Computer Science
Scientific paper
Apr 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989e%26psl..92..371d&link_type=abstract
Earth and Planetary Science Letters, Volume 92, Issue 3-4, p. 371-385.
Computer Science
2
Scientific paper
Metabasites from the Pelona-Orocopia-Rand (POR) schist, a presumed subduction complex in southern California, have been analyzed for major, minor, and trace element concentrations to investigate the nature, origin, and tectonic implications of these rock bodies. Element abundances indicate that these rocks are tholeiitic and alkalic basalts generated from several sources. Most samples (group 1) resemble normal to transitional mid-ocean ridge basalts (N-type to T-type MORB). Variation of MORB-like samples can be accounted for by low-pressure crystal fractionation. A second group (group 2), which includes five samples from the Rand Mountains and one from the San Gabriel Mountains, has elemental abundances similar to those of tholeiitic ocean-island basalts or E-type MORB, although phosphorus is unusually low. Several samples of group 2 have high MgO, Ni, and Cr, characteristics which are commonly associated with crystal accumulation. A final group (group 3) consists of two samples from the Orocopia Mountains that resemble alkalic ocean-island basalts. The analyzed samples were collected from six different bodies of POR schist. There seem to be no major differences in basalt type which would imply a unique and separate source for any one area.
Various sites of accumulation have been suggested for the protoliths of the POR schist: open ocean, Gulf of California-type basin, trapped back-arc basin, and rifted back-arc basin. The first three settings are entirely consistent with the basalt geochemistry. The last option is less likely, but not impossible.
Dawson Robert M.
Jacobson Carl E.
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