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Published 2009 | public
Book Section - Chapter

Perspectives on the architecture of continental crust from integrated field studies of exposed isobaric sections


Depth-dependent variations in the structure and composition of continental crust can be studied via integrated investigations of isobaric terranes. In this contribution, we summarize three isobaric terranes in Archean to Proterozoic crust. In western Canada, 35–45-km-deep lower crust is exposed over an area of more than 20,000 km^2. The Upper Granite Gorge of Grand Canyon, Arizona, provides a transect of 20–25-km-deep middle crust. The Proterozoic basement of central Arizona represents an isobaric exposure of 10–15-km-deep middle crust. Isobaric terranes yield a conceptual image of continental crust that can be compared to seismic images, xenolith data, and drill core data to clarify rheology, coupling/decoupling of crustal levels, and the interplay between deformation, metamorphism, and plutonism. General observations include: (1) The crust is heterogeneous at all levels and cannot be accurately modeled as a simple progression from quartz-rich to feldspar-rich lithologies or from felsic to mafic bulk compositions. (2) The crust is segmented into foliation domains that alternate between steeply dipping and shallowly dipping. (3) Magmatism is expressed differently at different depths due to different background temperatures and a general upward distillation from mafic to felsic composition, and may be the most important control on crustal architecture and rheology. The strength of continental crust (and its potential for low-viscosity flow) is not simply a function of temperature, depth, and compositional layering, but is controlled by the size and distribution of rheological domains. The rheological character of a particular layer can vary in space and time at any crustal level.

Additional Information

© 2009 Geological Society of America. Accepted 24 February 2009. The authors thank Scott Johnson, David Schneider, and Bob Miller (Guest Editor) for their careful and very helpful reviews of an earlier draft of this manuscript. This paper has benefited from discussions with a large number of people including: S.A. Bowring, M. Jercinovic, R. Flowers, J. Baldwin, C. Hetherington, N. Price, C. Kopf, D. Gibson, P. Goncalves, and many others. Work in the Athabasca granulite terrane has been supported by National Science Foundation (NSF) Grant EAR-0609935. Southwestern U.S. research has been supported by NSF EAR-9206045, 9508096, and 9305459. Electron Microprobe monazite geochronology technique development has been supported under EAR-0549639.

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August 20, 2023
January 13, 2024