NEAR-ULTRAHIGH PRESSURE PROCESSING OF SUBDUCTED
CONTINENTAL CRUST: MIOCENE CRUSTAL XENOLITHS FROM THE
PAMIRS
HACKER, Bradley1, LUFFI, Peter2, LUTKOV, Valery3, MINAEV, Vladislav3,
RATSCHBACHER, Lothar4, PATIÑO-DOUCE, Alberto5, DUCEA, Mihai6,
MCWILLIAMS, Michael7, and METCALF, James8, (1) Geological Sciences, Univ of
California, Santa Barbara, CA 93106, hacker@geology.ucsb.edu, (2) Geology and
Geophysics, Univ of Bucharest, Bucharest, 70139, Romania, (3) Geological Institute,
Tajik Academy of Sci, Dushanbe, 734063, Tajikistan, (4) TU Bergakademie Freiberg,
Bernhard-von-Cotta Strasse 2, Freiberg/SA, 09596, Germany, (5) Department of
Geology, Univ of Georgia, Athens, GA 30602, (6) Geosciences, Univ of Arizona,
Tucson, AZ 85721, (7) Geological and Environmental Sciences, Stanford Univ, Stanford,
CA 94305, (8) Geological and Environmental Sciences, Stanford Univ, Stanford, CA
94305-2115
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