transmission electron microscope analyses of alteration phases in martian meteorite mil 090032 abstract the nakhlite group of martian meteorites found in the antarctic contain varying abundances of both martian and terrestrial secondary alteration phases the aim of this study was to use transmission electron microscopy tem to compare martian and terrestrial alteration embodied within a single nakhlite martian meteorite find mil 090032 martian alteration veins in mil 090032 are composed of poorly ordered fe smectite phyllosilicate this poorly ordered smectite appears to be equivalent to the nanocrystalline phyllosilicate hydrated amorphous gel phase previously described in the martian alteration veins of other nakhlites chemical differences in this nanocrystalline phyllosilicate between different nakhlites imply localised alteration which occurred close to the martian surface in mil 090032 both structurally and compositionally the nakhlite nanocrystalline phyllosilicate shows similarities to the amorphous poorly ordered phase recently discovered in martian soil by the mars curiosity rover at rocknest gale crater terrestrially derived alteration phases in mil 090032 include jarosite and gypsum amorphous silicates and fe oxides and hydroxides similarities between the mineralogy and chemistry of the mil 090032 terrestrial and martian alteration phases suggest the alteration conditions on mars were similar to those in the antarctic at both sites a small amount of fluid at low temperatures infiltrated the rock and became acidic as a result of the conversion of fe2 to fe3 under oxidising conditions

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

aqueous alteration in the northwest africa 817 nwa 817 martian meteorite samples of a new martian meteorite of the nakhlite family nwa 817 contain traces of an iron rich alteration product textural arguments indicate that this alteration product has been formed on the parent body of the meteorite mars the chemical composition and structural data x ray diffraction transmission electron microscopy and vibrational spectroscopy show that the alteration mineral is a hydrous phase from the smectite family major elements and rare earth elements suggest that the formation of the alteration phase is related to the circulation of an aqueous fluid which composition is controlled by the dissolution of feldspars to account for a positive eu anomaly olivine and possibly apatite hydrogen isotope data display negative deltad values ranging from 60 to 280parts per thousand in olivine and pyroxenes and from 140 to 181parts per thousand in the alteration phase the values of deltad for the alteration product show a small scatter with a mean value of 170 14parts per thousand these values are lower than those previously obtained on other martian meteorites which give mainly positive deltad values these positive values have been interpreted as resulting from the interaction of the martian meteorites with water from the martian atmosphere ruling out the effect of terrestrial alteration it is suggested that alteration in the nwa 817 meteorite was likely produced on mars by the circulation of an aqueous fluid originating from a chemical reservoir such as the martian mantle which has not equilibrated with a fractionated martian atmosphere c 2002 elsevier science b v all rights reserved

a new martian meteorite from morocco the nakhlite north west africa 817 north west africa nwa 817 is a single stone of 104 g found in the sahara morocco by meteorite hunters in november 2000 the meteorite is an unbrecciated medium grained olivine bearing clinopyroxenite with a cumulate texture it consists of zoned euhedral subcalcic augite wo 42 en 38 22 f 20 36 olivine spanning a wide range of compositions from fa 56 in the core to fa 86 with rare magmatic inclusions and an intercumulus mesostasis made of fe bearing albitic plagioclase si rich glass ti magnetite with unusual skeletal growth morphologies containing ilmenite exsolutions acicular pyroxene olivine and cristobalite trace minerals are sulfide droplets and cl apatite mineral modes in vol are augite 69 olivine 10 mesostasis 20 and fe ti oxides 1 pervasive alteration produced a reddish clay mineral hydrous ferrous silicate in both olivine crystals and the mesostasis the major element composition of nwa 817 is very similar to that of the other nakhlites high feo mgo and cao concentrations reflect the abundance of cumulus augite and olivine key element ratios such as feo mno 37 na al 0 40 k la 449 ga al 3 9 x 10 4 and oxygen isotopic composition delta 17 o 0 37parts per thousand are clear evidence for a martian origin the incompatible trace element pattern as in nakhla displays a strong light rare earth element enrichment relative to chondrite la n yb n 4 89 however when compared to the other nakhlites nwa 817 has specific features 1 a higher modal proportion of mesostasis 2 quench textures of ti magnetite and fe rich clinopyroxene 3 more mg rich olivine core compositions whereas the augite core composition is identical for all nakhlites 4 a stronger fe enrichment toward crystal rims of these cumulus minerals the intercumulus minerals ti magnetite with skeletal growth morphology acicular chains of clinopyroxene and fe3 rich feldspar indicate rapid crystallization in response to a high degree of undercooling at the end of the sample story c 2002 elsevier science b v all rights reserved

sulfur isotope partitioning during experimental formation of pyrite via the polysulfide and hydrogen sulfide pathways implications for the interpretation of sedimentary and hydrothermal pyrite isotope records we show that the sulfur isotopic composition of sedimentary and hydrothermal pyrite is a good approximation of the average sulfur isotopic composition of the dissolved sulfide sources from which the pyrite formed consequently pyrite sulfur isotope systematics normally provide little evidence of the pyrite forming mechanism in most natural systems stable sulfur isotope partitioning during pyrite fes2 synthesis via the polysulfide and h2s pathways was investigated between 80 and 120 c iron monosulfide fes was reacted with hydrogen sulfide h2s or tetrasulfide s42 in aqueous solution under strictly anoxic conditions the results provide independent confirmation of the hydrogen sulfide and polysulfide mechanisms the measured isotopic composition of the synthesized pyrite is compared with 1 isotopic mixing models of the reactant reservoirs and 2 predictions based on the suggested mechanisms for the hydrogen sulfide and polysulfide pathways for pyrite formation the isotopic composition of the pyrite product is consistent with the result predicted from the reaction mechanisms pyrite produced via the h2s pathway has a composition reflecting isotopic contributions from both fes and h2s reservoirs pyrite formed via the polysulfide pathway inherits an isotopic composition dominated by the polysulfide reservoir in both cases solubility driven isotope exchange between fes and aqueous s species contribute to the final pyrite composition we show that published experimental sulfur isotope data for pyrite formation which apparently support conflicting pyrite forming pathways are consistent with pyritization via the polysulfide and h2s pathways formation rates of natural pyrite however may be too slow compared to solubility exchange for the influence of the reaction pathway on the isotopic composition to be significant

foredeeps versus subduction zones the geologic characteristics of foredeeps and accretionary wedges suggest that these features are distinguishable on the basis of the direction of the associated subduction east north east dipping subduction related accretionary wedges show high relief and broad outcrops of metamorphic rocks they are associated with shallow foredeeps with low subsidence rates in contrast west dipping subduction related accretionary wedges show low relief and involve mainly sedimentary cover the related foredeeps are deep and have high subsidence rates this differentiation is useful both for oceanic and continental subductions e g eastern vs western pacific subductions or east dipping alpine vs west dipping apenninec subductions in a cross section of the alps the ratio of the area of the orogen to the area of the foredeeps is at least 2 1 whereas this ratio is 0 22 1 for the apennines these ratios explain why foredeeps related to east or northeast dipping subduction are quickly filled and are bypassed by clastic rocks whereas foredeeps related to west dipping subduction maintain a deep water environment longer these differences support the presence of an eastward asthenospheric counterflow relative to the westward drift of the lithosphere detected in the hot spot reference frame even in the mediterranean where no hot spots are present in this interpretation the apennines foredeep was caused by the eastward push of the mantle acting on the subducted slab whereas the foredeeps in the alps were caused by the load of the thrust sheets and the downward component of movement of the upper adriatic plate these forces contrast with the upward component of the eastward mantle flow

gold and tin mineralisation in the ultramafic hosted cheoeum vent field central indian ridge the cheoeum vent field cvf is the first example of an inactive ultramafic hosted seafloor massive sulphide sms deposit identified in the middle part of the central indian ridge here we report on the detailed mineralogy and geochemistry of ultramafic hosted sulphide sample atop a chimney together with a few small fragments hydrothermal chimneys are characterised by high concentrations of au up to 17 8 ppm and sn up to 1720 ppm the sulphide mineralisation in the cvf shows 1 early precipitation of anhedral sphalerite and pyrite marcasite aggregates under relatively low temperature 250 c fluid conditions 2 intensive deposition of subhedral pyrrhotite isocubanite chalcopyrite fe rich sphalerite sp iii and electrum from high temperature 250 365 c and reduced fluids in the main mineralisation stage and 3 a seawater alteration stage distinguished by the mineral assemblage of marcasite pseudomorphs altered isocubanite phase covellite amorphous silica and fe oxyhydroxides electrum 2 m in size is the principal form of au mineralisation and is mainly associated with the main mineralisation stage the consistently high fineness of electrum 801 to 909 is indicative of the selective saturation of au over ag in the fluid during high temperature mineralisation which differs from the au mineralisation associated with typical basaltic hosted hydrothermal systems on mid ocean ridges tin is mainly substituted in structures of sphalerite isocubanite and chalcopyrite as a solid solution and not as mineral inclusions the continuously ascending hydrothermal fluids enable the early formed sn bearing sulphide to be dissolved and reprecipitated producing significantly sn enriched replacement boundaries between isocubanite and sp iii this study suggests that au sn mineralisation could be facilitated by the low redox potential of ultramafic hosted hydrothermal systems such as in the cvf which may be a common occurrence along slow spreading mid ocean ridges

chemistry and mineralogy of outcrops at meridiani planum analyses of outcrops created by the impact craters endurance fram and eagle reveal the broad lateral continuity of chemical sediments at the meridiani planum exploration site on mars approximately ten mineralogical components are implied in these salt rich silicic sediments from measurements by instruments on the opportunity rover compositional trends in an apparently intact vertical stratigraphic sequence at the karatepe west ingress point at endurance crater are consistent with non uniform deposition or with subsequent migration of mobile salt components dominated by sulfates of magnesium striking variations in cl and enrichments of br combined with diversity in sulfate species provide further evidence of episodes during which temperatures ph and water to rock ratios underwent significant change to first order the sedimentary sequence examined to date is consistent with a uniform reference composition modified by movement of major sulfates upward and of minor chlorides downward this reference composition has similarities to martian soils supplemented by sulfate anion and the alteration products of mafic igneous minerals lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the rock abrasion tool survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid h2o in this region since the time of crater formation

raman spectroscopy for mineral identification and quantification for in situ planetary surface analysis a point count method quantification of mineral proportions in rocks and soils by raman spectroscopy on a planetary surface is best done by taking many narrow beam spectra from different locations on the rock or soil with each spectrum yielding peaks from only one or two minerals the proportion of each mineral in the rock or soil can then be determined from the fraction of the spectra that contain its peaks in analogy with the standard petrographic technique of point counting the method can also be used for nondestructive laboratory characterization of rock samples although raman peaks for different minerals seldom overlap each other it is impractical to obtain proportions of constituent minerals by raman spectroscopy through analysis of peak intensities in a spectrum obtained by broad beam sensing of a representative area of the target material that is because the raman signal strength produced by a mineral in a rock or soil is not related in a simple way through the raman scattering cross section of that mineral to its proportion in the rock and the signal to noise ratio of a raman spectrum is poor when a sample is stimulated by a low power laser beam of broad diameter results obtained by the raman point count method are demonstrated for a lunar thin section 14161 7062 and a rock fragment 15273 7039 major minerals plagioclase and pyroxene minor minerals cristobalite and k feldspar and accessory minerals whitlockite apatite and baddeleyite were easily identified identification of the rock types kreep basalt or melt rock from the 100 location spectra was straightforward

terrestrial analogs of martian sulfates major and minor element systematics of alunite jarosite from goldfield nevada alunite and jarosite from goldfield nevada show spectacular relationships between early alunite and later jarosite in some cases jarosite overgrows alunite with the same crystallographic orientation and sharp contacts electron microprobe analyses of these phases show that they fall in the alunite jarosite quadrilateral defined by alunite kal3 so4 2 oh 6 natroalunite naal3 so4 2 oh 6 jarosite kfe33 so4 2 oh 6 and natrojarosite nafe33 so4 2 oh 6 a large compositional gap occurs between alunite natroalunite and jarosite natrojarosite this gap has no crystal chemical basis because al and fe3 can readily substitute for each other in octahedral site coordination we believe the on off switch behavior between early alunite and later jarosite is caused by an oxidant entering the system oxidizing fe2 in solution to fe3 raising the eh and possibly oxidizing h2s to lower the ph and thus stabilizing jarosite relative to alunite the activity of fe as fe2 increased in the solution because of prolonged alunite crystallization but could not readily enter the crystal structure until it was oxidized to fe3 the jarosite overgrowths show striking oscillatory zoning of na and k rich bands this reflects up to an order of magnitude change in the fluid k na ratio these textures are interpreted to represent rapid growth and kinetic control of delivery of free na and k to the crystal fluid interface this could be due to some combination of na and k diffusion rates in the solution and complex ion breakdown involving na and k

deformation history of a subducted continental crust gran paradiso western alps continuing crustal shortening during exhumation eclogite facies continental basement in the western alps outcrops as tectonic windows below the oceanic units in the gran paradiso massif eclogite facies assemblages in mafic rocks display a n s stretching lineation da1 the main phase foliation formed under epidote amphibolite facies conditions da2 and defines a regional dome structure for the whole gran paradiso massif structural data including new detailed mapping microstructural analyses and metamorphic studies in the northern part of the gran paradiso cogne valley reveal the occurrence of major thrusts in this continental basement associated with the da2 deformation e w trending stretching lineations and fold axes are associated with this second and main deformation nappe stacking of the different units was achieved by top to the west shearing during exhumation of the eclogite facies basement the antiformal doming of the gran paradiso basement is thus produced by the nappe stacking during exhumation under epidote amphibolite facies

alteration assemblages in the nakhlites variation with depth on mars secondary mineral assemblages in the nakhlite meteorites lafayette governador valadares gv nakhla yamato y 000593 y 000749 have been studied using scanning electron microscopy transmission electron microscopy and electron probe micro analysis the different nakhlites have distinctive secondary assemblages in their olivine grains and mesostases showing compositional fractionation correlated with their relative depths below the martian surface fracture filled veins in lafayette at the bottom of the pile consist of a siderite phyllosilicate fe oxide hydrated silicate gel assemblage corresponding veins in nakhla and gv further up the pile are predominantly a siderite gel assemblage with additional evaporites including gypsum y 000593 y 000749 veins are dominated by gel the gel s mg mg fe ratio decreases from lafayette 0 37 to gv 0 32 nakhla 0 24 and y 000593 0 15 we suggest that hydrothermal fluid flowed up this depth profile initiated by melting of buried h2o co2 ice our results show a complex mix of fe rich phyllosilicate within the veins and mesostasis of lafayette with d spacings of 0 7 1 1 nm suggesting a mixture of smectite and serpentine the phyllosilicate formed at close to neutral ph 150 c we also suggest that water rock ratios w r of 1 10 occurred in lafayette with smaller values for the other nakhlites this is reflected in the volume of alteration minerals 10 of olivine in lafayette to 3 in nakhla textural evidence of rapid cooling together with the w r and likely fluid velocities suggest that the secondary assemblages formed quickly e g within months a model is proposed in which the secondary assemblages formed in an impact induced hydrothermal system terminated by precipitation of the gel and evaporation of soluble salts

laihunite and jarosite in the yamato 00 nakhlites alteration products on mars 1 nakhlites martian clinopyroxenites are believed to have experienced aqueous alteration on the martian surface on the basis of the presence of reddish brown iddingsite on the rim and along cracks of large olivine crystals amorphous to poorly crystalline phyllosilicates smectites and carbonates are major products of aqueous alteration of the yamato 00 nakhlites the yamato 000593 nakhlite and its pair yamato 000749 contain large olivine crystals having opaque black material intimately associated with iddingsite on their rims and along cracks synchrotron radiation x ray diffraction micro raman spectroscopy and transmission electron microscopy revealed that the opaque material is the nonstoichiometric olivine type mineral laihunite 0 42 mg2 fe2 0 79fe3 0 79si1 00o4 typically formed as a high temperature oxidation product under nonequilibrium conditions because laihunite has been decomposed into a mixture of magnetite and amorphous silicate near the fusion crust it is preterrestrial in origin this is the first observation of large olivine crystals in martian meteorites being replaced by laihunite although its presence in olivine in the mesostasis of the miller range 03346 nakhlite has been suggested by micro raman spectroscopy because laihunite in the nakhlites does not form nanometer sized intergrowth with iron oxides fluid assisted high temperature oxidation may have played an important role in transporting away free fe2 cations liberated from olivine during laihunite formation although the yamato 00 nakhlites also contain jarosite we could not confirm the presence of preterrestrial jarosite based only on its occurrences

depositional setting of the late archean fe oxide and sulfide bearing chert and graphitic argillite in the shaw dome abitibi greenstone belt canada abstract interbedded chert rich exhalite and graphitic argillite are the only sedimentary rocks deposited in deep water settings during long lived hiatuses in mafic to ultramafic volcanism within the hart area of the shaw dome in the late archean abitibi greenstone belt in canada the fe oxide and sulfide bearing but predominantly cherty exhalite lithological unit in the hart area can be traced laterally to iron formation elsewhere in the shaw dome whole rock as well as fe and s isotope geochemistry suggest that the exhalite unit was formed as a result of direct precipitation from seawater distally from hydrothermal centres fractionation of fe isotopes through the precipitation of iron oxyhydroxides in a neutrally buoyant hydrothermal plume removed the heavier isotopes of fe resulting in the negative 56fe values observed in the exhalite in the hart area archean seawater is generally considered to be anoxic but moderate mn enrichments up to 1 87 wt mno in exhalite along with negative fe isotope values resulting from partial fe ii oxidation suggest the presence of oxygen in the upper part of the water column along the pathway of hydrothermal plumes from their source to the depositional site in the abitibi greenstone belt in contrast the graphitic argillite contains abundant pyrite nodules and bands that exhibit systematic negative fe isotope values but does not show mn enrichment this unit likely formed in a zone of upwelling of nutrient rich waters from deeper parts of the basin resulting in high organic productivity both exhalite and graphitic argillite have negative 33s values suggesting that sulfur was derived from seawater sulfate which is consistent with an anoxic atmosphere with sulfate aerosols produced by photochemical reactions combined our data indicates disequilibrium between anoxic atmosphere and partially oxygenated upper part of the water column during periods of volcanic quiescence in the 2 7 ga abitibi greenstone belt supporting the existence of oxidized oases within the archean ocean

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

petrology and chemistry of mil 03346 and its significance in understanding the petrogenesis of nakhlites on mars antarctic meteorite miller range mil 03346 is a nakhlite composed of 79 clinopyroxene 1 olivine and 20 vitrophyric intercumulus material we have performed a petrological and geochemical study of mil 03346 demonstrating a petrogenetic history similar to previously discovered nakhlites quantitative textural study of mil 03346 indicates long 1 x 101 yr residence times for the cumulus augite whereas the skeletal fe ti oxide fayalite and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling probably as a lava flow from the relatively high forsterite contents of olivine up to fo43 compared with other nakhlites and compositions of augite cores wo38 42en35 40fs22 28 and their hedenbergite rims we suggest that mil 03346 is part of the same or a similar martian cumulate rich lava flow as other nakhlites however mil 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date calculated trace element concentrations based upon modal abundances of mil 03346 and its constituent minerals are identical to whole rock trace element abundances parental melts for augite have ree patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients this parallelism reflects closed system crystallization for mil 03346 where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization a model for the petrogenesis of mil 03346 and the nakhlites nakhla governador valadares lafayette yamato 000593 northwest africa nwa 817 nwa 998 would include 1 partial melting and ascent of melt generated from a long term lree depleted mantle source 2 crystallization of cumulus augite olivine magnetite in a shallow level martian magma chamber 3 eruption of the crystal laden nakhlite magma onto the surface of mars 4 cooling crystal settling overgrowth and partial equilibration to different extents within the flow 5 secondary alteration through hydrothermal processes possibly immediately succeeding or during emplacement of the flow this model might apply to single or multiple flow models for the nakhlites ultimately mil 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks on mars with analogous petrogenetic histories to pyroxene rich terrestrial lava flows and to komatiites

complex mineral zoning patterns caused by ultra local equilibrium at reaction interfaces chemically zoned minerals are useful records of temporal variations in ambient conditions and bulk chemical composition of the fl uid from which the minerals precipitate in fl buffered systems zoning of mineral compositions is expected to refl ect directly the evolution of fl composition here we show that during rapid fl uid rock reactions ultra local equilibrium can form complex mineral zoning patterns even when the overall system is highly fl uid buffered we reacted cleaved calcite single crystals with aqueous arsenate phosphate solutions with molar ratios of as as p between 0 01 and 0 15 at 250 c and water saturated pressure we fithat complex zoning patterns and solid solution between hydroxylapatiteand arsenate bearing hydroxylapatite that pseudomorphically replaced calcite formed within hours and these zoning patterns were destroyed within days during secondary reactions we propose a two stage reaction process in the formation of the fi nal reaction product 1 on an hour time scale calcite is dissolved and replaced by compositionally heterogeneous apatite the thin reaction interface fllayer becomes extremely enriched in arsenic at an ultra local scale as the reaction removes phosphate faster than the interface fl uid can re equilibrate with the bulk fl uid 2 the heterogeneous apatite is replaced by homogeneous apatite that refl ects the bulk fl uid composition over a longer days time scale through interface coupled dissolution precipitation this paper highlights the complexity that can arise from ultra local fl uid composition variations due to rapid fl uid rock interaction in a short lived fl uid fl ow event for example during a seismic cycle subsequent interpretation of complex zoning patterns as refl ecting the evolution of bulk fl uid would be erroneous

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

comment on alpine thermal and structural evolution of the highest external crystalline massif the mont blanc by p h leloup n arnaud e r sobel and r lacassin in this comment we discuss the approach used and the significance of ar ar dating of synkinematic phengite within low grade alpine shear zones and we comment the geodynamic models that can be derived from this method the paper by leloup et al 2005 is a good step forward in the tectonic comprehension of the mont blanc area and provides a good synthesis of preexisting data leloup et al 2005 have proposed a polyphase alpine history for the mont blanc massif west alps based on a multidisciplinary approach ar ar on biotite for the higher pressure temperature events of the mont blanc and ar ar on k feldspar fission tracks ft on zircon and apatite for its later exhumation stages however at this point of our knowledge of alpine deformation in the mont blanc range the polyphased tectonic evolution in particular the timing of thrust and back thrust events are not in agreement with recently obtained ar ar data

neogene to ongoing normal faulting in the inner western alps a major evolution of the late alpine tectonics 1 widespread brittle extension occurs in the internal zones of the southwestern alps forming a dense fault network which overprints the compressional structures the extension has been followed by transcurrent motions in terms of paleostress this extension is radial to the belt close to the crustal penninic front and multidirectional in the eastern part of the internal zones the paleostress field of the strike slip phase is coherent with the extensional one and compatible with dextral shear along longitudinal faults globally we propose that the internal zones of the southwestern alps underwent a single neogene transtensive tectonic regime to strengthen our structural results the current tectonics has been analyzed using seismotectonic tools this approach allowed the recognition of several active faults moreover the ongoing tectonics is coherent with the observed brittle deformation the fault network controls the present day seismicity the combined seismotectonic and structural approaches give coherency and continuity from the neogene to ongoing extensional tectonics in the southwestern alps in the framework of the whole western alps a synthesis of our results with neotectonic related data allowed us to provide an accurate map of the neogene to present kinematics of the belt extension which appears as a major feature of the internal zones has been coeval with the propagation of thrusts in the outer zones during neogene times the geodynamic processes which rule this major tectonic evolution of the belt remain a matter of debate

mossbauer mineralogy of rock soil and dust at gusev crater mars spirit s journey through weakly altered olivine basalt on the plains and pervasively altered basalt in the columbia hills 1 the mossbauer spectrometer on spirit measured the oxidation state of fe identified fe bearing phases and measured relative abundances of fe among those phases for surface materials on the plains and in the columbia hills of gusev crater eight fe bearing phases were identified olivine pyroxene ilmenite magnetite nanophase ferric oxide npox hematite goethite and a fe3 sulfate adirondack basaltic rocks on the plains are nearly unaltered fe3 fet px and minor npox and magnetite columbia hills basaltic rocks are nearly unaltered peace and backstay moderately altered woolypatch wishstone and keystone and pervasively altered e g clovis uchben watchtower keel and paros with fe3 fet 0 6 0 9 fe from pyroxene is greater than fe from olivine ol sometimes absent and fe2 from ol px is 40 49 and 9 24 for moderately and pervasively altered materials respectively ilmenite fe from ilm 3 6 is present in backstay wishstone keystone and related rocks along with magnetite fe from mt 10 15 remaining fe is present as npox hematite and goethite in variable proportions clovis has the highest goethite content fe from gt 40 goethite feooh is mineralogical evidence for aqueous processes because it has structural hydroxide and is formed under aqueous conditions relatively unaltered basaltic soils fe3 fet 0 3 occur throughout gusev crater 60 80 fe from ol px 10 30 from npox and 10 from mt pasorobles soil in the columbia hills has a unique occurrence of high concentrations of fe3 sulfate 65 of fe magnetite is identified as a strongly magnetic phase in martian soil and dust

hydrothermal evolution and ore genesis of the laozuoshan au skarn deposit northeast china constrains from mineralogy fluid inclusion and o c s pb isotope geochemistry abstract the laozuoshan mine located in the central jiamusi block is the largest gold skarn deposit in northeast china it comprises three ore zones east middle west with complex stratigraphic and structural controls the skarn type orebodies mainly occur in the east and middle ore zones along the contact zones between hercynian granite and precambrian metasedimentary rocks the earliest stage of alteration is characterized by potassium hornfels subsequently prograde skarn formation occurred characterized by garnet in the grossular andradite series and pyroxene in the hedenbergite diopside series this was followed by a retrograde skarn overprint of hydrous silicates and ore minerals three types of garnet with distinct textures and elemental compositions are recognized which indicate fluctuating physicochemical conditions in the hydrothermal fluids the fluids associated to the prograde skarn are characterized by high temperature and high salinity which underwent fluid boiling that led to precipitation of minor pyrite and arsenopyrite the main gold and sulfide mineralization is related to the retrograde skarn overprint where cooling and strong fluid rock interactions occurred gold precipitation is estimated to have occurred at temperatures of 380 470 c based on the arsenopyrite geothermometer and fluid inclusion microthermometry the fluid inclusion and c o isotope data indicate that the ore forming fluids were dominated by magmatic water during the prograde skarn stage and the main ore forming stages mixing between meteoric and magmatic fluids occurred during the latest stages of the retrograde skarn formation both sulfur and lead isotope compositions of sulfides support a magmatic origin for the ore forming materials on the basis of the available geological and geochemical evidence we propose that the laozuoshan deposit is a reduced gold skarn deposit genetically related to the granitic pluton

early fimiston and late oroya au te ore paringa south mine golden mile kalgoorlie 4 mineralogical and thermodynamic constraints on gold deposition by magmatic fluids at 420 300 c and 300 mpa the golden mile deposit 1767 t au in the archean yilgarn craton western australia is controlled by d2 strike slip and d3 reverse faults displacing folded tholeiitic greenstones granodiorite and monzodiorite dykes emplaced into the faults predate and are synchronous with propylitic and sericite ankerite alteration overprinted by the ore arsenopyrite and chlorite thermometry and fluid inclusion data indicate ore formation at 420 30 c and 300 mpa and cooling to the ambient temperature at 10 km depth 250 300 c fimiston refractory ore 7 g t au in propylitic golden mile dolerite is zoned from inner albite ankerite to outer ankerite phengite quartz replacement pyrite magnetite is overprinted by pyrite hematite anhydrite arsenical pyrite encloses chalcopyrite tennantite gold and tellurides gold thio sulfide complexes buffered by magmatic so2 and h2s in the fluid were destabilised during the ankerite pyrite replacement of propylitic chlorite a reaction releasing hydrogen ions for the hydrolitic alteration of adjacent albite gold deposition was assisted by declining gold silver tellurium and sulfur solubility as the fluid cooled dissolved sulfate is recorded in pyrite by negative 34s 10 to 5 at magmatic 33s 0 0 2 oroya ore bodies are subdivided into oxidised pyrite lodes 5 g t au in propylitic gmd and reduced lodes 30 120 g t au characterised by stage 1 silica pyrite and siderite chlorite replacement in ankerite rich wall rocks rapid cooling an acidic fluid and the retrograde solubility of ankerite facilitated replacement and the deposition of minor arsenopyrite pyrrhotite chalcopyrite sphalerite and gold locally the h2s rich fluid log fs2 5 8 0 5 bar at 420 c was reduced by organic methane oroya stage 2 ore fills crosscutting veins and cements breccia quartz chalcedony dolomite ankerite calcite v muscovite v chlorite and v tourmaline form the gangue of pyrite telluride magnetite ore altaite tellurium myrmekites were deposited at 400 c as melt droplets together with tellurantimony altaite calaverite montbrayite and petzite as fluid temperature and tellurium fugacity declined free gold krennerite coloradoite and melonite also crystallised joined by sylvanite and hessite below 350 c finally trace covellite and digenite precipitated at high fluid sulfidation states

clues to martian brines based on halogens in salts from nakhlites and mer samples 1 chlorine and br abundances in fracture filling secondary salts in nakhla veins determined in this study by synchrotron x ray microprobe br and electron microprobe cl techniques compare well to the halogens determined recently by apxs instruments in soils and rock rinds at the gusev and meridiani sites the salts in these mars rocks arise from martian brines that have undergone evaporative or freezing concentration the halogen abundances in these salts are corrected for dilution effect because of mixing with halogen poor phases to obtain their true abundances which seem to be close to the halogen abundances in terrestrial sea brines consistent with the petrographic evidence for evaporative salt deposition sequence of carbonate sulfate halite in nakhlite meteorites nakhla veins yield high br 250 ppm and low cl br ratios 10 50 suggesting possible salt deposition from concentrated brines whereas lafayette iddingsite with low br 11 ppm and high cl br ratios 250 300 indicates salt deposition from dilute brines on mars the low cl br ratios 20 to 80 in salts from gusev and meridiani rock rinds indicate that they presumably originate from concentrated subsurface martian brines the high cl br ratio 270 in salts deposited by dilute solutions in lafayette and adirondack is similar to the chondritic cl br ratio which seems to characterize the dilute brines on mars prior to halite precipitation including early mars waters noachian or earlier our results seem to be consistent with the burt knauth model involving density stratification during evaporation freezing of brine solutions in martian regolith

opal a in the nakhla meteorite a tracer of ephemeral liquid water in the amazonian crust of mars the nakhlite meteorites are clinopyroxenites that are derived from a 1300 million year old sill or lava flow on mars most members of the group contain veins of iddingsite whose main component is a fine grained and hydrous fe and mg rich silicate siderite is present in the majority of veins where it straddles or cross cuts the fe mg silicate this carbonate also contains patches of ferric oxy hydroxide despite 40 years of investigation the mineralogy and origins of the fe mg silicate is poorly understood as is the paragenesis of the iddingsite veins nanometer scale analysis of fe mg silicate in the nakhla meteorite by electron and x ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal a this hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine each opal a nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine siderite crystallized subsequently and from solutions that were alkaline and reducing and replaced both the nanoparticles and olivine the fluids that formed both the opal a ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the martian atmosphere the last event recorded by the veins was alteration of the carbonate to a ferric oxy hydroxide that probably took place on mars although a terrestrial origin remains possible these results support findings from orbiter and rover based spectroscopy that opaline silica was a common product of aqueous alteration of the martian crust

lateral displacement during neogene convergence in the western and central alps although major deformation in the western alps is clearly the result of north northwest directed thrust tectonics there is evidence suggesting that orogen parallel deformation may have been important in the late tectonic history of the western alps the authors propose that this northeast trending deformation includes 1 southwest directed normal fault movement along the simplon line 2 a diffuse zone of northeast striking dextral strike slip deformation along the rhone valley in switzerland between the mont blanc and aiguilles rouges massifs and through the belledonne massif and 3 southwest directed thrusting in the embrunais ubaye and digne nappe systems of southeastern france the correlation of these three broad regions of deformation is based on similar amounts of minimum displacement consistent kinematics and timing of deformation

characterization of porosity in sulfide ore minerals a usans sans study porosity plays a key role in the formation and alteration of sulfide ore minerals yet our knowledge of the nature and formation of the residual pores is very limited herein we report the application of ultra small angle neutron scattering and small angle neutron scattering usans sans to assess the porosity in five natural sulfide minerals violarite marcasite pyrite chalcopyrite and bornite possibly formed by hydrothermal mineral replacement reactions and two synthetic sulfide minerals violarite and marcasite prepared experimentally by mimicking natural hydrothermal conditions usans sans data showed very different pore size distributions for these minerals natural violarite and marcasite tend to possess less pores in the small size range 100 nm compared with their synthetic counterparts this phenomenon is consistent with a higher degree of pore healing or diagenetic compaction experienced by the natural violarite and marcasite surprisingly nanometer sized 20 nm pores were revealed for a natural pyrite cube from la rioga spain and the sample has a pore volume fraction of 7 7 both chalcopyrite and bornite from the massive sulfide assemblage of the olympic dam deposit in roxby downs south australia were found to be porous with a similar pore volume fraction 15 but chalcopyrite tends to have a higher proportion of nanometer size pores centered at 4 nm while bornite tends to have a broader pore size distribution the specific surface area is generally low for these minerals ranging from 0 94 to 6 28 m2 g and the surfaces are generally rough as surface fractal behavior was observed for all these minerals this investigation has demonstrated that usans sans is a very useful tool for analyzing porosity in ore minerals we believe that with this quantified porosity information a deeper understanding of the complex fluid flow behavior within the porous minerals can be expected

gold refining by bismuth melts in the iron oxide dominated nico au co bi cu w deposit nwt canada the nico au co bi cu w deposit is located in the great bear magmatic zone nwt canada where numerous polymetallic iron oxide dominated mineralized systems have been recognized petrographic electron microprobe analysis empa and laser ablation inductively coupled plasma mass spectrometry la icp ms studies of host rock alteration and ore mineralogy together with sulfarsenide geothermometry have been carried out to constrain the nature of alteration and or mineralization assemblages in this deposit metasedimentary rocks of the treasure lake group host nico and are pervasively altered to an assemblage of ferrohornblende i actinolite i biotite i magnetite i orthoclase which is cut by barren veins composed of quartz ferrohornblende orthoclase calcite set 1 these alteration events are overprinted by metasomatic prograde and retrograde mineralized assemblages and both brittle and ductile deformation accompanied the metasomatism the prograde assemblage 400 c consists of cobaltite co rich loellingite and co rich arsenopyrite stage i magnetite ii ferrohornblende ii actinolite ii biotite ii pyrite and minor scheelite and orthoclase the earliest retrograde mineralization consists of arsenopyrite stages ii and iii which contains variable amounts of co together with native bi bismuthinite and au with lesser magnetite marcasite pyrite hastingsite and minor quartz the preservation of solidified native bi droplets suggests a temperature range of 270 to 400 c for precipitation of this assemblage the final stage of retrograde mineralization consists of a chalcopyrite bismuthinite hematite chlorite assemblage together with hastingsite emplectite which formed at temperatures of less than 270 c textural and trace element evidence indicates that the au and bi present within arsenides and sulfarsenides in the nico system resulted from the initial partitioning of structurally bound au and or invisible nanometer sized particles of au and bi into the prograde sulfarsenide and arsenide phases which contain up to 81 ppm au the au and bi were remobilized following retrograde alteration of those minerals to arsenopyrite ii molten bi droplets are interpreted to have scavenged au insitu resulting in the formation of the bi au inclusions observed in arsenopyrite ii the second mechanism of gold refining is explained by the occurrence of contemporaneous bi te melt and hydrothermal fluids that also could have fractionated gold during transport in solution and deposited it in fractures interstitially to earlier mineral grains and as disseminations within ca fe amphibole magnetite biotite altered rocks overall the gold upgrading at nico is consistent with the liquid bismuth collector model suggesting that this process was an important control on gold concentration in this and potentially other au bi te fe as s rich iron oxide copper gold iocg deposits

a combined electron microprobe emp and raman spectroscopic study of the alteration products in martian meteorite mil 03346 1 we examine the secondary alteration products in mil 03346 using raman spectroscopic and electron microprobe traverses discussion focuses on the single olivine in 177 supplemented with observations from 168 and 169 traverses start at the rim and progress into the interior dark brown nearly opaque laihunite fe2 fe3 2 sio4 2 is present as overgrowths and 20 50 m veins of reddish brown stilpnomelane k na ca 4 ti0 1 al2 3 fe3 35 5 mn0 8 mg9 3 si63al9 o oh 206 n h2o occur inside the olivine stilpnomelane crosscuts and postdates the laihunite veins are in sharp contact with the host olivine but lined by 5 m films of jarosite kfe3 3 so4 2 oh 6 from a later generation of alteration an interstitial laihunite also hosts stilpnomelane the most recent secondary phases are gypsum and bassanite in our x ray maps of 168 and 169 ca sulfates were not observed in x ray maps of 177 but were detected in our raman point count all sulfates are believed to be martian the groundmass of mil indicates rapid cooling from elevated temperatures with fo2 near qfm reports of laihunite synthesis by olivine oxidation at elevated temperatures 100 800 c suggest the overgrowths formed during consolidation in terrestrial rocks stilpnomelane is a product of late diagenesis to garnet grade metamorphism in mil stilpnomelane appears to be a secondary phase formed at the lower end of this stability range at conditions akin to diagenesis raman spectra indicate that the stilpnomelane jarosite and ca sulfates are hydrated the stilpnomelane contains cl and was followed by jarosite a product of acid alteration and the deposition of ca sulfates and halide salts from more neutral chloride solutions

spatial distributions of secondary minerals in the martian meteorite mil 03346 168 determined by raman spectroscopic imaging miller range mil 03346 is a nakhlite meteorite that has been extensively studied due to its unique complex secondary mineral phases and their potential implications for the hydrologic history of mars we conducted a set of raman spectroscopic and raman imaging studies of mil 03346 168 focusing on the secondary mineral phases and their spatial distributions with a goal to better understand the possible processes by which they were generated on mars this study revealed three types of calcium sulfates a solid solution of k na jarosite and two groups of hydrated species with low crystallinity hslc in the veins and or mesostasis areas of the meteorite the most abundant ca sulfate is bassanite that suggests two possible paths for its direct precipitation from a ca s h2o brine either having low water activity or with incomplete development producing bassanite with gypsum microcrystals on mars the second most abundant ca sulfate is soluble caso4 which raises a new question on the origins of this phase in the martian meteorite since caso4 readily hydrates in the laboratory but is apparently stable in atacama desert the close spatial relationship of k na jarosite solid solutions with rasvumite kfe2s3 magnetite hslc and fine grained low crystallinity alkali feldspar in mesostasis suggests a potential in situ formation of mesostasis jarosite from these fe k na s o h2o species

the oligocene alps domal unroofing and drainage development during early orogenic growth abstract the source of huge volumes of quartzofeldspathic detritus feeding oligo miocene foredeep turbidites of the apennines has long remained an unsolved geological enigma in this article we reinterpret the available sandstone petrography fission track stratigraphic and geomorphological evidence to demonstrate that the adriatic foredeep was dominantly sourced by a himalayan type tectonic aneurysm growing in the central alps since the late oligocene the lepontine dome the lepontine dome is the envelope of distinct subdomes that formed stepwise from east to west during northwestward indentation of adria beneath the axial alps focused erosion of domal culminations cut by antecedent drainage started suddenly in the late oligocene with unroofing of recently emplaced plutons and young amphibolite facies gneisses exhumation was tectonically driven and possibly accelerated by positive feedback between erosion and uplift of hot weak rocks from depth the huge volumes of resulting detritus gonfolite macigno clastic wedge were transported southward for hundreds of kilometers along the rapidly subsiding foredeep formed since middle eocene times in front of the alpine retrobelt and nascent apennine forebelt such massive sediment influx following 15 2 myr of starved foredeep sedimentation testifies to rapid formation of mountain relief in the central alps synchronous to dextral activity along the insubric fault the lepontine dome remains today as the only deeply dissected region in the alps where medium grade metamorphic rocks of the axial belt are extensively exposed the relationships between geological structures and drainage patterns still mirror those formed originally at oligocene times river headwaters have not been significantly displaced since then and their thalwegs constrain finite lateral displacement relative to the southalpine retrowedge to a maximum of 10 20 km our reconstruction has wide implications not only for a better understanding of the tertiary evolution of the alps apennines orogenic couple but also for general relationships among tectonic activity relief formation drainage development erosion distribution and long distance sediment transfer during continental collision and orogenic growth

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

miocene lateral extrusion in the inner western alps revealed by dynamic fault analysis 1 from early miocene to the present day the core parts of the western european alps experienced brittle extensional deformations mostly in a strike parallel direction here we present new data constraining the brittle deformation of the vanoise area french alps and a synthesis of 312 paleostress tensors in the whole arc of the internal western alps the data show a continuous change in the direction of extension from n065 simplon area to n s vanoise area and to nnw sse briancon area the abundance of orogen perpendicular 3 axes increases from the north to the south in the brianconnais area an extensional reactivation of the basal penninic thrust seems to be the origin of the e w to ne sw oriented 3 in light of these new data and the regional paleostress synthesis we propose a predominant orogen parallel extension in the internal zone as a whole this orogen parallel extension is related to the indentation rotation of the apulian microplate and to the opening of the ligurian sea during the lower middle miocene the locally observed orogen perpendicular extension is interpreted as an effect of the exhumation of the internal crystalline massifs the uplift of the external crystalline massifs and or the present day geodynamics postorogenic gravitational collapse some transcurrent tectonics older than the extension in the valais area and younger than the extension farther south is observed in the entire inner western alps strike slip movements are correlated with the apulian rotation and local permutation of stress axes

experimental study of the formation of chalcopyrite and bornite via the sulfidation of hematite mineral replacements with a large volume increase chalcopyrite cufes2 and bornite cu5fes4 are the most abundant cu bearing minerals in hydrothermal cu deposits forming under a wide range of conditions from moderate temperature sedimentary exhalative deposits to high temperature porphyry cu and skarn deposits we report the hydrothermal synthesis of both chalcopyrite and bornite at 200 300 c under hydrothermal conditions both minerals formed via the sulfidation of hematite in solutions containing cu i as a chloride complex and hydrosulfide at ph near the pka of h2s aq over the whole temperature range polycrystalline chalcopyrite formed first followed by bornite assuming that fe behaves conservatively the transformation of hematite to chalcopyrite involves a large increase in volume 290 the reaction proceeds both via direct replacement of the existing hematite and via overgrowth around the grain chemical exchanges between bulk solution and hematite are enabled by a network of micrometer size pores however in some cases the chalcopyrite overgrowth develops large grain sizes with few apparent pores and in these cases fluid transport may have been via a network of fractures similarly to the replacement of hematite by chalcopyrite bornite forms via the replacement of chalcopyrite the reaction has a large positive volume 230 and proceeds both via chalcopyrite replacement and via overgrowth this study shows that replacement reactions can proceed via coupled dissolution reprecipitation even where there is a large volume increase between parent and product mineral this study also provides further evidence about the controls of reaction pathways onto the final mineral assemblage in this case the host initial fluid was undersaturated with respect to fe bearing minerals upon slow release of fe at the surface of hematite a mineral assemblage of chalcocite bornite and finally chalcopyrite is expected however in practice chalcocite did not nucleate on the surface of hematite rather relatively slow nucleation of bornite enabled high concentrations of fe to build up near the dissolving hematite so that chalcopyrite high sulfidation experiments or chalcopyrite pyrite low sulfidation crystallized first

aqueous alteration of the martian meteorite northwest africa 817 probing fluid rock interaction at the nakhlite launch site the nakhlite meteorites characteristically contain iddingsite a hydrous iron magnesium silicate that formed by aqueous alteration on mars iddingsite is most abundant in northwest africa nwa 817 and alteration products in this meteorite also have the lowest deuterium hydrogen ratio of any nakhlite taken together these distinctive properties could be interpreted to show that nwa 817 was altered under different physico chemical conditions than the other nakhlites and by liquid water from a separate reservoir here this interpretation is tested through a petrographic mineralogical chemical and isotopic study of nwa 817 we find that its iddingsite occurs as olivine hosted veins of nanocrystalline smectite and fe oxyhydroxide strong similarities in the mineralogy of iddingsite between nwa 817 and other nakhlites suggest that these meteorites were altered under comparable physico chemical conditions with the fe rich composition of nwa 817 olivine grains rendering them especially susceptible to aqueous alteration analyses of nwa 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium hydrogen ratios but owing to terrestrial weathering of this meteorite the hydrogen isotopic data cannot be used with confidence to infer the origin of martian aqueous solutions nwa 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system one interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of mars and flowed through the nakhlite lava pile under the influence of gravity

application of laser raman micro analyses to earth and planetary materials abstract raman spectroscopy contributed greatly in the past 30 years or so for the advances of our understanding of earth and planetary materials and their associated geological processes after a brief introduction of the history and basic theory of raman spectroscopy the advantages and disadvantages of this spectroscopic analysis method were listed and examples were given when appropriate for its applications to the analyses of earth materials which include minerals and organic materials silicate glasses and melts aqueous solutions and gases and h2o gas systems previous works were discussed and cited this was followed by a review on applications of raman spectroscopic studies of minerals and fluids to petrogenesis and crustal evolution in which several p t diagrams were given to show metamorphic evolution of ultra high pressure units as well as a schematic cross section of the earth s outer shells showing recycling of crustal materials in different tectonic regimes for its applications to the analyses of planetary materials which include lunar samples martian meteorites and other extraterrestrial materials a brief history on the starting and development of raman spectroscopy technique was given we then discussed raman point counting and quantitative chemical analysis methods developed for obtaining quantitative information on mineral proportions and mineral chemistry in planetary surface explorations respectively finally new developments and future works which include quantitative analyses raman mapping portable raman systems and raman effects resonance raman spectroscopy cars sers and their associated applications were discussed

reaction mechanism for the replacement of calcite by dolomite and siderite implications for geochemistry microstructure and porosity evolution during hydrothermal mineralisation carbonate reactions are common in mineral deposits due to co2 rich mineralising fluids this study presents the first in depth integrated analysis of microstructure and microchemistry of fluid mediated carbonate reaction textures at hydrothermal conditions in doing so we describe the mechanisms by which carbonate phases replace one another and the implications for the evolution of geochemistry rock microstructures and porosity the sample from the 1 95 moz junction gold deposit western australia contains calcite derived from carbonation of a metamorphic amphibole plagioclase assemblage that has further altered to siderite and dolomite the calcite is porous and contains iron rich calcite blebs interpreted to have resulted from fluid mediated replacement of compositionally heterogeneous amphiboles the siderite is polycrystalline but nucleates topotactically on the calcite as a result the boundaries between adjacent grains are low angle boundaries 10 which are geometrically similar to those formed by crystal plastic deformation and recovery growth zoning within individual siderite grains shows that the low angle boundaries are growth features and not due to deformation low angle boundaries develop due to the propagation of defects at grain faces and zone boundaries and by impingement of grains that nucleated with small misorientations relative to each other during grain growth the cores of siderite grains are aligned with the twin planes in the parent calcite crystal showing that the reactant fe entered the crystal along the twin boundaries dolomite grains many of which appear to in fill space generated by the siderite replacement also show alignment of cores along the calcite twin planes suggesting that they did not grow into space but replaced the calcite where dolomite is seen directly replacing calcite it nucleates on the fe rich calcite due to the increased compatibility of the fe bearing calcite lattice relative to the pure calcite both reactions are interpreted as fluid mediated replacement reactions which use the crystallography and elemental chemistry of the calcite experiments of fluid mediated replacement reactions show that they proceed much faster than diffusion based reactions this is important when considering the rates of reactions relative to fluid flow in mineralising systems

reaction pathways and textural aspects of the replacement of anhydrite by calcite at 25 c the replacement of sulfate minerals by calcium carbonate polymorphs carbonation has important implications in a variety of geological processes occurring in earth surface environments in this paper we report the results of an experimental study of the interaction between anhydrite 100 010 and 001 surfaces and na2co3 aqueous solutions under ambient conditions carbonation progress was monitored by glancing incidence x ray diffraction gixrd and scanning electron microscopy sem we show that the reaction progresses through the dissolution of anhydrite and the simultaneous growth of calcite the growth of calcite occurs oriented on the three anhydrite cleavage surfaces and its formation is accompanied by minor vaterite the progress of the carbonation always occurs from the outer ward to the inner ward surfaces and its rate depends on the anhydrite surface considered with the 001 surface being much more reactive than the 010 and 100 surfaces the thickness of the formed carbonate layer grows linearly with time the original external shape of the anhydrite crystals and their surface details e g cleavage steps are preserved during the carbonation reaction textural characteristics of the transformed regions such as the gradation in the size of calcite crystals from 2 m in the outer region to 17 m at the calcite anhydrite interface the local preservation of calcite crystalographic orientation with respect to anhydrite and the distribution of the microporosity mainly within the carbonate layer without development of any significant gap between at the calcite anhydrite interface finally we compare these results on anhydrite carbonation with those on gypsum carbonation and can explain the differences on the basis of four parameters i the molar volume change involved in the replacement process in each case ii the lack existence of epitactic growth between parent and product phases iii the kinetics of dissolution of the different surfaces and iv the chemical composition amount of structural water of the parent phases

aqueous corrosion of olivine in the mars meteorite miller range mil 03346 during antarctic weathering implications for water on mars abstract several nakhlites clinopyroxenite meteorites from mars contain olivine phenocrysts with corrosion features identical in size shape and distribution to the smaller etch pits of well characterized weathered terrestrial olivine miller range mil 03346 is an antarctic nakhlite find recovered after long exposure to antarctic conditions the distribution of discrete olivine etch pits almost exclusively within a few hundred microns of allocation mil 03346 171 s documentably exposed surface suggests that they formed by terrestrial weathering in antarctica the small size of olivine etch pits in mil 03346 171 relative to commonly much larger etch pits in even incipiently weathered terrestrial examples suggests that the duration of its exposure to weathering conditions was short or the weathering conditions to which it was exposed did not favor olivine corrosion in the form of etch pit formation or both time scales for the formation of etch pits estimated from experimentally determined dissolution rates of olivine over a range of phs are comparable to the measured terrestrial age of the meteorite and short relative to the time available for possible similar corrosion on mars etch pits of the observed size on mil 03346 olivine phenocrysts would be relatively easy to form supraglacially under brief episodic acidic antarctic conditions but the terrestrial age of mil 03346 is long enough that its olivine might have been weathered to the observed state by englacial films of alkaline antarctic water the paucity of similar etch pits in olivine from the interior of mil 03346 suggests that olivine in this mars meteorite was exposed to even less aqueous alteration after iddingsitization during its 1 3 billion years on mars than its exterior was subjected to during its pleistocene holocene exposure to antarctic weathering conditions

interplay between erosion and tectonics in the western alps bedrock fission track analysis high resolution petrography and heavy mineral analyses of sediments are used to investigate the relationships between erosion and tectonics in the western alps along the aosta valley cross section exhumation rates based on fission track data are higher in the fault bounded western block than in the eastern block 0 4 1 5 vs 0 1 0 3 mm yr 1 erosion rates based on the analysis of bed load in the dora baltea drainage display the same pattern and have similar magnitudes in the relative sub basins 0 4 0 7 vs 0 04 0 08 mm yr 1 results highlight that climate relief and lithology are not the controlling factors of erosion in the western alps the main driving force behind erosion is instead tectonics that causes the differential upward motion of crustal blocks

fault motion and curved slickenlines a theoretical analysis slickenlines record on a fault surface the nature of relative movement of the faulted blocks an assemblage of straight slickenlines indicates linear translational fault motion curved slickenlines on the other hand may arise either due to rotational translational fault motion or due to fault motions where the translation direction changes continuously curvilinear translational fault motion the analysis of roto translational fault motion involves the ratio of relative rate of rotation vs translation whereas that of curvilinear translational fault motion involves the ratio of rate of change of translation direction to the rate of translation the analyses reveal that an assemblage of curved slickenlines where each slickenline differs in shape from the other is indicative of roto translational fault motion whereas an assemblage where the slickenlines are of similar shape is the consequence of curvilinear translational fault motion

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

experimental hydrothermal alteration of partially metamict zircon we present the results of a series of hydrothermal experiments on grains from two partially metamict zircon samples from sri lanka in the temperature range 350 to 650 c and with different solutions 2 m alcl 3 2 m cacl 2 pure h 2 o and a multi cation solution under these conditions sharply bounded reaction fronts penetrated into the zircon grains and developed complex lobate and rim structures that resemble structures found in natural zircon systems the reaction zones are characterized by a marked increase in the cathodoluminescence intensity a decrease of the back scattered electron emission and an increased degree of structural order as revealed by micro raman and infrared spectroscopy sensitive high resolution ion microprobe and electron microprobe measurements revealed that the altered areas gained solvent cations e g ca 2 ba 2 mg 2 al 3 from the solution and lost variable amounts of zr si hf the ree u th as well as radiogenic pb a comparison between dry and hydrothermal annealing trends shows that the kinetics of structural recovery including recrystallization of the amorphous phase in metamict zircon is strongly enhanced under hydrothermal conditions this finding suggests that water catalyzes structural recovery processes in metamict zircon we found that the structure of the reacted areas does not resemble that of crystalline zircon i e is still characterized by a temperature dependent degree of disorder which would not be expected if the reaction is controlled by a coupled dissolution and re precipitation process instead the alteration process can be described best by a diffusion reaction recrystallization model in this model it is postulated that the diffusion of water into the metamict structure is the driving force for moving recrystallization fronts we found that the rate and the extent of solid state recrystallization of the amorphous phase is an important factor in determining the mobility of trace elements this interpretation is indicated by the observation that trace elements including u and th were preferentially lost during the reaction with a fluid at low temperatures where recrystallization of the amorphous material was slow or not activated at all the observed chemical alteration patterns are believed to reflect a competition between the kinetics of long range diffusion and ion exchange and the kinetics of the short range diffusion necessary for the recrystallization process

strain partitioning in the axial nw alps since the oligocene 1 this work analyzes the postmetamorphic evolution of the northwestern alps thanks to a multiscale field geology study integrated by fission track analysis it illustrates how the fission track method constraining throws along major faults and age of mesoscale deformation provides interpretation keys to detangle complex structural data sets results are discussed within the framework of the alps apennines knot and give new insights on strain partitioning within transpressional orogenic belts the axial nw alps acted since the late oligocene as an orogen scale shear zone accommodating in the aosta valley dextral strike slip coeval with forward propagation of external thrusts within this transcurrent belt right lateral deformation was partitioned between the fast exhuming western block and the already unroofed eastern block these blocks show contrasting structural characters the former is cut by first order longitudinal structures bounding major tectonostratigraphic units the latter is fragmented by complex patterns of lower order faults interpreted as subsidiary shears the onset of mesoscale extension widespread in the eastern block is diachronous across the belt and migrated through time toward the european foreland transition from syncollisional shortening to orogen scale transcurrence observed in the nw alps corresponds to a regional strain field variation documented in the mid oligocene all around the alps apennines knot which is possibly related to a change of the adria trajectory relative to europe since the late oligocene deformation associated with oblique plate convergence was partitioned between strike slip in the axial belt and thrusting in external areas most of the shortening was accommodated in the helvetic chains 102 km deformation was limited elsewhere to an order of 101 km

neogene lateral extension during convergence in the central alps evidence from interrelated faulting and backfolding around the simplonpass switzerland abstract the simplon fault zone occurs at the western end of the lepontine metamorphic dome in the central alps and represents a major low angle 25 dip normal fault associated with wsw ene directed lateral extension movement began in the early miocene and continued until at least 3 ma accumulating a total vertical throw of around 10 km corresponding to 24 km displacement parallel to the fault this displacement is partitioned between a broad zone of ductile mylonites in the footwall and a more discrete cataclastic detachment fault the simplon line in the central region simplon village to zwischbergen some 3 km of the total vertical displacement is accommodated by the discrete cataclastic zone due to the higher exposed structural level the importance of the cataclastic component increases towards the northwest in the northern steep belt around the simplonpass retrograde greenschist facies mylonite formation and younger cataclastic faulting associated with lateral extension occurred contemporaneously with sse vergent large scale backfolding representing nnw sse shortening and crustal thickening the combined effect was an overall shortening across the orogen accommodated by an extension parallel to the orogen allowing lateral escape of continental material normal faulting and the resultant lateral escape was not just superficial it extended to depths of at least 15 km and probably to depths exceeding 25 km the overall geometry and kinematics of the simplon fault zone and in particular the interplay between folding and faulting is very similar to that described from the metamorphic core complexes and detachment faults of the cordillera of the southwestern usa within the central alps extension was associated with rapid exhumation of the lepontine metamorphic dome as evidenced by very rapid cooling rates determined from mineral ages in the footwall similar to the cenozoic tectonics of the himalayas and tibet orogen parallel extension in the mountain belt may have been promoted by an overall reduction in the horizontal compressive stress in this direction more limited extension of the same age and orientation is known from a large area of the european foreland greater extension in the mountain belt compared with the foreland was accommodated by major strike slip transfer fault systems and was linked to coeval overthrusting of the lowlands towards the southwest in the external southwestern alps of haute provence france coeval folding and orogen parallel extension such as at the simplonpass were developed in a dextral transpressive regime due to oblique wnw ese convergence across the alps during the neogene

fayalite oxidation processes in obsidian cliffs rhyolite flow oregon this study investigates the oxidation of fayalite fe22 sio4 that is present in lithophysae from a rhyolite flow obsidian cliffs oregon textural chemical and structural analyses of the successive oxidation zones are used to constrain 1 the oxidation processes of olivine and 2 the role of temperature chemical diffusion and meteoric infiltration petrologic analyses and thermodynamic modeling show that the rhyolite flow emplaced at 800 950 c fayalite bearing lithophysae formed only in the core of the lava flow variations in the gas composition inside the lithophysae induced the oxidation of fayalite to a laihunite 1 m zone fe12 fe23 1 sio4 2 this zone is made of nano lamellae of amorphous silica sio2 and laihunite 3 m fe2 1 6fe3 1 6 0 8 sio4 2 hematite fe2o3 it probably formed by a nucleation and growth process in the fayalite fractures and defects and at fayalite crystal edges the laihunite 1 m zone then oxidized into an oxyfayalite zone with the composition fe2 0 52fe3 2 32 1 16 sio4 2 this second oxidation zone is made of lamellae of amorphous silica sio2 and hematite fe2o3 with a possible small amount of ferrosilite fe2 sio3 a third and outer zone composed exclusively of hematite is also present the successive oxidation zones suggest that there may be a mineral in the olivine group with higher fe3 content than laihunite 1 m the transformation of laihunite 1 m to this oxyfayalite phase could occur by a reaction such as formula 1 this would imply that fe3 can also be incorporated in the m1 site of olivine 1 embed mml math 1 gif

arsenic in iron disulfides in a brown coal from the north bohemian basin czech republic arsenic in the coal studied is not bound to coal macerals it is concentrated in the inorganic part of coal specifically in the iron sulfides this paper reports the results of five crystal structure refinements that include natural 2 and synthetic 3 sulfides pyrite 3 and marcasite 2 powder 3 and single crystal 2 intensities used in the refinements were obtained by diffraction of x rays 4 and synchrotron radiation 1 the refined occupancy factors of sulfur and the unit cell parameters favor the possibility that as substitutes for s in both disulfides

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

a comparison of the iddingsite alteration products in two terrestrial basalts and the allan hills 77005 martian meteorite using raman spectroscopy and electron microprobe analyses 1 we document the secondary mineral assemblages in two occurrences of terrestrial iddingsite lunar crater nevada lc and mauna kea hawaii mk and compare these with the iddingsite in allan hills alha 77005 short raman spectroscopic traverses across olivine alteration fronts provide information about changes in mineralogy with alteration data from the raman traverses are combined with electron microprobe emp traverses at the same locations which provide information regarding element mobility and confirm mineral identifications made by raman spectroscopy this information is used with petrographic observations to argue for the martian origin of the iddingsite and jarosite infer the sequence of alteration and deliberate on the conditions and settings of alteration raman spectra indicate the presence of different iron oxides oxyhydroxides in each sample goethite in lc maghemite in mk and akaganeite in alha and the terrestrial samples show different element mobility trends loss of mgo and sio2 retention of feo than alha loss of mgo and feo influx of sio2 whose trends reflect the deposition of jarosite altered olivine occur throughout the lc samples but only in the exteriors of the mk samples the lc and mk alteration products formed by surface alteration but alha 77005 is a lherzolite and the olivine hosting the iddingsite are enclosed by orthopyroxene appear to be restricted to the light lithology suggesting that it formed at depth during magma consolidation the alha iddingsite is an example of deuteric alteration reaction with fluids that separated from the magma as crystallization progressed towards completion

present day geodynamics in the bend of the western and central alps as constrained by earthquake analysis summary the contrasted tectonics of the western central alps is examined using a synthesis of 389 reliable focal mechanisms the present day strain regime is mapped and interpolated for the entire alpine belt based on a newly developed method of regionalization the most striking feature is a continuous area of extension which closely follows the large scale topographic crest line of the alpine arc thrusting is observed locally limited to areas near the border of the alpine chain a majority of earthquakes within the alps and its forelands are in strike slip mode stress inversion methods have been applied to homogenous subsets of focal plane mechanisms in order to map regional variations in stress orientation the stress state is confirmed to be orogen perpendicular both for 3 in the inner extensional zones and 1 in the outer transcurrent transpressional zones extensional areas are well correlated with the part of the belt which presents the thickest crust as shown by the comparison with the bouguer anomaly and the average topography of the belt in the northwestern swiss alps extension is also correlated with currently uplifting zones these observations and our strain stress analyses support a geodynamic model for the western alps in which the current activity is mostly a result of gravitational body forces earthquakes do not provide any direct evidence for ongoing convergence in the alpine system but a relationship with ongoing activity of complex block rotations of the apulian microplate cannot be ruled out

replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 c an experimental study of reaction textures and mechanisms the transformation of pyrrhotite to fe disulfide pyrite and or marcasite under hydrothermal conditions was studied experimentally by probing the effects of temperature up to 220 c vapor saturated pressures s ii concentrations ph and availability of oxygen on reaction progress and on the resulting textures the pyrrhotite to fe disulfide reaction proceeded by a dissolution reprecipitation mechanism under all conditions marcasite and pyrite formed under both oxic and anaerobic conditions which is inconsistent with the traditionally assumed polysulfide route for fes2 formation oxidants required for polysulfide formation the nature of the products was controlled by the level of supersaturation of the solution with respect to fe disulfide minerals marcasite formed preferentially at low ph or s ii deficient solutions saturation index 1000 different textures were obtained for the replacement of pyrrhotite by either pyrite or marcasite pyrite formation proceeded by direct replacement of pyrrhotite and simultaneously by overgrowth from solution the pyrite crystals were 10 m in size and randomly oriented in comparison marcasite crystals were 1 m in size and no significant overgrowth was observed at ph21 c 3 the marcasite nanocrystals showed the well known crystallographic relationship with pyrrhotite but at ph21 c 3 96 the marcasite crystallites were randomly oriented these experimental results confirm that the preservation of the crystallographic orientation is not a distinguishing feature between dissolution reprecipitation and solid state reactions the different textures among pyrite and marcasite reflect the dominance of crystal growth pyrite vs nucleation marcasite as a precipitation mechanism

sulfide replacement processes revealed by textural and la icp ms trace element analyses example from the early mineralization stages at cerro de pasco peru the large cerro de pasco cordilleran base metal deposit in central peru is the result of three successive mineralizing stages comprising both low and high sulfidation mineral associations a several pyrrhotite pipes grading outward to sphalerite and galena replacement bodies b a massive funnel shaped pyrite quartz replacement orebody and c e w trending cu ag au zn pb enargite pyrite veins and well zoned zn pb bi ag cu carbonate replacement orebodies this superposition of hydrothermal events leads to complex replacement textures and crosscutting relationships a detailed study of the textures and mineral composition of the up to 15 m wide replacement front existing between the pyrrhotite pipes and the pyrite quartz body allows for clarification of the relative chronology of the hydrothermal events the results show that in contrast to previous interpretations the emplacement of the pyrrhotite pipes and their zn pb mineralized rims precedes that of the pyrite quartz body the replacement textures affecting pyrrhotite and arsenopyrite and the nature of the newly formed minerals have been used as a qualitative way to track the evolution of fs2 fo2 and ph of the mineralizing fluids two steps of pyrrhotite replacement have been recorded the first one takes place under moderate acidity and relatively reduced to moderately oxidized conditions and is marked by replacement of pyrrhotite by euhedral nonporous pyrite the second step occurs under more acidic and oxidized conditions and is characterized by replacement of pyrrhotite by porous marcasite and replacement of arsenopyrite by pyrite subsequently marcasite is partly replaced by fine grained euhedral nonporous pyrite la icp ms trace element analyses of the replaced pyrrhotite and arsenopyrite and of the newly formed marcasite and pyrite support dissolution reprecipitation as the main mechanism for replacement positive correlations between some of the elements e g pb sb pb ag are indicative of the possible presence of nanoscale solid inclusions as main carriers for those elements however coupled substitutions and incorporation of some of the elements at a ppm level into the pyrite and marcasite structures cannot be excluded the obtained as sb pb and bi values in pyrite are systematically higher than published data of pyrite in epithermal and porphyry systems nature and trace element content of the newly formed minerals yield information on the physicochemical conditions during their precipitation the initial trace element content of replaced minerals and the subsequently dissolved neighboring phases the results show that the metal concentration of the fluid is locally influenced by the composition of the dissolved minerals this study leads to a simpler interpretation of the fluid evolution than previously proposed with a progressive increase of fs2 fo2 and ph as a result of decreasing wall rock buffering during the three successive mineralizing stages at cerro de pasco

extracting olivine fo fa compositions from raman spectral peak positions the dominant feature of the olivine raman spectrum is a doublet that occurs in the spectral region of 815 825 cm 1 db1 and 838 857 cm 1 db2 these features arise from coupled symmetric and asymmetric stretching vibrational modes of the constituent sio4 tetrahedra the frequencies of both peaks show monotonic shifts following cation substitution between forsterite and fayalite we present a calibration for extracting olivine fo contents fo mg mg fe molar ratio fo0 100 from the peak positions of this doublet permitting estimates of chemical composition from raman spectra acquired in the laboratory or field as well as providing information on crystal structure distinction of polymorphs eight samples spanning the compositional range from forsterite to fayalite were used to develop the calibration equations for the db1 and db2 peaks individually and together the data indicate that the db1 peak is more reliable for calculating the compositions of fe rich olivine but that the db2 peak is better for magnesian compositions the two peak calibration overcomes the limitations of the single peak calibrations and is capable of calculating olivine compositions to within 10 fo units

counterclockwise rotation of the western alps since the oligocene new insights from paleomagnetic data 1 a paleomagnetic study of penninic units in the southern part of the alpine arc has been carried out more than 200 samples 23 sites were collected in brianconnais ammonitico rosso limestones of the high ubaye valley and the ligurian alps a characteristic component of magnetization of reverse polarity was isolated on most of the sites this component does not pass the fold test and is interpreted as a tertiary overprint related to alpine metamorphism mean directions in geographic coordinates are d 121 i 52 95 11 and d 72 i 48 95 15 for the ubaye and the liguria localities respectively indicating large counterclockwise rotations about vertical axis of 68 and 117 relative to stable europe these rotations in agreement with a previous study conducted in the briancon area together with other paleomagnetic data from the western alps show that the internal alps suffered a large but nonhomogeneous counterclockwise rotation since the oligocene the rotations are in agreement with the combination of earlier separately proposed processes the rotation of the adriatic plate accounts for about 25 of rotation remaining rotation and southward gradient would be related to left lateral shear accommodating the displacement between adria and europe at the southern border of the western alps furthermore the southward extrusion of the western alps south of the simplon fault zone may account for up to 10 of rotation rotations appear therefore as a major process accommodating deformation in the western alps since the oligocene

an experimental study of the mechanism of the replacement of magnetite by pyrite up to 300 c abstract we present the results of an experimental study into the sulfidation of magnetite to form pyrite marcasite under hydrothermal conditions 90 300 c vapor saturated pressures a process associated with gold deposition in a number of ore deposits the formation of pyrite marcasite was studied as a function of reaction time temperature ph sulfide concentration solid weight to fluid volume ratio and geometric surface area of magnetite in polytetrafluoroethylene lined autoclaves ptfe and a titanium and stainless steel flow through cell marcasite was formed only at ph 21 c 21 c 1 11 while pyrite predominated at ph 21 c 2 and formed even under basic conditions up to ph 21 c 12 13 marcasite formation was favored at higher temperatures fine grained pyrrhotite formed in the initial stage of the reaction together with pyrite in some experiments with large surface area of magnetite grain size 120 c 0 96 4 42 and that rate of the transformation increased from 120 to 190 c scanning electron microscope sem imaging revealed that micro pores 0 1 5 m scale existed at the reaction front between the parent magnetite and the product pyrite and that the pyrite and or marcasite were euhedral at ph 21 c 155 c 4 42 the experimental results are in good agreement with sulfide phase assemblage and textures reported from sulfidized banded iron formations pyrite marcasite and pyrrhotite have been found to exist or co exist in different sulfidized banded iron formations and the microtextures show no evidence of sub m scale pseudomorphism of magnetite by pyrite

multi stage thrusting at the penninic front in the western alps between mont blanc and pelvoux massifs the different segments of the tectonic boundary between external european and internal penninic units in the western alps the so called penninic front pf formed at different times and according to different kinematic scenarios during a first episode eocene the pf corresponds to a transpressive suture zone between penninic and european units north to nnw trending stretching lineations found along internal nappe contacts within the penninic units are related to this episode this subduction zone was sealed by the priabonian flysch of the aiguilles d arves a detrital trench formation that formed during the final stages of subduction during a second episode starting in mid oligocene times the pf imaged along the ecors crop profile acted as a wnw directed thrust this thrust the roselend thrust rt only partially coincides with the pf south of moutiers the rt propagates into the dauphinois units carrying the former eocene pf including the priabonian flysch passively in its hangingwall south of the pelvoux massif the rt finds its continuation along the brianconnais front an out of sequence thrust behind the embrunais ubaye nappes on a larger scale our findings indicate oblique sinistral collision within the future western alps during the eocene followed by westward indentation of the adriatic block

paleostresses associated with faults of large offset abstract in order to test empirically the limitations of paleostress analysis we used etchecopar s computer program to compute the orientations and relative magnitudes of paleostress principal values in two southern appalachian u s a thrust zones from minor fault and slickenside attitudes in both thrust zones faults are closely spaced many faults have offsets whose magnitudes exceed the distance to adjacent faults of comparable size and deformation was strongly non coaxial while even in the less deformed thrust zone bulk strains due to fault movement have axial ratios as high as 10 1 nearly 75 of the fault slickenside pairs in each thrust zone conform with paleostress tensors that indicate 1 sequential transport parallel compression transport parallel extension and extension oblique to transport and 2 low resolved shear stresses on the thrusts finite strains measured in one thrust zone share a principal plane with the first two tensors and the inclinations of the paleostress and finite strain principal directions in that plane are consistent with thrust parallel shearing relative magnitudes of paleostress and strain principal values do not correlate well moreover the locations and inferred origins of fault slickenside pairs inconsistent with paleostress tensors suggest that stresses in rocks between faults were not as is assumed in paleostress analyses uniform this complexity may also occur in faulted rocks where bulk strains are small paleostress tensors from rocks with large bulk strains may be viable but they must be interpreted cautiously

raman spectroscopy of fe ti cr oxides case study martian meteorite eeta79001 raman spectral features of chromite ulvospinel magnetite ilmenite hematite and some of their solid solutions are presented although most fe ti cr oxides produce relatively weak raman signals compared to oxyanionic minerals sufficient information can be extracted from their spectra to identify the end member mineral phases as well as some information about compositional variations in solid solutions correlations between raman spectral features and mineral chemistry are used to interpret the raman data of fe ti cr oxides found during raman point count measurements on rock chips of martian meteorite eeta79001 as an analog to mars on surface planetary investigations in general ulvospinel magnetite and chromite end members are readily distinguished by their raman spectral patterns as are ilmenite and hematite in the low signal to noise s n spectra generally obtained from the raman point count procedure the position and shape of the strongest peak of fe ti cr oxides in the region 660 680 cm 1 a1g mode is the most useful for discriminating fe3 ti cr al substitutions in the magnetite ulvospinel ulvospinel chromite and chromite spinel series but minor peaks in the range 300 600 cm 1 also assist in discrimination these spectral features are useful for investigating the variability among fe ti cr al oxide solid solutions in natural samples in eeta79001 a martian basaltic meteorite most of the oxide grains as measured with the electron microprobe are ulvospinel chromian ulvospinel and chromite but ilmenite titanian chromite and titanomagnetite are also observed the fe ti cr oxides identified by raman point count include end member ilmenite low al chromite spinel solid solutions ulvospinel magnetite solid solutions and more complex chromite spinel ulvospinel magnetite solid solutions the latter exhibit a wide range of main peak positions and broadened peak widths that may reflect structural disorder as well one raman spectrum suggests end member magnetite and one spectrum from a different rock chip appears to be that of non terrestrial hematite reflecting local oxidizing alteration which has not been observed previously in this meteorite these results show that analyses done in an automated mode on the surface of an unprepared martian rock sample can provide useful constraints on the fe ti cr oxide mineralogy present and on compositional variations within those minerals including an indication of oxygen fugacity

the mechanism and kinetics of the transformation from marcasite to pyrite in situ and ex situ experiments and geological implications despite the natural abundance of pyrite and marcasite and their intergrowth and a wealth of information they can provide on the physical chemical conditions of mineral deposits a complete mechanistic and kinetic study on the phase transformation from the thermodynamically metastable polymorph marcasite to the stable polymorph pyrite is yet to be made this limits the application of marcasite as an indicator mineral for low temperature geological environments here we report results from in situ synchrotron powder x ray diffraction and ex situ anneal quench experiments at 400 540 c demonstrating that the mechanism and kinetics of this transformation depend not only on temperature but also on particle size the presence of water vapor and the presence of pyrite inclusions in marcasite under dry conditions the transformation is limited by surface nucleation and occurs via epitaxial nucleation of pyrite on marcasite with 100 pyrite 101 marcasite and 001 pyrite 010 marcasite in contrast in the presence of water vapor there is little crystallographic orientation relationship between the two phases the transformation is still limited by surface nucleation but modification of the surface properties by water vapor results in a different nucleation mechanism and consequently different kinetics kinetic analysis estimates a half life of 1 5 ma at 300 c for the transformation under dry conditions with small and pyrite free marcasite grains but this estimation should be used with extreme caution due to the complexity of the transformation from synchrotron x ray fluorescence elemental mapping trace elements as and pb play an insignificant role in the transformation however the presence of a fluid phase changes the behavior of pb under dry conditions randomly oriented particles of galena formed in pyrite while under water vapor conditions arrays of nano to microparticles of galena precipitated in pores this study highlights that although the natural occurrence of marcasite can indicate low temperature environments precise estimation of temperature should not be made without considering the influences from various reaction parameters

invisible gold in arsenian pyrite and arsenopyrite from a multistage archaean gold deposit sunrise dam eastern goldfields province western australia the sunrise dam gold mine 11 1 moz au is the largest deposit in the archaean laverton greenstone belt eastern goldfields province yilgarn craton western australia the deposit is characterized by multiple events of fluid flow leading to repeated alteration and mineralization next to a major crustal scale structure the au content of arsenian pyrite and arsenopyrite from four mineralizing stages d1 d3 d4a and d4b and from different structural and lithostratigraphic environments was measured using in situ laser ablation inductively coupled plasma mass spectrometry pyrite contains up to 3 067 ppm au n 224 whereas arsenopyrite contains up to 5 767 ppm n 19 gold in arsenopyrite d4a stage was coprecipitated and remained as invisible gold nanoparticles and or lattice bound during subsequent deformation events in contrast gold in pyrite is present not only as invisible gold but also as micrometer size inclusions of native gold electrum and au ag tellurides pristine d1 and d3 arsenian pyrite contains relatively low au concentrations 26 ppm the highest au concentrations occur in d4a arsenian rich pyrite that has recrystallized from d3 pyrite textures show that this recrystallization proceeded via a coupled dissolution reprecipitation process and this process may have contributed to upgrading au grades during d4a in contrast au in d4b pyrite shows grain scale redistribution of invisible gold resulting in the formation of micrometer scale inclusions of au minerals the speciation of au at sunrise dam and the exceptional size of the deposit at province scale result from multiple fluid flow and multiple au precipitating mechanisms within a single plumbing system

marcasite inversion and the petrographic determination of pyrite ancestry pyrite formed by the inversion of marcasite or by oxidative leaching of pyrrhotite can be recognized in polished sections by the following characteristics compiled from synthetic pyrite after marcasite and natural samples of pyrite after marcasite and after pyrrhotite pyrite formed by inversion from marcasite is characterized by approximately 2 modal percent pore space no by products filling the pores optical anisotropy dark green to dark red anhedral shape and polycrystalline daughter pyrite domains in two orientations relative to the marcasite parent crystal pyrite or marcasite formed by oxidative dissolution as opposed to leaching of pyrrhotite exhibits up to 32 modal percent pore space gaps between the pyrite and parent pyrrhotite pores and gaps filled with by product siderite magnetite hisingerite or other fe bearing phase optically isotropic character for pyrite development of crystal faces and random orientation relative to the parent pyrrhotite marcasite formed by oxidative leaching of fe as opposed to complete dissolution from pyrrhotite also exhibits a large amount of pore space but has preferred orientation relative to the parent pyrrhotite pyrite after marcasite may be used as an indicator of ph 5 and t ca 240 degrees c during deposition of the parent marcasite marcasite precipitated following dissolution of pyrrhotite is also indicative of those conditions during alteration marcasite formed by oxidative leaching of pyrrhotite cannot be used as evidence of those conditions however

alpine thermal and structural evolution of the highest external crystalline massif the mont blanc 1 the alpine structural evolution of the mont blanc highest point of the alps 4810 m and of the surrounding area has been reexamined the mont blanc and the aiguilles rouges external crystalline massifs are windows of variscan basement within the penninic and helvetic nappes new structural 40ar 39ar and fission track data combined with a compilation of earlier p t estimates and geochronological data give constraints on the amount and timing of the mont blanc and aiguilles rouges massifs exhumation alpine exhumation of the aiguilles rouges was limited to the thickness of the overlying nappes 10 km while rocks now outcropping in the mont blanc have been exhumed from 15 to 20 km depth uplift of the two massifs started 22 myr ago probably above an incipient thrust the alpine sole thrust at 12 ma the ne sw trending mont blanc shear zone mbsz initiated it is a major steep reverse fault with a dextral component whose existence has been overlooked by most authors that brings the mont blanc above the aiguilles rouges total vertical throw on the mbsz is estimated to be between 4 and 8 km fission track data suggest that relative motion between the aiguilles rouges and the mont blanc stopped 4 myr ago since that time uplift of the mont blanc has mostly taken place along the mont blanc back thrust a steep north dipping fault bounding the southern flank of the range the european roof is located where the back thrust intersects the mbsz uplift of the mont blanc and aiguilles rouges occurred toward the end of motion on the helvetic basal decollement hbd at the base of the helvetic nappes but is coeval with the jura thin skinned belt northwestward thrusting and uplift of the external crystalline massifs above the alpine sole thrust deformed the overlying helvetic nappes and formed a backstop inducing the formation of the jura arc in that part of the external alps nw se shortening with minor dextral ne sw motions appears to have been continuous from 22 ma until at least 4 ma but may be still active today a sequential history of the alpine structural evolution of the units now outcropping nw of the pennine thrust is proposed

current strain regime in the western alps from continuous global positioning system measurements 1996 2001 four to six years of continuous measurements at 10 permanent global positioning system sites in the western alps show horizontal residual velocities of 2 mm yr with respect to stable europe uncertainties range from 0 3 to 1 4 mm yr these velocities and the associated strain rate field indicate that the central part of the range is currently dominated by east west extension whereas the southern part shows north south to northwest southeast compression the geodetic and seismotectonic data are consistent with a model where strain is essentially controlled by the counterclockwise rotation of the adriatic microplate with respect to eurasia this rotation together with the arcuate shape of the contact between the adriatic microplate and the alps induces dextral shear kinematic boundary conditions across the western alps with an additional divergence component in their central part and in switzerland and a convergence component in their southern part

precollisional multistage exhumation of subducted continental crust the sesia zone western alps 1 the sesia zone within the tertiary arc of the western alps is a relic of the subducted part of the adriatic continental margin along the se border of the tethyan ocean the sesia zone comprises three basement nappes which individuated during late cretaceous 65 80 ma subduction to different depths at high pressure hp blueschist eclogite facies conditions peak pressures of 1 0 1 2 1 0 1 5 and 1 5 2 0 gpa the thrusts bounding these nappes developed where the crust was previously thinned during jurassic rifting crustal scale shear zones partly overprinted these early thrusts and exhumed coherent slices of crust containing hp rocks initial exhumation of the internal part of the accreted margin involved thrusting d1 and transpressional shearing d2 along a subvertical e w trending mylonitic shear zone under retrograde blueschist to greenschist facies conditions this exhumation was nearly isothermal to a depth of about 25 km where the basement nappes were juxtaposed subsequent exhumation of these nappes to a common depth of about 15 20 km occurred in the footwall of a greenschist facies top se extensional shear zone d3 preserved in some of the highest mountain peaks of the sesia zone new rb sr mineral ages constrain d2 to have occurred at about 60 65 ma and d3 at about 45 55 ma thus top se extensional exhumation was broadly coeval with eocene se directed subduction of the liguro piemont oceanic lithosphere beneath the adriatic margin slow cooling and erosional denudation of the sesia zone from 45 to 30 ma occurred in the hanging wall of the gressoney extensional shear zone d4 which itself contributed to the exhumation of eocene hp and ultra hp oceanic rocks in its footwall by 30 ma hp rocks of the sesia zone were intruded by shallow granitic plutons which were eroded and redeposited within volcanoclastic sediments oligo miocene insubric backfolding and thrusting d5 only exhumed northeastern parts of the sesia zone where hp metamorphism is absent or was overprinted by tertiary temperature dominated metamorphism most exhumation of continental hp rocks in the sesia zone therefore preceded tertiary alpine collision and coincided with late cretaceous to early tertiary subduction of the adriatic and tethyan lithosphere the transition from d2 to d3 in the sesia zone is interpreted to mark a change from high stress oblique se directed subduction and accretion of the distal adriatic continental margin to nw retreating low stress subduction of the liguro piemont oceanic lithosphere

partitioning of arsenic between hydrothermal fluid and pyrite during experimental siderite replacement abstract arsenian pyrite is the major host mineral of gold in carlin type gold deposit ctgd and forms during the interaction of h2s bearing hydrothermal fluids with fe bearing carbonates e g siderite ankerite fe rich dolomite in the wall rock experimental replacement of siderite at hydrothermal conditions i e 200 c psat was used to study the parameters that control the formation of ctgd pyrite i e ph time ah2s and the partitioning of as between the hydrothermal fluid and newly formed pyrite hydrothermal pyrite formed via replacement of siderite in experiments mainly occurs as two types 1 porous massive pyrite at alkaline ph conditions or 2 clusters of dense euhedral to anhedral pyrite grains at slightly acidic conditions ph concentration of as in newly formed pyrite depends strongly on the as concentration of the hydrothermal fluid used in the experiment calculated partition coefficients vary between 300 and 1700 with lowest d values at high as concentrations of the fluid in the studied system as 1 substitutes for s 2 as indicated by the correlation of high as with low s concentrations experimental findings agree well with previous studies in natural ctgd on as substitution and the partitioning of as between ore stage pyrite and hydrothermal fluids trapped as fluid inclusions the newly constrained partition coefficients for as help to explain the large heterogeneity in natural ctgd pyrite compositions which is caused by changes in the fluid composition due to the strong partitioning of as into the forming pyrite

multi stage hydrothermal processes at the laozuoshan gold deposit in ne china insights from textures and compositions of sulfide assemblages abstract the laozuoshan gold deposit is a large gold deposit which experienced the early hydrothermal mineralization and the late hydrothermal mineralization in jiamusi massif northeast china the jiamusi massif hosts numerous gold deposits that are commonly considered as products of the metamorphic hydrothermal process during two oceanic subductions episodes in this study we report detailed textures observations identify the sulfides phases by the laser raman spectroscopy and obtain in situ composition data with electron probe micro analysis to further understand the formation and metasomatism of multi stage sulfides deposition in the laozuoshan gold deposit the paragenetic relationship between pyrite and marcasite at the nanoscale was also clarified by focused ion beam scanning electron microscopy and transmission electron microscopy according to the observed textural relationships among ore and gangue minerals the early hydrothermal mineralization period can be divided into three stages stage i to stage iii and the late hydrothermal mineralization period into four stages stage iv to stage vii the sulfides are mainly pyrrhotite po 1 in stage i with minor chalcopyrite arsenopyrite and pyrite the ag rich averaging 15 44 wt electrum au 1 is hosted in arsenopyrite which is also rich in cobalt averaging 2 69 wt pyrite py 2 is the main sulfide in stage ii with minor chalcedony and calcite the mineral stability relationships in both stage i and stage ii confirm that there was an increase in sulfur and oxygen fugacities and a decrease in temperature the sulfides are mainly arsenopyrite apy 2 in stage iii with minor native golds and tellurbismuth the native golds au 2 average 8 02 wt silver arsenopyrite geothermometers indicate precipitation temperatures between 420 and 390 c for stage iii the sulfur and oxygen fugacities of the ore related fluids were below the pyrite pyrrhotite buffer during stage iii revealing a reduced fluids system in the late hydrothermal mineralization period multiple magmatic activities caused multi stage hydrothermal fluids events in stage vi the pyrrhotite replaced by marcasite and pyrite through the dissolution reprecipitation mechanism indicating the increase in ph and oxygen fugacity of the fluids and alteration from weakly acidic and weakly reduced conditions to neutral and weakly oxidizing conditions the mineralogical and compositional evolution of the sulfides in the laozuoshan gold deposit constrain the physicochemical conditions of multi stage ore forming fluids which is of considerable significance in understanding the metamorphic hydrothermal superimposed gold bearing fluids evolved in the jiamusi massif

miocene to present differential exhumation in the western alps insights from fission track thermochronology 1 analysis of cooling age patterns yielded by low temperature thermochronometers provides key information about the role played by tectonic discontinuities during the late stages of exhumation of metamorphic belts in the western alps fission track data published so far are heterogeneously scattered and concentrated in few structural domains preventing analyses at the scale of the whole belt the new apatite fission track data reported in this work obtained with the external detector method as well as the population method in very low u content samples fill this gap they constrain the postmetamorphic evolution of the western alps along two transects from the foreland to the retroforeland unraveling the effective role played by some major faults during the exhumation of the belt at shallow crustal levels a clear regional pattern characterized by decreasing ages moving from the axial sector to the european external sector of the belt and by an along strike gradient with increasing ages from north to south has been unraveled evident breaks in this age pattern have been detected in correspondence of faults that are near parallel to the trend of the belt pointing to the occurrence of active tectonics during and after exhumation the most apparent breaks have been observed in the axial sector of the belt where the postmetamorphic deformation would have been negligible according to classic tectonic models faults located in the axial sector split the belt into two major blocks eastern and western since the miocene the western block experienced higher exhumation rates than the eastern one such differential exhumation was accommodated in the northern portion of the belt thanks to reverse motion along the internal houiller fault which occurred in a convergent transcurrent framework to the south it was accommodated instead by normal reactivation of the brianconnais front and by activity of the longitudinal fault system which occurred in a divergent transcurrent framework the tectonic activity affecting the axial sector of the belt in a context of regional dextral strike slip is coeval with the forward propagation of the external thrusts and of similar magnitude we suggest that the contrasting kinematic regimes i e convergent versus divergent transcurrence observed in the western alps moving along strike were responsible of the increasing exhumation rates toward the north revealed in both blocks by the along strike age gradient the higher exhumation rates recognized northward would be related to an increasing importance of crustal shortening that promoted erosion during the late stages of exhumation of the belt

dating deformation using rb sr in white mica greenschist facies deformation ages from the entrelor shear zone italian alps ages of deformation have been obtained by rb sr analysis of white micas whose microstructural and chemical characteristics indicate that they crystallized or recrystallized during shear fabric formation since white micas commonly define deformation fabrics in medium grade metamorphic rocks these ages can be directly related to structural geometries with regional context this direct method contrasts with estimates of midcrustal deformation ages derived from cooling histories because it does not rely on assumptions about the thermal structure of the crust it does require that the dated minerals attained isotopic equilibrium with the dominant sr reservoir at temperatures lower than the closure temperature this resetting was apparently achieved during dynamic recrystallization of white micas in greenschist facies metasediments and metagranitoid units in the western alps the results suggest that the sr isotopic composition of the new mica is buffered by the coexisting high sr phases calcite feldspar or epidote via the grain boundary network high strain rocks from the entrelor shear zone system of the western alps have yielded indistinguishable white mica rb sr ages along 30 km of individual and kinematically linked shear zones the age of the back thrusting event is constrained at 34 1ma the age yielded by the younger generation of synkinematically crystallized white micas this event was short lived involving at least 20 km of shortening in 1 m y or less an earlier variably overprinted component dating from 38 to 37 ma has been identified in the mica fabric but its kinematic significance is uncertain this method of dating strain fabrics offers a powerful tool for tectonic studies since isotopic resetting can be directly linked to structural geometries microstructural textures and pt conditions it allows testing of kinematic models in orogens and can provide important information on the rates of geological processes in the crust

structural analysis of the subbrianconnais and valais units in the area of moutiers savoy western alps paleogeographic and tectonic consequences valais and subbrianconnais units of the western alps of savoie underwent a common structural evolution postdating peak pressure conditions associated with high pressure metamorphism of internal parts of the valais units the first two phases due to roughly north south directed shortening are interpreted to be related to a nne ssw striking corridor of sinistral transpression between the internal western alps and the european foreland both phases led to nappe formation isoclinal folding and north south elongation only the third phase of deformation is related to wnw directed orogen perpendicular shortening thus far regarded as the predominant thrusting direction in the western alps late post 5 ma normal faulting evidenced by fission track dating reactivated the houiller front in the north and the penninic front in the south kinematics of movement observed along the present day houiller front and penninic front change from north to south in the north the houiller front indicates post d3 normal faulting while the penninic front preserved wnw directed thrusting d3 in the south the houiller front preserves syn d2 north directed thrusting whereas the penninic front is partly reactivated by post d3 normal faulting our observations clearly favor tectonic reasons for the disappearance of the valais units south of moutiers in present day map view

the aosta ranzola extensional fault system and oligocene present evolution of the austroalpine penninic wedge in the northwestern alps post nappe brittle structures across the austroalpine penninic wedge are representative of two principal deformation stages the former d1 developed during the late oligocene the latter d2 from the miocene to the present major d1 features are the e w aosta ranzola half graben and the ne sw ospizio sottile subvertical normal fault system oligocene extension was also characterized by hydrothermal activity and intrusion of calc alkaline to ultra potassic dikes from the miocene onwards d2 the ospizio sottile system was re activated as a se sinistral boundary of the pennine graian alps block of nappes bodily moving away from the simplon detachment to the sw inside the escaping block a number of d2 slightly diverging sublatitudinal splays aosta piccolo san bernardo system was generated as well as a regular set of nw trending normal faults from the simplon to the gran paradiso massif instead the aosta ranzola system was poorly reworked in that time more generally the short lived oligocene extension d1 was associated to slab break off of lower plate wedge rebound rapid uplift and thermal perturbation from the early miocene onwards the oligocene extension was replaced by renewed compression allowing the vertical extrusion of the lepontine dome and lateral escape of the overlying pennine graian alps block

jarosites and their application in hydrometallurgy the alunite supergroup consists of more than 40 minerals with the general formula dg 3 t o4 2 oh h2o 6 wherein d represents cations with a coordination number greater or equal to 9 and g and t represent sites with octahedral and tetrahedral coordination respectively smith et al 1998 the supergroup is commonly subdivided into various groups but the simplest primary subdivision is on the basis of the g cations for all of the minerals in the supergroup the dominant g cation is trivalent most of the minerals have g represented by fe3 or al3 but exceptions are the rare minerals gallobeudantite in which g is ga3 and springcreekite in which g is v3 table 1 thus the primary grouping adopted here is on whether formula fe3 exceeds or is subordinate to al3 the hierarchical sequence in mineralogy seems to be variable but here the decreasing sequence is given as supergroup family group and subgroup minerals with fe3 al3 are referred to as belonging to the jarosite family and those with a13 fe3 are allocated to the alunite family view this table table 1 minerals of the alunite supergroup subdivision of the alunite and jarosite families has also been variable scott 1987 for example used seven groups novak et al 1994 used six gaines et al 1997 used four and mandarino 1999 used three the arbitrary decision here is to use three groups which differ from those of mandarino 1999 but which in general indicate whether sulfate phosphate or arsenate predominates in the t o4 tetrahedra the three groups are the alunite group in which t o4 is dominated by so4 the crandallite group in which po4 is

are the alps collapsing abstract orogenic collapse is a process that transfers gravitational potential energy from regions of high potential energy to regions of lower potential energy this transfer is classically considered to be accomplished by extension in the orogenic core and by synchronous shortening in foreland regions of the orogen not all extensional features in collisional mountain belts need however reflect orogenic collapse normal faulting thrust faulting and strike slip faulting are all active in different parts of the alps today and reflect complex local responses to ongoing europe adria convergence the western alps is the only area today where extension and shortening radial to orogen trend occur synchronously and where orogenic collapse may be an important process elsewhere in the alps normal faults are oriented at a high angle to orogen trend and were primarily active in oligocene and miocene time most present day activity in the central and eastern alps is on strike slip faults that are accommodati

water and gas chemistry at lake kivu drc geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure 1 waters and dissolved gases collected along vertical profiles in the five basins main kabuno bay kalehe ishungu and bukavu forming the 485 m deep lake kivu democratic republic of the congo were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry the measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by 1 different contribution from long circulating fluid system containing magmatic co2 responsible of the huge co2 ch4 rich reservoir hosted within the deep lake water 2 spatial variations of the biomass distribution and or speciation and 3 solutes from water rock interactions the kabuno bay basin is characterized by the highest rate of magmatic fluid input accordingly this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the nyiragongo and nyamulagira volcanoes located a few kilometers north of the lake

petrology of martian meteorite northwest africa 998 nakhlite northwest africa nwa 998 is an augite rich cumulate igneous rock with mineral compositions and oxygen isotopic composition consistent with an origin on mars this 456 gram partially fusion crusted meteorite consists of by volume 75 augite core composition wo39en39fs22 9 olivine fo35 7 plagioclase ab61an35 as anhedra among augite and olivine 3 5 low calcium pyroxenes pigeonite and orthopyroxene replacing or forming overgrowths on olivine and augite 1 titanomagnetite and other phases including potassium feldspar apatite pyrrhotite chalcopyrite ilmenite and fine grained mesostasis material minor secondary alteration materials include iddingsite associated with olivine probably martian calcite crack fillings and iron oxide hydroxide staining both probably terrestrial shock effects are limited to minor cataclasis and twinning in augite in comparison to other nakhlites nwa 998 contains more low calcium pyroxenes and its plagioclase crystals are blockier the large size of the intercumulus feldspars and the chemical homogeneity of the olivine imply relatively slow cooling and chemical equilibration in the late and post igneous history of this specimen and mineral thermometers give subsolidus temperatures near 730 c oxidation state was near that of the qfm buffer from about qfm 2 in earliest crystallization to near qfm in late crystallization and to about qfm 1 5 in some magmatic inclusions the replacement or overgrowth of olivine by pigeonite and orthopyroxene with or without titanomagnetite and the marginal replacement of augite by pigeonite are interpreted to result from late stage reactions with residual melts consistent with experimental phase equilibrium relationships apatite is concentrated in planar zones separating apatite free domains which suggests that residual magma rich in p and ree was concentrated in planar fracture zones and possibly migrated through them loss of late magma through these zones is consistent with the low bulk ree content of nwa 998 compared with the calculated ree content of its parent magma

a halite siderite anhydrite chlorapatite assemblage in nakhla mineralogical evidence for evaporites on mars we report the results of a study of a halite siderite anhydrite chlorapatite assemblage in the shergotty nakhla chassigny snc martian meteorite nakhla these minerals are found associated with each other in interstitial areas with halite often being adjacent to or enclosing siderite we suggest the halite and other minerals are martian in origin because 1 the conditions of fall preclude significant amounts of terrestrial contamination or weathering having taken place 2 textures indicate that the minerals within this assemblage crystallized at the same stage as some silicate and oxide minerals within the nakhla parent and 3 the association with siderite which previous studies have shown has c and o isotopic compositions incompatible with an origin on the earth siderite has the range of compositions caco3 0 1 5 7 mgco3 2 0 40 9 feco3 23 2 87 0 mnco3 1 0 39 9 mol there are two compositional groupings high mnco3 30 mol and low mnco3 high feco3 with a gap identified between the two this may be a miscibility gap or alternatively the two compositional groupings may mark separate generations of carbonate we have not found any textural evidence for the latter explanation but acceptance of the presence of a miscibility gap would require independent work on fe mn carbonates to verify its existence trace element abundances have been determined by ion microprobe analysis on three siderite and one anhydrite grains siderite has light rare earth elements 2 2 7 3 c1 greater than heavy rare earth elements 0 32 0 79 c1 without ce or eu anomalies and the anhydrite has a similar pattern these abundances reflect the source composition rather than partitioning or complexing controls they are not typical of hydrothermal signatures which generally do not have such smooth ree abundance patterns the nature of the mineral assemblage suggests that its source rocks on mars were evaporites these may be common in the craters and flood plains of the martian southern highlands two models are suggested in this paper to explain the incorporation of evaporitic material into the nakhla igneous parent it may have happened as a low temperature process 200 c by crystallisation from an aqueous fluid an origin at low temperature is compatible with the available experimental data on siderite stability alternatively we suggest evaporitic material may have been incorporated into the nakhla parent while melt was still present and crystallized 800 c the latter model can more readily explain the trace element abundances and also the siderite textures that imply intergrowth with residual interstitial melt both high and low temperature models are consistent with the presence of evaporite sediments on mars

fe3 distribution in oxidized olivine a synchrotron micro xanes study synchrotron micro xanes spectroscopy smx is used to examine the amount and distribution of fe super 2 and fe super 3 in five samples of fayalite previously studied by mossbauer spectroscopy rockport fayalite is homogeneous and the fe in it is completely reduced olivine from qianan is almost completely oxidized and probably contains finely intergrown silica laihunite and hematite with hematite predominating pantelleria olivine has an oxidized rim around a reduced core suggesting either a post crystallization reaction with fayalite and oxygen going to laihunite and hematite or a change in prevailing oxidation during growth the texture of olivine from the mourne mountains suggests exsolution from a fayalite laihunite solid solution based on the substitution of three fe super 3 atoms for two fe super 2 and one vacancy that was stable at high temperature laihunite from the type locality lai he village shows 1 3 mu m mottling between light and dark areas in backscatter images but these areas cannot correspond to pure fayalite and laihunite exsolution because the bulk fe super 3 sigma fe of such a combination would not correspond to the smx value of 67 fe super 3 rather the texture observed in backscatter is interpreted to represent alternating areas of magnetite rich and laihunite rich compositions with a similar i e 67 fe super 3 sigma fe extent of oxidation