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UBC Theses and Dissertations

The Eastgate-Whipsaw metamorphic belt as Paleozoic underpinnings to the Nicola Group Oliver, Shelley Louise


The enigmatic Eastgate-Whipsaw metamorphic belt (EWm belt) is located on the western margin of the Late Triassic to Early Jurassic Nicola Group’s southernmost exposure in the Princeton area of south-central B.C. (NTS 092H/SE). Previously affiliated to the Nicola Group, new Early Permian ages of 281.3 ± 3.3 Ma and 282.7 ± 3.7 Ma show the EWm belt to be significantly older and is likely a southern manifestation of the Late Paleozoic Harper Ranch Group. This suggests a previously unrecognized potential in the Harper Ranch for hosting VHMS-style mineralization. The belt comprises metamorphically deformed, upper greenschist to lower amphibolite facies volcanic and volcanic-derived sedimentary rocks as well as pre- to syn-deformational intrusive phases. These rock types are divided into: 1) mafic volcanic amphibole-rich schists defining the western margin of the belt; 2) a thick, south-central package of quartzofeldspathic volcanic-derived sedimentary schists that transition northward into 3) a series of intercalated volcanic-derived sedimentary schists; 4) mafic volcanic amphibole (chlorite)-epidote schists on the south-east margin of the EWm belt; 5) a north-eastern package of felsic volcanic and volcanically-derived sedimentary schists that contain relict quartz and plagioclase phenocrysts, and 6) consanguinous meta-gabbro and foliated plagioclase porphyry intrusions of unknown ages. The EWm belt originated within an intra-arc or back-arc marine setting, as two geochemically distinct volcanic types. The eastern type 1 volcanic rocks comprise calkalkaline and tholeiitic compositions from LREE-enriched island arc basalts. The western type 2 volcanic rocks comprise a suite of back (or intra)-arc basin basalts. A complex set of foliations, the result of strong metamorphic deformation, is preserved within minor rock types of the EWm belt. The foliation set includes: 1) a dominant N-S, steeply westward dipping S₂ foliation that is predominantly continuous but also develops into differentiated crenulation cleavages, 2) a shallow east-dipping S₁ that is crenulated and progressively dextrally rotated by S₂-associated deformation, 3) a poorly-developed S₃ fabric that shallows the dominant S₂ foliation on the eastern side of the EWm belt. Equal metamorphic temperatures, equivalent to the greenschist to amphibolite facies transition, were established across the width of the EWm belt.

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