Branching Plagioclase, Isle of Rum
This project is on some unusual branching plagioclase in conjunction with H. Emeleus Durham University. The unusual textures are composed of dm-scale branching arrays of plagioclase within felspathic peridotite - troctolite of the Rum Central Complex. The work forms the M.Sc project of Francoise Labonté. The rocks were mapped and sampled in July 2001. Working hypotheses are that; the textures represent far from equilibrium crystal growth (e.g. Donaldson et. al., 1973), they are due to viscous fingering, or they are organized chains of plagioclase. Research is designed to test these hypotheses and to fully document the geometry and chemistry of the plagioclase texture in order to simulate its formation.
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Variolites of the Abitibi Greenstone Belt
For years these enigmatic textures were considered to be due to liquid silicate immiscibility. Strictly a variole is a centimetric-scale globular leucocratic texture found on the weathered surface of mafic (generally volcanic) rocks. Our work (Fowler et. al., 2002; Fowler et. al., 1986) shows that there are two types within the Archean Abitibi subprovince of Québec and Ontario. One group turns out to be plagioclase spherulites that were formed as a result of chilling superheated basalt. The other is composed of mingled rhyolitic and basaltic lavas. The latter type are the focus of on-going research. The aim here is to characterize the two lavas to better understand the generation of Archean rhyolites and the evolution of the mingled Archean rhyolites. The work has potential implications for gold mineralization in the area as shown by the recent M.Sc thesis by Ropchan (e.g. Ropchan et. al., 2002). Ph.D. student Etienne Dinel is working on some extremely well preserved sections of variolitic rocks from the Timmins and Harker-Holloway areas of the Abitibi. In addition, M.Sc. student Genévieve Leblanc is currently working on mineralized rocks in the Shining Tree area of the Abitibi.
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Komatiites
Former student Mark Shore and I have worked on the problem of olivine spinifex development (Shore and Fowler, 1999). Spinifex which is organized into spectacular sheave like structures results from rapid cooling. In essence the rapid and organized growth involves hydrothermal cooling of the propagating flow-crust along with constrained cooling of olivine. In this latter process the forsterite crystals transfer heat more efficiently than the liquid from which they grow. This cools the liquid directly ahead of the crystal thus promoting growth. Heat is transferred to the overlying hydrothermally cooled crust. Current work with Michel Houlé (Ph.D. student) and colleagues at Laurentian University and the Ontario Geological Survey is focused on the physical volcanology and facies architecture of komatiites.
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Rapakivi Granite
Gabriel Machado is studying the development of this texture for his Ph.D. in conjunction with Mike Higgins (Université du Québec à Chicoutimi) and Ilmari Happala (University of Helsinki). Samples have been collected and field measurements taken from the Eurajoki rapakivi/megacrystic granite of SW Finland. In order to test for ripening or other processes during the mineral growth Gabriel is doing crystal size distribition analyses.
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Oscillatory Mineral Zoning
Numerous minerals of which plagioclase is the archetype have a characteristic oscillatory zoning (Shore and Fowler, 1996). Our work and that of colleagues demonstrates that the zoning is inherent to the crystal growth dynamics and not a reflection of bulk changes within the system from which the crystal grows. The oscillatory growth mode appears under non-equilibrium conditions and involves a feedback between the crystal and the liquid from which it grows. Collaboration with Ivan L’Heureux in the department of physics has led to the development of quantitative models for the feldspar oscillatory growth, and recent findings have resulted in a data-driven model of zircon oscillatory growth (Fowler et. al., In press).
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Branching Mineral Growth
Some mineral growth results in fractal patterns that can be quantitatively described and modelled (Fowler et. al., 1989; Fowler and Roach, 1996). The realization that the textures are fractal objects and can be simulated using diffusion limited aggregation places constraints upon the conditions of growth. This can then be used to infer and understand geological conditions.

Dolores Durant recently completed her Ph.D. on the organization of orbicles from Fisher Lake California. The orbicules consist of shells of alternating mineral composition that have nucleated on cm-scale cores. Some of the minerals within the cores are characterized by a branching texture indicative of far from equilibrium growth conditions. In addition plagioclase and orythopyroxene are reversed zoned. Durant and Fowler (2002) demonstrate that the zoning and branching arises as a result of relatively fast growth during magma mingling.

We have documented branching galena associated with banded sphalerite of many Mississippi valley-type deposits (Fowler and L’Heureux, 1996). We think that in general the mineral patterning arises due to the introduction mixing of metliferous brines and their mixing with sulphurous gases within carbonate host rocks.

Ann Theriault recently completed her Ph.D. on the evolution of the Sudbury Igneous Complex. An outstanding feature of the complex are the widespread granophyres, and graphic textured rocks. These include branchng textures quartz and feldspar. We show that although the textures are what one expects of quickly cooled volcanic rocks, they formed in response to exsolution of a fluid phase at depth (Thériault et. al., 2002). Further study of the evolution of these textures and their associated inclusions may very well be useful in constraining the development of hydrothermal fluids of the area.
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Archean Volcanology
Through some of our early work on variolites former M.Sc. student Murray Jones discovered an intriguing and very well preserved volconoclastic deposit that recently we (with former students Craig, Scott and Dominque Richard) have determined to be a subaqueous pyroclastic flow. The rocks have clear evidence of having been deposited hot and under water (Scott et. al., Submitted). Much of graduate student work on projects within the Abitibi require careful mapping and the identification of volcanic lithofacies.
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Land Rovers
I grew up with these amazingly versatile though cantankerous (see the video The God's Must Be Crazy) vehicles and know them extremely well. As a consequence they (so-called series vehicles and defenders) are my vehicle of choice for exploration under difficult conditions. Unfortunately (?) this Land-Rover genetic defect seems to run in the family as my 20 year-old son is restoring the vehicle his grandfather used to drive over forty years ago!
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