Home – Home – Jornals – Russian Geology and Geophysics 2002 number 4

Pyroxenite xenoliths in Miocene Vitim picrite basalts were produced by polybaric fractional crystallization of melts in the mantle, as determined from their morphology and major- and trace-element chemistry. Black coarse-grained pyroxenites and megacrysts make a long trend (F# = 0.12-0.23) as a result of polybaric cotectic Gar-Cpx fractionation, possibly, during initiation of the feeding system for the basaltic eruption. Low-temperature black pyroxenites are products of interaction of residual melts with the lower crust into which they intruded. The highest-temperature hybrid websterites may result from mixing of basaltic melts with 5-10% partial melts from metasomatic mantle lherzolites. Anatectic Cr-pyroxenites were formed mostly by segregation of partial melts from lherzolite material and remelting of former veins. Low-temperature hybrid garnet pyroxenites were produced by interaction of metasomatic lherzolites (or earlier Cr-diopside veins) and differentiated basaltic melt enriched with volatiles. Remelting of earlier mineral generations, which occurs in all rising melt systems, is reflected by mirror peaks on spidergrams, and LREE and HFSE (and ore element) enrichment.