Fig. 5: Diffusive exchange between IBC melt and ambient mantle.
From: Titanium-rich basaltic melts on the Moon modulated by reactive flow processes
The reaction between the IBC melt and ambient olivine- and orthopyroxene-dominated cumulates drives diffusive elemental transport and kinetic isotope fractionation. a, Diagram displaying the covariation between δ26/24Mg and δ44/40Ca (relative to reference material SRM 915a) in lunar high-Ti basalts resulting from Ca loss to orthopyroxene and diffusion of Mg from olivine and orthopyroxene into the IBC melt. Low-Ti basalts display homogeneous Mg–Ca isotope compositions consistent with partial melting of orthopyroxene-rich cumulate source rocks. The IBC melts field represents low-degree partial melts of ilmenite-bearing cumulates16 (Supplementary Fig. 5). For both partial melt fields, the Mg and Ca isotope compositions were calculated through an isotopic mass balance (Methods). Uncertainties for δ26/24Mg are 2 s based on the pooled 2 s.d. of 13 reference material measurements (Supplementary Fig. 1). Calcium isotope composition data and 2 s uncertainties for the samples are from ref. 32. b, Median and range for Mg (this study) and Fe isotope41,42,43 compositions (δ57/54Fe relative to reference material IRMM-014) of low-Ti and high-Ti basalts. c, Median and range for Mg (this study) and Ti isotope44,45 compositions (δ49/47Ti relative to reference material OL-Ti) of low-Ti and high-Ti basalts. d, The direction of elemental transport and kinetic isotope fractionation in the reaction between ambient olivine–orthopyroxene mantle and an IBC partial melt. The IBC melt composition is shifted to lower δ26/24Mg and higher Al2O3/CaO, Mg#, δ44/40Ca and δ57/54Fe.
