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Near-ultrahigh pressure processing of subducted continental crust: Miocene crustal xenoliths from the Pamirs

Domenii publicaţii > Ştiinţele pământului şi planetare + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: Hacker, B., Luffi, P., Lutkov, P., Minaev, V., Ratschbacher, L., Patino-Douce, A., Ducea, M., McWilliams, M. and J. Metcalf

Editorial: Journal of Petrology, 46 (8), p.1661-1687, 2005.

Rezumat:

Xenoliths of deep origin hosted by Miocene ultrapotassic rocks in the Southern Pamir
bear important new information regarding the geological processes accompanying
tectonism during the Indo?Eurasian collision. Four types have been studied: sanidine
eclogites (omphacite, garnet, sanidine, quartz, biotite, kyanite), felsic granulites (garnet,
quartz, sanidine and kyanite), basaltic eclogites (omphacite and garnet), and a glimmerite
(biotite, clinopyroxene and sanidine). Apatite, rutile and carbonate are the most abundant
minor phases. Hydrous phases (biotite and phengite in felsic granulites and basaltic
eclogites, amphiboles in mafic and sanidine eclogites) and plagioclase form minor
inclusions in garnet or kyanite. Solid-phase thermobarometry reveals recrystallization at
mainly ultrahigh temperatures of 1000?1100°C and near-ultrahigh pressures of 2.5?2.8
GPa. Textures, parageneses and mineral compositions suggest derivation of the xenoliths
from subducted basaltic, tonalitic and pelitic crust that experienced high-pressure
dehydration melting, K-rich metasomatism, and solid-state re-equilibration. The timing of
these processes is constrained by zircon ages from the xenoliths and 40Ar/39Ar ages of the
host volcanic rocks to 57?11 Ma. These xenoliths reveal that deeply subducted crust may
undergo extensive dehydration-driven partial melting, density-driven differentiation and
disaggregation, and sequestration within the mantle. These processes may also contribute
to the alkaline volcanism observed in continent-collision zones.

Cuvinte cheie: ultra high pressure, Pamir, xenoliths