prolonged magmatism juvenile nature and tectonic evolution of the chinese altai nw china evidence from zircon u pb and hf isotopic study of paleozoic granitoids abstract paleozoic granitoid magmatism played an important role in the tectonic evolution of the chinese altai and zircon u pb and hf isotopic compositions have been determined for samples from eleven granitic plutons batholiths the jiadengyu gneissic granitic pluton yielded a zircon u pb age of 479 ma and thus it does not represent precambrian basement as suggested previously our results and published data demonstrate that voluminous granitoids were continuously emplaced over more than 30 area of the chinese altai during the period from 447 ma to 368 ma with a climax at ca 400 ma ages for zircon overgrowth rims demonstrate additional thermal events at ca 360 and 280 ma respectively positive e hf t values 0 to 9 of normal magmatic zircons suggest that the granitoid magmas were derived from juvenile sources xenocrystic zircon cores are 543 421 ma old and also give positive e hf t values 2 5 to 12 suggesting their origin as early crystallized minerals in the magma chambers or as inherited cores from newly accreted meterials the strong magmatism at ca 400 ma significantly changed the hf isotopic composition of the magma source by substantial input of juvenile material in a relatively short period geophysical geological and geochemical data support that ridge subduction was a possible mechanism for the strong magmatism ca 400 ma and the above mentioned change of hf isotopic composition in the magma source

the crustal structure from the altai mountains to the altyn tagh fault northwest china 1 we present a new crustal section across northwest china based on a seismic refraction profile and geologic mapping the 1100 km long section crosses the southern margin of the chinese altai mountains junggar accretional belt and eastern junggar basin easternmost tianshan mountains and easternmost tarim basin the crustal velocity structure and poisson s ratio which provide a constraint on crustal composition were determined from p and s wave data despite the complex geology the crustal thickness along the entire profile is nearly uniform at 50 km the thickest crust 56 km occurs at the northern end of the profile beneath the altai mountains and the thinnest 46 km crust is beneath the junggar basin beneath surficial sediments the crust is found to have three layers with p wave velocities vp of 6 0 6 3 6 3 6 6 and 6 9 7 0 km s respectively the southern half of the profile including the eastern tianshan mountains and eastern margin of the tarim basin shows low p wave velocities and 0 25 to a depth of 30 km which suggests a quartz rich granitic upper crustal composition the northern half of the profile below the altai mountains and junggar accretional belt has a higher poisson s ratio of 0 26 0 27 to a depth of 30 km indicative of an intermediate crustal composition the entire 1100 km long profile is underlain by a 15 30 km thick high velocity 6 9 7 0 km s 0 26 0 28 lower crustal layer that we interpret to have a bulk composition of mafic granulite at the southern end of the profile a 5 km thick midcrustal low velocity layer vp 5 9 km s 0 25 underlies the tianshan and the region to the south and may be indicative of a near horizontal detachment interface pn velocities are 7 7 7 8 km s between the tianshan and the junggar basin and 7 9 8 0 km s below the altai mountains and eastern margin of the tarim basin we interpret the consistent three layer stratification of the crust to indicate that the crust has undergone partial melting and differentiation after paleozoic terrane accretion the thickness 50 km of the crust appears to be related to compression resulting from the indo asian collision

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

a brine interface in the salton sea geothermal system california fluid geochemical and isotopic characteristics data from 71 geothermal production intervals in 48 wells from the salton sea geothermal system ssgs indicate that fluids in that system cluster into two distinct populations in terms of their salinity and their stable isotopic compositions the distinctive hot hypersaline brine typically 20 wt total dissolved solids for which the ssgs is known is overlain by a cooler 260 c fluid with distinctly lower salinity typically 10 wt total dissolved solids hypersaline brines have high and rather consistent 18o shifts produced by water rock interaction and have a very narrow range in d values low tds fluids on the other hand show a wide range in both d and 18o production of both types of fluid from closely spaced geothermal wells in many regions of the ssgs indicates that a relatively sharp salinity interface exists over much of the field the fluid interface typically cross cuts sedimentary bedding but is consistently found where reservoir temperatures are approximately 260 c at these temperatures hypersaline brines have densities of approximately 1 0 gm cm3 while the low tds fluids have densities as low as 0 85 gm cm3 this stable density stratified interface acts as a barrier to convective heat and mass transfer in the ssgs isolating the hypersaline reservoir from overlying dilute fluids a lithologic cap implied by previous ssgs models is unnecessary in such a stratified system since heat and mass transfer across the interface must occur by slow conductive diffusional and interface mixing processes regardless of local permeability

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

classification and mineralization potential of the pegmatites of the eastern brazilian pegmatite province the potential for nb ta li sn mineralization as well as for precious stones for the eastern brazilian pegmatite province ebpp has been evaluated on the basis of 530 k feldspar and 550 muscovite major and trace element analyses the ebpp is situated mainly in the state of minas gerais but encompasses also parts of the states of bahia espirito santo and rio de janeiro the ebpp is the largest pegmatite province of south america it was divided into the pegmatite districts of itambe aracuai safira nova era aimores and espera feliz this was done to test whether the pegmatites of these districts differ in their mineralization potential and how geotectonic setting influences mineralization potential the fractionation diagrams such as cs zn li be ba versus k rb cs versus ta ta nb and u na2o versus k cs for the pegmatite districts of aracuai and safira show the widest range in fractionation these pegmatite districts are leaders in the production of gem quality tourmaline aquamarine morganite and contain abundant spodumene tantalite and columbite in contrast the espera feliz and aimores pegmatite districts are the most primitive districts examined and have a corresponding lack of rare element mineralization literature data indicate that all studied pegmatites are of brasiliano age i e formed between 600 and 480 ma the pegmatites of transamazonic age 1 9 ga found rarely in the study area are of economic importance in the context of emerald mineralization but seem to be of less importance for rare metal and other gemstone mineralization

petrogenesis of the lijiagou spodumene pegmatites in songpan garze fold belt west sichuan china evidence from geochemistry zircon cassiterite and coltan u pb geochronology and hf isotopic compositions abstract spodumene and other pegmatites in the lijiagou area are located in the central songpan garze fold belt sgfb west sichuan these pegmatites are hosted within the giant songpan garze polymetallic belt a lack of precise geochronological constraints on the magmatic crystallization of the pegmatite suite and nearby plutonic granitoids has precluded definitive statements on genetic links between spodumene ore formation and the magmatic suite systematic zircon cassiterite and coltan u pb dating hf isotope and whole rock geochemical analysis were undertaken two mica granite and muscovite albite granite have s type granite affinities and chemical compositions suggesting a post orogenic setting and the albite spodumene pegmatites belong to the lct li cs ta group of pegmatites zircon la mc icp ms u pb dating of the two mica granite muscovite albite granite albite pegmatite and albite spodumene pegmatite give crystallization ages of 219 2 2 3 ma mswd 0 55 217 2 8 ma mswd 0 47 202 8 4 9 ma mswd 3 9 and 200 1 4 6 ma mswd 3 1 respectively zircons from the same units yield ehf t values of 39 17 to 6 81 22 73 to 2 83 11 17 to 8 14 and 4 92 to 2 4 respectively consistent with mixed crustal sources for the pegmatite and granite magmas cassiterite from albite spodumene pegmatite yields a concordia intercept age of 211 4 3 3 ma mswd 2 9 while coltan yields a weighted mean age of 211 1 1 0 ma mswd 0 97 the u pb zircon ages of the two mica granite and muscovite albite granite are interpreted as ages of magmatic crystallization metamictization of zircon in both albite and albite spodumene pegmatites makes their u pb zircon ages liable to inaccuracy due to pb loss the coltan u pb age is regarded as an accurate measure of the magmatic crystallization age of the albite spodumene pegmatite given the differences in magmatic ages and ehf t ranges between albite spodumene pegmatite and both the two mica granite and the muscovite albite granite the albite spodumene pegmatites probably represent anatectic melts and not fractionation products of either of the granitic magmas u pb coltan and u pb cassiterite dating are more likely to provide accurate crystallization ages of albite spodumene pegmatites than u pb zircon ages

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

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

mo deposits in northwest china geology geochemistry geochronology and tectonic setting abstract northwest china covering northern xinjiang northern gansu and westernmost inner mongolia mainly includes junggar basin and its surrounding mountains such as chinese altay junggar chinese tianshan and beishan it lies at the junction of siberia tarim and kazakhstan plates and is a key sector of the central asian orogenic belt caob characterized by multistage phanerozoic continental growth herein at least nine mo only or mo dominated fourteen cu mo two w mo and one be mo deposits have been discovered these 27 deposits occur in altay west jungar west tianshan east tianshan and beishan areas and have been formed during accretionary or collisional orogenies the majority of the deposits are porphyry type followed by the skarn and quartz vein types the orebodies occur mainly as veins lens pods in the positions from inner intrusions through contact zones to the hostrocks distal to causative intrusions the host rocks are variable in lithologies including granites porphyries volcanic breccias and tuffs and sedimentary rocks outward from orebodies to hostrocks the wallrock alteration is zoning from potassic k feldspar quartz mica through phyllic quartz sericite chlorite epidote to propylitic or argillic alterations with skarn specifically occurring in skarn type systems hydrothermal mineralization generally includes four stages from early to late represented by 1 potassic feldspar quartz veins or veinlets 2 quartz molybdenite stockworks 3 quartz polymetallic sulfide stockworks and 4 quartz carbonate fluorite veins or veinlets the ore forming fluids were initially magmatic in origin and shew high temperature and high salinity containing daughter mineral and or co2 bearing fluid inclusions and eventually evolved to low temperature low pressure low salinity and co2 poor meteoric water the porphyry mo deposits can be further subdivided into two subtypes i e dabie and endako types the endako type mo deposits e g suyunhe and hongyuan together with all the cu mo systems were formed in the palaeozoic subduction related magmatic arcs the dabie type porphyry mo deposits represented by giant donggebi and baishan together with the mo only mo dominated and w mo or be mo deposits were formed in syn to post collisional tectonic setting with isotope ages ranging 260 213 2 ma with the kumutage skarn type mo system being an exception aged 319 ma the dabie type porphyry mo deposits are characterized by the co2 bearing fluid inclusions that cannot be observed in the endako type porphyry mo systems the re contents in molybdenites from porphyry and porphyry skarn cu mo systems are mainly 100 ppm suggesting a source significantly contributed by the mantle whereas the re contents in molybdenites from the mo only or w mo deposits are mainly

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

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

age of the dahongliutan rare metal pegmatite deposit west kunlun xinjiang nw china constraints from la icp ms u pb dating of columbite fe and cassiterite abstract dahongliutan is a medium size li be ta nb rare metal pegmatite deposit in the tianshuihai terrane west kunlun orogenic belt nw china in this paper la icp ms u pb ages of columbite fe and cassiterite are reported to constrain the metallogenic age columbite fe with high u and low th yielded a late triassic weighted mean 206 pb 238 u age of 211 9 2 4 ma whilst cassiterite yielded a 206 pb 238 u 207 pb 235 u concordia lower intercept age of 218 12 ma and a tera wasserburg lower intercept age of 218 12 ma which is identical to the columbite fe u pb age and thus represents the emplacement age of the pegmatite dikes the ore hosting pegmatite dikes are intimately time space related to the dahongliutan s type granite ca 220 217 ma indicating that they may have been cogenetic integrating new and published geological data we suggest that the dahongliutan pegmatites may have evolved from the granitic magma represented by the dahongliutan s type pluton in a post collisional tectonic setting regionally the tianshuihai terrane is the western extension of the songpan ganzi block and thus the kunlun li mineralization belt may have been connected to the songpan ganzi li mineralization belt which contains eleven lithium deposits with about 9 8 of li 2 o reserves in china implying that the dahongliutan pegmatite deposit may also have favorable ore forming conditions the similar columbite fe and cassiterite ages demonstrate that these minerals can be precisely dated and could provide useful alternatives to accurately constrain the timing and evolution of rare metal mineralization

crystallization of the little three layered pegmatite aplite dike ramona district california subhorizontally layered pegmatite aplite bodies are characterized by fine grained sodic to granitic aplite that is usually juxtaposed abruptly above by much coarser grained commonly graphic potassic pegmatite although well studied there currently is little concensus as to how such dikes form the little three dike near ramona california is representative of such zoned bodies in this and other regions and contains discontinuous miarolitic pockets near the base of the graphic pegmatite zone tourmaline garnet biotite and muscovite show no changes in major or minor element compositions indicative of progressive magmatic fractionation until the immediate vicinity of the main miarolitic zone where they record abrupt and extreme enrichments in li f and mn there is no correlation of chemical changes in the dike with the appearance of small miarolitic vugs well below the main miarolitic zone nor is there any indication that the aplite graphic pegmatite or miarolitic pockets represent separate magma injections the chemistries of tourmaline garnet and micas however preclude conventional models of rayleigh fractionation or traditional zone refining textural features and modeled cooling histories indicate that the dike cooled quickly and might have solidified partially or totally to glass before crystallization commenced geothermometry based on the compositions of coexisting plagioclase and homogeneous nonperthitic k feldspar indicates inward crystallization of the dike from 400 435 c at the margins to 350 390 c within 20 30 cm of the pocket horizon then a sharp decrease to 240 275 c in the pockets where k feldspar is perthitic we interpret the feldspar geothermometry except perhaps in the miarolitic cavities to reflect the temperatures at crystallization fronts that advanced into the pegmatite first from the foot wall and eventually joined by a similar front downward from the hanging wall crystallization down from the hanging wall may have commenced after 70 80 of the foot wall aplite had crystallized the very abrupt increases of li mn and f in tourmaline and garnet near the miarolitic zone appear to be explained best by the process of constitutional zone refining in which a fluxed crystallization front sweeps an incompatible element enriched boundary layer through a solid or semi solid after these two highly fluxed boundary layers merged near the main miarolitic zone compositional evolution could have proceeded by crystal melt fractionation

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

palaeozoic accretionary and convergent tectonics of the southern altaids implications for the growth of central asia the southern altaids present a unidirectional section from mongolia to china through an accretionary orogen that youngs progressively from neoproterozoic in the north to permian in the south the orogen formed by forearc accretion of island arcs accretionary wedges ophiolites and precambrian microcontinents this regularity was upset by early growth within the ocean of arcs that later collided at the accreting continental margin by imbrication of old ophiolites with young arcs and by himalayan style thrust nappe tectonics when an arc collided into a microcontinent lateral growth of the southern altaids represents a massive addition of juvenile material to the palaeozoic crust

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

late permian triassic metallogeny in the chinese altay orogen constraints from mica 40ar 39ar dating on ore deposits abstract the central asian orogenic belt caob constitutes the largest phanerozoic accretionary orogen on earth it extends over 5000 km and hosting numerous metal deposits the chinese altay orogen an important element of the caob hosts abundant devonian ca 410 370 ma deposits the 40 ar 39 ar dating of seven mica separates from the representative samples syngenetic with orogenic type mineralization is summarized to record a poorly studied permian to triassic metallogenic episode in the chinese altay orogen the kelan and maizi basins in the chinese altay orogen which likely represent an arc accretionary complex contain a series of polymetallic lode deposits hosted in low grade metamorphic volcano sedimentary rocks two muscovite and five biotite separates were obtained from the ore forming veins paragenetically associated with au bearing polymetallic sulfides in the keketale pb zn wulasigou cu tiemurt pb zn dadonggou pb zn and sarekuobu au deposits these separates yielded 40 ar 39 ar plateau ages ranging from 260 ma to 205 ma integration of these results with other published geological and geochronological data indicates that the au cu pb zn mineralization post dated the final caob assembly with fluid movement and mineralization possibly driven by regional metamorphism and deformation it is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the caob results into the formation of the deposits

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

boron isotope evidence for the involvement of non marine evaporites in the origin of the broken hill ore deposits identifying the palaeogeographic setting and mode of origin of stratabound ore deposits can be difficult in high grade metamorphic terranes where the effects of metamorphism may obscure the nature of the protoliths here we report boron isotope data for tourmalines from the early proterozoic broken hill block in australia which hosts giant lead zinc silver sulphide deposits with one exception the 11b 10b ratios are lower than those for all other tourmalines from massive sulphide deposits and tour malinites elsewhere in the world we propose that these low ratios reflect leaching of boron from non marine evaporitic borates by convecting hydrothermal fluids associated with early proterozoic continental rifting a possible modern analogue is the salton sea geothermal field in california

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

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

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

early paleozoic sedimentary record of the chinese altai implications for its tectonic evolution abstract the chinese altai is a typical part of the central asian orogenic belt caob but its tectonic evolution is not well understood geochemical study of early paleozoic metasedimentary rocks was conducted to better constrain their provenance and tectonic environment these rocks have relatively low cia values 49 to 79 with icv values 0 73 1 36 higher than that of post archean australian average shale paas suggesting that they experienced relatively weak chemical weathering and were mainly derived from an immature source compared to paas and upper crust the samples mostly have relatively lower high field strength elements hfse e g zr hf nb ta and large ion lithophile element lile contents e g rb sr ba th u pb however their relatively high rb concentrations 40 ppm low rb sr 0 04 3 24 and th u th u 3 8 ratios are indicative of an acidic intermediate igneous source that had undergone weak chemical weathering all of the samples are moderately enriched in lree light ree and show relatively flat chondrite normalized hree heavy ree patterns la n yb n 3 2 12 6 with various negative eu anomalies eu eu 0 4 0 9 meta arenaceous samples have moderate sio 2 average 72 9 wt al 2 o 3 average 11 5 wt fe 2 o 3 t mgo average 7 16 wt contents and moderate al 2 o 3 sio 2 average 0 16 k 2 o na 2 o average 0 93 ratios similar to those of graywackes from continental island arcs or active continental margins however meta argillaceous samples have high sio 2 average 60 8 wt al 2 o 3 average 17 2 wt fe 2 o 3 t mgo average 12 2 wt contents and high k 2 o na 2 o average 3 45 al 2 o 3 sio 2 average 0 28 ratios similar to mudstones from continental arc basins this kind of tectonic environment is also manifested in tectonic discrimination diagrams including th sc zr 10 and la th sc these geochemical characteristics suggest that the metasedimentary rocks were deposited in an active continental margin or continental arc setting this does not favor the previously proposed passive continental margin model therefore this study supports an arc accretion model for the chinese altai

geochronology petrogenesis and tectonic significance of peraluminous granites from the chinese altai nw china abstract the paleozoic granites in the chinese altai are important for the study of tectonic evolution and crustal growth in the central asian orogenic belt caob four representative peraluminous granitic intrusions were selected for systematic studies of zircon u pb and hf isotopic compositions and whole rock geochemical and nd sr isotopic analyses these rocks have high asi alumina saturation index al 2 o 3 cao na 2 o k 2 o 1 01 1 46 molecular ratios with 0 6 5 6 wt of normative corundum and are characterized by moderately negative eu anomalies eu eu 0 38 0 98 and strong depletion in ba nb and sr elements our data suggest that these intrusions were emplaced from 419 to 393 ma consistent with a period of intensive magmatic activities and high temperature metamorphism in the chinese altai while in situ zircon hf isotopic analyses for these granites give predominantly positive e hf t values 0 8 to 12 8 a few inherited zircons yield negative e hf t values from 12 5 to 1 53 the u pb age and hf isotopic data of these inherited zircons are similar to that of the widespread metasediments in addition the peraluminous granitic rocks have near zero or negative e nd t values 3 3 to 0 5 and relatively high initial 87 sr 86 sr ratios 0 7079 0 7266 distinct from those of the i type granites in the study region but similar to the early paleozoic habahe sediments these isotopic compositions suggest that the newly accreted metasediments of habahe group may be the major source rock of the peraluminous granites the geochemical compositions indicate that their precursor magmas were derived from a relatively shallow crustal level p 5 kbar and zircon saturation temperatures suggest that these granitic intrusions were emplaced at 672 861 c the peraluminous granitic magmas were generated by dehydration melting of newly accreted materials which were possibly brought to at least middle crustal depth by subduction related processes in an active margin and were subsequently molten by strikingly high ambient temperature probably caused by upwelling of the hot asthenosphere associated with ridge subduction in the paleozoic

origin and evolution of uraniferous pegmatite a case study from the xiaohuacha granite pegmatite system and related country rocks in the shangdan uranium mineralization district of north qinling orogenic belt china abstract the shangdan district in the north qinling orogenic belt hosts the largest pegmatite type uraniferous province in china the xiaohuacha u mineralization in this district occurs along the contact zone between biotite pegmatite and its host rock of biotite gneiss adjacent to the composite huichizi batholith which is composed mainly of biotite monzogranite and syenogranite zircon u pb dating of these granitoids reveals two stage magmatism namely the early silurian for biotite monzogranite 438 5 4 4 ma and the early devonian for syenogranite 417 8 3 2 ma the biotite pegmatite shows an age of 415 8 3 8 ma for the mineralized marginal zone and similar ages of 414 6 4 3 ma and 413 2 3 5 ma are obtained for the barren marginal and intermediate zones respectively the biotite monzogranite exhibits a restricted range of positive zircon ehf t values of 5 3 to 7 8 with tdm2 ages of 0 93 1 08 ga suggesting magma derivation from mainly pre existing basaltic rocks in the orogenic root magmatic oxygen fugacity fo2 was estimated by ti in zircon thermometry and ce incorporation within zircons the biotite monzogranite was emplaced at a temperature of 736 24 c with log fo2 values of 22 28 to 14 19 in contrast the syenogranite zircons have ehf t values of 1 4 to 2 4 and tdm2 ages of 1 25 1 49 ga indicating a derivation from the mesoproterozoic crust with some mantle input pristine zircon domains from different zones of the biotite pegmatite display ehf t values of 2 8 to 1 8 and tdm2 ages of 1 29 1 58 ga similar to those of the syenogranite indicating they share a common magma source combination of petrographical geochronological isotopic and mineral chemical data supports a petrogenetic relationship between the high t 842 14 c syenogranite and biotite pegmatite 756 21 c and 709 26 c for the uncontaminated marginal and intermediate zones respectively through magmatic differentiation from the same magma source during a period of tectonic extension processes of segregation and emplacement of the pegmatitic magma are consistent with open system assimilation and fractional crystallization afc leading to decreasing log fo2 values from the syenogranite 11 23 to 7 02 to biotite pegmatite through a fractionation trajectory however log fo2 values increase from the uncontaminated pegmatite marginal 15 88 to 10 9 to intermediate 17 86 to 6 14 zones with closed system pegmatite internal evolution the interaction hybridization between magma and gneiss induced decrease of oxidation state and k na al as well as modifications to zircon compositions in the mineralized pegmatite marginal zone we propose a model with decreasing of fo2 and k na al during afc being the main controls on the formation of the u deposit

age geochemistry and tectonic implications of a late paleozoic stitching pluton in the north tian shan suture zone western china the central asian orogenic belt is the largest tectonic assembly of continental and oceanic terranes on earth due to closure of the paleo asian ocean in the phanerozoic among major suture zones in the north xinjiang region of western china the north tian shan suture zone because of collision between the yili terrane in the south and the junggar terrane in the north contains the youngest ophiolitic rocks and may represent the terminal stage of development of the central asian orogenic belt in western china but the timing of the suture zone remains poorly constrained a sensitive high resolution ion microprobe shrimp zircon u pb age of 316 3 ma i e the beginning of the late carboniferous from the undeformed sikeshu pluton which crosscuts the suture zone places a crucial upperage bound for the time of collision between the yili and junggar terranes this event occurred later than or nearly concurrent with other accretion collision events in the north xinjiang region implying that fi nal terrane amalgamation was completed in the late carboniferous the sikeshu pluton shares geochemical characteristics of the widespread late carboniferous to permian postcollisional a type and i type granitoids with depleted mantle like sr nd isotopic signatures in the north xinjiang region they all occurred during a protracted ca 320 270 ma episode of postcollisional magmatism that may have been induced by basaltic under plating due to either slab breakoff or delamination of thickened mantle lithosphere beneath the central asian orogenic belt the same postcollisional magmatism also generated cu ni sulfi de bearing mafi c ultramafi c magmatic complexes adakites and porphyry type coppermolybdenum bearing magmatic rocks in the north xinjiang region

contrasting deep crustal compositions between the altai and east junggar orogens sw central asian orogenic belt evidence from zircon hf isotopic mapping abstract there are long standing uncertainties over the deep crustal composition and basement nature of the chinese altai and junggar orogens of the southwestern central asian orogenic belt caob zircon lu hf isotopic tracer techniques applied to granitoids are helpful in distinguishing old from young deep crustal compositions this study aims to characterize the basement nature ancient juvenile of the chinese altai and east junggar orogens using hf isotopic mapping of granitoids 510 200 ma zircon hf isotopic data 18 new and 79 published samples indicate that the study area can be divided into six hf isotopic provinces on the basis of tdmc ages province i 1 4 ga ii 1 4 1 2 ga iii 1 2 1 0 ga iv 1 0 0 8 ga v 0 8 0 6 ga and vi 0 6 0 4 ga provinces i ii and iii occur mainly in the central units 2 and 3 and southern unit 4 altai orogen and have slightly positive zircon ehf t values of 0 5 to 9 1 with slightly old tdmc ages of 1 53 0 81 ga provinces iv and v are mainly distributed in the northern unit 1 and southernmost unit 5 altai orogen with zircon ehf t values of 7 5 to 11 1 and young tdmc ages of 0 84 0 60 ga in contrast province vi east junggar orogen has zircon ehf t values of 11 6 to 14 9 with much younger tdmc ages of 0 59 0 35 ga except for the small taheir area with a negative ehf t value of 2 5 and an older tdmc age of 2 5 ga there is a sharp contrast between the deep crustal compositions of the altai and junggar orogens which are ancient in central altai and relatively juvenile in east junggar this confirms that significant neoproterozoic phanerozoic continental crustal growth occurred in the southern altai and junggar orogens with juvenile crust occupying 78 of the study area and that the caob is a site of significant phanerozoic continental growth the distribution of juvenile and ancient crust in the altai and east junggar orogens provides new evidence for the tectonic division of the two orogens by the erqis fault zone and explains the heterogeneity of crustal growth in the southwestern caob

zircon indicators of fluid sources and ore genesis in a multi stage hydrothermal system the dongping au deposit in north china abstract the syenite hosted dongping gold deposit represents the largest gold deposit on the northern margin of the north china craton here we present new u pb age trace element concentration and hf isotope data from magmatic and hydrothermal zircons to better constrain the timing and genesis of gold mineralization geochronological data combined with field and petrologic results document two mineralization events the earlier event in the mid devonian 380 ma was associated with the intrusion of the shuiquangou syenite whereas the later event in the early cretaceous 140 ma was related to the emplacement of the shangshuiquan granite devonian hydrothermal zircons extracted from gray auriferous quartz veins were formed via metasomatic alteration of magmatic zircons derived from the syenite by an oxidizing f rich fluid in contrast cretaceous hydrothermal zircons hosted in the altered shangshuiquan granite and milky gold rich quartz ores were precipitated directly from a high temperature zr saturated aqueous fluid that was contaminated by basement materials possessing a substantially different hf isotopic composition from the contemporaneous magmatic zircons we propose that the devonian au mineralization event at dongping involved a magmatic fluid and auto metasomatism during crystallization of the shuiquangou syenite complex whereas the cretaceous au mineralization event involved a fluid exsolved from the shangshuiquan alkaline pluton results from this study highlight the potential utility of zircons as indicators of fluid sources and ore genesis in a multi stage hydrothermal system

recognition of early carboniferous alkaline granite in the southern altai orogen post orogenic processes constrained by u pb zircon ages nd isotopes and geochemical data the altai orogen forms the southern part of the central asian orogenic belt caob the world s largest accretionary orogen however its tectonic evolution par ticularly during the late paleozoic is still not well under stood u pb zircon analyses for the bulgen alkaline granite yield crystallization ages of 358 4 ma shrimp and 354 4 ma la icp ms these ages are significantly younger than published emplacement ages for subduction collision related syn orogenic granitoids 460 375 ma in this region the bulgen granite has high sio2 total alkalis rare earth elements hfse th zr hf nb and ce and low ba sr with pronounced negative anomalies in eu ba sr p and ti showing a clear a type geochemical signa ture the granite records high end t values of 6 3 to 6 4 and young model ages tdm of ca 600 ma the bulgen alkaline granite is largely undeformed as opposed to the early middle paleozoic counterparts which form elongated deformed bodies parallel to the prevailing tec tonic fabric nw direction available data suggest that magmatism in the southern altai region evolved from early middle paleozoic i type tholeiitic and calc alkaline granitoids to late paleozoic a type alkaline granitoids the high end t values of the bulgen alkaline granite indicate a homogeneous juvenile mantle source whereas the early middle paleozoic granitoids are characterized by lower and more variable end t values 2 6 to 4 2 these differ ences provide an important insight into the late paleozoic orogenic processes of the chinese altai and indicate a significant change of the tectonic regime from a syn oro genic regional compression setting to a post orogenic extensional one major tectonic movements in this region ceased after the early carboniferous

noyon uul syncline southern mongolia lower mesozoic sedimentary record of the tectonic amalgamation of central asia to explore the hypothesis that a regionally extensive early mesozoic collisional foreland basin existed on strike to the east of documented mesozoic foreland basins in western china we conducted a reconnaissance study of a 5 km section of upper permian lower jurassic nonmarine strata exposed in the noyon uul syncline in southern mongolia this paper documents the depositional settings of these poorly known strata their provenance and their regional tectonic significance in the context of the mesozoic amalgamation of central asia we interpret noyon uul strata to be composed of 1 a coarse grained braided fluvial facies 2 a meandering fluvial facies and 3 a poorly oxygenated lacustrine facies that represent three principal depositional environments sandstone compositions are dominantly volcanic mean compositions qm 20 f 23 lt 57 qp 13 lv 82 ls lm 5 likely reflecting derivation from carboniferous and older volcanic arc sequences increased proportions of alkalic granite pebbles and cobbles above the first coarse grained braided fluvial unit and the first stratigraphic appearance of detrital k feldspar in basal coarse grained braided fluvial strata suggest unroofing of permian alkalic granites the noyon uul deposits likely are syntectonic as suggested by their thickness environments of deposition coarse grained character and accumulation rates overlap of the noyon uul syncline by relatively undeformed upper jurassic and lower cretaceous strata together with the presence of a regional unconformity between middle and upper jurassic rocks requires a phase of middle late jurassic deformation the erosional remnants of a middle upper jurassic north verging thrust belt have been documented just 100 km south of noyon uul suggesting that the noyon uul deposits may be foreland in origin specifically triassic thrusting has not been recognized in southern mongolia but permian jurassic contractile deformation associated with the collisional amalgamation of asia is documented or reasonably inferred for extensive areas of china to the south and west although sedimentary attributes of the noyon strata are most compatible with a foreland interpretation it is possible that the noyon deposits and their deformation may be related to strike slip faulting neither the attributes of the noyon deposits nor their ages are compatible with widespread late jurassic early cretaceous rifting that occurred across southeastern mongolia

nd sr isotopic mapping of the chinese altai and implications for continental growth in the central asian orogenic belt article i nfo the chinese altai orogen is a typical domain of the central asian orogenic belt and in previous syntheses was divided into six tectonic units or terranes in this paper 41 new and 36 published whole rock nd and sr isotopic data for granitoid intrusions and mafic dykes within units 2 and 3 of the central altai and units 4 to 6 of the southern altai were used for isotopic mapping the age of the samples used is known from u pb zircon dating end t values range from 4 to 2 in the central altai units 2 and 3 and from 1 4 to 6 in the southern altai units 4 and 5 and up to 8 4 in unit 6 correspondingly nd model ages tdm decrease from 1 6 1 1 ga in the central altai to 1 0 0 5 ga in the southern altai except for a continental fragment in unit 4 isr is elevated in the central units decreasing to b0 705 in the southern units 5 and 6 these results demonstrate that the central altai contains widespread old crustal components in its basement whereas the southern altai comprises a higher proportion of juvenile crust when integrated with published u pb zircon ages our data show that new crust grew southwards in the chinese altai in addition our data suggest that units 2 and 3 are a single tectonic unit whereas the southern altai unit 4 which previously was regarded as a single young accretionary terrane should be subdivided into two units a younger arc and an older continental fragment the granitoids in the chinese altai can be divided into syn and post non orogenic groups the syn orogenic granitoids have ca 50 80 mantle derived component whereas the post non orogenic granitoids contain ca 70 90 the generation of syn and post non orogenic granitoids represents horizontal lateral and vertical crustal growth which contributed ca 18 28 and 7 8 respectively to the area of the chinese altai this work shows that isotopic mapping is an effective approach to elucidate terrane composition in the central asian orogenic belt and thereby better constrain palaeozoic crustal growth

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

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

timing is everything in a game of two hemispheres what causes ice ages and other episodes of violent climate change one clue comes from a new study of ice cores which unexpectedly seems to show rapid warming events happening first in the southern hemisphere

sediment recycling and crustal growth in the central asian orogenic belt evidence from sr nd hf isotopes and trace elements in granitoids of the chinese altay felsic igneous rocks are common constituents of volcanic arcs and contain valuable information about subduction related magmatism in this study we investigate nine granitoids with s type volcanic arc affinity from the chinese altay emplaced from 507 to 391 ma in an active subduction zone during the early middle paleozoic these granitoids are characterized by moderate to high sio2 contents 61 01 75 30 wt moderate total alkalis na2o k2o 3 43 7 64 wt and high al2o3 contents 13 29 17 18 wt negative epsilon nd t values 6 1 to 1 0 the wide range of epsilon hf t values 7 0 to 9 0 and enrichment of liles such as pb th and u all suggest that the granitoids were probably derived from the partial melting of subducting oceanic sediments and the associated mantle wedge this inference is further supported by the nd isotope data the high initial sr 87 sr 86 ratios 0 703963 0 719428 low ba th ratios 7 00 118 93 and uniformly negative end t values 6 1 to 1 0 indicate that slab derived aqueous fluids were vital in generating the initial magma of these granitoids and assimilation played only a minor role our data demonstrate that residual zircon retains a substantial amount of hf during the partial melting of oceanic sediments therefore hf may not be an effective tracer for the input of recycled sediments we conclude that sediment recycling played an important role in the generation of arc magmatism and the growth of the central asian orogenic belt caob c 2016 international association for gondwana research published by elsevier b v all rights reserved

zircons reveal multi stage genesis of the xiangdong dengfuxian tungsten deposit south china abstract as a typical tungsten deposit of the xitian ore field nanling range south china the xiangdong deposit is a quartz vein type w deposit related to a triassic jurassic granitic complex with total ore reserves of 7 mt wo3 30 kt in this study zircon cl and bse imaging la mc icp ms u pb dating trace element and hf isotopic analyses were carried out on the fluid altered granites and related w ores in the xiangdong deposits aiming to reveal the genesis of the deposit zircon u pb dating yielded three age clusters pre triassic 250 ma n 19 triassic 227 214 ma or 220 ma n 111 and jurassic 159 149 ma or 150 ma n 27 zircon morphology and geochemistry suggest that triassic granites and jurassic quartz veins experienced stronger influences from high temperature hydrothermal fluids than other geological bodies in the deposit high contents of p y pb and u are found in triassic granite zircons whereas high concentrations of nb and ta occur in jurassic quartz vein zircons indicating different hydrothermal fluid systems during the triassic and jurassic the triassic and jurassic zircons yield high y ho ratios up to 35 representing fractionated non chondritic compositions which are indicative of a late stage residual melt that co existed with f rich fluids decreases in zircon ce ce and eu eu ratios from the triassic to the jurassic suggest a decline in fo2 that is likely to have facilitated large scale jurassic w mineralization high 176yb 177hf and 176lu 177hf ratios in the hydrothermally altered jurassic zircons indicate intense fluid exsolution from the source magma whereas the more variable 176hf 177hf ratios and hf model ages of the triassic zircons suggest multiple fluid sources and more complex alteration processes a new ore genesis model is proposed for the xiangdong w deposit initial enrichment of ore materials during the late triassic followed by large scale tungsten precipitation during the late jurassic the triassic granite provided the initial w source whereas granite derived fluids successively formed magma differentiated ore veins and infilling metasomatic ore veins during the jurassic

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

petrogenesis of the late mesozoic guposhan composite plutons from the nanling range south china implications for w sn mineralization voluminous granite plutons were emplaced in the late mesozoic in the nanling range south china accompanied by large scale polymetallic deposits most plutons are composite composed of major phase granites and highly differentiated late stage granites previous studies have proposed fractionation of both granite types and polymetallic deposits from a common magma we choose to study the ages chemistry and nd hf isotopes of the guposhan complex from the range and propose a different model for the origin of the granite and relationship with associated polymetallic mineralization in the nanling range the major phase granites of the guposhan complex contain medium coarse grained biotite granite and hornblende bearing biotite granite with mafic microenclaves mmes emplaced at 161 1 ma on the contrary the late stage granite is fine grained with apparent zircon ages of 154 3 ma the major phase granites show large variation in chemical compositions and in whole rock nd and zircon hf isotope ratios with end t 6 0 to 1 9 and ehf t 4 5 to 1 5 respectively we suggest that their origin is attributable to a magma mixing process between felsic magma derived from melting of proterozoic basement rocks and mantle derived mafic magma the mafic magma could be represented by the parental magma of the mmes within the plutons which have low sio2 high mgo and high end t values up to 1 8 the late stage granite shows end t and ehf t values similar to the major phase granites but are chemically more evolved sio2 75 80 more reduced and water deficient and in particular are fluorine bearing numerical geochemical modeling and the petrological data indicate that the late stage granite was produced during a new thermal event rather than being produced due to fractional crystallization of the earlier major phase granite the polymetallic deposits are genetically linked with the late stage granite we suggest that a break off of the flat subducted pacific slab beneath the cathaysia block in the late mesozoic resulted in the upwelling of asthenosphere and formation of basaltic magma that underplated and triggered partial melting of the basement rocks forming felsic melts and followed by mixing of the mafic and felsic magmas in an extensional regime

zircon trace element and isotopic sr nd hf pb effects of assimilation fractional crystallization of pegmatite magma a case study of the guangshigou biotite pegmatites from the north qinling orogen central china abstract evidence for open system magmatic processes related to wallrock assimilation accompanied by fractional crystallization afc is present in the guangshigou biotite pegmatites north qinling orogen the biotite pegmatite gneiss contacts generally coincide with the greatest enrichment of u and th zircon u pb dating constrains the crystallization ages of the biotite pegmatite rim zone 415 2 6 ma internal zone 413 5 2 5 ma in line with a pyrite pb pb isochron age 413 22 ma metamict areas in zircon show generally elevated concentrations of trace elements and expulsion of radioactive pb internal zone samples representing uncontaminated magma have negative to positive zircon 413 ma ehf t 1 53 3 24 low end t values 2 4 and old hf and nd model ages tdm2 1 5 1 19 ga t2dm 1 35 ga respectively indicating a dominantly recycled mesoproterozoic lower crustal material with involvement of some juvenile materials in the source region the magmatic oxygen fugacity fo2 and crystallization temperatures ranges from 24 81 to 13 34 of log fo2 and 570 c to 793 c respectively compared to the internal zone pegmatite rim samples display a variable and lower end t values 3 9 to 2 8 and t2dm 1 47 1 37 ga but similar hf isotopic compositions favouring a three component isotopic mixing model recycled mesoproterozoic lower crust materials juvenile materials and host gneiss pronounced variations of ti y u th hf and ree concentrations in zircon from grain to grain in individual samples and from area to area within individual grains suggest a fluctuating crystallization environment in hybridized magma from which the rim hosted zircons crystallized variable and high radiogenic pb ratios of pyrites forming in the hybridized magma were inherited from the matrix zircons from both zones exhibit similar hf isotope patterns indicating the rim hosted zircons crystallized during the early stage of hybridization of magma however the heterogeneous nd isotopic composition in individual pegmatites imply an incorporation of wallrock derived melt with less radiogenic nd

sequence of events from the onset to the demise of the last interglacial evaluating strengths and limitations of chronologies used in climatic archives the last interglacial lig represents an invaluable case study to investigate the response of components of the earth system to global warming however the scarcity of absolute age constraints in most archives leads to extensive use of various stratigraphic alignments to different reference chronologies this feature sets limitations to the accuracy of the stratigraphic assignment of the climatic sequence of events across the globe during the lig here we review the strengths and limitations of the methods that are commonly used to date or develop chronologies in various climatic archives for the time span 140 100 ka encompassing the penultimate deglaciation the lig and the glacial inception climatic hypotheses underlying record alignment strategies and the interpretation of tracers are explicitly described quantitative estimates of the associated absolute and relative age uncertainties are provided recommendations are subsequently formulated on how best to define absolute and relative chronologies future climato stratigraphic alignments should provide 1 a clear statement of climate hypotheses involved 2 a detailed understanding of environmental parameters controlling selected tracers and 3 a careful evaluation of the synchronicity of aligned paleoclimatic records we underscore the need to 1 systematically report quantitative estimates of relative and absolute age uncertainties 2 assess the coherence of chronologies when comparing different records and 3 integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations finally we provide a sequence of major climatic events with associated age uncertainties for the period 140 105 ka which should serve as a new benchmark to disentangle mechanisms of the earth system s response to orbital forcing and evaluate transient climate simulations

fertile granites of precambrian rare element pegmatite fields is geochemistry controlled by tectonic setting or source lithologies abstract a total of twenty fertile granites and their rare element pegmatite aureoles was examined to correlate their tectonic position relative to the preceding orogenic event with their geochemical signature namely li rb cs be ga sn nb ta y ree sc ti zr be th u f nyf the range of t time difference between metamorphism and or deformation and granite intrusion is 20 to 465 ma for the examined cases there is some tendency toward syn to late orogenic origin of lct s as opposed to post to anorogenic timing of nyf s but the correlation is poor compared to the previously accepted stereotype similarly both metaluminous and peraluminous fertile granites are about equally spread among syn late and anorogenic environments lct systems are largely associated with peraluminous granites whereas all metaluminous to peralkaline plutons bear the nyf signature tectonic control on geochemistry of granite pegmatite suites is poor and secondary to the fundamental influence of the source lithologies yielding granitic melts the lct type suites are derived from undepleted upper crustal lithologies suffering their first anatectic event which mobilizes the most volatile components into low temperature low percentage melts supracrustal sequences as well as ortho and para lithologies of their basement serve as protoliths with variable degrees of involvement the nyf type suites whose plutons have the geochemical signature of a granites may be derived by melting of depleted lower crustal sources residual after preceding anatectic events or possibly by melting of juvenile lithologies with short crustal residence differentiation from mantle derived magmas is highly improbable volatile extraction of nyf elements from the mantle and their pre enrichment in protoliths or melts seems to be required the few mixed systems with variable expressions of a nyf lct signature are derived basically as nyf suites but contaminated by the lct elements from undepleted upper crust via several possible mechanisms

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

dating the xiaobaishitou skarn w mo deposit eastern tianshan nw china constraints from zircon u pb muscovite 40ar 39ar and molybdenite re os system abstract the xiaobaishitou deposit 36 264 tonnes 0 78 wt wo3 in the eastern tianshan orogenic belt is a medium sized skarn deposit characterized by w mo ore bodies that developed along contacts between triassic biotite granite and mesoproterozoic carbonaceous rocks scheelite and molybdenite are the dominant metallic minerals in this deposit and mostly precipitated during the retrograde stage and or quartz sulfide stage respectively laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms zircon u pb dating of the mineralization related biotite granites from underground openings and outcrops yields ages of 247 9 1 7 ma 1 n 22 mswd 0 69 and 252 2 3 0 ma 1 n 12 mswd 1 60 implying they were emplaced in the early triassic a muscovite 40ar 39ar weighted plateau age of 247 6 2 3 ma 2 mswd 2 03 and molybdenite re os model ages ranging from 235 8 5 7 ma to 249 6 3 6 ma weighted mean age 251 1 1 6 ma 2 mswd 0 70 are interpreted as the time of the hydrothermal activity mineralization the excellent agreement among the u pb 40ar 39ar and re os chronometers confirms that the xiaobaishitou deposit formed in the early triassic the re contents of the molybdenites range from 18 477 to 130 447 ng g suggesting that the ore forming materials were derived from continental crust together with the involvement of abundant mantle components as one of the representative triassic deposit in eastern tianshan the xiaobaishitou provides important chronological evidence for metallogenic regularity in the eastern tianshan and the central asian orogenic belt the new ages reported here confirm that the xiaobaishitou deposit represents one of the magmatic hydrothermal mineralization events that occurred in the eastern tianshan orogenic belt in lithospheric extension during the triassic it is suggested that mantle material played a role in producing the triassic mineralization and associated magmatism

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