Geothermal and rheological regime in the Po plain sector of Adria (Northern Italy)

Alfio Viganò(1), Bruno Della Vedova(2), Giorgio Ranalli(3), Silvana Martin(4) & Davide Scafidi(5)
(1) Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Trento, Via Mesiano, 77 - 38123 Trento, Italy. Corresponding author: E-mail: alfio.vigano@ing.unitn.it; tel: +39 0461 282610; fax: +39 0461 282672. (2) Dipartimento di Ingegneria Civile e Architettura, Università degli Studi di Trieste, Via Valerio, 10 - 34127 Trieste, Italy. (3) Department of Earth Sciences and Ottawa-Carleton Geoscience Centre, Carleton University, 1125 Colonel By Drive, Ottawa K1S 5B6, Canada. (4) Dipartimento di Geoscienze, Università degli Studi di Padova, Via Gradenigo, 6 - 35131 Padova, Italy. (5) DipTeRis, Università degli Studi di Genova, Viale Benedetto XV, 5 - 16132 Genova, Italy.

We present a thermo-rheological study of the Adriatic crust in the central Po plain (Northern Italy), which records the convergence of the Alpine and Apennine external fronts. The present thermal regime of the crust is inferred from geological and geophysical data from oil exploration. A set of temperature data from 37 deep boreholes (bottom hole, drill stem, and production test temperatures) is used to estimate undisturbed formation temperatures down to 6-7 km of depth. Best quality data are used to estimate upper crustal geotherms, which are subdivided into four groups taking into considerations the following factors: i) presence/absence of relevant fluid circulation; ii) conductive thermal refraction; iii) recent sedimentation, and iv) other disturbing tectonothermal processes (e.g., recent tectonics). Assuming average corrections for temperature data affected by recent sedimentation effects, geotherms fall within the same range and provide a homogeneous thermal signal. Temperature measurements in the upper ~7 km are used to constrain a 1-D thermal model at the crustal scale. The best fitting geotherm gives a thermal gradient of ~23 ± 5 mK m-1 (over 7 km of depth), a surface heat flow of ~46 ± 9 mW m-2, and an estimated Moho temperature of 620 ± 80 °C. Using the estimated crustal structure and composition and the best-fitting geotherm, a representative strength envelope is obtained. For hydrostatic and supra-hydrostatic pore pressures, the calculated total crustal strength of this sector of the Adria microplate (not including the upper mantle contribution) is in the 1.8-2.5 TN m-1 range. Considering also the lithospheric mantle contribution, the total lithospheric strength is estimated to be between 23 (wet peridotite) and 39 (dry peridotite) TN m-1.

Temperature measurements, Deep boreholes, Geothermal gradients, Moho temperature, Crustal rheology, Adriatic crust.