CHLORITE AND FLUID INCLUSION THERMOMETRY AS A TOOL TO INQUIRE INTO THE TECTONO-THERMAL EVOLUTION OF OROGENS: AN EXAMPLE FROM THE LA MOLINA V1 (LATE ORDOVICIAN) AND V2 (ALPINE) QUARTZ VEINS

Veins formed under low fluid/rock ratios are a paleorecord of the P-T conditions within the enclosing rocks, and their study may shed light on the evolution of orogens. In the La Molina area (Canigó massif, Eastern Pyrenees), two generations of metric quartz veins (V1 and V2) are distinguished by their distribution patterns and their relationships to the deformational macro, meso, and microstructures. P-T formation conditions are obtained by combining chlorite geothermometry and fluid inclusion microthermometry data. Different formation temperatures for chlorites located at different positions within the veins are discussed, concluding that the temperature discrepancy is a result of chlorite Fe³⁺content variations, and so that the veins grew in a low fluid/rock ratio. V1 veins can be related to the Late Ordovician ("Sardic") syn-sedimentary faulting episode as revealed by their distribution patterns, formation mechanisms, and fluid-rock interactions. We propose an Alpine age for the V2 veins, based on their structure and the emplacement conditions of 318 ± 12°C and 2.4 ± 0.2kbar, with an estimated geothermal gradient of 34°C∙km^-1 and a burial depth of ca. 9km. Several questions are raised, for instance, how representative are these data in the broader context of the Central and Eastern Pyrenees, and/or, what is the relationship between these metric veins and the larger ones spread throughout the pre-Alpine basement of the Eastern Pyrenees.