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

boron isotope ratios in meteorites and lunar rocks abstract the 11b 10b ratios of thirty two meteorite falls and nine lunar rocks were measured as cs2bo2 using thermal ionization mass spectrometry the 11b 10b ratios of meteorites vary from 4 011 to 4 098 i e their 11b values relative to nist srm 951 range from 10 5 to 19 2 however excluding two outliers mokoia and norton county the range of most meteorites is smaller 10 5 to 7 5 the average of two c11 meteorites ivuna and orgueil is 3 3 in the middle of the range the 11b values of the lunar rocks vary less than those of meteorites from 6 0 to 3 9 the average 11b of ci1 chondrites is 3 3 similar to that of terrestrial fresh mid ocean ridge basalts 6 5 to 1 2 and to the estimated mantle value of 0 2 ishikawa and nakamura 1992 which is the best representative of the whole earth the similarity of 11b values in meteorites lunar rocks and those parts of the earth unaffected by water implies that the boron isotopic composition of the solar system is rather homogeneous recently chaussidon and robert 1995 reported larger variation of 11b values in chondrules of three chondrites from 50 to 40 this degree of heterogeneity is absent from bulk meteorites

theoretical and experimental studies of coupled seepage pipe flow to a horizontal well abstract this study proposes a new approach which describes a finite diameter horizontal well and flow inside the pumping well jointly this approach utilizes a new treatment for in well hydraulics thus eliminating the flux or head based boundary condition along the horizontal well an equivalent hydraulic conductivity concept is applied for treating the horizontal wellbore this conceptual model is more general than previous models that describe the horizontal wellbore the description of in well hydraulics depends on the reynolds number a sample case of horizontal well pumping underneath a river is first used to illustrate the solution of the proposed approach a physical laboratory model was constructed and hydraulic heads and the well flow rate were carefully monitored and compared with the numerically calculated results using the proposed model the experimental data agree well with the numerical solution

contrasting styles of mineralization in the chinese altai and east junggar nw china implications for the accretionary history of the southern altaids abstract the chinese altai east junggar collage in the southern altaids hosts three metallogenic belts which are from north to south 1 a volcanogenic massive sulphide vms cu pb zn belt 2 a belt of shear zone related gold deposits 3 a porphyry cu au mo belt the vms deposits formed in two pulses c 405 ma and c 375 ma in the chinese altai arc the porphyry deposits developed in three pulses in the east junggar arc the first two synchronous with the vms mineralization and the third at c 330 ma the shear zone related gold deposits developed in the late carboniferous to permian at the contact between the chinese altai and east junggar arcs time space distributions of diverse ore deposits across the altai east junggar collage indicate that the collage developed from two independent arcs the chinese altai and the east junggar the vms and porphyry deposits developed in the chinese altai and east junggar arcs respectively the chinese altai arc is interpreted to be a japanese type arc and the east junggar arc a mariana type arc during the latest palaeozoic the two arcs were juxtaposed by the erqis fault when many shear zone related lode gold deposits were emplaced these metallogenic distributions were a likely response to spatially localized mechanisms of crust growth and to the tectonic evolution of the altai east junggar collage and they are consistent with interpretation of the altaids as a multiple subduction accretion collage

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

la mc icp ms u pb dating of zircons from volcanic rocks and subvolcanic intrusions in ashele cu zn ore district xinjiang and its geological implications the ashele cu zn deposit is representative volcanogenic massive sulfide vms deposit in china s altay region the deposit occurs in the marine volcano sedimentary sequence of the ashele formation in the ashele basin no main ore body occurs in the stratiform form between tuff and basalt and mineralization occurs in massive densely massive banded laminated densely disseminated and veinlet forms the hydrothermal alteration and mineralization also occur in the sub dacite lots of research work has been carried out in the ashele deposit but the ages of its ore hosting volcanic rock subvolcanic rock and mineralization have not yet been clearly determined in this paper la mc icp ms zircon u pb dating was used for studying the tuff and basalt from the direct host rocks of the ore bodies sub dacite and quartz diorite in the asele cu zn district the u pb ages are 387 0 4 2 ma 388 2 3 3 ma 379 4 0 8 ma 378 5 0 9 ma for tuff basalt sub dacite and quartz diorite respectively suggesting that the ashele formation is early middle devonian in age the ashele cu zn deposit is an syngenetic deposit and no main ore body occurs between tuff and basalt the ages of the tuff and basalt suggest that the mineralization in the sedimentary exhalative period occurred in the late early devonian 388 387 ma the u pb age of the sub dacite is 379 4 0 8 ma imrplying that the magmatic hydrothermal mineralization took place in the middle devonian the u pb ages of the older zircons from tuff basalt sub dacite and quartz diorite range from 743 to 2505 ma which represent the forming age of the precambrian crystalline basement in altay region

re os isotope systematics of sulfides from felsic igneous rocks application to base metal porphyry mineralization in chile dating sulfides and determining the source of ore forming metals have been limiting factors in our understanding of processes that produce hydrothermal ore deposits here we analyze sulfides from base metal porphyry deposits from chile to demonstrate the potential of the re os system to determine both the age and the source of metals for hydrothermal mineralization cogenetic chalcopyrite bornite pyrite and sphalerite from el teniente ca 5 ma have 187 re 188 os ratios from 0 3 to 21 8 and initial 187 os 188 os ratios from 0 17 to 0 22 a paragenetically late pyrite that has an initial 187 os 188 os of 0 88 indicates that the ore deposit is not isotopically homogeneous in os throughout the formation of the deposit pyrite samples from andacollo ca 100 ma have 187 re 188 os ratios from 15 to 3600 and different isochrons yield ages between 87 and 103 ma consistent with different sericite k ar ages initial 187 os 188 os ratios of 0 2 to 1 1 are similar to those of el teniente the relatively homogeneous 187 os 188 os ratios 0 19 for cogenetic sulfides from el teniente suggest that most of the os in the ore was from the causal intrusive the latestage pyrite probably incorporated os leached from the country rock by meteoric fluids which mixed with magmatic fluids at the periphery of the hydrothermal system we demonstrate that the re os isotope system can be a powerful geochronological tool in hydrothermal ore deposits the large range in re os ratios of sulfides permits the age of mineralization to be well constrained despite isotopic heterogeneities of the hydrothermal fluids

re os dating of pyrite from the tuolugou stratabound co au deposit eastern kunlun orogenic belt northwestern china abstract the tuolugou cobalt gold deposit in the northeastern margin of the qinghai tibetan plateau and central part of the eastern kunlun orogenic belt is the most recently discovered large cobalt gold discovery in qinghai province nw china exploration to date has identified a cobalt resource of greater than 20 000 t co with significant potential for expansion mineralization is largely confined to an e w striking volcano sedimentary sequence consisting of four lithological units that underwent extensive greenschist facies metamorphism and deformation all orebodies occur in stratiform or lenticular bodies within quartz albitite and sericite quartz schists and are concordant with lithological contacts the ores contain various amounts of pyrite the dominant ore mineral and display massive 80 pyrite banded 30 to 50 pyrite and disseminated re os dating shows that pyrite from different ore types has very low re and os concentrations in the range of 0 122 8 988 ppb and 0 003 0 054 ppb respectively isotope data on seven pyrite samples yield an isochron age of 429 29 ma 2 with an initial 187 os 188 os ratio of 0 2 mean square weighted deviates 7 9 on the 187 re 188 os 187 os 188 os plot which are close to the age of the host strata suggesting that primary cobalt mineralization in the tuolugou deposit may have formed from syngenetic exhalative processes in addition our results not only provide new evidence for plate rifting and mineralization taking place during the early silurian in the eastern kunlun orogenic belt but also suggest that the age of the regionally widespread nachitai group is early paleozoic

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

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

boron abundances and isotopic ratios of olivine grains on itokawa returned by the hayabusa spacecraft we report the b abundances and isotopic ratios of two olivine grains from the s type asteroid itokawa sampled by the hayabusa spacecraft olivine grains from the dar al gani dag 989 ll6 chondrite were used as a reference since we analyzed polished thin sections in both cases we expect the contribution from the solar wind b rich in 10b to be minimal because the solar wind was implanted only within very thin layers of the grain surface the itokawa and dag 989 olivine grains have homogeneous b abundances 400 ppb and 11b 10b ratios compatible with the terrestrial standard and bulk chondrites the observed homogeneous b abundances and isotopic ratios of the itokawa olivine grains are likely the result of thermal metamorphism which occurred in the parent asteroid of itokawa which had a similar composition as ll chondrites the chondritic b isotopic ratios of the itokawa samples suggest that they contain little cosmogenic b from cosmic ray spallation reactions rich in 10b this observation is consistent with the short cosmic ray exposure ages of itokawa samples inferred from the small concentrations of cosmogenic 21ne if other itokawa samples have little cosmogenic b as well the enrichment in 10b found previously on the surface of another itokawa particle as opposed to the bulk grain study here may be attributed to implanted solar wind b

a review of the geological characteristics and geodynamic setting of late paleozoic porphyry copper deposits in the junggar region xinjiang uygur autonomous region northwest china abstract in this review we describe the geological characteristics of porphyry copper deposits in junggar region xinjiang and place these into their metallogenic tectonic context these porphyry copper deposits are mainly found in four metallogenic belts 1 a late silurian to early devonian cu mo metallogenic belt in the qiongheba area 2 the late devonian kalaxiange er cu metallogenic belt 3 the early carboniferous xilekuduke suoerkuduke porphyry skarn cu mo metallogenic belt and 4 the late carboniferous baogutu porphyry cu metallogenic belt the ages of mineralization can be divided into three broad intervals

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

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

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

boron in chondrules isotopic compositions and abundances of boron were measured in sixteen chondrules from seven chondrites by ion microprobe mass spectrometry the chondrules are of the porphyritic barred and radial type and host meteorites include carbonaceous ordinary and enstatite chondrites boron abundances are generally low with average boron concentrations of between 80 and 500 ppb these abundances are lower than those of bulk chondrites 0 35 to 1 2 ppm zhai et al 1996 confirming earlier suggestions that boron is mostly contained in the matrix no significant variation in the 11b 10b ratio is observed among these chondrules outside our experimental error limits of several permil and b isotopic compositions agree with those reported for bulk chondrites the lack of a significant isotope fractionation between chondrules and matrix implies that the low boron abundances are not the result of a rayleigh fractionation during chondrule formation isotopic heterogeneities within individual chondrules are constrained to be 20 0 at 95 confidence level at a spatial scale of 20 30 m significantly lower than the value of about 40 0 previously reported for chondrules from carbonaceous and ordinary chondrites chaussidon and robert 1995 1998 the observed b isotopic homogeneity does not conflict with the presence of decay products from extinct 10be with 10be 9be 0 10 3 as was inferred for calcium aluminum rich inclusions extinct 10be in chondrules would shift the abundance ratio 11b 10b at best by several permil because of their commonly observed low be b ratios 2 the results show that potential b isotopic heterogeneities in the solar nebula due to the presence of components with different b isotopic signatures such as boron produced by high energy galactic cosmic rays 11b 10b 2 5 or by the hypothetical low energy particle irradiation 11b 10b 3 5 11 or boron from type ii supernovae 11b 10b 1 did not survive the chondrule formation processes to a measurable extent

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

early development of karst systems 2 turbulent flow a simulation model developed to explore patterns of fracture enlargement within incipient limestone karst aquifers has been extended to turbulent flow in contrast to the highly selective passage enlargement that occurs early in cave network development under laminar flow the transition to turbulent flow results in more general passage enlargement leading to maze networks when initial fractures are large and hydraulic gradients are high these results support previously published hypotheses for the development of maze patterns including formation within structural settings that have created initially large fractures or within flow systems periodically inundated by flooding maze development is also favored under turbulent flow when passages are entirely water filled and where the groundwater flow system is long lived by contrast branched patterns are most common when passages become free surface subterranean streams because depression of the piezometric surface along main passages downcutting along main passages and possible infilling with sediment of side passages limit the sharing of discharge among interconnected fractures or bedding planes that promote maze development

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

melting of a subducting slab and production of high mg andesite magmas unusual magmatism in sw japan at 13 15 ma characteristic high mg andesite magmas were produced in the sw japan arc at 13 15 ma that was synchronous with the commencement of subduction of a very young 11 m y lithosphere of the shikoku basin numerical simulation suggests that temperature at the surface of such a young subducting plate is high enough for partial melting both of the subducting sediments and oceanic crust at the beginning of the subduction high mg andesite magmas were likely to be produced by interaction between silicic slab melts and the overlying mantle wedge hma magmas may be commonly produced in the archean subduction zones under relatively high mantle temperature conditions contributing to making continental crusts

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

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

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

the abagong apatite rich magnetite deposit in the chinese altay orogenic belt a kiruna type iron deposit abstract the abagong apatite rich iron deposit is located in the kelang volcano sedimentary basin in the southern margin of the chinese altay orogenic belt aob which is an important polymetallic belt in china the ore bodies are interbedded with the upper silurian to lower devonian metamorphosed calc alkaline felsic volcanic rocks that show well preserved porphyritic and volcaniclastic textures the ore mineralization is aligned along faults that controlled their emplacement and occurs as lenses veins and stratoids bodies that generally cut the host rocks at a high angle and show sharp contacts the ore bodies and host rocks have undergone greenschist facies metamorphism deformation and folding the iron ores have massive densely disseminated banded and brecciated structures magnetite from the abagong deposit is low in ti tio 2 0 002 0 129 wt and the apatites from different ore types p poor and p rich ores are typical igneous fluorapatites with minor cl contents apatites of different forms and from different ore types show similar rare earth element ree and trace element normalized patterns with weak to moderate enrichment in light ree th u and pb depletion in sr ba nb ta and ti and negative eu anomalies indicating a common source and genesis the similar ree patterns for the magnetite apatite and volcanic host rocks suggest their close genetic linkage and support a magmatic origin for the deposit the abagong deposit shows the typical characteristics of kiruna type deposits with regard to the mineral assemblages ore texture and structure and the apatite and magnetite geochemistry we propose that the kiruna type abagong apatite rich iron deposit was derived from fe p rich melt through liquid immiscibility and the activity of hydrothermal fluids

analytical 1d dual porosity equivalent solutions to 3d discrete single continuum models application to karstic spring hydrograph modelling abstract one dimensional analytical porosity weighted solutions of the dual porosity model are derived providing insights on how to relate exchange and storage coefficients to the volumetric density of the high permeability medium it is shown that porosity weighted storage and exchange coefficients are needed when handling highly heterogeneous systems such as karstic aquifers using equivalent dual porosity models the sensitivity of these coefficients is illustrated by means of numerical experiments with theoretical karst systems the presented 1d dual porosity analytical model is used to reproduce the hydraulic responses of reference 3d karst aquifers modelled by a discrete single continuum approach under various stress conditions simulation results show the relations between the dual porosity model coefficients and the structural features of the discrete single continuum model the calibration of the equivalent 1d analytical dual porosity model on reference hydraulic responses confirms the dependence of the exchange coefficient with the karstic network density the use of the analytical model could also point out some fundamental structural properties of the karstic network that rule the shape of the hydraulic responses such as density and connectivity

origin and chronology of chondritic components a review abstract mineralogical observations chemical and oxygen isotope compositions absolute 207pb 206pb ages and short lived isotope systematics 7be 7li 10be 10b 26al 26mg 36cl 36s 41ca 41k 53mn 53cr 60fe 60ni 182hf 182w of refractory inclusions ca al rich inclusions cais and amoeboid olivine aggregates aoas chondrules and matrices from primitive unmetamorphosed chondrites are reviewed in an attempt to test i the x wind model vs the shock wave model of the origin of chondritic components and ii irradiation vs stellar origin of short lived radionuclides the data reviewed are consistent with an external stellar origin for most short lived radionuclides 7be 10be and 36cl are important exceptions and a shock wave model for chondrule formation and provide a sound basis for early solar system chronology they are inconsistent with the x wind model for the origin of chondritic components and a local irradiation origin of 26al 41ca and 53mn 10be is heterogeneously distributed among cais indicating its formation by local irradiation and precluding its use for the early solar system chronology 41ca 41k and 60fe 60ni systematics are important for understanding the astrophysical setting of solar system formation and origin of short lived radionuclides but so far have limited implications for the chronology of chondritic components the chronological significance of oxygen isotope compositions of chondritic components is limited the following general picture of formation of chondritic components is inferred cais and aoas were the first solids formed in the solar nebula 4567 4568 myr ago possibly within a period of 10 and have 26al 27al 0 similar to those in chondrules 5 nebular gas the majority of chondrules within a chondrite group may have formed over a much shorter period of time

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

isotope geochemistry of the tieluping silver lead deposit henan china a case study of orogenic silver dominated deposits and related tectonic setting the tieluping silver deposit which is sited along ne trending faults within the high grade metamorphic basement of the xiong er terrane in the qinling orogenic belt is part of an important recently discovered mesozoic orogenic type ag pb belt ore formation includes three stages an early barren quartz pyrite stage e an intermediate polymetallic sulfide ore stage m and a late barren carbonate stage l carbon sulfur and lead isotope systematics indicate that the e stage fluids are deeply sourced the l stage fluids are shallow sourced meteoric water whereas the m stage fluids are a mix of deep sourced and shallow sourced fluids sulfur and lead isotope data show that the ore forming fluids must have originated from a source with elevated radiogenic lead and low 34s values that differs significantly from exposed geologic units in the xiong er terrane the lower crust and the mantle this supports the view that the carbonate shale chert sequences of the guandaokou and luanchuan groups south of the machaoying fault might be the favorable sources although little is known about their isotopic compositions a tectonic model that combines collisional orogeny metallogeny and hydrothermal fluid flow is proposed to explain the formation of the tieluping silver deposit during the mesozoic collision between the north china craton and south china block early mid triassic indosinian orogeny crustal slabs containing the carbonate shale chert sequences of the guandaokou and luanchuan groups locally rich in organic matter carbonaceous shale were thrust northwards beneath the xiong er terrane along the machaoying fault metamorphic devolatilisation of this underthrust slab probably provided the ore forming fluids to develop the ag pb ore belt which includes the tieluping silver deposit fluids and magmas were emplaced during extensional stages related to the jurassic cretaceous yanshanian orogeny

a model comparison of karst aquifer evolution for different matrix flow formulations the evolution of permeability and flow in a karst aquifer is studied by numerical simulations the aquifer considered consists of a large central fracture a network of finer fissures and a porous rock matrix enlargement of both the central fracture and the fissures by chemical dissolution is possible hence the conductivities in the fracture and the fissure system can increase with time no dissolution is allowed in the porous rock matrix which has a constant conductivity flow is driven by a simple fixed head boundary condition representative for the initial phase of karstification a systematic parameter study is carried out by varying the initial width of the fissure network and the conductivity of the rock matrix while keeping the initial width of the central fracture fixed key parameters such as flowrates breakthrough times and conductivities for the different models are compared if either the conductivity of the rock matrix is high enough or the initial width of the fissures is large enough to carry flow breakthrough times of the aquifer are significantly reduced when compared to a model with low matrix conductivity and small fissures however due to the dissolutional widening of fissures the evolution of the aquifer is distinctively different for models with rock matrix simulated by a porous medium or a fissure network

geodynamics of magmatic cu ni pge sulfide deposits new insights from the re os isotope system in this study we reassess crustal contamination and sulfide ore forming processes in some of the largest magmatic ore deposits using published re os isotope data and a modeling methodology that incorporates the r factor defined as the effective mass of silicate magma with which a given mass of sulfide magma has equilibrated in an re os isotope mixing equation we show that there is less disparity between conclusions based on re os isotope data compared to other isotopic systems if the r factor is considered komatiite associated ni sulfide ore systems typically have high os concentrations low re os ratios and near chondritic initial os isotope compositions for magmatic sulfide ores that are interpreted to have experienced relatively low r factors 10 000 for noril sk talnakh and the j m reef stillwater complex in these very dynamic magmatic ore systems crustal contamination processes are more difficult to assess using re os isotopes as the effects of contamination are masked by the r factor process in which sulfide magma equilibrates with extensive amounts of asthenospheric mantle derived magma sulfide protore for these systems may then have been very radiogenic and of crustal origin prior to r factor processes that occurred during transport in feeder conduits and in upper crustal magma chambers this study therefore highlights the need for caution when interpreting the re os isotope geochemistry of sulfide ores from dynamic magmatic systems the results of our reinvestigation of these giant ore deposits suggest that geodynamic processes associated with large magmatic systems including major lithospheric pathways to the surface changes in flow regime coupled magma flow through and magma mixing providing enhanced r factors may be critical to our understanding of the emplacement localization and quality of magmatic sulfide deposits thus the timing and exact mechanism of sulfide saturation may be subordinate to dynamic magmatic processes in the localization of economic concentrations of magmatic sulfides

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

early silurian 440 ma adakitic andesitic and nb enriched basaltic lavas in the southern altay range northern xinjiang western china slab melting and implications for crustal growth in the central asian orogenic belt abstract as an important part of the central asian orogenic belt caob the altay range contains large scale paleozoic magmatic rocks however owing to the lack of precise age constraints the tectonic setting and petrogenesis of the magmatic rocks in this area have been controversial which has led to the debate on phanerozoic crustal growth mechanisms and accretionary orogenic processes in the caob herein we report geochronological and geochemical data of the suoerkuduke adakitic andesitic and nb enriched basaltic neb lavas in the southern margin of the southern altay range la icp ms zircon u pb analyses for five adakitic andesitic and neb samples indicate that they were coevally generated in the early silurian 440 ma the adakites and basaltic andesites are geochemically characterized by high na 2 o k 2 o sr y al 2 o 3 sr e nd t and zircon e hf t values and relatively low 87 sr 86 sr i ratios the nebs are sodium rich and have higher tio 2 p 2 o 5 zr nb and nb u values than those of typical arc basalts they also have positive e nd t values and positive and variable zircon e hf t values we suggest that the suoerkuduke adakites were derived by a partial melting of the subducted oceanic crust with minor overlying sediments and the continuous compositional variations between adakites and basaltic andesites confirm that the interaction between slab melts and mantle peridotite played an important role in the formation of basaltic andesites the associated nebs were possibly generated by a partial melting of mantle wedge peridotites metasomatized by slab derived adakitic melts and minor fluids in combination with the occurrence of voluminous silurian devonian granitoids coeval ophiolite melanges and a series of intra arc basins a slab window model triggered by slab tearing is proposed to account for the formation of the suoerkuduke adakite basaltic andesite neb suites the upwelling of the asthenospheric mantle through the slab window probably caused significant extension in the overlying lithosphere extensive melting of the subducted oceanic crust mantle and juvenile lower crust and intense interaction between slab derived melts or fluids and the mantle wedge slab tearing and subsequent asthenospheric upwelling possibly played an important role in the crustal growth of the caob during the phanerozoic

carbonic fluid overprints in volcanogenic massive sulfide deposits examples from the kelan volcanosedimentary basin altaides china the tiemurte and the dadonggou zn pb cu volcanogenic massive sulfide vms deposits situated in the devonian kelan volcanosedmentary basin of the south margin of the chinese altaides were metamorphosed and overprinted by metamorphic sulfide quartz veins during early carboniferous to early permian two mineralizing periods of ore mineral growth can be identified 1 disseminated banded and massive sulfide ores related to a primary depositional sea floor volcanic hydrothermal activity and 2 the foliated sulfide quartz veins q1 related to synorogenic metamorphism and late chalcopyrite bearing quartz veins q2 cutting the schist related to a younger metamorphic overprinting event carbonic co 2 ch 4 n 2 fluid inclusions are ubiquitous in q1 and q2 veins a few carbonic fluid inclusions may be primary and some may be pseudosecondary whereas the vast number of carbonic fluid inclusions are secondary representing later events a microthermometry study shows that primary carbonic fluid inclusions in q1 and q2 have tm co2 ranging from 64 5 to about 59 4 c with th co2 13 4 to about 18 6 c the secondary carbonic fluid inclusions exhibit two behaviors when cooling and heating the tm co2 of the first group l co2 ranges from 63 3 to 57 7 c and that of the second group l co2 ch4 n2 ranges from 83 4 to 61 c the second group of carbonic fluids has much higher ch 4 and or n 2 proportions than the first group the trapping temperatures for the carbonic inclusions have been estimated to be 243 1 to 412 1 c for tiemurte and 216 to 430 c for dadonggou on the basis of some l co2 l h2o inclusions associated with carbonic inclusions and the trapping pressures have been estimated to be 120 to 340 mpa which are consistent with deformation p t conditions of quartz and slightly less than the p t conditions of the biotite and garnet metamorphic zones these abundant carbonic inclusions at the tiemurte and the dadonggou deposits were not a part of a volcanogenic ore producing system but represent a much younger event possibly having originated from a synorogenic metamorphism which may have contributed to orogenic gold

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

in situ la mc icp ms u pb geochronology of igneous rocks in the ashele basin altay orogenic belt northwest china constraints on the timing of polymetallic copper mineralization abstract the altay orogenic belt of kazakhstan hosts a world class polymetallic copper volcanogenic massive sulfide vms metallogenic belt and the eastern margin of this belt extends into the southern chinese altay the ashele basin is located at the western end of the chinese altay and borders kazakhstan the basin hosts the large ashele copper zinc deposit which is a typical vms deposit and the largest deposit in the ashele basin and it hosts the subvolcanic hosted medium sized sarsuk polymetallic gold deposit both of these deposits are hosted in the ashele formation volcanic sequence the ashele copper zinc orebodies are stratabound orebodies located between basalt and tuff units and were formed during exhalative sediment deposition in comparison the sarsuk gold copper lead zinc orebodies are hosted by rhyolite porphyry that contains disseminated veinlet and veinlet stockwork ore that formed during intrusion of the rhyolite porphyry this study presents new zircon la mc icp ms u pb analyses of six volcanic and subvolcanic units and dikes associated with the sarsuk and ashele deposits the ore bearing rhyolite porphyry diabase dike basalt tuff and dacite porphyry samples analyzed during this study yielded ages of 382 0 382 8 381 7 388 2 387 0 and 379 4 ma respectively these data indicate that the ashele formation formed during the early mid devonian 375 402 ma whereas the ashele copper zinc deposit formed during the middle devonian 388 387 ma and the sarsuk polymetallic copper gold deposit formed during the latest middle devonian 382 ma inherited zircons within the six samples analyzed during this study yielded u pb ages of 618 2294 ma suggesting the presence of precambrian crystalline basement within the altay orogenic belt

a revised stratigraphic and tectonic framework for the ashele volcanogenic massive sulfide deposit in the southern chinese altay evidence from stratigraphic relationships and zircon geochronology abstract the ashele volcanogenic massive sulfide vms deposit is the largest and most representative vms deposit in the chinese altay metallogenic belt but its stratigraphic sequence tectonic framework and morphology are debated in this paper on the basis of previous research field investigations excavation pits drill core sampling and new la icp ms u pb analyses of zircons from mafic and felsic volcanic rocks we show that the main structure of the ashele deposit is an overturned tightly closed syncline and that the primary orebody is controlled by this structure moreover we show that the ashele vms deposit displays a double layer structure made up of a feeder zone of veinlet disseminated and stockwork orebodies overlain by massive stratiform orebodies that are folded we revise the stratigraphy of the ashele formation into five conformable sedimentary subsequences based on new field investigations and the zircon geochronology of each subsequence from bottom to top we divide the formation into a siliceous tuff layer 405 1 1 8 ma a dacitic layer 395 9 403 ma a rhyolitic layer 390 9 0 83 ma an orebody layer ca 387 ma and a basalt layer 387 377 ma the early to middle devonian ashele formation unconformably underlies the late devonian qiye formation

metamorphosed pb zn ag ores of the keketale vms deposit nw china evidence from ore textures fluid inclusions geochronology and pyrite compositions abstract the keketale pb zn deposit is located in the devonian volcanic sedimentary maizi basin of the altay orogenic belt the mineralization at keketale is hosted in marbles and deformed volcanic tuffs and biotite garnet chlorite schists folded into a series of overturned synclines formed in multiple deformation events keketale contains economic amounts of pb 0 89 mt 1 51 wt zn 1 94 mt 3 16 wt and ag 650 t 40 g t detailed petrographic studies have defined two main generations of sulfide development the banded pyrite of the early stage a is commonly stratiform with minor galena sphalerite and chalcopyrite stage b is characterized by a large amount of polymetallic sulfides including pyrrhotite chalcopyrite sphalerite and galena with minor pyrite hosted in quartz veins three types of fluid inclusions fis including mixed carbonic aqueous c type pure carbonic pc type and aqueous w type have been recognized in quartz of stage b the c type fis have homogenization temperatures of 150 326 c and salinities of 0 2 16 6 wt nacl equivalent the pc type fis are dominated by co2 with minor ch4 and n2 and have initial ice melting temperatures of 57 5 to 56 7 c co2 homogenization temperatures of 11 14 1 c the w type primary fis were completely homogenized at temperatures of 124 359 c with salinities of 5 0 14 6 wt nacl equivalent such co2 rich fluid inclusions are consistent with those discovered in orogenic type deposits in the altay area and elsewhere muscovite separates from the polymetallic quartz veinlets of stage b yield a well defined 40ar 39ar isotopic plateau age of 259 33 2 56 ma with an isochron age of 259 62 2 65 ma this age is coeval with the closure of the paleo asia ocean and reactivation of the ertix fault system la icp ms analyses of two generations of pyrite indicate that the banded pyrite of stage a is relatively depleted in metallic elements and contains low contents of cu 0 39 ppm ag 0 20 ppm au below the detection limits pb 17 43 ppm and zn 14 38 ppm whereas the pyrite in quartz polymetallic sulfide veinlets of the stage b is relatively rich in metallic elements e g cu 2 56 ppm ag 3 07 ppm au 0 01 ppm pb 1047 ppm and zn 1136 ppm the trace amounts of cu pb zn au and ag are interpreted to have been initially locked in the lattice of type a pyrite and then liberated and precipitated as micromineral inclusions with type b pyrite during subsequent metamorphism and deformation two key factors are considered vital to the formation of economic ores of the keketale pb zn deposit namely the original devonian banded pyrite formed in a vms system and subsequent permian deformation and metamorphic processes that liberated cu pb zn au and ag from the lattice of type a pyrite to form galena sphalerite and chalcopyrite with minor muscovite in quartz veinlets the model provides a new interpretation of vms pb zn deposit occurring in back arc basin environments followed by collision and new insights into the unique regional fe cu pb zn au mineralization in the altay orogenic belt

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

late paleozoic tectonic evolution and polymetallic ore forming processes in southern altay and northern junggar studies show that late paleozoic tectonic evolution and metallogenesis of southern altay and northern junggar are mainly controlled by the formation and evolution of the paleo asian ocean tectonic evolution of the paleo asian ocean during late paleozoic might be divided into three stages in early devonian the subduction of the paleo asian ocean plate began and some rift basins were formed on the continental margin of southern altay the ore forming processes of such metals as lead zinc copper and iron occurred contemporaneously in these basins at the same time adakitic magma and copper deposits were produced by partial melting of subducted paleo asian ocaen plate in middle devonian forearc basins were formed along with continuous subduction and copper lead and zinc metallogenesis occurred in these basins the collision of siberian plate and kazakhstan junggar plate occurred in carboniferous some gold deposits and rare metal deposits were formed along the ertixi suture zone and in southern altay due to this extrusion in early permian extension occurred around the ertixi suture zone and resulted in some mantle magma activities some copper and nickel processes represen ted by kelatongke took place in this stage according to the relationship between tectonic evolution and metallogenesis of north xinjiang the authors hold that polymetallic ore forming processes and perspective areas in north xinjiang include lead zinc copper and iron deposits in early devonian volcano sedimentary basins of southern altay early devonian copper deposits related to adakites copper polymetallic deposits in middle devonian forearc basins gold deposits and rare metal deposits related to carboniferous collision within ertixi suture zone and southern altay and copper nickel polymetallic deposits related to permian extension

subduction of diverging plates and the principles of slab window formation consumption of an ocean basin by subduction commonly brings a sea floor spreading ridge toward a deep sea trench if plate divergence and convergence continue after the ridge intersects the subduction zone a slab window forms between the subducted parts of the diverging oceanic plates producing anomalous thermal physical and chemical effects in the surrounding asthenospheric mantle in turn these conditions alter the tectonic and magmatic evolution of the overriding plate usually disturbing ordinary fore arc and arc regimes differential lithospheric stresses on opposite sides of the triple junction contribute to disturbances in the overriding plate anomalous magmatism from fore arc to back arc may be accompanied by fore arc metamorphism strike slip faulting uplift extension and in extreme cases rifting the shape and size of the window are controlled mainly by the pre subduction ridge transform trench configuration slab dip angles and vectors of plate convergence subducted ridge segments expand into windows whose margins approximately parallel the motion vectors between the triple junction and the subducting plates subducted transform faults continue to be active usually as oblique slip faults until the plates separate as transform faults subduct they become longer on the plate which occupies the acute angle between ridge and trench and shorter on the other plate trains of isolated windows produced by subduction of a segmented ridge transform system progressively expand during descent commonly merging together to form a composite slab window oblique subduction of a highly segmented ridge is likely to produce two or more fraternal slab windows one at each site of ridge trench intersection above a slab window arc volcanism diminishes and may be replaced by volcanism of mid ocean ridge or rift affinity the change in chemical character reflects various processes including elevated heat flow decreasing hydration of the upper mantle juxtaposition of supra and sub slab mantle reservoris asthenospheric upwelling and melting of the trailing plate edges if the slab window migrates the anomalous magmatic regime may be replaced by renewed arc volcanism identifying the effects of slab windows in ancient convergent margin assemblages requires an understanding of slab window principles and implications

fluid inclusion characteristics and mineralization of dadonggou pb zn ore deposit in altay xinjiang the dadonggou pb zn ore deposit is located in the kelan volcanic sedimentary basin the biggest basin on the southern margin of the altay mountains with the attitude of its ore bodies the same as that of the strata the ore bearing wall rock is mainly volcanic sedimentary rock of the lower devonian kangbutiebao formation and the ores occur in bedded disseminated and veinlet forms ore minerals consist simply of galena sphalerite and pyrite in this paper the authors carried out systemic measurements of homogeneous and freezing temperatures and salinities of fluid inclusions in quartz calcite and sphalerite formed at different ore forming stages in the dadonggou pb zn deposit chromatographic analysis of quartz samples and laser raman spectroscopic analysis of fluid inclusions in quartz and sphalerite were also conducted three main types of fluid inclusions namely nacl h2o inclusions co2 h2o ch4 inclusions and co2 h20 nacl inclusions were identified the homogenization temperatures of the fluid inclusions vary remarkably from 97 3 to 480 mostly in the range of 140 300 the salinities w nacleq of fluids range from 0 2 to 57 1 mostly between 3 2 and 14 8 the gas components of fluid inclusions are mainly co2 and h2o with minor amounts of such components as ch4 n2 and h2 the liquid components of fluid inclusions are mainly na ca2 f and cl subordinately k and so42 and small amounts of mg2 br and no 3 with the calculated ion concentration ranging from 36 6 to 58 0 according to previously analyses of the isotopic composition of c h o and s of the ores the 13cv pdb values of calcite range from 4 2 to 0 4 the dv smow of the inclusions in quartz range from 89 to 127 and the 18oh2o values of quartz and calcite range from 11 4 to 7 6 it is suggested that the ore forming fluid was mainly derived from the mixed meteoric water and magmatic water the carbon in the ore fluid was mainly derived from marine carbonates the change of physicochemical conditions and the immiscibility of co2 h2o exerted the main effect on the ore forming process of the dadonggou pb zn ore deposit

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

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

keketuohai mafic ultramafic complex in the chinese altai nw china petrogenesis and geodynamic significance abstract devonian magmatism was very intensive in the tectonic evolutionary history of the chinese altai a key part of the central asian orogenic belt caob the devonian keketuohai mafic ultramafic complex in the chinese altai is a zoned intrusion consisting of dunite olivine gabbro hornblende gabbro and pyroxene diorite the pyroxene diorite gives a zircon u pb age of 409 5 ma variations in mineral assemblage and chemical composition suggest that the petrogenesis of the keketuohai complex was chiefly governed by fractional crystallization from a common magma chamber low sio 2 k 2 o and na 2 o contents negative covariations between p 2 o 5 tio 2 and mg value suggest insignificant crustal assimilation contamination thus the positive e nd t values 0 to 2 7 and slight enrichments in light rare earth elements e g la yb n 0 98 3 64 suggest that their parental magma was possibly produced by partial melting of the lithospheric mantle model calculation suggests that their parental magma was high mg mg 66 tholeiitic basaltic melt the keketuohai intrusion was coeval with diverse magmatism high temperature metamorphism and hydrothermal mineralization which support a previously proposed model that ridge subduction most likely played an important role in the tectonic evolution of the chinese altai

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

linear kernels for karst aquifers karst aquifers contain significant water reserves in many parts of the world but development and management of these reserves is difficult because of the complexity of the aquifers this paper presents a method of characterizing karst aquifers based on the use of single linear kernel functions the kernels are identified with a deconvolution technique proposed by neuman and de marsily 1976 by using estimated groundwater recharge during isolated storms as the system input and the rapid storm response of spring flow as the system output derived kernels for large springs from data for different storms are similar in shape and time to peak average kernels derived from spring flow responses for multiple storms differ in shape for different springs but suggest a regularity in the response of individual springs to precipitation the derived kernel functions presently cannot be validated because of the use of a scaling factor in the moisture balance for the springs they can be used however to predict the storm response of a spring if the total volume of the rapid spring flow response is known

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

the study of molybdenites through the187re 187os chronometer we determined the re and os concentrations in 11 molybdenites of various ages 30 2700 m y and from various areas no common osmium has been detected and os was found to be purely radiogenic therefore by comparing the concentrations we were able to determine 187 re 187 os ages for most samples these ages are in good agreement with those measured in surrounding rocks and probably correspond to the age of mineralization however two or three re os ages seem unreliable being probably related to some rhenium leaching through later metamorphic and or hydrothermal events this shows that the petrographic characteristics of ores and the type of crystallization of mos 2 are important in choosing samples suitable for dating re and os determinations combined with careful petrographic investigations may give important clues on the genesis and evolution of molybdenum ores

metallogeny of the sarsuk polymetallic au deposit in the ashele basin altay orogenic belt xinjiang nw china constraints from mineralogy fluid inclusions and he ar isotopes the sarsuk polymetallic au deposit is located in the devonian volcano sedimentary ashele basin of the altay orogenic belt aob xinjiang mineralization in the deposit is confined to an area of 400 m long and 50 120 m wide and occurs as dense massive banded disseminated stockwork and veinlet ore structures exhalative sedimentary subvolcanic hydrothermal and supergene periods have been distinguished although syn depositional ores can be found the main orebodies from this period have been eroded thus the orebodies being mined are hosted mainly in a rhyolite porphyry subvolcanic intrusion within the volcanic conduit of a hydrothermal system electron microprobe analysis of the main ore minerals indicates that pyrite is the main au bearing mineral the au occurs mainly as either inclusions or in fissures in the form of tellurides and is closely associated with ag zn fe ratios of sphalerite vary from 11 37 to 251 36 with an average of 96 65 and the formation temperatures of chlorites are 155 206 c with an average of 175 c the compositions of sphalerite and chlorite indicate that the main mineralization occurred in a low to moderate temperature environment homogenization temperatures of fluid inclusions from ores of the main mineralization stage vary generally from 130 c to 390 c with peaks at 140 c 190 c and 310 c their corresponding salinities range from 3 0 to 10 0 wt nacl equivalent with densities from 0 56 to 1 03 g cm3 the main mineralizing fluid of the deposit is characterized by high low temperatures moderate low salinities and moderate low densities the 3he 4he ratios of fluid inclusions in pyrite are 0 02 to 0 44 ra and the percentage of mantle derived he ranges from 0 06 to 7 45 40ar 36ar ratios range from 319 6 to 458 5 and the percentage of 40ar varies from 7 53 to 35 55 both fluid characteristics and he and ar isotope compositions suggest that the ore forming fluids were a mixture of magmatic fluid and seawater the co2 rich fluids in the ores suggest that boiling occurred the mixing of a high temperature and high pressure magmatic fluid with deeply circulating seawater caused a decrease in temperature and phase separation in the ore forming fluids thus the precipitation of the most economically important ore materials was the result of this mixing process

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

tectonic setting of eocene boninite magmatism in the izu bonin mariana forearc abstract middle eocene boninites were simultaneously generated over a large region during the early history of the izu bonin mariana ibm arc however widespread boninite magmatism is not recognised in younger subduction zones of similar dimensions this suggests that an additional tectonic or thermal factor influenced the generation of the ibm boninite suite regional uplift ocean island basalt style magmatism and high heat flow also characterised the northern philippine sea plate psp at the start of the middle eocene these features are similar to those observed in large volume basaltic volcanic provinces such as the early tertiary north atlantic and suggest that the ibm boninite suite may have been produced because there was already a thermal anomaly in the mantle beneath the psp the reconstructed middle eocene location of the ibm arc and west philippine basin lies close to the present day manus basin where petrological and geochemical evidence indicate the presence of a mantle plume a calculated plume track linking these locations through time also passes close to the eauripik rise an aseismic ridge on the caroline plate during the oligocene and miocene therefore we propose that a thermal anomaly or mantle plume influenced the magmatic and tectonic development of the western pacific from the middle eocene until the present day

a review of the geological characteristics and mineralization history of iron deposits in the altay orogenic belt of the xinjiang northwest china abstract in this review we describe the geological characteristics and metallogenic tectonic origin of fe deposits in the altay orogenic belt within the xinjiang region of northwestern china the fe deposits are found mainly within three regions ordered from northwest to southeast the ashele kelan and maizi basins the principal host rocks for the fe deposits of the altay orogenic belt are the early devonian kangbutiebao formation the middle to late devonian altay formation with minor occurrences of lower carboniferous and early paleozoic metamorphosed volcano sedimentary rocks the principal mineral forming element groups of the deposits are fe fe cu fe mn fe p fe pb zn fe au and fe v ti the fe deposits are associated with distinct formations such as volcanic rocks skarn deposits pegmatites granite related hydrothermal vein mineralization and mafic pluton related v ti magnetite deposits the fe deposits are most commonly associated with volcanic rocks in the upper kangbutiebao formation in the volcano sedimentary kelan basin and in skarn deposits at several localities including the lower kangbutiebao formation in the volcano sedimentary maizi basin and the altay formation at jiaerbasidao kekebulake region homogenization temperatures of fluid inclusions in the prograde retrograde and sulfide stages of the skarn type deposit are mainly medium to high temperature cluster between 200 and 500 c medium temperature cluster between 200 and 340 c and low to medium temperature cluster between 160 and 300 c respectively ore fluids in the sedimentation period in the volcano sedimentary type deposit are characterized by low to medium temperature with a peak around 190 c low to moderate salinity 3 23 to 22 71 wt nacl equiv ore fluids in the pegmatite type deposit are characterized by low to medium temperature with a peak at 240 c low salinity with a peak around 9 wt nacl equiv an analysis of the isotopic data for fe deposits from the altay orogenic belt indicates that the sulfur was derived from several sources including volcanic rocks and granite as well as bacterial reduction of sulfate from seawater the present results indicate that different deposit types were derived from various sources the ree geochemistry of rocks and ores from the fe deposits in the altay orogenic belt suggests that the ore forming materials were derived from mafic volcanic rocks based on isotopic age data the timing of the mineralization can be divided into four broad intervals early devonian 410 384 ma middle devonian 377 ma early permian 287 274 ma and early triassic c 244 ma the ore forming processes of the fe deposits are closely related to volcanic activity and the emplacement of intermediate and felsic intrusions we conclude that fe deposits within the altay orogenic belt developed in a range of tectonic settings including continental arc post collisional extensional settings and intracontinental settings

the formation of the suyunhe large porphyry mo deposit in the west junggar terrain nw china zircon u pb age geochemistry and sr nd hf isotopic results abstract newly discovered suyunhe mo deposit 0 57 mt mo metal located in the barluk mountains of the west junggar terrain xinjiang nw china is the largest porphyry mo deposit discovered in xinjiang so far the suyunhe mo deposit is associated with the suyunhe intrusive complex which was emplaced into the volcano sedimentary sequences of the middle devonian barluk group the suyunhe complex consists of the deep granite intrusion and the shallow granite porphyry granodiorite porphyry monzonitic granite porphyry and tonalite porphyry stocks which are cut by the felsic dikes dominant mo mineralization is hosted in the barluk group volcano sedimentary rocks but is minor in the granite granite porphyry granodiorite porphyry and monzonitic granite porphyry of the suyunhe complex we report in situ zircon u pb ages whole rock geochemistry sr nd isotopic and zircon lu hf isotopic data for the ore bearing intrusive rocks from the suyunhe deposit secondary ion mass spectrometry sims zircon u pb dating indicates that the deep granite emplaced at 298 4 1 9 ma 295 3 3 ma and the shallow granodiorite porphyry intruded during 294 7 2 1 ma 293 7 2 3 ma the suyunhe granite intrusion including fine and medium grained granite belongs to the high k calc alkaline series most of them have low zr nb y ce 2 7 values showing a geochemical affinity to i type granite these granites are enriched in light rare earth elements lree and depleted in heavy rare earth elements hree and eu ba sr nb p and ti indicating that they have experienced advanced fractional crystallization they have low initial 87sr 86sr ratios 0 70318 0 70380 high whole rock end t values 4 4 to 6 0 high zircon ehf t values 10 8 to 14 6 and young whole rock nd and zircon hf model ages they also show low mg 0 35 these features demonstrate that the ore bearing granite formed by partial melting of the juvenile lower crust and experienced advanced fractional crystallization the suyunhe granite porphyry and monzonitic granite porphyry are compositionally similar to the granite indicating that they share a common magma source and process with the granite the suyunhe granodiorite porphyries belong to slightly high k calc alkaline series and have lree enrichment and hree nb and ti depletion they have low 87sr 86sr i ratios 0 70421 0 70444 high end t values 4 9 to 6 2 high zircon ehf t values 9 6 to 15 2 and young whole rock nd and zircon hf model ages they also show low mg

an integrated linear non linear flow model for the conduit fissure pore media in the karst triple void aquifer system most karstic aquifer media may be characterized as the triple void media with highly varied hydraulic properties including matrix pore fissure and conduit in which liner flow may co exist with non linear flow in this paper an attempt is made to couple linear flow with non linear flow in a single unified flow governing equations by introducing the concept of equivalent hydraulic conductivity ehc and deriving a general darcy s law for various flow the expression of ehc in the karst conduit and fissure are also derived the procedures of numerical implementation are demonstrated via an ideal model and a case study of karst aquifer system in the beishan ore formation area guangxi autonomous region china

high mg diorites derived from sanukitic hma magmas kyushu island southwest japan arc evidence from clinopyroxene and whole rock compositions abstract high mg diorites that have similar whole rock composition to high mg andesites hmas should not be simply interpreted as rocks solidified from the hma magmas because the high mg diorites may be mafic cumulates derived from a different magma from the hmas the hmas contain unique clinopyroxenes with higher mg and si than those of other sub alkaline series igneous rocks the mg and si are controlled by the source magma composition rather than its crystallized conditions such as pressure and temperature the chemical composition of clinopyroxenes would present important information for the investigation of the source of high mg diorites we considered the source of early cretaceous high mg diorites on kyushu island southwest japan arc based on their clinopyroxene and whole rock compositions the clinopyroxenes have similar chemical characteristics to those in hmas rather than those in other sub alkaline rocks moreover the whole rock compositions are equivalent to the sanukitic hma and do not show features of mafic cumulates this indicates that the high mg diorites solidified from sanukitic hma magmas it is generally believed that the sanukitic hma magmas involve the subduction of a young and or hot oceanic slab was situated in their genesis therefore the occurrence of the high mg diorites suggests that kyushu was situated in the tectonic setting of young and or hot slab subduction in the early cretaceous

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

simulation of the development of karst aquifers using a coupled continuum pipe flow model 1 this paper is intended to provide insight into the controlling mechanisms of karst genesis based on an advanced modeling approach covering the characteristic hydraulics in karst systems the dissolution kinetics and the associated temporal decrease in flow resistance karst water hydraulics is strongly governed by the interaction between a highly conductive low storage conduit network and a low conductive high storage rock matrix under variable boundary conditions only if this coupling of flow mechanisms is considered can an appropriate representation of other relevant processes be achieved e g carbonate dissolution transport of dissolved solids and limited groundwater recharge here a parameter study performed with the numerical model carbonate aquifer void evolution cave is presented which allows the simulation of the genesis of karst aquifers during geologic time periods cave integrates several important features relevant for different scenarios of karst evolution 1 the complex hydraulic interplay between flow in the karst conduits and in the small fissures of the rock matrix 2 laminar as well as turbulent flow conditions 3 time dependent and nonuniform recharge to both flow systems 4 the widening of the conduits accounting for appropriate physicochemical relationships governing calcite dissolution kinetics this is achieved by predefining an initial network of karst conduits protoconduits which are allowed to grow according to the amount of aggressive water available due to hydraulic boundary conditions the increase in conduit transmissivity is associated with an increase in conduit diameters while the conductivity of the fissured system is assumed to be constant in time the importance of various parameters controlling karst genesis is demonstrated in a parameter study covering the recharge distribution the upgradient boundary conditions for the conduit system and the hydraulic coupling between the conduit network and the rock matrix in particular it is shown that conduit diameters increase in downgradient or upgradient direction depending on the spatial distribution local versus uniform of the recharge component which directly enters the conduit system

the lack of potassium isotopic fractionation in bishunpur chondrules in a search for evidence of evaporation during chondrule formation the mesostases of 11 bishunpur chondrules and melt inclusions in olivine phenocrysts in 7 of them have been analyzed for their alkali element abundances and k isotopic compositions except for six points all areas of the chondrules that were analyzed had 41k compositions that were normal within error typically 3 2s the six anomalous points are probably all artifacts experiments have shown that free evaporation of k leads to large 41k enrichments in the evaporation residues consistent with rayleigh fractionation under rayleigh conditions a 3 enrichment in 41k is produced by 12 loss of k the range of l chondrite normalized k al ratios a measure of the k elemental fractionation in the areas analyzed vary by almost three orders of magnitude if all chondrules started out with l chondrite like k abundances and the k loss occurred via rayleigh fractionation the most k depleted chondrules would have had compositions of up to 41k 200 clearly k fractionation did not occur by evaporation under rayleigh conditions yet experiments and modeling indicate that k should have been lost during chondrule formation under currently accepted formation conditions peak temperature cooling rate etc invoking precursors with variable alkali abundances to produce the range of k al fractionation in chondrules does not explain the k isotopic data because any k that was present should still have experienced sufficient loss during melting for there to have been a measurable isotopic fractionation if k loss and isotopic fractionation was inevitable during chondrule formation the absence of k isotopic fractionation in bishunpur chondrules requires that they exchanged k with an isotopically normal reservoir during or after formation there is evidence for alkali exchange between chondrules and rim matrix in all unequilibrated ordinary chondrites however melt inclusions can have alkali abundances that are much lower than the mesostases of the host chondrules which suggests that they at least remained closed since formation if it is correct that some or all melt inclusions remained closed since formation the absence of k isotopic fractionation in them requires that the k isotopic exchange took place during chondrule formation which would probably require gas chondrule exchange potassium evaporated from fine grained dust and chondrules during chondrule formation may have produced sufficient k vapor pressure for gas chondrule isotopic exchange to be complete on the timescales of chondrule formation alternatively our understanding of chondrule formation conditions based on synthesis experiments needs some reevaluation

simulation of groundwater flow within observation boreholes for confined aquifers summary observation wells around a pumping well are the primary means of monitoring the change of hydraulic head in an aquifer pipe flow in open observation boreholes will affect the measurement of hydraulic head in the observation wells and alter the flow patterns around the wells but the influences of non darcian pipe flow in observation wells on the accuracy of hydraulic head measurements are not fully recognized this paper presents a coupled seepage pipe flow theory which integrates the aquifer and well as a continuous medium for assessing the influences the objective of this study is to examine the pipe flow effects in observation wells of varied diameters under several pumping scenarios including different penetration lengths of the pumping well a numerical model based on the galerkin finite element method and the finite difference method was developed for the study numerical simulations were conducted for a homogeneous and isotropic confined aquifer in which a pumping well penetrated a different thickness of the aquifer and a number of full penetrating observation wells were placed to obtain drawdowns the simulation results indicated that vertical pipe flow within the observation wells was significant and the flow was non linear the pipe flow resulted in a conduit effect that disturbed the distribution of the hydraulic head within the observation wells after comparing with the results of the hantush 1961 integral by using the case study which neglected the wellbore effect on the groundwater flow system the authors found that the hantush integral may be only conditionally applicable for estimating the drawdown within the observation wells when well diameter is greater than 0 20 m and radial distance is greater than the thickness of the aquifer our study suggests that use of hydraulic heads from observation wells for the evaluation of groundwater flow systems must be cautious before the pipe flow effect can be assumed to be negligible

re os isotopic systematics of the voisey s bay ni cu co magmatic ore system labrador canada abstract re and os concentrations and os isotopic compositions have been obtained for massive matrix and disseminated sulphide ores from three environments within the voisey s bay intrusion the ovoid eastern deeps and discovery hill zone in order to assess the role of crustal contamination in the genesis of this large cu ni co deposit these samples have high re concentrations 148 to 288 ppb in 100 sulphide for their common os concentrations 4 8 to 24 ppb in 100 sulphide yielding high re os ratios 12 to 33 these data confirm that the magma parental to the voisey s bay ore system was broadly basaltic in major element chemistry rather than picritic consistent with the low ni cu ratio of the ores 1 5 re os isotopic data exhibit a limited spread in 187 re 188 os 57 to 157 and define an imprecise 1323 135 ma model 3 isochron likely the result of small r factor variations within the ore system the re os isochron age is within error of 1334 ma u pb ages obtained for baddeleyite from the ore bearing troctolites demonstrating that whole rock re os isotopic systematics have remained closed since crystallisation the initial os isotopic composition of the isochron os 1040 200 implies significant magma interactions with radiogenic os that most likely resides in the nain churchill province crust these data are therefore consistent with the parental magma achieving sulphide saturation as a result of contamination by radiogenic crustal components with further addition of base and precious metals as a function of r factor analyses of sulphide separates from the proterozoic tasiuyak churchill and archaean nain gneisses confirm that both units contained significant os 8 6 ppb and 0 38 ppb respectively that was very radiogenic at 1334 ma os 1908 and 5202 respectively yielding crustal residence tchur model ages of 2200 to 2400 ma however these model ages may have been affected by re and or os mobility during the 1 85 ga torngat and 1 1 ga grenville orogeny re os isotopic modelling suggests that a reasonable fit to the ore data may be obtained via bulk crustal contamination of magmas parental to the nain plutonic suite nps with either tasiuyak 2 contamination or nain 16 contamination gneiss followed by an r factor process 200 to 1000 which improved the tenor of the sulphide liquid during transport in active magma conduits or after deposition in an active replenished voisey s bay intrusion magma chamber however the dominance of plagioclase rich high al2o3 magmas in the mafic members of the nps troctolites and anorthosites may indicate that other deeper forms of lithospheric interaction potentially involving mafic lower crust may be crucial to understanding this style of magmatic sulphide ore system

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

tectonic setting and geochronology of the sarsuk au polymetallic deposit in xinjiang nw china constraints from pyrite re os zircon u pb dating and hf isotopes abstract the sarsuk au polymetallic deposit is located in the ashele volcano sedimentary basin of the south altay orogenic belt aob northwest china within the deposit rhyolite porphyry and diabase are widespread and emplaced into the strata the orebodies of the sarsuk deposit are hosted by the rhyolite porphyry while diabase cuts through the rhyolite porphyry and part of the orebody rhyolite porphyry 1 yields a zircon u pb age of 384 1 2 ma mswd 0 69 and the diabases yield a zircon u pb age of 380 0 74 ma mswd 3 1 four auriferous pyrite samples from vein sulfide ores and one pyrite sample from massive ores display a re os isochron age of 383 11 ma mswd 1 2 these data show that the bimodal devonian magmatism and rhyolite porphyry hosted ore bodies emplaced in a narrow interval during 384 380 ma diabases have the geochemical characteristics of tholeiitic basalts with relatively high mg values 49 4 61 4 cr and ni a slight positive eu anomaly eu 0 98 1 12 and relatively low concentrations of sr and la yb n rhyolite porphyries have similar characteristics to those of sanukitoide in terms of high mg values 47 6 55 7 an obvious negative eu anomaly eu 0 33 0 35 and enrichments of large ion lithophile elements and light rare earth elements the aforementioned chemical characteristics indicate that the sarsuk deposit was located in the arc environment of a subduction zone during the early to middle devonian hf isotope analyses of the diabases exhibited ehf t values of 4 86 to 8 96 the two stage hf model age tdm2 was 805 1064 ma hf isotope analyses of the rhyolite porphyry exhibited a ehf t value range of 1 78 to 8 49 and the two stage hf model age tdm2 was 449 528 ma the original diabase and rhyolite porphyry magmas were derived from a mixing of the depleted mantle and juvenile crust material the pyrite re os system indicated that crust derivedand s rich sediments also contributed to the ore formation accordingly based on the results of this study and a review of the regional magmatic framework we can conclude that the sarsuk deposit was formed at 383 ma in an island arc subduction environment furthermore we establish that the magmatic rocks and ore are co genetic

ore geology and fluid inclusion geochemistry of the tiemurt pb zn cu deposit altay xinjiang china a case study of orogenic type pb zn systems abstract the tiemurt pb zn cu deposit is hosted in a devonian volcanic sedimentary basin of the altay orogenic belt and is thus interpreted to have formed by sea floor hydrothermal exhalation in previous studies our investigation discovered that the deposit is not stratiform or stratabound but structure controlled instead the hydrothermal ore forming process can be divided into the early middle and late stage represented by pyrite quartz polymetallic sulfide quartz and carbonate quartz veinlets respectively the early stage veins and contained minerals are structurally deformed and brecciated suggesting a compressional or transpressional tectonic regime the middle stage veinlets intrude and infill the fissures of the early stage assemblages and show no deformation suggesting a tensional shear setting the late stage veinlets mostly infill open space fissures that crosscut veins and replacements formed in the earlier stages four types of fluid inclusions fis including aqueous type w carbonic aqueous type c pure carbonic type pc and solid bearing type s are identified at the tiemurt deposit the early stage minerals contain the c and w type primary fis that are totally homogenized at temperatures of 330 390 c with low salinities of 0 8 11 9 wt nacl eqv whilst the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 118 205 c and salinities of 1 4 3 4 wt nacl eqv this indicates that the ore fluid system evolved from co2 rich probably metamorphic to co2 poor meteoric fluids and that a significant co2 escape must have occurred all the four types of fis can be only observed in the middle stage minerals and even in a microscopic domain of a crystal representing an association trapped from a boiling fluid system these fis homogenize at temperatures ranging from 270 to 330 c with two salinity clusters of 1 9 14 5 and 37 4 42 4 wt nacl eqv respectively this implies that metal precipitation resulted from fluid boiling co2 escape and transient oversaturation the estimated trapping pressures of fis range from 130 to 380 mpa suggesting an alternating lithostatic hydrostatic fluid system controlled by a fault valve at the depth of 13 km therefore the tiemurt pb zn cu deposit is likely an example of orogenic pb zn cu systems formed in collision orogeny rather than a pre collision vms or sedex system developed in devonian and a new metallogenic model is proposed to interpret the formation of the tiemurt pb zn cu deposit

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

petrogenesis of the devonian high mg rock association and its tectonic implication for the chinese altai orogenic belt nw china abstract the chinese altai is a key region to decipher the accretionary history of the gigantic caob one of the largest accretionary orogenic belts on the earth however tectonic implication of the widely distributed paleozoic magmatic rocks remain debated in this study a suite of igneous rocks including high mg dacite of the kangbutiebao formation and the associated gneissic granodiorites have been studied for their petrogenesis and tectonic implication the high mg dacite is dated at 400 2 ma which broadly resembles the emplacement age of the high mg gneissic granodiorites of 406 9 ma possibly suggesting that they were generated in the same tectono magmatic event both rocks have predominant zircon inheritances of 500 ma which is consistent with the age of predominant zircon population for the widespread habahe sedimentary sequence indicating that their precursor magmas were probably mainly derived from the habahe sediments the high mg rock association has similar ree and trace element patterns to those of the habahe sediments and they plot close to the field of the habahe sediments in th ta versus la ta diagram their high a cnk ratios 1 33 2 05 imply magma source dominated by sedimentary rocks similarly their high la sm ratios also suggest a greater contribution of sediments rather than altered oceanic crust in the magma generation however the high mg values 51 of the studied rocks argue against derivation purely from remelting of the habahe sediments in order to explain the high mg values of these rocks the participation of mantle derived melt into the precursor magma is considered zircons from this rock association mostly yield e hf t values from 0 85 to 9 71 supporting the involvement of juvenile materials in the magma generation samples from the high mg rock association fall in the same field as the sanukitoids in tio 2 versus mg and sr y versus y diagrams and they plot in the fractional crystallization trend of differentiated sanukitoids in harker diagram possibly suggesting a petrogenetic process like the typical sanukitoid magma elsewhere this study shows that similar to the sanukitoids in the setouchi area our high mg rock association also involved melting of subducted sediments in a hot subduction regime combined with previous work a ridge subduction regime is considered to interpret the early devonian tectonic evolution of the chinese altai

modeling of storm responses in conduit flow aquifers with reservoirs abstract in aquifers containing large voids such as karst aquifers with caves or basaltic aquifers with lava tubes hydrographs at wells or springs are used to analyze the structure and response of the hydrogeological system numerical modeling of hydrograph response is commonly based on either inverse techniques or postulated flow geometries however the range of mechanisms for generating hydrograph responses have not been fully investigated physical modeling of these complex non darcian systems permits better understanding of the storm responses that conduit systems may generate using a numerical model of conduit flow systems which incorporates turbulent flow some of the mechanisms that can alter storm pulses were investigated by treating them as combinations of pipes that connect reservoirs the results indicate that the response of a conduit flow aquifer can range from what has been called diffuse or steady to conduit or flashy without employing a diffusive component a full range of behavior can be the result of changes from phreatic to epiphreatic conditions in a conduit changes in conduit geometry or multiple springs draining the same system the results provide a quantitative tool to assess spring and well hydrographs and illustrate mechanisms that can generate observed responses which have previously been qualitatively interpreted