Ospe-Luvtuaivench massif of metabasic rocks, Kola Peninsula, Russia: geologic structure and petrogeochemical and isotope geochemical evidence for its relation to the Imandra complex of layered intrusions

摘要

This paper reports the results of a combined study of the geology, petrochemistry, geochemistry, and isotope geochronology of the Ospe-Luvtuaivench massif of metabasic rocks in the Kola region consisting of three blocks (from northwest to southeast): Luvtuaivench, Ospe, and Ekostrov. The massif is approximately 17 km long and 6 km wide and is dominated by meso-and melanocratic orthoamphibolites (metagab-broids) with 5-15-m-thick layers of leucocratic epidote orthoamphibolite (metagabbro-anorthosite), which are changed upsection by metaferrogabbro with a horizon of ilmenite-magnetite ore at least 1 km in lateral extent and approximately 50 m thick. The petrogeochemical characteristics of metabasic rocks from the three blocks of the massif are identical and similar to those of the rocks of the Imandra complex of layered intrusions. In addition, metaultrabasic bodies (chlorite-actinolite, actinolite-chlorite-serpentine, and actinolite-serpentine rocks) of varying thickness were found in the Luvtuaivench and Ekostrov blocks. Based on their structural features differing from those of similar rocks of Imandra layered intrusions and petrogeochemical characteristics, these rocks were interpreted as xenolithic bodies. New U-Pb zircon ages were obtained for the metagabbroids of all blocks of the Ospe-Luvtuaivench massif: 2445 +/- 5 Ma for the Luv-tuaivench block, 2455.8 +/- 3.5 Ma for the Ospe block, and 2447 +/- 4 Ma for the Ekostrov block; these estimates characterize the time of massif crystallization and are similar to the age of formation of typical intrusions of the Imandra layered complex. A U-Pb zircon age of 2444 +/- 3 Ma was obtained for the crystallization of the Mount Yagel'naya gabbronorites of the Imandra complex. The following epsilon(Nd)(2450) values were obtained for the rocks of the massif: +0.61 for the Luvtuaivench block,-1.58 for the Ospe block, and -1.27 for the Eko-strov block; the gabbronorites of the Mount Yagel'naya massif yielded epsilon(Nd)(2450) =-0.99. These values are similar to those of the Paleoproterozoic layered intrusions. The similarity of the Ospe-Luvtuaivench massif to typical massifs of the Imandra complex in terms of internal structure, petrochemical and isotope geochemical characteristics, and age of rock formation provides compelling evidence for the interpretation of the massif as part of the Imandra complex.