LAUSR

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 ca. 66.7% at an average convergence rate of 8.8±0.6 cm/yr during the first stage at 250-200 Ma, when ca. 62.5-76.1% of the slabs associated with the MOO lithosphere were formed primarily through intra-oceanic 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, ca. 14.2-30.9% of the MOO slabs were formed and continental-oceanic convergence outpaced intra-oceanic subduction. In the last stage at 150-120 Ma, the convergence rate dropped to ca. 0.4-0.6 cm/yr with the formation of ca. 4.6-9.8% slabs associated with the MOO lithosphere. The final closure of the MOO remnant 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.