This section presents six chapters as an overview of hydrothermal processes occurring in this tectonically active region. The discovery of hydrothermal activity in the Guaymas Basin was relatively recent and the scientific implications, especially hydrothermal petroleum generation and migration, are yet to be realized.
Heat flow from both deep-seated and shallow sources (BECKER and FISHER) drive this hydrothermal system, and the values are anomalously high along the central axis of the south rift of the basin. Fluid circulation controls the mineralogy of the vent/mound precipitates (PETER and SCOTT) as well as the chemistry of the vent and subbottom interstitial waters (VON DAMM; GIESKES et al.). The fluid geochemistry and ore genesis in the Salton Trough geothermal system (WILLIAMS et al.) also are presented for comparison with the Guaymas Basin hydrothermal system. These represent a transition from a terrestrial-lithified to a marine-unconsolidated regime. Hydrothermal petroleum generation, expulsion and migration (SIMONEIT) were first discovered in the Guaymas Basin and occur generally in sedimented, active rift systems. The overall conversion of immature organic detritus to petroleum is highly efficient and rapid (“zero” geological time) in such hydrothermal systems, and the Guaymas Basin is described as an example.