TheMongol-Okhotsk Ocean, also known as theKhangai-Khantey Ocean, was a triangle-shapedancient ocean present fromPaleozoic to theMesozoic,[1] whose oceanic floor rocks are preserved in the Mongol-Okhotsk suture zone extending throughMongolia to theSea of Okhotsk. The ancient ocean began opening during the Early-Middle Paleozoic within the accretionary collage of theCentral Asian Orogenic Belt,[2] and gradually started closing from west to east starting in theLate Triassic with a bending of the Western Mongolian Blocks and the formation of the Tuva-Mongol Orocline, and eventually a rapid scissor-like closure resulting in the collision between theErguna Block and theSiberian Craton during theLate Jurassic andEarly Cretaceous.[1][3]
With the formation of thesupercontinentPangea in the mid- to late-Paleozoic, the vastPanthalassa ocean dominated 70 percent of the Earth's surface. TheTethys, Mongol-Okhotsk and various small domains of early Pacific Ocean crust constituted other small oceans. Paleomagnetic data collected between 1987 and 2010 suggest that the Mongol-Okhotsk oceanic crust subducted under theterranes of Mongolia in theLate Jurassic orEarly Cretaceous.
During the early Mesozoic, the Solonker Ocean, also known as the Intra-Asian Ocean closed bringing together two large continental blocks: Amuria and the North China Block. Amuria then collided with the Siberian Craton, preserving the Mongol-Okhotsk suture zone. Geologists debate why the suture zone ends abruptly near Kazakhstan and have used seismic tomography to develop different interpretations.
Most exposed rocks in the suture zone are thrusted accretionary wedges, often withophiolites.Uranium-lead dating ofbasalt,doleritegabbro as well asSilurian radiolarite gives ages constraints on the formation of the oceanic crust. Dated rocks in the Adaatsag ophiolite in the east are among the oldest at 325 million years old.[4][5]
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