ISOTOPE COMPOSITION AND ORIGIN OF WATER IN ANDESITE MAGMA

Abstract

Isotope data should help to clarify the problem of the origin of water participating in hydrothermal activity. Thus, isotope data suggest that water participating in calcalkalic magma generation is of crustal (oceanic) origin. Its likely source was the products of hydrothermal activity at depth or the sedimentary rocks that are now found as amphibolite schist blocks in andesite lavas. The amount of foreign material added apparently did not exceed 5 to 10 percent, as hardly affected the oxygen-isotope composition, although it could have markedly altered its petrochemical aspect.