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Both the Bowen and Fenner differentiation trends have been recognized in the Emeishan flood basalts. While the Longzhoushan lavas in Panxi paleorift evolved on a trend of silica enrichment (Bowen trend), the lavas from Guizhou evolved along the Fenner trend leading to the magmas with high Fe2O3 (23%) and low SiO2 (44%) contents. This provides evidence for the existence of Fe-rich and Si-poor magmas in nature. Such contrasting differentiation trends, marked by different timing of crystallization of Fe-Ti oxides, are correlated with the extent of crustal contamination of the magmas. Limited crustal contamination in the Guizhou lavas is coupled with the low oxygen fugacity which delayed the onset of magnetite crystallization. In contrast, significant involvement of crustal components in the Longzhoushan lavas increased ƒO2 which in turn triggered early crystallization of magnetite. The close spatial association between the Longzhoushan lavas and the synchronous V-Fe-Ti deposit-bearing layered intrusions suggests a potential relationship between them.

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, eNd (t) = −21.8–−24.4) to the Maotanchang Fm. volcanic rocks (87Sr/86Sr = 0.7086–0.7102, eNd= −19.2–−24.4), but significantly distinct from those of Xiaotian Fm. (87Sr/86Sr = 0.7076–0.7084, eNd= −17.2–−19.2). K-Ar dating results of its underlying and overlying volcanic sequences indicate that the conglomerate layers were deposited at −135 Ma. This suggests that the NDOC was rapidly exhumed to the surface during or shortly before −135 Ma and became the important provenance of the late Mesozoic volcano-sedimentary basins in the NHB. In combination with the regional volcano-sedimentary correlation, we divided the Mesozoic stratigraphic sequence in the NHB from base to top into Fanghushan Fm. (>160 Ma), Yuantongshan Fm. (/middlelower segment of Sanjianpu Fm.) (160–149 Ma), Maotanchang Fm. (/Zhougongshan Fm./upper segment of Sanjianpu Fm./Fenghuangtai Fm.) (149–135 Ma) and Xiaotian Fm. (/Baidafan Fm./Heshidu Fm.) (135–116 Ma).

The SHRIMP zircon U-Pb geochronology of three typically Indosinian granitic plutons with peraluminous and potassium-rich affinities (Tangshi ultraunit for Weishan and Baimashan, and Longtan ultraunit for Guandimiao) is presented in Hunan Province, South China. The analyses of zircons from biotite monozonite granites for Weishan, Baimashan and Guandimiao plutons show the single and tight clusters on the concordia, and yield the weighted mean 206Pb/238U ages of 244 ± 4, 243 ± 3 and 239 ± 3 Ma, respectively, representing the crystallized ages of these Indosinian granites. These data suggest that the Indosinian granitic plutons as previously thought formed at a narrow age span. In combination with other data, it is inferred that the Indosinian granites within the South China Block probably distributed in Hunan, Jiangxi, Guangxi and Guangdong provinces as planar shape, and were the derivation of the crustal materials in the intracontinental thickening setting. These precisely geochronological data provide important constraints for better understanding the spatiotemporal pattern of the Indosinian peraluminous granites and early Mesozoic tectonic evolution of the South China Block.