An 1800 km cross section of the lithosphere through the northwestern North American plate: lessons from 4.0 billion years of Earth's history

Abstract

The Lithoprobe Slave – Northern Cordillera Lithospheric Evolution (SNORCLE) study across northwestern North America, in combination with related crustal studies, has been synthesized into an 1800 km long cross section of the lithosphere that is constrained by high-resolution geophysical data (seismic reflection, refraction, electromagnetic, potential fields) and detailed bedrock geology. The cross section offers one of the longest "continuous" profiles of the continental lithosphere anywhere in the world that is constrained by combined geophysical measurements and electromagnetic properties and exposed bedrock geological relationships. The primary conclusion of the study is that, during all major orogenic episodes recorded from Archean to present in that part of Earth's lithosphere, the crust, and perhaps much of the mantle, was reorganized and redistributed rather than being differentiated from the mantle at the time of orogenesis. The observed subsurface geometries of relict subduction zones, accretion boundaries, and magmatic arcs all lead to the inference that the crust includes a dominant proportion of reworked material. A similar conclusion appears applicable for the origin of subcrustal lithosphere in the region, i.e., that much of the lithosphere, whether Archean in the Slave Province or Proterozoic in the Cordillera, is old and thus that the amount of "new" lithosphere added to the plate during orogenesis is surprisingly small. A corollary is that many accreted rocks at surface that record orogenic complexity are detached from their originally underlying lithosphere and were emplaced upon unrelated crust and mantle during deformation.

Initial results from wide-angle seismic refraction lines in the southern Cape

“…The average velocity at a depth of 20 km is approximately 6.5 km/s. Other studies of northwestern Canada (e.g., Fernandez-Viejo and Clowes, 2003;Cook and Erdmer, 2005) produce similar results, and these patterns are very similar to the ones obtained by us for southern Africa.…”

CrustalVSstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

“…Our images of crustal velocity (Figure 11) are different than the mantle images ( Figure 15) in that they do not show a strong contrast across the deformation front that can be interpreted in terms of temperature. To gain a better understanding of the mechanisms that control crustal velocities in this region, we analyze our 3-D model with earlier results from the Lithoprobe program, specifically the Slave-Northern Cordillera Lithosphere Evolution (SNORCLE) project [e.g., Cook and Erdmer, 2005]. The SNORCLE transects consist of seismic reflection and refraction data acquired along four lines (Figure 1b).…”

“…We utilize broadband stations from the Canadian Northwest Experiment (CANOE), the Canadian National Seismograph Network (CNSN), and the Portable Observatories of Lithospheric Analysis and Research Investigating Seismicity (POLARIS). We compare our results to detailed images of the subsurface along active source reflection and refraction transects across the region, which were gathered as part of the Lithoprobe Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) project [Cook and Erdmer, 2005]. The surface waves measured with ambient noise cross correlation have a larger wavelength and do not resolve such fine details, but they allow coverage over a much larger area, thereby complementing the scale of information provided by the reflection and refraction lines.…”

“…[55] A Proterozoic metasedimentary wedge is only one possible explanation for the observed reflectivity; Cook and Erdmer [2005] and Cook et al [2004] discuss alternatives, including fabrics resulting from ductile flow and layered igneous intrusions. Indeed, the images of P wave speed obtained from refraction data along Lines 2a and 3, which are crucial to the interpretation as both lines show a tapering wedge of subhorizontal reflectivity in the middle and lower Figure 16.…”

Chronostratigraphy of the Hottah terrane and Great Bear magmatic zone of Wopmay Orogen, Canada, and exploration of a terrane translation model

“…1, 2;Fraser et al 1972;Badham 1973;Hoffman 1973Hoffman , 1980Hoffman , 1984Hoffman , 1988aHoffman and McGlynn 1977;Hoffman et al 1976;King 1986, 1987;Villeneuve et al 1991Villeneuve et al , 1993Aspler et al 2003;Cook and Erdmer 2005;Jackson 2008;Hildebrand et al 1987aHildebrand et al , 1987bHildebrand et al , 2010aHildebrand et al , 2010bJackson and Ootes 2012;Jackson et al 2013;Ootes et al 2013). The Coronation margin includes Archean crust, the ca.…”