TY - JOUR
T1 - The lunar magma ocean
T2 - Reconciling the solidification process with lunar petrology and geochronology
AU - Elkins-Tanton, Linda T.
AU - Burgess, Seth
AU - Yin, Qing Zhu
N1 - Funding Information:
The authors thank Rick Carlson, Larry Nyquist, and John Longhi for their thoughtful and expert reviews that greatly improved this paper. This work is funded through an NSF Astronomy CAREER grant to Elkins-Tanton, and NASA LASER and Lunar Institute funding. Q.-Z. Y. acknowledges the support by NASA Cosmochemistry grant ( NNX08AG57G ).
PY - 2011/4/15
Y1 - 2011/4/15
N2 - The Moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded. Ages of anorthositic crust range over at least 200. million years. The model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine (1) the final thickness of flotation crust generated by a fractionally solidifying magma ocean, (2) the timescale of crystallization before plagioclase is a stable phase, (3) the timescale of solidification after the formation of the plagioclase flotation crust, and (4) the post-overturn lunar mantle composition and structure. We find that magma oceans of as much as 1000. km depth are consistent with creating an anorthositic crust 40 to 50. km in thickness. Solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000. years, and complete solidification would require additional ten to tens of millions of years. Reconciling these short model timescales with radiometric dates of crustal samples requires either a very late-forming Moon combined with finding older crustal ages to be incorrect, or calling on tidal heating of the crust by the early Earth to prolong solidification. Gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar Mg suite of crustal rocks. Further, we find that upon crystallization, the Moon likely began with an azimuthally heterogeneous, gravitationally stable mantle, after magma ocean cumulate overturn. This result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials.
AB - The Moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded. Ages of anorthositic crust range over at least 200. million years. The model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine (1) the final thickness of flotation crust generated by a fractionally solidifying magma ocean, (2) the timescale of crystallization before plagioclase is a stable phase, (3) the timescale of solidification after the formation of the plagioclase flotation crust, and (4) the post-overturn lunar mantle composition and structure. We find that magma oceans of as much as 1000. km depth are consistent with creating an anorthositic crust 40 to 50. km in thickness. Solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000. years, and complete solidification would require additional ten to tens of millions of years. Reconciling these short model timescales with radiometric dates of crustal samples requires either a very late-forming Moon combined with finding older crustal ages to be incorrect, or calling on tidal heating of the crust by the early Earth to prolong solidification. Gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar Mg suite of crustal rocks. Further, we find that upon crystallization, the Moon likely began with an azimuthally heterogeneous, gravitationally stable mantle, after magma ocean cumulate overturn. This result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials.
KW - Anorthosite
KW - Geochronology
KW - Magma ocean
KW - Moon
UR - http://www.scopus.com/inward/record.url?scp=79953030651&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79953030651&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2011.02.004
DO - 10.1016/j.epsl.2011.02.004
M3 - Article
AN - SCOPUS:79953030651
SN - 0012-821X
VL - 304
SP - 326
EP - 336
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 3-4
ER -