LATE VENDIAN AGE OF THE HAN-TAISHIRI OPHIOLITE COMPLEX IN WESTERN MONGOLIA

The age of ophiolite plagiogranites from the Han-Taishiri ophiolite complex, western Mongolia, was determined by the U-Pb zircon method as 568.1 ± 4.0 Ma. This complex is a rare fragment of the ancient Central Asian blocks where real geological relationships within large tectonic slabs making up the ridge have been established between all ophiolite sequences but ultrabasic rocks: pyroxenite and gabbro from banded sequence, basic rocks of dike complex, dolerite sills, basic pillow lava, and deep-water clay-siliceous sediments. The Neoproterozoic age of the Han-Taishiri ophiolite complex suggests the presence of a Vendian island-arc system within the Central Asian Fold Belt. The model for this system was described for the first time by L. P. Zonenshain and O. Tomurtogoo on geologic objects of western Mongolia from the Dzavhan River to the northern slopes of the Mongolian Altai Ridge (Dzavhan, Gobi-Altai, Han-Taishiri, Naran, Ulan-Shanda, and Kuroi subzones). This system obviously included the Daribi ophiolites of western Mongolia; the Agardag and Shishkhid ophiolites of Tuva; the Dzhida and Ol’khon fragments of island-arc system; the belt of layered subduction massifs of Northern Baikal and eastern frame of the Muya block; the Naran, Eastern Sangilen, Southern Khamar-Daban, Ol’khon, and Bodaibo fragments of sedimentary basin; the Dzavhan, Hovsgol-Bokson, Western Baikal, and Baikal-Patom shelf fragments. Ocean lithosphere was represented by Bayan-Khongor ophiolites.