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Article

Coronitic Associations at Gabrish in the Kovdozero Layered Complex in the Southern Part of the Lapland—Belomorian Belt, Kola Peninsula, Russia

by
Andrei Y. Barkov
1,*,
Robert F. Martin
2,
Larisa P. Barkova
1 and
Vladimir N. Korolyuk
3
1
Research Laboratory of Industrial and Ore Mineralogy, Cherepovets State University, 5 Lunacharsky Avenue, 162600 Cherepovets, Russia
2
Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC H3A 0E8, Canada
3
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Science, 3 Avenue “Prospekt Koptyuga”, 630090 Novosibirsk, Russia
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(6), 565; https://doi.org/10.3390/min15060565
Submission received: 3 April 2025 / Revised: 19 May 2025 / Accepted: 23 May 2025 / Published: 26 May 2025
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)
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Abstract

:
The Paleoproterozoic Kovdozero complex, one of largest in the Fennoscandian Shield, was emplaced in a peripheral region of the SB–TB–LBB (Serpentinite Belt–Tulppio Belt–Lapland–Belomorian Belt) megastructure. Coronitic rocks of ultrabasic–basic compositions, investigated along a cross-section in the Gabrish area, are members of a cryptically layered series. They crystallized from the northern margin inward, as indicated by variations in mineral compositions and geochemical trends. Unsteady conditions of crystallization arose because of uneven cooling of the shallowly emplaced complex. Rapid drops in temperature likely caused the forced deposition of different generations of variously textured pyroxenes and chromian spinel or resulted in the unique development of narrow recurrent rims of orthopyroxene hosted by olivine. The unstable conditions of crystallization are expressed by (1) textural diversity, (2) broad variations in values of Mg#, and (3) virtual presence of double trends of Mg# as a function of distance. The coronitic textures are intimately associated with interstitial grains of plagioclase (An≤65), also present as relics in a rim of calcic amphibole. The coronas are results of (1) rapid cooling leading to unsteady conditions of crystallization, which caused the sudden cessation of olivine crystallization and the development of an orthopyroxene rim on olivine and (2) an intrinsic enrichment in H2O (and essential Cl in scapolite) coupled with a progressive accumulation of Al and alkalis, giving rise to fluid-rich environments in the intercumulus melt at advances stages of crystallization. These processes were followed by deuteric composite rims of calcic amphibole and reaction of fluid with early rims or grains of pyroxenes and late plagioclase. The coronitic sequences Ol → Opx → Cpx → calcic Amp → Pl (plus Qz + Mca) observed at a microscopic scale reproduce, in miniature, the normal order of crystallization in an ultrabasic–basic complex. A composite orthopyroxene + calcic amphibole corona resembles some rocks in complexes of the Serpentinite Belt. The prominence of such coronas may well be characteristic of the crystallization of komatiite-derived melts.

1. Introduction

The Kovdozero (Kovdozerskiy) layered complex of ultrabasic–basic rocks is one of the largest in the Fennoscandian Shield [1,2]. Its platinum-group element (PGE) potential is implied by occurrences of Pt–Pd mineralization [3]. The complex is exposed over 20 km in the Kovdozero Lake area, close to Kandalaksha Bay on the White Sea in the southern Kola Peninsula. A U–Pb zircon age of 2440 ± 10 Ma recorded in the Puakhta block [4] is notably younger than the date obtained in the Gabrish area of this complex, 2514 ± 5 Ma (Barkov et al., in prep.). The complex belongs to a huge structure, the Lapland–Belomorian Belt (LBB) of Paleoproterozoic age [5,6,7,8,9], which includes, in its central portion, the Perchatka layered intrusion with coronitic textures [10]. Results of Sm–Nd dating of the Perchatka body (2485 ± 51 Ma) agree well with those reported for the Pados–Tundra layered intrusion (2485 ± 38 Ma) [11,12], a member of the complementary Serpentinite Belt–Tulppio Belt (SB–TB) megastructure.
The Kovdozero complex is an important component in the development of the overall LBB and SB–TB megastructure produced by a large-scale plume of Al-undepleted komatiitic magma in the northeastern Fennoscandian Shield [13,14,15,16,17]. The recent documentation of spinifex-textured clinopyroxene crystallites having a hypermagnesian composition in the Tepsi complex in the northern LBB [18] supports such a source of komatiitic magma. Coronitic textures are characteristic attributes, formed by a combination of magmatic and autometasomatic processes at shallow settings, at Perchatka in the LBB [10] as well as at Chapesvara and Lyavaraka in the SB [19].
The present study is a next step in the characterization of key members of the LBB–SB–TB megastructure. We have investigated a differentiated series of corona-textured rocks exposed in the Gabrish area in the western portion of the Kovdozero complex. Our findings shed new light on the formation and petrogenetic significance of various combinations of coronitic sequences, some of which are, in fact, most unusual.

2. Regional Geology and Sampling

The Kovdozero complex is one of the largest members of the LBB megastructure (Figure 1). The Perchatka, Rogomu, Yanisvaara, and Tepsi complexes, located northwest of Kovdozero, are also important members of the LBB system. Further north, ultrabasic–basic suites in subsynchronous and subvolcanic (or subplutonic) Paleoproperozoic complexes, namely Khanlauta, Pados–Tundra, Chapesvara, Lotmvara, and Lyavaraka, belong to the complementary SB–TB megastructure [20,21,22,23,24,25,26,27,28,29,30] that extends across the Finnish border (Figure 1). Also, subsynchronous suites of komatiites and komatiitic basalts are exposed in the Windy Belt (Vetrenyi) [31,32]. In addition, many layered intrusions were emplaced at ~2.45–2.5 Ga [33] in the eastern Fennoscandian Shield in a context of continental rifting. Regional metamorphism in rocks of the Lapland Belt attained the granulite facies at 1.92–1.93 Ga. These are overlain by rocks of the Belomorian province metamorphosed under conditions of the amphibolite facies ([34] and references therein).
The Kovdozero complex consists of a long strip (~20 km) of blocks of ultrabasic–basic rocks interspersed chaotically with fragments of Archean rocks (biotite gneiss and granitic gneiss) of the Lower Keret’sky series (Figure 2). In general, ultrabasic rocks prevail. They are represented by olivine pyroxenite (commonly websterite), orthopyroxenite, and peridotite (lherzolite), interlayered with olivine gabbronorite. Zones of basic rocks consist of gabbronorite, gabbro-diabase or microgabbro with subordinate exposures of gabbro-amphibolite. The eastern part of the Kovdozero Lake is relatively poor in outcrops of basic–ultrabasic rocks, although outcrops of separate blocks have been mapped [1].

3. Materials and Methods

Our materials consist of twenty-seven samples of coronitic rocks of ultrabasic–basic compositions collected along a ~3-km cross-section oriented across the complex (profile AB: Figure 3) in a remote portion of Kovdozero Lake.
The analyses were conducted at the Analytical Center for Multi-Elemental and Isotope Studies, Institute of Geology and Mineralogy, SB RAS, in Novosibirsk. The minerals were analyzed using a JEOL JXA-8230 instrument (JEOL Ltd., Akishima, Tokyo, Japan) in wavelength-dispersion spectrometry mode (WDS). An accelerating voltage of 20 kV and a probe current of 20–50 nA were used. We employed Kα analytical lines for all elements except for Cr, where the Kβ1 line was used because of peak overlap. Periods of measurements at the peaks were 20 or 10 s. The superposition of the TiKβ1 line on the VKα line and of the VKβ line on the CrKα line were accommodated. The beam diameter was ~1 μm. Natural specimens of olivine (Mg, Si, Fe, and Ni) and chromiferous or manganiferous garnet (Ca, Cr, and Mn) were used as standards for olivine. A natural specimen of magnesian chromite (for Cr, Fe, Mg, and Al); manganiferous garnet (Mn); ilmenite (Ti); and synthetic oxides NiFe2O4 (Ni), ZnFe2O4 (Zn), and V2O5 (V) were used as standards for chromian spinel. Grains of orthopyroxene and amphiboles were analyzed using pyrope (Si, Al, and Fe), a glass Ti standard (GL-6), chromiferous garnet (Cr), diopside and pyrope (Mg and Ca), manganiferous garnet (Mn), albite (Na), and orthoclase (K). Clinopyroxene was analyzed with essentially the same set of standards, and diopside was used for Si, Ca, and Mg. The following standards were applied in the analysis of plagioclase: orthoclase (Si, Al, and K), diopside (Ca), pyrope (Fe), and albite (Na). The WDS analyses of mica-group minerals and scapolite were conducted using a phlogopite standard (synthetic) for K and F, and chlorapatite (also synthetic) for Cl. The above-mentioned garnet standards were used for Ca, Mg, Mn, Fe, Si, Al, and Cr. A synthetic glass was used for Ti. The data were processed with the ZAF method of corrections. Chalcopyrite was the standard used for S. The calculated limits of detection (1σ criterion) are ≤0.01 wt.% for Ti, Cr, Fe, Ni, Ca, Zn, Mn, and K and 0.02 wt.% for Na and Al.
The whole-rock abundances of trace elements were established at the same center by inductively coupled plasma-mass spectrometry (ICP-MS) using a high-resolution Finnigan MAT mass spectrometer (model ELEMENT). Analytical details are provided in [35]. Contents of major oxides in the rocks were established at the same center by X-ray fluorescence (XRF). The XRF analysis was carried out using molten tablets. First, the analyzed sample was dried at 105 °C for 1.5 h, and then it was calcined at 960 °C for 2.5 h and mixed with a flux (66.67% lithium tetraborate plus 32.83% lithium metaborate and 0.5% lithium bromide) in a ratio of 1:9. The total weight of the mixture was 5 g. The mixture was melted in platinum crucibles in the induction furnace Lifumat-2.0-Ox. Measurements were performed on an ARL-9900XP X-ray fluorescence spectrometer (Thermo Fisher Scientific Ltd., Waltham, MA, USA). The following set of state-approved standards were used to build calibration relationships and control the correctness of the analysis: MU-1, MU-3, MU-4, SA-1, SChT-1, SChT-2, SDO-1, SDU-1, SG-1A, SG-2, SG-3, SGD-1, SGD-2, SGKh-1, SGKh-5, SGKhM-2, SGKhM-3, SI-1, SI-2, SNS-1, SNS-2, SOP-1, and ST-1, plus synthetic mixtures based on components of MgO, SiO2, Al2O3, TiO2, CaO, CaSO4, Cr2O3, and Fe2O3. The analytical accuracy corresponds to the category OST 41-08-205-99. The analytical data are provided in Supplementary Tables S1–S9.

4. Results and Observations

Our investigation documented a great variety of rock types along profile A–B in the Gabrish area (Figure 2 and Figure 3). Some islands or large outcrops (Figure 4) entirely consist of ultrabasic rocks.
The cryptically and modally layered sequences consist of lherzolite, olivine- and plagioclase-bearing websterite, orthopyroxenite, olivine-bearing norite, olivine-bearing gabbro, norite, and gabbronorite (some with minor amounts of quartz). These rocks are quite fresh, commonly with only slight deuteric influence, and are undeformed. Fine-grained and “taxitic” textures (inhomogeneity in grain size) are not rare in our specimens.
Representative examples of textures and mineral associations are presented in Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12. Intergrowths of the three major phases (olivine, orthopyroxene, and clinopyroxene) are characteristic (Figure 5a and Figure 7d). Such examples are considered to be primocrystic. Owing to an inferred prolonged interval of crystallization, relative to olivine and orthopyroxene, clinopyroxene commonly occurs as an interstitial phase. In contrast, plagioclase is present only as an intercumulus phase.
The existence of two generations of orthopyroxene grains is inferred at Gabrish. The large early-generation grains are subhedral and distinctly more strongly magnesian, commonly with greater amounts of Ca, Al, and Cr (~1 wt.% Cr2O3) in solid solution. Note that some of the Fe-rich grains may also be chromiferous. The second generation represents well-formed crystals attributed to a sudden drop in temperature, resulting in grains 1–1.5 mm across (Figure 7c and Figure 10c). Some of the pyroxene grains are strikingly zoned; note the presence of olivine granules trapped in the core (Figure 8b). Orthopyroxene also occurs as a rim-like phase on olivine (Figure 5b and Figure 6), as a common rim after olivine (Figure 5c, Figure 7c, Figure 8d, Figure 11c and Figure 12a), or as an unusual aggregate of grains with calcic amphibole at the boundary of a large grain of orthopyroxene in contact with plagioclase (Figure 9d). The rim of the orthopyroxene is typically less strongly magnesian and has a low level of Cr and Ca in solid solution. In addition, exsolution-induced lamellae of orthopyroxene are locally present in grains of clinopyroxene (Figure 10b).
The various types of reaction rims or sequences are presented in Table 1. With rare exceptions, coronitic textures are invariably developed in direct contact with intercumulus grains of plagioclase (Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12). In the case of the double rims of amphibole (Figure 9b and Figure 11c), the Amp-1 rim, deposited around orthopyroxene, is composed of variants of actinolite-tremolite. The Amp-2 rim, precipitated in direct contact with plagioclase, typically represents pargasite or aluminous variants of magnesio-hornblende. Interestingly, relics of plagioclase are present in a rim of calcic amphibole (Figure 8c). Also of special interest are crystallites of mica (phlogopite—annite series) nucleated on the surface of orthopyroxene grains and in direct contact with plagioclase (Figure 5d and Figure 7a,b). In addition, separate grains or veins of clustered grains of mica are commonly present as components of coronitic associations (Figure 11a,b,d and Figure 12d). Note that in some cases only, plagioclase forms what looks like a rim (Figure 12b,c). However, normally interstitial grains of plagioclase are observed in these rocks, some with symplectitic quartz.
Interestingly, Cl-bearing meionite occurs as an alteration product after plagioclase (Figure 13). Its composition (WDS data) is SiO2 48.30 wt.% (47.45–49.89), Al2O3 26.48 wt.% (25.57–27.00), CaO 15.25 wt.% (13.96–16.09), FeO 0.09 wt.% (0.06–0.22), Na2O 4.59 wt.% (3.37–5.60), K2O 0.49 wt.% (0.46–0.56), Cl 1.07 wt.% (0.96–1.20), Cl≡O 0.24, F not detected (≤0.02 wt.%), S not detected (≤0.03 wt.%), and total 96.03 wt.% (sample KVDOZ-27; n = 12). Its formula, based on 24 oxygen atoms per formula unit, is (Ca2.37Na1.29K0.09)Σ3.75[(Al4.53Si7.00)Σ11.53O24](CO3)0.74Cl0.26. This is the second occurrence of Cl-bearing scapolite in the entire megastructure SB–TB–LBB; previously, it was reported from the Lyavaraka complex, SB [11].

4.1. Overall Variations and Cryptic Layering

The cryptic variations recorded for olivine in the Gabrish area correspond to Mg# 86.4–73.3 (based on 82 data-points: n = 82). The WDS compositions of orthopyroxene and clinopyroxene gave Mg# 88.2–63.3 (n = 233) and 89.0–77.2 (n = 152), respectively. Note that the clinopyroxene trend follows along the augite–wollastonite vector (Figure 14), which is unusual, but was reported from the related Perchatka complex in the same belt [10]. Plagioclase varies from An64.7 to An13.8 (n = 171); zoned grains of plagioclase were also analyzed.
Accessory grains of chromian spinel display a series that extends along the Cr–Al axis (Figure 15; n = 115). The spinel-group oxides consist of chromite or members of the hercynite-spinel series. Both are present in the same association, based on their appearance and compositions (enriched in Cr or Al). The coexistence of the two generations of spinel is known in other complexes of the megastructure, e.g., at Perchatka [10].
The variations and trends recorded in olivine, pyroxenes, and chromian spinels along the profile A–B are especially informative (Figure 16a–d): (1) Values of Mg# generally decrease from the margin of the intrusion inward. (2) Double trends are recognized based on maximums and minimums of the values. This feature is likely related to the documented presence of different generations or textural variants of these minerals, e.g., two generations and a coronitic rim of orthopyroxene all presumably formed over a range of temperatures. (3) The clinopyroxene “maximum” trendline is remarkably constant (Figure 16d), which likely points to its nucleation during the attainment of relative equilibrium in a large volume of differentiated melt after the early crystallization of the Ol + Opx paragenesis. On the other hand, late generations of clinopyroxene, which crystallized from the remaining melt, consistently show a steep decrease in slope inward in the “minimum” values.

4.2. Geochemical Trends

A drop in MgO, NiO, and Cr2O3, along with a stepped buildup in SiO2, are combined with the normal decrease in Al2O3, CaO, TiO2, and V2O3, all occurring as consequences of fractional crystallization. Contents of Co vary sympathetically with Ni, whereas Cu behaves incompatibly during crystallization (Figure 17a–i). A series of plots show the sympathetic behavior of the rare-earth elements and high-field-strength elements (Figure 18 and Figure 19).
In general, the microcoronitic series observed at Gabrish displays greater extents of fractional crystallization and differentiation compared with ultrabasic complexes in the Serpentinite Belt–northwestern Lapland–Belomorian Belt (Figure 20). The mean contents of MgO (32.28 wt.%) and SiO2 (44.46 wt.%) based on a total of 225 bulk-rock analyses [37] agree well with a komatiitic source suggested for the entire megastructure [10,13,14,15,16,17,18,19], cf. [38,39,40].

5. Discussion

5.1. Crystallization of the Kovdozero Complex Based on Evidence at Gabrish

As noted, the Kovdozero complex is an important constituent of the Paleoproterozoic SB–TB–LBB megastructure in the Fennoscandian Shield. We suggest that this complex formed from a large input of komatiitic melt derived from the magmatic feeder of the large-scale plume in the Pados–Tundra–Chapesvara area (Figure 1). The composition of olivine, as the first phase to nucleate, is a reliable monitor of the progressive decrease in values of Fo (max.) from Fo93 (Pados–Tundra) and Fo92 (Chapesvara), Fo91 (Tepsi), and Fo87 at Perchatka and Rogomu [13,14,18] to Fo86 (Gabrish in the Kovdozero complex). In addition, the compositional and geochemical trends (Figure 16a–d, Figure 18a–f and Figure 19a–f) all point unequivocally to an advance of the crystallization front at Gabrish inward from the northern margin to close to the outer contact. This path of crystallization is similar to that inferred for the Perchatka body in the central LBB [10]. As noted, the mean bulk-rock contents (n = 225) of MgO and SiO2, 32.28 and 44.46 wt.%, respectively (Figure 20), correspond to the komatiitic source of the initial magma in the large-scale plume [10,13,14,15,16,17,18,19]. The spinifex-textured crystallites of hypermagnesian Cpx recorded in the Tepsi complex in the same belt [18] provide direct evidence of the komatiite melt that rose in the plume. Note that the plume-type magmatism is known in other parts of the Fennoscandian Shield [41].
We believe that the Kovdozero complex is hypabyssal and that its internal structure is not made up of a single body. Rather, it is subdivided into suites of chonolithic segments of different size, separated by blocks and clusters of granite-gneissic rocks. Such an array is likely caused by the following circumstances: (1) the shallow setting of the complex, (2) insufficient volume of the magma chamber or space available to accommodate the intrusion, and (3) rapid crystallization, which precluded an efficient assimilation of trapped blocks of wallrock. On the other hand, the presence of well-established patterns of cryptic layering and geochemical trends indicates that large volumes of magma could communicate and convect.
Doubled trends of variation in Mg# illustrating the maximal and minimal values are documented at Gabrish (Figure 16a–d). These trends are attributes of unsteady conditions of crystallization related to rapid changes and drops in temperature because of uneven cooling in a hypabyssal setting. Presumably, grains of olivine coexisting with chromite and the chromian spinel–hercynite series crystallized first as the temperature dropped in the chamber. These parageneses were likely most sensitive to rates of cooling and thus display steeper trends of decreasing Mg# inward (Figure 16a,c). Grains of orthopyroxene display a similar but less prominent decrease in Mg# (Figure 16b). A steady trendline is observed for early-formed clinopyroxene in the three-phase intergrowths Ol + Opx + Cpx (Figure 7d). We thus suggest that the constant maximal Mg# values reflect uniform conditions of crystallization of clinopyroxene grains over a large volume of differentiated magma. In contrast, the minimal values of Mg# decrease sharply (Figure 16d) thus indicating the deposition of late variants of clinopyroxene (intercumulus or rim-like) formed at lower temperatures and at greater distances from contacts with the host rock.
The anomalous trend of clinopyroxene crystallization displayed in Figure 14 is yet another sign of rapid crystallization. A growth vector away from the wollastonite apex is consistent with a metastable crystal–liquid partition [42] and closely resembles that in the lherzolitic martian meteorite 77,005 [43], among others.

5.2. Origin of the Coronas

At Gabrish, coronitic textures are developed on a microscopic scale in members of the cryptically layered sequence; these are fresh or only slightly modified by autometamorphic (deuteric) processes. A regional metamorphic origin can thus be ruled out. Records of non-metamorphic coronas were previously reported [10,19,44,45].
The inferred order of deposition of participating minerals, provided in Table 1 and, schematically, in Figure 21a–g, involves an intimate association with grains of intercumulus plagioclase (An≤65). These textures likely formed at an advanced stage of crystallization as consequences of (1) a rapid cooling leading to unsteady conditions of crystallization in a shallow setting, which caused the appearance of an orthopyroxene rim after olivine; (2) an accumulation of Al and alkalis in the remaining intercumulus melt that coexisted with a locally Cl-bearing aqueous fluid; and (3) deuteric deposition of single or double rims of calcic amphibole (Figure 7c, Figure 9b and Figure 11c) as a result of reactions of H2O-bearing fluid with early pyroxenes and late plagioclase. Note that the double rims consist of inner Amp-1 rim, formed around grains of orthopyroxene and composed of members of the actinolite-tremolite series. The Amp-2 rim, deposited directly in contact with plagioclase, corresponds to pargasite or an aluminous magnesio-hornblende. The inferred change in the composition accounting for Amp-1 → Amp-2 thus involves a buildup in alkalis, Al, plus Ti, followed by a notable decrease in Mg#. These changes are attributed to a process of crystallization in the fluid-rich deuteric system. Relics of plagioclase (Figure 8c) are present in some of the Amp-2 rims, which clearly indicate that plagioclase was involved directly in the rim-forming reactions at a low temperature or possibly as a result of a solid-state reaction. Also, note the existence of overgrowths of oriented grains of mica, deposited on the edges of orthopyroxene grains from an aqueous fluid (Figure 5d and Figure 7b). Mafic components in these crystallites were presumably released by a local dissolution of pyroxene, whereas Al and alkalis were provided by the plagioclase.

6. Concluding Statements

The Paleoproterozoic Kovdozero complex formed in a hypabyssal setting by input of a large volume of differentiated komatiitic magma emplaced in a peripheral region of the SB–TB–LBB (Serpentinite Belt–Tulppio Belt–Lapland–Belomorian Belt) megastructure. The coronitic rocks of ultrabasic–basic compositions investigated at the Gabrish area are members of a cryptically layered series. The complex represents a system of chonolithic bodies that were somehow connected with each other during crystallization; these chonoliths are hosted by clusters or detached blocks of surrounding granite-gneiss of Archean age. The complex crystallized beginning from its northern margin inward as indicated by variations in mineral compositions and geochemical trends.
Unsteady conditions of crystallization arose because of uneven cooling of the shallowly emplaced complex. Rapid drops in temperature likely caused the forced deposition of different generations of variously textured pyroxenes and chromian spinel and even resulted in the unusual development of recurrent orthopyroxene as a narrow rim on olivine (Figure 21a–g).
The unstable conditions of crystallization are expressed in (1) textural diversity, (2) broad variations in values of Mg# (per sample for Ol, Opx, Cpx, and Chr), (3) virtual presence of double trends of Mg# (“maximum” and “minimum” trendlines) vs. distance in patterns of cryptic layering, and (4) coronitic textures.
The origin of coronitic textures is not a result of regional metamorphism in the investigated rocks. These textures and mineral associations are intimately associated with interstitial grains of plagioclase (An≤65), recorded as undigested relics in a rim of calcic amphibole (Figure 8c). The coronas formed as consequences of the following important factors: (1) a rapid cooling leading to unsteady conditions of crystallization, which caused the sudden cessation of olivine crystallization with a development in its place of an orthopyroxene rim and (2) an intrinsic enrichment in H2O (and essential Cl in scapolite) coupled with a progressive accumulation of Al and alkalis, giving rise to fluid-saturated environments in portions of intercumulus melt at advances stages of crystallization. These processes were followed by a deuteric deposition of composite rims of calcic amphibole as a result of accumulation of H2O and reaction of H2O-bearing fluid with early rims or grains of pyroxenes and late plagioclase.
Interestingly, the coronitic sequences Ol → Opx → Cpx → calcic Amp → Pl (plus Qz + Mca) observed at a microscopic scale (Figure 5c, Figure 7a and Figure 21e) reproduce in miniature the normal order of phase crystallization in an ultrabasic–basic complex. Also, the composite coronas, composed of orthopyroxene + calcic amphibole (Figure 9d), resemble some specific amphibole-orthopyroxene rocks described in the Lyavaraka complex, Serpentinite Belt [16].
Results of our examinations of coronitic textures in several suites of the megastructure [10,19], as well as the present findings, imply that the development of coronas can well represent a characteristic feature of crystallization of komatiite-derived melts.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min15060565/s1.

Author Contributions

A.Y.B. (investigation, project administration, funding acquisition, writing—original draft preparation); R.F.M. (writing—original draft preparation, writing—review and editing); L.P.B. (writing—original draft preparation, data curation); V.N.K. (formal analysis, methodology, data curation). All authors have read and agreed to the published version of the manuscript.

Funding

AYB acknowledges that the beginning of this study was supported by the Russian Science Foundation (grant #22-27-00419).

Data Availability Statement

The analytical data are provided in Tables S1–S9.

Acknowledgments

We thank the four referees and editors for constructive comments and suggestions. VNK acknowledges that this study was carried out within the framework of the state assignment of the Sobolev Institute of Geology and Mineralogy of the SB of the RAS, supported by the Ministry of Science and Higher Education of the Russian Federation (project 122041400171-5). We appreciate the professional help of the staff at the Analytical Center for Multi-Elemental and Isotope Studies, SB RAS, Novosibirsk, Russia. We also thank the staff of the Russian Geological Research Institute (VSEGEI) and the Federal Subsoil Resources Management Agency (Rosnedra) for providing an access to sets of geological maps.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Geological setting of the Gabrish area in the Kovdozero complex (KVDOZ) relative to other ultrabasic–basic suites of Paleoproterozoic age in the Lapland–Belomorian Belt (LBB) and to related subsynchronous complexes of dunite–harzburgite–orthopyroxenite sequences in the Serpentinite Belt–Tulppio Belt (SB–TB). The locations and boundaries are after [18], based on published maps [1,20,21,22,23,24,25,26,27,28]. Suites of the complementary Tulppio Belt (TB) are represented after [29,30], for which a Neoarchean age was previously proposed. The following labels are shown: LVR Lyavaraka, LTM Lotmvara, CHP Chapesvara, PDS Pados–Tundra, KHN Khanlauta, TPST Tepsi, YANA Yanisvaara, ROGO Rogomu, and PRCH for the Perchatka layered complex. The Gabrish area is shown on the insert.
Figure 1. Geological setting of the Gabrish area in the Kovdozero complex (KVDOZ) relative to other ultrabasic–basic suites of Paleoproterozoic age in the Lapland–Belomorian Belt (LBB) and to related subsynchronous complexes of dunite–harzburgite–orthopyroxenite sequences in the Serpentinite Belt–Tulppio Belt (SB–TB). The locations and boundaries are after [18], based on published maps [1,20,21,22,23,24,25,26,27,28]. Suites of the complementary Tulppio Belt (TB) are represented after [29,30], for which a Neoarchean age was previously proposed. The following labels are shown: LVR Lyavaraka, LTM Lotmvara, CHP Chapesvara, PDS Pados–Tundra, KHN Khanlauta, TPST Tepsi, YANA Yanisvaara, ROGO Rogomu, and PRCH for the Perchatka layered complex. The Gabrish area is shown on the insert.
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Figure 2. Regional geology of the western Kovdozero complex is based on mapping in [1] with minor modifications. Boundaries of the area investigated at Gabrish are outlined. The intense blue color indicates deeper water (and lighter blue indicates shallower level) in the waters of Lake Kovdozero.
Figure 2. Regional geology of the western Kovdozero complex is based on mapping in [1] with minor modifications. Boundaries of the area investigated at Gabrish are outlined. The intense blue color indicates deeper water (and lighter blue indicates shallower level) in the waters of Lake Kovdozero.
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Figure 3. Locations of corona-textured samples collected in the Gabrish area projected on a satellite SAS.Planet image (version 230909). The profile A–B shown by a dashed line is oriented north-to-south, from the northern margin of the complex inward. This area is shown on the geological map (Figure 2). Dark areas are all parts of Kovdozero Lake. The order of sample numbers seems random because of repeated visits to collect additional materials.
Figure 3. Locations of corona-textured samples collected in the Gabrish area projected on a satellite SAS.Planet image (version 230909). The profile A–B shown by a dashed line is oriented north-to-south, from the northern margin of the complex inward. This area is shown on the geological map (Figure 2). Dark areas are all parts of Kovdozero Lake. The order of sample numbers seems random because of repeated visits to collect additional materials.
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Figure 4. One of the rocky outcrops investigated in the Gabrish area of the Kovdozero layered complex. The investigator gives an idea of scale.
Figure 4. One of the rocky outcrops investigated in the Gabrish area of the Kovdozero layered complex. The investigator gives an idea of scale.
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Figure 5. (a–d). Back-scattered electron (BSE) images show corona-type features developed in samples KVDOZ-4, 6, 10, and 11 (see Figure 3 for sample locations). The following symbols are used: Ol for olivine, Opx for orthopyroxene, Cpx for clinopyroxene, Pl for plagioclase, Chr for chromian spinel, Amp for calcic amphibole, Mca for mica, and Kfs for potassic feldspar.
Figure 5. (a–d). Back-scattered electron (BSE) images show corona-type features developed in samples KVDOZ-4, 6, 10, and 11 (see Figure 3 for sample locations). The following symbols are used: Ol for olivine, Opx for orthopyroxene, Cpx for clinopyroxene, Pl for plagioclase, Chr for chromian spinel, Amp for calcic amphibole, Mca for mica, and Kfs for potassic feldspar.
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Figure 6. A magnification of a portion of Figure 5b displays the odd existence of two layers of recurrent orthopyroxene (Opx), which are hosted by a grain of olivine (Ol). Minor inclusions of calcic amphibole (Amp) and chromian spinel (Chr) are present (sample KVDOZ-6).
Figure 6. A magnification of a portion of Figure 5b displays the odd existence of two layers of recurrent orthopyroxene (Opx), which are hosted by a grain of olivine (Ol). Minor inclusions of calcic amphibole (Amp) and chromian spinel (Chr) are present (sample KVDOZ-6).
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Figure 7. (a–d). BSE images show corona-type features developed in samples KVDOZ-13, -17, and -19 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 5a–d. The additional symbols are Mca for mica (phlogopite—annite series) and Qz for quartz.
Figure 7. (a–d). BSE images show corona-type features developed in samples KVDOZ-13, -17, and -19 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 5a–d. The additional symbols are Mca for mica (phlogopite—annite series) and Qz for quartz.
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Figure 8. (a–d). BSE images show corona-type phenomena developed in samples KVDOZ-20, -21, and -23 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 7a–d.
Figure 8. (a–d). BSE images show corona-type phenomena developed in samples KVDOZ-20, -21, and -23 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 7a–d.
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Figure 9. (a–d). BSE images show corona-type features developed in samples KVDOZ-25, -26, and -27 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 7a–d.
Figure 9. (a–d). BSE images show corona-type features developed in samples KVDOZ-25, -26, and -27 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 7a–d.
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Figure 10. (a–d). BSE images show coronitic and reaction features developed in samples KVDOZ-28, -29, and -31 (sample locations are given in Figure 3). The symbols used are the same as in Figure 7a–d.
Figure 10. (a–d). BSE images show coronitic and reaction features developed in samples KVDOZ-28, -29, and -31 (sample locations are given in Figure 3). The symbols used are the same as in Figure 7a–d.
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Figure 11. (a–d). BSE images show coronitic and reaction features developed in samples KVDOZ-31, -32, and -33 (sample locations are presented in Figure 3). The symbols used are the same as in Figure 7a–d.
Figure 11. (a–d). BSE images show coronitic and reaction features developed in samples KVDOZ-31, -32, and -33 (sample locations are presented in Figure 3). The symbols used are the same as in Figure 7a–d.
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Figure 12. (a–d). BSE images show coronitic phenomena developed in samples KVDOZ-34, -36, and -37 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 7a–d.
Figure 12. (a–d). BSE images show coronitic phenomena developed in samples KVDOZ-34, -36, and -37 (sample locations are provided in Figure 3). The symbols used are the same as in Figure 7a–d.
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Figure 13. Irregular patches are composed of a scapolite-group mineral (Scp: Cl-bearing), associated with calcic amphibole (Amp), which both occur as products of alteration of plagioclase (Pl). In addition, the amphibole forms a coronitic rim around an orthopyroxene grain (Opx).
Figure 13. Irregular patches are composed of a scapolite-group mineral (Scp: Cl-bearing), associated with calcic amphibole (Amp), which both occur as products of alteration of plagioclase (Pl). In addition, the amphibole forms a coronitic rim around an orthopyroxene grain (Opx).
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Figure 14. Compositional series of grains of orthopyroxene and clinopyroxene in corona-type rocks at Gabrish, plotted on the triangular diagram enstatite (En)–ferrosilite (Fs)–wollastonite (Wo) (expressed in mol.%). The symbol Di is diopside, Hd is hedenbergite, and Aug is augite. The nomenclature is after [36].
Figure 14. Compositional series of grains of orthopyroxene and clinopyroxene in corona-type rocks at Gabrish, plotted on the triangular diagram enstatite (En)–ferrosilite (Fs)–wollastonite (Wo) (expressed in mol.%). The symbol Di is diopside, Hd is hedenbergite, and Aug is augite. The nomenclature is after [36].
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Figure 15. Compositional series of grains of chromian spinel in corona-type rocks at Gabrish, plotted on the triangular diagram Cr–Al–Fe3+ (expressed in atomic %).
Figure 15. Compositional series of grains of chromian spinel in corona-type rocks at Gabrish, plotted on the triangular diagram Cr–Al–Fe3+ (expressed in atomic %).
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Figure 16. (a–d). Variations in values of the Mg# index, 100 Mg/(Mg + Fe2+ + Mn), recorded in compositions of olivine (a), orthopyroxene (b), chromian spinel (c), and clinopyroxene (d) in rocks with coronitic textures, sampled along the profile A–B (shown in Figure 3). The distance is given in meters.
Figure 16. (a–d). Variations in values of the Mg# index, 100 Mg/(Mg + Fe2+ + Mn), recorded in compositions of olivine (a), orthopyroxene (b), chromian spinel (c), and clinopyroxene (d) in rocks with coronitic textures, sampled along the profile A–B (shown in Figure 3). The distance is given in meters.
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Figure 17. (a–l). Variations in bulk-rock contents of SiO2 (a), TiO2 (b), Al2O3 (c), CaO (d), MgO (e), Na2O (f), and K2O (g) expressed in weight % (XRF data) along with contents of Cr (h), V (i), Ni (j), Co (k), and Cu (l) expressed in ppm (ICP-MS data), recorded in compositions of rocks with coronitic textures sampled along the profile A–B (shown in Figure 3). The distance is expressed in meters. The arrowhead line shows variation trends observed for these values as a function of the relative distance from A to B along the profile. These results are based on the XRF and ICP-MS analyses of the following samples: KVDOZ-2, 10, 11, 25, 28, 31, and 32 (see Figure 3 for locations).
Figure 17. (a–l). Variations in bulk-rock contents of SiO2 (a), TiO2 (b), Al2O3 (c), CaO (d), MgO (e), Na2O (f), and K2O (g) expressed in weight % (XRF data) along with contents of Cr (h), V (i), Ni (j), Co (k), and Cu (l) expressed in ppm (ICP-MS data), recorded in compositions of rocks with coronitic textures sampled along the profile A–B (shown in Figure 3). The distance is expressed in meters. The arrowhead line shows variation trends observed for these values as a function of the relative distance from A to B along the profile. These results are based on the XRF and ICP-MS analyses of the following samples: KVDOZ-2, 10, 11, 25, 28, 31, and 32 (see Figure 3 for locations).
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Figure 18. (a–f). Variations in bulk-rock contents of Sc (a), Sr (b), Y (c), Zr (d), Nb (e), and Ba (f) expressed in ppm (ICP-MS data), in rocks with coronitic textures sampled along the profile A–B (shown in Figure 3). The distance is expressed in meters. The arrowhead line shows variation trends observed as a function of relative distances from A to B along the profile. These results pertain to the following samples: KVDOZ-2, 10, 11, 25, 28, 31, and 32 (see Figure 3 for locations).
Figure 18. (a–f). Variations in bulk-rock contents of Sc (a), Sr (b), Y (c), Zr (d), Nb (e), and Ba (f) expressed in ppm (ICP-MS data), in rocks with coronitic textures sampled along the profile A–B (shown in Figure 3). The distance is expressed in meters. The arrowhead line shows variation trends observed as a function of relative distances from A to B along the profile. These results pertain to the following samples: KVDOZ-2, 10, 11, 25, 28, 31, and 32 (see Figure 3 for locations).
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Figure 19. (a–f). Variations in bulk-rock contents of La (a), Ce (b), Nd (c), Yb (d), Hf (e), and Th (f) expressed in ppm (ICP-MS data), in rocks with coronitic textures sampled along the profile A–B (shown in Figure 3). The distance is expressed in meters. The arrowhead line shows variation trends observed as a function of relative distances from A to B along the profile. These results pertain to the following samples: KVDOZ-2, 10, 11, 25, 28, 31, and 32 (see Figure 3 for locations).
Figure 19. (a–f). Variations in bulk-rock contents of La (a), Ce (b), Nd (c), Yb (d), Hf (e), and Th (f) expressed in ppm (ICP-MS data), in rocks with coronitic textures sampled along the profile A–B (shown in Figure 3). The distance is expressed in meters. The arrowhead line shows variation trends observed as a function of relative distances from A to B along the profile. These results pertain to the following samples: KVDOZ-2, 10, 11, 25, 28, 31, and 32 (see Figure 3 for locations).
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Figure 20. Plot of bulk-rock contents of MgO vs. SiO2 both expressed in weight %, showing schematically compositional variations of the microcoronitic series at Gabrish (GBR) compared with the compositional field of the Pados–Tundra layered complex (PDS; the symbol OPXZ pertains to the Orthopyroxenite Zone, and DB refers to the Dunite Block of the Dunite Zone), with the differentiated flow of the Mount Khanlauta suite (KHNL) and the Yanisvaara complex (YANA), after [37]. A red point (SB) displays the mean composition of ultramafic complexes in the Serpentinite Belt–northwestern Lapland–Belomorian Belt, which is based on a total of 225 bulk-rock analyses [37] performed at Pados–Tundra, Malyi Pados, Chapesvara-I and -II, Lotmvara-I and -II, Lyavaraka, Khanlauta, Yanisvaara, Kareka–Tundra, and Tepsi (Urochishche Tepsi). Also shown for comparison are schematic boundaries of typical fields of boninites, komatiitic basalts, and komatiites of the Barberton Belt in South Africa, Gorgona Island in Columbia, and the Munro area in Ontario, Canada, after [38].
Figure 20. Plot of bulk-rock contents of MgO vs. SiO2 both expressed in weight %, showing schematically compositional variations of the microcoronitic series at Gabrish (GBR) compared with the compositional field of the Pados–Tundra layered complex (PDS; the symbol OPXZ pertains to the Orthopyroxenite Zone, and DB refers to the Dunite Block of the Dunite Zone), with the differentiated flow of the Mount Khanlauta suite (KHNL) and the Yanisvaara complex (YANA), after [37]. A red point (SB) displays the mean composition of ultramafic complexes in the Serpentinite Belt–northwestern Lapland–Belomorian Belt, which is based on a total of 225 bulk-rock analyses [37] performed at Pados–Tundra, Malyi Pados, Chapesvara-I and -II, Lotmvara-I and -II, Lyavaraka, Khanlauta, Yanisvaara, Kareka–Tundra, and Tepsi (Urochishche Tepsi). Also shown for comparison are schematic boundaries of typical fields of boninites, komatiitic basalts, and komatiites of the Barberton Belt in South Africa, Gorgona Island in Columbia, and the Munro area in Ontario, Canada, after [38].
Minerals 15 00565 g020
Minerals 15 00565 g021aMinerals 15 00565 g021b
Figure 21. (a–g). A schematic representation of sequences of deposition of coronitic associations observed in the Gabrish area. The dashed trendline (e) displays the entire sequence with the order Ol → Opx → Cpx → Amp → Pl. The symbols are the same as in Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12. The label Act is actinolite, Tr is tremolite, Prg is pargasite, Mhbl is magnesio-hornblende, and Phl is phlogopite.
Figure 21. (a–g). A schematic representation of sequences of deposition of coronitic associations observed in the Gabrish area. The dashed trendline (e) displays the entire sequence with the order Ol → Opx → Cpx → Amp → Pl. The symbols are the same as in Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12. The label Act is actinolite, Tr is tremolite, Prg is pargasite, Mhbl is magnesio-hornblende, and Phl is phlogopite.
Minerals 15 00565 g021aMinerals 15 00565 g021b
Table 1. Reactions and mineral sequences observed in rims or shells in coronitic associations in the Gabrish area of the Kovdozero complex.
Table 1. Reactions and mineral sequences observed in rims or shells in coronitic associations in the Gabrish area of the Kovdozero complex.
#SampleCoronitic Successions#SampleCoronitic Successions
1KVDOZ-2Ol → Srp + Amp → Pl 15KVDOZ-27Opx → Amp → Pl
2KVDOZ-4Cpx → Pl16KVDOZ-27Opx-1 → Opx-2 + Amp → Amp → Pl (zoned)
3KVDOZ-6Ol → Opx-1 → Ol → Opx-2 17KVDOZ-28Cpx → Amp-1 → Amp-2 → Pl
4KVDOZ-10Ol → Opx → Cpx → Amp → Pl 18KVDOZ-29Opx → Amp → Pl
5KVDOZ-11Opx → Amp → Pl19KVDOZ-31Ol → Opx + Amp → Pl
6KVDOZ-13Opx → Amp → Mca → Qz20KVDOZ-31Ol → Amp → Mca
7KVDOZ-13Opx → Mca → Pl21KVDOZ-32Opx → Cpx → Mca
8KVDOZ-17Ol → Opx → Amp-1 → Amp-2 → Pl22KVDOZ-33Ol → Opx → Amp → Pl
9KVDOZ-19Ol (Opx) → Amp23KVDOZ-33Ol → Opx → Mca
10KVDOZ-20Opx → Amp + Pl24KVDOZ-34Ol → Opx → Amp → Pl
11KVDOZ-21Opx → Amp + Pl → Pl25KVDOZ-36Cpx→ Amp + Pl
12KVDOZ-23Ol → Opx + Amp → Pl26KVDOZ-37Opx + Amp-1 → Amp-2 → Pl → Pl + Qz
(symplectite)
13KVDOZ-25Cpx → Amp-1 → Amp-2 → Pl27KVDOZ-37Opx → Mca + Amp
14KVDOZ-26Opx → Amp-1 → Amp-2 → Pl
Note. The following symbols are used: Ol olivine, Opx orthopyroxene, Cpx calcic pyroxene, Srp serpentine-group mineral, Amp calcic amphibole, Pl plagioclase, Mca mica (phlogopite—annite series), and Qz quartz. See Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12 for details.
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Barkov, A.Y.; Martin, R.F.; Barkova, L.P.; Korolyuk, V.N. Coronitic Associations at Gabrish in the Kovdozero Layered Complex in the Southern Part of the Lapland—Belomorian Belt, Kola Peninsula, Russia. Minerals 2025, 15, 565. https://doi.org/10.3390/min15060565

AMA Style

Barkov AY, Martin RF, Barkova LP, Korolyuk VN. Coronitic Associations at Gabrish in the Kovdozero Layered Complex in the Southern Part of the Lapland—Belomorian Belt, Kola Peninsula, Russia. Minerals. 2025; 15(6):565. https://doi.org/10.3390/min15060565

Chicago/Turabian Style

Barkov, Andrei Y., Robert F. Martin, Larisa P. Barkova, and Vladimir N. Korolyuk. 2025. "Coronitic Associations at Gabrish in the Kovdozero Layered Complex in the Southern Part of the Lapland—Belomorian Belt, Kola Peninsula, Russia" Minerals 15, no. 6: 565. https://doi.org/10.3390/min15060565

APA Style

Barkov, A. Y., Martin, R. F., Barkova, L. P., & Korolyuk, V. N. (2025). Coronitic Associations at Gabrish in the Kovdozero Layered Complex in the Southern Part of the Lapland—Belomorian Belt, Kola Peninsula, Russia. Minerals, 15(6), 565. https://doi.org/10.3390/min15060565

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