Τίτλος:
The Methana Volcano – Geothermal Resource, Greece, and its relationship to regional tectonics
Γλώσσες Τεκμηρίου:
Αγγλικά
Περίληψη:
Geophysical methods of analysis were applied, in order to investigate the deep structure and the geothermal potential of the Methana Volcano (NE Peloponnesus, Greece). The study is based on a re-evaluation and reinterpretation of legacy magnetotelluric (MT) data with modern analysis methods, as well as 3-D inversion of aeromagnetic data constrained by in situ measurements of magnetic susceptibility. Magmatic systems are located in regions of active tectonic processes that often play a controlling role. The MT method is effective in delineating low resistivity functional elements of volcanic systems, such as magma chambers, vents, thermal fluid reservoirs and thermal fluid circulation conduits, the latter two of which are typically associated with active faults. The aeromagnetic data can assist in mapping the configuration, hence emplacement modes of volcanic rocks at depth. Accordingly, the joint interpretation of these lines of evidence, together with structural and geochemical information, is expected to allow insight into the influence of contemporary tectonics on the inception and evolution of the volcano. The contemporary stress field is mainly extensional, NNE-SSW oriented and overall homogeneous; in the area of Methana it allows for the formation of WNW-ESE north-easterly dipping normal faults, W-E faults consistent with the synthetic (dextral) R-shear direction of Riedel's shear theory and NW-SE faults consistent with the antithetic (sinistral) R′-shear direction; all such features have been mapped on Methana Peninsula. The magnetotelluric data imaged a significant geothermal reservoir developing around an intersection of the three active fault zones (normal, R and R′) at depths of 1–1.5 km below the centre of the peninsula, as well as elongate epiphenomenal conductivity anomalies associated with the circulation of thermal fluids along all three fault zones. The 3-D magnetic susceptibility model strongly suggests that the intrusion and emplacement of magmas were guided by the same active fault zones, with particular reference to the R and R′ shears whose influence is imprinted on the configuration of volcanic rocks at depth. The joint interpretation of all lines of evidence indicates that magmatism and volcanism at Methana are almost completely controlled by tectonic activity in a manner analogous to the situation of the large Santorini Volcanic Complex. It also indicates that the reservoir is replenished through the weak permeable zone created by the intersection of the R and R′ shears, which is very probably collocated with the main vent of intrusive magmatic activity and may connect with a shallow magma chamber at depths greater than 4.5 km. The apparently common origin and similarities/differences in the circulation paths of thermal fluids may amply explain both the individual characteristics and similarities/differences in the chemical composition of thermal spring discharges, which have been reported by hitherto geochemical investigations. © 2020 Elsevier B.V.
Συγγραφείς:
Tzanis, A.
Efstathiou, A.
Chailas, S.
Lagios, E.
Stamatakis, M.
Περιοδικό:
Journal of Volcanology and Geothermal Research
Λέξεις-κλειδιά:
Geochemistry; Geothermal fields; Geothermal springs; Magnetic susceptibility; Magnetotellurics; Petroleum reservoir evaluation; Volcanic rocks; Volcanoes, Chemical compositions; Conductivity anomalies; Geochemical investigations; Geothermal potential; Geothermal reservoir; Geothermal resources; Individual characteristics; Magnetotelluric data, Fault slips, aeromagnetic survey; geothermal system; inverse analysis; magnetic susceptibility; magnetotelluric method; tectonics; volcano, Greece
DOI:
10.1016/j.jvolgeores.2020.107035
