Geological characteristics of the Sokli carbonatite complex, Finland

Vartiainen, H.; Paarma, Heikki

doi:10.2113/gsecongeo.74.5.1296

Cited by 47 publications

(31 citation statements)

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“…Examples include Sokli (Vartiainen and Woolley, 1976;Notholt, 1979); Fen (Verschure and Maijer, 2005); Kangankunde and Chilwa Island, Malawi (Woolley, 1969); Homa Mountain, Kenya (Clarke and Roberts, 1986); Dicker Willem, Namibia (Reid and Cooper, 1992); Toror Hills, Uganda (Sutherland, 1965b) and Okorusu, Namibia (Bhn et al, 2002). The brecciated transition zone between fenite and carbonatite at Sokli is highlighted by a reduction in gravity and low seismic velocities on geophysical surveys (Vartiainen and Paarma, 1979).…”

Section: Brecciasmentioning

confidence: 99%

Fenites associated with carbonatite complexes: A review

Elliott

Wall

Chakhmouradian

et al. 2018

Ore Geology Reviews

161

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A B S T R A C TCarbonatites and alkaline-silicate rocks are the most important sources of rare earth elements (REE) and niobium (Nb), both of which are metals imperative to technological advancement and associated with high risks of supply interruption. Cooling and crystallizing carbonatitic and alkaline melts expel multiple pulses of alkali-rich aqueous fluids which metasomatize the surrounding country rocks, forming fenites during a process called fenitization. These alkalis and volatiles are original constituents of the magma that are not recorded in the carbonatite rock, and therefore fenites should not be dismissed during the description of a carbonatite system. This paper reviews the existing literature, focusing on 17 worldwide carbonatite complexes whose attributes are used to discuss the main features and processes of fenitization. Although many attempts have been made in the literature to categorize and name fenites, it is recommended that the IUGS metamorphic nomenclature be used to describe predominant mineralogy and textures. Complexing anions greatly enhance the solubility of REE and Nb in these fenitizing fluids, mobilizing them into the surrounding country rock, and precipitating REE-and Nb-enriched micro-mineral assemblages. As such, fenites have significant potential to be used as an exploration tool to find mineralized intrusions in a similar way alteration patterns are used in other ore systems, such as porphyry copper deposits. Strong trends have been identified between the presence of more complex veining textures, mineralogy and brecciation in fenites with intermediate stage Nb-enriched and later stage REE-enriched magmas. However, compiling this evidence has also highlighted large gaps in the literature relating to fenitization. These need to be addressed before fenite can be used as a comprehensive and effective exploration tool.

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Section: Brecciasmentioning

confidence: 99%

Fenites associated with carbonatite complexes: A review

Elliott

Wall

Chakhmouradian

et al. 2018

Ore Geology Reviews

161

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“…2), while the alkaline complexes of Sokli (Finland), Kovdor, Kandagubskiy and Turiy Mys form an E-Wtrending belt spatially associated with the Kandalaksha deep fracture zone, an older structure initiated in the Neoproterozoic ( Fig. 3; Vartiainen & Paarma, 1979). Igneous activity may have started as early as 460 Ma and large alkaline lava xenoliths at Lovozero and Kontozero record an early phase of volcanic activity at ~404 Ma before the injection of the large alkaline intrusions at 380-360 Ma ( Arzamastsev et al, 2010( Arzamastsev et al, , 2013.…”

Section: 'K' -Devonian Lavas 'L' -Phanerozoic Dykes 'M' -Phoscoritementioning

confidence: 99%

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Hall¹

2015

NJG

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Contrasting views exist on the stability of the Earth's shield regions over the last 1 Ga that have major implications for reconstructing erosion patterns on shields and the supply of sediment to intra-cratonic and marginal basins. This paper explores Phanerozoic denudation rates and patterns on the northern part of the Fennoscandian Shield in the Kola Peninsula, Northwest Russia. This shield region was intruded by magmatic rocks of the Kola Alkaline Province (KAP) in the Devonian and Early Carboniferous. The KAP comprises a varied suite of alkali-ultramafic plutonic and hypabyssal intrusions, diatremes and dykes that was emplaced at various depths in the crust and allows assessment of depths and rates of erosion during and since the KAP magmatic episode. Further evidence of long-term denudation is provided by Mesoproterozoic and Neoproterozoic cover rocks found around the margins of the Kola Peninsula and in the White Sea. The burial and exhumation history is compared to available Apatite Fission Track (AFT) data for the Kola Peninsula and adjacent areas. Post-Devonian denudation rates on the shield rocks of the Kola Peninsula have varied in space and time. Around the periphery of the Kola Peninsula, low long-term denudation of shield rocks is indicated by the survival of Riphean cover rocks and Late Devonian lavas, kimberlite crater facies and near-surface emplacement of dykes. In contrast, in the main belts of KAP intrusions, 4-6 km of rock was removed in response to doming between 460 and 360 Ma. Deep denudation is indicated by the emplacement depths of alkaline intrusions and Phoscorite-Carbonatite pipes (PCPs). Erosion on the Kola Peninsula since 360 Ma has been far more limited. Extensive, shallow, late-stage magmatism associated with PCPs, dykes and the large alkaline intrusions in the KAP indicates that erosion depths nowhere exceeded 2 km. PostDevonian denudation has removed <1 km of rock from the margins of the Kola Peninsula and from the backslope of the Saariselkä-Karelia scarp in northern Finland. AFT data point to an important phase of erosion in the early Mesozoic but depths of unroofing of 3-5 km based on AFT cooling ages for this later phase are in conflict with the evidence of lesser erosion provided by the late-stage KAP intrusions and also require unrealistic depths of former Devonian to Triassic cover rocks. Mean denudation rates were greatest (up to 40 m/Myr) during the KAP magmatic phase. Post-Devonian rates across the Kola Peninsula and adjacent shield areas were much lower (<3-6 m/Myr) and are compatible with low long-term denudation rates for other cratons. Further resolution of long-term denudation patterns and rates on the Kola Peninsula requires the application of low-temperature thermochronometry, detailed examination of the regional geomorphology and firmer dating of ancient weathering episodes.

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“…Inset; Map of the Kola Alkaline Province (after Bell et al, 1996). trenching with detailed geophysical investigations (Vartiainen and Paarma, 1979;Vartiainen, 1980;Lee et al, 2004). The overall outline of the complex is a vertical pipe with about 6.4 km in diameter on the surface level and walls steeply dipping inward.…”

Section: General Geology and Petrographymentioning

confidence: 99%

Pyrochlore chemistry from the Sokli phoscorite-carbonatite complex, Finland: Implications for the genesis of phoscorite and carbonatite association

Lee

García

et al. 2006

Geochem. J.

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The phoscorite-carbonatite complex in the Sokli alkaline-carbonatite massif, northern Finland, comprises five stages of intrusions of phoscorites and carbonatites (P1-C1, P2-C2 and P3-C3 for phoscorites and calcite carbonatites; D4 and D5 for dolomite carbonatites). The phoscorites and calcite carbonatites at Sokli usually occur as pairs with the same mineral assemblages. Pyrochlore is found in the majority of rock types in the Sokli phoscorite-carbonatite complex, shows wide compositional variation and seems to preserve evolution trends of host rocks. Crystallization of pyrochlore begins from the P2-C2 phoscorite and calcite carbonatite and continues up to the latest D5 dolomite carbonatite. Pyrochlore in the early stage P2-C2 rocks has high U and Ta contents. These elements suddenly decrease from the P3-C3 rocks, on the other hand, Th and Ce contents increase. The compositions of the late generations from the D4 and D5 rocks are close to that of an ideal end-member pyrochlore with formula (Ca,Na) 2 Nb 2 O 6 F. The Nb/Ta ratio and F content of pyrochlore increase from P2-C2 to the latest D5 dolomite carbonatite. The composition and evolutionary history of pyrochlore from the phoscorites are distinguished from those of the associated calcite carbonatites. Pyrochlore from the calcite carbonatites shows larger A-cation deficiencies compared to those from the paired phoscorites. Ta and Zr contents are slightly higher in pyrochlore from the calcite carbonatites, whereas Ti is generally higher in pyrochlore from the associated phoscorites. Moreover, pyrochlore from the phoscorites always shows a longer and more complex crystallization history compared to that of the same stage carbonatites. This indicates that the chemical condition was clearly different in the two systems during the crystallization of pyrochlore. Based on these results, together with the previous mineralogical and geochemical studies on the Sokli phoscorite-carbonatite complex, we propose a liquid immiscibility process as the most possible segregation mechanism of the two associated rocks. The composition of pyrochlore in the late dolomite carbonatites is distinct and always lies on the evolutional trend of the earlier varieties. This implies that the dolomite carbonatites are the final magmatic products of the Sokli phoscorite-carbonatite system. Keywords: pyrochlore, phoscorite, carbonatite, Sokli, liquid immiscibility diopside (±phlogopite or tetraferriphlogopite). Phoscorites and the paired carbonatites generally show an extremely intricate association (at the meter scale) and share the same mineral assemblages which evolve from stage to stage.Genetic relationships between alkali silicate rocks and associated carbonatites have been examined in detail through previous experimental and isotopic studies. They show that carbonatites can originate from parental carbonated silicate melts by crystal fractionation or carbonate-silicate immiscibility (e.g., Lee and Wyllie, 1998 and references therein), and can also be generated from direct partial meltin...

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Geological characteristics of the Sokli carbonatite complex, Finland

Cited by 47 publications

References 0 publications

Fenites associated with carbonatite complexes: A review

Fenites associated with carbonatite complexes: A review

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Pyrochlore chemistry from the Sokli phoscorite-carbonatite complex, Finland: Implications for the genesis of phoscorite and carbonatite association

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