MAGMATISM RELATED TO THE EASTERN SIBERIA RIFT SYSTEM AND THE GEODYNAMICS

Based on the variation in space and time oi the composition of rift-re lated volcanic rocks in the Trans-Baikal region, the Cenozoic deep-sea ted processes are shown to be inherited from the tectonic and magmatic activity during the Mid-Paleozoic to Mesozoic. The Eastern Siberia ri ft system is divided into three groups of rift basins : the Tunka-Erav na group with associated volcanics formed in the Late Cretaceous to Mi d-Cenozoic, and the essentially non-volcanic Baikal-Chara and Khubsugu l-Darkhat groups which formed during the Late Cenozoic. Although devel opment oi the Eastern Siberia rift system was contemporaneous with the Indian-Asian collision, the relative rotation of terranes separated b y the Baikal-Chara group of rift basins around the pole at its northea stern termination, indicates that extensional forces were local. A hot spot model which proposed to explain the geodynamics within the Easte rn Siberia rift system, implies a powerful heat impulse along the sout hern edge of the Siberian craton from -29 to -12 My (Late Oligocene to Miocene). This was expressed by doming, rifting and vigorous mildly a lkaline basaltic volcanism. A migrating sequence of volcanism within t he western area of the Khubsugul-Darkhat group might indicate a slow ( 0.8-0.9 cm/yr) eastward motion of the Eurasian plate overriding a fixe d mantle hot plume.