Defining diagnostic criteria to describe the role of rift inheritance in collisional orogens: the case of the Err-Platta nappes (Switzerland)

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)

“…Epin et al () presented, using the example of the Err and Platta nappes, a detailed analysis of the role of rift inheritance during reactivation of a hyperextended and exhumed rift domain. This study builds on the work of Epin et al () and previous studies, in which the main Alpine and pre‐Alpine structures in the Err nappe have been described (see Figures , Epin et al, ). The main Alpine structures and deformation phases can be described as follows: The D1 phase (e.g., Trupchun phase of Froitzheim et al, ) is related to the major, top‐to‐west Alpine shortening manifested by the emplacement of the Austroalpine nappe stack during Late Cretaceous convergence (Froitzheim et al, ).…”

“…In the study area, this phase is responsible for the sandwiching of the Err nappe between the underlying Platta nappe (exhumed mantle and proto‐oceanic crust) and the overlying Bernina nappe (hyperextended continental crust) along major D1 thrust faults (black dotted fault, Figure ). Second‐order D1 thrusts (black thin fault, Figure ) subdivide the Err nappe in the Upper, Middle, and Lower Err units (for more details, see Manatschal & Nievergelt, ; Epin et al, ). The D2 phase (e.g., Ducan‐Ela phase of Froitzheim et al, ) is mainly expressed by normal faults (gray fault, Figure ) reactivating and/or crosscutting older D1 structures (e.g., Handy et al, ; Manatschal & Nievergelt, ). The D3 phase (e.g., Blaisun phase of Froitzheim et al, ) affected the Err nappe by north and south directed thrust splays and kilometer‐scale (not representing on the map, Figure ), upright east west striking open folds. The D4 and D5 phases of Froitzheim et al () are manifested in the study area by late east‐west directed high‐angle faults (light gray fault, Figure ) already mapped by Cornelius (). Handy () suggested that these faults are related to the Engadin fault that postdate the Bergell intrusion (30myr).…”

“…The southern segment of the Middle Err unit, around Piz Rocabella, Piz d'Emmat Dadora, and Grevasalvas, is the most affected by Alpine reactivation. It corresponds to a stacking of different subunits that preserve internally pre‐Alpine rift‐related contacts (Epin et al, ). Between Piz Bardella and Piz d'Emmat Dadora (Figures and ), there is a remnant of a Jurassic detachment that can be correlated across the valley with the Jenatsch detachment flooring the Bardella block (blue line).…”

“…In the past, the complex rift structures and in particular the lack of continuity of prerift and synrift sedimentary sequences made it difficult to describe and evaluate the Alpine overprint in the Err nappe. Only more recently, Epin et al (2017) were able to distinguish between pre-Alpine and Alpine structures and to describe the role of rift inheritance during Alpine convergence. This study enabled to recognize and map new parts of an extensional detachment system, from which parts were previously described by Froitzheim and Eberli (1990), Handy et al (1993), Handy (1996), Froitzheim and Manatschal (1996), Manatschal and Nievergelt (1997), Masini et al (2011), and Masini and Manatschal (2014), and to demonstrate that the extensional detachment system consists of multiple faults that formed in sequence.…”

“…In the study area, this phase is responsible for the sandwiching of the Err nappe between the underlying Platta nappe (exhumed mantle and proto-oceanic crust) and the overlying Bernina nappe (hyperextended continental crust) along major D1 thrust faults (black dotted fault, Figure 1). Second-order D1 thrusts (black thin fault, Figure 1) subdivide the Err nappe in the Upper, Middle, and Lower Err units (for more details, see Manatschal & Nievergelt, 1997;Epin et al, 2017). 2.…”