华北陆块早元古代基性岩墙群及其构造意义

华北陆块中部带的晋冀蒙地区早元古代未变形变质基性岩脉形成于1781~1765 Ma。东部陆块鲁西地区早元古代类似的基性岩脉形成时间约为1841 Ma。中部带基性岩脉依据其FeOt含量、(Nb/La)N和(Th/Nb)N值的差异能划分为组1、组2和组3三类。它们的元素-同位素组成变化表明,组1样品起源于再循环大陆玄武质组分参与的交代岩石圈地幔,组2样品源于交代富铁岩石圈地幔与MORB组分的混杂源区,组3样品则是受辉长质组分混染的、经俯冲改造而成的岩石圈地幔产物。相反,鲁西地区基性岩脉亏损HFSE,具MORB型钕同位素组成。上述地球化学特征支持华北陆块中部带约1780 Ma的基性岩脉与早期俯冲碰撞作用的关系密切,而东部陆块约1840 Ma基性岩脉类似于弧后盆地构造背景产物。

Early Proterozic Mafic Dikes in the North China Craton and Their Tectonic Implications

This paper synthetically presents the geochronological, elemental and isotopic data for the unmetamorphosed dikes from the Sangganhe, Lueliang and Hengshan, Fuping, Wutai and Taihang in the Central Zone, and western Shangdong in the Eastern Zone of the North China Craton respectively. The doleritic dikes, which is dated as 1781-1765 Ma, from the Central zone are tholeiitic basaltic compositions and can be geochemically classified into Group 1, 2 and 3. However, the dikes from the Eastern Block are subalkaline basalts and basaltic andesite, with dated age of about 1840 Ma. Petrological and geochemical analyses suggest that Group 1 dikes of the Central Zone were derived from a metasomatised lithospheric mantle with the involvement of recycled continental basaltic materials during subduction. Group 2 dikes originated from a mixture of subduction-modified lithospheric mantle with MORB component whereas Group 3 dikes are derived from the lithospheric mantle contaminated by subducted gabbroic componet. These dikes are closely asoociated with early stage of subduction/collision. The geochemical features of depleted HFSE and MORB type Nd isotopic compositions for the dikes from the Eastern Block suggest these dikes were products in a back-arc basin setting.