Initiation of the Himalayan Orogen as an Early Paleozoic Thin-skinned Thrust Belt

Abstract

Research by many workers in various regions of the Himalaya, combined with our recent geologic and geochronologic studies in Nepal, indicate that fundamental aspects of the Himalayan orogen originated in an early Paleozoic thrust belt and are unrelated to Tertiary India-Asia collision. Manifestations of early Paleozoic tectonism include ductile deformation, regional moderate-to highgrade metamorphism, large-scale southvergent thrusting, crustal thickening and the generation of granitic crustal melts, uplift and erosion of garnet-grade rocks, and accumulation of thick sequences of synorogenic strata. Determining the relative contributions of early Paleozoic versus Tertiary tectonism constitutes a significant challenge in understanding the Himalayan orogen.

Petrographic features as an effective indicator for the variation in strength of granites

“…Ma) granitoids intruding in LHS and GHS (DeCelles et al, 1998(DeCelles et al, , 2000(DeCelles et al, , 2004Godin et al, 2001;Gehrels et al, 2003;Booth et al, 2004;Lee and Whitehouse, 2007;Quigley et al, 2008) indicate an early Paleozoic orogenic event in Himalayan terrane.…”

“…Argles et al, 1999;Catlos et al, 2000Catlos et al, , 2002Foster, 2000;Godin et al, 2001;Gehrels et al, 2003Gehrels et al, , 2006aGehrels et al, , 2006bKohn et al, 2004) across wide areas of the Himalayas.…”

“…Garzanti et al, 1986;Brookfield, 1993). The lower Ordovician basal conglomerate unconformably overly the Cambrian strata in Kathmandu, Nepal (Kumar et al, 1978;Funakawa, 2001;Gehrels et al, 2003). Similarly in Spiti and Zanskar region of NW India, the Cambrian lithologies are unconformably overlain by coarse Ordovician conglomerates (Hughes, 2002;Myrow et al, 2006a, b).…”

Tectonic interleaving along the Main Central Thrust, Sikkim Himalaya

“…These include an event at c. 500 Ma (Bhargava 1995;Marquer et al 2000;Miller et al 2001;Ghosh et al 2005;Richards et al 2005) and an earlier Neoproterozoic event at c. 800 Ma (DiPietro & Isachsen 2001;Singh et al 2002;Ghosh et al 2005;Richards et al 2006;Spencer et al 2012). A widespread Cambro-Ordovician tectonic event has been documented across the Greater Himalayan Sequence (Argles et al 1999;Marquer et al 2000;Gehrels et al 2003Gehrels et al , 2006. This has been termed the 'Bhimpedian orogeny' (Cawood et al 2007), and has been related to the Cambrian formation of Gondwana (Yin et al 2010b).…”

Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction

“…Channel flow models predict that the STD should be the locus for large relative particle displacement, implying a different origin for the GHS and the Tethyan sedimentary sequence . Recent structural restorations and isotopic studies, however, propose the lower Tethyan sedimentary sequence as a potential protolith for some of the GHS (Vannay & Grasemann 2001;Argles et al 2003;Gehrels et al 2003;Searle & Godin 2003;Richards et al 2005). The STD is generally interpreted as either a d6collement surface (stretching fault), where the thick pile of continental margin rocks (Tethyan sedimentary sequence) has been decoupled without much internal disturbance to the stratigraphy, or a passive roof thrust within the MCT system, with a hanging-wall flat-footwall flat geometry (Searle et al 1988;Yin 2002).…”