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

Understanding 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.