Triassic orocline in East Asia: Insights from a transition from passive margin to foreland basin in eastern North China Block

Abstract

The characteristics and evolution of a continental margin is of key importance in constructing the tectonic framework of a plate boundary. In the eastern North China Block (NCB), there is still controversy regarding the tectonic attribution and types of its continental margin during Paleozoic times, which yielded an understanding of convergence between the NCB and South China Block. In this study, we integrated the previous stratigraphic and sedimentologic results in the NCB to reconstruct the tectono‐paleogeographic evolution of its continental margin. The sedimentary records from Paleozoic to Early Mesozoic times in the eastern and southeastern margin of the NCB can be divided into 3 tectono‐stratigraphic sequences. The Early Paleozoic (Cambrian–Ordovician) sediments that are widespread in the eastern NCB reveal the well‐preserved drifting passive margin successions that consist of enormous thicknesses of limestone and dolomite. During the Late Carboniferous to Early Permian, the eastern NCB was dominated by clastic rocks interbedded with limestones, which implies a convergent passive margin. The Late Permian to Middle Triassic fluvial‐lacustrine units in the eastern NCB have developed in a syn‐collisional foreland basin. We emphasize that the Early Paleozoic passive margin of the eastern NCB directly converted to a convergent platform during the Late Paleozoic, which is consistent with a southeastward subduction rather than a transition to an active continental margin with a northwestward indentation. We suggest that the 3 tectono‐stratigraphic sequences are related to the opening and closure of the Proto‐ and Paleo‐Tethys Ocean in the eastern segment of the northern margin of Gondwana. Moreover, the transition of marine to terrestrial environments is associated with a collisional model about an orocline in East Asia.