The Late Riphean-Paleozoic history of the Uda-Vitim island arc system in the Transbaikalian sector of the Paleoasian ocean

摘要

New structural, petrological, chemical, isotope, and paleomagnetic data have provided clues to the Late Riphean-Paleozoic history of the Uda-Vitim island arc system (UVIAS) in the Transbaikalian sector of the Paleoasian ocean, as part of the Transbaikalian zone of Paleozoids. The island arc system consists of three units corresponding to main evolution stages: (i) Upper Riphean (Late Baikalian), (ii) Vendian-Lower Paleozoic (Caledonian), and (iii) Middle-Upper Paleozoic (Hercynian). The earliest stage produced the base of the system composed of Late Riphean ophiolite (971-892 Ma, U-Pb) and volcanic (837-789 Ma, U-Pb) and sedimentary rocks (hemipelagic siliceous sediments and dolerite sills) which represent the Barguzin-Vitim oceanic basin and the Kelyana island arc. The main event of the second stage was the formation of the large UVIAS structure (over 150,000 km2) which comprised the Transbaikalian oceanic basin, the forearc and backarc basins, and the volcanic arc itself, and consisted of many volcanic-tectonic units exceeding 100 km~2 in area (Eravna, Oldynda, Abaga, etc.). Lithology, stratigraphy, major-element compositions, and isotope ages of Vendian-Cambrian volcanic rocks and associated sediments indicate strong differentiation of calc-alkaline series and the origin of the island arc system upon oceanic crust, in a setting similar to that of the today's Kuriles-Kamchatka island arc system. The Middle-Upper Paleozoic stage completed the long UVIAS history and left its imprint in sedimentary and volcanic rocks in superposed trough basins. The rocks were studied in terms of their biostratigraphic and isotope age constraints, as well as major- and trace-element compositions, and were interpreted as products of weathering and tectonic-magmatic rework of the UVIAS units.