Intra-continental Orogeny: Insights from Magnetotelluric Data into the Mesozoic Uplift History of the Eastern Jiangnan Orogen in South China

Despite extensive efforts to understand the tectonic evolution of the Jiangnan Orogen in South China, the orogenic process and its mechanism remain a matter of dispute. Previous geodynamic studies have mostly focused on collisional orogeny, which is commonly invoked to explain the Jiangnan Orogen. However, it is difficult for such hypotheses to reconcile all the geological and geophysical data, especially the absence of ultrahigh-pressure metamorphic rocks. Based on the magnetotelluric data, we present a group of resistivity models produced through the combination of two -dimensional and three-dimensional inversions, revealing the geo-electrical structures of Jiangnan and a typical collisional orogen. In our models, the resistive crust is separated into three parts by a prominent conductive layer with opposite dipping directions on both sides. A special thrust-nappe system, which is different from that developed in a typical collisional process, is revealed in the Jiangnan Orogen. This structure suggests a process different from the simple collisional orogeny. To interpret our observations, an 'intra-continental orogeny' is proposed to address the development of the Jiangnan Orogen in the Mesozoic. Furthermore, this 'reworked' process may contain at least two stages caused by the decoupling of the lithosphere, which is revealed by an extra conductive layer beneath Jiangnan.