Hornblende gabbro sill complex at Onion valley, California, and a mixing origin for the Sierra Nevada batholith

Article Abstract:

The Sierra Nevada batholith has formed because of the massive underplating of the crust by arc basaltic magmas. Some evolved wet basaltic magmas that leaked to shallow depths and created the mafic intrusive sill complex at Onion valley, California. The buoyancy of their parent hydrous magmas resulted in the prevalence of the hornblende mafic intrusive rocks. Compared to the dry basaltic melts, the hydrous basaltic and basaltic andesite magmas have low liquidus temperatures and hence, can rise through the crust. The dry basaltic magmas are insufficiently buoyant and stay at depth.

Analysis, Natural history, Sierra Nevada (United States), Sills (Geology)

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Temperatures and H2O content of low-MgO high-alumina basalts

Article Abstract:

The water content of low-MgO high-alumina basalts (HAB)and basaltic andesites (BA) were determined to show the conditions under which these rocks have formed, relate their formation to similar processes in magmatic arcs and study the major aspects on the origin of magma. The results of experiments accounted for low-MgO HABs as having 4% or more water content while in the liquid state at crustal pressures and indicated that it formed through simple crystallization differentiation of mantle-derived hydrous primary basalts.

Composition, Origin

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Experimental investigations of the role of H2O in calc-alkaline differentiation and subduction zone magmatism

Article Abstract:

The role of H2O in the magmatic differentiation of calc-alkaline melts and subduction zone magmatism was determined through rock melting experiments. The liquids used were low-MgO high-alumina basalt, or basaltic andesite, saturated with olivine, calcic plagioclase, and pyroxene or hornblende. The addition of H2O caused lower appearance temperatures of crystalline silicate minerals, but H2O had a lesser effect in the spinel, and promoted the development of a calc-alkaline differentiation trend.

Magmatism

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