NEOPROTEROZOIC METABASALTS OF THE TYYA COMPLEX OF THE OLOKIT RIFT TROUGH (Baikal-Muya Belt): COMPOSITION, U-Pb AGE, ISOTOPE-GEOCHEMICAL CHARACTERISTICS, AND GEODYNAMIC EFFECTS
D.A. Orsoev1, I.V. Gordienko1, A.N. Bulgatov1, R.A. Badmatsyrenova1, S.I. Dril'2, V.F. Possokhov1
a:2:{s:4:"TEXT";s:283:"1Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh’yanovoi 6, Ulan-Ude, 670047, Russia
2A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia";s:4:"TYPE";s:4:"html";}
Keywords: Metavolcanic rocks, tholeiitic basalts of back-arc basins, minerals, subductional component, geochemistry, geochronology, isotopy, Olokit trough, Nyurundukan island arc
Abstract
We present results of new mineralogical, geochemical, geochronological, and isotope (Sm-Nd, Rb-Sr, and O) studies of the volcanic rocks of the Tyya complex in the Olokit trough. These are normal tholeiitic basalts and scarcer basaltic andesites forming a fractionated series with mg# = 45-65, medium TiO2 contents (0.73-1.62 wt. %), low P2O5 contents (0.04-0.25 wt. %), and a significant domination of Na over K (Na2O/K2O = 2.1-50.0). The rocks are metamorphosed to greenschists, which are composed of chlorite, actinolite, epidote, and albite with quartz, titanite, ilmenite, and magnetite impurity. The metabasalts have is an age of 915 ± 5 Ma (zircon U-Pb dating) and are characterized by wide variations in εNd(T) (-3.5 to -11.9) and 87Sr/86Sr (0.70602-0.70732) and high δ18O values (9.0-15.2 ‰) as compared to the mantle ones. According to the isotope-geochemical characteristics, the studied metabasalts have features of both IAB and E-MORB. The Tyya metabasalts might have resulted from the melting of the lithospheric mantle with a subductional component. Comparison of the studied rocks with volcanic rocks of recent geodynamic settings shows their similarity to basalts of back-arc basins. The Tyya metabasalts might belong to a back-arc basin of the late Mesoproterozoic Nyurundukan island arc system.
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