geology of the sari gunay epithermal gold deposit northwest iran the sari gunay epithermal gold deposit is located within a mildly alkaline latitic to trachytic volcanic complex in central northwest iran intrusive and volcanic rocks that host the deposit have been dated at between 11 7 and 11 0 ma with one younger sample at 8 0 ma 40ar 39ar dating of igneous biotite and hornblende whereas sericitic alteration associated with an early stage of hydrothermal activity occurred between 10 8 and 10 3 ma the best age estimate is 10 7 ma obtained by 40ar 39ar dating of sericite the main hydrothermal system was structurally localized by a diatreme breccia complex centered on the sari gunay hill earliest hydrothermal activity only encountered at depth 300 m below surface produced weak potassic alteration and quartz sulfide magnetite veining with low grades of cu and au mineralization reminiscent of shallow level 1 5 km depth porphyry gold systems paragenetically later quartz tourmaline breccias and veins followed the south southwest north northeast trend of the diatreme breccias and produced strong sericitic alteration and silicification in igneous clasts and wall rocks fluid inclusions indicate temperatures of 246 to 360 c and salinities of 34 4 to 46 1 wt percent nacl equiv in hypersaline inclusions coexisting with low density co2 bearing vapor phase inclusions these fluids do not appear to have deposited gold but the breccias provided further structural permeability for flow of later mineralizing epithermal fluids invisible gold occurs in solid solution in fine grained arsenical pyrite and minor arsenopyrite deposited in the early stages of quartz adularia pyrite stibnite veins late stage minerals in these veins include realgar orpiment cinnabar and extremely rare wire gold liquid rich fluid inclusions in these veins have an average homogenization temperature trapping temperature of 199 24 c salinities of 3 6 1 1 wt percent nacl equiv and coexist with low density co2 bearing vapor phase inclusions suggesting low pressure conditions phase separation may have been a contributory cause of gold deposition but precipitation of sulfides in response to rapid cooling of the system may have been the main control on deposition of pyrite hosted gold the sari gunay gold deposit and its host volcanic system form part of the takab belt of structurally controlled middle miocene mildly alkaline volcano plutonic complexes the sediment hosted zarshuran gold deposit located 190 km to the north northwest along the belt is also related to middle miocene magmatism the takab belt is marginally younger than and displaced to the southwest of the extensive eocene miocene urumieh dokhtar calk alkaline volcanic arc which hosts several large porphyry cu deposits e g sar cheshmeh meiduk rocks of the takab belt are also distinctly more alkaline than the urumieh dokhtar rocks viewed in the context of plate tectonic models for neogene closure of a neo tethys ocean between the afro arabian and eurasian plates these differences may reflect a normal subduction zone origin for the urumieh dokhtar arc and contained porphyry cu deposits but a collisional origin for the slightly younger takab belt volcanic rocks and epithermal gold deposits the sari gunay deposit may thus be classified as a collision related alkalic type epithermal system although it is less alkaline than classic deposits of this group such as porgera emperor or cripple creek the latter apparently being related to postcollisional or back arc extensional rather than syncollisional processes

amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

accumulation of particles in propagating fronts field observations imply that accumulation and advection of invertebrate larvae and other plankton by propagating fronts provides an efficient mechanism for the cross shelf transport and subsequent coastal settlement of larvae and plankton gravity currents propagating into a heavier uniform density fluid are known to have near surface velocities u that exceed the propagation speed c of the gravity current nose it is shown by simple dam break laboratory experiments and through corresponding numerical solutions of two dimensional stratified flow and lagrangian particle advection that this characteristic of gravity currents can lead to accumulation in the gravity current nose of particles that originate well behind the gravity current head however efficient particle accumulation and transport with the speed c only occurs for particles with sufficient vertical buoyancy or vertical swimming capability weakly buoyant or neutral particles are swept down and back away from the gravity current head by the circulation in this region a dam break into an ambient fluid with stratification two layered could result in the transport of some particles that are initially trapped in the forepart of the leading disturbance an undular bore however this situation does not result in significant accumulation of particles at the leading edge of the disturbance the numerical solutions show that particles that originate in the dense fluid ahead of the gravity current are much less likely to be accumulated at the gravity current nose a simple scaling criterion for the minimum vertical buoyancy velocity for efficient accumulation and transport of buoyant particles based on the gravity current and particle characteristics is developed and compares favorably with the numerical results the implications of these results for transport of larvae in coastal environments are discussed the dynamics of marine benthic invertebrate populations are greatly affected by larval transport for near shore populations larval transport prior to settlement includes at least three processes cross shore advection because larvae are generally very small and cannot control their cross shore position by swimming alone larval behavior because by swimming vertically larvae might be able to exploit some depth dependent cross shore flows and accumulation by convergent circulation in propagating features because cross shore advection of larvae is often dependent on the retention of larvae at the propagating features several hypotheses of onshore larval transport namely surface slicks over linear internal waves shanks 1983 internal bore warm fronts pineda 1994 and upwelling relaxation fronts farrell et al 1991 invoke concentration of larvae at propagating features these hypotheses state that larvae become concentrated at convergent features aligned parallel to the coastline and that larval transport occurs as these linear features propagate shoreward the interplay between transport and accumulation is poorly understood issues include 1 the dependency of transport on accumulation and of accumulation on larval behavior and 2 whether the frontal larvae originate onshore or off

episodic and short lived granitic pulses in a post collisional setting evidence from precise u pb zircon dating through a crustal cross section in corsica abstract in western corsica a large granitoid batholith was emplaced during carboniferous and permian times these rocks display an evolution through time from high mg k calc alkaline to calc alkaline then alkaline affinities moreover the magmatic processes can be observed at different crustal levels new and precise isotope dilution and thermo ionisation mass spectrometry id tims u pb dating suggests that granite magmatism in corsica did not simply reflect the continuous thermal evolution of a thickened crust a precise timing for the post collisional magmatism is documented with four distinct short lived episodes respectively at 345 338 305 and 280 ma separated by periods of inactivity these four magma pulses display variable nd isotopic signatures related to mantle crust interactions granite magma generation and emplacement is strongly connected to the thermal and tectonic activity of the lithosphere an increasing contribution of a depleted mantle to the magmatic processes is documented for the last igneous event this is interpreted to reflect the emplacement of depleted mantle materials in the lower crust which enhanced heat flow and triggered partial melting of previously underplated mafic rocks this increasing contribution of mantle materials marks the onset of a new geodynamic cycle characterised by an extensional tectonic regime preluding to the opening of the alpine orogenic tract

seasonal cross shelf flow structure upwelling relaxation and the alongshelf pressure gradient in the northern california current system abstractmoored observations are used to investigate the seasonal change in vertical structure of the cross shelf circulation at a midshelf location in the northern california current system a streamwise normal coordinate system is employed to eliminate meander and eddy induced biases in the cross shelf flow that are unaccounted for with an alternative commonly applied approach the resulting flow structure develops an organized pattern midway through the upwelling season in particular under upwelling favorable conditions an onshore return layer occurs just beneath the offshore surface flow and a third offshore directed layer exists at depth that does not appear to satisfy ekman dynamics to within 9 m of the bottom both subsurface layers strengthen in time over the upwelling season mechanisms to explain the mean structure are evaluated and it is suggested that the timing of the development and strengthening of both the interior onshore return flow and the offshore near bottom layer are consisten

large diurnal temperature fluctuations in the nearshore water column abstract large daily temperature fluctuations in the nearshore water column have been observed at several sites along the coast of central and northern chile particularly during summertime these fluctuations are often on the order of the seasonal fluctuation in sea surface temperature for the area and are capable in certain locations of penetrating deep 10 15 m into the water column during the course of a single day we explain this phenomenon by a combination of solar heating of the sea surface and wind driven transport and accumulation of these warm surface waters near shore measurements of surface heat flux agree roughly with observed daytime changes in the heat content of the nearshore water column the strength of these diurnal fluctuations is shown to vary with the strength of coastal upwelling in the area the potential consequences of this process for nearshore larval transport are unknown but we briefly speculate about its importance

the transition from porphyry to epithermal style gold mineralization at ladolam lihir island papua new guinea a reconnaissance study the exceptionally large gold resource at ladolam 1 300 metric tons of gold lihir island resulted from the transition of an early stage low grade porphyry gold system to a low sulfidation epithermal gold event this transition was probably triggered by rapid decompression during the partial slope failure of luise stratovolcano and accompanied by the ingress of seawater the original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite magnetite altered monzodiorite with disseminated pyrite chalcopyrite and poorly developed pyrite quartz stockwork veins the breccias are overprinted by biotite magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite the breccias are cut by late stage epithermal quartz chalcedony illite adularia pyrite veins and associated illite adularia alteration that locally contain bonanza gold grades of up to 120 g t isotope data suggest a magmatic source of sulfur in the gold bearing fluids at ladolam electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0230 y

cenozoic k rich adakitic volcanic rocks in the hohxil area northern tibet lower crustal melting in an intracontinental setting it is generally accepted that the cenozoic potassic volcanic rocks of northern tibet were derived from a lithospheric mantle source here we report new chronological geochemical and isotopic data for the miocene ca 18 15 ma k rich adakitic volcanic rocks from the hohxil area of the songpan ganzi block in northern tibet we contend that these rocks were generated by partial melting of the mafic lower crust in an intracontinental setting unrelated to subduction of oceanic crust the hohxil rocks exhibit high sr y and la yb ratios high sr and la contents but low yb and y concentrations similar to adakites formed by slab melting associated with subduction however their relatively low e n d values 2 09 to 4 58 high 8 7 sr 8 6 sr 0 7072 0 7075 th u th ba and rb ba ratios and distinctive potassium enrichments k 2 o na 2 o are very different from the composition of typical adakites in addition those k rich adakitic rocks with the highest sio 2 contents 61 wt exhibit the lowest 8 7 sr 8 6 sr ratios and highest e n d values and are the oldest cenozoic volcanic rocks exposed in the songpan ganzi block suggesting that they were derived neither directly from a mantle source nor by differentiation of a shoshonitic magma taking into account the composition of lower crustal mafic xenoliths in tibet as well as the tectonic and geophysical evidence we conclude that the hohxil adakitic magmas were produced by partial melting of amphibole bearing eclogites with a k rich mafic bulk composition in the lower part 55 km of the thickened northern tibetan crust partial melting of the lower crust may have been triggered by dehydration release of fluids from sedimentary materials in the southward subducted continental lithosphere

circulation and larval distribution in internal tidal bore warm fronts internal tidal bore warm fronts were observed during the summer of 1996 off the coast of southern california warm bore fronts had concentrating currents resulting from high frequency internal motions and from a larger two way flow the two way flow featured surface currents onshore and bottom currents offshore a sharp thermocline depression and high frequency large amplitude internal motions followed the leading edge of the bore with downwelling currents on the trailing side of the crest of the nonlinear internal waves and upwelling currents in front of the crest warm bores propagated onshore with a propagation speed c that ranged from 10 6 to 19 6 cm s 1 while time averaged frontal currents varied from 11 2 to 17 6 cm s 1 in the shallowest bin in one out of three cases c which implied that there were faster currents than the rate of advance of the front and which implied that the origin of surface frontal material is behind the front not in front of it three invertebrate larval taxa were found at all sites across fronts but only two intertidal barnacles pollicipes polymerus and chthamalus spp were concentrated at the front s surface while the subtidal bryozoan membranipora spp was not frontal pollicipes were more concentrated than were chthamalus the frontal downwelling currents observed suggested that concentrated larvae would have to swim upward in order to maintain depth pollicipes were abundant on the offshore warm side of the fronts but were absent or rare on the onshore colder side suggesting that the origin of frontal pollicipes was behind the front although an alternative cannot be ruled out conclusively chthamalus were more abundant at depth than at the surface at all sites except at the front where this pattern was reversed the origin of frontal chthamalus is uncertain membranipora were more abundant on the onshore colder side of the fronts and abundances were usually higher at depth than at surface lack of accumulation in this species may be due to its limited swimming capability

the relationship between epithermal and porphyry hydrothermal systems within the tavua caldera fiji the shoshonitic tavua caldera in viti levu fiji defines the volcanic center of the tavua volcano the caldera occurs at the intersection of the northeast trending viti levu lineament and a northwest trending lineament locally manifested by the nasivi shear zone fault related subsidence which contributed to the evolution of the tavua caldera the central inner caldera and the structural preparation for mineralization occurred on these two regional fault systems and local concentric normal faults a continuum of mineralization and alteration styles is evident along the nasivi shear zone caused by a northwesterly evolution and migration of intrusion and hydrothermal activity porphyry style subeconomic copper gold mineralization and associated alteration occurred at depth in the nasivi shear zone at the center of the caldera approximately contemporaneously with the development of the inner caldera acid sulfate style epithermal alteration and minor gold mineralization immediately postdated and were superimposed on this porphyry style alteration farther northwest along the nasivi shear zone transitional ac d sulfate to adularia sericite epithermal alteration and minor gold mineralization occur variation in hydrothermal style is considered to reflect an increasing distance from magmatic source combined with an increasing proportion of meteoric water mixing with the hydrothermal fluid northwest of this system at the intersection of the nasivi shear zone and the viti levu lineament the 4 4 m oz adularia sericite style epithermal emperor gold mine occurs high level epithermal mineralization and alteration occur 4 km northeast of the emperor gold mine in an area which has a demonstrable present day hydraulic connection with the mine variations in fluid inclusion homogenization temperatures from the mine indicate that fluids entered the structurally prepared mine area via the nasivi shear zone emperor epithermal mineralization postdated magmatism by approximately 0 4 ma stable isotope data the presence of albitic alteration beneath mineralization and high salinities within the mine indicate that the emperor northern prospects hydrothermal system is related to an intrusion into the nasivi shear zone beneath the mine this is consistent with a demonstrable northwesterly migration of intrusions with time along the nasivi shear zone albitic phyllic and propylitic assemblages comprise the main porphyry style alteration types in the caldera center calculated temperatures of formation of chlorite in these assemblages indicate that these three alteration facies formed in the temperature range 270 degrees to 340 degrees c in good agreement with available fluid inclusion data and the stability ranges of the mineral assemblages kubler indices of illite likewise imply that these assemblages formed at relatively high temperature epithermal lode alteration mineralization at emperor is shown by fluid inclusion data to have formed around 200 degrees c kubler indices of illite confirm that this alteration formed at significantly lower temperatures than did porphyry alteration and that chlorites in the emperor mine have calculated temperatures of formation mostly below 200 degrees c high level epithermal alteration occurring northeast of emperor is inferred to have formed at even lower temperatures

larval retention entrainment and accumulation in the lee of a small headland recruitment hotspots along windy coasts we surveyed crustacean larvae in the plankton in the lee of bodega head california for 2 months during late spring and summer and cross correlated the larval abundance and stage of development of 16 taxa with 8 indicators of upwelling relaxation conditions larvae in all stages of development for 11 of these taxa were entrained and accumulated in a recirculation feature in bodega bay found in the lee of this small headland as soon as upwelling favorable winds began and persisted until winds weakened the remaining taxa were more prevalent during relaxation events when the recirculation feature dissipated and a poleward coastal current transported larvae into and through the bay during upwelling conditions a vertically sheared flow occurs in the lee of the headland that accounts for the accumulation of plankton however larval behavior did not have a substantial effect on density and persistence in the lee of the headland regardless of whether taxa were more prevalent during upwelling or relaxation conditions or whether they developed entirely nearshore or migrated offshore later in development thus larvae and postlarvae of many diverse taxa are concentrated in the plankton in the lee of small headlands in upwelling areas which is consistent with previously reported recruitment hot spots in small upwelling bays these headland related hot spots increase spatial structure in population density and community structure in recruitment limited upwelling regions and other wind driven coasts

meroplanktonic distribution and circulation in a coastal retention zone of the northern california upwelling system previous studies have shown that settlement of several crab species along the coast north of point reyes 38 00 n 123 00 w occurs primarily during relaxation from upwelling when warm water flows poleward from the gulf of the farallones during 1994 and 1995 we sampled planktonic larval distributions and hydrography both south and north of point reyes during upwelling to test whether high concentrations of crab and rockfish larvae were concentrated in the source of the relaxation flow to the south of point reyes an upwelling plume off point reyes and an upwelling shadow indicated by warmer less saline water in the northern gulf were evident in both years as were frontal regions that marked the boundaries between water types of three different types 1 newly upwelled 2 oceanic and 3 san francisco bay outflow in addition there was a fourth type termed gulf water that was a mixture of these three types concentrations of larvae of cancrid pinnotherid and coastal crabs and rockfishes were high south of point reyes but were low or absent in the newly upwelled water north of the point within the upwelling shadow these meroplankton taxa were associated with different water masses several intertidal crab species and early stage cancrid crabs were concentrated in san francisco bay outflow water and coastal gulf water late stage cancrid crabs early and late stage pinnotherid crabs and rockfishes were concentrated at the frontal region between newly upwelled and gulf water of the taxa examined only rockfishes were found offshore in oceanic water the high concentrations of meroplankton observed suggest that the gulf of the farallones is an important retention area for larvae that settle into coastal populations in the gulf and to the north via poleward transport during upwelling relaxation

upwelling relaxation and estuarine plumes 1 after coastal upwelling the water properties in the nearshore coastal region close to estuaries is determined by the race between the new estuarine plume traveling along the coast and the upwelled front a marker for the old upwelled plume and the coastal pycnocline returning to the coast under downwelling winds away from an estuary downwelling winds can return the upwelled front to the coast bringing less dense water nearshore near the estuary the estuarine plume can arrive along the coast and return less dense water to the nearshore region before the upwelled front returns to the coast where the plume brings less dense water to the coast first the plume keeps the upwelled front from returning to the coast in this region only the plume and the anthropogenic input and larvae associated with the plume waters influence the nearshore after upwelling we quantify the extent of the region where the plume is responsible for bringing less dense water to the nearshore and keeping the upwelled front from returning to the coast after upwelling we successfully tested our predictions against numerical experiments and field observations of the chesapeake plume near duck north carolina we argue that this alongshore region exists for other estuaries where the time integrated upwelling and downwelling wind stresses are comparable

intraplate type magmatism in a continent island arc collision zone porgera intrusive complex papua new guinea cogenetic volatile rich alkali basalts and gabbros hawaiites and mugearites occur in the late miocene age epizonal porgera intrusive complex which is temporally and spatially associated with rich gold silver mineralization the least evolved rocks show enrichments in light rare earth elements la yb sub cn 15 19 and other incompatible elements e g ba la approx 8 10 la nb approx 0 6 0 7 sr nd approx 25 characteristic of intraplate alkalic basalts and have isotopic compositions sup 87 sr sup 86 sr approx 0 7035 epsilon sub nd approx 6 sup 206 pb sup 204 pb approx 18 66 sup 207 pb sup 204 pb approx 15 56 sup 298 pb sup 204 pb approx 38 55 consistent with derivation from a time averaged depleted mantle source the porgera intrusive complex was emplaced at 6 ma in jurassic cretaceous shelf facies sedimentary rocks near the edge of the australasian plate intrusion appears to have occurred in a back arc environment during subduction of an oceanic microplate segment on two sides beneath the continental margin and an island arc we suggest that this unusual tectonic setting promoted partial melting of asthenospheric source materials that were perhaps modified by deep 150 km subduction processes to form alkalic magmas with intraplate character

cross shelf transport causes recruitment to intertidal populations in central california the control of recruitment to intertidal barnacle populations along the central california coast was examined from april to mid october 1988 four recruitment pulses occurred during periods of relaxation in alongshore winds and cessation of coastal upwelling in each case recruitment ended when strong equatorward winds reappeared and upwelling resumed data on sst salinity adjusted sea level and satellite avhrr images revealed alternating periods of onshore and offshore transport of the surface water layer the onset ofthe largest recruitment pulse was associated with the advection of warm clear low salinity water into the nearshore region this oceanic water mass also contained a different zooplankton assemblage than the water mass it replaced

examination of the deep levels of an island arc evidence from the tonsina ultramafic mafic assemblage tonsina alaska the tonsina ultramafic and mafic assemblage located in the northern chugach mountains along the trans alaska crustal transect tact is interpreted to be the remains of a magma chamber that crystallized at the base of a mature interoceanic island arc it is one of a number of isolated masses of peridotite and gabbro that comprise the basal part of the peninsular terrane along the northern fringe of the chugach mountains in southern alaska these masses the roots of a mid jurassic island arc have been uplifted along the north dipping border ranges fault system and crop out sporadically for 700 km from kodiak island to eastern alaska the tonsina ultramafic mafic assemblage is a layered sequence whose basal rocks are dunite and harzburgite 1 km thick overlain by a narrow zone of websterite and clinopyroxenite above these ultramafic rocks is a 5 to 6 km thick layered gabbro that is garnet bearing at its base textural relationships and chemical trends throughout the series of dunite pyroxenite garnet bearing gabbro and spinel gabbronorite point to an origin by igneous accumulation from a hydrous tholeiitic parent magma at deep levels i e at the base of a mature island arc before being emplaced along the border ranges fault the rocks were crystallized from a melt at pressures between 9 5 and 11 kbar 28 to 33 km depth and equilibrated at temperatures of 800 to 90o c based on phase relationships in the cumulus assemblages pyroxene thermobarometry and olivine spinel thermometry transitional sequences from ultramafic to mafic rocks are characterized by increasingly al rich pyroxenes and spinels or garnet and the absence of olivine plagioclase assemblages deep level fractionation of al poor phases such as olivine and pyroxene at moderately high pressures and temperatures resulted in concentration of al in the evolving magma as crystallization continued the phases recorded this alumina concentration and the resultant gabbros are al rich this observed trend supports the theory of high alumina basalt generation by fractional crystallization of olivine and pyroxene comparison of the tonsina rocks with aleutian lower crustal xenoliths as well as other exposures of arc related lower crustal magma chambers in japan pakistan and western north america indicates that this process is a common mechanism for island arc magma evolution at depth

magmatism and metallogenic mechanism of the ga erqiong and galale cu au deposits in the west central lhasa subterrane tibet constraints from geochronology geochemistry and sr nd pb hf isotopes abstract the ga erqiong galale ore district in the bangong nujiang metallogenic belt hosts two large skarn cu au deposits associated with voluminous late cretaceous volcanism and plutonism in this study we present new zircon u pb age and hf isotopic data whole rock geochemical and sr nd pb isotopic data to constrain the geodynamic mechanisms of late cretaceous magmatism and metallogenesis within the ga erqiong galale ore district the intrusive rocks in the district include diorite quartz diorite granodiorite granite and dioritic porphyrite zircon u pb analyses suggest those rocks mainly emplaced at early late cretaceous 84 95 ma which coincide with the ore forming age of ga erqiong and galale deposits 87 and 88 ma respectively geochemically the granodiorite and dioritic porphyrite are metaluminous with depletion of nb ta and ti and characterized by high mgo 2 68 4 16 wt mg 55 87 sr 414 616 ppm sr y 30 56 cr 22 5 105 0 ppm and ni 26 6 59 7 ppm low y 10 6 14 0 ppm and heavy rare earth elements hree showing geochemical signatures of high mg adakitic rocks four dioritic porphyrite and three granodiorite samples exhibit homologous sr nd pb isotope compositions and have positive whole rock end t values of 1 1 to 3 0 87sr 86sr i values of 0 7045 0 7048 206pb 204pb t ratios of 18 42 18 73 207pb 204pb t ratios of 15 58 15 63 and 208pb 204pb t ratios of 38 54 38 88 besides 116 analyses from the ga erqiong galale adakitic rocks give positive zircon ehf t values 4 3 to 12 1 the geochemical and isotopic data indicate that the early late cretaceous high mg adakitic rocks in the ga erqiong galale ore district originated from the delaminated juvenile lower mafic crust that has been modified by the previously subduction partial melting of previously subduction modified delaminated juvenile lower crust not only formed the hydrous adakitic melts in highly oxidation state but also provided the ore metals e g cu au mo for the subsequent mineralization such melts reacted with surrounding mantle peridotite to elevate the contents of metallic elements again then the melts experienced varying degrees of fractional crystallization process in the shallow magma chamber to form the dioritic and granodioritic magmas those magmas emplaced into the limestone of duo ai and jiega formation to form the ga erqiong and galale skarn cu au deposits respectively field observation together with geochronological and geochemical data indicate that the early late cretaceous mineralization events in the northern and central lhasa subterranes took place in a transition tectonic setting from collisional orogeny to extension and the input of subduction modified juvenile crust play an important role in the late cretaceous ore forming events

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

recruitment of coastal fishes and oceanographic variability in central california abstract recruitment of pelagic larval fishes to the nearshore environment is dependent on a suite of biological and physical processes operating at many spatial and temporal scales nearshore circulation processes associated with coastal upwelling are widely upheld as major determinants of year class strength for many rockfishes sebastes spp but the mechanism by which these processes drive recruitment is largely unknown we used standard monitoring units for the recruitment of fishes smurfs to monitor recruitment of two rockfish complexes sebastes spp and cabezon scorpaenichthys marmoratus from march to september of 2004 and 2005 at 3 sites along the central california coast we examined the relationship between recruitment of these fishes and measurements of oceanographic variability associated with upwelling dynamics including in situ water temperature avhrr sea surface temperature the bakun upwelling index and an index of alongshore surface water transport we found that rockfish comprising the kcgb complex sebastes atrovirens sebastes caurinus sebastes carnatus sebastes chrysomelas recruit during early summer while fishes of the byo complex sebastes melanops sebastes flavidus sebastes serranoides as well as cabezon recruit during late summer our results provide limited support for an association between the arrival of juvenile pelagic rockfish and cabezon to the nearshore environment and physical processes related to upwelling and relaxation beyond the limitations of our bimonthly sampling scheme the lack of a clear pattern may be related to the near absence of upwelling relaxation cycles along this stretch of coast during these two study periods moreover the settlement and recruitment of nearshore fishes may be closely tied to processes occurring earlier in the larval stage

time varying across shelf ekman transport and vertical eddy viscosity on the inner shelf abstract the event scale variability of across shelf transport was investigated using observations made in 15 m of water on the central oregon inner shelf in a study area with intermittently upwelling favorable winds and significant density stratification hydrographic and velocity observations show rapid across shelf movement of water masses over event time scales of 2 7 days to understand the time variability of across shelf exchange an inverse calculation was used to estimate eddy viscosity and the vertical turbulent diffusion of momentum from velocity profiles and wind forcing depth averaged eddy viscosity varied over a large dynamic range but averaged 1 3 10 3 m2 s 1 during upwelling winds and 2 1 10 3 m2 s 1 during downwelling winds the fraction of full ekman transport present in the surface layer a measure of the efficiency of across shelf exchange at this water depth was a strong function of eddy viscosity and wind forcing but not stratification transport fractions ranged from 60 d

volcanogenic massive sulfide deposits and the missing complement to the calc alkaline trend evidence from the jurassic talkeetna island arc of southern alaska

potassic ultrapotassic intrusions at the southwestern margin of the yangtze craton southwestern china petrogenesis and implications for the metal and fluid source of non arc porphyry cu mo au deposits abstract magmatic rocks can reveal partial melting processes in the lower crust and mantle therefore the petrogenesis of both ore barren and ore bearing magmatic rocks can provide key insights into the deep geological processes that control porphyry cu mo au deposits pcds here we investigate the petrogenesis of potassic ultrapotassic igneous rocks in the southwestern yangtze craton swyc to constrain their magmatic sources and assess their role in the formation of pcds these igneous rocks can be divided into three suites ore barren granite porphyry lamprophyre and ore bearing quartz monzonite u pb dating of zircons indicates that these potassic ultrapotassic intrusions crystalized simultaneously between 35 4 and 33 6 ma the lamprophyres have low sio2 contents and high mgo and k2o contents exhibiting an ultrapotassic affinity they are depleted in high field strength elements hfses nb ta zr hf and ti and enriched in large ion lithophile elements liles rb k sr and ba the enriched sr nd and hf isotopic compositions of the ore barren lamprophyres suggest that they were derived from low degree partial melting of lithospheric mantle that had been metasomatized by subduction related fluids during the proterozoic the ore barren granite porphyries have high sio2 and k2o contents with high k calc alkaline to shoshonitic characteristics these rocks have low mgo cr ni and co contents all samples exhibit high sr y ratios and highly fractionated rare earth elements rees patterns with weak eu anomalies combined with their low total ree contents 75 81 ppm and ehf t values which are similar to neoproterozoic granulite xenoliths we conclude that the ore barren porphyries are adakites derived from thickened neoproterozoic lower crust the ore bearing intrusions show variable sio2 and high na2o k2o contents plotting in the monzonite to quartz monzonite fields in a sio2 vs na2o k2o diagram these samples have much higher total ree contents 346 671 ppm than the ore barren intrusions the homogeneous sr nd isotopic compositions and linear trends on harker diagrams suggest that the magma that formed the ore bearing rocks underwent fractional crystallization of mainly amphibole and accessory minerals water contents are estimated to have been 9 12 wt at 0 8 gpa on the basis of the retention of plagioclase and low zircon saturation temperatures which suggests that the primitive magmas of the ore bearing intrusions were derived from water fluxed melting rather than dehydration melting the additional water required to promote water fluxed melting was probably derived from underplated poassic ultrapotassic mafic magmas the high total ree contents sr y and la yb n ratios indicate that the primitive magmas of ore bearing intrusions were probably derived from partial melting of potassic ultrapotassic lower crust formed by the underplating of mantle derived potassic ultrapotassic magma these results combined with previous research show that mantle derived potassic ultrapotassic magmas can provide metals and fluids required for the formation of pcds

relaxation from upwelling in the coastal ocean dynamics experiment a relaxation of the upwelling system on the northern california shelf occurs when upwelling favorable winds decay or reverse observations from the coastal ocean dynamics experiment are used to investigate this process with emphasis on the near surface temperature evolution models of relaxation warming are tested for the surface layer 0 30 m over midshelf with the result that the surface heat flux and poleward alongshelf advection can account for the observed temperature behavior onshore advection of the upwelled isopycnal field is a relatively unimportant contribution the warming patterns that are observed and which provide the gradients for the advective process have wedgelike shapes warmest inshore and in the south of the experimental area these patterns appear to be related to a topographic influence of point reyes possibly through the generation of gradients in the wind field remote advection of warm water from as far south as san francisco occasionally occurs as well the nature of the relaxation mechanism has general implications a new warm saline nutrient rich water mass may be formed in the surface layer since the warming processes are not the reverse of the cooling an important asymmetry is present it causes time variable upwelling to generate conditions very different from steady upwelling a new upwelling front is created during each event with upwelled water seaward of it and reversed alongshelf flow contributes to the warming and exchange mechanisms the system cannot be described or understood without the irreversible processes during upwelling and relaxation or without a mixed layer

petrology and geochemistry of post collisional middle eocene volcanic units in north central turkey evidence for magma generation by slab breakoff following the closure of the northern neotethys ocean the eocene volcano sedimentary units of northern anatolia are confined into a narrow zone trending parallel to the intra pontide and izmir ankara erzincan sutures along which the northern branch of the neotethys ocean was closed during a period between late maastrichtian and paleocene the middle eocene formations overlie both the imbricated and highly deformed units of the suture zone which are paleocene or older in age as well as the formations of adjacent continental blocks with a regional disconformity therefore they can be regarded to be post collisional these units are composed of subaerial to shallow marine sedimentary beds i e the orencik formation at the base and a subaerial volcanic unit i e the hamamozu formation in the middle and at the top this sudden facies change from marine to subaerial environment in the middle eocene is a common phenomenon across northern turkey implying that a regional uplift event occurred possibly across the suture zone before the initiation of the volcanism during lutetian the middle eocene lavas span the whole compositional range from basalts to rhyolites and display a calc alkaline character except for alkaline to mildly alkaline lavas from the top of the sequence all lavas display a distinct subduction signature our geochemical data indicate that calc alkaline lavas were derived from a subduction modified source whereas alkaline to mildly alkaline lavas of the late stage were possibly sourced by an enriched mantle domain magmas evolved in magma chambers emplaced possibly at two different crustal levels magmas in deeper 13 km and possibly larger chambers fractionated hydrous mafic minerals e g amphibole and biotite two pyroxenes and plagioclase and assimilated a significant amount of crustal material intermediate to acid calc alkaline lavas and pyroclastics were derived from these chambers magmas in the shallower chambers on the other hand 12 km crystallized anhydrous mineral assemblages assimilated little or no crustal material and fed basic to intermediate lavas in the region both deep and shallow chambers were periodically replenished by mafic magmas we argue that a slab breakoff model explains better than any alternative model i why the volcanism during the middle eocene was confined into a rather narrow belt along the suture zone ii why it initiated almost contemporaneous with a regional uplift after the continental collision event iii why it postdated arc volcanism along the pontides in the north by 15 20 my iv why it assimilated significant amount of crustal material and v why alkalinity of lavas increased in time

seasonal cycles of currents temperatures winds and sea level over the northeast pacific continental shelf 35 n to 48 n seasonal cycles of coastal wind stress adjusted sea level asl shelf currents and water temperatures off the west coast of north america 35 n to 48 n are estimated by fitting annual and semiannual harmonics to data from 1981 1983 longer records 9 34 years of monthly asl indicate that these two harmonics adequately represent the long term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles we characterize the differences between fall winter and spring summer as follows for fall winter monthly mean winds north of 35 n are northward for 3 6 months longer in the north than in the south south of 35 n the mean winds are near zero or weakly southward monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures for spring summer monthly mean wind stresses are southward at all latitudes for 3 6 months longer in the south than in the north sea levels are low and water temperatures are relatively cool monthly mean currents at 35 m depth over the shelf are southward for 1 6 months longer at the shelf break than over midshelf and longer in the north than in the south while the deeper currents are less southward or northward the magnitudes of the seasonal cycles of all variables are maximum between approximately 38 n and 43 n generally decreasing slightly to the north and greatly to the south at each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1 2 months the seasonal cycles of all variables show a south to north progression south leads north by 1 2 months at 48 n annual mean currents at 50 m depth over the shelf break oppose the annual mean wind northward wind and southward current similarly at 35 n annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind southward wind and northward current from 35 n to 43 n both summer and winter regimes are dominated by strongly fluctuating currents

subduction arc reversal and the origin of porphyry copper gold deposits in island arcs the tertiary quaternary porphyry copper gold deposits of the southwest pacific rim particularly in luzon mainland papua new guinea bougainville guadalcanal and fiji mostly formed after a reversal of arc polarity where this reversal has not occurred e g new zealand and japan porphyry copper gold deposits are absent or scarce hence older porphyry copper gold deposits may be useful clues to tectonic history enrichment of magmas in gold may have resulted from two stage melting the tectonic setting of porphyry copper gold deposits differs from that inferred for volcanic hosted massive sulfide deposits

volatility of se and te during subduction related distillation and the geochemistry of epithermal ores of the western united states subduction partial melting of mantle and magma generation and ultimately magma degassing can lead to the preferential mobilization of volatile elements and compounds research indicates that devolatilization reactions in a subducted slab can cause the overlying mantle to be enriched in volatile ore forming constituents water co2 sulfur metal loid s this process of mantle enrichment plays an important role in subsequent magma generation and initiation of ore genesis furthermore the relative volatility of metal loid s appears to play a role in the ultimate geochemistry of shallow epithermal epizonal hydrothermal ores in the western united states for example there is a general west to east geographic zonation of tertiary ores from se rich to te rich it is proposed that this geographic geochemical zonation is the direct result of the higher geochemical volatility of se as compared to te previously au ag te se hg as sb and tl have been referred to as the epithermal suite of elements it is suggested here that their geochemical cycles are linked by their similar volatile behavior through subduction partial melting in the mantle and subsequent magma degassing processes essentially specific tectonomagmatic events that affected the western united states e g oligocene eocene magmatism in the great basin and southern rocky mountains mid miocene magmatism associated with the inception of the yellowstone hotspot in the pacific northwest were distillation events that drove devolatilization of fertile mantle after the laramide shallow slab event furthermore the metal loid volatility behavior likely occurs in other regions affected by subduction and may play a fundamental role in the metal endowment of these regions

oceanic variability off the central california coast abstract mesoscale variability off the central california coast is strongly influenced by coastal upwelling and related processes off point sur there is significant space time variability in oceanic properties over periods of days and distances of several tens of km however the internal density field averaged over space ca 120km alongshore and time ca 18 days reveals the expected characteristics of a coastal upwelling regime including an equatorward surface jet 25km to 40km offshore and weaker poleward flow below 150m and within 20km of the coast upper ocean circulation is strongly influenced by the bathymetry offshore to water depths of at least 1000m based on repeated horizontal grids of oceanographic stations horizontal correlation scales for temperature are of the order of 30km in the upper 100m hence a horizontal sampling rate of ca 10km is desirable vertical correlation scales for temperature are of the order of 100m hence a vertical sampling rate of ca 10m is desirable similarly there are indications of a temporal correlation scale of a few weeks hence a temporal sampling rate of ca a few days is desirable empirical orthogonal functions eofs in the cross shore vertical plane suggest the influence of coastally trapped motions within 40km of the coast with an intense alongshore near surface transient coastal jet located ca 20km offshore sudden spring transitions to coastal upwelling conditions are often pronounced in coastal temperature records and they may precede the offshore migration of the major upwelling front by at least a month or more the spring transitions occur over a period of about a week in 1980 the spring transition propagated poleward along the california coast at a speed of ca 64km d 1 during spring and summer movement of a coastal upwelling front often located between 15km and 50km offshore is a major contributor to cross shore variability the upwelling front meanders with an alongshore scale of about 80km a time scale of 30 to 40 days and an amplitude scale of 10km rms based on satellite infrared ir imagery the along shore mean position of the major upwelling front migrates offshore during spring and summer offshore displacement of the front may be caused by ekman transport over periods of days to weeks and by rossby wave dispersion over longer periods during summer a time dependent offshore scale based on rossby wave dynamics was more appropriate than the baroclinic rossby radius every three to four years during 1971 through 1984 el nino episodes produced interannual variability in coastal sea surface temperature sst off central california most of the warming occured during fall and winter el nino episodes were often followed by major spring transitions the recent 1982 1983 episode was 2 to 3 c warmer than the three previous episodes over the past 14 years and its influence lasted almost twice as long

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

late paleozoic calc alkaline to shoshonitic magmatism and its geodynamic implications yuximolegai area western tianshan xinjiang article i nfo continuous late paleozoic magmatic activity in the western tianshan xinjiang china temporally overlapped the late carboniferous collision between the tarim and the kazakhstan yili plates isotopic dating whole rock geochemistry and isotopic characteristics of a suite of calc alkaline to shoshonitic rocks from yuximo legai area in the eastern end of the awulale mountains help define the tectonic evolution of this part of the tianshan zircon u pb ages of a quartz diorite and a quartz syenite porphyry are 310 8 2 1 ma and 284 4 3 6 ma respectively the geochemical and isotopic characteristics of late carboniferous igneous rocks including the quartz diorite as well as basaltic andesite and k rich trachyandesite indicate an evolu tion from calc alkaline towards shoshonitic series this was generated by the partial melting of the hydrated mantle wedge induced by changing subduction angles the younger quartz syenite porphyry however was more likely derived from the partial melting of a thickened crust in a post collisional setting or the partial melting of hot juvenile basalt in the lower crust during early permian delamination of the subcontinental lithospheric mantle therefore the generation of the calc alkaline to shoshonitic igneous rocks in yuximole gai area is genetically linked to the geodynamic evolution of the western tianshan from convergent subduc tion to collision during the late paleozoic

saline and particle driven interfacial intrusions this paper presents a theoretical and experimental investigation into saline and particle driven intrusions along the interface between two layers of dierent densities the conditions at the nose of an intrusion are described in an analysis similar to that applied by benjamin 1968 to boundary gravity currents equations for propagation velocity and front position as functions of relative density are derived these are used in an integral model for intrusions which also includes the eects of sedimentation of particles and detrainment of interstitial fluid the model describes the time evolution of the length of the intrusion and the sediment distribution it produces laboratory experiments were carried out with lock releases of a xed volume of saline or particleladen fluid into a two layer stratication measurements were taken of the intrusion propagation intrusion position and sediment distribution and are found to be in good agreement with the solutions of the integral model horizontal density gradients in a fluid may give rise to gravity currents sometimes called density currents the density gradients can be due to dierences in fluid composition phase temperature or concentration of suspended particulate in a suciently quiescent environment a sharp front may be formed across which a density dierence exists between the current and the surroundings this density dierence drives the mainly horizontal motion of the gravity current when the surrounding fluid is vertically stratied the gravity current can enter it at intermediate levels where its density is comparable with that of the ambient and is then called a gravity intrusion gravity intrusions occur frequently in the atmosphere when rising buoyant air reaches levels where its density matches the ambient density and spreads out horizontally a striking example is the outflow above volcanic plumes which carry ash high into the atmosphere and then spread laterally over many thousands of kilometres gravity intrusions are also an important phenomenon in oceanography a much quoted example is the warm but saline outflow from the mediterranean in the eastern atlantic ocean which produces a saline intrusion at about 1000 m depth particle driven intrusions in the ocean can occur when material is suspended by a river outflow by an underwater landslide from a shelf edge or even articially

source of copper in the giant shimensi w cu mo polymetallic deposit south china constraints from chalcopyrite geochemistry and oxygen fugacity of ore related granites abstract porphyry type copper mineralization is generally considered to be related to ore forming fluid exsolution from oxidized magnetite bearing intermediate to felsic magmas however copper deposits associated with ilmenite bearing per aluminous evolved granites also exist and their origin remains obscure the shimensi w cu mo polymetallic deposit located in the northern segment of the jiangnan orogen south china composed mainly of the neoproterozoic shuangqiaoshan group meta sediments volcanic rocks and biotite granite is one of the largest tungsten deposits in the world the w cu mo polymetallic orebodies occur at the contact zone between the mesozoic ilmenite bearing fluorite bearing f rich highly fractionated granite and the neoproterozoic granite the reason for the accompanying cu mineralization within ilmenite bearing granites is unclear in this paper we present a detailed study of chalcopyrite geochemistry including s pb isotopes trace elements and nd isotopes and oxygen fugacity fo2 of ore related granites in the shimensi deposit to constrain the origin of copper sulfur isotope values of the sulfides give a narrow 34s interval of 3 3 to 0 5 mean 1 5 n 32 suggesting the ore forming fluid is of magmatic origin the similarity of pb isotopes of the majority of sulfides and k feldspars from mesozoic granites indicates their genetic relationship however chalcopyrite samples show a wider range of pb isotopic compositions than that of k feldspars suggesting an extra source for the ore forming fluids chalcopyrite from the ore deposit show features of lree enriched patterns variable eu negative anomalies eu eu 0 26 0 75 and la sm n values 0 77 5 93 while the two figures for the mesozoic f rich evolved granites are eu eu 0 18 0 45 and la sm n 2 42 4 09 this along with and the larger range of end values 12 4 to 2 7 of the chalcopyrites than for the mesozoic granites and neoproterozoic granite therein 8 6 to 6 2 suggest that the ore forming fluids cannot be attributed to the mesozoic granites alone the local cu enriched neoproterozoic shuangqiaoshan group rocks should have contributed to the mineralization the low bulk rocks fe3 fe2 ratios 0 02 1 00 average 0 22 fe2 enriched biotite compositions fe2 fe3 5 64 143 average 22 combined with the low ce4 ce3 ratios 3 509 average 142 negative eu anomalies eu eu 0 05 0 56 average 0 25 and low fo2 fmq 3 4 1 9 fmq 1 5 1 7 for the mesozoic magmatic zircons suggest that the granites in the shimensi deposit are relatively reduced the low oxygen fugacity below nno of granites is favorable for significant tungsten mineralization accompanying by minor cu mineralization

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

flow modifications over a tropical coral reef system abstract hydraulic jumps transitions from supercritical to subcritical flows tend to maintain suspended particles in the water column and enhance biological productivity near the surface transitions occur from flow adjustments as the flow moves through a cross section reduction such as a reef crest hydraulic jumps can also inhibit the settlement of coral larvae and bivalve mollusks but could favor connectivity among reefs by dispersing planktonic organisms to surrounding areas the veracruz reef system vrs was chosen as a case study of hydraulic jumps produced over reef crests this system is located in the southwestern part of the gulf of mexico gom and features 50 coral reef structures the area is influenced by vertical stratification that modifies its dynamics hydrographic and yearlong current data collections in the area during 2009 identified fronts and a cyclonic recirculation on the other hand the presence of a hydraulic jump weakened the cyclonic recirculation on the leeward side of the reefs the vertical gradient of the horizontal velocity suggested the influence of vertical eddies at least 35 of the time throughout the entire year moreover the current velocity profiles showed a bidirectional behavior in spring and summer conditions of stratified waters these bidirectional flows contrasted the unidirectional structure caused by frictional dynamics during northerly winds

experimental determination of ree partition coefficients between amphibole and basaltic to andesitic liquids at high pressure abstract amphibole liquid partition coefficients for the ree damph liqree obtained from natural rocks increase systematically with bulk rock compositional change from basalt to rhyolite and are higher for the middle to heavy ree five new experimentally determined sets of dree la sm eu2 ho lu and 4 published sets are similar to these data and provide values for use in geochemical modelling of magmatic processes involving amphibole over a range of temperature pressure and oxygen fugacity the partition coefficients increase significantly with decreasing temperature and increase slightly with increasing oxygen fugacity pressure does not appear to have a major effect although one data set suggests increased pressure lowers damph liqree in a basaltic composition

copperore potential of adakitic intrusives in gangdese porphyry copper belt constrains from rock phase and deep melting process the gangdese porphyry cu mo system in southern tibet 13 6 16 9 ma was generated during the post collision crustal extension the pre ore porphyries mainly consist of granodiorite porphyries with ages older than 17 ma whereas the porphyries of the ore forming stage are mostly composed of monzonitic granite and adamellite porphyries with zircon shrimp ages ranging between 14 5 and 17 6 ma the post ore porphyries are comprised of granite porphyries with a young ar ar age of 11 2 ma geochemical studies indicate that these porphyries are of shoshonitic and high k calc alkaline series and show geochemical affinity with adakites derived from partial melting of a thickened basaltic lower crust the pre ore porphyries have the lowest contents of ree 27 10 6 45 10 6 y 2 9 10 6 3 4 10 6 and the lowest sm yb ratio 3 0 4 9 coupled with the highest zr sm ratio 50 118 the post ore porphyries have the highest contents of ree 122 10 6 197 10 6 and y 8 2 10 6 and intermediate ratios of sm yb 5 9 6 2 and zr sm 34 44 the porphyries of the ore forming stage are transitional between the pre and post ore porphyries in terms of y content and sm yb and zr sm ratios but their sr nd isotopic signature is similar to that of the adakitic rocks from cordillera blanca major trace elements and sr nd geochemistry of these adakitic porphyries indicates that partial melting of a thickened lower crust beneath southern tibet involves input of materials derived from the depleted mantle which provides necessary heat and metals cu au for the generation of cu bearing adakitic melts upward migration of the melt zone from basal amphibole eclogite to upper garnet amphibolite proceeds gradually with time but the transition of residual phase from amphibole bearing to garnet bearing assemblages in the garnet amphibolite source during melting is the fundamental and important process for the formation of the fertile adakite and porphyry cu systems in southern tibet