Isotopic characteristics of Hannuoba basalts, eastern China: Implications for their petrogenesis and the composition of subcontinental mantle
Isotopic characteristics of Hannuoba basalts, eastern China: Implications for their petrogenesis and the composition of subcontinental mantle
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DOI：
10.1016/0009-2541(90)90102-d
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发表时间：
1990-10
期刊：
影响因子：
3.9
通讯作者：
Yan Song;F. Frey;X. Zhi
中科院分区：
文献类型：
--
作者：
Yan Song;F. Frey;X. Zhi
中国东部汉诺坝地区的碱性玄武岩和拉斑玄武岩具有87Sr86Sr和143Nd144Nd144Nd值，范围从普遍的地幔(PREMA)场到推断的块体地球比值。206Pb204Pb值范围为17.10~17.94，所有样品的207Pb204Pb值和208Pb204Pb值均显著高于北半球参考线。虽然最古老的汉诺坝熔岩是碱性玄武岩，但碱性熔岩和拉斑玄武岩是夹层的，它们在同位素上是不同的。与碱性熔岩相比，拉斑玄武岩具有较高的87Sr86Sr值，较低的143Nd144Nd值和较低的放射性成因铅同位素比值。所有汉诺坝熔岩的同位素比值和不相容元素趋势与同位素和成分上不同成分的混合是一致的。我们推断，碱性玄武岩是由软流圈来源的少量熔融形成的，类似于某些大洋玄武岩所需的熔融程度。然而，拉斑玄武岩中含有与大洋地幔中的EMI类似的富集地幔成分，可能存在于上升软流圈或陆下岩石圈地幔中。这些地幔组分之间的混合可能发生在40 Ma前导致中国∼东北伸展的裂谷事件期间。具体地说，我们认为上升软流圈内的熔融形成了汉诺坝碱性熔岩，而以年轻为主的拉斑玄武岩是大陆岩石圈部分熔融的结果，大陆岩石圈被上升的软流圈加热。对于美国西部和英国第三纪省喷发的大陆玄武岩，也提出了类似的模型。
Alkalic and tholeiitic basalts from the Hannuoba region of eastern China have 87 Sr 86 Sr and 143 Nd 144 Nd ranging from the prevalent mantle (PREMA) field to inferred bulk Earth ratios. Ratios of 206 Pb 204 Pb range from 17.10 to 17.94 and all samples have 207 Pb 204 Pb and 208 Pb 204 Pb ratios significantly above the Northern Hemisphere reference line (NHRL). Although the oldest Hannuoba lavas are alkalic basalts, alkalic and tholeiitic lavas are intercalated, and they are isotopically distinct. Relative to the alkalic lavas, tholeiitic lavas have higher 87 Sr 86 Sr, lower 143 Nd 144 Nd and less radiogenic Pb isotope ratios. The isotopic ratios and incompatible-element trends defined by all Hannuoba lavas are consistent with mixing of isotopically and compositionally distinct components. We infer that the alkalic basalts were generated by small degrees of melting of an asthenospheric source, similar to that required for some oceanic basalts. However, the tholeiitic basalts contain an enriched mantle component, similar to EMI in the oceanic mantle, which may have resided in the upwelling asthenosphere or subcontinental lithospheric mantle. Mixing between these mantle components may have occurred during the rifting event that caused extension in northeast China∼ 40 Ma ago. Specifically, we propose that melting within the upwelling asthenospheric created the Hannuoba alkalic lavas whereas the dominantly younger tholeiitic lavas resulted from partial melting of continental lithosphere that was heated by the ascending asthenosphere. Similar models have been proposed for continental basalts erupted in the western USA and British Tertiary Province.