Evolution of the Mongol-Okhotsk Ocean as constrained by new palaeomagnetic data from the Mongol-Okhotsk suture zone, Siberia

Abstract

Summary This paper presents new data from palaeomagnetic investigations on the Upper Palaeozoic and Mesozoic geological units from the Siberian platform and the Mongol–Okhotsk suture zone. Within the southern portion of the Mongol–Okhotsk suture we collected palaeomagnetic samples from the Late Permian Belektuy formation (Borzya region; 50.7°N, 116.9°E) and the Middle–Late Jurassic Shadaron formation (Unda‐Daya; 51.5°N, 117.5°E). We sampled the Late Permian Alentuy formation (Khilok region; 50.8°N, 107.2°E), the Early to Middle Jurassic Irkutsk sedimentary basin (ISB; 52.0°N, 104.0°E), the Late Jurassic Badin formation (Mogzon region; 51.8°N, 112.0°E), and the Early Cretaceous Gusinoozesk formation (Gusinoe Lake region; 51.2°N, 106.5°E) additionally in the northern region of the Mongol–Okhotsk suture. Apart from the results of the ISB and Gusinoozersk formations, which show very large ellipses of confidence and might be the present‐day geomagnetic field overprint, our results allow us to constrain the evolution of the Mongol–Okhotsk Ocean palaeomagnetically from the Late Permian to the Middle–Late Jurassic. They confirm that this large Permian ocean closed during the Jurassic, ending up in the late Jurassic or the beginning of the Cretaceous in the eastern end of the suture zone, as suspected on geological grounds. However, although geological data suggest a Middle Jurassic closure of the Mongol–Okhotsk Ocean in the west Trans‐Baikal region, our data show evidence of a still large palaeolatitude difference between the Amuria and Siberia blocks. This is interpreted as a result of the quite fast closure of the ocean after the Middle Jurassic. Finally, our new palaeomagnetic results exhibit very large tectonic rotations around local vertical axes, which we interpret as probably arising both from collision processes and from a left‐lateral shear movement along the suture zone, due to the eastward extrusion of Mongolia under the effect of the collision of India into Asia.

Three-step continental-crust growth from subduction accretion and underplating, through intermediary differentiation, to granitoid production

“…This means that an abundance of subducted oceanic slabs remained in depth until this time. During late Middle through early Late Jurassic time, the combined North China-Mongolia block collided with the Siberia plate along the Mongol-Okhotsk suture to the north (Zorin et al 1995;Kravchinsky et al 2002). Thus, the eastern segment of CAOB remains confined or under a compressional regime.…”

Outcrops, isotopic ages, terranes and the undesirable fate of tectonic interpretations

“…Certainly not. Şengör and his co-workes have clearly shown that the Mongol-Okhotsk Ocean did not close until the end of the Jurassic using not only age but also stratigraphic, structural and petrographic data, and their conclusion is corroborated by more recent palaeomagnetic observations (Kravchinsky et al, 2002).…”

The latest geodynamics in Central Asia: primary and secondary mantle melting anomalies in the context of orogenesis, rifting, and lithospheric plate motions and interactions

“…Стабильный структурный ансамбль до-кембрийских каледонских террейнов Северного мегаблока, включающий Тувино-Монгольский ми-кроконтинент, сформировался к концу ордовика. Этот мегаблок осложнен структурой Монголо-Охотского залива Палеопацифика, последователь-но закрывавшегося с запада на восток в позднем палеозое и мезозое с быстрым смыканием берегов в конце юры -начале мела [Şengör, Natal'in, 1996;Zorin, 1999;Kravchinsky et al, 2002]. Герцинские (силлурийско-каменноугольные) островные дуги Южного мегаблока (как части Южномонгольско-Хинганской или Тяньшань-Южнохингалинской зо-ны) отделялись от Северо-Китайского кратона и аккретированных к нему террейнов Солонкерским швом [Yanshin, 1974;Belichenko, Boos, 1990;Tseden et al, 1992;Kozakov et al, 2007;Windley et al, 2007;Parfenov et al, 2003;Wan, 2010].…”