| 扬子西缘奥陶纪—志留纪之交斑脱岩锆石U-Pb年龄、Hf同位素特征及其地质意义 |
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| 关键词:western margin of the Yangtze block Ordovician–Silurian bentonite zircon U-Pb age Hf isotope |
| 基金项目:本文由中国地质调查局地质调查项目(编号: DD202601103305; DD20220987; DD202308404)和国家自然科学基金项目(编号: 42172035)联合资助。 |
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| Zircon U-Pb Ages and Lu-Hf Isotope of the Bentonite during the Ordovician–Silurian Transition in the Western Yangtze Block and Their Geological Significance |
| In this study, 10 layers of bentonite were identified in the Linxiang Formation–Xintan Formation during the Ordovician–Silurian transition in the Western Yangtze Block. The first layer of bentonite was at the bottom of the Linxiang Formation, and the tenth layer of bentonite in the Xintan Formation was discovered for the first time. To study the geochronology, protolith type and tectonic setting of the bentonite, zircon U-Pb dating, zircon trace element, and Hf isotope analysis were conducted on the bentonite at the bottom of the Linxiang Formation and the bentonite at the top of the Xintan Formation. The Zircon U-Pb results of the bentonite from the bottom of the Linxiang Formation were (447.9±1.7) Ma, εHf(t) = 1.3–4.9, TDM2=1 119–1 330 Ma. The Zircon U-Pb results of the bentonite at the top of the Xintan Formation were (436.1±2.2) Ma, εHf(t) = –9.4– –14.2, TDM2=2 017–2 316 Ma. The sedimentary record of volcanic activity during the Ordovician–Silurian transition in the Yangtze region is well-defined. The age provides a chronological reference for the sedimentary environment evolution of the Ordovician–Silurian in the Zhaotong area of the Upper Yangtze. The transformation from the platform carbonate facies of the Baota Formation to deep-water shelf facies began at approximately 447.8 Ma. The shallow-water shelf facies of the Xintan Formation entered the platform carbonate deposition facies of the Huanggexi Formation at about 436.1 Ma. The characteristics of zircon trace elements and Hf isotopes of the bentonite indicate that two types of protoliths were generated in different source areas and tectonic backgrounds existing in the Yangtze area: the early (449–444.7 Ma) magma was mainly partial basic magma from the new lower crust, which formed in an extensional environment. In the late stage (443–438 Ma), the magmatic material was mainly derived from the ancient mature crust, which formed in an arc environment of acidic magma. The transformation of tectonic environment occurred near the boundary between the Linxiang Formation and Wufeng Formation. By comparing with the volcanic activity records, magma types, and tectonic background of the same period around the Yangtze, the bentonite may be derived from the arc-backarc volcanism in the North Qinling area during the Ordovician–Silurian period. |
| YUAN Yongsheng,TANG Feng,WANG Wanneng,ZHANG Yaotang,LI Wenhui,ZHANG Honghui,ZHANG Liyuan,LOU Yuanlin.2026.Zircon U-Pb Ages and Lu-Hf Isotope of the Bentonite during the Ordovician–Silurian Transition in the Western Yangtze Block and Their Geological Significance[J].Acta Geoscientica Sinica,47(4):733-749. |
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