molybdenum mineralization in an active geothermal system valles caldera new mexico shallow sub ore grade molybdenite mineralization has been discovered in the active high temperature geothermal system penetrated by continental scientific drilling program corehole vc 2a at sulfur springs in the western ring fracture zone of the valles caldera new mexico this mineralization is hosted by fractured quartz sericitized intracaldera ash flow tuffs younger than 1 12 ma the molybdenite is an unusual poorly crystalline variety that occurs in vuggy veinlets and breccia cements also containing quartz sericite illite pyrite and fluorite as well as local sphalerite rhodochrosite and chalcopyrite fluid inclusion data suggest that this assemblage was deposited from very dilute solutions at temperatures near 200 sup 0 c geochemical modeling indicates that under restricted ph and fo sub 2 conditions at 200 sup 0 c the molybdenite and associated phases would be in equilibrium with hydrothermal fluids now circulating in the deep subsurface the shallow molybdenite zone intersected in vc 2a may be the near surface expression of deep climax type stockwork molybdenum mineralization

estimation of quality factors from cmp records estimates of the quality q factor are commonly obtained from vertical seismic data or stacked surface seismic data this paper describes a method that allows q factor to be estimated directly from common midpoint cmp gathers absorption of the wavefield is dependent on three parameters frequency traveltime in the medium and medium q factor assuming that the amplitude spectrum of the seismic source signature may be modeled by that of a ricker wavelet we derive an analytical relation between q factor and seismic data peak frequency variation both along offset and vertical time direction the q factor is estimated from cmp gathers using a layer stripping approach

conodont color and textural alteration an index to regional metamorphism contact metamorphism and hydrothermal alteration experimental and field data are used to extend the utility of conodonts as semi quantitative thermal indices into the regimes of regional and contact metamorphism as well as hydrothermal alteration an arrhenius plot of data from induced conodont color alteration by pyrolysis in air at 1 atm was used to generate the geologic temperatures for conodont color alteration indices cai above 300 c that is for cai values of 5 through 8 such cai values occur in very low to medium grade regionally metamorphosed contact metamorphosed and hydrothermally altered rocks the uniformity or variability of cai values within a sample together with conodont texture can help to distinguish grades and environments of metamorphism particularly in metacarbonate sequences induced cai by pyrolysis in a water methane mixture at kbar results in retardation of cai and in a disparate mixture of both low and high cai values within each experimental sample in this system color alteration processes above a cai of 2 to 3 seem to change from predominantly carbonization to predominantly loss of organic matter presumably by oxidation and volatilization of oxides these experiments approximate the type of cai mixture characteristically found in conodonts recovered from hydrothermally altered rocks these data indicate that cai values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization

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

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

zeolites in hydrothermally altered rocks over the past 40 years two universally accepted maxims of geology dealing with zeolite minerals have been shown to be incorrect the first is that zeolites occur primarily as cavity fillings in basaltic igneous rocks and the second is that these zeolites crystallized from so called hydrothermal solutions i e thermal waters from depth we recognize today that enormous quantities of zeolites occur as low temperature low pressure alteration products of pyroclastic material in sedimentary rocks and that many of the zeolites filling vugs and cavities in basalts and traprocks are actually diagenetic in origin having precipitated directly from ground water percolating through the rock mass see walker 1951 1959 1960a see walker b nashar and davies 1960 this is not to say that zeolite deposits of hydrothermal origin do not exist far from it the extensive zones of zeolites surrounding hot spring and geothermal activity in yellowstone national park wyoming wairakei new zealand reykjavik iceland pauzhetsk kamchatka russia lardello italy and takenoyu japan and in the vicinity of magmatic ore deposits such as the kuroko deposits of northern japan suggest that waters arising and or heated from below have indeed played an important role in their formation hydrothermal alteration can be defined as the crystallization of mineral material or the alteration of preexisting mineral material that has taken place in the presence of hot solutions the composition and temperature of which were wholly or partially the result of a deep seated magmatic body these reactions usually take place under comparatively high solution solid ratios over a wide temperature range and under low pressure conditions hydrothermal alteration is controlled by many factors including solution chemistry temperature rock permeability and the composition and stability of the starting material although hydrothermal solutions are very diverse in composition alkaline solutions are generally most favorable for formation of zeolites the temperature

hydrothermal brecciation in the jemez fault zone valles caldera new mexico results from continental scientific drilling program core hole vc 1 an unusual breccia sequence penetrated in the lower 30 m of continental scientific drilling program core hole vc 1 total depth 856 m records a complex hydrothermal history culminating in hydraulic rock rupture and associated alteration at the edge of the quaternary valles caldera the breccias both tectonic and hydrothermal in origin were formed in the jemez fault zone near the intersection of this major regional structure with the caldera s ring fracture margin tectonic breccias in the sequence are contorted crushed and sheared coexisting hydrothermal breccias lack such frictional textures but display matrix flow foliation and prominent clast rounding features characteristic of fluidization these hydrothermal breccias were intensely altered during at least five major stages to quartz illite phengite pyrite aggregates traces of molybdenite occur locally this assemblage indicates interaction with hydrothermal fluid at temperatures in excess of 200 c the extrapolated present maximum temperature of 184 c in the breccia zone therefore represents considerable cooling since these phases were formed fluid inclusions in the breccias also preserve evidence of the prior passage of hotter fluids the inclusions are principally two phase liquid rich secondary in origin and concentrated in hydrothermal quartz older high salinity inclusions unrelated to brecciation homogenize in the temperature range 189 246 c younger inclusions in part of interbreccia origin are low salinity and homogenize in the temperature range 230 283 c locally coexisting liquid and vapor rich inclusions document periodic boiling of the dilute fluids these fluid inclusion data along with the probable age of the hydrothermal breccias 1 5 ma the assumed depth at which they developed about 515 m and the contemporaneous state of stress extensional can be combined to model hydrothermal brecciation at the vc 1 site the minimum fluid pressure pfr required to hydrofracture these rocks was probably about 7 5 mpa 0 0146 mpa m a boiling point versus depth curve based on these pfr values graphically defines the physical conditions prevailing when the breccias were formed when fluid pressure at the assumed depth of brecciation exceeded that curve in response to rapid release of confining pressure possibly augmented by renewed heating flashing hydrothermal fluid fractured the enclosing rock large overpressures most likely induced by sudden seismic cracking of a hydrothermally sealed portion of the jemez fault zone led to local fluidization of the resulting breccias late quartz veining hydrothermal alteration and molybdenite mineralization were probably produced by the fluids responsible for brecciation

a petrogenetic model for the origin and compositional variation of the martian basaltic meteorites the major element trace element and isotopic compositional ranges of the martian basaltic meteorite source regions have been modeled assuming that planetary differentiation resulted from crystallization of a magma ocean the models are based on low to high pressure phase relationships estimated from experimental runs and estimates of the composition of silicate mars from the literature these models attempt to constrain the mechanisms by which the martian meteorites obtained their superchondritic cao al2o3 ratios and their source regions obtained their parent daughter 87 rb 86 sr 147 sm 144 nd and 176 lu 177 hf ratios calculated from the initial sr nd and hf isotopic compositions of the meteorites high pressure experiments suggest that majoritic garnet is the liquidus phase for mars relevant compositions at or above 12 gpa early crystallization of this phase from a martian magma ocean yields a liquid characterized by an elevated cao al2o3 ratio and a high mg olivine pyroxene garnet dominated cumulates that crystallize subsequently will also be characterized by superchondritic cao al2o3 ratios melting of these cumulates yields liquids with major element compositions that are similar to calculated parental melts of the martian meteorites furthermore crystallization models demonstrate that some of these cumulates have parent daughter ratios that are similar to those calculated for the most incompatible element depleted source region i e that of the meteorite queen alexandra que 94201 the incompatible element abundances of the most depleted que 94201 like source region have also been calculated and provide an estimate of the composition of depleted martian mantle the incompatible element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted earth s mantle melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of que 94201 e g ba th k p hf zr and heavy rare earth elements fairly well but does not reproduce the abundances of rb u ta and light rare earth elements the source regions for meteorites such as shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile melting of this hybrid source yields liquids with major element abundances and incompatible element patterns that are very similar to the shergotty bulk rock

efficient 3 d frequency domain mono parameter full waveform inversion of ocean bottom cable data application to valhall in the visco acoustic vertical transverse isotropic approximation computationally efficient 3 d frequency domain full waveform inversion fwi is applied to ocean bottom cable data from the valhall oil field in the visco acoustic vertical transverse isotropic vti approximation frequency domain seismic modelling is performed with a parallel sparse direct solver on a limited number of computer nodes a multiscale imaging is performed by successive inversions of single frequencies in the 3 5 10 hz frequency band the vertical wave speed is updated during fwi while density quality factor qp and anisotropic thomsen s parameters and are kept fixed to their initial values the final fwi model shows the resolution improvement that was achieved compared to the initial model that was built by reflection traveltime tomography this fwi model shows a glacial channel system at 175 m depth the footprint of drifting icebergs on the palaeo seafloor at 500 m depth a detailed view of a gas cloud at 1 km depth and the base cretaceous reflector at 3 5 km depth the relevance of the fwi model is assessed by frequency domain and time domain seismic modelling and source wavelet estimation the agreement between the modelled and recorded data in the frequency domain is excellent up to 10 hz although amplitudes of modelled wavefields propagating across the gas cloud are overestimated this might highlight the footprint of attenuation whose absorption effects are underestimated by the homogeneous background qp model qp 200 the match between recorded and modelled time domain seismograms suggests that the inversion was not significantly hampered by cycle skipping however late arrivals in the synthetic seismograms computed without attenuation and with a source wavelet estimated from short offset early arrivals arrive 40 ms earlier than the recorded seismograms this might result from dispersion effects related to attenuation the repeatability of the source wavelets inferred from data that are weighted by a linear gain with offset is dramatically improved when they are estimated in the fwi model rather than in the smooth initial model the two source wavelets estimated in the fwi model from data with and without offset gain show a 40 ms time shift which is consistent with the previous analysis of the time domain seismograms the computational efficiency of our frequency domain approach is assessed against a recent time domain fwi case study performed in a similar geological environment this analysis highlights the efficiency of the frequency domain approach to process a large number of sources and receivers with limited computational resources thanks to the efficiency of the substitution step performed by the direct solver this efficiency can be further improved by using a block low rank version of the multifrontal solver and by exploiting the sparsity of the source vectors during the substitution step future work will aim to update attenuation and density at the same time of the vertical wave speed

gas geochemistry of the valles caldera region new mexico and comparisons with gases at yellowstone long valley and other geothermal systems abstract noncondensible gases from hot springs fumaroles and deep wells within the valles caldera geothermal system 210 300 c consist of roughly 98 5 mol co 2 0 5 mol h 2 s and 1 mol other components 3 he 4 he ratios indicate a deep magmatic source r r a up to 6 whereas 13 c co 2 values 3 to 5 do not discriminate between a mantle magmatic source and a source from subjacent hydrothermally altered paleozoic carbonate rocks regional gases from sites within a 50 km radius beyond valles caldera are relatively enriched in co 2 and he but depleted in h 2 s compared to valles gases regional gases have r r a values 1 2 due to more interaction with the crust and or less contribution from the mantle carbon sources for regional co 2 are varied during 1982 1998 repeat analyses of gases from intracaldera sites at sulphur springs showed relatively constant ch 4 h 2 and h 2 s contents the only exception was gas from footbath spring 1987 1993 which experienced increases in these three components during drilling and testing of scientific wells vc 2a and vc 2b present day valles gases contain substantially less n 2 than fluid inclusion gases trapped in deep early stage post caldera vein minerals this suggests that the long lived valles hydrothermal system ca 1 myr has depleted subsurface paleozoic sedimentary rocks of nitrogen when compared with gases from many other geothermal systems valles caldera gases are relatively enriched in he but depleted in ch 4 n 2 and ar in this respect valles gases resemble end member hydrothermal and magmatic gases discharged at hot spots galapagos kilauea and yellowstone

temporal relations of volcanism and hydrothermal systems in two areas of the jemez volcanic field new mexico two hydrothermal alteration events 8 07 ma one sample 6 51 5 60 ma six samples related to the waning stages of late miocene volcanism ge 13 to le 5 8 ma are recognized at the cochiti district southeast jemez mountains most of the k ar dates 0 83 plus minus 0 11 0 66 plus minus 0 21 ma four samples in the hydrothermally altered caldera fill rocks of core hole vc 2a at sulfur springs valles caldera indicate post valles caldera hydrothermal alteration a sample from acid altered landslide debris of postcaldera tuffs from the upper 13 m of the core hole was too young to be dated by the k ar method and is possibly associated with current hot spring activity and the youngest pulses of volcanism oxygen isotope data from illite smectite clays in the cochiti district are zonally distributed and range from minus 2 15 per thousand to plus 7 97 per thousand smow depending upon temperature extent of rock fluid interaction and composition the samples from vc 2a get lighter with depth minus 0 20 per thousand to plus 1 62 per thousand the k ar and oxygen isotope data provide strong evidence that the epithermal quartz vein hosted gold silver mineralization at cochiti and the sub ore grade molybdenite at vc 2a were deposited in the late miocene 5 99 5 60 ma and mid quaternary approximately 0 66 ma respectively by hydrothermal fluids composed primarily of meteoric water

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

thermal maturity patterns of cretaceous and tertiary rocks san juan basin colorado and new mexico horizontal and vertical thermal maturity patterns and time temperature modeling of cretaceous and tertiary rocks in the san juan basin of southwestern colorado and northwestern new mexico indicate that the high levels of thermal maturity in the northern part of the basin are due to either 1 convective heat transfer associated with a deeply buried heat source located directly below the northern part of the basin or 2 the circulation of relatively hot fluids into the basin from a heat source north of the basin located near the san juan mountains vitrinite reflectance r m well profiles through cretaceous and tertiary rocks in the basin are commonly nonlinear with two to four segments having different gradients the different gradients most likely represent the combined effects of contrasting thermal conductivities associated with lithologic variations and differences in heat transfer processes conductive versus convective time temperature and kinetic modeling of nonlinear r m profiles indicates that present day heat flow is insufficient to account for the measured levels of thermal maturity furthermore in order to match the nonlinear r m profiles it is necessary to assign artificially high thermal conductivity values to some of the stratigraphic units these unrealistically high thermal conductivities are interpreted as evidence of convective heat transfer

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

white island new zealand volcanic hydrothermal system represents the geochemical environment of high sulfidation cu and au ore deposition the white island volcanic hydrothermal system new zealand is thought to closely represent the chemical conditions that lead to the formation of high sulfidation cu au ore deposits the amounts of cu and au produced over a 10 ka period of activity largely from degassing magma are calculated to be 106 and 45 t respectively altered andesite blocks ejected from recent vents contain alunite anhydrite and pyrite their s isotopic composition indicates vein filling at 380 c at this temperature cu and au are highly soluble in acid solutions which may explain the depletion of cu and absence of au in the ejecta mass balance calculations however suggest that cu and au are precipitated in cooler zones before the acid solutions discharge at the surface

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

comparison of hydrothermal alteration of carboniferous carbonate and siliclastic rocks in the valles caldera with outcrops from the socorro caldera new mexico abstract continental scientific drilling program csdp drill hole vc 2b total depth 1761 7 m 5780 ft maximum temperature 295 c was continuously cored through the sulphur springs hydrothermal system in the western ring fracture zone of the 1 14 ma valles caldera among other units the hole penetrated 760 2 m 2494 1 ft of paleozoic carbonate and siliciclastic strata underlying caldera fill and precaldera volcanic and epiclastic rocks comparison of the vc 2b paleozoic rocks with corresponding lithologies within and around the 32 1 ma socorro caldera 192 km 119 miles to the south southwest provides insight into the variability of alteration responses to similar caldera related hydrothermal regimes the pennsylvanian madera limestone and sandia formation from vc 2b preserve many of the sedimentological and diagenetic features observed in these units on a regional basis and where unaffected by high temperatures or hydrothermal activity micrites in these formations in vc 2b are generally altered and mineralized only where fractured or brecciated that is where hydrothermal solutions could invade carbonate rocks which were otherwise essentially impermeable alteration intensity and correspondingly inferred paleopermeability is only slightly higher in carbonate packstones and grainstones low to intermediate in siltstones and claystones and high in poorly cemented sandstones hydrothermal fracture filling phases in these rocks comprise sericite and phengite chlorite allanite apatite an unidentified zeolite and sphene in various combinations locally with sphalerite galena pyrite and chalcopyrite terrigenous feldspars and clays are commonly altered to chlorite and seriate and euhedral anhydrite porphyroblasts with minor chlorite occur in sandia formation siltstone fossils are typically unaltered but the walls of some colonial bryozoans in the madera limestone are altered to the assemblage chlorite sericite epidote allanite la ce and nd are present in an unidentified hydrothermal mineral occurring throughout much of the vc 2b pennsylvanian sequence carboniferous carbonate and siliciclastic formations within and around the socorro caldera show a similar style of alteration and mineralization to their valles caldera counterparts but by contrast locally host commercial caldera related base metal sulfide deposits as in the valles rocks mineralization and alteration in those of the socorro caldera were strongly controlled by porosity unless disrupted by fractures breccias or karst cavities not identified in valles caldera drill holes the rocks remained relatively unaltered where these features allowed ingress of mineralizing hydrothermal solutions base metal sulfides and rare earth element bearing minerals were precipitated

hydrothermal alteration in the baca geothermal system redondo dome valles caldera new mexico thermal fluids circulating in the active hydrothermal system of the resurgent redondo dome of the valles caldera have interacted with their diverse host rocks to produce well zoned alteration assemblages which not only help locate permeable fluid channels but also provide insight into the system s thermal history the alteration shows that fluid flow has been confined principally to steeply dipping normal faults and subsidiary fractures as well as thin stratigraphic aquifers permeability along many of these channels has been reduced or locally eliminated by hydrothermal self sealing alteration from the surface through the base of the miocene paliza canyon formation is of three distinctive types argillic propylitic and phyllic argillic alteration forms a blanket above the deep water table in formerly permeable nonwelded tuffs beneath the argillic zone pervasive propylitic alteration is weakly developed in felsic host rocks but locally intense in deep intermediate composition volcanics strong phyllic alteration is commonly but not invariably associated with major active thermal fluid channels phyllic zones yielding no fluid were clearly once permeable but now are hydrothermally sealed high temperature alteration phases at baca are presently found at much lower temperatures we suggest either that isotherms have collapsed due to gradual cooling of the system that they have retreated without overall heat loss due to uplift of the redondo dome that the system has shifted laterally or that it has contracted due to a drop in the water table the deepest well b 12 3423 m in the dome may have penetrated through the base of the active hydrothermal system below a depth of 2440 m in this well hydrothermal veining largely disappears and the rocks resemble those developed by isochemical thermal metamorphism the transition is reflected by temperature logs which show a conductive thermal gradient below 2440 m this depth may mark the dome s neutral plane which separates an upper permeable zone of extensional fracturing from a lower less permeable compressional regime the baca hydrothermal system is similar to those which have formed ore deposits in other calderas particularly creede colorado type epithermal silver base metal veins and stockworks recent scientific drilling has also intersected a deep zone of strong phyllic alteration and molybdenum mineralization in the valles caldera s ring fracture system a setting which localized a large stockwork molybdenite orebody in the nearby questa caldera

prestack depth migration with compensation for absorption and dispersion in prestack depth migration using explicit extrapolators the attenuation and dispersion of the seismic wave has been neglected so far we present a method for accommodating absorption and dispersion effects in depth migration schemes extrapolation operators that compensate for absorption and dispersion are designed using an optimization algorithm the design criterion is that the wavenumber response of the operator should equal the true extrapolator both phase velocity and absorption macro models are used in the wavefield extrapolation in a model with medium to high absorption the images obtained are superior to those obtained using extrapolators without compensation for absorption

seismic attenuation tomography using the frequency shift method we present a method for estimating seismic attenuation based on frequency shift data in most natural materials seismic attenuation increases with frequency the high frequency components of the seismic signal are attenuated more rapidly than the low frequency components as waves propagate as a result the centroid of the signal s spectrum experiences a downshift during propagation under the assumption of a frequency independent q model this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically the frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation in comparison to some other methods of estimating attenuation our frequency shift method is relatively insensitive to geometric spreading reflection and transmission effects source and receiver coupling and radiation patterns and instrument responses tests of crosswell attenuation tomography on 1 d and 2 d geological structures are presented

constraints on the petrogenesis of martian meteorites from the rb sr and sm nd isotopic systematics of the lherzolitic shergottites alh77005 and lew88516 abstract detailed rb sr and sm nd isotopic analyses have been completed on the lherzolitic shergottites alh77005 and lew88516 alh77005 yields a rb sr age of 185 11 ma and a sm nd age of 173 6 ma whereas the rb sr and sm nd ages of lew88516 are 183 10 and 166 16 ma respectively the initial sr isotopic composition of alh77005 is 0 71026 4 and the initial end value is 11 1 0 2 these values are distinct from those of lew88516 which has an initial sr isotopic composition of 0 71052 4 and an initial end value of 8 2 0 6 several of the mineral and whole rock leachates lie off the rb sr and sm nd isochrons indicating that the isotopic systematics of the meteorites have been disturbed the sm nd isotopic compositions of the leachates appear to be mixtures of primary igneous phosphates and an alteration component with a low 143nd 144nd ratio that was probably added to the meteorites on mars tie lines between leachate residue pairs from lew88516 mineral fractions and whole rocks have nearly identical slopes that correspond to rb sr ages of 90 1 ma this age may record a major shock event that fractionated rb sr from lattice sites located on mineral grain boundaries on the other hand the leachates could contain secondary alteration products and the parallel slopes of the tie lines could be coincidental nearly identical mineral modes compositions and ages suggest that these meteorites are very closely related nevertheless their initial sr and nd isotopic compositions differ outside analytical uncertainty requiring derivation from unique sources assimilation fractional crystallization models indicate that these two lherzolitic meteorites can only be related to a common parental magma if the assimilant has a sr nd ratio near 1 and a radiogenic sr isotopic composition further constraints placed on the evolved component by the geochemical and isotopic systematics of the shergottite meteorite suite suggest that it a formed at 4 5 ga b has a high la yb ratio c is an oxidant and d is basaltic in composition or is strongly enriched in incompatible elements the composition and isotopic systematics of the evolved component are unlike any evolved lunar or terrestrial igneous rocks its unusual geochemical and isotopic characteristics could reflect hydrous alteration of an evolved martian crustal component or hydrous metasomatism within the martian mantle

full waveform inversion and distance separated simultaneous sweeping a study with a land seismic data set abstract dense wide aperture and broad frequency band acquisition improves seismic imaging and potentially allows the use of full waveform inversion for velocity model building the cost of dense acquisitions however limits its applicability blended or simultaneous shooting could lead to a good compromise between cost and dense acquisition although the cross talk between simultaneous sweeps may reduce imaging capabilities onshore a compromise is achieved with distance separated simultaneous sweeping acquisition because the shots are easily separated when the processing focuses on pre critical reflected events full waveform inversion for velocity model building however relies on post critical reflected refracted and diving events these events can interfere in a distance separated simultaneous sweeping acquisition by using a single vibrator single receiver data set recorded in inner mongolia china a distance separated simultaneous sweeping data set is created to study the robustness of full waveform inversion in this acquisition context this data set is well suited for full waveform inversion since it contains frequencies down to 1 5 hz and offsets up to 25 km full waveform inversion after a crude deblending of the distance separated simultaneous sweeping data set leads to a result very similar to the one obtained from the single vibrator single receiver data set the inversion of the blended data set gives a slightly less good result because of the cross talk but it is still quite satisfactory

inverse theory applied to multi source cross hole tomography part 1 acoustic wave equation method1 frequency domain methods are well suited to the imaging of wide aperture cross hole data however although the combination of the frequency domain with the wavenumber domain has facilitated the development of rapid algorithms such as diffraction tomography this has also required linearization with respect to homogeneous reference media this restriction and association restrictions on source receiver geometries are overcome by applying inverse techniques that operate in the frequency space domain in order to incorporate the rigorous modelling technique of finite differences into the inverse procedure a nonlinear approach is used to reduce computational costs the method of finite differences is applied directly to the frequency domain wave equation the use of high speed high capacity vector computers allow the resultant finite difference equations to be factored in place in this way wavefields can be computed for additional source positions at minimal extra cost allowing inversions to be generated using data from a very large number of source positions synthetic studies show that where weak scatter approximations are valid diffraction tomography performs slightly better than a single iteration of non linear inversion however if the background velocities increase systematically with depth diffraction tomography is ineffective whereas non linear inversion yields useful images from one frequency component of the data after a single iteration further synthetic studies indicate the efficacy of the method in the time lapse monitoring of injection fluids in tertiary hydrocarbon recovery projects

mineral and organic material in matrices and coatings of framboidal pyrite from pennsylvanian sediments england abstract analytical sem observations show that the inorganic fraction of interstitial matrix and coatings of pyrite framboids consists only of a1 and si compounds xrd patterns from bulk concentrates of the pyrite reveal the presence of both kaolinite and quartz in this fraction from marine and nonmarine mud rocks and dominantly quartz with little or no kaolinite from coal these minerals are inferred to be present within framboidal interstices and coatings and can be alternate to or in association with organic matter in these positions the strata are of westphalian c age at the gastrioceras listeri marine horizon near sheffield england the mineral and organic material are regarded as early diagenetic the kaolinite and quartz being syndepositional with the pyrite the organic com onent may be of this age or later probably having undergone some subsequent maturation

two dimensional velocity models from wide angle seismic data by wavefield inversion summary modern wide angle surveys are often multi fold and multi channel with densely sampled source and receiver spacings such closely spaced data are potentially amenable to multi channel techniques involving wavefield propagation methods such as those commonly used in reflection data processing however the wide angle configuration requires techniques capable of handling very general wave types including those not commonly used in reflection seismology this is a situation analogous to that faced in cross borehole seismics where similar wave types are also recorded in a real cross borehole example we compare pre stack migration traveltime tomography and wavefield inversion we find that wavefield inversion produces images that are quantitative in velocity as are the tomograms but are of significantly higher resolution the wavefield inversion results have a resolution comparable to that of the qualitative pre stack migration images we seek to extend this novel development to the larger scale problem of crustal imaging an essential element of the approach we adopt is its formulation entirely within the temporal frequency domain this has three principal advantages 1 we can choose to decimate the data by selecting only a limited number of frequency components to invert thus making inversion of data from large numbers of source positions feasible 2 we can mitigate the notorious non linearity of the seismic inverse problem by progressing from low frequency components in the data to high frequency components and 3 we can include in the model any arbitrary frequency dependence of inelastic attenuation factors q and indeed solve for the spatial distribution of q an initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly this is related to the fact that the reconstruction is obtained from forward scattered waves under these conditions the method thus behaves much like tomography a second test with a deeper more extensive anomaly yields an image with the correct velocity polarity and the correct location but with a deficiency in low and high wavenumbers in this case this is because the reconstruction is obtained from backscattered waves under these conditions the method behaves not like tomography but like migration a more extensive test based on a large wide angle survey in south eastern california and western arizona demonstrates a real potential for high resolution imaging of crustal structures although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today the images are sufficiently encouraging to warrant future research the problem of local minima in the objective function is the most significant practical problem with our method but we propose that appropriate layer stripping methods can handle this problem

investigating the use of 3 d full waveform inversion to characterize the host rock at a geological disposal site the u k government has a policy to dispose of higher activity radioactive waste in a geological disposal facility gdf which will have multiple protective barriers to keep the waste isolated and to ensure no harmful quantities of radioactivity are able to reach the surface currently no specific gdf site in the united kingdom has been chosen but once it has the site is likely to be investigated using seismic methods in this study we explore whether 3 d full waveform inversion fwi of seismic data can be used to map changes in physical properties caused by the construction of the site specifically tunnel induced fracturing we have built a synthetic model for a gdf located in granite at 1000 m depth below the surface since granite is one of the candidate host rocks due to its high strength and low permeability and the gdf could be located at such a depth we use an effective medium model to predict changes in p wave velocity associated with tunnel induced fracturing within the spatial limits of an excavated disturbed zone edz modelled here as an increase in fracture density around the tunnel we then generate synthetic seismic data using a number of different experimental geometries to investigate how they affect the performance of fwi in recovering subsurface p wave velocity structure we find that the location and velocity of the edz are recovered well especially when data recorded on tunnel receivers are included in the inversion our findings show that 3 d fwi could be a useful tool for characterizing the subsurface and changes in fracture properties caused during construction and make a suite of suggestions on how to proceed once a potential gdf site has been identified and the geological setting is known

multiparameter full waveform inversion of multicomponent ocean bottom cable data from the valhall field part 1 imaging compressional wave speed density and attenuation multiparameter full waveform inversion fwi is a challenging quantitative seismic imaging method for lithological characterization and reservoir monitoring the difficulties in multiparameter fwi arise from the variable influence of the different parameter classes on the phase and amplitude of the data and the trade off between these in this framework choosing a suitable parametrization of the subsurface and designing the suitable fwi workflow are two key methodological issues in non linear waveform inversion we assess frequency domain visco acoustic fwi to reconstruct the compressive velocity vp the density or the impedance ip and the quality factor qp from the hydrophone component using a synthetic data set that is representative of the valhall oil field in the north sea we first assess which of the vp and vp ip parametrizations provides the most reliable fwi results when dealing with wide aperture data contrary to widely accepted ideas we show that the vp parametrization allows a better reconstruction of both the vp and ip parameters first because it favours the broad band reconstruction of the dominant vp parameter and secondly because the trade off effects between velocity and density at short to intermediate scattering angles can be removed by multiplication to build an impedance model this allows for the matching of the reflection amplitudes while the broad band velocity model accurately describes the kinematic attributes of both the diving waves and reflections then we assess different inversion strategies to recover the quality factor qp in addition to parameters vp and a difficulty related to attenuation estimation arises because on the one hand the values of qp are on average one order of magnitude smaller than those of vp and and on the other hands model perturbations relative to the starting models can be much higher for qp than for vp and during fwi in this framework we show that an empirical tuning of the fwi regularization which is adapted to each parameter class is a key issue to correctly account for the attenuation in the inversion we promote a hierarchical approach where the dominant parameter vp is reconstructed first from the full data set i e without any data preconditioning to build a velocity model as kinematically accurate as possible before performing the joint update of the three parameter classes during a second step this hierarchical imaging of compressive wave speed density and attenuation is applied to a real wide aperture ocean bottom cable data set from the valhall oil field several geological features such as accumulation of gas below barriers of claystone and soft quaternary sediment are interpreted in the fwi models of density and attenuation the models of vp and qp that have been developed by visco acoustic fwi of the hydrophone data can be used as initial models to perform visco elastic fwi of the geophone data for the joint update of the compressive and shear wave speeds

evolution of the western valles caldera complex new mexico evidence from intracaldera sandstones breccias and surge deposits scientific core drilling in the pleistocene valles caldera complex encompassing the valles 1 13 ma and coaxial toledo 1 50 ma calderas of north central new mexico has provided new insight into the origins of sandstones breccias and pyroclastic surge deposits interbedded with the thick intracaldera ignimbrite sequence these rocks were previously interpreted from geothermal drill cuttings as dominantly fluvial in origin as such representing significant erosional intervals they formed much of the basis for subdividing the intracaldera ignimbrite sequence up to 2000 m in apparent thickness where drilled into four major units the lower tuffs 1 50 ma the otowi 1 50 ma and tshirege 1 13 ma members of the bandelier tuff and a new unit the upper tuffs believed to be post bandelier in age 1 13 ma all but the upper tuffs correspond to mapped outflow facies ignimbrite sheets however continental scientific drilling program core holes vc 2a completed in 1986 and vc 2b completed in 1988 in the sulphur springs area of the valles caldera have provided continuous cores revealing for the first time that some intracaldera rocks previously thought to be exclusively clastic actually have multiple origins some of these rocks are probably pyroclastic surge deposits others could be lithic rich breccias of various origins incorporated nearly instantaneously in ignimbrites during ash flow eruption and concomitant caldera collapse these new findings demonstrate the value of continuous core for subsurface characterization and correlation of complex intracaldera lithologies they also necessitate revision of nielson and hulen s 1984 cuttings based intracaldera stratigraphic framework for example the hematitic s2 sandstone was initially interpreted as marking an erosional interval between the tshirege member of the bandelier tuff and the overlying petrographically similar upper tuffs core from vc 2a and vc 2b however shows that the s2 cuttings could also represent disaggregated permian red bed rich lithic lag breccias or caldera collapse mesobreccias if this is the case then most or all of the upper tuffs are actually uppermost tshirege member ignimbrites in similar fashion and upon review of previously applied correlation criteria the lower tuffs of the western valles caldera complex could represent both genuine pre bandelier ignimbrites and those of the lowermost otowi member the core however shows that in the sulphur springs subsurface the lower tuffs are separated from overlying ignimbrite sheets by prominent erosional and eruptive breaks they appear to be slightly more mafic than the overlying tuffs and host distinctive pumice lapilli at this site the lower tuffs almost certainly predate the otowi member and are probably correlative with the outflow facies san diego canyon ignimbrites 1 78 ma cores from vc 2a and vc 2b support earlier interpretation of the s3 sandstone as a major marker horizon separating the intracaldera otowi and tshirege members of the bandelier tuff but clearly shows that this important unit is not as previously thought entirely a simple intracaldera epiclastic apron in vc 2a the s3 has the superficial appearance of a sandstone but contains abundant blocky shards as well as accretionary and armored lapilli it is also soft sediment deformed and invades overlying nonwelded tuff as small clastic dikes we believe that here the s3 was emplaced by a wet pyroclastic surge in nearby corehole vc 2b the s3 consists of a basal massive sediment gravity flow sandstone overlain by sandstone and dacite breccias with accretionary and armored lapilli bearing tuffaceous matrices these deposits are probably caldera collapse mesobreccias that were formed simultaneously with early tshirege member ash flow eruptions through or into a toledo caldera lake

seismic migration with inverse q filtering 1 taking account the earth q effect i e frequency dependent amplitude decay and velocity dispersion during seismic migration simultaneously the resultant seismic image is expected to be high resolution with true amplitude and correct timing we present here a stabilized algorithm for such a migration incorporating inverse q filtering scheme so that the imaging technique is applicable to seismographs with long recording time the earth model is assumed to be 1 d with continuous variations vertically in velocity and attenuation and the imaging algorithm is implemented easily and efficiently in the frequency wavenumber domain although such a 1 d model suits mostly to the cases in lithospheric scale regional geophysics it is sometimes also suitable to the exploration seismic studies the method is demonstrated using a real data example from exploration seismics with an attempt to recover a target reflection underneath a group of strong coal seam reflections