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Eruption of the continental flood basalts at -259 Ma in the Emeishan Large Igneous Province, SW China: Evidence from Laser Microprobe ^(40)Ar/^(39)Ar Dating

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Acta Geologica Sinica(English Edition) 2006年第4期80卷 514-521页

作者： HOU Zengqian CHEN Wen LU Jiren Institute of Geology Chinese Academy of Geological Science Beijing 100037 Institute of Mineral Resources Chinese Academy of Geological Science Beijing 100037

A suite of continental flood basalts sampled over a vast exposure and stratigraphic thickness in the Emeishan large igneous province （LIP）, SW China was investigated for laser microprobe ^40Ar/^39Ar dating. There are two ^40Ar/^39Ar age groups for these basalts, corresponding to 259-246 Ma and 177-137 Ma, respectively. A well-defined isochron gives an eruption age of huge quantities of mafic magmas at 258.9±3.4 Ma, which is identical to previous dating and paleontological data. Much younger ^40Ar/^39Ar ages for some basalts with Iow-greenschist metamorphic facies probably recorded a late thermo-tectonic event caused by collision between the Yangtze and Qiangtang continental blocks during the Mesozoic, which resulted in the reset of argon isotope system. The ^40Ar/^39Ar age data, we present here, combined with previous dating and paleontological data, suggest relatively short duration （about 3 Ma） of mafic volcanism, which have important implication on mantle plume genesis of the Emeishan continental flood basalts in the LIP.

关键词： laser microprobe ^40Ar/^39Ar age continental flood basalts Emeishan large igneous province

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Petrology, Mineralogy and Geochemistry of the Emeishan continental flood basalts, SW China: Evidence for Activity of Mantle Plumes

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Acta Geologica Sinica(English Edition) 2004年第1期78卷 40-51页

作者： ZHANGZhaochong HAOYanli WANGFusheng JohnJ.MAHONEY InstituteofGeology ChineseAcademyofGeologicalSciencesBeijing100037China SchoolofOceanandEarthScienceandTechnology UniversityofHawaiiHonoluluHI96822USA

Electronic microprobe analyses for olivine, clinopyroxene and Cr-spinel in picrites, which we have discovered recently in the Emeishan continental flood basalt province (ECFBP), show that the olivine is rich in Mg, and that Cr-spinel is rich in Cr. Based on the olivine-melt equilibrium, the primary parental melt compositions are calculated. The high-Mg olivine-hosted picrite can be regarded as parental melt. Thus, the melting temperature and pressure are estimated: T=1600℃ and P=4.5 GPa. It suggests that the picrites are connected with the activity of mantle plumes. Their major element composition is comparable to many other CFBs by their high Fe8, (CaO/Al2O3)8 and low Na8, indicating a high pressure. All rocks display a similar chondrite-normalized REE patterns, i.e., enrichment of LREE, relative depletion of HFSE and absence of negative Nb and Ta but depletion in P and K. Some incompatible element ratios, such as La/Ta, La/ Sm, (La/Nb)PM, (Th/Ta)PM, are in a limited range, show that they were derived from the mantle plume, and there was no or little crustal contamination during magma ascent en route to the surface. They were generated by 7% partial melting of garnet peridotite. The axis of the plume might be located beneath Lijiang Town, Yunnan province.

关键词： continental flood basalts picrite geochemistry Emeishan

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The Bikou basalts in the northwestern Yangtze block,South China:Remnants of 820-810 Ma continental flood basalts?

The Bikou basalts in the northwestern Yangtze block,South Ch...

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中国科学院地质与地球物理研究所2008学术年会

作者： Xuan-Ce Wang Xian-Hua Li~+ State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,P.O.Box 9825, Beijing 100029,China Key Laboratory of Isotope Geochronology and Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, Guangzhou 510640,China Wu-Xian Li Key Laboratory of Isotope Geochronology and Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, Guangzhou 510640,China Zheng-Xiang Li Institute for Geoscience Research,Department of Applied Geology,Curtin University of Technology,GPO Box U1987,Perth,WA 6845, Australia Ying Liu Key Laboratory of Isotope Geochronology and Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, Guangzhou 510640,China Yue-Heng Yang State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,P.O.Box 9825, Beijing 100029,China Xi-Rong Liang Xiang-Lin Tu Key Laboratory of Isotope Geochronology and Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, Guangzhou 510640,China

Mantle plume or superplume activities have often been invoked as a cause for the breakup of the Neoproterozoic supercontinent ***,associated Neoproterozoic continental flood basalts,a requisite product of mantle plume activities,have rarely been *** sensitive high-resolution ion microprobe(SHRIMP) U-Pb zircon ages,geochemical,and Hf-Nd isotopic data are reported here for the Bikou Group basalts,the largest Neoproterozoic volcanic units in the northwestern Yangtze block, South *** Bikou basalts are mainly tholeiitic in composition,and they can be stratigraphically subdivided into the lower and upper *** U-Pb zircon dating of intercalated rhyolites indicates that the lower and upper group basalts were erupted at 821±7 Ma and 811±12 Ma,respectively. The two basalt groups define two populations on most elemental and isotopic diagrams. The lower group basalts display strong subcontinental lithospheric mantle affinities and large variableεNd(t)) andεHf(t)) values that correlate negatively with Th/Ta and positively with *** upper group basalts,on the other hand,show ocean-island basalt(OIB) affinities and highly positiveεHf(t)) andεNd(t)) values. Numerical modeling indicates that the lower and upper group basalts were formed at melting temperatures of>1350℃and>1450℃and mantle potential temperatures of 1400- 1488℃and 1550±30℃,***, the upper group basalts were derived from an anomalously hot asthenosphere mantle,～160℃hotter than the contemporary ambient mid-ocean-ridge basalt(MORB) source *** results are at clear variance with the alternative tectonic model that the Bikou basalts were part of a continental magmatic *** work suggests that the Bikou basalts are likely the remnants of Neoproterozoic continental flood basalts that formed in response to a mantle plume starting ca.825 Ma during the breakup of the supercontinent Rodinia.

关键词： Neoproterozoic continental flood basalts Nd-Hf isotopes Yangtze block South China mantle plume Rodinia

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溢流玄武岩成因过程中的岩浆补给作用:同位素证据（英文）

溢流玄武岩成因过程中的岩浆补给作用:同位素证据（英文）

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2016中国地球科学联合学术年会

作者：俞恂陈立辉曾罡南京大学地球科学与工程学院同济大学海洋地质国家重点实验室

continental flood basalts are thought to be the volcanic manifestations of large volumes of magma derived from Earth’s mantle including mantle compositions with variable elemental and isotopic compositions(Zhang et al., 2006;Hooper et al., 2007;Sobolev et al., 2009, 2011). Understanding the compositional record of continental flood basalts is thus crucial for a better understanding of mantle compositional variations and ultimately the dynamics that lead to these variations. Radiogenic isotope systematics of melts derived from a mantle source may provide clues on the formation mechanisms(e.g., plume versus nonplume) of continental flood basalts. Isotopic compositions of continental flood basalts are essential to understand their genesis and to constrain the character of their mantle sources. Because of potential crustal contamination, it needs to be evaluated if and to which degree these basalts record primitive isotopic signals of their mantle sources and/or crustal signatures. This study examines the Sr, Nd, Hf, and Pb isotopic compositions of the late Cenozoic Xinchang-Shengzhou(XS) flood basalts, a small-scale continental flood basalt field in eastern China. The basalts show positive correlations between 87Sr/86 Sr and 143Nd/144 Nd, and negative correlations between 143Nd/144 Nd and 176Hf/177 Hf, which deviate from compositional arrays of crustal contamination and instead highlight variations in magmatic recharge intensity and mantle source compositions. The lava samples formed by high-volume magmatic recharge recorded signals of recycled sediments in the mantle source, which are characterized by moderate Ba/Th(91.9–106.5), excess 208Pb/204 Pb relative to 206Pb/204 Pb, and excess 176Hf/177 Hf relative to 143Nd/144 Nd. Thus, we propose that magmatic recharge buffers the original isotopic compositions of magmas against crustal contamination. Identifying and utilizing the isotope systematics of continental flood basalts generated by high volumes of magmatic recharge

关键词： continental flood basalts mantle heterogeneity magmatic recharge crustal contamination

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