The northern boundary of the Proto-Tethys Ocean: Constraints from structural analysis and U-Pb zircon geochronology of the North Qinling Terrane

The North Qinling Terrane, including the Kuanping, Erlangping and Qinling groups, is located in the northern part of the Qinling Orogen. Here we present results from structural analyses of the North Qinling Terrane and its surrounding regions. Three episodes of deformation (D-1, D-2 and D-3) are recognized. The D-1 deformation is characterized by NNE-dipping and SSW-dipping penetrative foliations (S-1). The S-1 foliations are mainly marked by a strong preferred orientation of hornblende crystals, and they were subsequently overprinted by the D-2 deformation. The D-2 deformation is marked by tight asymmetric folds with NNE-dipping and SSW-dipping axial plane foliations (S-2). We propose that the D-1 and D-2 deformations mainly occurred during similar to 440-400 Ma after the peak ultra-high pressure metamorphic event (similar to 520-480 Ma). And so these two deformation events could constrain the collision and exhumation processes of the North Qinling Terrane, which probably indicates the closure of the Kuanping Ocean located between the North Qinling Terrane and the North China Block in the early Paleozoic. These two deformations are overprinted by the D-3 deformation characterized by ENE-trending upright open folds. Two detrital zircon age spectra for the Kuanping Group with the youngest zircon of,similar to 640 Ma and similar to 510 Ma, respectively, are different from those recorded for the North China Block, which may reveal the continuous southward subduction of the Kuanping Ocean during the Neoproterozoic to early Paleozoic interval. We propose that the Kuanping Ocean marks the northern boundary of the Proto-Tethys Ocean in the study area. (C) 2015 Elsevier Ltd. All rights reserved.