Mineralogy from three peralkaline granitic plutons of the Late Permian Emeishan large igneous province (SW China): evidence for contrasting magmatic conditions of A-type granitoids

TheEmeishan large igneous province contains a diverse assemblage of igneous rocks includingmildly peralkaline granitic rocks ofA-type affinity. The granitic rocks from the Panzhihua, Baima andTaihe plutons are temporally, spatially and chemically associatedwith layeredmafic-ultramafic intrusions. Electronmicroprobe analyses of themajor and accessoryminerals along with major and trace element data were used to document the magmatic conditions of the three peralkaline plutons. The amphiboles show magmatic/subsolidus trends and are primarily sodic-calcic in composition (i.e., ferrorichterite or richterite). Sodic (i.e., riebeckite-arfvedsonite) amphiboles are restricted to the Panzhihua and Taihe plutons. The amphiboles from the Panzhihua and Taihe granites are very similar in composition whereas amphiboles from the Baima syenites have higher MgO wt% and lower FeOt wt% and TiO2 wt%. Whole-rock Zr saturation temperature estimates indicate the initial average magma temperatures were 940 21 C for the Panzhihua pluton, 860 17 C for the Baima pluton, and 897 14 Cfor theTaihepluton.The initial Fmelt(wt%)valueswere calculated to be1.1 0.1, 0.8 0.1 and1.1 0.1wt%for the Panzhihua, Baima and Taihe plutons, respectively. The estimated Fmelt(wt%) values are higher than what can be accounted for in the Panzhihua and Taihe plutons and indicate that they may have lost F during crystallization. In contrast the Fmelt(wt%) value for the Baima pluton can be accounted for. The presence of titaniteþmagnetiteþ quartz in theBaima syenites indicates oxidizing fO2 conditionswhereas the presence of aenigmatite and ilmenite in the Panzhihua and Taihe granites indicate that they were relatively reducing. Although the Atype granitoids formed by the same processes (i.e., fractional crystallization of mafic magmas), their differences in major element and mineral chemistry are likely related to a combination of initial bulk magma composition and magmatic oxidation state. Key-words: ferrorichterite, peralkaline, A-type granite, Zr saturation thermometry, oxygen fugacity, aenigmatite.