Paleozoic Decollement Displaced the Surface Trace of Iapetus Ocean Closure in Northern Appalachians

Abstract

The northern Appalachians record accretion of Laurentia‐ and Gondwana‐derived terranes to Laurentian margin during the formation of Pangea. Terrane bounding structures, key to reconstructing this history, are poorly understood at depth. We use teleseismic receiver functions to probe the crust beneath Appalachian terranes in Québec and Maine. We identify an eastward‐dipping intra‐crustal boundary extending beneath the trace of the Iapetus Ocean closure that separates the peri‐Laurentian Dunnage and the peri‐Gondwanan Gander terranes. Systematic fabric in rocks is a likely cause of anisotropic seismic properties associated with it. Depth and position associate this boundary with a previously identified décollement separating authochtonous Laurentian basement from rocks emplaced during Pangea's assembly. Neither the décollement nor the crust‐mantle boundary under our profile change beneath the surface trace of the Iapetus Ocean closure, suggesting that it has been transported to the northwest relative to the actual boundary between mantle lithospheres of former Laurentia and Gondwana.