Tectonic evolution of the Eocene–Oligocene Lushi Basin in the eastern Qinling belt, Central China: Insights from paleomagnetic constraints

Abstract

The eastern Qinling orogenic belt, located in the conjoint region between the Neo-Tethys tectonic domain and the western Pacific tectonic domain, is key to understanding the tectono-sedimentary evolution of the East Asian interior. Extensive Late Cretaceous–Cenozoic fluvial and lacustrine deposits within the eastern Qinling orogen provide ideal archives of tectono-sedimentary evolution in Fenwei, the eastern Qinling orogen. We present an integrated rock magnetism and anisotropy of magnetic susceptibility (AMS) study of a Middle Eocene–Early Oligocene succession in the Lushi Basin, eastern Qinling region. Our rock magnetic results suggest that hematite and magnetite are the main magnetic carriers of remanence, while χ−T curves, hysteresis loops, and low values of bulk susceptibility indicate that paramagnetic minerals are major contributors to AMS in the Lushi Basin. Nevertheless, the anomalous magnetic fabrics in the Zhangjiacun and Lushi Formations may result from the contribution of the iron-bearing carbonates in deposits. The clustering of the minimum principal axes nearly vertical to the bedding plane and the well-defined NW–SE magnetic lineation almost parallel to the dip of the bounding fault suggest that the AMS of the Dayu Formation is not a sedimentary fabric but an incipient deformation magnetic fabric. The pronounced NW–SE magnetic lineation indicates the NW–SE stretching of the Lushi Basin during the Late Eocene–Earliest Oligocene, which may have been caused by the combined effects of the India–Eurasia collision and the subduction of the western Pacific plate.