geodetic observations and modeling of magmatic inflation at the three sisters volcanic center central oregon cascade range usa abstract tumescence at the three sisters volcanic center began sometime between summer 1996 and summer 1998 and was discovered in april 2001 using interferometric synthetic aperture radar insar swelling is centered about 5 km west of the summit of south sister a composite basaltic andesite to rhyolite volcano that last erupted between 2200 and 2000 yr ago and it affects an area 20 km in diameter within the three sisters wilderness yearly insar observations show that the average maximum displacement rate was 3 5 cm yr through summer 2001 and the velocity of a continuous gps station within the deforming area was essentially constant from june 2001 to june 2004 the background level of seismic activity has been low suggesting that temperatures in the source region are high enough or the strain rate has been low enough to favor plastic deformation over brittle failure a swarm of about 300 small earthquakes m max 1 9 in the northeast quadrant of the deforming area on march 23 26 2004 was the first notable seismicity in the area for at least two decades the u s geological survey usgs established tilt leveling and edm networks at south sister in 1985 1986 resurveyed them in 2001 the latter with gps and extended them to cover more of the deforming area the 2001 tilt leveling results are consistent with the inference drawn from insar that the current deformation episode did not start before 1996 i e the amount of deformation during 1995 2001 from insar fully accounts for the net tilt at south sister during 1985 2001 from tilt leveling subsequent insar gps and leveling observations constrain the source location geometry and inflation rate as a function of time a best fit source model derived from simultaneous inversion of all three datasets is a dipping sill located 6 5 2 5 km below the surface with a volume increase of 5 0 10 6 1 5 10 6 m 3 yr 95 confidence limits the most likely cause of tumescence is a pulse of basaltic magma intruding the upper crust along the brittle ductile interface a process that must occur episodically beneath the cascade range but in the past would have escaped detection in the absence of unusual seismicity we speculate that such intrusive episodes last from days to years and are separated by quiescent periods of decades to centuries the likelihood that the current episode at three sisters will culminate in an eruption is judged to be low but the impact of an eruption could be great the usgs has updated its volcano hazards assessment for the three sisters region notified appropriate agencies and the public and is helping to prepare an emergency coordination and communication plan

continuing inflation at three sisters volcanic center central oregon cascade range usa from gps leveling and insar observations uplift of a broad area centered 6 km west of the summit of south sister volcano started in september 1997 onset estimated from model discussed in this paper and was continuing when surveyed in august 2006 surface displacements were measured whenever possible since august 1992 with satellite radar interferometry insar annually since august 2001 with gps and leveling surveys and with continuous gps since may 2001 the average maximum displacement rate from insar decreased from 3 5 cm yr during 1998 2001 to 1 4 cm yr during 2004 2006 the other datasets show a similar pattern i e surface uplift and extension rates decreased over time but deformation continued through august 2006 our best fit model to the deformation data is a vertical prolate spheroidal point pressure source located 4 9 5 4 km below the surface the source inflation rate decreased exponentially during 2001 2006 with a 1 e decay time of 5 3 1 1 years the net increase in source volume from september 1997 to august 2006 was 36 5 41 9 x 106 m3 a swarm of 300 small mmax 1 9 earthquakes occurred beneath the deforming area in march 2004 no other unusual seismicity has been noted similar deformation episodes in the past probably would have gone unnoticed if as we suspect most are small intrusions that do not culminate in eruptions

magma at depth a retrospective analysis of the 1975 unrest at mount baker washington usa mount baker volcano displayed a short interval of seismically quiescent thermal unrest in 1975 with high emissions of magmatic gas that slowly waned during the following three decades the area of snow free ground in the active crater has not returned to pre unrest levels and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval a relative microgravity survey revealed a substantial gravity increase in the 30 years since the unrest while deformation measurements suggest slight deflation of the edifice between 1981 83 and 2006 07 the volcano remains seismically quiet with regard to impulsive volcano tectonic events but experiences shallow 10 km long period earthquakes reviewing the observations from the 1975 unrest in combination with geophysical and geochemical data collected in the decades that followed we infer that elevated gas and thermal emissions at mount baker in 1975 resulted from magmatic activity beneath the volcano either the emplacement of magma at mid crustal levels or opening of a conduit to a deep existing source of magmatic volatiles decadal timescale multi parameter observations were essential to this assessment of magmatic activity

co eruptive and inter eruptive surface deformation measured by satellite radar interferometry at nyamuragira volcano d r congo 1996 to 2010 abstract interferometric synthetic aperture radar insar measurements of surface deformation at nyamuragira volcano between 1996 and 2010 reveal a variety of co eruptive and inter eruptive signals during 7 of the 8 eruptions in this period deformation was measured that is consistent with the emplacement of shallow near vertical dykes feeding the eruptive fissures and associated with a nnw trending fissure zone that traverses the summit caldera between eruptions the caldera and the summit part of this fissure zone subsided gradually

increasing long wavelength relief across the southeastern flank of the sierra nevada california abstract a high degree of correlation between present day relative rock uplift measured using continuous gps geodesy and spatially averaged surface elevations suggests that long wavelength topographic relief is presently increasing along the southeastern flank of the sierra nevada range and within an adjacent portion of the northern basin and range province current estimates for erosion rate are an order of magnitude smaller than the relative rates determined by geodesy thus although the uplift serves to enhance long wavelength relief it cannot be explained entirely as an isostatic response to erosion if uplift rates have been constant through time the duration over which the uplift could have been active

origin of sio2 rich components in ordinary chondrites abstract silica rich objects are common minor components in ordinary chondrites oc occurring as fragments and as chondrules their typical paragenesis is orthopyroxene sio 2 with bulk sio 2 65 wt and occasionally with additional olivine and or spinel individual silica rich components src have previously been studied in various types of ocs although there is only one comprehensive study of these objects by brigham et al brigham c a murrell m t yabuki h ouyang z el goresy a 1986 silica bearing chondrules and clasts in ordinary chondrites geochim cosmochim acta 50 1655 1666 several different explanations of how srcs formed have been published the main question is how silica enrichment was achieved because ci chondritic atomic mg si ratio is 1 07 and as a consequence only olivine and pyroxene but no free silica should be stable there are two basic possibilities for the sio 2 enrichment 1 a redox mechanism or magmatic fractionation on the parent body and 2 fractional condensation or recycling of chondrule mesostasis in the solar nebula to better constrain the origin of these objects we measured major and rare earth elements in srcs of various types of ordinary chondrites and in addition we studied silica polymorphism in these objects using an in situ micro raman technique bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene the srcs extend these lines to an sio 2 end member in contrast magmatic trends grossly deviate from these mixing lines concentrations of cao al 2 o 3 and ree in the pyroxenes of the srcs are low 0 01 to 1 ci and the ci normalized ree patterns are virtually flat typical of bulk chondrules but untypical of magmatic trends we therefore conclude that sio 2 rich objects are not of magmatic origin they are the result of fractional condensation in the solar nebula the silica in srcs occurs mainly as tridymite and sometimes as cristobalite or in very rare cases as quartz some sio 2 phases yielded a yet unknown micro raman spectrum which we were unable to identify the often chondrule like shape of srcs as well as the presence of high temperature sio 2 polymorphs lead to the following model for the origin of srcs formation of sio 2 rich precursors in the solar nebula by fractional condensation reheating to temperatures between 1140 and 1968 k thereby forming the srcs probably during the chondrule forming process followed by rapid cooling

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

presolar diamond sic and graphite in primitive chondrites abundances as a function of meteorite class and petrologic type abstract acid resistant residues were prepared for eighteen meteorites from seven chondrite classes using improved procedures designed to minimize loss of presolar grains noble gases were measured by stepped pyrolysis and the abundances of five exotic noble gas components were used to determine abundances of diamond sic and graphite diamond separates were prepared to check diamond abundances determined from noble gases diamond and sic were found in unmetamorphosed members of all seven chondrite classes and evidence for graphite was found in orgued ci and ll3 0 3 1 chondrites our data and noble gas and stable isotope data in the literature show that presolar grains were incorporated into all chondrite classes the grains are sited in the fine grained matrix and their abundances within the matrix reflect mainly the degree of metamorphism suffered by the host meteorite the pattern of metamorphic destruction differs from class to class in unequilibrated ordinary chondrites uocs graphite is most easily destroyed followed by sic and then diamond no presolar grains remain in uocs of petrologic type 3 8 whose matrices have been completely recrystallized in eh chondrites diamond and sic survive much more severe metamorphism than in uocs with sic apparently more stable than diamond presolar graphite was not detected in cv3 and c03 chondrites diamond appears to be more stable than sic and graphite again is missing inferred premetamorphic diamond abundances matrix normalized vary by a factor of 2 2 between classes with eh cv and co chondrites having higher initial abundances than orgueil similar diamond sic ratios are observed in most classes and differences in the ratio can be tied to secondary processing suggesting that all chondrite classes sampled the same solar system wide reservoir of presolar grains differences in initial abundances between classes appear to correlate with chemical and physical properties of the host meteorites these bulk properties and variations in presolar grain abundances both may be the result of thermal processing of presolar dust in the accretion disk

quantifying the error of 2d bulk chondrule analyses using a computer model to simulate chondrules simchon bulk chondrule compositions are important to many questions in cosmochemistry however the number of available bulk chondrule data sets is still small a main reason for this is the difficulties of determining bulk chondrule compositions a commonly used technique is to obtain 2d bulk chondrule compositions from meteorite sections this technique has an error that we quantify here for the first time using a mathematical model of a chondrule called simchon the theoretically calculated errors are compared to errors that we determined from serial sectioning of eight efremovka chondrules the errors obtained from both approaches are in excellent agreement proving that our mathematical model produces reliable errors that can be assigned to 2d bulk chondrule compositions these errors allow a much better interpretation of 2d bulk chondrule data we provide a table that contains typical errors for 2d bulk compositions of porphyritic chondrules the errors are in the range of 1 30 relative this should be acceptable for many problems in cosmochemistry the effect of a chemical layering inside chondrules and the occurrence of a rim around them as well as the occurrence of opaque and other accessory phases have been studied a spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition bo chondrules have a negligible error but it is impossible to provide reasonable error estimates for bo chondrules with an igneous rim radial pyroxene chondrules have negligible errors

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

the origin of sulfide rimmed metal grains in ordinary chondrites abstract we report results from an experimental study of sulfide chemistry during metamorphism on ordinary chondrite parent bodies artificial ll chondrite material composed of silicate iron metal and sulfide grains was placed in sealed evacuated silica tubes and heated to either 500 c or 900 c these temperatures are representative peak metamorphic temperatures experienced by type 3 and type 6 ordinary chondrites respectively rapid sulfur mobilization occurs during heating and results in the formation of sulfide rims around the metal grains and sulfur loss from the original sulfide crystals the newly formed sulfide rims have two distinct layers that incorporate nearby silicate grains we also observe narrow sulfide trails that follow silicate grain boundaries and connect separate sulfide rimmed metal grains the morphologies of the sulfide rims suggest that vapor transport is the main mechanism for sulfur mobilization sulfur loss is observed along cracks and crystal boundaries of the initial sulfide grains after extensive reaction patches of iron metal appear at the outer edges of the sulfide crystals and large pore spaces form throughout the original sulfides the experimental metal sulfide assemblages resemble those found in low metamorphic grade ordinary chondrites this suggests metamorphism is mainly responsible for the observed metal sulfide textures in these chondrites

strain accumulation and rotation in western oregon and southwestern washington 1 velocities of 75 geodetic monuments in western oregon and southwestern washington extending from the coast to more than 300 km inland have been determined from gps surveys over the interval 1992 2000 the average standard deviation in each of the horizontal velocity components is 1 mm yr 1 the observed velocity field is approximated by a combination of rigid rotation euler vector relative to interior north america 43 40 n 0 14 119 33 w 0 28 and 0 822 0 057 myr 1 clockwise quoted uncertainties are standard deviations uniform regional strain rate eee 7 4 1 8 een 3 4 1 0 and enn 5 0 0 8 nstrain yr 1 extension reckoned positive and a dislocation model representing subduction of the juan de fuca plate beneath north america subduction south of 44 5 n was represented by a 40 km wide locked thrust and subduction north of 44 5 n by a 75 km wide locked thrust

textural equilibria of iron sulfide liquids in partly molten silicate aggregates and their relevance to core formation scenarios the influence of the coexistence of silicate and iron sulfide melts on the wetting of mantle olivine by iron sulfide melt is investigated the dihedral angle between iron alloy and olivine is unaffected by the presence of silicate melt at 1 5 gpa and 1370 1410 c and is much greater than the maximum allowable dihedral angle for melt connectivity at low melt fractions in experimental charges where silicate and sulfide melt occupy the same melt pocket the sulfide melt adheres to olivine grain faces rather than forming discrete droplets the relative interfacial energy between iron sulfide and basaltic silicate melt is lower than that of iron sulfide with olivine but the contrast is not sufficient for basaltic silicate melt to wet fes olivine grain boundaries this result implies that very large silicate melt fractions are necessary to mobilize iron sulfide melts in partially molten silicate phase assemblages therefore segregation of fe rich metallic melts by porous flow at low melt fraction is not a likely process for metal separation the experiments also investigated the influence of the presence of a thermal gradient on sulfide melt migration although the sulfide melt can not migrate through the olivine network by porous flow evidence in the experiments indicates mobility of sulfide through the interconnected silicate melt network the sulfide melt pools in contact with silicate melt at the hot top part of the experimental charges grow over time at the expense of the silicate melt pools in the cooler part of the charge this points to a diffusive transport mechanism for local sulfide redistribution we review literature data on metal olivine wetting angles and find that the metal composition has a dominant influence on the wetting behavior of a metallic liquid on an olivine matrix iron rich metallic liquid compositions are characterized by large dihedral angles 90 the metal olivine dihedral angle decreases with increasing amounts of dissolved light element s c o for light element contents in excess of 59 at the dihedral angle approaches 60 and the wetting behavior of a metallic liquid is similar to that of a silicate liquid

an accurate and efficient method for including the effects of topography in three dimensional elastic models of ground deformation with applications to radar interferometry topography has a large effect on the results predicted by elastic surface deformation models in regions of significant relief in some cases topography may have more influence on the predicted deformation field than do model source parameters we have developed an approximate analytical technique for including topographic effects that retains most of the computational simplicity of elastic half space models while providing an accurate representation of topographic effects we use a series expansion of the elastic half space solution with a small slope approximation yielding a set of higher order corrections the integrated effect of these corrections is evaluated using fourier methods we investigate the effectiveness of our method by comparing predicted results for a tilted triaxial ellipsoid with those predicted by finite element models the resulting displacements and displacement gradients are in good agreement with finite element results both for relatively smooth topography synthetically generated and for the greater relief in the vicinity of mount etna volcano we then compare the results of our method with those predicted by traditional elastic half space models using different reference elevations and with a previously proposed method of estimating topographic effects our new method provides a significantly better fit to the finite element results than do the other methods our method is able to accurately portray both the number and the horizontal pattern of fringes in a synthetic interferogram when compared with finite element results in particular the method accurately represents the broadening of fringes that is observed in regions of high relief as well as reproducing the location of the fringe center and the topographically induced deviation of the fringes from a regular pattern elastic half space models typically show a fringe center that is displaced with respect to the finite element results indicating that parameter inversions based on such a model would provide incorrect estimates of the horizontal source position the lack of topographically generated fringe distortions in elastic half space results would also likely lead to inaccuracies in the predicted magnitude and orientation of proposed deformation sources our new technique over comes these limitations and should be useful when evaluating either traditional geodetic results or the greater areal coverage provided by interferometric observations

strain accumulation near yucca mountain nevada 1993 1998 a 50 km aperture geodetic network centered on the proposed high level radioactive waste disposal site at yucca mountain nevada was surveyed with gps in 1993 and 1998 the average deformation rate across the area is described by the principal strain rates 22 8 8 8 nstrain yr 1 n77 6 w 13 5 and 8 8 11 9 nstrain yr 1 n12 5 e 13 5 extension reckoned positive and a clockwise rotation rate about a vertical axis of 9 6 7 4 nrad yr 1 relative to fixed north america quoted uncertainties are standard deviations those strain rates are consistent with the geodetic strain rates 2 12 nstrain yr 1 n87 12 w and 22 12 nstrain yr 1 n03 12 e previously reported by savage et al 1999 for the 1983 1998 interval and with the low extension rate 5 20 nstrain yr 1 marrett et al 1998 inferred from the geologic record none of those strain rates is consistent with the 50 9 nstrain yr 1 n65 w extension rate for the area reported by wernicke et al 1998

deciphering the nebular and asteroidal record of silicates and organic material in the matrix of the reduced cv3 chondrite vigarano we have conducted scanning electron microscope sem and transmission electron microscope tem studies of a variety of occurrences of matrix in the reduced cv3 chondrite breccia vigarano matrix which occurs as clastic interchondrule material and finer grained rims is dominated by morphologically variable olivines that host submicron hercynitic spinel and carbonaceous inclusions clastic matrix and fine grained rims show significant differences in their olivine morphologies abundance and composition of olivine inclusions and characteristics of the carbonaceous matter we suggest that these differences are the result of different degrees of alteration of clastic matrix and rims and are not due to variability in their precursor materials textural and compositional characteristics of olivine in the matrix are consistent with formation by growth possibly from an amorphous precursor material during asteroidal metamorphism in the presence of limited quantities of aqueous fluids spinel inclusions in olivine may be nebular condensates that acted as seeds for nucleation of olivine or may have formed during metamorphism and were subsequently overgrown by olivine carbonaceous material occurs as nanometer sized inclusions within olivine in both fine grained rims and clastic matrix but is most abundant as 100 200 nm grains interstitial to matrix olivines most carbonaceous material is amorphous but poorly graphitized carbon pgc also occurs as a minor component in both olivine inclusions and interstitial c the widespread occurrence of fine grained amorphous carbon grains in the interstitial regions between olivine grains may preserve the distribution and grain size of nebular organic material no clear textural relationships exist between carbonaceous grains and the other mineralogical components of vigarano matrix that could help constrain the origin of the organic grains i e evidence for fischer tropsch type reactions finally there are considerable differences between matrix olivines in vigarano in comparison with those in oxidized cv3 chondrites in particular the mineralogy and morphology of the matrix olivines and the nature composition and distribution of inclusions in the olivine grains are distinct based on these differences we conclude that matrix in the oxidized cv3 chondrites could not have formed by thermal processing of vigarano like material

vapor condensed phase processes in the early solar system abstract equilibrium thermodynamic calculations of the sequence of condensation of phases from a cooling gas of solar composition at total pressures thought to have prevailed in the inner part of the solar nebula successfully predict the primary mineral assemblages of refractory inclusions in cm2 and cv3 chondrites many refractory inclusions in cm2 chondrites contain a relatively sio2 poor assemblage spinel hibonite grossite perovskite corundum that represents a high temperature stage of condensation and some may be pristine condensates that escaped later melting compact type a and type b refractory inclusions consisting of spinel melilite perovskite ca rich clinopyroxene anorthite in cv3 chondrites are more sio2 rich and equilibrated with the solar nebular gas at a slightly lower temperature textures of many of these objects indicate that they underwent melting after condensation crystallizing into the same phase assemblage as their precursors the ti3 ti4 ratio of their pyroxene indicates that this process occurred in a gas whose oxygen fugacity was approximately 8 5 log units below that of the iron wustite buffer making them the only objects in chondrites known to have formed in a system whose composition was close to that of the sun relative to ci chondrites these inclusions are uniformly enriched in a group of elements e g ca ree zr ta ir that are chemically diverse except for their high condensation temperatures in a system of solar composition the enrichment factor 17 5 can be interpreted to mean that these objects represent either the first 5 7 wt of the condensable matter to condense during nebular cooling or the residue after vaporization of 94 3 of a ci chondrite precursor the mg and si isotopic compositions of types a and b inclusions are mass fractionated by up to 10 and 4 amu respectively when interpreted in terms of rayleigh fractionation during evaporation of mg and si from the inclusions while they were molten the isotopic compositions imply that up to 60 of the mg and up to 25 of the si were evaporated and that approximately 80 of the enrichment in refractory cao al2o3 relative to more volatile mgo sio2 in the average inclusion is due to initial condensation and approximately 20 due to subsequent evaporation the mineralogical composition including the ti3 ti4 ratio of the pyroxene in inti a particle sampled from comet wild 2 by the stardust spacecraft is nearly identical to that of a type b inclusion indicating that comets contain not only the lowest temperature condensates in the form of ices but the highest temperature condensates as well the feo feo mgo ratios of olivine and pyroxene in the matrix and chondrules of carbonaceous and ordinary chondrites are too high to be made in a system of solar composition requiring s only 1 or 2 log units below iron wustite more than 105 times higher than that of a solar gas various ways have been devised to generate cosmic gases sufficiently oxidizing to stabilize significant feo in olivine at temperatures above those where fe mg interdiffusion in olivine ceases one is by vertical settling of dust toward the nebular midplane enriching a region in dust relative to gas because dust is enriched in oxygen compared to carbon and hydrogen relative to solar composition a higher results from total vaporization of the region but the factor by which theoretical models have so far enriched the dust is 10 times too low another is by transporting icy bodies from the outer part of the nebula into the hot inner part where vaporization of water ice occurs not only does this method fail to make the needed by a factor of 30 1000 but it also ignores simultaneous evaporation of carbon bearing ices that would make the even lower

sulfur isotope composition of putative primary troilite in chondrules from bishunpur and semarkona the sulfur isotopic compositions of putative primary troilite grains within 15 ferromagnesian chondrules 10 feo poor and 5 feo rich chondrules in the least metamorphosed ordinary chondrites bishunpur and semarkona have been measured by ion microprobe some troilite grains are located inside metal spherules within chondrules since such an occurrence is unlikely to be formed by secondary sulfidization processes in the solar nebula or on parent bodies those troilites are most likely primary having survived chondrule forming high temperature events if they are primary they may be the residues of evaporation at high temperatures during chondrule formation and may have recorded mass dependent isotopic fractionations however the supposed primary troilites measured in this study do not show any significant sulfur isotopic fractionations 104 106 k h would be required to avoid a large degree of sulfur isotopic fractionation in the chondrule precursors this heating rate may provide a new constraint on the chondrule formation processes

partitioning of na between olivine and melt an experimental study with application to the formation of meteoritic na2o rich chondrule glass and refractory forsterite grains abstract we report experimentally determined 1 atm olivine melt d na partitioning data for low f o2 a variety of melt compositions and a temperature range of 1325 1522 c we demonstrated that high current electron microprobe analyses epma i 500 na 600 s on the peak allow quantitative determination of na 2 o in olivine down to 10 g g the mean olivine melt d na from 12 experimental runs is 0 0031 0 0007 1 this is the recommended value for low pressures and a wide range of natural compositions this result is applied to the problem of the origin of alkalis in chondrules and the formation of chondritic refractory forsterite grains the data on semarkona ll3 0 chondrules show that na 2 o is primordial and was present during olivine crystallization for refractory forsterite grains from murchison cm2 we demonstrate that high cao contents are not a result of equilibration with na 2 o rich melts but require high activities of cao during their formation

role of gas melt interaction during chondrule formation abstract it is generally believed that most chondrules formed in the protoplanetary disk by melting of fine grained solid precursor materials and that during these melting events chondrules behaved as closed systems both chemically and isotopically i e the observed range in chondrule bulk chemistry and modal mineralogy was entirely inherited from solid precursors that experienced melting to varying degrees followed by igneous crystallization accompanied by very limited if any evaporation recondensation our mineralogical and chemical study of magnesium rich porphyritic type i chondrules in primitive ordinary and carbonaceous chondrites revealed that chondrule glasses are not located on the subtraction lines of olivine or low ca pyroxene in appropriate phase diagrams indicating that type i chondrules do not obey closed system crystallization we suggest that gas melt interaction played a major role in evolution of mineralogy bulk chemical and isotopic compositions of type i chondrules chondrules are thus complex objects composed of an inherited solid component and a melt component that equilibrated with nebular gas suggesting that chondrules formed in regions with high ambient gas partial pressures as a result chondrule glasses melts are therefore thermochemical and isotopic sensors of the surrounding nebular gas in the chondrule forming regions of the protoplanetary disk and can be used for evaluating its physico chemical conditions

coseismic deformation from the 1999 mw 7 1 hector mine california earthquake as inferred from insar and gps observations we use interferometric synthetic aperture radar insar and global positioning system gps observations to investigate static deformation due to the 1999 m w 7 1 hector mine earthquake that occurred in the eastern california shear zone interferometric decorrelation phase and azimuth offset measurements indicate regions of surface and near surface slip which we use to constrain the geometry of surface rupture the inferred geometry is spatially complex with multiple strands the southern third of the rupture zone consists of three subparallel segments extending about 20 km in length in a n45 w direction the central segment is the simplest with a single strand crossing the bullion mountains and a strike of n10 w the northern third of the rupture zone is characterized by multiple splays with directions subparallel to strikes in the southern and central the average strike for the entire rupture is about n30 w the interferograms indicate significant along strike variations in strain which are consistent with variations in the ground based slip measurements using a variable resolution data sampling routine to reduce the computational burden we invert the insar and gps data for the fault geometry and distribution of slip we compare results from assuming an elastic half space and a layered elastic space results from these two elastic models are similar although the layered space model predicts more slip at depth than does the half space model the layered model predicts a maximum coseismic slip of more than 5 m at a depth of 3 to 6 km contrary to preliminary reports the northern part of the hector mine rupture accommodates the maximum slip our model predictions for the surface fault offset and total seismic moment agree with both field mapping results and recent seismic models the inferred shallow slip deficit is enigmatic and may suggest that distributed inelastic yielding occurred in the uppermost few kilometers of the crust during or soon after the earthquake

time dependent changes in volcanic inflation rate near three sisters oregon revealed by insar 1 an extensive area near the three sisters volcanic center oregon has been actively uplifting since 1996 in this study we use interferometric synthetic aperture radar insar to assess the three sisters uplift in time and space from 1992 through 2010 we present the first insar line of sight time series of the deformation refine the onset of volcanic intrusive activity assess the changes in deformation through time and determine whether inflation is still occurring we model insar data to determine the source geometry that best describes the uplift and create an inflation time series of the deformation our results reveal an intrusion located at 5 7 km depth with a cumulative volume of magma of 5 7 107 m3 as of fall 2010 the input of magma started gradually around the summer of 1996 increased significantly from 1998 to 2003 and then decreased in rate from 2004 through 2010 we present evidence that a swarm in 2004 was associated with the decrease in the source inflation rate

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

semipermanent gps spgps as a volcano monitoring tool rationale method and applications abstract semipermanent gps spgps is an alternative to conventional campaign or survey mode gps sgps and to continuous gps cgps that offers several advantages for monitoring ground deformation unlike cgps installations spgps stations can be deployed quickly in response to changing volcanic conditions or earthquake activity such as a swarm or aftershock sequence spgps networks can be more focused or more extensive than cgps installations because spgps equipment can be moved from station to station quickly to increase the total number of stations observed in a given time period spgps networks are less intrusive on the landscape than cgps installations which makes it easier to satisfy land use restrictions in ecologically sensitive areas spgps observations are preferred over sgps measurements because they provide better precision with only a modest increase in the amount of time equipment and personnel required in the field we describe three applications of the spgps method that demonstrate its utility and flexibility at the yellowstone caldera wyoming a 9 station spgps network serves to densify larger preexisting networks of cgps and sgps stations at the three sisters volcanic center oregon a 14 station spgps network complements an sgps network and extends the geographic coverage provided by 3 cgps stations permitted under wilderness land use restrictions in the basin and range province in northwest nevada a 6 station spgps network has been established in response to a prolonged earthquake swarm in an area with only sparse preexisting geodetic coverage at three sisters the estimated precision of station velocities based on annual 3 month summertime spgps occupations from 2009 to 2015 is approximately half that for nearby cgps stations conversely spgps derived station velocities are about twice as precise as those based on annual 1 week sgps measurements after 5 years of spgps observations at three sisters the precision of velocity determinations is estimated to be 0 5 mm yr in longitude 0 6 mm yr in latitude and 0 8 mm yr in height we conclude that an optimal approach to monitoring volcano deformation includes complementary cgps and spgps networks periodic insar observations and measurements from in situ borehole sensors such as tiltmeters or strainmeters this comprehensive approach provides the spatial and temporal detail necessary to adequately characterize a complex and evolving deformation pattern such information is essential to multi parameter models of magmatic or tectonic processes that can help to guide research efforts and also to inform hazards assessments and land use planning decisions

recent unrest of changbaishan volcano northeast china a precursor of a future eruption 1 over 12 years of continuous monitoring of changbaishan volcano in the border region of china and north korea by means of volcanic seismicity ground deformation and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006 in this so called active period the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background inactive periods the active period was also accompanied by ground inflation high values of co2 he h2 and high ratios of n2 o2 and 3he 4he in volcanic gases released from three hot springs near the caldera rim the monitoring evidence implies pressurization of the magma chamber possibly caused by incremental magma recharge the ground deformation data from both gps and precise leveling are modeled to suggest the corresponding deformation source is at 2 60 km depth beneath the volcano s summit where earthquake swarms were detected in 2002 and 2003 our findings suggest that the magma chamber beneath changbaishan volcano has awakened and resumed activity after remaining dormant since ad 1903 there is an urgent need to keep close watch on this active and very hazardous volcano in northeast china

sulfur and sulfides in chondrules abstract the nature and distribution of sulfides within type i po pop and pp chondrules of the carbonaceous chondrite vigarano cv3 have been studied by secondary electron microscopy and electron microprobe they occur predominantly as spheroidal blebs composed entirely of low ni iron sulfide troilite fes or troilite magnetite but in less abundance in association with metallic fe ni beads in opaque assemblages troilites are mainly located within the low ca pyroxene outer zone and their amounts increase with the abundance of low ca pyroxene within chondrules suggesting co crystallization of troilite and low ca pyroxene during high temperature events we show that sulfur concentration and sulfide occurrence in chondrules obey high temperature sulfur solubility and saturation laws depending on the f s 2 and f o 2 of the surrounding gas and on the melt composition mainly the feo content sulfur dissolved in chondrule melts may eventually reach a concentration limit the sulfur content at sulfide saturation scss at which an immiscible iron sulfide liquid separates from the silicate melt the occurrence of both a silicate melt and an immiscible iron sulfide liquid is further supported by the non wetting behavior of sulfides on silicate phases in chondrules due to the high interfacial tension between their precursor iron sulfide liquid droplets and the surrounding silicate melt during the high temperature chondrule forming event the evolution of chondrule melts from po to pp towards more silicic compositions very likely due to high p sio g of the surrounding nebular gas induces saturation of fes at much lower s content in pp than in po chondrules leading to the co crystallization of iron sulfides and low ca pyroxenes conditions of co saturation of low ca pyroxene and fes are only achieved in non canonical environments characterized by high partial pressures of sulfur and sio and redox conditions more oxidizing than iw 3 fe and s mass balance calculations also suggest the occurrence of an external source of iron very likely gaseous during chondrule formation we therefore propose that enrichments in sulfur and other volatile and moderately volatile elements from po to pp type i bulk chondrule compositions towards chondritic values result from progressive reaction between partially depleted olivine bearing precursors and a volatile rich gas phase

condensation of major elements during chondrule formation and its implication to the origin of chondrules abstract two glassy refractory al rich chondrules in semarkona ll3 0 the most primitive unequilibrated ordinary chondrite provide direct evidence for condensation of si and mg on melt droplets during cooling the chondrules are completely rounded rich in ca and al and poor in fe and alkalis they have extraordinarily abundant glass 70 80 vol with a subordinate amount of forsterite as the only crystalline phase that occurs mostly rimming the chondrule edge the groundmass glass is concentrically zoned in terms of si with an outward increase which is overlapped with local heterogeneity of mg and al induced by crystallization of forsterite the outward increase of si mostly compensated by al cannot be formed solely by crystallization of forsterite from a homogeneous melt in a closed system combined with skeletal or dendritic morphology and sector zoning of forsterite it is suggested that si condensed onto totally molten droplets initial melts accompanied by nucleation and rapid growth of forsterite with lowering temperature the initial melts the compositions of which were estimated from the ca contents of the first crystallized forsterite are very similar to type c cai but are notably poorer in mg and si than the bulk chondrules indicating condensation of mg in addition to si with an atomic ratio of mg si 3 2 the condensation after the nucleation of forsterite took place below 1300 c under cooling at 70 c h and amounted to 30 wt of the current chondrule this study suggests a model that a short time and local shock heating event induced melting of type c cai and concomitant evaporation of dusts ferromagnesian chondrules of earlier generation and their fragments to generate mg and si rich gas which condensed onto the melt droplets upon cooling accompanying condensation of type i chondrules

chondrules and other components in c o and e chondrites similarities in their properties and origins we describe three types of chondrules that are common to h3 ll3 cm2 co3 and cv3 chondrites low and high feo porphyritic olivine chondrules contain olivine with fa0 3 8 and fa5 50 respectively and can easily be distinguished petrographically poikilitic pyroxene chondrules have 1 20 vol olivine fa0 2 8 enclosed by low ca pyroxene fs0 5 7 and also occur in e chondrites these three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups metallic fe ni grains containing 0 1 1 cr si and p are present in low feo olivine chondrules from all type 2 and least metamorphosed type 3 chondrites metal compositions reflect reduction during chondrule formation in the nebula not nebular condensation opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy and probably have related origins we conclude that chondrules in all known chondrite groups share similar nebular origins

determination of the petrologic type of cv3 chondrites by raman spectroscopy of included organic matter abstract this paper reports the first reliable quantitative determination of the thermal metamorphism grade of a series of nine cv3 chondrites allende axtell bali mokoia grosnaja efremovka vigarano leoville and kaba the maturity of the organic matter in matrix determined by raman spectroscopy has been used as a powerful metamorphic tracer independent of the mineralogical context and extent of aqueous alteration this tracer has been used along with other metamorphic tracers such as fe zoning in type i chondrules of olivine phenocrysts presolar grain abundance and noble gas abundance bulk and p3 component the study shows that the petrologic types determined earlier by induced thermoluminescence were underestimated and suggests the following values pt allende axtell 3 6 pt bali mokoia grosnaja 3 6 pt efremovka leoville vigarano 3 1 3 4 pt kaba 3 1 the most commonly studied cv3 allende is also the most metamorphosed bali is a breccia containing clasts of different petrologic types the attribution suggested by this study is that of clasts of the highest petrologic types as pointed out by iom maturity and noble gas bulk abundance cv3 chondrites have complex asteroidal backgrounds with various degrees of aqueous alteration and or thermal metamorphism leading to complex mineralogical and petrologic patterns fe mg chemical zoning in olivine phenocrysts on the borders of type i chondrules of porphyritic olivine and pyroxene rich textural types has been found to correlate with the metamorphism grade this suggests that chemical zoning in some chondrules often interpreted as exchanges between chondrules and nebular gas may well have an asteroidal origin furthermore the compositional range of olivine matrix is controlled both by thermal metamorphism and aqueous alteration this does not support evidence of a nebular origin and does not necessarily mirror the metamorphism grade through fe mg equilibration on the other hand it may provide clues on the degree of aqueous alteration vs thermal metamorphism and on the timing of both processes in particular mokoia experienced significant aqueous alteration after the metamorphism peak whereas grosnaja which has similar metamorphism grade did not

repeated magmatic intrusions at el hierro island following the 2011 2012 submarine eruption abstract after more than 200 years of quiescence in july 2011 an intense seismic swarm was detected beneath the center of el hierro island canary islands culminating on 10 october 2011 in a submarine eruption 2 km off the southern coast although the eruption officially ended on 5 march 2012 magmatic activity continued in the area from june 2012 to march 2014 six earthquake swarms indicative of magmatic intrusions were detected underneath the island we have studied these post eruption intrusive events using gps and insar techniques to characterize the ground surface deformation produced by each of these intrusions and to determine the optimal source parameters geometry location depth volume change source inversions provide insight into the depth of the intrusions 11 16 km and the volume change associated with each of them between 0 02 and 0 13 km 3 during this period 20 cm of uplift was detected in the central western part of the island corresponding to approximately 0 32 0 38 km 3 of magma intruded beneath the volcano we suggest that these intrusions result from deep magma migrating from the mantle trapped at the mantle lower crust discontinuity in the form of sill like bodies this study using joint inversion of gps and insar data in a post eruption period provides important insight into the characteristics of the magmatic plumbing system of el hierro an oceanic intraplate volcanic island

zoned chondrules in semarkona evidence for high and low temperature processing at least 15 of the 10w feo chondrules in semarkona ll3 0 have mesostases that are concentrically zoned in na with enrichments near the outer margins we have studied zoned chondrules using electron microprobe methods x ray mapping plus quantitative analysis ion microprobe analysis for trace elements and hydrogen isotopes cathodoluminescence imaging and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved mesostases in these chondrules are strongly zoned in all moderately volatile elements and h interpreted as water calcium is depleted in areas ofvolatile enrichment titanium and cr generally decrease toward the chondrule surfaces whereas al and si may either increase or decrease generally in opposite directions to one another mn follows na in some chondru1es but not in others fe and mg are unzoned d h ratios increase in the water rich areas of zoned chondrules mesostasis shows cathodoluminescence zoning in most zoned chondrules with the brightest yellow color near the outside mesostasis in zoned chondrules appears to be glassy with no evidence for devitrification systematic variations in zoning patterns among pyroxene and olivine rich chondrules may indicate that fractionation oflow and high ca pyroxene played some role in ti cr mn si ai and some ca zoning but direct condensation ofelements into hot chondrules secondary melting oflate condensates into the outer portions of chondrules and subsolidus diffusion of elements into warm chondrules cannot account for the sub parallel zoning profiles ofmany elements the presence ofh20 or elemental abundance patterns zoning ofmoderately volatile elements and ca may have been produced by hydration ofchondrule glass without devitrification during aqueous alteration on the parent asteroid this could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material calcium was mainly lost during this process and other nonvolatile elements may have been mobile as well some unzoned 10w feo chondrules appear to have fully altered mesostasis

upper crustal structure of newberry volcano from p wave tomography and finite difference waveform modeling 1 seismic tomography combined with waveform modeling constrains the dimensions and melt content of a magma body in the upper crust at newberry volcano we obtain a p wave tomographic image by combining travel time data collected in 2008 on a line of densely spaced seismometers with active source data collected in the 1980s the tomographic analysis resolves a high velocity intrusive ring complex surrounding a low velocity caldera fill zone at depths above 3 km and a broader high velocity intrusive complex surrounding a central low velocity anomaly at greater depths 3 6 km this second upper crustal low velocity anomaly is poorly resolved and resolution tests indicate that an unrealistically large low velocity body representing 60 km3of melt could be consistent with the available travel times the 2008 data exhibit low amplitude first arrivals and an anomalous secondary p wave phase originating beneath the caldera two dimensional finite difference waveform modeling through the tomographic velocity model does not reproduce these observations to reproduce these phases we predict waveforms for models that include synthetic low velocity bodies and test possible magma chamber geometries and properties three classes of models produce a transmittedp phase consistent with the travel time and amplitude of the observed secondary phase and also match the observed lower amplitude first arrivals these models represent a graded mush region a crystal suspension region and a melt sill above a thin mush region the three possible magma chamber models comprise a much narrower range of melt volumes 1 6 8 0 km3 than could be constrained by travel time tomography alone

ree bearing sulfide in bishunpur ll3 1 a highly unequilibrated ordinary chondrite abstract this is a report of the first unambiguous discovery of rare earth elements ree in iron sulfide fes in an ordinary chondrite the content and the pattern of ree as well as the reduced state of the chondrules with the ree containing sulfide suggest that the sulfide inside the bishunpur ll3 1 chondrules is of igneous origin formed during crystallization of the chondrule melts the similarities in the content and the pattern of ree between chondrule sulfide and matrix sulfide in bishunpur indicate a genetic relationship the presence of igneous sulfide inside chondrules provides constraints on the ambient nebular temperature and the duration of chondrule formation the results of this study allow on the basis of ree content and pattern discrimination of igneous sulfide from condensate and secondary sulfide in chondrites and other interplanetary materials

rate of dissolution of carbonate sediments by microboring organisms davies reef australia abstract skeletal carbonate sediments on the lagoon floor of davies reef great barrier reef australia are subject to intense attack by microboring organisms principally algae the rate at which this microboring process dissolves carbonate was measured experimentally fresh unbored molluscan sand samples placed in the shallow lagoon 5 m water depth experienced a weight loss of about 0 9 g 30 g sample or 3 in one year due to dissolution of carbonate by microborers revealed by direct measurement of weight change and point count analysis this figure may be converted to about 350 g caco3 dissolved m2 lagoon floor year which is equivalent to between 18 and 30 of the sediment influx rate to this lagoon averaged over the past 9 000 years consideration of the exp rimental design suggests that the experiment underestimated the true rate of microboring in lagoon floor sediments we conclude that the extent of microboring in carbonate sands may provide information on the rate of sediment deposition and that dissolution of carbonate sediments by microborers is a significant factor in whole reef caco3 budgets

the mechanics of unrest at long valley caldera california 1 modeling the geometry of the source using gps leveling and two color edm data we surveyed 44 existing leveling monuments in long valley caldera in july 1999 using dual frequency global positioning system gps receivers we have been able to tie gps and leveling to a common reference frame in the long valley area and computed the vertical deformation by differencing gps based and leveled orthometric heights the resurgent dome uplifted 74 7 cm from 1975 to 1999 to define the inflation source we invert two color edm and uplift data from the 1985 1999 unrest period using spherical or ellipsoidal sources we find that the ellipsoidal source satisfies both the vertical and horizontal deformation data whereas the spherical point source cannot according to our analysis of the 1985 1999 data the main source of deformation is a prolate ellipsoid located beneath the resurgent dome at a depth of 5 9 km 95 bounds of 4 9 7 5 km this body is vertically elongated has an aspect ratio of 0 475 95 bounds are 0 25 0 65 and a volume change of 0 086 km3 95 bounds are 0 06 0 13 km3 failure to account for the ellipsoidal nature of the source biases the estimated source depth by 2 1 km 35 and the source volume by 0 038 km3 44

deformation and seismicity in the coso geothermal area inyo county california observations and modeling using satellite radar interferometry interferometric synthetic aperture radar insar data collected in the coso geothermal area eastern california during 1993 1999 indicate ground subsidence over a 50 km 2 region that approximately coincides with the production area of the coso geothermal plant the maximum subsidence rate in the peak of the anomaly is 3 5 cm yr 1 and the average volumetric rate of subsidence is of the order of 10 6 m 3 yr 1 the radar interferograms reveal a complex deformation pattern with at least two irregular subsidence peaks in the northern part of the anomaly and a region of relative uplift on the south we invert the insar displacement data for the positions geometry and relative strengths of the deformation sources at depth using a nonlinear least squares minimization algorithm we use elastic solutions for a prolate uniformly pressurized spheroidal cavity in a semi infinite body as basis functions for our inversions source depths inferred from our simulations range from 1 to 3 km which corresponds to the production depths of the coso geothermal plant underpressures in the geothermal reservoir inferred from the inversion are of the order of 0 1 1 mpa except a few abnormally high underpressures that are apparently biased toward the small source dimensions analysis of the insar data covering consecutive time intervals indicates that the depths and or horizontal extent of the deformation sources may increase with time this increase presumably reflects increasing volumes of the subsurface reservoir affected by the geothermal exploitation we show that clusters of microearthquakes associated with the geothermal power operation may result from perturbations in the pore fluid pressure as well as normal and shear stresses caused by the deflation of the geothermal reservoir

troilite in the chondrules of type 3 ordinary chondrites implications for chondrule formation abstract the presence of primary troilite in chondrules requires that nebular temperatures were 1170 k but much less ni at lower temperatures because this is far higher than the metamorphic temperature inferred for semarkona 670 k the troilite must be primary primary troilite fitting the three criteria occurs in a smaller fraction of low feo feo feo mgo in olivine and or low ca pyroxene not greater than 0 075 than high feo porphyritic chondrules in semarkona 9 vs 33 coarse grained low feo porphyritic chondrules appear to contain somewhat more troilite on average than those of medium grain size we found a few troilite free metallic fe ni bearing low feo chondrules that contain na2o bearing augite and na2o and k2o rich mesostasis these chondrules were probably formed after ambient nebular temperatures cooled below 910 k the 50 condensation temperature of na and before they reached 650 k literature reports of rare fayalitic microchondrules in the rims around a few normal size chondrules suggest that chondrule formation persisted until nebular temperatures cooled below 500 k secondary troilite occurs in a few percent of semarkona chondrules as thin veins mobilized by shock troilite or pyrrhotite in the outer portions of some chondrules occur within opaque assemblages containing magnetite carbide ni rich sulfide awaruite and co rich kamacite produced by parent body hydrothermal alteration

sustained water loss in california s mountain ranges during severe drought from 2012 to 2015 inferred from gps drought struck california during 7 of the 9 years from 2007 to 2015 reducing the state s available water resources pumping of central valley groundwater has produced spectacular land subsidence uplift of the adjacent sierra nevada mountains has been proposed to be either tectonic uplift or solid earth s elastic response to unloading of central valley groundwater we find that of the 24 mm of uplift of the sierra nevada from october 2011 to october 2015 just 5 mm is produced by central valley groundwater loss less than 2 mm is tectonic uplift and 17 mm is solid earth s elastic response to water loss in the sierra nevada we invert gps vertical displacements recording solid earth s elastic response to infer changes in water storage across the western u s from january 2006 to october 2017 we find water changes to be sustained over periods of drought or heavy precipitation the sierra nevada lost 15 19 km3 of water during drought from october 2006 to october 2009 gained 18 14 km3 of water during heavy precipitation from october 2009 to october 2011 and lost 45 21 km3 of water during severe drought from october 2011 to october 2015 95 confidence limits such large changes are not in hydrology models snow accumulation in october is negligible and long term soil moisture change is small we infer that there must be large loss of either deep soil moisture or groundwater in river alluvium and in crystalline basement in the sierra nevada the results suggest there to be parching of water in the ground during the summer of years of drought and seeping of melting snow into the sierra nevada in the spring of years of heavy precipitation

non spherical lobate chondrules in co3 0 y 81020 general implications for the formation of low feo porphyritic chondrules in co chondrites non spherical chondrules arbitrarily defined as having aspect ratios 1 20 in co3 0 chondrites comprise multi lobate distended and highly irregular objects with rounded margins they constitute 70 of the type i low feo porphyritic chondrules in y 81020 75 of such chondrules in alha77307 and 60 of those in colony although the proportion of non spherical type i chondrules in ll3 0 semarkona is comparable 60 multi lobate oc porphyritic chondrules with lobe heights equivalent to a significant fraction of the mean chondrule diameter are rare if the non spherical type i chondrules in co chondrites had formed from totally molten droplets calculations indicate that they would have collapsed into spheres within 10 3 s too little time for their 20 m size olivine phenocrysts to have grown from the melt these olivine grains must therefore be relicts from an earlier chondrule generation the final heating episode experienced by the non spherical chondrules involved only minor amounts of melting and crystallization the immediate precursors of the individual non spherical chondrules may have been irregularly shaped chondrule fragments whose fracture surfaces were rounded during melting because non spherical chondrules and circular chondrules form a continuum in shape and have similar grain sizes mineral and mesostasis compositions and modal abundances of non opaque phases they must have formed by related processes we conclude that a large majority of low feo chondrules in co3 chondrites experienced a late low degree melting event previous studies have shown that essentially all type ii high feo porphyritic chondrules in y 81020 formed by repeated episodes of low degree melting it thus appears that the type i and type ii porphyritic chondrules in y 81020 and presumably all co3 chondrites experienced analogous formation histories because these two types constitute 95 of all co chondrules it is clear that chondrule recycling was the rule in the co chondrule formation region and that most melting events produced only low degrees of melting the rarity of significantly non spherical multi lobate chondrules in semarkona may reflect more intense heating of chondrule precursors in the ordinary chondrite region of the solar nebula

strain accumulation near yucca mountain nevada 1983 1993 over the decade 1983 1993 the u s geological survey has measured the deformation of a 50 km aperture trilateration network centered on yucca mountain the proposed disposal site for high level nuclear waste in the united states the network was surveyed in 1983 1984 and 1993 the average annual principal strain rates are 0 010 0 020 strain yr n90 w 24 and 0 009 0 021 strain yr n00 e 24 indicating no significant strain accumulation the southeast corner of the network was disturbed on june 29 1992 by the little skull mountain earthquake ms 5 4 the epicenter of which is about 20 km southeast of the yucca mountain site using the seismically determined fault plane dip 54 s55 e we find that 0 580 0 075 m of normal slip on a 5 km square rupture surface at a depth of about 8 km provides a good fit to the observed deformation in the southeast corner of the network the inferred seismic moment is 4 4 0 6 1017 n m which compares well with the observed seismic moment of 4 1 1017 n m