early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

magmatic evolution of the eastern coast plutonic complex bella coola region west central british columbia the eastern coast plutonic complex in west central british columbia 51 54 n consists of a broad belt of jurassic to eocene granitic to dioritic intrusive rocks that collectively represent more than 140 m y of nearly continuous subduction related magmatism seven distinct intrusive suites have been identified in the bella coola region including from oldest to youngest the howe lake stick pass firvale desire fougner big snow and four mile suites pre late cretaceous rocks were produced by episodic subduction related magmatism characterized by partial melting of preexisting lower arc crust with minimal incorporation of evolved continental material the eastern coast plutonic complex experienced a magmatic lull between ca 110 and 95 ma coincident with sinistral transpression potentially linked to translational displacement of the wrangellia alexander composite terranes crustal thickening in late cretaceous time ca 100 90 ma possibly due to underplating of the wrangellia alexander terrane produced a deep crustal root 40 km that likely extended into the eclogite transition zone adakitic magmas ca 95 67 ma were produced by partial melting of an amphibolitic protolith in this thickened lower arc crust adakitic plutons are pre syn and postkinematic with respect to late cretaceous high angle shear zones and they are coeval and spatially associated with postkinematic two mica granites ca 70 75 ma having a hybrid a type geochemistry we suggest that delamination of this dense crustal root led to voluminous magmatism extension and crustal exhumation in paleocene eocene time the successive intrusive events in the eastern coast plutonic complex may reflect a predictable evolutionary progression common to all continental arc systems

late permian early triassic orogeny in japan piling up of nappes transverse lineation and continental subduction of the honshu block abstract field surveys in the oga atetsu and yamaguchi areas of southwest japan have been conducted in order to precise the structure of the permian orogen a stack of nappes is recognized comprising from top to bottom 1 the oga nappe which is considered to be a seamount complex 2 hp sangun metamorphics 3 the permian yakuno ophiolite and 4 the permian detrital maizuru group which is interpreted as the sedimentary cover of a continental block called here the honshu block outcropping as the older granite this stack of nappes is overthrust by the paleozoic hida basement consisting of ht gneisses granites and late carboniferous shallow water sediments microtectonic analysis of the sangun schists shows that the subhorizontal schistosity bearing a submeridian lineation was formed during the synmetamorphic phase asymmetric pressure shadows shear bands and sigmoidal minerals show that the synmetamorphic deformation corresponds to a ductile shear from north to south the permian early triassic orogeny is interpreted as the result of a collision between the hida gneiss or south china block and the honshu block the intervening oceanic area gave rise to southward directed nappes the permian orogenic belt extends at least from taiwan to central japan

geodynamics of the ogcheon belt south korea abstract the ogcheon belt is a stack of synmetamorphic southeastward verging nappes resulting from the deformation of a volcanosedimentary sequence deposited in an early palaeozoic rift which was affected by polyphase tectonics its pre cretaceous structure results from three main orogenic events the ogcheon late silurian devonian indosinian late permian triassic and yenshanian middle jurassic early cretaceous tectonic phases the external autochthonous or para autochthonous units represent platform zones with shallow water deposits whereas rift facies characterize the internal domain the yeongweol sequence forming an outer shelf on the southeastern margin of the rift displays affinities with the jiangnan basin of south china it is in wrench fault contact with the easternmost duwibong sequence correlated with the north china north korea platform in the internal metamorphic units post cambrian early ordovician pelitic and turbiditic rift metasediments overlie a thin cambrian or cambrian ordovician early platform sequence two subdomains are distinguished the upper units chung ju and pibaryeong units representing the deep axial part of the basin contain distal flyshoids and large olistoliths derived from the northwestern narrow margin the lower units turung san poeun and iwharyeong are related to the wide margin located between the deep rift domain and the stable southeastern platform the latter transitional domain is characterized by thick submarine debris flows and volcanics of alkali or transitional tholeiitic affinity the volcanic activity and mass gravity flow sedimentation are closely related to the crustal thinning and subsequent rifting and tilting lithostratigraphic evidence allows the correlation of the unfossiliferous rift metasediments with the cambrian ordovician platform sequence in one single basin the post middle silurian pre mid carboniferous ogcheon ensialic orogeny resulted in the closure of the rift with relatively minor effects in the platform area it gave rise to an intracontinental fold thrust belt without ophiolites this tectonic event may have been contemporaneous with early palaeozoic tectonism in the quinling belt in central china and in the southeast china fold belt the definitive constitution of the sino korean craton took place before the mid carboniferous and molasse sedimentation was initiated on a single platform located on the western edge of the yakuno oceanic basin of southwest japan in late permian and early triassic times the closure of the oceanic area and the subsequent westward collision of the honshu block are marked in korea by the intracratonic indosinian tectonism since late triassic times predominantly transcurrent movements have occurred along nne ssw faults associated with syntectonic intermontane troughs and important granitization

mercury evidence from the sino korean block for emeishan volcanism during the capitanian mass extinction a prominent large negative 13 c org excursion and a coeval notable spike in mercury hg total organic carbon ratio are observed in the middle upper permian gohan formation in central korea located in the eastern sino korean block skb which may represent the capitanian mass extinction event the skb was separated from the south china block by the eastern palaeo tethys ocean this finding from the skb supports the widespread hg loading to the environment emitted from the emeishan volcanic eruptions in sw china this study demonstrates that the hg cycle was globally perturbed in association with global carbon cycle perturbation that occurred during the capitanian extinction

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

provenance derived from the geochemistry of late paleozoic early mesozoic mudrocks of the pyeongan supergroup korea late carboniferous early triassic pyeongan supergroup korea was deposited in paralic to nonmarine environments developed disconformably on a lower paleozoic platformal sequence pyeongan supergroup mudrocks show progressive upsection changes in major trace and rare earth element compositions mudrocks in the lower and middle parts of the pyeongan supergroup are strongly depleted in cao and na2o while those in the upper part are enriched in these elements in parallel with cao and na2o the ratio of k2o al2o3 in the lower and middle sections is less than 0 3 while uppermost strata are enriched in k2o having k2o al2o3 ratios greater than 0 3 the index of compositional variability a measure of compositional maturity is less than 0 6 in the lower to middle section whereas in the uppermost strata it is greater than 0 7 similar trends are reflected in a cn k space compared to paas mudrocks of the pyeongan supergroup except for those in uppermost units they are depleted in mn ca and na and are slightly depleted in mg and p contrasting major oxide trends between the lower and middle parts of the pyeongan and the uppermost units are due to decreasing proportions of clay minerals and a concomitant increase in the proportion of nonclay silicate minerals due to increasing input of first cycle detritus excursions marked by increases in mgo na2o and cao reflect large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift incompatible elements are generally enriched in mudrocks of the pyeongan supergroup relative to paas while transition metals co ni cr and v are progressively depleted in younger parts of the section total rare earth element concentrations are higher than paas but chondrite normalized patterns display the typical lree enriched pattern of paas eu anomalies for most mudrocks are close to that of paas the youngest mudrocks in the pyeongan supergroup have the most negative values these trends can be explained by a sedimentary system dominated by detritus derived from recycled highly weathered granitic materials in the lower to middle pyeongan section with an increased proportion of less weathered detritus derived from fractionated granitic materials in uppermost strata such an interpretation is consistent with the results of studies on coarse grained sediments of the pyeongan supergroup

relay mountain group tyaughton methow basin southwest british columbia a major middle jurassic to early cretaceous terrane overlap assemblage the upper middle jurassic to lower cretaceous relay mountain group is the lower part of the northern tyaughton methow basin southwestern british columbia the relay mountain group consists of 2700 3400 m of clastic rocks that we subdivide into three formal formations the callovian and lower oxfordian tyoax pass formation is marine shale and sandstone turbidites the teepee mountain formation consists of upper oxfordian to valanginian shallow marine clastic rocks with common buchia and fluvial and marginal marine facies in the upper part of the unit in the northwest these rocks overlie the lower formation across an abrupt conformable to disconformable contact the hauterivian and barremian potato range formation consists of clastic rocks that are marine in the southeast mainly nonmarine to the northwest and derived from the west this unit displays an abrupt conformable to disconformable contact with the middle formation and locally rests above the lower formation across an angular unconformity t

kinematics and tectonic significance of transpressive structures within the coast plutonic complex british columbia abstract structural data from the coast plutonic complex near prince rupert british columbia are consistent with a deformational history dominated by dextral transpression from campanian to paleocene time penetrative east side up southwest directed ductile shearing produced moderately northeast plunging overturned kilometer scale isoclinal folds these folds are dextrally sheared and refolded into kilometer scale upright northwest plunging folds and steeply dipping transposed foliations with moderate to shallow northwest plunging lineations along their western side an east side up component to the transcurrent shearing is kinematically compatible with east side up shearing found within the great tonalite sill kinematic and geometric gradients and the spatial distribution of the finite stretching direction are interpreted to result from partitioning of transpression the location of these structures and overprinting relationships suggest the great tonalite sill intruded late kinematically into a crustal scale dextral transpressive shear zone these results indicate this shear zone could form part of the baja b c fault system that would have accommodated large northward displacements of the terranes making up western british columbia and southeast alaska this conclusion is based on 1 it is favorably located to accommodate the proposed displacements 2 deformation occurred during the time period of proposed large displacement 83 59 ma 3 the 15 km thickness of the shear zone indicates it records large displacements

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

sandstone detrital modes central utah foreland region stratigraphic record of cretaceous paleogene tectonic evolution abstract within a sedimentary basin the analysis of sandstone petrofacies defined by detrital modes of framework grains is a powerful means to detect areal or temporal changes in provenance related to evolving paleotectonics and paleogeography in the central utah foreland the regional tectonic transition from thin skinned sevier thrusting during the late cretaceous to deep seated laramide deformation during the paleogene is recorded by four contrasting petrofacies in uppermost cretaceous and paleogene sandstones of fluvial and deltaic facies coeval subaqueous environments were marine during the cretaceous and lacustrine during the paleogene the cretaceous quartzose petrofacies qm93 f1 lt6 of mainly campanian age was derived from sedime tary sources in the active sevier thrust belt and transported into a broad adjacent foreland basin by transverse paleocurrents the heterogeneous cretaceous quartzolithic petrofacies qm40 70 f5 20 lt25 40 of uppermost campanian age was derived from the sevier orogenic belt during the waning phases of sevier tectonism and was distributed by longitudinal paleocurrents within a foreland basin whose floor had begun to be deformed by incipient laramide tectonism the paleogene feldspathic petrofacies qm50 f35 lt15 in paleocene and eocene strata is composed of arkosic detritus that was derived principally from basement rocks then exposed in the extensive san luis uplift of laramide age in south central colorado the feldspathic sand was transported to the laramide uinta basin and vicinity in utah by a trunk river which flowed generally northwestward between monoclinal laramide uplifts of the colorado plateau the paleogene quartzolithic petrofacies qm75 f2 lt23 of dominantly eocene age was derived mainly from sedimentary sources in the laramide uinta uplift to the north but also in part from similar sources in the dormant sevier thrust belt to the west in the rocky mountain and intermountain regions more widespread and systematic use of petrofacies analysis in combination with standard paleocurrent and lithofacies analyses could lead to better definition of the timing of laramide uplift and improved understandi g of the evolution of complex laramide paleogeography

late palaeozoic to early mesozoic geodynamic evolution of the circum pacific orogenic belt in south korea and southwest japan abstract a review of the overall features of the late palaeozoic early mesozoic orogen of southwest japan and its korean hinterland allows a new geodynamic model for the building of the east asian margin to be proposed during middle carboniferous to early permian times an oceanic basin formed in a passive margin environment at a moderate spreading rate as the honshu continental block drifted away from the sino korean continent during that period paralic platform conditions and extensional synsedimentary tectonics prevailed in korea in middle permian times the closure of the oceanic area was responsible for yakuno ophiolite obduction and high pressure metamorphism while highly subsiding coal basins developed in the emerged korean hinterland thereafter in late permian times when the honshu block collided with the asian margin akiyoshi orogeny locally derived terrestrial clastic sedimentation in korea has succeeded coal measure deposition with local unconformity in early triassic times the collision was completed and regional uplift of the thickened crust resulted in the deposition of thick distal siliciclastic rocks in rapidly subsiding hinterland troughs korea and flyschoid deposition in the tamba foreland basin outer zone of southwest japan middle to late triassic medium to low pressure metamorphism large scale transcurrent tectonics and associated calc alkaline synkinematic plutonism in the hida and ogcheon belts represent a post collisional feature of the akiyoshi orogenic event post tectonic intrusives and terrestrial deposits post date intracratonic tectonics at ca 200 ma thus the akiyoshi orogeny of southwest japan is a result of continental drift and ensuing collisional rewelding of a fragment of sino korea the honshu microcontinent

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

coast plutonic complex a mid cretaceous contractional orogen early late cretaceous east vergent thrusts deform much of the eastern margin of the coast plutonic complex in western british columbia similarities in timing and style suggest that the faults represent a system of backthrusts to a west vergent thrust belt on the west side of the complex this geometry and the rarity of mid cretaceous strike slip faults indicate that the coast plutonic complex was a strongly contractional orogen in mid cretaceous time

tectonometamorphic evolution of the permo triassic songrim indosinian orogeny evidence from the late paleozoic pyeongan supergroup in the northeastern taebaeksan basin south korea the deformed and metamorphosed middle pennsylvanian to early triassic rocks of the pyeongan supergroup occurring in northeastern flank of the paleozoic taebaeksan basin east central south korea record the impact of the late permian triassic songrim indosinian collisional orogeny in the eastern eurasia margin analysis of meso and microstructures and their relationship with porphyroblast growth has revealed that these metasedimentary rocks were affected by four deformation events d1 d4 during the polyphase deformations successive foliations with alternately steep s1 and s3 and flat lying s2 and s4 orientations were produced with growth of chloritoid andalusite and kyanite porphyroblasts during d1 and d2 and growth of garnet staurolite and andalusite porphyroblasts during d3 and d4 shrimp u pb detrital zircon ages 330 310 ma from metapelites in the oldest unit of the pyeongan supergroup in the study area combined with the previous data on sandstone compositions indicate magmatic activity that was contemporaneous with the initial deposition of the pyeongan supergroup this also suggests that the pyeongan supergroup was deposited in an arc related foreland basin at an active continental margin during the late carboniferous and permian time two contractional deformation events d1 and d3 and two events related to gravitational flattening d2 and d4 along with barrovian type medium pressure regional metamorphism may have resulted from the late permian triassic songrim orogeny related to collision between the north and south china blocks and or collision between the eastern eurasia margin and the proto japan terrane

sandstone composition of the upper jurassic emuerhe formation from the mohe basin china the sandstone composition analysis carried out on the samples from three different sections western section middle section and eastern section of the upper jurassic emuerhe formation in the mohe basin northeastern china reveals that the okhotsk orogenic belt and the ergun massif basement are the source areas for the emuerhe formation the source area of the western section and the a segment of the middle section is the okhotsk orogenic belt the tectonic attributes of the okhotsk orogenic belt are those of a dissected arc the transportation distance of clastic rocks from these sections gradually lengthened and the uplift rate of the okhotsk orogenic belt gradually increased the source area of the eastern section and the b segment of the middle section is the ergun massif basement compared with the okhotsk orogenic belt the tectonic attributes and uplift rate of the ergun massif basement are different from the former the attributes of the ergun massif basement are those of basement uplift the transportation distance of clastic rocks from the eastern section and the b segment of the middle section gradually shortened and the uplift rate of the ergun massif basement gradually decreased these conclusions are consistent with the characteristics of a foreland basin thus we can draw the conclusion that the mohe basin belongs to the foreland basin

is the southeast coast plutonic complex the consequence of accretion of the insular superterrane evidence from u pb zircon geochronometry in the northern washington cascades zircon u pb geochronometry of orthogneisses and plutons in the southwestern crystalline core of the north cascades coupled with fabric and textural studies of the orthogneisses plutons and their metamorphic host rocks indicates extensive synmetamorphic plutonism at 89 96 ma metamorphic mineral assemblages define a culmination composed of an axial kyanite sillimanite zone rimmed by lower grade zones high grade index minerals are typically syntectonic to posttectonic metamorphic fabrics are characterized by an orogen parallel northwest striking steep foliation that contains a subhorizontal stretching and mineral lineation interpreted to be the product of ductile strike slip deformation this fabric is crosscut by 96 92 ma plutons yet is imprinted on 92 89 ma orthogneisses suggesting spatially diachronous fabric development during orogeny documentation of the spatial and temporal coincidence of magmatism with the peak of orogeny together with the kinematic significance of the metamorphic fabric precludes generation of the metamorphic fabric and plutons in response to thrust loading the authors suggest that this part of the coast plutonic complex evolved as a transpressional magmatic arc

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

provenance evolution and unroofing history of a modern arc continent collision evidence from petrography of plio pleistocene sandstones eastern taiwan abstract plio pleistocene sandstones from the coastal range of eastern taiwan provide a record of shifting source areas and unroofing events in adjacent arc and accretionary wedge terranes during the early stages of are continent collision in latest miocene and early pliocene time arc derived sediments were deposited in a precollisional forearc basin between the luzon volcanic arc and the manila trench sandstones of this age are rich in zoned plagioclase volcanic lithic fragments and pelagic foraminifera and contain only minor quartz and sedimentary metasedimentary lithic fragments in contrast lower pliocene to lower pleistocene sandstones are poor in feldspar and volcanic fragments and contain abundant sedimentary and metasedimentary lithic fragments this reflects a provenance shift f om the volcanic arc to the uplifted meta sedimentary accretionary wedge of proto taiwan which resulted from the early pliocene onset of arc continent collision a refined classification of sedimentary and metasedimentary lithic fragments is introduced here and used to interpret the early evolution of the collisional orogen lithic fragments are rich in pelitic minerals and are divided into 1 sedimentary ls mudstone shale siltstone chert and argillite 2 low grade metamorphic lm1 slate slatey siltstone and quartzite and 3 medium grade metamorphic lm2 phyllite schist phyllitic quartzite and quartz mica albite aggregate a good correlation is observed between these lithic fragment types and bedrock lithologies exposed in the present day central range of taiwan based on this correlation the change in relative abundance of sedimentary and metasedimentary lithic fragments through time has been used to interpret an unroofing sequence for the collisional fold and thrust belt lower pliocene taiwan derived sandstones are rich in sedimentary lithic fragments ls which were shed from the accretionary wedge during the earliest stages of arc continent collision from early pliocene to early pleistocene time sandstones became progressively depleted in ls lithic fragments and enriched first in lm1 and later in lm2 fragments as deeper levels in the metamorphic complex were uplifted and exposed to erosion regional metamorphism of biotite grade rocks lm2 occurred at about 4 5 ma at depths of 12 15 km ernst 1983 and were uplifted to the surface by about 1 4 ma this study these ages give an uplift rate of 4 to 5 km m y which is in good agreement with independent estimates based on fission track studies raised coral reefs quaternary elevation changes and present day denudation rates thus it appears that sandstone detrital modes of clastic orogenic sequences can be used to interpret specific aspects of unroofing and tectonic evolution in nearby active mountain belts

driving mechanisms for 40 km of exhumation during contraction and extension in a continental arc cascades core washington 1 in the nw north american cordillera the cascades core region of the coast plutonic complex underwent late cretaceous 96 ma to locally 73 ma sw ne contraction and crustal thickening followed by dextral transpression 73 to 55 ma then transtension 3 mm yr by local thrusting in regions undergoing crustal thickening in the central part of the core chelan block 40 km of exhumation occurred between 91 and 45 ma about half of which occurred during early contraction driven by thrusting and half during top to north arc oblique shear during reactivation of a midcrustal cretaceous thrust the dinkelman decollement the footwall of this thrust consists of the swakane biotite gneiss a cretaceous metaclastic assemblage with recorded pressures of 10 12 kbar no arc related magmatism and structures dominated by pervasive top to north shearing the hanging wall consists of the napeequa complex an oceanic assemblage with recorded pressures of 6 12 kbar voluminous arc related magmatism and complex structures indicating early top to wsw shearing younger top to north shearing and widespread folding in the napeequa top to north shearing started by 73 ma during melt present conditions at pressures 6 kbar top to north shearing in both hanging wall and footwall continued during exhumation 1 6 mm yr and cooling to greenschist facies conditions during which slip became increasingly localized eventually resulting in formation of pseudotachylite on discrete slip surfaces we suggest that arc oblique extension was driven by along arc heterogeneity in displacements erosion initially during transpression and underplating of continental sediments and later during transtension

formation of new continental crust in western british columbia during transpression and transtension crustal growth in the coast mountains along the leading edge of the canadian cordillera was the result of processes associated with horizontal flow of material during transpression and subsequent transtension and the vertical accretion of mantle derived melts from 85 to 58 ma as exotic terranes were translated northward during transpression the crust was thickened to about 55 km and melt that originated from a mix of mantle derived basalt with partial melt of the thickened crust intruded into crustal scale transpressive shear zones when the orogen extended between 58 and 50 ma there was large scale decompression melting in the mantle and dehydration melting in the lower crust voluminous emplacement of sub horizontal sills facilitated by ductile flow of the gneissic country rocks partially filled space created as the crust was pulled apart and as 15 to 20 km of tectonic exhumation occurred across low angle normal ductile shear zones by 50 ma the final crustal thickness of the new continental crust was about 34 km comparison of seismic data with other crustal sections suggests that the crust forming processes identified in western british columbia have general applicability to models for the formation of continental crust

strain partitioning in an obliquely convergent orogen plutonism and synorogenic collapse coast mountains batholith british columbia canada 1 we describe the crustal structure of the coast mountains batholith between 54 and 55 n within the canadian cordillera with emphasis on emplacement of the 7 km thick kasiks sill complex ksc kinematic patterns that developed during emplacement of the ksc are the result of interactions between magma transport magma accumulation and regional deformation the sills were emplaced during nw directed normal shearing and flattening of country rocks that host the ksc a 2 km thick shallowly ne dipping mylonite zone cuts the eastern side of the ksc kinematic indicators within the mylonite zone record top to the east normal displacements structural analysis shows that mylonite formation occurred during subvertical shortening and east northeast subhorizontal extension u pb zircon age dates show that ene directed normal shearing along the eastern side of the ksc and wnw directed normal shearing within the ksc occurred contemporaneously between 54 and 51 ma indicating strong strain partitioning between the mylonite and the ksc this pattern of strain partitioning is interpreted to have been driven by return flow of melt laden crust in response to tectonic denudation of the upper crust seismic profiling shows that many of these structures extend to mid and lower crustal depths comparison of our results with other regions within the canadian cordillera indicates that orogen scale right lateral strike slip faults deformed synchronously with wide spread magmatism and formation of extensional gneiss domes thus the crustal structure of the coast mountains batholith was the result of early tertiary batholith construction during dextral oblique convergence and synorogenic collapse

petrology of late paleozoic early mesozoic pyeongan group sandstones gohan area south korea and its provenance and tectonic implications abstract carboniferous to triassic strata of the pyeongan group crop out in the gohan area northeastern south korea these strata consist in ascending order of the hongjeom sadong gobangsan and nogam formations sandstones in these formations comprise three distinct framework mineral suites suite 1 sandstones hongjeom formation through the middle member of gobangsan formation are quartz and quartzose arenites wackes that contain abundant quartz little or no feldspar and few acid volcanic clasts heavy minerals are mainly tourmaline rutile and zircon suite 2 sandstones upper member of gobangsan formation are lithic arenites wackes characterized by moderate quartz content low amounts of feldspar and moderate to abundant volcanic clasts sphene is the predominant heavy mineral suite 3 sandstones nogam formation are feldspathic arenites wackes distinguished by low quartz content moderate to abundant feldspar and low amounts of acid volcanic clasts the heavy mineral assemblage of the nogam formation is characterized particularly by epidote and sphene feldspar poor suite 1 sandstones were derived from a source terrain rich in quartzite and quartzose sandstone abundant quartz and stable heavy minerals were supplied initially during late carboniferous time to a shallow marine shelf which changed gradually near the end of carboniferous time to a nonmarine paralic platform setting electron probe microanalysis shows that suite 1 tourmaline was derived originally from li poor granitoids pegmatites and ca poor aplite and metapsammite petrographic evidence demonstrates that the scarcity of feldspars in suite 1 sandstones is not the result of diagenetic intrastratal solution major changes in mineralogy from suite 1 into suite 2 and suite 3 sandstone indicate changes in provenance suite 2 sandstones were derived from diorite granodiorite acid volcanic rocks and possibly some metamorphic rocks which furnished feldspars and sphene the appearance of feldspars and volcanic rock fragments in these sandstones reflects orogenic changes and uplift resulting from incipient collision of the asian mainland and the honshu block of southwest japan compositionally immature suite 3 sandstones were derived mainly from granite granodiorite and granitic gneiss indicating continuing uplift these source rocks provided quartz k feldspar plagioclase epidote and sphene acid volcanic rocks supplied minor amounts of rock fragments

the tectonic setting of the eastern margin of the sino korean block inferred from detrital zircon u pb age and nd isotope composition of the pyeongan supergroup upper palaeozoic lower triassic korea the upper palaeozoic succession pyeongan supergroup in central eastern korea is well correlated with the equivalent successions distributed in north china suggestive of the korean upper palaeozoic being part of the sino korean block detrital zircon u pb ages and sm nd isotope compositions of the pyeongan supergroup in the samcheok coalfield of the taebaeksan basin were analysed a single predominant zircon age peak at c 1 9 ga 70 is marked in all sedimentary units followed by varying amounts of minor late palaeozoic grains up to 30 the rarity of meso to neoproterozoic and silurian aged zircons confirms that sediment influx from the south china and qinling blocks was insignificant the 2 0 1 8 ga dominated zircon age pattern and the nd isotope composition average end 0 15 5 4 0 of the pyeongan supergroup most closely reflect the signature of the yeongnam massif basements which supports a previous hypothesis that the pyeongan supergroup was mostly derived from a palaeo orogen located to the east southeast relatively higher end 0 values 10 1 in the lowermost and the upper parts of the succession are closely matched by the increased occurrence of syn depositional aged zircons which indicates considerable mixing of juvenile materials at c 320 ma and 260 ma both arc related magmatic events are interpreted to have been related to oceanic subduction suggesting that the eastern margin of the sino korean block was an active continental margin during late palaeozoic times

lithostratigraphy and depositional environments of the pyeongan supergroup carboniferous permian in the taebaek area mid east korea abstract the pyeongan supergroup carboniferous permian consists of a thick siliciclastic sequence 1700 m thick recent sedimentological work in the taebaek area has refined the lithostratigraphic units manhang geumcheon jangseong hambaeksan dosagok gohan and donggo formations in ascending order the entire sequence is represented by thirteen sedimentary facies which can be organized into seven facies associations fa the lower part of the manhang formation fa 1 moscovian consists of crudely cross stratified conglomerate massive sandstone and gray homogeneous siltstone formed in shoreface off river mouth whereas purple siltstone and grainstone of the upper part fa 2 probably formed in a coastal plain environment the geumcheon jangseong formation moscovian artinskian consists of dark gray sandstone dark gray shale coal and bioturbated wackestone fa 3 formed in a lagoonal environment the hambaeksan formation kungurian comprises milky white crudely stratified conglomerate gray coarse sandstone and partly laminated black shale fa 4 representing a shoreface progradation the dosagok formation late permian is characterized by an alternation of purple fine sandstone and conglomerate fa 5 formed in a bedload dominated fluvial system the gohan formation late permian is mostly composed of upward fining units massive sandstone to dark gray siltstone fa 6 suggesting a restricted inter distributary bay environment the donggo formation late permian consists of cross stratified coarse sandstone and purple sandstone fa 7 interpreted as deposits of perennial sandy braided river system

is the ogcheon metamorphic belt of korea the eastward continuation of the nanhua basin of china abstract the ogcheon metamorphic belt in central korea has been interpreted to be the eastward extension of the nanhua basin aulacogen of southeast china in this paper comparisons are made between the two regions based on stratigraphic thermal tectonic and other considerations from this comparison correlation of geological events between the nanhua basin and ogcheon metamorphic belt are at best equivocal the closest similarity is the presence in both regions of two major diamictite units of glacial origin and neoproterozoic age 750 690 ma range in china but of controversial origin and uncertain age in korea volcanic rocks in both regions appear to have similar petrological and geochemical traits and are interpreted to be rift related however their ages are different mostly 795 780 ma in the nanhua basin and c 750 ma in central korea so correlation remains uncertain more isotopic data from both regions may shed light on this comparison correlation between other pre carboniferous stratigraphic units in the two regions is hampered by the uncertainty about the stratigraphic age and succession in the ogcheon metamorphic belt stemming mainly from the absence of fossils and the strong tectonic metamorphic overprint both regions appear to have undergone deformation and metamorphism during the middle triassic indosinian songrim in some uncertain way related to the collision between the north and south china plates in the ogcheon metamorphic belt there has been no confirmation of a mid palaeozoic event but in the nanhua basin that event is recorded by stratigraphic and palaeogeographic evidence in the nanhua basin there is no evidence for an early permian metamorphic event that appears on isotopic grounds to have affected the ogcheon metamorphic belt this apparent difference has been interpreted as a result of diachronous deformation during late palaeozoic early mesozoic plate collisions that took place earlier in the east in korea than in the west in china

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

the pyeongan supergroup upper paleozoic lower triassic in the okcheon belt korea a review of stratigraphy and detrital zircon provenance and its implications for the tectonic setting of the eastern sino korean block abstract the tectonic setting of the okcheon belt in the korean peninsula has long been regarded as one of the important topics in discussing east asian tectonics the controversial tectonic setting of the okcheon belt before the triassic collision between north and south china limits proper understanding of the late paleozoic tectonics of east asia focusing on the upper paleozoic to lower triassic pyeongan supergroup coeval sedimentary records in different parts of the okcheon belt are reviewed this study has a clear advantage over previous assessments that build upon comparison between meta sedimentary units of unknown age in the region the pyeongan supergroup sediments show high similarity in both stratigraphy and detrital zircon u pb ages throughout the okcheon belt they are distinct from their age equivalents in south china while sharing characteristics with those in north korea and north china critical criteria include marine influence and enrichment of organic materials at each time period and relative proportion of mesoproterozoic silurian components in detrital zircon age population the combined results agree with the view that the entire okcheon belt was a single tectonic unit at least by the late carboniferous the results of this study favor the idea of the sino korean block encompassing the whole korean peninsula and cast doubts on the tectonic models that attribute the southern part of the korean peninsula to the south china block a retroarc foreland basin setting of the okcheon belt with detritus mainly provided from a subduction related orogen in the continent sided japan is inferred from the provenance characteristics of the detrital zircons

exceptions to the relationship between plate tectonics and sandstone composition abstract routine use of qfl qplsmlvm and lmlslv plate tectonic provenance diagrams has led to the recognition of error populations for these sandstones the interpretation of tectonic setting based on data exclusive of petrography does not coincide with the interpretation of tectonic setting based on their location on compositional diagrams the anomalous sandstones can be separated into at least four categories i sandstones deposited during the transition between tectonic regimes may be derived in part from relict source rocks ii the relative enrichment of sandstones in detrital quartz by weathering and or depositional reworking may lead to an inaccurate interpretation of tectonic setting from compositional data iii sandstones deposited in tectonic settings as yet unrepresented on he provenance diagrams may plot between the provenance fields or overlap existing fields iv the role of detrital carbonate rock fragments directly affects the location of data points on provenance diagrams and is an unresolved problem the first two categories represent permanent problems in the use of sandstone composition as an indicator of plate tectonic setting whereas the last two may only be temporary problems that can be solved by more data and a consensus on determining detrital modes recognition of anomalous sandstones in the rock record will reduce the probability of erroneous interpretations of tectonic setting and enhance the use of sandstone petrology as an indicator of plate tectonic setting

quartz grain types in holocene deposits from the spanish central system some problems in provenance analysis holocene sands of the spanish central system were exclusively derived from plutonic middle upper grade and low grade metamorphic rocks modal composition of studied sands is mostly controlled by grain size and source area lithology thus sands derived from slates and schists plot near the qr edge on the qfr diagram for ali grain size fractions sands derived from granitic or gneissic rocks have a wide dispersion on the qfr diagram from the r pole to the qf edge depending on sand grain size percentages of quartz types in granitic derived sands are qnu42 qu40 qp2 314 and qp 34 sands of gneissic origin have qnu 51 qu 1 5 qp2 323 and qp 311 sands derived from slates and schists have qnu 20 qu 1 2 qp2 35 and qp 363 quartz types easily discrimina te sands of low grade origin but distinction of sands derived from plutonic rocks from those derived from middle upper grade metamorphic rocks is difficult because of the highly variable qu content of plutonic rocks related to strain history and crystallization conditions thus quartz types mus be used with caution in source discrimination if plutonic rocks are present in the source area

petrology of holocene sand peninsular ranges california and baja norte mexico implications for provenance discrimination models abstract the peninsular ranges of southern california and baja california norte mexico represent an uplifted and variably dissected mesozoic magmatic arc they are composed mostly of cretaceous plutonic rocks and mesozoic greenschist to amphibolite facies metasedimentary and metavolcanic rocks in order to evaluate the reliability of the diamond shaped qnuquqp provenance discrimination diagram developed by basu et al 1975 and the qfl provenance discrimination diagram developed by dickinson et al 1983 we collected 62 samples of holocene sand from four drainage basins along the west side of the peninsular ranges the qfl composition of each specimen was determined by the gazzi dickinson point counting method the relative percentages of med um grained fragments of qnu qu and qp were determined by counting 100 grains in each specimen the results of our study indicate that holocene sands derived from the peninsular ranges have the following average petrological characteristics 1 sands derived mostly or exclusively from plutonic rocks are composed of 16 46 percent q 54 83 percent f and 0 2 0 5 percent l the medium grained quartz population produced by erosion of mostly or exclusively plutonic rocks consists of 61 77 percent qnu 4 17 percent qu and 13 27 percent qp 2 sands originating from the erosion of metasedimentary rocks are composed of 63 percent q 13 percent f and 24 percent l the medium grained quartz population derived from a metasedimentary source is made up of 25 percent qnu 9 percent qu and 66 percent qp 3 sands produced by the erosion of mostly or exclusively metavolcanic rocks are composed of 19 percent q 39 44 percent f and 38 43 percent l the medium grained quartz population originating from a mostly or exclusively metavolcanic source consists of 48 74 percent qnu 6 percent qu and 20 46 percent qp petrological data obtained during this study indicate that the qfl provenance discrimination model generally yields a correct interpretation of tectonic setting when applied to holocene sand from the peninsular ranges data however also show that local source areas produce sands that when interpreted on the basis of their position on the qfl provenance discrimination diagram yield an erroneous interpretation of tectonic setting data obtained from counting varieties of medium grained quartz show that detrital quartz populations produced by plutonic rocks are discriminated from those derived from metasedimentary rocks by the qnuquqp provenance discrimination diagram in contrast quartz populations originating from a mostly or exclusively metavolcanic source are difficult to interpret on the qnuquqp diagram therefore we recommend that the qfl provenance discrimination model be used with caution when sand or sandstone samples are from a limited geographic area and that the qnuquqp provenance discrimination diagram be used with prudence when metavolcanics are suspected in the provenance

two stage exhumation of midcrustal arc rocks coast mountains british columbia 1 new geologic data from the central gneiss complex along douglas channel help delineate the burial and exhumation of the late cretaceous to eocene coast mountains magmatic arc arc plutonism was on going between 90 and 60 ma replaced by formation of dikes to 52 ma supracrustal rocks were buried to midcrustal levels by 90 ma and garnet and kyanite grew from 90 through 70 ma subsequent exhumation was nearly isothermal and took place in two stages the first occurred from 70 to 59 ma as the arc contracted obliquely and sillimanite replaced kyanite exhumation was slow 0 5 mm yr probably accomplished by erosion aided by coaxial crustal thinning exhumation rates about doubled in the second stage of exhumation after 59 ma and before 52 ma penetrative deformation ended prior to intrusion of the quottoon pluton at 59 ma and 6 5 kbar production of cordierite rims on garnet at 4 5 kbar and 700 c signaled the end of near isothermal decompression prior to 52 ma rapid cooling 100 c 106 years of the central gneiss complex followed cordierite growth temperatures dropped to 250 by 48 ma the increase in exhumation rate and the subsequent rapid cooling are attributed to excision of 6 km of crust on a detachment system on the northeastern side of the central gneiss complex comparison to other parts of the coast mountains arc the sierra nevada and fiordland new zealand shows that the amount and tempo of exhumation vary greatly within and between arcs suggesting that the processes accommodating exhumation vary significantly

calcium and calcium isotope changes during carbon cycle perturbations at the end permian negative carbon and calcium isotope excursions as well as climate shifts took place during the most severe mass extinction event in earth s history the end permian 252 ma investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events such as the end permian may help resolve the intricacies between the coupled calcium carbon cycles as well as provide a tool for constraining the causes of mass extinction here we identify the deficiencies of a simplified calcium model employed in several previous studies and we demonstrate the importance of a fully coupled carbon cycle model when investigating the dynamics of carbon and calcium cycling simulations with a modified version of the long term ocean atmosphere sediment carbon cycle reservoir model which includes a fully coupled carbon calcium cycle indicate that increased weathering rates and ocean acidification potentially caused by siberian trap volcanism are not capable of producing trends observed in the record as previously claimed our model results suggest that combined effects of carbon input via siberian trap volcanism 12 000 pg c the cessation of biological carbon export and variable calcium isotope fractionation due to a change in the seawater carbonate ion concentration represents a more plausible scenario this scenario successfully reconciles 13c and 44ca trends observed in the sediment record as well as the proposed warming of 6 c

provenance of the qingshuijian formation late carboniferous ne china implications for tectonic processes in the northern margin of the north china block the upper carboniferous qingshuijian formation in the western hill ne china was deposited disconformably on a lower paleozoic platformal carbonate sequence the provenance and the tectonic setting of the source area of the qingshuijian formation were studied using sandstone petrography and mudstone geochemistry sandstones consist mainly of quartz and meta sedimentary lithic fragments and are classified as litharenite feldspar is lacking in sandstones and negative eu anomalies similar to those displayed by post archean australian shale paas along with depleted ca na cs and rb and low k2o al2o3 ratios in mudstones all suggest that feldspar was scarce in the source terrane abundant sedimentary lithic fragments in sandstones low values of the index of compositional variability 1 values of chemical index of alteration higher than paas depleted transition metals higher total ree abundances and more fractionated ree patterns than paas all indicate that the source area was dominated by sedimentary rocks geochemical and sandstone tectonic discrimination diagrams suggest that the provenance of the qingshuijian formation was a recycled orogen composed of quartzose to lithic sedimentary rocks that were deposited originally in a passive margin setting the yinshan uplift located in the northern margin of the north china block that formed as a result of the collision between the north china block and the mongolian continent is interpreted to be the provenance for the qingshuijian formation during collision the intervening sea floor was subducted northward and an accretionary prism was elevated forming a barrier to arc derived sediments

petrography and major element geochemistry of the permo triassic sandstones central india implications for provenance in an intracratonic pull apart basin abstract detrital mode composition of feldspars and heavy minerals and major element chemistry of sandstones from the permo triassic succession in the intracratonic satpura gondwana basin central india have been used to investigate provenance the talchir formation the lowermost unit of the succession comprises glacio marine and glacio fluvial deposits the rest of the succession base to top comprising the barakar motur bijori pachmarhi and denwa formations largely represent variety of fluvial depositional systems with minor fluvio deltaic and fluvio lacustrine sedimentation under a variety of climatic conditions including cold warm arid sub humid and semi arid qfl compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault bounded basement uplift tectonic setting compositional maturity of sandstones gradually increases upwards from the early permian talchir to the middle triassic denwa but is punctuated by a sharp peak of increased maturity in the barakar sandstones this temporal change in maturity was primarily controlled by temporal variation in fault induced basement uplift in the craton and was also influenced by climatic factors plots of different quartz types suggest plutonic source rocks for the talchir sandstones and medium to high rank metamorphic plus plutonic source rocks for the younger sandstones composition of alkali feldspars in the permo triassic sandstones and in different precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks compositions of plagioclase in the talchir and bijori sandstones are comparable with those of granite acid volcanic and metasedimentary rocks of the precambrian basement suggesting the latter as possible source rare presence of high k plagioclase in the talchir sandstones however indicates minor contribution from volcanic source rock exclusively plagioclase bearing metasedimentary rock tonalite gneiss and mafic rocks are the probable sources of plagioclase in the upper denwa sandstones quartz rich nature of the sandstones predominance of k feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic pull apart basin like the satpura gondwana basin composition of garnet and its comparison with that from the precambrian basement rocks suggests mica schist and amphibolite as possible sources predominance of dravite variety of tourmaline in the permian sandstones suggests sediment supply from metasedimentary rocks presence of both dravite and schorl variety of tourmaline in subequal amount in the triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks however schorl bearing rocks are absent in the basement complex of the study area a cn k plot suggests granites acid volcanic rock and meta sediments of the basement as possible sources of the talchir sandstones and metasedimentary rocks for the barakar to pachmarhi sandstones the denwa sandstones were possibly derived from k feldspar free plagioclase bearing metasediments mafic rocks and tonalite gneiss chemical index of alteration cia values suggest low intensity source rock weathering for the talchir sandstones and higher intensity source rock weathering for the others various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

the scotia quaal metamorphic belt a distinct assemblage with pre early late cretaceous deformational and metamorphic history coast plutonic complex british columbia the scotia quaal metamorphic belt extends from hawkesbury island to work channel between the early late cretaceous ecstall and the paleogene quottoon plutons the belt consists of a proterozoic paleozoic metasedimentary and metavolcanic sequence the middle devonian big falls orthogneiss early jurassic orthogneiss and jurassic or cretaceous mafic and ultramafic intrusive rocks the assemblage may be correlative with nisling terrane lithologies and may have shared a common history at least from early jurassic time on with rocks of stikine terrane strong planar and linear fabrics abundant folds and scarcity of kinematic indicators characterize the belt s deformational style development of a strong foliation followed by three episodes of folding occurred between emplacement of the middle devonian big falls orthogneiss and early late cretaceous ecstall intrusion paleogene fabrics occur in the quottoon pluton and in the easternmost 1 5 km of the scotia quaal belt if a major paleogene shear zone is po

batholith emplacement at mid crustal levels and its exhumation within an obliquely convergent margin abstract emplacement of the central part of the coast mountains batholith of northern coastal british columbia occurred within a regime characterized by oblique convergence between the farallon kula and north american plates we use new structural kinematic and u pb isotopic data to show that the locations geometry and mechanisms of pluton emplacement within this batholith were controlled by displacements within a network of normal faults and transtensional shear zones these data also show that the most active period of pluton emplacement from 67 to 51 ma coincided with a change in style of deformation within the batholith prior to 67 ma plutons were emplaced within an arc dominated by regional scale contractional shear zones in contrast emplacement of 67 51 ma plutons occurred in an arc increasingly dominated by normal faults with arc parallel to oblique displacement and by sinistral transtensional shear zones we have identified and mapped the structure of three plutonic complexes composed of 67 to 51 ma plutons the khyex sill complex arden lake plutonic complex and quottoon plutonic complex shear zone controlled emplacement of plutons within the batholith accounts for the widely different orientations and structural features that characterize plutons within these three complexes during and after this latest cretaceous paleogene period of intense plutonic activity and accompanying deformation the deep roots of the batholith were rapidly unroofed by ductile normal faulting prior to 50 ma

detrital modes of the pyeongan supergroup late carboniferous early triassic sandstones in the samcheog coalfield korea implications for provenance and tectonic setting abstract medium to coarse sandstones of the carboniferous to early triassic pyeongan supergroup in the samcheog coalfield korea were studied to infer the provenance and tectonic settings of the source areas sandstone detrital modes change upwards stratigraphically sandstone types from the manhang to dosagog formations low to middle in the sequence are quartzarenite and sublitharenite to litharenite whereas sandstones of the gohan and donggo formations high in the sequence are feldspathic litharenite and arkose respectively using various ternary diagrams the provenance of the manhang to gohan formations is suggested to be a recycled orogen setting some gohan formation sandstones plot within the arc related setting field and the donggo formation sandstones plot within both continental block and recycled orogen fields results of quartz grain petrography are consistent with those of detrital modes quartz in sandstones of all units except the donggo formation indicates derivation from low rank metamorphic sources quartz in donggo sandstones was derived from medium to high rank metamorphic and plutonic source rocks considering the sandstone composition and palaeocurrent data the pyeongan supergroup probably was deposited in a molasse foreland basin and was derived from a synbasinal orogenic belt probably the akiyoshi orogen located in southwest japan

geology of the fuding inlier in southeastern china implication for late paleozoic cathaysian paleogeography abstract the age and composition of the basement rocks underlying the mesozoic volcanic rocks in southeastern china have been long debated new field investigation stratigraphical and sedimentological studies of the fuding inlier in eastern cathaysian block have identified the presence of three stratigraphic units the upper carboniferous carbonate unit composed of silicified limestone deposited on carbonate platform in a continental shelf environment the lower permian siliciclastic unit consisting of slate and phyllite with minor arenites deposited on shallow semi restricted shelf the third unit is a suite of jurassic conglomerates and sandstones deposited in alluvial fan environment provenance data indicate that the fuding inlier was part of the wuyishan terrane in the eastern cathaysian block the u pb age and hf isotope of detrital zircons indicate that extensive magmatic activity happened during 280 360 ma in the source area the e hf values of detrital zircons point to magmatic mixing of juvenile material and precambrian crust the similarities in rock compositions and detrital zircon ages among the yeongnam massif in the korean peninsula the tananao complex in taiwan and the fuding inlier have led to the conclusion that these three regions most likely belonged to the wuyishan terrane eastern cathaysia during the late paleozoic

sandstone petrofacies expressions of multiphase basinal tectonics and arc magmatism permian triassic north bowen basin australia abstract modal analyses of 209 sandstone samples from the permian triassic succession of the northern bowen basin eastern australia identify two stratigraphically and compositionally distinct petrofacies the lower to mid upper permian back creek group is characterised by petrofacies a which is quartz rich q82f8l10 it was sourced primarily from cratonic basement terranes to the west where relief was subdued and the quartz content of the sandstones may also reflect some reworking in the marine realm with a consequent loss of labile grains petrofacies b is volcanolithic and characterises alluvial sediments of the upper permian blackwater and lower triassic rewan groups it was sourced from an undissected to transitional magmatic arc provenance located in the contemporary new england orogen to the east which supplied abundant pyroclastic debris to the depositional complex petrofacies b of the northern bowen basin was derived primarily from felsic volcanics compared to an intermediate association recorded for the southern basinal sector indicating significant along arc variation in volcanic style as a consequence its framework grain population is enriched in quartz and is not readily accommodated in the schemes of provenance interpretation currently in use the consistency of framework detrital modes for sandstones distributed throughout the blackwater group q24f10l66 allows the recognition of subpetrofacies b1 and shows that the volcanism associated with the magmatic arc system was remarkably uniform in character and activity during deposition of the entire group the magmatic arc delivered almost identical sedimentary debris over a period of some 9 my in the late permian relative enrichment of quartz within the early triassic rewan group q49f6l45 relative to the blackwater group discriminates subpetrofacies b2 and is attributed to a climatic change and shift in palaeotemperature at the permian triassic boundary the contact between the marine back creek group petrofacies a and the coal bearing blackwater group petrofacies b represents an abrupt switch in provenance with little or no evidence of source mixing the boundary marks the onset of volcanism and associated tectonic uplift in the northern part of the new england orogen to the east sediment from the new source prograded rapidly westwards across the basin coincident with regression direct evidence of contemporaneous volcanism is widespread in the blackwater group as shown by tuffs and tonsteins which are distributed throughout the entire late permian succession