petroleum formation by fischer tropsch synthesis in plate tectonics a somewhat speculative hypothesis of petroleum genesis in the upper lithosphere is proposed based on fischer tropsch synthesis this hypothesis is distinct from both the organic biogenic model and the inorganic model of hydrocarbon degassing from the earth s interior fischer tropsch synthesis is a well known industrial process whereby millions of tons of hydrocarbon oil resembling petroleum are produced annually from carbon monoxide or carbon dioxide and hydrogen gases reacting on a metallic iron or iron oxide catalyst like natural petroleum this synthetic oil consists of gas gasoline diesel oil and wax fractions all rich in saturated aliphatic hydrocarbons and enriched in the light 12c isotope the hypothesis presented in this paper proposes that petroleum liquids form by fischer tropsch synthesis on magnetite and hematite catalysts when carbon dioxide derived by massive metamorphic or igneous decarbonation of subducted sedimentary carbonates reacts with hydrogen generated by the serpentinization in the absence of air of shallow mantle lithosphere and ophiolite thrust sheets oblique plate movements may favor hydrocarbon formation by creating deep faults that aid fluid flow and serpentinization the world s richest oil provinces including those of the middle east may be tentatively interpreted to have formed by this mechanism

sediment delivery after a wildfire we use a record of sedimentation in a small reservoir within the cerro grande burn area new mexico to document postfire delivery of ash other fine grained sediment carried in suspension within floods and coarse grained sediment transported as bedload over a five year period ash content of sediment layers is estimated using fallout 137 cs as a tracer and ash concentrations are shown to rapidly decrease through a series of moderate intensity convective storms in the first rainy season after the fire over 90 of the ash was delivered to the reservoir in the first year and ash concentrations in suspended sediment were negligible after the second year delivery of the remainder of the fine sediment also declined rapidly after the first year despite the occurrence of higher intensity storms in the second year fine sediment loads after five years remained significantly above prefire averages deposition of coarse grained sediment was irregular in time and was associated with transport by snowmelt runoff of sediment stored along the upstream channel during short duration summer floods coarse sediment delivery in the first four years was strongly correlated with snowmelt volume suggesting a transport limited system with abundant available sediment transport rates of coarse sediment declined in the fifth year consistent with a transition to a more stable channel as the accessible sediment supply was depleted and the channel bed coarsened maximum impacts from ash and other fine grained sediment therefore occurred soon after the fire whereas the downstream impacts from coarse grained sediment were attenuated by the more gradual process of bedload sediment transport

holocene vegetation and climate history of the northern bighorn basin southern montana records of holocene vegetation and climate change at low elevations 2000 m are rare in the central rocky mountain region we developed a record of holocene vegetation and climate change from 55 14c dated woodrat middens at two low elevation sites 1275 to 1590 m currently vegetated by juniperus osteosperma woodlands in the northern bighorn basin macrofossil and pollen analyses show that the early holocene was cooler than today with warming and drying in the middle holocene during the holocene boreal juniperus communis j horizontalis and montane species j scopulorum were replaced by a great basin species j osteosperma j osteosperma colonized the east side of the pryor mountains 4700 14c yr b p downward movement of lower treeline indicates wetter conditions between 4400 and 2700 14c yr b p increased aridity after 2700 14c yr b p initiated expansion of j osteosperma from the east to west side of the pryor mountains

holocene lake level trends in the rocky mountains u s a abstract the availability of water shapes life in the western united states and much of the water in the region originates in the rocky mountains few studies however have explicitly examined the history of water levels in the rocky mountains during the holocene here we examine the past levels of three lakes near the continental divide in montana and colorado to reconstruct holocene moisture trends using transects of sediment cores and sub surface geophysical profiles from each lake we find that mid holocene shorelines in the small lakes 4 110 ha were as much as 10 m below the modern lake surfaces our results are consistent with existing evidence from other lakes and show that a wide range of settings in the region were much drier than today before 3000 2000 years ago we also discuss evidence for millennial scale moisture variation including an abruptly initiated and terminated wet period in colorado from 4400 to 3700 cal yr bp and find only limited evidence for low lake stands during the past millennium the extent of low water levels during the mid holocene which were most severe and widespread ca 7000 4500 cal yr bp is consistent with the extent of insolation induced aridity in previously published regional climate model simulations like the simulations the lake data provide no evidence for enhanced zonal flow during the mid holocene which has been invoked to explain enhanced mid continent aridity at the time the data including widespread evidence for large changes on orbital time scales and for more limited changes during the last millennium confirm the ability of large boundary condition changes to push western water supplies beyond the range of recent natural variability

what moved where the impact of velocity uncertainty on microseismic location and moment tensor inversion with the rise of unconventional resources microseismic monitoring is becoming increasingly important because of its cost effectiveness this has led to significant research activity on how best to locate events and characterize their moment tensors locations tell us where fracturing is occurring allow the tracking of fluid movement and fracture propagation moment tensors help to determine the type of failure occurring which is beneficial in planning and interpreting the results of hydraulic fracturing jobs and in monitoring production the rising number of methods to determine parameters raises important questions about how uncertainties in the input parameters are translated into uncertainties in the final locations and moment tensors we present a framework for assessing these uncertainties and use it to demonstrate how velocity uncertainty as well as uncertainties in arrival times and amplitudes translates into uncertainties on the recovered quantities of location and moment tensor parameters

fluid events and exhumation history of the main central thrust zone garhwal himalaya india mineral thermobarometric and fluid inclusion studies were carried out on the low to medium grade metamorphics which occur at different tectonic levels of the main central thrust mct zone in garhwal himalaya mct i in north mct ii in the centre and the southern most mct iii the augen gneiss and pelitic schists present in this zone show an increase in the grade of metamorphism from chlorite to kyanite towards the north the pressure calculated from garnet biotite muscovite plagioclase phase equilibria increases from 1 9 to 8 kbar and the temperature obtained through garnet biotite and chlorite geothermometer varies between 360 and 5628c the mineral assemblages and these thermobarometric estimates reveal that the grade of metamorphism in the mct zone increases from south to north considering the inclusion types it is apparent that the carbonic fluid increases towards the mct i which is related to increase in p t conditions whereas the aqueous phase is more pronounced near the mct iii reflecting fluid assisted retrogression this observation is also substantiated by the systematic increase in co2 density from 0 75 g cm 3 in co2 h2o inclusions near mct iii to 1 01 g cm 3 in pure co2 inclusions near mct i the pressure and temperature estimated using fluid isochores varies from 1 9 to 4 8 kbar and 360 to 5628c when compared with mineral phase thermobarometry these p t conditions suggest a post peak metamorphic nature of the fluids a smooth trend of mineral and fluid phase p t conditions is observed in the mct zone based on combined mineral p t data and fluid isochores a decompressional uplift path is suggested the decrease in p t and the evidence of movement along well distributed shear fabric across the mct zone indicate that exhumation from north to south occurred under decreasing p t conditions q 2001 elsevier science ltd all rights reserved

earthquakes produce carbon dioxide in crustal faults abstract fourier transform infrared ftir microanalysis of pseudotachylytes i e friction induced melts produced by seismic slip from the nojima fault japan reveals that earthquakes almost instantaneously expel 99 wt of the wall rock co 2 content carbon is exsolved because it is supersaturated in the friction melts by extrapolation to a crustal scale fault rupture large events such as the m7 2 kobe earthquake 1995 may yield a total production of 1 8 to 3 4 10 3 tons co 2 within a few seconds this extraordinary release of co 2 can cause a flash fluid pressure increase in the fault plane and therefore enhance earthquake slip or trigger aftershocks it may also explain the anomalous discharge of carbon monitored in nearby fault springs after large earthquakes because carbon saturation in silicate melts is pressure dependent ftir can be used as a new tool to constrain the maximum depth of pseudotachylyte formation in exhumed faults

late holocene climate change in the big belt mountains central montana usa carroll college and the helena national forest are working in a 6 year research partnership designed to investigate the relationship between paleoclimate change and human adaptation in the big belt mountains of central montana usa this ongoing project is designed to gather archaeological and paleoenvironmental data from three diverse ecosystems within one drainage basin high altitude park areas 1800 2100 m mid altitude conifer forests 1200 1500 m and low altitude locales under 1500 m along the missouri river these data will represent paleoecological and archaeological changes through time and will detect synchrony and diversity across an elevation gradient thus far excavation of two mid altitude sites dating to 2400 and 4500 bp and one high altitude site dated to 2400 bp revealed evidence of a significant drought period about 2000 years ago to date the excavated sites evidence a shift in pollen to drier species a shift to higher sedimentation rates and changes in snail and vertebrate

the concentration and isotopic composition of carbon in basaltic glasses from the juan de fuca ridge pacific ocean the abundance and 13c12c ratios of carbon were analyzed in basaltic glass from twenty locations along the juan de fuca ridge using a 3 step combustion extraction technique carbon released during the first two combustion steps at 400 500 c and 600 650 c is interpreted to be secondary and only the carbon recovered during a final combustion step at 1200 c is thought to be indigenous to the samples for carbon released at 1200 c glasses analyzed as 1 2 mm chips contained 23 146 ppm c with 13c values of 4 8 to 9 3 whereas samples crushed to 38 63 m or 63 90 m yielded 56 103 ppm c with 13c values of 6 1 to 9 2 the concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean ridge basalts the juan de fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor evidence of disequilibrium includes 1 1 a large range of carbon contents among glasses collected at similar depths 2 2 a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample and 3 3 a lack of correlation between vesicle abundance carbon concentration and depth of eruption variations in carbon concentration and 13c ratios along the ridge do not correlate with major element chemistry the observed relationship between carbon concentrations and 13c values may be explained by late stage variable degrees of open system rayleigh like degassing

holocene vegetational history of the kootenai river valley montana abstract pollen records in the kootenai and fisher river drainages in western montana reveal a fivezone sequence of holocene vegetation change deposition of glacier peak ash layer g ca 10 540 660 yr b p in the lowermost sediments clay intermixed with pebbles at tepee lake gives a minimum date for the initiation of sedimentation initial vegetation on the newly deglaciated terrain was dominated by pinus probably white bark pine with small amounts of gramineae picea and abies reflecting a relatively cool moist macroclimate two vegetation units appear to contribute to pollen zone ii ca 11 000 7100 yr b p arboreal communities with pines along with pseudotsuga or larix or both and treeless vegetation dominated by artemisia pollen zone ii represents an overall warmer macroclimate than occurred upon ice withdrawal after ca 7100 yr b p pollen zone iii diploxylon pines became a major pollen contributor near both tepee lake and mckillop creek pond indicating an expansion of xerophytic forest p contorta and p ponderosa along with an increase in the prominence of pseudotsuga menziesii or larix occidentalis or both artemisia briefly expanded coverage near tepee lake concomitant with the mazama ashfall ca 6700 yr b p a short term climatic trend with more available water began after ca 4000 yr b p as abies probably a grandis along with picea engelmannii became a more regular component of the forest surrounding both sites emergence of the modern macroclimate is indicated primarily with the first regular appearance of tsuga heterophylla in the pollen record by ca 2700 yr b p synchronous with the development of western hemlock forest within the same latitudes in northern idaho and northeastern washington

the effect of velocity uncertainty on migrated reflectors improvements from relative depth imaging we have studied the problem of uncertainty quantification for migrated images a traditional migrated image contains deterministic reconstructions of subsurface structures however input parameters used in migration such as reflection data and a velocity model are inherently uncertain this uncertainty is carried through to the migrated images we have used bayesian analysis to quantify the uncertainty of the migrated structures by constructing a joint statistical distribution of the location of these structures from this distribution we could deduce the uncertainty in any quantity derived from these structures we have developed the proposed framework using a simple model with velocity uncertainty in the overburden and we estimated the absolute positions of the horizons and the relative depth of one horizon with respect to another by quantifying the difference in the corresponding uncertainties we found that in this case the relative depths of the structures could be estimated much better than their absolute depths this analysis justifies redatuming below an uncertain overburden for the purposes of the uncertainty reduction

seasonal climate change across the roman warm period vandal minimum transition using isotope sclerochronology in archaeological shells and otoliths southwest florida usa abstract archaeological evidence suggests that southwest florida experienced variably warmer and wetter climate during the roman warm period rwp 300 bc 550 ad relative to the vandal minimum vm 550 800 ad this hypothesis was tested by reconstructing seasonal scale climate conditions for the latter part of the rwp 1 550 ad by using high resolution oxygen isotope ratios 18o of archaeological shells mercenaria campechiensis and otoliths ariopsis felis eight shells radiocarbon dated to 150 550 ad recorded that the rwp summers at 150 250 ad were insignificantly different from today and the rwp summers at 250 350 ad and 450 550 ad were drier relative to today eight otoliths indicate that the winters were variable during the rwp colder than today at 150 200 ad and 250 300 ad similar to today at 200 250 ad 300 350 ad and 450 500 ad and warmer than today at 500 550 ad the climate reconstructions agree with archaeological observations and are partially coherent with the history of sea level change with a drying and cooling trend at the 95 confidence level across the rwp vm transition the climate transition is not only consistent with falling sea level but also coherent with reduced solar radiation reduced solar radiation may have triggered a change in atmospheric circulation patterns that precipitated the observed climate transition

isotopic composition of co2 and dissolved carbon species in basalt glass the isotopic composition of coexisting fluid and dissolved carbon species in morb glass have been studied using a combination of replicate stepped heating experiments vacuum crushing and grain size analysis stepped heating carbon release profiles demonstrate the presence of isotopically light carbon released by combustion below 600 degree c ltc and isotopically heavier carbon released above 600 degree c htc up to 95 of the ltc component which mostly resides on the surface of the glass can be removed by extraction in dichloromethane combustion at 400 and 600 degree c ensures its complete removal prior to extraction of htc species above 600 degree c assuming that htc consists of fluid i e co sub 2 trapped within vesicles and dissolved i e carbonate ion complexes species limits on the net difference between the isotopic composition of coexisting fluid and dissolved carbon have been estimated from stepped heating data the apparent magnitude of carbon isotopic fractionation between co sub 2 vapor and basaltic melt is greater than 1 per thousand but significantly less than 4 5 per thousand and localized fractionation processes associated with magma degassing are associated with delta sub co sub 2 sub basalt melt values of approx 2 per thousand

co 2 co fluid inclusions in a composite peridotite xenolith implications for upper mantle oxygen fugacity fluid inclusions occur in a composite xenolith from the lunar crater volcanic field nevada u s a the xenolith is an amphibole bearing wehrlite that is cut by an andesine amphibole vein the compositions of individual fluid inclusions in both portions of the xenolith have been determined using microthermometry and micro laser raman spectroscopy fluids in the host wehrlite are nearly pure co2 99 mol whereas those in the vein contain from 8 5 to 12 0 mol co in co2 chemical modelling shows that the composition of the vein fluids at t room is representative of the composition at the high p t conditions of trapping graphite has not been observed by optical microscopy in any of the fluid inclusions graphite is probably absent although stable at t 800 c most probably because of the kinetically unfavorable co decomposition reaction and rapid quenching by combining the measured fluid compositions with fluid p v t data and the chemical equilibrium co2 co 1 2 o2 we have calculated the oxygen fugacity of the fluid inclusions at 1200 c log f o 2 8 6 vein and 6 host if the f o 2 of the fluid in the vein represents that in equilibrium with the magma that crystallized to produce the vein then the f o 2 of the basalt magma is near qfm at 1200 c and 10 3 kbar this is similar to values reported for extrusive basaltic lavas if the much lower intrinsic oxygen fugacity values for divines and spinels from alkali basalt nodules are representative of upper mantle conditions then oxidation of basaltic magmas must occur in the upper mantle prior to ascent to the surface implications for the origin of co2 rich fluids and carbon isotope geochemistry are also discussed

oxidation state of the mantle abstract phase equilibrium relations are established in a system mg fe si h o with and without c at high pressures and temperatures high pressure temperature equations of state for the fluids including non ideal mixing are used in the calculations the computed equilibrium data show that an olivine of appropriate mantle composition 10 to 14 mole fayalite is stable over a wide range of temperature and oxygen fugacities in the carbon free system if c is introduced such that the equilibrium assemblage may contain graphite or diamond the fluid phase in the peridotite water system consists mostly of h2o and little co2 and ch4 however the fluid composition is strongly affected by the fe content of the system if fe is increased within 10 by moles of the total fe in the mantle from undersaturation i e no free fe present in equilibrium to that of saturation i e fe stable as a phase the ch4 content of the fluid changes from a low of 1 to a high of 89 the calculated results show a fluid with as much as 75 methane could be in equilibrium with olivine 13 mole fayalite without metallic fe as a coexisting phase the fo2 of the primitive mantle with such a fluid composition would be several log units below that of the quartz fayalite magnetite buffer

constraints on graphite crystallinity in some spanish fluid deposited occurrences from different geologic settings epigenetic vein type graphite mineralization originates by deposition from c o h fluids in high temperature environments consequently fluid deposited graphite is uniformly highly crystalline in volumetrically large occurrences this work examines the factors controlling graphite crystallinity in fluid deposited occurrences with reference to some case studies from southern spain where vein type graphite is associated with a variety of host rocks possible causes influencing high crystallinity of graphite in these occurrences include 1 large graphite occurrences are generated from large volumes of fluids that maintain their temperatures for long periods of time which is easier at higher temperatures 2 high temperature conditions are required for a fluid to precipitate a major part of its dissolved carbon during a small temperature decrease 3 carbon is incorporated into c o h fluids mainly through devolatilization reactions which also require high temperatures 4 highly crystalline graphite generated at high t high p conditions is less susceptible to resorption as p decreases or by subsequent fluid flow 5 graphite precipitation involves high activation energy that can be overcome only if the temperature is high enough these causes can be extrapolated to most vein type graphite deposits worldwide

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

thermal decomposition of carbonates in fault zones slip weakening and temperature limiting effects 1 during an earthquake the heat generated by fault friction may be large enough to activate the devolatilization of minerals forming the fault rocks in this paper we model the mechanical effects of calcite thermal decomposition on the slip behavior of a fault zone during an earthquake to do so we introduce the coupled effects of calcite volume loss heat consumption and co2 production in the theoretical analysis of shear heating and thermal pressurization of pore fluids we consider a rapidly deforming shear band consisting of a fluid saturated carbonate rock the equations that govern the evolution of pore pressure and temperature inside the band and the mass of emitted co2 are deduced from the mass and energy balance of the multiphase saturated medium and from the kinetics of the chemical decomposition of calcite numerical simulation of seismic slip at depths of 5 to 8 km show that decarbonation has two critical consequences on fault slip first the endothermic reaction of calcite decomposition limits the coseismic temperature increase to less than 800 c corresponding to the initiation of the chemical reaction inside the shear band second the rapid emission of co2 by decarbonation significantly increases the slip weakening effect of thermal pressurization the pore pressure reaches a maximum and then decreases due to the reduction of solid volume causing a restrengthening of shear stress our theoretical study shows on the example of decarbonation that the thermal decomposition of minerals is an important slip weakening process and that a large part of the frictional heat of earthquakes may go into endothermic devolatilization reactions

methane rich fluids in the oceanic crust analyses of fluid inclusions in plutonic rocks recovered from the slow spreading southwest indian ridge swir record ch4 concentrations of 15 40 times those of hydrothermal vent fluids and of basalt hosted volcanic gases and provide the first direct sampling of co2 ch4 h2o h2 c bearing fluids in the oceanic crust compositional thermal and spatial analyses of these fluids are used to model the evolution of volatiles during the crystallization and cooling of mid ocean ridge magma chambers and to assess the potential importance of carbon bearing fluids in geochemical processes in the lower crustal component of hydrothermal systems results from these analyses show that the earliest fluids to be exsolved from the melts are dominated by co2 rich vapors which with progressive fractionation evolved to more h2o rich compositions these later fluids were most likely exsolved under immiscible conditions and involved the development of co2 h2o rich vapors and co2 h2o nacl brines that were trapped during mineral growth as well as during later high temperature fracturing events co2 ch4 h2o rich fluids in olivine and plagioclase minerals that contain up to 30 50 mol co2 and 33 mol ch4 may reflect respeciation of magmatic co2 during cooling and attendant graphite precipitation phase equilibria suggest that these fluids reequilibrated at 500 600 c and at fo2 s 3 log units below to close to qfm conditions alternatively the inclusions may record respeciation of magmatic fluids attendant with the inward diffusion of h2 into the inclusions and reduction of entrapped co2 during degassing and cooling of the gabbros throughout the subsolidus regime subsequent seawater reaction at minimum temperatures of 400 c with mafic rich layers within the gabbroic rocks or with ultramafic material that underlies the plutonic sequence resulted in the formation of ch4 h2o fluids that contain up to 40 mol ch4 molecular h2 and graphite daughter minerals these data provide strong evidence that the ch4 h2o rich fluids produced during serpentinization reactions were trapped under equilibrium conditions in the presence of graphite at very near to qfm conditions the ubiquitous occurrence of ch4 rich fluids in oceanic crustal layer 3 rocks from the swir indicates that these fluids may be a significant and previously unrecognized source for these volatile species in some hydrothermal systems venting on the seafloor and that the deep seated fluids most likely play an important role in the transfer of carbon from the lithosphere to the hydrosphere

leading order seismic imaging using curvelets curvelets are plausible candidates for simultaneous compressionofseismicdata theirimages andtheimagingoperator itself we show that with curvelets the leading order approximation in angular frequency horizontal wavenumber and migrated location to common offset co kirchhoff depth migration becomes a simple transformation of coordinates of curvelets in the data combined with amplitude scaling this transformation is calculated using map migration whichemploysthelocalslopesfromthecurveletdecomposition of the data because the data can be compressed using curvelets the transformation needs to be calculated for relatively few curvelets only numerical examples for homogeneous media show that using the leading order approximationonlyprovidesagoodapproximationtocomigrationfor moderate propagation times as the traveltime increases and raysdivergebeyondthespatialsupportofacurvelet however the leading order approximation is no longer accurate enough this shows the need for correction beyond leading order evenforhomogeneousmedia

a 28 000 year history of vegetation and climate from lower red rock lake centennial valley southwestern montana usa abstract a sediment core extending to 28 000 cal yr bp from lower red rock lake in the centennial valley of southwestern montana provides new information on the nature of full glacial vegetation as well as a history of late glacial and holocene vegetation and climate in a poorly studied region prior to 17 000 cal yr bp the eastern centennial valley was occupied by a large lake pleistocene lake centennial and valley glaciers were present in adjacent mountain ranges the lake lowered upon erosion of a newly formed western outlet in late glacial time high pollen percentages of juniperus poaceae asteraceae and other herbs as well as low pollen accumulation rates suggest sparse vegetation cover inferred cold dry conditions are consistent with a strengthened glacial anticyclone at this time between 17 000 and 10 500 cal yr bp high picea and abies pollen percentages suggest a shift to subalpine parkland and warmer conditions than before this is attributed to the northward shift of the jet stream and increasing summer insolation from 10 500 to 7100 cal yr bp pollen evidence of open dry forests suggests warm conditions which were likely a response to increased summer insolation and a strengthened pacific subtropical high pressure system from 7100 to 2400 cal yr bp cooler moister conditions promoted closed forest and wetlands increases in picea and abies pollen percentages after 2400 cal yr bp suggest increasing effective moisture the postglacial pattern of pseudotsuga expansion indicates that it arrived later on the atlantic side of the continental divide than on the pacific side the divide may have been a physical barrier for refugial populations or it delimited different climate regions that influenced the timing of pseudotsuga expansion

high temperature mass spectrometric degassing of enstatite chondrites implications for pyroclastic volcanism on the aubrite parent body wilson and keil 1991 argued that a few hundred ppm of expanding volatiles present in early partial basaltic melts on the aubrite parent body or on other differentiated asteroids 925 c principally co 1580 2830 ppm n2 110 430 ppm cl 120 450 ppm s see discussion for abundance are indigenous the precise host phases and host sites of the indigeneous volatiles are uncertain 2 2 n2 release appears to be associated with the melting of the fe ni sulfide cotectic at 950 c the amounts of gas released are not unlike those previously measured for iron meteorites and sulfides in irons but exceed by several orders of magnitude the equilibrium n2 solubility in metallic fe ni for solar nebula pressures this suggests that either partial pressures during n2 incorporation were much higher than solar values or n2 is trapped in lattice defects and microcracks possibly in sulfides 3 3 co release over a narrow temperature interval of 1025 1255 c is violent and results in pronounced vesiculation of the residue co may be trapped in microvesicles and cracks in silicates or less likely may form by a reduction reaction during heating between carbon graphite and the minor ferrosilite in the enstatite 4 4 cl release beginning at 950 eh s and 1025 c el s appears not to be associated with lawrencite which should sublime at t as low as 325 c in eh s some may be released from djerfisherite 5 5 gas release and textural studies suggest that metamorphic reheating of eh s and el s was to less than about 950 c el s did not form during metamorphic reheating of eh s by draining of cotectic fe ni sulfide liquid 6 6 sinoite present in some el6 s did not form by condensation from the solar nebula but during parent body metamorphism at t 950 c via the reaction of sio2 gaseous n2 and si in solid solution in the metallic fe ni 7 7 as little as 1 by volume partial melting in an asteroid of any size will generate excess pressures in the melt much greater 10 s of mpa than the tensile strength of silicate materials and will initiate formation of cracks this process will be enhanced by expansion of any exsolved or trapped gas phase in the asteroid and will lead to the formation of pathways cracks growing into dikes for melt migration 8 8 the pressure gradients implied when these pathways intersect the asteroid surface coupled with the observed amounts of indigenous volatiles released from eh s and el s are easily sufficient to drive the pyroclastic volcanic eruptions envisaged by wilson and keil 1991

rare gases water and carbon in kaersutites abstract kaersutites from kakanui new zealand and from three localities in the southwestern united states have been analyzed for rare gases water and carbon to investigate the volatile signature of the sub continental mantle this study does not confirm the high 3 he 4 he and 21 ne 22 ne ratios reported by saito et al 1 for the kakanui kaersutite instead a 3 he 4 he ratio of 6 r a and atmospheric 21 ne 22 ne ratios were measured which are consistent with our current knowledge of the earth s mantle a low 40 ar 36 ar of 320 and more than 10 8 cm 3 g of 36 ar confirms the argon results of saito et al and indicates that significant quantities of 36 ar reside in this portion of the mantle kaersutites from the southwestern united states arizona have a heterogeneous helium isotope signature ranging from 8 8 r a at san carlos to 0 46 at hoover dam all d h ratios for the water in kaersutites 56 to 78 represent typical mantle values with no apparent correlation with 3 he 4 he the correlation of increasing carbon content 140 400 ppm with increasing 13 c 24 5 to 16 7 may reflect differences in the proportions of oxidized and reduced carbon in these samples

storage of f and cl in the upper mantle geochemical implications abstract electron microprobe analyses yielded mean values of f 0 43 and cl 0 08 wt for primary textured phlogopites in coarse depleted garnet lherzolite xenoliths from kimberlites most secondary textured phlogopites have too low cl 0 01 0 08 wt to be metamorphic precursors of primary textured phlogopites marid suite phlogopites and many megacrysts in kimberlites have low cl 0 02 wt and some but not necessarily all secondary micas may result from infiltration of kimberlite into peridotite xenoliths a good correlation between p and f in some oceanic basalts and gabbros might suggest that these elements are derived mainly from f rich apatite inthe mantle and that whitlockite is not present in the source region mantle derived mica and amphibole have such low cl that it is necessary to attribute cl in oceanic basalts and gabbros either to substantial cl in the source apatite or to cl from invading solutions or both three apatites from the mantle contain 0 8 1 0 wt cl and others contain lower amounts the halogen contents of kimberlitic magmas can be explained by incorporation of cl bearing mica and f rich apatite during melting of peridotites but compositional constraints are weak

holocene seasonal variability inferred from multiple proxy records from crevice lake yellowstone national park usa article i nfo a 9400 yr old record from crevice lake a semi closed alkaline lake in northern yellowstone national park was analyzed for pollen charcoal geochemistry mineralogy diatoms and stable isotopes to develop a nu anced understanding of holocene environmental history in a region of northern rocky mountains that re ceives both summer and winter precipitation the limited surface area conical bathymetry and deep water 31 m of crevice lake create oxygen deficient conditions in the hypolimnion and preserve annually laminated sediment varves for much of the record pollen data indicate that the watershed supported a closed pinus dominated forest and low fire frequency prior to 8200 cal yr bp followed by open parkland until 2600 cal yr bp and open mixed conifer forest thereafter fire activity shifted from infrequent stand replacing fires initially to frequent surface fires in the middle holocene and stand replacing events in recent centuries low values of 18 o suggest high winter precipitation in the early holocene followed by steadily drier conditions after 8500 cal yr bp carbonate rich sediments before 5000 cal yr bp imply warmer summer conditions than after 5000 cal yr bp high values of molybdenum mo uranium u and sulfur s indicate anoxic bottom waters before 8000 cal yr bp between 4400 and 3900 cal yr bp and after 2400 cal yr bp the diatom record indicates extensive water column mixing in spring and early summer through much of the holocene but a period between 2200 and 800 cal yr bp had strong summer stratification phosphate limita tion and oxygen deficient bottom waters together the proxy data suggest wet winters protracted springs and warm effectively wet summers in the early holocene and less snowpack cool springs warm dry sum mers in the middle holocene in the late holocene the region and lake experienced extreme changes in win ter spring and summer conditions with particularly short springs and dry summers and winters during the roman warm period 2000 cal yr bp and medieval climate anomaly 1200 800 cal yr bp long springs and mild summers occurred during the little ice age and these conditions persist to the present although the proxy data indicate effectively wet summer conditions in the early holocene and drier conditions in the middle and late holocene none point specifically to changes in summer precipitation as the cause in stead summer conditions were governed by multi seasonal controls on effective moisture that operated over multiple time scales

volatiles in amphiboles from xenoliths vulcan s throne grand canyon arizona usa abstract analyses of major element and volatile components of amphiboles from vulcan s throne a recent volcano on the north rim of the grand canyon arizona usa have been performed by using the electron microprobe and high temperature mass spectrometry the amphiboles occur as megacrysts as oikocrysts in peridotite and pyroxenite xenoliths in amphibole rich selvages on lherzolite xenoliths and as grains in hornblendite xenoliths total volatiles range from 1 27 to 1 75 wt in all samples h 2 o is the principal volatile species lesser amounts of structurally bound fluorine chlorine and oxygen were also released the amphiboles studied are hydroxyl deficient the o 3 site is probably partially occupied by o 2 which was detected as o 2 during degassing of the amphibole ti shows a strong positive correlation with the amount of hydroxyl deficiency in the amphiboles except for one oxidized sample thus ti probably is significant in charge balancing the substitution of o 2 for oh and the substitution probably occurred during crystallization rather than by dehydrogenation small amounts of both oxidized and reduced carbon and sulfur bearing volatile species e g co 2 co ch 4 so 2 h 2 s were detected in all samples the observation of reduced carbon species supports the hypothesis that the oxygen fugacity of at least portions of the upper mantle is probably less than the quartz fayalite magnetite buffer

deep seated abiogenic origin of petroleum from geological assessment to physical theory the theory of the abyssal abiogenic origin of petroleum is a significant part of the modern scientific theories dealing with the formation of hydrocarbons these theories include the identification of natural hydrocarbon systems the physical processes leading to their terrestrial concentration and the dynamic processes controlling the migration of that material into geological reservoirs of petroleum the theory of the abyssal abiogenic origin of petroleum recognizes that natural gas and petroleum are primordial materials of deep origin which have migrated into the earth s crust experimental results and geological investigations presented in this article convincingly confirm the main postulates of the theory and allow us to reexamine the structure size and locality distributions of the world s hydrocarbon reserves

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

halogens in volcanic systems the transport degassing and atmospheric release of halogens from active volcanism on earth have been the focus of increasing interest over the last few decades and have recently been the subject of the 1st workshop on halogens in volcanic systems and their environmental impacts that was held in december of 2007 at yosemite lodge in yosemite national park california as an introduction to this chemical geology special issue collecting contributions from many of the participants at the workshop we review here recent advances in this field including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems we discuss previous research on several aspects of halogen geochemistry including halogen abundances in the mantle and magmas on earth the effects of halogens on phase equilibria and melt viscosities their partitioning between melt and fluid phase s upon decompression cooling and crystallisation of magmas in the earth s crust and their final atmospheric release as volcanic gases the role of halogens in the genesis of hydrothermal systems and in the transport of ore forming metals is also reviewed and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere and their consequent impacts in spite of these recent advancements our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary and the key questions that require answers from future research are summarised in our conclusions

joint location of microseismic events in the presence of velocity uncertainty the locations of seismic events are used to infer reservoir properties and to guide future production activity as well as to determine and understand the stress field thus locating seismic events with uncertainty quantification remains an important problem using bayesian analysis a joint probability density function of all event locations was constructed from prior information about picking errors in kinematic data and explicitly quantified velocity model uncertainty simultaneous location of all seismic events captured the absolute event locations and the relative locations of some events with respect to others along with their associated uncertainties we found that the influence of an uncertain velocity model on location uncertainty under many realistic scenarios can be significantly reduced by jointly locating events many quantities of interest that are estimated from multiple event locations such as fault sizes and fracture spacing or orientation can be better estimated in practice using the proposed approach

probabilistic full waveform inversion based on tectonic regionalization development and application to the australian upper mantle we present a first study to investigate the feasibility of a probabilistic 3 d full waveform inversion based on spectral element simulations of seismic wave propagation and monte carlo exploration of the model space through a tectonic regionalization we reduce the dimension of the model space to 12 and we incorporate complete seismograms in order to exploit all available information in the period range from 60 to 200 s s wave velocity variations in the australian archean and proterozoic lithospheres are generally well constrained and strongly positive in agreement with previous inferences from deterministic tomography the maximum likelihood model reveals significantly elevated p velocities while consistent with body wave studies they are however not well constrained by our data thereby providing an interesting example of a comparatively insignificant maximumlikelihood model our data are notably affected by 3 d density variations the effect however appears to be misleading both the maximum likelihood model and the posterior probability densities strongly prefer unrealistically large positive density variations that are inconsistent with independent information from geodynamics and mineral physics this suggests that highly probable and less extreme density models may be hidden in small and hardly detectable subvolumes of the 12 d model space it follows that deterministic full waveform inversions for density may require particularly accurate initial models from a methodological perspective we must conclude that a transition to significantly higher dimensions would currently be difficult available computing power clearly imposes restrictions however even when moore s law continues to hold the largest obstacle appears to be our inability to efficiently map small high dimensional subvolumes with high probability

late holocene relationships among fire climate and vegetation in a forest sagebrush ecotone of southwestern idaho usa the forest sagebrush ecotone is characterized by a more arid climate than forested regions therefore establishing fire histories using traditional methods e g fire scars from trees charcoal in lake sediments is problematic this study uses radiocarbon dating of charcoal preserved in alluvial deposits to reconstruct a record of fire and geomorphic response in southwestern idaho samples indicate three primary periods of fire related activity 4400 4000 2000 1400 and 650 400 cal yr bp charcoal macrofossil identification and comparison with other regional records indicate this area has likely alternated between a fuel limited system fires limited by lack of fuels and a moisture limited system fires limited by too much moisture with changes in holocene climate over the past 2000 yr samples from this site indicate most fires occurred during wetter times than the record average during overall wetter periods e g little ice age lia 600 100 cal yr bp tree density may have increased

volatiles in basalts and andesites from the galapagos spreading center 85 to 86 w abstract glasses from submarine lavas recovered by the alvin submersible from the galapagos spreading center gsc near 86 w have been analyzed by electron microprobe for major elements and by high temperature mass spectrometry for volatiles the samples studied range in composition from basalt to andesite and are more evolved than typical morbs previous studies indicate that they are related to normal morb by extensive crystal fractionation in small isolated magma chambers the h 2 o cl and f contents of these lavas are substantially higher than any previously reported for morbs h 2 o cl and f abundances increase linearly with p 2 o 5 content which is used as an indicator of the extent of crystal fractionation the fe 2 o 3 feo fe 2 o 3 ratios measured in the andesite glasses progressively decrease with increasing p 2 o 5 content and are probably related to fractionation of fe tioxides reduced carbon gas species principally ch 4 and co were discovered in these glasses the presence of reduced carbon species in gsc glasses may be indicative of a more reduced oxidation state of the upper mantle than is commonly assumed

volatiles in basaltic glasses from the east pacific rise at 21 n implications for morb sources and submarine lava flow morphology pillow rim glasses from a suite of moderately evolved lavas erupted along the axis of the east pacific rise epr at 21 n were analyzed by high temperature mass spectrometry for volatile content concentrations of h2o f and cl in the 21 n glasses are low and correlate inversely with mg yielding well defined trends these and other geochemical data indicate derivation of the 21 n glasses from similar parental magmas produced from a highly depleted nearly homogeneous source 1 total volatile h2o f and s contents are lower and co2 content is somewhat higher in these samples than in previously analyzed mid atlantic ridge mar glasses 21 n glasses are similar in volatile content to glasses from the galapagos spreading center gsc at 95 w except in cl lower and co2 higher unlike most mar and gsc glasses co2 is the dominant volatile in all of the 21 n glasses with mg 62 all of the epr and gsc glasses contain reduced carbon species co and ch4 unlike most previously analyzed mar samples these data indicate that sources for mid ocean ridge basalts are extremely volatile poor 0 10 wt and are probably dominantly reduced below quartz fayalite magnetite buffer sheet flow and pillow basalts contain identical volatile contents thus volatile abundance is not a factor controlling flow morphology extrusion rate and or surface topography are probably the most important factors influencing flow morphology in submarine basalts h2o release patterns are however related to flow morphology mass pyrograms for sheet flow and pillow basalt glasses both show bimodal h2o release behavior at the same temperatures 800 c and1000 c 50 c however the dominant h2o release peak for sheet flow glasses is at the lower temperature for pillow rim glasses it is at the higher temperature infrared spectroscopic studies indicate that h2o in these glasses is present only as hydroxyl groups thus the cause of differences in the bimodal h2o release and how it is related to flow morphology is unclear

volatile contents of phlogopite micas from south african kimberlite phlogopite micas from nodules in south african kimberlites were analyzed for major elements with the electron microprobe and for volatile contents by high temperature mass spectrometry the micas are from primary deformed and secondary undeformed textured grains in perodotite xenoliths glimmerites marid mica amphibole rutile ilmenite diopside suite nodules and a mica megacryst the major element and volatile contents of micas exhibiting these modes of occurrence overlap to a greater extent than indicated in previous studies concentrations of volatile species occupying structurally defined crystallographic sites h2o f cl are greater for many of the micas than predicted on the basis of the mica formula particularly for the glimmerite and marid suite samples a correlation exists between micas with tetrahedral and octahedral cation deficiencies and those with excess h2o f and cl substitution of h for tetrahedral and possibly octahedral cations may be responsible for the excess h2o in these micas except for one sample the major element and volatile data for the peridotite glimmerite and marid suite micas indicate that they crystallized at oxygen fugacities below the quartz fayalite magnetite buffer f and k2o are in the correct proportion in the micas to provide the source for these elements in alkali basalts but not in mid ocean ridge basalts kaersutite amphibole is a more likely source of potassium and fluorine in mid ocean ridge basalts

experimentally determined carbon isotope fractionation in and between methane bearing melt and fluid to upper mantle temperatures and pressures abstract the behavior of melts and fluids is at the core of understanding formation and evolution of the earth to advance our understanding of their role high pressure temperature experiments were employed to determine melt and fluid structure together with carbon isotope partitioning within and between ch 4 h 2 o h 2 saturated aluminosilicate melts and ch 4 h 2 o h 2 fluids the samples were characterized with vibrational spectroscopy while at temperatures and pressures from 475 to 850 c and 92 to 1158 mpa respectively the solution equilibrium is 2 ch 4 q n 2 ch 3 h 2 o q n 1 where the superscript n in the q n notation describes silicate species where n denotes the number of bridging oxygen the solution equilibrium affects the carbon isotope fractionation factor between melt and fluid melt fluid moreover it is significantly temperature dependent the melt fluid 1 with temperatures less than about 1050 c and is greater than 1 at higher temperature methane bearing melts can exist in the upper mantle at f o 2 f o 2 mw mysen et al 2011 reduced c h species in present day upper mantle magma therefore are likely during melting and crystallization in this environment the 13 c of melts increases with temperature at a rate of 0 6 c from the simple system data presented here at t 1050 c melt in equilibrium with a peridotite ch 4 h 2 o h 2 bearing mantle source will be isotopically lighter than fluid at higher temperatures melts will be isotopically heavier degassing at t 1050 c will shift 13 c of degassed magma to more positive values whereas degassing at t 1050 c will reduce the 13 c of the degassed magma

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

fire related sedimentation events on alluvial fans yellowstone national park u s a abstract we document initiation and flow processes deposit facies and geomorphic effects of forest fire related sedimentation on small alluvial fans in yellowstone national park brief intense convective storm precipitation on steep basins burned in the 1988 fires produced sedimentation events involving a variety of depositional processes on fans over the course of all documented events flows on fans progressed from higher to lower sediment concentration events were often dominated by either debris flows or relatively sediment poor streamflow processes in some events however flows ranging a over wide spectrum of sediment concentration produced significant fan deposits debris flows were generated by progressive sediment bulking involving pervasive surface runoff and rill erosion on st ep upper basin slopes followed by deep incision as flows progressed down channels debris flow deposits show a marked decline in thickness and coarse gravel content downfan often with extensive distal gravel poor facies we recognized a relatively minor percentage of noncohesive debris flow and hyperconcentrated flow facies with sorting and stratification intermediate between muddy debris flow and streamflow facies these were deposited where dilute flows bulked with coarse sediment by eroding channel alluvium or earlier deposits of the event below incised fan channels streamflows expanded as sheetfloods which prograded lower fans with distally fining deposits basins 3 km2 typically produced streamflow events on fans but sediment texture and availability on slopes and in channels are primary factors determining flow processes on fans of smaller basins burned soil surfaces provided abundant silt and clay for debris flow generation but because soil surface sediment was stripped and or compacted over time the lack of available fines resulted in dominance of streamflow processes in later events

sodium rich metasomatism in the upper mantle implications of experiments on the pyrolite na2o rich fluid system at 950 c 20 kbar abstract sodium rich metasomatism in the upper levels of the mantle has been modelled by reacting pyrolite with alkali bearing h2o fluids containing minor co2 and concentrations of na2o and na2o k2o k k na 0 1 up to 4 0 g alkalies 10 g h2o at 20 kbar and 950 c with increasing alkali concentration the amounts of amphibole pargasite edenite and olivine increase as orthopyroxene and clinopyroxene decrease amphiboles show progressive increases in na and k and si concentrations and decreases in al and ca concentrations suggesting the dominant substitution mechanism is na k sial ca these results and least squares mass balance calculations suggest the reaction of clinopyroxene orthopyroxene spinel produces amphibole olivine in nature upper mantle spinel lherzolite is commonly veined by a variety of rock types which may contain ti pargasite as a magmatic crystallization product pargasite edenite occurs interstitially in spinel iherzolite often spatially related to ti pargasite and may be produced by hydrous fluids evolved during late stage crystallization of the veined rocks this is supported by the close compositional correlation between the natural pargasite edenite amphiboles and those produced in this study the present study suggests that up to 43 wt amphibole may be accommodated in pyrolite in the presence of na2o rich h2o co2 fluids this represents 0 8 wt h2o and 1 7 wt na2o in the hydrated pyrolite composition and indicates the importance of sodium in determining the extent of metasomatism sodium also lowers the solidus temperature of pyrolite by more than 50 c over the h2o saturated pyrolite system at 20 kbar

fire and vegetation history from the coastal rain forest of the western oregon coast range high resolution charcoal and pollen analyses were used to reconstruct a 4600 yr long history of fire and vegetation near taylor lake in the wettest forests of coastal oregon today fires in these forests are rare because the season of ignition does not coincide with months of dry fuels from ca 4600 to 2700 cal yr b p fire episodes occurred at intervals of 140 30 yr while forest vegetation was dominated by disturbance adapted taxa such as alnus rubra from ca 2700 cal yr b p to the present fire episodes have become less common occurring at intervals of 240 30 yr and firesensitive forest taxa such as tsuga heterophylla and picea sitchensis have become more prominent fire occurrence during the midholocene was similar to that of the more xeric forests in the eastern coast range and suggests that summer drought was widespread after ca 2700 cal yr b p a decrease in fire episode frequency suggests that cooler conditions and possibly increased summer fog allowed the establishment of present day picea sitchensis forests within the watershed these results provide evidence that fire has been an important disturbance agent in the coast range of oregon and variations in fire frequency and climate have led to the establishment of present day forests c 2002 university of washington

new insight into polycrystalline diamond genesis from modern nanoanalytical techniques abstract technical developments in analytical methods that reach nanometer spatial resolution have enabled the interrogation of smaller submicron sized inclusions in diamond that had previously been elusive this has inspired and enabled studies of non classical diamond species from different geological settings resulting in a strongly faceted and dynamic picture of diamond formation this article reviews the leap of knowledge achieved by employing state of the art analytical methods with high spatial resolution to polycrystalline diamonds from different settings i e from kimberlite from crustal ultra high pressure metamorphic terranes and alluvial carbonados while crustal metamorphic diamonds are generally formed under oxidizing conditions polycrystalline diamond from the earth s mantle and carbonado have inclusion suites reflecting variable and sometimes extreme redox conditions diamond fluid compositions however fall in the same compositional field for worldwide diamond fluids regardless of their geodynamic environment on the basis of thermodynamic equilibrium data for c h o fluids in the mantle we argue that submicron inclusions in diamonds are products of local remobilization connected to fluid fluxed partial melting and redox freezing thus evidence from these inclusions complements information from classical work on larger inclusions and allows a unique direct insight into the medium in which diamond formed

volatile lines of descent in submarine plutonic environments insights from stable isotope and fluid inclusion analyses microthermometric and isotopic analyses of fluid inclusions in primitive olivine gabbros oxide gabbros and evolved granitic material recovered from ocean drilling program hole 735b at the southwest indian ridge provide new insights into the evolution of c o h nacl fluids in the plutonic foundation of the oceanic crust the variably altered and deformed plutonic rocks span a crustal section of over 1500 m and record a remarkably complex magma hydrothermal history magmatic fluids within this suite followed two chemically distinct paths during cooling through the subsolidus regime the first path included formation of co21ch41h2o1c fluids with up to 43 mole ch 4 the second path produced hypersaline brines that contain up to 50 nacl equivalent salinities subsequent to devolatilization respeciation of magmatic co2 attendant graphite precipitation and cooling from 800 c to 500 c promoted formation of ch 4 enriched fluids these fluids are characterized by average d 13 c ch4 values of 227 1 6 4 3 n5 45 with associated d 13 c co2 compositions ranging from 224 9 to 21 9 n539 and average dd values of exsolved vapor of 241 6 12 n523 in pods veins and lenses of highly fractionated residual material hypersaline brines formed during condensation and by direct exsolution in the absence of a conjugate vapor phase entrapped co21ch41h2o rich fluids within many oxide bearing rocks and felsic zones are significantly depleted in 13 c with d 13 c co2 values down to about 225 and contain co 2 concentrations higher than those predicted by equilibrium devolatilization models we hypothesize that lower effective pressures in high temperature shear zones promoted infiltration of highly fractionated melts and compositionally evolved volatiles into focused zones of deformation significantly weakening the rock strength in felsic rich zones volatile build up may have driven hydraulic fracturing of gabbroic wall rocks resulting in the formation of magmatic breccias comparison of isotopic compositions of fluids in plutonic rocks from 735b the mark area of the mid atlantic ridge and the mid cayman rise indicate 1 that the carbon isotope composition of the lower oceanic crust may be far more heterogeneous than previously believed and 2 that carbon bearing species in the oceanic crust and their distribution at depth are highly variable copyright 2001 elsevier science ltd

garnet peridotite and associated high grade rocks from sulawesi indonesia abstract the effects of collision between three major plates define the geological development of eastern indonesia garnet peridotite and associated granulite facies contact rocks are described from two sites within the valley of the active palu koro left lateral strike slip fault crossing central sulawesi disrupted parts of a medium to low grade metamorphic complex intruded by neogene granite occur on both sides of the fault thermobarometry on minerals and fluids in the garnet peridotite reveals a re equilibration path from a depth of 60 km upward chemistry points to metasomatic effects isolated trace element enrichment by a co 2 rich liquid and fluid in a peridotite of oceanic affiliation the granulite shows an increase in t and incipient melting at the arrival of peridotite the sequence of fluid inclusions of an evolving co 2 ch 4 n 2 h 2 o bearing fluid defines a concave decompression path suggesting rapid uplift trace element chemistry of granulite with basaltic to peraluminious rhyolitic composition indicates island arc affinity the described history may well reflect the processes beneath a mantled gneiss dome present as a coeval metamorphic aureole around the garnet peridotite outcrops

postglacial vegetation and climate in the northwestern great plains of montana abstract two pollen records from the northern great plains of montana portray vegetational and climatic changes during the last 12 200 yr in a region where few other data are available a 6 4 m core from guardipee lake east of the rocky mountains in the area formerly covered by the two medicine glacial lobe contains the glacier peak g and mt st helens jy volcanic ashes pollen percentage data are dominated by pinus poaceae artemisia and chenopodiaceae amaranthaceae high nonarboreal percentages and small amounts of juniperus alnus salix and populus pollen in sediments deposited between ca 12 200 and ca 9300 yr b p suggest a temperate grassland with shrubs growing locally in mesic settings after ca 9300 yr b p an increase in chenopodiaceae amaranthaceae pollen and a concomitant decline in artemisia indicate the development of more xerophytic grassland and the beginning of the altithermal period the lake probably was intermittently dry thoughout the holocene a high sedimentation rate and the presence of cereal taxa characterize the last ca 100 yr of euroamerican settlement lost lake at the northern margin of the highwood mountains yielded a 16 94 m core with no volcanic ashes that spans the last 9400 yr high amounts of chenopodiaceae amaranthaceae artemisia and poaceae pollen from ca 9400 to ca 6000 yr b p suggest the presence of xeric grassland and a climate drier than at present after ca 6000 yr b p chenopodiaceae amaranthaceae values declined and artemisia poaceae pinus picea salix alnus and betula increased the inferred spread of shrubs in wet habitats at this time and the expansion of forest in nearby mountain ranges indicate the end of the altithermal period and the onset of cooler moister conditions

simple models of co2 release from metacarbonates with implications for interpretation of directions and magnitudes of fluid flow in the deep crust simple one dimensional models of coupled advection hydrodynamic surroundings can account for basic t fluid composition reaction dispersion reaction are used to investigate processes of co2 release progress relationships observed in much of the acadian orogen of from metacarbonate beds during deep crustal 8 kbar acadian new england the results provide an alternative to up t flow prograde metamorphism in new england usa two broad models scenarios that account for these relationships by large pervasive in which reaction progress is controlled by gradients in h2o co2 horizontal fluid fluxes up regional t gradients fluid composition between diverent rock types are presented in the first divusional exchange of volatiles across lithologic contacts is significant co2 generated during prograde temperature t rise is transported away from metacarbonate layers to surrounding 1 metapelitic layers which generate h2o by dehydration and or 2 key words metamorphism fluid flow flow direction carbon dioxide

strain localization driven by thermal decomposition during seismic shear field and laboratory observations show that shear deformation is often extremely localized at seismic slip rates with a typical deforming zone width on the order of a few tens of microns this extreme localization can be understood in terms of thermally driven weakening mechanisms a zone of initially high strain rate will experience more shear heating and thus weaken faster making it more likely to accommodate subsequent deformation fault zones often contain thermally unstable minerals such as clays or carbonates which devolatilize at the high temperatures attained during seismic slip in this paper we investigate how these thermal decomposition reactions drive strain localization when coupled to a model for thermal pressurization of in situ groundwater building on rice et al 2014 we use a linear stability analysis to predict a localized zone thickness that depends on a combination of hydraulic frictional and thermochemical properties of the deforming fault rock numerical simulations show that the onset of thermal decomposition drives additional strain localization when compared with thermal pressurization alone and predict localized zone thicknesses of 7 and 13 m for lizardite and calcite respectively finally we show how thermal diffusion and the endothermic reaction combine to limit the peak temperature of the fault and that the pore fluid released by the reaction provides additional weakening of 20 40 of the initial strength

evidence of magmatic co 2 rich fluids in peraluminous graphite bearing leucogranites from deep freeze range northern victoria land antarctica fine grained peraluminous synkinematic leuco monzogranites skg of cambro ordovician age occur as veins and sills up to 20 30 m thick in the deep freeze range within the medium to high grade metamorphics of the wilson terrane secondary fibrolite graphite intergrowths occur in feldspars and subordinately in quartz four main solid and fluid inclusion populations are observed primary mixed co2 h2o inclusions al2sio5 brines in garnet type 1 early co2 rich inclusions brines in quartz type 2 early co2 ch4 up to 4 mol h2o inclusions graphite fibrolite in quartz type 3 late ch4 co2 n2 inclusions and h2o inclusions in quartz type 4 densities of type 1 inclusions are consistent with the crystallization conditions of skg 750 c and 3 kbar the other types are post magmatic densities of type 2 and 3 inclusions suggest isobaric cooling at high temperature 700 550 c type 4 inclusions were trapped below 500 c the skg crystallized from a magma that was at some stage vapour saturated fluids were co2 rich possibly with immiscible brines co2 rich fluids brines characterize the transition from magmatic to post magmatic stages progressive isobaric cooling t 670 c led to a continuous decrease off o 2 can entering in the graphite stability field at the same time the feldspars reacted with co2 rich fluids to give secondary fibrolite graphite decrease oft andf o 2 can explain the progressive variation in the fluid composition from co2 rich to ch4 and water dominated in a closed system in situ evolution the presence of n2 the late stages indicates interaction with external metamorphic fluids

fluids at crustal pressures and temperatures the pressure volume temperature data of several gases h2 o2 co ch4 n2 and co2 have been used to obtain the following corresponding states equation p 1 kbar t 400 k z 0 0878 a bp r cp r 2 21 where z is the compressibility factor p r reduced pressure p critical p t r reduced temperature t critical t and the coefficients are given by a 1 0 5917 t r 2 b 0 09122 t r 1 c 1 4164 10 4t r 2 2 8349 10 6 ln t r p 1 kbar t 400 k at pressures below 1 kbar z is given by z 0 0761 1 bp r cp r 2 23 where b 0 09827 t r 1 0 2709 t r 3 c 0 01472 t r 4 0 00103 t r 1 5 for water p 1 kbar t 400 k z 0 0209 a bp cp2 22 where a 0 7025 1 16 10 3t 99 6799 t 1b 0 2143 t 1 3 1423 10 14t3c 2 249 10 6t 1 0 1459 t 3 2 1690 10 15t2 at pressure below 1 kbar the equation is p 100 bar t 673 k z 0 0601 1 b v c v2 24 where b 2 20960 t0 5 3 35460 10 8 t3c 3 4569 10 5t2 5 64 9764 ln t fugacities of the gases may be obtained by integrating the z equations separately and combining the results as follows int limits 1 p vdp rt text left int limits 1 1000 z 23 pdp int limits 1000 1 z 21 pdp right 26 the subscript in z denotes the equation which is to be used for calculating z

volatiles in pillow rim glasses from loihi and kilauea volcanoes hawaii abstract volatiles and major elements in submarine glasses from loihi seamount and kilauea volcano hawaii were analyzed by high temperature mass spectrometry and the electron microprobe loihi glasses are subdivided into three groups tholeiitic transitional and alkali basalts the glasses are evolved mg numbers range from 48 58 the alkalic lavas are the most evolved total volatiles range from 0 73 to 1 40 wt h 2 o shows a positive linear correlation with k 2 o content h 2 o 0 83 09 k 2 o 0 08 06 concentrations of h 2 o are higher in the alkalic lavas but cl and f abundances are highly variable variations in ratios of incompatible elements k 2 o p 2 o 5 h 2 o indicate that each group was derived from a distinct source co 2 contents range from 0 05 to 0 19 wt but show no systematic correlation with rock type or mg a well defined decrease in glass co 2 content with increasing vesicularity is shown by the alkalic lavas co 2 may have been outgassed from the tholeiitic and transitional magmas prior to eruption during storage in a shallow magma chamber reduced carbon species co and ch 4 were found in small amounts in most of the alkalic samples although the redox histories of hawaiian lavas are poorly known these new data indicate the presence of a reduced source for loihi magmas the kilauea tholeiitic glasses are evolved mg 48 3 to 55 and have higher h 2 o contents av 0 54 wt than loihi tholeiites av 0 42 wt at the same mg 55 cl is distinctly lower in kilauea glasses 0 01 wt compared to loihi glasses 0 09 wt the data indicate significant source differences for the two volcanoes consistent with results of other geochemical studies loihi tholeiites have distinctly higher 3 he 4 he ratios than kilauea tholeiites and are the highest measured in submarine basalts kurz et al 1983 these high ratios have been used to invoke a primitive source for loihi basalts the high cl content of these basalts the highest we have ever measured in submarine basalts may be a fingerprint of this primitive source as previously noted for icelandic basalts schilling et al 1980

the nature and distribution of carbon in submarine basalts and peridotite nodules primary carbonaceous material has been identified in submarine basaltic glasses and mantle derived peridotite nodules from alkali basalts using electron microprobe techniques in the submarine rocks carbon occurs 1 in quench produced microcracks in glasses and phenocrysts 2 in vesicles where it is preferentially concentrated on the sulfide spherules attached to vesicle walls and 3 in microcracks and co2 rich bubbles in inclusions of glass completely enclosed by phenocrysts in peridotite nodules carbon exists in intergrain cracks along grain boundaries and on the walls of fluid inclusions disposed in two dimensional arrays the carbonaceous material is believed to consist of a mixture of graphite other forms of elemental carbon and possibly small amounts of organic matter it is suggested that carbon precipitates by disproportionation of co according to the reaction 2 co c co2 and that this reaction is catalyzed by sulfide oxide surfaces in vesicles once deposition has begun the reaction continues on carbon surfaces as well based on the large amounts of condensed carbon observed in some vapor inclusions and the apparent lack of oxidation features associated with them it is proposed that carbon condensed from a magmatic vapor in which co was a significant constituent this implies that oxygen fugacities of undegassed basaltic melts under confining pressures of the shallow crust are typically lower than those of the qfm buffer at equivalent temperatures this is in agreement with some intrinsic oxygen fugacity measurements on similar undegassed materials regardless of the mechanism of its formation the presence of carbon in co2 rich vesicles and inclusions in basaltic glasses and mantle nodules adds uncertainty to estimates of minimum pressures of entrapment based on measurements of fluid densities condensed carbon also accounts for some of the carbon isotopic characteristics of these rocks

fluid evolution in the el sid gold deposit eastern desert egypt auriferous quartz carbonate veins in the el sid mine cut through the western margin of the fawakhir granitic intrusion and the immediate country ophiolites gold mineraliz ation is spatially and temporally associated with ene wsw fault shear zones developed late in the deformational history of the area field and microscopic studies suggest two distinct ore stages namely an early gold fe as sulphide and a late gold base metal mineralization new microthermometric and raman data suggest gold deposition as a result of a complex history of fluid immiscibly dilution of low salinity aqueous carbonic fluids in the early mineralization stage while wall rock alteration and pressure loss precipitated au from intermediate salinity aqueous ore fluids during the late stage fluid inclusion isochoric reconstructions combined with oxygen and sulphur isotope data indicate conditions of 320 20 8c and 1 3 0 2 kbar for the early gold fe as sulphide mineralization and c 200 15 and 0 6 0 9 kbar for the late gold zn pb cu sulphide stage the clockwise evolution path in pressure temperature space likely documents gold mineralization under post peak metamorphic conditions the calcu lated sulphide d 34 sh2s equilibrium values 29 04 to 4 75 may refer to a variable redox state of sulphur in the ore fluids from the early to late mineralization stages the stable isotope signature of the vein quartz and calcite suggest mixed magmatic and metamorphic fluid sources d 18 o h2o 4 9 to 7 4 unusually low d 13 c values of calcite in the late mineralization 213 9 to 214 7 may reflect input of magmatic co2 and or oxidized carbonaceous mate rial in the infiltrating fluid gold bearing quartz veins associated with variably tectonized ophiolitic and island arc rocks or adja cent to their interferences are common in the southern and central sectors of the eastern desert of egypt whereas gold occurrences confined to granitic intrusions that are in some cases associ ated with felsic subvolcanic porphyries is a com mon feature in the northern eastern desert e g moharram et al 1970 sabet bordonosov 1984 klemm et al 2001 botros 2004 based on sev eral geological and mineralogical studies a gold granitoid association in the eastern desert has been suggested by many authors e g garson

calculated fluid evolution path versus fluid inclusion data in the cohn system as exemplified by metamorphic rocks from rogaland south west norway fluid evolution paths in the cohn system can be calculated for metamorphic rocks if there are relevant data regarding the mineral assemblages present and regarding the oxidation and nitrodation states throughout the entire p t loop the compositions of fluid inclusions observed in granulitic rocks from rogaland south west norway are compared with theoretical fluid compositions and molar volumes the fluid parameters are calculated using a p t path based on mineral assemblages which are represented by rocks within the pigeonite in isograd and by rocks near the orthopyroxene in isograd surrounding an intrusive anorthosite massif the oxygen and nitrogen fugacities are assumed to be buffered by the coexisting fe ti oxides and cr carlsbergite respectively many features of the natural fluid inclusions including 1 the occurrence of co2 n2 rich graphite absent fluid inclusions near peak m2 metamorphic conditions 927 c and 400 mpa 2 the non existence of intermediate ternary co2 ch4 n2 compositions and 3 the low molar volume co2 rich fluid inclusions 36 42 cm3 mol 1 are reproduced in the calculated fluid system the observed co2 ch4 rich inclusions with minor n2 5 mol should also include a large proportion of h2o according to the calculations the absence of h2o from these natural high molar volume co2 ch4 rich inclusions and the occurrence of natural ch4 n2 rich inclusions are both assumed to result from preferential leakage of h2o this has been previously experimentally demonstrated for h2o co2 rich fluid inclusions and has also been theoretically predicted fluid deficient conditions may explain the relatively high molar volumes but cannot be used to explain the occurrence of ch4 n2 rich inclusions and the absence of h2o

geochemistry of high h2 and ch4 vent fluids issuing from ultramafic rocks at the rainbow hydrothermal field 36 14 n mar the flores diving cruise was part of the mast iii amores 1995 1998 program funded by the european union one of the major achievements of the flores cruise was the discovery of the rainbow hydrothermal field hosted in ultramafic rocks south of the amar segment on the mid atlantic ridge mar the rainbow hydrothermal fluids exhibit temperatures of 365 c ph of 2 8 high chlorinity 750 mmol kg and low silica 6 9 mmol kg the uniformity in endmember major minor trace element concentrations and gas contents suggests that all rainbow fluids originate from the same deep source although h2s content is relatively low 1 20 mmol kg all vent fluids show extraordinary high h2 16 mmol kg ch4 2 5 mmol kg and co 5 mol kg endmember concentrations compared to fluids collected from other vent sites along the mar hydrogen represents more than 40 of the total gas volume extracted from the fluids at rainbow h2 production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization given that exposures of ultramafic rock may be common particularly along slow spreading ridges the production of h2 may have important implications for microbial activity at and beneath the seafloor

thermal maturity in the shimanto accretionary prism southwest japan with the thermal change of the subducting slab fluid inclusion and vitrinite reflectance study abstract the p t path of the cretaceous shimanto accretionary complex western shikoku southwest japan was determined by a combination of vitrinite reflectance data and homogenization temperatures of fluid inclusion analysis within the complex the p t paths of the upper cretaceous yokonami melange and surrounding coherent strata were compared no p t difference was found between the yokonami melange and surrounding strata at least two types of fluids methane rich and water rich fluids migrated at different stages during metamorphism within the complex the methane rich fluid was initially trapped in vein quartz under pressures of 260 mpa and a geothermal gradient of 24 c km the water rich fluid was included in calcite at 95 125 mpa and a geothermal gradient of 50 c km the complex sequence of occurrence of the vein minerals and radiometric age data suggest that the water rich fluid was trapped during the kula pacific ridge subduction into the shimanto accretionary complex the paleoheat flow values for the two stages of subduction are consistent with the changes in the inferred slab age the metamorphism of the shimanto accretionary complex was predominantly controlled by the thermal condition of the subducting plate

estimating and interpreting velocity uncertainty in migrated images and avo attributes estimating a suitable velocity field for use in prestack depth migration is inherently uncertain because of limitations on the available data and estimation techniques this uncertainty affects both the migrated depth of structures and their amplitudes in the inverted images these effects can be estimated by performing multiple migrations with a set of velocity fields and colocating features in the migrated images this lets us examine the imaging procedure s sensitivity to changes in the velocity field so we can assess both structural and amplitude uncertainties in migrated images these two types of uncertainties affect interpretation in different ways for instance with structural uncertainty interpretation we consider the change in migrated location of structures when deciding on drilling locations optimizing well trajectories or computing uncertainty in volumetric calculations with amplitude uncertainty or amplitude versus offset avo uncertainty interpretation we consider 1 uncertainty in c

the fina nagu volcanic complex unusual submarine arc volcanism in the rapidly deforming southern mariana margin in the mariana convergent margin large arc volcanoes disappear south of guam even though the pacific plate continues to subduct and instead small cones scatter on the seafloor these small cones could form either due to decompression melting accompanying back arc extension or flux melting as expected for arc volcanoes or as a result of both processes here we report the major trace and volatile element compositions as well as the oxidation state of fe in recently dredged fresh pillow lavas from the fina nagu volcanic chain an unusual alignment of small closely spaced submarine calderas and cones southwest of guam we show that fina nagu magmas are the consequence of mantle melting due to infiltrating aqueous fluids and sediment melts sourced from the subducting pacific plate into a depleted mantle wedge similar in extent of melting to accepted models for arc melts fina nagu magmas are not as oxidized as magmas elsewhere along the mariana arc suggesting that the subduction component responsible for producing arc magmas is either different or not present in the zone of melt generation for fina nagu and that amphibole or serpentine mineral destabilization reactions are key in producing oxidized arc magmas individual fina nagu volcanic structures are smaller in volume than mariana arc volcanoes although the estimated cumulative volume of the volcanic chain is similar to nearby submarine arc volcanoes we conclude that melt generation under the fina nagu chain occurs by similar mechanisms as under mariana arc volcanoes but that complex lithospheric deformation in the region distributes the melts among several small edifices that get younger to the northeast

high ti amphibole as a petrogenetic indicator of magma chemistry evidence for mildly alkalic hybrid melts during evolution of variscan basic ultrabasic magmatism of central iberia central iberian variscan granite batholiths and anatectic complexes are punctuated by coeval stocks of hydrous high k calc alkaline ultrabasic to intermediate rock series despite their overall calc alkaline affinity the mafic ultramafic members contain high ti amphibole oikocrysts rimmed by lower ti amphibole cummingtonite and high ti amphibole replacing early phlogopite to understand the factors controlling the saturation of high ti amphibole in the parental magmas clinopyroxene melt phlogopite melt and amphibole melt relationships are reviewed this analysis reveals that for melts with intermediate compositions the affinity of tio2 for amphibole rises in alkalic magmas accordingly mildly alkalic trachytoid to subalkaline medium to high k andesite and dacite compositions are estimated for interstitial high ti amphibole saturated melts amphibole ce pb ratios reveal a mantle crust hybrid nature for interstitial melts with subalkaline trachytoid compositions the hydrous character of the variscan basic magmas favoured an overall magmatic evolutionary trend with a low rate of variation of na2o with respect to silica during amphibole crystallization

fluid inclusion and mineral isotopic compositions hco in eclogitic rocks as tracers of local fluid migration during high pressure metamorphism eclogite facies metagabbros from the monviso ophiolitic complex italian western alps provide a unique opportunity to trace fluid migration processes in a portion of the oceanic crust that has undergone subduction at a depth of 40 km we have determined the omphacites 18o and the abundance d and 13c of hydrous and carbonaceous compounds present in whole rocks which are believed to trace the residual phases of what was mobilized in the original rocks during subduction prograde dehydration reactions and eclogitization of hydrothermally altered oceanic metagabbros was accompanied by approximately 90 fluid loss the remaining fluid was trapped as primary water rich fluid inclusions in omphacite megacrysts that developed at the expense of the precursor magmatic pyroxene deformation of the eclogitic rocks resulted in continuous recycling of fluid between mylonites and omphacite veins without further fluid loss from the host ductile shear zone oxygen isotopes of omphacite omp and hydrogen isotopes of water in the fluid inclusions fi analyzed in low strain rocks mylonites and undeformed deformed veins show marked variations 18oomp and dfi values ranging from 3 0 to 5 3 and from 31 to 93 respectively detailed isotopic analysis of several individual vein wallrock pairs show that the scale of isotopic equilibration is of the order of one centimeter therefore the eclogitic minerals and fluids filling the veins are concluded to be locally derived our results argue against recent models which suggest large scale mass flushing of isotopically homogeneous fluids during subduction zone metamorphism on average the h2o contents and dfi value are within the upper mantle range the carbon has been inherited from the metamorphic transformation of the original carbon present in the oceanic crust and has a mean 13c value of 24 2 1 2 two carbonaceous components can be recognized condensed carbon which represents the major carbon species and carbonate daughter crystals present in fluid inclusions 18oomp values are significantly lower than those reported for mantle minerals and are similar to pyroxene and whole rock values from hydrothermally altered oceanic crust it is suggested that the isotopic imprint of the monviso eclogitic minerals and fluids represents the signature of mid ocean ridge hydrothermal alteration and subduction zone eclogitization processes the rocks studied could be the missing link between altered oceanic gabbros and eclogitic xenoliths in addition the range in 18oomp values recorded in the different microstructural domains covers most of the 18o values reported in type a b and c eclogitic xenoliths implying that caution must be exercised when using oxygen isotopes as an indicator of the origin of eclogitic xenoliths

sensitivity analysis of seismic depth migrations depth migration is the processing step that can position seismic reflectors in their proper spatial locations beneath the earth9s surface accurate seismic imaging assists in structural interpretation and determination of optimum drilling locations there are many migration algorithms to perform this depth imaging step many of these algorithms and their applications to foothills data have been summarized by lines et al 1999 as mentioned by parkes and hatton 1987 most depth migration algorithms and seismic time measurements are quite accurate but to improve the migrated image greater emphasis needs to be placed on improving the accuracy of the input velocity field in addition a greater awareness of depth imaging errors due to velocity inaccuracy is crucial parkes and hatton 1987 state that depth migration uncertainty is primarily a result of the velocity field uncertainty used to map seismic data from time to space

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

methane rich fluid inclusions from ophiolitic dunite and post collisional mafic ultramafic intrusion the mantle dynamics underneath the palaeo asian ocean through to the post collisional period abstract the protracted development history of the palaeo asian ocean starting from 1000 ma to 320 ma and continuation of mantle derived magmatism right through the post collisional period as manifested by the widespread mafic ultramafic intrusion and alkaline peralkaline granite suggest a vigorous long running mantle dynamo using the micro laser raman spectrometer we analyzed olivine and plagioclase hosted fluid inclusions from ophiolitic dunite kudi of the western kunlun range and post collisional mafic ultramafic intrusions of the xiangshan and the huangshandong eastern chinese tienshan mountains our results show that fluids brought from the mantle by these rocks are rich in h 2 o and ch 4 with variable amounts of n 2 estimation of the redox state pressure and depth of formation for the melt ch 4 h 2 o n 2 fluid systems from the 3 rock suites of the xinjiang and comparison of these parameters with those of the peridotite fluid parageneses for the sub cratonic upper mantle give meaningful results these fluids were formed in the asthenosphere were originally ch 4 n 2 rich primordial mantle fluid but have been progressively diluted with h 2 o and become oxidized by repeated subduction of oceanic slab we propose that repeated redox melting in the mantle due to dilution of ch 4 with h 2 o and oxidation caused formation of the long lived palaeo asian ocean brought about extensive intrusion of mafic ultramafic complexes and alkaline peralkaline granites right through the post collisional period and consequently resulted in significant phanerozoic continental growth in the central asian orogenic belt rise of atmospheric o 2 and the earth s major oxidation occurred at about 2 4 to 2 2 ga oxidation of the earth s mantle promoted the mantle melting and magma input to the crust resulting in major continental growth after 2 5 ga however much postponed oxidation of the primordial mantle underneath the central asian orogenic belt led to significant continental growth in the phanerozoic times

role of fluids in migmatites co2 h2o fluid inclusions in leucosomes from the deep freeze range migmatites terra nova bay antarctica the metasedimentary sequence of the deep freeze range northern victoria land antarctica experienced high t low f metamorphism during the cambro ordovician ross orogeny the reaction bt sil qtz grt crd kfs melt was responsible for the formation of migmatites peak conditions were c 700 750 c c 3 5 5 kbar and xh2oc 0 5 distribution of fluid inclusions is controlled by host rock type 1 co2 h2o fluid inclusions occur only in graphite free leucosomes 2 co2 ch4 h2o fluid inclusions are the most common type in leucosomes and in graphite bearing mesosomes and gneiss and 3 co2 n2 ch4 fluid inclusions are observed only in the gneiss and subordinately in mesosomes co2 h2o mixtures 41 co2 58 h2o 1 nad mol are interpreted as remnants of a synmig matization fluid their composition and density are compatible p t ah2o conditions of migmatization c 750 c c 4 kbar xh2oc 0 5 co2 h2o fluid in graphite free leucosomes cannot originate via partial melting of graphite bearing mesosomes in a closed system this would have produced a mixed co2 ch4 fluid in the leucosomes by a reaction such as bt sil qtz c h2o grt crd kfs l co2 ch4 we conclude that an externally derived oxidizing co2 h2o fluid was present in the middle crust and initiated anatexis high density co2 rich fluid with traces of ch4 characterizes the retrograde evolution of these rocks at high temperatures and support isobaric cooling p t anticlockwise path in unmigmatized gneiss mixed co2 n2 ch4 fluid yields isochores compatible with peak metamorphic conditions c 700 750 c c 4 4 5 kbar they may represent a peak metamorphic fluid that pre dated the migmatization

high temperature reduced granulite facies nature of garnetites in the khabarny mafic ultramafic massif southern urals evidence from fluid and mineral analyses