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The Dizi Series is exposed within the Southern Slope zone of the Greater Caucasus, in the core of the Svaneti anticlinorium. It is mainly composed of terrigenous, volcanogenic and carbonate rocks faunistically dated from the Devonian to the Triassic inclusive. Regional and contact metamorphism of the Dizi Series rocks was studied. It is stated that the degree of regional metamorphism corresponds to the chlorite-sericite subfacies of the greenschist facies, occurring at a temperature of 300–350°C and a pressure of 1.5–2.3 kbar. As a result of the action of the Middle Jurassic intrusive rock bodies, the regionally metamorphosed rocks of the Dizi Series underwent contact metamorphism. Three zones of contact metamorphism were distinguished corresponding to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies. Contact metamorphism took place at a significantly higher temperature and lower pressure than the preceding regional metamorphism. The maximum temperature of the contact metamorphism reached ≈ 570°С, while pressure varied within the range of ≈ 0.3–0.8 kbar. The evolution of rock associations of regional and contact metamorphism of the Dizi Series was studied. The fields of facies and subfacies of regional and contact metamorphism are shown in the Ps-T diagram. Three age populations of zircons were identified using U-Pb LA-ICP-MS dating of the diorite-porphyrite intrusion in the Dizi Series: Zrn1 (ca. 2200 Ma) and Zrn2 (458 ± 29 Ma) that were captured by the diorite-porphyrite magma from the ancient magmatic and metamorphic rocks of the crystalline basement, and Zrn3 (166.5 ± 4.6 Ma) that corresponds to the age of diorite-porphyrite crystallization.

<p>The Loki crystalline massif and adjacent territories are exposed in South Georgia within the northern marginal part of the Beiburt-Sevan terrane. It is part of the Loki-Karabakh tectonic zone. The Loki massif is a large anticlinal structure with a pre-Alpine crystalline basement exposed in the core surrounded by a Mesozoic-Cenozoic sedimentary cover. According to the complex study of the massif, it was established that it is composed of autochthonous Upper Devonian gneissose quartz-diorites, allochthonous pre-Late Paleozoic Moshevani and Sapharlo-Lok-Jandari overthrust sheets of metasediments, Precambrian Lower Gorastskali ofiolite sheet and Upper Gorastskali mélange sheet. All these rocks are cut by Late Paleozoic, Jurassic and Cretaceous intrusions. All sheets, except for ophiolite one, were metamorphosed during the Caledonian orogeny and then were overthrust during Bretonian and Early Cimmerian orogenies. The Loki massif is a part of the northern active continental margin of the Paleotethys oceanic basin, where supra-subduction regional metamorphism and granite formation occurred during Variscan orogeny. During the Late Bretonian orogeny, the obduction of Precambrian ophiolite rocks and the overthrusting of Paleozoic metamorphic sheets onto the continental margin took place. Later they were intruded by granites. Along the entire perimeter, the crystalline basement and granites are transgressively covered by Mesozoic-Cenozoic deposits. On the basis of detailed studies of terrigenous deposits in the section of the r. Gorastskali gorge on nanoplankton new age data have been obtained. Based on these data, for three lithostratigraphic units – Moshevani (conglomerates and quartz sandstones), Lokchay (mica sandstones) and Jandari (argillites) suites, the following ages were established: Norian - Rhaetian, Hettangian - Low Pliensbachian and Upper Pliensbachian - Aalenian, respectively. Triassic deposits were discovered in this area for the first time. With the accumulation of new data on the Loki massif and surrounding area, a new corrected digital geological map, lithostratigraphic column and 3D section were compiled.</p>

<p>The Greater Caucasus - the complex geological structure of the Caucasus is an integrated part of the Mediterranean (Alpine-Himalayan) collision orogenic belt. The Dizi series is exposed within the Greater Caucasus Southern Slope zone, in the core of Svaneti anticlinorium. It is composed of faunistically dated from the Devonian to the Triassic inclusively thin-striped and crenulated terrigenous deposits, various volcanites and marbles. Despite the well-studied stratigraphy and tectonics of the Dizi series, the issues of metamorphism, unlike the other rocks of the pre-Alpine crystalline basement of the Greater Caucasus are less studied. The rocks of the Dizi series underwent regional metamorphism of the greenschist facies chlorite-sericite sub-facies under a temperature of 300-340°С and pressures of ≈ 2-2.5 kbar. Characteristic mineral assemblages are established on the basis of microprobe analysis of chlorite, K-mica, plagioclase, actinolite, actinolitic hornblende and prehnite. Due to the contact impact of the Bathonian intrusions on the regionally metamorphosed rocks of the Dizi series, various hornfelses, spotted schists and skarns were formed. Composition of minerals of contact-metamorphism - biotite, cordierite, muscovite, plagioclase, cummingtonite, hornblende, chlorite, clinopyroxene, clinozoisite and K-feldspar is determined. According to the results of studies of key mineral assemblages of contact-metamorphosed rocks, three exocontact zones are distinguished, corresponding to the albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels sub-facies conditions. The first zone is marked by the appearance of biotite, muscovite and plagioclase of oligoclase-andesine series in metapelites; hornblende, biotite and clinozoisite in metabasites and amphibole schists; wollastonite and clinozoisite in carbonate-silicate schists. The beginning of the second zone is marked in the appearance of cordierite, corundum in metapelites and of scapolite in metabasites and carbonate-silicate schists. By the disappearance of chlorite in the metapelites, the appearance of cummingtonite in metabasites and garnet in carbonate-silicate schists, a transition to the third zone is established. In the high-temperature part of the last zone, in the metapelites fibrolite is formed. The maximum temperature in the aureole of contact metamorphism is 550⁰С, and the pressure is about 0.5-1 kbar. Due to very low pressure during the re-crystallization of rocks pyralspite garnet is missing in the mineral associations of the Dizi series rocks. Instead of garnet, the association of chlorite-quartz-muscovite appeared. Under the conditions of increasing temperature during the metamorphism a change in the characteristic features of the mineral composition is shown graphically. Based on the accessible data the authors have drawn the contact metamorphism fields on the existing general scheme of facies and subfacies of regional metamorphism.</p>

<p>The Dizi Series is exposed within the Southern slope zone of the Greater Caucasus that occurs as a complex geological structure, which constitutes an integral part of the Mediterranean (Alpine-Himalayan) collisional orogenic belt. It is built up of terrigenous and volcanogenic-sedimentary rocks faunistically dated from the Devonian to Triassic inclusive (Somin, 1971; Somin, Belov, 1976; Kutelia 1983). Most of them are metamorphosed under conditions of chlorite-sericite subfacies of the greenschist facies of regional metamorphism (chlorite-phengite-albite±quartz, graphite-sericite-quartz phyllites and marbleized limestones), and only a minor part represented by clay-carbonaceous, phengite-chlorite-carbonaceous and prehnite-chlorite-carbonate schists underwent anchimetamorphism (Shengelia et al., 2015). The Dizi Series is intruded by numerous magmatic bodies of gabbro-diabases, diabases, diorites, diorite-porphyries, syenites, monzo-syenites and granitoids. The age of the intrusions was defined by K-Ar method at 176-165 Ma (Dudauri, Togonidze, 1998) and by U-Pb LA-ICP-MS zircon dating at 166.5 ± 4.6 Ma (authors` unpublished data) and corresponds to the Bathonian orogeny. The Middle Jurassic intrusions caused intense contact metamorphism of the rocks of the Dizi Series resulted in the formation of various hornfelses containing andalusite, cordierite, corundum, biotite, plagioclase, potassium feldspar, clinozoisite, hornblende, cummingtonite, clinopyroxene, wollastonite and scapolite. These rocks correspond to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies of the contact metamorphism (Javakhishvili et al., 2020). The analogues of the Dizi Series rocks have not previously been established either in the Greater Caucasus or in the neighboring regions. In our view, Paleozoic rocks similar to the Dizi Series occur under the Cretaceous and Jurassic deposits within the folded basement of the plain Crimea where they were recovered by wells. Most of these rocks, as in the Dizi Series, underwent metamorphism of chlorite subfacies of the greenschist facies and, to a lesser extent, deep epigenesis (clayey-carbonaceous, sericite-carbonaceous, actinolite-chlorite-prehnite, muscovite-albite-chlorite, epidote-actinolite-chlorite and graphite-talc-quartz schists) (Chernyak, 1969). These rocks are also intruded by Middle Jurassic igneous rocks, including gabbro-diabases, diabases, diorites, syenites, monzo-syenites, granite-porphyries, etc. (Shniukova, 2016; Shumlyanskyy, 2019). As a result of the contact metamorphism of the basement rocks, muscovite-quartz-cordierite and cordierite-quartz-feldspar micaceous hornfelses were formed. Quartz syenite yielded a K-Ar age of 158 Ma (Scherbak, 1981), while monzo-syenite was dated at 170 ± 5 Ma applying 40Ar/39Ar method (Meijers, 2010). Thus, based on the rock associations, the nature of metamorphism, the age of the metamorphic and igneous rocks, and on the spatial position of the Dizi Series and folded basement of the plain Crimea we assume that these units developed coevally in similar environment and geological conditions.<br><br>Acknowledgements.This work was supported by Shota Rustaveli National Science Foundation (SRNSF) [PHDF-19-159, Regional and Contact Metamorphism of the Dizi Series].</p>