A review of the relationships between granitoid types.
Chemical classification of the Archean granitoids: An essay to visit the Yilgarn Craton, W.A.Granitoids associated with Archean greenstones fall into one of three categories: gneissic complexes and batholiths, diapiric syntectonic plutons of variable composition, and late discordant granite plutons (Martin, 1994; Sylvester, 1994).In this classification most Cordilleran granitoids are magnesian and calc-alkalic or calcic; both metaluminous and peraluminous types are present.
The A-type Granitoids Defined by Loiselle and Wones (1979) A stands for Anorogenic or Anhydrous Magmas are emplaced in post-collisional or within plate settings, i.e., an extensional environment. May be produced by the melting of a lithospheric source from which a previous melt had been extracted or by differentiation of a basalt magma.A granitoid or granitic rock is a variety of coarse grained plutonic rock — granite or similar — which mineralogically is composed predominantly of feldspar, quartz and mica. Examples of granitoid rocks include granite, quartz monzonite, quartz diorite, syenite, granodiorite, tonalite and trondhjemite.Many are created by continental volcanic arc subduction or the collision of sialic masses.
The A-type granitoids can be divided into two chemical groups. The first group (A 1) is characterized by element ratios similar to those observed for oceanic-island basalts.The second group (A 2) is characterized by ratios that vary from those observed for continental crust to those observed for island-arc basalts.It is proposed that these two types have very different sources and tectonic.
