Boron Concentrations and Isotopic Compositions in Volcanic Arc Lavas Provide Unique Insights into Subduction Processes
Abstract
The B geochemistry of volcanic arc lavas provides potentially unique petrogenetic insights into subduction zone processes including thermal and dehydration evolution of subducting slabs, sources of fluids, and magma generation. Particular advantages include: low concentrations in 'normal' mantle and lower crustal rocks, generally high concentrations in subducted slab materials, distinct isotopic ranges for many relevant slab lithologies, and high solubility in aqueous fluids but otherwise strong incompatible element behavior. High B concentrations and B/Zr, B/Nb and similar ratios in arc lavas indicate that B is selectively enriched - implicating aqueous fluids as the dominant transport medium as opposed to silicate melts. Correlation of B enrichments with such tracers as 10Be provides compelling evidence that this signal is slab-derived. Intra- and inter-arc variations in B enrichment and isotopic composition are systematically related to geodynamic parameters and generally explicable in terms of slab thermal evolution. Subduction zone thermal models and B data available from at least ten volcanic arcs are used to 'calibrate' these relations, and they are applied to the Tonga-Kermadec-New Zealand and Andean arcs in an attempt to map relative variations in slab thermal state using geochemical 'tomography'.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2006
- Bibcode:
- 2006AGUSM.V33A..05L
- Keywords:
-
- 3613 Subduction zone processes (1031;
- 3060;
- 8170;
- 8413);
- 3619 Magma genesis and partial melting (1037);
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413);
- 1041 Stable isotope geochemistry (0454;
- 4870);
- 3060 Subduction zone processes (1031;
- 3613;
- 8170;
- 8413)