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

Bradley Hacker, Peter Lufffi, Valery Lutkov, Vladislav Minaev, Lothar Ratschbacher, Terry Plank, Mihai Ducea, Alberto Patiño-Douce, Michael McWilliams, Jim Metcalf

Research output: Contribution to journalArticle

138 Scopus citations

Abstract

Xenoliths of subducted crustal origin hosted by Miocene ultrapotassic igneous rocks in the southern Pamir provide 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.

Original languageEnglish (US)
Pages (from-to)1661-1687
Number of pages27
JournalJournal of Petrology
Volume46
Issue number8
DOIs
StatePublished - Aug 2005

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Keywords

  • High-pressure
  • Pamir
  • Subduction
  • Tibet
  • Xenolith

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Hacker, B., Lufffi, P., Lutkov, V., Minaev, V., Ratschbacher, L., Plank, T., Ducea, M., Patiño-Douce, A., McWilliams, M., & Metcalf, J. (2005). Near-ultrahigh pressure processing of continental crust: Miocene crustal xenoliths from the Pamir. Journal of Petrology, 46(8), 1661-1687. https://doi.org/10.1093/petrology/egi030