isotope geochemical characteristics of auriferous quartz veins from medium and great depths of xiaoqinling area central china and their significance h o s he and ar isotopes of gold bearing quartz veins from the medium and great depths of xiaoqinling area in central china were studied in this paper the data obtained indicate that the ore forming fluids were dominantly derived from the upper mantle and gradually mixed with crustal fluids along with the metallogenic process according to the temporal and spatial link between the gold mineralization and the tectonic evolution of regional extension in combination with other researchers achievements the authors hold that the main gold mineralization in xiaoqinling area occurred at the post collisional stage of late mesozoic being products of the regional extension resulting from the deep process the extensional tectonic system provided dilatational space for migration mixing and water rock interaction of the ore forming fluids as well as gold enrichment and deposition

coupling of the surface and near bottom currents in the gulf of mexico coupling between the surface and near bottom currents in the gulf of mexico gom has been reported in many case studies however geographical variations of this coupling need more examination in this study surface geostrophic currents derived from satellite observed sea surface height and subsurface currents from a collection of deep ocean moorings are used to examine the surface and bottom coupling in different parts of the gom the short period 30 90 days fluctuations generated by the loop current lc and the lc eddies lces have a more vertically coherent structure and stronger deep ocean expressions than the long period fluctuations 90 days in addition the strength of the coupling is modulated by the long period variations of the lc and lce sheddings moreover the surface and bottom coupling varies geographically in the lc region the surface fluctuations along the eastern side of the lc are important in causing the bottom current fluctuations through baroclinic instability under the lc and through traveling topographic rossby waves trws north of the lc in the central deep gom the bottom currents are affected by the upper fluctuations of the northern lc through both local baroclinic instability and remote trw propagation in the northwestern gom the bottom current fluctuations are largely related to the remote surface variability from the west side of the lc by trws propagating northwestward this study will help us better understand mechanisms of the bottom current fluctuations that are important for the dispersal of deep ocean materials and properties

observations of turbulence in a tidal beam and across a coastal ridge during a microstructure survey off california in monterey bay we found a midwater beam of strong turbulence emanating from the shelf break along the ray path of the semidiurnal m2 internal tide within the 50 m thick beam the turbulence kinetic energy dissipation rate e exceeded 10 6 w kg 1 and the diapycnal eddy diffusivity k was 0 01 m2 s 1 the beam extended 4 km off the shelf break several factors suggest that this beam of strong turbulence resulted from the breaking of semidiurnal internal tides the beam appeared to originate from the shelf break which is a potential generation site for semidiurnal internal tides the beam closely followed the ray path of the semidiurnal internal tide the average e off the shelf break varied by a factor of 100 with a semidiurnal tidal periodicity the isopycnal displacement confirmed the presence of semidiurnal internal tides processes associated with the breaking of internal tides are intermittent and sporadic at the same location we also observed equally intense turbulence in a 100 m thick layer of stratified water across the ridge of a sea fan this layer of strong turbulence was separated from the bottom and was clearly not generated by bottom friction although less well resolved in time the strong turbulence above the bottom seemed to vary with the semidiurnal tide and existed at the lee of the ridge where the isopycnal surface dipped and rebounded in a pattern resembling that of internal hydraulic jumps on the basis of the behavior of the density field we believe that the deep mixing was most likely produced by the across ridge current of internal tides the breaking of internal tides at middepth where the richardson number is close to the critical value is likely due to shear instability the presence of the coastal ridge provides an alternative pathway for converting energy from internal tides to turbulence via internal hydraulics multiplying the average e in the midwater beam by the length of the global coastline gives 31 gw only a small fraction of the estimated 360 gw dissipated globally by m2 internal tides our observations suggest that either most internal tides are generated away from shelf breaks or most internal tides generated at shelf breaks propagate away from their generation sites rather than dissipate locally and eventually contribute to pelagic mixing

spatial and temporal distribution of gold deposits in the urals during the past 10 years the paleozoic urals mountain belt has been the subject of internationally based deep seismic and ancillary geologic studies aimed at improving our knowledge of the lithospheric evolution of the orogenic belt in general and its prominent crustal root in particular in view of its wide ranging mineral endowment especially for gold this work also provides important keys to help clarify relationships between collisional tectonic processes and gold mineralization following an outline of current ideas on the tectonic evolution of the urals we present an overview of the distribution of the majority of known gold deposits this information together with the available isotopic and geologic age data of associated alteration assemblages is compared to available geochronological data for various magmatic and deformation episodes spatial and temporal relationships suggest that hydrothermal mineralizing processes and the geodynamic evolution of the orogen are linked in an attempt to analyze the deep structural framework of the orogen down to the mantle we have also examined a number of subcontinental and regional scale continuous geophysical datasets the urals have been subdivided traditionally into a series of north south striking tectonic zones but more recently into three principal tectono magmatic sectors which comprise a suture sector along the main uralian fault zone and two sectors with tectonically imbricated island arc transitional viewed as active continental margin and continental zones gold deposits are found in all tectono magmatic sectors of the orogen minor gold occurs in siluro devonian volcanic hosted massive sulfide deposits magnetite copper skarns and porphyry copper deposits in a number of cases younger structures shear zones faults and their intersections have controlled the deposition of higher gold grades in the urals this has led to the concept of progressive concentration of gold during later tectonic overprinting and the understanding that regional deformation and hydrothermal fluid rock interaction in the late carboniferous to early triassic upgraded gold contents of earlier deposits during the late carboniferous to early triassic gold bearing quartz vein lodes which effectively encompass the majority of the larger gold deposits in the urals were also formed in structural chemical traps some deposits such as mindyak that is hosted by tectonic melanges along the main uralian fault zone are clearly typical late orogenic lode gold deposits others occur within and along the margins of early to middle carboniferous older granite and although local orthomagmatic relationships have been described most recent observations now favor a strong structural control on the lodes and no direct genetic association with granite intrusion in the two largest gold deposits kochkar and berezovskoe gold mineralization was controlled by structural and combined structural chemical traps in dilational jogs in both shear and contact zones locally gold mineralization has been shown to occur during a change from orthogonal to transpressional compression the inferred ages of the lode gold deposits suggest they are mostly coeval with the generally undeformed permian early triassic younger granites however a spatial relationship with gold mineralization has not been observed the younger granites were formed in an extensional regime following ural wide magma generation caused by a thermal flux attributed to underplating of the crust by mantle derived mafic magmas the widespread distribution of this late thermal event during changes in stress regime and the involvement of magma generating mantle processes suggest regional delamination in the lithosphere and concomitant upwelling of the asthenosphere these processes may have largely occurred prior to the formation of the prominent crustal root of the urals which formed during subsequent transpressional convergence another triassic ural wide phase of hydrothermal alteration has been recognized but associated gold deposits have been documented in only two cases we tentatively attribute this phase to destabilization of the lithosphere of the wider altaids reflected by the formation of the west siberian and central asian basins east of the urals during the mesozoic the integrated analysis of magnetic bouguer gravity heat flow and crustal thickness data suggests that a major indenter of the east european craton is responsible for a singular transcrustal sidewall ramp in the subsurface of the middle urals this ramp may extend into the mantle and formed the principal conduit zone for mineralizing fluids the world class kochkar and berezovskoe gold deposits are adjacent to this proposed conduit

40ar 39ar constraints on a temporal link between gold mineralization magmatism and continental margin transtension in the jiaodong gold province eastern china abstract the jiaodong gold province is the largest gold repository in china both mineralization and granitoid hosts are spatially related to the crustal scale tan lu strike slip fault system which developed along the mesozoic continental margin in eastern china a series of 40ar 39ar laser incremental heating analyses of hydrothermal sericite muscovite from three major gold deposits jiaojia xincheng and wangershan and igneous biotite from the granodiorite hosts were performed to establish a possible temporal link between gold mineralization magmatism and movement along the tan lu fault zone magmatic biotite crystals yield well defined and concordant plateau ages between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewco

the geochemical study of fluvio lacustrine aquifers in the kathmandu basin nepal and the implications for the mobilization of arsenic the geochemical analyses of fluvial lacustrine aquifer sediments of the kathmandu valley have been made as a step in assessing the environment for the mobilization of arsenic in groundwater elements measured by x ray fluorescence xrf include 4 major oxides fe2o3 tio2 cao p2o5 and 14 trace elements as pb zn cu ni cr v sr y nb zr th sc and ts elution tests of 15 selected core samples were also carried out to determine the potential leaching of arsenic from the sediments the xrf results show that average bulk concentrations of the major oxides and trace elements are similar to modern unconsolidated sediments and average upper continental crust however the abundance of elements varies with grain size with higher concentrations in finer size grades variations in elemental abundances within the basin are strongly controlled by sediment facies the elution tests show that greater amounts of arsenic are generally eluted from the fine sediments although the rates are variable the results overall suggest that as concentrations in the bulk sediments are not a controlling factor for elevated as in the kathmandu basin groundwater and the roles of other factors such as redox conditions and organic matter contents are likely to be more significant

east asian gold deciphering the anomaly of phanerozoic gold in precambrian cratons early cretaceous orogenic gold deposits in eastern asia are globally unique in that large phanerozoic lode gold deposits occur in archean paleoproterozoic cratons in the northern pacific region ca 125 ma orogenic gold deposits in the north china yangzte and siberian craton margins as well as in young terranes in california may ultimately relate to the giant cretaceous mantle plume in the southern pacific basin and the relatively rapid tectonic consequences along both continental margins from resulting pacific plate reconfigurations in eastern asia such consequences include reactivation of and fluid flow along major fault systems with fluid focusing into simultaneously forming isolated core complexes of uncertain genesis deposition of gold ores in previously devolatilized high grade precambrian metamorphic rocks requires an exotic source of ore fluid most likely subducted mesozoic oceanic crust and or overlying sediment an implication is that phanerozoic metamorphic core complexes in other destabilized craton margins could host large gold resources

surface generated mesoscale eddies transport deep sea products from hydrothermal vents atmospheric forcing which is known to have a strong influence on surface ocean dynamics and production is typically not considered in studies of the deep sea our observations and models demonstrate an unexpected influence of surface generated mesoscale eddies in the transport of hydrothermal vent efflux and of vent larvae away from the northern east pacific rise transport by these deep reaching eddies provides a mechanism for spreading the hydrothermal chemical and heat flux into the deep ocean interior and for dispersing propagules hundreds of kilometers between isolated and ephemeral communities because the eddies interacting with the east pacific rise are formed seasonally and are sensitive to phenomena such as el nino they have the potential to introduce seasonal to interannual atmospheric variations into the deep sea

geological geochronological pyrite geochemical and stable isotope studies of the tantou gold deposit in central china abstract the tantou au deposit is a large scale gold deposit in the xiong ershan area a geochemical study of pyrite was conducted using laser ablation inductively coupled plasma mass spectrometry two types of hydrothermal pyrite were identified in the ores and wall rocks i e the fine euhedral pyrite in brecciated ores py1 and coarse grains disseminated in the quartz sulfide veins py2 the trace elements of the two pyrite types exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes both pyrites of the two mineralization stages were hydrothermal pyrite however the au as co ni and zn were more rich in py1 while ag cu mo sb and pb were favored in py2 the growth rims of py1 suggest several pulses of fluid activities hydrothermal sulfides from the main ore forming stage have a rb sr isochron age of 124 2 3 1 ma placing the gold mineralization in the early cretaceous the initial 87sr 86sr value of the sulfides is 0 71124 0 00010 suggesting an ancient crust source the paleoproterozoic xiong er group in situ s isotope data acquired from the main sulfides suggest that the ore forming materials underwent isotopic fractionation because of oxidation of the ore forming fluids during the hydrothermal process the c o isotope values of calcite from the postore stage indicate that magmatic fluids were likely the principle sources of carbon and that low temperature alteration has had a significant effect on the levels of co2 and carbonate ions together these results suggest that the tantou au deposit is genetically related to the destruction of the north china craton as a result of lithospheric thinning during the early cretaceous

a census of tehuantepec and papagayo eddies in the northeastern tropical pacific 1 we use a 12 year 1992 2004 time series of satellite altimetry to characterize long lived wind generated anticyclonic eddies originating in the gulfs of tehuantepec and papagayo in the northeastern tropical pacific a total of 42 tehuantepec and 26 papagayo eddies were observed eddy merging usually of a tehuantepec papagayo pair was observed on 16 occasions on average the eddy season began in late october and lasted approximately 250 days until early july with 3 5 tehuantepec and 2 2 papagayo eddies formed each year minimum average eddy lifespan was 143 days and 84 days for tehuantepec and papagayo eddies respectively there was considerable interannual variability in eddy activity with greater fewer number of eddies more intense weaker eddies and a longer shorter eddy season during el nino la nina years eddy intensification was consistently observed at the east pacific rise

gold distribution and source of the j4 gold bearing breccia pipe in the qiyugou district north china craton constraints from ore mineralogy and in situ analysis of trace elements and s pb isotopes abstract the qiyugou district is one of the most important gold deposit distribution areas in the xiong ershan region north china craton these deposits are hosted in archean taihua supergroup rocks as gold bearing breccia pipes here we report a detailed in situ analysis of trace elements and s pb isotopes in sulfides from different ore stages in combination with electron probe microanalysis of ore minerals from the gold bearing j4 breccia pipe in the qiyugou district to unravel the gold distribution and their textural relationships to pyrite the metal sources and s pb isotopic composition variations during the ore forming processes the qiyugou breccia pipes hosted gold ore over 70 t au average grade of 2 5 g t that formed in four mineralization stages i e an early k feldspar biotite magnetite quartz pyrite py 1 stage i that can be further divided into two substages namely the ia k feldspar biotite magnetite stage and the ib quartz pyrite stage a gold pyrite py 2 quartz stage ii a gold quartz polymetallic sulfide py 3 stage iii and a late quartz carbonate stage iv the visible native gold and electrum grains occur as small inclusions and disseminations in the fractures within py 2 and py 3 tellurides and bi pb minerals are widespread in the stage ii stockworks and veins as is intergrowth with visible native gold and py 2 in situ la icp ms trace element analysis reveals the presence of invisible gold hosted in three types of pyrite with extremely low au content py 1 0 05 ppm py 2 0 03 ppm py 3 0 02 ppm concentrations of te bi and pb in pyrite are high and correlate well with au concentrations but as content is low therefore the te bi and pb played a significant role in gold mineralization in as deficient ore fluids in the j4 gold bearing breccia pipe from the qiyugou district high precision in situ laser ablation multiple collector inductively coupled mass spectrometry la mc icp ms lead isotope analyses indicate that the sulfides have 206pb 204pb 207pb 204pb and 208pb 204pb ratios from 17 250 to 17 629 from 15 401 to 15 621 and from 37 649 to 38 290 respectively which are similar to the granite porphyry in the district and indicative of their similar lead sources high precision in situ la mc icp ms sulfur isotope analyses of pyrite show a large 34s variation e g from 18 1 to 11 1 per mil for py 1 from 12 2 to 6 6 per mil for py 2 and from 4 9 to 1 6 per mil for py 3 with a remarkable increasing trend from stage i stage iito stage iii this trend may record a decreasing oxygen fugacity of the ore forming fluids during mineralization

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

surface manifestation of internal tides in the deep ocean observations from altimetry and island gauges the sea surface height signatures of internal tides in the deep ocean amounting to a few centimeters or less are studied using two complementary measurement types satellite altimetry and island tide gauges altimetry can detect internal tides that maintain coherence with the astronomical forcing island gauges can monitor temporal variability which in some circumstances is due to internal tides varying in response to changes in the oceanic medium this latter mechanism is at work at hilo and other stations on the northern coasts of the hawaiian islands by detecting spatially coherent low frequency internal tide modulations the tide gauges along with inverted echo sounders at sea suggest that the mean internal tide is also spatially coherent satellite altimetry confirms this at hawaii and in many other places topex poseidon altimetry detects mean surface waves spatially coherent and propagating great distances 1000 km before decaying below background noise when temporal variability is small the altimetry plus information on ocean density sets useful constraints on energy fluxes into internal tides at the hawaiian ridge 15 gw of tidal power is being converted from barotropic to first mode baroclinic motion examples elsewhere warn that a simplistic interpretation of the altimetry without regard to variability noise or in situ information may be highly misleading with such uncertainties extension of the hawaiian results into a usefully realistic estimate of the global internal tide energy balance appears premature at this time

rb sr sm nd and pb isotope systematics of pyrite implications for the age and genesis of lode gold deposits lode gold deposits commonly consist of pyrite and lesser amounts of lead and zinc sulfides accompanied by quartz and calcite their exact origin remains controversial mainly because of the scarcity of reliable geochronological data here we present direct rb sr dating of pyrite from a lode gold deposit and propose the method as a useful geochronological technique for gold mineralization for which age data are poor a positive correlation between present day 87 sr 86 sr and 87 rb 86 sr ratios of pyrite fes 2 subsamples from the linglong gold mine of china corresponds to an age of 122 123 ma which dates the age of gold mineralization the sr nd and pb isotopic compositions of pyrites and the associated rocks suggest that the hydrothermal fluids responsible for the pyrite and gold mineralization were probably derived from a mixed source i e degassing of mafic magmas and meteoric water that had leached the country rocks

subinertial variability in the deep ocean near the east pacific rise between 9 and 10 n 1 the subinertial variability of deep ocean currents near the crest of the east pacific rise in the tropical east pacific is examined using observations from a collection of moored instruments augmented with sea surface height data the moored velocity observations reveal low frequency currents with characteristic time scales of 1 3 months and maximum speeds up to 10 cm s directly over the ridge axis the subinertial motions are dominated by the along axial meridional velocities which are coherent in phase and amplitude along the entire length of the ridge segment between 9 and 10 n with increasing distance from the ridge crest the low frequency currents become weaker and less dominated by the along axial flow component lag correlations between the velocity records indicate westward signal propagation with a speed on the same order as the speed of westward propagating sea surface height anomalies which are also associated with characteristic time scales of 1 3 months as furthermore the subinertial velocities at depth are significantly correlated with geostrophic near surface currents estimated from sea surface height data we conclude that the subinertial velocity field near the epr crest is mainly a superposition of velocities associated with eddies propagating westward across the ridge and topographic flows such as trapped waves and boundary currents

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

the early cretaceous yangzhaiyu lode gold deposit north china craton a link between craton reactivation and gold veining the yangzhaiyu gold deposit is one of numerous lode gold deposits in the xiaoqinling district southern margin of the north china craton gold mineralization is hosted in neoarchean to early paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein proximal alteration zone ore related hydrothermal alteration is dominated by sericite quartz sulfide assemblages close to gold veins and biotite quartz pyrite chlorite epidote alteration generally distal from mineralization pyrite is the predominant sulfide mineral locally coexisting with minor amounts of chalcopyrite sphalerite and galena gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with au bearing tellurides mainly petzite and calaverite coexisting with hessite tellurobismuthite and altaite fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures 175 313 c from aqueous or aqueous carbonic fluids with moderate salinity 5 14 wt nacl equiv 34s values of sulfide minerals range mainly from 2 0 to 4 4 whereas auriferous quartz vein samples have 18o values of 12 4 to 9 6 with calculated 18oh2o values of 6 0 to 3 2 gold related pyrite grains yield elevated 3he 4he ratios 1 51 0 32 ra relative to crustal reservoirs and mantle like 20ne 22ne and 21ne 22ne ratios 9 90 9 68 and 0 029 respectively the stable and noble gas isotopes thus suggest deep seated most likely magmatic and mantle derived sources for the ore fluids sulfur and by inference other components in the ore system 40ar 39ar dating of ore related sericite and biotite separates indicates two episodes of gold genesis at 134 5 to 132 3 and 124 3 to 123 7 ma the mineralization ages overlap zircon u pb ages of 141 0 1 6 to 125 8 1 4 ma 2 for the wenyu and niangniangshan monzogranite plutons and a number of mafic to intermediate dikes intruding these plutons all being proximal to the yangzhaiyu gold deposit the synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur the geochronologic data also suggest that gold veining took place billions of years after the stabilization of the north china craton and associated metamorphism in the late archean to early paleoproterozoic this contrasts sharply to lode gold deposits in other precambrian cratons that formed predominantly in late archean to paleoproterozoic temporarily and genetically related to regional high grade metamorphism and compressional or transpressional tectonism available data have demonstrated that the north china craton was reactivated in the late mesozoic as marked by voluminous igneous rocks faulted basin formation high crustal heat flow and widespread metamorphic core complexes in the eastern part of the craton it is thus suggested that the yangzhaiyu gold deposit together with other deposits of similar ages in the xiaoqinling district were products of this craton reactivation event lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy fluid and sulfur required for the formation of the gold deposits

multistage exhumation of the anjiayingzi gold deposit northern north china block geodynamic settings and exploration implications abstract post mineralisation exhumation is pivotal because of its strong effects on the preservation of ore deposit the jiguanzi quartz monzonite hosts the anjiayingzi au deposit at the centre of the kalaqin antiform or kalaqin metamorphic core complex in the northern north china block ncb we can link the exhumation of the deposit with regionally geodynamic events and evaluate its exploration implications using low temperature thermochronology from the quartz monzonite host sericite 40ar 39ar dating of auriferous quartz sulphide veins indicates that gold mineralisation timing is 130 1 ma zircon fission track ages of fresh samples from the host quartz monzonite vary from 118 6 to 99 4 ma and apatite fission track ages vary from 99 6 to 66 5 ma a four stage post mineralisation exhumation history is revealed by combining the binomial peak fitting of single grain ages and low temperature thermal history inverse modelling the first exhumation event is dated at ca 130 100 ma and characterised by the most rapid exhumation rate of 167 m ma and ca 5 km rise this movement is related to the top to nw and a se ductile brittle extensional deformation of the kalaqin antiform regionally it is also contemporaneous with the formation of extensional metamorphic core complexes development of basins and increasing heat flow and decreasing thermal lithospheric thickness in the eastern ncb all of these synchronous events can be linked to the back arc setting of the subducting izanagi oceanic plate and resulted geodynamic changes beneath the ncb the relatively slow stage 2 exhumation dated at ca 100 65 ma with an exhumation rate of 20 m ma was triggered by the collision between the izanagi oceanic plate and eastern china at ca 100 ma and following change in the drift direction of the izanagi oceanic plate sedimentation of basins in the ncb was continuous during this period resumed stage 3 exhumation ca 65 45 ma 27 m ma and synchronous sedimentary inversion are products of regional compression event related to the collision between india and the eurasian plates change of the pacific oceanic plate drifting direction at ca 50 ma finally induced the monotonic cooling and exhumation of stage 4 19 m ma the estimated post mineralisation exhumation is 7 1 km and the ore forming depth of the anjiayingzi au deposit is between 5 1 and 10 1 km in combination with previously published data the differential exhumation history exhumation degree and preservation potential of major gold provinces in ncb are confirmed which further indicate that their gold prospectivity must be assessed individually

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

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

the mesozoic cenozoic east china rift system abstract the mesozoic cenozoic rift system of eastern china extends in a n s direction over a distance of some 4000 km and has a width of 600 1000 km to the east it reaches into the coastal areas of the east and south china sea and extends onto the continental shelf this very large rift system evolved on a heterogenous basement consisting of a number of terranes which were amalgamated during the indosinian orogeny a first rifting phase spanned late jurassic early cretaceous times it was followed by a period of relative tectonic quiescence and thermal relaxation a latest cretaceous phase of compressional tectonics giving rise to partial basin inversion was followed by a renewed rifting cycle spanning eocene early neogene times development of the east china rift system involving vertical as well as lateral crustal movements was probably induced by physico chemical changes within the earth s mantle that can be related to activity along the pacific subduction zones the mesozoic cenozoic east china rifts contain some important hydrocarbon provinces which rely to a large extent on syn rift sediments for source and reservoir rocks

geology fluid inclusions isotope geochemistry and geochronology of the paishanlou shear zone hosted gold deposit north china craton abstract the paishanlou gold deposit lies along the northern margin of north china craton gold province the third largest au province in china the deposit is mainly hosted in archean metamorphic rocks of the jianping group and is structurally controlled by two sets of ductile shear zones gold mineralization is closely associated with intense hydrothermal alteration along the ductile shear zones with a typical greenschist facies alteration assemblage of sericite chlorite calcite biotite quartz and a distinct alteration zoning of inner pyrite sericite zone middle carbonate zone and outer epidote biotite chlorite zone from orebody to wall rock fluid inclusion petrography and microthermometric results suggest that four types of fluid inclusions are present at the deposit type 1 co 2 rich inclusions have homogenization temperatures of 22 4 27 9 c type 2 h 2 o co 2 inclusions show salinities of 4 6 12 3 wt nacl equivalent and th tot of 242 to 337 c type 3a primary aqueous inclusions have salinities of 5 9 11 2 wt nacl equivalent and th tot of 187 289 c while type 3b secondary aqueous inclusions have salinities of 3 1 8 3 wt nacl equivalent and th tot of 128 239 c type 4 multiphase inclusions have salinities ranging from 31 4 to 35 2 wt nacl equivalent and th tot of 370 447 c the close association of co 2 rich inclusions and h 2 o rich inclusions in groups and along the same trail suggests the presence of fluid immiscibility estimated p t values range from 1 4 to 1 9 kbar at 322 417 c the 18 o values of the ore forming fluids are calculated to range from 3 8 to 7 4 and the d values from 87 3 to 116 2 indicating a mixed source of deep seated magmatic water and shallower meteoric water the 34 s values 0 3 7 5 of sulfide ore minerals are similar to those of both pyrite from metamorphic country rocks and whole rock sulfur of metamorphic country rocks the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb of sulfide ores range within 16 40 17 0 15 21 15 37 and 36 69 37 38 respectively with the model ages of 397 727 ma consistent with those of late mesozoic granites and lying between archean metamorphic rock lead and the proterozoic dolomitic marble lead these sulfur and lead features reflect the fact that the ore forming materials originated mainly from multiple wall rock sources the well defined ar ar plateau age 126 6 1 1 ma of biotite from the nne ductile shear zone provides a possible temporal link between au mineralization magmatism and deformation at the paishanlou deposit the concordance of the biotite age with other well constrained mineralization ages for the deposit and the intrusion age of the granite suggests that au mineralization was essentially contemporaneous with late mesozoic granitic magmatism and the second stage of mylonitization in terms of its genetic linkage with the subduction process at the leading northern edge of the north china craton the paishanlou deposit can be favored as an orogenic gold deposit its formation benefited from the combined action of protracted activity of ductile fault zones hydrothermal circulation associated with granitoid intrusion and preferred structural setting favoring gold deposition the major geodynamic switch towards generalized extensional tectonics that occurred during uplift and thinning of the upper crust after the collisional stages in the northern edge of the north china craton may be the key factors controlling au concentration and enrichment in the paishanlou deposit

gold deposits of the northern margin of the north china craton multiple late paleozoic mesozoic mineralizing events the northern margin of the north china craton is well endowed with lode gold deposits hosting a resource of approximately 900 tonnes t of gold the 1 500 km long region is characterized by east trending blocks of metamorphosed archean and proterozoic strata that were episodically uplifted during variscan indosinian and yanshanian deformational and magmatic events at least 12 gold deposits from the daqinshan yan liao includes the zhangjiakou yanshan and chifeng gold districts and changbaishan gold provinces contain resources of 20 100 t au each most deposits are hosted in uplifted blocks of precambrian metamorphic rocks although felsic paleozoic and mesozoic plutons are typically proximal and host 30 of the deposits the lodes are characterized by sulfide poor quartz veins in brittle structures with low base metal values and high au ag ratios although phyllic alteration is most common intensive alkali feldspar metasomatism characterizes the wulashan dongping and zhongshangou deposits but is apparently coeval with variscan alkalic magmatism only at wulashan stepwise 40ar 39ar geochronology on 16 samples from gangue and alteration phases combined with unpublished shrimp u pb dates on associated granitoids suggest that gold mineralizing events occurred during variscan indosinian and yanshanian orogenies at circa 350 250 200 180 150 and 129 ma however widespread permo triassic 250 ma and early jurassic 180 ma thermal events caused variable resetting of most of the white mica and k feldspar argon spectra as well as previously reported k ar determinations compiled and new stable isotope and fluid inclusion data show that most 18o values for ore stage veins range from 8 to 14 indicating a fluid in equilibrium with the precambrian metamorphic basement rocks d values from fluid inclusions range widely from 64 to 154 which is indicative of a local meteoric component in some veins and highly variable 34s data 7 to 17 even within individual deposits indicate various local country rock sources for sulfur fluid inclusions from all districts show variable homogenization temperatures between 240 and 400 c and are consistently characterized by low salinity h2o co2 ch4 n2 solutions although the data are largely consistent with that from orogenic gold veins intrusion related veins and epithermal veins are also recognized the multiple episodes of mineralization are coincident with episodic tectonic reactivations and associated magmatism along the northern margin of the north china craton electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0239 2

geochronology of the pengjiakuang and rushan gold deposits eastern jiaodong gold province northeastern china implications for regional mineralization and geodynamic setting the jiaodong gold province the largest gold producing district in china is located in the jiaodong peninsula at the eastern margin of the north china craton and bounded by the continental scale tan lu fault 40 kin to the west previous geochronological studies suggest that pervasive gold deposition took place in the western part of the province between 122 and 119 ma here we report high quality ar 40 ar 39 ages of the pengjiakuang and rushan deposits from the eastern part of the jiaodong gold province placing additional chronological constraints on the timing of regional mineralization seven sericite grains extracted from auriferous alteration assemblages at the pengiiakuang deposit yielded well defined plateau ages between 120 9 0 4 and 119 1 0 2 ma 2 sigma three separates of igneous biotite from a sample of the queshan gneissic granite adjacent to the pengjiakuang deposit gave reproducible plateau ages of 124 6 0 6 to 123 9 0 4 ma 2 sigma six sericite separates front two samples in the rushan deposit yielded ar 40 ar 39 plateau ages at 109 3 0 3 to 107 7 0 5 ma 2 sigma whereas biotite from the kunyushan monzogranite that hosts the rushan deposit had plateau ages ranging from 129 0 0 6 to 126 9 0 6 ma 3 separates front one sample the apparent age gap between hydrothermal sericite and magmtic biotite from both deposits together with the similar argon closure temperatures for these mica minerals suggest that gold mineralization had no direct relationship to the granitoid magmatism instead gold deposition coincided with the emplacement of mafic to intermediate dikes widespread in the jiaodong gold province which have been dated at ca 122 to 119 ma and less commonly at 110 to 102 ma the new ar 40 ar 39 ages from the eastern jiaodong peninsula when combined with published data from the western part suggest that gold mineralization was broadly contemporaneous throughout the district the early cretaceous gold mineralization also is widely developed in four other major gold districts along the tan lu fault the temporal and spatial correlation of these gold deposits with mafic to intermediate dikes commonly found in most mineralized areas the presence of well documented metamorphic core complexes and half graben basins along the tan lu fault and voluminous basalts therein suggest that the early cretaceous was an important period of lithospheric extension possibly caused by the late mesozoic lithospheric thinning beneath the eastern block of the north china craton lithospheric thinning and extension could have resulted in abnormally high heat and fluid fluxes necessary for large scaled gold mineralization

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

giant mesozoic gold provinces related to the destruction of the north china craton abstract lode gold deposits in precambrian cratons represent the world s major gold source and were mostly generated during formation and stabilization of the cratons however there is an extraordinary exception in the north china craton ncc where lode gold deposits formed after prolonged stabilization of the craton molybdenite re os and hydrothermal sericite and biotite 40 ar 39 ar dating of major gold deposits from the xiaoqinling district southern ncc bracket their emplacement in the range of 154 1 1 1 to 118 9 1 2 ma n 23 postdating formation of the craton by more than 1 7 billion years fluid inclusions extracted from gold bearing pyrite have elevated 3 he 4 he ratios 1 52 0 22 ra and mantle like ne isotopes 20 ne 22 ne 10 02 9 22 and 21 ne 22 ne 0 033 0 027 indicating presence of mantle derived fluids in the ore system measured 34 s of pyrite and d and 18 o of hydrothermal micas and fluid inclusion waters in auriferous quartz further confirm a magmatic mantle source for sulfur and ore fluids gold deposits of similar ages also widely occur in the eastern and northern margins of the ncc which together with those in the xiaoqinling district have a total reserve of 2500 t gold forming the only known giant late mesozoic gold province in the world s precambrian cratons these deposits formed coevally with extensive felsic to mafic magmatism development of intracontinental rift basins and exhumation of metamorphic core complexes across the eastern ncc events interpreted as indicating thinning and destruction of the lithosphere beneath the craton rising of asthenosphere coupled with destruction of the lithosphere has generated voluminous mafic and felsic magmas that provided sufficient fluids sulfur and by inference other ore components to form the giant gold provinces

morb type neon in an enriched mantle beneath etna sicily abstract noble gas elemental and isotopic compositions were determined for five co 2 ch 4 samples collected around etna sicily to investigate the geochemical features of the mantle beneath the volcano the samples contain mantle derived noble gases the measured helium isotopic ratios 3 he 4 he vary between 5 9 and 6 4 times atmospheric ratio r a 1 4 10 6 which are comparable to the ratios of olivines 6 1 8 2 r a in the lavas of the same volcano 1 neon in the samples is enriched in both 20 ne and 21 ne 20 ne 22 ne 9 95 10 7 21 ne 22 ne 0 030 0 037 indicating derivation from the mantle the 20 ne 22 ne 21 ne 22 ne values are identical with that of mid ocean ridge basalts morb indicating a similarity in the time integrated u ne ratio between the etnean magma source and the depleted upper mantle morb source argon in the samples has 40 ar 36 ar ratios up to of 1800 which are higher than in atmosphere these ratios are positively correlated with the 20 ne 22 ne ratios indicating a mantle origin of the radiogenic argon compared with olivines from the etnean lavas 1 the argon in our natural gas samples is less contaminated by atmospheric argon two samples from a co 2 well show small but resolvable excess of 129 xe and 134 136 xe the volcanic rocks of etna ranging from tholeiites to alkaline are enriched in incompatible elements nd sr and pb isotopes of the volcanic rocks indicate that the magma source is isotopically heterogeneous and contain a component with high sr pb and low nd isotopic ratios derived from a mantle region which has been enriched in incompatible elements for a few million years 2 3 4 relative to the depleted upper mantle the helium isotopic ratios of the gas samples are lower than those of morb and are consistent with geochemical signatures of the solid elements in the etnean volcanic rocks however the observed morb type neon is on a morb correlation array without accumulation of nucleogenic 21 ne this apparent decoupling may be explained by a recent mixing of the depleted upper mantle morb source with fluid enriched in both incompatible elements and radiogenic 4 he when the fluid was formed with a small degree of partial melting fractionation of radiogenic 4 he from nucleogenic 21 ne could have occurred because of smaller partition coefficient of he than ne

direct breaking of the internal tide near topography kaena ridge hawaii abstract barotropic to baroclinic conversion and attendant phenomena were recently examined at the kaena ridge as an aspect of the hawaii ocean mixing experiment two distinct mixing processes appear to be at work in the waters above the 1100 m deep ridge crest at middepths above 400 m mixing events resemble their open ocean counterparts there is no apparent modulation of mixing rates with the fortnightly cycle and they are well modeled by standard open ocean parameterizations nearer to the topography there is quasi deterministic breaking associated with each baroclinic crest passage large amplitude small scale internal waves are triggered by tidal forcing consistent with lee wave formation at the ridge break these waves have vertical wavelengths on the order of 400 m during spring tides the waves are nonlinear and exhibit convective instabilities on their leading edge dissipation rates exceed those predicted by the open ocean parameterizations by up to a factor of 100 with the disparity in

gold distribution in as deficient pyrite and telluride mineralogy of the yangzhaiyu gold deposit xiaoqinling district southern north china craton the mesozoic yangzhaiyu lode gold deposit is situated in the southern edge of the north china craton gold mineralization is hosted in archean amphibolite facies metamorphic rocks and consists mainly of auriferous quartz veins pyrite is the predominant sulfide mineral with minor amounts of chalcopyrite sphalerite and galena based on morphology and paragenesis there are three generations of pyrite termed as first generation g1 second generation g2 and third generation g3 they have distinct contents occurrences and distribution patterns of gold the coarse grained euhedral g1 pyrite contains negligible to low levels of gold whereas both invisible and visible gold are present in the fine to medium grained g2 pyrite that is characterized by abundance of microfractures and porosities forming a foam like texture laser ablation inductively coupled plasma mass spectrometry la icp ms depth profiles indicate that invisible gold occurs either as solid solution or as nanoparticles of gold bearing tellurides in the g2 pyrite visible gold is widespread and present as irregular grains and stringers of native gold mostly along grain boundaries or filling microfractures of pyrite likely resulting from remobilization of invisible gold once locked in the g2 pyrite the g3 pyrite invariably intergrown with chalcopyrite sphalerite and galena contains the highest levels of invisible gold there is a positive correlation between au ag and te indicating that gold occurs as submicroscopic au bearing telluride inclusions in the host minerals whenever gold either invisible or visible is present as is always below or only marginally higher than the detection limit of la icp ms this indicates that as played an insignificant role in gold mineralization tellurides are widespread in the auriferous quartz veins consisting mainly of petzite calaverite hessite altaite and tellurobismuthite native gold commonly occurs as intergrowths with tellurides textural evidence indicates a precipitation sequence in a temporal order of calcaverite petzite altaite tellurobismuthite and hessite little amount of sulfide phases has been found in association with the tellurides indicating that tellurides were deposited under low s fugacity fs2 and or high te fugacity fte2 conditions the textural relationships when combined with fluid inclusion microthermometric data of auriferous quartz veins and tellurides thermodynamic data permit estimation for logfte2 during telluride formation which are 6 8 to 10 8 at 300 c and 9 6 to 17 6 at 250 c available geochronological and geochemical data suggest that te was most likely derived from the late mesozoic magmatic rocks widespread in the xiaoqinling district and other parts of the southern north china craton which were emplaced broadly contemporaneous with gold mineralization at yangzhaiyu this study highlights the role of te and tellurides as important gold scavengers in as deficient ore fluids

an estimate of tidal energy lost to turbulence at the hawaiian ridge abstract an integrated analysis of turbulence observations from four unique instrument platforms obtained over the hawaiian ridge leads to an assessment of the vertical cross ridge and along ridge structure of turbulence dissipation rate and diffusivity the diffusivity near the seafloor was on average 15 times that in the midwater column at 1000 m depth the diffusivity atop the ridge was 30 times that 10 km off the ridge decreasing to background oceanic values by 60 km a weak factor of 2 spring neap variation in dissipation was observed the observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide e and the depth integrated dissipation d such that d e1 0 5 at sites along the ridge this kinematic relationship is supported by combining a simple knife edge model to estimate internal tide generation with wave wave interaction time scales to estimate dissipation the along ridge kinematic relationship and the observed vertical and cross ridge st

observations of tidal internal wave beams at kauai channel hawaii abstract to observe the across ridge structure of internal tides density and velocity were measured using seasoar and a doppler sonar over the upper 400 600 m of the ocean extending 152 km on each side of the hawaiian ridge at kauai channel eighteen sections were completed in about 18 days with sampling intentionally detuned from the lunar semidiurnal m2 tide so that averaging over all sections was equivalent to phase averaging the m2 tide velocity and displacement variance and several covariances involving velocity and displacement showed one m2 internal wave beam on each side of the ridge and reflection of the beams off of the surface theoretical ray slopes aligned with the observed beams and originated from the sides of the ridge energy flux was in agreement with internal wave generation at the ridge inferred turbulent dissipation was elevated relative to open ocean values near tidal beams energy flux was larger than total dissipation almost everywhere across the ridge internal wave energy fl

incoherent nature of m2 internal tides at the hawaiian ridge abstractmoored current temperature and conductivity measurements are used to study the temporal variability of m2 internal tide generation above the kaena ridge between the hawaiian islands of oahu and kauai the energy conversion from the barotropic to baroclinic tide measured near the ridge crest varies by a factor of 2 over the 6 month mooring deployment 0 5 1 1 w m 2 the energy flux measured just off the ridge undergoes a similar modulation as the ridge conversion the energy conversion varies largely because of changes in the phase of the perturbation pressure suggesting variable work done on remotely generated internal tides during the mooring deployment low frequency current and stratification fluctuations occur on and off the ridge model simulations suggest that these variations are due to two mesoscale eddies that passed through the region the impact of these eddies on low mode internal tide propagation over the ridge crest is considered it appears that eddy related changes in stratif

internal hydraulic jumps and overturning generated by tidal flow over a tall steep ridge abstract recent observations from the hawaiian ridge indicate episodes of overturning and strong dissipation coupled with the tidal cycle near the top of the ridge simulations with realistic topography and stratification suggest that this overturning has its origins in transient internal hydraulic jumps that occur below the shelf break at maximum ebb tide and then propagate up the slope as internal bores when the flow reverses a series of numerical simulations explores the parameter space of topographic slope barotropic velocity stratification and forcing frequency to identify the parameter regime in which these internal jumps are possible theoretical analysis predicts that the tidally driven jumps may occur when the vertical tidal excursion is large which is shown to imply steep topographic slopes such that dh dxn 1 the vertical length scale of the jumps is predicted to depend on the flow speed such that the jump froude number is of order unity the numerical results agree with the theoreti

petrogenesis of the early cretaceous intermediate and felsic intrusions at the southern margin of the north china craton implications for crust mantle interaction abstract new major and trace element whole rock sr and nd isotopes and zircon u pb ages and hf isotope data are presented for rocks from the early cretaceous tianqiaogou dioritic and taishanmiao granitic plutons at the southern margin of the north china craton ncc in order to investigate their petrogenesis and geological evolution la icp ms u pb analyses for zircons from these two plutons yield similar 206 pb 238 u ages of 122 ma and 115 125 ma respectively monzodiorites from the tianqiaogou pluton have whole rock e nd t values ranging from 6 2 to 1 3 and zircon e hf t values from 2 9 to 6 2 they are variably enriched in ra ba and sr and depleted in nb ta zr hf and ti indicating that they were derived from a depleted mantle and underwent subsequent magma differentiation and crustal contamination the taishanmiao pluton is composed of metaluminous to peraluminous highly fractionated i type granites that have high sio 2 na 2 o k 2 o rb th and u and low p ba sr ti and eu contents the granites have strong negative whole rock e nd t values 16 1 to 7 5 and zircon e hf t values 20 9 to 6 1 their nd t dm ages 1 19 to 2 01 ga and zircon hf t c dm ages 1565 to 2490 ma are much younger than the basement rocks beneath the southern margin of the ncc suggesting derivation from an ancient crustal source with minor involvement of mantle derived components therefore rocks from the tianqiaogou dioritic pluton were partial melts of the mantle source underplating of the mafic magmas initiated partial melting of the ancient continental crust resulting in the formation of the taishanmiao granitic pluton their complex petrogenesis reflects a strong crust mantle interaction process related to lithospheric thinning beneath the southern margin of the ncc in early cretaceous

destruction mechanism of the north china craton insight from p and s wave mantle tomography abstract the eastern part of the north china craton ncc was reactivated and its lithosphere was destructed during the mesozoic to cenozoic several destruction models have been proposed by geochemical and geologic studies in this work we determined detailed p and s wave velocity and poisson s ratio structures under the ncc which show different structural patterns in different blocks of the ncc the present results provide important new constrains on the ncc evolution mechanism integrating geochemical and geologic observations and our tomographic results we consider that deep subduction of the pacific slab under east asia caused local or regional scale lithospheric delamination that first took place along some special locations such as the trans north china orogen dabie sulu and yanshan orogenic belts in early mesozoic or paleoproterozoic as a result asthenospheric upwelling in the big mantle wedge above the stagnant pacific slab led to widespread magmatism in and around the eastern part of the ncc hence the thermal erosion and or chemical metasomatism might be a main dynamic mechanism for the lithospheric evolution of eastern ncc during the mesozoic to cenozoic we suggest that the tanlu fault zone and trans north china orogen may have acted as two main conduits for the asthenospheric upwelling which have played an important role in the mesozoic cenozoic destruction of the pre existing archean lithospheric mantle

rapid dewatering of the crust deduced from ages of mesothermal gold deposits the large scale migration of fluids through the continental crust has been well documented but there is no consensus regarding the timing of fluid migration relative to orogenic episodes or rates of crustal dewatering1 here we present40ar 39ar dates for muscovites from quartz veins along a major shear zone in southeast alaska which show that the veins were emplaced in the early eocene during the late stages of orogenic deformation hydrother mal activity took place for only about 1 myr and along a distance of at least 200 km the fluids were generated by metamorphic reactions in subducted crust along the north american plate margin and were apparently trapped in the crust by the low permeabilities accompanying a convergent tectonic regime until 56 myr ago the rapid dewatering event coincided with a change in plate motion at 56 55 myr which caused a shift from convergent to partly transcurrent tectonics we suggest that this change in tectonic regime led to increased crustal permeabilities and hence the possibility of large scale fluid migration

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

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

two periods of zircon from dongping gold deposit in zhangjiakou xuanhua area northern margin of north china constraints on metallogenic chronology the dongping gold deposit is located in zhangjiakou xuanhua area of hebei province on the northern margin of the north china craton this ore deposit is mainly hosted by the medium fine grained syenite in the southern part of the shuiquangou alkaline complex there are two types of gold ores in this deposit namely the telluride mineral bearing and low sulfide quartz veins and the intense k feldspar alteration type the authors performed a systematic mineralogical and u pb geochronologic study of zircon minerals from no 1 auriferous quartz vein two types of zircons were recognized in this vein i e magmatic and hydrothermal ones the magmatic zircon is characterized by euhedral subhedral crystals with the prismatic form dark gray color in the backscattered electron bse image and clear magmatic oscillatory zoning in the cathodoluminescence cl image the hydrothermal zircon occurs mainly in irregular forms and occasionally as anhedral grains fills the magmatic zircon and shows grayish white color in the bse image and dark black color non luminescent in the cl image u pb analyses of the magmatic zircon indicate a devonian event with a weighted mean 206pb 238u age of 380 5 2 6 ma therefore the rock forming process of the shuiquangou alkaline complex is confidently constrained in late devonian compared with the magmatic zircon the hydrothermal zircon has not only much higher th u content and th u ratios but also much younger u pb age of 140 2 1 3 ma therefore the ore forming period of the dongping gold deposit is confidently constrained in early cretaceous obviously there is a time gap of about 240 ma between the rock forming process of the alkaline complex and the ore forming process in the dongping gold deposit it is therefore concluded that there is no direct genetic relationship between the shuiquangou alkaline complex and the dongping gold deposit according to local geological background the authors hold that the ore forming fluids might be genetically associated with mesozoic magmatism in this area

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

ore genesis of the fancha gold deposit xiaoqinling goldfield southern margin of the north china craton constraints from pyrite re os geochronology and he ar in situ s pb isotopes abstract the fancha gold deposit is one of the representative lode type deposit in the xiaoqinling goldfield four stage mineralization process were identified namely i the barren quartz stage ii the pyrite dominated stage iii the quartz polymetallic sulfides stage and iv the quartz carbonate stage correspondingly pyrite crystal can be divided into three generations i e py1 py2 and py3 according to their different textures and paragenesis during the first three mineralization stages in order to better understand the ore genesis an integrated analysis on re os he ar s pb multi isotopes was carried out for each mineralization stage to delineate the timing of the mineralization and the origins of the ore forming materials in detail gold bearing pyrite yields a re os isochron age of 124 3 2 6 ma mswd 1 9 overlapping with the previous hydrothermal mica 40ar 39ar ages suggesting that gold mineralization occurred in the early cretaceous the 3he 4he r ra and 40ar 36ar values of the py2 are 0 68 to 1 17 and 656 55 to 7384 2 and those of the py3 are 0 20 to 0 33 and 647 67 to 8913 55 respectively which reveal a significant contribution of mantle component in the ore forming fluids and the content of crust fluid is increasing in the later evolution in situ 34s values of the sulfides and tellurides in the auriferous quartz veins including the pyrite py1 py2 and py3 chalcopyrite sphalerite galena bismuthinite and tetradymite display a relatively narrow range 4 9 to 3 6 consistent with magmatic sulfur which are quite different from those of the pyrite in surrounding rock 7 8 to 9 3 in situ pb isotopic compositions of the galena and bismuthinite of stage iii are homogeneous with values of 208pb 204pb 207pb 204pb and 206pb 204pb being 37 482 37 508 15 392 15 523 16 995 17 006 and 39 279 39 287 15 588 15 590 18 283 18 288 respectively indicating a mixed pb sources with obvious proportions of mantle combined with previous data we suggest that the ore forming fluids and metals of the fancha gold deposit stemmed directly from the regional mantle derived magmatic hydrothermal system which is coupled with the large scale lithospheric extension and thinning in the eastern north china craton during the early cretaceous

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

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

the liaonan metamorphic core complex southeastern liaoning province north china a likely contributor to cretaceous rotation of eastern liaoning korea and contiguous areas abstract the mesozoic liaonan metamorphic core complex mcc of the southeastern liaoning province north china is an asymmetric cordilleran style complex with a west rooting master detachment fault the jinzhou fault a thick sequence of lower plate fault related mylonitic and gneissic rocks derived from archean and early cretaceous crystalline protoliths has been transported ese ward from mid crustal depths u pb ages of lower plate syntectonic plutons ca 130 120 ma 40 ar 39 ar cooling ages in the mylonitic and gneissic sequence ca 120 110 ma and a cretaceous supradetachment basin attest to the early cretaceous age of this extensional complex the recent discovery of the coeval and similarly west rooting waziyu mcc in western liaoning darby b j davis g a zhang x wu f wilde s yang j 2004 the newly discovered waziyu metamorphic core complex yiwulushan western liaoning province north china earth science frontiers 11 145 155 indicates that the gulf of liaoning which lies between the two complexes was the center of a region of major crustal extension clockwise crustal rotation of a large region including eastern liaoning province and the korean peninsula with respect to a non rotated north china block has been conclusively documented by paleomagnetic studies over the past decade the timing of this rotation and the reasons for it are controversial lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 proposed that a clockwise rotation of 22 5 10 2 was largely post early cretaceous in age and was the consequence of extension within a crustal domain that tapers southwards towards the bohai sea of which the gulf of liaoning is the northernmost part paleomagnetic studies of early cretaceous strata ca 134 120 ma in the yixian fuxin supradetachment basin of the waziyu mcc indicate the non rotation of north china and the basin zhu r x shao j a pan y x shi r p shi g h li d m 2002 paleomagnetic data from early cretaceous volcanic rocks of west liaoning evidence for intracontinental rotation chinese science bulletin 47 1832 1837 such upper plate non rotation supports our conclusion that the lower plates of the waziyu and liaonan metamorphic core complexes were displaced ese ward in an absolute sense away from the stable north china block thus contributing to the rotation of korea and contiguous areas rotation is inferred to have affected only the upper crust above mid crustal levels into which we believe the jinzhou and waziyu detachment fault zones flattened if this is the case the regional tan lu fault that lies between the two core complexes was truncated at mid crustal depth since in areas to the south it forms the boundary between the north and south china lithospheric blocks it is noteworthy that the two extensional complexes lie not far north of the bohai bay the area proposed by lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 as the site of the pole of rotation for korea s clockwise displacement lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 were unaware of the liaonan and waziyu mcc s and argued that most of the regional block rotation was post early cretaceous and in part early cenozoic however the ca 130 120 ma ages of the two liaoning mcc s and a songliao basin mcc xujiaweizi the latter discovered only by recent drilling through its younger stratigraphic cover support our and some korean coworkers conclusions that most of the clockwise rotation was early cretaceous

geology mineralization and geochronology of the qianhe gold deposit xiong ershan area southern north china craton the qianhe gold deposit in the xiong ershan area is located along the southern margin of the archean paleoproterozoic north china craton the deposit consists of six orebodies that are hosted in paleoproterozoic andesites to basaltic andesites and structurally controlled by roughly ew trending faults individual orebodies comprise auriferous quartz veins and disseminated au bearing pyrite within hydrothermally altered rocks on both sides of or close to the veins ore related hydrothermal alteration has produced various mixtures of k feldspar quartz sericite chlorite epidote carbonate and sulfides pyrite is the most important ore mineral associated with minor amounts of galena sphalerite and chalcopyrite other trace minerals include molybdenite arsenopyrite scheelite rutile xenotime and parisite gold occurs mostly as native gold and electrum enclosed in pyrite or along microfractures of sulfides and quartz microthermometric measurements of primary inclusions in auriferous quartz suggest that gold and associated minerals were precipitated in the range of 160 305 c from aqueous or carbonic aqueous fluids with salinities of 6 22 wt nacl equiv samples of molybdenite coexisting with au bearing pyrite have re os model ages of 134 135 ma whereas ore related hydrothermal sericite separates yield 40ar 39ar plateau ages between 127 and 124 ma the re os and 40ar 39ar ages are remarkably consistent with zircon u pb ages 134 5 1 5 and 127 2 1 4 ma 1 of the biotite monzogranite from the heyu intrusive complex and granitic dikes in and close to the qianhe gold mine indicating a close temporal and thus possibly genetic relationship between gold mineralization and granitic magmatism in the area fluid inclusion waters extracted from auriferous quartz have d values of 80 to 72 whereas the calculated 18oh2o values range from 3 1 to 3 8 the hydrogen and oxygen isotopes from this study and previous work indicate that ore fluids were likely derived from degassing of magmas with addition of minor amounts of meteoric water gold mineralization at qianhe is temporarily coincident with pervasive bimodal magmatism widespread fault basin formation and well development of metamorphic core complexes in the whole eastern north china craton that have been interpreted as reflecting reactivation of the craton in the late mesozoic after prolonged stabilization since its formation in the late paleoproterozoic it is therefore concluded that the qianhe gold deposit formed as a result of this craton reactivation event

semidiurnal tidal currents in the deep ocean near the east pacific rise between 9 and 10 n spatial and temporal variations of the semidiurnal tidal currents especially the baroclinic components in the deep ocean near a segment of the east pacific rise epr are examined using observations from a set of current meter moorings over the ridge crest the baroclinic semidiurnal tidal current is dominated by the zonal component and is coherent along the observed ridge segment in the direction across the ridge crest the baroclinic semidiurnal tidal current is not coherent and its magnitude decreases away from the ridge crest vertically the baroclinic semidiurnal tidal current covaries in a few hundred meters near the seafloor both the semidiurnal kinetic energy ke and shear show significant subinertial temporal variations by comparing with background forcings the author found that the subinertial variation of the semidiurnal tides over the ridge crest is related to both the spring neap cycles and the eddy induced low frequency flows in the deep ocean particularly their cross ridge components the observation that the baroclinic tidal currents at the axial stations flowing perpendicularly to the ridge crest suggests that the baroclinic semidiurnal tides at the axial stations are generated locally it is therefore probable that the subinertial variation of the baroclinic semidiurnal tides near the epr is due to the eddy modulated internal tide generation since the mesoscale eddies in the eastern tropical pacific vary with the state of the climate the observed eddy modulated internal tide generation connects climate change and variability to the physical and biogeochemical dynamics in the deep ocean and implies an unexplored feedback mechanism potentially affecting the climate system

interannual variability of tehuantepec eddies 1 topex poseidon satellite altimeter observations and the naval research laboratory layered ocean model simulations show interannual variability in the number and intensity of tehuantepec eddies off the mexican southwest coast analysis of the results illustrates that downwelling coastally trapped waves which are generated in the equatorial pacific play a crucial role in the modulation and generation of tehuantepec eddies and a dominant role in tehuantepec eddy interannual variability this introduces a new paradigm in which the generation and modulation of tehuantepec eddies is not exclusively explained in terms of the strong and intermittent tehuantepec wind events in fact the results show anticyclonic eddy formation during periods of calm tehuantepec winds that is specifically exemplified by the formation of two anticyclonic tehuantepec eddies during a 5 month period of weak gulf of tehuantepec winds during summer of 1997 furthermore the satellite observed and nlom simulated proliferation of tehuantepec eddies during el nino years is explained by the corresponding increase in downwelling coastally trapped waves and a lack of increase in the number and strength of tehuantepec wind events during el nino years

internal tides in the southwestern japan east sea abstract this paper investigates the internal tidal energy distribution in the southwestern japan east sea using vertical round trip travel time data from 23 pressure sensor equipped inverted echo sounders pies the records are analyzed by bandpass filtering to separate time dependent variability of the semidiurnal and diurnal bands the semidiurnal internal tides exhibit a horizontal beam pattern of high energy propagating into the open basin they originate from a restricted portion of the shelf break where the korea strait enters the ulleung basin the generation appears to occur at 200 m water depth near 35 5 35 7 n and 130 131 e where the slope of bottom topography matches that of the wave characteristics coinciding with the location where the semidiurnal barotropic cross slope tidal currents are strongest maximum vertical displacement of the thermocline interpreted as a long wave first baroclinic mode from the measured is about 25 m near the generation region annual and monthly var

magma mixing revealed from in situ zircon u pb hf isotope analysis of the muhuguan granitoid pluton eastern qinling orogen china implications for late mesozoic tectonic evolution in this paper we present zircon u pb age and hf isotope data to document the significance of magma mixing in the formation of late jurassic granitoid intrusions in the eastern qinling orogen china the muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite all containing abundant hornblende rich cumulates dioritic xenoliths and mafic magmatic enclaves mmes the monzogranite and granodiorite are intruded by a number of lamprophyre dykes both a cumulate and a dioritic xenolith samples have concordant zircon u pb ages of ca 161 1 ma but possess contrasting hf isotopic compositions the cumulate has more radiogenic zircon hf isotopes with negative ehf t values 7 9 to 2 5 and tdm1 ages of 0 9 1 1 ga indicating its derivation likely from basaltic rocks of the neoproterozoic to early paleozoic kuanping group in the area the dioritic xenolith has much lower zircon ehf t values of 19 5 to 8 8 and tdm2 ages of 2 4 1 7 ga consistent with a juvenile paleoproterozoic crust source presumably represented by the metabasic rocks of the qinling group in the area individual samples of the monzogranite mme and a lamprophyre dyke have u pb ages of 150 1 152 1 and 152 1 ma respectively demonstrating coeval mafic and felsic magmatism in the late jurassic the lamprophyre dyke has homogeneous highly negative zircon ehf t values 29 8 to 24 8 and archean tdm2 ages 3 0 2 7 ga and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source zircons from the fine grained mme show a large range of ehf t between 29 1 and 9 8 overlapping values of the monzogranite and lamprophyre dyke samples zircon u pb age and hf isotopes of the mmes are consistent with their formation by mixing of crustal and enriched mantle derived magmas the main group of zircons from the monzogranite has ehf t values 17 9 to 9 3 and tdm2 ages 2 3 1 8 ga that are compatible with the dioritic xenoliths indicating that the former was produced by partial melting of paleoproterozoic crustal source with involvement of mantle derived magmas mafic magmatism revealed from the muhuguan pluton indicates that the eastern qinling orogen was dominated by lithospheric extension during the late jurassic compilation of existing geological and geochronological data suggests that this extensional event started in late jurassic ca 160 ma and persisted into the early cretaceous until ca 110 ma the jura cretaceous extension may have resulted from the late mesozoic westward subduction of the pacific plate beneath the east asian continental margin

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

propagation of low mode internal waves through the ocean abstract the baroclinic tides play a significant role in the energy budget of the abyssal ocean although the basic principles of generation and propagation are known a clear understanding of these phenomena in the complex ocean environment is only now emerging to advance this effort a ray model is developed that quantifies the effects of spatially variable topography stratification and planetary vorticity on the horizontal propagation of internal gravity modes the objective is to identify baroclinic shoals where wave energy is spatially concentrated and enhanced dissipation might be expected the model is then extended to investigate the propagation of internal waves through a barotropic mesoscale current field the refraction of tidally generated internal waves at the hawaiian ridge is examined using an ensemble of mesoscale background realizations derived from weekly ocean topography experiment topex poseidon altimetric measurements the path of mode 1 is only slightly affected by typical cur

internal tide reflection and turbulent mixing on the continental slope abstract observations of turbulence internal waves and subinertial flow were made over a steep corrugated continental slope off virginia during may june 1998 at semidiurnal frequencies a convergence of low mode onshore energy flux is approximately balanced by a divergence of high wavenumber offshore energy flux this conversion occurs in a region where the continental slope is nearly critical with respect to the semidiurnal tide it is suggested that elevated near bottom mixing k 10 3 m2 s 1 observed offshore of the supercritical continental slope arises from the reflection of a remotely generated low mode m2 internal tide based on the observed turbulent kinetic energy dissipation rate the high wavenumber internal tide decays on time scales o 1 day no evidence for internal lee wave generation by flow over the slope s corrugations or internal tide generation at the shelf break was found at this site

the surface expression of semidiurnal internal tides near a strong source at hawaii part ii interactions with mesoscale currents abstract observations of semidiurnal surface currents in the kauai channel hawaii are interpreted in the light of the interaction of internal tides with energetic surface intensified mesoscale currents the impacts on internal tide propagation of a cyclone of 55 km diameter and 100 m vertical decay scale as well as of vorticity waves of 100 km wavelength and 100 200 m vertical decay scales are investigated using 3d ray tracing the doppler shifted intrinsic frequency is assumed to satisfy the classic hydrostatic internal wave dispersion relation using the local buoyancy frequency associated with the background currents through thermal wind or gradient wind balance the m2 internal tide rays with initial horizontal wavelength of 50 km and vertical wavelength of o 1000 m are propagated from possible generation locations at critical topographic slopes through idealized mesoscale currents approximating the observed currents despite the lack of scale separation between the internal waves and backgroun

coherence of internal tide modulations along the hawaiian ridge long time series of sea level from tide gauges along the north side of the hawaiian ridge and shorter series of dynamic heights inferred from inverted echo sounders moored just north of the main hawaiian islands are examined for evidence of internal tides at the m2 frequency we find that the amplitudes and phases of the m2 tidal components have low frequency variability which is consistent with a superposition of an internal tide with the larger barotropic tide further the low frequency variability is correlated with low frequency changes in the depth of the pycnocline which suggests a simple physical mechanism to account for the low frequency modulations in the internal tidal amplitude these modulations are coherent for long distances along the hawaiian ridge indicating a coherent generation of the internal tide that is consistent with acoustic observations in the north pacific and with recent analyses of sea surface heights from satellite altimetry

variation in noble gas isotopic composition of gas samples from the aegean arc greece abstract in contrast to most other arcs with oceanic plate subduction the aegean arc is characterized by continent continent subduction noble gas abundances and isotopic compositions of 45 gas samples have been determined from 6 volcanoes along the arc 2 islands in the back arc region and 7 sites in the surrounding areas the 3he 4he ratios of the samples ranged from 0 027ra to 6 2ra ra denotes the atmospheric 3he 4he ratio of 1 4 10 6 demonstrating that even the maximum 3he 4he ratio in the region is significantly lower than the maximum ratios of most oceanic subduction systems which are equal to the morb value of 8 1 ra regional variations in the 3he 4he ratio were observed both along and across the arc the maximum 3he 4he ratio was obtained from nisyros volcano located in the eastern end of the arc and the ratio decreased westward possibly reflecting the difference in potential degree of crustal assimilation or the present magmatic activity in each volcano across the volcanic arc the 3he 4he ratio decreased with an increasing distance from the arc front reaching a low ratio of 0 063ra in macedonia which suggested a major contribution of radiogenic helium derived from the continental crust at nisyros a temporal increase in 3he 4he ratio due to ascending subsurface magma was observed after the seismic crisis of 1995 1998 and mantle neon was possibly detected the maximum 3he 4he ratio 6 2ra in the aegean region which is significantly lower than the morb value is not probably due to crustal assimilation at shallow depth or addition of slab derived helium to morb like mantle wedge but inherent characteristics of the subcontinental lithospheric mantle sclm beneath the aegean arc

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

internal tide generation by seamounts ridges and islands a numerical investigation is made into the generation of semidiurnal internal tides by tidal flow over steep topographic features in the deep ocean a fully three dimensional free surface nonlinear hydrostatic model the princeton ocean model is used with real stratification representative tidal forcing and gaussian shaped seamounts ridges and islands for the topography the efficiencies of the different topographies in extracting energy from the barotropic tide and in generating an internal tide are considered each topography produces an internal tide characterized by signals propagating away from the feature as beams that follow internal wave characteristic paths the strength of the signals however varies markedly for different topographies this is largely attributed to the way in which the barotropic tide interacts with the three dimensional topography internal wave generation requires a significant vertical displacement of stratified water by the barotropic tide as it flows over topography it is found that for symmetric seamounts and islands the barotropic flow tends to go around the feature producing only a weak internal tide when elongated into a ridge barotropic flow is forced across isobaths generating an energetic internal tide changing the horizontal aspect ratio of the topography from 1 1 a seamount to 3 1 a ridge increases the resulting baroclinic energy flux by nearly an order of magnitude the slope of the topography relative to that of the internal wave characteristics is also shown to be important with strongest generation occurring at regions of critical or supercritical topographic slope

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

geodynamic setting of mesothermal gold deposits an association with accretionary tectonic regimes mesothermal gold provinces of phanerozoic age are characteristically associated with regional structures along which allochthonous terranes have been accreted onto continental margins or arcs a recurring sequence of transpressive deformation uplift late kinematic mineralization and shoshonitic magmatism is consistent with thermal reequilibration of tectonically thickened crust mesothermal gold camps in the superior province are spatially associated with large scale structures that have been interpreted as zones of transpressive accretion of individual subprovinces or allochthonous terranes these boundary structures are characterized by the sequence of significant horizontal shortening uplift late kinematic mineralization and shoshonitic lamprophyres and therefore may have the same geodynamic significance as phanerozoic counterparts in this model thermal re equilibration of underplated and subducted oceanic lithosphere and sediments in a transpressive regime over time scales of 10 to 40 m y is a necessary precursor to gold mineralization hydrothermal fluids are released along boundary faults and their splays during uplift the uniform temperature low salinity and mole co2 signify uniform source conditions whereas the variable o c sr and pb isotopic compositions of fluids reflect lithological complexity of the source regions and conduits ou the basis of this model it is suggested that mesothermal lode gold deposits are the product of subduction related crustal underplating and deep late metamorphism rather than magmatic or metamorphic events in the supracrustal rocks secular variations in the generation of archean proterozoic and phanerozoic mesothermal au provinces reflect the timing of collisional orogenies within terranes of these eras

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

pacific microplate and the pangea supercontinent in the early to middle jurassic new biostratigraphic data based on radiolarians recovered from deep within the oceanic crustal section of ocean drilling program hole 801c in the western pacific along with existing radiometric information date this oceanic crust as late bajocian early bathonian 170 165 ma the overlying basal sediments at hole 801c are essentially identical in age middle bathonian 164 162 ma to the basal sediments at deep sea drilling program hole 534a in the central atlantic we estimate the time of formation of the pacific plate as 175 170 ma and the time of initial separation of the pangea supercontinent in the central atlantic as 190 180 ma we also identify a time of extensive subduction zone magmatism 175 159 ma at the eastern and western edges of pangea we suggest that the initial plate separation of pangea increased subduction rates at its outer margins and altered the plate boundaries in the pacific superocean leading to formation of the pacific plate

temporal variability of diapycnal mixing in the northern south china sea temporal variability of diapycnal mixing over 7 months in the northern south china sea was examined based on mclane moored profiler observations from 850 to 2200 m by employing a finescale parameterization intensified diffusivity exceeding the order of 10 3 m2 s in magnitude was found over the first half of october 2014 and from 2 december 2014 to 21 january 2015 a typical wintertime strong internal tides and winds in winter were the likely candidates for the high level diapycnal mixing in winter as for the enhanced mixing during october 2014 we suspect the generation of near bottom near inertial waves through the interaction of mesoscale eddies and unique bottom topography was the cause

mantle dynamics of western pacific and east asia insight from seismic tomography and mineral physics abstract recent results of high resolution seismic tomography and mineral physics experiments are used to study mantle dynamics of western pacific and east asia the most important processes in subduction zones are the shallow and deep slab dehydration and the convective circulation corner flow processes in the mantle wedge the combination of the two processes may have caused the back arc spreading in the lau basin affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan and contributed to the formation of the continental rift system and intraplate volcanism in northeast asia which are clearly visible in our tomographic images slow anomalies are also found in the mantle under the subducting pacific slab which may represent a small mantle plumes b upwellings associated with the slab collapsing down to the lower mantle or c sub slab dehydration associated with deep earthquakes caused by the reactivation of large faults preserved in the slab combining tomographic images and earthquake hypocenters with phase diagrams in the systems of peridotite water we proposed a petrologic model for arc volcanism arc magmas are caused by the dehydration reactions of hydrated slab peridotite that supply water rich fluids to the mantle wedge and cause partial melting of the convecting mantle wedge a large amount of fluids can be released from hydrated morb at depths shallower than 55 km which move upwards to hydrate the wedge corner under the fore arc and never drag down to the deeper mantle along the slab surface slab dehydration reactions at 120 km depth are the antigorite related 5 reactions which supply water rich fluids for forming the volcanic front phase a and mg surssasite breakdown reactions at 200 and 300 km depths below 700 c cause the second and third arcs respectively moreover the dehydration reactions of super hydrous phase b phases d and e at 500 660 km depths cause the fluid transportation to the mantle boundary layer mbl 410 660 km depth the stagnant slabs extend from japan to beijing china for over 1000 km long indicating that the arc trench system covers the entire region from the japan trench to east asia we propose a big mantle wedge bmw model herein where hydrous plumes originating from 410 km depth cause a series of intra continental hot regions fluids derived from mbl accumulated by the double sided subduction zones rather than the india asia collision and the subsequent indentation into asia are the major cause for the active tectonics and mantle dynamics in this broad region

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