Early Proterozic mafic dikes in the North China Craton and their tectonic implications

Abstract

This paper synthetically presents the geochronological, elemental and isotopic data for the unmetamorphosed dikes from the Sangganhe, Lüliang 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.