Vendian and Permian-Triassic Plagiogranite Magmatism of the Ust-Belaya Mountains, West Koryak Fold System, Northeastern Russia

摘要

Vendian and Permian-Triassic plagiogranite magmatism is distinguished for the Ust-Belsky and Algansky terranes of West Koryak fold system. The UPb zircon ages from Vendian and Permian-Triassic plagiogranites are 556 +/- 3 Ma (SIMS), 538 +/- 7 Ma (LA-ICP-MS) and 235 +/- 2 Ma (SIMS), respectively. It is revealed that Vendian and Permian-Triassic plagiogranites are mainly low-K and low-Al. SrNd isotopy and rare earth element patterns make it possible to suggest their formation as partial melting of primarily mantle substrate or fractional crystallization of the basic magma. Vendian plagiogranites formed within active margin in ensimatic island arc simultaneously with deposition of the lower part of the volcano-sedimentary complex of Otrozhninskaya sheet. We suggest that the Permian-Triassic plagiogranites were formed within the limits of the Ust-Belsky segment of the Koni-Taigonos arc during partial melting of melanocratic ophiolite material built up as fragments in the accretionary structure of that arc or by fractional crystallization of basic magmas melted from a similar substrate.