late paleozoic closure of the ob zaisan ocean along the irtysh shear zone nw china implications for arc amalgamation and oroclinal bending in the central asian orogenic belt the largest accretionary orogen in the world the central asian orogenic belt has evolved through the assembly of various oceanic and continental blocks understanding the processes associated with the development of this orogenic belt relies on precise recognition of the boundaries between various terranes one such major suture zone which records the collisional history of the siberian marginal arc system chinese altai with intra oceanic arc systems east west junggar is the irtysh shear zone in nw china the spatial continuity and the tectonic nature of this shear zone are still poorly understood but its development has supposedly made a significant impact on the architecture of the western central asian orogenic belt and the formation of the kazakhstan orocline here we provide new insight into the evolution of this shear zone based on detrital zircon ages hf isotope composition structural data and ar ar age constraints on the timing of deformation our results show a major discrepancy in detrital zircon populations and hf model ages across the southern chinese altai and the northern east west junggar thus allowing us to map the exact location of the tectonic boundary detrital zircon data constrain the initial closure of the ob zaisan ocean to the late carboniferous 323 ma and new structural and ar ar geochronological data shed light on the subsequent collisional processes we propose that the collisional zone between the chinese altai and the east west junggar was initially subjected to crustal thickening at ca 323 295 ma followed by orogen parallel extension ca 295 ma and transpressional deformation ca 286 253 ma the closure of the ob zaisan ocean in nw china postdates the initial phase of oroclinal bending in the western central asian orogenic belt thus indicating that oroclinal bending initiated during subduction based on our new constraints and other available geological data we suggest that the early stage of oroclinal bending was likely driven by slab rollback

transpressional deformation strain partitioning and fold superimposition in the southern chinese altai central asian orogenic belt transpressional deformation has played an important role in the late paleozoic evolution of the western central asian orogenic belt caob and understanding the structural evolution of such transpressional zones is crucial for tectonic reconstructions here we focus on the transpressional irtysh shear zone with an aim at understanding amalgamation processes between the chinese altai and the west east junggar we mapped macroscopic fold structures in the southern chinese altai and analyzed their relationships with the development of the adjacent irtysh shear zone structural observations from these macroscopic folds show evidence for four generations of folding and associated fabrics the earlier fabric s 1 is locally recognized in low strain areas and is commonly isoclinally folded by f 2 folds that have an axial plane orientation parallel to the dominant fabric s 2 s 2 is associated with a shallowly plunging stretching lineation l 2 and defines similar to nw se tight close upright macroscopic folds f 3 with the doubly plunging geometry f 3 folds are superimposed by similar to nnw sse gentle f 4 folds the f 3 and f 4 folds are kinematically compatible with sinistral transpressional deformation along the irtysh shear zone and may represent strain partitioning during deformation the sub parallelism of f 3 fold axis with the irtysh shear zone may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear dominant deformation f 3 in fold zones the strain partitioning may have become less efficient in the later stage of transpressional deformation so that a fraction of trans current components was partitioned into f 4 folds c 2016 elsevier ltd all rights reserved

thermochronological constraints on the late paleozoic tectonic evolution of the southern chinese altai abstract the chinese altai as an accretionary orogen developing from the cambrian to carboniferous was modified by permian deformation metamorphism and magmatism in response to the collision with the east junggar the tectonic processes of the collision and the timing of related deformation and metamorphism are still enigmatic here we present new 40 ar 39 ar dating results for granitic gneisses and amphibolites exposed in the qiongkuer domain in two areas alahake and fuyun of the southern chinese altai the amphiboles from both aalaheke and fuyun areas yield consistent 40 ar 39 ar plateau ages at 265 9 1 7 ma and 270 1 3 1 ma in contrast the biotites from two areas show distinct 40 ar 39 ar ages of 232 0 2 1 ma and 226 8 1 7 ma for the alahake area and 245 1 1 5 ma and 264 5 2 2 ma for the fuyun area respectively given that 40 ar 39 ar ages are younger than the permian high temperature metamorphism at 299 277 ma as constrained by metamorphic zircons in the qiongkuer domain we interpret these 40 ar 39 ar ages to record the cooling history of two areas compatible amphibole ages in both areas indicate a similar exhumation age along the qiongkuer domain cooling through 550 c at 270 265 ma which may have been associated with the development of the sinistral erqis shear zone during the collision between the chinese altai and the east junggar the subsequent exhumation processes were variable in different areas of the qiongkuer domain as showed by the distinct biotite ages which may indicate along strike variation of cooling processes from 550 c to 300 c in the qiongkuer domain

a synthesis of zircon u pb ages and hf isotopic compositions of granitoids from southwest mongolia implications for crustal nature and tectonic evolution of the altai superterrane abstract granitoid magmatism is extensively developed in the altai superterrane but the timing of magmatic events is not so well determined in this study twelve granitoid intrusions from southwest mongolia were dated by the zircon u pb method and analyzed for zircon hf isotopic compositions the new age data indicated three phases of magmatic emplacement middle paleozoic 398 350 ma late paleozoic 317 289 ma and triassic ca 244 211 ma the first phase magmatism is mainly composed of hornblende bearing i type granitoids formed during a long lasting subduction process in the early to middle paleozoic the second phase magmatism was manifested by a few small intrusions primarily distributed along the erqis fault zone and probably formed in a transitional tectonic regime from subduction to post tectonic setting in the late paleozoic the third phase magmatism was represented by post tectonic granitoids emplaced in an intraplate extensional setting model ages that were calculated using the composition of new continental crust are predominantly neoproterozoic to early paleozoic indicating that the protoliths of granitoids were likely dominated by paleozoic juvenile crust with minor neoproterozoic materials the altai superterrane was a huge paleozoic tectonic collage produced by amalgamation of subduction accretion complexes in the margin of the siberian continent and the tuva mongol microcontinent

spatial and temporal distribution of the orogenic gold deposits in the late palaeozoic variscides and southern tianshan how orogenic are they abstract a principal uncertainty in models of orogenic ore deposits concerns their ages relative to orogenic processes the yardstick of the relation has resided loosely in the peak of metamorphism age estimates in the variscides and tianshan indicate that most orogenic ore deposits were formed in the course of the late carboniferous to middle triassic with a peak between 305 and 280 ma their locations settings and ages suggest an association with coeval lithosphere scale strike slip deformation which played a role in the destruction of the orogenic system following crustal shortening this destruction tends to invalidate the orogenic association of the orogenic ore deposits observation of a mantle signature in some of these ore deposits and in coeval magmatic rocks suggests that the strike slip belts tapped into sub crustal levels here lithological composition had been modified by subduction during the stage of construction consequently any orogenic element in the ore deposit models is apart from location only an element of inheritance of subduction modified lithosphere features acquired during construction of the orogen these features may however well have been crucial for the formation of the ore deposits in view of the translithospheric extent of the strike slip belts fluids which contributed to the ore deposits may have come from at least the entire in part metasomatized lithosphere column the ore deposits could probably not have been formed without these deep reaching strike slip systems a model is proposed for the geological setting of the orogenic gold deposits in the variscides and the southern tianshan it consists of plutono metamorphic elements in the mantle in the lower and in the middle crust within a transpressional to transtensional tectonic framework of translithospheric faults and associated domes and pull apart basins with shallow marine to terrestrial sediments and interlayered felsic and mafic volcanics the thermal engines of these systems were probably in localized upwellings of the asthenosphere prompted and controlled by the lithosphere scale deformation at the time at an even larger scale oroclinal bending of the old orogenic backbone may have played yet another role in the localization of the ore deposits the thesis of specific localized tectono thermal engines is at odds with the original proposals of a relation between orogenic ore deposits and regional metamorphism it suggests that the late palaeozoic gold antimony mercury ore deposits in the variscides and the southern tianshan are more akin to the intrusion related ore systems

nature and timing of the solonker suture of the central asian orogenic belt insights from geochronology and geochemistry of basic intrusions in the xilin gol complex inner mongolia china the solonker suture zone of the central asian orogenic belt caob records the final closure of the paleo asian ocean the nature and timing of final collision along the solonker suture has long been controversial partly because of an incomplete record of isotopic ages and differing interpretations of the geological environments of key tectonic units the xilin gol complex consisting of strongly deformed gneisses schists and amphibolites is such a key tectonic unit within the caob lenticular or quasi lamellar amphibolites are dispersed throughout the complex intercalated with biotite plagioclase gneiss both rock types experienced amphibolite facies metamorphism the protolith of the amphibolite is a basic rock that intruded into the biotite plagioclase gneiss at 319 4 ma based on la icpms zircon u pb dating the basic intrusion was sourced from a modified magma that experienced crystal fractionation and was admixed with slab derived fluids the slab derived fluids which formed during early paleozoic oceanic subduction along the north dipping sonidzuoqi xilinhot subduction zone mixed with the magma source and produced subduction related geochemical signatures superimposed on volcanic arc chemistry after early paleozoic oceanic subduction and arc continent collision a transient stage of extension occurred between 313 and 280 ma in the sonidzuoqi xilinhot area deformation and recrystallization during the switch from compression to extension and reheating by the later magmatic intrusions reset the isotope systems of minerals in the xilin gol complex recorded by a 312 2 1 5 ma biotite 40ar 39ar age from biotite plagioclase gneiss a 309 12 ma zircon intercept age and a 307 5 3 5 ma hornblende 40ar 39ar age from amphibolites in the complex there was an arc forearc related marine basin at the southern margin of the xilin gol complex during the permian the closure of the oceanic basin led to late paleozoic middle triassic north dipping subduction beneath the xilin gol complex and induced the amphibolite facies metamorphism of the complex the final suturing of the solonker zone occurred from 269 to 231 ma this latest amphibolite facies metamorphism with pressures of 0 31 0 39 gpa and temperatures of 620 660 c was recorded at 263 4 1 4 ma to the xilin gol complex as indicated by the hornblende 40ar 39ar age from the amphibolites as well as several zircon ages of 260 3 231 3 ma the xilin gol complex documented the progressive accretion of a single long lived subduction system at the southern margin of the south mongolian microcontinent from the early paleozoic 452 ma to middle triassic 231 ma the caob shows protracted collision prior to final suturing

peralkaline granitoid magmatism in the mongolian transbaikalian belt evolution petrogenesis and tectonic significance article i nfo the central asian orogenic belt caob is well known for its massive generation of juvenile crust in the phanerozoic in eastern caob voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanics were emplaced in three stages from early permian to late mesozoic 295 270 ma 230 190 ma and 150 120 ma they occur as huge granitoid belts in extensional tectonic settings and form a complex network of about 12 million km 2 in area among them the 2500 km long mongolian transbaikalian belt mtb is the most spectacular and it comprises more than 350 granite syenite plutons and stocks with numerous co genetic volcanic fields the three stages of granitoids have similar chemical compositions but show temporal variation in nd isotopic composition initial end t values range from 1t o 5 for the early permian 0 to 4 for the early mesozoic and 2t o 3 5 for the late mesozoic granitoids the negative end t values observed in the mtb are not typical of the caob granitoids which are generally characterized by positive values however several pieces of evidence suggest that the mtb peralkaline and alkali feldspar granitoids were produced from enriched mantle derived sources the evidence includes 1 felsic and mafic rocks formed in the same stage have similar initial nd sr isotopic ratios and sm nd model ages tdm 2 the granitoid belts extend over thousands of kilometers and intersect distinct crustal provinces but no correlation is found in chemical compositions between the granitoids and country rocks 3 the abundant syenites are considered to be cogenetic or in some cases parental to the granites experimental and isotope data argue for the derivation of syenites from an enriched mantle source thus the granites and comendites are regarded as mantle derived 4 a study of melt inclusions in quartz phenocrysts of comendite indicates a high liquidus temperature of 1000 1100 c for the magma generation this suggests that the silicic magma was generated in an unusually high temperature condition which is likely produced by basaltic magma that underplated the lower crust the generation of voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanic rocks represents an important addition of juvenile crustal mass to the earth s continental crust during a time span of about 150 ma from late paleozoic to late mesozoic

hidden eoarchean crust in the southwestern central asian orogenic belt abstract u pb and hf isotope analyses of zircon xenocrysts from drilling sampled carboniferous volcanic rocks suggest the presence of unexposed eoarchean crust beneath the junggar basin nw china southwestern central asian orogenic belt caob the oldest zircon population with u pb ages of 3 8 ga shows chondritic ehf t of 0 7 to 0 7 and hf model ages of 3900 3952 ma tdm and 3973 4062 ma tcrust three slightly younger populations at 3 7 3 62 and 3 45 ga have ehf t of 5 7 to 2 4 tdm of 3 6 3 9 ga and tcrust of 3 7 4 1 ga the youngest xenocrysts yield u pb ages of 2 55 ga with ehf t values of 3 7 to 8 0 crustal mineral inclusions and the trace element compositions of all these zircons show that they probably crystallized from granitic magmas the observation of deeply hidden archean crust significantly older than the exposed phanerozoic upper crust suggests that the juvenile origin in caob may be overestimated and the study of crustal growth rates through time for young orogens will require revision by comparing the hf isotopic signatures of ancient zircons 3 4 ga worldwide we infer that there may have been a great change in early crustal evolution at the hadean archean transition 3 9 ga possibly linked to the late heavy bombardment lhb

denudation and cooling of the lake teletskoye region in the altai mountains south siberia as revealed by apatite fission track thermochronology abstract lake teletskoye occupies a narrow graben located in the northwestern sector of the altai fold belt in south siberia the lake basin is thought to have formed during the pleistocene as a distant result of the cenozoic collision of india and eurasia that caused a tectonic reactivation of the palaeozoic gorny altai ga and west sayan ws blocks the present work reports of a pilot fission track study performed on 13 apatite separates collected from rocks that were sampled along two profiles in close proximity of the lake the age length data and aft thermochronological modelling reveal two important phases of cooling in the altai mountains a first one during the late jurassic early cretaceous and a second one that started in the miocene pliocene and that persists until today the first event is interpreted to result from uplift induced denudation probably related to the closure of the mongol okhotsk ocean the second event can be linked to the young cenozoic movements that lie at the origin of the formation of the lake teletskoye basin

mineralization and ore genesis of the qiaoxiahala fe cu au deposit in the northern margin of east junggar terrane central asian orogenic belt constraints from fluid inclusions and stable isotopes abstract the qiaoxiahala fe cu au deposit 1 44 mt ore 43 53 fe 0 55 2 21 cu and 0 13 2 4 g t au is located in the northern margin of east junggar terrane nw china the deposit is hosted in the upper part of the middle devonian beitashan formation mafic and felsic volcanic rocks and sedimentary interbeds and is spatially closely related to local fractures six hypogene hydrothermal stages have been identified including stage i early skarn stage ii late skarn stage iii magnetite mineralization stage iv magnetite pyrite mineralization stage v chalcopyrite mineralization and stage vi late veins these six stages include three major mineralization events as represented by the stage iii magnetite epidote k feldspar quartz calcite stage iv magnetite pyrite garnet quartz calcite and stage v chalcopyrite chlorite assemblages the stage iii magnetite mineralization fluids were likely of high temperature 354 386 c low medium salinity 9 9 14 7 wt nacl equiv mg fe rich and organic rich with lithostatic pressure of 1 3 1 5 kbar and corresponding depth of 4 3 4 8 km oxygen and hydrogen isotopes showed that the 18o rich 9 7 11 2 and d rich 26 3 fluids were possibly modified from the early carboniferous seawater interacting with the beitashan formation organic rich limestone or tuff in comparison the stage iv magnetite pyrite mineralization fluids were likely of medium high temperature 272 453 c low medium salinity 2 9 19 5 wt nacl equiv mg fe rich with pressure of 0 8 1 2 kbar and corresponding depth of 2 6 4 0 km the stage v chalcopyrite mineralization fluids were likely of low medium temperature 186 270 c low medium salinity 1 4 21 8 wt nacl equiv ca or na rich with pressure of 0 4 0 6 kbar and corresponding depth of 1 2 km hydrogen and oxygen isotopic compositions stage iv dwater 141 to 92 18owater 8 9 11 1 stage v dwater 104 18owater 7 2 suggest that the ore fluids were of connate marine origin furthermore stage iv 13cwater values 0 6 to 0 also indicate interactions between seawater and sedimentary wall rocks the negative sulfur isotopic compositions of chalcopyrite and pyrite 4 2 to 0 2 may demonstrate a biogenic sulfur source compared with the arc related iocg deposits in the central andean orogen the qiaoxiahala fe cu au deposit shares many common features in geology mineralization alteration and various sources of fluids indicating a possible iocg like mineralization style and potential to discover other late paleozoic arc related iocg deposits in east junggar

reconstructing multiple arc basin systems in the altai junggar area nw china implications for the architecture and evolution of the western central asian orogenic belt abstract the altai junggar area in northwestern china is a critical region to gain insights on the tectonic framework and geological evolution of the western central asian orogenic belt caob in this study we report results from integrated geological geochemical and geophysical investigations on the wulungu depression of the junggar basin to determine the basement nature of the basin and understand its amalgamation history with the chinese altai within the broad tectonic evolution of the altai junggar area based on borehole and seismic data the wulungu depression is subdivided into two nw trending tectonic units suosuoquan sag and hongyan high by southward vergent thrust faults the suosuoquan sag consists of the middle late devonian basaltic andesite andesite dacite tuff tuffaceous sandstone and tuffite and the overlying early carboniferous volcano sedimentary sequence with lava flows and shallow marine sediments from a proximal juvenile provenance zircon e hf t 6 0 14 9 compared to the late carboniferous andesite and rhyolite in the hongyan high zircon sims u pb ages for dacites and andesites indicate that these volcanics in the suosuoquan sag and hongyan high erupted at 376 3 ma and 313 4 ma respectively the middle late devonian basaltic andesites from well lc1 are calc alkaline and exhibit primitive magma like mgo contents 7 9 8 6 and mg values 66 68 with low initial 87 sr 86 sr 0 703269 0 704808 and positive e nd t values 6 6 7 6 and relatively high zr abundance 98 2 116 0 ppm and zr y ratios 5 1 5 4 enrichment in lrees and liles e g th and u and depletion in nb ta and ti suggesting that they were probably derived from a metasomatized depleted mantle in a retro arc extensional setting the well lc1 andesitic tuffs well l8 dacites well wl1 dacitic tuffs and well l5 andesites belong to calc alkaline and metaluminous to peraluminous a cnk 0 8 1 7 series and display low mg values 35 46 and variably positive e nd t 4 5 8 5 and e hf t 10 2 16 8 values as well as young isotopic model ages these devonian carboniferous intermediate felsic volcanics are interpreted as the products of partial melting of a juvenile lower crust with some contributions from mantle components in an evolved island arc setting from immature to mature island arc the basin filling pattern and the distribution of arc volcanics and their zircon hf model ages with the eruptive time suggest that the wulungu depression represents an island arc basin system with the development of a carboniferous retro arc basin in combination with previous work we propose that the northern junggar area comprises three arc basin belts from south to north the darbut luliang karamaili wulungu yemaquan and saur fuhai dulate such tectonic subdivisions are consistent with the regional gravity and magnetic anomaly data the recognition of the wulungu arc basin system demonstrates that the junggar basin is likely underlain by juvenile continental crust rather than ancient precambrian basement and also implies that the caob was built by amalgamation of multiple linear arcs and accretionary complexes

the 390 ma high t metamorphic event in the chinese altai a consequence of ridge subduction high grade rocks occur in the chinese altai but the timing of metamorphism is poorly constrained which hinders our understanding of the thermo tectonic history of the region representative high grade samples from the sillimanite zone extending from hanas to fuyun were selected for zircon u pb dating and temperature estimation la icp ms analyses of zircon overgrowth rims and recrystallized domains give consistent ages of 390 ma which is interpreted to record a regional metamorphic event temperature t estimations using the amphibole plagioclase quartz amp pl qtz and garnet biotite gb geothermometers give relatively high temperatures ranging from 650 to 700 c the zircon metamorphic rims yield temperature estimates of 720 c by using the ti in zircon thermometer these data suggest that a high temperature metamorphic event took place in the chinese altai in the middle devonian and may imply a tectonic environment involving an unusually elevated heat flux from a deep seated source our data support possible ridge subduction around 390 ma that caused upwelling of the hot asthenosphere and triggered the high t metamorphism this model can also account for coeval volcanic activity with a range of geochemical characteristics diverse mafic intrusions and extensive hydrothermal mineralization in the altai orogen

late palaeozoic to mesozoic kinematic history of the talas ferghana strike slip fault kyrgyz west tianshan as revealed by 40ar 39ar dating of syn kinematic white mica abstract the nw trending talas ferghana fault tff in kyrgyzstan central asia is one of the largest intracontinental strike slip faults in the world it extends over a distance of more than 2000 km from southern tourghai to western tarim and exhibits a maximum dextral offset of 200 km during the late palaeozoic to present the history of the fault provides important insights for the understanding of the evolution of southern central asia but remains poorly constrained due to lack of reliable geochronological data we present new ar ar ages and structural data from the kyrgyz west tianshan that elucidate the kinematic history of the tff in the palaeozoic and mesozoic 40ar 39ar ages on mylonitic white micas document a deformational history consisting of several episodes a late carboniferous age of 312 4 ma point to initiation of top to the south and dextral transpressional deformation during a metamorphic overprint in precambrian and palaeozoic rocks along the northern compartment of the tff the main phase of dextral motion along the entire fault occurred in the permian as suggested by minimum ages of 260 290 ma obtained at two different locations in the nw and central parts of the tff partial isotopic resetting occurred between 240 and 210 ma and younger ages of the ar ar mineral ages and structural data argue for a major phase of dextral shearing affecting the entire region from the west tianshan to mongolia in the late permian and leading to formation of almost equally spaced major nw trending dextral strike slip faults the uniform character of this deformation indicates that the process of amalgamation in this part of the caob ended prior to the late permian and central asia evolved as a single coherent continental block since that time

geology and ore forming fluid evolution of the aktogai giant porphyry cu deposit kazakhstan abstract the aktogai group more than 12 5mt of cu and 80t of au is located in the western part of the central asian orogenic belt caob the mineralization of the aktogai deposit is associated with the early carboniferous tonalite porphyry which intruded into the koldar complex the ore forming tonalite porphyry has higher oxygen fugacity and sulfur contents than those of wall rocks based on results of mineralogical chemistry analyses hydrothermal fluid activities result in the potassic sericite chlorite and propylitic alteration and are associated with disseminated and or vein mineralization the alteration and mineralization include three stages potassic stage is characterized by hydrothermal k feldspar biotite magnetite a veins and disseminated mineralization sericite chlorite stage that partly overprinted on potassic stage is characterized by sericite chlorite c veins and disseminated mineralization propylitic stage is characterized by chlorite epidote and c veins and develops in the tonalite porphyry and wall rocks five types of fluid inclusions have been recognized in the aktogai deposit including liquid rich l type vapor rich v type daughter mineral bearing s type co2 bearing c type and minor so2 bearing fluid inclusions in the potassic stage ore forming fluid belongs to h2o nacl co2 system with four types fluid inclusions homogeneous temperatures and salinities of fluid inclusions are 320 c to 448 c and 0 35 wt to 51 08 wt respectively in the sericite chlorite stage the fluid belongs to h2o nacl co2 system with l type v type and c type fluid inclusions homogeneous temperatures and salinities of fluid inclusions are 243 c to 315 c and 1 22 wt to 13 27 wt respectively in the propylitic stage the fluid belongs to h2o nacl system with l type and v type fluid inclusions homogeneous temperatures and salinities of fluid inclusions are 211 c to 328 c and 0 35 wt to 11 46 wt respectively a relatively negative 34s values 4 61 to 3 18 indicate that the sulfur derived from a high oxygen fugacity magma decreases of the temperature pressure and oxygen fugacity of the ore forming fluid result in metal precipitation in the aktogai deposit

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

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

u pb ages and hf o isotopes of zircons from late paleozoic mafic ultramafic units in the southern central asian orogenic belt tectonic implications and evidence for an early permian mantle plume abstract u pb age and hf o isotope data of zircons from the mafic ultramafic complexes and their related rhyolites and granites in the eastern tianshan and beishan regions were obtained by sims and la icpms the hf o isotopic composition and hf model age of the zircons are closely related to their tectonic setting and formation age the zircons from the mafic ultramafic complexes in the bogeda haerlike and jueluotage belts have higher ehf t 8 17 and lower 18o 4 6 whereas most of the zircons in the gabbros granites and rhyolite from the middle tianshan massif and beishan rift display lower ehf t 0 8 and higher 18o 5 8 the positive ehf t and relatively lower 18o values suggest that these mafic ultramafic complexes were derived from depleted mantle which was subjected to subduction related modification processes the hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the central asian orogenic belt during the paleozoic the hf model ages of the analyzed zircons together with the regional geology suggest that the beishan area had a northward subduction possibly from ca 900 ma to ca 400 ma whereas the eastern tianshan had a south directed subduction most likely from ca 600 ma to ca 310 ma additionally zircons with ca 280 ma u pb ages display wider and more scattered ehf t and 18o variations than the relatively older and younger ones which further support the early permian mantle plume model

recognition of ocean plate stratigraphy in accretionary orogens through earth history a record of 3 8billion years of sea floor spreading subduction and accretion abstract ocean plate stratigraphy ops is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust substratum from the time it forms at a spreading center to the time it is incorporated into an accretionary prism at a convergent margin in this study we review the major geological characteristics of relict cenozoic to early archean oceanic crust and ops persevered in alaska japan california franciscan complex central asia british isles canada slave province australia pilbara craton and greenland isua and ivisaartoq belts an assessment of ops in accretionary orogens spanning the duration of earth s rock record shows remarkable similarities between ops of all ages in terms of structural style major rock components sequence of accretion and trace element geochemical signatures volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts island arc picrites mid ocean ridge basalts back arc basalts oceanic plateau basalts ocean island basalts and boninites with extremely rare komatiites this demonstrates that sea floor spreading lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum and accretion at convergent margins have been major earth processes since at least 3 8 ga ago there have been some secular changes in the rock types in ops such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in phanerozoic times but absent in the precambrian but overall there have been few changes in the style of ops accretion with time komatiites and banded iron formations occur predominantly in archean orogenic belts reflecting higher mantle temperatures and less oxic seawater composition respectively before 2 5 ga this is clear documentation that plate tectonics including the lateral movement of oceanic lithosphere has been a major heat loss mechanism on earth since the early precambrian

crustal melting and magma mixing in a continental arc setting evidence from the yaloman intrusive complex in the gorny altai terrane central asian orogenic belt abstract granitoids and their hosted mafic enclaves may retain important information on crust mantle interaction and thus are significant for study of crustal growth and differentiation an integrated petrological geochronological and geochemical study on the granitoid plutons of the yaloman intrusive complex from the gorny altai terrane northwestern central asian orogenic belt was conducted to determine their source nature petrogenesis and geodynamics mafic enclaves are common in the plutons and a zircon u pb age 389 ma 4 ma indicates that they are coeval with their granitoid hosts ca 393 387 ma petrographic observations reveal that these mafic enclaves probably represent magmatic globules commingled with their host magmas the relatively low sio2 contents 46 0 60 7 wt and high mg 38 9 56 5 further suggest that mantle derived mafic melts served as a crucial component in the formation of these mafic enclaves the granitoid hosts including quartz diorites and granodiorites are i type in origin possessing higher sio2 contents 60 2 69 9 wt and lower mg 32 0 44 2 their zircon hf and whole rock nd isotopic compositions indicate that the magmas were dominated by remelting of neoproterozoic 0 79 1 07 ga crustal materials meanwhile the geochemical modeling together with the common occurrence of igneous mafic enclaves and the observation of reversely zoned plagioclases suggests that magma mixing possibly contributed significantly to the geochemical variation of the granitoid hosts our results imply that mafic magmas from the mantle not only provided substantial heat to melt the lower crust but also mixed with the crust derived melts to form the diverse granitoids the oxidizing and water enriched properties inferred from the mineral assemblages and compositions imply that the granitoid plutons of the yaloman intrusive complex were possibly formed in a continental arc related setting which is also supported by their geochemistry the devonian granitoids from the gorny altai terrane show remarkable temporal spatial petrogenetic affinities to the counterparts from the altai mongolian terrane indicating that these two terranes were possibly under subduction of the same oceanic plate i e the ob zaisan ocean the voluminous granitoids signify significant crustal recycling and growth as a response to the underplating of extensive mantle derived basaltic melts

geochemical study of the cambrian ordovician meta sedimentary rocks from the northern altai mongolian terrane northwestern central asian orogenic belt implications on the provenance and tectonic setting abstract the altai mongolian terrane am is a key component of the central asian orogenic belt caob but its tectonic nature has been poorly constrained this paper reports geochemical compositions of cambrian ordovician meta sedimentary rocks from the northern am to trace their source nature and depositional setting which in turn place constraints on the geodynamic evolution of the am the cambrian ordovician meta sedimentary rocks from the northern am show variable major element compositions with negative correlation between sio2 and tio2 al2o3 fe2o3t mgo and k2o their high icv values 1 18 2 53 and relatively low cia values 37 9 76 3 indicate that the sediments were immature and probably underwent mild to moderate chemical weathering the low sio2 samples are characterized by relatively restricted sio2 al2o3 mostly 2 60 6 07 and low rb sr ratios 0 02 1 89 implying their proximal deposition without obvious sedimentary sorting and recycling in contrast the high sio2 samples show much higher sio2 al2o3 ratios 15 4 19 9 possibly due to sedimentary sorting and or silicification all these samples yield relatively high al2o3 tio2 ratios 15 6 22 8 strong lrees hrees differentiation la yb n 4 86 10 7 and obvious negative eu anomalies eu 0 61 0 83 combined with their th sc zr sc la th and co th ratios comparable with intermediate acidic magmatic rocks we infer that these kinds of magmatic rocks served as a major source for the investigated meta sedimentary rocks the tio2 al2o3 and fe2o3t mgo concentrations are mostly higher than typical sediments from passive margin and the th u la sc th sc eu eu zr hf zr th and la th ratios are quite similar to sediments from continental arcs these data suggest that the cambrian ordovician meta sedimentary rocks from the northern am were most likely deposited in an environment related to a continental arc setting rather than a passive regime these rocks show strong similarities to their counterparts in the chinese altai ca southern am and tseel terrane southeastern extension of the ca in western mongolia in terms of geochemical compositions and depositional setting with combination of recent isotopic studies for detrital zircons our data suggest that the am probably represented a coherent accretionary prism along a continental arc in the early paleozoic

tectonic evolution of the paleozoic barluk continental arc west junggar nw china abstract the barluk arc situated in west junggar is an important component of the kazakhstan domain in the central asian orogenic belt caob however the nature of the barluk arc active continental margin or oceanic island arc is in debate the igneous rocks in the shiwu area barluk arc have diagnostic petrologic geochronologic and geochemical signatures that uncover the attributes of the barluk arc in this paper we report detailed petrology whole rock geochemistry and sr nd isotopic zircon u pb dating and hf isotopic data of igneous rocks in the shiwu area our results reveal that 1 except for 302 2 ma gabbro igneous rocks from barluk arc in the shiwu area are dioritic and granitic have ages ranging from 323 8 to 310 5 ma and they have geochemical signatures originated from typical continental arcs including calc alkaline series rocks enrichment of lile depletion of hfse and higher th yb and ta yb values 2 the granitic porphyry and rhyolite in barluk arc have old tdm2 hf ages up to 1091 ma suggesting the existence of precambrian crust or similar materials as their sources and 3 the 302 2 ma gabbro dike has high values of end t 7 54 and ehf t 12 8 to 15 5 and a young t2dm nd age 455 ma and therefore it was possibly related to upwelling of asthenosphere mantle in a post subduction extensional tectonic setting based on these parameters we suggest that the barluk arc is defined as a late paleozoic continental margin arc along the margin of the kazakhstan continent westward subduction of the junggar oceanic plate in the barluk area started in early devonian and continued to the late carboniferous 310 ma subsequent post collisional tectonic processes between the junggar oceanic plate and kazakhstan continent continued to the late carboniferous 302 ma

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

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

iron oxide copper gold mineralization of the devonian laoshankou deposit xinjiang nw china in the central asian orogenic belt abstract the laoshankou iron oxide cu au iocg deposit 41 km southwest of qinghe city xinjiang nw china is the most important magnetite deposit with economic cu and au metal reserve 3 26 mt fe 33 5 36 4 9 8 kt cu 0 2 0 4 and 0 14 t au 0 5 1 3 g t in the east junggar terrane of the central asian orogenic belt caob the deposit is hosted by volcanic rocks of the middle devonian beitashan formation in this study four hypogene hydrothermal alteration stages have been identified including the ca silicate alteration stage i amphibole epidote magnetite alteration mineralization stage ii pyrite chalcopyrite mineralization stage iii and late hydrothermal veining stage iv mineralogical fluid inclusion including laser raman spectroscopy and mineral sulfur oxygen hydrogen and carbon isotope analyses were carried out to elucidate the nature and origin of the hydrothermal fluids at laoshankou stage i hydrothermal fluids were likely derived from a 590 c magmatic fluid with 18 o water 9 2 9 7 subsequently the magnetite epidote amphibole assemblage may have precipitated from the fluids 530 c formed by the mixing of high temperature magmatic fluids with the seawater that reacted with 18 o rich wall rocks the fluid rock reactions are reflected from the 18 o water 9 6 10 7 and d water 25 5 23 8 values the sub economic stage iii a pyrite epidote quartz garnet mineralization likely occurred at 415 c and was formed by fluids with 34 s fluid 3 7 0 5 d water 110 94 and 18 o water 7 92 8 9 the lower temperature and presence of organic matter of the stage iii a fluids may have reflected the involvement of meteoric water and organic matter from the wall rocks the economic cu mineralization stage iii b was probably formed by the mixing of a meteoric water dominated fluid medium temperature low salinity and na dominated and a ca rich formation water in equilibrium with the volcanic wall rocks medium temperature medium salinity and ca fe mg dominated with 34 s fluid 2 6 18 o water 5 6 5 8 13 c water 3 3 3 1 and d water 92 95 towards the end of the fluid evolution meteoric water incursion may have continued and generated the ore barren low temperature low salinity and na dominated fluids although the laoshankou deposit contains distinct skarn alteration the ore mineral assemblage and ore fluid features indicate that it is not a typical skarn deposit but share many similarities with many central andean iocg deposits we conclude that the iocg ore forming setting in the devonian east junggar was analogous to the cretaceous central andes in that they both occurred during basin inversion in a volcanic arc setting

ordovician carboniferous tectono sedimentary evolution of the north nuratau region uzbekistan westernmost tien shan abstract the tien shan is a c 2500 km long orogenic belt of which the nuratau region of eastern uzbekistan forms the western part petrographical and field analysis of the ordovician carboniferous succession in the north nuratau region provided the basis for a reconstruction of the depositional settings along part of the northern margin of the alai continent and their evolution during the period of closure of the turkestan ocean which separated the alai and the kazakh kyrgyz continents initial sedimentation ordovician was broadly carbonate dominated although by mid late ordovician times siliciclastic input predominated in some areas these variations between clastic and carbonate dominated regions may have been related to tectonic activity within the alai continent carbonate sedimentation was reestablished in the wenlock with broad shelf systems forming along the continental margin volcanic activity in the early devonian records a period of tectonic instability and this was followed by the reestablishment of the carbonate mosaic albeit with a greater degree of instability as indicated by stratigraphic gaps than in the silurian this pattern extended up into the carboniferous culminating in backarc related magmatic activity final closure of the turkestan ocean involved significant folding and thrusting as well as a major change from compressional to strike slip movement

jurassic paleogeography of the tian shan an evolution driven by far field tectonics and climate abstract the strongly intracontinental tian shan region in central asia represents a key area to understand the long term evolution of continents in general and asia in particular if its paleozoic and cenozoic geodynamics are well understood its mesozoic evolution remains poorly constrained in order to decipher the paleogeographic and large scale tectonic evolution of the tian shan area during the jurassic we compiled detailed field analyses of sedimentary rocks acquired within and around the chinese tian shan region together with previously published data we present three paleogeographical maps corresponding to the late early early middle jurassic late middle early late jurassic and late jurassic early cretaceous transition periods we provide a large scale picture of the jurassic paleogeographic and climatic evolution of the tian shan region and discuss the geological evolution of the range together with the possible driving mechanisms during the early to early middle jurassic the topographic evolution of the tian shan range was dominated by progressive planation of late paleozoic to early mesozoic relief locally interrupted by short lived tectonic uplift throughout the region contemporaneous sedimentation was characterized by alluvial to lacustrine strata deposited under humid conditions during this period recurrent limited deformation events associated with strike slip and compressive tectonics occurred that cannot be explained by far field effect of the qiangtang collision but could instead be associated to the coeval subduction related extension affecting the caspian turan domains during the late middle to early late jurassic the planation of the paleozoic early mesozoic tian shan range then continued a shift to more semi arid conditions during the late jurassic is also recorded in the sedimentary series all over the region at that time few evidences of deformation exists in the tian shan or within the caspian turan domains we propose that the late middle early late jurassic corresponded to a period of relative tectonic quiescence in the area finally the late jurassic early cretaceous transition was marked by a tectonic reactivation leading to the inversion of the yarkand fergana basin and to localized relief building in the tian shan this renewed transpressive deformation phase could be mainly related to the coeval accretion of the helmand block to the south west and possibly to the onset of the accretion of the lhasa block along the southwestern margin of eurasia finally this period was also characterized by the climax of aridification which played a major role on the emplacement of extensive alluvial fan systems in the basins surrounding the range

the early paleozoic tectonic evolution of the russian altai implications from geochemical and detrital zircon u pb and hf isotopic studies of meta sedimentary complexes in the charysh terekta ulagan sayan suture zone abstract the charysh terekta ulagan sayan suture zone was regarded as a tectonic boundary separating two distinct subduction accretion systems in the central asian orogenic belt caob in the north magmatic arcs such as the gorny altai terrane formed in the southwestern periphery of the siberian continent whereas in the south arc prism systems such as the altai mongolian terrane formed around the so called kazakhstan baikal composite continent with gondwana affinity when did these two systems amalgamate and whether the metamorphic complexes in the suture zone represent precambrian micro continental slivers are critical for our understanding of the accretionary orogenesis and crustal growth rate in the caob a combined geochemical and detrital zircon u pb hf isotopic study was conducted on the meta sedimentary rocks from the ulagan also referred to bashkaus and teletsk complexes in the suture zone the results indicate that the protoliths of these rocks were dominated by immature sediments deposited in a time period between 500 and 420 ma thus precambrian micro continental slivers may not exist in the suture zone and even in the whole altai orogen the meta sedimentary rocks from the ulagan complex yield geochemical compositions between those of common intermediate and felsic igneous rocks implying that these kinds of rocks possibly served as dominant sources detrital zircons from this complex consist of a major population of ca 620 500 ma a subordinate one of ca 931 671 ma and rare grains of ca 2899 1428 ma this age spectrum is compatible with the magmatic records of the western mongolia we propose that the ulagan complex possibly represents part of a subduction accretion complex built upon an active continental margin of the western mongolia in the early paleozoic the remarkable similarities in source nature provenance and depositional setting to the early paleozoic meta sedimentary rocks from the northern altai mongolian terrane imply that the ulagan complex was possibly fragmented from this terrane the meta sedimentary rocks from the teletsk complex show similar detrital zircon populations but contain higher proportions of mafic sediments and have more depleted whole rock nd isotopic compositions our data suggest that the detritus mostly came from the same source as that for the ulagan complex but those from the gorny altai terrane also contributed this implies that the gorny altai and altai mongolian terranes possibly amalgamated prior to the early devonian rather than in the middle devonian to early carboniferous as previously thought thus the widespread devonian to early carboniferous magmatism within these two terranes was possibly generated in a similar tectonic setting moreover the dominant neoproterozoic to early paleozoic detrital zircons from the teletsk complex yield largely varied hf t values of 23 8 to 12 4 indicating that crustal growth and reworking are both important in the accretionary orogenesis

implications of palaeozoic ophiolites from western junggar nw china for the tectonics of central asia western junggar nw china contains fragments of several palaeozoic island arcs accretionary prisms and ophiolites which were accreted to each other and possibly to the southern margin of eurasia by the end of the palaeozoic the ophiolites of western junggar are important in reconstructions of these events four ophiolite belts are recognized from south to north these are tangbale mayila dalabute and barleik honggulueleng hebukesair they record the production and destruction of oceanic tracts in this region from the cambrian to the carboniferous the following characteristics are representative of them all 1 the ophiolitic successions are strongly deformed 2 sheeted dyke swarms are not preserved 3 basic igneous rocks show a range of chemical characteristics from depleted island arc tholeiite to ocean island basalt altered n type mid ocean basalts may be represented 4 large scale thrusts typically directed towards the southeast lie at the base of many individual ophiolitic bodies 5 the ophiolites rarely mark the position of possible sutures between arcs they are normally highly deformed and imbricated with other lithologies accretion of palaeozoic arcs and obduction of ophiolites was complete by the end of the carboniferous but the timing and sequence of events remain obscure no continental collisions occurred during this period of assembly crustal growth occurred by the amalgamation of non continental blocks

mid late miocene deformation of the northern kuqa fold and thrust belt southern chinese tian shan an apatite u th sm he study abstract the kuqa fold and thrust belt developed in response to cenozoic southward shortening between the chinese tian shan and the tarim basin this study aims to constrain the timing of the late cenozoic deformation by determining the onset time of enhanced rock cooling using apatite u th sm he thermochronometry eight sedimentary samples were collected from triassic to cretaceous strata exposed along a 17 km n s transect cross cutting the northern kuqa fold and thrust belt single grain ahe ages from these samples mostly cluster around 8 16 ma and are younger than their depositional ages older ahe ages show a positive relationship with eu a proxy for radiation damage modelling of the observed age eu relationships suggest a phase of enhanced cooling and erosion initiated at mid late miocene time 10 20 ma in the northern kuqa fold and thrust belt this result is consistent with a coeval abrupt increase of sedimentation rate in the foreland kuqa depression south of the study area indicating a mid late miocene phase of shortening in the northern kuqa fold and thrust belt

geochemical signature of porphyries in the baogutu porphyry copper belt western junggar nw china article i nfo the baogutu porphyry copper belt lies in the darbut transitional island arc of the western junggar in the western section of the central asian orogenic belt in nw china our new petrographic results for the ore bearing porphyry stocks in the baogutu porphyry copper belt recognize them as diorite porphyry stocks rather than the granodiorite porphyry stocks as previously identified the copper mineralization is hosted in the diorite diorite porphyries and related breccias of the diorite porphyry stocks geochemical data indicate that the ore bearing porphyries have a predominantly intermediate composition with a transitional character from tholeiite to calc alkaline and are enriched in large ion lithophile elements lile and depleted in highfield strength elements hfse with a clear negative nb anomaly ree patterns show distinctenrichmentsin lree relative to hree the rocks also exhibit high initial end t 2 7to 6 3 ratios and low initial 87 sr 86 sr values 0 70359 0 70397 many samples are chemically similar to adakites

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

pyrite re os and zircon u pb dating of the tugurige gold deposit in the western part of the xing an mongolia orogenic belt china and its geological significance abstract the tugurige gold deposit in the northeastern margin of the north china craton ncc and western part of the xing an mongolia orogenic belt xmob is a large tonnage quartz vein type deposit with a resource of 24 t at about 4 g t au gold mineralization is hosted by porphyritic syenogranite and controlled by nw trending faults our study provides the first precise age for the tugurige gold mineralization and host porphyritic syenogranite the u pb age of zircons from the syenogranite is 276 2 ma and re os dating of six pyrite separates from the deposit yields an isochron age of 268 15 ma the results show that the ages of syenogranite and gold mineralization are the same within error furthermore geological and geochronological evidence indicate that the syenogranite and gold mineralization have very close genetic relationships and that they are products of permian magmatism related to post collisional extension of the central asian orogenic belt caob the initial os isotopic compositions 187 os 188 os 1 26 0 69 of pyrite indicate that the source of os and by inference other ore related materials are derived from the crust the late paleozoic is an important period in which economic gold mineralization was deposited in the caob

basin evolution in a folding lithosphere altai sayan and tien shan belts in central asia abstract central asia is a classical example for continental lithospheric folding in particular the altay sayan belt in south siberia and the kyrgyz tien shan display a special mode of lithospheric deformation involving decoupled lithospheric mantle folding and upper crustal folding and faulting both areas have a heterogenous crust with a long history of accretion collision subsequently reactivated as a far field effect of the indian eurasian collision thanks to the youthfulness of the tectonic deformation in this region peak deformation in late pliocene early pleistocene the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures a review of the paleostress data and tectono stratigraphic evolution of the kurai chuya basin in siberian altai zaisan basin in kazakh south altai and issyk kul basin in kyrgyz tien shan suggests that they were initiated in an extensional context and inverted by a combination of fault controlled deformation and flexural folding in these basins fault controlled deformation alone appears largely insufficient to explain their architecture lithospheric buckling inducing surface tilting uplift and subsidence also played an important role they form typical basins in a folding lithosphere flb their characteristic basin fill and symmetry inner structure folding wavelength and amplitude thermal regime time frame are examined in relation to basement structure stress field strain rate timing of deformation and compared to existing modelling results

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

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

new evidence on the neogene uplift of south tianshan constraints from the u th he and aft ages of borehole samples of the tarim basin and implications for hydrocarbon generation we identified a neogene rapid uplift denudation event of the south tianshan based on apatite u th he and apatite fission track aft ages in tertiary rocks of the tarim basin using borehole samples the u th he thermochronology can be used to reveal the tectono thermal events with lower temperature than that of aft thermochronology and has not been used previously to study the uplift of the tianshan mountain using these data we show the relationship between the uplift of the south tianshan and the subsidence deposition of the northern tarim basin during the neogene the apatite helium ages reveal the migration of uplift erosion and deposition in the northern tarim basin a rapid uplift of the south tianshan during the miocene and a corresponding rapid subsidence in the northern tarim basin occurred however in the pliocene the kuqa depression and south tianshan uplifted and eroded at the same time and in turn provided the detrital source rocks for the northern uplift of the tarim basin in contrast to earlier studies we arrive at the conclusion that the south tianshan experienced rapid uplift in the miocene based on u th he data of apatite obtained from borehole samples collected in the tarim basin itself and not from the bordering mountain chain combined apatite u th he and fission track thermochronometry enables reconstruction of thermal histories of sedimentary rocks between 40 and 120 c and this has implications for the generation of liquid hydrocarbon in the 65 120 c range in the basin thermal and burial histories of typical samples were also modelled to show the rapid uplift in our study our works not only provide a new evidence for the south tianshan uplift but also indicate that there is a coupling between uplift and subsidence in the south tianshan and adjacent northern part of the tarim basin which controlled hydrocarbon accumulation in the kuqa depression and northern uplift of the tarim basin

nonlinear seismic response in the western l aquila basin italy numerical fem simulations vs ground motion records abstract in the western l aquila basin italy six seismic stations of the italian strong motion network which were used on both soil and rock outcrops recorded a huge amount of weak and strong motion data near an active fault during the 2009 l aquila seismic sequence this paper analyzes the ground motion records of events with magnitudes ranging between 1 6 and 6 3 and compares the observed peak accelerations and the h v and v h spectral ratios with those revealed from numerical simulations the finite element method is considered herein to perform 2d dynamic modeling on a geologic cross section of the upper aterno river valley which is 1000 m wide and 50 m deep based on the reviewed geologic geotechnical and geophysical investigations that were performed in previous studies the martin finn seed s pore water pressure model is used in the simulations the observed peak accelerations the frequencies and the levels of maximum amplification are correctly estimated using the fem simulations the consistency between the computed and the experimental results shows a seismic response that is sensitive to the level of earthquake magnitude and mainly depends on the rock and soil elastic and dynamic properties the intensity and the depth of the seismic impedance contrast the water table depth the two dimensional irregular configuration the dip angle of strata the shape and the frequency content of the input motion record the seismic motion amplification is usually higher at station aqv which is located near the valley center where a peak acceleration value of 0 66 g was recorded both the pga amplification factor and the maximum amplification frequency of the horizontal component decrease when the earthquake magnitude level increases which shows a nonlinear seismic response at the stations aqg on fractured and weathered rock aqa and aqv on alluvium the simulation of the 2009 mw 6 3 l aquila earthquake confirms the observed nonlinear effective stress behavior and allows us to relate it to the generation of excess pore water pressure which ranges between 50 and 300 kpa

the sino korean craton and supercontinent history problems and perspectives abstract the sino korean craton skc is an enigmatic block in the history of supercontinents older than pangea its accretion to eurasia and the effect of the broad region of mesozoic cenozoic extension in northern eurasia that crosses the eastern part of the skc are among several problems that need to be resolved in understanding the configuration of skc and the overprinting of earlier histories in this block we present a synopsis of these problems and perspectives for future research

tectonic evolution of the east junggar terrane evidence from the taheir tectonic window xinjiang china abstract the taheir tectonic window is located at the southern part of the yemaquan magmatic arc in east junggar this paper reports detailed petrology mineral chemistry whole rock and sr nd isotope geochemistry hornblende 40ar 39ar dating in situ zircon u pb dating and hf isotope analyses from igneous and meta igneous rocks from this region our new results show that the taheir tectonic window consists of metamorphic and deformed ordovician volcanic rocks and granitic porphyries ordovician silurian granites and undeformed silurian devonian granitic diorite diorites and rhyolitic porphyries the ordovician volcanic rocks and granitic porphyries and ordovician silurian granites in the taheir tectonic window exhibit distinct features of andean type continental arc such as enrichment in pb k and u depletion in nb p and ti negative eu anomalies high la yb th yb and ta yb values a high proportion of dacite rhyolite and andesite of the calc alkaline series massive contemporary granitic intrusions mixtures of the juvenile material and 2 5 ga crust and extensive crystallization differentiation these ordovician volcanic rocks witnessed a series of tectonic events including burial associated with the intrusion of 454 449 ma granitic porphyries underthrusting and subsidence to a depth in the middle crust associated with the intrusion of 443 432 ma granites the formation of albite hornblende schists hornblende albite quartz leptynites and amphibolites the transformation from continental to continental island arc at approximately 432 ma the exhumation associated with the intrusion of 416 406 ma diorites with geochemical signatures of continental island arc and exhumation and erosion between 398 ma and 390 ma are also identified the arc types that are associated with the taheir tectonic window and its host the yemaquan magmatic arc changed from andean type continental arc to continental island arc after the intra arc rifting that began at 432 ma on the basis of the new evidence the tectonic regime of the east junggar terrane is redefined and a new model is proposed it is suggested that the east junggar terrane is related to the southward subduction of the paleo asian ocean plate beneath the junggar continent in the early paleozoic and later shift to intra oceanic subduction

formation of the kokchetav subduction collision zone northern kazakhstan insights from zircon u pb and lu hf isotope systematics abstract the kokchetav subduction collision zone is located in the western part of the ancestral central asian orogenic belt this zone is built up by the precambrian kokchetav microcontinent which includes a hp uhp metamorphic belt and the north kokchetav tectonic zone nktz which represents an accretionary complex between the kokchetav microcontinent and the adjacent stepnyak island arc the entire region is widely intruded by palaeozoic granitoids which were emplaced after the collision of the stepnyak island arc with the kokchetav microcontinent we present zircon u pb ages and lu hf systematics in zircon to better characterize the tectonic evolution of the kokchetav subduction collision zone the lu hf results indicate that the kokchetav basement rocks are derived from late neoarchaean early palaeoproterozoic 2 5 ga crust for the granite gneiss basement of the kokchetav microcontinent early mesoproterozoic grenville age 1 17 1 14 ga zircon u pb crystallization ages were obtained for the nktz two main age components were recognized 1 an oldest mesoproterozoic age component 1 20 1 05 ga similar as for the kokchetav microcontinental zircons and 2 a younger early cambrian 540 520 ma or late cambrian early ordovician 490 480 ma age component th u ratios 0 1 and are typical of a magmatic protolith the distinction between both zircon types is supported by characteristic cathodoluminescence images these results confirm previous observations indicating early palaeozoic high grade metamorphism 540 520 ma and collisional deformation 490 480 ma of the mesoproterozoic kokchetav zone as a result of subduction accretion and collision of the stepnyak island arc to the kokchetav microcontinent for two additional samples of the balkashin granitic complex early devonian 415 395 ma zircon crystallization ages magmatic th u ratios were obtained the occurrence of a mesozoic xenocryst within these leucogranites may indicate that they were emplaced in a continental arc setting

devonian volcanic rocks of the southern chinese altai nw china petrogenesis and implication for a propagating slab window magmatism induced by ridge subduction during accretionary orogenesis abstract ridge trench interaction is a common tectonic process of the present day pacific rim accretionary orogenic belts and this process may facilitate slab window magmatism that can produce significant thermal anomalies and geochemically unusual magmatic events however ridge trench interaction has rarely been well documented in the ancient geologic record leading to grossly underestimation of this process in tectonic syntheses of plate margins the chinese altai was inferred to have undergone ridge subduction in the devonian and a slab window model is proposed to interpret its high temperature metamorphism and geochemically unique magmatic rocks which can serve as an excellent and unique place to refine the tectonic evolution associated with ridge subduction in an ancient accretionary orogeny for this purpose we carried out geochemical and geochronological studies on devonian basaltic rocks in this region secondary ion mass spectrometry sims zircon u pb dating results yield an age of 376 2 2 4 ma suggesting an eruption at the time of late devonian geochemically the samples in this study have variable sio2 43 3 58 3 wt low k2o 0 02 0 07 wt and total alkaline contents 2 16 5 41 wt as well as fe2o3t mgo ratios showing typical tholeiitic affinity on the other hand the basaltic rocks display morb like ree patterns la yb n 0 90 2 57 and ga yb n 0 97 1 28 and have moderate positive end t values 4 4 to 5 4 which collectively suggest a derivation from a mixing source comprising morb like mantle of a mature back arc basin and subordinate arc mantle wedge these basaltic rocks are characterized by low la yb 1 26 3 69 dy yb 1 51 1 77 and sm yb 0 83 1 32 ratios consistent with magmas derived from low degree 10 partial melting of the spinel lherzolite source at a quite shallow mantle depth considering the distinctive petrogenesis of the basaltic rocks in this region the late devonian basalts in the southern chinese altai is suggested to have witnessed the propagating process of slab window magmatism that was induced by ridge subduction in a nascent rifting stage of a back arc basin

late permian palaeomagnetic data east and west of the urals summary we studied upper permian redbeds from two areas one between the urals and the volga river in the southeastern part of baltica and the other in north kazakhstan within the ural mongol belt which are about 900 km apart a limited collection of lower middle triassic volcanics from north kazakhstan was also studied a high temperature component that shows rectilinear decay to the origin was isolated from most samples of all three collections for the late permian of north kazakhstan the area mean direction of this component is d 224 3 i 56 8 k 161 95 2 7 n 18 sites palaeopole at 53 4 n 161 3 e the fold test is positive the triassic result d 55 9 i 69 1 k 208 95 4 2 n 7 sites pole at 57 0 n 134 1 e is confirmed by a positive reversal test the corresponding palaeomagnetic poles from north kazakhstan show good agreement with the apwp for baltica thus indicating no substantial motion between the two areas that are separated by the urals our new mean late permian direction for se baltica d 42 2 i 39 2 k 94 95 3 5 n 17 sites palaeopole at 45 6 n 170 2 e is confirmed as near primary by a positive tilt test and the presence of dual polarity directions the corresponding pole also falls on the apwp of baltica but is far sided with respect to the coeval reference poles as the observed mean inclination is shallower than expected by 13 4 in principle lower than expected inclinations may be attributed to one or more of the following causes relative tectonic displacements quadrupole and octupole terms in the geomagnetic field higher order harmonics incl secular variation of the same field random scatter non removed overprints or inclination error during remanence acquisition and or diagenetic compaction our analysis shows that most mechanisms from the above list cannot explain the observed pattern leaving as the most likely option that it must be accounted for by inclination shallowing comparison with selected coeval results from eastern baltica all within russia shows that all of them are biased in the same way this implies that they cannot be used for analysis of geomagnetic field characteristics such as non dipole contributions without a more adequate knowledge of the required correction for inclination shallowing

basin structures and sediment accumulation in the baikal rift zone implications for cenozoic intracontinental processes in the central asian orogenic belt abstract in this paper we present a review of sedimentological geomorphological lithological geochronological and geophysical data from major minor and satellite basins of the baikal rift zone brz and discuss various aspects of its evolution previously the most detailed sedimentological data have been obtained from the basins of the central brz e g baikal tunka and barguzin and have been used by many scientists worldwide we add new information about the peripheral part and make an attempt to provide a more comprehensive view on brz sedimentation stages and environments and their relations to local and regional tectonic events a huge body of sedimentological data was obtained many years ago by soviet geologists and therefore is hardly accessible for an international reader we pay tribute to their efforts to the extent as the format of a journal paper permits we discuss structural and facial features of brz sedimentary sequences for the better understanding of their sedimentation environments in addition we review tectono sedimentation stages neotectonic features and volcanism of the region finally we consider the key questions of the brz evolution from the sedimentological point of view in particular correlation of mesozoic and cenozoic basins bilateral growth of the baikal rift miocene sedimentation environment and events at the miocene pliocene boundary pliocene and pleistocene tectonic deformations and sedimentation rates the data from deep boreholes and surface occurrences of pre quaternary sediments the distribution of the pleistocene sediments and the data from the baikal and hovsgol lakes sediments showed that 1 brz basins do not fit the mesozoic extensional structures and therefore hardly inherited them 2 the miocene stage of sedimentation was characterized by low topography and weak tectonic processes 3 the rifting mode shifted from slow to fast at ca 7 5 ma 4 the late pleistocene high sedimentation rates reflect the fast subsidence of basin bottoms

late paleozoic early mesozoic geodynamics of central asia abstract correlation and synthesis of published and new structural paleomagnetic and geochronological data from central asia show the important role of strike slip faulting in their evolution the pattern of major strike slip faults outlines a terrane collage produced by a late devonian early carboniferous collision of the gondwana derived altai mongolia tuva composite microcontinent with siberia and a late carboniferous permian collision of east europe and kazakhstan with siberia the accreted continental margins were cut by strike slip faults and conjugate thrusts into numerous terranes which mixed with one another and disturbed the previous structural and facies framework those complex and multi stage deformations resulted from the late devonian early carboniferous collision of gondwana derived terranes the deformations reached their peak in the late carboniferous permian due to the collision of the kazakhstan east european baltica and siberian continents a system of sinistral strike slip faults formed a mosaic block structure of central asia along the margin of the siberian continent as a result of the late carboniferous permian collision this resulted in the formation of the northern eurasia continent early mesozoic strike slip faulting and conjugate thrusting resulted from the rotation of the siberian and east european cratons

magnetism of south mongolian middle paleozoic ophiolites abstract this paper presents new paleomagnetic data from south mongolia middle paleozoic rocks were studied from three different tectonic zones within the south mongolian fold belt from north to south these are the gobi altai zone in terms of paleotectonic position the north shelf of the paleobasin the trans altai zone ophiolite complexes and the south gobia zone the south shelf several paleomagnetic field tests including conglomerate baked contact and fold tests were carried out to determine magnetic stability in addition principal component analysis of the stepwise thermal demagnetization data was used the ophiolites are characterized by three ancient components one magnetic component is pre folding and directed to the south with a very gentle inclination declination d 180 210 inclination i 6 2 k 120 two post folding magnetic components were observed also the first post folding magnetic component has d 282 4 i 36 4 k 30 3 and the second has d 318 6 i 33 0 k 60 5 the final magnetic component is very close to the permian paleomagnetic direction expected from the north china platform the first post folding component of magnetization may have been acquired during the variscan accretion in early carboniferous time when the basin was closed the south mongolian paleo ocean was located in equatorial latitudes near the tarim block the south china platform and probably the north china platform in the devonian

late paleozoic volcanic record of the eastern junggar terrane xinjiang northwestern china major and trace element characteristics sr nd isotopic systematics and implications for tectonic evolution article i nfo the eastern junggar terrane of the central asian orogenic belt includes a late paleozoic assemblage of volcanic rocks of mixed oceanic and arc affinity located in a structurally complex belt between the siberian plate the kazakhstan block and the tianshan range the early history of these rocks is not well constrained but the junggar terrane was part of a cordilleran style accreted arc assemblage by the late carboniferous late paleozoic volcanic rocks of the northern part of the east junggar terrane are divided from base to top into the early devonian tuoranggekuduke formation fm middle devonian beitashan fm middle devonian yundukala fm late devonian jiangzierkuduke fm early carboniferous nanmingshui fm and late carboniferous batamayineishan fm we present major element trace element and sr nd isotopic analyses of 64 ultra mafic to intermediate volcanic rock samples of these formations all devonian volcanic rocks exhibit remarkably negative nb ta and ti anomalies on the primitive mantle normalized trace element diagrams and are enriched in more highly incompatible elements relative to moderately incompatible ones furthermore they have subchondritic nb ta ratios and their zr nb and sm nd ratios resemble those of morbs characteristics of arc related volcanic rocks the early devonian tuoranggekuduke fm middle devonian beitashan fm and middle devonian yundukala fm are characterized by tholeiitic and calc alkaline affinities in contrast the late devonian jiangzierkuduke fm contains a large amount of tuff and sandstone and its volcanic rocks have dominantly calc alkaline affinities we therefore propose that the jiangzierkuduke fm formed in a mature island arc setting and other devonian fms formed in an immature island arc setting the basalts from the nanmingshui fm have geochemical signatures between n morb and island arcs indicating that they formed in a back arc setting in contrast the volcanic rocks from the batamayineishan fm display geochemical characteristics of continental intraplate volcanic rocks formed in an extensional setting after collision thus we propose a model that involves a volcanic arc formed by northward subduction of the ancient junggar ocean and amalgamation of different terranes during the late paleozoic to interpret the formation of the late paleozoic volcanic rocks in the eastern junggar terrane and the altai and junggar terranes fully amalgamated into a cordilleran type orogen during the end of early carboniferous to the middle late carboniferous

ordovician 40ar 39ar phengite ages from the blueschist facies ondor sum subduction accretion complex inner mongolia and implications for the early paleozoic history of continental blocks in china and adjacent areas we obtained 453 21 8 ma and 449 41 8 ma 2 laser step heating 40 ar 39 ar plateau ages for phengite from quartzite mylonites from the blueschist facies ondor sum subduction accretion complex in inner mongolia northern china these ages are within error of the inverse isochron ages calculated using the plateau steps and the weighted mean ages of total fusion of single grains the compositional change from glaucophane in the cores to crossite in the rims of blue amphiboles as revealed by electron microprobe analysis points to decompression probably caused by progressive exhumation of the subducted material the late ordovician ages were not affected by excess argon incorporation because in all likelihood the oceanic sediments were wet on arrival at the trench and free of older detrital mica the ca 450 ma ages are hence interpreted as the time of crystallization during mylonitization under high fluid activity at fairly low temperatures this means that accretion of the quartzite mylonite unit occured about 200 ma before final closure of the paleo asian ocean amalgamation of the siberian tarim and north china cratons and formation of the end permian solonker suture zone we argue that the early paleozoic evolution of the ondor sum complex occurred along the northeastern cimmerian margin of gondwana which was composed of micro continents fringed by subduction accretion complexes and island arcs the later evolution took place during the building of the eurasian continent following middle devonian and younger rifting along the east gondwanan margin and northward drift of the detached north china craton an extensive review shows that this type of two stage scenario probably also applies to the geodynamic evolution of other micro continents like south china tarim a number of kazakh terranes alashan qaidam and kunlun as well as south kitakami and correlatives in japan and probably indochina like the north china craton these were bordered by early paleozoic subduction accretion complexes island arcs or contained calc alkaline volcanic mar gins like for example the central tienshan north qinling north qaidam altun north qilian and kunlun belts in china as well as the oeyama and miyamori ophiolites and matsugadaira motai blueschist belt of japan and the dismembered sergeevka ophiolite of the southern part of the russian far east this implies that a vast orogenic system comprising an archipelago of micro continents seems to have existed along the cimmerian margin of east gondwana in early paleozoic time in which the ultrahigh pressure metamorphism that characterizes the early evolution of many of the asian micro continents occurred introduction and aim

pharmacokinetic modelling of multi decadal luminescence time series in coral skeletons abstract as corals grow they incorporate chemical indicators of seawater conditions into their aragonite skeleton after they have traversed an outer living tissue layer long lived massive coral skeletons can record decade and century long time series of seawater status one such environmental clue is luminescence intensity which can correspond to river flow patterns and has been attributed to humic acid incorporation seawater humic acid levels are linked to river flow as rainfall extracts them from catchment soils to then flow into rivers and coastal seas however discrepancies exist when validating coral luminescence records against river flow data with intense luminescence sometimes occurring in the absence of increased flows this contributes to uncertainty when reconstructing pre instrumental river flows and rainfall from coral luminescence here we demonstrate that a major portion of coral core luminescence time series can be explained using a single compartment pharmacokinetic model that incorporates river flow measurements as the equivalent of drug dose the model was robust for luminescence series in corals from near shore reefs regularly influenced by river flow the model implies that after floods a proportion of subsequent luminescence peaks can be derived from the initial flood this explains why some luminescence peaks after floods often do not correspond to additional significant river flows this provides the first mechanism based explanation for temporal changes in coral skeleton luminescence that incorporates a mathematical link between two independent time series making this proxy even more robust for reconstructing river flow and rainfall

geochronological geochemical and sr nd hf isotopic studies of the baiyanghe a type granite porphyry in the western junggar implications for its petrogenesis and tectonic setting abstract zircon u pb dates sr nd hf isotopic compositions and major element and trace element geochemistry were determined for the baiyanghe granite porphyry in the western junggar nw china the porphyry has a zircon u pb age of 313 4 2 3 ma is high in sio 2 76 34 78 30 wt and k 2 o na 2 o 8 04 8 85 wt relatively low in mgo 0 01 0 03 wt and cao 0 29 0 39 wt and shows characteristics typical of a type granites because its y nb ratio 0 33 0 51 is lower than 1 2 it can be classified into a 1 group moreover due to its positive values of end t 4 06 5 29 and ehf t 8 18 11 07 and high concentrations of incompatible elements including rb th u and nb the baiyanghe granite porphyry is suggested to have been derived from an oceanic island basalt like mantle source their extremely high initial 87 sr 86 sr ratios 0 7143 0 7469 and high la sm n values 5 13 8 44 could be caused by the involvement of marine sediments the low ba sr and eu concentrations and high values of di 97 3 98 0 of the granite porphyry suggest that its magma had undergone a high degree of fractional crystallization characterized by the features of within plate granites a back arc basin tectonic setting is favored for the petrogenesis of the baiyanghe granite porphyry such a setting indicates that the subduction of the irtysh zaysan oceanic lithosphere beneath the zharma saur arc was still active during the late carboniferous and the collision between the siberia and kazakhstan blocks probably occurred between ca 316 ma and 307 ma

s pb isotopic geochemistry u pb and re os geochronology of the huanggangliang fe sn deposit inner mongolia ne china abstract the huanggangliang fe sn deposit is located in the eastern section of the central asian orogenic belt caob and in the southern segment of the great hinggan range polymetallic belt this deposit is the largest tin based polymetallic ore deposit in the northern part of the north china plate the fe sn mineralization principally occurs in skarn zones which formed in the contact areas between granite intrusions and marbles twenty one 34 s v pdb values for sulfides from the huanggangliang fe sn deposit range from 2 3 to 2 7 with an average of 0 38 and these values are interpreted to reflect a deep magmatic source of the sulfur contained within the ore minerals of the deposit the distribution of lead isotopic compositions from sulfides in the huanggangliang fe sn deposit exhibits a generally concentrated field indicating that those sulfides have homogeneous lead isotopes and may derive from the same metallic source the existence of such identical pb isotopic compositions of sulfides and host granites suggests that granitic magmatism was probably largely responsible for the huanggangliang mineralization zircon la icp ms u pb dating from the huanggangliang granite exhibits a tight cluster on the concordia plot and yields a weighted mean 206 pb 238 u age of 139 96 0 87 ma which is considered to be the best estimate of the crystallization age of the huanggangliang granite results obtained from the molybdenite re os isotopic analysis indicate re os model ages of 133 6 to 141 5 ma and a weighted mean age of 135 1 2 3 ma the molybdenite re os dating yields an isochron age of 134 9 5 2 ma and an initial 187 os 188 os ratio of 0 22 0 35 the molybdenite re os isochron age is largely consistent with the zircon u pb age indicating that both granite intrusion and fe sn mineralization were associated with the mesozoic magmatism in ne china based on ore deposit geology isotope geochemistry and geochronology of the huanggangliang fe sn deposit and regional geodynamic evolution the formation of this deposit is believed to be related to lithospheric thinning which was caused by delamination and subsequent upwelling of the asthenosphere under the intra continental extension in ne china the dynamic setting for the geological processes should be linked to the nnw subduction of the izanagi plate beneath the eurasian plate during the mesozoic this subduction triggered intensive magmatism and mineralization events in the great hinggan range of ne china making this district an important cu mo sn fe ag pb zn metallogenic province

geochemistry and petrogenesis of early carboniferous volcanic rocks in east junggar north xinjiang implications for post collisional magmatism and geodynamic process abstract early carboniferous volcanic rocks in the batamayineishan formation overlie unconformably the molasse deposits and the ophiolitic melanges and are restricted in narrow zones along both sides of the kalamaili orogenic belt in north xinjiang southern central asian orogenic belt these rocks demonstrate the post collisional setting in east junggar commenced in tournaisian and also mark an important transitional period from the final amalgamation to late paleozoic voluminous juvenile granitoids in east junggar the volcanic rocks are composed of basalt basaltic andesite andesite trachyte and rhyolite both mafic and felsic rocks are characterized by enrichments in large ion lithophile elements light rare earth elements and depletion in nb and ta low initial 87sr 86sr and high positive nd t three groups of mafic rocks have been identified shoshonitic group 1 has the highest mgo cao ni and cr and the lowest na2o al2o3 la ba la yb and ba th with primary magma features group 2 calc alkaline and high k calc alkaline mafic rocks have the lowest k2o p2o5 th and th nb and the highest tio2 and group 3 shoshonitic to potassic alkaline has the highest k2o p2o5 la ba la yb and th nb and the lowest tio2 the a type like felsic rocks were derived from the differentiation of the mafic magma geological and geochemical evidences indicate that the batamayineishan formation was generated from the process of slab breakoff detachment group 1 samples are produced by decompressional melting of the upwelling asthenosphere mainly composed of spinel and garnet 50 50 lherzolite which has been enriched by overlying metasomatized lithosphere during ascent group 2 is derived from 5 10 partial melting of shallower spinel bearing lithospheric mantle induced by the hot rising asthenosphere where the contribution of slab derived fluid is predominant low partial melting 3 5 of the mantle wedge and or thickened lithospheric mantle enriched by slab derived components generates group 3 slab breakoff as an important geodynamic process accounts for the post collisional magmatism between 343 5 ma 330 ma providing a model for post collisional crust mantle interaction in the caob