Archean Rocks of the Diorite Window Block in the Southern Framing of the Monchegorsk (2.5 Ga) Layered Mafic-Ultramafic Complex (Kola Peninsula, Russia)

Abstract

The intermediate rocks classified as diorite-gneisses occur within the southern part of the Monchegorsk (2.5 Ga) layered mafic-ultramafic complex (Kola Peninsula, Russia). These diorite-gneisses belong to a block historically known as the diorite window (DW) block. The same rocks occur in a framing of the Monchegorsk complex. The DW block is predominantly composed of diorite-gneisses and, to a lesser degree, of amphibolites. Multi-ordinal banding, complex folding, boudinage and metamorphic transformations, garnet porphyroblasts, and tourmaline veinlets are typical of the diorite-gneisses. In accordance with the U-Pb isotope data, the age of the diorite-gneisses in the DW block is 2736.0 ± 4.6 Ma. The Sm-Nd mineral (garnet, biotite, and tourmaline) isochron for the DW rocks has yielded an age of 1806 ± 23 Ma (related to the processes of the Svecofennian orogeny). The DW diorite-gneisses are compared with the metadiorites of the Gabbro-10 massif. The latter is a part of the Monchegorsk complex, with U-Pb crystallization age of 2498 ± 6 Ma. On the basis of geological and isotope-geochemical data, it is shown that the DW rocks belong to the Archean basement while the Gabbro-10 metadiorites probably represent one of the late-magmatic phases of the Monchegorsk complex.

Accessory Cr-Spinels in the Section of the Nude-Poaz Massif in the Monchegorsk (2.5 Ga) Mafic-Ultramafic Layered Complex (Kola Peninsula, Russia): Comparison with Ore-Forming Chromites

“…Since the Monchepluton is a polyphase massif [10,14,15,47], the composition of Crspinels reflects the evolution of intrusion of these phases. Ore chromites occur in early ultramafic phases composing the lower parts of the section (Dunite block with the Sopcheozero chromite deposit).…”

“…Notably, considering the Monchetundra intrusion and Monchepluton as one complex is reasoned by their spatial proximity, in addition to geochronological data. The former is very important as we believe the Monchetundra intrusion includes, apart from itself, the South Sopchinsky and Gabbro-10 massifs [14].…”

“…Several authors [12][13][14] believe that MC consists of two large fragments, i.e., the Monchetundra intrusion (or massif) and Monchepluton (Figure 1). Despite their close age (2497 ± 3-2501 ± 8 Ma) [15,16], the Monchetundra intrusion and Monchepluton have complicated interrelations that reflect different sequences of intrusion of their major magmatic phases [10,14] and got shaded by intense postmagmatic tectonic processing. Thus, compiling the consolidated geological column of MC is quite challenging.…”

The geotectonic setting, age and mineral deposit inventory of global layered intrusions

“…Complex comprises dunite-hosted Cr seams (Chashchin et al 1999), marginal contact-style PGE-Cu mineralisation (Grokhovskaya et al 2003;Karykowski et al 2018a), massive Ni-Cu sulphide veins (Bekker et al 2016;Karykowski et al 2018a), PGE reef deposits (Sopcha and Vuruchuaivench; Grokhovskaya et al 2000;Karykowski et al 2018b), and Fe-Ti-V mineralisation in the Gabbro-10 massif (Pripachkin et al 2020). The 2.45 Ga lopolithic Burakovsky complex is among the largest layered intrusion in Europe (~ 700 km 2 ).…”

Editorial for Special Issue “Ore Genesis and Metamorphism: Geochemistry, Mineralogy, and Isotopes”

“…The paper by Pripachkin et al [5] provides comparative analysis of diorites observed in the Monchegorsk pluton (Kola Peninsula) and its basement. The Monchegorsk complex is primarily known for its complex Cu-Ni-PGE-Cr-Fe-Ti-V mineralization.…”