A THREE-DIMENSIONAL DYNAMIC MODEL TO UNDERSTAND THE THERMAL AND CHEMICAL EVOLUTION OF THE LUNAR MAGMA OCEAN
Seminars
Summer Semester
2023 – now: Staff Scientist, LMU Munich, Germany
2019 – 2023: CSH Fellow, Center for Space and Habitability (CSH), University of Bern, Switzerland
2018 – 2019: Deep Carbon Observatory (DCO) Postdoc, University of Oxford, UK
2016 – 2018: Newton International Fellow, University of Oxford, UK
2009 – 2016: Ph.D., Yale University, US
2005 – 2009: B.Sc. in Geochemistry, Peking University, China.
Returned samples of the lunar crust show an anorthite-rich feature, leading to the lunar magma ocean (LMO) hypothesis in which olivine/pyroxene fractionally crystallized and sunk to form cumulates, whereas late-stage plagioclase precipitated and floated up to form the anorthositic crust. Such a conventional thinking, however, does not agree with the data-derived, ~200 Ma lunar crust formation timescale. One possible avenue to sustaining such a lifetime of the LMO is the waning convective cooling of the mushy-state LMO. To systematically quantify this process, we devise a 3D numerical model based on CitcomS, where we consider viscous melt segregation, elastic melt extraction, thermal and chemical convection, as well as parameterized partial melting/freezing. With this 3D model, we find that melt segregation and subsequent extraction to the surface expedite the cooling of the LMO; however, the lunar crust formation timescale can still last for ~200 Ma given the high viscosities of the convecting solids. Furthermore, due to differential buoyancy between the parameterized anorthite and olivine components, a new mechanism of overturn is found during the Moon's mushy stage, potentially reconciling the magma ocean theory with the age data that show a temporal overlap between the lunar Mg-suite and ferroan anorthosites. This potential overturn mechanism is subject to future test because the current model does not consider iron-bearing components which strongly affect chemical buoyancy.