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Petrography Section
This section presents rocks of various ages (from Late Proterozoic to Pliocene) and of structures (from ultrabasic to acidic and alkaline) of the territory of Armenia.
The most ancient rocks (Middle (?) – Upper Proterozoic), which form the crystalline basement of the territory, are outcropped in Tsaghkunyats massif and are presented by various mica-schists, marbles, dolomites, amphibolites, phyllites, porphyritoids, porphyroids, which are metamorphosed primary sedimentary and volcanic rocks. From ancient intrusive rocks trondhjemites (~680 million years), albitites (~650 million years), and granitogneisses (~610 million years) are exhibited. Intrusive formations, mainly located in Tsaghkunk-Zangezur and Somkheto(Virahayots)-Kharabakh areas, are widely presented in the Section. The largest Meghri pluton (~1200sq/km) of Lesser Caucasus in Syunik region is represented by different types of rocks, the formation of which took place during the three main phases (41÷21 million years interval) in the post collision period of region. The rocks of the first phase (~41÷31million years) are represented with gabbroids, monzonites (from the southern and central parts of the pluton), syenite-granites, and different alkaline rocks. Here are exhibited the rocks of the second phase (~31÷28 million years) represented by monzonites and syenito-diorites of the pluton’s north-eastern part, and the porphyric granites and granodiorites of the third phase (~24÷21 million years).
From different composition dyke rocks wide spread in Meghri pluton, the most widely spread granodiorite-porphyries dykes are exhibited, the thickness of which reaches up to 25-30 meters.
Outside Meghri pluton borders, northwards, the intrusive massifs of Bargushat (Svarants, Gekhi, Surbqar, Lake Kazan etc.) are outcropped, the formation of which mainly corresponds to the Meghri pluton formation principles. From mentioned intrusive massifs, Svarants olivine gabbros and troctolites, Gekhi granodiorites, and other skarns of various mineral compositions are exhibited.
From the northern and central parts of Armenian territory are exhibited the gabbros and granodiorite-porphyries of Banush intrusive (~46 million years); the granodiorites and quartz diorites from Bazum intrusive massif; the gabbros and spherical gabbros from Lermontov massif; the quartz monzonites and aplitic dykes (intersecting them) from Aghavnadzor massif.
Middle Jurassic (~165 million years) plagiogranite (Haghpat, Tavush, Khndzorut, etc.) and Upper Jurassic (156÷150 million years) tonalitic (Koghb-Shnokh, Tsaghkashat, Tsaghkashen, etc.) intrusions are located within the Somkheto-Karabakh tectonic zone boundaries, which is considered (?) the southern part of the Eurasian plate. Plagiogranites, quartz diorites, pink granites of Tavush and Haghpat massifs, as well as tonalites, quartz diorites, gabbro-diorites, and hybrid formations of Tsav intrusion from Kapan block are also exhibited.
Upper Jurassic age tonalite intrusive massifs are widespread in the northern section of Tsaghkunq-Zangezur zone and were formed in the island-arc conditions. The Aghveran, Artavaz, Hankavan, Gegharot and other intrusions are represented with tonalites, quartz diorites, granodiorites, pegmatite dykes.
Ophiolite association rocks that are widespread in Sevan, Amasia, Stepanavan, and Vedi areas are among the important and characteristic geological formations in the territory of Armenia. Genetically, they are part of the disappeared Tethys oceanic remains, which were obducted on the northern margin of South-Armenian microcontinent in the Late Cretaceous. The mantle and crustal peridotites and serpentinites, crustal plutonic rocks (dunites, pyroxenites, gabbros, anorthosites, plagiogranites) and volcanites (basalts, diabases), as well as radiolarites (as a part of the volcanogenic-sedimentary cover) are demonstrated in a separate showcase.
Demonstrated several metamorphic rock samples, such as the glaucophane and garnet-amphibole schists and amphibolites, are the result of the metamorphism of primary basic composition rocks. According to the isotope (U-Pb, Ar/Ar) dating (178-165 Ma) in gabbros and plagiogranites, and to the paleontological dating in radiolarites , the ophiolite rocks (in the narrow sense) of this association have at least Middle and Upper Jurassic ages, while the superposed alkaline basalts have late Lower Cretaceous age (117 million years, Ar/Ar).