Tcctonophysics, 41 (1977) 101-112 @ Elsevier Scientific Publishing Company, Amsterdam -. Printed in The Netherlands 101 HEAT-FLOW MEASUREMENTS ON THE NORTHERN APENNINE ARC M. BOCCALETTI *, M. FAZZUOLI l, M. LODDO 2 and F. MONGELLI z ’ ktituto di Gcologia dell’linioersita di Firenzc, 50121 Firenze (Italy) 2 Istituto di Gcodcsia c Geofisica dell’Uniuersita di Bari, 70100 Bari (Italy) (Received February 10, 1977) ABSTRACT Boccaletti, M., Fazzuoli, M., Loddo, M. and Mongelli, F., 1977. Heat-flow measurements on the Northern Apennine arc. In: A.M. Jessop (editor), Heat Flow and Geodynamics. Tectonophysics, 41: 101-112. Temperature and thermal-conductivity measurements have been carried out for six boreholes along a profile crossing the Northern Apennine chain. The heat flow varies from 95 mWmM2 in Tuscany to 23 mWmu2 in Romagna. In the light of global tectonics these values support the hypothesis that the Northern Apennine chain is a continental arc with high heat flow in the retroarc basin (Tuscany) and low heat flow in the trough (Romagna). INTRODUCTION The Northern Apennine chain is very interesting from a geodynamic point of view. Its arcuate shape, complicated geology, seismicity and geothermal fields have drawn the attention of many geologists, but few geophysical surveys have been made. The present work is a contribution to the knowledge of geophysical aspects of the Northern Apennines. A set of preliminary heat-flow measurements have been carried out in six boreholes located within a narrow zone crossing the Apennines from the Tyrrhenian Sea to the Adriatic Sea. GEOLOGICAL SETTING The Northern Apennine chain is a folded continental arc, formed by a series of tectonic units superimposed during the erogenic phases of Alpine- Apennine age (Fig. 1). These units may be grouped in the following main complexes according to their tectonic position (from top to bottom) and to their original paleogeographic location (from east to west). (Abbate et al., 1970; Ogniben et al., 1973; Elter, 1973). (1) Post-erogenic and late-erogenic complexes, deposited after the main tectonic phase of Tortonian age (Units la-d of Fig. 1). During Pliocene