The nature, ascent and emplacement of granitic magmas

The address is a wide-ranging commentary on the physical aspects of granitic magma and deals especially with the mode of emplacement. Recommendations on the nomenclature of plutons and batholiths involve both a description of the actual shape and their modeling by experimental and salt-diapir analogues. The nature of granitic crystal-mushes, wet or dry, is discussed in the light of the special properties of pseudoplastics, particularly the influence of the physical state on the sinking of crystals and xenoliths, on magma mobility in zoned plutons, and on the final rock structure. The longevity of plutonic events and their episodic character are commented on in relation to the subduction process. The generation of granitic magmas, their upwelling and the structural control of their intrusion, whether forceful or permissive, are discussed. The structural form of batholiths in depth is described in terms of a batholith denudation series particularly in the circum-Pacific context. Finally, two main orogenic environments of granites are contrasted in terms of the Hercynotype and Andinotype, and composition and structure are interrelated in a proposed general model for the emplacement of batholiths.