adakite like and normal arc magmas distinct fractionation paths in the east serbian segment of the balkan carpathian arc are used to assess petrogenetic and regional geodynamic processes associated with late cretaceous subvolcanic intrusions within the sparsely studied timok magmatic complex tmc and ridanj krepoljin zone rkz of eastern serbia the tmc and rkz form part of the apuseni banat timok srednogorie abts magmatic belt a cu au mineralized calc alkaline magmatic arc related to closure of thetethys ocean that extends through romania serbia and bulgaria in se europe zircon ages based on u pb laser ablation inductively coupled plasma mass spectrometry supplemented by existing isotope dilution thermal ionization mass spectrometry data respectively range from 89 to 79 ma and from 76 to 71 ma for the tmc and rkz this age pattern corresponds to cross arc younging away from the european continent adakite like trace element signatures y 18 ppm are linked with samples that extend across the arc these overlap in space and time with samples that conform to a normal arc differentiation trend we performed energy constrained assimilation fractional crystallization ec afc modeling of sr la nd yb concentrations and sr and nd isotopic data results suggest that the two distinct fractionation trends may be explained in terms of a common mantle derived parental magma but distinct fractionation and assimilation paths in the lower and upper crust petrogenesis of the adakite like magmas is consistent with extensive high pressure amphibole fractionation in the lower crust followed by ascent and plagioclase dominant fractionation and assimilation in the upper crust in contrast normal arc signatures appear to have evolved exclusively via an upper crustal differentiation process overall our interpretation supports mantle wedge melting related to weak extension during progressive rollback of a subducting slab

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

miocene to present activity along the red river fault china in the context of continental extrusion upper crustal rotation and lower crustal flow detailed mapping of field relationships along the red river fault reveals information about the distribution and magnitude of slip along the fault about its interactions with other regional fault systems and the relationship between river incision and growth of the eastern margin of the tibetan plateau the red river fault is complex consisting of up to four strands and is dominated by right lateral strike slip displacement evidence for an extensional component of displacement is strongest along the northern part of the fault and decreases to the southeast to zero southeast of a major bend in the fault results of this study indicate dextral displacement on the red river fault is probably at least 40 km 15 16 km of which predates incision of the red river in pliocene time or later and probably also predates plateau growth and development of other regional fault systems long term average slip rate on the red river fault is a minimum of 5 mm yr however regional active tectonics are characterized by rotation of the upper crust around the eastern himalayan syntaxis bounded to the east by the xianshuihe xiaojiang fault system which deflects but does not cut the red river fault the distributed nature of the xianshuihe xiaojiang fault system as it approaches the red river fault is important for accommodating shearing across the strong crustal anisotropy formed by the red river fault and ailao shan shear zone the red river fault appears to terminate in the extending dali fault system in northwest yunnan pliocene surface uplift river incision and rotation around the eastern himalayan syntaxis are inconsistent with the pre pliocene displacement on the red river fault and lateral extrusion along the ailao shan shear zone advocated by the extrusion model this suggests a significant change in crustal conditions on the southeast margin of the tibetan plateau in pliocene time possibly the result of lower crustal flow

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

crustal and upper mantle velocity structure in yunnan southwest china abstract four wide angle seismic profiles acquired in analogue form in the 1980s from yunnan southwest china are re digitized and re interpreted for a detailed p wave velocity structure of the crust and lithospheric mantle the results reveal that the crust can be divided roughly into upper middle and lower crusts with bottom depths of 17 25 26 33 and 33 56 km respectively the moho depth varies from 56 km in the north of yunnan to about 33 km in the southern part and from 38 40 km in the west of yunnan to 42 km in the eastern zone the velocity anisotropy in the lower crust is of 4 4 in contrast with the very low values estimated for the upper middle crust which are close to 1 6 this suggests that the surface deformation in the yunnan area is decoupled from the lower crustal flow the seismic velocity discrepancy along different azimuths in the lower crust and upper mantle beneath the profiling cross points leads to a flow regime in the north south direction that agrees with contemporary tectonic deformation and also provides evidence for the rotation of the lower crust upper mantle medium around the east himalayan foreland high velocity anomalies in the lower crust might be explained as intrusions of mantle material or remaining patches of ancient oceanic crust

unusually thickened crust beneath the emeishan large igneous province detected by virtual deep seismic sounding abstract the emeishan large igneous province elip in southwest china represents the erosional remnant of a vast basalt field emplaced during the permian period spanning 0 25 million km2 the elip occupies a relatively small area relative to other large igneous provinces lips such as the siberian traps and ontong java plateau the original volume of an ancient lip can be constrained from estimates of its intrusive component we used virtual deep seismic sounding vdss to detect the boundary between the crust and the upper mantle moho beneath the elip a strong set of reflections from depths of 60 70 km indicate an unusually thick crust having a p wave velocity of 7 0 7 4 km s located beneath the inner zone of the elip a high velocity lower crustal body hvlcb of this thickness may have been formed by ponding magmas derived from the emeishan mantle plume and associated fractionated materials combined images of crustal structure allow re estimation of emeishan magmatic volume with a total estimated volume of 1 76 3 2 106 km3 the elip appears to have been a typical sized plume generated lip relative to other global examples

structure of the crust beneath the southeastern tibetan plateau from teleseismic receiver functions abstract southeastern tibet marks the site of presumed clockwise rotation of the crust due to the india eurasian collision and abutment against the stable sichuan basin and south china block knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region here we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method we find that the crustal thickness decreases gradually from the tibetan plateau proper to the sichuan basin and yangtze platform but that significant intra crustal heterogeneity exists on shorter lateral scales 0 30 are detected beneath the southeastern margin of tibet but in the sichuan basin and southeastern yangtze platform the values are close to the global average combined with high regional heat flow and independent evidence for mid crustal layers of high electric conductivity the large intra crustal s wave velocity reduction 12 19 and the intermediate to high average crustal poisson s ratios are consistent with partial melt in the crust beneath parts of southeastern tibet these results could be used in support of deformation models involving intra crustal flow with the caveat that significant lateral variation in location and strength of this flow may occur

crustal structure across longmenshan fault belt from passive source seismic profiling 1 we analyse receiver functions from 29 broad band seismographs along a 380 km profile across the longmenshan lms fault belt to determine crustal structure beneath the east tibetan margin and sichuan basin the moho deepens from about 50 km under songpan ganzi in east tibet to about 60 km beneath the lms and then shallows to about 35 km under the western sichuan basin the average crustal vp vs ratios vary in the range 1 75 1 88 under songpan ganzi in east tibet 1 8 2 0 under the lms and decrease systematically across the nw part of the sichuan basin to less than 1 70 a negative phase arrival above the moho under songpan ganzi and sichuan basin is interpreted as a ps conversion from the top of a low velocity layer in the lower crust the very high crustal vp vs ratio and negative polarity ps conversion at the top of lower crust in east tibet are inferred to be seismic signatures of a low viscosity channel in the eastern margin of the tibetan plateau the lateral variation of moho topography crustal vp vs ratio and negative polarity ps conversion at the top of the lower crust along the profile seem consistent with a model of lower crust flow or tectonic escape

crustal structure and deformation of the se tibetan plateau revealed by receiver function data we analyze a large amount of receiver function data recorded by regional seismic networks of the china earthquake administration to estimate crustal structure and deformation beneath the southeast margin of the tibetan plateau and its surrounding areas we develop a comprehensive analysis method that facilitates robust extraction of azimuthal seismic anisotropy from receiver function data the method includes an estimate of fast polarization direction and splitting time by a joint analysis of radial and transverse receiver function data and an evaluation of measurement reliability by statistical and harmonic analysis we find significant seismic anisotropy with a splitting time of 0 5 0 9 s beneath the se margin of the tibetan plateau both the splitting time and fast polarization direction are comparable to those estimated from sks skks data suggesting that crustal anisotropy is the main cause of shear wave splitting of the sks skks wave this also suggests that deformation in the upper mantle is either weak or predominantly vertical and is obviously different from the one in the crust a vertical flow in the upper mantle combined with the observation of a thin lithosphere beneath the study area leads to the inference that part of the mantle lithosphere may have been removed and is descending into deep mantle stations located in the surrounding areas on the other hand exhibit very little to no crustal anisotropy the estimated moho depth and vp vs ratio also show a distinct difference between the se tibetan plateau and the surrounding regions stations on the tibetan plateau have a vp vs ratio of 1 79 which is substantially higher than those measured at the yunnan guizhou yungui plateau 1 69 our observations here are consistent with the scenario that the se tibet has been built by lower crustal flow they also suggest that the mantle lithosphere beneath the margin may have been mechanically decoupled from the upper crust

evolution of magmatic vapor to gold rich epithermal liquid the porphyry to epithermal transition at nevados de famatina northwest argentina fluid inclusions in the subeconomic porphyry cu mo au system at nevados de famatina and closely associated high sulfidation epithermal cu au ag as sb te veins at la mejicana northwest argentina were studied to reconstruct the evolution of hydrothermal fluids from their deep magmatic source to the shallow epithermal environment field geology vein petrography fluid inclusion microthermometry and single inclusion microanalysis by laser ablation inductively coupled plasma mass spectrometry la icp ms were combined to determine the evolution of pressure temperature and ore metal concentrations in the fluids cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequence of the fluid inclusion populations aqueous liquid inclusions of 5 wt percent nacl equiv salinity trapped in quartz sericite pyrite qsp veins between 360 and 325 c contain unusually high concentrations of cu 400 5 000 ppm as 200 ppm sb and te both up to 100 ppm and au several ppm along with other ore forming elements these veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor and high sulfidation epithermal veins with high au grades which are preserved along a high ridge adjacent to the porphyry stock low density vapor and hypersaline liquid i e brine inclusions were trapped in early formed quartz of the porphyry stockwork veins between 450 and 600 c the brine contains lower cu and au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped in phenocrysts and some stockwork veins the latter may be equivalent to a parental fluid the low and intermediate density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz sericite pyrite veins fluid inclusions and geologic time relations indicate that the transitional quartz sericite pyrite veins were the channelways for metal rich aqueous liquids that generated the high sulfidation epithermal cu au deposit these mineralizing liquids are interpreted to have evolved by continuous density increase contraction from a low salinity s rich magmatic fluid of low to intermediate density this vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic hydrothermal complex and probably underwent minor brine separation prior to reaching the present level of exposure epithermal mineral precipitation occurred upon dilution of the low salinity magmatic fluid with meteoric water which entered the hydrothermal system as it was cooled and successively eroded during continued magmatic fluid ascent

anisotropic h k stacking and revisited crustal structure in the southeastern margin of tibet abstract p receiver functions prfs and the h k stacking technique are tools often used to constrain the thickness of the crust and the ratio between the velocities of p and s waves both the crustal depth and the poisson s ratio are very important parameters to study the tectonic evolution of the lithosphere but they can be significantly affected by the presence of crustal anisotropy in order to address this problem we have extended the isotropic stacking approach to include six converted p to s phases that are generated in the anisotropic case instead of only three phases considered in the isotropic case and we have examined the feasibility of the stacking technique using synthetic and real data based on prfs acquired by 108 permanent broadband seismic stations deployed in the southeastern margin of tibet including the sichuan and yunnan areas we have applied the anisotropic h k stacking scheme to investigate the crustal thickness and poisson s ratio the results reveal that the crustal thickness varies from 60 km in the songpan ganzi fold system and the northern part of the sichuan yunnan diamond shaped block near the eastern himalayan syntaxis to 33 km in southern yunnan and that the poisson s ratio varies mostly from 0 24 to 0 32 the highest values of 0 28 0 30 are found along the axis formed by the longmenshan fault the lijiang jinhe fault and the xiaojiang fault and are attributed to the accumulation of lower crustal flow in front of the sichuan basin the highest value of 0 32 is observed at the tengchong volcano area to the north of the indochina block and is attributed to the upwelling of hot mantle associated to the eastward subduction of the indian plate rather than to the expansion of east tibet comparing with the results provided by the isotropic stacking scheme it is appreciated that the crustal depth determined by the anisotropic stacking method well adjusts the observed pattern of gravity anomaly we conclude that the results obtained by anisotropic stacking yield a much better constraint on the estimation of the crustal depth and poisson s ratio when compared to those achieved by isotropic stacking

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

seismic signature of the collision between the east tibetan escape flow and the sichuan basin abstract gps displacement vectors show that the crust in east tibet is being squeezed in an easterly direction by the northward motion of the indian plate and the sichuan basin is resisting this stream and redirecting it mainly towards indochina the longmen shan containing the steepest rise to the high plateau anywhere in tibet results from the strong interaction between the east tibetan escape flow and the rigid yangtze block sichuan basin but the kinematics and dynamics of this interaction are still the subject of some debates we herein present results from a dense passive source seismic profile from the sichuan basin into eastern tibet in order to study the deep structure of this collision zone using p and s receiver function images we observe a sudden rise of the lithosphere asthenosphere boundary lab from 120 to 150 km beneath the sichuan basin and from 70 to 80 km beneath eastern tibet in contrast the depth of the crust mantle boundary moho increases from 36 to 40 km beneath the sichuan basin and from 55 to 60 km beneath eastern tibet the 410 km discontinuity is depressed below eastern tibet by about 30 km although the 660 remains at nearly the same depth throughout the lms from these observations we conclude that the mode of collision that occurs between tibet and the sichuan basin is very different to that found between india and tibet in southern tibet we observe in essence the subduction of the indian plate which penetrates northwards for several hundred kilometers under central tibet the very thin mantle part of the lithosphere beneath eastern tibet may indicate delamination or removal of the bottom of the lithosphere by hot asthenospheric escape flow this process leads to the exceptionally steep topography at the eastern tibetan margin as a result of gravitational buoyancy this view is supported by the very unusual depression of the 410 km discontinuity beneath eastern tibet which could be caused by the dynamics of the sub vertical downward asthenospheric flow

two crustal low velocity channels beneath se tibet revealed by joint inversion of rayleigh wave dispersion and receiver functions abstract competing geodynamic models such as rigid block extrusion continuous deformation and the mid lower crustal flow have been proposed to describe the growth and expansion of eastern tibet however the dynamic processes responsible for plateau evolution and deformation remain poorly understood partly due to resolution limitations of previous models of lithospheric structure on the basis of joint inversion of rayleigh wave dispersion and receiver functions using data from a newly deployed seismic array we have obtained a high resolution 3d image that reveals the distribution of low velocity zones lvzs with unprecedented clarity the prominent feature of our model is two low velocity channels that bound major strike slip faults in se tibet and wrap around the eastern himalaya syntaxis consistent with the clockwise movement of crustal material in this region most large earthquakes in this region occurred in the boundaries of the lvzs we propose that ductile flow within these channels in addition to shear motion along strike slip faults played a significant role in accommodating intensive lithospheric deformation during the eastward expansion of tibet in the cenozoic

geology and alteration geochemistry of the porphyry cu au deposit at bajo de la alumbrera argentina this paper describes the igneous geology alteration mineralogy and geochemistry as well as the ore mineralization history of bajo de la alumbrera a world class porphyry copper gold deposit in northwestern argentina the deposit occurs in the k rich calc alkaline farallon negro volcanic complex located 200 km east of the main andean porphyry copper belt of chile the deposit consists of a composite stock of dacitic porphyry intrusions and extends into the surrounding andesitic volcanic rocks two of the earliest intrusions now occupying the center of the intrusive complex show intense hydrothermal alteration and mineralization these two porphyries host the highest ore grades and were subsequently intruded by several weakly mineralized or barren porphyries intense quartz magnetite k feldspar alteration pervades the first mineralized porphyry whereas similar but lower intensity alteration affected the second laterally this alteration grades into potassic alteration secondary k feldspar and biotite which affects all porphyries except the latest dikes andesitic wall rocks within a hundred meters of the intrusions are dominated by dark hydrothermal biotite an outer halo of propylitic alteration epidote chlorite albite calcite extends up to 1 km into the andesites feldspar destructive alteration sericite pyrite clay minerals gypsum overprints the potassic and propylitic alteration in the volcanic rocks and all porphyries the alteration is locally controlled by faults and late fractures and developed most pervasively upon the outer part of the potassic zone and toward the transition to propylitic alteration in the upper part of the deposit mass balance calculations show small positive changes in net volume for the potassic alteration and minor volume decreases for the chlorite epidote and feldspar destructive alteration the intensely quartz magnetite veined sample of quartz magnetite alteration indicates a total volume increase of 350 percent copper and gold are intimately associated at all scales they occur as composite gold sulfide grains chalcopyrite rarely bornite show a close correlation of ore grades in sample assays and have a closely overlapping distribution on the mine scale a well developed ore shell coincides with potassic alteration and partly with the distribution of intense quartz magnetite veins even though the bulk of the ore minerals now occupy texturally late positions in vugs and fractures a barren zone with intense quartz magnetite potassic alteration and veins but little or no sulfides is interpreted as the focus of upflow of high temperature ore fluids prior to ore mineral saturation and coprecipitation of copper sulfides and gold in the ore shell

the bingham canyon porphyry cu mo au deposit iii zoned copper gold ore deposition by magmatic vapor expansion fluid inclusion microthermometry and laser ablation icpms microanalysis are combined with geological and textural observations to reconstruct the spatial and temporal evolution of magmatic fluids that formed the subvolcanic porphyry cu au mo ore deposit at bingham canyon utah the bingham canyon orebody is exposed over 1 6 km vertically and has the shape of an inverted cup with distinct metal zoning fluid inclusions in the barren but highly veined and potassically altered deep center of the system have intermediate density 0 6 g cm 3 and a salinity of 7 wt percent nacl equiv they have subequal concentrations of na k fe and cu and contain minor co2 the intermediate density fluids were trapped as a single phase mostly at 500 c and 800 bars the au cu rich center near the top of the orebody contains low density vapor inclusions 0 2 g cm 3 coexisting with brine inclusions containing 45 wt percent nacl equiv the vertical transition of different inclusion types indicates phase separation of the single phase input fluid upon volume expansion associated with a pressure drop to 200 100 bars mass balance calculation based on all analyzed inclusion components indicates that the mass of the vapor phase exceeded that of the brine by 9 1 the vapor contained cu as its dominant cation 1 5 wt and contributed about 95 percent of the total amount of copper transported to the base of the orebody bornite chalcopyrite and native gold were precipitated in a narrow temperature interval from 430 to 350 c into secondary pore space created by local redissolution of vein quartz as a result of retrograde quartz solubility in the vapor dominated fluid system intermediate density fluid inclusions in the deepest parts of the peripheral copper ore zone have identical density and composition including similar gold contents as those in the deep center microthermometry and statistical estimation of phase proportions in the inclusions show that the vapor in the peripheral cu rich but au poor ore zone remained denser and the separating brine was less saline 36 wt nacl equiv compared to vapor and brine in the central au cu ore zone this indicates that the peripheral fluids experienced a lower degree of phase separation due to slightly higher fluid pressure at equivalent temperature compared to more strongly expanding fluids in the center of the system the systematic zoning of au cu within the ore shell despite compositionally similar input fluids is interpreted to have resulted from slightly different pressure temperature density evolution paths of magmatic fluids copper was selectively precipitated in the peripheral ore zone in contrast to complete coprecipitation of au and cu in the central upflow zone of the vapor plume the formation of particularly rich cu au ore in the center of the upward expanding fluid plume is consistent with published experimental data showing that the solubility of metals in hydrous vapor decreases sharply with falling pressure due to destabilization of the hydration shell around metal complexes in expanding vapor this interpretation supports the classic vapor plume model for porphyry copper ore formation but additionally emphasizes the role of sulfur bearing complexes as a key chemical control on magmatic hydrothermal metal transport and the deposition of cu and au in porphyry ores our interpretation of selective cu au precipitation as a function of vapor density can explain the more general observation that most gold rich porphyry copper deposits are formed in shallow sub volcanic environments whereas deeper seated porphyry cu mo deposits are generally gold poor

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

crustal structure variation along 30 n in the eastern tibetan plateau and its tectonic implications abstract we determined crustal structure along the latitude 30 n through the eastern tibetan plateau using a teleseismic receiver function analysis the data came mostly from seismic stations deployed in eastern tibet and western sichuan region from 2004 to 2006 crustal thickness and vp vs ratio at each station were estimated by the h k stacking method on the profile the mean crustal thickness and vp vs ratio were found to be 62 3 km and 1 74 in the lhasa block 71 2 km and 1 79 near the bangong nujiang suture 66 3 km and 1 80 in the qiangtang block 59 8 km and 1 81 in the songpan garze block and 42 9 km and 1 76 in the yangtze block respectively the estimated crustal thicknesses are consistent with predictions based on the topography and the airy isostasy except near the bangong nujiang suture and in the qiangtang block where the crust is 5 10 km thicker than predicted indicating that the crust may be denser possibly due to mafic underplating we also inverted receiver functions for crustal velocity structure along the profile which reveals a low s wave velocity zone in the lower crust beneath the eastern tibetan plateau although the extent of the low velocity zone varies considerably the low velocity zone together with previous results suggests limited partial melting and localized crustal flow in the lower crust of the eastern tibetan plateau

the formation of plagioclase chains during convective transfer in basaltic magma the basaltic rock in the lower part of the thick holyoke lava flow in connecticut and massachusetts has been shown to have a remarkable texture with crystals of feldspar linked together in a continuous three dimensional network of chains1 heating experiments have revealed that this network persists to temperatures where the rock is 75 liquid2 and therefore the network was interpreted to have formed at an early stage of crystallization and to have played an important role in the compaction of crystal mush in the lower part of the flow3 4 despite the texture s importance to our understanding of how such basalt flows form the origin of the texture has remained uncertain1 2 3 here we show that although the network is present in the lower third of the flow it was actually formed in the upper solidification front and was transported down in plumes of dense crystal mush convection of this type has been postulated for intrusive magma chambers but corroborative field evidence has been equivocal especially in lava lakes and flows preservation of the roof generated texture in the lower part of a thick flood basalt flow therefore constitutes important evidence for the role of convection in the solidification and differentiation of a simple magma sheet

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

heterogeneous melt and hypersaline liquid inclusions in shallow porphyry type mineralization as markers of the magmatic hydrothermal transition cerro de pasco district peru recently identified occurrences of porphyry style mineralization evidence the link of the world s second largest known epithermal base metal cerro de pasco deposit peru to a porphyry system emplaced at depth they consist of i quartz monzonite dykes and ii the south western part of the large diatreme dome complex adjacent to the main ore bodies of cerro de pasco and iii stockwork of banded quartz magnetite chalcopyrite pyrite porphyry type veinlets crosscutting trachyte porphyritic intrusion cropping out at surface in the central part of the diatreme dome complex the latter porphyry type mineralization observed at the same erosion level as the main epithermal base metal carbonate replacement ore bodies is the subject of this work geological constraints indicate a shallow emplacement level depth 1 km p 270 bar implying rather unusual low pressure and high temperature environment for the formation of porphyry style mineralization the banded porphyry type veinlets record a multiphase history of formation with two successive high temperature n600 c stages followed by a lower temperature b350 c stage more than 90 of the quartz in veinlets precipitates during the first two high temperature stages stage 1 is characterized by the entrapment in hydrothermal quartz of inclusions containing variable proportions of both silicate melt and metal rich hypersaline n90 wt nacl eq liquid hereafter referred to as heterogeneous silicate melt inclusions hsmis the latter are rarely described in porphyry type mineralization we suggest that during stage 1 the inclusions result from heterogeneous entrapment of an evolved hydrous rhyolitic melt mixed with a hypersaline fluid phase at low pressure 270 bar and high temperature n600 c the stage 2 is marked by the entrapment of metaland sulfur rich hypersaline liquid inclusions with salinity around 70 wt nacl eq originated from the adiabatic ascent of magmatic hypersaline fluids transferred fromdeeper parts of the system the lower temperature stage 3 is characterized by an important temperature drop from n600 c to b350 c as revealed bymicrothermometry of aqueous two phase liquid vapor l v inclusions quartz textures revealed by sem cl imaging allowascribing the sulfide precipitation to the low temperaturemineralization stage 3 in situ sims 18o 16o isotope analyses of quartz across the veinlets are indicative of a magmatic signature of the fluids during the first two stages while quartz from stage 3 has oxygen isotopic compositions suggestive of minor contribution of meteoric waters to a predominantly magmatic aqueous fluid 10 vol of meteoric input which probably triggered cu fe sulfide precipitation in the stockwork high metal and sulfur contents of hsmis and hypersaline liquid inclusions determined by la icp ms are interpreted to represent the fluid composition prior to the main sulfide precipitation event the similar pb zn ratio of the bulk ore extracted from the epithermal ore bodies at cerro de pasco and the hsmis and hypersaline liquid inclusions suggest a common source of the fluids associated with the different mineralization styles at cerro de pasco

hydrothermal alteration mineralization and structural geology of the zijinshan high sulfidation au cu deposit fujian province southeast china zijinshan is a world class au cu district located in southwest fujian province southeast china it contains a diverse array of ore deposits hosted by the zijinshan granite complex and surrounding volcano sedimentary rocks associated deposits include high sulfidation epithermal gold copper intermediate sulfidation epithermal polymetallic silver base metal and porphyry molybdenum copper deposits the zijinshan high sulfidation au cu deposit is located in the middle of the zijinshan district and ore zones are hosted in below and adjacent to the zijinshan lithocap the host rocks are part of a jurassic granite complex emplaced between 165 and 157 ma 40ar 39ar age spectra of hydrothermal alunite indicate that hydrothermal activity at zijinshan occurred at 102 86 0 61 to 101 19 0 60 ma and was associated with dacite porphyry dikes that intruded at 104 8 0 9 ma hydrothermal activity produced pervasive silicic and advanced argillic alteration assemblages that are zoned from a central massive quartz alteration domain outward to massive quartz dickite disseminated quartz alunite dickite and disseminated quartz muscovite dickite zones copper sulfides occur in hydrothermally cemented breccias veins and minor disseminations in granite copper minerals include covellite digenite and minor enargite oxide au ores are associated with strongly weathered silicic alteration in the upper parts of the deposit a set of subvertical ne striking faults were active prior to mineralization at zijinshan during mineralization a nw striking fault system controlled the emplacement of veins breccias and dacite dikes kinematic indicators show that most of the nw striking faults were active as normal oblique faults during mineralization postmineralization ene striking dextral strike slip faults are associated with minor conjugate nnw striking faults the premineralization structures at zijinshan likely formed during nw directed compression synmineralization structures formed under subvertical contraction and subhorizontal nne plunging extension postmineralization structures developed in a strike slip regime defined by a nw oriented axis of compression and ne trending axis of extension changes in the styles of pre and synmineralization structures are related to fluctuations in the regional stress regime the transition from compression to extension was fundamental to mineralization postmineralization faults are related to transient local stress regime variations at the deposit scale

receiver functions of seismic waves in layered anisotropic media application to the estimate of seismic anisotropy abstract we investigate the effect of seismic anisotropy on p wave receiver functions calculating synthetic seismograms for p wave incidence on multilayered anisotropic structure with hexagonal symmetry the main characteristics of the receiver functions affected by the anisotropy are summarized as 1 appearance of seismic energy on radial and transverse receiver functions 2 systematic change of p to s ps converted waveforms on receiver functions as ray back azimuth increases and 3 reversal of the ps phase polarity on the radial receiver function in a range of the back azimuth another important influence is shear wave splitting of the ps converted waves and other later phases reverberated as s wave by numerical experiments using synthetic receiver functions we demonstrate that the waveform cross correlation analysis is applicable to splitting ps phases on receiver functions to estimate the seismic anisotropy of layer structure advantages to utilizing the ps phases are 1 they appear more clearly on receiver functions than on seismograms and 2 they inform us about what place along the seismic ray path is anisotropic real analysis of shear wave splitting is executed to the moho generated ps phases that are identified on receiver functions at six seismic stations in the chugoku district southwest japan the time lags between the two arrivals of the split ps phases are estimated at 0 2 0 7 sec and the polarization directions of the fast arrival components are from north south to northeast southwest this result is consistent with recent results of shear wave splitting measurements and the trend of linear epicenter distributions of crustal earthquakes and active fault strikes in the chugoku district

crustal anisotropy from moho converted ps wave splitting analysis and geodynamic implications beneath the eastern margin of tibet and surrounding regions abstract in addition to crustal thickening distinctly different mechanisms have been suggested to accommodate the huge convergences caused by the continental collision between india and eurasia as the transition zone between the two grand tectonic domains of asia the tethys and the pacific east tibet and its surrounding regions are the ideal places to study continental deformation pervasive rock deformation may produce anisotropy on the scale of seismic wavelengths thus seismic anisotropy provides insight into the deformation of the crust and mantle beneath tectonically active domains in this study we calculated receiver function pairs of radial and transverse components at 98 stations located in sichuan and yunnan provinces china we selected 7423 pairs with high signal to noise ratio snr and unambiguous moho converted ps phases pms to measure the pms splitting owing to the crustal anisotropy both the crustal thickness and the average crustal vp vs ratio were calculated simultaneously by the h k stacking method the geodynamic implications were also investigated in relation to surface geological features gps velocities absolute plate motion apm sks skks splitting and other seismological observations in addition to the fast polarization directions fpds of the crustal anisotropy we observed a conspicuous sharper clockwise rotation around the eastern himalayan syntaxis than was revealed by gps velocities the distributed fpds within and near the main active fault zones also favored the directions parallel to the faults this implied that the deformation of a continuous medium revealed by gps motions is a proxy for the deformation of the brittle shallow crust only while the main active faults and the deep crustal interiors both play important roles in the deep deformation our results suggest that the deformation between the crust and upper mantle within the northernmost section of the indochina block is decoupled due to the large difference in the directions between the observations related to the crust gps and crustal anisotropy and mantle apm and mantle anisotropy focusing on the transition zone between the plateau and the south china and indochina blocks we suggest that the motion of the central yunnan sub block is a southeastward extrusion by way of tectonic escape there is less deformation in the deep crust and the motion is controlled by the active boundary faults of the ailaoshan red river shear zone to the west and the xianshuihe xiaojiang fault to the east the lower crustal flow within the plateau southeastward reached the lijiang xiaojinhe fault but further south it was obstructed by the central yunnan sub block

sulfosalt melts evidence of high temperature vapor transport of metals in the formation of high sulfidation lode gold deposits in enargite gold high sulfidation vein deposits magmatic fluid is considered responsible for the transport of metals and sulfur into the depositional regime new data from field emission sem analyses of sulfosalt mineral assemblages primarily enargite and tennantite from el indio chile and summitville colorado provide direct evidence of high temperature deposition including the following 1 the preservation of delicate euhedral quartz assemblages in sulfosalts 2 a range of discrete sb rich sulfosalt quartz feldspar and flourapatite vug filling minerals and 3 symplectic sulfosalt chalcopyrite textures that are arguably quenched melts together these features indicate formation from the vapor phase at high temperatures furthermore euhedral quartz crystals from el indio contain high temperature vapor rich fluid inclusions combined these observations are interpreted as suggestive of deposition in response to vapor phase decompression within fracture arrays that may be considered the analogues of the feeder fractures beneath large low grade silver gold deposits such as yanacocha peru

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

crustal anisotropy estimated by splitting of ps converted waves on seismogram and an application to se tibetan plateau abstract the traditional method to study anisotropy of the crust is utilizing ps converted waves on receiver functions we try to measure the splitting parameters of ps converted waves on seismogram directly ps converted waves on teleseismic seismograms will be unclear due to the interference signals such as the tail of p waves scattering waves and noises however interference signals and ps converted waves have different polarization characteristics through theoretical and observational studies we found that the minimum energy method is applicable to obtain the correct splitting parameters of ps converted waves on seismograms and the time window is relatively easily chosen we selected triennial teleseismic records snr greater than 7 from 51 seismic stations operated by earthquake administration of yunnan province which located in southeastern tibetan plateau and sichuan yunnan area we applied a narrow filter range 0 2 0 6 hz to minimize the interference of the tail of p waves scattering waves and noises finally we obtained 41 measurements from 51 seismic stations with the minimum energy method through the comparison with geodetic data geophysical data and previous anisotropic studies we conclude that the eastward extrusion of the tibetan plateau affects the anisotropic property of the whole crust in southeastern tibetan plateau and its surrounding areas

the carpatho balkanides and adjacent area a sector of the tethyan eurasian metallogenic belt the tethyan eurasian metallogenic belt temb was formed during mesozoic and post mesozoic times in the area of the former tethyan ocean on the southern margin of eurasia with the afro arabian and indian plates to the south it extends from western mediterranean via the alps and southeastern europe through the lesser caucasus the hindu kush and the tibet plateau to burma and sw indonesia linking with the west pacific metallogenic belt the carpatho balkan region is one of the sectors of the temb characterized by some specific features the emplacement of ore deposits is related to a definite time interval and to specific tectonic settings such as

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

analysis of the crustal thickness and poisson s ratio in eastern tibet from teleseismic receiver functions summary crustal thickness and poisson s ratio are two key parameters for investigating tectonic setting and evolution the h k technique has become popular to determinate their values in recent years however ifacomplexstructureexistsinthecrust thereverberatedphasesfromdifferent depths may interfere with each other resulting in reduction or even absence of the ppps phase from the moho such that the h k algorithm may not reveal unambiguous estimates of these two parameters in this paper the h k technique is applied to process a synthetic receiver function for a test case the result of which is compared with that from direct picking of the time delays of the converted and reverberated phases then we process the observational data recorded at two stations in eastern tibet determine the crustal thickness and the velocity ratio using the two methods compare the result with that obtained by xu et al a t the same location and analyse the potential causes for discrepancy as well as the reliability of the two methods finally the crustal thickness and the poisson s ratio in eastern tibet and sichuan basin are determined from the receiver functions recorded at 51 broad band stations using the two different methods the results indicate that the crustal thickness from the time delays is thicker than that from the h k algorithm near the eastern himalayan syntaxis and the crustal poisson s ratio in the rigid sichuan basin from the time delays ranges from 0 26 to 0 28 which are more reasonable than that from the h k 0 28 to 0 34 additionally the poisson s ratio under the faults from the time delays is found to be higher than those on the two sides which is consistent with the tectonic background and previous study

kinematics and dynamics of the southeastern margin of the tibetan plateau summary on the southeastern margin of the tibetan plateau lies a large region which seismicity and gps data show to be actively deforming this paper describes the active faulting in the region and how it relates to the velocity field observed with gps in places the velocity field is accommodated by rotations about vertical axes and most or all of the strain at the surface in the region appears to be released seismically gps velocities are then compared to velocities calculated using a model for deformation driven by gravitational driving forces using rheologies estimated from experimentally derived mineral flow laws the model provides velocities that are in good agreement with observed gps velocities it is not possible to uniquely determine the rheology or flow velocity at depth and there are two forms of model solution which match the observed horizontal surface velocities in one of these vertical planes deform by pure shear and in the other vertical gradients of horizontal velocity are present within the crust two distinct regions of normal faulting earthquakes are present in the region and have mechanisms which are most easily explained by gravity driven deformation

constraining melt geometries beneath the afar depression ethiopia from teleseismic receiver functions the anisotropic h κ stacking technique understanding the nature of the crust has long been a goal for seismologists when imaging the earth this is particularly true in volcanic regions where imaging melt storage and migration can have important implications for the size and nature of an eruption receiver functions and the h stacking h technique are often used to constrain crustal thickness h and the ratio of p to s wave velocities in this paper i show that it is essential to consider anisotropy when performing h i show that in a medium with horizontally transverse isotropy a strong variation in with back azimuth is present which characterizes the anisotropic medium in a vertically transverse isotropic medium no variation in with back azimuth is observed but is increased across all back azimuths thus estimates of are more difficult to relate to composition than previously thought i extend these models to melt induced anisotropy and show that similar patterns are observed but with more significant variations and increases in based on these observations i develop a new anisotropic h stacking technique which inverts h data for melt fraction aspect ratio and orientation of melt inclusions i apply this to data for the afar depression and show that melt is stored in interconnected stacked sills in the lower crust which likely supply the recent volcanic eruptions and dike intrusions this new technique can be applied to any anisotropic medium where it can provide constraints on the average crustal anisotropy

fluid and mass transfer during metabasalt alteration and copper mineralization at mount isa australia metabasalts surrounding the metasediment hosted base metal deposit at mount isa have been modified by metamorphism polyphase deformation and several stages of hydrothermal alteration this study aims to understand the large scale hydrothermal processes that determined the chemical composition of syn to postmetamorphic ore brines prior to being focused into chemicaly anomalous metasediments that acted as a chemical trap for localized copper precipitation field mapping of the metabasalts provided the framework to determine the relative timing of district scale alteration events which were then studied by mineralogic observations and bulk mass balance measurements microthermometry raman microspeetrometry and br cl analyses of fluid inclusions and h o c and s stable isotope measurements on vein minerals were used to characterize the hydrothermal fluids associated with the alteration events all fluids are moderately to highly saline variably ca enriched with high br cl compared to modern seawater and isotopiealy most akin to modern evolved basin or low grade metamorphic brines the timing and fluid tracer observations in conjunction with thermodynamic mass transfer modeling permit the following correlation between district scale alteration processes and the mine scale hydrothermal events associated with copper deposition at mount isa district scale epidote sphene alteration of metabasalts temporally overlapped with the peak of greenschist facies metamorphism and deformation and is widely distributed in flow top breccias and as halos around synmetamorphic quartz calcite veins it is associated with calcic brines with 12 to 38 wt percent cacl 2 nacl equiv and thermodynamic modeling suggests that the observed mineralogy and bulk mass changes can be explained by focusing of metabasalt equilibrated fluids and by reaction with similar rocks at somewhat higher temperature similar timing and fluid characteristics are associated with dolomitic alteration at the mount isa mine where mixing of metabasalt derived calcic brine with metamorphic co 2 from the metasediments led to massive dolomite precipitation kilometer scale fracture zones associated with carbonate fe oxide alteration calcite albite magnetite or hematite or biotite or chlorite cut all penetrative foliations in the metabasalts east of mount isa they are locally associated with uranium mineralization and are characterized by medium salinity nacl rich fluid inclusions 8 93 wt nacl equiv carbonate fe oxide alteration is interpreted to mark channelways of infiltration by oxidized sulfate bearing brines from outside the metabasalt sequence possibly from an overlying evaporitic cover sequence fluid characteristics evidence for extreme copper mobility and timing criteria of alteration relative to deformation suggest a temporal and possibly genetic correlation with the main copper and silica deposition stage at the mount isa mine mg chlorite rutile alteration is restricted to metabasalts immediately below the copper deposit and the vicinity of the mount isa fault zone where higher grade amphibolite facies metabasalts were upthrust against the greenschist facies metabasalts and metasediments now hosting the copper ore bodies mg chlorite rutile alteration of metabasalts and copper mineralization in the adjacent reduced sediments can both be explained by fluid focusing along an actively extending contact zone between the oxidized metabasalts and the reducedmetasediments the brines focused into this contact zone were initially oxidized as a result of infiltration through the carbonate fe oxide fracture zones and less altered metabasalts and became reduced by reaction with the metasediments the unusual geochemical and isotopic low 13 c and high 34 s composition of mg chlorite rutile alteration can be explained as a result of back flow of reduced fluids from the metasediments into the metabasalts although mg chlorite rutile alteration of metabasalts probably liberated some of the copper now present in the orebodies this alteration may be a relatively localized effect associated with the site of ore deposition rather than an essential sourcing mechanism for the copper the regional feature of greatest significance to ore formation at mount isa and to exploration for similar high grade copper deposits elsewhere is not the somewhat elevated initial copper content of the metabasalts nor their locally significant copper depletions but their moderately high oxidation state evident from the ubiquitous occurrence of fe rich epidote and the large scale fe oxide altered fracture zones oxidation of the basalts or any other silicate rocks favored high copper solubility along extensive transport paths and provided the essential chemical contrast to the depositional environment which was anomalously reduced and sulfide rich as a result of an earlier process of sedimentary to diagenetic pb zn fe s mineralization

quantitative textural analysis of packings of elongate crystals the spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush and in turn is controlled by the rate of crystal growth and accumulation a predominant non spherical habit for igneous minerals brings into question the use of spherical particles in reference packings used for quantification of spatial distribution furthermore variations of crystal clustering ordering with length scale require spatial statistics which take into account the distribution of particles beyond nearest neighbours using random close packings of spherocylinders we demonstrate the importance of aspect ratio for the aggregation index usually known as r and show that packings of spherical particles have more structure than packings of rods the spatial distribution functions demonstrate that the plagioclase grains in the colonnade from the holyoke basalt are clustered on a length scale of 0 5 mm understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques to well understood environments

crustal structure beneath the eastern margin of the tibetan plateau and its tectonic implications 1 two crustal cross sections through the eastern margin of the tibetan plateau are jointly determined from deep seismic sounding the e w trending line aa passes through the western sichuan plateau including the songpan garze terrane and the longmenshan fault belt and ends in the sichuan basin a part of the yangtze craton line bb has a trend of nne and crosses the songpan garze terrane two dimensional crustal structures along the profiles were jointly determined by the additional use of existing deep seismic sounding data our seismic velocity models indicate that the western sichuan plateau and the sichuan basin have crustal thicknesses of 62 and 43 km average crustal p wave velocities of 6 27 and 6 45 km s and lower crustal vp 6 5 km s thicknesses of 27 and 15 km respectively density models constructed from the seismic velocity models are consistent with observed bouguer gravity anomalies we infer that collision between the tibetan plateau and the yangtze craton has caused thickening of the lower crust and uplift of the western sichuan plateau we detect a low velocity layer in the upper crust of the western sichuan plateau but observe no equivalence in the sichuan basin west dipping thrusts may detach into this low velocity layer the seismic phase pmp in the western sichuan plateau has low amplitude suggesting high attenuation in the lower crust qp of 100 300 we suggest that the high attenuation is a consequence of lower crustal flow caused by the large lower crustal thickness beneath the western sichuan plateau

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

disaggregated anisotropy and deformation style of the upper and lower crust in the southeastern tibetan plateau abstract the arrival times of the converted p to s phase at an intra crustal discontinuity pis or the moho pms provide a powerful diagnostic tool for detecting anisotropy with horizontal symmetry axis in this study we used pis and pms arrival times on p receiver functions to determine the anisotropy of the crust from the seismic data recorded by 285 temporary broadband stations and 3 permanent stations deployed in the southeast margin of tibet first we measured the splitting parameters of the upper crust by fitting the pis phase arrival and then we adjusted the pms phase arrival to obtain the splitting parameters of the lower crust after correcting for the effect of the anisotropic upper crust on the pms arrivals so we achieved 75 double layer splitting measurements in the upper crust the splitting times vary between 0 05 s and 1 34 s with an average of 0 53 s 0 29 s while in the lower crust they range from 0 06 s to 1 42 s with an average of 0 62 s 0 33 s the results confirm that the crust is remarkably anisotropic in the southeastern margin of tibet in the upper crust the fast wave polarization directions clearly show a clockwise rotation around the eastern himalayan syntax suggesting that the extensional fluid saturated microcracks induced by rigid extrusion from central tibet are mostly responsible for the observed anisotropy in contrast the lattice preferred orientation of anisotropic minerals induced by a channel flow is the main contributor to the lower crust anisotropy

refined timing of porphyry copper formation in the serbian and bulgarian portions of the cretaceous carpatho balkan belt the bor district in serbia and the panagyurishte district in bulgaria are part of the mineralized late cretaceous carpatho balkan igneous belt 40 ar 39 ar laser probe radiometric age information from porphyry copper deposits of the two districts in this study provides new constraints on the timing of host rock emplacement and the hydrothermal alteration that is linked to the porphyry mineralization in the bor district igneous hornblende from the host intrusions has an average plateau age at 84 0 1 5 ma 2 the timing of alteration is constrained by white mica with an average inverse isochron age of 85 4 1 8 ma and an average plateau age at 86 6 1 0 ma elevated by a small excess 40 ar contribution together these analyses indicate that porphyry mineralization occurred around 85 ma in the panagyurishte district previous isotopic studies have produced much older host rock ages in the northwest than mineralization ages in the southeast ages of igneous and alteration mineral separates from elatsite and medet in the northwestern and central parts of the district from the present study confirm pluton emplacement at 90 8 0 8 ma but much younger alteration at 79 5 0 5 ma it is proposed that two episodes of magmatic hydrothermal activity have affected the district one at 91 ma with the emplacement of the majority of the plutonic rocks and one at 79 to 80 ma during which the alteration micas were reset integration of these new ages with existing radiometric age information emphasizes the complex history of magmatic hydrothermal activity along the immature late cretaceous carpatho balkan convergent margin

three dimensional velocity structure of crust and upper mantle in southwestern china and its tectonic implications using p and s arrival times from 4625 local and regional earthquakes recorded at 174 seismic stations and associated geophysical investigations this paper presents a three dimensional crustal and upper mantle velocity structure of southwestern china 21 34 n 97 105 e southwestern china lies in the transition zone between the uplifted tibetan plateau to the west and the yangtze continental platform to the east in the upper crust a positive velocity anomaly exists in the sichuan basin whereas a large scale negative velocity anomaly exists in the western sichuan plateau consistent with the upper crustal structure under the southern tibetan plateau the boundary between these two anomaly zones is the longmen shan fault the negative velocity anomalies at 50 km depth in the tengchong volcanic area and the panxi tectonic zone appear to be associated with temperature and composition variations in the upper mantle the red river fault is the boundary between the positive and negative velocity anomalies at 50 km depth the overall features of the crustal and the upper mantle structures in southwestern china are a low average velocity large crustal thickness variations the existence of a high conductivity layer in the crust or and upper mantle and a high heat flow value all these features are closely related to the collision between the indian and the asian plates

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

pn anisotropic tomography and dynamics under eastern tibetan plateau we present a new anisotropic tomographic model of the uppermost mantle around eastern tibet using pn traveltime data from a newly deployed temporary seismic array and recent observation bulletins of chinese provincial networks our results are generally consistent with previous results but provide new insights into the dynamics of tibetan plateau prominent high velocity high v anomalies are visible under alashan block and qaidam and sichuan basins which clearly outline their tectonic margins a distinct high v zone representing the double sided subduction of indo eurasian plates is imaged from lhasa block to the south of qaidam basin a pronounced low velocity low v zone is observed from songpan ganzi block to southern chuan dian diamond block suggesting the existence of hot material upwelling there crustal strong earthquakes frequently occurred around high v anomalies or transition zones from high v to low v anomalies suggesting that these earthquakes could be related to lateral heterogeneities in the mantle the pn fast direction approximately rotates around eastern himalayan syntaxis and it is tangential to the margins of sichuan basin suggesting that the mantle material flow of tibetan plateau may have affected east china in the yunnan region to the south of 26 n the pn fast direction is different from sks splitting results indicating that the mantle lithosphere could be mechanically decoupled at certain depth below the uppermost mantle which might be attributable to the subduction of indian or burma slab although the correlation between anisotropy and velocity is complicated anisotropy strength could be associated with the pattern of velocity anomalies in the region

seismic anisotropy due to preferred mineral orientation observed in shallow crustal rocks in southern alaska laboratory velocity measurements and structural field relations explain the observation of a significant seismic anisotropy within highly foliated rocks in southern alaska the orientation of the principal compressive stress indicates that this anisotropy is not related to extensive dilatancy but can be satisfactorily explained by the foliation of the metasedimentary rocks laboratory measurements indicate a significant anisotropy within these rocks even at pressures well above those thought to close microcracks these observations document that anisotropy related to preferred mineral orientation may be widespread in continental rocks thus pervasive foliation can play a more important role in causing anisotropy than dilatancy and inferences of principal stress orientations solely from anisotropy may be erroneous

3 geochronology and geodynamics of late cretaceous magmatism and cu au mineralization in the panagyurishte region of the apuseni banat timok srednogorie belt bulgaria abstract the apuseni banat timok srednogorie abts belt europe s most extensive belt of calc alkaline magmatism and cu au mineralization is related to the subduction of the tethys ocean beneath the european continental margin during the late cretaceous phase of the alpine himalayan orogeny economic deposits are restricted to certain segments along the belt and all major porphyry style and high sulphidation ore deposits in bulgaria are aligned on the panagyurishte corridor a narrow zone obliquely crossing the abts belt this paper reviews the geology geochemistry and geochronology of igneous and hydrothermal events along this corridor in a profile extending from the european continental basement in the north to the accretionary complex of the rhodopes in the south extensive u pb dating of zircons from subvolcanic intrusions and major plutons supplemented by published age data for magmatic rocks and hydrothermal ore deposits obtained by other methods reveals a general younging of magmatism from ca 92 ma in the north elatsite to ca 78 ma in the south capitan dimitrievo cu au deposits are restricted to the northern and central parts of the profile ranging in age from 92 to 86 ma while the southernmost part exposes more deeply eroded mid crustal plutons devoid of economic mineralization the age progression correlates with a north to south geochemical trend of decreasing crustal input into mantle derived magmas magmatism and ore formation in individual magmatic hydrothermal complexes along the profile is much shorter lived for example subvolcanic intrusions and porphyry cu au mineralization at the elatsite deposit and andesitic volcanism and high sulphidation au as cu mineralization at chelopech all occurred within a time span of about 1 million years the age progression of calc alkaline magmatism within the panagyurishte region bulgaria from north to south is explained as a consequence of slab retreat during oblique subduction this led to transtensional block faulting and subsidence and thus to the preservation of near surface magmatic hydrothermal products including economic cu au deposits accretion of continental fragments in the rhodopes south of the abts belt led to greater uplift of the youngest late cretaceous intrusions this removed any ore deposits that might have been formed in this area

fluid inclusion studies of the chinkuashih high sulfidation gold copper deposits in taiwan epithermal high sulfidation au cu deposits at chinkuashih in northeastern taiwan are found both within pleistocene calc alkaline volcanic rocks and the miocene sedimentary rocks the deposits consist of gold copper veins of the penshan group and breccia pipes of the tushihshan changjen group primary two phase inclusions in hydrothermal quartz and secondary two phase inclusions in hydrothermal quartz as well as igneous quartz phenocrysts probably represent fluids related to mineralization these inclusions have homogenization temperatures generally between 1908c and 2808c and salinities mostly from 0 5 5 0 wt nacl eq in the penshan group microthermometric data indicate that variable amounts of boiling mixing and cooling occurred in the hydrothermal system based on the th of inclusions trapped from boiling fluids and the co contents of the inclusions the hydrostatic pressure is estimated at 6 9 7 9 mpa in the tushihshan 2 changjen group the microthermometry of sulfur gas bearing secondary two phase fluid inclusions from hydrothermal quartz shows bimodal contents for a certain th value perhaps due to the intermittent incursion of brine at depth by phreatic or phreato magmatic explosions the presence of poly phase liquid q vaporq halite sylvite opaques fluid inclusions with high th 3078c 4848c and high salinities 30 51 wt nacl eq in one sample suggests a dense brine of probable magmatic derivation circulated in the chinkuashih system halite bearing inclusions which were homogenized by vapor disappearance coexisting with low salinity vapor rich inclusions in this sample may have been trapped in an immiscibility field at vapor pressures from 7 5 to 21 5 mpa halite bearing inclusions which were homogenized by halite dissolution after the vapor disappearance may have been trapped under even greater pressures fluid inclusion gas in samples were analyzed with a qms the results of bulk analyses indicate that these inclusions contain 99 45 99 67 mol h o 0 27 0 52 mol 2 co 0 015 0 066 mol n 0 0015 0 015 mol ch and small amounts of so in three samples these data suggest that 22 4 2 the inclusion fluids are dominantly meteoric waters that interacted with host rocks and accumulated upward fluxing magmatic volatiles the fluid inclusion data indicate that the hydrothermal fluids related to the ore deposition of the high sulfidation au cu deposits at chinkuashih are characterized by the interaction of magmatic fluids with meteoric water under epithermal conditions q 1999 elsevier science b v all rights reserved

silicate replacive high sulfidation massive sulfide orebodies in a porphyry cu au system bor serbia the cu au deposit of bor serbia represents a continuum of mineralization styles from porphyry style ore occurring in quartz magnetite chalcopyrite veins and chalcopyrite disseminations to high sulfidation epithermal cu au ores in pyrite chalcopyrite and anhydrite sulfide veins decisive for the great economic importance of bor is the presence of exceptionally rich high sulfidation massive sulfide orebodies composed of pyrite covellite chalcocite digenite and minor anhydrite and enargite they form irregular bodies measuring 0 5 10 million tons of ore grading up to 7 cu hosted by andesites and surrounded by intense argillic alteration this study focuses on a small but rich underground orebody mined out recently where limited drillcore is preserved for quantitative geochemical study this paper documents the vein relationships within the deep porphyry style orebody of borska reka the transitional porphyry epithermal veins and the overlying and laterally surrounding epithermal massive sulfides of the bor deposit geological observations indicate that the formation of massive sulfide orebodies concludes the ore formation mass balance calculations recast into geologically realistic bulk fluid rock reactions confirm textural evidence that near isovolumetric replacement of andesite host rocks is the dominant formation mechanism of massive sulfide orebodies at bor whereby all lithophile elements including si are dissolved and only ti stays relatively immobile while net volume changes for individual mineralization styles within the massive sulfide orebody vary from 16 volume loss to 127 volume gain overall volume change for the whole massive sulfide orebody was probably slightly negative brecciation is important only as means of creating channelways for reactive fluid that turns the andesite protolith into massive sulfide whereas net breccia infill occurred only locally

flux of volatiles and ore forming metals from the magmatic hydrothermal system of satsuma iwojima volcano the satsuma iwojima volcano southwest japan degasses 5 x 10 6 t yr h 2 o 9 x 10 4 t yr s and 6 x 10 4 t yr cl from high temperature 880 c fumaroles atop a now altered rhyolite dome that erupted 1200 yr ago acidic hot springs ph 1 1 1 8 discharge 20 x 10 6 t yr h 2 o to the sea this water is composed of 1 part magmatic vapor absorbed by 6 parts meteoric ground water the cl and so 4 in solution originate from the vapor whereas cation components are derived largely by dissolution of the rhyolite the flux of pb zn cu and mo in the vapor and acidic springs ranges from 0 1 to 10 t yr each whereas the au flux is 10 5 and 10 3 t yr respectively the low concentrations of nacl and metals in the vapor are due to the condensation of a hypersaline liquid from the vapor during ascent and depressurization meaning that the atmospheric pressure vapor does not reflect the composition of the fluid exsolving from the magma neither this low pressure vapor nor the acidic waters can account for high sulfidation cu au ore deposits deduced to have formed in this environment such mineralization requires the subsequent ascent of a metal rich fluid

alunite 40ar 39ar and zircon u pb constraints on the magmatic hydrothermal history of the zijinshan high sulfidation epithermal cu au deposit and the adjacent luoboling porphyry cu mo deposit south china implications for their genetic association

microthermometry of enargite hosted fluid inclusions from the lepanto philippines high sulfidation cuau deposit abstract the spatial relation between porphyry and high sulfidation epithermal deposits is particularly well revealed in the mankayan mineral district of northern luzon philippines where the lepanto high sulfidation cu au deposit lies over and adjacent to the far southeast fse porphyry cu au deposit consequently a study was undertaken to characterize the fluids responsible for epithermal mineralization in this environment the ore stage at lepanto consists of enargite luzonite cu 3 ass 4 pyrite tennantite tetrahedrite and chalcopyrite infrared petrography of the enargite reveals variable transparency with growth banding and twinning visible in euhedral specimens two phase liquid vapor fluid inclusions occur as primary and secondary types ranging from t h of fluid inclusions in enargite were measured from within the lateral 3 0 km and vertical 0 5 km extent of the enargite mineralization these values show a cooling trend toward the northwest away from the area over the porphyry deposit with average t h ranging from 285 c proximal to 166 c distal ice melting temperatures t m were measured using a cycling technique as ice was usually not visible in frozen inclusions apparent salinities range from 4 5 to 0 2 eq wt nacl with samples from the margins of the deposit showing a general decrease in apparent salinity with lower t h secondary fluid inclusions in quartz phenocrysts tend to have a higher average t h and lower apparent salinities compared to enargite hosted inclusion fluids from the same locations several samples of pyrite are also transparent to ir radiation and show internal features such as growth banding and in one instance a two phase liquid vapor fluid inclusion this inclusion yielded a salinity of 1 2 eq wt nacl there is a large discrepancy in t h and apparent salinities between the enargite mineralization and the subjacent porphyry deposit despite contemporaneous formation suggesting that the hot 500 c hypersaline magmatic brines associated with porphyry mineralization did not directly ascend to the elevation of the enargite deposit however absorbtion of magmatic vapors into overlying meteoric water may have created the mineralizing fluid of the lepanto deposit as this liquid moved to the northwest along the lepanto fault it was cooled and diluted by mixing with groundwater resulting in enargite deposition

crustal structure and deformation under the longmenshan and its surroundings revealed by receiver function data abstract the convergence of india and eurasia and the obstruction from the rigid sichuan basin cause the longmenshan lms to have the steepest topographic gradient at the eastern margin of the tibetan plateau however the mechanisms of surface uplift are still controversial in this paper we estimate the crustal structure and deformation under the lms and its surroundings by analyzing a large amount of receiver function data recorded by regional seismic networks of the china earthquake administration we apply a comprehensive splitting measurement technique on ps conversion phase at the moho moho ps splitting to calculate crustal anisotropy from azimuthal variations of receiver functions our results show that most of the seismic stations beneath the lms area exhibit significant seismic anisotropy with the splitting time of 0 22 0 94 s and a fast polarization direction of nw se while less or even no crustal anisotropy has been observed under the sichuan basin comparing the fast polarization directions of moho ps splitting with the indicators of lithospheric deformation such as shear wave splitting absolute plate motion and global positioning system imply a consistent tendency of deformation between the lower crust and upper mantle but decoupling deformation in the crust beneath the lms area we further compare moho ps splitting time to that estimated from previous sks splitting indicating that crustal anisotropy is an important source of the sks splitting time in this study area in addition a thick crust 50 km with high vp vs values 1 74 1 86 is also observed using the h stacking method these seismic observations are consistent with the scenario that the lms area has been built by the lower crustal flow combined with the seismic reflection refraction profile and geology studies we further suggest that the lower crustal flow may extrude upward into the upper crust along the steeply dipping strike faults under the lms area resulting in the surface uplift of the lms

magmatic underplating and crustal growth in the emeishan large igneous province sw china revealed by a passive seismic experiment abstract in an attempt to characterize the subsurface structure that is related to fossil mantle plume activity a comprehensive geophysical investigation was conducted in the emeishan large igneous province elip the nature and geometry of the crust were examined within the scheme of the domal structure of elip which comprises the inner intermediate and outer zones which are defined on the basis of the biostratigraphy of pre volcanic sediments the bulk crustal properties within the inner zone are characterized by high density high p wave velocity high vp vs ratios and large crustal thickness a visible continuous seismic converter is present in the upper part of the crust in the whole intermediate zone and the eastern part of the inner zone but it is absent in the inner zone where another seismic converter is observed in the lower part of the crust the geometric configuration of these converters is attributable to the addition of mantle derived melts to the pre existing crust and subsequent interaction between them the crustal geometry which is delineated by the migrated image of receiver functions from the passive seismic experiment and the crustal properties collectively suggest that a mafic layer of 15 20 km thickness and 150 180 km width exists at the base of the crust in the inner zone such a mafic layer reflects a vertical crustal growth through magmatic underplating at the base of the crust and intraplating within the upper crust the salient spatial correlation between the deep crustal structure and the dome strongly supports a genetic link between crustal thickening and plume activity if the pre volcanic domal uplift is generated by the permian emeishan mantle plume this arrangement is further supported by the consistency of the extent of crustal uplift estimated by isostatic equilibrium modeling and sedimentary data this study therefore characterizes and provides evidence for a plume modified crust in a large igneous province

on the formation and evolution of the pannonian basin constraints derived from the structure of the junction area between the carpathians and dinarides 1 the large number and distribution of rollback systems in mediterranean orogens infer the possibility of interacting extensional back arc deformation driven by different slabs the formation of the pannonian back arc basin is generally related to the rapid miocene rollback of a slab attached to the european continent a key area of the entire system that is neglected by kinematic studies is the connection between the south carpathians and dinarides in order to derive an evolutionary model we interpreted regional seismic lines traversing the entire serbian part of the pannonian basin the observed deformation is dominantly expressed by the formation of miocene extensional detachments and half grabens the extensional geometries and associated synkinematic sedimentation that migrated in time and space allow the definition of a continuous and essentially asymmetric early to late miocene extensional evolution this evolution was followed by the formation of few uplifted areas during the subsequent latest miocene quaternary inversion the present day extensional geometry changing the strike across the basin is an effect of the clockwise rotation of the south carpathians and apuseni mountains in respect to the dinarides our study infers that the carpathian rollback is not the only mechanism responsible for the formation of the pannonian basin an additional middle miocene rollback of a dinaridic slab is required to explain the observed structures furthermore the study provides constraints for the pre neogene orogenic evolution of this junction zone including the affinity of major crustal blocks obducted ophiolitic sequences and the sava suture zone

comprehensive crustal structure and seismological evidence for lower crustal flow in the southeastern margin of tibet revealed by receiver functions abstract the lower crustal flow model has become an interesting proposal to describe the growth and expansion of eastern tibet to date however the geophysical results are not definitive due to the non uniqueness of the solutions found through data inversion and the resolution limitations in this study the polarity of p to s converted phases at intra crustal interfaces are analyzed in order to reveal evidence for low seismic velocity and lower crustal flow in southeastern tibet we are interested in a joint study that is both a mapping of the crustal structure moho topography and poisson s ratio and an attempt to constrain an iclvz we have determined the crustal thickness and poisson s ratio from p prfs and s srfs receiver functions acquired in 108 permanent seismic stations deployed in the sichuan and yunnan areas also we have obtained 98 measurements of pms phase splitting parameters at the array stations the crustal thickness provided by prfs is consistent with that given by srfs it varies from 60 km in the songpan ganzi sg fold system and the northern part of the sichuan yunnan diamond shaped block sydsb near the eastern himalayan syntaxis to 33 km in southern yunnan the poisson s ratio varies mostly from 0 24 to 0 32 the highest values 0 28 0 32 are found along the axis formed by the longmenshan fault the lijiang jinhe fault and in the tengchong volcano area the value of 0 28 observed in sydsb and the sg fold system is attributed to the presence of a low velocity zone in the lower crust and partly to the great sediment thickness in sichuan basin the crust is clearly anisotropic in the southeastern margin of tibet the fast wave polarization direction exhibits a nw se regional bias while the time delay varies between 0 07 s and 1 27 s being the average 0 54 s 0 12 s implying the existence a strong shear zone in the lower crust based on the negative polarity observed after the direct p wave in teleseismic receiver functions we have detected an intra crustal low velocity zone iclvz in a wide region including east and southeast of tibet and southern yunnan so both the shear zone and iclvz suggest the existence of lower crustal flow the reverberation ppps and psps ppss phases at the moho are clearly weaker in sydsb and the sg fold system than in the indochina block and eastern yunnan implying that sydsb has a structure and tectonic history different from indochina on its west side and eastern yunnan on its east side the above results provide seismological evidence for a lower crustal flow spreading from the eastern tibet and that in its advance southward has invaded sydsb widely crossed the lijiang jinhe fault and reached southern yunnan

three dimensional s velocity structure of the crust in the southeast margin of the tibetan plateau and geodynamic implications abstract the lower crustal flow model is one of several competing models considered to interpret the growth and expansion of southeastern tibet however the dynamic processes involved in the evolution and deformation of the tibetan plateau remain poorly understood due to the absence of reliable geophysical observations in this study 159 earthquakes of magnitude ms 6 2 were selected which were recorded by 50 permanent broadband stations deployed in southwest china and 1873 pairs of p wave receiver functions with high signal to noise ratio were isolated on the basis of a linearized inversion algorithm a two step inversion procedure was implemented that not only reduced the dependence of the inversion results on the initial models but also provided a statistical estimation of the solution thus we obtained an accurate 3d image of the s wave velocity structure of the crust and uppermost mantle in the southeast margin of the tibetan plateau our results reveal that an extensive intracrustal low velocity zone spreads beneath southwest china and further suggest that a lower crustal flow coming from eastern tibet is blocked by the jinshajiang red river fault to the west and the xiaojiang fault to the east and extends largely by the sichuan yunnan diamond shaped block this crustal flow along the southeastern margin of tibet does not appear to be restricted to two narrow low velocity channels as was advanced but rather reflects the southeastward extrusion of crustal material as a way of tectonic escape

seismic upper mantle discontinuities beneath southeast tibet and geodynamic implications abstract in this study a total of 13 080 p receiver functions and 2800 s receiver functions recorded by 116 stations in southeast tibet are used to determine the depths of the moho the lithosphere asthenosphere boundary lab and the 410 km and 660 km discontinuities the results show that the lab depth increases from 80 100 km beneath southern yunnan to 140 180 km beneath sichuan most of the 410 km discontinuity is flat and at 410 km depth with a slight depression of 10 20 km beneath the longmenshan lms fault the central sichuan yunnan sy diamond shaped block and southeastern yunnan for the 660 km discontinuity the greatest depth occurs beneath the lms and southern yunnan reaching 670 680 km the deepening of 660 km discontinuity is attributed to compositional heterogeneity within the mtz or dynamic pressure on the discontinuity additionally the velocity of movement in the crust and upper mantle beneath sy is different in yunnan crustal movement is southeastward whereas across the red river fault part of the crustal motion is redirected southwest by the westward rollback of the mantle beneath myanmar the interaction between the asthenosphere moving northeastward from myanmar and southeastward from tibet near latitude 26 n causes the crust and lithospheric mantle beneath southern yunnan to have different movement directions

seasonal patterns of 3d crustal motions across the seismically active southeastern tibetan plateau abstract we study the three dimensional 3d seasonal crustal deformation and its relationship with local seismicity based on continuous gps cgps mass loading models and seismicity data covering the period from 2010 to 2018 in the southeastern tibetan plateau setp of the 3d seasonal motions vertical motion is the most significant followed by the northward and eastward directions with average annual amplitudes from cgps of 9 28 mm 1 62 mm and 0 72 mm respectively the annual motions predicted by the hydrological mass loading hydl model in all directions are about 3 4 times larger than that of the atmospheric mass loading atml model but smaller than the cgps measurements the initial phase difference between the cgps and loading models can be nearly eliminated by combining the atml and hydl models which helps to fit the cgps results better the average weighted root mean square wrms reduction ratios of the atml hydl model and their combination are 0 30 0 77 and 0 88 respectively this indicates that the seasonal vertical crustal motions observed by cgps in the setp are dominated by seasonal loading motions from the atml and hydl in four subregions where no m 4 earthquakes had occurred in the past decade we observe an anti correlation between equivalent water height ewh from the grace gravity recovery and climate experiment and the vertical displacement derived by cgps it shows an anti correlation relationship between the ewh and seismicity in three subregions and positive correlation in one subregion which underscores the importance of hydrological loading on seismicity in the setp

a new statistical description of the spatial distribution of minerals in rocks we propose a new method to describe quantitatively rock textures with a special emphasis on the spatial distributions of minerals the method employs a statistical approach and examines probabilities for particular mineral pairs to occur for variable interpoint distances the probability is measured by counting the number of point pairs on digitized images of rock textures that are obtained with a computer aided digital image processor several problems in obtaining textural images and processing the data that were encountered in the actual procedures are reviewed the method is applied to two rock samples granite and contact metamorphic hornfels the method is useful in examining the extent of homogeneity and randomness of mineral distributions and spatial correlations among minerals of different kinds

tectonic configuration of the apuseni banat timok srednogorie belt balkans south carpathians constrained by high precision r e o s molybdenite ages the apuseni banat timok srednogorie magmatic metallogenic belt abts belt forms a substantial metallogenic province in the balkan south carpathian system in southeastern europe the belt hosts porphyry skarn and epithermal deposits mined since pre roman times generally the deposits prospects and occurrences within the belt are linked to magmatic centers of calc alkaline affinity fifty one rhenium osmium re os ages and re concentration data for molybdenites define systematic geochronologic trends and constrain the geochemical metallogenic evolution of the belt in space and time from these data and additional existing geologic geochemical data a general tectonic history for the belt is proposed mineralization ages in apuseni banat timok and panagyurishte the central district of the larger e w srednogorie zone range from 72 83 81 88 and 87 92 ma respectively and clearly document increasing age from the northwestern districts to the southeastern districts further re os ages suggest rapidly migrating pulses of late cretaceous magmatic hydrothermal activity with construction of deposits in 1 m y districts in 10 m y and the entire 1 500 km belt in 20 m y ages in both timok and panagyurishte show systematic younging while deposit ages in banat and apuseni are less systematic reflecting a restricted evolution of the tectonic system systematic differences are also observed for molybdenite re concentrations on the belt scale re concentrations generally range from hundreds to thousands of parts per million typical of subduction related cu au mo pge porphyry systems associated with the generation of juvenile crust the geochronologic and geochemical trends are compatible with proposed steepening of subducting oceanic slab and relaxation of upper continental plate compression resulting influx of sub continental mantle lithosphere scml and asthenosphere provide a fertile metal source and heat while the subducting slab contributes connate and mineral dehydration fluids which facilitate partial melting and metal leaching of scml and asthenosphere cu au mo pge porphyry deposits may develop where melts are trapped at shallow crustal levels often with associated volcanism and epithermal style deposits south banat timok and panagyurishte mo fe pb zn skarn deposits may develop where felsic melts are trapped adjacent to mesozoic limestones at moderate crustal levels north banat and apuseni systematic spatial variations in deposit style commodity enrichment re os ages and re concentrations support specific tectonic processes that led to ore formation in a post collisional setting subduction of vardar oceanic crust may have stalled causing slab steepening and rollback the slab rollback relaxes compression facilitating and enhancing orogenic collapse of previously thickened balkan south carpathian crust the progression of coupled rollback orogenic collapse is evidenced by the width of late cretaceous extensional basins and northward younging of re os ages from panagyurishte 60 km 92 87 ma to timok 20 km 88 81 ma to apuseni banat 5 km 83 72 ma generation of a well endowed mineral belt such as the abts requires a temporally and spatially restricted window of magmatic hydrothermal activity this window is quickly opened as upper plate compression relaxes thereby inducing melt generation and ingress of melt to higher crustal levels the window is just as quickly closed as upper plate compression is reinstated the transient tectonic state responsible for economic mineralization in the abts belt may be a paleo analogue to transient intervals in the present subduction tectonics of se asia where much mineral wealth has been created in the last few million years

subaqueous environment and volcanic evolution of the late cretaceous chelopech au cu epithermal deposit bulgaria abstract a detailed field and petrographic study constrains the volcanic evolution and environment setting of the volcano sedimentary hosted chelopech cu au epithermal deposit bulgaria magmatic activity and associated high sulfidation epithermal mineralization occurred at about 91 ma in the panagyurishte ore district of the eastern european banat timok srednogorie metallogenic belt volcanic and hydrothermal activity took place in a complex subaqueous setting resulting in the intercalation of quartz sandstone with andesitic volcanic and volcaniclastic breccia there are also hypabyssal andesite intrusion phreatomagmatic breccia and interbeds of pyroclastic oolithic and bioclastic rocks the presence of altered cerebroid ooid bearing sedimentary units characteristic of salty environment is in accordance with a lagoon environment predating the mineralization at chelopech four principal stages of evolution for the chelopech district are proposed based on field and petrographic observations initial volcanism occurred in a lake or in a coastal shallow lagoon environment above crystalline basement the chelopech phreatomagmatic breccia and subsurface andesites were emplaced at this time subsequent hydrothermal activity produced the different hydrothermal breccia types advanced argillic and quartz phyllic alteration and au cu vein and replacement mineralization the end of volcanism and hydrothermal activity was associated with opening of a pull apart basin that covered the chelopech environment with a sedimentary flysch tertiary compression faulting juxtaposed various rocks and tilted the ore deposit during the alpine orogeny

magmatism and metallogeny of the ridanj krepoljin belt eastern serbia and their correlation with northern and eastern analogues in the southwestern carpathians of sw romania and e serbia calc alkaline upper cretaceous paleogene subduction related magmatic rocks occur in two main zones the ridanj krepoljin belt e serbia represents the southern part of the western zone in this belt early maastrichtian dacites and subordinate andesites occur but there are indications of an unexposed granodioritic magmatism about 60 ma old pb zn ag and only subordinate cu mineralization is associated with this igneous activity the timok magmatic complex e serbia composed of upper cretaceous paleocene andesites and analogue intrusives represents the eastern zone south of the danube associated with this magmatism are cu au and very subordinate zn pb mineralization to the north sw romania in both zones mainly intrusive bodies diorites quartz diorites granodiorites monzonites of campanian paleocene age are exposed porphyry copper mo and in north pb zn cu mineralization are related to those intrusives the petrological and geochemical features of all these calc alkaline rocks are very similar it appears however that the associated polymetallic and the copper mineralization are both spatially and vertically separated

seismic fracture anisotropy in the earth s crust an overview fluid filled fractures and microcracks are the most stress sensitive component of crustal rock and often determine the pathways and volume of crustal fluid movement if we are to comprehend the role of fractures and fluids in tectonic processes to formulate an accurate hypothesis for phenomena precursory to catastrophic seismic failure or to monitor hydrocarbon and geothermal reservoirs for the presence or absence of major fluid pathways we must understand how seismic waves interact with the fracture crack and microcrack structures within the rock mass a salient feature of fracture related rock structure is the effective seismic anisotropy of aligned fractures and microcracks with the advent of large volume digital seismic data sets it is feasible to use polarized shear waves to explore the anisotropic fracture properties of the crust crustal fracture structures which may be monitored by polarized shear waves range in dimensions from the 10 100 km scale of crustal stress orientation and preseismic stress buildup through the 100 1000 m scale of fluid reservoir structure and characterization and the 1 10 scale of mining and geoengineering rock strain monitoring to millimeter and micrometer or possibly smaller fluid filled inclusions determining the elastic response of the intact rock mass to focus developments in seismic anisotropic studies of crustal fracture phenomena the american geophysical union and the society of exploration geophysicists sponsored a chapman conference on seismic anisotropy in the earth s crust held may 31 to june 4 1988 at the lawrence berkeley laboratory of the university of california this was the third international workshop on seismic anisotropy 3iwsa nineteen conference papers are presented in this special section of the journal of geophysical research

late cenozoic to holocene deformation in southwestern sichuan and adjacent yunnan china and its role in formation of the southeastern part of the tibetan plateau from at least 2 4 ma to present crust in the southeastern part of the tibetan plateau west of the convex east xianshuihe xiaojiang fault system has deformed internally and rotated clockwise around the eastern himalayan syntaxis the northwest striking ganzi fault zone bounds the rotating crust on the north and has a total left slip of 78 100 km of which 60 km is transferred to the xianshuihe fault zone across a diffuse transfer zone and 22 40 km is absorbed by bending of older structures and crustal shortening crustal shortening is expressed along and east of the eastern end of the ganzi fault zone by mountains capped by permanent glaciers locally rising nearly 1000 m above the average elevation of the tibetan plateau a similar transfer of left slip into shortening occurs farther south across the xianshuihe fault in the high mountains around and east of gongga shan 7556 m the northwest striking convex east left lateral litang fault zone lies southwest of the ganzi xianshuihe xiaojiang fault zone and appears to be less well developed but otherwise similar to the ganzi fault zone the batang chenzhi and other northeast striking right lateral faults of small displacement occur within the rotating crustal fragment together with the left slip faults they accommodate east west shortening northeast of the eastern himalayan syntaxis south of this region of shortening the crust is extending to form grabens within the dali and southern xiaojiang fault systems and in the tengchong volcanic province the progressive change from shortening southward into extension is related to variations in strain that characterize the region from northeast to southeast of the eastern himalayan syntaxis the assemblage of structures in southwestern sichuan geometrically resembles structures of eocene to miocene age in southern yunnan that were positioned northeast of the eastern himalayan syntaxis similar to present day southwestern sichuan at the time of their development the similarity in the structural development in the two areas indicates that crust northeast of the syntaxis underwent a common evolution as the syntaxis migrated northward during the past 50 m y structures in sichuan are less fully developed than older structures in southwestern yunnan and can serve as a guide to reconstruct the progressive tectonic development in the region of the syntaxis deformation in these areas indicates that plateau formation has been complex inhomogeneous and diachronous at scales from 1000 km to less than 100 km

insight into the origin of the tengchong intraplate volcano and seismotectonics in southwest china from local and teleseismic data received 18 june 2008 revised 22 february 2009 accepted 10 march 2009 published 13 may 2009 1 a high resolution tomographic image of the crust and upper mantle under yunnan province in southwest china was determined by using a large number of teleseismic data measured precisely from digital seismograms as well as local earthquake arrival times recorded by the dense yunnan seismic network the grid spacing of the tomographic model is 70 km 78 km in the horizontal directions and 4 70 km in depth our resulting model shows a clear low velocity low v 0 3 with respect to the average one dimensional velocity model column extending from the surface down to about 400 km depth under the active tengchong volcano and some high velocity high v anomalies existing in the mantle transition zone furthermore the low vanomaly extends horizontally toward the northeast at 250 to 400 km depth combining our tomographic results with geochemical and geological investigations we infer that the tengchong volcano is a rift related volcano caused by the subduction and dehydration of the indian plate as well as corner flow in the mantle wedge though the subducted slab is a continental plate our results show that the upwelling flow under tengchong originates at 400 km depth a prominent low v anomaly along the red river fault zone extends down to the upper mantle 100 km depth reflecting that the red river fault zone may have cut through the crust to the upper mantle the two dayao earthquakes m 6 1 and m 6 2 in 2003 occurred on the margin of high v anomalies and are underlain by a prominent low v anomaly in the lower crust and upper mantle suggesting that the dayao earthquakes may be associated with fluids released from the dehydration of the subducted indian slab these results are significantly improved compared with previous studies and provide new seismic constraints on the dynamic processes of the india asia collision

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others

pn wave velocity and anisotropy underneath the central segment of the north south seismic belt in china abstract we present a pn wave velocity and anisotropy model of the central segment of the north south seismic belt in china where there are numerous stable basins and active faults making this segment attractive for extensive studies the model was obtained by a tomographic analysis of 49 973 pn wave phase readings collected by the china earthquake networks center and temporary stations in yunnan and sichuan the tomographic velocity model shows that the average pn wave velocity is 8 06 km s prominent high velocity high v anomalies are visible under the sichuan basin the zoige basin and the ordos block which clearly outline their tectonic margins a pronounced low velocity low v zone is observed from the songpan ganzi block to the chuan dian and daliangshan blocks suggesting the presence of hot material upwelling the station delay data show a gradual variation from negative to positive values possibly reflecting a crustal thickness variation from the southwest to the northeast of the study area a correlation between the pn wave anisotropy and the distribution of velocity anomalies is observed anisotropy is relatively weaker in the high v anomaly zones beneath stable basins while it is stronger in the low v anomaly zones and the high to low v anomaly transition zones the high resolution velocity and anisotropy tomographic model that we obtained could also provide a better understanding of the study area seismicity since the occurrence of strong earthquakes seems to be related to the presence and strength of lateral heterogeneities at the uppermost mantle level

eastward expansion of the tibetan plateau by crustal flow and strain partitioning across faults the tibetan plateau is expanding eastwards but the modes of deformation are poorly understood high resolution seismic images from the region identify localized zones of weak crustal rocks as well as deep faults implying that deformation occurs through a combination of crustal flow and movement of rigid blocks of crust