Volcanic activity at Mt. Karacadağ, SE Turkey, developed between ∼11 and ∼0.01 Ma. In this paper we investigate the oldest products (older than 2.6 Ma) that created a large volcanic plateau and a N-S aligned volcanic edifice in the form of a shield volcano. These igneous rocks are mildly alkaline to transitional olivine-clinopyroxene phyric basalts with minor hawaiites, basanites and very rare differentiated lithologies (mugearites and benmoreites). The poor correlation of major elements with MgO in these lavas is qualitatively consistent with polybaric depths of magma production, variable degrees of partial melting (from ∼2 to ∼10 %), heterogeneous mantle sources and differences in the fractionating crystal assemblage. Primitive mantle-normalized patterns resemble typical anorogenic magma compositions, with peaks at HFSE (Nb, Ta, Hf, Zr) and high HFSE/LILE ratios. REE contents are compatible with derivation of the basanites from a mixed garnet-spinel facies peridotite after ∼2 % partial melting. Alkali basalts are compatible with higher degrees of melting (between 5 and 10 %) from the same type of source. Initial ⁸⁷Sr/⁸⁶Sr ratios range from 0.70349 to 0.70522 while those of ¹⁴³Nd/¹⁴⁴Nd range from 0.512853 to 0.512659. Early-stage lavas show higher ⁸⁷Sr/⁸⁶Sr and lower ¹⁴³Nd/¹⁴⁴Nd compared to plateau-stage lavas. The Sr-Nd isotopic variations and their relation with major and trace elements cannot be explained by AFC-like (Assimilation and Fractional Crystallization) processes involving average crustal lithologies. More likely, the Sr-Nd isotopic ratios are related to the existence of heterogeneous mantle sources with only minor involvement of AFC-like processes. The Cenozoic lavas in a 200 × 800 km area between the Karasu Valley and the Syria-Iraq-Turkey border in south-eastern Anatolia form a distinct igneous province which can be characterised on the basis of Sr-isotope signatures. The lithospheric mantle beneath this area is characterized by anomalously enriched ⁸⁷Sr/⁸⁶Sr compositions (up to 0.7055) as well as more isotopically depleted compositions (⁸⁷Sr/⁸⁶Sr down to 0.7030).

The Early Paleoproterozoic Monchegorsk Complex comprises two independent large layered mafic-ultramafic intrusions: the Monchegorsk pluton and the Main Range massif formed about 2.50 and 2.46 Ga ago, respectively. They are composed of similar cumulates, though they differ somewhat in the isotopic parameters of rocks, cumulate stratigraphy and derived from siliceous high-Mg series melts that arose in the same large long-living volcanic center. The economic syngenetic Ni-Cu-PGE sulfide mineralization related to the earlier Monchegorsk pluton is represented by two types of ores. The first type, pertaining to fractionation of the primary melt, is opposite to the reef formed due to injection of a special ore-bearing melt into the solidifying intrusive chamber. The primary magmatic mineralization is largely composed of Ni-Fe-Cu sulfides and Pd-Pt sulfides, bismuthides, and tellurides. Only small PGE and probably chromite occurrences are related to the Main Range massif. In the Mid-Paleoproterozoic (2.0-1.9 Ga), the complex was transformed into a collage of tectonic blocks confined to the regional fault zone. The Monchegorsk pluton was retained better, and only rocks of its southern framework were involved into tectonic and metamorphic reworking with the formation of economic metamorphic low-sulfide PGE mineralization with widespread Pd and Pt telluro-bismuthides, arsenides, stannides, antimonides, and selenides. The ore formation was accompanied by PGE redistribution and segregation of lenticular orebodies with diffuse contours. Thus, the Monchegorsk ore cluster is characterized by juxtaposition of unaltered primary magmatic deposits and those formed as a result of their metamorphism and distinguished from the former by structure and composition. The comparative study of these deposits opens up new possibilities for comprehending ore-forming processes in the same situations.

The Early Paleoproterozoic Monchegorsk Complex is exposed over an area of 550 km² and comprises two layered mafite-ultramafite intrusions of different age: the Monchegorsk pluton of ultramafic and mafic rocks and the predominantly gabbroid Main Range Massif (also referred to as the Moncha-Chuna-Volch’i Tundras Massif), which are separated by a fault. Both massifs consists of intercalating cumulates (first of all, Ol ± Crt, Ol + Opx ± Crt, Opx, Opx + Pl ± Cpx, and Pl), they were produced by similar melts of siliceous high-Mg series but differ in the stratigraphy of their cumulates: while the Monchegorsk pluton is dominated by ultramafites, the Main Range Massif consists mostly of gabbroids, first of all, of gabbronorites. The complex is accompanied by PGE-Cu-Ni ore mineralization, low-sulfide Pt-Pd mineralization, and chromite mineralization. Judging from geological data and isotopic dates, the Monchegorsk Complex is a long-lived magmatic center, which evolved over a time span of 50 Myr at 2.50–2.46 Ga. The Main Range Massif is younger and likely truncates the western continuation of the Monchegorsk pluton. The complex is spatially restricted to the zone of the Middle Paleoproterozoic regional Central Kola Fault and is now tectonic collage whose rocks were variably affected by overprinted metamorphism in the course of deformations. These processes most significantly affected rocks along the peripheries of the Monchegorsk pluton in the south. These rocks were completely transformed under greenschist-facies conditions but often preserved their primary textures and structures. The processes overprinted both the marginal portions of the pluton itself and the rocks of its second phase, which are accompanied by economic low-sulfide PGE deposits. The PGE-Cu-Ni ore mineralization of the Monchegorsk Complex is genetically related to two distinct evolutionary episodes with a quiescence period in between: The emplacement of large layered mafite-ultramafite intrusions at 2.5–2.45 Ga. Economic deposits of sulfide Cu-Ni ores with subordinate PGE mineralization occur within the Monchegorsk pluton, and the moderate-grade low-sulfide PGE ores are related to its second evolutionary phase (in the foothills of Vuruchuaivench and in the Moroshkovoe Lake, and Southern Sopcha areas). The primary magmatic ore mineralization is predominantly Cu-Fe-Ni sulfide with PGE bismuthides-tellurides. The Monchegorsk Complex was involved in the zone of the Central Kola Fault at 2.0–1.9 Ga and was broken in a collage of tectonic blocks. The rocks were sheared along the boundaries of the blocks and were affected by overprinted metamorphism, which proceeded under greenschist-facies conditions in the structures surrounding the Monchegorsk pluton in the south. Thereby the primary PGE-Cu-Ni ore mineralization underwent metamorphic processes was recrystallized with the formation of Pt-Pd arsenides, stannides, antimonides, selenides, etc. This processes was associated with the partial redistribution of PGE with their local accumulation (up to economic concentrations), and the orebodies themselves acquired diffuse outlines. In other words, the second episode was marked by the transformation of the older primary magmatic ore mineralization.

The paper presents a study of zircon from the Middle Paleoproterozoic Elet’ozero high-Ti layered ultramafic-mafic-alkaline intrusive complex with carbonatites and Sm-Nd isotope system of rock-forming minerals in ferrogabbro sample from this complex. Zircons extracted from syenite and ferrogabbro samples have similar pattern and experienced two main independent episodes of secondary transformation. The first episode was accompanied by the partial or complete replacement of the magmatic zircon with oscillatory zoning by porous zircon with a complex irregular inner structure, while a rim of CL-homogenous zircon around primary and porous zircons was produced during the second episode. The primary magmatic zircon is characterized by the elevated HREE, lowered LREE contents and positive Ce anomaly. The porous zircon is enriched in LREE, Ca, Ti, and frequently, in Th. While both varieties are mainly depleted in U. The REE distribution pattern in a homogenous zircon shell is similar to that of the magmatic zircon, but differs in much lower REE, especially HREE and MREE contents. The porous zircon contains microinclusions of thorite, barite, yttrialite, as well as other rare-metal and rare-earth minerals (calciosamarskite, pyrochlore, and hatchettolite), which indicates it was reworked by fluids containing not only F and Th, but also Y, U, Nb, Ta, Ba, Fe, Ti, and Ca. These components were presumably released during metamorphism-related replacement of magmatic minerals by metamorphic assemblages with fairly limited isomorphic capacity. U-Pb SHRIMP-II geochronological study of zircon showed its age varies within a wide range and correlates with peculiarities of its inner structure, which is explained by a style of superimposed processes. However, age estimations, especially for the domains dispersed alongside with porous zircon or “penetration” of shell material, often have younger values. The oldest ages (2086 ± 53 and 2086 ± 30 Ma for syenites and 2070 ± 24 Ma for ferrogabbroids) are presumably closest to the crystallization age of the intrusion. According to geological data, syenites intrude gabbroids. Therefore, the age obtained for syenites (2086 ± 30 Ma) seems to be the more preferable for the real formation age of the intrusion. Age values of porous zircon also widely vary, which is explained by the presence of relics (domains) of primary zircon in a porous matrix. We suggest that the minimum obtained dates (1.8–1.9 Ga) are the closest to the crystallization age of porous zircon. This age coincides with the Svecofennian tectonometamorphic processes, which presumably spanned the rocks of the Elet’ozero Complex, caused the metamorphism of all kind of rocks under the epidote-amphibolite facies conditions and formation of porous zircon. CL-light zircon shells were presumably formed later by interaction of zircon with a crustal fluid during the Meso- and Neoproterozoic, and even Caledonian events. The age of ferrogabbroids determined by Sm-Nd isochron method (1988 ± 63 Ma) is comparable within error with results of U-Pb dating of porous zircon, thus confirming that magmatic rocks of the complex underwent intense secondary transformations during the Svecofennian orogeny. The Middle Paleoproterozoic Elet’ozero Complex is the oldest manifestation of the high-Ti moderately alkaline magmatism at the Karelian Craton.

The first Sm-Nd and Rb-Sr dates were obtained for the dynamometamorphic processes associated with the origin and evolution of the Moncha Tundra fault, Kola Peninsula, which separates two large Early Paleoproterozoic layered intrusions: the Monchegorsk Ni-bearing mafic-ultramafic intrusion and the Main Range massif of predominantly mafic composition. The fault belongs to the regional Central Kola fault system, whose age was unknown. The material for the dating included metamorphic minerals from blastomylonitic rocks recovered by structural borehole M-1. Mineralogical thermobarometry suggests that the metamorphism occurred at 6.9–7.6 kbar and 620–640°C, which correspond to the amphibolite facies. The Sr and Nd isotopic systems were re-equilibrated, and their study allowed us to date the dynamometamorphic processes using mineral isochrons. It was established that the Moncha Tundra fault, and, respectively, the whole Central Kola fault system appeared in the middle of Paleoproterozoic ∼2.0–1.9 Ga, simultaneously with the Svecofennian orogen in the central part of the region and the Lapland-Kola orogen in its northeastern part. Another episode of dynamometamorphism that occurred at 1.60–1.65 Ga is envisaged.