Two-stage formation of the alcaline volcano-plutonic complexes in the Ketkap-Yuna igneous province of the Aldan Shield: New isotopic data

Abstract

1322 Recently, traditional views on the time limits accepted for the formation of many geological objects have been revised based on dates obtained for monom ineral fractions by high precision U–Pb and 40Ar/39Ar methods. The Ketkap–Yuna igneous province representing a tectonotype of the zones of Mesozoic tectono mag matic activation in the Adan Shield is one such object (Fig. 1; a geological–structural map of the province is available in [9]). The Ketkap–Yuna igneous province is a unique structure characterized by several polyformation mag matic complexes, which are discretely distributed through the latter. Its western segment (Bokur vol cano pluton of the Ulakhan massif) demonstrates wide development of alkaline, volcanic (Bokur Com plex), and subvolcanic (Kurung Complex) rocks. The central and eastern parts of the province are character ized by prevalence of hypabyssal bodies of subalkaline diorites and granitoids, including gold bearing variet ies. Alkaline intrusive rocks (Dar’ya Complex) occur sporadically in form of dike “swarms,” a system of small sills, and small stocks. Alkaline volcano plutonic and intrusive magma tism in zones of tectono magmatic activation is thought to be related to the second stage of Mesozoic magmatism of the Aldan Shield [1, 2, and others]. According to published data, its K–A ages fall into the interval of 168 to 70 Ma (Table 1 and data from [1–8]).