Anatomy of a low temperature zircon outgrowth |
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| Authors: | Duncan C Hay Tim J Dempster Martin R Lee David J Brown |
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| Institution: | (1) Department of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Glasgow, G12 8QQ, UK; |
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| Abstract: | Outgrowths of zircon and xenotime are abundant on detrital zircon in a greenschist facies regional metamorphic slate from
the Scottish Highlands. Back-scattered electron images reveal that ca. 3-μm wide zircon outgrowths are porous, inclusion-rich
and contain fine-grained intergrowths with xenotime. Focused ion beam milling, transmission electron microscopy and low-voltage
scanning transmission electron microscopy show that the outgrowth microstructure is complex, composed of mis-orientated nano-crystalline
zircon and a poorly crystalline zircon–xenotime complex. Well-defined micron-sized xenotime is also present within the outgrowth.
Micro-textures show that the outgrowth developed in a polyphase history during cooling and exhumation. Accommodation space
for the outgrowth is probably generated by a combination of thermal decompaction and the migration of defects in adjacent
quartz driven by the force of crystallisation. Zircon may be unique in its ability to record textural evidence of events during
uplift and exhumation that are not recorded in major silicate phases. |
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