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Master of Science (MS)
Talbot, James L.
Brown, Edwin H.
Burmester, Russell F.
Metamorphosed oceanic and arc-related lithologies of the Slollicum, Cogburn and Settler packages crop out to the east of Harrison Lake, B.C., within the southern Coast Plutonic Complex and represent the northern extension of the Cascade orogenic belt. The Cretaceous Spuzzum plutons intruded the packages in late syn- to post-metamorphic time, and several early Tertiary stocks intruded all units after deformation.
The Slollicum package is dominated by graphitic to politic phyllite, and felsic to mafic arc volcanics intercalated with marble, conglomerate and quartzite. The sediments dominate western exposures, and eastern exposures are mainly volcanics. U-Pb analysis of zircon in a volcanic interbed gives a concordant 146 Ma depositional age for the Slollicum package. The Cogburn package is composed of structurally juxtaposed blocks of graphitic phyllite, mafic metavolcanics, banded chert and marble. Serpentinite is common. The Settler package is dominated by politic schist interlayered with quartzite, amphibolite and conglomerate.
Foliations generally strike northwest, dip northeast and are accompanied by down-dip stretching lineations. Kinematic indicators show orogen-normal reverse-slip. Cleavage in the Slollicum package exhibits a strong influence of pressure solution. Cogburn and Settler packages each show two foliations, one preserved in poikiloblastic minerals and a dominant crenulation cleavage. The Harrison Lake shear zone is a late stage, right-lateral strike-slip shear zone that locally prints across the earlier fabrics after Spuzzum plutonism and prior to the intrusion of the early Tertiary stocks.
Metamorphic grade increases eastward from the chlorite and biotite zones of the greenschist facies in the Slollicum package to the garnet zone of the greenschist facies and the oligoclase/hornblende zone of the amphibolite facies in the Cogburn package through the staurolite zone to the sillimanite zone of the amphibolite facies in the Settler package.
Geothermobarometry indicates pressures of 3 to 4.5 kb in the biotite zone and 5.5 kb in the sillimanite zone. Temperatures in the sillimanite zone range up to approximately 750 ° C. A poly-metamorphic history is indicated by pseudomorphs of kyanite after andalusite in the Settler package.
Lineation-parallel slip on foliation planes, evidenced by augenshaped and boudinaged metamorphic minerals Indicates syn- to postmetamorphic deformation. Fabric relations indicate that this deformation primarily occurred prior to the intrusion of the Spuzzum plutons.
Early low-pressure metamorphism is interpreted to have been followed by higher grade, amphibolite facies metamorphism prior to and during deformation followed by the intrusion of the Spuzzum plutons coeval with peak metamorphism.
Spuzzum plutons, Southern Coast Plutonic Complex, Cascade orogenic belt
Western Washington University
Harrison Lake Region (B.C.)
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Bennett, Jeffrey D. (Jeffrey Dale), "Timing and Conditions of Deformation and Metamorphism of the Structural Packages East of Harrison Lake, B.C." (1989). WWU Graduate School Collection. 649.