Geochemistry and petrogenesis of the C retaceous A ‐type granites in the L aoshan granitic complex, eastern C hina

Major element and trace element compositions, and Sr , Nd and Pb isotopic compositions for postcollisional granites from the L aoshan granitic complex, in the eastern side of the T riassic suture between the South C hina and North C hina tectonic blocks were determined. The granites are alkaline, A ‐type and can be further classified as A 1 granites. The trace element composition of these granites is transitional between those of oceanic island basalt and enriched mid‐oceanic ridge basalt, with depletions in Ba , Sr , P , and Ti that can be ascribed to mineral fractionation and enrichments in Cs , Rb , Th and U possibly resulted from the involvement of slab fluids. The isotopic signature of L aoshan granites represent a mixture between an enriched mantle type 1 ( EMI )‐like end‐member and lower continental crust ( LCC ). We propose that the magmas that formed the L aoshan A 1 granites are a mixture between those derived from the EMI ‐like delaminated eclogitic rocks (subsequently enriched by fluids released from M esozoic P acific subducted slab) and those derived from the LCC , which consists of granulites or metamorphic residues from the prior generation of I ‐type granites in the region. The mixed magmas then experienced a strongly alkali feldspar‐dominated fractionation prior to their emplacements as A ‐type granites in the L aoshan granitic complex.