Abstract:It is probable that granitic magma ascent does not result from the intrinsic properties of the magmas. Within the uppermost crust, neither the reduced viscosity nor the density contrast between magma and surroundings are themselves sufficient to induce either low-inertia flow (diapirism) or fracture-induced magma propagation (dyking). Igneous diapirism is intrinsically restricted to the lower, ductile crust. Dyking is therefore the most probable ascent mechanism for granitic magmas that reach shallow crustal levels. A neutral buoyancy level in the crust, at which magma ascent should stall, is never observed. This,is demonstrated by coeval emplacement of magmas with different compositions and densities, and the negative gravity anomalies measured over many granitic plutons. We suggest that deformation, through strain partitioning, is necessary to magma ascent. Pluton formation is controlled by local structures and rock types rather than by intrinsic magma properties. As a result of its intermittent character, deformation (both local and regional) induces magma pulses, and this may have important consequences for the chemical homogeneity of intruded magmas.Ascent of granitic (leucogranitic to tonalitic) magma in the continental lithosphere is the most potent means of mass transfer and chemical segregation between the lower and upper crust. Granitic magmatism contributes to crustal recycling and, to a lesser extent, continental growth. In rapidly accreted crust, granitic rocks can occupy up to one-third of the volume of the middle crust (Meissner 1986). Together with shear zones, they are the most conspicuous effects of plate convergence and collision in orogenic zones. Consequently, they are a key element in understanding the evolution of Earth's mechanical workings.As most felsic magmas are emplaced in a liquid, or near-liquid state, at temperatures over 800~ a major heat source must be involved in their genesis. The existence of such a heat source also has consequences for the deformation regime of the crust. Commonly, a large temperature rise in the lithosphere will also increase the capacity of crustal material to respond to stress (by deformation). Such a thermal anomaly will contribute to the dissipation of energy and thus buffer the temperature effects. The stress regime will be imposed externally by the tectonic processes operating at the time. As a reaction to a significant increase in crustal heat flow, the rheological capacity of rocks to sustain stresses decreases, and this activates deformation. Therefore, most departures from a 'normal' heat distribution in the lithosphere will trigger deformation (e.g. formation of extensional rift zones, or shear zones in convergent situations).