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UBC Theses and Dissertations

Geology and metamorphism of the Mitchell Mountains ultramafite, Fort St. James map area, British Columbia Elliot, Andrew James Mather

Abstract

The area mapped includes two ultramafites of the alpine type, emplaced in, and with inclusions of, rocks of the Cache Creek Group. Northwest lies the Mitchell Patholith, a Late Jurassic (?) intrusion of diorite to granite. The argillite, chert, greenstone, and limestone of the Cache Creek Group are strongly to isoclinally folded about north-northeasterly trending axes. They have mineral assemblages characteristic of the middle to upper green-schist facies. The ultramafic rocks are fractured and sheared in a north-northeasterly direction, and may be folded. The overall shape of the Mitchell Mountains Ultramafite is not known. The Mitchell Mountains Ultramafite has three metamorphic zones, parallel to the edge of the Mitchell Patholith. They consist of serpentinite, talc-olivine rock, and olivine-enstatite-anthophyllite rock. The Goat Mountain Ultramafite consists mostly of serpentinate, The observed mineral assemblages may be explained in terms of the system CaO-MgO-SiO₂-H₂O-CO₂. At an assumed pressure of 2000 bars, the temperature during metamorphism ranged from 380°C at the eastern edge of the Mitchell Mountains Ultramafite, to almost 700° at the western edge. This contact metamorphism was caused by the Mitchell Patholith.

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