modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

equilibrium and disequilibrium degassing of a phonolitic melt vesuvius ad 79 white pumice simulated by decompression experiments abstract equilibrium and disequilibrium degassing of a volatile phase from a magma of k phonolitic composition was investigated to assess its behavior upon ascent decompression experiments were conducted in ar pressurized externally heated pressure vessels at superliquidus temperature 1050 c in the pressure range 10 200 mpa using pure water as fluid phase all experiments were equilibrated at 200 mpa and then decompressed to lower pressures with rates varying from 0 0028 to 4 8 mpa s isobaric saturation experiments were performed at the same temperature and at 900 950 c to determine the equilibrium water solubility in the pressure range 30 250 mpa the glasses obtained from decompression experiments were analyzed for their dissolved water content vesicularity and bubble size distribution all decompressed samples presented a first event of bubble nucleation at the capsule melt interface homogeneous bubble nucleation in the melt only occurred in fast decompressed experiments 4 8 and 1 7 mpa s for p 100 mpa for these decompression rates high water over saturations were maintained until a rapid exsolution was triggered at p 150 mpa for slower rates 0 0028 0 024 0 17 mpa s the degassing of the melt took place by diffusive growth of the bubbles nucleating at the capsule melt interface this process sensibly reduced water over saturation in the melt preventing homogeneous nucleation to occur for decompression rates of 0 024 and 0 17 mpa s low water over saturations were attained in the melt gradually declining toward equilibrium concentrations at low pressures a near equilibrium degassing path was observed for a decompression rate of 0 0028 mpa s experimental data combined with natural pumice textures suggest that both homogeneous and heterogeneous bubble nucleations occurred in the phonolitic magma during the ad 79 vesuvius plinian event homogeneous bubble nucleation probably occurred at a depth of 3 km in response to a fast decompression of the magma during the ascent

atmospheric oxygenation caused by a change in volcanic degassing pressure around two and a half billion years ago following the end of the archaean eon the atmosphere turned from anoxic to weakly oxic in what is known as the great oxidation event using a model of volcanic degassing gaillard et al demonstrate that a preceding period of continental crust formation may have been the trigger they propose that as continents emerged and volcanoes became increasingly subaerial rather than submarine magmatic volatiles were degassed at lower pressures leading to a progressive oxidation of the gases released this shift to a release of sulphur as sulphur dioxide rather than as hydrogen sulphide could then have fed marine sulphate reduction and the eventual oxygenation of earth s atmosphere the precambrian history of our planet is marked by two major events a pulse of continental crust formation at the end of the archaean eon and a weak oxygenation of the atmosphere the great oxidation event that followed at 2 45 billion years ago this oxygenation has been linked to the emergence of oxygenic cyanobacteria1 2 and to changes in the compositions of volcanic gases3 4 but not to the composition of erupting lavas geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3 5 billion years ago5 6 here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation using thermodynamic calculations simulating gas melt equilibria in erupting magmas we suggest that mostly submarine archaean volcanoes produced gases with so2 h2s 1 and low sulphur content emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late archaean then led to widespread subaerial volcanism which in turn yielded gases much richer in sulphur and dominated by so2 dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere

understanding etna flank instability through numerical models abstract as many active volcanoes mount etna shows clear evidence of flank instability and different mechanisms were suggested to explain this flank dynamics based on the recorded deformation pattern and character shallow and deep deformations mainly associated with both eruptive and seismic events are concentrated along recognised fracture and fault systems mobilising the eastern and south eastern flank of the volcano several interacting causes were postulated to control the phenomenon including gravity force magma ascent along the feeding system and a very complex local and or regional tectonic activity nevertheless the complexity of such dynamics is still an open subject of research and being the volcano flanks heavily urbanised the comprehension of the gravitative dynamics is a major issue for public safety and civil protection the present research explores the effects of the main geological features in particular the role of the subetnean clays interposed between the apennine maghrebian flysch and the volcanic products and the role of weakness zones identified by fracture and fault systems on the slope instability process the effects of magma intrusions are also investigated the problem is addressed by integrating field data laboratory tests and numerical modelling a bi and tri dimensional stress strain analysis was performed by a finite difference numerical code flac and flac 3d mainly aimed at evaluating the relationship among geological features volcano tectonic structures and magmatic activity in controlling the deformation processes the analyses are well supported by dedicated structural mechanical field surveys which allowed to estimate the rock mass strength and deformability parameters to take into account the uncertainties which inevitably occur in a so complicated model many efforts were done in performing a sensitivity analysis along a wnw ese section crossing the volcano summit and the valle del bove depression this was mainly devoted to evaluate the effect of topography geometry and rheological behaviour of the structural units the 3d numerical model extended 40 60 km was implemented to simulate the volcano deformation pattern first the role of the pleistocene subetnean clays was investigated then two structural weakness zones the pernicana fault system and the ne rift were introduced and their effects on the flank instability evaluated two extreme hydrogeological conditions drained and undrained were analysed the results are expressed in terms of stress strain field displacement pattern plasticity states and shear strain increments two main instability mechanisms were identified one at shallow depth with the sliding surface located inside the subetnean quaternary clay and another deep seated mechanism with a not continuous and less evident sliding surface developed inside the apennine maghrebian chain flysch bordered by active structures both mechanisms contribute to explain the present deformation pattern and some of the main structures of the etna flank the effect of magma pressure exerted on the active dyke walls during eruptions was then simulated and relations between magmatic activity and flank instability were preliminarily investigated

controls on the composition of ni cu sulfide deposits as illustrated by those at noril sk siberia the ni cu pge ore deposits of the noril sk region have developed in feeder channels for permo triassic continental flood basalt volcanism particularly within 100 to 300 m thick elongate stratified intrusions that merge with an extensive system of peripheral sills through which the magma is thought to have continued to surface the mineralization is centered within two ore junctions the noril sk and talnakh ore junctions principal ore types include massive ore which occurs typically below or at the lowest margin of the intrusions disseminated ore in picritic and taxitic gabbrodolerite which constitute the lower part of the intrusions and copper ore which either forms an impregnation in hornfelsic country rock adjacent to massive ore or occupies the matrix of breccia zones that have developed at the front and upper contact of the intrusions although showing a close spatial relationship to the intrusions the massive ore particularly that underlying the northwest talnakh intrusion appears to have been injected separately over 500 samples have been analyzed for ni cu s pt pd rh ru ir os and au by nis fire assay acid dissolution and neutron activation the massive ore of the kharayelakh orebody beneath the northwest talnakh intrusion has fractionated as injection proceeded from east to west with the fractionated liquid moving progressively farther west this liquid has also soaked into the surrounding hornfels to produce the cu rich mantle and above the western part of the kharayelakh orebody where the cu enrichment is most pronounced has also affected the lower part of disseminated ore zones within the intrusion study of the disseminated ore has revealed that this has not fractionated to a great degree and that adequate sampling gives an average composition close to that of the primary sulfide liquid disseminated ore from different parts of the talnakh ore junction are characterized by very different metal tenors with rh ranging from 4 000 to 10 000 ppb the composition of the disseminated ore is modeled as the result of initial low tenor sulfides becoming trapped in the ore bearing intrusions and then interacting with successive surges of new magma passing along the feeder channels represented by their host intrusions on the way to the surface the different tenors of the different ore junctions and parts of ore junctions are the consequence of the effective number of times the magma passing through a particular channel exceeds the amount of sulfide within the channel higher ratios leading to higher tenors

role of degassing of the noril sk nickel deposits in the permian triassic mass extinction event the largest mass extinction event in earth9s history marks the boundary between the permian and triassic periods at circa 252 ma and has been linked with the eruption of the basaltic siberian traps large igneous province slip one of the kill mechanisms that has been suggested is a biogenic methane burst triggered by the release of vast amounts of nickel into the atmosphere a proposed ni source lies within the huge noril sk nickel ore deposits which formed in magmatic conduits widely believed to have fed the eruption of the slip basalts however nickel is a nonvolatile element assumed to be largely sequestered at depth in dense sulfide liquids that formed the orebodies preventing its release into the atmosphere and oceans flotation of sulfide liquid droplets by surface attachment to gas bubbles has been suggested as a mechanism to overcome this problem and allow introduction of ni into the atmosphere during eruption of the slip lavas here we use 2d and 3d x ray imagery on noril sk nickel sulfide combined with simple thermodynamic models to show that the noril sk ores were degassing while they were forming consequent bubble riding by sulfide droplets followed by degassing of the shallow sulfide saturated and exceptionally volatile and cl rich slip lavas permitted a massive release of nickel rich volcanic gas and subsequent global dispersal of nickel released from this gas as aerosol particles

faulting structure above the main himalayan thrust as shown by relocated aftershocks of the 2015 mw7 8 gorkha nepal earthquake the 25 april 2015 m w 7 8 gorkha nepal earthquake ruptured a shallow section of the indian eurasian plate boundary by reverse faulting with nne ssw compression consistent with the direction of current indian eurasian continental collision the gorkha main shock and aftershocks were recorded by permanent global and regional arrays and by a temporary local broadband array near the china nepal border deployed prior to the gorkha main shock we relocate 272 earthquakes with m w 3 5 by applying a multiscale double difference earthquake relocation technique to arrival times of direct and depth phases recorded globally and locally we determine a well constrained depth of 18 5 km for the main shock hypocenter which places it on the main himalayan thrust mht many of the aftershocks at shallower depths illuminate faulting structure in the hanging wall with dip angles that are steeper than the mht this system of thrust faults of the lesser himalaya may accommodate most of the elastic strain of the himalayan orogeny

sulfur isotope exchange and metal enrichment in the formation of magmatic cu ni pge deposits sulfur isotope measurements provide a useful means of evaluating the source of sulfur in magmatic cu ni pge deposits although low sulfur pge rich deposits e g j m reef of the stillwater complex merensky reef of the bushveld complex show little or no isotopic evidence for the involvement of crustally derived sulfur several high sulfur deposits e g noril sk duluth complex show strong evidence for contamination of mafic magmas by sulfur of crustal origin processes such as magma degassing or redox changes accompanying crystallization are ineffective in significantly modifying sulfur isotope signatures of sulfides that crystallize from immiscible liquids that exsolve from the mafic magmas for this reason 34s values are primarily dependent on sulfur source characteristics and variations can often be treated using a two component mixing approach however deposits such as those at noril sk and voisey s bay that appear to have formed in magma conduit systems present another possibility for modification of sulfur isotope signatures these deposits are thought to have been upgraded in metal tenor by reaction with uncontaminated mantle derived melts that traversed the accumulated sulfide on their way to the surface our calculations illustrate the efficiency of reactions that involve the exchange of fe for cu ni or pge in producing increases in the metal tenor of the accumulated sulfide sulfur isotope exchange between the crustally contaminated sulfide ore accumulation and sulfur of mantle origin may accompany chalcophile element exchange and is capable of masking or limiting the degree of isotopic evidence for the initial stage of ore genesis that involved crustal sulfur sulfur isotope exchange is distinct from the addition of sulfur in the form of immiscible sulfide droplets from a sulfide saturated magma to the accumulated sulfide although both additive mixing and exchange can lead to similar isotopic effects stable isotopic exchange provides a mechanism in addition to additive mixing that may lead to decoupling of different isotopic systems

assimilation of sulfate and carbonaceous rocks experimental study thermodynamic modeling and application to the noril sk talnakh region russia most of the intrusions in the noril sk talnakh region siberia are hosted in thick sedimentary sequences including abundant evaporitic and terrigenous sedimentary rocks three mafic ultramafic intrusions in this region contain unusually thick massive sulfide deposits which represent one of the world s largest economic concentrations of ni cu and pge the interaction of siberian magmas with sulfate and organic matter rich sedimentary rocks has been proposed as a possible mechanism for the origin of these exceptional sulfide deposits but the interaction process and the reaction paths have never been fully investigated here we clarify by both experimental petrology and thermodynamic modeling how sulfate and organic matter assimilation occur in mafic ultramafic magmas affecting magma composition crystallization and sulfide saturation interaction experiments were conducted at conditions relevant to the emplacement of noril sk type intrusions 1200 c 80 mpa to simulate the assimilation of sulfate and or organic compounds by ultramafic magmas we used a picrite from noril sk1 intrusion and coal and anhydrite from the area as starting materials the experimental results show that the incorporation of anhydrite into the magma occurs by chemical dissolution in the melt which increases the magma s sulfur content but suppresses sulfide saturation and reduces olivine crystallization extreme assimilation leads to sulfate saturation in the magma and high dissolved sulfur contents of 0 9 0 1 wt s conversely coal assimilation promotes sulfide segregation and magma crystallization while decreasing the dissolved h2o content of the melt and increasing the amount of coexisting fluid phase we also employed gas melt thermodynamic calculations to quantify the effect of these assimilations on the redox conditions and the s content of the magma and investigate the role of temperature pressure and initial gas content of the magma in the assimilation process we quantify how sulfate assimilation strongly oxidizes the magma and increases its s content both effects are intensified by increasing pressure from 50 to 100 mpa in this study decreasing temperature from 1350 to 1200 c in this study and decreasing amounts of fluid phase initially coexisting with the magma from 2 to 0 wt the interaction with organic matter ch in this study induces a strong reduction of the magma even for extremely low degrees of assimilation few tenths of wt and the dehydration of the melt we therefore suggest that in the noril sk talnakh district 1 additional s was supplied to mantle derived magmas by the assimilation of evaporitic rocks and was transported during magma ascent in the form of dissolved oxidized s 2 a substantial reduction of the magma inducing sulfide segregation and important crystallization then occurred due to the interaction with carbonaceous sediments this mechanism can potentially produce massive sulfide deposits by important sulfate assimilation locally higher than 3 wt caso4 and minor organic matter assimilation few tenths of wt ch however if one of the two steps does not occur or the assimilation in 1 is not large enough disseminated sub economic or no sulfide deposits are produced we conclude that exceptional conditions favoring substantial assimilation of sediments are needed to generate exceptional ore deposits like those of the noril sk talnakh district

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

focal depths and fault plane solutions of earthquakes and active tectonics of the himalaya synthetic seismograms were compared with long period body waves for nine earthquakes with epicenters in the himalayan arc to determine depths of foci and to improve fault plane solutions focal depths are shallow 10 20 km inferred slip vectors are locally perpendicular to the mountain range they plunge very gently about 10 deg in the eastern sections of the range and more steeply about 25 deg in western sections assuming india to be a rigid plate the radially oriented slip vectors imply that southern tibet extends at about half the rate of underthrusting in the himalaya and therefore probably at about 5 10 mm yr the shallow depths and gentle dips of the fault planes at least for the events in the eastern half of the range are consistent with coherent underthrusting of the indian plate beneath at least the lesser himalaya the steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the greater himalaya

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

p and s wave tomography and anisotropy in northwest pacific and east asia constraints on stagnant slab and intraplate volcanism we determined three dimensional p and s wave velocities and p wave azimuthal anisotropic tomography of the northwest pacific subduction zones by inverting 1 225 086 p wave and 335 117 s wave arrival times from 13 413 earthquakes our results show some differences between p and s wave images for the stagnant pacific slab in the mantle transition zone mtz beneath northeast china the stagnant slab looks thicker in the p wave image than that in the s wave image which may reflects the effects of both hydration and lower temperature in the mtz though differences in the resolution of p and s wave tomography may also have some effects the changbai intraplate volcanism is caused by hot and wet upwelling in the big mantle wedge above the stagnant pacific slab our p wave anisotropy tomography shows that the fast velocity direction fvd in the subducting philippine sea plate beneath the ryukyu arc is ne sw trench parallel which is consistent with the spreading direction of the west philippine basin during its initial opening stage suggesting that it may reflect the fossil anisotropy a striking variation of the fvd with depth is revealed in the subducting pacific slab beneath the northeast japan arc which may be caused by slab dehydration that changed elastic properties of the slab with depth the fvd in the mantle wedge beneath the northeast japan and ryukyu arcs is trench normal which reflects subduction induced convection beneath the kuril and izu bonin arcs where oblique subduction occurs the fvd in the mantle wedge is nearly normal to the moving direction of the downgoing pacific plate suggesting that the oblique subduction together with the complex slab morphology have disturbed the mantle flow

tomographic inversion of pn travel times in china 1 pn travel times are useful for studying crustal and uppermost mantle structure and regional tectonics because they are affected by crustal velocity and thickness as well as uppermost mantle velocity and anisotropy we obtained 57 740 pn travel time picks from 5433 earthquakes and 307 stations from chinese national and provincial earthquake bulletins and the international seismological center bulletins to invert for pn velocity variation and anisotropy and station delays in china our inversion reveals significant features that correlate with surface geology the main results are as follows 1 the pn velocities show a mosaic of very fast and very slow anomalies mirroring the heterogeneous geology of china at the surface the pn velocities are high beneath the major basins in the west sichuan qaidam west tarim tulufan and junggar and low in areas of active volcanoes myanmar and western yunnan and quaternary volcanism in northern tibet in seismically active areas in north china and tien shan and in the southern part of south china the hainan plume 2 the pn anisotropy beneath the major basins in the west is generally weak strong anisotropy is found beneath high deformation regions the tibetan plateau southeastern margin of the tibetan plateau western tien shan and part of north china suggesting the anisotropy is likely related to recent large scale tectonic activity 3 a large area of north china shows prominent low pn velocity beneath archean basement with thin crust our observations are consistent with rifting lithospheric thinning and mantle upwelling in the region the pn anisotropy is consistent with a dextral simple shear in the nne direction in the lithosphere mantle during the last and ongoing major deformation period 4 the pn velocity in northern tibet is generally lower than that in the south southern tibet has significant e w structure low velocity anomalies can be traced from northern tibet across southwestern tibet and south central tibet to near the india plate anisotropy is absent beneath much of the himalaya block but consistent anisotropy with e w fast direction is present beneath the lhasa block and large anisotropy up to 4 is observed in low velocity regions of the northern and western tibet complex station delays in the eastern margin of the plateau suggest that the whole crust may be highly deformed the anisotropy pattern in the southeastern margin of the tibetan plateau suggests a mantle lithospheric deformation similar to the clockwise rotation of material observed at the surface 5 crustal thicknesses inferred from our station delays are consistent with previous models which correlate well with surface topography

a minimum upb age for siberian flood basalt volcanism abstract establishing an accurate and precise age for siberian flood basalt volcanism is of great importance in evaluating causes for the unequaled mass extinction of flora and fauna at the permian triassic boundary we report a new minimum u pb age obtained from zircon and baddeleyite from the mineralized noril sk i intrusion that cuts the lower third of this rapidly deposited 3500 m thick volcanic sequence near noril sk this 251 2 0 3 2 ma age is within analytical error of the shrimp u pb age for zircon from the permian triassic boundary at meishan south china 251 1 3 6 ma 2 and confirms siberian basaltic volcanism as a possible contributor to the mass extinction

current shortening across the himalayas of nepal summary underthrusting of the indian lithosphere beneath the himalayas occurs during the quaternary period along a gently north dipping main basal detachment main himalayan thrust mht from which the southernmost emergent ramp main frontal thrust mft branches historical seismicity shows that slip on the mht is frequently accommodated through m 8 shallow earthquakes but shows a seismic gap in western nepal this absence of major historical earthquakes in western nepal can be explained either by an aseismic slip on the mht or a longlived elastic strain accumulation to test these hypotheses the present day displacement field has been measured for a gps network formed of 35 sites the updated solution presented in this paper combines data from 1995 1997 1998 and 2000 measurements the lack of deformation less than 3 10 8 yr 1 through the outer belt does not fit with a regional aseismic slip along the southern part of mht a less than 3 mm yr 1 aseismic slip could nonetheless affect restricted areas of the outer belt in contrast a strain accumulation of more than 30 10 8 yr 1 is measured south of the higher himalayas in a zone where an intense microseismicity reflects a stress build up it is presumably generated by locking of the aseismic creep that occurs along the mht beneath the higher himalayas and tibet the displacement field is simulated by a dual dislocation model that takes into account the pattern of microseismicity and particularly a segmentation between central and western nepal the best fit between the measured and simulated displacement fields is obtained with 19 mm yr 1 thrust and 0 1 mm yr 1 dextral strike slip components along a 117 ne dislocation locked to a depth of 20 21 km beneath western nepal and 19 20 mm yr 1 thrust and 0 2 mm yr 1 dextral strike slip components along a 108 ne dislocation locked to a depth of 17 21 km beneath central nepal the width of the locked zone between the main frontal thrust and the creeping zone is of the same order but rather greater in western nepal than in central nepal therefore it is expected that m 8 earthquakes could occur in western nepal

slip distribution beneath the central and western himalaya inferred from gps observations summary underthrusting of the indian plate beneath the himalaya has been the cause of many hazardous thrust faulting earthquakes along the arc moderate earthquakes with magnitudes of 5 occur frequently in this region releasing the elastic strain accumulated over many years around the plate boundary these events can be attributed to slip deficits where the indian and eurasian plates are locked during interseismic periods geodetic measurements can help discriminate the distribution of the interlocking areas and the steadily slipping areas beneath the himalaya to understand the deformation across the central and western himalaya and the associated slip on thrust faults campaign mode gps data were collected in the garhwal kumaun region of the western himalaya gps sites velocities show that the deformation is currently concentrated between the lesser and higher himalaya horizontal velocities are used to estimate the slip distribution for the estimation a model of the interseismic surface deformation caused by buried non uniform creep dislocation nuc on a curved fault surface is used the slip distribution shows that there might be structural discontinuity on the fault between the kumaun and garhwal regions of the himalaya the estimated slip rate at the depth around 20 40 km in the central himalaya and at the depth of 15 km in the western himalaya is 10 mm yr 1 the nuc model indicates that the shallow part 20 km of the thrust fault system along the plate boundary is almost locked the locking depth appears to be deep in the central himalaya and shallower in the western himalaya further most of the historical large seismic events are observed to have occurred in an area with a slip velocity less than 10 mm yr 1 i e in a locked zone at the plate interface

temperature dependence of sulfide and sulfate solubility in olivine saturated basaltic magmas abstract the sulfur concentration at pyrrhotite and anhydrite saturation in primitive hydrous basaltic melt of the 2001 2002 eruption of mt etna was determined at 200 mpa t 1050 1250 c and at log fo2 from fmq to fmq 2 2 fmq is fayalite magnetite quartz oxygen buffer at 1050 c au sample containers were used a double capsule technique using a single crystal olivine sample container closed with an olivine piston embedded in a sealed au80pd20 capsule was developed to perform experiments in s bearing hydrous basaltic systems at t 1050 c pyrrhotite is found to be a stable phase coexisting with melt at fmq fmq 0 3 whereas anhydrite is stable at fmq 1 4 fmq 2 2 the s concentration in the melt increases almost linearly from 0 12 0 01 to 0 39 0 02 wt s at fes saturation and from 0 74 0 01 to 1 08 0 04 wt s at anhydrite saturation with t ranging from 1050 1250 c the relationships between s concentration at pyrrhotite and or anhydrite saturation mgo content of the olivine saturated melt t and log fo2 observed in this study and from previous data are used to develop an empirical model for estimating the magmatic t and fo2 from the s and mgo concentrations of h2o bearing olivine saturated basaltic melts the model can also be used to determine maximum s concentrations if fo2 and mgo content of the melt are known the application of the model to compositions of melt inclusions in olivines from mt etna indicates that the most primitive magmas trapped in inclusions might have been stored at log fo2 slightly higher than fmq 1 and at t 1100 1150 c whereas more evolved melts could have been trapped at t 1100 c these values are in a good agreement with the estimates obtained by other independent methods reported in the literature

kinetic controls on the partitioning of trace elements between silicate and sulfide liquids mass transfer between sulfide and silicate liquids is often discussed elements pge has resulted from liquation immiscible by reference to a mass ratio between hypothetical liquid reservoirs liquid phase separation of sulfide liquid from mafic or at equilibrium defined as r in an open system not at equilibrium ultramafic silicate magma a central assumption of modthe mass of silicate melt from which a growing sulfide droplet els of magmatic sulfide deposit formation is that the base appears to have scavenged chalcophile elements will depend on metals and pge are strongly partitioned into the sulfide diffusivities di and dfes of the element and of the fes component melt previous discussions of the process by which sulfide in the silicate melt respectively on the degree of supersaturation of liquids become enriched in chalcophile metals have fothe melt with fes c o on the radius a of the droplet and on the cused almost exclusively on models in which coexisting velocity v with which the droplet is advected through the melt so bodies of sulfide and silicate melt are considered to be that in equilibrium at all times the intent of this paper is to demonstrate that natural sulfide deposits preserved in igneous rocks will in many r 1 c fes o di 1 2 adiv dfes 1 2 adfesv instances record metal distributions that never attained equilibrium as a result of the kinetic constraints on metal chalcophile elements are expected to show inter element variations partitioning between phases the consequences are that in d spanning several orders of magnitude in some melts leading different elements will seem to show evidence for equito large inter element variations in effective r in a given sulfide libration at different silicate sulfide mass ratios within body these variations in effective r will lead to spatial separations single sulfide bodies i describe the time dependent evolubetween zones of maximum enrichment of chalcophile elements tion of metal distributions in silicate sulfide melt systems produced during fractional segregation of sulfide in layered intrusions starting with analytical solutions for simple boundary whereas it has proven impossible to model the generation of spatially conditions and then adapting them to more complex offset stratiform horizons in the australian munni munni layered systems as numerical models intrusion using equilibrium partition coefficients the present kinetic model reproduces the observed patterns with great fidelity

anhydrite solubility in differentiated arc magmas abstract the solubility of anhydrite in differentiated arc magmas was experimentally studied at 200 mpa and 800 1000 c over a range of oxygen fugacities from 0 5 log units above the ni nio buffer to the hematite magnetite buffer anhydrite is stable only at oxidizing conditions fo2 re reo2 whereas sulfides only form under reducing conditions the solubility of anhydrite in the melt ultimately regulates the amount of sulfur available to partition between melt and fluid phase during the eruption at oxidizing conditions the solubility product of anhydrite increases with temperature nbo t and melt water content we provide a new calibration of the anhydrite solubility product ksp xcao xso3 which reproduces all available experimental data with greatly improved accuracy ln k sp anhydrite 8 95 146 5 nbo t 2 696 10 4 t k 19 72 nbo t 10 4 t k 0 409 h 2 o wt in this equation the molar fractions xcao and xso3 in the melt as well as the number of non bridging oxygen atoms per tetrahedron nbo t are calculated on an anhydrous basis h2o refers to the melt water content t is temperature in kelvin we apply our model to estimate the sulfur yield of some recent volcanic eruptions and we show that the sulfur yield of the 1991 mt pinatubo dacite eruption was unusually large because only a small fraction of the sulfur was locked up in anhydrite in general high sulfur yields are expected when anhydrite solubility in the melt is high i e for somewhat depolymerized melts for rhyolitic systems most of the available sulfur will be locked up in anhydrite so that even very large eruptions may only have a small effect on global surface temperatures our model therefore allows improved predictions of the environmental impact of explosive volcanic eruptions

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

micro scale s isotope studies of the kharaelakh intrusion noril sk region siberia constraints on the genesis of coexisting anhydrite and sulfide minerals abstract the coexistence of magmatic anhydrite and sulfide minerals in non arc related mafic magmas has only rarely been documented likewise the s isotope fractionation between sulfate and sulfide in mafic rocks has infrequently been measured in the kharaelakh intrusion associated with the world famous noril sk ore district in siberia coexisting magmatic anhydrite and sulfide minerals have been identified sulfur isotope compositions of the anhydrite sulfide assemblages have been measured via both ion microprobe and conventional analyses to help elucidate the origin of the anhydrite sulfide pairs magmatic anhydrite and chalcopyrite are characterized by 34 s values between 18 8 and 22 8 and 9 3 and 13 2 respectfully coexisting anhydrite and chalcopyrite show values that fall between 8 5 and 11 9 anhydrite in the kharaelakh intrusion is most readily explained by the assimilation of sulfate from country rocks partial reduction to sulfide led to mixing between sulfate derived sulfide and sulfide of mantle origin the variable anhydrite and sulfide 34 s values are a function of differing degrees of sulfate reduction variable mixing of sulfate derived and mantle sulfide incomplete isotopic homogenization of the magma and a lack of uniform attainment of isotopic equilibrium during subsolidus cooling the 34 s values of sulfide minerals have changed much less with cooling than have anhydrite values due in large part to the high sulfide sulfate ratio variations in both sulfide and anhydrite 34 s values indicate that isotopically distinct domains existed on a centimeter scale late stage hydrothermal anhydrite and pyrite also occur associated with ca rich hydrous alteration assemblages e g thomsonite prehnite pectolite epidote xonotlite 34 s values of secondary hydrothermal anhydrite and pyrite determined by conventional analyses are in the same range as those of the magmatic minerals anhydrite pyrite values are in the 9 1 10 1 range and are smaller than anticipated for the low temperatures indicated by the silicate alteration assemblages the small values are suggestive of either sulfate sulfide isotopic disequilibrium or closure of the system to further exchange between 550 and 600 c our results confirm the importance of the assimilation of externally derived sulfur in the generation of the elevated 34 s values in the kharaelakh intrusion but highlight the sulfur isotopic variability that may occur in magmatic systems in addition our results confirm the need for more precise experimental determination of sulfate sulfide sulfur isotope fractionation factors in high t systems

crustal density structure from 3d gravity modeling beneath himalaya and lhasa blocks tibet abstract the himalaya and lhasa blocks act as the main belt of convergence and collision between the indian and eurasian plates their crustal structures can be used to understand the dynamic process of continent continent collision herein we present a 3d crustal density model beneath these two tectonic blocks constrained by a review of all available active seismic and passive seismological results on the velocity structure of crust and lower lithosphere from our final crustal density model we infer that the present subduction angle of the indian plate is small but presents some variations along the west east extension of the orogenic belt the dip angle of the moho interface is about 8 9 in the eastern and western part of the orogenic belt and about 16 in the central part integrating crustal p wave velocity distribution from wide angle seismic profiling geothermal data and our crustal density model we infer a crustal composition model which is composed of an upper crust with granite granodiorite and granite gneiss beneath the lhasa block biotite gneiss and phyllite beneath the himalaya a middle crust with granulite facies and possible pelitic gneisses and a lower crust with gabbro norite troctolite and mafic granulite beneath the lhasa block our density structure

line of sight displacement from alos 2 interferometry mw 7 8 gorkha earthquake and mw 7 3 aftershock interferometric synthetic aperture radar insar is a key tool for the analysis of displacement and stress changes caused by large crustal earthquakes particularly in remote areas a challenge for traditional insar has been its limited spatial and temporal coverage especially for very large events whose dimensions exceed the typical swath width of 70 100 km this problem is addressed by the alos 2 satellite whose palsar 2 instrument operates in scansar mode enabling a repeat time of 2 weeks and a swath width of 350 km here we present insar line of sight displacement data from alos 2 palsar 2 observations covering the mw 7 8 gorkha nepal earthquake and its mw 7 3 aftershock that were acquired within 1 week of each event the data are made freely available and we encourage their use in models of the fault slip and associated stress changes the mw 7 3 aftershock not only extended the rupture area of the main shock toward the east but also left a 20 km gap where the fault has little or no coseismic slip we estimate this unslipped fault patch has the potential to generate a mw 6 9 event

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

seismotectonics of the april may 2015 nepal earthquakes an assessment based on the aftershock patterns surface effects and deformational characteristics occurrence of the april 25 2015 mw 7 8 earthquake near gorkha central nepal and another one that followed on may 12 mw 7 3 located similar to 140 km to its east provides an exceptional opportunity to understand some new facets of himalayan earthquakes here we attempt to assess the seismotectonics of these earthquakes based on the deformational field generated by these events along with the spatial and temporal characteristics of their aftershocks when integrated with some of the post earthquake field observations including the localization of damage and surface deformation it became obvious that although the mainshock slip was mostly limited to the main himalayan thrust mht the rupture did not propagate to the main frontal thrust mft field evidence supported by the available insar imagery of the deformation field suggests that a component of slip could have emerged through a previously identified out of sequence thrust active thrust in the region that parallels the main central thrust mct known in the literature as a co linear physiographic transitional zone called pt2 termination of the first rupture triggering of the second large earthquake and distribution of aftershocks are also spatially constrained by the eastern extremity of pt2 mechanism of the 2015 sequence demonstrates that the out of sequence thrusts may accommodate part of the slip an aspect that needs to be considered in the current understanding of the mechanism of earthquakes originating on the mht c 2015 elsevier ltd all rights reserved

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

elastic modeling of the alto tiberina normal fault central italy geometry and lithological stratification influences on the local stress field abstract two dimensional elastic plane strain finite element models fems are generated to study the state of stress and failure induced by a low angle normal fault the alto tiberina fault of the northern apennines central italy it is beyond the scope of the present work to show that slip can occur on such a fault the numerical study was performed to evaluate the influences on the local stress field of the litho mechanical stratification of formations surrounding the fault and those induced by the geometry of the fault the performed models have shown the important role played by evaporites and basement formations of the umbria marche succession as seismogenetic layers the model results have also underlined that the flat ramp geometry of the fault induces high relative concentration of stresses in correspondence with the low angle east dipping synthetic normal faults observed today in shallow depth near the alto tiberina surface trace the stress regime predicted by the final model in which the behavior of the alto tiberina together with the antithetic normal fault of gubbio was simulated reconciles available geological and geophysical observable to a greater extent the numerical results can assist interpretation of the tectonic evolution of the region

insights into ore genesis of ni cu pge sulfide deposits of the noril sk province russia evidence from copper and sulfur isotopes abstract combined cu s isotope data for ni cu pge sufides from the economic deposits hosted in the noril sk 1 talnakh and kharaelakh intrusions from the subeconomic deposits in the chernogorsk zub marksheider and vologochan intrusions and from the non economic occurrences in the nizhny talnakh intrusion in the noril sk province russia and the j m reef in the stillwater complex usa are presented for the first time most sulfide samples including the ores from the talnakh intrusion and the stillwater complex have a restricted range of 65 cu values from 1 1 to 0 whereas those from the kharaelakh and noril sk 1 intrusions have more variable 65 cu values of 2 3 to 1 0 samples from the three economic deposits in the noril sk province have distinct mean 65 cu values of 1 56 0 27 for kharaelakh 0 55 0 41 for talnakh and 0 23 0 28 for noril sk 1 consistent with those for carbonaceous chondrite and iron meteorites the variation of 65 cu values is interpreted to represent a primary signature of the ores although a magmatic fractionation of cu isotopes and or assimilation from an external source cannot be ruled out particularly in the case of the kharaelakh ores collectively the eight investigated intrusions have an overall sulfur 34 s range from 0 7 to 13 8 disseminated and massive ores of the same intrusion have similar 34 s values the disseminated and massive ores of the khraelakh intrusion have a mean 34 s value of 12 57 0 54 and 12 76 0 42 respectively which are distinctly different from those of the disseminated 10 97 0 44 and massive ores 10 88 0 77 of the talnakh intrusion the different 34 s values of the intrusions may be attributed to sulfur fractionation in deep seated magma chambers rather than at shallow levels or the present emplacement site the mean 34 s value of the disseminated ores from the subeconomic ni cu pge deposits and non economic occurrences spans over 10 5 averaging 0 39 with a standard deviation of 1 55 for the highly contaminated zub marksheider rocks 6 38 1 89 for nizhny talnakh 6 90 1 17 for vologochan and 10 86 0 43 for chernogorsk samples from the zub marksheider intrusion have mantle like s isotope signatures consistent with a deep seated origin although individual mineralized instrusions have a restricted range the overall trend they define of falling 34 s with rising 65 cu values might be a useful indicator of the economic potential of ni cu pge sulfide deposits

himalayan megathrust geometry and relation to topography revealed by the gorkha earthquake the himalayan mountain range has been the locus of some of the largest continental earthquakes including the 2015 magnitude 7 8 gorkha earthquake competing hypotheses suggest that himalayan topography is sustained and plate convergence is accommodated either predominantly on the main plate boundary fault or more broadly across multiple smaller thrust faults here we use geodetic measurements of surface displacement to show that the gorkha earthquake ruptured the main himalayan thrust fault the earthquake generated about 1 m of uplift in the kathmandu basin yet caused the high himalaya farther north to subside by about 0 6 m we use the geodetic data combined with geologic geomorphological and geophysical analyses to constrain the geometry of the main himalayan thrust in the kathmandu area structural analyses together with interseismic and coseismic displacements are best explained by a steep shallow thrust fault flattening at depth between 5 and 15 km and connecting to a mid crustal steeper thrust we suggest that present day convergence across the himalaya is mostly accommodated by this fault no significant motion on smaller thrust faults is required furthermore given that the gorkha earthquake caused the high himalayan mountains to subside and that our fault geometry explains measured interseismic displacements we propose that growth of himalayan topography may largely occur during the ongoing post seismic phase

structural interpretation of the great earthquakes of the last millennium in the central himalaya abstract a major question about the himalaya remains open does a great earthquake like the mw 8 1 1934 earthquake release all the strain stored by the tibet india convergence during the preceding interseismic period and only that strain or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events to consider this question the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of kathmandu trenches through surface ruptures isoseismal damage mapping seismites and the instrumental record in the kathmandu basin the location of the epicenter of the 1934 earthquake was determined from the arrival of high energy p waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth the epicenter of the mw 7 6 1833 earthquake can therefore be determined analogously from dike orientation and its location to the ne of kathmandu indicates an overlap with the mw 8 1 1934 rupture the 1934 earthquake released strain not released by the 1833 earthquake comparison of the historical records of earthquakes in kathmandu with 14c ages from paleo seismic trenches along the himalayan front suggests that 1 the 1344 kathmandu event ruptured the surface as far away as kumaon and was therefore a giant mw 8 6 earthquake and 2 the 1255 event that destroyed kathmandu is attested by surface ruptures in central and western nepal and by seismites in soft sediment as far away as kumaon geometric and rheologic controls for the different types of ruptures during the medium mw 7 great mw 8 and giant mw 8 4 earthquakes are illustrated in structural cross sections it is found that the epicenters of great himalayan earthquakes are located on the basal thrust farther north or close to the locked zone which is defined from geodetic measurements of regional deformation during the interseismic period this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes the extent of which depends on the dip of the main himalayan thrust the succession of the great earthquakes during the last millennium has released all the 20 m millennial himalayan convergence even in the central seismic gap which has been locked since 1505 the millennial seismic release rate is close to the convergence rate nonetheless no evidence of a succession of characteristic earthquakes has been found the 1100 1833 and 1934 earthquakes in the eastern himalaya are characterized neither by constant displacement nor by constant recurrence furthermore some great earthquakes do not release all the strain elastically stored by the himalayan and tibetan upper crust after the 1255 event there was still the potential for a slip of several meters for the mw 8 1 1505 event this suggests a rather random release of seismic energy great earthquakes could occur anytime and in any part of the central himalaya furthermore a future giant earthquake of mw 8 6 cannot be excluded

cretaceous deformation history of the middle tan lu fault zone in shandong province eastern china abstract based on field analysis of fault slip data from different rock units of the cretaceous basins along the middle part of the tan lu fault zone shandong province eastern china we document polyphase tectonic stress fields and address the changes in sense of motion of the tan lu fault zone during the cretaceous the cretaceous deformation history of the tan lu fault zone can be divided into four main stages the first stage during the earliest cretaceous was dominated by n s extension responsible for the formation of the jiaolai basin we interpret this extension to be related to dextral strike slip pull apart opening guided by the tan lu fault zone the second stage during the middle early cretaceous was overwhelmingly rift dominated and characterized by widespread silicic to intermediate volcanism normal faulting and basin subsidence it was at this stage that the tan lu parallel yi shu rift was initiated by e w to wnw ese extension the tectonic regime then changed during the late early cretaceous to nw se oriented transpression causing inversion of the early cretaceous rift basin and sinistral slip along the tan lu fault zone during the late cretaceous dextral activation of the tan lu fault zone resulted in pull apart opening of the zhucheng basin which was subsequently deformed by ne sw compression this deformation chronology of the tan lu fault zone and the associated cretaceous basins allow us to constrain the regional kinematic models as related to subduction along the eastern margin of asia or related to collision in the tibet region

has focused denudation sustained active thrusting at the himalayan topographic front the geomorphic character of major river drainages in the himalayan foothills of central nepal suggests the existence of a discrete west northwest trending break in rock uplift rates that does not correspond to previously mapped faults the 40 ar 39 ar thermochronologic data from detrital muscovites with provenance from both sides of the discontinuity indicate that this geomorphic break also corresponds to a major discontinuity in cooling ages samples to the south are proterozoic to paleozoic whereas those to the north are miocene and younger combined these observations virtually require recent pliocene holocene motion on a thrust sense shear zone in the central nepal himalaya 20 30 km south of the main central thrust field observations are consistent with motion on a broad shear zone subparallel to the fabric of the lesser himalayan lithotectonic sequence the results suggest that motion on thrusts in the toe of the himalayan wedge may be synchronous with deeper exhumation on more hinterland structures in central nepal we speculate that this continued exhumation in the hinterland may be related to intense sustained erosion driven by focused orographic precipitation at the foot of the high himalaya

the effect of water and fo2 on the ferric ferrous ratio of silicic melts new experiments on the effect of dissolved water on the ferric ferrous ratio of silicic melts have been performed at 200 mpa between 800 c and 1000 c and for fo2 between nno 1 35 and nno 6 6 water saturated conditions were investigated compositions studied include six metaluminous synthetic melts with feotot progressively increasing from 0 47 to 4 25 wt two natural obsidian glasses one peraluminous and the other peralkaline and a synthetic rhyolitic glass having the composition of the matrix glass of the june 15 1991 pinatubo dacite ferrous iron was analyzed by titration and feotot by electron microprobe variation of quench rate was found to have no detectable effect on the ferric ferrous ratio of the hydrous silicic melts investigated at nno no dependence of the ferric ferrous ratio with temperature is observed at fo2 nno 1 the experimental ferric ferrous ratios are equal or lower than calculated the peralkaline samples show the same type of behaviour a non linear relationship between xfe2o3 xfeo and fo2 implies that a term for dissolved water must be added to the kc equation if it is to be applied to the calculation of ferric ferrous ratios of hydrous silicic melts above nno 1 the ferric ferrous ratio is essentially controlled by the anhydrous melt composition and fo2 however differences exist between measured and calculated ferric ferrous ratios of silicic melts that are not all attributable to the effect of dissolved water additional work is needed to describe more precisely the dependence of the ferric ferrous ratio on anhydrous melt composition the oxidizing effect of water is restricted to relatively reduced magmatic liquids in oxidized calk alkaline magma series the presence of dissolved water will not largely influence melt ferric ferrous ratios

textural development in sulfide matrix ore breccias in the voisey s bay ni cu co deposit labrador canada abstract magmatic ni cu sulfide ores at voisey s bay contain complex assemblages of extremely heterogeneous rocks these range from polymict breccias with rock fragments in sulfide rich and or sulfide poor matrices to heterogeneous vari textured gabbros with rapid short range variations in grain size and content of hydrous phases rock fragment populations in the breccias include endogenous olivine gabbros cumulate and non cumulate and cumulate peridotites along with extensively depleted plagioclase hercynite gneisses interpreted as restites from extensive partial melting of country rock quartzo feldspathic paragneisses using a combination of desk top microbeam xrf mapping at cm scale and 3d x ray tomography we show that both sulfide poor and sulfide rich breccias comprise heterolithic assemblages of clasts within a matrix of olivine gabbro this matrix is characterised by an interconnected 3d framework of plagioclase crystals highly variable in grain size at mm to cm scale with interstitial olivine and poikilitic clinopyroxene and is texturally indistinguishable from clast free olivine gabbro sulfide forms interconnected networks at cm to dm scale and possibly larger much of the plagioclase developed by outgrowth from the margins of paragneiss xenoliths when the porosity was occupied by silicate melt the observed range of textures is explained by a model of percolation of molten sulfide through variably crystalline inter clast matrix displacing the silicate melt to leave the refractory plagioclase olivine or in some cases plagioclase only component now entirely within a sulfide matrix the process is analogous to that believed to have formed interspinifex ore in komatiite hosted deposits biotite rims on plagioclase enclosed in sulfide are interpreted as the result of reaction between plagioclase olivine and a hydrous component derived from the sulfide melt itself with a possible component of migrating residual silicate melt wicking along sulfide silicate contacts this sulfide infiltration model offers an alternative to the current model for upward emplacement of a slurry of silicate melt sulfide melt and breccia fragments as a late stage injection into the dyke sill complex the preserved range of textures is interpreted as being due to gravity driven percolation of sulfide liquid through a pre existing partially molten intrusion breccia in this model the breccia serves as a physical trap site accumulating downward migrating sulfide liquid however the invariable close mutual association of sulfide and rock fragments at voisey s bay implies a common derivation

southward extrusion of tibetan crust and its effect on himalayan tectonics the tibetan plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during india asia collision and the contrast in potential energy between the plateau and its surroundings strongly influences the modern tectonics of south asia the distribution of potential energy anomalies across the region derived from geopotential models indicates that the himalayan front is the optimal location for focused dissipation of excess energy stored in the plateau the modern pattern of deformation and erosion in the himalaya provides an efficient mechanism for such dissipation and a review of the neogene geological evolution of southern tibet and the himalaya shows that this mechanism has been operational for at least the past 20 million years this persistence of deformational and erosional style suggests to us that orogens like other complex systems can evolve toward steady state configurations maintained by the continuous flow of energy the capacity of erogenic systems to self organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far field plate interactions

upper mantle tomography and dynamics beneath the north china craton 1 a high resolution tomographic model of the upper mantle beneath the north china craton ncc is determined using a large number of precisely hand picked teleseismic p wave arrival times the results are generally consistent with previous results but high quality arrivals provide new insights into the dynamics beneath the ncc obviously north south trending low velocity low v zones are revealed down to 300 400 km depth under the shanxi rift and tanlu fault zone while a north south trending high velocity high v zone representing the remainder of detached lithosphere is visible down to 200 km depth under the western portion of eastern ncc high v anomalies representing the detached lithosphere are detected at 200 400 km depth under central and eastern ncc under the ordos block high v anomalies are visible above 400 km depth indicating intact lithosphere broad high v anomalies representing the stagnant pacific slab are imaged with a low v anomaly from datong volcano to the edge of bohai sea in the mantle transition zone beneath eastern and central ncc suggesting that the pacific slab has subducted to central ncc but with a gap a continuously y shaped low v structure is clearly imaged under datong volcano and bohai sea from the lower mantle through this gap in the mantle transition zone to the upper mantle indicating the existence of a lower mantle plume these results suggest that in addition to the subduction of the pacific plate the plume has also played an important role in lithospheric destruction by thermal erosion of the asthenosphere and detachment of the lithosphere beneath the ncc

assessing quaternary reactivation of the main central thrust zone central nepal himalaya new thermochronologic data and numerical modeling we study the recent dynamics of the central nepal himalaya focusing on possible reactivation of the footwall of the main central thrust which is marked by an abrupt topographic transition different tectonic mechanisms such as overthrusting of a major crustal ramp underplating or out of sequence thrusting have been suggested to explain the morphology and exhumation patterns in this area we present 25 new apatite fission track ages collected along a north south transect in central nepal as well as two age elevation profiles ages are consistently younger than 3 ma old in the main central thrust zone and increase continuously to 4 6 ma old in the south no jump in apatite fission track ages is observed across the topographic transition apparent exhumation rates from age elevation relationships vary from 0 46 0 13 0 09 km ma in the palung granite south of kathmandu to 4 4 4 8 1 5 km ma in the main central thrust zone the latter rate is probably overestimated by a factor of two due to topographic effects as shown by a new numerical model these strongly varying exhumation rates can be explained by overthrusting of a crustal ramp which exerts a primary control on age patterns and do not require out of sequence reactivation of thrusts in the main central thrust zone

sulfur isotopic studies of continental flood basalts in the noril sk region implications for the association between lavas and ore bearing intrusions previous studies of both ore and non ore bearing intrusives in the permo triassic flood basalts of the siberian platform in the noril sk area have shown that high grade ni cu platinum group elements pge mineralization is associated with anomalously high 34s values of 8 to 12 in addition several researchers have proposed that observed depletions in the cu ni and pge content of basaltic lavas of the nadezhdinsky nd formation are related to diffusional exchange with and upgrading in metal tenor of sulfides in the volcanic conduit system sulfur isotopic studies of the lavas at noril sk were initiated to determine if interaction with crustally derived sulfur in the conduit system was evident and if the nd lavas in particular were characterized by an anomalous isotopic signature 34s values of the lavas range from 4 5 to 8 7 vienna canon diablo troilite vcdt with s concentrations from 40 to 1373 ppm the majority of 34s values range from 0 to 4 and are similar to those from s poor intrusions in the noril sk area although textural data are not supportive of early sulfide saturation and the presence of immiscible sulfide droplets in the lavas recrystallization may have erased expected mineralogical and textural evidence mineralogical data indicate that hydrothermal alteration of the lavas has occurred but s redistribution has been restricted to localized areas and 34s values have not been affected the relatively low s concentrations of the lavas are thought to be due in large part to degassing of the lavas in the shallow conduit system and during eruption our calculations are consistent with the premise that degassing of basaltic magmas at temperatures in excess of 900 c at qfm leads to only minor 34s depletion of sulfur remaining in the melt and decreases in 34s values of less than 2 at 90 degassing for this reason all lavas with 34s values in excess of 2 require a contribution of 34s enriched country rock sulfur because of the high s content and 34s value 16 20 of evaporites in the country rocks at noril sk contamination of less than 0 5 is required to explain the most 34s enriched lavas the nd lavas have an average 34s of 2 9 but show no difference in s isotopic composition relative to the other lavas suggesting that metal depletion involved only limited s transfer or that exchange between mantle derived s and s of crustal origin buffered 34s values to less than 5 anomalously positive 34s values similar to those of the ore bearing intrusives in the noril sk region are not consistently found in low s rocks either lavas or intrusives although the mechanism for the derivation of sulfide in the ore bearing intrusions remain speculative it is clear that the formation of sulfide ores characterized by high metal tenors proceeded only in the presence of sulfur of crustal origin

geodetically accurate insar data processor we present a new interferometric synthetic aperture radar insar processing approach that capitalizes on the precise orbit tracking that is available with modern radar satellites our method uses an accurate orbit information along with motion compensation techniques to propagate the radar echoes to positions along a noninertial virtual orbit frame in which the location and focusing equations are particularly simple so that images are focused without requiring autofocus techniques and are computed efficiently motion compensation requires two additional focus correction phase terms that are implemented in the frequency domain if the images from an interferometric pair or stack are all computed along the same reference orbit flat earth topographic correction is not needed and image coregistration is simplified obviating many difficulties that are often encountered in insar processing we process several data sets collected by the alos palsar instrument and find that the geodetic accuracy of the radar images is 10 20 m with up to 20 m of additional image distortion needed to align 100 km 100 km scenes with reference digital elevation models we validated the accuracy by using both known radar corner reflector locations and by the registration of the interferograms with digital maps the topography corrected interferograms are free from all geometric phase terms and they clearly show the geophysical observables of crustal deformation atmospheric phase and ionospheric phase

new insights into the 2012 emilia italy seismic sequence through advanced numerical modeling of ground deformation insar measurements 1 we provide new insights into the two main seismic events that occurred in 2012 in the emilia region italy we extend the results from previous studies based on analytical inversion modeling of gps and radarsat 1 insar measurements by exploiting radarsat 2 data moreover we benefit from the available large amount of geological and geophysical information through finite element method fem modeling implemented in a structural mechanical context to investigate the impact of known buried structures on the modulation of the ground deformation field we find that the displacement pattern associated with the 20 may event is consistent with the activation of a single fault segment of the inner ferrara thrust in good agreement with the analytical solution in contrast the interpretation of the 29 may episode requires the activation of three different fault segments and a block roto translation of the mirandola anticline the proposed fem based methodology is applicable to other seismic areas where the complexity of buried structures is known and plays a fundamental role in the modulation of the associated surface deformation pattern

extremely reducing conditions reached during basaltic intrusion in organic matter bearing sediments redox conditions in magma are widely interpreted as internally buffered and closely related to that of their mantle source regions we use thermodynamic calculations to show that high temperature interaction between magma and organic matter can lead to a dramatic reduction of the magma redox state and significant departure from that of the original source field studies provide direct evidence of the process that we describe with reported occurrences of graphite and native iron in igneous mafic rocks implying very reducing conditions that are almost unknown in average terrestrial magmas we calculate that the addition of 0 6 wt organic matter in the form of ch or ch2 to a standard basalt triggers graphite and native iron crystallization at depths of few hundred meters interaction with organic matter also profoundly affects the abundance and the redox state of the gases in equilibrium with the magma which are co dominated with h2 as the second most abundant species on a molar basis h2o and co2 being minor constituents the assimilation of only 0 1 wt organic matter by a basalt causes a decrease in its oxygen fugacity of 2 orders of magnitude the assimilation of 0 6 wt organic matter at depths 500 m implies minimum co content in the magma of 1 wt other gas components being less than 0 1 wt in the light of our calculations we suggest that the production of native iron bearing lava flows and associated intrusions was most likely accompanied by degassing of co rich gases whose fluxes depended on the magma production rates

petrogenesis of the massive chromitite layer from the jacurici complex brazil evidence from inclusions in chromite the jacurici complex hosts the largest chromite deposit in brazil in an up to 8 m thick chromitite layer within a tectonically segmented 300 m thick intrusion the ore has been interpreted as the result of crustal contamination driven crystallization in a magma conduit this study addresses the stratigraphy mineralogical and textural relationships and mineral chemistry of the monte alegre sul segment focusing on chromite hosted inclusions from the main chromitite layer to understand the role of volatiles in the genesis of the massive chromitite silicate inclusions enstatite phlogopite magnesiohornblende diopside and olivine are commonly monomineralic and sub to euhedral and crystallized prior to or coeval with the chromite crystallization carbonate inclusions dolomite and magnesite are irregular or have negative crystal shapes suggesting entrapment as melt droplets sulfides pentlandite millerite heazlewoodite polydymite pyrite and chalcopyrite are often polymineralic irregular or hexagonal shaped indicating entrapment as sulfide melt and as monosulfide solid solution the inclusions indicate an h2o and s saturated resident magma with immiscible droplets of carbonate melt during chromite crystallization inclusion rich and inclusion free chromites that occur together have similar compositions and are considered to have formed from the same magma in response to variations in the degree of cr saturation hot primitive magma might have heated and mobilized co2 and probably water from devolatized and assimilated carbonate rich wall rocks increasing fo2 and triggering chromite crystallization we propose that the formation of the chromitite layer started as in situ crystallization with additional material added by slumping of locally remobilized chromite slurries facilitated by the presence of volatiles

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

droplets and bubbles solidification of sulphide rich vapour saturated orthocumulates in the norilsk talnakh ni cu pge ore bearing intrusions

cenozoic faulting of the bohai bay basin and its bearing on the destruction of the eastern north china craton abstract the cenozoic bohai bay basin is located at the center of the eastern block of the north china craton the structural architecture of this basin provides important clues on the deep seated lithosphere thinning of the north china craton the cenozoic regional stress field is characterized by nw oriented extension however the various cenozoic structural patterns of normal faulting and related transverse folding in the bohai bay basin are controlled not only by cenozoic stress field but also by strain field and mesozoic basement fault assemblages in this area regionally the cenozoic tectonic features and the dynamic evolution of the eastern north china craton are dominated by two lithosphere penetrating fault systems including the sinistral tan lu fault system and the dextral lan liao fault system to the west of the lan liao fault system cenozoic extensional tectonics includes nne trending listric normal faults that controlled half grabens however between these two fault systems are wnw trending half grabens which show basement involved faulting in the north and overlapping relations between sedimentary cover and basement in the south to the east of the tan lu fault the north yellow sea basin is a wnw trending fault depression with faulting in the south and overlapping relations in the north these structural features are inherited from the mesozoic tectonic framework of this area whose tectonic characteristics were completely controlled by two opposite strike slipping faults the trans extensional or oblique rifting in the paleogene followed by extensional faulting and subsequent subsidence furthermore the culmination of the decratonization of the north china craton was also related to an eastward jump of cenozoic subduction of the pacific plate and the far field effect of eastward extrusion of cenozoic subduction of the indian plate and was not essentially restricted to the early mesozoic processes therefore the cenozoic especially 25 ma marks the time of cessation of the processes that led to lithosphere thinning and destruction of the eastern block of the north china craton

slip model of the 2015 mw 7 8 gorkha nepal earthquake from inversions of alos 2 and gps data we use surface deformation measurements including interferometric synthetic aperture radar data acquired by the alos 2 mission of the japanese aerospace exploration agency and global positioning system gps data to invert for the fault geometry and coseismic slip distribution of the 2015 mw 7 8 gorkha earthquake in nepal assuming that the ruptured fault connects to the surface trace of the main frontal thrust mft fault between 84 34 e and 86 19 e the best fitting model suggests a dip angle of 7 the moment calculated from the slip model is 6 08 1020 nm corresponding to the moment magnitude of 7 79 the rupture of the 2015 gorkha earthquake was dominated by thrust motion that was primarily concentrated in a 150 km long zone 50 to 100 km northward from the surface trace of the main frontal thrust mft with maximum slip of 5 8 m at a depth of 8 km data thus indicate that the 2015 gorkha earthquake ruptured a deep part of the seismogenic zone in contrast to the 1934 bihar nepal earthquake which had ruptured a shallow part of the adjacent fault segment to the east

magmatic anhydrite sulfide assemblages in the plumbing system of the siberian traps we report the first discovery of magmatic anhydrite sulfide assemblages in a subvolcanic intrusion associated with the siberian traps the 34s values of anhydrite and coexisting sulfide crystals analyzed by ion probe are 18 22 and 9 11 respectively more than 50 of the total sulfur in the intrusion is estimated to derive from marine evaporites in the footwall strata the contaminated magma was highly oxidized and able to dissolve up to one order of magnitude more sulfur than pure mantle derived basaltic magma such contaminated magma if erupted would have released far more so2 into the atmosphere than is generally appreciated

phase relations and liquid lines of descent in hydrous ferrobasalt implications for the skaergaard intrusion and columbia river flood basalts crystallization experiments using a hydrous ferrobasalt as starting material conducted at 200mpa 940 12008c at a wide range of water activities 0 1 1 and redox conditions qfm 3 to qfm 4 where qfm is the quartz fayalite magnetite oxygen buffer show that h2o influences significantly the differentiation history of ferrobasaltic magmas a combination of our data with published experiments on dry ferrobasalt at 1atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical fe rich tholeiitic system under both dry and hydrous conditions the addition of h2o decreases liquidus temperatures and changes significantly the proportions temperature range and sequence of crystallizing mineral phases the dry liquidus is at about 11708c whereas the liquidus for h2o saturated melts is at 10608c the main phases crystallizing from h2o bearing ferrobasalt at the investigated conditions are olivine ol clinopyroxene cpx plagioclase pl magnetite mt hematite hm ilmenite ilm and amphibole am the phase assemblage is similar to that of the dry system except for the presence of hm at extremely oxidizing conditions and am at low temperatures 59508c and h2o saturated conditions the important observation made in this study is that the stability of fe ti oxides and in particular mt as well as the simultaneous coprecipitation of mtand ilm are almost independent of the activity of h2o ah2o in the system whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing ah2o the stabilities of oxides are controlled mainly by the redox conditions prevailing in the system the most pronounced effect of ah2o on the liquidus temperatures of silicates is observed for pl which shows a considerable delay in crystallization with progressive magma differentiation early crystallization of fe ti oxides in h2o bearing ferrobasaltic compositions precludes any significant fe enrichment during differentiation as fe enrichment is a characteristic feature of the skaergaard intrusion it implies that the skaergaard parental magma did not contain considerable amounts of water on the other hand our experiments indicate that the differentiation of some ferrobasaltic series from the columbia river flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles 0 5 3 wt h2o

geology and geochemistry of intrusions and flood basalts of the noril sk region ussr with implications for the origin of the ni cu ores geochemical studies indicate that five principal magma types characterize the 3 8 km vertical thickness of flood basalt of the noril9sk region from base to top these are 1 a fractionated type with alkalic affiliations ivakinsky and syverminsky 2 an ni rich suite including picritic basalt gudchichinsky 3 a primitive but ni depleted suite with fiat rare earth element ree profiles and also including picritic basalts tuklonsky 4 a light ree enriched crustally contaminated suite lower nadezhdinsky nd 1 above 4 there is a transitional suite upper nadezhdinsky nd 2 and morongovsky mr 1 and mr 2 which is overlain by the fifth type a second primitive suite without picrites mokulaevsky similar but not identical in its chemistry to the tuklonsky type this is followed by tuffs and basalts of the kharayelakhsky kumginsky and samoyedsky suites which are largely composed of similar uncontaminated tholeiitic magma the latter three suites have not been studied by us intrusions of the region fall into five main groups 1 alkalic intrusions 2 ti rich dolerite dikes 3 dolerite sills and dikes 4 differentiated bodies not related to ore junctions and 5 differentiated bodies related to ore junctions the ni cu ores are associated with ni and cr rich type 5 olivine rich intrusions with flat ree profiles that are geochemicaly similar to the mokulaevsky magma light ree enriched ni and cr poor olivine rich type 5 intrusions with uneconomic mineralization occur closely associated with the strongly mineralized variants and resemble geochemically the basalts transitional between the lower nadezhdinsky and upper morongovsky they are cut by the strongly mineralized bodies indicating that the latter are of late morongovsky to mokulaevsky age the mineralized intrusions are associated with about 1 5 to 1 10 of their mass in sulfides this is a factor of 25 to 50 more than could have been carried in solution and deposited by in situ liquation from the magma of these intrusions the platinum group element pge concentrations in the ores require that the sulfides giving rise to them equilibrated with 15 to 200 times more magma than is represented by the intrusions much of the ore is very massive and crosscuts the host intrusions the sequence of igneous activity and mineralization in the immediate vicinity of noril9sk and talnakh from the base of the nadezhdinsky upward is thus interpreted to be 1 extrusion of highly crustally contaminated ni and cu poor basalt 2 extrusion of a series of basalt flows each progressively less contaminated and less ni and cu depleted than the preceding one accompanied by intrusion of contaminated ni depleted magma with weak mineralization 3 extrusion of uncontaminated ni and cu rich basalt accompanied by intrusion of uncontaminated ni rich magma with strong mineralization followed very closely by introduction of associated massive ore and 4 continued extrusion of ni and cu rich basalt it is proposed that crustal contamination of the original ni and cu rich magma occurred at the top of a vertically extensive fault controlled magma chamber and caused segregation of immiscible sulfides with a low r factor these depleted this magma in chalcophile elements and settled deeper in the chamber as they settled they reacted with less contaminated magma scavenging additional chalcophile elements they finally came to rest near the base of the chamber to form a zone of sulfide and thus chalcophile element enriched magma eruption and in some instances intrusion of progressively stratigraphically lower less contaminated and thus less depleted layers in the chamber gave rise to the observed sequence of basalts and intrusions the answer to the strong enrichment in ni cu and pge associated with the ore bearing intrusions is that these metals came from the magma that is now represented by the depleted basalts

contemporary tectonics of the himalayan frontal fault system folds blind thrusts and the 1905 kangra earthquake the sub himalayan fold thrust belt consists of deformed late cenozoic and older deposits south of the main boundary thrust mbt in pakistan east of the indus river the sub himalaya comprises the potwar plateau and the salt range which is thrust southward over the jhelum river floodplain along the salt range thrust although an estimated 9 14 mm a 1 shortening has been taken up on the salt range thrust during the last 2 ma the range front scarp does not show signs of recent faulting shortening may be shifting southward to the lilla overpressured anticline which rises from the jhelum floodplain as a fault propagation fold farther east shortening is partitioned among several anticlines underlain by foreland and hinterland dipping blind thrusts southeast of the main deformation zone the pabbi hills overpressured anticline is best explained as a fault propagation fold throughout the potwar plateau and salt range thrusts and folds rise from a basal decollement horizon in eocambrian evaporites the pakistani part of the decollement horizon could generate large earthquakes only if these evaporites die out northward at seismogenic depths in india and nepal the sub himalaya is narrower reflecting the absence of evaporites and a steeper slope of the basement towards the hinterland the southern boundary of the sub himalaya is the himalayan front fault discontinuous because part of the shortening is expressed at the surface by folding broad alluvial synclinal valleys dun valleys are bounded on the south by rising barrier anticlines of siwalik molasse the 1905 kangra earthquake m8 produced uplift on the mohand anticline and the dehra dun valley suggesting that this earthquake occurred on a decollement horizon above basement downdip from the fold if so the kangra event is the largest known earthquake on a blind thrust expressed at the surface as a fold

coseismic stress and strain field changes investigation through 3 d finite element modeling of dinsar and gps measurements and geological seismological data the l aquila italy 2009 earthquake case study

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

geology of the western flanks of the oktyabr skoe deposit noril sk district russia evidence of a closed magmatic system the oktyabr skoe deposit in the northern siberian platform is one of the world s largest deposits in terms of platinum group elements and nickel reserves the genesis of this deposit has been inferred from the inner geological structure of its central portion and remains a matter of long lasting and heated discussions the current dominant hypothesis is that the ores were produced in an open magmatic system this study is devoted to only one aspect of the complicated problem of ore formation i e the geological structure of the kharaelakh intrusion to which the huge orebodies are related recently new data have been acquired on the structure and composition of the western flanks of the kharaelakh intrusion which pinches out in this direction and does not coincide with basalts as has been suggested in many publications a distinctive feature of this part of the deposit is that it is cut by numerous relatively thin intrusions of contrasting compositions from picritic gabbro dolerite to leucogabbro that are spatially separated in contrast with the central portion of the deposit where these rocks occur as discrete layers of a single intrusion these bodies taper off westward and are blind apophyses of the intrusion to which various ore types are related the inner structure of this part of the vertical section of the intrusion is analyzed based on detailed data on the core material recovered by a number of boreholes and on the chemical and mineralogical characteristics of the ores which differ from those in the main orebodies in that they possess lower cu and pge concentrations up to 3 5 wt and 9 ppm respectively and hence result in the dominance of pyrrhotite and limited amounts and smaller grain sizes of platinum group minerals peripheral sills of the kharaelakh intrusion were formed by portions of initial magma with different melt cumulus minerals proportions forming separate bodies of picritic and olivine bearing gabbro dolerite the last rock varieties comprise disseminated ore in contrast with the central parts of the intrusion where these ores are located in the picritic and taxitic horizons no peripheral sills or dikes connected with lava flows have been found inside the studied area these facts evidence ore formation in a closed magmatic system

mineralogy geochemistry and stratigraphy of the maslovsky pt cu ni sulfide deposit noril sk region russia implications for relationship of ore bearing intrusions and lavas we report new data on the stratigraphy mineralogy and geochemistry of the rocks and ores of the maslovsky pt cu ni sulfide deposit which is thought to be the southwestern extension of the noril sk 1 intrusion variations in the ta nb ratio of the gabbro dolerites hosting the sulfide mineralization and the compositions of their pyroxene and olivine indicate that these rocks were produced by two discrete magmatic pulses which gave rise to the northern and southern maslovsky intrusions that together host the maslovsky deposit the northern intrusion is located inside the tungusska sandstones and basalt of the ivakinsky formation the southern intrusion cuts through all of the lower units of the siberian trap tuff lavas including the lower nadezhdinsky formation demonstrating that the ore bearing intrusions of the noril sk complex post date that unit rocks in both intrusions have low tio2 and elevated mgo contents average mean tio2 1 and mgo 12 wt that are more primitive than the lavas of the upper formations of the siberian traps which suggests that the ore bearing intrusions result from a separate magmatic event unusually high concentrations of both hree dy yb er lu and y up to 1 2 and 2 1 ppm respectively occur in olivines fo79 5 and 0 25 nio from picritic and taxitic gabbro dolerites with disseminated sulfide mineralization thus accumulation of hree y and ni in the melts is correlated with the mineral potential of the intrusions the tio2 concentration in pyroxene has a strong negative correlation with the mg of both host mineral and mg of host rock sulfides from the northern maslovsky intrusion are predominantly chalcopyrite pyrrhotite pentlandite with subordinate and minor amounts of cubanite bornite and millerite and a diverse assemblage of rare precious metal minerals including native metals au ag and pd sn pd pt bi pb compounds and fe pt alloys sulfides from the southern maslovsky intrusion have 34s 5 6 up to 10 8 in two samples whereas the country rock basalt have 34s 3 4 implying there was no in situ assimilation of surrounding rocks by magmas

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

ground deformation and source geometry of the 24 august 2016 amatrice earthquake central italy investigated through analytical and numerical modeling of dinsar measurements and structural geological data we investigate the ground deformation and source geometry of the 2016 amatrice earthquake central italy by exploiting alos2 and sentinel 1 coseismic differential interferometric synthetic aperture radar dinsar measurements they reveal two nnw sse striking surface deformation lobes which could be the effect of two distinct faults or the rupture propagation of a single fault we examine both cases through a single and a double dislocation planar source subsequently we extend our analysis by applying a 3 d finite elements approach jointly exploiting dinsar measurements and an independent structurally constrained 3 d fault model this model is based on a double fault system including the two northern gorzano and redentore vettoretto faults ngf and rvf which merge into a single wsw dipping fault surface at the hypocentral depth 8 km the retrieved best fit coseismic surface deformation pattern well supports the exploited structural model the maximum displacements occur at 5 7 km depth reaching 90 cm on the rvf footwall and 80 cm on the ngf hanging wall the von mises stress field confirms the retrieved seismogenic scenario

transport of metals and sulphur in magmas by flotation of sulphide melt on vapour bubbles emissions of sulphur 1 2 and transition metals 3 4 from magmas in the shallow crust have global impacts on human society by affecting climate after volcanic eruptions 5 6 and by forming giant copper and gold ore deposits which are massive anomalies of sulphur as well as of the ore metals themselves 3 4 7 8 these emissions vastly exceed the amounts that could have been derived from the associated magmas themselves 2 intrusion of denser hotter vapour and sulphide saturated magma beneath the cooler and more buoyant bodies that are finally erupted is the most probable source of the excess sulphur and metals in eruptive or hydrothermal systems 1 4 9 10 however the mechanism for the selective upward transfer of sulphur and metals remains poorly understood because their main carrier phase sulphide melt is dense and is generally assumed to settle to the bottoms of magma bodies here we show by experimental observation and by gas speciation and mass balance models that such transfers may be achieved by the flotation of compound drops 11 comprising droplets of sulphide melt attached to vapour bubbles by proposing and demonstrating the feasibility of a novel physical mechanism for upward mobility of sulphide liquids our work provides a mechanism for massive atmospheric releases of sulphur and contradicts widely held assumptions that dense sulphide liquids rich in sulphur copper and gold will remain sequestered in the crust

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

a new genetic model for the giant ni cu pge sulfide deposits associated with the siberian flood basalts the kharaelakh intrusion is one of several sill like multiphase gabbroic intrusions that host world class ni cu pge deposits in the noril sk talnakh region the sulfide ores of the kharaelakh intrusion are characterized by elevated 34s values 10 12 and high pge concentrations e g up to10 ppm pt the 34s values require addition of crustal s with elevated isotope ratios such as evaporite bearing country rocks 34s 20 and r factors magma sulfide mass ratios of 2 000 if pt content in the magma is similar to the values in the coeval most undepleted lavas 10 ppb such a discrepancy can be explained by sulfide resorption by a new flux of mantle derived magma into a deep staging chamber to form pge enriched magma interaction of the pge enriched magma with evaporite bearing country rocks in the plumbing system at higher crustal levels could have produced sulfide liquids with high pge contents as well as elevated 34s values mass balance calculations indicate that 0 9 wt percent anhydrite assimilation from evaporite bearing country rocks is required to explain the elevated 34s values of the sulfide ores this model although developed purely based on data from the kharaelakh deposit can also be applied to other coeval ni cu pge deposits for the coeval noril sk i and talnakh deposits different depths of anhydrite assimilation in the respective plumbing systems are required this model differs from the previously proposed models in detail but reenforces the idea that chalcophile element depletion in continental flood basalts is a useful exploration tool for ni cu pge deposits associated with coeval subvolcanic intrusions

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

rupture process of the mw 7 9 2015 gorkha earthquake nepal insights into himalayan megathrust segmentation we investigate the rupture process of the 25 april 2015 gorkha earthquake mw 7 9 using a kinematic joint inversion of teleseismic waves strong motion data high rate gps static gps and synthetic aperture radar sar data the rupture is found to be simple in terms of coseismic slip and even more in terms of rupture velocity as both inversion results and a complementing back projection analysis show that the main slip patch broke unilaterally at a steady velocity of 3 1 3 3 km s this feature likely contributes to the moderate peak ground acceleration 0 2 g observed in kathmandu the 15 km deep rupture occurs along the base of the coupled portion of the main himalayan thrust and does not break the area ranging from kathmandu to the front the limitation in length and width of the rupture cannot be identified in the preearthquake interseismic coupling distribution and is therefore discussed in light of the structural architecture of the megathrust

teleseismic p wave crustal tomography of the weifang segment on the tanlu fault zone a case study based on short period dense seismic array experiment abstract the 1896 high quality relative travel time residuals are collected by applying the multi channel cross correlation technique to the waveform data of teleseismic events recorded by a short period dense seismic array consisting of 302 stations in the weifang segment of the tanlu fault zone using the fast marching teleseismic tomography technique these residuals are inverted for a fine p wave crustal velocity model under the study region down to 30 km depth with the resolution of 20 km in horizontal directions and 30 km in depth we image obvious high velocity anomalies to the west of the fault zone from the surface down to a depth of 30 km and striking low velocity anomalies appear within the fault zone around 36 5 n where the changle volcano exists on the surface whilst to the east velocity anomalies exhibit a complicated pattern meanwhile our tomographic images roughly show a boundary between the fault zone and its surrounding areas we infer that the fault zone provides a plausible channel for continuous upwelling of hot and wet materials from the mantle to the surface when it intruded into the crust the process of upwelling of hot and wet materials from the mantle could be associated with mantle dynamics of the big mantle wedge due to the stagnation and dehydration of the subducted pacific slab in the mantle transition zone under the region our present study demonstrates that it is possible that a fine crustal velocity structure can be obtained by teleseismic tomography with a short period dense seismic array

compositional variations of olivine and sulfur isotopes in the noril sk and talnakh intrusions siberia implications for ore forming processes in dynamic magma conduits olivine from the noril sk i main and northwestern talnakh ore bearing intrusions in the noril sk region occurs as inclusions discrete grains and poikilitic crystals the original compositions of olivine inclusions have been well preserved by their host oikocrysts from reaction with interstitial silicate and sulfide liquids in contrast the compositions of discrete and poikilitic olivine crystals have been variably modified by reequilibration with trapped silicate and sulfide liquids there are abrupt changes in the contents of nickel in olivine inclusions 500 1 500 ppm between different rock units in all three intrusions which indicates that the different rock units in these intrusions are not related to each other via in situ differentiation of a common parental magma but rather are consistent with separate pulses of magma with variable degrees of differentiation possibly involving olivine crystallization and assimilation of siliceous crustal material in a staging chamber the 34s values of the samples with high sulfur contents 800 ppm sulfur from all three ore bearing intrusions vary between 8 and 14 per mil two sulfur poor samples 600 ppm sulfur from the northwestern talnakh intrusion yield 34s values of 1 5 and 3 6 per mil these values are similar to the values of the sulfur poor rocks from the ore barren intrusions in the region and illustrate the fact that high sulfur contents couple with increasing 34s values such a relationship is consistent with the addition of crustally derived 34s enriched sulfur to the magma of the ore bearing intrusions in contrast to other models of sulfide segregation in closed systems we propose that sulfide segregation occurred in an open system and the magma involved was undersaturated in sulfur and undepleted in chalcophile elements we envision that the 34s enriched sulfur was introduced via circulating fluids that transported sulfur from evaporite in the underlying sedimentary sequence to the magma in a dynamic magma conduit the immiscible sulfide liquids that segregated during sulfur contamination settled down in the wider parts of the conduit as the magma continued to travel successive pulses of new magma entered the conduit reacted with the early sulfide and displaced much of the early magma in the conduit the ore bearing intrusions are thought to have crystallized within the wider parts of the conduits and their voluminous sulfide poor peripheral sills represent some if not all of the magma that flowed out of the conduits

insight into the origin of the tengchong intraplate volcano and seismotectonics in southwest china from local and teleseismic data received 18 june 2008 revised 22 february 2009 accepted 10 march 2009 published 13 may 2009 1 a high resolution tomographic image of the crust and upper mantle under yunnan province in southwest china was determined by using a large number of teleseismic data measured precisely from digital seismograms as well as local earthquake arrival times recorded by the dense yunnan seismic network the grid spacing of the tomographic model is 70 km 78 km in the horizontal directions and 4 70 km in depth our resulting model shows a clear low velocity low v 0 3 with respect to the average one dimensional velocity model column extending from the surface down to about 400 km depth under the active tengchong volcano and some high velocity high v anomalies existing in the mantle transition zone furthermore the low vanomaly extends horizontally toward the northeast at 250 to 400 km depth combining our tomographic results with geochemical and geological investigations we infer that the tengchong volcano is a rift related volcano caused by the subduction and dehydration of the indian plate as well as corner flow in the mantle wedge though the subducted slab is a continental plate our results show that the upwelling flow under tengchong originates at 400 km depth a prominent low v anomaly along the red river fault zone extends down to the upper mantle 100 km depth reflecting that the red river fault zone may have cut through the crust to the upper mantle the two dayao earthquakes m 6 1 and m 6 2 in 2003 occurred on the margin of high v anomalies and are underlain by a prominent low v anomaly in the lower crust and upper mantle suggesting that the dayao earthquakes may be associated with fluids released from the dehydration of the subducted indian slab these results are significantly improved compared with previous studies and provide new seismic constraints on the dynamic processes of the india asia collision

finite element modelling of the 2015 gorkha earthquake through the joint exploitation of dinsar measurements and geologic structural information abstract we investigate the co seismic effects of the mw 7 8 gorkha earthquake through a finite element modelling approach that jointly exploits space borne dinsar deformation measurements and geologic structural information our model permits to retrieve the coseismic displacements with a very good accuracy and to confirm the finding of earlier studies suggesting that the slip reaches a maximum value of about 7 m at a depth of 7 15 km along the main himalayan thrust mht and occurs in an area about 30 km northern of kathmandu in particular the main shock ruptured the deep part of the seismogenic zone of mht with rather small displacement values retrieved along the splay faults main frontal thrust mft main boundary thrust mbt in the southern region a relevant aspect of our results is the imaging of about 3 m of displacement in correspondence to the shallow portion of the main central thrust mct to the north and of the munsiari mahabharat thrust mt to the south this finding may be associated to a possible mechanism for accommodating the mht sourced deformation on the adjacent thrusts highlighting a passive role of the hinterland structures as receiver faults of the displacements transferred from earthquakes originating on the mht in addition the proposed model allow us to map the stress field distribution evaluated through von mises failure criteria associated to the main seismic event this result is in good agreement with the hypocentral distribution and mechanism of the investigated aftershocks

geochemistry and origin of the intrusive hosts of the noril sk talnakhcu ni pge sulfide deposits the world class deposits of cu ni and platinum group elements pge of the noril sk talnakh district in russia are hosted by relatively small complex mafic ultramafic bodies that intrude permian sedimentary rocks and the lowermost suites of the siberian continental flood volcanic sequence the noril sk type ore bearing intrusions immediately overlie and are probably penecontemporaneous with weakly mineralized intrusions of the lower talnakh type which have similar petrological features but contrasting and much more variable nd os and sr isotopic compositions several types of spatially associated intrusions were emplaced after the ore bearing intrusions and the flood volcanic sequence to clarify relations between the various types of igneous bodies flood volcanic rocks noril sk type intrusions lower talnakh type intrusions and later intrusions and to help understand the formation of the ore deposits we undertook a detailed geochemical and nd os and sr isotopic study of eight of the more important intrusions the data indicate that these intrusions formed by the input of a series of magma pulses each of which produced rocks with distinctive petrology and chemical compositions these compositions are interpreted to have formed from mixtures of mantle derived magmas and different types of crustal rock which were encountered and assimilated during passage to the surface some of these variations may be superimposed on heterogeneities inherited from the mantle source the magmas that formed the lower talnakh type intrusions became contaminated with large amounts of crustal rock in a deep staging chamber the chemical and isotopic characteristics of the resultant hybrid magmas are broadly similar to those of basalts of the lower and middle nadezhdinsky lava subsuites nd 1 2 which are located about one third of the way through the overlying lava sequence these magmas became saturated in sulfur during contamination and segregation of sulfides resulted in the depletion of chalcophile elements recorded in the nd 1 2 lavas magmas feeding the ore bearing intrusions had trace element and isotopic compositions similar to those of the basalts in the upper two thirds of the volcanic sequence these magmas underwent lower degrees of contamination in a deep staging chamber and sulfur saturation was not reached these magmas therefore contained a full compliment of chalcophile elements when they encountered anhydrite rich sediments during passage toward the surface assimilation of these sediments led to the segregation of sulfides to form the ores two aspects of our data impose important constraints on the ore forming process the first is the os isotopic composition of the ore sulfides avg os 7 which is similar to that of mantle rocks and very different from those of sulfides that segregate from highly contaminated magma the second is the absence of ni depletion in olivine in rocks from the ore bearing intrusions most notably in the ore rich picritic gabbrodolerites the simplest explanation is that the sulfides segregated from magmas that were not highly contaminated and were transported into the intrusions by magmas different from those that yielded the sulfide if this explanation is correct it imposes some modifications to earlier models of sulfide ore deposition in the conduits of flood basalts

intensity magnitude location and attenuation in india for felt earthquakes since 1762 a comprehensive consistently interpreted new catalog of felt intensities for india martin and szeliga 2010 this issue includes intensities for 570 earth quakes instrumental magnitudes and locations are available for 100 of these events we use the intensity values for 29 of the instrumentally recorded events to develop new intensity versus attenuation relations for the indian subcontinent and the himalayan region we then use these relations to determine the locations and mag nitudes of 234 historical events using the method of bakun and wentworth 1997 for the remaining 336 events intensity distributions are too sparse to determine mag nitude or location we evaluate magnitude and location accuracy of newly located events by comparing the instrumental with the intensity derived location for 29 cali bration events for which more than 15 intensity observations are available with few exceptions most intensity derived locations lie within a fault length of the instrumen tally determined location for events in which the azimuthal distribution of intensities is limited we conclude that the formal error bounds from the regression of bakun and wentworth 1997 do not reflect the true uncertainties we also find that the regression underestimates the uncertainties of the location and magnitude of the 1819 allah bund earthquake for which a location has been inferred from mapped surface deformation comparing our inferred attenuation relations to those developed for other regions we find that attenuation for himalayan events is comparable to intensity attenuation in california bakun and wentworth 1997 while intensity attenuation for cratonic events is higher than intensity attenuation reported for central eastern north america bakun et al 2003 further we present evidence that intensities of intraplate earth quakes have a nonlinear dependence on magnitude such that attenuation relations based largely on small to moderate earthquakes may significantly overestimate the magnitudes of historical earthquakes

an overview of chalcophile element contents of pyrrhotite pentlandite chalcopyrite and pyrite from magmatic ni cu pge sulfide deposits we have compiled the trace element concentrations in pyrrhotite pentlandite chalcopyrite and pyrite from magmatic ni cu pge ore deposits with the aim of understanding their petrogenesis and whether these minerals can be used as indicator minerals among the samples there are some of the most studied world class ni cu aguablanca duluth jinchuan noril sk talnakh kharaelakh sudbury voisey s bay and others and pge dominated bushveld lac des iles stillwater great dyke and penikat deposits crustal assimilation may be constrained using as se and sb se ratios in pentlandite the degree of interaction between the silicate and sulfide liquids r factor can be estimated by the content of highly chalcophile elements dsulf liq sil liq above 1000 in sulfide minerals the fractional crystallization of the sulfide liquid can be traced using se te ratios of pentlandite pyrite formed by exsolution from mss has higher rh ru ir and os than co existing pyrrhotite whereas pyrite formed by hydrothermal alteration of pyrrhotite inherits the rh ru ir and os contents of the pyrrhotite it replaced sulfide minerals are preserved in transported glacial cover and their trace element chemistry can be used to discriminate their source pentlandite from ni cu deposits has much lower rh and pd concentrations than those from pge dominated deposits pyrite from magmatic deposits has higher co sb and se as ratios relative to pyrite from hydrothermal deposits and chalcopyrite from magmatic deposits has much higher ni and lower cd concentrations than those from hydrothermal deposits