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At least 361 records · Page 20Linked to original sources
USGS1991

The Wasatch fault zone, utah-segmentation and history of Holocene earthquakes

The Wasatch fault zone (WFZ) forms the eastern boundary of the Basin and Range province and is the longest continuous, active normal fault (343 km) in the United States. It underlies an urban corridor of 1.6 million people (80% of Utah's population) representing the largest earthquake risk in the interior of the western United States. We have used paleoseismological data to identify 10 discrete segments of the WFZ. Five are active, medial segments with Holocene slip rates of 1–2 mm a −1 , recurrence intervals of 2000–4000 years and average lengths of about 50 km. Five are less active, distal segments with mostly pre-Holocene surface ruptures, late Quaternary slip rates of <0.5 mm a −1 recurrence intervals of ≥10,000 years and average lengths of about 20 km. Surface-faulting events on each of the medial segments of the WFZ formed 2–4-m-high scarps repeatedly during the Holocene; latest Pleistocene (14–15 ka) deposits commonly have scarps as much as 15–20 m in height. Segments identified from paleoseismological studies of other major late Quaternary normal faults in the northern Basin and Range province are 20–25 km long, or about half of that proposed for the medial segments of the WFZ.

Journal of Structural Geology↗
USGS1991

Segmentation and the coseismic behavior of basin and range normal faults. Examples from east-central Idaho and southwestern Montana, USA

The range-front normal faults of the Lost River and Lemhi Ranges, and the Beaverhead and Tendoy Mountains in east-central Idaho and southwestern Montana have well-preserved fault scarps on Quaternary deposits along much of their lengths. Fault-scarp morphology, the age of deposits displaced by the faults, and the morphology of the range fronts provide a basis for dividing the faults into segments that are typically 20-25 km long. Four characteristics are recognized that help to identify segment boundaries: (1) major en echelon offsets or pronounced gaps in the continuity of fault scarps; (2) distinct, persistent, along-strike changes in fault-scarp morphology that indicate different ages of faulting; (3) major salients in the range front; and (4) transverse bedrock ridges where the cumulative throw is low compared to other places along the fault zone. Only features whose size is measured on the scale of kilometers are regarded as significant enough to represent a segment boundary that could inhibit or halt a propagating rupture. The ability to identify segments of faults that are likely to behave as independent structural entities will improve seismic-hazard assessment. However, one should not assume that the barriers at segment boundaries will completely stop all propagating ruptures.

Journal of Structural Geology↗
USGS1993

Kinematic stratification in the hinterland of the central Scandinavian Caledonides

A transect through west-central Norway illustrates the changing geometry and kinematics of collision in the hinterland of the central Scandinavian Caledonides. A depth section through the crust is exposed on Fosen Peninsula, comprising three tectonic units separated by two shear zones. The lowest unit, exposed in the Roan window, is a modestly deformed, Caledonian granulite complex framed by a subhorizontal décollement, with NW-SE oriented lineations and kinematic indicators showing top-to-the-northwest transport. The middle unit, the Vestranden gneiss complex, contains relict granulites, but was penetratively deformed at amphibolite facies to produce an orogen-parallel family of structures during translation on the décollement. Shallow plunging lineations on steep schistosities are subparallel to fold axes of the dominant, upright, non-cylindrical folds. A small component of sinistral strike slip is also recorded. In contrast, southernmost Fosen Peninsula contains an abundance of cover rocks infolded with Proterozoic basement in a fold nappe, with shallow, E-dipping schistosities, down-dip lineations, and orogen-oblique, top-to-the-west shear sense indicators. A NE-striking, sinistral shear zone separates the gneisses from southern Fosen. Deformation in the Scandian hinterland was partitioned both in space and time, with orogen-parallel extension and shear at middle structural levels and orogen-oblique transport at shallower levels.

Journal of Structural Geology↗
USGS1993

High-pressure deformation of calcite marble and its transformation to aragonite under non-hydrostatic conditions

We conducted deformation experiments on Carrara marble in the aragonite and calcite stability fields to observe the synkinematic transformation of calcite to aragonite, and to identify any relationships between transformation and deformation or sample strength. Deformation-induced microstructures in calcite crystals varied most significantly with temperature, ranging from limited slip and twinning at 400°C, limited recrystallization at 500°C, widespread recrystallization at 600 and 700°C, to grain growth at 800–900°C. Variations in confining pressure from 0.3 to 2.0 GPa have no apparent effect on calcite deformation microstructures. Aragonite grew in 10 −6 -10 −7 s −1 strain rate tests conducted for 18–524 h at confining pressures of 1.7–2.0 GPa and temperatures of 500–600°C. As in our previously reported hydrostatic experiments on this same transformation, the aragonite nucleated on calcite grain boundaries. The extent of transformation varied from a few percent conversion near pistons at 400°C, 2.0 GPa and 10 −4 s −1 strain rate in a 0.8 h long experiment, to 98% transformation in a 21-day test at a strain rate of 10 −7 s −7 , a temperature of 600°C and a pressure of 2.0 GPa. At 500°C, porphyroblastic 100–200 μm aragonite crystals grew at a rate faster than 8 × 10 −1 m s −1 . At 600°C, the growth of aragonite neoblasts was slower, ≈6 × 10 −1 m s −1 , and formed ‘glove-and-finger’ cellularprecipitation-like textures identical to those observed in hydrostatic experiments. The transformation to aragonite is not accompanied by a shear instability or anisotropic aragonite growth, consistent with its relatively small volume change and latent heat in comparison with compounds that do display those features.

Journal of Structural Geology↗
USGS1993

Experimental dynamic metamorphism of mineral single crystals

This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a - β quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite → clinoenstatite and w u &#x308; rtzite &#x2192; sphalerite "> würtzite→sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO · n Al 2 O 3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl 2 O 3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures.

Journal of Structural Geology↗
USGS1993

Structural analysis of sheath folds in the Sylacauga Marble Group, Talladega slate belt, southern Appalachians

Remnant blocks of marble from the Moretti-Harrah dimension-stone quarry provide excellent exposure of meter-scale sheath folds. Tubular structures with elliptical cross-sections (4 ≤ R yz ≤ 5) are the most common expression of the folds. The tubes are elongate subparallel to stretching lineation and are defined by centimeter-scale layers of schist. Eccentrically nested elliptical patterns and opposing asymmetry of folds (‘S’ and ‘Z’) are consistent with the sheath-fold interpretation. Sheath folds are locally numerous in the Moretti-Harrah quarry but are not widely distributed in the Sylacauga Marble Group; reconnaissance in neighboring quarries provided no additional observations. The presence of sheath folds in part of the Talladega slate belt indicates a local history of plastic, non-coaxial deformation. Such a history of deformation is substantiated by petrographic study of an extracted hinge from the Moretti-Harrah quarry. The sheath folds are modeled as due to passive amplification of initial structures during simple shear, using both analytic geometry and graphic simulation. As indicated by these models, relatively large shear strains ( y ≥ 9) and longitudinal initial structures are required. The shear strain presumably relates to NW-directed displacement of overlying crystalline rocks during late Paleozoic orogeny.

Journal of Structural Geology↗
USGS1994

Geometry of an outcrop-scale duplex in Devonian flysch, Maine

We describe an outcrop-scale duplex consisting of 211 exposed repetitions of a single bed. The duplex marks an early Acadian (Middle Devonian) oblique thrust zone in the Lower Devonian flysch of northern Maine. Detailed mapping at a scale of 1:8 has enabled us to measure accurately parameters such as horse length and thickness, ramp angles and displacements; we compare these and derivative values with those of published descriptions of duplexes, and with theoretical models. Shortening estimates based on line balancing are consistently smaller than two methods of area balancing, suggesting that layer-parallel shortening preceded thrusting.

Journal of Structural Geology↗
USGS1995

The role of microcracking in shear-fracture propagation in granite

Microcracking related to the formation of a laboratory shear fracture in a cylinder of Westerly granite has been investigated using image-analysis computer techniques. Well away from the fracture (farfield), the deformed granite has about twice the crack density (crack length per unit area) of undeformed granite. The microcrack density increases dramatically in a process zone that surrounds the fracture tip, and the fracture tip itself has more than an order of magnitude increase in crack density over the undeformed rock. Microcrack densities are consistently higher on the dilational side of the shear than on the compressional side. Microcracks in the undeformed rock and in the far-field areas of the laboratory sample are concentrated within and along the margins of quartz crystals, but near the shear fracture they are somewhat more abundant within K-feldspar crystals. The energy release rate, g II , for mode II fracture progagation is estimated from the microcrack density data to be ≥ 1.7–8.6 kJ m −2 . The microcracks that formed during the experiment are principally tensile cracks whose orientations reflect the local stress field: those formed prior to the nucleation of the fault are roughly parallel to the cylinder axis (loading direction), whereas those generated in the process zone make angles averaging 30 ° to the overall fault strike (and 20 ° to the cylinder axis). The preferred orientation and uneven distribution of microcracks in the process zone tends to pull the propagating fracture tip towards the dilational side, even though the trend is away from the overall fault strike. As a result, the propagating shear follows the microcrack trend for some distance and then changes direction in order to maintain an overall in-plane propagation path. This recurring process produces a zig-zag or sawtooth segmentation pattern similar to the sawtooth geometries of faults such as the San Andreas fault.

Journal of Structural Geology↗
USGS2004

Coal facies studies in the eastern United States

Coals in the eastern United States (east of the Mississippi River) have been the subject of a number of coal facies studies, going back to the 19th century. Such studies would not necessarily fall within a strict modern classification of coal facies studies, but if a study encompassed some aspects of paleobotany, palynology, petrology, geochemistry, or sedimentology, we assumed that some data and interpretations may be of use in evaluations of the facies. References are presented, as a guide for further research, with annotation in the tables. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2004

Functional group and individual maceral chemistry of high volatile bituminous coals from southern Indiana: Controls on coking

The individual maceral chemistries of two Pennsylvanian, high volatile bituminous coals, the Danville Coal Member (Dugger Formation, R o=0.55%) and the Lower Block Coal Member (Brazil Formation, R o=0.56%) of Indiana, were investigated using electron microprobe and Fourier Transform Infrared Spectrometry (FTIR) techniques, with the purpose of understanding differences in their coking behavior. Microprobe results reveal that carbon contents are highest in inertinite and sporinite, followed by desmocollinite and telocollinite. Oxygen and organic nitrogen are most abundant in telocollinite and desmocollinite; sporinite and inertinite contain lesser amounts of these two elements. Organic sulfur contents are highest in sporinite, lowest in inertinite, and intermediate in desmocollinite and telocollinite. Vitrinites within the Danville and Lower Block coals are very similar in elemental composition, while Lower Block inertinites and sporinites have higher carbon, lower oxygen, and sulfur contents which, when combined with the inertinite-and sporinite-rich composition of the Lower Block seam, strongly influences its whole coal chemistry. Fourier transform infrared spectrometry revealed greater aromatic hydrogen in the Lower Block coal, along with higher CH2/CH3 ratios, which suggest that liptinites contribute considerable amounts of long-chain, unbranched aliphatics to the overall kerogen composition of the Lower Block coal. Long-chain, unbranched aliphatics crack at higher temperatures, producing tar and oily byproducts during coking; these may help increase Lower Block plasticity. Electron microprobe and FTIR results indicate that individual maceral chemistries, combined with the maceral composition of the seam, are the primary control of better coking properties of the Lower Block coal. ?? 2003 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2004

Potential health impacts of burning coal beds and waste banks

Uncontrolled release of pollutants from burning coal beds and waste banks presents potential environmental and human health hazards. On a global scale, the emissions of large volumes of greenhouse gases from burning coal beds may contribute to climate change that alters ecosystems and patterns of disease occurrence. On regional and local scales, the emissions from burning coal beds and waste banks of acidic gases, particulates, organic compounds, and trace elements can contribute to a range of respiratory and other human health problems. Although there are few published reports of health problems caused by these emissions, the potential for problems can be significant. In India, large numbers of people have been displaced from their homes because of health problems caused by emissions from burning coal beds. Volatile elements such as arsenic, fluorine, mercury, and selenium are commonly enriched in coal deposits. Burning coal beds can volatilize these elements, which then can be inhaled, or adsorbed on crops and foods, taken up by livestock or bioaccumulated in birds and fish. Some of these elements can condense on dust particles that can be inhaled or ingested. In addition, selenium, arsenic, lead, tin, bismuth, fluorine, and other elements condense where the hot gaseous emissions come in contact with ambient air, forming mats of concentrated efflorescent minerals on the surface of the ground. These mats can be leached by rainwater and washed into local water bodies providing other potential routes of exposure. Although there are little data linking burning coal beds and waste banks to known health problems, a possibly analogous situation exists in rural China where mineralized coal burned in a residential environment has caused widespread and severe health problems such as fluorosis and arseniasis. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2004

Evaluation of coalbed gas potential of the Seelyville Coal Member, Indiana, USA

The Seelyville Coal Member of the Linton Formation in Indiana potentially contains 0.03 trillion m3 (1.1 TCF) of coalbed gas. The gas content determined by canister desorption technique ranges from 0.5 to 5.7 cm3/g on dry ash free basis (15.4 to 182.2 scf/ton). The controls on gas content distribution are complex, and cannot be explained by the coal rank alone. Ash content and the lithology of the overlying strata, among other factors, may influence this distribution. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2004

From in-situ coal to fly ash: A study of coal mines and power plants from Indiana

This paper presents data on the properties of coal and fly ash from two coal mines and two power plants that burn single-source coal from two mines in Indiana. One mine is in the low-sulfur (<1%) Danville Coal Member of the Dugger Formation (Pennsylvanian) and the other mines the high-sulfur (>5%) Springfield Coal Member of the Petersburg Formation (Pennsylvanian). Both seams have comparable ash contents (???11%). Coals sampled at the mines (both raw and washed fractions) were analyzed for proximate/ultimate/sulfur forms/heating value, major oxides, trace elements and petrographic composition. The properties of fly ash from these coals reflect the properties of the feed coal, as well as local combustion and post-combustion conditions. Sulfur and spinel content, and As, Pb and Zn concentrations of the fly ash are the parameters that most closely reflect the properties of the source coal. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2004

Modes of occurrence of mercury and other trace elements in coals from the warrior field, Black Warrior Basin, Northwestern Alabama

The mineralogic residence and abundance of trace metals is an important environmental issue. Data from the USGS coal quality database show that potentially toxic elements, including Hg, As, Mo, Se, Cu, and Tl are enriched in a subset of coal samples in the Black Warrior Basin of Alabama, USA. Although the coal as-mined typically is low in these elements, localized enrichments occur in high-pyrite coals and near faults. Microscopic analyses demonstrate that the residence of these elements is dominantly in a late-stage pyrite associated with structurally disrupted coal. Further, our data suggest addition of Hg to the coal matrix as well. The source of these trace elements was hydrothermal fluids driven into the Black Warrior Basin by Alleghanian age tectonism. ?? 2004 Published by Elsevier B.V.

International Journal of Coal Geology↗
USGS2004

Application of SAXS and SANS in evaluation of porosity, pore size distribution and surface area of coal

This paper discusses the applicability of small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) techniques for determining the porosity, pore size distribution and internal specific surface area in coals. The method is noninvasive, fast, inexpensive and does not require complex sample preparation. It uses coal grains of about 0.8 mm size mounted in standard pellets as used for petrographic studies. Assuming spherical pore geometry, the scattering data are converted into the pore size distribution in the size range 1 nm (10 A??) to 20 ??m (200,000 A??) in diameter, accounting for both open and closed pores. FTIR as well as SAXS and SANS data for seven samples of oriented whole coals and corresponding pellets with vitrinite reflectance (Ro) values in the range 0.55% to 5.15% are presented and analyzed. Our results demonstrate that pellets adequately represent the average microstructure of coal samples. The scattering data have been used to calculate the maximum surface area available for methane adsorption. Total porosity as percentage of sample volume is calculated and compared with worldwide trends. By demonstrating the applicability of SAXS and SANS techniques to determine the porosity, pore size distribution and surface area in coals, we provide a new and efficient tool, which can be used for any type of coal sample, from a thin slice to a representative sample of a thick seam. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2004

Carbon dioxide and methane sorption in high volatile bituminous coals from Indiana, USA

Samples of coals from several coalbeds in Indiana were analyzed for CO2 and CH4 sorption capacity using a high-pressure adsorption isotherm technique. Coal quality and petrographic composition of the coals were determined to study their relationships to the volume of CO2 and CH4 that could be sorbed into the coal. At the temperature of 17 ??C and 400 psi (??? 2.8 MPa), the coals can sorb (on dry ash-free basis) from 4 to 6.3 m3/ton (128-202 scf/ton) of CH4 and 19.5-24.6 m3/ton4 (624 to 788 scf/ton) of CO2. The ratio of CO2/CH4 at these conditions ranges from 3.5 to 5.3 and decreases with an increasing pressure for all coals. The coals studied are of a very similar coal rank (Ro from 0.48 to 0.62%) but of varying petrographic composition, and CO2 sorption volumes appear to be positively correlated to the content of maceral telocollinite. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2005

Mineralogy and geochemistry of a Late Permian coal in the Dafang Coalfield, Guizhou, China: Influence from siliceous and iron-rich calcic hydrothermal fluids

This paper describes the influence of siliceous and iron-rich calcic low-temperature hydrothermal fluids (LTHF) on the mineralogy and geochemistry of the Late Permian No. 11 Coal (anthracitic, Rr =2.85%) in the Dafang Coalfield in northwestern Guizhou Province, China. The No. 11 Coal has high contents of vein ankerite (10.2 vol.%) and vein quartz (11.4 vol.%), with formation temperatures of 85 and 180 ??C, respectively, indicating that vein ankerite and vein quartz were derived from low-temperature calcic and siliceous hydrothermal fluids in two epigenetic episodes. The vein quartz appears to have formed earlier than vein ankerite did, and at least three distinct stages of ankerite formation with different Ca/Sr and Fe/Mn ratios were observed. The two types of mineral veins are sources of different suites of major and trace metals. Scanning electron microscope and sequential extraction studies show that, in addition to Fe, Mg, and Ca, vein ankerite is the dominant source of Mn, Cu, Ni, Pb, and Zn in the coal, and the contents of these five elements are as high as 0.09% and 74.0, 33.6, 185, and 289 ??g/g, respectively. In contrast, vein quartz is the main carrier mineral for platinum-group elements (PGEs) Pd, Pt, and Ir in the coal, and the contents of Pd, Pt, and Ir are 1.57, 0.15, and 0.007 ??g/g, respectively. Sequential extraction showed a high PGE content in the silicate fraction, up to 10.4 ??g/g Pd, 1.23 ??g/g Pt, and 0.05 ??g/g Ir, respectively. It is concluded that the formation of ankerite and quartz and the anomalous enrichment of trace elements in the No. 11 Coal in the Dafang Coalfield, Guizhou, result from the influx of calcic and siliceous low-temperature hydrothermal fluids. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2005

Functional groups of fossil marattialeans: Chemotaxonomic implications for Pennsylvanian tree ferns and pteridophylls

Marattialean-fossil foliage, assigned to Pecopteris Brongniart, was an important and widespread floral component in Late Pennsylvanian mires, with phylogenetic affinity to extant marattialean taxa in tropical regions. Marattialean fossil taxonomy is, however, still uncertain. Specimens from the Pilsen limnic Basin, Westphalian D, Czech Republic, represent fertile marattialean foliage of Pecopteris (Asterotheca) nyranensis and Pecopteris (Asterotheca) miltonii, and sterile foliage of Pecopteris aspidioides and Pecopteris polypodioides. Taxonomic parameters for their assignments included cuticle, stomatal morphologies (studied for the first time), and in situ reproductive organs and spores. Chemotaxonomic interpretations hinge on fidelity of preservation of compounds, or molecular fragments thereof, that were synthesized by the once-living plants. This preservation state was possibly due to the thermal history (maximum temperature of 130 ??C) in the Pilsen Basin, acidic preservation conditions, lithology and facies stability. Although subtle, the four pecopterid species are differentiable from one another by combined FTIR characteristics, supporting taxonomy. The ratio of CH2/CH3 is hypothesized to be a chemotaxonomic parameter for Pennsylvanian pteridophylls, both in seed and true ferns that have previously been studied. It will, however, be supplemented by additional biochemical markers. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗