Cumulus processes and melt-migration in layered intrusions and the use of image analysis to quantify microscopic textures in cumulates.
This thesis presents three studies carried out to
investigate the relationship between small scale structures
and large scale processes in layered intrusions.
The first is a field-based study from the Eastern Layered
Series of the Rhum intrusion. Lateral variations were found
to be significant in the allivalite of unit 12 on Hallival,
and the cumulate stratigraphy was shown to thin by
approximately 50% over less than 800 metres down-dip. This
thinning was associated with the development of layeringparallel
zones of intense deformation and the entire
cumulate package is interpreted to have evolved as a
sequence of alternating troctolitic and peridotitic mass
flows initiated by the intrusion of basaltic melts into
marginal cumulates. In addition, a series of gabbroic
cumulates were interpreted as preserving melt-migration
pathways within still-porous cumulates. Cumulus textures
were found to control porosity-permeability relationships
in the crystal pile. The effect of anisotropy on the
movement of melts was studied.
Core material from the Muskox layered intrusion was
analysed to constrain compaction and showed it to be a
widespread process which reduced melt contents to -10% over
cumulate depths of 1000 metres, in less than 600 years.
Progressive contamination of Muskox primary melts resulted
in a change from olivine-rich to pyroxene-rich cumulates
and this lea to an increase in matrix viscosity from
<5x10 15 Pa s to -4x1016.
The final part of the thesis concentrates on the
quantification of interfacial curvature, a parameter which
dominates the evolution of textures by surface energy
minimization. Software is presented to allow the
determination of variations in two dimensional grain
boundary curvatures by curve-fitting method using a cubic
spline. The software is tested on experimental olivinebasalt