Large scale rhyolitic volcanism is an important process at some convergent plate margins because it leads to chemical differentiation of the upper.-crust and is responsible for the production of long lived near surface thermal anomalies; the Taupo Volcanic Zone is.a Quaternary example._x000D_
The main features of the magmatic systems-of the zone. are the existence of large high level chambers containing homogeneous silicic magma which erupt at intervals of thousands to tens of thousands of years._x000D_
Geochemical work on the deposits resulting from these eruptions has shown that with few exceptions the magmas have been remarkably uniform in their . composition throughout the history of the zone although individual batches with lifespans of the order of. one hundred thousand years can be recognised by subtle differences in trace element ratios._x000D_
Basalt is a rare proportion of the rocks exposed at the surface but has played a major role as a medium for heat transfer and as an end member in chemical mixing processes.