Abstract
Independent models of P wave and S wave velocity anomalies in the mantle derived from seismic tomography help to distinguish thermal signatures from those of partial melt, volatiles, and compositional variations. Here we use seismic data from SW Europe and NW Africa, spanning the region between the Pyrenees and the Canaries, in order to obtain a new S-SKS relative arrival-time tomographic model of the upper mantle below Iberia, Western Morocco, and the Canaries. Similar to previous P wave tomographic results, the S wave model provides evidence for (1) subvertical upper-mantle low-velocity structures below the Canaries, Atlas Ranges, and Gibraltar Arc, which are interpreted as mantle upwellings fed by a common lower-mantle source below the Canaries; and (2) two low-velocity anomalies below the eastern Rif and Betics that we interpret as the result of the interaction between quasi-toroidal mantle flow induced by the Gibraltar slab and the mantle upwelling behind it. The analysis of teleseismic P wave and S wave arrival-time residuals and the conversion of the low-velocity anomalies to temperature variations suggest that the upwellings in the upper mantle below the Canaries, Atlas Ranges, and Gibraltar Arc system may be solely thermal in nature, with temperature excesses in the range ~100–350 °C. Our results also indicate that local partial melting can be present at lithospheric depths, especially below the Atlas Ranges. The locations of thermal mantle upwellings are in good agreement with those of thinned lithosphere, moderate to high heat-flow measurements, and recent magmatic activity at the surface.
| Original language | English |
|---|---|
| Pages (from-to) | 1781-1801 |
| Number of pages | 21 |
| Journal | Journal of Geophysical Research: Solid Earth |
| Volume | 124 |
| Issue number | 2 |
| Early online date | 10 Jan 2018 |
| DOIs | |
| Publication status | Published - Feb 2019 |
Funding
The present research is supported by the Fundação para a Ciência e a Tecnologia under the Project SPIDER (PTDC/GEO‐FIQ/2590/2014). We would like to thank the many scientists involved in the collection of data used in this study. Most of the data provided for this study are archived at the ORFEUS data center (https://www. orfeus‐eu.org). The Instituto Geográfico Nacional (Spain) provided us with restricted seismic data recorded from stations deployed in the Canary Islands (http://www.ign.es/web/ign/portal), and NEAREST OBS data are available upon request ([email protected]). The seismic experiments/projects involved are the Catalan Seismic Network (Institut Cartogràfic i Geològic de Catalunya‐Institut d'Estudis Catalans, 1996), Geofon (GEOFON Data Centre, 1993), MedNet (MedNet Project Partner Institutions, 1990, January 1), the Western Mediterranean Seismic Network (San Fernando Royal Naval Observatory (ROA) et al., 1995), PICASSO (Levander et al., 2009), IberArray (Institute Earth Sciences "Jaume Almera" CSIC (ICTJA Spain), 2007), the University of Munster (Thomas, 2010), and WILAS (Dias et al., 2010). The 3D P wave and S wave tomographic models are available for download as a digital supplement. We thank Saskia Goes for her constructive comments, which helped us improve our manuscript. Thanks to Javier Fullea for providing the surface heat flow compilation and the lithospheric thickness values to build Figure 9 and Catarina Matos for providing us with the geological units in GMT format to plot Figure 1.
| Funders | Funder number |
|---|---|
| Catalan Seismic Network | |
| Institut Cartogràfic i Geològic de Catalunya-Institut d'Estudis Catalans | |
| Instituto Geográfico Nacional | |
| University of Munster | |
| WILAS | |
| Western Mediterranean Seismic Network | |
| Fundação para a Ciência e a Tecnologia | PTDC/GEO‐FIQ/2590/2014 |
| Consejo Superior de Investigaciones Científicas |
Keywords
- Ibero-western Maghreb region
- Lower-upper mantle connection
- Quasi-toroidal mantle flow
- Relative arrival-time residuals
- S-wave tomography
- Thermal mantle upwellings
