Thermal history of the Aragón-Béarn basin (Late Paleozoic, western Pyrenees, Spain); insights into basin tectonic evolution

Organic and inorganic thermal indicators throughout the Late Paleozoic sedimentary fill of the Aragon-Bearn Basin in the western Pyrenees, integrated with stratigraphic and structural data, point to a two-stage tectonic evolution: (i) High heat flow values and widespread magmatic intrusions driven by deeply rooted strike-slip faults characterized the first stage. This regime accompanied the rapid and localized deposition of the lower sedimentary succession and ended with uplift and erosion. (ii) The second stage was characterized by lower heat flow values, shallower strike-slip faults active during the deposition of an upper transgressive sedimentary succession and minor magmatic intrusions. The upper portion of the succession (Unidad Roja Superior, mainly Upper Permian in age) records maximum temperatures between 100-110 and 150 degrees C as indicated by KI values between 0.57 and 0.94 420, illite content in mixed layer illite-smectite of 85-92%, and fluid inclusions in host-rock quartz-calcite cements. Local thermal maturity anomalies affected selected portions of the Late Paleozoic sedimentary succession with organic matter and clay minerals reaching respectively Ro%: 4.2-4.7% and KI up to 0.32 420 in the lower sequence, and Ro% 2.9% in the upper sequence. These localized anomalies with respect to the basin thermal signature are the result of contact metamorphism related to the emplacement of magmatic intrusions across the sedimentary fill during two different magmatic events.