Quaternary volcanism in the Salton Sea geothermal field, Imperial Valley, California

摘要: The Salton Sea geothermal field lies in the Trough, landward extension of Gulf California, an area active crustal spreading. Surface volcanic rocks consist five small rhyolite domes extruded onto Quaternary sediments Colorado River delta. Two are linked by subaqueous pyroclastic deposits; others single extrusions with or without marginal lava flows. low-calcium, alkali 1 to 2 percent crystals. Similar silicic found wells have been extensively altered brines. Basaltic occur as xenoliths and subsurface dikes, sills, low-potassium tholeiitic basalt similar that East Pacific Rise. Subsurface basaltic mineralogically but undergone extensive hydrothermal alteration. Numerous partly melted granitic show various degrees either cotectic melting along quartz-feldspar grain boundaries disequilibrium incongruent hydrous ferromagnesian minerals. These sodic granite containing notably higher SiO/sub 2/, CaO, Na/sub 2/O lower total iron than enclosing rhyolite. Compositions textures suggest fragments basement rather crystallized equivalentsmore » magma. bimodal basalt-rhyolite assemblage is believed formed partial fusion two stages mantle peridotite, forming successive rhyolitic melts. After formation, magma was contaminated continental crust material.« less