Geochronology and geochemistry of Permian bimodal volcanic rocks from central Inner Mongolia, China: Implications for the late Palaeozoic tectonic evolution of the south-eastern Central Asian Orogenic Belt

Zircon U-Pb ages, geochemical data and Sr-Nd isotopic data are presented for volcanic rocks from the lower Permian Dashizhai Formation. These rocks are widely distributed in the south-eastern Central Asian Orogenic Belt in central Inner Mongolia, China. The volcanic rocks mainly consist of basaltic andesite and rhyolite, subordinate dacite and local andesite, and exhibit bimodal geochemical features. The results of zircon U-Pb dating indicate that the volcanic rocks formed during the early Permian (292279 Ma). The mafic volcanic rocks belong to low-K tholeiitic to medium-K talc-alkaline series. These mafic volcanic rocks are also characterised by moderately enriched light rare earth element (LREE) patterns; high abundances of Th, U, Zr and Hf; negative Nb, Ta and Ti anomalies; initial Sr-87/(86) Sr ratios of 0.70514-0.70623; and positive epsilon(Nd)(t) values (+1.9 to +3.8). These features indicate that the mafic volcanic rocks were likely derived from the high-percentage partial melting of subduction-related metasomatised asthenospheric mantle. The felsic rocks show an A-type affinity, with enrichments in alkalis, Th, U and LREEs. The felsic rocks are depleted in Ba, Sr, Nb, Ta and Ti and exhibit moderately LREE-enriched patterns (La-N/Yb-N = 2.09-6.45) and strongly negative Eu anomalies (Eu/Eu* = 0.04-0.25). These features, along with the positive cNd(t) values (+2.6 to +7.7) and young T-DM2 ages (T-DM2 = 435-916 Ma), indicate that the felsic rocks Were likely derived from a juvenile crustal source that mainly consisted of juvenile mid-ocean ridge basalt-related rocks. The volcanic association in this study and in previously published work widely distributed in central Inner Mongolia. The observations in this study suggest that the lower Permian volcanic rocks formed in an identical tectonic environment. The regional geological data indicate that the bimodal volcanic rocks from the lower Permian Dashizhai Formation in the study area formed in an extensional setting that was likely related to post-collisional delamination. (C) 2017 Elsevier Ltd. All rights reserved.National Key Basic Research Program of China [2013CB429801]; Geological Survey Project of China [1212010050503]; National Natural Science Foundation of China [41372225]SCI(E)ARTICLE370-38913