Seismic reflection profiles across deep continental crust exposed in the Kapuskasing uplift structure

Abstract

SEISMIC imaging of Precambrian cratons holds the promise of deep structural mapping and interpretation of fundamental crustal construction processes. Deep structures may be identified by tracing reflections to the surface¹, particularly in exposed crustal cross-sections² elevated along deeply penetrating faults, but many such cross-sections have structural orientations too steep for successful reflection imaging (like the Ivrea zone³) or occur in plate-boundary settings not representative of continental interiors. By contrast, the Archaean greenstone terrain exposed in the Kapus-kasing uplift of Canada^{4, 5} has gently dipping structures, and an intracratonic setting within the Superior Province, thus providing an opportunity to examine the third dimension of continental crust down to 25–30 km palaeodepth⁶. Here we present new seismic reflection data which, although generally supportive of structural models based on surface geology⁴, gravity modeling⁵ and seismic-refraction studies^7,8, also indicate that the Kapuskasing structure is a relatively thin thrust sheet containing seismically reflective sequences of high-grade rock which may be analogues of seismi-cally reflective in situ lower crust.