Spatial and temporal influence of Pacific subduction on South China: geochemical migration of Cretaceous mafic–intermediate rocks

The Cretaceous igneous rocks in the South China Block (SCB) were associated with the slab subduction and roll-back of the Pacific Plate. Thus, they provide excellent opportunities to examine the spatial–temporal geochemical migration of magmatism in the retreating subduction margins. The Cretaceous mafic–intermediate igneous rocks from the southeastern SCB were aged between 142 and 71 Ma, and can geochemically be subdivided into three groups: Group A (126–129 Ma and 83– 93 Ma), Group B (126–142 Ma and 71–108 Ma) and Group C (116–142 Ma and 70–110 Ma). Group A and B were mainly distributed in the SCB interior and derived from asthenosphere and asthenosphere–lithosphere interaction sources, respectively. Group C occurred to the east of the Ganjiang Fault and originated from slab–lithosphere interaction. From the coastal provinces to the interior, these mafic–intermediate igneous rocks show increasing incompatible element ratios and Nd isotopic compositions, reflective of a westerly decreasing involvement of slab-derived components. They show two similar age-pulses at c. 125 Ma and c. 90 Ma as well as the Cretaceous A-type granites, indicating two episodes of subduction retreat of the Pacific slab during the Cretaceous. This spatial–temporal pattern of the Cretaceous mafic–intermediate igneous rocks suggests that the Cretaceous slab metasomatism of Pacific subduction retreat was limited to the east of the Ganjiang Fault