the 1 85 ga mo mineralization in the xiong er terrane china implications for metallogeny associated with assembly of the columbia supercontinent abstract the east qinling region in china hosting several tens of mesozoic magmatic hydrothermal mo deposits is one of the largest molybdenum belts in the world the recently discovered longmendian mo deposit luoning county henan province occurs within the xiong er terrane of the east qinling mo belt here the mo mineralization is confined to altered amphibolite which is replaced by microcline actinolite tremolite epidote and carbonate molybdenite is also observed in microcline dominated felsic differentiates but occurs within the altered amphibolite enclaves here we report re os isotope analyses of five molybdenite and four pyrite samples from longmendian which yield re os isochron ages of 1853 36 ma and 1855 29 ma respectively these ages are in good agreement with the metamorphic age of the taihua supergroup 1 87 1 84 ga the re os data presented in this study indicate that the period of 1 85 ga was a time of widespread melting generating leucocratic microcline dominated granitic melts the timing also coincides with the collision of the eastern and western blocks of the north china craton and its final cratonization at 1 85 ga coinciding with the incorporation of the north china craton within the paleoproterozoic supercontinent columbia

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

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

late 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

a 1 78 ga large igneous province in the north china craton the xiong er volcanic province and the north china dyke swarm abstract the 1 78 ga xiong er volcanic province xvp and coeval north china giant mafic dyke swarm ncds are the most important magmatic events occurring after the amalgamation of the north china craton ncc the xvp consists of 3 7 km of extrusive volcanics and some feeder dykes sills located along the southern margin of the ncc and extending over an area 0 06 m km2 compositions vary from basalt to rhyolite but are predominantly intermediate in terms of silica content there are also minor sedimentary intercalations and pyroclastic units the sedimentary interlayers indicate an environment changing from continental facies to oceanic facies up section the xvp is characterized by fractional crystallization from an em i type mantle source and both continental arc andean type and rift environments have been proposed the ncds is widespread in the central ncc with an outcrop area 0 1 m km2 and are exposed at variable depths up to 20 km deepest in the north dyke compositions vary from basalt to andesite and dacite but are dominantly mafic and comprise two series of magmatism previous studies revealed that the ncds recorded assimilation and fractional crystallization of an em i type magma source with a minor dm contribution in the younger magmas both syn collisional and intra continental anorogenic environments have been proposed spatial and petrogenic correlations suggest a cogenetic relationship between the ncds and xvp and considered together they define a large igneous province lip of 0 1 m km2 in area and 0 1 m km3 in volume which is also notable for its continuous compositional range from mafic to felsic with no gap at intermediate compositions the petrology is explained by a common magma source that undergoes a silica poor and iron enriched fractionation trend at depth followed by a silica rich and iron poor fractionation trend in shallow level magma conduits dykes and surface lavas a mantle plume is favored as the cause of this 1 78 ga north china lip

constraining past seawater δ18o and temperature records developed from foraminiferal geochemistry paired measurements of magnesium to calcium ratios mg ca and the stable oxygen isotopic composition 18o in foraminifera have significantly advanced our knowledge of the climate system by providing information on past temperature and seawater 18o 18osw a proxy for salinity and ice volume however multiple sources of uncertainty exist in transferring these downcore geochemical data into quantitative paleoclimate reconstructions here we develop a computational toolkit entitled paleo seawater uncertainty solver psu solver that performs bootstrap monte carlo simulations to constrain these various sources of uncertainty psu solver calculates temperature and 18osw and their respective confidence intervals using an iterative approach with user defined errors calibrations and sea level curves our probabilistic approach yields reduced uncertainty constraints compared to theoretical considerations and commonly used propagation exercises we demonstrate the applicability of psu solver for published records covering three timescales the late holocene the last deglaciation and the last glacial period we show that the influence of salinity on mg ca can considerably alter the structure and amplitude of change in the resulting reconstruction and can impact the interpretation of paleoceanographic time series we also highlight the sensitivity of the records to various inputs of sea level curves transfer functions and uncertainty constraints psu solver offers an expeditious yet rigorous approach to test the robustness of past climate variability inferred from paired mg ca 18o measurements

geological geochronological pyrite geochemical and stable isotope studies of the tantou gold deposit in central china abstract the tantou au deposit is a large scale gold deposit in the xiong ershan area a geochemical study of pyrite was conducted using laser ablation inductively coupled plasma mass spectrometry two types of hydrothermal pyrite were identified in the ores and wall rocks i e the fine euhedral pyrite in brecciated ores py1 and coarse grains disseminated in the quartz sulfide veins py2 the trace elements of the two pyrite types exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes both pyrites of the two mineralization stages were hydrothermal pyrite however the au as co ni and zn were more rich in py1 while ag cu mo sb and pb were favored in py2 the growth rims of py1 suggest several pulses of fluid activities hydrothermal sulfides from the main ore forming stage have a rb sr isochron age of 124 2 3 1 ma placing the gold mineralization in the early cretaceous the initial 87sr 86sr value of the sulfides is 0 71124 0 00010 suggesting an ancient crust source the paleoproterozoic xiong er group in situ s isotope data acquired from the main sulfides suggest that the ore forming materials underwent isotopic fractionation because of oxidation of the ore forming fluids during the hydrothermal process the c o isotope values of calcite from the postore stage indicate that magmatic fluids were likely the principle sources of carbon and that low temperature alteration has had a significant effect on the levels of co2 and carbonate ions together these results suggest that the tantou au deposit is genetically related to the destruction of the north china craton as a result of lithospheric thinning during the early cretaceous

deformation history of the paleoproterozoic liaohe assemblage in the eastern block of the north china craton the paleoproterozoic liaohe assemblage and associated liaoji granitoids represent the youngest basement in the eastern block of the north china craton various structural elements and metamorphic reaction relations indicate that the liaohe assemblage has experienced three distinct deformational events d1 to d3 and four episodes of metamorphism m1 to m4 the earliest greenschist facies event m1 is recognized in undeformed or weakly deformed domains wrapped by the s1 schistosity suggesting that m1 occurred before d1 the d1 deformation produced small mostly meter scale isoclinal and recumbent folds f1 an associated penetrative axial planar schistosity s1 a mineral stretching lineation l1 and regional scale ductile shear zones concurrent with d1 was m2 metamorphism which occurred before d2 and produced low to medium pressure amphibolite facies assemblages regionally divergent motion senses reflected by the asymmetric f1 folds and other sense of shear indicators together with the radial distribution of the l1 lineation surrounding the liaoji granitoids imply that d1 represents an extensional event the d2 deformation produced open to tight f2 folds of varying scales s2 axial crenulation cleavages and ene ne striking thrust faults involving broadly nw se compression following d2 was m3 metamorphism that led to the formation of sillimanite and cordierite in low pressure type rocks and kyanite in medium pressure rocks the last deformational event d3 formed nw wnw trending folds f3 axial planar kink bands spaced cleavages s3 and strike slip and thrust faults which deflect the earlier d1 and d2 structures d3 occurred at a shallow crustal level and was associated with or followed by a greenschist facies retrograde metamorphic event m4 the liaohe assemblage and associated liaoji granitoids are considered to have formed in a paleoproterozoic rift the late spreading of which led to the occurrence of the early extensional deformation d1 and the m1 and m2 metamorphism and the final closing of which was associated with the d2 and d3 phases of deformation and m3 and m4 metamorphism

upb zircon age and geochemical constraints on tectonic evolution of the paleozoic accretionary orogenic system in the tongbai orogen central china abstract the tongbai orogen is located in a key tectonic position linking the qinling orogen to the west and the dabie sulu orogen to the east this orogen comprises a paleozoic accretionary orogenic system in the north and a permo triassic collisional orogenic system in the south hence it may serve as an ideal place to unravel the tectonic evolution from the initial oceanic subduction accretion to the final continental collision between the sino korean and yangtze cratons u pb zircon geochronology of metasedimentary and metaigneous rocks and geochemical characterization of metabasalts indicate a close genetic relationship between the individual tectonic units of the paleozoic accretionary orogenic system 1 the kuanping group as a neoproterozoic ordovician subduction accretion complex which received sediments from the qinling microcontinent 2 the erlangping group and huanggang diorite granodiorite complex as an ordovician silurian island arc evolving from backarc basin 3 the qinling group as a precambrian microcontinent converted into continental arc during the ordovician 4 the guishan complex as a mixture of the qinling continental arc and devonian forearc sediments and 5 the nanwan flysch as a devonian forearc sequence deposited on the newly accreted active margin of the sino korean craton consequently the northern and southern boundaries of the paleozoic accretionary orogenic system represent two sutures of the qinling microcontinent with the sino korean and yangtze cratons the new and previously published data reveal that the tectonic evolution of the tongbai orogen involved a series of events from ordovician early silurian ca 490 440 ma oceanic subduction and arc magmatism silurian early devonian ca 440 400 ma arc continent collision carboniferous ca 340 310 ma oceanic subduction and accretion late permian triassic ca 260 200 ma continental subduction and collision to cretaceous ca 140 90 ma extension and lateral eastward extrusion the entire accretionary orogenic processes until the final collision between the sino korean and yangtze cratons may have lasted more than 200 ma

u pb age and hf isotopic data of detrital zircons from the devonian and carboniferous sandstones in yimin area ne china new evidences to the collision timing between the xing an and erguna blocks in eastern segment of central asian orogenic belt abstract new u pb age data and hf isotope systematics on zircons from middle devonian and lower carboniferous units from ne china provide evidence for the depositional age of these poorly constrained units as well as for the timing of the collision between the erguna ergun in some references and xing an blocks in the eastern end of central asian orogenic belt caob the detrital zircons from the devonian and carboniferous sandstones yielded similar age spectra in probability diagrams showing three distinct peaks at 450 ma 500 ma and 540 ma respectively along with proterozoic and archean age groups except for a relatively young age population at 360 ma detected for zircons from the hongshuiquan fm the dating results suggest that the depositional time of the niqiuhe fm should be younger than late silurian as indicated by the youngest 422 ma detrital zircon from this fm and that of the hongshuiguan fm with a youngest detrital age of ca 338 ma is younger than middle mississippian visean which is in accordance with those inferred from biostratigraphic data these dominant age groups are widely found in the erguna and xing an blocks it is suggested that the sediments of the studied sandstones from niuqiuhe and hongshuiquan fms come mainly from the erguna and xing an blocks the e hf t value of dated zircons from our sandstones has a wide range 21 to 16 which shows a mixed signature of that from paleozoic granitoids in xing an block 6 17 and erguna block 2 to 6 indicating that erguna and xing an blocks had connected before the middle devonian deposition of the niqiuhe fm 422 5 ma combined with the age data we suggest that the erguna and xing an blocks started to accrete at 540 ma reached the peak of collision at 500 ma and went into the post collision stage from 490 to 450 ma the study provides more evidences and constraints for the early paleozoic evolutions of the inter continental block amalgamations and accretions in caob

anatomy of zircons from an ultrahot orogen the amalgamation of the north china craton within the supercontinent columbia abstract we report shrimp u pb rare earth element hf isotope and laser raman spectroscopic data on zircons from ultrahigh temperature uht granulites from the jining complex of the khondalite belt in the western block of the north china craton ncc these uht rocks form part of an ultrahot orogen that formed along the collisional margin of the ncc associated with the tectonics of assembly of the paleoproterozoic supercontinent columbia despite the core rim textures displayed by some of the uht zircons their age values sharply converge within error yielding weighted mean 207pb 206pb ages of ca 1 92 ga indicating growth by recrystallization under extreme thermal conditions in general the zircons show moderate heavy rare earth element enrichment with sharp positive ce and negative eu anomalies the hf isotope data from the uht zircons also display a fairly uniform character with the majority of them characterized by positive ehf values without any indication of mixing between reworked crust and

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

mantle and slab contributions in arc magmas destructive plate margins are major sites of terrestrial magmatism that have long had a key role in models for the generation of continental crust and the development of chemical heterogeneities in the upper mantle in these models it is important to evaluate the nature and size of contributions from preexisting crust in the generation of magmas above subduction zones and to constrain the size of the fluxes of different elements from the subducted crust and the overlying mantle wedge in arc magmas kay 1 980 hawkesworth ellam 1 989 hawkesworth et al 1 99 1 a mcculloch gamble 1 99 1 the more mobile components of the subducted oceanic crust are the products of element fractionation processes in the upper continental crust the ocean basins and hydrothermal systems on the ocean floor they therefore have distinctive isotope and even trace element ratios that in principle should be readily distinguished from those in peridotite in the mantle wedge prior to subduction in practice however element ratios are almost certainly fractionated during shallow level dehydration of sub ducted material and at greater depths where material from the slab appears to contribute in the generation of arc magmas moreover the isotope signal of slab derived material may be heavily diluted by exchange with

geochronology geochemistry and petrogenesis of the late palaeoproterozoic a type granites from the dunhuang block se tarim craton china implications for the break up of the columbia supercontinent the discovery of c 1 77 ga a type granite in the tarim craton tc provides the first evidence that supports an extensional event related to fragmentation of the columbia supercontinent in the late palaeoproterozoic we present laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages lu hf isotopic data and the whole rock geochemical and nd isotopic data of a type granites in the dunhuang area in the se tarim craton zircon u pb dating for three granite samples indicate that they were emplaced at c 1 77 ga zircons from these granites have e hf t values ranging from 5 9 to 8 7 corresponding to two stage model ages of 1 9 2 7 ga these granites exhibit the following petrological geochemical characteristics that are typical of a type granite a high content of sio 2 and alkalis i e high k 2 o na 2 o with k 2 o na 2 o 1 enrichment of high field strength elements hfse and rare earth elements ree except for eu and extreme depletion of ba sr p ti and eu b 10000 ga al ratios in the dunhuang granites of 3 5 4 4 with an average value of 3 79 which is similar to the global average of 3 75 for a type granites c the presence of characteristic minerals such as amphibole sphene and perthite and d zirconium saturation temperature results indicate that the dunhuang granites have high initial magmatic temperatures in the range 887 950 c similar to those of typical of a type granites whole rock e nd t values range from 2 5 to 6 2 and t dm model ages from 2 3 to 2 7 ga nd hf isotopic and whole rock geochemical data indicate that these granites were most likely derived from the late archean crustal source in a post collisional post orogenic extensional tectonic environment the late palaeoproterozoic a type granites in the tc could be correlated with those of the north china craton ncc india and the canadian shield thus demonstrating extensional tectonics and break up of the columbia supercontinent

tectono sedimentary evolution of the mesoproterozoic basins in the southern yan liao and mianchi queshan areas insights from stratigraphic pattern and detrital zircon geochronology the widespread mesoproterozoic successions around the world have recorded the breakup of the ancient supercontinent columbia in the north china craton ncc the mesoproterozoic basins in the yan liao and southern ncc are the important evidence to study the nature and evolution of the mesoproterozoic basins in this study we scrutinized the stratigraphic pattern and detrital zircon u pb geochronology in the southern yan liao and mianchi queshan areas in the southern ncc to investigate the evolutionary relationship between the mesoproterozoic basins in the north and south of ncc detrital zircons from the mesoproterozoic sequence in the southern yan liao areas showed monotonous source with age peak at ca 2500 ma corresponding well with the ages of the neoarchean complex in the central ncc however the mesoproterozoic sequence in the mianchi queshan areas which is represented by the ruyang group exhibited significantly different characteristics with influx of much younger zircons the southern yan liao and mianchi queshan areas showed distinct similarity in the stratigraphic pattern reflected by the mesoproterozoic successions in these two areas being both bracketed by two sequence boundaries and further divided into two sequences under a uniform sea level change the mesoproterozoic strata in these two areas probably possessed a correlative relationship in the stratigraphic patterns and basin evolutionary history

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

detrital zircon u pb dating hf isotopes and whole rock geochemistry from the songshan group in the dengfeng complex constraints on the tectonic evolution of the trans north china orogen abstract the dengfeng taihua and zhongtiao complexes are located in the southernmost segment of the trans north china orogen along which the western and eastern blocks amalgamated to form the north china craton the dengfeng complex consists of the neoarchean granitoids and supracrustal rocks of which the latter are subdivided into the dengfeng and songshan groups the songshan group consists of basal conglomerates quartzites schists with minor dolomites and phyllites geochemistry of the songshan schists and quartzites are indicative of felsic source rocks and display continental island arc and passive continental margin signatures respectively u pb ages of detrital zircons from the songshan group yielded three age populations of 3700 3100 ma 3000 2550 ma and 2550 1950 ma the dominant 3000 2550 ma detrital zircons were most likely sourced from the ttg gneisses of the dengfeng and taihua complexes the subordinate 2550 1950 ma detrital zircons were probably derived from the paleoproterozoic granitoid plutons and meta rhyolites in the dengfeng and zhongtiao complexes and minor amounts of 3700 3100 ma detrital zircons may have been derived from the paleoarchean and mesoarchean crust of the eastern block the youngest detrital zircon age peaks in the luohandong and wuzhiling formations constrain their maximum depositional ages at 2350 ma and 1960 ma respectively in combination with the 1775 ma undeformed granitoids that cut the songshan group the depositional age of the songshan group can be constrained in the period between 2350 and 1780 ma considering the lithostratigraphic feature provenance and depositional age the songshan group is interpreted as having deposited in a retroarc foreland basin which is consistent with the model that the collision between the eastern and western blocks to form the trans north china orogen occurred at 1 85 ga after long lived subduction

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

development of the north china craton during the late archaean and its final amalgamation at 1 8 ga some speculations on its position within a global palaeoproterozoic supercontinent abstract new data obtained over the past few years indicate that by the end of the archaean the north china craton consisted of two major crustal entities identified as the eastern and western blocks the formation of island and magmatic arcs along the western margin of the eastern block record the latest archaean events so far identified the location of the western block at this time is unknown however the occurrence of palaeoproterozoic passive margin sediments similar in age to those occurring in the eastern block indicates essentially similar conditions and possible separation by an ocean of unknown dimensions re initiation of east dipping subduction beneath the western margin of the eastern block resulted in closure of this palaeoproterozoic ocean bringing the western block into close proximity continued subduction resulted in a major continental continental collision and the western margin of the eastern block was again reactivated leading to extensive thrusting high pressure metamorphism and the generation of crustal melts this occurred between 1 88 and 1 79 ga ago resulting in the formation of the trans north china orogen and final amalgamation of the north china craton although information is sparse to non existent we have reviewed the possible location of the north china craton at the time of collision and note a similarity in terms of age lithology and distribution of major crustal components between the north china craton and baltica although speculative we present this model in the hope that it will stimulate debate and lead to further research in these areas

mesoproterozoic ophiolitic melange from the se periphery of the indian plate u pb zircon ages and tectonic implications abstract the kanigiri melange within the proterozoic nellore khammam schist belt in southern peninsular india includes ophiolitic fragments that represent the remnants of an oceanic plate the ophiolitic units were accreted along a ne trending suture that juxtaposes the proterozoic eastern ghats granulite belt eggb against the archean nellore schist belt of the dharwar craton the ophiolite components in the kanigiri melange include plagiogranites and gabbros which show mutually intrusive relations indicating their coeval nature we report laser ablation icp ms age data and ree geochemistry of zircons from the gabbro and granite the zircons from both gabbro and granite show high ree contents prominent hree enrichment and a conspicuous negative eu anomaly suggesting a common melt source zircon ree abundances and normalized patterns show little intersample and intrasample variations u pb dating of the zircons reveals prominent mesoproterozoic ages for the plagiogranite with the ca 1 33 ga age of the kanigiri ophiolitic melange offering important clues for arc continent collision during the final stages of amalgamation of the columbia derived fragments within the neoproterozoic supercontinent assembly

crustal growth in the north china craton at 2 5ga evidence from in situ zircon u pb ages hf isotopes and whole rock geochemistry of the dengfeng complex abstract the dengfeng complex is located on the southern margin of the north china craton ncc and belongs to the southern portion of the trans north china orogen this terrane is important to understand the formation and evolution of ncc during late neoarchean 2 5 ga the dengfeng complex is well exposed in the junzhao region and comprises two distinct lithologic units supracrustal assemblage and plutonic rocks la icpms magmatic zircon u pb age data shows that the rocks formed within the range of 2547 2504 ma the available hf isotope data indicate that the majority of ca 2 5 ga zircons from the dengfeng complex have high e hf t values close to the initial hf isotope ratios of the contemporaneous depleted mantle these data indicate that the rocks in the dengfeng represent juvenile crust the ttg gneisses in the dengfeng complex display low mg 41 48 mgo 59 69 mgo 3 5 6 6 wt ni 82 130 ppm and cr 148 237 ppm abundances elevated sr 1759 1927 ppm and ba 1742 2289 ppm concentrations and high lree la n 38 487 such geochemical features are similar to archean sanukitoids a two stage model is applied here to explain the genesis of metadiorites of dengfeng complex 1 firstly the mantle is metasomatized either by melts or by aqueous fluids from a subducted slab 2 subsequently sanukitoid magmas were produced by partial melting of the hybridized mantle furthermore the amphibolites of supracrustal rocks have a mixture of morb and arc like geochemical affinities suggesting the development of a back arc in the southern ncc at ca 2 5 ga the contemporary late neoarchean ttgs sanukitoids and morb back arc association may represent a late neoarchean tectonic melange implying a neoarchean subduction accretion process which would suggest that modern style plate tectonics processes was probably initiated in the southern ncc by 2 5 ga

crustal evolution of the north qinling terrain of the qinling orogen china evidence from detrital zircon u pb ages and hf isotopic composition abstract the north qinling terrain reveals a different geological history from the north china block to the north and the south qinling micro continental block to the south the timing of events and geochemical features of the north qinling terrain are essential for understanding the evolution of the qinling orogenic belt that joins the north and south china blocks this study presents detrital zircon ages and hf isotopic compositions from the guandaokou group a cover sequence of the north china block and from the kuanping group an upper basement sequence of the north qinling terrain the youngest detrital zircon u pb ages constrain the initiation of sedimentation in the guandaokou group to 1 85 ga and the maximum depositional age of the kuanping group to 640 ma zircon u pb ages and hf data testify to a major phase of magmatism in the north qinling terrain at 1000 900 ma the magmatic rocks were largely produced from reworking of early paleoproterozoic 2 5 2 0 ga crust with minor contribution of late paleoproterozoic 1 7 ga juvenile material this age record differs in time from the two important thermal events of 1 85 ga and 2 5 ga widely manifested in the north china block the north qinling terrain can thus be regarded as a separate micro continent with a pre neoproterozoic evolution different from that of the north china block the final assembly of the north qinling terrain to the north china block took place after about 640 ma

zircon u pb chronology hf isotope analysis and whole rock geochemistry for the neoarchean paleoproterozoic yudongzi complex northwestern margin of the yangtze craton china abstract the archean paleoproterozoic high grade basement of yudongzi complex is a key to understanding the early precambrian crustal evolution of the yangtze craton it comprises mainly orthogneiss paragneiss and amphibolite whose protoliths are tonalitic trondhjemitic granitic ttg sedimentary and basic intermediate volcanic rocks respectively the ttg gneiss amphibole plagiogneiss and biotite plagiogneiss yield magmatic zircon la icp ms u pb ages of 2815 18 ma mswd 0 92 2692 26 ma mswd 0 59 and 2449 4 ma mswd 0 94 respectively metamorphic overgrowths on zircon from amphibolite have an age of 1848 5 ma mswd 0 71 ttg gneisses show medium sr y and variable high la yb n ratios with low y and yb contents they are characterized by positive eu anomaly and distinct depletion of hree together with negative nb ta and ti implying amphibole garnet and minor rutile as residual phases their positive e hf t values of 2 1 to 8 1 with t dm2 of ca 2 80 3 10 ga suggest significant reworking of juvenile crust amphibole plagiogneisses display a strong enrichment of lrees and depletion of nb ta and ti additionally a relative enrichment of ba rb pb and zr as well as high cr and ni contents and mg values imply a mantle source with the addition of continental crust material zircon e hf t values vary between 0 9 and 3 9 suggesting a proportionally significant input of juvenile material and therefore interaction between the mantle and pre existing continental crust biotite plagiogneisses show negative e hf t values between 3 4 and 0 1 with a few positive e hf t values ranging from 0 1 to 1 5 together with t dm2 ages of ca 2 80 3 00 ga these e hf t values suggest that these rocks were mainly generated by reworking of ancient crust thus the yudongzi complex exposed in the northern part of the yangtze craton has experienced significant reworking of juvenile crust at ca 2 80 ga and subsequent crustal growth at ca 2 70 ga followed by a second stage of reworking of ancient crust at ca 2 45 ga during the late paleoproterozoic the yudongzi complex was probably involved in the amalgamation of the paleoproterozoic supercontinent columbia and affected by a post collisional metamorphic event at ca 1 85 ga

pb sr nd isotope constraints on the fluid source of the dahu au mo deposit in qinling orogen central china and implication for triassic tectonic setting abstract the dahu au mo deposit is a structure controlled lode system occurring in the northern xiaoqinling terrane huaxiong block qinling orogen this paper reports a new sr nd pb isotope dataset obtained for ore sulfides and the hostrocks within the taihua supergroup in an attempt to constrain the source of the ore forming fluids from a new dimension 16 sulfide samples yield i sr ratios of 0 70470 0 71312 with an average of 0 70854 e nd t values between 13 5 and 18 1 with average of 15 1 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios of 17 033 17 285 15 358 15 438 and 37 307 37 582 with averages of 17 162 15 405 and 37 440 respectively 5 gneiss samples from the taihua supergroup yield i sr ratios of 0 70947 0 73201 averaging 0 72294 e nd t values of 20 0 to 31 1 averaging 25 1 and 206 pb 204 pb i 207 pb 204 pb i 208 pb 204 pb i ratios of 17 127 18 392 15 416 15 604 and 37 498 37 814 with averages of 17 547 15 470 and 37 616 respectively these data show that the ore sulfides have less radiogenic sr nd pb isotope systematics than the hostrocks and suggest that the ore forming fluids which interacted with the wallrocks to form ores must be sourced from a depleted mantle or a depleted subducted oceanic slab in combination with the spatial scenario and geochemical signatures of the triassic magmatites and mineral systems we argue that in the triassic the mianlue ocean was not completely closed and that the northward oceanic plate subduction still survived along the mian lue suture which caused the late triassic magmatism and associated mineralization in qinling orogen including the au mo dahu deposit

geochemical and isotopic study of the xiong er volcanic rocks at the southern margin of the north china craton petrogenesis and tectonic implications abstract the xiong er volcanic rocks constitute a large paleo mesoproterozoic volcanic belt along the southern margin of the north china craton the volcanic rocks can be petrographically and geochemically classified into the basaltic andesite andesite and dacite rhyolite series with the former being the dominant component of the xiong er volcanic rocks the volcanic rocks of the dacite rhyolite series have been derived from the wet and low temperature differentiation of the basaltic andesite andesite series at shallow depth suggested by regional geological lithological and geochemical studies in addition crustal assimilation was involved in the magmas to form volcanic rocks of the dacite rhyolite series as suggested by low nd t values 8 09 to 9 99 and high th yb ratios 1 7 2 7 some of volcanic rocks from the basaltic andesite andesite series show features of high mg andesites hma being characterized by high mgo contents and mg numbers representing the most primitive end member of the

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

paleomagnetism of ca 1 35ga sills in northern north china craton and implications for paleogeographic reconstruction of the mesoproterozoic supercontinent abstract we report paleomagnetic data on precisely dated mesoproterozoic sills in zircon and baddeleyite 207pb 206pb ages of 1345 12 and 1353 14 ma respectively intruding the xiamaling and wumishan formations in north china with an aim of evaluating how the north china craton ncc was involved in the evolution of the columbia supercontinent from ca 1 78 to 1 35 ga after systematic thermal demagnetization we isolate a high temperature characteristic remanence from 18 sites with a tilt corrected site mean direction of d 294 4 i 31 7 and 95 4 3 corresponding to a mean paleomagnetic pole at 5 9 n 359 6 e n 18 with angular standard deviation of 10 0 and a95 4 3 rock magnetic experiments light microscopy and scanning electron microscopy all indicate that the main magnetic minerals in the sampled sill rocks are medium sized titanomagnetites the positive fold test and fresh titanomagnetite grains suggest that the characteristic remanence is likely to be a primary acquired at ca 1 35 ga the preliminary paleogeography reconstruction based upon the well matched apparent polar wander paths between the laurentia baltica siberia united block and the ncc supports the interpretation that the ncc may have drifted together with this united block before ca 1 35 ga during the late history of the columbia supercontinent we argue that the ncc was located in low latitudes and kept tight connections with the siberian and indian cratons during the interval between ca 1 8 and 1 35 ga and that the ca 1 35 ga sills widely developed in the mesoproterozoic xiamaling and wumishan formations as well as the ca 1 3 1 2 ga magma events well developed in siberia and northern margin of the ncc may represent the complete fragmentation of the ncc with the neighboring cratons

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

geochemistry isotope systematics and petrogenesis of the volcanic rocks in the zhongtiao mountain an alternative interpretation for the evolution of the southern margin of the north china craton abstract the xiong er volcanic rocks constitute a large paleo mesoproterozoic volcanic belt along the southern margin of the north china craton which are composed primarily of basaltic andesites and andesites with minor dacites and dacitic rhyolites the basaltic andesites and andesites from the xiong er volcanic rocks in the zhongtiao mountain show consistent nd t la nb and th nb values irrespectively of sio 2 which preclude significant crustal contamination during ascent both of these volcanic rocks share similar incompatible ratios e g la sm zr nb la nb indicating that the basaltic andesites and andesites originated from the same source the basaltic andesites are characterized by high mg number 45 55 precluding the possibility of their derivation from the melting of the lower crust variable ti eu zr sm and nb la ratios for the basaltic andesites with higher partial melting degree suggest that amphiboles remained as residues in the magma source indicating that the xiong er volcanic rocks were derived from hydrous magma non radiogenic nd isotopes for the xiong er volcanic rocks are inherited from a mantle source which had been enriched by the subduction related crustal recycling during archean to paleoproterozoic time basaltic andesites show hfse enrichments especially nb 4 7 ppm and high fe ti contents comparable with nb enriched basalts suggesting that the xiong er volcanic rocks were derived from a metasomatized mantle source similar to that of nb enriched basalts therefore the mantle source of the xiong er volcanic rocks in the zhongtiao mountain has been enriched in fe ti oxides and hfse by equilibrium reactions with the slab melts during late archean and paleoproterozoic subduction processes as evidenced by nd isotopes in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative anomalies on the nb ta ti similar to arc related volcanic rocks produced by the hydrous melting of the metasomatized mantle wedge in the paleo mesoproterozoic the xiong er volcanic rocks in the zhongtiao mountain were produced by the slab dehydration induced melting of an existing metasomatized mantle source and the fluids from the slab dehydration introduced significant lile and lree to the source masking its inherent hfse enriched characteristics the arc related characteristics of the xiong er volcanic rocks in the zhongtiao mountain suggest the xiong er volcanic belt constructs a subduction zone along the southern margin of the north china craton in the paleo mesoproterozoic implying that the craton may have recorded the outbuilding history of the columbia supercontinent during paleo mesoproterozoic time

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

early mesozoic mo mineralization in the qinling orogen an overview abstract as one of the most important mo provinces in the world the qinling orogen is host to mainly late mesozoic late jurassic early cretaceous porphyry mo systems recently additional early mesozoic mainly triassic plus minor early jurassic mo deposits have been identified which occur as fault controlled quartz veins or as carbonatite veins and as such they are fundamentally different from the commonly observed porphyry systems furthermore early mesozoic porphyry systems are also present but they are different from those of late mesozoic age thus early mesozoic mo systems not only offer a new and comprehensive view of the mo metallogenesis but also provide unique insight into the tectonic evolution of the qinling orogen taking into consideration the role of mineral deposits as ideal probes of the geodynamic evolution the known early mesozoic mo deposits in qinling can be classified into three types based on their geological and geochemical features porphyry carbonatite and orogenic systems porphyry mo systems including porphyry porphyry skarn and intrusion related veins are spatially and genetically associated with granitic porphyries they display typical porphyry type alterations and are formed by magmatic water carbonatites are considered as mantle derived igneous rocks and mo mineralization is associated with magmatic fluids orogenic mo systems occur as fault controlled quartz lodes and the ore forming fluids are medium high temperature co2 rich metamorphic fluids spatially early mesozoic porphyry mo systems are concentrated in the western and middle part of the qinling orogen whereas carbonatite veins and orogenic mo systems are located in the northeastern part temporally orogenic mo deposits were the earliest mainly between 220 and 250 ma followed by carbonatite veins mainly between 205 and 225 ma and porphyry mo systems mainly between 190 and 205 ma with some exceptions there is generally a trend of decreasing deposit ages toward the western part of the orogen detailed comparison reveals that the early mesozoic porphyry mo systems in the qinling orogen are different from the late mesozoic ones in terms of their economic importance spatial distribution ore causative intrusions hydrothermal alteration and the ore forming fluids to explain the above geological and geochemical features the triassic qinling is considered as an active continental margin caused by the northward subduction of the mian lue oceanic plate a transition from continental arc to back arc basin is suggested for the formation of triassic orogenic and carbonatite vein mo deposits whereas continental arc is host to the early mesozoic porphyry mo systems

geology geochemistry and ore genesis of the wenyu gold deposit xiaoqinling gold field qinling orogen southern margin of north china craton abstract the wenyu giant gold deposit is hosted in the precambrian taihua supergroup metamorphic rocks within the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided into three stages quartz pyrite veins early quartz sulfide veins middle main and carbonate quartz veinlets late with gold being mainly introduced in main stage quartz formed in two earlier stages contains three compositional types of fluid inclusions i e pure co2 co2 h2o and nacl h2o but the late stage minerals only contain the nacl h2o inclusions the inclusions in quartz formed in the early main and late stages yield total homogenization temperatures of 262 417 c 236 407 c and 114 239 c respectively with salinities no higher than 13 wt nacl equiv trapping pressures estimated from co2 h2o inclusions are 139 399 mpa and 111 316 mpa in the early and main stages corresponding to mineralization depths of 14 km and 11 km respectively fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co2 rich to co2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18owater values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology fluid inclusion and c h o s pb isotope geochemistry we conclude that the wenyu gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

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

two episodes of ree mineralization in the qinling orogenic belt central china in situ u th pb dating of bastnasite and monazite recent exploration revealed a number of rare earth element ree deposits that are distributed along the qinling orogenic belt central china these deposits have an estimated total reserve of about 2 mt ree2o3 thus making this belt a world class ree metallogenic province understanding the metallogenesis of the belt requires direct dating of ree minerals in this study la icp ms u th pb dating on bastnasite and monazite from the huangshuian taipingzhen and miaoya deposits in different units of the belt was used to precisely determine the timing of the ree mineralization the huangshuian deposit in the north is a carbonatite related mo ree deposit in which the ree minerals are closely associated with molybdenite after correction for common pb and excessed 206pb decayed from 230th a weighted average 206pb 238u age of 207 4 ma n 17 mswd 1 9 is obtained for bastnasite grains from this deposit such an age is slightly younger than that of the final collision peak at 230 220 ma of the qinling orogenic belt thus indicating that the mo ree mineralization is likely related to a post collisional extension setting the taipingzhen ree deposit in the middle contains sheet like ore bodies composed of veins where bastnasite the dominant ree mineral is closely associated with quartz fluorite and barite in situ bastnasite u th pb dating shows that the ree mineralization in this deposit has formed at 421 7 ma n 17 mswd 1 5 synchronous with extension related magmatism in the region the miaoya deposit in the south is the largest one in the belt and it is essentially a ree mineralized syenite carbonatite complex in this deposit the monazite grains are closely associated with major minerals of the syenites or carbonatites e g k feldspar or calcite but commonly exhibit complex internal textures different domains of monazite yield two groups of u pb ages at 414 11 ma n 5 mswd 0 91 and 231 2 ma n 21 mswd 3 1 whereas the bastnasite has an age of 206 4 ma n 14 mswd 1 5 the early age of 414 ma is obtained from homogenous monazite grains and in good agreement with zircon u pb ages of the miaoya syenite carbonatite complex and thus is considered to represent the timing of the major ree mineralization in the deposit the younger ages of 231 206 ma are obtained from monazite grains with complex internal textures and bastnasite in late veinlets thus recording secondary consecutive ree remobilization events likely related to the compression process during formation of the qinling orogenic belt our new u th pb ages in combination with previously geochronological data demonstrate that there are two episodes of ree mineralization at 440 410 ma and 220 200 ma in the qinling orogenic belt

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

are the south and north liaohe groups of north china craton different exotic terranes nd isotope constraints abstract the liaohe group is an important paleoproterozoic stratigraphic unit in the northeastern part of the north china craton and is traditionally subdivided into the north and south liaohe groups associated with both the north and south liaohe groups are voluminous paleoproterozoic granitoid rocks named the liaoji granitoids different tectonic models including terrane amalgamation continent arc collision and rift closure have been proposed to interpret the tectonic setting and evolution of the north and south liaohe groups and associated liaoji granitoids at the centre of the controversy between these models is whether or not the north and south liaohe groups developed on the same archean basement nd isotopic geochemistry of the liaoji granitoids provides important constraints on this controversial issue the liaoji granitoids associated with the north and south liaohe groups display similar e nd values restricted to a narrow range from 0 to 2 implying that these granitoid rocks were derived from the same or a similar magma source moreover the liaoji granitoids associated with the north and south liaohe groups have similar nd model ages t dm ranging from 2 4 to 2 6 ga suggesting that the protoliths of the liaoji granitoids associated with both groups may have formed simultaneously and that the basement rocks underneath the liaoji granitoids and associated north and south liaohe groups belong to the same continental block rather than two different blocks combining lithological structural and geochronological considerations we interpret the north and south liaohe groups as having developed on a single late archean basement that underwent paleoproterozoic rifting associated with the intrusion of the liaoji granitoids and the formation of the liaohe group and closed upon itself in the paleoproterozoic

petrogenesis and tectonic setting of volcanic rocks in the xiaoshan and waifangshan areas along the southern margin of the north china craton constraints from bulk rock geochemistry and sr nd isotopic composition abstract as part of the xiong er volcanic belt along the southern margin of the north china craton volcanic rocks in the xiaoshan and waifangshan areas have a compositional range from the basaltic andesite andesite dacite to rhyolite which display consistent variation trends in terms of their major and trace elements and sr nd isotopic compositions the variable yb contents with nearly constant la yb and tb yb ratios of volcanic rocks in two areas suggest that the fractional crystallization may have played an important role in the differentiation from the basaltic andesite through andesite and dacite to rhyolite the volcanic rocks in these two areas are characterized by the lile and lree enrichments and negative hfse anomalies implying hydrous melting of a mantle wedge in a subduction zone variable sr nd ratios of the basaltic andesite and andesite are interpreted as a result of the fluid addition from a subducting slab non radiogenic nd isotopic compositions as well as high zr y and nb y ratios suggest that the volcanic rocks in these areas were derived from an enriched mantle source on the other hand the volcanic rocks of the basaltic andesite and andesite possess markedly higher fe ti and hfse concentrations than those of typical intra oceanic arcs implying that the mantle source from which the volcanic rocks were derived was metasomatised by siliceous melts during the archean to paleoproterozoic subduction collision in the trans north china orogen these data suggest that in the paleo mesoproterozoic the southern margin of the north china craton was most likely an andean type continental arc in which slab dehydration not only induced the melting of a pre existing metasomatised mantle source but also released lile enriched fluids into the mantle source masking the inherent hfse enriched characteristics of the volcanic rocks along the southern margin of the craton the results of this study indicate that the north china craton like many other continental components e g north america greenland baltica amazonia australia etc of the supercontinent columbia nuna also underwent a subduction related outgrowth along its southern margin during the paleo mesoproterozoic time

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

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

high field strength element ratios in archean basalts a window to evolving sources of mantle plumes abstract in terms of high field strength element ratios nb th zr nb nb y and zr y most basalts from non arc type archean greenstones are similar to oceanic plateau basalts suggestive of mantle plume sources a large number of these basalts have ratios similar to primitive mantle composition perhaps the archean mantle was less fractionated than at present and primitive mantle comprised much of the deep mantle and made a significant contribution to mantle plumes the near absence of archean greenstone basalts similar to nmorb in composition is also consistent with a relatively unfractionated mantle in which a shallow depleted source dm was volumetrically insignificant the element ratios in basalts also indicate the existence of recycled components himu em1 em2 in the mantle by the late archean this suggests that oceanic lithosphere was recycled into the deep mantle and became incorporated in some mantle plumes by the late archean high field strength element ratios also indicate an important contribution of continental crust or and subcontinental lithosphere to some non arc archean greenstone basalts this implies that at least thin continental lithosphere was relatively widespread in the archean

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

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

possible southwestward extrusion of the ordos block in the late paleoproterozoic constraints from kinematic and geochronologic analysis of peripheral ductile shear zones abstract the paleoproterozoic is a pivotal period of the tectonic evolution of the north china craton ncc various models have been postulated by previous researchers through the study of petrology and metamorphism but the lack of structural analyses has hampered further understanding of the tectonic evolution of the ncc a series of well exposed ductile shear zones developed on the northern northwestern and eastern edges of the ordos block in the western part of the ncc we carried out detailed field studies along with isotopic dating focused on the kinematics and geochronology of the ductile shear zones on the north margin of the ordos block the wulashan daqingshan ductile shear zone is characterized by an e w trending shearing foliation that steeply dips 75 80 to the north or south with subhorizontal stretching lineation plunging 10 15 toward the east or west and dextral strike slip shearing kinematics on the west margin of the ordos block is the zongbieli ductile shear zone with top to the nw thrusting kinematics on the east margin of the ordos block is the xueling ductile shear zone with top to the se thrusting accompanied by sinistral strike slip shearing kinematics the 40ar 39ar ages of deformed minerals from mylonitic high grade metamorphic rocks and la icp ms u pb dating results of zircons from syn tectonic anatectic granites reflect that the ductile shear zones surrounding the ordos block deformed between 1 85 and 1 81 ga the similar deformation ages indicate that the ductile shear zones might be genetically correlated the geometry kinematics and geochronology characteristics of the wulashan daqingshan ductile shear zone on the north margin the zongbieli ductile shear zone on the west margin and the xueling ductile shear zone combined with the zhujiafang sinistral ductile shear zone on the east margin defined the possible southwestward extrusion of the ordos block in the late paleoproterozoic which might have resulted from the westward subduction collision of the eastern block under the western block at approximately 1 85 ga and which is correlated with the amalgamation of the columbia supercontinent

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

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

u pb dating of baddeleyite and zircon from the shizhaigou diorite in the southern margin of north china craton constrains on the timing and tectonic setting of the paleoproterozoic xiong er group abstract the xiong er volcanism marks an important thermal event in the southern margin of the north china craton during the paleoproterozoic precise u pb ages of zircon and baddeleyite from the shizhaigou diorite which intruded the majiahe formation of the upper part of the xiong er group were determined in this study by multi collector sims the mean 207 pb 206 pb ages are 1789 3 5 ma for baddeleyite and 1780 11 ma for zircon from shizhaigou diorite respectively the major and trace elements and sr nd isotopic compositions indicate an em i mantle type signature and crustal contamination features combining with previous chronological data it is proposed that the age of the xiong er volcanism is between 1770 ma and 1800 ma with a peak at 1780 ma our result supports the view that the xiong er volcanic rocks formed in an extensional rift environment

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

u pb and hf isotopic study of detrital zircons from the wulashan khondalites constraints on the evolution of the ordos terrane western block of the north china craton abstract detrital zircons from the wulashan khondalites in the ordos terrane western block of the north china craton give u pb ages between 1 84 and 2 32 ga showing that their provenance was dominated by paleoproterozoic rocks much younger than those exposed in the eastern block these zircons have oscillatory growth zoning and possess e hf values between 8 and 9 suggesting derivation of their precursor magmas from old crust and juvenile materials from the mantle the lowest e hf values of zircons with different ages give a line that intersects the depleted mantle line at about 2 6 ga in a e hf vs time diagram this may imply that the precursor magma source in the deep level of the crust was largely separated from the mantle 2 6 ga ago and therefore 2 6 ga may be an important crustal formation period for the terrane one khondalite sample has detrital zircons with a single age population at 2 0 ga and positive e hf values from 1 to 9 clearly recording the significant addition of juvenile materials at 2 0 ga in the source region this may inspire us to seek whether there was a connection between a mantle superevent and the formation of columbia supercontinent data of this study exclusively demonstrate that the ordos terrane was developed independently from the eastern block until assembly of the columbia supercontinent therefore tectonic models involving that the whole north china craton was cratonized 2 5 ga ago should be dismissed

origin of the late paleoproterozoic low δ18o a type granites on the southern margin of the north china craton and their geodynamic mechanism abstract a type granites with 18o depletion signatures are rather enigmatic as regards not only their typology and petrogenesis but also their rock forming geodynamic mechanism here we report a suite of late paleoproterozoic low 18o a type granites from the longwangzhuang pluton on the southern margin of the north china craton sims zircon u pb dating showed that the longwangzhuang pluton was emplaced at 1613 4 ma combined with previous data it is clear that the mineral components of longwangzhuang granites are variable and consist of perthite quartz plagioclase biotite and amphibole calcic hastingsite ferroedenite and sodic ferrogedrite geochemically they are metaluminous to peraluminous and have high alkali contents k2o na2o 8 76 wt k2o na2o 1 feot feot mgo 0 95 ratios zr nb ce y 993 ppm contents and 10000 ga al 4 31 ratios resembling a type granites in situ oxygen isotope analysis displayed low zircon 18o values between 4 0 and 4 9 with a weighted average of 4 4 based on the archean two stage zircon hf and whole rock nd model ages coupled with the low la yb cn ratios negative anomalies of eu and sr and high zr saturation temperatures and the presence of low pressures 3 3 5 7 kbar amphiboles the longwangzhuang a type granites were generated by self cannibalizing pre existing low 18o old rocks i e the taihua complex and emplaced at shallow depth combined with regional geological observations i e coeval tuffites a passive rift setting was the most plausible explanation for the generation of the late paleoproterozoic low 18o a type granites on the southern margin of the north china craton such a rifting could likely have lasted at least till 1 6 ga

shrimp u pb and cameca 1280 oxygen isotope results from ancient detrital zircons in the caozhuang quartzite eastern hebei north china craton evidence for crustal reworking 3 8 ga ago the caozhuang quartzite located in eastern hebei province in the eastern part of the north china craton has long been known to contain the oldest detrital zircon population in china a suite of 30 zircons with preliminary ages 3 7 ga were selected for detailed shrimp u pb and cameca 1280 oxygen isotope analyses shrimp u pb dating reveals that ages range from 3860 to 3135 ma the former being the oldest 207 pb 206 pb zircon age so far obtained from the north china craton values of 18 o range from 5 4 to 7 5 permil similar to archean igneous zircons worldwide but the average value for the 30 zircons is 6 6 permil which is 0 3 permil higher than suite averages for detrital zircons from the jack hills and beartooth mountains and nearly 1 permil higher than magmatic zircons from igneous rocks of the superior province and barberton these elevated values of 18 o suggest reworking of a significant amount of juvenile crust older than 3 8 ga that underwent a low temperature supracrustal history and was distributed throughout the source region in northeast china

reconstruction and interpretation of giant mafic dyke swarms a case study of 1 78 ga magmatism in the north china craton

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

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

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

the late paleoproterozoic i and a type granites in luliang complex north china craton new evidence on post collisional extension of trans north china orogen abstract the late paleoproterozoic granitoids from luliang complex can provide pivotal constraints on the amalgamation process between eastern and western blocks of north china craton along the trans north china orogen la icp ms zircon dating gives emplacement ages of 1854 20 ma for the huijiazhuang granite 1830 21 ma for the xiyupi granite vein and 1760 20 ma for the dacaoping porphyritic granite respectively the huijiazhuang granite and xiyupi granite dyke have variable sio2 66 71 74 31 wt high k2o 5 09 6 35 wt low p2o5 0 02 0 16 wt al2o3 13 92 15 31 wt right inclined ree patterns with medium negative eu anomalies enrichment in lile depletion in hfse especially nb ta consisting to high k i type granite in a post collisional setting the sr y 7 36 59 95 end t 5 7 to 4 1 with tdm 2381 ma to 2570 ma from whole rock sm nd isotope and ehf t 9 6 to 2 3 with tcdm 2360 ma to 3070 ma from zircon lu hf isotope suggest that they are produced by partial melting of slightly thickened neoarchean paleoproterozoic basement materials including both meta sedimentary and meta igneous rocks the dacaoping porphyritic granites are characterized by high sio2 70 83 74 30 wt k2o 4 84 5 60 wt feot feot mgo 0 86 0 92 seagull type ree pattern with strong negative eu anomaly eu 0 16 0 35 and higher 10000 ga al 2 99 3 36 hfse zr nb ce y 378 583 ppm showing an affinity of a2 type granite they have low sr y 1 17 8 62 end t 6 1 to 6 4 with tdm 2690 ma to 2776 ma from whole rock sm nd isotope and ehf t 7 9 to 5 2 with tcdm 2775 2938 ma from zircon lu hf isotope indicating a result from the melting of thinned neoarchean calc alkaline intermediate basement taking into account the temporal spatial distributions of late paleoproterozoic rocks in the trans north china orogen it suggests a post collisional extension occurred during 1 89 1 76 ga and the crust is thinned visibly since 1 82 ga

did south america and west africa marry and divorce or was it a long lasting relationship abstract the 2 1 2 0 ga transamazonian orogen in south america can be well correlated with the 2 1 2 0 ga eburnean orogen along the western margin of west africa both the orogens are characterized by early tangential tectonics marked by large scale thrusts and sinistral strike slip faults followed by later transcurrent tectonics marked by dextral shear zones metamorphic evolution of the two orogens involved an initial phase of crustal thrusting and thickening followed by exhumation and final cooling these suggest that south america and west africa may have been jointed along the transamazonian eburnean orogen at 2 1 2 0 ga this is supported by the presence of 2 0 ga fluvio deltaic formations in nearly every craton in south america and west africa the available paleomagnetic data also indicate that between 2 1 1 5 ga coeval rocks in west africa and south america recorded similar polar wander paths if south america and west africa remained coherent from their amalgamation at 2 1 2 0 ga until their incorporation into gondwana at 0 6 0 5 ga the positions of south america and west africa in the present configurations models of rodinia need to be re evaluated since these configurations did not bring the two blocks into close proximity

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

shrimp and la icp ms zircon geochronology of the xiong er volcanic rocks implications for the paleo mesoproterozoic evolution of the southern margin of the north china craton the paleo mesoproterozoic xiong er volcanic rocks along the southern margin of the north china craton are lithologically and geochemically similar to those formed in subduction related continental margin volcanic arcs the volcanic rocks are primarily composed of basaltic andesites and andesites with minor dacites and dacitic rhyolites traditionally the xiong er volcanic rocks have been divided from lower to upper into the xushan jidanping and majiahe formations but the ages of volcanic rocks in these formations have not been well constrained which has hindered further understanding the tectonic significance of the xiong er volcanic belt at the southern margin of the north china craton shrimp and la icp ms u pb zircon analyses combined with cathodeluminescence cl images have enabled resolution of xenocrystic and magmatic zircons that can be directed toward determination of the ages of the xiong er volcanic rocks shrimp and la icp ms u pb analyses on magmatic zircons from two basaltic andesite samples one dacite sample and one rhyolite sample of the xushan formation known as the lowest sequence of the xiong er volcanic rocks indicate that the volcanic eruption of this formation occurred at 1 78 ga but most xenocrystic inherited zircons in these samples yielded 207pb 206pb ages ranging from 2 55 ga to 1 91 ga of three samples collected from the jidanping formation two rhyolite samples 05xe015 and 05xe100 yielded weighted mean 207pb 206pb ages of 1778 5 5 ma and 1751 14 ma respectively similar to the ages of the volcanic rocks in the xushan formation whereas one dacite sample 05xe066 gave a weighted mean 207 pb

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

the geochemistry of young volcanism throughout western panama and southeastern costa rica an overview oblique aseismic subduction below western panama and southeastern costa rica has produced recent arc related volcanism the aseismicity is probably related to the subduction of relatively hot oceanic lithosphere the volcanism throughout this region over the past 2 ma has been quite distinct consisting of felsic magmas andesites to rhyolites but mainly dacites with geochemical signatures suggesting a metamorphosed basaltic source it is believed that the subduction of young oceanic crust sets up conditions under which the slab melts rather than the overlying mantle wedge rocks with slab melt geochemistries and associated with young subducted crust have been termed adakites elsewhere the young adakite melts are sometimes associated with a few rare young high nb basalts but there is no obvious genetic link between them through differentiation high nb basalts may also be derived from the partial melting of the subducted oceanic crust high nb basalt migmatites have been found with pegmatites of adakite compositions in the exposed subduction terrain of the catalina schist california alternatively the high nb basalts may be partial melts of phlogopite rich mantle that has previously reacted with adakite magmas eruption of adakites and high nb basalts was preceded by a 2 3 ma period of relative quiescence prior to this there was a 7 ma period of calc alkaline volcanism typical of the present day magmatism associated with a distinct benioff zone found throughout the central american arc the abrupt transition in volcanism with time from an early calc alkaline sequence to a later adakite high nb basalt sequence may record a change in the tectonic setting of western panama and southeastern costa rica over the past 12 ma

neoproterozoic amalgamation of the northern qinling terrain to the north china craton constraints from geochronology and geochemistry of the kuanping ophiolite abstract the proterozoic tectonic evolution of the qinling orogenic belt is a key to understanding the convergent processes between the north china and south china blocks the widely exposed kuanping ophiolite melange between the north qinling terrain and the north china block provides important constraints on the meso neoproterozoic tectonic evolutionary processes between the north qinling terrain and north china block detailed geological mapping reveal that the kuanping ophiolite melange consists of an ophiolite and a meta sedimentary unit according to our new geochemical investigations the ophiolite unit can be briefly divided into two groups 1 n morb and 2 e morb the former is characterized by depletion in light rare earth elements large ion lithophile elements and non differentiation in high field strength elements the latter shows slight enrichment in light rare earth elements large ion lithophile elements and minor differentiation in high field strength elements accordingly it is inferred that the kuanping ophiolite likely represents remnants of an oceanic crust named as kuanping ocean between the north qinling terrain and the north china block one metamorphosed n morb sample from the kuanping ophiolite was selected for la icpms zircon u pb dating which displays an age of 1445 60 ma probably represents the formation time of the kuanping ocean integrated with the regional geological geochemical and geochronological data we propose that the north qinling terrain amalgamated to the north china block after a southward subduction of a mesoproterozoic ocean represented by the kuanping ophiolite

isotopic characteristics of subduction fluids in an intra oceanic setting izu bonin arc japan new radiogenic isotope and trace element data are presented for the volcanic sequences along 600 km of the active izu bonin arc the oligocene izu arc and their associated rift basins as with many intra oceanic island arcs the pliocene recent izu bonin frontal arc lavas are highly depleted in zr nb and the rare earth elements relative to typical mid ocean ridge basalt morb indicating that the mantle wedge source has undergone a previous episode of melting ratios between these elements such as nb zr and la sm as well as 143nd 144nd do not vary significantly along the length of the frontal arc these parameters suggest that each of the arc volcanoes is derived from similar melt fractions of the mantle wedge however ba zr ba rb and 87sr 86sr increase along the frontal arc to the north this leads us to propose that a variable enrichment in ba and radiogenic sr is superimposed on the mantle wedge sr nd and pb nd isotope variation indicate that both sr and pb become more radiogenic after fluid addition however pb isotope ratios do not correlate with increases in pb concentration or ratios such as ba zr and nb pb in other words the pb isotopic composition of the arc lavas appears to be independent of the amount of pb introduced by subduction fluids into the mantle source this buffering of pb isotopes along the frontal arc means that the isotopic composition of the lavas is indistinguishable from that of the fluid isotopic mixing models presented for the arc are only illustrative of the many plausible combinations of components and quantities despite this we are able to determine that the mantle wedge has isotopic characteristics similar to indian ocean morb and that the subduction fluid solute is primarily derived from subducted oceanic basalt with a 2 contribution from subducted sediment lavas in the oligocene izu arc and fore arc basin were derived from a mantle wedge of similar composition to the active arc despite levels of pb enrichment comparable to those of the modern arc the pb isotopes of the oligocene volcanics indicate a lower sediment input into the melting region

zircon u pb geochronology and hf isotopic composition of the hongqiyingzi complex northern hebei province new evidence for paleoproterozoic and late paleozoic evolution of the northern margin of the north china craton abstract the hongqiyingzi complex located at the northern margin of the north china craton was previously defined as a paleoproterozoic unit it consists of volcanic and sedimentary rocks which underwent greenschist to amphibolite facies metamorphism this study presents zircon u pb ages and hf isotopic composition and whole rock nd isotopic composition of metamorphosed igneous and sedimentary rocks from the hongqiyingzi complex the age dating results show that different gneisses of this complex contain mainly late paleoproterozoic 1800 ma and late paleozoic 275 to 300 ma zircons and minor late archean zircons late paleozoic zircons either occur as magmatic grains or as metamorphic overgrowth and both types of zircon can be distinguished by their th u ratios and internal structures most zircon grains of a paleozoic magmatic rock sample hq14 have high e hf t values of 1 5 to 10 8 suggesting significant contribution of mantle or juvenile crustal material to the magma source s the results imply that the hongqiyingzi complex contains precambrian supracrustal sequences and paleozoic rocks of magmatic origin that underwent strong metamorphism and deformation during the late paleozoic related to the closure of the paleo asian ocean between siberia and the north china craton

ore genesis of the fancha gold deposit xiaoqinling goldfield southern margin of the north china craton constraints from pyrite re os geochronology and he ar in situ s pb isotopes abstract the fancha gold deposit is one of the representative lode type deposit in the xiaoqinling goldfield four stage mineralization process were identified namely i the barren quartz stage ii the pyrite dominated stage iii the quartz polymetallic sulfides stage and iv the quartz carbonate stage correspondingly pyrite crystal can be divided into three generations i e py1 py2 and py3 according to their different textures and paragenesis during the first three mineralization stages in order to better understand the ore genesis an integrated analysis on re os he ar s pb multi isotopes was carried out for each mineralization stage to delineate the timing of the mineralization and the origins of the ore forming materials in detail gold bearing pyrite yields a re os isochron age of 124 3 2 6 ma mswd 1 9 overlapping with the previous hydrothermal mica 40ar 39ar ages suggesting that gold mineralization occurred in the early cretaceous the 3he 4he r ra and 40ar 36ar values of the py2 are 0 68 to 1 17 and 656 55 to 7384 2 and those of the py3 are 0 20 to 0 33 and 647 67 to 8913 55 respectively which reveal a significant contribution of mantle component in the ore forming fluids and the content of crust fluid is increasing in the later evolution in situ 34s values of the sulfides and tellurides in the auriferous quartz veins including the pyrite py1 py2 and py3 chalcopyrite sphalerite galena bismuthinite and tetradymite display a relatively narrow range 4 9 to 3 6 consistent with magmatic sulfur which are quite different from those of the pyrite in surrounding rock 7 8 to 9 3 in situ pb isotopic compositions of the galena and bismuthinite of stage iii are homogeneous with values of 208pb 204pb 207pb 204pb and 206pb 204pb being 37 482 37 508 15 392 15 523 16 995 17 006 and 39 279 39 287 15 588 15 590 18 283 18 288 respectively indicating a mixed pb sources with obvious proportions of mantle combined with previous data we suggest that the ore forming fluids and metals of the fancha gold deposit stemmed directly from the regional mantle derived magmatic hydrothermal system which is coupled with the large scale lithospheric extension and thinning in the eastern north china craton during the early cretaceous

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

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

extreme crustal metamorphism during columbia supercontinent assembly evidence from north china craton abstract a vast supracrustal belt of khondalites granulite facies metapelites occur along the northern margin of the north china craton we report here for the first time spinel quartz equilibrium assemblage from these rocks in two textural settings 1 high zno up to 14 47 wt spinel with quartz as inclusions within garnet porphyroblasts defining pressure above 12 kbar and temperature of 900 c and 2 low zno down to 1 2 wt spinel in association with quartz in the matrix assemblage formed during peak ultrahigh temperature conditions ca 975 c and 9 kbar we present a unique case of decompression where the metamorphic conditions of the rocks traversed mostly through the spinel quartz extended stability field monazite grains in textural association with both types of spinel quartz textures were analysed for age determination and the data define two age peaks at 1927 11 ma and 1819 11 ma since the peak thermal regime of the khondalites was close to or exceeded the theoretical closure temperature of pb in monazite we infer the 1819 11 ma age as the timing of ultrahigh temperature event in this craton our data lend support to the idea of ca 1 9 1 8 ga e w collisional orogen at the northern margin of the north china craton we correlate the extreme crustal metamorphism with tectonics associated with the assembly of the north china craton within the columbia supercontinent

fluid inclusion geochemistry and ore genesis of the longmendian mo deposit in the east qinling orogen implication for migmatitic hydrothermal mo mineralization abstract the 1 85 ga longmendian mo deposit in east qinling is the oldest mo system recognized in china it is unique for three reasons 1 quartzofeldspathic orebodies are away from any intrusion or fault 2 it is closely associated with migmatitic rocks and 3 it has remarkably high re content in molybdenite 504 to 1660 ppm the origin of the deposit is poorly constrained in the longmendian deposit strong mo mineralization is always associated with hydrothermally altered migmatitic amphibolites to probe into ore genesis detailed fluid inclusion studies are carried out on both mineralized migmatitic amphibolites and ore barren rocks four compositional types of fluid inclusions are observed including co 2 ch 4 pc type co 2 h 2 o c type daughter mineral bearing s type and h 2 o nacl w type quartz in mesosome and melanosome of mineralized migmatitic amphibolites contains all of the four types of inclusions measurements of immiscible inclusion assemblages in the ores constrain the mo mineralization temperatures and pressures to be 225 390 c and 114 265 mpa respectively primary fluid inclusions in barren migmatitic gneisses are dominated by s type and minor of c and pc types which are identical to those in the leucosome of migmatitic amphibolites these inclusions yield lower homogenization temperatures than those in the mineralized mesosome and melanosome of migmatitic amphibolites suggesting that the ore causative injected melts should have higher temperatures and originated from depths such features of the ore forming fluids indicate that the longmendian deposit was a migmatitic hydrothermal system caused by high temperature melt injection this interpretation can also be supported by the observations below 1 tourmaline is abundant in melanosome but absent in mesosome 2 the consistent quartzofeldspathic composition of leucosome is independent of mesosome 3 leucosome in migmatitic amphibolite crosscuts each other 4 halite bearing fluid inclusions are prevalent in studied samples which is the feature of granitic rocks instead of the scenarios of in situ migmatites and 5 the trapping temperatures of fluid inclusions in mineralized migmatitic amphibolite are much lower than those required for partial melting but higher than those obtained from barren migmatitic rocks

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

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

early paleozoic tectonic evolution of the north qinling orogenic belt in central china insights on continental deep subduction and multiphase exhumation abstract the north qinling orogenic belt is an important component of qinling composite orogen in central china high pressure and ultra high pressure hp uhp rocks occur as lenses or layers surrounded by gneissic rocks in the northern central and southern qinling complex of the north qinling belt considered to have formed through deep continental subduction the magmatic protoliths of the hp uhp metamorphic rocks show formation ages ca 800 ma geochemical characteristics and pb nd isotopic compositions similar to those of the neoproterozoic igneous rocks of the south qinling belt continental materials of the south qinling belt were dragged down to mantle depths by the shangdan oceanic crust subducted and subjected to hp uhp metamorphism at ca 500 ma the erlangping and kuanping backarc basin formed in response to subduction of the shangdan ocean and might have developed into a limited small ocean basin at ca 500 ma the hp uhp rocks yielded retrograde metamorphic ages of ca 470 450 ma and ca 420 400 ma these ages are identical to the age of magmatic events in the north qinling hp uhp belt at 500 ma 450 ma and 420 ma related to deep subduction collision slab breakoff and crustal thinning during post collisional extension the dominant ca 500 400 ma ages of detrital zircons from the liuling group of the south qinling belt match well with those from the three stages of magmatic rocks and hp uhp rocks in the qinling complex this correlation suggests that the magmatic rocks and hp uhp metamorphic rocks in the north qinling belt initially exhumed to the surface eroded and were then deposited in the liuling basin in a post orogenic extensional setting during middle to late devonian new evidence suggests that the qinling complex is a tectonic complex rather than a uniform stratigraphic unit or a microcontinent as previously believed and is mainly composed of the exhumed hp uhp metamorphic rocks deep subduction exhumation related magmatic rocks and the early neoproterozoic granites together with the host rocks from the over riding plate at an active continental margin the early paleozoic tectonic history of the nqb includes oceanic slab subduction and formation of arc backarc spreading continental deep subduction arc continent collision break off and multi stage exhumation of the deep subducted slab as well as extension and thinning and associated erosion and deposition

the burnsville fault evidence for the timing and kinematics of southern appalachian acadian dextral transform tectonics there has been a conspicuous absence of documented acadian structures in the blue ridge province of the southern appalachians even though a growing body of evidence suggests that the middle paleozoic acadian orogeny affected the rocks of this region new mapping along with structural petrologic and geochronologic data from western north carolina show that the contact between the metasedimentary and metavolcanic rocks of the ashe metamorphic suite and the grenville basement rocks of the western blue ridge corresponds to a devonian high grade dextral strike slip fault zone the burnsville fault timing of motion on the burnsville fault is constrained by field relationships metamorphic fabrics and assemblages and radiometric ages a u pb zircon crystallization age for a pegmatite sheared by the burnsville fault shows that the last movement on the fault must he younger than 377 ma previously published 4 0 ar 3 9 ar cooling ages show that the burnsville fault must be older than ca 360 ma we have mapped the burnsville fault for 100 km in northwest ern north carolina the gossan lead fault of northwesternmost north carolina and southwestern virginia is the likely continuation of the burnsville fault to the north east southwest of asheville north carolina the burnsville fault may connect to the devonian dahlonega shear zone or may be cut by post devonian thrust faults associated with the alleghanian orogeny diachroneity of acadian elastic wedge the presence of silurian devonian pull apart basins the presence of devonian high grade dextral shearing in the inner piedmont and recent plate reconstructions for the middle paleozoic support the interpretation that the late phase of the acadian orogeny in the southern appalachians was primarily a dextral transpressional event the burnsville fault and the inner piedmont formed the boundaries of a dextral transform margin that may have extended the length of the appalachian orogen this interpretation requires that models for the paleozoic tectonics of the appalachians incorporate major pre alleghanian dextral displacement

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

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

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