Genesis of the oldest continental crust retains a marked trace in the Earth's evolution over its 4.5 Ga history. Despite ample isotope data on the role of the continental crust in the Earth's evolution, there has been much debate on the origin of grey gneisses and tonalite-trondhjemite-granodiorites (TTG). Precise U-Pb (ID-TIMS) and SHRIMP data on single zircon for paragneisses and TTG (3158.2 ± 8.2 Ma) have indicated the Central-Kola and Belomorian (White Sea) megablocks of the Fennoscandian Shield to be 3.16 Ga and 3.70 Ga, respectively. The newly obtained ages of zircon from these megablocks indicate the origin of the discrete continental crust to be 3.16 and 3.70 Ga. It is close to the Nordsim zircon data on the Siurua TTG (Finland), which are 3.45 and 3.73 Ga in the core. The new summarized data on the Earth's oldest rocks (basement and continental crust) indicate the younger age of the rocks in the Fennoscandian Shield as compared to those in Australia (Kronendonk et al., 2019).

Baddeleyite is a significant mineral successfully applied in the U-Pb geochronology for the precise dating of mafic rocks from layered intrusions with the platinum group element (PGE) and Cu-Ni mineralization. The Fennoscandian Shield hosts several layered Pt-Pd, Co-Cr-Ni, and Ti-V occurrences in the Northern (Karelian) and Southern (Karelian-Finnish) belts. The aim of this study is to estimate the content and distribution of rare earth elements (REE) in baddeleyite and to calculate temperatures (Т, ̊С) of the U-Pb system closure and baddeleyite crystallization compared to zircon from Cu-Ni and Pt-Pd deposits in the north-eastern Fennoscandian Shield. For the first time, baddeleyite crystals from Cu-Ni (Monchepluton) and Pt-Pd (Monchetundra) reefs of the Monchegorsk ore area have been studied in situ by the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to measure the U-Pb age of formation and the REE content.

Аннотация. Проведено локальное SHRIMP II датирование бадделеита и циркона из пижонитавгитовых диоритов расслоенного массива Ярва-варака, расположенного в Мончегорском районе. Ранее на основе геолого-петрологических исследований была предложена импактная модель происхождения массива. Возраст бадделеита, относящегося к раннему парагенезису породы составляет 2498 ± 6 млн. лет. Возраст циркона, отражающего кристаллизацию поздней гранофировой составляющей равен 2492 ± 3 млн. лет. Полученные данные наряду с геологическими доказательствами импактного происхождения массива Ярва-варака, позволяют утверждать, что на сегодняшний день, астроблема Ярва-варака является самой древней из известных на Фенноскандинавском щите. Ключевые слова: циркон, бадделеит, импактные структуры, расслоенные интрузии, Мончегорский рудный район.

<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>

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