Investigating the metamorphic evolution of the Bancroft Terrane (Grenville Province, Canada) using advanced equilibrium assemblage diagrams

• Applicant: Dr. Erik Duesterhoeft
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 281306778

The 1 Ma old Canadian Grenville Province is a Mesoproterozoic orogen, which developed during the formation of the supercontinent Rodinia. The Central Metasedimentary Belt is a part of the Grenville Province and its evolution is highly debated in the literature. Two hypothesis exits: a) it is a relict back-arc-basin or b) it is a composite arc belt, accreted to the southern margin of Proterozoic Laurentia. Since the early 70ties, many petrological, geochemical and geophysical studies investigate the complex tectonic history of the Central Metasedimentary Belt. However, some parts of the Central Metasedimentary Belt, like the Bancroft Terrane, are understudied in terms of P-T conditions. The reason for the lack of data is that previous studies only used conventional thermobarometric methods (e.g., using garnet-pyroxene thermometers and garnet-clinopyroxene-plagioclase-quartz barometers). This approach highly depends on the existing mineral assemblage of a sample. Because the Bancroft Terrane is mainly composed of non-garnet-bearing rocks, it is quite obvious that most geothermobarometers cannot be applied. This is the main reason for the lack of data within the Bancroft Terrane. The principal propose of this project is to unravel the multi-stage metamorphic history of the Bancroft Terrane, applying advanced equilibrium assemblage diagrams (also called pseudosections). Preliminary work has shown, that applying equilibrium assemblage diagrams can give essential insights into metamorphic history of the region. Thus, it was possible to model the P-T conditions of a presumable early metamorphic event, which differs from the proposed P-T conditions of the region. In order to decipher this petrological record of an earlier metamorphic event, affecting the Bancroft Terrane, there is a crucial need for systematic sampling during fieldwork combined with advanced thermodynamic modeling. The samples taken will be prepared for thermodynamic calculations, yielding the P-T conditions of the samples. The gained data will be visualized in a metamorphic map of the Bancroft Terrane. Consequently, the new map and data will help to understand the complex tectonic evolution of the Central Metasedimentary Belt and the whole Grenville Province.

• DFG Programme: Research Grants
• International Connection: Canada
• Cooperation Partner: Professor Dr. Fred Gaidies