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UBC Theses and Dissertations

A petrological study of intrusive rocks along the Fraser Canyon near Hell's Gate, British Columbia Morris, Peter Gerald


A study was made of rocks outcropping along a road section in the vicinity of Hell's Gate, some 12 miles south of Boston Bar, British Columbia. Biotite schists belonging to the Hozameen group (Carboniferous or Permian in age), were the oldest rocks found. The Custer granodiorite, a heterogeneous igneous body having the average composition of a hornblende granodiorite, intrudes the biotite schists. The age of the Caster granodiorite is believed to be Upper Jurassic. Large numbers of pegmatite and aplite dykes intrude the Custer granodiorite. Two types of pegmatites, magmatic and metasomatic were distinguished. The Hell's date granodiorite, a uniform igneous body of trondjhemitic composition, intrudes the Custer granodiorite and also post dates the pegmatite and aplite dykes. The age of the Hell's Qate granodiorite is believed to be Upper Jurassic or possibly Lower Cretaceous. Sight plagioclase porphyry dykes, classified into one of three groups, (staple, multiple, and protoclastic types) were found. The plagioclase porphyry dykes are believed to be genetically related to the Hell's Gate granodiorite. Six dykes having an andesitic composition were found; the dykes have been classified into light colored and dark colored andesites. The rocks along the road section have been intensively fractured. Faulting has taken place close to the southern contact between the two granodiorites. The narrow N-S trending outcrop of Custer granodiorite in the area could possibly have been produced by faulting, and its shape suggests a horst structure, A study, using a method suggested by Gorai, was made of the plagioclase twins occurring in the Hell's Gate rocks. The conclusions drawn from this work largely confirms the conclusions drawn from the field evidence.

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