Genesis and exhumation of the Kongur-Muztaghata and Maeryang gneiss domes in NE Pamir since the Mesozoic

Abstract

The Kongur-Muztaghata-Maeryang terrane in NE Pamir is considered to be the western extension of the Songpan-Ganze terrane located in the northern Tibetan Plateau. The Kongur-Muztaghata gneiss dome (KMGD) is situated in the north while the Maeryang gneiss dome (MYGD) is in the south. The KMGD comprises Triassic granites and granitic gneiss in the core and Early Paleozoic-Triassic sediments in the mantle that underwent Barrovian-type and Buchan-type metamorphisms. Based on geochemical and geochronological data, the Kongur-Muztaghata magmatic arc was formed around ∼252–204 Ma due to northward subduction of the Paleo-Tethys Jinsha oceanic slab. The collision of the Kongur-Muztaghata magmatic arc and the Qiangtang terrane occurred subsequently. Previous research suggested that the KMGD was formed in the Miocene (21–8 Ma). However, our new in-situ monazite U–Pb data for the mantled metasediment shows that the KMGD was initially formed at ∼198 Ma.

The MYGD is comprised of an Early Paleozoic-Triassic metasediment mantle and a Cambrian anatexis complex core that underwent Barrovian-Buchan metamorphisms. Our new structural, geochemical, and geochronological data suggest that the protolith of the Maeryang orthogneiss was formed around ∼519-513 Ma, with the surrounding Early Paleozoic metavolcanic rocks erupted at ∼519-508 Ma. Together, they formed the Early Cambrian magmatic complex. In-situ U–Pb dating of monazites and zircon metamorphic rims for the Triassic metamorphic rocks in the mantle indicate that the Barrovian-Buchan metamorphism in the MYGD occurred around ∼206-187 Ma, likely caused by anatexis in the deep crust of the gneiss dome core. Thus, we propose that the KMGD and MYGD underwent a two-stage exhumation: the initial uplift during the Late Triassic-Early Jurassic thermo-tectonic event associated with the Cimmerian orogeny and the late rapid exhumation since the Miocene driven by the collision between the Eurasian and Indian plates.