modeling of the transport and deposition of tungsten in the scheelite bearing calc silicate gneisses of the montagne noire france scheelite bearing calc silicate gneisses csg oceur in the montagne noire within a series of dominant micaschists detailed petrographical and mineralogical studies reveal three successive stages of metamorphism and hydrothermal alteration 1 stage 1 a regional metamorphism at 550 c and 4 5 kb where no mineralization is formed 2 stage 2a a hydrothermal alteration at 500 to 450 c and 4 to 3 kb which is characterized by an intense sericitization of feldpars and deposition of sn in sn bearing cale silicates and 3 stage 2b a hydrothermal alteration characterized by the crystallization of idocrasegrossular in csg with concomittant precipitation of scheelite tungsten was transported through the micaschist environment and deposited as scheelite only in the csg of stage 2b at relatively low pressures to characterize the mechanism of tungsten transport tungsten speciation at high p t and scheelite solubility in aqueous solations buffered by the csg and by the micaschists assemblages were calculated it was found that h2wo 0 4 hwo 4 and wo 2 4 are the dominant tungsten aqueous species in h2o nacl one molal solutions at 500 c and 2 4 kb calculations also indicate that scheelite deposition is controlled by decreasing pressure and increasing activity of aqueous calcium in this system this is consistent with the petrographical and mineralogical observations the consequences of the presence of volatiles n2 ch4 co2 in the regional fluids were examined by determining the effect of n2 on tungsten speciation and scheelite solubility the addition of n2 up to 10 mol to the mineralizing fluids results in a marked increase in h2wo 0 4 and hwo 4 concentrations relative to wo 2 4 and in a large decrease of scheelite solubility this mechanism favours scheelite precipitation and accounts for the commonly observed association of w and sn deposits with graphitic series generating mixed volatiles fluids

geochemical characteristics of biotite from felsic intrusive rocks around the sisson brook w mo cu deposit west central new brunswick an indicator of halogen and oxygen fugacity of magmatic systems abstract the sisson brook w mo cu deposit was formed by hydrothermal fluids likely related to the nashwaak granites muscovite biotite granite group i and biotite granite group ii and related dykes biotite granitic dykes group iii and a feldspar biotite quartz porphyry dyke group iv chemical data obtained using epma and la icp ms data of primary magmatic biotites were used to investigate magmatic processes and associated hydrothermal fluids trace element features of biotite in the group i two mica granite suggest other magmatic processes along with a simple fractional crystallization the k rb ratios and compatible elements cr ti co v and ba in biotite from groups ii iii and iv decrease whereas incompatible elements including ta tl ga cs li and sn increase with magma fractionation no correlation of cu w and mo with k rb ratios is evident suggesting that partitioning of cu w and mo into biotite may not be entirely controlled by magma fractionation halogen fugacity of the parental magma of the nashwaak granites and related dykes calculated from zircon saturation temperature shows that group i has high f hf f cl ratios broadly higher than 0 similar to the plutons at the henderson porphyry mo deposit the f hf f cl ratios of the other groups are generally lower than 0 comparable to the santa rita porphyry cu deposit the f h 2 o f hcl and f h 2 o f hf ratios inferred from biotite in the nashwaak granites and related dykes range from 3 to 5 and from 4 to 5 respectively the inferred oxygen fugacity shows that the dyke phases groups iii and iv have the oxygen fugacity around the nickel nickel oxide buffer the plutonic phases groups i and ii have the oxygen fugacity around the quartz fayalite magnetite qfm buffer at high temperatures and oxidized to nickel nickel oxide buffer at lower temperatures this oxidation process in the plutonic phases groups i and ii could be caused by h 2 release at or near h 2 o vapor saturation at high h 2 o fe 2 the magma associated with the biotite dykes group iii is more likely the source of the hydrothermal fluids at the sisson brook deposit since it has the highest differentiation degree and seems to have formed in an oxidized setting necessary for mo to concentrate in the late stage fluids

paragenetic constraints on the cantung mactung and lened tungsten skarn deposits canada implications for grade distribution abstract the cantung mactung and lened w skarn deposits located in northwest territories and yukon of canada are part of a large metallogenic belt that contains all major tungsten deposits in western north america in this study we evaluate the paragenesis and mineral compositions in these deposits to determine the parameters that control the distribution of high grade w mineralization in these skarn deposits the mineral compositions of the cantung mactung and lened deposits are indicative of reduced fluids grossular rich garnet hedenbergite rich pyroxene abundant pyrrhotite which is characteristic of high grade w deposits local mineral assemblages indicative of oxidizing conditions are observed at lened the smallest of the deposits but are interpreted to be induced by sporadic barite rich facies within the host rock and not by an oxidized fluid therefore the redox state of the skarn does not necessarily lessen the exploration potential for the lened deposit a correlation between high sulfide and scheelite cawo4 contents at cantung mactung and lened has been reported previously and observed in this study however petrographic observations from this study show that scheelite and sulfides precipitated at different times scheelite crystallized throughout the entire history of skarn development but peaked at different stages for each deposit in contrast sulfides have mainly crystallized as late stage minerals postdating the silicates and scheelite variations in the host rock texture and porosity and therefore permeability are proposed to be the main factor controlling scheelite sulfide distribution this control would be manifested such that areas of greater permeability focused fluid flow which favored the precipitation of both scheelite and sulfides at different times in the history of the system

seismic images of continental lithosphere seismic reflection profiles in usa and west germany over thirty years ago showed strong reflections from the lower crust but technical advances through the 1970s were needed for the method to image the continental lithosphere the british institutions reflection profiling syndicate birps found advantage in working offshore and has obtained over 12 000 km of profiles around britain during the past decade giving the densest regional coverage anywhere reflections are observed from strata in sedimentary basins from low angle faults that can be followed from surface to mid crust from a laterally variable reflective zone in the lower crust from the moho and from fault like features in the upper mantle there is evidence around britain that faults bounding sedimentary basins are older structures which have been reactivated it is argued that lower crustal reflectivity around britain is mainly due to anastomosing ductile shears which accommodate extension in the lower crust commensurate with extension in the upper crust by faulting and block rotation there is also evidence of reflections preserved from older orogenic features so that reflections interpreted as extensional ductile shears in the lower crust may also derive from older features that have been reactivated most reflections in the lower crust arise from rocks that have been highly strained evidence of lateral variability in the reflective character of the moho suggests that the moho has been actively involved in the structural evolution of the lithosphere upper mantle reflections are interpreted as shear zones which transfer crustal deformation through the lithosphere

the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

tectonosphere of the earth upper mantle and crust interaction abstract the endogenic geological processes which include tectonic magmatic and metamorphic processes form regular combinations called endogenic regimes these regimes are geosynclinal orogenic platform rift tectonic magmatic activation diwa taphrogenic plateau basalt oceanic basins and mid oceanic ridges the endogenic regimes are connected with the peculiarities of the structure composition and state of the entire tectonosphere i e not only of the crust but of the upper mantle as well heat flow is a major factor controlling the type of the regime the other conditions are the temperature distribution in the tectonosphere and the degree and type of penetrability of the tectonosphere to melts and fluids there is a certain regular succession of regimes the structural evolution of the tectonosphere and the transformation of the matter in it are in close relationship the main trend in the development of the tectonospheric material is directed towards geochemical depletion of the upper mantle by fractioning at the initial stages fractioning occurred mostly by degassing and under these conditions the continental crust was formed rich in non compatible elements at that stage the calc alkaline magmas prevailed as the upper mantle was depleted and began to lose its volatiles the mechanism of fractioning changed degassing was substituted for selective melting and in this environment most of the tholeiitic magmas were formed this change in magma composition and in fractioning mechanism was combined with the destruction of the continental crust and the formation of the oceanic crust the diwa regime and the rifts were the first steps in the destruction of continental crust the stages that followed were represented by taphrogenic regimes at various levels these kinds of regimes were manifested in deep continental and marine depressions compensated and not compensated by sediments taphrogenic regimes are advancing from the east and west onto the eurasian continent in the east they form marginal seas and cause subsidence of the eastern parts of the chinese platform in the west they produce collapses of the crust in the mediterranean area the major crisis occurred between the palaeozoic and mesozoic and since that time the process of substitution of the continental crust by the oceanic crust has proceeded over increasingly large territories the evolution of the tectonosphere instigated by the changes in its matter was further complicated by temporal and spatial irregularities in deep heat escape which caused the alternation of excited and quiescent endogenic regimes tectonomagmatic periodicity and their co existence the combination of all these phenomena creates the structural inhomogeneity of the earth s crust at any stage of its history

controls on marine carbonate cement mineralogy review and reassessment abstract commonly cited models for controls on variations in carbonate mineralogy are only partly successful in accounting for natural mineralogical trends this limited success may result in part from a failure to recognize or address the ramifications of assumptions inherent to such models in general changes from calcite to aragonite or vice versa and variations in mgco3 incorporation in calcite are interpreted as resulting from 1 kinetic rather than thermodynamic effects 2 the effects of fluid chemistry rather than hydrologic biological or substrate effects 3 the effects of single parameters of fluid chemistry rather than the interactive or aggregate effects of several components and or 4 inorganic rather than organic parameters of fluid chemistry recent laboratory data suggest the necessity of a new approach to modeling controls on mineralogy these data indicate that no single fluid parameter is likely to be a sole or dominant control on carbonate mineralogy in natural environments in some cases thermodynamic stability differences may be as important as kinetic factors in determining mineralogy furthermore the effects of substrate hydrologic and biological factors and of organic compounds cannot be ruled out for most natural situations although at present reliable data are lacking to quantify the influence of these factors on mineralogy future models of controls on carbonate mineralogy need to consider the aggregate and interdependent effects of all of these factors

evaporites and strata bound tungsten mineralization discoidal gypsum crystal cavities occur in quartzites that host varying amounts of strata bound scheelite mineralization near halls creek in western australia the host quartzites have been regionally metamorphosed to greenschist facies and are contained within a middle proterozoic sequence that includes pelites mafic and felsic volcanics and volcaniclastic rocks textural fluid inclusion and oxygen isotope data indicate that scheelite was present in the host quartzites prior to regional metamorphism the presence of crystal cavities after gypsum in the quartzites implies an evaporitic origin for this sequence the continental sabkha playa basins of the mojave desert california are suggested to be possible modern analogs e g searles lake where the tungsten content is up to 70 ppm wo sub 3 in brines and 118 ppm in muds and exceeds the amount of tungsten in all known deposits in the united states metamorphism of a continental evaporitic sequence containing tungsten could produce an assemblage of rocks very similar to those reported from several stratabound tungsten deposits some of these such as at halls creek may be related to original accumulations of tungsten in nonmarine evaporitic environments

origin of the muguayuan veinlet disseminated tungsten deposit south china constraints from in situ trace element analyses of scheelite abstract the late triassic muguayuan w deposit is located in the middle of the jiangnan orogen south china this deposit is characterized by veinlet disseminated w mineralization that developed in the sanxianba granitic porphyry stock the ore minerals are mainly scheelite with minor molybdenite and wolframite scheelite mineralization was closely related to greisenization and phyllic alteration and took place in two stages stage i involved scheelite wolframite molybdenite quartz veinlet and disseminated mineralization whereas stage ii resulted in scheelite quartz sericite veinlet mineralization sulfide and quartz calcite pyrite veinlets formed during the post ore stage scheelites from the two mineralization stages have different textures and compositions cathodoluminescence cl images of stage i scheelites reveal two generations of growth i a and i b stage i a scheelite is dark under cl with oscillatory zoning and has light rare earth element lree enriched chondrite normalized patterns negative eu anomalies and high total ree contents stage i b scheelite forms rim overgrowths on stage i a scheelite is bright under cl and shows positive eu anomalies and relatively low ree contents although stage ii scheelites are nearly uniform under cl they can be subdivided into two generations according to their ree systematics stage ii a scheelite yields middle ree mree enriched chondrite normalized patterns with negative eu anomalies whereas stage ii b scheelite has mree depleted patterns with positive eu anomalies minor amounts of apatite formed in both stages of mineralization stage i apatite contains 1370 1930 ppm mn and 97 7 127 ppm sr whereas stage ii apatite has lower mn 111 158 ppm and higher sr 2170 4690 ppm concentrations the distinct trace elements compositions of the scheelite and apatite from the two stages identify two ore forming fluids that had different origins and compositions the ore forming fluids in stage i a were relatively reduced magma derived fluids with high mo mn nb and ta and low sr fluid modeling shows that the initial fluids of stage i a were lree enriched with negative eu anomalies similar to the sanxianba granitic porphyry precipitation of early apatite and scheelite as well as plagioclase decomposition altered the fluid composition and led to relative depletions in ree nb and ta and increases of eu and sr in the stage i b fluids cooling of these fluids and the addition of recycled meteoric water led the fluids to become relatively oxidized and sr rich stage ii scheelite precipitated from these fluids precipitation of stage ii a scheelite resulted in the stage ii b fluids becoming progressively mree depleted extensive alteration especially greisenization and phyllic alteration led to plagioclase decomposition which provided the ca necessary for scheelite mineralization this process was important in generating the w mineralization in the muguayuan deposit and perhaps for other granite hosted veinlet disseminated scheelite deposits in the jiangnan orogen

role of crustal stretching on subsidence of the continental crust abstract the principal areas of subsidence of the continental crust are wide intracontinental basins and passive continental margins in many intracontinental basins crustal extension amounts to only a few percent and is unable to explain their subsidence as shown for the timan pechora pre caspian and west texas basins the deep black sea and south caspian basins are underlain by highly attenuated continental crust having velocities in the 7 km s range that shows no evidence for significant extension in passive margins upper crustal extension ranges between 10 and 40 whereas the lower crust is attenuated by 2 3 times e g campos basin north biscay margin large discrepancy between upper crustal stretching and lower crustal attenuation is seen in the crustal configuration of many intracontinental grabens e g baikal and dniepr prypyat basins only in highly extended areas such as the basin and range province and the east china rift system does crustal stretching account for the observed crustal thinning the observed discrepancy between upper extension and crustal thinning across intracontinental rifts and passive margins and particularly in some wide intracontinental basins suggests that crustal stretching alone cannot account for the subsidence of these basins phase transformations in the lower crust probably facilitated by the presence of hydrous fluids can cause rapid 1 ma as well as long term 200 1500 ma upward displacement of the moho discontinuity resulting in high amplitude subsidence of the crust in areas of crustal extension this mechanism can overprint subsidence induced by thermal relaxation of the lithosphere the case of the black sea and south caspian basins shows that density increase of the lithosphere can also occur independently of crustal stretching

genesis of the vein type tungsten mineralization at nyakabingo rwanda in the karagwe ankole belt central africa the vein type tungsten deposit at nyakabingo in the central tungsten belt of rwanda is located in the eastern flank of the complex bumbogo anticlinal structure the host rock is composed of alternating sequences of sandstones quartzites and black pyritiferous metapelitic rocks two types of w mineralized quartz veins have been observed bedding parallel and quartz veins that are at high angle to the bedding which are termed crosscutting veins both vein types have been interpreted to have been formed in a late stage of a compressional deformation event both vein types are associated with small alteration zones comprising silicification tourmalinization and muscovitization dating of muscovite crystals at the border of the veins resulted in a maximum age of 992 4 1 5 ma this age is within error similar to the ages obtained for the specialized g4 granites i e 986 10 ma the w bearing minerals formed during two different phases the first phase is characterized by scheelite and massive wolframite while the second phase is formed by ferberite pseudomorphs after scheelite these minerals occur late in the evolution of the massive quartz veins sometimes even in fractures that crosscut the veins the ore minerals precipitated from a h2o co2 ch4 n2 nacl kcl fluid with low to moderate salinity 0 6 13 8 eq wt nacl and minimal trapping temperatures between 247 and 344 c the quartz veins have been crosscut by sulfide rich veins based on the similar setting mineralogy stable isotope and fluid composition it is considered that both types of w mineralized quartz veins formed during the same mineralizing event given the overlap in age between the g4 granites and the mineralized quartz veins and the typical association of the w deposits in rwanda but also worldwide with granite intrusions w originated from the geochemically specialized g4 granites intense water rock interaction and mixing with metamorphic fluids largely overprinted the original magmatic hydrothermal signature

shear wave velocity structure beneath europe the northeastern atlantic and western asia from waveform inversions including surface wave mode coupling summary waveforms of 449 seismograms have been inverted for s wave velocity structures beneath europe the northeastern atlantic and western asia down to a depth of 670 km recorded waveforms were used in the time window starting at the s wave arrival and ending after the fundamental mode rayleigh wave arrival the inversion method is based on the partitioned waveform inversion nolet 1990 with the difference that synthetic seismograms are calculated taking surface wave mode coupling into account in order to model body waves in laterally heterogeneous media more accurately the partitioning of the inversion procedure makes non linear optimization feasible even for inversions including surface wave mode coupling the non linear inversion of the waveforms resulted in linear constraints on the 3 d velocity structure in a second step these constraints were used in a linear inversion for the 3 d shear wave velocity model beneath europe the northeastern atlantic and western asia the eur sc 95 model is presented which is characterized by a wide range of length scales of the velocity structures in central europe where the ray density is highest small scale structures are recovered such as the presence of high velocities associated with the hellenic subduction zone on the edges of the inversion model where the ray density and therefore also the resolution is poorer we find larger scale features such as the relatively laterally homogeneous high velocity structure beneath the russian platform to a depth of 300 km in this paper we discuss the inversion method data processing parametrization difficulties due to the introduction of surface wave mode coupling spatial resolution of the model and structures in the eur sc 95 model

u th stratigraphy of a cold seep carbonate crust on continental margins oxidation of methane rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor the biogeochemical processes involved during this carbonate precipitation are increasingly understood but little is known about the duration or mode of carbonate crust formation here we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement which provide the first stratigraphy for a cold seep carbonate crust the 5 5 cm thick crust nl7 cc2 was collected by submersible on the nile deep sea fan in an area of active fluid venting u th analyses must be corrected for initial th and measurement of co existing sediments indicates the presence of both scavenged and detrital initial 230th which must be considered during this correction the calculated 230th u age depth profile for nl7 cc2 provides evidence for continuous downward carbonate precipitation at the studied location over the last 5000 years three distinct phases can be distinguished from top to bottom with average growth rates of 0 4 5 and 0 8 cm kyr respectively corresponding to carbonate precipitation rates ranging from 7 to 92 mol m2 h 1 rates consistent with previous estimates high resolution 13c profiles gontharet s pierre c blanc valleron m m rouchy j m fouquet y bayon g foucher j p woodside j mascle j the nautinil scientific party 2007 nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the nile deep sea fan eastern mediterranean sea deep sea res ii 54 1292 1311 and major elements across nl7 cc2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition we suggest that these changes primarily reflect modification of the diagenetic environment i e a progressive depletion of dissolved sulphate through anaerobic oxidation of methane caused by the initial carbonate crust formation and the resulting reduction in bioirrigation overall u th dating of cold seep carbonates offers a promising tool to bring new insights into biogeochemical processes at cold seeps and to assess the timing and duration of fluid venting on continental margins

scheelite apatite calcite and tourmaline compositions from the late archean hutti orogenic gold deposit implications for analogous two stage ore fluids abstract gold mineralization at hutti southern india has occurred in two stages stage 1 mineral assemblage comprises biotite chlorite plagioclase calcite epidote actinolite tourmaline arsenopyrite pyrite pyrrhotite and gold whereas the stage 2 mineral assemblage is represented by sericite chlorite calcite scheelite tourmaline apatite titanite pyrrhotite arsenopyrite and gold we report here the occurrence of scheelite from the stage 1 assemblage and compare major and trace element compositions of scheelite fluorapatite f 4 wt calcite and tourmaline from the two stages with an emphasis on the second stage in which they are best represented scheelite displays three types of ree patterns these are the type i middle ree mree enriched with negative eu anomaly type ii heavy ree hree enriched with minor positive negative eu anomaly and type iii that varies from slightly mree enriched to mree depleted with correspondingly increasing positive eu anomaly the stage 1 scheelites display type i pattern while stage 2 scheelites display type ii and type iii patterns textural and compositional evidence suggest asynchronous precipitation of scheelite fluorapatite and calcite in the stage 2 mineralization indicating precipitation from cyclic fluid flow the occurrence of rare minute scheelite grains in the stage 1 mineralization assemblage is most likely because of prevalent high temperature 350 477 c whereas during the stage 2 mineralization abundant scheelite precipitation evidenced by the presence of scheelite rich carbonate quartz veins was favored by the decrease in temperature 300 c additionally repeated fluid pressure fluctuations due to fault valve mechanism would have further enhanced precipitation of scheelite in stage 2 the fewer scheelites in stage 1 mineralization resulted in their mree enriched pattern with high ree the mree depleted patterns of stage 2 scheelites on the other hand do not necessarily indicate a compositionally different fluid but are due to rapid removal of mree in early formed mree enriched scheelites making them less and less available in the fluid for later crystallizing scheelites this is supported by the observation that except for the slight remobilization of lree the rees are conserved in the altered rocks trace element ratios y ho zr hf nb ta in fluorapatite and calcite are chondritic indicating little fractionation of these element pairs and cannot be diagnostic of fluid composition tourmalines from both the stages record equally low contents of na liles and hfses and comparably low fe 3 fe 2 ratios suggesting very similar nature of the two fluids which were low in salinity trace element poor and reducing in nature indicating a metamorphic parentage

three dimensional interpretation of gravity data from sedimentary basins using an exponential density depth function in mapping the topography of the basement of deep sedimentary basins by gravity modelling the accuracy can be improved by incorporating an exponential increase in density with depth for calculating the gravity effect of a three dimensional 3d structure with such an exponential density depth relation a frequency domain forward algorithm based on series expansion is presented the numerical evaluation of which can be performed efficiently by fast fourier transform the algorithm can be applied in a recursive procedure to give the inverse solution in terms of basement relief the inversion procedure is satisfactorily tested on a 2d synthetic example and a 3d field example of gravity data from the western margin of the pannonian basin in eastern austria where up to 2 2 km of tertiary sediments overlie an igneous or metamorphic basement the results are confirmed by basement intersections in several wells

time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from gulf of mexico gas hydrate seafloor observatory article i nfo authigenic carbonate rocks recovered from the gulf of mexico gas hydrate seafloor observatory in mississippi canyon block 118 mc118 at approximately 900 m water depth were studied using mineralogical bulk geochemical and lipid biomarker analyses carbonate rocks occurred as fractured blocks and nodular masses incorporated in carbonate breccias the carbonates were comprised mainly of high mg calcite and aragonite the stable carbon isotope composition

effect of grossular content in garnet on the partitioning of fe and mg between garnet and biotite in contrast to ferry 1980 x ca values in garnet even lower than 0 1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the fe and mg paritioning between garnet and biotite garnet compositions and mg fe distribution coefficients from samples of the eoalpine staurolite in zone in the southern otztal are related by the quadratic regression equation ink d 1 7500 0 0226 2 978 0 5317 x ca gt 5 906 2 359 x ca gt 2 temperatures derived by the ferry and spear 1978 calibration using chemistry corrected k d values are petrologically realistic analysis of our data supports non ideal mixing of grossular with almandine pyrope solid solution the derived excess mixing energies are quite small for the almandine pyrope solution w femg 133 cal mole and about 2775 cal mole for the difference between pyrope grossular and almandine grossular solutions w mgca w feca at metamorphic conditions of 570 c and 5 000 bar the mixing parameters proposed by ganguly and saxena 1984 are not confirmed by our data as they would result in significantly lower temperatures

roles of carbonate co2 in the formation of quartz vein wolframite deposits insight from the crystallization experiments of huebnerite in alkali carbonate aqueous solutions in a hydrothermal diamond anvil cell abstract quartz vein type wolframite deposits are a primary type of tungsten deposits traditionally f and cl were considered as important agents in tungsten transportation during ore formation process however ore forming fluids enriched in co2 were commonly observed in natural fluid inclusions associated with quartz vein type wolframite deposits indicating that carbonate or co2 could be important for their formation in this paper we report experiments of the dissolution and crystallization of huebnerite in the mnwo4 li2co3 or na2co3 h2o system using a hydrothermal diamond anvil cell hdac the results showed that mnwo4 dissolved in alkali carbonate aqueous solutions and in some cases in associated carbonate melts during heating and subsequently huebnerite crystallized into needle and column shaped crystals during cooling in situ raman spectra obtained during heating of the experimental charge in the sample chamber of the hdac showed that wo42 was the only tungsten bearing ion detected in the carbonate melt or aqueous solution the dissolution of mnwo4 mainly attributed to the alkaline environment in the alkali carbonate aqueous solution furthermore the weak alkali condition in the carbonate solutions enhanced the crystallization of huebnerite when the temperature and pressure were decreased the experimental results indicate that although the crystallization temperature pressure conditions of huebnerite vary in a wide range conditions lower than approximately 200 mpa and 450 c are not favorable for huebnerite crystallization our experimental results also suggest that the alkali carbonate aqueous solution could serve as a medium for the transport of tungsten in the ore forming process

implications of earthquake focal mechanism data for the active tectonics of the south caspian basin and surrounding regions summary the south caspian basin is a relatively aseismic block within the alpine himalayan belt but is surrounded by zones of high seismicity we used the focal mechanisms of 16 earthquakes whose source parameters we determined from inversion of body waves and the mechanisms of 15 other earthquakes to determine the style of faulting in the seismic belts surrounding the south caspian basin earthquakes beneath the talesh mountains of north west iran and immediately off shore in the south west caspian sea have shallow thrust mechanisms showing that the continental crust of north west iran is overthrusting the oceanic like crust of the south caspian basin earthquakes south of the caspian sea in northern iran show a mixture of focal mechanisms both high angle reverse faulting and left lateral strike slip faulting mechanisms are observed in the high alborz mountains farther south on the edge of the central iran plateau oblique left lateral reverse mechanisms are observed it appears that the ne direction of shortening between central iran and the south caspian basin is partitioned into pure left lateral strike slip and thrusting in the wnw trending high alborz but is accommodated by oblique faulting in lower elevations earthquakes in the kopet dag mountains east of the caspian sea also show a mixture of high angle reverse and strike slip faulting mechanisms and may be another example of the partitioning of oblique slip into strike slip and thrust motion normal faulting mechanisms at centroid depths of 35 50 km dominate in the belt of seismicity that extends across the central caspian sea the significance of the normal faulting earthquakes is enigmatic it is improbable that these events represent the motion between the southern caspian basin and eurasia for they imply a sense of motion that is incompatible with the observed topography and folding in the sediments two shallow earthquakes at about 12 km depth in this belt one a small event and the other a large second subevent of a multiple earthquake have thrusting mechanisms suggesting that shortening occurs as the continental crust of the northern caspian sea is thrust over the oceanic like crust of the southern caspian basin shortening is also suggested by the orientations of folds in the sedimentary cover south of the central caspian sea seismic belt we suggest that this shortening does indeed represent a nne motion of the caspian sea relative to eurasia but that the motion is slow and has not produced many earthquakes the deeper normal faulting events may be related to bending or down dip extension of the incipient subducted slab if the motion of the caspian sea relative to eurasia is indeed slow then the motion in the alborz between central iran and the south caspian basin will be almost the same as that between iran and eurasia as has previously been assumed the combined effect of the overthrusting of the south caspian basin by the talesh alborz mountains in the south and by the continental crust of the northern caspian sea in the north will lead to the eventual destruction of the south caspian basin and the possible formation of an intermediate depth dipping seismic zone within the continental interior similar to that presently observed in the hindu kush

interpretation of geoid anomalies in the contact zone between the east european craton and the palaeozoic platform i estimation of effects of density inhomogeneities in the crust on geoid undulations summary in our paper we compile a detailed 3 d velocity model of the crust for the territory of poland and investigate the effect of a 3 d density distribution in the crust on geoid undulations the major tectonic feature in the study area is the trans european suture zone tesz separating the precambrian east european craton from younger tectonic units of palaeozoic europe high resolution seismic models of the crust and upper mantle from recent controlled source experiments were interpolated into a 3 d p wave velocity model for the whole poland the model was converted to a density model assuming different equations connecting seismic velocities to densities for crustal rocks sediments and the uppermost mantle the crustal density model was used to calculate synthetic geoid undulations for the territory of poland and to estimate influence of separate layers topography sediments crust and uppermost mantle on the geoid to calculate the gravity effect of a large scale 3 d density model we developed a code based on a point mass algorithm as well as prisms algorithm that uses some easy to implement optimizations the synthetic geoid undulations were compared to an existing gravimetric quasi geoid solution the modelling showed that the difference in crustal structure between the east european platform and palaeozoic platform explains significant part of the observed geoid undulations in the study area the remained residual could be related to density inhomogeneities in the upper mantle

shear wave velocity variations in the upper mantle beneath central europe summary a new model eur s91 of shear wave velocity variations in the upper mantle beneath central europe and surrounding regions down to a depth of 670km is presented the model is derived from the inversion of the waveforms of 217 seismograms using the partitioned waveform inversion method for the seismogram in the time window from the s wave arrival to the fundamental mode of the rayleigh wave the seismograms were mostly assembled from digitally recording long period and broad band stations in europe the resulting 3 d model accurately predicts most of the observed waveforms in a wide band of frequencies body waves were fit for frequencies up to 60mhz the fundamental rayleigh mode which at high frequencies is more prone to scattering and multipathing was generally low passed at 25 mhz the resolving power of the data set depends strongly on the density of available wave paths and varies as a function of geographical position small scale heterogeneities like the subducted lithosphere in the hellenic collision zone were imaged in the region with the highest density of wave paths which indicates an optimum resolution of better than 200 km the main new results of this study pertain to the transition between east and central europe we present new information about the structure below the tornquist teisseyre zone ttz the ttz is generally regarded as the boundary between the precambrian crust of the baltic shield russian platform and the younger crust of central europe our 3 d s velocity model reveals that below this line a sharp lateral boundary extends down to at least 140 km depth with high velocities beneath the baltic shield and russian platform contrasting to the low velocities beneath the younger regions of europe the observed velocity contrast across the ttz is largest between the pannonian basin and the russian platform where it is equal to 12 per cent at 80 km depth at depths of 300 400 km the ttz is underlain by a zone of low s velocity which indicates a local thinning of the deeply rooted high velocity structure or tectosphere that underlies most of eastern europe in addition to these new results on the transition region between east and central europe a number of features that are present in other tomographic results have been confirmed the precambrian provinces of europe are characterized by high s velocities low velocities are found beneath the pannonian basin the western mediterranean northern aegean sea turkey and a small region south west of the massif central the lithosphere beneath the paris basin has a positive s velocity anomaly the resolution of all these anomalies has been established with sensitivity tests

three dimensional gravity modelling of the european mediterranean lithosphere summary residual gravity anomalies characterizing the density heterogeneities in the upper mantle of the alpine belt of western europe are determined residual anomalies were calculated on a 1 x 1 grid by subtracting the gravity effect of the density model for the earth s crust from the observed gravity field our 3 d density model consists of two regional layers of varying thicknesses with a lateral variation in average density the sedimentary cover and the crystalline crust offshore the model is supplemented by a sea water layer this 3 d density model is based on a generalized velocity model represented by structure maps of the main seismic horizons the seismic basement and the moho boundary and a map of the average p wave velocity in the consolidated crust the density distribution within the model layers was obtained using the correlation functions between p wave velocity and density for sediments sediment consolidation with depth was taken into account the gravity effect of the model approximated by parallelepipeds 1 x 1 in planar size was calculated by a program designed for solving 3 d gravity problems the program takes into account the spherical configuration of the earth this method also permits the estimation of the isostatic state of the crust a mantle origin of residual gravity anomalies is confirmed by their close correlation with upper mantle velocity heterogeneities established by both seismic tomography and thermal regime data the residual gravity field is inverted into the distribution of anomalous density within the uppermost mantle layer between the moho and a bottom level at 200 km depth the most important anomalies are the high density domains caused by the thick lithosphere of the adriatic plate and by the lithosphere roots beneath the alps and the calabrian arc negative density anomalies over the pannonian basin and the western mediterranean basins reach 0 04 to 0 05 x lo3 kg m 3 due to thermal expansion of the asthenosphere

crustal temperature and mantle heat flow in europe abstract the map of the surface heat flow in europe was supplemented by the crustal thickness pattern and data on crustal radioactivity and transformed to the mantle moho heat flow distribution using a model of radioactivity decreasing exponentially with depth a z a 0 exp z d with a0 2 wm 3 and d 10km we computed generalized one dimensional steady state conductive temperature depth curves for the major tectonic units of europe the available information on the heat flow tectonic age heat flow heat generation and heat flow crustal thickness relationships were summarized and discussed in terms of crustal structure the mohorovicic discontinuity is clearly not an isothermal surface neither is the outflow of heat from the upper mantle constant but both parameters may vary within broad limits the moho temperature can be as low as 280 c in the shield areas however it can exceed 900 c in some young intrarnontane depressions or rift structures regional variations of the moho heat flow can be as large as 30 40 mwm 2 the value of the moho temperature reflects primarily the tectonic stabilization of the crust as a result of the deep seated processes in the upper mantle

biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux the tex86 tetraether index of tetraethers consisting of 86 carbon atoms is a proxy for sea surface temperature sst based on the distribution of isoprenoidal glycerol dialkyl glycerol tetraether gdgt membrane lipids synthesized by marine pelagic thaumarchaeota one of the caveats of this proxy is the production of additional gdgts by sedimentary euryarchaeota involved in anaerobic oxidation of methane aom that occurs at deep sea methane seeps but is also widespread in many continental shelf settings here gdgt distributions are investigated through the sulfate methane transition zone smtz in aarhus bay denmark to examine the extent the tex86 proxy is compromised in such a continental shelf setting where aom is characterized by a diffusive rather than rapid advective methane flux both free extractable and non extractable lipid fractions were analyzed as it was expected that pelagic derived and sediment derived gdgts could become incorporated into the molecular and sedimentary matrix to a different extent the results show a large change of tex86 values mainly due to the relative high amounts of gdgt 2 produced by aom related archaea both in the free and non extractable lipid fractions this additional gdgt input renders calculation of ssts based on tex86 inappropriate at the smtz the aom related gdgt signature however did not persist into deeper sediments perhaps reflecting rapid remineralization of the gdgts at the smtz although the process of aom at aarhus bay might not be representative for all continental margin settings it illustrates that aom in a variety of settings not just cold seeps can influence sedimentary gdgt distributions

wolframite solubility and precipitation in hydrothermal fluids insight from thermodynamic modeling abstract wolframite a solid solution series between hubnerite mnwo4 and ferberite fewo4 is the main tungsten bearing ore mineral in vein type tungsten deposits much progress has been made on characterizing the mineralizing fluids precipitating wolframite but it remains poorly understood what are the mechanisms depositing wolframite effectively and the variables controlling mn fe ratios in wolframite this study examines chemical controls on wolframite solubility in hydrothermal fluids and mn fe ratios in wolframite using thermodynamic models for fluids in the systems of w mn cl na o h and w fe cl na o h the fluid buffered models are established based on the characteristics of vein type tungsten deposits the modeling results indicate that solubilities of hubnerite and ferberite in hydrothermal fluids at typical w mineralizing conditions 300 400 c 500 1500 bars 5 15 wt nacl equivalent ph 4 6 reach up to hundreds of ppm the predominant tungsten manganese and iron species in fluids are h w o 4 m n c l 2 0 and f e c l 4 2 respectively an increase in ph and a decrease in fluid temperature and salinity are efficient mechanisms precipitating hubnerite and ferberite from acidic hydrothermal fluids hubnerite and ferberite are also significantly dissolved in alkaline hydrothermal fluids but their solubilities in alkaline fluids are insensitive to fluid temperature and salinity this may affect w mineralization at stages with different ph levels e g the greisen stage and the alkaline stage the mn fe ratio of mineralizing fluids is the principal variable controlling mn fe ratios in wolframite more supply of fe than mn from the fertile magma tends to produce fe rich mineralizing fluids this may be one of reasons why ferberite is more common than hubnerite in tungsten deposits and why hubnerite is more likely to precipitate at an early stage

combined analysis of seismic and gravimetric data in the adriatic plate abstract the presence of a structural heterogeneity between the northern part of the adriatic plate central mediterranean and its southernmost sector was hypothesised by different authors and also confirmed recently by 3d velocity models obtained through surface wave tomography and local earthquake tomography however the seismological data leave some uncertainty about the location of the lateral limits of this heterogeneity and about its structural meaning the analysis of the bouguer anomalies observed on a profile running from nw to se along the italian side of the plate has allowed to obtain a laterally improved and better constrained integrated model of the area in particular the gravimetric data have been interpreted through a 2 1 2 d density modelling developed adopting the seismic tomography model as starting point the obtained results support the hypothesis of a 10 km thinning of the crust from nw to se compensated by the presence of a thick transition zone under the crust in the southern part of the adriatic plate the location of the boundary of this lateral heterogeneity was better defined being marked by an increase of the bouguer anomalies the estimated density contrasts of the transition zone with respect to the contiguous layers of lower crust and mantle about 0 5 and 0 1 g cm3 respectively and the comparison with the corresponding velocity contrasts suggest that the material constituting this transition zone might have a composition more similar to that of the mantle

activity variations attending tungsten skarn formation pine creek california an integrated geochemical analysis of the well exposed pine creek california tungsten skarn deposit has been undertaken to evaluate changes in chemical gradients across various lithologies thermodynamic calculations using available experimental and thermodynamic data allow limits to be assigned to the activities of important chemical components in the metasomatic environment quantifiable changes in non volatile component activites cao mgo al2o3 fe2o3 wo3 and in fugacities o2 f2 have been traced across the system the activities of al2o3 fe2o3 and wo3 generally increase from the marble 102 10 6 10 5 respectively through the outer skarn zone and into the massive garnet skarn 10 1 7 0 3 10 3 4 0 4 10 4 8 0 1 while cao and mgo activities decrease for the same traverse from 10 5 and 10 2 1 1 respectively to 10 5 7 and 10 3 calculated oxygen fugacities are 10 23 5 1 0 at t 800 k 527 c about one log unit below qfm and more reducing than that required by mt py po the high variance of the garnet pyroxene quartz assemblages adds sufficient uncertainty to the calculated activities for individual specimens that only the large scale trends survive the small scale scatter none of the chemical variables emerge as major independent or controlling factors for the mineralogy or phase compositions changes in the activity of one component may be offset by compensatory changes in another resulting in an environment that while different from pine creek could still host scheelite mineralization mass balance calculations indicate that the exposed endoskarn cannot have supplied the necessary chemical components to convert the country rock to skarn

authigenic carbonates from methane seeps of the northern congo fan microbial formation mechanism abstract authigenic carbonates were collected from methane seeps at hydrate hole at 3113 m water depth and diapir field at 2417 m water depth on the northern congo deep sea fan during rv meteor cruise m56 the carbonate samples analyzed here are nodules mainly composed of aragonite and high mg calcite abundant putative microbial carbonate rods and associated pyrite framboids were recognized within the carbonate matrix the 13c values of the hydrate hole carbonates range from 62 5 to 46 3 pdb while the 13c values of the diapir field carbonate are somewhat higher ranging from 40 7 to 30 7 pdb indicating that methane is the predominant carbon source at both locations relative enrichment of 18o 18o values as high as 5 2 pdb are probably related to localized destabilization of gas hydrate the total content of rare earth elements ree of 5 hno3 treated solutions derived from carbonate samples varies from 1 6 ppm to 42 5 ppm the shale normalized ree patterns all display positive ce anomalies ce ce 1 3 revealing that the carbonates precipitated under anoxic conditions a sample from hydrate hole shows a concentric lamination corresponding to fluctuations in 13c values as well as trace elements contents these fluctuations are presumed to reflect changes of seepage flux

40 ma of hydrothermal w mineralization during the variscan orogenic evolution of the french massif central revealed by u pb dating of wolframite we present u pb thermal ionization mass spectrometer tims ages of wolframite from several granite related hydrothermal w sn deposits in the french massif central fmc located in the internal zone of the variscan belt the studied wolframite samples are characterized by variable u and pb contents typically 10 ppm and show significant variations in their radiogenic pb isotopic compositions the obtained u pb ages define three distinct geochronological groups related to three contrasting geodynamic settings i visean to namurian mineralization 333 327 ma coeval with syn orogenic compression and emplacement of large peraluminous leucogranites ca 335 325 ma ii namurian to westphalian mineralization 317 315 ma synchronous with the onset of late orogenic extension and emplacement of syn tectonic granites ca 315 310 ma and iii stephanian to permian mineralization 298 274 ma formed during post orogenic extension contemporaneous with the permian volcanism in the entire variscan belt the youngest ages 276 274 ma likely reflect the reopening of the u pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration e g ferberitization our results demonstrate that w sn mineralization in the fmc formed during at least three distinct hydrothermal events in different tectono metamorphic settings over a time range of 40 ma

comment on formation and evolution processes of the salanfe w au as skarns aiguilles rouges massif western swiss alps by chiaradia m mineralium deposita 38 154 168

volcanogenic exhalative tungsten mineralization of proterozoic age near santa fe new mexico and implications for exploration a stratabound tungsten scheelite occurrence is exposed in proterozoic 1650 1720 ma metamorphic terrane near santa fe new mexico and may be the first volcanogenic exhalative tungsten deposit recognized in the united states the tungsten bearing horizon is composed of disseminated scheelite within epidote actinolite rock exhibits pronounced mineralogic zoning and anomalous metal contents and is localized along the contact between sulfide bearing felsic tuffs and cherts and barren basalts and mafic sediments it is interpreted as a syngenetic tungsten deposit exhaled as a chemical sediment at the close of a volcanic cycle and subsequently metamorphosed to lower amphibolite facies and deformed we suggest that other tungsten deposits in precambrian terrane in the western united states may also be volcanogenic exhalative application of this model to exploration could lead to additional discoveries

microbial activity in surficial sediments overlying acoustic wipeout zones at a gulf of mexico cold seep 1 down core concentration gradients of dissolved methane and sulfate isotope gradients of methane dissolved inorganic carbon and authigenic carbonate and organic matter elemental ratios are incorporated into a vent evolution model to describe spatial and temporal variability of sedimentary microbial activity overlying acoustic wipeout zones at mississippi canyon mc 118 gulf of mexico we tested the hypothesis that these zones indicate areas where sediments are exposed to elevated fluid flux and therefore should contain saturated methane concentrations and enhanced microbial activity from sulfate reduction sr anaerobic oxidation of methane aom and methanogenesis mp thirty surficial cores between 22 and 460 cm deep were collected from sediments overlying and outside the wipeout zones and analyzed for pore water and solid phase constituents outside the wipeout zones sulfate and methane concentrations were similar to overlying water values and did not vary with depth indicating low microbial activity above the wipeouts nine cores showed moderate activity with gently sloping sulfate and methane concentration gradients methane concentrations 20 m and isotope depth gradients indicative of organic matter oxidation in stark contrast to this moderate activity four cores showed high microbial activity where sulfate concentrations were depleted by 50 cm below seafloor maximum methane concentrations in the decompressed cores were above 4 mm and down core profiles of 13c ch4 and 13c dissolved inorganic carbon dic indicated distinct depth zones of sr aom and mp bulk organic matter analysis suggested that the high activity was supported by an organic source that was enriched in carbon c n 15 and depleted in 15n and 13c compared to other activity groups possibly due to the influx of petroleum or chemosynthetically fixed carbon within high activity cores the 13c dic values were similar to the 13c caco3 values a result expected for authigenic carbonate recently precipitated however these values were dissimilar in moderate activity cores suggesting that microbial activity was higher in the past this study provides evidence that the fluid flux at mc 118 varies over time and that the microbial activity responds to such variability it also suggests that sediments overlying wipeout zones are not always saturated with respect to methane which has implications for the formation and detection of gas hydrate

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

magmatism and the geodynamics of rifting of the pripyat dnieper donets rift east european platform abstract the distribution of volcanism in the late devonian pripyat dnieper donets rift within the east european platform based upon the results of deep drilling indicates that pre existing basement structures and the major rift bounding faults played an important role in channelling the magmas towards the surface major and trace element and sr nd isotopic studies of the most primitive basic and ultrabasic magmas combined with estimates of the amount of extension 1 1 to 1 3 strongly suggest that magmatism was triggered by the upwelling of a thermally and geochemically anomalous mantle plume from the deep mantle during the late frasnian the peak of the magmatism occurred in the famennian coincident with the maximum amount of lithospheric extension magmatism rifting and domal basement uplife were contemporaneous at several localities within the eep suggesting that the thermal and geodynamic evolution of the platform could have been influenced by a cluster of mantle plumes during the late devonian

epcrust a reference crustal model for the european plate summary we present a new crustal model for the european plate derived from collection and critical integration of information selected from the literature the model covers the whole european plate from north africa to the north pole 20 n 90 n and from the mid atlantic ridge to the urals 40 w 70 e the chosen parametrization represents the crust in three layers sediments upper crust and lower crust and describes the 3 d geometry of the interfaces and seismologically relevant parameters isotropic p and s wave velocity plus density with a resolution of 0 5 0 5 on a geographical latitude longitude grid we selected global and local models derived from geological assumptions active seismic experiments surface wave studies noise correlation receiver functions model epcrust presents significant advantages with respect to previous models it covers the whole european plate it is a complete and internally consistent model with all the parameters provided also for the sedimentary layer it is reproducible it is easy to update in the future by adding new contributions and it is available in a convenient digital format epcrust could be used to account for crustal structure in seismic wave propagation modelling at continental scale or to compute linearized crustal corrections in continental scale seismic tomography gravity studies dynamic topography and other applications that require a reliable crustal structure because of its resolution our model is not suited for local scale studies such as the computation of earthquake scenarios where more detailed knowledge of the structure is required we plan to update the model as new data will become available and possibly improve its resolution for selected areas in the future

lipid biomarker patterns of methane seep microbialites from the mesozoic convergent margin of california abstract in order to reconstruct biogeochemical pathways at mesozoic methane seeps a set of late jurassic tithonian to early cretaceous aptian albian 13 c depleted seep limestones from forearc strata in western california were subjected to detailed molecular isotopic biomarker analyses two of the microbial carbonate deposits are turbidite hosted fault related whereas one is hosted in serpentinite in a diapir related setting the limestones contain 13 c depleted archaeal lipid biomarkers such as crocetane 13 c 80 and pmi 100 indicative of an involvement of anaerobic oxidation of methane aom in carbonate precipitation isotopically depleted crocetane in the tithonian sample represents the oldest reported occurrence of this compound at methane seeps in the set of samples a series of strongly 13 c depleted regular c 21 to c 24 isoprenoids possibly results from diagenetic alteration of archaeal sesterterpanylglycerol diethers as suggested by the presence of the putative intermediate 3 7 11 15 19 pentamethylicosanoic acid 13 c depleted 17 h 21 h and 17 h 21 h hopanes c 30 c 34 with 22 s and 22 r isomer couplets c 31 are present in all samples in distributions indicative of a moderate thermal maturity low 13 c values 78 to 60 suggest that these are derived from anaerobic bacteria involved in aom notably 22 s isomers are consistently enriched in 13 c relative to their 22 r counterparts our samples represent 70 myr of seepage activity and aom along the mesozoic margin of western california filling the gap between the currently oldest methane seep biomarker record from the oxfordian late jurassic and the more widely recognised cenozoic examples

biogeochemical controls on authigenic carbonate formation at the chapopote asphalt volcano bay of campeche abstract the campeche knolls in the bay of campeche southern gulf of mexico were investigated through detailed seafloor mapping rov surveys and sediment and pore water sampling the knolls are elongated submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor several of the knolls are associated with sea surface oil slicks identified from satellite data indicating the presence of hydrocarbon seeps on the seafloor one of the knolls named chapopote was studied in detail during two international research expeditions so174 2 and m67 2 and is characterized by extensive hydrocarbon seepage including large asphalt flows oil and gas seeps and seafloor gas hydrate deposits chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward diffusing seawater and hydrocarbon rich pore fluids at shallow sediment depth authigenic carbonates are characterized by aragonite exhibit a porous texture and are cemented by a matrix of microsparitic to sparitic aragonite macropores of the carbonates were completely filled with liquid oil carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism banded botryoidal aragonite cements line the intra and bioclasts and incompletely fill the pore spaces the stable carbon isotopic composition of authigenic aragonite varies between 28 6 and 17 9 pdb identifying oil oxidation as the primary source of carbon to the dic pool while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane aom these observations indicate the presence of additional aom independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the gulf of mexico basin oxygen isotope data of authigenic aragonite vary from 2 5 to 3 8 pdb indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids

the molybdenite re os isotope chronology in situ scheelite and wolframite trace elements and sr isotope characteristics of the chuankou tungsten ore field south china abstract the chuankou tungsten ore field situated in the central area of the qing hang ancient suture zone in south china is characterized by predominantly quartz vein type tungsten mineralization that formed near the contact between the chuankou granite and slightly metamorphosed silt bearing sericite slate based on field work cathodoluminescence molybdenite re os dating and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms analysis the chuankou tungsten ore was formed at 230 6 2 9 ma to 229 4 2 6 ma in a typical indosinian metallogenic event in addition three distinct generations of scheelite and two types of wolframite can be clearly distinguished type 1 wolframite has a semiautomorphic grain or brecciated vein structure with a high heavy rare earth element hree content and an obvious negative eu anomaly type 2 wolframite grains are strongly altered as residual pseudomorphic structures by ore forming fluids and have relatively low ree contents sch 1 scheelite is present in the interior of the type 2 wolframite grains the sch 1 scheelite grains have an elevated ree content and low 87sr 86sr ratios with a strongly negative eu anomaly which suggests an inheritance signal of the host rocks comparatively sch 2 and the altered sch 1 scheelite have characteristic extremely low ree contents and remarkably strong positive eu anomalies these scheelites also have increased 87sr 86sr ratios and low 88sr signals sch 3 is idiomorphic with perfect oscillating zoning the ree content of sch 3 which typically has the lowest 87sr 86sr ratios is higher than those in sch 1 and sch 2 and the extremely high 88sr signals indicate a distinct thermal fluid event that was directly derived from the host rock the correlations between the ree and nb of scheelite imply a type b substitution of sch 1 and sch 2 but a type c substitution for sch 3 the correlation of eun and eun shows an eu3 substitution process for stages sch 1 and sch 2 and an eu2 substitution process for stage sch 3 thus we confirm that ore bearing hydrothermal rocks must undergo early stage metasomatism and filling middle stage fluid mixing between wall rocks and magmatic hydrothermal activity and refilling of late stage magmatic hydrothermal activity during the metallogenic process during the indosinian period the mineralization stages of polymetallic deposits in the indosinian were composed of stage 1 240 to 220 ma and stage 2 220 to 200 ma the chuankou tungsten ore field can be considered as the typical representation of the stage 1 metallogenic event in south china this ore field is derived from remelting of the ancient basement and was reduced by regional extension under the dominant compression regime in the south china block

tectonic evolution of the mid polish trough modelling implications and significance for central european geology abstract the polish basin forms the easternmost part of the permian mesozoic northwest european basin the depocentral axis of the polish basin the mid polish trough mpt is superimposed on the boundary between the west european phanerozoic and east european proterozoic crustal domains within the trans european suture zone the presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the mpt concentrating stresses during post variscan wrench and extensional tectonics in central europe tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the polish basin indicates the occurrence of an initial late permian early triassic 255 241 ma rifting phase that was followed by subsequent episodes of increased tectonic subsidence during the oxfordian kimmeridgian 157 152 ma and beginning in the cenomanian 97 ma the oxfordian kimmeridgian episode is interpreted as corresponding to a second extensional event which correlated with intersified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin while the cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest cretaceous and paleocene forward modelling results in view of existing geophysical interpretations which show the presence of a deep moho and a very velocity lower crustal layer beneath thempt suggest that permo mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning

crustal thinning and subsidence in the north sea we present here the results of a detailed study of subsidence and crystal thinning across the central graben of the north sea basin two independent lines of evidence have been used to test how well the uniform extensional model1 2 can account for the evolution of the north sea basin a long range seismic profile was shot perpendicular to the central graben from edinburgh to southern norway and data were analysed from 11 exploration wells situated close to the seismic line fig 1 the estimates of the increase in surface area due to extension from the crustal structure determined using the seismic data and from the well subsidence patterns are both compatible with a simple uniform extensional mechanism for the post palaeozoic evolution of the north sea

lithospheric thermal regimes in europe abstract the heat flow pattern of europe derived from more than 8000 observations is dominated by a general northeast to southwest increase in geothermal activity which is the consequence of the tectonic evolution of the whole continent this paper reviews the history of the geothermal mapping of europe and describes the recently compiled set of geothermal maps of europe surface heat flow is correlated with the age of the last tectonothermal event with the near surface heat production and with the crustal thickness deep temperature distributions within the crust lithosphere are calculated for 1 d 2 d and simple 3 d models characteristic temperature depth curves are given for some of the major tectonic provinces and the results of various techniques are compared the value of the crustal heat contribution is assessed and a regional moho heat flow pattern is proposed the mohorovicic discontinuity is clearly not an isothermal surface neither is the heat flow from below the crust constant

the eclogite facies rocks of the montagne noire france eclogite facies rocks are very rare in the montagne noire the local typical metamorphism being a low pressure type with extensive development of migmatites the cabardes and le jounie eclogites garnet omphacite quartz rutile 700 800 c 9 2 kbar derive from tholeiitic basalts interbedded in paragneisses very close to the orthogneissic basement both are strongly retromorphosed and re equilibrated in the conditions of the amphibolite facies metamorphism of the surrounding gneisses the eclogite facies garnet ultramafite of the airette pod derives from a ferromagnesian calc alkalic cumulate its reactional mineral associations show a complex polyphase evolution a primary spinel websterite cpx opx pleonaste chromite is reset in the eclogite facies where garnet develops as coronas on the spinel a further retromorphic evolution leads to a paragenesis hornblende tremolite picotite olivine fo70 phlogopite and finally to the paragenesis chlorite amphibole those rocks may be interpreted either as tectonically emplaced slabs or as the only remnants of a medium to high pressure regional metamorphism but it must be pointed out that all these rocks occur only in the southern part of the axial zone of the montagne noire i e in the root zone of the large penninic nappes which characterize this part of the hercynian belt

the evolution of pegmatite hosted sn w mineralization at nong sua thailand evidence from fluid inclusions and stable isotopes abstract the nong sua aplite pergmatite complex contains two dominant styles of sn w ta nb mineralization cassiterite nb ta ti oxide minerals are disseminated in the pegmatite and cassiterite and wolframite are hosted by quartz tourmaline veins which are contained solely within aplite the orthomagmatic fluid at nong sua is preserved as primary fluid inclusions in the cores of magmatic garnet crystals that have high tin concentrations garnet cores without fluid inclusions do not contain elevated tin concentrations these fluid inclusions have a composition of 3 wt nacl eq the low salinity suggests that at vapor saturation tin was partitioned in favour of the melt which allowed cassiterite to initially crystallize directly from the melt primary pseudosecondary and secondary fluid inclusions in cassiterite tourmaline and quartz record three component mixing of the orthomagmatic fluid with high salinity aqueous and with co2 rich fluids the orthomagmatic water is interpreted to have had 18 o value of 8 7 to 9 9 per mil and a d value of 72 to 78 per mil from 18o analyses of muscovite and quartz and d of muscovite the 18o composition of muscovite decreased from 10 1 to 8 0 per mil and d increased from 106 to 85 per mil from the magmatic to the hydrothermal stages of pegmatite evolution these changes are consistent with an influx of metamorphic fluids or evolved meteoric waters we consider that the saturation of the melt with vapor caused the pressure in the pegmatite to rise to approximately 3 8 kbar at a temperature of 650 c fluid overpressure caused the aplite to fracture and veins to form from fluids which migrated into the fracture induced low pressure zones this event can be modeled by an isothermal decompression to 2 7 kbar cassiterite deposition was probably controlled by increasing fo2 whereas wolframite deposition resulted from the mixing of w rich with fe mn rich fluids in both cases decompression cooling and addition of volatiles may have also contributed to mineralization

distributions and carbon isotopic compositions of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abstract we investigated the distributions and 13c values of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abundant highly 13c depleted archaeal and bacterial biomarkers revealed that anaerobic oxidation of methane aom is associated with carbonate authigenesis at the hakon mosby mud volcano hmmv and the nyegga pockmark field no conclusive evidence for aom was found in the crust sample from the storegga slide anme 2 methanotrophic archaea and sulfate reducing bacteria from the desulfosarcina desulfococcus cluster were inferred from lipid fingerprints distinct patterns of 13c depleted non isoprenoid dialkyl glycerol diethers dages are possibly associated with unknown microbial partners in the aom

tracing the origin of ore forming fluids in the piaotang tungsten deposit south china constraints from in situ analyses of wolframite and individual fluid inclusion abstract the piaotang vein type tungsten deposit hosted by cambrian metasedimentary rocks is one of the largest vein type hydrothermal deposits in south china wolframite is the dominant ore mineral and intergrown with quartz and cassiterite in the main mineralization stage wolframite cassiterite and quartz crystals have 18o values ranging from 2 5 to 6 8 6 1 to 7 2 10 3 to 13 7 respectively d values of fluid inclusions in these minerals are very homogenous and lie mostly between 66 1 and 78 3 chondrite normalized ree patterns of wolframite show hree enrichment with significant negative eu anomalies which are different from those of hosting metasedimentary rocks h o isotopes of fluid inclusions and trace elements of wolframite indicated that the ore forming fluids in the piaotang tungsten deposit are dominantly magmatic in origin metamorphic and meteoric fluids were not involved in the main mineralized stage although the wolframite quartz veins were hosted by metasedimentary rocks element pairs zr hf and y ho of wolframite are remarkably fractionated zr hf 13 4 34 6 y ho 10 0 14 4 almost all the analyses of wolframite display unusual tetrad effect ree patterns te1 3 1 1 these peculiar trace element characteristics of wolframites indicate that ore forming fluids have high ligands f and or cl contents la icp ms analyses of individual fluid inclusion show that ore forming fluids contain all elements necessary for the formation of wolframite w fe mn and incompatible elements e g li rb cs cs na ratios are positively correlated with rb na ratios we conclude that the ore forming fluids were reduced in nature and likely exsolved from the highly evolved granite that concealed in the vicinity of the deposit wolframite precipitation resulted from decreasing temperature and pressure of magmatic fluids during infilling along fracture rather than fluid mixing and fluid rock interaction

the association of tourmalinite with stratiform scheelite deposits three types of stratiform scheelite deposits are recognised they all commonly have a close spatial association with tourmalinite regional prograde calc silicate rocks in precambrian rift settings commonly contain 100 ppm wo3 with enrichment to 0 5 1 wo3 in retrograde metamorphic assemblages at fold hinges joints faults shears and granite and pegmatite dyke contacts the calc silicate progenitor was probably a impure dolomitic carbonate sediment amphibolite hosted scheelite deposits occur in metamorphosed altered mafic volcanics formed in a narrow rift graben scheelite occurs both as stratiform and stratabound footwall stringer ore which has undergone minor remobilization during tectonism tourmalinites are rarely the host for stratabound quartz scheelite wolframite veins remobilized from the host tourmalinite and associated metavolcanics during tectonism

subcrustal density inhomogeneities of northern eurasia as derived from the gravity data and isostatic models of the lithosphere for the territory of northern eurasia 6 e 165 w 30 75 n the distribution of anomalous masses in the lithosphere has been estimated in accordance with the lithosphere isostatic model the method of model construction is based on the admittance technique the experimental admittance presents a relation between the part of the outer load uncompensated by the moho undulations and the residual gravity field and is used to select the best model the 1 1 averaged values of topography elevations basement and moho depths sedimentary cover density and gravity anomalies have been used as initial data according to the correlation equation relating the outer load and moho depths the mean density contrast between the lower crust and the subcrustal lithosphere is 0 43 g cm3 but the moho undulation can not provide complete isostatic equilibrium in some areas the part of the outer load uncompensated by moho undulations may be as large as 107 kg m2 and the residual gravity field is as intensive as 260 mgal assuming that for loads of wavelength 200 km local isostatic compensation is valid in accordance with the admittance analysis the anomalous masses compensating for the part of the outer load which is not compensated by moho undulations have to be located partly in the lower crust and in the subcrustal layer the regional trend of anomalous compensating masses is negative under western europe the mediterranean eastern asia and adjacent marginal seas and positive under the east european platform and western and central asia the local compensating masses correspond to particular tectonic units the isostatic gravity anomalies of northern eurasia have been determined and the long wave component of the field reflecting anomalous masses under the isostatic compensation level has been evaluated

3 d density model for the lithosphere of europe construction method and preliminary results summary a map of the observed gravity field of europe has been constructed by averaging anomalies on a 1 x 1 grid in a combined reduction of bouguer anomalies on land and free air anomalies offshore on the basis of the observed gravity field and recent seismic data on crustal structure a 3 d density model for the lithosphere of europe has been calculated the model is represented by two complementary parts each obtained by its own specific method for the south of eastern europe the 3 d density model of the earth s crust comprising the sedimentary cover and three layers within the crystalline crust upper intermediate and lower crust was obtained by the following procedure 1 the velocity model was transformed into a density distribution using the velocity density relation 2 the gravity field of this density distribution was calculated by solving the 3 d direct gravity problem 3 the residual gravity field was obtained by subtracting the total gravity effect of the model and the regional component from the oberved gravity field 4 the isostatic equilibrium of the model was evaluated 5 in accordance with the residual anomalies and isostasy estimates some changes mainly in density distribution within the sedimentary cover were entered into the initial density model and the final version of the density model was obtained for the consolidated crust as well as for areas with density inhomogeneities within the upper mantle the correlation between moho traveltimes and crustal gravity influence obtained from the results of 3 d modelling for the south of eastern europe supplemented by 2 d modelling data available over western europe makes it possible to estimate without solving the direct gravity problem the crustal gravity field for the whole european continent residual anomalies due to subcrustal density inhomogeneities have been interpreted in the light of seismic tomography and heat flow distribution for both parts of the model geological and geodynamical interpretations of the results have been made in particular differences in the deep structure of the two major geoblocks of the continent the west and east european platforms have been confirmed regions of relatively light upper mantle have been outlined beneath the east and north west of the east european platform while a heavier upper mantle has been distinguished below the alps the caucasus and the calabrian arc as well as under the south caspian depression

cold seep carbonates of the middle and lower continental slope northern gulf of mexico authigenic carbonates from cold seeps on the middle and lower continental slope of the northern gulf of mexico gom exhibit a wide range of mineralogical and stable isotopic compositions these carbonates consist of concretions and nodules in surface sediments hardgrounds of crusts and isolated slabs and mounded buildups of blocks and slabs of up to over 10 meters in relief above the surrounding seafloor mineralogically the carbonates are dominated by high mg calcite hmc and aragonite however low levels 5 wt of dolomite are present in most samples petrographically mg calcite peloidal matrix and acicular to botryoidal aragonitic void filling cements are the most frequent associations the carbon isotopic compositions of the carbonates range from 60 8 to 14 0 pdb indicating complex carbon sources that include 13c depleted biogenic and thermogenic methane biodegraded crude oil seawater co2 and 13c enriched residual co2 from methanogenesis a similarly large variability in 18o values 2 5 to 6 7 pdb demonstrates the geochemical complexity of the slope with some samples pointing toward an 18o enriched oxygen source that is possibly related to advection of 18o enriched formation water and or to the decomposition of gas hydrate a considerable range of mineralogical and isotopic variations in cold seep carbonate composition was noted even within individual study sites however common trends occur across multiple geographic areas this situation suggests that local controls on fluid and gas flux types of seep hydrocarbons the presence or absence of gas hydrate in the near surface sediment and chemosynthetic communities as well as the temporal evolution of the local hydrocarbon reservoir all may play a part in determining carbonate mineralogy and isotope geochemistry the carbon isotope data clearly indicate that between site variation is greater than within site variation seep carbonates formed on the middle and lower continental slope of the gom do not appear to be substantially different from those found on the upper slope 1000 m water depth the highly variable fluids and gases that leave their geochemical imprints on seep carbonate of the middle and lower continental slope are similar to their outer shelf and upper slope counterparts

lithosphere structure of european sedimentary basins from regional three dimensional gravity modelling abstract a three dimensional 3d density model approximated by two regional layers the sedimentary cover and the crystalline crust offshore a sea water layer was added has been constructed in 1 averaging for the whole european continent the crustal model is based on simplified velocity model represented by structure maps for main seismic horizons the seismic basement and the moho boundary laterally varying average density is assumed inside the model layers residual gravity anomalies obtained by subtraction of the crustal gravity effect from the observed field characterize the density heterogeneities in the upper mantle mantle anomalies are shown to correlate with the upper mantle velocity inhomogeneities revealed from seismic tomography data and geothermal data considering the type of mantle anomaly specific features of the evolution and type of isostatic compensation the sedimentary basins in europe may be related into some groups deep sedimentary basins located in the east european platform and its northern and eastern margins peri caspian dnieper donets barents sea basins fore ural trough with no significant mantle anomalies basins located on the activated thin crust of variscan western europe and mediterranean area with negative mantle anomalies of 150 to 200 10 5 ms 2 amplitude and the basins associated with suture zones at the western and southern margins of the east european platform polish trough south caspian basin characterized by positive mantle anomalies of 50 150 10 5 ms 2 magnitude an analysis of the main features of the lithosphere structure of the basins in europe and type of the compensation has been carried out

the lithosphere in central europe seismological and petrological aspects abstract the lithosphere thickness in the variscan belt of central europe varies between about 60 and 150 km with typical values of 100 120 km our estimates derived from directionally independent representative p wave residuals are in good agreement with magnetotelluric determinations of a layer with increased conductivity in the upper mantle the large scale anisotropies of the subcrustal lithosphere beneath four seismological stations determined from spatial variations of relative p residuals vary between 6 5 and 15 2 for p velocities the s wave anisotropies determined from sks polarizations vary between 2 2 and 6 7 these values are in reasonable agreement with the anisotropies of peridotites determined in laboratory systematic spatial variations of the directional terms of relative residuals in dependence on azimuths and incidence angles suggest the existence of large dipping anisotropic structures in the subcrustal lithosphere the residual patterns at most stations in the saxothuringicum rhenohercynicum and in the massif central imply northwesterly orientated dips of the anisotropic structures while stations in the moldanubicum the alpine foredeep and most of the alps north of the insubric line suggest southeasterly orientated dips in our interpretation the dipping anisotropic structures may represent paleosubductions which retain olivine preferred orientations originating from an ancient oceanic lithosphere the variscides of central europe may thus represent a collision zone characterized by two systems of paleosubductions divergent relative to the suture between the moldanubicum and the saxothuringicum

3 d gravity analysis of the dniepr donets basin and donbas foldbelt ukraine abstract the dniepr donets basin ddb is a linear nw se trending late palaeozoic and younger sedimentary basin on the east european platform separating the ukrainian shield from the voronezh massif its northwestern dniepr segment has the characteristics of a typical rift basin to the southeast through a transition zone of approximately 200 km length the ddb is progressively uplifted and compressionally deformed into the correlatable donbas foldbelt df along the axis of the dniepr segment a series of gravity highs has been previously explained by high density crystalline crust beneath the axis of the basin caused by intrusion of mafic and ultramafic rocks in this paper the results of a 3 d gravity analysis using a gravity backstripping technique is described that investigates the crustal and upper mantle structure in the region of the ddb df transition zone and df a residual gravity field i obtained by subtracting the gravity influence of the sedimentary succession of the ddb from the observed field reveals a distinct positive anomaly along the axis of the rift basin increasing in amplitude to the southeast in concert with increasing sedimentary thickness a residual gravity field ii derived by removing the gravity effects of a modelled homogeneous crystalline crust from residual field i reaches 200 and 100 mgal amplitude in the df for two respective moho models based on different interpretations of the published crust and upper mantle seismic velocity models the first of these model a assumes crustal thickening beneath the transition zone and df to a moho depth up to 50 km whereas the second model b assumes a moho shallowing to depths in the range 35 37 km along the whole basin axis for each residual anomaly ii the best fitting 3 d distribution of average density in the crystalline crust has been computed both models indicate the existence of a high density body in the crystalline crust along the ddb axis increasing in density from the dniepr segment to the df with higher average crustal density required in the case of moho model a 3 17 103 kg m 3 versus 3 06 103 kg m 3 for model b the preferred interpretation of the density models is one in which the denser crystalline crust underlying the ddb df transition zone and df is explained by intrusion of mafic and ultramafic rocks during late palaeozoic rifting processes invocation of processes related to the uplift and inversion in the df are not required to explain the observed gravity field although reworking of the crust during permian and younger tectonism in the df cannot be ruled out

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

high pressure and temperatures during the early stages of tungsten deposition at panasqueira revealed by fluid inclusions in topaz the variscan vein type panasqueira w sn cu deposit one of the main tungsten deposits in western europe has a long and complicated geological history the first vein infillings which consist of the quartz wolframite association as well as the first generation of topaz underwent significant deformation as a consequence most fluid inclusions of the earliest hydrothermal event are deformed and destroyed two preserved fluid inclusion assemblages are however found in the topaz overgrowth band and are dense aqueous carbonic inclusions as well as dense co2 dominated fluid inclusions the p t conditions of fluid trapping are constrained by using the intersection between isochores as well as graphite water equilibrium data and yield the following trapping conditions 500 20 c and 250 20 mpa these p t conditions are incompatible with fluid unmixing fluid chemistry results from water graphite equilibrium probably in metapelites at two distinct temperatures around 450 500 c for the predominant aqueous carbonic fluid and higher temperatures of maximal 550 c for the co2 rich fluid enriched in n2 these p t estimates are consistent with deep crustal levels around 8 10 km depth and a high geothermal gradient around c 60 c km 1 the ascending non magmatic fluids enriched in volatiles are essential in the ore genesis the high thermal gradients may be related either to new magma pulse after the formation of the panasqueira granite intrusion or to anomalous heat flux produced by the hot fluids ascending from migmatitic levels present at greater depth this hypothesis necessitates to consider the role of a crustal weakness which is attested both by the successive intrusions of several granitic magmas at the same place and the presence of inherited quartz filled structures so called seixo bravo found only in the panasqueira area