Olonkhuduk Anorthosite Pluton of the Baidaric Terrane of the Central Asian Orogenic Belt: Geological Position and Age

Abstract

Abstract???Anorthosites of the Olonkhuduk pluton of the Central Asian Orogenic Belt are dated at 1772 ?? 1 Ma (ID TIMS U-Pb zircon method). Similar age estimate (1784 ?? 10 Ma) was previously obtained for anorthosite of the Khungilingol pluton from the Ider block of the Tarbagatai terrane. These data indicate a significant time gap (70???60 Ma) between the collision that formed the Early Precambrian blocks of the Baidaric and Tarbagatai terranes in the range 1860???1850 Ma and the emplacement of the anorthosites. The termination of accretion-collision processes and consolidation of the Early Precambrian block of the Baidaric terrain are marked by the postkinematic subalkaline granites with an age of 1825 ?? 5 Ma. Geochemically, the anorthosites of the Olonkhuduk and Khungilingol plutons are similar to the typical anorthosites of ancient cratons. Sm-Nd isotopic data indicate a mixed source of these anorthosites: juvenile mantle component of Paleoproterozoic age and crustal component of Neoarchean age. It can be assumed that the primary mafic magma of the anorthosites experienced a significant crustal contamination. Based on the similar geologic setting, age, and composition, the anorthosites of the Olonkhuduk and Khungilingol plutons can be ascribed to a single within-plate complex. The age values obtained for the anorthosites coincide with the estimated age of rift magmatism in the North China craton at 1.8???1.75 Ga and the emplacement time of mafic dikes swarms at 1778 ?? 3 Ma (SIMS U-Pb method). Thus, the considered Early Precambrian blocks by the end of the Paleoproterozoic (about 1900???1850 Ma) could be a part of the Columbia supercontinent (Rogers and Santosh, 2002).