First characterization of the cooling of the paleo-geothermal system of Terre-de-Haut (Les Saintes archipelago, Guadeloupe): Application of fluid inclusion and chlorite thermometry

International audienceDue to its geodynamic location in the Lesser Antilles arc, Basse-Terre of Guadeloupe displays an active volcanism which is favourable to the development of high-enthalpy geothermal energy. An exhumed analogue of the Bouillante geothermal reservoir has been recently characterized in Terre-de-Haut island (Les Saintes archipelago), giving an opportunity to study the cooling of a natural geothermal system and the related alterations.By coupling chlorite geothermometry and primary fluid inclusions in associated zoned quartz crystals located in N70 trending fractures, new insights on the Terre-de-Haut paleo-geothermal evolution can be inferred by distinguishing three new different episodes during functioning and cooling of this system: (i) a temperature of at least 240–270 °C in fluid inclusions trapped in the quartz core, (ii) chlorite formation at about 120 °C, and (iii) temperatures of ~50 °C - or less - in fluid inclusions of the quartz outer growth zones. Fluid inclusions also reveal that the hydrothermal fluid is of low salinity (2 wt% NaCl), probably of meteoric and sea water origin. Additionally, a second type of fluid inclusions observed in a banded quartz vein indicates at least an episode of a CO2-(H2O) fluid, with traces of H2S. Hence, some similarities can be highlighted between Terre-de-Haut and the Bouillante active geothermal systems in term of the highest temperatures of circulation events and gas composition, despite a difference in fluid origin. This study shows that some alteration episodes also occur at low temperature during the cooling of the geothermal system. Moreover, the N70 trending fractures, that have been identified as drains for the hot temperature fluids, have to be considered for future geothermal exploration

Recording of the thermal evolution of limestones undergoing experimental accelerated ageing tests

International audienceSodium sulfates are widely regarded as the most destructive salts for porous stone, concrete and brick. Thenardite (Na2SO4), mirabilite (Na2SO4, 10H2O) and heptahydrate (Na2SO4, 7H2O) are the common phases that occur under surface conditions. The heptahydrate phase has been largely neglected in most modern work about salt weathering. However, several recent publications suggest that it could play an important role in geochemical and planetary processes. Therefore its role in the Na2SO4-H2O system should be clarified.We present here results of accelerated ageing experiments performed on samples of a micritic limestone under two different ambient temperatures: 20°C (i.e. below the upper limit of metastability of the heptahydrate), and 30°C (i.e. above this limit and also below the upper limit of stability of mirabilite). Thermocouples were placed into the samples in order to follow the evolution of the temperature of the stones during the weathering tests. This method allows the recording of exo- and endothermic reactions that are linked to physicochemical processes, such as crystallization, wetting, evaporative cooling, etc.The experiments show significant differences in the pattern and degree of damage. In the experiment at 20°C, the loss of material is noticeable, and occurs as crumbling and scaling. In the experiment at 30°C, we observe just efflorescence with no visible loss of material. The recorded thermal evolution is also different for the two experiments, which provides some clues as to the different physicochemical processes occurring in each situation, depending on the ambient temperature

Aggregate’s influence on thermophysical concrete properties at elevated temperature

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Influence of recycled coarse aggregates on normal and high performance concrete subjected to elevated temperatures

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