Structural pattern and CO 2–CH 4 degassing of Ustica Island, Southern Tyrrhenian basin

• Published in: Journal of volcanology and geothermal research Vol. 88; no. 4; pp. 291 - 304
• Main Authors: Etiope, G, Beneduce, P, Calcara, M, Favali, P, Frugoni, F, Schiattarella, M, Smriglio, G
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1999
• Subjects: Active structures; Mesostructural analyses; Pleistocene volcanics; Soil gases; Active structures; Mesostructural analyses; Soil gases; Pleistocene volcanics
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/S0377-0273(99)00010-4

Brittle tectonics and ground degassing, including fracture-field, soil–gas and exhalation flux analyses of CO 2 and CH 4, were studied at Ustica Island, a Pleistocene volcanic complex in the Southern Tyrrhenian Sea. The mesoscopic fracture pattern perfectly fits an E–W-trending left-lateral strike–slip master fault, in agreement with the main morpho-structural submarine alignment including Ustica Island and Anchise Seamount. Along the SW–NE high-angle normal Arso Fault, geological evidence of reactivation with different kinematics (left- to right-lateral displacements) was recognised. Major CO 2 and CH 4 degassing (with fluxes up to 93,750 and 20 t km −2 a −1, respectively, and soil–gas concentrations of 11.3% and 5.7 ppm) occur over the Arso Fault. Although this fault is mapped just in the SW sector of the island, soil–gas CO 2 anomalies point out its clear continuation up to the NE margin of the island. These data, together with those of previous geophysical and geochemical results from off-shore Ustica, suggest that the Arso Fault is the local evidence of a more important active, gas-bearing structure. This tectonic feature is interpreted as a reactivation of a preexistent SW–NE trend, inherited as a second-order structure of the E–W deep shear zone. The reactivation is related to the interplay among different structures of the Southern Tyrrhenian basin.