New Nd-Sr isotope-geochronological evidence of its affinity to the East-Scandinavian Large Igneous Province (The Kandalaksha-Kolvitsa gabbro-anorthosite complex, Russia)

<p>The article provides new Sm-Nd and Nd-Sr isotope-geochronological data on rocks of the Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex.</p><p>The Sm-Nd and Rb-Sr studies have provided data on isotope compositions of neodymium and strontium in rocks of both massifs. The isotope compositions of neodymium (eNd) range from -0.02 in norites of the Kandalaksha massif to -5.53 in lens bodies of gneiss granites of the Kolvitsa massif</p><p>Weakly radiogenic values of eNd = -1.0 – -1.2 dominate, which complies with characteristic values of Paleoproterozoic layered intrusions in Fennoscandia. Isotope compositions of strontium ranging from 0.7013 to 0.7025 also reflect typical values of a Paleoproterozoic igneous province [.</p><p>New data suggest that the Kandalaksha-Kolvitsa gabbro-anorthosite complex is confined to the East-Scandinavian Large Igneous Province with a protracted evolution at the turn of 2.53-2.39 Ga. According to geochronological and isotope Nd-Sr data, rocks of the Kandalaksha-Kolvitsa complex seem to have the same anomalous mantle source with Paleoproterozoic layered intrusions in the Baltic Shield (Fig. 3). The latter include Cu-Ni-Co-Cr+PGE deposits in the Monchegorsk ore area and Pechenga, Cr ores in the Pados massif, Fe-Ti-V Kolvitsa deposit, PGE and Cu-Ni Fedorovo-Pana layered complex  and Burakovsky intrusion, Cu-Ni-Co+PGE deposits in Finland, i.e. Kemi, Penikat, Akanvaara, Kontelainen, Tornio and many other. These deposits formed at two episodes, 2.53-2.39 Ga and 2.0-1.8 Ga, that refer to the beginning of rifting and the late rifting stage of the Fennoscandian Shield evolution, respectively.</p><p>Rocks of these intrusions referred to the pyroxenite-gabbronorite-anorthosite formation have similar isotope-geochemical features:</p><p>1) according to U-Pb and Sm-Nd geochronological data, the formation time span is 2530 to 2380 Ma;</p><p>2) the mantle reservoir feeding magmas that formed the massifs is rich in lithophile elements;  I<sub>Sr</sub> values vary from 0.702 to 0.706, ε<sub>Nd</sub>(T) varies from +2 to -6;</p><p>3) the model Sm-Nd ages of T<sub>DM</sub> protoliths are 2.8-3.3 Ga.</p><p>The scientific research has been carried out in the framework of the State Research Contract of GI KSС RAS No. 0226-2019-0053, RFBR grant No. 18-05-70082 «Arctic’s Resources» and Presidium RAS Program No. 8.</p>

The Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex (Fennoscandian Shield): new U-Pb, Sm-Nd and Nd-Sr (ID-TIMS) isotope data on the age of formation, metamorphism and geochemical features of zircon (LA-ICP-MS)

<p>The paper provides new U-Pb, Sm-Nd and Nd-Sr isotope-geochronological data on rocks of the Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex. REE contents in zircons from basic rock varieties of the Kandalaksha-Kolvitsa area have been defined in situ using LA-ICP-MS. Plots of REE distribution have been constructed, confirming the magmatic origin of zircon. Temperatures of zircon crystallization have been estimated, using a Ti-in-zircon geochronometer. For the first time, the U-Pb method with <sup>205</sup>Pb artificial tracer has been applied to date single zircon grains (2448±5 Ma) from metagabbro of the Kolvitsa massif. The U-Pb analysis of zircon from anorthosites of the Kandalaksha massif has dated the early stage of the granulite metamorphism at 2230±10 Ma. The Sm-Nd isotope age has been estimated on metamorphic minerals (apatite, garnet, sulfides) and the rock at 1985±17 Ma (granulite metamorphism) for the Kolvitsa massif, 1887±37 Ma (high-temperature metasomatic transformations) and 1692±71 Ma (regional fluid reworking) for the Kandalaksha massif. The Sm-Nd model age of metagabbro is 3.3 Ga with negative value εNd=4.6, which corresponds either with processes of crustal contamination, or with primary enriched mantle reservoir of primary magmas.</p><p>This research was funded by the Scientific Research Contract of GI KSC RAS No. 0226-2019-0053, grants of the Russian Foundation for Basic Research NoNo. 18-05-70082 «Arctic Resources», 18-35-00246 mol_a, and the Presidium RAS Program No. 8.</p><p> </p>