15. OCEAN CRUST GEOTHERMAL PROCESSES: A PERSPECTIVE FROM THE VANTAGE OF LEC 54 DRILLING

ABSTRACT-Two distinct sedimentary facies produced by sea-floor hydrother-mal activity were cored during Deep Sea Drilling Project Leg 54. The first is equivalent to the typical basal iron- and manganese-rich, clayey mud recovered at many DSDP sites. It was tampled as a dispersed component throughout the cores taken in small \ediment ponds in several sites within 120 km of the Eart Pacific Rise at 9"N. We infer that this component was originally deposited as iron hydroxides dis-persed from high-temperature bents over the axial magma chamber of the East Pacific Rise. In the \ediments, the iron hydroxides have reacted diagenetically with siliceous microfossil tests and detrital clays to form K- and Fe-rich clays with variable SiO2/FezO3 and Fe20,/A120, ratios.-The second facies was cored in the active Galapagos Mounds hy-drothermal field 21 km south of the Galapagos Rift. Mounds \edi-ments consist of a capping of Mn oxides and up to 15 meters of gree