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Geology: Recent submissions
Now showing items 281-300 of 480
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Late Silurian plutons in Yucatan
(American Geophysical Union, 1996-08-10)U-Pb measurements of zircons from two composite plutons in the Maya Mountains of the Yucatan Block (Belize) give Late Silurian ages. Zircons from one of the five compositional phases of the Mountain Pine Ridge pluton yield ... -
Large-magnitude miocene extension in the central Mojave Desert: Implications for Paleozoic to Tertiary paleogeography and tectonics
(American Geophysical Union, 1990-01-10)The main Cenozoic extensional structure in the central Mojave Desert is the Waterman Hills detachment fault, which places brittlely deformed synorogenic Miocene rocks on ductilely and cataclastically deformed footwall ... -
Geologic evolution of Iron Mountain, central Mojave Desert, California
(American Geophysical Union, 1993-04)Geologic mapping, structural analysis, petrologic study, and U-Pb geochronology at Iron Mountain, 20 km southwest of Barstow, California, place important constraints on the paleogeographic affinities of metasedimentary ... -
Geochemistry of crustally derived leucocratic igneous rocks from the Ulugh Muztagh Area, Northern Tibet and their implications for the formation of the Tibetan Plateau
(American Geophysical Union, 1990-12-10)Igneous rocks collected from the Ulugh Muztagh, 200 km south of the northern rim of the Tibetan Plateau (36°28′N, 87°29′E), form intrusive and extrusive bodies whose magmas were produced by partial melting of upper-crustal, ... -
Evolution of extensional basins and basin and range topography west of Death Valley, California
(American Geophysical Union, 1989-06)Neogene extension in the Death Valley region, SE California, has produced a variety of sedimentary basins. Diachronous movements on an array of strike-slip and normal fault systems have resulted in the uplift and preservation ... -
Evolution of a mafic volcanic field in the central Great Basin, south central Nevada
(American Geophysical Union, 1996-08-10)Evolution of a mafic volcanic field is investigated through a study of Pliocene age rocks in the Reveille Range in south central Nevada. Pliocene activity began with the eruption of relatively abundant hawaiite (episode ... -
Evidence of Uppermost Proterozoic to Lower Cambrian miogeoclinal rocks and the Mojave-Snow Lake Fault: Snow Lake Pendant, central Sierra Nevada, California
(American Geophysical Union, 1990-12)Displaced uppermost Precambrian to Lower Cambrian miogeoclinal strata occur within Snow Lake pendant in the central Sierra Nevada. These rocks have been correlated with the Stirling Quartzite, the Wood Canyon Formation, ... -
Evidence for the generation of juvenile granitic crust during continental extension, Mineral Mountains Batholith, Utah
(American Geophysical Union, 1992-07-10)Field, chemical and isotopic data from the Miocene Mineral Mountains batholith in southwest Utah are consistent with the batholith being derived through differentiation of material recently separated from the lithospheric ... -
Connection between igneous activity and extension in the central Mojave metamorphic core complex, California
(American Geophysical Union, 1995-06-10)The development of metamorphic core complexes and associated low-angle detachment faults commonly is intimately associated with synextensional igneous activity. In most areas studied to date, the relation of magmatism to ... -
A mantle melting profile across the Basin and Range, SW USA
(American Geophysical Union, 2002-01)The major and trace element composition of late Cenozoic basalts (0–10 Ma) across the Basin and Range province (B&R) preserve a clear signal of mantle melting depth variations. FeO, Fe8.0, and Tb/Yb increase, whereas Si8.0 ... -
Monitoring pumping test response in a fractured aquifer using ground-penetrating radar
(American Geophysical Union, 2001-05)Fractured aquifers present a number of problems when attempting to characterize flow on the well scale (less than 100 m). Standard hydraulic testing methods are expensive because of the need for installation of monitoring ... -
Comparing flux-averaged and resident concentration in a fractured bedrock using ground penetrating radar
(American Geophysical Union, 2010-09)Saline tracer transport experiments were performed to compare flux-averaged and resident concentration in a single subhorizontal fracture in sandstone bedrock. Tracer migration over a 14 m distance was monitored at an ... -
GPR imaging of dual-porosity rocks: Insights to fluid flow
(Society of Exploration Geophysicists, 2008-11)Dual-porosity rocks, such as those that are fractured and/or karstic, are highly heterogeneous and present a great challenge to predicting fluid-flow properties. -
Ultra-shallow seismic imaging of the top of the saturated zone
(American Geophysical Union, 2010-04-08)We collected ultra-shallow seismic-reflection data to image the near-surface stratigraphy of a Kansas River point bar. We were successful in identifying a discontinuous clay layer and the top of the saturated zone at depths ... -
Shallow seismic AVO variations related to partial water saturation during a pumping test
(American Geophysical Union, 2007-11-27)High-resolution shallow seismic reflection experiments were conducted during and after a pumping test of an agricultural irrigation well to image the cone of depression. Although variations in the reflection time from the ... -
Investigating multi-polarization GPR wave transmission through thin layers: Implications for vertical fracture characterization
(American Geophysical Union, 2006-10-18)We investigate the controls governing the response of ground-penetrating radar (GPR) wave transmission through thin layers in order to explore the use of variable polarization GPR signals for remote characterization of ... -
Complex fabric development revealed by englacial seismic reflectivity: Jakobshavn Isbræ, Greenland
(American Geophysical Union, 2008-05-21)High-resolution reflection seismic data from Jakobshavn Isbræ, Greenland, reveal complex fabric development. Abundant englacial reflectivity occurs for approximately half the thickness of the ice (the lower half), and ... -
Ground-penetrating-radar response to fracture-fluid salinity: Why lower frequencies are favorable for resolving salinity changes
(Society of Exploration Geophysicists, 2008-08-26)Time-lapse ground-penetrating-radar (GPR) surveys exploit signal-amplitude changes to monitor saline tracers in fractures and to identify groundwater flow paths. However, the relationships between GPR signal amplitude, ... -
Fixed-source and fixed-receiver walkaway seismic noise tests: A field comparison
(Society of Exploration Geophysicists, 2006-09-21)Seismologists and geophysical literature often use the term “walkaway” to describe any survey used to analyze wavetrains based on source-to-receiver offset. A distinction should be made between receiver-group moveout ... -
Application of the multiaxial perfectly matched layer (M-PML) to near-surface seismic modeling with Rayleigh waves
(Society of Exploration Geophysicists, 2011-05)Perfectly matched layer (PML) absorbing boundaries are widely used to suppress spurious edge reflections in seismic modeling. When modeling Rayleigh waves with the existence of the free surface, the classical PML algorithm ...