Migration and storage of geothermal fluids in the upper crust are mostly controlled by permeable rock volumes corresponding to crustal sectors affected by brittle deformation. Understanding how hot (250°-350°C) to super-hot (>350°C) fluids circulate and interact with host rocks in fault-controlled upper continental crust is a challenging task. The results from structural, fluid inclusion, Sr isotope, petrographic and mineralogical studies of the Terranera Fe-hydrothermal mineralisation, considered an exhumed palaeo-geothermal system, describe how hot to super-hot fluids were controlled by the increased permeability resulting from the interplay between low-angle normal faults and high-angle oblique-slip faults, the latter being part of a regional transfer zone (Zucchi et al., 2024). The study area is located in the eastern Elba Island (northern Tyrrhenian Sea, Italy), where the emplacement of a Messinian felsic intrusion has allowed hydrothermal fluids to circulate in relation to a fault-related permeability of the order of 10-15 to 10-13 m2. Magmatic fluids reacted with the host rocks (carbonate and phyllite) to form Fe-ore deposits hosted within the fault zones that controlled the fluid flow. Fluid inclusions trapped in quartz crystals indicate that the fluids consisted of saline solutions (salinity from 18.0 to 26.6 wt.% NaCl eq.), which later mixed with low salinity waters of probable meteoric origin. The fluid temperature during the main hydrothermal stage ranged between about 300° and 360°C under an estimated maximum hydrostatic pressure of 28–30 MPa. In contrast, the maximum possible temperature was about 400°C at a lithostatic pressure of 89 MPa. The hydraulic breccias formed as a result of the transient fluid pressurisation up to lithostatic values, due to the self-sealing process and the subsequent pressure drop, down to hydrostatic values, as framed in the hydrofracturing processes. The results provide useful input for the identification of geothermal and ore body targets in those geological settings where fluids of magmatic and meteoric origin are controlled by active faults in an extensional tectonic regime. Zucchi M. et al. (2024) - Migration of hot to super-hot palaeo-fluids in an extensional setting (eastern Elba Island, Italy). Tectonophysics, 874, 230210, https://doi.org/10.1016/j.tecto.2024.230210.
Tracing the palaeo-circulation of geothermal fluids in the shallow crust exposed in the eastern Elba Island (Tuscany, Italy)
Zucchi M.;Brogi A.;Liotta D.;Fregola R. A.;Caggianelli A.;Ventruti G.;Ruggieri G.
2024-01-01
Abstract
Migration and storage of geothermal fluids in the upper crust are mostly controlled by permeable rock volumes corresponding to crustal sectors affected by brittle deformation. Understanding how hot (250°-350°C) to super-hot (>350°C) fluids circulate and interact with host rocks in fault-controlled upper continental crust is a challenging task. The results from structural, fluid inclusion, Sr isotope, petrographic and mineralogical studies of the Terranera Fe-hydrothermal mineralisation, considered an exhumed palaeo-geothermal system, describe how hot to super-hot fluids were controlled by the increased permeability resulting from the interplay between low-angle normal faults and high-angle oblique-slip faults, the latter being part of a regional transfer zone (Zucchi et al., 2024). The study area is located in the eastern Elba Island (northern Tyrrhenian Sea, Italy), where the emplacement of a Messinian felsic intrusion has allowed hydrothermal fluids to circulate in relation to a fault-related permeability of the order of 10-15 to 10-13 m2. Magmatic fluids reacted with the host rocks (carbonate and phyllite) to form Fe-ore deposits hosted within the fault zones that controlled the fluid flow. Fluid inclusions trapped in quartz crystals indicate that the fluids consisted of saline solutions (salinity from 18.0 to 26.6 wt.% NaCl eq.), which later mixed with low salinity waters of probable meteoric origin. The fluid temperature during the main hydrothermal stage ranged between about 300° and 360°C under an estimated maximum hydrostatic pressure of 28–30 MPa. In contrast, the maximum possible temperature was about 400°C at a lithostatic pressure of 89 MPa. The hydraulic breccias formed as a result of the transient fluid pressurisation up to lithostatic values, due to the self-sealing process and the subsequent pressure drop, down to hydrostatic values, as framed in the hydrofracturing processes. The results provide useful input for the identification of geothermal and ore body targets in those geological settings where fluids of magmatic and meteoric origin are controlled by active faults in an extensional tectonic regime. Zucchi M. et al. (2024) - Migration of hot to super-hot palaeo-fluids in an extensional setting (eastern Elba Island, Italy). Tectonophysics, 874, 230210, https://doi.org/10.1016/j.tecto.2024.230210.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
