Evolutionary stages of the continental crust in the buried basement of theeastern Siberian platform: Sm-Nd isotopic data

Nd isotopic data are presented for rock samples from the buried basement an d crustal xenoliths in kimberlite pipes of the Siberian craton. Based on th e comparison of these results with preexisting geochronological and isotopi c data on crystalline basement outcrops of the Siberian craton, the followi ng stages in the evolution of the continental crust of the buried basement were recognized: Early Archean, Late Archean, and Early Proterozoic. The Ea rly Archean stage was recognized in the Tungusska (similar to 3.4 Ga), Maga n (similar to 3.6-3.1 Ga), and Anabar [from 3.3-3.2 Ga, T-Nd(DM-2st) to 3.5 Ga] geoblocks. The most active crustal buildup is typical of the Late Arch ean stage of the geoblocks. This stage was marked by the development of the continental crust in the basement of the Tungusska (similar to 3.0-2.8 Ga) , Magan (similar to 3.1-2.6 Ga), and Anabar (similar to 3.2-2.7 Ga) geobloc ks. The Early Proterozoic stage was responsible for the formation of the co ntinental crust in the Khapchan terrane of the Olenek geoblock. In the Tung usska, Magan, and Anabar geoblocks, Proterozoic crustal growth proceeded lo cally, and traces of these processes are discernible only in occasional roc k samples recovered by holes from the buried basement and in some crustal x enoliths. Our Nd isotopic data are the first to suggest the existence of a Late Proterozoic (similar to 1.6-1.0 Ga) stage in the evolution of the cont inental crust in the buried basement of the Siberian craton, Indications of this process were detected within the Batomgskii block of the Aldan geoblo ck, in the Olenek geoblock, and in the Akitkan foldbelt. The reliable estab lishment of this stage requires further isotopic and geochronological studi es on the basis of more representative material. The Archean and Early Prot erozoic stages distinguished in the continental crust of the buried basemen t of the Siberian Platform coincide with the stages of crust-forming proces ses recognized in the Anabar and Aldan shields. Considered collectively, av ailable Nd isotopic data make it possible to distinguish an Archean and an Early Proterozoic isotopic provinces of the Siberian craton. The Archean pr ovince comprises the Tungusska, Magan, and Anabar geoblocks, whose main cru st-building processes occurred in the Archean. The Early Proterozoic isotop ic province includes the Khapchan block of the Olenek geoblock and the East ern Aldan block of the Aldan geoblock, which were produced mainly by crust- building processes of Early Proterozoic age.