New models for evolution of magma-poor rifted margins based on a review of data and concepts from West Iberia and the Alps

Abstract

Direct observation and extensive sampling in ancient margins exposed in the Alps, combined with drillhole and geophysical data from the present-day Iberia margin, result in new concepts for the strain evolution and near-surface response to lithospheric rupturing at magmapoor rifted margins. This paper reviews data and tectonic concepts derived from these two margins and proposes that extension, leading to thinning and final rupturing of the continental lithosphere, is accommodated by three fault systems, each of them characterized by a specific temporal and spatial evolution during rifting of the margin, by its fault geometry, and its surface response. The data presented in this paper suggest that margin architecture and distribution of rift structures within the future margin are controlled first by inherited heterogeneities within the lithosphere leading to a contrasting behaviour of the future distal and proximal margins during an initial stage of rifting. The place of final break-up appears to be determined early in the evolution of the margin and occurs where the crust has been thinned during a first stage to less than 10 kilometres. During final break-up, the rheology of the extending lithosphere is controlled by the thermal structure related to the rise of the asthenosphere and by serpentinization and magmatic processes.

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

“…The ultramafic rocks in such settings mainly represent inherited sub-continental lithospheric mantle exhumed onto the seafloor and the structurally interleaved sedimentary rocks represent its syn-to post-rift cover (Manatschal 2004;Péron-Pinvidic and Manatschal 2009). The complex polyphase structural history and the relatively high pressures recorded in the mafic schist (Willner et al 2012) are another feature typical of OCT zones, e.g.…”

“…Müntener and Manatschal 2006;Bernoulli et al 2003) or may change over time from magmapoor to magma-rich (e.g. Osmundsen and Ebbing 2008 Manatschal 2004;Manatschal et al 2007Manatschal et al , 2011Sutra and Manatschal 2012). This final asymmetric phase of extension may be superimposed on an earlier phase of more symmetric extension (Huismans and Beaumont 2002) during which mantle detachments can form below both extending margins (e.g.…”

High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the North Pyrenean passive paleomargin

“…In addition, its relative impermeability due to high clay content must have consistently limited the penetration of basinal and meteoric water in the system, hence annihilating convective cooling . In contrast with the starved paleotethys margin (Manatschal and Bernoulli, 1999;Manatschal, 2004;Masini et al, 2012) and Iberian margin (Shipboard Scientific Party, 1987;Manatschal and Bernoulli, 1999;Soares et al, 2012), the Pyrenean paleomargin seems to have developed in a sedimentrich environment, favorable to a marked blanketing effect.…”

“…The understanding of the processes controlling their structural and thermal evolution hence requires the comparison with exhumed analogs of fossil passive margins. The first and moststudied analogs have been the paleomargins exposed along the Alpine arc (Lemoine et al, 1987;Froitzheim and Eberli 1990;Manatschal and Nievergelt 1997;Manatschal 2004). …”

The Valais units in Savoy (France): a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps

“…Frisch 1979;Stampfli 1993;Stampfli et al 1998) or non-existence (e.g. Schärer et al 2000;Manatschal 2004;Beltrando et al 2007;Masson et al 2008) of a Cretaceous age Valais ocean. Finally, we will briefly discuss the significance of these new findings for the palaeotectonic and orogenic evolution of the Western Alps.…”