PB, SR AND BE-10 ISOTOPIC STUDIES OF VOLCANIC-ROCKS FROM THE NORTHERN MARIANA-ISLANDS - IMPLICATIONS FOR MAGMA GENESIS AND CRUSTAL RECYCLING IN THE WESTERN PACIFIC

Abstract

We report Sr and Pb isotope analyses for an extensive suite of volcanic rocks from the N. Mariana arc together with Sr and Pb isotope analyses of sediments from the nearby Mariana and Nauru basins. In addition ten of the most recent volcanic samples were analysed for 10Be. The Sr isotope compositions cluster tightly around 87Sr 86Sr = 0.7035 being slightly but significantly higher than the Pacific ocean floor basalts on either side of the arc and agreeing well with previous data. In contrast, the large number of new Pb isotopic data presented significantly extends the observed range of Pb isotope compositions for volcanic rocks from the Mariana arc to more radiogenic compositions. The conce..