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A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units
Author(s) -
Dygert Nick,
Lin JungFu,
Marshall Edward W.,
Kono Yoshio,
Gardner James E.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl075703
Subject(s) - mafic , crust , plagioclase , geology , anorthosite , geochemistry , magma , magmatism , petrology , viscosity , oceanic crust , geophysics , thermodynamics , volcano , tectonics , subduction , quartz , physics , paleontology
Much of the lunar crust is monomineralic, comprising >98% plagioclase. The prevailing model argues the crust accumulated as plagioclase floated to the surface of a solidifying lunar magma ocean (LMO). Whether >98% pure anorthosites can form in a flotation scenario is debated. An important determinant of the efficiency of plagioclase fractionation is the viscosity of the LMO liquid, which was unconstrained. Here we present results from new experiments conducted on a late LMO‐relevant ferrobasaltic melt. The liquid has an exceptionally low viscosity of 0.22 − 0.19 + 0.11to 1.45 − 0.82 + 0.46 Pa s at experimental conditions (1,300–1,600°C; 0.1–4.4 GPa) and can be modeled by an Arrhenius relation. Extrapolating to LMO‐relevant temperatures, our analysis suggests a low viscosity LMO would form a stratified flotation crust, with the oldest units containing a mafic component and with very pure younger units. Old, impure crust may have been buried by lower crustal diapirs of pure anorthosite in a serial magmatism scenario.