Lithospheric structure of the Yukon, northern Canadian Cordillera, obtained from magnetotelluric data

Abstract

[1] Two goals of Lithoprobe's 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 Canada's 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 42 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, as a result of the complex structural evolution of the lithosphere.

Granitic and magmatic bodies in the deep crust of the Son Narmada Region, Central India: constraints from seismic, gravity and magnetotelluric methods

“…The output of the sensitivity values is the sum of the squares of each column and represent the sum over all the data (stations and frequencies) (Rodi and Mackie, 2001). In this study, the structures with sensitivity matrix values >0.0001 were con- sidered to be resolved features, which is in agreement with other recent works, such as those by Brasse et al (2002) and Ledo et al (2004). Most of the Chinchpada-Godhra profile shows (Fig.…”

Geoelectric structure of the Proterozoic Wopmay Orogen and adjacent terranes, Northwest Territories, Canada

“…Deformation and metamorphism of ocean lithosphere containing a fluid phase can disperse carbon (Mareschal et al 1992), and enhanced conductivity is observed in continental crust above presently actively subducting plates such as above the Juan de Fuca plate in Oregon, Washington, and southern British Columbia (Wannamaker et al 1989;Kurtz et al 1990; see also Jones 1993). In SNORCLE corridors 2 and 3 in the northern Cordillera (Yukon and northern British Columbia), a conductive anomaly is observed in a region in which subduction ceased at 40 Ma and is, therefore, attributed to a mineralogical constituent created by the subduction process rather than remnant fluid or thermal sources (Wennberg et al 2002;Ledo et al 2003). It is of note that the deformation associated with the Fort Simpson -Hottah collision involved significant fluid movement and subsequent melting of continental crust as indicated by the presence of calc-alkaline magmatism in the Fort Simpson magmatic arc.…”

Contrasting seismic characteristics of three major faults in northwestern Canada

“…The moderate velocities to the east appear to correlate with the Middle and Late Cretaceous(?) Deadman Creek batholith (Gordey et al 1998) as do high conductivities (Ledo et al 2004). The thickest near-surface section of low-velocity (<4.3 km/s) rocks occurs between the fault traces and beneath the Teslin River valley.…”