Diverse Origins of Xenoliths from Seamounts at the Continental Margin, Offshore Central California |
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| Authors: | Davis A S; Clague D A; Paduan J B |
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| Institution: | Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039-9644, USA |
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| Abstract: | A diverse assemblage of small mafic and ultramafic xenolithsoccurs in alkalic lava from Davidson and Pioneer seamounts locatedat the continental margin of central California. Based on mineralcompositions and textures, they form three groups: (1) mantlexenoliths of lherzolite, pyroxenite, and dunite with olivineof >Fo90; (2) ocean crust xenoliths of dunite with olivine<Fo90, troctolite, pyroxene-gabbro, and anorthosite withlow-K2O plagioclase; (3) cumulates of seamount magmas of alkalicgabbro with primary amphibole and biotite and anorthosites withhigh-K2O plagioclase. The alkalic cumulates are geneticallyrelated to, but more evolved than, their host lavas and probablycrystallized at the margins of magma reservoirs. Modeling andcomparison with experimentally derived phases suggest an originat moderate pressures ( 0·5–0·9 GPa). Thehigh volatile contents of the alkalic host lavas may have pressurizedthe magma chambers and helped to propel the xenolith-bearinglavas directly from deep storage at the base of the lithosphereto the eruption site on the ocean floor, entraining fragmentsof the upper mantle and ocean crust cumulates from the underlyingabandoned spreading center. KEY WORDS: basaltic magmatism; continental margin seamounts; geothermobarometry; mineral chemistry; xenoliths |
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| Keywords: | : basaltic magmatism continental margin seamounts geothermobarometry mineral chemistry xenoliths |
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