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

Baddeleyite is an important mineral geochronometer. It is valued in the U-Pb (ID-TIMS) geochronology more than zircon because of its magmatic origin, while zircon can be metamorphic, hydrothermal or occur as xenocrysts. De-tailed mineralogical (BSE, KL, etc.) research of baddeleyite started in the Fennoscandian Shield in the 1990s. The mineral was first extracted from the Paleozoic Kovdor deposit, the second-biggest baddeleyite deposit in the world after Phalaborwa (2.1 Ga), South Africa. The mineral was successfully introduced into the U-Pb systematics. This study provides new U-Pb and LA-ICP-MS data on Archean Ti-Mgt and BIF deposits, Paleoproterozoic layered PGE intrusions with Pt-Pd and Cu-Ni reefs and Paleozoic complex deposits (baddeleyite, apatite, foscorite ores, etc.) in the NE Fennoscandian Shield. Data on concentrations of REE in baddeleyite and temperature of the U-Pb systematics closure are also provided. It is shown that baddeleyite plays an important role in the geological history of the Earth, in particular, in the break-up of supercontinents.

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] for 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.

Materials and Methods
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] is the 37 th "piece" in the "Late Archean record puzzle" [7].
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 208 Pb and 205 Pb 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/cm 2 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] glasses 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].
LA-ICP-MS has been applied to study zircons from dike rocks that intersect the Olenegorsk BIF, comprising the Kirovogorskoye deposit. Figure 3, Table 2 and Table 3 provide data on concentrations and distribution of REE in the Kirovogorskoye deposit. Temperatures of the zircon crystallization and closure of the U-Pb systematics have been estimated (Table 4) according to [27].
Spectra of REE distribution in zircon crystals show minor amount of LREE and major amount of heavy REE. It explains a steep positive incline of the graphs complicated by negative Eu anomalies and positive Ce anomalies, which complies with the trend of the REE distribution in zircon grains of the magmatic origin ( Figure 3).
Gabbronorites intersecting the Kirovogorskoye deposit of the Olenegorsk BIF have been studied using LA-ICP-MS. This method has been applied to study zircons of 3 morphotypes with an average total amount of REE from 826 to 1099 ppm ( Table 2). Since LREE are minor, values of (La/Yb) N are low (0.000337 -    1 The ratios are corrected for blanks of 0.08 ng for Pb and 0.04 ng for U and for mass discrimination 0.12% ± 0.04%. 2 Correction for common Pb are determined for the age according to [26].  0.002518). Zircons are rich in Ce, because the value of (Ce/Ce*) N varies in the range of 4.6 -27.4, and poor in Eu, because the value of (Eu/Eu*) N is 0.24 -0.27 [29]. Along with the study of the REE concentrations in zircon crystals, Ti contents and crystallization temperatures of zircon grains have been estimated, using a Ti-in-zircon thermometer [27]. An average temperature of the zircon crystallization in gabbronorites is 771˚С (Table 3). This temperature seems to show that zircon formed at the latest stage of the gabbronorite dike crystallization. Table 4 shows the concentration of REE in zircons from the Tsaga Ti-Mgt deposit. Figure 4 shows a trend of the REE distribution in zircon from the Tsaga Ti-Mgt deposit. Table 6 shows the temperature of the zircon crystallization in the Tsaga Ti-Mgt deposit.
Three types of zircon from monzogabbro of the Tsaga Ti-Mgt deposit have been studied, using LA-ICP-MS. The analyzed zircon samples show high total amounts of REE from 1871 to 2264 ppm ( Table 4). Spectra of the REE distribution in crystal zircons have the same low amount of LREE and high amount of heavy REE. It explains a steep positive incline of the graphs complicated by positive Eu and Ce anomalies, which complies with the trend of the REE distribution in zircon grains of the magmatic origin ( Figure 4).
Notably, values of (La/Yb) N are low (0.000889 -0.017590). It indicates a minor amount of LREE. Zircons are rich in Ce, since the value of (Ce/Ce*) N varies in the range of 1.0 -2.1, and rich in Eu, since the value of (Eu/Eu*) N is 1.67 -5.52 [29].  Along with the study of the REE concentrations in zircon crystals, Ti contents and crystallization temperatures of zircon grains have been estimated, using a Ti-in-zircon thermometer. An average temperature of the zircon crystallization in monzogabbro from the Tsaga Ti-Mgt massif is 724˚С (Table 5). Table 6 and Figure 5 provide data on concentration and distribution of REE in zircons from carbonatites of the Siilinjarvi deposit. Table 8 shows temperature of the zircon crystallization in the Siilinjarvi deposit.
The precise LA-ICP-MS analysis has been applied to study three types of zircon from carbonatites of the Siilinjarvi deposit. Average total amounts of REE in the zircon grains vary from 33 to 1099 ppm (Table 7). LREE are minor, therefore, values of (Yb/La) N are low (0.000193 -0.05101). Spectra of the REE distribution have a positive incline of the graphs complicated by positive Eu and Ce anomalies ( Figure 5). Crystallization temperatures of zircon grains from metagabbro have been estimated, using a Ti-in-zircon thermometer [27]. An average temperature of the U-Pb systematics closure in measured areas of zircon from the Siilinjarvi carbonatites is 646˚С (Table 7).

Baddeleyite in Paleoproterozoic Co-Cu-Ni, Cr-Ti-V-Mgt and PGE Layered Intrusions with Pt-Pd and Cu-Ni Reefs
The formation time of these large igneous provinces (LIPs) is 2.53 Ga to 2.       *All ratios are corrected for the blank pollution of 1 pg for Pb and 10 pg for U and mass-discrimination of 0.12% ± 0.04%. **Correction for the common lead admixture is determined by age [26]. D is the % discordance. Isotopic ratios are measured on a Finnigan MAT-262 (RPQ) 7-channel mass-spectrometer in the static regime. All errors are given at the level 2 σ. The coordinates of points and parameters of the U-Pb isochron are calculated in the Isoplot program [33] [34], considering commonly accepted decay constants. Baddeleyite is chemically decomposed following the procedure described in [17] [30].

Baddeleyite in Paleozoic Complex Deposits
The Paleozoic marked the origin of the largest (Kovdor, Vuoriyarvi, etc.) and super largest (Khibiny and Lovozero) alkaline-subalkaline intrusions with carbonatites.
Baddeleyite has been separated and dated using the U-Pb analysis and LA-ICP-MS. For the first time, the REE distribution and concentrations of Ti and Zr have been studied based on the known temperature of the U-Pb systematics closure (Figure 11(a), Figure 11(b), Table 11). U-Pb, Sm-Nd and Rb-Sr analyses using rocks, accessory and rock-forming minerals from kimberlitic pipes, carbonatites and dike series reflect formation of the biggest mantle reservoirs for primary magma of alkaline-ultra alkaline magmatism in a time span of 465 -325 Ma (more than 140 Ma) [13] [35]. According to isotope data (ε Nd + 4; I Sr -0.703 -0.704; T Dm -980 -700 Ma; enriched by LILE REE; 3 He/ 4 He up to 3.5 × 10 −5 ) on reference rocks, they originated from the primary mantle reservoirs DM and HIMU [36]. Isotope-geochemical data on U-Pb and LA-ICP-MS dating of baddeleyite from carbonatite and dike complexes suggest that these rocks result from primary magmatic plume activity of Paleozoic magmatism. This magmatism, in its turn, is associated with the break-up of the Pangea supercontinent [37].   Table  10) [28].  Table 10) [28].  Figure 10. Chondrite normalized REE patterns for baddeleyite from vein pegmatites of the gabbronorite composition (Terrace Cu-Ni deposit, Mt. Nyud) (Sample 3 in Table 10) [28].  According to new data on the distribution and concentration of REE, Ti and Zr in baddeleyite grains from the Kovdor ( Figure 12) and Vyoriyarvi ( Figure  13) massifs measured by LA-ICP-MS (ELAN 9000), the temperature of the U-Pb systematics closure in baddeleyite is higher (984˚C) than that in zircon (-888˚C).

Discussion
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] for 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.   Table 12) [28].   Table 13) [28].   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.
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

Conclusions
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 Open Journal of Geology 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].

Funding
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.