Ion microprobe dating of fissure monazite in the Western Alps: insights from the Argentera Massif and Piemontais and Briançonnais Zones
- 1University of Geneva, Department of Earth Sciences , Switzerland (emmanuelle.ricchi@unige.ch)
- 2Natural History Museum of Geneva, Route de Malagnou 1, 1208 Geneva, Switzerland
- 3Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
- 4Institute of Earth Sciences, University of Lausanne, Geopolis, Lausanne, 1015 Switzerland
Ion probe 208Pb/232Th fissure monazite ages from high pressure regions of the Western Alps and from the Argentera Massif provide new insights on the tectonic evolution of the Western Alps during Cenozoic times. Fissure monazite is a hydrothermal mineral crystallizing during cooling/exhumation in Alpine fissures, an environment where monazite is highly susceptible to fluid-mediated dissolution-(re)crystallization. Fissure monazite ages directly record chemical disequilibrium occurring in a fissure environment, but growing evidences indicate that fissure monazite commonly register tectonic activity. Fissure monazite age domains from this study show that monazite crystallization occurred between ~32-30.5 Ma and ~31.5-30 Ma in the Piémontais and Briançonnais Zone of the High Pressure regions, and between ~17-15 Ma and in the north-eastern border of the Argentera Massif. So far, monazite ages were recorded between ~32-23 Ma and at ~20.5 Ma in the Briançonnais Zone and in the south-western border of the Argentera Massif respectively. Thus the presented dataset corroborate and complement already reported fissure monazite 208Pb/232Th ages from the Western Alps. This new fissure monazite ages compilation supports that Late Oligocene thrusting affected the High Pressure regions of the Western Alps, and that Early and Middle Miocene dextral strike-slips movements respectively affected the south-western and north-eastern margins of the Argentera Massif. Chemical observations provide new hints on fissure monazite growth conditions (e.g. leached host-rock minerals, oxidation conditions) encouraging to pursue chemical studies with a larger dataset on natural fissure monazite to better understand growth conditions under cleft environment.
How to cite: Ricchi, E., Gnos, E., Rubatto, D., and Pettke, T.: Ion microprobe dating of fissure monazite in the Western Alps: insights from the Argentera Massif and Piemontais and Briançonnais Zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18344, https://doi.org/10.5194/egusphere-egu2020-18344, 2020