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

forty years of ttg research abstract ttgs tonalite trondhjemite granodiorite are one of the archetypical lithologies of archaean cratons since their original description in the 1970s they have been the subject of many studies and discussions relating to archaean geology in this paper we review the ideas concepts and arguments brought forward in these 40 years and try to address some open questions both old and new the late 1960s and the 1970s mark the appearance of grey gneisses ttg in the scientific literature during this period most work was focused on the identification and description of this suite and the recognition that it is a typical archaean lithology ttgs were already recognised as generated by melting of mafic rocks this was corroborated during the next decade when detailed geochemical ttg studies allowed us to constrain their petrogenesis melting of garnet bearing metamafic rocks and to conclude that they must have been generated by archaean geodynamic processes distinct from their modern counterparts however the geodynamic debate raged for the following 30 years as many distinct tectonic scenarios can be imagined all resulting in the melting of mafic rocks in the garnet stability field the 1990s were dominated by experimental petrology work a wealth of independent studies demonstrated that melting of amphibolites as well as of mafic eclogites can give rise to ttg liquids whether amphibolitic or eclogitic conditions are more likely is still an ongoing debate from 1990s onwards one of the key questions became the comparison with modern adakites as originally defined these arc lavas are reasonably close equivalents to archaean ttgs pending issues largely revolve around definitions as the name ttg has now been applied to most archaean plutonic rocks whether sodic or potassic irrespective of their hree contents this leads to a large range of petrogenetic and tectonic scenarios a fair number of which may well have operated concurrently but are applicable only to some of the rocks lumped together in the ever broadening ttg bin

an exotic mesoarchean microcontinent the coorg block southern india abstract sandwiched between the dharwar craton in the north and the neoarchean proterozoic crustal blocks to the south the coorg block in southern india is composed dominantly of a suite of arc magmatic rocks including charnockites ttg tonalite trondhjemite granodiorite related granitoid suite and felsic volcanic tuffs together with minor accreted oceanic remnants along the periphery of the block coeval mafic and felsic magmatism with magma mixing and mingling in an arc setting is well represented in the block here we present the petrology geochemistry zircon u pb geochronology and lu hf isotopes of all the major lithologies from this block computation of metamorphic p t conditions from mineral chemical data shows consistent granulite facies p t conditions of 820 870 c and up to 6 kbar our geochemical data from major trace and ree on representative samples of the dominant rock types from the coorg block corroborate an arc related signature with magma generation in a convergent margin setting the zircon data yield weighted mean 207pb 206pb ages of 3153 4 9 to 3184 0 5 5 ma for syenogranites 3170 3 6 8 ma for biotite granite 3275 5 1 ma for trondhjemite 3133 12 to 3163 8 6 9 ma for charnockites 3156 10 to 3158 3 8 2 for mafic enclaves 3161 16 ma for diorite and 3173 16 ma for felsic volcanic tuff an upper intercept age of 3363 59 ma and a lower intercept age of 2896 130 ma on zircons from a charnockite as well as an evaluation of the th u values of the zircon domains against respective 207pb 206pb ages suggest that the mesoarchean magma emplacement which probably ranged from 3 3 to 3 1 ga was immediately followed by metamorphism at ca 3 0 to 2 9 ga the ages of magmatic zircons from the charnockites and their mafic granulite enclaves as well as those from the volcanic tuff and biotite granite are all remarkably consistent and concordant marking ca 3 1 ga as the peak of subduction related crust building in this block within the tectonic milieu of an active convergent margin the majority of zircons from the coorg rocks show hf isotope features typical of crystallization from magmas derived from juvenile sources their hf crustal model ages suggest that the crust building might have also involved partial recycling of basement rocks as old as ca 3 8 ga the crustal blocks in the southern granulite terrane in india preserve strong imprints of major tectonothermal events at 2 5 ga 2 0 ga 0 8 ga and 0 55 ga associated with various subduction accretion collision or rifting events however the coorg block is exceptional with our data suggesting that none of the above events affected this block importantly there is also no record in the coorg block for the 2 5 ga pervasive regional metamorphism that affected all the other blocks in this region the geochronological data raise the intriguing possibility that this block is an exotic entity within the dominantly neoarchean collage in the northern domain of the southern granulite terrane of india the mesoarchean arc related rocks in the coorg block suggest that the magma factories and their tectonic architecture in the early earth were not markedly different from those associated with the modern style plate tectonics

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

contrasting zircon hf and o isotopes in the two episodes of neoproterozoic granitoids in south china implications for growth and reworking of continental crust abstract the genetic links among rift magmatism crustal growth and water rock interaction are an important issue about mass and heat transfer between mantle and crust during supercontinent breakup a combined study of hf and o isotopes in zircons from neoproterozoic granitoids in south china provides evidence for growth and reworking of juvenile and ancient crusts with different styles of water rock interactions along rift tectonic zones two generations of the granitoids show contrasting features in both zircon hf and o isotope compositions indicating their distinct petrogenesis the 825 ma granitoids exhibit negative ehf t values of 3 4 0 8 to 1 6 0 8 with old model hf ages of 1 81 0 07 to 1 92 0 10 ga and high 18o values of 8 7 to 10 4 these indicate that the source material of granitoid magmas was derived from melting of paleoproterozoic basement that has the hf isotope signature similar to the enriched mantle but experienced chemical weathering process before anatexis reworking of ancient crust is demonstrated to occur at 825 ma in the orogenic collapse zone with overprinting of subsolidus hydrothermal alteration during magma emplacement in contrast the 760 750 ma bimodal intrusives are characterized by positive ehf t values of 3 5 0 8 to 9 9 0 8 with young model hf ages of 0 94 0 06 to 1 18 0 06 ga and both low and high 18o values of 4 2 to 6 2 relative to 5 3 0 3 for the normal mantle zircon prompt reworking of juvenile crust is suggested to occur at 750 ma in the rifted tectonic zone with occurrence of supersolidus hydrothermal alteration and local low 18o magmatism during supercontinent breakup contributions of the depleted mantle to their magma sources are contrasting in the two episodes of magmatism in association with breakup of the supercontinent rodinia while the change in melt source from the crust to the mantle keeps pace with the advance from continental rifting to supercontinent breakup significant transport of both heat and material from the depleted mantle to the continental crust only occurred along the active rifting zone in either case the growth and reworking of continental crust are episodically associated with rift magmatism

paleoproterozoic arc continent collision in the north china craton evidence from the zanhuang complex abstract the trans north china orogen tnco marks the major ca 300 km wide paleoproterozoic collisional suture between the eastern and western blocks of the north china craton ncc which also incorporates several microblocks or complexes here we investigate the zanhuang complex along the eastern margin of tnco we present petrological geochemical zircon u pb and lu hf data on a suite of quartz mica schist metavolcanics and diorite from the central zanhuang domain czd as well as granitoids and amphibolite that constitute the basement rocks of the western zanhuang domian wzd and eastern zanhuang domain ezd our study represents a cross section across two continental margins and covers the paleo ocean tract in between the metavolcanics show calc alkaline to tholeiitic affinity and negative correlations of la sm n vs p nd ti ti ce ce and positive with nb nb the granitoids fall within the vag field the iab and morb features of the volcanic suite are consistent with magma derivation in arc to back arc environment from an enrichment source the magmatic suite also displays lree enrichment positive rb k la pb nd anomalies and negative ta nb ce ti anomalies la cipms u pb geochronology of detrital zircon grains shows two age populations in the quartz mica schist with 207pb 206pb mean ages of 2499 14 ma and 2252 22 2216 39 ma and the timing of deposition is estimated as ca 2 3 2 2 ga zircons from the granodioritic gneiss yield 207pb 206pb mean age of 2508 14 ma representing neoarchean continental basement the metavolcanics and two diorite samples yield ages of 2302 30 ma 2089 63 ma marking the timing of an active arc the metamorphic zircons from these rocks show an age of 1882 15 ma the zircon lu hf data yield both positive and negative ehf t values suggesting depleted mantle source mixed with crustal components their crustal residence ages t dm c range from 3875 to 2224 ma and depleted model ages t dm range from 3415 to 2092 ma suggesting mixed juvenile and reworked crustal components and possible vestiges of mesoarchean basement we propose that the zanhuang complex is one of the paleoproterozoic arcs within the tnco which was accreted to the neoarchean continent along the eastern block of the ncc during the suturing along the tnco the tectonics associated with crustal growth and recycling in the tnco and the arc continent collision broadly coincided with the building of the columbia supercontinent

cycle anatomy and variability in the storm dominated type cincinnatian upper ordovician coming to grips with cycle delineation and genesis although parasequence and sequence are scale independent terms they are frequently applied only to specific scales of cycles for example meter scale cycles are commonly assumed to be parasequences or pacs in the upper ordovi cian kope and fairview formations of northern kentucky we examined a succession of 50 meter scale cycles that have been variously interpreted as deepening upward shallowing upward or showing no relationship with water depth our analysis shows that these cycles characterized by shifts in storm bed proximality are highly variable in their thickness and internal construction most cycles are best considered high frequency sequences because deepening upward intervals are common and many cycles contain evidence of abrupt basinward shifts in facies as expected at sequence boundaries a minority fit the parasequence model of shallowing upward cycles bounded by flooding surfaces larger 20 m scale cycles are defined by systematic thickening and thinning trends of meter scale cycl

neoarchean paleoproterozoic crustal growth and tectonic evolution of the trans north china orogen north china craton evidence from granite greenstone successions in the dengfeng complex granite greenstone successions and associated tonalite trondhjemite granodiorite ttg suites constitute dominant components of precambrian cratons here we present petrology geochemistry zircon u pb geochronology and lu hf isotopes on monzonite granodiorite granite and amphibolite from the dengfeng complex in the southern part of the north china craton ncc zircon u pb data yield weighted mean 207pb 206pb ages of 2498 6 ma for monzonite 2481 16 ma for granodiorite and 2475 21 ma for granite lu hf isotope systematics show ehf t values ranging from 1 3 to 6 7 and crustal model ages t text dm text c in the range of 2584 2934 ma for the rocks the monzonite granodiorite and granite show moderate total rare earth element ree contents enrichment in light rees lree and depletion in heavy rees hree negative nb ta and ti anomalies high al2o3 sr y and la yb n ratios with low cr and ni indicating that the magma was possibly sourced from partial melting of the lower crust the geochemical features of amphibolites are characterized by low sio2 na2o k2o sr y la yb n and high feo low total rees values limited lree hree fractionation and absence of obvious ce anomaly showing similarity to island arc magmatic rocks our results are consistent with the model of subduction and arc continent collision in the trans north china orogen during the neoarchean to paleoproterozoic

episodic crustal growth in the southern segment of the trans north china orogen across the archean proterozoic boundary abstract the dengfeng and taihua complexes are well exposed neoarchean to paleoproterozoic units in the southern segment of the trans north china orogen tnco zircon u pb dating shows that the dengfeng complex records two episodes 2568 11 ma and 2306 6 ma of tonalite trondhjemite granodiorite ttg magmatism all of the ttg rocks are characterized by high sio2 66 7 75 4 wt na2o 3 20 5 06 wt and relatively low mgo 0 40 1 78 wt the late neoarchean ttg gneisses have very low contents of hree ybn 0 69 2 75 and y 1 73 7 07 ppm with moderate la yb n 24 1 53 8 and high sr y 65 1 291 3 ratios the early paleoproterozoic ttg gneisses have low contents of hree ybn 2 93 6 37 and y 6 7 11 0 ppm with moderate la yb n 10 1 27 0 and sr y 10 6 52 1 ratios both suites show pronounced negative nb ta p and ti anomalies but positive sr and pb anomalies the late neoarchean ttg gneisses all have similar bulk rock nd and zircon hf model ages with mainly positive nd t and are interpreted as resulting from the melting of dominantly juvenile thickened lower crust with residual garnet and amphibole the early paleoproterozoic ttg gneisses have extremely variable nd t 6 23 to 4 23 and heterogeneous zircon hf t 3 3 to 3 1 which are also best interpreted as resulting from the partial melting of thickened lower crust with residual amphibole and garnet the taihua complex in the xiaoqinling area records three episodes of early paleoproterozoic ttg magmatism 2 48 ga at caotan 2 31 ga at houjiacun and 2 16 ga at bayuan younger than the taihua complex in the lushan area 2 85 2 72 ga all rocks have relatively low contents of hree ybn 1 03 8 32 and y 2 84 24 ppm with moderate la yb n 8 7 88 4 and sr y 19 8 125 8 ratios and show negative ta nb and ti anomalies and positive sr and pb anomalies the caotan gneisses at 2 48 ga and the houjiacun ttg gneisses at 2 31 ga have low mg 0 14 0 45 low cr the geochronology of the dengfeng complex in the dengfeng area and the taihua complex in the lushan xiong er and xiaoqinling areas reveals at least four magmatic episodes in the southern segment of the tnco from the late mesoarchean to early paleoproterozoic 2 85 2 72 ga 2 57 2 48 ga 2 34 2 30 ga and 2 20 2 07 ga the rocks of the two early episodes are dominantly of juvenile compositions with mostly positive whole rock nd t and zircon hf t values suggesting two episodes of crustal growth formed in a subduction tectonic setting the magmatic rocks of the third episode consist of both the juvenile and pre existing crustal materials with variable whole rock nd t and zircon hf t values which were generated in a subduction zone during the initial assembly of the ncc within the columbia supercontinent cycle the final episode of magmatism lacks juvenile materials with whole rock nd t and zircon hf t values being consistently negative these may have resulted from the orogenic collapse the episodic continental growth recorded in the southern segment of the tnco was caused by subduction and consequent orogeny consistent with global supercontinent cycles within the late archean and early paleoproterozoic

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

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

geochronological and geochemical constraints on the petrogenesis of the early paleoproterozoic potassic granite in the lushan area southern margin of the north china craton abstract we conducted a geochronological and geochemical study on the paleoproterozoic potassic granites in the lushan area southern margin of the north china craton ncc to understand the tectonic regime of the ncc at 2 2 2 1 ga this rock suite formed at 2194 29 ma the rocks are rich in sio2 76 10 77 73 wt and k2o 5 94 6 90 wt with high k2o na2o contents from 7 56 wt to 8 48 wt but poor in cao 0 10 0 28 wt p2o5 0 02 0 05 wt and mgo 0 01 0 30 wt mg 1 08 27 3 indicating they experienced fractional crystallization major element compositions suggest the potassic granites share an affinity with high k calc alkaline granite even though the lushan potassic granitic rocks have high a cnk ratios 1 11 1 25 which can reach peraluminous feature the very low p2o5 contents and negative correlation of p2o5 and sio2 ruling out they are s type granites different from peralkaline a type granites the lushan potassic granites have variable zr concentrations 160 344 ppm 226 ppm on average and 10 000 ga al ratios 1 76 3 00 together with high zircon saturation temperatures tzr 826 885 c indicating they are fractionated aluminous a type granites enriched lree la yb n 9 72 81 8 negative eu anomalies and low sr y with no correlations in sr y and sr zr versus cao suggest the possible presence of ca rich plagioclase and absence of garnet in the residual magmatic zircon grains have variable ehf t values 2 4 to 7 3 with zircon two stage hf model ages tdmc varying from 2848 ma to 2306 ma mostly around ca 2 5 ga and are plotted in the evolution line of crustal felsic rock we propose that the rocks mainly formed by partial melting of ca 2 50 ga tonalitic granodioritic crust as a result of upwelling mantle derived magmas which provided thermal flux and source materials in an intra continent rifting the ca 2 2 ga magmatism suggests that intra continental rifting occurred at 2 35 1 97 ga at least in the southern margin of the ncc after its final cratonization in the late neoarchean

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

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

petrogenesis of the archean tonalite trondhjemite granodiorite ttg and granites in the lushan area southern margin of the north china craton implications for crustal accretion and transformation abstract tonalite trondhjemite granodiorite ttg assemblages and abundant high k calc alkaline magmatism are considered to be closely related to craton stabilization and usually record a tectonic transition three episodes of granitic magmatism are identified in the lushan area at the southern margin of the north china craton ncc on the basis of new la icp ms zircon u pb ages and whole rock geochemical data they are ttg gneisses sodic potassic granite spg suite and potassic granite dated at 2840 ma 2760 ma and 2570 ma respectively the ttg gneisses have high sio 2 variable mg cr and ni contents with high la yb n and sr y ratios suggesting that the parental magmas were derived by partial melting of subducted oceanic crust they show no obvious correlations between sr y and dy yb or la yb n and dy yb and all have negative nb and ta but positive zr and hf anomalies and variable dy yb nb ta zr hf and zr sm ratios suggesting melting of a deep source 45 km with rutile eclogite and garnet amphibolite in the residue the ttg samples have positive hf t values 2 6 to 7 0 with the youngest t dm c 2896 ma close to the crystallization age indicating that they were produced by partial melting of juvenile crustal materials in an arc setting rocks of the spg suite have high sio 2 contents variable na 2 o k 2 o ratios 0 41 10 91 and low y and yb contents with high sr y ratios indicating an affinity to i type granites they display depleted and concave upward ree patterns between middle and heavy rees and higher zr sm than ttg gneisses possibly resulting from amphibole removal by fractional crystallization or as a residual phase during melting meanwhile the rocks have a large variation of dy yb without obvious correlations between sr y and dy yb and la yb n and dy yb in combination with variable but uniformly low y contents therefore we suggest that the spg samples were derived from partial melting with garnet in the residue magmatic zircons have hf t values from 4 3 to 4 2 with t dm c ages from 3200 ma to 2877 ma indicative of older mafic lower crustal sources the rocks formed within a short time interval with the ttg and their emplacement was accompanied by regional granulite and amphibolite metamorphism implying that they may also have formed in an arc setting the potassic granite has high sio 2 74 79 wt and k 2 o na 2 o 9 22 wt contents with a low 10 000ga al 1 89 ratio and t zr 670 c magmatic zircons have a narrow range of hf t values 2 0 to 4 1 with t dm c ages 2942 2692 ma older than the formation age but consistent with the formation age ca 2760 ma of the lushan spg suite the potassic granite has a hf isotope composition identical to that of the spg suite and is enriched in lree and depleted in y with a positive eu anomaly suggesting that the spg suite is the main source one zircon yielded an inherited age of 2837 36 ma consistent with the age of the ttg gneisses indicating that the gneisses could also be the source of the potassic granite the two types of source rocks indicate a shallow crust depth hence the heat required for partial melting of granodioritic rocks to form the potassic granite could have been provided by the upwelling of mantle or mantle derived melts in an extensional setting therefore the ttg gneisses spg suite and potassic granite in the lushan area record a tectonic transition from a compressive to an extensional setting in the southern margin of the ncc between 2 85 and 2 50 ga

geochemical changes in baslts and andesites across the archean proterozoic boundary identification and significance abstract to identify accurately changes in rock composition across the archean proterozoic boundary it is necessary to compare rocks from similar lithologic associations to constrain the effect of tectonic setting most basalts and andesites from the greenstone association volcanic dominated submarine supracrustal rocks possess a geochemical subduction zone component similar to their counterparts from modern arc systems basalts with island arc geochemical affinities dominate in archean greenstones while those with calc alkaline affinities are most abundant in proterozoic greenstones basalts with morb or oceanic within plate geochemical characteristics are rare in precambrian greenstones of all ages preserved early archean greenstone basalts 3500 ma reflect mantle sources less depleted than late archean greenstone basalts 2500 3500 ma proterozoic greenstone basalts are derived from relatively enriched mantle sources compared to all archean sources a feature which may be due to recycling of continental sediments into the mantle following rapid late archean continental growth precambrian andesites are geochemically similar to andesites from modern arcs but archean andesites are unique in that they are depleted in heavy ree and y results are consistent with archean andesite production by partial melting of descending mafic crust with amphibole garnet remaining in the residue while proterozoic and younger andesites are produced by fractional crystallization of basalts

late neoarchean magmatism and tectonic evolution recorded in the dengfeng complex in the southern segment of the trans north china orogen abstract the dengfeng complex exposed in songshan area in the southern segment of the trans north china orogen tnco mainly consists of late neoarchean tonalite trondhjemite granodiorite ttg gneiss metadiorite and amphibolite the sanhuangzhai amphibolite records the earliest mafic magmatism 2658 5 ma in the region which is enriched in lree and lile with negative nb ta and ti anomalies and positive initial e nd t and e hf t values suggested to be the remnant of an arc related juvenile mafic crust the shipaihe amphibolite at the end of neoarchean 2492 7 ma is characterized by flat ree pattern slightly negative nb ta and ti anomalies and positive initial e nd t and e hf t values which is interpreted as large degree partial melt of metasomatised mantle source in a back arc basin zircon u pb dating shows two episodes of ttg magmatism 2 57 2 55 ga and 2 55 2 50 ga within the dengfeng complex all ttg gneisses have high sio 2 and na 2 o but low mg cr ni yb n and y with high la yb n and sr y the early ttg gneiss 2 57 2 55 ga in the eastern songshan area has variable whole rock hf nd isotopes e hf t 2 14 4 64 e nd t 0 11 3 35 respectively and its protolith is interpreted as the result of partial melting of a thickened lower crust with residual garnet and amphibole in the source but the later ttg gneiss 2 55 2 50 ga in the western songshan area has depleted whole rock hf nd isotopes e hf t 5 59 6 08 e nd t 2 42 3 86 respectively suggesting an overall juvenile source and its protolith is interpreted as the partial melt of flat subducting oceanic crust the shipaihe metadiorite is characterized by high mg cr ni sr ba highly fractionated ree patterns and strong negative nb ta and ti anomalies resembling to sanukitoid suite which is interpreted as the partial melt of a mantle wedge metasomatised by subduction derived fluids melts integrated geochronology and geochemical data of the dengfeng complex in songshan area reveal the late neoarchean crustal accretion process from subduction to arc continental collision accretionary orogeny followed by post collisional extension back arc basin implying an active continental margin arc environment in the southern segment of the north china craton

geochronology and geochemistry of 2 5 to 2 4 ga granitic plutons from the southern margin of the north china craton implications for a tectonic transition from arc to post collisional setting abstract the xutai and lujiagou plutons exposed in the songshan jishan area in the southern margin of the north china craton ncc are studied to constrain the tectonic regime of the ncc between 2 5 and 2 4 ga the xutai pluton dated at 2509 33 ma mainly consists of tonalite and monzogranite with a calc alkaline affinity rittmann index

petrogenesis of the 2 1 ga lushan garnet bearing quartz monzonite on the southern margin of the north china craton and its tectonic implications abstract the lushan garnet bearing quartz monzonite was emplaced into the western taihua complex at 2134 17 ma on the southern margin of the north china craton ncc the rocks contain sio 2 contents of 56 98 59 05 wt with high k 2 o na 2 o 7 46 9 14 wt and al 2 o 3 15 87 17 58 wt and low cao 2 38 2 77 wt and mgo 1 18 1 50 wt contents and belong to an intermediate shoshonitic series magmatic garnet grains in the rocks are chemically homogeneous with relatively high cao 6 36 7 92 wt but low mno 1 45 1 94 wt and mgo 2 47 3 45 wt contents and high fe mn ratios they contain 61 94 66 39 mol almandine 18 60 23 40 mol grossular 10 06 15 11 mol pyrope and 1 09 4 32 mol spessartine similar to high pressure garnets formed from m type magma but different from those found in s type granites and metapelites phase equilibrium diagrams in combination with trace element distribution coefficients between zircon and garnet suggest whole rock zircon saturation temperatures varying from 891 c to 951 c and the mineral assemblage of garnet plagioclase amphibole or biotite in these rocks is stable at 15 kbar and 890 950 c with h 2 o t 800 c all of the rocks are enriched in lile and lree with low nb la ratios 0 24 0 61 similar to those of lithospheric mantle which has a nb la ratio of 0 5 therefore the garnet and whole rock chemical compositions indicate that the lushan quartz monzonite possibly formed by small degrees of partial melting of a phlogopite bearing lithospheric mantle the variable zircon hf t values 3 5 to 4 1 with t dm c from 2 34 ga to 2 51 ga suggest involvement of crustal materials the rocks have slightly negative nb and ta anomalies characteristics of island arc basalts iab however their high zr 598 926 ppm and zr y ratios 17 1 21 8 suggest an affinity with ocean island basalt oib hence the mixed iab and oib like geochemical signatures are indicative of continental intra plate rifting possibly related to extension and thinning of the lithosphere and upwelling of asthenosphere our study proposes that an intra continental rifting event occurred at 2 2 2 0 ga on the southern margin of the ncc after the final amalgamation of ncc

discrimination and origin of the sanukitoid series geochemical constraints from the neoarchean western karelian province finland abstract neoarchean late to post tectonic sanukitoid intrusions are found in the western part of the karelian province in finland variable sized even grained to k feldspar porphyritic intrusions form a series of diorites tonalites and granodiorites that are calc alkaline to alkali calcic magnesian and mostly peraluminous the major and trace element geochemistry of the intrusions show typical sanukitoid affinities a mantle signature high content of mg ni cr and high mg and enrichment in lile especially k ba and sr the intrusions form a distinctive series that can be distinguished from the ttg series of the karelian province by their high ba sr signature low na 2 o k 2 o ratio and uniform hree pattern the sanukitoid series can be compositionally constrained as follows sio 2 55 70 wt na 2 o k 2 o 0 5 3 mgo 1 5 9 wt mg 45 65 k 2 o 1 5 5 0 wt ba sr 1400 ppm and gd er n 2 6 the probable source was enriched subcontinental lithosphere mantle with high lile concentrations in phlogopite and or sanidine the accumulation of k ba and sr in the mantle source may have occurred as a consequence of two separate metasomatic events 1 by subduction related fluids melts and 2 by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff the slab breakoff at the end stage of subduction is also a viable trigger for the sanukitoid magmatism

geochemical and nd hf isotopic constraints on the origin of the 1 74 ga damiao anorthosite complex north china craton abstract the 1 74 ga damiao complex in the north china craton consists of anorthosite 85 norite 10 mangerite 4 and minor troctolite 75 would have been required to form the parental high al gabbroic magma from the lower crust we propose that the crustal rocks were dragged into the upper mantle during amalgamation of the north china craton where the ambient temperature was high enough 1271 c at 12 kbar to cause extensive melting producing a deep seated magma chamber the melt then evolved through polybaric crystallization producing anorthositic magmas with abundant suspended plagioclase that were finally injected at mid crustal depth to form the damiao complex

age and tectonic setting of late archean greenstone gneiss terrain in henan province china as revealed by single grain zircon dating the authors report precise u pb zircon ages for single grains of a metarhyodacite from the late archean dengfeng greenstone belt in henan province china near the southern margin of the north china craton most grains belong to an igneous population whose u pb isotopic systematics define a straight line intersecting concordia at 2512 12 ma and this is interpreted as the time of crystallization of the original greenstone volcanics several grains are distinctly older between 2576 9 and 2945 44 ma and the authors interpret the older grains as xenocrysts of pre greenstone continental crust that provide evidence for crustal derivation or crustal contamination of the original rhyodacitic lava the xenocrysts suggest evolution of the dengfeng greenstone belt in a continental environment that may be represented by the taihua high grade gneisses bordering the dengfeng greenstones and for which the authors obtained ages of 2806 7 and 2841 6 ma the data add evidence to the now widely held concept that most archean greenstones developed on or near older continental crust and were therefore prone to crustal contamination in such cases conventional zircon dating may not always record the precise age of rock formation

2 7ga crust growth in the north china craton abstract numerous u pb zircon geochronological data show that rocks of the precambrian basement from the north china craton ncc have two age peaks at 1 8 1 9 and 2 5 ga respectively whether the most prominent peak at 2 5 ga really registered a period of major crustal growth in the ncc thus making it different from the global major crustal growth period of 2 7 ga is uncertain in this paper we carried out in situ u pb and hf isotopes of zircons and whole rock chemical and sr nd isotopic analyses for six precambrian samples from the ncc in order to understand crustal growth and reworking the samples have u pb zircon ages of 1 8 1 9 2 5 and 2 7 ga respectively the two samples with u pb zircon ages of 2 7 ga have zircon hf model ages t hf dm and or whole rock nd model ages t nd dm close to their u pb zircon ages it is clear that they represent juvenile crust generation thus providing direct evidence that 2 7 ga was a period of new crustal addition the samples with u pb zircon ages of 1 8 and 2 5 ga also have t hf dm and or t nd dm similar to those of the 2 7 ga samples indicating that these samples also have a mantle extraction time of 2 7 0 1 ga and their 1 8 and 2 5 ga ages may represent periods of reworking of the 2 7 0 1 ga crust rather than juvenile crust generation the reworking is manifested either as metamorphism or as lower crustal derived magmatism specifically the 2 5 ga tonalitic gneiss sample is thought to be derived by melting of the 2 7 ga lower crust since many 2 5 ga tonalite trondhjemite granodiorites ttgs and calc alkaline granitoids in the ncc contain 2 7 ga xenocrystic and inherited zircons we postulate that they are probably also derived mainly from the 2 7 0 1 ga crust our data imply that the quantity of 2 7 ga continental crust in the ncc is probably greater in extent than that exposed today

neoarchean paleoproterozoic terrane assembly and wilson cycle in the north china craton an overview from the central segment of the trans north china orogen abstract the north china craton ncc is one of the important precambrian nuclei of the globe as well as an integral component of the paleoproterozoic supercontinent columba the ncc is considered in popular models as an assembly of two major crustal blocks the eastern and western blocks which were sutured along the trans north china orogen tnco which represents a major paleoproterozoic collisional orogen the central segment of the tnco preserves important keys to unravel the tectonic history of amalgamation and cratonization of the ncc here we present an overview on the lithology geochemistry geochronology lu hf isotopes and metamorphic history of the neoarchean to paleoproterozoic rocks in the major basement terranes from the central segment of the tnco the available data allow us to re construct the major precambrian events from the heart of the ncc as follows 1 2 58 2 48 ga amalgamation of three microblocks ordos qianhuai and xuchang along the wutai granite greenstone belt and its branch at the zanhuang area together with the convergence of major microblocks along other 2 5 ga granite greenstone belts leading to the initial cratonization of the ncc 2 2 50 2 45 ga post collisional extension as represented by undeformed mafic dykes and granitoid dykes or plutons resulting in the opening of an oceanic basin along the hengshan and huai an xuanhua complexes 3 2 45 2 12 ga subduction in the hengshan huai an xuanhua and luliang complexes and simultaneous rifting in the fuping wutai and zanhuang complexes 4 2 12 1 98 ga opening of oceanic basins in the wutai and fuping areas followed by double subduction of the oceanic lithosphere and arc magmatism in the fuping wutai and luliang complexes with coeval rifting in the northern part as represented by the hengshan and huai an xuanhua complexes and the southern side as represented by the zanhuang complex 5 1 96 1 80 ga the assembly of the separated terranes or complexes driven by the amalgamation of the western and eastern blocks the collisional event may have occurred at 1 96 1 90 ga and the 1 88 1 80 ga metamorphic ages might represent the retrograde cooling during exhumation 6 termination of the collisional event represented by post collisional intrusions of granitoids charnockites and pegmatites until ca 1 74 ga thus the central segment of the tnco records a prolonged wilson cycle following the initial cratonization of the ncc during neoarchean and involved multiple rift subduction and collisional processes in the paleoproterozoic resulting in the unified ncc and its incorporation into the supercontinent columbia

a 2 5 ga fore arc subduction accretion complex in the dengfeng granite greenstone belt southern north china craton abstract the dengfeng granite greenstone belt dggb located in the southern segment of the central orogenic belt cob of the north china craton ncc consists of a volcano sedimentary assemblage intruded by tonalite trondhjemite granodiorite ttg suite diorite granites and late mafic dikes the volcano sedimentary assemblage in the dggb mainly consists of tectonically imbricated basaltic amphibolites meta gabbroic rocks with minor ultramafic rocks and metagreywacke marble and quartzite consistent with characterisitics of typical phanerozoic subduction accretion complexes the basaltic amphibolites yield a metamorphic zircon 207pb 206pb age of 2507 26 ma interpreted to represent the peak age of amphibolite facies metamorphism that took place during subduction accretion of the basaltic protolith the basaltic amphibolites are characterized by a tholeiitic affinity and flat lree patterns with minor negative nb and zr anomalies based on mixed morb and arc affinities the basaltic amphibolites in the dggb are interpreted to have formed in a fore arc tectonic setting one late potassic granite dike cutting across the fabrics of the volcano sedimentary assemblage yields an intrusion age of 2492 35 ma constraining the minimum deformation age for tectonic assembly of the package the ttg gneisses and diorites intruded the western margin and the center of the subduction accretion complex respectively one ttg sample and one diorite sample yield igneous zircon 207pb 206pb ages of 2514 26 ma and 2518 36 ma respectively constraining their intrusion ages the ttg gneisses display high ratios of la yb cn and sr y and depletion in hfse with negative nb ta and ti anomalies consistent with those of typical archean ttgs the ttg gneisses are therefore considered to be generated from partial melting of a shallowly subducting oceanic slab and or accreted arc amphibolites the diorites have high concentrations of mgo 2 89 6 05 wt ni 148 178 ppm and cr 85 7 120 6 ppm and highly fractionated ree patterns and are depleted in hfses with negative nb ta zr hf and ti anomalies we suggest that the high mg diorites in the dggb may have been derived from a hydrated mantle wedge which was previously metasomatized by subduction derived melts and or fluids collectively a neoarchean subduction accretion collision event is therefore proposed to have generated the dggb the volcano sedimentary assemblage in the dggb represents a fore arc subduction accretion complex which is interpreted to be related to the suture zone of ca 2 5 ga arc continent collision between a ttg dominated arc terrane in the cob and the eastern block of the ncc we further propose a long n s striking neoarchean suture zone occurring in the eastern margin of the cob mainly consists of the ca 2 5 ga subduction accretion complex in the dggb to the south the ca 2 5 ga melange belt in the zanhuang complex in the central and the ca 2 5 ga ophiolitic melange belt in the zunhua dongwanzi structural belt to the north which separate an arc terrane in the cob from the eastern block of the ncc

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

comment on the mesozoic margin of the maghrebian tethys in the rif belt morocco evidence for polyphase rifting and related magmatic activity by gimeno vives et al

ttg and potassic granitoids in the eastern north china craton making neoarchean upper continental crust during micro continental collision and post collisional extension as the major component archean granitoids provide us with an insight into the formation of the early continental crust we report the study of a series of neoarchean granitoids including tonalite trondhjemite granodiorite ttg and potassic granitoids in the xingcheng region of the eastern north china craton zircon u pb dating shows that the ttg granitoids were emplaced in the neoarchean within a 75 myr period 2595 2520 ma with coeval mafic magmatic enclaves followed by intrusion of potassic granitoids the geochemistry of the ttg granitoids is consistent with partial melting of mesoarchean enriched mafic crustal sources at different depths up to 10 12 kbar equivalent pressure during a continental collision event the potassic granitoids are derived from either low degree melting of mesoarchean enriched mafic crustal sources or remelting of mesoarchean ttgs in response to post collisional extension and were hybridized with neoarchean mantle derived mafic melts to various degrees the ttg and potassic granitoids in the xingcheng region record the evolution from collision of micro continental blocks to post collisional extension consistent with other studies suggesting that the amalgamation of micro continental blocks is what gave rise to the cratonization of the north china craton at the end of the archean the rock assemblage of these granitoids resembles those of syn and post collisional magmatism in phanerozoic orogenic belts and the estimated average composition is similar to that of the present day upper continental crust suggesting that a prototype upper continental crust might have been developed at the end of the archean from a mixture of ttg and potassic granitoids together with concurrent high grade metamorphism in the north china craton we conclude that collisional orogenesis is responsible for continental cratonization at the end of the archean in the north china craton