Mapping the nature of mantle domains in Western and Central Europe based on clinopyroxene and spinel chemistry: Evidence for mantle modification during an extensional cycle
Abstract Systematic differences in mineral composition of mantle peridotites are observed in ophiolites and peridotitic bodies from the Alpine Tethys, the Pyrenean domain, the Dinarides and Hellenides, and the Iberia Newfoundland rifted margins. These differences can be understood in the context of the evolution of rifted margins and allow the identification of 3 major mantle domains: an inherited domain, a refertilized domain and a depleted domain. Most clinopyroxene from the inherited domain equilibrated in the spinel peridotite field and are too enriched in Na2O and Al2O3 to be residues of syn rift melting. Clinopyroxene from the refertilized domain partially equilibrated with plagioclase and display lower Na2O and Al2O3, and elevated Cr2O3 contents. The refertilized domain is a hybrid zone, which locally preserves remnants from the inherited domain and overlapping chemical compositions. Depleted domains with clinopyroxene similar to abyssal peridotites are rare and Nd isotopic studies indicate that they represent ancient periods of melting unrelated to the opening of the Jurassic and Cretaceous oceanic basins of the Alpine Tethys and southern North Atlantic. In many studied sections of mantle rocks in exposed ophiolites a systematic spatial distribution of the different domains with respect to the evolution of rifted margins can be identified. This new approach integrates observations from exposed and drilled mantle rocks and proposes that the mantle lithosphere evolved and was modified during an extensional cycle from post orogenic collapse through several periods of rifting to seafloor spreading. The defined chemical and petrological characteristics of mantle domains based on clinopyroxene and spinel compositions are compiled on present day and paleogeographic maps of Western and Central Europe. These maps show that the observed distribution of mantle domains are linked to processes related to late post Variscan extension, rift evolution and refertilization associated to crustal/lithospheric extension, and the development of embryonic oceanic domains.