late cenozoic transpressional ductile deformation north of the nazca south america antarctica triple junction abstract the southern andes plate boundary zone records a protracted history of bulk transpressional deformation during the cenozoic which has been causally related to either oblique subduction or ridge collision however few structural and chronological studies of regional deformation are available to support one hypothesis or the other we address along and across strike variations in the nature and timing of plate boundary deformation to better understand the cenozoic tectonics of the southern andes two east west structural transects were mapped at puyuhuapi and aysen immediately north of the nazca south america antarctica triple junction at puyuhuapi 44 s north south striking high angle contractional and strike slip ductile shear zones developed from plutons coexist with moderately dipping dextral oblique shear zones in the wallrocks in aysen 45 46 top to the southwest oblique thrusting predominates to the west of the cenozoic magmatic arc whereas dextral strike slip shear zones develop within it new 40ar 39ar data from mylonites and undeformed rocks from the two transects suggest that dextral strike slip oblique slip and contractional deformation occurred at nearly the same time but within different structural domains along and across the orogen similar ages were obtained on both high strain pelitic schists with dextral strike slip kinematics 4 4 0 3 ma laser on muscovite biotite aggregates aysen transect 45 s and on mylonitic plutonic rocks with contractional deformation 3 8 0 2 to 4 2 0 2 ma fine grained recrystallized biotite puyuhuapi transect oblique slip dextral reverse kinematics of uncertain age is documented at the canal costa shear zone 45 s and at the queulat shear zone at 44 s published dates for the undeformed protholiths suggest both shear zones are likely late miocene or pliocene coeval with contractional and strike slip shear zones farther north coeval strike slip oblique slip and contractional deformation on ductile shear zones of the southern andes suggest different degrees of along and across strike deformation partitioning of bulk transpressional deformation the long term dextral transpressional regime appears to be driven by oblique subduction the short term deformation is in turn controlled by ridge collision from 6 ma to present day this is indicated by most deformation ages and by a southward increase in the contractional component of deformation oblique slip to contractional shear zones at both western and eastern margins of the miocene belt of the patagonian batholith define a large scale pop up structure by which deeper levels of the crust have been differentially exhumed since the pliocene at a rate in excess of 1 7 mm year

geochemistry of thermal waters in the southern volcanic zone chile implications for structural controls on geothermal fluid composition abstract thermal waters in the southern volcanic zone svz of chile between 36 41 s were studied using major and selected trace element relationships to characterize their geochemistry formation mechanisms and to explore the influence of regional structural controls on fluid composition three sets of waters were identified based on physicochemical characteristics i nacl waters ii acid sulfate waters and iii bicarbonate hco3 waters nacl waters are the most abundant type in the studied region and their chemistry is controlled by significant water rock interaction they are characterized by an alkaline ph 7 2 9 3 generally lower temperatures avg 55 c and relatively high concentrations of cl na b as li and cs acid sulfate waters are typically associated with volcanoes and have a strong magmatic volcanic component due to the absorption of magmatic vapors they are acidic ph 892 ppm in the region and are similar in temperature 6 2 to nacl waters they have elevated concentrations of most cations ca k na mg ba sr as a result of intense shallow cation leaching due to the absorption of co2 rich volcanic vapors on the peripheries of geothermal systems the thermal waters were also characterized according to their spatial relation with the dominant fault systems of the region the nne striking intra arc liquine ofqui fault system lofs and the wnw striking andean transverse faults atf the inherent differences in fault nature between these fault systems constitutes the primary structural control influencing geothermal fluid development in the svz the chemistry of waters spatially associated with the lofs as a whole is defined by high vertical permeability networks and lack magmatic reservoir development therefore these waters tend to have higher cl b ratios and strong correlations between trace alkali metals and cl due to rapid efficient upflow pathways in contrast waters spatially associated with the atf have lower cl b ratios and show no correlation between trace alkali metals and cl due to degassing magma chambers and decreased vertical permeability the relationship between water type and structural domain in cl b ratios and trace metal behavior provides evidence that fault geometry and kinematics exert a fundamental control on geothermal fluid development in the svz of chile

a numerical method for determining the state of stress using focal mechanisms of earthquake populations application to tibetan teleseisms and microseismicity of southern peru the numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms this method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane the proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes this enables one to test the data homogeneity furthermore this restricts the space where the principal stress axes have to be searched then for each principal stress reference whose location is constrained by above confined zones the r value chosen equal to 2 1 3 1 is computed which fits the slip vector on each nodal plane this permits one to select a set of preferred seismic fault planes from a set of auxiliary planes finally a state of stress is computed from the preferred seismic fault plane set using the non linear simplex method already applied to fault populations this algorithm is constructed so as to avoid two major difficulties misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions this calculation does not take into account possible changes of the strike and dip of the nodal planes however we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress tibetan teleseisms and southern peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions this suggests that major seismic events may give a good evaluation of the regional mean state of stress focal mechanisms of the small events are also modelled by a mean stress deviator but this differs significantly from the regional state of stress in southern peru deduced from quaternary faulting this may be due to imprecise location of the small events however some movements are strongly different from those predicted by the computed mean stress deviator this suggests that small fault kinematics surely depend on the regional state of stress but that local effects may control the small deformations

evaluating isotopic equilibrium among sulfide mineral pairs in archean ore deposits case study from the kidd creek vms deposit ontario canada recent developments in the measurement of 34s and 33s in sulfide minerals provide a new framework to evaluate isotopic equilibrium among sulfide minerals and a new tool to investigate mineralizing processes or sources of sulfur in ore forming systems isotopic equilibrium requires that values of 34s and 33s are highly correlated between mineral pairs and that deviations quantified as 33s from a reference mass dependent fractionation are the same for both minerals within experimental error in this contribution we apply this framework for the first time to natural samples and evaluate isotopic equilibrium among sulfide minerals from the archean kidd creek volcanogenic massive sulfide deposit in ontario canada two of eight sulfide mineral pairs showed clear isotopic disequilibrium in agreement with interpreted paragenetic relationships six other pairs have isotopic compositions that are consistent with equilibrium we discuss the implications of these results for the interpretation of mineral paragenesis and sulfur isotope geothermometry at kidd creek this technique offers new possibilities for evaluating sulfur isotope systematics in archean 2 45 ga ore deposits in which the range of 34s values is small but non zero values of 33s are common

contractional tectonics and magma paths in volcanoes abstract this study aims to contribute a possible explanation for magma migration within volcanoes located in contractional tectonic settings based on field data and physically scaled experiments the data demonstrate the occurrence of large stratovolcanoes in areas of coeval reverse faulting in spite of the widely accepted idea that volcanism can develop only in extensional transcurrent tectonic settings the experiments simulate the propagation of deformation from substrate reverse faults with different attitudes and locations into volcanoes the substrate fault splits into two main shear zones within the volcano a shallow dipping one with reverse motion propagates towards the lower volcano flank and a steeper dipping one with normal motion propagates upwards in plan view the reverse fault zone is arcuate and convex outwards whereas the normal fault zone is rectilinear structural field surveys at volcanoes located in contractional settings show similar features the plio quaternary trohunco and los cardos centinela volcanic complexes argentina lie above plio quaternary reverse faults the late pleistocene holocene el reventador volcano ecuador is also located in a coeval contractional tectonic belt these volcanoes show curvilinear reverse faults along one flank and rectilinear extensional fracture zones across the crater area consistent with the experiments these data consistently suggest that magma migrates along the substrate reverse fault and is channelled along the normal fault zone across the volcano

primary origin of marginal ni cu pge mineralization in layered intrusions δ33s evidence from the platreef bushveld south africa the margins of layered igneous intrusions can host ore deposits of nickel copper and platinum group elements pges these marginal deposits are characterized by a complex geologic history which obscures direct evidence for the mineralization process mass independent fractionation of sulfur isotopes is a distinguishing feature of archean sedimentary rocks and reflects processes operating solely in the archean surface environment as a result mass independent fractionation of sulfur isotopes is a chemically conservative tracer that indicates the involvement of crustal sulfur in marginal ni cu pge deposits in this study we use mass independent fractionation of sulfur isotopes to evaluate the sulfur budget of the platreef the marginal pge bearing horizon of the northern limb of the bushveld complex south africa our multiple sulfur isotope measurements demonstrate that crustal sulfur in the platreef originated from a restricted stratigraphic horizon the duitschland formation in the platreef footwall as this signature is spread out over the 100 km strike length of the platreef it does not reflect sulfur inputs from the local footwall nonlocal crustal sulfur isotope anomalies are unexpected given the high metal tenors in the platreef these features can be reconciled if a preformed ni cu pge rich sulfide melt assimilated sulfur in a staging chamber bounded completely by the duitschland formation and then was emplaced into the platreef such a model is supported by long standing observations of lithologic geochemical and stratigraphic similarities between the merensky reef and the platreef as well as by recent suggestions that the northern limb represents an escape structure for the rest of the bushveld complex crustal sulfur assimilation is often thought to initiate the ore forming process by producing an immiscible sulfide melt that can collect base metals and pges in the platreef however crustal sulfur assimilation apparently diluted a preexisting pge rich sulfide melt instead

the multiple sulfur isotope architecture of the golden mile and mount charlotte deposits western australia the golden mile and mount charlotte deposits in the kalgoorlie terrane western australia display three main mineralization styles fimiston comprised of interconnected shear zones associated with ankerite pyrite hematite magnetite gold telluride alteration oroya made up of breccia bodies with v muscovite ankerite pyrite pyrrhotite gold telluride alteration and mount charlotte which consists of vein arrays with symmetrical ankerite sericite albite pyrite pyrrhotite gold alteration pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes the 34s 33s and 36s analyses on pyrite grains from the different mineralization styles including oxidized and reduced sulfide oxide assemblages reveal 1 a large variation in 34s from 12 6 to 23 5 and 2 a previously unrecognized occurrence of anomalous 33s and 36s signatures from 1 0 to 1 1 and from 2 3 to 0 9 respectively it is argued that the mineralizing fluids that formed the golden mile and mount charlotte deposits record mixing among three components mantle sulfur oxidized seawater sulfur e g so4 and reduced elemental sulfur e g s8 petrographic evidence in conjunction with 33s and 36s data suggest that mif s was acquired during the deposition of shales and basalts present in the kalgoorlie terrane and later mixed with mantle derived sulfur during the mineralization events the negative 34s values that predominate in fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore forming process as reflected by the presence of hematite pyrite magnetite gold assemblages conversely the positive 34s values that dominate in the mt charlotte and oroya mineralization styles reflect a reducing environment as reflected by the presence of pyrite pyrrhotite gold assemblages

a revised classification scheme of pyrite in the witwatersrand basin and application to placer gold deposits abstract pyrite is the most abundant ore mineral in gold bearing quartz pebble conglomerates qpcs of the witwatersrand basin and similar archaean sedimentary units much of the pyrite in archaean conglomerates is detrital in origin implying that it survived weathering transport and reworking under anoxic conditions detrital pyrite is generally found together with authigenic pyrite formed in situ as a result of syn to post depositional processes as pyrite is frequently associated with gold mineralization many authors have developed different pyrite classification schemes in order to better understand the nature and origin of the mineralization although the different classifications cannot always be easily compared as they are largely based on inferred pyrite genesis we propose a revised entirely descriptive classification scheme for detrital and authigenic pyrite in archaean qpcs the scheme was created in order to provide a consistent framework for the petrographic description of pyrite in clastic sedimentary rocks detrital pyrite is subdivided into massive inclusion bearing and coarsely crystalline types authigenic pyrite includes euhedral overgrowth infill aggregate and pseudomorphic types we evaluate the methods used in pyrite classification propose formation pathways for detrital and authigenic pyrites and apply the classification scheme to some well known occurrences of detrital pyrite bearing conglomerates

morphometric analysis of the submarine arc volcano monowai tofua kermadec arc to decipher tectono magmatic interactions morphometric analysis of multibeam bathymetry and backscatter data is applied to monowai a submarine volcano of the active tofua kermadec arc to map and document the structure and evolution of the volcanic centre low rates of erosion and sedimentation and pervasive tectonic and magmatic processes allow quantification through detailed structural analysis and measurement of deformation the slope aspect curvature rugosity and hydrology flow tools of arcgis provide a robust structural interpretation and the development of a model of monowai evolution a nested caldera structure with a volume of 31 km3 and a stratovolcano of 18 km3 dominate the magmatic constructs the outer caldera is elongate along 125 and the inner caldera along 135 numerous parasitic cones and fissure ridges are also observed oriented at 039 and 041 respectively northeast trending faults with a regional average strike of 031 are widespread within this part of the backarc forming a nascent rift graben to the west of the monowai caldera complex the distribution of throw varies spatially reaching a maximum total along rift of 320 m and across rift of 120 m with greater throw values measured in the west elongation directions of the two nested calderas are near perpendicular to the trends of faults and fissure ridges the inner caldera is more orthogonal to the magmatic constructs fissure ridges and aligned vent cones and the outer caldera is approximately orthogonal to the regional fault fabric suggesting a strong interaction between magmatic and tectonic processes and the directions of the horizontal principal stress we present a detailed morphometric analysis of these relationships and the data are used to interpret the spatial and temporal evolution of the tectono magmatic system at monowai and classify the type of rifting as transtensional similar analysis is possible elsewhere in the kermadec backarc and within other regions of submarine volcanism

stress tensor analysis of the 1998 1999 tectonic swarm of northern quito related to the volcanic swarm of guagua pichincha volcano ecuador the phreatic activity and the subsequent dacitic dome growth in 1998 1999 at guagua pichincha volcano ecuador were associated with two seismic swarms one located in the northern part of quito population 1 500 000 and another one just below the active volcano about 15 20 km sw from the first one quito swarm tectonic events have high frequencies from 1 to 10 15 hz we registered more than 3200 events among which 2354 events of 1 4 m l 4 2 between june 1998 and december 1999 at the 2 and 17 km depth the volcanic events below the guagua pichincha caldera have high from 1 to 10 15 hz and low less than 3 hz frequencies approximately 130 000 events were registered between september 1998 and december 1999 at the 2 4 and 3 5 km depth here we study the stress tensors of these two swarms deduced from the polarities of p first motions and compare them to the regional stress tensor deduced from cmt harvard focal mechanisms the quito swarm stress tensor is relatively close to the regional stress tensor the 1 axis was oriented n117 e close to the n102 e direction of the plate motion found by the gps measurement and 3 is nearly vertical the difference may be due to the action of the closely active guagua pichincha volcano the guagua pichincha stress tensor is very different from the regional tectonic one the 1 axis of the volcano is oriented n214 e almost perpendicular to the 1 of the swarm of quito and 3 is almost horizontal even if these two tensors are different they can be explained in a more general tectonic scheme the almost horizontal direction of 3 just below the volcano is compatible with an extensional horizontal direction that may be expected in the shallow extrados part of a compressional region and consistent with an opening of the top of the guagua pichincha volcano the movement of the fluids magma gas and or groundwater produced by the closely active guagua pichincha volcano seems to have an influence in the acceleration of the generation of seismic events

sources of sulphur for the proterozoic kiggavik uranium deposit nunavut canada the thelon basin is temporally and spatially related to the athabasca basin in saskatchewan canada which hosts the highest grade unconformity related uranium deposits in the world several uraniu

relationship between tectonism and volcanism along the great sumatran fault zone deduced by spot image analyses abstract satellite images provide evidence for numerous stepovers pull apart grabens and volcanic structures along the nw trending right lateral great sumatran fault zone high resolution spot images permit us to analyze the relationship between volcanic and tectonic structures this analysis reveals that releasing stepovers and pull aparts are ephemeral structures along the great sumatran fault zone and that the geometry of the strike slip fault evolves permanently through time the interpretative structural maps obtained from spot image analysis reveal that the formation of huge peculiarly shaped volcanic calderas has occurred in large releasing stepover fault zones and that the bounding faults of rectangular pull apart basins are analogous to the circular ring faults of calderas in particular detailed study of the segments at the southernmost 150 km long termination of the great sumatran fault zone from northwest of ranau lake to semangka bay allows us to describe the development of the ranau collapse caldera this caldera is located within a pull apart basin bounded by a stepover its peculiar rectangular shape and its relatively large size about 200 km 2 are controlled by the evolution of the extinct ranau releasing stepover similarly the toba elliptical caldera one of the largest volcanic caldera in the world is elongated parallel to the present trace of the great sumatran fault and appears to be related to a releasing stepover associated with a wide pull apart basin that is not active at present

physicochemical models of effusive rhyolitic eruptions constrained with insar and dem data a case study of the 2011 2012 cordon caulle eruption abstract the 9 month long 2011 2012 eruption of cordon caulle southern andes chile is the best instrumentally recorded rhyolitic eruption to date and the first time that the effusion of a rhyolitic flow has been observed in detail we use interferometric synthetic aperture radar insar with time lapse digital elevation models dems and numerical models to study the dynamics of coupled magma reservoir deflation and lava effusion insar recorded 2 2 2 5 m of subsidence after the first three days of the eruption which can be modeled using a spheroidal magma reservoir at a depth of 5 km 20 km long and with a pressure drop of 20 30 mpa the source is elongated in the nw se direction and its large dimensions imply a large plumbing system active throughout the eruption and spanning neighboring volcanoes with a slight change in the geometry halfway through the effusive phase tandem x and pleiades dems record the extrusion of both the rhyolitic lava flow and the intrusion of a shallow laccolith around the eruptive vent after the third day of the eruption with a total volume of 1 45 km3 dre the laccolith was emplaced during the first month of the eruption during both the explosive and effusive stages of the eruption both the reservoir pressure drop and the extruded volume time series follow quasi exponential trends and can be explained by a model that couples the reservoir pressure decrease time and pressure dependent variations in the magma properties inside of the reservoir and conduit flow this model predicts both the temporal evolution and amplitude of both time series during the effusive phase and a magma compressibility of 10 10 pa 1 half the reported compressibility of the magma of the sub plinian explosive phase further we estimate that the reservoir contained 1 3 wt dissolved h2o at the onset of lava effusion with no exsolved co2 and h2o in the reservoir throughout the effusive phase this implies that the magma was significantly degassed after the explosive phase the remaining volatiles in the magma after the explosive stage might have caused magma fragmentation consistent with the hybrid explosive effusive style observed during the waning of the eruption

transient shallow reservoirs beneath small eruptive centres constraints from mg fe interdiffusion in olivine abstract small eruptive centres commonly have more primitive lavas than those associated with stratovolcanoes an observation that has been taken to indicate a short magma residence in the crust relative to those reservoirs below stratovolcanoes the caburgua cones of the andean southern volcanic zone from a basaltic small eruptive centre where this can be tested here we use melts simulations and the available thermobarometry data to determine the conditions of olivine crystal rim formation and the mg fe diffusion modelling to determine the magma residence times of those rims in the crust results yield timescales varying from a few days to dozens of days and if freezing is to be avoided can only be explained by some form of storage or slow transport through at least one shallow magma body the longest durations of magma residence seen in the olivine rim zones are up to 471 days these timescales are shorter than those estimated decadal from the nearby more differentiated and well established stratovolcano villarrica which has a dominantly basaltic andesite composition for caburgua cones we propose the existence of a transient reservoir in contrast to a long lived reservoir such as that inferred beneath the adjacent villarrica stratovolcano

sulfur isotope and trace element data from ore sulfides in the noranda district abitibi canada implications for volcanogenic massive sulfide deposit genesis we examine models for volcanogenic massive sulfide vms mineralization in the 2 7 ga noranda camp abitibi subprovince superior province canada using a combination of multiple sulfur isotope and trace element data from ore sulfide minerals the noranda camp is a well preserved vms deposit rich area that is thought to represent a collapsed volcanic caldera due to its economic value the camp has been studied extensively providing a robust geological framework within which to assess the new data presented in this study we explore previously proposed controls on mineralization within the noranda camp and in particular the exceptional au rich horne and quemont deposits we present multiple sulfur isotope and trace element compositional data for sulfide separates representing 25 different vms deposits and showings within the noranda camp multiple sulfur isotope data for this study have 34sv cdt values of between 1 9 and 2 5 and 33sv cdt values of between 0 59 and 0 03 we interpret the negative 33s values to be due to a contribution of sulfur that originated as seawater sulfate to form the ore sulfides of the noranda camp vms deposits the contribution of seawater sulfate increased with the collapse and subsequent evolution of the noranda caldera an inference supported by select trace and major element analyses in particular higher concentrations of se occur in samples with 33s values closer to 0 as well as lower fe zn ratios in sphalerite suggesting lower pressures and temperatures of formation we also report a relationship between average au grade and 33s values within au rich vms deposits of the noranda camp whereby higher gold grades are associated with near zero 33s values from this we infer a dominance of igneous sulfur in the gold rich deposits either leached from the volcanic pile and or directly degassed from an associated intrusion

morpho structural evolution of the cordon caulle geothermal region southern volcanic zone chile insights from gravity and 40ar 39ar dating the cordon caulle geothermal region 40 5 s is a 13 km 6 km nw se elongate volcano tectonic depression hosting numerous monogenetic volcanic centers fumaroles and hot springs most of which occur spatially associated with the edges of the depression volcanism started at approximately 0 3 ma with dominantly mafic effusions and expressed ultimately in post glacial and historic dacite rhyolite eruptions 1921 1922 and 1960 three ne trending gravimetric profiles were carried out across the depression of cordon caulle yielding a residual negative anomaly with the greatest amplitude 20 mgal at the center of the depression a 2d gravity model given by a 490 m thick shallow body with a density contrast 650 kg m3 interpreted as a shallow package of dacite rhyolite lavas and tephra was found to match the residual anomaly a dense rock equivalent volume of felsic material on the order of 28 km3 25 of the total output of cordon caulle is derived from this thickness previous workers explain the origin of felsic rocks at cordon caulle in terms of the orientation of the borders of cordon caulle relative to the maximum stress direction 1 i e ne trending prevailing during the quaternary according to which nw trending domains were compressional favoring stagnation storage and differentiation of magmas the dominantly monogenetic style of volcanism the plateau like morphology and the negative bouguer anomaly on the contrary are interpreted as an indication of extensional tectonics intra arc extension is proposed to be related to coseismic or postseismic stress relaxation accompanying major thrust events such as the great 1960 chilean earthquake which is consistent at cordon caulle with the direction of propagation of dikes of the 1960 eruption i e coseismic extension and present day subsidence inferred from insar data i e postseismic extension prior to the quaternary 8 2 1 6 ma nearly east west compression prevailed at the intra arc zone a 5 44 0 04 ma old granodiorite intrusion bracketed by two sub parallel branches of the regional margin parallel liquine ofqui fault zone lofz in a prominent pop up structure 15 km to the east of cordon caulle accounts for reverse reactivation of the lofz and rapid fault related exhumation of basement rocks 1 mm year we argue that under compression reverse reactivation of the lofz was facilitated by the combined effect of cyclic increase in fluid pressure induced by magmatic hydrothermal input and removal of lithostatic load induced by glacial erosion 1 5 mm year in the vicinity of cordon caulle

contrasting nature of deformation along an intra arc shear zone the liquine ofqui fault zone southern chilean andes abstract the liquine ofquifault zone lofz cuts the patagonian batholith and the modern volcanic arc of southern chile for ca 1000 km the rock fabric along three transects of the lofz combined with new and published geochronological data suggest marked differences in the nature and timing of deformation along strike in the liquine transect 39 s a 1 km wide northeast striking subvertical mylonitic zone shows north plunging stretching lineations this mylonitic zone has been juxtaposed by high angle reverse faulting against a nearly undeformed miocene granitoid metamorphic assemblages and microstructures in the mylonites indicate greenschist facies conditions and sinistral reverse displacement deformation pre dates a 100 2 ma undeformed porphyritic dike hornblende 40ar 39ar mean age in the reloncavi transect 41 42 s deformation in cretaceous and miocene plutons is predominantly brittle kinematic analysis of two fault populations yields compressional and dextral strike slip stress regimes interpreted as late miocene in age in the hornopiren transect 42 43 s a 4 km wide mylonitic zone developed in plutons and wallrocks shows subhorizontal stretching lineations and dextral displacement a single fault population overprinting the mylonites supports a dextral strike slip stress regime available u pb k ar and 40ar 39ar dates on deformed cenozoic plutons and wallrock range from 9 to 13 ma on hornblende and from 6 to 3 ma on biotite microstructures and mineral assemblages indicate that the youngest ductile fabrics in the plutons formed at greenschist facies similar to the biotite ar closure temperature subparallel magmatic and solid state fabrics combined with geochronology suggest that dextral displacement was continuous during emplacement and cooling of the plutons dextral oblique subduction of the nazca plate beneath western south america has driven long term intra arc deformation at the southern andes plate boundary zone ridge collision in turn has favored dextral displacement at the leading edge of the continent since the pliocene

multiple sulfur isotopes reveal a magmatic origin for the platreef platinum group element deposit bushveld complex south africa the platreef ore horizon of the bushveld complex south africa is the third largest platinum group element ore deposit in the world but the origin of its ore remains enigmatic a complex contact relationship between the igneous and footwall rocks of the bushveld complex coupled with evidence for widespread late stage hydrothermal processing obscures the original mineralization history of the platreef we constrain the parental magmatic origin of the platreef by exploiting multiple sulfur isotope contrasts across bushveld complex contact zones in order to see through the effects of postmineralization hydrothermal activity we report s isotope measurements made on samples collected along two profi les through the platreef into underlying metapelitic and metacarbonate footwall rocks in both profi les igneous rocks far from the contact have low 33 s values average 33 s 0 15 whereas metasedimentary rocks far from the contact have high 33 s values 33 s to 5 04 with a smoothly varying profi le between the two end members the midpoint in both isotope profi les is displaced into the footwall defi ning a classic advective dispersive tracer geometry this geometry is not present in the associated 34 s values the displacement of the 33 s front suggests fl uid transport and advection of s into the country rocks this was accompanied by back diffusion of the s isotope tracer into the platreef the platreef magma was apparently s saturated prior to emplacement and counterintuitively lost s during the formation of the present platreef ore horizon

pyrite paragenesis and multiple sulfur isotope distribution in late archean and early paleoproterozoic hamersley basin sediments abstract the sulfur isotope record in late archean and early paleoproterozoic rocks is of considerable importance because it provides evidence for changes in early earth atmospheric oxygen levels and potentially constrains the origin and relative impact of various microbial metabolisms during the transition from an anoxic to oxic atmosphere mass independently fractionated mif sulfur isotopes reveal late archean and early paleoproterozoic sulfur sources in different pyrite morphologies in western australia s hamersley basin multiple sulfur isotope values in late archean pyrite vary according to morphology fine grained pyrite has positive sulfur mif indicating a reduced elemental sulfur source whereas pyrite nodules have negative sulfur mif potentially derived from soluble sulfate via microbial sulfate reduction the hamersley basin 34 s 33 s record suggests that the extent of oxygenation of the surface ocean fluctuated through the late archean from at least 2 6 ga more than 150 million yr before the great oxidation event in the early paleoproterozoic there is less distinction between pyrite morphologies with respect to sulfur isotope fractionation and pyrite from the brockman iron formation trends toward modern sulfur isotope values an important exception to this is the strong negative mif recorded in layer parallel pyrite in paleoproterozoic carbonate facies iron formation this may suggest that deeper water hydrothermal environments remained anoxic while shallower water environments became more oxidised by the early paleoproterozoic the results of the current study indicate that sulfide paragenesis is highly significant when investigating archean and early paleoproterozoic multiple sulfur isotope compositions and sulfur sources

sulfur isotope and metal variations in sulfides in the bif hosted orogenic cuiaba gold deposit brazil implications for the hydrothermal fluid evolution abstract textural chemical and multiple sulfur isotope analyses of sulfides from the archean world class cuiaba orogenic au deposit quadrilatero ferrifero district brazil were conducted to track distinct trace element signatures from syngenetic to epigenetic hydrothermal pyrite types in different host units and to deduce the nature and source of the mineralizing fluids gold mineralization in cuiaba is hosted in greenschist facies volcanic and sedimentary host rocks belonging to the archean rio das velhas supergroup especially in association with quartz veins and sulfide minerals the bif hosted fonte grande sul orebody is controlled by quartz veins and disseminated gold bearing pyrite pyrrhotite and arsenopyrite in the wall rocks five pyrite types are classified based on textural relations as spongy syngenetic py1 porous early py2 smooth main py3 and smooth isolated and overgrown late stage py4 and py5 types variably present in metamorphosed carbonaceous pelites bif and andesite besides pyrite pyrrhotite and arsenopyrite are also defined according to textural and paragenetic differences and they display significant trace element contents trace element abundance maps and la icp ms analyses display trace element incorporations in py1 present only in carbonaceous pelite py2 and py3 in all host rocks and py4 and py5 only in bif py1 yields high as co ni pb and ag concentrations whereas py2 formed by agglomeration of py1 maintains high trace element concentrations with slightly less of those elements trace element incorporation in py3 is similar to py1 in carbonaceous pelite early stage py2 and main stage py3 in bif and andesite have increased co and ni but have less au and as late stage py4 is characterized by lower trace element concentrations whereas py5 is further enriched in as bi co ni and pb the hydrothermal alteration is divided into early main and late stage which correlate to the sulfide hydrothermal evolution the study shows that carbonaceous pelite is pre enriched in co ni and pb whereas certain elements like ag au bi and as are only hydrothermally concentrated either during the early main or late stage in bif and andesite this geochemical pattern supports a syngenetic versus hydrothermal origin of distinct elements including some trace elements now in the ore zones multiple sulfur isotope data suggest that mineralizing fluids at the cuiaba gold deposit reflect a complex mixing of sulfur evolved from three possible sources seawater mantle and reduced elemental sulfur spongy syngenetic py1 yields 33s values ranging from 2 28 to 0 25 separated into two ranges the first from 2 28 to 1 97 and the second from 0 96 to 0 25 the first range suggests py1 in the carbonaceous pelite was deposited in a seawater environment these pyrites probably mixed with later mantle sulfur carrying a near zero 33s signature which is indicated by the second 33s range or could have mixed with fluids sourced from sedimentary rocks at depth carrying a positive 33s signature the second scenario is more common in sedimentary and diagenetic pyrites an unequivocal contrast is shown by early main and late stage pyrite types py2 py3 py4 and py5 in carbonaceous pelite bif and andesite which present a continuous process of crustal assimilation values towards increasingly positive 34s and 33s values this confirms evidence for a sedimentary derived sulfur source as also indicated by fluid inclusion data of the andesite hosted orebody at the cuiaba deposit

recent volcanism in the puyehue cordon caulle region southern andes chile 40 5 s petrogenesis of evolved lavas

paleomagnetic rotation pattern of the southern chile fore arc sliver 38 s 42 s a new tool to evaluate plate locking along subduction zones the chile fore arc at 37 s 47 s represents the coseismic deformation zone of the 1960 mw 9 5 valdivia earthquake here we report on the paleomagnetism of 43 oligocene pleistocene volcanic sites from the fore arc sliver between 38 s and 42 s sites were gathered west of the 1000 km long liquine ofqui dextral fault zone lofz that represents the eastern fore arc sliver boundary nineteen reliable sites reveal that the fore arc is characterized by counterclockwise ccw rotations of variable magnitude except at 40 s 41 s where ultrafast 50 myr clockwise cw rotations occur within a 30 km wide zone adjacent to the lofz ccw rotation variability even at close sites and rapidity 10 myr suggest that the observed block rotation pattern is related to nw se seismically active sinistral faults crosscutting the whole fore arc according to previously published data cw rotations up to 170 also occur east of the lofz and have been related to ongoing lofz shear we suggest that the occurrence and width of the eastern fore arc sliver undergoing cw rotations is a function of plate coupling along the subduction zone interface zones of high coupling enhance stress normal to the lofz induce high lofz strength and yield a wide deformation zone characterized by cw rotations conversely low coupling imply a weak lofz a lack of cw rotations and a fore arc entirely dominated by ccw rotations related to sinistral fault kinematics our locking inferences are in good agreement with those recently derived by gps analysis and indicate that seismotectonic segment coupling has remained virtually unchanged during the last 5 ma

the southern andes between 36 and 40 s latitude seismicity and average seismic velocities abstract the project issa 2000 integrated seismological experiment in the southern andes consists of a temporary seismological network and a seismic refraction profile a network of 62 seismological stations was deployed across the southern andes at 38 s three hundred thirty three local seismic events were observed in a 3 month period p and s arrival times of a subset of high quality data were inverted simultaneously for 1 d velocity structure hypocentral coordinates and station delays seismic refraction data along a transect at 39 s provide further constraints on the crustal structure low crustal velocities beneath the forearc may be either due to subducted trench sediments or serpentinized mantle material of the continental lithosphere the continental moho is not clearly observed in this region average velocities of the crust beneath the arc are higher than those beneath the forearc crustal thickness is about 40 km crustal seismicity concentrates in the forearc region along the bio bio and gastre fault zones the area between these two prominent fault zones seems to be nearly devoid of crustal seismicity but shows highest uplift and topography in the forearc region benioff seismicity is observed down to 150 km depth resulting in the first accurate image of the benioff zone in the southern andes a maximum of seismicity at 60 km depth may be caused by dehydration embrittlement

multiple sulfur isotope evidence for surface derived sulfur in the bushveld complex abstract the rustenberg layered suite of the bushveld complex originated in the mantle but is characterized by variably radiogenic strontium neodymium lead and osmium initial isotope ratios and more elevated 18 o values than expected from a partial melt of primitive mantle it is not clear whether bushveld magmas assimilated material from the crust or whether they were instead generated from an eclogitic mantle source that contained crustal material here we report the 33 s of fifteen whole rock and sulfide separate samples from both the main and critical zones of the bushveld including the ug2 chromitite and the merensky reef all samples have positive 33 s values 0 11 0 02 1 and 34 s values 2 2 0 6 1 non zero 33 s is fundamentally a surface process since high temperature processes are not known to produce significant change in 33 s the positive 33 s indicates that the bushveld sulfur contains a sedimentary or surface derived component the homogeneity of 33 s values for this suite of samples contrasts with the heterogeneity displayed by strontium neodymium lead and osmium initial isotope ratios of the bushveld and requires that the sulfur contamination occurred prior to the emplacement of the bushveld in the upper crust possible sources of contamination include lower crust and sub continental lithospheric mantle limited multiple sulfur isotopic measurements of these reservoirs exist more work needs to be done to constrain whether they contain surface derived sulfur with non zero 33 s and if they do whether the concentrations and isotopic compositions of these reservoirs can explain the measured 33 s of the bushveld

multiple sulfur isotope analyses support a magmatic model for the volcanogenic massive sulfide deposits of the teutonic bore volcanic complex yilgarn craton western australia we report sensitive high mass resolution ion microprobe stable isotopes shrimp si multiple sulfur isotope analyses 32s 33s 34s to constrain the sources of sulfur in three archean vms deposits teutonic bore bentley and jaguar from the teutonic bore volcanic complex of the yilgarn craton western australia together with sedimentary pyrites from associated black shales and interpillow pyrites the pyrites from vms mineralization are dominated by mantle sulfur but include a small amount of slightly negative mass independent fractionation mif anomalies whereas sulfur from the pyrites in the sedimentary rocks has pronounced positive mif with 33s values that lie between 0 19 and 6 20 with one outlier at 1 62 the wall rocks to the mineralization include sedimentary rocks that have contributed no detectable positive mif sulfur to the vms deposits which is difficult to reconcile with the leaching model for the formation of these deposits the sulfur isotope data are best explained by mixing between sulfur derived from a magmatic hydrothermal fluid and seawater sulfur as represented by the interpillow pyrites the massive sulfide lens pyrites have a weighted mean 33s value of 0 27 0 05 mswd 1 6 nearly identical with 0 31 0 08 mswd 2 4 for pyrites from the stringer zone which requires mixing to have occurred below the sea floor we employed a two component mixing model to estimate the contribution of seawater sulfur to the total sulfur budget of the two teutonic bore volcanic complex vms deposits the results are 15 to 18 for both teutonic bore and bentley much higher than the 3 obtained by jamieson et al 2013 for the giant kidd creek deposit similar calculations carried out for other neoarchean vms deposits give value between 2 and 30 which are similar to modern hydrothermal vms deposits we suggest that multiple sulfur isotope analyses may be used to predict the size of archean vms deposits and to provide a vector to ore deposit but further studies are needed to test these suggestions

emplacement of volcanic vents and geodynamics of central anatolia turkey abstract observations on synthetic aperture radar sar scenes of the european remote sensing ers satellite and digital elevation models dems complemented by field structural analysis permit a new understanding of relationships between tectonics and volcanism since the late miocene 10 ma in central anatolia volcanic edifices form elongate stratovolcanoes linear clusters and volcanic ridges they indicate emplacement on tension fractures and tail crack or horsetail features for instance the kara dag volcano is rooted on a tail crack which accommodates a horizontal left lateral throw component at a fault termination caldera complexes of cappadocia are associated with horsetail fault patterns the emplacement of volcanoes also benefits from larger scale tectonic structures the erciyes dag volcano is localized by the sultan saz releasing bend which opens along the sinistral strike slip ecemis fault deformation has been analysed from tension fractures which are perpendicular to the direction of extension and from field structural analysis on a regional scale the tectonic regime responsible for the distribution of volcanic vents in this area of convergence and lateral extrusion is not compression but extension the central taurus range is the thermally uplifted shoulder of the adana cilicia basin which is related to lithosphere thinning westward movements in the northwestern part of the studied area are influenced by the active back arc aegean extension situated to the west farther to the south the direction of motion turns southwest and south under the influence of the opening of the adana cilicia basin we interpreted that extension in the central anatolian plateau is related to crustal blocks moving above sub horizontal detachment surfaces located in the lower crust this is based on several facts the tuz golu fault zone is a within crust detachment the tuz golu basin does not affect the whole lithosphere because otherwise it would have been bordered by thermally uplifted shoulders movements change trend within a small 50 km region

geologic evolution of the late archean abitibi greenstone belt of canada the southern volcanic zone svz of the late archean abitibi belt of the superior province of canada is dominated by komatiitic to tholeiitic volcanic plateaus and large bimodal mafic felsic volcanic centers these volcanic rocks were erupted between about 2717 and 2700 ma in a series of rift basins that formed as a result of wrench fault tectonics they overlie and juxtapose a volcano plutonic assemblage characterized in the northern abitibi belt the age of the assemblage is about 2720 ma or older and it comprises basaltic to andesitic and dacitic subaqueous massive volcanics cored by comagmatic sills and layered anorthositic complexes and overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 2 ma a tectonic model is proposed in which the svz formed in a series of rift basins that dissected an earlier formed volcanic arc comparisons are made with rift environments that have been postulated for phanerozoic areas such as the hokuroko basin of japan the taupo volcanic zone of new zealand and the sumatra and nicaragua arcs

strategies for high temperature oxygen isotope thermometry a worked example from the laramie anorthosite complex wyoming usa abstract an understanding of the factors that affect the magnitude and direction of isotopic exchange is fundamental to the application of oxygen isotope geothermometers this is particularly true in high temperature rocks where retrograde exchange between minerals commonly results in the calculation of spurious isotopic temperatures herein we present an approach to isotope thermometry that combines numerical modelling techniques with a directed sampling strategy to retrieve peak or near peak temperature information from rocks that have behaved as closed systems on the hand sample scale during cooling the isotopic composition of minerals in such samples changes in predictable fashion on cooling these so called isotope exchange trajectories iet can be calculated for any mineral given the whole rock isotopic composition the modal abundance of each mineral in the rock and the fractionation factors between the minerals model temperatures can be obtained for both single and multiple hand samples through the calculation of iets temperatures for single samples are determined by locating the intersection between a mineral s calculated iet and its measured isotopic composition on plots of 18 o vs 1 t 2 the resulting temperature represents either the closure temperature of the mineral or the maximum temperature attained by the rock whichever is lower the multiple sample method relies on the premise that at high temperatures isotopic equilibrium is effectively achieved over a large area typically on the scale of meters or larger this method permits the retrieval of temperatures that are significantly higher than the closure temperature of any individual mineral multiple sample temperatures are calculated by determining the intersection of the iets of a given mineral in two or more samples the intersection of these iets represents the temperature at which the isotopic composition of the mineral was the same in both samples i e the last temperature of large scale isotopic equilibrium our methods allow for a rigorous determination of uncertainties in the calculated temperatures these numerical techniques can be used on any samples precise temperature estimates however require samples with specific mineralogic and modal characteristics the best samples for use with the single sample method are those that contain small amounts of a slow diffusing mineral and large fractionation factors between this mineral and the other minerals in the rock the multiple sample method requires two or more samples with widely different modal proportions of a mineral that strongly fractionates oxygen isotopes such samples are present in many terrains but are commonly overlooked because their mineral assemblages are not well suited for conventional thermobarometry these methods yield excellent results when applied to rocks from the sybille fe ti oxide quarry a late magmatic segregate of the laramie anorthosite numerical modelling of single sample and multiple samples from this quarry yield temperatures of 1000 and 1080 c respectively the single sample temperatures record the closure temperature of ilmenite whereas the multiple sample temperatures correspond closely to the experimentally determined solidus for these rocks these model temperatures are higher than any other conventional oxygen isotope temperatures yet reported from slowly cooled rocks

euxinia in the neoarchean the starting point for early oxygenation in a brazilian craton abstract geochemical evidence for local redox transitions is observed 300 ma years prior to the great oxygenation event goe ca 2400 ma and suggests evolving environmental conditions through a continuous sequence where euxinia anoxic and sulfidic preceded the expansion of more oxidizing conditions based on multiproxy data such as iron speciation fepy fehr 0 7 and mo enrichments varying from 3 to 64 we present one of the oldest records of euxinia from the archean pitangui greenstone belt 2700 ma minas gerais brazil the sulfur isotopic composition of sedimentary sulfides indicates early inputs of sulfate from oxidative weathering and an attenuation of sulfur mass independent fractionation that combined with other geochemical signatures fehr fet ce anomalies and rare earth element fractionation is consistent with the expansion of oxygen availability and suggests localized oxic conditions before the goe

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

temporal and spatial variation of local stress fields before and after the 1992 eruptions of crater peak vent mount spurr volcano alaska we searched for changes in local stress field orientation at mount spurr volcano alaska between august 1991 and december 2001 this study focuses on the stress field orientation beneath crater peak vent the site of three eruptions in 1992 and beneath the summit of mount spurr local stress tensors were calculated by inverting subsets of 140 fault plane solutions for earthquakes beneath crater peak and 96 fault plane solutions for earthquakes beneath mount spurr we also calculated an upper crustal regional stress tensor by inverting fault plane solutions for 66 intraplate earthquakes located near mount spurr during 1991 2001 prior to the 1992 eruptions and for 11 months beginning with a posteruption seismic swarm the axis of maximum compressive stress beneath crater peak was subhorizontal and oriented n67 76 e approximately perpendicular to the regional axis of maximum compressive stress n43 w the strong temporal correlation between this horizontal stress field rotation change in position of the 1 3 axes relative to regional stress and magmatic activity indicates that the rotation was related to magmatic activity and we suggest that the crater peak stress field rotation resulted from pressurization of a network of dikes during the entire study period the stress field beneath the summit of mount spurr also differed from the regional stress tensor and was characterized by a vertical axis of maximum compressive stress we suggest that slip beneath mount spurr s summit occurs primarily on a major normal fault in response to a combination of gravitational loading hydrothermal circulation and magmatic processes beneath crater peak online material regional and local fault plane solutions

seismological aspects of the 1988 1989 lonquimay chile volcanic eruption abstract more than 1600 earthquakes were recorded in a four month period on portable seismographic stations installed in the lonquimay area immediately after the initiation of the volcanic eruption of december 25 1988 hypocentral parameters were calculated on a subset of 150 events showing clear p and s arrivals seismic activity was restricted to a north south elongated region that included the main crater of the lonquimay volcano the new navidad crater lies along the eastern margin of the area of seismicity most of the hypocenters are located at depths shallower than 6 km and none have depths exceeding 10 km the largest earthquakes of the sequence took place on dec 28 m 4 7 jan 12 13 m 4 8 and 5 0 and feb 24 m 5 3 the number of events per day varied it peaked on dec 27 with more than 260 events and more than 200 events were recorded on jan 13 both of which corresponded to the days of large earthquakes the relation of large to small events given by the b value of the magnitude frequency distribution log n a bm is typical of volcanic sequences b 1 7 and much larger than the equivalent for tectonic environments the rate of decay of the number of aftershocks of each large earthquake is proportional to t p with p increasing from 0 63 to 1 08 as the eruption progressed in time initial low values of p indicate a slow stress release in the region larger absolute values of p are comparable with tectonic environments and might be indicators of the last stages of the eruption process the total seismic energy release is 9 6 10 19 ergs about five orders of magnitude less than the estimated thermal energy the spatial distribution of earthquakes suggests that the sources of stress change associated with the eruption are located under and possibly to the south of the main crater of the lonquimay volcano and that the evacuation channels of magma occupied a zone of weakness in the region of the new crater

multiple sulphur and iron isotope composition of detrital pyrite in archaean sedimentary rocks a new tool for provenance analysis abstract multiple s 34 s and 33 s and fe 56 fe isotope analyses of rounded pyrite grains from 3 1 to 2 6 ga conglomerates of southern africa indicate their detrital origin which supports anoxic surface conditions in the archaean rounded pyrites from meso to neoarchaean gold and uranium bearing strata of south africa are derived from both crustal and sedimentary sources the latter being characterised by non mass dependent fractionation of s isotopes 33 s as negative as 1 35 and large range of fe isotope values 56 fe between 1 1 and 1 2 most sediment sourced pyrite grains are likely derived from sulphide nodules in marine organic matter rich shales sedimentary exhalites and volcanogenic massive sulphide deposits some sedimentary pyrite grains may have been derived from in situ sulphidised fe oxides prior to their incorporation into the conglomerates as indicated by unusually high positive 56 fe values sedimentary sulphides without significant non mass dependent fractionation of s isotopes were also present in the source of some conglomerates the abundance in these rocks of detrital pyrite unstable in the oxygenated atmosphere may suggest factors other than high p o 2 as the cause for the absence of significant non mass dependent fractionation processes in the 3 2 2 7 ga atmosphere rounded pyrites from the c 2 6 ga conglomerates of the belingwe greenstone belt in zimbabwe have strongly fractionated 34 s 33 s and 56 fe values the source of which can be traced back to black shale hosted massive sulphides in the underlying strata the study demonstrates the utility of combined multiple s and fe isotope analyses for provenance reconstruction of archaean sedimentary successions

melting of a subducting oceanic crust from u th disequilibria in austral andean lavas understanding crustal genesis at convergent plate boundaries is important for determining mass transfer between different geochemical reservoirs in the earth s mantle and for deciphering the long term growth of the continental crust most arc magmas are thought to be generated from fluid induced melting of the mantle wedge above slabs of subducting oceanic crust1 such magmas frequently display 238u enrichments or radioactive equilibrium2 3 between 238u and its radiogenic product 230th but where a young and hot oceanic crust is being subducted it may itself partially melt and produce calc alkaline andesites and dacites termed adakites4 here we report a uniform excess of 230th over 238u but variable th isotope ratios in young adakites from the andean austral volcanic zone south of the triple junction where the chile ridge subducts beneath south america we show that these results are compatible with the adakites having been formed by approximately 20 equilibrium melting due to amphibole decomposition in a heterogeneous5 oceanic crust moreover both the degree of melting of the oceanic crust and its thermal structure appear to be uniform under most of the andean austral volcanic zone such partial melting of subducted oceanic slabs may have occurred throughout the earth s history where young oceanic plates were subducted

neotectonics in the foothills of the southernmost central andes 37 38 s evidence of strike slip displacement along the antinir copahue fault zone 1 the antinir copahue fault zone acfz is the eastern orogenic front of the andes between 38 and 37 s it is formed by an east vergent fan of high angle dextral transpressive and transtensive faults which invert a paleogene intra arc rift system in an out of sequence order with respect to the cretaceous to miocene fold and thrust belt 3 1 1 7 ma volcanic rocks are folded and fractured through this belt and recent indicators of fault activity in unconsolidated deposits suggest an ongoing deformation in spite of the absence of substantial shallow seismicity associated with the orogenic front neotectonic studies show the existence of active faults in the present mountain front the low shallow seismicity could be linked to the high volumes of retroarc derived volcanic rocks erupted through this fault system during pliocene and quaternary times this thermally weakened basement accommodates the strain of the antinir copahue fault zone absorbing the present convergence between the south america and nazca plates

eruptive history geochronology and magmatic evolution of the puyehue cordon caulle volcanic complex chile forty three 40 ar 39 ar age determinations of lava flows domes ignimbrites and dikes plus 14 c dates from seven distal tephra layers combined with stratigraphy geochemistry and sr and th isotope data establish an eruptive chronology for the puyehue cordon caulle volcanic complex at 40 5 s in the andean southern volcanic zone svz the complex preserves 131 km 3 of lava and tephra that erupted from numerous vents widely separated in time and space approximately 80 of the total volume consists of basaltic to andesitic lava that formed two broad shield volcanoes between 314 and 70 ka the modern puyehue stratovolcano was built on the southerly shield during the past 69 k y following a hiatus of 25 k y puyehue has erupted 15 km 3 of basaltic to rhyolitic magma that spans the entire compositional range found in the southern svz and evolved via at least six phases including 1 basaltic andesitic to dacitic lavas between 69 and 32 ka 2 a shift to bimodal magma compositions that is first expressed by a rhyodacite mingled with inclusions of mgo rich basaltic andesite at 34 ka 3 dacitic to rhyolitic flows and domes from 19 to 12 ka 4 basaltic to basaltic andesitic flows between 15 and 12 ka 5 subsequent rhyolitic dome growth in several effusive and explosive stages between 7 and 5 ka followed by 6 a powerful series of phreatomagmatic and sub plinian eruptions at ca 1 1 ka that obliterated the preceding rhyolite domes and formed the present 2 5 km diameter 280 m deep summit crater along the cordon caulle fissure zone 5 km 3 of rhyodacitic to rhyolitic lavas domes and cones have formed during the past 16 5 k y including explosive and effusive eruptions in 1921 1922 and 1960 eruptive rates were nonuniform over time with background growth at 0 04 km 3 k y or less punctuated by spurts at up to 0 90 km 3 k y the time averaged rate 0 42 km 3 k y is nearly double that at the tatara san pedro complex 500 km to the north during the past 300 k y these findings indicate that within a single arc the magmatic and eruptive fluxes at individual frontal volcanoes can be highly variable the last three stratocone building events on puyehue began during periods of deglaciation suggesting a relationship between unloading of ice and ease of magma ascent puyehue basalt exhibits subtle changes in 238 u 230 th 87 sr 86 sr and trace element composition over time that signal shifts in the composition and degree of melting of the mantle wedge or the extent to which basalt was modified by assimilation of heterogeneous crustal melts the complex has become exceptionally bimodal and more explosive over time with recent rhyolites evolving by extreme crystal fractionation of mafic magma and lesser volumes of andesite and dacite created via mixing of rhyolite and basalt despite the high flux of basalt during the past 300 k y no large silicic magma reservoir formed in the upper crust instead 238 u 230 th data favor rapid ascent of several small bodies of basaltic and silicic magma from the lower crust promoted perhaps by conduits that reflect strike slip faulting beneath the complex

multiple sulfur isotopes and the evolution of earth s surface sulfur cycle abstract the distribution of sulfur isotopes in geological materials reveals information about earth history and biogeochemical processes research during the last several decades has used sulfur isotope geochemistry as a tool to better understand microbial processes harrison and thode 1958 kaplan 1975 monster et al 1979 peck 1959 peck 1962 rees 1973 and sediment diagenesis berner 1969 berner 1982 canfield et al 1993b earth historians also realized this potential as there exists a rich record of environmental change within the sedimentary records canfield and teske 1996 claypool et al 1980 goodwin et al 1976 habicht et al 2002 kah et al 2004 monster et al 1979 shen et al 2001 strauss 1993 thode and goodwin 1983 these applications have championed the use of the two most abundant sulfur isotopes 32s and 34s and provide a rich introduction to what the sulfur isotope record has to offer see canfield 2004 canfield and raiswell 1999 within the last decade this information has been supplemented by new data derived from the less abundant isotopes 33s and 36s the measurement of all four stable sulfur isotopes multiple sulfur isotope geochemistry has expanded our understanding of biological evolution and activity atmospheric chemistry and transport crustal recycling and many more fields related to earth surface processes see farquhar and wing 2003 here i present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and earth surface evolution

uranium and 10 be enrichments by fluids in andean arc magmas volcanic rocks from subduction settings frequently contain 10be enrichments that have been attributed to sediment subduction1 6 and are often characterized by 238u 230th ratios greater than unity in contrast to mid ocean ridge and ocean island basalts7 8 here we report such an excess of 238u over 230th in historic lavas from the southern volcanic zone of chile 33 42 s the greatest uranium excess is found south of 39 s where 10be 9 be ratios are highest and the trench is filled with sediment these features suggest that both u and 10be enrichments result from preferential partitioning of u and be into a fluid phase during dehydration of the recently subducted sediments the presence of strong 238u 230th disequilibria in basaltic magmas of the southern volcanic zone suggests that the timescale for dehydration melting and eruption in this arc is probably less than 20 000 yr

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

evidence of magmatic degassing in archean komatiites insights from the wannaway nickel sulfide deposit western australia abstract magmatic degassing from komatiite lava flows potentially influenced the geochemical evolution of the archean atmosphere and hydrosphere we argue that the escape of so2 rich volatiles from komatiites impacted on the mineralogical geochemical and isotopic composition of associated nickel sulfide mineralization leaving behind detectable and measurable footprints that can be best observed where the polarity of the magmatic sequence is clearly recognizable here we focus on the ore bearing sequence of the archean komatiite hosted n01 nickel sulfide orebody at wannaway yilgarn craton western australia this deposit displays a volcanic sequence with a well defined succession of stratigraphically correlated facies comprising a massive sulfide horizon at the base of the channelized komatiite flow overlain by matrix and disseminated sulfide mineralization pyrrhotite is the dominant sulfide phase in the lower part of the ore profile the amount of troilite gradually increases from the base of the matrix ore over several meters up sequence eventually becoming dominant at the expense of pyrrhotite in the upper portion of the mineralized sequence troilite is associated with accessory mn sulfide alabandite mns which is usually reported in reduced terrestrial and extra terrestrial environments such mineralogical and volcanological features are consistent with upwards decreasing in fs2 and fo2 away from the basal contact of the komatiite flow after evaluating the possible role of metamorphism the pyrrhotite troilite alabandite assemblage and the progressive up sequence decrease of the pyrrhotite troilite ratio across the upper part of the mineralized sequence are interpreted as magmatic and indicative of progressive loss of sulfur with concomitant establishment of reducing conditions within the sulfide melt ponding at the base of the komatiite lava in this context the investigation of spatially constrained sulfur isotopic signatures allows to isolate the multiple sulfur fractionation processes that impacted on sulfide mineralization and ultimately permits the identification of the isotopic shift associated with magmatic degassing following this approach we recognize two distinct sulfur isotope exchanges processes triggered by 1 assimilation of sulfidic shales during emplacement of the komatiite flow and 2 equilibration between the sulfide melt and the sulfur dissolved in the silicate melt we finally correlate the remaining 34 s depletion up stratigraphy with the loss of heavy sulfur isotopes through magmatic degassing of so2 rich volatiles from the ultramafic flow the emission of so2 upon emplacement and cooling of the magma flow would also explain the progressive reducing fo2 and f s 2 conditions indicated by variations in mineral assemblages from the base of the komatiite upwards

multiple sulfur isotope fractionation and mass transfer processes during pyrite precipitation and recrystallization an experimental study at 300 and 350 c abstract equilibrium multiple sulfur isotope fractionation factors 33s 32s and 34s 32s between aqueous so4 h2s and coexisting pyrite under hydrothermal conditions were determined experimentally at 300 350 c and 500 bars two different experimental techniques were used to determine the fractionation factors and the rate of s isotope exchange between pyrite and constituent aqueous species h2s and so4 1 closed system gold capsule pyrite h2s exchange experiments and 2 complimentary time series experiments at 300 and 350 c 500 bars using flexible gold cell hydrothermal equipment which allowed monitoring the multiple s isotope composition of dissolved s species during pyrite precipitation and subsequent recrystallization the three isotope technique was applied to the multiple s isotope data to demonstrate equilibrium s isotope fractionation between pyrite and h2s results at 350 c indicate ln 34 pyrite h 2 s 1 9 and ln 33 pyrite h 2 s 1 0 the ln 34 pyrite h 2 s is not only different in magnitude but also in sign from the commonly used value of 1 from ohmoto and rye 1979 this experimental study also demonstrated initial s isotope disequilibrium amongst the aqueous s species and pyrite during rapid precipitation despite aqueous speciation indicating pyrite saturation at all stages textural crystallographic and s isotope interpretations suggest that pyrite formed by means of the fes pathway the initial s isotope disequilibrium between formed pyrite and dissolved s species was effectively erased and approached isotopic equilibrium upon recrystallization during the course of 4297 h interpretation of seafloor hydrothermal vent sulfides using the revised equilibrium 34s 32s fractionation between pyrite and h2s suggests that pyrite is close to s isotope equilibrium with vent h2s contrary to previous conclusions the experimental data reported here broaden the range of pyrite formation mechanisms at seafloor hydrothermal vents in that mineral formation pathway and equilibration rates need to be considered to account for the well recognized s isotope variability that often characterizes these systems

co eruptive subsidence and post eruptive uplift associated with the 2011 2012 eruption of puyehue cordon caulle chile revealed by dinsar abstract the 2011 2012 eruption of the puyehue cordon caulle volcanic complex southern andes chile was associated with complex surface deformation affecting an area of roughly 50 by 50 km we report here differential sar interferometry dinsar results of pre co and post eruptive deformation from envisat asar cosmo skymed and alos 2 palsar scenes acquired between early 2011 and early 2017 no clear pre eruptive deformation is observed during five months before the eruption although some patterns could be interpreted as showing inflation occurring between april and may 2011 co eruptive interferograms show a complex deformation pattern consisting in a major deflation lobe 120 cm los lengthening centered 10 km nw of the eruption vent accompanied by smaller uplift and subsidence regions in the vicinity of the vent re inflation began immediately after the end of the eruption a first pulse lasted 3 years between 2012 and 2015 accumulating 70 cm uplift we detect here a second pulse beginning in june 2016 and still ongoing in february 2017 reaching 12 cm in half a year inverse modeling with spherical cavity and spheroidal sources locates re inflation sources at a depth ranging between 8 and 11 km under the surface it suggests re filling of the reservoir occurring after the draining of a shallow magma chamber during the 2011 2012 eruption

mass independently fractionated sulfur in archean paleosols a large reservoir of negative δ33s anomaly on the early earth abstract results of multiple sulfur isotope analyses from five archean paleosols show the widespread presence of mass independently fractionated sulfur in the regolith developed on the pre 2 5 ga earth analysis of sulfur from a small set of diamictite samples gave similar results all values of 33 s are negative indicating that the archean surface environments preferentially retained atmospheric s from the so 4 2 pathway which carried a negative 33 s signal whereas a portion of the s from the s 8 pathway with a positive 33 s was transferred to the oceans the soil so 4 2 was then converted to sulfide by bacterial sulfate reduction with terrestrial organic matter in the weathering horizon acting as a reductant some s from the s 8 pathway also included which resulted in a net soil 33 s anomaly from atmospheric s in the range 0 3 to 0 6 similar to values for pyrites from floodplain sediments excess s 8 derived s was carried to the oceans resulting in the negative positive dichotomy between terrestrial and marine systems pyrite that formed in paleosols and pyrite grains that formed in flood plain deposits both carrying the terrestrial 33 s signal were then recycled into detrital pyrite grains now found in sandstones and conglomerates deposited before the rise of atmospheric oxygen therefore the earth s early regolith constituted a reservoir of s with negative 33 s values that could be important for balancing the predominantly positive 33 s signature found in marine sediments

in situ trace element and sulfur isotope analysis of pyrite in a paleoproterozoic gold placer deposit pardo and clement townships ontario canada extensive pyrite bearing auriferous cobble and boulder conglomerates are present in the basal 30 in of the mississagi formation in pardo and clement townships ontario canada the sedimentology of the conglomerates combined with regional geology indicates limited fluvial transport in a gravel bed braided river with local hyperconcentrated flows with material derived from a highly restricted catchment area postdepositional overprinting of the conglomerates is related to the penokean orogeny at 1 85 to 1 5 ga and alkali metasomatism at similar to 1 7 ga several pyrite varieties including detrital and postdepositional recrystallized and altered grains are present in the conglomerates detailed in situ laser ablation inductively coupled plasma mass spectrometry la icpms analysis of pyrite revealed that the gold in the deposit is intimately associated to large detrital pyrite grains as invisible au with lesser amounts of free gold postdepositional pyrite and pyrite overgrowths have very low au content elements such as pb bi sb te ag and hg together with au were mobilized during hydrothermal alteration and dissolution of detrital pyrite grains small scale transport and reprecipitation formed part of the postdepositional pyrite and free gold in immediate contact with postdepositional grains in contrast ni co and as were not mobilized external fluid infiltration is negligible and is indicated only by minor compositionally distinct late sulfide veinlets crosscutting the conglomerates sulfur isotope analysis of detrital pyrite yields generally positive delta 34 s values 0 97 9 26 0 the delta 34 s sulfur isotope composition of pyrite overgrowths and postdepositional grains overlaps the isotopic range of the detrital grains suggesting a near closed s system during postd epositional processes however the detrital pyrite tends to have slightly negative delta 33 s while the postdepositional and overgrowth pyrite are either neutral or slightly positive the s isotope composition of the detrital pyrite is compatible with an origin of s as dissolved sulfate in an ocean under a low oxygen atmosphere the potential source of the au bearing detrital pyrite appears to have been an as yet undiscovered archean deposit located within 1 to 8 kin of the placer deposit

volcano morphology as an indicator of stress orientation in the java volcanic arc indonesia abstract stress fields in the earth s crust are important indicators leading to better understanding of geologic processes one way to acquire stress data is through morphometric analysis of volcanoes here we evaluate 141 quaternary age monogenetic and polygenetic volcanoes and volcanic fields in java indonesia using a 30 m srtm dem an 8 m demnas aerial photos published geological maps and landsat and google earth satellite imagery we analyze parameters that imply the geometry of the shallow magma plumbing system and ascent pathways crater ellipticity and elongation axis and the orientation of crater breaching bisectors the dominant trend of all of these parameters should indicate the direction of the maximum horizontal compressive stress hmax while the minimum horizontal stress hmin should be perpendicular to it the goal here is to estimate the principal stress axes at the time of dike emplacement to recognize any spatial variations in stress orientations and assess factors controlling the emplacement the resulting orientation of hmax in the western part of java is ne sw and the trend gradually rotates to nw se moving eastward abrupt changes in stress orientations and anomalies are also observed in the vicinity of prominent geologic structures highlighting the influence of preexisting structures on dike emplacement and eruption characteristics results of the morphometric analysis of volcanoes and volcanic fields conducted in this study help to estimate the past and present stress orientations in java and provide valuable understanding regarding the relationship between volcanic emplacement and crustal structures complementing other types of analysis

rapid reinflation following the 2011 2012 rhyodacite eruption at cordon caulle volcano southern andes imaged by insar evidence for magma reservoir refill cordon caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921 1960 and 2011 2012 there was significant ground deformation observed before and during the 2011 2012 eruption here we use c and x band insar time series results to document post eruptive uplift up to 0 8 m between march 2012 and may 2015 with los rates up to 45 cm yr that have been largely aseismic along with subsidence in the 2011 2012 lava flow the 2012 uplift rate is one of the largest for silicic systems and was likely produced by the intrusion of 0 125 km3 of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions nevertheless the uplift ended before the reservoir refilled with the erupted volume maybe due to a change in the pressure gradient produced by the 2011 2012 eruption

investigating sulfur pathways through the lithosphere by tracing mass independent fractionation of sulfur to the lady bountiful orogenic gold deposit yilgarn craton abstract as sulfur is the primary complexing ligand for gold transport in aqueous fluids recent work has demonstrated that the archean systems can preserve mass independent fractionation of sulfur mif s to yield near zero values 33s1 0 0 5 in such cases interpretation of the geological significance of such isotopic signatures may be compromised as it is known that mass dependent fractionation of sulfur mdf s can yield small 33s values herein as 33sb often owing to geobiological reactions involving sulfur in this study we reassess the range of possible values of 33sb from the traditionally accepted value of 0 0 2 to demonstrate that this range is not constant but rather directly linked to the degree of 34s fractionation we present a multiple sulfur isotope dataset from the neoarchean lady bountiful orogenic gold deposit from the yilgarn craton western australia this deposit contains pyrite with an isotopic composition of 34s 2 1 0 8 and 33s 0 14 0 06 2sd on the mean the analysis of these results as well as of a data compilation from other 2 65 ga orogenic gold deposits of the yilgarn craton indicates that 33s1 values are too large to be the result of purely mdf s processes in addition when compared to a compilation of 3400 33s0 measurements of archean sedimentary rocks which shows highly variable positive and negative signals the remarkably constant positive mif s1 signature of gold deposits from the yilgarn craton with 33s1 values between 0 and 0 6 is evidence that the source of the auriferous fluids equilibrated at depth by mixing with a non mif s0 bearing sulfur reservoir by enhancing the application of mif s1 33s1 as a powerful and indelible tracer to understand the source and emplacement pathways of gold bearing fluids through the lithosphere the outcomes from this study demonstrate the recorded 33s1 signature in the auriferous fluids reflects the presence of sulfur that was at least partially sourced from an archean sediment reservoir

the fluid evolution of the nimbus ag zn au deposit an interplay between mantle plume and microbial activity abstract the nimbus ag zn au volcanic hosted massive sulfide vhms deposit represents an exceptional orebody in the yilgarn craton of western australia it is located in a zone of juvenile crust running n s through the eastern goldfields superterrane however unlike most other vhms occurrences associated with the 2690 2680 ma rift sequence teutonic bore jaguar bentley erayinia it is hosted by the ca 2705 ma plume related stratigraphy which is more typically associated with komatiite hosted nickel sulfide mineralization the nimbus deposit displays hybrid vhms epithermal characteristics resulting from low temperature and shallow water conditions which developed a quartz carbonate sericite dominated alteration assemblage in the dacite host rocks sulfide mineralization comprises pyrite sphalerite galena arsenopyrite ag sb pb bi sulfosalts and rare chalcopyrite in this study we applied a combination of in situ analytical techniques to monitor the evolving sulfur isotope signature of the mineralizing fluids and propose that the nimbus vhms deposit developed as a result of a bimodal fluid history in the first stage the hydrothermal system powered by plume related magmatism deposited a series of barren pyrite lenses with colloform textures their variable but consistently negative mass independent sulfur isotope fractionation signature 33s 0 81 reflects the interaction between mantle derived magmatic fluids and archean seawater the ubiquitous presence of carbon rich porous textures and the remnants of carbonaceous nests in colloform pyrite also indicate a significant contribution of microbial sulfate reducers during the incipient stages of sulfide precipitation the gradual formation of colloform lenses eventually sealed the hydrothermal system establishing a physical barrier that limited the interaction with seawater this process promoted the onset of higher temperature and pressure conditions required to form the high grade zn ag mineralization sourcing sulfur and fluids largely from a magmatic reservoir 33s 0 09 whereas the identification of a predominantly magmatic sulfur source is supported by sulfur isotope signatures the recognition of a magmatic origin of the fluid may only be inferred indirectly it is consistent with the observed quartz sericite alteration style and the proposed mechanism of sulfide deposition via decompression which does not require any interaction with seawater the trace element distribution of the ore related sulfides also supports a closed hydrothermal system developed through multiple fluid pulses indeed this ore forming scenario is commonly favored by high confining pressures which at nimbus were established following the deposition of the colloform pyrite lenses that progressively sealed the hydrothermal system creating the favorable conditions for mineralization

paleoarchean sulfur cycling multiple sulfur isotope constraints from the barberton greenstone belt south africa mass dependent and mass independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the barberton greenstone belt 3550 3215 ma south africa provide constraints for sulfur cycling on the early earth four different sample suites were studied komatiites and tholeiites barite massive and disseminated sulfide ores and non mineralized black shales variable but generally slightly positive 34s values between 0 7 and 5 2 negative 33s values between 0 50 and 0 09 and a negative correlation between 34s and 33s as well as between 33s and 36s for komatiites and tholeiites from the komati formation and from the weltevreden formation are outside the expected range of unfractionated juvenile sulfur instead results suggest alteration of oceanic crustal rock sulfur through interactions with fluids that most likely derived their sulfur from seawater barite from the mapepe formation displays positive 34s values between 3 1 and 8 1 and negative 33s values between 0 77 and 0 34 the mass independent sulfur isotope fractionation indicates an atmospheric sulfur source notably photolytic sulfate whereas the positive 34s values suggest bacterial sulfate reduction of the marine sulfate reservoir non mineralized black shale samples from the presumed stratigraphic equivalent of the mapepe formation show positive 34s values between 0 0 and 1 3 and positive 33s values between 0 59 and 2 45 these results are interpreted to result from the reduction of photolytic elemental sulfur carrying a positive 33s signature positive 34s values ranging from 0 7 to 3 5 and slightly negative 33s values between 0 17 and 0 12 characterize massive and disseminated sulfides from the bien venue prospect results suggest unfractionated juvenile magmatic sulfur source as the primary sulfur source but a contribution from recycled seawater sulfate which would be indicative of submarine hydrothermal activity cannot be ruled out massive and disseminated sulfides from the m hlati prospect are distinctly different from massive and disseminated sulfide from the bien venue prospect they show negative 34s values between 1 2 and 0 1 and positive 33s values between 2 66 and 3 17 thus displaying a sizeable mass independent sulfur isotopic fractionation again these samples clearly exhibit the incorporation of an atmospheric mif s signal the source of sulfur for these samples has positive 33s values suggesting a connection with photolytic elemental sulfur in conclusion the sulfur isotope signatures in paleoarchean rocks from the barberton greenstone belt are diverse and indicate the incorporation of different sources of sulfur for komatiites and tholeiites barite and massive and possibly also disseminated sulfides from bien venue multiple sulfur isotopes are related to ambient seawater sulfate and its photolytic origin while massive and disseminated sulfides from m hlati and non mineralized black shales are related to a second photolytic elemental sulfur end member

mass independent isotope effects in archean 2 5 to 3 8 ga sedimentary sulfides determined by ion microprobe analysis we report sulfur isotope anomalies with 33 s the deviation from a mass dependent fractionation line for the three isotope system 34 s 32 s vs 33 s 32 s ranging up to 2 within individual archean sedimentary sulfides from a variety of localities our measurements which are made in situ by multicollector secondary ion mass spectrometry unequivocally corroborate prior bulk measurements of mass independent fractionations mif in sulfur and provide additional evidence for an anoxic atmosphere on the earth before 2 ga this technique also offers new opportunities for exploring ancient sulfur metabolisms preserved in the rock record the presence of mif sulfur in sulfides from a 3 8 ga fe rich quartzite from akilia island west greenland is consistent with a marine sedimentary origin for this rock copyright 2003 elsevier science ltd

evolution of the late paleozoic accretionary complex and overlying forearc magmatic arc south central chile 38 41 s constraints for the tectonic setting along the southwestern margin of gondwana stratigraphic structural metamorphic and geochronologic studies of basement rocks in the andean foothills and coast ranges of south central chile 39 41 s suggest a protracted late paleozoic to middle mesozoic deformational and metamorphic history that imposes important constraints on the tectonic development of the southwestern gondwana margin in the study area the late paleozoic paired metamorphic belt coeval magmatic arc and overlying triassic sedimentary units preserve a record of late carboniferous to early permian subduction and arc magmatism subsequent deep exhumation of the western series subduction complex and diminished uplift and erosion of the eastern series arc forearc region by the late triassic late paleozoic structural elements and metamorphic assemblages formed during early subduction and arc magmatism collectively referred to as dl are largely erased in the western series by the dominant d2 schistosity and lower greenschist grade metamorphism d1 structural features as well as original sedimentary textures are relatively well preserved in the less penetratively deformed eastern series the regional distribution of late paleozoic arc magmatism suggests that the late paleozoic convergent margin deviated from a n s trend north of this area to a nw se trend near this latitude and faced an open marine environment to the southwest a transition from f2 isoclinal folding to more open larger scale f3 folds interpreted as change in ductility during differential uplift of the western series is not apparent in the eastern series despite a lesser degree of uplift during the main exhumational d2 event delineation of unconformities and u pb dating of detrital zircons and intrusions into the eastern series allow tighter constraints to be placed on timing of uplift and denudation of the eastern series than on that in the western series a regional unconformity exposed in the lake district that separates more highly deformed eastern series lithologies from late triassic shallow marine to continental deposits suggests that substantial uplift also affected the inner forearc and magmatic arc region during the d2 event we propose that dextral oblique convergence initiated during the middle permian along this segment of the gondwana margin resulted in the transpressional uplift and juxtaposition of high pressure temperature p t western series against low p t eastern series lithologies and culminated with deposition of late triassic continental to shallow marine coarse clastic sedimentary rocks in fault bounded strike slip basins adjacent to the exhumed western series large scale dextral transpression and northward displacement of the accretionary complex during late permian to late triassic time along the chilean margin of gondwana are synchronous and kinematically compatible with widespread regional transpression extension and silicic magmatism inboard of the southern gondwana margin at this time we thank c mpodozis m gardeweg and j munoz of the servicio de geologia y mineria de chile sernageomin for their support of this work fruitful discussions with n blanco f herve h moreno c mpodozis and f munizaga have aided in our understanding of the geology of the region the hard work by the staff of sernageomin s puerto varas office is graciously appreciated we thank j d walker and w r van schmus at the university of kansas for allowing mwm use of their u pb and mass spectrometer facilities and j vargas and the staff of sernageomin s geochemistry laboratory for their assistance in this project f munizaga allowed us to cite an unpublished 40ar 39ar date we thank g ya nez for access to aeromagnetic data t kato wishes to thank w g ernst comments by i dalziel s kay and v ramos helped clarify ideas presented in this paper and are greatly appreciated this work is dedicated to our friend and colleague alberto campos c who died in a climbing accident on calbuco volcano 1996

structural controls of volcanism in transversal chains resheared faults and neotectonics in the cordon caulle puyehue area 40 5 s southern andes abstract the nature of the relationship between tectonics and volcanism in a specific area is the result of the interaction between the crustal structures of the basement and ongoing regional stress field in the southern andes different kinematic environments represented by two nearly orthogonal active fissure systems show apparently incompatible arrays of volcanic chains moreover a local quaternary compressive regime is inferred from basement faults however these mutually orthogonal chains which are also oblique to the volcanic front have contrasting magma evolution and eruptive styles that can be related with their tectonic setting whereas northeast trending monogenetic cones carran los venados can be interpreted as resulting from magma upwelling along regional tension cracks in a quaternary dextral transpressive compressive domain northwest striking fissure system cordon caulle volcanic complex can be the result of extensional fault reactivation and long magma residence in the upper crust different kinematic environments cause contrasting magma evolution and eruptive styles a two way coupling mechanism is suggested for to explain local depart of the regional stress field geometric array of extensional features and final magmatic evolution in these volcanic domains of the southern andes

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

analysis of geometry of volcanoes and faults in terceira island azores evidence for reactivation tectonics at the eur afr plate boundary in the azores triple junction abstract the late pliocene to quaternary 5 ma volcanism in the central and eastern azores archipelago is related to the eurasia africa divergence but a clear deformation pattern has not yet been established at this location this work focuses on the contribution of synthetic aperture radar sar scenes and digital elevation models dem complemented with geophysical geodetic and morpho structural data to establish the geometric relationships between volcanic edifices and tectonic structures in the central and eastern azores archipelago bathymetric data were also used to extend field observations to the significant submarine area of the azores plateau strikes of extension fractures directly observed or inferred from elongated volcanic vents or linear volcanic clusters in terceira island indicate that volcanism is mainly controlled by regional extension as given by nuvel 1a plate motion model additionally other directions were also detected for extension fractures around the santa barbara volcano defining a radial pattern and in the central part of the island exhibiting an s shape pattern although most of the volcanic vents are controlled by extension fractures some seem to be controlled by faulting such as the case of the ones rooted in releasing bends along strike slip or oblique slip faults in the central part of the island concerning the azores plateau most of the structures have directions that do not directly fit with present day direction of relative motion n70 between eurasia and africa directions ranging from n110 to n125 found mainly along the terceira rift are interpreted as ancient transform directions reactivating as transtensional fault zones due to the present day plate motion n s directions are also visible in the plateau being interpreted as former middle oceanic rift faults reactivated as left lateral fault zones these results contrast with the volcanic expression in other hotspot dominated oceanic islands such as the canaries or the hawaii islands chain probably due to the tectonic complexity promoted by the azores triple junction instability through time

compressional and transpressional stress pattern for pliocene and quaternary brittle deformation in fore arc and intra arc zones andes of central and southern chile kinematic analysis of fault slip data for stress determination was carried out on late miocene to quaternary rocks from the fore arc and intra arc regions of the chilean andes between 33 and 46 south latitudes studies of neogene and quaternary infilling the central depression as well as plutonic rocks of the north patagonian batholith along the liquine ofqui fault zone have revealed various compressional and or transpressional states of stress in the pliocene the maximum compressional stress 1 was generally oriented east west during the quaternary the deformation was partitioned into two coeval distinctive states of stress in the fore arc zone the state of stress was compressional with 1 oriented in a n s to nne ssw direction in the intra arc zone the state of stress was transpressional with 1 striking ne sw along the coast in one site 37 30 s the quaternary strain deformation is extensional with an e w direction which can be explained by a co seismic crustal bending readjustment

formation of the abitibi greenstone belt by arc trench migration volcanic and plutonic rocks of archean greenstone belts in the abitibi subprovince become younger southward plutonic rocks are 10 30 m y younger than volcanic rocks the abitibi greenstone belt has an upper crust of 2 75 2 70 ga oceanic supracrustal assemblages and a middle crust of 2 70 2 68 ga granitic and gneissic rocks the greenstone belt upper crust is greenschist facies with upright structures and low reflectivity and the middle crust is amphibolite facies with moderate to shallowly dipping structures and strong reflectivity we propose that the age progression and crustal layering resulted from accretion of oceanic assemblages followed by extensive mid crustal magmatism linked to southward migration of an arc trench system thermal softening of the middle crust during magmatism caused ductile flow now represented by strong mid crustal reflectivity upward heat flow following magmatism caused late tectonic 2 67 2 65 ga low pressure metamorphism observed in the upper crust

the 1960 chilean earthquakes an unusual foreshock sequence that began with an earthquake of moment 2 0 1021 n m and rupture length of about 150 km preceded the great 1960 chilean earthquake earthquake relocations of the sequence show a progression of seismic activity toward the initiation of the main shock the rupture length of the great 1960 chilean earthquake is estimated from the distribution of aftershocks and crustal deformation to be 920 100 km the source mechanisms of a foreshock and two aftershocks are determined and used to constrain the source mechanism of the main shock the first event in the sequence ruptured the segment of the peru chile trench between 37 03 s and 38 74 s whereas the great 1960 chilean main shock ruptured the adjoining segment to the south the great 1960 chilean main shock initiated within the rupture area of the first event and terminated near the intersection of the chile ridge with the peru chile trench 46 5 s

critical metals in manganese nodules from the cook islands eez abundances and distributions abstract the cook islands cis exclusive economic zone eez encompasses 1 977 000 km2 and includes the penrhyn and samoa basins abyssal plains where manganese nodules flourish due to the availability of prolific nucleus material slow sedimentation rates and strong bottom currents a group of cis nodules was analyzed for mineralogical and chemical composition which include many critical metals not before analyzed for cis nodules these nodules have varying sizes and nuclei material however all are composed predominantly of mno2 and x ray amorphous iron oxyhydroxide the mineralogy fe mn ratios rare earth element contents and slow growth rates mean 1 9 mm 106 years reflect formation primarily by hydrogenetic precipitation the paucity of diagenetic input can be explained by low primary productivity at the surface and resultant low organic matter content in seafloor sediment producing oxic seafloor and sub seafloor environments the nodules contain high mean contents of co 0 41 ni 0 38 ti 1 20 and total rare earth elements plus yttrium rey 0 167 and also high contents of mo nb v w and zr compiled data from a series of four cruises by the japan international cooperation agency and the mining agency of japan from 1985 to 2000 were used to generate a map that defines the statistical distribution of nodule abundance throughout the eez except the manihiki plateau the abundance distribution map shows a belt of high nodule abundance 19 45 kg m2 that starts in the southeast corner of the eez runs northwest and also bifurcates into a sw trending branch small isolated areas contain abundances of nodules of up to 58 kg m2 six 20 000 km2 areas of particularly high abundance were chosen to represent potential exploration areas and maps for metal concentration were generated to visualize metal distribution and to extrapolate estimated metal tonnages within the six sites and the eez as a whole grades for mn cu and ni are low in cis nodules in areas of high abundance however ti co and rey show high contents where nodule abundances are high of the six areas identified to represent a range of metal contents one at the northern end of the n s abundance main belt optimizes the most metals and would yield the highest dry metric tons for mn 61 002 292 ni 1 247 834 mo 186 166 v 356 247 w 30 215 and zr 195 323 when compared with the clarion clipperton zone the cis nodules show higher nodule abundances 25 kg m2 over 123 844 km2 and are more enriched in the green tech high tech and energy metals co ti te nb rey pt and zr the cis eez shows a significant resource potential for these critical metals due to their high prices high demand and the high nodule abundance which will allow for a smaller footprint for a 20 year mine site and therefore smaller environmental impact

extension and basin formation in the southern andes caused by increased convergence rate a mid cenozoic trigger for the andes the southern andes between 33 and 45 s latitude are characterized by a series of complex basins that spanned the contemporaneous active continental margin which itself was characterized by volcanic activity the basins are filled with thick up to 3000 m accumulations of interbedded sedimentary and volcanic strata of late oligocene early miocene age we interpret that these basins developed during a phase of moderate extension within the plate margin system triggered by an increased rate of convergence of the farallon nazca and south american plates between 28 and 26 ma this history is inconsistent with models of convergence that link high rates of convergence of a continental margin and an oceanic plate to strong compressional coupling although extensional basins of this age are only well described in the southern andes the convergence history and volcanic chronology are similar farther north in the central andes 18 33 s leading to the speculation that extension may have characterized the late oligocene early miocene interval regionally we hypothesize that this extension was a necessary condition to subsequent building of the modern andes mountains

evidence of local sourcing of sulfur and gold in an archaean sediment hosted gold deposit abstract determining the source of sulfur in an ore deposit is key to understanding the nature of the ore forming processes the neoarchaean paulsens sediment hosted gold deposit 1 moz 7 6 g t located in the pilbara craton of western australia exhibits many of the characteristics of phanerozoic shale hosted gold deposits e g huijiabao trend northern carlin trend and sukhoi log in that 1 black shales are the dominant host rock 2 gold is hosted in pyrite as both free gold and dissolved gold in the lattice of the pyrite and 3 multiple generations of pyrite have formed due to a variety of geological processes in this contribution we utilised secondary ion mass spectrometer sims to measure the in situ quadrupole 32 s 33 s 34 s and 36 s sulfur isotope compositions of the different generations of pyrite our results indicate that the both diagenetic and hydrothermal pyrite generations display similar and anomalous 33 s signatures up to 0 4 further the 33 s 36 s arrays in the hydrothermal pyrite generations lie on a slope which is similar to that of the diagenetic pyrite these data support the hypothesis that the sulfur in the ore zones came from the host hardey formation black shales we also performed trace element analyses of syn sedimentary and early diagenetic pyrite from the hardey formaiton using nano secondary ion mass spectrometry nanosims electron probe microanalysis epma and laser ablation inductively coupled plasma mass spectrometry la icpms all of which show that the syn sedimentary and early diagenetic pyrite contain high concentrations of many trace elements as ni co cu ag se te bi including up to 1 5 ppm au these metals contents are also abundant in the several generations of mineralised hydrothermal pyrite and form clear patterns of growth associated with couple dissolution reprecipitation reactions these findings clearly indicate that the fluid that transported the au must have also been enriched in the base and precious metals that are contained in the early syn diagenesis pyrite data from this study clearly support the hypothesis that in some sediment hosted gold systems all the sulfur and gold required to form the deposit are sourced from the local sedimentary package by using the presence of anomalous mass independent sulfur isotope signatures as chemically conservative and indelible tracers it is possible to fingerprint the source of sulfur in a wide range of mineral systems thus enhancing predictive exploration strategies at the regional to camp scales

multiple sulfur isotopes and the evolution of the atmosphere interest in multiple sulfur isotope analyses has been fueled by recent reports of mass independent sulfur isotope signatures in the geologic record a non zero multiple isotopic signature of sulfur 33s and 36s is produced primarily through photochemical reactions and it is an almost perfect tracer of the source of sulfur once the signature is passed on to a given sulfur reservoir it will be preserved unless there is addition of sulfur with a different 33s or 36s in the geological record this signature has been used to study the evolution of the earth s atmosphere and to trace movement of sulfur through geological systems early in earth s history recently small but significant mass independent signatures have been reported for some younger samples raising the possibility of additional applications of multiple isotope studies the purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous but not uncommon isotopic signatures

trace elemental and sulfur lead isotopic variations in metamorphosed volcanogenic massive sulfide vms mineralization systems an example from the keketale pb zn ag deposit nw china abstract the effects of post vms volcanogenic massive sulfide deformation metamorphism on sulfide trace element and sulfur lead isotopic compositions remain unclear the greenschist to lower amphibolite facies metamorphosed keketale vms pb zn ag deposit located in the devonian maizi volcanic sedimentary basin in the chinese altay nw china provides an opportunity to resolve the abovementioned issue two mineralization stages are recognized at keketale including 1 primary banded massive and disseminated ores derived from sea floor hydrothermal mineralization and 2 ore remobilization as represented by intensively deformed ores and quartz polymetallic sulfide ore veins that crosscut the primary ores sulfide trace elements data suggest that stage ii pyrite and pyrrhotite have higher contents of cu zn ag sb and pb whereas contents of these elements are higher in stage i sphalerite and galena than their stage ii counterparts such elemental remobilization was probably caused by the rapid intragrain diffusion and subsequent fluid mediated liberation with trace elements re precipitated as particles within the same grain and nearby minerals respectively the 34scdt values in both stages show a trimodal distribution 25 9 to 22 7 17 0 to 10 6 and 0 6 to 2 1 sulfide mineral pairs formed during primary vms mineralization are not in sulfur isotopic equilibrium and only localized re equilibration occurs during deformation and metamorphism in addition the lead isotopic values of galena from remobilized sulfide veins overlap with those of the stage i galena and pyrite these data indicate that regional deformation and metamorphism of the keketale deposit can be approximated as a closed system in terms of sulfur lead isotopes whilst the presence of the anomalously low 34s values minimum 25 9 and the distinct lead isotopic ratios of sulfides from the calcite quartz veins argue for that in the late part of the metamorphic event some exotic lead and light sulfur were sourced from outside the ore field in situ 34s values of stage i sulfides vary widely 17 0 to 2 1 suggesting that the sulfur was originated from bacterial sulfate reduction bsr of marine sulfates with probably some magmatic input lead isotopes of the sulfides and mineralized meta sedimentary volcanic rocks display a linear distribution between the mantle and upper crust line in the 206pb 204pb vs 207pb 204pb diagram the lead source may be derived from both felsic volcanic rocks and mafic igneous rocks and or magmatic volatiles and the sulfur lead isotopes may result from a shallow level seawater circulating process an additional group of lead isotopic compositions of the meta volcanic rocks show elevated present day 206pb 204pb 207pb 204pb and 208pb 204pb values probably due to decay of th and u carried by deeply penetrative circulation 13 km of co2 f cl rich hydrothermal metamorphic fluids both syn vms shallow seawater and post vms deep metamorphic fluids circulation processes are critical for the metal concentration at keketale

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

seismic potential for large and great interplate earthquakes along the chilean and southern peruvian margins of south america a quantitative reappraisal the seismic potential of the chilean and southern peruvian margins of south america is reevaluated to delineate those areas or segments of the margin that may be expected to experience large or great interplate earthquakes within the next 20 years 1984 2004 long term estimates of seismic potential or the conditional probability of recurrence within a specified period of time are based on 1 statistical analysis of historic repeat time data using weibull distributions and 2 deterministic estimates of recurrence times based on the time predictable model of earthquake recurrence both methods emphasize the periodic nature of large and great earthquake recurrence and are compared with estimates of probability based on the assumption of poisson type behavior the estimates of seismic potential presented in this study are long term forecasts only as the temporal resolution or standard deviation of both methods is taken to range from 15 to 25 of the average or estimated repeat time at present the valparaiso region of central chile 32 35 s has a high potential or probability of recurrence in the next 20 years coseismic uplift data associated with previous shocks in 1822 and 1906 suggest that this area may have already started to rerupture in 1971 1973 average repeat times also suggest this area is due for a great shock within the next 20 years flanking segments of the chilean margin coquimbo illapel 30 32 s and talca concepcion 35 38 s presently have poorly constrained but possibly quite high potentials for a series of large or great shocks within the next 20 years in contrast the rupture zone of the great 1960 earthquake 37 46 s has the lowest potential along the margin and is not expected to rerupture in a great earthquake within the next 100 years in the north the seismic potentials of the mollendo arica 17 18 s and arica antofagasta 18 24 s segments which last ruptured during great earthquakes in 1868 and 1877 are also high but poorly constrained

active tectonics in the lesser caucasus coexistence of compressive and extensional structures detailed spot image analysis which completed field data and a microseismicity study was done on the central caucasian mountain belt georgia armenia and eastern turkey north of the front of the arabian collision in order to clarify the relationships between compression extension and volcanism in fact this region is characterized by relatively complex active tectonics associating both n s compressive e w thrusts and folds and e w extensional n s normal faults and dikes structures accompanied by considerable neogene to quaternary volcanism and ne sw left lateral and nw se right lateral strike slip faults these different structures are all intricately imbricated and can be observed at different scales the general layout implies an important variation in the stress state for instance this passes from a n s compression in the spitak earthquake fault zone to an e w extension at the aboul samsar volcanic axis these results agree well with the n s convergence between arabia and eurasia and the e w lateral expulsion of the anatolian and iranian blocks a detailed cartographic network of active structures was drawn and their kinematic relationships were specified in places recent offsets on strike slip faults were estimated at about 500 to 1000 m suitable sites for future determination of fault velocity displacements were also selected this study shows that some strike slip faults behave partly like faults which transform the e w extension of the n s striking normal faults into a n s compression along the e w thrusts one of the characteristics of this region is the continuous important volcanic activity at least from the jurassic until now this persistence evidences a lithospheric thinning which remained in spite of the recent arabian eurasian collision because of the e w extension linked to the opposite lateral expulsion of the anatolian and iranian blocks this geodynamic evolution can explain the juxtaposition and superimposition of volcanic structures and thrusts in a general compressive context

magmatic evolution of the puyehue cordon caulle volcanic complex 40 s southern andean volcanic zone from shield to unusual rhyolitic fissure volcanism abstract magmas erupted from quaternary volcanoes of southern andes between 37 and 46 s latitude are mainly basaltic to andesitic however pccvc 40 s shows a singular magmatic evolution due to the abnormal evacuation of rhyolites especially in the last 100 ka in addition pccvc is the result of juxtaposing products from the nw trending alignment of cordillera nevada caldera cordon caulle fissure volcano and the puyehue stratocone using 40 ar 39 ar and 14 c geochronology it can be established that they evolved since ca 500 ka as coeval but separated vents with a first stage of shield volcanism followed by repeated collapses that formed an internal nw elongated graben from ca 100 ka volcanic activity occurred in both a fissure system cordon caulle and a central volcano puyehue holocene explosive eruptions mainly in the puyehue crater accompanied the dome growing along a nw trending fissure system last historical eruptions were in 1921 and 1960 when nw fissures of cordon caulle fed rhyodacitic lava flows in 1960 the fissure eruption was triggered by a remote mw 9 5 thrust earthquake cordillera nevada caldera presents a reduced compositional range 52 63 sio 2 and geochemical features of low pressure magma mixing and assimilation instead cordon caulle and puyehue volcanoes have a wide silica range 48 71 sio 2 and an outstanding affinity which can be modelled with initial high pressure fractional crystallization moderate magma mixing and subsequent low pressure fractional crystallization from a common parental source the exceptional magmatic evolution and eruptive style of pccvc in southern andes could be related with the physics of the plumbing system which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime

the regional intraplate stress field in south america a compilation of lithospheric stress directions for continental south america and the inferred major patterns of the regional intraplate stress field are presented stress orientations are based primarily on earthquake focal mechanisms and quaternary fault slip inversion published in the literature four new focal mechanisms based on short period p wave modeling and selected centroid moment tensor solutions published by u s geological survey consistent with p wave first motions at south american and other world wide standard seismograph network stations are also included in the data base the observed patterns of intraplate stresses may be useful in constraining numerical models of the plate driving forces in the south american plate in the andean plateau altitudes greater than 3000 m n s extensional stresses predominate e w compressional stresses are observed in the sub andean and platform regions extending up to about 1000 km east of the andes the maximum horizontal stress shmax is uniformly oriented in the e w direction throughout western south america averages of the shmax direction at grid points spaced 2 5 o were taken as representing the regional field the e w direction of this regional field is not affected by the change of strike of the andean chain nor by the contact of a flat subducted slab underneath the regional shmax direction is oriented 15 o more clockwise than the direction of the nazca plate convergence the difference between the regional shmax orientations and the absolute plate motion may be only about 6 o this may indicate that contact forces with the nazca plate may not be the only major contributor to the intraplate stresses in western south america the eastern limit of this andean stress province seems to coincide with aseismic regions in the upper amazon basin and in the paraml basin in the central amazonian region seismicity and stress data suggest a seismic province with n s compressional stresses the origin of these stresses is not yet clearly understood but could possibly be related to lower crustal loading along the middle amazon basin in northeastern brazil seismicity is characterized by upper crustal strike slip earthquakes bordering the potiguar marginal basin a model is proposed for this region in which the stress field is the result of a superposition of regional e w compressional stresses and local extensional stresses oriented perpendicular to the continental margin possibly related to density contrasts and sediment loading in the continental shelf

an insar based survey of volcanic deformation in the southern andes we use interferometric synthetic aperture radar insar to search for surface deformation in the southern andes 40 s 46 s and 49 s 53 s associated with magmatic processes although the available data are not optimal we can constrain the amount of volcanic deformation at about 27 holocene volcanoes between the years 1993 1999 we detect inflation of cerro hudson volcano following its 1991 eruption and use spherical and non spherical models to constrain the source of deformation to be between 4 and 8 km below sea level we measure the rate of deformation to be about 5 cm year in the radar line of sight and infer that the maximum deformation could exceed 10 cm year in the center of the caldera within the errors of the measurements the rate of deformation is constant from 1993 1998 10 30 10 6 m 3 year at this rate 100 200 years is required to accumulate the volume of material erupted in 1991

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved

sulfur isotope characteristics of metamorphosed zn cu volcanogenic massive sulfides in the areachap group northern cape province south africa zn and cu rich massive sulfide ores of volcanogenic origin volcanogenic massive sulfide vms deposits occur as stratiform stratabound lenses of variable size hosted by gneisses amphibolites and schists of the areachap group in the northern cape province of south africa the areachap group represents the highly deformed and metamorphosed remnants of a mesoproterozoic volcanic arc that was accreted onto the western margin of the kaapvaal craton during the 1 0 1 2 ga namaquan orogeny sulfur isotope data 34s are presented for 57 sulfide separates and one barite sample from five massive sulfide occurrences in the areachap group although sulfides from each site have distinct sulfur isotope values all 34s values fall within a very limited range 3 0 to 8 5 barite has a 34s value of 18 5 very different from that of associated sulfides at one of the studied sites kantienpan a distinct increase in 34s of sulfides is observed from the massive sulfide lens into the disseminated sulfides associated with a distinct footwall alteration zone sulfide sulfide and sulfide barite mineral pairs which recrystallized together during amphibolite and lower granulite facies metamorphism are not in isotopic equilibrium sulfur isotope characteristics of sulfides and sulfates of the zn cu ores in the areachap group are however very similar to base metal sulfide accumulations associated with modern volcanic arcs and unsedimented mid ocean ridges it is thus concluded that profound recrystallization and textural reconstitution associated with high grade regional metamorphism of the massive sulfide ores of the areachap group did not result in extensive sulfur isotopic homogenization this is similar to observations in other metamorphosed vms deposit districts and confirms that massive sulfide ores remain effectively a closed system for sulfur isotopes for both sulfides and sulfates during metamorphism