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University of Cambridge > Talks.cam > Bullard Laboratories Wednesday Seminars > Origin of carbonatites using the triple-isotope approach
Origin of carbonatites using the triple-isotope approachAdd to your list(s) Download to your calendar using vCal
If you have a question about this talk, please contact Megan Holdt. Carbonatites are rare carbonate-rich igneous rocks derived from carbon and carbonate-rich regions of Earth’s mantle. Although a number of igneous processes are recognized to have controlled their compositions, the origin of the carbonate-rich nature of these magmas remains debated and has been linked to various mantle-related processes, including subduction and plume–lithosphere interaction. High-precision isotope measurements can provide insights into carbonatite petrogenesis, including the identification of subducted crustal material in their source region. In particular, combining mass-dependent and kinetically corrected Mg isotope data, also known as the triple-isotope approach, provides insights into mass fractionation processes driving mass dependent fractionation, which in turn allows to distinguish between equilibrium and kinetic processes. In this work, we report high-precision Mg stable isotope data for 59 carbonatites and associated silicate rocks from different localities and ages ranging from 3000 Ma to present-day. In addition, we also report Mg isotope data for 17 Phanerozoic carbonate rocks, with the aim of identifying the isotopic signature of carbonate-rich material potentially recycled to the carbonatite mantle source regions. We observe positive residual deviations after kinetic mass fractionation correction of the Mg isotope data for our carbonatites; an isotope signal that is also present in Phanerozoic carbonates. This observation establishes that a component of the Mg present in these samples experienced mass-dependent equilibrium isotopic fractionation processes, which are significantly larger at low temperatures. Given that the Mg results do not covary with C and O isotopic signals, the magnitude of the fractionation following the equilibrium law observed in carbonatites provides strong evidence for recycled material from the Earth’s surface in the mantle source of Ca- and Mg-rich carbonatites. Furthermore, associated silicate rocks present mantle-like Mg isotopic compositions in contrast with the genetically linked carbonatites – based on the Sr isotopes – for some complexes, which is best explained if the carbonatites and associated silicate rocks represent distinct generation of partial melts of a mantle source containing recycled carbonate. This talk is part of the Bullard Laboratories Wednesday Seminars series. This talk is included in these lists:
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