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The geodynamic significance of UHP exhumation: New constraints from Tso Morari Complex, NW Himalaya
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  • Anna Bidgood,
  • Andrew J Parsons,
  • Nicholas M W Roberts,
  • David Waters,
  • Simon Tapster,
  • Phillip Gopon
Anna Bidgood
Carnegie Institution for Science

Corresponding Author:[email protected]

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Andrew J Parsons
University of Plymouth
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Nicholas M W Roberts
NERC Isotope Geosciences Laboratory
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David Waters
Oxford University
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Simon Tapster
British Geological Survey
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Phillip Gopon
University of Leoben
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The burial and exhumation of continental crust to and from ultrahigh-pressure (UHP) is an important orogenic process, often interpreted with respect to the onset and/or subduction dynamics of continent-continent collision. Here, we investigate the timing and significance of UHP metamorphism and exhumation of the Tso Morari complex, North-West Himalaya. We present new petrochronological analyses of mafic eclogites and their host-rock gneisses, combining U-Pb zircon, rutile and xenotime geochronology (high-precision CA-ID-TIMS and high-spatial resolution LA-ICP-MS), garnet element maps, and petrographic observations. Zircon from mafic eclogite have a CA-ID-TIMS age of 46.91 ± 0.07 Ma, with REE profiles indicative of growth at eclogite facies conditions. Those ages overlap with zircon rim ages (48.9 ± 1.2 Ma, LA-ICP-MS) and xenotime ages (47.4 ± 1.4 Ma; LA-ICP-MS) from the hosting Puga gneiss, which grew during breakdown of UHP garnet rims. We argue that peak zircon growth at 47-46 Ma corresponds to the onset of exhumation from UHP conditions. Subsequent exhumation through the rutile closure temperature, is constrained by new dates of 40.4 ± 1.7 and 36.3 ± 3.8 Ma (LA-ICP-MS). Overlapping ages from Kaghan imply a coeval time-frame for the onset of UHP exhumation across the NW Himalaya. Furthermore, our regional synthesis demonstrates a causative link between changes in the subduction dynamics of the India-Asia collision zone at 47-46 Ma and the resulting mid-Eocene plate network reorganization. The onset of UHP exhumation therefore provides a tightly constrained time-stamp significant geodynamic shifts within the orogen and wider plate network.
29 Feb 2024Submitted to ESS Open Archive
05 Mar 2024Published in ESS Open Archive