In-situ Charakterisierung von Spurenelement-Signaturen, mit besonderer Berücksichtigung der REE Gehalte, Ca-reicher Mineral- und Fluid-Einschlüsse in Diamanten einer Fundstelle mit supertiefem Ursprung.
Zusammenfassung der Projektergebnisse
The aim of the project was to characterize the trace element signature, including REE pattern of inclusions in diamonds from super-deep sources. As in-situ techniques like S-XRF, which allow to measure inclusions without the need of polishing, have detection limits of a few ppm, the plan was to concentrate on Ca-rich phases and if available fluid inclusions. Several new and unexpected findings led to a thematic extension towards the origin and processes of non-carbonaceous mineral phases involved. The publications which are based on the outcome of this project show that: a) Breyite, a common Ca-rich inclusion in diamonds having a super-deep origin can be formed by a larger number of processes and pathways, which are not restricted to the lower mantle as back transformation from a precursor CaSiO3 perovskite, b) Raman-spectroscopy is a very powerful tool to identify Ca-rich inclusions and their paragenetic phases, c) the peridotitic composition and hydrous conditions extend at least across the transition zone and into the lower mantle. This is based on the petrological character of the inclusions ringwoodite (∼Mg1.84Fe0.15SiO4) which broke down into bridgmanite (∼Mg0.93Fe0.07SiO3) and ferropericlase (∼Mg0.84Fe0.16O) in a water-saturated environment at the 660 km discontinuity, d) in contrast to previous findings diamonds can be transported downwards in a subducting slab after formation and trapping of mineral phases, e) in some cases, Breyite found as inclusion in diamond was indeed trapped as CaSiO3-pervoskite and transformed to its lower pressure polymorph during ascend, which is in contrast to previous calculations that diamond should not be able to compensate the large volume change between these CaSiO3-polymorphs. Further results of the project, for which manuscript drafts are written and will be submitted soon are: a) the finding of several high-pressure Ca-phosphates (tuite) as inclusion in diamond from different tectonic settings in the upper and lower mantle tracking the Earth´s deep phosphorous cycle. b) Complex Ti-rich Ca-silicate an carbonate compound inclusions, which include Ti-bearing phases like CaTiO3-perovskite and CaTiSiO5-titanite. We are able to show that the Ti-content of Ca(Si,Ti)O3-perovskite solid solution determines at which pressures the phases stabilize ranging from <5 GPa at CaTiO3-rich to ~13 GPa at the CaSiO3-rich end. The Ti-rich mineral assemblage determined within this specific diamond gives evidence for phase stabilization within upper mantle depths indicating that the phases have been trapped as direct crystallization products at a pressure of ~9 GPa from a Ti-bearing, Ca-rich lithology within the upper mantle at a depth of about 250 km. In summary, our work on Ca-rich and other related inclusions in diamonds having a super deep origin extended our knowledge and understanding of deep Earth processes like the global phosphorus cycle, the transport of sedimentary and crustal components and the deep water storage.
Projektbezogene Publikationen (Auswahl)
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Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist, 106(1), 38-43.
Brenker, Frank E.; Nestola, Fabrizio; Brenker, Lion; Peruzzo, Luca & Harris, Jeffrey W.
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Hydrous peridotitic fragments of Earth’s mantle 660 km discontinuity sampled by a diamond. Nature Geoscience, 15(11), 950-954.
Gu, Tingting; Pamato, Martha G.; Novella, Davide; Alvaro, Matteo; Fournelle, John; Brenker, Frank E.; Wang, Wuyi & Nestola, Fabrizio
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Raman Identification of Inclusions in Diamond. Reviews in Mineralogy and Geochemistry, 88(1), 451-473.
Smith, Evan M.; Krebs, Mandy Y.; Genzel, Philomena-Theresa & Brenker, Frank E.
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Ringwoodite and zirconia inclusions indicate downward travel of super-deep diamonds. Geology, 50(9), 996-1000.
Lorenzon, Sofia; Novella, Davide; Nimis, Paolo; Jacobsen, Steven D.; Thomassot, Emilie; Pamato, Martha G.; Prosperi, Loredana; Lorenzetti, Alessandra; Alvaro, Matteo; Brenker, Frank; Salvadego, Franco & Nestola, Fabrizio
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Geobarometric evidence for a LM/TZ origin of CaSiO3 in a sublithospheric diamond. Geochemical Perspectives Letters, 25, 41-45.
Genzel, P.-T.; Pamato, M.G.; Novella, D.; Santello, L.; Lorenzon, S.; Shirey, S.B.; Pearson, D.G.; Nestola, F. & Brenker, F.E.
