New Data on the U-Pb Age of Granitoids of the NudyMi Complex in the Bilyakchan Zone of the Okhotsk Massif and Siberian Craton Junction

摘要

The Bilyakchan zone of the Okhotsk Massif and Siberian Craton junction is a narrow (10-25 km wide) band of Paleoproterozoic rocks that extends along the deep Bilyakchan fault in the meridional direction for more than 230 km. This zone separates the southeastern margin of the Siberian Craton and the thrust-fold structures of the South Verkhoyansk Synclinorium from the Verkhnyaya Maya Uplift of the Okhotsk Massif in the west and the Okhotsk-Chukotka volcanic belt in the east. In recent works, this zone has been regarded as a northern part of the anorogenic Bilyakchan-Ulkan volcanoplutonic belt that extends for no less than 750 km and is characterized by a distinct asymmetric structure. Its southwestern sector, which crosses the Stanovoi Megablock, is composed of large anorthositic bodies. The central segment of the belt incorporates the Ulkan Massif, which mainly consists of silicic volcanic rocks and comagmatic medium-alkaline and alkaline granites. The geological survey data and results of our investigations show that the northern part of the belt markedly differs from the southern areas. Terrigenous rocks obviously prevail over basic volcanics; silicic volcanics are scarce; anorthosites are lacking altogether; and granitoids occur only locally. According to, the formation of the Bilyakchan-Ulkan Belt was related to within-plate crustal extension at the end of the Paleoproterozoic (approximately 1736-1705 Ma ago).