Grenvillian evolution of the Qaidam block and its position in Rodinia constrained by U–Pb–Hf composition of detrital zircons from the Altyn Tagh, Northern Tibet

Abstract

The U–Pb ages and Hf isotopic composition of detrital zircons provide important constraints on basin evolution and paleogeography. The Qaidam block, a continental fragment along the northeastern margin of the Tibetan Plateau, has been suggested to have been either in an internal or a peripheral position in Rodinia. We present a systematic study of late Mesoproterozoic to Ediacaran sedimentary sequences from the Altyn Tagh belt, a part of the Qaidam block displaced by the Altyn Tagh fault, in an effort to establish its position within Rodinia. The (meta-)sedimentary rocks of the Altyn Complex of South Altyn can be correlated with the Taxidaban Group, the part of the basement(meta-)sedimentarysequence of Central Altyn, on the basis of lithological and geochronological similarities. Both of these were deposited in the late Mesoproterozoic to early Neoproterozoic. The early Neoproterozoic Suoerkuli Group of Central Altyn and its coeval magmatism formed in an extensional setting. This extensional episode facilitated thinning of the lithosphere during the late Tonian–Ediacaran when the sedimentary protoliths of the Hongliuquan Complex were deposited. Detrital zircon grains from late Mesoproterozoic to Ediacaran sedimentary sequences in the Altyn Tagh orogenic belt show a wide distribution of Meso- and Paleoproterozoic ages between 1800 and 1000 Ma, which match well with contemporaneous supracrustal sequences in northeastern Laurentia. In combination with the similarity in late Mesoproterozoic to Ediacaran tectono-thermal events, we propose the Qaidam block was located along the northeast Laurentian margin during the late Meso- to Neoproterozoic assembly of Rodinia.