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

comment on rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals rubin et al reports 16 june 2017 p 1154 proposed that gradients in lithium abundance in zircons from a rhyolitic eruption in new zealand reflected short lived residence at magmatic temperatures interleaved with long term cold 650 c storage important issues arise with the interpretation of these lithium gradients and consequent crystal thermal histories that raise concerns about the validity of this conclusion

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

formation of columbite and microlite after alteration of nb and ta bearing biotite from the lizaizhai pegmatite guangning ore district guangdong south china identification of a new potential nb ta mineralization type abstract the lizaizhai pegmatite is located in guangning guangdong province south china unlike common rare element li sn nb ta pegmatites in guangning which contain muscovite as the dominant mica the lizaizhai pegmatite represents a different type of rare element mineralization with biotite as the dominant mica our detailed study shows that the lizaizhai pegmatite can be divided into a border zone and a core zone biotite in the border zone contains lower contents of ta mean 121 ppm and higher contents of ti mean tio2 0 31 wt and nb mean 409 ppm compared with biotite in the core zone which contains slightly more ta mean 381 ppm than nb mean 375 ppm and ti mean tio2

petrogenesis and magmatic hydrothermal evolution time limitation of kelumute no 112 pegmatite in altay northwestern china evidence from zircon upb and hf isotopes abstract granitic pegmatites and associated rare metal deposits unique features in the altay orogen are located in a key tectonic position of the southern central asian orogenic belt caob and document the tectonic evolution of the paleo asian ocean the kelumute no 112 pegmatite which intruded into the jideke two mica granites hosts abundant rare metal e g li be nb ta ore deposits and ranks only second to the koktokay no 3 pegmatite in both size and reserves to explore the evolution time limitation of magmatic magmatic hydrothermal and hydrothermal stages in the pegmatite magma system the tectonic setting and the genetic relationship between pegmatites and granites this study presents zircon u pb and hf isotopic compositions of the kelumute no 112 pegmatite and the wall rocks two mica granite and biotite granite as determined by la icpms and la mc icpms the weighted mean 206 pb 238 u ages of the internal textural zones of the pegmatite including zones i ii iii v and vi are 238 3 2 0 ma 233 5 3 7 ma 188 3 1 7 ma 218 8 1 9 ma and 210 7 1 6 ma respectively wall rocks of two mica granite and biotite granite are dated at 445 6 4 3 ma and 455 6 5 4 ma respectively zircons from the kelumute no 112 pegmatite have lower positive e hf t values 0 03 to 2 35 with t dm model ages of 1112 1225 ma wall rocks show similar zircon e hf t values 1 41 to 4 13 and t dm model ages 1172 to 1515 ma however three xenocrystic zircons from the granites are characterized by larger negative ehf t values 5 85 to 9 83 and older t dm model ages 1839 to 2090 ma thus the following conclusions can be drawn 1 the kelumute no 112 pegmatite and its wall rocks jideke two mica granite and biotite granite have no genetic relationship as indicated by the large gaps between their formation ages however they did originate from a common source composed of ancient crust and mantle derived materials under two different tectonic settings 2 the magmatic magmatic hydrothermal transition and hydrothermal stages of the no 112 pegmatite magma lasted for 5 ma 23 ma and 22 ma respectively and 3 the no 112 pegmatite magma was most likely formed in a post collision tectonic setting indicating that block amalgamation and collisional orogeny of the caob continued into the triassic

petrogenetic relationships between pegmatite and granite based on geochemistry of muscovite in pegmatite wall zones black hills south dakota usa abstract the compositions of large samples of granitic pegmatite wall zones have been determined for a suite of ten pegmatites of diverse geochemical character and degree of compositional evolution in the keystone area of the black hills whole rock compositions are strongly peraluminous and they deviate substantially from the granite minimum composition in quartz albite orthoclase normalized components showing considerably more scatter than harney peak granite whole rocks wall zone minerals are commonly coarsely segregated leading to large modal variability among whole rocks these features make whole rock samples of wall zones unsuitable for the determination of initial pegmatite bulk compositions trace and minor element compositions of muscovite separates from the wall zones were thus determined to eliminate the effects of modal variability on trace element concentrations so that geochemical differences between pegmatites could be modeled estimates of initial pegmatite melt trace element concentrations range from 800 4000 ppm rb 100 1000 ppm cs 200 2000 ppm li and 1 50 ppm ba trace element concentrations of muscovite from a given pegmatite generally cluster together although several show considerable intra pegmatite scatter and there are large overlaps among different pegmatites the geochemical characteristics of samples from the etta pegmatite indicate mixing with and assimilation of country rocks exceptionally low rb cs ratios of muscovite from the etta pegmatite are similar to those of muscovite from k feldspar rich assemblages of other pegmatites where the rb concentration of melt may have been buffered by crystallizing assemblages that had bulk rb distribution coefficients close to 1 the large degree of scatter of geochemical parameters among these pegmatites precludes derivation of the entire suite by either single stage crystallization or partial melting processes nor can the pegmatites be satisfactorily related by any fractionation trajectory from a single starting composition fractional crystallization is difficult to model due to an apparent geochemical decoupling that exists among several of these elements in different pegmatites e g rb from cs or li from rb cs and nonsystematic variation of ba concentrations however the magnitude of observed rare element enrichments could be achieved by 75 90 fractional crystallization of melts that crystallized harney peak granite in nearby exposures the inter pegmatite scatter and apparent geochemical decoupling that characterize the suite indicate an origin by partial melting of a heterogeneous source rock or rock sequence followed by an intermediate episode of fractional crystallization prior to final emplacement of the pegmatite melts additional compositional variations among samples from the wall zones of individual pegmatites were caused by processes during or after emplacement including local interaction with host metamorphic rocks and fractionation during internal evolution of the pegmatites as they crystallized

a synthesis of mineralization styles and geodynamic settings of the paleozoic and mesozoic metallic ore deposits in the altay mountains nw china abstract the altay mountains within the xinjiang region of northwestern china hosts major metallic ore deposits here we review the geological characteristics metallogenic features and tectonic settings of these deposits the metallic ore deposits in the altay mountains occur mainly within four regions north altay central altay south altay and erqis we recognize seven types of metallic ore deposits in the altay mountains vms submarine volcanogenic iron magmatic skarn pegmatite hydrothermal vein cu zn fe and orogenic gold among these types the vms pegmatite orogenic gold and skarn deposits are the most common most of the rare metal pegmatite deposits are distributed in central altay with only a few in south altay the vms submarine volcanogenic type iron and skarn type deposits are distributed in south altay whereas the orogenic type gold deposits are distributed in the erqis fault belt the hydrothermal vein type deposits occur in the erqis fault belt and chonghu er basin in south altay magmatic type deposits are mostly in the erqis fault belt and central altay based on isotopic age data the vms submarine volcanogenic type fe and skarn type cu pb zn fe mineralization occurred during early middle devonian 410 377 ma orogenic type au magmatic type cu ni and a small number of skarn type fe hydrothermal vein type cu zn pegmatite type rare metal deposits in early middle permian 293 261 ma pegmatite type rare metal deposits few skarn type fe deposit in early middle triassic 248 232 ma and dominantly represented by pegmatite type rare metal deposits in late triassic early jurassic 223 180 ma the metallic ore deposits in the altay mountains formed in various tectonic settings such as the early middle devonian continental arc and oceanic island arc early middle permian post collisional extensional setting and triassic early jurassic intracontinental setting

zircon u pb geochronology and hf isotopic composition of granitiods in russian altai mountain central asian orogenic belt the central asian orogenic belt caob consists of many tectonic terranes with distinct origin and complicated evolutionary history understanding of individual block is crucial for the reconstruction of the geodynamic history of the gigantic accetionary collage this study presents zircon u pb ages and hf isotopes for the granitoid rocks in the russian altai mountain range including gorny altai altai mongolian terrane and ctus suture zone between them in order to clarify the timing of granitic magmatism source nature continental crustal growth and tectonic evolution our dating results suggest that granitic magmatism of the russian altai mountain range occurred in three major episodes including 445 429 ma 410 360 ma and 241 ma zircons from these granitoids yield comparable positive ehf t values and neoproterozoic crustal model ages which favor the interpretation that the juvenile crustal materials produced in the early stage of the caob were probably dominant sources for the paleozoic magmatism in the region the inference is also supported by widespread occurrence of short lived juvenile materials including ophiolites seamount relics and arc assemblages in the northern caob consequently the paleozoic massive granitic rocks maybe do not represent continental crustal growth at the time when they were emplaced but rather record reworking of relatively juvenile proterozoic crustal rocks although mantle derived mafic magma was possibly involved to serve as heat engine during granitic magma generation the early triassic granitic intrusion may be a product in an intra plate environment as the case of same type rocks in the adjacent areas the positive ehf t values 1 81 7 47 and corresponding hf model ages 0 80 1 16 ga together with evidence of petrology are consistent with the interpretation that the magma source of the triassic granitic intrusion was derived from enriched mantle and melted under an usually high temperature condition likely due to basaltic magma that underplated the lower crust our data combined with evidence of the regional geology enable us to conclude that the gorny altai and altai mongolian terranes possibly have similar tectonic natures but represent two separate accretionary systems before devonian collision the accretion and amalgamation processes resulted in the paleozoic granitoid magmatism and caused the two terranes to merge as a composite tectonic domain at the siberian continental margin

geochronology and origin of the sarekoubu gold deposit southern altaides china ar ar dating of vein quartz and cu zn fe isotopes abstract the sarekoubu gold deposit located north to altay city china has an unusual feature for abundant carbonic co2 ch4 n2 bearing fluid inclusions for many years the ages and origin of the sarekoubu deposit have been still controversial the gold deposit occurs in the fractured zone parallel to the strata of lower devonian kangbutiebao formation d1k22 and has three hydrothermal mineralizing stages i disseminated pyrite and white quartz vein stage ii fine quartz and pyrite veinlet stage and iii polymetallic sulfides grey quartz stage stages ii and iii are the main gold mineralization stages two gold bearing chalcopyrite quartz vein samples from stage iii were selected for 40ar 39ar age study the result shows that fluid inclusions in quartz of mineralizing stage have isochronal ages of 216 9 6 7 ma and 218 0 6 3 ma and inverse isochronal ages of 218 3 6 1 ma and 216 7 6 4 ma the fe isotope analysis shows that the sarekoubu gold deposit is different from vms sedex deposits the 56fe values of pyrite from main mineralization stages in the sarekoubu gold deposit have a large variation of fe isotope range from 0 498 to 0 759 which can be regarded as a closed hydrothermal system for fe isotopes the 65cu values of chalcopyrite both from the sarekoubu gold deposit and overprint gold mineralization of adjacent tiemurte deposit have a narrow range 0 28 0 922 which are not the same as vms deposits with a wide range of 65cu values the gold mineralization in the sarekoubu deposit is younger than the gold deposits near regional irtysh tectonic belt this may be related with the evolution of the thrust of the irtysh tectonic belt in the southern altaides

geochronology of metarhyolites from the kangbutiebao formation in the kelang basin altay mountains xinjiang implications for the tectonic evolution and metallogeny abstract the altay orogenic belt aob situated in the middle part of the central asian orogenic belt caob is one of the most important metallogenic belts in china the kangbutiebao formation is a late paleozoic stratigraphic unit that hosts many important iron and pb zn deposits the kangbutiebao formation consists of intercalated volcanic and sedimentary rocks that have undergone regional greenschist to lower amphibolite facies metamorphism and mainly outcrops in three nw trending fault bounded volcano sedimentary basins including the maizi kelang and chonghuer basins shrimp analyses of zircons from three metarhyolites of the kangbutiebao fm in the kelang basin yield weighted mean 206 pb 238 u ages of 412 6 3 5 ma 408 7 5 3 ma and 406 7 4 3 ma respectively which can be interpreted as the eruption age of the kangbutiebao silicic volcanic rocks in the kelang basin these ages indicate that the kangbutiebao formation was formed during the late silurian to early devonian they also demonstrate that the deposits hosted in the kangbutiebao formation were formed after 412 407 ma they play a key role in understanding the paleozoic tectonic evolution and metallogenesis of the southern margin of the chinese aob

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

petrogenesis and tectonic settings of volcanic rocks of the ashele cu zn deposit in southern altay xinjiang northwest china insights from zircon u pb geochronology geochemistry and sr nd isotopes abstract the early mid devonian ashele formation of the southern margin of the chinese altay hosts the ashele cu zn volcanogenic massive sulfide vms deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist facies metamorphism we studied the petrography zircon u pb geochronology geochemistry and sr nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution two dacites yielded la mc icp ms zircon u pb ages of 402 6 ma and 403 2 ma the dacites are calc alkaline and characterized by high na 2 o k 2 o ratios 3 6 9 3 and high mg values 47 63 enrichment in large ion lithophile elements lile and light rare earth elements lree depletion in nb ta ti and p and relatively positive e nd t values 3 6 to 7 5 collectively suggesting a sanukitic magma affinity the variations in the major and trace elements of the dacites indicate that fe ti oxide plagioclase and apatite were fractionated during their petrogenesis the basalts are tholeiitic and are characterized by high mg values 66 73 and negative nb and ta anomalies the geochemical characteristics of the basalts are similar to those of n morb those characteristics together with the positive e nd t values 6 8 to 9 2 of the basalts indicate that the precursor magma was derived mainly from an n morb type depleted asthenospheric mantle in an island arc setting the geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case possibly related to ridge subduction

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

neodymium and strontium isotope study of the blue tier batholith ne tasmania and its bearing on the origin of tin bearing alkali feldspar granites the middle to late devonian plutons of the blue tier and eddystone batholiths of ne tasmania intrude quartz wacke and mudstone of the ordovician devonian mathinna beds four granitoid types are recognized hornblende biotite granodiorite biotite granite biotite cordierite garnet granite and alkali feldspar granite afg minor diorite bodies and dolerite dykes are also present tin w mineralisation is genetically associated with the afg major granitoid types other than afg of the blue tier and eddystone batholiths all have similar 143nd 144nd initial ratios nd 5 0 to 6 5 at ma more fractionated felsic samples within individual plutons have lower nd values suggesting progressive involvement up to about 5 of the sedimentary country rocks which have nd of about 11 at 370 ma the source rock model age for all granitoids except afg based on a depleted mantle evolution model tdm is about 1 6 ga on the basis of geochemical data 87sr 86sr initial ratios 0 707 0 713 oxygen isotope ratios 180 9 to 12 and rb sr and k ar isotopic age dates 368 to 388 ma the major plutons were interpreted to have been generated independently from heterogeneous crustal sources geochemical variation within each major granitoid type with the possible exception of the afg is due to fractional crystallisation accompanied by some country rock assimilation integrated nd sr and o isotopic systematics of the blue tier batholith of the bassian terrain are different from granite batholiths in the mainland of the lachlan fold belt similarity of isotopic systematics of the blue tier batholith to those of devonian granites in central victoria reinforces the geological correlation between western tasmania and south australia in the early paleozoic two competing hypotheses for the generation of sn w mineralized afg have been proposed on the basis of geological relationships chemical and mineralogical trends and stable and radiogenic isotopes the first hypothesis groves et al 1977 higgins et al 1985 higgins 1990 links the afg with the country rock more mafic poimena granite through processes of fractional crystallisation and subsequent metasomatic modification the second hypothesis suggests that these afg are unrelated to the poimena granite they are specialised granites derived from a different parent with distinctive chemical isotopic systematics sun et al 1986 mackenzie 1986 mackenzie et al 1988 1990 according to the first hypothesis the afg exhibit a range in nd initial values from 5 9 to 2 2 however there is no known isotopic mechanism which can produce this range within the geological time frame of intrusion and solidification at this time the authors favour the second hypothesis because of chemical and isotopic correlations on the basis of a distinct discontinuity between poimena and afg on a y versus ga al plot there is also a clear grouping of initial nd for the poimena granite around 6 and the afg 2 4 it is argued that those few afg having much lower nd than 2 4 are either samples of altered poimena granite two samples with nd 6 8 and 9 1 or a result of extensive metasomatic modification one sample nd 5 9 involving circulation of fluids in equilibrium with the country rocks poimena granite initial nd 6 and mathinna beds 11 hydrothermal minerals from the anchor tin deposit show a range in initial nd and 87sr 86sr correlated with paragenesis apatite formed during albitisation of the lottah granite has nd and sr isotopic compositions intermediate between those of the lottah and poimena granites greisen fluorites have initial nd between 4 0 and 4 6 closer to the lottah average composition while initial 87sr 86sr approaches that of the metasedimentary country rock 0 729 fluorites formed during sericitic alteration have lower nd compositions 0 721 these data support an origin of tin mineralisation through mixing of an afg derived magmatic fluid with a externally derived meteoric groundwater dominated fluid

new precise timing constraint for the keketuohai no 3 pegmatite in xinjiang china and identification of its parental pluton abstract the keketuohai pegmatite field is one of the pegmatite rich regions in the altay orogen with abundant pegmatites and voluminous granite magmatism the keketuohai no 3 pegmatite is renowned for its deposits of rare metals but despite a lot of in depth research the geochronology of the pegmatite remains the subject of dispute and there is a lack of precise geochronological evidence to support the view that the aral granite represents the parental magma of the pegmatite to further our understanding of this pegmatite field one sample was collected from the aral granite in the northern part of the ore district and six molybdenite samples were taken from the marginal zone of the keketuohai no 3 pegmatite the geological context of the molybdenite samples indicates an origin by hydrothermal metasomatism in the zone between the margin of the pegmatite and the wall rock and the time of its formation should coincide with or immediately follow the formation of the pegmatite margin this allows the lower time limit of the pegmatite formation to be set la mc icp ms dating of zircons from the aral granite gives 206 pb 238 u ages that range from 209 0 to 215 6 ma from 16 spot analyses and the plotted data are mainly distributed on or around the concordant line the weighted mean age is 211 4 0 8 ma mswd 1 4 which may represent the crystallization age of the granite the re os isotopic model ages for the six molybdenite samples range from 207 8 to 212 2 ma the weighted mean age of 209 9 1 3 ma mswd 0 69 and the re os isochron age of 208 8 2 4 ma mswd 0 89 are consistent within error if decoupling of the re os isotope system in molybdenite is neglected this consistency in the age data may indicate the time at which molybdenite was deposited from fluids after researching in detail the previously published chronological data we propose that earlier views on the ages of the keketuohai no 3 pegmatite and the aral granite may be incorrect and we now suggest that the pegmatite started to form around 209 210 ma in the late triassic the agreement between the newly determined u pb ages for the aral granite and the re os ages of the molybdenite in the pegmatite strongly indicates a close relationship between the crystallization of the aral granite and the formation of the pegmatite and its rare metals deposits it also points to the aral granite being the parent of the no 3 pegmatite

geochronology and geochemistry of the chuanwulu complex in the south tianshan western xinjiang nw china implications for petrogenesis and phanerozoic continental growth abstract the south tianshan collisional belt stcb formed by the collision between the tarim and central tianshan blocks is pivotal for understanding the complex and prolonged tectonic evolution of the central asian orogenic belt caob the chuanwulu complex is located in the eastern part of the stcb xinjiang province nw china it consists of a gabbro diorite unit unit i and a monzonite syenite unit unit ii which are both cut by some granite dykes unit iii based on la icp ms u pb zircon dating the units i and ii were emplaced at 287 8 4 3 ma and 286 4 2 5 ma respectively the sio 2 contents of the samples from the complex display a wide range from 50 52 wt to 70 64 wt and most samples are of alkaline affinities the magma mixing process during the formation of the complex is suggested by considerable petrographic and geochemical evidence such as mafic microgranular enclaves mees that occur within unit ii disequilibrium textures linear negative correlations between sio 2 and some major elements and a wide range of 87 sr 86 sr t ratios and 18 o smow values unit i is characterized by relatively low sio 2 contents 50 52 55 05 wt high mgo contents 3 29 5 43 wt with mg 0 50 0 56 high sr contents 1646 3101 ppm pronounced negative nb ta anomalies and light rare earth element lree enrichment in combination with their isotopic compositions 87 sr 86 sr t 0 70543 0 70751 e nd t 2 3 to 1 8 18 o smow 5 7 9 4 e hf t 0 2 4 9 these features indicate that they are derived from an incompatible element enriched lithospheric mantle the sio 2 contents of units ii and iii range from 58 88 wt to 65 91 wt and 67 10 wt to 70 64 wt respectively they exhibit pronounced positive zr hf anomalies and negative p and ti anomalies and relatively elevated sr and o isotopic compositions 87 sr 86 sr t 0 70543 0 70751 18 o smow 8 9 9 1 in addition samples of unit iii have high sr 600 ppm to 1201 ppm contents and sr yb 373 to 1905 and low y yb 8 to 12 ratios the felsic rocks units ii and iii have a c type adakite like geochemical signature and are comparable with those of rocks derived from an ancient garnet bearing amphibolite facies lower crust our study complied with other geological evidence indicate that the collision between the central tianshan and tarim blocks and the final amalgamation of the caob should have occurred during late carboniferous on the regional scale we propose that the recycling of ancient lithosphere is the predominant mechanism which is able to account for phanerozoic continental evolution in stcb differing from other tectonic units in caob

numerical modelling of the three dimensional stress field in southwestern japan abstract it has been inferred from the focal mechanism of earthquakes and their hypocenter distribution shiono 1977 that the stress field in southwestern japan indicates complicated features a nw se compression at shallow depths along the nankai trough an e w or ese wnw compression in the inland crust an extension parallel to the leading edge of the philippine sea plate at subcrustal depths in the region from the southern chubu to northwestern shikoku and a down dip tension beneath the kyushu island in order to investigate possible sources of these complex features of the stress state a three dimensional finite element method is employed to model the configuration of the subducting philippine sea plate taking into consideration the following three possible types of forces 1 1 a negative buoyancy due to the density contrast between the subducting plate and the surrounding mantle 2 2 a northwestward compressive force generated by the movement of the philippine sea plate 3 3 a westward compressive force due to the movement of the pacific plate for various combinations of different magnitudes of these forces and of different elastic moduli the stresses at a number of selected sites are calculated and their directions are compared with those inferred from the focal mechanism and other geophysical information it is found that the observed extensional stresses parallel to the leading edge of the subducting philippine sea plate may be caused mainly by the negative buoyancy the northwestward compressive force may not play an important role in generating the complex stress field in southwestern japan the observed e w compressional stress field prevailing in the inland region appears to result mainly from the westward moving pacific plate the present results suggest that if a thin low velocity transitional layer exists just above the subducting philippine sea plate it could give appreciable effects on the mechanism of low angled thrust faulting off the kii peninsula and the shikoku island the magnitude of the shear stress in the continental crust and in the subducting plate is estimated to be of the order of several hundred bars although the calculated shear stresses are considerably affected by the configuration of the subducting plate and also by the applied forces it is interesting that the stress distribution appears to have some relations to seismicity of subcrustal earthquakes and to the rupture process of large thrust earthquakes along the plate boundary

melt inclusions in quartz from an evolved peraluminous pegmatite geochemical evidence for strong tin enrichment in fluorine rich and phosphorus rich residual liquids abstract we have investigated the magmatic evolution of a late stage f and p rich pegmatite forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally crystallized melt inclusions in quartz and analyzing the quenched glass by epma and sims the quartz phenocrysts were sampled from a pegmatite that occurs in a variscan granite genetically associated with cassiterite and wolframite mineralized greisen veins at the ehrenfriedersdorf sn w deposit central erzgebirge se germany the melt inclusion compositions imply that the pegmatite forming liquid achieved extreme levels of chemical differentiation it contained high abundances of sn f p li rb cs nb ta and be and abnormally low concentrations of ca y sr and ree for a granite and it was strongly peraluminous the molar al 2 o 3 cao na 2 o k 2 o ranged from 1 3 to 2 0 fractions of the pegmatite forming liquid were extremely enriched in p 2 o 5 f al 2 o 3 and the molar abundances of f p in the glasses correlate strongly with moles of network modifying al ions implying that the bulk liquid included f p and al bearing complexes formation of these complexes reduced the activities of f p and al in bulk liquid suppressed the crystallization of magmatic topaz and p rich minerals and allowed the liquid to become enriched in these constituents some fractions of the ehrenfriedersdorf aluminosilicate liquid contained 1000 2000 ppm sn these levels of sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineralized metaluminous and peraluminous igneous materials and are consistent with some experimentally derived sn solubilities in cassiterite saturated granitic liquids at geologically relevant pressures and temperatures this concordance implies that cassiterite could have crystallized directly from this highly evolved p and f rich peraluminous granitic liquid without the involvement of hydrothermal fluids

geochemical and isotopic studies of the sedimentary and granitic rocks of the altai orogen of northwest china and their tectonic implications the altai orogen northwest china represents the southwestern margin of the central asian orogenic belt geochemical and nd sr isotope analyses were carried out on the palaeozoic sedimentary and granitic rocks in order to trace their sources and to evaluate the pattern of continental growth of the orogen nd isotopic data for both the granites and sediments suggest a significant proportion of middle proterozoic crust beneath the altai orogen however addition of juvenile material arc back arc oceanic crust during palaeozoic times is also significant trace elements and isotopic data of sediments suggest their sources were immature they represent mixtures between a palaeozoic juvenile component and an evolved continental crust the early palaeozoic sediments show e nd t 3 4 to 5 0 t dm 1 5 1 8 ga and i sr 0 710 0 712 they represent a passive margin setting with a predominance of evolved crustal material in the source the devonian sequences however might have been deposited in a back arc basin setting produced by subduction of the junggar oceanic crust along the irtysh fault a significant addition of arc material into the sedimentary basin is responsible for the highly variable e nd values 6 to 0 and i sr 0 711 0 706 the carboniferous rocks were also deposited in a back arc basin setting but with predominantly arc material in the source as suggested by an abrupt increase in e nd t 6 to 3 and decrease in i sr 0 7045 0 7051 voluminous syn orogenic granitoids have e nd t 2 1 to 4 3 i sr 0 705 0 714 and t dm 0 7 1 6 ga they were not derived by melting of local metasedimentary rocks as suggested by previous workers but by melting of a more juvenile source at depth post orogenic granites have higher e nd t 4 4 than the syn orogenic granitoids indicating their derivation from a deeper crustal level where juvenile crust may predominate

argon loss by alkali feldspars abstract ar loss is generally thought to preclude the use of alkali feldspars for dating old rocks by the k ar method and has been thought to occur via structural features such as the boundaries of perthite lamellae or twins we have done a 40 ar 39 ar step heating study of a suite of alkali feldspars from the klokken syenite intrusion u pb age 1166 4 ma which have been fully characterized by transmission electron microscopy all are low albite low microcline intergrowths but some are non turbid strain controlled cryptoperthites while others are turbid coarse microperthites geological and textural evidence suggests that the turbidity developed by fluid rock interactions during the initial cooling of the pluton in the stability field of low microcline 5 a after crystallization the finest cryptoperthites have numerous fully coherent perthite lamellar boundaries lamellar periodicity 40 nm and twin composition planes the have retained radiogenic 40 ar and yield total degassing ages as high as 1125 16 ma and maximum ages on the age spectra of 1162 16 ma the coarse turbid microperthites with patchy intergrowths and twins on the mm scale gave total degassing ages as low as 650 ma maximum age 750 ma argon leakage occurs least in feldspars with the most lamellar interfaces but in proportion to the degree of turbidity which is thought to be caused by large numbers of micropores strain controlled intergrowths in perthites allow the recognition of volumes of alkali feldspar crystals which have not interacted with deuteric fluids these retain argon and can give reliable k ar ages in old rocks saddle shaped age spectra appear to result from the preferential degassing at 1000 c of part of the feldspar structure which has lost more of its argon in nature the laboratory degassing does not occur in a manner analogous to that which has occurred naturally

a new style of rare metal granite with nb rich mica the early cretaceous huangshan rare metal granite suite northeast jiangxi province southeast china

sr nd and pb stable isotopes of surface dust on urumqi glacier no 1 in western china stable isotopic ratios of strontium sr neodymium nd and lead pb provide a means of identifying a geological source of substances and are used as tracers of elements in biological and geochemical processes we analyzed these isotopic ratios of surface dust cryoconite collected on urumqi glacier no 1 tien shan china the dust was separated chemically into five fractions four minerals and organic matter and the isotopic ratios of each fraction were measured the sr and nd isotopic ratios in the fractions extracted with ultrapure water saline minerals hydrogen peroxide solution organic matter and acetic acid carbonate minerals were low and invariable whereas those extracted by hydrochloric acid phosphate minerals and the residual fraction silicate minerals were higher the difference was likely due to the original source of each fraction the isotopic ratios of the surface dust collected from different sites showed no significant difference suggesting that they were spatially uniform across the glacier the isotopic ratios of the silicate fraction were closer to those of desert sand reported in china than those of the soil and bedrock around the glacier this suggests that the silicate minerals on the glacier were derived from distant deserts the isotopic ratios in saline carbonate and phosphate fractions were also close to those of evaporites and apatite in that desert region suggesting that these minerals were also derived from that source the sr isotopic ratios in the organic fraction were closer to ratios in the saline and carbonate fractions rather than the silicate or phosphate fractions and may therefore reflect the isotopic ratios of the elements when they are incorporated into living microbes on the glacier

la icp ms u pb zircon columbite tantalite and 40ar 39ar muscovite age constraints for the rare element pegmatite dykes in the altai orogenic belt nw china the chinese altai is renowned for its rich rare element resources nine representative rare element rel pegmatites were dated using la icp ms and 40ar 39ar methods the columbite grains yield a weighted mean 206pb 238u age of 239 6 3 8 ma for the dakalasu be nb ta pegmatite and concordia u pb ages of 258 1 3 1 ma and 262 3 2 5 ma for the xiaokalasu li nb ta pegmatite the zircons display a weighted mean 206pb 238u age of 198 5 2 5 ma for the husite be pegmatite and concordia u pb ages of 194 3 1 6 ma and 248 2 2 2 ma for the qunkuer be and taerlang barren pegmatites the muscovite 40ar 39ar dating gives plateau ages of 286 4 1 6 ma 297 0 2 6 ma 265 2 1 5 ma 178 8 1 0 ma 162 2 0 9 ma 237 7 1 3 ma 237 4 1 2 ma and 231 9 1 2 ma for the talate li be nb ta baicheng nb ta kangmunagong barren husite be qunkuer be nb ta xiaokalasu li nb ta weizigou be and taerlang barren pegmatites respectively these new ages coupled with previous geochronological work suggest that the rel pegmatites in the chinese altai formed during early permain late jurassic time the rel pegmatites located in the central altaishan terrane are younger than those in the qiongkuer abagong terrane showing a correlation with the coeval and adjacent granites the formation of the rel pegmatites and these granites indicates frequent and strong magmatic activity in the post orogenic and anorogenic setting the spatial and temporal distribution of pegmatites and granites reveals a magmatism path from the se of age early middle permian to the nw middle permian middle triassic and finally to the central part middle triassic jurassic of the chinese altai

a new model for the granite pegmatite genetic relationships in the kaluan azubai qiongkuer pegmatite related ore fields the chinese altay pegmatites commonly form in the waning stage of magma evolution by fractional crystallization of volatile rich magmas and may be important host rocks of strategic metals e g li be cs ta and nb and high quality gem minerals this study reports new zircon u pb dating results and hf isotopic compositions of the kla803 pegmatite the azb 01 pegmatite the jmk 09 pegmatite abbreviated as the k a j pegmatites and the halong granite from the chinese altay to determine the potential petrogenetic relationships between them the geochronological data document that the k a j pegmatites were emplaced at 224 6 2 3 ma 191 6 2 0 ma and 192 0 2 3 ma respectively and they are characterized by negative to low positive epsilon hf t values from 1 0 to 63 and old model ages t dm with the t dm1 from 874 to 597 ma and t dm2 from 1298 to 833 ma in contrast the halong granite has an emplacement age of 398 3 2 4 ma and is characterized by higher positive epsilon hf t values from 9 9 to 15 2 and younger model ages t dm with the t dm1 from 626 to 414 ma and t dm2 from 760 to 423 ma they all have intruded into the kulumuti group stratum which has negative initial epsilon nd t values from 4 3 to 0 2 and old t dm model ages between 1 22 and 1 56 ga based on the calculated results of the mixing ratios f of the initial magmas and the prevailing paleozoic tectonic framework of the chinese altay we establish two petrogenetic models for the k a j pegmatites model 1 refers to that these pegmatites originated from a mixed magma that was composed of 72 91 wt depleted mantle components and 9 28 wt lower crust components and model 2 refers to that they were derived from the partial melting of 38 83 wt halong granite and 17 62 wt sedimentary rocks from the kulumuti group we also suggest that the initial magma of the halong granite was significantly contributed by juvenile materials with a slight involvement of crustal materials in model 1 because lct type pegmatites classified as li cs ta enriched pegmatites associated with s type granite that was produced by the partial melting of preexisting sedimentary rocks have close geochemical affinities with crustal materials the excessively high weight percentages 72 91 wt of the depleted mantle components in the initial magma of the k a j pegmatites indicate that this model is unrealistic therefore we consider that model 2 is more reasonable at present for interpreting the petrogenesis of the k a j pegmatites and it needs to be verified in other pegmatite fields of the chinese altay c 2016 elsevier ltd all rights reserved

complex trace element effects of mixing fractional crystallization composite processes applications to the alaer granite pluton altay mountains xinjiang northwestern china abstract complex patterns of intersection of linear with power function curvilinear data point arrays are observed on ratio ratio correlation plots of trace elements in the alaer palaeozoic granite pluton altay mts xinjiang northwestern china data points in the linear array are relatively lower in sio 2 content and differentiation index d i and they become progressively decreased rightwards along the array in abundances of zr and hf which could be better explained by mixing between zircon rich restite and the granite melt data points in curvilinear arrays are higher in sio 2 content and d i value and therefore have presumably suffered more extensive fractional crystallization the complex patterns cannot be resolved with the classical models two models for the complex trace element effects of mixing fractional crystallization are developed in the paper with which the patterns can be resolved in all models we begin with a linear data array formed by simple two component mixing and then superpose fractional crystallization trends to generate a family of curves model 1 d 1 d 3 d 2 d 3 or d 1 d 3 d 2 d 3 in the general situation fractional crystallization curves assume a cluster of concave up or convex up power function curves which intersect the initial mixing line sloping positively special cases 1 3 d 1 d 2 d 3 or d 1 d 2 d 3 or d 2 d 1 d 3 the fractional crystallization curve is transformed into a straight line special case 4 d 1 d 2 d 3 the fractional crystallization line coincides with the initial mixing line model 2 d 1 d 3 d 2 or d 1 d 3 d 2 fractional crystallization curves assume the form of hyperbolic curves which intersect the initial mixing line sloping negatively in all of the two models the iso fraction lines are uniformly steeper d 1 d 2 or more gentle d 1 d 2 than the initial mixing line iso fraction lines increase d 1 d 2 or decrease d 1 d 2 progressively in slope with the decrease of residual liquid mass fraction f through modelling of the data point arrays on ratio ratio correlation plots of trace elements one can discern and distinguish between simple mixing pure fractional crystallization and mixing fractional crystallization composite processes initial compositions of the magma and the mixing modes can also be constrained through modelling the functional form concavity or convexity and the power index of the fractional crystallization curves the relative incompatibility of trace elements can be estimated semi quantitatively and the incompatibility sequence can be established it is demonstrated through modelling that the alaer granite pluton experienced mixing fractional crystallization composite processes the mixing mode is probably described by the restite model the incompatibility sequence of the 7 concerned trace elements is d th d la d y d nb d ta d hf d zr this incompatibility sequence may be applicable to the anatectic granites

reconnaissance fluid inclusion study of the morefield pegmatite amelia county virginia over 90 of the fluid inclusions in quartz topaz and beryl from the morefield pegmatite amelia co virginia contain mixed co 2 h 2 o fluids in order of abundance there are four inclusion types 1 three phase l l v 2 two phase h 2 o rich 3 three or four phase l v s and l l v s and 4 two phase co 2 rich co 2 rich inclusions formed by necking of inclusions containing mixed fluids topaz and quartz contain all four inclusion types and all types occur throughout the pegmatite although no h 2 o rich inclusions occur in beryl quartz from gneiss that hosts the pegmatite contains dominantly h 2 o rich inclusions most inclusions are secondary and occur along healed fractures possible primary inclusions occur only among those that contain solids all inclusions homogenize into the liquid phase a few homogenize to liquid co 2 h 2 o rich inclusions with 2 o rich and mixed fluid inclusions with 3 7 wt nacl eq and homogenization temperatures 290 degrees c contain fluids interpreted to derive primarily from the pegmatite inclusions with salinities between 3 13 wt nacl eq and intermediate homogenization temperatures are in part cooled equivalents of the pegmatite fluids but the origin of those with salinity 7 wt nacl eq is uncertain homogenization temperatures for co 2 indicate average co 2 densities near 0 65 g cm 3 for mixed fluids homogenizing near 300 degrees c and this co 2 density the trapping pressure is estimated to be 2 5 kb neither age relations nor physical proximity tie the morefield pegmatite to known granitic intrusions fluid compositions preclude a genetic relation between the pegmatite and its host gneisses

sequence of mineral assemblages in differentiated granitic pegmatites revised sequence is 1 plagioclase quartz muscovite 2 plagioclase quartz 3 quartz perthite plagioclase 4 perthite quartz 5 quartz plagioclase perthite spodumene or petalite amblygonite 6 quartz spodumene or petalite 7 quartz microcline or perthite 8 quartz and 9 lepidolite or lithian mica plagioclase quartz microcline modified journal abstract

evolution source and tectonic significance of early mesozoic granitoid magmatism in the central asian orogenic belt central segment abstract numerous early mesozoic granitoids have been recognized from the central segment of the central asian orogenic belt caob they can be broadly classified into two groups according to zircon u pb ages an early stage group covering the time span from early to middle triassic 250 230 ma and a late stage group emplaced during late triassic to early jurassic ca 230 190 ma early stage 250 230 ma granitoids are mainly distributed in the western central mongolia erguna belt cmeb the western altai belt ab the south mongolia xing an belt smxb and the beishan inner mongolia jilin belt bijb they consist mainly of quartz diorites granodiorites and monzogranites mostly of i type with minor mafic intrusions with some of them showing adakite like signatures and some with s type features late stage 230 190 ma granitoids mainly occur in the north mongolia transbaikalia belt nmtb the eastern cmeb erguna massif and the eastern altai belt ab they are predominately syenogranites monzogranites and syenites associated with many alkaline granites and mafic intrusions and are a type and transitional i a type or highly fractionated i type granites whole rock sr nd and zircon hf isotopic data have been compiled for regional isotopic mapping the end t values show large variations from 7 0 to 7 4 and nd model ages tdm from 0 46 ga to 1 43 ga as well as the initial sr isotopic ratios sri from 0 7023 to 0 7174 the zircon ehf t values vary from 4 6 to 15 3 and give two stage hf model ages tdm2 from 0 30 ga to 2 09 ga the extremely large variations of whole rock sr nd and zircon hf isotopes demonstrate strong isotopic heterogeneity of the source regions that are mainly dominated by juvenile components with significant old crustal participation furthermore the late stage granitoids in the nmtb the cmeb and the ab generally have more negative end t values and more variable zircon ehf t values than those of the early stage granitoids in the same belt implying an increasing crustal signature from early to late stage in the assumed heterogeneous source regions within the same belt which probably results from melting of shallower crust in parallel with a shift to more alkaline chemistry of the late granitoid magmas by contrast most late stage granitoids in the smxb and the bijb have more positive end t values and homogeneous zircon ehf t values than those of the early stage granitoids in the same belt indicating more juvenile contribution to the source of the these granitoids the generation of the early mesozoic granitoid magmas in the nmtb and the cmeb was dominated by the ongoing closure of the mongol okhotsk ocean and some was probably related to a mantle plume process they were possibly derived from subducted materials melting or juvenile components with some probable contributions from ancient continental crust early mesozoic granitoid magmas in the smxb the ab and the bijb were generated in a post non orogenic setting after the closure of the paleo asian ocean and were the results of partial melting of crustal components in response to underplating of mantle derived magmas most likely linked to lithospheric thickening and delamination and asthenospheric upwelling early mesozoic granitoid magmatism provides critical information on mesozoic post accretionary tectonic evolution of the paleo asian ocean and transitional tectonic regimes from early mesozoic subduction to late mesozoic closure of the mongol okhotsk ocean as well as post accretionary continental growth

geochemistry of the rare metal bearing pegmatite no 3 vein and related granites in the keketuohai region altay mountains northwest china abstract the chemical composition of a barren biotite granite a two mica granite and a rare metal bearing pegmatite the no 3 vein in keketuohai altay mountains northwest china along with mineral separates of apatite and mica were analyzed and compared in the present work bulk chemistries of biotite granite two mica granite and pegmatite rim are consistent with fractional crystallization trend from granites toward pegmatite changes in pegmatite composition can be explained mainly by fractional crystallization of biotite rb sr isochrons yield 248 8 7 5 ma for the biotite granite 247 8 6 3 ma for the two mica granite and 218 4 5 8 ma for the pegmatite rim similar geochemical characteristics including initial e nd t values ranging from 0 76 to 3 04 for apatites similar initial e nd t values for whole rock samples of studied granites and pegmatite ranged from 1 40 to 3 21 and for biotites from granites ranged from 2 75 to 3 15 suggest that these rocks were derived from a common magma source old continental crust may have played a significant role in magma generation based on these data we interpret the evolution of the keketuohai granite pegmatite by magma differentiation from a common source biotite granite was the first to crystallize followed by two mica granites the residual melt was probably stored in a granitic batholith the pegmatite veins were injected 30 m y later during another episodic tectono magmatic event in the altay mountains