Isotopic evidence for lithospheric thinning during extension: Southeastern Great Basin

Journal Article · Sat Feb 01 00:00:00 EST 1992 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1992)020<0104:IEFLTD>2.3.CO;2· OSTI ID:7031615

Daley, E E; DePaolo, D J ^[1]

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1. Univ. of California, Berkeley (United States) Lawrence Berkeley Lab., CA (United States)

Mafic rocks erupted during late Cenozoic extension near Las Vegas, Nevada, show temporal patterns of variation in Nd and Sr isotope ratios and in bulk chemistry. The patterns indicate that depths of magma generation were varying through time and that lithospheric mantle was partially replaced with asthenospheric mantle as extension proceeded. In alkalic rocks, {epsilon}{sub Nd} changed through time from {minus}9.1 (typical of lithospheric mantle in this area) before the onset of major (16 Ma) extension to +6.4 (typical of asthenospheric mantle) after extension (4.6 Ma). Near the end of the period of major extension (10-6 Ma), tholeiitic rocks erupted, the {epsilon}{sub Nd} of which ranged from {minus}10.1 to {minus}7.9; this indicates that the lithosphere had not thinned sufficiently by that time to bring asthenospheric mantle into the depth range of tholeiitic magma generation (33-50 km). The lithosphere in the Las Vegas area appears to have thinned by about 50%, less than would be predicted by the magnitude of upper crustal extension (a factor of 3 or 4), and indicative of a nonuniform lithospheric response to extension.

• OSTI ID: 7031615
• Journal Information: Geology; (United States), Vol. 20:2; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GREAT BASIN
PETROCHEMISTRY
PETROGENESIS
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CONTINENTAL CRUST
EARTH MANTLE
GEOCHEMISTRY
GEOLOGIC HISTORY
ISOTOPE RATIO
MAGMA
NEODYMIUM ISOTOPES
NEVADA
PLATE TECTONICS
STRONTIUM ISOTOPES
ALKALINE EARTH ISOTOPES
CHEMISTRY
DEVELOPED COUNTRIES
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IGNEOUS ROCKS
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