Mineralogy and chemical composition of ferromanganese crusts from the Cruzeiro do Sul Lineament - Rio Grande Rise, South Atlantic

Type Article
Date 2021-06
Language English
Author(s) Sousa I.M.C.1, Santos R.V.1, Koschinsky A.2, Bau M.2, Wegorzewski A.V.3, Cavalcanti J.A.D.4, Dantas E.L.1
Affiliation(s) 1 : Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, 70910-900, Brasília – DF, Brazil
2 : Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany
3 : BGR , Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655, Hannover, Germany
4 : CPRM , Geological Survey of Brazil, Av. Brasil 1731, 30140-002, Belo Horizonte, MG, Brazil
Source Journal Of South American Earth Sciences (0895-9811) (Elsevier BV), 2021-06 , Vol. 108 , P. 103207 (18p.)
DOI 10.1016/j.jsames.2021.103207
WOS© Times Cited 11
Keyword(s) Rio grande rise, Ferromanganese crusts, Atlantic ocean, Cruzeiro do sul lineament, Phosphatization

Samples dredged from the Cruzeiro do Sul Lineament exhibit ferromanganese crusts precipitated above phosphate-rich substrates (phosphorites, phosphate-impregnated volcanic rocks and older phosphatized ferromanganese crusts). Co-chronology of the crusts, paleontological data and 87Sr/86Sr ratios of the phosphatized substrate indicate that the last phosphatization event in the region happened between 17.6 and 14.6 Ma ago. When the event ceased, oxic conditions were resumed and hydrogenetic crust precipitation started at a maximum rate of 1.6–3.0 mm/Ma, forming layers of Fe-vernadite above the phosphorites. These crusts differ in composition from crusts that formed prior to the phosphatization, which were impregnated by carbonate fluorapatite and recrystallized forming a 10 Å Mn-phase, in expense of a lower crystallinity Mn-phase. Mn/Fe ratios of non-phosphatized crusts vary from 1.05 to 1.41. The Mn/Fe ratios as well as the metal content (Co = 0.65–1.04 wt%, Zn = 0.04–0.06 wt%, Cu = 0.02–0.06 wt% and Ni = 0.29–0.48 wt%) are similar to hydrogenetic crusts described in other parts of the world.

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Sousa I.M.C., Santos R.V., Koschinsky A., Bau M., Wegorzewski A.V., Cavalcanti J.A.D., Dantas E.L. (2021). Mineralogy and chemical composition of ferromanganese crusts from the Cruzeiro do Sul Lineament - Rio Grande Rise, South Atlantic. Journal Of South American Earth Sciences, 108, 103207 (18p.). Publisher's official version : https://doi.org/10.1016/j.jsames.2021.103207 , Open Access version : https://archimer.ifremer.fr/doc/00679/79086/