Introduction to the Guaymas Basin and Hydrothermal Symposium

This, the second symposium of the Leg 64 Initial Reports, is a collection of papers on the principal results of drilling in the Guaymas Basin floor (Figs. 1 and 2). Two sites, Sites 477 and 481, were drilled into active spreading axes of opening of the Gulf of California. The third site, Site 478, was drilled in what had been interpreted to be somewhat older rocks of the basin floor. Objectives of this drilling were to test the tectonic model of formation and locus of generation of new oceanic crust, to investigate the sediments deposited in this environment, to determine the nature of the expected sediment-basalt mixtures and to explore for possible hydrothermal alteration products in this region of known high heat flow. An important secondary objective was to investigate the content and early maturation of hydrocarbons believed to occur in this region of high heat flow. Results of organic geochemistry studies were reported in the preceding collection of papers. The following papers include