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Caledonian orogeny is another important tectonic event in South China Block after the breakup of the Rodinia supercontinent. With a view to constrain the tectonic evolution and proto–basin in South China, this paper reports the geochemical and zircon U‐Pb dating data of the Ordovician strata in central Hunan, South China. Geochemical features and paleocurrent directions suggest that the lower Ordovician deposited in a passive continental margin basin with a provenance of quartzose components and showing an affinity with the Yangtze Block. U‐Pb age data for 260 detrital zircons from upper Ordovician identify three major age populations as: 900–1200 Ma, 1400–1800 Ma and 2400–2700 Ma. The detrital zircon age spectrum as well as the paleocurrent directions suggest that upper Ordovician deposited in a foreland basin and showing a close affinity with the Cathaysia Block. It is also suggest that the lower Ordovician continuously accepted the mineral from the Yangtze Block, whereas the provenance of the upper Ordovician sedimentary basin changed from the Yangtze Block to the Cathaysia Block. This change implies a tectonic movement, which caused the transformation of the proto–basin in the Hunan area in SCB from passive continental margin basin to foreland basin probably took place during late Ordovician. This fact also demonstrate that the Caledonian orogeny in South China Block began no later than 453 Ma, and a new crustal evolution model is proposed. [ABSTRACT FROM AUTHOR]

The mafic igneous activities in the late Triassic play an important role in the tectonic evolution of the South China Block (SCB). In this paper, relevant data of the bojites in Yajiangqiao area, eastern Hunan Province, South China were provided, including zircon U–Pb ages, whole‐rock geochemical data, Sr–Nd–Pb isotopic data, and zircon Hf isotope data. These data indicate that the bojites were crystallized at ~ 215.7 Ma, and thus are coeval with biotite monzonitic granites of Yajiangqiao pluton. The bojite samples feature a low SiO2 content of 48.84–49.94 wt%, a low ALK (K2O + Na2O) content of 5.13–6.13 wt%, a relatively high Al2O3 content of 17.64–21.22 wt%, a moderate MgO content of 4.32–7.07 wt%, and a moderate FeOT content of 5.66–7.33 wt%. In addition, the samples have a total rare earth element (REE) content of 108–163 ppm. They display right‐declined REE patterns, enriched in light rare earth elements and large‐ion lithophile elements (such as Rb, K, Th, and U) and depleted in high field strength elements (such as Nb, Ta, P, and Ti). All the samples have homogeneous Sr–Nd–Pb and zircon Hf isotopic compositions, with the (87Sr/86Sr)i ratio varying from 0.708 202 to 0.709 515, (143Nd/144Nd)i ratio from 0.512 156 to 0.512 229, (206Pb/204Pb)t ratio from 18.185 to 18.264, (207Pb/204Pb)t ratio from 15.667 to 15.672, (208Pb/204Pb)t ratio from 38.510 to 38.587, and initial 176Hf/177Hf ratio ranging from 0.282 428 to 0.282 530. Meanwhile, the calculated εNd(t) and εHf(t) values range from −4.0 to −2.6 and from −7.9 to −4.1, respectively, with two‐stage Nd model ages of 1.20–1.32 Ga and two‐stage Hf model ages of 1.35–1.56 Ga, respectively. As indicated by geochemical data, the primitive magmas of the bojites in Yajiangqiao area were derived from lithospheric mantle in post‐collisional extensional environment, which underwent low‐degree partial melting (1–5 %) of spinel‐garnet lherzolites (spinel > garnet) and was subjected to metasomatism of slab‐derived fluids. Furthermore, it can be concluded from these data and previous data that the SCB was transformed from syn‐collisional compression to post‐collisional extension in the late Triassic (~ 234 Ma) and the post‐collisional extension lasted until 215 Ma. [ABSTRACT FROM AUTHOR]