Crustal Cross Sections from the Western North American Cordillera and Elsewhere: Implications for Tectonic and Petrologic Processes / Разрез коры западных североамериканских Кордильер и иных местах: значение для тектонических и петрологических процессов

The nature of petrologic and structural properties and processes that characterize the middle and lower continental crust is a long-standing problem in the earth sciences. During the past several decades signifi cant progress has been made on this fundamental problem by synthesizing deep-crustal seismic-refl ection imaging, laboratory-based seismic-velocity determinations, xenolith studies, and detailed geologic studies of exposed crustal cross sections. Geological, geochemical, and geophysical studies of crustal sections provide a crustal-scale context for a variety of important problems in the earth sciences. Crustal sections are widely used to evaluate crustal composition and petrogenesis, including lateral and vertical variations in rock types. Evidence from deep levels of crustal sections suggests seismic shear-wave anisotropy and seismic lamination result from widespread subhorizontal contacts, shear zones, and transposition fabrics, and in some sections from metamorphosed m- to km-thick, intraplated and/or underplated mafi c magmatic sheets and plutons. Crustal sections also facilitate the evaluation of crustal rheology in natural settings from regional to outcrop scale. Magmatism, metamorphism, partial melting, and relatively small lithological differences control rheology, localize strain, and lead to markedly heterogeneous deformation over a wide range of crustal levels. Finally, crustal sections provide unique views of the architecture and deformation patterns of fault zones in the deep crust. <...>