Squeezing out the slab - modelling the release of Li, Be and B during progressive high-pressure metamorphism.

Marschall, Horst R., Altherr, Rainer and Rüpke, Lars (2007) Squeezing out the slab - modelling the release of Li, Be and B during progressive high-pressure metamorphism. Chemical Geology, 239 (3/4). pp. 323-335. DOI 10.1016/j.chemgeo.2006.08.008.

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Abstract

A model for the release of Li, Be and B from progressively dehydrating altered oceanic crust during subduction is presented. Combining clinopyroxene/fluid partition coefficients determined experimentally in an earlier study Brenan et al. [Brenan, J.M., Ryerson, F.J., Shaw, H.F., 1998. The role of aqueous fluids in the slab-to-mantle transfer of boron, beryllium, and lithium during subduction: Experiments and models. Geochim. Cosmochim. Acta 62, 3337–3347] with apparent mineral/clinopyroxene partition coefficients as observed in natural high-pressure metamorphic rocks Marschall et al. [Marschall, H.R., Altherr, R., Ludwig, T., Kalt, A., Gméling, K., Kasztovszky, Zs., 2006a. Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks. Geochim. Cosmochim. Acta 70, 4750–4769] results in a set of mineral/fluid partition coefficients for high-pressure metamorphic minerals. Mineral modes of altered oceanic crust as a function of pressure and temperature along a given subduction path can be derived from thermodynamic calculations using the program PerpleX. Combination of these modes with mineral/fluid partition coefficients results in whole rock/fluid partition coefficients at any stage of the P–T path including information on the amount of fluid released at any depth. Based on these data, the concentrations of Li, Be and B in subducting rocks and released fluids along a given P–T path can be modelled. The derived information on B concentrations in rocks and fluids are combined with the temperature-dependent fractionation of B isotopes in order to model the B isotopic evolution of subducting rocks and released fluids. Model calculations are performed for two slightly different chemical compositions (hydrous MORB without K and with 0.5 wt.% K2O), in order to demonstrate the impact of phengite on the boron budget. Provided the necessary input data are available, the concept of such a model could be employed to quantify the trace element release from the slab from any lithology along any reasonable P–T path.

Document Type: Article
Keywords: Lithium, Beryllium, Boron isotopes, Subduction zone, Dehydration
Research affiliation: OceanRep > SFB 574 > C5
OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.chemgeo.2006.08.008
ISSN: 0009-2541
Projects: Future Ocean
Contribution Number:
ProjectNumber
SFB 574109
Date Deposited: 25 Jan 2010 10:53
Last Modified: 11 Dec 2017 11:24
URI: http://oceanrep.geomar.de/id/eprint/2004

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