The distribution of adakite-like rocks in South Anhui province, China
0
Citation
0
Reference
20
Related Paper
Cite
Cite
Citations (0)
Cite
Citations (0)
Cite
Citations (0)
Geological survey
Cite
Citations (1)
Northwest Zhejiang Province (NWZJ) is located in the southeastern Lower Yangtze River Belt, southeastern China. Here we document the occurrence of both magnesian (149–131 Ma) and ferroan (162–121 Ma) granitoids in NWZJ. The magnesian granitoids are calc-alkalic peraluminous in composition, with a wide range of SiO2 (58–72 wt%) contents. They have high K2O/Na2O, Sr/Y, and (La/Yb)N ratios, with insignificant Eu anomalies, whereas the calc-alkalic peraluminous ferroan granites have high SiO2 (76–77 wt%) contents, Fe indices (FeO*/(FeO*+MgO)), and Ga/Al ratios. The ferroan granites also have low Ce/Pb and Nb/U ratios, with strong Ba, Sr, and Eu negative anomalies. Most of the rocks have similar zircon Lu-Hf isotopes (εHf(t)=−6.0 to −0.7). However, rocks from two ferroan granitic bodies (Huangshitan and Jiuligang) have more depleted Hf isotopes, with εHf(t) ranging from −1.9 to 5.9. The whole-rock Nd isotopes of the ferroan granites (εNd(t)=−6.5 to −3.2) are slightly more depleted than those of magnesian granitoids (εNd(t)=−8.8 to −5.1). In addition, all ferroan granites show similar and high present-day whole-rock Pb isotopic ratios (18.3–18.8 for 206Pb/204Pb, 15.6–15.7 for 207Pb/204Pb, and 38.5–39.0 for 208Pb/204Pb). On the basis of published data and our new results, we propose that the magnesian granitoids were generated by partial melting of lower-crustal materials, whereas the ferroan granites were derived from a similar source but some more-depleted materials were added into their source after ∼135 Ma. The water contents of the magma may have played an important role in determining the different geochemical affinities of the felsic magmatism. The felsic magmatism occurred under an extensional setting during the period 162–121 Ma. The extension of the lithosphere was further enhanced and followed by upwelling of asthenospheric mantle after ∼135 Ma. This study suggests that a change in the tectonic regime occurred at ∼135 Ma in NWZJ, which may have been triggered by the rollback of the subducted Paleo-Pacific Plate.
Petrogenesis
Cite
Citations (4)
Cite
Citations (52)
Cite
Citations (0)
Terrestrial Jurassic rocks are widespread in China, whereas marine Jurassic rocks are confined to Xizang (Tibet), South Qinghai, South Xinjiang, and, in limited parts of the sequence, to West Yunnan, Guangdong, South Hunan, and East Heilongjiang. Geographically, occurrences of Jurassic deposits may be divided into three regions and 13 districts: (I) the Xizang–Qinghai region, with the South Tethyan Himalayan, North Tethyan Himalayan, Lhasa, Xanza–Shiquanhe, Bangon–Dengqen, Karakorum–Tanggula, and Qamdo districts; (II) the Coastal Volcanic region of East China, with the Guangdong–Hunan, Fujian–Zhejiang, Heilongjiang, and Northeast China districts; and (III) the Stable Giant Basin region of West China, with the Sichuan–Yunnan and Northwest China districts. These regions and districts are described briefly, and preliminary biostratigraphic sequences and palaeogeography are presented. The upper and lower boundaries of the Jurassic System in China are briefly discussed.The Jurassic seas of China evidently were extensions of the Mediterranean (Tethyan) Sea and of the Pacific Ocean. The main transgressions occurred during Sinemurian, Bathonian–Callovian, and Tithonian – Early Cretaceous times. All three transgressions of the Mediterranean Sea were important, whereas only the earlier two transgressions from the Pacific Ocean were important.The relief and climate of China during the Jurassic Period are also discussed briefly. After Triassic tectonism, the ancient mountains, such as the Altai, Tian Shan, Kunlun, Altun, Hengduan, Qilian, Qinling, Dabei, North China Plateau, Huaibei Plateau, and Yunnan–Guizhou Plateau, originated. Latitudinal and longitudinal tectonic belts were important in the geological development of China and significantly influenced biogeography, palaeogeography, and climate.
Palaeogeography
Tethys Ocean
Cite
Citations (11)
Cite
Citations (0)