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Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China

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Science Bulletin 2003年第16期48卷 1663-1669页

作者： WANG Jian1, LI Xianhua2, DUAN Taizhong3, LIU Dunyi4, SONG Biao4, LI Zhongxiong1 & GAO Yonghua5 1. Chengdu Institute of geology and mineral resources, China Geologi-cal Survey, Chengdu 610082, China 2. Guangzhou Institute of Geochemistry, chinese Academy of Sciences, Guangzhou 510640, China 3. Colorado School of Mines, Golden, CO 80401-1887, USA (Present address: Marathon Oil Company, Houston, TX 77056-2725, USA) 4. Institute of geology, chinese Academy of Geological Sciences, Bei-jing 100037, China 5. Graduate School of the chinese Academy of Geological Sciences, Beijing 100037, China Correspondence should be addressed to Wang Jian (e-mail: jianwang@ ***) Chengdu Institute of geology and mineral resources China Geological Survey Chengdu China Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou China Colorado School of Mines Golden USA Institute of geology Chinese Academy of Geological Sciences Beijing China Graduate School of the chinese Academy of Geological Sciences Beijing China

The continental volcanic rocks and volcaniclas-tic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan province, consisting of a wedge-shaped succession of Neoproterozoic strata that over-lie with high-angle unconformity the flysch turbidites of the Lengjiaxi Group in the Upper Mesoproterozoic Eonothem. SHRIMP zircon U-Pb dating gives a weighted mean age of 814 12 Ma for the dacitic volcanic agglomerates from the lowest part of the volcanic rocks in the Cangshuipu Forma-tion. This age is younger than previously reported values of 921—933 Ma for the volcanic rocks from the Cangshuipu Formation. Our new dating represents the lower boundary age of the Neoproterozoic System in the studied area. The younger age for the Cangshuipu volcanic rocks is supported by the following observations: （1） Lower Neoproterozoic strata （814—1000 Ma） are missing in the studied area; （2） the Nanhua rift system was initiated at about 820 Ma; and （3） an age of820 Ma may be taken as the lower boundary tim-ing of the Nanhua System （even Neoproterozoic） in South China.

关键词： Zicon U-Pb dating Neoproterozoic volcanics rift basin Nanhua System.

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Geophysical implications for the formation of the Tamu Massif–the Earth's largest single volcano–within the Shatsky Rise in the northwest Pacific Ocean

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Science Bulletin 2017年第1期62卷 69-80页

作者： Jinchang Zhang Jie Chen Key Laboratory of Marginal Sea geology South China Sea Institute of Oceanology Chinese Academy of Sciences Key Laboratory of Marine mineral resources Ministry of Land and Resources South China Sea Institute of Planning and Environmental Research State Oceanic Administration Key Laboratory for Ecological Environment in Coastal Areas State Oceanic Administration Key Laboratory of Integrated Marine Monitoring and Applied Technologies for Harmful Algal Blooms State Oceanic Administration

Recent geophysical research programs survey the Tamu Massif within the Shatsky Rise oceanic plateau in the northwest Pacific Ocean to understand the formation of this immense volcano and to test the forma- tion hypotheses of large igneous province volcanism. Massive sheet basalt flows are cored from the Tamu Massif, implying voluminous eruptions with high effusion rates. Seismic reflection data show that the Tamu Massif is the largest single volcano on Earth, characterized by a central volcanic shield with low- gradient flank slopes, implying lava flows emanating from its center and spreading massive area on the seafloor. Velocity model calculated from seismic refraction data shows that crustal thickness has a negative correlation with average velocity, implying a chemically anomalous origin of the Tamu Massif. Seismic refraction and reflection data reveal a complete crustal structure across the entire vol- cano, featured by a deep crust root with a maximum thickness of -30 kin, and Moho geometry is consis- tent with the Airy lsostasy. These recent findings provide evidence for the two end-member formation models： the mantle plume and the plate boundary, Both are supported by some results, but both are not fit with some either. Consequently, plume-ridge interaction could be a resolution that awaits future investigations.

关键词： Oceanic plateauLarge igneous province Plume-ridge interaction Marine geophysics Plate tectonics

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Tectonics of the Indo-Australian Plate Near the Ninetyeast Ridge Constrained from Marine Gravity and Magnetic Data

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Journal of Ocean University of China 2017年第3期16卷 403-410页

作者： CHEN Jie ZHANG Jinchang South China Sea Institute of Planning and Environmental Research State Oceanic Administration Key Laboratory for Ecological Environment in Coastal Areas State Oceanic Administration Key Laboratory of Integrated Marine Monitoring and Applied Technologies for Harmful Algal Blooms State Oceanic Administration Key Laboratory of Marginal Sea geology South China Sea Institute of OceanologyChinese Academy of Sciences Key Laboratory of Marine mineral resources Ministry of Land and Resouces

Although the Indo-Australian plate near the Ninetyeast Ridge is important for understanding the formation of new plate boundaries, its tectonic problems are complex and most of them are poorly known. This paper made a detailed tectonic analysis based on the data of bathymetry, gravity and magnetics. Bathymetry and gravity maps show morphological features of many folds, which are related to the intraplate deformation of the Indo-Australian plate due to the collision between the Indian and Asian plates. Gravity anomalies show the structure of fracture zones, which are caused by the seafloor spreading and transform faulting. The characteristics of the folds and fracture zones are consistent with the hypothesis that diffuse plate boundaries and redefined plate components would occur within the Indo-Australian plate. In addition, compiled magnetic data demonstrate magnetic lineations, abandoned spreading centers, southward ridge jumps and plate motions. These features provide useful information for rebuilding the tectonic evolution history of the study area. Magnetic anomalies suggest that an additional plate boundary of transform fault type is developing.

关键词： Indian Ocean Ninetyeast Ridge Indo-Australian plate plate tectonics marine geophysics

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