HYDROTHERMAL ACTIVITY AND PETROLEUM GENERATION IN THE GUAYMAS BASIN

Hydrothermal activity associated with ocean plate accretion is responsible for the rapid conversion of sedimentary organic matter to petroleum-like bitumens in the Guaymas Basin. The combination of plate accretion by dike and sill intrusions into recent diatomaceous hemipelagic sediments and the concomittant hydrothermal circulation coupled to the cooling of a subaxial magma chamber provides the heat necessary to readily pyrolyze (crack) the immature organic matter, which consists mainly of degraded microbial and diatomaceous marine detritus. Subsequent leaching/transport of the organic pyrolysate by the circulating hydrothermal fluids results in its upward migration to the seabed, where the more volatile and soluble components (<C-10) disperse into the ambient seawater and the heavier fractions (>C-10) condense/solidify within the mineral matrix of the hydrothermal mounds. Petroleum products on mound surfaces and sediments constitute an important source of carbon for microbiota that support the rich macrofaunal communities in the basin.