The bending of a supra-subduction zone produced crustal thickening and arc migration of the Mongolian Orocline

Orogenic curvatures have been widely recognized along global convergent plate boundaries. Understanding the impact of such curvatures on the tectonic evolution of orogens and their three-dimensional architecture has been challenging. Here we address this issue by studying magmatism around the tightly curved Mongolian Orocline in Central Asia. Our results show that during the Permian–Triassic, arc magmatism around the inner hinge of the orocline became younger towards the core of the orocline. During the same period, the crust was thickened, as indicated by Lanthanum–Ytterbium ratio proxy. These findings, together with the observation that the present-day hinge zone of the Mongolian Orocline is wider, indicate that this zone was subjected to significant crustal-scale contraction. This contractional deformation accounts for the relatively thicker crust around the inner hinge of the Mongolian Orocline, and offers a novel perspective on the formation of elevated topography around the hinge of curved plate boundaries.