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Abstract

The Salton Sea geothermal system (SSGS) of the Salton Trough is the northernmost of a series of active hydrothermal systems found along the East Pacific Rise-San Andreas fault zone plate boundary transition. The sediment-smothered, saline nature of the SSGS is a consequence of deposition of the Colorado River delta over the fragmented rift system and creation of a saline lake environment in the northern Salton Trough. Intrusion of rift-related magma into the base of this saline sediment pile induces brine diapirism and localizes sulfide and oxide mineral deposition at a stable, density-controlled interface between rising brines and shallower lower-salinity basin fluids. The heated brines interact with the abundant lacustrine sediments, pervasively altering them to greenschist facies assemblages at depths of 2 to 3 km. Reaction with evaporitic sulfates in the host sediments keeps the brines relatively oxidized and provides a source of H2S via hydrothermal SO4-2 reduction. The high salinity, moderately high oxidation state, and near-neutral pH of the fluids keeps the dissolved metal content high and the sulfur content low. Compared with the East Pacific Rise and Guaymas Basin systems, the SSGS reflects the progressive influence of continental sediments and tectonics on an oceanic ridge system as it impinges upon a continental margin.

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