Using titanium-in-quartz geothermometry and geospeedometry to recover temperatures in the aureole of the Ballachulish Igneous Complex, NW Scotland
D. J. Morgan, M. C. Jollands, G. E. Lloyd, D. A. Banks, 2014. "Using titanium-in-quartz geothermometry and geospeedometry to recover temperatures in the aureole of the Ballachulish Igneous Complex, NW Scotland", Deformation Structures and Processes within the Continental Crust, S. Llana-Fúnez, A. Marcos, F. Bastida
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‘Titanium-in-Quartz’ geothermometry suggests quartzites could yield reliable temperature estimates. We here apply four calibrations of the titanium-in-quartz geothermometer to contact-metamorphosed quartzites surrounding the Ballachulish Igneous Complex, Scotland. Two agree broadly with thermal modelling and pre-existing geothermometry; two give temperatures consistently too low. As reported in earlier studies, the technique suffers from difficulties in analysing low titanium (Ti) levels with high spatial and analytical precision. However, this study finds that the critical problem is one of Ti heterogeneity, which poses difficulties in constraining the chemical activity of Ti during quartz growth under metamorphic conditions. Scanning electron microscope-cathodoluminescence (SEM-CL) textures support an interpretation of extensive Ti disequilibrium despite the presence of rutile, indicating dynamic interplay between grain boundary diffusion, fluid/melt percolation and grain growth. The strong zonation suggests a possible geothermometer based on apparent volume diffusion of Ti-in-quartz to derive grain growth histories. Analysis of rutile–quartz interaction implies peak contact temperatures of 645±12 °C, precise but reliant on external estimates of cooling rate from thermal models. Our conclusions support caution in applying Ti-in-quartz geothermometry in aureole settings. However, rutile–quartz juxtaposition prior to heating to >600 °C defines a Ti diffusion couple, employable as a thermometer if cooling rates are constrained by other means.
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Deformation Structures and Processes within the Continental Crust
This volume presents a selection of papers showing the current focus of studies of deformation structures and processes within the continental crust. The selected contributions use a large range of analytical techniques suited to the full range of structure sizes and fine-tuned to the physical process that controls the deformation, from the grain boundary at the micro-scale, the lithological contact at the meso-scale to the plate boundary at the global scale.
The papers in the volume are grouped into three sections relating to specific lines of research within the analysis of rock deformation structures and processes, in particular in respect to the continental crust: structures within shear zones and faults; magmatic structures, and microstructures and rheology. These sections include papers describing field studies, experimental rock deformation and numerical modelling of deformation processes.