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

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

anthropogenic stable cesium in water and sediment of a shallow estuary st louis bay mississippi abstract st louis bay slb mississippi is a small shallow estuary with moderate local residential and industrial development dissolved stable cs i e 133 cs was significantly enriched in bay waters up to 1570 nm as compared to river 2 refinery located on the north shore of the bay is the likely source of the cs given that the highest cs concentrations were found in waters and in surface sediments up to 49 g g near the refinery outfall this setting presented a unique opportunity to study remobilization of cs in a shallow estuarine system where sediment resuspension is frequent remobilization up to 3 fold increase of dissolved cs was observed during sediment resuspension events a weak correlation between cs and clay strong correlations among cs silt and particulate organic carbon poc and simple numerical approaches indicate that desorption from resuspended particulate matter is the likely mechanism of cs remobilization cs enriched slb waters can be traced to nearshore mississippi sound waters but not into mississippi bight waters further offshore the findings from this study also suggest that caution needs to be taken when interpreting the radio cesium distribution in shallow estuarine and coastal systems

geochemistry and u pb zircon ages of metamorphic volcanic rocks of the paleoproterozoic luliang complex and constraints on the evolution of the trans north china orogen north china craton abstract the paleoproterozoic luliang complex is situated in the central part of the western margin of the trans north china orogen and consists of volcanic rocks sedimentary rocks and paleoproterozoic granitoid intrusions the volcanic rocks and earlier granitoid rocks were strongly deformed and metamorphosed into the greenschist to amphibolite facies these metamorphosed volcanic rocks are dominated by basalts to basaltic andesites the parental mafic magmas of these metamorphosed volcanic rocks were mainly derived from the 5 to 30 partial melting of spinel lherzolites to spinel garnet lherzolites which had been enriched by the subduction melts mafic magma experienced fractional crystallization and crustal assimilation u pb zircon dating on two metamorphosed volcanic rocks from the yejishan and luliang groups reveals that they formed at 2210 13 ma and 2213 47 ma respectively and were metamorphosed at 1832 ma this suggests that the metamorphosed volcanic rocks in the yejishan and luliang groups formed synchronously in the paleoproterozoic these new ages integrated with recently reported u pb zircon ages for the jiehekou group and paleoproterozoic granitoids suggest that all of the lithological assemblages of the luliang complex formed and were metamorphosed in the paleoproterozoic not in the neoarchean petrological geochronological and geochemical data suggest that the geodynamic evolution of the paleoproterozoic luliang complex was involved in the development of a magmatic arc system at an active continental margin generating widespread arc related magmatism at 2 2 ga the luliang complex then underwent intense deformation and metamorphism and was incorporated into the trans north china orogen during the 1 88 1 83 ga collisional event which was followed by post collision extension at 1 80 ga

shrimp u pb zircon ages of granitoid rocks in the luliang complex implications for the accretion and evolution of the trans north china orogen abstract the luliang complex is situated in the central segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of supracrustal and granitoid rocks of which the latter can be subdivided into pre tectonic ttg gneisses including the yunzhongshan guojiazhuang and chijianling guandishan gneisses syn tectonic gneissic granites represented by the huijiazhuang gneissic granite and post tectonic granites including the luyashan charnockite luchaogou porphyritic granite and tangershang guandishan massive granite the pre tectonic ttg gneisses are mostly calc alkaline and considered to have formed in a magmatic arc environment shrimp u pb analyses reveal that the yunzhongshan gneisses were emplaced at 2499 9 ma representing the earliest arc related magmatic event in the luliang complex this was followed by the intrusion of the guojiazhuang gneisses at 2375 10 ma the most widespread arc related magmatic event in the region was the emplacement of the chijianling guandishan granitoid gneisses of which the tonalitic granodioritic and monzogranitic gneisses were emplaced at 2199 11 ma 2180 7 ma and 2173 7 ma respectively metamorphic zircon overgrowth rims from a tonalitic gneiss yielded a weighted mean 207 pb 206 pb age of 1872 7 ma consistent with the metamorphic age range of 1880 1820 ma defined by metamorphic zircons from various high grade rocks in the tnco thus the evolution of the luliang complex involved emplacement of the yunzhongshan granitoids at 2499 ma the guajiazhuang granitoids at 2375 ma and the chijianling guandishan granitoids at 2199 2173 ma with the final collision between the eastern and western blocks in this area occurring at 1872 7 ma the whole series of magmatic events lasting nearly 650 ma this suggests that the trans north china orogen represents a long lived magmatic arc the new shrimp zircon data combined with structural and petrological studies also reveal the existence of both syn and post collisional granites in the luliang complex the former is represented by the huijiazhuang gneissic granite that was emplaced at 1832 11 ma whereas the latter include the 1815 5 ma luyashan charnockite 1807 10 ma luchaogou porphyritic granite 1798 11 ma guandishan massive granite and 1790 14 ma tangershan massive granite

structural pattern of the wutai complex and its constraints on the tectonic framework of the trans north china orogen abstract wutai complex is a key to test controversial models for the tectonic evolution of the trans north china orogen tnco along which the eastern and western blocks amalgamated to form the north china craton three stages of deformation d 1 to d 3 were identified in the wutai complex d 1 is characterized by ne sw trending foliations s 1 and nw se orientated lineations l 1 indicating an initial nw se directed compression associated with d 1 was prograde metamorphism m 1 d 2 progressively overprinted d 1 and generated z shaped folds and nee sww trending ductile shear zones d 2 resulted in a fan shaped structural pattern of the complex with top to the nw thrusting in the northwestern part and opposite top to the se thrusting in the southeastern part during d 2 the crust was doubled through thickening leading to peak metamorphism m 2 d 3 developed during post collision exhumation and deformed the early fabrics to be open folds resulting in near isothermal decompression m 3 and late cooling metamorphism m 4 the overall structure of the wutai complex is characterized by a fan shaped pattern with structural divergence structural features of the wutai complex combined with those of the adjacent hengshan and fuping complexes indicate that the tnco is characterized by a fan shaped orogenic wedge with opposite senses of thrust this orogenic wedge could have resulted from an eastward subduction and collision between the western and eastern blocks to finally form the tnco at 1 85 ga

geochemistry of neoarchean ca 2 55 2 50 ga volcanic and ophiolitic rocks in the wutaishan greenstone belt central orogenic belt north china craton implications for geodynamic setting and continental growth discussion we read with interest the contribution by polat et al 2005 1 on the origin of neoarchean volcanic and ophiolitic rocks in the wutaishan greenstone belt northern china and their geo dynamic setting we do not dispute the quality of the authors data and their interpretations but we disagree

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

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

geochronological and geochemical constraints on the luliang group in the luliang complex implications for the tectonic evolution of the trans north china orogen abstract the luliang complex is located at the western margin of the middle segment of the trans north china orogen along which the western and eastern blocks amalgamated to form the basement of the north china craton the complex consists of the late neoarchean to paleoproterozoic granitic plutons and meta supracrustal rocks of which the latter are subdivided into the jiehekou luliang yejishan and heichashan lanhe groups the luliang group is composed mainly of siliciclastic rocks in the lower part and volcanic rocks in the upper part all of which have been metamorphosed from greenschist to amphibolite facies u pb ages of detrital zircons from meta sedimentary rocks in the luliang group yield four populations of 3061 2920 ma 2790 2600 ma 2599 2280 ma and 2211 2202 ma suggesting that their provenances were derived mainly from the luliang and taihua complexes in the trans north china orogen the meta volcanic rocks give igneous zircon u pb ages of 2209 2178 ma and e hf t values of 0 8 to 3 6 geochemically they are subalkaline basalts and andesites that can be classified into two groups of which one group has flat lrees weak enrichment in lrees relative to hrees and flat hrees and displays e morb like spider diagrams with the exception of insignificantly negative nb ta zr hf and ti anomalies in contrast the other group displays stronger lree fractionation stronger enrichment in lrees relative to hrees and mildly fractionated hrees and is characterized by spiky spider diagrams similar to arc volcanic rocks the first group is interpreted to have originated from a neoarchean e morb source whereas the second group shows inputs of newly subduction derived fluids in the mantle source these geochronological and geochemical signatures indicate the existence of an 2 2 2 1 ga continental back arc system in the luliang complex of the trans north china orogen which is consistent with the model that the collision between the eastern and western blocks to form the coherent basement of the north china craton in the paleoproterozoic not at the end of neoarchean

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

high cesium concentrations in groundwater in the upper 1 2 km of fractured crystalline rock influence of groundwater origin and secondary minerals abstract dissolved and solid phase cesium cs was studied in the upper 1 2 km of a coastal granitoid fracture network on the baltic shield aspo hard rock laboratory and laxemar area se sweden there unusually high cs concentrations up to 5 6 g l 1 occur in the low temperature 1 median laxemar 3 7 g l 1 and groundwater with marine origin aspo hrl 4 2 g l 1 overall lower but variable cs concentrations were found in other types of groundwater the similar concentrations of cs in the saline groundwater which had a residence time in the order of millions of years and in the marine groundwater which had residence times in the order of years shows that duration of water rock interactions is not the single and primary control of dissolved cs in these systems the high cs concentrations in the saline groundwater is ascribed to long term weathering of minerals primarily cs enriched fracture coatings dominated by illite and mixed layer clays and possibly wall rock micaceous minerals the high cs concentrations in the groundwater of marine origin are in contrast explained by relatively fast cation exchange reactions as indicated by the field data and predicted by 1d solute transport modeling alkali cations with low energy hydration carried by intruding marine water are capable of nh 4 in particular and k to some extent replacing cs on frayed edge fes sites on illite in the fracture coatings the result is a rapid and persistent at least in the order of decades buildup of dissolved cs concentrations in fractures where marine water flows downward the identification of high cs concentrations in young groundwater of marine origin and the predicted capacity of nh 4 to displace cs from fracture solids are of particular relevance in the disposal of radioactive nuclear waste deep underground in crystalline rock

a morb arc basalt adakite association in the 2 5 ga wutai greenstone belt late archean magmatism and crustal growth in the north china craton abstract the wutai fuping and hengshan complexes form part of a major 2 5 ga late archean arc system in the northern part of the north china craton the wutai complex is a well preserved greenstone belt dominated by mafic intermediate and felsic volcanic rocks with a mid ocean ridge basalt morb arc back arc basalt adakite association multi element plots for morb type mafic volcanic rocks are characterised by depletion of th nb ta and la nearly flat or lree depleted ree patterns and nb u and nb th ratios greater than primitive mantle values back arc basin basalt babb type rocks have nearly flat trace element patterns with nb ti and y troughs and lree depleted or near flat ree patterns island arc basalt iab type rocks are characterized by negative anomalies of nb ta zr hf ti and y and by lree enrichment the felsic volcanic rocks conform to most compositional criteria for cenozoic adakites including low y and yb high la smn la yb and zr sm ratios and similar trace element and ree patterns trends defined by the association are consistent with magma mixing between morb like melts and subduction slab related melts intra oceanic subduction coupled with contemporary morb type mantle upwelling related to back arc basin extension can account for the interaction between the two components subduction accretion or back arc basin collapse led to accretion of the wutai intra oceanic arc back arc complexes with the magmatic arcs of the fuping and hengshan terranes that are dominated by high grade tonalite trondhjemite granodiorite ttg gneisses this geodynamic interpretation is different from many tectonic models for archean greenstone belts in which magmatism and crustal growth were dominated by mantle plumes or interaction between subduction zones and mantle plumes the final disposition of the arc complexes was controlled by the collision of the eastern and western blocks of the north china craton during the paleoproterozoic resulting in extensive tectonic interleaving within a major orogenic belt that extended throughout the central portion of the north china craton

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

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

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

deformation history of the hengshan wutai fuping complexes implications for the evolution of the trans north china orogen abstract the trans north china orogen separates the north china craton into two small continental blocks the eastern and western blocks as one of the largest exposure in the central part of the orogen the hengshan wutai fuping complexes consist of four lithotectonic units the wutai hengshan and fuping complexes and the hutuo group the hengshan complex contains high pressure mafic granulites and retrograded eclogites structural analysis indicates that most of the rocks in these complexes underwent three distinct episodes of folding d 1 to d 3 and two stages of ductile thrust shearing stz 1 between d 1 and d 2 and stz 2 after d 3 the d 1 deformation formed penetrative axial planar foliations s 1 mineral stretching lineations l 1 and rarely preserved small isoclinal folds f 1 in the hengshan and fuping complexes in the wutai complex however large scale f 1 recumbent folds with sw vergence are displayed by sedimentary compositional layers penetrative transposition resulted in stacking of thrust sheets which are separated by ductile shear zones stz 1 the kinematic indicators of stz 1 in the hengshan and wutai complexes show top to the s230 w thrusting likely related to northeastward oblique pre collisional subduction d 1 resulted in crustal thickening with resultant prograde peak metamorphism the hutuo group did not undergo the d 1 deformation either because sedimentation was coeval with the d 1 deformation or because it was at a high structural level and was not influenced directly by the early deformation the d 2 deformation produced nw verging asymmetric and recumbent folds the d 2 deformation is interpreted to have resulted from collision between the eastern and western blocks of the north china craton in the hutuo group and the fuping complex the development of ese verging asymmetric tight folds is associated with d 2 the structural pattern resulting from superimposition of d 1 and d 2 is a composite synform in the hengshan wutai fuping complexes all four lithotectonic units were superposed during the later d 3 deformation the d 3 deformation developed nw trending open upright folds ongoing collision led to development of transpressional ductile shearing stz 2 forming the transpressional zhujiafang dextral ductile shear zone between the northern hengshan complex and the southern hengshan complex and generating the sinistral longquanguan ductile shear zone between the fuping complex and the wutai complex respectively the stz 1 and d 2 deformation were possibly responsible for fast syn collisional exhumation of the high pressure mafic granulites and retrograded eclogites the structural patterns and elucidation of the deformation history of the hengshan wutai fuping complexes places important constraints on the tectonic model suggesting that an oceanic lithosphere between the eastern and western blocks underwent northeastward directed oblique subduction beneath the western margin of the eastern block and that the final closure of this ocean led to collision between the two blocks to form the coherent basement of the north china craton

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

measuring the specific caesium sorption capacity of soils sediments and clay minerals abstract two methods to quantify the specific cs sorption capacity of soils and sediments which is generally believed to be associated with the frayed edge sites fes of illitic clay minerals are described in detail and are critically reviewed the first method is a direct measurement of the fes capacity while the second quantifies the combined parameter k d cs k k c k cs fes i e the product of the fes capacity and the affinity of these sites for cs both methods use the bulky agtu complex to mask non specific sorption sites for cs and are applied to a number of different soils and pure minerals measurement of the fes capacity of pure illite is straightforward it is shown that the measured capacity is independent of the saturating ion but does depend on particle size this method could not be successfully applied to a peat bog soil with 90 organic matter because the necessary correction for non specific cs sorption by the large pool of organic exchange sites overpasses the capacity of the small fes fraction measurement of the combined parameter k d cs k is shown to be more appropriate in such cases application of the fes capacity method to the hydrous aluminosilicate mineral allophane an important soil constituent of andisols shows that the agtu complex is unable to block all non specific sorption sites for cs on this mineral the k d cs k measurements show evidence of a very small number of specific cs sorption sites on allophane much smaller than inferred from the fes capacity measurement the fes capacity of the clay mineral vermiculite is difficult to quantify because the high cs concentrations that are needed to measure the fes capacity probably cause a collapse of the vermiculite interlayers thereby creating more high affinity sites for cs the k d cs k method in which only trace concentrations of cs are used is shown to be more appropriate for soils containing substantial amounts of vermiculite it is concluded that both the direct fes capacity measurement and the measurement of the combined parameter k d cs k can be very useful methods to isolate and characterise cs selective sorption sites in soils and sediments but that results should be interpreted with great care

geomagnetic variation on decadal time scales what can we learn from empirical mode decomposition 1 the effects of core fluid dynamics are observable as variations in the geomagnetic field at time scales of decades to many thousands of years a non classical method empirical mode decomposition emd is performed on globally distributed observatory records of declination and inclination to study decadal variations of the geomagnetic field we use waveform analysis to test the robustness of emd and find an 11 5 year signal consistent with the solar cycle periods of 30 5 62 and 81 years are also identified in the observations and compared with results from core flow inversions these signals are likely to be of internal origin potentially the manifestation of torsional oscillations in the fluid core finally we analyse a new 600 year time series from munich and suggest that a longer 160 year period exists

single zircon grains record two paleoproterozoic collisional events in the north china craton abstract the western block of the north china craton consists of the yinshan block in the north and the ordos block in the south which were amalgamated along the east west trending khondalite belt at 1 95 ga the western block then collided with the eastern block to form the coherent basement of the north china craton along the north south trending trans north china orogen at 1 85 ga the huaian complex a high grade terrrane located at the conjunction of the khondalite belt and trans north china orogen records metamorphic events associated with both collisions the complex consists of lithologies from both the khondalite belt and trans north china orogen of which the former consist of graphite garnet sillimanite gneiss garnet quartzite felsic paragneiss calc silicate rock and marble together called the khondalite series zircons in the graphite garnet sillimanite gneiss can be divided into three types 1 spherical grains without internal structures 2 grains with a core and rim structure and 3 grains with a dark core surrounded by double rims except for the dark core in type 3 all other types of zircon domains are structureless and highly luminescent with very low th u ratios typical of a metamorphic origin analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 26 and 1947 22 ma similar to previously determined metamorphic ages from the khondalite belt and thus interpreted as the time of collision between the yinshan and ordos blocks analyses on type 1 zircons rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 15 and 1857 16 ma interpreted as the time of collision between the eastern and western blocks thus zircons in the graphite garnet sillimanite gneiss of the huaian complex record both of the paleoproterozoic collisional events in the north china craton

growth and reworking of the early precambrian continental crust in the north china craton constraints from zircon hf isotopes abstract we synthesize more than 2600 hf isotope data on the archean paleoproterozoic zircons from the north china craton ncc recalculation of the data based on single stage and two stage hf model ages of the eastern block of the ncc shows peak ages of 3902 13 ma and 3978 18 ma respectively and also small peaks at 3 5 4 0 ga the majority of zircon ehf t values are positive suggesting the possibility of the crust and the mantle differentiation at ca 3 9 4 0 ga in the eastern block of the ncc most magmatic zircons from the whole of ncc have their hf model age range of 2 4 2 9 ga and the single stage model ages is cluster at 2698 4 ma whereas the two stage model ages concentrate at 2714 5 ma implying that the protoliths were juvenile crustal rocks the most prominent peak at 2 7 ga indicates that this period marks the most important stage of the crust mantle differentiation and crust formation of the ncc the widespread 2 5 ga rocks in the ncc and the absence of the 2 5 ga peaks in hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2 5 ga furthermore the 2 5 1 7 ga zircon hf isotope features are also related to the reworking of the crustal rocks our results from the integration of a large database suggest that the eastern block and the trans north china orogen have undergone similar crust mantle differentiation and magmatism leading to the conclusion that the essential cratonization of the north china took place at the end of neoarchean

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

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

charnockite magmatism during a transitional phase implications for late paleoproterozoic ridge subduction in the north china craton abstract the trans north china orogen tnco is a major paleoproterozoic collisional belt along which the western and eastern blocks of the north china craton were amalgamated the luliang complex occurs along the western margin of this belt and incorporates several arc magmatic suites supracrustal sequences granitoids and charnockites here we investigate the luyashan charnockite suite as well as the surrounding granitoids from this complex we present results from petrology fluid inclusions mineral chemistry whole rock geochemistry and zircon u pb and lu hf isotopic studies the charnockites are dominantly anhydrous with the typical presence of orthopyroxene microthermometric and laser raman spectroscopic data on fluid inclusions in the charnockite characterize the trapped fluids as dominantly co2 with traces of n2 and ch4 geochemically the charnockite suite shows compositional variation from monzogabbro through gabbroic diorite and diorite to monzodiorite they are dominantly calc alkaline and ferroan type and display distinct enrichment in large ion lithophile elements with depletion in hree they also show prominent negative anomalies of nb ta sr and ti and positive anomalies of rb pb zr and hf indicating crustal components in the magma source the majority of the granitoid suite shows 207pb 206pb mean ages in the range of 2172 2032 ma correlating with similar ages reported from various groups in the luliang complex the formation of which is correlated with subduction along an active convergent margin however the charnockites which intrude the granitoids and their dioritic enclaves are clearly younger and show tightly constrained emplacement ages in the range of 1853 1872 ma the recrystallized zircons in the older granitoids also show similar ages suggesting a prominent thermal event at this time these ages are close to the timing of final collision between the western and eastern blocks of the north china craton and associated high grade metamorphism at ca 1 85 ga the zircon lu hf isotope data reveal dominantly negative hf t values 8 7 to 0 1 and their tdmc 2477 3042 ma suggest that the magma sources mainly involved meso to neoarchean reworked crustal components with limited input of paleoproterozoic juvenile components our study reveals that charnockite magmatism and regional metamorphism in the western margin of the tnco broadly overlap in space and time the geochemical features mineral assemblages and fluid inclusion characteristics of the charnockites suggest that the rocks were derived from high temperature 900 1000 c co2 enriched and anhydrous less than 3 h2o magmas the magma evolved into more hydrous conditions during cooling marked by the crystallization of amphiboles at 800 850 c the geochemical features of the charnockite suite also suggest that these rocks were formed during a transitional phase from syn subduction to collision such a scenario is compatible with a tectonic setting involving the subduction of an oceanic ridge when flushing of heat and co2 rich fluids from asthenosphere into the overriding plate might have occurred through the slab window generating hot and anhydrous magmas through melting of the basement rocks the slab window mechanism would also account for broadly coeval high temperature and high pressure granulites reported from the tnco we therefore speculate that the formation of the luyashan charnockite suite might have been associated with ridge subduction at the terminal stage of the convergence