Ancient primary boninitic melts of the Gorny Altai (65-105 km, 1410-1590 °C) were studied from the composition of melt inclusions in clinopyroxenes. We estimated their parameters and the conditions for the onset of magma crystallization in an intermediate chamber at a depth of about 30-35 km, which appear similar to the reference boninitic magmatism of the modern Izu-Bonin island arc. A combined analysis of the composition of inclusions and clinopyroxenes from Gorny Altai boninites shows that within a range of minimum temperature values (1140-1120 °C), the crystallizing material continuously ascends from a depth of 12 to 0.6 km. The pattern is different in case of higher-temperature magmas, and three zones of pyroxene crystallization are distinguished: 18.0-13.8 km (1245-1205 °С), 12.0-3.5 km (1240-1185 °С), and 3.3-0.6 km (1185-1145 °С). Actually, these zones correspond to the intermediate deep-seated magmatic chambers typical of modern island-arc subduction zones [Dobretsov et al., 2016]. Based on the detailed study of zonal phenocrysts of clinopyroxene in boninites from the Kuray ophiolites, we established the parameters of the evolution of the ascending boninite melts. Three temperature intervals (1220-1200 °С, 1235-1210 °С, and 1120-1220 °С) and three pressure ranges (1.5-11.5 kbar, 2.0-6.0 kbar, and 2.0-0.3 kbar) are distinguished. One case shows a significant pressure drop (from 11.5 to 1.5 kbar) with a small drop in temperature (from 1220 °C to 1200 °C). In the second case, the pressure rises from 2.0 to 6.0 kbar, and the crystallization temperature decreases from 1235 to 1210°C. In the third case, crystallization begins at a stable temperature (1120-1140 °C) and a stable pressure (1.4-2.0 kbar); then, in the near-surface conditions, the temperature increases to 1220 °C, and the pressure decreases sharply to 0.3 kbar.
The carried out researches with the help of 40Ar/39Ar analysis have shown a coincidence of formation (about 490 million years) of Paleozoic picrite and basalt complexes of the basement of the Western Siberian Plate. The data on petrochemistry, geochemistry of rare and rare-earth elements, and also on compositions of clinopyroxenes, testifies to formation of picrites of borehole № 11 (Chkalovsky area) as a result of action of intra plate magmatic systems of oceanic islands - OIB. Calculations on the basis of clinopyroxene compositions speak about considerable parameters of crystallization of picrite porphyrite minerals: 1215-1275 °C, 4.5-8 kbar. As a whole, it is established that considered picrite basalt complexes were formed with the assistance of enriched plume magmatic systems in intra plate conditions of ancient ocean near to its active margin.
Комплексные исследования колчеданного раннекембрийского Кызыл-Таштыгского месторождения (Восточная Тува) позволили реконструировать палеогидротермальные системы, выяснить физикохимические условия гидротермальных процессов, а также установить особенности существования древней пригидротермальной биоты в зонах действия растворов, участвовавших на всех стадиях формирования рудоносных структур, начиная с воздействия постмагматических флюидов и заканчивая низкотемпературными гидротермами. Представительные данные по биоте были получены при изучении объектов, находившихся в зоне влияния относительно низкотемпературных гидротермальных систем. В одних случаях находки микроорганизмов приурочены к вмещающим рудные тела базальтовым комплексам, а в других случаях найденная фауна связана с железисто-кремнистыми отложениями. Выяснено, что микроорганизмы в миндалинах базальтов развивались при температурах около 110-140 °С под воздействием гидротермальных растворов. Гораздо более низкие температуры (до 100 °С) существовали при развитии микрофоссилий в кварц-гематитовых гидротермальных постройках Кызыл-Таштыгского месторождения.Ключевые слова: кембрийская пригидротермальная биота, колчеданные месторождения, флюидные включения, микрофоссилии, гидротермальные растворы
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