Exhumation history of a section of the Sikkim Himalayas, India: Records in the metamorphic mineral equilibria and compositional zoning of garnet

Jibamitra Ganguly, Somnath Dasgupta, Weiji Cheng, Sudipta Neogi

Research output: Contribution to journalArticle

109 Scopus citations

Abstract

The exhumation history of pelitic migmatite samples from the High Himalayan Crystalline Complex (HHC) near the South Tibetian Detachment System in the Sikkim-Darjeeling section has been determined on the basis of thermobarometric analyses, retrograde breakdown reactions and compositional zoning of garnet. The peak metamorphic condition is estimated to be Ο10.4 kbar, 800°C from thermo-barometric and phase equilibrium constraints. The observed retrograde breakdown of garnet to spinel and cordierite requires near isothermal and, hence, extremely rapid (15 mm/yr) exhumation up to the depth of Ο15 km. Numerical modeling suggests that the initial rapid exhumation must have been followed by a much slower process, 2 mm/yr, up to at least 5 km depth, to lead to the development of the observed compositional zoning of garnet. The dramatic change of the exhumation velocity (Vz) might reflect a process of tectonic thinning followed by erosion and/or horizontal flow at shallow depth. Assuming that the Vz did not change significantly below 5 km depth, these results suggest that the HHC samples studied in this work exhumed from a depth of 34 km within 8 Ma.

Original languageEnglish (US)
Pages (from-to)471-486
Number of pages16
JournalEarth and Planetary Science Letters
Volume183
Issue number3-4
DOIs
StatePublished - Dec 1 2000

Keywords

  • Crystal zoning
  • Exhumation
  • Himalayas
  • P-T conditions
  • Sikim India

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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