20. AUTHIGENIC MINERALS IN VOLCANOGENIC SEDIMENTS CORED DURING DEEP SEA DRILLING PROJECT LEG 601

Eocene to Pleistocene volcanogenic sediments from the Mariana Trough and the Mariana arc-trench system have been studied by X-ray diffraction, X-ray fluorescence, and atomic absorption, and with a scanning electron microscope with an X-ray-energy-dispersive attachment. The mineralogical composition of the volcaniclastic sediments (tuffs) is the same as that of the other associated sediments (mudstones). Diagenetic alterations are significant and seem to result from two processes. The first (low-temperature alteration) develops with age and depth; it consists of the genesis of pure smectite, coupled with zeolites (phillipsite, clinoptilolite). The second is limited to sediments immediately overlying basalts and to the altered basalts themselves. It consists of the massive development of palygorskite, and seems to be linked with hydrothermal activity in the igneous basement. SITE DESCRIPTION The following stratigraphies are summarized from the site chapters in this volume. During Leg 60 in the South Philippine Sea, four sites were drilled in the Mariana Trough (Fig. 1). Site 453 (17°54.42'N-143° 40.95'E) is about 10 km from the eastern edge of th