The P-wave velocity structure of the mantle below the Iberian Peninsula: evidence for subducted lithosphere below southern Spain

Abstract

Abstract The P-wave velocity structure of the mantle below the Iberian Peninsula is investigated with the method of delay-time tomography. More than 200,000 delay-times are inverted for simultaneous estimates of P-wave velocity anomalies, event mislocation and origin time errors, and station corrections. Below the Betic-Alboran area we find a positive anomaly between 200 and 700 km depth which in shape and amplitude resembles the image of a subducted lithosphere slab. Laterally this anomaly exhibits a clear SW-NE trend. In view of the low level of spatial resolution encountered we focus in our analysis on assessing the reliability of the slab-like image. Arguments in favor of the existence of a slab structure in the upper mantle are developed from inversions of subsets of the data. The resolving power for imaging a slab below the Betic-Alboran region is investigated using sensitivity analyses with a velocity model for a subducted slab. We conclude that a slab-structure exists in the mantle below the Betic and Alboran region and that it can be imaged with sufficient reliability. We interpret the anomaly as the image of subducted lithosphere. The slab is presumably detached from the surface. We propose that subduction took place during at least part of the Oligocene followed by slab detachment in the early Miocene.