Premium
Structural kinematics, metamorphic P–T profiles and zircon geochronology across the Greater H imalayan Crystalline Complex in south‐central T ibet: implication for a revised channel flow
Author(s) -
Wang J. M.,
Zhang J. J.,
Wang X. X.
Publication year - 2013
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/jmg.12036
Subject(s) - geology , sillimanite , migmatite , main central thrust , kyanite , leucogranite , orogeny , geochemistry , shear zone , metamorphism , zircon , geochronology , metamorphic rock , petrology , geomorphology , paleontology , gneiss , tectonics , quartz , biotite
A specific question about the H imalayas 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 H imalayan Crystalline Complex ( GHC ) in the Nyalam region, south‐central T ibet. 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 T ibetan 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 H imalayan orogen, while discrete thrusting occurred in a later period as a secondary process.