This program will focus on a petrological and geochemical characterization of the intra-transform spreading centers in the Siqueiros transform fault, on determining the structural histroy along the transform domain through ALVIN field mapping, structural studies of deformed rocks recovered from the walls of each fault scarp, and on understanding the tectonci processess that have influenced the development of the Siqueiros tranform for the past 4 Ma. There will be eighteen ALVIN dives in the transfrom and a night-time program of rock coring and dredging that will provide additional samples from along the spreading axis and at various sites along the strike- slip faults. SeaBeam will be used at night to produce detailed 10 m contour maps of each spreading axis. Questions to be addressed include: What processes are responsible for initiating intra-transform spreading? What is the evolutionary sequence of lava types erupted when a new spreading center start? What is the nature of major transform-affiliated compositional discontinuities in the mantle? What is the scale of chemical heterogeneity in the mantle? Are unique magma types generated along transform faults?
