Résumé
The study of the serpentinization process in ultramafic rocks has been revived in recent years in response to the problems of natural hydrogen generation. Serpentinization results in the formation of magnetite, which is often observed in the most serpentinized peridotites, at concentrations of up to a few percentage. In this study, we propose a novel experimental approach to test the formation of magnetite at temperatures of 100°C, 200°C and 300°C. The aim is to test whether magnetite can be produced at low temperatures in variably serpentinized peridotites, and how the degree of serpentinization can influence this production. This experimental approach exploits the properties of newly formed magnetites to record the magnetic field applied during the experiment. To achieve this, a study was conducted on Pyrenean peridotites, which encompassed variable degrees of serpentinization. The findings suggest that magnetite formation commences at 100°C, irrespective of the initial rock's degree of serpentinization. At 200°C, the production of magnetite remains comparable to that at 100°C. However, at 300°C, the production of magnetite is an order of magnitude higher. The most noteworthy outcome of our investigation is the demonstration that the production of magnetite is directly proportional to the initial nanomagnetite content of the peridotite. This finding suggests that magnetite may act as a catalyst, with strongly serpentinized peridotite exhibiting a greater propensity for magnetite production than weakly serpentinized peridotite under natural conditions.