Final Report Summary - EMAS (Geochemical study of hydrated and dehydrated ultramafic rocks from the Cerro del Almirez (southern Spain): implications for element mobilization in subduction zones and the composition of arc magmas)
Executive Summary:
The subduction zones are the margins of lithospheric plates where chemical elements are recycled on the global scale. Reactions involving volatiles are fundamental in order to understand the significance of the mass-transfer taking place in subduction zones, the origin of the chemical composition of the associated arc volcanism, and the physical properties of the rocks that control the dynamic behaviour of subduction settings. The main reactions that occur in the subducting plate include the dehydration and dehydration-melting reactions of oceanic sediments and igneous crust, the transition gabbro-eclogite in the oceanic crust, and the dehydration of serpentinite to chlorite harzburgite in the lithospheric mantle.
The ultramafic rocks of the Cerro del Almirez (southern Spain) consist of strongly foliated antigorite serpentinite and massive chlorite harzburgite with different microstructures. These rocks preserve unique examples of the dehydration reactions in serpentinite, including the dehydration reaction of antigorite to form olivine and enstatite that took place at ~ 2 GPa (~ 70 km) and 650 ºC. The results of this project has provided new insights into how chemical elements and radiogenic isotopes are mobilized during hydration and dehydration of serpentinite, how different sources of fluids participate in the formation of dehydrated serpentinite, and which minerals control the fractionation of trace elements during reaction and their transfer to the source regions of arc magmas. To achieve these goals, the researcher performed major, trace element and isotopic analyses of whole-rocks and minerals in samples representative of the lithological variability of the Cerro del Almirez. Moreover, he collaborated with leading scientists specialized in the geochemistry of volatiles (i.e. boron, water, carbon and sulphur) to evaluate the impact of serpentinite dehydration on the global cycles of these chemical species. Additional collaborations focused on the study of the physical mechanisms related to the production of serpentinite fluids, and on the thermobarometry of ultramafic rocks.
The experience acquired during the realization of the project has given the researcher a strong level of independence and the skills necessary to autonomously manage his research. The confidence attained with several cutting-edge geochemical techniques enabled him to build up fruitful collaborations with some of the best geochemical laboratories in the world and contribute to set up a new ultra-clean lab for isotopic analyses in the host institution. The results of the project have been presented in several of the most important international meetings and published in some of the top journals in Geosciences. Additional manuscripts using the data of the project are currently in preparation. This activity has been fundamental for the researcher to obtain a tenure track contract of 5 years at the University of Granada, with the commitment to be finally hired as permanent scientist.