Origin of chemical heterogeneities in the subcontinental lithospehric mantle: Insights from the westernmost Mediterranean orogenic peridotites and allied crustal rocks

Abstract

Understanding the mechanisms and processes responsible for the generation of mantle heterogeneities is crucial for improving our knowledge about the composition and differentiation of the Earth at different scales. Orogenic peridotite massifs provide an exceptional opportunity to investigate in situ the nature and scale of compositional mantle heterogeneities. This Ph.D. thesis aims to shed new light on the role of melt-rock reaction processes and recycling of oceanic and continental crustal material in creating chemical heterogeneities in the mantle. To achieve this objective, this study focuses on mantle rocks exposed in orogenic peridotites from the Betic-Rif Cordillera in the westernmost Mediterranean, and their allied crustal rocks. Two processes related to the development of geochemical heterogeneities in the Earth’s upper mantle are addressed in this work: (i) the formation of secondary lherzolites by melt-rock reaction processes, and (ii) the genesis of ultrahigh pressure garnet pyroxenites and its implications for crustal recycling into the mantle. Furthermore, this thesis explores (iii) to what extent Betic crustal rocks were involved in the geochemical signature of magmatism recorded in the subcontinental lithospheric mantle (SCLM), and in the Miocene Alborán Sea basin volcanism. The westernmost Mediterranean records an Alpine history of subduction and slab roll-back that resulted in the creation of the Alborán Sea basin. Mantle rocks and their allied crustal rocks in the Betic-Rif belt hence provide a unique natural laboratory for studying large scale recycling of crustal components in the SCLM.