Crystal growth rate effect on Mg/Ca and Sr/Ca partitioning between calcite and fluid : An in situ approach

Gabitov, R. I. and Sadekov, A. and Leinweber, A. (2014) Crystal growth rate effect on Mg/Ca and Sr/Ca partitioning between calcite and fluid : An in situ approach. Chemical Geology, 367. pp. 70-82. ISSN 0009-2541 DOI 10.1016/j.chemgeo.2013.12.019

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Official URL: http://dx.doi.org/10.1016/j.chemgeo.2013.12.019

Abstract

Partition coefficients of Mg and Sr (K Mg and K Sr ) between calcite and fluid were determined in crystals grown under different rates (V), where V is defined as the crystal extension per unit of time (nm/s). Addition of rare earth elements (REE) into the fluid, leads to REE preservation in the calcite. This preservation allows for a direct determination of the values of V by measuring the widths of the REE spiked zones. The edge to edge spot analyses of Mg/Ca, Sr/Ca, and REE/Ca in the individual crystals were conducted using Secondary Ion Mass Spectrometry (SIMS). The Mg/Ca and Sr/Ca ratios in the fluids, from which calcites precipitated, were also measured with In- ductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES). This allowed for the first time, to evaluate K Mg in situ in the individual crystals without averaging the data from the multiple calcite crystals. Results show that K Sr increases by a factor of six with increasing calcite growth rate from 0.001 to 4 nm/s. K Mg decreases by a factor of three with the same increase of V values. These K Sr and K Mg behaviors were described quantitatively using a growth entrapment model (GEM). According to the GEM simulations, Sr is enriched and Mg is depleted in the near-surface layer of calcite relative to the bulk lattice. This distinct outermost region of the crystal may be fully or partially captured by its lattice during rapid growth. This process causes disequilibrium partitioning of Sr and Mg through growth entrapment.

Item Type: Article
Uncontrolled Keywords: 2014AREP; IA67;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Chemical Geology
Volume: 367
Page Range: pp. 70-82
Identification Number: 10.1016/j.chemgeo.2013.12.019
Depositing User: Sarah Humbert
Date Deposited: 27 Feb 2014 22:53
Last Modified: 29 May 2014 16:14
URI: http://eprints.esc.cam.ac.uk/id/eprint/2978

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