Post-collisional alkaline granites

Alkaline (A-type and highly fractionated felsic I-type) granites that may have formed in post-collisional plate tectonic environments are present in the Alaskan Cordillera, the New England and Lachlan Fold Belts of Australia, and the Arabian-Nubian Shield. Their emplacement is associated with diffuse extension and/or strike-slip shear movements that follow the proposed collisional events by ~25 to 75 Ma. The post-collisional alkaline granites are compositionally most similar to within-plate (anorogenic) alkaline granites, but also show affinities with volcanic arc and syn-collisional granites. Their source rocks are just as likely to be previously unmelted mafic meta-tonalites as they are to be restite from which I-type granitic melt has been extracted earlier. -from Author