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Title: The isotope geochemistry and petrology of Dalradian metacarbonate rocks
Author: Thomas, Christopher Walter
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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This thesis presents a detailed petrographic and geochemical study of several Dalradian metacarbonate and calc-silicate rock units from Scotland and Northern Ireland, which were metamorphosed at greenschist to middle amphibolite facies conditions during the Ordovician Grampian Orogeny. The study aimed: a) to determine the extent to which metamorphic fluid-rock interaction has modified original sedimentary/diagenetic chemical signatures, b) to relate original signatures to the pre-metamorphic history of the carbonate rocks, and c) to elucidate and quantify the nature and mechanisms of metamorphic fluid-rock interaction. Conventional bulk carbonate d18O, d13C and 87Sr/86Sr ratios were determined at a range of sample scales, including whole-rock samples from outcrops, small-sale samples from within hand specimens, and mini-core samples from a drilled profile. Oxygen isotope and trace element compositions of two metalimestones were studied on grain and subgrain sales by Secondary Ion Mass Spectrometry (SIMS), aided by cathodoluminescence imaging. This work elucidated fluid infiltration pathways and mechanisms, the extent of altered domains, timescales and mechanisms of isotope exchange, and the true scale of isotope equilibration. The work also aided interpretation of the bulk carbonate data. Petrographical and microchemical analysis of calc-silicate rocks from Glen Rinnes, NE Grampian Highlands, indicate varied and complex buffering of the fluid phase. The lack of diopside, the presence of plagioclase + calcite and zoisite breakdown textures indicate local buffering of the fluid phase to more XCO2-rich compositions along unvariant equilibria and to invariant points. This implies local buffering of fluid composition by the rock, mitigating against infiltration of very water-rich fluids. Stable and strontium isotope data show that pervasive metamorphic fluid infiltration of the limestones did not commonly occur and primary/near-primary d13C and 87Sr/86Sr ratios have been widely preserved. 87Sr/86Sr ratios of metadolostones are markedly different to those in metalimestones and probably relate to dolomitisation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available