The eclogite, blueschists in central Qiangtang, Tibet, China: The record of Triassic subduction belt

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Zhai, Qingguo۱; Xiao, Xuchang۱; Li, Cai۲
Holding Date 29 September 2008

Widespread evidence for high-pressure (HP)/low-temperature (LT) metamorphism was reported in central Qiangtang area, North Tibet. This includes blueschists with glaucophane, crossite and lawsonite. These lines of evidence demonstrate that a HP/LT metamorphic belt occurs in central Qiangtang area. Recently, low temperature eclogite occur as lens or blocks was reported in this HP/LT belt. Garnet - omphacite - phengite geothermobarometry yields metamorphic conditions of 370-538،و and 14.1-26.2Gpa for eclogite. SHRIMP U-Pb dating on zircons from the eclogite show age of 243،ہ4Ma. The inclusions in zircons from the eclogite are mainly phengite, omphacite, garnet, barroisite, quartz, and so on, which are all the eclogite facies minerals, so this age reflects an eclogite facies metamorphism. The amphibole 40Ar/39Ar dating yields plateau age of 237،ہ2.2Ma, which records an amphibole facies metamorphism after eclogite. The219،ہ2Ma and 217.2،ہ1.8Ma 40Ar/39Ar ages of the phengite from the eclogite and its country rock , respectively, indicate the exhumation to the Earth’s surface in Late Triassic. The petrological and chronological data demonstrate the existence of a Triassic subduction zone in central Qiangtang area, North Tibet.