Reinvestigating the relationships between the Badenoch Group, Dalradian Supergroup and the Grampian Shear Zone

Evason, Lewis Alexander

Abstract

In situ monazite and titanite U-Pb LA-ICP-MS geochronology and combined petrological and microstructural analysis has revealed both Neoproterozoic and Ordovician deformation within the Grampian Shear Zone (GSZ), central Scotland. The Grampian Shear Zone has been posited to separate the Dalradian Supergroup from the Badenoch Group, representing either, a structural break, an orogenic unconformity or a shear zone that predominantly affects the top of the Glen Banchor Subgroup. New monazite U-Pb data gave Neoproterozoic ages which provide a youngest age of deformation/monazite growth within the GSZ at 824 ± 2.73Ma, with subsequent Neoproterozoic resetting of the monazite at 751.81 ± 3.56Ma and a further resetting during the Early Ordovician/Late Cambrian at 485.85 ± 2.63Ma, from within sample RG1716. Monazite U-Pb data from sample RG1718 Ruthven Semipelite of the Corrieyairack Sub-Group (Grampian Group, of the Dalradian Supergroup) produced two distinct populations of monazite, one population of monazite growth associated with the Grampian Orogeny at 475.03 ± 1.11Ma, the other population from a detrital domain within the monazite produced lower intercept age of 475.51 ± 2.84Ma and an upper intercept age of 3004.7 ± 58Ma, revealing that the Ruthven Semipelite shows a distinct lack of Neoproterozoic deformation. The titanite U-Pb data collected produced an age of 467.45 ± 1.84Ma from Sample RG1703 a sheared garnet amphibolite from within the GSZ and 469 ± 0.3Ma from sample RG1710 a Badenoch Group lithology. The titanites dated within the Garnet amphibolite are from a titanite population within the garnet cores and must date or predate the onset of garnet growth. These garnets subsequently developed large strain shadows indicating a reactivation of the GSZ after the garnet growth. Sample RG1710s titanite population contains rare rutile cores, biotite quartz intergrowth textures and, cordierite pseudomorphs indicating a higher grade mineralogy predating the titanites. This mineralogy may be related to eclogite deformation within the Badenoch Group which predates migmitization of the Dava Sub-Group.

Citation

Evason, L. A. Reinvestigating the relationships between the Badenoch Group, Dalradian Supergroup and the Grampian Shear Zone. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4223712

• Thesis Type: Thesis
• Deposit Date: Dec 1, 2021
• Publicly Available Date: Feb 24, 2023
• Keywords: Geology
• Public URL: https://hull-repository.worktribe.com/output/4223712
• Additional Information: Department of Geography, Geology and Environment, The University of Hull
• Award Date: May 1, 2021