Magma mixing/mingling in Salmas granodiorite, NW Iran: evidence from mafic microgranular enclaves

Abstract

The interaction of mafic–intermediate and felsic rocks of the Salmas plutonic rocks produced mixed rocks (granodiorites) which contain mafic microgranular enclaves (MMEs). Enclaves ranging from a few millimeters to centimeters in size, and from ellipsoidal to rounded in shape. Based on both field observation and mineralogical compositions, MMEs are composed of quartz diorite whereas the felsic host rocks comprise mainly granodiorite. MMEs are characterized by a microporphiritic texture and revealed some types of microscopic textures, e.g., prismatic-cellular plagioclase with spike zones and rounded plagioclase megacrysts, blade-shaped biotite and acicular apatite. The host rocks show textures such as oscillatory- and reversely zoned plagioclase with spike zone. Compositions of plagioclases (An41 to An48) of MMEs are similar to those of host rocks (An38 to An45) which suggest partial to complete equilibration during mafic–felsic magma interactions. The individual petrographic and microstructural textures and mineral chemistry similarities between the MMEs and their host rocks and diorites indicate that the enclaves are of mixed origin and most probably formed by interaction of lower crust magma (granitic melt) and evolved mantle-derived magmas (diorites).