ISSN 1028-334X, Doklady Earth Sciences, 2015, Vol. 461, Part 2, pp. 334–338. © Pleiades Publishing, Ltd., 2015. Original Russian Text © N.V. Popov, I.Yu. Safonova, A.A. Postnikov, A.A. Terleev, Tsuyoshi Komiya, D.A. Tokarev, 2015, published in Doklady Akademii Nauk, 2015, Vol. 461, No. 5, pp. 558–562. 334 The Siberian Platform is the largest structure of Northeast Asia, which records practically its entire geological history since the Early Archean. The base- ment of the platform crops out in the Aldan Shield in the southeast, Anabar Shield, Olenek Uplift in the north, and as small inliers along its southwestern periphery (Kan, Sharyzhalgai, Irkutnyi, and Angara– Kan) (Fig. 1). The remaining part of the platform is overlain by a thick cover of Phanerozoic sedimentary and igneous rocks. The age and composition of the buried basement of the Siberian Platform is deter- mined by analogy with the well-known metamorphic and igneous rocks cropping out in the above-men- tioned shields and inliers. The data on the occurrence, depth, thickness, and lateral distribution of regional rock complexes of the basement under the cover are usually derived from geophysical data whole-rock composition of blocks (terranes) and specific features of boundaries between these blocks (Fig. 1). Over 20 boreholes of those drilled in the Siberian Platform during the last 20–30 years have recovered the Precambrian basement in its western and central parts [e.g., 1–3]. The data yielded by these boreholes combined with information on the areas of the plat- form accessible for observations and from crustal xenoliths of kimberlite pipes make it possible to deter- mine the composition of the basement in this region. In connection with the recent intensive and exten- sive development of East Siberia, the problem of defining the main stages of the formation of the Sibe- rian Platform including the age and composition of its Precambrian basement remains debatable. The first isotopic dates obtained by the Pb–Pb thermionic emission method for zircons extracted mainly from granitoids and, to lesser extent, metamorphic rocks recovered by deep boreholes correspond to the interval of 2950 to 1720 Ma [4, 5]. Subsequently, more Sm– Nd age estimates were obtained, using the samples from deep boreholes and kimberlite xenoliths, for a protolith of basement rocks, i.e., for the time corre- sponding to the separation of matter protolithic mate- rial from the mantle [2, 3, 6, and others]. The obtained dates can be divided into three groups corresponding to different stages of Earth evolution. The Early Archean blocks correspond to the global stages in the formation of the early cratons of the Earth [3, 7]. The Paleoproterozoic blocks were likely related to the for- mation of the Columbia supercontinent, i.e., collision and amalgamation of Archean cratons or “conti- nents,” which are considered to record the main stages in crust-forming processes [3, 8]. The Mesoprotero- zoic rocks mark the formation of orogenic belts along the margins of the Siberian craton [3]. At the same time, the problem of correct dating of the basement of the Siberian Platform, particularly in its central parts, is still far from a solution mostly because of a deficiency of reliable isotopic dates for borehole rock samples. In this paper, we present first geochemical and geochronological data (U–Pb zir- con age) from granitoids of the southern Siberian Plat- form by the Mogdinskaya-6 exploration borehole, which was drilled at the Nizhnyaya Tunguska–Vilyui river watershed in the Chona River basin, a right trib- utary of the Vilyui River approximately 300 km south- west of Mirnyi (Fig. 1). The borehole was drilled in connection with the exploration of hydrocarbon deposits. According to various models, the basement in this area consists of the Archean West Yakutia cra- tonic block or Magan–Vilyui granite–greenstone ter- rane [3], or Magan granulite–gneiss terrane [6], or Paleoproterozoic Granitoids from the Basement in the Central Part of the Siberian Platform (Borehole Mogdinskaya-6): U–Pb Age and Composition N. V. Popov a , I. Yu. Safonova b, c *, A. A. Postnikov a , A. A. Terleev a , Tsuyoshi Komiya d , and D. A. Tokarev a Presented by Academician A.E. Kontorovich October 21, 2013 Received October 15, 2013 DOI: 10.1134/S1028334X15040145 a Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia b Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia c Novosibirsk State University, Novosibirsk, Russia d University of Tokyo, Tokyo, Japan *e-mail: inna@igm.nsc.ru GEOLOGY