Tectonic Evolution of Tuvinian Trough (Northern Part of Central Asian Orogenic Belt): Synthesis of Geological Data and Results of Feldspar Ar‒Ar Dating

The Tuvinian rift trough, located in the northern part of the Central Asian orogenic belt (CAOB), was formed in the Early Devonian on late Proterozoic (?)‒Early Paleozoic terranes as a result of the activity of the Altai-Sayan mantle plume. The sedimentary record from the middle Paleozoic to the middle Mesozoic, preserved in the Tuvinian trough, and the middle Paleozoic igneous complexes confined to the structures of the trough, reflect the stages of evolution of the Earth’s crust in the Tuva segment, that necessary for understanding the history of the geological development of the CAOB as a whole. Dating of accessory and rock-forming minerals from igneous rocks using low-temperature geochronology methods allows us to obtain additional information about post-magmatic processes and thereby update the model of tectonic evolution of the region. In this study, we have reconstructed the stages of tectonic development of the Tuvinian trough in the northern part of the CAOB based on the analysis of geological data and new Ar‒Ar dating data on feldspars from mafic intrusions. As a result of this study, the chronology of the previously known stages of post-magmatic processes manifested in the Tuvinian trough was clarified, and new stages were identified according to the tectonic evolution of the CAOB. Ar‒Ar dating of feldspars carried out on eight samples showed four age groups: (i) Late Devonian, (ii) middle Carboniferous, (iii) early Permian and (iv) Early Jurassic. Late Devonian (~377 and 375 Ma) ages record an impulse of mafic magmatism, widely manifested in the northern segments of the CAOB (~380‒365 Ma). Middle Carboniferous (~320 and 319 Ma) dates may be associated with the closure of the Ob-Zaisan branch of the Paleo-Asian ocean as a result of the Kazakhstan-Siberian collision. Early Permian (~290–279 Ma) ages are consistent with the formation of late Carboniferous–Early Permian (~305–275 Ma) large igneous provinces in connection with rifting processes in the northern segments of the CAOB. Finally, a single Early Jurassic (~188 Ma) age marks tectonic reorganization of the CAOB in Late Triassic‒Early Jurassic in response to (i) closure of the Paleotethys ocean with subsequent collision of the Cimmerian blocks and the southern margin of the Eurasian continent and/or (ii) activity of the Mongolian mantle plume.