The big picture: A lithospheric cross section of the North American continent
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A lithospheric cross section constructed within a 6000-km-long corridor across southern Canada and its margins at 45–55°N illuminates the assembly of the North American continent at an unprecedented scale. Based on coordinated, multidisciplinary research, the profile emphasizes lithospheric-scale relationships between orogens—plate collisions and accretions have sequentially stacked orogen upon orogen such that the older crust forms basement to the next younger. This large-scale perspective highlights the similarities among crustal structures produced by orogenic processes despite the broad range of age from the Mesoarchean to the present. Heterogeneities in the lithospheric mantle suggest that, in certain situations, relict subducted or delaminated lithosphere can remain intact beneath, and eventually within, cratonic lithospheric mantle. In contrast, the dominantly subhorizontal Moho appears to be re-equilibrated through mechanical and/or thermal processes; few crustal roots beneath orogens are preserved.
Manuscript received 31 Mar. 2010; accepted 12 Dec. 2010