a possible genetic relationship between orogenic gold mineralization and post collisional magmatism in the eastern kunlun orogen western china abstract controversies in orogenic gold deposits remain especially regarding the relative contribution of magmatic fluids to the mineralization the shuizhadonggou huanglonggou gold deposit in the wulonggou gold field of the eastern kunlun orogen western china consists mainly of sulfide disseminations in hydrothermally altered rocks with minor amounts of quartz sulfide veins coeval to or overprinting the disseminated ores gold mineralization is hosted in diverse lithologies i e early palaeozoic metamorphic rocks late silurian syenogranite and late triassic porphyritic granodiorite and quartz diorite and is structurally controlled by a second order nw trending sinistral normal ductile shear zone and its subsidiary structures along the first order central kunlun fault gold related hydrothermal alteration formed chlorite sericite quartz and calcite with associated sulfide minerals dominated by pyrite arsenopyrite lollingite and pyrrhotite two types of hydrothermal sericite separates from a gold mineralized syenogranite yielded two 40 ar 39 ar ages of 237 0 2 0 ma and 230 8 1 7 ma respectively which postdated the early triassic regional metamorphism and ductile deformation by 13 m y field relationships suggest that gold mineralization also overprinted 220 ma porphyritic granodiorites and quartz diorites these data indicate three gold mineralization events in the late triassic overlapped with post collisional magmatism in the orogen gold bearing sulfides have 34 s values mostly in the range of 2 0 5 5 consistent with a magmatic source of sulfur quartz from quartz pyrite sericite veins has calculated 18 o h2o values of 1 8 6 1 and d h2o of 63 to 107 the stable isotopic and geochronological data suggest a magmatic origin for the ore forming fluids therefore the shuizhadonggou huanglonggou and other gold deposits in the eastern kunlun orogen share many features of orogenic gold deposits e g multiple order ore controlling structures hydrothermal alteration mineralization styles close association between mineralization and magmatism and h o s stable isotope compositions and are genetically related to late triassic post collisional magmatism

intermediate mafic dikes in the east kunlun orogen northern tibetan plateau a window into paleo arc magma feeding system abstract the contemporaneous mafic and intermediate dikes of a continental magmatic arc provide a window into the magma feeding system at depth here we integrate data on the elemental and sr nd hf isotope geochemistry petrology mineralogy and zircon geochronology of late permian dikes in the east kunlun orogen northern tibetan plateau discuss the petrogenesis of the dikes and reconstruct the nature and relationship of different magma reservoirs the dikes are porphyritic diabases lamprophyres and diorite porphyries that crystallized between 259 and 255 ma coeval with their host granodiorites geochemical and sr nd hf isotopic data indicate the parental magma of the porphyritic diabases and lamprophyres was derived from enriched lithospheric mantle this magma underplated the crust and underwent varying degrees of magma recharging crustal assimilation and fractional crystallization dominated by olivine pyroxene and hornblende this evolved basaltic magmas ascended through the crust undergoing further differentiation and some magma entered mid crustal reservoirs occupied by felsic crystal mushes rejuvenating the mushes the subsequent mixing of mafic and felsic materials formed the precursor magmas of the intermediate dikes our new data reveal that the magmas stagnated mainly in reservoirs at two levels 26 32 and 9 18 km based on hornblende barometry the underplating assimilation and replenishment of basaltic magmas in the lower crust and their eventual emplacement and differentiation in a mid crustal reservoir controlled the mineralogy and geochemistry of the mafic dikes while the rejuvenation of crystal mushes the mixing of mafic and felsic materials and differentiation account for the compositional features of the diorite porphyries this study shows that the trans crustal magma feeding system which controls the compositions of several dispersed but interconnected magma reservoirs is the key to understanding the compositional diversity and igneous petrogenesis in continental arcs

magmatic hydrothermal origin of the early triassic laodou lode gold deposit in the xiahe hezuo district west qinling orogen china implications for gold metallogeny the xiahe hezuo district in the west qinling orogen contains numerous au as sb and cu au w deposits the district is divided into eastern and western zones by the xiahe hezuo fault the western zone is exposed at a shallow level and contains sediment hosted disseminated au as sb deposits whereas the eastern zone is exposed at a deeper level and contains cu au w skarn and lode gold deposits within or close to granitic intrusions the laodou gold deposit in the eastern zone consists of auriferous quartz sulfide tourmaline and minor quartz stibnite veins that are structurally controlled by fault zones transecting the laodou quartz diorite porphyry stock and enveloped by potassic and phyllic alteration both the veins and alteration halos commonly contain quartz sericite tourmaline pyrite and arsenopyrite with minor galena sphalerite chalcopyrite tetrahedrite and enargite gold occurs mainly as invisible gold in pyrite or arsenopyrite and locally as inclusions less than 50 m in diameter the zircon u pb age of 247 6 1 3 ma 2 on the host quartz diorite porphyry and the sericite 40ar 39ar plateau ages of 249 1 1 6 and 249 0 1 5 ma 2 on two ore related hydrothermal sericite samples are within analytical errors of one another at the formation temperature 275 c inferred from microthermometric measurements of fluid inclusion sericite and tourmaline yield calculated dh2o values of 70 to 45 and 18oh2o of 5 8 to 9 7 while quartz yields calculated 18oh2o values of 5 1 5 7 hydrothermal tourmaline in quartz sulfide tourmaline veins has 11b of 11 2 to 0 9 mean of 6 3 that are similar to the values of magmatic tourmaline 8 9 to 5 5 with a mean of 6 8 in the host quartz diorite porphyry the 34s values of sulfide minerals range from 5 9 to 5 8 with a mean of 0 6 that is typical of magmatic sulfur pyrite from hydrothermally altered quartz diorite porphyry and quartz sulfide tourmaline veins have relatively homogeneous lead isotopic compositions compatible with granitic intrusions in the district the geochronological and isotopic data combined support a magmatic origin for the laodou gold deposit most likely formed from fluids exsolved from the laodou quartz diorite porphyry or associated intrusive phases at deeper levels beneath the stock orogenic and carlin like gold deposits in the west qinling orogen have been commonly thought to have formed from metamorphic fluids this study however highlights the role of magmatic derived fluids in the formation of lode gold deposits synthesis of geochronological geological and geochemical data on magmatic rocks and ore deposits in and surrounding the xiahe hezuo district indicates that gold mineralization predominantly occurred within a subduction related magmatic arc prior to collision between the yangtze and north china cratons that produced the west qinling orogen

propagation tectonics and multiple accretionary processes of the qinling orogen abstract the qinling orogen was built through collision between the north china and south china blocks previous detailed geological geochemical and geochronological investigations revealed that the mountain range can be divided into four tectonic units with distinct tectono lithostratigraphy which are from north to south the southern sector of the north china block north qinling belt south qinling belt and northern sector of the south china block separated by the kuanping shangdan and mianlue sutures according to the petrology geochemistry and geochronology of ophiolitic melanges and related magmatic rocks as well as the features of sedimentary units we think that the north china block the north qinling belt and the south china block were originally independent continental units while the south qinling belt had been the northern part of the south china block these units experienced three episodes of accretionary tectonic processes and amalgamation from south to north the neoproterozoic accretion took place along the luonan luanchuan fault and kuanping ophiolitic melange belt as a result of southward subduction and subsequent collision between the north qinling and north china blocks during ca 1 0 0 8 ga related to the formation of the supercontinent of rodinia the paleozoic accretion occurred along the shangdan suture resulted from northward subduction of oceanic lithosphere in the early paleozoic and subsequent continental subduction in the late paleozoic late triassic accretion took place along the mianlue suture between the south qinling and south china blocks due to northward subduction of the mianlue oceanic lithosphere during the permian early triassic and subsequent collision in the late triassic after the late triassic collision along the mianlue suture the whole qinling mountain range entered the phase of intense intracontinental deformation

low permeability rocks laboratory measurements and three dimensional microstructural analysis traditional techniques for measuring permeability and traditional models relating permeability to porosity are inadequate for low permeability or 10 sup 18 m sup 2 geologic materials special techniques have been developed for measuring fluid flow through such rock samples and for quantifying their three dimensional pore microstructure permeability is measured by a modified transient pulse technique pore structure is quantified using a computerized microgeometric modeling system and portable three dimensional display is produced by an optical imaging system results of applying this processing to a low porosity tight gas sandstone from the cotton valley formation agree with the well documented diagenetic history of these samples we find that the porosity distribution is very inhomogeneous and skewed the pore system is slightly anisotropic which is consistent with the differences in permeability measured in two orthogonal directions we indicate how such data could be used to develop more geologically and geometrically realistic models relating porosity and permeability in low permeability gas formations

tin metallogenesis associated with granitoids in the southwestern sanjiang tethyan domain nature deposit types and tectonic setting article i nfo tin mineralization in the southwestern sanjiang tethys sn metallogenic domain extends from the southeast asia tin belt in the south the eastern part of the domain does not contain significant sn deposits whereas the central part of the domain composed of the changning menglian sn belt and related to ca 239 178 ma s type granitoids generated by the collision between tengchong baoshan and simao blocks carries wide spread the hydrothermal vein type mineralization the western part of the domain composed of the tengchong baoshan sn metallogenic belt is related to both 136 113 ma and 89 52 ma s type granitoids the former granitoids resulted from the collision between western burma and tengchong baoshan blocks and generated skarn type tin deposits the younger groups correspond to the india asia continental collision and are associated with the xiaolonghe and lailishan greisen type sn deposits

reply to the comment by zhang et al on first finding of a type and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination we greatly thank zhang et al 2008 this issue for their comments on our recent paper zhang et al 2007 regarding the tectonic setting of the indosinian granitoids in the songpan garze fold belt as it gives us an opportunity to further clarify our viewpoints the discrepancy between zhang et al 2008 this issue and zhang et al 2007 h f zhang r parrish l zhang w c xu h l yuan s gao and q g crowley a type granite and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination lithos 97 2007 pp 323 335 article pdf 1219 k view record in scopus cited by in scopus 7 zhang et al 2007 is focused on the interpretation of the tectonic setting of the indosinian a type granite 211 1 ma and adakitic magmatism 216 221 ma in the songpan garze fold belt we emphasize that these magmatic rocks formed in post collisional tectonic setting while zhang et al 2008 this issue suggest that they were related to the northward subduction of the jinsajian tethys

design criteria for laboratory measurements of low permeability rocks the advantages and limitations of two versions of the pulse technique for laboratory measurements of low permeabilities 10 16 to 10 24 m are discussed the transient pulse technique developed by brace et al 1968 is the preferred method because of the ease of data reduction the modified transient pulse technique developed by trimmer et al 1980 can be used when the assumptions inherent in the transient pulse technique are invalid the systematic error associated with the transient pulse technique is a function of the ratio of the effective sample pore volume to the reservoir volumes if this ratio is less than 0 25 then the error associated with the transient technique is less than 10 the modified transient pulse technique does not suffer from this systematic error criteria are also presented for optimizing the experimental configuration for measurement durations as well as ease of data reduction

influence of maturity on carbazole and benzocarbazole distributions in crude oils and source rocks from the sonda de campeche gulf of mexico abstract carbazole geochemistry has been studied for a petroleum system in which vertical migration is prominent and where reservoirs are locally sourced an essentially uniform organofacies of organicrich tithonian source rocks from the sonda de campeche gulf of mexico covering a well defined maturity sequence 0 36 1 29 rr and associated crude oils 0 49 0 92 rc from palaeocene reservoirs formed the sampling base comparison of the distribution of alkylcarbazoles and benzocarbazoles in rock bitumens and oils revealed that fractionation due to primary expulsion had no effect on the distribution of shielded exposed carbazoles within crude oils perhaps more importantly the benzocarbazole ratio in both rock extracts and crude oils increased with maturity indicating that this parameter cannot be directly used as a migration indicator in petroleum systems where vertical migration through faults and fissures represents the main avenues of oil migration

a geochemical study of oil migration at source rock reservoir contacts stable isotopes abstract whereas organic geochemical analyses of oils and potential source rocks have enabled correlations to be drawn and have been utilized to suggest modes of migration only limited data has been published relating a known source rock in contact with an oil filled reservoir this paper presents initial results from the examination of an approximately 100 m continuous core through the kimmeridge shale of the north sea the variability in extractable source rock hydrocarbon contents kerogen toc asphaltene and their carbon isotopic contents are documented nitrogen isotopic content of kerogens and asphaltenes as well as kerogen and asphaltene ton are relatively constant carbon isotopic compositions of kerogen extractable hydrocarbons and asphaltenes covaried significantly as did nitrogen isotopic compositions of kerogen and asphaltenes average isotopic compositions of the asphaltene free extracts and asphaltenes were nearly identical to the oil in the primary reservoir small chemical differences are noted among extracts

cassiterite u pb geochronology of the kekekaerde w sn deposit in the baiganhu ore field east kunlun orogen nw china timing and tectonic setting of mineralization abstract the baiganhu w sn ore field in the northwestern area of the east kunlun orogen nw china contains three economically important w sn deposits namely kekekaerde baiganhu and bashierxi timing of the w sn mineralization remains under debates due to lack of precise isotope dating directly conducted on ore minerals we herewith report la mc icp ms laser ablation multi collector inductively coupled plasma mass spectrometry and id tims isotope dilution thermal ionization mass spectrometry cassiterite u pb ages for the kekekaerde w sn deposit in the baiganhu w sn ore field the id tims cassiterite 206 pb 238 u results yield a weighted mean age of 416 1 ma 95 confidence mswd 0 8 and the la mc icp ms analytical data give a 206 pb 207 pb 238 u 207 pb isochron age of 426 13 ma 95 confidence mswd 0 1 these two ages are same within errors suggesting that the mineralization in the baiganhu w sn ore field occurred at ca 416 ma these new ages and understandings are consistent with the previously reported zircon u pb ages of 430 420 ma for the ore bearing granites in the ore field and with the 40 ar 39 ar plateau ages of ca 412 ma for the hydrothermal muscovite from ore bearing quartz veins and greinsenized granite it shows that the granite magmatism and its associated hydrothermal mineralization resulted from the caledonian orogeny that accommodated the closure of the proto tethys followed by the continental collision between the central kunlun northern kunlun terranes and the qaidam block

displacement and timing of left lateral faulting in the kunlun fault zone northern tibet inferred from geologic and geomorphic features abstract the e w to wnw ese striking kunlun fault zone extending about 1600 km is one of the large strike slip faults in the northern tibet china as a major strike slip fault it plays an important role on the extrusion of tibet plateau in accommodating northeastward shortening caused by the india asia convergence however the time of initiation left lateral faulting of the kunlun fault zone is still largely debated ranging from the middle to late triassic 240 200 ma to early quaternary 2 ma we document displaced basement rocks and geomorphic features along the kunlun fault zone based on tectono geomorphic interpretation of satellite remote sensing images and field geologic and geomorphic observations our results show that the largest cumulative offset of basement rocks is likely to be 100 20 km meanwhile a series of pull apart basins kusai xiugou and tuosu lake basins and pressure ridges east deshuiwai and maji snow mountains each 45 70 km long and 8 12 km wide are developed along the kunlun fault zone which resulted from long term tectono geomorphic growth since the late miocene or early pliocene geologic evidence indicates that the kunlun fault zone had a long term slip rate of ca 10 mm yr during the late quaternary this slip rate is similar to that shown by present day gps measurements thus we estimate that the kunlun fault zone probably began left lateral faulting at 10 2 ma based on a total displacement of 100 20 km and assuming a constant long term slip rate of ca 10 mm yr for several millions of years and this timing constraint on initiation of left lateral faulting of the kunlun fault zone is consistent with widespread tectonic deformation which occurred in the tibetan plateau

early paleozoic high mg diorite granodiorite in the eastern kunlun orogen western china response to continental collision and slab break off abstract phanerozoic high mg diorites and granodiorites are known to be related to diverse subduction styles at convergent margin settings but have not been linked to collision processes the santonggou complex in the eastern kunlun orogen is composed of a dominant granodiorite intruded by small stocks and dykes of porphyritic granodiorites and diorites which are all characterized by high mgo and ni but low yb and y contents mafic microgranular enclaves mmes occur in the granodiorite and the porphyritic granodiorites la icpms u pb analyses of zircon from the granodiorite porphyritic granodiorite and porphyritic diorite yield similar ages of 432 2 ma 432 2 ma and 427 3 ma respectively plagioclase in the granodiorite exhibits complex zonations with resorbed and patchy cores plagioclase and hornblende phenocrysts in the porphyritic granodiorites and diorites also show textural and compositional zonations the highest e nd t value of 0 6 in mmes suggests asthenosphere derived mafic magma these lines of mineralogical and geochemical evidence together with results from geochemical modeling suggest that the porphyritic diorites were derived from mantle metasomatized slab melts the porphyritic granodiorites and the granodiorite were generated by simultaneous assimilation and fractional crystallization of the magma approximated by the porphyritic diorites plus mixing of asthenosphere derived mafic and evolved granodioritic magmas pressure estimates from the al in hornblende geobarometer suggest that the granodiorite had been uplifted to near the surface before the emplacement of the porphyritic granodiorites partial melting of the slab upwelling of the asthenosphere and rapid orogenic uplift at 430 ma suggest that the cessation of subduction and the initiation of collision as well as slab break off occurred almost simultaneously in the eastern kunlun orogen

fish from the upper devonian of the shan thai terrane indicate proximity to east gondwana and south china terranes we report the first discovery of abundant devonian vertebrates from thailand an unusual form of coronodontid shark tooth with six equal sized cusps occurs only in the upper devonian of thailand shan thai terrane and south china and a new species of phoebodus is reported that occurs elsewhere only in south china and australia east gondwana terrane the occurrence of the chondrichthyan harpagodens thrinacodus ferox turner 1982 in the late devonian of thailand australia and south china predates the appearance of this species in euramerica early carboniferous these data suggest late devonian proximity of the shan thai south china and east gondwana terranes and is in accord with recent paleomagnetic data

permeability of illite bearing shale 2 influence of fluid chemistry on flow and functionally connected pores 1 bedding parallel permeability of illite rich shale of the wilcox formation has been investigated using distilled water and 1 m solutions of nacl kcl and cacl2 as pore fluids despite low modal concentrations of swelling clays specimens expand upon fluid saturation and permeabilities depend on fluid composition permeabilities to flow of 1 m cacl2 are 3 5 times greater than values measured for the other pore fluids suggesting sensitivity to exchange of divalent cations for monovalent cations at clay mineral surfaces permeabilities of individual samples exhibit nonrecoverable changes with sequential changes in composition of incoming fluid permeabilities k at varying effective pressure pe fit a cubic law k k0 1 pe p1 m 3 where m and p1 are independent of fluid composition and k0 is greater for transport of 1 m cacl2 than that for transport of the other pore fluids assuming that fluid conduits have crack like dimensions the lack of sensitivity of m and p1 to fluid composition suggests that surface roughness and asperity stiffness of conduits are unaffected by cation exchange while changes in k0 reflect changes in the clay fluid interfaces of the connected pore space index terms 5114 physical properties of rocks permeability and porosity 5139 physical properties of rocks transport properties 1832 hydrology groundwater transport 3947 mineral physics surfaces and interfaces 1045 geochemistry low temperature geochemistry keywords permeability shale fluid chemistry citation kwon o b e herbert and a k kronenberg 2004 permeability of illite bearing shale 2 influence of fluid chemistry on flow and functionally connected pores j geophys res 109 b10206 doi 10 1029 2004jb003055

a brief review of ophiolites in china abstract ophiolites are widely distributed in western southwestern and northern china where they fall into four principal age groups neoproterozoic early paleozoic late paleozoic and mesozoic cenozoic neoproterozoic ophiolites are known only in the north qinling orogenic belt in ne jiangxi province and in western sichuan province phanerozoic ophiolites are grouped into the paleo asian tethyan and circum pacific series the paleo asian ophiolites crop out in the western and northern parts of china between the siberian and north china blocks and range in age from early to late paleozoic all of these ophiolites are of the franciscan formerly cordilleran type and many are superimposed on one another suggesting repeated accretion of arc assemblages in an environment similar to the present day western pacific ocean mediterranean type formerly tethyan type ophiolites are confined to sw china particularly tibet and yunnan province paleo tethyan ophiolites are characterized by morb type lavas and are typically bounded by old continental lithosphere suggesting that they formed in small intercontinental ocean basins neo tethyan ophiolites contain a range of lava types including morb iat and boninite indicating formation in a variety of suprasubduction zone ssz environments circum pacific ophiolites occur sporadically in taiwan and ne china where they form tectonic melanges composed mainly of metaperidotite gabbro and basalt

injection of tibetan crust beneath the south qaidam basin evidence from indepth iv wide angle seismic data 1 the international deep profiling of tibet and the himalaya phase iv indepth iv active source seismic profile in northeast tibet extends 270 km roughly north south across the songpan ganzi terrane the predominantly strike slip north kunlun fault along the kunlun suture the east kunlun mountains and the south qaidam basin refraction reflection and gravity modeling provide constraints on the velocity and density structure down to the moho the central qaidam basin resembles average continental crust whereas the songpan ganzi terrane and east kunlun mountains exhibit thickened lower velocity crust also characteristic of southern tibet the crustal thickness changes from 70 km beneath the songpan ganzi terrane and east kunlun mountains to 50 km beneath the qaidam basin this jump in crustal thickness is located 100 km north of the north kunlun fault and 45 km north of the southern kunlun qaidam boundary farther north than previously suggested ruling out a moho step caused by a crustal penetrating north kunlun fault the qaidam moho is underlain by crustal velocity material 6 8 7 1 km s for 45 km near the crustal thickness transition the southernmost 10 km of the qaidam moho are underlain by a 70 km reflector that continues to the south as the tibetan moho the apparently overlapping crustal material may represent songpan ganzi lower crust underthrusting or flowing northward beneath the qaidam basin moho thus the high tibetan plateau may be thickening northward into south qaidam as its weak thickened lower crust is injected beneath stronger qaidam crust

under stress permeability determination of the meuse haute marne mudstone abstract in the underground waste isolation projects such as the andra one in the site of bure the transport properties of the surrounding rock mass is of fundamental importance to measure very low permeability we use the modified version of the pulse test proposed by hsieh et al hsieh p a tracy j v neuzil c e bredehoeft j d silliman s e 1981 a transient laboratory method for determining the hydraulic properties of tight rocks i theory int j rock mech min sci geomech abstr vol 18 pp 245 252 which enables the intrinsic permeability k and the specific storage coefficient s s of rocks such as mudstone to be characterized in this paper the special effort performed on the laboratory apparatus design to ensure a good sensitivity of the rock response with respect to both parameters k and s s is presented in addition two parameters identification procedures are proposed the graphical method given by hsieh et al hsieh p a tracy j v neuzil c e bredehoeft j d silliman s e 1981 a transient laboratory method for determining the hydraulic properties of tight rocks i theory int j rock mech min sci geomech abstr vol 18 pp 245 252 and a parameter identification based on the solution of an inverse problem the efficiency of the apparatus design and the parameters identification procedures is then demonstrated though some pulse tests performed on the meuse haute marne mudstone

fluid and metal sources of the wenquan porphyry molybdenum deposit western qinling nw china the wenquan porphyry moybdenium deposit western qinling nw china with a resource of 247 million tonnes at 0 048 mo formed during triassic collision between south china and north china blocks ore fluids at wenquan vary widely in composition from single phase low salinity aqueous to low salinity vapor and hypersaline inclusions fluid inclusion assemblages in a quartz molybdenite vein contain 60 vol vapor are equant to negative crystal shaped and form clusters or distinct inclusion trails they yield homogenization temperatures of 285 295 c with an estimated trapping temperature of 425 c suggesting a paleodepth of about 5 km calculated at a pressure correction of 100 150 mpa hydrothermal k feldspar from early stockwork veins related to potassic alteration have calculated 18ofluid values of 1 9 to 1 9 hydrothermal sericite from an overprinting phyllic alteration associated with late quartz pyrite veins has calculated dfluid values between 68 and 60 and 18ofluid values from 3 7 to 1 4 these isotopic data suggest that both early and late stage fluids are dominated by magmatic fluids with influx of meteoric water during the late stage exsolution of volatiles from magma in a late stage open system results in more variable d values than an earlier closed system molybdenite and pyrite have 34s values ranging from 1 1 to 6 6 indicating that sulfur at wenquan had a magmatic source a linear relationship between 34s values of sulfides separated from early potassic alteration and late phyllic alteration could reflect incorporation of isotopically heavy evaporate sulfate into source magmas from underlying devonian sedimentary rocks during late alteration the 56fe whole rock values of altered porphyries range from 0 08 to 0 26 similar to 56fe values of 0 15 0 32 for pyrite from quartz veins related to both the potassic and phyllic alteration assemblages the 56fe values of pyrite are positively correlated to but in general slightly lighter than those of altered porphyries indicating similar metal sources moreover both altered porphyries and the pyrite are progressively enriched in heavy fe isotopes from biotite through potassic to late phyllic alteration consistent with isotopic evolution from an early lithostatic load to a late hydrostatic load the triassic intrusive rocks and fluids responsible for mineralization were derived from a deeply sourced hybrid mantle crustal magma crystallizing at a paleodepth of 5 km under lithostatic load external late triassic meteoric or devonian formational fluids became a part of the hydrothermal system during the post fracturing final stage of ore formation under a hydrostatic regime the formation of the wenquan magmatic hydrothermal systems spans the ductile brittle transition based on a normal thermal gradient as constrained by the temperature range of 550 300 c the early high temperature potassic alteration developed under a ductile regime whereas the later low temperature phyllic alteration correlates to a brittle environment where hydraulic rock fracturing enhances permeability and fluid circulation most sulfur and metals were precipitated from vapor rich fluids resulting from cooling and expansion of a single phase fluid exsolved from a hybrid magma

geochronology geochemical and sr nd hf pb isotopic compositions of the granitoids in the yemaquan orefield east kunlun orogenic belt northern qinghai tibet plateau implications for magmatic fractional crystallization and sub solidus hydrothermal alteration abstract a general consensus has emerged that high field strength elements hfse can mobile to some extent in a hydrothermal fluid however there are hot debates on whether sub solidus hydrothermal alteration can lower the nb ta ratio in evolved melts in this study we present petrography geochronology and geochemistry of the barren and mineralized rocks in the yemaquan skarn iron deposit northern qinghai tibet plateau to probe magmatic hydrothermal transition the barren rocks consist of diorites granodiorites granites and syenogranites whereas the porphyritic granodiorites are associated with mineralization for an excellent consistency between the magmatic zircon u pb age 225 2 ma and the hydrothermal phlogopite 40 ar 39 ar age 225 1 5 ma the sr nd hf pb isotopic data demonstrate that the yemaquan granitoids are originated from a relatively homogenous enriched mantle with different degrees of crust contamination assimilation fractional crystallization afc trace elements signatures indicate that the porphyritic granodiorites related to mineralization display amphibole crystallization for high water contents whereas the barren granites have gone through biotite crystallization due to potassium enrichment by continuous upper crust contamination both of which are responsible for their nb ta ratios respectively modeling results suggest that a basaltic melt with nb ta ratio of 15 3 can reach a minimum nb ta ratio of 12 in the producing granodioritic melt by amphibole fractional crystallization based on partition coefficients of nb and ta between amphibole and melts from previous experiments this may explain the average nb ta ratio 13 7 of the barren granodiorites while it cannot account for the average nb ta ratio 8 4 of the mineralized porphyritic granodiorites and it is even lower than that of the granites 10 3 with biotite fractional crystallization exsolution of a magmatic hydrothermal fluid is inevitable when a water saturated magma emplaced in shallow crust leading to a transportation of certain chemical components from the magmatic melts to exsolved fluids because nb seems more mobile than ta in fluorine bearing fluids we contend that a preferentially transport nb over ta by sub solidus hydrothermal alteration can further lower the nb ta ratios of the mineralized porphyritic granodiorites which may also result in a broad range of hfse contents and their ratios in the altered porphyritic granodiorites formed in a post magmatic process

sr nd os s isotope and pge geochemistry of the xiarihamu magmatic sulfide deposit in the qinghai tibet plateau china the newly discovered xiarihamu ni cu deposit is located in the eastern kunlun orogenic belt in the northern part of the qinghai tibet plateau western china it is the largest magmatic ni cu sulfide deposit found thus far in an arc setting worldwide and ranks second in china in terms of total ni resources fe ni cu sulfide mineralization occurs in a small ultramafic body that is part of a larger mafic ultramafic complex formed by protracted silurian early devonian basaltic magmatism the mineralized ultramafic body is composed predominantly of lherzolite and olivine websterite with minor dunite websterite and orthopyroxenite here we report new pge platinum group element data and the results of a new integrated sr nd os s isotope study the initial concentrations of rh and pd in the parental magma are estimated to be 0 014 ppb and 0 24 ppb respectively which are more than one order of magnitude lower than those in undepleted mantle derived magmas such as many continental picrites the observed pge depletions in the xiarihamu parental magma are attributed to sulfide retention in the source mantle because the degree of partial melting required to generate the xiarihamu primary magma was not high enough for a magma of that composition to dissolve all sulfides in the source the 87sr 86sr i ratios and end t of the xiarihamu host rocks range from 0 7062 to 0 7105 and from 1 97 to 5 74 respectively indicating 5 30 wt crustal contamination in the xiarihamu magma these data also reveal that the source mantle for the xiarihamu magma is isotopically sr nd more enriched than that for the average cenozoic arc basalt the os t and 34s values of sulfide ores from the xiarihamu deposit range from 78 to 1393 and from 2 to 6 respectively these values clearly indicate addition of crustal os and s to the xiarihamu parental magma metal tenors such as ni and rh are inversely correlated with os t and 34s values this indicates that mixing between different pulses of magma with different isotope compositions took place during magma emplacement at xiarihamu and that external s played a critical role in the formation of the xiarihamu magmatic ni cu sulfide deposit

geochemical constraints on models for secondary petroleum migration along the upper devonian rimbey meadowbrook reef trend in central alberta canada abstract the upper devonian rimbey meadowbrook reef trend of central alberta canada is one of the classical examples that was originally used to support gussow s model of differential hydrocarbon entrapment however the clear discrepancies existing between the ideal hydrocarbon distribution predicted by this model and the one actually observed led to several alternative geological models most of which have not been constrained by organic geochemical data the present study uses a wide range of bulk and molecular parameters to determine the oil source characteristics and thermal maturity along the reef trend the concentrations and isomeric distributions of alkylcarbazoles and non alkylated benzocarbazoles in oils are employed to study petroleum migration pathways and to constrain the existing secondary petroleum migration models the data indicates that gussow s principle is generally applicable as the oils in the up dip direction generally have longer implied migration distances although this is not always the case other factors not recognized previously such as the presence of two subfamilies of the duvernay formation sourced oils may also have contributed significantly to the discrepancies in the oil and gas distributions between the model predictions and the actual observational data

uhp metamorphism recorded by coesite bearing metapelite in the east kunlun orogen nw china the east kunlun orogen eko is the nw part of the central china orogenic belt which records the evolutionary history of the proto and palaeo tethys oceans from the cambrian to the triassic an early palaeozoic eclogite belt has been recognized in recent years which extends discontinuously for 500 km as three eclogite bearing terranes in this study we report an integrated study of zircon grains from mica schists accompanying the eclogites in terms of mineral inclusions u pb age systematics and p t conditions the presence of coesite is identified as inclusions within the metamorphic domain of zircons which provides unambiguous evidence for subducted terrigenous clastic rocks of the proto tethys ocean exhumed from coesite forming depths u pb dating of the metamorphic zircons yields a concordia age of 426 5 0 88 ma which is likely to be the time of ultrahigh pressure metamorphism in the kehete terrane p t calculations suggest that metapelite may have experienced a clockwise p t path with peak p t conditions of 685 41 c and 28 kbar and equilibrated at 482 566 c and 5 6 8 9 kbar during subsequent exhumation the high pressure ultrahigh pressure hp uhp metamorphic belt within the eko may have formed by collision between the qaidam block and the south kunlun block as a consequence of the closure of the proto tethys ocean

fractionation of azaarenes during oil migration abstract a comparative study of alkylbenzoquinolines in crude oils and rock extracts bitumens from japan and sumatra shows that the ratios of nitrogen masked isomers nmis to nitrogen exposed isomers neis and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens also a regular increase in the ratios of nmis to neis with increasing migration distance is observed for a series of crude oils from the sarukawa oil field northeastern japan these results are attributed to the preferential migration of nmis caused by their weak adsorption on clay minerals and or their low solubility in interstitial water and the selective removal of lower honologs caused by their irreversible adsorption onto clays during oil migration which are regarded as geochromatographic phenomena it is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration

geochronology petrology and hf s isotope geochemistry of the newly discovered xiarihamu magmatic ni cu sulfide deposit in the qinghai tibet plateau western china this paper reports the first set of data for the newly discovered xiarihamu magmatic ni cu sulfide deposit in the eastern kunlun paleozoic arc terrane which is located in the northern part of the qinghai tibet plateau an on going drilling campaign reveals 100 million tons of sulfide mineralization with the average grade of 0 8 wt ni and 0 1 wt cu for the deposit this makes the xiarihamu deposit one of the 20 largest magmatic ni cu sulfide deposits in the world and the largest ever found in arc settings the deposit is hosted in a small ultramafic body intruding older gabbroic and metamorphic rocks new zircon u pb isotope age data reveal that the ultramafic body 411 6 2 4 ma is 20 ma younger than the host gabbroic intrusion 431 3 2 1 ma the ultramafic body is composed predominantly of lherzolite and olivine websterite with minor dunite websterite and orthopyroxenite mineralization mainly occurs as sub horizontal to gently dipping 30 disseminated sulfide zones that are generally concordant with the lithological structure of the ultramafic intrusion the lateral extension and thickness of individual mineralized zones are up to 200 m and 100 m respectively sulfide mineral assemblages are composed of pyrrhotite pentlandite and chalcopyrite the xiarihamu ultramafic rocks show light ree enrichments and pronounced negative nb anomalies plus significant ca depletion in olivine 700 ppm ca which are characteristic of many arc basalts in the world olivine crystals in the xiarihamu ultramafic rocks have relatively primitive compositions with fo contents up to 90 mol close to the mantle value the contrasting ni contents of olivine crystals with similar fo contents from different sulfide mineralized zones in a single drill core indicate that at least two pulses of sulfide laden magma with different ni compositions were involved in the development of the deposit estimated parental magma for the xiarihamu lherzolites contains 52 4 wt sio2 and 9 8 wt mgo which are within the ranges of boninites worldwide supporting the interpretation that the xiarihamu sulfide ore bearing ultramafic intrusion is the product of subduction related boninitic magmatism the ehf t values of zircon crystals from the xiarihamu ultramafic rocks vary from 1 to 5 indicating minor crustal contamination of the parent magma the involvement of external sulfur in the genesis of the xiarihamu magmatic sulfide deposit is evident from higher 34s values of sulfide ores 3 5 to 6 8 than typical mantle value 0 2 although the actual contaminants are yet to be identified

petrogenesis of granitoids in the dewulu skarn copper deposit implications for the evolution of the paleotethys ocean and mineralization in western qinling china abstract the tethyan tectonic domain hosts numerous world class mineral deposits among these the dewulu skarn copper deposit in western qinling china belongs to the paleotethys ore belt the skarn and orebodies here occur as stratoids or lenses at the contact between the triassic dewulu intrusive complex and permian marine clastic and carbonates alteration minerals include prograde skarns garnet diopside wollastonite plagioclase hornblende actinolite tremolite epidote chlorite calcite quartz and sericite the main ore types include early disseminated skarn type replacement orebodies and late stage quartz sulfide veins chalcopyrite is the major ore mineral along with pyrite bornite and sphalerite the dewulu intrusive complex comprises quartz diorite quartz diorite porphyry and dioritic mafic microgranular enclaves mme the mmes are spheroidal in shape and have igneous mineral assemblages acicular apatites complex oscillatory zoned plagioclase and quartz megacrysts surrounded by mafic minerals the mmes are metaluminous and calc alkaline to high k calc alkaline and possess relatively high ni cr and mgo contents and mg values they display sub parallel patterns in trace element spider diagrams and rare earth element ree plots they are also characterized by the enrichment of rb u and th depletion of ba sr nb and ta and negative eu anomaly zircon la icp ms u pb dating of the dioritic mme yields an age of 247 0 2 2 ma coeval with the host quartz diorite quartz diorite porphyry and ore related sericite 40ar 39ar plateau ages within analytical uncertainties oxygen fugacity estimated from trace element compositions of zircons from the dioritic mme shows fmq 3 3 the zircons have negative ehf t values in a range of 8 0 to 3 3 corresponding to two stage model ages ranging from 1 48 to 1 78 ga the integrated data from petrology geochronology and bulk geochemistry suggest that the early triassic granitoids associated with cu skarn mineralization at dewulu were products of arc magmatism and involved magma mixing in an active continental margin setting the magma was sourced through partial melting of enriched sub continental lithospheric mantle that had been previously modified by slab derived melt during the continuous northward subduction of the paleotethys oceanic slab

the ophiolites of the tibetan geotraverses lhasa to golmud 1985 and lhasa to kathmandu 1986 ophiolite belts are found in tibet along the zangbo banggong and jinsha river sutures and in the anyemaqen mountains the eastern extension of the kunlun mountains where studied the zangbo suture ophiolites are characterized by apparently thin crustal sequences 3 3 5 km an abundance of sills and dykes throughout the crustal and uppermost mantle sequences common intraoceanic melanges and unconformities and an n morb petrological and geochemical composition the ophiolites probably formed within the main neo tethyan ocean and the unusual features may be due to proximity to ridge transform intersections rather than to genesis at very slow spreading ridges as the current consensus suggests the banggong suture ophiolites have a supra subduction zone petrological and geochemical composition although at least one locality in the ado massif shows morb characteristics however it is also apparent that the dykes and lavas show a regional chemical zonation from boninites and primitive island arc tholeiites in the south of the ophiolite belt through normal island arc tholeiites in the central belt to island arc tholeiites transitional to n morb in the north the ophiolites could represent fragments of a fore arc island arc back arc complex developed above a jurassic northward dipping subduction zone and emplaced in several stages during convergence of the lhasa and qiangtang terranes the ophiolites of the jinsha river suture have a n morb composition where analysed but more information is needed for a proper characterization the anyemaqen ophiolites where studied have a within plate tholeiite composition and may have originated at a passive margin it is not however certain whether true oceanic lithosphere as opposed to strongly attenuated continental lithosphere existed in this region

petrographical and petrophysical characterization of the late cretaceous naparima hill formation central range trinidad west indies abstract the late cretaceous naparima hill formation in the south trinidad basin southeast caribbean is a prolific source rock with a potential for unconventional hydrocarbon exploration it is exposed across the central range and extends to the city of san fernando this study characterized the naparima hill source rock using petrographic analysis techniques x ray diffraction and thin section analysis and petrophysical techniques these techniques were applied to outcrop samples that were collected from 11 locations firstly petrographic analysis was used to determine the mineral composition and lithofacies secondly plugs were taken perpendicular to bedding and the bulk density was determined in dry conditions thirdly porosity and grain density were determined using a porosimeter at ambient conditions finally permeability measurements were obtained at 10 mpa to 130 mpa effective pressures using the transient pulse decay technique the results show that the source rock is dominated by silica with carbonate as secondary minerals four lithofacies were identified a siliceous calcareous mudstone b calcareous mudstones interbedded with black chert c carbonate rich mudstone with nodular chert and d siliceous mudstone ranges of 5 9 to 30 8 2362 to 2668 kg m3 and 1804 to 2350 kg m3 were determined for porosity grain density and bulk density respectively the permeability ranges from 3 96 10 20 to 5 94 10 18 m2 and shows very little dependence on the effective pressure permeability and porosity are moderately correlated r2 0 6 there is no relationship between permeability and mineralogical composition the observed microfractures diagenetic processes and grain sorting are factors that have affected the permeability porosity relationship to varying degrees however none of these factors can be considered as the main intrinsic factor controlling the permeability of the samples overall it is difficult to predict the permeability of the naparima hill formation with any of the proxies density mineralogy and porosity determined in this study

early mesozoic magmatism within the tibetan plateau implications for the paleo tethyan tectonic evolution and continental amalgamation

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

the tectonic evolution of the east kunlun orogen northern tibetan plateau a critical review with an integrated geodynamic model abstract the east kunlun orogen is an integral component of the northern qinghai tibet plateau here we synthesize the geologic geochemical geochronological and stratigraphical dataset and propose an integrated geodynamic model to illustrate the tectonic evolution of this orogen this review also provides important insights on the complex phanerozoic plate tectonic processes we envisage the protracted multi stage accretion and collision of a collage of terranes during the subduction and closure of the south kunlun and anemaqen oceans from the neoproterozoic to early mesozoic the east kunlun orogen is tectonically divided into the north kunlun terrane nkt south kunlun terrane skt muz tagh anemaqen terrane mat and hoh xil bayan har terrane hbt from the north to south of which evolution can be divided into six stages from late neoproterozoic early mesozoic age 550 ma 200 ma i ca 540 481 ma ii ca 481 424 ma iii ca 424 370 ma iv ca 370 271 ma magmatic gap v ca 271 224 ma and vi ca 224 201 ma the nkt as an active continental margin initiated at ca 450 ma as a consequence of backarc ocean lithosphere subduction in the late ordovician middle silurian stage ii the closure of back arc basin led to an oblique collision between the nkt and skt during the early middle silurian stage ii and to a post collisional environment in the late silurian middle devonian stage iii the skt and mat developed as a young island arc both carrying large amounts of ocean island arc granitoids oags and ssz supra subduction zone type ophiolites together with island arc tholeiite iat as a consequence of bidirectional subduction of proto tethys ocean stage i during the collision between skt and nkt the skt transformed from a young island arc into a mature island arc with thickening crust and the granitoids geochemically evolved from the oags to cags continental arc granitoids wpgs within plate granitoids in the late ordovician middle silurian stage ii the collision between skt and mat probably occurred after the middle devonian stage iii as evidenced from the absence of the upper devonian strata in the skt the skt and mat is interpreted as an exotic terrane that has been accreted onto the continental margin and contributed significantly to the continental growth in this orogenic belt a magmatic quiescence occurred during ca 370 270 ma stage iv associated with subduction polarity reversal a new subduction zone initiated at the southern margin of the mat after the middle permian stage v which subsequently resulted in extensively development of calc alkaline granitoids in the nkt skt and mat the progressive chronology change of granitoids from nkt to further south maybe the joint results of flat subduction and slab rollback which make magmatism center retrograde migrate towards the trench the final closure of the anemaqen ocean might have occurred in the late triassic stage vi as indicated by the upper triassic babaoshan terrestrial molasse formation and development of cags and wpgs in the hbt which resulted in the accretion of the north qiang tang microcontinent

provenance analysis of the mesozoic hoh xil songpan ganzi turbidites in northern tibet implications for the tectonic evolution of the eastern paleo tethys ocean 1 mesozoic strata of the hoh xil songpan ganzi complex in northern tibet are exposed in a vast 370 000 km2 triangle shaped orogenic belt bound by the longmen shan thrust belt in the east the kunlun terrane and north china block in the north and the qiangtang terrane and yidun arc in the south these strata consist of middle upper triassic submarine fan and deep marine facies rocks that were deposited in the paleo tethys ocean late triassic early jurassic contractional deformation in the eastern hoh xil songpan ganzi complex marks the demise of the paleo tethys ocean basin and the accretion of the gondwana derived qiangtang terrane to eurasia we conducted geological mapping regional stratigraphic analyses and u pb geochronology of detrital zircons n 4128 on the mesozoic sequences exposed in the hoh xil songpan ganzi complex kunlun terrane and qiangtang terrane we identify for the first time marine silciclastic sandstone and shale of jurassic age in the northwestern hoh xil songpan ganzi complex that unconformably overlie upper triassic turbidites zircon age data indicate that the middle upper triassic marine gravity flow deposits of the hoh xil songpan ganzi complex were shed from the north and south china blocks and middle late triassic ultrahigh pressure qinling dabie orogenic belt as well as the kunlun and qiangtang terranes in addition the detrital zircon results suggest vast sediment source to sink distances 1500 km for the middle upper triassic hoh xil songpan ganzi strata which is consistent with tectonic models for the paleo tethys ocean basin that incorporate significant components of horizontal tectonic transport like opening of large back arc basins in response to oceanic slab rollback

subduction and accretionary tectonics of the east kunlun orogen western segment of the central china orogenic system abstract the kunlun orogen is generally divided into the east kunlun orogenic belt e kob and the west kunlun orogenic belt w kob by the altyn tagh fault the e kob forms part of the western segment of the central china orogenic system ccos and is considered to have formed by the collision between the qaidam block and qiangtang or bayanhar terrane as a consequence of the closure of the kunlun ocean branch of the paleo tethyan ocean based on a compilation recently published high quality data this contribution provides an overview of the composition nature and ages of the principal tectonic elements including ophiolitic melanges and related volcanic rocks intrusive plutons and sedimentary cover sequences in the e kob according to multiple lines of evidence from these tectonic elements we proposed herewith a paleozoic triassic subduction and accretionary tectonic model to interpret the spatiotemporal tectonic framework plate subduction polarity and tectonic processes from accretion to collision of the e kob three main ophiolitic melange zones are identified in the e kob from north to south they are the qimantagh xiangride ophiolitic melange zone qxm the aqikekulehu kunzhong ophiolitic melange zone akm and the muztagh buqingshan anemaqen ophiolitic melange zone mbam according to these ophiolitic melange zones the e kob is divided into four major tectonic units the north qimantagh belt the central kunlun belt the south kunlun belt and the bayanhar terrane based on several lines of evidence from geology geochemistry and geochronology the south kunlun belt is interpreted as a paleozoic to triassic fore arc and accretionary complex related to northward subduction of the kunlun ocean during the ordovician triassic time the akm mabm and the south kunlun belt constitute a wide accretionary complex along the kunlun suture zone that marks final closure of the major paleo tethyan ocean while the qxm represents the best expression of another suture that records final closure of the qimantagh back arc basin the central kunlun belt as a long lived island arc terrane from ordovician to triassic times rifted from the qaidam block due to the spreading of the qimantagh back arc basin during the period of ca 485 425 ma taken into all the geological geochemical and geochronological lines of evidence together a trench arc back arc basin tectonic system in the e kob was built up and evolved into a protracted and long lived northward subduction and accretion along the kunlun suture during paleozoic and triassic time

detrital heavy mineral constraints on the triassic tectonic evolution of the west qinling terrane nw china implications for understanding subduction of the paleotethyan ocean we have examined the triassic sediments in the west qinling terrane northeastern tibet these sediments consist mainly of flysch and shallow sea and fluvial deposits with abundant lithic and heavy mineral detritus sandwiched between and overlying late paleozoic and early middle triassic ophiolitic melanges volcanic and metamorphic detritus dominates the lithic component of lower triassic sandstones accompanied by high cr spinel pyroxene and magnetite contents indicating a mixed ophiolite and metamorphic source detrital mineral geochemistry further suggests that ophiolitic high grade metamorphic basic and intermediate acidic igneous rocks must have been exposed and deeply eroded in their source area abundances of zircon rutile garnet tourmaline and epidote are greater in the middle triassic samples and granitic and volcanic sources are the major contributors of detrital clasts considering these new observations on sedimentary petrography and detrital heavy mineral geochemistry along with published data on paleocurrents detrital zircon u pb ages sedimentary facies and regional magmatism we suggest that these triassic sediments represent the sedimentary fill of a forearc basin that overlies a late paleozoic ophiolitic complex a south facing andean type convergent continental margin system developed along the southern margin of the north china block during the triassic in response to northward subduction of the paleotethyan ocean

age geochemistry and tectonic setting of buqingshan ophiolites north qinghai tibet plateau china abstract the buqingshan ophiolite complex is a sector of the a nyemaqen ophiolite belt in the east kunlun southern marginal suture zone in the northern part of the qinghai tibet plateau the wnw trending ophiolite complex consists of metaperidotite gabbro diabase pillow basalt massive basalt and pelagic sedimentary rocks including radiolarian chert we have determined that early paleozoic and early carboniferous early permian ophiolites are present in this ophiolite complex that were previously thought of permian middle triassic age a zircon u pb age of 467 2 0 9 ma for gabbro and a rb sr isochron age of 481 130 ma for diabase and gabbro have been obtained from the early paleozoic ophiolite slice and middle late ordovician acritarchs have been found in the melange matrix that envelopes the sliver we interpret the first two ages to represent the formation age of the ophiolite granodiorite tonalite plutons with a zircon u pb age of 402 24 ma intrude the slice early carboniferous early permian radiolarians have been discovered in cherts and argillaceous cherts in the second ophiolite slice geochemistry indicates that metaperidotites in the first slice represent a depleted ocean lithosphere mantle most mafic rocks in the early paleozoic ophiolite are of n morb type with small amount of t morb and they resulted from the magma from the depleted oceanic lithosphere mantle with little crustal contamination the basalts in the early carboniferous early permian ophiolite have similar characteristics to the mafic rocks and also show dupal anomaly and a mixed source of dmm and em ii the original formation environments of the two stage ophiolites are both mid ocean ridges these lines of evidence suggest that a mature early paleozoic kunlun qilian qinling ocean basin and a mature paleotethyan ocean basin once existed in the study area

ophiolites of the kunlun mountains china and their tectonic implications abstract three ophiolite belts ranging in age from cambrian to triassic provide valuable data on the tectonic evolution of the kunlun mountains which lie along the northern margin of the tibetan plateau all of the ophiolites contain dismembered but nearly complete assemblages of peridotite mafic and ultramafic cumulates pillow and massive lavas and radiolarian cherts 1 the oldest belt contains ophiolites of cambrian age but the initial spreading of the ocean basin most likely began in the late proterozoic these ophiolites outcrop in the central part of the eastern kunlun extend for at least a few hundred kilometers and are believed to reflect a small ocean basin closure of this ocean led the accretion of south kunlun block to the north kunlun block and tarim craton ophiolitic lavas in this belt have island are affinities 2 a second belt of early carboniferous ophiolites extends nearly 600 km along the northern margin of the western kunlun lavas in this belt are basalt basaltic andesite and andesite all of which have compositions characteristic of volcanic arcs this ocean basin possibly developed on the basis of the early paleozoic oceanic basin closure of this ocean basin by southward subduction in the early permian produced a suite of calc alkaline volcanic rocks in what is now the central part of the western kunlun 3 the third belt extends nearly 1200 km along the southern margin of the eastern kunlun and contains numerous ophiolites of early permian to middle triassic age these ophiolites are highly tectonized containing volcanic rocks with the geochemical characteristics of mid ocean ridges oceanic islands and volcanic arcs this belt is tentatively interpreted as the suture zone between gondwana and eurasia

triassic turbidites in the west qinling mountains nw china part of the collisional songpan ganzi basin or an active forearc basin abstract lower to middle triassic clastic rocks in the west qinling mountains along ne margin of the qinghai tibet plateau are generally regarded as part of the songpan ganzi flysch basin however relatively little attention has been paid to the age and provenance of these units new petrological and geochemical results demonstrate that these sediments accumulated along an active continental margin and are dominated by feldspathic litharenite and lithic arkose with low mineral and compositional maturity they were derived primarily from a continental arc source dominated by intermediate to felsic igneous rocks with a minor contribution from older metamorphosed and sedimentary sources turbidite samples yielded two primary detrital zircon u pb age populations of ca 273 ma and ca 435 ma which is different from the early triassic ca 252 ma and middle silurian ca 427 ma age populations that dominate the songpan ganzi basin these data together with paleocurrent results indicate that the south qilian belt was the primary source origin because this belt contains both early paleozoic andean type igneous and magmatic rocks and has a basement of precambrian metamorphosed rocks regionally an andean type arc traverses the south qilian belts and extends into the west qinling mountains and kunlun orogen which formed by north directed subduction of the paleo tethyan ocean during the early to middle triassic voluminous detritus that originated from the qilian and kunlun orogens as they were uplifted and eroded was transported to the south and deposited in the forearc area in front of the a nimaqen mianlue suture

the early triassic andean type halagatu granitoids pluton in the east kunlun orogen northern tibet plateau response to the northward subduction of the paleo tethys ocean abstract voluminous granitoids located in the east kunlun orogen eko play an important role in characterizing the crustal growth and northward subduction of the paleo tethys oceanic lithosphere this paper presents new petrological whole rock geochemical zircon u pb isotope geochronological and sr nd hf isotopic data for the halagatu granitoids hg pluton the hg pluton comprises several different textural and compositional types i e medium to fine grained granodiorites mg porphyritic monzogranites pmg coarse grained monzogranites cmg and dark mafic microgranular enclaves me u pb dating of zircons from the hg pluton yielded a weighted mean 206pb 238u age of 248 244 ma which represents the crystallization age of the hg pluton the whole rock geochemical data indicate that the pmg cmg and mg have similar geochemical features for example they are classified as high k calc alkaline metaluminous to wildly peraluminous i type granitoids with negative nb ta and ti anomalies low mg and al2o3 feot mgo tio2 values and high th y ratios these characteristics suggest the parent magmas were crustally derived in contrast the me are characterized by medium k calc alkaline and metaluminous compositions low th y ratios and relatively high mg cr and ni values likely suggesting these magmas were derived from a mantle source furthermore the host granodiorites and microgranular enclaves have consistent sr nd hf isotopic features with end t values of 6 10 to 4 30 and zircon ehf t values of 7 8 to 0 4 indicating an enriched subcontinental lithospheric mantle sclm on the basis of these values and the whole rock geochemistry the hg pluton magmas were the result of mixing between lithospheric mantle derived and crust derived magmas and that fractional crystallization fc played an important role in the formation of the hg pluton the combination of these new data with previously published data reveals that the hg pluton was emplaced in a continental magmatic arc setting by the northward subduction of a branch of the paleo tethys ocean buqingshan ocean beneath the east kunlun qaidam terrane ekt and that the buqingshan ocean began to subduct strongly northward in the late permian ca 260 ma with subduction terminating during the late middle triassic ca 240 ma

effect of maturity and petroleum expulsion on pyrrolic nitrogen compound yields and distributions in duvernay formation petroleum source rocks in central alberta canada abstract a quantitative study of pyrrolic nitrogen compounds was conducted on a series of marine carbonate petroleum source rock extracts taken from the upper devonian duvernay formation in the central alberta portion of the western canada sedimentary basin with increasing thermal maturity concentrations of various pyrrolic nitrogen compounds in the rock extracts increase drastically together with significant compositional variations related to alkyl substitution position the study provides circumstantial evidence for adsorptive interactions operating between organic nitrogen compounds and solid organic mineral phases in subsurface sedimentary rocks during petroleum generation and expulsion the absolute concentrations and relative distributions of pyrrolic nitrogen compounds in the extracts of different maturity ranges provide background information for the calibration of such data in migrated petroleums as an independent measurement of secondary oil migration range of duvernaysourced oils in the basin

constraints of late cambrian mafic rocks from the qushi ang ophiolite on a back arc system in a continental margin east kunlun orogen western china abstract early palaeozoic ophiolites emplaced in the central east kunlun fault zone cekf offer critical clues to the tectonic evolution of the proto tethys ocean and the accretionary process of cekf the qushi ang ophiolite located within the eastern segment of the cekf consists of dismembered serpentinites meta gabbros and meta basalts this study presents petrologic whole rock geochemical and in situ zircon u pb and hf isotope data for basic rocks both metagabbros and metabasalts from the qushi ang ophiolite to constrain the formation age and tectonic setting of the ophiolite zircons from two meta gabbro samples yield concordant u pb ages of ca 498 ma and ca 505 ma indicating that the qushi ang ophiolite was formed in the late cambrian the meta gabbros and meta basalts show significant enrichment in large ionic lithophile elements liles such as cs rb ba u and pb and depletion in high field strength elements hfses such as nb ta zr and ti suggesting the influence of fluids derived from a subducting oceanic slab on the n morb normalized trace element diagrams these rocks share similar features with arc basalts and back arc basalts and far away from fore arc basalts fabs and normal mid ocean basalts n morbs low zircon ehf t values 2 9 to 0 2 for the meta gabbros further indicate that the qushi ang ophiolite likely originated from an weakly enriched mantle wedge source geochemical discrimination diagrams show that the qushi ang ophiolite formed in a back arc basin setting our new analyses combined with previous data suggest that the qushi ang ophiolite represents a relict of a nascent back arc basin similar to the scenario of the okinawa trough in western pacific

origin of devonian mafic magmatism in the east kunlun orogenic belt northern tibetan plateau implications for continental exhumation

continuity of the north qilian and north qinling orogenic belts central orogenic system of china evidence from newly discovered paleozoic adakitic rocks abstract adakitic intrusive rocks of 430 450 ma were discovered in the north qilian orogenic belt the western section of the central orogenic system cos in china these adakitic rocks were lower crust melts rather than slab melts as indicated by their crustal ce pb nb u ti eu and nd sm ratios and radiogenically enriched 87sr 86sr i of 0 7053 0 7066 and end t of 0 9 to 1 7 while they are all characterized by low yb 65 and la yb n 13 7 ratios these adakitic rocks are classified into the low mgo ni cr and high mgo ni cr groups the low mgo samples were derived from partial melting of thickened lower crust whereas the high mgo samples were melts from delaminated lower crust which subsequently interacted with mantle peridotite upon ascent adakitic rocks from the adjacent north qinling orogenic belt also originated from thickened lower crust at 430 ma in addition the north qilian and north qinling orogenic belts both consist of lithological assemblages varying from subduction accretionary complexes at south to central arc assemblages which include adakitic rocks then to backarc phases at north such a sequence reflects northward subduction of the qilian and qinling oceans in these two orogenic belts the occurrence of adakitic rocks of common origin and ages together with the similarities in tectonic configurations and lithological assemblages are considered to be the evidence for the continuity between eastern qilian and western qinling forming a 1000 km early paleozoic orogenic belt in such a tectonic configuration the qilian and qinling oceans that subducted from south possibly represent parts of the large proto tethyan ocean this inference is supported by the coexistence of early paleozoic coral and trilobite specimens from asia america and australia in the north qilian orogenic belt post 400 ma volcanic rocks occur in the north qinling orogenic belt but are absent in the north qilian orogenic belt indicating that these two orogenic belts underwent distinct evolution history after the closure of the proto tethyan ocean 420 ma

permeability of illite bearing shale 1 anisotropy and effects of clay content and loading direction relative to bedding clay content 40 65 and effective pressure pe 2 12 mpa permeability k is anisotropic at low pe measured k values for flow parallel to bedding at pe 3 mpa exceed those for flow perpendicular to bedding by a factor of 10 both for low clay content lc and high clay content hc samples with increasing pe k becomes increasingly isotropic showing little directional dependence at 10 12 mpa permeability depends on clay content k measured for lc samples exceed those of hc samples by a factor of 5 permeability decreases irreversibly with the application of pe following a cubic law of the form k k0 1 pe p1 m 3 where k0 varies over 3 orders of magnitude depending on orientation and clay content m is dependent only on orientation equal to 0 166 for bedding parallel flow and 0 52 for flow across bedding and p1 18 27 mpa appears to be similar for all orientations and clay contents anisotropy and reductions in permeability with pe are attributed to the presence of crack like voids parallel to bedding and their closure upon loading respectively index terms 5114 physical properties of rocks permeability and porosity 5139 physical properties of rocks transport properties 5112 physical properties of rocks microstructure 1832 hydrology groundwater transport keywords permeability shale connected pore space

multiple episodes of gold mineralization in the east kunlun orogen western central orogenic belt china constraints from re os sulfide geochronology abstract the gouli goldfield 110 t au located in the east kunlun orogen western central orogenic belt of china is one of the most important goldfields in this area in the last decade a number of orogenic gold deposits e g guoluolongwa and annage have been shown to be hosted by rock units of different lithology and ages rhenium osmium re os geochronology of sulfides from gold bearing veins was performed to define the chronologic relationships between gold mineralization present in the metamorphic rocks proterozoic and silurian of the east kunlun orogen sulfides pyrite and chalcopyrite from pyrite quartz vein and polymetallic sulfides quartz vein in the guoluolongwa gold deposit yield re os isochron dates of 374 15 ma mswd 4 6 initial 187os 188os ratio osi 0 06 0 22 and 354 7 ma mswd 0 18 osi 0 13 0 01 respectively similar ages are also revealed by the pyrite mineral separates from the annage gold deposit 383 8 ma and 349 6 ma these ages are interpreted to record the timings of the formation of the two vein types in these deposits which are nominally separated by 20 ma the new re os ages presented here identify the first two late paleozoic devonian and early carboniferous gold mineralizing events in the east kunlun orogen and thus indicate at least two mineralization epochs in this area given ages late triassic of other gold systems and field observations considering the geological background and temporal distribution of gold deposits in adjacent areas western qinling and qaidam qilian we suggest that gold deposits in the western central orogenic belt were formed in collisional post collisional settings being controlled by common tectonic magmatic activities related to the evolution of both the prototethys ocean proterozoic paleozoic and paleotethys ocean paleozoic early cenozoic further the initial os osi obtained from the re os isochron suggest that for the two vein types in the guoluolongwa gold deposit the os and by inference the ore metal au were derived from a mantle like source osi values 0 12 0 13 which should be related to the contemporaneous mantle like magmatism in contrast the pyrite quartz vein in the annage gold deposit possesses a significantly radiogenic osi value 3 65 0 51 given the similar timing of mineralization between the guoluolongwa and annage deposits it is considered that the ore metal likely has a similar origin i e a mantle like source however at annage the hydrothermal fluid interacted with the proterozoic metamorphic host rocks and leached radiogenic os that masks any evidence of a mantle like source

the wulonggou metaluminous a2 type granites in the eastern kunlun orogenic belt nw china rejuvenation of subduction related felsic crust and implications for post collision extension abstract the wulonggou pluton is located in wulonggou area eastern segment of the eastern kunlun orogenic belt nw china and consists of mainly alkali feldspar granites covering an area of about 150 km2 petrogenesis of these granitoids has been investigated through an integrated study of petrography zircon u pb ages whole rock geochemistry and hf nd isotopic compositions u pb dating of magmatic zircons indicated these granites crystallized during 426 424 ma in the middle silurian the granites display high sio2 75 26 77 55 wt k2o na2o 7 98 9 03 wt extremely low mgo 0 04 0 19 wt cao 0 28 0 61 wt and tio2 0 05 0 09 wt contents showing metaluminous calcic alkali and ferroan features enrichment in rb and some hfses zr u nb ta and y depletion in sr ba p and ti mostly right inclined ree curve flat hree patterns high 10 000 ga al and intensively negative eu anomalies exhibiting an a2 type granite affinity with y nb 1 2 mostly the primitive magma of these large quantities of granites was generated under a high temperature low pressure reduced and anhydrous environment indicating intense upwelling of asthenosphere combining with the positive uniform zircon ehf t values of 0 2 to 3 8 and decoupled end t values of 4 9 to 2 1 at t 424 ma it can be concluded that subduction related juvenile materials probably calc alkaline granitoids are the source of these a type granites geochemical studies of wulonggou granites spatial and temporal distributions of regional magmatism metamorphism and sedimentary records throughout the eastern kunlun orogen belt jointly indicate that the whole orogenic belt was in a typical post collision extension setting and experienced an isostatic uplift during the middle silurian triggered by delamination after the convergence of the northeastern margin of gondwana

closure of the east paleotethyan ocean and amalgamation of the eastern cimmerian and southeast asia continental fragments abstract the phanerozoic record of southeast asia preserves the history of opening and subsequent consumption of the paleotethyan ocean and the assembly of continental fragments into asia as part of the broader scale reconstruction of pangea however uncertainty remains as to which of the many suture zones in southeast asia represents the relict of the main ocean when final ocean closure occurred and the assembly history of the eastern cimmerian and southeast asia continental fragments our overview of the geological features of the suture zones the bounding continental fragments and their magmatic metamorphic and sedimentary records resolves many of these key issues the sedimentary biogeographical structural lithological geochemical and geochronological data from the changning menglian inthanon and bentong raub suture zones argue for their linkage with the longmu co shuanghu suture zone in central tibet and together constitute the main east paleotethyan ocean relict the eastward subduction of the ocean resulted in the development of a series of magmatic arc back arc basin and continental fragments in southeast asia including from west to east the lincang sukhothai east malaya arc the jinghong nan sa kaeo back arc basin the simao west indochina fragment the luang prabang loei back arc basin the south indochina fragment the wusu and truong son back arc basins the north indochina fragment the jinshajiang ailaoshan song ma branch back arc basin and the south china block assembly of these fragments resulted in indosinian high temperature and high pressure metamorphism and related tectonothermal event available data indicate a switch from subduction of the main east paleotethyan ocean to the collision of the sibumasu with simao indochina blocks at 237 ma with subsequent syn and post collisional events at 237 230 ma and 230 200 ma respectively along the changning menglian inthanon and bentong raub suture zones the timing of initial syn and post collision events along the jinshajiang ailaoshan song ma suture zone with its record of back arc basin closure is at 247 ma 247 237 ma and 237 200 ma generally 10 ma older than that along the changning menglian inthanon and bentong raub suture zones our synthesis of all available data enables establishment of a comprehensive geodynamic model for the east paleotethyan evolution this model links the spatial temporal pattern across southeast asia into a series of tectonic events including ocean back arc basin opening subduction closure subsequent assemblage and orogenic collapse along with associated igneous metamorphic and sedimentary activities

new cambrian and ordovician paleomagnetic poles for the north china block and their paleogeographic implications multicomponent magnetization has been revealed in several cambrian and ordovician sedimentary units from localities in hebei and shandong provinces of the north china block ncb a well defined component with lower unblocking temperature is characterized by northerly declination and moderate to steep inclination with both polarities and postdates the late cretaceous folding the pole position derived from the overprinted directions is close to both the cretaceous pole for the ncb as well as the present north pole the overprint is not a simple thermal remanent magnetization but is probably a chemical remanent magnetization imposed at moderately elevated temperature during the major episode of regional deformation in the late mesozoic the higher unblocking temperature characteristic components pass reversal baked contact and fold tests and are internally consistent with rocks of different lithologies from widely distributed localities moreover the data exhibit an overall similarity in the magnetic polarity pattern in the stratigraphic sequence at sampled localities hence the high unblocking temperature characteristic component was probably acquired at or near the time of deposition the cambrian and ordovician paleopoles are somewhat different from the other coeval poles for the ncb which are based on much less data and do not pass as many reliability tests but all imply that the ncb was in the equatorial zone in the early paleozoic

heishan mafic ultramafic rocks in the qimantag area of eastern kunlun nw china remnants of an early paleozoic incipient island arc abstract the heishan mafic ultramafic complex in the qimantag mountains of the eastern kunlun orogen consists of olivine pyroxenites pyroxenites gabbros and massive basalts zircons from the gabbros have magmatic sector zoning with th u ratios of 0 5 2 3 and yield a shrimp age of 486 6 ma mswd 0 31 which is taken as the time of magma crystallization spinel pyroxene and plagioclase mineral compositions indicate that the rocks formed in an island arc environment the cumulates have low la yb n ratios 0 6 0 8 and depleted lree patterns high abundances of cr 3031 1185 ppm co 119 50 ppm and ni 953 291 ppm and end t values of about 8 0 the massive basalts have somewhat higher contents of tio2 1 0 1 3 na2o 2 6 2 8 total ree and mg s 55 63 than those of the cumulates the la yb n ratios of the basalts range from 0 8 to 1 2 and the chondrite normalized ree patterns are flat end t values of the basalts range from 7 7 to 9 4 the compositions of the cumulates and volcanic rocks especially their similar nd isotopes suggest that the rocks were derived from similar depleted mantle sources the primary magmas were probably generated in an initial arc environment we conclude that the heishan mafic ultramafic complex in the qimantag area preserves a record of proto tethyan oceanic lithosphere formed in the early paleozoic it possibly marks a suture between the qaidam and north kunlun terranes in the western segment of the eastern kunlun orogen

petrogenesis and tectonic implication of the permian triassic syenogranites from the eastern segment of the east kunlun orogen china abstract permian triassic granitoids are widespread in the east kunlun orogen eko and are influential in the re construction of paleo tethyan tectono magmatic activities in this contribution zircon u pb dating and lu hf isotopic as well as whole rock major and trace elements analysis have been conducted on a series of syenogranite plutons from the eastern segment of the eko to constrain their petrogenesis and tectonic implication the syenogranites are characterized by dominant mineral assemblages of k feldspars and minor plagioclase and biotite in contrast to the coexisting granodiorites that are rich in amphibole and plagioclase zircon u pb dating reveals that the studied syenogranites represent a two stage magmatism from middle permian to late triassic ca 265 ma and 235 232 ma geochemical and mineralogical evidences show that the syenogranites are classified as high k calc alkaline weakly peraluminous highly fractionated di 93 95 and moderately fractionated di 82 91 i type granites they yield negative hf t values 13 25 to 0 11 which together with their high th nb 0 73 4 88 th la 0 29 2 65 and la nb 1 07 4 48 ratios and moderate pressure conditions 7 10 kbar imply magma generation through partial melting of the normal thickened lower crust the magma underwent extensive plagioclase and subordinate k feldspar fractionation during evolution given the old two stage hf model ages tdm2 1270 2100 ma we interpret the ancient lower crust as their dominant source rocks with limited contribution from the juvenile lower crust our new data in tandem with published data show that the middle permian ca 265 ma jialuhe syenogranites were formed during a period of local extension concomitant with the northward subduction of the paleo tethyan ocean in contrast the late triassic qingshuihe 235 ma keri 234 ma wutuo 232 ma and balong syenogranite plutons were generated in response to asthenospheric upwelling lower crust delamination and subsequent continental rifting in a post collisional extension stage along the convergent plate margins

hualong complex south qilian terrane u pb and lu hf constraints on neoproterozoic micro continental fragments accreted to the northern proto tethyan margin abstract the neoproterozoic hualong complex dominates the south qilian terrane it contains mafic to felsic magmatic rocks cherts and turbiditic sediments some of which have been metamorphosed to amphibolite grade and is traditionally regarded as a pre cambrian micro continental block rifted from the south china plate new u pb geochronology of morphologically complex zircons sheds light on the history of the complex garnet bearing amphibolite and quartzite have detrital zircon u pb main peak ages of 1 47 1 78 ga with youngest u pb ages of 967 ma and 964 ma they are intruded by neoproterozoic orthogneisses that crystallized between ca 850 and 940 ma psammitic paragneisses are dominated by 940 780 ma detrital zircon populations with a youngest u pb weighted mean age of 721 3 ma and a main peak at 906 ma metamorphic overgrowths on older zircons record amphibolite facies metamorphism of the hualong complex and correspond to the emplacement of the younger plutonic rocks during the early paleozoic northward subduction of proto tethyan oceanic lithosphere 426 ma and 455 ma detrital zircon populations that originated from synkinematic granitoids dominate quartz mica schist negative to positive hf t values for both 940 850 ma granitic orthogneisses and intruding 460 410 ma granites suggest a crustal mantle mixture source hf t dm1 model ages and inherited zircon u pb ages are the same as those for garnet bearing amphibolites and psammitic gneiss indicating that late magmatic rocks were formed by melting of the accreted neoproterozoic rocks

migration of hydrocarbons in carbonate source rocks of the stasfurt member ca2 of the permian zechstein borehole aue 1 germany the role of solution seams abstract the effects of petroleum migration from carbonate source rocks through preferential expulsion of hydrocarbons from stylolites is investigated this type of expulsion is associated with compositional fractionation saturated hydrocarbons and nso compounds are expelled preferentially pristane and phytane show higher relative expulsion efficiencies than n c 17 and n c 18 alkanes aromatic hydrocarbons especially trimethylnaphthalenes are fractionated by the expulsion processes triterpanes and steranes are not fractionated by expulsion from solution seams and could be valuable tools for oil source rock correlation in carbonate rocks

improved accuracy of u pb zircon dating by selection of more concordant fractions using a high gradient magnetic separation technique abstract a loop of soft iron wire or a paper clip or a ferromagnetic grid mounted between the poles of an electromagnet picks up and allows further magnetic separation of zircons previously found to be non magnetic on a frantz isodynamic separator tests on previously analysed samples indicate that most such zircons that are fairly discordant say 10 can be picked up and isolated from associated grains that are more concordant tests on new samples indicate that even when most grains can be picked up the last few percent of the sample contain less uranium and are more concordant than the bulk sample the degree of discordance is the dominant factor affecting the uncertainty of u pb zircon ages both because of the error amplification in projections and because the assumption of a simple two stage system may not be valid only by eliminating or reducing discordance can errors approaching the uncertainty in a single analysis say 2 m y for 2700 m y rocks be achieved rutile normally concentrated with zircon as non magnetic has been successfully removed from a small amount of low uranium zircon using the high intensity separation technique

geochemistry and zircon u pb geochronology of granitic rocks in the buqingshan tectonic melange belt northern tibet plateau china and its implications for prototethyan evolution abstract the yikehalaer intrusives are distributed in the buqingshan tectonic melange belt at the southern margin of east kunlun china they tectonically intruded the conglomerate of permian gequ formation to the south and the marble of mesoproterozoic kuhai group to the north these intrusives mainly consist of off white coarse and fine grained granodiorite and granite u pb dating of zircons from the intrusive samples yielded weighted mean 206pb 238u ages of 436 7 ma and 437 6 ma indicating early silurian crystallization age the intrusives are high silica na rich i type calc alkalic rocks they are divisible into two subgroups on the basis of their trace element content adakitic rocks in the northern part and normal calc alkalic arc rocks in the southern part rocks in the northern part exhibit high sr 280 493 ppm low y 3 8 11 7 ppm high sr y ratios 23 9 125 0 high light rare earth elements lree heavy rare earth elements hree 15 1 35 7 and invisible eu eu they resemble adakites formed by slab melting in subduction zones however the rocks in the southern part possess the attributes of normal arc rocks in addition the ehf t values of the intrusives are consistently positive 0 6 7 6 implying that they were generated by melting of an isotopically depleted mantle source with insignificant contributions from crustal materials the source residues likely contained 10 20 garnet and hornblende and plagioclase was either absent or totally consumed during partial melting combining the regional tectonic data we conclude that the buqingshan paleo ocean may have started to subduct in middle cambrian until early silurian 436 ma generating an important adakitic magma event during the late stage of oceanic crust subduction moreover the proto tethyan ocean closed and the bayan har east kunlun and qaidam blocks collided during the middle late silurian

the closure of palaeo tethys in eastern myanmar and northern thailand new insights from zircon u pb and hf isotope data abstract two of the major granite belts of southeast asia are the main range and eastern province together these are interpreted to represent the magmatic expression of the closure of palaeo tethys during late palaeozoic to early mesozoic times recent geochronological and geochemical work has better delineated these belts within peninsular malaysia thereby providing important constraints on the timing of palaeo tethys suturing however the northern extension of this palaeo tethyan suture is less well understood here we present new ion microprobe u pb zircon age data from northern thailand and eastern myanmar measured ages of 219 and 220 ma from the kyaing tong granite imply northern extension of the main range province into eastern myanmar the tachileik granite in far eastern myanmar yields an age of 266 ma consistent with published eastern province ages and this therefore constrains the northern extension of the palaeo tethys suture in eastern myanmar we further discuss how this suture may extend northwards into yunnan a late cretaceous age 70 ma measured in thailand represents later magmatic activity and is similar to published magmatic ages from central myanmar this younger magmatism is interpreted to be related to the subduction of neo tethys prior to india asia collision further we present new laser ablation zircon hf isotope data from eastern myanmar which suggest that palaeoproterozoic crust underlies both the main range and eastern province granites our ehf model age of ca 1750 ma from sibumasu the basement underlying eastern myanmar lies within the range of other model ages reported thus far for the baoshan block north in yunnan interpreted by some to be the northern extension of sibumasu

early paleozoic paleomagnetic poles from the western part of the north china block and their implications abstract we collected 917 oriented drill core samples 124 sites from 22 units spanning the early cambrian to middle ordovician formations of the north china block ncb to construct an apparent polar wander path apwp of the early paleozoic for the ncb sampling areas are located in the helanshan tongchuan hancheng and yuncheng luliang regions along the margin of the ordos basin characteristic remanent magnetizations for five periods between the cambrian and ordovician are isolated from 281 samples by careful demagnetization directions cluster around northwesterly direction with upward shallow inclination and its antipode after tilt correction reliability of these five directions is ascertained through positive fold and reversal tests the five cambrian and ordovician paleopoles plot in the present atlantic ocean which is consistent with previously reported paleomagnetic poles a newly constructed apwp between the cambrian and ordovician indicates that the ncb was located in the southern hemisphere around 15 s during cambro ordovician time motion of the ncb between the early and middle cambrian comprised a counterclockwise rotation of 22 3 7 0 and a northward latitudinal displacement of 7 2 6 8 combining the paleobiogeographic and paleoclimatic data with the paleomagnetic implies that the ncb was probably located in east gondwana in the early cambrian and may have separated from gondwana in post early cambrian time the ncb is also inferred to have been located close to siberia and north america during the middle ordovician

geochemical and geochronologic constraints for paleozoic magmatism related to the orogenic collapse in the qimantagh south altyn region northwestern china abstract voluminous and discrete early paleozoic bimodal magmatic suites are thought to be the result of post collisional extension following the amalgamation of east kunlun and altyn tagh in this paper four representative magmatic units were studied for their geochemical fingerprint in conjunction with geochronological studies the 467 445 ma mangya mafic suite shows e morb type rare earth element ree patterns that are the result of asthenospheric interaction with a metasomatized subcontinental lithosphere high k calc alkaline granodiorites intruded at ca 450 ma are characterized by high mg the least fractionated ree pattern without an eu anomaly as well as high sr and low rb sr ratio we interpret these geochemical signals to result from lower crustal melting of garnet amphibolite at pressures between 16 and 22 kbar a 430 420 ma a type granite is interpreted to result from the melting of metaigneous rocks at middle to lower crustal depths lastly a late magmatic pulse occurs between 400 and 380 ma and is represented by the alk granite the alk granite is interpreted to be a product of metapelite melts and is associated with a smaller volume of mafic melts u pb zircon geochronology of paleozoic igneous rocks of the qimantagh south altyn reveals that most of the magmatic episodes are either coeval with or post extensional deformation this phase of extension is supported by the exhumation of hp uhp metamorphic rocks and crustal anatexis collectively the evolutionary stages documented in this study correspond to a succession of post collisional postorogenic and ultimately within plate magmatic episodes the overall features support orogenic collapse via removal of a thickened lithospheric root beneath the east kunlun altyn tagh collisional orogen during early paleozoic

petrogenesis and tectonic significance of the late permian middle triassic calc alkaline granites in the balong region eastern kunlun orogen china numerous calc alkaline granitoid intrusions in the eastern kunlun orogen provide a valuable opportunity to constrain the evolution of the orogen the age and genesis of these intrusions however remain poorly understood the granitoid intrusions near the balong region eastern kunlun orogen consist of granodiorite diorite and syenogranite the granodiorite contains crystallized segregations abundant mafic microgranular enclaves mmes and small quartz diorite stocks in situ zircon u pb dating reveals that the granodiorites and quartz diorites were emplaced between 263 and 241 ma whereas the syenogranite was produced at c 231 ma the granodiorite and quartz diorite have a calc alkaline affinity and are metaluminous and na rich with slightly enriched sr nd isotope compositions the granodiorite is characterized by fractionated ree patterns whereas the quartz diorite displays a relatively flat ree pattern the mmes are consistent with the granodiorite in terms of incompatible elements and sr nd isotope composition compared to the granodiorite and diorite the syenogranite has higher sio 2 k rb th and sr contents and a lower rb sr ratio the results presented here when combined with regional geological data indicate that the granodiorite and quartz diorite were derived from dehydration melting of mafic lower crustal rocks during the n directed subduction of the anyemaqen ocean lithosphere in late permian middle triassic times whereas the syenogranite was produced at a higher crustal level in a syn collisional setting compared to the granodiorite

fractionation of benzocarbazoles between source rocks and petroleums the concentrations of the a and c isomers of benzocarbazoles in a number of crude oils and source rock bitumens were obtained by in house methods and from reported published data the changes in benzocarbazole concentrations and the benzocarbazole a a c ratio relating to source maturity facies and migration are described with increasing source maturity in north sea oils and source rocks up to 0 85 vitrinite reflectance equivalent benzocarbazole concentrations increase due to generation followed by a decrease above 0 85 vitrinite reflectance equivalent due to expulsion dilution by newly generated hydrocarbons comparison of benzocarbazole concentrations between reservoired petroleum and related source petroleum revealed a concentration bias in favour of source petroleum where concentrations of benzocarbazoles reached up to 10 times that found in equivalent reservoired petroleum the differences in benzocarbazole concentrations between related oils and source rocks indicate that the major fractionation is introduced during primary migration and expulsion because when secondary migration is limited as in the miller field we see extensive benzocarbazole fractionation between reservoired petroleum and associated source petroleum the relationships between source rock toc content and petroleum benzocarbazole concentrations and a a c ratios indicate that source organic matter exerts a strong influence on benzocarbazole distributions the introduction of a reservoir source fractionation parameter rsfp defined as the ratio between the concentrations of benzo a benzo c carbazole in reservoired petroleum versus the concentration of benzo a benzo c carbazole in source petroleum enables description of the relationship between reservoired petroleum and source petroleum from different petroleum systems petroleum deriving from clastic source rocks demonstrated high levels of benzocarbazole fractionation between reservoired petroleum and source petroleum during primary and secondary migration compared to petroleum deriving from carbonate systems the rsfp parameter may also be used to examine fractionation effects during migration between different compound types the more polar benzocarbazoles are fractionated more strongly than dibenzothiophene and phenanthrene between reservoired petroleum and source petroleum whereas sometimes source maturity signals do dominate the benzocarbazole signals in migrated oils in other circumstances often associated with clastic source rocks no clear maturity signal is transferred to migrated oils

discovery of early paleozoic eclogite from the east kunlun western china and its tectonic significance abstract eclogites discovered in the eastern part of the east kunlun mountains western china are primarily composed of garnet omphacite quartz rutile the garnets show end member components of 48 55 almandine 1 2 spessartine 19 29 grossularite and 16 29 pyrope and the omphacite has a jadeite content of 21 63 the peak metamorphic assemblage of eclogites records a p t condition of 1 6 gpa and 590 c 650 c zircon u pb dating of the inherited magmatic zircons from fine grained eclogite reveals a neoproterozoic age of 934 ma representing the protolith age of the eclogite zircons from the coarse grained eclogite contain inclusions of garnet omphacite and rutile and yield a weighted mean age of 428 ma indicating the metamorphic age of eclogite the eclogites together with the late cambrian 508 ma high pressure granulite to the west constitute an early paleozoic high pressure metamorphic belt in the east kunlun

migration of hydrocarbons in the tampen spur area norwegian north sea a reservoir geochemical evaluation abstract this paper describes the application of reservoir geochemical protocols to a study of oil field and regional petroleum compositional variations in the major fields in the tampen spur area the tampen spur high is located in the middle of several oil mature to gas mature source rock kitchens and most of the structures might receive petroleum from several different directions based on the definition of several different petroleum populations within the tampen spur area we define five major petroleum charging systems correlating the petroleum population variations with geological information allows us to derive likely migration fill scenarios for many of the oil fields and requires us to invoke a new upper jurassic carrier system in parts of the area connecting brent group reservoirs across major faults based on this hypothesis two exploration wells were drilled on structures to test this carrier and petroleum was found in one of the structures an understanding of the migration pathways and petroleum drainage efficiency of the basins is of great economic interest because most of the smaller substructures are marginally economic thus it is important to provide an effective risk analysis and ranking of the satellite prospects prior to drilling this study has demonstrated that filling and migration in a geological province are controlled by a series of complex processes and that the filling history of the structures within the tampen spur is more complicated than suggested earlier

crustal structure of the paleozoic kunlun orogeny from an active source seismic profile between moba and guide in east tibet china abstract we herein present a new seismic refraction wide angle reflection profile that crosses the songpan ganzi terrane the animaqing suture zone and the eastern kunlun mountains comprised of the south kunlun and middle kunlun blocks separated by the middle kunlun fault the profile is 380 km long and extends from moba to guide in eastern tibet the crustal thickness is about 62 km under the songpan ganzi terrane 62 64 km under the south kunlun and 60 km under the middle kunlun block the songpan ganzi flysch seems to be present up to a depth of 15 km south of the animaqing suture zone and up to a depth of 10 km in the middle kunlun block with thicknesses elsewhere that depend on assumptions about the likely lithologies the profile exhibits clear lateral variations both in the upper and lower crust which are indicative of different crustal blocks juxtaposed by the kunlun fault system whether or not the songpan ganzi flysch was originally deposited on oceanic crust at the longitude of our profile 100 e it is now underlain by continental crust and the presence of continental crust beneath the songpan ganzi terrane and of a continental arc under the south kunlun block suggest paleozoic continent continent arc collision in the eastern kunlun mountains comparison of crustal velocity columns from all wide angle seismic profiles across the eastern kunlun mountains indicates a remarkable west to east change in the moho topography across the kunlun fault system 15 20 km moho step at 95 e but only 2 5 km along our profile at 100 e lower crustal thickness of the kunlun terranes is rather uniform about 35 km from 80 95 e which suggests that similar thrust thickening processes have played a role where the qaidam basin abuts the kunlun fault but thins to 20 25 km at 100 e east of the qaidam basin the increased crustal thickness from 93 to 98 e compared to that at 100 e may be due to the differences in the thickness of the crust of the two plates before their collision and or largely achieved by thickening of the lower crust perhaps indicating a crustal flow mechanism operating more strongly in the western region

reply to comment by w liu and b xia on age and geochemistry of western hoh xil songpan ganzi granitoids northern tibet implications for the mesozoic closure of the paleo tethys ocean

proto tethys magmatic evolution along northern gondwana insights from late silurian middle devonian a type magmatism east kunlun orogen northern tibetan plateau china abstract the east kunlun orogen records the geological evolutions of the neoproterozoic early paleozoic proto tethyan ocean and late paleozoic mesozoic paleo tethys ocean along northern gondwana however the late stage evolution of the proto tethyan ocean and the configuration of peri gondwana microcontinents during the silurian devonian is under debate here we report new geochronological and geochemical data of a type granites from the western wulonggou and the eastern gouli areas in the east kunlun orogen to deepen our understanding of these problems zircon la icp ms u pb data reveal that the danshuigou monzogranite and shenshuitan syenogranite from the western wulonggou area were emplaced simultaneously at 418 3 ma while the niantang syenogranite from the eastern gouli area was emplaced at 403 2 ma all these rocks display high k calcic alkalic to shoshonitic and metaluminous to slight peraluminous signatures with relatively low cao al2o3 mgo and sr and high feot mgo ga al zr and nb indicating their a type affinity their moderate whole rock end t 5 3 to 0 6 and zircon ehf t 6 3 6 4 are different from those of depleted mantle and old basement rocks but similar to those of the ordovician silurian granitoids in the east kunlun orogen these chemical signatures together with the anhydrous low pressure and high temperature characteristics of the magmas indicate that partial melting of the ordovician silurian granitoids generated these a type granites regionally these a type granites and previously reported a type granites in the east kunlun orogen compose a late silurian middle devonian a type granite belt this belt together with the regionally coeval molasse formation and mafic ultramafic rocks indicate a post collisional extensional regime for the east kunlun orogen during the late silurian middle devonian given that extensive contemporaneous post collision related magmatic rocks have also been revealed in the neighboring west kunlun altyn qilian and qinling blocks terranes we contend that the neoproterozoic early paleozoic proto tethyan ocean that separated these blocks terranes from gondwana had closed by the late silurian middle devonian which resulted in the re welding of the above blocks terranes to northern gondwana or gondwana derived microcontinents

chemical weathering in the three rivers region of eastern tibet abstract three large rivers the chang jiang yangtze mekong lancang jiang and salween nu jiang originate in eastern tibet and run in close parallel over 300 km near the eastern himalayan syntaxis seventy four river water samples were collected mostly during the summer season from 1999 to 2004 their major element compositions vary widely with total dissolved solids tds ranging from 31 to 3037 mg l reflecting the complex geologic makeup of the vast drainage basins the major ion distribution of the main channel samples primarily reflects the weathering of carbonates evaporite dissolution prevails in the headwater samples of the chang jiang in the tibetan plateau interior as evidenced by the high tds 928 and 3037 mg l and the na cl dominant major element composition local tributary samples of the mekong and salween draining the lincang batholith and the tengchong volcano show distinctive silicate weathering signatures we used five reservoirs rain halite sulfate carbonate and silicate in a forward model to calculate the contribution from silicate weathering to the total dissolved load and to estimate the consumption rate of atmospheric co 2 by silicate weathering carbonate weathering accounts for about 50 of the total cationic charge tz in the samples of the mekong and the salween exiting the tibetan plateau in the exit sample of the chang jiang 45 of tz is from halite dissolution inherited from the extreme headwater tributaries in the interior of the plateau and carbonates contribute only 26 to the tz the net rate of co 2 consumption by silicate weathering is 103 121 10 3 mol km 2 year 1 lower than the rivers draining the himalayan front gis based analyses indicate that runoff and relief can explain 52 of the spread in the rate of atmospheric co 2 drawdown by silicate weathering but other climatic temperature precipitation potential evapotranspiration and geomorphic elevation slope factors also show collinearity only qualitative conclusions can be drawn for the significance of lithology due to lack of digitized lithologic information the effect of the peculiar drainage pattern due to tectonic forcing is not readily apparent in the major element composition or in increased chemical weathering rates the 87 sr 86 sr ratios and the silicate weathering rates are in general lower in the three rivers than in the rivers draining the himalayan front

the formation of pangea abstract the making of pangea is the result of large scale amalgamation of continents and micro continents which started at the end of the neoproterozoic with the formation of gondwana as pieces were added to gondwana on its south american antarctica and australia side ribbon like micro continents were detached from its african and south chinese side cadomia in the late neoproterozoic avalonia and hunia in the ordovician galatia in the devonian and cimmeria in the permian cadomia was re accreted to gondwana but the other ribbon continents were accreted to baltica north china laurussia or laurasia finding the origin of these numerous terranes is a major geological challenge recently a global plate tectonic model was developed together with a large geological geodynamic database at the lausanne university covering the last 600 ma of the earth s history special attention was given to the placing of gondwana derived terranes in their original position using all possible constraints we propose here a solution for the variscan terranes another paper deals with the altaids the galatian super terrane was detached from gondwana in the devonian during the opening of paleotethys and was quickly separated into four sub terranes that started to by pass each other the leading terranes collided at the end of the devonian with the hanseatic terrane detached from laurussia in the carboniferous gondwana started to impinge onto the amalgamated terranes creating the variscan chain and the pangean super continent east of spain paleotethys remained opened until the triassic subducting northward under laurasia roll back of the paleotethyan slab triggered the collapse of most of the european variscan orogen which was replaced by series of permian rifts some of them becoming oceanized back arc basins during the triassic major force changes at the pangean plate limits at the end of the triassic provoked its break up through the opening of the proto caribbean central atlantic alpine tethys oceanic seaways

triassic sedimentary filling and closure of the eastern paleo tethys ocean new insights from detrital zircon geochronology of songpan ganzi yidun and west qinling flysch in eastern tibet

volcanic rocks of the 1985 tibet geotraverse lhasa to golmud volcanic rocks encountered during the tibet geotraverse have been studied in the field in thin section and by major and trace element geochemistry in order to determine their most probable original eruptive environment rocks from a total of eleven distinct volcanic provinces were studied in this way they provide evidence for an active continental margin or post collision province of probable devonian early carboniferous age in the northern kunlun mountains an active continental margin of late carboniferous age in the southern lhasa terrane permian continental rifts in the central qiangtang and central kunlun terranes triassic volcanic arcs in the southern lhasa and northern qiangtang terranes a triassic active continental margin dyke swarm in the northern kunlun mountains a jurassic post collision or back arc rifting province in the southern qiangtang terrane a jurassic island arc in the northern lhasa terrane a cretaceous post collision province in the northern lhasa terrane possibly extending into the southern qiangtang terrane and a palaeogene active continental margin in the southern lhasa terrane an oligocene trachyte plug in the northern qiangtang terrane was the only evidence encountered during the geotraverse of volcanism post dating the palaeogene india eurasia collision however the composition of this plug coupled with new and published analyses from miocene volcanics in the southern lhasa terrane and from the pliocene recent volcanic province of northwest tibet places important constraints on models for post collision underplating of tibet by continental lithosphere any underplating is likely to have been a much later than the start of collision b directed beneath tibet from the north as well as the south and c limited in extent

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

parametric analyses of the transient method of measuring permeability analyses are made to compare the two approaches of using the transient method to determine permeability of rocks the simplified version and the numerical version the simplified version assumes that when the sample volume is much smaller than the reservoir volume the fluid storage in a rock sample can be neglected and the pressure decay in the upstream reservoir can be approximated by an exponential function of time the numerical version uses finite difference method to solve the differential equation of pressure decay and matches the observed pressure decay with the calculated decay curves the pressure decay calculated by the numerical version is not generally a simple exponential function of time as suggested by the simplified version our analyses show that the numerical version fits to the observed data very well the permeability value determined by the simplified version tends to be greater than that determined by the numerical version the difference in apparent permeability between the two depends on many factors such as rock properties porosity and compressibility sample size reservoir volumes etc a relative fluid storage is used to illustrate the difference of these two approaches for a relative fluid storage value of greater than 0 03 the difference in permeability between the two is more than 30 for a system with a fluid storage of less than 0 01 these two versions agree with each other well

crustal structure across the kunlun fault from passive source seismic profiling in east tibet abstract the crust beneath the northeastern ne tibetan plateau records the imprints on paleozoic kunlun orogen and far field effects from continental collision and convergence between the indian and eurasian plates a passive source seismic profile was conducted across eastern kunlun mountains also called animaqing suture belt receiver function imaging and h k stacking results with this dataset demonstrate that 1 crust slightly thins from about 64 km under the songpan ganzi terrane to about 56 62 km under the qaidam kunlun block and the qilian block 2 moho topography is relatively smooth with gradual undulation beneath east kunlun orogeny belt in contrast to 2 5 km moho step at the akms kunlun fault from previous deep seismic soundings or even no moho topography variation from recent deep seismic reflection profiling 3 the average crustal vp vs ratios display an increasing trend to the kunlun fault belt from 1 76 to 1 85 in songpan ganzi terrane while decreases from 1 83 to 1 65 away from the fault belt in qaidam kunlun block 4 the high vp vs ratio in songpan ganzi terrane is similar to previous results from the profile across longmenshan fault belt the normal to low vp vs ratio distribution in qaidam kunlun block supports the viewpoint that the deformation occurring in ne tibet is predominated by upper crustal thickening and 5 the thickness of non seismogenic layer varies slightly about 40 km between 90 and 100 e then decreases to less than 20 km around 106 e along the kunlun fault the change of the non seismogenic layer thickness is consistent with the change of the lower crust thickness derived from deep seismic sounding the increased crustal thickness may be due to the differences in the thickness of the crust of the two plates before their collision and or largely achieved by thickening of the lower crust perhaps indicating a crust flow mechanism operating more strongly in the western region

a type granite and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination abstract the songpan garze fold belt covers a huge triangular area 200 000 km2 confined by the south china yangtze north china and tibetan plateau continental blocks in the songpan garze fold belt triassic adakitic granitoids have been identified however whether there are triassic a type granites is unclear here we report our first finding of an a type granite nianbaoyeche which occurs in the central part of the songpan garze fold belt the nianbaoyeche granite 820 km2 is characterized by arfvedsonite in its mineral assemblage using both la icpms and tims u pb zircon dating methods we obtain a magma crystallization age of 211 1 ma which is slightly younger than triassic adakitic granitoids 216 221 ma in the songpan garze fold belt the nianbaoyeche granite is enriched in si k na rb ree hfse nb ta zr hf with elevated feotot feotot mgo and ga al ratios but is depleted in al mg ca ba and sr the ree compositions show moderately fractionated patterns with la yb n 2 67 7 54 and eu eu 0 09 0 34 these geochemical characteristics indicate that the nianbaoyeche granite has an a type affinity geochemical data and u pb zircon age combined with regional studies show that the nianbaoyeche granite formed in a post collisional tectonic setting sr nd isotopic data for the granite exhibit isr 0 7090 0 7123 and end t 2 72 to 4 26 with tdm 1 15 1 51 ga suggesting that the magma has a dominantly crustal source though a minor contribution from the mantle cannot be ruled out melting to produce an a type granite may have resulted from triassic lithospheric delamination after triassic crustal thickening of the songpan garze fold belt due to convergence between the yangtze north china and north tibet continental blocks the lithospheric delamination model also helps to explain the triassic adakitic magma generation in the songpan garze belt we conclude that association of a type granite and adakitic granitoids in post collisional environment could be a useful indicator of lithospheric delamination

geochronology and geochemistry of the yazidaban ophiolitic melange in qimantagh constraints on the early paleozoic back arc basin of the east kunlun orogen northern tibetan plateau the east kunlun orogenic belt of the northern tibetan plateau can be divided by the qimantagh xiangride aqikekulehu kunzhong and muztagh buqingshan sutures into from north to south the northern qimantagh central kunlun and southern kunlun belts the yazidaban ophiolitic melange located in the westernmost region of the qimantagh xiangride suture between the northern qimantagh and central kunlun belts consists predominantly of serpentinite basalt diabase and andesite the serpentinites are characterized by low total rare earth element ree concentrations and depletion of mid rees showing an ophiolitic ultramafic affinity the basalts have low ree concentrations a slight enrichment in light rees depletion of large ion lithophile elements and insignificant fractionation of high field strength elements which are attributed to an incompatible element enriched mid ocean ridge basalt both diabases and andesites are characterized by high ree strong enrichment in light rees depletion of nb ta p and ti and significant fractionation of high field strength elements these geochemical characteristics indicate that the diabase and andesite were mostly generated in a subduction related setting igneous zircons from the diabase yielded a 206pb 238u age of 421 5 2 2 ma mswd 0 44 representing the formation time of the subduction related rocks together with the regional geology these constraints on the ultramafic rock basalt andesite and diabase suggest that the yazidaban ophiolitic melange represents the remnants of oceanic crust from a back arc basin and the associated subduction related magmatic rocks supplementary material details of u th pb laser ablation inductively coupled plasma mass spectrometry data of zircons from the diabase and major and trace element compositions for the samples from the qimantagh melange east kunlun orogen are available at https doi org 10 6084 m9 figshare c 4283219

carbazole distributions in carbonate and clastic source rocks abstract carbazole the benzocarbazoles and their alkyl derivatives have been studied from rock extracts to assess the contribution of facies and maturity in controlling their distribution carbonates from the keg river formation elk point group middle devonian western canada consisting of two different facies reflecting deposition under trangressive and regressive events were used to assess facies influences to study maturation a uniform organo facies of organic rich posidonia shale lower toarcian jurassic northern germany from 0 48 to 1 45 r r was used the organic rich lower keg member deposited under photic zone anoxia contained predominantly c 4 c 5 carbazoles by contrast the upper keg river member deposited under regressive higher salinity environment contains predominantly carbazole itself 1 methylcarbazole and a high abundance of benzo c carbazole relative to benzo a carbazole the distribution of the c 1 to c 3 carbazoles was seen to vary with facies an examination of the carbazole derivatives within the posidonia shale reveals that maturation strongly influences the distribution of carbazole methylcarbazoles 1 8 dimethylcarbazole 1 ethylcarbazole benzo a carbazole and benzo c carbazole quantitative determination of these compounds indicates a maximum yield at 0 88 r r for all derivatives with the exception of carbazole which displays as a maximum at 0 53 r r a systematic variation of compound ratios with maturity to 0 88 r r suggests that selective isomerisation destruction generation of carbazole derivatives may occur in contrast to earlier publications which stress the importance of carbazoles as migration markers in migrated oils the results presented here indicate that facies and maturation do play a significant role in controlling the distribution of carbazole derivatives in source rocks and other sediments

multi stage tectono magmatic events of the eastern kunlun range northern tibet insights from u pb geochronology and u th he thermochronology article i nfo to understand the magmatic and tectonic events in the eastern kunlun range we conducted systematic zircon u pb geochronology and paired zircon zhe and apatite ahe u th he themchronology investigations in the central and eastern segments of this range zircon u pb ages show two stage magmatic events of late silurian and latest permian early jurassic zhe and ahe ages and multi system thermochronometers reveal multi stage rapid cooling events from a combination of these data with previously published geochronological and thermochronological ages and regional geological setting we confirm several important phanerozoic tectono magmaticeventsinthisregion whereasthesiluriangranitesmightberelatedtoasmallpaleo oceansub duction and subsequent collision the latest permian early triassic granitoids were produced by northward sub duction of the songpan ganzi paleo tethyan ocean the late triassic earliest jurassic granitoids and late triassic early jurassic exhumation are interpreted as response to the collision between kunlun qaidam and qiangtang samples close to the kunlun fault show rapid late oligocene early miocene exhumation 1 3 1 6 km ma whereas those from the northern part of central segment display extremely low exhumation rates 0 02 0 05 km ma this heterogeneous denudation during 30 20 ma between northern and southern part of the central segment requires that crustal thickening was completed by lower crustal underthrusting with littleex humation or crustal thickening in pre cenozoic times the activity of the kunlun fault and associated normal faulting component were probably responsible for this stage of rapid exhumation in the southern part the com plex tectono magmatic evolution of the eastern kunlun range is controlled by pre cenozoic paleo ocean subduc tions and subsequent continent collisions and paleogene india asia collision

insights into ore genesis of the jinding zn pb deposit yunnan province china evidence from zn and in situ s isotopes abstract the jinding zn pb deposit located in the mesozoic cenozoic lanping basin of southwest china has ore reserves of 220 mt with an average grade of 6 1 zn and 1 3 pb the mineralization is hosted by sandstone in the early cretaceous jingxing formation and limestone breccia in the paleocene yunlong formation mineralization in both types of host rocks is characterized by a paragenetic sequence beginning with marcasite sphalerite stage 1 followed by pyrite marcasite sphalerite galena stage 2 and then galena sphalerite pyrite sulfate carbonate stage 3 pyrite from these stages have different 33 s compositions with pyrite from stage 1 averaging 9 6 stage 2 averaging 8 9 and stage 3 averaging 0 3 sphalerite hosted by the sandstone has similar 66 zn values ranging from 0 10 to 0 30 in all stages of the mineralization but sphalerite samples from the limestone breccia hosted ore show variable 66 zn values between 0 03 and 0 20 our data on sphalerite precipitated during the earlier stages of mineralization has a constant 66 zn value and cogenetic pyrite displays a very light sulfur isotope signature which we believe to reflect a sulfur source that formed during bacterial sulfate reduction bsr the stage 3 sphalerite and pyrite precipitated from a late influx of metal rich basinal brine which had a relatively constant variable 66 zn isotopic composition due to open system isotope fractionation and a near zero 33 s composition due to the influence of abiotic thermochemical sulfate reduction from observed sulfates in the host rock