Zircon U-Pb geochronology of the volcanic rocks from Fanchang-Ningwu volcanic basins in the Lower Yangtze region and its geological implications

被引:60
作者
Yan Jun [1 ]
Liu HaiQuan [1 ]
Song ChuanZhong [1 ]
Xu XiSheng [2 ]
An YaJun [1 ]
Liu Jia [1 ]
Dai LiQun [1 ]
机构
[1] Hefei Univ Technol, Sch Resources & Environm Engn, Hefei 230009, Peoples R China
[2] Nanjing Univ, State Key Lab Mineral Deposits Res, Dept Earth Sci, Nanjing 210093, Peoples R China
来源
CHINESE SCIENCE BULLETIN | 2009年 / 54卷 / 16期
基金
中国国家自然科学基金;
关键词
Zircon U-Pb dating; volcanic rocks; Early Cretaceous; extensional setting; Lower Yangtze region; NORTHERN DABIE COMPLEX; CONTINENTAL-CRUST; EASTERN CHINA; ISOTOPE EVIDENCE; ANHUI PROVINCE; IGNEOUS ROCKS; LOWER REACHES; OROGEN; AREA; GEOCHEMISTRY;
D O I
10.1007/s11434-009-0110-x
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapotassic volcanic rocks of the Niangniangshan Formation, respectively. The representative volcanic rocks of the two Formations were selected for LA-ICPMS zircon U-Pb dating. The results indicate that there exist a large amount of magmatic zircons as indicated by high Th/U ratios in these volcanic rocks. The weighted mean age of 21 analyses is 130.7 +/- 1.1 Ma for the Kedoushan Formation, and that of 20 analyses is 130.6 +/- 1.1 Ma for the Niangniangshan Formation. These U-Pb ages are interpreted to represent the formation times of the volcanic rocks. In combination with other known geochronological data for Mesozoic volcanic rocks from the Lower Yangtze region, it is proposed that the latest volcanic activations in the Jinniu, Luzong, Fanchang and Ningwu volcanic basins probably came to end prior to ca. 128 Ma. There is no significant time interval between the early and later volcanic activities in the Luzong and Ningwu basins, suggesting a short duration of volcanic activities and thus implying the onset of an extensional tectonic setting at about 130 Ma in the Lower Yangtze region. Integrated studies reveal that the Early Cretaceous magmatic activities and their geochronological framework in the Lower Yangtze region are a response to progressively dynamic deep processes that started with the transformation of tectonic setting from compression to extension, followed by delaminating of the lower part of the thickened lithosphere, lithospheric thinning, asthenosphere upwelling, and crust-mantle interaction.
引用
收藏
页码:2895 / 2904
页数:10
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