We report zircon for from ophiolitic and high-grade rocks of the Neoproterozoic Baikal-Muya belt of Siberia that occupies an arc-shaped area on the southeastern margin of the Siberian craton. It consists of arc-related plutonic, metavolcanic and metasedimentary rocks as well as fragmented ophiolites and high-grade metamorphic assemblages. Magmatic zircons from two plagiogranite dyke samples of the Mamakan ophiolite complex in the Sredne-Mamakan massif of the eastern Baikal-Muya belt yielded similar and concordant SHRIMP mean Pb-206/U-238 ages of 640.0 +/- 4.1 and 650 +/- 6 Ma, respectively, that reflect the time of dyke emplacement and from which we suggest an age of ca. 645 Ma as the most likely time of ophiolite formation.Enderbitic gneisses of the North Baikal area, in the western part of the Baikal-Muya belt, contain complex zircon populations that reflect variable recrystallization, Pb-loss and metamorphic overgrowth during granulite-facies metamorphism. LA-ICP-MS dating of these zircons yielded inconclusive results that led us to undertake a detailed study of cathodoluminescence images combined with U-Pb SHRIMP dating. Well-preserved magmatic domains in zircons from enderbite sample 2821 yielded concordant results with a mean Pb-206/U-238 age of 640 +/- 5 Ma, slightly higher but broadly comparable with the data obtained by LA-ICP-MS. The zircon populations of two more enderbitic gneiss samples are more complex, and their LA-ICP-MS data constitute broad swaths along concordia between ca. 840 and 600 Ma, reflecting two end-member isotopic components, namely an igneous crystallization event at ca. 800 Ma and a Pb-loss and recrystallization event at ca. 600 Ma. SHRIMP analyses of magmatic zircon domains of these samples yielded concordant data with identical mean Pb-206/U-238 ages of 826 +/- 7.5 Ma and 826 +/- 8 Ma, respectively, whereas low-U metamorphic rims crystallized at 640 +/- 7 Ma. Newly crystallized ball-round metamorphic zircons in one sample produced a mean Pb-206/U-238 age of 640 +/- 6 Ma. We suggest that the protoliths of the enderbitic gneisses crystallized at 826 +/- 7.5 Ma and experienced granulite-metamorphism at 640 +/- 6 Ma. The LA-ICP-MS analyses are fully compatible with this interpretation.Our geochronological data and previously published ages for Neoproterozoic igneous rocks of the BaikalMuya belt define two age groups at 830-780 and 650-640 Ma. We interpret that the older group reflects the evolution of a large arc system in the Baikal-Muya belt and the eastern Sayan-northwestern Mongolia region, whereas the younger group documents collision between the above arc system and the southern margin of the Siberian craton. (c) 2015 Elsevier Ltd. All rights reserved.

В работе приведены новые геологические, геохимические и изотопно-геохимические данные по магматическим породам детально изученного участка западной части Байкало-Муйского пояса – представительного сегмента неопротерозойского обрамления Сибирского кратона. В строении района исследования принимают участие три ассоциации горных пород: гранулит-эндербит-чарнокитовый, ультрамафит-мафитовый комплексы и наиболее поздняя тоналит-плагиогранит-гранитная серия пород, по геохимическим характеристикам отвечающая адакитам. Показано, что комплекс тоналитов и гранитов интрудирует как породы метаморфической ассоциации, так и габброиды мыса Тонкий, Слюдинского и Курлинского массивов. Для тоналитов получены геохронологические данные по цирконам – 595 ± 5 млн лет, указывающие, с учетом геологической информации, что не более чем за несколько десятков миллионов лет после формирования гранулиты были выведены в верхние уровни литосферы. Sm-Nd изотопные данные свидетельствуют о присутствии ювенильного материала в составе серии гранитоидов – Nd(t) 3.2–7.1. Проведен обзор данных по комплексам – индикаторам геодинамических условий, существовавших в неопротерозое в Байкало-Муйском поясе: офиолитам, островодужным сериям, эклогитам и молассовым толщам. Обсуждается роль пространственно связанных гранулитов и ультрамафит-мафитовых интрузий, а также гранитоидов с адакитовыми геохимическими характеристиками, для палеогеодинамических реконструкций западной части Байкало-Муйского пояса во взаимосвязи с другими элементами структуры Центрально-Азиатского пояса, прилегающими к южной части Сибирской платформы.

The paper presents new geological, geochemical, and isotopic data on igneous rocks from a thoroughly studied area in the western Baikal-Muya Belt, which is a representative segment of the Neoproterozoic framework of the Siberian Craton. Three rock associations are distinguished in the studied area: granulite-enderbite-charnockite and ultramafic-mafic complexes followed by the latest tonalite-plagiogranitegranite series corresponding to adakite in geochemical characteristics. Tonalites and granites intrude the metamorphic and gabbroic rocks of the Tonky Mys Point, as well as Slyudyanka and Kurlinka intrusions. The tonalites yielded a U-Pb zircon age of 595 ± 5 Ma. The geochronological and geological information indicate that no later than a few tens of Ma after granulite formation they were transferred to the upper lithosphere level. The Sm-Nd isotopic data show that juvenile material occurs in rocks of granitoid series (ɛ Nd (t) = 3.2–7.1). Ophiolites, island-arc series, eclogites, and molasse sequences have been reviewed as indicators of Neoproterozoic geodynamic settings that existed in the Baikal-Muya Belt. The implications of spatially associated granulites and ultramafic-mafic intrusions, as well as granitoids with adakitic geochemical characteristics for paleogeodynamic reconstructions of the western Baikal-Muya Belt, are discussed together with other structural elements of the Central Asian Belt adjoining the Siberian Platform in the south.