early devonian alkaline intrusive complex from the northern north china craton a petrological monitor of post collisional tectonics abstract laser ablation inductively coupled plasma mass spectrometry zircon u pb dating and geochemical data document the early devonian sandaogou alkaline complex 409 ma from the northern margin of the north china craton the rock suite includes pyroxene syenite quartz syenite and monzonite these rocks exhibit high contents of k 2 o 5 13 wt strong enrichments in large ion lithophile elements and light ree slightly negative eu anomalies and pronounced depletions in high field strength elements they are characterized by moderate 87 sr 86 sr i ratios of 0 7052 0 7071 low e nd t values of 12 7 to 17 9 and zircon e hf t values from 27 8 to 32 3 these geochemical features and quantitative isotopic modelling suggest that they might have been formed through simultaneous fractional crystallization and lower crustal assimilation of a metasomatized mantle derived alkali basaltic magma these trachytic rocks together with the middle devonian alkaline rocks and mafic ultramafic complex from neighbouring regions constitute a linear post collisional magmatic belt along the northern north china craton possibly formed under a tectonic regime of slab breakoff they serve not only as a magmatic milestone for marking the termination of early palaeozoic orogenic cycle around the northern north china craton but also as a spatial tracer for locating the position of the potential ancient slab breakoff at the surface supplementary material analytical methods mineral composition data field and zircon cathodoluminescence cl photographs are available at http www geolsoc org uk sup18403

geochemical characteristics of the permian basins and their provenances across the solonker suture zone assessment of net crustal growth during the closure of the palaeo asian ocean abstract the solonker suture zone is commonly recognised as the location of the late permian to early triassic closure of the palaeo asian ocean in the southeastern segment of the central asian orogenic belt however the absence of typical suture related features as a consequence of uncommon collisional geometries gave it a cryptic nature thus the tectonic setting which led to suturing still remains enigmatic a geochemical characterisation of permian sedimentary and volcanic rocks across the suture was carried out supplemented with hf and nd isotopic analyses this approach enables not only a better definition of such regional suture but also estimates on the long controversial issue of net crustal growth in accretionary tectonic environments the results indicate short sedimentary transport distances between the arc basins and their provenances of which the studied volcanic rocks were a major contributor similar enrichment and depletion patterns with respect to n morb and average continental crust further corroborate a close source sediment relationship immobile element provenance analyses indicate that the active continental northern margin of the north china craton was a major source for arc basins to the south of the solonker suture zone to its north arc basins are interpreted to be sourced by a more complex mixture of provenances e g the baolidao volcanic arc suite and the heterogenous precambrian basement of southern mongolia an overall collisional tectonic setting across the suture is recognised the geochemical signature of sedimentary rocks to the south of the suture points at an active continental arc setting whereas the bimodal geochemical distribution of the samples to the north shows a contemporaneous active oceanic island arc as well as a passive margin environment these features favour a double sided subduction of the palaeo asian ocean beneath the north china craton and the mongolian arcs throughout the palaeozoic including back arc basin opening north of the suture in the permian analysis of hf and nd isotopic compositions revealed that magmas to the south were produced involving significant crustal contamination thus having less radiogenic compositions north of the suture however isotopic compositions tend to be more radiogenic implying a more juvenile contribution however the bulk isotopic compositions are close to present day chur suggesting that crustal reworking appears to be equally balanced by juvenile addition during the palaeozoic closure of the palaeo asian ocean across the solonker suture zone

episodic fluid migration in the fennoscandian shield recorded by stable isotopes rare earth elements and fluid inclusions in fracture minerals at forsmark sweden abstract drilling through the palaeoproterozoic bedrock at forsmark central sweden during the site investigation for a potential geological repository of highly radioactive nuclear waste has provided high quality drill core material from the upper 1 km of the fennoscandian shield analyses of stable isotopes 13c 18o 34s 87sr 86sr rare earth elements and fluid inclusions in fracture filling calcite and pyrite from these drill cores have resulted in the discrimination of several episodes of fracture mineralisations these events represent migration of fluids during a wide range of conditions ranging from high temperature hydrothermal to present day groundwater circulation four major events have been distinguished 1 precipitation of epidote chlorite and quartz under hydrothermal conditions t 150 200 c during the proterozoic sometime between 1 8 and 1 1 ga 2 hydrothermal circulation at temperatures close to 200 c with precipitation of adularia albite prehnite laumontite calcite and chlorite most of these minerals precipitated during a tectonothermal event between 1 1 and 1 0 ga possibly in response to far field effects of the sveconorwegian orogeny 3 precipitation of mainly quartz calcite pyrite and asphaltite occurred during the palaeozoic at temperatures between 60 and 190 c mainly at

final amalgamation of the tianshan and junggar orogenic collage in the southwestern central asian orogenic belt constraints on the closure of the paleo asian ocean abstract the tianshan and junggar orogenic collage occupies the southwestern part of the central asian orogenic belt and was assembled by collision accretion of several continental blocks and island arcs during late paleozoic early mesozoic time following the consumption of the junggar and south tianshan oceanic basins in the western segment of the paleo asian ocean considerable and continuing controversy has surrounded when where and how this orogenic collage was eventually amalgamated which plays a crucial role in understanding the formation of the central asian orogenic belt this review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains a comprehensive data compilation indicates that the formation of ophiolites along major sutures in the tianshan and junggar region lasted to the early carboniferous for the kalamaili suture zone to the mid carboniferous for the west junggar region and the north tianshan suture zone and to the late carboniferous for the south tianshan suture zone ca 325 310 ma ultra high pressure metamorphism along the western part of the south tianshan suture occurred nearly synchronously with the collision between the tarim craton and the central tianshan yili block the oceanic closure and collision events were sequentially followed by widespread and intensive a type granitic and bimodal magmatism which commenced in the mid carboniferous along the kalamaili belt and in the latest carboniferous to earliest permian in other regions contemporaneously large scale strike slip shearing took place along major faults subparallel to main sutures with a dominant dextral sense and deformation time since the carboniferous permian transition available data and geological evidence support an eastward propagating scissor like closure of the western segment of the paleo asian ocean along the south tianshan and north tianshan suture zones over a period from the mid to end carboniferous with the south tianshan belt representing the final suturing site in the early permian the tarim mantle plume likely merely affected the southwestern part of the assembled tarim and tianshan region as indicated by regional discrepancy in type and geochemistry of early permian a type granitoids the amalgamation of the tianshan and junggar orogenic collage was associated with the tectonic bending of the kazakhstan orocline leaving a piece of trapped oceanic crust in its middle part beneath the present junggar basin

increasing restriction of the egyptian shelf during the early eocene new insights from a southern tethyan carbonate platform the evolution of the isolated galala carbonate platform has been studied intensively with respect to the paleocene eocene thermal maximum petm and the strong climatic variability from the late paleocene to the early eocene in this study we compare the results of different approaches which deal with the early palaeogene evolution of the egyptian shelf including new data from the galala platform microfacies analyses along a platform to basin transect reveal a sedimentological response to a massive tectonic uplift along the syrian arc fold belt in the early eocene this uplift triggered the restriction of the egyptian shelf by modulating and weakening tethyan onshore currents from the north the increasing deposition of quartz and proliferating gastropods green algae and radiolaria which indicate elevated nutrient levels reflect an intensified eutrophication of shallow marine platforms and deeper marine shelf environments strongly depleted carbon isotope ratios in the sediments of the galala succession strongly suggest the presence of restricted conditions throughout the early eocene we assume that a strong climatic divergence with arid conditions on the shelf and humid conditions at the african hinterland triggered intensified chemical weathering at the nubian arabian craton the enhanced riverine transport of terrestrial organic material to the north african shelf caused the increased availability of trophic resources and a strong negative shift of carbon isotope ratios between np10 and np14a the recovery to open ocean conditions is linked to the termination of tectonic uplift along the syrian arc fold belt in the latest early eocene and to stronger ocean currents caused by increasing latitudinal temperature gradients additionally the post petm carbon isotope evolution at the galala platform indicates at least two further negative carbon isotope excursions which reflect hyperthermal events on a global scale the associated reorganization of shallow marine assemblages as described for example for the larger foraminifera turnover at the petm boundary event is however missing we assume that the absence of a foraminiferal reorganization in this region can be linked to an increasing robustness of the major early eocene platform organisms larger benthic foraminifera and their adaption to unfavorable conditions and repeated environmental shifts 2011 elsevier b v

kick starting ancient warming rapid global warming marked the boundary between the palaeocene and eocene periods 55 6 million years ago but how the temperature rise was initiated remains elusive a catastrophic release of greenhouse gases from the kilda basin could have served as a trigger

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

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

the permian triassic granitoids in bayan obo north china craton a geochemical and geochronological study abstract granitoids near the bayan obo giant rare earth element ree deposit at the north margin of the north china craton ncc the world s largest light ree lree deposit have been taken by some authors as the key factors that controlled the mineralization in contrast others proposed that the ree deposit has been partially destructed by these granitoids here we report systematic studies on geochronology and geochemical characteristics of granitoids of different distances from the orebodies to investigate the genesis and their relationship to the giant bayan obo deposit granitoids studied here including granites and quartz monzonites are peraluminous with a cnk 0 99 1 11 lree enriched and heavy ree hree depleted with variable ree concentrations total ree 54 330 ppm and large negative eu anomaly eu 0 19 0 70 the ree patterns are distinct from those of ore bearing dolomites some samples have slightly higher lree concentrations which may have been contaminated by the orebodies during intrusion trace elements of the granitoids are characterized by positive pb anomaly strong negative ti anomaly and nb ta and sr anomalies the granites exhibit negative ba anomaly the granitoids plot within the post collision granite field in the pearce diagram which is consistent with the tectonic regime the quartz monzonites and one granite have a type granite characteristics and belong to the a 2 subgroup zircons in these granitoids have high th u values which are typical for magmatic zircons high precision u pb dating for these zircons by secondary ion mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms yields permian triassic 206 pb 238 u ages ranging from 243 2 to 293 8 ma the formation of the granitoids is 55 ma later than the latest ore forming age the zircons have low la concentrations 0 02 12 ppm high sm la n 0 8 685 and ce ce 1 4 80 the ti in zircon temperature of the granitoids ranges from 590 to 770 c all these evidences suggest that the granitoids have no contribution to the formation of the bayan obo deposit granitoids that are close to the orebodies had limited interaction with it and gained some lree enriched characteristics during magmatisms nevertheless their effects to the orebodies are subtle all the granitoids formed in a post collisional tectonic regime at convergent margins which is consistent with plate subduction during the closure of the palaeo asian ocean which started in the neoproterozoic and lasted until the carboniferous permian

a rift system in southeastern central asian orogenic belt constraint from sedimentological geochronological and geochemical investigations of the late carboniferous early permian strata in northern inner mongolia china abstract the late carboniferous early permian is the most controversial period for the tectonic evolution of the southeastern central asian orogenic belt caob in this study we performed sedimentological and detrital zircon dating on the clastic sediments as well as zircon u pb age and geochemical analysis on the rhyolitic rocks of the late carboniferous early permian strata from northern inner mongolia china the sedimentological analysis showed that the late carboniferous early permian sediments are composed of continental clastic and volcanic rocks with basal conglomerate overlying the devonian strata the detrital zircon study revealed three age peaks at 300 ma 440 ma and 530 ma indicating that the clastic rocks derived from paleozoic magmatic rocks and pre carboniferous sediments from northern inner mongolia the age data revealed that rhyolitic rocks from northern inner mongolia extruded in two stages at late carboniferous and latest carboniferous early permian the late carboniferous rhyolites show i to a type granitic affinities whereas the latest carboniferous early permian rhyolites have a type granitic characteristics the difference suggests a transition of tectonic setting from post collisional extension to intraplate rift the late carboniferous early permian strata from northern inner mongolia and south mongolia show similar sedimentary facies detrital zircon age distribution and geochemistry features hence they were probably deposited in the same tectonic setting a unified block was finally proposed in northern inner mongolia and south mongolia where a rift system provided an intra continental sedimentary basin and induced intense syn rift magmatic activities the intra continental basin and syn rift magmatism indicate that the xing an airgin sum songliao hunshandake and south mongolia blocks in southeastern caob have been welded into a single continental block before the late carboniferous

is methane driven deglaciation consistent with the ice core record the rapid climate changes at the terminations marking the end of the last glaciation are poorly understood this study uses the cambridge two dimensional atmospheric model to investigate the impact of a large marine sediment slump or permafrost rupture releasing 4000 tg of ch 4 into the high latitudes of the northern hemisphere with particular emphasis on the evolution of atmospheric ch 4 concentrations which may have led to an associated direct radiative effect of the order of 1 w m 2 persisting for a few decades because of enhanced levels of atmospheric ch4 the model generated ch 4 concentrations were converted into synthetic ice core signals for 66 n and 85 s representing arctic and antarctic cores respectively a range of possible averaging times was considered the results show that irrespective of the site or enclosure time chosen with the current sampling interval of 300 years it is not possible to discount completely the existence of a spike as a result of the instantaneous release of 4000 tg of ch 4 detection or refutation of a ch 4 spike would however be probable if the sampling interval were reduced to around 50 100 years

different sources involved in generation of continental arc volcanism the carboniferous permian volcanic rocks in the northern margin of the north china block abstract new zircon u pb dating results on the carboniferous permian volcanic rocks in the northern margin of the north china block ncb indicate their eruption during the early carboniferous to late permian from 347 3 ma to 258 1 ma and a slight decrease of the upper limits of the volcanic sequences from west to east they have a main rock association of basalt basaltic andesite andesite dacite rhyolite tuff and tufaceous sandstone most of them have calc alkaline compositions and exhibit variable sio2 contents from 48 2 wt to 77 1 wt there is no significant gap between the mafic and felsic volcanic rocks in major and trace element classification diagrams indicating that they are not bimodal in composition the carboniferous permian volcanic rocks exhibit subduction related geochemical features such as negative nb and ta anomalies of mafic to intermediate rocks on primitive mantle normalized diagrams indicating they were formed in an andean type continental arc during southward subduction of the paleo asian oceanic plate beneath the northern ncb however their wide range of whole rock sr nd and zircon hf isotopic compositions indicate that their source areas are very complex and different sources were involved in generation of these volcanic rocks geochemical and sr nd hf isotopic results show that the basalt and some andesite were produced by fractional crystallization of mafic magma derived from partial melting of mantle wedge and subducted oceanic crust however most of the intermediate to felsic volcanic rocks were derived from partial melting of lower continental crust there is an increasing input of crustal materials from the carboniferous to permian as indicated by increasing volumes of felsic volcanic rocks in the volcanic sequences the results show that origin of the continental arc volcanism is very complex and both materials from the subducted oceanic crust and sediments mantle wedge and arc continental crust could be involved in their generation for the permian andesite dacite and rhyolitic volcanic rocks there is a striking correlation between their sr nd hf isotopic compositions and those of the underlying basement sr nd hf isotopic differences between the permian intermediate to felsic volcanic rocks from either side of the northern boundary fault of the north china craton suggest that mixture and homogenization of the magmas in the melting assimilation storage hybridization mash zone within this continental arc was incomplete and incomplete homogenization of magmas is likely a common feature of many mash zones within continental arcs our results on the volcanic rocks also show that the final closure of the paleo asian ocean along the solonker suture zone has not been finished prior to the middle permian and the decease of the paleo asian oceanic subduction beneath the northern ncb in its middle western parts is a little earlier than that in its eastern part

magmatic evidence for middle late permian tectonic evolution on the northern margin of the north china craton abstract late paleozoic tectonic evolution of the northern margin of the north china craton ncc remains controversial especially for the mechanism and time during the late stage oceanic consumption of the paleo asian ocean pao we address this issue through geochronological geochemical and lu hf isotopic studies on felsic mafic volcanic rock suites and granite plutons from the damao area in the western segment of the ncc s northern margin zircon u pb dating reveals that the volcanic suites with eruptive unconformities in between erupted primarily at 275 260 ma while the granites emplaced later at 255 ma the volcanic rocks contain rhyolites and dacites having an a type affinity with high feot mgo k2o na2o cao and ga al ratios enriched th u zr hf and depleted ba sr and eu contents the basaltic rocks display low mgo and tio2 contents negative nb ta ti anomalies as well as negative hf t values we suggest that the 275 260 ma volcanic suites were generated in a post collisional setting with the dominant rhyolites and dacites derived from the mixing between mantle and crustal magmas and subordinate basalts from the partial melting of enriched sub continental lithospheric mantle the sudden and intensive occurrence of these 275 260 ma felsic dominant bimodal post collisional magmatism and their sudden increase of zircon hf t values imply a significant mantle contribution to their sources possibly due to the slab breakoff of the subducting pao plate the 255 ma granites also have an a type affinity and a large spread of negative hf t values 3 6 to 30 5 indicating a prominent involvement of continental crust materials that was likely related to crustal reworking after the slab breakoff overall these 275 255 ma magmatic suites document a significant post collisional crustal extension at the western segment of the northern ncc in this region the southward subduction of the pao likely ceased prior to 275 ma on the basis of a regional comparison

solonker suture in east asia and its bearing on the final closure of the eastern segment of the palaeo asian ocean abstract the location and tectonic nature of the solonker suture in east asia and hence the late palaeozoic to early mesozoic closure of the palaeo asian ocean have notoriously been enigmatic in the past decades due to limited rock exposure and the absence of unambiguous collision related regional features several tectonic models have been proposed since but in many cases these models were derived only from single key exposures or methodologies often being over simplified or interpreted leading to questionable extrapolations on regional and global scales despite the complexity of the palaeozoic accretionary tectonic framework now the regionally consistent availability of geochronological geochemical stratigraphic and palaeo geographic data enables us to integrate these into a highly detailed and coherent palaeozoic tectonic review of the suture the region across the solonker suture can generally be subdivided into three major palaeozoic tectonic provinces e g i a sino cratonic province that resembles the active palaeozoic northern margin of the north china craton to the south of the suture ii a mongolian province that comprises the south eastern margin of the mongolian terrane to the north of the suture and iii an east asian pre pacific province in north east china that accreted with the late permian initiation of pacific plate subduction the sino cratonic province experienced episodic tectonic activity that includes the accretion of the initially ensialic bainaimiao arc onto the passive northern margin of the north china craton at 437 453 ma subsequent southward directed subduction activity beneath the amalgamated margin until at least 400 ma followed by a temporary cessation of magmatic activity accompanied by a switch from north to southward directed continental drift and finally concluded by renewed subduction activity until the final closure of the palaeo asian ocean the mongolian province is suggested to have been more closely associated with the siberian craton before the presumably late devonian opening of the mongol okhotsk ocean the east asian pre pacific province originally rifted away from the eastern margin of gondwana at 600 750 ma recorded early palaeozoic 500 ma orogenic processes along the then northern margin of the siberian craton the baolidao arc system successively developed along the present day south eastern margin of the mongolian province due to continued subduction activity throughout the palaeozoic after the middle carboniferous opening of the hegenshan back arc basin renewed subduction beneath a matured baolidao arc during carboniferous and permian times led to the obduction of the hegenshan ophiolite not earlier than 270 ma shortly after the palaeo asian ocean diachronously closed from west to east along the solonker suture in the late permian to early triassic the east asian pre pacific province re attached itself by the mid mesozoic followed by a change in the regional stress regime controlled by palaeo pacific plate subduction a divergent double sided subduction model for the closure of the palaeo asian ocean provides based on the reviewed data a tectonic model that is not only able to reasonably well explain the absence of typical collision related features in the region but also the abundance of mesozoic a type granitic magmatism in north east china

seasonal signals in lake malawi sediments the sedimentary record of lake malawi one of the large rift valley lakes of east africa contains thick sequences of biologically undisturbed finely laminated muds and silts laminated sequences were recovered in cores from the extensive diatom ooze and silty diatom clay facies of the lake basin that is permanently anoxic below 250 m the sequences consist of light dark laminae couplets with average thickness of 1 mm the light laminae are completely dominated by the diatom genus melosira with a relatively minor contribution from the genus stephanodiscus the dark laminae consist of 50 diatoms equal proportions of melosira and stephanodiscus few nitzschia and occasional littoral diatom genera and 50 terrestrial plant debris mineral grains and fine clay and organic material based on a 210pb and 14c calculated sedimentation rate of 1 mm yr 1 for lake malawi basin sediments and the well defined seasonal variations in fluvial input and diatom productivity levels our data suggest that the lamination couplets are annual varves representing biannual sedimentation sequences the light laminae result from diatom blooms occurring during the dry windy season april october when the upper 250 m of the lake is well mixed localized upwelling occurs and the epilimnion becomes enriched with nutrients the dark laminae represent sedimentation in the rainy low wind velocity season november march when runoff and allochthonous terrestrial input are at a maximum and primary productivity is at a minimum

natural uranium in forsmark sweden the solid phase u bearing solid phases from forsmark sweden a proposed host for radioactive waste repositories havebeen identified and characterized elevated dissolved u was found in some groundwater samples d

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

a hybrid origin for the qianshan a type granite northeast china geochemical and sr nd hf isotopic evidence abstract major and trace element whole rock sr and nd isotope and zircon hf isotope data are reported for a suite of a type granites and mafic microgranular enclaves from the early cretaceous 126 2 ma qianshan pluton liaodong peninsula northeast china with the aim of investigating the sources and petrogenesis of a type granites the qianshan pluton includes hornblende alkali feldspar granite graphic biotite granite and mafic microgranular enclaves the hornblende alkali feldspar granites have high sio 2 fe 2 o 3t mgo k 2 o na 2 o rb zr and lree contents and low ba and sr concentrations with strongly negative eu anomalies their high rb sr 87 rb 86 sr 16 76 24 15 and initial 87 sr 86 sr ratios 0 7215 to 0 7283 negative e nd t values 14 1 to 16 5 and zircon e hf t values 18 9 to 11 5 indicate they were mainly derived from a crustal source but with involvement of high e nd t and e hf t materials graphic biotite granites have similar geochemical features and sr nd hf isotopic compositions to enclaves indicating they were the result of crystal fractionation of evolved mafic magmas but with involvement of low e nd t and e hf t materials the mafic enclaves have an igneous texture and contain acicular apatite suggesting quenching of mafic magmas that have co mingled with the host granites they have low initial 87 sr 86 sr ratios 0 7097 0 7148 negative e nd t 14 5 to 11 9 and zircon e hf t 17 1 to 6 9 values and are enriched in liles and lrees and depleted in hfses when coupled with the high mgo mg up to 54 this indicates derivation from an enriched lithospheric mantle source but contaminated by crustal materials geochemical and sr nd and zircon hf isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mantle derived mafic and crustal derived magmas coupled with crystal fractionation is compatible with the data this example shows that at least some a type granites formed through a complex process involving mantle and crustal derived magma mixing crystal fractionation and infracrustal melting

late paleocene middle eocene benthic foraminifera on a pacific seamount allison guyot odp site 865 greenhouse climate and superimposed hyperthermal events we investigated the response of late paleocene middle eocene 60 37 5 ma benthic foraminiferal assemblages to long term climate change and hyperthermal events including the paleocene eocene thermal maximum petm at ocean drilling program odp site 865 on allison guyot a seamount in the mid pacific mountains seamounts are isolated deep sea environments where enhanced current systems interrupt bentho pelagic coupling and fossil assemblages from such settings have been little evaluated assemblages at site 865 are diverse and dominated by cylindrical calcareous taxa with complex apertures an extinct group which probably lived infaunally dominance of an infaunal morphogroup is unexpected in a highly oligotrophic setting but these forms may have been shallow infaunal suspension feeders which were ecologically successful on the current swept seamount the magnitude of the petm extinction at site 865 was similar to other sites globally but lower diversity postextinction faunas at this location were affected by ocean acidification as well as changes in current regime which might have led to increased nutrient supply through trophic focusing a minor hyperthermal saw less severe effects of changes in current regime with no evidence for carbonate dissolution although the relative abundance of infaunal benthic foraminifera has been used as a proxy for surface productivity through bentho pelagic coupling we argue that this proxy can be used only in the absence of changes in carbonate saturation and current driven biophysical linking

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

shrimp u pb zircon ages of the fuping complex implications for late archean to paleoproterozoic accretion and assembly of the north china craton the fuping complex is situated in the central part of the north china craton and consists of four major lithological assemblages fuping tonalitic trondhjemitic granodioritic gneisses longquanguan augen gneisses wanzi supracrustal assemblage and nanying granitic gneisses shrimp u pb geochronology combined with u th and cathodoluminescence cl imaging of zircon enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the fuping complex cl images reveal the coexistence of magmatic and metamorphic zircons in nearly all rock types of the fuping complex the metamorphic zircons occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores and are all characterized by nebulous zoning or being structureless with extremely high luminescence and very low th contents these features make them distinct from magmatic zircons that are characterized by concentric oscillatory zoning comparatively low luminescence and high th and u contents shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic plutons of the fuping gneisses were emplaced at 2523 14 ma 2499 10 ma and 2486 8 ma respectively whereas the monzogranitic and granitic plutons of the longquanguan augen gneisses were intruded respectively at 2510 22 ma and 2507 11 ma prismatic and oscillatory zoned zircons dominate in the pelitic rocks of the wanzi supracrustal assemblage and are interpreted as detritus from igneous source rocks the concordant and discordant u pb ages of 2502 5 ma and 2507 14 ma obtained from two pelitic rock samples indicate these rocks must have been deposited no earlier than 2507 ma ago in addition a zoned zircon grain in one pelitic rock sample has a near concordant age of 2109 5 1 ma which may provide a maximum depositional age for the wanzi supracrustal rocks shrimp results also reveal that granitic magmatism assigned to the nanying granitic gneisses occurred over a protracted interval from 2077 13 ma to 2024 21 ma the nebulously zoned zircon grains and overgrowth recrystallization zircon rims from different rocks yielded similar concordant 207pb 206pb ages in the range 1875 to 1802 ma interpreted as approximating the age of regional metamorphism of the fuping complex timing of primary zircon crystallization and regional metamorphism of the fuping complex is in general agreement with recent u pb zircon ion probe results for the wutai and hengshan complexes that bound the fuping complex to the northwest these areas are characterized by the emplacement of major granitoid bodies at around 2 50 ga to 2 48 ga ago deposition of supracrustal rocks in the paleoproterozoic intrusion of paleoproterozoic granitic bodies at 2 1 to 2 0 ga and regional metamorphism at 1 875 to 1 802 ga these data indicate that the fuping and hengshan complexes do not represent an older crystalline basement to the wutai complex as suggested in previous tectonic models but together with the wutai complex represent elements of a single late archean to paleoproterozoic magmatic arc system that has been subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western north china blocks at 1 85 ga which resulted in the final assembly of the north china craton

modeling the climate response to a massive methane release from gas hydrates 1 the climate response to a massive release of methane from gas hydrates is simulated in two 2500 year long numerical experiments performed with a three dimensional global coupled atmosphere sea ice ocean model of intermediate complexity two different equilibrium states were used as reference climates the first state with preindustrial forcing conditions and the second state with a four times higher atmospheric co2 concentration these climates were perturbed by prescribing a methane emission scenario equivalent to that computed for the paleocene eocene thermal maximum petm similar to55 5 ma involving a sudden release of 1500 gt of carbon into the atmosphere in 1000 years in both cases this produced rapid atmospheric warming up to 10degreesc at high latitudes and a reorganization of the global overturning ocean circulation in the ocean maximum warming 2 4degreesc occurred at intermediate depths where methane hydrates are stored in the upper slope sediments suggesting that further hydrate instability could result from the prescribed scenario

slab breakoff a model for caledonian late granite syn collisional magmatism in the orthotectonic metamorphic zone of scotland and donegal ireland abstract none of the existing models for calc alkaline late granite siluro devonian genesis in the metamorphic caledonian orogenic belt of ireland and scotland fully explains their spatial age or chemical character a consistent model must involve the closure of iapetus ocean where slab breakoff is a natural consequence of attempted subduction of continental crust expected outcome is a long linear belt of high k calc alkaline magmas some with characteristic trace element signatures specifically high ba sr and zr other features include the critical magmatic association of coeval appinite and granite rapid uplift erosion and the low grade regional metamorphism in the southern uplands the linear heat pulse on breakoff is spatially intensity and time limited producing small volume melts emplaced as separated plutons over a short time span magmatism in the caledonian metamorphic belt is accurately accounted for by slab breakoff on collision of baltica with the scoto greenland margin during the scandian orogeny following iapetus ocean closure the two chemically isotopically and areally distinctive suites in the metamorphic belt in scotland viz the argyll and cairngorm suites can be modelled by reference to the donegal granites where sequential partial melting of new lamprophyric underplated crust then shallower old crust as heat conduction moved up through the crust on slab breakoff produced magmas characteristic of the two suites

geochemistry and geochronology of the delinggou intrusion implications for the subduction of the paleo asian ocean beneath the north china craton abstract the formation and evolution of the central asian orogenic belt caob are intimately related to the opening and closure of the paleo asian ocean the final closure led to amalgamation or collision between the caob and north china craton however the issue about the subduction polarity and final closure of the paleo asian ocean has long been debated in order to resolve this issue we carried out a detailed geochemical and age study on the delinggou intrusion from the siziwangqi area of central inner mongolia at the northern margin of the north china craton the delinggou intrusion consists predominantly of diorite and quartz diorite with minor gabbroic diorite u pb zircon dating indicates that the intrusion was emplaced during early carboniferous 330 to 343 ma geochemically the rocks are metaluminous and belong to the calc alkaline series they are enriched in large ion lithophile elements lile e g rb sr and ba and depleted in high field strength elements hfse e g zr nb hf ta and ti the delinggou rocks were probably generated by partial melting of an enriched subcontinental lithospheric mantle further contaminated by crustal material during the magmatic differentiation in a continental arc setting we conclude that the paleo asian ocean underwent southward subduction beneath the north china craton and the subduction initiated in the carboniferous 343 330 ma but the final ocean closure time is not yet constrained

reconstructions of east asian blocks in pangea preface abstract pangea is the youngest supercontinent in earth s history forming about 300 250 ma ago as supported by large amounts of geological paleomagnetic and paleontonlogical data there is little debate on the positions of major continental blocks in pangea however controversy has long surrounded the relations of east asian blocks with pangea most pangea reconstructions assume that the east asian blocks were not the components of pangea but separated from pangea by the paleo tethys ocean these reconstructions were mainly based on geological and paleomagnetic data before the 1990 s but did not fully consider recent data especially for major orogenic belts that formed through the subduction and closure of the proto tethys paleo asian and paleo tethys oceans in east asia to determine where when and how these oceans were closed and whether or not the east asian blocks were added to pangea the national natural science foundation of china nsfc set up a nsfc major program entitled reconstructions of east asian continental blocks in pangea which started in 2012 and was completed in 2016 in the past five years the researchers of this project carried out extensive field based geological and paleomagnetic investigations on the east asian blocks and their intervening mountain belts and produced large amounts of data and competing interpretations which provide constraints on the paleogeographic evolution of the east asian blocks from the breakup of rodinia to the assembly of pangea this forms the justification for organizing this special issue in which we collected ten papers that timely summarize these new data and interpretations and present new models for the reconstructions of the east asian continental blocks in pangea

regional uplift gas hydrate dissociation and the origins of the paleocene eocene thermal maximum much of the north atlantic region experienced hundreds of metres of transient uplift during the latest paleocene regional uplift should cause dissociation of gas hydrates stored in marine sedimentary strata and the subsequent release of carbon to the atmosphere should enhance warming through the greenhouse effect we have developed models of the spatial distribution of uplift to match observational constraints from sedimentary basins fringing the north atlantic in order to provide quantitative estimates of the carbon released upon uplift these models are coupled to a simple parameterisation of carbon storage in sub seafloor gas hydrates results of modelling indicate that large quantities of carbon can be released by uplift with some models generating over 2000 gt of carbon release the possibility that latest paleocene regional uplift occurred over the same time interval as onset of the paleocene eocene thermal maximum petm around 30 kyr cannot be ruled out using current stratigraphical observations or mantle convection models in this case the uplift mechanism alone can account for the magnitude and timing of the carbon isotope excursion associated with the petm alternatively if the duration of latest paleocene uplift was closer to the upper bound of around 1 myr or if other paleocene uplift events were equally significant then gas hydrate dissociation upon uplift could have contributed to longer term changes in ocean temperature and carbon isotope composition through the late paleocene these temperature changes in combination with development of the north atlantic land bridge during the latest paleocene culmination of uplift may be able to force rapid changes in ocean circulation and cause phenomena such as the petm

multiple early eocene hyperthermals their sedimentary expression on the new zealand continental margin and in the deep sea the paleocene eocene thermal maximum petm ca 55 5 ma was a geologically brief interval characterized by massive influx of isotopically light carbon extreme changes in global climate and profound variations in earth system processes an outstanding issue is whether it was an isolated event or the most prominent example of a recurring phenomenon recent studies of condensed deep sea sections support the latter but this finding remains uncertain here we present and discuss lithologic and carbon isotope records across two lower eocene outcrops on south island new zealand the petm manifests as a marl rich horizon with a significant negative carbon isotope excursion cie above in sediment deposited between 54 and 53 ma are four horizons with similar though less pronounced expressions marl beds of all five horizons represent increased terrigenous sedimentation presumably linked to an accelerated hydrological cycle five corresponding clay rich horizons and cies are found in deep sea records although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution the presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 c depleted carbon during the early eocene

contrasting late carboniferous and late permian middle triassic intrusive suites from the northern margin of the north china craton geochronology petrogenesis and tectonic implications two contrasting intrusive suites have been identified from the northern margin of the north china craton a late carboniferous dioritegranodiorite suite mainly made up of quartz diorite diorite granodiorite tonalite and hornblende gabbro and a late permian middle triassic suite of granitoid intrusions consisting of monzogranite syenogranite and quartz monzonite plutons from the late carboniferous suite exhibit variable sio2 contents and calc alkaline or high k calc alkaline metaluminous geochemical features most have low negative whole rock nd t values where t is the crystallization age of 17 1 to 11 5 and zircon hf t values of 38 3 to 11 2 indicating that they were derived mainly from anatectic melting of the ancient lower crust with some involvement of mantle materials however an older pluton in the suite exhibits higher nd t values of 11 5 to 9 9 nd model ages of 1 82 1 64 ga lower initial 87sr 86sr ratios of 0 7046 0 7048 and it contains some zircon grains that are characterized by high negative to positive zircon hf t values of 8 7 to 1 2 indicating strong involvement of juvenile materials derived from the lithospheric mantle the late carboniferous plutons are interpreted as subduction related and to have been emplaced in an andean style continental margin arc during the southward subduction of the paleo asian oceanic plate beneath the north china craton rocks from the late permian middle triassic intrusive suite display geochemical signatures ranging from highly fractionated i type to a type they exhibit higher zircon hf t values of 14 9 to 6 7 whole rock nd t values of 10 6 to 8 8 and younger hf and nd model ages than most of the late carboniferous plutons indicating that they could have been produced by extreme fractional crystallization of hybrid magmas resulted from mixing of coeval mantle and crust derived melts they are interpreted as postcollisional postorogenic granitoids linked to lithospheric extension and asthenosphere upwelling due to slab break off and subsequent sinking after final collision and suturing of the mongolian arc terranes with the north china craton these two contrasting intrusive suites suggest that the final closure of the paleo asian ocean and collision between the mongolian arc terranes and the north china craton occurred during the late permian and these events were followed by postcollisional postorogenic extension large volume magmatism and significant continental growth no significant syncollisional crustal thickening high pressure metamorphism or s type granitoid magmatism occurred during the collision process

paleomagnetic constraints on the paleogeography of the east asian blocks during late paleozoic and early mesozoic times abstract although the axial and dominant geocentric character of the earth s magnetic field means that paleolongitude is indeterminate paleomagnetism is otherwise the only truly quantitative method available to the earth scientist for constraining paleogeography and reconstructing the kinematic evolution of continental blocks during the past half century numerous paleomagnetic results have provided substantial quantitative constraints on the origin and tectonic evolution of the major tectonic divisions now comprising eastern asian in this paper we first assess the available early paleozoic to early cretaceous paleomagnetic results from the south china north china and tarim blocks using internationally recognized reliability criteria we then construct a running mean through a 20 ma window by weighting the poles according to their q factors and fit a spherical spline with smoothing factor of 300 to derive apparent polar wander apw paths for these three major blocks during this early paleozoic to late mesozoic time interval together with late paleozoic to early mesozoic paleomagnetic poles from the qaidam qiangtang lhasa sibumasu indochina and some other smaller blocks terranes of east asia we produce a series of paleogeographic reconstructions for these major blocks and lesser terranes of east asia between mid ordovician and late jurassic times 460 160 ma which although based primarily upon paleomagnetic evidence aim to embrace the geological constraints finally we discuss the current evidence for closure times of the paleo asian mianlue and east paleo tethyan oceans which incorporate fundamental issues concerning the formation of the east asian continental collage and collision with the northern main body of the pangean supercontinent we use the collective evidence to argue that these major paleo oceans had closed by the late triassic and that the east asian sector of the supercontinent had united to become an integral part of pangea by that time 220 ma

geochemistry and zircon u pb hf isotopes of paleozoic intrusive rocks in the damao area in inner mongolia northern china implications for the tectonic evolution of the bainaimiao arc abstract the tectonic evolution of the central asian orogenic belt caob is related to the subduction and closure of the paleo asian ocean pao considerable controversy still surrounds whether when and how the pao subducted underneath the northern margin of the north china craton ncc this study carries out whole rock geochemical and zircon u pb hf isotopic investigations on paleozoic intrusive rocks in both the bainaimiao arc and the northern margin of the ncc zircon u pb dating of gabbroic diorite and diorite in the bainaimiao arc and the granite and diorite at the northern margin of the ncc yielded crystallization ages of 458 2 ma 428 2 ma 326 2 ma and 258 2 ma respectively in the bainaimiao arc the middle silurian diorite as the main body of the arc related intrusive rocks there show geochemical characteristics of continental margin arc magma with negartive hf t values and old hf model ages on the other hand the middle ordovician gabbroic diorite mainly shows typical calc alkaline continental arc geochemical characteristics with positive hf t values and relative young hf model ages indicative of the southward propagating reworking and arc accretion processes thus we interpret these rocks as a consequence of southward subduction of the pao beneath the bainaimiao arc here termed as bainaimiao arc terrane bat the early carboniferous granite and late permian diorite at the northern margin of the ncc show geochemical characteristics similar to post collisional adakites and typical continental arc rocks respectively combined with previous work the early carboniferous post collisional adakite shows limited distribution and corresponds to the subsequent effect of the amalgamation between the bat and the ncc whereas most of the carboniferous permian magmatic rocks ca 342 258 ma at the northern margin of the ncc are arc related and resulted from the continued effect of the southward subduction of the pao moreover the southward subduction in the early paleozoic was transformed from relative high angle subduction beneath the bat to shallow subduction beneath the unity of the ncc and the bat in the late paleozoic which lasted until the late permian ca 258 ma

dynamics of co2 driven lake eruptions on 21 august 1986 a massive release of carbon dioxide from lake nyos in cameroon killed about 1 700 people a similar event occurred on 15 august 1984 at lake monoun also in cameroon it was suggested1 5 that the co2 released was initially dissolved in the hypolimnion dense lower layer of the lake and was released by eruptive outgassing because of its violence the nyos outburst was at first thought6 to have been volcanic but undisturbed sediments and other evidence indicate that no large volcanic eruption occurred7 9 recent experiments10 11 have shown that decompression of co2 saturated water is able to power explosive eruptions here i analyse the dynamics of co2 driven lake water eruptions by deriving an equation of state for gas liquid mixtures and using it to integrate the bernoulli equation which describes the dynamics of the bubbly flow i find that under certain conditions these eruptions can be violent the lake surface exit velocity of an initially gas saturated water parcel may reach 89m s 1 for lake nyos and 51m s 1 for lake monoun the dynamics are similar to those of water driven volcanic eruptions which are also powered by gas exsolution from a liquid

the end of the ice age methane gas hydrates may have contributed to the rapid rise in atmospheric ch4 co2 and global temperatures at the end of the last major glaciation about 13 500 years ago given suitable orbital conditions and insolation at high latitude a small triggering event such as the release of one or more arctic gas pools may have initiated massive release of methane from hydrate under ice and in permafrost the consequent greenhouse warming would have provided strong positive feedback amplifying emission this warming driven by ch4 may have induced the release of co2 from the oceans to the biosphere stabilizing the interglacial carbon cycle

single zircon grains record two paleoproterozoic collisional events in the north china craton abstract the western block of the north china craton consists of the yinshan block in the north and the ordos block in the south which were amalgamated along the east west trending khondalite belt at 1 95 ga the western block then collided with the eastern block to form the coherent basement of the north china craton along the north south trending trans north china orogen at 1 85 ga the huaian complex a high grade terrrane located at the conjunction of the khondalite belt and trans north china orogen records metamorphic events associated with both collisions the complex consists of lithologies from both the khondalite belt and trans north china orogen of which the former consist of graphite garnet sillimanite gneiss garnet quartzite felsic paragneiss calc silicate rock and marble together called the khondalite series zircons in the graphite garnet sillimanite gneiss can be divided into three types 1 spherical grains without internal structures 2 grains with a core and rim structure and 3 grains with a dark core surrounded by double rims except for the dark core in type 3 all other types of zircon domains are structureless and highly luminescent with very low th u ratios typical of a metamorphic origin analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 26 and 1947 22 ma similar to previously determined metamorphic ages from the khondalite belt and thus interpreted as the time of collision between the yinshan and ordos blocks analyses on type 1 zircons rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 15 and 1857 16 ma interpreted as the time of collision between the eastern and western blocks thus zircons in the graphite garnet sillimanite gneiss of the huaian complex record both of the paleoproterozoic collisional events in the north china craton

late paleozoic subduction and collision processes during the amalgamation of the central asian orogenic belt along the south tianshan suture zone abstract the provenance of late paleozoic siliciclastic sedimentary strata on the northern margin of the tarim craton and the south tianshan orogenic belt provides important insights into subduction and collision processes during the formation of the southern central asian orogenic belt detrital zircons from carboniferous and permian sedimentary rocks in the south tianshan belt show two predominant age populations of 500 400 and 305 270 ma and three subordinate clusters around 2 5 ga 2 0 1 7 ga and 1 2 0 6 ma such age patterns are similar to major magmatic episodes in the tarim craton but are distinct from those in the central tianshan yili block implying that the carboniferous permian strata in the south tianshan belt were deposited on the northern margin of the tarim craton these data in combination with carboniferous passive margin deposition along the south tianshan and northern tarim regions and intense arc magmatism in the central tianshan area support the northward subduction of the south tianshan oceanic crust the abrupt decrease of zircon e hf t values at 310 ma indicates the tectonic transformation from oceanic subduction to continental collision however syn and post collisional sediments in the south tianshan and northern tarim regions did not contain detritus from the central tianshan yili block as evidenced by the absence paucity of 380 310 ma detrital zircons in the late paleozoic strata and by the stratigraphic record in the regions insignificant surface erosion and uplifting during the collision and ultra high pressure rock exhumation require divergence in the frontal wedge we propose that the switch from a convergent to a divergent regime was triggered by the arrival of the tarim mantle plume in the latest carboniferous which possibly had profound effects on regional sedimentation and exhumation of ultra high pressure rocks in the orogenic belt

tempo and scale of late paleocene and early eocene carbon isotope cycles implications for the origin of hyperthermals abstract the upper paleocene and lower eocene are marked by several prominent 1 carbon isotope 13c excursions cie that coincide with transient global warmings or thermal maxima including the paleocene eocene thermal maximum petm the cie which are recorded mainly in marine sedimentary sequences have also been identified in continental sequences occurred episodically and yet appear to be paced or triggered by orbital forcing to constrain the timing and scale of the cie relative to long term baseline variability we have constructed a 4 52 million year myr long high resolution 3 kyr bulk sediment carbon isotope record spanning the lower eocene to upper paleocene c25r c24n from a pelagic sediment section recovered at odp site 1262 in the southeast atlantic this section which was orbitally tuned utilizing high resolution core log physical property and geochemical records is the most stratigraphically complete upper paleocene to lower eocene sequence recovered to date time series analysis of the carbon isotope record along with a high resolution fe intensity record obtained by xrf core scanner reveal cyclicity with variance concentrated primarily in the precession 21 kyr and eccentricity bands 100 and 400 kyr throughout the upper paleocene lower eocene in general minima in 13c correspond with peaks in fe i e carbonate dissolution both of which appear to be in phase with maxima in eccentricity this covariance is consistent with excess oceanic uptake of isotopically depleted carbon resulting in lower carbonate saturation during periods of high eccentricity this relationship includes all late paleocene and early eocene cie confirming pacing by orbital forcing the lone exception is the petm which appears to be out of phase with the 400 kyr cycle though possibly in phase with the 100 kyr cycle reinforcing the notion that a mechanism other than orbital forcing and or an additional source of carbon is required to account for the occurrence and unusual scale of this event

biostratigraphic evidence for evolving palaeoenvironments in the lower paleogene of the faeroe shetland basin the results of biostratigraphic analysis of the palaeocene to lower eocene section in four faeroe shetland basin wells are presented the succession of bioevents is shown to be the same as that documented for wells in the north sea evolution of microfossil assemblages within the basin reflects the change from an open marine setting in the danian to more restricted marine and non marine conditions in the late thanetian and early ypresian this change is accompanied by a number of microfossil extinctions that form useful regional biomarkers for the faeroe shetland and north sea basins these events include the extinction of planktonic foraminifera close to the danian selandian boundary and the extinction of dinocyst taxa palaeoperidinium pyrophorum and areoligera cf coronata at the selandian thanetian boundary within the thanetian section the extinction of areoligera coincides with an abrupt reduction in numbers and diversity of agglutinated foraminifera the thanetian ypresian boundary is marked by the extinction of apectodinium augustum well 208 19 1 lies in the marine northeastern part of the basin which was connected to the north sea by a narrow seaway however upper thanetian to lower ypresian biofacies become increasingly restricted when traced southwestwards along the basin axis with this interval being non marine in 204 24 1a

microfossil turnover across the uppermost danian at caravaca spain paleoenvironmental inferences and identification of the latest danian event abstract the latest danian event lde or top chron c27n hyperthermal event has been identified in the caravaca section southern spain by means of calcareous nannofossil biozones subzone ntp7b and the recognition of a prominent negative 0 6 per mille carbon isotope excursion measured in benthic foraminiferal tests this is the first time that this danian hyperthermal event has been identified in a deep water middle to lower bathyal setting from the western tethyan realm the analysis of benthic foraminiferal assemblages shows gradual changes in the assemblages prior to the onset of the lde and an increase in food supply to the seafloor during the lde in agreement with results from shallower southern tethyan settings the benthic assemblage changes across the lde at caravaca share some characteristics with other hyperthermal events including the negative carbon isotope excursion the increased abundance of buliminids or the common occurrence of a aragonensis an opportunistic species that proliferated during other paleogene hyperthermal events in addition the increased abundance of nuttallides truempyi a dissolution resistant form that thrived during the paleocene eocene thermal maximum and the abundance of calcareous infaunal morphogroups which calcify in less carbonate undersaturated pore waters indicate slightly caco3 corrosive bottom waters during the lde turnover of calcareous plankton across the lde is similar to other sites globally distributed including the evolution of photosymbiotic foraminiferal lineages and the radiation of the nannofossil fasciculiths group the occurrence of innovative morphostructures diantholitha and lithoptychius towards the base of the lde may indicate a more efficient biological pump this hypothesis is supported by increased percentages of benthic infaunal morphogroups and a decrease in the abundance of oligotrophic species a reworked interval has been identified immediately above the lde higher up in the section benthic and planktic assemblages from the post lde interval point to the recovery of the environmental conditions including a decrease in the food supply to the seafloor

late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block constraints on the composition and evolution of the lithospheric mantle abstract the late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block ncb are used to constrain the isotopic composition and evolution of mantle reservoirs during different tectonic stages prior to the initiation of lithosphere destruction in the late mesozoic zircon u pb ages show that emplacement of the mafic ultramafic complexes occurred in at least three stages middle devonian ca 395 ma late carboniferous early permian 308 276 ma and triassic 250 220 ma most of the middle devonian complexes display low initial 87sr 86sr ratios of 0 70467 0 70492 weak to moderate negative end t values from 6 3 to 1 5 and weakly negative to weakly positive zircon ehf t values from 11 5 to 5 5 indicating that the parent magma was derived from slightly enriched lithospheric mantle the late carboniferous early permian complexes are characterized by low initial 87sr 86sr ratios of 0 70521 0 70604 significant negative end t values from 14 1 to 9 3 and zircon ehf t values from 17 0 to 10 5 and were probably derived from metasomatized lithospheric mantle the early triassic complexes exhibit initial 87sr 86sr ratios of 0 70656 0 70825 and significant negative end t values from 17 1 to 8 2 indicating their derivation from enriched lithospheric mantle however the late triassic mafic ultramafic complexes display weakly negative to weakly positive end t values of 4 4 to 0 5 and zircon ehf t values from 2 9 to 1 7 indicating that magma sources likely resulted from mixing of depleted asthenospheric mantle and enriched lithospheric mantle zircon ages geochemistry and sr nd hf isotopic studies suggest that the lithospheric mantle beneath the northern ncb had a slightly enriched signature during the middle devonian but it became significantly enriched during the late carboniferous to early permian due to metasomatism of lithospheric mantle during the southward subduction of the paleo asian oceanic plate after final closure of the paleo asian ocean and amalgamation of the mongolian arc terranes with the northern ncb in the latest permian to earliest triassic enriched lithospheric mantle still existed beneath the northern ncb during the early triassic however in the late triassic involvement of asthenospheric mantle became significant owing to strong upwelling of asthenospheric mantle and post collisional lithospheric delamination in the early late triassic these results suggest that the cratonic lithospheric mantle beneath the northern ncb underwent multiple stages of modification prior to its destruction and thinning initiation of lithospheric destruction and thinning in the northern ncb likely occurred during the early late triassic which is much earlier than in other parts of the ncb where it occurred in the late mesozoic it appears likely that lithospheric destruction and thinning of the ncb initially started at the northern and eastern margins of the craton as a result of post collisional lithospheric delamination and then spread to the interior of the craton

could changing ocean circulation have destabilized methane hydrate at the paleocene eocene boundary 1 during the paleocene eocene thermal maximum petm 55 ma marine and terrestrial carbon isotope values exhibit a negative shift of at least 2 5 indicative of massive destabilization of marine methane hydrates releasing 2000 gigatons of methane carbon the cause of the hydrate destabilization is unknown but has been speculated to be warming due to a change from high latitude to low latitude deepwater formation here we present results from a numerical ocean model indicating that a sudden switch of deepwater formation from southern to northern high latitudes caused middepth and deep ocean warming of 3 5 c the switch is caused by a slow increase in the intensity of the atmospheric hydrologic cycle as expected under increasing temperatures and consistent with petm sedimentary evidence deepened subtropical subduction prior to the thermohaline circulation switch causes warming of 1 4 c in limited areas at thermocline through upper intermediate depths which could destabilize methane hydrates gradually and at progressively greater depths warming accompanying a south to north switch in deepwater formation would produce sufficient warming to destabilize seafloor gas hydrates over most of the world ocean to a water depth of at least 1900 m

adakite like volcanism of ecuador lower crust magmatic evolution and recycling in the northern andes of ecuador a broad quaternary volcanic arc with significant across arc geochemical changes sits upon continental crust consisting of accreted oceanic and continental terranes quaternary volcanic centers occur from west to east along the western cordillera frontal arc in the inter andean depression and along the eastern cordillera main arc and in the sub andean zone back arc the adakite like signatures of the frontal and main arc volcanoes have been interpreted either as the result of slab melting plus subsequent slab melt mantle interactions or of lower crustal melting fractional crystallization and assimilation processes in this paper we present petrographic geochemical and isotopic sr nd pb data on dominantly andesitic to dacitic volcanic rocks as well as crustal xenolith and cumulate samples from five volcanic centers pululagua pichincha ilalo chacana sumaco forming a nw se transect at about 0 latitude and encompassing the frontal pululagua pichincha main ilalo chacana and back arc sumaco chains all rocks display typical subduction related geochemical signatures such as nb and ta negative anomalies and lile enrichment they show a relative depletion of fluid mobile elements and a general increase in incompatible elements from the front to the back arc suggesting derivation from progressively lower degrees of partial melting of the mantle wedge induced by decreasing amounts of fluids released from the slab we observe widespread petrographic evidence of interaction of primary melts with mafic xenoliths as well as with clinopyroxene and or amphibole bearing cumulates and of magma mixing at all frontal and main arc volcanic centers within each volcanic center rocks display correlations between evolution indices and radiogenic isotopes although absolute variations of radiogenic isotopes are small and their values are overall rather primitive e g end 1 5 to 6 87sr 86sr 0 7040 0 70435 rare earth element patterns are characterized by variably fractionated light to heavy ree la ybn 5 7 34 and by the absence of eu negative anomalies suggesting evolution of these rocks with limited plagioclase fractionation we interpret the petrographic geochemical and isotopic data as indicating open system evolution at all volcanic centers characterized by fractional crystallization and magma mixing processes at different lower to mid crustal levels as well as by assimilation of mafic lower crust and or its partial melts thus we propose that the adakite like signatures of ecuadorian rocks e g high sr y and la yb values are primarily the result of lower to mid crustal processing of mantle derived melts rather than of slab melts and slab melt mantle interactions the isotopic signatures of the least evolved adakite like rocks of the active and recent volcanoes are the same as those of tertiary normal calc alkaline magmatic rocks of ecuador suggesting that the source of the magma did not change through time what changed was the depth of magmatic evolution probably as a consequence of increased compression induced by the stronger coupling between the subducting and overriding plates associated with subduction of the aseismic carnegie ridge

marine and terrestrial environmental changes in nw europe preceding carbon release at the paleocene eocene transition environmental changes associated with the paleocene eocene thermal maximum petm 56 ma have not yet been documented in detail from the north sea basin located within proximity to the north atlantic igneous province naip the kilda basin and the northern rain belt paleolatitude 54 1n during the petm this is a critical region for testing proposed triggers of atmospheric carbon release that may have caused the global negative carbon isotope excursion cie in marine and terrestrial environments the cie onset is identified from organic matter d 13 c in exceptional detail within a

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago