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Geological Cross-section of Southern British Columbia
Interpreted lithospheric cross section from the Pacific Ocean to the Rocky Mountains was derived from synthesis
of many geoscience studies. Old rocks (greater than 1800 Ma) of the North American craton to the east extend
below younger rocks as far west as the Fraser Canyon. In a series of collisions during the past 200Ma,
blocks of lithosphere 500 Ma old and younger collided with early North America, pushing up the sediments
deposited on the old shelf to form the Rocky Mountains. In so doing the blocks lost much of their lower
lithosphere (into the mantle below), with the upeer part remaining. Today young (less than 20 Ma) oceanic crust
of the Juan de Fuca plate is being pushed under North America at rates of about 50 mm/year as the
tectonic plates continue to collide. This subduction causes the many earthquakes in the region.
Open arrows in the mantle show material flow of the Juan de Fuca plate and of the continental asthenosphere
below the more rigid lithosphere above it. The open stars indicate major earthquake hypocenters.
Abbreviation details: AW - accreted wedge; BR - Bridge River terrane; CD - Cadwallader terrane;
CT - Crescent terrane; CWF - Coldwater fault; DF - deformation front; FF - Fraser fault; gr - granites;
GVB - Garibaldi volcanic belt; HA - Harrison terrane; Hi V, p - high velocity and density; Lo V - low velocity;
M - Moho; MD - Monashee decollement; MR - mantle reflector; MT - Methow terrane;
NA - North American cratonic basement; OVF - Okanagan Valley fault; PRT - Pacific Rim terrane;
QCF - Quilchena Creek fault; SH - Shuksan terrane; SLF - Slocan Lake fault.
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