an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

nd isotopic and geochemical constraints on the provenance and tectonic setting of the low grade meta sedimentary rocks from the trans north china orogen north china craton abstract in the trans north china orogen tnco of the north china craton low grade supracrustal successions extensively occur in the wutai luliang zanhuang zhongtiao and dengfeng complexes from north to south meta sedimentary samples from the wutai and zhongtiao complexes were collected for geochemical and nd isotopic studies and several samples from the zanhuang and dengfeng complexes were also analyzed for nd isotopic studies for comparative purpose most of the meta siltstones and meta sandstones from the wutai and zhongtiao complexes are characterized by depletions in mobile elements like cao sr and na2o high chemical index of weathering ciw values and strong positive correlation between al2o3 and tio2 indicating intense weathering conditions significant post depositional k metasomatism is indicated in the a cn k diagrams for most of the analyzed samples and the relatively high pre metasomatized chemical index of alteration cia values 43 87 also imply a high degree of source weathering depleted transitional trace elements ni cr co and sc fractionated light rare earth elements patterns mild negative eu anomalies in the majority of these meta sedimentary samples point toward felsic source rocks including the 2 5 ga granitics ttg gneisses and the paleoproterozoic granitics in the tnco minor contribution from mafic rocks is evidenced from relative high contents of mgo fe 2 o 3 t sc and lower la ybn ratios in some older sequence set samples from the zhongtiao complex our geochemical and nd isotopic data combined with previous studies in the lithostratigraphic sequence provenance and depositional age suggest that the older and younger sequence sets of the low grade supracrustal successions in the tnco were deposited in the different depositional environments the older sequence set was deposited in a back arc basin between the andean type continental margin arc and the eastern block after 2 1 ga whereas the younger sequence set formed in a foreland basin between 1 88 and 1 80 ga which is consistent with the model that the collision between the eastern and western blocks to form the trans north china orogen occurred at 1 85 ga

provenances of the mesozoic sediments in the ordos basin and implications for collision between the north china craton ncc and the south china craton scc abstract to constrain the provenance of the ordos basin and the evolution history of the qinling orogen belt from the triassic to the jurassic 10 samples from the dongsheng area and 28 samples from the yan an area were analyzed for u pb ages and lu hf and sm nd isotopic compositions the results indicate that middle jurassic sediments in the dongsheng area were derived from the khondalite belt langshan mountain and the yinshan terrane mesozoic sediments in the yan an area consist of two parts one part is derived from the north china craton ncc which has u pb age groups of 1 8 ga and 2 5 ga and hf model ages of 2 8 ga the other part is derived from the qilian qinling orogenic belt which has u pb age groups of 600 1500 ma and 100 500 ma and nd and hf isotopic model ages of less than 2 2 ga combining the u pb ages with the hf and nd isotopic model ages mesozoic detrital zircons with u pb age groups of 1 8 ga and 2 5 ga in the yan an area are found to also be derived from the khondalite belt langshan mountain and the yinshan terrane not from the trans china orogen belt from the late late triassic sediments of the yan an area the low average values of the hf 2 03 ga and nd 2 03 ga model ages and the characteristic age population of 600 1500 ma reveal that the main collision or continental subduction between the ncc and the south china craton scc occurred in the late late triassic after the main collision or continental subduction the proportion of sediments from the qinling qilian orogenic belt began to decrease recorded in the early jurassic samples which may be in response to the gradual slowing of the uplift speed of the qinling orogenic belt in the early middle jurassic the sediments have a main u pb age population of 100 500 ma low detrital zircon hf model ages average value is 1 17 ga and low whole rock nd model ages average value is 1 13 ga which suggests that the qilian qinling orogenic belt may have a fast uplift history in the early middle jurassic

destruction of ancient lower crust through magma underplating beneath jiaodong peninsula north china craton u pb and hf isotopic evidence from granulite xenoliths abstract zircons from granulite xenoliths entrained in a late cretaceous mafic dike in the jiaodong peninsula north china craton ncc show three distinct u pb age populations part of the old zircon grains yield discordant data that project to ages of about 2 4 to 2 5 ga a few grains indicate growth at about 2 0 ga and a third group yield cretaceous ages with peaks at 120 and 90 ma the oldest zircons give hf t dm model ages of 2 6 2 8 ga these results demonstrate the existence of original archean lower crust in the jiaodong region zircons of 2 0 ga have similar hf t dm model ages as the neoarchean paleoproterozoic grains suggesting that these zircons were products of metamorphic recrystallization due to thermal event without juvenile input early cretaceous zircons yield ehf t values of 21 to 12 and late cretaceous zircons large variable ehf t from 4 to 50 these data suggest that magmatic underplating occurred in the neoarchean to earliest proterozoic lower crust of the ncc both in the early and late cretaceous it is suggested that the mesozoic magma underplating which also provided the heat source for the voluminous mesozoic magmatism in the ncc significantly modified the composition of the archean to paleoproterozoic lower crust of the ncc

genetic relationship between 1780 ma dykes and coeval volcanics in the lvliang area north china abstract the 1780 ma dykes and coeval volcanics constitute a large igneous province in the north china craton however whether these dykes and volcanic rocks of varying compositions originated from one or multiple sources remains controversial the ca 1780 ma lvliang dykes are characterized by widespread e w oriented dykes and minor n w oriented diabase dykes the e w oriented dykes are bimodal and comprise two subgroups one is dominated by acidic high silica dykes sio 2 63 wt while the other is dominated by mafic to intermediate relatively low silica dykes sio 2 sims u pb dating on zircons from one high silica dyke and a rhyolite volcanic layer yields 207 pb 206 pb ages of 1783 7 ma and 1776 6 ma respectively and sims u pb dating on baddeleyites from a low silica dyke yields a 207 pb 206 pb age of 1789 5 ma they are all tholeiitic in composition mgo 0 3 6 1 wt sio 2 51 74 wt enriched in light rare earth elements la yb n 7 9 20 2 and show negative anomalies in nb ta sr and eu eu eu 0 3 0 9 they also have similar in situ hf isotopes of baddeleyite zircon ehf values of 14 5 to 1 8 and bulk rock end 6 7 to 3 0 isotopes furthermore immiscible textures are identified from the xiaoliangling group volcanics which are characterized by some silica rich melts globules in the fe rich magma these spatiotemporal affinities and geochemical similarities as well as the identified immiscible textures reveal that the low silicate dykes are conduits for the basalt andesite with significant fractionation of clinopyroxene and plagioclase while the high silica dykes are conduits for the rhyolite dacite with distinct immiscible segregation prior to eruption in addition there is a sharp change of ehf values at 1780 1730 ma and their hf t dm ages are 2750 1950 ma as these rocks originated from the subcontinental lithospheric mantle this may indicate that the subcontinental lithospheric mantle was metasomatized during this time period possibly by a paleo plume event

late paleozoic retrograded eclogites from within the northern margin of the north china craton evidence for subduction of the paleo asian ocean abstract retrograded eclogites from the central part of the northern margin of the north china craton hebei province china occur as separate tectonic lenses or boundins within garnet biotite plagioclase gneisses of the paleoproterozoic hongqiyingzi complex characterized by amphibolite facies paragneisses the petrographic features and mineralogical compositions represent three main metamorphic stages 1 the peak eclogite facies stage p 1 40 1 50 gpa t 680 730 c 2 the granulite facies stage and 3 the amphibolite facies stage p 0 67 0 81 gpa t 530 610 c formed during decompression the major and trace element and sm nd isotopic data suggest that most of the retrograded eclogite samples had protoliths of tholeiitic oceanic crust with geochemical characteristics of mid ocean ridge basalt morb or island arc tholeiite iat environment and were contaminated by crustal components during subsequent subduction zircon shrimp isotopic dating of two different textural varieties of retrograded eclogite defines a weighted mean age of 325 ma which is interpreted as the peak metamorphic age of the eclogites and reflects the occurrence of eclogite facies metamorphism related to subduction of paleo asian oceanic crust beneath the north china craton during the late paleozoic finally we show that the retrograded eclogite from hebei province is not related to the baimashi retrograded eclogite at the northern foot of the heng mountains approximately 300 km to the southwest

phase equilibria modelling and zircon age dating of pelitic granulites in zhaojiayao from the jining group of the khondalite belt north china craton the jining group occurs as the eastern segment of the khondalite belt north china craton and is dominated by a series of granulite facies rocks involving normal pelitic granulites recording peak temperatures of 850 c and ultrahigh temperature uht pelitic granulites recording peak temperatures of 950 1100 c the p t paths and ages of these two types of granulites are controversial three pelitic granulite samples in the jining group comprising two sillimanite garnet gneiss samples j1208 and j1210 and one spinel garnet gneiss sample j1303 were collected from zhaojiayao where normal pelitic granulites occur for determination of their metamorphic evolution and ages samples j1208 and j1210 are interpreted to record cooling paths from the tmax stages with p t conditions respectively of 870 890 c 7 8 kbar and 840 c 7 5 kbar constrained from the stability fields of the observed mineral assemblages and the isopleths of plagioclase garnet and biotite compositions in pseudosections sample j1303 is interpreted to record pre tmax decompression from the kyanite stability fields to the tmax stage of 950 1020 c 8 9 kbar and a post tmax cooling path revealed mainly from the stability field of the observed mineral assemblage the plagioclase zoning and the biotite composition isopleth in pseudosections the post tmax cooling stage can be divided into suprasolidus and subsolidus stages the suprasolidus cooling may not result in an equilibrium state at the solidus in a rock therefore different minerals may record different p t conditions along the cooling path the inferred maximum temperature is commonly higher than the solidus as well as different solidi being recorded for different samples from the same outcrop but experiencing different degrees of melt loss plagioclase compositions especially its zoning in plagioclase rich granulites are predicted to be useful for recording the higher temperature conditions of a granulite s thermal history the three samples studied seem to record the temperature range covering those of the normal and uht pelitic granulites in the jining group suggesting that uht conditions may be reached in normal granulites without diagnostic uht indicators la icp ms zircon u pb data provide a continuous trend of concordant 207pb 206pb ages from 1 89 to 1 79 ga for sample j1210 and from 1 94 to 1 80 ga for sample j1303 these continuous and long age spectrums are interpreted to represent a slow cooling and exhumation process corresponding to the post tmax cooling p t paths recorded by the pelitic granulites which may have followed the exhumation of deeply buried rocks in a thickened crust region resulted from a collision event at c 1 95 ga as suggested by the pre tmax decompression p t path

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

shrimp u pb zircon geochronology of the fuping complex implications for formation and assembly of the north china craton abstract the fuping complex located within the central zone of the north china craton is composed of amphibolite to granulite facies orthogneisses interleaved with minor supracrustal rocks at similar metamorphic grade the oldest components recognised are hornblende gneiss enclaves within the predominant biotite orthogneiss which have a shrimp u pb zircon age of 2708 8 ma we consider these enclaves to represent fragments of 2 7 ga continental materials incorporated in the biotite gneiss the biotite gneiss has a shrimp u pb zircon age of 2513 12 ma interpreted to be time of magmatic crystallisation of the igneous precursor based on the igneous characteristics of the zircons this indicates a major magmatic episode at 2 52 ga in the fuping complex identical to the age of felsic volcanism within the low grade wutai complex which crops out immediately to the west a gneissic granite that intrudes the biotite gneisses has a poorly defined 207pb 206pb age of 2045 64 ma this is within error of the age of 2097 46 ma obtained from a fine grained gneiss interlayered with amphibolite of the wanzi supracrustal suite wss interpreted to be volcanic in origin zircons from both these samples have strong oscillatory zoning and provide the first indication of a palaeoproterozoic magmatic event in the area again similar in age to magmatic events recently recognised in the adjacent wutai complex these data indicate a comparable history for the fuping and wutai complexes and support geochemical evidence that they had a common origin and formed part of a late archaean arc affected by later palaeoproterozoic re activation low uranium zircons without oscillatory zoning separated from a sample of biotite gneiss yield data clustered at 1817 26 ma which is interpreted to reflect a period of new zircon growth during a major metamorphic event these data support the recently proposed tectonic model that amalgamation of the north china craton occurred due to collision of the eastern and western blocks along the central zone at 1 8 ga ago

petrogenesis and tectonic implications of the 2 1 2 0 ga granitoids in fuping complex north china craton constraints from petrology geochemistry and zircon u pb hf isotopes abstract mid paleoproterozoic 2 2 2 0 ga magmatism in the trans north china orogen tnco is of great significance for the paleoproterozoic geological evolution of the entire north china craton ncc in this paper we present geochemical shrimp zircon u pb and hf isotopic data on the 2 1 2 0 ga granitoids in the fuping complex of the tnco these include the nanying granitic gneiss which yielded ages of 2075 13 ma 2079 9 ma and 2073 10 ma the gangnan granitic gneiss dated at 2081 8 ma 2082 14 ma and 2063 7 ma the baiyangling granite with ages of 2077 6 ma 2070 19 ma and 2069 12 ma and the shangzhuang granite which yielded ages of 2072 12 ma and 2070 12 ma the 2 1 2 0 ga granitic rocks in fuping complex are enriched in sio2 k2o na2o rare earth elements rees except eu high field strength elements like zr nb ga and y and depleted in cao al2o3 and sr their ga al ratios and absolute zr nb y ce contents are high and their average zr saturation temperatures are as high as 890 c all of which are consistent with the features of a type granite the ehf t values of zircon in all samples are much lower than that of the depleted mantle at the same stage while hf model tdm1 tdmc ages have ranges of 2 3 2 7 ga and 2 4 2 9 ga respectively which are much older than the age of the granitoids these zircon hf model ages are similar to those of the neoarchean ttg tonalite trondhjemite granodiorite gneisses in the fuping complex therefore based on a combination of petrology geochemistry and isotopic characteristics we infer that these four 2 1 2 0 ga granitic plutons in the fuping complex are partial melts of the neoarchean ttg gneiss generated in an extensional environment based on extensive data the 2 1 2 0 ga a type granites and the mafic dikes in the fuping complex represent a bimodal magma association considering the sedimentary rocks of the gantaohe group deposited in the same period we deduce that the 2 1 2 0 ga a type granite in the tnco fuping complex was emplaced in an intra continental rift setting in the ncc this evidence indicates that the north china craton was initially stabilized at the end of the neoarchean

p t t path and tectonic significance of pelitic migmatites from the luliang complex in xiyupi area of trans north china orogen north china craton abstract in order to reveal the metamorphic evolution of the luliang complex a combined study of petrography phase equilibria modeling and zircon u pb dating is carried out on two mesosome of pelitic migmatites from the jiehekou group in the luliang complex sample 15xyp 02 preserved the thermal peak assemblage of garnet biotite k feldspar sillimanite quartz and ilmenite without plagioclase it recorded two near isothermal decompressional indicators that rutile was moated by ilmenite and garnet was replaced by cordierite small plagioclase occurred in the rim of k feldspar and garnet four stages m1 m4 of metamorphic evolution have been identified based on the mineral assemblages and p t pseudosection it is interpreted to record pre tmax decompression from rutile stability field m1 represented by rutile relicts in matrix and biotite sillimanite quartz inclusions in garnet porphyroblasts at 8 9 kbar to the tmax stage m2 characterized by garnet rim with ilmenite and biotite k feldspar sillimanite quartz in matrix of 815 838 c the following suprasolidus post tmax cooling comprises m3 stage represented by appearance of cordierite in the assemblage of garnet biotite k feldspar sillimanite ilmenite quartz of 780 838 c 5 0 6 3 kbar and m4 stage defined by the final mineral assemblage of garnet biotite k feldspar plagioclase sillimanite cordierite ilmenite quartz of 775 c 5 0 kbar another sample 15xyp 21 preserved the thermal peak assemblage of garnet biotite plagioclase k feldspar sillimanite quartz it also records pre tmax decompression from rutile stability field at 9 0 kbar to the tmax stage of 796 821 c 6 4 7 1 kbar followed by suprasolidus post tmax cooling stage of 778 803 c 5 0 5 7 kbar the clockwise p t paths are consistent with those of orogenic belt furthermore the zircon u pb dating on mesosome and leucosome of pelitic migmatite yield metamorphic ages of 1 95 ga and 1 91 ga respectively in which the former represents the early stage of cooling after tmax nearly close to the time of pressure peak metamorphism combined with those granulites in the trans north china orogen a common long lived continent continent collision processes was proposed which may culminated at 1 95 ga and followed by a prolonged cooling process

geochronology geochemistry and nd hf isotopes of the xiaokouzi granite from the helanshan complex constraints on the paleoproterozoic evolution of the khondalite belt north china craton abstract the khondalite belt is one of the three paleoproterozoic mobile belts in the north china craton and was formed by a continental collision between the yinshan and ordos blocks at ca 1 95 ga although the metamorphism geochemistry and geochronology of the khondalite belt have been extensively studied the provenance and depositional setting of the khondalite protoliths remain controversial in this study u pb zircon ages and geochemistry of the xiaokouzi granite in the southern helanshan complex part of the khondalite belt are investigated zircon u pb dating indicates that the xiaokouzi granite was formed between 2023 14 ma and 2034 16 ma the granite shows variable sio2 64 33 74 14 wt moderate al2o3 14 75 17 23 wt and a cnk values 1 09 1 66 low cao 0 33 2 35 wt tio2 0 30 0 66 wt tfe2o3 2 58 5 76 wt mgo 0 82 2 32 wt and k2o 2 57 4 96 wt contents these features indicate that the xiaokouzi granite is a peraluminous s type granite the xiaokouzi granite has cr and ni contents of 32 7 84 5 ppm and 10 7 19 3 ppm respectively the granite is enriched in cs k pb and zr and depleted in nb ta p and ti the granite displays variable nd t values 1 7 to 3 5 with a corresponding two stage nd model age of 2 2 2 5 ga in addition the granite has high initial 176hf 177hf ratios 0 281569 0 281789 and positive hf t values 1 1 to 8 1 with a two stage hf model age of 2 2 2 6 ga suggesting a juvenile source the crystallization age of the xiaokouzi granite is synchronous with the peak in the detrital zircon age population from metasedimentary rocks in the khondalite belt in addition hf isotope values from the xiaokouzi granite are consistent with the detrital zircons from metasedimentary rocks together with other paleoproterozoic igneous rocks in the khondalite belt it is inferred that paleoproterozoic magmatic rocks in the khondalite belt may be the potential provenance for khondalite protoliths combined with previous geological data from the khondalite belt we propose that the helanshan khondalite protoliths were most likely deposited in an active continental margin near the ordos block

prolonged anatexis of paleoproterozoic metasedimentary basement first evidence from the yinchuan basin and new constraints on the evolution of the khondalite belt north china craton abstract discerning the history of burial residence at depth and exhumation of high grade metamorphic rocks from an orogen is essential to understanding crustal differentiation and orogenesis such high grade rocks are inferred to exist beneath the yinchuan basin which is overlain by a thick covering of younger sediments and is located at the inferred southwest boundary of the paleoproterozoic khondalite belt in the northwestern north china craton the metamorphic basement sampled from a recently completed deep borehole in the yinchuan basin is migmatitic and contains an assemblage of garnet biotite sillimanite plagioclase quartz minor k feldspar and local occurrences of muscovite phase equilibrium modelling in the na2o cao k2o feo mgo al2o3 sio2 h2o tio2 o system constrains the peak p t conditions of anatexis to 6 10 kbar at 760 810 c followed by final crystallization at 4 5 5 5 kbar and 690 710 c ti in zircon thermometry for the narrow metamorphic zircon rims provides a temperature range of 687 753 c demonstrating formation during retrogression to the solidus nanosims u pb analyses on the metamorphic overgrowths of zircon grains yields an upper intercept age of 1895 36 ma chronological and chemical analyses of monazite indicate irregular bright gray domains with relatively high th and low y and hree contents developed during prograde metamorphism 1962 8 ma conversely dark domains with low th and high y and hree overgrew during retrograde cooling 1892 14 ma that was synchronous with the development of metamorphic zircon rims la icp ms u pb analyses of detrital zircons reveal that the metamorphic basement beneath the yinchuan basin has a sedimentary protolith of paleoproterozoic age the results directly confirm the existence of paleoproterozoic basement beneath the yinchuan basin and the well constrained p t t path supports the involvement of the basement as part of the western khondalite belt in burial and exhumation processes during the 1 96 1 89 ga period during which anatexis occurred for 70 ma

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

geochemistry and detrital zircon u pb and hf isotopes of the paragneiss suite from the quanji massif se tarim craton implications for paleoproterozoic tectonics in nw china abstract the delingha paragneiss suite in the quanji massif southeastern tarim craton is composed of mica schist paragneiss leptynite and quartzite similar to the khondalite suites described from elsewhere in the world the mica schist is rich in al2o3 up to 26 wt and contains graphite and diagnostic minerals including sillimanite and garnet with metamorphism under amphibolite facies to locally granulite facies conditions as manifested by association with amphibolite and granulite the detrital zircon u pb ages and geochemical data indicate that the protolith materials of the delingha paragneiss suite were mainly sourced from 2 20 to 2 45 ga granites felsic volcanic rocks and ttg and were deposited at 2 17 1 92 ga the detrital zircon hf and whole rock nd isotopes document important crustal growth at 2 5 2 7 ga the detrital zircon age spectra the whole rock nd and zircon hf model ages the low maturity of the protolith and short distance transportation suggest that the detritus were derived from the underlying delingha complex and the lower dakendaban sub group the timing of magmatic activities in the source region the depositional age and metamorphic histories of the delingha paragneiss suite are all comparable to those recorded in the khondalite belt along northern margin of the ordos block in the north china craton our study shows that the 2 2 2 45 ga magmatic rocks were generated in arc or active continental margin settings suggesting a prolonged subduction and accretion history prior to final amalgamation 2 5 1 8 ga to form the unified north china craton and the assembly of the tarim craton in nw china

modvolc near real time thermal monitoring of global volcanism modvolc is a non interactive algorithm developed at the hawaii institute of geophysics and planetology higp that uses low spatial resolution 1 km pixel size infrared satellite data acquired by the moderate resolution imaging spectroradiometer modis to map the global distribution of volcanic thermal anomalies in near real time modvolc scans the level 1b modis data stream on a pixel by pixel basis for evidence of pixel and sub pixel sized high temperature radiators once a hot spot has been identified its details location emitted spectral radiance time satellite observation geometry are written to ascii text files and transferred via ftp to higp from where the results are disseminated via the internet http modis higp hawaii edu in this paper we review the underlying principles upon which the algorithm is based before presenting some of the results and data that have been obtained since its inception we show how modvolc reliably detects thermal anomalies at a large number of persistently and sporadically active volcanoes that encompass the full range of common eruptive styles including erebus antarctica colima mexico karymsky kamchatka popocatepetl mexico etna italy and nyiragongo democratic republic of congo amongst others we also present a few cautionary notes regarding the limitations of the algorithm and interpretation of the data it provides

thermobarometry of garnet clinopyroxene hornblende granulites from the kapuskasing structural zone amphibole mixing properties and standard state properties for the end members tremolite tschermakite pargasite ferrotremolite ferrotschermakite and ferropargasite have been refined through analysis of relevant phase equilibrium experiments coexisting cummingtonite hornblende pairs and natural mineral parageneses when merged with the mineral properties given by r g berman these amphibole properties allow the calculation of numerous equilibria suitable for thermobarometry in a wide range of bulk compositions at amphibolite to granulite metamorphic grades the method was applied to texturally equilibrated garnet pyroxene hornblende gneisses and compared both to results based on anhydrous assemblages and to those for garnet biotite gneisses from the kapuskasing structural zone thermometer resetting is apparent only in garnet biotite gneisses whereas touching garnet pyroxene pairs in mafic gneiss show little evidence of retrograde fe mg exchange computed metamorphic temperatures garnet clinopyrox

zircon u pb ages and lu hf isotope compositions from clastic rocks in the hutuo group further constraints on paleoproterozoic tectonic evolution of the trans north china orogen abstract the hutuo group as one of the classic examples of paleoproterozoic strata plays an important role in establishing evolutionary processes in the trans north china craton in this contribution we present petrologic detrital zircon u pb ages and lu hf isotopes from three subgroups of the hutuo group sandstones in the doucun and dongye subgroups are dominated by q monocrystalline and polycrystalline quartz and f k feldspar and plagioclase with minor lithic fragments suggesting that the detrital components were mainly derived from both the continental block and recycled orogen in contrast clastic components in the guojiazhai subgroup are mainly q and lithic fragments indicating they were derived predominantly from the recycled orogen the ages of detrital zircons from sandstones in the doucun and dongye subgroups are mainly concentrated at ca 2 5 ga and 2 2 2 1 ga with minor 2 7 ga zircons also present which indicates they were dominantly sourced from 2 5 ga wutai fuping and zanhuang complexes and paleoproterozoic intrusives the guojiazhai subgroup displays a different zircon age population of ca 2 4 ga 2 2 2 1 ga and 2 0 1 9 ga which indicates likely derivation from paleoproterozoic intrusives in the wutai luliang and hengshan areas based on the observation that sandstone clastic components in the doucun and dongye subgroups are dominantly quartz feldspar and sedimentary lithic fragments but not volcanic lithics we propose that they were deposited in a rift related setting zircons from the lower sequence of the hutuo group yielded a young population of 2140 ma considering the volcanic rocks of 2140 14 ma at the base of the group and 2 2 2 0 ga magmatism along the tnco we propose that doucun and dongye subgroups formed at 2 2 2 0 ga the youngest ca 1 9 ga zircons in the guojiazhai subgroup indicate this group was deposited during closure of the rift at 1 9 1 8 ga the two stage model ages of the detrital zircons mainly range from 2 6 to 2 9 ga with a minor 2 5 ga contribution therefore we infer that 2 6 2 9 ga represents a period of intensive crustal growth in the trans north china orogen but that some degree of crustal growth continued to 2 5 ga

determining precambrian crustal evolution in china a case study from wutaishan shanxi province demonstrating the application of precise shrimp u pb geochronology

geological evolution of venus rises plains plumes and plateaus crustal plateaus and volcanic rises major physiographic features on venus both formed over mantle plumes crustal plateaus were produced by large degrees of plume melting beneath thin lithosphere the oldest tectonic features in crustal plateaus are ribbon like troughs indicating early uplift and tensile stretching their shallow depths suggest that surface temperature there was higher in the past widespread volcanic plains derived from the broad upwellings of internally heated mantle convection were continually erupted during the time of crustal plateau formation discrete volcanic rises younger than crustal plateaus formed over a thicker lithosphere with less plume partial melting the presence of only one transitional form indicates that the lithosphere thickened rapidly thermal and magmatic models show that the formation of these major features can be tied to an expected change in mantle convective style about 1 billion years ago

garnet orthopyroxene plagioclase quartz barometry refinement and application to the english river subprovince and the minnesota river valley recent experimental theoretical and thermodynamic studies permit better calibration of two reactions for geobarometry grossular pyrope quartz anorthite enstatite grossular almandine quartz anorthite ferrosilite if both reactions are applied using the same thermodynamic data and activity models they should yield the same pressure for a given garnet pyroxene plagioclase quartz assemblage application to a variety of high grade terrains generally yielded excellent results however poor results have been obtained for high fe rocks which can be traced to errors in activity models for garnet and or pyroxene either a two site ideal mixing model for orthopyroxene cf wood and banno 1973 underestimates enstatite activity for high fe orthopyroxenes or the ganguly and saxena 1984 model overestimates pyrope activity in low mg garnets

in situ zircon u pb dating and whole rock geochemistry of metasedimentary rocks from south liaohe group jiao liao ji orogenic belt constraints on the depositional and metamorphic ages and implications for tectonic setting abstract the liaohe group is an important paleoproterozoic lithostratigraphic unit of the jiao liao ji orogenic belt and traditionally subdivided into the north and south liaohe groups however their tectonic setting and evolution are still a matter of debate the precise depositional and metamorphic data of the studied metasedimentary rocks from the south liaohe group provide important information on the controversial discussion of the tectonic setting and evolution based on cathodoluminescence cl imaging and connecting la icp ms u pb geochronology zircon grains separated from metasedimentary rocks of different formations of the south liaohe group were subdivided into detrital and metamorphic zircons or zircon domains igneous zircon cores of detrital zircons of the li eryu gaojiayu dashiqiao and gaixian formations yield u pb age peaks at 2130 ma 2520 ma 2160 ma 2500 ma and 2040 ma indicating that their sediments were transported from the liaoji granitoids the archean basement rocks of the adjacent complex in addition deposition age of the sedimentary precursors was investigated which must have taken place at some time after 2 05 ga 2 07 ga 2 04 ga and 1 92 ga respectively these new geochronological data can be well explained by 1 a continent arc collision model which suggests that the south liaohe group formed an intervening island arc and foreland basin sandwiched between the longgang and nangrim complexes and 2 a northward subduction of the nangrim complex source rocks of the south liaohe group these source rocks were successively deposited along the margin of the two complexes

proterozoic polymetamorphism in the quanji block northwestern china evidence from microtextures garnet compositions and monazite chime ages abstract the quanji block situated close to the triple junction of three major precambrian terranes in china i e the north china craton the yangtze block and the tarim block is composed of precambrian metamorphic crystalline basement and an unmetamorphosed mesozoic paleozoic sedimentary cover it has been interpreted as a remnant continental fragment microtextural relationships garnet trace element compositions and monazite chime ages in paragneisses schists and granitic leucosomes show two episodes of regional metamorphism in the quanji block basement the first regional metamorphism and accompaning anatexis took place at 1 93 ga the second regional metamorphism occurred between 1 75 and 1 71 ga mineral compositions of the first metamorphism including those of monazite were significantly disturbed by the second event these two regional metamorphic episodes were most likely linked to assembly and breakup of the supercontinent columbia respectively

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

structural evolution and 40ar 39ar dating of the zanhuang metamorphic domain in the north china craton constraints on paleoproterozoic tectonothermal overprinting abstract the zanhuang domain in the hinterland of the north china craton consists of archaean paleoproterozoic mesoproterozoic and palaeozoic rocks and was previously considered a mesozoic metamorphic core complex our reappraisal of regional structural history and mineral 40 ar 39 ar geochronology shows that the domain was subjected to a number of deformation events and had a heterogeneous uplift cooling history during the paleoproterozoic four primary deformation events have been recognized in the domain the first event reflects the earliest deformation in the region however only closed and rootless folds are preserved d2 was dominated by wnw ese shortening and top to ese thrusting in a collisional environment d3 was a divergent extensional and ductile shearing event driven by the post collisional extensional collapse and exhumation of the thickened crust in the domain d4 was characterized by localized ductile shearing with the development of three nne trending ductile shear zones the 40 ar 39 ar plateau ages derived from the thermochronology analyses of the biotite concentrates from the metamorphic rocks are interpreted as cooling ages through biotite 40 ar 39 ar closure temperature 300 c and this allows us to constrain the timing of deformation events in conjunction with the evidence from structural analyses and previous geochronological data we conclude that 1870 and 1870 1826 ma define the timing of d1 and d2 events respectively while 1826 1793 ma represents the age of d3 the last event d4 occurred at 1689 1633 ma as constrained by 40 ar 39 ar plateau ages of biotite concentrates from the mylonites within the ductile shear zones these data together with k feldspar 40 ar 39 ar geochronology allows us to depict the cooling history of the region during the paleoproterozoic and mesoproterozoic it appears that the uplift cooling rate varies temporally and spatially in the region

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

la icp ms u pb zircon ages of the liaohe group in the eastern block of the north china craton constraints on the evolution of the jiao liao ji belt abstract as a major lithostratigraphic unit of the palaeoproterozoic jiao liao ji belt in the eastern block of the north china craton the liaohe group consists of an assemblage that is transitional from a lower arkose and volcanic rich sequence langzishan li eryu and gaojiayu formations through a middle carbonate rich sequence dashiqiao formation to an upper argillaceous sequence gaixian formation tectonically associated with the liaohe group are large volumes of granitoid rocks named the liaoji granite whose emplacement age has been dated at about 2 1 2 2 ga regionally the liaohe group and the associated liaoji granite extend along a nee trending belt that is flanked by 2 45 2 55 ga basement gneisses u pb zircon data and cathodoluminescence cl imaging are used to constrain the maximum depositional and metamorphic ages of the liaohe group which are critical in understanding the tectonic setting and history of the jiao liao ji belt cathodoluminescence images reveal that most detrital zircon grains from the liaohe group are characterized by concentric oscillatory zoning with comparatively low luminescence and high th u ratios suggesting magmatic origin but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low th u ratio indicating metamorphic origin results of this study show that the detrital zircon grains of the langzishan formation the lowest sequence of the liaohe group have concordant u pb ages ranging from 2 05 to 2 24 ga suggesting that the liaohe group was deposited at some time after 2 05 ga although most overgrowth or recrystallization rims are too narrow to be analyzed some rims yield concordant or upper intercept ages around 1 93 ga interpreted as the peak metamorphic age of the liaohe group detrital zircon grains from the dashiqiao formation in the middle sequence of the liaohe group have concordant u pb ages ranging from 2 25 to 2 53 ga some of which are similar to those of the basement gneisses in the area this study indicates that the liaohe group was deposited after the emplacement of the liaoji granite and the latter may be a major component of the provenance for the langzishan formation in contrast the protoliths of the middle sequence of the liaohe group were most probably derived from the basement gneisses these new zircon ages for the liaohe group and recent data for the liaoji granite combined with lithological structural and metamorphic considerations support a rifting model for the evolution of the jiao liao ji belt

2090 2070 ma a type granitoids in zanhuang complex further evidence on a paleoproterozoic rift related tectonic regime in the trans north china orogen abstract the xuting pluton located at the north section of the zanhuang complex contains potassic and sodic granite in both of which shallow level emplacement is shown by graphic texture feldspar and quartz intergrowth two potassic granite and one sodic granite samples yielded zircon 207 pb 206 pb ages of 2066 17 ma 2092 14 ma and 2071 14 ma respectively suggesting that the xuting pluton emplaced between 2070 ma and 2090 ma which is coeval with the paleoproterozoic gantaohe group dominated by mafic volcanic and sedimentary rocks the potassic granite is enriched in sio 2 total feo rees except eu zr nb ga and y and depleted in mgo cao al 2 o 3 sr v cr and ni with high tfeo mgo ratios consistent with the features of a type granite except for the high mgo and low k 2 o contents the sodic granite also presents most of the features of a type granites the zircon saturation temperatures from the potassic and sodic granites range from 855 to 998 c and 853 to 933 c respectively indicating that they are from the high temperature magma the potassic granites have the e hf t ranging from 5 9 to 1 33 and hf model ages of 2 5 2 8 ga which are identical with the ages of neoarchean ttg gneisses in the zanhuang complex we propose that the potassic granite in the xuting pluton derived from the partial melting of neoarchean ttg gneisses the sodic granites also present negative e hf t values from 4 81 to 0 76 and hf model ages of 2 5 2 8 ga suggesting that they come from the partial melting of the neoarchean crust however with relative enrichment in mgo and total feo and lower k 2 o and rb the sodic granite was derived from a mafic source in the lower crust the likely heat source was high heatflow associated with mantle upwelling the a type xuting pluton and mafic volcanic rocks in the gantaohe group constitute a bimodal lithologic association from a paleoproterozoic continental rift environment 2 2 2 0 ga magmas are widely distributed along the trans north china orogen tnco and also present a bimodal character we propose that 2 2 2 0 ga bimodal magmas throughout the tnco were likely formed in a paleoproterozoic rifting setting considering the widespread 2 2 2 0 ga magmatic rocks in the north china craton ncc we infer that the magmatism likely occurs in tensional environment after the initial amalgamation of the ncc in the late archean

petrogenesis and thermal overprint of s type granites in helanshan region north china craton constraints on the 1 90 ga khondalites decompression melting and 1 32 ga tectono thermal event abstract widespread paleoproterozoic s type granites and khondalites high grade sillimanite garnet gneisses are exposed in the khondalite belt of the north china craton ncc porphyritic biotite granites in the helanshan region from the western khondalite belt exhibit a gradual contact relationship with the neighboring khondalites in order to constrain the petrogenesis of these granites and their genetic relationship with the khondalites detailed geochronological data as well as geochemical and whole rock sm nd and zircon lu hf isotope compositions of these granites are reported la icp ms zircon u pb dating on magmatic zircon cores yields an emplacement age of 1902 22 ma whereas metamorphic rims define a metamorphic age of 1356 57 ma the unpolished surfaces of zircon crystals selected based on the presence of rims visible in cathodoluminescence were further analyzed by sims depth profiling which gave a more precise metamorphic age of 1317 18 ma the helanshan granites display typical s type geochemical characteristics e g high a cnk 1 16 1 29 and k2o 5 09 5 86 wt contents but low feot mgo 2 39 4 88 and p2o5 0 15 0 23 wt contents similar trace and rare earth element patterns and consistent zircon hf model ages 2366 2483 ma and whole rock nd model ages 2407 2499 ma between the porphyritic biotite granites and the khondalites suggest that they were derived from partial melting of khondalites the geochemical character of the porphyritic biotite granites including significant negative eu anomalies high rb ba and rb sr ratios and variable hree contents and la yb n ratios suggest that they are probably related to the post peak decompression stage that was characterized by biotite breakdown and the progressive replacement of garnet with the presence of k feldspar and plagioclase in the residues homogeneous zircon ehf t values mostly from 0 5 to 1 7 combined with low bulk rock fe2o3t content and cao na2o ratios preclude the contribution from mafic magma following the continental collision the emplacement of the porphyritic biotite granites at ca 1 90 ga provides the latest limit on the timing of post peak decompression metamorphism of the khondalites and their formation supports a post collisional mantle upwelling model to account for the 1 92 1 90 ga regional metamorphic magmatic events on the other hand the metamorphic zircon rims indicate that s type granites were overprinted by a 1 32 ga tectono thermal event which was probably related to the breakup of the columbia supercontinent

plume formation in the d double prime layer and the roughness of the core mantle boundary numerical simulations of the formation of thermal plumes in the d layer at the base of the earth s mantle show that plumes are initiated by coalescence of small scale convective instabilities within the low viscosity region immediately above the core mantle boundary cmb these instabilities support topographic roughness on the cmb having horizontal scales of 20 50 km and provide a source for scattered p waves seen as precursors to the phases pkikp and pkkp the calculated structure of fully developed plumes emerging from d consists of 5 50 cm yr 1 flow confined to 50 100 km thick vertical conduits with strongly temperature dependent viscosity plumes exhibit time dependent behaviour including upward propagating solitary conduit waves which may contribute to episodicity in hotspot volcanism

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

age and evolution of a late archean to paleoproterozoic upper to lower crustal section in the wutaishan hengshan fuping terrain of northern china abstract the taihangshan wutaishan area forms part of the central north china craton and consists of three main components the hengshan and fuping complexes containing predominantly ductilely deformed late archean to paleoproterozoic high grade granitoid orthogneisses intruded by mafic dykes of gabbroic composition and the low grade late archean wutai greenstone belt developed between the high grade terrains and consisting of bimodal volcanic rocks and metasediments associated with coeval granitoids zircon dating shows that both the hengshan and fuping complexes were intruded by major granitoid bodies between 2 52 and 2 48 ga with rare occurrences of 2 7 ga gneisses wutai granitoids adjacent to the fuping complex also contain 2 7 ga xenocrysts all possibly reflecting the same older basement rare granitic gneisses in the hengshan have emplacement ages of 2 35 ga and show the same structural features as the older rocks indicating that the main deformation occurred after 2 3 ga deposition of supracrustal rocks and emplacement of mafic dykes occurred in the paleoproterozoic together with intrusion of granitic bodies at 2 1 2 0 ga and all underwent regional metamorphism at 1 88 1 85 ga we interpret the hengshan and fuping granitoid gneisses as the lower plutonic part of a late archean to early paleoproterozoic japan type magmatic arc with the upper volcanic part represented by the wutai complex components of this arc may have evolved at a continental margin as indicated by the 2 7 ga zircons virtually all magmatic events are recorded in all three complexes however the 1 85 ga metamorphic event is only recorded in the higher grade portions of the wutai since low grade and presumably high crustal level precluded metamorphic zircon growth shear zones in the hengshan are interpreted as major lower crustal discontinuities post dating the peak of high pressure granulite metamorphism we suggest that they formed during orogenic collapse and uplift of the hengshan complex in the late paleoproterozoic 1800 ma

application of the two feldspar geothermometer to ultrahigh temperature uht rocks in the khondalite belt north china craton and its implications the paleoproterozoic khondalite belt in the north china craton preserves evidence for ultrahigh temperature uht crustal metamorphism associated with the collision of the yinshan and ordos blocks here we apply two feldspar geothermometry to uht granulites from two localities newly reported in this study tuguishan and xuwujia and another two localities from previous studies dajing tuguiwula and dongpo in the khondalite belt the presence of abundant perthite mesoperthite in these rocks reflects post peak slow cooling the minimum estimated peak metamorphic temperatures are 832 998 819 952 844 1037 and 966 1019 c computed at 8 kbar for the dajing tuguiwula dongpo tuguishan and xuwujia areas respectively these results confirm the previous report of extreme metamorphism at dajing tuguiwula and dongpo and reveal similar conditions in the new localities reported here suggesting that uht metamorphism is widespread in the khondalite belt of the north china craton our study demonstrates that uht metamorphism can be recognized using the two feldspar geothermometry in rocks that do not possess other key uht assemblages

thermal evolution of two textural types of mafic granulites in the north china craton evidence for both mantle plume and collisional tectonics mafic granulites from the north china craton can be divided into two textural types referred to as a and b types a type mafic granulites display garnet quartz symplectic coronas and outcrop in the eastern and western zones of the craton whereas b type mafic granulites exhibit orthopyroxene plagioclase clinopyroxene symplectites or coronas and are mainly exposed in the central zone of the craton most a type mafic granulites preserve the prograde m 1 peak m 2 and post peak near isobaric cooling m 3 assemblages which are represented respectively by inclusions of hornblende plagioclase quartz a peak mineralogy of orthopyroxene clinopyroxene plagio clase quartz garnet and overprinted by garnet quartz symplectic coronas these mineral assem blages and their p t pressure temperature estimates define anticlockwise p t evolutionary paths the b type mafic granulites preserve the peak m 1 post peak near isothermal decompression m 2 and cooling m 3 assemblages which are represented by the peak assemblage of orthopyroxene clinopyroxene plagioclase quartz garnet hornblende post peak orthopyroxene plagioclase clinopyroxene symplectites or coronas and later hornblende plagioclase magnetite symplectites respectively these mineral assemblages and their p t estimates define clockwise p t paths the anticlockwise p t paths of the a type mafic granulites in the eastern and western zones of the north china craton are consistent with a model of underplating and intrusion of mantle derived magmas in combination with lithological structural and geochronological data the eastern and west ern zones of the north china craton are considered to represent two continental blocks that devel oped through the interaction of mantle plumes with the lithosphere from the palaeoarchaean to the neoarchaean era the b type mafic granulites and associated rocks in the central zone represent a magmatic arc that was metamorphosed and deformed during amalgamation of the eastern and west ern continental blocks in the late palaeoproterozoic era the mineral reaction relations and clockwise p t paths of the b type mafic granulites from the central zone record the tectonothermal history of the collision that resulted in the final assembly of the north china craton at c 1800 ma

u pb dating and hf isotope study of detrital zircons from the zhifu group jiaobei terrane north china craton provenance and implications for precambrian crustal growth and recycling abstract the zhifu group exposed in the northeastern jiaobei terrane is subdivided from base to top into the laoyeshan bingying and dongkou formations and comprises mainly quartzites and muscovite and tourmaline bearing quartz schists in order to define its provenance and depositional age and to constrain the crustal growth and recycling of the source regions we have conducted la icp ms u pb dating and in situ hf isotopic study of detrital zircons from three quartz schists samples collected from the zhifu group most of the analyzed zircon grains have oscillatory zoning and th u ratios 0 4 suggesting igneous origins 270 detrital zircons u pb analyses yield u pb ages of 1709 3679 ma that cluster into three major age populations of 1 7 1 9 ga with a peak at 1844 ma 1 9 2 0 ga with a peak at 1936 ma and 2 4 2 55 ga with a peak at 2465 ma and two minor age populations of 2 2 2 35 and 2 6 2 7 ga the peaking age of 1844 ma for the youngest age population indicates that the zhifu group must be deposited after 1844 ma detrital zircons with ages of 1 7 2 35 ga can be linked to pre and post tectonic polyphase magmatic events along the jljb and most of the zircons have negative hf t values from 1 76 to 18 02 and two stage hf model ages t dm2 concentrating at 2 7 3 0 ga indicating that source rocks of these zircons were derived from recycling of ancient crusts detrital zircons with ages of 2 4 2 9 ga may have been sourced from the archean granitoid mainly ttg gneisses in the jiaobei terrane and these zircons have hf t values from 6 4 to 7 53 and t dm2 of 2 6 3 4 ga peak at 2 7 3 0 ga suggesting that source rocks of these zircons were mainly derived from juvenile crusts associated with a major crustal growth at 2 7 3 0 ga and a limited amount of ancient crustal component the two detrital zircons with ages of 3631 and 3679 ma have negative hf t values of 4 42 and 1 51 and t dm2 of 4137 and 4000 ma respectively implying the recycling of ancient continental crust 3 6 ga and crustal growth prior to 4 1 ga in the ncc

petrogenesis and tectonic implications of the iron rich tholeiitic basalts in the hutuo group of the wutai mountains central trans north china orogen abstract the hutuo group located in the wutai mountains area is characteristic of paleoproterozoic strata in the north china craton and plays an important role in establishing evolutionary processes in the trans north china orogen we present petrological observations along with geochemical and nd isotopic data for basalts in the qingshicun and hebiancun formations of the hutuo group these basalts are enriched in tfeo 11 97 18 01 wt consistent with occurrences of iron rich basalt world wide they also display relatively high mgo 4 95 12 25 wt ni 79 121 ppm and cr 37 101 ppm and low in sio 2 41 37 51 95 wt therefore the iron rich character of the hutuo group basalts originated with their parental magma rather than via shallow crustal fractionation at low oxygen fugacity as inferred for many high iron basalts the hutuo group basalts exhibit weak to moderate differentiation of light ree over heavy ree la lu cn 2 61 6 79 with minor or slight eu anomalies eu eu 0 77 1 41 and also show the nb and ti troughs without obvious zr and hf anomalies the nd t values of the basalts range from 1 23 to 0 81 with t dm of 2489 2664 ma the basalts most plausibly originated from the fertile subcontinental lithosphere mantle and in the case of the qingshicun formation basalts also underwent the crustal contamination basalts in the hutuo group also have the high zr hf ratios and present high ti v values of 24 55 and zr y ratios ranging from 4 6 to 13 6 suggesting that they were emplaced in a within plate setting considering the sedimentary associations and detrital fragments in the hutuo and gantaohe groups and bimodal magmatism along the trans north china orogen we propose that 2 2 2 0 ga geological events within the orogen were rift related but did not result from subduction or island arc processes

precambrian geology of china preface abstract the north china south china and tarim cratons compose the tectonic framework of china in the last decade extensive structural metamorphic geochemical geochronological and geophysical investigations have been carried out on these cratonic blocks producing an abundant amount of new data and competing interpretations which have resulted in refinement of and in some cases significant reinterpretations of the precambrian crustal formation and evolution of china this forms a justification for organizing this special issue in which we invited representative experts working in the north china south china and tarim cratons to present overviews or detailed studies on the formation and tectonic evolution of major precambrian blocks in china twenty four contributions collected in this special issue provide current knowledge of the components and tectonic evolution of major precambrian blocks in china and discuss some key issues based on new data and interpretations which will provide important insights into understanding the precambrian geology of china

zircon ages and geochemistry of late neoarchean syenogranites in the north china craton a review abstract at the end of the neoarchean continental evolution voluminous syenogranites were emplaced in the north china craton together with other magmatic rocks trondhjemite tonalite granodiorite ttg monzogranite diorite gabbro syenogranites are widely distributed in anshan benxi qinhuangdao and western shandong and also occur in southern jilin northern liaoning northwestern hebei and central henan based on geological relationships degree of metamorphism deformation and magmatic zircon ages two phases of syenogranite magmatism are recognized rocks produced during the first phase show a gneissic texture and were formed between 2 53 and 2 52 ga and locally comprise abundant ttg rocks of the second phase cut late neoarchean ttg and supracrustal rocks display a massive structure and mainly formed between 2 52 and 2 50 ga all syenogranites share the same features in major element compositions being high in sio2 and low in cao total feo mgo tio2 and p2o5 however they are different in trace and ree compositions and can be subdivided into three types 1 type 1 shows a large variation in total ree contents low la yb n ratios strong negative eu eu anomalies and ba depletion 2 type 2 is similar to type 1 but has higher la yb n ratios 3 type 3 shows a large variation in total ree and la yb n ratios and significantly do not show strongly negative eu eu anomalies and ba depletion whole rock sm nd isotopic compositions show large variations in nd t values and tdm nd modal ages ranging from 9 49 to 4 72 and 3 70 to 3 25 ga type 1 0 55 1 03 and 2 77 2 71 ga type 2 and 2 35 to 1 23 and 2 93 2 66 ga type 3 respectively hf isotopic compositions of zircons from three samples have hf t values and tdm1 hf ages of 0 7 7 2 and 2 84 2 56 ga type 1 2 6 7 4 and 2 74 2 56 ga type 2 and 2 1 6 3 and 2 76 2 60 ga type 3 it is concluded that syenogranites were generated by melting of continental crust with different mean crustal residence ages and most of them were emplaced during the second phase 2 52 2 50 ga in an extensional tectonic regime the formation of these voluminous syenogranites marks a tectono magmatic event resulting in stabilization of the north china craton at the end of the neoarchean

two types of precambrian high grade metamorphism inner mongolia china archaean and proterozoic granulite facies complexes of inner mongolia differ in lithological association tectonic style mineral assemblage and metamorphic p t path a nearly isobaric cooling path for archaean high grade metamorphic rocks is suggested by reaction textures and geothermobarometry early proterozoic metamorphic rocks show nearly isothermal decompression archaean metamorphism may have been caused by magmatic accretion whereas early proterozoic metamorphism suggests a major continental thickening event followed by exhumation

u pb and hf isotopic study of zircons of the helanshan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the helanshan complex is located at the westernmost segment of the khondalite belt a continent continent collisional belt along which the yinshan block in the north collided with the ordos block in the south to form the western block of the north china craton the complex consists of s type granites and high grade pelitic granulite gneiss felsic paragneiss quartzite calc silicate rock and marble together called the khondalite series rocks la q icp ms u pb geochronology and la mc icp ms lu hf isotopic data of zircons combined with cathodoluminescence cl imaging enable the resolution of magmatic and metamorphic events that can be directed towards understanding the formation and evolution of the khondalite belt in the western block of the north china craton cl images reveal the coexistence of magmatic type detrital zircons and metamorphic zircons in most of the khondalite series rocks of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating magmatic type detrital zircon cores la q icp ms u pb analyses on magmatic type detrital zircons reveal two distinct age populations with one in the archaean 2 85 2 53 ga and the other in the palaeoproterozoic 2 2 2 0 ga suggesting that the sedimentary protoliths of the khondalite series rocks in the helanshan complex must have been deposited at some time after 2 0 ga the hf analyses show that the archaean detrital zircons possess negative ehf t values from 7 64 to 0 15 with depleted mantle model ages ranging from 3 34 to 3 10 ga this implies the existence of a paleo mesoarchaean 3 34 3 10 ga crust in the western block which underwent a recycling event in the period 2 85 2 53 ga nearly all palaeoproterozoic 2 2 2 0 ga detrital zircons possess positive ehf t values 0 86 9 38 with depleted mantle model ages of 2 45 2 15 ga suggesting a significant crustal growth event in the western block in the palaeoproterozoic metamorphic zircons yield two groups of age with one at 1 95 ga and the other at 1 87 ga of which the former is considered as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the latter is consistent with the age of 1 86 ga from two s type granites which are considered to have formed by the partial melting of pelitic granulites gneisses at the stage of the exhumation of the helanshan complex

pressure temperature time paths and a tectonic model for the evolution of granulites petrologic studies and application of well calibrated mineralogic thermometers and barometers reveal several important features common to many granulite terrains 1 peak metamorphic pressure and temperature conditions cluster around values of 7 5 pm 1 kbar and 800 pm 50 c implying average geothermal gradients of 30 35 c km 2 in comparison with upper amphibolite facies rocks especially in paired amphibolite granulite terrains it is evident that granulites are distinguished from amphibolites by the former s higher metamorphic temperatures but not higher pressure 3 initial cooling of granulite terrains from peak conditions is nearly isobaric for garnet closure temperatures of 600 pm 50 c the dp dt retrograde paths inferred from compositionally zoned garnet rims are 2 8 b c in most granulites 4 primary coarse sillimanite is found in most granulites and retrograde kyanite is known in a few these data suggest that granulites form as a result of anomalous thermal gradients

p t t paths and tectonic history of an early precambrian granulite facies terrane jining district south east inner mongolia china abstract the widespread khondalite series of south east inner mongolia consists largely of biotite sillimanite garnet gneiss and quartzo feldspathic gneiss with some marble and mafic granulite layers it has experienced two metamorphic events at c 2500 and 1900 2000 ma a pre peak stage of the first metamorphism at t 600 700 c and p 6 7 kbar is recognized by the relict amphibolite facies assemblage ky grt bt pl qtz and protected inclusions of biotite hornblende sodic plagioclase and quartz in garnet or orthopyroxene the peak stage with t c 800 50 c and p 8 10 kbar is characterized by the widespread granulite facies assemblages sil grt bt kfs pl qtz in gneiss and opx cpx pl hbl grt in granulite the p t t path suggests that the supracrustal sequence was buried in the lower crust by tectonic thickening during d1 d2 the beginning of the second metamorphism is characterized by further temperature rise to 700 c or more at lower pressure this stage is manifested by the appearance of cordierite after garnet fibrolite sil2 after biotite in gneiss and transformation of hbl1 into opx2 and cpx2 in granulite coronas of symplectitic opx2 pl2 surrounding grt1 and cpx1 in mafic granulite are interpreted as products of near isothermal decompression the p t t path may be related tectonically to waning extension of the crust by the end of the early proterozoic

on the formation of granulites the tectonic settings for the formation and evolution of regional granulite terranes and the lowermost continental crust can be deduced from pressure temperature time p t time paths and constrained by petrological and geophysical considerations p t conditions deduced for regional granulites require transient average geothermal gradients of greater than 35 c km 1 implying minimum heat flow in excess of 100 mwm 2 such high heat flow is probably caused by magmatic heating tectonic settings wherein such conditions are found include convergent plate margins continental rifts hot spots and at the margins of large deep seated batholiths however particular p t time paths do not allow specific tectonic settings to be distinguished at this time under different conditions both clockwise cw pmax attained before tmax and anticlockwise acw pmax attained slightly after tmax paths are possible in the same tectonic setting both cw and acw end member paths can yield nearly isobaric cooling ibc paths such cooling paths are clearly not an artefact of thermobarometry but can be constrained by solid solid and devolatilization equilibria and geophysical modelling in terms of understanding the evolution of the deep crust a potentially significant group of regional granulite terranes are those that show evidence for acw ibc paths such paths are the likely result of i episodic igneous activity resulting in intrusions within all levels of the crust ii thickening of the crust by magmatic underplating iii slow uplift as a result of the formation of a deep garnet rich crustal root and iv excavation resulting from a later tectonic event unrelated to that resulting in the formation of the granulites the later event might be triggered by the delamination of the garnet rich lowermost crust

epma u th pb monazite and shrimp u pb zircon geochronology of high pressure pelitic granulites in the jiaobei massif of the north china craton the jiaobei massif constitutes the southern segment of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton and contains high pressure hp mafic and pelitic granulites the hp pelitic granulites contain four distinct mineral assemblages garnet kyanite biotite muscovite rutile m1 garnet kyanite ternary feldspar biotite muscovite rutile m2 garnet sillimanite biotite perthite anti perthite m3 and biotite muscovite sillimanite plagioclase m4 of which m2 is a typical hp pelitic assemblage the origin of these hp granulites is important for understanding the tectonic evolution of the jiao liao ji belt but the timing of the hp event still remains unknown this study applied the epma u th pb monazite and shrimp u pb zircon dating techniques to determine the metamorphic ages of the hp pelitic granulites in the jiaobei massif cl images and th u ratios show that all monazite and zircon grains in the analyzed samples are of metamorphic origin eighty two epma analyses on 16 monazite grains from two samples yielded three age groups at 1895 to 1882 ma 1814 to 1813 ma and 1706 to 1692 ma and the ages of 16 shrimp analyses on 14 zircon grains from one sample range from 1864 to 1803 ma the oldest ages of 1895 to 1882 ma were yielded from high y monazite grains enclosed in garnet and sillimanite pseudomorph after kyanite and thus interpreted as the time of the hp m2 granulite facies metamorphism the epma monazite ages of 1814 to 1813 ma and shrimp zircon ages of 1864 to 1803 ma are interpreted as the approximate ages of the post hp granulite facies metamorphism m3 most probably resulting from the exhumation of the hp granulites to the medium pressure granulite facies levels the youngest age group of 1706 to 1692 ma obtained from low y monazite grains in the matrix can be interpreted as the age of late cooling and retrograde metamorphism m4 that occurred when the hp pelitic granulites were exhumed to the upper crust the presence of paleoproterozoic hp mafic and pelitic granulites in the southern segment of the jiao liao ji belt suggests that the evolution of the jiao liao ji belt in the eastern block of the north china craton must have been involved in subduction or collision related tectonic processes

far field lithospheric deformation in tibet during continental collision 1 crustal deformation along the present day northern margin of the tibetan plateau has occurred since mid to late eocene time soon after india collided with eurasia assuming that on these distance and time scales the lithosphere can be approximated using a thin viscous sheet we show that far field lithospheric deformation caused by an indenting boundary is expected to start shortly after collision begins when a strong region analogous to cratonic lithosphere like that of the tarim basin is included in the calculations shear and vertical strain rates concentrate along the southern edge of the strong region resulting in enhanced deformation there in calculations scaled to the dimensions of india and the tibetan plateau shear and vertical strain rates on the northern edge of the plateau increase soon after collision begins crustal thickening accelerates later in the calculations we propose that the apparent increased exhumation and perhaps surface uplift around 10 ma may signal the arrival of the thickening front

microblock amalgamation in the north china craton evidence from neoarchaean magmatic suite in the western margin of the jiaoliao block abstract the archaean earth is considered to have been characterized by microcontinents that formed dominantly through the accretion of oceanic arcs and plateaus the north china craton ncc provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the archaean here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks the jiaoliao block that forms part of the composite eastern block of the ncc we present petrological geochemical and zircon u pb geochronological data from the taipingzhai charnockite suite and associated amphibolites metagabbros and orthogneisses from the qianxi complex geochemically the rocks show a wide range of sio 2 charnockite suite 52 57 75 50 wt metagabbro 43 71 wt amphibolite 50 24 wt garnet bearing biotite 63 73 wt and mgo charnockite suite 0 89 5 01 wt metagabbro 3 99 wt amphibolite 6 23 wt garnet bearing biotite 2 08 wt the composition of the felsic units straddle from diorite through syeno diorite to granite with both alkalic and subalkalic affinity with dominantly magnesian composition and arc related features their immobile trace element relationships suggest calc alkaline affinity they show positive pb ba la nd and gd and negative nb ta sr th and ti anomalies with slightly negative anomalies of ce and y attesting to arc related features in tectonic classification diagrams the rocks plot in the vag syn colg field or the vag area suggesting subduction related origin the dominant population of zircons in all these rocks displays magmatic crystallization features including high th u values with core rims textures indicating subsequent thermal events the zircon u pb data yield upper intercept ages of 2587 10 ma to 2543 17 ma and 207 pb 206 pb mean ages of 2578 7 3 ma to 2536 8 ma for the charnockite suite marking the timing of emplacement of the arc magmas the overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207 pb 206 pb ages between 2533 ma to 2490 ma zircons in the metagabbro preserve upper intercept ages of 2556 20 ma representing the crystallization age of this rock the younger ages of 2449 58 ma upper intercept age and 1845 25 ma 207 pb 206 pb spot age are interpreted to represent subsequent multiple thermal events in this area zircons in the amphibolite preserve the 207 pb 206 pb mean age of 2539 9 ma representing the crystallization age of this rock the garnet bearing biotite gneiss shows an upper intercept age of 2562 10 ma mswd 0 66 n 36 and the 207 pb 206 pb mean age of 2561 9 ma mswd 0 63 n 33 which is taken to represent the crystallization age of this rock some inherited zircons are also identified with 207 pb 206 pb ages of 2664 26 ma and 2628 26 ma zircon lu hf data show dominantly positive ehf t values and combined with crustal residence ages the results suggest mesoarchean to neoarchean juvenile crust formation in the ncc we interpret the data presented here to represent a phase of major late neoarchaean arc magmatism along the western margin of the jiaoliao block related to the birth of microcontinental nuclei within the ncc our data suggest that the western and eastern blocks might not have existed as discrete crustal blocks and that the construction of the ncc is a result of the assembly of several microblocks or terranes at the end of archaean similar archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early earth

is the ordos basin floored by a trapped oceanic plateau abstract the ordos basin in china has about 10 km of neoarchean to quaternary sediments covering an enigmatic basement of uncertain origin the basement is tectonically stable has a thick mantle root low heat flow few earthquakes and has been slowly subsiding for billions of years the basement has geophysical signatures that indicate it is dominantly intermediate to mafic in composition and is similar to some other cratons world wide and also to several major oceanic plateaus it was accreted to the amalgamated eastern block and central orogenic belt of the north china craton ncc in the paleoproterozoic then involved in several proterozoic tectonic events including being over thrust by an accretionary orogen and intruded by andean arc related magmas and then involved in a continent continent collision during amalgamation with the columbia supercontinent thus the basement rocks are deformed metamorphosed to granulite facies and determining their initial origin is difficult we suggest that the data is consistent with an origin as an oceanic plateau that accreted to the ncc and later experienced different episodes of differentiation associated with later subduction and collisions formation of cratonic lithosphere by accretion of oceanic plateaus may be one mechanism to create stable cratons other cratons that apparently formed by partial melting of underplated and imbricated oceanic slabs are stable in some cases but also re activated and de cratonized in some cases in asia where they have been affected by younger subduction hydration slab roll back and melt peridotite reactions this suggests that the initial mode of craton formation may be a factor in the preservation of stable cratons and de cratonization is not only influenced by younger tectonic activity

deformation history of the hengshan complex implications for the tectonic evolution of the trans north china orogen structural analysis indicates that the hengshan complex underwent five distinct episodes of deformation d1 d5 the d1 episode formed small isoclinal folds f1 penetrative axial planar foliations s1 and mineral stretching lineations l1 d1 fabrics were reworked by following d2 deformation associated with d2 was the development of nw verging asymmetric folds and accompanying thrust faults both d1 and d2 resulted from crustal thickening and coherent with prograde and peak metamorphism d2 deformation was followed by transpressional dextral shearing d3 including top to nw oblique slip shearing and nne ssw dextral strike slip shearing ongoing collision led to development of the zhujiafang ductile shear zone d4 a near e w trending high strain belt across the hengshan complex d5 deformation is characterized by f5 open folds and associated normal faults probably related to exhumation of the complex structural patterns of the hengshan complex can place important insights into a recently proposed tectonic model suggesting that an ocean between the eastern and western blocks underwent eastward directed subduction beneath the western margin of the eastern block and closure of this ocean finally led to collision between the two blocks to form the coherent north china craton

archean to paleoproterozoic continental crust growth in the western block of north china constraints from zircon hf isotopic and whole rock nd isotopic data abstract this study presents new zircon hf isotopic data which combined with previous zircon u pb geochronological in situ hf and whole rock nd isotopic data from the western block of the north china craton ncc provide a new insight into global scale continental crustal growth and evolution of early earth in particular igneous zircons and detrital zircons from the yinshan block yield 207 pb 206 pb ages of 2446 2733 ma with an age peak at 2524 ma of those 86 have positive e hf t values and archean hf model ages t dm c 2 6 2 9 ga peaking at 2840 ma this indicates that those basement rocks of the western block are most likely derived from a depleted mantle source implying a crust mantle differentiation event at 2 8 2 7 ga followed by extensive reworking at 2 5 ga more than 95 detrital zircons from the khondalite belt have ages converging on 2 2 2 0 ga and their e hf t values vary from 5 43 to 9 54 of which 80 are positive and yield hf model ages t dm c peaking at 2250 ma these characteristics of e hf t values in the khondalite belt are also documented in the basement rocks of the ordos block under same age frame of 2 2 2 0 ga this suggests that the ordos block may be a juvenile crust with addition of older materials the initiation of subduction under the southern margin of the ordos block leads to the formation of a 2 2 2 0 ga magmatic arc which is likely related to the assembly of the supercontinent columbia

3800 to 2500 ma crustal evolution in the anshan area of liaoning province northeastern china shrimp u pb zircon geochronology has revealed several generations of granitoids and gneisses from the anshan area of northeastern china two samples of the baijiafen granite sensu lato 3804 5 and 3812 4 ma chentaigou granite 3306 13 ma lishan granite 3142 7 ma east and west anshan granites 3001 4 and 2994 8 ma tiejiashan granite 2962 4 and 2964 6 ma and qidashan granite 2475 ma the 3800 ma baijiafen granite consists of banded migmatitic trondhjemitic gneisses and forms only a small part of the area nonetheless they are the oldest known rocks in asia and are one of very few locations in the world where rocks of this antiquity have been found the younger suites are predominantly granite sensu stricto in composition and although foliated they have not been transformed into banded gneisses nd isotopic data suggest that the 3800 ma granites were produced at least in part by remelting of very ancient lree enriched sources perhaps like the exposed remnants of the 3800 ma rocks the chentaigou supracrustals contain layered mafic and ultramafic rocks banded iron formation bif and siliceous layered rocks of probable volcanogenic origin a sample of the latter has yielded a concordant u pb zircon age of 3362 5 ma interpreted as the age of deposition a trondhjemitic sheet cutting these rocks has yielded a u pb zircon age of 3342 6 ma the chentaigou supracrustals are the oldest recognised in the area younger supracrustal sequences collectively known as the anshan group contains the main economic bif units in the area bif is intruded by the 2475 ma qidashan granite indicating that the anshan group is archaean or earliest proterozoic in age

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

polyphase deformation of the fuping complex trans north china orogen structures shrimp u pb zircon ages and tectonic implications abstract the fuping complex is located in the central part of the trans north china orogen tnco a paleoproterozoic collisional belt along which the eastern and western blocks were assembled to form the north china craton three stages of deformation d 1 d 3 have been identified in the fuping complex d 1 formed tight to isoclinal folds f 1 penetrative foliation s 1 and mineral lineation l 1 which resulted from the early nw se orientated thrusting and shearing d 2 progressively overprinted d 1 and was dominated by mostly nw se shortening and top to the se e thrusting under a compressive environment d 1 and d 2 occurred in association with the peak metamorphism m 1 d 3 occurred during the exhumation after the crustal thickening producing regional scale nww see trending open folds f 3 and associated low angle detachment faults and was responsible for the isothermal decompression m 2 metamorphism of the complex following the d 3 deformation the complex was exhumed to shallow crustal levels where the rocks underwent the retrogressive cooling m 3 metamorphism syn tectonic leucocratic dykes are widespread in the fuping complex two leucocratic dykes that did not experience d 1 but underwent d 2 yield shrimp zircon ages of 1843 12 ma and 1844 18 ma which indicate that d 1 must have occurred at some time earlier than 1844 ma whereas d 2 must have occurred at some time later than this age two weakly deformed post d 2 leucocratic dykes yield shrimp zircon ages of 1817 14 ma and 1815 45 ma suggesting that the d 2 deformation occurred in the period 1843 1815 ma the new shrimp data indicate that the collision related deformation of the fuping complex must have occurred in the paleoproterozoic not in the late archean structural and geochronological data presented in this study in association with previous lithological and geochemical data suggest that the fuping complex may have been located in the hinterland of an eastward subduction zone and underwent intensive deformation and metamorphism involved in the final collision between the western and eastern blocks at 1 85 ga