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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 919 records · Page 51Linked to original sources
USGS2015

Regional tectonic setting for the Trinidad earthquake swarms (2000-2012) from gravity and magnetic data

Earthquakes in the Raton basin near Trinidad, Colorado, (Figure 1) are located (Rubenstein et. al., 2014) near a major gravity and magnetic boundary. These earthquakes also occur in an area of hydrocarbon production that includes several high-capacity produced water injection wells. This presentation gives a very basic outline of the relation between the earthquakes, the potential field data, and possible basement structure.

Colorado, New Mexico↗
USGS2001

Minimum age of the Neoproterozoic Seven Hundred Acre Island Formation and the tectonic setting of the Islesboro Formation, Islesboro block, Maine

Two plat formal stratigraphic sequences occur on Islesboro, Penobscot Bay, Maine. The older Seven Hundred Acre Island Formation is at least 200 m thick, its base is not exposed, and it makes up fault-bounded blocks of siliceous colour-banded dolomitic marble, muscovite-rich quartzite, coarse-grained splendent muscovite-garnet-staurolite-andalusite schist, and calcareous metapelite, with minor garnet amphibolite and amphibolite. It was initially metamorphosed to lower amphibolite facies and was later retrograded to lower greenschist facies. The lower amphibolite facies metamorphism is Neoproterozoic (670 to 650 Ma) as inferred from the 40 Ar/ 39 Ar high temperature release spectra of hornblende separates. A U-Pb zircon age of 646.7 ± 2.7 Ma obtained for a pegmatite that intruded deformed rocks is taken to be the minimum age of the Formation. The platformal Islesboro Formation probably unconformably overlies the Seven Hundred Acre Island Formation. It is primarily turbiditic pelite with many beds of quartzite, impure dolomitic marble, some conglomerate, and a few feldspar-rich volcaniclastic beds and is thought to be either Neoproterozoic or Cambrian. It was metamorphosed only to lower greenschist facies, possibly in the same event that retrograded the Seven Hundred Acre Island Formation. Geochemical interpretations of minor and trace element analyses of six amphibolite and four schist samples from the Seven Hundred Acre Island Formation show that the protoliths of the amphibolite samples were intermediate between tholeiitic and within-plate type basaltic flows or dikes that intruded attenuated continental crust, or were eroded from these basalts. Four amphibolite and three schist samples analyzed for Pb isotopes were found to be enriched in radiogenic Pb. The Pb isotopic compositions are similar to those in peri-Gondwanan basement rocks from Atlantic Canada. The peri-Gondwanan Islesboro block was placed against the peri-Gondwanan Middle and Late Cambrian Ellsworth terrane on the cast by significant Late Silurian strike-slip faulting. The Late Silurian or Early Devonian Turtle Head dextral strike-slip fault separates the Islesboro block from the peri-Gondwanan St. Croix terrane to the west. The timing and nature of the movements of these faults are given from offsets of the isograds around the zircon-dated Laic Silurian Sedgwick Granite (419.5 ± 1.4 Ma) and South Penobscot Intrusive Suite (419.2 ± 2.2 Ma). These terranes and others like them in Atlantic Canada make up a composite terrane that is different from the composite Avalonian terranes sensu stricto of southeastern New England and Atlantic Canada. The composite peri-Gondwanan terrane that included the Islesboro block was amalgamated with the margin of ancestral North America in the Silurian.

Maine↗
USGS1995

Silurian tectonic history of Penobscot Bay region, Maine

Early Paleozoic amalgamation of composite terranes was contemporaneous at widely separated regions that were later accreted to either ancestral North America or to Gondwana as those two continents approached each other. Peri-Gondwanan terranes formed from Late Cambrian and Early Ordovician rocks were amalgamated in the Late Ordovician and Early Silurian to form the Salinic orogenic belt. Salinic orogenic activity involved extensive thrust faulting and metamorphism, large strike-slip faults, and plutonism. In the Penobscot Bay region, Maine, the peri-Gondwanan St. Croix terrane was thrust northwest in the Silurian(?) upon middle amphibolite facies Ordovician and Early Silurian rocks of the Fredericton trough. The strike-slip faults are interpreted to either remain steep until they reach the sole of the thrust sheet or to become listric within the thrust sheet. -from Authors

Maine↗
USGS2007

Influence of tectonic folding on rockfall susceptibility, American Fork Canyon, Utah, USA

We examine rockfall susceptibility of folded strata in the Sevier fold-thrust belt exposed in American Fork Canyon in north-central Utah. Large-scale geologic mapping, talus production data, rock-mass-quality measurements, and historical rockfall data indicate that rockfall susceptibility is correlated with limb dip and curvature of the folded, cliff-forming Mississippian limestones. On fold limbs, rockfall susceptibility increases as dip increases. This relation is controlled by several factors, including an increase in adverse dip conditions and apertures of discontinuities, and shearing by flexural slip during folding that has reduced the friction angles of discontinuities by smoothing surface asperities. Susceptibility is greater in fold hinge zones than on adjacent limbs primarily because there are greater numbers of discontinuities in hinge zones. We speculate that susceptibility increases in hinge zones as fold curvature becomes tighter.

Natural Hazards and Earth System Sciences↗
USGS1981

Plate-tectonic mechanism of Laramide deformation.

The Laramide compressive deformation of the craton was caused by a clockwise rotation of about 2-4o of the Colorado Plateau region relative to the continental interior, during late Late Cretaceous and early Tertiary time. Late Paleozoic and Neogene deformation of the craton also were produced by motion of a southwestern subplate relative to the continental interior. -from Author

Contributions to Geology - University of Wyoming, ↗
USGS1988

Tectonic significance of dikes of Westerly Granite, southeastern Connecticut and southwestern Rhode Island

Undeformed Early Permian Westerly Granite dikes cut gneisses of the southeastern New England Avalon zone along coastal southeastern Connecticut and adjacent Rhode Island. Most dikes dip southward at a low angle. The Westerly dikes were emplaced in relatively warm rock penecontemporaneously with the Narragansett Pier Granite during a narrow time interval shortly after cessation of pervasive Alleghanian ductile deformation but probably before final localized movement on major shear zones. The gentle dips indicate subhorizontal release at the end stage of the Alleghanian compressive event. Doming, intrusion of granite, and subsequent rapid uplift and cooling are attributed to the underplating of Avalonian crust by an African plate during the Alleghanian. -Author

Northeastern Geology↗
USGS1997

Bimodal magmatism, basaltic volcanic styles, tectonics, and geomorphic processes of the eastern Snake River Plain, Idaho

Geology presented in this field guide covers a wide spectrum of internal and surficial processes of the eastern Snake River Plain, one of the largest components of the combined late Cenozoic igneous provinces of the western United States. Focus is on widespread Quaternary basaltic plains volcanism that produced coalescent shields and complex eruptive centers that yielded compositionally evolved magmas. The guide is constructed in several parts beginning with discussion sections that provide an overview of the geology followed by road directions, with explanations, for specific locations. The geology overview briefly summarizes the collective knowledge gained, and petrologic implications made, over the past few decades. The field guide covers plains volcanism, lava flow emplacement, basaltic shield growth, phreatomagmatic eruptions, and complex and evolved eruptive centers. Locations and explanations are also provided for the hydrogeology, groundwater contamination, and environmental issues such as range fires and cataclysmic floods associated with the region.

Brigham Young University Geology Studies↗
USGS1999

Middle Miocene paleotemperature anomalies within the Franciscan Complex of northern California: Thermo-tectonic responses near the Mendocino triple junction

This study documents three localities in the Franciscan accretionary complex of northern California, now adjacent to the San Andreas fault, that were overprinted thermally between 13.9 and 12.2 Ma: Point Delgada-Shelter Cove (King Range terrane); Bolinas Ridge (San Bruno Mountain terrane); and Mount San Bruno (San Bruno Mountain terrane). Vein assemblages of quartz, carbonate, sulfide minerals, and adularia were precipitated locally in highly fractured wall rock. Vitrinite reflectance (Rm) values and illite crystallinity decrease away from the zones of metalliferous veins, where peak wall-rock temperatures, as determined from Rm, were as high as 315??C. The ??18O values of quartz and calcite indicate that two separate types of fluid contributed to vein precipitation. Higher ??18O fluids produced widespread quartz and calcite veins that are typical of the regional paleothermal regime. The widespread veins are by-products of heat conduction and diffuse fluid flow during zeolite and prehnite-pumpellyite-grade metamorphism, and we interpret their paleofluids to have evolved through dehydration reactions and/or extensive isotopic exchange with accreted Franciscan rocks. Lower ??18O fluids, in contrast, evolved from relatively high temperature exchange between seawater (or meteoric water) and basaltic and/or sedimentary host rocks; focused flow of those fluids resulted in local deposition of the metalliferous veins. Heat sources for the three paleothermal anomalies remain uncertain and may have been unrelated to one another. Higher temperature metalliferous fluids in the King Range terrane could have advected either from a site of ridge-trench interaction north of the Mendocino fracture zone or from a "slabless window" in the wake of the northward migrating Mendocino triple junction. A separate paradox involves the amount of Quaternary offset of Franciscan basement rocks near Shelter Cove by on-land faults that some regard as the main active trace of the San Andreas plate boundary. Contouring of vitrinite reflectance values to the north of an area affected by A.D. 1906 surface rupture indicates that the maximum dextral offset within the interior of the King Range terrane is only 2.5 km. If this fault extends inland, and if it has been accommodating most of the strike-slip component of San Andreas offset at a rate of 3-4 cm/yr, then its activity began only 83-62 ka. This interpretation would also mean that a longer term trace of the San Andreas fault must be nearby, either offshore or along the northeast boundary of the King Range terrane. An offshore fault trace would be consistent with peak heating of King Range strata north of the Mendocino triple junction. Conversely, shifting the fault to the east would be compatible with a slabless window heat source and long-distance northward translation of the King Range terrane after peak heating.

Geological Society of America Bulletin↗
USGS1998

Tectonic controls on fault-zone permeability in a geothermal reservoir at Dixie Valley, Nevada

To determine factors controlling permeability variations within and adjacent to a fault-hosted geothermal reservoir at Dixie Valley, Nevada, we conducted borehole televiewer observations of wellbore failure (breakouts and cooling cracks) together with hydraulic fracturing stress measurements in six wells drilled into the Stillwater fault zone at depths of 2 to 3 km. Measurements in highly permeable wells penetrating the main geothermal reservoir indicate that the local orientation of the least horizontal principal stress, Shmin, is nearly optimal for normal faulting on the Stillwater fault. Hydraulic fracturing tests from these wells further show that the magnitude of Shmin is low enough to lead to frictional failure on the Stillwater and nearby subparallel faults, suggesting that fault slip is responsible for the high reservoir productivity. Similar measurements were conducted in two wells penetrating a relatively impermeable segment of the Stillwater fault zone, located approx. 8 and 20 km southwest of the geothermal reservoir (wells 66-21 and 45-14, respectively). The orientation of Shmin in well 66-21 is near optimal for normal faulting on the nearby Stillwater fault, but the magnitude of Shmin is too high to result in incipient frictional failure. In contrast, although the magnitude of Shmin in well 45-14 is low enough to lead to normal faulting on optimally oriented faults, the orientation of the Stillwater fault near this well is rotated by approx. 40?? from the optimal orientation for normal faulting. This misorientation, coupled with an apparent increase in the magnitude of the greatest horizontal principal stress in going from the producing to nonproducing wells, acts to inhibit frictional failure on the Stillwater fault zone in proximity to well 45-14. Taken together, data from the nonproducing and producing wells thus suggest that a necessary condition for high reservoir permeability is that the Stillwater fault zone be critically stressed for frictional failure in the current stress field.

Conference Paper↗
USGS2004

Holocene alluvium around Lefkosia (Nicosia), Cyprus: An archive of land-use, tectonic processes, and climate change

Holocene alluvium of the Pedhicos River around Lefkosia (Nicosia), Cyprus, was studied. Alluvial stratigraphy was found to present serial flood deposits underlying river terraces and an extensive alluvial fan. It was found that the stratigraphy and geomorphology of the alluvium can be interpreted to distinguish not only the effects of climate change, but also land-use change, and the impact of particular engineering works. It was suggested that details of the physical properties of the flood deposit sequences and paleosols can contribute to modeling various geophysical and engineering properties and in predicting response to vertical acceleration during earthquakes.

Conference Paper↗