HEAT-FLOW IN THE VALENCIA TROUGH - GEODYNAMIC IMPLICATIONS

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 +/- 4 mW/m2 to the north of Menorca to 88 +/- 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.