Metal Stable Isotopes in Paleoceanography

Abstract

Considered esoteric only a few years ago, research into the stable isotope geochemistry of transition metals is moving into the geoscience mainstream. Although initial attention focused on the potential use of some of these nontraditional isotope systems as biosignatures, they are now emerging as powerful paleoceanographic proxies. In particular, the Fe and Mo isotope systems are providing information about changes in oxygenation and metal cycling in ancient oceans. Zn, Cu, Tl, and a number of other metals and metalloids also show promise. Here we review the basis of stable isotope fractionation as it applies to these elements, analytical considerations, and the current status and future prospects of this rapidly developing research area.

Multiple sulphur and iron isotope composition of detrital pyrite in Archaean sedimentary rocks: A new tool for provenance analysis

“…Fe isotope fractionation occurs during redox changes, fluid-mineral interactions and biological processes (see Dauphas and Rouxel, 2006, Anbar and Rouxel, 2007 for recent reviews). While igneous rocks and siliciclastic sedimentary rocks with low carbon and sulphur contents have limited Fe isotope variations, diagenetic pyrites in Archaean black shales show highly variable and mostly negative values ranging from -3.5 to +0.5 ‰ (Rouxel et al, 2005;Yamaguchi et al, 2005;Archer and Vance, 2006).…”

Subduction fluxes through geologic time

“…Figure 1 (Anbar and Rouxel, 2007) provides a schematic view of the sequence from the production of oceanic crust at ridges to its subduction in convergent margins. The ocean crust matures through cooling and interaction with sea-water and also through hydrothermal exchange with cooling magma bodies in the deep ocean crust.…”

“…Inputs into the subduction factory from altered oceanic crust and entrained sediments. Adapted from Anbar and Rouxel (2007).…”

“…Below, I speculate on some consequences of changing subduction regimes through time. There are numerous examples, some are highly speculative, but there is a renewed interest in early Earth processes due to our abilities to apply new geochemical tracers to the early Earth (Anbar and Rouxel, 2007) and I hope we will soon be able to apply firm constraints to some of the speculations below.…”

“…High U/Pb mantle sources may not have been formed until the Proterozoic. Indeed, they may have been formed preferentially in the Proterozoic when large quantities of Fe, U, and other elements susceptible to oxidation (e.g., molybdenum- Anbar and Rouxel, 2007) were sequestered on the ocean floor and thus made available for input to the subduction factories of the Proterozoic.…”