The LITHOPROBE trans-continental lithospheric cross-sections: Imaging the internal structure of the North American continent

Three lithospheric cross-sections, with Earth curvature, provide a continental-scale synthesis of more than two decades of coordinated multidisciplinary research. The LITHOPROBE cross-sections show seismic reflection images, velocity models from refraction data and interpretations of these based on a broad range of geological, geochemical, geochronological and other geophysical data. The dataset derives from remnants of nearly every kind of tectonic regime and the geologic history of the entrained rocks spans the Present to the Mesoarchean. The unprecedented scale of the cross-sections illuminates the assembly of the North American continent. The 6000 km-long Trans-Canada corridor traverses the North American continent at 45-55°N. The profile crosses the Juan de Fuca ridge and active Cascadia subduction zone, the Cordilleran, Albertan, and Trans-Hudson orogens, the Superior Province, the Keweenawan rift, the Grenville and Appalachian orogens, and the Atlantic passive margin. The two northern cross-sections include a 2000 km-long corridor in northwestern Canada (54-63°N) crossing the Cordilleran, Wopmay and Slave orogens, and a 1600 km-long corridor in northeastern Canada (52-61°N) crossing the New Quebec and Torngat orogens, the Nain craton, and the Makkovik and Grenville orogens. Relationships between orogens are emphasized; plate collisions and accretions have sequentially stacked orogen upon orogen such that one forms basement to the next. Boundary relationships between adjacent terranes as well as structure within terranes are preserved and linked from outcrop to the upper-to-mid crust by correlating seismic reflections with structures and stratigraphy. The orogens exhibit subcretion (mechanical underplating) as is observed in subduction/accretion zones, mid-crustal tectonic wedging and crustal ramping up a full crustal-scale décollement from the Moho. First-order observations show that these stacked and wedged bivergent orogens are replicated across the continent with remarkable similarity in style despite the range of complexity and age of the orogens involved. Reflections extending from the crust into the uppermost mantle are observed in the majority of orogens, demonstrating that subducted or subcreted lithosphere can remain intact beneath and eventually within cratonic lithospheric mantle. The dynamic nature of the seismic Moho contrasts with the preservation of some crustal structures that extend into lithospheric mantle. Syn- or post-orogenic re-equilibration of the Moho is required; the Moho remains remarkably flat across the entire continent despite the great diversity of overlying topography and crustal properties. The seismic data also provide convincing evidence that horizontal plate collisional processes played important, if not dominant, roles in the Neoarchean (2.5-2.7 Ga) and perhaps earlier. The LITHOPROBE continental-scale lithospheric cross-sections provide a unique perspective on the assembly of the North American continent.