On the rates of emplacement, crystallization and cooling

Abstract

We know very little with certainty about the times required to melt, segregate, crystallize and cool granitic magmas. Calculation is bedevilled by imponderables such as the effect of crustal depth, tectonic environment and mode of emplacement, and the extent to which fresh draughts of magma thermally recharge the system. It is extremely unlikely that a pluton ever represents a closed system insulated from the enveloping heat plume within which it rises, and from its source of magma replenishment. Nevertheless, it seems worth while to attempt to identify constraints and assign minimum time spans to the several parts of the evolutionary history — that is, the initial partial melting and the melt assembly, its ascent and intrusion, and its crystallization and final cooling to the ambient temperature of the country rock. However, I do so in the reverse of this natural order in accord with the reliability of the data.