The first author appreciates the opportunity to have been a shipboard petrologist on Leg 149, the guidance and co-operation of Co-Chief scientists Dale Sawyer and Bob Whitmarsh, and the support of an excellent technical staff and facilities on the ship. Data gathering for this study was supported by USSSP Grant# 0040 to the first author. This manuscript has been greatly improved by the constructive reviews of Bob Cullers and Bob Shuster as well as the comments of the ODP editorial staff.