Possible role of midcrustal igneous sheet intrusions in cratonic arch formation

Abstract

Factors controlling widespread cratonic arch formation across western North America from the Early Paleozoic to the Middle Mesozoic remain poorly understood. While a number of causes, such as mantle hot spots, lithospheric contraction, mantle flow, and lithospheric flexure due to surface loading, have been suggested to explain the localized uplift of basement blocks on otherwise tectonically quiescent margins, a variety of mechanisms may be at work. Here, we test the hypothesis that seismically detected packages of discrete midcrustal igneous sheet intrusions impart rheological contrasts within the crust, which act as seeds for cratonic arch formation in the presence of weak intraplate compression, using finite element modeling of intraplate deformation. We find that the seismically resolved sills can generate significant surface uplift in the presence of modest strain rates over reasonable orogenic timescales. Cratonic arch formation would be enhanced in the presence of additional thin, seismically unresolvable sills. While midcrustal sheet intrusions may be just one of many factors influencing cratonic arch formation, their presence in northern Alberta, Canada, can help explain the asymmetric configuration of the well‐studied Peace River Arch.