AQUEOUS HIGH-TEMPERATURE AND HIGH-PRESSURE ORGANIC GEOCHEMISTRY OF HYDROTHERMAL VENT SYSTEMS

Hydrothermal systems associated with oceanic spreading centers are now recognized as relatively common phenomena, and the organic chemical a lterations occurring there are rapid and efficient. In the marine hydr othermal systems at water depths > 1.5 km, the conditions driving chem ical reactions are high temperatures (up to > 400-degrees-C), confinin g pressures (> 150 bar), and other parameters such as pH, Eh, and mine ralogy in an aqueous open flow medium. Continental hydrothermal system s may also be of interest, as, for example, in failed or dormant rifts and regions around piercement volcanoes. Organic matter alteration by reductive reactions to petroleum hydrocarbons occurs in hydrothermal systems over a wide temperature window (approximately 60 to > 400-degr ees-C), under elevated pressure, and in a brief geological time (years to hundreds of years). The products are rapidly moved as bulk phase o r in fluids from the regions at higher temperatures to areas at lower temperatures, where the high molecular weight material separates from the bulk. These conditions are conducive to organic chemistry which yi elds concurrent products by primarily reduction (due to mineral buffer ing), oxidation (high thermal stress), and synthesis reactions. This c hemistry is just beginning to be elucidated by the geochemical communi ty, but there are various industrial applications which provide useful preliminary insight. Therefore, the behavior of organic matter (inclu sive of methane to high molecular weight compounds > C40) in warm to s upercritical water needs to be characterized to understand the implica tions of this novel phenomenon in geological and geochemical processes , and the chemistry occurring over the full temperature spectrum of hy drothermal systems is of relevance to origins of life research.