Role of sediment in generating contemporaneous, diverse “type” granitoid magmas

Abstract Granite typology categorizes granitoid rocks based upon distinguishing characteristics that are interpreted to indicate sources, conditions of generation, and, by implication, tectonic setting. Complexities elemental and isotopic geochemistry, however, commonly preclude simple typological interpretation suggest more complex petrogenetic histories. Granitoids from the Songpan-Ganzi terrane in eastern Tibetan Plateau were emplaced within a short interval (~15 m.y.). They display mineralogical geochemical consistent with wide range proposed typologies (I-, S-, A-type; high Ba-Sr adakitic variants). Despite their close spatial temporal association, these granitoids exhibit diversity indicates broad spectrum contributing sources. Radiogenic isotope data reveal continuum primitive evolved crustal compositions; i.e., 87Sr/86Sr(t) = 0.704–0.715 ?Nd(t) +2 ?11. All “types” have variable but zircon ?18O (+4.1‰ +11.6‰) low whole-rock Li-B-Mg ratios compared mantle and/or seawater (?7Li +5.1‰ ?3.2‰; ?11B ?10.7‰ ?16.5‰; ?26Mg ?0.23‰ ?0.59‰). These stable compositions granitic magmas all had contributions sediment, ranging minor dominant. The highly rule out single homogeneous source for diverse yet contemporaneous granitoids. Their compositional variability may been significantly influenced sedimentary contributions, results demonstrate difficulty straightforward assignment using conventional typology.