Abstract
Among the Riphean–Vendian dyke complexes of the basic composition, which intersect the Precambrian strata of the Bashkirian meganticlinorium (Southern Urals), one of the most common is the Kurgas gabbro-dolerite complex dated to the Early – Middle Riphean. This article presents the isotopic dating, petrological and geochemical features of the rocks belonging to the Kurgas complex. It gives the first description of the regional geochemical zoning that is reflected in a decrease in SiO 2 contents from the north to the south along the Bashkirian meganticlinorium, and an increase in MgO contents in the same direction, which is attributed by the authors to an increase in the permeability of the crust to the south during opening of the Mashak riftogenic structure. New data on isotopic ages were obtained for the dyke that cuts the Satka formation of the Lower Riphean – 1318±10 ( 40 Ar/ 39 Ar), the intrusion in the exocontact zone of the Berdyaush rapakivi granite massif – 1349±11 Ma (U-Pb), and the andesite dyke among the metamorphic rocks of the Taratash complex – 1365.6±6.6 Ma (U-Pb). These ages, in combination with the previously obtained data, suggest that the complex formed during a rather long period of time (from 1385 to 1318 Ma, as a minimum), which corresponds to the beginning of the Middle Riphean. Isotopic U-Pb age of the dyke that cuts the contact zone of the Berdyaush massif, suggests that the major portion of the massif had already crystallized by that time and was exhumed into the shallow zone of brittle deformation.
Highlights
New data on isotopic ages were obtained for the dyke that cuts the Satka formation of the Lower Riphean – 1318±10 (40Ar/39Ar), the intrusion in the exocontact zone of the Berdyaush rapakivi granite massif – 1349±11 Ma (U-Pb), and the andesite dyke among the metamorphic rocks of the Taratash complex – 1365.6±6.6 Ma (U-Pb)
which intersect the Precambrian strata of the Bashkirian meganticlinorium
the Kurgas gabbro-dolerite complex dated to the Early – Middle Riphean
Summary
FOR CITATION: Khotylev A.O., Tevelev A.V., Bychkova Ya.V., Latyshev A.V., Anosova M.B., 2020. Среди рифейско-вендских дайковых комплексов основного состава, секущих докембрийские толщи Башкирского мегантиклинория (Южный Урал), одним из самых распространенных является кургасский габбро-долеритовый раннесреднерифейский комплекс. В соче тании с полученными ранее, указывают на формирование комплекса на достаточно большом протяжении времени – как минимум от 1385 до 1318 млн лет, что отвечает началу среднего рифея. Получены новые изотопные данные по трем дай кам (пробы 1036, 18102-7, Р51002) габбро кургасского комплекса, а также геохимические и петрографические данные для 30 тел габброидов из Бакало-Саткинского и Кусинского районов Челябинской области, предпо ложительно относящихся к этому комплексу. Геохи мические данные для тел кургасского комплекса, про рывающих на самом севере Башкирского мегантикли нория архейско-раннепротерозойский тараташский комплекс (Тараташский выступ), приведены в работе [Khotylev et al, 2017].
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