Rate of palagonitization and manganese coating on basaltic rocks from the Rift Valley in the Atlantic Ocean near 36°50′N

Abstract

Various types of rocks consisting of plagioclase basalts, olivine basalts, pyroxene basalts, picritic basalts and volcanoclastics were found in the Rift Valley between 36°52′N and 36°47′N in the Atlantic Ocean. Palagonite and manganese are the main coating materials encountered on the chilled margins of the pillow-lava fragments. Palagonite is often associated with montmorillonite and chlorite. The thickness of palagonite coating the chilled margins increases in the fragments found from the innerfloor axis towards the walls of the Rift Valley. There is a linear correlation between the thickness of palagonite and that of the manganese encrustation. Considering a rate of manganese and palagonite accumulation of about 3μ 10 3 year it is speculated that the age of a hill located near the axis of the inner floor near 36°50′N is between 3,000 and 12,000 years. The relative age of the inner floor near the intersection of the Rift Valley walls is less than 120,000 years. The specimens having a thicker manganese and palagonite crust located at 4–6 km away from the inner floor axis are 130,000–482,000 years old.