Illustrated Field Guide to the Geology of Cap de Creus

Argumento de Illustrated Field Guide to the Geology of Cap de Creus

In the early seventies, Jordi Carreras thesis on the general structural and metamorphic trends of the area and his later M.Sc. research on shear zones and mylonites can be regarded as a milestone for the Cap de Creus geology. Nowadays, and after 40 years of research, this area has become a worldwide reference place for structural geology. The main reason for this is the exceptional quality of outcrops and structures exposed. This fact, together with that in the nineties the Cap de Creus stood as one of the unique landscapes preserved in the Catalan coast, lead the Catalan Government to protect vast areas of the Cap de Creus Peninsula, designating the Cap de Creus Natural Park. This has been essential to avoid the landscape and outcrop destruction due to the rampant urbanization that took place since the sixties elsewhere along the eastern Spanish coast. However, some spectacular geological outcrops are located in areas that suffered from uncontrolled touristic development. This is the case of the Roses lighthouse area, which, to make matters worse, was not later included in the Cap de Creus Natural Park because of its closeness to urban areas.

The geological value of the Cap de Creus area lies on the fact that it displays a great variety of key structures. Most of the exposed structures are “self-explanatory” and there is no need for speculation or extrapolations.

The relevance of the Geology of the Cap de Creus was first disseminated internationally in 1979 with the International Conference on Shear Zones in Rocks (the 3rd precursor of the present-day DRT meetings). From Catalan universities, Pere Santanach, Vicente Morales, Joan Manel Orta, Mariona Losantos, Joan (Ramírez) Palau, Josep Maria Casas, Amparo García-Celma and Felip Ortuño joined the research in Cap de Creus. In the early nineties Elena Druguet started her research in the area that continues nowadays. Albert Griera also did his Ph.D. thesis in this area. Many foreign researchers have visited the region, some of them being involved in research. Among them, Stan White and Carol Simpson were the first to collaborate with Jordi. Later, Gerard Bossière, Donny Hutton, Cees Passchier, Pia Victor, Paul Bons, Ian Alsop, Peter Hudleston, Dyanna Czeck and Isadora Mariani have collaborated with the MIET research group. Others, like Sandra Piazolo and Florian Fusseis, impressed by the suitability of the structures, also performed their investigations here.

Pere Enrique, K.W. Damm, Joan Carles Melgarejo, Mercè Corbella, Pura Alfonso, Montserrat Liesa and Marina Navidad have also done research in Cap de Creus from the petrological, mineralogical or geochronological perspectives, particularly devoted to the study of the pegmatite dyke swarm and the pre-Variscan igneous rocks.

An outstanding quality of the area is that it allows conclusions to be drawn that are beyond the regional interest, it is simply full of textbook examples of structures. Most of the thematic subjects are related to shear zones. One of the first papers relating folds in a shear zone with shear sense came out in 1973 using examples from the Cala Prona - el Llimac shear zone. Later, accurate studies on sheath fold evolution were presented using examples from here. The first published example of shear bands was taken from the Cala Sardina shear zone. A better understanding of the peculiarities of shear zones in foliated rocks was also based on Cap the Creus examples. In 1977, the relationship between fabric asymmetries and shear sense was first reported at the Leiden Conference (DRT precursor), using quartz-mylonite fabrics from this area. The subsequent discussion on c-axis quartz fabric rotations versus constant orientation with regard to the shear plane was based on published data from Cap de Creus. The present-day ongoing discussion of shear zones nucleating as buckling instabilities or evolving from brittle precursors is based, among others, on Cap de Creus examples.

More recently, Cap de Creus has furnished many examples of the problems associated with relating local strain regime with regional strain, and the complex relations between rock symmetries and asymmetries and kinematics. It has also provided important insights into the relationships between deformation, metamorphism, anatexis and magmatism, and the significance of some magmatic structures, such as the apparent boudinage of dykes and anatectic leucosomes. Another aspect that transcends the regional interest of the area is the well documented LP/HT metamorphism and granitoid emplacement in a transpressive regime.

The area is well suited to educational and research purposes. Each year many Universities visit Cap de Creus, where teaching and research will likely continue and increase in the coming years. As Win Means stated when he visited the area, a detail study of an appropriate square meter can furnish enough information to develop a whole Ph.D. thesis. The authors of this guide are ready to continue their research in Cap de Creus and are open to collaborate with researchers that share the same enthusiasm and dedication.0