HIGH-RATES OF HYDROTHERMAL ACTIVITY AT THE WEST RIFT OF THE EASTER MICROPLATE DEDUCED FROM METALLIFEROUS SEDIMENT COMPOSITION

Based on the mineralogy and composition of sediment cores from three l ocations along the East Pacific Rise, sediments from 12 degrees 58' N are shown to contain about 34% metalliferous sediment (on a carbonate- and salt-free basis) whereas those from 23 degrees 50' S and 27 degre es 24' S each contain about 73% metalliferous sediment. The latter two cores are situated near the West Rift of the Easter Microplate. The m etalliferous contents of the sediments at 23 degrees 50' S and 27 degr ees 24' S are among the highest recorded on the East Pacific Rise. The distribution of elements with depth in these cores indicates that the hydrothermal activity has lasted more than 100,000 years. These data suggest that the West Rift of the Easter Microplate is a highly prospe ctive site for submarine hydrothermal minerals. This is in accord with the high rate of ocean spreading (15-16 cm/yr) and the complex proces ses of plate extension and rotation there.