Absolute reconstruction of the closing of the Mongol‐Okhotsk Ocean in the Mesozoic elucidates the genesis of the slab geometry underneath Eurasia

Abstract

AbstractUnderstanding the present‐day fast seismic velocity anomalies in the mantle requires an accurate kinematic reconstruction of past convergent tectonics. Using the paleomagnetism‐based absolute reconstruction method from Wu and Kravchinsky (2014), we present here the restoration of the closing of the Mongol‐Okhotsk Ocean (MOO) that existed between Siberia and North China‐Amuria (NCA) during the Mesozoic. Three stages, i.e., 250–200 Ma, 200–150 Ma, and 150–120 Ma, are identified from the time‐varying convergence rates of Siberia and NCA. The spherical distance between the suture margins was reduced by approximately 66.7% at an average convergence rate of 8.8 ± 0.6 cm/yr during the first stage at 250–200 Ma, when approximately 62.5–76.1% of the slabs associated with the MOO lithosphere were formed primarily through intraoceanic convergence. In the second stage at 200–150 Ma, the spherical distance was reduced by another 21.1% with a convergence rate of 3.6 ± 0.3 cm/yr. During this stage, approximately 14.2–30.9% of the MOO slabs were formed and continental‐oceanic convergence outpaced intraoceanic subduction. In the last stage at 150–120 Ma, the convergence rate dropped to approximately 0.4–0.6 cm/yr with the formation of approximately 4.6–9.8% slabs associated with the MOO lithosphere. The final closure of the remnant MOO basin could have been accomplished by 130–120 Ma, which explains the origin of the fast‐velocity anomalies inside the restored continents at 120 Ma near the suture margins.