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Tatiana Donskaya, Institute of the Earth?s crust, Siberian Branch of the Russian Academy of Sciences (Russian Federation)
Dmitry Gladkochub, Institute of the Earth?s crust, Siberian Branch of the Russian Academy of Sciences (Russian Federation)
Anatoly Mazukabzov, Institute of the Earth?s crust, Siberian Branch of the Russian Academy of Sciences (Russian Federation)
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Resent geological and geochronological data on igneous and metamorphic complexes allow us to distinguish principal stages of evolution of the northern segment of the Central Asian orogenic belt (Cisbaikalia and Transbaikalia). First stage (ca. 500-460 Ma) was related to accretion and collision of several microcontinents and island arcs of the Paleo-Asian ocean to the southern part of the Siberian craton. This stage is marked by high-grade metamorphic complexes, syn- and post-collision granitoids. All these metamorphic and igneous complexes are united in the Baikal collision belt which located along the southern flank of the Siberian craton. Second stage (ca. 420 Ma) was related to following accretion event when other island arc chains were attached to the Siberian craton margin.
This stage is fixed by upper amphibolite facies rocks and syn-folded granitoids located northward from 500-460 Ma high-grade metamorphic complexes. We assume that mentioned above metamorphic and igneous complexes related to the Early Paleozoic accretion and collision events could be traced up to hundreds kilometres along the "Baikalian" margin of the Siberian craton. The indicators of ca. 330-300 Ma compression events (metamorphic complexes, foliated granitoids) are widespread in the western segments of Transbaikalia. These compression events could be linked with closure of relict paleobasins. Ca. 300-270 Ma granitoids and bimodal volcanic associations were intruded for the post-orogenic stage related to 330-300 Ma compression. Next igneous episode in Transbaikalia was caused by subduction of the Mongol-Okhotsk oceanic crust under the southern margin of the Siberian continent (present coordinates). This subduction gave rise to abundant calc-alkaline to peralkaline intrusions and lavas produced within Mesozoic active continental margin. Igneous complexes of this stage are dated at ca. 240-195 Ma. Closure of the Mongol-Okhotsk ocean in the early/mid Jurassic in eastern Mongolia and Transbaikalia led to intraplate magmatic activity in late Mesozoic in the region studied. A-type granitoids and bimodal basalt-rhyolite association were formed ca. 180-150 Ma.
The final stage (ca. 135-120 Ma) of tectonic and igneous activity within the area studied is marked by metamorphic core complexes which testify on large-scale regional extension within Transbaikalia (Russia), Mongolia and northern China. After metamorphic core complexes exhumation the northern segment of Central Asian orogenic belt exhibited insignificant intraplate extension accompanied by basaltic volcanism.
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