an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

the 1 85 ga mo mineralization in the xiong er terrane china implications for metallogeny associated with assembly of the columbia supercontinent abstract the east qinling region in china hosting several tens of mesozoic magmatic hydrothermal mo deposits is one of the largest molybdenum belts in the world the recently discovered longmendian mo deposit luoning county henan province occurs within the xiong er terrane of the east qinling mo belt here the mo mineralization is confined to altered amphibolite which is replaced by microcline actinolite tremolite epidote and carbonate molybdenite is also observed in microcline dominated felsic differentiates but occurs within the altered amphibolite enclaves here we report re os isotope analyses of five molybdenite and four pyrite samples from longmendian which yield re os isochron ages of 1853 36 ma and 1855 29 ma respectively these ages are in good agreement with the metamorphic age of the taihua supergroup 1 87 1 84 ga the re os data presented in this study indicate that the period of 1 85 ga was a time of widespread melting generating leucocratic microcline dominated granitic melts the timing also coincides with the collision of the eastern and western blocks of the north china craton and its final cratonization at 1 85 ga coinciding with the incorporation of the north china craton within the paleoproterozoic supercontinent columbia

propagation tectonics and multiple accretionary processes of the qinling orogen abstract the qinling orogen was built through collision between the north china and south china blocks previous detailed geological geochemical and geochronological investigations revealed that the mountain range can be divided into four tectonic units with distinct tectono lithostratigraphy which are from north to south the southern sector of the north china block north qinling belt south qinling belt and northern sector of the south china block separated by the kuanping shangdan and mianlue sutures according to the petrology geochemistry and geochronology of ophiolitic melanges and related magmatic rocks as well as the features of sedimentary units we think that the north china block the north qinling belt and the south china block were originally independent continental units while the south qinling belt had been the northern part of the south china block these units experienced three episodes of accretionary tectonic processes and amalgamation from south to north the neoproterozoic accretion took place along the luonan luanchuan fault and kuanping ophiolitic melange belt as a result of southward subduction and subsequent collision between the north qinling and north china blocks during ca 1 0 0 8 ga related to the formation of the supercontinent of rodinia the paleozoic accretion occurred along the shangdan suture resulted from northward subduction of oceanic lithosphere in the early paleozoic and subsequent continental subduction in the late paleozoic late triassic accretion took place along the mianlue suture between the south qinling and south china blocks due to northward subduction of the mianlue oceanic lithosphere during the permian early triassic and subsequent collision in the late triassic after the late triassic collision along the mianlue suture the whole qinling mountain range entered the phase of intense intracontinental deformation

eocene onset and late miocene acceleration of cenozoic intracontinental extension in the north qinling range weihe graben insights from apatite fission track thermochronology abstract intracontinental extension in central china is accommodated by cenozoic grabens flanking the ordos block such as the weihe graben which accommodate 5 6 mm yr of extension to define the onset and evolution of major cenozoic extension we examine the cooling history of exhumed footwall rocks in the north qinling range adjacent to the weihe graben we present results from 47 new apatite fission track aft samples primarily from two vertical transects of 1 5 2 5 km relief located on the northern flank of the north qinling footwall aft ages that get progressively older with increasing distance from the active range bounding normal fault suggest that cenozoic uplift and southward tilting was a response to range parallel extension correlations between aft ages and both elevation and track lengths combined with thermal modeling of representative samples reveal that the north qinling experienced two major stages of cenozoic exhumation 1 relatively slow exhumation in response to a small magnitude of extension that initiated at 50 ma 2 relatively rapid exhumation in response to a large magnitude of accelerated extension that initiated at 10 ma in addition small changes in cooling rate at 35 ma and 25 ma may reflect minor changes in faulting rate we interpret initial extensional at 50 ma to be a far field effect of initial india asia continental collision in contrast accelerated extension after 10 ma along the qinling is likely linked to the upward and outward growth of the tibetan plateau alternatively lower crustal flow beneath the qinling may have progressively accelerated exhumation in late miocene time

crustal extension ag pb zn veins in the xiong ershan district southern north china craton constraints from the shagou deposit the shagou vein type ag pb zn deposit in the xiong ershan district southern margin of the north china craton is hosted within amphibolite facies metamorphic rocks of the late archean to early paleoproterozoic taihua group the ag pb zn veins are localized in ne to nne trending brittle faults and typically display symmetrical zoning consisting of siderite quartz sphalerite galena and quartz calcite from the margin toward the center of each vein ore related hydrothermal alteration is well developed on both sides of the veins dominated by silicification sericitization chloritization and carbonatization sericite separates extracted from a major ag pb zn vein yield a 40 ar 39 ar plateau age of 140 0 1 0 ma 1 and isochron age of 141 1 1 6 ma 1 indicating that mineralization occurred at the beginning of early cretaceous field and textural relationships indicate four hydrothermal stages marked by assemblages of quartz siderite stage i quartz sphalerite ankerite stage ii quartz galena silver minerals ankerite stage iii and quartz calcite stage iv respectively silver minerals are abundant in all veins and are composed of in paragenetic order argentiferous tetrahedrite polybasite jalpaite argentite and native silver these silver minerals commonly occur as replacements of galena chalcopyrite and other sulfides or as fillings of microfractures in sulfides and quartz microthermometric measurements of primary fluid inclusions in quartz carbonates and sphalerite from various hydrothermal stages indicate that ore minerals were deposited at intermediate temperatures 267 157 c from aqueous carbonic to aqueous fluids with moderate salinities 7 2 15 9 wt nacl equiv coexisting galena sphalerite pair yields sulfur isotope equilibrium temperatures of 205 to 267 c consistent with the overall homogenization temperatures of fluid inclusions the microthermometric data also indicate that both fluid mixing and fluid rock interaction were important mechanisms for ore precipitation carbonate minerals siderite ankerite calcite spanning the entire mineralization history have 13 c v pdb values of 5 2 to 1 4 and 18 o v smow of 10 9 to 15 0 corresponding to calculated values for the ore fluids of 6 5 to 1 8 and 1 4 to 5 4 respectively 34 s v cdt values of sulfide minerals pyrite sphalerite galena range from 1 1 to 5 5 consistent with a deep seated sulfur source galena separates have 206 pb 204 pb ratios of 17 472 to 17 813 207 pb 204 pb ratios of 15 411 to 15 498 and 208 pb 204 pb ratios of 38 178 to 38 506 the isotope data together with geological and geochronological evidence favor a primary metamorphic source for sulfur and other components in the ore fluids a synthesis of available data suggests that the shagou deposit is a typical vein type ag pb zn deposit that formed under an extensional geodynamic setting associated with tectonic reactivation of the north china craton during the late mesozoic a time period that is manifested by pervasive magmatism widespread formation of metamorphic core complexes and development of faulted basins throughout the eastern part of the craton metamorphic devolatilization of the meso neoproterozoic marine sedimentary rocks previously subducted beneath the xiong ershan district facilitated by extensive magmatism and elevated heat flow due to lithospheric extension could have provided large amounts of ore fluids responsible for the ag pb zn mineralization the ne to nne trending faults affiliated with the transcrustal machaoying fault may have acted as pathways for the upward migration of deep seated metamorphic fluids mixing of the metamorphically derived fluids with meteoric waters ultimately resulted in deposition of the ag pb zn veins in brittle extensional structures

formation and evolution of the paleoproterozoic meta mafic and associated supracrustal rocks from the lushan taihua complex southern north china craton insights from zircon u pb geochronology and whole rock geochemistry abstract the upper taihua complex in the lushan area is one of the best preserved paleoproterozoic metamorphic basements exposed in the southern north china craton which is mainly composed of khondalite dominated supracrustal rocks and associated meta mafic intrusions amphibolites and granitic plutons detrital zircon u pb ages of four paragneisses from the supracrustal rocks can be divided into two groups 2 39 2 10 ga and 1 97 1 83 ga concordant 207 pb 206 pb ages from the older group show typical magmatic features with a distinct peak around 2 31 2 23 ga whereas the metamorphic zircons define a remarkable age peak at 1 93 ga magmatic zircons from the amphibolite sample have a weighted mean 207 pb 206 pb age of 2128 29 ma representing the crystallization age of the protolith therefore the depositional age of the supracrustal rocks in the upper taihua complex can be well constrained at 2 23 2 13 ga geochemically the amphibolites are classified as subalkaline high fe tholeiitic basalts in compositions and characterized by slightly enrichment in lree flat hree and weakly negative eu anomalies with depleted high field strength elements e g nb ta and ti inconsistent with typical rocks derived from the asthenospheric mantle the high feo t 13 59 wt cao 6 67 wt low al 2 o 3 th e nd t values and crustal contamination sensitive elements suggest that crustal assimilation was limited during magma evolution the varied e nd t values 2 99 to 0 44 and nd model ages 2 65 2 98 ga suggest that they were likely originated from archean subcontinental lithospheric mantle sclm which have been refertilized by metasomatic processes these geochronological and geochemical signatures indicate the meta mafic rocks and associated supracrustal rocks of the upper taihua complex in the lushan area were most likely formed in an intra continental rift setting implying the extensional tectonic scenario rather than subduction related regime occurred between 2 2 and 2 0 ga at least in the southern margin of the ncc metamorphic ages suggest that the taihua complex in the lushan area was involved in subduction collision processes from 1 97 ga to 1 83 ga

a 1 78 ga large igneous province in the north china craton the xiong er volcanic province and the north china dyke swarm abstract the 1 78 ga xiong er volcanic province xvp and coeval north china giant mafic dyke swarm ncds are the most important magmatic events occurring after the amalgamation of the north china craton ncc the xvp consists of 3 7 km of extrusive volcanics and some feeder dykes sills located along the southern margin of the ncc and extending over an area 0 06 m km2 compositions vary from basalt to rhyolite but are predominantly intermediate in terms of silica content there are also minor sedimentary intercalations and pyroclastic units the sedimentary interlayers indicate an environment changing from continental facies to oceanic facies up section the xvp is characterized by fractional crystallization from an em i type mantle source and both continental arc andean type and rift environments have been proposed the ncds is widespread in the central ncc with an outcrop area 0 1 m km2 and are exposed at variable depths up to 20 km deepest in the north dyke compositions vary from basalt to andesite and dacite but are dominantly mafic and comprise two series of magmatism previous studies revealed that the ncds recorded assimilation and fractional crystallization of an em i type magma source with a minor dm contribution in the younger magmas both syn collisional and intra continental anorogenic environments have been proposed spatial and petrogenic correlations suggest a cogenetic relationship between the ncds and xvp and considered together they define a large igneous province lip of 0 1 m km2 in area and 0 1 m km3 in volume which is also notable for its continuous compositional range from mafic to felsic with no gap at intermediate compositions the petrology is explained by a common magma source that undergoes a silica poor and iron enriched fractionation trend at depth followed by a silica rich and iron poor fractionation trend in shallow level magma conduits dykes and surface lavas a mantle plume is favored as the cause of this 1 78 ga north china lip

properties of geothermal resources in kebilli region southwestern tunisia the kebilli region is located in the southwestern part of tunisia and is characterized by the presence of deep and shallow geothermal systems continental intercalary and complex terminal chemical and isotopic contents are used to classify the type and determine the origin of thermal water an evaluation of reservoir temperature and a possible geothermal fluid mixing are also carried out both continental intercalary deep aquifer and complex terminal shallow aquifer are of na ca cl so4 mixed water type the use of different geothermometers and the computation of saturation indexes for different solid phases suggests that the thermal reservoir temperature of the continental intercalary is between 92 and 105 c while the fluid temperature from the shallow complex terminal aquifer ranges from 50 to 75 c also the isotopic data indicates the old origin of all groundwater of southwestern tunisia mixing effects characterizing the continental intercalary and the complex terminal aquifers were identified using 2h and 18o relationship it appears that the upward movement of thermal water from the deep aquifer to shallow ones is probably due to the abundant fractures in the research area

geodynamics of heterogeneous gold mineralization in the north china craton and its relationship to lithospheric destruction abstract the north china craton ncc hosts some of the world class gold deposits on the globe which can be classified into distinct types as the jiaodong type explosive breccia type and skarn type the jiaodong type gold deposits were formed at ca 120 130 ma both in the margins and interior of the ncc two explosive breccia gold deposits formed at ac 180 ma and 120 ma and are located in the southern margin and the interior of the ncc important skarn gold deposits of ca 128 ma formed within the interior of the ncc although the formation and distribution of these gold deposits are temporally and spatially heterogeneous they are commonly related with the lithospheric destruction of the ncc the interplay of several factors such as basement architecture inhomogeneous decratonization crust mantle interaction mantle dynamics magmatic characteristics high heat flow and massive flux of deep derived ore forming fluids operated in generating the gold endowment all the three types of gold systems are closely related with granitoid plutons and different types of dykes the magmas for which were sourced from the lower crust near the moho discontinuity and involved the mixing and mingling of felsic and mafic magmas the ore forming fluids display prominent magmatic signature and were largely derived from deep domains with probable input from the asthenosphere mantle the heterogeneous distribution of the giant gold systems in the ncc was geodynamically controlled by the destruction of the craton the regions at the confluence of two or three precambrian micro continental blocks are generally characterized by thinned lithosphere and high heat flow constituting the potential sites of giant gold deposits the mantle beneath these regions shows em2 characteristics implying the involvement of subducted oceanic components the magmatic intrusions associated with the gold systems crystallized under high oxygen fugacity conditions and were rich in volatiles

neoproterozoic paleozoic and mesozoic granitoid magmatism in the qinling orogen china constraints on orogenic process abstract the qinling orogen is one of the main orogenic belts in asia and is characterized by multi stage orogenic processes and the development of voluminous magmatic intrusions the results of zircon u pb dating indicate that granitoid magmatism in the qinling orogen mainly occurred in four distinct periods the neoproterozoic 979 711 ma paleozoic 507 400 ma and early 252 185 ma and late 158 100 ma mesozoic the neoproterozoic granitic magmatism in the qinling orogen is represented by strongly deformed s type granites emplaced at 979 911 ma weakly deformed i type granites at 894 815 ma and a type granites at 759 711 ma they can be interpreted as the products of respectively syn collisional post collisional and extensional setting in response to the assembly and breakup of the rodinia supercontinent the paleozoic magmatism can be temporally classified into three stages of 507 470 ma 460 422 ma and 415 400 ma they were genetically related to the subduction of the shangdan ocean and subsequent collision of the southern north china block and the south qinling belt the 507 470 ma magmatism is spatially and temporally related to ultrahigh pressure metamorphism in the studied area the 460 422 ma magmatism with an extensive development in the north qinling belt is characterized by i type granitoids and originated from the lower crust with the involvement of mantle derived magma in a collisional setting the magmatism with the formation age of 415 400 ma only occurred in the middle part of the north qinling belt and is dominated by i type granitoid intrusions and probably formed in the late stage of a collisional setting early mesozoic magmatism in the study area occurred between 252 and 185 ma with the cluster in 225 200 ma it took place predominantly in the western part of the south qinling belt the 250 240 ma i type granitoids are of small volume and show high sr y ratios and may have been formed in a continental arc setting related to subduction of the mianlue ocean between the south qinling belt and the south china block voluminous late stage 225 185 ma magmatism evolved from early i type to later i a type granitoids associated with contemporaneous lamprophyres representative of a transition from syn to post collisional setting in response to the collision between the north china and the south china blocks late mesozoic 158 100 ma granitoids located in the southern margin of the north china block and the eastern part of the north qinling belt are characterized by i type i to a type and a type granitoids that were emplaced in a post orogenic or intraplate setting the first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process these suggest that the tectonic evolution of the qinling orogen is very complicated

shrimp u pb zircon ages of granitoid rocks in the luliang complex implications for the accretion and evolution of the trans north china orogen abstract the luliang complex is situated in the central segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of supracrustal and granitoid rocks of which the latter can be subdivided into pre tectonic ttg gneisses including the yunzhongshan guojiazhuang and chijianling guandishan gneisses syn tectonic gneissic granites represented by the huijiazhuang gneissic granite and post tectonic granites including the luyashan charnockite luchaogou porphyritic granite and tangershang guandishan massive granite the pre tectonic ttg gneisses are mostly calc alkaline and considered to have formed in a magmatic arc environment shrimp u pb analyses reveal that the yunzhongshan gneisses were emplaced at 2499 9 ma representing the earliest arc related magmatic event in the luliang complex this was followed by the intrusion of the guojiazhuang gneisses at 2375 10 ma the most widespread arc related magmatic event in the region was the emplacement of the chijianling guandishan granitoid gneisses of which the tonalitic granodioritic and monzogranitic gneisses were emplaced at 2199 11 ma 2180 7 ma and 2173 7 ma respectively metamorphic zircon overgrowth rims from a tonalitic gneiss yielded a weighted mean 207 pb 206 pb age of 1872 7 ma consistent with the metamorphic age range of 1880 1820 ma defined by metamorphic zircons from various high grade rocks in the tnco thus the evolution of the luliang complex involved emplacement of the yunzhongshan granitoids at 2499 ma the guajiazhuang granitoids at 2375 ma and the chijianling guandishan granitoids at 2199 2173 ma with the final collision between the eastern and western blocks in this area occurring at 1872 7 ma the whole series of magmatic events lasting nearly 650 ma this suggests that the trans north china orogen represents a long lived magmatic arc the new shrimp zircon data combined with structural and petrological studies also reveal the existence of both syn and post collisional granites in the luliang complex the former is represented by the huijiazhuang gneissic granite that was emplaced at 1832 11 ma whereas the latter include the 1815 5 ma luyashan charnockite 1807 10 ma luchaogou porphyritic granite 1798 11 ma guandishan massive granite and 1790 14 ma tangershan massive granite

re os dating of molybdenites from au mo deposits in xiaoqinling gold ore district and its geological significance molybdenum mineralization with economic value was recently discovered in the dahu gold deposit and its nearby quanjiayu gold bearing quartz veins in the xiaoqinling gold ore district henan province for the purpose of studying the chronology of the molybdenum mineralization in this district the authors purified molybdenite from the dahu gold deposit and the quanjiayu gold bearing quartz veins re os dating of these molybdenite minerals yielded modal ages of 223 0 2 8 ma 223 7 2 6 ma and 232 9 2 7 ma for the three samples from dahu and 129 1 1 6 ma and 130 8 1 5 ma for the two samples from quanjiayu these results indicate that au mo mineralization in the xiaoqinling gold ore district took place not only at the yanshanian stage but also at the indo chinese stage different from things of jinduicheng huanglongpu and other mo deposits the molybdenites from the dahu and quanjiayu deposits have a very low content of re showing a crustal source for ore forming materials

multiple episodes of tectono thermal disturbances in the huayangchuan u nb pb polymetallic deposit in the xiaoqinling region central china and their significances on metallogeny abstract the huayangchuan u nb pb polymetallic deposit is hosted in a suite of neoarchean to paleoproterozoic gneisses in the xiaoqinling region central china the deposit is composed mainly of discrete small scale carbonatite veins emplaced largely along shallow lying brittle fractures various regimes of deformation from ductile flow to brittle fracturing are documented in the deposit and its adjacent areas these include an earliest phase of contracting deformation d1 manifested as well developed boudinages abundant relict rootless folds and penetrative compositional bands i e gneissosity generally trending e w a subsequent phase of disperse dextral ductile shear d2 along the e w trending gneissosity and a following phase of general ne sw compression d3 resulting in local contraction deformation bands and abundant sinistral ductile shear along the e w trending gneissosity all of which are affected by an overwhelming nne ssw compression d4 with hemi ductile to brittle deformation behaviors the deformation after d4 is generally brittle and may arise from an earlier regime of dominant compression nw se d5 and a later regime of extensive extension d6 multiple thermal events are superimposed on gneisses as revealed by 40ar 39ar dating on biotite collected from various lithologies in the deposit and its adjacent areas which yields ages ranging from late triassic 238 203 ma through earliest cretaceous 139 134 ma and middle cretaceous 117 92 ma to latest cretaceous 72 ma and even early cenozoic 53 ma this sequence of thermal disturbances unlikely predates the d4 deformation given that it is the last ductile deformation experienced by the precambrian rocks ore bearing carbonatite veins have their shallowly lying attitudes consilient with the d4 and d5 deformation and ages compatible with the first two thermal overprints accordingly a two stage mineralization model is proposed for the huayangchuan polymetallic deposit with an early phase of ore veining in the late triassic to latest jurassic during the nearly n s collision between the south and north china blocks and a late phase of ore veining or more possibly reworking in the early cretaceous related to the yanshanian orogeny due to a generally nw directed subduction of the paleo pacific oceanic plate beneath the eastern asia continent

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

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

episodic crustal growth in the southern segment of the trans north china orogen across the archean proterozoic boundary abstract the dengfeng and taihua complexes are well exposed neoarchean to paleoproterozoic units in the southern segment of the trans north china orogen tnco zircon u pb dating shows that the dengfeng complex records two episodes 2568 11 ma and 2306 6 ma of tonalite trondhjemite granodiorite ttg magmatism all of the ttg rocks are characterized by high sio2 66 7 75 4 wt na2o 3 20 5 06 wt and relatively low mgo 0 40 1 78 wt the late neoarchean ttg gneisses have very low contents of hree ybn 0 69 2 75 and y 1 73 7 07 ppm with moderate la yb n 24 1 53 8 and high sr y 65 1 291 3 ratios the early paleoproterozoic ttg gneisses have low contents of hree ybn 2 93 6 37 and y 6 7 11 0 ppm with moderate la yb n 10 1 27 0 and sr y 10 6 52 1 ratios both suites show pronounced negative nb ta p and ti anomalies but positive sr and pb anomalies the late neoarchean ttg gneisses all have similar bulk rock nd and zircon hf model ages with mainly positive nd t and are interpreted as resulting from the melting of dominantly juvenile thickened lower crust with residual garnet and amphibole the early paleoproterozoic ttg gneisses have extremely variable nd t 6 23 to 4 23 and heterogeneous zircon hf t 3 3 to 3 1 which are also best interpreted as resulting from the partial melting of thickened lower crust with residual amphibole and garnet the taihua complex in the xiaoqinling area records three episodes of early paleoproterozoic ttg magmatism 2 48 ga at caotan 2 31 ga at houjiacun and 2 16 ga at bayuan younger than the taihua complex in the lushan area 2 85 2 72 ga all rocks have relatively low contents of hree ybn 1 03 8 32 and y 2 84 24 ppm with moderate la yb n 8 7 88 4 and sr y 19 8 125 8 ratios and show negative ta nb and ti anomalies and positive sr and pb anomalies the caotan gneisses at 2 48 ga and the houjiacun ttg gneisses at 2 31 ga have low mg 0 14 0 45 low cr the geochronology of the dengfeng complex in the dengfeng area and the taihua complex in the lushan xiong er and xiaoqinling areas reveals at least four magmatic episodes in the southern segment of the tnco from the late mesoarchean to early paleoproterozoic 2 85 2 72 ga 2 57 2 48 ga 2 34 2 30 ga and 2 20 2 07 ga the rocks of the two early episodes are dominantly of juvenile compositions with mostly positive whole rock nd t and zircon hf t values suggesting two episodes of crustal growth formed in a subduction tectonic setting the magmatic rocks of the third episode consist of both the juvenile and pre existing crustal materials with variable whole rock nd t and zircon hf t values which were generated in a subduction zone during the initial assembly of the ncc within the columbia supercontinent cycle the final episode of magmatism lacks juvenile materials with whole rock nd t and zircon hf t values being consistently negative these may have resulted from the orogenic collapse the episodic continental growth recorded in the southern segment of the tnco was caused by subduction and consequent orogeny consistent with global supercontinent cycles within the late archean and early paleoproterozoic

preliminary heat flow density data from tunisia and the pelagian sea heat flow density values at 78 sites in tunisia and the pelagian sea are derived from oil exploration wells bottom hole temperatures bht are systematically corrected for mud circulation cooling effects either by a horner technique when several temperature records are available at a given depth or by a statistical method based on the comparison of all bht with test temperatures dst that are representative of the actual formation temperatures thermal conductivities are estimated from detailed studies of stratigraphic and geophysical logs an inverse technique is used to estimate heat flow density for each borehole as well as interpolated temperatures at constant depths results are discussed with maps that include heat flow density data in neighbouring areas algeria and the strait of sicily the general trend corresponds remarkably to the recent structural evolution of the tunisian margin with high values in the pelagian sea and decreasing values toward the stable platform

the luanchuan mo w pb zn ag magmatic hydrothermal system in the east qinling metallogenic belt china constrains on metallogenesis from c h o s pb isotope compositions and rb sr isochron ages abstract the luanchuan mo w pb zn ag polymetallic ore district is located in the east qinling metallogenic belt on the southern margin of the north china craton two ore fields nannihu and yuku are recognized in the district and three types of deposits are identified from the two ore fields as follows 1 the 6 proximal porphyry skarn type mo w deposits occurring at the inner contact zone of the granite porphyries 2 the 3 middle skarn hydrothermal type zn deposits and 3 the 8 distal hydrothermal type pb zn ag deposits at the periphery of the porphyry we present c h o isotope compositions of hydrothermal quartz and calcite s pb isotope compositions of sulfide minerals and sphalerite rb sr isochron ages from the 17 deposits the geochemical and geochronological data from the two ore fields all show systematic temporal and spatial variation and primarily lead to the following inferences 1 the temperatures and salinities of the ore forming fluids decreased during mineralization the ore forming fluids gradually evolved from magmatic water to mixed magmatic meteoric water 2 the metallogenic components were primarily derived from igneous rocks with increasing proportions of the materials from the ore bearing rocks 3 the mineralization ages of these deposits are close 147 136 ma which correspond to the emplacement of the granite intrusions 4 the three types of deposits and the ore related late mesozoic intrusives constitute a unified magmatic hydrothermal mineralization system finally we also suggest exploration strategies for the luanchuan ore district

late neoarchean to early paleoproterozoic tectonic evolution of the southern north china craton evidence from geochemistry zircon geochronology and hf isotopes of felsic gneisses from the taihua complex abstract the archean paleoproterozoic taihua complex extending from east to west along the southern margin of the north china craton ncc is an ideal window to understand the tectonic evolution of the early earth here we present new data on petrology zircon geochronology whole rock geochemistry and isotopes of ttgs granitic gneisses and felsic leucosomes of migmatites from the taihua complex in the xiaoqinling area zircon la icp ms analyses of rocks yield the formation ages of 2564 2503 ma for ttgs 2481 2476 ma for felsic leucosomes and 2359 2334 ma for granitic gneisses respectively the zircon lu hf isotopes suggest that crustal growth occurred in the late neoarchean and crustal reworking occurred in the end of neoarchean and the early paleoproterozoic the ttg gneisses are characterized by high na2o k2o la yb sr y and low nb ta ratios and they were likely generated by partial melting of subducted juvenile oceanic crust with garnet or amphibole in residuals a mechanism similar to the slab melting model both the felsic leucosomes and granitic gneisses have high sio2 contents and various hf isotopic compositions and they probably were formed in an extensional setting attributing to partial melting as well as mixing of the preexisting ttg suite statistically we report a major transitional phase in the tectonic milieu of the southern ncc from compression to extension during the late neoarchean ca 2 57 2 42 ga the compressional tectonics can be attributed to amalgamation of micro continental blocks during the late neoarchean ca 2 57 2 5 ga as the leading period of crustal growth and associated multistage ttg magmatism in contrast the extensional phase occurred during the end of neoarchean ca 2 5 2 42 ga that may represent the end of cratonic stabilization period and formation of large amounts of k rich granitic rocks widespread high grade metamorphism and migmatites additionally the formation of a large amount of crust derived granites and mafic dykes during the early paleoproterozoic in southern ncc reflect another stage ca 2 36 2 24 ga of crustal extension which represents an episode of initial worldwide rifting events probably linking to the great oxygen event goe therefore the present study proposes a new profile on multi stage crustal growth reworking and craton stabilization during neoarchean paleoproterozoic period along the southern ncc and provides useful insights on complex and heterogeneous evolutionary processes of early earth

timing and genesis of the adakitic and shoshonitic intrusions in the laoniushan complex southern margin of the north china craton implications for post collisional magmatism associated with the qinling orogen abstract the nww striking qinling orogen formed in the triassic by collision between the north china and yangtze cratons triassic granitoid intrusions mostly middle to high k calc alkaline are widespread in this orogen but contemporaneous intrusions are rare in the southern margin of the north china craton an area commonly considered as the hinterland belt of the orogen in this paper we report zircon u pb ages elemental geochemistry and sr nd hf isotope data for the laoniushan granitoid complex that was emplaced in the southern margin of the north china craton zircon u pb dating shows that the complex was emplaced in the late triassic 228 1 to 215 4 ma indicating that it is part of the post collisional magmatism in the qinling orogen the complex consists of from early to late biotite monzogranite quartz diorite quartz monzonite and hornblende monzonite which span a wide compositional range e g sio2 55 9 70 6 wt k2o na2o 6 6 10 2 wt and mg of 24 to 54 the biotite monzogranite has high al2o3 15 5 17 4 wt sr 396 1398 ppm and ba 1284 3993 ppm contents and relatively high la yb mostly 14 30 and sr y mostly 40 97 ratios but low yb mostly 1 3 1 6 ppm and y mostly14 19 ppm contents features typical of adakitic rocks the quartz monzonite hornblende monzonite and quartz diorite have a shoshonitic affinity with k2o up to 5 58 wt and k2o na2o ratios averaging 1 4 the rocks are characterized by strong lree hree fractionation in chondrite normalized ree pattern without obvious eu anomalies and show enrichment in large ion lithophile elements but depletion in high field strength elements nb ta ti the biotite monzogranite 228 ma has initial 87sr 86sr ratios of 0 7061 to 0 7067 end t values of 9 2 to 12 6 and ehf t values of 9 0 to 15 1 whereas the shoshonitic granitoids mainly 217 215 ma have similar initial 87sr 86sr ratios 0 7065 to 0 7075 but more radiogenic end t 12 4 to 17 0 and ehf t 14 1 to 17 0 the sr nd hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions as partly confirmed by the widespread presence of early paleoproterozoic inherited zircons mafic microgranular enclaves mmes characterized by fine grained igneous textures and an abundance of acicular apatites are common in the laoniushan complex compared with the host rocks they have lower sio2 48 6 53 7 wt and higher mg 51 56 cr 122 393 ppm and ni 24 79 ppm but equivalent sr nd isotope compositions indicating that the mmes likely originated from an ancient enriched lithospheric mantle the abundance of mmes in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the laoniushan complex collectively it is suggested that the laoniushan complex was a product of post collisional magmatism related to lithospheric extension following slab break off formation of the adakitic and shoshonitic intrusions in the laoniushan complex indicates that the qinling orogen had evolved into a post collisional setting by about 230 210 ma

apatite fission track thermochronological constraints on the pattern of late mesozoic cenozoic uplift and exhumation of the qinling orogen central china abstract the qinling orogen of central china was formed by intracontinental collision between the north and south china blocks the orogen comprises several micro blocks bounded by sutures and faults and has undergone long term intracontinental deformation since the late triassic the micro blocks include the southern margin of the north china block s ncb the northern qinling belt nqb the southern qinling belt sqb and the northern margin of the south china block n scb under a uniform tectonic setting in late mesozoic cenozoic these micro blocks have been subjected to a range of deformation styles as demonstrated by their structural deformation history of magmatism and the development of sedimentary basins to investigate the differences among the micro blocks and to quantify their uplift and exhumation we obtained 45 rock samples from eight mesozoic granites in these micro blocks and conducted apatite fission track aft thermochronological modeling the results reveal that the qinling orogen underwent four distinct stages of rapid cooling histories during the late mesozoic cenozoic and showed variation in uplift and exhumation whereby the intracontinental deformation started in the south the n scb and propagated to the north s ncb in the first stage during the late jurassic early cretaceous ca 160 120 ma rock cooling occurred mainly in the n scb attributed to the clockwise rotation and northward subduction of the south china block beneath the qinling orogen in the second stage compression and extension related uplift was initiated during the late early cretaceous early late cretaceous ca 120 90 ma in the sqb consistent with the southward subduction of the north china block and broadly extensional deformation in the eastern china continent in the third stage a gentle regional scale cooling event that occurred during the latest cretaceous paleocene ca 90 50 ma started in the nqb and became widespread in the qinling orogen this regional scale uplift and exhumation event was probably a response to the opposite polarity subduction beneath the qinling orogen combined with the effects of subduction of the pacific plate from the southeast the fourth stage eocene oligocene ca 50 20 ma was marked by another phase of rapid cooling in the s ncb the nqb and the nw sqb and is interpreted as being cause by the eastward tectonic escape of tibetan plateau related to india asia collision furthermore the record of variable timings and rates of cooling of these micro blocks together with regional structural analysis indicates that the late mesozoic cenozoic intracontinental deformation in the qinling orogen was characterized by a spatiotemporally variable and propagating style uplift and exhumation of the micro blocks and the predominant deformation was through displacement across various boundary sutures and faults

petrogenesis and geochronology of the neoarchean paleoproterozoic granitoid and monzonitic gneisses in the taihua complex episodic magmatism of the southwestern trans north china orogen abstract the taihua metamorphic complex exposes in the southern trans north china orogen tnco and records at least three episodes of magmatism the shanxian ttg gneisses obtained at 2 54 2 48 ga have high sio 2 variable mg with high la yb n and sr y ratios 15 08 93 26 with average of 37 31 and 7 33 115 05 with average of 49 59 respectively they show negative nb and ta but positive zr and hf anomalies with low nb ta and gd yb and high zr hf and zr sm ratios 4 97 18 8 1 92 6 37 23 71 50 26 and 29 18 75 23 respectively and have positive e hf t values 1 7 to 7 9 and e nd t values 0 72 to 2 55 indicating that they were possibly produced by partial melting of lower crust derived from metasomatized lithospheric mantle with the residue of minor garnet the sihe granitic gneisses recorded at 2 35 2 30 ga are enriched in silica al 2 o 3 contents 13 59 15 33 k 2 o na 2 o ratios 1 13 1 7 defined as high al ttg they exhibit high sr y zr sm and zr hf ratios and low nb ta and gd yb ratios 44 71 83 09 47 79 62 58 36 05 37 43 12 04 16 36 and 2 95 3 68 respectively with negative eu anomaly combined with hf and nd isotopes 2 5 to 4 7 and 0 74 to 0 36 the sihe granitic gneiss was possibly generated from partial melting of lower crust with minor ancient material contributions leaving residual amphibole and minor garnet in the source the muce monzonitic gneisses emplaced at 2 17 2 16 ga have high mg ni and cr contents constant sr y and la yb n 42 39 50 33 19 8 41 4 33 6 74 2 31 32 34 14 and 15 32 16 7 respectively with relatively low and constant dy yb ratio 1 82 1 85 together with hf and nd isotopes 6 5 to 0 9 and 2 07 to 2 86 the muce monzonitic gneisses might be derived from partial melting of neoarchean pre existing crustal materials possibly in an arc setting it is therefore found that four episodes of crustal growth and or reworking in the southern segment of the tnco have occurred at 2 85 2 72 ga 2 57 2 48 ga 2 35 2 30 ga and 2 2 2 0 ga respectively likely to connect with the subduction collision between the eastern and western blocks along the tnco in the north china craton

triassic mineralization with cretaceous overprint in the dahu au mo deposit xiaoqinling gold province constraints from shrimp monazite u th pb geochronology abstract the xiaoqinling terrane in central china is the second largest gold producing area in china previous application of age constraints has yielded ages for the gold mineralization ranging from paleoproterozoic through triassic indosinian to jurassic and cretaceous yanshanian shrimp u th pb dating of hydrothermal monazite in a mo mineralized quartz vein from the dahu au mo deposit in the northern xiaoqinling terrane identifies two mineralization episodes hydrothermal monazite intergrown with molybdenite yields an initial precipitation age of 216 5 ma which is identical to but more precise than the molybdenite re os isochron age of 218 41 ma a younger generation of monazite is distinguished by data falling on a mixing array it is inferred that the younger monazite was formed at the expense of the older ones during the yanshanian probably during a single event that occurred at 125 ma combining these results with available geochronological data and geological evidence we conclude that molybdenum mineralization accompanied by monazite deposition took place in the indosinian followed by a yanshanian tectono hydrothermal event that resulted in large scale gold mineralization in the xiaoqinling terrane our observation demonstrates that monazite is sensitive to hydrothermal overprint and thus is useful for dating fluid infiltration event

adsorption of organic compounds on carbonate minerals 3 influence on dissolution rates abstract this is the third in a series of papers to investigate the role of organic compounds on wettability porosity and permeability of carbonate rocks these are important reservoir characteristics that influence the performance of petroleum reservoirs this paper reports dissolution studies to address diagenetic effects on carbonate porosity and permeability comparative dissolution measurements were performed to assess the influence of adsorbed organic material on the reactivity of calcite and dolomite in the geologic environment organic compounds that adsorb strongly on carbonate minerals fatty acids and carboxylated polymers were found to dramatically inhibit dissolution while weak adsorbates and nonadsorbates showed little or no effect on the dissolution rates experiments were performed at 20 50 and 80 c to examine the role of organic adsorbates at reservoir temperatures and the strong adsorbates inhibited dissolution at all temperatures experiments from various initial ph s confirmed that strong adsorption is an ionic interaction and demonstrated that the inhibition of dissolution is limited to ph s above 4 5 5 0

abiotic interactions of natural dissolved organic matter and carbonate aquifer rock abstract abiotic interactions between natural dissolved organic matter ndom and carbonate aquifer rock may be controlling factors of biogeochemical processes and contaminant fate in carbonate aquifer systems the importance and effects of these interactions were examined using batch adsorption experiments of soil ndom and representative carbonate sorbents from the floridan aquifer adsorption of ndom carbon to aquifer rocks was well described using a modified linear model and was mostly reversible significant adsorption was observed at higher ndom concentrations while the release of indigenous organic matter from the rocks occurred at lower concentrations longer interaction periods led to more adsorption indicating that adsorption equilibrium was not achieved for relatively pure carbonate rock samples sorbent surface area was found to be the most important controlling factor of adsorption whereas the presence of indigenous organic matter and subdominant mineral phases were more important when they occurred preferential adsorption of a high over low molecular weight and humic over fulvic components of ndom onto carbonate sorbents was detected using liquid size exclusion chromatography and excitation emission fluorometry respectively the presence of ndom inhibited mineral dissolution though this inhibition was not proportional to ndom concentration as surface area and mineralogy of carbonate sorbents played additional roles though the ndom carbonate rock adsorption mechanism could not be completely determined due to the heterogeneity and complexity of ndom and sorbent surfaces it is speculated that both rapid and weak outer sphere bonding and stronger but slower hydrophobic interaction occur these results have important implications for groundwater quality and hydrogeologic projects such as aquifer storage and recovery

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

a synthetic approach integrating surface and subsurface data for prospecting deep aquifers the southeast tunisia the southeast tunisia has remarkable thermal springs that have been used for bathing since many years currently studies are being carried out to investigate the possible use of the hot water for heating buildings and for greenhouses springs with discharge temperatures between 26 8 and 58 c exist in the area the flow rates range between 7 and 66 l s with total dissolved solids tds varying between 2 020 and 4 030 mg l both geological hydrogeological setting and the similarity in chemical characteristics between the zarat spring and nearby water wells suggest that the hot water from this spring may be related to the senonian aquifer however the hydrogeothermal approach shows that the depth of the reservoir that supplies the zarat spring is greater than that of the senonian aquifer in fact geothermometry approach indicates that fluids emerging from the lower cretaceous sandstones reach temperatures of approximately 78 c at depth while the fluid temperature from the nearby water wells is 32 c through the integration of various types of data we found that the thermal water of southeast tunisia is of meteoric origin this water infiltrates deeply into the lower cretaceous sandstones and reaches a high temperature before rising upwards to supply the hot springs and well discharge zones it appears that the upward movement of hot water from the deep aquifers to shallow ones is probably due to the abundant fractures in the area

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

geochemistry isotope systematics and petrogenesis of the volcanic rocks in the zhongtiao mountain an alternative interpretation for the evolution of the southern margin of the north china craton abstract the xiong er volcanic rocks constitute a large paleo mesoproterozoic volcanic belt along the southern margin of the north china craton which are composed primarily of basaltic andesites and andesites with minor dacites and dacitic rhyolites the basaltic andesites and andesites from the xiong er volcanic rocks in the zhongtiao mountain show consistent nd t la nb and th nb values irrespectively of sio 2 which preclude significant crustal contamination during ascent both of these volcanic rocks share similar incompatible ratios e g la sm zr nb la nb indicating that the basaltic andesites and andesites originated from the same source the basaltic andesites are characterized by high mg number 45 55 precluding the possibility of their derivation from the melting of the lower crust variable ti eu zr sm and nb la ratios for the basaltic andesites with higher partial melting degree suggest that amphiboles remained as residues in the magma source indicating that the xiong er volcanic rocks were derived from hydrous magma non radiogenic nd isotopes for the xiong er volcanic rocks are inherited from a mantle source which had been enriched by the subduction related crustal recycling during archean to paleoproterozoic time basaltic andesites show hfse enrichments especially nb 4 7 ppm and high fe ti contents comparable with nb enriched basalts suggesting that the xiong er volcanic rocks were derived from a metasomatized mantle source similar to that of nb enriched basalts therefore the mantle source of the xiong er volcanic rocks in the zhongtiao mountain has been enriched in fe ti oxides and hfse by equilibrium reactions with the slab melts during late archean and paleoproterozoic subduction processes as evidenced by nd isotopes in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative anomalies on the nb ta ti similar to arc related volcanic rocks produced by the hydrous melting of the metasomatized mantle wedge in the paleo mesoproterozoic the xiong er volcanic rocks in the zhongtiao mountain were produced by the slab dehydration induced melting of an existing metasomatized mantle source and the fluids from the slab dehydration introduced significant lile and lree to the source masking its inherent hfse enriched characteristics the arc related characteristics of the xiong er volcanic rocks in the zhongtiao mountain suggest the xiong er volcanic belt constructs a subduction zone along the southern margin of the north china craton in the paleo mesoproterozoic implying that the craton may have recorded the outbuilding history of the columbia supercontinent during paleo mesoproterozoic time

zircon u pb dating and hf isotope analysis on the taihua complex constraints on the formation and evolution of the trans north china orogen abstract precise age determination and source tracing of the granitic and pegmatitic gneisses of the taihua complex in the xiaoqinling area are important to address the debates on the timing and processes of the amalgamation of the western and eastern blocks along the trans north china orogen this paper conducted zircon dating of metamorphic rocks from the xiaoqinling area the results demonstrate that the collision between the western and eastern blocks occurred in the paleoproterozoic laser ablation inductively coupled plasma mass spectrometry la icpms zircon uranium lead u pb analyses yielded consistent results the early paleoproterozoic the first period age of 2346 28 ma was determined for granitic gneiss in the taihua complex and 2328 14 ma for the xiaohe granite pluton that intruded into the granitic gneiss the gneissose pegmatitic granite and granitic veins that intruded into the granitic gneiss yielded la icp ms zircon ages of 1881 24 and 1866 19 ma respectively these paleoproterozoic ages strongly indicate that the ocean between the eastern and western blocks were completely subducted at 1 85 ga the hf t values of the zircons from the granitic gneiss can be divided into a positive group 0 44 to 3 77 and a negative group 3 11 to 1 27 the two stage hafnium hf model ages tdm2 hf corresponding to the positive values are between 2672 and 2887 ma the hf t values of the zircons from the xiaohe granite range from 2 49 to 2 58 with the hf isotope model ages ranging from 2742 to 3022 ma thus the xiaohe granite could have resulted from the partial melting of the late archean lower crust caused by subduction and the presence of juvenile mantle material the primary magma of the granitic gneiss of the paleoproterozoic taihua complex was derived from the differentiation of the depleted late archean mantle source with a small portion derived from the remelting of the subducted lower crust

gold metallogeny associated with craton destruction a geophysical perspective from the north china craton abstract currently ranking as the largest producer of gold in the world china s gold reserves are spread over 200 major gold deposits and several minor deposits a large part of these belong to the late mesozoic gold deposits in the north china craton ncc that occur along craton margins as well as within the cratonic interior in reactivated paleo sutures and show a close spatio temporal relationship with zones of lithospheric thinning and craton destruction here we integrate and evaluate geophysical information from the ncc through an analysis of receiver function and tomography that suggest mantle upwelling accompanied by lower crustal or lithospheric delamination our results identify that the major gold belts in the ncc are largely located above zones of mantle upwelling and craton destruction the faults and paleo sutures provided the pathways for migration of ore bearing fluids with the granitoids offering favorable conditions for gold deposition

early mesozoic mo mineralization in the qinling orogen an overview abstract as one of the most important mo provinces in the world the qinling orogen is host to mainly late mesozoic late jurassic early cretaceous porphyry mo systems recently additional early mesozoic mainly triassic plus minor early jurassic mo deposits have been identified which occur as fault controlled quartz veins or as carbonatite veins and as such they are fundamentally different from the commonly observed porphyry systems furthermore early mesozoic porphyry systems are also present but they are different from those of late mesozoic age thus early mesozoic mo systems not only offer a new and comprehensive view of the mo metallogenesis but also provide unique insight into the tectonic evolution of the qinling orogen taking into consideration the role of mineral deposits as ideal probes of the geodynamic evolution the known early mesozoic mo deposits in qinling can be classified into three types based on their geological and geochemical features porphyry carbonatite and orogenic systems porphyry mo systems including porphyry porphyry skarn and intrusion related veins are spatially and genetically associated with granitic porphyries they display typical porphyry type alterations and are formed by magmatic water carbonatites are considered as mantle derived igneous rocks and mo mineralization is associated with magmatic fluids orogenic mo systems occur as fault controlled quartz lodes and the ore forming fluids are medium high temperature co2 rich metamorphic fluids spatially early mesozoic porphyry mo systems are concentrated in the western and middle part of the qinling orogen whereas carbonatite veins and orogenic mo systems are located in the northeastern part temporally orogenic mo deposits were the earliest mainly between 220 and 250 ma followed by carbonatite veins mainly between 205 and 225 ma and porphyry mo systems mainly between 190 and 205 ma with some exceptions there is generally a trend of decreasing deposit ages toward the western part of the orogen detailed comparison reveals that the early mesozoic porphyry mo systems in the qinling orogen are different from the late mesozoic ones in terms of their economic importance spatial distribution ore causative intrusions hydrothermal alteration and the ore forming fluids to explain the above geological and geochemical features the triassic qinling is considered as an active continental margin caused by the northward subduction of the mian lue oceanic plate a transition from continental arc to back arc basin is suggested for the formation of triassic orogenic and carbonatite vein mo deposits whereas continental arc is host to the early mesozoic porphyry mo systems

two episodes of ree mineralization in the qinling orogenic belt central china in situ u th pb dating of bastnasite and monazite recent exploration revealed a number of rare earth element ree deposits that are distributed along the qinling orogenic belt central china these deposits have an estimated total reserve of about 2 mt ree2o3 thus making this belt a world class ree metallogenic province understanding the metallogenesis of the belt requires direct dating of ree minerals in this study la icp ms u th pb dating on bastnasite and monazite from the huangshuian taipingzhen and miaoya deposits in different units of the belt was used to precisely determine the timing of the ree mineralization the huangshuian deposit in the north is a carbonatite related mo ree deposit in which the ree minerals are closely associated with molybdenite after correction for common pb and excessed 206pb decayed from 230th a weighted average 206pb 238u age of 207 4 ma n 17 mswd 1 9 is obtained for bastnasite grains from this deposit such an age is slightly younger than that of the final collision peak at 230 220 ma of the qinling orogenic belt thus indicating that the mo ree mineralization is likely related to a post collisional extension setting the taipingzhen ree deposit in the middle contains sheet like ore bodies composed of veins where bastnasite the dominant ree mineral is closely associated with quartz fluorite and barite in situ bastnasite u th pb dating shows that the ree mineralization in this deposit has formed at 421 7 ma n 17 mswd 1 5 synchronous with extension related magmatism in the region the miaoya deposit in the south is the largest one in the belt and it is essentially a ree mineralized syenite carbonatite complex in this deposit the monazite grains are closely associated with major minerals of the syenites or carbonatites e g k feldspar or calcite but commonly exhibit complex internal textures different domains of monazite yield two groups of u pb ages at 414 11 ma n 5 mswd 0 91 and 231 2 ma n 21 mswd 3 1 whereas the bastnasite has an age of 206 4 ma n 14 mswd 1 5 the early age of 414 ma is obtained from homogenous monazite grains and in good agreement with zircon u pb ages of the miaoya syenite carbonatite complex and thus is considered to represent the timing of the major ree mineralization in the deposit the younger ages of 231 206 ma are obtained from monazite grains with complex internal textures and bastnasite in late veinlets thus recording secondary consecutive ree remobilization events likely related to the compression process during formation of the qinling orogenic belt our new u th pb ages in combination with previously geochronological data demonstrate that there are two episodes of ree mineralization at 440 410 ma and 220 200 ma in the qinling orogenic belt

carbonate dissolution in the guts of benthic deposit feeders a numerical model abstract we present a numerical model to quantify calcite dissolution in the guts of deposit feeding invertebrates deposit feeder guts were modeled as constantly stirred reactors cstrs following terminology from digestion theory saturation state and dissolution of calcium carbonate were calculated from changes in total dissolved carbon dioxide and alkalinity resulting from sediment passage through the digestive tract while accounting for dissolution of calcite and respiration of organic carbon typical dissolution rates for a gut volume of 1 ml ranged between 0 5 4 mg calcite d 1 sensitivity analysis revealed gut ph sediment organic matter om content and om reactivity to be the critical parameters determining calcite dissolution rate carbonate dissolution rate was inversely related to gut ph however calcite dissolution was found to be possible even at alkaline gut ph due to respiration by intestinal microbes the kinetics of calcite dissolution had only marginal influence on daily calcite dissolution rates varying the calcite dissolution rate constant by six orders of magnitude affected calcite dissolution rates by less than a factor of 10 calcite dissolution rates were calculated for 4 different hydrographic regimes that differed in their content of sedimentary calcite and om and furthermore in their om reactivity highest dissolution rates were calculated for the shallow water setting where relatively high om content facilitated high microbial respiration rates depressing gut ph however dissolution rates for the deep sea setting were only slightly lower due to greatly elevated ingestion rates resulting from low om content as a consequence of much higher faunal abundances shallow water benthos is likely to contribute the vast majority of gut mediated carbonate dissolution nevertheless the fraction of sedimentary calcite that dissolves during one gut passage is probably too small to be observable by simple gravimetric analysis this may explain the notable scarcity of evidence for gut mediated carbonate dissolution in the literature to date assuming depth dependent calcite dissolution rates and deposit feeder abundances we estimate gut mediated carbonate dissolution to contribute approximately 5 of the annual global sedimentary carbonate dissolution rate which corresponds to an average calcite dissolution rate of approximately 0 5 mg m 2 d 1 for the entire ocean floor

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

origin and assembly of the tethyside orogenic collage at the expense of gondwana land abstract the tethysides are a superorogenic complex flanking the eurasian continent to the south and consisting of the cimmerides and alpides products of palaeo and neo tethys respectively we here review their evolution mainly on the basis of new maps showing the distribution of sutures magmatic rocks certain palaeobiogeographically and palaeoclimatologically significant taxa and facies and fragments of pan african 900 450 ma orogenic system forming the basement of many tethyside blocks these are supplemented by palaeomagnetic data reported in the literature a fundamental tenet of this paper is that major sutures which contain ophiolite fragments represent tectonic sections between continental blocks where oceanic crust has been subducted palaeo tethys came into existence largely in late carboniferous time coevally it began to be consumed by both internal and peripheral subduction zones which continued into the permian some of these had been inherited from pre tethyan times in the later permian rifting subparallel with the northern margin of gondwana land began between the zagros and malaysia separating a cimmerian continent from n gondwana land and thus heralding the opening of neo tethys and other smaller oceans that were back arc basins of palaeo tethys this rifting possibly also extended farther west into crete and mainland greece however the north china block yangtze block huanan block the eastern moity of the qangtang block north tibet and annamia all originally pieces of the end proterozoic early palaeozoic gondwana land had already separated from it in pre late carboniferous times possibly during the devonian all of these blocks and the cimmerian continent were characterized by cathaysian floral elements in late palaeozoic time palaeomagnetic and palaeontological data showing the original gondwana land affinity of these continental blocks are supplemented by correlating late proterozoic early palaeozoic pan african sutures orogenic belts and sedimentary basin fragments across tethyside sutures late permian foraminiferal provinces are related to this palaeogeographical interpretation by triassic times most cimmeride subduction zones were already in existence the cimmerian continent accelerated its separation from gondwana land and locally in the late permian began disintegrating internally along the waser rushan pshart banggong co nu jiang mandalay ocean by late triassic time all of the chinese blocks except lhasa and annamia had collided with each other and with laurasia the resulting enormous orogenic collage had a soft cushion between itself and laurasia in the form of the enormous accretionary complex of the songpan ganzi this connection enabled laurasian land vertebrates to reach south east asia by late triassic time in late triassic to middle jurassic times most major cimmeride collisions were completed widespread aridity in central asia occurred in late jurassic time probably in the rain shadow of the newly formed cimmeride mountain wall neo tethyan subduction systems formed along the s margin of the cimmerides or within neo tethyan oceanic lithosphere during the jurassic most if not all were north or east dipping they continued the northerly migration of the tethyside blocks evolution of the tethysides influenced the distribution of marine and terrestrial organisms and affected sea level changes and patterns of atmospheric circulation during much of the mesozoic and cainozoic it is likely to have reflected the surface expression of a persistent trend in the large scale convective circulation in the mantle that continuously transported material northward into the tethyan domain

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

metallogeny and craton destruction records from the north china craton abstract the link between metallogeny and craton destruction in the north china craton ncc remains poorly understood particularly the mechanisms within the interior of the craton in this overview we summarize the major stages in the history of formation and evolution of the ncc the spatio temporal distribution and types of major ore species as well as mantle contribution to the metallogeny in an attempt to evaluate the geodynamic settings of metallogeny and the mechanisms of formation of the ore deposits the early precambrian history of the ncc witnessed the amalgamation of micro blocks and construction of the fundamental tectonic architecture of the craton by 2 5 ga the boundaries of these micro blocks and the margins of the ncc remained as weak zones and were the principal locales along which inhomogeneous destruction of the craton occurred during later tectonothermal events these zones record the formation of orogeny related gold copper iron and titanium during the early to middle paleoproterozoic with ages ranging from 2 5 to 1 8 ma the early ordovician kimberlite and diamond mineralization at ca 480 ma the late carboniferous and early to middle permian calc alkaline i type granitoids and gold deposits of 324 300 ma and the triassic alkaline rocks and gold silver polymetallic deposits occurring along these zones and the margins of the blocks correlate with rising mantle plume southward subduction of the siberian plate and northward subduction of the yangtze plate respectively the voluminous jurassic granitoids and cretaceous intrusives carrying gold molybdenum copper lead and zinc deposits are also localized along the weak zones and block margins the concentration of most of these deposits in the eastern part of the ncc invokes correlation with lithosphere thinning associated with the westward subduction of the pacific plate although magmatism and mineralization have been recorded along the margins and few places within the interior of the ncc in the jurassic their peak occurred in the cretaceous in the eastern part of the ncc marking large scale destruction of the craton at this time the junctions of the boundaries between the micro continental blocks are characterized by extensive inhomogeneous thinning we propose that these junctions are probably for future mineral exploration targeting in the ncc

behaviour of major elements and some trace elements li rb cs sr fe mn w f in deep hot waters from granitic areas abstract analyses of selected hot springs in more than sixty areas in granites from europe are presented concentrations of major elements and of some trace elements li rb cs sr fe mn w f in high ph waters are not significantly affected by processes during uprise from the deep reservoir to the surface re equilibrations mixing with surficial waters normalized to k or na concentrations of all other elements are related to the aquifer temperature the knowledge of aquifer temperature and total electric charge of mobile elements cl s possibly f allows us to predict both major elements within 50 and trace elements within a factor 2 or 3 concentrations in alkaline waters from granites

early yellowstone hotspot magmatism and gold metallogeny abstract high grade epithermal gold deposits in the northern great basin have long been associated with regional miocene basaltic to rhyolitic volcanism previous models for the low sulfidation epithermal gold ores in this region have generally portrayed the bimodal magmas as a source of heat to drive large scale convection of meteoritic water that leached gold from crustal sources and deposited it in hydrothermal vein systems or required that the gold evolve from fractionated silicic magmas new data of the present study indicate a more direct genetic link to the plume related basaltic magmas of the region laser 40ar 39ar incremental heating plateau ages for single crystals of adularia from several of these low sulfidation epithermal gold deposits range from 16 6 ma to 15 5 ma adularia from the jumbo deposit yields three concordant plateau ages with a combined statistical result of 16 54 0 04 ma 95 confidence level mswd 0 23 plateau ages for adularia from other deposits in the region and from gold bearing veins in the owyhee mountains of southwestern idaho yield similar ages up to 16 5 ma however some veins are as young as ca 15 5 ma and the grain to grain ages for a given sample can vary by up to ca 0 5 ma observed variations in age among the adularia crystals of a given rock sample indicate varying amounts of extraneous argon and also loss of radiogenic 40ar among the population of grains for a particular sample the single crystal results are interpreted to indicate a 16 5 15 5 ma interval for formation of gold bearing adularia veins in the region the initiation and duration of this gold forming event appears contemporaneous within uncertainties with the basaltic volcanism at the steens mountain section and an ensuing one million year episode of basaltic volcanism from multiple centers in the region brueseke et al 2007 trace amounts of lead are alloyed with gold in the deposits studied the isotopic compositions of this lead are not compatible with regional crustal units that host the gold ores or the silicic igneous lithologies of the region but have the same lead isotopic composition as basalts of the earliest yellowstone plume represented by the earliest lavas of the columbia river basalt province the steens basalts and stonyford volcanic complex hanan et al 2008 we propose that the gold studied and its traces of alloyed lead were derived together from the mantle released from basaltic magma chambers of the province and carried by low density fluids into shallow geothermal systems during the earliest stages of yellowstone hotspot magmatism

geochronology and geochemistry of the late paleoproterozoic aluminous a type granite in the xiaoqinling area along the southern margin of the north china craton petrogenesis and tectonic implications abstract the occurrence of extensional related a type granites with a high k nature in some early precambrian blocks hints a possible link with the orogeny and may imply the ending of the orogenic processes and the beginning of craton stabilization the newly recognized late paleoproterozoic a type granite the guijiayu pluton composed of monzogranites in the xiaoqinling area of the southern margin of the north china craton ncc is a promising locus to investigate the late paleoproterozoic tectonic evolution of the ncc la icp ms zircon u pb dating shows that the guijiayu pluton was emplaced at 1 80 ga petrologically the guijiayu granites contain perthite annite and calcic amphibole but are lack of alkali mafic minerals geochemically all the rocks are enriched in silicon and total alkali and depleted in mgo cao and p2o5 with high feot mgo tio2 mgo and 10 000 ga al ratios and high hfses i e zr nb ce y concentrations as well as negative eu sr p and ti anomalies they are also characterized by high melting temperatures and metaluminous to weakly peraluminous natures taken together the guijiayu granites show an affinity to aluminous a type granite their geochemical characteristics e g obviously negative eu and sr anomalies along with the low zircon ehf t values 13 9 to 7 0 and whole rock end t values 5 81 to 5 65 indicate that the guijiayu aluminous a type granite was derived from partial melting of the crustal calc alkaline granitoids dominated by the granodiorite of the taihua group in the study area combined with the regional data especially for the identification of the clockwise p t paths of paleoproterozoic metamorphism in the southern margin of the ncc even coeval granites and regional retrograde metamorphism in other areas in the ncc it is most likely that the peak of continent continent collision had finished in the study area at least before 1 80 ga and that the generation of the guijiayu aluminous a type granite was related to the underplating of mafic magmas in a post collisional regime

formation and tectonic evolution of the khondalite series at the southern margin of the north china craton geochronological constraints from a 1 85 ga mo deposit in the xiong ershan area abstract the taihua complex is an important metamorphic rock suite at the southern margin of the trans north china orogen and hosts important mineral deposits its protolith and metamorphic ages are still controversial the 1 85 ga longmendian mo deposit in the xiong ershan is hosted by the khondalite series of the duangou formation taihua complex three kinds of rocks are collected for shrimp cameca u pb dating including the meta sedimentary rock that occurred as wallrock the mo mineralized meta gabbro that intruded the meta sedimentary rock and the leucosome that cut both the meta sedimentary rock and the meta gabbro zircon u pb analyses reveal that the precursor of the meta sedimentary rock was crystallized between 2200 4 and 2742 18 ma with most before 2500 ma whereas the protolith of the meta gabbro was formed at 2178 6 ma anatexis zircons in the leucosome yield a weighted mean age of 1943 8 ma that is indistinguishable with the metamorphic age of the meta gabbro 1952 4 ma in the intensively altered meta gabbro hydrothermal titanites were formed by at least two pulses of crystallization at 1940 7 ma and 1916 9 ma respectively the new data reveal that the khondalite series of the duangou formation were formed between 2200 ma and 2178 ma the results are inconsistent with previous subdivision of the taihua complex into the upper taihua and lower taihua subgroup instead they fit well with the tripartitite divison into the beizi group 3 0 2 55 ga the dangzehe group 2 55 2 3 ga and the shuidigou group 2 3 2 1 ga compiling zircon u pb ages indicate that in the trans north china orogen the 1 95 ga and 1 85 ga metamorphic events are widespread and prominent

a possible model for the lithospheric thinning of north china craton evidence from the yanshanian jura cretaceous magmatism and tectonism it is well known that the north china craton was largely formed in the archean and was reactivated and transformed during the jura cretaceous yanshanian time into an orogenic belt which is believed to be related to the lithospheric thinning recent debate is centered on the mechanisms and processes of the lithospheric thinning there are two prevailing models for the lithosphere thinning 1 thermal erosion or and chemical metasomatism allowed the lower part of the lithospheric mantle to be transformed into asthenosphere 2 delamination of the lithospheric mantle and perhaps also the lowermost crust in this paper we attempt to explain how the buoyant cratonic lithosphere may be transformed into a denser one allowing delamination to take place on the basis of field observation tectonic analysis and petrologic data on igneous rocks formed during the yanshanian we recognize four episodes of contractional deformation that resulted in significant crustal shortening and vertical thickening the counter clockwise pressure temperature time path of the tectonomagmatic events suggests that the underplating basaltic magma may have heated and weakened the existing cold and strong crust this crustal change in rheology may have facilitated the contractional deformation and crustal thickening petrologic data of the contemporary igneous rocks and the lower crustal xenoliths suggest that the crust had reached 50 65 km in thickness it suggests that input of large amount of asthenosphere derived mafic magmas is required to cause crustal melting thus a large amount of eclogite may be formed at the lowermost crust following the transient thickening events the dense eclogite may trigger the lithosphere delamination

the geothermal gradient map of central tunisia comparison with structural gravimetric and petroleum data abstract five hundred and fifty temperature values initially measured as either bottom hole temperatures bht or drill stem tests dst from 98 selected petroleum exploration wells form the basis of a geothermal gradient map of central tunisia a global statistical method was employed to correct the bht measurements using the dst as references the geothermal gradient ranges from 23 to 49 c km comparison of the geothermal gradient with structural gravimetric and petroleum data indicates that 1 1 the general trend of the geothermal gradient curves reflects the main structural directions of the region 2 2 zones of low and high geothermal gradient are correlated with zones of negative and positive bouguer anomalies and 3 3 the five most important oil fields of central tunisia are located near the geothermal gradient curve of 40 c km such associations could have practical importance in petroleum exploration but their significance must first be established through further investigation and additional data

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

age and geochemistry of the early mesoproterozoic a type granites in the southern margin of the north china craton constraints on their petrogenesis and tectonic implications abstract a type granites are a spectrum of especial felsic rocks that are produced commonly within an extensional environment they are rare before middle paleoproterozoic but present abundantly since the late paleoproterozoic probably indicating a causal change of tectonics and geodynamic mechanism in the continental evolution of the earth an early mesoproterozoic a type granite belt was recognized in the southern margin of the north china craton ncc in recent decades the occurrence of this type of rocks indicates a possible spatial temporal link between the tectonic evolution of the ncc and the breakup of the columbia supercontinent during the mesoproterozoic the zhangjiaping granitic pluton is located in the southern margin of the ncc and one part of the a type granite belt it can be divided into three zones according to their textural and compositional differences of the rocks with a gradually increasing degree of evolution inwards wall zone intermediate zone and core zone la icp ms zircon u pb dating shows that it was emplaced at ca 1 53 ga petrologically the zhangjiaping granites contain perthite and calcic amphibole but are lack of alkali mafic minerals geochemically all the zhangjiaping granitic rocks show an affinity to fractionated aluminous a type granites with enrichment in silicon and total alkali and depletion in mgo cao and p2o5 with negative eu sr and ti anomalies as well as high feot mgo tio2 mgo and ga al ratios and high hfses i e zr nb ce y concentrations such signatures along with their low ehf t values 12 5 to 4 0 of all the granites from the zhangjiaping pluton obviously indicate that the zhangjiaping aluminous a type granites were derived from partial melting of the crustal calc alkaline granitoids i e the granodiorites of the taihua complex in the study area and experienced fractional crystallization during magmatic evolution their generation would be related to the underplating of mafic magmas in an extensional regime integrated with regional data the zhangjiaping aluminous a type granites were the products of anorogenic magmatism likely corresponding to the breakup of the columbia supercontinent

shrimp and la icp ms zircon geochronology of the xiong er volcanic rocks implications for the paleo mesoproterozoic evolution of the southern margin of the north china craton the paleo mesoproterozoic xiong er volcanic rocks along the southern margin of the north china craton are lithologically and geochemically similar to those formed in subduction related continental margin volcanic arcs the volcanic rocks are primarily composed of basaltic andesites and andesites with minor dacites and dacitic rhyolites traditionally the xiong er volcanic rocks have been divided from lower to upper into the xushan jidanping and majiahe formations but the ages of volcanic rocks in these formations have not been well constrained which has hindered further understanding the tectonic significance of the xiong er volcanic belt at the southern margin of the north china craton shrimp and la icp ms u pb zircon analyses combined with cathodeluminescence cl images have enabled resolution of xenocrystic and magmatic zircons that can be directed toward determination of the ages of the xiong er volcanic rocks shrimp and la icp ms u pb analyses on magmatic zircons from two basaltic andesite samples one dacite sample and one rhyolite sample of the xushan formation known as the lowest sequence of the xiong er volcanic rocks indicate that the volcanic eruption of this formation occurred at 1 78 ga but most xenocrystic inherited zircons in these samples yielded 207pb 206pb ages ranging from 2 55 ga to 1 91 ga of three samples collected from the jidanping formation two rhyolite samples 05xe015 and 05xe100 yielded weighted mean 207pb 206pb ages of 1778 5 5 ma and 1751 14 ma respectively similar to the ages of the volcanic rocks in the xushan formation whereas one dacite sample 05xe066 gave a weighted mean 207 pb

groundwater evolution in the continental intercalaire aquifer of southern algeria and tunisia trace element and isotopic indicators abstract the geochemical processes taking place along an 800 km flow line in the non carbonate continental intercalaire aquifer ci aquifer in north africa are described using chemical major and trace element and isotopic indicators the aquifer is hydraulically continuous from the atlas mountains in algeria to the chotts of tunisia and the geochemical evidence corroborates this the highest discharge temperature is 73 c but silica geothermometry indicates a maximum temperature of 94 c at depth chloride concentrations increase from 200 to 800 mg l 1 and the br cl ratios confirm the dissolution of non marine evaporites or interstitial waters as the main source of salinity fluoride concentrations are low and are likely to be derived from rainfall recording oscillations in source radiocarbon ages except near outcrop are at or near detection limits and the 18o and 2h values indicate a cooler recharge regime with rainfall having lower primary evaporation than today this is shown by the fact that mean isotope ratios of ci waters are around 3 lighter than the present day weighted mean value for rain major ion ratios and most trace elements indicate that despite the complex structure and stratigraphy uniform evolution with continuous water rock interaction takes place along the flow lines which are only disturbed near the tunisian chotts by groundwater converging from additional flow lines the ageing of the water can also be followed by the smooth increase in several indicator elements such as li k and mn which are least affected by solubility controls similarly the influence of marine facies in the tunisian sector may be recognised by the changing mg ca and higher br cl as well as trace element indicators the groundwaters are oxidising up to 300 km from outcrop dissolved o2 has persisted for at least 20 ka and within this zone the concentrations of several elements forming oxy anions such as u and cr increase and no3 remains conservative beyond 300 km from outcrop the groundwaters are reducing and contain high fe concentrations the basin contains huge reserves of fresh brackish waters but these need careful development due to the limiting high salinity and scaling tendency resulting from the high temperatures and mineral super saturation caused during abstraction as well as high concentrations of some harmful elements such as cr in the oxidising section

regional variations in the chemical and helium carbon isotope composition of geothermal fluids across tunisia abstract tunisia has numerous thermo mineral springs previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology however little work has been done so far to study the isotopic composition of volatiles associated with these geothermal manifestations here we report on the results of an extensive survey of both natural hot springs and production wells across tunisia aimed at investigating the spatial distribution of thermal fluids geochemical characteristics and he c isotopic composition the chemistry of the analyzed samples highlights the heterogeneity of the water mineralization processes in tunisia as a consequence of the complex geological and tectonic setting of the country in terms of chemical composition we are able to conclude however that dissolution of halite and gypsum plays a key control on groundwater chemistry helium and carbon isotope systematics confirm the prevalently crustal origin of the volatiles interacting with the aquifer systems consistent with the absence of any recent magmatism most samples are characterized by crustal type helium 3 he 4 he in the range 0 02 ra 0 4 ra associated with a co 2 predominantly metamorphic in origin with the exception of the saharan platform where the carbon content is low and mostly organically derived in eastern tunisia however a few samples have he c isotope compositions which suggest at least partial mantle derivation of the dissolved gas phase the 3 he 4 he ratio reaches 2 4 ra corresponding to 30 of mantle derived helium at the ain garci site a co 2 rich mineral spring located some 30 km south of the city of zaghouan this mantle signature is consistent with the fact that the pelagian block to which eastern tunisia belongs has been deeply affected by extensional and transtensional tectonics since the opening of the tethys a process which is still ongoing in the sicily channel pantelleria rift as a whole however our results show that the italian mantle gas anomaly only marginally extends to northwestern africa

the shanggong gold deposit eastern qinling orogen china isotope geochemistry and implications for ore genesis abstract the shanggong au deposit in the xiong er terrane east qinling china has resources of about 30 ton au making it one of the largest orogenic mesothermal au deposits hosted in volcanic rocks of the mesoproterozoic xiong er group three stages of hydrothermal activity are recognized early middle and late of which two early and middle were ore producing and characterized by quartz pyrite and polymetallic sulfides respectively the third and late stage is represented by a carbonate quartz assemblage hydrogen oxygen and carbon isotope systematics of the shanggong deposit from a previous work suggest that the early stage fluids were derived from magmatic and or metamorphic devolatilization of sedimentary rocks at depth this is supported by new c s and published sr and pb isotopic data presented in this paper these new data 13c values ranging from 1 5 for early stage ankerite to 2 2 for late stage ankerite negative 34s values for sulfides from the middle stage 19 2 to 6 3 suggest a contribution from organic matter and that the ore fluid evolved from deeply sourced to shallowly sourced with those of the middle stage representing a mixture of these two fluid systems the comparison of the hydrogen oxygen carbon sulfur lead strontium isotope systematics between the shanggong deposit and the main lithologies in the xiong er terrane shows that neither these nor the underlying lower crust and mantle or combinations thereof could be considered as the source of ore fluids for the shanggong au deposit a likely source was a carbonaceous carbonate sandstone shale chert sequence in the underthrusted guandaokou and luanchuan groups exposed south of the xiong er terrane ar ar and rb sr isochron ages for mineral phases of the early middle and late stages together with geological field data constrain the timing of the hydrothermal activity and au metallogenesis at 242 10 167 7 and 112 7 ma respectively this metallogenesis and associated granitic magmatism can be related to the continental collision between the yangtze and north china cratons that resulted in the formation of the qinling orogen led to the different hydrothermal systems that were responsible for the three stages that formed the shanggong au deposit over a period of about 130 myrs

diverse and multistage mo au ag pb zn and cu deposits in the xiong er terrane east qinling from triassic cu mineralization abstract the xiong er terrane is one of the representative regions in east qinling orogenic belt various polymetallic deposits have been discovered in the xiong er terrane such as porphyry mo carbonatite hosted type mo quartz vein type mo breccia pipes type au and orogenic type au ag pb zn deposits indicating that diverse significant mineralization occurred in the xiong er terrane recently numerous cu deposits have been observed in the xiong er terrane xianglugou is a quartz vein type copper mineralization which was discovered in xiayu district southern of the xiong er terrane four chalcopyrite samples from xianglugou yield re os isochron age of 230 31 ma 2 mswd 0 8 this is the first evidence for triassic cu mineralization in the xiong er terrane this not only shows the xiong er terrane contains considerable mo au and ag pb zn reserve but also indicates that there is a great potential of cu mineralization the discoverable cu mineralization can further emphasize the significance of the widespread triassic mineralization and widened exploration ideas and goals in the future in the xiong er terrane the xiong er terrane experienced three polymetallic mineralization events including paleoproterozoic triassic and late jurassic to early cretaceous deposits during the qinling orogen evolution these metallogenic events may be related to multiple tectonic events the paleoproterozoic mineralization was associated with the continental outgrowth occurred along the southern margin of the north china craton before 1760 ma the triassic cu mineralization may be associated with the northward subduction of the north qinling orogen beneath the huaxiong block during the collision between north china craton and yangtze craton late jurassic to early cretaceous mineralization perhaps caused by decompressional extension of the qinling orogenic belts and the north china craton intense destruction and lithospheric thinning which is now generally related to the westward subduction of paleo pacific plate

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

hydrogeological investigations of thermal waters in the sfax basin tunisia the sfax basin in eastern tunisia is bounded to the east by the mediterranean sea thermal waters of the sfax area have measured temperatures of 23 36 c and electrical conductivities of 3 200 and 14 980 s cm most of the thermal waters are characterized as na cl type although there are a few na so4 cl waters they issue from miocene units which are made up sands and sandstones interbedded with clay the quaternary sediments cap the system the heat source is high geothermal gradient which are determined downhole temperature measurements caused by graben tectonics of the area the results of mineral equilibrium modeling indicate that the thermal waters of the sfax basin are undersaturated with respect to gypsum anhydrite and fluorite oversaturated with respect to kaolinite dolomite calcite microcline quartz chalcedony and muscovite assessments from various chemical geothermometers na k mg ternary and mineral equilibrium diagrams suggest that the reservoir temperature of the sfax area can reach up to 120 c according to 18o and 2h values all thermal and cold groundwater is of meteoric origin

tunisian geothermal data from oil wells since direct measurements of steady state temperatures are not readily available in tunisia a geothermal investigation has been made using 1319 values of bottom hole temperatures bhts obtained from 217 petroleum exploration wells an empirical relation based on the differences between bht and dst drill stem tests was used to correct bhts and estimate geothermal gradients the estimated geothermal gradient of the country varies between 21 and 52 c km a few regions with similar gradients have been identified and similarities between gradient contours and the main structural directions are noted furthermore for 25 points from 12 wells it was possible to apply the horner plot method to determine the equilibrium formation temperature tf comparison of tf values with those calculated by the estimated gradients reveals a good correlation r 97 percent between the two estimates this agreement permits greater confidence in the statistical method used and consequently in the estimated gradients for

a review of the geological characteristics and geodynamic setting of the late early cretaceous molybdenum deposits in the east qinling dabie molybdenum belt east china abstract the east qinling dabie molybdenum belt which is located in the nearly east west trending qinling dabie orogen east china is the largest mo belt in the world and is characterized by extensive mesozoic mineralization although the late early cretaceous ca 120 100 ma is the latest stage of the mo mineralization in the east qinling dabie mo belt this period shows relatively intensive mo mineralization such as the world class shapinggou mo deposit all of the late early cretaceous mo deposits are closely related to granitic magmatism some of which are typical porphyry type deposits e g donggou tangjiaping shapinggou homogenization temperatures of fluid inclusions in the late early cretaceous mo deposits range from 115 to 550 c with salinities ranging from 0 02 to 62 1 wt nacl equivalent different amount of co2 have been recognized in the hydrothermal systems of these mo deposits indicating h2o nacl co2 systems the ore forming fluids in these mo deposits were magmatic water mixed with different amount of meteoric water except the donggou deposit the 34s values of sulfides from the late early cretaceous mo deposits have a narrow range of 0 4 6 3 suggesting a deep magmatic source for the sulfur the donggou mo deposit has slightly higher 34s values 7 5 9 4 reflecting that the ore sulfur was mainly derived from magma probably with some upper crust materials available isotopic data show that the ore associated magmas of the late early cretaceous mo deposits were mainly derived from crustal materials probably with some contribution of mantle or newly added crust the donggou tangjiaping and shapinggou mo deposits are genetically related to a type magmatism suggesting that they formed in an extensional setting the late early cretaceous mo deposits in the east qinling dabie mo belt formed in an intraplate extensional setting accompanied by the lithospheric thinning and asthenospheric upwelling

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

paleo position of the north china craton within the supercontinent columbia constraints from new paleomagnetic results abstract several new paleomagnetic and geological studies focused on the reconstruction of the north china craton ncc within the paleo mesoproterozoic columbia supercontinent in spite of these new data there are still widely divergent opinions regarding supercontinental reconstructions in addition to qualitative correlations of orogenic belts rift basin ages stratigraphy and distribution of igneous provinces paleomagnetic data can provide key constraints on the positioning of individual cratons on the globe in this paper we report a detailed paleomagnetic study on the coeval 1780 ma mafic dyke swarm and xiong er volcanic province which extended for more than one thousand kilometers in the central ncc rock magnetic studies including thermomagnetic curves hysteresis loops and the progressive acquisition of isothermal remanence conducted in selected samples indicate that the dominant magnetic carriers are psd magnetite stepwise thermal demagnetization isolated higher temperature components directed to nne ssw with shallow inclinations from 37 sampling sites 16 sites in yinshan area 13 sites in taihang area and 8 sites in xiaoshan area a baked contact test conducted on two yinshan dykes intruded by a younger dyke demonstrates the magnetization in the yinshan dykes pre dates 1320 ma the existence of dual polarity magnetizations in both taihang and xiong er areas support our contention that the chrm was acquired during the cooling of the magma the primary origin of the chrm is also supported by a positive fold test on the xiong er data and a coherent regional test between the results from the taihang and xiong er areas two different site mean directions were compiled from these new results along with previous publications the first direction from the taihang and xiong er areas yields declination d inclination i 12 4 3 7 20 5 95 4 3 n 57 sites the second from the yinshan area is at d 36 7 i 12 4 86 8 95 2 7 n 32 sites we argue that the difference is due to mesozoic and or cenozoic vertical axis rotation of the taihang and xiong er areas with respect to the fixed yinshan ordos basin the corresponding paleopoles for the yinshan dykes falls at 245 2 e 35 5 n a95 2 4 a comparison between the ncc laurentia siberia and baltica is consistent with possible links between these four blocks in a perhaps even larger continent the proximity of australia and india to the ncc is also evaluated

gold deposits in the xiaoqinling xiong ershan region qinling mountains central china the gold rich xiaoqinling xiong ershan region in eastern shaanxi and western henan provinces central china lies about 30 50 km inland of the southern margin of the north china craton more than 100 gold deposits and occurrences are concentrated in the xiaoqinling west xiaoshan middle and xiong ershan east areas late archean gneiss of the taihua group and middle proterozoic metavolcanic rocks of the xiong er group are the main host rocks for the deposits mesozoic granitoids ca 178 104 ma are present in most gold districts but deposits are typically hosted in the precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones deposits in the xiaoqinling and xiaoshan areas are best classified as orogenic gold deposits with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks alteration assemblages are dominated by quartz sericite pyrite and carbonate minerals the ore forming fluids were low salinity co2 rich and characterized by isotopically heavy 18o four deposits dongchuang wenyu yangzhaiyu and dahu in the xiaoqinling area each contain resources of about 1 moz au some of the gold deposits in the xiong ershan area represent more shallowly emplaced tellurium enriched orogenic systems which include resources of approximately 1 1 5 moz au at shanggong and beiling or tantou others are epithermal deposits e g qiyugou and dianfang that are hosted in volcanic breccia pipes isotopic dates for all gold deposits although often contradictory generally cluster between 172 99 ma and are coeval with emplacement of the post kinematic granitoids the gold deposits formed during a period of relaxation of far field compressional stresses clearly subsequent to the extensive paleozoic early mesozoic accretion of arc terranes and the yangtze craton onto the southern margin of the north china craton hydrothermal and magmatic events occurred locally where extension related precambrian basement uplifting took place along the craton margin fluids for the orogenic gold deposits in the xiaoqinling xiaoshan and xiong ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones alternatively for the epithermal gold deposits at shallower levels in the xiong ershan area gold transporting fluids were mainly exsolved from coeval magmas although meteoric water was also involved in these hydrothermal systems

further evidence for 1 85 ga metamorphism in the central zone of the north china craton shrimp u pb dating of zircon from metamorphic rocks in the lushan area henan province abstract this paper reports shrimp zircon u pb dating of precambrian supracrustal and granitic rocks from the lushan area henan province in the southern portion of the central zone also referred to as the trans north china orogen of the north china craton a graphite garnet sillimanite gneiss sample tw0006 1 of the shangtaihua group gives a range of inherited zircon ages from 2 73 to 2 26 ga and a metamorphic zircon age of 1 84 0 07 ga a garnet bearing gneissic granitoid sample twj358 1 which is considered to intrude the shangtaihua group gives a magmatic zircon age of 2 14 0 02 ga and a metamorphic zircon age of 1 87 ga the metamorphic zircon ages of 1 87 1 84 ga obtained in this study indicate that an important tectonothermal event occurred at the end of the paleoproterozoic in the lushan area this supports the southern continuation of a central zone in the north china craton that workers have recently considered to result from continent continent collision it is also evident that the shangtaihua group was formed during the paleoproterozoic between 2 26 and 2 14 ga and not during the archean as previously considered

silurian devonian provenance changes of south qinling basins implications for accretion of the yangtze south china to the north china cratons abstract the north china and yangtze south china cratons are the most important tectonic units of china the two cratons finally coalesced through collision with the formation of the e w trending qinling mountains that are considered to be the eastern extreme of the paleotethys the north qinling and south qinling belts constitute the southern active margin of the north china craton and the northern passive margin of the yangtze craton respectively we have studied chemical compositions of 573 fine grained clastic sedimentary rocks of all the early proterozoic to neogene ages from the north china craton the yangtze craton and the north and south qinling orogenic belts as well as their ten tectonostratigraphic subunits the purpose of this study is to investigate possible provenance changes that are expected to have been recorded in the phanerozoic clastic sediments of the south qinling basins if north and south china had approached and accreted because the north china craton north qinling belt and yangtze craton have distinct upper crustal and provenance compositions both the north china and yangtze cratons and the north qinling belt are characterized by a relatively uniform non evolutionary composition of clastic sediments in la th sc co systematics during post archean times they can be however distinguished from each other in provenance in terms of the la th sc th th co as well as k2o na2o ratios in contrast there is a significant provenance change in the silurian devonian clastic sediments from the baiyun zhashui liuba yunxian and western xichuan subunits of the south qinling belt the late sinian 700 600 ma cambrian and ordovician pelites show characteristics that are consistent with the yangtze craton being high in la th 3 5 10 and sc th 1 4 2 4 and low in th co 0 2 1 0 and lacking la th ratios 3 5 these are accompanied by the increasing immaturity of the silurian devonian clastic sediments illustrated by the decreasing k2o na2o ratio which is attributed to the near source of the north qinling belt dominated by low k2o island arc igneous suites and immature metagraywackes we propose that the south qinling basins except the eastern xichuan subunit had been in a close proximity and accreted to the north qinling belt in silurian devonian times the result agrees well with recent studies of benthic faunas granite distribution age of granulite and clastic provenance directions of the south qinling devonian sediments but it is apparently inconsistent with the age of coesite and diamond bearing ecologite in the dabie mountains to the east and with paleomagnetic data both suggesting an important triassic jurassic collision event between north and south china it is likely that the silurian devonian and the mesozoic represent two different episodes phases of accretion and collision between north and south china new models regarding the phanerozoic tectonic evolution of east china are needed to reconcile the contrasting evidence