late archaean to palaeoproterozoic evolution of the trans north china orogen insights from synthesis of existing data from the hengshan wutai fuping belt

biogenic influence on the growth of ferromanganese micronodules in the central indian basin abstract in a 20 cm core collected from the central indian basin with increasing depth the abundance of ferromanganese micronodules decreases as their size increases and the surface texture changes from rough to smooth biological debris including radiolarian fragments diatom tests and bacterial cells were found associated with the micronodules dissolution of biological debris with increasing core depth was evident ferromanganese oxides are present as fine imprints and coarse lumpy growths on the biological debris they are also present in different crystal forms in vugs and cavities in the micronodules electron microprobe spot analyses indicate that the micronodules are particularly high in manganese and iron in the upper and lower levels of the sediment column respectively diagenetic effects may account for the metal enrichment it appears that biological debris play an important role in the growth of the micronodules

late paleoproterozoic 1900 1800ma nappe stacking and polyphase deformation in the hengshan wutaishan area implications for the understanding of the trans north china belt north china craton abstract the hengshan wutaishan area forms part of the trans north china belt developed in response to the final amalgamation of the north china craton the hengshan wutaishan domain and the adjacent fuping massif constitute the largest and the most representative rock exposure of the belt a structural study allows us to redefine the lithological and tectonic units that compose the architecture of the hengshan wutaishan domain and to propose that the trans north china belt was built up through a polyphase tectonic evolution within the period 1900 1800 ma the first event d1 corresponds to the emplacement of lower and upper nappes herein called the orthogneiss and volcanites unit ovu and the low grade mafic unit lgmu respectively the ovu mainly consists of rocks formed in an arc system and metamorphosed under amphibolite facies conditions whereas the lgmu represents oceanic crust rocks with an arc component that underwent greenschist facies metamorphism the syn metamorphic d1 deformation is characterized by a nw se stretching and mineral lineation with a top to the se sense of shear that corresponds to the sense of nappe motion u th pb epm chemical dating on monazite from three metapelites of the ovu gives isochron ages of 1884 11 ma 1886 5 ma and 1887 4 ma interpreted as the age of the prograde amphibolite facies metamorphism coeval with nappe stacking during the d1 event the d2 event corresponds to a widespread crustal melting of the ovu and underlying basement rocks in hengshan related to the exhumation of deep structures about 20 30 ma after nappe emplacement the migmatite contains blocks of retrograded eclogite or hp granulitic restites and is characterized by the development of a pervasive foliation and lineation a late d2 event represents the folding stage of the migmatitic foliation during the completion of a dome the orthogneiss and volcanics unit and the low grade mafic unit are unconformably covered by weakly metamorphosed to unmetamorphosed sediments belonging to the hutuo supergroup these rocks were deformed by a ductile d3 event characterized by a nw se trending stretching lineation south verging folds associated with an axial planar slaty cleavage and an e w crenulation lineation lastly a left lateral wrenching along the zhujiafang shear zone separates the northern and southern parts of hengshan our structural study shows that there is no significant difference between the southern part of hengshan and the lower part of wutaishan both areas belong to ovu and show a structural continuity we suggest that this polyphase deformation developed in response to a north westward subduction of an old ocean named the luliang ocean beneath the western block followed by collision with a micro continent named the fuping block at 1890 1880 ma

geological and isotopic geochemical constraints on the evolution of the fuping complex north china craton abstract the neoarchean to paleoproterozoic fuping complex together with the adjacent hengshan and wutaishan complexes form the middle part of the central zone that separates the north china craton into the eastern and western archean continental blocks the fuping complex comprises three major lithological assemblages the 2 50 ga fuping trondhjemite tonalite granodiorite ttg gneisses the wanzi paragneisses and the 2 08 and 2 02 ga nanying granitic gneisses the ttg gneisses contain abundant enclaves of highly metamorphosed supracrustal rocks including 2 70 ga mafic granulites and amphibolites with endt of 3 29 to 3 96 and tdm of 2 72 2 82 ga and are characterized by tdm of 2 76 3 04 ga and a linear correlation between endt 1 64 to 0 96 and 1 nd indicative of mixing of melts derived from the 2 70 ga metabasic rocks and 3 0 ga crustal materials mafic dikes along the chengnanzhuang shear zone were most likely emplaced at 2 31 ga and have endt of 2 24 to 4 78 and tdm of 2 34 2 59 ga the nanying granitic gneisses with endt of 4 04 to 5 24 were most likely related to partial melting of the 2 70 ga supracrustal rocks and or the 2 50 ga ttg gneisses these geological relationships and isotopic data suggest that the fuping complex probably formed from the following five major tectonomagmatic events 1 mafic magmatism and early crustal growth at 2 7 ga with the possible existence of older 3 0 ga crust s 2 collision related crustal thickening underplating of basaltic magma high grade metamorphism crustal anatexis and ttg magmatism at 2 5 ga 3 extensional deformation and emplacement of the mafic dikes and the nanying granitic plutons along the chengnanzhuang shear zone 2 5 to 2 0 ga 4 s type granitic magmatism and associated amphibolite facies metamorphism 2 0 to 1 80 ga and 5 emplacement of granitic pegmatite dikes at 1 80 ga

pb and nd isotopic constraints on paleoproterozoic crustal evolution of the northeastern yeongnam massif south korea abstract we report pb isotopic ages and nd isotopic signatures of paleoproterozoic basement rocks from the pyeonghae area northeastern yeongnam massif south korea the pbsl lead step leaching garnet data of the wonnam group precambrian metasediments yield a 207pb 206pb age of 1840 26 ma which can be regarded as the timing of amphibolite to upper amphibolite facies metamorphism and associated garnet growth whole rock data for the pyeonghae gneiss intruding the wonnam group give a 207pb 206pb age of 2093 86 ma denying the possibility of a direct link between the intrusion of the pyeonghae gneiss and the regional metamorphism of the wonnam group our results confirm the significance of the 2 1 ga and 1 8 ga episodes that have been broadly constrained in the yeongnam massif the depleted mantle nd model ages of metasedimentary rocks from the wonnam group 2 63 2 47 ga are slightly younger than those of the pyeonghae gneiss samples 2 71 2 57 ga this nd isotopic signature also precludes a direct derivation of the pyeonghae gneiss from the wonnam group instead implying the presence and involvement of the older probably late archean crustal materials during the 2 1 ga magmatism in the northeastern yeongnam massif compiled pb and nd isotope data from the yeongnam and gyeonggi massifs suggest a similar geologic history for them arguing against the conventional idea that the gyeonggi and yeongnam massifs are separate continental blocks respectively correlated to the south and north china blocks the whole rock pb isotope data of basement rocks from the two massifs form a well defined 207pb 206pb linearity of around 2 0 ga suggesting their common crustal evolution process for the past two billion years a broad coincidence of major tectonic episodes in the two massifs is confirmed by reviewed geochronological data the nd model ages of basement rocks from the two massifs support a probable existence of archean crusts in south korea the nd model ages both archean and proterozoic of the gyeonggi and yeongnam massifs agree with neither those of the north china block predominantly archean nor those of the south china block predominantly proterozoic our compiled isotope data together with recent estimation for the age of the honam shear zone appear to refute the presence of suture zone between the two south korean precambrian massifs which leaves the imjingang belt as the possible suture zone

ree geochemistry of early precambrian charnockites and tonalitic granodioritic gneisses of the qianan region eastern hebei north china abstract the charnockites and gneisses from the qianan area eastern hebei province china were investigated for their isotope and trace element abundances the majority of the charnockites are acid in composition only a few samples have a composition corresponding to intermediate to basic rocks a rb sr whole rock isochron of the charnockites gives an age of 2 65 0 05 ga the highly fractionated ree patterns and the variable ce yb n ratios in these rocks are interpreted as being a result of igneous processes it is believed that the charnockitic rocks are related to each other by fractional crystallization under high temperatures and low p h 2 o conditions the major precipitating phases are thought to be orthopyroxene and plagioclase by contrast the qianan gneisses are mainly of tonalitic and granodioritic composition however a few samples have composition corresponding to granite s s probably produced by metasomatic processes a rb sr whole rock isochron of the qianan gneisses yields an age of 2 13 0 06 ga and this age probably represents a remobilization event the qianan gneisses do not contain hypersthene they have strongly fractionated ree patterns similar to those found in many archaean tonalitic rocks of the world in addition the total ree abundances and the magnitudes of the eu anomaly show regular variation with the sio 2 content this may suggest that the qianan gneisses might have evolved under hydrous conditions with hornblende exerting a major control on their trace element chemistry

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

archean crustal evolution in china the taishan complex and evidence for juvenile crustal addition from long term depleted mantle abstract the main framework for crustal evolution of the late archean taishan complex in the shandong province of china is constructed using data from field investigation petrographic examination geochemical analysis and isotopic age determination the history of the complex began with emplacement of basic and tonalitic magmas about 2 7 2 75 ga ago which were metamorphosed designated as metamorphism i to amphibolites and grey gneisses shortly after their emplacement these rocks constitute a metamorphic basement termed the wangfushan gneisses the basement gneisses were later intruded by a plutonic association including 1 alkali and light rare earth element lree enriched dioritic rocks and their differentiates 2 6 ga ago 2 granites and trondhjemites collectively termed the hushan granites also 2 6 ga ago and 3 the aolaishan type granites sensu stricto 2 4 2 5 ga ago the plutonic association in conjunction with the older basement gneisses was later subjected to a second period of deformation and metamorphism metamorphism ii 2 ga ago as inferred from published k ar biotite dates the chronological order of all the above events has been determined by a multichronometric approach and the age results in ma with 2 uncertainties are summarized as follows the relatively low i sr initial 87 sr 86 sr ratio and high positive nd t values for the wangfushan gneisses and the diorite group provides strong evidence for continental growth by addition of juvenile material ultimately separated from long term depleted mantle sources by contrast the sr and nd isotopic data for the aolaishan type granites coherently suggest that they are likely to be derived by anatexis of the basement gneisses at shallow depths crustal evolution of the taishan complex offers an additional example supporting the concept of a continental accretion differentiation superevent that during such a worldwide tectonothermal episode particularly in the archean important differentiation of the upper mantle has contributed to the growth of the continental crust by addition of juvenile material

u pb dating on single detrital zircon grains from the triassic songpan ganze flysch central china provenance and tectonic correlations the songpan ganze flysch belt central china covers a huge triangular area of more than 200 000 km and is bounded by the continental blocks of south china north china and the tibetan plateau detrital zircons extracted from three flysch samples collected in the central part of the belt were analyzed grain by grain using the u pb method two samples of middle triassic sandstones collected at different locations in the belt provide identical results which suggests similar source regions the detrital zircons yield a wide range of ages and indicate their principal derivation from mid proterozoic 1 8 2 0 ga source rocks with minor contribution from late archean ca 2 5 2 6 ga material the discordance and pb loss patterns from low u zircons indicate disturbances during a subsequent event which may be of caledonian age as suggested by concordant zircon grains at ca 420 and 450 ma one sample collected within the palang shan pass zone provides concordant zircon grains at around 230 ma 231 1 ma and 233 1 ma these triassic ages are synchronous to flysch deposition and suggest intense geological activity calc alkaline volcanism at that time in the area close to the basin the data support an origin of the clastic material mainly from a northeastern landmass corresponding to the southern margin of the sino korean craton to a lesser degree inputs from the yangtze craton and possibly from the northern margin of the basin kunlun arc are also detected the age spectrum from the upper triassic sandstone is significantly different and shows predominance of sinian ca 760 ma grains probably derived from the yangtze craton this change in the source region is interpreted as reflecting the tectonic evolution of this area and in particular as being linked to the late triassic collision between south china and north china in the middle triassic while subduction of the songpan sea northward beneath the north china plate was still taking place continental subduction of south china in the dabie region was responsible for uplift of the overriding plate i e the sino korean craton which supplied large volumes of sediments during the late triassic clockwise rotation of the south china block uplifted the indo sinian part of the qinling belt and closed the basin as the accretionary wedge was thickening along the southern margin of north china detritus derived from this source region were unable to reach the flysch basin the age spectrum presented by detrital zircons indicates

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

extensional collapse and uplift in a polymetamorphic granulite terrain in the archaean and palaeoproterozoic of north china abstract the archaean granulite terrain in the datong huai an area north china comprises a basement complex of felsic and mafic granulite overlain by a sedimentary sequence dominated by metapelite and metapsammite both lithological associations are separated by a tectonic contact and structural textural and stratigraphic data indicate that the terrain was affected by two prominent tectono thermal cycles c a and c b associated with two granulite facies events m1 and m2 which probably occurred 2500 ma and 1800 ma ago respectively of these m1 events were dominant and associated with all major structures in the area in the basement gneiss m1 reached peak metamorphic conditions of 12 14 kbar and 800 900 c during a foliation forming event d 2ba which transposed an earlier s 1ba foliation of unknown age and origin in the allochthonous cover sediments m1 peak conditions of about 8 kbar and 800 c were reached after a prograde thickening event d 1co associated with the formation of a bedding parallel foliation while large amounts of s type granites were emplaced the localised d 2ba and d 1co structures are interpreted as spatially distinct responses at different crustal levels to one metamorphic event juxtaposition of basement and allochthonous cover along a large low angle normal shear zone occurred during d 3 this detachment zone accommodated extension after crustal thickening and allowed unloading of the footwall resulting in a rise of the basement rocks through 4 6 kbar as deduced from syn d 3 decompression textures coeval cooling textures in the allochthonous cover sequence indicate that lateral rather than vertical displacements occurred in the hanging wall of the detachment during c b m2 peak conditions of about 4 6 kbar and 650 700 c were reached coeval with the development of discrete left lateral strike slip zones d 4 that transect both basement and allochthonous cover and accommodated some uplift the deduced c a and c b p t paths have equivalents in many precambrian granulites in general decompressional paths like the one recorded in the basement rocks are linked to processes involving crustal thickening followed by extensional collapse in the datong huai an area it can be shown that low angle detachments may have played an important role in the uplift and cooling history of granulite belts as long ago as the archaean proterozoic boundary

upb zircon geochronology of late archaean metamorphic rocks in the taihangshan wutaishan area north china abstract a geochronological study has been made in the taihangshan wutaishan area shanxi province on a sequence of precambrian supracrustal rocks and stratigraphically related intrusives these constitute part of the north china basement block the oldest rocks of the fuping group consist predominantly of mafic granulites paragneisses quartzites and amphibolites this group was always considered archaean and early k ar measurements yielded some minimum ages as old as 2300 ma and others as young as 1500 1900 ma the unconformably overlying wutai group is considered as the base of the proterozoic succession and consists of amphibolite grade paragneisses carbonates and amphibolites in its lower part and greenschist grade clastic sediments and volcanics in its upper part it has given apparent k ar mineral ages between 1500 and 2000 ma present investigations have employed the u pb zircon approach on selected parts of the sequences to provide direct depositional ages or age constraints for the fuping and wutai groups and to find the age s of subsequent metamorphic processes a minimum age for the fuping group and maximum age for the wutai group has been derived from zircon age measurements on the lanzhishan granite 2560 9 ma which intrudes the fuping group and is unconformably overlain by the wutai group this late archaean result can be interpreted as the age of an igneous crystallization event and therefore a maximum for the depositional age of the wutai group the above result is well substantiated by zircon dating of the wutai group itself zircons from a low grade metamorphosed keratophyric lava in the upper part of the group give a volcanic crystallization age of 2520 17 ma this provides close constraints for the age of deposition of the wutai group at between 2560 and 2520 ma ago if the wutai group is indeed basal proterozoic the archaean proterozoic boundary in this part of china is also dated at between 2560 and 2520 ma further evidence as to the antiquity of the wutai group comes from a u pb zircon age of 2520 30 ma for the ekou granite which intrudes the wutai group sequence the age of the underlying late archaean rocks in the tainhangshan wutaishan area the fuping group could not be directly determined because of the paucity of volcanic markers and the higher grade of metamorphism its minimum age is 2560 ma see above but only an approximate maximum age can be gleaned from the zircon systematics in granulite and amphibolite grade paragneiss samples these data indicate a degree of pb inheritance which combined with metamorphic disturbance and more recent pb loss inhibit any further interpretation other than that they indicate an approximate maximum age of around 2800 ma several of the paragneisses and one amphibolitic schist contain zircon systems which are interpreted as having completely responded to a well defined amphibolite facies metamorphic event at 2500 ma ago a younger but less well defined metamorphism caused complete pb loss from zircon and recrystallization in the amphibolite and granulite facies terrains at between 2000 and 1800 ma ago rocks which show evidence of this younger metamorphic event were not recognized from the field or structural data base but from the distribution of the few such samples analyzed it seems possible that this younger terrain may now be interpretable as a cross cutting proterozoic mobile belt this proterozoic metamorphic province is also reflected by k ar mica ages between 1600 and 2000 ma and some preliminary rb sr total rock ages at 1700 ma on nearby paragneisses whose u pb zircon age is 2500 ma

tectonic evolution in the archaean and proterozoic kre high heat flow probably favoured global hotspot activity with crustal growth of iceland type through vertical magmatic accretion the tectonic environment for the generation of about 3 9 2 5 ga granite gneiss greenstone terrains with volurnlnous production of tonalite trondhjemite granodlorite magmas is still uncertain and both piate ma and intrapiate scenarios arc possible deformanon atylea in greenstones and adjacent high grade orthognersses with intercalated shallow water supracrustal assemblages suggest extensive horizontal shortening and crustal interstacking this probably resulted from collisional and or rotational motion and produced significant intracrustal melting as early as 3 9 ga by the end of the archaean and locally much earlier crustal thicknesses reached 35 50 km or more and the cxtl aordinary hhlding to erogenic deformation may have been due to delamination and crustal subduction towards the end of the proterozoic evidence for modern style plate tectonics becomes abundant through the recognition of laland a16 accretion ophiolite obducdon foreland thrust and fold belts and exotic terranes one of the best documented example for this tectonic environment is the arabian nubian shield 4lthough it is doubtful whether modern plate tectonic settings can serve as analogues for all precambrian tectonic styles it i clear that global crustal evolution since the early archaean was governed by the motion of plates which repeatedly came togethel tv fotm supercontinents and then dlspersetl again we shall not understand the detailed mechanism of precambrian crustal itlton cs before we learn horn lo irltejpret recent large scale crustal deformation and its causes

tectonic evolution of the early mesozoic blueschist bearing qiangtang metamorphic belt central tibet this is the published version copyright 2003 american geophysical union all rights reserved

subdivision of precambrian time recommendations and suggestions by the subcommission on precambrian stratigraphy abstract the subcommission on precambrian stratigraphy consisting at the time of its last formal meeting in 1982 of 12 titular members and 30 correspondents has been actively working toward an acceptable subdivision of precambrian time for more than a decade comprehensive time rock charts have been prepared for major precambrian shields and this composite record has been analysed for patterns and events common to several or to all a geochronologic subdivision scheme has evolved that reflects these patterns of major events in earth history while still recognizing that those events are typically varied in intensity and timing from one region to another time unit boundaries have been selected so as to enclose or delimit principal cycles of sedimentation orogeny and magmatism but the boundaries are defined in years without specific reference to any bodies of rock several recommendations developed sequentially at formal meetings held at intervals of 2 4 years and announced in geologic journals with calls for comment and criticism are proposed 1 1 the recommendation to establish two major time units of eon rank proterozoic and archaean archean separated by a time boundary at 2500 ma is reaffirmed 2 2 the provisional recommendation to subdivide the proterozoic eon into three units of era rank provisionally labelled proterozoic i ii and iii with time boundaries at 2500 1600 900 and about 570 ma respectively is confirmed and 3 3 further subdivision of the proterozoic into eight time units of period rank as yet unnamed with time boundaries at 2500 2100 1800 1600 1400 1200 900 700 and about 570 ma respectively is provisionally recommended the nature of the subcommission s deliberations and the guidelines developed are described herein comment and criticism both on the procedure followed and on the recommendations themselves are invited

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

zircon u pb ages and hf isotopes of the huai an gneisses from the tianzhen xinpingbu area implications for the tectonic evolution of the trans north china orogen abstract one of the major advancements in understanding the formation and evolution of the north china craton was the recognition of a himalayan type collisional belt in the central part of the craton called the trans north china orogen tnco along which two micro continental blocks named the eastern block and western block joined together to form a coherent craton however controversy still remains about the pre collisional tectonic setting and architectures of the tnco in this contribution field based zircon u pb and lu hf isotopic investigations were carried out on the huai an gneisses from the tianzhen xinpingbu area in the northern part of the tnco the huai an gneisses consist predominantly of tonalitic trondhjemitic granodioritic ttg gneisses with minor gabbroic dioritic and granitic gneisses our zircon u pb results show that the plutonic protoliths of the huai an gneisses were emplaced at 2 51 2 40 ga and experienced a granulite facies metamorphic event at 1 86 1 80 ga the magmatic zircons of these samples yield e hf t values from 1 9 to 7 0 and t dm c ages of 2862 2619 ma these positive e hf t values associated with the lack of old inherited zircons suggest the derivation of their precursor magmas from a juvenile crust without contamination of old continental crust the t dm c model ages indicate that 2 8 2 6 ga is the best estimation of the mantle extraction time for the source rocks in the huai an gneisses revealing a major period of juvenile crustal growth thus it can be inferred that the partial melting of subducted oceanic crust slab produced the magmas of the huai an gneisses which subsequently interacted with overlying mantle wedge during the ascent suggesting an intra oceanic arc environment for the huai an gneiss complex taken together the development of the huai an gneiss complex was involved in a subduction related magmatic event in an intra oceanic arc at 2 5 ga followed by collision between the eastern and western blocks at 1 85 ga

constraints of volcanic rocks of the wutai complex shanxi province northern china on a giant late neoarchean intra oceanic arc system in the trans north china orogen abstract the wutai complex is located in the central part of the trans north china orogen the complex consists of neoarchean to paleoproterozoic granitoids and low grade metamorphosed volcanic and sedimentary rocks of the wutai group the group is subdivided into the shizui taihuai and gaofan subgroups meta volcanic rocks from the taihuai subgroup have igneous zircon u pb ages of 2548 2538 ma and e hf t values of 4 10 to 8 84 with xenocrystic zircons of 3 6 2 7 ga geochemically the meta volcanic rocks can be classified into four groups group 1 low ti tholeiites have the highest nb la pm ratios and the lowest la sm cn ratios flat to slightly light ree depleted chondrite normalized patterns and lower tio 2 and yb contents compared to v they were most likely derived from partial melting of depleted mantle in a fore arc setting group 2 island arc tholeiites displays flat to mildly right declined ree patterns and moderately negative nb ta zr and ti anomalies group 3 mature arc calc alkaline basalts display strongly fractionated chondrite normalized ree patterns and evidently negative nb ta and ti anomalies group 2 and 3 basalts formed by partial melting of sub arc depleted mantle wedge modified by different degrees of slab derived melts group 4 meta andesites and rhyolites have high la and low yb contents and strongly fractionated ree patterns and may have formed by fractionational crystallization of magma of group 3 basalts with clinopyroxene as a major mineral phase the 2 55 2 52 ga wutai group represents an intra oceanic arc underlain in part by a 2 7 ga continental nucleus derived fragment

shrimp u pb zircon geochronology of the huai an complex constraints on late archean to paleoproterozoic magmatic and metamorphic events in the trans north china orogen the huai9an complex is situated in the northern segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete archean eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of six distinct lithologic units the huai9an ttg gneisses the manjinggou high pressure mafic granulites the khondalite series the dongjiagou granitic gneiss the huai9an charnockite and the dapinggou k feldspar granite shrimp u pb geochronology combined with th and u data and cathodoluminescence cl imaging of zircons enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the tnco cl images reveal the coexistence of magmatic and metamorphic zircons in most lithologies of the huai9an complex of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating oscillatory zoned magmatic zircon cores shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic protoliths of the huai9an ttg gneisses were emplaced at 2515 20 ma 2499 19 ma and 2440 26 ma respectively much earlier than the emplacement of the dongjiagou granitic gneiss dated at 2036 16 ma however their metamorphic zircons yield similar concordant 207pb 206pb ages of 1847 17 ma 1842 10 ma and 1847 11 ma for the tonalitic trondhjemitic and granodioritic gneisses respectively and 1839 46 ma for the dongjia granitic gneiss these ages demonstrate that the huai9an complex underwent a regional metamorphic event at 1850 ma which is further supported by a mean 207pb 206pb age of 1848 19 ma for metamorphic zircons in the manjinggou high pressure mafic granulite and 1849 10 ma and 1850 17 ma for igneous zircons in the anatectic huai9an charnockite and dapinggou garnet bearing s type granite respectively the timing of late archean to paleoproterozoic magmatism and regional metamorphism in the huai9an complex is in general agreement with recent shrimp zircon data for other metamorphic complexes in the tnco these data prove that the high grade gneiss complexes were not the basement to the low grade granite greenstone terranes in the tnco furthermore the lithologies of the orogen are considered to have developed as a long lived magmatic arc that was subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western blocks at 1 85 ga leading to final assembly of the north china craton

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

archean geodynamics in the central zone north china craton constraints from geochemistry of two contrasting series of granitoids in the fuping and wutai complexes abstract the archean to paleoproterozoic central zone of the north china craton is situated between the eastern and western archean continental blocks and contains two contrasting series of neoarchean granitoids the 2523 2486 ma tonalite trondhjemite granodiorite ttg gneisses in the fuping complex and the 2555 2525 ma calc alkaline granitoids tonalite granodiorite granite and monzogranite in the wutai complex the fuping ttg gneisses most likely formed from partial melting of 2 7 ga basalts at 50 km with an involvement of 3 0 ga crustal material the wutai granitoids have higher k 2 o lile and rb sr but lower sr y and la n yb n than the fuping ttg gneisses are characterized by nd t dm from 2 5 to 2 8 ga and e nd t from 0 49 to 3 34 and are derived from partial melting of a juvenile source at the geochemistry of these two contrasting series of neoarchean granitoids provides further evidence that the wutai complex originated and evolved separately from the fuping complex the wutai complex most likely formed as an oceanic island arc with volcanism and synvolcanic granitoid intrusions at 2555 2525 ma the wutai complex was subsequently accreted onto the eastern archean continental block and was probably responsible for crustal thickening and ttg magmatism at 2523 2486 ma in the fuping complex as part of the taihangshan hengshan block at the western margin of the eastern archean continental block

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

volumetric changes in weathered profiles iso element mass balance method questioned by magnetic fabric abstract a major issue in understanding weathering processes is to determine to what extent fabrics structures and volumes from the parent rock are preserved through the weathering profile iso element mass balance methods imb are often used to estimate volume changes during progressive weathering based on the assumption that a given element either ti zr or th is not mobile the petrofabric of the weathered material is often characterized by a mimetic replacement of primary minerals that fully preserve the primary fabric this suggests an isovolume weathering as volume change must be associated with shape change due to boundary conditions not allowing horizontal strains so collapse or dilation should induce vertical compaction or constriction respectively the weak petrofabric of weathered materials may be precisely quantified using the anisotropy of low field magnetic susceptibility technique ams this paper reports for the first time a combined imb and ams study of two different environments a complex lateritic sequence on precambrian metamorphic rocks in cameroon and a weathering profile on a pleistocene basaltic flow in morocco the lateritic profile divided into a lower saprolite zone 12 m and an upper nodular iron rich unit 4 m is characterized by neoformed magnetic minerals goethite hematite spinels and a weak but rather consistent magnetic fabric saprolitization which induces low susceptibility values 50 10 9 m3 kg preserves the linear tectonic fabric of the parent gneiss ams evidence for isovolumetric weathering agrees with th based imb while ti and zr partly indicate apparent collapse and dilation up to 50 respectively ferralitization in the nodular iron crust which enhances susceptibilities 500 to 700 10 9 m3 kg due to spinel phases induces drastic reductions in anisotropy due to multiple generation of neoformed minerals destroying primary fabric however a weak horizontal planar magnetic fabric suggests compaction in agreement with th and ti based imb while zr would indicate isovolume weathering conversely in the one meter thick weathering profile on basalt the strong susceptibility 1 5 to 3 10 6 m3 kg is dominated by inherited titanomaghemite grains which totally preserve the weak magmatic fabric of the fresh basalt this again suggests that volume change is minor while ti and zr based imb indicate 20 to 50 of dilation in both examples large volume changes inferred from the imb in units showing preserved primary ams fabric appear unrealistic our ams study together with the large discrepancies between the imb results produced by various elements indicate that the assumption of immobility of a given element is probably not fulfilled all along these profiles isovolumetric weathering in the saprolitic zone may be more widespread than suggested by imb results

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

magnetic fabric and post orogenic uplift and cooling magnetisations in a precambrian granulite terrain the datong huai an region of the north china shield abstract the polymetamorphic terrain in the datong huai an region of the north china shield records two metamorphic m1 and m2 and associated deformational d1 d3 and d4 episodes in granulite facies the magnetic fabric is dominated by the d3 foliation imparted by emplacement of allochthonous cover rocks onto basement during compression and subsequent collapse and uplift magnetite is present in four generations as 1 discrete grains 2 exsolution lamellae in mafic minerals 3 corona rims formed during regional decompression and 4 a filling of microfractures it is the dominant ferromagnetic phase and carries a stable high blocking temperature remanence of dual polarity linked to magnetite grain sizes and shapes of generations 2 to 4 remanence was acquired during later stages of uplift and cooling after the m2 metamorphism and d4 deformation and during rapid decompression a ne to nw migration of the palaeofield direction during this time is identified palaeomagnetic directions are not constrained to lineation in the older magnetic anisotropy but lie close to the dominant d3 foliation although no satisfactory methods presently exist for correcting remanence for anisotropy qualitative considerations from petrology and comparisons between sites of contrasting ams fabric suggest that palaeodirections are not prominently deflected into the d3 plane the pole positions define a continuous swathe plotting between 50 e 20 s and 170 e 35 s summarised by group mean poles a1 51 e 20 s dp dm 8 15 a2 80 e 33 s dp dm 6 11 a3 106 e 48 s dp dm 7 13 and a4 164 e 40 s dp dm 11 21 they are assigned to the interval ca 2000 1840 ma and extend the apparent polar wander record for the north china shield backwards in time from the record derived from supracrustal successions

lithotectonic elements and geological events in the hengshan wutai fuping belt a synthesis and implications for the evolution of the trans north china orogen the hengshan wutai fuping belt is located in the middle segment of the trans north china orogen a palaeoproterozoic continental collisional belt along which the eastern and western blocks amalgamated to form the north china craton the belt consists of the medium to high grade hengshan and fuping gneiss complexes and the intervening low to medium grade wutai granite greenstone terrane and most igneous rocks in the belt are calc alkaline and have affinities to magmatic arcs previous tectonic models assumed that the hengshan and fuping gneiss assemblages were an older basement to the wutai supracrustal rocks but recent studies indicate that the three complexes constitute a single long lived neoarchaean to palaeoproterozoic magmatic arc where the wutai complex represents an upper crustal domain whereas the hengshan and fuping gneisses represent the lower crustal components forming the root of the arc the earliest arc related magmatism in the belt occurred at 2560 2520 ma marked by the emplacement of the wutai granitoids which was followed by arc volcanism at 2530 2515 ma forming the wutai greenstones extension driven by widespread arc volcanism led to the development of a back arc basin or a marginal sea which divided the belt into the hengshan wutai island arc japan type and the fuping relict arc at 2520 2480 ma subduction beneath the hengshan wutai island arc caused partial melting of the lower crust to form the hengshan tonalitic trondhjemitic granodioritic ttg suites whereas eastward directed subduction of the marginal sea led to the reactivation of the fuping relict arc where the fuping tonalitic trondhjemitic granodioritic suite was emplaced in the period 2360 2000 ma sporadic phases of isolated granitoid magmatism occurred in the hengshan wutai fuping region forming 2360 ma c 2250 ma and 2000 2100 ma granitoids in the hengshan complex the c 2100 ma wangjiahui and dawaliang granites in the wutai complex and the 2100 2000 ma nanying granitoids in the fuping complex atc 1920 ma the hengshan wutai island arc underwent an extensional event possibly due to the subduction of an oceanic ridge leading to the emplacement of pre tectonic gabbroic dykes that were subsequently metamorphosed together with their host rocks to form medium to high pressure granulites at 1880 1820 ma the hengshan wutai fuping arc system was juxtaposed intensely deformed and metamorphosed during a major and regionally extensive orogenic event the l uliang orogeny which generated the trans north china orogen through collision of the eastern and western blocks the hengshan wutai fuping belt was finally stabilized after emplacement of a mafic dyke swarm at 1780 1750 ma

a neoarchean subduction polarity reversal event in the north china craton abstract subduction polarity reversal events following arc continent arc arc or continent continent collisions have been well documented from cenozoic mesozoic and paleozoic orogens but not from the archean we here document a neoarchean subduction reversal event after an arc continent collision between the eastern block of the north china craton ncc and the fuping arc using field geochemical and geochronological data we focus our work on the wangjiazhuang granite in the zanhuang massif located along the eastern margin of the central orogenic belt cob of the ncc and a regional tectonic comparison with other granitic rocks with similar ages geochemical and petrogenetic characteristics the ca 2 5 ga a type wangjiazhuang granite intrudes the neoarchean zanhuang melange belt and contains mafic and felsic inclusions it has positive end t values 0 12 to 1 13 and tdm2 ages between 2784 ma and 2869 ma this work shows clearly from field structural relationships geochemistry and geochronology that the wangjiazhuang granite formed after an arc continent collision between the eastern block which is defined as a continental block and the fuping arc after a subduction polarity reversal event placed a new slab beneath the collisionally modified margin of the eastern block and converted it to an andean type margin the subduction polarity reversal event at ca 2 5 ga resulted in melting of the enriched mantle meanwhile the rising magma induced partial melting of the old and thickened ttg crust leading to the intrusion of ca 2 5 ga wangjiazhuang granite into the neoarchean zanhuang melange there are other granitic rocks with similar ages and geochemical and petrogenetic features in the central orogenic belt and eastern block of the north china craton suggesting that they formed in a similar tectonic setting as the circa 2 5 ga granites across the eastern block the neoarchean subduction polarity reversal event and prior arc continent collision provide strong evidence that plate tectonics was operating by the end of the neoarchean

contrasted tectonic styles for the paleoproterozoic evolution of the north china craton evidence for a 2 1 ga thermal and tectonic event in the fuping massif structural analysis along with 40ar 39ar and u pb datings in the fuping massif provide new insight into the evolution of the eastern part of the trans north china belt north china craton from 2 7 ga to 1 8 ga d1 is responsible for the development of a dome and basin structure coeval with crustal melting giving rise to migmatite and nanying gneissic granites at 2 1 ga this dome and basin architecture resulted from the interference between a n s compression of a weak ductile crust and gravity driven vertical flow in a high thermal regime the next events involved flat lying ductile thrusting d2 and normal faulting d3 dated at around 1880 ma and 1830 ma respectively the d2 and d3 events belong to the trans north china orogeny that results in the final amalgamation of the north china craton the d1 deformation is considered as evidence for an earlier orogen developed around 2 1 ga prior to the trans north china orogeny the change in the deformation style between the 2 1 ga and 1 8 ga could be viewed as a consequence of the cooling of the continental crust in the north china craton

archean crustal evolution in china u pb geochronology of the qianxi complex abstract the qianxi complex formerly the qianxi group in eastern hebei province is a key terrain for studying the archean crustal evolution of the sino korean craton in china the evolution of the complex involved several stages of supracrustal deposition and magmatic intrusion except for a few post tectonic intrusives all rock assemblages have been metamorphosed to high grade granulite and amphibolite facies the evolution of the complex has spanned more than 1 ga since about 3 5 ga ago in the present work two areas in the qianan region qianan county have been investigated for u pb age study 1 the caozhuang area in the south and 2 the shuichang yangyashan area in the north important tectonothermal events and magmatic episodes of the qianxi complex were identified by the u pb isotopic analyses of zircons extracted from various rock types the results of age determination and the most likely interpretation in terms of temporal evolution of the complex are summarized schematically the oldest zircons 3 65 3 67 ga of china have been found in a fuchsite bearing quartzite in association with the 3 5 ga sm nd isochron age amphibolites in the caozhuang area this emphasizes the existence of early archean sialic crust in the qianxi complex however no ages older than 2 9 ga have been revealed for grey gneisses enclosing the ca 3 5 ga amphibolite enclaves in the caozhuang area but a leptynite sample of dacitic composition gave a minimum 207pb 206pb age of 3 3 ga obtained by a single zircon stepwise evaporation analysis this age and the 3 5 ga sm nd isochron age for amphibolites suggest that the earliest deposition of supracrustal rocks took place about 3 5 3 3 ga ago the deposition of fuchsite quartzite could have taken place contemporaneously or in an earlier period up to 3 6 ga but its precise stratigraphic positions remains to be determined nevertheless the presence of very ancient zircons clearly advocate for the existence of sialic crust at least 3 6 ga in china in the shuichang yangyashan area a supracrustal sequence containing abundant banded iron formations was intruded by a granitic gneiss dated at 2 96 ga by the conventional multigrain zircon method sm nd model ages of about 3 3 ga were obtained for two amphibolite enclaves in a charnockitic gneiss it appears that supracrustal deposition of the qianxi complex might have migrated to the north and took place in the period of 3 3 3 0 ga in addition to supracrustal rocks the qianxi complex is characterized by polyphase granitoid intrusions except for the contaminated grey gneisses sm nd tdm 3 2 3 3 ga in the caozhuang area and the ca 3 ga granitic gneiss in the yangyashan area most granitoid intrusions are of late archean ages the period of 2 7 2 5 ga has undoubtedly recorded the most important tectonothermal events in the evolution of the sino korean craton the present zircon age study and available age data in the literature demonstrate that the archean crustal development in china culminated towards the end of the archean

the wutaishan orogenic belt within the shanxi province northern china a record of late archaean collision tectonics abstract the archaean crust of northeastern shanxi province northern china is dominated by three distinct terranes the high grade gneiss terranes hengshan in the north and fuping in the southeast and the intervening low grade terrane of the wutaishan belt the 2 5 ga beitai arc complex which constitutes the major part of the wutaishan belt is interpreted as a pre collision magmatic arc there was a marginal sea basin between the beitai arc and the fuping terrane at the fore arc collision stage the passive margin deposits which occurred along the western margin of the fuping terrane became a foreland fold thrust belt after the closure of the marginal sea basin the remnants of sea floor occur as a melange zone along the suture zone between the beitai arc and fuping terrane nearly at the same time at 2 5 ga the back arc oceanic lithosphere started to subduct beneath the hengshan terrane then the hengshan terrane came into collision with the arc and the fuping terrane some dismembered sea floor rocks are preserved as a back arc melange zone between the hengshan terrane and the beitai arc the term wutaishan orogeny should be reserved for the processes which lasted from 2600 to 2450 ma

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

shrimp data on zircons from the wanzi series constraints on the rock formation time and implications of migmatization at 2 1 2 0 ga in the fuping complex north china craton in most of the rocks of the fuping complex in the trans north china orogen a large quantity of leucocratic veins dykes and granitic intrusions are present as migmatites the incongruent partial melting of biotite to hornblende suggests the water fluxed anatexis of the migmatization of which the melt is manifested by the euhedral crystallization of some quartzofeldspathic minerals and presence of albite rim on earlier plagioclase or k feldspar importantly some melt may be segregated in the sillimanite gneisses or extracted and injected as faint dispersed melt into the competent metasedimentary quartzite of the wanzi series rocks the quartzite has plenty of zircon ages cluster at c 2 5 ga and some at c 2 1 2 0 ga the former may be detrital zircon age while the latter represents the age of migmatization or crystallization of the injected melt not detrital zircon ages as conventionally believed the data have constrained that the sedimentation time of the protolith of the quartzite of the wanzi series was between c 2 5 ga and c 2 1 2 0 ga not younger than c 2 1 2 0 ga as once proposed therefore it must be cautious in applying detrital zircon ages in constraining the time of sedimentation if the rocks have undergone middle high grade metamorphism especially when migmatization was involved in the metamorphism process

neoarchean paleoproterozoic magmatic arc evolution in the wutai hengshan fuping area north china craton new perspectives from zircon u pb ages and hf isotopic data abstract the wutai granite greenstone belt which formed in the neoarchean paleoproterozoic with the adjoining high grade metamorphic hengshan fuping region record important transitions in crustal and tectonic evolution although these evolutionary processes have still been in dispute in this study new u pb and lu hf la icp ms zircon analyses were obtained from eight metamorphosed magmatic rocks in the wutai hengshan fuping area in north china craton ncc the results reveal that most of wutai granitoids yield emplacement ages of 2 56 2 52 ga with corresponding ehf t2 of 4 7 to 8 3 the tonalitic gneiss from dongshandi intrusion however gives a new age of 2482 ma and ehf t2 of 2 5 to 4 6 which are similar with yixingzhai pluton marked by ages of 2501 2499 ma and ehf t2 of 3 2 to 4 4 also 2 7 ga and 2 5 ga continental crust generation are further revealed but 2 5 ga crustal growth is more complicated due to the involvement of old crustal components which can be identified by variable ehf t2 values ranging from 1 8 to 7 5 thus based on the distinctions of hf isotopes compositional and spatial features two consecutive groups of 2 56 2 52 ga and 2 52 2 48 ga are recognized and a two step tectonic evolution model for the wutai hengshan fuping area is proposed during 2 56 2 52 ga intra oceanic subduction led to the formation of wutai oceanic island arc accompanied mainly by the development of wutai granitoids ehf t2 of 4 7 to 8 3 and coeval volcanics predominant arc tholeiitic chemical affinity corresponding to the juvenile crustal growth between 2 52 ga and 2 48 ga with intervening oceanic crust between intra oceanic arc and continent consumed the wutai intra oceanic arc then collided and was obducted onto the western edge of the hengshan fuping continental block large amounts of ttg gneisses produced in both the wutai and hengshan fuping ehf t of 1 8 to 7 5 along with calc alkaline volcanism in wutai possibly in response to the thickening through arc accretion and commencing the continental arc this proposed two step tectonic evolution model combined with a late neoarchean 2 6 2 5 ga intra oceanic arc system along the northwestern of the eastern block eb probably provides a better explanation for the fundamental geodynamic mechanism for continental arc development at the proterozoic dawn

in situ zircon u pb dating and o isotopes of the neoarchean hongtoushan vms cu zn deposit in the north china craton implication for the ore genesis abstract the hongtoushan volcanogenic massive sulfide vms deposit is the largest archean cu zn deposit in china located in the qingyuan greenstone belt on the northern margin of the north china craton the cu zn mineralization was stratigraphically controlled by the interbeds 100 m in thickness of mafic felsic volcanic sets and overlain by banded iron layers however the relationship between vms deposits and associated volcanics has not been examined this study ultimately clarifies the times and sources of the volcanics and mineralization based on in situ zircon u pb and o isotope on vms hosting mafic felsic volcanic rocks banded and massive sulfide ores and postmineralization pegmatite vein we considered that there were two main formation stages for the qingyuan cu zn deposits one was exhalative hydrothermal sedimentation and another was further cu zn enriched by later hydrothermal processes the timing of the first stage occurred at 2571 6 ma based on the magmatic zircons in the vms hosting mafic volcanic rocks from which the inherited zircons also indicate the existence of 2 65 3 12 ga ancient supercrustal rocks in the qingyuan district a modern mantle like 18 o zircon value of 5 5 0 1 2sd for this volcanism was well preserved in the inherited core domains of ore samples it suggests that the mafic volcanics was most likely sourced from partial melting of juvenile crust e g ttg granites a large scale metamorphic or hydrothermal event is documented by the recrystallized zircons in sulfide ores the timing is tightly constrained by the hydrothermal zircon u pb ages they are 2508 4 ma for the banded ore 2507 4 ma for the massive ore and 2508 2 ma for the postmineralization pegmatite vein these indistinguishable ages indicate that the 2507 ma hydrothermal systems played a significant role in the upgrading of the vms cu zn orebodies the weighted 18 o values of hydrothermal zircons show a successively increasing trend from 6 0 0 1 2 for the banded ore 6 6 0 2 2 for the massive ore to 7 3 0 2 2 for the later pegmatite vein this variation might be induced by gradual inputting of the 18 o rich oceanic crust and or oceanic sediment during the hydrothermal cycling system considering its modern mantle like oxygen isotope composition of 2571 ma volcanism a submarine volcanic hydrothermal system involving mantle plumes is a preferred setting for the neoarchean vms cu zn deposits in the qingyuan greenstone belt

petrochemistry and sr pb and nd isotopic geochemistry of early precambrian rocks wutaishan and taihangshan areas china abstract in the wutaishan and taihangshan region china the lowermost high grade metamorphic complex of grey gneiss and amphibolite the fuping complex gives a 2 2 0 2 ga pb pb isochron age with a first stage growth 7 73 and a 2 37 0 07 ga sm nd isochron age with 143nd 144nd 0 0 50963 0 00005 or nd t 1 50 nd depleted mantle model dates tdm of amhibolites 2 48 to 2 60 ga those of gneisses are 2 43 to 2 46 ga the unconformably overlying medium to low grade metavolcanic complex the wutai complex gives a 2 0 0 1 ga rb sr isochron age with 87 86sr 0 0 7025 2 a 2 27 0 02 ga pb pb isochron date with afirst stage growth 7 73 and a 2 26 0 06 ga sm nd isochron first stage 143nd 144nd 0 0 5097 2 or nd t 1 08 individual sample nd depleted mantle model date are 2 5 ga metavolcanic samples from low grade metasedimentary rocks of the hutuo group all lie close to a 2 3 ga reference line on a rb sr isochron plot have nd tdm 2 32 2 34 and 2 62 ga from previous geological work published u pb zircon dating and ourisotopic and geochemical results we infer that the fuping rocks formed 2 6 ga ago in an environment like a modern island arc the wutai complex formed by 2 5 ga ago mostly formed in a tectonic setting similar to that of the fuping complex with the exception that one volcanic cycle formed in an environment like a modern mor and one unit formed in an environment transitional between modern within plate and plate margin settings the hutuo group formed 2 4 ga ago in a within plate tectonic environment there is no evidence for continental crust before 2 6 ga in the wutaishan and taihangshan region this contradicts previous assignment of the fuping complex to 2 8 ga ol older the fuping complex is not an early nucleus of the sino korean craton the new data also confirm that the wutai complex is older than its original assignment as early proterozoic the sm nd systems for metabasaltic rocks in the region either in amphibolite facies or in greenschist facies are all significantly disturbed in contrast with the undisturbed sm nd reported in previous studies of the sino korea craton this study provides further evidence that the archean igneous rocks in china formed at different times from heterogeneous and depleted mantle sources

granitoid evolution in the late archean wutai complex north china craton abstract two temporally discrete episodes of granite magmatism have been identified in the wutai complex of the north china craton based on shrimp u pb zircon dating of all major granitoid bodies in the area the older period is latest archean and ranges in age from 2560 to 2515 ma whereas the younger episode is paleoproterozoic with magmatism at 2170 and 2120 ma archean magmatism can be further separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the wutai complex the early phase of archean activity is represented by the lanzhishan ekou and portions of the chechang betai granites with ages ranging from 2560 to 2540 ma the lanzhishan granite is the only one at wutaishan that contains inherited zircon with a number of cores and individual grains giving ages in excess of 2700 ma these are relatively evolved granitoids interpreted to be derived from older basement of the eastern block of the north china craton the shifo guangmingshi the main grey phase of the wangjiahui granite and the major components of the chechang betai granite have ages of 2540 2515 ma and are coeval with felsic volcanism in the wutai complex which is a consequence of subduction and related arc magmatism the dawaliang granite and pink phase of the wangjiahui granite are considerably younger with paleoproterozoic ages of 2170 and 2120 ma respectively these are also evolved granitoids most likely derived by partial melting of the older basement although we have found no evidence of inheritance the petrogenesis of the granitoids reflects the precambrian amalgamation history of the north china craton indicating derivation along the western edge of the eastern block during development and amalgamation of the wutai arc and prior to collision with the western block of the craton 1 8 ga ago

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

characteristics of palaeoproterozoic stromatolites in china in china palaeoproterozoic stromatolites are best represented by taxa from the hutuo group of the wutai mountains and the changchengian group of the yanshan range which all belong to palaeoproterozoic rocks with a time range from 2500 to 1600 ma from the present data palaeoproterozoic stromatolite assemblages are mainly characterized by the following features 1 1 the palaeoproterozoic stromatolite succession contains many special elements such as forms of pilbaria externia kussoidella confunda discorsia vertexa tibia dongyeella jiananella shugongsiella yaochicunia zhongtiaoshania which so far have not been found in meso and neoproterozoic rocks 2 2 the assemblages of the palaeoproterozoic stromatolites cannot be compared wich those of the meso and neoproterozoic stromatolites in representative elements 3 3 the microstructures of the palaeoproterozoic stromatolites are dominated by banded and streaky types but grumelous type which is found frequently in meso to neoproterozoic rocks has been found only occasionally 4 4 the stromatolite building microorganisms of the palaeoproterozoic stromatolites are dominated by quite thin filaments 5 m in width and solitary coccoids and display more primitive characteristics in their morphology and structure and are of a lower grade in evolution failure to distinguish between the palaeoproterozoic stromatolite succession and the meso to neoproterozoic one using tge above characteristics can result in incorrect correlations in the study of proterozoic stratigraphy

depositional age and provenance of the wutai group evidence from zircon u pb and lu hf isotopes and whole rock geochemistry abstract the hengshan wutai fuping area is situated in the middle segment of the trans north china orogen and consists of the upper amphibolite to granulite facies hengshan and fuping complexes and the intervening greenschist to lower amphibolite facies wutai complex the wutai complex is composed of neoarchean to paleoproterozoic granitoids and low grade metamorphosed supracrustal rocks of which the latter are further divided into the wutai and hutuo groups geochemistry of the meta sedimentary samples from the wutai group indicates weak to moderate source weathering dominantly compositional variation trend and major felsic with few mafic source rocks on the tectonic discrimination plots most of the samples display continental island arc and active continental margin features u pb ages of detrital and xenocrystic zircons from the wutai group yield two major age populations of 2565 2465 ma and 2729 2676 ma and a subordinate age population of 2372 2331 ma the major 2522 ma and 2699 ma zircons were most likely derived from the wutai meta volcanic rocks the minor 2348 ma zircons are only found from the upper gaofan subgroup and most likely sourced from the 2360 2330 ma orthogneisses in the hengshan complex the maximum depositional ages of 2535 2516 ma from the meta sedimentary rocks are consistent with the eruption ages of 2548 2513 ma from meta volcanic rocks in the lower shizui and middle taihuai subgroups indicating coeval sedimentation and volcanism in a fore arc or intra arc basin this favors a tectonically juxtaposed contact rather than a layer cake model however the maximum depositional age of 2348 ma and the 2176 2161 ma felsic intrusions suggest a much younger formation age for the gaofan subgroup

age and tectonic setting of the jingangku besshi type volcanogenic massive sulfide deposit from the northern shanxi north china craton abstract the jingangku volcanogenic massive sulfide deposit is one of the largest archean deposits in china it is located in the wutai greenstone belt in the northern part of the central orogenic belt in the north china craton the deformed deposit is hosted in a suite of neoarchean metamorphosed volcano sedimentary rocks mica quartz schist plagioamphibolite plagioclase schist and bif the orebodies are characterized by massive pyrite and contain varied amounts of chalcopyrite pyrrhotite and sphalerite the country rock of the jingangku vms ores shows intense chloritization silicification sericitization and carbonation the vms hosted pyrite and copper deposit is represented by the jingangku deposit that yielded a la icp ms zircon age of 2500 15 ma mswd 0 87 the other two vms hosted pyrite and copper deposits are represented by the houping and haoditang deposits that formed between 2494 ma and 2507 ma the late neoarchean vms deposits can be interpreted to have formed in a forearc setting and subsequently tectonically transported in melange belts during continental collision quite similar to the younger besshi type deposits in japan analyses of fluid inclusions from ore bearing magnetite quartzite showed the composition of metamorphic fluid to be h2o nacl co2 ch4 n2 h2 the analysis also showed that during the peak of metamorphism the fluid was characterized by medium high temperature 322 473 and low salinity 2 2 6 74 sulfide orebodies are closely associated with the magnetite quartzite and therefore it is proposed that both the sulfide and magnetite quartzite were derived from the same material source and have the same formation age and underwent the same history of deformation and metamorphism consequently the jingangku deposit most likely formed from submarine exhalative sedimentation and later superimposed and transformed by metamorphic fluid

early proterozoic tectonic styles and associated mineral deposits of the north china platform abstract the remarkable change in tectonic style from archean granite greenstone belts and high grade terrains to linear sedimentary basins marks the beginning of the early proterozoic in china the different evolutionary histories of and accumulations in the early proterozoic basins result in different archean early proterozoic boundaries two time limits 2 8 and 2 5 ga are significant for the boundary in eastern china early proterozoic basins displaying different tectonic styles contain different mineral deposits the liaodong peninsula type of early proterozoic basin contains the most abundant mineral resources and deposit types including stratabound b fe and pb zn deposits in the eugeosynclinal facies of the liaojitite suite and pyrite p and magnesite deposits in miogeosynclinal facies rocks the magnesite deposits in liaodong peninsula are the largest in the world and were formed in a unique geological setting

palaeomagnetism rock magnetism and magnetic fabrics in precambrian metamorphic terranes of the huabei shield china abstract this study has investigated magnetic remanence rock magnetism and anisotropy of magnetic susceptibility ams in granulite and amphibolite grade metamorphic terranes of the huabei shield between inner mongolia in the west and the bohai sea in the east rock magnetic studies identify annealed metamorphic magnetite grains with multidomain properties as the remanence carriers a widely recorded stable remanence was probably fixed by grain shape effects granulite facies terranes are typically between one and two orders more strongly magnetised than amphibolite terranes and ams fabrics correlate mostly with metamorphic mineral fabrics observed in the country rocks progressive thermal demagnetisation identifies a range of two and three component structures resident in magnetite an important component recognised as a partial or complete remagnetisation by late mesozoic tertiary tectonic magmatic activity is present in basement at the southern margin of the outcrop miyun terrane and where extensive granite plutonism has occurred zhunhua terrane these components have directions corresponding to remanence in the yunmeng shan granite 119 114 ma d i 33 58 39 samples a 95 3 5 palaeopole at 201 e 64 n most remanence elsewhere was probably acquired during post tectonic uplift and cooling of the basement between 2200 and 1850 ma because palaeomagnetic directions are removed from the phanerozoic palaeofield path and they are distinct from the palaeomagnetic record in the overlying jixian supergroup deposited at 1840 900 ma these latter magnetisations are considered reliable indicators of the palaeofield during late palaeoproterozoic times because deformation of overlying supracrustal rocks is mostly slight and no prominent deflection of magnetic remanence by magnetic fabrics is observed palaeofield directions and poles attributed to the time of uplift related cooling are qian an terrane d i 215 71 a 95 9 17 samples pole at 99 e 10 n and north qianxi terrane d i 44 45 a 95 4 41 samples pole at 79 e 11 s in addition a more widely preserved shallow northerly component correlates with a nw e swathe of components recorded by uplift related cooling within the datong huan an granulite terrane in the west of the shield a preliminary palaeo mesoproterozoic apparent polar wander path for the huabei shield is defined from the palaeoproterozoic record in the metamorphic basement rocks and the meso neoproterozoic record in the overlying jixian supergroup it incorporates a loop between 2200 and 1850 ma and exhibits a general east to west trend in subsequent times

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

geochemistry of the paleoproterozonic nanying granitic gneisses in the fuping complex implications for the tectonic evolution of the central zone north china craton abstract the nanying granitic gneisses represent a major 2 0 ga magmatic event in the fuping complex of the central zone of the north china craton they occur in the chengnanzhuang shear zone which is chiefly developed along the contact between the neoarchean fuping tonalite trondhjemite granodiorite ttg gneisses and the wanzi paragneisses the nanying granitic gneisses were derived from monzogranite and syenogranite with minor amounts of quartz diorite and granodiorite and belong to the metaluminous to peraluminous high potassium calc alkaline series correlations between major and trace elements and similarities in chondrite normalized rare earth element ree patterns support field relationships e g gradational contacts indicating that the nanying granitic gneisses originated from similar magmas the granodioritic monzogranitic and syenogranitic gneisses have similar ranges of initial 87sr 86sr values 0 7030 0 7093 0 7021 0 7193 and 0 7049 0 7111 respectively although these variations are partly attributable to local resetting of the isotopic system during late deformation hydrothermal alteration the whole rock 208pb 204pb 206pb 204pb and 207pb 204pb values of the nanying granitic gneisses are 37 32 76 8 15 24 23 82 and 14 92 17 92 respectively these sr pb isotope systematics together with previously published nd isotope compositions suggest that the nanying granitic gneisses were derived from partal melting of the 2 50 ga fuping ttg gneisses with local assimilation involving the wanzi paragneisses the nanying granitic gneisses are geochemically similar to the cca and ccl groups of granitoids except for a few samples which plot in the hlo group the nanying granitic gneisses exhibit depletion in rb sr ba ti and u and enrichment in th nb zr hf and ree similar to those of syn shear high potassium calc alkaline granitoids and late shear alkaline granitoids they therefore represent the product of a syn collisional to post collisional magmatic event this collisional event which is significantly older than the 1 84 1 80 ga event that has been proposed for the juxtaposition of the eastern and western archean continental blocks in the final stabilization of the north china craton supports a tectonic model involving multiple collisional events for the amalgamation of the internal lithotectonic domains within the central zone and the assembly of the north china craton as a whole