K-Ar dating of late Mesozoic volcanism and geochemistry of volcanic gravels in the North Huaiyang Belt, Dabie orogen: Constraints on the stratigraphic framework and exhumation of the northern Dabie orthogneiss complex

<正>Two eruption episodes are identified through systematic field investigations and K-Ar dating of the late Mesozoic volcanic rocks in the North Huaiyang belt (NHB), Dabie orogenic belt, of which the earlier volcanic suite termed Maotanchang Fm. (Fm.) occurring at Jinzhai, Xianhualing and Maotanchang, etc., was erupted from 149 Ma to 138 Ma. The other named Xiaotian Fm. mainly distributed at Xiaotian, Shucheng, etc., was formed between 132 Ma and 116 Ma. During the eruption gap of the two volcanic suites deposited a volcano-sedimentary conglomerate layer, which are composed of the multi-compositional gravels, including the North Dabie orthogneiss complex (NDOC), volcanic gravels, etc. These volcanic gravels in the conglomerate layer show identical geochemical and isotopic compositions (87Sr/86Sr(t) =0.7084-0.7092,εNd(t) =-21.8--24.4) to the Maotanchang Fm. volcanic rocks (87Sr/86Sr = 0.7086-0.7102,εNd = -19.2-24.4), but significantly distinct from those of Xiaotian Fm. (87Sr/86Sr = 0.7076-0.7084, εNd= -1