Peculiarites of clay minerals formation in the Pleistocene sediments under specific tectonomagmatic and hydrothermal conditions of the Central Hill (Escanaba Trough, Gorda Ridge, Pacific Ocean). Communication 2. Holes ODP 1038A and 1038H

Clay minerals were studied in Pleistocene sediments from Holes 1038А, 114.50 m deep, and 1038Н, 192.80 m deep, which were drilled near a hydrothermal spring with a temperature of 217°C on Central Hill, 275 m east of Hole 1038B. In the sediments from Hole 1038A, at a depth of 8.52 m, the fraction <0.001 mm consists completely of chlorite. In the rest of the sediment section from Hole 1038A clay minerals consist of chlorite (from ~64 to ~98%) and illite. In sediments from Hole 1038H clay minerals also consist of chlorite and illite. Their formation occurred under conditions that arose at the intrusion of a basaltic melt in the form of a laccolith into the Escanaba trough and the heating under its influence of a solution, during the interaction of which with sediments at a high-temperature stage biotite was formed. With the subsequent slow cooling of the laccolith and fluid, the newly formed biotite was completely replaced by chlorite. Illite was precipitated from a hydrothermal solution. At a depth of 183 m, in sediments from Hole 1038H, clay minerals consist of biotite, chlorite and dioctahedral smectite, just as in sediments from Hole 1038B when they were formed under conditions of rapid cooling of the laccolith flank and penetration of sea water into the sediments. The similarities and differences in the processes of formation of clay minerals are shown in the Pleistocene sediments of the Central Hill, located above the slowly cooling part of the laccolith (Holes 1038A and 1038H), and in sediments located above the rapidly cooling flank of the laccolith (Hole 1038B).