The colloidal structure of bitumen: Consequences on the rheology and on the mechanisms of bitumen modification

Geological atlas of western and central Europe

Evolution of the European Cenozoic Rift System: interaction of the Alpine and Pyrenean orogens with their foreland lithosphere

The circum-Mediterranean anorogenic Cenozoic igneous province

More than 100 offshore mass-movement deposits have been studied in Holocene and Pleistocene sediments. The processes can be divided into three main types: slides/slumps, plastic flows, and turbidity currents, of which 13 main varieties have been recognized. The three types are differentiated mainly by motion, architecture, and shape of failure surface. For slides, the morphology of deposits can usually be linked to a process, but for plastic flows and turbidity currents, information about the motion is mainly provided by the sedimentary record. A static classification based on these features is given, and is related to a dynamic classification system to try to underline the morphological transformation of an offshore event from initiation to deposition.

Classification of offshore mass movements

Comparison of analogue experiments at crustal and lithospheric scale provides essential information concerning the mode of deformation during lithospheric extension. This study shows that during extension, lithospheric deformation is controlled by the development of shear zones in the ductile parts. At lithospheric scale, the global deformation is initiated by the rupture of the brittle mantle lithosphere. This failure generates the formation of conjugate and opposite shear zones in the lower crust and the ductile mantle lithosphere. The analysis of the internal strain of the ductile layers suggests that the two opposite shear zones located below the asymmetric graben in the lower crust and the ductile mantle lithosphere prevail. Experiments show that from a similar initial stage, the relative predominance of these shear zones originates two different modes of deformation. If the crustal shear zone prevails, a major detachment-like structure crosscuts the whole lithosphere and controls its thinning. In this model named the simple shear mode, the resulting geometry shows that crustal and lithospheric thinning are laterally shifted. If the mantle shear zone predominates, the lithospheric thinning is induced by the coeval activity of the two main shear zones. This process called the necking mode leads to the vertical superposition of crustal and mantle lithospheric thinning. Applied to natural laboratories (West European rift, Red Sea rift and North Atlantic), this conceptual model allows a plausible explanation of the different geometries and evolutions described in these provinces. The North Atlantic and the Red Sea rift systems may result from a simple shear mode, whereas the necking mode may explain part of the evolution of the West European rift especially in the Massif Central and the Eger graben.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002TC001435

Mode of lithospheric extension: Conceptual models from analogue modeling

Two of the most improtant segments of the west European Rift, the Rhinegraben and the Massif Central grabens, show in plan and cross section a very different crustal structure.

https://hal.archives-ouvertes.fr/hal-01242821/document

Crustal structures of the Rhinegraben and the Massif Central grabens: An experimental approach

Seismic records from La Reunion Island very broadband Geoscope station are investigated to constrain the link between the 2007 eruptive sequence and the related caldera collapse of the Piton de la Fournaise volcano. Tilt estimated from seismic records reveals that the three 2007 eruptions belong to a single inflation-deflation cycle. Tilt trend indicates that the small-volume summit eruption of 18 February occurred during a phase of continuous inflation that started in January 2007. Inflation decelerated 24 days before a second short-lived, small-volume eruption on 30 March, almost simultaneous with a sudden, large-scale deflation of the volcano. Deflation rate, which had stabilized at relatively low level, increased anew on 1 April while no magma was erupted, followed on 2 April by a major distal eruption and on 5 April by a summit caldera collapse. Long-term tilt variation suggests that the 2007 eruptive succession was triggered by a deep magma input.

/pdf/the-2007-eruptions-and-caldera-collapse-of-the-piton-de-la-eiwhori3cq.pdf

The 2007 eruptions and caldera collapse of the Piton de la Fournaise volcano (La Réunion Island) from tilt analysis at a single very broadband seismic station

We performed a microstructural study of Piton des Neiges (La Reunion Island) to understand how intrusions and stresses control each other in basaltic volcanoes. Our study reveals that three perpendicular intrusions trends coexisted during the 2 Myr history of the volcano: a N120–140°E rift zone, a perpendicular dike trend, and swarms of subhorizontal intrusions hereafter called “sill zones”. Independently, the inversion of fault-slip data shows that incompatible paleostress fields recurrently occurred along with the intrusions: a dominant NNE-SSW extension, a perpendicular extension, and strike-slip or compressional regimes. The orientations of paleostresses are consistent with the orientations of the three perpendicular intrusion populations. We propose that stress accumulation in the edifice under the effect of repeated magma injections resulted in permutations of the principal axes of the stress tensor, causing a reorientation of subsequent intrusions. Stress permutations were cyclical. Each cycle started with dike injections in an extensional stress field, reducing the deviatoric stress and switching the axes of principal stresses, and finished with sill intrusions in a compressional stress field. Sill zones acted as detachment planes, restoring the extensional stress field and initiating a new cycle of permutations. Our model of stress permutations is in agreement with the pattern of eruptions and deformation observed at Piton de la Fournaise. In contrast with the Hawaiian model of spreading on a decollement, stress permutations in La Reunion's volcanoes imply that the basal deformation of the edifices, if any, is not sufficient to compensate the reduction of deviatoric stress caused by intrusions.

/pdf/deformation-of-basaltic-shield-volcanoes-under-cointrusive-39u1jjh9ba.pdf

Laurent Michon

Papers

Mode of lithospheric extension: Conceptual models from analogue modeling

Crustal structures of the Rhinegraben and the Massif Central grabens: An experimental approach

The 2007 eruptions and caldera collapse of the Piton de la Fournaise volcano (La Réunion Island) from tilt analysis at a single very broadband seismic station

Deformation of basaltic shield volcanoes under cointrusive stress permutations

Interaction between structural inheritance and extension direction during graben and depocentre formation: An experimental approach