First-principles investigation of equilibrium magnesium isotope fractionation among mantle minerals: Review and new data

Fe and Mg Isotope Compositions Indicate a Hybrid Mantle Source for Young Chang’E 5 Mare Basalts

“…Our predicted MgO and FeO contents for LMO cumulates and Fe-Mg isotope compositions of cumulate and residual melt are shown in Figure 3. The Fe and Mg isotope compositions are unfractionated during the olivine crystallization stage (<53 PCS) because petrology experiments and theoretical calculations show that olivine has similar Fe and Mg isotope compositions to basaltic melts (e.g., Nie et al 2021;Wang et al 2023). The modeling results further suggest that the pyroxene crystallization controls the Fe-Mg isotope evolution of LMO.…”

“…The 1000lnβ of minerals and melts can be calculated by 1000lnβ = a × 10 6 /T 2 +b × (10 6 /T 2 ) 2 +c × (10 6 /T 2 ) 3 . T is the crystalizing temperature in kelvins and a, b and c are polynomial fitting parameters reported by Wang et al (2023) and references therein (Table A5):…”

Heavy magnesium isotopic signatures in arc lavas may be attributed to dehydration of subducting hydrated mantle

“…While the lighter Mg isotope signatures in arc lavas from subduction zones like Costa Rica and Kamchatka could be linked to recycled carbonates from the subducting slabs 16 , the sources contributing to the elevated δ 26 Mg values observed in arc lavas from other subduction zones remain a perplexing enigma. Crust assimilation or fractional crystallization may drive the evolving magmas toward higher δ 26 Mg values 31,[33][34][35][36] . Their impacts are particularly pronounced in samples with MgO content below 3 wt%, whereas samples with MgO content exceeding 3 wt% are anticipated to show minimal influence from these processes 33,36 .…”

“…Crust assimilation or fractional crystallization may drive the evolving magmas toward higher δ 26 Mg values 31,[33][34][35][36] . Their impacts are particularly pronounced in samples with MgO content below 3 wt%, whereas samples with MgO content exceeding 3 wt% are anticipated to show minimal influence from these processes 33,36 . Notably, elevated δ 26 Mg values have been widely observed in arc lava samples with MgO content higher than 3 wt% 16,31 .…”

“…Previous experimental studies on the equilibrium Mg isotope fractionation of hydrous minerals are restricted to brucite with its coexisting aqueous solutions at ambient pressure conditions 37,38 . Alternatively, first-principles calculations based on density functional theory (DFT) have been widely used to ascertain equilibrium isotope fractionation factors for many systems, including Mg 36,[39][40][41][42][43][44][45] . However, the computational studies concerning aqueous fluids and Mg isotopes are restricted to 0 GPa 39,40,44,45 , which does not align with the conditions associated with the dehydration of subducting slabs.…”