Britholite-group minerals as sensitive indicators of changing fluid composition during pegmatite formation: evidence from the Keivy alkaline province,Kola peninsula,NW Russia

Mineralogy and Petrology - The Keivy alkaline province, Kola Peninsula, NW Russia, consists of vast alkali granite massifs and several dike-like nepheline syenite bodies. It contains numerous...     

Native elements in rocks of the banded iron formation,Kola Peninsula

Eleven native minerals and intermetallic alloys were identified in rocks of the banded iron formation (BIF) in the Kola Peninsula: copper, silver, gold, electrum, auricupride, cuproauride, tetraauricupride, bismuth, sulfur, tellurium, and graphite. Graphite is a common mineral of sulfide-bearing BIF and gneiss. Sulfur occurs in supergene-altered sulfide-bearing BIFs together with Fe- and Ca-sulfates. Gold of low fineness (electrum) in association with electrum, acanthite, auricupride, volynskite, hessite, cervelleite, pavonite, petzite, and bismuth is related to the areas of hydrothermally altered skarnoids with greenalite, chamosite, aegirine, and Na-Ca amphibole. Redeposited gold of high fineness associated with auricupride, hessite, silver, electrum, kostovite, cuproauride, tetraauricupride, and sperrylite occurs in low-temperature zonal hydrothermal segregations hosted in aluminous gneiss and which formed under the effect of alkalized, highly siliceous solutions at the regressive stage of BIF metamorphism.     

Stages of the lower crust formation of the Belomorian mobile belt,Kola Peninsula

Doklady Earth Sciences -     

The formation conditions of labuntsovite-group minerals in the Kovdor massif,Kola Peninsula

In the Kovdor massif, labuntsovite-group minerals occur in dolomite carbonatite veins (labuntsovite-Mg), in a natrolite-calcite vein (lemmleinite-Ba and labuntsovite-Fe), and in calcite pockets and veinlets cutting fenites (late labuntsovite-Mg). They are closely intergrown with paragenetic carbonates, and this makes it possible to estimate their crystallization temperature from the fluid inclusions entrapped in dolomite (≥265°C) and calcite (175–225°C). The earlier labuntsovite-Mg was formed under relatively acidic conditions, whereas later labuntsovite-calcite mineralization was derived from alkaline solutions.     

Dolomite-calcite textures in early carbonatites of the Kovdor ore deposit,Kola peninsula,Russia: their genesis and application for calcite-dolomite geothermometry

In early calcite carbonatites of the Kovdor ore deposit four morphological types of dolomite are represented. In the first type, dolomite microcrystals occur as lamellae enclosed by optically continuous calcite. In the second, dolomite microcrystals occur as segmented rods, plates and xenomorphic grains, enclosed by optically discontinuous calcite, and in the third, dolomite is represented by grains of various morphologies, situated along calcite grain boundaries. The fourth type of dolomite occurs as a fine-grained aggregate, which develops along grain boundaries and cleavage cracks of calcite. From microscopic, scanning electron microscope and microprobe studies of these different types of dolomite microcrystals, as well as the calcite associated with them, it can be concluded that the first type of dolomite was exsolved from magnesian calcite during cooling. The second, and the third types of dolomite microcrystals were formed by recrystallization. The fourth type of dolomite was formed by metasomatic dolomitization. As the result of these two processes-recrystallization and metasomatic dolomitization-early dolomite microcrystals seldom occur. The composition of the early-formed primary magnesian calcite yielded temperatures of exsolution of dolomite from magnesian calcite between 665 and 700°C.     

Duration of the formation and sources of the granitoids of the Litsk-Araguba Complex, Kola Peninsula

Postorogenic granitoids of the Litsk-Araguba Complex compose a chain of intrusive bodies around 850 km² in area, which are confined to the NE-trending deep-seated fault zone. Results of U-Pb zircon dating indicate that the formation of granitoids of the Litsk-Araguba Complex lasted 28 ± 9 Ma. Note that the rocks of the first-fourth phases have similar age within (1774–1762 Ma), while quartz syenites of the fifth phase were formed much later (1746 ± 8 Ma). The study of Sm-Nd isotopic system revealed that the quartz syenites plot in the field of the Nd isotopic evolution of the lower crust represented mainly by the Paleoproterozoic garnet granulites with model ages T_Nd(DM) = 2.4–2.7 Ga and ?_Nd(T) from ?5.6 to ?6.3. It was found that the near-contact syenites of the Litsk Massif contain composite zircons with an age of 1758 ± 9Ma. They differ from zircons in coeval porphyraceous granites in lowered U and Th concentrations, which are close to those in zircons from the lower crustal garnet granulites of this region. These data in combination with internal structure of the crystals determine xenogenic lower-crustal origin of zircons from syenites and confirm geochemical data on the lower crustal input in the formation of granitoid melts.     

Die Halbinsel Kola

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Structural and compositional zoning and formation conditions of the Greater Eastern Litsa BIF occurrence, Kola Peninsula

New geological and geochronological data on the Greater Eastern Litsa banded iron formation (BIF) occurrence demonstrate its similarity to the BIF of the Olenegorsk iron district in geology (lenticular orebodies with exponential distribution of their sizes), age (2.8 Ga), and typical structural and compositional zoning of orebodies. The temperature of ore formation (600–780°C) and BIF composition depend on the intensity of folding expressed in the fractal dimension D = 1.0–1.3 of a single layer. All BIF deposits of the Kola-Norwegian Megablock, including the Greater Eastern Litsa occurrence pertain to the one system. Variation m their composition is controlled by the size of orebodies (capacity of oxygen buffer) and the energy of metamorphic reactions, which strongly depend on the intensity of folding.     

Sources of terrigenous material in formation of metasedimentary rocks of the archean complex cored by the Kola superdeep borehole

The basement of the Paleoproterozoic Pechenga structure was cored by the Kola superdeep borehole SD-3 at the depths of 6842–12 262 m. It consists mainly of alternating strata of metavolcanic daciteplagiorhyodacite rocks and high-alumina gneisses; the protoliths of these rocks corresponded to siltstones, graywackes, arkoses, polymictic sandstones, and silt-pelitic and pelitic argillites. Resulting from the examination of zircons from metaterrigenous rocks of the 1st, 3rd, and 9th strata of the SD-3, the detrital, anatectic, metamorphogenic, and contact-metasomatic genetic types have been identified. Detrital zircons include several age groups. The most homogeneous, i.e., comparable to zircons from tonalite gneisses (bottoms of the SD-3 section) and from analogous rocks from surrounding rocks, zircons have appeared to be those from gneisses of the deepest 9th stratum. The data on the age of these zircons, along with a poor rounding of the grains, signifies formation of the host gneisses’ protoliths owing to washing-out and redeposition of material. Widening of alimentation areas, which supplied terrigenous material into sedimentation basins, took place during formation of alumina gneisses of the 3rd and especially 1st strata of the section. Detrital zircons of the 1st stratum are characterized by a good rounding of crystals and a broad age spectrum (from 2.79 to >3.1 Ga). By composition, they are close to zircons from Neoarchean tonalite gneisses of the SD-3 borehole and its surroundings, and gneisses of the Kola Series; however, they differ from zircons of the most ancient granitoids from the north of the Baltic Shield by the higher content of common lead.     

Paleomagnetism of the Istria peninsula, Yugoslavia

280 core samples were collected from Upper Jurassic, Cretaceous and Eocene sediments outcropping in the Istria peninsula (Yugoslavia). Due to the very low intensities of the initial natural remanent magnetizations, more than 50% of the collection, consisting mainly of rock samples of Jurassic and Eocene sediments, was not suitable for paleomagnetic studies.The Cretaceous samples yield a mean paleomagnetic pole (lat. 53°, long. 275° and α₉₅ = 4.8°), which is significantly different from the African and European paleomagnetic poles of the same age. The position of the Istria peninsula on the autochthonous Adriatic platform allows the result to be interpreted as applicable to all the autochthonous Periadriatic region. This new paleomagnetic result indicates that the autochthonous Adriatic platform rotated counterclockwise over an angle of about 30° with respect to Africa in post-Mesozoic times.     

Upper-mantle structure under the Arabian peninsula

The phase velocity of Rayleigh waves across the Arabian Peninsula has been measured for profiles SHI-HLW, JER-SHI in the northern part and SHI-AAE in the southern part of the peninsula. The phase velocities for the Arabian stable shelf are lower than those for the Canadian shield and higher than those for the Gulf coastal plain of the United States. Shear-velocity models obtained from the inversion of these experimental data show a pronounced low-velocity channel for S-waves which is found throughout the region with a velocity of S in the channel of 4.25–4.45 km/sec. The top of the channel is at 100–140 km depth. This structure differs from those under the Canadian shield and the Gulf Coast. Crustal thickness is 35 ± 8 km.