Mineral distribution in the clay fraction of the sediments from Mexico Central Pacific.

The clay fraction distribution from 90 samples collected in the R/V El Puma , during the Oceanographic Cruise Mimar II, realized on 1986 on a portion of the Mexican Central Pacific were estimated. The mineralogy of the clay fraction was studied by X-ray diffraction method. The main minerals found on this fraction were: montmorillonite, illite, kaolinite and quartz. Montmorillonite is richer near the East Pacific Rise area, meanwhile illite has apparently less basic vulcanic influence. Montmorillonite enrichment is associated with an illite decrease, while kaolinite and quartz remain without appreciable concentration changes on their horizontal and vertical distributions. The intermediate portions of the sediment cores studied in the East Pacific Rise area show an increase on montmorillonite concentration, which suggests a higher degree of basic vulcanism in the near past. A close relationship was observed between montmorillonite distribution on surface sediments and the East Pacific Rise, Socorro, San Benedicto and Roca Partida Islands which supports the argument that montmorillonite and basic vulcanism are associated.