Structural kinematics, metamorphic P–T profiles and zircon geochronology across the Greater Himalayan Crystalline Complex in south‐central Tibet: implication for a revised channel flow

Abstract

A specific question about the Himalayas is whether the orogeny grew by distributed extrusion or discrete thrusting. To place firm constraints on tectonic models for the orogeny, kinematic, thermobarometric and geochronological investigations have been undertaken across the Greater Himalayan Crystalline Complex (GHC) in the Nyalam region, south‐central Tibet. The GHC in this section is divided into the lower, upper and uppermost GHC, with kinematically top‐to‐the‐south, alternating with top‐to‐the‐north shear senses. A new thrust named the Nyalam thrust is recognized between the lower and upper GHC, with a 3 kbar pressure reversion, top‐to‐the‐south thrust sense, and was active after the exhumation of the GHC. Peak temperature reached ∼749 °C in the cordierite zone, and decreased southwards to 633–667 °C in the kyanite and sillimanite‐muscovite zones, and northwards to greenschist facies at the top of the South Tibetan Detachment System (STDS). Pressure at peak temperature reached a maximum value in the kyanite zone of 9.0–12.6 kbar and decreased northwards to ∼4.1 kbar in the cordierite zone. Zircon U‐Pb ages of a sillimanite migmatite and an undeformed leucogranite dyke cutting the mylonitized rocks in the STDS reveal a long‐lived partial melting of the GHC, which initiated at 39.7–34 Ma and ceased at 14.1 Ma. Synthesizing the obtained and collected results, a revised channel flow model is proposed by considering the effect of heat advection and convection by melt and magma migration. Our new model suggests that distributed processes like channel flow dominated during the growth of the Himalayan orogen, while discrete thrusting occurred in a later period as a secondary process.

Oligocene HP metamorphism and anatexis of the Higher Himalayan Crystalline Sequence in Yadong region, east-central Himalaya

“…The garnets of the studied migmatites contain multiphase inclusions, representing a peritectic phase as described above. Therefore, the obtained Wang et al, 2013;Zhang et al, 2015). This longer time span covers the Eohimalayan and Neohimalayan stages of metamorphism as described above, suggesting that the HHCS underwent a continued but episodic metamorphic process.…”

“…Cordierite is common in the HHCS migmatites and leucogranites (Neogi et al, 1988;Ganguly et al, 2000;Goscombe et al, 2006;Rubatto et al, 2013;Sorcar et al, 2014). The upper structural level of the HHCS in the central Himalayas is characterized by the presence of cordierite-bearing migmatites, and thus was traditionally assigned to the HT and low pressure (LP) metamorphic cordierite zone (e.g., Goscombe et al, 2006;Imayama et al, 2010Imayama et al, , 2012Streule et al, 2010;Warren et al, 2011;Wang et al, 2013).…”

Long-lived high-temperature granulite-facies metamorphism in the Eastern Himalayan orogen, south Tibet

“…40-13 Ma (Fig. 9), such as 32-17 Ma (Searle et al, 2003), 33-13 Ma (Cottle et al, 2009a;Kali et al, 2010) and 37-20 Ma (Kohn and Corrie, 2011); (3) in Central and Eastern Himalayas, the HHC also underwent a longlived partial melting, such as 40-14 Ma (Wang et al, 2013), 33-18 Ma (Imayama et al, 2012), 25-9 Ma (Guo and Wilson, 2012), 36-17 Ma (Rubatto et al, 2013) and even as early as 46-42 Ma (Aikman et al, 2008;Hou et al, 2012;Zeng et al, 2011); (4) the channel flow model predicts that the HHC underwent a prolonged granulite-facies metamorphism with the HP metamorphism (P max.) at ca.…”

“…Zhang et al, 2004). Therefore, although many studies have focused on petrology and geochronology of the HHC, initiation and duration of HT granulite-facies metamorphism and associated anatexis are still far from being universally demonstrated (Groppo et al, 2010;Kali et al, 2010;Kohn and Corrie, 2011;Rubatto et al, 2013;Searle, 2013;Wang et al, 2013).…”

Tectonics of the Himalayas

“…; Imayama et al, 2012 , Corrie andKohn, 2011;, Wang et al, 2013;, Regis et al, 2014 High Himalayan Discontinuity; Figs. 4a, 5a -MCT MCT Kohn et al, 2001;Imayama et al, 2010MCT -Harris et al, 2004Imayama et al, 2010Imayama et al, , 2012 Khaghn valley Nanga Parbat syntaxis Tso Morari Fig Pressure-temperature (P-T) diagram with equilibrium curves for fluid-saturated melting and mica dehydration reactions.…”