The significance of mafic microgranular enclaves in the petrogenesis of the Qorveh granitoid complex, northern Sanandaj-Sirjan zone, Iran

The Sanandaj-Sirjan Zone originated during subduction of the Neo-Tethys oceanic crust beneath the Central Iranian microplate. Magmatic rocks exposed in this region are represented by a wide compositional range, with a preponderance of granitoids. The calc-alkaline Qorveh Granitoid Complex (QGC), located to the southeast of Qorveh, includes granodioritic and granitic intrusions that host mafic microgranular enclaves (MMEs). Geochemical, textural and mineral chemistry features of granitoid host rocks and MMEs are presented here. The host rocks and enclaves show disequilibrium textures (e.g., tabular plagioclase with inclusions of biotite+hornblende, resorbed plagioclases, needles of apatite and overgrowth of feldspar crystals). Field, textural and geochemical evidence suggest that these features result from incomplete mixing with the enclosing host rocks. Physicochemical conditions and mesoscopic features suggest that the enclaves cooled quickly without pervasive changes. Considering all data, the MMEs most likely formed by magma mingling processes. The injection and rapid cooling of successive pulses of mafic magma into granodioritic-granitic magma resulted in the formation of the observed enclaves. Rheological properties of these magmas inhibited mixing, but inter-diffusion of trace elements between melts was partly efficient.