Zircon U-Pb dating and Lu-Hf isotope study of intermediate-mafic sub-volcanic and intrusive rocks in the Lishui Basin in the middle and lower reaches of Yangtze River  

作　　者：Lijuan Wang Jianping Huang Jinhai Yu W. L. Griffin Rucheng Wang Shaoqin Zhang Yinghe Yang 

机构地区：[1]Key Laboratory of Earth Fissures Geological Disaster, Ministry of Land and Resources, Geological Survey of Jiangsu Province [2]Department of Earth Sciences, State Key Laboratory for Mineral Deposits Research, Nanjing University [3]Department of Earth and Planetary Science, ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC Key Centre, Macquarie University, NSW 2109,Australia

出　　处：《Chinese Science Bulletin》2014年第27期3427-3440,共14页

基　　金：supported by National Natural Science Foundation of China (41102123, 41330208);a Grant (1212011120864) from China Geological Survey

摘　　要：Eight Mesozoic sub-volcanic and intrusive rocks in the Lishui Basin have been selected for zircon U-Pb dating and Lu-Hf isotopic analysis. The Laohutou, Datongshan,Daweizhuang, Yeshanao, Yanwaqiao, Xibeishan, Changshantou and Jianshan porphyrites yield concordant early Cretaceous ages of 130.5 ± 1.6 Ma, 136.0 ± 3.4 Ma, 132.7 ±2.7 Ma, 127.0 ± 1.9 Ma, 129.4 ± 1.7 Ma, 133.2 ± 2.1 Ma,131.1 ± 2.3 Ma and 127.4 ± 1.8 Ma, respectively. Zircon eHf(t) values for these rocks range from-3.54 to-9.11, mostly between-3.54 and-5.93, suggesting sources similar to those for coeval igneous rocks in other volcanic basins along the middle and lower reaches of Yangtze River. Considering the geochemical characteristics of coeval magmatic rocks in the middle and lower reaches of Yangtze River and its adjacent areas, this paper proposes a model of slab rollback to explain the Mesozoic magmatism in the east-central part of China continent. In the middle-late Jurassic to early Cretaceous(170–135 Ma), the Pacific plate started to subduct beneath the Eurasian continent, producing a compressive tectonic setting,and magmatism progressed from coast to the inland. The magmas of this period were derived mostly from partial melting of ancient crust. After *135 Ma, the subduction weakened, and the rollback of the subducted Pacific plate produced an extensional environment. This led to the formation of volcanic basins, the partial melting of enriched mantle sources and less ancient crust, and the intrusion of voluminous intermediate-mafic igneous rocks.Eight Mesozoic sub-volcanic and intrusive rocks in the Lishui Basin have been selected for zircon U-Pb dating and Lu-Hf isotopic analysis. The Laohutou, Datongshan, Daweizhuang, Yeshanao, Yanwaqiao, Xibeishan, Chang- shantou and Jianshan porphyrites yield concordant early Cretaceous ages of 130.5 ±1.6 Ma, 136.0 ± 3.4 Ma, 132.7± 2.7 Ma, 127.0 ± 1.9 Ma, 129.4 ± 1.7 Ma, 133.2± 2.1 Ma, 131.1 ± 2.3 Ma and 127.4 ± 1.8 Ma, respectively. Zircon εHf（t） values for these rocks range from - 3.54 to - 9.11, mostly between -3.54 and -5.93, suggesting sources similar to those for coeval igneous rocks in other volcanic basins along the middle and lower reaches of Yangtze River. Considering the geochemical characteristics of coeval magmatic rocks in the middle and lower reaches of Yangtze River and its adjacent areas, this paper proposes a model of slab rollback to explain the Mesozoic magmatism in the east-central part of China continent. In the middle-late Jurassic to early Cretaceous （170-135 Ma）, the Pacific plate started to subduct beneath the Eurasian continent, producing a compressive tectonic setting, and magmatism progressed from coast to the inland. The magmas of this period were derived mostly from partial melting of ancient crust. After- 135 Ma, the subduction weakened, and the rollback of the subducted Pacific plate produced an extensional environment. This led to the formation of volcanic basins, the partial melting of enriched mantle sources and less ancient crust, and the intrusion of voluminous intermediate-mafic igneous rocks.

关 键 词：锆石U-Pb定年 长江中下游 Hf同位素 火山盆地 次火山岩 侵入岩 丽水 基性 

分 类 号：P588.1[天文地球—岩石学] P597[天文地球—地质学]