The Influence of Lithospheric Mantle Scars and Rheology on Intraplate Deformation and Orogenesis: Insights From Tectonic Analog Models

Abstract

Structural heterogeneities in the deep lithosphere have been identified as an important factor in crustal tectonics, particularly where inherited deep zones of weakness may initiate orogenesis in continent interiors. Aside from structural heterogeneity, the rheological strength of the lithosphere may also have a primary role affecting the kinematics of deformation in the lithosphere. To investigate the interplay of rheology and pre‐existing structures, we designed a set of physical scaled analogue experiments for a convergent setting that tests: a) the presence and absence of a pre‐existing weak zone in the lithospheric mantle; and b) the effects of the rheological strength of the lithospheric mantle. Tectonic evolution of the model is recorded to acquire a time‐series dataset of the velocity field and subsequently strain in the model. Results show that a weak zone in the lithospheric mantle allows deformation to be accommodated by displacement along this zone and into the overlying lower and upper crust, regardless of lithosphere strength. In contrast, a model absent of a weak zone accommodates deformation by folding and thickening of the viscous layers. The viscous lithosphere in models with a strong lithospheric mantle tends to buckle creating a sequence of brittle faulting in the upper crust. Specifically, the rheology of the lithosphere dictates the distribution of strain. Our results are considered in the context of the formation of the Eurekan fold and thrust belts in an intraplate setting on Ellesmere Island, where deformation may be related to the influence of deep lithosphere structure(s) and deep lithosphere strength.