ON THE AGE OF THE CHARNOCKITOIDS OF THE TASHLYK COMPLEX OF THE INHUL REGION OF The UKRAINIAN SHIELD

Zircons from charnockitoids of the Tashlyk complex from the Pryinhul syncline were studied and dated in order to determine their chronostratigraphic position. Zircons of two age generations were identified, namely the Early Archean (ca. 3 Ga) and the Early Proterozoic (2.0±0.1 Ga). The presence of the former generation indicates that the protolith for charnockites have been represented by the rocks older than the Spasove Series, which is considered to be Proterozoic in age. At ca. 2.0±0.1 Ga Archean rocks together with rocks of the Inhul-Inhulets Series, underwent granulite metamorphism. This event resulted in crystallization of the second (Paleoproterozoic) generation of zircon in charnockites. Archean zircons found in the rocks of the Tashlyk complex, which correspond morphologically to granitoid of the amphibolite facies, differ from Eoarchean zircons in enderbites of the Haivoron complex, which partially retain their appearance during the Neoarchean and Paleoproterozoic tectonic-magmatic events.

Fluid inclusion and thermobarometric study of interaction between mafic xenoliths and plagiogranites in the Lotta River Area, Lapland Granulite Belt

<p>Thermobarometric data and fluid inclusions data of conditions of interaction between mafic granulite xenoliths and plagiogranites in the Lotta river area, Lapland Granulite Belt, confirm the conclusion that leucocratic garnet-bearing plagiogranites of the Lapland complex are associated with the anatexis of country khondalites during peak of metamorphism.</p><p>The formation of plagiogranitic magmas, probably, occurred at depths of about 25-30 km. As they ascended, they captured numerous xenoliths (Kozlov, Kozlova, 1998). The most remarkable of them are two-pyroxene-plagioclase granulite xenoliths (orthopyroxene ± clinopyroxene + plagioclase ± quartz + magnetite + ilmenite + pyrrhotite). The xenoliths show extensive amphibole formation, which is manifested as coronas of K-bearing pargasite-edenite amphibole and coarse-grained amphibole-quartz symplectites in contacts of pyroxenes, magnetite, ilmenite and pyrrhotite with plagioclase.</p><p>The more calcic composition of plagioclase and the lower Mg-number of pyroxenes in the amphibolized portions of xenoliths correspond to the amphibole formation via reaction: Opx + Ilm + Mt + Pl = Amph ± Qtz. Amphibole formation is locally accompanied by biotite, indicating the addition of potassium into the xenoliths.</p><p>A pressure of 6.0-6.4 kbar was estimated from the equilibrium of clinopyroxene + orthopyroxene + plagioclase + quartz in non-amphibolized portions of xenoliths. The corresponding temperatures 800-860°C are within the range of temperatures estimated for the plagiogranite crystallization (Kaulina et al., 2014) as well as peak temperatures of the M2 tectonic-thermal event in the Lapland complex (Mints et al., 2007). Amphibole-plagioclase equilibrium (Blundy, Holland, 1990) recorded the temperatures of the amphibole formation 740-780°C at a pressure of 5.0-5.5 kbar. Compositional variations of amphibole toward tremolite indicate further cooling. It was, probably, due to the interaction of an essentially aqueous fluid issued from plagiogranitic magma with xenoliths as they were captured and transported.</p><p>Indeed, xenoliths are crossed by plagiogranitic veins. Abundance of aqueous-salt (17-20 wt. % NaCl eq.) inclusions and the subordinate amount of carbon dioxide inclusions in plagiogranite minerals confirm this assumption. Thus, plagiogranites of the Lapland complex and associated fluids were formed inside the complex at P-T parameters comparable to the peak conditions of granulite metamorphism. During ascension, these granite magmas could only produce fluid effects on the country rocks including xenoliths.</p>

The Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex (Fennoscandian Shield): new U-Pb, Sm-Nd and Nd-Sr (ID-TIMS) isotope data on the age of formation, metamorphism and geochemical features of zircon (LA-ICP-MS)

<p>The paper provides new U-Pb, Sm-Nd and Nd-Sr isotope-geochronological data on rocks of the Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex. REE contents in zircons from basic rock varieties of the Kandalaksha-Kolvitsa area have been defined in situ using LA-ICP-MS. Plots of REE distribution have been constructed, confirming the magmatic origin of zircon. Temperatures of zircon crystallization have been estimated, using a Ti-in-zircon geochronometer. For the first time, the U-Pb method with <sup>205</sup>Pb artificial tracer has been applied to date single zircon grains (2448±5 Ma) from metagabbro of the Kolvitsa massif. The U-Pb analysis of zircon from anorthosites of the Kandalaksha massif has dated the early stage of the granulite metamorphism at 2230±10 Ma. The Sm-Nd isotope age has been estimated on metamorphic minerals (apatite, garnet, sulfides) and the rock at 1985±17 Ma (granulite metamorphism) for the Kolvitsa massif, 1887±37 Ma (high-temperature metasomatic transformations) and 1692±71 Ma (regional fluid reworking) for the Kandalaksha massif. The Sm-Nd model age of metagabbro is 3.3 Ga with negative value εNd=4.6, which corresponds either with processes of crustal contamination, or with primary enriched mantle reservoir of primary magmas.</p><p>This research was funded by the Scientific Research Contract of GI KSC RAS No. 0226-2019-0053, grants of the Russian Foundation for Basic Research NoNo. 18-05-70082 «Arctic Resources», 18-35-00246 mol_a, and the Presidium RAS Program No. 8.</p><p> </p>

The Paleoproterozoic Kandalaksha-Kolvitsa Gabbro-Anorthosite Complex (Fennoscandian Shield): New U–Pb, Sm–Nd, and Nd–Sr (ID-TIMS) Isotope Data on the Age of Formation, Metamorphism, and Geochemical Features of Zircon (LA-ICP-MS)

The paper provides new U–Pb, Sm–Nd, and Nd–Sr isotope-geochronological data on rocks of the Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex. Rare earth element (REE) contents in zircons from basic rock varieties of the Kandalaksha-Kolvitsa area were analyzed in situ using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Plots of REE distribution were constructed, confirming the magmatic origin of zircon. Temperatures of zircon crystallization were estimated using a Ti-in-zircon geochronometer. The U–Pb method with a 205Pb artificial tracer was first applied to date single zircon grains (2448 ± 5 Ma) from metagabbro of the Kolvitsa massif. The U–Pb analysis of zircon from anorthosites of the Kandalaksha massif dated the early stage of the granulite metamorphism at 2230 ± 10 Ma. The Sm–Nd isotope age was estimated on metamorphic minerals (apatite, garnet, sulfides) and whole rock at 1985 ± 17 Ma (granulite metamorphism) for the Kolvitsa massif and at 1887 ± 37 Ma (high-temperature metasomatic transformations) and 1692 ± 71 Ma (regional fluid reworking) for the Kandalaksha massif. The Sm–Nd model age of metagabbro was 3.3 Ga with a negative value of εNd = 4.6, which corresponds with either processes of crustal contamination or primary enriched mantle reservoir of primary magmas.

Age of rocks of the Shurmak Formation according to U-Pb dating of zircon by LA-ICP-MS method (south-eastern Tuva)

At the south-eastern part of Tuva, early Proterozoic volcanogenic-sedimentary deposits have been studied including conglomerates from Shurmak formation. As the result of U-Pb zircon dating from tuff with andesitic composition, conglomerate matrix and volcanicomictic sandstones from this formation, it has been established that it was accumulated at around 500 Ma. The dating results for zircons from tuff are a geochronological date and indicate the time of manifestation of andesitic volcanism synchronous with accumulation of Shurmak Formation deposits. Given the close age of zircons of the main populations in both tuff and clastic rocks, one can assume that the formation of the latter is related directly to the manifestations of volcanism on this territory at this time. The presence in the tuff of xenogenic zircons and in volcanicomictic sandstones and matrix of Shurmak Formation of detrital zircons with Neoproterozoic and Paleoproterozoic age, as well as Sm-Nd isotopic data indicate that these volcanic and sedimentary processes in the early Cambrian time took place within the range if Precambrian block of earth’s crust. The main supplier of clastic material during the formation of the Early Cambrian Shurmak Formation were volcanic events synchronous with sedimentation. Other sources of clastic material entering the sedimentation basin were Neoproterozoic granitoids and, less commonly, Paleoproterozoic and Neoarchean rocks. Combination with the underlying rocks of the Mugur Formation of the Erza metamorphic complex occurred as a result of tectonic processes in the post-Cambrian time, since the sedimentation of the Shurmak Formation deposits and the processes of granulite metamorphism in the rocks of the metamorphic complex occurred almost simultaneously.

Granulite-gneiss (high grade) belts: geodynamic view

On the basis of analysis and generalization of modern data the features of the structure and tectonic evolution of granulite-gneiss (high-grade) belts of the Earth are considered. Their continental collisional tectonic nature, polycyclic and inherited character of development, expressed in repeated manifestations in the same belt of several stages of granulite metamorphism, separated by intervals of several hundred million years, are confirmed. Granulite-gneiss belts are permanent mobility structures that maintain endogenous activity in all stages of their existence, including intraplate environments. The relationship between high-grade belts and supercontinental cyclicity is revealed, which is expressed in the spatial coincidence of the majority of them to the outskirts of the young oceans that arose during the breakup of Pangea; in the control of assembly and breakup of ancient supercontinents along granulite belts; in correlation of manifestations of different types of granulite metamorphism in these belts with the stages of the supercontinent cycle. In the evolution of these belts there is a complex interaction of plate-tectonic and mantle-plume mechanisms, which is expressed in the combination of continental collision and underplating processes. The possibility of using granulite-gneiss belts in paleotectonic analysis along with other indicators of geodynamic settings is shown.