Metallogenic Setting and Evolution of the Pados-Tundra Cr-Bearing Ultramafic Complex, Kola Peninsula: Evidence from Sm–Nd and U–Pb Isotopes

Abstract

The article presents new Sm–Nd and U–Pb geochronological data on rocks of the poorly studied Pados-Tundra Cr-bearing complex. It is part of the Notozero mafic–ultramafic complex (western Kola Peninsula) and occurs at the border of the Paleoproterozoic Lapland Granulite Belt and the Archean Belomorian composite terrain. The Pados-Tundra complex hosts two major zones, the Dunite and Orthopyroxenite Blocks. Dunites are associated with four levels of chromite mineralization. Isotope Sm–Nd studies of dunites, harzburgites, and orthopyroxenites from the central part of the complex have been carried out. The isochron Sm–Nd age on 11 whole-rock samples from a rhythmically layered series of the complex is 2485 ± 38 Ma; the mineral Sm–Nd isochron for harzburgites shows the age of 2475 ± 38 Ma. It corresponds with the time of large-scale rifting that originated in the Fennoscandian Shield. When the rhythmically layered series of the intrusion and its chromite mineralization were formed, hornblendite dykes intruded. The U–Pb and Sm–Nd research has estimated their age at ca. 2080 Ma, which is likely to correspond with the occurrence of the Lapland–Kola Ocean. According to isotope Sm–Nd dating on metamorphic minerals (rutile, amphibole), the age of postmetamorphic cooling of rocks in the complex to 650–600 °C is 1872 ± 76 Ma. The U–Pb age on rutile from a hornblendite dyke (1804 ± 10 Ma) indicates further cooling to 450–400 °C. The conducted research has determined the early Proterozoic age of rocks in the rhythmically layered series in the Pados-Tundra complex. It is close to the age of the Paleoproterozoic ore magmatic system in the Fennoscandian Shield that developed 2.53–2.40 Ga ago. Later episodes of alterations in rocks are directly related to main metamorphic episodes in the region at the turn of 1.9 Ga. Results of the current study expand the geography of the vast Paleoproterozoic East Scandinavian Large Igneous Province and can be applied for further studies of similar mafic–ultramafic complexes.

Zones of PGE–Chromite Mineralization in Relation to Crystallization of the Pados-Tundra Ultramafic Complex, Serpentinite Belt, Kola Peninsula, Russia

“…These suites are members of a transregional megastructure, the "Serpentinite belt-Tulppio belt" or SB-TB structure [22], an important component of the Fennoscandian Shield. This structure has a Paleoproterozoic age, as indicated by results of Sm-Nd dating of the Pados-Tundra complex: 2485 ± 38 Ma [21].…”

“…In addition, suites of the Vetrenyi belt differ in their lower level of whole-rock Mg content and appear to exhibit greater degrees of differentiation relative to the Serpentinite belt. Comagmatic associations of the Vetrenyi belt vary from komatiite sensu stricto (18)(19)(20)(21)(22)(23)(24)(25)(26)(27) [37]. The authors considered that the juvenile magma of the plume was contaminated by a felsic crustal material to the extent of 4 to 15%.…”

“…The process of double-front crystallization documented at Chapesvara represents the first example reported in a highly magnesian subvolcanic complex [20]. A Paleoproterozoic age is indicated for the Pados-Tundra complex on the basis of the Sm-Nd and U-Pb isotopic systems [21]. Our objectives here are to further characterize the Pados-Tundra complex texturally and mineralogically, and to build on comparisons with the closely associated comagmatic suites at Chapesvara [19,20] and Khanlauta [22].…”

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

“…The measurements of Sm and Nd concentrations and isotope Nd composition in Samples OK-7 and OK-8 were made using a seven-channel solid-source mass-spectrometer, Finnigan-MAT 262 (Waltham, MA, USA), (equipped with an Retarding Potential Quadrupole (RPQ)), in the static mode using rhenium and tantalum double filaments. Isotopic investigations were carried out according to the technique described in detail in [16]. The calculation of isochron parameters was executed using the ISOPLOT software [17].…”

The Sulfide/Silicate Coefficients of Nd and Sm: Geochemical “Fingerprints” for the Syn- and Epigenetic Cu-Ni-(PGE) Ores in the NE Fennoscandian Shield

“…The dated deposits were formed in two major episodes, at 2.53-2.39 Ga and 2.0-1.8 Ga, corresponding to the early [1,2,39,48,[52][53][54][55][56][57][58][59] and late [40,42,60] stages of rifting in the Fennoscandian Shield.…”