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Contributions to the geology of Bowen Island Leitch, Henry Cedric Browning

Abstract

Bowen Island is situated within six and one-half miles of the University of British Columbia and is accessible at all seasons. The island contains a great variety of rocks and offers an excellent opportunity for the student geologist to study batholithic and minor intrusives, acidic to basic extrusives, pyroclastics and sediments. The writer studied the rocks and is submitting, for a Master's degree in Geological Engineering, this paper encompassing the results of his study. Roughly two-thirds of the island were visited in reconnaissance survey. Mapping was done by means of pacing, compass and barometer. A compilation map showing the writer's observations and those of earlier observers is presented. A small area, roughly half a mile square, was studied in detail and is the main basis of the paper. The area studied in detail was found to be composed of volcanics, sediments, quartz-diorite and minor intrusives. The earliest rocks in the detailed area are a series of volcanics with some interbedded sediments. The volcanics and interbedded sediments are highly metamorphosed and intruded by basic porphyry dykes which are in turn metamorphosed to a lesser degree. All the above are cut by quartz-diorite and minor acid intrusions. This places the basic porphyry dykes as later than the volcanics and earlier than the quartz-diorite and related rocks. Basic dykes of trachytic texture represent the closing period of intrusion. Pleistocene and post-pleistocene sediments lie unconformably on the earlier rocks. There are three types of metamorphism present: a) dynamic metamorphism; b) thermal metamorphism; c) contact metamorphism. In addition to these, paulopost juvenile action and propylitization have caused considerable alteration of the volcanics and related dykes. The age of the batholith is accepted provisionally as Upper Jurassic. Material which is believed to be from fossilized organisms but which has not yet proved identifiable, is found in limey inclusions in the volcanics of Wharf Point. The inclusions may indicate an earlier limestone formation or mud formation contemporaneous with the flow rocks. Structures in the pre-batholith volcanics are of questionable assistance in determining top from bottom of a formation.

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