Unravelling the interaction between tectonic and sedimentary processes during lithospheric thinning in the Alpine Tethys margins

Abstract

The discovery of exhumed continental mantle and hyper-extended crust in present-day magma-poor rifted margins is at the origin of a paradigm shift within the research field of deep-water rifted margins. It opened new questions about the strain history of rifted margins and the nature and composition of sedimentary, crustal and mantle rocks in rifted margins. Thanks to the benefit of more than one century of work in the Alps and access to world-class outcrops preserving the primary relationships between sediments and crustal and mantle rocks from the fossil Alpine Tethys margins, it is possible to link the subsidence history and syn-rift sedimentary evolution with the strain distribution observed in the crust and mantle rocks exposed in the distal rifted margins. In this paper, we will focus on the transition from early to late rifting that is associated with considerable crustal thinning and a reorganization of the rift system. Crustal thinning is at the origin of a major change in the style of deformation from high-angle to lowangle normal faulting which controls basin-architecture, sedimentary sources and processes and the nature of basement rocks exhumed along the detachment faults in the distal margin. Stratigraphic and isotopic ages indicate that this major change occurred in late Sinemurian time, involving a shift of the syn-rift sedimentation toward the distal domain associated with a major reorganization of the crustal structure with exhumation of lower and middle crust. These changes may be triggered by mantle processes, as indicated by the infiltration of MOR-type magmas in the lithospheric mantle, and the uplift of the Briançonnais domain. Thinning and exhumation of the crust and lithosphere also resulted in the creation of new paleogeographic domains, the Proto Valais and Liguria-Piemonte domains. These basins show a complex, 3D temporal and spatial evolution that might have evolved, at least in the case of the Liguria-Piemonte basin, in the formation of an embryonic oceanic crust. The re-interpretation of the rift evolution and the architecture of the distal rifted margins in the Alps have important implications for the understanding of rifted margins worldwide, but also for the paleogeographic reconstruction of the Alpine domain and its subsequent Alpine compressional overprint.

Evidence of Late Ediacaran Hyperextension of the Laurentian Iapetan Margin in the Birchy Complex, Baie Verte Peninsula, Northwest Newfoundland: Implications for the Opening of Iapetus, Formation of Peri-Laurentian Microcontinents and Taconic – Grampian Orogenesis

“…It is inferred that Dashwoods started out as a keystone between conjugate normal faults (hanging wall block) associated with thinning of the lithosphere. This part of the model follows the structural evolution proposed by Mohn et al (2010) for the isolation of the BrianHonnais block through formation of the Valais and Ligurian -Piemonte oceanic seaways in the Alpine Tethys. B.…”

“…Burton and Southworth 2010). An alternative model involving protracted hyperextension of the Humber margin similar to the margins along the Alpine Tethys Ocean Manatschal and Müntener 2009;Mohn et al 2010) has not been previously explored but forms a viable solution to these seemingly conflicting datasets.…”

“…Karabinos et al 1998;Hibbard et al 2007;van Staal and Hatcher 2010;Allen et al 2010;Chew et al 2008Chew et al , 2010 initially could have formed, at least to a first approximation, as H-blocks or large extensional allochthons, analogous to the BrianHonnais crustal block in the Alps Mohn et al 2010). The crust of H-blocks is commonly thinned to less than 20 km and is generally associated with marked retardation of subsidence (Péron-Pinvidic and Manatschal 2010).…”

“…Formation of H-blocks and/or large extensional allochthons during hyperextension would remove the necessity of having two discrete rifting events along the Humber margin, resulting in two coeval spreading centres Waldron and van Staal 2001;Burton and Southworth 2010). This is analogous to the BrianHonnais crustal block in the Alps Mohn et al 2010), which separates the Valais oceanic basin to the north from the Piemonte -Liguria Ocean to the south. In this analogy (Fig.…”

New stratigraphic data from the Lower Penninic between the Adula nappe and the Gotthard massif and consequences for the tectonics and the paleogeography of the Central Alps

“…We explain this protracted history as follows (partly inspired by Manatschal et al (2006Manatschal et al ( , 2007, Mohn et al (2010) and Péron-Pinvidic et al (2007), Manatschal, 2009 andPéron-Pinvidic et al, 2010):…”