A multi-chronometric perspective on timing and rates of fold-thrust belt development during Himalayan orogenesis: insights from eastern Nepal Himalaya

Tshering Sherpa, University of Washington
Peter DeCelles, The University of Arizona
Barbara Carrapa, The University of Arizona
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Abstract

The Himalayan fold-thrust belt is a natural laboratory to investigate patterns of fold-thrust belt kinematics in a classic continental orogen. Integrating different chronometers with kinematic models derived from balanced cross sections provides a means of coupling and assessing regional deformation with temporal constraints. Here, we combine new and published monazite petrochronology,leucogranite zircon U-Pb geochronology, muscovite 40Ar/39Ar, zircon (U-Th)/He, zircon and apatite fission track dates to resolve regional patterns of thrust belt development in the Sagarmatha (Mt. Everest) region of eastern Nepal Himalaya. Broadly, average shortening rates are ~26-23 mm/yr during the Early Miocene, 17-15 mm/yr during the Middle Miocene, and <10 mm/yr during the Late Miocene. These first order approximation of shortening rates, in comparison with modern shortening rates (~20 mm/yr), indicate that the eastern Nepal Himalaya has accommodated shortening variably since collision. Rapid shortening rates during ca. 23-15 Ma and ca. 15-8 Ma are consistent with slip on Main Central thrust and Ramgarh thrust. Subsequent ca. 8-5 Ma shortening reflects smaller increments of slip on individual thrusts that built the Lesser Himalayan duplex. Together, these results demonstrate that thrust-belt development in the Himalaya proceeded episodically, with shortening rates that varied during different phases of orogenesis.

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