论文摘要
Global-scale mantle heterogeneities have been recognized through geochemical studies of oceanic basalts（Hart, 1984）. The origins, properties and histories of such chemical heterogeneities provide keys to a better understanding of global mantle evolution during Earth history. One way to decipher the geology of the mantle is through long-lived radiogenic isotopes（Castillo, 1988）. In this respect, Pb isotopes are a very powerful tool because Pb has four naturally occurring isotopes-the ～nonradiogenic 204Pb and radiogenic 206Pb,207Pb and 208Pb isotopes, the half-lives of the radioactive parent elements U and Th are relatively short, and these radioactive parents are geochemically different from each other. These make 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb isotope ratios sensitive tracers of different mantle reservoirs. Ophiolites, pieces of ocean floor that are occasionally preserved on land, are interesting to study in this context since their trace element and isotopic characteristics generally reflect those of the composition and evolution of their underlying mantle（Xu and Castillo, 2004; Liu et al., 2014）. They are an important source of direct information on the nature of their sources and can also provide opportunities to extrapolate mantle evolution through time（Mahoney, 1998; Xu and Castillo, 2004）. The Paleo-Asia and Tethys are two extinct ancient oceans. Paleo-Tethyan Ocean（PTO）and Paleo-Asian Ocean（PAO） have existed on Earth throughout the Paleozoic. Ophiolites representing relict fragments of the PAO and PTO crusts are preserved along the Central Asian Orogenic Belt and Tethyan Tectonic Zone, respectively. We analyze the geochemical and Pb, Nd and Sr isotopic compositions of representative mafic rocks from several Paleo-Asian Ocean ophiolites to constrain the isotopic evolution of its mantle domain that, in turn, will help us better understand mantle geodynamics during Earth’s history. Data suggest that the Sr isotopic composition of PAO ophiolites do not represent primary magmatic composition due to alteration. Combined with similar data for mafic rocks from Paleo-Tethyan Ocean ophiolites, the Nd and Pb isotopic composition indicates the sub-PAO and-PTO mantles have had similar long time-integrated history of Sm/Nd enrichment but marked differences in their Th/Pb and U/Pb fractionation. The sub-PAO mantle produced a Pacific MORB-type mantle with lower 207Pb/204Pb（t） and 208Pb/204Pb（t） for given 206Pb/204Pb ratios than the sub-PTO mantle.
论文目录
文章来源
类型: 国际会议
作者: LIU Xijun,XIAO Wengjiao,XU Jifeng,Paterno R.CASTILLO,ZHANG Zhiguo
来源: 第九届世界华人地质科学研讨会 2019-06-01
年度: 2019
分类: 基础科学
专业: 地质学
单位: Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration and Guangxi Collaborative Innovation Centre of Hidden Non–ferrous Metallic Ore Deposits Exploration and Development of Materials, Guilin University of TechnologyXinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of SciencesSchool of Earth Sciences and Resources, China University of GeosciencesScripps Institution of Oceanography,UCSD
分类号: P597
DOI: 10.26914/c.cnkihy.2019.028395
页码: 207
总页数: 1
文件大小: 75k
下载量: 2