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E. A. Du Bray

Publications and source records attributed to E. A. Du Bray.

At least 19 recordsLinked to original sources
USGS2008

Compilation of Stratigraphic Thicknesses for Caldera-Related Tertiary Volcanic Rocks, East-Central Nevada and West-Central Utah

The U.S. Geological Survey (USGS), the Desert Research Institute (DRI), and a designee from the State of Utah are currently conducting a water-resources study of aquifers in White Pine County, Nevada, and adjacent areas in Nevada and Utah, in response to concerns about water availability and limited geohydrologic information relevant to ground-water flow in the region. Production of ground water in this region could impact water accumulations in three general types of aquifer materials: consolidated Paleozoic carbonate bedrock, and basin-filling Cenozoic volcanic rocks and unconsolidated Quaternary sediments. At present, the full impact of extracting ground water from any or all of these potential valley-graben reservoirs is not fully understood. A thorough understanding of intermontane basin stratigraphy, mostly concealed by the youngest unconsolidated deposits that blanket the surface in these valleys, is critical to an understanding of the regional hydrology in this area. This report presents a literature-based compilation of geologic data, especially thicknesses and lithologic characteristics, for Tertiary volcanic rocks that are presumably present in the subsurface of the intermontane valleys, which are prominent features of this area. Two methods are used to estimate volcanic-rock thickness beneath valleys: (1) published geologic maps and accompanying descriptions of map units were used to compile the aggregate thicknesses of Tertiary stratigraphic units present in each mountain range within the study areas, and then interpolated to infer volcanic-rock thickness in the intervening valley, and (2) published isopach maps for individual out-flow ash-flow tuff were converted to digital spatial data and thickness was added together to produce a regional thickness map that aggregates thickness of the individual units. The two methods yield generally similar results and are similar to volcanic-rock thickness observed in a limited number of oil and gas exploration drill holes in the region, although local geologic complexity and the inherent assumptions in both methods allow only general comparison. These methods serve the needs of regional ground-water studies that require a three-dimensional depiction of the extent and thickness of subsurface geologic units. The compilation of geologic data from published maps and reports provides a general understanding of the distribution and thickness of tuffs that are presumably present in the subsurface of the intermontane valleys and are critical to understanding the ground-water hydrology of this area.

Data Series↗
USGS2002

Composition, age, and petrogenesis of Late Cretaceous intrusive rocks in the central Big Belt Mountains, Broadwater and Meagher counties, Montana

Cretaceous intrusions hosted by the Proterozoic Newland Formation. The northern intrusion, centered on Boulder Baldy, consists of outer, intermediate, and core zones composed of aegirine-augite quartz monzonite, hornblende quartz monzodiorite, and biotite granodiorite, respectively. The southern intrusion, north of Mount Edith, is compositionally indistinguishable from the intermediate zone of the northern intrusion.

Montana↗
USGS1998

Geology, age, and tectonic setting of the Cretaceous Sliderock Mountain Volcano, Montana

The Sliderock Mountain stratovolcano, part of the Upper Cretaceous continental magmatic arc in southwestern Montana, consists of volcaniclastic strata and basaltic andesite lava flows. An intrusive complex represents the volcano's solidified magma chamber. Compositional diversity within components of the volcano appears to reflect evolution via about 50 percent fractional crystallization involving clinopyroxene and plagioclase. 40Ar/39Ar indicate that the volcano was active about 78?1 Ma.

Professional Paper↗
USGS1994

Reconnaissance geologic map of the Sliderock Mountain area, Sweet Grass and Stillwater counties, Montana

The remains of a deeply eroded Late Cretaceous stratovolcano centered near Sliderock Mountain dominate the map area. The volcano consists mostly of lahars, although basaltic andesite lava flows are also present. An extensively eroded, weakly mineralized hypabyssal intrusive complex, inferred to represent the volcano's solidified magma chamber, intrudes previously erupted lava flows and associated lahars. Cretaceous sandstone and shale and Paleozoic sedimentary rocks, principally limestone of the Madison Group, host the stratovolcano; remnants of these rocks are preserved as large xenoliths and roof pendants.

Montana↗
USGS1994

Campground talk and slide show on volcanoes for Chiricahua National Monument

The slides and the accompanying script presented here are based on a campground presentation at Chiricahua National Monument in 1994. Examples of eruptions at active volcanoes are used to help the audience visualize events that took place in the National Monument 27 million years ago. This presentation stresses the following themes: 1) The National Monument lies on the flank of an ancient volcano known as the Turkey Creek caldera. 2) This volcano produced giant explosive eruptions, much larger than any in the 20th century. Similar volcanoes that are still capable of producing giant eruptions exist today, and include examples in the United States. 3) We can learn how these giant volcanoes operate and what their typical "life histories" are by examining ancient analogues such as the Turkey Creek caldera that have been dissected by erosion. Studies of ancient volcanoes provide the conceptual framework for evaluating hazards at active volcanoes. 4) Large eruptions of the type that occurred in the Chiricahua Mountains are highly explosive. As a result, the molten rock, or magma, that feeds such eruptions is "blown to bits", producing volcanic ash and pumice instead of lava flows. 5) The volcanic history of Chiricahua National Monument can be reconstructed by geologic mapping and by "reading" the record of past eruptions from the layers of rock that were deposited by the volcano. The slides and script follow the format of the 1994 campground presentation. Slides are keyed to the script by number. Italic print is used to identify the subject and source of each slide, and to provide additional background information. This document is intended to be used by interpreters at the National Monument for presentations on geology. It may be used as a complete "packaged" talk or as background material for customized presentations. Additional information for the non-specialist on the geology of Chiricahua National Monument is available in a separate report (Pallister and others, 1993).

Open-File Report↗