granodioritic

Granodioritic is a term used in geology to describe igneous rocks with granodiorite-like composition. Such rocks are intermediate between granite and diorite in their mineralogy and chemistry, and they are typically felsic to intermediate in overall character. The name reflects a balance in mineral proportions that is coarser and coarser-grained than many basalts but finer than pure felsic rhyolites in some cases.

The defining minerals of granodioritic rocks are quartz and plagioclase feldspar as the dominant constituents, with potassium feldspar present in lesser amounts. Plagioclase is commonly calcic to andesine-oligoclase, and quartz is a significant component. Mafic minerals, such as biotite, hornblende, or minor pyroxene, occur in variable amounts and give the rock its color index. Accessory minerals may include magnetite, apatite, zircon, and sometimes allanite.

Texture is typically phaneritic, indicating slow crystallization at depth. Granodioritic rocks form in plutonic settings, often as large intrusions such as batholiths or laccoliths, and are commonly associated with continental crust and subduction-related tectonic environments. They are the intrusive counterparts of granitic compositions that crystallized beneath the surface.

Geochemically, granodiorites are silica-rich and belong to the felsic to intermediate range. In field relationships, granodioritic rocks are distinguished from granite by a relatively higher plagioclase-to-alkali feldspar ratio and a notable amount of quartz; they are distinguished from diorite by their quartz content and the presence of both feldspars. Granodioritic rocks are widely discussed in studies of crustal differentiation and continental arc magmatism.