PETROLOGO-GEOCHEMICAL FEATURES AND GEODYN AMIC CONDITIONS OF THE FORMATION OF ORE-BEARING GRANITOIDS ON THE CHUKCHI-PENINSULA

Cretaceous granitoids from the three main ore regions of the Chukchi P rovince - Chaun, Iultin, and Telekai - have been studied petrologicall y and geochemically. It is shown that the granitoids are characterized by common petrologo-geochemical similarities to evidence their belong ing to the same large stage of granite formation as well as by the dif ferences indicating the areal pattern of granite magmatism in the regi on. The granitoid areas formed under the conditions of changing geodyn amic regimes. There are three successive stages of the orogenic cycle responsible for granite formation and three corresponding geochemical types of granitoids: early subduction stage involved with latite and a ndesite series, intermediate collision stage accompanied with the form ation of the main volume of granitoids of the main intrusive phases of geochemical type of plumasite rare-metal granites, and the late stage of reflected tectonomagmatic activity induced by the formation of the marginal Okhotsk-Chukchi volcanogenic belt and leading to local intru sions of the late, most rare-metal, leucogranites of the preceding geo chemical type. The formation of granitoid magmatic chambers is involve d with melting of the crustal bedrock under the effect of the mantle-d erived potassium alkali-basaltoid magma.