Thermal and structural evolution of the Grenville Channel shear zone, Coast Plutonic Complex, British Columbia

Michael Robert Mansfield, University of Texas at El Paso


Understanding the genesis of transpressive structures is important to modern structural geology because of the ubiquitous occurrence of transpression along plate margins. A key question is how strain partitioning occurs in regions of transpression. We report on a sequence of supercrustal and plutonic rocks from the western Coast Plutonic Complex exposed along Grenville Channel. Grenville Channel is a major topographic lineament which coincides with a Cretaceous aged sinistral shear zone. This shear zone, called the Grenville Channel shear zone (GCSZ), separates panels of rocks intruded by the 109 Ma Capitan Cove pluton to the west from rocks intruded by the 90 Ma Ecstall pluton on the east. The GCSZ is subvertical and northwest striking and contains rocks with mylonitic fabrics. Lineations have moderate to shallow plunges in the shear zone. Folds adjacent to the GCSZ rotate in a counterclockwise sense into parallelism with the shear zone indicating a shear zone directed increasing strain gradient. Geothermobarmetric studies conducted on metamorphosed country and igneous samples indicate pressures variations for the eastern side of the shear from 8 kbars in the north to a low of 5.2 kbars in the middle before a return to near 8 kbars at the southern terminus of the channel. Rocks to the west of the shear zone record homogenous pressures between 6.4 and 7.3 kbars. We interpret the structural data as evidence for strain partitioning during transpression between areas adjacent to the shear zone which were dominated by horizontal shorting and the shear zone itself which was dominated by sinistral transcurrent displacement. This pattern of strain partitioning produced differential uplift and exhumation along the shear zone causing the observed pressure differences.

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Recommended Citation

Mansfield, Michael Robert, "Thermal and structural evolution of the Grenville Channel shear zone, Coast Plutonic Complex, British Columbia" (2004). ETD Collection for University of Texas, El Paso. AAI1423733.