Fracturación y migración de fluidos durante la evolución tectónica neogena en el Sector Central de las Cadenas Costero Catalanas

Abstract

The Neogene rift in the Catalan Coastal Ranges, located in the NE part of the Eastern Iberian Margin, corresponds to a system of grabens formed in the north-western margin of the Valencia Trough. Extensional activity was superimposed on to earlier, Eocene strike-slip movements related to the Alpine compression. In the Penedés graben and the adjacent Carrafhorst, tectonic structures (faults and joints) affect Mesozoic limestones as well as Miocene deposits which fill the grabens. Seven generations of fractures formed during different geodynamic stages (prerifl, synrift, early postrift and late postrift) have been distinguished. The fractures are filled with calcite cement, and locally by internal sediment and dolomitic cement. The fillings present different petrographic, minor and trace elements (Mg, Sr, Na, Fe and Mn), stable isotopes (8 laO y 8 13C) and 87Sr/86Sr ratio features. The prerift stage presents two fluid regimes: in the first (Fractures 1 and 2) the fluids related to the Alpine compression suggest a relatively closed hydrogeological system and high fluid-rock interaction; and in the second (Fractures 2 and 4) the fluids are meteoric in origin and present low fluid-rock interaction. The synrift stage is characterized by formation fluids (Fractures 5) suggesting an open hydrogeological system and low fluid-rock interaction. The early postrift stage was a period of low tectonic activity and the fluids have not been studied. The late postrift stage presents two fluid regimes: in the first (dolomite cement on Fractures 7) the fluids are hydrothermal and present a high fluid-rock interaction; in the second (calcite cement on Fractures 7) the fluids are meteoric and present an open hydrogeological system and low fluid-rock interaction