Jerram, D., Mock, A., Davidson, J., Petford, N. and Marsh, D.B., 2005. 3D crystal packing variation through a rythmic layer in the Dais Intrusion, Dry Valleys Antarctica: initial insights through 3D micro CT analysis. In: American Geophysical Union, Fall Meeting 2005, 5-9 Dec 2005, San Francisco, USA.
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Crystal populations provide a solid cornerstone of information to help understand magmatic processes and timescales. However, intruding magmas are often laced with varying amounts of existing crystals upon emplacement constraining newly developing crystal populations. High modal abundance of pre- existing crystals may change magma flow dynamics and modify the crystallising sequence on a local scale by dynamically changing the relative abundance of solid phases. In the late stages of intrusion of the basal Sill in the Dry Valleys of Antarctica (c180 Ma), a large layered intrusion developed called the Dais. This was formed when magma laced with OPX crystals invaded the lowermost parts of the magma plumbing system and spread out to deveolop an OPX rich zone known as the OPX Tongue. As the OPX rich magma invaded the basal sill, rhythmic layering developed on a variety of scales from cm to meter. In this study, we have investigated on a cm scale a boundary between an OPX rich and an OPX poor layer. 3D micro CT analysis of this boundary zone allows the characterisation of the 3D packing arrangement and size distribution of the crystals. The layers are characterised by varying modal abundances of plagioclase and OPX/CPX. The analysis shows that a touching framework of OPX + CPX crystals exists throughout the layer studied over a 25% modal variation from 70-45% pyroxene crystals. The relative abundance of CPX increases into the plagioclase rich zone and its acicular skeletal morphology suggests that it was able to grow more freely into the plagioclase rich melt as the layers developed. Such variations in packing will be used to calculate emplacement and flow dynamics on a cm scale and highlight the importance of the pyroxene crystal framework for the evolution of this layered intrusion.
|Item Type:||Conference or Workshop Item (Paper)|
|Additional Information:||Abstract #V13H-07|
|Subjects:||Science > Earth Sciences|
|Group:||University Executive Team|
|Deposited By:||Ms MJ Bowden|
|Deposited On:||13 Aug 2007|
|Last Modified:||07 Mar 2013 14:44|
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