paleoproterozoic granitoids in the basement of bangladesh a piece of the indian shield or an exotic fragment of the gondwana jigsaw abstract we present the first precise age for precambrian basement rocks in bangladesh these lie within the dinajpur block located between the indian craton to the southwest and the shillong massif to the east there are no surface outcrops and the rocks were intersected by drill holes they consist of a suite of tonalitic and granodioritic rocks variously deformed to granitic gneiss and intruded by younger monzogranite a tonalite obtained at a depth of 227 48 m in drill hole bh 2 at maddhapara in northwestern bangladesh records a shrimp zircon 207pb 206pb magmatic age of 1722 6 ma paleoproterozoic rocks with similar magmatic ages are unknown in the adjacent indian blocks of the chotanagpur plateau indian craton or shillong massif this lack of comparable ages may be due to the paucity of precise radiometric ages from the indian terrains or more likely because there are real age differences with the buried rocks at maddhapara representing a separate and discrete microcontinental fragment the dinajpur block that was trapped by the northward migration of india during gondwana dispersal

paleoproterozoic tectonic transition from collision to extension in the eastern cathaysia block south china evidence from geochemistry zircon u pb geochronology and nd hf isotopes of a granite charnockite suite in southwestern zhejiang abstract the badu complex and associated paleoproterozoic granitoids are among the oldest known rocks in the cathaysia block in south china the paleoproterozoic units of the badu complex are dominantly composed of metapelitic rocks and meta greywackes here we report la ss icp ms laser ablation split stream inductively coupled plasma mass spectrometry zircon u pb data from a newly discovered garnet bearing granite which show an emplacement age of 1929 15 ma and metamorphism at 1872 34 ma we also report u pb ages of 1886 16 ma 1858 7 ma 1848 11 ma from a gneissic granodiorite and two charnockites respectively the garnet bearing granite is peraluminous with a cnk range from 1 1 to 1 3 the rock shows relatively high sio2 k2o and rb contents and low total ree sr cao and ferromagnesian components typical of leucogranites the whole rock nd two stage model age tdm2 nd of this rock is ca 2 7 ga zircon hf crustal model ages tdmc hf peak at about 2 7 ga and abundant inherited zircons occur with u pb ages in the range of 2044 to 2803 ma evidences from zircon u pb age and hf isotope compositions whole rock nd isotopes and whole rock major and trace elements suggest a metasedimentary protolith and that the garnet bearing granite leucogranite was derived by partial melting in a thickened crust at about 1 93 ga the gneissic granodiorite and charnockites show indistinguishable major and trace element features as well as zircon hf and whole rock nd isotope compositions indicating that they were generated from the same source rocks the gneissic granodiorite and charnockites are ferroan calc alkalic and metaluminous with a cnk range from 0 80 to 0 98 they display relatively low sio2 contents and ga al ratios suggesting their a type affinity their zircon tdmc hf age peak is 2 9 ga and whole rock tdm2 nd ages range from 2 8 to 2 9 ga these high temperature rocks were generated possibly through the partial melting of ancient amphibolites 2 9 ga with heat input from asthenosphere upwelling and magmatic underplating in an extensional setting at about 1 85 1 88 ga combined with data from previous studies we suggest three episodes of major crustal growth in this region at 1 8 1 9 ga 2 7 ga and 2 9 ga during the 1 8 1 9 ga event extensive reworking also took place from the 1 93 ga syn collision leucogranite garnet bearing granite the 1 88 1 85 ga post collision a type granites and charnockites the granite charnockite suite and the1 85 1 77 ga intraplate basaltic rocks li 1997 and xiang et al 2008 in the region a paleoproterozoic orogenic cycle can be deciphered in the cathaysia block the rapid transition of tectonic regime from collision to post collisional extension can be correlated to the assembly of the supercontinent columbia

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

isotopic constraints on the structural relationships between the lesser himalayan series and the high himalayan crystalline series garhwal himalaya nd and sr isotope systematics may provide important constraints on the location of major thrust systems that separate lithologically similar sedimentary sequences the potential of the technique is illustrated by this isotopic study of the main central thrust system of the himalaya nd isotope data from the garhwal himalaya indicate that metasedimentary rocks from the vaikrita group nd 14 to 19 correlate closely with those from the high himalayan crystalline series which constitutes the hanging wall lithologies of the main central thrust in contrast metasedimentary rocks from the munsiari group nd 23 to 28 show marked similarities to the lesser himalayan series in the footwall of the main central thrust sr isotopes support the correlations in that the vaikrita group shows partial reequilibration at 500 ma whereas the munsiari group has not undergone sr isotope homogenization since 1800 ma thus the vaikrita thrust that juxtaposes these two formations is recognized as the main central thrust in garhwal himalaya the thrust coincides approximately with the location of the kyanite isograd confirming that inverted metamorphism is characteristic of both hanging wall and footwall of the main central thrust along the tons thrust known locally as the srinagar thrust 50 km south of the main central thrust low grade quartzarenites with nd sr isotope and trace element characteristics typical of lesser himalayan formations have been emplaced on phyllites and siltstones with geochemical characteristics of the high himalayan crystalline series the field relationships most probably result from out of sequence thrusting in which lesser himalayan series rocks to the north were emplaced over low grade equivalents of the high himalayan crystalline series preserved in the external part of the orogen this study establishes the value of isotope data for lithostratigraphic correlations within orogenic belts

where was south china in the rodinia supercontinent evidence from u pb geochronology and hf isotopes of detrital zircons abstract u pb geochronology and lu hf isotopic studies on detrital zircons from late neoproterozoic sediments of the cathaysia block south china show abundant grenville age 1 0 ga and neoarchaean populations and minor eoarchaean 3 8 ga paleo to mesoarchaean 3 3 3 0 ga mesoproterozoic 1 7 1 4 ga and pan african 0 70 0 54 ga populations this is the first report of 3 8 ga material in the crust of the cathaysia block the presence of euhedral 1 0 ga zircons indicates that a grenville orogenic belt was within or very close to the southern cathaysia block however the provenance containing the 3 8 ga 3 3 3 0 ga 2 5 ga 1 0 ga and 0 70 0 54 ga zircon populations cannot be found in the south china block the combination of zircon age distributions and the rounded strongly abraded shapes of the archean zircons suggesting long transport is consistent with derivation from other continental terranes previously linked with the southern part of the south china block comparison with the tectono magmatic history and compositions of rocks in western laurentia eastern australia and eastern india east antarctica western australia we suggest that these late neoproterozoic sediments may have originated mainly from eastern india east antarctica this indicates that the south china block was linked with the eastern india east antarctica continents in the late neoproterozoic rather than being located between the western laurentia and eastern australia continental blocks u pb and hf isotope studies on detrital zircons provide an important independent constraint on the palaeogeography of the south china block in the context of the breakup of rodinia and the subsequent assembly of gondwana in late neoproterozoic time and insights into the relationship between the cathaysia and yangtze blocks

tectonothermal events in central indian tectonic zone citz and its implications in rodinian crustal assembly abstract the precambrian crust of central india comprising bundelkhand craton bkc in the north and bastar craton bc in the south were accreted along a ene wsw trending proterozoic central indian tectonic zone citz the citz is an ensemble of several low to medium grade supracrustal belts gneisses granitoids and a few linear tracts of granulite belts a number of crustal scale shear zones define the boundaries of the supracrustal belts and discrete terrains available data suggest polyphase tectonothermal events in citz spanning from palaeoproterozoic to early neoproterozoic each event is characterized by contractional tectonic regime and attendant metamorphism and magmatism a new plate tectonic model in contrast to the earlier one of yedekar et al geol surv india spec publ 28 1990 is proposed according to the present model a northward dipping subduction system leading to continent continent collision explains the growth and assembly of the citz the continent continent collision is tentatively placed at ca 1 5 ga which is comparable to similar tectonothermal event in chotanagpur gneissic complex further east while the suturing event predates the global grenvillian orogeny ca 1 3 1 0 ga the sausar tectonothermal event ca 1 1 0 9 ga of citz is correlatable with the latter

the mesoproterozoic supercontinent atlantica in the brazilian shield review of geological and u pb zircon and sm nd isotopic evidence abstract supercontinent atlantica was formed in south america by the orogenies of the trans amazonian cycle namely the accretionary encantadas orogeny 2250 2100 ma and the collisional camboriu orogeny 2100 2000 ma large belts 500 to more than1000 km long formed during the trans amazonian cycle in the three major cratons of south america in the northern part of the amazon craton in the sao francisco craton and in the rio de la plata craton however other large 1000 km segments of archean crust remained little deformed in the cratonic interior of supercontinent atlantica such as a major portion of the tocantins province in central brazil in addition smaller fragments up to 100 km of trans amazonian cycle continental crust are present inside the neoproterozoic brasiliano cycle orogenic belts in the eastern half of extra andean south america in contrast the dominant volume about 90 of neoproterozoic belts was formed by reworking of archean and paleoproterozoic crust zircon u pb geochronology associated with nd isotopes indicates the widespread presence of supercontinent atlantica crust in south america and sensitive high mass resolution ion microprobe investigation of zircons indicates that crust in southern brazil was formed mostly in the trans amazonian cycle zircon geochronology also reveals that supercontinent atlantica was preceded by an intra cratonic period lasting about 300 my and was succeeded by an intra cratonic period of about 1000 to 1300 my many of the trans amazonian cycle belts and crustal fragments may have been accreted to south america during the neoproterozoic the demonstration that they all were once part of supercontinent atlantica must await further multi technique investigations

late paleoproterozoic magmatism in delhi fold belt nw india and its implication evidence from epma chemical ages of zircons abstract zircons from six granitoid plutons occurring in the northern part of the delhi fold belt nw india have been chemically dated using an electron microprobe most of the zircons occurring in the granites are chronologically unzoned and gave ages around 1 78 1 71 ga but younger ages of 1 1 0 9 ga have also been obtained from the rim of some grains monazite and zircons from the metasediments of delhi supergroup adjacent to the granitoids were also analyzed the older age of 1 9 1 7 ga obtained for monazites could possibly indicate their provenance age detrital zircon grains mostly rounded in the delhi metasediments which gave older ages of 1 9 ga could possibly have been derived from the archaean basement rocks exposed in this aravalli delhi fold belt the geochemical signatures of these granitoids are consistent with an extensional tectonic regime it is quite likely that contrary to the prevailing assumption of the granitoids being intrusive our geochronologic data suggests them to be the basement for sedimentation the new geochronologic information on these granitoids in the northern part of the delhi fold belt and their comparison with other correlative events establishes a widespread thermal event during late paleoproterozoic

correlation of lithotectonic units across the eastern himalaya bhutan clastic sediments deposited in foreland basins and offshore fans allow the evolution of an orogen to be reconstructed provided their source regions are properly characterized isotopic data from the lithotectonic units of the eastern himalaya bhutan indicate clear isotopic differences directly comparable with the equivalent units from the central himalaya zircons from metaquartzites of the high himalayan series that range in age from 980 to 1820 ma and an orthogneiss intruded at 825 9 ma bracket deposition to between 816 and 980 ma model ages derived from nd isotopes of associated metapelites range from 1700 to 2200 ma in contrast zircons from a metaquartzite from the lesser himalayan series range from 1850 to 2550 ma a paleoproterozoic deposition age ca 1750 ma is inferred from the age of a metarhyolite associated with the sediments model nd ages of metapelites from the lesser himalayan series range from 2500 to 2600 ma the bhutanese himalayan units can be correlated more than 1000 km westward along strike from catchments of the brahmaputra to the headwaters of the sutlej on the basis of their structural position provenance and isotopes because current discharge from the brahmaputra carries the dominant sedimentary flux into the bengal fan results from this work validate the interpretation of isotopic variations observed in offshore deposits in terms of the unroofing history of the component lithologies of the himalaya

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

composite nature of the north china granulite facies belt tectonothermal and geochronological constraints granulite facies rocks are intermittently exposed in a roughly e w trending belt that extends for approximately 2000 km across the north china craton from the helanshan qianlishan wulashan daqingshan guyang and jining complexes in the western block through the huai an hengshan xuanhua and chengde complexes in the trans north china orogen to the jianping western liaoning eastern hebei northern liaoning and southern jilin complexes in the eastern block the belt is generally referred to as the north china granulite facies belt previously interpreted as the lowest part of an obliquely exposed crust of the north china craton recent data indicate that the north china granulite facies belt is not a single terrane instead it represents components of three separate terranes the eastern and western blocks and trans north china orogen each of these units records different metamorphic histories and reflect the complex tectonic evolution of the ncc during the late archean and paleoproterozoic mafic granulites in the eastern block and the yinshan terrane western block underwent medium pressure granulite facies metamorphism at about 2 5 ga with anticlockwise p t paths involving near isobaric cooling following peak metamorphism reflecting an origin related to intrusion and underplating of mantle derived magmas pelitic granulites in the khondalite belt western block underwent medium pressure granulite facies metamorphism at about 2 0 1 9 ga with clockwise p t paths which record the paleoproterozoic amalgamation of the yinshan and ordos terranes to form the western block mafic and pelitic granulites in the trans north china orogen experienced high to medium pressure granulite facies metamorphism at 1 85 ga with clockwise p t paths involving nearly isothermal decompression following peak metamorphism which are in accord with the final collision between the eastern and western blocks to form the north china craton at 1 8 ga the ncgb cannot therefore represent a separate unique terrane instead it reflects the amalgamation of three separate granulite terranes that evolved independently and at different times d 2005 international association for gondwana research published by elsevier b v all rights reserved

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

tectonic implications of palaeoproterozoic anatexis and late miocene metamorphism in the lesser himalayan sequence sutlej valley nw india unravelling the kinematic evolution of orogenic belts requires that the defining tectonostratigraphic units and structural elements that bound them are properly identified and characterized in the sutlej valley western himalaya the munsiari and vaikrita thrusts have both been correlated with the main central thrust the sequence of amphibolite grade rocks the jutogh group bounded by these faults has been variously assigned to the lesser himalayan sequence based on provenance ages and to the greater himalayan sequence from its metamorphic grade trace element and geochronological data from leucogranites in the jutogh group 1 indicate crustal melting at c 1810 ma before the deposition of the greater himalayan sequence thus correlating the jutogh group with the lesser himalayan sequence and 2 record proterozoic metamorphism overprinted at 10 5 1 1 ma established from u pb analysis of uraninite during the himalayan orogeny pressure temperature time data indicate that the jutogh group and greater himalayan sequence represent distinct tectonic units of the metamorphic core that were decoupled during their extrusion this precludes extrusion along a single widening channel and requires a southward shift of the locus of movement during the late miocene coincident with present day precipitation patterns

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

correlations between the eastern block of the north china craton and the south indian block of the indian shield an archaean to palaeoproterozoic link abstract recent tectonometamorphic data reveal that the north china craton formed by amalgamation of an eastern block eb and a western block wb along the trans north china orogen tnco and the indian shield formed by amalgamation of the south indian block sib and the north indian block nib along the central indian tectonic zone citz the eb of the north china craton and the sib of the indian shield share many similar magmatic and sedimentary features the early archaean supracrustal sequences in both the eb and sib consist of 3 6 3 4 ga fuchsite quartzites pelitic gneisses calc silicates marbles banded magnetic quartzites and amphibolites called the caozhuang group in the eb and the older metamorphic group omg in the sib the middle archaean assemblages in both the blocks can be divided into an early 3 4 3 3 ga phase represented by the chentaigou supracrustal rocks and orthogneisses in the eb and the holenarsipur supracrustal rocks and the gorur orthogneisses in the sib and a late 3 1 2 9 ga phase represented by the qianan supracrustal rocks and the yangyashan orthogneiss in the eb and the sargur group and the peninsular gneiss in sib the late archaean taishan group and its equivalents in the eb are stratigraphically similar to the dharwar supergroup in the sib moreover both the eb and sib are characterised by near contemporaneity of late archaean granitoid intrusive and metamorphic events in addition dome and basin structures are dominant in both the eb and sib and anticlockwise p t paths charaterise the metamorphic evolution of the late archaean granulites in the two blocks the palaeoproterozoic sedimentary volcanic rocks in both blocks comprise lower clastic rich middle volcanic rich and upper clastic carbonate sequences the strong resemblance of the archaean to palaeoproterozoic magmatic and sedimentary records suggests that it is possible that the eb and sib are dispersed remnants of what was once a single continent a possible fit is proposed for the reconstruction of the eb and sib where the northern margin of the eb is placed adjacent to the western margin of the sib with the tnco and wb representing the continuations respectively of the citz and nib this fit suggests that the eb sib and the wb nib represent two discrete continental blocks that joined along the tnco citz orogen during a palaeoproterozoic collisional event fragmentation of the eb and sib may have occurred at the beginning of the mesoproterozoic and by 1 4 ga the eb and sib may have separated into two different continental blocks as evidenced by striking differences in the mesoproterozoic sedimentary successions and associated bimodal volcanics in the two blocks

an overview of the upb geochronology of the paleoproterozoic torngat orogen northeastern canada abstract the paleoproterozoic torngat orogen northern labrador and northeastern quebec canada is the result of oblique collision between the nain north atlantic and rae cratons a comprehensive set of u pb ages allows the chronology of events to be closely bracketed subduction occurred below the nain craton from ca 1910 1870 ma and collision between the cratons may have occurred between 1869 and 1844 ma sinistral deformation continued along the intervening abloviak shear zone until ca 1824 ma and convergence was ultimately impeded by the partial subduction of the southern rae craton post collisional isostatic uplift of the southern rae craton initiated deformation in the komaktorvik zone ca 1798 ma a prominent bend in the abloviak shear zone may be the result of differential uplift of the western side of the orogen in the south sinistral strike slip and east as well as west side up deformation continued episodically in the komaktorvik zone until at least 1710 ma the tectonic development of the orogen can be explained in terms of modern plate tectonic processes

evolution of reworked paleoproterozoic basement rocks within the ribeira belt neoproterozoic se brazil based on u pb geochronology implications for paleogeographic reconstructions of the sao francisco congo paleocontinent abstract geological geochemical and geochronological data suggest that the basement exposed in the occidental terrane of the neoproterozoic ordovician ribeira belt represents the continuation of the sao francisco paleocontinent which was amalgamated at the end of the rhyacian transamazonian orogeny the mantiqueira complex represents a cordilleran type active margin of the archean paleocontinent while the juiz de fora complex represents juvenile paleoproterozoic material probably developed within an oceanic setting primitive arc or plateau the latter unit was probably accreted to the active margin of the paleocontinent during the latest stages of the transamazonian orogeny around ca 2 05 ma causing the deformation and metamorphism of the mantiqueira complex at this time to the west and on the cratonic foreland concurrent deformation of the minas passive margin and sedimentation of the sabara basin took place subsequent to the transamazonian orogeny the basement associations were intruded by intraplate alkaline and basic rocks related to rifting events between ca 1 7 and 1 3 ga that resulted in the development of intracratonic basins the paleoproterozoic suture located between the mantiqueira and juiz de fora paleoproterozoic terranes probably controlled the neoproterozoic passive margin tectonics and also the development of a major thrust surface during the neoproterozoic cambrian brasiliano convergence

geochemical evolution of peraluminous paleoproterozoic bandal orthogneiss nw himalaya himachal pradesh india implications for the ancient crustal growth in the himalaya abstract paleoproterozoic 1900 100 ma granites along a 2000 km linear belt in the lesser himalaya are significant in terms of their tectonic setting and emplacement as they form the basement for younger sedimentary cover rocks the geochemistry and petrogenesis of one granitic body bandal orthogneiss 1904 70 ma from the lesser himalayan belt has been studied and correlated with the other plutons in the belt the paleoproterozoic bandal orthogneiss covering 500 sq km surface area occupies the core of the kulu rampur window himachal pradesh nw lesser himalaya the orthogneiss is s type peraluminous and can be subdivided into two suites a muscovite biotite granite suite i coarse grained porphyritic gneiss cpg and fine grained gneiss fg and a tourmaline muscovite granite suite ii leucogranite lg the two mica granites suite i form the bulk of the bandal orthogneiss whereas the tourmaline bearing granite which cuts across suite i occurs in the central part of the main pluton comparison of their bulk composition with melt experimental data suggest formation of lg from a water undersaturated magma of minimum melt composition at pressures around 3 4 kbar whereas the tourmaline free granites may have been derived by melting due to biotite dehydration at pressures 5 kbar high concentrations of mgo feo ba sr rb sr and ti of the two mica granites reflect higher extents of melting derived from biotite dehydration melting of a metasedimentary source tourmaline leucogranites with higher rb sr and low ba sr ratios represent low fraction melts extracted from their protoliths under conditions of low water activity the striking similarities in terms of the geological setting geochemical characteristics and the age data between bandal orthogneisses and the adjoining wangtu gneisses suggest that they were formed under similar tectono magmatic environment during paleoproterozic period the wide spread occurrence of paleoproterozoic gneisses in the lesser himalayan belt strongly suggest that they represent the granitic basement on which the younger sedimentary rocks were deposited the geochemical studies on the overlying sedimentary rocks chail and jutogh formations in the lesser himalaya suggest that the huge volumes of granitic magmatism played a significant role in changing the crustal composition of the himalayan rocks from mafic to felsic during the post archean

tectonic implications of palaeoproterozoic post collisional high k felsic igneous rocks from the kimberley region of northwestern australia abstract palaeoproterozoic high k i type granites high level porphyry intrusions and felsic volcanic rocks of the whitewater volcanics dominate the hooper and lamboo complexes in the kimberley region of northwestern australia the granites porphyries and volcanic rocks are gradational into each other in the field and they have the same mineralogy similar major and trace element abundances and indistinguishable shrimp u pb zircon ages of 1865 1850 ma there is evidence of widespread mingling between the granites and coeval gabbros magma mixing may be important in the formation of some of the mafic granites but most of the rocks probably formed from felsic parent magmas that underwent variable degrees of fractional crystallization the felsic igneous rocks may have formed by partial melting of intermediate to felsic calc alkaline rocks along the southern and eastern margins of the kimberley craton following accretion of various earlier palaeoproterozoic terranes to the craton therefore models for palaeoproterozoic high k granites in northern australia that invoke intracratonic rifting of a stable archaean craton may need to be revised

petrogenesis of juvenile type birimian paleoproterozoic granitoids in central cote d ivoire west africa geochemistry and geochronology abstract the birimian paleoproterozoic granitoids of central cote d ivoire are associated either with greenstone belts or with basin sedimentary rocks field data indicate two stages of granitoid emplacement which according to singlezircon and monazite 207 pb 206 pb age determinations occurred within a short period of time the first generation of granitoids 2123 2108 ma intruded and metamorphosed the greenstone belts whereas the second generation 2108 2097 ma intruded and metamorphosed the sedimentary pile and subordinate andesitic volcanic rocks of the bandama basin unconformably overlying the greenstone belts geochemical and isotopic data show that the various granitoids belong to four magmatic groups 1 sodic calc alkaline nacg 2 potassic calc alkaline kcg 3 peraluminous alg and 4 alkaline alkg all the granitoids show juvenile features with mantle like low initial sr isotopic compositions 0 700 0 702 and positive epsilon nd values 1 5 2 7 these data indicate that a the nacg may have formed by partial melting of a garnet amphibolite crust b the kcg and alkg derived from partial melting of crustal mafic to intermediate metaigneous rocks and c the alg epsilon nd 1 5 represent infracrustal melting of young sialic igneous materials during a regional crustal shortening in a transcurrent tectonic context sm nd model ages 2 25 2 4 ga preclude the existence of an archean crust reworked in the birimian magmas an underplating model is discussed

timing constraints of orogeny to cratonization thermochronology of the paleoproterozoic trans hudson orogen manitoba and saskatchewan canada abstract a comprehensive thermochronometric investigation across a 600 km transect of the paleoproterozoic trans hudson orogen tho in canada has resolved two first order thermal events 1 widespread peak metamorphism at 1 82 1 79 ga associated with terrane amalgamation and 2 a late collisional metamorphic episode at ca 1 77 ga that is characterized by significant strike slip deformation and rapid cooling geophysical observations of the lithosphere beneath the tho reveal crust that is markedly different on either side of the crustal scale tabbernor sturgeon weir tsw strike slip fault system which offsets lower crustal reflectors the tho east of the fault system records u pb titanite and total pb monazite domain ages that are relatively indistinguishable from 40ar 39ar hornblende and mica cooling ages indicating rapid cooling and perhaps exhumation following 1 77 ga metamorphism seismic imaging indicates the eastern orogen is an irregular package of stacked crustal blocks and our thermochronometric data demonstrate it behaved as a single coherent element shortly 20 30 m y following cessation of convergence in contrast rocks located west of the tsw fault system cooled distinctly later preserving 40ar 39ar muscovite and biotite ages between 1 74 and 1 72 ga this crustal architecture delineated from seismic surveys illustrates a more homogeneous slightly 5 km thinner crust in the case of this orogen apparent stabilization and cratonization occurred ca 100 m y after peak terrane amalgamation and notably the orogen was likely cratonized as two blocks east and west of the tsw fault system

shrimp zircon u pb geochronological and whole rock geochemical evidence for an early neoproterozoic sibaoan magmatic arc along the southeastern margin of the yangtze block abstract it has been generally accepted that the south china block was formed through amalgamation of the yangtze and cathaysia blocks during the proterozoic sibaoan orogenesis but the timing and kinematics of the sibao orogeny are still not well constrained we report here shrimp u pb zircon geochronological and geochemical data for the taohong and xiqiu tonalite granodiorite stocks from northeastern zhejiang southeastern margin of the yangtze block our data demonstrate that these rocks dated at 913 15 ma and 905 14 ma are typical amphibole rich calc alkaline granitoids formed in an active continental margin combined with previously reported isotopic dates for the 1 0 ga ophiolites and 0 97 ga adakitic rocks from northeastern jiangxi the timing of the sibao orogenesis is thus believed to be between 1 0 and 0 9 ga in its eastern segment it is noted that the sibao orogeny in south china is in general contemporaneous with some other early neoproterozoic 1 0 0 9 ga orogenic belts such as the eastern ghats belt of india and the rayner province in east antarctica indicating that the assembly of rodinia was not finally completed until 0 9 ga

post taltson sedimentary and intrusive history of the southern rae province along the northern margin of the athabasca basin western canadian shield abstract the southern rae province of the western canadian shield underwent extensive reworking during paleoproterozoic time widespread granitic plutonism and poorly defined metamorphism resulting from the ca 2 5 to 2 3 ga arrowsmith orogen was followed by more intense thermotectonic overprints attributed to the 1 99 1 92 ga taltson orogen in the west and ca 1 91 1 90 ga tectonic activity associated with the snowbird tectonic zone in the east the thluicho lake group is a fining upwards conglomerate arkose argillite succession deposited in an intermontane setting towards the end of the taltson orogen following deposition the thluicho lake group underwent two phases of regional folding and greenschist facies metamorphism marking the latest taltson and snowbird overprints respectively prior to the emplacement of extensive 1 82 ga mafic dykes these depositional constraints support correlation of the thluicho lake group with the lithologically similar nonacho group in the northwest territories whereas petrological similarities and coeval emplacement ages indicate that the mafic dykes represent a southeastward extension of the sparrow dykes mafic volcanic rocks geochemically linked to the dykes are intercalated within the martin group a continental redbed succession deposited in trans tensional basin settings indicating that deposition was ongoing at 1 82 ga similarities in age lithological association and depositional setting suggest that the martin group is broadly correlative with the baker lake group of the lower dubawnt supergroup in nunavut widespread lamprophyre dykes of the type that fed minette volcanic rocks of the christopher island formation in the baker lake group are also spatially associated with the martin group the broadly coeval hudson granites which extend over much of the same ground as the lamprophyres in nunavut also appear to have analogs in the southern rae province the formation of widespread trans tensional basins together with extensive dyke emplacement implies a period of intense brittle to brittle ductile deformation throughout the western churchill province at about 1 83 1 82 ga this deformation is attributed to a broadly east west stress regime imposed by accretion of the nahanni fort simpson terrane to the west combined with terminal collision in the trans hudson orogen to the east

shrimp u pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in northwestern fujian cathaysia block china tectonic implications and the need to redefine lithostratigraphic units abstract northwestern fujian province is one of the most important pre palaeozoic areas in the cathaysia block of south china metavolcano sedimentary and metasedimentary rocks of different types ages and metamorphic grades granulite to upper greenschist facies are present and previously were divided into several formations and groups tectonic contacts occur between some units whereas deformed unconformities have been reported between others new shrimp u pb zircon ages presented here indicate that the original lithostratigraphy and the old group and formation terminology should be abandoned thus the tianjingping formation was not formed in the archaean or palaeoproterozoic as previously considered but must be younger than its youngest detrital zircons 1790 ma but older than regional metamorphism 460 ma besides magmatic zircon ages of 807 ma obtained from metavolcano sedimentary rocks of the nanshan formation and 751 728 ma for the mamianshan group many inherited and detrital zircons with ages ranging from 1 0 to 0 8 ga were also found in them these ages indicate that the geological evolution of the study area may be related to the assembly and subsequent break up of the rodinia supercontinent the new zircon results poorly constrain the age of the mayuan group as neoproterozoic to early palaeozoic 728 458 ma and not palaeoproterozoic as previously thought many older inherited and detrital zircons with ages of 3 6 2 8 2 7 2 6 2 5 2 0 1 8 and 1 6 ga were found in this study a 3 6 ga detrital grain is the oldest one so far identified in northwestern fujian province as well as throughout the cathaysia block nd isotope tdm values of eight volcano sedimentary and clastic sedimentary rock samples centre on 2 73 1 68 ga being much older than the formation ages of their protoliths and thus showing that the recycling of older crust played an important role in their formation these rocks underwent high grade metamorphism in the early palaeozoic 458 425 ma during an important tectono thermal event in the cathaysia block

crustal evolution and age of thermotectonic reworking in the western hinterland of the trans hudson orogen northern saskatchewan abstract the hearne province in northern saskatchewan forms the western hinterland of the trans hudson orogen it is a fault bounded terrane lying structurally and geographically between the rae province to its west and the wathaman batholith and orogenic internides to its east the hearne province is comprised primarily of high grade metamorphic archean rocks structurally overlain by archean or proterozoic metasedimentary rocks and intruded by paleoproterozoic granites whereas the rae terrane on its west boundary is comprised primarily of still higher grade archean rocks the calc alkaline wathaman batholith was intruded at ca 1 855 ga and the orogenic internides to the east of it include mostly high grade mafic and intermediate volcanic rocks crystallized between 1 92 and 1 86 ga terminal collision and orogenesis in the internides have been constrained to be later than 1 82 ga and earlier than 1 78 ga mineral u pb data presented here unequivocally demonstrate that high grade metamorphism and large volume anatexis across the southern hearne province were approximately synchronous with terminal collision and high grade metamorphism across the trans hudson orogen zircon data for most samples form complex arrays in concordia space but demonstrate a high grade metamorphic overprint at 1810 1800 ma zircons typically have inherited components of archean age suggesting the presence of extremely old material in the hearne and a potential archean connection with the rae province sm nd data indicating ca 3500 ma model ages for similar parageneses in both terranes further support the proposed archean connection between hearne and rae province and the great antiquity of hearne crust sm nd data also elucidate the similarity of the ca 1 80 ga anatectic granites of the hearne to the 1 82 ga junction granite which intruded the virgin river shear zone and constrains the timing of final motion on that structure monazite 207 pb 206 pb ages are not older than 1812 ma or younger than 1769 ma and rutile 207 pb 206 pb ages and u pb ages are tightly constrained at about 1750 ma these data in combination with results of standard thermobarometric analysis permit determination of post orogenic cooling and denudation rates high cooling 7 c ma and denudation 240 m ma rates suggest fault accomodated uplift during post orogenic collapse

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

detrital zircon ages improving interpretation via nd and hf isotopic data abstract the bulk of sedimentary provenance studies use similarities in the detrital zircon age patterns or barcodes in sedimentary systems and potential source regions to make interpretations about palaeogeographic settings while this age only approach is generally considered to be effective it is limiting because the timing of zircon growth events may not be unique to specific terrains and important rock forming events may be associated with little zircon growth to a significant extent these limitations can be overcome by employing additional isotopic data sets such as sm nd and lu hf that provide information on the crustal evolution of the source region and allow comparisons with sedimentary packages as an example the age spectra of detrital zircons in palaeoproterozoic metasedimentary rocks in the eastern gawler craton in southern australia are virtually identical to the dominant zircon growth timelines in adjacent older domains of the gawler craton presenting a prima facie case that it was the source region however whole rock nd isotopic data indicate that the pre existing proto gawler craton was isotopically too crustally evolved e nd 1850 ma 10 to have supplied the bulk of the sediment to the relatively more juvenile metasedimentary units e nd 1850 ma 1 to 5 in addition zircon hf isotopic compositions from ca 2000 ma detrital zircons in the metasedimentary rocks e hf 2000 ma 2 to 5 are significantly more juvenile than 2000 ma rocks in the adjacent gawler craton e hf 2000 ma 2 to 5 the combination of bulk rock nd and hf zircon data suggest that the gawler craton is not a viable source region for the metasedimentary packages despite the striking similarity between detrital zircon ages and zircon crystallisation events within the craton

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

geological framework of the archean and paleoproterozoic tanami region northern territory the tanami region a poorly exposed mostly paleoproterozoic province within the north australian craton hosts a number of significant gold deposits in diverse settings rare exposures of 2 520 2 500 ma amphibolite facies archean gneiss and metasedimentary rocks form basement to the thick overlying metasedimentary succession of the 1 880 1 830 ma tanami group the basal unit of the tanami group is the dead bullock formation a fining upward deep water succession dominated by siltstone carbonaceous siltstone iron rich siltstone and mafic sills carbonaceous and iron rich lithologies in the upper dead bullock formation represent important hosts for gold mineralization the conformably overlying killi killi formation represents turbiditic sedimentary rocks that are correlated with the widespread lander rock beds of the arunta region sedimentation of the tanami group was terminated by regional deformation and greenschist to amphibolite facies metamorphism during the tanami event d1 m1 at around 1 830 ma the tanami group is unconformably overlain by rhyolite siliciclastic sedimentary rocks and felsic ignimbrite of the ware group that were deposited at about 1 825 1 810 ma subsequent ese wnw to se nw directed shortening d2 followed by ne sw to e w directed shortening d3 has resulted in open ne f2 and nw f3 trending folds in both the tanami and ware groups voluminous granitoids dominated by i type biotite granodiorite and monzogranite were intruded in the interval 1 825 1 790 ma and have been subdivided using geochemical criteria into the birthday frederick and grimwade suites basalt and immature sedimentary rocks of the mount charles formation are restricted in extent to the tanami mine corridor and are interpreted to reflect a continental rift succession that was deposited around 1 800 ma with an early archean sedimentary provenance steep s to se dipping f4 fold structures of tanami and ware group metasedimentary rocks many spatially associated with 1 825 1 790 ma granitoid intrusions indicate a period of sse directed regional shortening d4 syn to post the regional granitoid intrusive phase a network of n to nw striking faults several of which are interpreted as oblique thrusts with a component of left lateral movement indicates a period of d5 convergence during wsw ene to e w directed shortening the tanami mine corridor fault system comprises a network of n ne to ene striking d5 faults that merge with n to nw striking faults and probably accommodated movement between granite core domains d5 faulting is associated with the main phase of gold mineralization in suitable structural lithological traps the paleoproterozoic basement of the tanami region is unconformably overlain by quartz sandstone lithic arenite and conglomerate of the pargee sandstone pargee sandstone may represent syn tectonic sedimentation related to the 1 730 ma strangways orogeny and is unconformably overlain by the late paleoproterozoic platform cover succession of the birrindudu group the paleoproterozoic basement and cover sequences have subsequently undergone several episodes of faulting collectively termed d6 the paleoproterozoic evolution of the tanami region is interpreted to have occurred in an intracratonic setting but was fundamentally influenced by tectonic events in the adjacent halls creek orogen 1 835 1 805 ma halls creek orogeny and arunta region 1 815 1 800 ma stafford event the boundaries between the tanami region and kimberley region to the northwest and the arunta region to the southeast are transitional and are largely defined by the presence or absence of identifiable dead bullock formation

paleoproterozoic crustal growth in the western block of the north china craton evidence from detrital zircon hf and whole rock sr nd isotopic compositions of the khondalites from the jining complex detrital zircons from the khondalites in the western block of the north china craton were mainly derived from a 1 9 to 2 1 ga paleoproterozoic provenance most of the more than 200 detrital zircons analyzed in this study have positive initial ehf values and a wide range of hf depleted mantle model ages tdmc that range from 2 08 ga to 2 74 ga with a peak at 2 24 to 2 40 ga the whole rock nd isotopic analyses for the khondalite samples give quite uniform 143nd 144nd ratios from 0 511188 to 0 511858 corresponding to initial end 2 10ga values ranging from 1 6 to 0 6 in contrast sr isotopic compositions of these samples are more varied with initial 87sr 86sr ratios at 2 10 ga ranging from 0 7017 to 0 7076 in the end versus 87sr 86sr correlation diagram most samples plot near the mixing hyperbola of the depeleted mantle and crust with the contribution of depleted mantle about 65 to 75 percent these results suggest that a large amount of juvenile materials from the depleted mantle was accreted to the western block at 2 1 ga a period of magmatic quiescence in many cratons of the world

the oldest known rocks in south western china shrimp u pb magmatic crystallisation age and detrital provenance analysis of the paleoproterozoic dahongshan group abstract the paleoproterozoic dahongshan group outcrops along the present day southwest margin of the yangtze craton it is the oldest rock found in the region and forms the basement for the late mesoproterozoic sedimentary successions the dahongshan group is a sequence of volcanic and sedimentary rocks which have undergone structural deformation and metamorphism to upper greenschist lower amphibolite facies some of the original sedimentary features such as unimodal cross bedding in quartzite and rounded conglomerate clasts are still preserved suggesting deposition in a fluvial environment abundant carbonate rocks also found within the sedimentary sequence indicate periods of shallow marine or lagoonal conditions a weighted mean shrimp 206pb 207pb age of 1675 8 ma for a tuffaceous schist unit confirms the paleoproterozoic formation age of the group shrimp and lam icp ms u pb analysis of detrital zircon grains from metasedimentary units indicate a late archean to paleoproterozoic ca 2780 1860 ma source region the age spectrum of the detrital zircons is similar to that of the late archean and early paleoproterozoic basement rocks previously identified in the yangtze craton but includes a population of paleoproterozoic grains ca 2400 2100 ma which have no known source region in the exposed yangtze craton

isotopic constraints on the age and provenance of the lesser and greater himalayan sequences nepalese himalaya the main central thrust of the central himalaya juxtaposes the lesser himalayan sequence footwall with the greater himalayan sequence hanging wall both of which are regarded as components of the northern passive margin of india considerable uncertainty surrounds their respective ages and sedimentary derivation u pb and sm nd isotopic studies of samples from the langtang area central nepal demonstrate important distinctions between the two rock packages the greater himalayan sequence had a sedimentary provenance that included a major source of 0 8 1 0 ga zircons implying a late proterozoic age the source of the precambrian part of the lesser himalayan sequence contained 1 87 2 60 ga zircons and its depositional age is probably middle proterozoic nd isotopic characteristics of the two sequences are different at 21 ma the greater himalayan rocks had end values between 14 6 and 18 5 while their lesser himalayan counterparts had values between 21 4 and 25 9 giving rise to major differences in their model ages the lesser and greater himalayan sequences at langtang are interpreted as correlative to the lower and upper parts of the vindhyan supergroup currently exposed south of the gangetic plain in northern india on the basis of available age data the exposed hanging wall of the main central thrust in central and eastern nepal contains no archean early proterozoic basement if the fault does root into the basement at depth it must do so farther north than recently published cross sections indicate this implies a total displacement on the fault that is substantially greater than the 140 210 km required by tectonic overlap in the eastern himalayas

neoproterozoic arc related mafic intrusions along the northern margin of south china implications for the accretion of rodinia abstract south china has been considered as part of the rodinian supercontinent during neoproterozoic time although its paleogeographic position within this supercontinent is still a matter of debate the wangjiangshan and bijigou complexes along the northern margin of south china are among the largest mafic intrusions in china new shrimp zircon u pb results indicate that these two intrusions have crystallization ages of 820 ma and 780 ma respectively enrichment of large ion lithophile and light rare earth elements and depletion of high field strength elements in these intrusions suggest derivation from an active arc along a continental margin this interpretation of these intrusions as part of a continental arc assemblage is in contrast with the previous view that they were products of a neoproterozoic mantle plume that initiated the breakup of rodinia the presence of a neoproterozoic magmatic arc suggests that rodinian oceanic lithosphere was subducted beneath the present northern margin of south

proterozoic crustal evolution in the nw himalaya india as recorded by circa 1 80 ga mafic and 1 84 ga granitic magmatism abstract single zircon dating of the rampur metabasalts of the larji kullu rampur window in the lesser himalayas yielded an evaporation age of 1800 13 ma the zircon age is considerably younger than the previously published whole rock sm nd age of 2510 90 ma suggesting that the sm nd age may be geologically meaningless and that the sm nd whole rock array may have resulted from mixing in the nw himalaya there is also evidence for extensive silicic melt generation in the paleoproterozoic zircons from a metarhyodacite in the larji kullu rampur window yielded an evaporation age of 1840 16 ma which we interpret as the minimum age of magmatism the main central thrust granitic mylonites are interpreted as the basement of the neoproterozoic haimanta group metasediments together with the granitic rocks from the lesser himalaya they were derived from pre existing continental crust prior to 1 84 ga the nd depleted mantle model ages are in the range of 2 6 2 4 ga suggesting a contribution of archean crust a recycled archean component is also documented by a 2 9 ga domain in one of the zircons

anion exclusion effects in compacted bentonites towards a better understanding of anion diffusion abstract diffusion of 36cl in compacted bentonite was studied using through diffusion out diffusion and profile analysis techniques both the bulk dry density of the bentonite and the composition of the external solution were varied increasing the bulk dry density of the bentonite resulted in a decrease of both the effective diffusion coefficient and the cl accessible porosity increasing the ionic strength of the external solutions resulted in an increase of both the effective diffusion coefficient and the cl accessible porosity this can be explained by anion exclusion effects donnan exclusion at high ionic strength values i 1 m nacl the cl accessible porosity approaches the interparticle porosity this interparticle porosity is the difference between the total and interlayer porosity of the bentonite the interlayer porosity was found to depend on the degree of compaction up to a bulk dry density of 1300 kg m 3 the interlayer is built up of 3 water layers between 1300 and 1800 kg m 3 the interlayer water is reduced from 3 to 2 layers of water above 1800 kg m 3 evidence for a further decrease to 1 layer of water was found these findings are in agreement with x ray data found in the literature showing a decrease of the basal spacing of montmorillonite the main clay mineral in bentonite with increasing degree of compaction the relationship between the effective diffusion coefficient of cl and the diffusion accessible porosity can be described by an empirical relationship analogous to archie s law to predict the effective diffusion coefficient of cl in compacted bentonite the diffusion coefficient of cl in water the bulk dry density and the ionic strength of the pore water have to be known

paleoproterozoic orogeny in south korea evidence from sm nd and pb step leaching garnet ages of precambrian basement rocks abstract geology and tectonics of the korean peninsula have been considered to be closely associated with those of the adjacent chinese continent although phanerozoic connections between the two areas have been reasonably well worked out precambrian ones are less well established we obtained sm nd and u pb garnet ages of 12 metamorphic rocks from widely separated parts of the gyeonggi and yeongnam massifs in south korea to better understand their precambrian history the two massifs consist of late archean to paleoproterozoic basement rocks and meso to neoproterozoic supracrustal rocks previous studies have shown that the two massifs experienced upper amphibolite to granulite facies metamorphism of medium pressure type with clockwise p t time paths suggesting that the two massifs may represent remnants of a collisional orogen pb pb and u pb garnet ages give two distinct age groups ten paleoproterozoic 1989 34 to 1835 56 ma ages of basement rocks from the two massifs and one late permian 265 8 ma age of a supracrustal rock from the gyeonggi massif that corroborates previous estimates of permo triassic 298 245 ma metamorphic age for the supracrustal rocks on the other hand sm nd garnet ages are less precise and display a wide range of ages from 2257 to 413 ma for the basement rocks when we compare the sm nd and pb pb ages from the same sample the sm nd age is similar to or younger than the pb pb age suggesting that the blocking temperature of the sm nd garnet system may be lower than that of the u pb system 800 c we interpret the pb pb and u pb ages as representing the timing of metamorphic garnet growth since the blocking temperature of the u pb garnet system is similar to or higher than the metamorphic temperature of the analyzed samples apparently the younger metamorphism possibly associated with the permo triassic collision between the north and south china cratons was not strong enough to reset the older metamorphic age similar paleoproterozoic metamorphic ages for basement rocks of the two massifs suggest that they may have come from the same precambrian terrane the metamorphic ages of the basement rocks of south korea agree very well with those of the central zone orogenic belt in the north china craton suggesting a possible correlation between the two terranes

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

shrimp u pb analyses of detrital zircon a window to understanding the paleoproterozoic development of the tanami region northern australia poorly exposed paleoproterozoic turbiditic to shallow marine sedimentary rocks of the tanami basin nt australia are largely the erosional products of either the 1 87 1 85 hooper orogeny and or magmatism associated with the 1 87 ga nimbuwah event dating of detrital zircon from six of the principal sedimentary units shows that deposition spanned at least the period 1 84 1 77 ga collectively the detrital zircon ages reveal a progression in provenance that is a record of the development of the orogen the basal dead bullock formation contains only zircon derived from archean basement and no contemporaneous products of orogeny its deposition age is inferred to be 1 87 1 84 ga orogenic 1 86 ga zircon appears in the overlying killi killi formation deposited between 1 84 1 82 ga and persists probably due to recycling in all overlying units except one the mount charles formation the accepted stratigraphic position of this unit might be incorrect

the kinematic evolution of the nepalese himalaya interpreted from nd isotopes neodymium nd isotopes from the himalayan fold thrust belt and its associated foreland basin deposits are useful for distinguishing between himalayan tectonostratigraphic zones and revealing the erosional unroofing history as controlled by the kinematic development of the orogen neodymium isotopic data from the himalayan fold thrust belt in nepal n 35 reveal that the lesser himalayan zone consistently has a more negative nd 0 value than the greater and tibetan himalayan zones our data show the average nd 0 value in the lesser himalayan zone is 21 5 whereas the greater and tibetan himalayan zones have an average nd 0 value of 16 these consistently distinct values throughout nepal enable the use of nd isotopes as a technique for distinguishing between lesser himalayan zone and greater himalayan zone rock the less negative nd 0 values of the greater himalayan rocks support the idea that the greater himalayan zone is not indian basement but rather a terrane that accreted onto india during early paleozoic time neodymium isotopic data from eocene through pliocene foreland basin deposits n 34 show that sediment provenance has been dominated by greater and tibetan himalayan detritus across nepal the nd t values in the synorogenic rocks in western and central nepal generally show an up section shift toward more negative values and record the progressive unroofing of the different tectonostratigraphic zones at 10 ma in khutia khola and 11 ma in surai khola a shift in nd t values from 16 to 18 marks the erosional breaching of a large duplex in the northern part of the lesser himalayan zone this shift is not seen in eastern nepal where the nd t values remain close to 16 throughout miocene time because there has been less erosional unroofing in this region

himalayan architecture constrained by isotopic tracers from clastic sediments we report the first geochemical traverse to integrate u pb ages and hf data on single detrital zircons with bulk rock sm nd rb sr isotopic measurements across the breadth of the himalayan orogen in northwest india our dataset from key tectonostratigraphic units in the sutlej valley provides detailed insights into both the provenance of the sedimentary formations and their tectonic history whole rock nd data provide information on the mean age of source areas contributing detritus to the sedimentary units in the mountain belt regardless of their current metamorphic grade u pb ages of detrital zircons from the same units identify the age of melt formation in the source rocks while lu hf isotope data from zircons resolve discrete crust formation ages in the multiple eroding terrains complex whole rock sr systematics hint at the extent of pre himalayan thermal events our data confirm the geochemical distinction between the older lesser himalayan formations and those of the depositionally younger units including the high himalayan crystalline series that has been recorded along the strike of the himalaya from the western syntaxis to nepal palaeoproterozoic metasediments of the jutogh group and rampur formation yield end 500 values below 17 whereas neoproterozoic and younger metasediments yield end 500 above 13 the latter group encompasses the vaikrita group gneisses of the high himalayan crystallines and the overlying haimanta group but also includes a number of units in thrust sheets north of the main boundary thrust in the lesser himalayan zone designated the douter lesser himalayat to distinguish them from the palaeoproterozoic dinner lesser himalayat zircon populations from the inner lesser himalaya are characterised by palaeoproterozoic late archaean ages 2 6 1 8 ga whereas the depositionally younger units contain populations both of this age and a younger period meso to neo proterozoic 1 1 0 8 ga detrital zircon ages are younger than their respective hf isotope derived crustal formation ages by 0 7 2 1 ga indicating that the source regions of the detrital zircons consisted of older terranes with considerable amounts of reworking and renewed magmatism the

la icp ms u pb zircon ages of the liaohe group in the eastern block of the north china craton constraints on the evolution of the jiao liao ji belt abstract as a major lithostratigraphic unit of the palaeoproterozoic jiao liao ji belt in the eastern block of the north china craton the liaohe group consists of an assemblage that is transitional from a lower arkose and volcanic rich sequence langzishan li eryu and gaojiayu formations through a middle carbonate rich sequence dashiqiao formation to an upper argillaceous sequence gaixian formation tectonically associated with the liaohe group are large volumes of granitoid rocks named the liaoji granite whose emplacement age has been dated at about 2 1 2 2 ga regionally the liaohe group and the associated liaoji granite extend along a nee trending belt that is flanked by 2 45 2 55 ga basement gneisses u pb zircon data and cathodoluminescence cl imaging are used to constrain the maximum depositional and metamorphic ages of the liaohe group which are critical in understanding the tectonic setting and history of the jiao liao ji belt cathodoluminescence images reveal that most detrital zircon grains from the liaohe group are characterized by concentric oscillatory zoning with comparatively low luminescence and high th u ratios suggesting magmatic origin but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low th u ratio indicating metamorphic origin results of this study show that the detrital zircon grains of the langzishan formation the lowest sequence of the liaohe group have concordant u pb ages ranging from 2 05 to 2 24 ga suggesting that the liaohe group was deposited at some time after 2 05 ga although most overgrowth or recrystallization rims are too narrow to be analyzed some rims yield concordant or upper intercept ages around 1 93 ga interpreted as the peak metamorphic age of the liaohe group detrital zircon grains from the dashiqiao formation in the middle sequence of the liaohe group have concordant u pb ages ranging from 2 25 to 2 53 ga some of which are similar to those of the basement gneisses in the area this study indicates that the liaohe group was deposited after the emplacement of the liaoji granite and the latter may be a major component of the provenance for the langzishan formation in contrast the protoliths of the middle sequence of the liaohe group were most probably derived from the basement gneisses these new zircon ages for the liaohe group and recent data for the liaoji granite combined with lithological structural and metamorphic considerations support a rifting model for the evolution of the jiao liao ji belt

geochronological constraints on paleoproterozoic crustal evolution and regional correlations of the northern outer hebridean lewisian complex scotland abstract ion microprobe u th pb geochronological data are presented for four samples from paleoproterozoic belts in the lewisian of the northern outer hebrides north west scotland two of these samples a tonalite sheet associated with the south harris igneous complex and a psammite from the leverburgh metasupracrustal belt south harris yield zircons with a dominant ca 1 87 ga age these are interpreted as the igneous crystallisation age for the tonalite and the source rock for the psammite and their age concordance suggests that the latter was developed in an arc basin sequence derived largely from contemporaneous igneous rocks and buried during collision which resulted in documented 1 83 ga high grade metamorphism a diorite from the paleoproterozoic shear zone at the northern tip of lewis has a probable 2 7 2 8 ga protolith age although its zircons have strongly been affected by pb loss during later events culminating in development of low th u overgrowths at ca 1 86 ga zircons from a tonalite from berneray in the sound of harris yield an archean crystallisation age of ca 2 83 ga with no indication of later disturbance thus providing a southern limit to the region affected by paleoproterozoic tectonothermal events the paleoproterozoic arc in south harris represents a major tectonic boundary active margin in the lewisian of the outer hebrides possibly correlated with the laxford or gairloch shear zones of the mainland lewisian contrasts in the flanking region geology and geochronology possibly reflecting lateral heterogeneities may be introduced by major thrusts and or extensional faults e g the outer isles fault developed between the shear zones on a broader regional scale evidence for a magmatic arc in the lewisian is consistent with the tectonic style of other ca 1 9 ga paleoproterozoic collisional orogens throughout laurentia fennoscandia suggesting a reappraisal of the formerly proposed intracratonic evolution of the lewisian at this time

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

preliminary stratigraphic and structural architecture of bhutan implications for the along strike architecture of the himalayan system article i nfo preliminary mapping and stratigraphic correlation of lesser himalayan rock in eastern bhutan using field characteristics u pb detrital zircon dating and nd geochemistry define the first order stratigraphic architecture of the indian passive margin sequence in the eastern himalaya we use this new image of the lateral and vertical relationships of the original stratigraphy to determine the structural framework of the eastern himalayan fold thrust belt in bhutan we propose that lesser himalayan rock in bhutan can be divided into lower lesser himalayan rocks with a paleoproterozoic detrital zircon signal and upper lesser himalayan rocks with detrital zircon signals of 1000 500 ma the 500 ma detrital grains are from rocks in the frontal portions of the fold thrust belt north of the main boundary thrust as well as directly in the footwall of the main central thrust in the hinterland our preliminary stratigraphic study coupled with mapping allows us to construct a composite balanced cross section through the kuru chu valley in eastern bhutan which provides the first image of the geometry and amount of shortening through bhutan the main frontal thrust tilts a 6 km of thick section of neogene foreland basin deposits these deposits are separated from folded and faulted upper lesser himalayan rocks by the main boundary thrust north of the main boundary thrust we propose two duplex systems the southernmost duplex contains 9 repeated sections of upper lesser himalayan units including the permian gondwana sequence and the cambrian or younger baxa group the northernmost duplex is located in the footwall of the main central thrust and is comprised of two repeated sections of the proterozoic shumar and daling formations the southern boundary of this northern duplex is the shumar thrust which acts as a roof thrust for the southern duplex system and may correlate to the ramgarh thrust in nepal and india we propose that the development of the duplex systems passively folded overlying tethyan and greater himalayan rocks minimum shortening for this part of the himalayan fold thrust belt is 359 km all of which has occurred from 22 ma to present defining a long term shortening rate of 16 mm yr

detrital zircon u pb hf isotopes and whole rock geochemistry of neoproterozoic cambrian successions in the cathaysia block of south china implications on paleogeographic reconstruction in supercontinent abstract paleogeographic reconstruction of the cathaysia block of south china and its link with orogeny associated with rodinia and gondwana remain enigmatic leading to controversial models proposed for supercontinental configuration this study presents detailed provenance analysis of late neoproterozoic to early paleozoic sedimentary successions from the cathaysia block to trace the sedimentary provenance that was essentially linked to previously adjacent continents blocks zircon u pb dating combined with published paleontological evidence suggests an ediacaran depositional age range 633 542 ma for the lechangxia group while deposition of the bacun group most likely commenced during early cambrian the older strata were sourced mainly from recycling of quartz rich sedimentary rocks while the younger one received sediments dominantly from felsic igneous rocks high sio2 contents 54 6 79 3 wt and k2o na2o ratios 0 69 35 7 detrital zircon age distribution and abundant monocrystalline quartz indicate a passive setting for ediacaran and early cambrian successions in great contrast the middle cambrian strata was likely deposited in collisional setting considering relatively lower sio2 contents 67 9 74 5 wt and k2o na2o ratios 0 97 1 63 plus absence of old zircons this tectonic transition is consistent with the change from quartz arenite to arkose that could be related to a disconformity between early and middle cambrian strata dominant late mesoproterozoic detritus 1250 1050 ma in the lechangxia group was possibly sourced from older grenville orogens 1300 1050 ma in western australia and east antarctica because rocks of these ages are rare in the cathaysia block similarly abundant early neoproterozoic clastic 1000 950 ma in the late ediacaran and early cambrian successions imply an increasing input from younger grenville orogens 990 950 ma in east antarctica and eastern india thus the cathaysia block was a part of the east gondwana assembly and was linked to eastern india east antarctica and western australia during ediacaran and cambrian the source change was coeval with the pinjarra orogeny 550 520 ma and the early stage of the kuunga orogeny 570 550 ma in middle cambrian strata the middle neoproterozoic sediments 850 700 ma were mainly derived from intrinsic sources likely to be the wuyishan terrane this provenance variation can be linked to the middle cambrian uplift of the cathaysia block in synchronous with the later phase of the kuunga orogeny 530 480 ma

a relationship between d104 value and composition in the calcite disordered dolomite solid solution series x ray diffraction has been widely used in analyzing ca mg carbonates compositions of biogenic and inorganic ca mg co3 crystals are often calculated by comparing their d 104 values with published empirical curves however previous studies suggested that these curves do not apply to very high mg calcite and disordered dolomite based on synthesized high mg calcite and disordered dolomite a new empirical curve between values of magnesian calcite d 104 and mgco3 content in the calcite disordered dolomite solid solution series is constructed this new curve is consistent with the significant cell parameter changes accompanying the mg ca cation disorder in dolomite and it can help the characterization of the mgco3 content of both natural and synthetic magnesian calcite and disordered dolomite especially for the mineral mixtures that are not suitable for other analysis methods

age and evolution of a late archean to paleoproterozoic upper to lower crustal section in the wutaishan hengshan fuping terrain of northern china abstract the taihangshan wutaishan area forms part of the central north china craton and consists of three main components the hengshan and fuping complexes containing predominantly ductilely deformed late archean to paleoproterozoic high grade granitoid orthogneisses intruded by mafic dykes of gabbroic composition and the low grade late archean wutai greenstone belt developed between the high grade terrains and consisting of bimodal volcanic rocks and metasediments associated with coeval granitoids zircon dating shows that both the hengshan and fuping complexes were intruded by major granitoid bodies between 2 52 and 2 48 ga with rare occurrences of 2 7 ga gneisses wutai granitoids adjacent to the fuping complex also contain 2 7 ga xenocrysts all possibly reflecting the same older basement rare granitic gneisses in the hengshan have emplacement ages of 2 35 ga and show the same structural features as the older rocks indicating that the main deformation occurred after 2 3 ga deposition of supracrustal rocks and emplacement of mafic dykes occurred in the paleoproterozoic together with intrusion of granitic bodies at 2 1 2 0 ga and all underwent regional metamorphism at 1 88 1 85 ga we interpret the hengshan and fuping granitoid gneisses as the lower plutonic part of a late archean to early paleoproterozoic japan type magmatic arc with the upper volcanic part represented by the wutai complex components of this arc may have evolved at a continental margin as indicated by the 2 7 ga zircons virtually all magmatic events are recorded in all three complexes however the 1 85 ga metamorphic event is only recorded in the higher grade portions of the wutai since low grade and presumably high crustal level precluded metamorphic zircon growth shear zones in the hengshan are interpreted as major lower crustal discontinuities post dating the peak of high pressure granulite metamorphism we suggest that they formed during orogenic collapse and uplift of the hengshan complex in the late paleoproterozoic 1800 ma

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

depositional and tectonic setting of the paleoproterozoic lower aillik group makkovik province canada evolution of a passive margin foredeep sequence based on petrochemistry and u pb tims and lam icp ms geochronology abstract the paleoproterozoic lower aillik group is a deformed metasedimentary metavolcanic succession located in the makkovik province of labrador eastern canada the group is situated near the boundary between reworked archaean gneiss of the nain north atlantic craton and juvenile paleoproterozoic crust that was both tectonically accreted and formed on or adjacent to this craton during the ca 1 9 1 78 ma makkovikian orogeny the lower aillik group is structurally underlain by archaean gneiss and structurally overlain by ca 1860 1807 ma bimodal dominantly felsic volcanic and volcaniclastic rocks of the upper aillik group we present geochemical data from metavolcanic rocks and u pb geochronological data from several units of the lower aillik group in order to address the depositional and tectonic history of this group u pb data were obtained using both thermal ionization mass spectrometry tims and laser ablation microprobe inductively coupled plasma mass spectrometry lam icp ms two quartzite units near the structural base of the lower aillik group contain detrital zircons only of archaean age and are interpreted to have been deposited on the nain craton during post 2235 ma rifting and initiation of a passive continental margin overlying mafic metavolcanic rocks contain thin horizons of intermediate tuff one of which is dated at 2178 4 ma this relatively old age and an inferred stratigraphic relationship with underlying sedimentary units suggest that the volcanic rocks represent transitional oceanic crust consistent with their geochemical similarity to tholeiitic rifted margin sequences of mesozoic age in eastern north america a package of interlayered psammitic and semipelitic metasedimentary rocks that appears to stratigraphically overlie the mafic volcanic unit is dominated by paleoproterozoic detrital zircons but also contains archaean grains this package was deposited after 2013 ma the age of the youngest concordant zircon the u pb data imply a minimum 165 m y time gap between mafic volcanism and sedimentation and are consistent with deposition of the psammite semipelite unit in an evolving foredeep that heralded the approach of a paleoproterozoic arc terrane accretion of this terrane to the nain cratonic margin at ca 1 9 ga initiated the makkovikian orogeny although the lower aillik group is highly deformed and may contain internal tectonic boundaries or be incomplete the u pb and geochemical data allow quantitative assessment of a prolonged rift drift basin closure cycle that characterized the early paleoproterozoic evolution of the southern nain cratonic margin

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

u pb zircon and sm nd isotopic study of the huangtuling granulite dabie sulu belt china implication for the paleoproterozoic tectonic history of the yangtze craton sims data demonstrate archean 2 9 to 2 7 ga and paleoproterozoic 1991 43 ma ages for rounded detrital zircon cores and unzoned rims respectively in a graulite sample collected from huangtuling dabie sulu orogenic belt china the granulite rocks in this locality have pelitic compositions and represent an exposure of the northern margin of the yangtze craton the rounded zircon cores show oscillatory zoning and have th u ratios 0 17 0 78 systematically higher than those of the unzoned luminescent rims 0 005 0 03 the age of the detrital zircon cores and whole rock nd isotope model age suggest that the huangtuling granulite was possibly derived from a provenance dominated by archean rocks similar to the kongling complex exposed 200 km in the southwest multiple phases of metamorphism have been identified for the granulites with the dominant granulite facies mineral assemblage defining an early clock wise metamorphic p t path orthopyroxene plagioclase and whole rock material define a linear trend in a 147sm 144nd 143nd 144nd diagram corresponding to an age of 1926 146 ma this result and the u pb data for the zircon rims suggest that a collisional event may have occurred along the northern margin of the yangtze craton at 2 0 ga inviting further study on whether the yangtze craton was involved in the assembly of the recently proposed paleo mesoproterozoic supercontinent columbia

low pressure metamorphism and leucogranite magmatism northeastern yeongnam massif korea implication for paleoproterozoic crustal evolution abstract the northeastern yeongnam massif consists primarily of pelitic to psammopelitic metasedimentary rocks together with garnet bearing leucogranites and granitic gneisses metapelitic mineral assemblages define three progressive metamorphic zones of the low pressure facies series cordierite sillimanite and garnet zones with increasing temperature metamorphic grade ranges from lower amphibolite to lower granulite facies reaching 750 800 c and 4 6 kbar in migmatitic gneisses geochemical characteristics such as the enrichments of rb and ba relative to sr high k contents and negative e nd 1 9 ga values indicate that peraluminous leucogranites were produced primarily by the fluid absent melting of supracrustal rocks trace element characteristics of leucogranites are generally compatible with those of volcanic arc granites and the widespread crustal melting may be attributed largely to magmatic heat flux in an arc environment whole rock pb pb ages suggest that leucogranite intruded at ca 1 93 1 86 ga into the granitic gneiss formed by an earlier magmatic episode at ca 1 95 ga these ages are compatible with those of felsic magmatism reported from other parts of the yeongnam massif our results in conjunction with the available geochronologic data suggest that four stages of precambrian crustal evolution are represented in the yeongnam massif 1 the formation of proto crust at ca 2 9 2 5 ga and felsic magmatic episodes primarily at 2 ca 2 1 ga 3 1 95 ga and 4 1 9 ga in particular the last tectonothermal event produced widespread low pressure type metamorphism in association with the emplacement of leucogranite and is correlative with the luliangian orogeny in north china

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

timing of metamorphism in the paleoproterozoic jiao liao ji belt new shrimp u pb zircon dating of granulites gneisses and marbles of the jiaobei massif in the north china craton abstract the paleoproterozoic jiao liao ji belt lies in the eastern block of the north china craton with its southern segment extending across the bohai sea into the jiaobei massif high pressure pelitic and mafic granulites have been recently recognized in the paleoproterozoic jingshan group jiaobei massif new shrimp u th pb geochronology combined with cathodoluminescence cl imaging of zircon has been applied to the determination of the timing of the metamorphism of the high temperature and high pressure granulites and associated gneisses and marbles metamorphic zircons in these high pressure granulites gneisses and marbles occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores metamorphic zircons are all characterized by nebulous zoning or being structureless with high luminescence and relatively low th u values metamorphic zircons from two high pressure mafic granulites yielded 207pb 206pb ages of 1956 41 ma and 1884 24 ma one metamorphic zircon from a garnet sillimanite gneiss also gave an apparent 207pb 206pb age of 1939 15 ma these results are consistent with interval of ages of c 1 93 1 90 ga already obtained by previous studies for the north and south liaohe groups and the laoling group in the northern segment of the jiao liao ji belt metamorphic zircons from a high pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207pb 206pb ages of 1837 8 ma 1821 8 ma and 1836 8 ma respectively two diopside olivine phlogopite marbles yielded weighted mean 207pb 206pb ages of 1817 9 ma and 1790 6 ma these paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c 1 85 ga produced from the ji an group in the northern segment of the jiao liao ji belt and c 1 86 1 80 ga obtained for the high pressure pelitic granulites from the jingshan group in the southern segment as this metamorphic event was coeval with the emplacement of a type granites in the jiao liao ji belt and its adjacent areas it is interpreted as having resulted from a post orogenic or anorogenic extensional event

episodic growth of the gondwana supercontinent from hafnium and oxygen isotopes in zircon it is thought that continental crust existed as early as 150 million years after planetary accretion but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records for example the striking global peaks in juvenile igneous activity 2 7 1 9 and 1 2 gyr ago imply rapid crustal generation in response to the emplacement of mantle super plumes rather than by the continuous process of subduction yet uncertainties persist over whether these age peaks are artefacts of selective preservation and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle these model ages are only meaningful if the host magma lacked a mixed or sedimentary source component but the latter can be diagnosed by oxygen isotopes which are strongly fractionated by rock hydrosphere interactions here we report the first study that integrates hafnium and oxygen isotopes all measured in situ on the same precisely dated detrital zircon grains the data reveal that crust generation in part of gondwana was limited to major pulses at 1 9 and 3 3 gyr ago and that the zircons crystallized during repeated reworking of crust formed at these times the implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts

a mesoproterozoic supercontinent evidence from the indian shield abstract geophysical signatures of late paleoproterozoic collisional sutures fold belts between the deccan protocontinent and bundelkhand craton and between the bundelkhand and mewar cratons of the north indian shield are presented the aravalli and satpura orogenies evolved during these continent continent collision episodes both the orogenic episodes are associated with granulite facies metamorphism and metallogeny serpentinised ultramafic breccia in ophiolitic melange is present in both regions structural discontinuities and oppositely dipping reflection fabrics with high conductivity anomalies are the characteristic features of these collision zones a major gravity high is also observed all along the strike of these fold belts to a distance of 700 1000 km paleoproterozoic 1 8 2 1 ma ages corresponding to compressional activity have also been observed in the southern granulite terrain and other gondwana fragments extensive granites and gneisses of 1900 ma age are observed in the lower himalayas and nanga parbat ranges late paleoproterozoic orogenic activity is also observed in all of the earth s shields intense orogenic activity of this period observed in various widely separated cratonic blocks is related to global plate tectonic processes and supercontinental episodes the available geophysical evidences in various parts of the globe suggest the presence of a supercontinent referred to as columbia during the early mesoproterozoic period

evolution of polycyclic basement complexes in the aracuai orogen based on u pb shrimp data implications for brazil africa links in paleoproterozoic time paleoproterozoic basement of the aracuaorogen is composed of amphibolite and granulite facies orthogneiss units known as mantiqueira and juiz de fora complexes six u pb shrimp crystallization ages for the mantiqueira complex range from 2137 19 to 2041 7 ma studied samples are characterized by the abundance of inherited archean zircon grains tdm model ages ranging from 2 9 to 3 2 ga and strongly negative end t 9t o 13 gneiss protholits were mainly generated by partial melting of older continental material and the mantiqueira complex is related to active margin and syn collisional magmatism high grade gneiss samples of the juiz de fora complex yields crystallization ages of 2119 16 and 2084 13 and inherited zircon grains are absent this plutonic unit much probably evolved within an oceanic magmatic arc setting or on a very stretched continental crust the mantiqueira and juiz de fora complexes together with the kimezian basement of the west congo belt were parts of a paleoproterozoic orogenic system disrupted and deeply reworked during the evolution of the aracuacongo orogen neoproterozoic metamorphic overprint is dated at ca 590 574 ma 2007 elsevier b v all rights reserved

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

geochemistry zircon ages and whole rock nd isotopic systematics for palaeoproterozoic a type granitoids in the northern part of the delhi belt rajasthan nw india implications for late palaeoproterozoic crustal evolution of the aravalli craton determination of zircon ages as well as geochemical and sm nd isotope systematics of granitoids in the khetri copper belt of the aravalli mountains nw india constrain the late palaeoproterozoic crustal evolution of the aravalli craton the plutons are typical a type within plate granites derived from melts generated in an extensional tectonic environment they display ree and multi element patterns characterized by steep lree enriched and almost flat hree profiles and distinct negative anomalies for sr p and ti initial e nd values range from 1 3 to 6 2 and correspond to crustal sources with mean crustal residence ages of 2 5 to 2 1 ga a lower mafic crustal anatectic origin is envisaged for these granitoids and the heterogeneous e nd t values are inferred to have been acquired from the magma source region zircon pb pb evaporation and u pb ages indicate widespread rift related a type magmatism at 1711 1660 ma in the northern delhi belt and also suggest a discrete older magmatic event at around 1800 ma the emplacement ages of the compositionally distinct a type granitoid plutons and virtually coeval granulite metamorphism and exhumation in another segment of the aravalli mountains further signify that part of the aravalli crust evolved during a widespread extensional event in late palaeoproterozoic time

u pb and hf isotopic study of zircons of the helanshan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the helanshan complex is located at the westernmost segment of the khondalite belt a continent continent collisional belt along which the yinshan block in the north collided with the ordos block in the south to form the western block of the north china craton the complex consists of s type granites and high grade pelitic granulite gneiss felsic paragneiss quartzite calc silicate rock and marble together called the khondalite series rocks la q icp ms u pb geochronology and la mc icp ms lu hf isotopic data of zircons combined with cathodoluminescence cl imaging enable the resolution of magmatic and metamorphic events that can be directed towards understanding the formation and evolution of the khondalite belt in the western block of the north china craton cl images reveal the coexistence of magmatic type detrital zircons and metamorphic zircons in most of the khondalite series rocks of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating magmatic type detrital zircon cores la q icp ms u pb analyses on magmatic type detrital zircons reveal two distinct age populations with one in the archaean 2 85 2 53 ga and the other in the palaeoproterozoic 2 2 2 0 ga suggesting that the sedimentary protoliths of the khondalite series rocks in the helanshan complex must have been deposited at some time after 2 0 ga the hf analyses show that the archaean detrital zircons possess negative ehf t values from 7 64 to 0 15 with depleted mantle model ages ranging from 3 34 to 3 10 ga this implies the existence of a paleo mesoarchaean 3 34 3 10 ga crust in the western block which underwent a recycling event in the period 2 85 2 53 ga nearly all palaeoproterozoic 2 2 2 0 ga detrital zircons possess positive ehf t values 0 86 9 38 with depleted mantle model ages of 2 45 2 15 ga suggesting a significant crustal growth event in the western block in the palaeoproterozoic metamorphic zircons yield two groups of age with one at 1 95 ga and the other at 1 87 ga of which the former is considered as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the latter is consistent with the age of 1 86 ga from two s type granites which are considered to have formed by the partial melting of pelitic granulites gneisses at the stage of the exhumation of the helanshan complex

diffusion of landfill leachate through compacted natural clays containing small amounts of carbonates and sulfates abstract diffusion of a synthetic urban landfill leachate through compacted natural illitic clays and the role of reactive accessory minerals carbonates and gypsum in the geochemical behavior of major soluble ions are evaluated the leachate is composed of nh 4 and na 0 25 m balanced by cl 0 25 m acetate 0 1 m and hco 3 0 15 m the ph is 7 8 and it is typical of the mature stage of organic matter degradation within an urban landfill laboratory scale diffusion tests were performed over 4 months long term experiment lt and 2 weeks short term experiment st the st experiments were designed to allow the measurement of the cl gradient as a diffusion tracer in the compacted clay in the lt experiments the chemical gradients were already at steady state but geochemical reactions involving dissolution of gypsum and precipitation of calcite were observed evolution of pore water chemistry mineralogy cation exchange properties and the specific surface of clays were determined numerical simulations were carried out using the geochemical code retraso chloride transport precipitation of carbonates ph buffering and ca2 nh 4 cation exchange reactions took place in the laboratory tests apparent cl diffusion coefficients were determined by direct modeling of the st tests and validated with the lt experiments these coefficients were considered in the simulation of transport coupled with experimentally calculated exchange constants and dissolution precipitation reactions of gypsum and carbonates sulfate reduction coupled with acetate oxidation has been proven to be relevant in the sample with significant concentration of so 4 2 bailen this process also includes significant precipitation of carbonates mainly calcite and causes a decrease of so 4 2 in the porewater

tectonic setting and significance of 2 3 2 1ga magmatic events in the trans north china orogen new constraints from the yanmenguan mafic ultramafic intrusion in the hengshan wutai fuping area abstract a detailed study of the 2 2 ga yanmenguan mafic ultramafic intrusion in the hengshan area is presented with the aim of clarifying the tectonic history of the trans north china orogen in the north china craton during the period 2 3 2 1 ga shrimp u pb dating of magmatic zircons from a gabbro indicates emplacement at 2193 ma the whole rock and mineral geochemistry of this intrusion are akin to alaskan type complexes and are typical of subduction related magmas the parental magma likely originated from the depleted mantle wedge above a subduction zone and experienced fractional crystallization of olivine and clinopyroxene the continental arc represented by the mafic ultramafic intrusions and contemporary granitic and volcanic rocks together with the luliang back arc basin constitute a marginal arc back arc basin system that evolved between 2 3 and 2 1 ga based on geochronological datasets and available data on magmatism metamorphism and structural deformation a comprehensive new tectonic model for the evolution of the tnco during the neoarchean to paleoproterozoic is constructed 1 2 5 ga intra oceanic arc back arc basin system and its accretion at the end of the neoarchean 2 a long hiatus in magmatism and tectonism between 2 5 and 2 3 ga 3 2 3 2 1 ga marginal arc back arc basin magmatism developed in the accreted hengshan wutai fuping arc terranes and the luliang terrane 4 2 1 ga collision resulting in closure of the 2 3 2 1 ga luliang back arc basin accretion of the luliang hengshan wutai fuping arc terranes and their attachment to the western block of the north china craton 5 the intrusion of 1970 1910 ma post collisional mafic dykes in an extensional event 6 final collision between the western and eastern blocks between 1 9 and 1 8 ga resulting in extensive magmatism tectonism and metamorphism and lastly 7 post 1 8 ga crustal extension

lithostratigraphic correlations in the western himalaya an isotopic approach we present the results of a whole rock nd isotopic study of two contrasting regions of the western himalaya using the neodymium model age approach on the scale of a single orogen high grade metasedimentary rocks from zanskar yield model ages t dm that are similar to those of the high himalayan crystalline series t dm 1 2 2 0 ga nd 6 to 16 and distinct from values from the lesser himalaya t dm 2 3 3 4 ga nd 18 to 27 hence these two lithological sequences can be recognized for 2000 km along the strike of the orogen data for the basement of the nanga parbat massif at the western extremity of the himalaya t dm 2 3 2 8 ga nd 18 to 30 suggest that these rocks are not equivalent to the high himalaya as previously supposed but have affinities with the lesser himalaya a thin metasedimentary cover sequence on the margins of the nanga parbat massif is isotopically indistinguishable from the high himalaya t dm 1 6 1 8 ga nd 10 to 14 the prior misidentification of the provenance of the massif stems from its high metamorphic grade characteristic of the high himalaya but in this case related to the unique neogene history of the nanga parbat massif which has exhumed a higher grade equivalent of the lesser himalaya that is not seen elsewhere

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

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

u pb geochronology and hf nd isotopic geochemistry of the badu complex southeastern china implications for the precambrian crustal evolution and paleogeography of the cathaysia block abstract the oldest rocks of the cathaysia block south china comprise the badu complex and paleoproterozoic granites in the wuyishan area southern zhejiang and northwestern fujian provinces new zircon u pb ages hf isotopes and trace elements for metamorphic rocks from the badu complex and bulk nd isotope compositions of these rocks and granites in the wuyishan area provide important constraints on the precambrian crustal evolution of the cathaysia block inherited cores of zircon grains from the metamorphic rocks are of magmatic origin predominantly formed at ca 2 5 ga while overgrowth rims reflect two episodes of granulite facies metamorphism related to collisional orogeny at 1 89 1 88 ga and 252 234 ma the unimodal age distribution 2 5 ga of detrital zircons and the positive hf t of most neoarchean zircons suggest that the detritus of these sedimentary protoliths of the badu complex came from a proximal volcanic arc and that they were deposited in an arc basin synchronously with 2 5 ga volcanism zircon u pb ages and hf isotopes with whole rock nd isotopes suggest that the juvenile crust of the eastern cathaysia block was generated mainly at 2 5 ga and 2 8 ga and minor at 3 5 3 3 ga with some evidence for the generation at 3 7 3 6 ga and 4 0 ga a strong 1 9 ga orogeny and the 3 3 3 0 ga thermal event only involved the reworking of older crust material paleoproterozoic 1 89 1 86 ga granitic magmatic activity and high grade metamorphism in the eastern cathaysia block were synchronous with the assembly of the columbia supercontinent using integrated geochronological hf nd isotopic and petrologic data as a barcode we compare the cathaysia block with other paleoproterozoic orogens worldwide and argue that its closest affinity is with the south korean peninsula and the lesser himalaya of nw india consequently the eastern cathaysia block and the south korean massif as the united cathay south korea terrane was close to the lesser himalaya terrane in the paleoproterozoic configuration of the columbia supercontinent the spatial linkage was maintained for ca 1 ga until the fragmentation of the rodinia supercontinent during neoproterozoic time

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

proterozoic collisional tectonism in the trans hudson orogen saskatchewan isotopic and structural data from the juvenile reindeer zone of the trans hudson orogen northern saskatchewan indicate a pre 1 85 ga thermotectonic event possibly reflecting arc continent collision followed by a more extensive nappe forming ca 1 83 1 80 ga thermotectonism during terminal continent continent collision preliminary data from the adjacent ensialic cree lake zone suggest high grade reworking of archean crust by the pre 1 85 ga event in the rae province to the west high grade metamorphism and reworking of archean crust occurred about 2 0 ga and may be related to the formation of the coeval taltson magmatic zone

freshwater distribution in the arctic ocean simulation with a high resolution model and model data comparison 1 a high resolution numerical simulation of the arctic ocean is analyzed in order to study the fate of river runoff and freshwater fluxes in the arctic ocean the model is driven by realistic winds and thermodynamic forcing from the european centre for medium range weather forecasting ecmwf reanalysis data set dye tracers have been added to visualize the pathways followed by low salinity water from the major arctic rivers and bering strait inflow the model is spun up using repeated forcing with the 1979 annual cycle for 20 years then the 1979 through 1998 atmospheric forcing is applied under the influence of the 1979 through early 1980s winds a large plume of river runoff exits the broad eurasian shelf seas along the lomonosov ridge starting in about 1985 the locus of shelf to basin transport shifts eastward to the alpha mendeleyev ridge complex this shift in the model output is related to changes in the sea surface height ssh fields which we attribute primarily to shifts in surface wind stresses model resolution runoff inputs and relaxation terms in the lena river delta region are analyzed in detail to expose issues with model performance at boundaries with freshwater inflow suggestions are made for improving future simulations of river runoff in basin scale models

neoproterozoic bimodal magmatism in the cathaysia block of south china and its tectonic significance shrimp u pb zircon age geochemical and sm nd isotopic results are reported for the mamianshan volcanic rocks in the cathaysia block of southeastern south china the mamianshan volcanic rocks are bimodal in composition and are dominantly transitional to mildly alkaline basalts and subordinate alkaline rhyolite with an eruption age of 818 9 ma the basaltic samples are characterized by lree enriched and humped trace element patterns similar to many alkali basalts in continental rifts variablend t values between 3 33 and 4 35 indicate that the primary magma of these basalts was derived from an oib like mantle source and underwent fractional crystallization plus crustal contamination the rhyolitic rocks are highly enriched in th ta nb ree zr hf and y and depleted in sr p eu and ti sharing affinity to a 1 type granites combined with their slightly positive nd t values 0 22 to 0 92 the mamianshan felsic rocks were most likely generated by partial melting of the regional paleoproterozoic mayuan amphibolites the mamianshan bimodal volcanic rocks in the cathaysia block are coeval with the widespread intraplate magmatism around the yangtze block our results support the idea that a coherent south china craton was formed during the ca 1 0 ga sibao orogeny and it subsequently underwent extensive continental rifting related to mantle plume or superplume activities beneath rodinia since ca 825 ma 2004 elsevier b v all rights reserved

a kinetic approach for simulating redox controlled fringe and core biodegradation processes in groundwater model development and application to a landfill site in piedmont italy a three dimensional model for predicting redox controlled multi species reactive transport processes in groundwater systems is presented the model equations were fully integrated within a modflow family reactive transport code rt3d the model can simulate organic compound biodegradation coupled to different terminal electron acceptor processes a computational approach which uses the spatial and temporal distribution of the rates of different redox reactions is proposed to map redox zones the method allows one to quantify and visualize the biological degradation reactions occurring in three distinct patterns involving fringe pseudo core and core processes the capabilities of the numerical model are demonstrated using two hypothetical examples a batch problem and a simplified two dimensional reactive transport problem the model is then applied to an unconfined aquifer underlying a leaking landfill located near the city of turin in piedmont italy at this site high organic load from the landfill leachate activates different biogeochemical processes including aerobic degradation denitrification manganese reduction iron reduction sulfate reduction and methanogenesis the model was able to describe and quantify these complex biogeochemical processes the proposed model offers a rational framework for simulating coupled reactive transport processes occurring beneath a landfill site

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

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

complex precambrian crustal evolution beneath the northeastern yangtze craton reflected by zircons from mesozoic volcanic rocks of the fanchang basin anhui province abstract our knowledge of the precambrian accretion and reworking history of deep crust beneath the northeastern yangtze craton is still sparse zircons from volcanic rocks can not only give accurate crystallization ages for zircons within the host magmas but also provide unique information on the history of deep crustal rocks sampled during magma ascent in situ u pb ages and hf isotopes were analyzed on zircons from two trachyandesites from the late mesozoic zhongfencun and kedoushan formations in the fanchang basin anhui province the zircons exhibit relatively complex internal structures four zircons in the zhongfencun trachyandesite yield a lower intercept 206 pb 238 u age of 133 0 3 2 ma with hf model ages of 2 8 2 4 ga t crust and significantly negative hf t 25 15 to 18 72 demonstrating that this lava formed in early cretaceous time zircons in the kedoushan biotite trachyandesite yield a 206 pb 238 u age of 126 1 ma as well as negative but relatively high hf t values up to 4 34 revealing it formed roughly coeval with the cretaceous a type granites and bimodal magmatism in this region more significantly u pb ages and hf isotopes for proterozoic zircon xenocrysts in the fanchang volcanic rocks reveal that the northeastern yangtze deep crust probably contains unexposed archean e g 3 4 2 9 ga and 2 8 2 5 ga components rarely identified from the outcrops in this area and has undergone complex evolutional history including the addition of juvenile mantle derived materials at 3 4 2 9 ga ca 2 65 ga and ca 0 8 ga and reworking of the precambrian crust at ca 2 0 1 8 ga ca 0 8 ga and 133 126 ma the history of the continental crust s accretion and reworking of the northeastern yangtze craton may not fully coincide with the major episodes of crustal evolution in the wider yangtze craton especially during the archean to paleoproterozoic periods

zircon u pb age and trace element evidence for paleoproterozoic granulite facies metamorphism and archean crustal rocks in the dabie orogen abstract zircon u pb ages and trace elements were determined for granulites and gneiss at huangtuling which are hosted by ultrahigh pressure metamorphic rocks in the dabie orogen east central china cl images reveal core rim structure for most zircons in the granulites the cores show oscillatory zoning relatively high th u ratios and hree enriched patterns consistent with a magmatic origin they gave a weighted mean 207pb 206pb age of 2766 9 ma interpreted as dating magma emplacement of the protolith the rims are characterized by sector or planar zoning low th u ratios negative eu anomalies and flat hree patterns consistent with their formation under granulite facies metamorphic conditions zircon u pb dating yields a weighted mean 207pb 206pb age of 2029 13 ma which is interpreted to record a metamorphic event possibly during assembly of the supercontinent columbia the gneiss has a protolith age of 1982 14 ma which is younger than the zircon age of the granulite facies metamorphism suggesting a generally delay between ht metamorphism and the intrusion of post collisional granites a few inherited cores with igneous characteristics have 207pb 206pb ages of 2 90 3 28 and 3 53 ga suggesting the presence of mesoarchean to paleoarchean crustal remnants in the yangtze craton a few cretaceous metamorphic ages were also obtained suggesting the influence of post collisional collapse in response to cretaceous extension of the dabie orogen it is inferred that the recently discovered archean basement of the yangtze craton occurs as far north as the dabie orogen

early proterozoic granulites in central korea tectonic correlation with chinese cratons abstract a coherent granulite complex has been discovered in the central part of the korean peninsula formerly regarded as the eastern imjingang belt this granulite complex hwacheon granulite complex hgc experienced two cycles of tectonometamorphic events the first event corresponded to crustal thickening followed by peak granulite facies metamorphism and associated partial melting the quasi isobaric cooling path suggested by the occurrences of secondary garnet mantling orthopyroxene and secondary kyanite in mafic and pelitic granulites respectively indicates substantial residence time at midcrustal levels prior to exhumation of the hgc the timing of peak metamorphism was dated from the unzoned overgrowth rims on zircons in a migmatitic granulite at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra