Baddeleyite, or zirconium dioxide (ZrO₂), was discovered in Sri Lanka (Ceylon) more than 100 years ago. It was found by tea magnate Joseph Baddeley and called after him [1]. The mineral occurs in numerous terrestrial and lunar rocks [1]. Just like zircon, it was first studied using U-Pb isotope analysis only in the 1990s by T. Krogh and his associates F. Corfu, S. Kamo, L. Heaman and others. In U-Pb studies with the isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and precise dating of reference complexes, baddeleyite benefits from its best-preserved U-Pb isotope systematics, high concentrations of U and Pb and a low discordance degree, compared to zircon. However, it is difficult to separate baddeleyite because of its minor amounts in silica-undersaturated rocks: gabbro, anorthosites, carbonatites, diabase dikes, etc. Besides, concentrations of baddeleyite are lower and findings are fewer than those of zircon [1].2].3]. First publications on the REE distribution in baddeleyite are provided by [4].or Phalaborwa deposit (South Africa).

The purpose of this work is 1) to study the distribution and concentrations of rare earth elements (REE) in baddeleyite, using the laser ablation inductively coupled plasma (LA-ICP-MS) mass spectrometry (ELAN 9000 DRC-e mass spectrometer), and 2) to estimate the precise age of the U-Pb system closure using ID-TIMS and crystallization temperatures of baddeleyite compared to zircon from Neoarchean Ti-Mgt and BIF deposits, than Paleoproterozoic Co-Cu-Ni, Ti-Cr-V-Mgt, Pt-Pd layered intrusions and Paleozoic complex deposits of the NE Fennoscandian Shield.

The paper presents a novel technique of estimating concentrations and distribution of REE in samples from major deposits of the NE Fennoscandian Shield and provides important information on REE contents in the studied objects.

For the first time, this paper provides a modeled link between the break-up of supercontinents and complex deposits with baddeleyite, since all complex deposits are derivates of LIPs from the Archean to Paleozoic.

The NE Fennoscandian (Baltic) Shield (Figure 1) is composed of grey and tonalite-trondhjemite gneisses (TTG) in the Paleoarchean Murmansk (I) and Central Kola (II) megablocks [5]. Recently, cores of single zircon grains from high aluminous gneisses of the Central Kola megablock near Murmansk have been dated at 3.7 Ga, using the SHRIMP-II technique [6]. According to [7]. 35 age estimates of the world-oldest zircons had been obtained by 2003. Later on, the 36^th age has been estimated for zircon in TTG from Syria (Finland) [8]. The age reported in [6].s the 37^th “piece” in the “Late Archean record puzzle” [7].

The Neoarchean Kolmozero-Voronja (III) Greenstone Belt divides the Murmansk and Central Kola megablocks. The latter hosts the largest BIF deposits of Olenegorsk (1) and Kirovogorsk (with U-Pb on baddeleyite from Neoarhaean dikes) [9].

The Keivy terraine (IV) contains Neoarhaean alkaline granite [10].11].nd

Ti-Mgt Tsaga (2) deposits. They have been U-Pb dated as Neoarchean [12]. For the first time, the U-Pb method has been applied to date baddeleyite from carbonatites [12].n the Siilinjarvi deposit (Finland) [13].

Besides, the Central Kola megablock comprises superlarge Proterozoic Cu-Ni deposits, i.e. the Pechenga (3), Monchegorsk (4) and Fedorovo-Pana (5) ore areas with Pt-Pd, Cr and Pt-Pd reefs and major deposits. This megablock also hosts the superlarge Paleozoic Khibiny (6) and Lovozero (7) massifs with complex foscorite-apatite-nepheline ores.

The NE Fennoscandian Shield is the second-biggest PGE-bearing province in Russia after the Norilsk (Figure 1) ore area [14]. It is commercially important owing to Co-Cu-Ni (Monchegorsk area), Cr-Ti-Fe-V (Imandra lopolith) and low-sulfide Pt-Pd ores with Au + Aq (Fedorovo-Pana complex) [14].

The Paleoproterozoic Pechenga-Imandra-Varzuga Greenstone Belt (V) separates the Central Kola megablock from the Belomorian belt, which is a thick subduction zone [15]. This complex terrain includes giant deposits of the ring-like Paleozoic Kovdor (8) and Vuorijarvi intrusions (9). The Lapland Paleoproterozoic granulite belt (VII) is located in the southern part of the Pechenga structure [5].16].

Baddeleyite has been sampled from Archean to Paleozoic deposits in the north-eastern part of the Fennoscandian Shield (Figure 1). It has been separated from a 50 - 100 kg reference sample using the technique described in [3].13].17].

Isotope U-Pb (ID-TIMS) studies have been performed using a 7-channel mass spectrometer Finnigan-MAT 262 with a quadrupole RPQ, following the technique with ²⁰⁸Pb and ²⁰⁵Pb tracers suggested in [3].17]. LA-ICP-MS has been adjusted to study concentrations and distribution of REE in baddeleyite only recently [4].18].19].

A new technique of estimating concentrations and distribution of REE in samples using LA-ICP-MS (ELAN 9000 DRC-e, UP 266 MAKRO) has been applied in the Tananaev Institute of Chemistry KSC RAS (Apatity, Russia) to study REE in zircon crystals [20]. Microprobe analyses of resin-mounted samples have been carried out using LEO-1415. Analytical points have been selected on baddeleyite crystals based on analyses of their BSE and CL-images (LEO-1415), as well as optic images (LEICA OM 2500 P, camera DFC 290). Trace and REE analyses of baddeleyite crystals have been carried out in situ on polished thin sections by laser ablation inductively coupled plasma mass spectrometry, using a Perkin Elmer ELAN 9000 DRC-e quadrupole mass spectrometer equipped with a 266 nm UP-266 MAСRO laser (New Wave Research).

Experiments have been carried out using argon with a repetition rate of 10 Hz, pulse duration of 4 ns, energy density of 14 - 15 J/cm² at a spot with a diameter of 35 - 100 µm. External calibration was carried out using NIST 612 glass with the known concentration of REE, U, Th of 40 ppm as a multi-point calibration forced through the origin after blank correction. A diameter of the laser beam has been changed, while all of the rest parameters were stable: from 35 to 240 µm (r = 0.999). Sample NIST SRM 610 with the concentration of 450 ppm has been used to check the accuracy of estimations [20].21].22]. The NIST SRM 610 and NIST SRM 612 [23].24].25].lasses are silicate glass reference materials produced by the National Institute of Standards and Technology. Considering calibration standards, measurements of the elements are within the range of 15% relative deviations. The precision was typically 15% RSD for all isotopes after internal correction of diameter of the laser beam. The determination limits are in the range of 0.01 ppm, when a diameter of the laser beam is 155 µm. It complies with the available data [4].18].19]. The results have been verified in inter-laboratory cross-checks and analyses of internationally approved standard zircon samples 91500, TEMORA 1 and Mud Tank [20].21].22].

For the first time, baddeleyite has been defined in Neoarchean rocks of major BIF and Ti-Mgt deposits, Pt-Pd and Cu-Ni reefs of Proterozoic intrusions and Paleozoic complex deposits in the NE Fennoscandian Shield. Since geochronological analysis of baddeleyite is challenging (especially SIMS and SHRIMP) [18].19].38]. the authors have applied the U-Pb (TIMS) method [3].13].17].30].or precise dating of the above mentioned deposits.

Compared to zircon, baddeleyite is a rarer mineral and a more reliable geochronometer for dating large and superlarge complex deposits using the U-Pb systematics. It is commonly magmatic [2].39].40].41]. as opposed to zircon that can be metamorphic, hydrothermal, detritic or occur as xenocrysts. Hence, baddeleyite is much promising for dating of large and superlarge deposits of strategic minerals in the Arctic region.

Isotope U-Pb studies of baddeleyite started in the 1990s. Large (70 - 100 kg) samples have been selected to extract zircon-baddeleyite concentrate for U-Pb

studies. The article provides U-Pb data on baddeleyite (2738 ± 6 Ma) from a gabbronorite dike intersecting ores of the Olenegorskoye BIF [9]. Nowadays, the most ancient U-Pb age on baddeleyite (2.7 Ga) is known for the Stillwater PGE deposit only [42].nd equals U-Pb data to baddeleyite from the Olenegorskoye BIF. U-Pb isotope data on baddeleyite have been recently obtained and compared to zircon ages [43]. The youngest Paleozoic age is estimated on baddeleyite from the Kovdor foscorite-baddeleyite deposit (380 - 348 Ma). Thus, baddeleyite is studied in the eastern Baltic Shield for the period of 2.7 Ga to 348 Ma, i.e. for the time span of more than 2.4 Ga.

LA-ICP-MS has been first applied to study concentrations and distributions of REE in baddeleyite from the deposits. Studying and applying Zr-Ti geochronometer for baddeleyite is considered important. New investigations yield higher temperatures of the baddeleyite grains formation and the U-Pb systematics closure (more than 10,000˚C), compared to zircon (less than 9000˚C) [20].21].22]. These newly obtained high temperatures of the U-Pb systematics closure and baddeleyite formation are close to other geochronometers, e.g. pyroxenes from mafic rocks, but require further study.

The content of Ti in grains varies widely. It is 10 - 37 ppm (21.2 on average) for sample Bd-300 and 28 - 72 ppm (44.8 on average) for sample Bd-300 (prismatic), 47 - 150 ppm (96.6 on average) for sample Bd-400 and 0.31% - 0.79% (0.49% on the average) for older baddeleyite M-2.

Average temperatures of the baddeleyite crystallization and U-Pb system closure have been detected using a zircon-applied method [27]. Ti-in-zircon thermometer has never been used for baddeleyite before. We apply this method for the first time as a test to check how it works for baddeleyite. They are calculated at 804˚C - 888˚C for Kovdor and 984˚C for Vuoriyarvi. Notably, baddeleyite from the Monchegorsk pluton has high crystallization temperatures of more than 1000˚C (Table 6).

Isotope-geochemical data based on Nd-Sr-He systematics for the rocks of PGE layered Paleoproterozoic intrusions and Ilm and Mgt minerals suggest the mantle impact of N-MORB, E-MORB and OIB sources to dike complexes [3].17].30].32]. Primary-mantle protolith is characterized by εNd 1 - 3; ISr 0.702 - 0.704; TDm 3.5 - 2.8 Ga; enriched by LILE REE elements; 3He/4He up to 1.5 × 10⁻⁶. Re-Os investigations suggest the plume origin of an enriched mantle reservoir EM-1 [Yang 2016]. Cu-Ni-Cr-Ti-V-Fe and PGE deposits formed in the Kola province owing to the large plume magmatism and probably the break-up of the oldest Kenorland supercontinent [3].14].17].

Baddeleyite has been sampled from important industrial deposits in the Arctic region and reference rocks of the Neoarchean BIF, Paleoproterozoic Сu-Ni and Pt-Pd layered intrusions, as well as Paleozoic alkaline and ultra-alkaline ore deposits. Analyses of the sampled minerals have indicated their primary magmatic

genesis. In terms of the U-Pb geochronology, baddeleyite is important in indicating the formation time and duration of magmatic activity. It is also crucial for the reconstruction of supercontinents.

Based on new precise U-Pb data on baddeleyite, we can assume that the major deposits formed in periods of the plume activity (Figure 14(b)). They, in turn, correlate with supercontinental cycles, as shown in Figure 14(a).

This article pioneers in linking the break-up of supercontinents and baddeleyite, which is used as a basis for paleo-reconstructions of the continents [7].37].44]. For the first time, this paper provides a modeled link between the break-up of supercontinents and complex deposits with baddeleyite, since all complex deposits are derivates of LIPs from the Archean to Paleozoic [45].

Conceptualization, T.B.; Methodology, T.B., S.D. and A.N.; Validation, T.B., E.S.; Formal Analysis, T.B., V.S., S.D. and A.N.; Investigation, T.B., V.S., S.D., A.N. and E.S.; Writing-Original Draft Preparation, T.B., E.S.; Writing-Review & Editing, T.B., A.N., S.D. and E.S.; Supervision, T.B.

The research has been carried out in the framework of the scientific research contract No. 0226-2019-0053, grants RFBR 18-35-00246, 18-05-70082 and Program by Presidium RAS No. 8.

This paper is dedicated to Academician F.P. Mitrofanov, who initiated baddeleyite studies in the Pt-bearing province in the Arctic region of the NE Fennoscandian Shield.

The authors declare no conflict of interest.

Bayanova, T., Subbotin, V., Drogobuzhskaya, S., Nikolaev, A. and Steshenko, E. (2019) Baddeleyite from Large Complex Deposits: Significance for Archean-Paleozoic Plume Processes in the Arctic Region (NE Fennoscandian Shield) Based on U-Pb (ID-TIMS) and LA-ICP-MS Data. Open Journal of Geology, 9, 474-496. https://doi.org/10.4236/ojg.2019.98031