PETROLOGICAL AND GEOCHEMICAL STUDY OF CRUSTAL XENOLITHS FROM 1961 ERUPTION OF CALBUCO VOLCANO, CHILE (LATITUDE 41 20 S )

Twenty four samples of xenoliths and country rocks from the 1961 lava flow of Calbuco volcano have been studied. Fourteen samples have been analyzed for major elements and P, Ni, Ba, Cr, V, Zr, Sc, Y, and Sr. Five of these samples were further analyzed for Sm, Nd, Sr, and Pb isotope ratios. Seventeen samples were analyzed under the microscope and three samples were analyzed by microprobe for their pyroxene composition. Based on petrograghic studies xenoliths were divided into three groups. Fine grained xenoliths (groups I and II) probably formed from metamorphosed MORB-like basalts , whereas coarse grained xenoliths (group III) were apparently derived from cumulate minerals that crystallized from the Calbuco magma. The fine grained xenoliths were probably entrained in magma at intermediate levels of the crust, near the stability limit of amphibole to form pyroxene and plagioclase. In the coarse grained xenoliths amphibole that form at depth dehydrated as the xenoliths were brought to the surface. The country rocks are apparently unrelated to the xenoliths.