Geochronology of granulitized eclogite from the Ama Drime Massif: Implications for the tectonic evolution of the South Tibetan Himalaya

Abstract

[1] The Ama Drime Massif (ADM) is an elongate north-south trending antiformal feature that extends $70 km north across the crest of the South Tibetan Himalaya and offsets the position of the South Tibetan Detachment system. A detailed U(-Th)-Pb geochronologic study of granulitized mafic eclogites and associated rocks from the footwall of the ADM yields important insights into the middle to late Miocene tectonic evolution of the Himalayan orogen. The mafic igneous precursor to the granulitized eclogites is 986.6 ± 1.8 Ma and was intruded into the paleoproterozoic (1799 ± 9 Ma) Ama Drime orthogneiss, the latter being similar in age to rocks previously assigned to the Lesser Himalayan Series in the Himalayan foreland. The original eclogite-facies mineral assemblage in the mafic rocks has been strongly overprinted by granulite facies metamorphism at 750°C and 0.7-0.8 GPa. In the host Ama Drime orthogneiss, the granulite event is correlated with synkinematic sillimanite-grade metamorphism and muscovite dehydration melting. Monazite and xenotime ages indicate that the granulite metamorphism and associated anatexis occurred at <13.2 ± 1.4 Ma. High-grade metamorphism was followed by postkinematic leucogranite dyke emplacement at 11.6 ± 0.4 Ma. This integrated data set indicates that high-temperature metamorphism, decompression, and exhumation of the ADM postdates mid-Miocene south directed midcrustal extrusion and is kinematically linked to orogen-parallel extension. Citation: Cottle,

Detrital provenance evolution of the Ediacaran–Silurian Nanhua foreland basin, South China

“…8a-c;Liu and Xu, 1994;Wang, 1985), and the age spectra of the Ediacaran-Cambrian samples do not match that of the Cathaysian crystalline basements (see Section 5.1), an external detrital source is therefore demanded for siliciclastic deposition over the Cathaysia Block. On the other hand, the age spectra grossly match that of similar-aged rocks in northern India (e.g., Schärer et al, 1986;Brookfield, 1993;Stern, 1994;Wiedenbeck et al, 1996;Mezger and Cosca, 1999;Miller et al, 2001;Singh et al, 2002;Cawood et al, 2007;Liu et al, 2007;Simmat and Raith, 2008;Cottle et al, 2009). We therefore interpret that the Cathaysia side of the Nanhua Basin probably shared a similar clastic source region with basins in northern India, Fig.…”

“…Ca. 2.5 Ga tectonomagmatic events are reported in northwestern India (Wiedenbeck et al, 1996), 1.6-1.4 Ga events in the Eastern Ghats Belt of eastern India (e.g., Mezger and Cosca, 1999;Simmat and Raith, 2008), 1.1-1.0 Ga, 880-820 Ma and 550-470 Ma in northern India (e.g., Schärer et al, 1986;Brookfield, 1993;Miller et al, 2001;Singh et al, 2002;Cawood et al, 2007;Liu et al, 2007;Cottle et al, 2009), and 680-500 Ma in the East African Orogen that was connected to northwestern India and supplied detritus during the assembly of Gondwanaland (e.g., Myrow et al, 2010 and references therein;Stern, 1994). All these regions likely contributed to the Cambrian sediments in the SCB.…”

Introduction to Higher Himalaya

“…The migmatitic orthogneisses contain a few hundred meter-thick boudins of metabasics, recording eclogite facies metamorphism (Groppo et al 2007). The orthogneisses are dated at 1.8 Ga, similar to the Ulleri orthogneisses of the Lesser Himalaya in west Nepal Liu et al 2007;Cottle et al 2009). These high-pressure granulites contain garnet, clinopyroxene, orthopyroxene, plagioclase, quartz, and biotite.…”

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

“…Field relationships and detailed geochronology suggest that, in contrast to other domes (e.g. Cottle and others, 2009), melting within the LPD occurred over a protracted period (>10 Ma). Melt production and mobilization into dikes and sills likely resulted from semi-continuous production of melt by in-situ partial melting of the metamorphic host rock at different structural positions immediately prior to, and/or during, exhumation of the LPD.…”