Abstract:
Analysis of the regional stress field in the upper crust of continents and oceans showed that the rocks here are undergoing active horizontal compression and subvertical extension. Hydrocarbons here are generated in the upper crust from both organic and inorganic components in sedimentary, metasedimentary and igneous rocks at temperatures that range widely from normal to 300°C. At higher temperatures, all hydrocarbons except methane are unstable and undergo thermal cracking. The oceanic crust, like the continental, also is inhomogeneous and layered. The following model of a fluid system was proposed for the oceanic crust. Because of the anomalously low formation pressures of fluids in the upper crust, seawater infiltrates the basement rocks. Then, as a result of thermo-osmosis, formation waters migrate into the third deformed regional layer, from which it is then discharged up subvertical faults. That is how the mechanism of global hydrothermal convection in the system seawater-oceanic crust can be broadly outlined. We think that the global fluid-bearing layer in the oceanic crust is a reactor where hydrocarbons are generated because rocks of the third oceanic crustal layer are mainly ultramafic, i.e., have high reducing potential. Being significantly deformed, they contain zones of stress relaxation and, consequently, mechanical energy dissipation and intensive mass exchange, which are the essential features of highly