Sedimentary processes and deformation styles of the Mesozoic sedimentary succession in the northern margin of the Mohe basin, NE China: Constraints on the final closure of the Mongol–Okhotsk Ocean

Abstract

• The depositional age of the Xiufeng Formation was estimated as 159 Ma. • The Mohe Formation has a bidirectional provenance from 150 Ma. • The tectonic setting transformed from compression to extension during 135–128 Ma. • A series of E-W and NE-SW-trending normal faults occurred since the Early Barremian . • The final closure of the Mongol-Okhotsk Ocean has been limited to 150–135 Ma. The Mohe basin is located to the south of the eastern Mongol–Okhotsk suture belt and contains critical stratigraphic records and thrust-nappe structures for understanding the closure of the eastern Mongol–Okhotsk Ocean. This paper discusses the formation ages, provenance, and tectonic setting of the Xiufeng and Mohe formations, and further reveals the timing of the final closure of the Mongol–Okhotsk Ocean and the tectonic evolution of the Mohe basin. The weighted mean 206 Pb/ 238 U ages for the youngest zircon of these samples indicate that the maximum depositional ages of the Xiufeng, Mohe and Tamulangou Formations were conservatively estimated at 159 Ma, 150 Ma and 128 Ma, respectively. From Late Triassic to Late Jurassic (150 Ma), the Mongol-Okhotsk Ocean was consumed by bidirectional subduction expressed by subduction under the Siberian Craton and the Erguna Block, respectively. The intense subduction led to the compression of the continental arc and the basement uplift of the Erguna Block, which provided abundant clastic sediments to the Xiufeng-Ershierzhan Formations. During the Late Jurassic-Valanginian (150–135 Ma), the Mongol-Okhotsk Ocean closed rapidly, which finally caused the collision between the Erguna Block and the Siberian Craton. Meanwhile, the southern margin of the Siberian Craton was uplifted and started furnishing sediments into the Mohe-Kaikukang Formations, which may have a bidirectional provenance. The subsequent crustal shortening associated with collision between the Erguna Block and the Siberian Craton led to nappe structures, syn‐collisional folds, and nearly N-S-trending reverse and oblique-slip faults occurred along the northwestern margin of the Mohe basin. Between 135 and 128 Ma, the Mohe basin entered the stage of tectonic setting transformation, which is the crucial period for the Mohe basin to transform from compression to extension. Since the Early Barremian (ca. 128 Ma), the compressional environment was transformed into a post-orogenic extensional tectonic environment, and a series of nearly E-W and NE-SW-trending normal faults occurred, which might have been controlled by the slab rollback of the Paleo-Pacific Plate and detachment of the Mongol-Okhotsk oceanic plate after the closure of the Mongol-Okhotsk Ocean.