Mesoproterozoic granitoid magmatism in the Trans-Angara segment of the Yenisei Range: U-Pb evidence

Abstract

Marginal parts of cratons yield valuable informa� tion on the evolution of the lithosphere, which is con� trolled by different geodynamic processes. This explains the interest in problems of reconstruction and development of accretionary-collisional continental structures at craton margins (1). The Yenisei Range representing a foldthrust belt in the southwestern margin of the North Asian Craton is geodynamically one of the most interesting regions of Siberia. Its TransAngara segment hosts widespread Proterozoic substantially metasedimentary rocks of the Tei Group. The basal part of its section corresponds to the Malaya Garevka and Nemtikha metamorphic complexes, pre� sumably Early Precambrian in age (2). The strati� graphic position and age of these rocks are debatable. Recent studies of presumably the oldest granitoids in the TransAngara part of the Yenisei Range using pre� cise geochronological methods revealed their Neopro� terozoic age (865-880 Ma) (3). Based on these data, many researchers have arrived at the conclusion that no Grenvillian collisional events related to the forma� tion of the supercontinent Rodinia took place in this region and that its stratified and intrusive complexes are Neoproterozoic in age, not older. The original geochronological data indicate devel� opment of Mesoproterozoic granitoid magmatism in this region. These results are important for periodiza� tion of the Precambrian and understanding the geody� namic evolution of the western North American Cra� ton as well as for solving the widely discussed problem concerning the probable position of this continental block in the ancient supercontinents Pangea I and Rodinia (4, 5). Periodization of the Mesoproterozoic is one of the fundamental problems dealing with the long geologi� cal period (1.6-1.0 Ga) spanning from termination of the intense growth of the continental crust to the for� mation of Rodinia. Inasmuch as Mesoproterozoic rocks are characterized by a limited distribution, the formation mode of the crust at this stage remains unclear, which prompts the question: did the super� continent exist continuously as a single block during this stage or was it first broken similarly to Pangea I (its predecessor) and then later amalgamated at the end of the Mesoproterozoic after the Grenvllian Orogeny to form epiGrenvilian Rodinia (1).