Late Mesozoic intrusive complexes in the coastal area of Fujian, SE China: the significance of the gabbro-diorite-granite association

The Pingtan and Daiqianshan igneous complexes, southeastern China, are typical of calc-alkaline series developed at active continental margins. These two complexes are dominated by granites or gabbros, with minor diorites and granodiorites, and these rock types closely coexisted both temporally and spatially. The major and trace element signatures of gabbros indicate they were crystallised from high aluminium basaltic magmas, which were generated from metasomatised upper mantle. The typical metaluminous calc-alkaline composition, trace element patterns and Sr-Nd isotopes indicate the granites in the complexes are I-type granites, which may have been generated from the deeper crust by a thermal contribution from the mantle. Field relationships, petrography and geochemistry favour a mechanical mingling together with a limited chemical mixing between high aluminium basaltic magma and granitic magma, resulting in the formation of diorites or granodiorites. The essentially bimodal character of these complexes reflects the general character of back-arc extensional magmatism, which was induced by the subduction of the Pacific plate beneath the Eurasian continent in late Mesozoic time.