Permian peralkaline, peraluminous and metaluminous A-type granites in the Panxi district, SW China: Their relationship to the Emeishan mantle plume

Numerous Permian granitic intrusions (plutons) in the Panxi region, SW China are spatially and temporally associated with the Emeishan large igneous province (ELIP). Granites from the 260 Ma Panzhihua and Taihe plutons are peralkaline (ASI=0.76-1.12; Na+K/AI=0.78-1.2) and have high Fe* values (0.92-0.99) with negative Eu anomalies (Eu/Eu*=0.22-0.98). Contrasted with the peralkaline plutons, syenites from the 260 Ma Woshui pluton are metaluminous (ASI=0.84-1.0,Na+K/AI=0.91-1.01) and have moderately high Fe* (0.79-0.81) and positive Eu-anomalies (Eu/Eu*=0.82-1.91). Both the peralkaline and metalurnmous rocks have mantle isotopic signatures (rNd((T))=+ 1.3-+3.2) and were derived from the ELIP mantle plume source. The peralkaline rocks were likely derived by fractional crystallization of the temporally, spatially and chemically associated layered mafic intrusions which host giant magmatic Fe-Ti-V oxide deposits. The metaluminous granitic rocks, although spatially related to the peralkaline granites and layered gabbros were likely generated by partial melting of underplated mafic rocks. Granites from the 211 Ma Ailanghe pluton are peraluminous (ASI=0.97-1.29) and have high Fe* (0.82-0.9l) values and negative Eu-anomalies (Eu/Eu*=0.10-0.37). Their crustal isotopic signature (epsilon Nd-(T)=-5.7 to -6.7) indicates possible derivation from melting of Yangtze Block basement rocks. The Ailanghe pluton is contemporaneous with other A-type granites in the region, supporting the view that ELIP magmatism was sporadic for at least 9 million years. The coexistence of three chemically exclusive A-type granites in the ELIP suggests that a variety of A-type granites can be generated in the same tectonic setting. (c) 2007 Elsevier BX. All rights reserved.