A mafic-ultramafic rock belt in the Fujian coastal area, southeastern China: a geochemical study

Abstract

Geological and geochemical evidence supports the non-ophiolitic origin of the mafic-ultramafic rocks exclusively exposed along the Changle-Nanao fracture zone in the Fujian coastal area, southeastern China. The spinels of the ultramafic rocks have very high Cr^#$\text{[}\text{100 × Cr}\text{(Cr + Al)}\text{= 0.85]}$, and the gabbros contain abundant calcic plagioclases, FeTi oxides and amphiboles, are are rich in TiO₂, total iron, and light rare earth elements. It is probable that the mafic-ultramafic rocks are originally formed at a local extensional environment on the continental side of the subduction zone and eventually thrust in the compressional environment onto the Jurassic volcanic rocks or metamorphic rocks in the Yenshan (upper Triassic-upper Cretaceous) orogen. It is likely that the Yenshan subduction zone exists along the East Taiwan longitudinal valley rather than the Changle-Nanao fracture zone. The pre-Cenozoic tectonic evolution of the eastern Fujian coastal area and Taiwan is also discussed.