Three‐Dimensional Architecture, Structural Evolution, and Role of Inheritance Controlling Detachment Faulting at a Hyperextended Distal Margin: The Example of the Err Detachment System (SE Switzerland)

Abstract

AbstractWhile extensional detachment systems linked to postorogenic or oceanic settings have been described from many places, examples linked to hyperextension and formation of magma‐poor rifted margins remain rare. Here we describe one of the best preserved examples of a detachment system that is exposed over 200 km2 in the Err nappe in SE Switzerland. Based on existing and new mapping, we realized a new map that enables to describe the 3‐D structure of a detachment system and its role in thinning the crust and controlling the architecture and structural evolution of a hyperextended margin. We show that the Err detachment system is formed by at least three in‐sequence detachment faults. The 3‐D architecture of these faults and of their hanging wall blocks is controlled by inherited structures and a prerift evaporite level. The geometrical relationships and the evolution of the detachment system show deviations from the classical rolling hinge model. From the observations it remains unclear how and where the detachment faults rooted at depth. The overall observations made in the Err nappe allow to describe how the final rift evolution preceding mantle exhumation can be explained by extensional detachment systems and how these structures shape the hyperextended continental wedge at distal margins. While these questions are difficult to answer at present‐day rifted margins, the use of a kilometer‐scale field analogue can help to upscale and to interpret extensional detachment systems at present‐day distal, magma‐poor rifted margins.