carboniferous permian tectonic transition envisaged in two magmatic episodes at the kuruer cu au deposit western tianshan nw china abstract the western tianshan in nw china is one of the most important gold provinces in the central asian orogenic belt caob the recently discovered kuruer cu au deposit has been interpreted to represent a transition from high sulfidation epithermal to porphyry mineralization system in this study we present new la icp ms zircon u pb ages for the many magmatic rock types at kuruer including the dahalajunshan formation andesitic tuff 333 2 1 6 ma diorite porphyry 269 7 2 0 ma slightly altered 264 4 2 6 ma and intensively altered 270 5 2 5 ma albite porphyry these ages reveal two distinct magmatic episodes the early carboniferous dahalajunshan formation wall rocks andesitic tuff samples contain narrow ranges of sio 2 60 29 61 28 wt tio 2 0 96 0 98 wt al 2 o 3 16 55 16 57 wt and fe 2 o 3 t 5 36 5 57 wt the tuff is characterized by lree enrichment and hfse depletion as well as lree hree enrichment la yb n 8 31 8 76 and negative eu anomalies eu 0 64 0 76 zircon e hf t values are 5 4 8 2 and two stage hf model ages t dm2 are 821 1016 ma indicating partial melting of a moderately depleted mantle wedge with precambrian continental crustal input the ore forming middle permian diorite porphyry and quartz albite porphyry have variable major oxide compositions e g sio 2 53 09 53 12 wt for the diorite porphyry 70 84 78 03 wt for the albite porphyry and 74 07 75 03 wt for the quartz albite porphyry but similar chondrite normalized ree and primitive mantle normalized multi element patterns these porphyries display lree enrichment and hfse depletion as well as elevated lree hree enrichment and negative eu anomalies the positive zircon e hf t values 11 7 15 9 for the diorite porphyry 8 9 14 9 for the albite porphyry and young two stage hf model ages t dm2 282 542 ma for the diorite porphyry 337 717 ma for the albite porphyry indicate a major juvenile continental crustal involvement we propose that the carboniferous and middle permian magmatism was formed in a continental arc and post collisional settings respectively with the latter episode responsible for the cu au mineralization

recent and past anthropogenic impact on a mediterranean lagoon lead isotope constraints from mussel shells abstract the aim of this study was to determine the variations of past and present anthropogenic impact on a coastal lagoon thau s france using mussel shells as indicators the concentrations and isotopic compositions of pb in recent shells from the edge and the center of a lagoon and in ancient shells bronze age and 1st 6th century have been determined to compare metal levels in different environments recent shells from the center of the lagoon show somewhat lower pb concentrations than shells from the edge of the lagoon using pb isotopes it is possible to constrain pb sources and their contribution to the shells on the basis of several natural and anthropogenic endmembers rocks road traffic sete harbour and water treatment plants recent lagoon shells are clearly influenced by anthropogenic input from the harbour and road traffic anthropogenic contributions vary with location the pb isotopic composition was also determined on ancient shells dating from the roman empire whose pb concentrations are similar to the recent shells from the lagoon center their isotopic compositions are compared to different pb sources local castings english and spanish ingots and regional mining districts it is suggested that local anthropogenic impact existed since the roman empire and is linked with population development in the area

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

lead isotope study of zn pb ore deposits associated with the basque cantabrian basin and paleozoic basement northern spain a total of forty three galena samples from syngenetic and epigenetic pb zn mineralizations emplaced in the lower cretaceous basque cantabrian basin and paleozoic basement of the cinco villas massif in the western pyrenees have been analyzed for pb isotopic composition galena from sedex mineralizations hosted in carboniferous clastic rocks in the cinco villas massif display an homogeneous lead isotopic signature 206pb 2044pb 18 43 207pb 204pb 15 66 208pb 204pb 38 69 suggesting a single lead reservoir these values are slightly more radiogenic than lead from other european hercynian deposits possibly reflecting the influence of a more evolved upper crustal source underlying paleozoic sediments are proposed as lead source for the cinco villas massif ores analyses from twenty six galena samples from the four strata bound ore districts hosted in mesozoic rocks reveal the existence of two populations regarding their lead isotopic composition galena from the western santander districts e g reocin is characterized by more radiogenic isotope values 206pb 204pb 18 74 207pb 204pb 15 67 208pb 204pb 38 73 than those from the central and eastern districts troya legorreta central and western vizcaya 206pb 204pb 18 59 207pb 204pb 15 66 208pb 204pb 38 73 in all districts the most likely source for these mineralizations was the thick sequence of lower cretaceous clastic sediments the existence of two separate lead isotopic populations could be the result of regional difference in the composition of the basement rocks and the clastic sediments derived of it or different evolution histories in both sub basins isotopic ratios indicate an increase in crustal influence as the age of the ores decreases

accreted seamounts in north tianshan nw china implications for the evolution of the central asian orogenic belt the carboniferous bayingou ophiolitic melange is exposed in north tianshan accretionary complex in the southwestern part of the central asian orogenic belt caob the melange is mainly composed of serpentinised ultramafic rocks including harzburgite lherzolite pyroxenite dunite and peridotite pillowed and massive basalts layered gabbros radiolarian cherts pelagic limestones breccias and tuffs and displays block in matrix structures the blocks of ultramafic rocks gabbros basalts cherts and limestones are set in a matrix of serpentinised ultramafic rocks massive basalts and tuffs the basaltic rocks in the melange show significant geochemical heterogeneity and two compositional groups one ocean island basalt like and the other mid ocean ridge like can be distinguished on the basis of their isotopic compositions and immobile trace element contents such as light rare earth element enrichment in the former but depletion in the latter the more enriched basaltic rocks are interpreted as remnants fragments of seamounts derived from a deep mantle reservoir with low degrees 2 3 of garnet lherzolite mantle melting the depleted basalts most likely formed by melting of a shallower spinel lherzolite mantle source with 15 partial melting it is probable that both groups owe their origin to melting of a mixture between plume and depleted morb mantle the results from this study when integrated with previous work indicate that the junggar ocean crust comprising a significant number of seamounts was likely to have been subducted southward beneath the yili central tianshan block in late devonian early carboniferous the seamounts were scraped off and accreted along with the oceanic crust in an accretionary wedge to form the bayingou ophiolitic melange we present a model for the tectonomagmatic evolution of this portion of the caob involving prolonged intra oceanic subduction with seamount accretion

basin evolution within and adjacent to the tien shan range nw china two late palaeozoic collisions produced the ancestral tien shan range extension following the younger collision preceded a phase of thermal subsidence associated with fluvial and lacustrine sedimentation throughout the jurassic cretaceous and early tertiary this thermal subsidence was interrupted by renewed movement on palaeozoic reverse faults caused by the mesozoic collisions at the southern margin of asia the india asia collision in the early tertiary has produced widespread thrusting in the tien shan which in turn is responsible for the formation of active foreland basins at the southern and northern margins of the range and similar basins within the range itself this compression produced uplift and relief and consequent erosion gave rise to alluvial fans braidplains and ephemeral lakes in an extremely arid environment

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

structural styles and zircon ages of the south tianshan accretionary complex atbashi ridge kyrgyzstan insights for the anatomy of ocean plate stratigraphy and accretionary processes abstract the anatomy of an ancient accretionary complex has a significance for a better understanding of the tectonic processes of accretionary orogens and complex because of its complicated compositions and strong deformation with a thorough structural and geochronological study of a fossil accretionary complex in the atbashi ridge south tianshan kyrgyzstan we analyze the structure and architecture of ocean plate stratigraphy in the western central asian orogenic belt the architecture of the atbashi accretionary complex is subdivisible into four lithotectonic assemblages some of which are melanges with block in matrix structure 1 north ophiolitic melange 2 high pressure hp ultra high pressure uhp metamorphic assemblage 3 coherent melange assemblage and 4 south ophiolitic melange relationships between main units are tectonic contacts presented by faults the major structures and lithostratigraphy of these units are thrust fold nappes thrusted duplexes and imbricated ocean plate stratigraphy all these rock units are complicatedly stacked in 3 d with the hp uhp rocks being obliquely southwestward extruded detrital zircon ages of meta sediments provide robust constraints on their provenance from the ili central tianshan arc the isotopic ages of the youngest components of the four units are late permian early middle triassic early carboniferous and early triassic respectively we present a new tectonic model of the south tianshan a general northward subduction polarity led to final closure of the south tianshan ocean in the end permian to late triassic these results help to resolve the long standing controversy regarding the subduction polarity and the timing of the final closure of the south tianshan ocean finally our work sheds lights on the use of ocean plate stratigraphy in the analysis of the tectonic evolution of accretionary orogens

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

two contrasting late paleozoic magmatic episodes in the northwestern chinese tianshan belt nw china implication for tectonic transition from plate convergence to intra plate adjustment during accretionary orogenesis abstract late carboniferous to early permian is a critical period for the final amalgamation of the central asian orogenic belt caob however as most of the accreted terranes of the caob are unclear in tectonic nature and origin the timing and processes of their mutual amalgamation have been poorly constrained to understand assembly of the west junggar terrane with the yili block a suite of the late paleozoic magmatic rocks including ignimbrite rhyolite and granite in northwestern chinese tianshan belt were studied for their petrogenesis and tectonic implications our new results of secondary ion mass spectrometry sims zircon u pb dating reveal two separate magmatic episodes ca 300 ma volcanism ignimbrite and rhyolite and ca 288 ma plutonsim biotite granite geochemically for the ca 300 ma volcanism the ignimbrites have low sio2 65 8 71 5 wt and mg 6 13 values and exhibit arc affinity with significantly enriched in large ion lithophile elements lile and depleted in high field strength elements hfse such as nb ta and ti the whole rock end t and zircon ehf t values range from 6 9 to 7 0 and 9 9 to 14 1 respectively indicating a juvenile basaltic lower crustal origin rhyolites have slightly high sio2 72 7 74 0 wt and k2o 3 86 4 53 wt contents high zircon 18o 11 67 13 23 values and low whole rock end t 2 9 to 3 8 and zircon ehf t 2 8 to 10 0 values which may suggest sediment involvements during magma generation in contrast for the ca 288 ma plutonism the biotite granites have obviously higher sio2 74 7 75 5 wt contents and whole rock end t 7 7 to 8 8 zircon ehf t 9 8 to 12 7 and lower zircon 18o 5 99 6 84 values than those of the ca 300 ma volcanic rocks which are consistent with signatures of juvenile magma source according to our estimates of zircon saturation temperatures together with their contrasting genesis we attribute the formation of ca 300 ma high temperature 815 938 c volcanism to oceanic slab break off during assembly of the west junggar terrane with the yili block and relate the generation of ca 288 ma low temperature 723 735 c plutonism to subsequent strike slipping of north tianshan fault that facilitated introduction of water fluxes triggering hydrous partial melting of juvenile lower crust the sequential magmatic episodes in the northwestern chinese tianshan belt may provide a crucial clue to a tectonic transition from plate convergence to intra plate adjustment during the formation of the kazakhstan orocline in the late paleozoic

geochemical discrimination of metabasalt rocks of the fan karategin transitional blueschist greenschist belt south tianshan tajikistan seamount volcanism and accretionary tectonics the fan karategin metamorphic belt south tianshan tajikistan is regarded to be an ancient subduction accretionary complex and is composed of three tectonostratigraphic units which display lithologies consistent with different tectonic settings the mafic schists which make up the major part of the older unit of the belt contain both alkali and tholeiitic metabasalts on the basis of rare earth and other immobile element characteristics the alkali metabasalts are akin to within plate ocean island basalts whereas the tholeiitic metabasalts resemble e type morb the association is interpreted to have been formed on seamount like structures under a within plate plume bedded cherts and marbles in the unit are regarded as ancient pelagic sediments and carbonate caps developed upon basaltic seamounts respectively dismemberment of the seamount related basalts and pelagic sediments and the high p low t prograde metamorphism of the unit rocks up to transitional blueschist greenschist facies was the result of paleoseamount submergence into a subduction zone this unit is tectonically overlain by arc derived metavolcanic unit and a disrupted mainly clastic unit of upper ordovician lower silurian age metavolcanic and metasedimentary rocks of the two upper units have geochemical characteristics compatible with subduction related origin the lithological assemblages of the individual units and their juxtaposition suggest an origin involving collision accretionary processes the fan karategin belt is a subduction accretionary complex which formed during subduction of oceanic crust under a volcanic arc and was subjected to tectonic juxtaposition and imbrication of seamount deep sea trench and volcanic arc sequences

lead isotope behaviour in a polyphased pb zn ore deposit les malines cevennes france les malines mine cevennes france provides an example of pb zn ore bodies that underwent a polyphased evolution on the pb pb diagram experimental points of the les malines ore types always plot in the central part of the field defined for the cevennes metallogenic province this homogeneity the similarities with the pb isotopic compositions of the surrounding rocks and the comparison with pb isotopes evolution of whole rocks and minerals of the neighbouring continental lands which emerged during triassic and liassic times rule out the participation of extraneous pb during the successive concentration stages and agree with an initial metal stock transformed and mobilized in a pb closed system hercynian k feldspars are the main source of the pb preconcentrated during triassic times most of the cevennes pb zn ore bodies could derive from this triassic metal stock nevertheless local pb isotopic anomalies suggest hydrothermal sources for some pb zn ore bodies located along the cevennes fault

crustal structures revealed from a deep seismic reflection profile across the solonker suture zone of the central asian orogenic belt northern china an integrated interpretation abstract the solonker suture zone is one of the most important tectonic boundaries in the southeastern part of the central asian orogenic belt caob an 630 km long reflection seismic profile across this suture was recently completed by the chinese sinoprobe project the processed seismic data show clear crustal structures and provide new constraints on the tectonic and crustal evolution models the moho is delineated as a relatively flat boundary between a strongly reflective lower crust and a transparent mantle at a depth of 40 45 km 14 5 s two way travel time which is in agreement with the refraction data recorded along the same profile in a broad view the profile images an orogen that appears bivergent with and approximately centered on the solonker suture zone the southern portion of this profile is dominated by a crustal scale cratonward propagating fold and thrust system that formed during the late permian and triassic through collision and subsequent convergence in a post collisional stage the major thrust faults are truncated by mesozoic granitoid plutons in the upper crust and by the moho at the base of the crust this geometry suggests that the moho was formed after the thrusting event the northern portion of the profile although partially obliterated by post collisional magmatic bodies shows major south dipping folding and thrusting bands of layered reflectors immediately overlying the moho are interpreted as basaltic sills derived from the mantle episodic mafic underplating may have occurred in this region giving rise to post collisional magmatic events and renewal of the moho a few mantle reflectors are also visible the overall geometry of these mantle reflectors supports the tectonic models that the southern orogen manchurides experienced south directed subduction and the northern orogen altaids underwent north directed subduction prior to collision along the solonker suture zone

s type granite from the gongpoquan arc in the beishan orogenic collage southern altaids implications for the tectonic transition abstract voluminous paleozoic intrusions occur in the beishan orogenic collage boc and their genesis and tectonic background are important to reconstruct the accretion collision processes in the southernmost altaids paleozoic is an important period for arc development in the boc where the gongpoquan and huaniushan arcs are located there are two pulses of magmatism in the huaniushan and gongpoquan arcs i e the ca 470 423 ma i type and ca 424 395 ma s and a type granitoids in this study we focus on two peraluminous granitic plutons in the gongpoquan arc i e the baitoushan muscovite granite and haergen two mica granite aiming at unraveling their petrogenesis and tectonic background zircon la icp ms u pb dating yields emplacement ages of ca 409 395 ma and ca 409 ma for the baitoushan and haergen plutons respectively both the granitic plutons are strongly peraluminous with a cnk ratios of 1 10 1 20 indicative of s type affinities the rocks are characterized by high sio 2 and k 2 o contents with high cao na 2 o ratios moreover the rocks possess low mgo contents rb sr and rb ba ratios together with their relatively high initial 87 sr 86 sr ratios 0 7139 0 7152 and less radiogenic end t values 3 15 to 5 17 implying a clay poor and plagioclase rich crustal source compared with earlier pulse of arc related magmatism ca 470 423 ma the latter pulse of magmatism ca 424 395 ma consists mainly of normal granite characterized by higher sio 2 66 and k 2 o contents weaker fractionated ree patterns and lower eu values and gabbroic to dioritic intrusions are only sporadic moreover the granitoids of the latter pulse show variable but more crust like sr nd isotopic compositions 87 sr 86 sr 0 0 7038 0 7327 end t 6 70 to 0 33 than the earlier ones 87 sr 86 sr 0 0 7024 0 7080 end t 2 56 to 8 86 indicating that the early devonian ca 424 395 ma experienced extensive crustal melting with minor involvement of mantle materials considering early devonian geological evidence the transition from i to s and a type magmatism probably reflects the early devonian amalgamation between the gongpoquan and huaniushan arcs which caused not only regional unconformity and strong deformation metamorphism but also extensive melting of the accreted crustal materials in the boc

geological context and plumbotectonic evolution of the giant almaden mercury deposit abstract the almaden mine has been the largest among several mercury deposits that represent the biggest mercury concentration in the world the deposits form a mining district which is located in a 30 km long and up to 15 km wide wnw ese oriented syncline where a thick lower ordovician upper devonian siliciclastic sedimentary sequence outcrops most of the deposits are located in the south subvertical syncline flank which has an opposite vergence to the rest of the region of special note is the presence of important nw se to wnw ese crustal structures that played a major role at several times during the regional geological history and controlled the sedimentary unit distribution volcanism and deformation one of these structures seems to have played an important role in the almaden area probably having been responsible for the anomalous syncline geometry this structure acted during the e w variscan shortening as a ductile fragile sinistral shear zone that resulted in a subvertical attitude of the southern almaden syncline flank affecting the sedimentary sequence longitudinally the hg deposits in the region correspond to two types stratabound and stockworks the former are hosted in well defined criadero quartzite orthoquartzite levels of ordovician silurian age these deposits were folded and sheared during the variscan deformation the stockwork deposits filled fractures and veins and partially replaced the volcanic rocks affected by the variscan shear zones the replacement process took place at the end of the e w variscan shortening the almaden deposit belongs to the stratabound type and has three mineralized levels one located in the lower part and the other two in the upper part of the criadero quartzite of minor relevance other small stockwork bodies replacing a volcanic breccia tuff known as frailesca rock have also been exploited this rock formed massive lenticular bodies that have been interpreted as pre variscan diatremes on the basis of field criteria we conclude that the frailesca rock emplacement took place later than cinnabar mineralization after the frailesca rock was formed it was cut by sills of quartz diabase that resulted from a new magmatic event both volcanic materials affect the mercury ore developing small aureoles of contact metamorphism and volatilizing the cinnabar the deposit shows three sectors separated by two straight dextral faults which cut the sinistral wnw ese shears bands the latter affect the mercury ore mostly in its western area lead isotopes from almaden cinnabar deposits show a broad range of values higher than those predicted for the stacey and kramers and cumming and richards crustal pb evolution models but largely tallying with the sardinia evolution line for this sector of the variscan basement quite well the data set plotted along the sardinia curve in several well defined clusters that could be interpreted as a lead extraction by means of large scale convective hydrothermal systems from a lead reservoir located in the upper crust at a time indicated by the sardinia curve the estimated ages for this lead model evolution indicate lead extraction as having occurred during the late silurian devonian 420 375 ma late variscan 300 ma permian triassic 290 220 ma late jurassic early cretaceous 200 150 ma and eocene oligocene 50 25 ma and are coincident with the main extensional tectonic episodes from late ordovician to devonian permian to triassic and late jurassic to early cretaceous this shows that cinnabar is likely to have been mostly remobilized crystallized during the regional extensional tectonic events capturing lead from the host sedimentary sequence this lead was mobilized by large scale long term hydrothermal convective cells at various times constituting a complex geotectonic history for the ore forming processes

the bertholene uranium deposit mineralogical characteristics and upb dating of the primary u mineralization and its subsequent remobilization consequences upon the evolution of the u deposits of the massif central france abstract in the southern part of the massif central france u ores of the rouergue area are spatially related to the unconformity of the permian carboniferous sedimentary terranes overlying the variscan basement the bertholene uraniferous orebody is located in the palanges precambrian orthogneiss close to the unconformity and in the vicinity of a highly deformed part of the orthogneiss massif marked by the occurrence of mylonitic bands for which a variscan age is assumed the u ore is mainly expressed as coffinite but primary u oxide was also identified hydrothermal alteration stages have been defined a first albitization stage is expressed on a regional scale and successive stages of argillization silicification and lastly carbonate crystallization have been described in the mining district the u oxide formation followed the silicification stage u pb systematics were used on coffinite and u oxide to define the evolution of the bertholene deposit 1 1 primary u oxide was found to be 173 9 ma old this phase of u concentration or remobilization has also been dated in the two other u deposits of the southern part of the massif central lodeve pierres plantees as well as in deposits located in limousin and morvan france the event which mobilized the u in these deposits is related to the consequences of the liassic pre rifting phase that preceded the opening of ligurian ocean during malm times 2 2 complex phenomena have affected the coffinite u pb system u pb and pb pb data show that 2 1 a unsupported isotopically heterogeneous radiogenic pb was in the coffinites during their genesis and may reflect the role of primary u oxide as their source 2 2 b in some coffinites rn loss phenomena controlled mainly the evolution of the u pb system two main types of coffinites were identified and the u pb data indicate that the coffinitization event occurred during oligocene times 40 30 ma or from the oligocene to actual times

formation of positive end t granitoids from the alataw mountains xinjiang china by mixing and fractional crystallization implication for phanerozoic crustal growth abstract syn collisional granitic plutons intruded into devonian and carboniferous sedimentary and volcanic rocks along the southern slope of the alataw mountains in the north tianshan fold belt these intrusions are 307 290 ma in age granitoids in the eastern part of the mountain show characteristics similar to i type affinity while those in the western part show s type affinity carboniferous volcanic rocks andesite to rhyolite cover the eastern part of the region they share many common geochemical characteristics with the eastern granitoids intermediate and acid igneous rocks show positive e nd t values ranging from 7 to about 0 and initial sr isotopic ratios of 0 702 0 711 carboniferous basalts exposed in the region give 87 sr 86 sr t 0 701 0 704 and e nd t 7 12 country rock and basement gneisses show 87 sr 86 sr t 0 707 0 715 and e nd t 5 to 8 the positive e nd t suggests that mantle derived material play an important role in petrogenesis of the alataw granitoids a common mantle derived component is much likely to be involved in the petrogenesis of the granites from northern xinjiang since the positive e nd t granites with early paleozoic ages are widespread in the entire central asia mongolia granitic belt our data provide a constraint on the sr and nd isotopic ratios of this mantle derived mafic component which may be similar to those of the carboniferous basalts but can also have lower e nd t of 3 7 positive e nd t values suggest large mantle input representing a contribution of mantle derived materials to the continental crust it is very likely that this event of continental growth took place in very late proterozoic or early paleozoic

pb isotope evidence for the origin of lead in strata bound pb zn deposits in triassic carbonates of the eastern and southern alps a comparison of ore lead isotope ratios of pb zn deposits hosted in triassic carbonates of the eastern and southern alps with the isotopic composition of trace leads of their host rocks of triassic volcanics and of the underlying clastic sediments shows that these rocks could have supplied only part of the ore lead the isotopic signature of feldspar lead from crystalline basement rocks however reveals that they must have contributed a significant amount of metal to these deposits the presence of barite and of thallium is also indicative that feldspars were the main source of lead arsenic is one of the few important trace elements in these deposits and is known to occur in some areas of lower paleozoic metasediments in unusually high concentrations any model explaining the origin of these deposits must consider the extensive leaching of the basement and to some extent of the overlying clastic sediments as well how the metal bearing solutions entered the lagoonal back reef areas is still open to question as feeder channels have not yet been positively identified the results further demonstrate that the basement also acted as a metal source for galena bearing deposits hosted in permian sediments vein type deposits in permian volcanics and probably the barite fluorite polymetallic deposits along a devonian erosional surface in the carnic alps as well

existence de mineralisations plombo zinciferes syngenetiques du substratum cambrien du district des malines gard france l essentiel du minerai actuellement exploite dans le district minier des malines gard france provient d amas plombo zinciferes apparamment constitues par le remplissage de cavites paleo karstiques post stephaniennes developpees dans la dolomie cambrienne a proximite de la surface de discordance qui la separe de sa couverture mesozoique l etude detaillee des mineralisations du substrat carbonate revele l existence de concentrations egalement plombo zinciferes mais stratoides et syngenetiques de la dolomie qui les supporte en effet ces mineralisations ont enregistre tous les phenomenes ayant affecte la dolomie encaissante figures de sedimentation et de deformation synmetamorphe orogenie varisque fracturation post schisteuse anterieure a la discordance permo triasique il est propose de considerer que ce type de mineralisation alimenta en metaux de base voire en soufre les pieges karstiques post hercyniens on en trouve notamment remanie a l etat d elements brechiques dans les remplissages paleo karstiques

paleozoic multiple accretionary and collisional processes of the beishan orogenic collage in the paper by xiao and others american journal of science v 310 p 1553 1594 1 please substitute figure 16 reproduced here for figure 16 that appears between pages 1573 and 1574 the original figure 16 2 was printed at an improper size figure 3 1 lookup volpage 310

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

geology mineralization and fluid inclusion characteristics of the kashkasu w mo cu skarn deposit associated with a high potassic to shoshonitic igneous suite in kyrgyzstan tien shan toward a diversity of w mineralization in central asia abstract the kashkasu deposit is part of the subduction related late paleozoic late carboniferous metallogenic belt of tien shan it is associated with a multiphase monzodiorite monzonite granodiorite granite pluton of the magnetite series high k calc alkaline to shoshonitic igneous suite the deposit contains zones of w mo cu oxidized prograde and retrograde skarns with abundant andraditic garnet magnetite locally scapolite and k feldspar as well as scheelite chalcopyrite and molybdenite skarns are overprinted by quartz carbonate sericite phyllic alteration zones with scheelite and sulfides prograde calcic skarn and initial retrograde skarns were formed from a high temperature 650 c to 450 550 c high pressure 2000 bars to 600 900 bars magmatic hydrothermal low to high salinity aqueous chloride fluid the gradual fluid evolution was interrupted by the intrusion of granodiorite and likely associated release of low salinity 7 8 wt nacl equiv fluid ascent of this fluid to shallower levels and or its cooling to 400 500 c has resulted in phase separation into low salinity 2 1 3 1 wt nacl equiv vapor and coexisting brine 35 40 wt nacl equiv the boiling was coincident with most intense scheelite deposition in retrograde skarn later retrograde skarn assemblages were formed from a gaseous low to moderate salinity 3 4 8 1 wt nacl equiv fluid and then from high salinity 37 42 wt nacl equiv aqueous chloride fluids the latter being enriched in ca 17 20 wt cacl2 that could also affect scheelite deposition another cycle of fluid exsolution from crystallizing magma corresponded to quartz carbonate sericite scheelite sulfide phyllic alteration stage with the early low salinity 5 3 8 4 wt nacl equiv fluid followed by later high salinity 33 5 38 2 wt nacl equiv fluid the sulfur isotope data 34s 5 1 to 9 0 suggest significant sulfur sourcing from sedimentary rocks enriched in seawater sulfate possibly evaporites

lead isotope zoning in galena an ion microprobe study of a galena crystal from the buick mine southeast missouri ion microprobe techniques have been used to determine the variations of pb isotope ratios within a single octahedral crystal of galena from the buick mine southeast missouri the crystal shows uniform concentric zonation of pb isotope ratios with a total variation of approximately 3 percent in 208 pb 206 pb and approximately 4 percent in 207 pb 206 pb and with the crystal margin being less radiogenic lower 206 204 than the core the range in the observed 208 pb 206 pb ratio is larger than that observed previously for bulk galena analyses from throughout the mine and is almost as large as the total variation reported for the whole southeast missouri ore district the ion probe results are demonstrated to be accurate to 0 1 0 2 percent by comparison with conventional mass spectrometric analyses performed on microsamples of the same crystal the ion probe technique holds promise for establishing a pb isotope chronostratigraphy for the ore bearing solutions which will be useful in delineating temporal and spatial aspects of the fluid circulation patterns

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

continental crust melting induced by subduction initiation of the south tianshan ocean insight from the latest devonian granitic magmatism in the southern yili block nw china abstract the tianshan belt of the southwestern central asian orogenic belt was generated by paleozoic multi stage subduction and final closure of several extinct oceans including the south tianshan ocean between the kazakhstan yili and tarim blocks however the subduction initiation and polarity of the south tianshan ocean remain issues of highly debated this study presents new zircon u pb ages geochemical compositions and sr nd isotopes as well as zircon hf isotopic data of the latest devonian to early carboniferous granitic rocks in the wusun mountain of the yili paleozoic convergent margin which together with the spatial temporal distributions of regional magmatic rocks are applied to elucidate their petrogenesis and tectonic linkage to the northward subduction initiation of the south tianshan ocean our zircon u pb dating results reveal that these granites were emplaced at the time interval of 362 0 1 2 360 3 1 9 ma suggesting a marked partial melting event of the continental crust in the latest devonian to early carboniferous these granites based on their mineral compositions and textures can be categorized as monzogranites and k feldspar granites geochemically both monzogranites and k feldspar granites have characters of i type granites with high k 2 o contents 4 64 4 83 wt and the k feldspar granites are highly fractionated i type granites while the monzogranites have features of unfractionated i type granites whole rock sr nd isotopic modeling results suggest that ca 20 40 mantle derived magmas may be involved in magma mixing with continental crust partial melts to generate the parental magmas of the granites the mantle derived basaltic magmas was inferred not only to be a major component of magma mixture but also as an important heat source to fuse the continental crust in an extensional setting which is evidenced by the high zircon saturation temperatures 713 727 c and 760 782 c of the studied granites the latest devonian to early carboniferous extensional setting in the wusun mountain region of the yili paleozoic convergent margin is addressed by the subduction initiation of the south tianshan ocean and constituted a late paleozoic nascent arc back arc system in the southwestern caob

lead isotopic composition of hercynian granitic k feldspars constrains continental genesis lead isotope compositions have been determined in many k feldspars from granitic rocks emplaced during the variscan hercynian orogeny sensu lato around 300 myr in various parts of europe and the eastern us the ratios show a regular geographical pattern with contours arched around southern france and parallel to the atlantic coast of the us this distribution parallels predriftpalaeogeographical zones during the palaeozoic the lead isotope pattern of variscan granitic rocks is similar to that of some orogenic volcanic suites but is better explained by crustal melting than by an hercynian mantle crust material mixing the continental crust from these areas must be older than 3 000 myr large scale fluid circulation in the crust during orogenic processes apparently explains the observed geographical patterns of lead isotopes

early carboniferous metamorphism of the neoproterozoic south tien shan karakum basement new geochronological results from baisun and kyzylkum uzbekistan abstract paleozoic evolution of the western tien shan which is built up on the basement of the karakum continent is poorly constrained compared to the better investigated tien shan terranes along the margin of the tarim craton we present magmatic metamorphic and detrital zircon ages for the regionally metamorphosed baisun block and the metasediments comprising the karakum basement in the westernmost parts of the south tien shan terrane age spectra of detrital zircon from metasediments of the baisun metamorphic block and the western south tien shan show remarkable similarities over the vast area extending for ca 500 km and are characterized by major neoproterozoic peak at 1200 600 ma and smaller peaks at 2300 1700 and 2700 2400 ma the 570 540 ma ages of the youngest grains define late neoproterozoic ediacaran early cambrian maximum depositional ages of the metasediments comparison of the obtained age spectra with those published for the adjacent tien shan terranes indicate that the detrital zircon grains in the studied ediacaran sediments were derived from the southern precambrian continents of karakum and tarim while transport from the northern tien shan was limited the age of the barrovian metamorphism in the baisun block is constrained by ages of anatectic granites in the range 352 340 ma corresponding to early carboniferous these ages well match the 340 330 ma ages established for the adjacent lolabulak and garm metamorphic blocks based on the regional distribution of suture zones we suggest that during the carboniferous the relatively small tectonic blocks of the south gissar comprised an archipelago located between the larger continents of karakum and tarim and possibly connected with the paleotethys ocean the archipelago scenario can explain hot and rapid metamorphic and tectonic processes documented in the south gissar similar to the ongoing collision along the australia se asia junction

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

the post variscan tectonic thermal activity in the southeastern metalliferous province of the french massif central revisited with k ar ages of illite abstract this study deals with k ar data of illite and illite rich mixed layers of cambrian and permian metasediments that were subjected to tectono thermal episodes in the montdardier and mas lavayre ore districts of the southeastern massif central france the objective was to differentiate events that altered the metal rich deposits from those that affected only barren host rocks close to the ores on the basis of combined mineralogical analyses and isotopic determinations of the clay material successive tectono thermal events induced illitization at 288 10 246 9 197 6 176 6 and 107 4 ma and probably at 136 4 ma the lack of major geodynamic activities near the studied ore deposits during these times hypothesizes periodic long distance migrations of fluids in the continental crust to explain their occurrences metals seem to have been concentrated at specific places but apparently they were not deposited or altered during post visean tectono thermal pulses recorded by the associated illite the tectonic thermal history of the les malines district confirms that repetitive geodynamic re activations induced local heat transfers however the episode at 246 9 ma apparently did not affect the earlier deposited ores while that at 35 40 ma found in coffinite at pierre plantees was probably not induced by a thermal event but by an alteration event that did not affect the k ar system of the surrounding clay material

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

carboniferous early permian magmatic evolution of the bogda range xinjiang nw china implications for the late paleozoic accretionary tectonics of the sw central asian orogenic belt abstract the late paleozoic magmatic evolution of the bogda range chinese north tianshan is important for understanding the accretionary history of the central asian orogenic belt we investigated the carboniferous and lower permian volcanic and sedimentary sequences of the daheyan section southern bogda range and present new zircon u pb ages and whole rock geochemical data for the volcanic rocks one carboniferous rhyolite is dated at 298 8 ma a permian basalt yielded many proterozoic zircon xenocrysts and its maximum age 297 ma is constrained by the detrital zircon ages of the sandstone that stratigraphically underlies it these volcanic rocks belong to calc alkaline series we further synthesize previous geochronological geochemical and isotopic data of magmatic and sedimentary rocks in the bogda range the available data indicate that the magmatism occurred continuously from 350 ma to 280 ma a comprehensive analysis allows us to propose that 1 the carboniferous to early permian magmatic rocks of the bogda range generally show consistent arc type features 2 increasing mantle input through time suggests intra arc extension in a supra subduction zone 3 the localized occurrence of early permian alkaline pillow basalts and deep water sediments close to the major shear zone advocate a transtensional crustal thinning during the transition from carboniferous convergence to early permian transcurrent tectonics 4 occurrence of a large number of proterozoic zircon xenocrysts in the late paleozoic magmatic rocks and proterozoic detrital zircons in the coeval clastic sediments suggest a continental or transitional basement of the bogda arc 5 subduction in the bogda area terminated prior to the deposition of middle permian terrestrial sediments

late orogenic large scale rotations in the tien shan and adjacent mobile belts in kyrgyzstan and kazakhstan abstract most of kazakhstan belongs to the central part of the eurasian paleozoic mobile belts for which previously proposed tectonic scenarios have been rather disparate of particular interest is the origin of strongly curved middle and late paleozoic volcanic belts of island arc and andean arc affinities that dominate the structure of kazakhstan we undertook a paleomagnetic study of carboniferous to upper permian volcanics and sediments from several localities in the ili river basin between the tien shan and the junggar alatau ranges in southeast kazakhstan our main goal was to investigate the permian kinematic evolution of these belts particularly in terms of rotations about vertical axes in the hope of deciphering the dynamics that played a role during the latest paleozoic deformation in this area this deformation in turn can then be related to the amalgamation of this area with baltica siberia and tarim in the expanding eurasian supercontinent thermal demagnetization revealed that most permian rocks retained a pretilting and likely primary component which is of reversed polarity at three localities and normal at the fourth in contrast most carboniferous rocks are dominated by postfolding reversed overprints of probably mid permian age whereas presumably primary components are isolated from a few sites at two localities mean inclinations of primary components generally agree with coeval reference values extrapolated from baltica whereas declinations from primary as well as secondary components are deflected counterclockwise ccw by up to 90 such ccw rotated directions have previously also been observed in other tien shan sampling areas and in the adjacent tarim block to the south however two other areas in kazakhstan show clockwise cw rotations of permian magnetization directions one area is located in the kendyktas block about 300 km to the west of the ili river valley and the other is found in the chingiz range to the north of lake balkhash and about 400 km to the north of the ili river valley the timing of the ccw as well as cw rotations is clearly later than the disappearance of any marine basins from northern tarim the tien shan and eastern kazakhstan so that the rotations cannot be attributed to island arc or andean margin plate settings instead we attribute the rotations to large scale east west present day coordinates sinistral wrenching in an intracontinental setting related to convergence between siberia and baltica as recently proposed by natal in and engor natal in b a and engor a m c 2005 late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure tectonophysics 404 175 202 our previous work in the chingiz and north tien shan areas on ordovician and silurian rocks suggested relative rotations of 180 whereas the permian declination differences are of the order of 90 between the two areas thus we assume that about 50 of the total post ordovician rotations are of pre late permian age with the other half of late permian earliest mesozoic age the pre late permian rotations are likely related to oroclinal bending during plate boundary evolution in a supra subduction setting given the calc alkaline character of nearly all of the pre late permian volcanics in the strongly curved belts

from oblique accretion to transpression in the evolution of the altaid collage new insights from west junggar northwestern china abstract along active margins tectonic features that develop in response to plate convergence are strongly controlled by subduction zone geometry in west junggar a segment of the giant palaeozoic collage of central asia the west karamay unit represents a carboniferous accretionary complex composed of fore arc sedimentary rocks and ophiolitic melanges the occurrence of quasi synchronous upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the west junggar latest carboniferous ca 300 ma alkaline plutons postdate this early phase of folding which was synchronous with accretion of the carboniferous complex the permian dalabute sinistral fault overprints carboniferous ductile shearing and split the west karamay unit ca 100 km apart oblique convergence may have been provoked by the buckling of the kazakh orocline and relative rotations between its segments depending upon the shape of the convergence zone either upright folds and fold with vertical axes or alternatively strike slip brittle faults developed in response to strain partitioning sinistral brittle faulting may account for the lateral imbrication of units in the west junggar accretionary complex

the baikalide altaid transbaikal mongolian and north pacific orogenic collages similarity and diversity of structural patterns and metallogenic zoning

geochronology petrogenesis and tectonic implications of triassic granitoids from beishan nw china abstract five triassic granitic plutons have been identified from the beishan orogen by zircon u pb dating that defines two age groups 240 238 ma and 225 217 ma they belong to the high k calc alkaline and shoshonitic series and have alkalic and alkali calcic characteristics and are weakly peraluminous metaluminous these granitoids are mainly highly fractionated i type granite and a type granite they have high i sr values 0 7049 0 7096 and negative e nd t values of 0 9 to 2 8 with nd model ages of 0 89 1 13 ga suggesting a crustal contribution they also exhibit relatively high zircon e hf t values 1 3 to 6 1 and two stage hf model ages of 1 34 0 87 ga suggesting a mixture of mantle and various amounts of crustal components the mantle component probably originated from underplated magmas produced by partial melting of lithospheric mantle metasomatized by fluids or melts possibly derived from pre existing subducted materials the mid triassic 240 238 ma pluton has relatively high sr y 15 9 41 8 ratios and mgo 1 22 3 77 contents with negligibly to weakly negative eu anomalies eu 0 57 0 80 indicating adakite like features this was likely the result of partial melting of crustal components in response to voluminous underplated mantle derived magmas probably linked to lithospheric delamination and asthenospheric upwelling the late triassic 217 225 ma granitic plutons show strong negative anomalies of eu ba nb ta sr p and ti these were likely the result of fractional crystallization and crustal contamination for the granitic magma emplaced in a post orogenic setting

structural control and geological significance of the zn pb ores formed in the benasque pass area central pyrenees during the post late ordovician extensional event of the gondwana margin abstract the benasque pass area central pyrenees is located in the eastern part of the variscan lys caillaouas massif where cambro ordovician rocks of the hesperian massif crop out in the area several zn pb deposits are located in variscan structures lead isotopes indicate a late ordovician early devonian model age for the deposits in the region an unconformity between pre late ordovician and late ordovician rocks has been defined by several authors and has been identified in the study area the first structures observed in the benasque pass area consist of a pre variscan cleavage which only affects the pre late ordovician rocks in the study area the main structures correspond to two variscan generations i e w trending north verging folds which are associated with the main foliation s 1 d 1 ii e w trending upright folds and associated small south directed thrusts d 2 d 2 structures are the ones hosting the zinc lead ore in the benasque pass area d 1 and d 2 variscan structures have developed under low grade metamorphic conditions some faults observed in the north and the south of the study area may have alpine movement in the benasque pass area the strongly silicified and brecciated zinc lead ore is mainly developed in the d 1 short limb of the mina peak syncline within which s 1 foliation is intensely folded and cross thrust by d 2 structures taking into account their model age all these zinc lead deposits seem to be stratiform stratabound or filling open spaces in origin and related to the pre variscan extension described for the central pyrenees however the zinc lead ore is hosted in strongly silicified and brecciated variscan structures the 34 s isotopic composition of sulfides indicates that the metamorphism and deformation did not completely obliterate the original isotopic composition suggesting that sulfur in the benasque pass has mainly come from the reduction of marine sulfate extracted from the rocks of the metasedimentary sequence in the benasque pass area the lead isotope ratios are homogeneous and have a pre variscan model age which is also the age of the host rocks in the case of the benasque pass the deposits occurred in variscan structures making it impossible to recognize their original pre variscan characteristics indicated by lead isotopes model age the correlation between the pb isotope data for deposits from the benasque pass and aran valley also located in the central pyrenees and those for other deposits from the southern european gondwana is evident and the isotopic data set closely fits the two stage pb evolution model for sardinia terrane the coherence of the pb isotope trends in all the deposits suggests that pb was extracted at various times from sources with similar time averaged u pb th pb and th u values through a process of leaching of the basement rocks by large volumes of hydrothermal fluids in the case of the pyrenees central and eastern the lead and other metals present in the deposit were extracted by hydrothermal fluids from the upper crust rocks during the post late ordovician extensional event of the gondwana margin

nd sr pb isotopic constraints on metal and fluid sources in w sb au mineralization at woxi and liaojiaping western hunan china this paper presents nd sr pb isotope data on scheelite inclusion fluids and residues of gangue quartz and sulfides from the w sb au ore deposits at woxi and liaojiaping ljp in the xuefeng uplift belt xub western hunan china sm and nd concentrations in scheelite from woxi are much lower than in scheelite from ljp and can be distinguished by their high 147sm 144nd ratios of 1 25 from the much lower ratios around 0 26 in scheelites from the ljp end values compared to values at 200 ma which is the average timing of granitoid emplacement during the indosinian yanshanian periods in the xub are around 10 for the ljp and compare well with the range of 5 to 11 defined by the granitoids whereas they are around 27 for scheelite from woxi this might indicate that rees in the mineralizing fluids at ljp originated from granitoids that are concentrated along the southern border of the xub whereas in the case of woxi the original fluids might have been masked by rees released during intense high temperature wall rock alteration of unexposed precambrian basement rocks at depth sr isotopes of scheelite from these two deposits show similar relations to host nearby rocks in that 87sr 86sr t 200 ma ratios of 0 721 for ljp scheelite agree with values ranging between 0 718 0 726 for granitoids whereas these ratios are much higher i e 0 745 for scheelite from woxi and correspond to the 87sr 86sr t 200 ma ratio range of 0 743 0 749 for precambrian host slates crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two point fluid residue tie lines in rb sr isochron diagrams however sr released from fluid inclusions generally reveals lower initial 87sr 86sr ratios than the respective residues and shows affinities to 87sr 86sr t 200 ma values of indosinian yanshanian granitoids both at woxi and ljp pb stepwise leaching of scheelite and sulfides did not result in sufficient spreads in pb isotope diagrams and therefore no information regarding exact mineralization ages in the two deposits could be deduced overall ore pb isotopes reveal upper crustal signatures and are compatible with pb isotope signatures of the predominant precambrian slates in the woxi area steep trajectories through late stage quartz sulfide mineralization in pb isotope diagrams may hint at mixing scenarios involving pb from the host rocks and a component with lower 207pb 204pb and 208pb 204pb ratios relative to 206pb 204pb ratios which cannot be linked to any known reservoir in the xub mining district sr isotopes of four out of seven residual sulfide samples from woxi plot along a paleomixing line at an age of 199 8 ma supporting a mixing scenario for the fluids indicated by the pb isotopes and pointing to a possible genetic relationship with the emplacement of indosinian yanshanian granitoids the budgets of rees rb sr and pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but after sealing of the major pathways the mineralizing fluids tend to have better preserved their original signatures these attest a genetic relationship between the metallogeny in the xub w sb au province and the emplacement of indosinian yanshanian granitoids during mesozoic intracontinental tectonic uplift and thrusting

ore lead isotope pattern from the iglesiente sulcis area sw sardinia and the problem of remobilization of metals in sw sardinia syngenetic to syndiagenetic pb zn ores occur in cambrian carbonates along the unconformity between the cambrian and ordovician in permo triassic karsts and in vein type deposits related to late hercynian granites which also contact metamorphosed some cambrian deposits in all types of deposits the leadisotope ratios show similarly high 238u 204pb and high w 232th 204pb values indicating a crustal origin for the lead most of the cambrian ores contain isotopically similar or identical leads whereas in the younger deposits the isotope ratios vary and suggest that especially the lead of permo triassic ores may consist to a large extent of remobilized cambrian possibly also ordovician ore lead plus a hercynian component

40 ma of hydrothermal w mineralization during the variscan orogenic evolution of the french massif central revealed by u pb dating of wolframite we present u pb thermal ionization mass spectrometer tims ages of wolframite from several granite related hydrothermal w sn deposits in the french massif central fmc located in the internal zone of the variscan belt the studied wolframite samples are characterized by variable u and pb contents typically 10 ppm and show significant variations in their radiogenic pb isotopic compositions the obtained u pb ages define three distinct geochronological groups related to three contrasting geodynamic settings i visean to namurian mineralization 333 327 ma coeval with syn orogenic compression and emplacement of large peraluminous leucogranites ca 335 325 ma ii namurian to westphalian mineralization 317 315 ma synchronous with the onset of late orogenic extension and emplacement of syn tectonic granites ca 315 310 ma and iii stephanian to permian mineralization 298 274 ma formed during post orogenic extension contemporaneous with the permian volcanism in the entire variscan belt the youngest ages 276 274 ma likely reflect the reopening of the u pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration e g ferberitization our results demonstrate that w sn mineralization in the fmc formed during at least three distinct hydrothermal events in different tectono metamorphic settings over a time range of 40 ma

accretionary and collisional orogenesis in the south domain of the western central asian orogenic belt caob abstract the central asian orogenic belt caob was the result of long lived multi stage tectonic evolution including proterozoic to paleozoic accretion and collision mesozoic intracontinental modification and cenozoic rapid deformation and uplift the accretionary and collisional orogenesis of its early history generated a huge orogenic collage consisting of diverse tectonic units including island arcs ophiolites accretionary prisms seamounts oceanic plateaus and micro continents these incorporated orogenic components preserved valuable detailed information on orogenic process and continental crust growth which make the caob a key region to understanding of continental evolution mantle crust interaction and associated mineralization the western caob refers to the west region in north xinjiang of china and circum balkash of kazakhstan with occurrences of the spectacular kazakhstan orocline and its surrounding mountain belts because orogenic fabrics of this part mostly preserve their original features caused by the interactions among the southern siberian active margin in the north and the tarim craton in the south the western caob can be regarded as an ideal region to study the processes of the accretionary and collisional orogenesis and associated mineralization since a large number of researchers have been working on this region research advances bloom strikingly in a short time period therefore we in this special issue focus on these new study advances on the south domain of the western caob including the kazakhstan collage system tianshan orogenic belt and beishan region and it is anticipated that this issue can draw more attention from the international research groups to be interested in the studies on orogenesis of the caob

geometry kinematics and tectonic models of the kazakhstan orocline central asian orogenic belt abstract the central asian orogenic belt caob is one of the largest accretionary orogens on earth and is characterized by the occurrence of tight oroclines kazakhstan and tuva mongolian oroclines the origin of these large scale orogenic curvatures is not quite understood but is fundamentally important for understanding crustal growth and tectonic evolution of the caob here we provide an outline of available geological and paleomagnetic data around the kazakhstan orocline with an aim of clarifying the geometry kinematics and geodynamic origin of the orocline the kazakhstan orocline is evident in a total magmatic image and can be traced by the continuation of high magnetic anomalies associated with the devonian volcanic belt and the late devonian to carboniferous balkhash yili arc paleomagnetic data show 112 126 clockwise rotation of the northern limb relative to the southern limb in the late devonian to early carboniferous as well as 15 28 clockwise rotation of the northern limb and 39 40 anticlockwise rotation of the southern limb relative to the hinge of the orocline during the late carboniferous to permian we argue that the kazakhstan orocline experienced two stage bending with the early stage of bending late devonian to early carboniferous 112 126 driven by slab rollback and the later stage late carboniferous to permian 54 68 possibly associated with the amalgamation of the siberian tarim and baltic cratons this new tectonic model is compatible with the occurrence of rift basins the spatial migration of magmatic arc and the development of large scale strike slip fault systems during oroclinal bending

late cenozoic tectonics of the kepingtage thrust zone interactions of the tien shan and tarim basin northwest china the kepingtage kalpin thrust zone northwest china is an actively deforming part of the india asia collision system it lies south of the tien shan has an area of 16 000 km2 and consists of arcuate emergent imbricates overall vergence is toward the interior of the tarim basin to the south thrust sheets typically expose upper cambrian to permian platformal strata thrusting is largely thin skinned thin upper cambrian evaporites are likely to be the main decollement horizon the kepingtage thrust zone is the only margin of the tarim basin to deform in this style in the cenozoic it is replaced to the east and west by thrust zones which have propagated shorter distances into the interior of the tarim basin thick up to 10 km mesozoic and cenozoic clastic successions are present and deformed in these regions such successions are not present in the kepingtage thrust zone or the adjacent bachu uplift within the tarim basin because of episodic activity on steep northwest southeast trending thrusts which define the margins of the bachu uplift these mesozoic cenozoic strata may have suppressed the ability of regions along strike from the kepingtage thrust zone to deform by thin skinned thrusting utilizing the upper cambrian decollement the along strike variation in active thrusting at the southern margin of the tien shan is an example of syntectonic sedimentation controlling thrust belt deformation style a balanced section across the thrust zone indicates 28 shortening equivalent to 35 km this is equivalent to an average slip rate of 1 8 mm yr 1 and a strain rate of 4 4 10 16 s 1 assuming deformation began at circa 20 ma active deformation is focused along the frontal thrust the kepingtage fault the northern boundary of the kepingtage thrust zone is formed by the south tien shan fault this major north dipping thrust is seismically active with published earthquake focal depths at midcrustal levels 14 and 18 km it juxtaposes upper carboniferous sedimentary rocks of different facies and different paleozoic deformation histories speculatively it represents a reactivation of a late paleozoic thrust which originated at the boundary between the platformal interior of the tarim block and a deeper water foreland basin to its north

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

devonian paleomagnetism of the north tien shan implications for the middle late paleozoic paleogeography of eurasia the ural mongol belt umb between siberia baltica and tarim is widely recognized as the locus of asia s main growth during the paleozoic but its evolution remains highly controversial as illustrated by the disparate paleogeographic models published in the last decade one of the largest tectonic units of the umb is the kokchetav north tien shan domain kntd that stretches from tarim in the south nearly to the west siberian basin the kntd comprises several precambrian microcontinents and numerous remnants of early paleozoic island arcs marginal basins and accretionary complexes in late ordovician time all these structures had amalgamated into a single contiguous domain its paleogeographic position is of crucial importance for elucidating the paleozoic evolution of the umb in general and of the urals in particular the aral formation located in kyrgyzstan in the southern part of the kntd consists of a thick upper devonian frasnian basalt andesite sequence paleomagnetic data show a dual polarity characteristic component dec inc 286 56 95 9 k 21 n 15 sites the primary origin of this magnetization is confirmed by a positive test on intraformational conglomerates we combine this result with other paleozoic data from the kntd and show its latitudinal motion from the late ordovician to the end of the paleozoic the observed paleolatitudes are found to agree well with the values extrapolated from baltica to a common reference point 42 5 n 73 e in our sampling area for the entire interval hence coherent motion of the kntd and baltica is strongly indicated for most of the paleozoic this finding contradicts most published models of the umb evolution where the kntd is separated from baltica by a rather wide ural ocean containing one or more major plate boundaries an exception is the model of engor and natal in a m c engor b a natal in paleotectonics of asia fragments of a synthesis in a yin and m harrison eds the tectonic evolution of asia cambridge university press cambridge 1996 486 640 in which coherent paleolatitudinal motion of baltica and the kntd is hypothesized the latter as part of the kipchak arc we suggest a parallel hypothesis which explains coherent motion of the kntd and baltica in particular we argue that if a basin with oceanic crust ever existed between the kntd and baltica it was a narrow one without significant active spreading in middle to late paleozoic time notably the paleogeographic position of siberia during the middle paleozoic and hence the width of the khanty mansi ocean between siberia on the one hand and baltica kntd on the other hand remains largely unconstrained because of the paucity of high quality silurian devonian and carboniferous paleomagnetic results from siberia

paleomagnetic study of late paleozoic rocks in the tacheng basin of west junggar nw china implications for the tectonic evolution of the western altaids abstract to better understand the tectonic evolution of west junggar in the western altaids we have conducted a combined paleomagnetic and geochronological study on late devonian d3 late carboniferous c2 and early permian p1 successions from the tacheng basin northwest of china both primary and secondary characteristic remanent magnetization components have been successfully isolated and yield three reliable paleomagnetic poles of c2 and late permian p2 ages the c2 and p2 poles reveal a significant clockwise rotation of 35 6 10 4 which is comparable to the rotation deduced in the western part of the chingiz range during the time interval c2 to p2 similar rotation patterns for the two units suggest that the chingiz west junggar has remained as a quasi rigid block by the p2 time and constituted the northeast limb of the kazakhstan orocline the differential rotation of ca 25 to 30 deduced between the northeast and middle limbs of the kazakhstan orocline further suggests that at least a part of the curvature of the balkhash arc was acquired during the c2 to p2 interval and was a continuation of the middle paleozoic oroclinal bending moreover the c2 poles for west junggar and the junggar block are significantly different while the p2 ones almost overlap supporting the view that final closure of the balkhash junggar ocean occurred during the c2 to p2 interval on the other hand a large scale counterclockwise rotation of ca 80 to 90 is observed in west junggar and junggar relative to the western part of the chingiz range since the p2 time and this rotation probably represents an important intra continental deformation within the western part of the altaids a reconstruction of the paleo asian ocean has been proposed in which the kazakhstan orocline was emphasized by using the paleomagnetic results and geological evidence

paleozoic early mesozoic gold deposits of the xinjiang autonomous region northwestern china the late paleozoic early mesozoic tectonic evolution of xinjiang autonomous region northwestern china provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major eastern asia cratonic blocks these sutures are now represented by the altay shan tian shan and kunlun shan ranges with the former two separated by the junggar basin and the latter two by the immense tarim basin in northernmost xinjiang final growth of the altaid orogen southward from the angara craton is now recorded in the remote mid to late paleozoic altay shan accreted early to middle devonian oceanic rock sequences contain typically small precious metal bearing fe cu zn vms deposits e g ashele orogenic gold deposits are widespread along the major irtysh e g duyolanasayi saidi taerde kabenbulake akexike shaerbulake and tuergen hongshanzui e g hongshanzui fault systems as well as in structurally displaced terrane slivers of the western junggar e g hatu and eastern junggar areas geological and geochronological constraints indicate a generally late carboniferous to early permian episode of gold deposition which was coeval with the final stages of altaid magmatism and large scale right lateral translation along older terrane bounding faults the tian shan an exceptionally gold rich mountain range to the west in the central asian republics is only beginning to be recognized for its gold potential in xinjiang in this easternmost part to the range northerly and southerly directed subduction accretion of early to mid paleozoic and mid to late paleozoic oceanic terranes respectively to the precambrian yili block central tian shan was associated with 400 to 250 ma arc magmatism and carboniferous through early permian gold forming hydrothermal events the more significant resulting deposits in the terranes of the southern tian shan include the sawayaerdun orogenic deposit along the kyrgyzstan border and the epithermal and replacement deposits of the kanggurtag belt to the east in the chol tagh range gold deposits of approximately the same age in the yili block include the axi hot springs epithermal deposit near the kazakhstan border and a series of small orogenic gold deposits south of urumqi e g wangfeng gold rich porphyry copper deposits e g tuwu define important new exploration targets in the northern tian shan of xinjiang the northern foothills of the kunlun shan of southern xinjiang host scattered small placer gold deposits sources for the gold have not been identified but are hypothesized to be orogenic gold veins beneath the icefields to the south they are predicted to have formed in the tianshuihai terrane during its early mesozoic accretion to the amalgamated tarim qaidam kunlun cratonic block

eocene and neogene volcanic rocks in the southeastern nechako basin british columbia interpretation of the canadian hunter seismic reflection surveys using first arrival tomography geological investigation of the near surface in the southeastern nechako basin is difficult shallow seismic reflection imaging is poor due in part to an extensive cover of eocene and neogene volcanic rocks outcrops of these volcanic rocks and the primarily cretaceous bedrock are commonly obscured by quaternary deposits and vegetation estimates of near surface p wave velocity are derived from the tomographic inversion of seismic first arrivals an effective tool when seismic imaging is poor tomographic model velocities are in agreement with sonic logs and laboratory samples except for those from the neogene chilcotin group cretaceous sedimentary rocks have velocities of 2800 4200 ms 1 the eocene endako and ootsa lake groups which have velocities of 3000 4200 ms 1 are not distinguishable based on velocity the velocity the character density focus and penetration depth of rays and ties with well and surface geology constrain the subsurface extent of the endako group adjacent to well b 82 c

unraveling the early middle paleozoic paleogeography of kazakhstan on the basis of ordovician and devonian paleomagnetic results abstract it is a common concept that different tectonic units in the western part of the central asian orogenic belt were united into the landmass of the kazakhstania continent in the paleozoic but many important details of its history remain enigmatic and controversial recently published paleomagnetic data from this region demonstrate that the 2000 km long horseshoe shaped devonian volcanic belt was created by oroclinal bending of an originally rectilinear active margin of kazakhstania still the silurian and devonian paleomagnetic results which this interpretation is based upon are limited and unevenly spread along the belt and additional middle paleozoic data are highly desirable accordingly we studied three mid paleozoic objects from different segments of this volcanic belt two of the three new objects yielded paleomagnetic directions that fit perfectly into the oroclinal scenario whereas the third one provided no interpretable data the earlier history of kazakhstania however remains misty we obtained three new ordovician results in north central kazakhstan and found similar inclinations but widely dissimilar declinations previously published data show a large scatter of ordovician declinations in south kazakhstan and kyrgyzstan as well we analyzed all seven middle late ordovician paleolatitudes and came to the conclusion that a nearly e w trending active margin of the kazakhstania landmass had existed at low 10 s latitudes at that time we hypothesize that this margin of the kazakhstania landmass collided with another island arc called baydaulet akbastau and with the aktau junggar microcontinent by the ordovician silurian boundary as a result of this collision subduction ceased and regional deformation magmatism and rotations of crustal fragments took place in most of kazakhstania in silurian time kazakhstania moved northward crossing the equator and rotating clockwise by 45 this changed the orientation of the kazakhstania to nw se and thereby established the rectilinear predecessor of the modern curved devonian volcanic belt

middle paleozoic paleomagnetism of east kazakhstan post middle devonian rotations in a large scale orocline in the central ural mongol belt abstract in order to test different hypotheses concerning the paleozoic evolution of the ural mongol belt umb and the amalgamation of eurasia we studied middle devonian basalts from two localities 11 sites and lower silurian volcanics redbeds and intra formational conglomerates from three localities 20 sites in the chingiz range of east kazakhstan the devonian rocks prove to be heavily overprinted in the late paleozoic and a high temperature presumably primary southerly and down component is isolated at only four sites from a homoclinal section most silurian redbeds are found to be remagnetized in the late paleozoic in contrast a bipolar near horizontal remanence isolated from silurian volcanics is most probably primary as indicated by positive tilt and conglomerate tests analysis of paleomagnetic data from the chingiz range shows that southward pointing directions in ordovician silurian and devonian rocks are of normal polarity and hence indicate large scale rotations after the middle devonian the chingiz paleomagnetic directions can be compared with paleozoic data from the north tien shan and with the horseshoe shaped distribution of subduction related volcanic complexes in kazakhstan both paleomagnetic and geological data support the idea that today s strongly curved volcanic belts of kazakhstan are an orocline deformed mostly before mid permian time despite the determination of nearly a dozen new paleozoic paleopoles in this study and other recent publications by our team significant temporal and spatial gaps remain in our knowledge of the paleomagnetic directions during the middle and late paleozoic however the paleomagnetic results from the chingiz range and the north tien shan indicate that these areas show generally coherent motions with siberia and baltica respectively

the malines cambrian carbonate shale hosted pb zn deposit france thermometric and isotopic h o evidence for pulsating hydrothermal mineralization microthermometric stable isotope d h 18o 16o and raman spectroscopic data are given for four different mineralization events located beneath a triassic unconformity these events include the pb zn bearing kii mineralization which fills geodes and fractures in the main karstic mineralization ki and the f mineralization which fills fractures in the cambrian carbonates and shales post ki pre kii and f mineralization fluids were hot 150 c moderately saline 10 equiv wt nacl and precipitated red dolomite subsequently equally hot but more saline 20 equiv wt nacl fluids deposited white dolomite and then sphalerite of the f mineralization they were followed by another generation of dolomite at about 70 c from fluids with about 15 equiv wt nacl and even later barites 165 c 10 equiv wt nacl variation in the homogenization temperature with salinity for the different dolomite generations suggests that the hot saline fluids were repeatedly diluted by a cooler less saline fluid the fluids are interpreted to be of formation water origin having possibly developed in the deep levels of the rhone basins to the southeast which was at least 3 km thick at the time of mineralization post hetangian the inferred metal bearing hot brines were probably episodically expulsed during the dewatering of the basin depositing their mineralization in the more permeable fault and karstic zones associated with the uplift of the st bresson horst cold surface waters probably invaded the mineralized zones between the pulses of hydrothermal solutions this hydrothermal model with the introduction of sulfides can account for the precipitation and dissolution textures associated with the hydrothermal mineralizations

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

an early permian epithermal gold system in the tulasu basin in north xinjiang nw china constraints from in situ oxygen sulfur isotopes and geochronology abstract the axi and jingxi yelmand gold deposits being the largest gold deposits in the chinese north tianshan nw china are located ca l0 km apart in the tulasu basin and are hosted by the late devonian early carboniferous dahalajunshan formation in situ la icp ms titanium analyses on quartz from the axi and jingxi yelmand deposits are broadly identical accordingly the calculated ore forming temperatures by ti in quartz thermometer give average temperatures of 279 c and 294 c respectively results of in situ sims analyses of oxygen and sulfur isotopes on quartz and pyrite from these two deposits are similar temperature corrected fluids of the axi deposit have 18 o values of 2 6 8 1 and 34 s values of 0 8 2 4 whereas the fluids of the jingxi yelmand deposit have 18 o of 6 4 8 9 and 34 s of 0 4 to 4 0 the oxygen and sulfur isotopes from the two deposits indicate a magmatic origin la icp ms zircon u pb ages of aqialehe formation sandstone provided a lower limit for the mineralization timing of the axi deposit 288 ma in situ sims u pb analyses on entrapped zircon 297 ma and newly recognized 284 5 ma columnar rhyolite implies that the jingxi yelmand deposit formed in the early permian based on the magmatic affinity of the ore fluids similar age and ore formation temperatures we propose that the axi and jingxi yelmand deposits comprise an epithermal gold system which was driven by the same permian magma in the tulasu basin the ore geological features together with our new results indicate that the axi and jingxi yelmand deposits are intermediate and high sulfidation type epithermal deposits respectively

re evaluation of lead isotopic data southern massif central france three independent pb isotope homogenizing processes operating on large volumes of rock material during limited intervals in the phanerozoic have been used to define a unique evolutionary curve for rock and ore lead isotopic compositions of the southern massif central france the model is begin gathered text x text t 18 641 text text 9 text 56 e text l1 t 1 text hfill text y text t 15 678 text text 0 text 06934 e text l2 t 1 text hfill text z text t 38 701 text text 30 text 8 e text l3 t 1 text hfill end gathered where xt yt and zt are the calculated isotopic ratios 206pb 204pb 207pb 204pb and 208pb 204pb respectively at time t years ago and l1 l2 and l3 are the decay constants of 238u 235u and 232th respectively the model gives the following ages for averages of the three sets of data used in its generation age of mineralization for carbonate hosted lead zinc ore of les malines ca 150 ma emplacement of the saint guiral liron granite ca 290 ma and an estimated average age of a group of cambrian syngenetic deposits ca 520 ma these ages are in close agreement with ages determined by independent methods

origin of a giant orebody at navan ireland the navan base metal deposit in ireland formed 360 myr ago1 and is one of the world s largest orebodies with 70 million tonnes of 12 zn pb much of the mineralization was sedimentary exhalative other well known examples of this class of the so called sedex deposits are mount isa in australia sullivan in canada and meggen in germany several models for the formation of such deposits have been suggested here we report the first systematic stratigraphic pb isotopic study of galenas in any giant exhalative zn pb orebody we document evidence that the sources of pb in the navan orebody evolved to produce increased dispersion and less radiogenic averages of lead isotopic compositions this is as expected if the orebody formed from a hydrothermal convection cell which expanded to scavenge metals from progressively deeper parts of the continental crust

metallogenic provinces and the remobilization process studied by lead isotopes lead zinc ore deposits from the southern massif central france the two main problems of ore genesis are the origin of metals and the process es of emplacement lead isotopes have proven to be a powerful tool for studying these questions we have studied pb zn mineralizations from montagne noire and cevennes southern massif central france by means of lead isotopes this study shows the existence of two populations of ore deposits defined by 17 76 206 pb 204 pb 17 94 and 18 25 206 pb 204 pb 18 63 a general model of lead evolution in these deposits is proposed after evolving in the earth s mantle until approximately 3 b y ago the lead became incorporated into a segment of continental crust then the less radiogenic population of ore deposits was emplaced contemporaneously with the formation of cambrian carbonate host rocks the second population is related to the emplacement of hercynian granitoids or in more general terms to fluid circulations associated with the hercynian orogeny it can also be shown that some of the deposits are remobilized from preexisting ore deposits

the dynamics of big mantle wedge magma factory and metamorphic metasomatic factory in subduction zones abstract the east asian continental margin is underlain by stagnant slabs resulting from subduction of the pacific plate from the east and the philippine sea plate from the south we classify the upper mantle in this region into three major domains a metasomatic metamorphic factory mmf subduction zone magma factory szmf and the big mantle wedge bmw whereas the convection pattern is anticlockwise in the mmf domain it is predominantly clockwise in the szmf and bmw along a cross section from the south here we define the mmf as a small wedge corner which is driven by the subducting pacific plate and dominated by h 2 o rich fluids derived by dehydration reactions and enriched in large ion lithophile elements lile which cause the metasomatism the szmf is a zone intermediate between mmf and bmw domains and constitutes the main region of continental crust production by partial melting through wedge counter corner flow large hydrous plume generated at about 200 km depth causes extensive reduction in viscosity and the smaller scale hydrous plumes between 60 km and 200 km also bring about an overall reduction in the viscosity of szmf more fertile and high temperature peridotites are supplied from the entrance to this domain the domain extends obliquely to the volcanic front and then swings back to the deep mantle together with the subducting slab the bmw occupies the major portion of upper mantle in the western pacific and convects largely with a clockwise sense removing the eastern trench oceanward sporadic formation of hydrous plume at the depth of around 410 km and the curtain flow adjacent to the trench cause back arc spreading we envisage that the heat source in bmw could be the accumulated ttg tonalite trondhjemite granodiorite crust on the bottom of the mantle transition zone the ongoing process of transportation of granitic crust into the mantle transition zone is evident from the deep subduction of five intra oceanic arcs on the subducting philippine sea plate from the south in addition to the sediment trapped subduction by the pacific plate and philippine sea plate the dynamics of mmf szmf and bmw domains are controlled by the angle of subduction a wide zone of mmf in sw japan is caused by shallow angle subduction of the philippine sea plate and the markedly small mmf domain in the mariana trench is due to the high angle subduction of pacific plate the domains in ne japan and kyushu region are intermediate between these two during the tertiary a series of marginal basins were formed because of the nearly 2000 km northward shift of the subduction zone along the southern margin of tethyan asia which may be related to the collision of india with asia and the indentation the volume of upper mantle under asia was reduced extensively on the southern margin with a resultant oceanward trench retreat along the eastern margin of asia leading to the formation of a series of marginal basins the western pacific domain in general is characterized by double sided subduction from the east by the oldest pacific plate and from the south by the oldest indo australian plate the old plates are hence hydrated extensively even in their central domains and therefore of low temperature the cracks have allowed the transport of water into the deeper portions of the slab and these domains supply hydrous fluids even to the bottom of the upper mantle thus a fluid dominated upper mantle in the western pacific drives a number of microplates and promote the plate boundary processes

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

petrogenesis of late paleozoic diorites and a type granites in the central eastern tianshan nw china response to post collisional extension triggered by slab breakoff abstract geological evolution of the eastern tianshan in the late paleozoic is significant to understanding the multiple accretions and final formation of the southern central asian orogenic belt here we report new whole rock geochemical and sr nd isotopic data and in situ zircon u pb ages for three typical a type granitic intrusions syenogranite k feldspar granite and monzonitic granite and one dioritic pluton in the central eastern tianshan nw china in order to constrain their petrogenesis tectonic setting and geodynamic evolution zircon la icp ms u pb ages indicate that the syenogranites and k feldspar granites were both formed during a short time interval in the early permian 284 286 ma whereas the diorites were crystallized at 293 6 ma the monzonitic granites were generated at 307 3 ma earlier than the other two granitic intrusions the three kinds of granites syenogranite k feldspar granite and monzonitic granite have high hfse hree and y nb ratios 1 68 2 84 and remarkably low sr and ba contents with the absence of aluminium rich minerals and show metaluminous to weakly peraluminous natures indicating geochemical characteristics of aluminous a2 type granites these granites show negative end t 3 32 to 4 40 values and mesoproterozoic two stage nd model ages tdm2 1 36 to 1 43 ga which suggest a relatively old crustal source for these rocks the sr nd isotopic compositions imply that the mesoproterozoic metamorphic basement of the central tianshan block can be considered as a potential magmatic source for these aluminous a2 type granites in addition they have geochemical characteristics similar to the experimental melt that was derived from partial melting of crustal metaigneous rocks at the depth of middle to lower crust levels therefore the granites were most likely produced by partial melting of metaigneous rocks in a post collisional extensional setting the diorites have low sio2 and high mgo with uniform 87sr 86sr i values 0 7055 negative end t values 4 11 to 4 59 and mesoproterozoic two stage nd model ages tdm2 1 41 to 1 45 ga they have higher ti zr 42 8 46 7 and ti y 280 359 ratios than continental crust and show negative nb ta ti anomalies which can be explained by partial melting of a relatively fertile mantle modified by old crustal materials of the central tianshan block the formation of the dioritic pluton was induced by an upwelling asthenosphere in an extensional geodynamic setting based on the zircon saturation temperatures of these a type granites and the distribution of late carboniferous to early permian mantle derived intrusions a slab breakoff model is suggested to interpret the formation of the studied a type granites and diorites we infer that the slab breakoff was initiated in the late carboniferous and ended in the early permian

the role of the kazakhstan orocline in the late paleozoic amalgamation of eurasia article i nfo the kazakhstan orocline a horseshoe shaped belt with volcanic arcs of devonian external and late paleozoic internal age is thought to have formed as a result of convergence between the cratons of siberia baltica and tarim leading to the amalgamation of eurasia paleomagnetic and geologic data indicate that in the middle devonian the arc which is now strongly curved was nearly straight near the northwest southeast trending volcanic margin of a kazakhstania continent to constrain the age of oroclinal bending we conducted a paleomagnetic study of late carboniferous to late permian subduction related volcanics from the middle nw and north eastern ne limbs of the orocline our new results indicate that the rotation of the middle arm of the orocline was essentially completed by the earliest permian while the ne arm probably was still 50 short of its final orientation with respect to baltica the rotation of or rotation within the ne arm was completed by the late permian the paleomagnetic data constraining the timing and rotation patterns lead us to propose the following scenario for the bending of the kazakhstan orocline the orogenic deformation scenario began in the late devonian when an initial collision with tarim pinned kazakhstania s southern corner while a dextral shear motion and a considerable clockwise rotation of siberia dragged its northern end relative convergence between siberia and tarim caused initial buckling of the kazakhstania continental element trapped between them subdividing the belt into three sw nw ne segments continued subduction under the established limbs of the orocline with an estimated outward directed subduction velocity of well less than 1 cm yr gradually led to closure of the intervening junggar balkhash oceanic basin and tightening of the orocline 2008 elsevier b v all rights reserved

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

geochemistry and genesis of the lengenbach pb zn as tl ba mineralisation binn valley switzerland the lengenbach pb zn as tl ba mineralisation is located in triassic dolostones of the penninic zone in the swiss alps where alpine metamorphism reached upper greenschist to lower amphibolite grade geochemical data are used to constrain the origin of this unique occurrence two metamorphic redox environments are present the as iii rich zone is controlled by barite pyrite while the reduced zone contains graphite or pyrrhotitepyrite and formally zerovalent as the as iii rich zone is characterised by a mineral assemblage consistent withfo2 in the stability field of barite pyrite an as pb tl rich sulphide melt coexisted with a hydrothermal fluid at 300 c in this zone mineralised dolostones are anomalous in as pb ag tl hg zn ba cd fe cu mo u v b ga cr and possibly sri and au in order of decreasing enrichment as pb and zn are present in the 0 1 to 1 range tl and ag reach several hundred ppm uraninite is concentrated in silicate rich bands and yields a late alpine u pb age of 18 5 0 5 ma pb and s isotopic variations are interpreted by metamorphic overprinting and re equilibration within an isochemically metamorphosed mineralisation hydrothermal sulphides are more strongly affected by uranogenic pb than massive pb as sulphides representing a former sulphide melt the least overprinted mineralisation is characterised by206pb 204pb 18 44 18 56 207pb 204pb 15 60 15 75 208pb 204pb 38 44 38 84 and 34s sulphide 25 2 s isotopic variations are largely a result of sulphide sulphate re equilibration yielding temperatures of 450 30 c 87sr 86sr ratios of mineralised samples are lower than or equal to host dolostones precluding major infiltration of basement derived fluids during alpine metamorphism the sr source 87sr 86sr close to 0 708 probably was seawater with a radiogenic detrital mineral component the genesis of the unique lengenbach mineralisation is interpreted as the result of isochemical metamorphic overprinting of a carbonate hosted stratiform sulphide mineralisation well crystallised sulphide minerals in fissures and druses formed during retrograde cooling of a sulphide melt in equilibrium with a hydrothermal fluid the primary mineralisation was probably formed at or close below the sea floor and fed by sulphide poor hydrothermal fluids sulphide was largely derived from seawater by open system bacterial sulphate reduction u v and mo may be seawater derived

moving metals ii provenancing scandinavian bronze age artefacts by lead isotope and elemental analyses the first part of this research published previously proved without doubt that the metals dated to the nordic bronze age found in sweden were not smelted from the local copper ores in this second part we present a detailed interpretation of these analytical data with the aim to identify the ore sources from which these metals originated the interpretation of lead isotope and chemical data of 71 swedish bronze age metals is based on the direct comparisons between the lead isotope data and geochemistry of ore deposits that are known to have produced copper in the bronze age the presented interpretations of chemical and lead isotope analyses of swedish metals dated to the nordic bronze age are surprising and bring some information not known from previous work apart from a steady supply of copper from the alpine ores in the north tyrol the main sources of copper seem to be ores from the iberian peninsula and sardinia thus from the results presented here a new complex picture emerges of possible connectivities and flows in the bronze age between scandinavia and europe

geochronology and geochemistry of the borohoro pluton in the northern yili block nw china implication for the tectonic evolution of the northern west tianshan orogen abstract the closure of the north tianshan ocean between the junggar terrane and the yili block is a longtime debated issue in literature because of the different understanding of the carboniferous volcanic rocks in the northern margin of the yili block this study presents new geochronological and whole rock geochemical data for the granitic rocks from the borohoro pluton to provide constraints on the tectonic regime for the northern west tianshan during the carboniferous la icp ms u pb dating results reveal two magmatic phases for the borohoro pluton the former magmatic activity in the early carboniferous formed the fine grained granodiorite 332 ma the later magmatic activity occurred during the late carboniferous 305 300 ma forming a diversity of granitic rocks involving quartz diorite granodiorite and granite geochemical and mineralogical studies reveal that the studied granitic rocks from the borohoro pluton all belong to metaluminous to weakly peraluminous calc alkaline i type granites they are characterized by enrichment in liles relative to hfses and depletion of nb ti and p typical of continental arc type granites the intermediate sio2 high al2o3 and relatively low fe2o3t mgo and tio2 contents reflect that these granitic rocks are mainly crust derived but the high mg values for most samples and the occurrence of microgranular mafic enclaves indicate that their magma sources were mixed by mantle derived components especially the late carboniferous rocks define an elegant mixing trend in both the rb rb v and the 1 v rb v diagrams consistent with mixing between magmas from subcontinental lithospheric mantle and mafic lower crust taking into consideration of the facts that all the devonian to carboniferous granitoids belong to calc alkaline i type granites and granitoids of a type didn t appear until the early permian we suggest that the subduction of the north tianshan ocean continued to the late carboniferous generating the granitic rocks of the borohoro pluton