VOLCANIC DEBRIS AND CLAY MINERALS IN THE DEEP-SEA SEDIMENTS OF THE WESTERN CENTRAL PACIFIC

The analyses on the volcanic debris and clay minerals of about 100 samples taken from 12 stations located in the Western Central Pacific are described in this paper. The volcanic debris is determined by means of microscope in the heavy mineeral laboratory, and the clay minerals br X-ray diffraction, thermal analysis and electronmicroscope in the clay mineral laboratory. The volcanic debris of the area studied is the product of oceanic volcanic eruption,which constitutes the main component and source of the deep-sea sediments.It has the character of tholeiite and andesite. The mineral association of the volcanic debris becomes complicated and metamorphosed due to the frequent eruptions of oceanic volcano in this area. The clay mineral composition of the said area is composed of montmorillonite, kaolinite, chlorite and illite, with montmorillonite predorninanting (50-70%). The volcanic debris (especially the volcanic ash) and the wind-transported matter are the main sources of the clay minerals in this area. It this area., the abundant montmorillonite results from the weathering and alteration of volcanic ash at the quiet deep-ocean floor where alkaline is weak(pH=7-8), Fa rich and Si:Al ratio high. The alternating changes of the climate from warm to cold during the geological history made the content of montmorillonite in the cores change correspondingly from a lower level to a higher. Therefore the studies of the volcanic debris and clay minerals are of great significance for th.e research on the proparcy, strength, mode oceanic volcanic action, the character of oceanic crust, on the physicochemical and geocilemical environments which a pelagic sediments are in,and on the determination of the sediment character and sediment process of the core.