Age and Geochemical Characteristics of Major Mafic Dyke Swarms in the Southern Part of the Siberian Craton

ages and geochemical characteristics cut Precambrian rocks of the southern part of the Siberian craton (Irkutsk Promontory). Each generation of dykes is related to a specific stage of Siberian evolution. Here, we present geochronological and geochemical data for Palaeoproterozoic ‒ Palaeozoic mafic dyke swarms, located within the Sharyzhalgai and Goloustnaya inliers of the Siberian craton. An older generation of Palaeoproterozoic dolerite dykes is exposed in the Kitoi area (Sharyzhalgai inlier). Zircon from the Kitoi dyke has yielded a U-Pb age of 1864 ± 4 Ma, while baddeleyite from the Malozadoisky dyke provides an age of 1863 ± 1 Ma (Ernst et al., 2016). The Malozadoisky dyke is 150-m-wide, whereas the Kitoi dykes are 0.5-mwide (Ernst et al., 2016). Compositionally, the Kitoi dolerites are sub-alkaline and alkaline tholeiites. The dolerite compositions are close both to OIB with high K2O and P2O2 contents of 2.28–2.52 and 0.74–0.77 wt.% respectively, and to arc basalts with moderate TiO2 (1.18– 1.25 wt.%) and Nb (12.4–14.7 ppm), high concentrations of Sr (907–989 ppm), La (116–120 ppm), and Th (7–12 ppm). It is likely that these dolerites originated from melting of a mixed mantle source. The emplacement of these dykes could be related to post-collisional extension following accretionary and collisional events responsible for amalgamation of the Siberian craton. Mesoproterozoic dykes are exposed along the coast of Lake Baikal near the village of Listvyanka (Sharyzhalgai inlier) and in the Goloustnaya area (Goloustnaya inlier). UPb baddeleyite–zircon ages are 1350 ± 6 Ma for the Listvyanka dolerites (Ernst et al. 2016) and ca. 1338 Ga for the Goloustnaya dolerites. Known exposures of the Listvyanka dykes include one relatively thick dyke (30 m) and several smaller dykes, whereas the width of Goloustnaya dykes varies from about 10 to 100 m. The chemical compositions of these dolerites are essentially sub -alkaline basalts (Na2O+K2O = 2.2–3.9 wt.%). The rocks are differentiates (Mg# = 36–54) of tholeiitic magmas with relatively high TiО2 (1.6–3.2 wt.%) and P2O5 (0.2 – 0.6 wt.%). A clear, positive Nb–Ta anomaly in normalized multi-element diagrams suggests an OIB affinity. These dykes are interpreted to have been generated during plumerelated Mesoproterozoic intra-continental extension, and likely represent part of the plumbing system of a Large Igneous Province (LIP). The Neoproterozoic (725 – 715 Ma) Irkutsk mafic dyke swarm (Ernst et al., 2016) is widespread in the Sharyzhalgai and Goloustnaya inliers, with individual dyke thicknesses ranging from 1 to 15 m. These dykes are subalkaline tholeiitic dolerites (Na2O + K2O = 1.4–4.2 wt.%). With Mg#’s that vary from 30 to 78, these dolerites include some of the most primitive chemical compositions among Tatiana V. DONSKAYA, Dmitry P. GLADKOCHUB, Richard E. ERNST, Sergei A. PISAREVSKY, Anatoliy M. MAZUKABZOV, Ulf SÖDERLUND, Michael T.D. WINGATE, Michael A. HAMILTON, and Elena I. DEMONTEROVA, 2016. Age and Geochemical Characteristics of Major Mafic Dyke Swarms in the Southern Part of the Siberian Craton. Acta Geologica Sinica (English Edition), 90 (supp. 1): 125-126.