the mineralogy of ordinary chondrites and implications for asteroid spectrophotometry abstract the normative mineralogies of 94 ordinary chondrites have been calculated from high quality bulk chemical analyses relative proportions of olivine orthopyroxene and metal are more variable within the h l and ll classes than has been recognized previously mineralogy within each chondrite class varies systematically with oxidation state these data have important implications for the design of reflectance spectroscopy studies that match asteroid and meteorite spectral features and for quantitative spectral interpretations of asteroids they also provide a tool with which to predict mineral abundances in unsampled asteroids that formed under different redox conditions

uranium series ages of travertines and timing of the last glaciation in the northern yellowstone area wyoming montana uranium series age determinations by mass spectrometric methods were done for travertines and associated carbonate veins related to clastic deposits of the last glaciation pinedale in the northern yellowstone area dramatic variations in the hydrologic head are inferred from variations in the elevation of travertine deposition with time and are consistent with the expected hydrologic effects of glaciation we determine the following chronology of the pinedale glaciation with the key assumption that travertine deposits and associated carbonate veins perched high above present thermal springs were deposited when glaciers filled the valley below these perched deposits 1 the early pinedale outlet glacier advanced well downvalley between 47 000 and 34 000 yr b p 2 the outlet glacier receded to an interstadial position between 34 000 and 30 000 yr b p 3 an extensive pinedale ice advance occurred between 30 000 and 22 500 yr b p 4 a major recession occurred between 22 500 and 19 500 yr b p 5 a minor readvance deckard flats culminated after 19 500 yr b p and 6 recession from the deckard flats position was completed before 15 500 yr b p this chronology is consistent with the general trend of climatic changes in the northern hemisphere as revealed by recent high resolution ice core records from the greenland ice sheet

travertine deposits of soda dam new mexico and their implications for the age and evolution of the valles caldera hydrothermal system uranium thorium disequilibrium dates and stable isotope analyses of travertine deposits at soda dam new mexico have been used to determine the age and to document the evolution of the valles caldera hydrothermal system soda dam discharges from paleozoic and precambrian rocks in san diego canyon southwest of the caldera and the canyon was filled with several hundred metres of upper bandelier tuff during formation of valles caldera 1 12 ma according to the dates the valles hydrothermal system is at least 106 yr old or nearly as old as the caldera the basic hydrology of the system has thus remained virtually unchanged during this time travertine ages indicate pulses in travertine deposition from 1 0 to 0 48 ma from 0 107 to 0 058 ma and from 0 005 ma to present the volume of various travertine deposits suggests that the hot spring system at soda dam was once larger than it is today possibly discharging as much as 5 to 10 times more fluid of na hco3 cl composition stable isotopes of the travertines indicate however that the hot spring system has probably never been more than about 10 c hotter than the present maximum temperature of 48 c stable isotopes also show that the 13c of co2 and 18o of h2o in hot spring waters has remained relatively constant for 106 yr the similar ages between caldera formation and the onset of large scale hydrothermal circulation and travertine deposition on pre bandelier tuff rocks imply that incision rates by the jemez river in bandelier tuff were relatively rapid as much as 400 m of tuff were cut by the ancestral jemez river in 105 yr or less

climatic eustatic and tectonic controls on quaternary deposits and landforms red sea coast egypt the degree to which local climatic variations eustatic sea level fluctuations and tectonic uplift have influenced the development of quaternary marine and fluvial landforms and deposits along the red sea coast eastern desert egypt was investigated using a combination of remote sensing and field data age determinations of corals and numerical simulations false color composites generated from landsat thematic mapper and spot image data digital elevation models derived from steieophotogrammetric analysis of spot data and field observations document that a 10 km wide swath inland from the coast is covered in many places with coalescing alluvial fans of quaternary age wadis cutting through the fans exhibit several pairs of fluvial terraces and wadi walls expose alluvium interbedded with coralline limestone deposits further three distinct coral terraces are evident along the coastline climatic eustatic and tectonic uplift controls on the overall system were simulated using a cellular automata algorithm with the following characteristics 1 uplift as a function of position and time as defined by the elevations and ages of corals 2 climatic variations driven by insolation changes associated with milankovitch cycles 3 sea level fluctuations based on u tb ages of coral terraces and eustatic data and 4 parameterized fluvial erosion and deposition results imply that the fans and coralline limestones were generated in a setting in which the tectonic uplift rate decreased over the quaternary to negligible values at present coralline limestones formed during eustatic highstands when alluvium was trapped upstream and wadis filled with debris during lowstands wadis cut into sedimentary deposits coupled with continuing uplift fans were dissected leaving remnant surfaces and wadirelated terraces were generated by down cutting only landforms from the past three to four eustatic sea level cycles i e 300 to 400 kyr are likely to have survived erosion and deposition associated with fluvial processes

epidote in calcalkaline magmas an experimental study of stability phase relationships and the role of epidote in magmatic evolution experiments on tonalite and granodiorite were performed at conditions ranging from 2 1 to 18 kbar and 550 to 850 c to establish the magmatic stability field of epidote as a function of p t and f02 at water saturated conditions and f02 buffered by nno epidote has a wide magmatic stability field in tonalite at 13 kbar this field extends from the wet solidus at 630 to 790 0c the low pressure intersection of the magmatic epidote crystallization reaction and the h20 saturated tonalite solidus and hence the minimum pressure for magmatic epidote occurs at about 5 kbar the clapeyron slopes of epidote melting reactions are moderately positive in p t space at pressures below the intersection of the epidote melting and the gamet in reactions at 13 kbar 790 c at this intersection epidote reaches its maximal thermal stability 790 c in tonalite h20 in the presence of garnet that is above 14 kbar epidote melting reactions have steep negative clapeyron slopes in p t space at p t conditions near the low pressure intersection of the epidote melting reaction with the water saturated solidus experiments were also performed with f02 buffered by hm at these oxidizing conditions the magmatic stability field of epidote is enlarged down to a pressure of about 3 kbar in granodiorite the stability of epidote has been investigated at pressures from 7 5 to 18 kbar with respect to the tonalite the epidote out reaction is located almost at the same p t conditions at 10 kbar but the maximum thermal stability is about 50 c lower toward higher pressures although few experiments indicate that epidote stability does not increase dramatically with decreasing water activity at present state it is not possible to predict melting and crystallization behavior of epidote at waterundersaturated conditions modal abundances of epidote are low 05 vol in the presence of major 40 vol melt fractions thus epidote in calc alkaline magmatic rocks is not likely to affect major elements strongly by fractional crystallization

initial results from vc 1 first continental scientific drilling program core hole in valles caldera new mexico valles caldera 1 vc 1 is the first continental scientific drilling program csdp core hole drilled in the valles caldera and the first continuously cored well in the caldera region the objectives of vc 1 were to penetrate a hydrothermal outflow plume near its source to obtain structural and stratigraphie information near the intersection of the ring fracture zone and the precaldera jemez fault zone arid to core the youngest volcanic unit inside the caldera banco bonito obsidian coring of the 856 m well took only 35 days to finish during which all objectives were attained and core recovery exceeded 95 vc 1 penetrates 298 m of moat volcanics and caldera fill ignimbrites 35 m of precaldera volcaniclastic breccia and 523 m of paleozoic carbonates sandstones and shales a previously unknown obsidian flow was encountered at 160 m depth underlying the battleship rock tuff in the caldera moat zone hydrothermal alteration is concentrated in sheared brecciated and fractured zones from the volcaniclastic breccia to total depth with both the intensity and rank of alterations increasing with depth alteration assemblages consist primarily of clays calcite pyrite quartz and chlorite but chalcopyrite and sphalerite have been identified as high as 450 m and molybdenite has been identified in a fractured zone at 847 m carbon 13 and oxygen 18 analyses of core show that the most intense zones of hydrothermal alteration occur in the madera limestone above 550 m and in the madera and sandia formations below 700 m this corresponds with zones of most intense calcite and quartz veining thermal aquifers were penetrated at the 480 540 and 845 m intervals although these intervals are associated with alteration brecciation and veining they are also intervals where clastic layers occur in the paleozoic sedimentary rocks

stratigraphic relations and lithologic variations in the jemez volcanic field new mexico over 100 radiometric dates and recent detailed geologic mapping allow some refinements of the stratigraphic relations of major units and generalization of temporal lithologic variations in the jemez volcanic field volcanism had begun in the area by about 16 5 ma with episodic eruptions of alkaline basalts by 13 ma alkaline volcanism had been replaced with eruptions of more voluminous olivine tholeiite high silica rhyolite derived from melts of lower crust also was erupting by about 13 ma basalt and high silica rhyolite continued to be erupted until about 7 and 6 ma respectively but effusions of dominantly andesitic differentiates of basalt that began as early as about 12 ma volumetrically overshadowed all other eruptive products between 10 and 7 ma from 7 to 3 ma the dominant erupted lithology was dacite which appears to have been generated by mixing of magmas whose compositions are approximated by earlier andesites and high silica rhyolites less than 4 3 ma volcanism was dominated by eruption of rhyolitic tuffs field relations geochemistry and dates specifically indicate the following with regards to stratigraphie relations 1 distinctions among basalt of chamisa mesa paliza canyon formation basalts and lobato basalt for other than geographic reasons are artificial basaltic volcanism was continuous in volcanic field from 13 to 7 ma 2 canovas canyon and bearhead rhyolites form a continuum of high silica rhyolite volcanism from 13 to 6 ma 3 hypabyssal and volcanic rocks of the cochiti mining district probably represent the exhumed interior of a keres group volcano s 4 temporal overlaps exist among the major stratigraphie groups which may imply some genetic relations and 5 the tewa group formation cerro rubio quartz latite may more appropriately be considered part of the tschicoma formation of the polvadera group preliminary analysis of hydrothermal alteration in the context of the volcanic stratigraphy suggests at least three distinct hydrothermal events have occurred in the volcanic field s history

radium isotopes alkaline earth diagenesis and age determination of travertine from mammoth hot springs wyoming u s a abstract travertine from active springs former vents and drill core from mammoth hot springs wyoming was analyzed for ra isotopes 226 ra 228 ra other alkaline earth elements mg sr ba and mineralogical composition thermal water also was analyzed travertine presently being deposited contains 3 0 15 3 pci g 226 ra and has a 228 ra 226 ra ratio identical to that in thermal water travertine precipitates mostly as aragonite and experiences a complete diagenetic transformation to calcite within 9 a estimated from 228 ra 226 ra value of youngest completely calcite travertine systematic compositional changes associated with this diagenetic transformation are enrichment of mg and depletion of sr ba and ra apparent mineral water distribution coefficients for mg sr and ba in aragonite and calcite are within the range of those determined experimentally implying near equilibrium conditions and high water rock ratios during travertine diagenesis impure travertine from near the base of the travertine section in the u s geological survey y 10 drill hole at 72 9 m depth has a 230 th 234 u isochron age of 7700 440a the content of 226 ra in normal subhorizontally layered porous travertine decreases with depth in y 10 the observed 226 ra vs depth relation is consistent with continuous deposition of travertine at the y 10 site from 7700 a bp to near present at a mean rate of 1 0 cm a and indicates minimal exchange of ra between travertine and pore water after the early diagenetic transformation of aragonite to calcite these data imply that under favorable conditions 226 ra measurements may be useful in determining ages and deposition rates for other travertines

hydrothermal sulfide and oxide deposits on seamounts near 21 n east pacific rise hydrothermal deposits were sampled by submersible from the calderas and summit benches of two seamounts 20 and 30 km west of the east pacific rise at 21 n the deposits document a wide variety of off axis hydrothermal activity including samples from the interiors of seafloor sulfide deposits in contrast to most mid ocean ridge deposits sulfide deposits on green seamount are rich in si fe and cu are poor in zn and contain abundant quartz sulfide chimneys grew by quenching of hydrothermal fluids and deposition of walls of colloform pyrite marcasite zn sulfide and minor galena whereas coarse grained pyrite and chalcopyrite were deposited at higher temperatures 250 c in chimney interiors as chimney walls grew outward into sea water increased temperatures in the inner walls resulted in recrystallization to pyrite and deposition of pyrite and chalcopyrite in pore space cooling in the outer portions of chimneys caused deposition of opal at temperatures of about 80 170 c as chimneys coalesced and opal rich material was heated in the interiors of sulfide edifices opal was recrystallized to chalcedony and quartz faulting has exposed the interiors of sulfide deposits where further recrystallization and deposition of chalcopyrite and quartz occurred at temperatures of 230 320 c clogging of chimneys changes in flow paths and cooling of the deposits led to the deposition of late mixed layer illite smectite iron sulfides fe poor sphalerite opal and barite the sulfide deposits formed over a time span of at least 140 000 to 70 000 yr ago probably coincident with caldera and pit crater formation the ages of the sulfide deposits provide constraints on the last volcanic and tectonic activity and they also suggest that it took a maximum of 260 000 yr for the seamount to reach its present height red seamount is presently hydrothermally active and deposits consisting predominantly of amorphous fe oxyhydroxide are forming on small pillow cones in the caldera at temperatures of 10 15 c hydrothermal nontronite deposits capped by mn oxide crusts cover much of the southern summit bench of red seamount and formed at temperatures of around 30 c iron rich talc and sulfide grains in nontronite provide evidence of former high temperature activity and suggest that a sulfide deposit is present nearby

238u 226ra and 210pb in some vent waters of the galapagos spreading center the concentrations of sup 226 ra sup 238 u and sup 210 pb have been measured in waters from the mussel bed and the rose garden thermal fields at the galapagos spreading center over a temperature range of approx 2 5 16 sup 0 c the sup 226 ra t plots yield slopes of 0 112 and 0 036 dpm kg sup 0 c for the mussel bed and the rose garden respectively yielding a global hydrothermal sup 226 ra flux less than 5 of that required to sustain the oceanic inventory sup 238 u concentration in waters 9 sup 0 c is the same as that in ambient sea water whereas water hotter than approx 9 sup 0 c shows a decreasing trend with temperature to zero sup 238 u at approx 29 sup 0 c sup 210 pb concentration in mussel bed increases with temperature and extrapolated to approx 350 sup 0 c yields a sup 210 pb concentration considerably less than that expected from sup 222 rn decay and basalt alteration

global distribution composition and abundance of olivine on the surface of mars from thermal infrared data 1 we used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of fo91 fo68 fo53 fo39 fo18 and fo1 olivine samples to mars global surveyor thermal emission spectrometer tes data over low albedo regions of mars the fo91 fo68 fo53 and fo39 spectral end members were confidently identified on mars a range of compositions wider than inferred from martian meteorites small less than hundreds of square kilometers occurrences of the fo91 spectral end member are present in the rims of the argyre and hellas impact basins and may represent martian mantle materials the fo68 spectral end member is common throughout the highlands chasmata outflow channels and nili fossae region the fo53 spectral end member occurs in eastern syrtis major the nili fossae region and smooth floored craters of the highlands although less abundant than fo68 and fo53 the distribution of the fo39 spectral end member suggests that some olivine on mars is more fe rich than olivine in martian meteorites global maps of olivine show that 1 materials containing 10 20 of olivine are common in the southern highlands of mars 2 olivine is most common near the topographic dichotomy boundary and 3 olivine becomes uncommon near the poles suggesting that it may be influenced by topography and or latitude climate olivine is found in early noachian to amazonian terrains some of which may be coeval with phyllosilicate and sulfate deposits detected by omega implying that any early noachian wet period of mars climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today

geology water geochemistry and geothermal potential of the jemez springs area canon de san diego new mexico abstract studies of the geology geochemistry of thermal waters and of one exploratory geothermal well show that two related hot spring systems discharge in canon de san diego at soda dam 48 c and jemez springs 72 c the hot springs discharge from separate strands of the jemez fault zone which trends northeastward towards the center of valles caldera exploration drilling to precambrian basement beneath jemez springs encountered a hot aquifer 68 c at the top of paleozoic limestone of appropriate temperature and composition to be the local source of the fluids in the surface hot springs at jemez springs comparisons of the soluble elements na li cl and b arguments based on isotopic evidence and chemical geothermometry indicate that the hot spring fluids are derivatives of the deep geothermal fluid within valles caldera no hot aquifer was discovered in or on top of precambrian basement it appears that low to moderate temperature geothermal reservoirs

climate driven variations in geothermal activity in the northern kenya rift valley high temperature continental geothermal systems are primarily associated with volcanic activity at plate margins1 it has long been known that the activity of these geothermal systems is intermittent and this is generally attributed to the effect of magmatic intrusions or fault motions recently however it has also been recognized2 4 that surface water hydrology and climate variations can influence the evolution of individual silicic caldera hosted geothermal systems although it is difficult to judge the general importance of such effects in controlling the long term behaviour of continental geothermal systems here we report uranium series ages for the hydrothermal deposits of past geothermal activity from several quaternary volcanic centres in the northern kenya rift valley we find that the ages correspond well to periods of high lake level within the rift suggesting that the elevated water table and increased availability of meteoric water associated with more humid climates can promote greater transfer of heat and mass from deep long lived heat sources to the surface

implications of temperature dependent near ir spectral properties of common minerals and meteorites for remote sensing of asteroids remote sensing analysis of common mafic silicates on bodies like asteroid 433 eros may be in error unless temperature effects are considered in this paper spectral sensitivity to temperature as a function of wavelength from 0 4 to 2 5 microns is quantified using new measurements of reflectance spectra of olivine and two ordinary chondrites the new data were obtained at higher temperature resolution and with greater accuracy than previous measurements we use a simple thermal model to show that the temperature difference between terrestrial ambient conditions and those prevailing on main belt asteroids as well as the temperature variations expected on the surfaces of individual asteroids during observations by spacecraft are large enough to cause easily detectable spectral differences therefore interpretations of asteroid spectra using spectra of minerals and meteorites obtained at terrestrial ambient conditions are suspect

hydrogen and major element concentrations on 433 eros evidence for an l or ll chondrite like surface composition a reanalysis of near x ray gamma ray spectrometer xgrs data provides robust evidence that the elemental composition of the near earth asteroid 433 eros is consistent with the l and ll ordinary chondrites these results facilitated the use of the gamma ray measurements to produce the first in situ measurement of hydrogen concentrations on an asteroid the measured value 1100 1600 700 ppm is consistent with hydrogen concentrations measured in l and ll chondrite meteorite falls gamma ray derived abundances of hydrogen and potassium show no evidence for depletion of volatiles relative to ordinary chondrites suggesting that the sulfur depletion observed in x ray data is a surficial effect consistent with a space weathering origin the newfound agreement between the x ray gamma ray and spectral data suggests that the near landing site a ponded regolith deposit has an elemental composition that is indistinguishable from the mean surface this observation argues against a pond formation process that segregates metals from silicates and instead suggests that the differences observed in reflectance spectra between the ponds and bulk eros are due to grain size differences resulting from granular sorting of ponded material

spectral properties and rotational spectral heterogeneity of 433 eros composite spectra of different rotational aspects of the s asteroid 433 eros were assembled from previous studies covering the wavelength range 0 33 2 5 m these data allow us to measure significant attributes of eros s spectrum its mafic mineral absorptions and the degree and nature of compositional heterogeneity of its surface we also evaluated previous s asteroid taxonomies using independent methods and from this test determined that the taxonomy of gaffey et al 1993 provides a sound basis for relating eros to other s asteroids on average eros resembles the s iv asteroids which bear the closest resemblance to ordinary chondrites in mafic mineralogy however eros also exhibits distinct rotational spectral variations comparable to the greatest yet recognized on an s asteroid one side of the asteroid has a shorter wavelength 1 m absorption and a stronger 2 m absorption than the global average and is interpreted to be richer in pyroxene the opposite face has a longer wavelength 1 m absorption and a weaker 2 m absorption and is interpreted to be richer in olivine the pyroxene rich side coincides with a facet like face identified in radar studies and the olivine rich side coincides with a convex shaped face each side of the asteroid exhibits spectral affinities with a different spectral class of s asteroids demonstrating that such subdivisions of s asteroids represent different parts of a compositional continuum high spatial resolution measurement of the mineralogic and elemental compositions and especially the geologic settings of these different materials by the near earth asteroid rendezvous mission will provide a great advance in the understanding of the origin and evolution of a candidate ordinary chondrite parent body

uranium series age determination of calcite veins vc 1 drill core valles caldera new mexico uranium series analysis sup 238 u sup 234 u sup 230 th of 13 calcite veins from the hydrothermally altered madera limestone in the vc 1 drill core was performed to determine the ages of the veins and their relation to the valles hydrothermal system thermal water from vc 1 and two hot springs in san diego canyon was analyzed for u and sup 234 u sup 238 u to help evaluate the constancy of initial sup 234 u sup 238 u the sup 230 th sup 234 u age of one of the veins is similar to 95 kyr and those of two other veins are similar to 230 and similar to 250 kyr five of the veins have near equilibrium sup 230 th sup 234 u and are probably older than similar to 0 3 m y uranium concentrations in the remaining veins are too low for analysis by the cap alpha spectrometry techniques employed in this study of the five veins near sup 230 th sup 234 u equilibrium suggesting ages greater than similar to 1 0 m y but one has sup 234 u sup 238 u 1 15 suggesting an age between similar to 0 3 and similar to 1 0 m y calculated initial sup 234 u sup 238 u of the veins yielding relatively young ages are neither equal to each other nor to sup 234 u sup 238 u in thermal water from vc 1 indicating inconstancy of initial supmore 234 u sup 238 u tht may be related to variations in groundwater mixing proportions three of the four veins that yield relatively young ages consist of coarse sparry vuggy calcite suggesting that this may be the type of calcite vein which forms under conditions resembling those encountered presently in vc 1 the analytical data are consistent with closed system behavior of u and th in the vc 1 calcite veins copyright american geophysical union 1988 less

local topographic effects on photometry and reflectance spectra of planetary surfaces an example based on lunar photometry the photometric properties of the average lunar surface are characterized using hapkes equations and whole disk observations ranging from 0 36 to 1 06 m synthetic spectra across a crater topographic profile arecreated using the modeling results the synthetic spectra are examined for spectral variations created by changes in lighting conditions induced by the topography changes above the modeling uncertainties are seen in both spectral slope and band depths though the most pronounced change is in band depth the data have insufficient spectral resolution to determine if there are any changes in band center due to photometric effects no additional absorption features are introduced by the photometry these results have serious implications on the interpretation of spectral observations in terms of abundance estimates and alteration processes as a function of location and association with geologic features

an estimate of hydrothermal fluid residence times and vent chimney growth rates based on210pb pb ratios and mineralogic studies of sulfides dredged from the juan de fuca ridge abstract the210pbpb ratios across two sulfide samples dredged from the juan de fuca ridge are used to estimate the growth rate of the sulfide material and the residence time of the hydrothermal fluid within the oceanic crust from the onset of basalt alteration 210pb is added to the hydrothermal fluid by two processes 1 high temperature alteration of basalt and 2 if the residence time of the fluid is on the order of the 22 3 year half life of210pb by in situ growth from222rn krishnaswami and turekian 1982 stable lead is derived only from the alteration of basalt the210pb pb ratio across one sample was 0 5 dpm 10 6 g pb and across the other it was 0 4 dpm 10 6 g pb these values are quite close to the238up b ratios of basalts from the area suggesting that the residence time of the hydrothermal fluid from the onset of basalt alteration is appreciably less than the mean life of210pb i e the time required for ingrowth from the radon an apparent growth rate of 1 2 cm yr is derived from the slope of the210pb pb curve for one of the samples this is consistent with its mineralogy and texture which suggest an accretionary pattern of development there is no obvious sequential growth pattern and virtually no gradient in210pb pb across the second sample this is consistent with alteration of the original210pb pb distribution by extensive remobilization reactions which are inferred from the mineralogic and textural relationships of the sample

the composition of 433 eros a mineralogical chemical synthesis abstract the near earth asteroid rendezvous near mission carried x ray gamma ray spectrometers and multi spectral imager near infrared spectrometer instrument packages which gave complementary information on the chemistry and mineralogy respectively of the target asteroid 433 eros synthesis of these two data sets provides information not available from either alone including the abundance of non mafic silicates metal and sulfide minerals we have utilized four techniques to synthesize these data sets venn diagrams which examine overlapping features in two data sets suggest that the best match for 433 eros is an ordinary chondrite altered at the surface of the asteroid or perhaps a primitive achondrite derived from material mineralogically similar to these chondrites normalized element distributions preclude feo rich pyroxenes and suggest that the x ray and gamma ray data can be reconciled with a common silicate mineralogy by inclusion of varying amounts of metal normative mineralogy cannot be applied to these data sets owing to uncertainties in oxygen abundance and lack of any constraints on the abundance of sodium matrix inversion for simultaneous solution of mineral abundances yields reasonable results for the x ray derived bulk composition but seems to confirm the inconsistency between mineral compositions and orthopyroxene clinopyroxene ratios a unique solution does not seem possible in synthesizing these multiple data sets future missions including a lander to fully characterize regolith distribution and sample return would resolve the types of problems faced in synthesizing the near data

hydrothermal alteration in the valles caldera ring fracture zone and core hole vc 1 evidence for multiple hydrothermal systems two types of hydrothermal mineral assemblages kaolinite alunite and sericite chlorite were recognized in outcrop and core samples from the jemez volcanic field new mexico active and fossil acid sulfate hydrothermal activity producing kaolinite alunite alteration occurs along the caldera ring fracture and within the resurgent dome whereas alterations of the chlorite sericite type are mostly confined to subsurface rocks k ar dates on illitic clays 2 m 2 0 25 m and 0 25 m separated from hydrothermally altered samples are used to document hydrothermal episodes in pre caldera rocks of the jemez volcanic field the clay separates are illitic 75 95 illite layers with k2o contents of 8 24 8 95 in the core samples and 4 22 6 67 in the outcrops three episodes of hydrothermal alteration are now recognized in the jemez mountains region based on k ar age dates of illites the earliest event 17 11 ma n 4 occurred within altered and illite rich 90 illite layers lowermost paleozoic rocks in core hole vc 1 and may correlate with the inception of volcanism in the jemez region 16 5 ma illitic clays from altered andesite and rhyolite from the topographic rim of the valles caldera were dated at 8 2 and 6 96 ma suggesting that a hydrothermal event related to the waning stages of the keres group volcanism 13 5 8 ma was responsible for the alteration these dates overlap minimum ages obtained on slightly altered basalt 8 05 ma and andesite lava 7 07 ma from the southern and northwestern topographic rim of the valles caldera respectively ages of 1 21 and 1 34 ma from illite rich 90 illite layers hydrothermally altered paleozoic sandstone at a depth of 479 m in vc 1 suggest hydrothermal activity contemporaneous with the formation of the toledo 1 45 ma and valles 1 12 ma calderas ore minerals of sphalerite chalcopyrite galena barite and molybdenite mineralization occur in the lower half of vc 1 and are related to the toledo and valles caldera forming eruptions

k ar dates of hydrothermal clays from core hole vc 2b valles caldera new mexico and their relation to alteration in a large hydrothermal system abstract seventeen k ar dates were obtained on illitic clays within valles caldera 1 13 ma to investigate the impact of hydrothermal alteration on quaternary to precambrian intracaldera and pre caldera rocks in a large long lived hydrothermal system 1 0 ma to present clay samples came from scientific core hole vc 2b 295 c at 1762 m which was spudded in the sulphur springs thermal area and drilled into the boundary between the central resurgent dome and the western ring fracture zone six illitic clays within quaternary caldera fill debris flow tuffaceous sediment and ash flow tuff 48 to 587 m depth yield ages from 0 35 to 1 09 ma illite from miocene pre caldera sandstone 765 m gives an age of 6 74 ma two dates on illite from sandstones in permian red beds 1008 and 1187 m are 4 33 and 4 07 ma respectively surprisingly three dates on illites from altered andesite pebbles within the red beds 1010 1014 m are 0 95 to 1 06 ma four illite dates on variably altered precambrian quartz monzonite 1615 1762 m range from 2 90 to 276 ma post valles age illite is not correlated with alteration style argillic to propylitic rather post valles ages are uniformly obtained from illites in highly fractured intensely altered caldera fill rocks and the permian volcanic clasts generally finer clay fractions from identical samples yield younger ages plots of 40 ar 36 ar versus 40 k 36 ar and 40 ar versus 40 k for the illites in caldera fill rocks lie close to a 1 ma isochron most illite dates older than valles caldera are difficult to interpret because they correspond to the ages of pre valles volcanic and hydrothermal episodes in the jemez volcanic field 13 ma in addition older dates may be caused by co mingling of different illites during sample preparation or by inherited argon or lost argon in illites from rocks with potentially complex hydrothermal histories however the range of ages obtained from illites in permian sands and pebbles and from precambrian crystalline rocks indicates that valles hydrothermal activity is overwhelming illite produced by earlier geologic events

thorium uranium disequilibrium in a geothermal discharge zone at yellowstone whole rock samples of hydrothermally altered biscuit basin rhyolite from yellowstone drill cores y 7 and y 8 were analyzed for sup 230 th sup 234 u sup 238 u and sup 232 th extreme disequilibrium was found with sup 230 th sup 234 u ranging from 0 30 to 1 27 values of sup 230 th sup 232 th and sup 234 u sup 232 th define a linear correlation with a slope of 0 16 0 01 which corresponds to a sup 230 th sup 234 age of approximately 19 ka the sup 230 th sup 234 u disequilibrium was apparently caused by u redistribution which occurred mostly at about 19 ka and is not related simply to the relative degree of hydrothermal alteration and self sealing of the rhyolite mass balance of u requires a large flux of u bearing ground water through the rhyolite at the time of u redistribution rough estimates of minimum water rock ratio range from 10 sup 2 to 10 sup 4 for a range of possible ground water u concentrations conservative hydraulic calculations indicate that the required ground water flux could have occurred within a period of hundreds of years prior to self sealing the disequilibrium data are consistent with a model involving u redistribution during the initial stages of development of a geothermal discharge zone that formed in response tomore the hydrogeologic effects of glacial melting and unloading during the decline of the pinedale glaciation less

meteoritic and other constraints on the internal structure and impact history of small asteroids studies of the internal structure of asteroids which are crucial for understanding their impact history and for hazard mitigation appear to be in conflict for the s type asteroids eros gaspra and ida spacecraft images and geophysical data show that they are fractured coherent bodies whereas models of catastrophic asteroidal impacts family and satellite formation and studies of asteroid spin rates and other diverse properties of asteroids and planetary craters suggest that such asteroids are gravitationally bound aggregates of rubble these conflicting views may be reconciled if 10 50 km s type asteroids formed as rubble piles but were later consolidated into coherent bodies many meteorites are breccias that testify to a long history of impact fragmentation and consolidation by alteration metamorphism igneous and impact processes ordinary chondrites which are the best analogs for s asteroids are commonly breccias some may have formed in cratering events but many appear to have formed during disruption and reaccretion of their parent asteroids some breccias were lithified during metamorphism and a few were lithified by injected impact melt but most are regolith and fragmental breccias that were lithified by mild or moderate shock like their lunar analogs shock experiments show that porous chondritic powders can be consolidated during mild shock by small amounts of silicate melt that glues grains together and by friction and pressure welding of silicate and metallic fe ni grains we suggest that the same processes that converted impact debris into meteorite breccias also consolidated asteroidal rubble internal voids would be partly filled with regolith by impact induced seismic shaking consolidation of this material beneath large craters would lithify asteroidal rubble to form a more coherent body fractures on ida that were created by antipodal impacts and are concentrated in and near large craters and small positive gravity anomalies associated with the psyche and himeros craters on eros are consistent with this concept spin data suggest that smaller asteroids 0 6 6 km in size are unconsolidated rubble piles c type asteroids which are more porous than s types and their analogs the volatile rich carbonaceous chondrites were probably not lithified by shock

mineralogical interpretation of reflectance spectra of eros from near near infrared spectrometer low phase flyby high signal to noise near infrared spectrometer nis spectra acquired during the low phase flyby of the near earth asteroid rendezvous near mission to 433 eros are analyzed to determine mineral chemistry and proportions of mafic silicates across the asteroid s surface at 2 68 5 50 km spatial resolution spectral band parameters are derived and compared with those of laboratory samples of known mineral composition grain size distribution and terrestrial meteoritic and lunar pyroxene spectral properties the nis derived band parameters are consistent with ordinary chondrite meteorites we invoke the presence of a clinopyroxene component in the spectra which is consistent with ordinary chondrite mineralogy and or some degree of partial melting of ordinary chondritic material spectra measured across the surface of eros can reveal small but real spectral variations most relative spectra are uniform to within 1 2 some areas suggest compositional variations of a few percent spectral slope variations of a few percent are seen indicating a non uniform distribution of materials affecting the slope parameter but with no resolved absorption bands we find no correlation of slope with viewing geometry or compositional variation the band parameter values do not consistently indicate a specific ordinary chondrite class but eros is definitely undifferentiated with possible compositional variations of no more than 1 2

the hydrothermal outflow plume of valles caldera new mexico and a comparison with other outflow plumes stratigraphic temperature gradient hydrogeochemical and hydrologic data have been integrated with geologic data from previous studies to show the structural configuration of the valles caldera hydrothermal ouflow plume hydrologic data suggest that 25 50 of the discharge of the valles outflow is confined to the jemez fault zone which predates caldera formation thermal gradient data from bores penetrating the plume show that shallow gradients are highest in the vicinity of the jemez fault zone up to 190 c km shallow heat flow above the hydrothermal plume is as high as 500 mw m 2 near core hole vc 1 jemez fault zone to 200 mw m 2 at fenton hill jemez plateau chemical and isotopic data indicate that two source reservoirs within the caldera redondo creek and sulphur springs reservoirs are parents to mixed fluids flowing in the hydrothermal plume however isotopic data borehole data basic geology and inverse relations between temperature and chloride content at major hot springs indicate that no single reservoir fluid and no single diluting fluid are involved in mixing the valles caldera hydrothermal plume is structurally dominated by lateral flow through a belt of vertical conduits jemez fault zone that strike away from the source reservoir stratigraphically confined flow is present but dispersed over a wide area in relatively impermeable rocks the valles configuration is contrasted with the configuration of the hydrothermal plume at roosevelt hot springs which is dominated by lateral flow through a near surface widespread permeable aquifer data from 12 other representative geothermal systems show that outflow plumes occur in a variety of magmatic and tectonic settings have varying reservoir compositions and have different flow characteristics although temperature reversals are commonly observed in wells penetrating outflow plumes reversals are not observed in all plumes less information is available on the absolute age of hydrothermal outflow plumes although the data show that they can be as old as 106 years and display episodic behavior

the paleomagnetic effects of reheating the ecstall pluton british columbia abstract paleomagnetic data of plutons from the western canadian cordillera are currently interpreted to indicate thousands of kilometers of latitudinal transport in situ tilting or post intrusion folding for the ecstall pluton of british columbia the inclination of magnetic remanence directions steepens to the east from 16 to 81 butler et al j geophys res 107 2002 between 24 and 12 km west of a thermal boundary with the coast mountains batholith cmb the cmb was at 700 800 c between 60 and 52 ma the stable remanent magnetization is in ilmenohematite grains with exsolved lamellae of ferrian ilmenite it has the characteristic properties of lamellar magnetism robinson et al nature 418 2002 517 520 which is acquired with exsolution in ilmenohematite below 390 c ghiorso phys chem minerals 25 1997 28 38 thus it is thermal chemical remanent magnetization tcrm our heat flow calculations show that the thermal effects of eocene cmb on the adjacent 91 ma ecstall pluton were enough to reset the remanent magnetization directions reheating to the temperatures necessary for tcrm is supported by k ar and ar ar cooling dates on hornblende and biotite which young from west to east towards the cmb in concert with the change in inclinations thus the progressive steepening of magnetization inclinations is attributed to reheating during the eocene of the 91 ma ecstall pluton by the cmb this reheating followed post solidification northward latitudinal displacement of the pluton the amount of translational displacement of the coastal terranes of british columbia prior to 60 ma hinges on the interpretation of discordant magnetizations from plutons that may have cooled slowly after emplacement in the mid to lower crust as was the case for the ecstall pluton many of these plutons contain ilmenohematite as an accessory magnetic phase our interpretation for the low temperature acquisition of tcrm in the ecstall pluton may have far reaching implications for understanding enigmatic discordant paleomagnetic directions reported from plutons of the western canadian cordillera

gaussian analysis of temperature effects on the reflectance spectra of mafic minerals in the 1 μm region gaussian band fitting analysis has been applied to the reflectance spectra of mafic silicates which are of geologic importance throughout much of the solar system reflectance spectra obtained over a sample temperature range of 80 to 448 k of olivine clinopyroxene and orthopyroxene were used in order to characterize the spectral changes in the 1 m wavelength region of these minerals as a function of temperature four gaussians are required to characterize the olivine while two gaussians are necessary to characterize both the orthopyroxene and clinopyroxene the trends of the individual gaussian parameters integrated area width and center position are presented as a function of temperature for each mineral the characterization by gaussian analysis of the 1 m absorption feature of all minerals yields consistent trends in center position integrated area and width that may prove useful in quantitative determination of these minerals in mineral mixtures the gaussian analysis of olivine for the three primary band components is qualitatively consistent with previous crystal field transition assignments of fe2 in the m 1 and m 2 crystallographic sites the trends of the determined olivine gaussian center positions imply that site symmetry is more important in determining transition energies than metal oxygen distances the result of the gaussian analysis for orthopyroxene is consistent with the need for two gaussians to describe an asymmetric band the gaussian analysis of the clinopyroxene is consistent with previous assignments of crystal field transitions due to fe2 in the m 1 and m 2 crystallographic sites

exploration drilling and reservoir model of the platanares geothermal system honduras central america abstract results of drilling logging and testing of three exploration core holes combined with results of geologic and hydrogeochemical investigations have been used to present a reservoir model of the platanares geothermal system honduras geothermal fluids circulate at depths 1 5 km in a region of active tectonism devoid of quaternary volcanism large artesian water entries of 160 to 165 c geothermal fluid in two core holes at 625 to 644 m and 460 to 635 m depth have maximum flow rates of roughly 355 and 560 l min respectively which are equivalent to power outputs of about 3 1 and 5 1 mw thermal dilute alkali chloride reservoir fluids tds 1200 mg kg are produced from fractured miocene andesite and cretaceous to eocene redbeds that are hydrothermally altered fracture permeabillity in producing horizons is locally greater than 1500 and bulk porosity is 6 a simple fracture dominated volume impedance model assuming turbulent flow indicates that the calculated reservoir storage capacity of each flowing hole is approximately 9 7 106 l kg cm 2 tritium data indicate a mean residence time of 450 yr for water in the reservoir multiplying the natural fluid discharge rate by the mean residence time gives an estimated water volume of the platanares system of 0 78 km3 downward continuation of a 139 c km conductive gradient at a depth of 400 m in a third core hole implies that the depth to a 225 c source reservoir predicted from chemical geothermometers is at least 1 5 km uranium thorium disequilibrium ages on calcite veins at the surface and in the core holes indicate that the present platanares hydrothermal system has been active for the last 0 25 m y

a u th calcite isochron age from an active geothermal field in new zealand we report here the first u th disequilibrium age for a hydrothermal mineral from an active geothermal system in new zealand vein calcite recovered from a depth of 389 m in well thm 1 at the tauhara geothermal field has an age of 99 44 ka bp this age was determined using a leachate leachate isochron technique on four silicate containing sub samples of calcite from a single vein although the error on this isochron age is considerable it is significantly younger than the earlier estimated age of 200 ka bp for the onset of activity at the tauhara system and probably records the date of brecciation and veining which may be associated with volcanic activity at the adjacent dacitic tauhara volcanic complex these results demonstrate that hydrothermal vein calcite can now be dated directly and opens the way for more detailed studies of the evolution of the new zealand geothermal systems

alteration in the madera limestone and sandia formation from core hole vc 1 valles caldera new mexico core hole vc 1 penetrated the southwestern ring fracture zone of the 1 1 ma valles caldera and at a depth of 333 m intersected the top of the paleozoic section including the abo formation madera limestone and sandia formation reaching a total depth of 856 m the paleozoic rocks which consist of thin bedded limestone siltstone mudstone sandstone and local conglomerate are overlain by volcanic rocks of the caldera moat that are less than 0 6 ma diagenetic and at least three hydrothermal alteration stages were identified in the madera limestone and sandia formation diagenetic clay alteration was pervasive throughout the sedimentary rocks volcanic activity at 16 5 ma and continuing through the formation of the valles caldera resulted in high thermal gradients which caused recrystallization of diagenetic clay minerals interstratified smectite illite is the most diagnostic clay mineral throughout the section structurally the illite component in the ordered interstratified illite smectite changes gradationally from 70 at the top of the madera limestone to 95 at the base of the section in the sandia formation pyrite that occurs as small clots and lenses as well as finely disseminated is interpreted as being of diagenetic origin especially in organic rich beds low permeability of much of the paleozoic section precluded the deposition of hydrothermal minerals except in fractures and intergranular space in some of the more permeable sandstone and brecciated horizons three stages of hydrothermal mineral deposition are defined stage i is widespread and includes mainly chlorite calcite pyrite and interstratified smectite illite that was formed prior to caldera development at temperatures approximating 200 c stage ii is characterized by quartz sericite and scarce sulfides deposited locally by fluids at approximately 275 c shortly before or at the time of early caldera related volcanism the stage iii hydrothermal event associated with formation of the valles caldera caused complex brecciation accompanied by deposition of phengite and molybdenite at temperatures locally approaching 300 c mostly in rocks underlying the madera limestone during the present drilling program thermal aquifers were encountered at 483 m 113 c 533 m 125 c and 845 m 184 c very close to the stage ii and iii mineralized zones however measured temperatures of the present hydrothermal system are much lower than during the main hydrothermal events good permeability has been maintained in these three levels for a long time while the rest of the madera limestone and sandia formation was sealed by hydrothermal mineral precipitation

microthermometry of fluid inclusions from the vc 1 core hole in valles caldera new mexico fluid inclusions in vein quartz and calcite from core samples of the vc 1 hole were studied with microscope heating freezing and crushing stages all samples originate from hydrothermally altered paleozoic rocks predating formation of the jemez mountains volcanic field and valles caldera most homogenization temperatures th of the liquid rich inclusions are above the present well temperature but some th of primary inclusions from 515 m and those of secondary inclusions from 723 m fit the present well temperature curve measured 10 months after completion of the well the maximum temperature recorded by the primary inclusions is 275 c from hydrothermal quartz in the sandia formation at 811 m depth the total range of th for samples from several depths 90 c indicates cooling from the maximum temperature the salinity of fluid inclusions in hydrothermal quartz and calcite is generally low 1 wt nacl eq high salinity fluid up to 5 wt nacl eq has been found in several calcite veins from the lower part of the madera limestone the salinity decreases with decrease of th of the secondary inclusions and that with lowest th at the lower part of the madera limestone is similar to those from the other depths these data show that early hot water circulation system involved several types of fluid whereas the later one was a homogeneous fluid the salinity of fluid inclusions in detrital quartz presumably inherited inclusions is higher than that in hydrothermal minerals some of these inclusions show extraordinary low temperatures of final melting point of ice about 40 c suggesting that a cacl2 component is present co2 contents in fluid inclusions were estimated by the bubble behavior on crushing crushing results indicate that co2 content of the early fluid is 0 35 wt and that of the later fluid is 0 2 0 3 wt geothermal fluid trapped in the fluid inclusions representing the present temperature regime is comparable in composition to those from the baca geothermal field inside the caldera and to those from hot springs in san diego canyon

precipitation source inferred from stable isotopic composition of pleistocene groundwater and carbonate deposits in the western desert of egypt an atlantic source of precipitation can be inferred from stable isotopic data h and o for fossil groundwaters and uranium series dated carbonate spring deposits from oases in the western desert of egypt in the context of available stable isotopic data for fossil groundwaters throughout north africa the observed isotopic depletions delta d 72 to 81 per thousand delta sup 18 o 10 6 to 11 5 per thousand of fossil ge 32 000 yr b p groundwaters from the nubian aquifer are best explained by progressive condensation of water vapor from paleowesterly wet oceanic air masses that traveled across north africa and operated at least as far back as 450 000 yr before the present the values of delta sup 18 o 17 1 to 25 9 per thousand for 45 000 to 450 000 yr old tufas and vein filling calcite deposits from the kharga and farafra oases are consistent with deposition from groundwaters having oxygen isotopic compositions similar to those of fossil groundwaters sampled recently at these locations

growth of bivalves at deep sea hydrothermal vents along the galapagos rift direct measurements of shell growth of an unclassified mussel from active hydrothermal vents along the galapagos rift reveal growth rates of approxmately 1 centimeter per year for mature specimens the largest mussel collected with shell length of 18 4 centimeters was estimated to be 19 7 years old at the time of sampling recorded growth rates are among the highest documented for deep sea species

fractures in mudrocks advances in constraining timing and understanding mechanisms abstract recent advances in fracture timing techniques have led to new insights about sequences and mechanisms of fracture formation in mudrocks methods to constrain fracture timing in mudrocks include i field evidence including crosscutting relationships and evidence of compaction ii petrographic evidence including signs of soft sediment deformation and diagnostic mineral assemblages or textures iii stable isotopic evidence iv thermometric dating using burial history modelling and v radiometric age dating in this contribution we briefly review each method with salient examples from the literature many documented examples of mudrock hosted fractures formed during early burial a non intuitive finding that demands a re assessment of our assumptions about what types of materials can develop opening mode fractures in general the style and distribution of fractures varies dramatically based on fracture timing highlighting the importance of constraining timing for predicting fracture patterns and interpreting their mechanisms including the role of fluid flow

radium geochemistry of ground waters in paleozoic carbonate aquifers midcontinent usa the purpose of this study was to elucidate the processes controlling the distribution and behavior of the longerlived ra isotopes in continuous paleozoic carbonate aquifers of parts of missouri kansas and oklahoma activities of 228 ra and 226 ra were analyzed in fresh and saline ground waters brines and rocks the fluids have a wide salinity range 200 250 000 mg l 1 total dissolved solids the 226 ra activity ranges from 0 66 7660 dpm kg 1 and correlates with salinity and other alkaline earth element ca sr and ba concentrations the range of 228 ra 226 ra ratios in the fluids 0 06 1 48 is similar to that in the aquifer rocks 0 21 1 53 the relatively low mean fluid 228 ra 226 ra ratio 0 30 reflects the low th u ratio of the predominant carbonate aquifer rock radium occurs mostly r77 as ra 2 species in the fluids salinity dependent sorption desorption processes with log k values from 10 0 10 4 and negatively correlated with salinity involving th enriched surface coatings on aquifer flow channels can explain the rapid solid fluid transfer of ra isotopes in the system and the correlation of ra with

eros shape topography and slope processes stereogrammetric measurement of the shape of eros using images obtained by near s multispectral imager provides a survey of the major topographic features and slope processes on this asteroid this curved asteroid has radii ranging from 3 1 to 17 7 km and a volume of 2535 20 km3 the center of figure is within 52 m of the center of mass provided by the navigation team this minimal difference suggests that there are only modest variations in density or porosity within the asteroid three large depressions 10 8 and 5 3 km across represent different stages of degradation of large impact craters slopes on horizontal scales of 300 m are nearly all less than 35 although locally scarps are much steeper the area distribution of slopes is similar to those on ida phobos and deimos regions that have slopes greater than 25 have distinct brighter markings and have fewer large ejecta blocks than do flatter areas the albedo patterns that suggest downslope transport of regolith have sharper boundaries than those on phobos deimos and gaspra the morphology of the albedo patterns their lack of discrete sources and their concentration on steeper slopes suggest transport mechanisms different from those on the previously well observed small bodies perhaps due to a reduced relative effectiveness of impact gardening on eros regolith is also transported in talus cones and in connected sinuous paths extending as much as 2 km with some evident as relatively darker material talus material in at least one area is a discrete superposed unit a feature not resolved on other small bodies flat floored craters that apparently contain ponded material also suggest discrete units that are not well mixed by impacts

boulders and ponds on the asteroid 433 eros abstract there are 300 features on the asteroid 433 eros that morphologically resemble ponds flat floored and sharply embaying the bounding depression in which they sit because boulders on eros are apparently eroding in place and because ponds with associated boulders tend to be larger than ponds without blocks we propose that ponds form from thermally disaggregated and seismically flattened boulder material under the assumption that repeated day night cycling causes material fatigue that leads to erosion of the boulders results from a simple boulder emplacement thermal erosion model with boulders emplaced in a few discrete events i e large impacts match well the observed size distribution under this scenario the subtle color differences of ponds somewhat bluer than the rest of the surface might be due to some combination of less space weathered material and density stratification of silicate rich chondrules and more metal rich matrix from a disaggregated boulder volume estimates of ponds derived from near laser rangefinder profiles are consistent with what can be supplied by boulders ponds are also observed to be concentrated in regions of low slope and high elevation which suggests the presence of a less mobile regolith and thus a contrast in the resistance to seismic shaking between the pond material and the material that makes up the bounding depression future tests include shake table experiments and temperature cycling fatigue of ordinary chondrites to test the thermal erosion mechanism

the geology of 433 eros the global high resolution imaging of asteroid 433 eros by the near earth asteroid rendezvous near shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small s type asteroid eros displays a variety of surface features and evidence of a substantial regolith large scale facets grooves and ridges indicate the presence of at least one global planar structure directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object as with other small objects impact craters dominate the overall shape as well as the small scale topography of eros depth diameter ratios of craters on eros average 0 13 but the freshest craters approach lunar values of 0 2 ejecta block production from craters is highly variable the majority of large blocks appear to have originated from one 7 6 km crater shoemaker the interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of phobos this lack of mechanical boundaries and the abundant evidence of regolith in nearly every high resolution image suggests a gradation in the porosity and fracturing with depth the density of small craters is deficient at sizes below 200 m relative to predicted slopes of empirical saturation this characteristic which is also found on parts of phobos and lunar highland areas probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith eros displays a variety of regolith features such as debris aprons fine grained ponded deposits talus cones and bright and dark streamers on steep slopes indicative of efficient downslope movement of regolith these processes serve to mix materials in the upper loose fragmental portion of the asteroid regolith in the instance of ponded materials and crater wall deposits there is evidence of processes that segregate finer materials into discrete deposits the near observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the near shoemaker spacecraft

age dating of sulfide deposits from axial and off axial structures on the east pacific rise near 12 50 n abstract during several cruises clipperton 1981 cyatherm 1982 and geocyarise leg 3 1984 conducted between 12 40 n and 12 54 n on the east pacific rise massive sulfide deposits have been dredged and recovered by the diving saucer cyana these well localized and documented samples have been analyzed for their 210 pb pb ratio and uranium series disequilibrium in view of dating the hydrothermal phenomenon using samples which are presently forming the initial 210 pb pb ratio has been established as 0 60 0 06 ten sulfide samples from the central graben near 12 50 n have ages less than about 10 years and are younger than most of the deposits found at 21 n on the east pacific rise one sample from the eastern rim of the graben presents an age of about 150 years two off axis structures with hydrothermal sulfide deposits were studied the first is a semi circular volcanic structure where low temperature hydrothermal vents were observed at 500 m and 1000 m from the rise axis sulfide samples collected from these sites yielded ages of about 2000 years further east about 6 km from the rise axis the second off axis structure called south eastern se seamount presents thick inactive sulfide deposits as well as mn rich and nontronite deposits an age around 20 000 years has been found for these deposits these ages are discussed and taking into account the asymmetrical structure of the ridge near 12 43 n it is concluded that the formation of the se seamount occurred 20 000 years ago on a basement of about 100 000 years old accompanied by an extensive hydrothermal event this indicates that an important eastward shift 4 5 km from the graben of the volcano hydrothermal activity took place in this area 12 43 n

age and isotopic constraints on pleistocene pluvial episodes in the western desert egypt abstract north africa has undergone drastic climatic changes over the past several hundred thousand years the timing of humid intervals called pluvials was investigated by uranium series disequilibrium dating of travertines from the kurkur oasis western desert egypt the youngest and best dated travertines 70 160 ka are found in wadi kurkur and include spring and lacustrine units exposed as 2 to 3 m high terraces travertines having an age of approximately 191 220 ka are exposed by differential erosion as linear mounds produced by spring systems over fracture zones in ancient wadis the oldest travertines having ages 260 ka are extensive cap limestone units above the oasis and were deposited in paludal and lacustrine environments oxygen isotope ratios were measured for the wadi travertines 18o values ranging from 16 7 to 19 1 smow and for spring mound travertines 18 5 20 5 equilibrium oxygen isotope fractionation calculations indicate that the kurkur travertines were deposited from waters having 18o values similar to ancient western desert groundwaters 11 sonntag et al 1978a b thorweithe 1990 sultan et al 1996 the ages of the travertines correspond to times of monsoonal maxima eustatic sea level high stands and interglacial maxima rainfall producing these groundwaters and travertines was significantly fractionated during atmospheric transport in contrast to modern meteoric waters 2 09 joseph et al 1992 implying a distant source for the pluvial waters increased precipitation recharge of western desert groundwaters and resultant travertine deposition are interpreted to be consequences of milankovitch insolation cycle forcing through enhanced atlantic and indian ocean monsoons during interglacial time periods

space weathering on eros constraints from albedo and spectral measurements of psyche crater we present combined multi spectral imager msi 0 95 m and near infrared spectrometer nis 0 8 2 4 m observations of psyche crater on s type asteroid 433 eros obtained by the near earth asteroid rendezvous near shoemaker spacecraft at 5 3 km in diameter psyche is one of the largest craters on eros which exhibit distinctive brightness patterns consistent with downslope motion of dark regolith material overlying a substrate of brighter material at spatial scales of 620 m spectrum psyche crater wall materials exhibit albedo contrasts of 32 40 at 0 946 m associated spectral variations occur at a much lower level of 4 8 2 4 we report results of scattering model and lunar analogy investigations into several possible causes for these albedo and spectral trends grain size differences olivine pyroxene and troilite variations and optical surface maturation we find that the albedo contrasts in psyche crater are not consistent with a cause due solely to variations in grain size olivine pyroxene or lunar like optical maturation a grain size change sufficient to explain the observed albedo contrasts would result in strong color variations that are not observed olivine and pyroxene variations would produce strong band correlated variations that are not observed a simple lunar like optical maturation effect would produce strong reddening that is not observed the contrasts and associated spectral variation trends are most consistent with a combination of enhanced troilite a dark spectrally neutral component simulating optical effects of shock and lunar like optical maturation these results suggest that space weathering processes may affect the spectral properties of eros materials causing surface exposures to differ optically from subsurface bedrock however there are significant spectral differences between eros proposed analog meteorites ordinary chondrites and or primitive achondrites and eros freshest exposures of subsurface bright materials after accounting for all differences in the measurement units of our reflectance comparisons we have found that the bright materials on eros have reflectance values at 0 946 m consistent with meteorites but spectral continua that are much redder than meteorites from 1 5 to 2 4 m most importantly we calculate that average eros surface materials are 30 40 darker than meteorites

detection of temperature dependent spectral variation on the asteroid eros and new evidence for the presence of an olivine rich silicate assemblage data obtained by the near infrared spectrometer carried by the near shoemaker spacecraft show that the spectral properties of the asteroid eros vary with temperature the manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface the near ir temperature dependent spectral properties of eros in the northern hemisphere and for two individual regions on the surface show clear evidence of the presence of the mineral olivine and are a close match to the temperature spectral behavior of ll type ordinary chondrite meteorites while the presence of other olivine rich meteorites cannot be excluded h type ordinary chondrites are clearly too pyroxene rich to be permitted as a major surface component of eros the results of the thermal spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of eros

quaternary deformation in the eastern pamirs tadzhikistan and kyrgyzstan active deformation in the eastern pamir of central asia is concentrated on the margins of the orogen with minor deformation within the high terrain along the trans alai mountain front at the northern perimeter of the orogen quaternary thrusting is documented by uplifted pediments now at 500 m above the piedmont holocene fault scarps and large earthquakes with n to nw oriented p axes seismicity in the interior of the orogen outlines a n s belt that includes normal faulting events with e w oriented t axes n s striking active normal faults in the interior lake karakul region are compatible with these earthquakes they define an asymmetric graben with a master fault at the western basin margin in the southern pamirs dextral strike slip faults root in the dextral karakorum fault which bounds the pamirs to the east a mixture of dextral and reverse offsets totalling 135 m in pleistocene terraces and 8 m in late pleistocene holocene deposits demonstrates contemporary transpression indicating average displacement rates of 1 mm yr the concentration of young thrusts along the trans alai the northward migration of thrusting and the scarcity of other large scale shortening features within the eastern pamirs suggest that this part of the orogen moves northward en bloc and causes the progressive annihilation of the intermontane alai valley widespread dextral shear in the eastern pamirs both to the south and north of the extensional karakul depression and combined dextral strike slip and normal faulting in the muji tashgorgan graben of the chinese pamirs are interpreted as localized space accommodation phenomena formed during progressive transfer of compressional deformation along a dextral strike slip deformation zone with extensional stepovers

possible temperature variation effects on the interpretation of spatially resolved reflectance observations of asteroid surfaces abstract the visible and near ir spectral reflectance of some minerals is a function of temperature hence surface temperature variation must be considered for mineralogical interpretation of spectral reflectance data obtained from a spatially resolved surface which has a temperature distribution an example is presented to illustrate the errors which can be encountered when interpreting the spectral reflectance of a silicate mineral assemblage measured at various temperatures that might be expected across an asteroid surface independent knowledge of the surface temperature distribution would allow the optimal extraction of mineralogical information in such cases

impact history of eros craters and boulders abstract preliminary measurements of craters and boulders have been made in various locations on eros from images acquired during the first nine months of near shoemaker s orbital mission including the october 2000 low altitude flyover we offer some very preliminary qualitative analysis of later laf images and very high resolution images obtained during near s landing on 12 february 2001 craters on eros 100 m diameter closely resemble the saturated crater population of ida eros is more heavily cratered than gaspra but lacks the saturated giant craters of mathilde these craters and the other large scale geological features were formed over a duration of very roughly 2 gyr while eros was in the main asteroid belt between the time when its parent body was disrupted and eros was injected into an earth approaching orbit probably tens of myr ago saturation equilibrium had been expected to shape eros crater population down to very small sizes as on the lunar maria however craters

caldera resurgence during magma replenishment and rejuvenation at valles and lake city calderas a key question in volcanology is the driving mechanisms of resurgence at active recently active and ancient calderas valles caldera in new mexico and lake city caldera in colorado are well studied resurgent structures which provide three crucial clues for understanding the resurgence process 1 within the limits of 40ar 39ar dating techniques resurgence and hydrothermal alteration at both calderas occurred very quickly after the caldera forming eruptions tens of thousands of years or less 2 immediately before and during resurgence dacite magma was intruded and or erupted into each system this magma is chemically distinct from rhyolite magma which was resident in each system 3 at least 1 km of structural uplift occurred along regional and subsidence faults which were closely associated with shallow intrusions or lava domes of dacite magma these observations demonstrate that resurgence at these two volcanoes is temporally linked to caldera subsidence with the upward migration of dacite magma as the driver of resurgence recharge of dacite magma occurs as a response to loss of lithostatic load during the caldera forming eruption flow of dacite into the shallow magmatic system is facilitated by regional fault systems which provide pathways for magma ascent once the dacite enters the system it is able to heat remobilize and mingle with residual crystal rich rhyolite remaining in the shallow magma chamber dacite and remobilized rhyolite rise buoyantly to form laccoliths by lifting the chamber roof and producing surface resurgent uplift the resurgent deformation caused by magma ascent fractures the chamber roof increasing its structural permeability and allowing both rhyolite and dacite magmas to intrude and or erupt together this sequence of events also promotes the development of magmatic hydrothermal systems and ore deposits injection of dacite magma into the shallow rhyolite magma chamber provides a source of heat and magmatic volatiles while resurgent deformation and fracturing increase the permeability of the system these changes allow magmatic volatiles to rise and meteoric fluids to percolate downward favouring the development of hydrothermal convection cells which are driven by hot magma the end result is a vigorous hydrothermal system which is driven by magma recharge

effects of temperature on remotely sensed mineral absorption features laboratory spectral reflectance of mafic silicates has been measured over a temperature range characteristic of solar system objects to study the variation of diagnostic mineral absorption bands this information has become increasingly important with recent improvements in the quality of remotely sensed planetary data and the concurrent increase in sophistication of quantitative and qualitative spectrum analysis techniques in this study visible and near ir reflectance spectra 0 4 2 5 m of pyroxenes and olivine were obtained over a sample temperature range of 80 448 k these are the first published reflectance data for these minerals at temperatures significantly below ambient 300 k additionally thermal radiation emitted from the samples at elevated temperatures was effectively removed disclosing for the first time the high temperature reflectance behavior of pyroxenes in the diagnostic 2 m spectral region as expected from basic physical considerations fe2 crystal field absorptions in all samples become narrower with decreasing temperature the three components of the composite olivine band centered near 1 m become better resolved with decreased temperature and show changes in relative absorption strength there is not however any significant wavelength shift of the olivine reflectance minimum both orthopyroxene and clinopyroxene spectra show dramatic changes in band symmetry with temperature with the greatest change in the longer wavelength edge despite these significant changes in shape little if any change is observed in the wavelength position of reflectance minima of pyroxene absorptions near 1 m the 2 m pyroxene absorptions in contrast demonstrate major shifts of reflectance minima but in different directions in orthopyroxene spectra the band shifts to longer wavelengths with increased temperature while for the clinopyroxene spectra the band shifts to shorter wavelengths this behavior results in greatly improved spectral differentiation of orthopyroxene and clinopyroxene components in a mixture such as a basalt at reduced temperatures application of the results presented here to remote sensing mineral characterization techniques currently in use for determination of pyroxene composition can provide a moderate improvement to quantitative interpretations from 5 to 20 wt feo for orthopyroxenes and 5 wt cao for clinopyroxenes depending on planetary surface temperature

mobility and depositional controls of radioelements in hydrothermal systems at the long valley and valles calderas abstract the loci and abundance of u and th were examined in tuffaceous rocks encompassing hydrothermal systems at the long valley caldera california and the valles caldera new mexico aspects of these systems may be analogous to conditions expected in a potential site for a high level waste repository in welded tuff examination of radioelements in core from scientific drill holes at these sites was accomplished by gamma ray spectrometry and fission track radiography in the lateral flowing hydrothermal system at the long valley caldera where temperatures range from 140 to 200 c u is concentrated to 20 ppm in fe rich zones of varved tuff and to 50 ppm with fe rich mineral phases in tuff fragments of a calcite cemented breccia u series disequilibrium in some of these samples suggests mobilization deposition of parent u and or its daughters in the vapor zone of the valles caldera s hydrothermal system temperature 100 c the concordance of high u low th u and decreasing whole rock o isotope ratios suggests that u was concentrated in response to hydrothermal circulation when the system was formerly liquid dominated in the underlying present day liquid dominated zone temperature to 210 c u up to several tens of parts per million occurs with pyrite and fe oxide minerals and in concentrations to several percents with a ti nb y rare earth mineral in the valles system s outflow zone u is also concentrated in fe rich zones as well as in carbonaceous rich zones in the paleozoic sedimentary rocks that underlie the quaternary tuff th associated with accessory minerals predominates in breccia zones and in a mineralized fault zone near the base of the paleozoic sedimentary sequence relatively high concentrations of u occur in springs representative of water recharging the valles caldera s hydrothermal system in contrast considerably lower u concentrations occur in hot waters 220 c and in the system s outflow plume suggesting that u is concentrating in the hotter part of the system the long valley and valles observations indicate that u and ra are locally mobile under hydrothermal conditions and that reducing conditions associated with fe rich minerals and carbonaceous material are important factors in the adsorption of u and thus can retard its transport in water at elevated temperature

borax lake a thermal lake confined within a biomorphic mound pueblo valley oregon usa abstract relations among geothermal system dynamics evolution of an 8 m thick biomorphic mound and requirements to protect critical habitat of gila boraxobius a fish protected under the endangered species act of 1973 were explored at borax lake a shallow thermal lake in the tectonically active northwestern basin and range province neutral ph thermal water at 105 c discharges within a carrot shaped vent at a depth of 29 m and rapidly mixes within the vent and lake which is mostly 1 and proximity of seismic sources indicates the mound may be susceptible to liquefaction and slope failure during dynamic earthquake loading borax lake is the unique product of the geothermal system and the biological communities it supports portions of the mound may have failed in the past during seismic loading eroded and been rebuilt by processes similar to those active today

strike slip deformation and u th dating of travertine deposition examples from north anatolian fault zone bolu and yenicag basins turkey the relation of the travertine deposition outcropping in the bolu and yenicaga basins located to the west of the north anatolian fault system nafs with the faulting of the zone nafz of the system in this part is examined these travertines are dated by u series travertine formations in the bolu and yenicaga basins are deposited in different ways and localities on pressure ridges in the releasing restraining bends of the strike slip faults and around the intersection of faults while the travertines of the uctepeler and belemur hill are deposited on the pressure ridges the travertines deposited in cigdem hill and cepni are deposited in the releasing restraining bends of the faults of the zone and the travertines in golkoy are deposited on the foot wall of the intersecting of the normal faults which encircles the west side of the basin as a result of the dating of the travertines on the study area by u series method the age data range between 52 649 8040 a and 96 308 17 674 a and between 17 962 1671 a and 133 463 76 882 a in the yenicaga and basins respectively information on fault activity is gained as a result of the dating of the travertines deposited due to the strike slip deformation on different segments of the nafz

olivine dominated asteroids and meteorites distinguishing nebular and igneous histories melting models indicate that the composition and abundance of olivine systematically co vary and are therefore excellent petrologic indicators however heliocentric distance and thus surface temperature has a significant effect on the spectra of olivine rich asteroids we show that composition and temperature complexly interact spectrally and must be simultaneously taken into account in order to infer olivine composition accurately we find that most 7 9 of the olivine dominated asteroids are magnesian and thus likely sampled mantles differentiated from ordinary chondrite sources e g pallasites however two other olivine rich asteroids 289 nenetta and 246 asporina are found to be more ferroan melting models show that partial melting cannot produce olivine rich residues that are more ferroan than the chondrite precursor from which they formed thus even moderately ferroan olivine must have non ordinary chondrite origins and therefore likely originate from oxidized r chondrites or melts thereof which reflect variations in nebular composition within the asteroid belt this is consistent with the meteoritic record in which r chondrites and brachinites are rare relative to pallasites