Geochemical expression of a major E-W trending lithospheric boundary at 37[degree] N latitude, southern Nevada

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5341792

Farmer, G L ^[1]; Scott, R B ^[2]; Weiss, S I; Noble, D C ^[3]

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1. Univ. of Colorado, Boulder, CO (United States). Dept. of Geological Sciences
2. Geological Survey, Denver, CO (United States)
3. Univ. of Nevada, Reno, NV (United States). Mackay School of Mines

Late Cenozoic hawaiites ([<=]16 Ma) in southern Nevada have long been recognized as having significantly higher [sup 87]Sr/[sup 86]Sr (0.7060--0.7080) and lower e[sub ND] values ([minus]8 to [minus]10) than volcanic rocks of similar age and composition elsewhere in the western US. These hawaiites are also characterized by high rare-earth element abundances ([Nd] = 43--80 ppm), low Rb/Sr ratios (0.01--0.06), and trace element patterns similar to those of island-arc basalts. New geochemical data from mafic volcanic rocks from 35 to 37 N latitudes illustrate that rocks with these characteristics are found as far east as the Pahranagat shear system in southeastern Nevada in southeastern Nevada and as far west as the California/Nevada border. In contrast, existing data have shown that young basalts north of 37 N in central Nevada lack these unique geochemical characteristics and have isotopic and trace element compositions more similar to those of ocean-island basalts (OIB). The geophysical properties have been interpreted to suggest that significant north-south variations occur in the buoyancy of the upper most mantle. The close geographic correspondence between the transition in basaltic rock geochemistry and in mantle buoyancy suggests that the two may share a common origin. The simplest interpretation of the hawaiite data is that they inherited their chemical and isotopic characteristics from this mantle lithosphere, although the possible effects of crustal contamination in these chemically evolved basalts have been poorly constrained. If derived from a lithospheric mantle source, the low basalt [epsilon][sub ND] values require that the basalts sources have been isolated from the convecting portions of the upper mantle since the Precambrian. In this case, latitude 37[degree]N may mark an important boundary in the Precambrian lithosphere of the western US.

• OSTI ID: 5341792
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
CHEMICAL COMPOSITION
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COMPARATIVE EVALUATIONS
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GEOCHEMISTRY
GEOLOGIC DEPOSITS
GEOLOGY
IGNEOUS ROCKS
ISOTOPE RATIO
MAGMATISM
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NORTH AMERICA
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PETROLOGY
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USA
VARIATIONS
VOLCANIC ROCKS