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

experimental zircon melt and zircon garnet trace element partitioning and implications for the geochronology of crustal rocks garnet is the most commonly used mineral in thermobarometry whereas zircon is the most robust chronometer to date high grade metamorphic rocks to provide a basis for correlation of zircon and garnet growth we determined experimentally the trace element partitioningbetweenzircon ahydrousgraniticmeltandgarnetat20kbarand800 1000 cforp y rareearthelements ree zr hf th andu inrespecttomelt zirconpreferentiallyincorporatesallinvestigatedelementsapartfromreewithatomicnumberlowerthansm at this pressure and in the chosen composition the distribution coefficient between zircon and melt d zrn melt for ree increases with increasingatomicnumberofthereeandwithdecreasingtemperature dyb is 20at1000 c butmorethananorderofmagnitude higher at800 c the solubilityofzrinhydrousgraniticmelts buffered by zirconisabouta factoroftwo lower at20kbar than what has been previously established for mid crustal pressures large garnet produced in the experiments allowed determination of garnet melt trace element partitioning d grt melt at temperatures of 800 1000 c conditions relevant for partial melting of crustal rocks there is a systematic increase indree with decreasing temperature zircon contains significantly more heavy ree than garnet at temperatures of 800 850 c zircon garnetpartitioncoefficientsofheavy reedecreasewithincreasingtemperaturefromdlu of12at800 cto 1 4at1000 c middle reepartitioningisclosetounityforthewholeinvestigatedtemperaturerange differentempiricallydetermined zircon garnet partition coefficients from granulites and ultra high temperature granulites can potentially be explained by the experimentallydeterminedchangeofpartitioningasafunctionoftemperature thesedatacanassistinestablishingequilibriumbetween garnetandzirconzonesinnaturalrocks andintheconstructionofdetailedpressure temperature timepathsinhigh grademetamorphic rocks

age of the dahongliutan rare metal pegmatite deposit west kunlun xinjiang nw china constraints from la icp ms u pb dating of columbite fe and cassiterite abstract dahongliutan is a medium size li be ta nb rare metal pegmatite deposit in the tianshuihai terrane west kunlun orogenic belt nw china in this paper la icp ms u pb ages of columbite fe and cassiterite are reported to constrain the metallogenic age columbite fe with high u and low th yielded a late triassic weighted mean 206 pb 238 u age of 211 9 2 4 ma whilst cassiterite yielded a 206 pb 238 u 207 pb 235 u concordia lower intercept age of 218 12 ma and a tera wasserburg lower intercept age of 218 12 ma which is identical to the columbite fe u pb age and thus represents the emplacement age of the pegmatite dikes the ore hosting pegmatite dikes are intimately time space related to the dahongliutan s type granite ca 220 217 ma indicating that they may have been cogenetic integrating new and published geological data we suggest that the dahongliutan pegmatites may have evolved from the granitic magma represented by the dahongliutan s type pluton in a post collisional tectonic setting regionally the tianshuihai terrane is the western extension of the songpan ganzi block and thus the kunlun li mineralization belt may have been connected to the songpan ganzi li mineralization belt which contains eleven lithium deposits with about 9 8 of li 2 o reserves in china implying that the dahongliutan pegmatite deposit may also have favorable ore forming conditions the similar columbite fe and cassiterite ages demonstrate that these minerals can be precisely dated and could provide useful alternatives to accurately constrain the timing and evolution of rare metal mineralization

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

la icp ms u pb geochronology of detrital zircons from the jining complex north china craton and its tectonic significance abstract la icp ms u pb zircon dating and cathodoluminescene cl image analysis were carried out to determine the protolith and metamorphic ages of high grade al rich gneisses named as khondalites from the jining complex of the north china craton ncc the analytical results of more than 200 detrital zircon grains from the khondalites show three main age populations 2060 ma 1940 ma and 1890 ma these data indicate that the provenance of the jining khondalites is paleoproterozoic in age but not archean as previously suggested and the sediments were derived from a provenance different from the eastern block and the yinshan terrane of the ncc the nearly concordant youngest age of 1842 16 ma 207pb 206pb age for the detrital zircons is interpreted as the maximum depositional age of the khondalites overgrowth rims of detrital zircons yield an age of 1811 23 ma which we interpret as the metamorphic age the new age data are consistent with the recent three fold tectonic subdivision of the ncc and support that the eastern and western blocks collided at 1 8 ga to form the coherent ncc

la icp ms u pb zircon ages of the qianlishan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the qianlishan complex is located in the westernmost part of the khondalite belt a continent continent collisional belt along which the yinshan block in the north and the ordos block in the south amalgamated to form the western block which then collided with the eastern block along the trans north china orogen to form the north china craton the complex is dominated by high grade supracrustal rocks and minor s type granites of which the supracrustals consist of graphite bearing sillimanite garnet gneiss garnet quartzite felsic paragneiss calc silicate rock and marble cl images reveal the existence of detrital and metamorphic zircons in major rocks of the qianlishan complex in most cases detrital zircons occur as either single grains with oscillatory zoning or oscillatory zoning cores typical of igneous origin which are surrounded by metamorphic overgrowth rims that are structureless high bright and low in th u ratio detrital zircons from the qianlishan complex yield nearly concordant 207 pb 206 pb ages ranging from 2 3 to 2 0 ga suggesting that the protoliths of the high grade supracrustal rocks in the qianlishan complex were deposited at some time after 2 0 ga metamorphic zircons yield two age populations with one at 1 95 ga and another at 1 92 ga of which the former is interpreted as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the later is considered to be the age of subsequent post orogenic extensional event minor s type granites were emplaced at 1 88 ga as a result of partial melting of supracrustals at the stage of the exhumation of the qianlishan complex these new zircon ages combined with structural and metamorphic considerations enable resolution of the tectonothermal events involving the collision between the yinshan and ordos blocks to form the western block followed by the post collisional extension and subsequent exhumation of the khondalite belt

sm nd and shrimp u pb zircon geochronology of high pressure granulites in the sanggan area north china craton timing of paleoproterozoic continental collision abstract high pressure hp mafic granulites are widely distributed as sheet like and lenticular bodies within highly deformed tonalitic gneisses in the sanggan area north china craton they have clockwise isothermal decompression and isobaric cooling p t paths implying continental collision tectonics whole rock analyses of 15 samples define a sm nd isochron yielding an age of 2547 87 ma with e nd t 2 7 corresponding nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites a combined sm nd mineral whole rock isochron from one of these samples yields an age of 1813 23 ma taken to represent the metamorphic age at an early stage on the cooling path shrimp u pb zircon analyses of three hp mafic granulite samples give uniform weighted mean 207 pb 206 pb ages of 1817 12 1817 12 and 1819 16 ma these ages are interpreted to date metamorphism of the hp granulites and with the sm nd mineral whole rock result strongly suggest that the time of continental collision was at ca 1 82 ga an additional sample records two age populations one at 1803 9 ma and an older one at 1872 16 ma the latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at 1 82 ga these results confirm the paleoproterozoic age for assembly of the north china craton

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

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

shrimp u pb zircon geochronology of the liaoji granitoids constraints on the evolution of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton abstract the paleoproterozoic jiao liao ji belt lies at the eastern margin of the eastern block of the north china craton and is composed mainly of the liaohe group and the liaoji granitoids the liaoji granitoids are divisible into pre tectonic magnetite and hornblende biotite monzogranitic gneisses and post tectonic or anorogenic porphyritic monzogranites and alkaline syenites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the paleoproterozoic jiao liao ji belt shrimp u pb zircon analyses reveal that the pre tectonic magnetite monzogranitic gneisses were emplaced in the period 2176 2166 ma and metamorphosed at 1914 ma and the pre tectonic hornblende biotite monzogranitic gneisses were emplaced at 2150 2143 ma these data demonstrate that the pre tectonic monzogranitic gneisses of the liaoji granitoids were not younger than the deposition of the liaohe group as previously considered since the latter contains a large amount of 2100 2000 ma detrital zircons in contrast the pre tectonic monzogranitic gneisses of the liaoji granitoids or similar aged granitoids may have been an important component of the provenance for the liaohe group shrimp u pb zircon analyses also reveal that the post tectonic porphyritic monzogranites and granites in the jiao liao ji belt were emplaced at 1875 10 and 1856 31 ma respectively simultaneously with the emplacement of the alkaline syenites that was dated at 1857 20 and 1843 23 ma similar post tecotnic or anorogenic granites are not only limited to the jiao liao ji belt but are also found in the north and south korea suggesting that the 1 85 ga post tectonic or anorogenic granitic magmatic event may have occurred in both the korean peninsula and the eastern block of the north china craton the shrimp zircon ages of this study combined with lithological structural metamorphic and geochemical data is consistent with a rift closure model which suggests that the archean complexes on the northern and southern sides of the jiao liao ji belt were originally situated on a single continental block that underwent paleoproterozoic rifting associated with the formation of the liaohe group and liaoji granitoids and closed upon itself at 1 9 ga

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

high pressure granulites in the sanggan area north china craton metamorphic evolution p t paths and geotectonic significance high pressure basic granulites are widely distributed as enclaves and sheet like blocks in the huaian ttg gneiss terrane in the sanggan area of the central zone of the north china craton four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles the p t conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers the low ca core of growth zoned garnet along with inclusion minerals defines a prograde assemblage m1 of garnet clinopyroxene plagioclase quartz yielding 700 c and 10 kbar the peak of metamorphism at about 750 870 c and 11 14 5 kbar m2 is defined by high ca domains in garnet interiors and inclusion minerals of clinopyroxene plagioclase and quartz kelyphites or coronas of orthopyroxene plagioclase magnetite around garnet porphyroblasts indicate garnet breakdown reactions m3 at conditions around 770 830 c and 8 5 10 5 kbar garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole plagioclase around garnet formed during the cooling process at about 500 650 c and 5 5 8 kbar m4 these results help define a sequential p t path containing prograde near isothermal decompression itd and near isobaric cooling ibc stages the clockwise hybrid itd and ibc p t paths of the hp granulites in the sanggan area imply a model of thickening followed by extension in a collisional environment furthermore the relatively high pressures 6 14 5 kbar of the four metamorphic stages and the geometry of the p t paths suggest that the hp granulites together with their host huaian ttg gneisses represent the lower plate in a crust thickened during collision the corresponding upper plate might be the tectonically overlying khondalite series which was subjected to medium to low pressure mp lp 7 4 kbar granulite facies metamorphism with a clockwise p t path including an itd segment both the hp and the mp lp granulite facies events occurred contemporaneously at c 1 90 1 85 ga in a collisional environment created by the assembly process of the north china craton

a late archean foreland fold and thrust belt in the north china craton implications for early collisional tectonics abstract the archean north china craton is divided into the western and eastern blocks along the central orogenic belt a 1600 km long archean foreland basin and thrust belt fringes the eastern side of the central orogenic belt rocks in the orogen form tectonically stacked east vergent fold and thrust sheets including foreland basin sediments 2 50 ga ophiolitic melange and an island arc complex foreland basin sediments overlie a passive margin sequence and include a 2 50 ga deep water turbidite sequence that grades upward and westward into shallow water molasse now disposed in structurally imbricated east verging thrusts and asymmetric folds that gradually migrated craton ward with deformation uplift and erosion of the orogen there is a strong linked relationship of the formation of the foreland basin to collision of the east and west blocks of the north china craton along the central orogenic belt at 2 50 ga the qinglong foreland basin and central orogenic belt of the north china craton represents one of the best preserved archean orogen to craton transitions in the world its classic internal to external zonation and flexural response to loading demonstrate that convergent tectonics in the archean were broadly similar to phanerozoic convergent margin processes

geochemical ar 40 ar 39 geochronological and sr nd isotopic constraints on the origin of paleoproterozoic mafic dikes from the southern taihang mountains and implications for the ca 1800 ma event of the north china craton abstract the wide occurrence of paleoproterozoic mafic dikes in the basement of the trans north china orogen provides important constraints on the major 1800 ma tectonothermal event of the north china craton these mafic dikes form a tholeiitic series dominated by basalts and basaltic andesites and can be geochemically classified into three groups the groups 1 and 2 rocks are characterized by high total feo contents 12 69 15 61 of which the group 1 rocks are more enriched in lile and lree contents and depleted in hfse th nb n 2 5 3 8 la yb cn 3 0 5 8 nb la n 0 27 0 38 and have more radiogenic nd isotopic ratios nd t 3 40 to 5 14 than the group 2 rocks th nb n 0 8 1 2 la yb cn 1 5 2 1 nb la n 0 65 0 87 nd t 0 60 to 1 67 in contrast the group 3 rocks are typified by low feot 7 86 11 04 and high mgo 5 62 9 56 contents higher la yb cn 4 22 7 13 ratios less radiogenic nd isotopic ratios nd t 2 75 to 5 52 and more significant th u and nb ta depletion are also apparent features 40ar 39ar geochronology of three representative samples from each group yielded plateau ages of 1780 7 0 5 ma 1765 3 1 1 ma and 1774 7 0 7 ma respectively these elemental and isotopic data suggest that the geochemical variations of these rocks cannot be simply explained by crystallization from a common parental magma involving crustal contamination during emplacement instead they most likely originated from variable sources under different degrees of partial melting the group 1 rocks were derived from relatively low degrees of partial melting of a refractory lithospheric mantle previously metasomatised by subduction related fluids whereas the group 2 rocks originated from a hybridized source involving ca 40 subduction modified lithospheric mantle similar to the group 1 and ca 60 n morb component in contrast the group 3 rocks show significant th u depletion that may mark the involvement of portions of gabbroic lower crust trapped in the source region during subduction based on all the available data we propose a tectonic model of a full subduction syncollision postcollision rifting cycle for the evolution of the ncc between 1870 and 1765 ma a variety of source regions beneath the southern taihang mountains initially developed during the period of subduction collision and subsequent extension rifting resulted in the melting of the subduction modified lithospheric mantle which produced widespread paleoproterozoic mafic dikes on the trans north china orogen in response to upwelling of convective mantle

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 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

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

zircon geochronology and metamorphic evolution of mafic dykes in the hengshan complex of northern china evidence for late palaeoproterozoic extension and subsequent high pressure metamorphism in the north china craton abstract magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the hengshan complex of the north china craton these dykes now occur as boudins and deformed sheets within migmatitic tonalitic trondhjemitic granodioritic and granitic gneisses and are conspicuous due to relics of high pressure granulite or even former eclogite facies garnet pyroxene bearing assemblages shrimp ages for magmatic zircons from two dykes reflect the time of dyke emplacement at 1915 ma whereas metamorphic zircons dated by both shrimp and evaporation techniques are consistently in the range 1848 1888 ma the youngest granitoid gneiss yet dated in the hengshan has an emplacement age of 1872 17 ma these results complement recent geochronological studies from the neighbouring wutai and fuping complexes to the se of the hengshan showing that a crustal extension event occurred in the late palaeoproterozoic this preceded a major high pressure collision type metamorphic event in the central part of the north china craton that occurred in the palaeoproterozoic and not in the late archaean as previously thought our data support recent suggestions that the north china craton experienced a major craton wide orogenic event in the late palaeoproterozoic after which it became cratonized and acted as a stable block

carbonic metamorphism at ultrahigh temperatures evidence from north china craton abstract the north china craton ncc constitutes one of the fundamental precambrian nuclei of asia the paleoproterozoic khondalite belt along the northern margin of the ncc shows evidence for extreme crustal metamorphism at temperatures exceeding 1000 c and pressures of 10 12 kbar with the formation of diagnostic ultrahigh temperature uht mineral assemblages including sapphirine quartz high alumina orthopyroxene sillimanite and high temperature mesoperthites here we record for the first time the common occurrence of co2 rich fluid inclusions in peak uht minerals in the mg al granulites of ncc and trace the fluid evolution history from microthermometric and laser raman spectroscopic studies we show that the syn metamorphic fluid in the uht rocks was pure co2 while very high density carbonic fluids are preserved in some cases corresponding to entrapment at peak conditions many of the inclusions underwent density modification during the rapid and near isothermal exhumation of the rocks following peak uht metamorphism and initial cooling at depth the present study area within the northern margin of the ncc defines a collisional orogenic belt where continental collision and deep subduction were possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusions of paleoproterozoic age that are seen emplaced within the granulite facies supracrustals the thermal anomaly displayed by the uht granulites may thus correlate with asthenospheric upwelling and emplacement of mafic magmas possibly associated with plume activity which provided the heat and co2 input to achieve extreme crustal metamorphism and generation of dry granulite facies assemblages our study is the first report of syn metamorphic co2 rich fluids in uht granulites from a paleoproterozoic ca 1 92 ga terrane and provide evidence for carbonic metamorphism at ultrahigh temperatures as north china craton joined the columbia supercontinent amalgam

a comparison of u pb and hf isotopic compositions of detrital zircons from the north and south liaohe groups constraints on the evolution of the jiao liao ji belt north china craton the jiao liao ji orogenic belt is one of the important paleoproterozoic mobile belts in the north china craton ncc and its central segment consists of the north and south liaohe groups and the liaoji granitoids the north and south liaohe groups consist of sedimentary and volcanic successions metamorphosed from greenschist to lower amphibolite facies and the liaoji granitoids are divisible into 2 2 2 1 ga pre tectonic monzogranitic gneisses and 1 88 1 85 ga post tectonic porphyritic monzogranites and alkaline syenites combined with cathodoluminescence cl imaging we report la icp ms laser ablation inductively coupled plasma mass spectrometry u pb and hf isotopic data for detrital zircons from the north and south liaohe groups zircons grains from both groups have igneous zircon cores that yielded two u pb age populations at 2 0 2 2 ga major and 2 5 ga minor indicating that their provenances were similarly dominated by paleoproterozoic liaoji granitoids and late archean basement rocks some structureless zircon rims in both groups yield concordant or upper intercept ages 1 9 ga interpreted as the peak metamorphic age of the two groups these results suggest that both groups were deposited in the period 2 0 1 9 ga shortly after the emplacement of the liaoji granitoids moreover zircons from both groups have similar hf model age peaks t c dm peaks at 2 66 2 75 ga and 2 80 3 00 ga

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

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

further evidence for 1 85 ga metamorphism in the central zone of the north china craton shrimp u pb dating of zircon from metamorphic rocks in the lushan area henan province abstract this paper reports shrimp zircon u pb dating of precambrian supracrustal and granitic rocks from the lushan area henan province in the southern portion of the central zone also referred to as the trans north china orogen of the north china craton a graphite garnet sillimanite gneiss sample tw0006 1 of the shangtaihua group gives a range of inherited zircon ages from 2 73 to 2 26 ga and a metamorphic zircon age of 1 84 0 07 ga a garnet bearing gneissic granitoid sample twj358 1 which is considered to intrude the shangtaihua group gives a magmatic zircon age of 2 14 0 02 ga and a metamorphic zircon age of 1 87 ga the metamorphic zircon ages of 1 87 1 84 ga obtained in this study indicate that an important tectonothermal event occurred at the end of the paleoproterozoic in the lushan area this supports the southern continuation of a central zone in the north china craton that workers have recently considered to result from continent continent collision it is also evident that the shangtaihua group was formed during the paleoproterozoic between 2 26 and 2 14 ga and not during the archean as previously considered