Open Collections

The Eastgate-Whipsaw metamorphic belt as Paleozoic underpinnings to the Nicola Group

University of British Columbia

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.

Text

2011-05-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/34982

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/