Molybdenum-isotope signals and cerium anomalies in Palaeoproterozoic manganese ore survive high-grade metamorphism

0504100 - GLÚ 2020 RIV GB eng J - Journal Article
Cabral, A. R. - Zeh, A. - Vianna, N. C. - Ackerman, Lukáš - Pašava, J. - Lehmann, B. - Chrastný, V.
Molybdenum-isotope signals and cerium anomalies in Palaeoproterozoic manganese ore survive high-grade metamorphism.
Scientific Reports. Roč. 9, č. 1 (2019), č. článku 4570. ISSN 2045-2322. E-ISSN 2045-2322
R&D Projects: GA ČR(CZ) GA17-15700S
Institutional support: RVO:67985831
Keywords : molybdenum * Cambrian * Mo isotope
OECD category: Geology
Impact factor: 3.998, year: 2019
Method of publishing: Open access
https://www.nature.com/articles/s41598-019-40998-5

Molybdenum (Mo) and its isotopes have been used to retrieve palaeoenvironmental information on the ocean–atmosphere system through geological time. Their application has so far been restricted to rocks least affected by severe metamorphism and deformation, which may erase or alter palaeoenvironmental signals. Environmental Mo-isotope signatures can be retrieved if the more manganese (Mn)-enriched rocks are isotopically depleted and the maximum range of δ⁹⁸Mo values is close to the ~2.7‰ Mo-isotope fractionation known from Mo sorption onto Mn oxides at low temperature. Here, we show that the Morro da Mina Mn-ore deposit in Minas Gerais, Brazil, contains Mn-silicate–carbonate ore and associated graphitic schist that likely preserve δ⁹⁸Mo of Palaeoproterozoic seawater, despite a metamorphic overprint of at least 600 °C. The extent of Moisotope fractionation between the Mn-silicate–carbonate ore and the graphitic schist is similar to modern Mn-oxide precipitates and seawater. Differences in δ⁹⁸Mo signals are broadly reflected in cerium (Ce) anomalies, which suggest an oxic–anoxic-stratified Palaeoproterozoic ocean.
Permanent Link: http://hdl.handle.net/11104/0295803