thermo rheological shear heating model for leucogranite generation metamorphism and deformation during the proterozoic trans hudson orogeny black hills south dakota abstract this paper evaluates thermotectonic models for metamorphism and leucogranite generation during the proterozoic trans hudson orogeny as recorded in rocks exposed in the black hills sd intrusion of the harney peak granite and associated pegmatites at 1715 ma occurred at the waning stages of regional deformation and staurolite grade regional metamorphism published consortium for continental reflection profiling cocorp results indicate that proterozoic sedimentary rocks were thrust over the archean wyoming province during the trans hudson collision isotopic compositions of the harney peak granite suggest that the exposed proterozoic and archean metasedimentary rocks in the black hills represent source rocks of the granites numerical simulations of the regional metamorphism and harney peak granite generation assuming crustal thickening by thrusting coupled with erosion show the following 1 doubling of the crust with normal distribution of radioactive elements does not yield sufficiently high temperatures to cause anatexis anywhere in the crust or growth of garnet in the now exposed part of the crust 2 a 35 km drop off length for internal heat production can yield sufficient temperature for garnet growth at the current erosion level it is however insufficient to produce staurolite and melting can occur only in the deepest parts of the crust 3 temperatures in crust with stable 70 km thickness for 40 ma and 35 km drop off length for heat production could become sufficient to produce staurolite at the current erosion level and subsequent rapid denudation of the crust could potentially trigger decompression melting of lower crustal rocks although this model could potentially explain the observed temporal relationship between regional metamorphism and leucogranite generation it is inconsistent with melting of upper crustal proterozoic source rocks that is indicated by isotopic compositions of the granites with lack of evidence for rapid denudation of the trans hudson orogen and with confinement of the leucogranites to the deformed proterozoic metapelitic rocks production of the harney peak granite and its relationship to regional metamorphism of the country rocks are best explained by shear heating at the interface between the wyoming province and overthrusted sedimentary rocks we suggest that with reasonable rheologic properties of metapelites and rates of plate convergence shear heating sufficiently perturbs locally the geotherms to cause anatexis in a deep shear zone system and growth of staurolite in the overlying crust modeling rheology of the lithologically stratified thickened crust with granitic basement and metapelitic upper plate shows that the currently exposed part of the crust and the granite source region were ductile through much of the orogeny which explains regional folding of the schists and predicts ductile shear zones in the granite source region because of the lithologic stratification the granitic basement is likely to become significantly weaker during crustal thickening than the upper crust dominated by schists a weak basement under a folded upper crust is likely to contribute to the observed relatively flat topography of high plateaus over thickened orogens

early mesozoic southward subduction history of the mongol okhotsk oceanic plate evidence from geochronology and geochemistry of early mesozoic intrusive rocks in the erguna massif ne china abstract in this paper we present new zircon u pb ages hf isotope data and whole rock major and trace element data for early mesozoic intrusive rocks in the erguna massif of ne china and we use these data to constrain the history of southward subduction of the mongol okhotsk oceanic plate and its influence on ne china as a whole the zircon u pb dating indicates that early mesozoic magmatic activity in the erguna massif can be subdivided into four stages at 246 ma 225 ma 205 ma and 185 ma the 246 ma intrusive rocks comprise a suite of high k calc alkaline diorites quartz diorites granodiorites monzogranites and syenogranites with i type affinities the 225 ma intrusive rocks consist of gabbro diorites and granitoids and they constitute a bimodal igneous association the 205 ma intrusive rocks are dominated by calc alkaline i type granitoids that are accompanied by subordinate intermediate mafic rocks the 185 ma intrusive rocks are dominated by i type granitoids accompanied by minor amounts of a types these early mesozoic granitoids mainly originated by partial melting of a depleted and heterogeneous lower crust whereas the coeval mafic rocks were probably derived from partial melting of a depleted mantle modified by subduction related fluids the rock associations and their geochemical features indicate that the 246 ma 205 ma and 185 ma intrusive rocks formed in an active continental margin setting related to the southward subduction of the mongol okhotsk oceanic plate the 225 ma bimodal igneous rock association formed within an extensional environment in a pause during the subduction process of the mongol okhotsk oceanic plate every magmatic stage has its own corresponding set of porphyry deposits in the southeast of the mongol okhotsk suture belt taking all this into account we conclude the following 1 during the early mesozoic the mongol okhotsk oceanic plate was subducted towards the south beneath the erguna massif but with a pause in subduction at 225 ma and 2 the southward subduction of the mongol okhotsk oceanic plate not only caused the intense magmatic activity but was also favorable to the formation of porphyry deposits

transformation from paleo asian ocean closure to paleo pacific subduction new constraints from granitoids in the eastern jilin heilongjiang belt ne china abstract the eastern jilin heilongjiang belt ejhb of ne china is a unique orogen that underwent two stages of evolution within the tectonic regimes of the paleo asian and paleo pacific oceans 158 available zircon u pb ages including 26 ages obtained during the present study and 132 ages from the literature were compiled and analyzed for the mesozoic and cenozoic granitoids from the ejhb and the adjacent russian sikhote alin orogenic belt saob to examine the temporal spatial distribution of the granitoids and to constrain the tectonic evolution of the east asian continental margin five stages of granitic magmatism can be identified early triassic 251 240 ma late triassic 228 215 ma latest triassic to middle jurassic 213 158 ma early cretaceous 131 105 ma and late cretaceous to paleocene 95 56 ma the early triassic granitoids are restricted to the yanbian region along the changchun yanji suture and show geochemical characteristics of magmas from a thickened lower crust source probably due to the final collision of the combined ne china blocks with the north china craton the late triassic granitoids with features of a type granites represent post collisional magmatic activities that were related to post orogenic extension marking the end of the tectonic evolution of the paleo asian ocean the latest triassic to paleocene granitoids with calc alkaline characteristics were ne trending emplaced along the ejhb and saob and young towards the coastal region and represent continental marginal arc magmas that were associated with the northwestwards subduction of the paleo pacific plate two periods of magmatic quiescence 158 131 and 105 95 ma correspond to changes in the subduction direction of the paleo pacific plate from oblique relative to the continental margin to subparallel taking all this into account we conclude that 1 the final closure of the paleo asian ocean occurred along the changchun yanji suture during the early triassic 2 the onset of the subduction of the paleo pacific plate beneath the east asian continental margin probably took place during the latest triassic ca 215 ma 3 changes in the drifting direction of the paleo pacific plate were responsible for the intermittent magmatic activities and 4 roll back of the subducted plate resulted in the oceanwards migration of the magmatic arc and large scale back arc extension throughout ne china during the early cretaceous

geological fluid inclusion h o s pb isotope and ar ar geochronology constraints on the genesis of the nancha gold deposit southern jilin province northeast china abstract the nancha gold deposit located in the central part of southern jilin province in the northeastern portion of the north china craton contains orebodies hosted in a proterozoic metamorphosed volcanic sedimentary sequence the distribution of the orebodies is controlled by nne trending brittle ductile shear zones and faults the gold orebodies consist of auriferous quartz veins and auriferous altered rocks mineralization can be divided into three stages 1 quartz pyrite 2 quartz gold polymetallic sulfide and 3 quartz carbonate with gold being introduced mainly in the second stage three types of fluid inclusions were identified in the vein mineral assemblages based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type and pure co 2 pc type crystals in the early quartz pyrite stage veins mainly contain c type primary fluid inclusions and rare pc type inclusions the fluid inclusions in these veins completely homogenize at temperatures of 273 432 c and show low salinities of 0 63 7 78 wt nacl equiv in the middle quartz gold polymetallic sulfide stage all three types of fluid inclusions were observed these fluid inclusions homogenize at temperatures of 132 to 255 c and show salinities of 0 83 11 72 wt nacl equiv in contrast crystals in the late quartz carbonate stage contain only w type fluid inclusions that show homogenization temperatures of 132 255 c and salinities of 0 35 7 86 wt nacl equiv these data indicate that the metallogenic system evolved from a co 2 rich metamorphogenic fluid to a co 2 poor fluid due to inputs of meteoric waters fluid boiling and mixing caused the rapid precipitation of sulfides and gold trapping pressures estimated from boiling c type fluid inclusions were 152 367 mpa in the ore forming stage this suggests an alternating lithostatic hydrostatic fluid system controlled by a fault valve activity at a depth of 13 8 15 2 km one hydrothermal sericite sample from an auriferous quartz vein yielded an 40 ar 39 ar isotopic plateau age of 170 1 1 9 ma indicating that mineralization occurred in the middle jurassic and was unrelated to the volcanics and intrusions in the mineralized area the characteristics of h o s pb isotopes and fluid inclusions suggest that the ore forming fluids were of metamorphic origin with the s originating from proterozoic crustal components and the pb originating from a mixture of ore forming metamorphogenic fluids and host rocks the results combined with existing data on the regional geology ore geology fluid inclusions h o s pb isotope geochemistry age of mineralization and tectonic setting indicate that the nancha gold deposit was an orogenic type system that formed in a middle jurassic accretionary orogenic regime following subduction of the paleo pacific plate beneath the eurasian continent

early paleozoic amalgamation of the songnen zhangguangcai range and jiamusi massifs in the eastern segment of the central asian orogenic belt geochronological and geochemical evidence from granitoids and rhyolites abstract to constrain the early paleozoic tectonic evolution of the songnen zhangguangcai range and jiamusi massifs we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic igneous rocks in the lesser xing an zhangguangcai range of eastern heilongjiang province ne china the zircons from one diorite two rhyolites and four granitoids are euhedral subhedral and display fine scale oscillatory growth zoning indicating a magmatic origin la icp ms zircon u pb age data indicate the occurrence of magmatic events in the late ordovician 443 451 ma and middle silurian 424 430 ma the late ordovician igneous rocks are composed mainly of diorite tonalite and rhyolite whereas the middle silurian igneous rocks consist mainly of monzogranites the early paleozoic igneous rocks have sio2 59 65 76 11 wt mgo 0 13 1 23 wt and na2o k2o 4 68 7 77 wt and are chemically a calc alkaline series they are characterized by enrichment in light rare earth elements and large ion lithophile elements and depletion in heavy rare earth elements and high field strength elements such as nb ta and ti consistent with the chemistry of igneous rocks from an active continental margin setting in situ hf analyses of zircons show that ehf t values of zircons that formed in the early ordovician captured and inherited zircons in late ordovician igneous rocks range from 0 1 to 7 1 those of zircons that formed in the late ordovician including captured and inherited zircons in middle silurian monzogranite vary from 2 6 to 5 6 and those of zircons that formed in the middle silurian vary from 3 0 to 3 2 the progressive decrease in zircon ehf t values from the early ordovician to the middle silurian suggests an increasing involvement of ancient crust in the magma sources corresponding to the transition from subduction to collision take together these data suggest that the formation of late ordovician diorite tonalite and rhyolite in the zhangguangcai range adjacent to the mudanjiang fault may have been related to the westward subduction of an oceanic plate between the songnen zhangguangcai range and jiamusi massifs in contrast coeval rhyolites from the lesser xing an range located far from the mudanjiang fault may have formed in the supra subduction zone the occurrence of a middle silurian monzogranite association combined with geochronological data for detrital zircons from early devonian sedimentary rocks in eastern heilongjiang province suggests that the amalgamation between the songnen zhangguangcai range and jiamusi massifs occurred in the middle silurian

isotopic analysis of the super large shuangjianzishan pb zn ag deposit in inner mongolia china constraints on magmatism metallogenesis and tectonic setting abstract the super large shuangjianzishan pb zn ag deposit is a newly discovered deposit located in the huanggang ganzhuermiao polymetallic metallogenic belt of inner mongolia ne china the deposit s resource includes 0 026 mt ag 1 1 mt pb and 3 3 mt zn the deposit is controlled by a nw trending ductile shear zone and ne and nw trending faults in black pelite assigned to the lower permian dashizhai formation lree enrichment hree depletion nb ta p and ti depletion and zr and hf enrichment characterize felsic magmatic rocks in the shuangjianzishan pb zn ag district the ages of porphyritic monzogranite rhyolitic crystal vitric ignimbrite and porphyritic granodiorite are 254 252 169 and 130 ma respectively pyrite sampled from the mineralization has re os isochron ages of 165 7 ma which suggest the mineralization is associated with the ca 169 ma magmatism in the shuangjianzishan district zircons extracted from the porphyritic granodiorite yield e hf t values of 11 34 to 1 41 with t dm2 dates of 1275 1901 ma the e hf t values of zircons in the rhyolitic crystal vitric ignimbrite and the ore bearing monzogranite porphyry are 7 57 16 23 and 10 18 15 96 respectively and their t dm2 ages are 177 733 and 257 632 ma respectively partial melting of depleted mantle resulted in the formation of the ca 254 252 ma ore bearing porphyritic monzogranite and the ca 169 ma rhyolitic crystal vitric ignimbrite dehydration partial melting of subducted oceanic crust resulted in the formation of the ca 130 ma porphyritic granodiorite the porphyritic monzogranite was emplaced during the late stages of closure of the paleo asian ocean during the transformation from a collisional to extensional tectonic setting the ca 170 and ca 130 ma magmatism and mineralization in the shuangjianzishan district are related to subduction of the mongolia okhotsk ocean and subduction of the paleo pacific ocean plate respectively

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

the marine permian of east and northeast asia an overview of biostratigraphy palaeobiogeography and palaeogeographical implications abstract the permian marine biostratigraphy faunal successions and mutual correlations where possible throughout east and northeast asia are synthesized region by region based on both published literature and the author s field observations in certain parts of the region the correlation of the permian marine successions of ne asia with the permian international timescale and in particular with gondwanan permian marine sequences remains a major challenge due to profound marine provincialism during the permian however by employing biogeographically mixed faunas from east asia se mongolia ne china south primorye of far east russia and the south kitakami terrane of japan as biostratigraphic gateways coupled with some bipolarly and bi temperately shared permian marine taxa and faunas it has been possible to correlate with reasonable confidence some of the high palaeolatitude permian marine rock units and faunas of ne asia with those of the tethyan region and gondwana palaeobiogeographically the permian marine faunas of east and ne asia are assigned to four major provinces verkolyman sino mongolian japanese cathaysian and panthalassan provinces on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages of these the sino mongolian japanese province has considerable significance for regional palaeogeographical plate tectonic and palaeoceanographical reconstructions during the middle permian because of its conspicuously mixed cool and warm water marine biota the origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors including the increased tectonic convergence between the bureya jiamusi terrane and the sino korean platform during the permian and the intermingling of both warm and cold water ocean currents off the eastern coastal areas of the bureya jiamusi terrane and the sino korean platform during the middle permian

permian bimodal volcanism in the zhangguangcai range of eastern heilongjiang province ne china zircon u pb hf isotopes and geochemical evidence abstract in this paper we report on zircon u pb dating hf isotopes major and trace elements and sr nd isotope data with the aim of constraining the petrogenesis and regional tectonic evolution of late paleozoic volcanic rocks in the zhangguangcai range of eastern heilongjiang province ne china located in the eastern segment of the central asian orogenic belt caob between the siberian and north china cratons the late paleozoic volcanic rocks in the zhangguangcai range are composed mainly of basalt basaltic andesite rhyolite and minor dacite the results of la icp ms zircon u pb dating for two basaltic rocks three rhyolites and one dacite indicate that they formed in the early permian ca 292 ma the mafic rocks have sio2 50 13 53 80 wt k2o 0 98 2 28 wt mg 0 51 0 71 cr 144 541 ppm ni 74 260 ppm 87sr 86sr i 0 7044 and end t 4 28 whereas the felsic rocks have sio2 69 12 77 98 wt k2o 3 09 5 33 wt mg 0 17 0 36 87sr 86sr i 0 7032 and end t 4 32 these data are typical of bimodal volcanism the mafic volcanic rocks are characterized by a strong enrichment in large ion lithophile elements liles such as rb ba sr and pb depletion in high field strength elements hfses such as nb ta and ti depletion in heavy rare earth elements hrees and weak negative eu anomalies eu eu 0 88 0 94 on the other hand the felsic rocks show a strong depletion in nb ta sr p and ti enrichment in th u and k and relatively large negative eu anomalies eu eu 0 28 0 95 taken together these data suggest that the mafic magma was derived from the partial melting of a depleted lithospheric mantle modified by subducted slab derived fluids and that the felsic magma originated by partial melting of newly accreted crust the early permian bimodal volcanic rocks together with the coeval a type granites indicate an extensional environment similar to a back arc basin such a setting was possibly related to subduction of the paleo asian oceanic plate beneath the jiamusi and songnen zhangguangcai range massifs

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

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

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

petrogenesis of early middle jurassic intrusive rocks in northern liaoning and central jilin provinces northeast china implications for the extent of spatial temporal overprinting of the mongol okhotsk and paleo pacific tectonic regimes abstract the mesozoic tectonic evolution of ne china was controlled mainly by the mongol okhotsk and paleo pacific tectonic regimes however the extent of the spatial and temporal overprinting of these two regimes is poorly understood here we report new zircon la icp ms u pb dating and geochemical analyses of jurassic intrusive rocks in northern liaoning and central jilin provinces northeast china to discuss their petrogenesis and outline the extent of spatial and temporal overprinting of these two tectonic regimes dating results indicate that jurassic magmatism occurred in two stages during the early ca 175 ma and middle jurassic 170 163 ma these rocks represent two stage typical bimodal igneous rock associations composed mainly of olivine gabbro gabbro and gneissic granitoids the early and middle jurassic gabbros have low rare earth element ree abundances positive eu anomalies depletion in high field strength elements hfses and positive ehf t values 4 0 to 10 3 except for one value of 17 8 suggesting that the primary magma was derived from partial melting of depleted lithospheric mantle metasomatized by subducted slab derived fluids the early jurassic monzogranite exhibit high ree abundances 195 201 ppm weak negative eu anomalies eu 0 63 0 64 and negative ehf t values 11 9 to 8 2 suggesting a primary magma that was derived from partial melting of lower continental crust of the ncc the middle jurassic granodiorites are enriched in light rees lrees and large ion lithophile elements liles and are depleted in heavy rees hrees and hfses as well as high sr y 29 132 and la yb n 15 44 ratios in addition the middle jurassic granitoids near or within the ncc exhibit negative ehf t values 18 9 to 0 2 whereas those within the xing an mongolia orogenic belt xmob have generally positive ehf t values 0 6 to 6 4 suggesting their origin from partial melting of thickened ancient ncc and newly accreted continental crust of the xmob respectively the above findings combined with regional geologic data suggest that the early jurassic bimodal igneous rocks formed in an extensional tectonic environment related to subduction of the paleo pacific plate beneath the eurasian continent the middle jurassic bimodal igneous rocks possibly formed in an extensional environment related to the collapse of a thickened region of the lower crust after closure of the mongol okhotsk ocean

triassic volcanism in eastern heilongjiang and jilin provinces ne china chronology geochemistry and tectonic implications abstract with the aim of constraining the early mesozoic tectonic evolution of the eastern section of the central asian orogenic belt caob we undertook zircon u pb dating and geochemical analyses major and trace elements sr nd isotopes of volcanic rocks of the luoquanzhan formation and daxinggou group in eastern heilongjiang and jilin provinces china the analyzed rocks consist mainly of dacite and rhyolite with sio2 contents of 68 52 76 65 wt three samples from the luoquanzhan formation and one from the daxinggou group were analyzed using laser ablation inductively coupled plasma mass spectrometry la icp ms u pb zircon techniques three zircons with well defined oscillatory zoning yielded weighted mean 206pb 238u ages of 217 1 214 2 and 208 1 ma and one zircon with oscillatory zoning yielded a weighted mean 206pb 238u age of 201 1 ma these ages are interpreted to represent the timing of eruption of the volcanic rocks the triassic volcanic rocks are characterized by high sio2 and low mgo concentrations enrichment in large ion lithophile elements liles and light rare earth elements lrees depletion in high field strength elements hfses and heavy rare earth elements hrees 87sr 86sr i 0 7040 0 7050 luoquanzhan formation and 0 7163 0 7381 daxinggou group and end t 1 89 3 94 luoquanzhan formation and 3 42 3 68 daxinggou group these geochemical features indicate an origin involving the partial melting of juvenile lower crust nd model ages tdm2 of 651 821 ma and that compositional variation among the volcanic rocks arose from mineral fractionation and minor assimilation these volcanic rocks formed within an extensional environment following collision of the ncc and jiamusi khanka massif during the late paleozoic early triassic

early jurassic mafic magmatism in the lesser xing an zhangguangcai range ne china and its tectonic implications constraints from zircon u pb chronology and geochemistry abstract la icp ms zircon u pb dating and geochemical data have been obtained from five representative mafic ultramafic intrusions in the lesser xing an zhangguangcai range ne china with the aim of improving our understanding of the mesozoic tectonic evolution in the region and in particular determining the time of initiation of the circum pacific tectonic system the selected zircons exhibit striped absorption in cathodoluminescence cl images and have high th u ratios 0 20 3 16 indicating a magmatic origin the zircon u pb dates indicate that most of these magmatic zircons other than a few relics that were captured and entrained in the magma formed in the late early jurassic 186 182 ma and not as previously supposed in the middle caledonian the five mafic ultramafic plutons are composed of olivine gabbro hornblendite gabbro hornblende gabbro and gabbro diorite the olivine gabbro and hornblendite display cumulate textures implying that fractional crystallization of olivine and plagioclase took place during magma evolution these mafic ultramafic igneous rocks have sio2 37 3 55 7 mgo 3 05 13 3 al2o3 11 8 23 8 mg 42 69 mg 100mg mg fe2 total and eu 0 88 1 32 and they display three types of rare earth element ree distribution patterns right slipped flat patterns or dome like the trace element spider diagrams show that the rocks are enriched in large ion lithophile elements liles such as ba k and sr and depleted in high field strength elements hfses such as nb ta zr and hf the zircons have ehf 186 182 ma 2 7 to 12 0 and tdm1 366 732 ma the geochemical data indicate that the early jurassic mafic magma originated in an extensional environment from the partial melting of a depleted mantle wedge that had been metasomatized by fluids released from a fossil subducted slab these data combined with information on the spatial variation of coeval igneous rocks indicate that the formation of the early jurassic mafic ultramafic rocks in the lesser xing an zhangguangcai range was related to the subduction of the paleo pacific plate beneath the eurasian continent and this event would mark the beginning of the circum pacific tectonic system

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

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

sm nd and rb sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at shuanghe in the dabie mountains central china abstract ultrahigh pressure metamorphic uhpm rocks at shuanghe area in the dabie mountains occur as a uhpm block within the regional granitic gneiss a sm nd isochron defined by garnet omphacite rutile from coesite bearing eclogite yield an age of 226 3 3 2 ma another sm nd isochron defined by garnet two phengites form uhp gneiss yield a similar age of 226 5 2 3 ma the two consistent sm nd ages defined by three uhpm minerals suggest that nd isotopic equilibrium between uhpm minerals in these rocks during uhp metamorphism has been achieved this may correspond to the age of peak metamorphism with an average metamorphic temperature of 800 c it is demonstrated that the retrograde metamorphism of uhpm rocks occurred in an open chemical system whereas the nd and sr isotopic systematics of uhpm minerals may have remained closed nd and sr isotopic disequilibrium between uhpm minerals and retrograde metamorphic minerals has been observed therefore the tie line of garnet or phengite and whole rock containing retrograde metamorphic minerals gives an old sm nd age and a young rb sr age respectively with no geologic significance however a rb sr ages of 219 0 6 6 ma defined by phengite garnet from a uhpm gneiss indicates that the uhpm rocks at shuanghe cooled down to 500 c at that time it suggests that the uhpm rocks at shuanghe experienced the first rapid cooling during 226 219 ma on the other hand the rb sr ages of 174 7 8 to 169 2 3 3 ma defined by retrograde minerals amphibole or biotite with closure temperature ranging from 450 to 300 c and intensely retrograded metamorphic rocks reflect a second rapid cooling during this time interval this is consistent with the rapid cooling time of 190 170 ma of the orthogneiss in the dabie su lu uhpm belt obtained by ar ar dating method in contrast to uhpm rocks the nd isotopic composition of the garnet in granitic gneiss has been reset during retrograde metamorphism and is in equilibrium with those of retrograde epidote and biotite which yields a sm nd isochron age of 213 5 ma indicating the retrometamorphic time corresponding to amphibolite facies in addition the biotites from the granitic gneiss yield rb sr ages of 171 173 ma similar to those of the uhpm rocks these data suggest that the country rocks granitic gneiss may have a similar cooling history to the uhpm rocks at shuanghe two stages of rapid cooling of uhpm rocks at shuanghe may correspond two stages of fast uplift the initial rapid uplifting and cooling of uhpm rocks during 226 219 ma may be caused by compression tectonics during subducting time of the continental crust whereas the later rapid cooling may reflect the exhumation of the entire subducted continental crust by extension during the early middle jurassic

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

early miocene anatexis identified in the western syntaxis pakistan himalaya abstract evidence for typical himalayan early to middle miocene anatexis has remained elusive in the nanga parbat massif in the western himalaya of pakistan previous work has identified only young plutonism 10 1 ma new u th pb data from the southern chichi granite a leucogranite in southern nanga parbat reveal that crustal melting occurred during the early miocene this largely undeformed fine grained pluton intrudes the indian metasedimentary cover sequence adjacent to the rupal shear a major shear zone at nanga parbat th pb ion microprobe analyses of monazites from the chichi granite yield ages between 22 ma and 16 ma with the majority of analyses lying at 19 18 ma u pb zircon analyses yield ages which fall along a chord with a lower intercept age of 19 ma the zircons also contain an 1850 ma inherited component these data indicate that the early miocene anatexis that is ubiquitous in central portions of the himalayan orogen unreported anywhere in the nw himalaya also occurred in the western himalayan syntaxis and demonstrates that nanga parbat has a protracted melting history a small granitic dike that cross cuts the outer portion of the rupal shear yields monazite ages between 22 ma and 9 ma where the young ages correlate with high u concentrations 40ar 39ar biotite ages from adjacent gneisses indicate cooling by 10 ma requiring significant displacement on this portion of the rupal shear to be older than 10 ma and possibly as old as 20 ma

mesozoic adakitic rocks from the xuzhou suzhou area eastern china evidence for partial melting of delaminated lower continental crust abstract adakitic rocks in the xuzhou suzhou area eastern china consist of dioritic and monzodioritic porphyries and were dated at 131 132 ma by the shrimp u pb zircon method these rocks have high mgo content 1 47 5 73 high mg values 0 49 0 61 and high la yb and sr y ratios these features are similar to rocks derived from partial melting of a subducted oceanic slab however their high initial 87sr 86sr 0 7053 0 7075 and low end t values 4 43 to 13 14 are inconsistent with the origin from slab melting these rocks often contain garnet residual crystals and eclogite garnet clinopyroxenite and garnet amphibolite xenoliths petrographical characteristics and estimated p t conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early mesozoic garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from precambrian basement of the north china craton the data also suggest that the lower continental crust in the eastern north china craton was thickened during the early mesozoic and delaminated in the early cretaceous the high mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport leaving garnet as the residual phase

petrology of the hegenshan ophiolite and its implication for the tectonic evolution of northern china abstract petrographic observations and mineralogical and geochemical analyses have revealed that the hegenshan ophiolite is of mid ocean ridge origin and has been subjected to dynamothermal metamorphism at medium p t conditions the metamorphism is characterized by a prograde change in paragenesis from the greenschist to epidote amphibolite facies with peak temperature conditions of 570 640 c at pressures of 4 10 kbar the amphiboles formed by this metamorphism show k ar ages of 110 130 ma the metamorphic conditions and k ar ages suggest that the hegenshan ophiolite is located at the suture between the siberian and north china continental blocks where the continental collision in this area took place in middle mesozoic time given the temporal and spatial distribution of the igneous activity around the da hinggan ling mountains it is suggested that the extensive yanshanian magmatism in this region resulted predominantly from a southward subduction of an oceanic plate prior to collision alternatively it may possibly have resulted from the collision itself at the final stage

late permian tectonic evolution at the southeastern margin of the songnen zhangguangcai range massif ne china constraints from geochronology and geochemistry of granitoids abstract this paper reports the la icp ms u pb zircon dating and geochemical data for the huangqigou xiaobeihu and lalagou granitic plutons at the southeastern margin of the songnen zhangguangcai range massif which will not only place important constraints on the rock forming ages source characteristics and tectonic setting of these granitic plutons but will also provide insights into understanding the tectonic evolution of the eastern segment of the central asian orogenic belt zircons from three plutons have distinct oscillatory zoning structures in their cathodoluminescene cl images which combined with the th u ratios of 0 28 1 06 indicate their magmatic origins zircon u pb dating results for these granitic plutons indicate that the granitic magmatism occurred mainly in the late permian 256 252 ma the granites have sio2 of 58 0 74 3 na2o of 2 74 3 76 k2o of 2 75 3 95 na2o k2o of 0 77 1 13 mg 100 mg mg fe2 of 21 8 39 9 and a cnk of 0 88 1 08 with ree patterns characterized by lree hree 7 75 12 82 la yb n 7 88 14 9 and eu 0 56 0 87 the trace element spider diagrams indicate that these granites are enriched in large ion lithosphile elements rb ba th u etc and relatively depleted in high field strength elements ti nb ta with sr and pb ranging from 205 to 350 ppm and from 2 02 to 3 60 ppm respectively the in situ hf isotope analysis reveals that ehf t values range from 2 22 to 11 65 and the two stage hf model ages tdm2 range between 641 and 1274 ma these geochemical characteristics indicate that the late permian granitic plutons at the se margin of the songnen zhangguangcai range massif can be assigned to metaluminous and weakly peraluminous high potassium calc alkaline i type granites with low sr and high yb features and that the magmas to have formed these granites were originated from the partial melting of mafic igneous rocks in the lower crust the source rocks are composed mainly of the juvenile crust with small contributions of ancient continental crust considering the existence of coeval mafic intrusive rocks and sedimentary basins we propose that the late permian magmatism in the study area occurred in a post collisional extensional setting following the collision of the xingkai block and the united jiamusi and songnen zhangguangcai range massifs

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

metallogenic age and hydrothermal evolution of the jidetun mo deposit in central jilin province northeast china evidence from fluid inclusions isotope systematics and geochronology abstract the jidetun deposit is a large porphyry mo deposit that is located in central jilin province northeast china the mo mineralization occurs mainly at the edge of porphyritic granodiorite as well as the adjacent monzogranite field investigations cross cutting relationships and mineral paragenetic associations indicate four stages of hydrothermal activity to determine the relationships between mineralization and associated magmatism and better understand the metallogenic processes in ore district we have undertaken a series of studies incluiding molybdenite re os and zircon u pb geochronology fluid inclusions microthermometry and c h o s pb isotope compositions the molybdenite re os dating yielded a well defined isochron age of 168 9 1 9 ma mswd 0 34 that is similar to the weighted mean 206 pb 238 u age of 173 5 1 5 ma mswd 1 8 obtained from zircons from the porphyritic granodiorite the results lead to the conclusion that mo mineralization occurred in the middle jurassic 168 9 1 9 ma was spatially temporally and genetically related to the porphyritic granodiorite 173 5 1 5 ma rather than the older monzogranite 180 1 0 6 ma fluid inclusion and stable c h o isotope data indicate that the initial h 2 o nacl fluids of mineralization stage i were of high temperature and high salinity affinity and exsolved from the granodiorite magma as a result of cooling and fractional crystallization the fluids then evolved during mineralization stage ii into immiscible h 2 o co 2 nacl fluids that facilitated the transport of metals mo cu and fe and their separation from the ore bearing magmas due to the influx of abundant external co 2 and heated meteoric water subsequently during mineralization stage iii and iv increase of ph in residual ore forming fluids on account of co 2 escape and continuous decrease of ore forming temperatures caused by the large accession of the meteoric water into the fluid system reduced solubility and stability of metal clathrates thus facilitating the deposition of polymetallic sulfides

late jurassic to early early cretaceous tectonic nature on the ne asian continental margin constraints from mesozoic accretionary complexes abstract it is widely accepted that subduction of the paleo pacific plate beneath eurasia began in the early mesozoic however the tectonic nature and processes of the ne asian continental margin in the late jurassic to early early cretaceous remain unclear in this contribution lithological provenance and metamorphic deformation data are used to constrain the formation of mesozoic accretionary complexes ac along the ne asian continental margin and determine the tectonic relationship between the ne asian continental margin and the paleo pacific plate in the late jurassic to early early cretaceous the mesozoic ac formed during the late jurassic including the raohe ac in ne china the khabarovsk samarka and taukha acs in the russian far east and the mino tamba ac in japan and early cretaceous including the shimanto ac in japan and the kiselevka manoma ac in the russian far east the jurassic ac underwent a complex evolution including the formation of seamounts middle late jurassic terrigenous clastic sedimentation adjacent to the trench collision of seamounts with eurasia northward migration of the ac early early cretaceous terrigenous clastic sedimentation a second period of accretion and final emplacement the earliest mesozoic ac arrived at the trench at ca 195 ma combined with the occurrence of early mesozoic calc alkaline igneous rocks along the ne asian continental margin we suggest that subduction of the paleo pacific plate beneath eurasia began in the early jurassic jurassic ac in japan was affected by a regional high p t metamorphic event at 160 ma which might have been related to subduction collision of seamounts with eurasia at the trench ages and hf isotopic compositions of detrital zircon grains from the middle upper jurassic and cretaceous ac sandstones together with paleontological and paleomagnetic data indicate that jurassic clastic sediments were sourced mainly from the south china block scb whereas the lower cretaceous sandstones were sourced from the eastern central asian orogenic belt caob the inferred northward migration of jurassic ac in the late jurassic to early early cretaceous indicates that the boundary between the ne asian continental margin and the paleo pacific plate was characterized by strike slip tectonics at this time likely due to a small angle of obliquity in the subduction of the paleo pacific plate beneath eurasia in the late early cretaceous westward subduction of the paleo pacific plate beneath eurasia resulted in the emplacement of the raohe and khabarovsk acs at 137 130 ma and the formation of acs in the russian far east and japan

p t t evolution of orogenic belts and the causes of regional metamorphism barrow 1893 introduced three important ideas that furthered understanding of metamorphic processes i the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional metamorphism ii the concept of progressive metamorphism and iii the concept of magmatic advection of heat as a possible cause of regional metamorphism this article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the p t t paths of metamorphic rocks and by considering the likely causes of the different kinds of regional metamorphism that we observe within orogenic belts understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum t and maximum p orogenic belts characterized by clockwise p t paths achieved maximum p before maximum t the metamorphic peak normally post dated early deformation within the belt and additional heating above the normal conductive flux has been related to the amount of overthickening by contrast orogenic belts characterized by counterclockwise p t paths achieved maximum t before maximum p the metamorphic peak normally pre dated or was synchronous with early deformation within the belt and additional heating above the normal conductive flux has been related to the emplacement of plutons techniques used to constrain portions of p t t paths include the use of mineral inclusion suites in porphyroblasts and reaction textures thermobarometry the use of fluid inclusions thermodynamic approaches such as the gibbs method radiogenic isotope dating fission track studies and numerical modelling we can utilize specific mineral parageneses in suitable rocks to determine individual p t t paths and a set of p t t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the metamorphism recent advances are reviewed with reference to collision metamorphism high temperature low pressure metamorphism granulite metamorphism and subduction zone metamorphism and some important directions for future work are indicated

cone in cone and beef mineralization associated with triassic growth basin faulting and shallow shale diagenesis edgeoya svalbard cone in cone cic and beef bf carbonate lenses ornament detachment zone faults underlying triassic growth basins on edgeoya field relationships place cic and bf growth as during early diagenesis and a transition from hydroplastic to a later brittle style of faulting that is marked by coarser calcite veining deformation is constrained to have occurred at 300 m depth multiple models exist for cic formation for the edgeoya example textural analysis of thin sections suggests that small tensile fractures and carbonate shell fragments nucleated development of calcite aggregates with cic and bf morphology within unconsolidated to poorly consolidated sediment to form asymmetric antitaxial tensile aggregates subparallel to bedding and fault surfaces the conical forms result from differential growth on stepped cleavage parallel faces of fibres facing host sediment with preferential inclusion incorporation at inner corners the preferred directions of calcite growth are attributed to local stresses and seepage flow associated with pore pressure gradients substantial framboidal pyrite in the sediments represents an early phase of microbially driven sulphate reduction which may have induced calcite mineralization the transition to brittle style faulting was marked by development of deformation twins in cic bf fibres and a transition to coarse blocky calcite growth in relay arrays of steeply oriented microveins this indicates local fault related stresses substantially changed during shallow diagenesis and lithification an evolution attributed to changing pore pressures seepage forces and material moduli calcite mineralizations at edgeoya track the very significant changes in mechanical properties and stress states that occur during synlithification deformation at very shallow crustal levels

petrogenesis of the middle triassic erenhot granitoid batholith in central inner mongolia northern china with tectonic implication for the triassic mo mineralization in the eastern central asian orogenic belt abstract voluminous post orogenic magmatism holds a key to monitoring important geodynamic processes and crustal evolution within an extensional accretionary orogen the middle triassic erenhot granitoid batholith from central inner mongolia northern china is tectonically located in the eastern central asian orogenic belt this batholith consists of monzogranite syenogranite alkali feldspar granite and albite granite with minor mafic to felsic enclaves and dykes the formation of this composite batholith involved distinct mafic and felsic magma end members concomitant episodic mafic felsic interaction and intra felsic magma evolution mafic diabasic and high mg intermediate dioritic dykes show enrichment in large ion lithophile elements depletion in high field strength elements and heterogeneous isotopic compositions indicative of a metasomatized lithospheric mantle source inherited from prior oceanic slab subduction the monzogranites and aplites have arc like elemental features and variable isotopic compositions isr t 0 706132 end t 0 4 zircon ehf t 2 8 to 7 4 zircon 18o 5 32 to 6 74 clearly suggesting that the felsic magma end member of a dual heritage was derived from dominant newly underplated mafic crust and subordinate ancient lower crust hybridization processes between mantle derived mafic magma and crust derived felsic magma result in the formation of monzonitic enclaves isr t 0 704850 end t 0 1 with an isotopic resemblance to the host granites fractional crystallization of the monzogranitic magmas endows the differentiated syenogranites and alkali feldspar granites with highly evolved elemental characteristics we further deduce that the magmatic immiscibility between k rich and na rich residual melts in a deep reservoir produces albite granites with distinct deformation imprints variable k2o contents and wide range of crystallization temperatures combining with coeval regional igneous episodes as well as concomitant sedimentary and structural events in the northern china mongolia tract the triassic erenhot composite batholith can be considered as post orogenic magmatic products possibly within a coupled geodynamic scenario between lithospheric dripping and concurrent gravitational collapse therefore the documentation of this large scale triassic post orogenic magmatism could not only lead to the characterization of the eventual closure of the paleo asian ocean but also capture a snapshot into the tectonic background for the widespread porphyry type mo mineralization in the eastern central asian orogenic belt during early mesozoic

geochemical constraints on the genesis of hercynian two mica leucogranites from the massif central france abstract late hercynian two mica leucogranites dated at 340 280 3a old occur across the entire massif central france and form dykes and stocks up to 130 km in length they are peraluminous molecular al 2 o 3 na 2 o k 2 o cao asi 1 16 1 25 and have low initial nd 8 2 to 6 1 indicating derivation from the metasedimentary lower crust as sampled in crustal xenoliths nd 340 8 6 to 4 3 nd 280 9 0 to 4 8 their high sio 2 70 78 wt p 2 o 5 up to 0 5 rb and ga and low ba sr and ree are mainly a result of partial melting processes rather than fractionation partial melting was initiated by underplating of the lower crust by mantle derived basic magmas between 360 and 270 ma and was intensified by granulite facies metamorphism between 300 and 280 ma from this model there is little similarity between the genesis of two mica leucogranite in the massif central and that in the himalaya with which it has previously been compared

geochronology and isotope geochemistry studies of an epithermal gold deposit in the northern lesser khingan range ne china the gaosongshan example abstract the gaosongshan epithermal gold au deposit is located in the northern margin of the lesser khingan range polymetallic ore belt northeast ne china and contains au resources of more than 23 tons at an average grade of 6 3 g t gold orebodies are mainly hosted in intensely altered volcanic rocks of the lower cretaceous banzifang formation and as exploration has continued gold has also been discovered in extensively altered porphyritic intrusions with the highest au grade of 70 g t however the ages of metallogenesis and related magmatism have not been well constrained yet which have hindered the summary of metallogenic regularities in this study laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating from the granite porphyry yields a weighted mean 206pb 238u age of 101 6 1 2 ma slightly older than the rb sr isotope age of 98 1 6 ma for the auriferous quartz samples indicating that the gaosongshan au mineralization is genetically related to the granite porphyry the fluid d and 18oh2o values vary from 136 to 111 and from 9 3 to 2 5 respectively and the 4he and 40ar isotope compositions range from 15 7 10 9 to 35 5 10 9 cm3 stp g and 13 4 10 7 cm3 to 34 1 10 7 cm3 stp g respectively the obtained isotopic data show that the ore forming fluids were mixtures of magmatic and meteoric water but were dominated by meteoric water the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of ores in the gaosongshan deposit are 17 752 18 856 15 514 15 674 and 38 005 39 921 respectively which are similar to those of the gaosongshan granite porphyry implying that pb and possibly au originated primarily from late early cretaceous magmatic intrusions combining these results with data from previous studies we propose that the gaosongshan au deposit formed in an extensional tectonic setting during the rollback of the paleo pacific oceanic plate in ne china

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

zircon u pb age and sr nd hf isotope geochemistry of permian granodiorite and associated gabbro in the songliao block ne china and implications for growth of juvenile crust abstract post orogenic granitic and associated mafic rocks from northeastern ne china consist of granodiorite and gabbro intrusions we report here upon new u pb zircon ages geochemical data and sr nd hf isotopic data for these rocks la icp ms u pb zircon analysis yields an age of 262 8 1 0 ma for the granitic rocks and a uniform age of 262 1 0 7 ma for the gabbro most of the granitic and mafic rocks are characterised by low k 2 o na 2 o and pertain to the subalkaline series in the total alkali silica diagram the granodiorite samples show low 87 sr 86 sr i ranging from 0 700 to 0 705 positive e nd t values from 0 3 to 0 8 and large variation in e hf t values of between 4 0 and 2 5 indicating that both newly underplated basalt 70 80 and ancient lower crustal sources 20 30 contributed to their origin furthermore positive e hf t values with two stage model ages t dm2 of 1123 1260 ma together with nd model ages 960 1000 ma suggest an important episode of crustal growth during the meso neoproterozoic beneath the songliao block in contrast the investigated gabbro is characterised by relatively high 87 sr 86 sr i ratios 0 707 0 708 negative e nd t 5 9 to 5 3 and e hf t values 5 0 to 2 3 implying that this was derived from an enriched mantle source the geochemical data indicate that the granitic magmas underwent separation of clinopyroxene hornblende k feldspar plagioclase ti bearing phases e g rutile ilmenite titanite apatite and zircon during their evolution whereas the gabbro is characterised by low mgo 2 92 3 92 wt mg 35 41 and compatible elements content such as cr 10 68 ppm co 16 31 ppm and ni 5 7 33 ppm features of a more evolved mafic magma there is no evidence that the granitic and mafic rocks were affected by crustal contamination during emplacement our interpretation is that the two coeval intrusive suites were both formed in a post orogenic extensional setting related to lithospheric delamination or collapse of the central asian orogenic belt caob xingmeng orogenic belt in china

some geodynamic and compositional constraints on postorogenic magmatism postorogenic magmatic suites are common to many orogens in many cases apparently just postdating the cessation of deformation they differ from preceding orogenic suites in that they have higher temperatures more primitive isotopic signatures and bimodal natures and thus are compositionally similar to suites found in extensional regimes we propose that thinning of the lithospheric mantle which may be an automatic response to orogenic lithospheric thickening is responsible for these magmatic suites mantle lithospheric thinning moves the asthenospheric lithospheric thermal boundary higher in the lithospheric column thereby raising the overall thermal budget of the orogen and the likelihood of basaltic magmatism this removal of much of the dense lithospheric mantle root of the orogen also invokes uplift capable of producing horizontal orogenic buoyancy forces that will oppose and potentially terminate deformation extreme fractionation of the magmas is promoted by high temperatures and a noncompressional or tensional lithospheric stress regime to produce accompanying felsic a type magmas this model explains why the cessation of deformation is coincident with high temperature bimodal magmatism and inferred uplift as well as the long noted similarity and confusion between postorogenic and extensional magmatic suites this arises because both reflect thinning of the lithospheric mantle not because both reflect extensional tectonics we suggest that these magmatic episodes may be important in transferring lithospheric mantle material and its compositional signatures into the crust

collision belt between the khanka block and the north china block in the yanbian region northeast china the pre jurassic geotectonics in northeast china and its adjacent regions are characterized by collision of microcontinental blocks the yanbian region lies between the north china block ncb and the khanka block kb along the dashanzui antu kaishantun collision belt the yanbian pre jurassic fold belt can be divided into two parts one part represents the western margin of the kb which consists of late proterozoic metamorphic basement and a permian active continental margin the other one is located at the eastern margin of the ncb and is composed of proterozoic passive margin deposits where the seluohe and qinglongcun groups are developed and rocks of the permian passive margin collision of these two parts took place along the dashanzui antu kaishantun collision zone during the late permian to early triassic as evidenced by the emplacement of syncollision granites and a type granites in northeast china and adjacent regions a series of microcontinental blocks collided with one other from the end of early paleozoic to the early triassic the collision event that took place in the yanbian region may represent the latest collision event in the paleo asian oceanic domain c 2003 elsevier ltd all rights reserved

origin of mesozoic adakitic intrusive rocks in the ningzhen area of east china partial melting of delaminated lower continental crust to the best of our knowledge modern adakites have not been documented in a nonarc environment we report geochemical and isotopic data for early cretaceous anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction the anjishan adakitic intrusive rocks which are exposed in the ningzhen area of east china have high sr y and la yb ratios coupled with low yb and y as well as relatively high mgo contents and mg numbers mg 0 4 0 6 similar to products from slab melting however low n d t values 6 8 to 9 7 and high 8 7 sr 8 6 sr i 0 7053 0 7066 are inconsistent with an origin by slab melting the tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust high sr y and la yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting implying that the crustal thickness exceeded 40 km in the early cretaceous the present thickness of the crust in the ningzhen area is only 30 km and therefore the crust appears to have been thinned by at least 10 km since the early cretaceous the relatively high mgo contents and mg of the anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks possibly coinciding with lower crustal delamination which would also account for the observed thinning

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

early cretaceous subduction related adakite like rocks of the gangdese belt southern tibet products of slab melting and subsequent melt peridotite interaction abstract the limited geochronology and geochemistry data available for the early cretaceous igneous rocks of the southern gangdese belt southern tibet has resulted in the proposal of conflicting geodynamic models for the generation of the widespread cretaceous igneous rocks in the middle and northern parts of the belt to explore this issue we present shrimp u pb zircon data and geochemical and sr nd pb hf isotopic data for the mamen andesites from the southern margin of the gangdese belt the mamen andesites emplaced at 136 5 ma are sodic na2o k2o 1 2 2 3 and have geochemical characteristics typical of adakites i e high al2o3 high la yb ratios and sr contents low y and hree contents and positive eu anomalies except for high cr ni and mgo contents the andesites have initial 87sr 86sr t ratios of 0 70413 0 70513 positive end t values of 3 7 5 8 and 206pb 204pb t ratios of 18 37 18 51 207pb 204pb t ratios of 15 59 15 65 and 208pb 204pb t ratios of 38 43 38 72 in situ hf isotopic analyses of zircons that had previously been dated by shrimp yielded positive initial ehf t values ranging from 11 0 to 15 5 a model calculation using trace element and sr nd pb isotopic data indicates that several percent of subducted sediment is required to generate the mamen andesites which were derived via the partial melting of subducted neo tethyan slab morb sediment fluid and subsequently hybridized by peridotite in the mantle wedge our data indicate that the neo tethyan oceanic crust was subducted northward beneath the gangdese belt during the early cretaceous at a high angle our results are inconsistent with a tectonic model that advocates the low angle or flat slab subduction of neo tethyan oceanic crust in generating the widespread cretaceous magmatism recorded in the gangdese belt

basanite to phonolite differentiation within 1550 1750 yr u th ra isotopic evidence from the a d 1585 eruption on la palma canary islands u th ra disequilibria of basanites tephrites and phonolites from the a d 1585 eruption on la palma canary islands constrain magma differentiation times in an ocean island rift zone the insignificant difference in 230th 232th implies differentiation from basanite to phonolite in 15 k y 226ra has a half life of 1600 yr however and permits higher temporal resolution 226ra 230th disequilibria are highest in the phonolites 46 54 and basanites 44 47 and lowest in the tephrites 38 41 the higher 226ra excesses in the end member compositions model basanite phonolite differentiation within 1550 1750 yr at a rate of 0 04 fractional crystallization per year such a short time interval is in sharp contrast to the 200 k y proposed for phonolite differentiation on the neighboring island of tenerife and could reflect different volcanic systems with a mantle fed rift system on la palma versus a crustal magma reservoir on tenerife

the ordovician igneous rocks with high sr y at the tongshan porphyry copper deposit satellite of the duobaoshan deposit and their metallogenic role abstract a strong link between high sr y arc magmas and porphyry cu mo au deposits has been recognized in recent years the tongshan and duobaoshan deposits are representative large cu mo au deposits in ne china we report la icp ms zircon u pb crystallization age of 471 5 1 3 ma for tongshan ore related granitoid re os isotopic analyses of the two chalcopyrite samples from tongshan deposit show a model age range of 470 2 477 1 ma the duobaoshan and tongshan ore related granitoids show higher sr y and la yb ratios the 34 s values of sulphides from the duobaoshan and tongshan deposits vary from 2 3 to 0 0 belonging to a magmatic hydrothermal system the pb isotopic ratios of the sulphides from the duobaoshan and tongshan deposit range from 17 201 to 18 453 for 206 pb 204 pb 15 445 to 15 551 for 207 pb 204 pb and 36 974 to 37 999 for 208 pb 204 pb indicating the addition of lower crustal material the duobaoshan and tongshan granitoids were formed in a subduction related continental arc setting produced by partial melting of juvenile hydrous basalts underplating the deep continental crust during the ordovician

geochronology and geochemistry of early mesozoic magmatism in the northeastern north china craton implications for tectonic evolution abstract this paper reports geochronological geochemical zircon u pb and hf o isotopic data of the late triassic and early jurassic intrusive rocks in the northeastern north china craton ncc with the aim of reconstructing the tectonic evolution and constraining the spatial temporal extent of multiple tectonic regimes during the early mesozoic zircon u pb ages indicate that the early mesozoic magmatism in the northeastern ncc can be subdivided into two stages late triassic 221 219 ma and early jurassic 180 177 ma late triassic magmatism produced mainly granodiorite and monzogranite which occur as a ne sw trending belt parallel to the sulu jingji belt geochemically they are classified as high k calc alkaline and metaluminous to weakly peraluminous granitoids and are enriched in large ion lithophile elements liles and light rare earth elements lrees and depleted in high field strength elements hfses e g nb ta ti and p and heavy rare earth elements hrees indicating an affinity to adakite combined with their ehf t values 17 9 to 3 2 and two stage model ages 2387 1459 ma we conclude that the late triassic granitoid magma in the northeastern ncc was derived from partial melting of the thickened lower crust of the ncc and was related to deep subduction and collision between the ncc and the yangtze craton yc the early jurassic magmatism is composed mainly of monzogranites which are classified as metaluminous high k calc alkaline and i type granite their ehf t values and two stage model ages are 16 7 to 4 2 and 2282 1491 ma respectively compared with the late triassic granitoids the early jurassic granitoids have relatively high hree contents similar to calc alkaline igneous rocks in an active continental margin setting these early jurassic granitoids together with the coeval calc alkaline volcanic rocks and gabbro diorite granodiorite association in the northeastern ne asian continental margin comprise a nne ssw trending belt parallel to the ne asian continental margin indicative of the onset of paleo pacific plate subduction beneath eurasia

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

u pb ages of zircons from mesozoic intrusive rocks in the yanbian area jilin province ne china transition of the paleo asian oceanic regime to the circum pacific tectonic regime abstract geology in the yanbian area ne china is a key to understanding the relationship between the paleo pacific tectonic regime and the older paleo asian oceanic regime especially the transition between the regimes during the mesozoic a compilation of 131 u pb zircon ages including 18 obtained in the present study shows that the late paleozoic to mesozoic magmatism in the yanbian area took place from 285 to 105 ma mainly 205 160 ma and that there was a peak of activity at 175 ma and a hiatus from the late jurassic to early cretaceous 150 130 ma provisionally we subdivide the magmatic activity into four dominant stages middle permian to middle triassic 280 240 ma late triassic 230 205 ma early to middle jurassic 205 160 ma and early cretaceous 130 105 ma middle permian intrusive rocks including pyroxenite gabbro diorite granodiorite tonalite and monzogranite are interpreted to have been emplaced along an andean style continental margin in association with the subduction of the paleo asian oceanic plate the late permian middle triassic intrusive rocks are mainly quartz monzonite monzogranite and syenogranite and are considered to have been the result of syn orogenic post collisional activities the late triassic magmatism involved not only the emplacement of mafic ultramafic intrusive rocks but also coeval i and a type granitoids indicating an extensional environment after the final closure of the paleo asian ocean since the jurassic the tectonic setting has been dominated by subduction of the paleo pacific oceanic plate previously published data for the yanbian area and age data from surrounding regions show that the entire region from the yanbian area to the korean peninsula and the japanese islands experienced peaks in igneous activities that ranged from 200 to 165 ma during the jurassic and 120 to 110 ma and 90 to 65 ma during the cretaceous the jurassic intrusive rocks were emplaced mainly in the west and cretaceous intrusive rocks in the east in other words there is a southeastwards younging of mesozoic intrusive rocks that appears to have been closely associated with the evolution of the paleo pacific ocean taking all this into account we conclude that the transition from the paleo asian oceanic regime to the circum pacific tectonic regime took place during the late triassic to early jurassic

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

geochronology geochemistry and deformation history of late jurassic early cretaceous intrusive rocks in the erguna massif ne china constraints on the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt abstract this paper presents new zircon and sphene u pb ages biotite and hornblende 40 ar 39 ar ages hf isotopic data and geochemical data for five mesozoic plutons in the erguna massif of ne china these data are used to constrain the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt this new dating when combined with previously published ages indicates that the late jurassic early cretaceous j 3 k 1 intrusive rocks can be subdivided into three stages that represent periods of magmatism during the late jurassic 155 ma early early cretaceous 137 ma and late early cretaceous 123 ma in addition the rocks have undergone later deformation recorded by peak ages of 137 and 123 ma the late jurassic and early early cretaceous intrusive rocks in the study area are dominantly syenogranites and are either a type granites or are classified as alkaline series suggesting that they formed in an extensional environment the late early cretaceous intrusive rocks in this area are generally monzogranitic and were emplaced as dikes in an extensional environment along with coeval bimodal volcanics these data combined with the presence of regional unconformities in the northern part of hebei province and western part of liaoning province and the spatial distribution of coeval volcanic rocks in ne china suggest the late jurassic and early early cretaceous magmatisms and the early early cretaceous deformation in this area occurred in an extensional environment related to the delamination of a thickened part of the crust after closure of the mongol okhotsk ocean in comparison the late early cretaceous deformation and magmatism occurred in an extensional environment related to either delamination of the previously thickened crust related to the mongol okhotsk tectonic regime or the subduction of the paleo pacific plate or the combined influence of these two tectonic regimes

genesis of the tianbaoshan pb zn cu mo polymetallic deposit in eastern jilin ne china constraints from fluid inclusions and c h o s pb isotope systematics abstract the tianbaoshan pb zn cu mo deposit is located in the eastern part of jilin heilongjiang region ne china which is considered to be the eastern segment of the central asian orogenic belt field and geochronological evidences indicate that this deposit experienced three types of mineralization including hercynian skarn cryptoexplosion breccia pipe and yanshanian quartz vein the early stages of the pb zn cu mineral systems in skarn and cryptoexplosion breccia pipe are characterized by a high temperature high salinity h 2 o co 2 nacl system of hydrothermal fluids that were possibly exsolved from the hercynian wall rock granodiorite these fluids show h o isotopic compositions similar to those of typical magmatic fluids by contrast the low temperature hydrothermal fluids of the later stages are represented by low salinity nacl h 2 o systems with low h o isotopic values the skarn and cryptoexplosive breccia pipe types of pb zn cu mineralization tend to have weakly negative 34 s values of 4 0 to 0 8 mean values of 2 31 and 2 16 respectively indicating that the sulfur was sourced from the hercynian magma therefore the early stage ore forming fluids of the skarn and cryptoexplosive breccia pipe were most likely sourced from high temperature and high salinity fluids closely related to the cooling and fractional crystallization of the hercynian granodiorite while the later stages changed to nacl h 2 o meteoric water influx whereas the ore forming fluids of the quartz vein type of mo mineralization were high temperature high salinity nacl h 2 o systems that differed from those of the skarn and cryptoexplosion breccia pipe but their h o isotopic compositions also indicate a magmatic fluid the weakly enriched 34 s values of molybdenite from the quartz vein type mo mineralization 34 s 0 2 2 8 average of 1 65 are comparable with those of other mesozoic yanshanian mo deposits 34 s 0 4 4 1 with an average of 1 39 3 15 but differ significantly from those of the hercynian pb zn cu skarn and cryptoexplosion breccia pipe this indicates that the sulfur of quartz vein type of mo originated from mesozoic yanshanian magmatism and that the ore forming fluids were derived from yanshanian magmatic rocks rather than being a product of the hercynian activity the 13 c values of the fluid inclusions in quartz from the skarn cryptoexplosion breccia pipe and quartz vein types are in a narrow range of 19 5 to 9 3 similar to those of the shanxiuling group which indicates that the carbon of the three types of mineralization had the same primary origin in the shanxiuling group the lead isotope compositions of ores from the skarn and cryptoexplosion breccia pipe types of mineralization 206 pb 204 pb 18 0725 18 3627 207 pb 204 pb 15 3721 15 5694 and 208 pb 204 pb 37 5542 38 8208 overlap with those of the hercynian granodiorite and shanxiuling group marble suggesting that the lead was probably derived from a mix of two different sources the shanxiuling group and the hercynian granodiorite whereas the lead isotope compositions of ores from the quartz vein type of mo mineralization 206 pb 204 pb 18 3837 18 6949 207 pb 204 pb 15 6824 15 7293 and 208 pb 204 pb 39 1009 39 1889 are significantly higher than those of the shanxiuling group marble and the hercynian granodiorite this indicates that the lead may be a product of yanshanian magmatic activity instead of the nearby hercynian granodiorite

zircon u pb and molybdenite re os dating and geological implications of the shimadong porphyry molybdenum deposit in eastern yanbian northeastern china the shimadong porphyry mo deposit is located in eastern yanbian in the eastern part of the north margin of the north china craton northeastern china here we present the whole rock major and tra

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

early permian plutons from the northern north china block constraints on continental arc evolution and convergent margin magmatism related to the central asian orogenic belt recent zircon dating identified several late carboniferous to early permian hornblende gabbro diorite quartz diorite granodiorite tonalite granite plutons in lithological assemblages at the northern margin of the north china block ncb that were previously regarded as archaean to palaeoproterozoic our geochronological results indicate that emplacement of these plutons was a continuous process during the late carboniferous to early permian from 324 6 to 274 6 ma and lasted for at least 50 ma in this paper the early permian components with compositions from gabbro to granite within the intrusive complex were studied the early permian plutons exhibit calc alkaline or high k calc alkaline metaluminous geochemical features and highly variable sio2 contents they have no significant eu anomaly in their ree patterns and in primitive mantle normalized spidergrams they display depletion in th u nb ta p and ti and enrichment in ba k pb and sr the granitoid bodies within these plutons display i type and adakitic geochemical signatures the early permian rocks exhibit low whole rock initial 87sr 86sr ratios from 0 70520 to 0 70615 and have negative whole rock e nd t values ranging from 17 4 to 9 3 and zircon e hf t values of 23 2 to 10 5 the gabbros exhibit higher e nd t values from 11 1 to 9 3 and e hf t values from 16 5 to 10 5 and one granodiorite exhibits an even lower e nd t value of 17 4 and zircon e hf t values of 23 2 to 15 1 geochemical sr nd and in situ zircon hf isotopic compositions suggest that the hornblende gabbros were derived from a metasomatized lithospheric mantle and the diorite and quartz diorite were generated from a gabbroic magma by fractional crystallization coupled with differential assimilation of ancient lower crustal material the granodiorite was likely derived from partial melting of ancient lower crust with involvement of some mantle components involvement of both lithospheric mantle and ancient lower crust in the generation of the early permian plutons indicates strong crust mantle interaction in the northern ncb petrological associations as well as geochemical and sr nd hf isotopic results show that the early permian plutons were emplaced along an andean type active continental margin during southward subduction of the palaeo asian oceanic plate beneath the ncb integration of our results with previously published data for late carboniferous and late permian to middle triassic intrusions suggests that the continental arc on the northern margin of the ncb existed for at least 50 ma during the late palaeozoic and final amalgamation of the mongolian arc terranes with the northern ncb likely occurred during a period from 270 to 250 ma i e in the late permian to earliest triassic

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

zircon u pb geochronology and petrogenesis of the late paleozoic early mesozoic intrusive rocks in the eastern segment of the northern margin of the north china block abstract zircon u pb dating and whole rock geochemical analysis have been undertaken on late paleozoic early mesozoic intrusive rocks of central jilin province ne china with the aim of constraining the tectonic evolution of the eastern segment of the northern margin of the north china block ncb during the late paleozoic early mesozoic zircon u pb dating indicates that late paleozoic early mesozoic magmatic events can be subdivided into four stages middle permian 270 ma late permian 259 255 ma early triassic 249 ma and late triassic 222 ma the middle permian magmatic event formed peraluminous garnet bearing monzogranites indicative of formation under a compressional tectonic regime related to collision between the ncb and the songnen zhangguangcai range massif the late permian magmatic event formed gabbros and syenogranites a bimodal association that is typical of magmatism within post collisional extensional setting the early triassic magmatic event formed adakitic monzogranites suggesting that they formed from magmas derived from partial melting of a thickened mafic lower crust the late triassic magmatic event formed a series of mafic ultramafic intrusive rocks together with coeval granitoids in adjacent regions and make up a typical bimodal association suggesting that they formed under an extensional environment related to the final amalgamation of the ncb and the songnen zhangguangcai range massif taken together we conclude that the northern margin of the ncb underwent multiple orogenic events between the middle permian and the late triassic with final amalgamation of the ncb and the songnen zhangguangcai range massif occurring in the early triassic an event that led to the final suturing of the solonker xra moron changchun zone

adakites without slab melting high pressure differentiation of island arc magma mindanao the philippines abstract new geochemical data for pleistocene magmatic rocks from the surigao peninsula eastern mindanao the philippines demonstrate typical adakitic traits including elevation of sr y and depletion of the heavy rare earth elements 87sr 86sr and 143nd 144nd ratios of the adakites do not support melting of the subducted philippine sea plate but resemble pliocene arc lavas generated in the same subduction zone excepting the heavy rare earth elements the adakites and arc lavas also possess similar ratios of incompatible elements suggesting that the adakites were ultimately derived from melting of the mantle wedge the wide range of sio2 in the adakites and its strong correlation with trace element concentrations and ratios indicate two possible mechanisms for generating the adakitic signature 1 adakitic melt was produced from basaltic arc magma by fractional crystallisation of a garnet bearing assemblage 2 solidified basaltic rock containing garnet melted to yield adakitic magma in either case the basaltic precursor was generated from fluid modified mantle then differentiated within the garnet stability field in surigao this requires differentiation within mantle the surigao example suggests that any subduction zone has the potential to produce adakitic magma if basalt crystallises at sufficient depth this has important implications for the geodynamics of modern and ancient subduction zones that have generated similar rocks

timing of deformation and location of the eastern liaoyuan terrane ne china constraints on the final closure time of the paleo asian ocean abstract the liaoyuan terrane lt in ne china formed as a result of accretion during the final closure of the paleo asian ocean between the north china and siberian cratons however the timing of the deformation and the location of the eastern lt remain controversial here we present structural data zircon u pb age dating and hf isotopic data to constrain the kinematics and timing of deformation and the southern boundary of the eastern lt in relation to the ne sw striking yilan yitong fault yyf one of two branches of the continental scale tan lu fault zone in ne china pre jurassic rocks in the eastern lt were widely involved in ductile deformation within wnw ese striking thrust belts the microstructures in these shear zones indicate a top to the ssw sense of shear and deformation temperatures of 450 500 c the northern margin of the north china craton ncc was also affected by the nne ssw contraction as shown by similar ductile deformation in the archean gneisses and wnw ese trending folds in the mesoproterozoic sedimentary cover the ages of crystallization in deformed and undeformed igneous rocks in the lt constrain the deformation to an interval between 241 and 193 ma u pb dating of zircons in syn kinematic migmatitic rocks indicates an age of 234 229 ma for the deformation we consider this middle triassic age to represent the final closure time of the paleo asian ocean along the eastern lt and this timing is consistent with the eastwards scissor style closure model lithological variations zircon age spectra ehf t values and model ages confirm the eastward extension of the lt across the yyf the data constrain the boundary between the lt and ncc to be roughly along the liao river to the west of the yyf and along the northern edge of the exposed archean gneisses to the east the boundary follows the bayan obo chifeng kaiyuan fault which was active as a thrust thrusting of material to the ssw during the middle triassic orogeny the newly determined boundary location indicates a 35 km sinistral displacement along the yyf

the hulan group its role in the evolution of the central asian orogenic belt of ne china the hulan group of central jilin province northeastern ne china consists of felsic volcanic and sedimentary rocks that underwent sub greenschist to amphibolite facies metamorphism and multiple phases of deformation during formation of the central asian orogenic belt young nd model ages of 1100 ma obtained in this study do not support earlier models that the hulan group was either rifted from the north china craton to the south or from the jiamusi block to the north since both these blocks have much older nd model ages detrital zircon u pb ages from a meta sedimentary rock of the hulan group define a maximum age of deposition of 287 6 ma not early palaeozoic as previously believed rb sr mineral isochron data indicate that metamorphism of the hulan group occurred at 250 ma this conclusion is further supported by an age of 248 4 ma for the dayushan granite which intruded the hulan group these new isotopic data together with evaluation of the regional geology indicate that final oceanic closure in the chinese segment of the central asian orogenic belt took place in the late permian the hulan area is located along the solonker xra moronchangchun suture that extends from inner mongolia across to central jilin province it is this zone that marks the final ocean closure resulting in the amalgamation of the north china and siberian cratons 2007 elsevier ltd all rights reserved