GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 283-5
Presentation Time: 9:00 AM-6:30 PM


QIU, Liang1, YAN, Dan-Ping2, WELLS, Michael L.3, CAO, Wentao4, LI, Xu-Tuo1, XU, Chen-Guang1, YANG, Wenxin1 and GAO, Tian1, (1)School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China, Beijing, 100083, China, (2)State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, Beijing, 100083, China, (3)Department of Geoscience, University of Nevada Las Vegas, 4505 S. Maryland Pkwy, Las Vegas, NV 89154-4010, (4)State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, 100083, China

Structural and thermochronologic studies of the Batang-Deqin area in eastern Tibetan Plateau provide constraints on the Paleo-Tethys orogeny. The NS-trending Paleo-Tethys orogen at Batang-Deqin includes ophiolitic mélange zone, magmatic belt, and fold-thrust belt. Two Paleo-Tethys deformation stages, i.e., the dextral oblique top-to-the-west thrusting (D1) and a top-down-to-the-southeast shearing (D2), and associated metamorphism, are identified in this area. The P-T estimates of the garnet schist of the Barrovian metamorphism suggest the formation condition of ~500-600 °C and ~5-6 kbars. The 40Ar/39Ar analyses on synkinematic and metamorphic micas of the garnet schist yield Late Permian to Early Triassic and Late Triassic ages throughout the Batang-Deqin area. The biotite 40Ar/39Ar and zircon (U-Th)/He analyses on the migmatite yield ages of ~190 Ma and Cenozoic ages, respectively. Integrated with previous 40Ar/39Ar and U-Pb ages, the reconstruction of cooling path for the garnet schist, plutons, and migmatites reveals a rapid cooling from crystallization of igneous zircons through closure temperature of mica (~700 ºC to ~300 ºC), between ~230 Ma to ~210 Ma. Therefore, we propose that the post-orogenic extension and ductile thinning (D2) cooled and exhumed the thickened Paleo-Tethys orogenic crust through the biotite 40Ar/39Ar temperature during the late Late Triassic.

Keywords: Paleo-Tethys tectonics; eastern Tibetan Plateau; Jinsha suture zone; thermochronology; structural analysis