Pattison, David Robert MaitlanForshaw, Jacob Benedict2021-12-202021-12-202021-12Forshaw, J. B. (2021). Bulk compositional control on the metamorphism of pelitic rocks with an emphasis on the Whetstone Lake area, Southeastern Ontario (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.http://hdl.handle.net/1880/114190Metapelites (metamorphosed shales and mudstones) are an important rock type for interpreting metamorphism. This thesis examines the influence of bulk rock composition on the metamorphism of pelites using a two-pronged approach: (i) analysis of large datasets compiled from the literature and (ii) detailed study of an exceptional metamorphic sequence, the Whetstone Lake area in southeastern Ontario. A database of 3225 published whole rock geochemical analyses from the literature was collated, an order of magnitude greater than any previous. Whilst metapelites worldwide appear geochemically similar, there are many metapelites whose composition lies outside the main cluster. Analysis reveals a decrease in volatile content with increasing metamorphic grade, whilst the proportion of the major elements remains relatively constant. The average metapelite from this database is (wt%): SiO2 = 62.24, TiO2 = 0.94, Al2O3 = 19.88, FeOtotal = 7.32, MnO = 0.13, MgO = 2.68, CaO = 0.92, Na2O = 1.57, K2O = 4.19, and P2O5 = 0.15; the average (± 1σ) XMg = MgO/(MgO+FeOtotal) in moles = 0.40 ± 0.09, and the average XFe3+ = Fe3+/(Fe2+ + Fe3+) in moles is 0.27 ± 0.17. A database of 785 published XFe3+ analyses in metapelitic minerals was collated. Average (± 1σ) XFe3+ values in biotite, white mica, chlorite, and staurolite are 0.11 ± 0.08, 0.55 ± 0.18, 0.08 ± 0.07, and 0.07 ± 0.06, respectively. Whilst there is little variation in XFe3+ with pressure and temperature, there is an increase in XFe3+ in both white mica and biotite from ilmenite- to magnetite- to hematite-bearing samples. Metapelites at Whetstone Lake showcase a diversity of mineral assemblages over a small range of grade, a result of wide differences in bulk composition. Whole rock XMg and XFe3+ exert the greatest control on mineral assemblages, whilst MnO, K2O, and Al2O3 have a secondary influence. The observed mineral assemblages, modal proportions, and mineral compositions from both the XFe3+ database and Whetstone Lake were compared with the predictions of thermodynamic modelling. There is acceptable agreement between predicted and observed mineral assemblages and modes, but consistent discrepancies are found for mineral compositions. These include the overestimation of XMg in garnet, staurolite, and cordierite, overestimation of Ti in staurolite and biotite, underestimation of Si in biotite, and overestimation of Al and underestimation of Fe3+, Fe2+, and Mg in muscovite.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.MetapelitePhase equilibrium modellingFerrous/ferricFe2+/Fe3+MetamorphismMineral assemblageWhole rock geochemistryGeochemistryGeologyMineralogydoctoral thesis10.11575/PRISM/39432