The continental crust has an observed stratification from mafic lower crust to granitic
shallow crust. How this stratification arises is one of the key unanswered questions in
igneous petrology. For this thesis a general coupled model of heat and mass transport
during buoyancy driven melt segregation has been developed and employed to simulate
the intrusion and subsequent evolution of sills in regions termed deep crustal hot zones.
A system of governing equations describing the conservation of heat, mass and momentum
in a two phase media undergoing buoyancy driven melt segregation has been
developed. Suitable numerical methods have been employed to solve the governing
equations and a computer code developed for their solution.
As sills are emplaced into the crust they cool and crystallise with the release of latent
heat warming and then melting the surrounding country rock. It is shown that contributions
from both the crust and intrusion are significant. Subsequent melt migration
leads to the development of high melt fraction layers able to fluidise and form mobile
magmas in geologically short time periods. The model can predict temperature and
melt fraction of these mobile magmas and from this the composition can be inferred.
Low temperature, evolved magmas are shown to develop which are able to leave the hot
zone and ascend to the shallow crust, driving crustal stratification.
The model is then extended to discuss the transport of major components during
melt migration and applied to several geologically significant systems. Binary systems
have been chosen due to their relative simplicity and the importance of several two
component phase diagrams in igneous systems. Mixing in a heterogeneous crust is
shown to lead to previously unobserved effects such as the formation of mobile magmas
at the interface between compositionally distinct layers. Finally trace element transport
during melt migration is investigated for both compatible and incompatible elements.
Large deviations from the current paradigms of trace element fractionation are observed
when the migration of species is modelled explicitly.
This thesis shows that melt migration is an important process in geological systems
and is a major influence during the formation of mobile magmas and their resultant
temperature, composition and trace element concentration.