Zircon U-Pb ages and Hf isotopes of Paleozoic metasedimentary rocks from the Habahe Group in the Qinghe area, Chinese Altai and their tectonic implications

Abstract

As one of the largest accretionary orogens in Earth's history, the Central Asian Orogenic Belt has attracted much attention in the past two decades, but there are still many unresolved issues regarding its tectonic nature and evolution. This is the case with the Chinese Altai whose tectonic provenance remains controversial, especially for the Paleozoic era. As the most widely exposed meta-sedimentary rocks in the Chinese Altai, the Habahe Group was previously considered as representing a component of Precambrian micro-continent, forming at a passive continental margin. Our new U-Pb data for detrital zircons from the Habahe Group in the Qinghe region of the eastern Chinese Altai indicate that the strata were deposited from the late Silurian to early Devonian (427–405 Ma) and experienced regional metamorphism in the middle Devonian (383 ± 9 Ma), as constrained by the age of youngest detrital zircons (427 ± 13 Ma), the age 405 ± 3 Ma of the tonalite that intrudes the Habahe Group, and the metamorphic age of 383 ± 9 Ma. Additionally, the majority of zircons from the Habahe Group have positive εHf(t) values (+0.22–+15.02). These data, combined with geochemical features and maturity of the sedimentary rocks, indicate an immature provenance for the Habahe Group, with the source materials mainly derived from a juvenile crust with some old continental components. The juvenile crust was most likely formed in a subduction zone, developing in the Chinese Altai during early-middle Paleozoic time. New geochemical data presented in this study suggest that the Chinese Altai was a transitional arc during early Paleozoic time, similar to the Japan-type arc with involvements of old continental components. Therefore, it is proposed that the Chinese Altai was likely rifted from the south margin of the Siberia Craton, probably related to the break-up of the Rodinia Supercontinent, and then experienced accretion and reworking with the subduction of the Paleo-Asian Ocean during early Paleozoic time.