Fault and fracture systems of the Northern Thor-Odin dome of the Monashee Complex, Southeastern Canadian Cordillera, British Columbia

Abstract

Fracture and fault systems of the Northern Thor-Odin dome of the Monashee Core Complex in the Omineca belt of the Southeastern Canadian Cordillera are studied. The objective of study is to classify the D5 fault systems and determine their relationships to each other, if any. Also the late lamprophyre and pegmatite dyke orientations are considered. The field area is divided into three zones based on geological domains. Zone 1 is in cover rock in the Northwest of the field area. Zone 2 is the largest of the zones and consists of rock near the basement-cover contact, which is exposed by upright F4 folding across the zone. Zone 3 is almost entirely in deeper basement, to the East of the field area. The orientation analysis reveals three prominent fracture groups. Group A is the most prominent and dips shallowly to the East; these fractures appear to be associated with normal faults genetically related to the Columbia River fault and similar extensional faults that caused the exhumation of the Monashee Complex in the early Tertiary. Group B fractures correspond to a prominent set of East-West trending lineaments that pervade the complex. These fractures have little evidence of displacement, but may have minor dextral strike slip movement. Group C fractures dip steeply to the West, and often show late normal displacement, possibly related to late denudation of the complex. A small number of wide (1-10 metre) North-South striking fault zones with potential strike slip displacement are also found, but their relation to the other systems is unclear. Pegmatites are early Tertiary syn- to post- Group A faulting, and lamprophyres are all Eocene, and are post- pegmatites and Group A faults. Neither pegmatites nor lamprophyres exploit the Group B or Group C fracture sets, implying that these faults may not have been active until after dyke intrusion.