Criteries and prospects of diamonds of the Vitebsk granulite massif

The article describes the history of studying the diamond content of tectonic structures of the territory of Belarus. Based on the results of magnetometric, mineralogical, tectonic studies carried out by industrial geologists and scientists over the past 50 years, new scientifically substantiated criteria for the search for explosion pipes have been developed using Clifford’s rule, according to which kimberlite explosion pipes are developed within the Archean cratons, where the thickness of the lithosphere is 175–270 km, and are absent in the zones of Early Proterozoic stabilisation and tectonomagmatic activation. Explosion tubes on the African-Arabian, East Siberian, Sino-Korean and East European platforms demonstrate their confinement to the Archean cratons and may be associated with zones of paleosubduction of the Proterozoic oceanic crust beneath the Archean cratons. Based on this, the authors scientifically substantiated the hypothesis that during the closure of the Early Proterozoic paleoocean separating the Fenno-Scandinavian craton from the Volga-Ural and Sarmatian cratons, subduction of the younger crust took place under these cratons, the southwestern corner of which on the territory of Belarus is the Vitebsk granulite massif. The article concludes that the Vitebsk granulite massif is the most promising in terms of diamond-bearing on the territory of Belarus, and within its limits – the Smolensk regional deep fault at the intersection of this fault of northeastern striking with the Odessa-Gomel regional deep fault of submeridional striking south of the city of Orsha. Recommendations are given for further study of promising areas in order to determine their diamond content.

SOME PROBLEMS GEOCHEMISTRY OF VOLCANITES OF THE PECHENGA STRUCTURE (KOLA PENINSULA)

Some problems of dating the most important stratigraphic units of the Early Proterozoic Pechenga Structure are considered. The structure is composed of rocks of the Pechenga Complex, which in turn is divided into well-studied formations of the North-Pechenga subcomplex and poorly studied formations – the South-Pechenga subcomplex. This structure is one of the most studied Early Precambrian structures in the world. Volcanites of the Pechenga Structure have been studied for nearly half a century. However, many determinations of the isotopic ages of reference levels of geological crossection were carried out by insufficiently accurate Rb-Sr, Sm-Nd, and other methods. Nevertheless, in recent years, using the modern U-Pb method, age characteristics of the most important stratigraphic units of the North-Pechenga subcomplex have been obtained.

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.

Two stage of gold-bearing sulfide ores of early Proterozoic gabbroids in the north Ladoga area

In a study based on Pb isotopes, it has been shown that the formation of gold-sulfide mineralization in the Early Proterozoic gabbros of the Northern Ladoga region is associated with different tectonic phases. This conclusion is based on a comparative study of isotopic data for feldspars and lead sulfides in two Early Proterozoic intrusions; Velimäki and Alattu-Päkylä. The investigated intrusions have similar geological settings at the junction of the Svecofennian accretionary complex and the Karelian craton. Both massifs are characterized by manifestations of noble metal sulfide mineralization associated with zones of local shear deformations. The formation of the studied ore massifs is attributed to the Svecofennian and Caledonian tectonic stages. Feldspars of Velimäki intrusion have parameters and model age of Pb significantly older than U-Pb age of zircon (1.9 Ga), although they correspond to the Svecofennian time of magmatic crystallization of gabbro and clinopyroxenites, while sulfide pyrite-pyrrhotite mineralization is associated with gold in these rocks with the Caledonian stage of fluid-thermal processing of the Early Proterozoic magmatic mineral paracenteses. Feldspars and sulfides of the Alattu-Päkylä intrusion have similar lead isotopic parameters and Pb model age (~ 2 Ga), also somewhat older than the U-Pb age of zircon, but at the same time indicating the formation of rock-forming and ore sulfide associations with gold during the Svecofennian (Early Proterozoic) plutonic and tectonic-thermal events. The source of lead sulfides of the Velimäki massif is characterized by the parameters of the upper crust with high µ2 = 238U / 204Pb, while the µ2 parameter of the minerals of the Alattu-Päkylä massif is slightly lower, which indicates the participation of the mantle-lower crustal reservoir material in the formation of magma.

THE PHENOMENON OF RAPID ACCUMULATION OF SEDIMENTS BELONGING TO THE UDOKAN GROUP AND THE FORMATION OF THE UNIQUE UDOKAN COPPER DEPOSIT (ALDAN SHIELD, SIBERIAN CRATON)

We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.

Were Neoarchean atmospheric methane hazes and early Paleoproterozoic glaciations driven by the rise of oxygen in surface environments?

Insofar as methane was the predominant greenhouse gas of the Archean and early Proterozoic eons, its wax and wane in Earth’s atmosphere would have contributed to climate change and the relative flux of harmful UV radiation to surface environments. If correct, understanding the first-order environmental controls (e.g., O2 or resource concentration) of the biological methane cycle might shed light on the repetition of biological, atmospheric and climatic events preserved in the sedimentary rock record between ~2.8 and 2.0 billion years ago. Environmental controls on the dynamics of methane cycling may further explain other repetitious events in deep time, as well as the present-day increase in the methane flux to the atmosphere from wetland environments. In this study, we developed an ecological interaction model to predict the conditions in which methane is preferentially released to the atmosphere, and found that the interplay of resource and O2 availability can cause complex cyclic patterns in methane dynamics that are unrelated to the size and efficiency of any of the microbial communities, to initial conditions, or to other model constraints. Based on these model results, we propose that the cyclicity of methane haze events and glacial episodes in the late Archean and early Proterozoic may have been linked to the progressive increase in oceanic and atmospheric O2 through the interval.