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Trace element diffusion in tephrite-phonolite couple experiments as a function of temperature, H2O contents and oxygen fugacity

Diego González-García1,2, Ingo Horn1, Felix Marxer1, François Holtz1

  • Affiliations:  1Institute of Earth System Sciences, Leibniz Universität Hannover, Germany; 2Department of Mineralogy and Petrology, Universidad Complutense de Madrid, Spain 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 77

  • Programme No: 1.2.22

  • Theme 1 > Session 2

Abstract

Trace element diffusion in magmas is of major importance, as trace elements are used as proxies for a large variety of igneous processes (magma recharge, crystal growth/dissolution or volatile exsolution) and their associated timescales. The database of diffusion coefficients (D) has increased significantly in the last decades, but gaps still exist for water-rich melts. Moreover, although alkaline melts constitute a significant volume of ocean island magmatism, such liquids are generally under-represented in the current trace element diffusion database. Therefore, a series of interdiffusion experiments between tephritic and phonolitic melts from the Canary Islands were run in internally heated pressure vessels at variable conditions (300 MPa, 1150-1300°C, 0.3-3.3 wt.% H2O). Concentrations of 13 trace elements (V, Zr, Nb, Co, Ta, Hf, U, Th, Sn, Sr, Ba, Rb and Cs) were determined by LA-ICP-MS and effective binary diffusion coefficients (D) were obtained by a modified Boltzmann-Matano analysis. Preliminary results show a systematic relationship between trace element diffusion and ionic radius (r) in all runs, with a maximum in diffusivity at r ~ 1 Å (Sn, Sr, Ba). As already observed for major elements [1], log D of trace elements show a non-linear relationship with melt H2O contents with a convergence of D towards the water-rich end at different temperatures. This dataset will allow constraining magma interactions and dynamics in bimodal eruptions, in Tenerife and other islands, where banded pumices resulting from mixing between basanite/tephrite and phonolite are common. [1] González-García, D. et al. (2024). Eur. J. Mineral. 36(4), 623--640. doi: 10.5194/ejm-36-623-2024