fluid inclusions and hydrothermal alteration on the dixie valley fault nevada footwall rocks of the 1954 rupture segment of the dixie valley fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages an early biotite feldspar assemblage is followed by later fe chlorite and epidote both chlorite and epidote are replaced by hydrothermal sericite and cross cut by calcite hematite and quartz calcite veins biotite is partially replaced by prehnite the latest hydrothermal minerals are stilbite laumontite kaolinite alunite smectite illite and pervasive replacement of rock units with fine grained quartz chalcedony and opal secondary fluid inclusions trapped in healed microfractures in igneous quartz include type i inclusions that contain a moderate salinity aqueous liquid and vapor type ii inclusions that contain a moderate salinity aqueous liquid and co2 type iii inclusions that show eutectic melting temperatures below the nacl h2o eutectic and contain substantial cacl2 and type iv inclusions containing halite and other daughter minerals microthermometric measurements on these inclusions yield variable compositions and homogenization temperatures salinities of type i inclusions vary from 0 1 to 12 9 wt nacl with the mode in the interval 0 to 1 salinities of type ii co2 bearing inclusions range from 0 62 to 6 81 wt nacl relative to h2o and salinities of type iii inclusions with low eutectic melting temperatures are 12 9 to 25 3 nacl equivalent wt salinities of halite bearing inclusions are 30 1 to 39 2 wt nacl homogenization temperatures span the range 120 to 400 c the processes of isochemical cooling with upward displacement of the footwall mixing of cool low salinity water with hotter components and mixing of cool evaporite brine with hotter components could be responsible for variable fluid inclusion compositions homogenization temperatures and densities the p t path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics the path includes a lithostatic fluid pressure at 305 c and 1570 bars along with cooling and escape of co2 from fluids the fluid p t path probably approaches hydrostatic pressure conditions at lower temperatures hydrothermal alteration product minerals fluid temperatures pressures and compositions in the footwall of the dixie valley fault constrain minimum fault age to 20 to 25 ma displacement to 6 km with about 3 km of pre 10 to 13 ma and 3 km of post 10 ma uplift fluid compositions and p t data suggest the following mechanism for rupture initiation and arrest ruptures may be initiated as a result of high fluid pressures then opening of dilatant fractures causes drastic decrease in fluid pressure separation of steam and co2 the drastic reduction in fluid bulk modulus that accompanies volatile phase separation permits propagation of the ruptures even though fluid pressure is reduced in areas where fluid pressure reduction is not accompanied by phase separation fractures are arrested by dilatant hardening

quartz recrystallization regimes c axis texture transitions and fluid inclusion reequilibration in a prograde greenschist to amphibolite facies mylonite zone ribeira shear zone se brazil abstract the crystal plastic behavior of quartz mylonites from the ribeira shear zone se brazil a major strike slip structure that was active during a prograde metamorphic phase related to the neoproterozoic brasiliano pan african orogeny was investigated using a multi method approach geothermobarometry results indicate deformational conditions ranging from 300 to 630 c and 500 700 mpa a strong correlation between mapped metamorphic zones and a dominance of different dynamic recrystallization mechanisms of quartz occurs within the mylonite zone bulging recrystallization blg dominates within the chlorite zone between 300 and 410 c subgrain rotation recrystallization sgr operates within the biotite zone from 410 to 520 c and grain boundary migration recrystallization gbm dominates in the garnet zone above 520 c the development of quartz c axis textures is mainly governed by temperature and dynamic recrystallization mechanisms textures from blg zone mylonites are characterized by maxima around z sgr zone mylonites display single girdles or asymmetric type i crossed girdles and gbm zone mylonites comprise maxima around y and intermediate between x and z the scarcity or absence of water bearing fluid inclusions in quartz mylonites from the sgr and gbm zones which are dominated by carbonic inclusions suggests water deficient conditions whereas blg zone mylonites are dominated by water bearing inclusions this evidence indicates that water was available in the protoliths but has been eliminated with increasing deformation and deformation temperature no effect of the water content variation on the quartz microstructural and recrystallized grain size evolution was detected and little influence on c axis texture development was observed most of the fluid inclusion densities were reequilibrated during the shear zone exhumation history recording a decompression in the range of 300 500 mpa while microstructural reequilibration effects related to the prograde metamorphism are largely preserved fluid inclusion microstructures and densities from two sgr zone samples preserved evidence for a near isothermal compression within the interior of the ribeira shear zone during the prograde metamorphism

syndeformational fluid trapping in quartz determining the pressure temperature conditions of deformation from fluid inclusions and the formation of pure co2fluid inclusions during grain boundary migration observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids our results imply that pure co2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation recrystallization process rather than representing a primary metamorphic fluid where the temperature of deformation can be deduced by other means the densities of fluid inclusions trapped during recrystallization which we call recrystallization primary fluid inclusions can be used to constrain the ambient pressure during deformation using these constraints the data imply that the post metamorphic hercynian exhumation in sardinia brought rocks at 300 c to within 3km of the surface this conclusion is similar to that described for the rapidly uplifted southern alps in new zealand

high resolution late maastrichtian early danian oceanic 87sr 86sr record implications for cretaceous tertiary boundary events a high resolution late maastrichtian early danian seawater 87 sr 86 sr reference curve is constructed from two cretaceous tertiary boundary k t boundary sections bidart france and el kef tunisia the 87 sr 86 sr curve shows maxima at 0 3 0 4 ma before the k t boundary and at the k t boundary the first maximum could mark the onset of a major outflow of the deccan traps the second maximum a rapid 0 000 06 87 sr 86 sr shift extends from 3 4 m below to 1 m above the k t boundary this profile probably results from diagenetic smoothing of an originally sharp k t boundary 87 sr 86 sr anomaly rather than from a gradual process the sharp shift could result from 1 the vaporization of the chicxulub target rocks 2 global wildfires and 3 acid rain leaching of soils and sialic surface rocks of these three possibilities only sr release by soil leaching combined with increased rainfall associated with the k t event appears to be sufficiently large to produce the observed k t 87 sr 86 sr anomaly

sr and 87sr 86sr in rivers draining the deccan traps india implications to weathering sr fluxes and the marine 87sr 86sr record around k t the concentration of dissolved sr and its 87sr 86sr has been measured in the headwaters of the krishna river system and west flowing western ghat rivers all of which have their drainage almost entirely in the deccan traps the sr concentration follows that of ca and mg with sr ca and sr mg ratios similar to that of deccan basalts suggesting that all these alkaline earths are released to waters nearly congruently from the deccan basalts during chemical weathering the 87sr 86sr range from 0 70614 to 0 70986 within that reported for the deccan basalts the dissolved sr flux from the deccan calculated from the measured data is 1 35 108 moles yr 1 0 4 of the global riverine flux which is nearly the same as the proportion of area covered by deccan basalts relative to the global drainage the flux however is a factor of 3 lower than that reported for the narmada tapti wainganga ntw rivers draining the northern deccan this difference in sr flux among rivers draining the various regions of deccan could be natural spatial temporal variations and or due to supply of sr to ntw rivers from nonbasaltic sources model calculations on the role of emplacement and weathering of deccan on marine sr isotope evolution around ktb and late tertiary show that deccan basalts can be an important contributor to the decline in 87sr 86sr during these periods it is shown that to account for the pre ktb dip in 87sr 86sr the flux requirement from deccan at that time would have to be several times the contemporary flux with 87sr 86sr of 0 705 0 708 considering that the area of deccan at ktb was about thrice the present area and that the weathering rate of deccan basalts may have been much higher in early stages following eruption such high fluxes at about ktb seem feasible the disproportionately higher flux requirement for sr is similar to that invoked to explain the pre ktb decrease in 187os 188os the calculations also show that the supply of unradiogenic sr from basalts can have significant control on the long term 66 to 55 ma decline of marine 87sr 86sr

uplift and erosional history of the deccan traps india evidence from laterites and drainage patterns of the western ghats and konkan coast abstract the western ghats escarpment in the western coastal region of peninsular india is locally capped by plateau remnants on which a regional high level laterite carapace is preserved geochemical fingerprinting studies show that the laterite has been developed from a protolith of panhala formation basalts the youngest known formation of the deccan sequence the high level laterite is in detail structurally concordant with its underlying basalts and hence it is concluded that it represents the original top of the lava pile a younger low level laterite carapace is developed on the konkan plain below the escarpment where it lies discordantly on basalts of the ambenali and poladpur formations from which it developed in situ the low level laterite rises topographically northwards in response to differential uplift probably at a maximum in the nasik region the main structures of the ghats region excluding the coastal monocline are the nasik dome and the mahabaleshwar anticline these have no effect on regional drainage patterns and it is argued that they are largely secondary features developing in response to post volcanic uplift

carbon isotope ratio of dissolved inorganic carbon dic in rivers draining the deccan traps india sources of dic and their magnitudes abstract chemical weathering of silicate and carbonate rocks by carbonic acid is important in the context of atmospheric co 2 sequestration and its delivery to the oceans via rivers as dissolved inorganic carbon dic in this work silicate weathering contribution to dic in the krishna river system draining the deccan basalts in south western india has been determined using a new approach based on 13 c si hco 3 systematics of the waters 13 c in the samples ranges from 8 5 to 20 7 and shows a strong linear inverse trend with si hco 3 r 2 0 80 the si hco 3 ratios in rivers vary from 0 55 to 0 10 the higher value matches the expected ratio for chemical weathering of deccan basalts based on their composition the 13 c si hco 3 trend suggests the mixing of two end members a carbonate derived endmember with low si hco 3 and enriched in 13 c and a silicate derived endmember with higher si hco 3 and depleted in 13 c small rivers of the western ghats are depleted in 13 c 13 c 18 7 2 and have high si hco 3 these properties are interpreted as signatures of basalt silicate weathering with co 2 from c 3 vegetation three samples from the krishna mainstream and two of its larger tributaries the bhima and the ghod are enriched in 13 c 13 c 8 5 to 15 with higher hco 3 and lower si hco 3 ratios indicating that a significant fraction of dic in these samples is derived from carbonate weathering carbonate dispersed in river sediments can be a likely source of dic

tectonics of the southern portion of the ribeira belt apiai domain abstract the name ribeira belt was originally used in a reference to a broad belt of deformed crust which strikes subparallel to the southeastern brazilian coastline it was originally believed to be neoproterozoic brasiliano panafrican but present investigations indicate that this age seems to be mainly related to the extensive arc related plutonism and tectono metamorphism that affected its most representative formations whereas the time of deposition of the supracrustals would be significantly older in this study the main tectono stratigraphic features of the apiai domain of the ribeira belt are described the lithostratigraphy is reviewed as well the paleogeographic structural geochemical and radiometric data and their implications for the tectonic evolution models for the region the marine sediments of the apiai domain were laid down on the borders of the parana and luis alves cratons and on an intervening mesoproterozoic 1 8 1 1 ga ocean crust they were intensively deformed by ocean closure and collision of the cratonic fragments and they constitute the majority of the local supracrustals designated as the acungui supergroup symmetrical continental passive margin deposits are represented to the northwest by a more proximal facies itaiacoca group probably related to the parana paleocontinent and by the capiru formation to the southeast between them lies the central domain formed by the votuverava group characterized by the remains of gradually deepening carbonatic platform sediments of the lajeado subgroup which grade eastward into distal turbiditic sequences of the ribeira subgroup where ocean floor and immature island arc magmatic rocks are present during the neoproterozoic the apiai domain behaved as a single continental mass into which basic rocks were intruded between 1 1 and 0 85 ga between 0 7 and 0 6 ga the apiai domain evolved into a cordilleran type magmatic arc related to the evolution of a subduction zone possibly situated to the southeast of the luis alves cratonic fragment this subduction caused metamorphism and migmatization of the supra and infra crustal rocks of the region and produced the extensive calc alkaline granitoid plutonism between 0 6 and 0 45 ga the majority of the southeastern continental blocks amalgamated during closure of the adamastor ocean followed by development of a system of regional dextral transcurrent shear zones related to oblique collision and or escape tectonics pull apart basins opened up and were filled with molasse sequences the region was intruded by post tectonic granitoids and then underwent regional cooling

juvenile contribution of the neoproterozoic rio negro magmatic arc ribeira belt brazil implications for western gondwana amalgamation abstract the ca 790 600 ma rio negro complex rnc of the ribeira belt brazil consists of a plutonic portion of a magmatic arc built by the e vergent subduction of the ese border of the sao francisco paleoplate during the amalgamation of western gondwana the plutonic series comprises low to medium k granitoids ca 790 620 ma and high k granitoids and shoshonite rocks ca 610 605 the age span of 185 m y is suggestive of a long history of arc related magmatism continuously or not in time the nd isotopic signatures of the rnc consist of end t ratios from 3 to 5 for the medium k series shoshonite series and from 14 to 3 for the younger high k group this time dependent trend of nd isotopes is indicative of progressive maturity of the arc over time the same evolution is indicated by sr data as the medium k rocks have 87sr 86sr initial ratios the role of transform fault zones such as the luanda shear zone is emphasized in order to explain the consumption of a wide oceanic plate in the inner portion of western gondwana

fault valve action and vein development during strike slip faulting an example from the ribeira shear zone southeastern brazil abstract fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of neoproterozoic cambrian age in the ribeira river valley area southeastern brazil geometric and microstructural constraints indicate that foliation parallel and extensional veins were formed during dextral strike slip faulting both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates and were crystallized in the presence of co2 ch4 and h2o co2 ch4 nacl immiscible fluids following unmixing from a homogeneous parental fluid contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels foliation parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values 319 397 c and 47 215 mpa which is compatible with predicted fluid pressure cycle curves derived from fault valve action growth of extensional veins occurred in shallower structural levels under pressure fluctuating from near hydrostatic to moderately subhydrostatic values 207 218 c and 18 74 mpa which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone fluid immiscibility and precipitation of quartz in foliation parallel veins resulted from fluid pressure drop immediately after earthquake rupture fluid immiscibility following a local pressure drop during extensional veining occurred in pre seismic stages in response to the development of fracture porosity in the dilatant zone late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity 0 2 to 44 wt equivalent nacl h2o nacl cacl2 fluid inclusions trapped in healed fractures mainly in foliation parallel veins which also exhibit subordinate h2o nacl cacl2 co2 ch4 and h2o co2 ch4 nacl fluid inclusions trapped under subsolvus conditions in single healed microcracks recurrent circulation of aqueous carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes a fluid evolution trending toward ch4 depletion for co2 ch4 bearing fluids and salinity depletion and dilution approximation of the system h2o nacl for aqueous saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history

double vein ore bearing vs ore free structures in the xitian ore field south china implications for fluid evolution and mineral exploration abstract two types of spatially and temporally associated hydrothermal veins ore bearing and ore free occur as double vein structures in the xitian ore field south china here we investigated the genetic relationship material provenance fluid properties and prospecting significance of the co developed veins in the granite related fault controlled vein type xiangdong w goudanlan w chaling pb zn and xinggao fluorite deposits of the xitian ore field focusing on two common minerals quartz and zircon petrographic cl microthermometric and h o isotopic analyses of stage i and stage ii quartz in both the ore bearing and ore free veins of these deposits document two episodes of hydrothermal activity the first episode involved a high temperature up to 370 high salinity up to 28 nacl equiv high 18o 2 1 to 7 2 and high 2h 82 to 54 mean 68 n 13 fluid that corresponds to the main magmatic hydrothermal stage of the deposits and the second episode involved a low temperature down to 90 low salinity down to 1 nacl equiv low 18o 8 8 to 5 3 and low 2h 83 to 60 mean 73 n 6 fluid that represents an accessary mineralization stage variations in fluid inclusion types and compositions indicate that the processes of fluid mixing boiling cooling and degassing played important roles in mineralization and that magmatic fluid became less important than meteoric water along during the formation of ore free veins la icpms u pb dating reveals totally different age populations for these veins zircons from the ore bearing quartz veins yield older and more variable ages pre devonian 400 ma n 68 that are similar to that of the local basement sedimentary rocks whereas zircons from the ore free quartz veins yield younger and less variable ages triassic 250 200 ma n 31 and jurassic 170 140 ma n 13 that are identical to those of the host granite zircons in addition the ore free veins show lower temperatures salinities and total rees as recorded by quartz but greater alteration as reflected by cl and trace element features of hydrothermally altered zircons and wider vein size than the ore bearing veins we propose a mineral water separation model to explain the formation of the double vein structures in this model ore bearing veins and ore free veins formed in succession during faulting events ore bearing veins formed first in the smaller fractures and were the dominant sites of mineralization whereas the ore free veins served as dissipating passageways for residual water and silica in larger fractures we suggest that the mineral water separation model has good application prospects in mineral exploration and that zircons can be applied as an indicative mineral to differentiate the mineralization potential of different types of quartz veins

fault valve behaviour in optimally oriented shear zones an example at the revenge gold mine kambalda western australia abstract quartz vein systems developed in and adjacent to shear zones host major gold deposits in the kambalda region of the norseman wiluna greenstone belt at the revenge mine two groups of mineralised reverse shear zones formed as conjugate near optimally oriented sets during ese subhorizontal shortening adjacent to a major transpressional shear system the shear zones developed at temperatures of about 400 c in a transitional brittle ductile regime deformation was associated with high fluid fluxes and involved fault valve behaviour at transiently near lithostatic fluid pressures during progressive evolution of the shear system early brittle and ductile deformation was overprinted by predominantly brittle deformation brittle shear failure was associated with fault dilation and the formation of fault fill veins particularly at fault bends and jogs a transition from predominantly brittle shear failure to combined shear along faults and extension failure adjacent to faults occurred late during shear zone evolution and is interpreted as a response to a progressive decrease in maximum shear stress and a decrease in effective stresses the formation of subhorizontal stylolites locally subvertical extension veins and minor normal faults in association with thrust faulting indicates episodic or transient reorientation of the near field maximum principal stress from a subhorizontal to a near vertical attitude during some fault valve cycles local stress re orientation is interpreted as resulting from near total shear stress release and overshoot during some rupture events previously described fault valve systems have formed predominantly in severely misoriented faults the shear systems at revenge mine indicate that fault valve action and associated fluctuations in shear stress and fluid pressure can influence the mechanical behaviour of optimally oriented faults

chemostratigraphic evidence of deccan volcanism from the marine osmium isotope record continental flood basalt cfb volcanism is hypothesized to have played a causative role in global climate change and mass extinctions uncertainties associated with radiometric dating preclude a clear chronological assessment of the environmental consequences of cfb volcanism our results document a 25 decline in the marine 187 os 188 os record that predates the cretaceous tertiary boundary ktb and coincides with late maastrichtian warming we argue that this decline provides a chemostratigraphic marker of deccan volcanism and thus constitutes compelling evidence that the main environmental consequence of deccan volcanism was a transient global warming event of 3 to 5 c that is fully resolved from the ktb mass extinction

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

development of fluid conduits in the auriferous shear zones of the hutti gold mine india evidence for spatially and temporally heterogeneous fluid flow abstract the gold mineralization of the hutti mine is hosted by nine parallel n s trending steeply dipping 2 10 m wide shear zones that transect archaean amphibolites the shear zones were formed after peak metamorphism during retrograde ductile d 2 shearing in the lower amphibolite facies they were reactivated in the lower to mid greenschist facies by brittle ductile d 3 shearing and intense quartz veining the development of a s 2 s 3 crenulation cleavage facilitates the discrimination between the two deformation events and contemporaneous alteration and gold mineralization ductile d 2 shearing is associated with a pervasively developed distal chlorite sericite alteration assemblage in the outer parts of the shear zones and the proximal biotite plagioclase alteration in the center of the shear zones d 3 is characterized by development of the inner chlorite k feldspar alteration which forms a centimeter scale alteration halo surrounding the laminated quartz veins and replaces earlier biotite along s 3 the average size of the laminated vein systems is 30 50 m along strike as well as down dip and 2 6 m in width mass balance calculations suggest strong metasomatic changes for the proximal biotite plagioclase alteration yielding mass and volume increase of ca 16 and 12 respectively the calculated mass and volume changes of the distal chlorite sericite alteration ca 11 ca 8 are lower the decrease in 18 o values of the whole rock from around 7 5 for the host rocks to 6 7 for the distal chlorite sericite and the proximal biotite plagioclase alteration and around 5 for the inner chlorite k feldspar alteration suggests hydrothermal alteration during two stage deformation and fluid flow the ductile d 2 deformation in the lower amphibolite facies has provided grain scale porosities by microfracturing the pervasive steady state fluid flow resulted in a disseminated style of gold sulfide mineralization and a penetrative alteration of the host rocks alternating ductile and brittle d 3 deformation during lower to mid greenschist facies conditions followed the fault valve process ductile creep in the shear zones resulted in a low permeability environment leading to fluid pressure build up strongly episodic fluid advection and mass transfer was controlled by repeated seismic fracturing during the formation of laminated quartz gold veins the limitation of quartz veins to the extent of earlier shear zones indicate the importance of pre existing anisotropies for fault valve action and economic gold mineralization

lower and upper neoproterozoic magmatic records in itaiacoca belt parana brazil zircon ages and lithostratigraphy studies abstract the itaiacoca belt is a sequence of metavolcanic and metasedimentary rocks that crop out east of parana and southeast of sao paulo states in southern brazil this geologic geochronologic study supports division of the itaiacoca belt into two major lithologic sequences the older is a carbonate platform sequence dolomitic meta limestones metamarls calc phyllites carbonate phyllites with minimum deposition ages related to the end of the mesoproterozoic beginning of the neoproterozoic 1030 908 ma u pb zircon of metabasic rocks the younger sequence contains mainly clastics deposits meta arkoses metavolcanics metaconglomerates metapelites with deposition ages related to the neoproterozoic 645 628 ma u pb zircon of metavolcanic rocks these ages are quite close to k ar ages fine fraction of the 628 610 ma interval associated with metamorphism and cooling of the itaiacoca belt the contact between the dolomitic meta limestones and meta arkoses is marked by intense stretching and high angle foliation suggesting that the discontinuity between these associations resulted from shearing it is proposed here that the term itaiacoca sequence should represent the dolomitic meta limestones and the term abapa sequence represents the meta arkoses metavolcanics phyllites in a major tectonic context these periods are related to the break up of rodinia supercontinent 1030 908 ma and the amalgamation of the gondwana supercontinent 645 628 ma

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

the la belliere gold and antimony district french armorican massif a two stage evolution model controlled by variscan strike slip tectonic the la belliere gold district in the ligerian domain of the armorican massif is the third one of france in term of production it shows gold bearing quartz veins neighboring with a complex network of sb veins hosted in the neoproterozoic metasedimentary basement of the mauges nappe new structural data mineralogical textural and geochemical assays have been carried out to clarify the gold and sb veins relationships our results favor of two step hydrothermal event with an early deep seated gold event followed by a late shallower sb event the gold bearing quartz veins are hosted by n60 e to n90 e sinistral strike slip faults these veins exhibit a four stage paragenesis 1 early barren quartz filling 2 arsenopyrite pyrite with minor scheelite assemblage 3 gold and base metal sulfides crystallized after a ductile brittle deformation stage and 4 pyrite carbonate coeval with a late brittle stage these results support a continuous evolution model from a deep emplacement level 12 to 9 km to a shallow one 7 to 5 km with a brutal change in the p t conditions that triggered the deposition of gold stage 2 controlled by a seismic valve mechanism on the contrary sb veins correspond to open space vein types hosted in a n20 w to n20 e conjugated strike slip fault network arranged in a riedel shear model controlled by n130 140 e regional dextral strike slip shear zone associated to the south armorican shear zone system a two stage evolution is recognized the first one consists of early pyrite arsenopyrite with microcrystalline quartz followed by a late stibnite stage formed after geodic quartz deposition quartz texture argues for a shallow emplacement 5 km of veins controlled by a suction pump mechanism chronologically the gold vein opening complies with a ne sw maximum shortening direction different from the late variscan stress field responsible for the dextral armorican shear zone during late carboniferous and constrains an indirect dating thus a visean age is proposed for the formation of gold veins the overall features of gold deposits are close to those of mesozonal orogenic gold deposits in europe conversely sb bearing veins are generated by a n s shortening during the late carboniferous the sb event distinct in time from the earlier gold one might correspond to a different expression of the so called epizonal type in the orogenic gold model it is proposed that the late carboniferous or 300 event is not the unique metallogenic period for gold deposition in the french variscan domain our study highlights the role of the sinistral strike slip shearing of possible visean age in the gold metallogenesis of the ligerian domain

strontium isotope profiles across k t boundary sequences in denmark and antarctica strontium isotope profiles derived from minimally altered samples across marine k t boundary sequences exposed at kjolby gaard and nye klov denmark and on seymour island antarctica show neither the boundary excursions nor the boundary spikes in 87sr 86sr that have been reported for k t boundary sequences from elsewhere nor do our data conform to modelled predictions of the sr isotopic response of the oceans to a positive spike in 87sr 86sr at the terminal cretaceous boundary values for 87sr 86sr with 95 confidence intervals are 0 707828 3 in denmark and 0 707832 7 in antarctica our data suggest that 87sr 86sr stopped increasing and started decreasing at least 90 ka before the k t boundary

chemical and strontium oxygen and carbon isotopic compositions of carbonates from the lesser himalaya implications to the strontium isotope composition of the source waters of the ganga ghaghara and the indus rivers samples of precambrian carbonate mostly dolomite outcrops collected across the lesser himalaya have been analysed for their mineralogy chemical composition and isotope ratios of sr o and c to assess the extent of their preservation and their role in contributing to the high radiogenic strontium isotope composition of the source waters of the ganga ghaghara and the indus their sr concentrations range from 20 to 363 ppm 18opdb 1 4 to 12 8 and mn 11 2036 ppm the petrography of the samples their low sr concentrations and wide range of 18o values are suggestive of their postdepositional alteration the 87sr 86sr of the bulk samples and their carbonate fractions are similar to one another with values ranging from 0 7064 to 0 8935 and are generally more radiogenic than that of contemporaneous seawater comparison of the 87sr 86sr and sr ca ratios among the carbonates and silicates from the lesser himalaya and the source waters of the ganga ghaghara and the indus shows that the values for the source waters overlap with those of the silicates but are much higher than those in carbonates an upper limit of carbonate sr in the various source waters is calculated to be between 6 and 43 assuming that all the ca in the rivers is of carbonate origin the results show that on the average weathering of the precambrian carbonates is unlikely to be a major contributor to the highly radiogenic strontium isotope composition of these source waters however they can be a dominant supplier of radiogenic sr to some rivers on a regional scale the silicate sr component in some of the source waters of the ganga bhagirathi bhilangna alaknanda and ganga ghaghara kali and sarju and the indus sutlej was calculated from the ca na sr na ratios and strontium isotope compositions of these rivers and the silicate endmember these calculations suggest that 33 89 of sr in the bhagirathi bhilangna alaknanda ganga and sarju rivers is of silicate origin whereas in the kali and the sutlej it is much lower only 8 the remaining sr to all these waters has to be supplied from other sources such as weathering of carbonates and evaporites this study underscores the importance of weathering of silicates carbonates and evaporites in contributing to the sr mass balance and 87sr 86sr of the source waters of the ganga ghaghara and the indus the present day silicate and carbonate sr contributions to the sr budget of the rivers vary considerably but among the major source waters of the ganga silicate sr exerts a more dominant control on their sr abundance and 87sr 86sr

hydrothermal transport and depositional processes in archean lode gold systems a review abstract compelling evidence now exists for the formation of archean lode gold deposits over a substantial range in metamorphic conditions and crustal depth the commonality of ore fluid isotopic and geochemical characteristics the extreme fluid rock ratios within actual ore zones and the observed depth continuity within individual orebodies all suggest that these deposits formed within vertically extensive crustal scale hydrothermal systems calculations based on new thermodynamic data and estimated ore fluid conditions suggest that gold would have been transported as au hs 2 over most of this range gold transport in the ore fluids that formed some diopside and diopside k feldspar class deposits t 550 c would have been as aucl2 whereas the au hs complex may have been significant in some of the lower temperature 270 c less alkaline ore fluids the high solubility of gold in lode gold ore fluids at amphibolite facies conditions 10 s to 1000 s ppb suggests that fluids may have been undersaturated in gold within their source regions promoting the ore fluid s capacity to retain gold in solution over the large transport distances involved ore depositional mechanisms were also likely to vary between crustal levels fluid rock interactions and wallrock sulphidation in particular appear to be the most important type of precipitation mechanism however with decreasing depth of formation the scope of other depositional mechanisms notably phase separation and fluid mixing becomes greater

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

comments on deccan flood basalts at the cretaceous tertiary boundary by v courtillot j besse d vandamme r montigny j j jaeger and h cappetta the age of the flood basalts of the deccan area and the length of the interval during which the outpourings took place are not known precisely the authors have tried to date those basalts and estimate how long the volcanic activity lasted on the basis of new paleomagnetic paleontological and geochronological data of the deccan effusives they came to the preliminary conclusion that the volcanic activity may have lasted less than 1 ma and that the majority of the lavas poured out during chron 29r unfortunately the authors were not familiar with our paper on paleomagnetism and radiomettic age determinations of deccan trap lavas 2 in our paper we presented the paleomagnetic data derived from 223 individual lava flows from 16 sections all over the deccan area and gave the k ar age determinations for 13 selected unaltered lava flows we agree that the enormous volume of deccan extrusives poured out in a relatively short interval and that the volcanic activity was probably concerned with the spreading in the central indian ocean in late cretaceous and early tertiary time

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

geology and geochronology of the betara region in south southeastern brazil evidence for possible statherian 1 80 1 75 ga and calymmian 1 50 1 45 ga extension events abstract the results of geological mapping chemical analysis and radiometric dating of metabasic rocks of betara formation and mapping and dating of those present in the betara basement nucleus together with mylonitic granodiorite and syenogranite are reported here u pb analysis of bulk zircon fractions from the metabasic rocks of the basement nucleus yielded a statherian age of 1790 22 ma while the metabasic rocks from the upper part of the betara formation yielded a calymmian age between 1500 and 1450 ma this age is a minimum for the deposition of the betara formation the older metabasic rocks are associated with post tectonic possibly anorogenic syenogranite while the younger ones are gabbro or very porphyritic ankaramite whose ree patterns are consistent with crystallization from an n morb parent magma the observations and data point to the probable events associated with extensional processes of the end of paleoproterozoic and early mesoproterozoic similar registers of statherian 1 80 1 75 ga and calymmian 1 50 1 45 ga extensional events are recorded in other parts of the south american and african continents the neoproterozoic witnessed the formation and junction of the tectonic slices which formed the apiai domain during the assemblage of western gondwana

the role of fluids in syntectonic mass transport and the localization of metamorphic vein type ore deposists abstract in low to medium grade metamorphic environments the mobilization of species is closely associated with the operation of solution precipitation creep processes during foliation development such deformation processes involve dissolution of material from source sites which are usually discrete dissolution surfaces having orientations controlled by the applied stress and displacement fields mass transfer occurs via solute diffusion in an essentially static fluid network or by transport of dissolved species in a migrating fluid precipitation of material removed from dissolution sites occurs in a variety of sink sites including pore surfaces grain scale microcracks and veins sink sites may be close to or distantly removed from source sites the transport of material during deformation involving solution precipitation creep is largely controlled by the mobility of metamorphic fluids in regions of high fluid mobility significant mass transfer may occur over large distances fluid flow mass transfer paths and the development of sink sites in such cases are constrained by the structurally controlled development of high fluid pressure domains and the consequent mechanical enhancement of permeability by hydraulic fracture processes and the development of grain scale dilatancy these processes may result in focussed fluid flow and precipitation of mobilized species in restricted regions a proportion of syntectonically mobilized material is precipitated to form vein type deposits in hydraulic fracture arrays which develop in high fluid pressure environments the microstructures developed in minerals deposited in these sites reflect the interaction of a range of nucleation and growth processes which usually involve multiple generations of fracture growth and mineral crystallization the formation of syntectonic gold quartz vein deposits in central victoria australia illustrates the importance of structural controls on both the large scale migration of metamorphic fluids and the development of sites suitable for the precipitation of metamorphically mobilized species

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

the bronzewing lode gold deposit western australia p t x evidence for fluid immiscibility caused by cyclic decompression in gold bearing quartz veins abstract the bronzewing lode gold deposit is located in the yandal greenstone belt in the yilgarn craton of western australia gold mineralization is hosted in tholeiitic basalt that is metamorphosed to greenschist facies individual ore bodies are controlled by a complex gold bearing quartz vein system that comprises shear and extension veins formed during a progressive d2 deformation event gold is localized in quartz along fractures and deformed grain boundaries and is interpreted to have formed late in the formation of the veins detailed petrography and microthermometry on primary pseudosecondary and secondary fluid inclusions trapped in gold bearing shear and extension veins revealed five types of fluid inclusions 1 co2 ch4 h2o nacl inclusions of variable salinity 0 1 to 17 5 eq wt nacl containing between 10 and 99 mol co2 and molar volumes that range from 22 to 76 cm3 2 h2o nacl inclusions of variable salinity 0 4 to 22 1 eq wt nacl 3 co2 ch4 inclusions with up to 58 mol ch4 and molar volumes between 54 and 73 cm3 4 ch4 h2o inclusions with ch4 ranging from 80 to 90 mol and 5 ch4 inclusions with low molar volumes of 19 to 23 cm3 types 1 2 and 3 constitute a fluid inclusion assemblage that occurs consistently in primary pseudosecondary and secondary trails and clusters within the gold bearing quartz vein system these co existing fluids are interpreted to have formed by fluid immiscibility of a low salinity homogeneous parent fluid at about 300 c and 1500 bars locally type 2 fluid inclusions exhibit total homogenization temperatures that are on average 100 c less than the co genetically trapped type 1 aqueous carbonic inclusions this discrepancy is interpreted to have involved co2 effervescence in response to fluid pressure fluctuations types 4 and 5 fluid inclusions are rare and are only present locally in secondary trails and clusters in extension veins significant pressure fluctuations but relatively constant homogenization temperatures for types 1 2 and 3 fluid inclusions suggest that cyclic decompression of the hydrothermal fluids due to seismic activity along the shear zones that host the gold bearing veins triggered fluid immiscibility the process of fluid immiscibility and subsequent lowering of gold solubility is interpreted to be the most efficient precipitation mechanism for gold in the d2 shear zone hosted vein system at bronzewing

structure and evolution of the abyssal jet in the vema channel of the south atlantic the vema channel represents the only major conduit through which the deepest and coldest 0 2 c potential temperature antarctic bottom water aabw flows from the argentine into the brazil basin from 2003 to 2007 two current meter moorings were present on each side of the vema sill close to the narrowest spot of the vema channel the data from the moorings are compared with earlier current and temperature observations on average the maximum current core lies 100 m above the bottom of the sill with a mean northward speed of 0 3 m s 1 farther up in the water column where lower circumpolar deep water and north atlantic deep water prevail one finds a level of sluggish currents with a southward tendency in the sub centimeter per second range the lower boundary of a layer of no motion was observed at 3700 m depth where the mean potential temperature amounts to 1 5 c the evolution of the abyssal warming phenomenon over the last decades with notable fluctuations at the choke point between the argentine and the brazil basin differs from the more stable attitude of deep horizontal currents starting with ctd observations in 1972 we find a steady increase of temperatures of the coldest aabw in the vema channel this general trend of rising abyssal potential temperatures of almost 2 mkelvin per year is based on mostly annual ctd observations the overall warming trend is fully compatible with our three year moored temperature series in agreement with earlier records with high temporal resolution distinct frequently fluctuating horizontal current shear between the western and eastern sides of the vema sill may be explained by two different catchment areas for aabw at the mouth of the vema channel one pathway originates at the american continental rise and advects bottom water in form of the deep western boundary current a second pathway is supplied by an eastern boundary current along the mid atlantic ridge in the argentine basin both source waters merge at the channel entrance mix and their respective strengths can alternate within the sill area

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

p t fluid deformation regime of the ediacaran serra do cavalo magro orogenic gold deposit ribeira belt brazil abstract the serra do cavalo magro orogenic gold deposit is located in the southern ribeira belt brazil gold quartz veins are hosted in calymmian 1500 1450 ma metasedimentary and metabasic rocks and ediacaran 610 600 ma granitic rocks geochronological data available in previous literature and structural petrological relationships with host rocks and shear zones indicate that the gold mineralization was formed within 580 540 ma during the late stage evolution of the brasiliano pan african orogeny related with gondwana supercontinent assembly petrological modeling indicates peak metamorphic conditions from 560 c and 7 kbar chlorite biotite phyllite to 625 c and 6 8 kbar garnet biotite phyllite recorded in immediate host rocks gold mineralization occurs in quartz shear and extensional veins structurally controlled by ne trending second and third order sinistral transcurrent shear zones the nnw trending subvertical and subhorizontal extensional veins are oriented 55 85 in relation to the fault planes indicating the shear zones were severely misoriented to frictional reactivation deformation within the shear zones was accommodated by bulging recrystallization of quartz aggregates while feldspar aggregates from the granitic protolith underwent cataclastic flow or were replaced by sericite epidote producing phyllonites gold precipitated during stages of vein deformation within microfractures in shear and extensional veins with quartz previously subjected to bulging recrystallization metamorphic ore bearing fluids are recorded in distinct assemblages of low to moderate salinities 1 18 wt nacleq h2o nacl cacl2 and h2o co2 n2 nacl cacl2 fluid inclusions and co2 n2 inclusions microthermometric data indicate entrapment conditions of 250 350 c and 0 3 2 3 kbar recording hydrostatic to supralithostatic fluid pressures in post peak metamorphic stages sharp fluid pressure fluctuations 0 4 1 6 kbar resulted from earthquake rupture events and the fault valve behavior induced circulation of fluids from distinct sources with limited partial fluid mixing favoring the gold transportation and precipitation

combined osmium and strontium isotopic study of the cretaceous tertiary boundary at sumbar turkmenistan a test for an impact vs a volcanic hypothesis osmium and strontium isotopic ratios at the cretaceous tertiary boundary at sumbar turkmenistan display a negative hyperbolic covariation superimposed on the long term trend which displays a positive covariation the minimum ratio for os and the maximum ratio for sr occur at the boundary clay volcanism with a mantle or crustal source cannot account for the isotopic data the low 187 o s 188 o s and the high 87 sr 86 sr ratios can be explained by an impact whereby os was derived from the bolide and the 87 sr 86 sr ratio was enhanced by acid rain and or a tsunami following the event

fluid regimes fault valve behavior and formation of gold quartz veins the morro do ouro mine ribeira belt brazil abstract fluid inclusion studies petrographic analyses and structural analyses for neoproterozoic auriferous veins from the morro do ouro mine ribeira belt southeastern brazil are presented the deposit is classified as an orogenic gold deposit the vein type au mineralization at the mine is restricted to structurally controlled domains in a low grade calymmian ca 1500 1450 ma metasedimentary sequence that also hosts syngenetic au mineralization two main auriferous quartz vein systems are present i nw trending subvertical extensional veins and ii ne trending subvertical veins parallel to the axial surface of tight folds the mineralized veins are adjacent to a major dextral transcurrent fault zone and their structural relationships indicate that this fault is severely misoriented for frictional reactivation the nw trending veins present a fluid inclusion assemblage dominated by co 2 n 2 ch 4 inclusions h 2 o co 2 n 2 ch 4 nacl cacl 2 inclusions and h 2 o nacl cacl 2 inclusions both with highly variable salinities 0 5 to 52 wt nacl equivalent while the ne trending veins are dominated by h 2 o co 2 n 2 ch 4 nacl cacl 2 and h 2 o nacl cacl 2 inclusions also of highly variable salinities 1 to 45 wt nacl equivalent the entrapment of fluids occurred at temperatures between 225 and 240 c in the nw trending veins and at approximately 208 c in the ne trending veins involving processes of fluid immiscibility and mixing between fluids of contrasting compositions the nw trending extensional veins were formed predominantly under pressure fluctuating between near lithostatic and strongly supralithostatic conditions 100 250 mpa during pre seismic failure stages the ne trending veins precipitated predominantly under subhydrostatic to lithostatic pressure conditions 10 150 mpa following the discharge of fluids from different reservoirs along the ruptured zone after earthquake rupture stages the hydrothermal fluids were probably enriched with gold through interactions with the host rocks and its precipitation is attributed to changes in physicochemical properties due to fluid immiscibility and mixing between fluids of highly contrasting salinities as a consequence of cyclic fluctuations in the values of fluid pressure and tectonic stresses accompanying episodes of seismogenic fault activity

source and differentiation of deccan trap lavas implications of geochemical and mineral chemical variations the basalt stratigraphy of the deccan trap between mahabaleshwar ghat and belgaum over steps the basement from north to south sr isotope and zr nb ratios and sr rb and ba concentrations correlate portions of the post poladpur stratigraphy over 250 km along the western ghats thereby confirming a southerly component of dip of 0 06 at the southwestern margin the stratigraphy extends upwards from the compositionally uniform ambenali formation cox hawkesworth 1984 into a sequence of grossly heterogeneous flow units which have been allocated to the mahabaleshwar and panhala formations lightfoot hawkesworth 1988 the mahabaleshwar formation is represented only by a sequence of highly fractionated flows termed the kolhapur unit with similar 87sr 86sr0 to the mahabaleshwar 0 7045 but with sr 2 25 succeeding the kolhapur unit are a series of flows with high 87sr 86sr0 0 7045 0 705 zr nb 13 and low sr 230 but trace element concentrations similar to the mahabaleshwar formation these have been allocated to the desur unit of the panhala geochemical variations in flows overlying the ambenali define two distinct trends one is attributed to gabbro fractionation and the other to variations in the compositions of the parental magmas and arguably their source regions there is little evidence for significant crustal contamination in these flows and the degree of fractionation and the composition of the phase extract are shown to vary along strike within the mahabaleshwar formation the high tio2 content of kolhapur unit flows is shown to be the result of shallow level gabbro fractionation rather than the presence of a primitive high ti magma mahabaleshwar formation basalts exhibit a broad negative correlation between the degree of fractionation and sr isotopic composition the endmember with lower 87sr 86sr0 has different zr y from the ambenali basalts and would appear to have been generated by lower degrees of melting of a similar source the other endmember has more radiogenic sr lower zr nb similar zr y but higher mg number the simplest interpretation is that these magmas were more primitive and hence hotter and more able to interact with the lithosphere en route to the surface and that they then mixed to produce the mahabaleshwar array the panhala formation basalts plot on the sr nd array defined by the mahabaleshwar formation and the desur unit basalts plot on an extension of this array this suggests that the source characteristics are also lithospheric the absolute elemental abundances may then be a function of melting and fractionation we are impressed by the apparent switch from crustal lithospheric contributions to mantle lithospheric contributions through the stratigraphy and suggest that this together with the more protracted fractionation of the magma reflects a change in the availability of the lithospheric components accompanying the southerly migration of the volcanic edifice

seawater sr isotopes at the cretaceous tertiary boundary abstract seawater 87 sr 86 sr values increase abruptly by 28 10 6 across the cretaceous tertiary boundary ktb this small but rapid shift is superimposed on the larger scale structure of the seawater sr isotope curve the time scale of radiogenic sr addition appears to be too rapid to reconcile with sources associated with volcanism and we show that the amount of sr required to produce even this small increase is too large to be derived from 1 a kt bolide of the size constrained by the ir anomaly 2 continental crust ejecta from the impact of such a bolide 3 soot from global wildfires initiated by an impact or 4 any combination of these sources the probable source of the radiogenic sr is enhanced continental weathering but the high rate of increase appears to rule out processes such as sea level regression glaciation or tectonism a plausible mechanism for rapid addition of radiogenic sr to the oceans is enhanced weathering associated with globally distributed acid rain ph 1 which is a proposed by product of a bolide impact 51 epsl vol 83

constraining the age of the iporanga formation with shrimp u pb zircon implications for possible ediacaran glaciation in the ribeira belt se brazil abstract the ribeira belt in se brazil is a neoproterozoic to early palaeozoic orogen whose architecture and history is not yet fully understood the depositional age of many of the sedimentary sequences in the ribeira belt remains unconstrained and with debate concerning their depositional environment and tectonic setting in this paper we present shrimp zircon u pb age constraints for one such problematic unit in the ribeira belt the iporanga formation and discuss the significance of this age with regards to the timing of neoproterozoic glacial events in southeast brazil using a felsic volcanic unit immediately under the iporanga formation and granite cobbles from breccias in its basal parts a reconnaissance shrimp u pb zircon maximum depositional age of 580 ma is assigned for the base of this unit this age is marginally younger than the 625 605 ma ages for intrusions into the lajeado and ribeira subgroups with which the iporanga formation is in tectonic contact this indicates that the lajeado and ribeira subgroups are not stratigraphically equivalent to the iporanga formation as thought previously by some workers the maximum depositional age of 580 ma also places a maximum time constraint on the tectonic juxtaposition of the iporanga formation with other supracrustal units and on the greenschist facies metamorphism and isoclinal folding that affected it the potential glacial origin for the iporanga formation if correct would place it in the late ediacaran provisionally equivalent to the gaskiers glaciation

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

ore forming fluids in archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec canada archean gold bearing quartz veins at the sigma mine occur in deformed metavolcanics intruded by two generations of preore porphyries the veins were emplaced during a late compressional tectonic event and they consist primarily of quartz tourmaline carbonates pyrite and scheelite vein minerals have been deformed and are also cut by abundant healed fractures outlined by fluid inclusions in the veins gold typically occurs in late fractures and in recrystallized quartz microthermometric sem eda leachate analysis and gas chromatographic techniques were used to study fluid inclusions in quartz most fluid inclusions at sigma occur in late fractures and are secondary the fluid inclusions are commonly found in fractures parallel to or less commonly within gold bearing fractures and are genetically related to the gold three types of fluid inclusions are identified 1 high salinity na ca cl aqueous inclusions 25 34 wt salt with small amounts of co 2 some containing halite calcite and nahcolite as daughter minerals 2 co 2 rich inclusions containing small amounts of h 2 o and ch 4 and 3 low salinity h 2 o co 2 inclusions 10 equiv wt nacl with co 2 contents which are variable but commonly in the range of 15 to 30 mole percent co 2 leachate analyses show that in addition to na and ca the aqueous fluids contain minor amounts of k fe mg and li homogenization temperatures of h 2 o co 2 inclusions with constant phase ratios range from 285 degrees to 395 degrees c those of aqueous inclusions range from 60 degrees to 295 degrees c the aqueous and co 2 rich inclusions are interpreted to have trapped two coexisting fluids resulting from the unmixing of a homogeneous h 2 o co 2 parent fluid itself occasionally trapped in late fractures the ore bearing fluid is interpreted to be a low salinity 10 equiv wt nacl fluid containing 15 to 30 mole percent co 2 at minimum temperatures in the range of 285 degrees to 395 degrees c the relatively low homogenization temperatures of aqueous inclusions are interpreted to be the result of co 2 effervescence from a co 2 saturated aqueous fluid due to pressure fluctuations at the time of entrapment it is also proposed that the onset of gold deposition is related to the onset of fluid unmixing

sedimentary fluids fault interaction during syn rift burial of the lodeve permian basin herault france an example of seismic valve mechanism in active extensional faults abstract during basin burial interstitial fluids initially trapped within the sedimentary pile easily move under thermal and pressure gradients as the main mechanism is linked to fluid overpressure such fluids play a significant role on frictional mechanics for fault reactivation and sediment deformation the lodeve permian basin herault france is an exhumed half graben with exceptional outcrop conditions providing access to barite sulfide mineralized systems and hydrocarbon trapped into syn rift roll over faults architectural studies show a cyclic infilling of fault zone and associated bedding parallel veins according to three main fluid events during dextral normal faulting contrasting fluid entrapment conditions are deduced from textural analysis fluid inclusion microthermometry and sulfur isotope geothermometer we conclude that a polyphase history of trapping occurred during permian syn rift formation of the basin the first stage is characterized by an implosion breccia cemented by silicifications and barite during an abrupt pressure drop within fault zone this mechanism is linked to the dextral strike slip motion on faults and leads to a first sealing of the fault zone by basinal fluid mineralization the second stage consists of a succession of barite ribbons precipitated under overpressure fluctuations derived from fault valve action this corresponds to periodic reactivations of fault planes and bedding controlled opening localized at sulphide rich micro shearing structures showing a normal movement this process formed the main mineralized ore bodies by the single action of fluid overpressure fluctuations undergoing changes in local stress distribution the last stage is associated with the formation of dextral strike slip pull apart infilled by large barite and contemporaneous hydrocarbons under suprahydrostatic pressure values this final tectonic activation of fault is linked to late basinal fluids and hydrocarbon migration during which shear stress restoration on the fault plane is faster than fluid pressure build up this integrated study shows the interplay action between tectonic stress and fluid overpressure in fault reactivation during basin burial that clearly impact potential economic reservoirs

fluid pressure transients on seismogenic normal faults abstract fluid inclusions in hydrothermally altered footwall rocks of the dixie valley fault nevada and the wasatch fault utah indicate that pore fluid pressure fluctuated minimum entrapment pressures for fluid inclusions consisting of h2o co2 nacl ranged from 295 mpa to 60 mpa in the temperature range 350 to 170 c on the wasatch fault and from 158 to 35 mpa in the temperature range 350 to 200 c on the dixie valley fault scatter in the pressure estimates at constant temperature is interpreted as paleo fluid pressure transients at depths of up to 11 km on the wasatch fault and 3 to 5 km on the dixie valley fault observed pressure transients range from 5 mpa within the limits of error in pressure determination to 120 mpa on the wasatch fault and 7 to 126 mpa on the dixie valley fault the pressure transients are greatest on both faults in the temperature range 270 to 310 c the fluids represented by fluid inclusions play a key role in nucleation and propagation of earthquake ruptures high fluid pressures may initiate rupture then dilatancy pore pressure reduction and dilatant hardening may arrest the rupture however decompression of the fluids and phase separation produces a decrease in fluid bulk modulus of 41 to 90 which reduces the dilatant hardening effect and may permit ruptures to propagate

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

fluid pressure and salinity variations in shear zone related veins central pyrenees france implications for the fault valve model abstract fluid inclusion microthermometry data is presented from quartz veins associated with high angle reverse shear zones cutting the neouvielle massif in the central french pyrenees a complex series of veins were formed during both normal and reverse movement on brittle faults within the shear zone brittle structures developed contemporaneously with quasi plastic deformation in the shear zones fluid inclusion data are presented from a variety of vein types and shows that a wide variation in fluid density and salinity is present in the fault system these variations occur both within individual veins and between different vein types temperatures at the time of vein filling are constrained to be in the range 310 360 c by chlorite microthermometry the variation in homogenisation temperature is too large to be accounted for by variations in the fluid temperature and is interpreted to reflect variations in fluid pressure between lithostatic 500 mpa and hydrostatic 200 mpa values at the time of quartz growth in the veins the shear zones carry modest displacements and may not themselves have been seismogenic a model is presented in which fluid pressure variations and stress cycling within the steeply dipping shear zones is controlled by the seismogenic cycle on large underlying thrust structures the model predicts that the highest maximum trapping pressures should occur in fluid inclusions from low angle veins formed in a high pfluid compressional regime immediately before earthquake rupture lower maximum pressures are expected in steep veins related to extension and normal fault movement across the shear zones immediately after rupture the fluid inclusion data support this model when maximum trapping pressures are considered but the majority of inclusions in all vein types formed at pressures well below lithostatic values this suggests that the dominant factor causing quartz precipitation was the sudden pressure drop immediately after earthquake rupture regardless of vein type

pressure fluctuation during uplift of the northern apennines italy a fluid inclusions study abstract p t conditions existing after the main syn collision tectonic phase in the western part of the northern apenninic chain italy e g in the tuscan nappe outcropping in the la spezia area were estimated on the basis of a detailed microstructural structural petrographic and fluid inclusion study of quartz of syn tectonic d2 veins developed in the tertiary flysch at the top of the tuscan nappe macigno formation three main fluid events have been distinguished as follows during retrograde metamorphism d1 to d2 phase fluids in equilibrium with turbidites from the tuscan nappe were h2o ch4 mixtures issued from water organic matter interactions in temperatures conditions that may have reached at least 260 c or more 280 c depending on the considered depth estimates and maximum pressures around 210 250 mpa evidence of strong fluid pressure fluctuation between lithostatic and hydrostatic within the metamorphic formations up to 100 150 mpa possibly linked to fault valve activity at the beginning of the uplift triggered phase separation of the water methane fluids and production of methane rich and water rich fluids fluctuations in pressure during these events played a crucial role in quartz crystallization especially in extensional fissures formed perpendicular to the d2 folds axial foliation changes in the fluid regime and sources with time are evidenced by the input of brines which mix to distinct degrees and are trapped in healing microfissures during retrograde fluid evolution such mixing processes are an indication of the connection between separate fluid reservoirs with different temperature conditions consequently mass and heat transfer have to be taken into account as the downward percolation of cooler fluids probably accelerated the rate of cooling of the exhumed formations these processes are certainly common to most orogenic terrains and can be quantitatively studied through p v t x reconstruction using fluid inclusion data on the drainage zones where the mixing processes occurred this work confirms that fluid inclusion studies can provide accurate quantitative estimates of fluid pressure variations during the evolution of orogenic terrains and could therefore constitute a useful tool in tectonic interpretations at the light of the models developed for pressure variations in the upper crust

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

fluid immiscibility in natural processes use and misuse of fluid inclusion data abstract many occurrences of fluid immiscibility in natural geologic systems have been reported recently most often from fluid inclusion studies however the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology in the tpx space of natural fluid systems for such reasons some authors have been misled to erroneous interpretations the term chemical immiscibility is unambiguously redefined as a multiphase multicomponent equilibrium the consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters temperature pressure volumes compositions to each other these equations already put constraints on the topology of the phase equilibria in fluid systems a particular expression of the phase rule is proposed which takes into account the multiphase constant bulk volume constant bulk composition constraints in fluid inclusions the consequences of such an expression are of major importance in fluid inclusion studies the phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed h2o nacl co2 ch4 h2o co2 h2o co2 nacl the effects of these topologies and of the supplementary constraints constant bulk composition and constant bulk volume assumed for fluid inclusions isopleth isochoric systems are discussed

uppermost campanian maestrichtian strontium isotopic biostratigraphic and sequence stratigraphic framework of the new jersey coastal plain firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units sequences we correlate the well developed uppermost campanian and maestrichtian sequences of the new jersey coastal plain to the geomagnetic polarity time scale gpts by integrating sr isotopic stratigraphy and biostratigraphy to do this we developed a maestrichtian ca 73 65 ma sr isotopic reference section at deep sea drilling project hole 525a in the southeastern atlantic ocean maestrichtian strata can then be dated by measuring their 87 sr 86 sr composition calibrating to the gpts of s c cande and d v kent 1993 personal commun and using the equation age ma 37 326 894 52 639 89 87 sr 86 sr sr stratigraphic resolution for the maestrichtian is estimated as 1 2 to 2 m y at least two unconformity bounded units comprise the uppermost campanian to maestrichtian strata in new jersey the lower one the marshalltown sequence is assigned to calcareous nannofossil zones cc20 21 nc19 and cc22b nc20 it ranges in age from 74 1 to 69 9 ma based on sr isotope age estimates the overlying navesink sequence is assigned to calcareous nannoplankton zones cc25 26 nc21 23 it ranges in age from 69 3 to 65 ma based on sr isotope age estimates the upper part of this sequence the tinton formation has no calcareous planktonic control sr isotopes provide an age estimate of 66 1 2 ma latest maestrichtian sequence boundaries at the base and the top of the marshalltown sequence match boundaries elsewhere in the atlantic coastal plain owens and gohn 1985 and the inferred global sea level record of haq et al 1987 they support eustatic changes as the mechanism controlling depositional history of this sequence however the latest maestrichtian record in new jersey does not agree with haq et al 1987 we attribute this to correlation and time scale differences near the cretaceous paleogene boundary high sedimentation rates in the latest maestrichtian of new jersey shrewsbury member of the red bank formation and the tinton formation suggest tectonic uplift and or rapid progradation during deposition of the highstand systems tract

scaling the 3 d mohr circle and quantification of paleostress during fluid pressure fluctuation application to understand gold mineralization in quartz veins of gadag southern india abstract in this study orientations of 157 quartz veins occurring in metabasalts of the gadag region dharwar craton southern india are used to plot the 3 d mohr stress circle which provides information about relative stress fluid pressure pf conditions as well as stress state during pf fluctuation to scale the 3 d mohr circle vein orientation data are integrated with a available estimates from fluid inclusions of highest recorded pf 390 mpa and lowest recorded pf 50 mpa and b intrinsic rupture criterion that empirically quantify rock properties based on the scaled 3 d mohr circle the absolute magnitudes of the three principal stresses are quantified for high and low pf of 157 veins investigated here 14 veins are identified as having favourable orientation for dilation at high as well as low pf these 14 veins have a mean strike of 150 which is similar to the orientation of the gold bearing quartz lodes reported in the region the effective normal stress n n pf prevalent during dilation of fracture fabric anisotropy with 150 strike is calculated to be 11 5 mpa at high pf and 1 0 mpa at low pf thus it is interpreted that in the gadag region a change in n of 10 5 mpa prevailed during pf fluctuation and associated separation of gold from the fluid

fluid inclusion evidence for p v t x evolution of hydrothermal solutions in late alpine gold quartz veins at brusson val d ayas northwest italian alps

structural and geochemical controls on the development of turbidite hosted gold quartz vein deposits wattle gully mine central victoria australia gold quartz vein deposits in the wattle gully mine arefault related structures developed in a low grade metamorphosed ordovician quartz rich flysch sequence the major mineralization is associated with a high angle reverse fault wattle gully fault that has a maximum displacement of 40 m over 10 6 metric tons t of vein quartz averaging 10 5 g t au occur within a dilatant jog in this structure fold geometry has controlled fault geometry and resulted in the localization of the jog segment where the wattle gully fault traverses an east dipping fold limb to link two more steeply dipping bedding parallel fault sediments on adjacent west dipping fold limbs gold mineralization is also associated with several minor east clipping reverse faults and a bedding parallel fault whose development is related to flexural slip during fold tightening mineralization occurs within fault fill veins and extension veins adjacent to faults the geometry and internal structures of veins indicate that vein growth has been controlled by repeated fluctuations in fluid pressure and shear stress associated with fault valve behavior vein mineralogy is dominated by quartz with minor carbonates chlorite white mica albite and apatite arsenopyrite and pyrite are the major sulfide phases but sphalerite galena chalcopyrite and pyrrhotite are also present the highest au grades tend to be localised in vein systems that are in proximity to carbonaceous slates wall rock alteration is minor and restricted mainly to narrow zones adjacent to major vein systems sulfur isotope fractionation between galena and sphalerite indicates mineralization occurred at temperatures around 300 degrees c the delta 34 s compositions of pyrite and arsenopyrite are nearly uniform throughout the mine 1 5 2 8 but are generally not in equilibrium with the delta 34 s values of associated base metal sulfides 0 7 5 3 the delta 18 o values for vein quartz vary between 15 6 and 18 0 per mil and correspond to delta 18 o values

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes