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AGU: Tectonics

 

Keywords

  • gneiss domes
  • Tibet
  • age dating

Index Terms

  • Tectonophysics: Continental tectonics: compressional
  • Geochronology: Radioisotope geochronology
  • Structural Geology: High strain deformation zones
  • Geochronology: Thermochronology
  • Tectonophysics: Dynamics: gravity and tectonics

Abstract

TECTONICS, VOL. 29, TC4013, 30 PP., 2010
doi:10.1029/2008TC002393

Out-of-sequence deformation and expansion of the Himalayan orogenic wedge: insight from the Changgo culmination, south central Tibet

Kyle P. Larson

Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario, Canada

Laurent Godin

Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario, Canada

William J. Davis

Geological Survey of Canada, Ottawa, Ontario, Canada

Don W. Davis

Jack Satterly Geochronology Laboratory, Department of Geology, University of Toronto, Toronto, Ontario, Canada

The Changgo culmination, one of the North Himalayan domes in south central Tibet, consists of a multiphase granite core surrounded by a deformed metasedimentary carapace. The granitic core records general non-coaxial shear with a top-to-the-south sense shear component. The contact between the core and the carapace is a shear zone, characterized by general non-coaxial shear with a top-to-the-north shear sense, interpreted to be the northern continuation of the South Tibetan detachment system (STDS). The shear zone contains lenses of leucogranite dated at 35.4 Ma. This is interpreted to reflect Eocene crustal thickening, coeval with the earliest shortening event recorded in the carapace. The main phase of the Changgo granite crystallized at 23.5 Ma, while undeformed aplite dikes, the youngest phase observed in the granite, were intruded at 22.1 Ma. Aplite dikes crosscut the main deformation fabric within the Changgo granite; therefore, that deformation and associated south directed shearing must have ended between 23.5 Ma and 22.1 Ma. The dikes are strained within the STDS, indicating that final displacement along the STDS must post-date 22 Ma, yet be older than 18.4 Ma, the cooling age of muscovite in the shear zone. It is proposed that the exhumation of the Changgo culmination is related to tectonically driven erosion in response to crustal thickening and rebuilding of the orogenic critical taper wedge. Subsequently, deformation in the wedge migrated toward the foreland, expanding the orogenic wedge laterally and moving the locus of displacement from the Main Central thrust structurally downward to the Main Boundary thrust.

Received 18 September 2008; accepted 2 March 2010; published 27 July 2010.

Citation: Larson, K. P., L. Godin, W. J. Davis, and D. W. Davis (2010), Out-of-sequence deformation and expansion of the Himalayan orogenic wedge: insight from the Changgo culmination, south central Tibet, Tectonics, 29, TC4013, doi:10.1029/2008TC002393.

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