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

While 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.

The syn‐rift tectono‐stratigraphic record of rifted margins (Part I): Insights from the Alpine Tethys

“…BB4 (Figure 3a and Table 1) comprises successive, in‐sequence long‐offset extensional detachment faults responsible for exhumation of mainly upper crustal levels at the seafloor (for details see Epin & Manatschal, 2018). The exhumed basement is locally overlain by allochthonous fragments of upper crust and pre‐rift and early syn‐rift sediments.…”

“…The type‐locality of BB4 is the Err‐detachment system exposed in the Lower Austroalpine Err Nappe north of the Julier Pass (Figure 4d,e) (e.g. Epin & Manatschal, 2018; Froitzheim & Eberli, 1990; Manatschal & Nievergelt, 1997; Masini et al., 2012). Another nearby example is the Bernina detachment system (Mohn et al., 2012) (Figure 4d,e).…”

“…The type locality is the Tasna ocean‐continent transition (OCT) exposed north of Scuol in the Lower Engadin valley (Florineth & Froitzheim, 1994; Manatschal et al., 2006; Ribes, Petri, et al., 2020) (Figure 4d,e). Other examples are the Upper Platta unit (Epin & Manatschal, 2018), Northern Lanzo (Kaczmarek & Müntener, 2008) or the External Ligurides (Marroni et al., 2002).…”

From rifting to hyperextension: Upper Jurassic–Lower Cretaceous tectono‐stratigraphy of the Porcupine Basin, Irish Atlantic Margin

“…Low‐angle faults may be formed by progressive rotation of initially high‐angle fault planes as extension increases with time and strain migrates towards the rift centre (Buck, 1988; Ranero & Pérez‐Gussinyé, 2010; Reston & McDermott, 2011, 2014). Major detachment faults may develop not from one single active fault, but from complex interaction of smaller faults with active extension migrating towards the rift axis through time, leading to exhumation of the upper mantle (Epin & Manatschal, 2018; Lymer et al., 2019). The migration of extensional strain towards the rift axis can lead to syn‐tectonic and post‐tectonic packages that are younger in the distal parts of rifted margins than in the proximal parts (Masini et al., 2014; Péron‐Pinvidic et al., 2013; Ribes et al., 2019).…”

The Role of Inherited Lithospheric Heterogeneities in Defining the Crustal Architecture of Rifted Margins and the Magmatic Budget During Continental Breakup

“…The continent‐ocean transition (COT) is best studied and understood in magma‐poor (i.e., nonvolcanic) margins. This is particularly true with respect to the present‐day Iberia‐Newfoundland margins, where there is an abundance of high‐resolution seismic data and deep ocean drillings (e.g., Manatschal, ; Péron‐Pinvidic & Manatschal, ; Sutra & Manatschal, ), and in the Alps, where the ancient Mesozoic Tethys margins are preserved and exposed providing excellent field analogs (e.g., Epin & Manatschal, ). Observations indicate that the COT forms during the final stage of rifting when deformation in the crust and subcontinental mantle becomes coupled.…”