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TitleWeakly magnetic crust in the Canadian Cordillera
AuthorPilkington, M; Snyder, D B; Hemant, K
SourceEarth and Planetary Science Letters vol. 248, issue 1-2, 2006 p. 476-485,
Alt SeriesEarth Sciences Sector, Contribution Series 2005010
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia; Alberta; Northwest Territories; Yukon
Lat/Long WENS-140.0000 -110.0000 70.0000 50.0000
Subjectsgeneral geology; geophysics; seismic data; magnetic surveys; magnetic anomalies; volcanic rocks; metamorphic rocks; seismic refraction surveys; seismic reflection surveys; non-magnetic crust
Illustrationslocation maps; magnetic anomaly maps; magnetic maps; diagrams; graphs
AbstractCurrent models of continental crust favor an increase in magnetization with depth. Here we report a counter example from the
Canadian Cordillera where almost a full thickness of non-magnetic continental crust is suggested by joint interpretation of magnetic
and seismic data. The magnetic field over the Cordillera is characterized by complex, short-wavelength (<100 km) anomalies
associated with intrusive, metamorphic and volcanic rocks that occur at shallow depths (<5 km) within accreted terranes. The longwavelength
(>100 km) portion of the Cordilleran field is subdued and mainly featureless, and suggests a lack of magnetic sources
at greater depths. Seismic reflection and refraction data from three major transects in the Yukon and British Columbia, Canada
support this interpretation and indicate that sedimentary-like formations make up the majority of the crust. The dominance of
shallow, upper crustal magnetization in the Canadian Cordillera contrasts with the generally-held view that the lower continental
crust is the primary source for long-wavelength magnetic anomalies. Sources for these anomalies are often assumed to be located in
the lower crust when surface magnetizations are insufficient to produce such anomalies or no correlation exists between the
magnetic field and the mapped surface geology. The Canadian Cordillera appears to be an example of a non-magnetic lower crust
overlain by a more magnetic upper crust that is, however, not magnetized strongly enough to produce significant long-wavelength
magnetic anomalies.

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