2016 PSPA - Juvenal Andrés - Curie-depth and thermal gradient map of the Iberian Peninsula and surrounding areas

The distribution of temperature at depth is a combination of past and present processes such as, collisions, thickening and thinning of the crust or subduction. Furthermore, the thermal structure of an area is dependent on the physical properties of the rocks (e.g. petrology, radiogenic heat production and thermal conductivity), hindering its understanding. The Curie point (CP) is the temperature at which magnetic minerals become paramagnetic. For the upper part of the lithosphere, the most abundant magnetic mineral is the magnetite, which has a CP of 580°C. Therefore, if we can calculate the depth at which we lose the magnetic signal we can get the depth of 580ºC isotherm. 

In this study, we have calculated a complete map of the Curie-Depth Point (CDP) (Fig.1) from a compilation of aeromagnetic data for the Iberian Peninsula and surrounding offshore areas by means of spectral analysis. The final magnetized layer appears on the range of 13 km to 27 km depth below topography onshore and bathimetry offshore. As expected, this isotherm is shallow in offshore zones, where the crust is thinner while in continental areas, the CDP appears deeper. 

We have compared our results with a Moho depth map of the same area. Offshore, the CDP is usually located beneath the Moho which may imply a magnetic upper mantle, partly formed by serpentinites. This serpentinized upper mantle might have played an important role in the evolution of some areas like the Western Mediterranean. On the contrary, for continental areas the CDP is located above the Moho, with NW Iberia featuring the deepest CDP values. We correlate these values with the late orogenic Variscan evolution that led to crustal thinning and intense thermal metamorphism that melted and re-equilibrated the crust. Finally, we have derived a complete map of the thermal gradient of the Iberian Peninsula and offshore areas.

Figure 1. Final distribution of calculated CDP (black dots) overlapped on ETOPO1 with major geological boundaries.

This work is supervised by Ramon Carbonell (ICTJA-CSIC) and Puy Ayarza (USAL). Economic support has been provided through CGL2014-56548-P project funded by the Spanish Ministry of Science and Innovation. We acknowledge GETECH Group Plc. for providing the magnetic data for the study.