Sequential fluid migration along a fold and thrust belt: se pyrenees from late cretaceous to oligocene
- Autores: David Cruset
- Directores de la Tesis: Anna Travé Herrero (dir. tes.), Jaume Vergés i Masip (codir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2019
- Idioma: español
- Materias:
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- Resumen
The south eastern Pyrenees allowed us to study the relationships between fluid flow and deformation in a complete section of a well-preserved fold and thrust belt. Furthermore, this study enables us to decipher the main controls in fluid flow and to perform a conceptual model of fluid migration in fold and thrust belts by comparing the southern Pyrenees with other orogens worldwide.
A combination of field-based and petrographic observations together with geochemical analyses was used to determine the origin of fluids from which these cements precipitated, the conditions of fluid migration and the fluid-rock relationships. These methods were applied to carbonate host rocks and in calcite and dolomite cements precipitated in fractures and in intergranular and vug porosities.
The integration of the methodology allowed us to define up to 20 fluid flow events for the Upper Pedraforca thrust sheet, Eight for the Lower Pedraforca thrust sheet, seven for the Vallfogona thrust, which is the southern margin of the Cadí thrust sheet, and two for both the Abocador thrust and the Puig-reig anticline, which are located in the foreland Ebro basin.
U-Pb geochronology applied to calcite cements related to the fluid flow events identified in each thrust sheet indicates that the fluid flow events identified for each thrust sheet are related to the Pyrenean compression. Furthermore, these results allow us to refine the sequence of deformation in the south eastern Pyrenees.
Stable, clumped and strontium isotopes together with elemental composition and rare earths + yttrium analysis indicate that during the emplacement of the Upper and Lower Pedraforca thrust sheets, from Late Cretaceous to middle Eocene, the fluid system was dominated by high-salinity formation fluids and meteoric waters at temperatures ranging between 70 and 90 ºC. In these thrust sheets, fluids migrated above evaporite detachments that acted as barriers for the input of deep sourced fluids. Contrarily, during the emplacement of the Cadí thrust sheet and during the deformation affecting the northern side of the Ebro foreland basin from middle Eocene to Oligocene, high-salinity hydrothermal fluids derived from the deeper parts of the Axial zone and at temperatures between 100 and 177 ºC, migrated through fractures to the thrust front. Hydrothermal fluid flow induced the development of thermal anomalies in the Vallfogona and Abocador thrusts and in the Puig-reig anticline, which are structures rooted at depth with the basement.
In all the studied thrust sheets and in the Ebro foreland basin, as the thrust front progressively emerged, low-temperature meteoric waters migrated downwards the foreland basin by topography-driven fluid flow and mixed at depth with the formation and hydrothermal fluids. However, the presence or absence of thick evaporitic units highly controls fluid composition. Whereas in thrusts not detached along thick evaporite units, mixed fluids are progressively more depleted in δ18O and have a lower temperature and lower Fe and Sr contents as the thrust front emerges, in thrust detachments through thick evaporite units, the mixed fluids are enriched in δ18O.
During the layer-parallel shortening stretching the Upper Pedraforca Lower Pedraforca and Cadí thrust sheet and the Ebro foreland basin, the paleohydrological system was closed and the fluid-rock interaction was low. In contrast, during later folding and thrusting the system opened to the input external fluids and the interaction between fluids and their adjacent host rocks decreased progressively.
The fluid flow patterns observed during the growth of the south eastern Pyrenean fold and thrust belt are similar to that observed in the western side of this orogen.
The evolution of the fluid regime during the growth of the southern Pyrenees has strong similarities to that observed in other orogens worldwide and allow us to perform a conceptual model of fluid flow in fold and thrust belts in which the style of deformation is one of the main controlling parameters. Whereas in thin-skinned fold and thrust belts the fluid system is controlled by formation, marine and meteoric waters, in thick-skinned fold and thrust belts the system is controlled by the input of deep-sourced hydrothermal fluids, which induce the formation of thermal anomalies. In both situations, the influence of meteoric fluids increases as these folds and thrust belts emerge and are exhumed.
