A petro-structural and geochronological study has been conducted in the Agly Variscan Massif loca... more A petro-structural and geochronological study has been conducted in the Agly Variscan Massif located in the Northern Pyrenean Zone (France). The Lower Gneiss Unit (LGU) displays highly ductile deformation with a NNE-SSW oriented stretching lineation and opposite senses of shear in the directions top-to-the-NNE and top-to-the-SSW. Field observations and thin section analysis show that these two senses of shear are coeval with bulk coaxial vertical shortening and horizontal lengthening. Focusing on syntectonic minerals located within shear bands, Th-U/Pb monazite and40Ar/39Ar mica dating yield a 94–127 Ma age bracket for the mylonitic deformation. The principal conclusion from these results is that the main ductile strain (i.e., stretching lineations and kinematic indicators) in the LGU should be ascribed to the Cretaceous rifting. A PTt path for the LGU is proposed showing the diachronism between the Cretaceous metamorphic evolution in the Agly Massif (peak temperature at 127 Ma) and...
The tectono-volcanic ensemble of the Chaîne des Puys and the Limagne fault, which is part of the ... more The tectono-volcanic ensemble of the Chaîne des Puys and the Limagne fault, which is part of the West European rift, was inscribed on the UNESCO World Heritage list in 2018 as the Chaîne des Puys–Limagne fault tectonic arena. This site includes (1) the western normal border fault of the graben (the Limagne fault), (2) the shoulder of the graben (the granitic Plateau des Dômes) on which lies a Quaternary volcanic alignment (the Chaîne des Puys), and (3) an inverted relief resulting from erosive action around a Pliocene volcanic lava flow (the Montagne de la Serre). It is shown that, when viewed in a global tectonic context, these structural and volcanic features can be described as a natural scale model, allowing everyone to understand the processes in operation at depth in a continental rift. The property is an inhabited environment that counts 30,000 inhabitants and traditional activities such as pastoral farming and agroforestry. Following its inscription on the World Heritage Lis...
Scaled experiments have been carried out on caldera collapse mechanisms, using silicone as analog... more Scaled experiments have been carried out on caldera collapse mechanisms, using silicone as analogue magma and dry sand as analogue rock. Experiments were carried out in two and three dimensions using a range of roof aspect ratios (thickness/width 0.2 to 4.5) appropriate for caldera collapse. They reveal a general mechanism of collapse, only weakly dependent on the shape of the
A petro-structural and geochronological study has been conducted in the Agly Variscan Massif loca... more A petro-structural and geochronological study has been conducted in the Agly Variscan Massif located in the Northern Pyrenean Zone (France). The Lower Gneiss Unit (LGU) displays highly ductile deformation with a NNE-SSW oriented stretching lineation and opposite senses of shear in the directions top-to-the-NNE and top-to-the-SSW. Field observations and thin section analysis show that these two senses of shear are coeval with bulk coaxial vertical shortening and horizontal lengthening. Focusing on syntectonic minerals located within shear bands, Th-U/Pb monazite and40Ar/39Ar mica dating yield a 94–127 Ma age bracket for the mylonitic deformation. The principal conclusion from these results is that the main ductile strain (i.e., stretching lineations and kinematic indicators) in the LGU should be ascribed to the Cretaceous rifting. A PTt path for the LGU is proposed showing the diachronism between the Cretaceous metamorphic evolution in the Agly Massif (peak temperature at 127 Ma) and...
The tectono-volcanic ensemble of the Chaîne des Puys and the Limagne fault, which is part of the ... more The tectono-volcanic ensemble of the Chaîne des Puys and the Limagne fault, which is part of the West European rift, was inscribed on the UNESCO World Heritage list in 2018 as the Chaîne des Puys–Limagne fault tectonic arena. This site includes (1) the western normal border fault of the graben (the Limagne fault), (2) the shoulder of the graben (the granitic Plateau des Dômes) on which lies a Quaternary volcanic alignment (the Chaîne des Puys), and (3) an inverted relief resulting from erosive action around a Pliocene volcanic lava flow (the Montagne de la Serre). It is shown that, when viewed in a global tectonic context, these structural and volcanic features can be described as a natural scale model, allowing everyone to understand the processes in operation at depth in a continental rift. The property is an inhabited environment that counts 30,000 inhabitants and traditional activities such as pastoral farming and agroforestry. Following its inscription on the World Heritage Lis...
Scaled experiments have been carried out on caldera collapse mechanisms, using silicone as analog... more Scaled experiments have been carried out on caldera collapse mechanisms, using silicone as analogue magma and dry sand as analogue rock. Experiments were carried out in two and three dimensions using a range of roof aspect ratios (thickness/width 0.2 to 4.5) appropriate for caldera collapse. They reveal a general mechanism of collapse, only weakly dependent on the shape of the
Uploads
Papers by Olivier Merle