Scientific publications

The gabbro-anorthosite massifs and related intrusions of subalkaline granites in the Keivy structure were studied. Based on the U-Pb (SHRIMP) dating of zircons, the crystallization age of the Tsaginsky and Achinsky massifs was established at 2.67–2.66 Ga, and the intrusion of the subalkaline dikes within the Tsaginsky gabbro-anorthosite massif was dated to 2671 ± 2 Ma BP. The isotopic age for igneous rocks of the Keivy structure obtained in this work, along with previous studies of other massifs of the Keivy structure, reflect the almost simultaneous crystallization of both gabbro-anorthosites and subalkaline and alkaline granites. The formation of the magmatic complexes was associated with partial melting of lower crustal basites due to magmatic underplating at the base of the lower crust. This inference follows from Sm-Nd (whole-rock) and Lu-Hf (zircon): ƐNd = –1,0÷+3,0; ƐHf = – 3,8÷+1,5 isotopic data with model ages of 3.1–2.9 Ga. The significant predominance of acid products over basic rocks in the Keivy structure is determined by the modern erosion level. The gabbro-anorthosite massifs in large regional faults are likely a part of significant volumes of basites located at greater depths. The subsequent evolution of the Keivy structure is associated with metasomatic processes and crystallization of rare metal and rare earth pegmatites of Paleoproterozoic age, 1.75–1.71 Ga.