triassic paragonite and garnet bearing epidote amphibolite from the hida mountains japan paragonite and garnet bearing high grade epidote amphibolite pgea in the ise area of the hida mountains japan is characterized by the high pressure hp epidote amphibolite facies parageneses m1 garnet hornblende clinozoisite paragonite quartz rutile paragonite and garnet of the peak m1 stage are locally replaced by retrograde albite oligoclase and chlorite m2 respectively phase equilibria constrain peak metamorphic conditions of p 1 1 1 4 gpa and t 530 570 c and a decompressional p t path for this rock mineral parageneses of prograde epidote amphibolite facies are comparable to some hp rocks from the hongan region of western dabie but differ from other hp mafic schists with cooling ages of c 330 ma in the hida mountains new paragonite k ar dating for the pgeayields a triassic cooling event at 210 ma that is coeval with regional cooling and exhumation of the sulu dabie qinling sdq belt both petrological and geochronological data of the triassic hp epidote amphibolite in hida mountains support our earlier hypothesis that the sdq belt extends across the korean peninsula to sw japan

evidence of early cretaceous transpression in the sulu orogenic belt eastern china abstract recent studies have documented marine turbidites with syn sedimentary deformation features in the central sulu orogenic belt of eastern china these units preserve essential information on the late mesozoic evolution of the sulu orogenic belt referred to as the baxiandun formation the turbidites exhibit similar lithologic characteristics to nearby units such as the lingshandao formation that have been well studied even though precise geochronologic constraints are lacking for a more precise correlation this study reports detrital zircon u pb age data that correlate the baxiandun formation turbidites of the central sulu orogenic belt to the early cretaceous lingshandao formation we also report al in hornblende emplacement depth estimates for granitic intrusions of the sulu orogenic belt s laoshan mountain a sharp contact between the laoshan granites and the marine baxiandun formation indicates that the baxiandun basin rapidly subsided to the emplacement depth of the laoshan plutons lateral correlation among the marine turbidites the lingshandao and baxiandun formations combined with information established by previous studies indicates initiation of transpressional tectonics at 122 121 ma transpression ceased with the emplacement of the laoshan granites whose a1 type composition indicates a return to extensional tectonics at ca 111 ma

k ar illite dating to constrain multiple events in shallow crustal rocks implications for the late phanerozoic evolution of ne asia abstract a recently developed illite age analysis iaa approach was applied to determine the multiple events for the chugaryeong fault belt korea each event was determined by a combined approach of the optimized illite polytype quantification and the k ar age dating of clay fractions separated from the fault clays the late cretaceous to paleogene events 76 5 0 8 69 1 0 6 59 3 0 7 and 48 2 0 7 ma were recognized by calculating the authigenic 1m 1m d illite ages on the iaa plots of the fault clays the early cretaceous ages 121 7 124 7 and 112 4 1 5 ma were also obtained from the convergent intercepts of 100 2m 1 illite on the iaa plots the absence of the 2m 1 illites in the host rock indicates that the early cretaceous ages represent the timings of high t hydrothermal events of 280 c the 2m 1 illites in the fault clays should be pre formed by a fluid rock interaction under a relatively high t subsurface condition and be mechanically reworked into the near surface along the fault by post tectonic events this is the first report determining the absolute age constraints of multi activated tectonic events from a fault these geochronological determinations of the multiple events recorded in the chugaryeong fault belt are crucial to establish the tectonic evolution of the korean peninsula since the late cretaceous

metamorphic evolution of the northwestern ogcheon metamorphic belt south korea the ogcheon metamorphic belt omb comprises late proterozoic to paleozoic metasedimentary and metavolcanic sequences which are intruded by mesozoic granitoid plutons to delineate the metamorphic evolution of the omb we have investigated mineral parageneses metamorphic reactions and p t conditions of pelitic and mafic schists in the chungju area northwestern part of the omb the regional metamorphic grade increases north westward from biotite to garnet zones although low pressure assemblages have developed in contact aureoles around jurassic granites garnet crystals show chemical zoning typical for prograde metamorphism with decreasing mn and increasing fe and mg from core to rim compositions of amphiboles constituting the common assemblage in the mafic schist are consistent with those of biotite and garnet zones documented in the medium pressure metabasites p t conditions of the garnet zone estimated from garnet biotite garnet chlorite and amphibole plagioclase geothermometers together with garnet plagioclase biotite muscoviterquartz geobarometers are in the range of 5 8 kbar and 520 5908c retrograde p t path based on fluid inclusion studies suggests that the exhumation of the omb has passed through the p trange of 1 3 kbar and 350 5008c following the isochore curves of the co inclusions in conjunction with structural and geochronologic data we conclude 2 that the omb has experienced a polycyclic p t evolution characterized by 1 crustal thickening during the middle paleozoic time and 2 regional retrograde metamorphism in the triassic our result further suggests that the triassic collision belt in east central china does not pass through the omb q 1998 elsevier science b v

polyphase tectono magmatic episodes as revealed by shrimp u pb geochronology and microanalysis of zircon and titanite from the central okcheon belt korea abstract the south central okcheon belt of the southern korean peninsula experienced polyphase granitic magmatism and deformation during the mesozoic this study presents integrated results of ion microprobe u pb geochronology and microtextural and microchemical analyses of zircon and titanite from pre tectonic baegnok and cheongsan and post tectonic boeun and sokrisan plutons with respect to the cheongsan shear zone the baegnok granodiorite sample yielded coherent zircon and titanite 206pb 238u ages of 225 6 1 8 and 223 9 4 4 ma indicating a rapid early cooling of the pluton the cheongsan k feldspar megacryst bearing biotite granite sample yielded a coeval zircon 206pb 238u age of 224 7 1 8 ma on the other hand the titanite grains from this rock are categorized into two age populations corresponding to the late triassic 214 3 7 9 ma and the late cretaceous 96 2 8 2 ma growth the older population is clearly of igneous origin considering partly preserved oscillatory zoning in back scattered electron images therefore the age indicates contrasting early cooling paths of the two pre tectonic plutons the younger population is interpreted to be the product of superimposed metasomatic reactions involving plagioclase ilmenite rutile epidote and calcite the two populations show different patterns in their atomic al fe ratios zircons from the boeun and sokrisan plutons yielded 206pb 238u ages of 172 2 2 1 and 94 2 2 1 ma respectively with the latter being indistinguishable from the younger titanite age of the cheongsan pluton the shrimp u pb age of syn deformational fine grained titanite grains lying on sigmoidal foliations in a mylonite from the cheongsan shear zone has a large error 165 47 ma due to their low u pb ratios possibly affected by post tectonic magmatic activities this study highlights the importance of detailed microanalysis prior to the isotopic dating of samples that have experienced complex tectono magmatic episodes

eclogite facies metamorphism in impure marble from north qaidam orogenic belt geodynamic implications for early paleozoic continental arc collision abstract in the north qaidam ultrahigh pressure uhp metamorphic belt impure marble and interbedded eclogite represent a particular sedimentary provenance and tectonic setting which have important implications for a controversial problem the dynamic evolution of early paleozoic subduction collision complexes in this contribution detailed field work mineral chemistry and whole rock geochemistry are presented for impure marble to provide the first direct evidence for the recycling of carbonate sediments under ultrahigh pressures during subduction and collision in the yuka terrane in the north qaidam uhp metamorphic belt according to conventional geothermobarometry pre peak subduction to 0 8 1 3 gpa 485 569 c was followed by peak uhp metamorphism at 2 5 3 3 gpa 567 754 c and cooling to amphibolite facies conditions at 0 6 0 7 gpa 571 589 c u pb dating of zircons from impure marble reveals a large group with ages ranging from 441 to 458 ma peak at 450 ma a smaller group ranging from 770 to 1000 ma peak at 780 ma and minor 1 8 ga zircon aged ca 430 ma uhp metamorphism the youngest detrital zircons suggest a maximum depositional age of ca 442 ma and a burial rate of ca 1 0 1 1 cm yr when combined with p t conditions and uhp metamorphic age the ree and trace element patterns of impure marble with positive sr and u anomalies negative high field strength elements nb ta zr hf and ti and ce anomalies imply that the marble had a marine limestone precursor impure marble intercalated with micaschist and eclogite was similar to limestone and siltstone protoliths deposited in continental fore arc or arc setting with basic volcanic activity therefore the yuka terrane most likely evolved in a continental island arc setting during the paleozoic these data suggest that metasediments were derived from a mixture of proterozoic continental crust and juvenile early paleozoic oceanic and or island arc crust in addition their protoliths were likely deposited in a terrigenous dominated forearc marine basin rather than an intracontinental basin environment further evidence that some continental arc volcanic rock may have been the source of eclogite in the north qaidam these sediments formed in a forearc basin close to the qaidam block to the north were transported in the subduction zone to 100 110 km depth with uhp metamorphism prior to exhumation meanwhile the new results suggest that subduction erosion occurred along the active continental margin during the qaidam block with north dipping subduction indicating that the north qaidam uhp metamorphic belt may have formed during continental arc collision

evidence against subduction related magmatism for the jiaoziyan gabbro northern dabie shan china the largest gabbroic intrusion jiaoziyan in the northern orthogneiss of the dabie shan was investigated to test whether such intrusions represent arc related or collision related magma as postulated in recent regional tectonic models the jiaoziyan intrusions comprise a gabbro monzogabbro suite and are locally characterized by cumulus textured anhydrous silicates petrologic indications against arc magmatism include 1 coexisting olivine plagioclase compositions beyond the documented range of arc gabbros and 2 a compositional trend of al ti ratios in the gabbroic clinopyroxenes that is significantly different from subduction related gabbros worldwide in contrast the jiaoziyan rocks are mineralogically similar to rift gabbros geochronologic and geometric arguments against collision related magmatism i e as a consequence of slab breakoff include the following 1 crystallization of the jiaoziyan mafic intrusion postdated the triassic 245 240 ma subduction and peak orogenic metamorphism by 100 m y and 2 the rocks of the dabie cretaceous magmatic suite including jiaoziyan are on the footwall plate rather than on the hanging wall of the triassic subduction zone framework and do not show a linear distribution these observations argue that the voluminous early cretaceous magmatism in the northern orthogneiss is geodynamically unrelated to the qinling dabie orogeny but was caused by extensional tectonism related to regional magmatic underplating beneath the thinned dabie crust

geology distribution and classification of gold deposits in the western qinling belt central china gold deposits of the western qinling belt occur within the western part of the qinling dabie sulu orogen which is located between the precambrian north china and yangtze cratons and east of the songpan ganzi basin the early paleozoic to early mesozoic orogen can be divided into northern central and southern zones separated by the shangdan and lixian shanyang thrust fault systems the northern zone consists of an early paleozoic arc accreted to the north china craton by ca 450 ma the central zone which contains numerous orogenic gold deposits is dominated by clastic rocks formed in a late paleozoic basin between the converging cratonic blocks the southern zone is characterized by the easternmost exposure of triassic sedimentary rocks of the songpan ganzi basin these early to late triassic turbidities in part calcareous of the immense songpan ganzi basin also border the western qinling belt to the west carlin like gold deposits are abundant 1 along a westward extension of the southern zone defined by a window of early paleozoic clastic rocks extending into the basin and 2 within the easternmost margin of the basinal rocks to the south of the extension and in adjacent cover rocks of the yangtze craton triassic and early jurassic synkinematic granitoids are widespread across the western qinling belt as well as in the songpan ganzi basin orogenic lode gold deposits along brittle ductile shear zones occur within greenschist facies highly deformed devonian and younger clastic rocks of the central zone mainly coarse grained gold along with pyrite pyrrhotite arsenopyrite and minor base metal sulfides occur in networks of quartz veinlets brecciated wall rock and are disseminated in altered wall rock isotopic dates suggest that the deposits formed during the late triassic to middle jurassic as the leading edge of the yangtze craton was thrust beneath rocks of the western qinling belt many gold bearing placers are distributed along the river systems that flow south from the lode bearing central zone carlin like gold deposits have only been identified during the last decade in the southern zone of the western qinling and in the northeastern corner of the songpan ganzi basin the deposits mainly contain micron diameter gold in arsenical pyrite are characterized by the common occurrence of cinnabar stibnite realgar and orpiment exhibit strong silicification carbonatization pyritization and decalcification dissolution textures and are structurally controlled the lack of reactive host lithologies may have prevented development of large 100 tonnes of gold stratigraphically controlled orebodies which are typical of the carlin deposits in the western usa these deposits are hosted by triassic turbidities and shallow water carbonates and an early paleozoic inlier in the songpan ganzi basin that extends in an east west belt for about 300 km rather than true carlin deposits these carlin like deposits may be some type of shallow crustal i e epithermal hybrid with features intermediate to nevada style carlin deposits and the orogenic gold deposits to the immediate north these carlin like deposits also overlap in age with the early mesozoic orogenic gold deposits and therefore also formed during the final stages of collision between the cratons and intermediate basin closure

contrasting plate tectonic styles of the qinling dabie sulu and franciscan metamorphic belts the dabie mountains are part of the 2000 km long qinling dabie sulu suture zone juxtaposing the sino korean and yangtze cratons an eastern extension apparently crosses korea and lies along the japan sea side of honshu as the imjingang and sangun terranes respectively a northeastern segment may be present in sikhote alin russian far east this orogenic belt records late paleozoic ocean floor consumption and the triassic collision of two precambrian continental massifs in east central china coesite and microdiamond inclusions in strong refractory minerals of eclogite facies ultrahigh pressure uhp metamorphic rocks in the dabie sulu area attest to profound subduction of a leading salient of the old cold yangtze craton now recovered through tectonic exhumation and erosion northward increase in intensity of subsolidus recrystallization of the suture complex is analogous to the internal progression in grade of high pressure hp and uhp metamorphism documented in the western alps in both regions subduction of narrow prongs of continental material uhp metamorphism and return toward midcrustal levels of relatively lower density buoyant microcontinental blocks resulted from delamination of these rocks from the descending higher density oceanic crust capped lithospheric plate such salients of continental crust represent an integral structural part of the downgoing slab remain intact and may be dragged to great depths before disengaging and rising differentially as coherent blocks uhp parageneses include trace mineralogic relics requiring peak metamorphic conditions of 700 900 c and 28 35 kbar or more in contrast pacific type hp metamorphic belts as represented by the franciscan complex of western california recrystallized under physical conditions up to 200 500 c 10 3 kbar in this setting voluminous quartzo feldspathic and graywacke debris was carried downward on oceanic crust capped lithosphere choking the subduction zone with incompetent material sited between both plates and strongly adhering to neither this buoyant largely sedimentary complex decoupled at 25 30 km depth and ascended toward the surface in both alpine type intracontinental collision and pacific type underflow light sialic material displaced dense mantle thus the return to midcrustal levels was propelled dominantly by body forces

subduction of continental margins and the uplift of high pressure metamorphic rocks abstract the mechanism by which high pressure metamorphosed continental material is emplaced at high structural levels is a major unsolved problem of collisional orogenesis we suggest that the emplacement results from partial subduction of the continental margin which because of its high flexural rigidity produces a rapid change in the trajectory of the descending slab we assume a two fold increase in effective elastic thickness of the lithosphere as the continental margin approaches the subduction zone and calculate the flexural profile of a thin plate for progressive downward migration of the zone of increased rigidity we assess the effect of changes in the flexural profile on the overlying accretionary prism and mantle wedge as the continent approaches by estimating the extra stresses that are imposed on the wedge due to the bending moment exerted by the continental part of the plate the wedges overlying the subduction zones and the subducting slab itself experience substantial extra compressional stress at depths of around 100 km and extensional stress at shallower depths as the continental margin passes through the zone of maximum curvature the magnitudes of such extra stresses are probably adequate to effect significant deformation of the wedge and or the descending plate and are experienced in a time interval of less than 5 m y for typical subduction rates the spatial variation of yield stresses in the region of the wedge and descending slab indicates that much of this deformation may be taken up in the crustal part of the descending slab which is the weakest region in the deeper parts of the subduction zone this may result in rapid upward migration of the crust of the partially subducted continental margin against the flow of subduction high pressure metamorphosed terranes emplaced by the mechanism envisaged in this paper would be bounded by thrust faults below and normal faults above movement on the faults would have been coeval and would have resulted in rapid unroofing of the high pressure terranes synchronous with arrival of the continental margin at the subduction zone and therefore relatively early in the history of a collisional orogen

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

phanerozoic polyphase orogenies recorded in the northeastern okcheon belt korea from shrimp u pb detrital zircon and k ar illite geochronologies abstract we present the shrimp u pb detrital zircon and k ar illite 1m d 1m and 2m 1 ages suggesting new insight into the phanerozoic polyphase orogenies preserved in the northeastern okcheon belt korea since the initial basin formation during neoproterozoic rifting through several successive contractional orogens the u pb detrital zircon ages from the early paleozoic strata of the taebaeksan zone suggest a cambrian maximum deposition age and are supported by trilobite and conodont biostratigraphy although the age spectra from two sedimentary groups the yeongwol and taebaek groups show similar continuous distributions from the late paleoproterozoic to early paleozoic ages a grenville age hiatus 1 3 0 9 ga in the continuous stratigraphic sequence from the taebaek group suggests the existence of different peripheral clastic sources along rifted continental margin s in addition we present the k ar illite 1m d 1m ages of the fault gouges which confirm fault formation reactivation during the late cretaceous to early paleogene ca 82 62 ma and the early miocene ca 20 18 ma the 2m 1 illite ages at least those younger than the host rock ages provide episodes of deformation metamorphism and hydrothermal effects related to the tectonic events during the devonian ca 410 ma and permo triassic ca 285 240 ma these results indicate that the northeastern okcheon belt experienced polyphase orogenic events namely the okcheon middle paleozoic songrim late paleozoic to early mesozoic daebo middle mesozoic and bulguksa late mesozoic to early cenozoic orogenies reflecting the phanerozoic tectonic evolution of the korean peninsula along the east asian continental margin

southward extrusion of eclogite bearing mafic ultramafic bodies in the sanbagawa belt central shikoku japan abstract several mafic rock masses which have experienced eclogite facies metamorphism are distributed in flat lying non eclogitic schists in an intermediate structural level thermal core of the sanbagawa belt the largest iratsu mass and an associated peridotite the higashi akaishi mass extend e w for about 8 km and n s for about 3 km and are surrounded by pelitic basic and quartz schists the iratsu mass consists of metabasites of gabbroic and basaltic origin with intercalations of ultramafic rocks felsic gneiss quartz schist and metacarbonate the iratsu mass can be divided into two layers along a wnw trending metacarbonate layer the higashi akaishi mass consists of peridotite with intercalations of garnet clinopyroxenite it is situated beneath the western half of the iratsu mass and their mutual boundary dips gently or steeply to the n or ne these masses underwent eclogite and subsequent epidote amphibolite facies metamorphism as has been reported elsewhere the iratsu higashi akaishi masses and the surrounding rocks underwent ductile deformation under epidote amphibolite facies or lower p t metamorphic conditions their foliation generally trends wnw and dips moderately to the nne and the mineral lineation mostly plunges to the n and ne in non eclogitic schists surrounding the iratsu higashi akaishi masses the foliation generally trends wnw and dips gently or steeply to the n or s and the mineral lineation mostly plunges to the nw n and ne kinematic analysis of deformation structures in outcrops and oriented samples has been performed to determine shear senses consistent top to the north normal fault displacements are observed in peridotite layers of the higashi akaishi mass and eclogite bearing epidote amphibolite layers of the iratsu mass top to the northeast or top to the northwest displacements also occur in non eclogitic pelitic quartz schists on the northern side of the iratsu mass in the structural bottom of the iratsu higashi akaishi masses and to the south reverse fault top to the south movements are recognized in serpentinized peridotite and non eclogitic schists these observations provide the following constraints on the kinematics of the rock masses 1 northward normal displacement of iratsu relative to higashi akaishi 2 northward normal displacement of non eclogitic schists on the north of the iratsu mass and 3 southward thrusting of the iratsu higashi akaishi masses upon non eclogitic schists in the south the exhumation process of the iratsu higashi akaishi masses can be explained by their southward extrusion

mesozoic episodic magmatism in south korea and its tectonic implication 1 ne trending granitoid batholiths in south korea are part of the huge phanerozoic granitoid belt in east asia the crystallization ages of granitoid plutons show three episodes of mesozoic magmatism in south korea triassic 248 210 ma jurassic 197 158 ma and late cretaceous early tertiary 110 50 ma with a late jurassic early cretaceous 50 m y hiatus the granitoid ages and kinematic analyses of the mesozoic structures in south korea suggest that the middle jurassic 180 170 ma dextral strike slip ductile shear zones formed by the northwest orthogonal subduction of the izanagi plate whereas the cretaceous sinistral faults formed by the northward oblique subduction of the same plate which generally agree with proposed reconstruction of plate motions albeit uncertain around east asia among the models proposed to explain magmatic lull in a continental arc shallow angle subduction associated with high convergence rate and subduction of oceanic plateaus might be the probable cause for the magmatic hiatus in south korea and japan the huge width 500 km of the east asian granitoid belt may be explained by oceanward retreat of subduction zone in the cretaceous in association with change in the movement direction of the subducting plate

multiple partial melting events in the sulu uhp terrane zircon u pb dating of granitic leucosomes within amphibolite and gneiss thin layers and lenses of granitic leucosome are widely distributed within amphibolites paragneisses and orthogneisses of the sulu uhp terrane they are parallel to or cross cut foliations in the host rocks at different scales and show evidence of coalescence and migration to form centimetre to decimetre scale segregations variously migmatized rocks extend at least 350 km from sw sulu maobei to ne sulu weihai in a band at least 50 km wide a combined study of mineral inclusions cathoduluminescence cl images u pb la icp ms dates and in situ trace element compositions of zircon provide clear evidence on the nature and timing of partial melting in these uhp rocks most zircon from the granitic leucosomes occurs as distinct overgrowths around inherited igneous or metamorphic cores or as new euhedral crystals the overgrowths and new crystals commonly show perfectly euhedral shapes have pronounced oscillatory zoning and contain felsic mineral inclusions such as kfs pl qtz ilm monazite mon in contrast the inherited igneous or metamorphic cores are rounded or irregular contain low p or uhp mineral inclusions and show clear dissolution textures these data suggest that the new zircon is anatectic in origin and that it grew during partial melting of the uhp rocks the ree patterns of the anatectic zircon show steep slopes from the hree to lree with strongly to moderately negative eu anomalies eu eu 0 31 0 72 and pronounced positive ce anomalies ce ce 6 8 26 5 abundant u pb spot analyses of the anatectic zircon reveal two discrete and meaningful ages of partial melting within the sulu uhp terrane anatectic zircon from 12 granitic leucosomes within amphibolites paragneisses and orthogneisses from sulu uhp slices ii and iii yields consistent mean u pb ages of 219 0 1 2 to 218 3 1 6 ma 218 8 2 0 to 217 3 1 7 ma and 218 2 1 4 to 215 0 1 5 ma respectively in contrast anatectic zircon from six granitic leucosomes within paragneisses and orthogneisses from sulu uhp slice iii records younger mean u pb ages of 151 9 1 3 to 151 1 1 8 ma and 155 9 1 8 to 153 7 1 7 ma respectively these data imply that the sulu uhp terrane experienced two mesozoic partial melting events the first partial melting event 219 215 ma was probably associated with a late triassic granulite facies stage of hot exhumation whereas the second 156 151 ma is interpreted as the result of middle late jurassic extension and thinning of the previously thickened crust of the sulu uhp terrane both partial melting events induced extensive retrograde metamorphism of the eclogites and their country rocks

the metamorphic evolution and tectonic significance of the sumdo hp uhp metamorphic terrane central south lhasa block tibet the lhasa terrane forming one of the main tectonic components of the himalayan tibetan orogen has received a lot of attention as it records multiple episodes of plate spreading subduction and collision within the realm of the paleo tethys ocean a review of the mineralogical petrological geochemical and geochronological data of eclogites associated blueschists and garnet bearing mica schists from the sumdo high and ultrahigh pressure metamorphic hp uhp complex in the central southern part of the lhasa terrane is present here so that the origin and tectono metamorphic evolution of this important suture can be deduced by re evaluating the original published p t conditions for the metamorphic rocks of the sumdo complex we consider that the sumdo complex has experienced low temperature hp uhp metamorphic conditions characteristic of fast subduction and exhumation in a typical oceanic subduction zone setting the original wide spread in the maximal peak p t conditions could be reduced in size due to thus far unknown inconsistencies in the usage of applied geothermobarometric techniques the remaining spread in the maximal p t conditions c 200 c 10 kbar of the hp uhp regions can be explained by a mechanism that the rocks from individual tectonic slices were subducted to different depths and followed by juxtaposition on their way back to the surface a re consideration of the isotopic ages of eclogites from the sumdo complex demonstrates that the opening of the paleo tethys ocean located in between the two major components of the lhasa terrane was initiated prior to c 280 ma and the eclogite facies metamorphism is likely to be of late permian c 260 ma to early triassic age 245 225 ma recording different ages of subduction from individual slices of the oceanic crust the closure of the paleo tethys ocean resulted no earlier than 210 ma in the final collision between the northern and southern lhasa blocks this final collision event may have been triggered by the initial subduction of the bangong nujiang tethys ocean in the north

timing of synorogenic granitoids in the south qinling central china constraints on the evolution of the qinling dabie orogenic belt abstract the ca 400 km long granitoid belt in the south qinling is believed to be a synorogenic product of the collision between the north and south china blocks along the qinling dabie orogenic belt in central china single and multigrain zircon u pb dating of six of these granitoid bodies indicate that the granitoids were formed between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 220 pm 1 end document and documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage m

evolutionary model for alpine corsica mechanism for ophiolite emplacement and exhumation of high pressure rocks a tectonic model of alpine corsica is proposed based on geological studies its evolution starts after the jurassic with intraoceanic subduction followed by mid cretaceous subduction of the european continental margin under the oceanic segment of the adriatic plate after subduction of the continental crust to a depth of 150 km slices of crustal material are buoyantly uplifted together with high pressure oceanic rocks ophiolites and schistes lustres high pressure low temperature continental gneiss units overthrust the outer segments of the european crust while producing a normal sense motion along the upper surface of the rising crustal body during the eocene the closure of the remnant ligurian oceanic basin separating the proto corsican belt and adria resulted in a second orogenic phase with the emplacement of unmetamorphosed ophiolitic nappes which overthrust the previously exhumed and eroded hp belt this corsican model suggests an original evolutionary path for orogenic belts when continental collision is preceded by intraoceanic subduction

polyphase formation and exhumation of high to ultrahigh pressure rocks in continental subduction zone numerical modeling and application to the sulu ultrahigh pressure terrane in eastern china 1 high to ultrahigh pressure hp uhp metamorphic rocks commonly form and exhume during the early continental collision and many questions related to their origin still remain unresolved we focus our study on explaining the poly metamorphic origins of many hp uhp terranes composed of tectonic units having strongly variable ages peak metamorphic conditions and p t paths these features are especially well characterized for the sulu uhp terrane in eastern china which we have chosen therefore as the reference case we conducted 2 d thermomechanical numerical modeling of continental subduction associated with formation and exhumation of hp uhp rocks our experiments suggest existence of several consequent episodes of u hp rocks exhumation related to the inherently cyclic origin of continental crust subduction detachment exhumation processes three major phases of these processes are identified in our reference model for the sulu uhp terrane 1 first and 2 second exhumation episodes of hp rocks originated in the subduction channel at lithospheric depths and 3 exhumation of uhp rocks originated at asthenospheric depths numerical models also suggest that subducted uhp rocks which are positively buoyant compared to the mantle may detach from the slab forming a flattened plume underplating the overriding lithosphere this sublithospheric plume may exist for several million years being heated to 800 900 c by the surrounding hot mantle at the later stage upward extrusion of hot partially molten rocks from the plume may exhume high temperature ht uhp complexes toward the surface

the formation of foliated garnet bearing granites in the tongbai dabie orogenic belt partial melting of subducted continental crust during exhumation foliated garnet bearing fgb granites are associated closely with and are usually the major wall rocks of the high pressure hp and ultrahigh pressure uhp metamorphic rocks in the tongbai dabie region the mid segment of the qinling dabie sulu orogenic belt in central china these granites appear either as small plutons or as veins which commonly intrude into or surround the hp and uhp metamorphic eclogites or gneisses the veins of fgb granites usually penetrate into the retrograded eclogites or gneisses along the foliations condensation rims can occasionally be found along the margins of granite veins these granites are rich in si and alkali with high ga al ratios and depleted in ca mg al ti sc v ni co cr and sr which are similar to a type granites in a chondrite normalized diagram the samples are light rare earth elements enriched with different extent of negative eu anomaly moreover rb nb ta sr p and ti show different degrees of negative anomalies whereas ba k la zr and hf show positive anomalies in the primitive mantle normalized diagram negative anomalies of eu and sr indicate strong influence of plagioclase in conventional discrimination diagrams these fgb granites belong to the a type granite with geochemical characteristics affinitive to post collisional granites the end 230 ma values 15 80 to 2 52 and tdm values 1 02 2 07 ga suggest that magma for the fgb granites were derived from a heterogeneous crustal source therefore the fgb granites may provide clues for deciphering the formation of post collisional granites it is proposed that the magma of the fgb granites both in the hp and uhp units was formed in an extensional tectonic setting slightly post dating the hp and uhp metamorphism most likely as a result of decompressional partial melting of uhp retrograded eclogites during exhumation

initial constraints on the timing of granitic magmatism in north korea using u pb zircon geochronology abstract the geology of north korea is very poorly known in this paper twenty seven granitic samples from the tumangang belt and the rangnim massif including diorite granodiorite and monzogranite were selected for in situ zircon u pb isotopic dating in the tumangang belt granites formed mainly in the jurassic with one sample giving a triassic age this is contrary to previous views that considered the granites to be permian to triassic in age in the rangnim massif precambrian granitic magmatism mainly took place at 2 1 and 1 9 1 8 ga no archean emplacement ages have been documented in this study although some inherited discordant zircon may be of this age mesozoic magmatism in this area can be divided into three stages with ages of 234 213 173 and 114 109 ma the triassic granites are mostly exposed in the north and the early cretaceous ones in the west the distribution of jurassic granites is less well documented and only one sample was identified in this study however previous data indicate they are more widely distributed in the area the 2 1 and 1 9 1 8 ga precambrian ages are comparable to paleoproterozoic magmatism in northeastern china indicating that the rangnim massif was most likely part of the north china craton during that time however the absence of 2 5 ga granites and the occurrence of 1 2 ga granites indicate that the rangnim massif was probably at the margin of the north china craton and affected by mesoproterozoic magmatism the similarity in age patterns of the mesozoic granites in north korea to surrounding areas of south korea and the liaodong peninsula of northeastern china indicate that they were controlled by subduction of the pacific ocean under eastern asia however roll back or retreat of the subduction zone resulted in a younging trend from northwest to southeast during the cretaceous

detrital zircon u pb ages of the jangsan formation in the northeastern okcheon belt korea and its implications for material source provenance and tectonic setting abstract the jangsan formation distributed in the taebaeksan basin central eastern korea is unfossiliferous and is composed of quartz arenite this formation is conventionally believed to be the lowermost stratigraphic unit of the lower paleozoic sequence deposited on the yeongnam massif in south korea corresponding to early cambrian in age u pb dating of detrital zircon grains using a laser ablation inductively coupled mass spectrometer yields ages ranging from archean to middle proterozoic 1738 67 ma to 3058 53 ma detrital zircons show no ages younger than 1 8 ga suggesting that the jangsan formation was deposited at some time after this age but much prior to ca 520 ma the depositional age of the immediately overlying myobong formation this interpretation is supported by the recent report on the presence of the unconformity between the jangsan and the myobong formations kim and lee 2006 zircon ages from jangsan sandstones define two major groups archean age grains with a maximum frequency at about 2 5 ga and paleoproterozoic age grains with maximum frequencies at about 2 1 and 1 8 ga the observed zircon age distribution in the jangsan sandstones may represent that of the yeongnam massif on which the jangsan formation was deposited such an age distribution of the yeongnam massif matches well with that the north china block suggestive of the yeongnam massif being a part of the sino korean craton during the precambrian

ar ar muscovite dating as a constraint on sediment provenance and erosion processes in the red and yangtze river systems se asia in this study we applied 40ar 39ar dating methods to muscovite grains in sands from the modern red and yangtze rivers in order to constrain palaeo and modern erosion patterns and sediment transport processes micas in the headwaters of the red river and its southern da river tributary are dominantly cenozoic while the northern lo river tributary shows a typical 160 220 ma population the lower reaches of the red river comprise 53 of such triassic grains indicating that the lo river is the most important net contributor to the modern delta however this contrasts with zircon u pb data indicating that the upper reaches of the red river dominate that mineral group we suggest that the mismatch reflects the rapid transport of mica relative to zircon in the river and the fact that the red river is not in equilibrium we hypothesize that the zircons were eroded 8 ka under a regime of stronger monsoon that enhanced erosion in the northern drainage basin while modern erosion is focused in the south especially in the song chay massif micas from the upper yangtze river are resolvably older than those in the red river 230 250 ma so that this method could be used to test for drainage capture in palaeo delta sediments micas in the modern yangtze delta are generally much younger than those in the upper reaches and indicate that erosion in the longmen shan sichuan and neighbouring regions is more important than the upper yangtze in supplying sediment reflecting the stronger monsoon rains in those areas

controls on sedimentation in distal margin palaeovalleys in the early tertiary alpine foreland basin south eastern france the influence of palaeodrainage characteristics palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems this study is an examination of the influence of source region vs downstream base level controls on the sedimentary architecture of a set of bedrock confined palaeovalleys developed along the distal margin of the alpine foreland basin in south eastern france three distinct facies associations are observed within the palaeovalley fills fluvial facies association a is mainly dominated by poorly sorted highly disorganized clast to matrix supported cobble to boulder conglomerates that are interpreted as streamflood deposits facies association b comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment estuarine marine facies association c comprises interstratified estuarine siltstones and clean well sorted washover sandstones the sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits in contrast distal palaeovalley segments which are located several kilometres downstream contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines and finally into estuarine marginal marine facies facies distributions suggest that the fluvial deposits form wedge shaped downstream thinning sediment bodies whereas the estuarine deposits form an upstream thinning wedge the vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock confined river valleys which drained a rugged upland terrain facies geometries suggest that a fluvial sediment wedge initially prograded downvalley in response to high bed load sediment yields subsequently palaeovalleys became drowned during the passage of a marine transgression with the establishment of estuarine conditions initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea level rise driven by flexural subsidence of the basin

multiple deformations along the honam shear zone in southwestern korea constrained by rb sr dating of synkinematic fabrics implications for the mesozoic tectonic evolution of northeastern asia abstract the honam shear zone dextrally running along the southern margin of the ogcheon belt korea has drawn much attention in reconstructing the mesozoic tectonic framework of northeastern asia here we present rb sr data for the middle to southwestern part of the honam shear zone in an attempt to directly determine ages of deformation in the middle part the younger limit of deformation is constrained to be 162 11 ma by feldspar biotite rb sr dating of the deformed sunchang granodiorite on the other hand an early cretaceous deformation age is estimated for synkinematic fibers in ultramylonites from the southwestern part by two reproducible rb sr errorchrons at 138 4 and 139 23 ma this deformational time scale is consistent with earlier interpretations based on field evidence magnetic susceptibility data and age data for jurassic plutons within the shear zone our data demonstrate that the honam shear zone is not a permian to triassic tectonic feature related to the chinese continental collision

climate change river redirected glaciers and ice sheets are retreating in response to climate warming an analysis of drainage patterns of a huge glacier in yukon canada shows that glacier retreat has led to a drastic change in the destination of its meltwater in spring 2016

granulite facies metamorphism in the punggi area northeastern yeongnam massif korea and its tectonic implications for east asia abstract in the punggi area of the northeastern part of the yeongnam massif one of precambrian basement terrains in korean peninsular the metamorphic grade increases from the amphibolite to the granulite facies zones towards the southeast the boundary of the granulite facies zone is defined by the orthopyroxene opx in reaction in metabasites as metamorphic grade increases across the opx in isograd the mineral assemblage in calcic metabasites is changed from clinopyroxene amphibole plagioclase to orthopyroxene clinopyroxene amphibole plagioclase and that in alkali metabasites from garnet orthoamphibole plagioclase to garnet orthopyroxene plagioclase the metamorphic rocks in the granulite facies zone were overprinted by upper amphibolite facies retrograde metamorphism during retrograde metamorphism cordierite and spinel formed in the migmatitic gneiss the p t conditions of granulite facies metamorphism are 767 815 c and 6 0 8 4 kb and the p t conditions for the retrograde stage are 595 707 c 4 7 6 4 kb a u pb zircon age of 1904 9 ma has been obtained from a garnet granitic gneiss and is inferred to date the emplacement of its precursor this is consistent with the intrusion age of precursors to most orthogneisses in other parts of the yeongnam massif the same sample has yielded a sm nd whole rock garnet age of 617 38 ma which is inferred to represent a late proterozoic metamorphic event of upper amphibolite facies

zircon u pb geochronology sr nd hf isotopic composition and geological significance of the late triassic baijiazhuang and lvjing granitic plutons in west qinling orogen the qinling orogen was a consequence of continental collision of the south china craton with the north china craton in the triassic and caused widespread granitoid magmatism however the petrogenesis of these granitoids remains controversial in this paper we choose the baijiazhuang bjz and lvjing lj plutons in the west qinling orogen for a combined study of the zircon u pb geochronology whole rock major and trace element compositions and sr nd hf isotopic characteristics we obtained zircon crystallization ages of similar to 216 ma and similar to 212 ma for the bjz and the lj plutons respectively the granitoid samples from both plutons have high k2o metaluminous to peraluminous compositions they are enriched in large ion lithophile elements liles light rare earth elements lrees and depleted in high field strength elements hfses with significant negative eu anomalies the bjz samples have initial sr isotopic ratios of 0 7032 to 0 7078 epsilon nd t of 10 99 to 8 54 and epsilon hf t of 1022 to 6 41 the lj granitoids have initial sr isotopic ratios of 0 7070 to 0 7080 epsilon nd t of 5 37 to 4 58 and epsilon hf t of 3 64 to 1 78 the enriched isotopic characteristics of the two plutons are consistent with their source being dominated by ancient continental crust however two bjz samples show depleted sr isotope compositions which may infer possible involvement of mantle materials mantle derived melt which formed from partial melting of mantle wedge peridotite facilitated by dehydration of the subducted subducting mianlue ocean crust provide the required heat for the crustal melting while also contributing to the compositions of these granitoids that is the two granitic plutons are magmatic responses to the closure of the mianlue ocean basin and the continental collision between the yangtze and south qinling crustal terranes c 2016 elsevier b v all rights reserved

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