Tectonophysics, 203 (1992) 11-97 Elsevier Science Publishers B.V., Amsterdam Heat flow in the Valencia trough: geodynamic implications J.P. Foucher a, A. Mauffret b, M. Steckler ‘, M.F. Brunet b, A. Maillard b, J.P. Rehault d, B. Alonso e, P. Desegaulx f, J. Murillas g and G. Ouillon a a Institut Franqais de Recherche pour I’Ekploitation de la Mer, B P 70, 29280 Plouzane, France b Groupe d’Etude de la Marge Continentale et de I’Ocean, URA 718, Universite’ Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris, France c Lament-Doherty Geological Observatory of Columbia Universify, Palisades, N.Y. 10964, USA d Universite’ de Bretagne Occidentale, 6 avenue Le Gorgeu, 29283 Brest Cedex, France e Institute de Ciencas de1 Mar, Paseo National, s/n, 08003 Barcelona, Spain f Institut Franqais du P&role, BP 311, 92506 Rueil-Malmaison Cedex, France s Institute of Earth Sciences “Jaume Almera”, Marti i Franques, s/n, 08028 Barcelona, Spain Received December 181990, revised version accepted April 24, 1991 ABSTRACI Foucher, J.P., Mauffret, A., Steckler, M., Brunet, M.F., Maillard, A., Rehault, J.P., Alonso, B., Desegaulx, P., Murillas, J. and Ouillon, G., 1992. Heat flow in the Valencia trough: geodynamic implications. In: E. Banda and P. Santanach (Editors), Geology and Geophysics of the Valencia Trough, Western Mediterranean. Tectonophysics, 203: 77-97. As part of the Valsis project, 110 heat-flow determinations were obtained in the axial, deep part of the Valencia trough during the Valsis 1 cruise of the R/V Le Suroit in 1988. The data gathered data provide a fairly comprehensive view of the regional heat-flow pattern. Regional heat flow increases from a value of 66 f 4 mW/m’ to the north of Menorca to 88 f 4 mW/m2 in the southern part of the rift between Valencia and Ibiza. A simple rifting model, assuming uniform stretching of the lithosphere during a single rifting event from 28 to 22 Ma ago, satisfactorily describes the observed heat flow and depth to sea floor in the northern part of the trough. In contrast, the southern Valencia trough has high heat flow and shallow sea floor that are difficult to reconcile with predictions of a uniform lithospheric stretching model even allowing for an initial elevation, a thin, hot lithosphere or a multi-episode history of rifting. Non-homogeneous lithospheric stretching models, assuming for example large-scale dike intrusion or a greater extension of the mantle than in the crust, provide potential explanations of the high heat flow and shallow sea floor in the southern Valencia trough. Yet, these models remain poorly constrained. Introduction The Valencia trough is an aborted rift formed during the opening of the western Mediterranean Sea (Biju-Duval et al., 1978; FontbotC et al., 1989; Maillard et al., 1992-this volume). The Valencia trough was created by the Late Oligocene-Early Miocene rifting of the Balearic promontory from the Spanish Meseta. As yet, the processes through which the trough was initiated and evolved to its present-day structure remain poorly understood. Correspondence to: J.P. Foucher, Institut Franfais de Recherche pour IExploitation de la Mer, B.P. 70, 29280 Plouzand, France. In this regard, the Valsis project has been a major step towards a better understanding of the deep structure of the trough and of the rifting processes that led to its formation. In addition to seismic studies (Maillard et al., 1992-this volume; Tome et al., 1992~this volume), the determination of the geothermal structure of the Valencia trough was a main objective of the Valsis project. This objective was chosen because the thermal struc- ture of basins formed by lithospheric extension is specific to the age of their formation and to the nature of the rifting processes (e.g., Royden and Keen, 1980; Buck et al., 1988; Louden et al., 1991). In this paper, we present the results of 110 successful heat-flow measurements made in the 0040-1951/92/$05.00 0 1992 - Elsevier Science Publishers B.V. All rights reserved