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Showing papers by "United States Geological Survey published in 1990"


Journal ArticleDOI
TL;DR: In this article, a qualitative model is presented that produces self-healing slip pulses, which is the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity, and the model has the following features: high static strength of materials (kilobar range), low static stress drops (in the range of tens of bars).

901 citations


Journal ArticleDOI
31 Aug 1990-Science
TL;DR: Synchrony of fire-free and severe fire years across diverse southwestern forests implies that climate forces fire regimes on a subcontinental scale; it also underscores the importance of exogenous factors in ecosystem dynamics.
Abstract: Fire scar and tree growth chronologies (1700 to 1905) and fire statistics (since 1905) from Arizona and New Mexico show that small areas burn after wet springs associated with the low phase of the Southern Oscillation (SO), whereas large areas burn after dry springs associated with the high phase of the SO. Through its synergistic influence on spring weather and fuel conditions, climatic variability in the tropical Pacific significantly influences vegetation dynamics in the southwestern United States. Synchrony of fire-free and severe fire years across diverse southwestern forests implies that climate forces fire regimes on a subcontinental scale; it also underscores the importance of exogenous factors in ecosystem dynamics.

661 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared the observed and predicted streamwater concentration of six solutes (alkalinity, sulfate, sodium, magnesium, calcium and dissolved silica), which are assumed to mix conservatively, and assessed the consistency of the implied hydrograph separation with the hydrological mechanisms that are believed to be operating in this catchment.

535 citations


Journal ArticleDOI
TL;DR: The metabolism of toluene, phenol, and p-cresol by GS-15 provides a model for how aromatic hydrocarbons and phenols may be oxidized with the reduction of Fe(III) in contaminated aquifers and petroleum-containing sediments.
Abstract: The dissimilatory Fe(III) reducer, GS-15, is the first microorganism known to couple the oxidation of aromatic compounds to the reduction of Fe(III) and the first example of a pure culture of any kind known to anaerobically oxidize an aromatic hydrocarbon, toluene. In this study, the metabolism of toluene, phenol, and p-cresol by GS-15 was investigated in more detail. GS-15 grew in an anaerobic medium with toluene as the sole electron donor and Fe(III) oxide as the electron acceptor. Growth coincided with Fe(III) reduction. [ring-14C]toluene was oxidized to 14CO2, and the stoichiometry of 14CO2 production and Fe(III) reduction indicated that GS-15 completely oxidized toluene to carbon dioxide with Fe(III) as the electron acceptor. Magnetite was the primary iron end product during toluene oxidation. Phenol and p-cresol were also completely oxidized to carbon dioxide with Fe(III) as the sole electron acceptor, and GS-15 could obtain energy to support growth by oxidizing either of these compounds as the sole electron donor. p-Hydroxybenzoate was a transitory extracellular intermediate of phenol and p-cresol metabolism but not of toluene metabolism. GS-15 oxidized potential aromatic intermediates in the oxidation of toluene (benzylalcohol and benzaldehyde) and p-cresol (p-hydroxybenzylalcohol and p-hydroxybenzaldehyde). The metabolism described here provides a model for how aromatic hydrocarbons and phenols may be oxidized with the reduction of Fe(III) in contaminated aquifers and petroleum-containing sediments. Images

463 citations


Journal ArticleDOI
TL;DR: In this article, a technique is developed whereby stream water can be predicted as a mixture of the observed soilwater classes or end-members, provided that a sufficient set of endmembers has been identified, a least squares technique can be used to estimate the contribution to the stream from each end-member, whenever streamwater samples have been taken.

428 citations


Journal ArticleDOI
TL;DR: In this article, stable isotope data for dissolved carbonate, sulfate, and sulfide were combined with water compo- sition data to construct geochemical reaction models along eight flow paths in the Madison aquifer in parts of Wyoming, Montana, and South Dakota.
Abstract: Stable isotope data for dissolved carbonate, sulfate, and sulfide are combined with water compo­ sition data to construct geochemical reaction models along eight flow paths in the Madison aquifer in parts of Wyoming, Montana, and South Dakota. The sulfur isotope data are treated as an isotope dilution problem, whereas the carbon isotope data are treated as Rayleigh distillations. All reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the Madison Limestone. The geochemical reaction models indicate that the dominant groundwater reaction in the Madison aquifer is dedolomitization ~calcite precipita­ tion and dolomite dissolution driven by anhydrite dissolution). Sulfate reduction, [Ca + + Mg2+ ]INa+ cation exchange, and halite dissolution are locally important, particularly in central Montana. The groundwater system is treated as closed to C02 gas from external sources such as the soil zone or cross-formational leakage but open to C02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer. The computed mineral mass transfers and modeled sulfur isotopic composition of Madison anhydrites are mapped throughout the study area. Carbon 14 groundwater ages, adjusted for the modeled carbon mass transfer, range from modem to about 23,000 years B.P. and indicate flow velocities of 7~7 ftlyr (2.1-26.5 rnlyr). Most horizontal hydraulic conductivities calculated from Darcy's Law using the average 14 C flow velocities are within a factor of 5 of those based on digital simulation. The calculated mineral mass transfer and adjusted 14 C groundwater ages permit determination of apparent rates of reaction in the aquifer. The apparent rate of organic matter oxidation is typically 0.12 JLIDOl/Uyr. Sulfate and, to a lesser extent, ferric iron are the predominant electron acceptors. The (kinetic) biochemical fractionation of 34 S between sulfate and hydrogen sulfide is approximately -44%o at 25•c, with a temperature variation of

405 citations


Journal ArticleDOI
TL;DR: The existence of a threshold pore pressure gradient below which water would not flow through clay-filled fault zones has been studied in this article, which has profound implications for the rheological properties of mature fault zones that contain large thickness of fault gouge.
Abstract: More than twenty-five years ago Miller and Low reported the existence of a threshold pore pressure gradient below which water would not flow through clay. Recent experimental observations of the shear strength of structured water on biotite surfaces have provided a physical basis for understanding this threshold gradient. The existence of this phenomenon has profound implications for the rheological properties of mature fault zones, such as the San Andreas, that contain large thickness of fault gouge. For example, a clay-filled fault zone about 1 km wide at the base of the surface could support core fluid pressure equal to the maximum principal stress over the entire seismogenic zone. As a result, the fault would have near-zero strength and the maximum principal stress measured on the flanks of the fault, would be oriented normal to the fault surface. Another consequence of the threshold gradient is that normal hydrostatic fluid pressures outside the fault zone could coexist with near-lithostatic fluid pressures in the interior of the fault zone without the need for continual replenishment of the overpressured fluid. In addition, the pore pressure at any point should never exceed the local minimum principal stress so that hydrofracture will not occur.

394 citations


Journal ArticleDOI
TL;DR: In this paper, the compositional differences between fulvic acids and humic acids from soil, stream and marine environments by five different methods (1H and 13C NMR spectroscopy, 14C age and δ13C isotopic analyses, amino acid analyses, pyrolysis-mass spectrometry).

381 citations


Journal ArticleDOI
01 Jun 1990-Geology
TL;DR: In this paper, the authors found that climate is a primary control on sediment flux from continental sources into sedimentary systems, and that siliciclastic input is greatest under highly seasonal rainfall.
Abstract: Climate is a primary control on sediment flux from continental sources into sedimentary systems. In warm climates, siliciclastic input is greatest under highly seasonal rainfall. Nonseasonal conditions favor formation of "end member" chemical rocks; perennially wet climates are conducive to coal formation, whereas dry climates produce carbonates and/or evaporites. Stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive-regressive events and tectonics.

381 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared and modeled the adsorption of selenium and other anions on a neutral to alkaline surface (amorphous iron oxyhydroxide) and an acidic surface (manganese dioxide).

376 citations


Journal ArticleDOI
TL;DR: In this paper, the volume of material removed by subduction erosion can be estimated quantitatively if the position of the volcanic arc, the positions of the paleotrench axis, and a paleo-depth reference surface are known.
Abstract: The volume of material removed by subduction erosion can be estimated quantitatively if the position of the volcanic arc, the position of the paleotrench axis, and a paleo-depth reference surface are known. Estimates based on these parameters along the Japan and Peru Trenches indicate rates of erosion comparable to well-known rates of accretion. Proposed erosional mechanisms along the plate boundary, where horsts on the lower plate abrade the upper one, appear insufficient to handle the minimum volumes of eroded material. Some mechanisms of tectonic erosion at the base of the trench slope can be observed at colliding seamounts and ridges where structures are large enough to be seismically imaged. Local tectonic erosion of the lower slope of the Japan Trench resulted when seamounts entered the subduction zone, uplifted the slope, and oversteepened it. The oversteepened slope failed, debris slumped into the trench axis, and much of it was then subducted. Where a seamount was subducted, a large re-entrant was left in the slope, which filled rapidly by local accretion of abundant sediment. Subduction of the oblique-trending Nazca Ridge off Peru produced many similar structures. Erosion is dominated by uplift and breakup of the lower slope, with subduction of the debris rather than abrasion under high-stress conditions. Another form of tectonic erosion occurs along the base of the upper plate. Its magnitude is indicated by massive subsidence along the margin; however, because of deep burial, the structure resulting from basal erosion is rarely imaged in seismic records. The volume of material eroded along the base of the upper plate exceeds that eroded from the front of the lower slope.

Journal ArticleDOI
TL;DR: A complex sequence of pyroclastic flows and surges erupted by Nevado del Ruiz volcano on 13 November 1985 interacted with snow and ice on the summit ice cap to trigger catastrophic lahars (volcanic debris flows), which killed more than 23,000 people living at or beyond the base of the volcano.

Journal ArticleDOI
TL;DR: In this paper, Radiocarbon-age estimations for materials that were deposited in the lake basins indicate that Lake Bonneville, Lake Russell and Lake Searles underwent a major period of lake-level change during the past 35,000 years.

Journal ArticleDOI
TL;DR: In this article, a simple graph relating elevation to lithosphere density and thickness provides an overview of expectable conditions around the earth and a simple test for consistancy of continental and oceanic lithosphere models.

Journal ArticleDOI
TL;DR: The combination of screening analysis by ELISA, which requires no sample preparation and works on 160 microL of sample, and confirmation by GC/MS was designed for rapid, inexpensive analysis of triazine herbicides in water.
Abstract: An enzyme-linked immunosorbent assay (ELISA) was compared to a gas chromatography/mass spectrometry (GC/MS) procedure for the analysis of triazine herbicides and their metabolites in surface water and groundwater. Apparent recoveries from natural water and spiked water by both methods were comparable at 0.2-2 micrograms/L. Solid-phase extraction (SPE) was examined also, and recoveries were determined for a suite of triazine herbicides. A significant correlation was obtained between the ELISA and GC/MS method for natural water samples that were extracted by SPE. Because ELISA was developed with an atrazine-like compound as the hapten with conjugation at the 2-position, it was selective for triazines that contained both ethyl and isopropyl side chains. Concentrations for 50% inhibition (IC50) were as follows: atrazine, 0.4 microgram/L; ametryne, 0.45 microgram/L; prometryn and propazine, 0.5 microgram/L; prometon, 0.7 microgram/L; simazine and terbutryn, 2.5 micrograms/L; hydroxyatrazine, 28 micrograms/L; deethylatrazine and deisopropylatrazine, 30 micrograms/L; cyanazine, 40 micrograms/L; didealkylatrazine had no response. The combination of screening analysis by ELISA, which requires no sample preparation and works on 160 microL of sample, and confirmation by GC/MS was designed for rapid, inexpensive analysis of triazine herbicides in water.

Journal ArticleDOI
TL;DR: In this paper, the mineral surface of Wyoming bentonite (clay) was modified by replacing inorganic ions by each of 10 quaternary ammonium compounds, and tetrachloromethane sorption to the modified sorbents from water was studied.
Abstract: The mineral surface of Wyoming bentonite (clay) was modified by replacing inorganic ions by each of 10 quaternary ammonium compounds, and tetrachloromethane sorption to the modified sorbents from water was studied. Tetrachloromethane sorption from solution to clay modified with tetramethyl-, tetraethyl-, benzyltrimethyl-, or benzyltriethylammonium cations generally is characterized by relatively high solute uptake, isotherm nonlinearity, and competitive sorption (with trichloroethene as the competing sorbate). For these sorbents, the ethyl functional groups yield reduced sorptive capacity relative to methyl groups, whereas the benzyl group appears to have a similar effect on sorbent capacity as the methyl group. Sorption of tetrachloromethane to clay modified with dodecyldimethyl(2-phenoxyethyl)-, dodecyltrimethyl-, tetradecyltrimethyl-, hexadecyltrimethyl-, or benzyldimethylhexadecylammonium bromide is characterized by relatively low solute uptake, isotherm linearity, and noncompetitive sorption. For these sorbents, an increase in the size of the nonpolar functional group(s) causes an increase in the organic carbon normalized sorption coefficient (K{sub oc}).

Book
01 Jan 1990
TL;DR: In this paper, the authors used 24 broadband teleseismic and 48 components of local strong motion velocity records of the 1989 Loma Prieta earthquake in a formal inversion to determine the temporal and spatial distribution of slip.
Abstract: We have used 24 broadband teleseismic and 48 components of local strong motion velocity records of the 1989 Loma Prieta earthquake in a formal inversion to determine the temporal and spatial distribution of slip. Separate inversions of the teleseismic data (periods 3-30 sec) or strong motion data (periods 1-5 sec) result in similar models. The data require bilateral rupture with relatively little slip in the region directly updip from the hypocenter. Slip is concentrated in two patches; one centered 6 km northwest of the hypocenter at a depth of 12 km and with a maximum slip of 350 cm, and the other centered about 5 km southeast of the hypocenter at a depth of 16 km and with a maximum slip of 460 cm. The bilateral nature of the rupture results in large amplitude ground motions at sites located along the fault strike, both to the northwest and the southeast. However, the northwestern patch has a larger moment and overall stress drop and is, consequently, the source of the largest ground motion velocities, consistent with the observed recordings. This bilateral rupture also produces relatively modest ground motion amplitudes directly updip from the hypocenter, which is in agreement with the velocity ground motions observed at Corralitos. There is clear evidence of a foreshock (magnitude between 3.5 and 5.0) or a slow rupture nucleation about 2 seconds before the main part of the rupture; the origin time implied by strong motion trigger times is systematically 2 seconds later than the time predicted from the high-gain regional network data. The seismic moment obtained from either of the separate data sets or both sets combined is about 3.0 x 10^(26) dyne-cm and the potency is 0.95 km^3.

Journal ArticleDOI
TL;DR: The rate estimates from geochemical modeling indicate that deep aquifers are among the most oligotrophic aquatic environments in which there is ongoing microbial metabolism, and laboratory incubations may greatly overestimate the in situ rates of microbial metabolism in deep subsurface environments.
Abstract: Rates of microbial metabolism in deep anaerobic aquifers of the Atlantic coastal plain of South Carolina were investigated by both microbiological and geochemical techniques. Rates of (2-{sup 14}C)acetate and (U-{sup 14}C)glucose oxidation as well as geochemical evidence indicated that metabolic rates were faster in the sandy sediments composing the aquifers than in the clayey sediments of the confirming layers. In the many aquifer sediments, estimates of the rates of CO{sub 2} production (millimoles of CO{sub 2} per liter per year) based on the oxidation of (2-{sup 14}C) acetate were 9.4 {times} 10{sup {minus}3} to 2.4 {times} 10{sup {minus}1} for the Black Creek aquifer, 1.1 {times} 10{sup {minus}2} for the Middendorf aquifer, and < 7 {times} 10{sup {minus}5} for the Cape Fear aquifer. These estimates were at least 2 orders of magnitude lower than previously published estimates that were based on the accumulation of CO{sub 2} in laboratory incubations of similar deep subsurface sediments. In contrast, geochemical modeling of groundwater chemistry changes along aquifer flowpaths gave rate estimates that ranged from 10{sup {minus}4} to 10{sup {minus}6} mmol of CO{sub 2} production could have been no more than 10{sup {minus}4} mmol per liter per year. Thus, laboratory incubations may greatly overestimate themore » in situ rates of microbial metabolism in deep subsurface environments. This has important implications for the use of laboratory incubations in attempts to estimate biorestoration capacities of deep aquifers. The rate estimates from geochemical modeling indicate that deep aquifers are among the most oligotrophic aquatic environments in which there is ongoing microbial metabolism.« less

Journal ArticleDOI
TL;DR: In this article, a high-charge smectite from Arizona (CEC) = 120 meq/100 g) and a low-charge tetrachylammonium (TMA)-clay from WYoming, USA, were used to prepare homoionic TMA-clay complexes for the adsorption of benzene, toluene, and o-xylene.
Abstract: A high-charge smectite from Arizona (cation-exchange capacity (CEC) = 120 meq/100 g) and a low-charge smectite from Wyoming (CEC = 90 meq/100 g) were used to prepare homoionic tetra- methylammonium (TMA)-clay complexes. The adsorption of benzene, toluene, and o-xylene as vapors by the dry TMA-clays and as solutes from water by the wet TMA-clays was studied. The adsorption of the organic vapors by the dry TMA-smectite samples was strong and apparently consisted of interactions with both the aluminosilicate mineral surfaces and the TMA exchange ions in the interlayers. In the adsorption of organic vapors, the closer packing of TMA ions in the dry high-charge TMA-smectite, compared with the dry low-charge TMA-smectite, resulted in a somewhat higher degree of shape-selective adsorption of benzene, toluene, and xylene. In the presence of water, the adsorption capacities of both samples for the aromatic compounds were significantly reduced, although the uptake of benzene from water by the low-charge TMA-smectite was still substantial. This lower sorption capacity was accompanied by increased shape-selectivity for the aromatic compounds. The reduction in uptake and increased se- lectivity was much more pronounced for the water-saturated, high-charge TMA-smectite than for the low-charge TMA-smectite. Hydration of the TMA exchange ions and/or the mineral surfaces apparently reduced the accessibility of the aromatic molecules to interlamellar regions. The resulting water-induced sieving effect was greater for the high-charge TMA-smectite due to the higher density of exchanged TMA- ions. The low-charge Wyoming TMA-smectite was a highly effective adsorbent for removing benzene from water and may be useful for purifying benzene-contaminated water. Key Wards--Adsorption, Aromatic hydrocarbons, Benzene, Charge density, Smectite, Tetramethylam- monium, Water.

Journal ArticleDOI
01 May 1990-Geology
Abstract: The middle Pliocene, {approximately}3.5-2.5 Ma, was a period of global warmth preceding the growth of major Northern Hemisphere ice sheets. The authors report on eustatic sea level for the middle Pliocene based on microspaleontologic study of marine deposits of the Duplin Formation of South Carolina and North Carolina. The Duplin was deposited during a middle Pliocene marine transgression that formed the Orangeburg scarp, a prominent wave-cut geomorphic paleoshoreline of the southeastern U.S. Atlantic Coastal Plain. They concluded that (1) the scarp in South Carolina was formed mostly during the middle Pliocene (3.5-3.0 Ma), (2) eustatic sea level was about 35 {plus minus} 18 m higher than modern sea level (the scarp has been uplifted about 50-65 m since the middle Pliocene), and (3) ocean-water temperatures along eastern North America were warmer when the scarp was formed that they are at present.

Journal ArticleDOI
01 Apr 1990-Nature
TL;DR: In this article, detailed aeromagnetic measurements from the sea floor offshore of the Grand Banks of Newfoundland were used to show that Iberia moved as part of the African plate from late Cretaceous to mid-Eocene time, with a plate boundary extending westward from the Bay of Biscay.
Abstract: THE rotation of Iberia and its relation to the formation of the Pyrenees has been difficult to decipher because of the lack of detailed sea-floor spreading data, although several models have been proposed1–7. Here we use detailed aeromagnetic measurements from the sea floor offshore of the Grand Banks of Newfoundland to show that Iberia moved as part of the African plate from late Cretaceous to mid-Eocene time, with a plate boundary extending westward from the Bay of Biscay. When motion along this boundary ceased, a boundary linking extension in the King's Trough to compression along the Pyrenees came into existence. Finally, since the late Oligocene, Iberia has been part of the Eurasian plate, with the boundary between Eurasia and Africa situated along the Azores–Gibraltar fracture zone.

Journal ArticleDOI
TL;DR: The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups as discussed by the authors : cratonic and transitional basalts.
Abstract: The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The “cratonic” basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in 87Sr/86Sr (0.70316 to 0.70512), 143Nd/144Nd (ɛNd) and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the “cratonic” basalts. In contrast, the “transitional” basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by 87Sr/86Sr=0.7039±0.0004, ɛNd, 206Pb/204Pb=18.60±0.08, 207Pb/204Pb=15.60±0.01, and 208Pb/204Pb=38.50±0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the “cratonic” basalts, are displaced to higher 87Sr/86Sr at a given 143Nd/144Nd and to higher 207Pb/204Pb at a given 208Pb/204Pb. The “transitional” basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the “cratonic” and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, δ18O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock δ18O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock δ18O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc to back-arc volcanism in southern South America. The “cratonic” basalts do not contain the slab-derived components that impart the higher Ba/La, Ba/Nb, La/Nb, Cs/Rb, 87Sr/86Sr at a given 143Nd/144Nd, 207Pb/204Pb at a given 208Pb/204Pb, and δ18O to Andean orogenic arc basalts. Instead, these basalts are formed by relatively low degrees of partial melting of heterogeneous lower continental lithosphere and/or asthenosphere, probably due to thermal and mechanical pertubation of the mantle in response to subduction of oceanic lithosphere below the western margin of the continent. The “transitional” basalts do contain components added to their source region by either (1) active input of slab-derived components in amounts smaller than the contribution to the mantle below the arc and/or with lower Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios than below the arc due to progressive downdip dehydration of the subducted slab; or (2) subarc source region contamination processes which affected the mantle source of the “transitional” basalts earlier in the Cenozoic.

Journal ArticleDOI
TL;DR: The authors showed that Saharan dust is the most important parent material for soils on all islands in the Lesser Antilles island arc and the Atlantic Ocean on the northeast trade winds for much of the Quaterary.

Journal ArticleDOI
TL;DR: Methane-hydrogen gas seeps with mantle-like C and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the Zambales ophiolite, Philippines.

Journal ArticleDOI
01 Oct 1990-Geology
TL;DR: In this article, aqueous fluid inclusions in calcite can be used to establish maximum temperature (T peak ), and the authors have compiled fluid inclusion T peak, mean random vitrinite reflectance (R m ), and present-day T peak from 46 diverse geologic systems that have been at T peak for 10 4 to 10 6 yr.
Abstract: Theory, laboratory experiments, and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating, and therefore some homogenization temperatures ( T h ) record a temperature close to the maximum reached by the rock. This characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature ( T peak ). To test this hypothesis, we have compiled fluid inclusion T peak , mean random vitrinite reflectance ( R m ), and present-day T peak from 46 diverse geologic systems that have been at T peak from 10 4 to 10 6 yr. Present T peak ranged from 65 to 345 °C, T h modes and means ranged from 59 to 350 °C, and R m data ranged from 0.4% to 4.6%, spanning the temperature and thermal maturity range associated with burial diagenesis, hydrothermal alteration, and low-grade metamorphism. Plots of T h and T peak data for systems thought to be currently at maximum temperature demonstrate close agreement between T h and present T peak in sedimentary basins. Although caution should be applied, the relation suggests that T h of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature. This study also compares T h to mean random vitrinite reflectance ( R m ) to offer further support for the use of T h as a measure of T peak , and to provide a better understanding of R m . T h correlates well with R m and results in a curve similar to R m vs. T peak calibrations determined by other workers. The strong correlation (correlation coefficient r = 0.93) between T peak and R m in these systems suggests that maximum temperature is the major control on thermal maturation.

Journal ArticleDOI
TL;DR: The Taylor Creek Rhyolite of southwest New Mexico comprises at least 20 lava domes and flows, each of the lavas was erupted from its own vent, and the vents are distributed throughout a 20 km by 50 km area.
Abstract: The Tertiary Taylor Creek Rhyolite of southwest New Mexico comprises at least 20 lava domes and flows. Each of the lavas was erupted from its own vent, and the vents are distributed throughout a 20 km by 50 km area. The volume of the rhyolite and genetically associated pyroclastic deposits is at least 100 km3 (denserock equivalent). The rhyolite contains 15%–35% quartz, sanidine, plagioclase, ±biotite, ±hornblende phenocrysts. Quartz and sanidine account for about 98% of the phenocrysts and are present in roughly equal amounts. With rare exceptions, the groundmass consists of intergrowths of fine-grained silica and alkali feldspar. Whole-rock major-element composition varies little, and the rhyolite is metaluminous to weakly peraluminous; mean SiO2 content is about 77.5±0.3%. Similarly, major-element compositions of the two feldsparphenocryst species also are nearly constant. However, whole-rock concentrations of some trace-elements vary as much as several hundred percent. Initial radiometric age determinations, all K−Ar and fission track, suggest that the rhyolite lava field grew during a period of at least 2 m.y. Subsequent 40Ar/39Ar ages indicate that the period of growth was no more than 100 000 years. The time-space-composition relations thus suggest that the Taylor Creek Rhyolite was erupted from a single magma reservoir whose average width was at least 30 km, comparable in size to several penecontemporaneous nearby calderas. However, this rhyolite apparently is not related to a caldera structure. Possibly, the Taylor Creek Phyolite magma body never became sufficiently volatile rich to produce a large-volume pyroclastic eruption and associated caldera collapse, but instead leaked repeatedly to feed many relatively small domes and flows.

Book ChapterDOI
01 Jan 1990
TL;DR: In this article, the best estimates of the collision rates with Earth of asteroids and comets and the corresponding production of impact craters are presented, based on the best available data.
Abstract: Significant advances in the knowledge and understanding of the flux of large solid objects in the neighborhood of Earth have occurred. The best estimates of the collision rates with Earth of asteroids and comets and the corresponding production of impact craters are presented. Approximately 80 Earth-crossing asteroids were discovered through May 1988. Among 42 new Earth-crossing asteroids found in the last decade, two-thirds were discovered from observations at Palomar Observatory and 15 were discovered or independently detected in dedicated surveys with the Palomar Observatory and 15 were discovered or independently detected in dedicated surveys with the Palomar 46 cm Schmidt. Probabilities of collision with Earth have been calculated for about two-thirds of the known Earth-crossing asteroids. When multiplied by the estimated population of Earth-crossers, this yields an estimated present rate of collision about 65 pct higher than that previously reported. Spectrophotometric data obtained chiefly in the last decade show that the large majority of obvserved Earth-crossers are similar to asteroids found in the inner part of the main belt. The number of discovered Earth-crossing comets is more than 4 times greater than the number of known Earth-crossing asteroids, but reliable data on the sizes of comet nuclei are sparse. The flux of comets almost certainly was highly variable over late geologic time, owing to the random perturbation of the Oort comet cloud by stars in the solar neighborhood.

Journal ArticleDOI
27 Apr 1990-Science
TL;DR: Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening, and one can determine the detailed geologic history of clays by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.
Abstract: Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.

Journal ArticleDOI
TL;DR: A bimodal volcanic suite with KAr ages of 0.05-1.40 Ma was collected from the Sumisu Rift using alvin. as mentioned in this paper showed that major element geochemistry of the basalts is most similar to that of basalts found in other, more mature back-arc basins.

Journal ArticleDOI
TL;DR: In this paper, a method was developed to extract soil water for determination of deuterium (D) and 18O content based on the observation that water and toluene form an azeotropic mixture at 84.1°C, but are completely immiscible at ambient temperature.