| dc.description.abstract | This thesis describes the occurence, mineralogy and assimilation of
basic Kenoliths hosted by Centre 3 syenites. Field work ‘was earned out in
two locations, one in the vicinity of Neys/Ashburton and the other a large
megaxenolith hosted by Centre 1 syenites in the vicinity of Wolf Camp Lake.
Least altered Menoliths consist of plagioclase, pyreo^ene. arnphibole,
biotite, apatite and opaque phases. 'With increasing assimilation this
changes to a combination of plagioclase, arnphibole, biotite, apatite, opaque
phases, alkali feldspar, calcite, fluorite, sphene, zircon, REE phases and
quartz.
Plagioclase is replaced by alkali feldspar in the form of oorphyroblasts
and crystals in the groundmass. Plagioclase is also decalcified to more
albitic compositions along with recrystallization. Arnphibole compositions
extend over the same range of arnphibole compositions in the host
ferro-edenite syenite. The general effect of xenolith assimilation is the
equilibrium of a xenolith’s mineral assemblage to that of the host syenite.
Assimilation processes seen at Wolf Camp Lake are similiar to those seen at Neys/Ashburton.
Bulk rock data along with mineralogical compositional variation in
clinopyroxenes, suggest a tholeiitic basalt parentage for x.enoliths in both
areas. Cr and Ni contents indicate an evolved nature to the parent volcanics.
Data also suggest the possible existence of a second undersaturated type of
volcanic xenolith present at Neys/Ashburton. Parental basalts are
postulated to be coeval volcanics related to the formation of the Coldwell
Complex.
Modelling by mass balance mixing calculations of contamination of host
syenites indicates that contaminated ferro-edenite syenites are the result
of direct assimilation of volcanic xenoliths by ferro-edenite syenite. Quartz
syenites are found to be unsuitable parents to contaminated ferro-edenite
syenites. | |
