230Th-238U disequilibrium in East Scotia backarc basalts: Implications for slab contributions
- S. Fretzdorff*1,
- K.M. Haase*1,
- P.T. Leat*2,
- R.A. Livermore*2,
- C.-D. Garbe-Schönberg*3,
- J. Fietzke*3 and
- P. Stoffers*3
- 1Institut für Geowissenschaften, Universität Kiel, Olshausenstrasse 40, 24089 Kiel, Germany
- 2British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
- 3Institut für Geowissenschaften, Universität Kiel, Olshausenstrasse 40, 24089 Kiel, Germany
Abstract
New U-series isotope data for lavas from the East Scotia backarc spreading center span a large range in (230Th/232Th) and (238U/232Th). Most of the backarc lavas have (238U/230Th) < 1, similar to the composition of mid-oceanic-ridge basalts (MORB). Lavas from two segments have (238U/230Th) > 1 and are enriched in fluid-mobile elements, implying a recent addition of a U-rich slab-derived component. The data from one segment suggest an influence from an aqueous fluid from altered MORB, whereas samples from the other slab-influenced segment show addition of a sediment melt. The slab-influenced samples form a distinct trend in the equiline diagram between aqueous fluid and sediment melt that is suggested to be a mixing line rather than an isochron.
Footnotes
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↵*E-mail addresses: sfgpi.uni-kiel.de; khgpi.uni-kiel.de; ptlebas.ac.uk; ralbas.ac.uk; cdggpi.uni-kiel.de; jfgpi.uni-kiel.de; pstgpi.uni-kiel.de
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- Accepted April 28, 2003.
- Received January 3, 2003.
- Revision received April 25, 2003.
- Geological Society of America
