Evidence for Two Distinct Hydrothermal Systems in the Guaymas Basin

Abstract

Detailed mineralogical, petrol., and O isotope analyses of unaltered and altered sediments and O isotope analyses of pore fluids at Sites 477, 481, and 478 in the Guaymas Basin indicate that 2 distinct hydrothermal systems operate in this section of the Gulf of California intercontinental rift. A minor system is caused by the intrusion of hot sills into highly porous, cold sediments and can be modeled as a closed hydrothermal system at 150-200 Deg. The major hydrothermal system of the Guaymas Basin, like ridge-crest hydrothermal systems, is driven by relatively shallow magma chambers and cannot be modeled as a closed system. Recharge of fluids at calcd. water/rock ratios (in wt. %) of 2-3 is required. The temp. range of this hydrothermal system is 300 +- 50 Deg. The vertical discharge of the hydrothermal fluids occurs through faults until they encounter sills, which force a horizontal flow towards another fault system. [on SciFinder (R)]