A major lithospheric boundary in eastern California defined by isotope ratios in Cenozoic basalts from the Coso Range and surrounding areas
Conference Proceedings: A major lithospheric boundary in eastern California defined by isotope ratios in Cenozoic basalts from the Coso Range and surrounding areas
AbstractSr and Nd isotope ratios of Miocene-Recent basalts in eastern California, when screened for crustal contamination, vary dramatically and indicate the presence of a major lithospheric boundary that is not obvious from surface geology. Tectonic and geochemical interpretation of this boundary is difficult, however, because there are so many potential explanations.Plio-Pleistocene lavas from Owens and Panamint valleys and Miocene lavas from the eastern Mojave Desert have high 87 Sr/ 86 Sr ( approximately 0.7050-0.7065) and low eNd ( approximately 0 to -4.5), whereas Plio-Pleistocene lavas from the Coso geothermal area and Miocene lavas from the central and western Mojave Desert have lower 87 Sr/ 86 Sr ( approximately 0.704) and higher eNd ( approximately 5 to 8). Isotope ratios from the Coso field form a bull's-eye pattern with very low 87 Sr/ 86 Sr (0.7033) centered just south of the geothermal area. The boundary between enriched (high 87 Sr/ 86 Sr) and depleted (low 87 Sr/ 86 Sr) domains is sharply defined in the Coso Range and coincides with the northeastern boundary of recent seismicity. The boundary strikes southeast from the Coso Range into the northeastern Mojave Desert and is thereafter coincident with the eastern edge of the Mojave block and southern projection of the Death Valley fault zone. There are several possible explanations for this isotopic gradient. It may mark juxtaposition of the truncated North American craton against oceanic lithosphere emplaced during Permo-Triassic tectonism. Alternatively, it may mark the western edge of enriched North American mantle that was not stripped away by shallow subduction in the Late Cretaceous. In the Coso region the boundary's sharpness may reflect the large flux of asthenospheric magma under the geothermal area. In any case, the boundary lies well east of the traditionally defined 0.706 line in the southern Sierra Nevada.
- Glazner, A.F.; Miller and J.S.
- Abstracts with Programs - Geological Society of America, 1/1/1997
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Glazner, A.F.; Miller, J.S. . 1/1/1997. A major lithospheric boundary in eastern California defined by isotope ratios in Cenozoic basalts from the Coso Range and surrounding areas. Proceedings of (!) ; (!) : Abstracts with Programs - Geological Society of America.