Archean Pon’goma-Navolok Granulite-Charnockite-Enderbite Complex, Northern Karelia: Geological Structure, Composition, and Parameters of Formation

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Abstract

The paper presents original detailed data on the Archean Pon'goma-Navolok granulite and charnockite massif in northern Karelia: a geological map of the massif and its surroundings, data on the petrography of the magmatic and metamorphic rocks, and the P–T parameters evaluated for major rock types by the techniques of multimineral thermomabometry and pseudosections. The Pon'goma-Navolok massif is determined to have been formed in two intrusive phases at different crustal levels. The first intrusive phase corresponds to the massif of clinopyroxene–orthopyroxene charnoenderbites that crystallized at 8–11.2 kbar and 730–740°C. The second phase is dikes of orthopyroxene–biotite charnockites, which were formed at 5.6–6.8 kbar and 830–850°C, and biotite granites, which crystallized at 6.8–7.0 kbar and 730–740°C. The dikes are most likely different temperature and water-activity facies. The charnockites and granites were formed by processes of charnockitization and granitization of the charnoenderbites under the effect of saline aqueous solutions. The granulite-facies metamorphic of the metabasite blocks hosted in the charnoenderbite intrusion was of contact nature and was induced by the thermal effect of the charnoenderbites on the roof and wall rocks of the magma chamber. The high metamorphic temperatures of the metabasites (>900oC) and the absence of migmatization aureoles are explained by low water contents in the enderbites.

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V. M. Kozlovskii

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences; Sergo Ordzhonikidze Russian State University for Geological Prospecting

Author for correspondence.
Email: bazily.koz@gmail.com
Russian Federation, Moscow; Moscow

E. B. Kurdyukov

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, Moscow

M. V. Strel'nikov

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, Moscow

V. V. Travin

Institute of 'Geology, Karelian Research Center

Email: bazily.koz@gmail.com
Russian Federation, Petrozavodsk

T. F. Zinger

Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, St. Petersburg

M. A. Golunova

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences; Korzhinskii Institute of Experimental Mineralogy, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, Moscow; Chernogolovka, Moscow district

I. S. Volkov

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, Moscow

S. A. Ushakova

Korzhinskii Institute of Experimental Mineralogy, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, Chernogolovka, Moscow district

V. I. Taskaev

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, Moscow

A. I. Yakushev

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

Email: bazily.koz@gmail.com
Russian Federation, Moscow

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2. Fig. 1. (a) Scheme of tectonic zoning of the Fennoscandian Shield (Slabunov, 2008) indicating the position of the Pongoma-Navolok massif. (b) Geological map of the Pongoma-Navolok granulite and charnockitoid massif and its metamorphic framework (according to the authors' data in 2017–2020 and updated in 2022). 1–3 – charnoenderbites: 1 – homogeneous, mainly massive, mesocratic; 2 – mesocratic and leucocratic gneissic; 3 – lenses of melanocratic charnoenderbites in mesocratic gneissic charnoenderbites; 4, 5 – metadiorites: 4 – massive homogeneous, 5 – gneissic; 6 – granitization zones and homogeneous coarse-grained plagiomicrocline granites; 7 – plagiomicrocline ceramic pegmatites, presumably of Paleoproterozoic age; 8 – metamorphosed dikes of the lherzolite-gabbronorite complex: a – small dikes outside scale, b – boudinage fragments of dikes in steeply dipping zones of plastic flow; 9 – metamorphosed dikes of ferruginous tholeiites: a – small dikes outside scale, b – large dikes within scale, c – boudinage fragments of dikes in steeply dipping zones of plastic flow; 10 – dikes of pegmatoid charnockites (out of scale); 11 – dikes of fine- to medium-grained charnockites (out of scale); 12 – dikes of leucocratic aplite-like plagiogranites (out of scale); 13 – Grt-Bt-Amph and Ep-Вt-Amph plagiomigmatized orthogneisses; 14 – Grt-Bt and Ky-Grt-Bt aluminous paragneisses; 15–17 – metabasites of different petrographic composition (banded amphibolites, apoamphibolite Cpx-(Opx)-Pl granulites, apoamphibolite Grt-Cpx-Pl eclogite-like rocks): 15 – unfragmented bodies of plate-like shape with characteristic metamorphic banding, 16 – subconcordant lenses in paragneisses, homogeneous with linear texture, 17 – zones of development of fragmented bodies of metabasites of different composition and texture (a – occurring as lenses in orthogneisses, as well as as remnants and small xenoliths in charnoenderbites and metadiorites, b – occurring as lenses in paragneisses); 18 – small zones of degneissification and blastomylonitization (out of scale); 19 – metamorphic veinlets of eclogite-like rocks of Grt-Cpx-Pl composition in metabasites (out of scale); 20 – geological boundaries: a – traced in outcrops, b – inferred; 21 – inferred boundaries: a – charnoenderbite intrusions of the first phase of the Pongoma-Navolok massif formation and metadiorite intrusions, b – gneissic rocks in steeply dipping zones of plastic deformations; 22 – orientation of planar textures: a – gneissosity and banding of rocks outside plastic flow zones (inclined and vertical), b – gneissosity and foliation of rocks in steeply dipping plastic flow zones (inclined and vertical); 23 – orientation of aggregate lineation in homogeneous charnoenderbites; 24 – geological domains with different structural-metamorphic history: I – zones of plastic flow and intense high-pressure metamorphism (Ia – north-eastern striking, Ib – sublatitudinal striking), II – rigid blocks of weakly deformed rocks with limited manifestation of high-pressure metamorphism (IIa – massif of Paleoproterozoic metadiorites (2.415 Ga), IIb – massif of charnoenderbites, charnockites, granites and basic granulites of Pongoma-Navolok (2.728 Ga) according to (Levchenkov et al., 1996). Inset (a): BMB – Belomorian mobile belt, KK – Karelian craton, MK – Murmansk craton, KP – Kola province, Nb – Norrbotten province, SP – Svecofennian province, KO – regions of the Caledonian orogeny, Pl – platform cover, Ko – Kolvitsa mélange zone, Up – Umbina granulite zone, Lp – Lapland granulite belt.

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3. Fig. 2. Geological relationships of different-aged intrusive rocks that make up the Pongoma-Navolok massif and its framing. (a) – charnoenderbite xenoliths (1) in metadiorites (2). (b) – apophysis of metadiorites (2) in charnoenderbites (1). Both metadiorites and charnoenderbites contain amphibolite xenoliths (3), however, the elongation of xenoliths and planar textures in them are oriented along different directions, which indicates different directions of material flow. (c) – veinlets of leucocratic charnoenderbites (4) form a branched network and are localized along cracks in mesocratic charnoenderbites of the main intrusive phase (1). (g) – pegmatoid charnockite dikes (5) cut the charnoenderbite massif (1); fine-medium-grained charnockite dikes (6) cut both the charnoenderbite massif (1) and the pegmatoid charnockite dikes (5). The marginal part of the fine-medium-grained charnockite dike has a pegmatoid structure. (a, b, d) – horizontal outcrops, (c) – inclined.

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4. Fig. 3. Geological relationships between charnoenderbites, metabasites, and garnet metagabbros. (a) – split fragments of amphibolites (1) in charnoenderbites (2). (b) – layered vein injections of charnoenderbites (2) along cracks in the amphibolite plate (1). (c) – igneous breccia formed in the bend zone of a large metabasite plate: disoriented fragments of apoamphibolite granulites (3) are cemented by charnoenderbite material (2). (d) – remobilized vein material of charnoenderbites (2) fills cracks in the contact zone of garnet metagabbros dikes (4). (a–d) – horizontal outcrops.

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5. Fig. 4. Geological map of the eastern segment of Pongoma-Navolok Island. 1 – Homogeneous mesocratic Cpx-Opx-charnoenderbites: a – massive, b – gneissic. 2 – metabasite remnants composed of amphibolites, Cpx-Opx-Pl apoamphibolite granulites and Grt-Cpx-Pl eclogite-like rocks. 3 – zones of lensed and boudinaged metabasite remnants among charnoenderbites. 4 – individual lenses and boudins of metabasites. 5 – large dikes of garnet metagabbros (ferruginous tholeiites) (to scale of the map). 6 – small dikes of garnet metagabbros (ferruginous tholeiites) (out of scale). 7 – small bodies of homogeneous coarse-grained Bt-granites. 8 – granitization (K-feldspathization) zones in charnoenderbites. 9 – veins of leucocratic pegmatoid and coarse-grained Cpx-Opx charnoenderbites (out of scale). 10 – veins and dikes of pegmatoid, coarse-, medium-, and fine-grained homogeneous granitoids of indeterminate composition (out of scale). 11 – veins and dikes of pegmatoid, coarse-, medium-, and fine-grained homogeneous Bt granites (out of scale). 12 – veins and dikes of pegmatoid and fine-crystalline Bt-Opx charnockites (out of scale). 13 – small zones of ductile flow (out of scale). 14 – metamorphic veinlets of Grt-Cpx-Pl composition in amphibolites (out of scale). 15 – elements of occurrence of metamorphic layering in metabasites or gneissicity in gneissified charnoenderbites. 16 – geological boundaries: a – reliable, b – assumed.

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6. Fig. 5. Geological manifestation of Paleoproterozoic metamorphism in the rocks of the Pongoma-Navolok massif and the surrounding rocks. (a) – shear and K-feldspathization zone (1) in metadiorites (2) and charnoenderbite xenolith in metadiorites (3). (b) – shear and K-feldspathization zone (1) crosscuts the charnoenderbite massif (3) and veins of pegmatoid charnockites (4). (c) – areas of spotted texture in the garnet metagabbro dike caused by glomeroporphyritic garnet aggregates (5); (6) – concentration of garnet segregations along cleavage cracks. (g) – amphibolites with primary metamorphic banding (7) are cut by a series of thin subparallel veinlets of Grt-Cpx-Pl eclogite-like rocks (8), oriented according to the north-eastern strike of a powerful zone of plastic flow in domain Ia within the framework of the massif.

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7. Fig. 6. TAS diagram (Sharapenyuk et al., 2013) for the compositions of charnoenderbites, charnockites and biotite granites of the Pongoma-Navolok massif (see text for explanations).

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8. Fig. 7. Modal composition of charnoenderbites, charnockites and granites of the Pongoma-Navolok massif on the diagram by V.M. Shemyakin (1976). Fields on the diagram: 1 - birkremites; 2 - alkali-feldspar charnockites; 3 - charnockites; 4 - charnoenderbites; 5 - enderbites; 6 - syeno-charnockites; 7 - monzocharnockites; 8 - monzoenderbites; 9 - mangeroenderbites. Rock composition points: 1–5 – charnock-enderbites: 1 – mesocratic, 2 – melanocratic, 3 – leucocratic, 4 – gneissic, 5 – charnockitized; 6 – fine- to medium-grained and pegmatoid charnockites; 7 – granites.

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9. Fig. 8. Structural and microstructural features of charnoenderbites from the Pongoma-Navolok massif. (a) – homogeneous hypidiomythic-granular structure of charnoenderbites. Cpx and Opx form short-prismatic grains with jagged uneven boundaries, and Na-K-Ca-Fsp form poorly formed tabular crystals. Pyroxenes contain feldspar inclusions and fill the interstices between its crystals. (b) – relationships between Opx and Cpx-I in charnoenderbites. Cpx-I of the magmatic association is usually less idiomorphic than Opx and sometimes overgrows it. Opx sometimes occurs as isometric inclusions in Cpx-I. The relationships of the minerals indicate that Cpx-I crystallized after Opx. (c) – zoned grain of clinopyroxene. The center of the Cpx-I grain belongs to the magmatic association and contains abundant inclusions of an ore mineral less than 1 μm in size (probably titanomagnetite or ilmenite). The inclusions were apparently formed as a result of the disintegration of the primary more ferruginous and titaniferous clinopyroxene during its cooling. The marginal part of Cpx-II does not contain inclusions; its formation is associated with the process of charnockitization of charnoenderbites. (d) – replacement of Na-K-Ca feldspar by alkali feldspar during charnockitization of charnoenderbites. A relic of Na-K-Ca feldspar is preserved in the core of the alkali feldspar grain in the form of a corroded fragment of irregular shape. (e) – development of the Grt crown between Na-K-Ca-Fsp and Fe-Mg minerals (Cpx, Opx, Ilm, Bt-I) in charnoenderbite from the marginal part of the massif, near the shear and gneiss zones. (e) – development of the Grt + Bt-II + Рl-II metamorphic association along the periphery of Bt-I segregations. Bt-II forms symplectite intergrowths with Рl-II and quartz. Plate crystals of Bt-I (formed in the earlier process of charnockitization) remain in the relics. (g) – retrograde amphibolization affecting the Fe-Mg minerals of charnoenderbite. Newly formed Amph develops as an aggregate of isometric grains around minerals of the magmatic stage and the charnockitization stage − Bt-I, Ilm, Opx. Photo at one nicol. (h) – replacement of orthopyroxene by chlorite during low-temperature epigenetic changes in minerals of charnoenderbites, charnockites and granulites. Photos (a, g) – at two nicols, (b, c, d, f, g, h) – at one nicol.

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10. Fig. 9. Compositions of clino- and orthopyroxenes from charnoenderbites, charnockites, and mafic granulites of the Pongoma-Navolok massif on the En–Fs–Wo diagram (Morimoto et al., 1988).

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11. Fig. 10. Heterogeneous structure of Cpx grains from charnoenderbites of the Pongoma-Navolok massif according to BSE data. (a) – thin parallel Opx lamellae and point inclusions of ore mineral (Ti-Mag or Ilm) in magmatic Cpx-I. (b) – zonal structure of Cpx grains. Magmatic Cpx-I, containing Opx lamellae and inclusions of ore mineral, is surrounded by a rim of Cpx-II along the edges, formed during charnockitization of charnoenderbites. The rim thickness is 10–15 μm.

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12. Fig. 11. Structural and microstructural features of charnockites of the Pongoma-Navolok massif. (a) – heterogeneous structure of charnockites. The uneven-grained structure is formed by large plagioclase crystals (probably relict, preserved from charnoenderbites of the protolith) and K-Na-feldspar metacrystals surrounded by an equigranular allotriamorphic-granular Pl-Kfs-Qz aggregate. (b) – metacrystal of alkali feldspar that replaced plagioclase in charnockite. Preserved relics of plagioclase are visible in the central part. (c) – heterogeneity of the perthitic structure of the alkali feldspar metacrystal from charnockite. The metacrystal core contains long perthite ingrowths, while the perthites in the peripheral part are discontinuous and wavy. (g) – equigranular allotriamorphic-granular structure of the charnockite mineral aggregate. (d) – graphic intergrowths of quartz and alkali feldspar in charnockite, indicating joint crystallization of these minerals. (e) – quartz-plagioclase intergranular symplectites adjacent to a grain of alkali feldspar in charnockite. The presence of intergrowths shown in Figs. (d) and (e) indicates that charnockite probably crystallized from a melt in the region close to the eutectic temperature minimum. Photos (a, b, d, e, e) – at two nicols, (c) – BSE image.

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13. Fig. 12. Structural and microstructural features of biotite granites of the Pongoma-Navolok massif. (a) – irregular-grained structure of biotite granite from the dike phase of the Pongoma-Navolok massif. (b) – regular-grained allotriamorphic-grained structure of homogeneous biotite granite. (c) – large metacrystal of alkali feldspar with preserved relics of plagioclase in an irregular-grained variety of biotite granite. (d) – quartz-potassium feldspar graphic intergrowths in biotite granite. (d) – intergranular quartz-plagioclase symplectite developing along the boundaries of alkali feldspar grains. (e) – garnet crowns around biotite-I and symplectite plagioclase and fine-flaked biotite-II, formed during Paleoproterozoic recrystallization of garnets in areas close to plastic deformation zones in the northwestern framing of the massif. Photos (a, b, c, d, e) – at two nicols, (e) – BSE image.

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14. Fig. 13. Structural and microstructural features of metabasites of the Pongoma-Navolok massif: (a) − equigranular granonematoblastic structure of amphibolites formed by elongated and oriented prismatic grains of amphibole-I and isometric grains of plagioclase-I. (b) − two-pyroxene-plagioclase granulite aggregate with homogeneous equigranular quasi-isotropic (hornfels) structure. Oriented prismatic crystals of amphibole have been preserved only in relics. (c) − fragment of a vein of recrystallized two-pyroxene-plagioclase granulites. Recrystallization is accompanied by coarsening of mineral grains, and plagioclase grains gradually acquire a tabular habit. (g) – nucleation of garnet grains at the contact of clinopyroxene and plagioclase. (d) – glomeroporphyritic intergrowth of garnet grains surrounded by clinopyroxene-II and plagioclase from the alteration zones of two-pyroxene-plagioclase granulites. (e) – enlarged fragment of Fig. (b). Two generations of amphibole in basic granulites. Amph-I – relict, forms oriented prismatic grains, Amph-II – late, forms isometric grains around ore minerals and Fe-Mg-silicates at the retrograde stage of metamorphism. Photos (a, b, c, e) – at one nicol, (g, d) – BSE image.

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15. Fig. 14. Morphology of fluid inclusions in quartz from pegmatoid charnockites, samples PNG-56, PNG-128 (a, b), and granite, sample PNG-95-1 (c, d). (a) – pseudo-secondary carbon dioxide inclusions, sample PNG-56; (b) – pseudo-secondary water-salt inclusions, sample PNG-128; (c) – isolated primary carbon dioxide inclusions, sample PNG-95-1; (d) – primary-secondary water-salt inclusions, sample PNG-95-1. Carbon dioxide inclusions (a) and (c) usually have the form of negative quartz; water-salt inclusions (b) and (d) are mainly localized along closed fractures.

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16. Fig. 15. P–T pseudosection for two-pyroxene charnoenderbite, sample PNG-58. Orange field is the area of ​​probable charnoenderbite crystallization. The field is contoured based on the intersection of mineral isopleths (see text for details). Yellow dotted rectangular contour corresponds to P–T parameters of the peak metamorphism of the main two-pyroxene granulites in sample PNG-132. Numbers designate the stability fields of mineral associations: 1 − melt(G) Gt(W) feldspar Cpx(HP) mic q ru H2O; 2 − melt(G) Gt(W) feldspar IlHm(A) Cpx(HP) q ru; 3 − melt(G) Gt(W) feldspar IlHm(A) Cpx(HP) q; 4 − Gt(W) feldspar IlHm(A) Cpx(HP) mic q ru H2O; 5 − Gt(W) Opx(W) feldspar IlHm(A) Cpx(HP) mic q ru H2O; 6 − Gt(W) feldspar IlHm(A) Cpx(HP) Amph(DHP) mic q ru H2O; 7 − melt(G) Gt(W) Opx(W) feldspar IlHm(A) Cpx(HP) mic q H2O; 8 − Gt(W) Opx(W) feldspar IlHm(A) Cpx(HP) Amph(DHP) mic q H2O; 9 − Gt(W) feldspar Mt(W) IlHm(A) Cpx(HP) Amph(DHP) mic q H2O; 10 − Gt(W) Opx(W) feldspar Mt(W) IlHm(A) Cpx(HP) mic q H2O; 11 − Gt(W) Opx(W) feldspar Mt(W) IlHm(A) Cpx(HP) Amph(DHP) mic q H2O; 12 − Gt(W) feldspar Mt(W) IlHm(A) Amph(DHP) mic q H2O; 13 − Gt(W) Opx(W) feldspar Mt(W) IlHm(A) Amph(DHP) mic q H2O; 14 − Opx(W) feldspar Mt(W) IlHm(A) Amph(DHP) mic q H2O; 15 − melt(G) Opx(W) feldspar IlHm(A) Cpx(HP) q H2O; 16 − melt(G) Opx(W) feldspar Mt(W) IlHm(A) Cpx(HP) q H2O. Isolines: f(Cpx) – clinopyroxene iron index, f(Оpx) – orthopyroxene iron index, An – anorthite fraction in plagioclase, V(melt) – melt volume, ρ(melt) – melt density, H2O(melt) – melt water content.

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17. Fig. 16. P–T pseudosection for charnockite, sample PNG-113. The orange field is the area of ​​probable charnockite crystallization. The field is contoured based on the intersection of mineral isopleths (see text for details). The yellow dotted rectangular contour corresponds to the P–T parameters of recrystallized coarse-grained basic granulites formed in cracks. For isoline designations, see Fig. 15.

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18. Fig. 17. P–T pseudosection for granites, sample PNG-281. Orange field – area of ​​probable granite crystallization. The field is contoured based on the intersection of An isopleths in plagioclase and isochores of primary and primary-secondary CO2 inclusions (see text for details). For contour designations, see Fig. 15.

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19. Fig. 18. T–logаH2O pseudosection constructed for charnockites (sample PNG-113) and reflecting the relationship of these intensive parameters in the charnoenderbite–charnockite–granite series of rocks (see text for explanation).

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20. Fig. 19. Estimates of P–T metamorphic conditions for various mineral associations of metabasites of the Pongoma-Navolok massif using the TWEEQU method (Berman, 1991). The lines of monovariant equilibria are constructed on the compositions of coexisting minerals from the amphibolite domain in granulites (sample PNG-132, green lines), from the two-pyroxene-plagioclase association of the peak of granulite metamorphism (sample PNG-132, red lines), from coarse-grained recrystallized veins of granulites (sample PNG-133, blue lines). Rectangles outline the P–T intervals obtained from the entire set of analyzes.

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21. Fig. 20. Scheme of the formation of the Pongoma-Navolok massif at three depth levels (see the text for explanations). P–T estimates of the melt generation area are taken from (Kozlovsky et al., 2023). The boundaries of metamorphic facies are drawn according to (Bushmin, Glebovitsky, 2008).

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22. Chemical and modal composition of granitoids of the granulite-charnockitoid massif of the Pongoma-Navolok
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23. Results of microprobe determinations of the compositions of rock-forming minerals (wt.%) from the rocks of the granulite-charnockitoid massif Pongoma-Navolok and their recalculation into crystallochemical formulas: ESM_1 – orthopyroxenes, ESM_2 – clinopyroxenes, ESM_3 – biotites, ESM_4 – amphiboles, ESM_5 – garnets, ESM_6 – plagioclases and Na-K-feldspars
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