cenozoic lithospheric evolution of the bohai bay basin eastern north china craton constraint from tectono thermal modeling abstract it is well established that the lithosphere beneath the eastern north china craton ncc had been thinned before the cenozoic a 2d multi phase extension model in which the initial crustal and lithospheric thicknesses are variable is presented to reconstruct the initial thicknesses of the crust and lithosphere in the early cenozoic and to further investigate the lithospheric evolution beneath the eastern ncc through the cenozoic we conduct thermal modeling along three profiles from east to west in the bohai bay basin which is the center of the lithospheric destruction and thinning of the ncc using multiple constraints such as tectonic subsidence the present day heat flow and the moho depth we determine the initial crustal and lithospheric thicknesses of the bohai bay basin before the cenozoic rift to be 33 36 km and 80 105 km respectively the model results show that the most rapid lithospheric thinning during the cenozoic occurred in the middle eocene for most depressions and the thinning activity ceased at the end of the oligocene reaching a minimum lithospheric thickness of 53 74 km followed by a thermal relaxation phase combined with previous studies we infer that the lithosphere beneath the eastern ncc experienced two stages of alternating thinning and thickening notable thinning in the early cretaceous and paleogene and thickening in the late cretaceous and late cenozoic we believe that thermo chemical erosion together with extension was probably the major mechanism of the significant lithospheric removal during the mesozoic whereas the cenozoic lithospheric thinning was mainly dominated by tectonic extension in the eastern ncc lithospheric thickening was generally a result of thermal cooling

uhp metamorphism and exhumation of the dabie orogen china evidence from shrimp dating of zircon and monazite from a uhp granitic gneiss cobble from the hefei basin a shrimp u pb study of zircons separated from an ultrahigh pressure uhp granitic gneiss cobble sample ds12 from the upper jurassic fenghuangtai formation of the hefei basin north of the dabie orogen has identified three different domains 1 cores some of which show straight boundaries and strong oscillatory zoning with th u ratios of 0 12 0 70 and an imprecise upper intercept age of 777 220 ma mswd 2 4 2 mantles variable in shape and cathodoluminescence cl intensity and containing many uhp mineral inclusions including coesite and omphacite and with th u ratios of 0 02 0 26 and a weighted mean 206pb 238u age of 244 5 ma mswd 4 7 and 3 rims which are more homogeneous and luminescent in cl than the mantles and contain fewer uhp mineral inclusions with th u ratios of 0 01 0 05 and a weighted mean 206pb 238u age of 226 2 ma mswd 0 65 monazites from the same sample do not contain coesite and omphacite inclusions but they do show sector zones and are composed of two contrasting domains the light domains in backscattered electron bse images have a th u ratio of 7 3 18 9 and a weighted mean 206pb 238u age of 221 2 ma mswd 0 94 the dark domains in bse have a th u ratio of 2 8 7 2 and have a weighted mean 206pb 238u age of 218 2 ma mswd 0 96 based on these data and a review of the literature it can be concluded that 1 the protolith of gneiss sample ds12 is a granitoid of neoproterozoic age 2 the ages of 244 and 226 ma for the mantle and rim domains of the zircons are time records of two discrete stages in the uhp evolution of dabieshan 3 the ages of 221 and 218 ma for the light and dark gray domains respectively of the monazites record the times of two stages of retrogressive metamorphism during exhumation of the uhp granitic gneiss to a higher crustal level 4 the exhumation rate of the gneiss is estimated to be 6 km ma and 5 the uhp metamorphic blocks of the dabie orogen provided significant detritus to the hefei basin in the jurassic

textures trace elements and pb isotopes of sulfides from the haopinggou vein deposit southern north china craton implications for discrete au and ag pb zn mineralization the haopinggou deposit in the xiong ershan district southern margin of the north china craton comprises numerous au and ag pb zn veins hosted in metamorphic rocks of the late archean to early paleoproterozoic taihua group two stages of mineralization have been recognized stage 1 pyrite quartz veins and stage 2 pb zn sulfide veins some pyrite quartz veins are surrounded or cut by pb zn sulfide veins others occur as independent veins six generations of pyrite have been identified at haopinggou py1 to py3 in stage 1 and py4 to py6 in stage 2 pyrites from stage 1 are enriched in au as co ni and bi whereas stage 2 pyrites contain higher ag pb zn sn and sb invisible au mostly occurs as lattice bound gold in py2 up to 92 ppm au and py3 up to 127 ppm au and has a close relationship with as native au grains are also present in py3 and likely resulted from mobilization and reprecipitation of the invisible au previously locked in the precursor pyrite this view is supported by extensive plastic deformation in stage 1 pyrite as revealed by electron backscatter diffraction analysis in stage 2 ag is mostly present as lattice bound silver closely associated with sb in galena up to 798 ppm ag a variety of silver minerals are also present as inclusions within galena or as interstitial grains these silver minerals were likely formed via ag cu exchange reaction between tetrahedrite and galena or represent exsolution from galena due to a temperature decrease pb isotopic compositions differ remarkably between stage 1 and stage 2 sulfides indicating different sources of lead pb in stage 2 pb zn sulfide veins is consistent with the haopinggou porphyry close to the veins the field textural compositional and lead isotopic data led us to conclude that the early gold bearing pyrite quartz veins and late silver bearing pb zn sulfide veins likely formed from distinct fluid systems related to discrete mineralization events our study suggests that au and ag pb zn veins hosted in the same metamorphic terrains may not be genetically related to each other

the 1 75 1 68ga anorthosite mangerite alkali granitoid rapakivi granite suite from the northern north china craton magmatism related to a paleoproterozoic orogen abstract the amgrs is a suite of anorthosite mangerite alkali granitoid rapakivi granite in the northern north china craton ncc new zircon shrimp and laser ablation inductively coupled plasma mass spectrometry la icpms u pb dating of the damiao anorthosite changsaoying k feldspar granite lanying anorthosite and quartz syenite and the gubeikou k feldspar granite yielded emplacement ages of 1726 9 ma 1753 23 ma 1739 43 ma 1712 15 ma and 1692 19 ma respectively combined with previous geochronological data from the damiao norite and mangerite and shachang rapakivi granite it indicates that the whole amgrs was intruded between 1750 ma and 1680 ma the damiao anorthosites and norites exhibit a high mg and this decreases from mafic up to 63 to felsic t dm c ages ranging from 2 32 ga to 2 43 ga and 2 70 ga to 2 88 ga respectively this suggests that these rocks are the fractional crystallization products of one parental magma zircon hf and whole rock sr nd pb isotopic systematics combined with high la yb 10 and intermediate th ta ratios suggest that the parental magma of the amgrs could have been derived from em i lithosphere mantle enriched by recycled archean continent crustal materials accompanied by some assimilation of lower crustal components the mafic to felsic compositions of the amgrs are different from typical bimodal rocks formed in an anorogenic intra continent rift setting but resemble those emplaced during post collisional post orogenic extensional tectonic setting this is compatible with their age of

exhumation of the ultrahigh pressure continental crust in east central china cretaceous and cenozoic unroofing and the tan lu fault the orogenic architecture of the world s largest ultrahigh pressure exposure the hong an dabie mountains of the triassic qinling dabie orogenic belt is dominated by cretaceous and cenozoic structures that contributed to its exhumation from 30 km depth cretaceous magmatic crustal recycling 50 for the entire dabie and heating 250 to 700 c were most prominent in dabie and exhumation magmatism and cooling were all controlled by cretaceous transtension exhumation was accomplished principally by an asymmetric cordilleran type extensional complex in the northern dabie northern orthogneiss unit between 140 and 120 ma at rates as fast as 2 mm yr and average horizontal stretching rates of up to 6 mm yr cretaceous reactivation occurred within a regional transtensional strain field as a result of far field collisions and pacific subduction the onset of crustal extension was preceded and possibly facilitated by a reheating of the hong an dabie crust 140 ma coeval with the onset of voluminous magmatism in eastern china 145 ma which resulted from a change in pacific subduction from highly oblique to orthogonal the tan lu continental scale fault was a normal fault zone in the mid cretaceous 110 90 ma and underwent 5 4 km dip slip and 4 km throw in the cenozoic during the india asia collision the qinling dabie belt acted as the structural discontinuity between the strike slip dominated escape tectonics south of the qilian qinling dabie belt and the rifting dominated tectonism north of it the most prominent cretaceous and cenozoic structures of the hong an dabie the xiaotian mozitang and the jinzhai fault zones respectively reactivated major lithospheric structures of the triassic orogen i e the huwan detachment zone and the suture

chronology and geochemistry of mesozoic granitoids in the bengbu area central china constraints on the tectonic evolution of the eastern north china craton abstract we performed zircon u pb dating and analyses of major and trace elements and sr nd pb isotopes for granitoids in the bengbu area central china with the aim of constraining the magma sources and tectonic evolution of the eastern north china craton ncc the analyzed zircons show typical fine scale oscillatory zoning indicating a magmatic origin zircon u pb dating reveals granitoids of two ages late jurassic and early cretaceous 206pb 238u ages of 160 ma and 130 110 ma respectively the late jurassic rocks jingshan intrusion consist of biotite syenogranite whereas the early cretaceous rocks huaiguang xilushan nushan and caoshan intrusions are granodiorite syenogranite and monzogranite the late jurassic biotite syenogranites and early cretaceous granitoids have the following common geochemical characteristics sio2 70 35 74 56 wt k2o na2o 0 66 1 27 mainly the occurrence of neoproterozoic magmatic zircons 850 ma and inherited early mesozoic 208 228 ma metamorphic zircons within the late jurassic biotite syenogranites together with the occurrence of neoproterozoic magmatic zircons 657 and 759 ma and inherited early mesozoic 206 231 ma metamorphic zircons within the early cretaceous nushan and xilushan granitoids suggests that the primary magmas were derived from partial melting of the yangtze craton yc basement in contrast the occurrence of paleoproterozoic and paleoarchean inherited zircons within the huaiguang granitoids indicates that their primary magmas mainly originated from partial melting of the ncc basement the occurrence of yc basement within the lower continental crust of the eastern ncc indicates that the yc was subducted to the northwest beneath the ncc along the tan lu fault zone during the early mesozoic

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

mesozoic and cenozoic tectono thermal reconstruction of the western bohai bay basin east china with implications for hydrocarbon generation and migration abstract studies on the tectono thermal evolution of the western bohai bay basin wbbb including the jizhong sub basin and cangxian uplift are important for further petroleum exploration and exploitation this study aims to reconstruct the tectono thermal history of the wbbb based on a combination of 125 vitrinite reflectance ro data and seven apatite fission track aft and nine apatite u th he ahe ages the effective aft ages range from 60 3 to 97 0 ma with mean track lengths of 10 86 12 64 m the variable single grain aft ages are explained to be due to the parameter dpar the effective ahe ages range from 21 1 ma to 75 0 ma two rapid cooling events revealed by the thermal modeling results occurred during the early late cretaceous 130 90 ma and late eocene early miocene 40 18 ma respectively the fuping complex which is located in the western margin of the wbbb and mainly composed of the paleo proterozoic high grade gneisses experienced the intensive extension detachment during the early late cretaceous along with the subduction of the izanagi plate that was probably responsible for the first cooling event the second cooling event was caused by the subduction of the pacific plate during the middle eocene early miocene 43 23 ma as well as the collision of the indian and eurasian plates and the rollback of the subducting pacific plate during the early miocene 23 18 ma the wbbb experienced two heat flow peaks of 75 and 80 mw m2 during the early cretaceous and the late eocene respectively during the late eocene early miocene rapid subsidence in the baxian depression one secondary tectonic unit of the jizhong sub basin coupled with the rapid uplift in the cangxian uplift caused the shahejie formation of the middle upper eocene to generate gas during the early miocene meanwhile tectonic movement during the early miocene also caused faults to become migration paths as revealed by the homogenization temperature of the fluid inclusion this study provides new insights regarding the tectonic and hydrocarbon evolution of the wbbb

confirming sharp bending of the pacific plate in the northern japan trench subduction zone by applying a traveltime mapping method abstract many destructive earthquakes have occurred in the northern japan trench region owing to the subduction of the pacific plate two plate bending points where the dip of the subducting plate changes markedly have been found and correlations between the bending points and the updip limits of large earthquake rupture zones have been previously found in the regions off aomori 40 n and off miyagi 38 n in this study we investigate whether sharp plate bending is also present in the region off iwate 39 n located approximately halfway between the off aomori and off miyagi regions we analysed the existing off iwate wide angle seismic experimental data by applying a new method in which observed reflection phases are directly projected onto the depth distance domain from the time distance domain as a result we found a plate bending point in the region off iwate this is the first time such a point has been found there distances between the three bending points and the trench axis are almost uniform and sharp plate bending is a common feature in the northern japan trench subduction zone the bending axis which is defined by connecting bending points approximately coincides with the updip limit of the rupture zones of large interplate earthquakes seismic swarm activities have been observed inside the subducting oceanic crust along the bending axis and we infer that some of these activities are caused by bending of the subducting plate in addition p wave velocities of the upper plate vary across the bending axis implying that the position of the bending axis is closely related to physical properties of the upper plate and to seismic activities

timing of destruction of the north china craton abstract the north china craton ncc is the typical example of destruction of an ancient craton however the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction which is the key to understanding the destruction processes based on temporal and spatial distributions of the igneous rocks and their sources and tectonic settings it is recognized that six stages of tectono magmatism occurred in the ncc during the phanerozoic i e carboniferous to early permian late permian to middle triassic late triassic jurassic early cretaceous and cenozoic among them cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern ncc the first four stages of magmatism and tectonism related to the southward subduction of the paleo asian plate and the assembly of sino korean and yangtze cratons are locally distributed in limited parts of the ncc reflecting a multiple stage modification of the ncc from the late carboniferous to jurassic however the intensive development of early cretaceous magmatism extensional deformation and associated gold mineralization with significant continental crustal growth indicate that the eastern ncc was destroyed during this time period this destruction was the result of paleo pacific subduction beneath the eastern asian continent with lithospheric removal and or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere

lower crustal processes leading to mesozoic lithospheric thinning beneath eastern north china underplating replacement and delamination abstract our recent studies show that the lower crust and lithospheric mantle in the eastern north china craton ncc was thinned in the mesozoic the lower crust played a key role in the tectonic mechanism that led to lithospheric thinning geochemical data from volcanic rocks and xenoliths support the idea that delamination of the lower crust and lithospheric mantle took place only along the northern and perhaps the southern margins of the ncc and this was linked to post collisional orogenic processes however it is difficult for the delamination process to act on the whole eastern ncc and remove 80 120 km of the lithosphere lower crustal xenoliths in mesozoic and cenozoic basalts within the ncc are of two kinds one is granulite facies metamorphosed two pyroxene gabbros and eclogite facies metamorphosed garnet pyroxenites formed at 140 120 ma the other is precambrian granulites that were strongly overprinted by mesozoic metamorphism large scale lower crustal replacement took place in the mesozoic beneath the ncc in other words some or perhaps most part of the present lower crust of the ncc is not precambrian the present lowermost crust is mostly composed of mesozoic meta gabbros and pyroxenites abundant late jurassic high sr granites in the ncc which are compositionally similar to a dakite probably formed by partial melting of the lowermost crust leaving a residue of eclogite or garnet amphibolite a hot upwelling mantle was necessary to partially melt the pre existing lowermost crust and underplate magma in order to form the present lower crust although eclogites could sink into the mantle it is hard to imagine that there was a thick enough eclogite layer that could drag 80 120 km of the lithosphere into the asthenosphere beneath the ncc magmatic underplating seems to be a better alternative mechanism thus the formation of the present lower crust through the underplating and replacement of the pre existing one was closely related to lithospheric thinning and represented a continuation of the same geodynamic process

zircon shrimp u pb ages and in situ hf isotopic analysis for the mesozoic intrusions in south taihang north china craton evidence for hybridization between mantle derived magmas and crustal components abstract the north china craton ncc was stabilized in paleo proterozoic times and the eastern part of it was remobilized in the mesozoic as is indicated by the presence of voluminous mesozoic magmas in eastern ncc in particular the lithospheric mantle beneath eastern ncc was significantly thinned during the intense mesozoic tectono magmatic activity which makes the ncc different from most other ancient cratons the mesozoic magmas may thus provide crucial evidence regarding the processes that transformed the ncc from craton to a tectonically active region the south taihang magmatic complex lies in the western part of the mesozoic magmatic zone in the ncc the complex falls into three main plutonic rocks the hongshan syenite the xishu gabbroic diorite monzonite and the wu an monzonitic rocks zircon u pb dating reveals that the three plutonic rocks were emplaced contemporaneously at 132 ma in situ hf isotopic analyses for the dated zircons indicate that the hongshan syenites show homogeneous hf t values 10 to 13 which are slightly lower than those 9 0 for the enriched subcontinental lithospheric mantle sclm as revealed by zircons from mafic rocks that originated from melting of sclm this suggests that the parental magma to the syenites was likely derived from melting of the enriched sclm and contaminated slightly by old lower continental crustal material during ascent the xishu and wu an gabbroic diorites to monzonitic rocks however show significantly varied hf isotopic compositions with hf t 9 2 to 16 and 15 5 to 24 respectively the wide range of hf t values for a single sample suggests that the xishu and wu an plutons formed through a process of hybridization between enriched mantle derived mafic magma and crustal components in variable proportions this is supported by the textural and compositional disequilibrium of plagioclase phenocrysts from the two plutons the wu an monzonitic rocks show lower hf t values than the xishu gabbroic diorite monzonite suggesting more incorporation of crustal components in the source the sudden surge of magmatic activity in the south taihang orogen took place as a result of lithospheric extension that caused partial fusion of the enriched portions of sclm generating voluminous mafic magmas underplating of the mafic magmas in the lower crust consequently caused partial melting of the old basement rocks to produce granitic melts which was followed by mixing between the mafic and granitic magmas

identifying mineral prospectivity using seismic and potential field data in the hongniangyu district inner mongolia china abstract since the discovery of several large porphyry mo deposits 0 1 mt mo in the jining region of inner mongolia china during the past decades the area has been receiving wide interest for mining activities however mineral exploration in this area is challenging because most of it is thickly covered by cenozoic sediments geophysical surveys especially the seismic method are becoming increasingly important for investigating deep seated ore controlling structures e g porphyry granites faults and even orebodies supporting the discovery of buried ore deposits recently potential field data and seismic reflection data have been acquired for the hongniangyu area south of jining region in this study we mainly use seismic reflection and potential field data to obtain subsurface geological model in support of mineral exploration targeting gravity and magnetic data were firstly used for spatial analysis of mineral system by mapping the distribution of the faults concealed granites and the sedimentary basin through wavelet analysis tilt angle and euler deconvolution to address the common problem of low signal to noise ratio of seismic reflection data obtained in hard rock terranes we applied a sophisticated workflow including refraction static correction noise filtering surface consistent deconvolution and velocity analysis the obtained post stack migrated seismic profile clearly imaged the geometry of the concealed graben located at the north end of the datong basin and the south east dipping kouquan normal fault controls the depression of the graben and offsets cenozoic sediments by several hectometers up to 500 m joint modeling of seismic gravity and magnetic data further provided evidence of the three buried belts of granites intriguingly one of the concealed granitic belts located in the north of hongniangyu area was found to have both significant chargeability and mo geochemical anomalies indicating a high potential of hosting porphyry type mo ore deposits as expected mo and w mineralized cores were discovered in this target area but limited to only one deep drilling hole the presented results provide the geological framework of hongniangyu district and guidelines for delineating new potential mo mineralization in the jining region

rapid exhumation and cooling of the liaonan metamorphic core complex inferences from 40ar 39ar thermochronology and implications for late mesozoic extension in the eastern north china craton the liaonan metamorphic core complex formed during crustal extension in the liaodong peninsula eastern north china craton and consists of the jinzhou detachment fault proterozoic paleozoic sedimentary rocks in its upper plate and exhumed high grade archean metamorphic rocks and early cretaceous granitic plutons in the lower plate exhumation of its footwall from mid crustal levels is evidenced in the detachment fault zone by the temporal transition from amphibolite facies mylonitization at depth through retrograde chloritic shearing and brecciation to brittle faulting during final uplift the footwall mylonite zone is 2 5 3 5 km thick and includes early cretaceous 128 118 ma granitic rocks together with older metamorphic rocks the 40ar 39ar ages of muscovite hornblende biotite and k feldspar from the mylonitic rocks record that the core complex cooled between ca 120 and 107 ma from the time of initial crystallization of zircons 122 118 ma at 700 800 c in syntectonic leucocratic dikes and granitic rocks to closure of argon diffusion in hornblende micas and k feldspar at 500 to 200 c throughout the eastern north china craton the synchroneity of cooling and exhumation of metamorphic core complexes the formation of pull apart basins and regional alkaline igneous activity reflects regional extensional tectonics in the early cretaceous this accompanied lithospheric thinning possibly resulting from the rollback of the subducted pacific plate along the eastern asian margin during the early cretaceous

the rapid drift of the indian tectonic plate the breakup of the supercontinent gondwanaland into africa antarctica australia and india about 140 million years ago and consequently the opening of the indian ocean is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the marion kerguelen and reunion plumes plate reconstructions based on palaeomagnetic data suggest that the indian plate attained a very high speed 18 20 cm yr 1 during the late cretaceous period subsequent to its breakup from gondwanaland and then slowed to approximately 5 cm yr 1 after the continental collision with asia approximately 50 myr ago the australian and african plates moved comparatively less distance and at much lower speeds of 2 4 cm yr 1 refs 3 5 antarctica remained almost stationary this mobility makes india unique among the fragments of gondwanaland here we propose that when the fragments of gondwanaland were separated by the plume the penetration of their lithospheric roots into the asthenosphere were important in determining their speed we estimated the thickness of the lithospheric plates of the different fragments of gondwanaland around the indian ocean by using the shear wave receiver function technique we found that the fragment of gondwanaland with clearly the thinnest lithosphere is india the lithospheric roots in south africa australia and antarctica are between 180 and 300 km deep whereas the indian lithosphere extends only about 100 km deep we infer that the plume that partitioned gondwanaland may have also melted the lower half of the indian lithosphere thus permitting faster motion due to ridge push or slab pull

multiple sources for the origin of granites geochemical and nd sr isotopic evidence from the gudaoling granite and its mafic enclaves northeast china geochemical and sr and nd isotopic data have been determined for mafic to intermediate microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china the rocks include monzogranite porphyric granodiorite and quartz diorite monzogranites have relatively high 87rb 86sr ratios 0 672 0 853 low initial 87sr 86sr ratios 0 7052 0 7086 and e nd t values 18 5 to 20 9 indicating that they were mainly derived from a newly underplated crustal source with a short crustal residence time quartz diorites have high initial 87sr 86sr ratios 0 7118 0 7120 and negative e nd t values 13 2 to 18 1 coupled with high al2o3 and mgo contents indicating they were derived from enriched lithospheric mantle with contributions of radiogenic sr from plagioclase rich metagreywackes or meta igneous rocks i e ancient lower crust two groups of enclaves with igneous textures and abundant acicular apatites are distinguished dioritic enclaves and biotite monzonitic enclaves dioritic enclaves have low al2o3 13 5 16 4 wt and high mgo mg 72 3 concentrations low initial 87sr 86sr ratios 0 7058 0 7073 and negative e nd t values 7 2 and are enriched in liles and lrees and depleted in hfses suggesting they were derived from an enriched lithospheric mantle source biotite monzonitic enclaves have sr and nd isotopic compositions similar to the monzogranites indicating they were crystal cumulates of the parental magmas of these monzogranites granodiorites have transitional geochemistry and nd and sr isotopic compositions intermediate between the monzogranites quartz diorites and the enclaves geochemical and sr and nd isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mafic mantle derived and juvenile crustal derived magmas coupled with crystal fractionation and assimilation of ancient lower crust is compatible with the data this example shows that at least some calc alkaline granitoids are not produced by pure intracrustal melting but formed through a complex multi stage hybridization process involving mantle and crustal derived magmas and several concomitant magmatic processes crystal fractionation crustal assimilation and crustal anatexis

influence of paleo trade winds on facies patterns of the cambrian shanganning carbonate platform north china abstract the shanganning carbonate platform scp of the north china craton ncc was located in the trade winds belt during the cambrian which influenced its facies development in recent years numerous drillcores have been recovered from these units but the depositional environments and facies architecture of this large 2 0 105 km2 carbonate platform system have not yet been reported in detail in this study we integrate sedimentological and magnetic fabric data collected from outcrops and drillcores in order to document variation in microfacies and facies associations within the scp to infer paleowind directions and constrain the paleogeographic location of the scp and to evaluate eolian controls on platform development this analysis documented numerous carbonate microfacies belonging to six fabric types mudstone wackestone packstone grainstone framestone and dolostone along with rarer siliciclastic sediments these microfacies belong to facies associations representing tidal flat open platform platform margin slope and deep basinal depositional environments anisotropy of magnetic susceptibility ams measurements yielded mean paleocurrent directions for the early middle and late cambrian of 114 63 and 83 30 from paleo north respectively that were relatively consistent for 12 out of 13 platform margin sites all vectors being corrected for a post cambrian 150 clockwise rotation of the ncc these wind orientations are consistent with the scp shifting from south of the paleo equator in the early cambrian to north of it by the middle cambrian paleo trade winds influenced facies patterns across the platform producing a distinct windward leeward zonation the windward margin is characterized by well sorted oolitic grainstone as well as favositids coral and dasycladacean algal sponge framestone and the leeward margin by poorly sorted oolitic wackestone grainstone and fine bioclastic sediments the present study is innovative in 1 integrating microfacies and ams analyses in order to establish paleowind patterns and influences on an ancient carbonate platform 2 documenting windward leeward variation in quantifiable sediment properties across the scp and 3 constraining the paleo hemispheric location of the ncc during the cambrian

paleozoic intrusive rocks from the dunhuang tectonic belt nw china constraints on the tectonic evolution of the southernmost central asian orogenic belt abstract the dunhuang tectonic belt dtb is of great importance for understanding the tectonic evolution of the southernmost central asian orogenic belt caob in this study the temporal spatial distribution petrogenesis and tectonic setting of the paleozoic representative intrusive rocks from the dtb were systematically investigated to discuss crustal evolution history and tectonic regime of the dtb during paleozoic our results reveal that the paleozoic magmatism within the dtb can be broadly divided into two distinct episodes of early paleozoic and late paleozoic the early paleozoic intrusive rocks represented by a suite metaluminous slight peraluminous and medium to high k calc alkaline i type granitoids crystallized at silurian ca 430 410 ma are predominantly distributed along the northern part of the dtb they were probably produced with mineral assemblage of eclogite or garnet amphibole rutile in the residue and were derived from magma mixing source of depleted mantle materials with various proportions of archean mesoproterozoic continental crust the late paleozoic intrusive rocks can be further subdivided into two stages of late devonian stage ca 370 360 ma and middle carboniferous stage ca 335 315 ma the former stage is predominated by metaluminous to slight peraluminous and low k tholeiite to high k calc alkaline i type granitic rocks distributed in the central part of the dtb they were also generated with mineral assemblage of amphibolite to eclogite facies in the residue and originated from magma source of depleted mantle materials mixed with different degrees of old continental crust the later stage is represented by adakite and alkali rich granite exposed in the southern part of the dtb the alkali rich granites studied in this paper were possibly produced with mineral assemblage of granulite facies in the residue and were generated by partial melting of thickened lower continental crust zircon hf isotopes and field distribution of those paleozoic intrusive rocks reveal that both the silurian and the late devonian magmatic activities predominantly represent crustal growth processes in the dtb accompanied by different degrees of reworking of pre existing continental crust however the middle carboniferous ca 335 315 ma magmatic activity reflects a crustal reworking process the silurian and late devonian intrusive rocks were most likely formed in the arc related subduction zones whereas the middle carboniferous intrusive rocks were possibly formed in a transitional tectonic setting from compression to extension representing the final stage of paleozoic orogeny in the dtb these paleozoic magmatic rocks further suggest that the dtb has reactivated from a stable block to an orogen and undergone two episodes the early paleozoic and the late paleozoic of orogeny during paleozoic it represents a paleozoic accretionary orogen of the southernmost margin of the caob between the tarim craton and north china craton and tectonically extends northward to the beishan orogen and westward to the eastern south tianshan belt

geometric and temporal evolution of an extensional detachment fault hohhot metamorphic core complex inner mongolia china the early cretaceous hohhot metamorphic core complex and its master hohhot detachment fault are 400 km west of beijing in the daqing shan mountains of inner mongolia the complex developed across the east trending yinshan fold and thrust belt within 4 m y following cessation of thrusting ca 125 ma see note added in proof in main text postcontractional extension was initiated within a mid crustal zone of mylonitic and ductile shear that was in part controlled by carboniferous strata sandwiched between its proterozoic and archean crystalline basement and an overlying thrust sheet of similar crystalline rocks the hohhot detachment fault appears to have rooted into deep kinematically active levels of the mid crustal shear zone higher inactive levels of the mylonitic section were transected by the fault and carried upward in its footwall geometries of the footwall mylonitic rocks indicate localized ramp flat geometries of the fault within and across them the crosscut top of the mylonitic sequence defines a mylonitic front that departs from the gently south dipping detachment fault and dips northward into its footwall early cretaceous extension was widespread elsewhere in northern china and was particularly pronounced in the yunmeng shan core complex north of beijing the gravitational collapse of orogenically thickened crust acting in concert with localized centers of deep seated plutonism appear to have led to the development of isolated metamorphic core complexes within a broad region of more distributed extensional deformation

partial melting of stagnant oceanic lithosphere in the mantle transition zone and its geophysical implications abstract widespread low velocity anomalies have been observed in the upper mantle around many oceanic subduction zones fluid or melt released from a stagnant slab may have contributed to the formation of these anomalies furthermore slab partial melting or dehydration is also thought to be closely related to the origin of intraplate volcanoes i e changbaishan however experimental evidence on the process of slab partial melting is very limited here our experimental results show that partial melting of stagnant oceanic lithosphere may occurs for temperatures above 1300 1400 c with residual phases composed of wadsleyite ringwoodite garnet clinopyroxene stishovite akimotite the density of melt was approximately 1 0 1 5 g cm 3 less dense than the surrounding mantle which provided a buoyancy force for ascent to the upper mantle across the 410 km seismic discontinuity the ascending melt may react with mantle peridotite leading to the formation of a variably metasomatized mantle which may contribute to the formation of the observed low velocity anomalies above stagnant slab re melting of the metasomatized mantle may have contributed to the origin of the intraplate volcanoes e g changbaishan volcanoes we suggest that partial melting of stagnant oceanic lithosphere in the mtz may have close relations with the origin of the big mantle wedge beneath eastern china

evolving magma sources during continental lithospheric extension insights from the liaonan metamorphic core complex eastern north china craton abstract the relation between magmatic activity and detachment faulting during continental lithospheric extension remains a persistent question this paper takes the liaonan metamorphic core complex mcc in the eastern north china craton as an example to explore how magma generation relates to detachment faulting in response to continental lithospheric extension due to the subduction of the paleopacific plate beneath the eurasian continent in the early cretaceous dating of lower plate granitic intrusions and trachy dacitic volcanic rocks in the supradetachment basin constrains a progressive exhumation of the mcc between ca 134 ma and 113 ma syn tectonic magmatism is grouped into three types i e early syn kinematic late syn kinematic and post kinematic magmatism in reference to detachment faulting the magmatic rocks exhibit obvious differences in whole rock sr nd isotopes implying varying sources e g lithospheric mantle juvenile and ancient lower crusts evolving magma sources during the progressive exhumation of the mcc are shown from one with a lithospheric mantle signature for the early syn kinematic intrusions to one with mixed derivations from both juvenile and ancient lower crust for the late syn kinematic plutons and volcanics and finally to a juvenile lower crust source for the post kinematic intrusions the source evolution of magmatism during the continental lithospheric extension implies that both crustal and mantle processes may have been involved in the magma generation the parallel extension tectonics model is applied to explain both the tectonic faulting and magmatic activities in the model the evolving magma sources accompanying the mcc exhumation were attributed to thinning of the cratonic lithosphere as a consequence of coupled crust mantle detachment faulting during tectonic extension the model can be applied to the variably extended provinces in the north china craton but integrated structural geochronological and geochemical studies are needed to present a comprehensive tectono thermal magmatic history of these provinces

cenozoic volcanic rocks of eastern china secular and geographic trends in chemistry and strontium isotopic composition abstract the cenozoic volcanic rocks of eastern china are subalkalic to alkalic basalts erupted in an early tertiary back arc rift environment and from scattered late tertiary and quaternary volcanic centers in a continental area crossed by active faults driven by subduction of the pacific plate and the collision of india and eurasia immobile trace elements and major elements conform very well to each other in classification of the 59 rocks for which complete data are reported and they correctly identify the tectonic setting lil element enrichments of the basalts lie between those of p morb and ocean island alkalic basalts and show a secular increase 87sr 86sr ratios of basalts vary from 0 7029 to 0 7048 alkalic basalts are systematically less radiogenic than geographically coextensive and contemporaneous tholeiitic basalts increase of radiogenic sr with increasing crustal thickness and crustal age and with silica enrichment of the magmas suggests crustal contamination but this is inadequate to explain the lil element enrichment patterns and variable lil element enrichments the preferred hypothesis is that the alkalic magmas come from a deeper source with long term lil element depletion and low rb sr ratio but relatively recent lil element enrichment conversely the tholeiitic magmas are melts of subcontinental mantle lithosphere that is more lil element depleted than the alkalic source at the time of magma genesis but has had an elevated rb sr ratio for much of its post consolidation history

trace element and isotope characteristics of cenozoic basalts around the tanlu fault with implications for the eastern plate boundary between north and south china a reply abstract cenozoic intraplate basalts in eastern china show variations of pb sr and nd isotope ratios that essentially correspond to major lithospheric domains with distinct tectonic histories whereas an enriched mantle em1 type isotope signature is commonly observed in basalts from the north china block an em2 type isotope signature appears to dominate in those from the south china block this study reports new trace element data for cenozoic basalts occurring around the tanlu fault zone a sinistral translithospheric fault related to the triassic continental collision between the north and south china blocks combining published isotope data basalts from the subei basin in the east of the tanlu fault exhibit the em1 type geochemical and isotopic features implying that their lithospheric mantle source region is structurally affiliated with the north china block this is consistent with the crustal detachment collision model that suggests a subsurface suture between the north and south china blocks

evolution of meso cenozoic lithospheric thermal rheological structure in the jiyang sub basin bohai bay basin eastern north china craton the meso cenozoic lithospheric thermal rheological structure and lithospheric strength evolution of the jiyang sub basin were modeled using thermal history crustal structure and rheological parameter data results indicate that the thermal rheological structure of the jiyang sub basin has exhibited obvious rheological stratification and changes over time during the early mesozoic the uppermost portion of the upper crust middle crust and the top part of the upper mantle had a thick brittle layer during the early early cretaceous the top of the middle crust s brittle layer thinned because of lithosphere thinning and temperature increase and the uppermost portion of the upper mantle was almost occupied by a ductile layer during the late early cretaceous the brittle layer of the middle crust and the upper mantle changed to a ductile one then the uppermost portion of the middle crust changed to a thin brittle layer in the late cretaceous during the early paleogene the thin brittle layer of the middle crust became even thinner and shallower under the condition of crustal extension currently with the decrease in lithospheric temperature the top of the upper crust middle crust and the uppermost portion of the upper mantle are of a brittle layer the total lithospheric strength and the effective elastic thickness t e in meso cenozoic indicate that the jiyang sub basin experienced two weakened stages during the late early cretaceous and the early paleogene the total lithospheric strength approximately 4 5 1013 n m 1 and t e approximately 50 60 km during the early mesozoic was larger than that after the late jurassic 2 7 1012 n m 1 and 19 39 km respectively the results also reflect the subduction and rollback of pacific plate is the geodynamic mechanism of the destruction of the eastern north china craton

observations and simulations of quasiperiodic ionospheric oscillations and large scale traveling ionospheric disturbances during the december 2006 geomagnetic storm 1 a numerical simulation was performed to investigate quasiperiodic ionospheric oscillations that were observed with periods of 4 5 h by the ionosonde network okinawa yamagawa kokubunji and wakkanai in japan during the 15 december 2006 magnetic storm this simulation used the coupled magnetosphere ionosphere thermosphere cmit 2 0 model the cmit model reproduced the main characteristics of the observed ionospheric oscillations although it remains a challenging task to simulate the observations in a quantitative sense term analysis of the ion continuity equation demonstrated that the ionospheric oscillations in this event were mainly induced by the disturbed neutral winds which were associated with the large scale thermospheric circulation and traveling atmospheric disturbances tads during the storm the tads simulated from the model were then compared with those observed by the gps earth observation network geonet in japan to validate the simulation results a prominent northward propagating large scale traveling ionospheric disturbance lstid during daytime seen by the geonet total electron content tec data was captured by the cmit model two southward lstids observed by geonet gps network were also reproduced by the cmit model however the model gave faster phase speeds for the southward propagating lstid occurred during 0620 0800 ut and the northward propagating lstid furthermore the model missed the lstid seen in the tec perturbation data during 0140 0220 ut finally both observations and simulations showed a strong hemispheric asymmetry for the tad propagation that occurred during 0000 0400 ut which may be associated with the hemispheric asymmetry of the change of joule heating at high latitude

contrasting late carboniferous and late permian middle triassic intrusive suites from the northern margin of the north china craton geochronology petrogenesis and tectonic implications two contrasting intrusive suites have been identified from the northern margin of the north china craton a late carboniferous dioritegranodiorite suite mainly made up of quartz diorite diorite granodiorite tonalite and hornblende gabbro and a late permian middle triassic suite of granitoid intrusions consisting of monzogranite syenogranite and quartz monzonite plutons from the late carboniferous suite exhibit variable sio2 contents and calc alkaline or high k calc alkaline metaluminous geochemical features most have low negative whole rock nd t values where t is the crystallization age of 17 1 to 11 5 and zircon hf t values of 38 3 to 11 2 indicating that they were derived mainly from anatectic melting of the ancient lower crust with some involvement of mantle materials however an older pluton in the suite exhibits higher nd t values of 11 5 to 9 9 nd model ages of 1 82 1 64 ga lower initial 87sr 86sr ratios of 0 7046 0 7048 and it contains some zircon grains that are characterized by high negative to positive zircon hf t values of 8 7 to 1 2 indicating strong involvement of juvenile materials derived from the lithospheric mantle the late carboniferous plutons are interpreted as subduction related and to have been emplaced in an andean style continental margin arc during the southward subduction of the paleo asian oceanic plate beneath the north china craton rocks from the late permian middle triassic intrusive suite display geochemical signatures ranging from highly fractionated i type to a type they exhibit higher zircon hf t values of 14 9 to 6 7 whole rock nd t values of 10 6 to 8 8 and younger hf and nd model ages than most of the late carboniferous plutons indicating that they could have been produced by extreme fractional crystallization of hybrid magmas resulted from mixing of coeval mantle and crust derived melts they are interpreted as postcollisional postorogenic granitoids linked to lithospheric extension and asthenosphere upwelling due to slab break off and subsequent sinking after final collision and suturing of the mongolian arc terranes with the north china craton these two contrasting intrusive suites suggest that the final closure of the paleo asian ocean and collision between the mongolian arc terranes and the north china craton occurred during the late permian and these events were followed by postcollisional postorogenic extension large volume magmatism and significant continental growth no significant syncollisional crustal thickening high pressure metamorphism or s type granitoid magmatism occurred during the collision process

zircon shrimp u pb and in situ lu hf isotope analyses of a tuff from western beijing evidence for missing late paleozoic arc volcano eruptions at the northern margin of the north china block abstract zircon shrimp u pb and in situ lu hf isotopic analyses via laser ablation microprobe inductively coupled plasma mass spectrometer lam icpms of a tuff within the upper paleozoic from western beijing were carried out to give new constraints on volcano eruption ages and source area of the tuffs within the north china block ncb shrimp u pb zircon dating of the tuff yielded a 206 pb 238 u weighted mean age of 296 4 ma 95 confidence mswd 3 3 which is very similar to the emplacement age of the newly discovered carboniferous calc alkaline i type continental arc granitoid plutons in the inner mongolia paleo uplift impu on the northern margin of the ncb in situ lu hf analysis results of most zircons from the tuff yielded initial 176 hf 177 hf ratios from 0 282142 to 0 282284 and e hf t values from 15 9 to 10 7 these lu hf isotopic compositions are very similar to those of the late carboniferous granitoids in the impu but are very different to those of the central asian orogenic belt caob together with the sedimentary and tectonic analyses results we inferred that the source area of the tuffs within the ncb is the impu instead of the caob therefore some arc volcanoes once existed in the impu on northern margin of the ncb during the late carboniferous but they were entirely eroded due to strong exhumation and erosion of the impu during the late carboniferous to early jurassic

petrogenesis of an alkali syenite granite rhyolite suite in the yanshan fold and thrust belt eastern north china craton geochronological geochemical and nd sr hf isotopic evidence for lithospheric thinning the yanshan fold and thrust belt in eastern china has been intruded by a series of alkalic igneous rocks ranging in composition from granite and rhyolite to syenite and trachyte laser ablation inductively coupled plasma mass spectrometry u pb analyses of zircon from three alkaline suites yield early cretaceous ages of 130 117ma three groups of rocks have been identified based on their mineralogical geochemical and sr nd hf isotope characteristics the alkali granites and rhyolites are ferroan and have low al2o3 mgo cao sr ba and eu concentrations and high sio2 total fe2o3 k2o nb ga ta th and heavy rare earth element abundances and ga al ratios geochemical data and sr ndand zircon hf isotopic compositions sr sr i1 4 0 7050 0 7164 end t 1 4 8 4 to 13 6 and ehf t 1 4 5 7 to 16 8 indicate that they were probably generated by shallow dehydration melting of biotiteor hornblende bearing granitoid crustal source rocks and then mixed with contemporaneous magma from a mantle and or lower crustal source ferroan syenites have distinct geochemical features from those of the alkaline granites and rhyolites suggesting that they were produced by clinopyroxene and plagioclase fractionation of melt derived from an enriched mantle source mixed with lower and upper crustal derived magmas the magnesian syenites and trachytes have sr ndand zircon hf isotopic compositions that are distinct from those of the ferroan syenites they were mainly derived from partial melting of lower crustal materials mixed with enriched mantle derived alkali basaltic magma the emplacement of an alkali syenite granite rhyolite suite coeval with the formation of metamorphic core complexes and pull apart basins in eastern china indicates they formed in an extensional setting possibly as a result of lithospheric thinning

geological control of the eastern great wall mountain basin relationships in the eastern north china craton abstract the e w trending yanshan belt an intraplate fold thrust belt located in the northern north china craton has experienced several episodes of mesozoic deformation which resulted in the widely distributed magmatism and mountain basin tectonics that completely re shaped the topography of the eastern north china craton the eastern part of the famous chinese great wall was built on the high range of the southeastern yanshan mountain belt juxta posed to the plain which directly relates to the bohai bay basin our study focuses on which tectonic processes created such mountain basin couple in mid late mesozoic times the u pb la icp ms dating of zircons yield ages of 114 to 201 ma for various granites and 115 to 116 ma for volcanic rocks from yixian and jiufotang fms the detrital zircons from the lower cretaceous sandstones yield four age groups of 2587 to 2460 ma 2222 to 1828 ma 297 to 190 ma and 187 to 100 ma which are all sourced from the qinglong and surrounding areas and indicating that the qinglong area started to uplift after the middle jurassic the qinglong area underwent multiple deformation by ne sw compression in the middle late jurassic times wnw ese compression in the late jurassic to early cretaceous ene wsw extension in the early cretaceous and nnw sse compression in the late cretaceous during the final stage of the yanshanian orogeny meanwhile widely distributed granite intrusions and emplacement of the upper jurassic lower cretaceous volcanic rocks indicate a large amount of magma input into the area the qinglong area with the great wall along its southern margin close to adjacent plain to the south was uplifted to form the qinglong highland and surrounding related basins by combination of the following three processes the multiple tectonic late jurassic and late cretaceous shortening processes related to yanshanian orogeny early cretaceous regional extension triggered by slab retreat of the paleo pacific ocean and inflation of large amount magma at depth during jurassic and early cretaceous

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

biostratigraphy and biofacies of the middle darriwilian ordovician conodonts from the laoshidan section in the western margin of the north china craton abstract middle ordovician conodonts from the sandaokan and zhuozishan formations of the laoshidan section at the western margin of the north china craton consist of 39 identified and six indeterminate species belonging to 21 genera and three taxa left in open nomenclature at both genus and species levels of particular biostratigraphic importance is the presence of morphologically advanced species of histiodella associated with several age diagnostic endemic taxa making it possible to recognize international conodont biozones in the main part of the sequence three histiodella based zones are recognized in the studied section including the histiodella cf holodentata histiodella kristinae and histiodella bellburnensis zones in ascending order they can be directly correlated with the conodont zonations established in western newfoundland canada and tarim western china and compared well with the conodont biozones of baltoscandia and yangtze central china however the same stratigraphic interval on the north china platform is barren of conodonts multivariate statistical studies on these conodonts allow recognition of four conodont biofacies scalpellodus biofacies panderodus biofacies drepanoistodus biofacies and phragmodus biofacies turnovers of the conodont biofacies are related to either sea level changes or mixing of shallow water conodonts due to down slope transportation excluding the effect of the allochthonous conodonts the transgressive regressive patterns demonstrated by the conodont biofacies compare closely to the published sea level curves for the western margin of the north china craton

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

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

decratonic gold mineralization evidence from the shangzhuang gold deposit eastern north china craton abstract the jiaodong peninsula in the eastern north china craton ncc hosts some of the world class gold deposits among these the shangzhuang gold deposit represents a typical fault zone hosted disseminated and stockwork style gold mineralization the mineralization is characterized by intense hydrothermal alteration halos in the wallrocks with the mineralized veins intruding into altered wallrocks zircon u pb isotope dating constrains the timing of emplacement of the guojialing granodiorite as 130 1 ma five molybdenite samples from the main mineralization stage veins yielded a well fitted isochron age of 126 2 ma mswd 1 3 marking the timing of gold mineralization four types of fluid inclusions are identified at shangzhuang and their petrographic and microthermometric features suggest fluid immiscibility followed by fluid mixing this inference is also supported by oxygen and hydrogen isotopic data of quartz veins from stage iii the measured 18 o values of quartz are 12 3 to 13 7 for stage ii and 11 7 to 12 0 for stage iii with calculated 18 o fluid values for stage ii ranging from 5 9 to 7 3 and for stage iii from 3 4 to 3 7 d values for stage ii and iii quartz range from 65 3 to 75 2 and 70 6 to 74 7 respectively the data suggest that the ore forming fluids were initially derived from magmatic sources followed by mixing with meteoric water sims in situ sulfur isotope analyses of two types of pyrite py i and py ii from different mineralization stages show different sulfur isotope features the 34 s values for py i 10 2 to 11 3 mean 10 8 n 25 are higher than those of the later mostly gold related py ii 4 1 to 6 8 mean 5 4 n 27 the higher 34 s values of py i are correlated to degassing of mantle wedge metasomatized by the slab fluids the relatively lower 34 s values of py ii might suggest increasing of f o2 through fluid mixing between ore forming fluids and meteoric water the temporal spatial and tectonic relations between the giant gold mineralization and destruction of the ncc suggest a genetic linkage the gold mineralization between 126 and 117 ma at jiaodong was probably initiated at the peak of decratonization ca 125 ma of the eastern ncc phanerozoic craton margin orogeny also played a critical role in the generation of the early cretaceous giant gold deposits in the eastern ncc integrated geological characteristics mineralization features metallogenic age sources of ore forming fluids and sulfur and tectonic settings favor a decratonic gold mineralization model for the shangzhuang gold deposit the geodynamic scenario proposed for the early cretaceous giant gold mineralization event in the eastern ncc includes the paleo west pacific plate subduction asthenospheric upwelling multiple subduction collision processes along the margins

evidence for intracontinental thrust related exhumation of the ultra high pressure rocks in china coesite and diamond bearing ultra high pressure metamorphic rocks produced during the triassic continental collision between the sino korean and yangtze plates are offset by about 530 km along the sinistral tanlu fault in eastern china the tanlu fault terminates abruptly south of the ultra high pressure metamorphic terrain in dabie shan and does not extend into the foreland fold belt along the yangtze river this suggests that in this region the mesozoic major sinistral displacement along the tanlu fault was transferred to southward directed thrusting which led to the exhumation of the ultra high pressure metamorphic rocks formed earlier postcollisional himalayan type intracontinental thrusting and concomitant erosion appear to be the main agents in the exhumation of the very high pressure metamorphic rocks in china

carboniferous granitic plutons from the northern margin of the north china block implications for a late palaeozoic active continental margin we report four late palaeozoic zircon sensitive high resolution ion microprobe shrimp u pb ages for granitic plutons from the inner mongolia palaeo uplift on the northern margin of the north china block these cast a new light on the poorly understood tectonic history of the northern margin of the north china block and the central asian orogenic belt during the late palaeozoic the plutons have for a long time been considered to belong to the early precambrian basement of the north china block our new shrimp u pb zircon dating of four plutons at longhua daguangding boluonuo and hushiha has yielded intrusive ages of 311 2 ma 324 6 ma 302 4 ma and 310 5 ma respectively geochemical data suggest that these granitoids have a calc alkaline subduction related i type signature indicating the existence of an andean style continental arc along the northern margin of the north china block during the late palaeozoic our results also indicate that the palaeo asian ocean still existed during latest carboniferous earliest permian time and that the final collision between the southern mongolia composite terranes and the north china block occurred later than c 290 ma we suggest that the northern margin of the north china block was an active continental margin and the inner mongolia palaeo uplift is a deeply exhumed mid crustal root of a late palaeozoic andean style continental arc

mineralization age and geodynamic background for the shangjiazhuang mo deposit in the jiaodong gold province china abstract the shangjiazhuang mo deposit is located on the jiaodong peninsula in eastern china which is famous for the ca 120 ma jiaodong type au deposits with total au endowment of over 3000 t in this paper we discuss the deposit geology mineralization age and geochemical features of the host granodiorite of the shangjiazhuang mo orebody using this information we aim to clarify the time and geodynamic mechanism for the mo deposit which is another constraint to understand the genesis of au deposits the mo mineralization generally occurs as quartz sulfide veins within the medium grained yashan granodiorite the alteration consists of potassic alteration silicification sericitization chloritization and carbonatization with a weak unclear zonation the ore minerals mainly include molybdenite chalcopyrite and pyrite we measured re os isotopes of molybdenite grains which yielded a weighted mean model age of 116 9 0 81 mswd 1 03 and a well constrained 187 re 187 os isochron age of 117 1 1 4 ma mswd 1 6 these ages are slightly younger than the age of au mineralization on the jiaodong peninsula rhenium contents of 5 84 29 99 ppm with an average of 16 4 ppm in molybdenites indicate a crustal source whole rock geochemical compositions show that the granodiorite is high k calc alkaline and metaluminous to peraluminous the samples show low y contents from 8 2 to 10 5 ppm and sr y ratios from 48 2 to 58 8 displaying an adakitic affinity the yashan granodiorite has high initial 87 sr 86 sr ratios of 0 7101 to 0 7104 low e nd t values of 17 6 to 16 7 and zircon e hf t values from 24 8 to 17 1 with corresponding hf model ages of 2 7 to 2 2 ga these isotopic data together with the adakitic affinity of the granodiorite indicate that the parental magma was derived from ancient crust mafic microgranular enclaves mme that are contemporaneous with the host granodiorite show sio 2 contents of 57 98 58 41 wt and depletion in nb ta the mmes show enriched initial 87 sr 86 sr ratios of 0 7102 to 0 7106 and low e nd t values of 17 3 to 16 3 the mmes are the products of mixing between the metasomatized lithospheric mantle derived mafic magma and the ancient crust derived felsic magma the early cretaceous mo mineralization 120 110 ma is slightly younger than the peak time of au mineralization 126 120 ma on the jiaodong peninsula but have a different spatial distribution which suggests different sources of au and mo the jiaodong type au deposits were probably related to the upwelling of metasomatized lithospheric mantle while the mo mineralization on the jiaodong peninsula may delineate a 120 110 ma mo metallogenic belt along the southern margin of the north china craton with the east qinling which is related to the melting of ancient crustal sources the subduction of the paleo pacific slab and accompanying asthenospheric upwelling triggered upwelling of metasomatized lithospheric mantle forming jiaodong type au deposits subsequently the ponding of mantle derived magmas resulted in partial melting of ancient crust and associated mo deposits

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

precisely dating paleozoic kimberlites in the north china craton and hf isotopic constraints on the evolution of the subcontinental lithospheric mantle abstract kimberlite a deep sourced ultramafic potassic rock carries not only diamond but also invaluable mantle xenoliths and or xenocrysts which are important for tracking the evolution of subcontinental lithospheric mantle sclm however it is challenging to accurately determine the emplacement age of kimberlite and its compositions of primary magma because of modifications by crustal and or mantle contamination and post emplacement alteration this paper reports emplacement ages of diamondiferous kimberlites in mengyin and fuxian of the north china craton ncc using three different dating methods for mengyin kimberlite single grain phlogopite rb sr dating yields an isochron age of 485 4 ma u th pb analyses on perovskite give a 238u 206pb age of 480 6 2 9 ma and a 232th 208pb age of 478 9 3 9 ma and baddeleyite yields a 207pb 206pb age of 480 4 3 9 ma for fuxian kimberlite baddeleyite gives a 207pb 206pb age of 479 6 3 9 ma indicating that the paleozoic kimberlites in the ncc were emplaced at 480 ma numerous lines of evidence indicate that the studied baddeleyites are xenocrysts from the sclm and can be used to constrain hf isotope compositions ehf t 6 of the sclm when kimberlite erupted combined with data from mesozoic cenozoic mantle derived rocks and xenoliths the hf isotope evolution trend of the sclm beneath ncc before craton destruction was tentatively constructed which suggested that the archean slcm was enriched by metasomatism at 1 3 ga further hf isotope investigations on additional sclm derived materials could be used to compare with the constructed hf isotope evolution trend before craton destruction to determine when lithospheric thinning occurred

from dextral contraction to sinistral extension of intracontinental transform structures in the yanshan and northern taihang mountain belts during early cretaceous implications to the destruction of the north china craton abstract mesozoic tectonics of the north china craton ncc is characterized by craton modification and destruction that resulted in varied degrees of craton instability the change from the end of the latest modification to the start of the final destruction of the ncc is regarded to be related to the subduction and roll back of the izanagi plate however the timing of this tectonic transition remains debated and the extent of the area where cratonic destruction occurred is still poorly constrained the joint part of the yanshan and taihang mountain belts has been viewed as the northwest margin of the destructed eastern ncc detailed geological mapping and geochronological studies of this area reveal two groups of transform structures 1 the dextral transform structures developed before 143 ma and 2 the sinistral transform structures formed after 129 ma the western boundary of the dextral transform structures separate the intact ncc and the modified ncc whereas the sinistral transform structures define the northwestern and northern boundaries of the destructed ncc the switching from dextral to sinistral movement occurred at ca 143 129 ma which is roughly coeval with the initial volcanism of the zhangjiakou formation whose age becomes younger eastward the western boundary of the sinistral transform structures migrated to the east for more than 120 km with respect to that of the dextral transform structures these indicate that the transition from the end of the latest modification to the start of the final destruction of the ncc occurred in 143 129 ma in regional geology this transition is consistent with the geodynamic setting of the transformation from the late jurassic flat slab subduction to slab roll back of the izanagi plate since 144 ma

paleogeography reconstruction of a multi stage modified intra cratonic basin a case study from the jurassic ordos basin western north china craton abstract post depositional modification is commonly found in sedimentary basins particularly in the eastern tethys tectonic domain and is related to special geological settings and evolution processes of the region the chinese continent is composed of numerous small scale blocks that underwent intensive tectonic movements paleogeography reconstruction for a modified basin is fundamental for objectively understanding the basin dynamics and exploration of hydrocarbon sandstone type uranium deposits and other mineral resources as a large scale intra cratonic depression basin in the western part of the north china craton ncc the mesozoic ordos basin underwent multi stage modification as a result only the western part was preserved in this study the paleogeography in bathonian oxfordian ages of the jurassic was reconstructed via integrated approaches including stratigraphic correlation sedimentary facies analysis provenance analysis and fission track analysis the original sedimentary boundary of the ordos basin during this period is approximately outlined we determine that the northern and southern borders reach the cenozoic hetao basin and the cenozoic weihe basin respectively and that the eastern northwestern and southwestern borders lie to the west of taihang mountain at the langshan bayanhot basin kexueshan and to the west of liupan mountain respectively the original sedimentary extent of the ordos basin was almost twice that of the present day residual basin the evolution of this basin in the mesozoic recorded the evolution and destruction processes of the ncc the ncc shows that n s and w e trending compressional setting occurred during the triassic and the jurassic respectively the interactive activities of adjacent tectonic domains played a critical role in subsidence dynamics for the intra cratonic ordos basin this study provides further insights for exploration of hydrocarbon and sandstone type uranium deposits in the ordos basin

petrogenesis of late triassic granitoids and their enclaves with implications for post collisional lithospheric thinning of the liaodong peninsula north china craton abstract major and trace element sr nd and hf isotope zircon u pb and hf isotope data are reported for mafic microgranular enclaves and host granitoids from the xiuyan pluton in the liaodong peninsula of the eastern north china craton in order to investigate their sources petrogenesis and tectonic implications the zircon u pb age of the enclaves 211 1 ma is identical to that of the host granite 210 1 ma establishing that the mafic and felsic magmas were coeval the enclaves have high mgo concentrations at low silica contents and positive ehf t values they are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements which can be explained as melts derived from a depleted asthenospheric mantle with some crustal contamination the host granitoids have high sio2 contents variable initial 87sr 86sr ratios and highly negative end t and ehf t values suggesting they were mainly derived from an ancient crustal source heated by the input of asthenospheric mantle derived magmas field observations geochronology geochemistry sr and nd isotopic and zircon hf isotopic compositions point to a complex petrogenesis where asthenospheric mantle and crust derived magma mixing was coupled with crystal fractionation thus explaining the genetic link between enclaves and host rocks identification of an asthenospheric mantle component in the xiuyan granitoids suggests asthenospheric mantle upwelling and decompressional melting of the mantle indicating that post collisional lithospheric thinning in the liaodong peninsula was initiated in the late triassic

geochronology and petrogenesis of the granites in malanyu anticline in eastern north china block abstract widespread mesozoic magmatism and intracontinental deformation is recorded in the north china block ncb but few studies have considered the link between the emplacement of the granite and deformation the malanyu anticline is a large scale east trending fold exposed in the eastern part of ncb and is intruded by many plutons whole rock geochemistry la icp ms zircon u pb ages sr nd isotopic composition as well as zircon hf isotopic data for eight granitic bodies in the anticline have been studied in detail and are reported in this contribution fourteen zircon la icp ms u pb ages have been obtained ranging from ca 218 to 126 ma spanning the triassic to cretaceous with a major population at ca 220 160 ma this age range is different from rest of the mesozoic igneous rocks in ncb indicating the emplacement of the granites in the anticline was structurally controlled although the regional tectonic setting during the mesozoic played an important role in magmatism in the region all of the granites in the malanyu anticline are enriched in light rare earth elements relative to heavy rare earth elements and have similar trace elements patterns with depletions in ba nb sr p and ti and enrichments in rb th u k la ce sm and tb the triassic to jurassic granites two stage depleted mantle nd model t2dm ages are both paleoproterozoic with similar end t values and two stage depleted mantle nd model ages their in situ zircon two stage depleted mantle hf model ages tdm2 range from ca 2861 to 1406 ma integrated with the sr nd hf data from previous studies the triassic dushan granite in the study area has high sr and low y assays derived from the partial melting of archean ttgs in the lower crust with a minor contribution from a depleted mantle source the emplacement was during a post collisional setting following the closure of the paleo asian ocean along the suolun suture in the north the emplacement of most of the jurassic granites involved the superimposition of the initial subduction of the paleo pacific ocean plate beneath ncb while the emplacement of the minor jurassic and cretaceous granites are probably related to the partial melting of the precambrian crust due to widespread extensional tectonics at the northern margin of the ncb

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

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

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

timing of multiple magma events and duration of the hydrothermal system at the yu erya gold deposit eastern hebei province china constraints from u pb and ar ar dating abstract the yu erya deposit is a large granite hosted gold deposit in the eastern hebei province classified as an intrusion related gold system the yu erya complex contains the causative intrusion which was the source of hydrothermal metal bearing fluids this composite granite complex contains miarolitic pegmatite like cavities and pegmatite veins a combination of detailed field observations and u pb dating by shrimp and la icp ms is used to document multiple magmatic events which occurred at 210 220 175 173 171 170 167 166 and 161 ma formed the yu erya granite complex the initiation of the hydrothermal system as determined via ar ar dating is closely related to the exsolution of a magmatic volatile phase from the g1 granite at ca 176 ma the hydrothermal system operated for 16 my 176 160 ma and produced multiple mineralising events 176 172 168 and 162 160 ma linked to emplacement of repeated magma pulses from 175 ma to 161 ma our results suggest that multiple magmatic hydrothermal events over a time period of several million years may be a fundamental factor responsible for the enrichment process during formation of intrusion related gold deposits and thus may be a requirement for forming economic orebodies

petrogenesis and geodynamics of late archean magmatism in eastern hebei eastern north china craton geochronological geochemical and nd hf isotopic evidence abstract the eastern part of the north china craton contains large volumes of late archean hornblenditic tonalitic dioritic granodioritic and granitic rocks la icpms zircon u pb dating of three plutons from eastern hebei eastern north china craton record emplacement ages of 2526 2515 ma and metamorphic ages of 2500 2490 ma for the diorite granodiorite and monzogranite and 2440 ma for the k feldspar granite hornblendites have high mgo 8 6 10 6 wt cr 674 1126 ppm ni 125 159 ppm and v 224 315 ppm at low basic silica contents sio2 45 7 49 0 wt they are enriched in light rare earth elements lrees and large ion lithophile elements liles and depleted in high field strength elements hfses with positive nd t values 1 2 to 2 0 indicating they were derived from an enriched mantle source the monzogranites have high sr and ba contents and sr y and la yb ratios low y and hrees abundances and positive nd t and zircon hf t values with nd and hf model ages less than 3 0 ga reflecting that they were derived from partial melting of a juvenile lower crust at high pressure however the k feldspar granites with low sr and ba concentrations and high hree and y contents are considered to have originated from partial melting of juvenile crustal materials at shallow crustal levels the diorites and granodiorites have variable major and trace element concentrations magmatic zircons from these rocks have heterogeneous hf t values but record uniform homogeneous u pb ages indicating they resulted from mixing of mafic and felsic magmas coupled with fractional crystallization because of the widespread distribution of late archean magmatism and evidence for magma mixing possibly related to mafic magma underplating it appears likely that this event in the eastern north china craton may relfect mantle plume activity that resulted in significant growth of continental crust during the late archean

timing of volcanism in the sierra nevada of california evidence for pliocene delamination of the batholithic root recent seismic experiments across the southern sierra nevada california show that the range lacks a thick crustal root xenolith studies indicate that delamination and loss of much of the lower crust may have occurred between 10 and 3 ma we estimate that delamination occurred ca 3 5 ma on the basis of a sudden pulse of mafic potassic magmatism within and just east of the sierra nevada from 4 to 3 ma this pulse interrupted the low level of volcanism that had prevailed regionally since 13 ma delamination could have promoted magmatism via decompression melting heating of the shallow lithosphere by upwelling asthenosphere and foundering of crustal rocks into the mantle and could have provided dynamic support to the range foundering of the lower crust may have occurred spontaneously owing to negative buoyancy or may have been triggered by extension between the sierra nevada and death valley

the nature of orogenic crust in the central andes 1 the central andes 16 22 s are part of an active continental margin mountain belt and the result of shortening of the weak western edge of south america between the strong lithospheres of the subducting nazca plate and the underthrusting brazilian shield we have combined receiver function and surface wave dispersion results from the banjo seda project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure the major results are as follows 1 the crust supporting the high elevations is thick and has a felsic to intermediate bulk composition 2 the relatively strong brazilian lithosphere is underthrusting as far west 65 5 w as the high elevations of the western part of the eastern cordillera ec but does not underthrust the entire altiplano 3 the subcrustal lithosphere is delaminating piecemeal under the altiplano ec boundary but is not completely removed beneath the central altiplano the altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation leading to lower crustal flow and flat topography in contrast in the high relief inland sloping regions of the ec and sub andean zone the upper crust is still strongly coupled across the basal thrust of the fold thrust belt to the underthrusting brazilian shield lithosphere subcrustal shortening between the altiplano and brazilian lithosphere appears to be accommodated by delamination near the altiplano ec boundary our study suggests that orogenic reworking may be an important part of the felsification of continental crust

structure of the mantle transition zone beneath the north china craton abstract detailed information on deep structural features can improve current understanding of lithospheric thinning and destruction of the north china craton in this study we analyzed receiver functions rfs from teleseismic p waveforms recorded by 246 seismic stations beneath the north china craton ncc to determine the topography of the mantle transition zone mtz the results reveal specific features in the 410 and 660 km discontinuities and outlined mtz thickness beneath the study area the mtz structure shows two anomalously thickened regions beneath the ncc up to 30 40 km thicker than the global average which are mainly concentrated in the eastern and western sections of the eastern ncc encc the thickened regions are discontinuous and separated by a distance of about 400 km double 660 km discontinuities also appear in the southeastern encc combining these results with previous findings we propose a model in which mtz thickening is caused by discrete remnants of the subducted western pacific slab discontinuities resulting from the stagnant slabs may retain evidence of changes in the rate of pacific plate subduction as well as the phase transition of the subducted slabs within the mtz

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

petrogenesis of cretaceous granitoids in the bengbu wuhe area southeastern north china craton implications for gold mineralization abstract sinistral slip along the tancheng lujiang fault zone tlfz during the mesozoic resulted in an offset of approximately 400 km between the dabie and sulu orogens the bengbu wuhe gold belt bwgb represents an extension of the zhaoyuan yexian gold belt to the west of the tlfz early cretaceous intrusions are widely distributed throughout the bwgb gold deposits in the bwgb are commonly associated with intermediate acid dykes that are roughly contemporaneous with mineralization and some orebodies are hosted in granitoids this paper investigates granitoids within the bwgb to constrain their petrogenesis tectonic setting and metallogenic significance using systematic whole rock elemental geochemistry apatite geochemistry zircon u pb dating zircon lu hf isotopes and whole rock sr nd and pb isotopes the timing of au mineralization 134 113 ma in the area is consistent with the age of intrusive adakite like rocks 130 115 ma and normal calc alkaline granitoids 114 109 ma the adakite like samples are characterized by pronounced enrichment in light rare earth elements ree depletion in heavy ree la yb n 30 5 66 2 an absence of eu anomalies high sr contents and sr y ratios low y and yb contents and fractionated ree patterns dy yb n 1 22 1 69 they have relatively low mg values 38 42 and variable sr nd pb hf isotopic compositions 87sr 86sr t 0 7083 0 7111 end t 22 2 to 14 9 206pb 204pb t 17 219 18 010 zircon ehf t 21 0 to 12 3 these features indicate that the parental magmas of the adakites were derived from partial melting of thickened lower crust of the south china plate and or the north china craton the normal calc alkaline granitoids have low sr y 6 0 40 5 la ybn 6 8 24 7 and dy ybn 0 90 1 28 ratios exhibit negative eu anomalies and have variable sr nd pb hf isotopic compositions 87sr 86sr t 0 7082 0 7085 end t 22 7 to 17 7 206pb 204pb t 16 686 16 713 zircon ehf t 24 9 to 19 0 indicating they were derived from the middle to lower crust of the north china craton compared with the normal calc alkaline granitoids the adakite like rocks have higher zircon ce4 ce3 higher apatite so3 and lower apatite mno contents lower and more variable zircon crystallization temperatures and higher apatite molar oh f and cl f ratios indicating that the adakitic magmas were more enriched in volatiles and more highly oxidized taken together field observations and geochemical data suggest that the adakite like rocks related to the subducted south china block are the ore causative rocks

genesis of the wulong gold deposit northeastern north china craton constraints from fluid inclusions h o s pb isotopes and pyrite trace element concentrations abstract the wulong vein type gold deposit located along the northeastern margin of the north china craton ncc contains 80 tonnes of gold at an average grade of 5 35 g t a total of 380 auriferous quartz veins are hosted in late jurassic gneissic two mica granite and early cretaceous granodiorite a paragenetic sequence representing three hydrothermal stages has been identified 1 quartz pyrite 2 quartz polymetallic sulfide and 3 quartz calcite pyrite petrography fluid inclusion microthermometry and laser raman spectroscopy revealed three types of fluid inclusions co2 ch4 type i h2o co2 ch4 type ii and h2o nacl type iii fluid inclusion data indicate that during mineralization fluid temperatures evolved from 283 to 395 c to 219 328 c to 144 255 c and salinities varied from 0 70 to 8 95 wt to 0 18 7 86 wt to 0 18 4 96 wt nacl equivalent quartz yielded 18oh2o smow and dsmow values of 0 9 7 3 and 65 to 48 respectively indicating that the ore forming fluids were derived from magmatic water and mixed with meteoric water during the later stages of mineralization sulfides have 34scdt sulfur isotopic compositions ranging from 0 9 to 3 9 suggesting that the s was derived from a magmatic source pb isotopic compositions of sulfides 206pb 204pb 17 488 17 718 207pb 204pb 15 565 15 631 and 208pb 204pb 38 190 38 766 indicate that the pb was derived primarily from the upper crust with minor input from the mantle in situ laser ablation inductively coupled plasma mass spectrometry la icp ms trace element analyses of three generations of pyrite py1 py2 and py3 reveal that gold concentrations in py2 are higher than those in py1 and py3 which indicates that gold mineralization occurred primarily during the middle stage high co ni ratios of pyrite are consistent with a hydrothermal origin we suggest that the wulong gold deposit formed during lithospheric thinning associated with destruction of the ncc this process was triggered by subduction of the paleo pacific plate during the early cretaceous

petrogenesis and tectonic implications of the mesozoic granitoid intrusions in the eastern liaoning peninsula ne china abstract mesozoic magmatic rocks are widely distributed in the eastern region of the north china craton ncc providing important information for understanding the mesozoic tectonic regimes in this area this paper reports newly obtained geological geochemical and zircon u pb lu hf isotope data for the xiaoheishan daheishan intrusion xdi and the yanghezhen dayingzhen intrusion ydi newly identified from precambrian metamorphic basement range in the eastern liaoning peninsula and provides a case study demonstrating that the petrogenesis of granitoid rocks was closely related to the tectonic regimes the middle late jurassic xdi granitoids commonly have the adakite like geochemical characteristics and their primary magma was derived from the partial melting of mafic rocks and neoarchean tonalites in the thickened lower crust the early cretaceous ydi granitoid rocks generally show diversified geochemical characteristics and their primary magma was generated by the partial melting of paleoproterozoic metagreywackes and neoarchean tonalites in the lower crust with minor addition of mantle derived magma these differences indicate that the granitoid magmatism in the eastern liaoning peninsula has occurred a significant variation during the jurassic to cretaceous the variation of late mesozoic granitoid magmatism may be responses to the regional tectonic transition from compression to extension in the eastern liaoning peninsula which is induced by the geodynamic regime of the paleo pacific plate from low angle subduction to slab rollback

lithospheric structure across the northeastern margin of the tibetan plateau implications for the plateau s lateral growth abstract variations of lithospheric structure across the northeastern tibetan plateau and its bounding asian blocks the alxa block to the north and the ordos block to the east are crucial for understanding the rise and lateral growth of the tibetan plateau using waveforms from high density seismic arrays in northeastern tibetan plateau and the surrounding regions we investigated the lithospheric structure with s and p wave receiver functions the results show strong and relatively simple negative velocity gradients in the depth range of mantle lithosphere 70 150 km under the ordos and alxa blocks similar to those under typical stable continental lithosphere in contrast under northeastern tibetan plateau including its marginal regions the velocity gradients are weak and diffusive for the mantle lithosphere which may be explained by elevated temperature and presence of partial melts the changes of lithospheric structures are sharp between the tibetan plateau and the bounding ordos and alxa blocks suggesting that these two blocks have restricted the lateral growth of the tibetan plateau as rigid boundaries however across the northeastern corner of the tibetan plateau to the yinchuan rift the lithospheric mantle structures are similar suggesting a lateral mantle flow from the tibetan plateau to the gap between the ordos and the alxa blocks the crustal structures along this transition show evidence of lateral growth of the tibetan plateau in particular the edge of thickened crust and evidence of moho superposition are found between the haiyuan fault and the tianjin shan fault which may have replaced the haiyuan fault as the front boundary of the laterally growing tibetan plateau in its northeastern corner

rapid exhumation of the northern jiaobei terrane north china craton in the early cretaceous insights from al in hornblende barometry and u pb geochronology abstract the guojialing and aishan plutons in the northern jiaobei terrane represent the magmatic products of the lithospheric thinning of the north china craton in the early cretaceous the exhumation history of the terrane in response to the thinning process and its effect on the formation and preservation of coeval gold deposits remain poorly constrained granodiorites from the guojialing pluton and monzogranites from the aishan pluton contain zircon grains with u pb ages of ca 130 ma and ca 116 ma respectively using the al in hornblende barometry the guojialing and aishan plutons had crystallization pressures of 3 2 5 4 kbar 12 km and 1 5 2 6 kbar 5 km respectively using the hornblende plagioclase thermometry the guojialing and aishan plutons had crystallization temperatures of 628 697 c and 702 745 c respectively fluid inclusion microthermometric data show that auriferous quartz veins in the daliuhang deposit formed at temperatures between 243 and 322 c at a depth of 7 11 km which was similar to the emplacement depth of the aishan pluton these thermobarometric and geochronological data reveal 7 km uplift between 130 ma and 116 ma but negligible exhumation for the gold deposits after its formation until 116 ma combining previous results we envisage that the exhumation magnitude of the guojialing intrusions were nearly the same in the wide area with slight differences between the core and margin of a single pluton numerous gold deposits in the jiaobei terrane formed during or after the late stage of rapid exhumation of granitoids and were uplifted with similar depths to the aishan pluton since ca 116 ma the rapid exhumation of the guojialing pluton was with the regional extension and might be genetically associated with the intensive delamination of destabilized lithospheric root and dense residues

origin of mafic enclaves from the taihang mesozoic orogen north china craton abstract the origin of mafic enclaves in intermediate and felsic granitoids has long been debated in this paper petrological and geochemical analyses whole rock geochemistry nd sr and zircon in situ hf isotopic compositions are used to address this controversial issue mafic enclaves in the taihang felsic plutons north china craton are fine grained and show typical magmatic textures they occur as rounded to ellipsoidal globules and are sometimes highly elongated without solid state deformation due to stretching within the partially crystallized convective felsic magma such occurrence suggests that the mafic enclaves and host rocks represent two co existing compositionally distinct magmas the mafic enclaves contain abundant hydrous phases hornblende and biotite and show the reaction relationship of clinopyroxene being rimmed by hornblende they also contain plagioclase xenocrysts showing compositional and textural disequilibrium in terms of nd hf isotopes mafic enclaves have end t values of 10 to 15 and host rocks have lower values as a whole 13 to 18 zircons from a single enclave show a large variation in hf isotopic compositions ehf t 5 to 20 a model is proposed whereby an evolved basaltic magma first mixed with a granitic magma of crustal origin at depth and then the mixed magma broke up into discrete globules upon entering the felsic magma chamber forming enclaves by convective motion or forceful injection in the host felsic magma this was followed by a double mechanical transfer of plagioclase crystals at the contact of the two magmas and by the diffusion of mobile elements e g si alkalis p y yb pb from felsic magma to enclave forming magma