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Defining the Main Central Thrust in the Hazara-Kashmir Syntaxis, Northern Pakistan: Evidence from New Isotopic Data
  • W Joel Schiffer,
  • Delores Robinson,
  • Shah Faisal
W Joel Schiffer
University of Alabama

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Delores Robinson
University of Alabama
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Shah Faisal
National Centre of Excellence in Geology, University of Peshawar
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Integrating detrital zircon U/Pb and whole-rock Nd data throughout the Himalayan arc provides the means to distinguish between the Tethyan (TH), Greater (GH), and Lesser Himalayan (LH) tectonostratigraphic zones within the thrust belt. In the Kaghan valley of northern Pakistan, debate exists over the existence and location of the Main Central thrust (MCT) and the tectonostratigraphic affinity of the rocks in the Hazara-Kashmir syntaxis. Three new detrital zircon U/Pb age spectra and two new εNd(0) values from the footwall rocks of the Batal fault yield 1.0-2.0 Ga age populations and an average εNd(0) value of -13.6. Four new detrital zircon U/Pb age spectra and two new εNd(0) values from the hanging wall rocks have primarily <1.2 Ga age populations and an average εNd(0) value of -16.7. Most detrital zircon analyses exhibit Pb-loss from younger (<600 Ma) intrusive or metamorphic events. The absence of zircon <1.0 Ga in the footwall samples indicates that they are LH rocks, while εNd(0) values indicate that they are not Paleoproterozoic LH rocks, but are comparable to other Meso- and Neoproterozoic LH rocks along the Himalayan arc. Neoproterozoic and younger detrital zircon age populations from the hanging wall samples and the presence of ~47 Ma intrusive leucogranite indicate that these are either TH or GH rocks, with εNd(0) values also consistent with TH or GH values. Combining these data show that the hanging wall rocks are either TH or GH rocks, and that the footwall rocks are Mesoproterozoic LH rocks. In most places, the MCT is defined as GH rocks thrust over LH rocks. However, in NW India, the GH/LH contact is buried in the subsurface, and the MCT at the surface is a TH/LH contact. Therefore, these data define the Batal fault in the Kaghan valley as equivalent to the MCT, with TH/GH rocks thrust over LH rocks, and link it with the Indus River valley to the west in Pakistan and NW India to the east.