Preservation of Proterozoic terrane boundaries within the Colorado Plateau and implications for its tectonic evolution

Abstract

During the Proterozoic, the North American continent grew by the accretion of arcs onto the Archean craton. Subsequent tectonic events affected much of the lithosphere of western North American resulting in the destruction of many of the features that reflect continental growth. The Colorado Plateau, which is centrally located within the tectonically active western portion of North America, experienced only minor amounts of volcanism during subsequent magmatic events, and has undergone comparatively little internal deformation during the remainder of the Precambrian and Phanerozic, despite the occurrence of some significant tectonic events. Because the lithosphere of the plateau has not been significantly reworked by tectonic events it may have retained structures since accretion that give insight into processes of continental growth. The crust of the southeastern portion of the Colorado Plateau, revealed here through seismic data recorded by the temporary SPE and LA RISTRA arrays, is greater than 40 km thick and possesses distinct changes in intercrustal layering and the character of the Moho. The Moho appears quite dim towards the center of the plateau and much brighter along its southeastern margins. Connecting changes in crustal features that are common between the two arrays indicates a northeastern structural trend that matches the pattern of gravity anomalies in the region. Differences in crustal structures between terranes extend across much of the crust suggesting that entire distinct crustal columns align with terrane boundaries. It is unlikely that extensive crustal flow, as required by some models of plateau evolution, could have traversed across the entire Colorado Plateau without producing features that cross-cut these boundaries.