Geochemistry of Ocean Floor and Fore-arc Serpentinites: Constraints on the Ultramafic Input to Subduction Zones

• Published in: Journal of Petrology
• Main Authors: Kodolányi, János, Pettke, Thomas, Spandler, Carl, Kamber, Balz S., Gméling, Katalin
• Format: Text
• Language: English
• Published: Oxford University Press 2012
• Subjects: Original Papers; Mid-Atlantic Ridge; Hess; Newfoundland
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/53/2/235; https://doi.org/10.1093/petrology/egr058

We provide new insights into the geochemistry of serpentinites from mid-ocean ridges (Mid-Atlantic Ridge and Hess Deep), passive margins (Iberia Abyssal Plain and Newfoundland) and fore-arcs (Mariana and Guatemala) based on bulk-rock and in situ mineral major and trace element compositional data collected on drill cores from the Deep Sea Drilling Project and Ocean Drilling Program. These data are important for constraining the serpentinite-hosted trace element inventory of subduction zones. Bulk serpentinites show up to several orders of magnitude enrichments in Cl, B, Sr, U, Sb, Pb, Rb, Cs and Li relative to elements of similar compatibility during mantle melting, which correspond to the highest primitive mantle-normalized B/Nb, B/Th, U/Th, Sb/Ce, Sr/Nd and Li/Y among subducted lithologies of the oceanic lithosphere (serpentinites, sediments and altered igneous oceanic crust). Among the elements showing relative enrichment, Cl and B are by far the most abundant with bulk concentrations mostly above 1000 µg g−1 and 30 µg g−1, respectively. All other trace elements showing relative enrichments are generally present in low concentrations (µg g−1 level), except Sr in carbonate-bearing serpentinites (thousands of µg g−1). In situ data indicate that concentrations of Cl, B, Sr, U, Sb, Rb and Cs are, and that of Li can be, increased by serpentinization. These elements are largely hosted in serpentine (lizardite and chrysotile, but not antigorite). Aragonite precipitation leads to significant enrichments in Sr, U and B, whereas calcite is important only as an Sr host. Commonly observed brucite is trace element-poor. The overall enrichment patterns are comparable among serpentinites from mid-ocean ridges, passive margins and fore-arcs, whereas the extents of enrichments are often specific to the geodynamic setting. Variability in relative trace element enrichments within a specific setting (and locality) can be several orders of magnitude. Mid-ocean ridge serpentinites often show pronounced bulk-rock U enrichment in ...