cretaceous stress field evolution and origin of the jiaolai basin eastern north china abstract the jiaolai basin to the east of the tan lu fault zone tlfz is a cretaceous ne trending basin in eastern north china and has a multi episodic evolution different from other contemporary nw trending en echelon graben systems west to the tlfz the origin of the jiaolai basin three episodes k1l 135 120 ma k2q 120 105 ma k2w 88 65 ma cannot be simply explained by the sinistral displacement of the tlfz at the beginning of the early cretaceous around ca 135 ma the purpose of this paper is to investigate the critical factors e g bounding faults tectonic setting stress field driving the development of the jiaolai basin and constraint its evolution three episodes of two dimensional finite element models were generated in order to determine the roles of the boundary conditions and to reveal the tectonic development of the basin when compared to the calculated maximum horizontal compressive stress hmax trajectories and the observed data along with a comparison between the von mises stress u von and the depocenters of the basin the calculated results can be well proved by the geological evidence both in stress field evolution and in the basin patterns our analysis show that the three episodes of the maximum principle stress trajectories changed from ne sw earlier early cretaceous k1l nne ssw later early cretaceous k1q then e w late cretaceous k2w moreover the results show a good consistency between the u von and the depocenters in the basin through geological cross sections via models we suggest that the origin and evolution of the jiaolai basin were controlled by three episodes of tectonic events i the reactivated bounding faults and the post orogenic extension of the sulu orogen during the earlier early cretaceous ii the lithospheric delamination of the thickened lithosphere during the later early cretaceous and iii the likely far field effects produced by the collision between the kohistan drags arc complex and asia during the late cretaceous the jiaolai basin evolved from extension to pull apart experiencing volcanic activity during the three episodes of the cretaceous

thermal gradient and geochronology of a paleozoic high grade terrane in the northeastern cathaysia block south china abstract the chencai terrane in the northeastern cathaysia block forms part of the northeast extension of the paleozoic orogeny in south china recent field investigations have revealed the occurrence of high grade rocks in this terrane including granulite facies metapelites khondalites and orthopyroxene bearing granulites however the thermal gradients and metamorphic history of this region have not been well constrained thus impeding a better understanding of the geodynamic history of the paleozoic orogeny in south china here we report results from a systematic study on the metamorphic pt conditions and geochronology of the orthopyroxene granulites and metasedimentary rocks metapelites from the chencai area the orthopyroxene granulites preserve granulite facies peak assemblage of opx grt pl kfs qtz and a retrograde p t trajectory peak pt conditions are 845 860 c and 0 83 0 86 gpa corresponding to a thermal gradient of 30 c km which is much hotter than the normal thermal gradient of continental crust mineral compositions of the metasedimentary rocks re equilibrated during retrograde metamorphism so that the peak pt conditions recorded by these rocks are much lower than those obtained from the orthopyroxene granulite peak pt conditions are 710 720 c 0 57 0 58 gpa for garnet biotite gneiss and 760 780 c 0 60 0 62 gpa for biotite garnetite zircon u pb dating shows that this episode of granulite facies metamorphism occurred at 430 450 ma and the detrital population shows minor or no contribution from the basement rocks of the cathaysia block the neoproterozoic rocks occurring along the jiangnan belt are considered to have provided the sedimentary source as indicated by the two main age peaks of 0 79 ga and 0 83 ga from the detrital zircon cores lu hf isotope data on the zircons indicates extensive alteration and little new zircon growth during the paleozoic metamorphism the ehf t values and model ages tdm1 of zircons suggest that the source rocks involved juvenile crustal components with hf model ages of 1 1 1 5 ga sedimentation of such a continental shelf sequence as well as the high thermal gradient of 30 c km confirm the previously proposed continental arc formation and maturation model in the chencai region

the xiaoqinling metamorphic core complex a record of early cretaceous backarc extension along the southern part of the north china craton

shear sense a new approach that resolves conflicts between criteria in metamorphic rocks investigation of microstructural relationships in major movement zones in metamorphic rocks where the sense of displacement is known from regional geological relationships indicates numerous problems with current concepts of shear sense criteria and their application the direction of apparent shearing commonly conflicts from one criterion to another e g from the symmetry of quartz c axis orientation diagrams to the asymmetry of extensional crenulation cleavages this implies that interpretations of shear sense along foliations from some mesoscale and microscale criteria have been erroneous a new approach to interpreting shear sense involving the use of strain fields resolves conflicts in mesoscopic and microscopic criteria and provides a method for determining coherent shear sense histories extending back before the last shearing event for any foliated metamorphic rock it also provides a powerful tool for determining the structural metamorphic path that a rock has followed within an orogen for determination of the shear sense on the last foliation developed in a rock this approach uses geometries developed around competent heterogeneities such as quartz pebbles pegmatite pods veins porphyroclasts porphyroblasts and breccia clasts a shear sense history is derived by applying this approach to earlier foliations preserved within the heterogeneities and their strain shadows

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

the reliability of asymmetric c axis fabrics of quartz to determine sense of vorticity abstract asymmetric c axis fabrics of quartz are commonly used to determine sense of vorticity in ductile shear zones this method seems to work if the fabric pattern resembles a model fabric proposed by lister and hobbs 1980 usually however c axis fabrics are rather vague the reliability of such vague fabrics was tested in a major shear zone with known sense of vorticity only 62 of the c axis fabrics predict the correct sense great care should therefore be taken in applying this method to determine sense of vorticity

petrogenesis and tectonic implications of early cretaceous s and a type granites in the northwest of the gan hang rift se china the gan hang rift trending at least 450 km in a ne sw direction is a part of a mesozoic basin and range province in southeastern china detailed shrimp zircon u pb chronology major and trace element and sr nd hf isotope data of three granitic plutons and a diabasic dike in the northwest of the gan hang rift are used to explore the origin of these granites and their relationship to the evolution of the gan hang rift shrimp zircon u pb dating shows that the granitic plutons and diabasic dike were emplaced in the early cretaceous 122 129 ma the tongshan and damaoshan plutons close to the gan hang rift consist mainly of weakly peraluminous granitic rocks which show a2 subtype affinity these granites have initial 87sr 86sr ratios of 0 7080 0 7103 end t values of 1 4 to 5 6 and ehf t in situ zircon values of 3 8 to 1 2 detailed elemental and isotopic data suggest that they were formed by partial melting of granulitized mesoproterozoic metamorphic basement including metasedimentary and metaigneous rocks in the shallow 30 km crust at a high temperature 823 c these pure crustal melts underwent crystal fractionation of biotite plagioclase and k feldspar forming the more felsic end member of granitic rocks the ehu pluton more distant from the gan hang rift is composed of two mica granites which are strongly peraluminous and are s type granites these granites have higher initial 87sr 86sr ratios 0 7162 0 7191 and lower end t 7 1 to 7 4 and ehf t 6 8 in situ zircon values than the tongshan and damaoshan granites detailed elemental and isotopic data suggest that the ehu granites were formed by partial melting of paleoproterozoic metasedimentary basement in the deep 40 50 km crust at a relatively low temperature 757 c with no fractional crystallization and mantle derived magma mixing in their evolution the coeval diabasic dike is calc alkaline and has initial 87sr 86sr ratio of 0 7085 end t value of 0 9 and ehf t in situ zircon value of 7 1 suggesting that it was derived from the asthenospheric mantle wedge that had been metasomatised via addition of subducted sediment derived melt with monazite in the residual phase the association of early cretaceous 122 129 ma s and a type granites in the northwest of the gan hang rift marks the onset of back arc extension or intra arc rift with ongoing extension the crust and lithospheric mantle became progressively thinned the upwelling of asthenosphere triggered partial melting of both metasedimentary and metaigneous rocks in the more thinned crust close to the gan hang rift forming the a type granitic magmas such as tongshan and damaoshan whereas partial melting of metasedimentary rocks in the less thinned crust farther from the gan hang rift formed the s type granitic magmas such as ehu the red sediments with the total thickness more than 10 000 m have been successively deposited in the gan hang rift valley since the late early cretaceous 105 ma suggesting that this region experienced the most back arc extension

liquefaction resistance of soils from shear wave velocity a simplified procedure using shear wave velocity measurements for evaluating the liquefaction resistance of soils is presented the procedure was developed in cooperation with industry researchers and practitioners and evolved from workshops in 1996 and 1998 it follows the general format of the seed idriss simplified procedure based on standard penetration test blow count and was developed using case history data from 26 earthquakes and 70 measurement sites in soils ranging from fine sand to sandy gravel with cobbles to profiles including silty clay layers liquefaction resistance curves were established by applying a modified relationship between the shear wave velocity and cyclic stress ratio for the constant average cyclic shear strain suggested by r dobry these curves correctly predicted moderate to high liquefaction potential for 95 of the liquefaction case histories and are shown to be consistent with the standard penetration test based curves in sandy soils a case study is provided to illustrate application of the procedure additional data are needed particularly from denser soil deposits shaken by stronger ground motions to further validate the simplified procedure

gold mineralization of the chencai suichang uplift and tectonic evolution of zhejiang province southeast china abstract a metallogenic model is proposed in which gold and base metal mineralization in se china is related to plate interactions along the pacific margin with southeast asia from about 900 to 70 ma all depositional orogenic and metallogenic processes can be explained by subduction events along northeast trending zones with progressive accretion and cratonization along the continental margin these subduction zones moved southeast for a distance of less than 150 km as a result the area is one of crustal reworking in which the rocks and mineral deposits of earlier events have been repeatedly modified the chencai suichang uplift is an uplifted crustal block in central zhejiang province of mainland china in which the proterozoic basement is exposed as tectonic windows in overlying mesozoic volcanics several gold and base metal deposits are located in these proterozoic windows as well as in the younger volcanics most economic deposits were formed during the last major tectono magmatic event affecting the area the yanshanian 160 170 ma event although there is evidence for earlier mineralization that has been remobilized during the yanshanian it is suggested that crustal reworking was particularly important in remobilising and upgrading gold mineralization the model presented is supported not only by local geology and isotopic data but also by the regional distribution of gold deposits which are arranged in a 50 km wide belt parallel to the yanshanian subduction zone three major episodes of mineralization occurred during 1 a subduction related period of metamorphism partial melting and mesothermal fluid generation and mineralization in the lower crust during the caledonian 2 subduction related volcano plutonic activity with epithermal mineralization during the early yanshanian and 3 hydrothermal mineralization during late yanshanian tectono magmatic event in the third two main categories of metallogenic control are recognized namely 1 hydrothermal fluid generation in the lower crust and 2 upper crust structural and lithological controls on mineralization

liquefaction potential of recent fills versus natural sands located in high seismicity regions using shear wave velocity abstractthe liquefaction potential of clean and silty sands is examined on the basis of the field measurement of the shear wave velocity vs the starting point is the database of 225 case histories supporting the andrus stokoe vs based liquefaction chart for sands silts and gravels only clean and silty sands with nonplastic fines are considered resulting in a reduced database of 110 case histories which are plotted separately by type of deposit a line of constant cyclic shear strain cl 0 03 is recommended for liquefaction evaluation of recent uncompacted clean and silty sand fills and earthquake magnitude mw 7 5 the geologically recent natural silty sand sites in the imperial valley of southern california have significantly higher liquefaction resistance as a result of preshaking caused by the high seismic activity in the valley a line of constant cyclic shear strain cl 0 1 0 2 is recommended for practical use in the imperial valley additional research including revisiting available vs

eastward tectonic migration and transition of the jurassic cretaceous andean type continental margin along southeast china abstract a mesozoic andean type active continental margin is believed to have developed along the southeast china continental margin which has been investigated in detail however the architecture and evolution of its retroarc arc forearc system which is important for us to understand the interaction or connection between continental and oceanic lithospheres are ambiguous using multiple disciplinary data comprising seismic profiles field observations and numerical paleo topographies this study synthetically focused on the jurassic cretaceous evolution and geodynamics of the andean type southeast china continental margin subduction of the paleo pacific plate was initiated during the early jurassic 200 ma generating a nne striking jurassic magmatic arc along the east china sea bounded by imbricate thrust faults on both sides and coinciding with a paleo topographic coastal mountain range while the jurassic arc erupted along an ene striking triassic suture zone in the northern south china sea dominated by the tethyan tectonic domain and overprinted by the pacific tectonic domain the jurassic coastal mountain range began to collapse and transited into a rift basin at 135 ma and then the andean type continental margin gradually switched to the western pacific type during the late cretaceous 100 72 ma accompanied by jurassic thrust faults inverting into cretaceous detachment faults and magmatic arc migrated eastward to the taiwan rukyu areas such eastward tectonic migration and transition is associated with the eastward retreat of the subducted paleo pacific slab then a regional latest cretaceous 72 66 ma compression prevailed southeast china probably related to ridge subduction when the pacific plate replaced the paleo pacific plate to subduct beneath east asia

a type granite belts of two chemical subgroups in central eastern china indication of ridge subduction abstract early cretaceous a type granites in the lower yangtze river belt central eastern china with both a 1 and a 2 chemical subgroups formed at 125 2 ma after a cretaceous ridge subduction remarkably a 1 and a 2 group granites are distributed in three zones roughly parallel to each other and to a slightly older adakite belt in general a 1 granites form in intraplate settings whereas a 2 granites near paleo convergent margins the alternate distribution of these two subgroup a type granites is compatible with a proposed cretaceous ridge subduction in the region the subduction of a dry and hot spreading ridge may have only released small amount of fluids so that metasomatism on the overriding lithosphere was undetectable correspondingly resulted in a 1 granites later on in contrast wetter and colder oceanic crust away from the spreading ridge was responsible for mantle metasomatism and consequently the formation of a 2 granites further away from the ridge the subduction angle was much steeper and dehydration of the slab had occurred earlier during the subduction and thus dramatically reduced mantle metasomatism corresponding to a 1 granites again both a 1 and a 2 granites formed within a short period of time due to slab window rollback after the ridge subduction the distribution of the a 1 and a 2 granites together with the adakite belt may be taken as discrimination indice for ancient ridge subduction

zircon u pb geochronology and geochemistry of two episodes of granitoids from the northwestern zhejiang province se china implication for magmatic evolution and tectonic transition abstract granitoids 175 80 ma representing a prominent yanshanian jurassic to cretaceous magmatic event in south china widely intrude the precambrian crystalline basement and paleozoic strata here we report zircon u pb age data geochemical characteristics and sr nd isotopes of the late jurassic and early cretaceous granitoids from the northwestern zhejiang province zxb of southeastern china our results reveal two distinct episodes for the yanshanian magmatism the jiemeng and datongkeng granodiorites formed at 148 6 1 1 ma whereas the huangshitan jiuligang and ruhong aluminous a type granites were generated between 129 0 0 6 ma and 126 1 1 1 ma the two magmatic phases represent a tectonic transition from an active continental margin to post orogenic setting during the late jurassic ca 150 ma to early cretaceous ca 128 ma geochemically these intrusions are granodioritic to granitic in composition and show an affinity of s type and a type granitoids respectively the s type granodiorites of jiemeng and datongkeng are characterized by moderate sio 2 65 0 69 6 wt high k 2 o na 2 o 5 0 7 6 wt k 2 o na 2 o 1 2 1 5 zr 31 109 ppm sr 71 190 ppm and high field strength elements low to intermediate mg and moderate nb depletion the a type granites of huangshitan jiuligang and ruhong are characterized by high sio 2 72 7 77 2 wt k 2 o na 2 o 6 9 8 8 wt k 2 o na 2 o 1 3 2 1 fe t fe t mg ga 17 29 ppm 20 ppm commonly zr 96 197 ppm and sr 8 45 ppm with slight nb depletion the s type granodiorites have higher mg a nk sr sr ba sr y la yb n and lree hree and lower sio 2 k 2 o na 2 o ga and zr with weak negative eu anomalies compared to those of the a type granites with negative eu anomalies all these rocks show y nb ratios 1 2 high initial 87 sr 86 sr i sr ratios and low e nd t and are depleted in nb ti and sr indicating crustal origin with subduction zone signatures we suggested that the zxb s type granitic bodies might have been derived from the mesoproterozoic metamorphic basement rocks through partial melting induced by mantle derived magma followed by limited fractional crystallization the zxb aluminous a type granites were also derived from a similar magma source but underwent fractional crystallization at higher crustal levels the a type granites in the zxb correlate with a post orogenic tectonic setting a geological comparison between zxb and adjacent areas indicates that the geochemical features of the zxb a type granites are comparable with the baijuhuajian a type granites and also the adjacent areas a type granites but are distinct from the late cretaceous a type granites 105 90 ma distributed along the southeastern coastal area of south china we correlate the formation of the zxb s type granodiorites to inland compression associated with the subduction and collision of the paleo pacific plate in the late jurassic 170 145 ma in contrast the a type granites formed under a post orogenic setting during the early cretaceous period 145 120 ma resulting from lithospheric thinning and continent extension accompanied by slab roll back of the paleo pacific plate following the subduction collision event

liquefaction potential map of charleston south carolina based on the 1886 earthquake a liquefaction potential map of the peninsula of charleston s c is presented in this paper liquefaction potential is expressed in terms of the liquefaction potential index developed by iwasaki et al and calculated using 44 cone penetration test profiles the cone profiles are supplemented with information from the 1 24 000 scale geologic map by weems and lemon several first hand accounts of liquefaction and ground deformation that occurred during the 1886 charleston earthquake and liquefaction probabilities determined by elton and hadj hamou based on standard penetration tests nearly all of the cases of liquefaction and ground deformation occurred in the holocene to late pleistocene beach deposits that flank the higher ground sediments of the wando formation to match the observed field behavior a deposit resistance correction factor of 1 8 is applied to cyclic resistance ratios calculated for the 100 000 year old wando formation no corrections are needed for the younger deposits in additional to 1886 field behavior the deposit resistance corrections are supported by ratios of measured to predicted shear wave velocity

magmatism along the southeast margin of the yangtze block precambrian collision of the yangtze and cathysia blocks of china the time and the environment of formation of igneous rocks along the southern margin of the yangtze continental block in southern anhui province and northeastern jiangxi province china are discussed sm nd dating for samples from two ophiolite suites give ages of about 1 ga late proterozoic granodiorites in the study area have ages of about 0 9 ga and have normal intrusive relations against banxi group metamorphic country rocks trace element abundances and initial nd isotope ratios for ophiolite and proterozoic granodiorites are consistent with formation in an island arc environment in contrast sr and nd isotopes for mesozoic granitoids of the region suggest that they are products of remelting of crustal sources similar to the basement of the yangtze block these relations do not support a recently proposed mesozoic overthrust tectonic model for southeast china but rather favor a late precambrian collision history for the yangtze and cathysia blocks

jurassic intraplate magmatism in southern hunan eastern guangxi 40ar 39ar dating geochemistry sr nd isotopes and implications for the tectonic evolution of se china the mesozoic geology of se china is characterized by intensive and widespread magmatism however the tectonic regime that accounted for the mesozoic magmatism has been an issue with little consensus a comprehensive study of ar 40 ar 39 dating geochemistry and sr nd isotopes has been conducted on basalts from southern hunan and syenite intrusions from eastern guangxi three episodes of jurassic magmatism i e alkaline basalts of c 175 ma in age syenitic intrusions of c 160 ma and high mg basalts of c 150 ma are identified the older c 175 ma alkaline basalts are characterized by low sr i sr 0 7035 0 7040 and high nd epsilon nd t 5 to 6 isotopic compositions and oib like trace element patterns e g nb la 1 in contrast the younger c 150 ma high mg basalts have high sr i sr c 0 7054 and low nd epsilon nd t c 2 isotopic compositions and incompatible trace element patterns of arc affinity the c 160 ma syenitic intrusions display a relatively large range of sr and nd isotopic compositions i sr 0 7032 0 7082 epsilon nd t 5 5 to 4 1 with the qinghu syenites having the lowest i sr highest epsilon nd t and oib type incompatible trace element patterns analogous to the c 175 ma alkaline basalts such a secular variation in rock types and geochemical and isotopic characteristics reveals changes in melt segregation depth and mantle sources which are inferred to have resulted from the post indosinian orogenic lithosphere extension and thinning the c 175 ma alkaline basalts are suggested to have formed by small degrees of decompression melting of the astheno sphere or an enriched lithospheric mantle source accreted by asthenosphere derived melts during the initial extension the c 160 ma syenitic and c 150 ma high mg basaltic rocks mainly originated from the enriched lithospheric mantle that melted owing to a raised geotherm caused by lithosphere thinning this interpretation is at odds with the active continental margin related to the subduction of palaeo pacific plate but consistent with continental rifting and extension for the mesozoic of se china

mesozoic extensional structures of the fangshan tectonic dome and their subsequent reworking during collisional accretion of the north china block the fangshan area sw of beijing lies at the junction of the nne trending taihang mountain range and the southeastern portion of the yanshan intraplate orogenic belt and has undergone at least five stages of deformation mid to late triassic extensional deformation d 1 is represented by the formation of the fangshan tectonic dome during se directed extensional tectonics this deformation was later modified by nnw directed thrusting in the late triassic d 2 and wnw directed thrusting in the late jurassic d 3 these d 1 d 3 structures were deformed by the arcuate beiling syncline d 4 which formed during the intrusion of the 133 128 ma fangshan pluton d 5 deformation is represented by cretaceous to quaternary nne striking high angle normal faults the ages of these events demonstrate that the principal ene trending tectonic framework of the yanshan intraplate orogenic belt was established mainly in the mid to late triassic the indosinian event the jurassic to cretaceous yanshanian deformation with thick skinned thrusting was associated with intrusion of numerous plutons and strongly modified the older structures the tectonic evolution of the fangshan tectonic dome was linked genetically with the collision of the north china block and the siberian craton and the later collision of the north and south china blocks

characteristics and dynamic origin of the large scale jiaoluotage ductile compressional zone in the eastern tianshan mountains china abstract the jiaoluotage ductile compressional zone jdcz in the eastern tianshan mountains china developed in volcanic and sedimentary rocks that were deposited in a carboniferous back arc basin situated between the jungar plate and middle tianshan terrane the ductile compressional zone 500 km long and 20 50 km wide consists of a number of east trending vertical foliation zones that display an augen geometry in plan view and a fan like geometry in transverse profiles ductile compressional deformation has produced pervasive foliation radial stretching lineations contemporaneous folds and various macroscopic to microscopic symmetric structures within the jdcz rotations of most clasts and porphyroclasts are bidirectional the preferred orientation patterns of the optical axes of calcite and quartz display axial or orthorhombic symmetry three kinds of strain patterns have been determined in the jdcz apparent flattening plane strain and apparent constriction the overall strain character of the jdcz is cream cake style the volcanic and sedimentary rocks within the jdcz were metamorphosed into greenschist facies with temperature of 400 600 c and pressure of 300 400 mpa development of the jdcz is interpreted as due to n s coaxial compression caused by the collision between the tarim plate and the middle tianshan arc jiaoluotage basin jungar plate system during the permian between 270 and 290 ma

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

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

sliding thrusting tectonics caused by thermal uplift in the yunmeng mountains beijing china abstract a ductile shear zone analogous to a normal fault with a low dip angle occurs on the southeastern flank of the yunmeng anticlinorium north of beijing in huairou county the southeast dipping shuiyu ductile shear zone is composed of mylonitic granitic gneiss and has an average width of about 1 km the structures in the area show a symmetrical pattern this pattern may be generated by a process of sliding and thrusting caused by thermal uplift an alternative possible model for the area is that for the north american cordilleran regions

vergence an evaluation abstract fold asymmetry is an independent concept distinct from facing fold vergence is a direction relating to the sense of asymmetry of folds the complementary concept of cleavage vergence is defined allowing asymmetry to be used to locate major fold traces where no minor folds exist cleavage vergence is a valuable tool in complex structural terrains both concepts can be used singly or in combination to identify refolding vergence can define structural way up where sedimentological or stratigraphic way up cannot be recognised

the liaonan wanfu metamorphic core complexes in the liaodong peninsula two stages of exhumation and constraints on the destruction of the north china craton 1 the liaodong peninsula early cretaceous extension province lep located in the eastern part of the north china craton ncc was highly extended in early cretaceous the liaonan and the wanfu metamorphic core complexes mccs are two most important elements in the province both are typical cordilleran type core complexes that are composed of a general three layered structure but show various differences shearing along the jinzhou detachment fault zone in the liaonan mcc generated ductile to brittle tectonites various deformation microstructures and several types of quartz c axis fabrics implying that the mcc has a complicated progressive exhumation history however medium temperature microstructures and fabrics are superimposed by low temperature features along the wanfu detachment fault zone suggesting a relatively short and simple exhumation history of the wanfu mcc magmatic zircon u pb geochronological dating reveals that the early cretaceous extension of the lep began with the initiation of shearing along the jinzhou detachment fault zone and exhumation of the liaonan mcc before ca 134 ma subsequently relatively slow cooling and exhumation of the lower plate accompanied a giant magmatic event from 130 ma to 120 ma exhumation of a new mcc i e the wanfu mcc was triggered by progressive extension after ca 120 ma rapid cooling and exhumation of the metamorphic lower plate of the two mccs are attributed to coeval detachment faulting along both the jinzhou and wanfu faults from 120 ma to 113 ma the extension ended at ca 107 ma these data provide reliable evidence that the two mccs were exhumed progressively and sequentially during two stages of crustal extension of the lep our results indicates that heterogeneous lithosphere extension and upper middle crust upper mantle detachment possibly due to the interaction between the paleo pacific and eurasian plates are among the most important processes during the early cretaceous thinning of the lithosphere tectonic extension may have led to the detachment in east asia which contributed to the thinning of the lithosphere and the destruction of the ncc a phase of uniform and consistent wnw ese extension was responsible for the generation of the extensional structures in the eastern asia continent and the destruction of the ncc

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

mesozoic felsic arc magmatism and continental olivine tholeiites in zhejiang province and their relationship with the tectonic activity in southeastern china abstract the mesozoic geology of zhejiang province in southeastern china is characterized by two distinct geodynamic settings separated by a major tectonic event during the late jurassic early cretaceous a continental magmatic arc developed with a westward subduction of the kula or izanagi plate under the south china block during the development of this magmatic arc microsyenite porphyries and quartz bearing porphyries were emplaced in western zhejiang about 124 ma ago these porphyritic rocks intruded felsic tuffs that rest unconformably on carboniferous and permian folded strata geochemically they are enriched in lil and light rare earth elements lree which are features of acid shoshonitic suites isotopically they are characterized by negative nd t 124 5 3 to 4 7 values and high initial 87 sr 86 sr ratios 0 7079 0 7084 later in eastern zhejiang quartz phyric ignimbrites and subordinate acid andesites were emplaced and intruded by nearly contemporaneous microsyenitic and rhyolitic domes during the cretaceous about 97 ma ago all these rocks belong to the high k calc alkaline suites they show geochemical features of volcanic arc granites emplaced in an active continental margin and are characterized by negative nd t 97 8 8 to 7 1 and high initial sr isotopic ratios 0 7081 0 7089 the negative nd t 97 values of all the cretaceous calc alkaline and shoshonitic rocks of intermediate to acid composition suggest that these rocks were probably derived from a mantle wedge source contaminated by variable amounts of old crustal components likely represented by the proterozoic basement rocks of the south china block the contemporaneous igneous rocks in vietnam as well as in the fujian and guangdong provinces china represent the lateral counterparts of the zhejiang calc alkaline plutonic and volcanic rocks in the late early cretaceous an important tectonic event occurred which provoked the ending of the inagazi or kula plate subduction and affected the continental magmatic arc this tectonic event is likely related to the collision of the china indochina margin with the west philippine block after this tectonic event in the beginning of the late cretaceous continental stretching and crustal attenuation affected the south china block leading to the development of ne sw faulted basins in which continental olivine tholeiites and minor alkaline rhyolites were erupted both characterized by low nd t 97 ratios ca 4 meanwhile continental conglomerates and sandstones were also deposited this rifting process began likely before the india asia indentation and lasted at least until the late tertiary

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

liquefaction potential assessment of pleistocene beach sands near charleston south carolina abstract liquefaction potential of four pleistocene beach sand deposits in the greater charleston area south carolina is assessed the assessment is based on a review of 51 sites of conspicuous craterlets and horizontal ground displacement that occurred in beach sand deposits during the 1886 charleston earthquake and an analysis of 82 seismic cone penetration tests with pore pressure measurements of the 51 ground failure sites 23 are associated with the ten mile hill beds 13 with the wando formation 13 with the silver bluff terrace and younger deposits that lie adjacent to the harbor rivers and creeks and two with the ladson formation liquefaction potential is analyzed using the seismic cone data with and without correction for age related processes diagenesis and then expressed in terms of the liquefaction potential index lpi probability curves are developed from the lpi calculations for different earthquake ground shaking parameters the probability curves for the wando formation overpred

petrogenesis of the cretaceous granitoids in zhejiang northeast south china block and their implications for episodic retreat and roll back of the paleo pacific plate

influence of nonplastic fines on shear wave velocity based assessment of liquefaction many false positives no liquefaction detected when the normalized shear wave velocity cyclic stress ratio vs1 csr combination indicated that it should have been are observed in the database used in the simplified liquefaction assessment procedure based on shear wave velocity two possible reasons for false positives are the presence of a thick surface layer of nonliquefiable soil and the effects of fines on cyclic shear resistance crr and vs1 about 67 of the false positives that could not have been caused by an overlying thick surface layer are associated with silty sands with less than 35 fines the effects of fines on the liquefaction resistance of silty sands and on the shear wave velocity are analyzed theoretical crrfield versus vs1 curves for silty sands containing 0 to 15 nonplastic fines are established they show that the theoretical crr vs1 correlations for silty sands with 5 to 15 nonplastic fines are all located to the far left of the semi empirical curves that separate liquefac

timing and processes of late mesozoic mid lower crustal extension in continental ne asia and implications for the tectonic setting of the destruction of the north china craton mainly constrained by zircon u pb ages from metamorphic core complexes abstract late mesozoic large scale crustal extension occurred across the northeastern section of continental asia and metamorphic core complexes mccs are the major features in this region this paper presents new zircon u pb and ar ar ages of biotite and hornblende for pre or syn mylonitized and post kinematic unmylonitized intrusions from these mccs and attempts to determine the timing of initiation duration and termination of the mid lower crustal ductile extension by integrating with geochronological data from previous studies these mccs have similar 40 ar 39 ar biotite and hornblende ages 130 to 110 ma mainly from 130 to 120 ma which are interpreted as the cooling ages and represent the timing of the late stage formation of the mccs zircon u pb ages for syn to post kinematic intrusions from some mccs suggest that the mid lower crustal extension probably initiated at ca 150 145 ma with a peak occurring 145 130 ma and continued to 130 120 ma which is older than that suggested by 40 ar 39 ar ages by 10 20 ma the early ductile extension most likely initiated in mongolia and northern china during the late jurassic 150 145 ma at a deeper level then propagated southwards 140 130 ma and finally developed throughout the entire continental ne asia 130 120 ma based on the timing and processes of the extension a geodynamic model and tectonic setting of the destruction of the north china craton ncc are proposed

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

mineral chemistry trace elements and sr nd hf isotope geochemistry and petrogenesis of cailing and furong granites and mafic enclaves from the qitianling batholith in the shi hang zone south china abstract the shi hang zone is an important ne trending mesozoic magmatic belt composed of granites with relative high end t values and young tdm model ages in south china however the petrogenesis and the tectonic environment for the shi hang zone magmatic rocks remain controversial we report here mineral chemistry geochemical and sr nd hf isotopic data for the cailing and furong granites and mafic microgranular enclaves mmes from the qitianling granite batholith in southern hunan province south china the qitianling granite batholith is a multi staged composite pluton with three phases cailing furong and huangtangling according to their ages and petrography the cailing 163 160 ma and furong 157 153 ma phases are mainly composed of porphyritic amphibole biotite monzogranite and they share similar geochemical and isotopic characteristics both of them show similar sio2 contents from 66 50 to 70 28 and metaluminous a cnk values of 0 80 to 0 98 the granites are characterized by high contents of large ion lithosphile elements lile such as rb th u pb high field strength elements hfse such as nb ta zr hf and zr nb ce y contents 350 ppm and high 10 000 ga al ratios 2 6 chondrite normalized ree patterns show relative enrichment of light rare earth elements lrees and significant negative eu anomalies mineralogical and geochemical features suggest that the cailing and furong granites are a type which can be further classified as a2 subtype they have relatively lower 87sr 86sr i ratios 0 7091 0 7132 higher end t values 5 5 to 7 6 and younger nd isotopic model ages 1 48 1 56 ga than those common s type granites in south china zircon ehf t values vary from 8 1 to 3 7 the mmes in the cailing phase show similar trace element and sr nd isotopic characteristics with the host granites but zircons from the mmes show different ehf t values 6 4 2 6 with those from the host granites 8 1 to 3 7 this indicates that the mmes and host granites were crystallized from different sources of magmas providing direct evidence for mafic felsic magma mixing processes the isotope data indicate that the cailing and furong granites from the qitianling batholith were derived from a hybrid magma consisting of about 80 felsic magma derived from old crust and about 20 mantle derived mafic magma the strong magma mixing at about 160 155 ma caused by intra arc rifting or back arc extension related to subduction of the paleo pacific plate is favored to explain the petrogenesis of the cailing and furong granites as well as the shi hang zone

north palawan block philippines its relation to asian mainland and role in evolution of south china sea the island of mindoro the northern part of palawan island and the reed bank area southwestern philippines together constitute a continental fragment the north palawan block lying within an island arc oceanic setting the permian to paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the philippine archipelago these rocks also suggest that the north palawan block once occupied a pre drift position contiguous with the south china mainland four prominent pre neogene regional unconformities are recognized both onshore and offshore the china mainland in taiwan and in the north palawan block the synchrony of these unconformities and the facies relation of the unconformity bounded sedimentary units strongly suggest a common pre neogene history for all these areas by contrast an important regional unconformity occurring at the top of the middle miocene throughout the palawan area is absent from the asian mainland extension in the south china sea basin since the mesozoic which has separated the north palawan block from the asian mainland has been approximately uniform from west to east however there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea floor spreading from the foregoing observations and using the most recent magnetic spreading anomaly data for the south china sea a suite of palinspastic reconstructions has been prepared which shows the evolution of the south china sea area from the late triassic to the pliocene the reconstructions illustrate 1 the convergent continental margin setting of the north palawan block during much of the jurassic and cretaceous 2 the late cretaceous inception of the philippine island arc system 3 the subsequent counter clockwise rotation of the arc system from the late eocene onward 4 the paleocene to middle miocene opening of the south china sea and 5 the early to middle miocene collision between the north palawan block and the palawan subduction system

structural evolution of the whipple and south mountains shear zones southwestern united states the whipple and south mountains of the southwestern united states have undergone a strikingly similar sequence of deformations in both ranges gently dipping mylonitic fabrics have been overprinted by successively more brittle structures associated with a low angle detachment fault kinematic indicators reveal that the mylonitic rocks brittle structures and detachment faults are kinematically coordinated and were all formed by top to the northeast shear the structural evolution of both areas can be explained in terms of major shallow dipping shear zones that accommodated tertiary crustal extension we suggest that detachment faults and associated zones of brecciation cataclasis and seismic slip were originally continuous downdip along the low angle shear zones into mylonitic gneisses formed below or near the ductile brittle transition as the mylonites were drawn out from beneath the brittlely extending upper plate they were progressively uplifted above the ductile brittle transition and were overprinted by successively more brittle structures

revisiting early middle jurassic igneous activity in the nanling mountains south china geochemistry and implications for regional geodynamics abstract early middle jurassic igneous rocks 190 170 ma are distributed in an e w trending band within the nanling tectonic belt and have a wide range of compositions but are only present in limited volumes this scenario contrasts with the uniform but voluminous middle late jurassic igneous rocks 165 150 ma in this area the early middle jurassic rocks include oceanic island basalt oib type alkali basalts tholeiitic basalts and gabbros bimodal volcanic rocks syenites a type granites and high k calc alkaline granodiorites geochemical and isotopic data indicate that alkaline and tholeiitic basalts and syenites were derived from melting of the asthenospheric mantle with asthenosphere derived magmas mixing with variable amounts of magmas derived from melting of metasomatized lithospheric mantle in comparison a type granites in the study area were probably generated by shallow dehydration related melting of hornblende bearing continental crustal rocks that were heated by contemporaneous intrusion of mantle derived basaltic magmas and high k calc alkaline granodiorites resulted from the interaction between melts from upwelling asthenospheric mantle and the lower crust the early middle jurassic magmatic event is spatially variable in terms of lithology geochemistry and isotopic systematics this indicates that the deep mantle sources of the magmas that formed these igneous rocks were significantly heterogeneous and magmatism had a gradual decrease in the involvement of the asthenospheric mantle from west to east these variations in composition and sourcing of magmas in addition to the spatial distribution and the thermal structure of the crust mantle boundary during this magmatic event indicates that these igneous rocks formed during a period of rifting after the indosinian orogeny rather than during subduction of the paleo pacific oceanic crust

geochemical and zircon u pb and hf isotopic study of the baijuhuajian metaluminous a type granite extension at 125 100 ma and its tectonic significance for south china abstract the early cretaceous baijuhuajian pluton is an a type granitic intrusion emplaced along the jiangshan shaoxing jssx fault zone in western zhejiang province se south china it intruded into a late jurassic volcanic basin bounded by proterozoic sandstone and siltstone the granite has a coarse grained porphyritic texture and is composed of alkali feldspar phenocrysts in a matrix of k feldspar quartz plagioclase and biotite the pluton has a clear a type geochemical signature e g it is metaluminous a cnk 1 0 and has high sio2 75 to 78 wt total alkalis na2o k2o 4 8 to 8 5 wt rare earth elements total ree 228 to 438 ppm hfse and fe feot feot mgo 0 87 to 0 97 on the other hand it is characterized by low cao 0 51 to 1 01 wt tio2 0 06 to 0 13 wt p2o5 below detection and sr 7 0 to 9 5 ppm the hypersolvus texture and fine grained groundmass indicate emplacement at a shallow depth shrimp u pb zircon dating yielded a weighted mean 206pb 238u age of 126 3 ma and zircons from this pluton give ehf t values between 0 52 and 4 24 suggesting the importance of juvenile material in the magma source most of the plutonic rocks in southeast china are calc alkaline subduction related intrusions of jurassic and cretaceous age previous studies suggested that the sparse a type granites in south china were emplaced in two episodes 190 155 ma in the inland area and 100 ma along the coastal area in se south china our study of the baijuhuajian granite together with the coeval suzhou a type granite 123 ma in jiangsu province defines an important extensional event between 125 and 100 ma considering the available data for the mesozoic igneous rocks in south china we suggest that subduction of the pacific plate in the mesozoic produced voluminous calc alkaline granitoids and volcanic rocks with a younging trend from west to east the a type granites were generated during periods of local extension at 190 155 ma and 125 100 ma perhaps corresponding to localized rollback of the pacific plate

a geochemical and geochronological study of the early cretaceous extension related honggong ferroan a type granite in southwestern zhejiang province southeast china the honggong pluton is the largest ferroan alkalic a type granite intrusion emplaced along the jiangshan shaoxing fault zone in southwestern zhejiang province and has important implications for understanding the late mesozoic tectonic evolution of se china u pb ages of 138 7 0 8 134 2 1 1 128 5 1 5 and 126 1 0 9 ma were obtained from zircon by laser ablation inductively coupled plasma mass spectrometry indicating that the honggong pluton formed in the early cretaceous the honggong pluton has a clear ferroan alkalic a type granite geochemical signature with for example high total alkali contents and feo t feo t mgo values the sr nd hf isotopic compositions suggest that there was juvenile material in the magma source geochemical evidence indicates that the pluton was derived through extensive fractionation of melts that contained both asthenospheric mantle and mesoproterozoic crustal components these rare granites in southern china were emplaced during five episodes at 235 225 190 165 155 100 90 and 140 120 ma the age of the honggong pluton suggests that localized extension in southwestern zhejiang province began as early as 138 ma and continued to 126 ma this early cretaceous extensional event was triggered by localized rollback of the subducting pacific plate

zircon u pb geochronology and hf isotopic compositions of the mesozoic granites in southern anhui province china abstract mesozoic magmatism is extensively developed in eastern china along the eastern asian continental margin but the geochronological framework is not well understood for each area in this study seventy eight samples were collected from the mesozoic igneous rocks in south anhui province east central china in order to precisely constrain their formation ages and contributions to crustal growth zircon u pb age determination using ion probe and laser ablation techniques indicate that magmatism in the area can be divided into two separate stages at 150 136 and 136 120 ma respectively the first stage of granitic rocks not documented in other areas of eastern china is mostly composed of hornblende bearing i type granodiorite and monzogranite and is considered to be formed by slab tearing during pacific subduction the second stage of magmatism coeval to that in other areas of eastern china is characterized by the occurrence of a type granite and syenite and their volcanic counterparts although i type granitic rocks are also developed locally these rocks are mostly distributed around and within the fault controlled volcanic basins and some are closely related to detachment shearing indicating their formation in an extensional setting zircon hf isotopic analyses indicate that archean material might be present in the area but that the main episode of crustal growth took place during the mesoproterozoic with very little juvenile material in the mesozoic

rapid change from compression to extension in the north china craton during the early cretaceous evidence from the yunmengshan metamorphic core complex abstract the yunmengshan metamorphic core complex ymmcc is situated in the northern part of the eastern north china craton ncc the main structures in the ymmcc area include the arcuate sihetang shear zone shtsz and the ne striking shuiyu shear zone sysz we present structural and geochronological evidence to show that the shtsz was a top to the ssw thrusting zone formed between 140 and 137 ma the sysz is an extensional top to the se shear zone developed between 131 and 114 ma in association with intense magmatism and the development of the huairou rifted basin in the hanging wall ductile shearing on the sysz was followed by isostatic rebound from 114 ma to the end of the early cretaceous and then was replaced by brittle normal faulting the normal displacement on the sysz and subsequent isostatic rebound led to the formation of the ymmcc the mechanism of formation is consistent with a rolling hinge model of detachment faulting and core complex formation the structural evolution of the yunmengshan area in common with the whole eastern ncc thus records a rapid switch from a nne ssw shortening regime to a nw se extension one in the earliest cretaceous the intense nw se extension of the early cretaceous as recorded by the ymmcc was associated with peak lithospheric thinning in the eastern ncc we attribute the shortening to the final closure of the mongol okhotsk ocean between the siberian craton and the north china south mongol block and the extension to the back arc deformation related to the subduction of the izanagi plate in the pacific ocean we suggest that the yunmengshan area illustrates how back arc compression can be driven by the overriding plate motion while connection of the overriding plate to a larger continent favors subduction related back arc extension

is the jurassic yanshanian intraplate tectonics of north china due to westward indentation of the north china block terra nova 24 333 338 2012 abstract the northern mountains of beijing are the type locality of the mesozoic yanshanian orogen our structural study emphasizes the importance of dextral strike slip for the formation of this intracontinental belt the south and north directed thrusts are positive flower structures rooted in strike slip faults this transpressional tectonics developed from late triassic to late jurassic early cretaceous through three deformation phases coeval with syntectonic sedimentation separated by two transtensional episodes coeval with magmatism the late jurassic early cretaceous tectonic event is also recognized in several places of north china strike slip faulting controls the deformation of the northern border of the north china block in the yanshan yinshan belt simultaneously east directed thrusts and folds develop along n s elongated ranges in helanshan shanxi highlands and taihangshan the jurassic tectonics of the north china block is interpreted in a unitary way as the result of the westward underthrusting of the north china block below the alashan block

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

structures kinematic analysis rheological parameters and temperature pressure estimate of the mesozoic xingcheng taili ductile shear zone in the north china craton abstract the ne to ene trending mesozoic xingcheng taili ductile shear zone of the northeastern north china craton was shaped by three phases of deformation deformation phase d 1 is characterized by a steep generally e w striking gneissosity it was then overprinted by deformation phase d 2 with ne sinistral shear with k feldspar porphyroclasts forming a subhorizontal low angle stretching lineation on a steep foliation during deformation phase d 3 lateral motion accommodated by ene sinistral strike slip shear zones dominated associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle to shallow crustal levels in some parts the older structures have been in turn overprinted by late stage sinistral d 3 shearing finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid l s tectonites near plane strain simple shear dominated general shear during d 3 deformation is probably of general significance the quartz c axis textures indicate prism gliding with a dominant rhomb slip and basal slip system formed mainly at low middle temperatures mineral deformation behavior quartz c axis textures quartz grain size and the kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 c dislocation creep is the main deformation mechanism at a shallow crustal level fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self similarities differential stresses deduced from dynamically recrystallized quartz grain size are at around 20 39 mpa and strain rates in the order of 10 12 to 10 14 s 1 this indicates deformation of granitic rocks in the xingcheng taili ductile shear zone at low strain rates which is consistent with most other ductile shear zones hornblende plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca 3 5 kbar and temperatures of 400 500 c within greenschist facies conditions the main d 3 deformation of the ene trending sinistral strike slip ductile shearing is related to the roll back of the subducting pacific plate beneath the north china craton

petrogenesis of late paleozoic diorites and a type granites in the central eastern tianshan nw china response to post collisional extension triggered by slab breakoff abstract geological evolution of the eastern tianshan in the late paleozoic is significant to understanding the multiple accretions and final formation of the southern central asian orogenic belt here we report new whole rock geochemical and sr nd isotopic data and in situ zircon u pb ages for three typical a type granitic intrusions syenogranite k feldspar granite and monzonitic granite and one dioritic pluton in the central eastern tianshan nw china in order to constrain their petrogenesis tectonic setting and geodynamic evolution zircon la icp ms u pb ages indicate that the syenogranites and k feldspar granites were both formed during a short time interval in the early permian 284 286 ma whereas the diorites were crystallized at 293 6 ma the monzonitic granites were generated at 307 3 ma earlier than the other two granitic intrusions the three kinds of granites syenogranite k feldspar granite and monzonitic granite have high hfse hree and y nb ratios 1 68 2 84 and remarkably low sr and ba contents with the absence of aluminium rich minerals and show metaluminous to weakly peraluminous natures indicating geochemical characteristics of aluminous a2 type granites these granites show negative end t 3 32 to 4 40 values and mesoproterozoic two stage nd model ages tdm2 1 36 to 1 43 ga which suggest a relatively old crustal source for these rocks the sr nd isotopic compositions imply that the mesoproterozoic metamorphic basement of the central tianshan block can be considered as a potential magmatic source for these aluminous a2 type granites in addition they have geochemical characteristics similar to the experimental melt that was derived from partial melting of crustal metaigneous rocks at the depth of middle to lower crust levels therefore the granites were most likely produced by partial melting of metaigneous rocks in a post collisional extensional setting the diorites have low sio2 and high mgo with uniform 87sr 86sr i values 0 7055 negative end t values 4 11 to 4 59 and mesoproterozoic two stage nd model ages tdm2 1 41 to 1 45 ga they have higher ti zr 42 8 46 7 and ti y 280 359 ratios than continental crust and show negative nb ta ti anomalies which can be explained by partial melting of a relatively fertile mantle modified by old crustal materials of the central tianshan block the formation of the dioritic pluton was induced by an upwelling asthenosphere in an extensional geodynamic setting based on the zircon saturation temperatures of these a type granites and the distribution of late carboniferous to early permian mantle derived intrusions a slab breakoff model is suggested to interpret the formation of the studied a type granites and diorites we infer that the slab breakoff was initiated in the late carboniferous and ended in the early permian

cretaceous magmatism and mo mineralization in the south china mo province u pb and re os geochronology constraints from the sanzhishu porphyry mo deposit abstract compared with the mesozoic w sn cu au pb zn ag mineralization in the south china mo province scmp detailed studies on mo deposits especially cretaceous mo deposits are rare due to limited exposures the sanzhishu porphyry mo deposit located in the scmp is characterized by disseminated and veinlet type molybdenite quartz veins within monzogranite zircon sims u pb analysis of the monzogranite yields a concordia age of 112 3 ma indicating that the emplacement of the sanzhishu monzogranite was in the early cretaceous six molybdenite samples yield re os ages between 111 and 112 ma with an isochron age of 111 6 4 ma which is consistent with the zircon age of the ore bearing monzogranite a new compilation of reliable re os isotope age data indicate that cretaceous mo mineralization in the scmp occurred during two major episodes at 130 145 ma and 90 120 ma with most deposits forming in the later episode during the cretaceous a back arc extensional setting in se china is evidenced by the occurrence of numerous high f mo deposits widespread a type granites and the development of pull apart basins the increasing trend in re contents of molybdenite from the early mo mineralization period to the late mo mineralization period in the scmp indicates that the area experienced stronger crust mantle interaction in the later mineralization episode based on geological evidence we propose that the early episode of mo mineralization formed in a tectonic setting associated with a metamorphosed subducted slab that experienced an increase in density and an increase in the gravitational pull on the slab itself which induced rollback of the subducting paleo pacific slab the late episode of mo mineralization developed in an extensional tectonic setting caused by the continued rollback and the eventual slab break off

centrifuge and large scale modeling of seismic pore pressures in sands cyclic strain interpretation abstractcentrifuge modeling of pore pressure buildup in a sand deposit as a result of shaking is evaluated by comparison with a large scale experiment in large scale test sg 1 a 5 6 m thick mildly sloping deposit of hydraulic fill clean ottawa sand of dr 40 was subjected to 5 s of low intensity base shaking 0 02g that induced excess pore pressures short of liquefaction three centrifuge experiments using various soil deposits and saturation fluids were conducted and compared with the large scale test one of these centrifuge simulations used the same ottawa sand and dr 40 of the prototype a viscous pore fluid and dry pluviation deposition which created a soil fabric stiffer than the prototype the other two centrifuge simulations used silty sand saturated with water the pore pressure buildup in one of the silty sand tests was in good agreement with the prototype while the other two centrifuge deposits did not develop any excess pore pressure the various responses in the four tests are expla

shear wave velocity based probabilistic and deterministic assessment of seismic soil liquefaction potential abstractshear wave velocity vs offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property this paper presents the results of an 11 year international project to gather new vs site data and develop probabilistic correlations for seismic soil liquefaction occurrence toward that objective shear wave velocity test sites were identified and measurements made for 301 new liquefaction field case histories in china japan taiwan greece and the united states over a decade the majority of these new case histories reoccupy those previously investigated by penetration testing these new data are combined with previously published case histories to build a global catalog of 422 case histories of vs liquefaction performance bayesian regression and structural reliability methods facilitate a probabilistic treatment of the vs catalog for performance based engineering applications where possible uncertainties of the variables comprising both the seismic demand an

geometric and kinematic evolution of basement cored structures intraplate orogenesis within the yanshan orogen northern china abstract detailed surface mapping lithology facies analysis drillcore data and aeromagnetic interpretation reveal the geometries of the basement involved structures of laowopu nantan liudaohe xinglong and malanyu to have been generated by folding and thrusting the resulting basement cored anticlines are asymmetric with a shallowly dipping top and backlimb and a steep to overturned forelimb and or frontal fault linked with a gently dipping synclinal limb both the fold axes and frontal faults trend roughly east west suggesting north south shortening north to northeast trending faults behave as tear lateral or oblique ramp structures and formed coevally with their frontal faults their trends may have been inherited from proterozoic synsedimentary faults and archaean basement ductile shear zones foliations and mafic dikes thin skinned thrusts and their three dimensional geometry are locally controlled by detachment within mechanically incompetent layers four types of interrelationships between the thick and thin skinned structures occur including 1 lateral changes along the length of a fault 2 displacement transfer between thick and thin skinned structures 3 buttressing of thin skinned thrusts against the basement involved structures and 4 generation of an out of the syncline thrust under thick skinned shortening most of the deformation within the study area involved brittle behaviour but ductile shear zones developed where fluid access was possible both the basement involved structures and the thin skinned structures formed in the early mesozoic as constrained by cross cutting relationships isotopic ages of igneous rock and syntectonic basins the model of geometric and kinematic evolution of the basement involved structures and their relationship with the thin skinned structures defined in this paper provides an alternative to the current metamorphic core complex model used for the yanshan intraplate orogen

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

correcting liquefaction resistance of unsaturated soil using wave velocity abstractexplicit empirical relationships for correcting liquefaction resistance of unsaturated soil below the groundwater table using compression wave velocity vp and shear wave velocity vs are derived and evaluated in this paper the relationships are derived using published laboratory test data for four different sands and one silt material the laboratory test data based on vp exhibit less scatter than the test data based on the ratio vp vs for this reason the vp based relationship is recommended for correcting the liquefaction resistance of unsaturated soil the influence of loading cycles and relative density on the recommended relationship is investigated from a review of 40 field case history sites it is found that in the critical layers at 20 of the sites average vp is less than 1 400 m s indicating unsaturated conditions liquefaction resistances computed for eight field case histories with vp 1 200 m s in the critical layers are corrected and plotted on penetration and vs based lique

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

zircon u pb and hf isotopic study of mesozoic felsic rocks from eastern zhejiang south china geochemical contrast between the yangtze and cathaysia blocks abstract the jiangshan shaoxing fault zone jsfz in zhejiang province has been proposed to represent a suture between the yangtze and cathaysia blocks in south china in this study in situ zircon u pb and hf isotopic analysis and whole rock major and trace element measurement of early to middle cretaceous felsic rocks across the fault zone were conducted to constrain the nature of the fault zone twelve cretaceous granitoid bodies were sampled from the nw and se sides of the fault zone respectively with composition ranging from diorite to granite sio2 56 2 76 6 wt these granitoids yielded u pb ages ranging from 135 100 ma with a systematic variation in zircon hf isotopic compositions ehf t 6 9 to 7 0 in the nw side vs 1 9 to 12 9 in the se side the tdm2 values for the granitoids from the nw side are 0 34 to 1 33 ga with two peaks at ca 876 and 1170 ma respectively whereas those from the se side are 0 70 to 1 62 ga with a single peak at ca 1126 ma the hf isotopic disparity for the two sides may indicate a fundamental difference in the lower crustal compositions of the yangtze and cathaysia blocks supporting that the jsfz is possibly a suture zone between the two blocks our results together with the available geological data suggest that the mesoproterozoic materials are important for both the yangtze and cathaysia basement and the neoproterozoic magmatic activities were important in the yangtze block possibly related to the break up of the rodinia supercontinent but less significant in the cathaysia block this may imply that the two blocks have not completely juxtaposed in the neoproterozoic

molybdenite re os dating zircon u pb age and geochemistry of granitoids in the yangchuling porphyry w mo deposit jiangnan tungsten ore belt china implications for petrogenesis mineralization and geodynamic setting abstract the yangchuling w mo deposit located in the jiangnan porphyry skarn jnb tungsten ore belt is the first recognized typical porphyry w mo deposit in china in the 1980 s stockworks and disseminated w mo mineralization occur in the roof pendant of a 0 3 km 2 monzogranitic porphyry stock that intruded into a granodiorite stock hosted by neoproterozoic phyllite and slate la icpms zircon u pb analyses suggest that of the monzogranitic porphyry and granodiorite were formed at 143 8 0 5 ma and 149 8 0 6 ma respectively six molybdenite samples yielded a re os weighted mean age of 146 4 1 0 ma geochemical data show that both granodiorite and monzogranitic porphyry are characterized by enrichment of large ion lithophile elements lile relative to high field strength elements hfse indicating a peraluminous nature a cnk 1 01 1 08 two granitoids are characterized by a negative slope with significant light ree heavy ree fractionation la yb n 8 38 23 20 and negative eu anomalies eu eu 0 69 0 76 the p 2 o 5 contents of the yangchuling granitoids range from 0 12 to 0 17 and exhibit a negative correlation with sio 2 reflecting that they are highly fractionated i type they have high initial 87 sr 86 sr ratios 0 7104 0 7116 low negative e nd t 5 05 to 5 67 and homogeneous e hf t between 1 39 and 2 17 indicating similar sources additionally two stage nd model ages t dm2 of 1 3 1 4 ga and two stage hf model ages t dm2 of 1 2 1 3 ga are consistent indicating that neoproterozoic crustal rocks of the shuangqiaoshan group could have contributed to form the yangchuling magmas considering the two groups of parallel late mesozoic ore belts namely the jiangnan porphyry skarn tungsten belt jnb in the south and the middle lower yangtze river porphyry skarn cu au mo fe ore belt yrb in the north the nanling granite related w sn ore belt nlb in the south the neighboring qin hang porphyry skarn cu mo hydrothermal pb zn ag ore belt qhb in the north as well as the southeastern coast porphyry skarn cu mo au ore belt scb recognized in south china in this paper we propose that the latest jurassic to earliest cretaceous granitoids and associated ores were formed during a tearing of the subducting izanagi slab this tearing of the subduction slab caused the upwelling of asthenosphere and the resulting mantle crust interaction the granitoid related w ore systems in jnb resulted from the remelting of the proterozoic crust the mafic ultramafic volcanic rocks of the shuangqiaoshan group intercalated with phyllite and slate ophiolitic melange and magmatic arc rocks mainly comprising i type granite basalt andesite rhyolite pyroclastics together with subduction related metasomatized lithospheric mantle would have provided additional mantle material in this case the partial melting of rocks of the shuangqiaoshan group can produce s i and transitional type granitoids after strong differentiation it formed tungsten bearing granitoids characterized by enrichment of high alkali silicon and volatile components in the yangchuling mine area the small monzogranitic porphyry stock has stronger fractionation volatile content and ore forming components than the older granodiorite resulting in the development of the porphyry w mo ore system

stacking of disparate volcanic and sedimentary units by thrusting in the archean favourable lake greenstone belt central canada abstract in the favourable lake greenstone belt older volcanic sedimentary units have been stacked concordantly on younger units by three thrust faults units above and below thrusts differ in age and or lithology and unlike many thrust terranes elsewhere there is no stratigraphic repetition the lack of repetition may reflect rapid lateral facies changes the lowest thrust sheet is at least 6 km thick and includes rock units of two distinct ages 2925 ma ultramafic to intermediate flows and intermediate fragmental rocks in the lower part and 2725 ma mafic flows and a conglomerate greywacke fan in the upper part this sheet was thrust northward over a 2734 ma felsic to intermediate stratovolcano at least 4 km thick this implies at least 7 km of vertical movement of the thrust sheet the stratovolcano is the facies equivalent of and probable provenance for the greywacke fan in the upper part of the thrust sheet the two upper thrust sheets are relatively thin and comprise rock units of 2870 2858 ma age rocks of this age were not found in underlying units the thrust faults apparently developed in a relatively undeformed volcanic sedimentary sequence they predated regional isoclinal folding many discordant faults and emplacement of bordering granitoid batholiths the root zone for the thrust sheets is hidden in an area now occupied by granitoid batholiths but thrusts could have been generated by either horizontal compression at colliding plate margins and or gravity sliding triggered by vertical uplift associated with emplacement of granitoid plutons