A Possible Late Jurassic Final Closure of the Mongol-Okhotsk Ocean in Its Eastern Segment: Constraints From New Paleomagnetic Investigations

Closure of the Mongol-Okhotsk Ocean (MOO) marks the final continental configuration of central Asia. Here we present a paleomagnetic study on the Upper Jurassic sedimentary rocks from the northern part of the Amuria Block (AMB) in northeastern China that is directly south of the Mongol-Okhotsk suture to constrain the timing of its final closure in the eastern segment. Rock magnetic experiments reveal that magnetite and hematite are magnetic carriers of the characteristic remanent magnetization. Site-mean directions isolated from 21 sites show antipodal normal and reversed polarities, passing both fold and reversal tests. After applying Elongation/Inclination correction of inclination shallowing, an age-mean direction is calculated at D_s/I_s = 196.7°/−68.2° (k = 71.9, α_95s = 1.3°) in stratigraphic coordinates, corresponding to a Late Jurassic paleomagnetic pole of λ/φ = 78.3°N/184.6°E (A₉₅ = 2.0°) for the AMB. Combining paleomagnetic data with regional geological evidence, we propose a possible Late Jurassic closure of the MOO in its eastern segment, marking the final closure of the MOO and the formation of the central Asian continent.