L.M. Stepanyuk. PALEOPROTEROZOIC AGE OF PORPHYRY granitEs OF THE JANVAR MASSIF OF THE VOLCHANSKIY BLOCK (AZOV MEGABLOCK)
PALEOPROTEROZOIC AGE OF PORPHYRY granitEs OF THE JANVAR MASSIF OF THE VOLCHANSKIY BLOCK (AZOV MEGABLOCK)
L.M. Stepanyuk 1, https://orcid.org/0000-0001-5591-5169
G.V. Artemenko 1, https://orcid.org/0000-0002-4528-6853
B.V. Borodynya 2
1 M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladin Ave., Kyiv, Ukraine, 03142
2 Public Enterprise "Pivdenukrgeologiya"
Dnipro, Ukraine, 49005
Mineralogical journal 2019, 41 (4): 40-49
Volchansk block is an anticlinal uplift situated in the north-western part of the Azov megablock of the Ukrainian Shield. Characteristic feature of the megablock is the presence of a large number of faults that subdivide it into numerous block structures where linear folds of higher ranks are observed. Of primary importance in the tectonic structure of the region is the system of faults of north-western strike. Horst and graben-like structures are associated with them. The horst-like ("dome") structures are composed of Archean gneisses of the West Azov series and granitoids of the Remiv complex, with graben-like being composed of metasedimentary rocks of the Volchansk thickness. According to geophysical data, the Shevchenko, Fedorivka, Ivanivka and Volchansk synclinal structures were identified in the northern and eastern frames of the Volchansk anticlinorium, which are considered to be the northwest continuation of the Central Azov synclinal structures. They are composed of low metamorphosed sedimentary rocks, which occur unconformable on the highly metamorphosed rocks of the West-Azov series and the Volchansk thickness. These metasedimentary rocks are intruded by granitoids of potassium-sodium composition, that form small granite massifs associated with faults. Geochronological studies of porphyritic granites of the January massif, which is located to the west of the Shevchenko and Fedoriv synclinal structures, are made. It has been established that the U-Pb isotopic age of the Janvar porphyry granitoids of the Janvar massif is 2.06 Ga. According to geochemical data, they have crustal origin and are probably produced by melting from Archean tonalite-trondhjemite-granodiorite (TTG) complex. The granitoids of the Janvar massif are comparable, by isotopic age, petrographic and petrochemical characteristics, with the granitoids of the Anadol complex. Their formation is probably associated with the collision phase of the Sarmatian and Volga-Ural microcontinents.
Keywords: Janvar massif, Volchansk block, Azov megablock, Ukrainian Shield, porphyry granite, monazite, U-Pb age, collision, Anadol complex.
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