Sr, Nd and Pb isotope constraints on the formation of the metalliferous sediments in the Nereus Deep, Red Sea

Delphine Bosch (1) , Joël Lancelot (1) , Jacques Boulègue (2)

1 UM2 - Université Montpellier 2 - Sciences et Techniques
2 Laboratoire de Géochimie et Métallogénie

Previous chemical analyses of sediments from Nereus Deep core 412, located in the northern part of the Red Sea at about 23°20′N, have demonstrated the occurrence of V-rich authigenic magnetites associated with Fe, Zn and Cu sulphides mostly located at the bottom of the core. The evolutionary stage of Nereus Deep is intermediate between that of the immature Shaban Deep and the more evolved Atlantis II Deep. Previous studies have proposed either MORB basalts (by analogy with East Pacific Rise sulphide deposits) or sediments as possible sources of the metals in the Red Sea metalliferous sediments. Sr, Nd and Pb isotope systematics, observed at ten levels in Nereus core 412, lead us to distinguish three types of sediments, (1) with predominantly basaltic fragments associated with loose titanomagnetite crystals (; ; ), (2) detrital or biogenic sediments with a continental isotopic imprint (; ; ), and (3) V-rich metalliferous sediments (; ; ). On SrNd and PbPb isotope diagrams this last group of sediments defines a field located between the fields of the first two groups. Our data suggest that the Sr, Nd and Pb in the studied metalliferous sediments were derived from overlying sedimentary beds in which the two main constituent detrital components show very distinct origins (Red Sea MORB and continental Arabo-Nubian Shield). These data clearly support a model of convective circulation within the Nereus Deep sedimentary pile. This model involves leaching two main components from the upper sedimentary layers of the core and a downward circulation of a hot fluid promoting the growth of V-rich magnetites and Fe, Zn and Cu sulphides when the fluid cooled by mixing with the pore water of sediments from the lower part of the core. A driving force, represented by magmatic activity located near the 412 core in the Nereus Deep, is required to explain the presence of hot convective fluids. These data also suggest that, for sedimented ridges, the isotopic imprint of a basaltic source in metalliferous sediments or a hydrothermal ore deposit may result by interaction of a hot fluid with detrital sediments that are enriched in basaltic clasts and loose magmatic crystals.

Domaines: Géochimie

Delphine Bosch, Joël Lancelot, Jacques Boulègue. Sr, Nd and Pb isotope constraints on the formation of the metalliferous sediments in the Nereus Deep, Red Sea. Earth and Planetary Science Letters, 1994, 123 (1-3), pp.299-315. ⟨10.1016/0012-821X(94)90275-5⟩. ⟨hal-03878329⟩