Metamorphic effects on agate found near the Shap granite, Cumbria, England: as demonstrated by petrography, X-ray diffraction and spectroscopic methods

摘要

Agates from a 430 Ma host at Stockdale Beck, Cumbria, England have been characterized The crystallite size of the Stockdale Beck agates was found to be approx 60 percent greater than any other agates from five regions aged 400-1100 Ma. Raman spectroscopy identified moganite in all agates tested excent those from Stockdale Beck. Infrared spectroscopy showed that the silanol content of the Stockdale Beck agates was near zero. The properties of agates from Stockdale Beck and the 1 84-3 48 Ga metamorphosed hosts found in Western Australia were similar but different from agates found in other hosts aged 400-1100 Ma. Cathodoluminescence demonstrates further differences between asates from hosts aged 13-1100 Ma and those from Stockdale Beck and Western Australia. Agates from the latter areas have a lower proportion of defects causing a red emission band (approx 660 nm) but an increased proportion of defects causing blue (approx 470 nm) and orange (approx 640 nm) emission bands Agates found in hosts aged 13-1100 Ma are also differentiated from the Stockdale Beck and Western Australian agates in a ternary plot of the relative intensities of violet to blue to orange emission bands Sinale scans producing this combination of colours are only found in the Stockdale Beck and Western Australian agates. The properties shown by the Stockdale Beck and Western Australian agates demonstrate that an agate or chalcedony infill can be used to identify post-deposition palaeoheating within a host rock