Journal
GEOLOGY
Volume 34, Issue 9, Pages 733-736Publisher
GEOLOGICAL SOC AMERICA, INC
DOI: 10.1130/G22793.1
Keywords
tectonics; crustal structure; superstructure; infrastructure; seismic reflectivity; Superior Province
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The historical superstructure-infrastructure concept (S-I) expressed contrasts in structural style and metamorphic grade between shallow and deep orogenic levels. Two-dimensional thermal-mechanical models provide a quantitative explanation in terms of progressive crustal shortening and thickening (phase 1), thermal relaxation and rheological weakening (phase 2), and ductile flow at depth (phase 3). Results predict an upper-crustal superstructure, dominated by early steep structures, separated across a subhorizontal high-strain zone from a ductile infrastructure with late gently dipping structures; this is consistent with observations from the western Superior Province. These models can account for contrasts in structural style, metamorphic grade, seismic reflectivity, and age between upper- and lower-crustal levels. In contrast to conventional thrust-tectonics models, the revived S-I model shows how young structures can form beneath older ones during progressive convergence, thereby encouraging reassessment of standard seismic reflection interpretations.
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