Nd–Sr isotope and REY geochemistry of metalliferous sediments in a low-temperature off-axis hydrothermal environment (Costa Rica margin)

• Published in: Marine geology 2012-06, Vol.315-318, p.132-142
• Main Authors: Steinmann, Marc, Bodeï, Sabine, Buatier, Martine
• Format: Article
• Language: English
• Subjects: 143Nd/144Nd; 87Sr/86Sr; authigenic minerals; Cocos plate; Earth Sciences; Environmental Sciences; Geochemistry; Global Changes; low-temperature hydrothermalism; rare earth elements; Sciences of the Universe
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/j.margeo.2012.04.005

Metalliferous deposits are ubiquitous in marine sediments and play a major role in the elemental cycles of iron, manganese, and other trace elements. The metalliferous sediments studied here were sampled near a basaltic seamount named “Dorado”, on the eastern flank of the East Pacific Rise, west of Nicoya Peninsula (Costa Rica). Based on heat flow data and porewater profiles, this site is an area of active low-temperature hydrothermal discharge. Most samples are from gravity core GC50, which is characterized by the presence of abundant authigenic minerals (mainly Fe–Mn-oxyhydroxides and apatites). Our data suggest that these minerals have initially precipitated during the Miocene from a high-temperature hydrothermal plume when the Dorado site was located near the East Pacific Rise. With increasing distance from the ridge axis, the plume precipitates were buried under hemipelagic sediments. After the onset of the present-day low temperature hydrothermal activity these precipitates were dissolved and re-precipitated higher up in the sediment pile to form the observed assemblage of authigenic minerals. The study thus shows that the metalliferous deposits of the Dorado seamount have a very complex origin, which could be unraveled by a combined approach based on Nd–Sr isotopes, REY data (rare earth elements and yttrium), and mineralogical observations. ► Metalliferous sediments from the Cocos plate (offshore Costa Rica) were studied. ► The site is in an area of active low-T hydrothermal discharge. ► Sediments contain authigenic Fe–Mn oxyhydroxides and apatite. ► Sm–Nd isotopes and REY data show a seawater signature for these authigenic phases. ► We interpret the data by remobilization of high-T plume deposits by low-T hydrothermalism.