Continental lithospheric mantle origin of 2.5 Ga old Monchegorsk layered intrusion from the Fennoscandian shield

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Petrology and geochemistry of xenoliths from the northern Baltic Shield: evidence for partial melting and metasomatism in the lower crust beneath an Archaean terrane

Lower crustal xenoliths entrained in a Paleozoic ultramafic lamprophyre breccia pipe on Elovy island, Kola peninsula, Russia, represent some of the oldest lower crustal material yet investigated from Europe. The xenoliths vary from feldspar-poor, garnetrich rocks which resemble eclogites, to feldspar-rich garnet granulites. Quartz-rich felsic granulites, as well as pyroxenites and amphibole-rich rocks are also present. The mafic granulites/eclogites represent a suite of gabbros and norites that is related by olivine fractionation. The igneous protoliths may have formed in a manner analogous to lower crustal rocks from most other European xenolith localities, i.e. by basaltic underplating, but magmatic cumulates are not in evidence. The Kola lower crust was subjected to one or more metasomatic events which introduced up to 45% phlogopite and/or amphibole into both eclogites/granulites and pyroxenites. The resulting rocks have strong enrichments in Rb, Ba, and K, indicating that the lower crust is not uniformly depleted in LIL and heat-producing elements. Siliceous (65% SiO2) and mafic (< 50% SiO2) lithologies coexist in migmatitic xenoliths, which provide evidence for partial melting processes and restite formation in mafic metaigneous lower crust. The relationship, if any, between partial melting and metasomatism is unclear

The oldest volcanic glass in the early paleoproterozoic boninite-type lavas, Karelian craton: Results of instrumental investigations

Since Early Precambrian volcanic rocks are typically strongly altered by superimposed processes, they retain primary composition and texture only in exceptional cases. Such a case is observed in the Early Paleoproterozoic volcanic rocks of the Vetrenyi Belt Formation of the synonymous riftogenic structure in southeastern Karelia, where volcanic glass is locally preserved [1-3]. The Sm-Nd, Re-Os, and U-Pb (zircon) ages of volcanic rocks of this formation range from 2.5 Ga in the lower parts to 2.41 Ga in the upper parts of the sequence [1-3]. Zolotykh and Ladygin [4, 5] also confirmed the presence of volcanic glass in these rocks. During short-term field works in 2000, we collected additional samples in the southeastern termination of the graben-shaped Vetrenyi Belt, where the least altered rocks were preserved. The samples were mainly treated at the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry

The oldest volcanic glass in the early paleoproterozoic boninite-type lavas, Karelian craton: Results of instrumental investigations

Since Early Precambrian volcanic rocks are typically strongly altered by superimposed processes, they retain primary composition and texture only in exceptional cases. Such a case is observed in the Early Paleoproterozoic volcanic rocks of the Vetrenyi Belt Formation of the synonymous riftogenic structure in southeastern Karelia, where volcanic glass is locally preserved [1-3]. The Sm-Nd, Re-Os, and U-Pb (zircon) ages of volcanic rocks of this formation range from 2.5 Ga in the lower parts to 2.41 Ga in the upper parts of the sequence [1-3]. Zolotykh and Ladygin [4, 5] also confirmed the presence of volcanic glass in these rocks. During short-term field works in 2000, we collected additional samples in the southeastern termination of the graben-shaped Vetrenyi Belt, where the least altered rocks were preserved. The samples were mainly treated at the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry