Program > Browse abstracts by speaker > Villamizar Blanco Julian

Silicate liquid immiscibility (SLI) is a common phenomenon in the genesis and differentiation of igneous suites in terrestrial and lunar settings. Ample evidence of this process in samples retrieved by the Apollo missions and previous experimental studies suggest it might have had an important role during the latest crystallisation stages of the Lunar Magma Ocean (LMO). In particular, existing LMO crystallisation models cannot explain the high 238U/204Pb (i.e., μ ratio) of urKREEP. SLI during LMO crystallisation holds promise for elevating the range of μ ratios to those required in the residual melt, representing urKREEP. However, the lack of accurate partitioning data relevant to lunar magmas has thus far hindered any reliable assessment of the importance of this process. Here, we provide new liquid-liquid partition coefficients (Dmafic/dacitic) for a variety of trace elements (Mn, Rb, Sr, Y, Zr, Nb, Cd, In, Sn, La, Nd, Sm, Gd, Lu, Hf, Ta, Pb, Th, U) at three different equilibration temperatures (T = 990, 975 and 950 °C) and two oxygen fugacities, +0.79 to +1.86 relative to the iron-wüstite (IW) buffer. The resulting Dmafic/dacitic values are proportional to 1/T for all studied elements, where, for those with Dmafic/dacitic > 1 (Mn, Sr, Y, Zr, Nb, Sn, La, Nd, Sm, Gd, Lu, Hf, Ta, Pb, Th, U), the slope is positive and for Dmafic/dacitic < 1 (Rb), the slope is negative. We find that, although SLI results in fractionation of U from Pb, the extent of liquid-liquid segregation required to explain the high μ ratio of urKREEP would produce mismatches in its Sm/Nd, Lu/Hf and Rb/Sr ratios. Consequently, it is likely that SLI could have shifted the isotopic signature and chemical cargo of the residual melt during the final stages of LMO crystallisation, but other processes, such as Pb volatilisation, are required to explain the high μ ratio of urKREEP.