automated detection and location of microseismicity at mount st helens with a large n geophone array in the summer of 2014 a dense array of 904 geophones was deployed at mount st helens along the road and trail system within 15 km distance of the summit crater the array recorded continuous data for approximately 2 weeks and presents an unprecedented seismic observation of an active volcano a reverse time imaging method is applied to short term average over long term average time series data to automatically detect and locate microseismicity these efforts resulted in an order of magnitude increase in earthquake detections over the normal monitoring operations of the pacific northwest seismic network earthquake locations resolve a narrow 1 km wide vertical lineament of seismicity which extends from the surface to 4 km depth directly beneath the summit crater this feature is interpreted as a fracture network that acts as a conduit connecting an underlying magma chamber to the surface

deciphering the hydrothermal evolution of a vms system by la icp ms using trace elements in pyrite an example from the bracemac mcleod deposits abitibi canada and implications for exploration textural and chemical characterization of pyrite was used to reconstruct the hydrothermal evolution of the bracemac mcleod archean volcanogenic massive sulfide vms deposits 6 mt in the matagami district abitibi canada the mineralization hosted in a bimodal volcanic sequence is divided into a 1 zn rich zone concordant to the key tuffite a marker horizon at the district scale 2 a cu rich zone which locally crosscuts the stratigraphic pile and 3 some localized magnetite rich zones replacing sphalerite and pyrite detailed petrographic and laser ablation inductively coupled plasma mass spectrometry la icp ms studies of whole pyrite grains including inclusions and zonation from the key tuffite and from the different ore zones of the deposits has revealed five pyrite types nodular pyrites i in the key tuffite and subidiomorphic pyrites from the low temperature 250 c zn rich zone ii have the same chemical signature suggesting that both precipitated under similar physicochemical conditions a wide range of trace elements cu zn ag sn sb te au pb bi tl are present in both but compared to the other types of pyrite they are significantly enriched in sb and tl subidiomorphic pyrites from the copper rich zone iii have a different signature enriched only in se co in pb and bi these pyrites commonly overgrow the nodular pyrites and are related to later higher temperature fluids 300 c pyrite preserved during a later magnetite replacement 350 c stage iv also are enriched in se but are depleted in all other elements a similar signature is found in idiomorphic metamorphic pyrite v which occurs at the district scale during high temperature recrystallization of pyrite iv and v only the contents of ni co as and se are mostly preserved whereas other base metals are expelled from the pyrite structure consequently only ni co as se sb and tl were useful to reconstruct the hydrothermal evolution of the vms system and used to build a suite of discrimination diagrams specifically the ratio se tl can discriminate pyrites from mineralized zn rich zone se tl 10 000 the innovative approach of this study based on la icp ms acquisition of the chemistry of entire pyrite grains makes our results directly applicable for exploration consequently pyrite concentrate samples analyzed for as tl and se by more classical mass spectrometric techniques have the potential to be used for vectoring to ore by using the proposed discrimination diagrams

a noachian source region for the black beauty meteorite and a source lithology for mars surface hydrated dust the martian surface is covered by a fine layer of oxidized dust responsible for its red color in the visible spectral range bibring et al 2006 morris et al 2006 in the near infrared the strongest spectral feature is located between 2 6 and 3 6 m and is ubiquitously observed on the planet jouglet et al 2007 milliken et al 2007 although this absorption has been studied for many decades its exact attribution and its geological and climatic implications remain debated we present new lines of evidence from laboratory experiments orbital and landed missions data and characterization of the unique martian meteorite nwa 7533 all converging toward the prominent role of hydroxylated ferric minerals martian breccias so called black beauty meteorite nwa7034 and its paired stones nwa7533 and nwa 7455 are unique pieces of the martian surface that display abundant evidence of aqueous alteration that occurred on their parent planet agee et al 2013 these dark stones are also unique in the fact that they arose from a near surface level in the noachian southern hemisphere humayun et al 2013 we used ir spectroscopy fe xanes and petrography to identify the mineral hosts of hydrogen in nwa 7533 and compare them with observations of the martian surface and results of laboratory experiments the spectrum of nwa 7533 does not show mafic mineral absorptions making its definite identification difficult through nir remote sensing mapping however its spectra are virtually consistent with a large fraction of the martian highlands abundant nwa 7034 7533 and paired samples lithologies might abound on mars and might play a role in the dust production mechanism

pb isotopic evidence for an early enriched crust on mars abstract martian meteorite nwa 7533 is a regolith breccia that compositionally resembles the martian surface measured by orbiters and landers nwa 7533 contains monzonitic clasts that have zircon with u pb ages of 4 428 ga the pb isotopic compositions of plagioclase and alkali feldspars as well as u pb isotopic compositions of chlorapatite in the monzonitic clasts of nwa 7533 have been measured by secondary ion mass spectrometry sims the u pb isotopic compositions measured from the chlorapatite in nwa 7533 yield an age of 1 357 81 ga 2 the least radiogenic pb isotopic compositions measured in plagioclase and k feldspar lie within error of the 4 428 ga geochron these data indicate that the monzonitic clasts in nwa 7533 are a product of a differentiation history that includes residence in a reservoir that formed prior to 4 428 ga with a value 238 u 204 pb of at least 13 4 1 7 2 and a value 232 th 238 u of 4 3 this value is more than three times higher than any other documented martian reservoir these results indicate either the martian mantle is significantly more heterogeneous than previously thought value of 1 14 vs 1 5 and or the monzonitic clasts formed by the melting of martian crust with a value of at least 13 4 therefore nwa 7533 may contain the first isotopic evidence for an enriched differentiated crust on mars

ancient impactor components preserved and reworked in martian regolith breccia northwest africa 7034 abstract northwest africa nwa 7034 and paired stones represent unique samples of martian polymict regolith breccia multiple breccia subsamples characterized in this work confirm highly siderophile element hse re os ir ru pt pd contents that are consistently elevated e g os 9 3 18 4 ppb above indigenous martian igneous rocks mostly 187 os 188 os ratios of 0 119 0 136 record a wider variation than observed for all major chondrite types combined with the measured 187 re 188 os ratios of 0 154 0 994 the range in os isotope ratios indicates redistribution of re and os from originally chondritic components early in the history of the regolith commencing at 4 4 ga superimposed recent re mobility reflects exposure and weathering at or near the martian and terrestrial surfaces elevated os concentrations 38 0 and 92 6 ppb os superchondritic os hse ratios and 187 os 188 os of 0 1171 and 0 1197 measured for two subsamples of the breccia suggest the redistribution of impactor material at 1 5 1 9 ga possibly overlapping with a partial resetting event at 1 4 ga recorded by u pb isotope systematics in the breccia martian alteration of the originally chondritic hse host phases to form os ir rich nuggets and ni rich pyrite implies the influence of potentially impact driven hydrothermal systems multiple generations of impactor component admixture redistribution and alteration mark the formation and evolution of the martian regolith clasts and matrix of nwa 7034 and paired meteorites from the pre noachian until impact ejection to earth

the south american rainfall dipole a complex network analysis of extreme events intraseasonal rainfall variability of the south american monsoon system is characterized by a pronounced dipole between southeastern south america and southeastern brazil here we analyze the dynamical properties of extreme rainfall events associated with this dipole by combining a nonlinear synchronization measure with complex networks we make the following main observations i our approach reveals the dominant synchronization pathways of extreme events for the two dipole phases ii while extreme rainfall synchronization in the tropics is directly driven by the trade winds and their deflection by the andes mountains extreme rainfall propagation in the subtropics is mainly dictated by frontal systems and iii the well known rainfall dipole is in fact only the most prominent mode of an oscillatory pattern that extends over the entir ec ontinent this provides further evidence that the influence of rossby waves which cause frontal systems over south america and impact large scale circulation patterns extends beyond the equator

the geochemistry of trace elements in geothermal fluids iceland abstract trace element geochemistry was studied in geothermal fluids in iceland the major and trace element compositions of hot springs sub boiling and two phase liquid and vapor wells from 10 geothermal areas were used to reconstruct the fluid composition in the aquifers at depth aquifer fluid temperatures ranged from 4 to 300 c ph values between 4 5 and 9 3 and fluids typically contained total dissolved solids

chalcophile and platinum group element pge concentrations in the sulfide minerals from the mccreedy east deposit sudbury canada and the origin of pge in pyrite magmatic sulfide deposits consist of pyrrhotite pentlandite chalcopyrite pyrite and platinum group minerals pgm understanding the distribution of the chalcophile and platinum group element pge concentrations among the base metal sulfide phases and pgm is important both for the petrogenetic models of the ores and for the efficient extraction of the pge typically pyrrhotite and pentlandite host much of the pge except pt which forms pt minerals chalcopyrite does not host pge and the role of pyrite has not been closely investigated the ni cu pge ores from the south range of sudbury are unusual in that sulfarsenide pgm rather than pyrrhotite and pentlandite are the main carrier of pge probably as the result of arsenic contribution to the sulfide liquid by the as bearing metasedimentary footwall rocks in comparison the north range deposits of sudbury such as the mccreedy east deposit have as poor granites in the footwall and the ores commonly contain pyrite our results show that in the pyrrhotite rich ores of the mccreedy east deposit os ir ru rh ipge and re are concentrated in pyrrhotite pentlandite and surprisingly in pyrite this indicates that sulfarsenides which are not present in the ores were not important in concentrating pge in the north range of sudbury palladium is present in pentlandite and together with pt form pgm such as ptpd tebi 2 platinum is also found in pyrite two generations of pyrite are present one pyrite is primary and locally exsolved from monosulfide solid solution mss in small amounts 2 wt together with pyrrhotite and pentlandite this pyrite is unexpectedly enriched in ipge as pt and the concentrations of these elements are oscillatory zoned the other pyrite is secondary and formed by alteration of the mss cumulates by late magmatic hydrothermal fluids this pyrite is unzoned and has inherited the low concentrations of ipge and re from the pyrrhotite and pentlandite that it has replaced

convective storm life cycle and environments near the sierras de cordoba argentina abstractsatellite observations have revealed that some of the world s most intense deep convective storms occur near the sierras de cordoba argentina south america a c band dual polarization do

magma reservoirs from the upper crust to the moho inferred from high resolution vp and vs models beneath mount st helens washington state usa the size frequency and intensity of volcanic eruptions are strongly controlled by the volume and connectivity of magma within the crust several geophysical and geochemical studies have produced a comprehensive model of the magmatic system to depths near 7 km beneath mount st helens washington state usa currently the most active volcano in the cascade range data limitations have precluded imaging below this depth to observe the entire primary shallow magma reservoir as well as its connection to deeper zones of magma accumulation in the crust the inversion of p and s wave traveltime data collected during the active source component of the imush imaging magma under st helens project reveals a high p wave vp s wave vs velocity anomaly beneath mount st helens between depths of 4 and 13 km which we interpret as the primary upper middle crustal magma reservoir beneath and southeast of this shallow reservoir a low vp velocity column extends from 15 km depth to the moho deep long period events near the boundary of this column indicate that this anomaly is associated with the injection of magmatic fluids southeast of mount st helens an upper middle crustal high vp vs body beneath the indian heaven volcanic field may also have a magmatic origin both of these high vp vs bodies are at the boundaries of the low vp middle lower crustal column and both are directly above high vp middle lower crustal regions that may represent cumulates associated with recent quaternary or paleogene neogene cascade magmatism seismicity immediately following the 18 may 1980 eruption terminates near the top of the inferred middle lower crustal cumulates and directly adjacent to the inferred middle lower crustal magma reservoir these spatial relationships suggest that the boundaries of these high density cumulates play an important role in both vertical and lateral transport of magma through the crust

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

orogenic convection in subtropical south america as seen by the trmm satellite abstractextreme orogenic convective storms in southeastern south america are divided into three categories storms with deep convective cores storms with wide convective cores and storms containing broad stratiform regions data from the tropical rainfall measuring mission satellite s precipitation radar show that storms with wide convective cores are the most frequent tending to originate near the sierra de cordoba range downslope flow at upper levels caps a nocturnally enhanced low level jet thus preventing convection from breaking out until the jet hits a steep slope of terrain such as the sierra de cordoba mountains or andean foothills so that the moist low level air is lifted enough to release the instability and overcome the cap this capping and triggering is similar to the way intense convection is released near the northwestern himalayas however the intense storms with wide convective cores over southeastern south america are unlike their himalayan counterparts in that they exhibit leadi

influence of the frontal systems on the day to day convection variability over south america abstract cold cloud top fractions derived from international satellite cloud climatology project images and latitude time diagrams are used to study the interaction of frontal systems with tropical convection over south america sa an 11 yr climatology for three frequent types of frontal system tropical convection interaction is built and the associated day to day convection variability is described using satellite images complex principal components and wavelet transforms type 1 is frequent throughout the year especially in austral summer and is characterized by the penetration of a cold front in subtropical sa that interacts with tropical convection and moves with it into lower tropical latitudes type 2 is also more frequent in austral summer and is characterized by amazon convection and enhancement of a quasi stationary northwest southeast oriented band of convection extending from the amazon basin to subtropical sa along the passage of a cold front in the subtropics when the type 2 pattern

halogen and cl isotopic systematics in martian phosphates implications for the cl cycle and surface halogen reservoirs on mars abstract the cl isotopic compositions and halogen cl f br and i abundances in phosphates from eight martian meteorites spanning most rock types and ages currently available have been measured in situ by secondary ion mass spectrometry sims likewise the distribution of halogens has been documented by x ray mapping halogen concentrations range over several orders of magnitude up to some of the largest concentrations yet measured in martian samples or on the martian surface and the inter element ratios are highly variable similarly cl isotope compositions exhibit a larger range than all pristine terrestrial igneous rocks phosphates in ancient 4 ga meteorites orthopyroxenite alh 84001 and breccia nwa 7533 have positive 37 cl anomalies 1 1 to 2 5 these samples also exhibit explicit whole rock and grain scale evidence for hydrothermal or aqueous activity in contrast the phosphates in the younger basaltic shergottite meteorites 37 cl anomalies 0 2 to 5 6 phosphates with the largest negative 37 cl anomalies display zonation in which the rims of the grains are enriched in all halogens and have significantly more negative 37 cl anomalies suggestive of interaction with the surface of mars during the latest stages of basalt crystallization the phosphates with no textural major element or halogen enrichment evidence for mixing with this surface reservoir have an average 37 cl of 0 6 supporting a similar initial cl isotope composition for mars the earth and the moon oxidation and reduction of chlorine are the only processes known to strongly fractionate cl isotopes both positively and negatively and perchlorate has been detected in weight percent concentrations on the martian surface the age range and obvious mixing history of the phosphates studied here suggest perchlorate formation and halogen cycling via brines which have been documented on the martian surface has been active throughout martian history

magma system recharge of mount st helens from precise relative hypocenter location of microearthquakes 1 four hundred forty seven well recorded earthquakes at mount st helens during the late 1990s are relocated with high precision using a combination of a cross correlation technique and then a procedure to obtain a one dimensional velocity structure solution together with station corrections the resulting high resolution pattern of the spatial temporal evolution of the earthquake activity along with focal mechanisms of events provide additional evidence for the presence of a magma reservoir in the depth range 5 5 10 km connected to the surface by a thin vertical conduit moreover the distribution of the events below 5 5 km yielded a much clearer view of the structures that generate the seismicity at that depth some of the deeper events occur along a sequence of faults under the influence of a radial stress field however a large number of the events occur on a nne ssw striking steeply dipping fault with slip consistent with magma being periodically injected into a truncated dike on the northwest side of this fault

systematic variations of trace element and sulfur isotope compositions in pyrite with stratigraphic depth in the skouriotissa volcanic hosted massive sulfide deposit troodos ophiolite cyprus the troodos ophiolite represents one of the best preserved fossil analogs of modern oceanic crust and includes numerous volcanic hosted massive sulfide deposits the skouriotissa deposit can be separated into a stockwork ore zone and an overlying massive sulfide lens that is covered by metalliferous sediments representing the former sulfide seawater interface pyrite is the dominant sulfide mineral within these ores the trace element composition of pyrite varies systematically with stratigraphic depth down to 150 mbsf probably reflecting fluid temperature variations and effects of phase separation co ni se te bi and cu metal remobilization due to hydrothermal zone refining zn sb and pb and fluid seawater mixing at the seafloor mo represent further important processes controlling the pyrite chemistry massive sulfide hosted sphalerite and euhedral pyrite probably formed from hot fluids 400 c while the occurrence of colloform pyrite indicates lower precipitation temperatures 400 c similar 18o quartz fluid equilibration temperatures 400 c in the stockwork zone suggest that the skouriotissa fluids did not cool significantly during the final 150 m of fluid ascent to the seafloor the 34s composition of deep stockwork pyrite 1 4 suggests that an isotopically light magmatic volatile phase 0 was added to the hydrothermal system of skouriotissa during further fluid ascent about 38 of cretaceous seawater 34s 18 19 was added leading to the precipitation of stockwork pyrite with positive 34s values 6 1 in addition the chemical and textural similarities between skouriotissa and modern seafloor vent systems and massive sulfide deposits suggest that the skouriotissa hydrothermal system has a modern analog

the distribution of gold in sub seafloor stockwork mineralization from dsdp hole 504b and the agrokipia b deposit cyprus the distribution of gold has been examined in sub seafloor stockworks from two sections of hydrothermally altered oceanic crust beneath the axial zones of fossil spreading centers deep sea drilling project hole 504b leg 83 contains a narrow zone of stockwork like sulfides in 6 ma old basalt from the transition zone between sheeted dikes and overlying pillow lavas 910 928 m mineralization occurred as a result of local mixing between ascending hydrothermal fluids 350 c and seawater that penetrated the top of the dike section previous studies indicate that a significant amount of gold was leached from the sheeted dikes during high temperature greenschist facies alteration but mineralized wall rock in the transition zone is not substantially enriched in gold sulfide concentrates from the narrow stockwork average 26 ppb au and one sample of as rich pyrite from a quartz epidote breccia contains 100 ppb au cyprus custal study project hole cy 2a contains an equivalent section of altered cretaceous p

the paris meteorite the least altered cm chondrite so far the paris chondrite provides an excellent opportunity to study cm chondrules and refractory inclusions in a more pristine state than currently possible from other cms and to investigate the earliest stages of aqueous alteration captured within a single cm bulk composition it was found in the effects of a former colonial mining engineer and may have been an observed fall the texture mineralogy petrography magnetic properties and chemical and isotopic compositions are consistent with classification as a cm2 chondrite there are 45 vol high temperature components mainly type i chondrules with olivine mostly fa0 2 mean fa0 9 with granular textures because of low mesostasis abundances type ii chondrules contain olivine fa7 to fa76 these are dominantly of type iia but there are iiab and iib chondrules ii a b chondrules with minor highly ferroan olivine and iia c with augite as the only pyroxene the refractory inclusions in paris are amoeboid olivine aggregates aoas and fine grained spinel rich ca al rich inclusions cais the cai phases formed in the sequence hibonite perovskite grossite spinel gehlenite anorthite diopside fassaite and forsterite the most refractory phases are embedded in spinel which also occurs as massive nodules refractory metal nuggets are found in many cai and refractory platinum group element abundances pge decrease following the observed condensation sequences of their host phases mn cr isotope measurements of mineral separates from paris define a regression line with a slope of 53mn 55mn 5 76 0 76 106 if we interpret cr isotopic systematics as dating paris components particularly the chondrules the age is 4566 44 0 66 myr which is close to the age of cai and puts new constraints on the early evolution of the solar system eleven individual paris samples define an o isotope mixing line that passes through cm2 and co3 falls and indicates that paris is a very fresh sample with variation explained by local differences in the extent of alteration the anhydrous precursor to the cm2s was co3 like but the two groups differed in that the cms accreted a higher proportion of water paris has little matrix 47 plus 8 fine grained rims and is less altered than other cm chondrites chondrule silicates except mesostasis cai phases submicron forsterite and amorphous silicate in the matrix are all well preserved in the freshest domains and there is abundant metal preserved metal alteration stage 1 of palmer and lauretta 2011 metal and sulfide compositions and textures correspond to the least heated or equilibrated cm chondrites category a of kimura et al 2011 the composition of tochilinite cronstedtite intergrowths gives a pcp index of 2 9 cronstedtite is more abundant in the more altered zones whereas in normal highly altered cm chondrites with petrologic subtype 2 6 2 0 based on the s sio2 and feo sio2 ratios in pcp or tochilinite cronstedtite intergrowths rubin et al 2007 cronstedtite is destroyed by alteration the matrix in fresh zones has ci chondritic volatile element abundances but interactions between matrix and chondrules occurred during alteration modifying the volatile element abundances in the altered zones paris has higher trapped ne contents more primitive organic compounds and more primitive organic material than other cms there are gradational contacts between domains of different degree of alteration on the scale of 1 cm but also highly altered clasts suggesting mainly a water limited style of alteration with no significant metamorphic reheating

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

local crustal extension at mount st helens washington seismicity and the orientation of fault planes from focal mechanisms indicate that mount st helens is located at a dextral offset along the st helens seismic zone shz earthquake swarms occurring in this offset are related to volcanic eruptions because motion on the shz is in a right lateral strike slip sense this dextral offset creates extension within a volume of the crust between the offset fault segments this offset geometry is similar to that of geothermal areas along the san andreas fault system we apply a model derived from these geothermal areas to mount st helens and find that the major differences between mount st helens and the geothermal areas can be related to the ratio of the width of the offset between fault segments l to the seismogenic depth h at mount st helens this ratio is 1 whereas in the geothermal areas the ratio is 1 we propose that when l h 1 as at mount st helens the regional minimum principal stress does not completely dominate the small volume under extension and as a consequence the opening geometry is poory established compared to the oblique crustal spreading that characterizes the geothermal areas where l h 1 late quaternary volcanic vents near mount st helens strike northeast similar to the strike of a set of pre quaternary faults and intrusive rocks that are mapped north of the volcano in addition the deepest earthquakes occurring within the extensional volume are aligned along a northeast striking fault since these northeast striking features are aligned approximately prependicular to the regional minimum principal stress we infer that the spatial position of mount st helens is controlled by the junction of the right stepping offset of the shz with the older set of fractures and that these fractures are favorably aligned with respect to the contemporary regional tectonic stress directions for the transport of magma through the brittle crust the sense of fault motions predicted by our model for local crustal extension is consistent with an apparent component of right lateral shear measured from geodetic lines around mount st helens during june and july 1980

siderophile element abundances in the upper mantle evidence for a sulfide signature and equilibrium with the core abstract measurements of the intrinsic oxygen fugacities of samples from the earth s upper mantle have shown that the characteristic oxidation state ranges from values close to fe ni metal saturation to more oxidized values tectonic processes can account for the progressive and variable oxidation of a mantle that was originally in equilibrium with metal so that the oxygen fugacity data give strong support to the possibility of protocore protomantle equilibrium the data for apparently overabundant siderophile elements in the mantle are reviewed and 2 groups group a ge au pd pt ru rh ir re os group b sn sb ag ga cu as co ni w mo are recognized group a abundances result from an overprinting by a late accreting chondritic component of a mantle that had suffered major extraction of the indigenous complement by core forming metal chou 1978 group b however are 10 more abundant than group a and may be distinguished as a group by their greater chalcophile tendencies this is highlighted for example by the large cl normalized sn ge ratio of the mantle which is unexpected as a result of metal silicate fractionation alone but can be accounted for if some sn together with sulfur was retained in the mantle during core separation industrial experience in the equilibrium of molten fe and silicate slags shows that sulfur is not overwhelmingly partitioned into metal so that the concept of partial 20 of original accreting component retention of sulfur and group b elements in the mantle has experimental and theoretical support following core separation progressive loss of sulfide from the mantle is indicated by the anomalously high ni at a given mg number in archaean basalts and siliceous mg poor sediments it is also a feature of oceanic and continental basalts that some u pb fractionation must have occurred in the mantle source regions following core separation and this is most satisfactorily achieved if pb is partially removed from u in a sulfide phase

rhodium gold and other highly siderophile element abundances in chondritic meteorites abstract the abundances of the highly siderophile elements hse re os ir ru pt rh pd and au and 187os 188os isotope ratios have been determined for a set of carbonaceous ordinary enstatite and rumuruti chondrites using an analytical technique that permits the precise and accurate measurement of all hse from the same digestion aliquot concentrations of re os ir ru pt and pd were determined by isotope dilution icp ms and n tims analysis the monoisotopic elements rh and au were quantified relative to the abundance of ir differences in hse abundances and ratios such as re os 187os 188os pd ir and au ir between different chondrite classes are further substantiated with new data and additional rh and au data including new data for ci chondrites systematically different relative abundances of rh between different chondrite classes are reminiscent of the behaviour of re carbonaceous chondrites are characterized by low average rh ir of 0 27 0 03 1s which is about 20 lower than the ratio for ordinary 0 34 0 02 and enstatite chondrites eh 0 33 0 01 el 0 32 0 01 r chondrites show higher and somewhat variable rh ir of 0 37 0 07 well defined linear correlations of hse in particular for bulk samples of ordinary and el chondrites are explained by binary mixing and or dilution by silicates the hse carriers responsible for these correlations have a uniform chemical composition indicating efficient homogenization of local nebular heterogeneities during or prior to the formation of the host minerals in chondrite components excepting rumuruti chondrites and au in carbonaceous chondrites these correlations also suggest that metamorphism alteration and igneous processes had negligible influence on the hse distribution on the bulk sample scale depletion patterns for rh pd and au in carbonaceous chondrites other than ci are smoothly related to condensation temperatures and therefore consistent with the general depletion of moderately volatile elements in carbonaceous chondrites fractionated hse abundance patterns of ordinary enstatite and rumuruti chondrites however are more difficult to explain fractional condensation combined with the removal of metal phases at various times and later mixing of early and late formed metal phases may provide a viable explanation planetary fractionation processes that may have affected precursor material of chondrite components cannot explain the hse abundance patterns of chondrite groups hse abundances of some but not all rumuruti chondrites may be consistent with solid sulphide liquid sulphide fractionation processes during impact induced melting

the ratio of tellurium and selenium in geological material as a possible paleo redox proxy abstract only few data for both tellurium and selenium in different geological materials including international reference materials have been available so far in this study the te se ratio has been investigated in more detail to provide a better understanding of the correlation of these two elements in the geological environment nine international reference materials irms and 79 different geological samples spanning a wide range of formation times and conditions from the paleoproterozoic to present were analyzed with quadrupole dynamic reaction cell drc icp ms these samples include basalts shales river and beach sediments loess dolomites a recent cold water coral precambrian manganese and iron formations and cenozoic marine ferromanganese nodules and crusts a wide range of concentrations between 0 01 and 1 5 g g for se and 0 01 and 90 g g for te was measured and the most interesting feature was found to be the te se ratio in the different geological matrices while most rock and sediment samples fall within the range of te se ratios typical of the average earth s crust a significant enrichment of te over se is evident for modern marine mn fe oxide precipitates with the most pronounced te enrichment found for hydrogenetic ferromanganese crusts which form under fully oxidizing conditions the apparent positive trend of the degree of te se fractionation with the redox potential of the formation environment suggests that the te se ratio may represent a potential paleo proxy for redox environments

comparative mineralogy and geochemistry of gold bearing sulfide deposits on the mid ocean ridges a comparative study of the mineralogy and geochemistry of sulfide deposits on mid ocean ridges in the northeast pacific and the mid atlantic reveals common characteristics associated with primary gold enrichment average gold contents of 0 8 to 5 ppm au occur in sulfides from southern explorer ridge and axial seamount northeast pacific and from the tag hydrothermal field and snakepit vent field mid atlantic ridge the enrichment of gold in these deposits is consistently related to a phase of late stage low temperature 1 ppm au occur exclusively in pyritic assemblages and commonly with abundant fe poor sphalerite and a suite of complex pb sb as sulfosalts amorphous silica and locally barite or carbonate are important constituents of the gold rich precipitates but do not contain gold themselves high temperature 350 c black smoker assemblages consisting dominantly of pyrite chalcopyrite pyrrhotite isocubanite and abundant anhydrite are uniformly gold poor 0 2 ppm au to the extent that individual sulfides can be mechanically separated chemical analyses by neutron activation indicate that gold is most abundant in sphalerite up to 5 7 ppm au but also occurs in pyrite and marcasite samples of sphalerite with abundant inclusions of fine grained sulfosalts locally contain up to 18 ppm au suggesting that sulfosalts may be repositories for gold no free gold has been observed at 4000 magnification of polished specimens indicating that the gold is present only as submicroscopic inclusions or as a chemical constituent within the sulfides samples from gold rich deposits in the northeast pacific and mid atlantic are compared with similar but relatively gold poor sulfides from the galapagos rift and 13 n on the east pacific rise epr and with barren sulfides from 11 n epr 21 n epr the endeavour ridge and the southern juan de fuca ridge trace element analyses of more than 170 samples show that gold enrichment in almost all of the deposits is associated with high concentrations of ag as sb pb and zn and locally with high cd hg tl and ga in contrast gold is typically depleted in samples with high co se and mo the close association of au with ag as sb and pb may reflect the common behavior of these metals as aqueous sulfur complexes e g au hs 2 at low temperatures similar mineralogical and geochemical associations are observed in sulfide deposits from modern back arc settings and in the ancient geologic record

severe convection and lightning in subtropical south america satellite radar and radiometer data show that subtropical south america has the world s deepest convective storms robust mesoscale convective systems and very frequent large hail we determine severe weather characteristics for the most intense precipitation features seen by satellite in this region in summer hail and lightning concentrate over the foothills of western argentina lightning has a nocturnal maximum associated with storms having deep and mesoscale convective echoes in spring lightning is maximum to the east in association with storms having mesoscale structure a tornado alley is over the pampas in central argentina distant from the maximum hail occurrence in association with extreme storms in summer flash floods occur over the andes foothills associated with storms having deep convective cores in spring slow rise floods occur over the plains with storms of mesoscale dimension this characterization of high impact weather in south america provides crucial information for socioeconomic implications and public safety

subseasonal variations of rainfall in south america in the vicinity of the low level jet east of the andes and comparison to those in the south atlantic convergence zone abstract regional and large scale circulation anomalies associated with variations in rainfall downstream of the south american low level jet are identified and compared to those in the south atlantic convergence zone sacz composites of precipitation associated with strong jets reveal an approximate doubling of the quantities one would expect from climatology with an evolution of the rainfall pattern from south to north the occurrence of extreme precipitation events follows a similar pattern meridional cross sections of composite wind reveal a distinct low level jet near 20 s and a baroclinic development farther south that appears to force the jet geopotential height temperature and large scale wind composites suggest that this developing disturbance is tied to a wave train that originates in the midlatitude pacific and turns equatorward as it crosses the andes mountains similar composites based on sacz rainfall reveal similar features but of opposite sign suggesting that the phase of the wave

variability in warm season atmospheric circulation and precipitation patterns over subtropical south america relationships between the south atlantic convergence zone and large scale organized convection over the la plata basin warm season precipitation variability over subtropical south america is characterized by an inverse relationship between the south atlantic convergence zone sacz and precipitation over the central and western la plata basin of southeastern south america this study extends the analysis of this south american seesaw precipitation dipole to relationships between the sacz and large long lived mesoscale convective systems llcss over the la plata basin by classifying sacz events into distinct continental and oceanic categories and building a logistic regression model that relates llcs activity across the region to continental and oceanic sacz precipitation a detailed account of spatial variability in the out of phase coupling between the sacz and large scale organized convection over the la plata basin is provided enhanced precipitation in the continental sacz is found to result in increased llcs activity over northern northeastern and western sections of the la plata basin in association with poleward atmospheric moisture flux from the amazon basin toward these regions and a decrease in the probability of llcs occurrence over the southeastern la plata basin increased oceanic sacz precipitation however was strongly related to reduced atmospheric moisture and decreased probability of llcs occurrence over nearly the entire la plata basin these results suggest that continental sacz activity and large scale organized convection over the northern and eastern sections of the la plata basin are closely tied to atmospheric moisture transport from the amazon basin while the warm coastal brazil current may also play an important role as an evaporative moisture source for llcss over the central and western la plata basin

climatology of the low level jet east of the andes as derived from the ncep ncar reanalyses characteristics and temporal variability abstract a climatology of the south american low level jet east of the andes sallj is developed using the 1950 2000 circulation and moisture fields from the ncep ncar reanalyses and available upper air observations made in bolivia and paraguay since 1998 upper and low level circulation fields were derived for seasonal means and sallj composites during the warm and cold seasons the bonner criterion 1 was applied for sites in central bolivia and downstream near northern paraguay to determine the spatial and temporal characteristics of the sallj on the circulation characteristics sallj composites during the warm season show the enhanced low level meridional moisture transport coming from equatorial south america as well as an upper level wave train emanating from the west pacific propagating toward south america the intensification of the warm season sallj follows the establishment of an upper level ridge over southern brazil and a trough over most of argentina the circulation anomalies at upper a

a 10 year radar based climatology of mesoscale convective system archetypes and derechos in poland abstractin this study a 10 year 2008 2017 radar based mesoscale convective system mcs and derecho climatology for poland is presented this is one of the first attempt for a european country to

chaco low level jet events characterization during the austral summer season 1 previous studies showed a relationship between convection maxima and the convergence of vapor flux over southeastern south america nicolini and saulo 2000 explored the hypothesis of an intensification of this mutual dependency during the chaco jet events they defined these events as extreme cases of low level jets east of the andes that penetrate southernmost to 25 s using eta operative products during the 1997 1998 austral warm season the interest of the present paper centers on the climatic characterization of the chaco jet events cjes and the possibility of researching this hypothesis using the european centre for medium range weather forecasts reanalyses era which cover a 15 year period 1979 1993 the cjes represent a subensemble of low level jet events east of the andes that are infrequent in the era data set their duration varies from 1 to 10 days more frequently extending from 1 to 5 days the outstanding features of the circulation and the thermodynamic field that represent this ensemble are a maximum contrast of air masses in a latitude close to 39 s the presence of a trough centered on 70 w within a baroclinic wave train penetrating from the pacific ocean and a maximum of heat and moisture over northen argentina and paraguay during the cjes there is an important flux of moisture and convergence at low and mid levels that is about 10 times more intense than the summer mean the intensity found in the water vapor flux anomaly reinforces the importance of studying these episodes for the purpose of determining the water balance over southeastern south america the statement that the cjes represent an important characteristic of the southeastern south american climate is founded on the fact that although the cjes only represent 17 of the austral summer days they account for a significant fraction of the precipitation a maximun of 55 over northeastern argentina however it is indispensable to contrast these results with future field experiments to test the hypothesis addressed in this paper

tectonics and seismicity of the southern washington cascade range abstract geophysical geological and seismicity data are combined to develop a transpressional strain model for the southern washington cascades region we use this model to explain oblique fold and fault systems transverse faults and a linear seismic zone just west of mt rainier known as the western rainier zone we also attempt to explain a concentration of earthquakes that connects the northwest trending mount st helens seismic zone to the north trending western rainier zone our tectonic model illustrates the pervasive effects of accretionary processes combined with subsequent transpressive forces generated by oblique subduction on eocene to present crustal processes such as seismicity and volcanism

subpolar high anomaly preconditioning precipitation over south america abstract the mechanisms associated with the intraseasonal variability of precipitation over south america during the spring season are investigated with emphasis on the influence of a quasi stationary anomalous circulation over the southeastern south pacific ocean sep a spectral analysis performed to the bandpass filtered time series of daily precipitation anomalies for the la plata basin lpb and the south atlantic convergence zone sacz regions revealed several statistically relevant peaks corresponding to periods of roughly 23 days and 14 16 days with the lower higher frequency peaks more prevalent for the sacz lpb the large scale circulation patterns preconditioning precipitation variability over both regions were explored by means of a regression analysis performed on the daily 500 hpa geopotential anomaly field provided by the ncep ncar reanalysis dataset the most prominent feature of the regression fields is the presence of a quasi stationary anomalous anticyclonic cyclonic circulation

convective initiation near the andes in subtropical south america abstractsatellite radar and radiometer data indicate that subtropical south america has some of the deepest and most extreme convective storms on earth this study uses the full 15 yr trmm precipitation radar dataset in conjunction with high resolution simulations from the weather research and forecasting model to better understand the physical factors that control the climatology of high impact weather in subtropical south america the occurrence of intense storms with an extreme horizontal dimension is generally associated with lee cyclogenesis and a strengthening south american low level jet sallj in the la plata basin the orography of the andes is critical and model sensitivity calculations removing and or reducing various topographic features indicate the orographic control on the initiation of convection and its upscale growth into mesoscale convective systems mcss reduced andes experiments show more widespread convective initiation weaker average storm intensity and more rapid propagation

geology of the mount st helens area record of discontinuous volcanic and plutonic activity in the cascade arc of southern washington the quaternary edifice of mount st helens volcano was built upon a deeply eroded terrane of gently folded and altered volcanic and plutonic rocks that represent the core of the tertiary cascade magmatic arc these rocks constitute an east dipping homoclinal sequence several kilometers thick of subaerially erupted mafic to silicic flows and volcaniclastic strata k ar ages from this section range from about 28 to 23 ma late oligocene and earliest miocene which corresponds to an apparent lull in cascade volcanism to the north of mount rainier volcanism was essentially continuous during this period of time and neither a well defined base nor top of the section is exposed within the mapped area basalt and basaltic andesite dominate the lower part of the mid tertiary section whereas andesitic and dacitic rocks comprise most of the upper part this section was intruded by numerous mafic to silicic dikes sills and irregular plutonic bodies most no more than a few million years younger than their host rocks and subjected to pervasive burial metamorphism and widespread hydrothermal alteration large areas of hornfelsed rock surrounding even relatively small intrusions indicate that the proportion of plutonic rock becomes significantly greater at shallow depth beneath the existing erosion surface a large granitic pluton intruded the mid tertiary section north of spirit lake at about 21 ma the earl porphyry copper deposit occurs within the pluton but appears too young 17 ma to be genetically related to it in contrast to the rather continuous and voluminous oligocene to early miocene activity volcanism since then in the mount st helens area has been localized and volumetrically minor products of three younger eruptive periods have been recognized a sequence of 15 m y old pyroxene andesite flows resting unconformably on mid tertiary strata south of mount st helens widespread shallow dikes and sills of pyroxene andesite between 10 and 8 m y old and compositionally diverse rocks erupted during the past 3 m y the quaternary lavas are more potassic than the tertiary lavas and typically contain phenocrysts of hornblende and biotite which are absent from the older rocks a number of tertiary structures define a broad nne trending zone that may reflect a deep seated lithospheric flaw that has controlled the locus of cascade magmatism in southern washington for the past 25 m y mount st helens lies within this zone at the intersection of the nnw striking st helens seismic zone shz and an ene trending alignment of pleistocene silicic plug domes no surface breakage has been detected along the shz which is apparently very young the linear zone of silicic vents is probably controlled by a fault that has been interpreted from seismic records to occur directly beneath the volcano this zone parallels the directions of regional maximum horizontal compressive stress and north america juan de fuca plate convergence mount st helens is an example of a low volume tectonically controlled magmatic system in an early stage of development

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

nickeliferous pyrite tracks pervasive hydrothermal alteration in martian regolith breccia a study in nwa 7533 martian regolith breccia nwa 7533 and the seven paired samples is unique among martian meteorites in showing accessory pyrite up to 1 by weight pyrite is a late mineral crystallized after the final assembly of the breccia it is present in all of the lithologies i e the fine grained matrix icm clast laden impact melt rocks climr melt spherules microbasalts lithic clasts and mineral clasts all lacking magmatic sulfides due to degassing pyrite crystals show combinations of cubes truncated cubes and octahedra polycrystalline clusters can reach 200 lm in maximum dimensions regardless of their shape pyrite crystals display evidence of very weak shock metamorphism such as planar features fracture networks and disruption into subgrains the late fracture systems acted as preferential pathways for partial replacement of pyrite by iron oxyhydroxides interpreted as resulting from hot desert terrestrial alteration the distribution and shape of pyrite crystals argue for growth at moderate to low growth rate from just saturated near neutral 6 fmq 2 log units it is inferred from the maximum ni contents 4 5 wt that pyrite started crystallizing at 400 500 c during or shortly after a short duration relatively low temperature thermal event that lithified and sintered the regolith breccias 1 4 ga ago as deduced from disturbance in several isotope systematics

sedimentary underplating at the cascadia mantle wedge corner revealed by seismic imaging earth s largest earthquakes occur at the boundary between subducting oceanic crust and the overriding plate yet the position of the plate boundaries remains uncertain analysis of zones of low seismic wave velocities beneath the northern cascadia subduction zone implies that the plate boundary here may be deeper than previously thought

chalcophile siderophile element systematics of hydrothermal pyrite from martian regolith breccia nwa 7533 unlike other martian meteorites studied so far martian regolith breccia nwa 7533 and 56 paired meteorites that have sampled 4 4 ga old impact lithologies show only sulfides of 57 hydrothermal origin mostly pyrite 1 the reasonably good positive correlation r 2 0 72 between se and 65 ni reflects a temperature control on the solubility of both elements apart from the chalcogens s se 66 and te pyrite appears to be a minor contributor 400 c temperature crystallization for nwa 7533 pyrite as deduced from 69 its se and ni contents ii magmatic sulfide depletion of brecciated early martian crust iii 70 precipitation from near neutral h 2 s hs h 2 o rich hydrothermal fluids that did not provide halogen 71 ligands for extensive transport of chalcophile siderophile metals it is suggested that the 1 4 ga 72 lithification event that precipitated hydrothermal pyrite left the chalcophile siderophile element 73 budget of the early martian crust nearly unmodified except for s se and te 74 75 76

cold season synoptic scale waves over subtropical south america the most active winter synoptic scale wave patterns over south america are identified using an extended empirical orthogonal function eeof technique and are physically diagnosed using composite methods results show that the leading modes of short timescale variability propagate along two main paths over the subtropical jet latitudes 308s and over the subpolar jet latitudes 608s this research focuses on the subtropical mode and its evolution over south america the observed structure of the systems associated with the subtropical mode resembles that of midlatitude baroclinic waves both cyclonic and anticyclonic perturbations display significant modifications in their threedimensional structure as they evolve over extratropical and subtropical south america while the upper level perturbations are mostly unaffected when moving eastward the lower level perturbations advance following the shape of the andes mountains and exhibit an abrupt equatorward migration at the lee side of the mountains as a result of such detachment smaller eddy heat fluxes are observed in the vicinity of the orography and consequently a weaker eddy baroclinic growth is observed once the upper level system is on the lee side the perturbations acquire a more typical baroclinic wave structure and low level intensification of the system occurs the latter is largest around 1000 km east of the orography where enhanced moisture transports from tropical latitudes along the eastern portion of the low level cyclone favor precipitation occurrence over southeastern south america those precipitation processes seem to provide a diabatic source of energy that further contributes to the strengthening of the low level cyclone in addition an intensification of the cyclone once over the ocean was found in 60 of the situations considered which is consistent with previous research suggesting an additional source of moisture and heat flux due to the warm waters of the brazil current

elevated mixed layers and associated severe thunderstorm environments in south and north america abstractthis study presents a climatological and composite analysis of elevated mixed layers emls in south and north america derived from the ncep climate forecast system reanalysis the emls are identified based on objective criteria applied to the reanalysis data composite analyses of synoptic scale conditions and severe weather parameters associated with spring eml cases are presented emls are more frequent immediately to the east of the andes and the rockies the north american emls form by surface heating over the higher terrain of the rockies with peak frequency occurring in spring and summer emls in south america are generated by differential temperature advection due to ageostrophic circulations east of the andes as indicated by the temperature lapse rate tendency equation which relates to the higher frequency of emls during the cold season in south america emls over north america are about 100 hpa lower than over south america due to the lower height of the rockies in comparison to the a

unique meteorite from early amazonian mars water rich basaltic breccia northwest africa 7034 we report data on the martian meteorite northwest africa nwa 7034 which shares some petrologic and geochemical characteristics with known martian meteorites of the snc i e shergottite nakhlite and chassignite group but also has some unique characteristics that would exclude it from that group nwa 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent rover and orbiter missions it formed 2 089 0 081 billion years ago during the early amazonian epoch in mars9 geologic history nwa 7034 has an order of magnitude more indigenous water than most snc meteorites with up to 6000 parts per million extraterrestrial h2o released during stepped heating it also has bulk oxygen isotope values of 17o 0 58 0 05 per mil and a heat released water oxygen isotope average value of 17o 0 330 0 011 per mil suggesting the existence of multiple oxygen reservoirs on mars

serial upstream propagating mesoscale convective system events over southeastern south america abstract serial mesoscale convective system mcs events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern south america from infrared satellite imagery during the spring and summer these events begin over the southern la plata river basin with individual convective systems generally moving eastward with the cloud layer mean wind however an important and common subset of these serial mcs events shows individual mcss moving to the east or southeast yet the region of convective development as a whole shifts upstream to the north or northwest analyses of the composite mean environments from 10 of these upstream propagating serial mcs events using ncep ncar reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the united states the serial mcs events form within an environment of strong low level warm advection and strong moisture advection between the surface and 700 hpa from the amazon

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

the influence of the andes mountains on the south american low level flow 1 a dry hydrostatic three dimensional primitive equation model is used to evaluate the mechanical effect of the andes mountains on the south american low level flow llf the model simulations reproduce the evolution of a baroclinic wave over the continent under winter and summer conditions in both seasons as a consequence of the interaction between the basic flow and the andes northerly llf was reproduced east of the andes which resembles the main characteristics of the observed flow moreover seasonal changes of cyclone activity have a significant impact on the location of maximum llf and its alignment which exhibits a nw se orientation during winter and more meridional orientation in the warm season

inventory of h2o in the ancient martian regolith from northwest africa 7034 the important role of fe oxides water rich martian regolith breccia northwest africa nwa 7034 was analyzed by fourier transform infrared spectroscopy and transmission electron microscopy to determine the inventory and phase distribution of h2o used herein to refer to both molecular h2o and oh structural components in hydrous minerals hydrous fe oxide phases hydromaghemite and an unidentified nanocrystalline fe bearing oxide phase observed with hydromaghemite and phyllosilicates saponite were identified as the primary mineralogic hosts for h2o with a minor contribution from cl rich apatite based on mass balance calculations and modal abundances of minerals constrained by powder x ray diffraction and petrography we can account for the entire 6000 ppm h2o measured in bulk rock analyses of nwa 7034 this h2o is distributed evenly between hydrous fe rich oxides and phyllosilicates indicating that fe oxides could be as important as phyllosilicates for h2o storage in martian surface material

geologic history of martian regolith breccia northwest africa 7034 evidence for hydrothermal activity and lithologic diversity in the martian crust the timing and mode of deposition for martian regolith breccia northwest africa nwa 7034 were determined by combining petrography shape analysis and thermochronology nwa 7034 is composed of igneous impact and brecciated clasts within a thermally annealed submicron matrix of pulverized crustal rocks and devitrified impact volcanic glass the brecciated clasts are likely lithified portions of martian regolith with some evidence of past hydrothermal activity represented lithologies are primarily ancient crustal materials with crystallization ages as old as 4 4 ga one ancient zircon was hosted by an alkali rich basalt clast confirming that alkalic volcanism occurred on mars very early nwa 7034 is composed of fragmented particles that do not exhibit evidence of having undergone bed load transport by wind or water the clast size distribution is similar to terrestrial pyroclastic deposits we infer that the clasts were deposited by atmospheric rainout subsequent to a pyroclastic eruption s and or impact event s although the ancient ages of igneous components favor mobilization by impact s despite ancient components the breccia has undergone a single pervasive thermal event at 500 800 c evident by groundmass texture and concordance of 1 5 ga dates for bulk rock k ar u pb in apatite and u pb in metamict zircons the 1 5 ga age is likely a thermal event that coincides with rainout breccia lithification we infer that the episodic process of regolith lithification dominated sedimentary processes during the amazonian epoch the absence of pre amazonian high temperature metamorphic events recorded in ancient zircons indicates source domains of static southern highland crust punctuated by episodic impact modification

magmatic system geometry at mount st helens modeled from the stress field associated with posteruptive earthquakes earthquakes following the may 18 1980 and june 12 1980 explosive eruptions of mount st helens were concentrated at depths below 6 km the hypocenters of these posteruption earthquakes define two seismic lobes separated by an aseismic volume of 2 km width that is located beneath the position of the crater the timing and location of the posteruption seismicity suggests that the earthquakes occurred in the country rock surrounding a magma body located within the aseismic volume the withdrawal of magma caused a pressure decrease within the reservoir and the earthquakes occurred as a brittle response to the resulting stress change focal mechanism solutions for posteruption earthquakes distributed within the seismic lobes are calculated using polarity and amplitude data results show that a perturbation from the regional stress field occurs between depths of 7 and 11 km this anomalous stress field is successfully modeled by a decrease in pressure within a cylindrical magma body located between the seismic lobes and subject to conditions representing the regional shear stress regime in the best fitting model the magma body is centered at 46 204 n 122 187 w 600 m to the north of the present dome and is under a regional shear stress of 20 bars the radius of the chamber is calculated to be between 0 65 and 0 75 km when using pressure drops within the cylinder of 220 and 150 bars respectively the magma body extends from 7 to 11 km and has a volume of between 5 and 7 km3 posteruption earthquakes located below 11 km fall on a northeast striking fault that is preferentially aligned with the regional tectonic stress regime this fault may be a conduit to transport magma to the shallow reservoir from greater depths within the crust

orographic rainfall hot spots in the andes amazon transition according to the trmm precipitation radar and in situ data the andes amazon transition along the eastern peruvian andes features hotspots with strong precipitation using 15 years of trmm pr data we established a robust relation between terrain elevation and mean surface precipitation with the latter peaking around 1000 masl coinciding with the moisture flux peak of the south american low level jet sallj there is strong diurnal variability with afternoon 13 18 lt convection in the amazon plains while on the eastern slopes 1000 2000 masl after the forcing associated with the thermal heating of the andes subsides convection grows during the night and surface precipitation peaks around 01 06 lt and organizes into mesoscale convective systems mcss these then displace downslope to an terrain elevation of 700 masl with stratiform regions spreading upslope and downslope and then decay during the remainder of the morning the large mcss contribute with at least 50 of daily rainfall 40 of the 01 06 lt rainfall on synoptic scales the large mcss are more common in stronger sallj conditions although subtropical cold surges are responsible for 16 of the cases

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

petrography and composition of martian regolith breccia meteorite northwest africa 7475 the northwest africa nwa 7475 meteorite is one of the several stones of paired regolith breccias from mars based on petrography oxygen isotope mineral compositions and bulk rock compositions its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten other clast types include crystallized impact melt rocks evolved plutonic rocks possible basalts contact metamorphosed rocks and siltstones impact spherules and vitrophyre shards record airborne transport and accreted dust rims were sintered on most clasts presumably during residence in an ejecta plume the clast assemblage records at least three impact events one that formed an impact melt sheet on mars 4 4 ga ago a second that assembled nwa 7475 from impactites associated with the impact melt sheet at 1 7 1 4 ga and a third that launched nwa 7475 from mars 5 ma ago mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to 5 and 15 gpa the mild postshock heating that resulted from these shock pressures would have been insufficient to sterilize this water bearing lithology during launch magnetite maghemite and pyrite are likely products of secondary alteration on mars textural relationships suggest that calcium carbonate and goethite are probably of terrestrial origin yet trace element chemistry indicates relatively low terrestrial alteration comparison of mars odyssey gamma ray spectrometer data with the fe and th abundances of nwa 7475 points to a provenance in the ancient southern highlands of mars gratteri crater with an age of 5 ma and an apparent diameter of 6 9 km marks one possible launch site of nwa 7475

mesoscale ascent in nocturnal low level jets abstracta theory for gentle but persistent mesoscale ascent in the lower troposphere is developed in which the vertical motion arises as an inertia gravity wave response to the sudden decrease of t

a composite model of mesoscale convective complexes abstract a composite analysis technique is used to investigate the evolution of mesoscale features of mesoscale convective complexes mccs the early stage of the mcc lifecycle is characterized by convergence vertical motion and heating being centered in the lower troposphere as the mcc matures the level of peak upward motion and heating shifts to the upper troposphere the system achieves and maintains its maximum divergence upward motion and anticyclonic vorticity in the upper troposphere during the latter half of the life cycle this is in contrast to gate tropical clusters where the maximum divergence upward motion and anticyclonic vorticity occurred at the mature stage of the cluster and then weakened this difference might be explained by an mcc being an inertially stable form of mesoscale convective system whose radius exceeds the rossby radius of deformation the mcc is shown to be an efficient rain producer exhibiting a precipitation efficiency exceeding 100 at the mature stage due to th

exsolution and shock microstructures of igneous pyroxene clasts in the northwest africa 7533 martian meteorite northwest africa nwa 7533 is a martian regolith breccia this meteorite and its pairings offers a good opportunity to study near surface processes that occurred on early mars here we have conducted a transmission electron microscope study of medium and coarse grained a few tens to hundreds of micrometers ca rich pyroxene clasts in order to define their thermal and shock histories the pyroxene grains have a high temperature magmatic origin as revealed by the well developed pigeonite augite exsolution microstructure exsolution lamella characteristics composition thickness and spacing indicate a moderately slow cooling some of the pyroxene clasts display evidence for local decomposition into magnetite and silica at the submicron scale this phase decomposition may have occurred at high temperature and occurred at high oxygen fugacity at least 2 3 log units above the qfm buffer after the formation of the exsolution lamellae this corresponds to oxidizing conditions well above typical martian magmatic conditions these oxidizing conditions seem to have prevailed early and throughout most of the history of nwa 7533 the shock microstructure consists of 100 mechanical twins which have accommodated plastic deformation other pyroxene shock indicators are absent compared with snc meteorites that all suffered significant shock metamorphism nwa 7533 appears only mildly shocked the twin microstructure is similar from one clast to another suggesting that the impact which generated the 100 twins involved the compacted breccia and that the pyroxene clasts were unshocked when they were incorporated into the nwa 7533 breccia

terrestrial impact melt rocks and glasses abstract the effects of meteorite and comet impact on earth are rock brecciation the formation of shock metamorphic features rock melting and the formation of impact structures i e simple craters complex craters and multi ring basins large events such as the 65 ma chicxulub impact are believed to have had catastrophic environmental effects that profoundly influenced the development of life on earth in this review an attempt is made to summarize some of the voluminous literature on impact melting one important aspect of planetary impact provide some comments on this process and to make suggestions for future research the products of impact melting are glasses impact melt rocks and pseudotachylites our treatise deals mainly with the geological setting petrography and major element chemistry of melt rocks and glasses impact glasses in several petrographic aspects are similar to volcanic glasses but they are associated with shock metamorphosed mineral and rock fragments and in places with siderophile element anomalies suggestive of meteoritic contamination they are found in allogenic breccia deposits within fall back suevite and outside fall out suevite impact craters and as spherules in distal ejecta large events such as the k t boundary chicxulub impact are responsible for the formation of worldwide ejecta horizons which are associated with siderophile element anomalies and shock metamorphosed mineral and rock debris impact glasses have a bulk chemical composition that is homogeneous but exemptions to this rule are common on a microscopic scale however impact glasses are commonly strikingly heterogeneous tektites are glasses ejected from craters over large distances they are characterized by very low water and volatile contents and element abundances and ratios that are evidence that tektites formed by melting of upper crustal sedimentary rocks four tektite strewn fields are known three of which can be tied to specific impact craters impact melt rocks form sheets lenses and dike like bodies within or beneath allogenic fallback breccia deposits in the impact crater and possibly on crater terraces and flanks dikes of impact melt rocks also intrude the rocks of the crater floor they commonly contain shock metamorphosed target rock and mineral fragments in various stages of assimilation and are glassy or fine to coarse grained chemically they are strikingly homogeneous but as with impact glasses exemptions to this rule do exist large and thick melt bodies such as the sudbury igneous complex sic are differentiated or may represent a combination of impact melt rocks sensu strictu and impact triggered deep crustal melts a concerted multidisciplinary approach to future research on impact melting and on other aspects of meteorite and comet impact is advocated impact models are models only and uncritical reliance on their validity will not lead to a better understanding of impact processes especially of melting excavation and deposition of allogenic breccias and the spatial position of breccias in relation to sheets and lenses of melt rocks within the crater impact triggered pressure release melting of target rocks beneath the excavation cavity may be responsible for the existence of melt rocks beneath the impact melt rocks sensu strictu this controversial idea needs to be tested by a re evaluation of existing data and models be they based on field or laboratory research only a relatively small number of terrestrial impact structures has been investigated in sufficient detail as it relates to geological and geophysical mapping in this review we summarize observations made on impact melt rocks and impact glasses in a number of north american brent haughton manicouagan new quebec sudbury wanapitei all in canada asian popigai russia zhamanshin kazakhstan two south african structures morokweng and vredefort the henbury crater field of australia and one european crater ries germany our tables listing major element chemical compositions of impact glasses and melt rocks however include also data from structures not dealt with in further detail

mesoscale convective systems over southeastern south america and their relationship with the south american low level jet abstract prior studies have shown that the low level jet is a recurrent characteristic of the environment during the initiation and mature stages of mesoscale convective systems mcss over the great plains of the united states the south american low level jet sallj over southeastern south america sesa has an analogous role advecting heat and moisture from the amazon basin southward into the central plains of southeastern south america generating ideal environmental conditions for convection initiation and growth into mcss this research has two purposes one is to describe the characteristics of a 3 yr mcs sample in south america south of the equator and its related geographical distribution of convection frequency the other is to advance the knowledge of the evolution of favorable environmental conditions for the development of large mcss specifically those that mature under sallj conditions high horizontal and temporal resolution satellite images are used to detect mcss in the area for the

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

environmental conditions associated with amazonian squall lines a case study abstract the environmental conditions associated with squall lines sl that were observed during the period of 13 april 13 may 1987 gte able 2b originating at the northern coast of south america and propagating over the amazon basin are documented the sl observed on 5 7 may are examined in more detail the sl days had in common a stronger and deeper low level jet when compared with the days without sl two possible explanations are found for the intensification of the low level jet propagating easterly waves in the tropical atlantic which eventually reach manaus and localized heat sources in the western amazon both were observed on 5 6 may it is suggested that numerical simulations should be performed to unravel the relative importance of each large scale mechanism

extreme summer convection in south america abstract tropical rainfall measuring mission trmm precipitation radar pr and national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data are used to indicate mechanisms responsible for extreme summer convection over south america the three dimensional reflectivity field is analyzed to define three types of extreme echo deep convective cores wide convective cores and broad stratiform regions the location and timing of these echoes are sensitive to midlatitude synoptic disturbances crossing the andes at the leading edges of these disturbances the nocturnal south american low level jet sallj transports moisture along the eastern edge of the andes from the tropical to the subtropical part of the continent where the sallj rises over lower but steep mountains on the east side of the southern central andes deep and wide convective cores are triggered in the evening when the sallj withdraws to the north as the disturbance passes nocturnal trig

life cycle variations of mesoscale convective systems over the americas abstract using goes 7 isccp b3 satellite data for 1987 88 the authors studied the evolution of the morphological and radiative properties of clouds over the life cycles of deep convective systems cs over the americas at both tropical and middle latitudes a deep convective cloud system is identified by adjacent satellite image pixels with infrared brightness temperatures tir 245 k 28 c that at some time contain embedded convective clusters that are defined by pixel values of tir 218 k 55 c the first part of the analysis computes parameters for each convective system that describe the system areal size number of convective clusters fractional convective area average and maximum size of the convective clusters shape eccentricity and orientation mean tir variance of tir tir gradient and the mean variance and gradient of collocated visible reflectances when available the second part of the analysis searches a 5 5 region centered on each convective system but in the subsequent

trace metal concentration and partitioning in the first 1 5 m of hydrothermal vent plumes along the mid atlantic ridge tag snakepit and rainbow abstract to determine the significance of metal fluxes from hydrothermal vents understanding the speciation reactivity and possible transformations of metals and metal sulfides within the hydrothermal plume is critical in this study we measure the concentration and partitioning of trace metals fe mn cu cd co pb ni and sulfide phases within the first 1 5 m of the rising plume at three vent fields tag snakepit and rainbow along the mid atlantic ridge a hcl hno3 leaching method was used to differentiate metals present in metal mono sulfides from those in pyrite and chalcopyrite at all three vent sites mn and fe are primarily in the

evidence from gravity data for an intrusive complex beneath mount st helens on the basis of gravity data aided by aeromagnetic magnetotelluric side looking radar and geologic information we tentatively identify a large shallow intrusive complex beneath mount st helens the complex is roughly 5 6 km thick and has apparently intruded a buried and compressed mesozoic forearc sedimentary sequence the lateral extent of the intrusive complex is uncertain and we give three alternative models varying from about 18 by 10 km to as much as 18 by 22 km the western boundary of the inferred mount st helens intrusion abuts several of a number of tertiary and younger plutons that crop out in the area the mount st helens intrusion apparently is adjacent to sedimentary rock or shallow volcanic rock along most of the remainder of its boundary a ringlike drainage pattern around mount st helens suggests subsidence caused by removing magma from deep beneath mount st helens and adding this mass to the mount st helens edifice and its underlying intrusion our analysis indicates that the average bulk density of the volcanic rock comprising mount st helens is about 2 15 g cm3

observations of deep long period dlp seismic events beneath aleutian arc volcanoes 1989 2002 abstract between october 12 1989 and december 31 2002 the alaska volcano observatory avo located 162 deep long period dlp events beneath 11 volcanic centers in the aleutian arc these events generally occur at mid to lower crustal depths 10 45 km and are characterized by emergent phases extended codas and a strong spectral peak between 1 0 and 3 0 hz observed wave velocities and particle motions indicate that the dominant phases are p and s waves dlp epicenters often extend over broad areas 5 20 km surrounding the active volcanoes the average reduced displacement of aleutian dlps is 26 5 cm2 and the largest event has a reduced displacement of 589 cm2 or ml 2 5 aleutian dlp events occur both as solitary events and as sequences of events with several occurring over a period of 1 30 min within the sequences individual dlps are often separated by lower amplitude volcanic tremor with a similar spectral character occasionally volcano tectonic earthquakes that locate at similar depths are contained within the dlp sequences at most aleutian volcanoes dlps appear to loosely surround the main volcanic vent and occur as part of background seismicity a likely explanation is that they reflect a relatively steady state process of magma ascent over broad areas in the lower and middle portions of the crust at mount spurr dlp seismicity was initiated by the 1992 eruptions and then slowly declined until 1997 at shishaldin volcano a short lived increase in dlp seismicity occurred about 10 months prior to the april 19 1999 eruption these observations suggest a link between eruptive activity and magma flux in the mid to lower crust and uppermost mantle

a small s mif signal in martian regolith pyrite implications for the atmosphere abstract the past martian atmosphere is often compared to the archean earth s as both were dominated by co2 rich and o2 poor chemistries archean earth rocks preserve mass independently fractionated sulfur isotopes s mif non zero 33s and 36s originating from photochemistry in an anoxic atmosphere thus martian crustal rocks might also be expected to preserve a s mif signature providing insights into past atmospheric chemistry we have used secondary ion mass spectrometry sims to investigate in situ the sulfur isotope systematics of nwa 8171 paired to nwa 7034 a martian polymict breccia containing pyrite that formed through hydrothermal sulfur addition in a near surface regolith setting in this meteorite pyrite grains have a weighted mean of 33s of 0 14 0 08 and 36s 0 70 0 40 2 s e m so the s mif signature is subtle sulfur isotope data for four additional shergottites yield 33s values that are not resolvable from zero as in previous studies of shergottites at first glance the result for the polymict breccia might seem surprising but no martian meteorite yet has yielded a s mif signature akin to the large deviations seen on earth we suggest that s mif bearing aerosols h2so4 and s8 were produced when volcanic activity pushed a typically oxidising martian atmosphere into a reduced state after rain out of these aerosols s8 would tend to be oxidised by chlorate dampening the s mif signal which might be somewhat retained in the more abundant photolytic sulfate then in the regolith mixing of aqueous surface derived sulfate with igneous sulfide the latter with zero mif to form the abundant pyrite seen in nwa 8171 would further dampen the s mif signal nonetheless the small negative 33s anomalies seen in martian meteorites imply that volcanic activity was sufficient to produce a reducing atmosphere at times this volcanically driven atmospheric evolution would tend to produce high levels of carbonyl sulfide ocs given that ocs is a relatively long lived strong greenhouse gas the s mif signal implies that volcanism periodically generated warmer conditions perhaps offering an evidence based solution to the young wet mars paradox

simulation of a serial upstream propagating mesoscale convective system event over southeastern south america using composite initial conditions abstract serial upstream propagating mesoscale convective system mcs events over southeastern south america are important contributors to the local hydrologic cycle as they can provide roughly half of the total monthly summer precipitation however the mechanisms of upstream propagation for these events have not been explored to remedy this situation a numerical simulation of the composite environmental conditions from 10 observed serial mcs events is conducted results indicate that the 3 day simulation from the composite yields a reasonable evolution of the large scale environment and produces a large region of organized convection in the warm sector over an extended period as seen in observations upstream propagation of the convective region is produced and is tied initially to the development and evolution of untrapped internal gravity waves however as convective downdrafts develop and begin to merge and form a surface cold pool in the simulation the cold pool and its interaction with the env

sulphide mineral evolution and metal mobility during alteration of the oceanic crust insights from odp hole 1256d fluxes of metals during the hydrothermal alteration of the oceanic crust have far reaching effects including buffering of the compositions of the ocean and lithosphere supporting microbial life an

record of the ancient martian hydrosphere and atmosphere preserved in zircon from a martian meteorite how the atmosphere hydrosphere and surface materials interacted on early mars is poorly understood oxygen isotopic composition of zircon grains in a martian meteorite reveals a prolonged history of exchange between martian regolith and atmosphere

regolith breccia northwest africa 7533 mineralogy and petrology with implications for early mars northwest africa 7533 a polymict martian breccia consists of fine grained clast laden melt particles and microcrystalline matrix while both melt and matrix contain medium grained noritic monzonitic material and crystal clasts the matrix also contains lithic clasts with zoned pigeonite and augite plus two feldspars microbasaltic clasts vitrophyric and microcrystalline spherules and shards the clast laden melt rocks contain clump like aggregates of orthopyroxene surrounded by aureoles of plagioclase some shards of vesicular melt rocks resemble the pyroxene plagioclase clump aureole structures submicron size matrix grains show some triple junctions but most are irregular with high intergranular porosity the noritic monzonitic rocks contain exsolved pyroxenes and perthitic intergrowths and cooled more slowly than rocks with zoned pyroxene or fine grain size noritic material contains orthopyroxene or inverted pigeonite augite calcic to intermediate plagioclase and chromite to cr bearing magnetite monzonitic clasts contain augite sodic plagioclase k feldspar ti bearing magnetite ilmenite chlorapatite and zircon these feldspathic rocks show similarities to some rocks at gale crater like black trout mara and jake m the most magnesian orthopyroxene clasts are close to alh 84001 orthopyroxene in composition all these materials are enriched in siderophile elements indicating impact melting and incorporation of a projectile component except for ni poor pyroxene clasts which are from pristine rocks clast laden melt rocks spherules shards and siderophile element contents indicate formation of nwa 7533 as a regolith breccia the zircons mainly derived from monzonitic melt rocks crystallized at 4 43 0 03 ga humayun et al 2013 and a 147sm 143nd isochron for nwa 7034 yielding 4 42 0 07 ga nyquist et al 2016 defines the crystallization age of all its igneous portions the zircon from the monzonitic rocks has a higher 17o than other martian meteorites explained in part by assimilation of regolith materials enriched during surface alteration nemchin et al 2014 this record of protolith interaction with atmosphere hydrosphere during regolith formation before melting demonstrates a thin atmosphere a wet early surface environment on mars and an evolved crust likely to have contaminated younger extrusive rocks the latest events recorded when the breccia was on mars are resetting of apatite much feldspar and some zircons at 1 35 1 4 ga bellucci et al 2015 and formation of ni bearing pyrite veins during or shortly after this disturbance lorand et al 2015

a case study of a chaco low level jet event abstract this paper concentrates on the analysis of the life cycle of the low level jet llj during a summer chaco jet event this is accomplished through the use of the eta centro de previsao del tempo e estudos climaticos cptec regional model in order to obtain high temporal and spatial detail of the main processes taking place both the low level circulation and the geopotential height evolution at different latitudes are analyzed to provide a more detailed description of the effects of topography and differential warming on the evolution of this current this study shows that the life cycle of the particular event analyzed is not the same at the different latitudes swept by this well organized northerly current expanding from 15 to 32 s during two consecutive days a common feature to all the examined latitudes is the presence of a diurnal cycle linked to local effects which is more evident during the first day and a half of the simulation this cycle was identified not only by a nocturnal maxi