Concentrically-Zoned Massifs of the Tamanvayam Group (Koryak–Kamchatka Platiniferous Belt): Structure, Age, Petrological and Geochemical Aspects

Resumo

The paper presents new geological, petrological, and geochemical data on the dunite–clinopyroxenite–gabbro massifs of the Tamanvayam area. The time of formation of the intrusions is specified using U–Pb zircon dating.
The Machevna Massif is mainly composed of gabbroids and clinopyroxenites, which are related by gradual facies transitions and intruded by amphibole gabbro, leucogabbro, and monzogabbro. The youngest rocks, cutting across all of the above-described varieties, are granites and granodiorites (tonalites), which make up composite injection bodies and small stocks in the central part of the massif.
According to the new U–Pb dates, all of the intrusive rocks of the Machevna and Poputny intrusions were formed in a narrow time range of 73.1–67.7 Ma. The obtained range overlaps the formation interval of the siliceous volcanogenic sequences of the Achaivayam Formation (biostratigraphic studies, retrospective data).
The geochemical similarity of the gabbroids and pyroxenites with intersecting amphibole gabbros and leuco- and monzogabbros allows us to attribute them to a single magmatic complex. The geochemical affinity and the penecontemporaneous formation of the intrusive rocks of the Tamanvayam area and volcanics of the Achaivayam Formation indicate their formation during a single tectonomagmatic event. At the same time, the gabbroids and pyroxenites can be considered as comagmatic rocks of the basalts and picrobasalts of the Achaivayam Formation. The high-Ca picrobasalts of the Achaivayam Formation that developed near the Machevna intrusion were presumably derived from parental melts of concentrically zonal massifs.