Elemental and Sr-Nd isotope geochemistry of microgranular enclaves from peralkaline A-type granitic plutons of the Emeishan large igneous province, SW China

Microgranular enclaves are common within intermediate to felsic granitic rocks that have I- and S-type affinity however they are rare within alkaline anorogenic granitoids of A-type affinity. The Permian (~260Ma) Emeishan large igneous province (ELIP) of southwest China contains two peralkaline silica saturated A-type granitic plutons that host microgranular enclaves. The enclaves from the Baima pluton are intermediate in composition and have lower SiO₂ and higher TiO₂, CaO and Mg# (SiO₂=57.2 to 63.0wt.%; TiO₂=0.8 to 1.8wt.%; CaO=1.7 to 3.3wt.%; Mg#=28 to 44) than their host (SiO₂=62.6 to 67.8wt.%; TiO₂=0.5 to 1.4wt.%; CaO=0.4 to 1.8wt.%; Mg#=15 to 31). The enclaves from the Taihe pluton are more felsic (SiO₂=63.8 to 71.3wt.%; TiO₂=0.3 to 0.6wt.%; CaO=0.6 to 2.3wt.%; Mg#=8 to 22) but are still less evolved than their host (SiO₂=69.8 to 75.1wt.%; TiO₂=0.2 to 0.6wt.%; CaO=0.4 to 0.8wt.%; Mg#=3 to 12). In both cases, the enclaves have very similar εNd_(T) values (Baima εNd_(T)=+2.8 to +3.2; Taihe εNd_(T)=+1.0 to +2.0) as their hosts (Baima εNd_(T)=+3.0 to +3.2; Taihe εNd_(T)=+1.5 to +1.9). The major and trace element trends of the enclave-host pairs suggest that fractional crystallization occurred and that element diffusion was likely minimal. The enclaves are interpreted as entrained accumulations of early formed crystals of a silicic magma which was originally produced by fractional crystallization of a mafic magma.