PETROCHEMICAL EVOLUTION AND GENESIS OF A POTASSIC PYROXENITE-ECLOGITE-GRANULITE ASSOCIATION: MANTLE AND CRUSTAL XENOLITHS IN NEOGENE FERGUSITES IN THE SOUTHERN PAMIRS, TAJIKISTAN

Abstract

Xenoliths of the pyroxenite-eclogite-granulite suite in alkaline mafic rocks of the Pamirs differ from pyroxenite-eclogite nodules in kimberlites and eclogites in metamorphic complexes in that they have anomalously high potassic alkalinity and widespread K-sanidine and micas. The xenoliths are proved to be related to the high-pressure crystallization of mantle melts at different lithospheric levels (under pressures of 20-36 kbar). The xenoliths are classified with two petrochemical suites (series): suite A, which is an analogue of shoshonite-latite volcanic complexes of mature island arcs, and suite B, which shows certain petrochemical features close to those of the tephrite-leucitite association of rift zones. The very thick (up to 75-80 km) crust of the Pamirs is thought to have been formed by magmatic underplating.