Major, trace element, and Nd, Sr and Pb isotope studies of Cenozoic basalts in SE China: mantle sources, regional variations, and tectonic significance
Major, trace element, and Nd, Sr and Pb isotope studies of Cenozoic basalts in SE China: mantle sources, regional variations, and tectonic significance
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DOI：
10.1016/s0009-2541(00)00243-6
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发表时间：
2000-12
期刊：
影响因子：
3.9
通讯作者：
H. Zou;A. Zindler;Xi‐sheng Xu;Q. Qi
中科院分区：
文献类型：
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作者：
H. Zou;A. Zindler;Xi‐sheng Xu;Q. Qi
测量了中国东南部含地幔捕虏体的新生代玄武岩的主量、微量元素和Nd-Sr-Pb同位素组成，以了解其地幔来源和过程的性质。应用改进的熔融动力学反演方法对中国东南部玄武岩的研究表明，女山玄武岩和方山玄武岩是由富含轻稀土元素的地幔源区部分熔融形成的，熔融程度为4-11%。143 Nd/144 Nd与206 Pb/204 Pb之间的负相关和87 Sr/86 Sr与206 Pb/204 Pb之间的正相关强烈地表明了研究区中等亏损的软流圈地幔源区和EM 2组分的混合。研究区EM 2信号的出现和自南向北逐渐减弱的特征与中国东南部为冈瓦纳大陆一部分的假设是一致的。此外，中国东南部玄武岩的同位素约束与Li [Li，Z.X.，1994.南北陆块碰撞：郯庐断裂以东地区陆块碰撞的地壳拆离模式。地质学，22，739-742]，华南和华北地块之间的地下缝合线向东穿过南京。结合已发表的中国东北地区新生代玄武岩的同位素数据，整个中国东部的玄武岩在给定的206 Pb/204 Pb下具有高的208 Pb/204 Pb和207 Pb/204 Pb，这是南半球Dupal洋岛玄武岩中常见的特征。206 Pb/204 Pb由南向北逐渐减小。中国东部Pb同位素组成的这种区域性变化不能简单地归因于两个地幔端元的混合，因为Nd和Sr同位素组成在中国东南部和东北部表现出相反的区域性变化。中国东南部的玄武岩反映了软流圈地幔与EM 2的混合，而中国东北部的玄武岩反映了软流圈地幔与EM 1的混合。中国中东部的女山、方山和塔山玄武岩具有最亏损的Nd和Sr同位素组成，可能代表了软流圈地幔的同位素组成。Pb-Dupal特征的出现可能意味着软流圈地幔在与EM 1或EM 2混合之前就已经具有Pb-Dupal特征。
Major, trace element, and Nd–Sr–Pb isotopic compositions of mantle xenolith-bearing Cenozoic basalts in southeastern China are measured to provide an insight into the nature of their mantle sources and processes. Application of a modified dynamic melting inversion (DMI) method presented here to SE China basalts suggests that Nushan and Fangshan basalts are formed by 4–11% partial melting of a light-rare-earth-element-enriched mantle source. The negative correlation between143Nd/144Nd and206Pb/204Pb and the positive relationship between87Sr/86Sr and206Pb/204Pb strongly suggest a mixing of an intermediate-depleted asthenospheric mantle source and an EM2 component in the study area. The occurrence of the EM2 signature and the diminishing of this signature from south to north in the study area are consistent with the hypotheses that SE China was a part of Gondwanaland. In addition, isotopic constraints from SE China basalts are consistent with the crustal detachment model of Li [Li, Z.X., 1994. Collision between the North and South China blocks: a crustal-detachment model for suturing in the region east of the Tanlu fault. Geology, 22, 739–742] that a subsurface suture between South China and North China Blocks runs eastward through Nanjing. When published isotopic data for Cenozoic basalts from NE China are included, basalts in the whole of eastern China have high208Pb/204Pb and207Pb/204Pb at a given206Pb/204Pb, a feature that is commonly observed in the Southern Hemisphere Dupal oceanic island basalts. In addition,206Pb/204Pb decreases from south to north. Such a regional variation of Pb isotopic compositions in the whole of eastern China cannot simply be attributed to mixing of two mantle endmembers because Nd and Sr isotopic compositions show opposite regional variations in SE China and NE China. The SE China basalts suggest mixing between an asthenospheric mantle and EM2, while the NE China basalts reflect mixing between an asthenospheric mantle and EM1. The central-eastern China basalts from Nushan, Fangshan, and Tashan have the most depleted Nd and Sr isotopic compositions that may represent the isotopic composition of the asthenospheric mantle. The occurrence of Pb-Dupal signatures in these central-eastern China basalts may imply that the asthenospheric mantle already had a Pb-Dupal signature before its mixing with EM1 or EM2.