¹J. F. Rapp,²D. S. Draper
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13086]
¹Jacobs JETS, NASA Johnson Space Center, Houston, Texas, USA
²Astromaterials Research Office, EISD, NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

We report results of systematic experimental simulation of fractional crystallization of a lunar magma ocean (LMO) with the Lunar Primitive Upper Mantle bulk composition. These results complement prior work that simulated equilibrium crystallization. In contrast to previous numerical models for investigating magma ocean solidification processes and implications, our combined program simulates these processes directly using petrologic experimentation. Our experiments mimic LMO crystallization that is fractional throughout the process, rather than switching from initially equilibrium to fractional crystallization partway through. To do this, we adopted an iterative approach in which the starting material for each run is synthesized using the composition of the melt phase from the prior run. We compare our results to those from long‐standing numerical models of LMO crystallization and show that although some features of those models are broadly reproduced, there are key differences in liquid lines of descent and the cumulate lithologies generated. Our results can be used to estimate the possible thickness of a primordial lunar crust formed from flotation of plagioclase during magma ocean solidification. Our estimate is greater than that from the recent Gravity Recovery and Interior Laboratory (GRAIL) mission, but consistent with the criteria on which the starting bulk composition was originally calculated. It assumes perfectly efficient separation of all plagioclase formed from the crystallizing magma ocean, which is likely not the case. We also demonstrate that a non‐chondritic bulk composition, with respect to trace elements, is not required in order to generate a KREEP (potassium, rare earth elements, and phosphorus) signature from magma ocean crystallization.

^1,2Masahiro Kayama,^3,4Toshimori Sekine,⁵Naotaka Tomioka,⁶Hirotsugu Nishido,³Yukako Kato,⁶Kiyotaka Ninagawa,⁷Takamichi Kobayashi,^8,9Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13092]
¹Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai, Japan
²Creative Interdisciplinary Research Division, Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Japan
³Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi‐Hiroshima, Japan
⁴Center for High Pressure Science and Technology Advanced Research, , Shanghai, China
⁵Kochi Institute for Core Sample Research, Japan Agency for Marine‐Earth Science and Technology, , Nankoku City, Kochi, Japan
⁶Department of Biosphere‐Geosphere Science, Okayama University of Science, , Okayama, Japan
⁷National Institute for Materials Science, , Tsukuba, Ibaraki, Japan
⁸National Institute of Polar Research, Tachikawa, Tokyo, Japan
⁹Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Tokyo, Japan
Published by arrangement with John Wiley & Sons

Cathodoluminescence (CL) analyses were carried out on maskelynite and lingunite in L6 chondrites of Tenham and Yamato‐790729. Under CL microscopy, bright blue emission was observed in Na‐lingunite in the shock veins. Dull blue‐emitting maskelynite is adjacent to the shock veins, and aqua blue luminescent plagioclase lies farther away. CL spectroscopy of the Na‐lingunite showed emission bands centered at ~330, 360–380, and ~590 nm. CL spectra of maskelynite consisted of emission bands at ~330 and ~380 nm. Only an emission band at 420 nm was recognized in crystalline plagioclase. Deconvolution of CL spectra from maskelynite successfully separated the UV–blue emission bands into Gaussian components at 3.88, 3.26, and 2.95 eV. For comparison, we prepared K‐lingunite and experimentally shock‐recovered feldspars at the known shock pressures of 11.1–41.2 GPa to measure CL spectra. Synthetic K‐lingunite has similar UV–blue and characteristic yellow bands at ~550, ~660, ~720, ~750, and ~770 nm. The UV–blue emissions of shock‐recovered feldspars and the diaplectic feldspar glasses show a good correlation between intensity and shock pressure after deconvolution. They may be assigned to pressure‐induced defects in Si and Al octahedra and tetrahedra. The components at 3.88 and 3.26 eV were detectable in the lingunite, both of which may be caused by the defects in Si and Al octahedra, the same as maskelynite. CL of maskelynite and lingunite may be applicable to estimate shock pressure for feldspar‐bearing meteorites, impactites, and samples returned by spacecraft mission, although we need to develop more as a reliable shock barometer.