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Osmium Recycling in Subduction Zones
1A. D. Brandon, S. B. Shirey, R. W. Carlson, Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC, USA, 20015. R. A. Creaser, Department of Earth and Atmospheric Sciences, University of Alberta, 126 Earth Sciences Building, Edmonton, Alberta, Canada T6G 2E3.
Science (New York, N.Y.)
|May 10, 1996
Summary
Subducting oceanic crust adds 5-15% material to Earth's mantle wedge, influencing its composition. This study shows osmium can be transported into the mantle via oxidized, chlorine-rich fluids or melts derived from subducting slabs.
Area of Science:
- Geochemistry
- Petrology
- Isotope Geochemistry
Background:
- Peridotite xenoliths provide insights into the Earth's mantle composition and evolution.
- Subduction zones are key tectonic settings where oceanic crust is recycled into the mantle.
- Understanding the fate of elements during subduction is crucial for mantle geochemistry.
Purpose of the Study:
- To investigate the isotopic composition of neodymium and osmium in peridotite xenoliths from the Cascade and Japan arcs.
- To determine the extent of subducted material addition to the present-day depleted mantle.
- To constrain the behavior and transport mechanisms of osmium during oceanic crust subduction.
Main Methods:
- Analysis of neodymium and osmium isotopic compositions in peridotite xenoliths.
- Geochemical modeling to quantify the proportion of subducted material.
- Interpretation of isotopic data in the context of subduction zone processes.
Main Results:
- Neodymium and osmium isotopic compositions indicate 5-15% subducted material addition to the mantle wedge.
- Osmium is shown to partition into oxidized and chlorine-rich slab-derived fluids or melts.
- Evidence suggests osmium can be transported into the mantle wedge via these fluids/melts.
Conclusions:
- Subduction of oceanic crust significantly contributes to the composition of the mantle wedge.
- Osmium's behavior during subduction is linked to oxidized and chlorine-rich fluids/melts.
- These findings provide new constraints on the mobility of osmium and potentially other platinum group elements in subduction zones.