Fluid-flow in the - palaeogeothermal system: insights for the Larderello- field Domenico Liotta(1), Andrea Brogi(2), Paolo Fulignati(3), Giovanni Ruggieri(4) & Andrea Dini(5)

(1) Dipartimento di Geologia e Geofisica, Università di Bari, Via Orabona 4, 70125 Bari. (2) Dipartimento di Scienze della Terra, Università di Siena, Via Laterina 8, 53100 Siena. (3) Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, 56100 Pisa. (4) CNR- Istituto di Geoscienze e Georisorse, Via G. La Pira, 4, 50121 Firenze. (5) CNR- Istituto di Geoscienze e Georisorse, Via G. Moruzzi, 1 - 56124 Pisa (), PISA .

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g l Larderello A Pomarance-Radicondoli Basin es bid gre Ma Ionian Sea represents a continuous task for successful exploration of geothermal Serrazzano Castelnuovo Val di Cecina resources. The fluid-flow pathway in the Larderello-Travale geothermal field is Bacino di Serrazzano few understood and object of a timely debate METHODOLOGY: to study the past for understanding the Present. Fluid inclusions

Montieri Monterotondo Ciciano of hydrothermal minerals and geometry of the mineralised geological bodies. M.mo

Boccheggiano STUDY AREA: Montieri-Boccheggiano area where a close relation among Plio- Pleistocene magmatism, genesis of hydrothermal fluid and main Pliocene-Pleistocene Boccheggiano Fault normal faults (particularly the Boccheggiano Fault) have been highlighted.

Massa Marittima Hydrothermal mineralisation characterised by mixed sulphides have been also

0 7 Km exploited in sub-horizontal cataclasites developed during the Late Oligocene-

stratigraphic contact Quaternary continental deposits Late Miocene marine Tuscan Nappe Late Miocene, away from the Pliocene-Pleistocene normal faults. sediments (Late Trias - Cretaceous) Miocene normal fault

Quaternary volcanites Ligurian Units Tuscan Nappe: evaporites Pliocene-Quaternary (Middle Jurassic-Eocene) (Late Trias) normal fault Late Pliocene-Pleistocene Subligurian Unit continental deposits Magmatic rocks Ligurian and (Paleocene-Eocene) (Paleozoic-Eocene) geothermal area subligurian Units Early-Middle Miocene marine Tuscan Nappe sediments (Cretaceous-Early Miocene ) Location of the analysed samples AIM OF THIS STUDY is to verify the possible relationships between the hydrothermal circulation within the Pliocene-Pleistocene normal fault and that within the oldest cataclasites, Cataclasites far away up to 10 km. within the Tuscan Nappe

Cretaceous - Pelagic-turbiditic Early Miocene succession Jur. Late Middle Jur. carbonate succession Early Jurassic

a Late Trias Late evaporiti

Poggio Montieri

1000 Poggio Prugnoli 1000 900 900 800 800 700 700 600 600 500 500 400 400 600 300 300 500 200 500 200 100 400 100 400 0 0 300 300 quartz vein with Ligurian Unit Tuscan Nappe -100 200 -100 200 mixed sulphides Jurassic - Eocene evaporites 0 500 m Late Triassic -200 100 -200 100 WSW ENE -300 mineralized Tuscan Nappe Tectonic pile composed of -300 0 0 cataclasite pelagic-turbiditc succession phyllite and evaporite levels -400 -100 -400 -100 Cretaceous - Early Miocene Paleozoic - Late Triassic -200 -200 Tuscan Nappe carbonate succession -300 -300 Late Triasic - Cretaceous -400 WSW ENE -400

MAIN RESULTS are: a) The Oligocene-Miocene cataclasites were dissected by the Boccheggiano Fault. The Boccheggiano Fault also dissected the magmatic body emplaced at depth in the Montieri area. b) Fluid inclusions indicate that the hydrothermal fluids circulated in the Montieri-Boccheggiano system were composed of meteoric water which interacted with the Late Triassic evaporites. c) Fluid inclusions indicate that the hydrothermal fluids were progressively coldest moving away from the Boccheggiano METEORIC WATER CONTENT Fault. INCREASING TEMPERATURE d) The sub-horizontal cataclasites related to the stacking of the meteoric water mineralized cataclasite meteoric water Tuscan Nappe Tuscan Nappe (Late Oligocene-Early Miocene) and extensional Ligurian Unit erosion since 3.6 Ma tectonics (Middle-Late Miocene) represented the reservoirs for the hydrothermal fluids. carbonate tectonic The hydrothermal fluid-flow model provides a common fluid mine area breccias deep fluids circulating both in the damage zone of the Boccheggiano Fault and Palaeozoic phyllites in the oldest cataclasites dissected by the fault. The Boccheggiano Fault could represents the main conduit for both meteoric waters infiltration and hydrothermal fluids upwelling, which dispersed in granodiorite: 2.2 Ma the oldest cataclasites dissected by the faults.