EARLY PALEOZOIC SNEZHNAYA GABBRO-SYENITE INTRUSION IN SOUTHWESTERN BAIKAL REGION (trace-element signature of crust/mantle mixing)
M.I. Grudinin, S.V. Rasskazov*, S.N. Kovalenko*, and A.M. Il'yasova*
Irkutsk State University, 3 ul. Lenina, Irkutsk, 664003, Russia
* Institute of the Earth's Crust, Siberian Branch of RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Early Paleozoic, collision, alkaline rocks, trace elements, Baikal region
Pages: 1043-1052
Abstract
The Snezhnaya gabbro-syenite intrusion is composed of medium-alkaline and transitional rocks, namely gabbroics, syenites, and granodiorites. It intruded after the formation of the metamorphic complex of the southwestern Baikal region associated with the Early Ordovician collision. Gabbroics crystallized at the early stage of intrusion and show mantle and subduction signature. Granodiorites are crosscut by thin veins of S-type gabbroics. The final intrusion stage produced syenite veins with I-type features. Besides magmatism, the Snezhnaya rocks bear traces of metasomatism which accompanied the intrusion of syenites. Many samples show better or worse pronounced Eu peaks or dips indicating fractionation of plagioclase. Ore gabbro has no Eu anomalies.
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