bluuebunny/crossref_metadata_2025 huggingface dataset:
Horizontal deformation in New York and Connecticut: Examining contradictory results from the geodetic evidence
Authors: Snay Richard A.
Published: February 2008

From the analysis of historical geodetic data, Zoback et al. (1985) (hereinafter referred to as ZPK) found evidence of significant horizontal crustal deformation for the 1862–1973 interval in southeastern New York and western Connecticut. I have reviewed pertinent geodetic data in this region, including the 30 observed angular changes used by ZPK plus over 3000 additional geodetic measurements. Using the same analysis technique (extended Frank) that ZPK employed and using the same data set, I corroborate their results; that is, a maximum right‐lateral shear strain rate
of 0.18 μrad/yr with a 1‐sigma error estimate of 0.05 or 0.07 μrad/yr depending on whether or not the uncertainty is to reflect data misfit to the assumed model. This maximum shear rate occurs across a vertical plane striking N3°E ± 7° or ± 10°. Analysis of the larger data set, however, which required the use of an alternative technique (simultaneous reduction), produced a
estimate of 0.032 ± 0.018μrad/yr across a vertical plane striking N3°W ± 17°. This latter
estimate is statistically indistinguishable from zero at the 95% confidence level, whereas the former estimate is statistically nonzero at this confidence level. To investigate the apparent contradiction between these two results, several experiments were performed. These experiments uncovered no problem with the software used. The experiments, however, do indicate that two of the 30 observed angular changes used by ZPK are of questionable quality. Moreover, if one of these two observed changes is excluded and the other is replaced by a change observed for the same angle over a different time period, then the resulting 29‐observation data set yields a
estimate that is statistically indistinguishable from zero at the 95% confidence level (0.122 ± 0.057 μrad/yr). Finally, the experiments provide tenuous evidence that part of the difference between results could also be due to spatial variation in the deformation.
Accretion, metamorphism, and brecciation of ordinary chondrites: Evidence from petrologic studies of meteorites from Roosevelt County, New Mexico
Authors: Scott Edward R. D. , Taylor G. Jeffrey , Keil Klaus
Published: February 2008

We have made petrologic studies of a suite of 29 newly discovered ordinary chondrites from Roosevelt County, New Mexico, including an H3 chondrite that is rich in solar wind gases and contains clasts of melt rock and graphite‐magnetite‐rich material, and an L5 chondrite with a unique igneous inclusion. Our data and published work show that mean CaO concentrations of low‐Ca pyroxene can be used to distinguish petrologic types in H, L, and LL groups. Mean CaO concentrations in olivine show significant variations among equilibrated chondrites, but these are not correlated with petrologic type; varied cooling rates could be responsible. The degree of heterogeneity of FeO concentrations in olivines of types 4–6 is also not correlated with degree of metamorphism; it may be controlled more by postmetamorphic brecciation and mixing of material than by metamorphism. Mean FeO concentrations of silicates show average increases of 3–5% from type 4 to type 6 in each group. This increase and the accompanying increase in bulk concentrations of siderophile elements appear to predate parent body formation. Correlation of nebula‐controlled bulk chemistry and planetary metamorphic effects could only have been produced under special conditions of accretion. One possible origin is runaway growth, which allowed parent bodies to form by accretion kilometer‐sized planetesimals to larger bodies, accompanied by differential movement of chemically distinct large and small bodies to produce radially zoned parent bodies that were subsequently metamorphosed by internal heating. Alternatively, ordinary chondrites may have been metamorphosed in a variety of planetesimals, each of which had a uniform chemical composition and metamorphic temperature. Correlations between composition and temperature may have arisen if both were correlated with another parameter, such as heliocentric distance.
Fluidization and hydrothermal alteration of the Suevite deposit at the Ries Crater, West Germany, and implications for Mars
Authors: Newsom Horton E. , Graup Günther , Sewards Terry , Keil Klaus
Published: February 2008

The formation, cooling, and alteration of the impact ejecta deposits at the Ries crater are an analog for impact processes and the formation of regoliths and soils on Mars. We have studied the suevite deposit, an impact‐melt‐bearing breccia found outside of the crater rim. This suevite contains large numbers of chimney‐like degassing pipes, apparently formed by high gas pressures in the hot (>500°C) fluidized suevite immediately after deposition of the suevite. The likely sources of the gas are volatiles from the melted and shocked basement inclusions. The suevite outside of the crater rim contains about 15 wt % clay, indicating a large amount of alteration of the suevite. The clay is an Fe‐rich montmorillonite with less than 5% interstratified illite, indicating that the temperature at which most of the alteration occurred was less than 100°–130°C. The duration of this low‐temperature period may have been extended by additional heating from the exothermal alteration reactions. The surfaces of the degassing pipes are not altered to clays, however, but have a thin Fe‐rich oxide or hydroxide coating. The absence of alteration in the pipes suggests that the main alteration event outside the crater occurred under unsaturated conditions, such that the walls of the pipes were dry. Suevite deposits are likely to exist on Mars, because of the presence of volatile‐rich target rock. Martian suevites may have also been fluidized and hydrothermally altered, contributing significantly to the formation of the clay‐like phases inferred to exist in the Martian soil.
Muong Nong type tektites from the moldavite and North American strewn fields?
Authors: Koeberl Christian
Published: February 2008

Muong Nong type tektites are a very important group of tektites because they differ from splash‐form tektites in several important characteristics (e.g., volatile element enrichment, major‐ and minor‐element inhomogeneities, bubbles, inclusions, layered and sometimes brecciated structure). They seem to have experienced a lower peak temperature and pressure, thus preserving the precursor material much better than the splash forms do. They lead to important conclusions about the impact process, especially regarding the behaviour of the trace elements during impact melting. To date they have been found only within the Australasian strewn field. Finding such tektites within other strewn fields would be very important in proving a genetic relationship between them and splash‐form tektites. Two samples, one bediasite (from the North American strewn field) and one moldavite (from the Czechoslovakian strewn field), that show some Muong Nong features (layered structure) have been analyzed for major and minor as well as trace elements to test for the presence of chemical Muong Nong signatures. Although these three samples show a somewhat larger internal variation of major elements than normal splash‐form tektites, this variation is not as large as that of typical Muong Nong tektites. Likewise, there is no enrichment in volatiles (at least no significant one), which is one of the most obvious characteristics of Muong Nong type. Thus these samples deviate to some extent from splash‐forms, but do not constitute real Muong Nong tektites, so no genetic relationship between Muong Nong tektites and normal splash forms has yet been established beyond doubt.
Relative sea level change from tide gauge records of western North America
Authors: Emery K. O. , Aubrey D. G.
Published: February 2008

Negligible success of investigators in relating tide gauge records of the west coast of North America to eustatic changes of sea level is the result of tectonic movements of the land reference level beneath the tide gauges. The vertical tectonic movements are caused by horizontal movements of oceanic crustal plates. Sinking of 12 mm/yr at Cordova, Alaska, is associated with intense subduction at the east end of the Aleutian Trench; rising by 6 mm/yr at Skagway may be caused by resistance to lateral crustal movement toward the filled trench; rising of 1 mm/yr in southern Alaska (uplift above slow subduction); little vertical movement between Sitka and Mendocino Fracture Zone (translation and slow subduction including fracture zones and thick sediments); sinking of 1 mm/yr west of the San Andreas fault (translation); and sinking of 2 mm/yr along northwestern Mexico (effects of cooling of late rifted crust and only diagonal subduction). Superimposed on this tectonism due to plate motion is broad scale isostatic adjustment (both rise and fall) resulting from deglaciation. Removal of rigid plate motion deltas helps resolve subplate tectonic processes. Higher‐frequency (0.05–0.5 cpy) sea level changes as well as large‐scale pressure fluctuations and wind stress events are associated with El Niño/Southern Oscillation. An apparent increase in relative sea level rise near 1935, also observed in other regions, remains to be explained.
Fractal geometry in the San Andreas Fault System
Authors: Okubo Paul G. , Aki Keiiti
Published: February 2008

It has been noted that the spatial distribution of earthquakes and the mode of strain release in the San Andreas fault system is related to the complexity of fault geometry. Because of their rough appearance over many length scales, faults can be regarded as fractal surfaces. Direct estimates of fractal dimension D of portions of the San Andreas fault system between the northern Gabilan Range and the Salton Sea, including the postulated extent of the great 1857 Fort Tejon earthquake, are obtained from measured fault lengths, analogous to the lengths of coastlines as discussed by Mandelbrot. Regions characterized by complicated fault geometry are associated with larger values of D. Based on fault traces mapped at a scale of 1:750,000, D is 1.3 for this reach of the fault defined as a 30‐km‐wide band about a main fault trace. For that part near Parkfield which could be associated with the nucleation of the 1857 earthquake, D is 1.1; at this same scale, D is 1.4 for the San Andreas and related faults near San Bernardino where the 1857 rupture stopped, compared to 1.2 for the San Andreas‐San Juan fault segments near the point of arrest of the 1966 Parkfield earthquake. At finer map scales (1:24,000 and 1:62,500) critical lengths of ∼ 500 m and 1 km are identified which might relate to the extent of off‐San Andreas fault offsets. The critical lengths also suggest that fault geometry is not self‐similar. If this fractal geometry persists through the seismic cycle, it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault.
Earthquakes, gravity, and the origin of the Bali Basin: An example of a Nascent Continental Fold‐and‐Thrust Belt
Authors: McCaffrey Robert , Nabelek John
Published: February 2008

We infer from the bathymetry and gravity field and from the source mechanisms and depths of the eight largest earthquakes in the Bali region that the Bali Basin is a downwarp in the crust of the Sunda Shelf produced and maintained by thrusting along the Flores back arc thrust zone. Earthquake source mechanisms and focal depths are inferred from the inversion of long‐period P and SH waves for all events and short‐period P waves for two of the events. Centroidal depths that give the best fit to the seismograms range from 10 to 18 km, but uncertainties in depth allow a range from 7 to 24 km. The P wave nodal planes that dip south at 13° to 35° (±7°) strike roughly parallel to the volcanic arc and are consistent with thrusting of crust of the Bali Basin beneath it. The positions of the earthquakes with respect to crustal features inferred from seismic and gravity data suggest that the earthquakes occur in the basement along the western end of the Flores thrust zone. The slip direction for the back arc thrust zone inferred from the orientation of the earthquake slip vectors indicates that the thrusting in the Bali Basin is probably part of the overall plate convergence, as it roughly coincides with the convergence direction between the Sunda arc and the Indian Ocean plate. Summation of seismic moments of earthquakes between 1960 and 1985 suggests a minimum rate of convergence across the thrust zone of 4 ± 2 mm/a. The presence of back arc thrusting suggests that some coupling between the Indian Ocean plate and the Sunda arc occurs but mechanisms such as continental collision or a shallow subduction of the Indian Ocean plate probably can be ruled out. The present tectonic setting and structure of the Bali Basin is comparable to the early forelands of the Andes or western North America in that a fold‐and‐thrust belt is forming on the continental side of an arc‐trench system at which oceanic lithosphere is being subducted. The Bali Basin is flanked by the Tertiary Java Basin to the west and the oceanic Flores Basin to the east and thus provides an actualistic setting for the development of a fold‐and‐thrust belt in which structure and timing of deformation can change significantly along strike on the scale a few hundred kilometers.
East Olkaria Geothermal Field, Kenya: 1. History match with production and pressure decline data
Authors: Bodvarsson Gudmundur S. , Pruess Karsten , Stefansson Valgardur , Bjornsson Sveinbjorn , Ojiambo Sebastian B.
Published: February 2008

A detailed three‐dimensional model of the present well field of the Olkaria geothermal field in Kenya (East Olkaria) has been developed. The model matches reasonably well flow rate and enthalpy data from all existing wells at East Olkaria. The history match shows that the effective permeabilities in the steam zone and the underlying liquid‐dominated zone are 7.5 and 4.0 mdarcy, respectively. These values are somewhat higher than those inferred from well test data. The effective fracture porosity in the liquid‐dominated zone is estimated to be 2% on the average, with spatial variations of 0.25–5%. The modeling studies suggest that the reservoir system is of rather uniform permeability and that no barriers to fluid flow are necessary to match the data. However, there appears to be a high permeability anomaly below a depth of 1000 m extending north‐south through some of the more productive wells (wells 12, 15, 16, and 20).
Measurements of plume flow from a hydrothermal vent field
Authors: Little Sarah A. , Stolzenbach Keith D. , Von Herzen Richard P.
Published: February 2008

Simultaneous velocity, temperature, and conductivity data were taken in the convective flow emanating from a hydrothermal vent field located at 10°56′N, 103°41′W on the East Pacific Rise. The horizontal profiles obtained indicate that the flow field approaches an ideal plume in the temperature and velocity distribution. Such parameters as total heat flow and maximum plume height can be estimated using either the velocity or the temperature information. The results of these independent calculations are in close agreement, yielding a total heat flow from this vent site of 3.7 ± 0.8 MW and a maximum height of 150 ± 10 m. The nonlinear effects of large temperature variations on heat capacity and volume changes slightly alter the calculations applied to obtain these values.
Variations in oceanic layer 2 elastic velocities near Hawaii and their correlation to lithospheric flexure
Authors: Brocher Thomas M. , ten Brink Uri S.
Published: February 2008

Analysis of the travel times and amplitude range distributions of both compressional and shear wave arrivals on 15 closely spaced refraction profiles reveals a significant, systematic, and symmetric dependence of average layer 2 velocities on their distance to the north and south of the Hawaiian ridge. Beyond the flexural arch surrounding the ridge the velocity‐depth solutions indicate a normal layer 2. Within the arch (approximately 155 km from the ridge) the average elastic velocities in layer 2 are lowered by 0.8–0.9 ± 0.2 km/s. Within 75 km of the ridge the average velocities are again normal. Elastic and elastic‐plastic flexural models for the regional compensation of the Hawaiian islands predict tensional stress drops of 0.8 kbar in the upper lithosphere for the region having lowered velocities in layer 2, which are similar in magnitude with laboratory measurements of the confining pressure drop necessary to reduce velocities in porous basalts by 0.5 km/s. A significant inverse relationship (correlation coefficient of 0.818) exists between the average elastic velocities in the upper 1.0 km of the igneous crust and the strain in the upper crust calculated from these flexural models. The correlation between lowered average velocities in layer 2 and increased tensional stresses and strains suggest that crack opening in the upper crust accompanies the flexure. These observations are the first reported for a midplate load and corroborate previous suggestions from seismic and flexural data at subduction zones.
Seismic waveform modeling in heterogeneous media by ray perturbation theory
Authors: Farra Veronique , Madariaga Raul
Published: February 2008

We study the propagation of rays, par axial rays, and Gaussian beams in a medium where slowness differs only slightly from that of a reference medium. Ray theory is developed using a Hamiltonian formalism that is independent of the coordinate system under consideration. Let us consider a ray in the unperturbed medium. The perturbation in slowness produces a change of the trajectory of this ray which may be calculated by means of canonical perturbation theory. We define par axial rays as those rays that propagate in perturbed medium in the vicinity of the perturbed ray. The ray tracing equation for par axial rays may be obtained by a linearization of the canonical ray equations. The linearized equations are then solved by a propagator method. With the help of the propagator we form beams, i. e. families of paraxial rays that depend on a single beam parameter. The results are very general and may be applied to a number of kinematic and dynamic ray tracing problems, like two‐point ray tracing, Gaussian beams, wave front interpolation, etc. The perturbation methods are applied to the study of a few simple problems in which the unperturbed medium is homogeneous. First, we consider a two‐dimensional spherical inclusion with a Gaussian slowness perturbation profile. Second, transmission and reflection problems are examined. We compare results for amplitude and travel time computed by exact and perturbed ray theory. The agreement is excellent and may be improved using an iterative procedure by which we change the reference unperturbed ray whenever the perturbation becomes large. Finally, we apply our technique to a three‐dimensional problem: we calculate the amplitude perturbation and ray deflection produced by the velocity structure under the Mont Dore volcano (central France). Again a comparison shows excellent agreement between exact and perturbed ray theory.
Apollo 17 KREEPy basalts: Evidence for nonuniformity of KREEP
Authors: Salpas Peter A. , Taylor Lawrence A. , Lindstrom Marilyn M.
Published: February 2008

Breccia 72275 contains pristine KREEPy basalt clasts that are not found among other samples collected at Apollo 17. These basalts occur as discrete clasts and as clasts enclosed within basaltic microbreccias. Mineral and whole‐rock chemical analyses reveal that the microbreccias are compositionally indistinguishable from the basalt clasts. Samples of the 72275 matrix also have the same compositions as the basalts and the basaltic microbreccias. 72275 was assembled in situ from a single flow or series of closely related flows of Apollo 17 KREEPy basalt before it was transported to the Apollo 17 site. As a rock type, Apollo 17 KREEPy basalts are distinct from Apollo 15 KREEP basalts. The Apollo 17 samples have lower REE concentrations, steeper negative slopes of the HREE, and are less magnesian than the Apollo 15 samples. The two basalt types cannot be related by fractional crystallization, partial melting, or assimilation. This is evidence for the compositional nonuniformity of KREEP as a function of geography.
Origin of lead from green glass of Apollo 15426: A search for primitive lunar lead
Authors: Tatsumoto Mitsunobu , Premo Wayne R. , Unruh Daniel M.
Published: February 2008

A major obstacle in lunar U‐Pb chronology is the elusiveness of the primary Pb isotopic composition and U/Pb ratio and therefore the Pb evolution for the early history of the moon. In an attempt to seek the primitive lunar Pb isotopic composition, green glass from lunar clod 15426,49 was studied for U‐Th‐Pb systematics because it is extremely Mg‐rich and known to be the most primitive among sampled lunar volcanic rocks. Green glass and yellow impact glass were handpicked, washed with water, then washed in an acid mixture (0.3 N HBr + 0.2 N HF), and the washes and residues were analyzed. In contrast to the Pb from Apollo 17 orange glass, Pb from the surface of the green glass spherules is totally different from that of the spherule interior, but is similar to lunar surface lead. Data for the interior Pb yield a 207Pb/206Pb age of 3.41 Ga. Because of the low Pb concentration and high U/Pb ratio observed for the interior, the initial Pb was poorly defined. Nevertheless, the data indicate that lunar Pb evolved in an environment with 238U/204Pb = 19–55, which is considerably lower than those for mare basalts (around 300) but higher than values for the earth (6–8).
The composition and history of breccia 67015 from North Ray Crater
Authors: Marvin Ursula B. , Lindstrom Marilyn M. , Bernatowicz T. J. , Podosek Frank A. , Sugiura Naoji
Published: February 2008

We have examined feldspathic fragmental breccia 67015 from the rim of North Ray Crater and found it to be the most diverse and complex of the Apollo 16 FFBs. It contains a wider range of clast types than any of the others and is not dominated by any single lithology. We have identified several crystalline lithologies, occurring in minor amounts, that we believe represent highland plutonic rocks. Plagioclase fragments are the most abundant breccia constituent, followed by clasts of impact melt rocks and granulites. The impact melts are of two main types: feldspathic fragment‐laden melts and mafic, KREEPy melt rocks of VHA basalt composition. Textural evidence indicates that some of the VHA melts were hot and plastic when they accumulated into the breccia. 40Ar‐39Ar dates show that both types of melts solidified about 3.9 × 109 years ago. Magnetic measurements on clasts show a scatter of NMR directions, making it impossible to read a consistent imprint of an ancient dipolar magnetic field. Previous studies of Apollo 16 stratigraphy suggested that KREEPy melt rocks were introduced to the site as Imbrium impact ejecta, about 3.8 × 106 years ago. Our results indicate that the highlands crust contained KREEP components as early as 3.9 × 109 years ago.
Quantitative abundance estimates from bidirectional reflectance measurements
Authors: Mustard John F. , Pieters Carle M.
Published: February 2008

A simplified approach to the problem of determining the relative proportion of minerals in a mixture from a reflectance spectrum of the mixture is presented. Fundamental to this approach is a priori information concerning reflectance spectra of the minerals in the mixture and some estimate of the particle sizes of the mixture components. Reflectance spectra of intimate mixtures are a systematic but nonlinear combination of the spectra of the minerals in the mixtures. Equations for bidirectional reflectance are used to linearize the systematics of spectral mixing for intimate mixtures. The equations are simplified by assuming that particulate media scatter light isotropically at phase angles between 15° and 40°. This method for linearizing the mixing systematics is used to determine mineral relative geometric cross sections (proportional to mass fraction/density × particle diameter) from reflectance spectra of mixtures of igneous rock‐forming minerals (olivine, magnetite, enstatite, and anorthite) and to determine endmember relative geometric cross sections from reflectance spectra of mixtures of terrestrial desert soils. Since particle diameters are known, the mass fractions of the mixture components are also calculated. For materials without strongly absorbing components, the accuracy of abundance determinations is better than 5%. The results indicate that the method presented can be used to accurately determine the relative proportions of components (minerals or complex endmembers) in a mixture from a reflectance spectrum of the mixture given information of the endmembers in the mixture, reflectance spectra of the endmembers, and an estimate of particle sizes of the respective mixture components.
A kinetic study of the hydrous alteration of amorphous MgSiO smokes: Implications for cometary particles and chondrite matrix
Authors: Nelson Robert , Nuth Joseph A. , Donn Bertram
Published: February 2008

We report measurements of the rate of hydrous alteration of amorphous Mg‐SiO smokes as a function of temperature as inferred by observing changes in the infrared spectra of these materials. We show that under the conditions reported for the nucleus of Comet Halley based on measurements made by the Vega and Giotto missions, amorphous, anhydrous Mg‐SiO smokes would become hydrated within several weeks in the dusty regolith observed on the surface. However, if such grains were released in “jets” or from loose ice fragments, then previously amorphous grains would retain their anhydrous nature. Similarly, brief periods of aqueous activity on meteorite parent bodies would convert amorphous, fine‐grained material to hydrated phyllosilictes much more rapidly than coarse mineral grains. A kinetic model might therefore be developed to explain the observed textural relationships in the matrices of carbonaceous chondrites such as Mokoia, where amorphous phyllosilicates are intimately associated with coarse anhydrous grains.
Nuclide production by primary cosmic‐ray protons
Authors: Reedy Robert C.
Published: February 2008

The production rates of cosmogenic nuclides in the solar system and in interstellar space were calculated for the primary protons in the galactic and solar cosmic rays. Only thin‐target production rates, which are directly applicable to small objects in space, were calculated; however, these results also are used to examine the relative variations in production rates that are possible for large objects. In small objects at 1 AU from the sun, the long‐term average fluxes of solar protons usually produce many more atoms of a cosmogenic nuclide than do the primary protons in the galactic cosmic rays (GCR)—the exceptions being nuclides made only by high‐energy reactions (such as 10Be). Because the particle fluxes inside meteorites and other large objects in space include many secondary neutrons, the production rates are much higher, and ratios inside large objects are often very different from those produced by just the primary GCR protons in small objects. The production rates of cosmogenic nuclides are calculated to vary by factors of about 2.5 between the extremes for a typical 11‐year solar cycle; this variation is in agreement with measurements of short‐lived radionuclides in recently fallen meteorites. The production of cosmogenic nuclides by GCR particles outside the heliosphere is higher by factors of ∼4 than that by the modulated GCR primaries normally in the solar system. However, there is considerable uncertainty about the fluxes of interstellar protons and, therefore, in the production rates of cosmogenic nuclides in interstellar space. Production rates and ratios for cosmogenic nuclides could be used to identify particles that were from small bodies in space or that were exposed to an unmodulated spectrum of GCR particles.
Distinct meteoroid families identified on the lunar seismograms
Authors: Oberst Jürgen , Nakamura Yosio
Published: February 2008

We reexamined the seismic events originating from impacts of meteoroids on the lunar surface, as recorded by the Apollo lunar seismic network, in terms of (1) difference in temporal distribution between large and small impacts, (2) clustering of impacts in a two‐dimensional space of the time of the year and the time of the month (lunar day), and (3) their relationship with terrestrial observations. The study led us to identify several distinct families of meteoroids impacting the moon. Most meteoroids producing small impact‐seismic events appear to approach from retrograde heliocentric orbits, including many that are associated with well‐known cometary showers. In contrast, most meteoroids associated with large impact‐seismic events appear to approach from prograde orbits. Although some of them may also be cometary, the observation is consistent with a hypothesis that many of them represent stony asteroidal material. A unique cluster of large‐amplitude impact events observed in June, 1975, appears to be associated with the Taurid cometary complex, suggesting that the Taurids contain more massive or even denser objects than other meteor showers. The previously reported discrepancy between lunar and terrestrial meteoroid‐flux estimates may be due to the differences in lunar and terrestrial detection efficiency among various families of meteoroids.
Eastern Asia in the Cretaceous: New paleomagnetic data from South Korea and a new look at Chinese and Japanese data
Authors: Gidong Lee , Besse Jean , Courtillot Vincent , Montigny Raymond
Published: February 2008

Lower Cretaceous continental sediments and volcanic rocks have been sampled in the Gyeongsang basin (South Korea). A detailed analysis of 160 specimens reveals two stable components of magnetization, a postfolding, low‐temperature (LT) component with normal polarity and a stable, high‐temperature (HT) component with both normal and reversed polarities. The blocking temperature of the HT component ranges from 540°C up to the Néel temperature of hematite. This component predates the folding of the series and yields a pole at λ = 68°N, Φ = 205°E, A95 = 6°. The prefolding magnetization indicates that South Korea stood at a latitude nearly identical to its present‐day latitude in the Lower Cretaceous. Comparison of Korean data with (revised) paleomagnetic data from North and South China and Japan shows that all these blocks of Eastern Asia occupied the same positions in term of latitude and were probably parts of a single craton since at least the Lower Cretaceous. The paleomagnetic directions of the Sino‐Korean block show large discrepancies with respect to the expected directions of the “stable” Eurasian (Siberian) block. An interpretation involving significant N‐S motion (∼1000 km) between either North and South China or between North China and Siberia appears to contradict geological data. A preferred interpretation is that the Siberian data are in serious error and that the combined China/Korea Lower Cretaceous pole provides a valid estimate for the Eurasian plate as a whole.
A stagnation point flow model for melt extraction from a mantle plume
Authors: Ribe Neil M. , Smooke Michell D.
Published: February 2008

We present a two‐dimensional dynamical model for melt extraction from a mantle plume. Mantle material rises at constant velocity Wo until it reaches a depth at which melting begins. The flow in the melt zone above this depth has the form of a stagnation point flow. Melt migrates through the unmelted matrix in response to the total nonhydrostatic pressure gradient, which is the sum of contributions from the deformation of the matrix and the buoyancy of the melt. Melt extraction is modeled as a melt flux through the upper surface of the melt zone. Our main conclusions are as follows: (1) The nonhydrostatic pressure gradient associated with the deformation of the matrix is small relative to the buoyancy of the melt everywhere within the melt zone, and the melt migration within the plume obeys Darcy's law. The rate of melt extraction from a mantle plume is therefore controlled by the buoyancy and viscosity of the melt itself, and not by the viscosity of the matrix. (2) Melt extraction from a plume occurs over an area comparable to that of the plume itself, and about 60–80% of the melt generated within the plume is extracted. Both the geometry and rate of extraction predicted by the model are consistent with observations in the Hawaiian Islands. (3) Layers of segregated melt (magma chambers) are likely to form at the the base of the lithosphere under intraplate volcanoes.
Geopotential orbit variations: Applications to error analysis
Authors: Wagner Carl A.
Published: February 2008

The position and velocity errors of a near‐circular orbit due to geopotential uncertainty are developed in Fourier series. Current satellite gravity models generate position uncertainties of up to 50 m alongtrack for close satellites (∼1000 km altitude) in shallow resonance (periods less than 5 days, from coefficients of order 13–14). Smaller radial errors are due to resonance and to first‐order terms poorly seen in current satellite geopotentials. Correlation of errors is strong by order and the same degree parity. Application of the development is made to (1) the prediction of errors for a future altimeter satellite, (2) the capability of earth‐based tracking of a close Mars orbiter in resolving that planet's gravity potential, and (3) improvement of the resolution of the low‐degree geopotential from the Geopotential Research Mission using tracking data from the Global Positioning System.
Columbia Glacier, Alaska: Changes in velocity 1977–1986
Authors: Krimmel Robert M. , Vaughn Bruce H.
Published: February 2008

The Columbia Glacier, a grounded, iceberg‐calving tidewater glacier near Valdez, Alaska, began to retreat about 1977. Drastic retreat occurred in 1984, and by early 1986, retreat amounted to 2 km. The glacier has thinned more than 100 m since 1974 at a point 4 km behind the 1974 terminus position. Between 1977 and 1985 the lower glacier ice velocity increased from 3–8 m/d to 10–15 m/d. Ice velocity in the region 0.5 km above the terminus was highest near the time the glacier was most receded (late fall), and lowest near the time of maximum length (early summer), for years 1977–1982. Velocity in the region 52–57 from the head of the glacier was highest in mid‐spring, and lowest in early fall from 1977 to 1985. Through the years 1983–1985, the dates of maximum and minimum velocities within 0.5 km of the receding terminus tended toward the dates of the 52–57 km maximum and minimums. This occurred because as the terminus receded, it was no longer strongly influenced by the reverse slope of the terminal moraine shoal. Velocities near the terminus fluctuated by 2–3 m/d during summer and fall, when liquid water input was variable, and were relatively constant during winter. Hourly variations in ice velocities are controlled by liquid water input to the glacier hydraulic system and tide stage. Velocity increases near periods of high surface water input and decreases during periods of high tide as a result of hydrostatic back pressure.
Compressibility of solids
Authors: Vinet P. , Ferrante J. , Rose J. H. , Smith J. R.
Published: February 2008

We have discovered that the isothermal equation of state for solids in compression has a simple, universal form. This single form is shown to accurately describe the pressure and bulk modulus as a function of volume for ionic, metallic, covalent, and rare gas solids.
Snow load effect on the Earth's rotation and gravitational field, 1979–1985
Authors: Chao B. Fong , O'Connor William P. , Chang Alfred T. C. , Hall Dorothy K. , Foster James L.
Published: February 2008

A global, monthly snow depth data set has been generated from the Nimbus 7 satellite observations using passive microwave remote‐sensing techniques. In this paper we analyze 7 years of data, 1979–1985, to compute the snow load effects on the earth's rotation and low–degree zonal gravitational field. A uniform sea level decrease has been assumed in order to conserve water mass. The resultant time series show dominant seasonal cycles. The annual peak‐to‐peak variation in J2 is found to be 2.3 × 10 −10, that in J3 to be 1.1 × 10−10, and believed to decrease rapidly for higher degrees. The corresponding change in the length of day is 41 μs. The annual wobble excitation is (4.9 marc sec, −109°) for the prograde motion component and (4.8 marc sec, −28°) for the retrograde motion component. The excitation power of the Chandler wobble due to the snow load is estimated to be about 25 dB less than the power needed to maintain the observed Chandler wobble. The superior quality of the satellite data over conventional data acquired by ground observations and modeling is demonstrated. We also discuss the role of atmospheric water and the problems arising from the lack of snow load observations over the Antarctic and Greenland ice sheets.
Evidence from gravity data for an intrusive complex beneath Mount St. Helens
Authors: Williams David L. , Abrams Gerda , Finn Carol , Dzurisin Daniel , Johnson Daniel J. , Denlinger Roger
Published: February 2008

On the basis of gravity data, aided by aeromagnetic, magnetotelluric, side‐looking radar, and geologic information, we tentatively identify a large, shallow intrusive complex beneath Mount St. Helens. The complex is roughly 5–6 km thick and has apparently intruded a buried and compressed Mesozoic forearc sedimentary sequence. The lateral extent of the intrusive complex is uncertain, and we give three alternative models varying from about 18 by 10 km to as much as 18 by 22 km. The western boundary of the inferred Mount St. Helens intrusion abuts several of a number of Tertiary and younger plutons that crop out in the area. The Mount St. Helens intrusion apparently is adjacent to sedimentary rock or shallow volcanic rock along most of the remainder of its boundary. A ringlike drainage pattern around Mount St. Helens suggests subsidence caused by removing magma from deep beneath Mount St. Helens and adding this mass to the Mount St. Helens edifice and its underlying intrusion. Our analysis indicates that the average bulk density of the volcanic rock comprising Mount St. Helens is about 2.15 g/cm3.
High precision relative locations of earthquakes at Mount St. Helens, Washington
Authors: Frémont Marie‐José , Malone Stephen D.
Published: February 2008

Several earthquake sequences have occurred at Mount St. Helens as clusters of shallow events with nearly identical waveforms (multiplets). We present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques. A multiplet is studied in pairs of events called doublets. Each doublet is made up of a reference event and one other event from the multiplet. The cross spectrum of a short window beginning just before the P arrival is used to compute differences in arrival times between seismograms from the same station for each doublet. These time differences, computed with a precision of 1–2 ms, are then used to locate each earthquake relative to the reference event. Engineering explosions with well‐known locations are used to test the relocation technique. Explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion. The relocation technique is applied to earthquakes preceding the September 10, 1984, and the May‐June 1985 dome‐building eruptions of Mount St. Helens. Forty events that occurred during a 12‐hour period in September 1984 are located in a volume, approximately 30 m in diameter, beneath the lava dome. The earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume. In the May‐June 1985 eruption we recognize three multiplet sets that took place successively in time. The multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit.
Detectability of minerals on desert alluvial fans using reflectance spectra
Authors: Shipman Hugh , Adams John B.
Published: February 2008

We analyzed the visible and near‐infrared reflectance spectra of soil samples collected from desert alluvial and colluvial surfaces in the Cuprite mining district, Nevada. These surfaces are downslope from hydrothermally altered volcanic rocks that contain spectrally characteristic minerals such as alunite and kaolinite. Coarse fractions of the soils on the alluvial fans are mineralogically variable and express the upslope lithologies; fine fractions are remarkably similar mineralogically and spectrally in all samples because of dilution of local mineral components by regionally derived windblown dust. Theoretical models for spectral mixing and for particle‐size effects were used to model the observed spectral variations. Diagnostic mineral absorption bands in the spectra of fan materials were enhanced by computationally removing the spectrum of the homogenous fine‐soil component. Detection limits for minerals were found to be controlled by the sensitivity of the instrument, the spectral contrast between the mineral and the background, and the relative brightnesses of the mineral and the background. These results show that spectral mixing models are useful for analyzing data with high spectral resolution obtained by field and aircraft spectrometers.
Uniformity and diversity in the composition of mineralizing fluids from hydrothermal vents on the southern Juan de Fuca Ridge
Authors: Philpotts J. A. , Aruscavage P. J. , Von Damm K. L.
Published: February 2008

Abundances of Li, Na, K, Rb, Ca, Sr, Ba, Mn, Fe, Zn, and Si have been determined in fluid samples from seven vents located in three areas on the southern Juan de Fuca Ridge. The hydrothermal component estimated from the Mg contents of the samples ranges from 7% to 76%. Concentrations of Fe and Si, among other elements, in acid‐stabilized solutions appear to be generally representative of the parental hydrothermal fluids, but some Zn determinations and most Ba values appear to be too low. Thermodynamic calculations indicate that the acidified samples remain supersaturated with respect to silica, barite, and pyrite; unacidified samples are supersaturated, in addition, with respect to ZnS, FeS, and many silicate phases. Within the constraints of limited sampling there appear to be differences in fluid compositions both within and between the three vent areas. Some uniform differences in the elemental abundances predicted for hydrothermal end‐member fluids might be due to inmixing of fresh seawater at depth in the hydrothermal system. The Juan de Fuca hydrothermal fluids contain more Fe but otherwise have relative elemental abundances fairly similar to those in 13°N (East Pacific Rise) fluids, albeit at higher levels. In contrast, fluids from 21°N (East Pacific Rise) and Galapagos have lower K/Rb and much lower Sr and Na abundances; these compositional features probably result from interaction of these fluids with a different mineral assemblage, possibly more mature greenstone.
Composition and dissolution of black smoker particulates from active vents on the Juan de Fuca Ridge
Authors: Feely Richard A. , Lewison Maureen , Massoth Gary J. , Robert‐Baldo Gillian , Lavelle J. William , Byrne Robert H. , Von Damm Karen L. , Curl Herbert C.
Published: February 2008

During two Atlantis II/Alvin cruises to the Juan de Fuca Ridge in 1984 active high temperature (140°–284°C) vents were sampled for black smoker particulates using the Grassle Pump. Individual mineral phases were identified using standard X ray diffraction and petrographic procedures. In addition, elemental compositions and particle morphologies were determined by X ray energy spectrometry and scanning electron microscope/X ray energy spectrometry techniques. The vent particulates from the southern Juan de Fuca Ridge vent sites were highly enriched in S, Si, Fe, Zn, and Cu and were primarily composed of sphalerite, wurtzite, pyrite, pyrrhotite, barite, chalcopyrite, cubanite, hydrous iron oxides, and elemental sulfur. Two additional unidentified phases which were prevalent in the samples included an Fe‐Si phase and a Ca‐Si phase. The grain sizes of the individual particle phases ranged from < 2 μm for the sphalerite and Fe oxide particles to > 100 μm for the Fe‐Si particles. Grain size and current meter data were used in a deposition model of individual phase dispersal. For many of the larger sulfide and sulfate particles, the model predicts dispersal to occur over length scales of only several hundreds of meters. The high‐temperature black smokers from the more northerly Endeavour Segment vents were highly enriched in Fe, S, Ca, Cu, and Zn and were primarily composed of anhydrite, chalcopyrite, sphalerite, barite, sulfur, pyrite, and other less abundant metal sulfide minerals. The grain sizes of the individual particles ranged from < 10 μm to slightly larger than 500 μm. The composition and size distributions of the mineral phases are highly suggestive of high‐temperature mixing between vent fluids and seawater. A series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals. The dissolution rates ranged over more than 3 orders of magnitude, from 3.2 × 10−8 cm s−1 for anhydrite to 1.2 × 10−12 cm s−1 for chalcopyrite. The results indicate that for some minerals, particularly anhydrite and marcasite, total dissolution occurs within a few hours to a few weeks of their formation. For other more stable minerals, including pyrite, sphalerite and chalcopyrite, the time required for total dissolution is much longer, and consequently, individual crystals may be expected to persist in the sediments for considerable periods of time after deposition.
Strain accumulation across the fairweather and Totschunda Faults, Alaska
Authors: Lisowski M. , Savage J. C. , Burford R. O.
Published: February 2008

Deformation across the Fairweather and Totschunda faults is estimated from repeated surveys of geodetic networks that span those faults. Surveys in 1967, 1983, and 1986 of networks crossing the Fairweather fault indicate that right‐lateral engineering shear strain is accumulating across the 1958 earthquake rupture at a rate of 1.6 ± 0.2 μrad/yr. This rate of deformation is one of the highest observed across a strike‐slip fault system, and it is several times greater than the secular rate of deformation across locked parts of the San Andreas fault. The rate of strain accumulation across the Fairweather fault was the same in the two intervals 1967–1983 and 1983–1986 and is thus believed to be a secular rate rather than a transient associated with the 1958 earthquake. The 1983–1986 line length changes are best fit by a model fault that is locked from the surface to a depth of 7 to 9 km and is slipping in a right‐lateral sense at a rate of 41 to 51 mm/yr below that depth. Models with the fault locked to any depth of ≥4 km fit the data almost equally well. The best‐fitting models indicate a slip rate comparable to the 48 to 58 mm/yr average late Holocene slip rate indicated by offset glacial moraines and to the 54 mm/yr component of relative motion between the Pacific and North American plates that is parallel to the Fairweather fault. No significant contraction was measured across the Fairweather fault. Only a small part of the relative plate motion is transferred across the Saint Elias Mountains to the colinear Totschunda fault. Surveys in 1909–1912 and 1985 of a geodetic network that extends for 72 km across the Totschunda fault indicate right‐lateral shear strain is accumulating at a rate of 0.11 ± 0.06 μrad/yr. This rate of strain accumulation suggests a slip rate of about 10 mm/yr on the Totschunda fault, a value at the lower end of the average Holocene slip rate of 10 to 20 mm/yr.