Chemical composition and crystallization conditions of trachybasalts from the Dzhida field, Southern Baikal volcanic area: Evidence from melt and fluid inclusions |
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| Authors: | V B Naumov M V Portnyagin M L Tolstykh V V Yarmolyuk |
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| Institution: | (1) Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia;(2) Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 109017, Russia |
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| Abstract: | Melt and fluid inclusions have been studied in olivine phenocrysts (Fo 81–79) from trachybasalts of the Southern Baikal volcanic area, Dzhida field. The melt inclusions were homogenized, quenched, and analyzed on an electron and ion microprobe. The study of homogenized glasses of nine inclusions showed that basaltic melts (SiO2 = 47.1–50.3 wt %, MgO = 5.0–7.7 wt %, CaO = 7.1–11.1 wt %) have high contents of Al2O3 (17.1–19.6 wt %), Na2O (4.1–6.2 wt %), K2O (2.2–3.3 wt %), and P2O5 (0.6–1.1 wt %). The volatile contents are low (in wt %): 0.24–0.31 H2O, 0.08 F, 0.03 Cl, and 0.02 S. Primary fluid inclusions in olivines from four trachybasalt samples contain high-density CO2 (0.73–0.87 g/cm3), indicating a CO2 fluid pressure of 4.3–6.6 kbar at 1200–1300°C and olivine crystallization depths of 16–24 km. Ion microprobe analyses of 20 glasses from melt inclusions for trace elements showed that the magmas of the Baikal rift were enriched in incompatible elements, thus differing from oceanic rift basalts and resembling oceanic island basalts. A comparison of our data on melt and fluid inclusions in olivine from trachybasalts of the Dzhida field with preexisting data on the Eastern Tuva volcanic highland in the Southern Baikal volcanic area showed that they had similar contents of volatiles, major, and trace elements. |
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