Geochemistry of Early Cretaceous calc-alkaline lamprophyres in the Jiaodong Peninsula: Implication for lithospheric evolution of the eastern North China Craton

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• 作者：Liang Ma ; Shao-Yong Jiang ; Ming-Lan Hou ; Bao-Zhang Dai ; Yao-Hui Jiang ; Tao Yang ; Kui-Dong Zhao ; Wei Pu ; Zhi-Yong Zhu ; Bin Xu
• 关键词：Calc-alkaline lamprophyres ; Geochemistry ; Jiaodong Peninsula ; Lithospheric evolution ; North China Craton
• 刊名：Gondwana Research
• 出版年：March, 2014
• 年：2014
• 卷：25
• 期：2
• 页码：859-872
• 全文大小：2992 K

文摘

Mesozoic lamprophyres are widely present in gold province in the Jiaodong Peninsula. In this study, we analyzed major and trace elements and Sr-Nd-Pb isotopic compositions of lamprophyres from the Linglong and Penglai Au-ore districts in the Jiaodong Peninsula, in an attempt to better understand Mesozoic lithospheric evolution beneath the eastern North China Craton. These lamprophyre dikes are calc-alkaline in nature, and are characterized by low concentrations of SiO₂, TiO₂ and total Fe₂O₃, high concentrations of MgO, Mg# and compatible element, enriched in LREE and LILE but variably depleted in HFSE. They display initial ⁸⁷Sr/⁸⁶Sr ratios of 0.709134-0.710314, 蔚_Nd(t) values of 鈭?#xA0;13.2 to 鈭?#xA0;18.3, ²⁰⁶Pb/²⁰⁴Pb of 17.364-17.645, ²⁰⁷Pb/²⁰⁴Pb of 15.513-15.571 and ²⁰⁸Pb/²⁰⁴Pb of 37.995-38.374. Interpretation of elemental and isotopic data suggests that the Linglong and Penglai lamprophyres were derived from partial melting of a phlogopite- and/or amphibole-bearing lherzolite in the spinel-garnet transition zone. The parental magma might have experienced fractionation of olivine and clinopyroxene, and minor crustal materials were incorporated during ascent of these mafic magmas. Before ~ 120 Ma of emplacement of these calc-alkaline lamprophyres, the ancient lithospheric mantle was variably metasomatized by hydrous fluids rather than melts from subducted/foundered continental crust. It is proposed that continuous modification by slab-derived hydrous fluids from the Paleo-Pacific plate converted the old cratonic lithospheric mantle to Mesozoic enriched lithospheric mantle. Geodynamic force for generation of these lamprophyres may be related to large scale lithospheric thinning coupled with upwelling of the asthenosphere beneath the North China Craton. Continental arc-rifting related to the Paleo-Pacific plate subduction is favored as a geodynamic force for the cratonic lithosphere detachment.