Towards a comprehensive boundary tectonism model for the late Paleozoic Ancestral Rocky Mountain orogeny

Abstract

The orientations of intra-cratonic uplifts are commonly used to posit modes of boundary tectonism on continental margins during the time of uplift generation. In North America, a quintessential example of this practice is the ongoing interpretation of the late Paleozoic Ancestral Rocky Mountain Orogeny (ARMO). Continental margins active during ARMO uplifts have been subsequently modified or destroyed, and direct evidence for the styles of coeval tectonism obscured by later deformation, especially within the western Cordillera. Thus, there is a sustained history of workers attempting to deduce the tectonic state of late Paleozoic Laurentian margins from the characteristics of recognized uplifts. Here, using a 3D Finite Element Method (FEM) we show that it is necessary to consider the complete picture of continental fringing tectonism to understand how the intracontinental stress field could be compatible with the ARMO uplifts. Of the preexisting models tested, the model including a transform boundary on the western continental margin is most consistent with ARMO uplifts. A new tectonism model is derived including a left-lateral transtensional boundary on the Laurentian western margin and a refined compressional history along the Appalachian-Marathon margin. Modeling suggests that contemporaneous extension along eastern Greenland may have limited northward growth of the ARMO.