Late Paleozoic sedimentation recording back-arc basin evolution in response to Chinese Altai−East Junggar convergence in Central Asia

Abstract

Sedimentological and geochronological data from late Paleozoic strata located between the East Junggar and Chinese Altai regions in NW China were examined, aiming to decipher the tectono-sedimentary evolution of this important tectonic boundary. Carboniferous sediments on the East Junggar side show arc-proximal depositional characteristics of the proximal Heishantou and Nanmingshui Formations and distal Beitashan and Yundukala Formations, while the Erqis complex on the Chinese Altai side is characterized by continental margin affinity. Lithological analysis revealed the dominant input of arc-related detritus for all these sequences and a uniform transition from volcaniclastic to siliciclastic components in their respective upper sections. The investigated East Junggar strata are dominated by Carboniferous zircons with positive εHf(t) values, sourced exclusively from the southerly Yemaquan-Jiangjunmiao arc domain, whereas the Erqis complex received detritus from the same arc domain but also evolved components from the northerly Chinese Altai. Combined with regional data, the examined strata are interpreted to have developed in a back-arc basin with regard to an arc that developed above the north-dipping Kalamaili subduction system. In contrast, the unmetamorphosed Lower Permian Tesibahan Formation, unconformably overlying the Erqis complex, received detritus mainly from the Chinese Altai. These sediments were deposited in an intracontinental piggyback or synformal basin following closure of the back-arc basin. The late Paleozoic sedimentation records support the interpretation that the Chinese Altai and East Junggar domains evolved from the same suprasubduction system prior to the Carboniferous rather than as independent terranes mutually juxtaposed during Permian lateral translation, as previously proposed.