Fe–Mg interdiffusion rates in clinopyroxene: experimental data and implications for Fe–Mg exchange geothermometers

Formation of fast-spreading lower oceanic crust as revealed by a new Mg–REE coupled geospeedometer

“…(A.12)) well reproduces the Mg diffusivities used for their model calibration (LaTourrette and Wasserburg, 1998;Van Orman et al, 2014) as well as those from diffusion experiments of Faak et al (2013) with excess silica (Fig. A.1a); however, systematic overestimations (Müller et al, 2013) and REE diffusion coefficients (Van Orman et al, 2001) in clinopyroxene at 1200 • C (orange) and 1000 • C (blue). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)…”

“…The recent measurements of Müller et al (2013) for diopside ( X Ca = 1.0 per six-oxygen) at 1 atm are similar to those of Dimanov and Wiedenbeck (2006); however, both are about one order of magnitude greater than Brady and McCallister's measurements. The differences may be attributed to the low-Ca clinopyroxene used in Brady and McCallister (1983) Thus, the Arrhenius expression of Müller et al (2013) is used in our diffusion model to simulate Mg diffusion in clinopyroxene. With the increase of anorthite content in plagioclase (e.g., An = 20-100), the relative differences in Mg diffusivities between clinopyroxene and plagioclase are reduced from about three orders of magnitude to less than a factor of two (Fig.…”

“…Interdiffusion coefficients of Ca-Mg-Fe in clinopyroxene were measured in three experimental studies (Brady and McCallister, 1983;Dimanov and Wiedenbeck, 2006;Müller et al, 2013). The recent measurements of Müller et al (2013) for diopside ( X Ca = 1.0 per six-oxygen) at 1 atm are similar to those of Dimanov and Wiedenbeck (2006); however, both are about one order of magnitude greater than Brady and McCallister's measurements.…”

“…This is also the case for REE in clinopyroxene, but does not remain true for Mg in clinopyroxene (e.g., Zhang et al, 2010). Practically, the interdiffusion coefficients of Mg-Fe-Ca in clinopyroxene at the relevant composition are often used as chemical diffusion coefficients for modeling of Mg and Fe diffusion in clinopyroxene (e.g., Müller et al, 2013).…”

“…Geospeedometers have the ability to extract cooling information of natural rocks from mineral compositions using analytical or numerical models (e.g., Dodson, 1973;Eiler et al, 1992;Ganguly and Tirone, 1999;Costa et al, 2003;Müller et al, 2013;Watson and Cherniak, 2015;Liang, 2017). Applying the closure temperature equation of Dodson (1973) to Ca in olivine, two research groups estimated cooling rates of oceanic gabbros from the Faak et al (2013) as a function of silica activity and (b) the differences of two existing silica activity models for a basaltic system.…”