Geochemistry of Seine River metaconglomerates from Mine Centre, Ontario: interpreting fluid flow and volume changes during deformation with implications for strain analysis

Detaya Johnson

Abstract


Interpretation of strain in ductile shear zones is made difficult by the presence of fluids; if volume loss due to fluid rock interactions occurred during deformation, that loss needs to be factored into strain estimates and can change the structural interpretation of the area. Even though fluid is such an important factor in deformation, it is difficult to study due to its transient nature, so geochemical analyses may be used to interpret fluid conditions during deformation. The Seine metaconglomerates were deposited, buried, deformed and metamorphosed in this dynamic tectonic environment. The Seine River Metaconglomerates have clasts with varied lithology from felsic to ultra-mafic volcanic clasts and granitoid clasts with a matrix comprised of sediment derived from intermediate-mafic volcanic rocks. As deformation occurred, the different competences of clasts had variable rheology that resulted in a range of strain magnitudes. Strain magnitude also varied across the region with, for example, low strain sites having strain magnitudes of ~0.6 and high strain sites having strain magnitudes of ~2.4 for mafic volcanic clasts. Geochemical analysis and evaluation for volume loss has not been performed on the samples collected from this region and was the focus of this study. Discrepancies in major elements from the high to low strained samples was analyzed using isocon plots. The primary significance of this project was to determine whether similar fluids migrated through the less deformed rocks as through the concentrated shear zones within the Seine metaconglomerates. This determination may lead towards a better understanding of shear zone hosted gold concentrations in the region. In addition, if it is determined that volume loss was associated with deformation, the strain ellipsoids determined by Czeck et al. (2009) will need to be revised and will change the current understanding of strain distribution in the area.

 


Keywords


Shear Zone, Geochemistry, Fluid-Rock Interaction

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