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Geology topics

Edward A. du Bray

Publications and source records attributed to Edward A. du Bray.

48 records · Page 3Linked to original sources
USGS1995

Geochemistry and petrology of Oligocene and Miocene ash-flow tuffs of the southeastern Great Basin, Nevada

The White River Narrows area of Southeast Nevada contains 18 regionally distributed middle Tertiary dacite to rhyolite ash-flow tuffs. Geochemical data provide an excellent opportunity to study stratigraphic and petrologic relations of these tuffs. Chemical data for each of the tuffs are distinctive and provide a significant addition to other data used to identify and correlate these units. Relatively minor compositional variation within the tuffs is noteworthy.

Professional Paper↗
USGS1991

Age and petrology of the Tertiary As Sarat volcanic field, southwestern Saudi Arabia

Harrat As Sarat forms the second smallest and southernmost of the basalt fields of western Saudi Arabia and is part of a voluminous Red Sea rift-related continental alkali basalt province. The rocks of the As Sarat were emplaced during the first stage of Red Sea rifting and represent the northernmost extension of the Tertiary Trap Series volcanics that occur mainly in the Yemen Arab Republic and Ethiopia. The field consists of up to 580 m of basalt flows, that are intruded by basaltic plugs, necks, minor dikes, and highly evolved peralkaline trachyte intrusions. K-Ar ages indicate that the As Sarat field formed between 31 and 22 Ma and contains an eruption hiatus of one million years that began about 25 Ma ago. Pre-hiatus flows are primarily hypersthene normative intersertal subalkaline basalt, whereas the majority of post-hiatus flows are nepheline normative alkali basalt and hawaiite with trachytic textures. Normative compositions of the basalts are consistent with their genesis by partial melting at varying depths. Trace element abundances in the basalt indicate that varying degrees of partial melting and fractional crystallization (or crystal accumulation) had major and minor roles, respectively, in development of compositional variation in these rocks. Modeling indicates that the pre-hiatus subalkaline basalts represent 8–10 percent mantle melting at depths of about 70 km and the post-hiatus alkali basalts represent 4–9 percent mantle melting at depths greater than 70 km.

southwestern Saudi Arabia↗
USGS1990

SAVEWARE I; a dozen programs designed to read DATASAVE files, perform various petrologic calculations, and produce printed and graphical data analysis, Part A - Documentation

SAVEWARE is a group of 12 programs that run on IBM and IBM compatible microcomputers. The programs were written in QuickBASIC and have been combined with input/output routines from DATASAVE. The programs (except ASCI2DSV) access data from DATASAVE format data files and perform various petrologic operations.

Open-File Report↗
USGS1983

Mineral potential of selected felsic plutons in the eastern and southeastern Arabian Shield, Kingdom of Saudi Arabia

Sixteen well-defined geochemical anomalies associated with felsic plutons and (or) muscovite-bearing plutons of Proterozoic age have been identified in the eastern and southeastern Arabian Shield. The majority of these plutons are highly evolved, granitophile-element-enriched muscovite-bearing granites that are weakly peraluminous. A followup study of the mineral potential of these plutons included detailed geologic mapping, extensive geochemical sampling, ground traverses, and petrographic and petrologic studies. A total of 212 samples were collected for geochemical analysis, and a lesser number were collected for petrographic studies. Most of the plutons studied are similar to metallogenically specialized granites described elsewhere in the world and found associated with deposits of tin, tungsten, or molybdenum and other rare metals. Only four of the plutons, the Sitarah, Tarban, and Gaharra monzogranites and the Bwana granite, contained highly anomalous amounts of tin, tungsten, or molybdenum and altered zones- and (or) numerous quartz veins and otherwise appeared to have noteworthy mineral potential. Additional work on at least these four plutons is suggested.

Open-File Report↗
USGS1978

Mapped offset on the right-lateral Kern Canyon fault, southern Sierra Nevada, California

The north-trending Kern Canyon fault, the longest fault within the southern Sierra Nevada, has been mapped from lat 36°00′N to its northern end near lat 36°40′N. The fault cuts and offsets granitic plutons as young as 80 m.y., but despite the fact that many recent earthquake foci plot close to the fault, it does not appear to offset an overlying 3.5-m.y.-old basalt flow. Seven granitic plutons are clearly offset by the fault in a right-lateral sense. In the area mapped, offset of plutonic contacts is 6.5 to 13 km and increases southward by 0.2 km/km.

California↗