petrology mineral chemistry and geochemistry of late triassic ni cu ore bearing mafic ultramafic intrusions hongqiling northeastern china petrogenesis and tectonic implications the hongqiling magmatic ni cu sulfide deposit situated on the southern margin of the eastern central asian orogenic belt caob is composed of over 30 mafic ultramafic intrusions these ore beari

melt mantle interaction and melt evolution in the sartohay high al chromite deposits of the dalabute ophiolite nw china the sartohay block of the dalabute ophiolite consists chiefly of mantle harzburgite and lherzolite with minor dunite these rocks host voluminous chromite deposits with lenticular or vein like shapes the podiform chromitites are associated with and cross cut by numerous troctolite dykes chromite in the chromitites has al2o3 23 31 wt tio2 0 29 0 44 wt and cr2o3 contents 45 wt with cr s 100cr cr al 60 typical of high al chromite deposits the host peridotites in sartohay have been texturally and geochemically modified by magmas from which the high al chromitites and mafic dykes formed dunites commonly envelop the podiform chromite bodies and show transitional contacts with the peridotites some of the peridotites and chromitites contain plagioclase that crystallized from impregnated melts the dunite locally grades into troctolite with increasing plagioclase contents as a result of melt impregnation peridotites and dunites show variable ca and al contents and lree enrichment the parental magma of the chromitites was likely tholeiitic in composition derived from partial melting of the asthenospheric mantle in a rising diapir the interaction between this magma and pre existing lithospheric mantle composed of depleted lherzolite would have formed a more silicic tholeiitic magma from which high al chromitites crystallized during this interaction harzburgite and dunite were depleted in modal pyroxene and enriched in some incompatible elements such as al ca and lree due to melt impregnation

depleted mantle source for the ulungur river a type granites from north xinjiang china geochemistry and nd sr isotopic evidence and implications for phanerozoic crustal growth abstract the ulungur river granites from north xinjiang china display two petrological trends 1 a peralkaline trend composed of alkali amphibole and alkali pyroxene bearing granites and dykes and 2 an aluminous trend represented by alkali granites monzogranites and aluminous granite dykes within the peralkaline granites rb sr whole rock isochron dating yielded an age of 300 ma for the emplacement of the peralkaline granites and 270 ma for the aluminous granites the ulungur river granites share all the geochemical features common to a type granites of the world the ulungur river granites are post orogenic and emplaced in a post collisional extensional environment the peralkaline and aluminous rocks have indistinguishable nd isotopic compositions they have unusually positive and relatively uniform nd t values ranging from 5 1 to 6 7 for the peralkaline rocks at 300 ma and from 5 5 to 5 9 for the aluminous rocks at 270 ma the initial 87sr 86sr ratios cannot be determined precisely by the whole rock isochron technique mainly because most samples are highly radiogenic and have high rb sr ratios in addition the large variation in sr isotopic compositions can partly be explained by crustal contamination during magma differentiation the nd isotopic data clearly indicate that both the peralkaline and aluminous rocks were derived from a long lived depleted mantle reservoir the formation of the ulungur river a type granites is hypothesized as follows 1 a depleted mantle was first metasomatised then subjected to partial melting leading to the generation of basic magmas now represented by the kalatongke mafic ultramafic complex in the ulungur river area 2 the basic magmas have undergone high degrees of fractional crystallisation with separation of biotite hornblende plagioclase potassium feldspar and other accessory phases such as apatite and ilmenite with the residual magmas forming the peralkaline granites during the magmatic differentiation the liquids were probably contaminated by crustal materials as evidenced by nb depletion and nd sr isotopic systematics on the other hand the formation of aluminous granites involved a replenishment of new mantle derived magmas into the differentiating magma chamber and followed by fractional crystallisation with retention of hydrous phases hornblende and biotite the petrological evolution of the ulungur river granites is thus from peralkaline to calc alkaline and not from calc alkaline to peralkaline as more often observed elsewhere the ulungur river granites in common with the voluminous granitoids occurring in the central asian orogenic belt represent a significant juvenile addition of the continental crust in the phanerozoic

geochemistry and geochronology of the amphibolite blocks in ophiolitic melanges along bangong nujiang suture central tibet abstract amphibolites occur as blocks within serpentinite matrix melange at dong tso and lagkor tso in the gertse area of central tibet where they are associated with the bangong nujiang suture bns geochemical data shows amphibolites have similar morb or arc like morb geochemical characteristics lagkor tso amphibolites show greater arc affinity whereas those from dong tso amphibolites are more morb like these characteristics are similar to basalts from continental back arc basin settings hornblendes from the amphibolites dated by the 40 ar 39 ar single grain laser fusion technique show similar metamorphic ages 170 177 ma which is interpreted to represent the timing of the main metamorphic event experienced in this region we suggest that the western and middle sectors of the bns contain the remnants of a short lived back arc basin the bangong nujiang ocean which partly opened and closed in the middle jurassic

genesis of the huangshannan high ni tenor magmatic sulfide deposit in the eastern tianshan northwest china constraints from pge geochemistry and os s isotopes abstract the huangshannan magmatic ni cu sulfide deposit is one of a group of permian magmatic ni cu deposits located in the southern central asian orogenic belt in the eastern tianshan northwest china it is characterized by elevated ni tenor concentrations in recalculated 100 sulfide in sulfide within ultramafic rocks 9 19 wt with values much higher than other deposits in the region sulfides of the huangshannan deposit are composed of pentlandite chalcopyrite and pyrrhotite and the host rock is relatively fresh indicating that the high ni tenor is a primary magmatic feature rather than formed by alteration processes it is shown that sulfides with high ni tenor can be generated by sulfide olivine equilibrium at an oxygen fugacity of qfm 0 5 for magmas containing 450 ppm ni and 20 olivine ores with 10 wt sulfur have relatively low pge and ni tenors compared to other ores r factor mass ratio of silicate to sulfide liquid modeling of ni indicates that they formed at moderate r values 150 600 based on this constraint on r values ores with 4 5 wt as sulfide rich samples are also depleted in cu and as interstitial sulfides in those samples are physically interconnected at a scale of several cms the low pt and pd anomalies are attributed to solid pt and pd phases crystallization and retention with the monosulfide solid solution mss and cu rich sulfide liquid percolation during mss fractionation this finding indicates that pt anomalies in sulfide rich rocks from magmatic ni cu deposits in the eastern tianshan are the result of sulfide fractionation rather than a hydrothermal effect 187 os 188 os 278ma values of the lherzolite samples vary from 0 27 to 0 37 and os 278ma values vary from 110 to 189 indicating significant magma interaction with crustal sulfides rich in radiogenic os well constrained os values and 34 s values 0 4 to 0 8 indicate that crustal contamination occurred at depth before the arrival of the magma in the huangshannan chamber regionally deposits with high ni tenor have not been reported other than the huangshannan deposit however many intrusions with high ni contents in olivine are present in nw china such as the erhongwa poyi and poshi intrusions those intrusions are capable of forming high ni tenor sulfides due to olivine sulfide silicate equilibrium and relative high ni content in parent magma making them attractive exploration targets

dinoflagellate cysts and mid oligocene chronostratigraphy in the central mediterranean region two new dinoflagellate cyst zones are proposed linking previously established zonal schemes for the eocene oligocene and oligocene miocene successions in the central mediterranean region the hystrichokolpoma pusillum hpu and chiropteridium lobospinosum clo interval zones are based on the contessa quarry and monte cagnero sections central italy and are correlated with previously established magnetostratigraphical and biostratigraphical schemes the base of the chattian is considered to correlate with chron cl0n in central italy the most distinct dinoflagellate cyst event associated with this chron is the first occurrence of distatodinium biffii marking the base of the distatodinium biffii dbi zone indirect evidence also suggests that the first occurrence of distatodinium biffii is above but close to the base of the chattian stage in its type area in northwest germany thus making it an important marker other possible markers for the base of the chattian are the last occurrence of areosphaeridium pectiniforme and the lowest acme of chiropteridium spp the latter may be related to the major mid oligocene sea level fall ta tb exxon supercycle boundary also considered to represent the base of the chattian and previously correlated with chron cl0n however in the contessa quarry section this dinoflagellate cyst event is associated with the older chron c11

final amalgamation of the tianshan and junggar orogenic collage in the southwestern central asian orogenic belt constraints on the closure of the paleo asian ocean abstract the tianshan and junggar orogenic collage occupies the southwestern part of the central asian orogenic belt and was assembled by collision accretion of several continental blocks and island arcs during late paleozoic early mesozoic time following the consumption of the junggar and south tianshan oceanic basins in the western segment of the paleo asian ocean considerable and continuing controversy has surrounded when where and how this orogenic collage was eventually amalgamated which plays a crucial role in understanding the formation of the central asian orogenic belt this review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains a comprehensive data compilation indicates that the formation of ophiolites along major sutures in the tianshan and junggar region lasted to the early carboniferous for the kalamaili suture zone to the mid carboniferous for the west junggar region and the north tianshan suture zone and to the late carboniferous for the south tianshan suture zone ca 325 310 ma ultra high pressure metamorphism along the western part of the south tianshan suture occurred nearly synchronously with the collision between the tarim craton and the central tianshan yili block the oceanic closure and collision events were sequentially followed by widespread and intensive a type granitic and bimodal magmatism which commenced in the mid carboniferous along the kalamaili belt and in the latest carboniferous to earliest permian in other regions contemporaneously large scale strike slip shearing took place along major faults subparallel to main sutures with a dominant dextral sense and deformation time since the carboniferous permian transition available data and geological evidence support an eastward propagating scissor like closure of the western segment of the paleo asian ocean along the south tianshan and north tianshan suture zones over a period from the mid to end carboniferous with the south tianshan belt representing the final suturing site in the early permian the tarim mantle plume likely merely affected the southwestern part of the assembled tarim and tianshan region as indicated by regional discrepancy in type and geochemistry of early permian a type granitoids the amalgamation of the tianshan and junggar orogenic collage was associated with the tectonic bending of the kazakhstan orocline leaving a piece of trapped oceanic crust in its middle part beneath the present junggar basin

petrogenesis of permian a type granitoids in the cihai iron ore district eastern tianshan nw china constraints on the timing of iron mineralization and implications for a non plume tectonic setting abstract the geochronology and geochemistry of granitoids in the eastern tianshan nw china provide important constraints on the timing of iron mineralization as well as in understanding evolution history of the southern central asian orogenic belt caob here we present results from a detailed study on granitoid rocks from the cihai iron ore district in the beishan region southern part of the eastern tianshan the granitoid rocks are composed of granodiorite quartz monzonite granite and monzonite zircon u pb analyses yielded the ages of 294 1 2 2 ma 286 5 0 7 ma 284 3 3 3 ma and 265 6 3 0 ma respectively suggesting they were formed in early middle permian among these granitoid rocks the ages of quartz monzonite and granite are close to the timing of iron mineralization 282 ma indicating they may provide a source of iron in the cihai ore district geochemically the granodiorite granite and quartz monzonite samples are characterized by high feo t feo t mgo and ga al ratios 0 84 0 94 and 2 28 3 27 respectively as well as high zircon saturation temperatures 781 908 c similar to those of typical a type granitoids isotopically they display consistently depleted hf isotopic compositions e hf t 1 18 to 15 37 geological geochemical and isotopic data suggest that the cihai a type granitoids were derived from melting of juvenile lower crust some early permian a type granitoids were recently identified in the tarim and eastern tianshan with the ages between 294 and 269 ma the a type granitoids in the eastern tianshan formed earlier between 294 284 ma and exhibit characteristics of a 2 type granitoids whereas the a type granitoids in the tarim formed later between 277 269 ma and show a 1 granitoids affinity we suggest that the permian tarim mantle plume does not account for the formation of the a type granitoids in the eastern tianshan area and the eastern tianshan was in a non plume tectonic setting during early permian time a slab break off event has been suggested as the possible tectonic mechanism that triggered the formation of early permian a type granitoids in the eastern tianshan

the liuyuan volcanic belt in nw china revisited evidence for permian rifting associated with the assembly of continental blocks in the central asian orogenic belt the basaltic pillow lavas in the liuyuan region of nw china considered to be part of an ophiolitic suite have been central to the models on tectonic setting evolution and timing of the final closure of the palaeo asian ocean new field evidence on the sedimentary units associated with the basalts reveals comparable sequences in the northern and southern flanks of the liuyuan volcanic belt with coarse to fine sediments from periphery to the centre the dacites and rhyolites formed coevally with the pillow basalts the pillow basalts are interlayered with lacustrine sandstone claystone and clayey lake deposits detrital zircons from these sediments yield zircon u pb ages of 291 285 ma andesites dacites and rhyolites from the basaltic sequence yield u pb ages of 280 277 ma similar to the 282 280 ma ages of gabbros that intrude the pillow lavas all these rocks cover the 460 440 ma granite and greenschist basement and have been intruded by gabbros of c 272 ma age with subsequent 230 227 ma north south contractional thrusting and folding the data from our study are incompatible with the existing models that consider the basalts as part of an ophiolitic suite along the northern continental margin of china from west to east the tarim dunhuang alxa and north china cratonic areas all show evidence for regional extension through rifting during early middle permian time these rift features and basaltic eruptions occurred coevally with the assembly of various microcontinental blocks against the siberian craton at c 300 250 ma synchronous with amalgamation of the central asian orogenic belt caob on the northern side of the liuyuan rift these events were also broadly synchronous with formation of the global supercontinent pangea

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

mineralization of an intra oceanic arc in an accretionary orogen insights from the early silurian honghai volcanogenic massive sulfide cu zn deposit and associated adakites of the eastern tianshan nw china the honghai volcanogenic massive sulfide vms deposit occurs in the kalatage inlier of the dananhu haerlik arc eastern tianshan in the southern altaids the deformed deposit hosted in a suite of early paleozoic basic to intermediate volcanic volcaniclastic and sedimentary rocks consists of lenticular massive to semimassive and sulfide silicate stockwork orebodies the orebodies are characterized by zoning of metallogenic elements and sulfide minerals outward from a central stockwork zone as follows fe cu fe cu zn au ag cu zn fe zn cu au ag zn cu and fe cu zn a typical vms hydrothermal alteration zone that formed around the foot of the massive orebodies is several times larger than the lenticular massive orebody the hydrothermally altered rocks contain sericite chlorite and epidote zones from the core outward re os and argon dating of pyrite and sericite shows that the honghai vms deposit formed in the early silurian 436 2 ma and was deformed in the early devonian 410 4 ma this is the first documented early paleozoic vms deposit in the eastern tianshan our multidisciplinary data indicate that the honghai cu zn deposit formed in an immature nascent island arc where early tholeiitic lavas evolved into transitional basic andesitic volcanic rocks and calc alkaline intrusions with relatively high epsilon nd t values 6 2 8 4 and low sr 87 sr 86 i ratios 0 70412 0 70541 the sr nd pb s isotopic and geochemical data suggest that the ore forming melts started in mantle derived volcanic rocks and deep subvolcanic intrusions and some alteration was influenced by seawater the deposit formed in a high level subvolcanic intrusion driven by sub seafloor co2 rich nacl cacl2 h2o hydrothermal fluids temperatures 99 377 degrees c salinities 6 18 nacl equivalent circulating in active extensional faults in a submarine caldera extension of the immature nascent intra oceanic arc was one of the important factors that controlled the development and preservation of the vms deposit future work will benefit from this improved understanding of the vms deposits formed in immature nascent intra oceanic arcs especially in early paleozoic island arcs in the eastern tianshan in the southern altaids

the liuyuan complex in the beishan nw china a carboniferous permian ophiolitic fore arc sliver in the southern altaids the tectonic history and time of closure of the palaeo asian ocean of the altaids are issues of lively current debate to address these issues this paper presents detailed geological petrological and geochemical data of the liuyuan complex lc in the beishan region in nw china located in the southernmost altaids in order to constrain its age origin and tectonic setting the lc mainly comprises massive basalts pillow basalts basaltic breccias gabbros and ultramafic rocks together with cherts and tuffs most prominent are gabbros and large volumes of basaltic lavas these mafic rocks have high tio 2 contents flat rare earth element ree patterns and show high field strength elements hfses similar to those of mid ocean ridge basalts morb the mafic rocks exhibit positive e nd t 6 6 9 0 values representing magmas derived from the mantle but these basic rocks are also enriched in th relative to rees and are systematically depleted in nb ta ti relative to rees there is also a large range in initial 87 sr 86 sr 0 7037 0 7093 all these variables indicate that mantle derived magma was contaminated by fluids and or melts from a subducting lithospheric slab and formed in a supra subduction zone ssz setting a gabbro intruded in the complex was dated by la icp ms on 20 zircons that yielded a 206 pb 238 u weighted average age of 286 2 ma considering the fact that all these basalts are imbricated against permian tuffaceous sediments and limestone we propose that the lc formed as an ophiolite in a fore arc in carboniferous permian time this indicates that the palaeo asian ocean still existed at 286 2 ma in early permian time and thus the time of closure of the palaeo asian ocean was in or after the late permian

the slip fiber chrysotile asbestos deposit in the zidani area northern greece abstract the chrysotile asbestos deposit of zidani in northern greece is an example of a slip fiber deposit associated with alpine type peridotites the deposit occurs in the northern part of an antigorite serpentinite and peridotite body tectonically emplaced on the pelagonian basement of the area a continuous retrograde alteration event is recognizable along the thrust fault between a metaclastic and carbonate sequence and the serpentinite body a phase of ductile deformation that formed antigorite mylonites was followed by a brittle one which formed schistose serpentinite the sense of shear of the overthrusting metaclastic mylonite coincides with that of the immediate underlying schistose and mylonite serpentinites thus retrogression of both groups of rocks is assumed to be the result of the thrust event the numerous altered amphibolite dikes crosscutting the ore created planar anisotropies during the thrust related deformation these planar anisotropies localized the deformation and consequently the formation of the schistose serpentinite and the asbestos ore in the northern part of the serpentinite body slip fiber chrysotile asbestos was formed along anastomosing non penetrating shear surfaces in the schistose serpentinite the chrysotile fibers replaced antigorite in situ in shear planes most likely at a transitional stage of deformation exhibiting both ductile and brittle fabrics however syntectonic filling of shear veins at the brittle stage is the major cause of the origin of the asbestos deposit

geochemical and isotopic constraints on the evolution of late paleozoic dyke swarms in west junggar xinjiang china abstract there are two sets nw and ne trending of basic to intermediate dykes emplaced into both the carboniferous volcanic sedimentary strata and undeformed plutons in the west junggar northern xinjiang china the early to middle permian nw trending dykes are mainly diorite and diorite porphyrite characterized by moderate mg 55 66 1 belonging to calc alkaline series the late permian ne trending dykes are diabase and diabase porphyritic belonging to tholeiitic series with low mg 41 4 58 3 both sets of dykes exhibit enriched liles depleted nb ta hrees and highly depleted isotopic signatures end 5 1 8 1 isr 0 70379 0 70675 trace element and isotopic data indicate that the nw trending dykes were generated by partial melting of a recently metasomatized subducted cold lithospheric mantle sclm coupled with variable assimilation of juvenile crustal materials whereas the ne trending dykes were derived from the partial melting of a similar sclm with lower degree of metasomatism than the nw trending dykes which were subsequently subjected to magma modification by the fractional crystallization of olivine pyroxene and or plagioclase the arc signatures exhibited by the trace element patterns of both sets of dykes in north xinjiang imply a recently metasomated mantle in this region formed during subduction prior to late paleozoic the mafic dyke swarms in this region are the products of phanerozoic continental growth in north xinjiang indicating widespread lithospheric extension

compositional variations of olivine from the jinchuan ni cu sulfide deposit western china implications for ore genesis the jinchuan ni cu sulfide deposit is hosted by an elongated olivine rich ultramafic body that is divided by subvertical strike slip faults into three segments central eastern and western the central segment is characterized by concentric enrichments of cumulus olivine crystals and interstitial sulfides pyrrhotite pentlandite chalcopyrite intergrowth whereas the eastern and western segments are characterized by an increase of sulfides toward the lower contacts in all segments sulfides are concentrated at the expense of intercumulus silicates olivine re crystallization is found to be associated with actinolite alteration in some samples the compositional variations of primary olivine from the sulfide poor samples can be explained by a small degree of olivine crystallization 50 modal and sulfide averaging 5 wt in the rocks are consistent with the interpretation that the jinchuan deposit was formed by olivine and sulfide laden magma successively ascending through a conduit to a higher now eroded level sulfide enrichment toward the center in the central segment and toward the lower contact in the eastern and western segments may have in part resulted from flow differentiation and gravitational settling during magma ascent respectively

world class ni cu pge deposits key factors in their genesis magmatic ni cu sulfide deposits form as the result of segregation and concentration of droplets of liquid sulfide from mafic or ultramafic magma and the partitioning of chalcophile elements into these from the silicate melt sulfide saturation of a magma is not enough in itself to produce an ore deposit the appropriate physical environment is required so that the sulfide liquid mixes with enough magma to become adequately enriched in chalcophile metals and then is concentrated in a restricted locality so that the resulting concentration is of ore grade the deposits of the noril sk region have developed within flat elongate bodies 15 2 0 2 km that intrude argillites evaporites and coal measures adjacent to a major trans crustal fault and immediately below the centre of a 3 5 km thick volcanic basin studies of the overlying basalts have shown that lavas forming a 500 m thick sequence within these have lost 75 of their cu and ni and more than 90 of their pge overlying basalts show a gradual recovery in their chalcophile element concentrations to reach normal values 500 m above the top of the highly depleted zone the ore bearing noril sk type intrusions correlate with those basalts above the depleted zone that contain normal levels of chalcophile elements the high proportion of sulfide 2 10 wt associated with the noril sk type intrusions the high pge content of the ores the extensive metamorphic aureole 100 400 m around the bodies and the heavy sulfur isotopic composition of the ores 8 12 34s are explicable if the ore bearing bodies are exit conduits from high level intrusions along which magma has flowed en route to extrude at surface the first magma to enter these intrusions reacted with much evaporitic sulfur at a low r value and thus gave rise to sulfides with low metal tenors successive flow of magma through the system progressively enriched the sulfides in the conduits losing progressively less of their chalcophile metals and thus accounting for the upward increase in metals in successive lava flows above the highly depleted flows the voisey s bay deposit lies partly within a 30 100 m thick sheet of troctolite interpreted as a feeder for the 1 334 ga voisey s bay intrusion and partly at the base of this intrusion where the feeder adjoins it studies of olivine compositions indicate that an early pulse of magma through the feeder and into the intrusion was ni depleted but that subsequent pulses were much less depleted trace element re os and s and o isotope data and mineralogical studies indicate that the magma pulses interacted with country gneiss probably principally in a deeper level intrusion extracting sio2 na2o k2o and possibly sulfur form the gneiss which accounts for the magma becoming sulfide saturated the jinchuan deposit of north central china occurs within a 6 km long dyke like body of peridotite the compositions of olivine within the dyke the igneous rocks themselves and the ore are all inconsistent with derivation of the body from ultramafic magma as originally supposed and indicate that the structure forms the keel of a much larger intrusion of magnesian basalt magma flow of magma into the intrusion has resulted in olivine and sulfide being retained where the keel was widening out into the intrusion the west australian komatiite related deposits occur in thermal erosional troughs which have developed due to the channelisation of magma flow and the resulting thermal erosion of underlying sediments and basalt by the hot komatiite magma the sediments are sulfide rich and may have contributed substantially to the sulfide of the ores the mineralisation in the duluth complex occurs in troctolitic intrusions along the western margin of the complex as a result of magma interacting with and extracting sulfur from the underlying graphite and sulfide bearing sediments no magma flow channels have been identified so far and the lack of magma flow subsequent to the development of sulfide immiscibility is regarded as the reason why these deposits are not of economic grade when most major ni cu sulfide deposits are compared they prove to have a number of features in common olivine rich magma proximity to a major crustal fault sulfide bearing country rocks chalcophile element depletion in related intrusive or extrusive rocks field and or geochemical evidence of interaction between the magma and the country rocks and the presence of or proximity to a magma conduit the features are thought to explain the three key requirements sulfide immiscibilty adequate mixing between sulfides and magma and localisation of the sulfides discussed and have important implications with respect to exploration

the middle permian hongshanliang manto type copper deposit in the east tianshan constraints from geology geochronology fluid inclusions and h o s isotopes abstract the hongshanliang copper deposit hosted in the tuff of the lower carboniferous yamansu formation is a typical copper deposit in the aqishan yamansu belt east tianshan based on crosscutting relationships of veins textural relationships and mineral assemblages five alteration mineralization stages at hongshanliang have been established chlorite sulfide stage stage i quartz pyrite stage stage ii quartz polymetallic sulfide stage stage iii late veins stage iv and supergene process stage v stage i has mineral assemblage of chlorite pyrite chalcopyrite quartz sericite and is commonly characterized by euhedral pyrite with silicates e g chlorite quartz and sericite and or chalcopyrite as its pressure shadow indicating an early mineralization event with apparent deformation stage ii is characterized by quartz pyrite chalcopyrite or locally quartz gypsum anhydrite pyrite veins cutting stage i chlorite pyrite the main mineralization stage stage iii at hongshanliang has typical mineral assemblages of quartz chalcopyrite chlorite calcite sericite quartz chalcopyrite sphalerite galena pyrite and quartz sphalerite galena chlorite with veins veinlets disseminations and local massive ore types similar to manto type copper deposits regarding mineralization and ore structures detailed fluid inclusion study shows temperature of fluids decreased from stage ii 307 484 c through stage iii peak at 160 180 c consistent with quartz chlorite oxygen isotope geothermometer of 190 c to stage iv 129 169 c with corresponding salinities of 2 7 26 2 wt nacl equiv peak at 8 wt 2 1 12 3 wt nacl equiv peak at 8 wt and 0 5 7 7 wt nacl equiv peaks at 4 6 wt respectively indicating an evolved hydrothermal ore forming system such fluid evolution can also be supported by h o isotopes during water rock reaction from stage ii 18ofluid 6 3 8 3 and dfluid 77 to 64 through stage iii 18ofluid 1 7 to 7 0 and dfluid 82 to 58 to stage iv 18ofluid 2 5 to 2 1 and dfluid 77 to 73 with a magmatic hydrothermal origin furthermore sulfur isotopes suggest that fluids of the two mineralization stages stage i and iii are predominantly magmatic hydrothermal with other influx contribution into the ore forming system i e minor early carboniferous seawater in stage i 34sfluid varying from 3 5 to 6 1 with peak at 0 and minor organic materials in stage iii 34sfluid varying from 6 5 to 4 1 with peak at 0 1 and detection of ch4 and c2h6 from fluid inclusions in combination of alteration paragenesis nature and source of ore forming fluids and comparison with other typical deposits we proposed that the hongshanliang copper deposit underwent two mineralization events with the main mineralization similar to manto type copper deposits 40ar 39ar dating of sericite from a massive chalcopyrite ore indicates the hongshanliang main mineralization formed at 269 0 0 4 ma generally coeval with regional k feldspar granite emplacement ca 272 ma integrating the regional tectonic setting magmatism and metallogenesis of the aqishan yamansu belt and the east tianshan we suggest that the aqishan yamansu belt has potential of mineral prospecting for the middle permian manto type copper deposits

experimental evidence for high temperature felsic melts formed during basaltic intrusion of the deep crust basaltic intrusion into the continental crust was simulated with melting experiments on layered charges of high alumina olivine tholeiite haot and metapelite at 11 kbar rapid diffusion of cao and na 2 o into the metapelite and h 2 o k 2 o sio 2 and al 2 o 3 into the basalt resulted in spectacular changes in the phase assemblage garnet megacrysts crystallized profusely across the basalt layer cumulate assemblages closely resembled rocks found in underplating localities and glass compositions graded from dacite to rhyolite even at temperatures as high as 1150 c silicic melts can be generated during interaction of basalt with metapelite at temperatures well above the h 2 o saturated granite minimum calculations based on these results and comparison with natural occurrences suggest that high temperature felsic melts with 2 o can form and segregate at rates of 1 cm yr

a review of the cu ni sulphide deposits in the chinese tianshan and altay orogens xinjiang autonomous region nw china principal characteristics and ore forming processes abstract several cu ni sulphide deposits and occurrences have recently been discovered along parallel deep faults in the chinese tianshan and altay orogenic belts xinjiang province nw china the kalatongke and several other cu ni mineralized intrusions are located along the irtysh fault which separates the altay orogenic belt from the junggar basin the huangshan huangshandong xiangshan tudun erhongwa tula ergen and hongling deposits occur along the kanggurtag suture which separates the jueluotage orogenic belt from the turpan hami tuha basin the baishiquan tianyu and tianxiang deposits are located along the arqikekuduke fault which separates the jueluotage orogenic belt from the central tianshan precambrian terrane the poyi poshi and luodong deposits are located along the baidiwa fault which separates the central tianshan precambrian terrane from the beishan paleozoic rift re os dating of cu ni sulphide ores reveals that these cu ni ore belts formed in a narrow age range of 298 282 ma this age range is about the same as those of associated intrusions and dykes dated by the shrimp zircon u pb method tectonic and geochronological constraints suggest that the amalgamation of continental blocks mainly occurred during the late carboniferous in the central asian orogenic belt large scale hydrothermal and magmatic metallogenesis in the region occurred during post collisional stages of latest carboniferous to early permian age the cu ni sulphide deposits are part of this metallogenic event the cu ni orthomagmatic sulphide deposits in northern xinjiang are represented by 1 net textured type deposits by segregation of a cu ni metal sulphide melt and 2 magma conduit type some mafic ultramafic suites exhibit lithological zoning caused by strong differentiation stratiform orebodies are hosted by ultramafic rocks at the base of the magma chamber good examples are the kalatongke huangshandong and poshi deposits others such as the xiangshan baishiquan tianyu and tula ergen deposits are hosted by magma conduits consisting of peridotite troctolite and pyroxenite these ultramafic rocks either occur within faults or are surrounded by gabbroic and dioritic intrusions these two types of orthomagmatic cu ni sulphide deposits are also distributed along the same ore belts for instance the differentiated sill related huangshandong deposit co exists with the magma conduit type tula ergen deposit in the jueluotage orogenic belt orthomagmatic cu ni sulphide deposits in northern xinjiang formed during post collisional extension and are possibly related to a late carboniferous early permian mantle plume event the mafic ultramafic suites and associated cu ni deposits are commonly accompanied by dyke swarms and are characterized by elongated outcrops occurring along parallel e w trending regional faults these mafic ultramafic suites and accompanying dyke swarms are generally fractionated implying that they were feeders of presently eroded flood basalts

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

kinetic controls on the partitioning of trace elements between silicate and sulfide liquids mass transfer between sulfide and silicate liquids is often discussed elements pge has resulted from liquation immiscible by reference to a mass ratio between hypothetical liquid reservoirs liquid phase separation of sulfide liquid from mafic or at equilibrium defined as r in an open system not at equilibrium ultramafic silicate magma a central assumption of modthe mass of silicate melt from which a growing sulfide droplet els of magmatic sulfide deposit formation is that the base appears to have scavenged chalcophile elements will depend on metals and pge are strongly partitioned into the sulfide diffusivities di and dfes of the element and of the fes component melt previous discussions of the process by which sulfide in the silicate melt respectively on the degree of supersaturation of liquids become enriched in chalcophile metals have fothe melt with fes c o on the radius a of the droplet and on the cused almost exclusively on models in which coexisting velocity v with which the droplet is advected through the melt so bodies of sulfide and silicate melt are considered to be that in equilibrium at all times the intent of this paper is to demonstrate that natural sulfide deposits preserved in igneous rocks will in many r 1 c fes o di 1 2 adiv dfes 1 2 adfesv instances record metal distributions that never attained equilibrium as a result of the kinetic constraints on metal chalcophile elements are expected to show inter element variations partitioning between phases the consequences are that in d spanning several orders of magnitude in some melts leading different elements will seem to show evidence for equito large inter element variations in effective r in a given sulfide libration at different silicate sulfide mass ratios within body these variations in effective r will lead to spatial separations single sulfide bodies i describe the time dependent evolubetween zones of maximum enrichment of chalcophile elements tion of metal distributions in silicate sulfide melt systems produced during fractional segregation of sulfide in layered intrusions starting with analytical solutions for simple boundary whereas it has proven impossible to model the generation of spatially conditions and then adapting them to more complex offset stratiform horizons in the australian munni munni layered systems as numerical models intrusion using equilibrium partition coefficients the present kinetic model reproduces the observed patterns with great fidelity

electron microprobe monazite geochronological constraints on the late palaeozoic tectonothermal evolution in the chinese tianshan electron microprobe monazite data from the early palaeozoic granitoid gneisses in the central tianshan tectonic zone provide two main ages 1 an age of 355 12 ma obtained on the chemically complex grains which is good agreement with the high pressure metamorphic age obtained on eclogite and blueschist rocks from the south tianshan tectonic zone 2 an age of 323 7 ma obtained on the complex and the monogenetic grains which is also closely consistent with the age for a major episode of cooling recrystallization of these high pressure rocks monazite from the schist of the xingxingxia complex yields a younger th pb u pb centroid age of 282 9 ma this younger age is interpreted as being linked to a magmatic episode possibly related to underplating extension and or shear activities these data provide timing constraints on the episodes of metamorphism and high pressure metamorphism and evidence for transition from compression to extension during the carboniferous to early permian for the chinese tianshan region moreover this study shows that electron microprobe dating of monazite together with recent statistical treatment can provide a reliable method to reveal a sequence of events within an orogenic cycle

the origin of rodingites from cassiar british columbia and their use to estimate t and p h2o during serpentinization abstract the cassiar serpentinite located in north central british columbia is a low grade alpine type serpentinite within the sylvester allochthon two stages of rodingitization have occurred at cassiar and these correlate with two stages of serpentinization that have occurred in the ultramafic rock the first stage is characterised by an increase in ca activity and decreases in mg and sio 2 activities in the rodingite culminating in the crystallization of grossular in the rodingite and by the formation of lizardite in the serpentinite at a later time a second event occurred characterised by a decrease in ca activity and increases in mg and sio 2 activities both in the rodingite and the serpentinite this was marked by the crystallization of diopside prehnite and lizardite in the rodingite and by the recrystallization of lizardite to chrysotile and antigorite in the serpentinite the serpentine recrystallization and the development of the second stage rodingite minerals indicate that the changes in rodingite and serpentine mineral assemblages were driven by similar changes in the bulk rock compositions this suggests that the second stage event in both rodingite and serpentinite was caused by an externally derived fluid measurements on fluid inclusions in the rodingite minerals clinozoisite grossular and diopside of the second event indicate that the externally derived fluid was co 2 poor but relatively saline 8 1 5 equiv wt nacl by combining the pressure dependant temperature measurements from fluid inclusions with the pressure independant temperature measurements on 18 o in coexisting serpentine magnetite pairs the pressure of formation can be estimated the second event of serpentine recrystallization and rodingitization was an isothermal process at 300 c 36 c p h 2 o

postcollisional eastward extrusion and tectonic exhumation along the eastern tianshan orogen central asia constraints from dextral strike slip motion and 40ar 39ar geochronological evidence abstractpostcollisional extrusion and tectonic evolution in the eastern tianshan orogenic belt etob remains poorly known especially the mechanism of dextral strike slip motion and associated tectonic exhumation to better constrain this development a structural and 40ar 39ar geochronological study was carried out on a syndextral strike slip intrusion the jueluotag batholith as well as on other granitic plutons in the etob 40ar 39ar analyses of hornblende biotite k feldspar and plagioclase from quartz mica diorite granodiorite and dioritic porphyry dykes were used to construct cooling histories of the etob hornblendes have cooling ages of 277 272 ma similar to the syntectonic granitic intrusions but biotite ages are 261 254 ma along the syndextral strike slip pluton from east to west the dextral strike slip motion cuts through 268 ma dioritic porphyry dikes as well from these data we conclude that dextral strike slip motion occurred from 270 to 245 ma based on the syntectonic granitic intr

constraints on the timing of fe cu metallogenesis in the eastern aqishan yamansu shaquanzi metallogenic belt eastern tianshan nw china abstract the aqishan yamansu shaquanzi belt is a well known fe cu au metallogenic belt located in the central asian orogenic belt nw china numerous fe rich ores as well as polymetallic mineralization including cu pb zn and co and related magmatic hydrothermal alteration are hosted in volcanic rocks especially those in the eastern part of this metallogenic belt the complex geology of the belt and the divergent geochronological data obtained by different investigators and analytical methods have led to contrasting opinions on the deposit types and metallogenesis of the belt the present study focuses on the shaquanzi yamansu and heifengshan fe cu polymetallic deposits in the eastern part of the belt these deposits display fe dominated metallogenesis related to volcanic sedimentary exhalative processes and polymetallic metallogenesis related to volcanic hydrothermal metasomatism and skarnization caused by subsequent intrusion processes the shaquanzi yamansu and heifengshan deposits have undergone multiple periods of metallogenesis and contain late fe cu pb mo fe cu zn co and fe cu mineralization respectively using zircon u pb dating by laser ablation multi collector inductively coupled plasma mass spectrometry two rhyolite samples at the base and lower middle part of the tugutubulak formation and a basaltic andesite and a diorite dyke in the shaquanzi ore district yield concordant ages of 327 9 2 6 ma mean square of weighted deviates or mswd 0 015 327 8 1 4 ma mswd 1 03 285 9 2 0 ma mswd 0 81 and 276 3 1 4 ma mswd 0 21 respectively basaltic andesite from the upper yamansu formation in the yamansu deposit area yields a concordant age of 327 6 6 4 ma mswd 0 54 whereas rhyolite diorite dyke and granite stock from the heifengshan deposit give concordant ages of 285 7 1 3 ma mswd 0 01 273 7 1 6 ma mswd 1 2 and 274 4 2 5 ma mswd 0 20 respectively hydrothermal molybdenite in the shaquanzi deposit yields a weighted mean re os age of 314 6 1 7 ma mswd 0 29 and an isochron age of 316 6 ma mswd 0 46 a collation of previously reported ages and our new age data show that extensive magmatism occurred during the carboniferous early permian ca 350 270 ma in the aqishan yamansu shaquanzi belt with a peak period between ca 335 and ca 305 ma the yamansu formation and tugutubulak formation volcanic rocks formed at ca 348 334 ma early carboniferous and between ca 328 and ca 303 ma late early carboniferous to late carboniferous respectively in the eastern part of the belt fe dominated mineralization resulting from volcanic sedimentary exhalative processes e g ca 334 ca 322 and ca 286 ma and polymetallic mineralization resulting from volcanic hydrothermal metasomatism e g ca 334 323 ma as well as skarnization and magmtic hydrothermal caused by intrusions occurred at different stages e g ca 322 316 ca 299 and ca 274 ma leading to the superimposition of polymetallic mineralization between ca 334 and ca 273 ma

neoproterozoic to paleozoic geology of the altai orogen nw china new zircon age data and tectonic evolution abstract we present a synthesis and a new account of the geological and tectonic history of the terranes of the chinese paleozoic altai orogen together with new single zircon ages for granitic and rhyodacitic rocks a central terrane consists of neoproterozoic to silurian amphibolite facies metasedimentary rocks and abundant devonian carboniferous granites the presence of precambrian basement is indicated by sinian fossils our xenocryst ages and published nd mean crustal residence ages of granites felsic arc type lavas on the southern margin of the terrane have a mean 207pb 206pb zircon age of 505 ma reflecting the time of arc volcanism and the presence of xenocysts with ages between 614 and 921 ma suggests derivation by intracrustal melting accordingly we suggest that a cambro ordovician continental magmatic arc was built on the southern margin of the central terrane by northward subduction a low grade ordovician andean type arc with a continental basement is situated above a normal fault on

revisiting the irtish tectonic belt implications for the paleozoic tectonic evolution of the altai orogen abstract the irtish tectonic belt is one of the most important suture zones in the central asian orogenic belt caob the various models invoked to explain the tectonic evolution of this belt in relation to paleozoic continental growth include 1 syn subduction strike slip duplication of a single long lived arc and 2 collision of many arcs and micro continents here we report new results from detailed field studies geochemistry and zircon u pb geochronology on the major rock units along the irtish belt both in kazakhstan and in the chinese altay our new results together with information from published data suggest that the altai mongolia terrain witnessed several episodes of subduction the junggar terrain which formed by multiple collisions of intra oceanic arcs seamounts and ophiolite suites prior to 330 ma subsequently amalgamated with the altai mongolia terrain at around 320 ma along the irtish suture zone following the clockwise rotation of the siberian craton and the n directed movement of the junggar terrain the sinistral strike slip motion along the irtish suture zone resulted in ductile shearing partial melting of the crustal material and the formation of mylonites syn tectonic migmatite and gneissic granites the sinistral strike slip deformation of the irtish suture zone culminated at ca 275 ma the diverse 275 250 ma magmatism mafic ultramafic complexes bimodal intrusives mafic and silicic dykes a type and i a type granites is related to magma pulses generated by the permian tarim mantle plume our model of multiple episodes of subduction below the altai arc is different from previous models and proposes that the subduction continued until triassic with the permian subduction under the altai arc and a late permian large scale south directed thrusting

geochemical and geochronological studies of granitoid rocks from the western tianshan orogen implications for continental growth in the southwestern central asian orogenic belt abstract the western tianshan orogen in northwestern china is part of the southwestern margin of the central asian orogenic belt caob which represents the largest tectonic assembly of accretionary complexes and the most significant area of phanerozoic continental growth in the world granitoid rocks have a widespread occurrence and occupy about 30 of the whole exposure of the orogen ages obtained for the granitoids vary from 896 ma to 247 ma while initial 87 sr 86 sr ratios vary from 0 70329 to 0 72070 and e nd values from 14 1 to 7 3 the occurrence of neoproterozoic granitic gneisses implies the presence of precambrian basement in this area during oceanic subduction continental growth occurred as a result of several combined processes i e by addition of oceanic crustal melts adakites the intrusion of basaltic magmas derived by partial melting of the metasomatized depleted mantle wedge and the upwelling of granitic magma derived from a mixed source of basaltic magmas and old continental basement however during the post collisional period vertical accretion of underplated juvenile mantle material may have been accomplished during slab breakoff delamination this study suggests a two stage model of continental growth of syn subduction lateral accretion of arc complexes and post collisional vertical accretion of underplated mantle material which may also be relevant for the western segment of the caob in the phanerozoic the reworking and involvement of old crust are more obvious in the western tianshan orogen compared to other parts of the caob comprising the western junggar eastern junggar alataw and altay terranes

the early paleozoic huangtupo vms cu zn deposit in kalatag eastern tianshan implications from geochemistry and zircon u pb geochronology of volcanic host rocks abstract the tianshan in china forms the southern part of the central asian orogenic belt caob and also hosts important polymetallic resources here we investigate the huangtupo medium size copper zinc deposit located in the central part of the kalatag copper polymetallic belt with a view to evaluate the nature and genesis of the early paleozoic volcanogenic massive sulfide vms cu zn deposits this deposit is correlated to intermediate felsic volcano sedimentary sequences of the early paleozoic daliugou formation which are mainly composed of andesite dacite and rhyolite with minor basalt as well as their pyroclastic equivalents the ore bodies are hosted in the contact zone between andesitic volcanic breccia and tuff representing an eruptive hiatus between the two volcanic cycles with massive sulphide lens at the top and stockwork zone at lower part of the daliugou formation we report new zircon u pb data major and trace element geochemistry and sr nd isotopes from the andesite dacite and andesitic tuff in the huangtupo deposit zircon from the dacite and the andesite occurring above the ore bodies yield and age of 440 1 1 2 ma and 439 7 0 95 ma and that from the andesitic tuff in footwall shows and age of 442 0 1 1 ma all samples show typical geochemical signatures of subduction related calc alkaline magmas with slight enrichment in lile and lree but depletion in nb and ti content relative to primitive mantle the andesites are characterized by high mgo 7 6 10 8 wt contents and mg values 64 72 with low sr y and la yb ratios belonging to sanukite both dacite and tuff have low mgo

sulfide saturation and magma emplacement in the formation of the permian huangshandong ni cu sulfide deposit xinjiang northwestern china the eastern tianshan orogenic belt northwestern china hosts 120 mafic ultramafic intrusions and at least six of them host significant ni cu sulfide mineralization of which the permian huangshandong intrusion is the largest the mafic ultramafic rocks of the huangshandong intrusion comprise lherzolite gabbronorite gabbro and diorite individual orebodies are composed of pyrrhotite pentlandite and chalcopyrite as disseminated to net textured or massive to semimassive sulfide mineralization oxide bearing sulfide mineralization contains 1 to 5 magmatic magnetite that has ilmenite and spinel exsolution lamellae silicate rocks and sulfide mineralization have variable whole rock platinum group elements pge 0 38 362 ppb cu 42 97 000 ppm and ni 26 33 000 ppm concentrations the mineralization is broken out into two types termed oxide rich and oxide poor the oxide rich sulfide mineralization has high pge concentrations with low 187re 188os ratios 38 9 151 whereas oxide poor sulfide mineralization has low pge concentrations with high 187re 188os 159 781 both oxide rich and poor sulfide mineralization have highly variable os values 49 189 and 30 278 respectively oxide rich sulfide mineralization contains magnetite with variable amounts of mgo tio2 al2o3 feototal cr v zn and sn indicating that they crystallized from different stages during magma differentiation we propose that the host intrusion and associated sulfide mineralization were derived from high mg basaltic magmas from a mantle source that was previously modified by subducted oceanic slab oxide poor sulfide mineralization of the huangshandong intrusion formed from a magma that underwent 0 03 sulfide removal before emplacement and was thus pge depleted oxide rich sulfide mineralization formed from magma that had much lower amounts of sulfide 0 003 removed in the early stage before entering the huangshandong magma chamber an early sulfide saturation event was likely associated with fractionation of silicate minerals in a deep staging magma chamber the second sulfide saturation event that formed the sulfide mineralization was probably triggered by selective crustal contamination and fractionation in the high level chamber where mixing of magmas and accumulation of immiscible sulfide occurred

geochemistry and geochronology of acidic rocks in the beishan region nw china petrogenesis and tectonic implications abstract the dacites and granites from the beishan region are characterized by highly fractionated ree enrichments in lile and depletion in nb ta and sr the dacites contain zircons with ages ranging from 265 to 748 ma these features suggest that they were probably derived from the older lower continental crust and were later on subjected to significant crustal assimilation the rhyolites diorites and diabases all of which share similar geochemical features such as trace element patterns zircon u pb ages of 280 ma positive ehf t and end t high initial 87sr 86sr i and 18o values were most likely derived from the juvenile crustal sources and subsequently experienced fractional crystallization and crustal contamination these acidic igneous rocks except dacites and granites and coeval mafic ultramafic intrusions form a bimodal igneous series this implies that the beishan region was a late paleozoic rift probably developed in association with the early permian mantle plume activity in the tarim basin

genesis of the giant caixiashan zn pb deposit in eastern tianshan nw china constraints from geology geochronology and s pb isotopic geochemistry abstract the caixiashan zn pb deposit is the largest carbonate hosted zn pb deposit in eastern tianshan nw china the deposit comprises the no iii and iv ore zones with a proven reserve of 131 mt ore at 3 95 pb zn the orebodies generally occur as irregular lenses and pods in altered carbonate rocks of the mesoproterozoic kawabulake group near faults the mineralization is characterized by massive disseminated and vein veinlet sulfides including pyrite pyrrhotite sphalerite and galena with minor arsenopyrite and chalcopyrite as well as sulfosalt minerals of ag as sb and pb the mineralization is associated with tremolite chlorite silica and carbonate alterations rb sr isotopic dating of sphalerite and pyrrhotite yields an isochron age of 337 2 5 7 ma which is interpreted as the mineralization age zircon u pb dating reveals that stocks of diorite quartz diorite k feldspar granite and monzonitic granite that occur in the deposit area were emplaced at 348 2 3 7 ma 351 9 3 5 ma 333 6 3 6 ma and 330 0 3 6 ma respectively these age data suggest that the mineralization is coeval with carboniferous granitic magmatism the 34sv cdt values of sulfides excluding the syn sedimentary pyrite range from 2 42 to 19 1 suggesting that the reduced sulfur was mainly derived from thermal sulfate reduction tsr of seawater derived sulfates in the marine sedimentary basement rocks and minor contribution by replacement of syn sedimentary pyrite as well as a possible input of magmatic sulfur the pb isotopic compositions of sulfides with 206pb 204pb ranging from 17 074 to 17 361 207pb 204pb from 15 422 to 15 614 and 208pb 204pb from 36 685 to 37 303 partly overlap with those of basement rocks of the mesoproterozoic kawabulake group and the carboniferous intrusions suggesting that the ore metals were derived from both the basement and carboniferous magmatism on the basis of the spatio temporal relations between hydrothermal alterations mineralization and carboniferous magmatism we conclude that the caixiashan zn pb deposit is a high temperature carbonate replacement deposit related to concealed granitic intrusions which were formed in an arc environment related to the subduction of the south tianshan ocean plate underneath the central tianshan massif during the carboniferous time the results of this study indicate that there is a great potential of finding more large scale zn pb deposits similar to caixiashan in eastern tianshan

new 40ar 39ar age constraints on the late palaeozoic tectonic evolution of the western tianshan xinjiang northwestern china with emphasis on permian fluid ingress laser probe dating of mylonite whole rock samples from the north tianshan main tianshan fault zone that cross cuts the north tianshan domain s southern margin yielded 40ar 39ar spectra with 255 285 ma ages biotite from an undeformed early carboniferous granite which cuts the steep mylonitic foliation in the proterozoic basement of the yili arcs s southern margin gave a 263 4 0 6 ma plateau age 1 pre carboniferous metasediments overlying this basement yielded plateau ages 1 of 253 3 0 3 muscovite and 252 3 0 3 biotite ma the permian ages of mylonites date movement on these ductile dextral strike slip shear zones whereas the mica ages are interpreted by recrystallisation as a result of fluid flow around such transcurrent faults we propose that the tianshan s permian syn tectonic bimodal magmatism was created in a non plume related yellowstone like extensional transtensional tectonic regime gold mineralisation tracing aqueous flow in the crust peaked in permian time and continued locally into the triassic the picture is emerging that a convective fluid system partly driven by magmatic heat existed in a strongly fractured and weakened crust with an elevated heat flow leading to regional scale isotope resetting we suggest that surprisingly young isotopic ages in the literature for early orogenic ultra high pressure metamorphism are similarly due to fluid mediated recrystallisation

cambrian ophiolite complexes in the beishan area china southern margin of the central asian orogenic belt abstract we present zircon ages and geochemical data for cambrian ophiolite complexes exposed in the beishan area at the southern margin of the central asian orogenic belt caob the complexes consist of the xichangjing xiaohuangshan and hongliuhe yushishan ophiolites which both exhibit complete ophiolite stratigraphy chert basalt sheeted dikes gabbro mafic and ultramafic cumulates and serpentinized mantle peridotites zircon grains of gabbro samples yielded 206 pb 238 u ages of 516 8 521 4 528 3 and 535 6 ma that reflect the timing of gabbro emplacement the geochemical data of the basaltic rocks show enrichment in large ion lithophile elements and depletion in the high field strength elements relative to normal mid oceanic ridge basalt nmorb in response to aqueous fluids or melts expelled from the subducting slab the gabbro samples have higher whole rock initial 87 sr 86 sr ratios and lower positive e nd t values than nmorb these geochemical signatures resulted from processes or conditions that are unique to subduction zones and the ophiolites are therefore likely to have formed within a supra subduction zone ssz environment we suggest that the cambrian ophiolite complexes in the beishan area formed within a ssz setting reflecting an early paleozoic subduction of components of the paleo central asian ocean and recording an early paleozoic southward subduction event in the southern caob along the northern margin of the tarim and north china cratons

subduction induced mantle heterogeneity beneath eastern tianshan and beishan insights from nd sr hf o isotopic mapping of late paleozoic mafic ultramafic complexes abstract extensive late paleozoic mafic ultramafic complexes in the eastern tianshan and beishan regions in the southern central asian orogenic belt caob represent an ideal opportunity to assess the characteristics of the mantle in this area whole rock nd sr and zircon hf o isotopic data from the mafic ultramafic complexes of the jueluotage belt middle tianshan massif and beishan rift were compiled for isotopic mapping end t and 87sr 86sr i values range from 5 5 to 9 5 and 0 702 to 0 706 respectively in the jueluotage belt and from 2 to 11 and 0 703 to 0 710 respectively in the middle tianshan and beishan zircon ehf t and 18o values are in the range of 6 0 17 0 and 4 14 8 00 respectively in the jueluotage belt 1 8 and 5 17 6 30 respectively in the middle tianshan and show large variations of 1 17 and 4 12 respectively in the beishan spatially the 87sr 86sr i ratios of mafic ultramafic complexes increase from the jueluotage belt and beishan to the middle tianshan while the end t values show an opposite trend and reflect a mixing character between depleted mantle and em ii reservoirs zircon ehf t and 18o values exhibit an apparent southward decreasing and increasing trends respectively from the jueluotage belt through middle tianshan to beishan rift their corresponding hf model ages increase continuously from north to south these observations demonstrate that the mantle sources beneath the eastern tianshan and beishan are compositionally heterogeneous which presumably result from significant and variable degrees of subduction related modification we therefore suggest that the late paleozoic subcontinental lithospheric mantle beneath the jueluotage belt was modified by slab derived melts and fluids during the subduction of the junggar ocean whereas the mantle beneath the beishan rift was influenced mainly by slab derived fluids during the subduction of the south tianshan ocean the unique similarities of the middle tianshan mafic ultramafic complexes reflect a two stage modification of their mantle source namely the sequential subduction of the early south tianshan ocean followed by subduction of the junggar ocean thus the subduction induced mantle heterogeneity beneath the caob is probably regional in scope

re os isotopic ages of pyrite and chemical composition of magnetite from the cihai magmatic hydrothermal fe deposit nw china the eastern tianshan orogenic belt of the central asian orogenic belt and the beishan terrane of the tarim block nw china host numerous fe deposits the cihai fe deposit 90 mt at 45 6 fe in the beishan terrane is diabase hosted and consists of the cihai cinan and cixi ore clusters ore minerals are dominantly magnetite pyrite and pyrrhotite with minor chalcopyrite galena and sphalerite gangue minerals include pyroxene garnet hornblende and minor plagioclase biotite chlorite epidotite quartz and calcite pyrite from the cihai and cixi ore clusters has similar re os isotope compositions with 14 to 62 ppb re and 10 ppt common os pyrrhotite has 5 to 39 ppb re and 0 6 ppb common os pyrite has a mean re os model age of 262 3 5 6 ma n 13 in agreement with the isochron regression of 187os vs 187re the re os age 262 ma for the cihai fe deposit is within uncertainty in agreement with a previously reported rb sr age 268 25 ma of the hosting diabase indicating a genetic relationship between magmatism and mineralization magnetite from the cihai deposit has mg al ti v cr co ni mn zn ga and sn more elevated than that of typical skarn deposits but both v and ti contents lower than that of magmatic fe ti v deposits magnetite from these two ore clusters at cihai has slightly different trace element concentrations magnetite from the cihai ore cluster has relatively constant trace element compositions some magnetite grains from the cixi ore cluster have higher v ti and cr than those from the cihai ore cluster the compositional variations of magnetite between the ore clusters are possibly due to different formation temperatures combined with regional tectonic evolution of the beishan terrane the re os age of pyrite and the composition of magnetite indicate that the cihai fe deposit may have derived from magmatic hydrothermal fluids related to mafic magmatism probably in an extensional rift environment

domainal failure of serpentinite in shear zones state line mafic complex pennsylvania u s a abstract deformation within 0 2 1 4 km wide dextral strike slip shear zones in the serpentinite portion of the state line mafic complex pennsylvania maryland is partitioned into two types anastomosing throughgoing mylonitic faults experienced a long relatively simple deformational history of unidirectional dextral transcurrent shearing the relatively less deformed lenticular shaped areas between these faults deformed in a complex sequence of faulting the lenticular pods contain early e striking extensional veins and brittle reverse faults with north strikes northeast striking dextral strike slip faults deformed the veins and reverse faults east striking shear bands developed in both the throughgoing faults and the mylonitic dextral faults within the lenticular pods northwest striking sinistral strike slip faults transected the lenticular pods and earlier faults the sinistral mylonites formed shear bands late in their movement history a similar sequence of faulting occurred in microscopic lenticular pods within mylonitic serpentinite these faults exhibit the same orientation and sequence as their larger counterparts but are clearly not synchronous with them each lenticular pod may have acted as a separate system and therefore like faults between pods of any size may not have been synchronous

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

crustal contamination and sulfide immiscibility history of the permian huangshannan magmatic ni cu sulfide deposit east tianshan nw china abstract the huangshannan mafic ultramafic intrusion is a permian ni cu sulfide bearing intrusion in the southern margin of the central asian orogenic belt the intrusion consists of an ultramafic unit which is composed of lherzolite and olivine websterite and a mafic unit which is composed of olivine gabbronorite gabbronorite and leuco gabbronorite this intrusion was formed by two separate pulses of magma a more primitive magma for the early ultramafic unit and a more evolved magma for the late mafic unit u pb isotope geochronology of zircon from the mafic unit yields an age of 278 2 ma according to its olivine and cr rich spinel compositions the estimated parental magma of lherzolite for the huangshannan intrusion has 12 4 wt mgo indicating picritic affinity fractional crystallization modeling results and the presence of rounded sulfide inclusions in an olivine crystal fo 86 7 indicate that sulfide immiscibility was achieved at the beginning of olivine fractionation co magmatic zircon crystals from gabbronorite have a 18o value close to 6 5 which is 1 2 higher than the typical mantle value and suggests significant crustal contamination 20 the positive ehf t values of co magmatic zircon which vary from 9 2 to 15 3 and positive whole rock end t values which vary from 4 7 to 7 8 also indicate that the parental magma was derived from a depleted mantle source and contaminated by 5 20 juvenile arc crust and then by 5 upper crustal materials however modeling results of sulfur content at sulfide saturation reveal that such a large amount of crustal contamination is not sufficient to trigger sulfide saturation in the parental magma which strongly suggests that external sulfur addition probably during contamination has played a critical role in causing sulfide immiscibility furthermore the arc magmatism geochemical signatures of the huangshannan intrusion such as significant nb and ta depletion relative to la and low ca contents in olivine are interpreted as the result of slab derived fluid modification during previous subduction we speculate that the contamination of juvenile arc crust may have occurred in the lower crust because of picritic magma underplating and that partial melting in the mantle was triggered by the impingement of a mantle plume or lithosphere delamination in a post subduction environment

tectonic evolution of the south tianshan orogen and adjacent regions nw china geochemical and age constraints of granitoid rocks geochemical and geochronological evidence was obtained from granitoids of the south tianshan orogen and adjacent regions which consist of three individual tectonic domains the kazakhstan yili plate the central tianshan terrane and the tarim plate from north to south the central tianshan terrane is structurally bounded by the early paleozoic nikolaev line north nalati fault and late paleozoic atbashy inyl chek south nalati qawabulak fault zones against the kazakhstan yili and tarim plates respectively the meta aluminous to weakly peraluminous granitic rocks which are exposed along the kekesu river and the bikai river across the central tianshan terrane have a tholeiitic calc alkaline or high potassium calc alkaline composition i type geochemical trace element characteristics and the y versus rb nb or y versus nb discrimination diagrams favor a continental arc setting for these granitoid rocks shrimp u pb and la icp ms u pb zircon age data indicate that the magmatism started at about 480 ma continued from 460 to 330 ma and ended at about 275 ma the earlier magmatism 470 ma is considered to be the result of a simultaneous southward and northward subduction of the terskey ocean beneath the northern margin of the tarim plate and the kazakhstan yili plate respectively the later magmatism 460 330 ma is related to the northward subduction of the south tianshan ocean beneath the southern margin of the kazakhstan yili central tianshan plate the dataset presented here in conjunction with previously published data support a late paleozoic tectonic evolution of the south tianshan orogen not a triassic one as recently suggested by shrimp u pb zircon dating for eclogites

magma generation and sulfide saturation of permian mafic ultramafic intrusions from the western part of the northern tianshan in nw china implications for ni cu mineralization compared to permian magmatic ni cu sulfide deposits in the eastern part of the northern tianshan such as huangshan and huangshandong those in the western part e g baixintan and lubei are poorly documented zircon id tims u pb age data 279 7 0 2 ma of lherzolite and la icpms u pb age data 277 8 3 4 ma of a hornblende gabbro suggest the lubei intrusion was emplaced in the early permian the baixintan and lubei mafic ultramafic intrusive rocks are characterized by enrichments of large ion lithophile elements and th and u relative to the high field strength elements as well as depletion of nb and ta relative to mid ocean ridge basalt the 87sr 86sr t 0 70354 0 70713 end t 2 80 to 7 05 and ehf t 2 50 18 4 values for the intrusions indicate that they have assimilated tianshan basement rocks whereas the se s ratios 181 10 6 418 10 6 and 34scdt values 0 13 to 0 90 of the sulfides suggest that crustal sulfur has not been incorporated into the magma the decrease in pd zr with increasing th nb pm indicates that sulfide saturation accompanied crustal contamination the olivine compositions and whole rock chalcophile elements of the baixintan and lubei intrusions imply that the parental magma of the intrusive rocks in the west contains higher chalcophile elements than those in the east which suggests that the mafic ultramafic intrusions in the western part of the northern tianshan should be regarded as favorable ni cu sulfide exploration targets

the early permian mafic ultramafic complexes in the beishan terrane nw china alaskan type intrusives or rift cumulates abstract the petrogenesis and geodynamic setting of the early permian mafic ultramafic complexes in the beishan terrane nw china have important bearing on the prospects of ni cu pge sulfide and ti fe oxide deposits as well as in understanding the history of evolution of the southern central asian orogenic belt caob here we present results from a detailed study on a representative suit of a mafic ultramafic rocks from the bijiashan complex in the beishan terrane the complex is composed of dunite troctolite olivine gabbro and gabbro without clinopyroxenite or hornblendite in addition to olivine and clinopyroxene orthopyroxene and plagioclase are also present in all these rock types in the absence of chromite or primary hornblende the minerals display marked compositional variations with the fo content in olivines ranging from 66 to 83 and the clinopyroxenes ranging from diopside to augite the whole rock geochemistry shows good correlations among the major elements and the trace elements are characterized by flat ree patterns with eu positive anomalies and hfse depletion relative to lile these features are comparable to other mafic ultramafic complexes in the beishan and eastern tianshan terranes but obviously deviate from the typical features of alaskan type intrusives the present study suggests that the beishan complexes were formed in a post orogenic extensional environment with potential for ni cu mineralization rather than in arc related setting with alaskan type pge mineralization our study confirms that the beishan area does not conform to an arc related setting but was located within a rift setting in permian probably related to permian mantle plume event suggesting that the subduction of the paleo asian ocean had culminated by this time and the southern caob witnessed a post orogenic extensional regime in late paleozoic

genesis of permian granites along the kangguer shear zone jueluotage area northwest china geological and geochemical evidence abstract permian mafic and felsic intrusions occur along the kangguer shear zone ksz in the jueluotage area eastern tianshan northwest china this study focuses on the permian felsic intrusions 288 276 2 ma systematic geological and geochemical investigations show that granite plutons in the western ksz dikan guandao and hongshi have lower al and higher alkali contents than those in the eastern ksz longdong huangshan and baishandong the western granite plutons experienced higher degrees of crystal fractionation than the eastern granite plutons both of the western and eastern permian granite intrusions along ksz were derived from juvenile crust the nd pb isotopic characteristics of which exhibit mixed compositions of dm and emii type mantles both of the western and eastern permian granites along ksz were formed within post collision background the dikan guandao and hongshi plutons in the west ksz sector were formed in an extensional tectonic setting whereas the longdong huangshan and baishandong plutons in the east ksz formed in a compressional tectonic setting

re os geochronology on sulfides from the tudun cu ni sulfide deposit eastern tianshan and its geological significance the tudun deposit is a medium sized cu ni sulfide deposit located at the westernmost edge of the huangshan jing erquan belt in the northern part of eastern tianshan nw china sulfide separates including pentlandite pyrrhotite and chalcopyrite from the tudun deposit contain re common os and 187os ranging from 40 46 to 201 2 0 8048 to 6 246 and 0 1709 to 0 9977 ppb respectively they have very low 187os 188os ratios of 1 224 2 352 the sulfides yield a re os isochron age of 270 0 7 5 ma mswd 1 3 consistent within uncertainty with the shrimp zircon u pb age for the tudun mafic intrusion gabbro of 280 0 3 0 ma the calculated initial 187os 188os ratio is 0 533 0 022 and os values range from 283 to 307 with a mean of 297 indicating significant crustal contamination of the parent melt prior to sulfide saturation the tudun deposit shares the same age and re os isotopic compositions with other orthomagmatic cu ni sulfide deposits in huangshan jing erquan belt suggesting that they have formed in early permian

a modified genetic model for the huangshandong magmatic sulfide deposit in the central asian orogenic belt xinjiang western china the huangshandong ni cu deposit is the largest magmatic sulfide deposit discovered to date in the central asian orogenic belt in northern xinjiang western china the host intrusion is a 274 ma composite mafic ultramafic intrusion consisting of four separate intrusive units a large layered gabbroic sequence phase i a sheet like ultramafic body phase ii a dyke like gabbronorite body phase iii and an irregular ultramafic unit phase iv important sulfide mineralization is present in the last three intrusive units predominantly as disseminated and net textured sulfides pyrrhotite pentlandite and chalcopyrite the huangshandong mafic ultramafic intrusive rocks are characterized by arc like geochemical signatures such as low ca content in olivine and negative nb ta anomalies in whole rocks this together with a post subduction setting for the east tianshan in the permian suggests that the source mantle was modified previously by slab derived fluids in the carboniferous the mantle derived magma was ponded in a staging chamber in the lower part of the newly formed arc crust the first batch of magma to arrive at huangshandong was most fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo67 300 ppm ni the second batch of magma was more primitive crystallizing more primitive olivine fo81 84 the third batch of magma was also highly fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo72 600 ppm ni the final batch of magma became more primitive again crystallizing the most primitive olivine fo81 86 the occurrence of rounded sulfide inclusions in olivine primocrysts in the huangshandong ultramafic rocks indicates that immiscible sulfide liquid droplets were present during olivine crystallization the ni tenors of disseminated sulfide ores in the gabbronorite dyke vary mainly between 5 and 8 wt which are too high to have been produced by the parental magma of the dyke the ni cu and platinum group elements pge tenors of disseminated sulfide ores in the dyke phase iii and the ultramafic sheet phase ii are remarkably similar these observations together with the sequence of magma emplacement suggest that the sulfide liquids entrapped in the magma of the dyke formed at depth by a previous pulse of more primitive magma the estimated parental magma for the most primitive lherzolites in the huangshandong intrusion contains 10 wt mgo modeling shows that sulfide saturation in the parental magma of the huangshandong lherzolites could have resulted from fractional crystallization significant pge depletions relative to ni and cu in the disseminated sulfide ores of the huangshandong deposit may be due to sulfide retention in the source mantle

sulfide saturation mechanism of the poyi magmatic cu ni sulfide deposit in beishan xinjiang northwest china abstract the poyi cu ni deposit is hosted by the early permian pobei mafic ultramafic complex along the northern margin of the tarim plate this series of multiple intrusions in the poyi deposit can be divided into four lithologies gabbro dunite hornblende peridotite and wehrlite the ore body consists mainly of disseminated sulfides hosted by hornblende peridotite all the poyi deposit sulfides show positive 33 s values from 0 004 to 0 221 and negative 34 s values from 0 8 to 3 5 high ni contents occur in the hornblende peridotites which exhibit the highest 33 s value of 0 221 and the lowest 34 s value of 3 5 indicating contamination by sulfides from archean sedimentary rocks this contamination was important during sulfide saturation in the poyi intrusions and likely occurred at depth before the emplacement of the poyi intrusions the intrusions incorporated country rocks during their emplacement and consolidation and the degree of assimilation increases from the central lithofacies i e the hornblende peridotite to the marginal lithofacies i e the wehrlite dunite olivine gabbro and gabbro higher ni contents are correlated with lower degrees of contamination thus we infer that the contamination by the country paleoproterozoic rocks which contain significant amounts of gneiss and marble hindered sulfide saturation the whole rock ni content is negatively correlated with the mgo and fo contents in the olivine and positively correlated with the feo and mno contents in the olivine during crystallization olivine becomes gradually richer in feo but poorer in mgo and mn tends to be enriched in the late stages of the melt we infer that the fractional crystallization of olivine was an important factor during sulfide saturation

the collision between the yili and tarim blocks of the southwestern altaids geochemical and age constraints of a leucogranite dike crosscutting the hp lt metamorphic belt in the chinese tianshan orogen article i nfo a ca 600 m long 0 5 20 m wide nw se trending granite dike crosscuts the high pressure low temperature hp lt tianshan metamorphic belt the foliation of which is parallel to the main ene regional trend in the chinese south tianshan orogen it is mainly composed of plagioclase k feldspar quartz muscovite biotite and secondary chlorite while fluorite zircon and xenotime occur as accessories the immediate country rock is a quartz biotite plagioclase schist which grades several tens of meters away from the granite dike into a chlorite mica albite schist the latter schist is intimately intercalated with blueschist layers and boudins the a cnk value of the granite dike samples varies from 1 15 to 1 27 indicating a strongly peraluminous composition cao na2o ranges from 0 06 to 0 17 and al2o3 tio2 from 240 to 525 similar to the ratios of strongly peraluminous sp granites exposed in high pressure collision zones such as the himalayas a zircon u pb age of 285 ma was obtained for the granite dike thus constraining the upper limit for the age of hp lt metamorphism the petrological and geochemical data suggest that the sp leucogranite dike intruded during the exhumation of overthickened crust in the post collisional setting between the yili central tianshan and tarim blocks the dataset presented here in conjunction with previously published data corroborate that the hp lt metamorphism must have occurred earlier than the permian in the tianshan orogen therefore the collision between the yili central tianshan and tarim blocks and the final amalgamation of the southwestern altaids must have been terminated in late paleozoic and not in triassic times as previously suggested

shear zone controlled post magmatic ore formation in the huangshandong ni cu sulfide deposit nw china abstract the huangshandong ni cu sulfide deposit located in the kangguer jing erquan ductile shear zone belongs to the jueluotage island arc belt in eastern tianshan of the central asian orogenic belt the huangshandong mafic ultramafic pluton which has a fusiform shape is believed to have intruded strongly foliated late carboniferous volcanic rocks during the development of the regional ductile shear zone some orebodies in the deposit show intense ductile deformation among them the no 17 orebody is entirely controlled and hosted by the ductile shear zone host rocks and ores from this orebody show intense deformation and alteration and could be called ore mylonites furthermore numerous anastomosing veinlets can be observed in copper rich carbonate sulfide veins in the ductile shear zone geological field investigation and ore petrography studies indicate that sulfide ores at huangshandong are composed of three types undeformed magmatic ores deformed magmatic ores and hydrothermal overprinted ores magmatic ores with net fabrics remain unaltered and undeformed and sulfide minerals in them show only brittle fractures silicate and sulfide minerals in deformed magmatic ores are characterized by intense deformation fabrics examples for such fabrics are kink bands wavy extinction of uralite domino structure of phlogopite and elongated grains of pyrrhotite and pentlandite hydrothermal overprinted ores are characterized by strong deformation flattened grains and recrystallization of pyrrhotite moreover annealing of pyrrhotite is frequently observed pyrrhotite pentlandite and chalcopyrite in hydrothermal overprinted ores have high ni and co concentrations in pyrrhotite a higher ni concentration in pentlandite and high ag and cd concentrations respectively we attribute ni and co in fluid overprinted ores mainly to the alteration of olivine and the dissolution of primary chalcopyrite is the likely source of copper in chalcopyrite rich hydrothermal overprinted ores during the intruding and cooling of the huangshandong pluton intense regional ductile shearing caused the ductile deformation of sulfide ores in the deposit and subsequently ore mylonites were formed gangue minerals in the deformed orebodies were crushed to fine grained minerals and altered to serpentine chlorite and uralite during these processes fluid and ore elements were released and reacted with deformed rocks and ores forming anastomosing veinlets on hydrothermal overprinted ores

geochronological and geochemical study of the darbut ophiolitic complex in the west junggar nw china implications for petrogenesis and tectonic evolution abstract the darbut ophiolitic complex consists of ultramafic rocks cumulates pillow lavas and abyssal radiolarian cherts and occurs in the sartuohai suluqiaoke area which is situated in the eastern part of the west junggar nw china southern altaids in the present study we report new geochronological and geochemical data obtained for gabbro and basalt blocks embedded in the darbut ophiolitic complex zircon u pb analyses from one representative gabbro sample by la icp ms yielded a weighted mean age of 391 6 ma showing that it was emplaced in the middle devonian the samples bear n morb e morb and arc like geochemical signatures they are tholeiitic in composition with low concentrations of na 2 o k 2 o varying from 1 36 to 4 09 wt mg and ti depleted large ion lithophile elements liles enriched with insignificant negative eu they also show negative nb ta anomalies and high positive e nd t values with relative high la nb ba nb ba la ba th and zr nb ratios we interpret that these volcanic rocks were derived from a slightly metasomatized depleted mantle source in a back arc basin setting which corresponds to 10 30 partial melting of a depleted spinel lherzolite mantle the data presented here in combination with previously published data suggest a northwestward subduction model for the west junggar during the period of the early devonian to early carboniferous the west junggar was dominated by normal northwestward subduction and the ridge subduction commenced in the late carboniferous

tectonic evolution from subduction to arc continent collision of the junggar ocean constraints from u pb dating and hf isotopes of detrital zircons from the north tianshan belt nw china the junggar ocean once situated north present coordinate of the yili and central tianshan blocks during early paleozoic to late carboniferous time was a major southern branch of the paleo asian ocean the opening expansion and final closure of which led to the development of the central asian orogenic belt between eastern europe siberia and tarim north china however the detailed evolution of the junggar ocean has not been well constrained this paper reports u pb and lu hf isotopic data of detrital zircons from sandstones in the north tianshan belt which can provide new insights into understanding the paleozoic development of the junggar ocean most detrital zircons exhibit oscillatory zoning and high th u ratios typical of igneous origin the predominant paleozoic zircons yield major age populations at ca 294 313 327 338 375 440 455 and 474 502 ma and are interpreted to have been derived from the long lived volcanic and island arc systems formed by the southward subduction of the junggar ocean and subsequent collisional and postcollisional magmatism the minor precambrian zircons yield ages scattering at ca 550 680 765 890 970 990 1160 1250 1500 1690 1750 1840 1970 2440 2500 and 2615 2700 ma which are nearly but not fully congruent with those from the adjacent beishan and kuluketage precambrian terranes therefore our results indicate that the central tianshan block was once part of the tarim block during precambrian time most of the 541 440 ma zircons possess low negative ehf t values while the 440 300 ma zircons exhibit dominantly positive ehf t values which can be linked to the junggar oceanic slab rollback since ca 440 ma this event subsequently gave rise to the opening of the south tianshan back arc basin ocean between the central tianshan and tarim blocks exhumation of high pressure granulites and formation of a series of island arcs in the junggar ocean combined with previous studies we suggest that the junggar ocean was probably closed at ca 300 ma in association with arc continent collision followed by postcollisional magmatism it deserves mentioning that the ca 0 5 and 1 4 1 5 ga detrital zircons and contemporaneous magmatic rocks only occur in the central tianshan block not in the tarim block therefore more detailed investigations are needed to better elucidate the origin and precambrian evolution of the central tianshan block

the most ancient ophiolite of the central asian fold belt u pb and pb pb zircon ages for the dunzhugur complex eastern sayan siberia and geodynamic implications abstract ophiolitic rocks with a zircon age of 1020 ma occur in the dunzhugur complex of east sayan siberia and are part of a neoproterozoic to early palaeozoic segment of the central asian fold belt the most spectacular suite is exposed along the oka and bokson rivers where a complete ophiolite sequence with mantle tectonites a layered sequence composed of dunite wehrlite and pyroxenite a gabbro section a sheeted diabase dyke complex and basaltic pillow lavas are exposed petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic ultramafic crustal section and support a supra subduction zone setting in a fore arc rifting environment for its origin two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean 207pb 206pb age of 1020 10 ma evaporation of three additional fractions of three to four grains each from the same sample produced a mean 207pb 207pb age of 1019 9 0 7 ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite this is the oldest ophiolite so far dated from the central asian fold belt the southern margin of the siberian craton and the palaeo asian ocean were established at the end of the mesoproterozoic at least 1000 ma ago during the time interval 1000 570 ma one or several large ocean basins existed between baltica siberia kazakhstan tarim and northern china and these blocks are therefore unlikely to have been part of the supercontinent rodinia rifting initiation of subduction and marginal basin formation began prior to 1000 ma and continued through 570 ma the dunzhugur ophiolite of eastern sayan provides evidence for the early opening of the palaeo asian ocean not later than 1000 ma ago

geochemistry and geochronology of carboniferous volcanic rocks in the eastern junggar terrane nw china implication for a tectonic transition the carboniferous tectonic setting of the junggar terrane northern xinjiang nw china has long been a matter of debate voluminous carboniferous volcanic rocks are widely distributed in the karamaili area the southern part of the eastern junggar terrane early carboniferous rocks comprise basalts and basaltic andesites with enrichment of lree and lile and depletion of hfse and uniformly high end t 3 7 to 4 0 late carboniferous rocks consist of basalts basaltic andesites rhyolites and minor dacites and can be subdivided into basic and felsic groups the basic rocks are depleted in hfse and show variable high end t 4 8 to 6 9 they have higher cr and ni and lower na2o u and th contents than early carboniferous basic rocks the felsic rocks show a type affinity with typical enrichment of alkalis lree and hfse and strong depletion in ba sr eu and ti they have high values of end t and zircon ehf t 11 6 to 17 9 new la icpms zircon u pb analyses constrain their emplacement to late carboniferous time 306 5 314 3 ma the carboniferous basic rocks show negative zr hf anomalies and low th ce 0 07 and th la 0 06 0 16 excluding significant crustal contamination during magma evolution they have low la ba 0 03 0 12 ce y 3 and tb yb n 2 and variable ba th 28 318 and ba la 3 1 34 suggesting that they were derived from a main spinel with minor garnet lherzolite mantle source metasomatized by slab derived fluids the late carboniferous felsic rocks were produced when upwelling asthenosphere triggered partial melting of juvenile lower crust the early carboniferous volcanism occurred in an island arc setting related to the southward subduction of the paleo junggar ocean plate whereas the late carboniferous rocks erupted in a post collisional extensional setting thus a rapid tectonic transition from arc to post collisional extension may have occurred between early and late carboniferous and probably resulted from slab break off or lithospheric delamination

decoupling of whole rock nd hf and zircon hf o isotopic compositions of a 284 ma mafic ultramafic intrusion in the beishan terrane nw china abundant permian mafic ultramafic intrusions in the beishan terrane nw china are parts of the tarim large igneous province among these intrusions luodong intrusion is composed of dunite wehrlite and gabbro these rocks have whole rock sr nd hf and zircon hf o isotope compositions that display significant decoupling the decoupling of these generally well correlated systems demonstrates contrasting evolving trends systematic compositional and mineralogical controls on decoupling have been investigated wehrlites and gabbros show morb like trace element patterns with negligible crustal contamination they have high initial 143nd 144nd end t 6 6 to 11 2 and 176hf 177hf ehf t 12 2 to 16 9 and low initial 87sr 86sr 87sr 86sr i 0 702949 0 704098 ratios and plot within the morb field indicating that their parental magmas were derived from a depleted mantle source the enrichment features are present in the zircon crystals separated from the gabbro these homogeneously unzoned zircon crystals have high u concentrations low th u ratios and a u pb age of 284 0 2 3 ma they are therefore interpreted as having formed rapidly in a highly fractionated evolved magma their ehf t and 18o values range from 9 3 to 6 7 and 10 25 to 11 42 respectively the decoupling is linked with crustal contamination by ancient crust probably proterozoic schist in the beishan terrane that occurred during zircon crystallization however the contamination signature in the whole rock composition was soon overprinted by magma mixing process the inference is evidenced by zoning textures preserved in plagioclase clinopyroxene spinel and particularly olivine and the presence of coeval diabase dykes cutting through the intrusion the isotope decoupling observed in this mantle plume related mafic ultramafic intrusion supports the idea that nd hf decoupling and lu hf and sm nd parent daughter variations exist only on a small hand size scale in a particular growth environment and prevailing kinetics

whole rock geochemistry and sr nd pb isotope systematics of the late carboniferous volcanic rocks of the awulale metallogenic belt in the western tianshan mountains nw china petrogenesis and geodynamical implications abstract the awulale metallogenic belt amb of the western tianshan nw china includes late carboniferous ca 320 ma ore bearing volcanic rocks of the dahalajunshan formation the petrogenesis and tectonic setting of these volcanic rocks are important for the understanding of the tectonic evolution and metallogeny of the western tianshan this paper presents new major and trace elements and sr nd pb isotope data from the dahalajunshan volcanic rocks which are mainly calc alkaline basaltic trachy andesite and trachy andesite with subordinate basalt trachy basalt and rhyolite the variations of major and trace elements in the mafic and intermediate volcanic rocks indicate the fractionation of pyroxene and magnetite or hornblende magnetite apatite and plagioclase respectively during their petrogenesis the dahalajunshan volcanic rocks have similar primitive mantle normalized diagrams and chondrite normalized rare earth element ree patterns suggesting their similar mantle source s they are characterized by enrichment in large ion lithophile elements liles and light rees lrees depletion in heavy rees lan ybn 2 80 to 9 59 and high field strength elements hfses and end t ranging from 1 2 to 6 0 at 86sr 87sr t 0 7047 0 7063 and 206pb 204pbi 17 49 18 19 both the geochemical and isotopic data indicate that the volcanic rocks were probably derived by low degree melting of sub arc lithospheric mantle modified by fluids in a continental arc setting our obtained results in conjunction with previous published data allow us to suggest that the southward subduction of junggar oceanic crust continued until the late carboniferous and was followed by a tectonic shift from continental arc to post collisional extension environment

zircon dating hf sr nd os isotopes and pge geochemistry of the tianyu sulfide bearing mafic ultramafic intrusion in the central asian orogenic belt nw china abstract the tianyu mafic ultramafic intrusion is one of many important sulfide bearing mafic ultramafic intrusions in the eastern tianshan terrane located in the southern margin of the central asian orogenic belt in north xinjiang nw china the origin of sulfide mineralization in these intrusions their relationship with permian basalts and a type granites and the geodynamic setting of the bimodal magmatism in the region are controversial in this paper we use zircon u pb age hf sr nd os isotope and lithophile chalcophile trace element constraints from the tianyu mafic ultramafic intrusion to address these important issues the u pb age of zircon from the tianyu intrusion determined by sims is 280 2 ma this confirms that the tianyu intrusion is coeval with most sulfide bearing mafic ultramafic intrusions and some basalts and a type granites in the tianshan region similar to coeval basalts in the nearby tuha basin the tianyu intrusive rocks are characterized by negative nb anomaly and elevated end values varying between 1 and 4 6 the negative nb anomaly in the tianyu intrusion is not as pronounced as in the coeval a type granites but the end values for these bimodal rocks are similar the ehf values of zircon from the tianyu intrusion are positive varying between 3 and 8 these values suggest that the parental magma of the tianyu intrusion was dominated by melt derived from a depleted source mantle the os values of pyrrhotite from the tianyu intrusion are high ranging from 725 to 995 which can be modeled by selective assimilation of sulfide from the lower and upper crusts negative pt anomaly is present in relatively sulfide rich samples such as semi massive and massive sulfide ores but not in sulfide poor samples which is more consistent with the effect of post magmatic hydrothermal alteration than the original signature of the parental magma the results of modeling using the compositions of selected disseminated sulfide samples suggest that the parental magma of the tianyu intrusion was depleted in all pge which is consistent with previous sulfide segregation at depth our data and modeling results support the model of decompression melting of upwelling asthenosphere due to slab break off during a transition from oceanic subduction to arc arc or arc continent collision in the permian decompression melting of the upwelling asthenosphere in the region produced mafic magma partial melting in the lower parts of a juvenile arc crust due to mafic magma underplating produced granitic melts mixing of the mafic magma with a small amount of granitic melts at depth followed by contamination with the upper crust at a higher level formed the parental magma of the tianyu intrusion pge depletion in the parental magma of the tianyu intrusion can be attributed to sulfide segregation associated to the first stage of crustal contamination at depth we suggest that the formation of sulfide ores in the intrusion was related to the second stage of crustal contamination in the upper crust

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

skarn mineralized porphyry adakites in the harlik arc at kalatage e tianshan nw china slab melting in the devonian early carboniferous in the southern central asian orogenic belt abstract the geodynamic control of mineralization in the accretionary evolution of the central asian orogenic belt caob has long been controversial here we report new field geochemical and geochronological data on recently defined porphyry and skarn type ore deposits devonian early carboniferous in the kalatage area in the middle of the harlik dananhu arc eastern tianshan nw china in the southern caob with the aim of better understanding the accretionary tectonics and genesis of porphyry and skarn type mineralization the yudai porphyry cu au deposits and the xierqu skarn cu fe au deposits are closely associated with middle devonian adakitic diorite porphyries 382 390 ma which are calc alkaline and characterized by high na2o k2o ratios and sr contents 310 1020 ppm strong depletion of hree e g yb 0 80 1 44 ppm and y 7 68 14 50 ppm and all enriched in rb sr ba k and depleted in nb and ti they are characterized by distinctive eu positive anomalies high na2o contents and morb like sr and nd isotope signatures high end t 6 1 to 7 0 and low 87sr 86sr i 0 70412 0 70462 these adakites most likely formed by melting of a young hot subducted oceanic slab and adakites in general are important carriers of porphyry cu au deposits early carboniferous adakites in the tuwu area south of kalatage are known to have similar features therefore skarn mineralized porphyry adakites get younger from north to south suggesting southward migration of the harlik dananhu arc from 390 ma to 322 ma these data indicate that partial melting of hot and or young oceanic crustal slabs were an important mechanism of accretionary crustal growth and mineralization in the southern caob

geochemistry of silurian devonian volcanic rocks in the coastal volcanic belt machias eastport area maine evidence for a pre acadian arc the coastal volcanic belt in easternmost maine consists of silurian devonian volcanic rocks related to the convergence of avalonia with the leading edge of composite laurentia just before and during early stages of the acadian orogeny new major and trace element analyses from the machias eastport area indicate that the early to late silurian volcanic rocks in the dennys edmunds and leighton formations formed in a continental arc environment in contrast to some earlier interpretations these rocks have a continuous compositional range from basalt through andesite to rhyolite the mafic rocks in these formations are calc alkaline and show subduction related geochemical signatures on various discrimination diagrams whereas the felsic rocks have geochemical characteristics of volcanic arc granites in contrast the thick volcanic deposits of the younger late silurian eastport formation are bimodal and tholeiitic and have transitional to within plate geochemical signatures thus the transition over time as the acadian seaway closed from subduction and arc settings to continental extension can been seen in this rock sequence and it constrains the time of avalonia s docking regionally volcanic rocks in the kingston terrane of southern new brunswick are likely correlatives of the earlier arc volcanic rocks dennys edmunds and leighton formations while eastport formation analogues are found in the coastal maine magmatic province cranberry island series and probably the passamaquoddy bay volcanic series which similarly appear to have formed after the transition to an extensional environment occurred although other extensional settings cannot be entirely ruled out basalts in the post acadian perry formation indicate continental extension was also active in the late devonian

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

origin and emplacement of the aguablanca magmatic ni cu pge sulfide deposit sw iberia a multidisciplinary approach a model is proposed for the origin and emplacement of the ca 341 ma aguablanca magmatic ni cu platinum group element pge sulfi de deposit sw iberia integrating petrological geochemical structural and geophysical data the aguablanca deposit occurs in an unusual geodynamic context for this ore type an active plate margin as an exotic magmatic subvertical breccia located at the northern part of the coeval gabbronorite aguablanca stock 341 1 5 ma structural and gravity data show that mineralized breccia occurs inside the inferred feeder zone for the stock adjacent to the cherneca ductile shear zone a variscan sinistral transpressional structure the orientation of the feeder zone corresponds to that expected for tensional fractures formed within the strain fi eld of the adjacent cherneca ductile shear two distinctive stages are established for the origin and emplacement of the deposit 1 initially the ore forming processes are attributed to magma emplacement in the crust assimilation of crustal s and segregation and gravitational settling of sulfi de melt a scenario similar to most plutonic ni cu sulfi de ores and 2 fi nal emplacement of the ni cu sulfi de bearing rocks by multiple melt injections controlled by successive opening events of tensional fractures related to the cherneca ductile shear zone

the origin of alpine peridotite hosted cross fiber chrysotile asbestos deposits cross fiber chrysotile asbestos deposits within serpentinized alpine type peridotites are syntectonic the asbestos veins fill tension fractures induced by regional stress fields moderated by local structural heterogeneities inverting this process by measuring the orientation of the veins yields the regional stress regime at the time the veins were formed measurements at several asbestos mines cassiar mine british columbia thetford mines quebec and woodsreef mine new south wales suggest that the asbestos develops during a change in the orientation of the regional stress which appears kinematically as a change from dip slip to strike slip fault motion this interpretation is compatible with other independent sets of structural data several factors determine whether or not an asbestos deposit is developed first the serpentinite must have a nonfoliated texture mineralogy does not appear to be important second it must be situated near a fault that is active during a change in the orientation of the stress field third the serpentinite must be in the stability field of chrysotile when the change in orientation occurs last subsequent deformation must not continue or temperature increase such that the fiber is destroyed

late paleozoic mafic ultramafic intrusions in southern central asian orogenic belt nw china insight into magmatic ni cu sulfide mineralization in orogenic setting abstract the mafic ultramafic intrusions hosting magmatic ni cu sulfide ore deposits usually present within the precambrian cratons and on their margin have been extensively studied whereas those occurring within the phanerozoic orogenic belts have received little attention the southern margin of the central asian orogenic belt is a region of late paleozoic mafic ultramafic intrusions emplaced during post orogenic stage in order to recognize the mineralization features this study compares barren or weakly mineralized mafic ultramafic intrusions in the beishan with those hosting ni cu sulfide ore deposit in the altay and eastern tianshan in petrology mineralogy and geochemistry aspects several mineralization features can be recognized with respects to petrology mineralogy and geochemistry from comprehensive comparisons among the mineralization indicators we highlight strong alteration accompanying sulfide emplacement post erosion exposure of magma conduit abundant primary hydrous minerals and potential transportation mechanism of ore forming elements other indicators are the presence of orthopyroxene and pyroxenite for potential sulfide formation through crystal fractionation restricted fo and ni ranges in olivines for sulfide segregation and some other special geochemical characteristics related to crustal contamination the variation in mineralization could be ascribed to different degrees of partial melting crustal assimilation and subduction related modification of a mantle source we suggest that the ni cu sulfide mineralization of mafic ultramafic intrusions within orogenic belts is remarkably different from that of cratonic and continental marginal settings in respects of petrogenesis and mineralizing mechanism magmatic conduit type ni cu sulfide ore deposit is a target for future prospecting and exploration for mafic ultramafic intrusions in the orogenic belts

late paleozoic post collisional magmatism in the eastern tianshan belt northwest china new insights from geochemistry geochronology and petrology of bimodal volcanic rocks abstract the late carboniferous to permian marks an important phase of terrane amalgamation through accretion collision in the central asian orogenic belt caob the tianshan belt forms part of this sequence where the post collisional event generated an e w trending bimodal volcanic zone that extends for ca 500 km from the southern bogda mt to the easternmost tianshan belt here we report the petrology geochemistry and geochronology of the bimodal volcanic rocks to characterize the post collisional tectonic evolution in late paleozoic the major element chemistry of the basalt and rhyolite samples indicates a bimodal high k calc alkaline affinity the basalts are characterized by high abundance in tio2 th u and pb and depletion in nb ta and p together with slight enrichment in lree contents and low hfse lree ratios the rhyolites show a close affinity to aluminous a type granites with enrichment in k na zr ce y and depletion in p nb ta and ti they also exhibit fractionated ree patterns with prominent negative eu anomalies the petrographic and geochemical data suggest that this bimodal rock series was generated in a post collisional setting the mafic rocks are likely derived from a metasomatized lithospheric mantle assimilation of different crustal components played a minor role in the genesis of these basaltic rocks the la icp ms analysis on zircons from four rhyolites and two basalts yielded similar ages ranging from 295 8 2 8 to 293 3 1 7 ma suggesting an early permian event zircons from the basalts show a wide ehf t range from 0 49 to 13 whereas those from the rhyolites show two groups of ehf t values from 5 to 3 and from 6 to 12 suggesting a mixing of crust mantle material the magmatic zircons from the bimodal volcanic rocks yielded two peaks of tdm2 between 600 820 ma and 1160 1360 ma probably representing two significant episodes of continental crust growth the bimodal volcanic rocks are correlated with the early stage of post collision our results suggest that vertical crustal growth through mantle derived magmas in post collisional setting also played a major role in the construction of the caob

a non plume model for the permian protracted 266 286 ma basaltic magmatism in the beishan tianshan region xinjiang western china abstract the convenient mantle plume model for the permian protracted mafic ultramafic intrusions and mafic dykes 266 286 ma in the beishan tianshan region northern xinjiang western china can be rejected because their temporal spatial distribution does not show a hotspot track predicted by such model new zircon u pb ages reveal that two small mafic dyke clusters podong 280 5 2 ma luodong 266 2 3 2 ma that are separated by only 20 km in the pobei area the southernmost part of the beishan tianshan region have a large age difference of 18 ma the older mafic dykes are characterized by nearly flat mantle normalized rare earth element patterns pronounced negative nb ta anomalies and positive e nd t values from 5 5 to 7 5 similar to the majority of the permian mafic ultramafic intrusions in the region the younger mafic dykes are characterized by significant light rare earth element enrichments as well as pronounced negative nb ta anomalies plus lower e nd t 1 2 to 2 6 values and higher initial 87 sr 86 sr ratios than the older mafic dykes the observed compositional variations can be explained by source mantle heterogeneity plus different degrees of crustal contamination overall the permian mafic ultramafic rocks in the beishan tianshan region are geochemically consistent with the products of basaltic magmatism induced by lithospheric delamination and asthenosphere upwelling in a convergent tectonic zone

late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block constraints on the composition and evolution of the lithospheric mantle abstract the late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block ncb are used to constrain the isotopic composition and evolution of mantle reservoirs during different tectonic stages prior to the initiation of lithosphere destruction in the late mesozoic zircon u pb ages show that emplacement of the mafic ultramafic complexes occurred in at least three stages middle devonian ca 395 ma late carboniferous early permian 308 276 ma and triassic 250 220 ma most of the middle devonian complexes display low initial 87sr 86sr ratios of 0 70467 0 70492 weak to moderate negative end t values from 6 3 to 1 5 and weakly negative to weakly positive zircon ehf t values from 11 5 to 5 5 indicating that the parent magma was derived from slightly enriched lithospheric mantle the late carboniferous early permian complexes are characterized by low initial 87sr 86sr ratios of 0 70521 0 70604 significant negative end t values from 14 1 to 9 3 and zircon ehf t values from 17 0 to 10 5 and were probably derived from metasomatized lithospheric mantle the early triassic complexes exhibit initial 87sr 86sr ratios of 0 70656 0 70825 and significant negative end t values from 17 1 to 8 2 indicating their derivation from enriched lithospheric mantle however the late triassic mafic ultramafic complexes display weakly negative to weakly positive end t values of 4 4 to 0 5 and zircon ehf t values from 2 9 to 1 7 indicating that magma sources likely resulted from mixing of depleted asthenospheric mantle and enriched lithospheric mantle zircon ages geochemistry and sr nd hf isotopic studies suggest that the lithospheric mantle beneath the northern ncb had a slightly enriched signature during the middle devonian but it became significantly enriched during the late carboniferous to early permian due to metasomatism of lithospheric mantle during the southward subduction of the paleo asian oceanic plate after final closure of the paleo asian ocean and amalgamation of the mongolian arc terranes with the northern ncb in the latest permian to earliest triassic enriched lithospheric mantle still existed beneath the northern ncb during the early triassic however in the late triassic involvement of asthenospheric mantle became significant owing to strong upwelling of asthenospheric mantle and post collisional lithospheric delamination in the early late triassic these results suggest that the cratonic lithospheric mantle beneath the northern ncb underwent multiple stages of modification prior to its destruction and thinning initiation of lithospheric destruction and thinning in the northern ncb likely occurred during the early late triassic which is much earlier than in other parts of the ncb where it occurred in the late mesozoic it appears likely that lithospheric destruction and thinning of the ncb initially started at the northern and eastern margins of the craton as a result of post collisional lithospheric delamination and then spread to the interior of the craton

constraining the potential temperature of the archaean mantle a review of the evidence from komatiites the maximum potential temperature of the archaean mantle is poorly known and is best constrained by the mgo contents of komatiitic liquids which are directly related to eruptive temperatures however most archaean komatiites are significantly altered and it is difficult to assess the composition of the erupted liquid relatively fresh lavas from the saskmar suite belingwe greenstone belt zimbabwe 2 7 ga include chills of 25 6 wt mgo and olivines ranging to fo93 6 implying eruption at around 1520 c a chill sample from alexo township ontario also 2 7 ga is 28 wt mgo and associated olivines range to fo94 1 implying eruption at 1560 c however inferences of erupted liquids containing 32 33 wt mgo from lavas in the barberton greenstone belt south africa 3 45 ga and from the perseverance complex western australia 2 7 ga may be challenged on the grounds that they contain excess cumulate olivine or were enriched in mg during alteration or metamorphism re interpretation of olivine compositions from these rocks shows that they most likely contained a maximum of 29 wt mgo corresponding to an eruption temperature of 1580 c this composition is the highest liquid mgo content of an erupted lava that can be supported with any confidence the hottest modern magma on gorgona island 0 155 ga contained 18 20 mgo and erupted at circa 1400 c if 1580 c is taken as the temperature of the most magnesian known eruption then the source mantle from which the liquids rose would have been at up to 2200 c at pressures of 18 gpa corresponding to a mantle potential temperature of 1900 c these temperatures are in excess of the mantle temperatures predicted by secular cooling models and thus komatiites can only be formed in hot rising convective jets in the mantle this result requires that archaean mantle jets may have been 300 c hotter than the archaean ambient mantle temperature this temperature difference is similar to the 200 300 c temperature difference between present day jets and ambient mantle temperatures an important subsidiary result of this study is the confirmation that spinifex rocks may be cumulates and do not necessarily represent liquid compositions

geochronology geochemistry and petrogenesis of early permian alkaline magmatism in the eastern tianshan implications for tectonics of the southern altaids abstract in the early permian large volumes of volcanic rocks developed in the eastern tianshan of the southern altaids the shaerhu alkaline complex which occurs along a nw trending transcurrent fault in the dananhu arc is composed of alkaline gabbro intrusions granites and rhyolites the gabbros and rhyolites have similar zircon crystallization ages of 286 5 2 1 ma and 286 7 2 1 ma respectively the granitic and rhyolitic rocks have typical a type granite geochemical signatures i e high oxide ratios in wt k2o na2o k2o na2o cao k2o mgo and sio2 high trace element values zr nb ga ce y and ree and high zr ce y and 10 000 ga al ratios however spidergrams and ree patterns indicate major depletions in ba sr p ti and eu the presence of positive end t values of 7 0 to 11 2 and low 87sr 86sr i 0 70148 0 70416 indicates that these alkaline rocks were derived from a depleted mantle and not from old continental crust the geochemical characters indicate that the rocks of the complex have the same source and that fractionation was important in their generation a type granitic rocks are the most highly fractionated of alkaline basic rocks in summary the shaerhu complex is a product of mantle derived alkaline magma fractionation which is one of the main mechanisms of a type granite genesis the felsic rocks of the shaerhu complex have the geochemical signature of an a2 type granite and thus were not derived from a rift or mantle plume in the early permian oblique subduction in the southern altaids gave rise to strike slip extensional faults which controlled the emplacement of large volumes of mantle derived melts

geochronological and geochemical study of the baixintan magmatic ni cu sulphide deposit new implications for the exploration potential in the western part of the east tianshan nickel belt nw china abstract several newly discovered magmatic ni cu sulphide deposits are located in the east tianshan nickel belt in the southern part of the central asian orogenic belt in nw china the baixintan magmatic sulphide deposit is one of these new discoveries the host mafic ultramafic intrusion of the baixintan deposit is composed of plagioclase bearing lherzolite pl bearing olivine websterite olivine norite and gabbro zircon crystals from olivine norite yielded a u pb age of 286 0 1 6 ma similar to the ages of other magmatic ni cu sulphide ore deposits in this belt disseminated sulphide mineralization is present in olivine bearing rocks the fo and ni contents of olivine crystals from the sulphide barren samples vary from 81 7 to 85 6 mol and from 956 to 2837 ppm respectively exhibiting a positive fo ni correlation that is consistent with the fractional crystallization of olivine plus removal of small amounts of immiscible sulphide liquid the baixintan mafic ultramafic rocks are characterized by light ree enrichment pronounced negative nb ta anomalies low initial 87sr 86sr ratios from 0 7035 to 0 7039 positive end chur 286 ma values from 6 0 to 7 4 and zircon ehf chur 286 ma values from 11 6 to 15 8 these data indicate that the parental magmas were derived from a depleted mantle source with moderate degrees of contamination by the upper crust the variations in pge tenor in the baixintan deposit which are characterized by positive correlations between ipge and ppge can be explained by variable r factors r 400 3000 mass balance calculations indicate that the parental magma was severely depleted in pge which could be likely due to prior sulphide segregation at depth or sulphide retention in the mantle during partial melting both fractional crystallization and crustal contamination may have played a role in triggering second stage sulphide saturation in the baixintan magma the similarities in ages lithological controls and bulk sulphide composition between the baixintan deposit and other known magmatic ni cu sulphide ore deposits in the east tianshan nickel belt encourage further exploration in the baixintan mafic ultramafic intrusion as well as expansion of the on going regional ni exploration program

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

petrology and geochemistry of mafic ultramafic fragments from the aguablanca ni cu ore breccia southwest spain aguablanca southwest spain is the first economic ni cu pge deposit found in southern europe two features make it an unusual example of magmatic sulfide ore it is related to the development of an andean type continental magmatic arc and it is hosted by a subvertical magmatic breccia the structural style and the geodynamic context of the deposit contrast with most plutonic ni cu pge deposits elsewhere which occur at specific levels of layered mafic intrusions in rift environments the ni cu deposit is hosted by the aguablanca intrusion a mafic body composed of gabbronorite and minor quartz diorite gabbro and norite sulfides are concentrated in a gabbronorite matrix along a subvertical dip of 70 80 n funnel like magmatic breccia that contains barren or slightly mineralized ultramafic mafic cumulate fragments modal compositions of the fragments reflect a wide variety of rock types including peridotite hornblende rich werhlite dunite and hornblende rich harzburgite pyroxenite ortho and clinopyroxenite gabbro gabbro gabbronorite and hornblende gabbro and anorthosite the primary silicate assemblage includes olivine fo91 fo79 orthopyroxene mg no 0 85 0 73 clinopyroxene mg no 0 93 0 62 plagioclase an99 an38 amphibole mg no 0 87 0 68 and phlogopite mg no 0 89 0 64 the wide range of rock types and the fe enrichment trends in the primary ferromagnesian silicates suggest magmatic differentiation processes from the parent melts with the fragments representing different stages of cumulate formation the ore bearing breccia contains both semimassive and disseminated sulfides in the gabbronorite matrix textures vary between meso and orthocumulate and the rock forming magmatic silicates are orthopyroxene mg no 0 83 0 74 clinopyroxene mg no 0 89 0 78 plagioclase an50 an77 and intercumulus amphibole mg no 0 86 0 70 phlogopite 0 84 0 69 and minor quartz the gabbronorite in the matrix of the breccia is petrographically and chemically very similar to that of the unmineralized parts of the main aguablanca intrusion and exhibits a similar differentiation trend suggesting that the matrix of the ore bearing breccia and the unmineralized rocks belong to a same magmatic suite the local presence of mafic ultramafic fragments in the barren aguablanca intrusion supports this suggestion the presence of highly ni depleted olivine whole rock cu zr ratios below 1 and the local occurrence of disseminations of magmatic sulfides in the peridotite fragments point to sulfide segregation before and or during the formation of the peridotite cumulates mantle normalized incompatible trace element patterns of the fragments along with published sulfur isotope data are consistent with crustal contamination suggesting that addition of crustal sulfur from pyrite bearing black slates led to sulfide saturation these results support a model in which sulfides segregated and settled during the differentiation of an unexposed mafic ultramafic complex now sampled as fragments in the breccia whereas the overlying silicate magma most probably fed by successive fresh magma injections underwent fractional crystallization giving rise to this cumulate sequence the emplacement of the ore breccia took place at temperatures above the monosulfide solid solution mss solidus but below the olivine and pyroxene solidus likely owing to the explosive injection of a new pulse of magma into the chamber which mingled with the sulfide liquid and disrupted the overlying cumulate sequence as a consequence fragments reached their current position in the breccia injected along with the sulfide and the silicate melts which subsequently formed the sulfide rich gabbronorite

compositional variations of olivine and sulfur isotopes in the noril sk and talnakh intrusions siberia implications for ore forming processes in dynamic magma conduits olivine from the noril sk i main and northwestern talnakh ore bearing intrusions in the noril sk region occurs as inclusions discrete grains and poikilitic crystals the original compositions of olivine inclusions have been well preserved by their host oikocrysts from reaction with interstitial silicate and sulfide liquids in contrast the compositions of discrete and poikilitic olivine crystals have been variably modified by reequilibration with trapped silicate and sulfide liquids there are abrupt changes in the contents of nickel in olivine inclusions 500 1 500 ppm between different rock units in all three intrusions which indicates that the different rock units in these intrusions are not related to each other via in situ differentiation of a common parental magma but rather are consistent with separate pulses of magma with variable degrees of differentiation possibly involving olivine crystallization and assimilation of siliceous crustal material in a staging chamber the 34s values of the samples with high sulfur contents 800 ppm sulfur from all three ore bearing intrusions vary between 8 and 14 per mil two sulfur poor samples 600 ppm sulfur from the northwestern talnakh intrusion yield 34s values of 1 5 and 3 6 per mil these values are similar to the values of the sulfur poor rocks from the ore barren intrusions in the region and illustrate the fact that high sulfur contents couple with increasing 34s values such a relationship is consistent with the addition of crustally derived 34s enriched sulfur to the magma of the ore bearing intrusions in contrast to other models of sulfide segregation in closed systems we propose that sulfide segregation occurred in an open system and the magma involved was undersaturated in sulfur and undepleted in chalcophile elements we envision that the 34s enriched sulfur was introduced via circulating fluids that transported sulfur from evaporite in the underlying sedimentary sequence to the magma in a dynamic magma conduit the immiscible sulfide liquids that segregated during sulfur contamination settled down in the wider parts of the conduit as the magma continued to travel successive pulses of new magma entered the conduit reacted with the early sulfide and displaced much of the early magma in the conduit the ore bearing intrusions are thought to have crystallized within the wider parts of the conduits and their voluminous sulfide poor peripheral sills represent some if not all of the magma that flowed out of the conduits

geological development and phanerozoic crustal accretion in the western segment of the southern tien shan kyrgyzstan uzbekistan and tajikistan abstract the tien shan form a high intracontinental mountain belt lying north of the main india asia collision mountains and consist of re activated paleozoic orogens the western segment of the southern tien shan lies northwest of the pamir and west of the talas fergana fault the stratigraphy lithology igneous and metamorphic petrology and geochemistry of this segment indicate that it was formed by the assembly of lower paleozoic arcs which developed into microcontinents with upper paleozoic mature shelf and slope clastic and carbonate sediments precambrian continental crust is confined to two small blocks along its southern margin the bulk of the southern tien shan consists of vendian to silurian oceanic and slope clastic rocks resting on oceanic lithosphere and overlain by thick passive margin devonian to mid carboniferous mature shelf clastics and carbonates these are unconformably overlain by syn and post orogenic immature clastic sediments derived from mountains on the north formed by closure of a carboniferus southern tajik and a northern vendian to carboniferous turkestan ocean with the southern tien shan microcontinent sandwiched between associated with these collisions are late carboniferous to permian intrusives which form three south to north though overlapping suites a southern calc alkaline granodiorite granite suite an intermediate gabbro monzodiorite granite suite and a northern alkaline monzodiorite granite alaskite suite the gabbro monzodiorite granite suite forms the earliest subduction related magmatism of the southern tien shan rare earth element patterns are consistent with derivation from a primitive or slightly enriched mantle the other suites show more crustal contamination rb and sr vary with depth and degree of partial melting and are consistent with progressive involvement of crustal material in partial melts during collision the gradual change in composition within each complex lasting in some cases from 295 to 250 ma the entire permian may be explained by a consecutive shift in the melting sedimentary cover of the subducting plate from oceanic crust through transitional crust to marginal continental crust like the central asian orogenic belt the main focus of igcp 420 the tien shan represent a net addition of continental crust during the phanerozoic very little of the belt has any precambrian precursor

re os isotope and platinum group element geochemistry of the pobei ni cu sulfide bearing mafic ultramafic complex in the northeastern part of the tarim craton a number of mafic ultramafic intrusions that host ni cu sulfide mineralization occur in the northeastern tarim craton and the eastern tianshan orogenic belt nw china the sulfide mineralized pobei mafic ultramafic complex is located in the northeastern part of the tarim craton the complex is composed of gabbro and olivine gabbro cut by dunite wehrlite and melatroctolite of the poyi and poshi intrusions disseminated ni cu sulfide mineralization is present towards the base of the ultramafic bodies the sulfide mineralization is typically low grade 4 wt samples from the pobei complex have end at 280 ma values up to 8 1 consistent with the derivation of the magma from an asthenospheric mantle source fo 89 5 mol olivine from the ultramafic bodies is consistent with a primitive parental magma sulfide bearing dunite and wehrlite have high cu pd ratios ranging from 24 000 to 218 000 indicating a magma that evolved under conditions of sulfide saturation the grades of ni cu and pge in 100 sulfide show a strong positive correlation a model for these variations is proposed where the mantle source of the pobei magma retained 0 033 wt sulfide during the production of a pge depleted parental magma the parental magma migrated from the mantle to the crust and underwent further s saturation to generate the observed mineralization along with its high cu pd ratio at an r factor varying from 100 to 1 200 the mineralization at poshi and poyi has very high os at 280 ma values 30 to 292 that are negatively correlated with the abundance of os in 100 sulfide 5 81 271 ppb and positively correlated with the re os ratios this indicates that sulfide saturation was triggered by the assimilation of crustal sulfide with both high os and re os ratios when compared to other permian mafic ultramafic intrusions with sulfide mineralization in the east tianshan the poyi and poshi ultramafic bodies were formed from more primitive magmas and this helps to explain why the sulfide mineralization has high ni tenor

recycling oceanic crust for continental crustal growth sr nd hf isotope evidence from granitoids in the western junggar region nw china abstract the juvenile component of accretionary orogenic belts has been declining since the archean as a result there is often controversy regarding the contribution of oceanic basalts to phanerozoic crustal growth as in the case of the central asian orogenic belt caob here we report on three groups of late carboniferous 316 305 ma granitoids in the western junggar region of northern xinjiang nw china which is part of the southwestern caob they consist of adakites and i and a type granites and as a whole have the most depleted isotopic compositions e nd t 6 9 87 sr 86 sr i 0 7030 0 7045 and e hf t 12 16 among the granitoids of the caob these features are nearly identical to those of pre permian ophiolites in northern xinjiang and are clearly different from those of carboniferous basalts in the western junggar region these relationships indicate that the granitoids were mainly derived from recycled oceanic crust by melting of subducted oceanic crust e g adakites and of the middle lower crust of intra oceanic arc that mainly consisted of oceanic crust e g i and a type granites based on evidence from the caob we suggest that recycling of oceanic crust has made a significant contribution to continental crustal growth and evolution during the phanerozoic

revisiting the age and emplacement process of the huangshandong ni cu deposit in the central asian orogenic belt northwestern china implications for multiple magma extractions from a short lived staging magma chamber abstract magmatic ni cu deposits that associated with mafic ultramafic intrusions in convergent settings could form from multiple magma pulses with age difference varying from 1 ma to 10 ma years the huangshandong deposit in nw china of the southern central asian orogenic belt was formed in such a setting the intrusion is composed of four units formed by four magma pluses a gabbroic sequence phase i crystallized from an evolved magma a sheet like ultramafic body phase ii crystallized from a relatively primitive magma a dike like gabbronorite body phase iii crystallized from an evolved magma and an irregular ultramafic unit phase iv crystallized from a relatively primitive magma our zircon sims u pb dating shows that the phase i and phase iv magmas of the huangshandong deposit were emplaced at 280 3 1 9 ma and 281 4 2 2 ma respectively indicating that the four magma pulses were intruded over a very short period and cannot be distinguished within the uncertainty of 2 ma moreover the zircon crystals in the four units record identical hf t values average of 12 1 13 5 and 18o values average of 6 3 6 5 however the intrusive relationships of the four units illustrate that the huangshandong complex cannot form by in situ fractionation therefore the indistinguishable hf o isotopic values together with their contemporaneous emplacements indicate that the four magma pulses could originate from a same staging magma chamber the overall enrichment of hf t value relative to that of the depleted mantle 16 and elevation of 18o values relative to the mantle value 5 3 suggest 15 20 crustal material incorporation additionally the magmas may have been contaminated prior to their arrival at the staging magma chamber where the magma has subsequently experienced variable olivine fractionations and relatively primitive magma replenishment for most mafic ultramafic intrusions which are characterized by long duration magmatism 10 ma in convergent settings e g intrusions in the kalatongke area tulaergen intrusions xiarihamu intrusions the most important ni cu mineralization are closely related to the last stage magmatism this finding suggests that the intrusions emplaced at the late stage of subduction and post collisional period of the orogenic process may have more potential for ni cu mineralization exploration

geochemistry of the permian kalatongke mafic intrusions northern xinjiang northwest china implications for the genesis of magmatic ni cu sulfide deposits the kalatongke cu ni sulfide deposit in northern xinjiang northwest china is located on the southern side of the regional irtysh fault zone which is the boundary between the early paleozoic altai orogenic belt to the north and the late paleozoic junggar terrane to the south in the kalatongke region there are 11 mafic intrusions which were emplaced in lower carboniferous strata economic ni cu sulfide ores are found within three of these intrusions which are well differentiated and compositionally zoned four rock types are recognized which from top to base of the three mineralized intrusions include biotite diorite biotite hornblende norite biotite hornblende olivine norite and biotite hornblende dolerite the biotite hornblende olivine norites and biotite hornblende norites are the most favorable host rocks for ni cu mineralization the initial 87sr 86sr t t 280 ma ratios of the intrusions vary from 0 70375 to 0 70504 and end t from 6 3 to 8 2 implying that the magmas originated from depleted asthenospheric mantle however the strong enrichment of lithophile elements such as k rb th u and lree the negative nb and ta anomalies and the high 18o values of whole rocks 5 4 10 6 suggest significant crustal contamination these patterns are present in almost all samples from the intrusions indicating that the contamination took place before the magma was emplaced at its present level in the crust crustal contamination is interpreted to have driven the magma to s saturation and brought orthopyroxene onto the liquidus convection or perhaps flow differentiation of the crystal bearing magma during ascent caused the dense sulfide melt with entrained olivine and orthopyroxene crystals to become concentrated in the center of the intrusions whereas the fractionated magmas formed other less mafic intrusions which intrude the nearby strata