Granite magma generation, ascent and

Crustal thickening during transpressive orogenesis may produce anatectic granites which may then localize deformation leading to transcurrent movement. Granites may be transported from sites of generation through the mid-crust in dyke-like channelways within relatively narrow strike-slip shear zones which link to major fault zones in the upper crust. Extensional jogs within fault systems provide developing sites for the assembly of plutons from magma arriving from below. The model is based upon obser-vations from the Cadomian belt of NW France which exposes sections through middle and upper levels of the late Precambrian crust within different elements of the orogen. The mechanism provides a favourable alternative to diapirism, and explains the common collocation of granites and shear zone/fault systems within orogenic belts. Growing realization that diapirism is not the dominant process by which granite magmas ascend through the crust (e.g. Bateman 1984) requires investigation of alternative mechan