PARTIAL MELTING OF CRUSTAL XENOLITHS FROM THE BASALTS OF THE BAIKAL-MONGOLIA REGION

Abstract

A study of crustal xenoliths from Cenozoic alkaline basalts revealed that almost all of the samples from the Baikal Rift Zone and roughly half of the collection of Mongolian xenoliths had been involved in partial melting. Some mineralogical and structural indicators of partial melting are described. The linear orientation of fine glass films, the interstitial melting zones similar to blastocataclastic zones, and the varying degree of partial melting in one rock sample suggest the association of partial melting with a heterogeneous deformation process. The chemical compositions of minerals and glasses from the xenoliths, as well as of the host basalts, are presented. The PT conditions of the emplacement of basalts and of the entrapment and partial melting of xenoliths are discussed. The process of partial melting is believed to have occurred under subisothermal decompression in the presence of alkaline fluids. It is postulated that some of the xenoliths might have been entrapped from crustal low-velocity layers.