Cabo Ortegal Complex

The Cabo Ortegal Complex is known to the mantle community for its ultramafic massifs that preserve some of the best outcrops of pyroxenite among orogenic massifs worldwide. The Herbeira massif of the Cabo Ortegal Complex preserves abundant primitive pyroxenites that intruded into mantle peridotites. It is a unique example of a delaminated arc root exhumed through a subduction zone.

PhD theses at Macquarie University

This locality was the case study of my PhD project (2013-2017), and of the related PhD project of H. Henry (2014-2018), both as co-tutelle between Macquarie University (Sydney, Australia) and Université Paul Sabatier (Toulouse, France) funded by international Macquarie Research Excellence Scholarships (iMQRES).

My thesis Petrology and geochemistry of pyroxenites from the Cabo Ortegal Complex, Spain (Tilhac, 2017) provided a systematic classification of the variety of pyroxenites in Cabo Ortegal and showed that they are characterized by high CaO/Al₂O₃ and LILE/HFSE, and crystallized from Ca-rich picritic/boninitic parental melts (Tilhac et al., 2016). Their REE and radiogenic-isotope compositions reflect the role of melt-peridotite interaction and slab-derived metasomatic fluids in the evolution of primary arc magmas at mantle depths (Tilhac et al., 2017, 2020).

Hadrien’s thesis Mantle pyroxenites: deformation and seismic properties focused on the pyroxenite microstructures, revealing that they all reacted to deformation in a similar way, independent of composition Henry_et al._2017. Petrofabrics suggested that layered pyroxenites can preserve structures and textures inherited from high-temperature deformation, could help to localize shearing, and may represent preferred pathways for later fluid percolation. His thesis also targeted peridotites and pyroxenites from the Trinity Ophiolite (California, USA).

Together, these works have contributed to understanding of the:

Petrogenesis of pyroxenites in the sub-arc mantle;
Overprint of subduction-related metasomatism and metamorphism;
Variability of source and timing of pyroxenite formation;
Formation of the continental crust and the recycling of elements within the Earth.
Deformation of pyroxenites in layered mantle domains;
Seismic properties of pyroxenite-rich mantle;

Links to articles

Tilhac, R., Ceuleneer, G., Griffin, W.L., O’Reilly, S.Y., Pearson, N.J., Benoit, M., Henry, H., Girardeau, J., Grégoire, M. 2016. Primitive arc magmatism and delamination: petrology and geochemistry of pyroxenites from the Cabo Ortegal Complex, Spain. Journal of Petrology, 57, 1921-1954. DOI Link to the PDF

Tilhac, R., Grégoire, M., O’Reilly, S.Y., Griffin, W.L., Henry, H., Ceuleneer, G. 2017. Source and timing of pyroxenite formation in the sub-arc mantle: Casestudy of the Cabo Ortegal Complex, Spain. Earth and Planetary Science Letters, 474, 490-502. DOI Link to the PDF

Henry, H., Tilhac, R., Griffin, W.L., O’Reilly, S.Y., Satsukawa, T., Kaczmarek, M.-A., Grégoire, M., Ceuleneer, G. 2017. Deformation of mantle pyroxenites provides clues to geodynamic processes in subduction zones: Case study of the Cabo Ortegal Complex, Spain. Earth and Planetary Science Letters, 472, 174-185. DOI Link to the PDF

Tilhac, R., Oliveira, B., Alard, O., Griffin, W.L., O’Reilly, S.Y., Schaefer, B.F., Alard, O., Ceuleneer, G., Afonso, J.C., Grégoire, M. 2020. Reworking of old continental lithosphere: Unradiogenic Os and decoupled Hf-Nd isotopes in sub-arc mantle pyroxenites. Lithos, 354-355, 105346. DOI Link to the PDF

7^th Orogenic Lherzolite Meeting

The mantle section of the Cabo Ortegal Complex was also recently the object of the pre-conference fieldtrip of the 7^th Orogenic Lherzolite Meeting, which I had the pleasure to co-organize. The fieldtrip was the opportunity to put together a fairly comprehensive field guide for the mantle section of the complex. The .pdf of the printed guide and an extended online version are both available on the conference website or directly on my personal webpage via the following links: