seismicity and stress distribution in the copiapo northern chile subduction zone using combined on and off shore seismic observations abstract historic as well as teleseismically and locally recorded seismicity of the subduction margin of copiapo northern chile is analysed an on and off shore temporary network was deployed during 2 months in the region in order to obtain a detailed definition of the wadati benioff zone an average dip angle of 20 along the subduction thrust interplate contact was determined this value is similar to that observed along the chilean margin suggesting that there are no variations in the dip angle of the nazca plate for depths less than 50 60 km locally recorded data do not provide seismic evidence to determine whether subhorizontal subduction exists north of latitude 28 s teleseismically recorded events exhibit a low rate of occurrence of inland earthquakes with a tendency for epicentres to be located off shore in contrast locally recorded seismicity reveals a homogeneous epicentral distribution without a predominance of off shore events along the subduction thrust contact there is a reverse stress regime with the greatest compression axis 1 horizontal and oriented perpendicular to the strike of the trench events located above the main decollement are in a normal stress regime with the minimum compressive stress axis 3 horizontally oriented parallel to the convergence direction the events located below the coupled interplate contact also lie in a normal faulting regime but the 3 axis plunges almost parallel to the subducting plate the intermediate depth fault plane solutions exhibit a substantial scatter suggesting a complicated faulting regime similar to that observed in previous studies of northern chile they are associated with a normal faulting stress regime in which 3 is oriented in a n14 e direction parallel to the strike of the trench high resolution bathymetric data and seismicity located above the thrust contact suggest that seamounts are being subducting

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

sample scale carbon isotopic variability and diverse biomass in the paleoproterozoic zaonega formation russia abstract the stratigraphic record of organic matter in the c 1 97 ga zaonega formation zf onega basin northwestern russia exhibits a distinct negative 13c excursion 13corg from 25 to 40 vpdb which was previously interpreted either to reflect a disturbance in the global carbon cycle after the great oxidation event or to have been caused by an increase in basinal methanotrophic activity in order to assess the nature of primary biomass and the effects of post depositional alteration we here report the sample scale carbon isotopic characteristics of organic matter in two drill cores from the zf covering 500 m of stratigraphy by using secondary ion mass spectrometry sims the results confirm that the organic matter has to a large extent preserved the primary isotopic signatures whereas secondary effects are limited

morphology and geology of the continental shelf and upper slope of southern central chile 33 s 43 s the continental shelf and slope of southern central chile have been subject to a number of international as well as chilean research campaigns over the last 30 years this work summarizes the geologic setting of the southern central chilean continental shelf 33 s 43 s using recently published geophysical seismological sedimentological and bio geochemical data additionally unpublished data such as reflection seismic profiles swath bathymetry and observations on biota that allow further insights into the evolution of this continental platform are integrated the outcome is an overview of the current knowledge about the geology of the southern central chilean shelf and upper slope we observe both patches of reduced as well as high recent sedimentation on the shelf and upper slope due to local redistribution of fluvial input mainly governed by bottom currents and submarine canyons and highly productive upwelling zones shelf basins show highly variable thickness of oligocene quaternary sedimentary units that are dissected by the marine continuations of upper plate faults known from land seismic velocity studies indicate that a paleo accretionary complex that is sandwiched between the present relatively small active accretionary prism and the continental crust forms the bulk of the continental margin of southern central chile

a double layered seismic zone in arica northern chile a double layered seismic zone is determined in arica northern chile using locally recorded events at depths 100 km two planes of seismicity can be observed one dipping at 30 e with 10 km of thickness and a second parallel plane 20 25 km deeper with the same average thickness fault plane solutions for both layers show a wide variability even between nearby events the genesis of the arica double seismic zone seems to be independent of the age the relative convergence rate and direction of the nazca plate because all of these parameters are almost the same along the whole northern chile and a clear separation of the seismicity into two layers is only observed around the arica elbow moreover it cannot be responsible of the double layered seismic zone because no similar significant changes are observed in the other well studied double seismic zones

chilean megathrust earthquake recurrence linked to frictional contrast at depth fundamental processes of the seismic cycle in subduction zones including those controlling the recurrence and size of great earthquakes are still poorly understood here by studying the 2016 earthquake in southern chile the first large event within the rupture zone of the 1960 earthquake moment magnitude mw 9 5 we show that the frictional zonation of the plate interface fault at depth mechanically controls the timing of more frequent moderate size deep events mw 8 5 we model the evolution of stress build up for a seismogenic zone with heterogeneous friction to examine the link between the 2016 and 1960 earthquakes our results suggest that the deeper segments of the seismogenic megathrust are weaker and interseismically loaded by a more strongly coupled shallower asperity deeper segments fail earlier 60 yr recurrence producing moderate size events that precede the failure of the shallower region which fails in a great earthquake recurrence 110 yr we interpret the contrasting frictional strength and lag time between deeper and shallower earthquakes to be controlled by variations in pore fluid pressure our integrated analysis strengthens understanding of the mechanics and timing of great megathrust earthquakes and therefore could aid in the seismic hazard assessment of other subduction zones the recurrence time of megathrust earthquakes in chile may be controlled by frictional contrasts at depth according to analyses of stress build up and release related to the december 2016 southern chile earthquake

evidence of sub vent biosphere enzymatic activities in 308 c deep sea hydrothermal systems at suiyo seamount izu bonin arc western pacific ocean abstract a high temperature deep sea hydrothermal system related to dacitic arc volcanism was drilled using a tethered submarine rock drill system as a part of the archaean park project the benthic multi coring system bms employed allowed for direct sampling of microorganisms rocks and fluids beneath hydrothermal vents the samples examined in this study were from sites apsk 05 and apsk 07 on the suiyo seamount of the izu bonin arc in the pacific ocean based on the vertical distribution of samples derived from this vigorous sub vent environment a model of deep sea subterranean chemistry and biology was determined detailing optimal microbial activities deep sea hydrothermal sub vent core samples of dacitic arc volcanism obtained at the suiyo seamount izu bonin arc western pacific ocean were analyzed for acid and alkaline phosphatase enzymatic activities useful biomarkers of acid phosphatase acp and alkaline phosphatase alp enzymatic activities were positively correlated against each other and was greatest at the partial middle core sequences acp and alp activities determined were as high as 5 10 and 6 80 nmol min g rock respectively biochemical indicators of acp and alp were consistent with the origin of biogenic amino acids occupied in the sub vent region and microbial cell number in the fluid the significant enzymatic activities demonstrated in this study provides crucial evidence that sub vent regions represent part of the previously unknown extreme environment biosphere extending the known subterranean habitable spaces of for example extremophilic microbes this boring trial was first example of discharging high temperature hydrothermal activities at the frontal arc volcanoes

karelian shungite an indication of 2 0 ga old metamorphosed oil shale and generation of petroleum geology lithology and geochemistry abstract the ca 2 0 ga old 600 m thick upper zaonezhskaya formation near lake onega nw russia contains unusually high concentrations of corg up to 98 averaging around 25 the formation contains an estimated 25 1010 tonnes of organic carbon accumulated within an area of 9000 km2 organic material is represented by shungite which forms a black dense amorphous or nanocrystalline mass consisting of c with traces of n o s and h autochthonous shungite occurs as disseminated organic material 0 1 50 corg which when mixed with migrated bitumen now pyrobitumen appears as coal like seams and lenses of semilustrous and semimat layer shungite rocks oil shales 50 75 corg the migrated bitumen originally petroleum represented by the lustrous vein and layer shungite conformably fills interbedding spaces or cross cutting joints and usually contains 80 98 corg the shungite bearing rocks of the upper zaonezhskaya formation represent one of the most richest accumulations of organic material reported from the palaeoproterozoic and one of the geologically earliest stages of petroleum generation the sediments of the zaonezhskaya formation were initially deposited in brackish water in a non euxinic lagoonal environment the high c s ratio 8 1000 with a zero intercept on the c s cross plot indicates that deposition occurred in sulphur poor water intensive synchronous volcanism may have contributed to both the enhanced delivery of nutrients and elevated sedimentation rate and eventually to the high degree of preservation of organic material the integrated data suggest that the organic material has a biogenic origin most likely algal or bacterial the organic material suffered complex catagenetic and metamorphic alteration which is reflected in 1 the four modal distribution of corg content with maxima at 5 30 65 and 95 2 highly variable 13 c org 45 to 17 3 bimodal distribution of 13 c org with maxima at 28 and 39 and 4 low h c ratios 0 005 0 2 abundant diagenetic carbonates associated with shungite rocks 13 c carb 5 to 26 and the presence of pyrite 34 s 22 to 31 reflects substantial loss of organic matter via bacterial reduction of sulphate during diagenesis the shungite rocks are characterised by a further substantial loss 50 of biologically produced organic material in the course of thermal maturation and by a depletion in 12 c 10 the isotopic composition of carbonate concretions does not indicate the involvement of fermentative diagenesis conservative estimates give 13corg of 34 as the best value of the initial biomass lustrous vein and layer shungite containing more than 80 corg are considered to be allochthonous migrated bitumen originally petroleum the semilustrous and semimat layer shungite rocks containing 55 75 corg represent oil shales with both migrated bitumen originally petroleum and autochthonous kerogen residues the oil source rocks were apparently hosted in the zaonezhskaya formation the generated oil has migrated both vertically and laterally with the highest concentration in cupola structures the locality at shunga represents the most significant volume of trapped petroleum from the study area

deep lithospheric structures along the southern central chile margin from wide angle p wave modelling p crustal and upper mantle structures of the subduction zone in south central chile between 42 degrees s and 46 degrees s are determined from seismic wide angle reflection and refraction data using the seismic ray tracing method to calculate minimum parameter models three profiles along differently aged segments of the subducting nazca plate were analysed in order to study subduction zone structure dependencies related to the age that is thermal state of the incoming plate the age of the oceanic crust at the trench ranges from 3 ma on the southernmost profile immediately north of the chile triple junction to 6 5 ma old about 100 km to the north and to 14 5 ma old another 200 km further north off the island of chiloe remarkable similarities appear in the structures of both the incoming as well as the overriding plate the oceanic nazca plate is around 5 km thick with a slightly increasing thickness northward reflecting temperature changes at the time of crustal generation the trench basin is about 2 km thick except in the south where the chile ridge is close to the deformation front and only a small 800 m thick trench infill could develop in south central chile typically three quarters 1 5 km of the trench sediments subduct below the decollement in the subduction channel to the north and south of the study area only about one quarter to one third of the sediments subducts the rest is accreted above similarities in the overriding plate are the width of the active accretionary prism 35 50 km and a strong lateral crustal velocity gradient zone about 75 80 km landward from the deformation front where landward upper crustal velocities of over 5 0 5 4 km s su 1 su decrease seaward to around 4 5 km s su 1 su within about 10 km which possibly represents a palaeo backstop this zone is also accompanied by strong intraplate seismicity differences in the subduction zone structures exist in the outer rise region where the northern profile exhibits a clear bulge of uplifted oceanic lithosphere prior to subduction whereas the younger structures have a less developed outer rise this plate bending is accompanied by strongly reduced rock velocities on the northern profile due to fracturing and possible hydration of the crust and upper mantle the southern profiles do not exhibit such a strong alteration of the lithosphere although this effect may be counteracted by plate cooling effects which are reflected in increasing rock velocities away from the spreading centre overall there appears little influence of incoming plate age on the subduction zone structure which may explain why the m w 9 5 great chile earthquake from 1960 ruptured through all these differing age segments the rupture area however appears to coincide with a relatively thick subduction channel

global nature of the paleoproterozoic lomagundi carbon isotope excursion a review of occurrences in brazil india and uruguay abstract positive carbon isotope excursion is reported from paleoproterozoic carbonates of the aravalli supergroup northwestern india the minas supergroup brazil and new sections of the paso severino formation uruguay the 2 42 ga gandarela formation minas gerais brazil contains red carbonate facies bif grading into dolostones and limestones and yielding 13 c values ranging from 1 6 to 0 4 v pdb the positive c isotope excursion up to 11 v pdb in marine shallow water carbonates in india and brazil jhamarkotra formation in northwestern india and cercadinho and fecho do funil formations in minas gerais state brazil is comparable to that observed in 2 22 2 1 ga carbonate successions worldwide that were deposited during the lomagundi excursion in uruguay 13 c values up to 11 6 v pdb in the deep water paso severino formation of the piedra alta terrane are compatible with deposition at ca 2 15 ga as indicated by the 2146 7 ma u pb age of dacites occurring at the top of the unit negative 13 c values are also present in carbonates of the paso severino formation but an origin related to organic matter remineralization cannot be ruled out thin carbonate beds in the rio itapicuru greenstone belt bahia state brazil are associated as in the paso severino formation with deep water black shales and have carbon isotope values up to 9 v pdb high metamorphic grade carbonates of the jacurici terrane in the medrado ipueira area bahia brazil have carbon isotope values up to 6 9 v pdb consistent with their minimum age of 2085 5 ma inferred from the intrusive contact with and the age of the medrado norite no evidence was found in india brazil or uruguay for paleoproterozoic glacial events recognized in the 2 45 2 22 ga sedimentary successions worldwide unconformities between the gandarela and cercadinho formations in brazil and the banded gneissic complex and the lower aravalli supergroup in india might explain the absence of glacial record compositional and isotopic data presented here for studied paleoproterozoic carbonate successions allow their integration into the global record of the paleoproterozoic evolution as well as correlation with other successions of similar age the study highlights the global nature of the lomagundi excursion furthermore it indicates that the lomagundi excursion is recorded in both shallow water aravalli and minas supergroups and deep water carbonates paso severino formation and rio itapicuru greenstone belt negating a significant impact of stromatolite productivity and hypersaline conditions on carbon isotope values of carbonates deposited in shallow water open marine and isolated basins

the andean subduction zone between 22 and 25 s northern chile precise geometry and state of stress abstract one year of seismicity recorded by a local network is used to obtain more precision about the geometry and the stress regime of the andean subduction between 22 and 25 s in the northern chile seismic gap a sharp image of the wadati benioff zone wbz is obtained down to 270 km in depth a seismically quasi quiescent zone is observed in the wbz below the volcanic arc between 150 and 210 km in depth hypocentres of distant intermediate depth earthquakes located with the local network are compared with worldwide seismic network hypocentres in order to evaluate the accuracy of the wbz image at depth greater than 100 150 km in depth no shallow microearthquakes have been observed in the continental crust but some seismic activity is likely to occur locally at the deep root of the atacama fault the stress field and the characteristics of faulting along the subducted slab are investigated underthrusting and localized reverse faulting earthquakes define the seismically coupled plate interface from 20 to 50 km in depth locked zone downdip intra slab normal faulting prevails tensile zone but some strike slip faulting is observed a transition between normal faulting with variable fault azimuth and normal faulting with nearly homogeneous nnw to nw oriented fault plane is found at about 80 km in depth it is found that the stress axes 1 and 3 in the locked zone are oriented in the convergence direction 75 80 e downdip in the tensile zone 3 has a mean azimuth 60 65 e there the slab is hence submitted to a tensional force slab pull oblique relatively to the convergence the transition between seismic underthrusting and intraplate normal faulting downdip occurs at the depth where the continental moho encounters the wadati benioff zone suggesting that a relationship exists between seismic coupling and the presence of continental crust at the plate interface the pre seismic state of this segment of the andean subduction zone is confirmed by the occurrence of strong earthquakes located by the global network around the presumed rupture area and by the stress regime found along the wadati benioff zone

biological origin for amino acids in a deep subterranean hydrothermal vent toyoha mine hokkaido japan abstract concentrations of amino acids were determined for the investigation of subterranean microbiological activities in geothermal environments at toyoha mines hokkaido japan samples used were three specimens collected in hydrothermal water and cores from a hydrothermal vein and a quartz vein total hydrolyzed amino acids thaa in the hydrothermal water were in the range of 2 5 mol l to 6 2 mol l d l ratios of aspartic acid glutamic acid and alanine of the three samples were quite low not more than 0 16 thaa in the hydrothermal vein rock and the quartz vein rock were 0 2 mol g rock and 0 1 mol g rock respectively d l ratios of samples imply that these amino acids were generated through microbiological activities not abiotic hydrothermal chemical synthesis

the 1960 chile earthquake inversion for slip distribution from surface deformation summary a total of 166 observations of sea level change 130 measurements of elevation difference and 16 determinations of horizontal strain provide an excellent view of the quasi static source process of the great 1960 chilean earthquake these surface deformation data were employed in classical uniform slip fault models as well as more recently developed models that allow spatial variability of slip the best uniform slip planar usp model is 850km long 130km wide and dips 20 seventeen metres of fault displacement contributed to a usp moment of 9 4 times 1022 n m the variable slip planar vsp model concentrates slip on a 900 km long 150 km wide band parallel to the coast several peaks of slip with dimensions of 50 100 km appear in this band and are thought to represent major subduction zone asperities important fractures of the oceanic lithosphere bound the 1960 rupture and are offered as a potential source of fault segmentation within the chilean subduction zone the vsp moment for 1960 earthquake totals 9 5 times 1022 n m about one fifth of the value estimated for the foreshock mainshock sequence from seismic methods except for areas out to sea geodetic resolution on the fault is fairly uniform thus it is unlikely that slip missed by the network could increase the vsp moment much beyond 1 8 times 1023 n m several patches of moment isolated from the main body at 80 110 km depth are found down dip in the vsp model and are presumably indicative of aseismic slip one patch at the northern end of the rupture is probably associated with the initiation phase of the mainshock although the time sequence of the relationship is unknown tide gauge records suggest that another patch between 40 and 43 s responsible for the observed strain and uplifts inland at those latitudes is not of coseismic origin but derives from in place post seismic creep over several years apparently great 1960 type events are not typical members of the 128 yr earthquake cycle in south central chile the nazca south america boundary here is characterized by a variable rupture mode in which major asperities are completely broken by great earthquakes only once in four or five earthquake cycles the more frequent large earthquakes that geographically overlap the great events fill in between the locked zones

occurrence of natural fullerenes in low grade metamorphosed proterozoic shungite from karelia russia abstract we report on the occurrence of fullerenes in proterozoic shungite 2 ga from the shungite mine kondopoga karelia russia 62 12 n 34 17 e the presence of fullerenes has been confirmed by mass spectrometry with peaks at 360 and 720 amu atomic mass unit powder x ray diffraction showing ten diffraction peaks corresponding to the fullerite structure with a 1 4201 5 nm and 13 c nuclear magnetic resonance nmr spectroscopic studies showing a peak at 143 2 ppm in the kondopoga shungite mine fullerenes occur in silty shales that have experienced greenshist facies metamorphism

late cenozoic geomorphic and tectonic evolution of the patagonian andes between latitudes 42 s and 46 s an appraisal based on fission track results from the transpressional intra arc liquine ofqui fault zone fission track ft thermochronology has been applied to investigate the low temperature cooling and denudation history of the patagonian andes along the southern part of the intra arc transpressional liquine ofqui fault zone between 42 and 46 s the liquine ofqui fault is shown to have been the focus of enhanced cooling and denudation initiated between ca 16 and 10 ma several fault blocks with different cooling histories are identified these are separated by major oblique or reverse slip faults proposed to form the eastern part of a major crustal scale dextral transpression zone local very fast rates of cooling and denudation between ca 7 and 2 ma were coeval with collision of the chile rise an active mid oceanic ridge with the peru chile trench between 47 and 48 s this location is close to the southern termination of the liquine ofqui fault implying that the collision of the ridge was a major force driving late cenozoic transpression the lack of significant cooling and denudation before ca 16 ma is indicative of pure strike slip or transtensional movement along the liquine ofqui fault before the collision of the ridge digital landscape analysis supports glacial and periglacial erosion as the main contributor to denudation since ca 7 ma leading to restriction of topographic development the combination of transpression induced rock uplift and glacial erosion is shown to be very effective at causing localized denudation anomalously young ft ages along the liquine ofqui fault are attributed to the existence of a late cenozoic localized heat flow anomaly along the fault

the chiloe mw 7 6 earthquake of 25 december 2016in southern chile and its relation tothe mw 9 5 1960 valdivia earthquake on 25 december 2016 a mw 7 6 earthquake broke a portion of the southern chilean subduction zone south of chiloe island located in the central part of the mw 9 5 1960 valdivia earthquake this region is characterized by repeated earthquakes in 1960 and historical times with very sparse interseismic activity due to the subduction of a young 15 ma and therefore hot oceanic plate we estimate the co seismic slip distribution based on a kinematic finite fault source model and through joint inversion of teleseismic body waves and strong motion data the coseismic slip model yields a total seismic moment of 3 94 1020 nm that occurred over 30 s with the rupture propagating mainly downdip reaching a peak slip of 4 2 m regional moment tensor inversion of stronger aftershocks reveals thrust type faulting at depths of the plate interface the fore and aftershock seismicity is mostly related to the subduction interface with sparse seismicity in the overriding crust the 2016 chiloe event broke a region with increased locking and most likely broke an asperity of the 1960 earthquake the updip limit of the main event aftershocks foreshocks and interseismic activity are spatially similar located 15 km offshore and parallel to chiloe islands west coast the coseismic slip model of the 2016 chiloe earthquake suggests a peak slip of 4 2 m that locally exceeds the 3 38 m slip deficit that has accumulated since 1960 therefore the 2016 chiloe earthquake possibly released strain that has built up prior to the 1960 valdivia earthquake

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

role of organic matter in the proterozoic oklo natural fission reactors gabon africa of the sixteen known oklo and the bangombe natural fission reactors hydrothermally altered elastic sedimentary rocks that contain abundant uraninite and authigenic clay minerals reactors 1 to 6 at oklo contain only traces of organic matter but the others are rich in organic substances reactors 7 to 9 are the subjects of this study these organic rich reactors may serve as time tested analogues for anthropogenic nuclear waste containment strategies organic matter helped to concentrate quantities of uranium sufficient to initiate the nuclear chain reactions liquid bitumen was generated from organic matter by hydrothermal reactions during nuclear criticality the bitumen soon became a solid consisting of polycyclic aromatic hydrocarbons and an intimate mixture of cryptocrystalline graphite which enclosed and immobilized uraninite and the fission generated isotopes entrapped in uraninite this mechanism prevented major loss of uranium and fission products from the natural nuclear reactors for 1 2 b y 24 refs 4 figs

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

reawakening of large earthquakes in south central chile the 2016 mw 7 6 chiloe event on 25 december 2016 the mw 7 6 chiloe earthquake broke a plate boundary asperity in south central chile near the center of the rupture zone of the mw 9 5 valdivia earthquake of 1960 to gain insight on decadal scale deformation trends and their relation with the chiloe earthquake we combine geodetic teleseismic and regional seismological data gps velocities increased at continental scale after the 2010 maule earthquake probably due to a readjustment in the mantle flow and an apparently abrupt end of the viscoelastic mantle relaxation following the 1960 valdivia earthquake it also produced an increase in the degree of plate locking the chiloe earthquake occurred within the region of increased locking breaking a circular patch of 15 km radius at 30 km depth located near the bottom of the seismogenic zone we propose that the chiloe earthquake is a first sign of the seismic reawakening of the valdivia segment in response to the interaction between postseismic viscoelastic relaxation and changes of interseismic locking between nazca and south america

petroleum surface oil seeps from a palaeoproterozoic petrified giant oilfield early palaeoproterozoic rocks from the onega basin in russian fennoscandia contain evidence for substantial accumulation and preservation of organic matter up to 75 wt total organic carbon with an estimated original petroleum potential comparable to a modern supergiant oilfield the basin contains a uniquely preserved petrified oilfield including evidence of oil traps and oil migration pathways here we report the discovery of the surface expression of a migration pathway along which petroleum was flowing from the sub surface this surface oil seep the first occurrence ever reported from the palaeoproterozoic appears as original bitumen clasts redeposited in palaeoproterozoic lacustrine turbidites the 13corg of clastic pyrobitumen ranges between 35 4 and 36 0 n 14 which is within the range of interbed and vein trapped fossil oil 46 and 24 suggesting similar source biogenic organic matter whose isotopic composition was modified during thermal maturation is the likely source for the migrated hydrocarbon

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

origins of fullerenes in rocks this article is a technical comment and author response to the the discovery of naturally occuring fullerenes in shunga rock samples the commenting researchers did not find detectable amounts of fullerenes in a variety of carbon rich rocks they hypothesize that the fullerenes found in the shunga sample were probably a localized event the original researchers buseck and tsipursky provide a rebuttal with further comments including parallels to other minerological occurences all agreed that more data are needed 10 refs

moho topography and subducting oceanic slab of the chilean continental margin in the maximum slip segment of the 1960 mw 9 5 valdivia chile earthquake from p receiver functions the maximum slip area of the 1960 mw 9 5 valdivia chile earthquake has been investigated down to 100 km depth by a receiver function survey along two trench perpendicular profiles at 39 3 and 39 5 s the data are compared with seismicity and local earthquake tomography we find a slab of ca 35 dip at depths similar to what is observed to the north and south of the study area the slab and the overlying mantle wedge show a local decrease in seismic velocities possibly caused by hydration or underplating of sediments the presence of hydrated or sedimentary rocks would reduce plate coupling in this region in agreement with recent gps measurements the moho is found at depths of 30 to 40 km deepening from the coast to the andes the moho topography is close to isostatic equilibrium under the volcanic centre of villarrica quetrupillan and lanin the moho conversion occurs about 10 km shallower than expected for a standard isostatic model this can be explained by a density reduction in the lower crust due to magmatic processes or by non compensated stress

structure and tectonics of the central chilean margin 31 33 s implications for subduction erosion and shallow crustal seismicity the pre and current collision of the juan fernandez ridge with the central chilean margin at 31 33 s is characterized by large scale crustal thinning and long term subsidence of the submarine forearc caused by subduction erosion processes here we study the structure of the central chilean margin in the ridge trench collision zone by using wide angle and multichannel seismic data the transition from the upper to middle continental slope is defined by a trenchward dipping normal scarp with variable offsets of 500 2000 m height beneath the scarp the 2 d velocity depth models show a prominent lateral velocity contrast of 1 s 1 that propagates deep into the continental crust defining a major lateral seismic discontinuity the discontinuity is interpreted as the lithological contact between the subsided collapsed outermost forearc composed of eroded and highly fractured volcanic rocks and the seaward part of the uplifted coastal cordillera made of less fractured metamorphic igneous rocks extensional faults are abundant in the collapsed outermost forearc however landward of the continental slope scarp both extensional and compressional structures are observed along the uplifted continental shelf that forms part of the coastal cordillera particularly at the landward flank of the valparaiso forearc basin 32 33 5 s shallow crustal seismicity has been recorded in 2008 2009 forming a dense cluster of thrust events of mw 4 5 the estimated hypocentres spatially correlate with the location of the fault scarp and they highlight the upper part of the seismic crustal discontinuity

active faulting and heterogeneous deformation across a megathrust segment boundary from gps data south central chile 36 39 s 1 this study focuses on the present day deformation mechanisms of the south central chile margin at the transition zone between two megathrust earthquake segments defined from historical data the valdivia and concepcion sectors new gps data and finite element models with complex geometries constrained by geophysical data are presented to gain insight into forearc kinematics and to address the role of upper plate faults on contemporary deformation gps vectors are heterogeneously distributed in two domains that follow these two earthquake segments we find that models which simulate only interseismic locking on the plate interface fail to reproduce surface deformation in the entire study area in the concepcion domain models that include a crustal scale fault in the upper plate better reproduce the gps observations in the valdivia domain gps data show regional scale vertical axis rotations which could reflect postseismic deformation processes at the edge of the mw 9 5 earthquake that ruptured in 1960 and or activity of another crustal fault related to motion of a forearc sliver our study suggests that upper plate faults in addition to earthquake cycle transients may exert an important control on the surface velocity of subduction zone forearcs

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

a giant palaeoproterozoic deposit of shungite in nw russia genesis and practical applications abstract occurrences of 2 0 ga mature organic material from the lake onega area nw russia constitute one of the most remarkable accumulations of organic carbon from the palaeoproterozoic the deposit occurs in a 1000 m sedimentary volcanic succession developed over an area of 9000 km 2 with an estimated total carbon reserve exceeding 25 10 10 tonnes the organic material occurs in the form of the mineraloid shungite which is a black non crystalline semi metallic material that contains 98 wt c the shungite bearing rocks were accumulated within a volcanic continental rift setting in a non euxinic brackish water lagoonal environment developed on the rifted margin of the archaean craton the occurrences of shungite bearing rocks represent a combination of a petrified oil field petrified organosiliceous diapirs and oil spills these are exemplified by three types of deposit i in situ stratified ii migrated diapirs and iii redeposited clastic in situ stratified deposits are composed of metamorphosed oil shales 80 wt c diapiric deposits form non stratified cupolas or mushroom shaped bodies composed of shungite containing 35 75 wt sio 2 and 20 55 wt c these are considered to represent organosiliceous rocks originally gels or mud the shungite rocks show abundant shrinkage cracks cryptic fluidal textures and brecciation caused by multiple fluidisation processes the current data are consistent with either diapiric or mud volcanic origins occurrences of clastic shungite are hosted by lacustrine volcanoclastic greywackes deposited from turbiditic flows shungite occurs in rocks as shungite has a heterogeneous molecular structure in which carbon occurs as 10 nm globules irregularly distributed within carbon showing no structure the unusual physicochemical and structural properties of shungite are used in diverse industrial and environmental applications including metallurgy water purification thermolysis and organosynthesis of cyclic hydrocarbons shungite is an effective sorbent for removal of organic and inorganic substances pathogenic bacteria and heavy metals from contaminated water

impact of megathrust geometry on inversion of coseismic slip from geodetic data application to the 1960 chile earthquake 1 we analyze the role of megathrust geometry on slip estimation using the 1960 chile earthquake mw 9 5 as an example a variable slip distribution for this earthquake has been derived by barrientos and ward 1990 applying an elastic dislocation model with a planar fault geometry their model shows slip patches at 80 110 km depth isolated from the seismogenic zone interpreted as aseismic slip we invert the same geodetic data set using a finite element model fem with precise geometry derived from geophysical data isoparametric fem is implemented to constrain the slip distribution of curve shaped elements slip resolved by our precise geometry model is limited to the shallow region of the plate interface suggesting that the deep patches of moment were most likely an artifact of the planar geometry our study emphasizes the importance of fault geometry on slip estimation of large earthquakes

tsunami earthquakes possibly widespread manifestations of frictional conditional stability 1 tsunami earthquakes shallow events that produce larger tsunamis than expected given their surface wave magnitudes ms typically have long durations and a source spectrum depleted in short period energy seven cases of underthrusting tsunami earthquakes provide information on the rupture processes but little constraint on geographic distribution or frequency we compare their rupture characteristics with smaller magnitude earthquakes on circum pacific interplate thrust faults comparable moment release time histories are found for large tsunami earthquakes and for many smaller shallow subduction zone earthquakes with significantly longer durations and additional source complexity than for events deeper than 15 km thus very shallow interplate earthquake ruptures are scale invariant with variable frictional properties on the plate interface controlling the depth dependent rupture process widespread occurrence of small shallow interplate earthquakes with long durations suggests that many subduction faults have frictional properties that may enable large tsunami generating earthquakes to occur fortunately large shallow ruptures are infrequent

structure of the seismogenic zone of the southcentral chilean margin revealed by local earthquake traveltime tomography we use traveltime data of local earthquakes and controlled sources observed by a large temporary amphibious seismic network to reveal the anatomy of the southcentral chilean subduction zone 37 39 s between the trench and the magmatic arc at this location the giant 1960 earthquake m 9 5 nucleated and ruptured almost 1000 km of the subduction megathrust for the three dimensional tomographic inversion we used 17 148 p wave and 10 049 s wave arrival time readings from 439 local earthquakes and 94 shots the resolution of the tomographic images was explored by analyzing the model resolution matrix and conducting extensive numerical tests the downgoing lithosphere is delineated by high seismic p wave velocities high vp vs ratio in the subducting slab reflects hydrated oceanic crust and serpentinized uppermost oceanic mantle the subducting oceanic crust can be traced down to a depth of 80 km as indicated by a low velocity channel the continental crust extends to approximately a 50 km depth near the intersection with the subducting plate this suggests a wide contact zone between continental and oceanic crust of about 150 km potentially supporting the development of large asperities eastward the crustal thickness decreases again to a minimum of about a 30 km depth relatively low vp vs at the base of the forearc does not support a large scale serpentinization of the mantle wedge offshore low vp and high vp vs reflect young fluid saturated sediments of forearc basins and the accretionary prism

triggered seismic activity in the liquine ofqui fault zone southern chile during the 2007 aysen seismic swarm summary we relocated the six large magnitude 5 2 mw 6 2 earthquakes of the destructive tsunamigenic aysen seismic swarm which occurred from 2007 january october in patagonian chile we used p and sh arrival times from near source stations of a temporary seismic network fortuitously deployed in the area when the swarm began and also traveltimes to stations of the permanent global networks to locate the 2007 january 23 mw 5 2 earthquake the first of the six large magnitude events this earthquake s hypocentre lies at shallow depth 10 km on the eastern strand of a major intraarc shear zone the dextral liquine ofqui fault zone using the hypocentre of the january 23 earthquake as a fixed location we relocated the five other large magnitude aysen earthquakes by joint hypocentral determination four of these five events also occurred at shallow depth on the eastern strand liquine ofqui fault whereas the 2007 april 2 earthquake occurred some 45 km to the west on the aysen fault a strike slip duplex fault that segments the area between the eastern and western liquine ofqui fault strands the five earthquakes on the liquine ofqui fault were all produced by dextral slip on n s nodal planes approximately parallel to the mapped trace of the fault the april 2 earthquake resulted from normal slip on the aysen fault modelling of coulomb stress changes on the nodal planes of the april 2 earthquake shows that the cumulative slip on the liquine ofqui fault strand could have triggered the april 2 earthquake similarly the april 2 earthquake may have triggered the mw 6 2 april 21 earthquake which caused mass wasting into aysen fjord generating a destructive tsunami the system of channels and fjords in the study region is a major shipping route around south america and therefore careful evaluation of the seismic hazard is warranted

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

comparative mass balance of volcanic edifices at the southern volcanic zone of the andes between 33 s and 46 s volcano edifice volume calculations are presented for 65 volcanoes of the 1400 km long chilean southern volcanic zone svz as a basic step in subduction zone mass budgets volume calculations are performed in a geographical information system that integrates digital elevation models based on of shuttle radar topography mission as well as aster gdem topographic data landsat satellite images and geological maps the method of volume calculation is straightforward for isolated morphologically well defined stratovolcanoes uncertainties increase for volcanic edifices that formed on pre existing rugged terrain for multi phase eruptive centers as well as for eroded edifices a revised segmentation of the arc is used to describe the spatial volume distribution of extruded magma along the svz and to discuss controlling tectonic factors peak volumes between arc and back arc are offset by 400 km the total volcanic extrusion is in the range of 10 13 km3 km ma major differences between the svz and the central american subduction system are notable with regard to volcano density and maximum volumes

vertical distribution of amino acids and chiral ratios in deep sea hydrothermal sub vents of the suiyo seamount izu bonin arc pacific ocean abstract a high temperature deep sea hydrothermal system related to dacitic arc volcanism has been drilled using a tethered submarine rock drill system as a part of the archaean park project the benthic multi coring system bms employed allows for direct sampling of microorganisms rocks and fluids beneath hydrothermal vents the samples examined in this study are from sites apsk 08 09 and 10 on the suiyo seamount of the izu bonin arc in the pacific ocean based on the vertical distribution and stereochemistry of amino acids in this vigorous sub vent environment a model of deep sea subterranean chemistry and biology is proposed describing optimal microbial activity rather than abiotically synthesized amino acids components total hydrolyzed amino acids in the hydrothermal sub vent core samples are of the order of 10 1 10 2 nmol g rock the ratios of alanine aspartic acid and aminobutyric acid glutamic acid are low consistent with a large microbial population and fresh subterranean bioorganic compounds the d l ratios of chiral amino acids such as aspartic acid glutamic acid and alanine in these rock samples were overall also quite low large enantiomeric excesses of l amino acids also support the existence of a vigorous subjacent microbial oasis in this seamount hydrothermal sub system the present findings represent crucial evidence that sub vent regions are a previously unknown extreme environment biosphere extending the known subterranean habitable spaces

accurate hypocentre determination in the seismogenic zone of the subducting nazca plate in northern chile using a combined on offshore network the coupled plate interface of subduction zones commonly called the seismogenic zone has been recognized as the origin of fatal earthquakes a subset of the after shock series of the great antofagasta thrust type event 1995 july 30 mw 8 0 has been used to study the extent of the seismogenic zone in northern chile to achieve reliable and precise hypocentre locations we applied the concept of the minimum 1 d model which incorporates iterative simultaneous inversion of velocity and hypocentre parameters the minimum 1 d model is complemented by station corrections which are influenced by near surface velocity heterogeneity and by the individual station elevations by relocating mine blasts which were not included in the inversion we obtain absolute location errors of 1 km in epicentre and 2 km in focal depth a study of the resolution parameters ale and dspr documents the importance of offshore stations on location accuracy for offshore events based on precisely determined hypo centres we calculate a depth of 46 km for the lower limit of the seismogenic zone which is in good agreement with previous studies for this area for the upper limit we found a depth of 20 km our results of an aseismic zone between the upper limit of the seismogenic zone and the surface correlates with a detachment zone proposed by other studies the results are also in agreement with thermal studies for the antofagasta forearc region

first seismic record for intra arc strike slip tectonics along the liquine ofqui fault zone at the obliquely convergent plate margin of the southern andes a temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike slip liquine ofqui fault zone lofz in southern chile seventy five shallow crustal events with magnitudes up to m tief w 3 8 and depths shallower than 25 km were observed in an 11 month period mainly occurring in different clusters those clusters are spatially related to the lofz to the volcanoes chaiten michinmahuida and corcovado and to active faulting on secondary faults further activity along the lofz is indicated by individual events located in direct vicinity of the surface expression of the lofz focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike slip mechanisms indicating a ne sw direction of the p axis for the lofz at this latitude the seismic activity reveals the present day activity of the fault zone the recent m tief w 6 2 event near puerto aysen southern chile at 45 4 s on april 21 2007 shows that the lofz is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region

volcano tectonic earthquakes a new tool for estimating intrusive volumes and forecasting eruptions abstract we present data on 136 high frequency earthquakes and swarms termed volcano tectonic vt seismicity which preceded 111 eruptions at 83 volcanoes plus data on vt swarms that preceded intrusions at 21 other volcanoes we find that vt seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from vei 0 to ultraplinian vei 6 at such previously long dormant volcanoes because large eruptions occur most commonly during resumption of activity at long dormant volcanoes vt seismicity is an important precursor for the earth s most dangerous eruptions vt seismicity precedes all explosive eruptions of vei 5 and most if not all vei 4 eruptions in our data set surprisingly we find that the vt seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption and rarely if ever starts beneath the eruption site itself the distal vt swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance beyond which hypocenter depths level out we summarize several important characteristics of this distal vt seismicity including swarm like nature onset days to years prior to the beginning of magmatic eruptions peaking of activity at the time of the initial eruption whether phreatic or magmatic and large non double couple component to focal mechanisms most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the vt seismicity from log10 v 0 77 log moment 5 32 with volume v in cubic meters and seismic moment in newton meters because the cumulative seismic moment can be approximated from the size of just the few largest events and is quite insensitive to precise locations the intruded magma volume can be quickly and easily estimated with few short period seismic stations notable cases in which distal vt events preceded eruptions at long dormant volcanoes include nevado del ruiz 1984 1985 pinatubo 1991 unzen 1989 1995 soufriere hills 1995 shishaldin 1989 1999 tacana 1985 1986 pacaya 1980 1984 rabaul 1994 and cotopaxi 2001 additional cases are recognized at frequently active volcanoes including popocateptl 2001 2003 and mauna loa 1984 we present four case studies pinatubo soufriere hills unzen and tacana in which we demonstrate the above mentioned vt characteristics prior to eruptions using regional data recorded by neic we recognized in near real time that a huge distal vt swarm was occurring deduced that a proportionately huge magmatic intrusion was taking place beneath the long dormant sulu range new britain island papua new guinea that it was likely to lead to eruptive activity and warned rabaul volcano observatory days before a phreatic eruption occurred this confirms the value of this technique for eruption forecasting we also present a counter example where we deduced that a vt swarm at volcan cosiguina nicaragua indicated a small intrusion insufficient to reach the surface and erupt finally we discuss limitations of the method and propose a mechanism by which this distal vt seismicity is triggered by magmatic intrusion

seismo tectonic structure of the aysen region southern chile inferred from the 2007 mw 6 2 aysen earthquake sequence summary on 2007 april 21 a mw 6 2 earthquake shook the aysen fjord southern chile in an unprecedented episode for this region characterized by low seismicity the area is intersected by the liquine ofqui fault system lofs a 1000 km long strike slip fault that absorbs part of the oblique convergence motion between nazca and south america plates to study the aftershock sequence of this main event we installed a seismic network of 15 stations in the area for a period of nearly 7 months we characterized the seismogenic structure of the zone by calculating a minimum 1 d local velocity model and obtaining precise hypocentral coordinates and uncertainty estimates by using a non linear probabilistic approach we also obtained fault plane solutions based on first motion polarities and sv p amplitude ratios the velocity model shows an average vp vs ratio of 1 76 for the area and low shear wave velocity values for the upper 3 km of crust the aftershock seismicity was located mainly between 4 and 10 km depth and disposed in 1 an n s trending alignment that follows the trace of the lofs and 2 an e w alignment at the east of the main fault furthermore we re analysed the previously published foreshock and early aftershock activity of the sequence including four of its largest events improving considerably previous location estimates selected focal mechanisms show a strong strike slip component that coincides with the nature of the lofs based on our new analysis we conclude that the 2007 aysen seismic sequence had a tectonic origin related to activity on the southern end of the lofs however not discarding the presence and potential action of fluids on the aftershock activity

amino acids in the 308 c deep sea hydrothermal system of the suiyo seamount izu bonin arc pacific ocean abstract deep sea hydrothermal systems are of significant interest as a new scientific frontier in a number of fields this report analyzes data obtained in ocean drilling surveys at submarine hydrothermal vents on the suiyo seamount in the izu bonin arc pacific ocean these surveys obtained direct data regarding subjacent extreme environments under extreme conditions of 308 c and greater than 14 mpa evaluation of the vertical distribution and stereochemistry of amino acids in such a vigorous hydrothermal system leads to a model of deep sea subterranean chemistry and biology that describes a lack of evidence of abiotically synthesized amino acids large enantiomeric excesses of l form amino acids supported the existence of a vigorous subjacent microbial oasis in a hydrothermal system

kolosjoki sedimentary formation a record in the aftermath of the paleoproterozoic global positive δ13c excursion in sedimentary carbonates abstract the kolosjoki sedimentary formation of the pechenga greenstone belt north eastern fennoscandia records the aftermath of the paleoproterozoic global positive 13 c excursion in sedimentary carbonates the lomagundi jatuli isotope excursion the goals of this research were to provide detailed new data on the 13 c trend in the kolosjoki sedimentary formation and generate a secular 13 c curve for the time period immediately succeeding the lomagundi jatuli isotope excursion for these purposes sedimentary carbonate samples from two new drillcores representing the kolosjoki sedimentary formation were collected in total 88 whole rock samples and 67 micro drilled subsamples ca 1 3 mg were analyzed for the isotope composition of c and o the whole rock elemental abundances and for the composition of the acid soluble fraction the kolosjoki carbonate rocks are dolostone or calcitic dolostone mg ca 0 50 0 67 with minor limestone mg ca 0 04 0 06 only weak correlation was observed between the mn sr ratios and the 13 c and 18 o values and the carbonate samples have likely retained their near primary 13 c values the sedimentary carbonate rocks show first low 13 c values at 2 to 1 and then a subtle upward increasing 13 c trend from ca 1 to 3 the increasing 13 c trend is interpreted to record a recovery from a 13 c minimum following the lomagundi jatuli isotope excursion

extending the upper temperature limit for life the upper temperature limit for life is a key parameter for delimiting when and where life might have evolved on a hot early earth the depth to which life exists in the earth s subsurface and the potential for life in hot extraterrestrial environments a combination of geological and

understanding kinematics of intra arc transcurrent deformation paleomagnetic evidence from the liquine ofqui fault zone chile 38 41 s the liquine ofqui fault zone lofz is a major 1000 km long dextral shear zone of southern chile likely related to strain partitioning of nazca plate oblique convergence with south america to understand block rotation pattern along the lofz we paleomagnetically sampled 55 sites 553 samples between 38 s and 41 s we gathered oligocene to pleistocene volcanics and miocene granites at a maximum distance of 20 km from the lofz and at both sides of it rotations with respect to south america evaluated for 36 successful sites show that crust around the lofz is fragmented in small blocks 1 to 10 km in size while some blocks at both fault edges undergo very large 150 170 rotations others do not rotate even adjacent to fault walls we infer that rotations affected equidimensional blocks while elongated crust slivers were translated subparallel to the lofz without rotating rotation pattern across the lofz is markedly asymmetric east of the fault and adjacent to it rotations are up to 150 170 clockwise and fade out 10 km east of fault these data support a quasi continuous crust kinematics characterized by small rigid blocks drag by the underlying ductile crust flow and imply 120 km of total fault offset conversely crust west of the lofz is cut by seismically active nw se sinistral antithetic faults and yields counterclockwise rotations up to 170 at 8 10 km from lofz besides the unrotated blocks further data from the chile fore arc are needed to understand block rotation kinematics and plate dynamics west of the lofz

a narrowly spaced double seismic zone in the subducting nazca plate 1 high precision relocations of intermediate depth earthquakes 80 130 km below the central andes reveal a fine scale double layered wadati benioff zone wbz upper and lower band of seismicity are separated by about 9 km and occur at the top of the oceanic crust and in the uppermost oceanic mantle respectively analysis of focal mechanisms and waveform similarities indicate that fluid processes are causing the events earthquakes in the oceanic crust occur on pre existing normal faults due to hydraulic embrittlement from metamorphic dehydration and on subvertical faults that connect the two layers in a narrow depth range extensional faulting predominates in both layers indicating that slab pull forces are the dominant stress source superseding possible unbending forces in this segment of the nazca plate

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

hydrothermal circulation and oil migration at the root of the heterogeneous micro structure of carbonaceous material in the 2 0 ga zaonega formation onega basin russia abstract organic rich rocks of the 2 0 ga zaonega formation karelia russia have been studied extensively to gain understanding of the global carbon cycle and reconstruction of paleo environments directly after the great oxidation event goe this formation has a complex history of alteration involving pervasive hydrothermal circulation hydrocarbon generation migration and mineral authigenesis several previous studies have focused on the description of these secondary effects and the identification of primary geochemical signals in the carbonaceous phases migration and infiltration of organic rich fluids appear to have had only limited effect on the primary carbon isotope record 13corg however the structural variability of carbonaceous material cm appears to have been strongly affected with a range of reported structures including carbon onion shaped nanostructures and mineral templated graphite films here we present a systematic raman spectroscopy based study of the structural variability of cm in a drill core representing the middle and upper strata of the zaonega formation the raman spectra of cm show a systematic difference in structural order between the bulk carbonaceous matrix matrix cm and the cm occurring near mineral contacts contact cm indicating that mineral templating was an important process affecting structural order in the formation the templating effect was observed on the surface of a wide range of minerals the difference in structural order between matrix cm and contact cm can be traced throughout the ca 400 m stratigraphy the structural order varied with the degree of alteration and hydrothermal circulation from highly ordered structures directly above a large gabbro intrusion at the bottom of the stratigraphy to less ordered structures higher up in the sequence this trend directly correlates with the 18o trend of secondary calcite and can be attributed to the decreasing influence and temperature regime of hydrothermal circulation upward in the stratigraphy the results presented here suggest that organic rich hydrothermal fluids can locally strongly enhance graphitization of carbonaceous materials and cause sample scale heterogeneities in the structural order of organic materials this has implications for the interpretation of carbonaceous materials in other ancient rocks experiencing circulation of organic rich hydrothermal fluids

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

a seismological study of the 1835 seismic gap in south central chile we study the possible seismic gap in the concepcion constitucion region of south central chile and the nature of the m 7 8 earthquake of january 1939 from 1 march to 31 may 1996 a seismic network of 26 short period digital instruments was deployed in this area we located 379 hypocenters with rms travel time residuals of less than 0 50 s using an approximate velocity distribution using the velest program we improved the velocity model and located 240 high precision hypocenters with residuals less than 0 2 s the large majority of earthquakes occurred along the wadati benioff zone along the upper part of the downgoing slab under central chile a few shallow events were recorded near the chain of active volcanos on the andes these events are similar to those of las melozas near santiago a few events took place at the boundary between the coastal ranges and the central valley well constrained fault plane solutions could be computed for 32 of the 240 well located events most of the earthquakes located on the wadati benioff zone had slab pull fault mechanism due to tensional stresses sub parallel to the downgoing slab this slab pull mechanism is the same as that of eight earthquakes of magnitude around 6 that are listed in the cmt catalog of harvard university for the period 1980 1998 this is also the mechanism inferred for the large 1939 chilean earthquake a very small number of events in the benioff zone had slab push mechanisms that is events whose pressureaxis is aligned with the slab these events are found in double layered wadati benioff zones such as in northern chile or japan our spatial resolution is not good enough to detect the presence of a double layer but we suspect there may be one 2002 elsevier science b v all rights reserved

interaction between forearc and oceanic plate at the south central chilean margin as seen in local seismic data we installed a dense amphibious temporary seismological network to study the seismicity and structure of the seismogenic zone in southern chile between 37 and 39 s the nucleation area of the great 1960 chile earthquake 213 local earthquakes with 14 754 onset times were used for a simultaneous inversion for the 1 d velocity model and precise earthquake locations relocated artificial shots suggest an accuracy of the earthquake hypocenter of about 1 km horizontally and 500 m vertically crustal events along trench parallel and transverse deep reaching faults reflect the interseismic transpressional deformation of the forearc crust due to the subduction of the nazca plate the transverse faults seems to accomplish differential lateral stresses between subduction zone segments many events situated in an internally structured planar seismicity patch at 20 to 40 km depth near the coast indicate a stress concentration at the plate s interface at 38 s which might in part be induced by the fragmented forearc structure

anatomy of the andean subduction zone three dimensional density model upgraded and compared against global scale models summary we present an upgraded version of a previously published 3 d density model of the andean subduction zone between 18 s and 45 s this model consists of 3 d bodies of constant density which geometry is constrained by independent seismic data and is triangulated from vertical cross sections these bodies define the first order morphology and internal structure of the subducted nazca slab and south american plate the new version of the density model results after forward modelling the bouguer anomaly as computed from the most recent version of the earth gravitational model egm2008 the 3 d density model incorporates new seismic information to better constrain the geometry of the subducted slab and continental moho cmh and has a trench parallel resolution doubling the resolution of the previous model as an example of the potential utility of our model we compare the geometry of the subducted slab and cmh against the corresponding global models slab1 0 and crust2 0 respectively this exercise demonstrates that although global models provide a good first order representation of the slab and upper plate crustal geometries they show large discrepancies up to 40 km with our upgraded model for some well constrained areas the geometries of the slab lithosphere asthenosphere boundary below the continent cmh and intracrustal density discontinuity that we present here as supporting information can be used to study andean geodynamic processes from a wide range of quantitative approaches

multiple sulphur isotope records tracking basinal and global processes in the 1 98 ga zaonega formation nw russia abstract the exceptionally organic rich rocks of the 1 98 ga zaonega formation deposited in the onega basin nw russia have refined our understanding of earth system evolution during the paleoproterozoic rise in atmospheric oxygen these rocks were formed in vent or seep influenced settings contemporaneous with voluminous mafic volcanism and contain strongly 13c depleted organic matter here we report new isotopic 34s 33s 36s 13corg and mineralogical major element total sulphur and organic carbon data for the upper part of the zaonega formation which was deposited shortly after the termination of the lomagundi jatuli positive carbon isotope excursion the data were collected on a recently obtained 102 m drill core section and show a 13corg shift from 38 to 25 sedimentary sulphides have 34s values typically between 15 and 25 reflecting closed system sulphur isotope behaviour driven by high rates of microbial sulphate reduction high sulphate demand hydrothermal activity and hydrocarbon seepage four intervals record 34s values that exceed 30 we interpret these unusually 34s enriched sulphides to be a result of limited sulphate diffusion into pore waters due to changes in sedimentation and or periods of basinal restriction additionally there are four negative 34s excursions that are interpreted to reflect changes in the open closed system behaviour of sulphate reduction or availability of reactive iron our findings highlight the influence of basinal processes in regulating sulphur isotope records and the need for care before interpreting such signals as reflecting global conditions

mineral templated growth of natural graphite films abstract organic material in sediments is progressively altered during diagenesis and metamorphism leading to the formation of kerogen and ultimately crystalline graphite bulk carbonaceous material in metamorphic terrains typically has attained an overall degree of structural order that is in line with peak metamorphic temperature on a micron to nano scale however carbonaceous material can display strong structural variation the main factor that drives this variation is the chemical and molecular heterogeneity of the precursor biologic material specific conditions during metamorphism however can also play a role in shaping the microstructure of carbonaceous material here we describe the structural variation of carbonaceous material in rocks of the 2 0 ga zaonega formation karelia russia raman spectroscopy indicates that bulk carbonaceous matter in these rocks has experienced peak temperatures between 350 and 400 c consistent with greenschist facies metamorphism on a nano scale however a strong structural heterogeneity is observed transmission electron microscopy tem reveals the occurrence of thin films of highly ordered graphitic carbon at mineral surfaces these graphite films consisting of 20 100 individual layers completely envelop quartz crystals and occur on specific crystal surfaces of chlorite it is proposed that minerals can act as templates for the parallel ordering of carbon crystallites causing enhanced graphitization within narrow zones at mineral surfaces alternatively oriented organic precursor molecules could have been adsorbed onto charged mineral surfaces leading to thin graphitic films during later metamorphic heating episodes overall the presented observations demonstrate that mineral surfaces can initiate and accelerate localized graphitization of sedimentary organic material during metamorphism and therefore cause distinct nano scale variation in structural order

intra arc crustal seismicity seismotectonic implications for the southern andes volcanic zone chile we examine the intra arc crustal seismicity of the southern andes volcanic zone svz our aim is to resolve inter seismic deformation in an active magmatic arc dominated by both margin parallel liquine ofqui fault system lofs and andean transverse faults atf crustal seismicity provides information about the schizosphere tectonic state delineating the geometry and kinematics of high strain domains driven by oblique subduction here we present local seismicity based on 16 months data collected from 34 seismometers monitoring a 200 km long section of the southern volcanic zone including the lonquimay and villarrica volcanoes we located 356 crustal events with magnitudes between mw 0 6 and mw 3 6 local seismicity occurs at depths down to 40 km in the forearc and consistently shallower than 12 km beneath the volcanic chain suggesting a convex shape of the crustal seismogenic layer bottom focal mechanisms indicate strike slip faulting consistent with ene wsw shortening in line with the long term deformation history revealed by structural geology studies however we find regional to local scale variations in the shortening axes orientation as revealed by the nature and spatial distribution of microseismicity within three distinctive latitudinal domains in the northernmost domain seismicity is consistent with splay faulting at the northern termination of the lofs in the central domain seismicity distributes along ene and wnw striking discrete faults spatially associated with hitherto seismic atf the southernmost domain in turn is characterized by activity focused along a n15 e striking master branch of the lofs these observations indicate a complex strain compartmentalization pattern within the intra arc crust where variable strike slip faulting dominates over dip slip movements

peculiar features of suiyo seamount hydrothermal fluids izu bonin arc differences from subaerial volcanism abstract this is the first report of the dissolved gas composition of a deep sea venting hydrothermal system originating from arc volcanism the origin of dissolved gases in hydrothermal fluids from the suiyo seamount in the southern izu bonin ogasawara arc is discussed on the basis of chemical and isotopic compositions twelve high temperature up to 310 c fluid samples were collected from three vents of the hydrothermal system using the submersible shinkai 2000 the average 3 he 4 he ratio of the dissolved he is 8 1 r r atm which is within the range of values reported for n morb the co 2 3 he ratio is 12 109 which is within the range of arc volcanic gas values the 13c values of co2 and ch4 are 1 and 8 5 respectively which is quite high compared with other subaerial arc volcanic gases and those from mid ocean ridges these results which do not accord with those from subaerial volcanism are unlikely to result from fractionation or addition of carbon sources during the fluid circulation but are regarded as characteristic of the magma source of suiyo seamount a simple mixing of 97 morb mantle with 3 subducting slab explains well the composition of the helium and carbon in the parent magma

seismicity and geometry of the south chilean subduction zone 41 5 s 43 5 s implications for controlling parameters in 2005 an amphibious seismic network was deployed on the chilean forearc between 41 75 s and 43 25 s 364 local events were observed in a 11 month period a subset of the p and s arrival times were inverted for hypocentral coordinates 1 d velocity structure and station delays main seismic activity occurred predominantly in a belt parallel to the coast of chiloe island in a depth range of 12 30 km presumably related to the plate interface the 30 inclination of the shallow part of the wadati benioff zone is similar to observations further north indicating that oceanic plate age is not controlling the subduction angle of the shallower part for the chilean subduction zone the down dip termination of abundant intermediate depth seismicity at approximately 70 km depth seems to be related to the young age and high temperature of the oceanic plate crustal seismicity is associated with the liquine ofqui fault zone and active volcanoes

water input and water release from the subducting nazca plate along southern central chile 33 s 46 s the age of the subducting nazca plate off chile increases northward from 0 ma at the chile triple junction 46 s to 37 ma at the latitude of valparaiso 32 s age related variations in the thermal state of the subducting plate impact on a the water influx to the subduction zone as well as on b the volumes of water that are released under the continental fore arc or alternatively carried beyond the arc southern central chile is an ideal setting to study this effect because other factors for the subduction zone water budget appear constant we determine the water influx by calculating the crustal water uptake and by modeling the upper mantle serpentinization at the outer rise of the chile trench the water release under fore arc and arc is determined by coupling fem thermal models of the subducting plate with stability fields of water releasing mineral reactions for upper and lower crust and hydrated mantle results show that both the influx of water stored in and the outflux of water released from upper crust lower crust and mantle vary drastically over segment boundaries in particular the oldest and coldest segments carry roughly twice as much water into the subduction zone as the youngest and hottest segments but their release flux to the fore arc is only about one fourth of the latter this high variability over a subduction zone of 1500 km length shows that it is insufficient to consider subduction zones as uniform entities in global estimates of subduction zone fluxes

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

testing for fullerenes in geologic materials oklo carbonaceous substances karelian shungites sudbury black tuff fullerenes have been reported from diverse geologic environments since their discovery in shungite from karelian russia our investigation is prompted by the presence of onionskin like structures in some carbonaceous substances associated with the fossil nuclear fission reactors of oklo gabon the same series of extractions and the same instrumental techniques laser desorption ionization and high resolution mass spectroscopy electron impact mass spectroscopy were employed to test for fullerenes in samples from three different localities two sites containing putative fullerenes sudbury basin and russian karelia and one new location oklo gabon we confirm the presence of fullerenes c 6 0 and c 7 0 in the black tuff of the onaping formation impact breccia in the sudbury basin but we find no evidence of fullerenes in shungite samples from various locations in russian karelia analysis of carbonaceous substances associated with the natural nuclear fission reactors of oklo yields no definitive signals for fullerenes if fullerenes were produced during sustained nuclear fission at oklo then they are present below the detection limit 100 fmol or they have destabilized since formation contrary to some expectations geologic occurrences of fullerenes are not commonplace

remarkably consistent thermal state of the south central chile subduction zone from 36 s to 45 s delineating rupture areas of subduction zone earthquakes is necessary for understanding the controls on seismic and aseismic slip for the largest recorded earthquake the 1960 chile event with moment magnitude 9 5 the rupture area is only loosely defined due to limitations in the global seismic network at the time the rupture extends 900 km along strike coastal deformation is consistent with either a constant rupture width of 180 200 km along the entire length or a narrower 115 km rupture in the southern half a southward narrowing of the seismogenic zone has been hypothesized to result from warming of the subduction zone to the south where the subducting plate is younger we present results of thermal models at 36 s 38 s 43 s and 45 s to examine potential along strike changes in thermal state models most consistent with observed surface heat flux include fluid circulation in the oceanic crust that advects heat to the ocean this ventilated hydrothermal circulation preferentially cools transects with young subducting lithosphere frictional heating preferentially warms transects with older subducting lithosphere the combined effects of frictional heating and hydrothermal circulation increase decollement temperatures in the 36 s and 38 s transects by up to 155 c and decrease temperatures in the 45 s transect by up to 150 c in our preferred models decollement temperatures 200 km landward of the trench in all four transects are 350 400 c this is consistent with a constant 200 km wide seismogenic zone for the 1960 mw 9 5 rupture with decreasing slip magnitude in the southern half of the rupture

carbonate deposition in the palaeoproterozoic onega basin from fennoscandia a spotlight on the transition from the lomagundi jatuli to shunga events abstract several deep drillholes were made in the onega palaeobasin by the fennoscandian arctic russia drilling early earth project far deep of the international continental scientific drilling program icdp these provided fresh core material documenting the lomagundi jatuli isotopic event ljie its termination and the start of the shunga event she of an enhanced accumulation of organic matter the cored section represents the most complete known record of the end of the ljie the late phase of the ljie recorded in far deep core 11a is represented by the upper part of the tulomozero formation tf a 300 m thick unit composed of variegated dolostones siltstones and shales accumulated under oxic conditions on a shallow water carbonate platform the tf hosts the earliest known thick formations of halite and massive anhydrite low temperature greenschist facies metamorphism caused partial recrystallisation of the rocks however a primary carbonate phase the dolomite exhibits a negligible degree of post depositional alteration of the carbon isotope system the dataset of 46 bulk carbonate analyses of carbon and oxygen isotopes yielded 13 c carb ranging between 6 8 and 11 8 and revealed a positive excursion from 8 to 11 8 followed by a decline to 8 towards the top of the 300 m thick succession the cored part of the overlying zaonega formation zf recovered in holes 12ab and 13a is an 800 m thick unit composed of mixed siliciclastic carbonate facies with numerous mafic lava flows and tuff beds intruded by gabbro sills the formation represents an unprecedented episode of enhanced accumulation of organic rich rocks and preserves the earliest known supergiant petrified oilfield all typifying the she the sedimentological petrographic geochemical and c and o isotopic study of over 800 m of core throughout the zf suggests that the initial carbonate deposition occurred in a lacustrine environment then rapidly proceeding through a lagoonal setting to a rifted deepwater shelf and finally to a carbonate platform both the deepwater shelf and the platformal settings are marked by organic rich environments the primary dolomite was potentially exposed to syn and post depositional hydrothermal metasomatic alterations organic matter diagenesis metamorphic mineral reactions co 2 degassing and finally a low temperature post metamorphic calcitisation resulting in overall large fluctuations of 13 c carb between 22 and 8 the dataset of over 413 bulk carbonate analyses of carbon and oxygen isotopes screened petrographically and geochemically against post depositional alteration revealed 28 least altered samples within three stratigraphic intervals suggesting multiple positive and negative 13 c carb excursions throughout over 1000 m of stratigraphy a shift from 5 to 9 followed by a drop to near zero values marks the lower part of the zf a 13 c carb decline from 8 to below zero in the middle and upper part of the zf defines the end of the ljie a subsequent prominent negative excursion down to 6 does not show convincing isotopic evidence for influence of methanogenesis and hence appears to be of primary depositional origin an erratic positive excursion in the uppermost part of the drilled section indicates return of 13 c carb to a near normal marine value

active crustal faults in the forearc region guerrero sector of the mexican subduction zone this work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate we present the results of geomorphic structural and fault kinematic analyses conducted on the convergent margin between the cocos plate and the forearc region of the overriding north american plate within the guerrero sector of the mexican subduction zone we aim to determine the active tectonic processes in the forearc region of the subduction zone using the river network pattern topography and structural data we suggest that in the studied forearc region both strike slip and normal crustal faults sub parallel to the subduction zone show evidence of activity the left lateral offsets of the main stream courses of the largest river basins gps measurements and obliquity of plate convergence along the cocos subduction zone in the guerrero sector suggest the activity of sub latitudinal left lateral strike slip faults notably the regional left lateral strike slip fault that offsets the papagayo river near the town of la venta named la venta fault shows evidence of recent activity corroborated also by gps measurements 4 5 mm year of sinistral motion assuming that during a probable earthquake the whole mapped length of this fault would rupture it would produce an event of maximum moment magnitude mw 7 7 even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike slip structures we hypothesize that these faults are active and suggest two probable explanations 1 these faults are characterized by long recurrence period i e beyond the instrumental record or 2 they experience slow slip events and or associated fault creep the analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate for the period between 1995 and 2008 revealed that frequent normal faults sub parallel to the trench could be reactivated in the current stress field related to the cocos subduction moreover these features could also be reactivated by subduction megathrust earthquakes

seismicity near the slip maximum of the 1960 mw 9 5 valdivia earthquake chile plate interface lock and reactivation of the subducted valdivia fracture zone understanding the processes behind subduction related hazards is an important responsibility and major challenge for the earth sciences few areas demonstrate this as clearly as south central chile where some of the largest earthquakes in human history have occurred we present the first observation of local seismicity in the villarrica region 39 40 s based on a temporary local network of 55 stations installed from the chilean coast into the argentinian back arc for one year while consistent with the chilean national catalog ssn our results allow us to observe smaller magnitudes with a completeness of about 2 0 and image the geometry of the wadati benioff zone from the chile trench down to 200 km offshore a gap in interplate seismicity is observed in the region of the 1960 valdivia earthquake slip above the interface two offshore seismicity clusters possibly indicate ongoing stress relaxation in the subducting nazca plate we find a prominent seismicity cluster along the extrapolated trace of the oceanic valdivia fracture zone vfz the seismicity cluster is observed between 70 and 130 km depth and comprises mainly strike slip events it indicates weakening and reactivation of the major vfz by dehydration of oceanic crust and mantle interpreting the subducted vfz section as a localized reservoir of potential fluid release offers an explanation for the villarrica volcanic complex that is located above the reactivated vfz and shows the highest volcanic activity in south america crustal seismicity is observed near puyehue volcano which recently started to erupt june 2011 key points we observe local seismicity near the 1960 valdivia maximum slip region the subducted valdivia fracture zone is reactivated by fluid release the seismogenic zone is free of seismicity events occur at faults and volcanoes

seismicity in the outer rise offshore southern chile indication of fluid effects in crust and mantle we examine the micro earthquake seismicity recorded by two temporary arrays of ocean bottom seismometers on the outer rise offshore southern chile on young oceanic plate of ages 14 ma and 6 ma respectively the arrays were in operation from december 2004 january 2005 and consisted of 17 instruments and 12 instruments respectively approximately 10 locatable events per day were recorded by each of the arrays the catalogue which is complete for magnitudes above 1 2 1 5 is characterized by a high b value i e a high ratio of small to large events and the data set is remarkable in that a large proportion of the events form clusters whose members show a high degree of waveform similarity the largest cluster thus identified consisted of 27 similar events average inter event correlation coefficient 0 8 for a 9 5 s window and waveform similarity persists far into the coda inter event spacing is irregular but very short waiting times of a few minutes are far more common than expected from a poisson distribution seismicity with these features high b value large number of similar events with short waiting times is typical of swarm activity which based on empirical evidence and theoretical considerations is generally thought to be driven by fluid pressure variations because no pronounced outer rise bulge exists on the very young plate in the study region it is unlikely that melt is accessible from decompression melting or opening of cracks a fluid source related to processes at the nearby ridge is conceivable for the younger segment but less likely for the older one we infer that the fluid source could be seawater which enters through fractures in the crust most of the similar earthquake clusters are within the crust but some of them locate significantly below the moho if our interpretation is correct this implies that water is present within the mantle hydration of the mantle is also indicated by a decrease of pn velocities below the outer rise seen on a refraction profile through one of the arrays contreras reyes e grevemeyer i flueh e r scherwath m heesemann m 2007 alteration of the subducting oceanic lithosphere at the southern central chile trench outer rise geochem geophys geosyst 8 q07003 the deepest events within the array on the 6 ma old plate occur where the temperature reaches 500 600 c consistent with the value observed for large intraplate earthquakes within the mantle 650 c suggesting that the maximum temperature at which these fluid mediated micro earthquakes can occur is similar or identical to that of large earthquakes

the first since 1960 a large event in the valdivia segment of the chilean subduction zone the 2016 m7 6 melinka earthquake abstract we present results for joint kinematic inversion of high rate gps strong motion and insar data for the 2016 m7 6 melinka earthquake we show that the source is a compact 35 s long rupture with 5 0 0 15 m of peak slip we find the melinka earthquake occurs inside the slip region for the 1960 m9 5 valdivia earthquake and within the highly locked portion of the megathrust inferred from inter seismic velocity analysis we show that there is very modest post seismic deformation at a nearby gps site qlln and argue that this indicates the melinka earthquake ruptures within the intermediate portion of the megathrust and is an isolated asperity surrounded by locked velocity weakening material further we find that the peak slip observed during this earthquake is larger than what has been accumulated in the intervening 57 years since the 1960 rupture and conclude that at least in the area of the melinka earthquake this is indicates that the 1960 valdivia event might not have used all the slip deficit available on the megathrust

synsedimentary diagenetic and metamorphic pyrite pyrrhotite and marcasite at the homestake bif hosted gold deposit south dakota usa insights on au as ore genesis from textural and la icp ms trace element studies the paleoproterozoic homestake deposit northern black hills south dakota is the largest banded iron formation bif hosted gold deposit in the world and one of the largest single gold deposits globally 1 300 t au mined at an average grade of 8 4 g t the origin of the deposit has remained in dispute from its discovery with views broadly falling into two groups 1 the gold and associated elements were externally sourced and deposited in a suitable structural and or chemical trap e g iron formation and 2 gold was indigenous to the host iron formation from which it was remobilized into dilatant structural zones during deformation and metamorphism in recent times most workers have favored the former model appealing to the broad synchroneity of paleoproterozoic metamorphism felsic magmatic activity and gold event timing la icp ms analysis of synsedimentary to early diagenetic sulfides at homestake and surrounding area indicates that the au in the orebodies may have originally had a significant syngenetic component in particular la icp ms mapping of multistage pyrites from carbonaceous shale in the upper poorman formation shows that au and a suite of trace elements co ni cu zn se mo ag sb te au hg tl pb and bi similar to those in diagenetic pyrite from around the globe are contained in anhedral sponge textured cores and nodules surrounded by relatively trace element barren au poor euhedral pyrite rims furthermore interelement ratios e g co ni ni ag of the trace element rich spongy and nodular pyrites are also similar to those of typical diagenetic pyrite la icp ms imaging of pyrrhotite in the same rocks reveals multistage growth in this mineral as well with the earlier generation having higher concentrations of ag sb pb tl and bi than its presumed metamorphic counterpart imaging of marcasite in the shales of the upper poorman formation demonstrates this mineral s high abundance of w and tl relative to all generations of pyrite and pyrrhotite mass balance calculations indicate that the volume of upper poorman formation in the mine area approx 12 km3 could potentially yield 4 500 t of au a value greater than the total mined resource by more than a factor of three these geochemical data and calculations suggest that a significant portion of the gold at homestake may have been sourced from the relatively thick carbonaceous and sulfidic black shale facies in the stratigraphic footwall to the host iron formation in a manner similar to other sediment hosted gold districts

paleotemperatures and paleofluids recorded in fluid inclusions from calcite veins from the northern flank of the ponta grossa dyke swarm implications for hydrocarbon generation and migration in the parana basin abstract the parana basin southern brazil has an atypical thermal and fluid history due to the occurrence of an episodic continental flood volcanism during the early cretaceous so far there are few data about the influence of this volcanic event on the paleotemperatures and paleofluids of the parana basin sedimentary rocks the teresina formation in the northern flank of the ponta grossa dyke swarm hosts high concentration of subsurface igneous rock bodies sills and dykes besides its covering by a hundreds meter thick volcanic rock cap in this study we used fluid inclusion analysis performed in horizontal and vertical calcite veins from the teresina formation and from a late cretaceous basic dyke to estimate paleotemperatures and to characterize the composition of diagenetic paleofluids homogenization temperatures of requilibrated fluid inclusions show that the teresina formation reached temperatures above 200 c horizontal parallel bedding calcite veins from the teresina formation record low to high salinity 2 26 wt nacl eq aqueous paleofluids the prevalence of high salinity fluid inclusions associated with light hydrocarbon fluid inclusions indicates deep buried fluids fluid inclusions in vertical calcite vein from basic dyke comprise only low salinity aqueous fluids 0 3 wt eq nacl interpreted as dominated by meteoric water the recorded paleotemperatures are attributed to the heating by the parana volcanic event during the early cretaceous with the thermal effect of the volcanic rock cap surpassing the effect of nearby sills and dykes estimated paleotemperatures higher than 200 c would allow the generation of light liquid and gaseous hydrocarbons overpressured compartments in the teresina formation allowed the expulsion of buried pore fluids high salinity aqueous fluids and hydrocarbons to fracture systems where they mixed with meteoric water the input of meteoric water through fracture systems connected with the surface favored hydrocarbons degradation in the early stages of source rock maturation during the early cretaceous

earthquake swarms and slow slip on a sliver fault in the mexican subduction zone the mexican subduction zone is an ideal location for studying subduction processes due to the short trench to coast distances that bring broad portions of the seismogenic and transition zones of the plate interface inland using a recently generated seismicity catalog from a local network in oaxaca we identified 20 swarms of earthquakes m

deep sea smokers windows to a subsurface biosphere since the discovery of hyperthermophilic microbial activity in hydrothermal fluids recovered from smoker vents on the east pacific rise the widely accepted upper temperature limit for life based on pure culture data has risen from below the boiling point of water at atmospheric pressure to approximately 115 degrees c many microbiologists seem willing to speculate that the maximum may be closer to 150 degrees c we have postulated not only higher temperatures than these under deep sea hydrostatic pressures but also the existence of a biosphere subsurface to accessible seafloor vents new geochemical information from the endeavour segment of the juan de fuca ridge indicative of subsurface organic material caused us to re examine both the literature on hyperthermophilic microorganisms cultured from deep sea smoker environments and recent results of microbial sampling efforts at actively discharging smokers on the endeavour segment here we offer the case for a subsurface biosphere based on an interdisciplinary view of microbial and geochemical analyses of endeavour smoker fluids a case in keeping with rapidly evolving geophysical understanding of organic stability under deep sea hydrothermal conditions

mantle subducting slab structure in the region of the 2010 m8 8 maule earthquake 30 40 s chile we present a new tomographic model of the mantle in the area of the 2010 m8 8 maule earthquake and surrounding regions increased ray coverage provided by the aftershock data allows us to image the detailed subducting slab structure in the mantle from the region of flat slab subduction north of the maule rupture to the area of overlapping rupture between the 1960 m9 5 and the 2010 m8 8 events to the south we have combined teleseismic primary and depth phase arrivals with available local arrivals to better constrain the teleseismic earthquake locations in the region which we use to conduct nested regional global tomography the new model reveals the detailed structure of the flat slab and its transition to a more moderately dipping slab in the maule region south of the maule region a steeply dipping relic slab is imaged from 200 to 1000 km depth that is distinct from the moderately dipping slab above it and from the more northerly slab at similar depths we interpret the images as revealing both horizontal and vertical tearing of the slab at 38 s to explain the imaged pattern of slab anomalies in the southern portion of the model in contrast the transition from a horizontal to moderately subducting slab in the northern portion of the model is imaged as a continuous slab bend we speculate that the tearing was most likely facilitated by a fracture zone in the downgoing plate or alternatively by a continental scale terrane boundary in the overriding plate

extending the record of the lomagundi jatuli carbon isotope excursion in the labrador trough canada the labrador trough in northern quebec and labrador is a 900 km long rhyacian orosirian orogenic belt containing mixed sedimentary volcanic successions despite having been studied intensively sinc

geological fullerenes review and analysis abstract fullerenes have been reported from numerous terrestrial and meteoritic sources but only at low concentrations the occurrences are associated with localized energetic events such as lightning impacts of extraterrestrial objects and wildfires great interest has also been generated by a series of papers that report noble gases with anomalous isotopic compositions encapsulated within fullerenes in spite of all of the published work many unresolved questions remain about the identity and formation of fullerenes in geological environments

the updip seismic aseismic transition of the sumatra megathrust illuminated by aftershocks of the 2004 aceh andaman and 2005 nias events great subduction earthquakes exhibit segmentation both within the rupture of individual events and in the long term history of the margin the 2004 december 26 aceh andaman and 2005 march 28 nias event in northern sumatra are two of the largest earthquakes in recent years with both co and post seismic displacements constrained in unprecedented detail using aftershock locations from a temporary seismic array in the boundary region between both events and waveform modelling of large aftershocks we demonstrate that the vast majority of aftershocks in the study region occur on the plate interface within a narrow band 20 km seaward of the outer arc high comparing the seismicity distribution to the co and post seismic displacements we infer that the seismic band marks the transition between the seismogenic zone and stable sliding the location of the band and therefore the transition appears to be correlated with the 500 m bathymetry contour this close correspondence is disrupted at the boundary between the two great earthquakes where the transition to seismogenic behaviour occurs further landward by 25 km to the west of simeulue where seafloor bathymetry throughout the forearc is deeper than 500 m the seismic band terminates abruptly and the focus of aftershock activity is found near the trench the seismic efficiency of afterslip varies dramatically along strike the segment below the banyak islands in the gap between the two main asperities of the nias earthquake accommodates a much larger proportion of afterslip seismically