The Supra-Detachment Sedimentary Evolution of Deep-Water Magma-Poor Rifted Margins: the Example of the Fossil Distal Alpine Tethys Margin Exposed in the Alps (SE Switzerland)
Abstract
Rifting processes leading to the formation of deep-water, magma-poor rifted margins are poorly understood due to the limited access to direct observation at present-day rifted margins. The available data from many present-day examples have shown that classical models are unable to explain the observed tectonic, sedimentary and subsidence history. Therefore, finding good field analogues preserving the syn-rift tectono-sedimentary evolution is a key to investigate the underlying processes and propose new tectono-sedimentary models for the formation of deep-water rifted margins. In the Jurassic Adriatic rifted margin preserved in the Central Alps in SE Switzerland, rift related structures and the associated syn-rift sedimentary sequences can be mapped and three main paleogeographic domains can be distinguished: a “proximal domain” showing classical tilted block geometries, a “necking zone” dominated by thinning structures, and a “distal domain” with exhumed crustal rocks and extensional allochthons that pass oceanwards into a zone of exhumed subcontinental mantle. The low sedimentation rates observed along the whole Adriatic margin gives an opportunity to study the exhumation history and related evolution of the sedimentary sources during final rifting. In our study we constrain the tectono-sedimentary evolution of a supra-detachment rift basin, which is preserved between the necking zone and the exhumed subcontinental mantle in the ocean continent transition. Its temporal evolution is recorded in four main stratigraphic units that are deposited on top of an evolving detachment system: (1) the Bardella Formation records the erosion of the hanging wall (pre-rift platform) along high-angle faults in the hanging wall of a major detachment system leading to the formation of local basins dominated by debris-flow processes. (2) the Saluver A Fm records the first local exhumation of the footwall (the basement) with a comparable dynamic. (3) the Saluver B Fm consists of the onset of axial sand-dominated turbiditic systems consecutive of the migration of sedimentary sources continentward (toward the necking zone). Upsection it records a progressive stopping of Bardella and Saluver A due to a migration of the local tectonic activity oceanwards. (4) the Saluver C Fm is related to the tectonic migration oceanwards into the exhumed mantle domain and shows a decrease in sedimentation rate and a retrogradation of turbiditic systems before the whole margin including the adjacent embryonic oceanic crust is sealed by pelagic post-rift sediments. To conclude, the fossil analogue exposed in the Alps shows the close relationship between tectonic and sedimentary processes during thinning, exhumation and continental breakup. Based on the investigation of such fossil analogues combined with seismic observations from present-day rifted margins, we aim to understand the general evolution of tectono-sedimentary systems related to final rifting and onset of seafloor spreading.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T31C1829M
- Keywords:
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- 8109 TECTONOPHYSICS / Continental tectonics: extensional