Abstract
Abstract The eastern Karakoram terrane, NW India, records crustal evolution in the core of the Himalayan–Tibetan orogen. Recent debate has centred on whether prograde metamorphism, anatexis and leucogranite emplacement were the result of localised shear heating and magma advection within the Karakoram Fault Zone (KFZ) or instead predate the KFZ and were the result of regional tectonometamophic events. Inclusions within andalusite porphyroblasts that grew during 15.7 Ma leucogranite emplacement have fabrics that are random or discordant to the KFZ matrix foliation, indicating that the KFZ initiated after this time. Therefore, earlier anatexis and metamorphism are the result of regional metamorphic events. Amphibole–plagioclase thermobarometry on a c. 17 Ma migmatite melanosome, later exhumed within a transpressional zone of the KFZ, shows that melting occurred at 688 °C and 522 MPa. Amphibolites record an older kyanite-grade metamorphic event that occurred at 677–736 °C and 875–1059 MPa. Metapelites also record a kyanite-grade event which is constrained by Ti-in-biotite thermometry to have occurred at 622 °C and > 650 MPa. The tectonometamorphic history of the eastern Karakoram correlates closely with that of the central Karakoram away from the KFZ. This correlation supports the interpretation that metamorphism and anatexis were regional in extent and also indicates a limited offset of
Highlights
Understanding the evolution of the continental crust during the orogenic cycle, the pressure–temperature paths experienced by metamorphic rocks and their relationship to magmatic and deformation processes are fundamental but challenging issues
Alternative prekinematic interpretations of the intrusions, based on regional mapping, thermochronology and field and microstructural criteria, have been put forward as evidence that the Karakoram Fault Zone (KFZ) initiated after c. 15.7 Ma and is a significantly more recent structure (Phillips and Searle, 2007; Phillips et al, 2004; Searle, 1996; Wang et al, 2011, 2013a,b). If this is the case the KFZ cannot have been the cause of anatexis and leucogranite generation between c. 22 and 16 Ma (Phillips et al, 2013). In this contribution we investigate metamorphism throughout the Eastern Karakoram Metamorphic Complex (EKMC) and its relationship to regional and local (i.e. KFZ) tectonic events
Cretaceous subduction and crustal thickening along the southern Karakoram terrane resulted in sillimanite-grade metamorphism of the Pangong Metamorphic Complex
Summary
Understanding the evolution of the continental crust during the orogenic cycle, the pressure–temperature paths experienced by metamorphic rocks and their relationship to magmatic and deformation processes are fundamental but challenging issues. Geographically links the central Karakoram with the Qiangtang terrane and contains exposures of basement lithologies exhumed from a range of depths Metamorphism in this region remains relatively less studied and has potential to further our understanding of these key terranes. Peak metamorphism adjacent to the KFZ predates strike-slip deformation on the fault (Streule et al, 2009) and can be correlated with metamorphic events away from the KFZ in the Hunza region of the Karakoram (Fraser et al, 2001; Palin et al, 2012). 22 and 16 Ma (Phillips et al, 2013) In this contribution we investigate metamorphism throughout the Eastern Karakoram Metamorphic Complex (EKMC) and its relationship to regional and local (i.e. KFZ) tectonic events
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