Detrital zircon U-Pb ages, Hf isotopes and tectonic implications for Palaeozoic sedimentary rocks from the Xing-Meng Orogenic Belt, Middle-East Part of Inner Mongolia, China

The Xing-Meng Orogenic Belt is the eastern extension of the Central Asian Orogenic Belt that marks the boundary between the North China Block and the Siberian Block. Studies of zircon U-Pb ages and Hf isotopic compositions show that four elastic sedimentary rock samples from different parts of the regional stratigraphic sequence were deposited at different ages, none earlier than Mid- or Early Silurian. Two sedimentary rocks were deposited during or after the Early Permian. Almost all zircons are of igneous origin. In Silurian and Devonian sediments, zircons show several modal age peaks, and in Permian sediments, zircons show a unimodal age peak. Based on the zircon age distribution of sedimentary rocks versus known ages from exposed rocks of the potential source regions, most of the zircons were derived from the Xing-Meng Orogen itself. A few came from the South Mongolian microcontinent or the Siberia Block, but none came from the North China Block. The zircons of a biotite-plagioclase paragneiss in Xilinhot have similar provenance to the sediments and were deposited during or after the Middle Devonian. Similarities between zircon age spectra and events in underlying rocks of sedimentary origin show that the sediments lie at their deposition site north of the Solonker suture zone because north-dipping subduction and elevation blocked deposition of material from farther afield. Hf isotope compositions show the crustal accretion stages of the provenance areas during the Meso- to Neoarchaean. Palaeoproterozoic and Early and Late Palaeozoic. A two-component mixing calculation based on Hf isotopes shows the large scale of the crustal accretion event of the region. Copyright (C) 2010 John Wiley & Sons, Ltd.