EARLY PRECAMBRIAN CRUSTAL EVOLUTION OF THE BELOMORIAN AND TRANS-NORTH CHINA OROGENS AND SUPERCONTINENTS RECONSTRUCTION

Comparative analysis of the crustal evolution of the Early Precambrian Belomorian and Trans-North China orogens (Fig. 1) has shown [Slabunov et al., 2015] that: Both belts were formed by the superposition of two Precambrian orogenies. The earth crust of the Belomorian belt was produced during the Mesoarchaean to Neoarchaean Belomorian collisional orogeny [Slabunov, 2008; Slabunov et al., 2006] and then was reworked during the Palaeoproterozoic Lapland-Kola collisional orogeny [Daly at al., 2006; Balagansky et al., 2014]. The earth crust of the Trans-North China orogen was formed during a Neoarchean accretionary orogeny and then was reworked during a Paleoproterozoic collisional orogeny [Zhao et al., 2012; Guo et al., 2012, 2005]. The Lapland granulite belt is the core of the Lapland-Kola Palaeoproterozoic collisional orogen in the Fennoscandian shield and the Khondolite belt occupies the same tectonic position in a Palaeoproterozoic collisional orogen in the North China craton.Comparative analysis of the crustal evolution of the Early Precambrian Belomorian and Trans-North China orogens (Fig. 1) has shown [Slabunov et al., 2015] that: Both belts were formed by the superposition of two Precambrian orogenies. The earth crust of the Belomorian belt was produced during the Mesoarchaean to Neoarchaean Belomorian collisional orogeny [Slabunov, 2008; Slabunov et al., 2006] and then was reworked during the Palaeoproterozoic Lapland-Kola collisional orogeny [Daly at al., 2006; Balagansky et al., 2014]. The earth crust of the Trans-North China orogen was formed during a Neoarchean accretionary orogeny and then was reworked during a Paleoproterozoic collisional orogeny [Zhao et al., 2012; Guo et al., 2012, 2005]. The Lapland granulite belt is the core of the Lapland-Kola Palaeoproterozoic collisional orogen in the Fennoscandian shield and the Khondolite belt occupies the same tectonic position in a Palaeoproterozoic collisional orogen in the North China craton

Early Precambrian Eclogites of the Belomorian Province, Fennoscandian Shield

Early Precambrian eclogites are widespread in the Belomorian Province of the Fennoscandian shield. There are three points of view on the their age: 1) Archean and Paleoproterozoic; 2) solely Mesoarchean; 3) solely Paleoproterozoic. The goal of this field trip is to show all these types of eclogites including Archean and Paleoproterozoic (from the authors' point of view) eclogites, eclogitized Paleoproterozoic coronitic gabbroids, Archean zoisitites and their structural position in the Gridino, Salma (Uzkaya Salma and Shirokaya Salma) and Kuru-Vaara areas of the Belomorian Province. The geological excursions provide a good opportunity for the participants and the reader to exanimate these contradicting points of view immediately at beautiful outcrops on islands of the White Sea, on the benches of the Kuru-Vaara quarry and in the walls of road pits in the Salma area. This Field Guidebook is of interest for geologists, petrologists and geochronologists who study the early evolution of the Earth and HP-UHP metamorphic processes

Reply to Skublov et al. Comment on “Volodichev et al. Archean Zircons with Omphacite Inclusions from Eclogites of the Belomorian Province, Fennoscandian Shield: The First Finding. <i>Minerals</i> 2021, <i>11</i>, 1029”

Early Precambrian retrogressed eclogites are abundant in the Archean Belomorian Province of the Fennoscandian Shield. Archean zircons with inclusions of omphacite have been found in these eclogites. Similar Archean zircons from the retrogressed eclogites also contain garnet inclusions. The Archean zircons display no negative Eu anomaly, which indicates their crystallization in plagioclase-free rock. Garnet, omphacite and clinopyroxene-plagioclase symplectite as a proxy of omphacite compose ≥75% of the studied rocks, with garnet and omphacite being major constituents and associating with rutile and quartz. These data strongly suggest that the studied rock is eclogite. In the majority of petrogenetic grids, P-T parameters calculated for these rocks fall in the eclogite-facies field. Thus, these findings and data provide evidence that eclogite-facies metamorphism occurred in the Neoarchean

Seismogeological section of the Earth's crust of North Karelia along the profile of Kandalaksha - Kem

CDP, DSS and seismotomographic section along the North Karelian portion of geotraverse 1-ЕВ (Kandalaksha - Kem) have made it possible for the first time to study in detail the earth crust under the Belomorian province within the limits of the Phenno-Scandian Shield. Correlation and integrated interpretation of CDP time sections, DSS multi-wave sections and geological data show that the results obtained by the seismic methods differ markedly, but the data obtained by both methods are important for geological interpretation because they emphasize different environmental characteristics. Tectonic dislocation zones, extending to M-discontinu-ity, were delineated and traced downwards. The crystalline crust of the Belomorian province was shown to have a nappe tectonics. Horizontal variation in velocity correlates with heterogeneities in crustal section responsible for its blocky geological structure. The heterogeneity pattern of the crust seems to reflect collision tectonics, and as a result tectonic slits of different composition were superposed

Chemical and isotopic compositions of zircons from an eclogitized gabbronorite dike at the Gridino village, Northern Karelia

A comprehensive (mineralogical, geochronological, and geochemical) study of zircons from an eclogitized gabbronorite dike was carried out in order to identify reliable indicators (mineralogical and geochronological) of genesis of the zircons in their various populations and, correspondingly, ages of certain geological events (magmatic crystallization of the gabbroids, their eclogitization, and overprinted retrograde metamorphism). Three populations of zircons separated from two rock samples comprised xenogenic, magmatic (gabbroic), and metamorphic zircons, with the latter found exclusively in the sample of retrograded eclogitized gabbroids. Group I zircons are xenogenic and have a Meso- to Neoarchean age. Mineral inclusions in them (quartz, apatite, biotite, and chlorite) are atypical of gabbroids, and geochemistry of these zircons is very diverse. Group II zircons contain mineral inclusions of ortho- and clinopyroxene and are distinguished for their very high U, Th, Pb, and REE concentrations and Th/U ratios. These zircons formed during the late magmatic crystallization of the gabbroids at temperatures of 1150-1160°C, and their U-Pb age 2389±25 Ma corresponds to this process. Eclogite mineral assemblages crystallized shortly after the magmatic process, as follows from the fact that marginal portions of prismatic zircons contain clinopyroxene inclusions with elevated contents of the jadeite end-member. Group III zircons contain rare amphibole and biotite inclusions and have low Ti, Y, and REE concentrations, low Th/U ratios, high Hf concentrations, contain more HREE than LREE, and have U-Pb age 1911±9.5 Ma, which corresponds to age of overprinted amphibolite-facies metamorphism

EARLY PRECAMBRIAN CRUSTAL EVOLUTION OF THE BELOMORIAN AND TRANS-NORTH CHINA OROGENS AND SUPERCONTINENTS RECONSTRUCTION

Comparative analysis of the crustal evolution of the Early Precambrian Belomorian and Trans-North China orogens (Fig. 1) has shown [Slabunov et al., 2015] that: Both belts were formed by the superposition of two Precambrian orogenies. The earth crust of the Belomorian belt was produced during the Mesoarchaean to Neoarchaean Belomorian collisional orogeny [Slabunov, 2008; Slabunov et al., 2006] and then was reworked during the Palaeoproterozoic Lapland-Kola collisional orogeny [Daly at al., 2006; Balagansky et al., 2014]. The earth crust of the Trans-North China orogen was formed during a Neoarchean accretionary orogeny and then was reworked during a Paleoproterozoic collisional orogeny [Zhao et al., 2012; Guo et al., 2012, 2005]. The Lapland granulite belt is the core of the Lapland-Kola Palaeoproterozoic collisional orogen in the Fennoscandian shield and the Khondolite belt occupies the same tectonic position in a Palaeoproterozoic collisional orogen in the North China craton