Аннотация
In the Phanerozoic, the production of the continental crust was associated with convergent geodynamic settings and, therefore, with intracontinental orogenic belts developed after the closure of paleooceans. Evaluation of the proportions of juvenile versus older recycled material is a key parameter for understanding how the crust in orogens formed and evolved. The Mongol-Okhotsk orogenic belt is one of the major structural part of Central Asia. Its central – Trans-Baikal part contains the well-reserved fragments of island-arc system as well as the entire spectrum of accretionary prism formations, allowing evaluation of the proportions of juvenile to recycled sedimentary material in the crust of this orogen. In this part of the belt, the best preserved fragments of juvenile crust are the Late Paleozoic volcanogenic-sedimentary sequences of the Kamensk and Urtui suites. The first suite is an indicator of the subduction along the northwestern margin of the Mongol-Okhotsk Paleocean beneath the Siberian paleocontinent, and the second one is an indicator of the subduction along the southeastern beneath the Argun superterrane. The entire compositional spectrum of volcanics from basalts to rhyolites demonstrate positive values εNd(254МА) = +1.4–(+3.8) and TNd(DM) = 896–920 MA. The basalts of the Urtui formation are also characterized by positive εNd(350МА) values, lying in the range of +1.7–(+6.0) at TNd(DM) = 773–939 MA. Therefore, the juvenile crust of the orogenic belt is characterized by positive ɛNd(t) values and model TNd(DM) age of <1000 Ma. The meta-sedimentary rocks of the accretion wedge of the Mongol-Okhotsk orogenic belt are significantly dominated by older recycled crustal material, whose source is likely the Late-Riphean formations of the Argun superterrane.