Tectonic setting of the Late Triassic magmatism in the Qinling Orogen: New constraints from the interplay between granite emplacement and shear zone deformation in the Shagou area

Abstract

Multidisciplinary studies of the Baliping granite pluton and the Shagou shear zone (East Qinling Orogen, Central China) have been conducted to reconstruct the emplacement and deformation processes of the Baliping pluton, to explore the relationship between granite pluton and shear zone deformation, and further to constrain the tectonic setting of the Late Triassic magmatism in the Qinling Orogen which remains controversial. Zircon U–Pb geochronology studies confirmed that the Baliping granites and the protolithes of the Shagou granitic mylonites crystallized from the same magmas at ca. 221 Ma since the two nearly have the same zircon U–Pb ages and Ti–in–zircon temperatures. Meanwhile, the 210 Ma of metamorphic zircons and the 201 Ma of syntectonic granitic vein provide precise limits on the timing of synkinematic deformation in response to Late Triassic orogeny. Anisotropy of magnetic susceptibility, microstructural observation, and shape preferred orientation were combined to study the internal structures. New fabrics datasets display a high degree of coupling between the Baliping pluton and the Shagou shear zone, indicating a syntectonic emplacement of the pluton. Microstructural data suggest that the magmatic to high‐temperature solid‐state deformation is a continuum process in which the fabrics were mainly acquired. We propose an integrated syntectonic emplacement model of the Baliping pluton, in which the shear zone deformation (sinistral transpression) play a significant role on the emplacement of the magma by creating rooms. Emplacement of the pluton, in turn, triggers the nucleation of Shagou shear zone by providing the protoliths and the heat. On the basis of this study, we argued that the Qinling Orogen was still under the convergent setting during 221–201 Ma.