TY - JOUR

T1 - Water-enhanced interdiffusion of major elements between natural shoshonite and high-K rhyolite melts

AU - González-García, Diego

AU - Behrens, Harald

AU - Petrelli, Maurizio

AU - Vetere, Francesco

AU - Morgavi, Daniele

AU - Zhang, Chao

AU - Perugini, Diego

N1 - Funding information: This research was funded by the European Research Council Consolidator Grant ERC-2013-CoG (No. 612776 – CHRONOS) to D. Perugini; and by the MIUR-DAAD Joint Mobility Project (grant number 57262582) to F. Vetere and H. Behrens. D. Morgavi thanks the project AEOLUS (No. MORGABASE2015) funded by the Fondo di Ricerca di Base of Department of Physics and Geology, University of Perugia. D. González-García wishes to acknowledge the kind help received from R. Balzer while performing the experiments, R. Almeev during the microprobe analysis, and J. Feige for the careful preparation of experiment sections, all of them at the Institute of Mineralogy, Hannover. In addition, we acknowledge A. Zezza for completing the first experiment under her M.Sc. thesis work. We are grateful to Y. Zhang and an anonymous reviewer, whose constructive reviews significantly improved the quality of this manuscript. We acknowledge R. Astbury as well for the review of the English in the manuscript.

PY - 2017/9/5

Y1 - 2017/9/5

N2 - The interdiffusion of six major elements (Si, Ti, Fe, Mg, Ca, K) between natural shoshonite and a high-K rhyolite (Vulcano island, Aeolian archipelago, Italy) has been experimentally measured by the diffusion couple technique at 1200 °C, pressures from 50 to 500 MPa and water contents from 0.3 (‘nominally dry’) to 2 wt%. The experiments were carried out in an internally heated pressure vessel, and major element profiles were later acquired by electron probe microanalysis. The concentration-distance profiles are evaluated using a concentration-dependent diffusivity approach. Effective binary diffusion coefficients for four intermediate silica contents are obtained by the Sauer-Freise modified Boltzmann-Matano method. At the experimental temperature and pressures, the diffusivity of all studied elements notably increases with dissolved H2O content. Particularly, diffusion is up to 1.4 orders of magnitude faster in a melt containing 2 wt% H2O than in nominally dry melts. This effect is slightly enhanced in the more mafic compositions. Uphill diffusion was observed for Al, while all other elements can be described by the concept of effective binary interdiffusion. Ti is the slowest diffusing element through all experimental conditions and compositions, followed by Si. Fe, Mg, Ca and K diffuse at similar rates but always more rapidly than Si and Ti. This trend suggests a strong coupling between melt components. Since effects of composition (including water content) are dominant, a pressure effect on diffusion cannot be clearly resolved in the experimental pressure range.

AB - The interdiffusion of six major elements (Si, Ti, Fe, Mg, Ca, K) between natural shoshonite and a high-K rhyolite (Vulcano island, Aeolian archipelago, Italy) has been experimentally measured by the diffusion couple technique at 1200 °C, pressures from 50 to 500 MPa and water contents from 0.3 (‘nominally dry’) to 2 wt%. The experiments were carried out in an internally heated pressure vessel, and major element profiles were later acquired by electron probe microanalysis. The concentration-distance profiles are evaluated using a concentration-dependent diffusivity approach. Effective binary diffusion coefficients for four intermediate silica contents are obtained by the Sauer-Freise modified Boltzmann-Matano method. At the experimental temperature and pressures, the diffusivity of all studied elements notably increases with dissolved H2O content. Particularly, diffusion is up to 1.4 orders of magnitude faster in a melt containing 2 wt% H2O than in nominally dry melts. This effect is slightly enhanced in the more mafic compositions. Uphill diffusion was observed for Al, while all other elements can be described by the concept of effective binary interdiffusion. Ti is the slowest diffusing element through all experimental conditions and compositions, followed by Si. Fe, Mg, Ca and K diffuse at similar rates but always more rapidly than Si and Ti. This trend suggests a strong coupling between melt components. Since effects of composition (including water content) are dominant, a pressure effect on diffusion cannot be clearly resolved in the experimental pressure range.

KW - Effective binary diffusion

KW - Hydrous melt

KW - Major elements

KW - Rhyolite

KW - Shoshonite

UR - http://www.scopus.com/inward/record.url?scp=85020675655&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2017.05.023

DO - 10.1016/j.chemgeo.2017.05.023

M3 - Article

AN - SCOPUS:85020675655

VL - 466

SP - 86

EP - 101

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

ER -