Geochemistry of Mesozoic Basalts and Mafic Dikes, Southeastern North China Craton, and Tectonic Implications
Geochemistry of Mesozoic Basalts and Mafic Dikes, Southeastern North China Craton, and Tectonic Implications
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DOI：
10.2747/0020-6814.44.4.370
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发表时间：
2002-04
影响因子：
2.6
通讯作者：
Hong‐fu Zhang;M. Sun
中科院分区：
文献类型：
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作者：
Hong‐fu Zhang;M. Sun
华北克拉通中生代玄武岩岩浆活动是探测中生代岩石圈地幔性质，包括显生宙岩石圈减薄过程的关键。早白垩世钙碱性玄武岩和基性岩脉广泛分布于华北盆地东南部的防城、蒙阴、即墨和胶东地区。两种岩石类型具有相似的地球化学特征；SiO2含量高；中等含量的MgO、CaO和Al2O3；高富集LREE （(Ce/Yb)N bbb10）和LILE (Rb, Ba， U, Th)；在HFSE （Ti和Nb）中耗尽。这些岩石的Sr-Nd同位素富集（87Sr/86Sri > 0.7072, εNd(t) = -11.5 ~ -17.5）， Pb同位素富集（206Pb/204Pb < 17.6, 207Pb/204Pb < 15.6, 208Pb/204Pb < 38.1）。它们的地球化学特征表明，这些玄武岩和基性岩脉来源于富集的岩石圈地幔，这与该地区古生代和新生代岩石圈有很大的不同。计算结果表明，中生代岩石圈受到了广泛的硅熔体改造，这是由俯冲的硅壳部分融合而来的。NCC岩石圈基底下的扬子陆壳构造底化已经建立。丰富岩石圈的广泛熔融和大陆根的构造崩塌为与大别碰撞有关的岩石圈减薄提供了可能的机制。
Mesozoic basaltic magmatism in the North China craton (NCC) is a key for probing the nature of the Mesozoic lithospheric mantle, including the process of lithosphere thinning over Phanerozoic time. Early Cretaceous calc-alkaline basalts and mafic dikes are widespread in the Fangcheng, Mengyin, Jimo, and Jiaodong regions of the southeastern NCC. Both rock types have similar geochemical signatures; are high in SiO2 content; moderately high in MgO, CaO, and Al2O3; highly enriched in LREE ((Ce/Yb)N > 10) and LILE (Rb, Ba, U, Th); and depleted in HFSE (Ti and Nb). These rocks are highly enriched in Sr-Nd isotopes (87Sr/86Sri > 0.7072, εNd(t) = -11.5 ∼ -17.5) and depleted in Pb isotopes (206Pb/204Pb < 17.6, 207Pb/204Pb < 15.6, 208Pb/204Pb < 38.1). Their geochemistry demonstrates that these basalts and mafic dikes were derived from enriched lithospheric mantle, which differs considerably from the Paleozoic and Cenozoic lithosphere of the region. Calculations indicate that the Mesozoic lithosphere was extensively modified by silicic melt, derived from the partial fusion of subducted silicic crust. Tectonic underplating of the Yangtze continental crust beneath the base of the NCC lithosphere is well established. Extensive melting of the enriched lithosphere and tectonic collapse of the continental root provide a possible mechanism for lithosphere thinning linked to the Dabie collision.