Structural Deformation and Genetic Mechanism of Qinghe Gneiss Dome in the Altai Orogen, Western China

Abstract

As a highly coupled aggregate of tectonism, magmatism, and metamorphism, a gneiss dome is usually taken as a vital window for understanding the crustal internal structure and the exchange of material and energy during orogenic exhumation. The Qinghe gneiss dome located in the eastern Chinese Altai orogen, lies in Qinghe County, Xinjiang, records important information of late accretionary orogeny associated with continental uplift and crustal growth. According to the field investigation, the dome shows core–mantle–margin domains, in which the core is composed of migmatized granite and gneiss, the mantle consists of banded gneiss, schist, and leptynite, and the margin has rock assemblages of phyllite, schist, and meta-sandstone. From the margin to the core, the dome can be divided into chlorite–sericite, andalusite–staurolite, sillimanite–biotite, and sillimanite–garnet metamorphic zones, recording progressive metamorphism. Detailed structural analyses in the Qinghe gneiss dome indicate progressive deformation from the margin to the core. Internal and external detachment faults are clarified, with the former characterized by inflow and outward migration of crustal material and the latter marked by brittle-ductile deformation with a lineation indicating lateral slip of the upper wall when the dome uplifted. Based on these faults, upper, middle, lower structural layers are observed from the outer to inner domains of the dome. Considering the general geological background and new data, the Qinghe gneiss dome probably predominantly underwent early ductile shear deformation and late heat-flow diapirism in the early Permian, closely related to upwelling of asthenosphere mantle that resulted from slab break-off in the extensional tectonic setting.