Abstract:
The North American Cordillera is composed of amalgamated allochthanous terranes that originated far southwest of their present-day location in the Panthalassic (paleo-Pacific) and Tethys oceans. Despite over thirty years of debate, the distance and mechanism of terrane transport continues to elude the geologic community. This is partially due to the fact that traditional geology and paleomagnetic studies yield contradictory results. Three main models have been proposed to reconcile the traditional geology and paleomagnetic data: 1) the Baja-British Columbia hypothesis, 2) the moderate tilt hypothesis, and 3) the westward subduction hypothesis. This paper presents case studies of the Triassic Nicola Group and the Early Cretaceous Spences Bridge Group – both exposed today in the Princeton, British Columbia region of Canada. Demagnetization results along with field tests indicate that the Nicola Group was remagnetized within the last 200 Ma and thus cannot be interpreted within the context of the terrane accretion debate. The Spences Bridge group’s characteristic remanent magnetization (ChRM) suggests either a pre-tilting or syn-tilting affiliation. If the ChRM is pre-tilting, it suggests about 3,400 km of transport northwards, whereas, if the ChRM is interpreted as syn-tilting, it indicates about 1,900 km of northward transport.
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