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Petrogenesis of Late Jurassic two-mica granites and associated diorites and syenite porphyries in Guangzhou, SE China
Lithos ( IF 3.5 ) Pub Date : 2020-07-01 , DOI: 10.1016/j.lithos.2020.105537 Xiao Liu , Qiang Wang , Lin Ma , Zong-Yong Yang , Wan-Long Hu , Yi-Ming Ma , Jun Wang , Tong-Yu Huang
Lithos ( IF 3.5 ) Pub Date : 2020-07-01 , DOI: 10.1016/j.lithos.2020.105537 Xiao Liu , Qiang Wang , Lin Ma , Zong-Yong Yang , Wan-Long Hu , Yi-Ming Ma , Jun Wang , Tong-Yu Huang
Abstract The South China Block (SCB) is considered to have undergone extensive reworking of continental crust. However, the mechanisms of this crustal reworking are unclear. Here, we report on Late Jurassic (162–155 Ma) two-mica granites and associated diorites and syenite porphyries from the Huolushan–Longyandong area of Guangzhou City, southeastern China. The two-mica granites have high SiO2 contents (69.6–73.6 wt%) and weakly peraluminous to strongly peraluminous compositions. These rocks have enriched Sr–Nd–Hf isotopic compositions ((87Sr/86Sr)i = 0.7094–0.7145; eNd(t) = −10.5 to −9.3; eHf(t) = −12.7 to −4.2). The Huolushan two-mica granites have variable zircon O isotopic compositions (δ18O = 6.8‰–10.4‰), whereas the Longyandong two-mica granites have homogeneous compositions (δ18O = 8.6‰–9.9‰). The Huolushan syenite porphyries have moderate SiO2 (59.6–60.1 wt%) and high alkaline (K2O + Na2O = 9.4–9.8 wt%) contents. Their Sr–Nd–Hf–O isotopic compositions ((87Sr/86Sr)i = 0.7105–0.7119; eNd(t) = −9.9 to −9.8; eHf(t) = −14.1 to −5.9; δ18O = 6.5‰–10.6‰) are similar to those of the Huolushan two-mica granites. The Huolushan diorites have moderate SiO2 contents (59.9–60.4 wt%) and are high-K calc-alkaline and metaluminous with Mg# values of 43.2–43.8. Their Sr Nd isotopic compositions ((87Sr/86Sr)i = 0.7106–0.7109, eNd(t) = −8.8 to −8.6) are less enriched than those of the two-mica granites and syenite porphyries. In addition, the diorites have high zircon δ18O values (7.8‰–8.9‰) and a wide range of zircon eHf(t) values (−13.4 to −5.6). We propose that the Huolushan two-mica granites were derived from a metagreywacke-dominated hybridized source with minor juvenile crustal rocks and that the Longyandong two-mica granites were generated by partial melting of metagreywackes. The Huolushan syenite porphyries were formed by the mixing of metasedimentary-rock-derived felsic magmas and minor enriched-mantle-derived alkaline magmas. The Huolushan diorites were most likely derived by partial melting of mafic lower crust, with the dioritic magmas undergoing assimilation and fractional crystallization (AFC) during ascent. All of these intrusive rocks were likely formed in an extensional intraplate setting. The mantle-derived magmas, which could have been triggered by lithospheric extension, underplated the middle–lower crust and provided heat for crustal reworking and materials for late Mesozoic crustal growth.
更新日期：2020-07-01
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