highly fractionated i type granites in ne china ii isotopic geochemistry and implications for crustal growth in the phanerozoic ne china is the easternmost part of the central asian orogenic belt caob the area is distinguished by widespread occurrence of phanerozoic granitic rocks in the companion paper part i we established the jurassic ages 184 137 ma for three granitic plutons xinhuatun lamashan and yiershi we also used geochemical data to argue that these rocks are highly fractionated i type granites in this paper we present sr nd o isotope data of the three plutons and 32 additional samples to delineate the nature of their source to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the phanerozoic despite their difference in emplacement age sr nd isotopic analyses reveal that these jurassic granites have common isotopic characteristics they all have low initial 87 sr 86 sr ratios 0 7045f0 0015 positive end t values 1 3 to 2 8 and young sm nd model ages 720 840 ma these characteristics are indicative of juvenile nature for these granites other late paleozoic to mesozoic granites in this region also show the same features sr nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two stage processes 1 formation of parental magmas by melting of a relatively juvenile crust which is probably a mixed lithology formed by pre existing lower crust intruded or underplated by mantle derived basaltic magma and 2 extensive magmatic differentiation of the parental magmas in a slow cooling environment the widespread distribution of juvenile granitoids in ne china indicates a massive transfer of mantle material to the crust in a post orogenic tectonic setting several recent studies have documented that juvenile granitoids of paleozoic to mesozoic ages are ubiquitous in the central asian orogenic belt hence suggesting a significant growth of the continental crust in the phanerozoic d 2003 elsevier science b v all rights reserved

single crystal 40ar 39ar dating of the olorgesailie formation southern kenya rift single crystal laser fusion sup 40 ar sup 39 ar analyses and several conventional bulk fusion sup 40 k sup 40 ar dates have been used to determine the age of volcaniclastic strata within the olorgesailie formation and of associated volcanic and sedimentary units of the southern kenya rift in the principal exposures along the southern edge of the legemunge plain the formation spans the interval from approximately 500 to 1 000 ka deposition continued to the east along the ol keju nyiro river where a tuff near the top of the formation has been dated at 215 ka in these exposures the formation is unconformably overlain by sediments dated at 49 ka a possible source for the olorgesailie tephra the ol doinyo nyokie volcanic complex contains as ash flow dated at approximately 1 ma extending the known age range of this complex to encompass that of virtually the entire olorgesailie formation in the legemunge plain these geologic examples illustrate the importance of the single crystal sup 40 ar sup 39 ar dating technique whereby contaminant altered or otherwise aberrant grains can be identified and eliminated from the determination of eruptive ages for reworked or altered pyroclastic deposits the authors have presented a computer modeling procedure based on an inverse isochron analysis thatmore promotes a more objective approach to trimming sup 40 ar sup 39 ar isotope data sets of this type less

a newly discovered earliest triassic chert at gaimao section guizhou southwestern china abstract the permian triassic ptb boundary section at gaimao huaxi district guiyang guizhou province records a unique lithological transition between the permian and triassic in south china thus bioclastic limestones of the changxing formation are overlain by radiolarian bearing siliceous rocks of the dalong formation and ultimately limestone mudstone alternations of the shabaowan formation conodont sampling of the section revealed well preserved elements that enabled a conodont biostratigraphy to be established the occurrences of hindeodus julfensis and hindeodus typicalis in changxing formation bioclastic limestone indicate a late permian age four conodont zones have been established in dalong and shabaowan formations in ascending order those are the isarcicella isarcica zone neogondolella or clarkina planata zone neogondolella krystyni zone and neospathodus dieneri zone the presence of typical griesbachian conodonts i isarcica and isarcicella staeschei in upper dalong formation indicates that this formation s radiolarian bearing siliceous mudrocks are of earliest triassic age and not restricted to the permian as previously thought thin section analysis reveals that the upper dalong formation contains spheroidal radiolarians but not a diverse assemblage of permian holdover taxa the new data proves that following the end permian mass extinction of radiolarian the abundance of these siliceous planktons was maintained at least locally enabling chert deposition to persist thus the gaimao section provides an exception to the early triassic chert gap the first of its kind in palaeo tethys and indicates that the end of chert deposition does not always mark the end permian mass extinction

geochemistry and zircon u pb hf isotopes of the mante aobao granite porphyry at east ujimqin banner inner mongolia implications for petrogenesis and tectonic setting we present detailed petrography geochemistry and zircon u pb hf isotopes of the mante aobao granite porphyry in east ujimqin banner inner mongolia with the aim of determining its age and petrogenesis important for understanding the early palaeozoic tectonic evolution of the xing an mongolian orogenic belt the mante aobao granite porphyry consists of plagioclase quartz and minor biotite but without amphibole zircon u pb analyses yield ages of 450 1 ma and 445 2 ma for the granite porphyry indicating that it formed during late ordovician time the granite porphyry is metaluminous to slightly peraluminous aluminous saturation index a cnk 0 98 1 11 with high sio 2 k 2 o and na 2 o concentrations and differentiation index di 85 90 chondrite normalized rare earth element ree patterns display enrichment of light rees lrees with high ratios of la yb n and negative eu anomalies in the mantle normalized multi element variation diagrams all samples are characterized by depletions of high field strength elements hfses nb ta and ti and enrichments of large ion lithophiles liles rb th u and k these geochemical features indicate that the granite porphyry is a highly fractionated i type granite and formed in a subduction related setting zircon grains have positive e hf t values of 9 2 to 11 2 and t dm2 hf ages of 691 821 ma suggesting that the granite porphyry was generated by partial melting of neoproterozoic juvenile crust with involvement of fractional crystallization during magmatic evolution it is likely that underplating of mantle derived magmas during late ordovician time provided the necessary heat to partially melt this juvenile crust combined with the regional geological data we infer that the mante aobao granite porphyry was emplaced in an active continental margin setting that was probably related to the northwards subduction of the paleo asian plate beneath the south mongolian terrane along the sonid zuoqi xilinhot axis

griesbachian earliest triassic palaeoenvironmental changes in the salt range pakistan and southeast china and their bearing on the permo triassic mass extinction abstract facies and faunal analysis from pakistan and china show that the permo triassic mass extinction of marine invertebrate faunas was associated with a spectacularly rapid griesbachian transgression which lead to the widespread establishment of deep water anoxic and dysoxic conditions the extinction event was thus caused by habitat loss due to the extensive development of inhospitable conditions the initial griesbachian transgression in pakistan produced extensive shallow normal marine conditions in which permian holdover taxa were able to survive until the development of dysaerobic facies in the late griesbachian the exceptionally complete sections of china show a three phased deepening and extinction event beginning in the latest permia by the late griesbachian a variety of dysaerobic and anaerobic facies were developed in all the regions studied several of these contain evidence for minimal sulphate reducing activity suggesting that marine productivity and thus organic matter flux to the sediments was very low in early triassic seas

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

reply to comment on mantle plume the invisible serial killer application to the permian triassic boundary mass extinction by e heydari n arzani and j hassanzadeh palaeogeography palaeoclimatology palaeoecology 264 2008 147 162 abstract in a recent paper heydari e arzani n hassanzadeh j 2008 mantle plume the invisible serial killer application to the permian triassic boundary mass extinction palaeogeography palaeoclimatology palaeoecology 264 147 162 the cause of the end permian mass extinction was once again associated with the eruption of the siberian traps however this work considered the vast outpouring of flood basalts to be an incidental sideshow to the main event the catastrophic release of huge volumes of methane to the atmosphere this was attributed to a selection of sources marine gas hydrates thermogenic methane and methane from permafrost that have been proposed by many authors previously uniquely they suggest that the mantle plume envisaged to have sourced the flood basalts impinged beneath oceanic crust to the north of the siberian flood basalts and that feeder dykes in the continental slope to the south heated sediments and released methane there is no evidence for either of these two new proposed facets to end permian volcanism the paper invokes an oceanic acid bath kill mechanism and dismisses claims for ocean anoxia at this time instead suggesting that end permian oceans were as well ventilated as those pertaining today this latter claim simply ignores a vast body of sedimentological palaeoecological and geochemical evidence for widespread anoxia in ocean and shelf settings at this time the former claim for ocean acidity is equally suspect and based on the notion that a transition from calcite to aragonite precipitating seas occurred at the permian triassic boundary however previous studies have suggested that this interval occurs within a phase of aragonite seas and it is significant that most of the principal contributors to carbonate sediment in the late permian calcareous algae and foraminifera secreted aragonite

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

evidence for a fungal event methane hydrate release and soil erosion at the permian triassic boundary in southern israel abstract the transition between the permian and the triassic systems in israel is evident only in the subsurface two cores from the makhtesh qatan 2 core 9 and avedat 1 core 5 drillholes in which the permian triassic boundary was found marked by a fungal event were sampled at close intervals and analysed for palynological petrographical mineralogical chemical and isotopic properties three palynozones were recorded lueckisporites virkkia zone late permian fungal event and endosporites papillatus zone early triassic the fungul event occurs in a narrow interval of 1 m and contains almost exclusively fungal remains and recycled woody particles the two cores consist of laminated sediments mainly siliciclastic that were deposited in very shallow to restricted marine environments with a minor presence of evaporites and no bioturbation green glauconitic material and framboidal pyrite suggest suboxic conditions even in the shallow waters reddish brown particles and plant fragments derived from nearby soils now outcropping on the northeast side of the dead sea these materials as well as recycled brown glauconitic grains suggest a drop in sea level and intense erosion before sedimentation which was apparently continuous major and trace element compositions including rare earth elements do not exhibit any particular pattern that might be related to the fungul event or to other core intervals the rare earth element patterns are basically normal and their concentration correlates with the clay content reflecting the provenance of the arabo nubian massif and its sedimentary rims iridium results were mostly at the background level and therefore the two distinct anomalous values are inconclusive microspherules mainly of 2 m size and al si composition were observed in a few samples in both cores their origin could not be determined though they are considered to be natural there was no evidence for shocked quartz 13corg excursion exhibits a marked negative shift in both cores just below the fungal event the lowest values 37 and 42 are among the lowest ever recorded near the permian triassic boundary and suggest large scale release of methane hydrates

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

the late paleozoic to mesozoic evolution of the eastern margin of the central asian orogenic belt in china abstract the north east central asian orogenic belt caob in china records terminal closure of the paleo asian ocean in the mid to late permian along the solonker xar moron changchun suture this marks the end of the overall northward movement of the chinese blocks from a peri gondwana position toward siberia and a switch in tectonic processes to those dominated by activity associated with the paleo pacific plate to the east four distinct changes in tectonic regime can be recognised here in the late paleozoic to early mesozoic i north south compression resulted in orogenesis and gave way to post collisional extension at 260 250 ma with the emplacement of a type granites ii almost coeval with this there was an the onset of east west extension from 250 to 225 ma along the extreme eastern margin of the caob when a seaway opened between the songliao and jiamusi khanka blocks iii the onset of westerly directed compression associated with subduction of the paleo pacific plate from 210 ma resulted in re amalgamation of the jiamusi khanka block with the caob by 190 180 ma and the massive generation of jurassic i type granitoids throughout the region finally iv a change to east west extension from 140 ma onward resulted from roll back of the paleo pacific plate this latter event was accompanied by the emplacement of s type granitoids and the development of sedimentary basins and core complexes it also accompanied a more widespread thinning or delamination of the lithosphere across most of north east china during the cretaceous

carboniferous and cretaceous mafic ultramafic massifs in inner mongolia china a shrimp zircon and geochemical study of the previously presumed integral hegenshan ophiolite abstract we present shrimp zircon ages and whole rock geochemical data to identify mafic ultramafic massifs of early carboniferous and early cretaceous ages from northern inner mongolia china the early carboniferous massifs chongenshan xiaobaliang wusnihei comprise predominantly lherzolite and minor gabbroic rocks zircons from a microgabbro e nd t 9 8 and a plagiogranite e nd t 9 yielded weighted mean 206 pb 238 u ages of 354 7 ma and 333 4 ma that we interpret as reflecting the time of zircon and magma crystallization a volcanic breccia resting unconformably on the ultramafic rocks serpentinites has an eruption age of 300 2 ma and provides a younger minimum time limit for the emplacement of the early carboniferous mafic ultramafic massifs in contrast the early cretaceous mafic ultramafic massifs hegenshan chaogenshan consist predominantly of harzburgite a pegmatoid gabbro and a rodingite e nd t 10 6 from the hegenshan massif have magmatic zircon ages of 139 2 ma and 132 7 ma respectively the chaogenshan massif is concentrically zoned with an ultramafic core dominantly harzburgite dunite subordinate lherzolite surrounded by gabbro with minor hornblendite and an outermost volcano sedimentary sequence metabasaltic flows metapelites we dated zircons from a leuocogabbro 125 2 ma e nd t 10 6 a coarse grained gabbro 142 4 ma and a metabasalt 134 2 ma zircon xenocrysts ca 152 492 ma are ubiquitous in these and other associated rocks a coarse grained gabbro and a diabase as in the hegenshan rocks ca 152 468 ma the youngest detrital zircon in outer zone garnet schist i e metapelite has an age of 132 2 ma accordingly we conclude that the northern inner mongolia lherzolite dominant and harzburgite dominant massifs are temporally and genetically unrelated their emplacement is attributed to asthenospheric upwelling and consequent lithospheric extension during periods of orogenic quiescence in the southern central asian orogenic belt

development of a largely anoxic stratified ocean and its temporary massive mixing at the permian triassic boundary supported by the sulfur isotopic record systematic sulfur isotope data for whole rock sulfides have been obtained from the chert dominated continuous pelagic sedimentary sequences spanning the permian triassic p tr boundary at tenjinmaru in the chichibu terrane and at sasayama in the tanba terrane in japan the p tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed cretaceous tertiary k t boundary claystone the observed data clearly demonstrate a significant bimodalism the 34s 32s ratios with respect to cdt are generally low throughout the middle permian ca 39 to 25 0 and show a remarkable increase beginning in the lower upper permian and persisting into the lower triassic ca 20 to 2 0 with a temporary and drastic negative shift down to roughly the same isotopic level as in the middle permian just at the suspected p tr boundary ca 41 to 23 0 interestingly the mode of isotopic excursion across the p tr boundary is in striking contrast to that across the k t boundary which was recently described at kawaruppu in hokkado japan the apparent extent of fractionation with respect to contemporaneous seawater sulfate in the high 34s 32s group lies within the range of 25 10 0 which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction and that in the low 34s 32s group mostly exceeds this range giving the values typically in the range of 45 10 0 which is similar to what is generally observed in the present day oceanic sediments the present data would provide strong evidence for the development of a largely stagnant anoxic stratified ocean which presumably began to form in the lower upper permian and persisted into the lower triassic and for a brief episode of its temporary massive mixing just at the suspected p tr boundary such an oceanic oxic anoxic history may account to some extent for the relatively high enrichments of chalcophile elements in basal triassic sediments in the world and add a significant constraint to the current arguments on the cause and consequence of the terminal permian mass extinction

zircon ages and geochemical compositions of the manlay ophiolite and coeval island arc implications for the tectonic evolution of south mongolia abstract numerous small dismembered ophiolite fragments occur in south mongolia but they are very poorly studied the lack of age data and geochemical analysis hampers our understanding of the paleozoic tectonic evolution of the region we conducted detailed studies on the manlay ophiolitic complex and huree volcanic rocks south of the main mongolian lineament mml to provide some constraints on these rocks the manlay ophiolite consists of dunite harzburgite pyroxenite gabbro plagiogranite basalt and chert locally with chromite mineralization in dunite the gabbro and plagiogranite yielded shrimp zircon weighted mean 206 pb 238 u ages of 509 5 ma and 482 4 ma respectively the basalt and dolerite samples of this complex show enrichment in lree and lile and negative nb ta and ti anomalies and the chrome spinel from the chromitite lens in the dunite is characterized by high cr and low tio 2 contents these features suggest a supra subduction zone ssz origin for the ophiolitic complex the huree volcanic rocks ranging from basalt to dacite display enrichment in lree and lile weak eu anomalies and distinctly negative nb ta and ti anomalies consistent with those of typical magmas in a subduction environment an andesite sample from this arc yielded a shrimp 206 pb 238 u zircon age of 487 5 ma which is the oldest reliable age for an island arc in south mongolia recognition of an early paleozoic ophiolitic complex and a coeval island arc indicates that south mongolia underwent a period of active volcanism during late cambrian to ordovician additionally the tuff overlying the ophiolitic complex and a granite intruding the ophiolite have shrimp zircon u pb ages of 391 5 ma and 304 4 ma respectively combining the available data we propose that the early paleozoic subduction accretionary complexes likely constitute the basement of the late paleozoic arc formations and correlate with the lake zone in western mongolia

final amalgamation of the central asian orogenic belt in ne china paleo asian ocean closure versus paleo pacific plate subduction a review of the evidence abstract the central asian orogenic belt caob evolved through complex closure of the paleo asian ocean from the neoproterozoic to the late phanerozoic this caused the chinese cratons to collide with eurasia and led to the formation of the world s largest phanerozoic orogenic belt ocean closure commenced in the west and was completed in the east near changchun closure of the paleo asian ocean in ne china was along the solonker xar moron changchun yanji suture and this was likely completed in the late permian although associated activity continued into the triassic there was an overlap in the latest permian early triassic between terminal activity associated with paleo asian ocean closure and the onset of tectonism associated with subduction of the paleo pacific plate this switch in geodynamic setting occurred at 260 250 ma and is reflected by a relaxing of north south directed compression and the onset of east west directed processes related to paleo pacific subduction by the early jurassic events associated with the westward advance of the paleo pacific plate dominated leading to extensive development of i type granites as far inland as the great xing an range from 140 ma the paleo pacific plate retreated eastward resulting in an extensional setting in the early cretaceous the effects of which were enhanced by regional thinning of the lithosphere commonly attributed to delamination throughout this period the eastern asian margin was tectonically complex the north south oriented jiamusi khanka bureya block was rifted away from the eastern margin of the caob in the late triassic but was then re united in the jurassic by westward advancing subduction that affected both the western and eastern margins of the block accretionary complexes continued to evolve in the cretaceous along the whole eastern margin of asia with final accretion of the nadanhada terrane part of the sikhote alin accretionary terrane with the caob at 130 ma followed by the emplacement of s type granites

structural and kinematic analysis of the early paleozoic ondor sum hongqi melange belt eastern part of the altaids caob in inner mongolia china we present a structural and kinematic study of an early paleozoic subduction melange and a magmatic arc that form the main elements of the southern orogen belt of inner mongolia which lies in the eastearn part of the altaids or central asia orogenic belt the structural analysis of the melange conducted in the hongqi and ondor sum areas western inner mongolia shows two phrases of ductile deformation the d1 event is responsible for the pervasive s1 foliation nw se striking l1 stretching lineation and f1 intrafolial folds these microstructures are coeval with a greenschist facies metamorphism during d2 nw verging f2 folds associated with a s2 axial planar cleavage deformed s1 and l1 the d1 kinematic criteria indicate a top to the nw sense of shear d1 and d2 developed before the unconformable deposition of the early devonian shallow water sandstone a lithosphere scale geodynamic model involving an early paleozoic southeast directed subduction beneath the north china craton and late silurian collision of the north china craton with an hypothetical microcontinent is proposed to account for the microstructural evolution

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

early permian a type granites from central inner mongolia north china magmatic tracer of post collisional tectonics and oceanic crustal recycling abstract a type granitoids constitute volumetrically minor but genetically important building blocks of most post archean continental landmasses on earth and their diversified genesis encapsulates key information for ascertaining critical geodynamic controls on continental crustal formation and differentiation this zircon u pb dating and geochemical study documents the early permian peralkaline granites from central inner mongolia of china eastern central asian orogenic belt caob these granites show an a type magmatic affinity with typical enrichment in alkalis ga zr nb and y depletion in sr and p and fractionated ree patterns showing strong negative eu anomalies they have meaningful initial 87 sr 86 sr ratio of 0 70594 e nd t of 4 25 to 6 05 zircon e hf t from 9 8 to 16 0 and 18 o values from 2 41 to 4 72 these elemental and isotopic characters argue for parental magmas from partial melting of a newly trapped charnockitic lower crustal protolith and their subsequent fractional crystallization with an inherent hydrothermally altered oceanic crustal heritage and possible tectonic linkage to post collisional slab breakoff this kind of a type granites could not only serve as an insightful temporal milestone for monitoring the amalgamation between various constituent terranes in the caob but also present a spatial magmatic proxy for marking the maturation stage of juvenile crustal reworking during the final phase of a large orogenic event

the mixing of magmas in plutonic and volcanic environments analogies and differences abstract magma mixing processes have been widely recognized in both the plutonic and volcanic environments but the quality and quantity of information that can be extracted from the two environments are substantially different understanding the advantages and limits associated with the study of plutonic and volcanic rocks is essential to establish precise methodological approaches to build the most complete conceptual model by merging information from these two complementary igneous environments in this work we review magmatic interaction processes in the plutonic and volcanic environments by considering several aspects of these geological phenomena in particular we first briefly report on the structural and geochemical evidence for magma mixing in both plutonic and volcanic rocks with the aim to provide a general picture of this natural phenomenon successively we discuss some recent results about magma mixing achieved using the concepts from chaos theory and discuss their potential impact on magma differentiation finally we attempt to build a general picture of this igneous process by merging present day information from both the plutonic and volcanic environments it emerges from the general picture that the time spent by the magmatic system in the molten or partially molten state is the crucial factor for the preservation of the fingerprints of magma mixing in the two environments we propose a conceptual model that may be useful to understand what kind of information we can obtain from volcanic and plutonic rocks and ultimately to maximize our knowledge about magma mixing

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

evidence for recurrent changes in lower triassic oceanic circulation of the tethys the δ13c record from marine sections in iran abstract stable carbon isotope curves derived from lower triassic carbonate rocks from three iranian sections are established to investigate changes in the carbon cycle during the early triassic in this area the sections are located in the south center abadeh north amol and northwest zal of iran all three curves show a similar pattern starting out with high 13 c values in the uppermost permian decreasing across the permian triassic boundary an increase toward more positive values during the griesbachian that slowly increase further up during the dienerian followed by a positive excursion to values as high as 8 near the dienerian smithian boundary during the smithian values return to below 0 whereas second positive excursion to values higher than 3 is recorded at the smithian spathian boundary again followed by a drop in 13 c into the spathian and a final excursion to positive values at the spathian anisian boundary the results from these iranian sections are consistent with previous studies from italy and china thus strongly suggesting that the recorded 13 c variability represents at least tethys wide geochemical signals moreover the new curves reveal evidence of high amplitude frequent oscillations pointing toward rapid and profound changes in the global carbon cycle during the lower triassic stratification of the ocean interrupted by episodic overturning transporting deep water to the ocean surface is a viable mechanism to account for the recorded isotope variations provided that the 13 c curve is representative of the global lower triassic ocean it has high potential for accurately dating sedimentary successions via chemostratigraphy

tectonic significance of the xilin gol complex inner mongolia china petrological geochemical and u pb zircon age constraints abstract the xilin gol complex consisting of strongly deformed and metamorphosed rocks is exposed as a large tectonic unit within the central asian orogenic belt caob it is located on the xilinhot sonidzuoqi north dipping thrust belt and near the solonker suture zone that is widely regarded to record the terminal evolution of the caob its genesis and tectonic origin are a key to test the existing tectonic models as to whether there was a single arc chain by successive accretion or multiple amalgamation involving some microcontinents this study reports petrological geochemical and zircon u pb age data of biotite plagioclase gneisses from the complex as migmatization is common in the gneiss restitic and magmatic components are identified in the gneiss by their petrographic features mineral chemistry indicates that the xilin gol complex was subjected to amphibolite facies metamorphism three groups of zircons are identified by cathodoluminescence cl images and th u ratios 1 the first and most abundant group is of magmatic origin and yields a weighted mean 206 pb 238 u age of 452 5 ma 2 the second scarcest group is of metamorphic origin and yields a weighted mean 206 pb 238 u age of 339 4 ma 3 the third group is minor of apparent detrital origin and yields 207 pb 206 pb ages from 1902 11 to 886 54 ma for the cores with a peak at 1150 to 900 ma whole rock major and trace element contents are representative for the upper continental crust with rb pb u th k lree enrichment and nb ta sr depletion this suggests the gneisses are sourced in the upper continental crust with some old sediment contamination the protolith of the biotite plagioclase gneiss is a sedimentary rock with detrital source ages between 1902 11 ma and 886 54 ma that was deposited at the southern active continental margin of the siberia craton during the amalgamation of the rodinia supercontinent partial melting and migmatization occurred at 452 5 ma in response to north dipping oceanic subduction in the sonidzuoqi xilinhot area many new magmatic materials formed in the xilin gol complex during this time while it resided in a continental marginal arc tectonic setting oceanic subduction started at 490 8 ma and lasted at least to 440 4 ma in the early paleozoic the caob was an advancing accretionary orogen the complex was mildly affected by a 320 310 ma magmatic event in the xilinhot sonidzuoqi area therefore the xilin gol complex recorded a long lived successive accretion along the southern margin of the siberia craton

the menengai tuff a 36 ka widespread tephra and its chronological relevance to late pleistocene human evolution in east africa abstract the east african rift preserves the world s richest middle and late pleistocene 780 12 ka geological archaeological and paleontological archives relevant to the emergence of homo sapiens this region also provides unparalleled chronological control for many important sites through tephrochronology the dating and correlation of volcanic ashes as widespread isochronous markers in the geological record there are many well characterized pliocene early pleistocene tephras that are widespread across east africa a comparable framework is lacking for the middle and late pleistocene a period characterized by spatially and temporally complex patterns of climate change as well as the emergence of modern homo sapiens and the dispersal of this species across and out of africa unraveling relationships among these spatial and temporally complex phenomena requires a precise chronology to this end we report the menengai tuff a widespread volcanic ash produced by the large scale caldera forming eruption in kenya and 40 ar 39 ar dated to 35 62 0 26 ka geochemical characterization of 565 glass shards from 36 samples by wavelength dispersive electron probe microanalysis show the menengai tuff was deposited over 115 000 km 2 and is found in the baringo chalbi elmenteita nakuru olorgesailie turkana and victoria basins all of which preserve rich late pleistocene paleoenvironmental and archaeological archives correlation and dating of the menengai tuff demonstrate that it is the most widespread tephra and largest eruption currently known from the late pleistocene of east africa as such it is a valuable marker in establishing a late pleistocene chronology for paleoclimatic archeological and paleontological records relevant to the study of human evolution

a permian triassic boundary section at quinn river crossing northwestern nevada and implications for the cause of the early triassic chert gap on the western pangean margin the upper permian lower triassic quinn river formation in northwestern nevada was previously thought to represent an incomplete permian triassic boundary sequence owing to an inferred disconformable relationship between permian radiolarian and spicule rich chert and overlying triassic siltstone petrographic and geochemical studies demonstrate that the siltstone is in fact a radiolarian bearing early authi genic dolomicrite with both the chert and dolomicrite deposited conformably in deep water chert production declined or ceased in the late permian and reappeared in the spathian forming a widespread chert gap in permian triassic sequences given the conformable lithofacies relationships deep water depositional setting new radiolarian data extending ranges of key taxa and the presence of the global chert gap sedimentation in the quinn river formation was apparently continuous across the permian triassic boundary this represents the first permian triassic boundary section in the united states portion of the north american cordillera and one of the few deep water sections worldwide organic carbon isotope stratigraphy of the quinn river formation displays multiple excursions through sediments of wuchiapingian anisian age with a negative excursion 1 54 m above the chert shale transition likely representing the permian triassic boundary the multiple excursions in the organic carbon record verify studies of the carbonate carbon record in china that suggest instability in the isotopic record throughout the early triassic and demonstrate that the permian triassic boundary isotope excursion was not an isolated event stratigraphic variation in redox sensitive trace metals indicates that seawater became less oxic slightly before the chert shale transition in turn impacting siliceous sponge communities and creating the widespread chert gap the distinctive dolomicrites in the quinn river formation represent a widespread lithofacies deposited in many localities during the late permian early triassic and express early authigenic formation of dolomite via microbial sulfate reduction in organic rich low oxygen environments

geochemistry of late permian to early triassic pelagic cherts from southwest japan implications for an oceanic redox change major trace and rare earth element abundances were determined for the southwestern japanese pelagic chert sequence from the early late permian to early early triassic to investigate a redox change in deep sea pelagic environments before and at the permo triassic boundary ptb 251 ma the sequence was primarily deposited in the deep sea of the superocean panthalassa and then was accreted to japan in the middle jurassic a remarkable lithostratigraphic change from red chert to siliceous carbonaceous claystone through gray chert is observed in this sequence constituent elements for these sedimentary rocks are essentially derived from two sources 1 an ancient seawater via biogenic mainly radiolarian hydrothermal and authigenic materials and 2 an average shale like terrigenous material the present measurement demonstrates significant stratigraphic changes of the ce cenon ter value estimated ce anomaly value of non terrigenous component recalculated by subtraction of terrigenous rees from bulk rees and the mn te sample mn te paas value excess mn component other than terrigenous one te terrigenous elements including ti al nb hf th paas post archean average australian shale in the permian chert the ce cenon ter values increase from 0 2 to 1 and the mn te sample mn te paas values decrease up section suggesting that the redox condition of deep sea open ocean changed from oxic to suboxic in an interval of approximately 10 myr the fe te sample fe te paas and mn te sample mn te paas values of carbonaceous claystone near or at the ptb are less than unity suggesting that reductive dissolution of iron and manganese occurred under an anoxic condition this supports the idea of the ptb oceanic anoxia in the superocean panthalassa the present data suggest that the anoxic condition prevailed in the deep sea pelagic regions for an extremely long period much more than 10 myr from the middle late permian to early early triassic this long term development of widespread oceanic anoxia may have been linked to the greatest mass extinction of the phanerozoic

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

high organic carbon content and a decrease in radiolarians at the end of the permian in a newly discovered continuous pelagic section a coincidence article i nfo the greatest mass extinction occurred at the end of the permian most records of the mass extinction are not from pelagic sediments but from shallow marine and terrestrial sediments although several pelagic sections that span the end permian mass extinction have been found these sections contain few index fossils and are often discontinuous because of small faults we found the index fossils albaillella cf triangularis radiolaria in siliceous claystone beds hindeodus parvus conodont in the overlying black claystone beds and neospathodus cf cristagalli and ns waageni conodont in the subsequent siliceous claystone beds in akkamori section 2 in northern japan these fossils suggest that this section ranges from the late permian to the early triassic including the early induan and olenekian stages furthermore the lithological changes in the section i e starting from bedded chert through siliceous claystone and black claystone to siliceous claystone are concordant with those of well known permian triassic pelagic sequences in japan there is no gap between each lithofacie of the akkamori section 2 critical lithological continuity between upper permian siliceous claystone beds and uppermost permian to lowermost triassic black claystone beds of the akkamori section 2 was recognized by observing hand polished specimens and thin sections such paleontological and sedimentological evidence implies that the akkamori section 2 is a continuous pelagic section that records the end permian mass extinction event the carbonaceous black claystone beds have high total organic carbon toc concentrations 1 06 3 31 wt suggesting oceanic anoxia at least deep and probably stable primary productivity a decrease in radiolarian abundance from 26 563 to 0 27 20 specimens cm 2 coincided with an increase in toc content from 0 01 0 16 to 1 06 3 31 wt at the boundary of the siliceous claystone and the overlying black claystone beds near the top of the permian implying that radiolarian extinction occurred at the end of the permian coinciding with oceanic anoxia although toc contents decreased in the early olenekian smithian radiolarian abundance did not increase at that time indicating that radiolarian recovery was delayed by n1 5 m y

geochronological and hf isotopic variability of detrital zircons in paleozoic strata across the accretionary collision zone between the north china craton and mongolian arcs and tectonic implications the central asian orogenic belt formed by accretion subsequent to the contraction of the paleo asian ocean and its southeastern segment terminated along the solonker suture zone amalgamating the mongolian arcs and the north china craton by the end of the early triassic since typical regional collisional features are absent its tectonic evolution remains speculative an investigation into the variability of detrital zircon u pb ages and hf ratios in permian strata along a southeast northwest transect from the mongolian arcs to the north china craton reveals distinct differences northern basins carry a broad mesoproterozoic to latest precambrian age signature and their sedimentary source terranes are of mixed juvenile to crustal magmatic origin in contrast southern basins contain detritus from the north china craton and their sources are of dominantly crustal contaminated magmatic origin provenance analysis suggests that in the early paleozoic ca 429 ma the paleo asian ocean was consumed along the uliastai arc and the north china craton initiating the formation of the northern and southern accretionary orogens respectively by the end of the middle carboniferous the mongolian arcs were consolidated after the accretion of the uliastai arc in the late carboniferous ca 314 ma the hegenshan back arc basin opened detaching the northern accretionary orogen while subduction continued there it may have temporarily ceased in the south after the accretion of a microcontinent ca 300 ma by the end of the middle permian ca 269 ma back arc basin closure led to the formation and obduction of the suprasubduction zone hegenshan ophiolite eventually the paleo asian ocean closed by double sided subduction such accretionary wedge wedge collision would not involve continental deep subduction unlike other continental collisions the early stages of the sequence likely resembled a pacific type scenario dominated by the subduction of oceanic lithosphere including a japanese sea type back arc basin opening the late stages involved the accretion of large scale continental blocks ultimately leading to final ocean closure which may be similar to the archipelago type setting of present day southeast asia

response late permian extinctions we agree with caldeira that the mechanism we proposed 1 to account for large decreases in the c isotopic composition of surface sea water during neoproterozoic and permo triassic can work only if the negative excursions lasted for less than 10 6 years it is likely that the permo triassic boundary excursion persisted no longer than the 10 5 year time scale permitted in kump s model 2 at the proposed permo triassic boundary stratotype at meishan china the stratigraphic interval containing the excursion is 1 meter thick 3 an earlier negative excursion described by jin 4 from a capitanian wujiapingian boundary section in southwestern china is confined to a comparably thin stratigraphic interval for the one neoproterozoic negative excursion closely constrained by radiometric data uranium lead zircon dates on volcanic rocks just below and just above the event are the same to within the measurement error of one million years 5

a mid permian chert event widespread deposition of biogenic siliceous sediments in coastal island arc and oceanic basins abstract radiolarian and conodont of permian siliceous rocks from twenty three areas in teh the circum pacific and mediterranean regions reveal a widespread permian chert event during the middle leonardian to wordian radiolarian and or sponge spicule rich siliceous sediments accumulated beneath high productivity zones in coastal island arc and oceanic basins most of these deposits now crop out in fault bounded accreted terranes biogenic siliceous sediments did not accumulate in terranes lying beneath infertile waters including the marine sequences in terranes of northern and central alaska the permian chert event is coeval with major phosphorite deposition along the western margin of pangea phosphoria formation and related deposits a well known analogue for this event is middle miocene deposition of biogenic siliceous sediments beneath high productivity zones in many parts of the pacific and concurrent deposition of phosphatic as well as siliceous sediments in basins along the coast of california interrelated factors associated with both the miocene and permian depositional events include plate reorientations small sea level rises and cool polar waters

geochemical changes in baslts and andesites across the archean proterozoic boundary identification and significance abstract to identify accurately changes in rock composition across the archean proterozoic boundary it is necessary to compare rocks from similar lithologic associations to constrain the effect of tectonic setting most basalts and andesites from the greenstone association volcanic dominated submarine supracrustal rocks possess a geochemical subduction zone component similar to their counterparts from modern arc systems basalts with island arc geochemical affinities dominate in archean greenstones while those with calc alkaline affinities are most abundant in proterozoic greenstones basalts with morb or oceanic within plate geochemical characteristics are rare in precambrian greenstones of all ages preserved early archean greenstone basalts 3500 ma reflect mantle sources less depleted than late archean greenstone basalts 2500 3500 ma proterozoic greenstone basalts are derived from relatively enriched mantle sources compared to all archean sources a feature which may be due to recycling of continental sediments into the mantle following rapid late archean continental growth precambrian andesites are geochemically similar to andesites from modern arcs but archean andesites are unique in that they are depleted in heavy ree and y results are consistent with archean andesite production by partial melting of descending mafic crust with amphibole garnet remaining in the residue while proterozoic and younger andesites are produced by fractional crystallization of basalts

petrogenesis of middle triassic post collisional granite from jiefangyingzi area southeast inner mongolia constraint on the triassic tectonic evolution of the north margin of the sino korean paleoplate abstract zircon u pb dating and geochemical data are reported for the jiefangyingzi and yongshenghao granitic plutons from the jiefangyingzi area to the northeast ne of chifeng city inner mongolia with the objective of revealing the tectonic nature of the northern margin of the sino korean paleoplate in early mesozoic zircons from these granitic intrusions are euhedral and subeuhedral in shape with typical oscillatory zoning indicating magmatic origin the dating results indicate that these plutons formed in late middle triassic 229 2 ma and 229 1 ma respectively rather than in late paleozoic as previously thought the jiefangyingzi and yongshegnhao granitic plutons are composed primarily of granodiorite and granite with compositions of sio 2 63 23 68 91 wt k 2 o 3 06 4 51 wt and a cnk 0 94 0 99 chemically they belong to the high k calc alkaline series and meta aluminous i type granites zircon e hf t values of both plutons range from 2 1 to 5 0 and 1 4 to 3 9 respectively whereas the whole rock e nd t values of yongshenghao pluton range from 1 2 to 0 7 indicating the participation of depleted mantle material in their magmatic source the petrological and geochemical characteristics suggest that these plutons are post collisional granitoids combined with regional geological data we conclude that these late middle triassic granitoids formed during the transitional period from the post collision setting to the post orogenic extension setting after the collision between the siberian and sino korean paleoplates

early paleozoic magmatic history of central inner mongolia china implications for the tectonic evolution of the southeast central asian orogenic belt to provide insights into the early paleozoic tectonic evolution of the southern portion of the long lived central asian orogenic belt we have conducted major and trace element analyses and zircon u pb dating of granitoid samples from central inner mongolia our study area covers three pre mesozoic tectonic units from north to south the wenduermiao subduction accretionary complex the bainaimiao magmatic belt and the northern margin of the north china craton our new geochronological and geochemical data show the temporal and genetic relationships between the three tectonic units accordingly we suggest that the wenduermiao subduction accretionary complex developed in the middle cambrian late silurian 509 421 ma comprising of coeval oceanic crust arc magmatism and forearc deposits the bainaimiao continental arc was developed during the late cambrian to early silurian 501 437 ma which superposed on the basement with the affinity of the north china craton the back arc basin opened prior to early silurian and lasted to the late silurian which is slightly younger than bainaimiao island arc the wenduermiao ocean between the wenduermiao subduction accretionary complex and the bainaimiao continental arc existed in early paleozoic

reply to the comments on permian triassic boundary interval in the abadeh section of iran with implications for mass extinction part 1 sedimentology by e heydari j hassanzadeh w j wade and a m ghazi palaeogeography palaeoclimatology palaeoecology 193 405 424 2003 reply

geochemistry and u pb zircon dating of the toudaoqiao blueschists in the great xing an range northeast china and tectonic implications abstract the toudaoqiao complex is a sequence of high pressure metamorphic rocks located along the suture zone that separates the xing an and erguna blocks in northeast china the rocks were metamorphosed up to epidote blueschist facies at p t conditions of approximately 0 9 1 1 gpa and 320 450 c lithological associations and major and trace element compositions indicate that the blueschists are metabasalts with ocean island basalt oib and normal mid ocean ridge basalt n morb affinities similar to those of the philippines intraoceanic accretionary complex formed by subduction of oceanic crust magmatic zircons extracted from two samples of the epidote blueschist facies metabasalts from the north mountain in the toudaoqiao complex exhibit 206pb 238u ages of 511 5 and 516 17 ma whereas a greenschist from the south mountain has a 206pb 238u age of 511 2 ma these data show that the protoliths of the toudaoqiao complex are of early paleozoic age in addition a granitic dike from the south mountain exhibits a weighted mean 206pb 238u age of 492 1 ma these ages constrain the timing of high pressure metamorphism in the toudaoqiao complex to 490 510 ma the new data support the view that the suture zone between the xing an and erguna blocks is the toudaoqiao xinlin fault rather than the derbugan fault as previously thought this suture which extends from xinlin through toudaoqiao and southern mongolia named the south mongolia toudaoqiao xinlin suture zone may be an important boundary between the central mongolia erguna and xing an blocks

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

anoxia as a cause of the permian triassic mass extinction facies evidence from northern italy and the western united states facies faunal and geochemical evidence from the permian triassic boundary sediments of the dolomites and idaho indicates a major anoxic event in the earliest triassic in both regions the basal beds consist of finely laminated micrites with common syngenetic pyrite the only fauna consists of occasional bedding plane assemblages of lingula or clacaria a typical lower dysaerobic assemblage this is a level where previous studies have shown a major negative carbon isotope excursion and a cerium anomaly in the dolomites the pyritic micrite directly overlies strata containing a diverse and typically permian marine fauna of algae foraminifers including fusulinids and articulate brachiopods implying an abrupt extinction in contradiction to many previous views sequence stratigraphic analysis of the dolomite boundary sediments reveals a minor sequence boundary in the late permian followed by extremely rapid transgression leading to the development of the relatively deep water pyritic micrite a maximum flooding surface at the permo triassic boundary a further pulsed deepening in the lower griesbachian recorded in both the dolomites and idaho lead to the widespread establishment of dysaerobic facies it is clear that most of the extinctions occurred at the erathem boundary although the subsequent failure of the marine benthos to fill the empty ecospace in the ensuing griesbachian may have been due to the widespread development of dysaerobic conditions

origin and deposition of organic matter in continental chert of the middle permian gufeng formation in the northeastern yangtze platform abstract the middle permian gufeng formation in the northeastern yangtze platform china contains radiolarian chert that is characterized by black color high content of fe mo ni cu and zn based on the inorganic geochemical features previous work concluded that the cherts were deposited under sulfate reducing conditions in this study organic carbon c org n and s contents of the cherts and h c and o c ratios of kerogen were examined to explore the origin of the organic matter the concentration of c org in the black chert is extremely high relative to other cherts in accretionary complexes and continental platforms the average c n ratio of organic matter is 35 indicating that the organic matter originates from land plants the kerogen from the chert is classed as type iv based on the h c and o c ratios suggesting that oxidized or reworked organic matter was supplied to the gufeng basin therefore the organic matter is considered to originate from terrestrial plants or reworked material from land due to the depositional setting on a continental platform nutrient supplied with organic matter from land probably played an important role in abundant biogenic productivity and sedimentation of the radiolarian chert on the continental platform

guidelines for reporting zircon hf isotopic data by la mc icpms and potential pitfalls in the interpretation of these data invited technical paper high quality analytical data are essential for the development of sound scientific interpretations to ensure the quality of the data published in chemical geology a new type of contribution has been introduced the invited technical paper when a particular technical issue needing discussion or clarification is identified specialists in the technique will be invited to share their expertise as is true for all articles published in the journal these contributions will be subject to peer review before publication the first topic to be treated concerns in situ hf isotopic measurements in zircon by laser ablation inductively coupled plasma mass spectrometry this is an extremely powerful and promising technique that has been adopted by many laboratories throughout the world however if insufficient care is taken during analysis and data processing inaccurate results can be obtained notably because of the existence of very large isobaric interferences on the isotope of interest to address this issue we have asked christopher fisher jeffery vervoort and john hanchar to provide a set of guidelines that can be adopted to assure that reliable hf isotopic data are obtained by this technique abstract over the past decade the hf isotope composition of zircon as determined in situ by laser ablation multicollector inductively coupled plasma mass spectrometry la mc icpms has been applied increasingly to a wide range of geological problems and has proven to be a valuable analytical tool there has been no uniformity however in the reporting of in situ hf isotopic data and quite often reviewers and readers of papers are not provided with sufficient information to assess data quality the goal of this invited contribution is to provide the non specialist with a brief outline and explanation of what is required for proper presentation and documentation of in situ hf isotopic data from zircon including details of how the challenging large isobaric interference corrections have been made in addition we discuss a number of potential pitfalls vis a vis the assignment of the incorrect age to the measured hf isotope composition non specialists should be aware of these important issues when doing their own analyses and evaluating the analyses done by others

the pre devonian tectonic framework of xing an mongolia orogenic belt xmob in north china abstract a new tectonic division of the xing an mongolia orogenic belt xmob in north china has been presented according to our research and a lot of new data of tectonics geochronology and geochemistry four blocks and four sutures have been recognized in the xmob including the erguna eb xing an airgin sum xab songliao hunshandake shb and jiamusi jb and xinlin xiguitu xxs xilinhot heihe xhs mudanjiang ms and ondor sum yongji sutures oys the framework of the xmob is characterized by a tectonic collage of the blocks and orogenic belts between them different precambrian basements have been found in the blocks including the neoproterozoic metamorphic rocks and plutons in the eb the neoproterozoic metamorphic rocks in western and eastern of segments of the xab mesoproterozoic and neoproterozoic metamorphic rocks in middle segments of the xab respectively the neoproterozoic metamorphic rocks and mesoproterozoic volcanic rocks and plutons in the shb and neoproterozoic metamorphic rocks in the jb the xxs resulted from a northwestward subduction of the xab beneath the eb during the cambrian which was followed by the forming of the xhs and oys in the northwest and south margins of the shb in the silurian respectively the ms was caused by a westward subduction of the jb beneath the east margin of the shb during the middle devonian the three cambrian silurian and middle devonian events indicate that the xmob belongs to a pre middle devonian multiple orogenic belt in the central asian orogenic belt caob forming of the xmob suggests that the southeast part of the paleo asian ocean closed before the middle devonian

hominin evolution in settings of strong environmental variability abstract investigations into how climate change shaped human evolution have begun to focus on environmental dynamics i e the nature and tempo of climate and landscape variability an approach that de emphasizes static reconstructions of early hominin habitats the interaction among insolation cycles is especially apparent in the paleoenvironmental records of the east african rift system where the longest records of human evolution are preserved however environmental indicators such as deep sea oxygen isotopes terrestrial dust flux paleosol carbon isotopes and lake sediments do not point consistently to any simple trend or climate driver of evolutionary change comparison of environmental indicators cautions against an exclusive focus on any given end member of environmental fluctuation driest or wettest warmest or coolest and argues for the impact of the entire range of variability in shaping evolutionary change a model of alternating high and low climate variability for tropical africa further implies that specific environmental indicators reflect different aspects of east african environmental dynamics the model may thus help reconcile some of the conflicting interpretations about the environmental drivers of hominin evolution first and last appearances of hominin lineages benchmark biogeographic events and the emergence of key adaptations and capacities to alter the surroundings are consistently concentrated in the predicted longest intervals of high climate variability the view that emerges is that important changes in stone technology sociality and other aspects of hominin behavior can now be understood as adaptive responses to heightened habitat instability

lower triassic δ13c isotope curve from shallow marine carbonates in japan panthalassa realm confirmation of the tethys δ13c curve abstract 13 c data from tethyan sections provide evidence of profound changes in the carbon cycle during the lower triassic sections from the panthalassa realm were investigated to establish whether these variations are also present there in the jurassic accretionary wedges in japan exotic blocks having a panthalassan affinity have been incorporated the majority of the blocks are pelagic cherts but rare shallow water carbonates are also present we present a 13 c study on the lower triassic of a shallow water carbonate succession deposited on a mid oceanic seamount and accreted to the chichibu belt japan two sections have been measured at kamura central kyushu island the carbon isotope curve shows depleted values across the permian triassic boundary ptb subsequently followed by an increase to heavier values into the dienerian culminating in a maximum of almost 4 v pdb before a steep drop at a stratigraphic gap low values are recorded in the smithian but rise to enriched 13 c values 3 5 near the smithian spathian boundary the observed trend of the stable carbon isotope curve from japanese sediments mirrors the curves derived from sections in the tethys e g italy iran turkey oman and the south china nanpanjing basin our results support the interpretation of this curve as representing a global trend across the ptb and in the lower triassic although some distinct features are absent around the dienerian smithian boundary profound variations of the carbon isotope curve in the lower triassic are presented for the first time from a marine section outside of the tethys they indicate severe global changes in the lower triassic carbon cycle and the causative processes must have significantly contributed to the delayed biotic recovery after the ptb large amounts of carbon were shifted between carbon reservoirs most probably between shallow and deep ocean waters and or ocean and sediment anoxia followed by overturn of the ocean water masses may have been the mechanism which quickly altered ecological conditions in the ocean leading to variable availability of nutrients and oxygen and changes in isotope composition of the available carbon in the surface waters that was incorporated in the precipitated carbonate

petrography of late cambrian to middle ordovician radiolarian chert in kazakhstan with special reference to the emergence of benthic animals in the pelagic realm

trace fossils of ordovician radiolarian chert and siliceous mudstone in newfoundland canada abstract ordovician radiolarian chert and siliceous mudstone in newfoundland are examined to elucidate the development of trace fossils in and on the early paleozoic ocean bottom chert sedimentation in the shoal arm formation saf is limited to a short interval but its sedimentation rate is high with few siliciclastic materials trace fossils are common in chert in the saf but their development is interrupted by frequent anoxic events the trace fossils are larger than trace fossils in the contemporary chert of other areas in contrast trace fossils in the strong island chert sic are moderately sized to small with a few sandstone beds interbedded with chert those characteristics reflect differences in the sedimentary environments rocks of the sic were deposited in a basinal part of a back arc basin whereas those in the saf were deposited on a small isolated basin red chert or siliceous rocks that underlie grey cherts and siliceous rocks of the sic and the saf bear small and simple trace fossils this is a common feature of oceanic red rocks radiolarian chert and siliceous rocks in newfoundland also showed that trace fossils are widespread by the middle ordovician in the deep sea environment the great ordovician biodiversification event is confirmed in the radiolarian siliceous rocks there

permian triassic mass extinction event recorded in bedded chert sequence in southwest japan rock types in southwest japan change across the permian triassic boundary late permian bedded chert grades upward into latest permian siliceous claystone carbonaceous mudstone of unknown age early triassic siliceous claystone with carbonaceous mudstone and chert interbeds and then into middle triassic to jurassic bedded chert these stratigraphic lithologic variation also accompany the decline and recovery of radiolarians in the changxingian stage and smithian stage respectively the permian triassic boundary is not precisely defined because of poor stratigraphic control but it is thought to occur at the boundary between the carbonaceous mudstone and the changxingian siliceous claystone or somewhere in the carbonaceous mudstone during the griesbachian stage there was deposition of carbonaceous mudstone in deep pelagic seas bioturbation structures and the massive nature of carbonaceous mudstone indicate dysaerobic but not anoxic condition in a strict sense the dramatic decrease in productivity of radiolarians preceded the sedimentation of carbonaceous mudstone which suggests that oxygen deficient conditions were not the primary cause of mass extinction red tide type conditions inferred from the increased primary productivity in the pelagic seas and the oxygen deficiency in the epicontinental seas are the last hit against the biosphere in the chain of events that started from late permian and caused the greatest mass extinction of the phanerozoic correlation between lithologic variations of bedded cherts and 13c excursions of carbonate rocks clarifies the processes of simultaneous massive decline and recovery of biomass as represented in both group of rocks

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

growth and demise of permian biogenic chert along northwest pangea evidence for end permian collapse of thermohaline circulation abstract the permian chert event pce was a 30 ma long episode of unusual chert accumulation along the northwest margin of pangea and possibly worldwide the onset of the pce occurred at about the sakmarian artinskian boundary in the sverdrup basin canadian arctic where it coincides with a maximum flooding event the ending of high frequency high amplitude shelf cyclicity the onset of massive biogenic chert deposition in deep water distal areas and a long term shift from warm to cool water carbonate sedimentation in shallow water proximal areas a similar and coeval shift is observed from the barents sea to the northwestern usa a landward and southward expansion of silica factories occurred during the middle and late permian at which time warm water carbonate producers disappeared completely from the northwest margin of pangea biotically impoverished and increasingly narrow cold water carbonate factories characterised by non cemented bioclasts of sponges bryozoans echinoderms and brachiopods were then progressively replaced by silica factories by late permian time little carbonate sediments accumulated in the barents sea and in the sverdrup basin where the deep to shallow water sedimentary spectrum was occupied by siliceous sponge spicules by that time biogenic silica sedimentation was common throughout the world silica factories collapsed in the late permian abruptly bringing the pce to an end in northwest pangea the end permian collapse of the pce was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions chert deposition resumed in the distal oceanic areas during the early middle triassic anisian after a 8 10 ma interruption early triassic chert gap the conditions necessary for the onset expansion and zenith of the pce were provided by the thermohaline circulation of nutrient rich cold waters along the northwestern and western margin of pangea and possibly throughout the world oceans these conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area created a nutrient and oxygen rich environment favouring siliceous biogenic productivity established cold sea floor conditions hindering silica dissolution while increasing calcium carbonate solubility and provided conditions adverse to organic and inorganic carbonate production the northwest margin of pangea was for nearly 30 ma bathed by cold waters presumably derived from the seasonal melting of northern sea ice the assumed engine for thermohaline circulation this process started near the sakmarian artinskian boundary intensified throughout middle and late permian time and ceased suddenly in latest permian time it led to oceanic conditions much colder than normally expected from the palaeolatitudes and the influence of cold northerly derived water was felt as far south southern nevada the demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production accumulation and preservation of biogenic silica

high productivity in the earliest triassic ocean black shales southwest japan abstract bedded cherts containing the permian triassic p t boundary exposed in the tanba and chichibu belts southwest japan contain interbedded organic rich black shales the organic carbon concentration of black shales before thermal maturation was evaluated to be about 3 average considering their maturity levels kerogens do not contain any debris of higher plant origins but are mostly composed of structureless amorphous kerogen black shales comprise organic matter derived mainly from plankton with additional organic matter derived from bacterial activity showing that the high primary production took place intermittently in the earliest triassic a stratified ocean with a well developed oxygen minimum layer rich in nutrients was intermittently disturbed due to tectonically and or climatically induced active ocean current systems in the earliest triassic resulting in upwelling causing remarkably high primary production to form organic rich black shales

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

an intercalibrated triassic conodont succession and carbonate carbon isotope profile kamura japan abstract the kamura section located in the chichibu belt of kyushu island in southern japan contains a succession of uppermost permian to upper triassic shallow marine atoll sediments from the mid panthalassic ocean in the present study carbonate microfacies conodont biostratigraphy and carbonate carbon isotopes were analyzed making it possible to construct a detailed biochronological framework for the triassic of the central panthalassic region a total of 14 conodont zones are recognized from the uppermost changhsingian to the upper norian the lower triassic contains the hindeodus parvus isarcicella isarcica and h postparvus zones griesbachian the neospathodus dieneri zone dienerian and the novispathodus ex gr waageni parachirognathus zone smithian while no evidence of the upper lower triassic spathian substage was recovered at kamura the overlying middle triassic section consists of the chiosella ex gr timorensis cratognathus paragondolella ex gr alpina pg ex gr excelsa budurovignathus hungaricus and b mungoensis zones followed in the upper triassic by the quadralella tadpole gladigondolella malayensis q lobata q carpathica primatella cf orchardi pr permica epigondolella rigoi pg hallstattensis and e ex gr bidentata norigondolella steinbergensis zones the exact stratigraphic intervals present at kamura were refined through intercalibration of the conodont biozonation data with its 13ccarb profile which shows a characteristic series of negative and positive excursions that correspond to well established global reference profiles the permian triassic boundary is placed 0 20 m above the mitai kamura formation contact a reference datum corresponding to the end permian extinction horizon 0 m based on the first appearance of h parvus and the olenekian anisian boundary is placed 17 60 m above the reference datum based on the first appearance of ch ex gr timorensis kamura carbonates were assigned to six fabric types and 17 microfacies the microfacies succession records a deepening immediately following the end permian mass extinction a strong shallowing during the mid to late smithian development of an unconformity spanning the entire spathian and minor sea level fluctuations during the middle and late triassic the spathian unconformity is attributed to a eustatic fall related to a sharp cooling event at or close to the smithian spathian boundary that exposed the kamura atoll the subsequent resumption of shallow marine sedimentation in the earliest middle triassic was probably due to continued thermal subsidence of the oceanic crustal basement beneath the atoll the present work is the most complete analysis to date of the conodont biostratigraphic carbon isotope chemostratigraphic and eustatic records of the triassic system in the central panthalassic ocean and should serve as a regional reference standard in the future

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

episodic euxinia in the changhsingian late permian of south china evidence from framboidal pyrite and geochemical data abstract a multiproxy study of a new upper permian lower triassic section xiaojiaba in sichuan province china documents large changes in marine productivity redox conditions and detrital input prior to the latest permian mass extinction marine productivity as proxied by total organic carbon content toc biogenic sio 2 and excess barium displays a long term decline through most of the changhsingian stage late late permian culminating in very low values around the permian triassic boundary concurrently redox proxies including pyrite framboid 34 s py mo auth and u auth and c org p document a shift from suboxic to dysoxic oxic conditions that was interrupted by several episodes of benthic euxinia and detrital siliciclastic proxies al hf nb and rees suggest an increased flux of weathered material from land areas the long term changes in productivity redox conditions and terrigenous detrital fluxes were probably caused by a regional sea level fall across the south china craton on the other hand the brief euxinic episodes occurring during the late permian had oceanographic causes probably related to the transient upward expansion of the chemocline at the top of the oceanic oxygen minimum zone these euxinic episodes may have been harbingers of the more widespread anoxia that developed concurrently with the latest permian mass extinction and that may have played a major role in triggering the largest biotic crisis of the phanerozoic

ostracods crustacea through permian triassic events abstract through geological times the main turnover of marine ostracod group occurred at the permian triassic boundary ptb when the palaeozoic world gave way to meso cenozoic world as quite all the groups ostracods intensively suffered of the end palaeozoic events but they have the particularity to pass the ptb and to be present in quite all marine environments we have studied the ostracod assemblages from the best preserved marine permian triassic sections through the world these sections are for most of them located along the palaeo tethys margins south china block and tibet r p china bukk mountains hungary dolomites italy taurus mountains turkey and elbourz mountains iran these areas present different environmental settings from very shallow water to deep shelf the biostratigraphy is well constrained by the presence of conodont index in deep environment from external shelf to slope all the permian ostracods disappear slightly before the ptb and are absent from the early triassic the last representatives of palaeopsychrospheric forms occur in the early anisian on the platforms during the late permian the ostracods are abundant and highly diversified everywhere along peri tethyan margins the typical palaeozoic forms are mixed with the very first meso cenozoic representatives the specific extinction rates in the latest permian vary from 74 to 100 during the earliest triassic two different settings have to be considered with or without microbialitic deposits the development of microbialites gives favorable ecological conditions to ostracods during the griesbachian the fauna is composed of both new comers and surviving palaeozoic forms the reduction of size is frequently observed this interval is called survival stage during the dienerian and the smithian the fauna are very scarce and poor these two substages represent the maximum of poverty for the ostracod fauna may be due to the development of anoxia on the platforms during the spathian occurs the beginning of the true recovery the very last palaeozoic representatives are found in the earliest anisian which is the radiation stage of ostracod fauna with typical new comers the interval of palaeozoic meso cenozoic ostracod turnover is quite long about 15 my

zircon ages and hf isotopic compositions of ordovician and carboniferous granitoids from central inner mongolia and their significance for early and late paleozoic evolution of the central asian orogenic belt abstract we present zircon ages and hf in zircon isotopic data for plutonic rocks and review the evolution of central inner mongolia china in the early and late paleozoic zircons of a granodiorite yielded a 206 pb 238 u age of 472 3 ma that reflects the time of early paleozoic magmatism zircon ages were also obtained for a tonalite 329 3 ma quartz diorite 320 3 ma and granite vein 297 2 ma our results in combination with published zircon ages and geochemical data document distinct magmatic episodes in central inner mongolia the dated samples are mostly granodiorite tonalite and quartz diorite in composition with intermediate to high silica high na 2 o 3 08 4 26 wt low k 2 o 0 89 2 86 wt and high na 2 o k 2 o and sr y ratios their chondrite normalized ree patterns are characterized by lree enrichment in mantle normalized multi element variation diagrams they show typical negative nb and ta anomalies and all samples display positive e hf t and e nd t values and low i sr the ordovician rocks however show higher sr y and la yb ratios than the carboniferous samples implying that the older granitoids represent adakitic granitoids and the carboniferous granitoids are typical subduction related arc granitoids but also with adakite like compositions the results are compatible with the view that the central asian orogenic belt caob in inner mongolia evolved through operation of several subduction systems with different polarities an early middle paleozoic subduction and accretion system along the northern margin of the north china craton and the southern margin of the mongolian terrane and late paleozoic northward subduction along the northern orogen and exhumation of a high pressure metamorphic terrane on the northern margin of the north china craton

deev jahi model of the permian triassic boundary mass extinction a case for gas hydrates as the main cause of biological crisis on earth the smoking gun revealing the secrets of the end permian mass mortality is a unique 1 2 m thick layer consisting of 5 20 cm long crystals of calcite that occurs precisely at the permian triassic boundary ptb in iran armenia turkey and china this layer is interpreted as synsedimentary abiotic seafloor cement indicative of precipitation from a highly carbonate supersaturated seawater its 13 c composition 13 c 0 pdb is 4 to 5 pdb lower than the typical upper permian values 4 to 5 pdb suggesting the involvement of massive amounts of gas hydrate ch 4 13 c 60 pdb the temporal coincidence of the cement layer with the ptb suggests that the process that promoted seafloor cementation was also responsible for the biological crisis a cementation model is developed based on accumulation dissociation cycle of gas hydrates which also explains the mass extinction at the ptb the upper permian accumulation period of gas hydrates ended abruptly adjacent to the ptb and the dissociation event began releasing 3 2 to 4 7 10 18 g ch 4 into the ocean oxidation of ch 4 in the water column created a seawater that was charged with co 2 an oceanic acid bath and had lower than normal o 2 content but not anoxic this oceanic acid bath first dissolved suspended fine grained carbonate particles and small calcareous organisms followed by extensive dissolution of platform carbonates raising ca 2 and hco 3 concentrations of seawater when the release of ch 4 declined the acid bath ocean became a soda ocean precipitating massive amount of seafloor cements observed globally at the ptb the study suggests that prior to cement precipitation the ptb ocean was charged with co 2 warm had low oxygen high ca 2 and high hco 3 concentrations these conditions collectively created stressful conditions causing the marine mass mortality the leakage of ch 4 to the atmosphere produced a super hot climate resulting in the biological devastation on land the proposed kill mechanism is developed on the basis of the physical clue the cement layer left behind by the killing process the change in ocean chemistry the accumulation dissociation cycles of gas hydrates also explain the 13 c pattern of marine carbonates and the periodicity of mass extinction events during the phanerozoic accumulation periods were long 5 to 20 my providing favorable conditions for ecosystem development pardeess phase the dissociation events were short and catastrophic 10 to 500 ky causing low oxygenation super hot climate and biological devastation doozakh phase it appears that most mass extinctions of the phanerozoic have been related to the internal working of the earth system during the phanerozoic methane has played the role of the deev jahi a female demon in persian mythology whose task is to attack the earth every so often to kill life on land and in sea

global warming leads to early triassic nutrient stress across northern pangea the largest extinction in earth history in the latest permian was followed throughout most of the early triassic by a prolonged period of ecologic recovery what factors delayed biotic recovery are still under debate and partly revolve around impacts of global warming on primary marine productivity we examined n isotope records from the festningen section on spitsbergen to examine changes in nutrient availability through the early to middle triassic along the northern margin of pangea our results show progressive decline in n availability throughout the griesbachian leading to severe nutrient limitations through the remainder of the early triassic until returning to a highly productive continental margin in middle triassic time these results are consistent with other studies from northern and western pangea and thus show regional nutrient limitations occurred in what should have been the main zone of marine primary productivity such nutrient limitation likely stressed primary production and consequently contributed to prolonged marine recovery we suggest this was driven by high ocean temperatures depressing the marine nutricline

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

an extraterrestrial impact at the permian triassic boundary becker et al 1 presented geochemical evidence that suggests that the largest mass extinction in earth history at the permian triassic boundary ptb 250 million years ago ma coincided with an extraterrestrial impact comparable in size to the one that likely caused the end cretaceous extinctions 65 ma 2 although becker et al analyzed material from sections in hungary japan and china the hungarian section yielded no extraterrestrial signature and their identification of the ptb in the japanese section is questioned in the accompanying comment by isozaki below thus only their analyses of the chinese section provide hitherto uncontested evidence for an impact at the boundary in the form of data on the abundance and composition of fullerenes in the boundary clay a volcanic ash layer called bed 25 at meishan china 3 although fullerenes may be purely terrestrial see e g 4 becker et al report that the fullerenes from the meishan ash carry extraterrestrial noble gases in the cage structure rich in 3 he and with distinctive 3 he 36 ar and 40 ar 36 ar ratios and that this signature therefore derived from a bolide impact here we report that we are able to detect fullerene hosted extraterrestrial 3 he neither in aliquots of the same meishan material analyzed by beckeret al nor any in samples of a second chinese ptb section and that we thus find no evidence for an impact

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

bounded by crises an overview of the evolution of marine ostracods during the triassic abstract the triassic was a turning in the history of biodiversity bracketed by two major biotic crises characterised by major biotic climatic and tectonic events it saw the transition from the palaeozoic to the modern evolutionary faunas herein we propose the first synthetic analysis of the diversity of marine and brackish water ostracods over the entire triassic in the light of palaeoecological palaeoenvironmental and palaeogeographical contexts although general diversity trends witnessed poor ostracod communities during most of the early triassic after the end permian crisis the roots of their triassic taxonomic rediversification were visible as early as the dienerian the explosive diversification of the spathian and anisian was followed by a high diversity plateau up to the brink of the end triassic extinction a morphological phylogeny proposes that all permian and triassic ornate bairdiidae derived from petasobairdia in the kungurian with the emergence of the ceratobairdia lineage and abrobairdia lineage while they are generally the poor cousin of trophic chain analyses traces of typical mesozoic drilling predation on late triassic ostracods unexpectedly document the increase in the efficiency of predators drilling abilities through the triassic finally the palaeogeographical distribution of ostracods was very dynamic during this interval with distinct peri palaeo tethyan and peri neotethyan biotas in the early triassic followed by a dispersal and thus a relative homogenisation from the anisian onwards

panthalassic oceanic anoxia at the end of the early triassic a cause of delay in the recovery of life after the end permian mass extinction abstract fossil data show that the recovery of life after the end permian mass extinction occurred in the anisian early middle triassic the process by which oceanic environments recovered from anoxia after the end permian event is uncertain to determine the timing of known recovery stages the nature of oceanic redox conditions and the health of cyanobacterial plankton populations this study analyses conodonts and organic molecules from siliceous claystones and cherts from accretionary complexes in japan that span the upper lower triassic to the lowermost middle triassic conodonts indicate that the study section ranges from upper olenekian to anisian and includes the olenekian anisian boundary an increase in polycyclic aromatic hydrocarbons probably derived from algae dominated organic matter and a decrease in methylhopane index 2 methylhopane hopane a measure of cyanobacterial activity are present in end olenekian black chert pristane phytane ratios a measure of redox conditions in all stratigraphic units are lower than 1 indicating the prevalence of deep sea anoxia during the late olenekian to anisian high concentrations of dibenzothiophene an index of anoxic depositional environments high sulphur carbon ratios and high organic carbon contents are present in two upper olenekian intervals and at the end of the upper olenekian suggesting development of anoxic deep water one of the anoxic events in the end of the upper olenekian coincided with decreased radiolarian diversity this implies that anoxic deep water in the panthalassic ocean reached intermediate water depths at the end of the early triassic killing marine organisms including radiolaria this event may be related to the delay in the recovery of life and environments after the end permian mass extinction

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

phanerozoic evolution of the inner mongolia daxinganling orogenic belt in north china constraints from geochronology of ophiolites and associated formations

quaternary history of the lake magadi basin southern kenya rift tectonic and climatic controls abstract sediments from the magadi basin south kenya rift preserve a one million year palaeoenvironmental record that reflects interactions between climatic volcanic and tectonic controls climate changes that impacted sedimentation include wet dry cycles on variable timescales and an overall progressive trend towards greater aridity volcanic influences involved inputs of tephra to the basin significant inflow of geothermal fluids and the effects of weathering erosion and transportation of clastics from trachyte and basalt terrains tectonic controls which were often step like reflect the influence of faults that provided pathways for fluids and which controlled accommodation space and drainage directions intensified aridity and evaporative concentration resulted in salinity and ph increasing with time which led to a change from calcite deposition in mildly saline lakes before 380 ka to the later formation of zeolites from reactions of volcaniclastic debris with highly alkaline lake and pore water after 105 ka hyperalkaline conditions led to trona accumulation and increasingly variable rare earth elements rees the presence of mixed saline and freshwater diatom taxa between 545 and 16 ka indicates climate variability and episodic inputs of fresh water to saline lakes calcrete formed in lake marginal settings during semi arid periods tectonic controls operated independently of climate but they interacted together to determine environmental conditions aquatic deposition was maintained during periods of increasing aridity because fault controlled ambient and geothermal springs continued to flow lakewards this recharge in turn limited pedogenesis palaeosols are common in other rift floor sequences trona formed when aridity and evapoconcentration increased but its precipitation also reflects increased magmatic co2 that ascended along faults basin fragmentation and north south fractures caused loss of cross rift east west drainage from rift marginal basalts resulting in reduced transition metals after 545 ka the magadi basin demonstrates how a careful reconstruction of these complex tectono climatic interactions is essential for accurate palaeoenvironmental reconstruction in continental rifts and in other tectonic settings

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

late early triassic climate change insights from carbonate carbon isotopes sedimentary evolution and ammonoid paleobiogeography the late early triassic sedimentary facies evolution and carbonate carbon isotopemarine record 13ccarb of ammonoid rich outer platform settings show striking similarities between the south china block scb and the widely distantnorthern indianmargin nim the studied sections are located within the triassic tethyshimalayan belt losar section himachal pradesh india and the nanpanjiang basin in the south china block jinya section guangxi province respectively carbon isotopes from the studied sections confirm the previously observed carbon cycle perturbations at a time of major paleoceanographic changes in the wake of the end permian biotic crisis this study documents the coincidence between a sharp increase in the carbon isotope composition and the worldwide ammonoid evolutionary turnover extinction followed by a radiation occurring around the smithian spathian boundary based on recent modeling studies on ammonoid paleobiogeography and taxonomic diversity we demonstrate that the late early triassic smithian and spathian was a time of a major climate change more precisely the end smithian climate can be characterized by a warm and equable climate underlined by a flat pole to equator sea surface temperature sst gradient while the steep spathian sst gradient suggests latitudinally differentiated climatic conditions moreover sedimentary evidence suggests a transition froma humid and hot climate during the smithian to a dryer climate fromthe spathian onwards by analogywith comparable carbon isotope perturbations in the latedevonian jurassic andcretaceouswe propose that high atmosphericco2 levels could have been responsible for the observed carbon cycle disturbance at the smithian spathian boundary we suggest that the end smithian ammonoid extinction has been essentially caused by a warm and equable climate related to an increased co2 flux possibly originating froma short eruptive event of the siberian igneous province this increase in atmospheric co2 concentrations could have additionally reduced the marine calcium carbonate oversaturation and weakened the calcification potential of marine organisms including ammonoids in late smithian oceans