Publication 91
Lithospheric structure of the Yukon, Northern Canadian Cordillera,
obtained from magnetotelluric data
Juanjo Ledo, Alan G. Jones, Ian J. Ferguson and Lisa Wolynec
Abstract
Two goals of LithoprobeÆs geoscientific studies in the Phanerozoic accretionary
cordillera of western North America were to define the subsurface geometries of the
terranes and to infer the physical conditions of the crust. These questions were
addressed in CanadaÆs southern cordillera a decade ago, and have more recently been
addressed in the northern cordillera, of which one component of the new studies is
magnetotelluric (MT) profiling from ancestral North American rocks to the coast.
We present a resistivity cross-section, and its interpretation, of the northern
cordillera derived from modeling data from forty-two MT sites along a 470-km-long
NE-SW profile. Beneath the Coast Belt (southwestern end of the profile) a deep crustal
low resistivity layer dips inland; we interpret the crustal part of this conductor as
being due to metasedimentary rocks emplaced and metamorphosed during Paleocene Kula
plate subduction. A strong lateral transition in lithospheric mantle resistivity exists
below the Intermontane Belt that is spatially coincident with changes in chemical and
isotopic characteristics of Tertiary to recent alkaline lavas, suggesting that
isotopically-enriched lithosphere related to the Coast Belt basalts extends partly
beneath the Intermontane Belt. The unusually high lower crustal resistivity in the
Intermontane and Omineca belts, similar in value to the resistivity found in the
unextended part of central British Columbia, excludes the presence of fluids or
conducting metasediments. Finally, our resistivity model displays strong lateral
variation of the middle and lower crust between different terranes within the same
belt which contrasts with a Westward Tapering Wedge (WTW) containing a uniform pattern
of seismic reflectivity. We take this resistivity variation as indicative of the
complex structural evolution of the lithosphere due to superimposed episodes of
accretion, subduction, sea-floor spreading and transform faulting.
Source
Journal of Geophysical Research, 109, B04410-1 - B04410-15, doi: 10.1029/2003JB002516, 2004.
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Alan G Jones / 10 June 2004 /
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