Petrology of mesozoic monzonite-syenite magmatism of the Ketkap-Yuna magmatic province in the Aldan Shield

Abstract

Genetic relationships between ore mineralization and associations of potassic basaltoids and comagmatic intrusions have been established in recent decades. The works of L.V. Tauson, O.A. Bogatikov, V.I. Kovalenko, and other researchers have shown that both alkaline basaltic and granitoid magmatism of the latite petrochemical type and related multiprofile mineralization were widespread in intracontinental consolidated areas during tectonomagmatic activation. Hence, problems of petrogenesis of latite magmatism and geodynamic regimes of its manifestation acquire great scientific and practical importance. In this context, we carried out petrological studies of the Ketkap trachydacite‐monzonite‐syenite complex of the Ketkap‐Yuna magmatogenic province (KYMP) on the Aldan Shield. A significant part of this rock complex can be derived from latite melts [8]. The formation of the Ketkap Complex is related to final stages of Mesozoic magmatism on the Aldan Shield [3‐8]. The complex exhibits four phases of evolution and is confined to the second cycle of tectonomagmatic reactivation (Table 1). Near the tectonomagmatic structures, the complex postdated intense phonotephrite‐phonolite‐ trachyte volcanism in the western KYMP (the Bokur Complex in the Bokur and Ulakhan calderas of the Ulakhan Massif). Its final stages are temporally and spatially close to alkaline syenite subintrusive magmatism (the Dariin Complex in the Usmun‐Dariin, Yuna‐Dan, and Ulakhan massifs [4, 5, 8]. The main phase of monzonite‐syenite magma intrusion is related to the fourth stage of Mesozoic magmatism on the Aldan Shield and is widely represented at the western flank of the Ketkap magmatogenic uplift of the KYMP. Moreover, small exposures of Ketkap monzonitoids are known in the KYMP in a series of other magmatogenic massifs in association with alkaline magmatites of the Dariin Complex. The fifth (final) stage of the Mesozoic magmatism was marked by the intrusion of a series of dikes of subalkaline potassic rocks, which also show spatiotemporal association with dikes of alkaline magmatites of the Dariin Complex. The geological position and petrographical features of the Ketkap Complex were described previously [3, 6, 8, and others]. Representative compositions of rocks and some of the results of their petrogeochemical and geodynamic typification are given in this work (Table 2). The rock complex includes feldspathoid-free rocks (shonkinites, syenites, monzonites, and quartz monzonites), monzodiorites, subvolcanic trachydacites,