Abstract

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.