| 广西崇左三叠系北泗组火山岩锆石U-Pb年龄、Hf同位素和地球化学特征——对古特提斯演化的指示 |
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| 关键词:zircon U-Pb age geochemistry volcanic rocks Beisi Formation Chongzuo Paleo-Tethys Ocean |
| 基金项目:本文由中国地质调查局地质调查项目(编号: DD20242336; DD20221689)资助。 |
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| Zircon U-Pb Ages, Hf Isotopes, and Geochemical Characteristics of the Triassic Beisi Formation Volcanic Rocks in Chongzuo, Guangxi: Implications for the Evolution of the Paleo-Tethys Ocean |
| The Chongzuo Liutang area exposes the northernmost rhyolite and dacite of the contemporaneous Beisi Formation volcanic rocks. We obtained high-precision LA-ICP-MS zircon U-Pb ages of (247.8±1.4) Ma and (248.0±1.4) Ma for these rocks. Statistical analysis indicates that volcanic rocks of the Beisi and Banba Formations in southwestern Guangxi Province were formed at 240–248 Ma and 248–250 Ma, respectively, which were the products of the Early-Middle Triassic tectonic movement. The geochemical analysis shows that the volcanic rocks of the Beisi Formation comprise high SiO2 and alkali (Na2O+K2O) contents and extremely low MgO, MnO, and CaO contents. The rhyolite and dacite REE contents both exhibit right-inclined LREE enrichment patterns, with δEu values of 0.14–0.16 and 0.16–0.18. Furthermore, they are enriched in Rb, K, Th, U, and Nd contents, and are depleted in Ba, Sr, P, Nb, Ta, and Ti, etc. The Hf isotope study shows that the rhyolites have εHf(t) values ranging from –14.1 to –4.4 and TDM2 values ranging from 1 553 Ma to 2 169 Ma, while the dacites have εHf(t) values ranging from –16.2 to –7.8 and TDM2 values ranging from 1 774 Ma to 2 296 Ma. It can be concluded that the volcanic rocks in this study originated from the partial melting of Paleoproterozoic metasedimentary rocks. Based on a comprehensive study, the Early–Middle Triassic volcanic rocks in southwestern Guangxi are interpreted to have formed in a continental margin arc setting associated with the subduction of the Paleo-Tethys Ocean. These rocks, together with the Early–Middle Triassic island arc volcanic rocks in the Funing–Napo–Chongzuo–Pingxiang area and the Babu–Cao Bang ophiolitic melange belt, constitute an oceanic crust subduction-accretion complex-arc system. Thus, the Liutang area volcanic rocks constrain the spatial extent and temporal limits of Paleo-Tethys oceanic subduction in southwestern Guangxi. |
| ZHANG Kun,LI Jianfeng,CHENG Shunbo,LI Kun,BAO Bo,LIU Asui,XIA Jie.2026.Zircon U-Pb Ages, Hf Isotopes, and Geochemical Characteristics of the Triassic Beisi Formation Volcanic Rocks in Chongzuo, Guangxi: Implications for the Evolution of the Paleo-Tethys Ocean[J].Acta Geoscientica Sinica,47(3):613-628. |
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