A-type volcanic–intrusive complex in the Huanggangshan Basin: Implications for early cretaceous crust–mantle interaction in the Gan-Hang Belt and adjacent areas, South China

Abstract

The origin and petrogenesis of Early Cretaceous A-type volcanic–intrusive complexes in the Gan-Hang Belt and adjacent areas of South China remain controversial. An A-type volcanic–intrusive complex in the Huanggangshan Basin of North Wuyi Mountain comprises syenite porphyry, granite porphyry, granite, and tuffaceous volcanic and pyroclastic rocks. These rocks were subjected to geochronological, geochemical, and isotopic analyses in order to investigate their age and petrogenesis, and crust–mantle interactions in South China. Field observations reveal that this A-type volcanic–intrusive complex contains abundant mafic microgranular enclaves. Zircon UPb dating of the various rock types yielded ages between 136 and 128 Ma. Geochemically, the rocks have A-type affinities, including high large-ion lithophile and high-field-strength element contents, Ga/Al ratios, and zircon saturation temperatures. (87Sr/86Sr)i values vary from 0.702704 to 0.711298, and εNd(t) = −10.63 to −7.28 and εHf(t) = −13.26 to −7.70. Three stages of magmatism are proposed to explain the petrogenesis of the A-type volcanic–intrusive complex in the Huanggangshan Basin: (1) syenitic magmas formed by mingling of crustally derived silicic and mantle-derived mafic magmas; (2) fractional crystallization of anorthitic plagioclase + biotite + ilmenite from the syenitic magmas generated A-type igneous rocks with SiO2 < 71 wt%; and (3) fractional crystallization of plagioclase + K-feldspar + biotite + apatite + allanite + ilmenite then generated A-type igneous rocks with SiO2 > 71 wt%. Combined with previous studies, we suggest that the Early Cretaceous A-type igneous rocks in the Gan-Hang Belt and adjacent areas might have been generated by crust–mantle-derived magma mixing, and the crust–mantle interaction was more intense from southwest to northeast. This increased crust–mantle interaction may have been a response to the Early Cretaceous back-arc extensional environment, possibly as a result of the rollback of the Paleo-Pacific Plate.