T219 Phase Relations, High P-T Terrains, P-T-ometry and Plate Pushing IV: A Tribute to W.G. Ernst

Wednesday, 5 November 2003
8:00 AM - 12:00 PM

NEAR-ULTRAHIGH PRESSURE PROCESSING OF SUBDUCTED CONTINENTAL CRUST: MIOCENE CRUSTAL XENOLITHS FROM THE PAMIRS

Paper number: T219-15
Program: Technical Sessions
Time: 11:30 AM – 11:45 AM

Authors

Abstract

Xenoliths erupted at 11 Ma in the southeastern Pamirs suggest that Gondwanan crust overprinted by a Cretaceous magmatic arc on the southern margin of Eurasia was subducted to near-ultrahigh-pressure depths of 90-100 km beneath Eurasia during Eocene(?)-Miocene intracontinental convergence. Combined with Tibetan xenoliths and surface exposures, these xenoliths suggest that the Pamirs and Tibet share similar crustal architectures--a southern lower crust composed of Gondwanan crust overprinted by a Cretaceous magmatic arc and a northern lower crust composed of clastic sedimentary rocks--produced by parallel tectonic evolutions. The Pamirs xenoliths reached temperatures of ~1075°C after they underwent dehydration melting, enrichment metasomatism, and melt injection during subduction. This processing at extreme temperatures and pressures caused significant changes in physical properties of the subducted crust: melting decreased buoyancy whereas melt injection/metasomatism increased buoyancy