TY - JOUR

T1 - The Lunar Mare Ring-Moat Dome Structure (RMDS) Age Conundrum

T2 - Contemporaneous With Imbrian-Aged Host Lava Flows or Emplaced in the Copernican?

AU - Zhang, F.

AU - Head, J.W.

AU - Wöhler, C.

AU - Basilevsky, A.T.

AU - Wilson, L.

AU - Xie, M.

AU - Bugiolacchi, R.

AU - Wilhelm, T.

AU - Althoff, S.

AU - Zou, Y.L.

N1 - An edited version of this paper was published by AGU. Copyright 2021 American Geophysical Union. Zhang, F., Head, J. W., Wöhler, C., Basilevsky, A. T., Wilson, L., Xie, M., et al. (2021). The lunar mare ring-moat dome structure (RMDS) age conundrum: Contemporaneous with Imbrian-aged host lava flows or emplaced in the Copernican?. Journal of Geophysical Research: Planets, 126, e2021JE006880. https://doi.org/10.1029/2021JE006880

PY - 2021/8/31

Y1 - 2021/8/31

N2 - Ring-moat dome structures (RMDSs) are small circular mounds of diameter typically about 200 m and ∼3–4 m in height, surrounded by narrow, shallow moats. They occur in clusters, are widespread in ancient Imbrian-aged mare basalt host units and show mineralogies comparable to those of their host units. Based on these close associations and similarities, a model has been proposed for the formation of RMDS as the result of late-stage flow inflation, with second boiling releasing quantities of magmatic volatiles that migrate to the top of the flow as magmatic foams and extrude through cracks in the cooled upper part of the flow to produce the small RMDS domes and surrounding moats. In contrast to this model advocating a contemporaneous emplacement of RMDSs and their host lava flows, a range of observations suggests that the RMDS formed significantly after the emplacement and cooling of their host lava flows, perhaps as recently as in the Copernican Period (∼1.1 Ga to the present). These observations include: (a) stratigraphic embayment of domes into post-lava flow emplacement impact craters; (b) young crater degradation age estimates for the underlying embayed craters; (c) regolith development models that predict thicknesses in excess of the observed topography of domes and moats; (d) landform diffusional degradation models that predict very young ages for mounds and moats; (e) suggestions of fewer superposed craters on the mounds than on the adjacent host lava flows, and (f) observations of superposed craters that suggest that the mound substrate does not have the properties predicted by the magmatic foam model. Together, these observations are consistent with the RMDS formation occurring during the period after the extrusion and solidification of the host lava flows, up to and including the geologically recent Late Copernican, that is, the last few hundreds of millions of years of lunar history. We present and discuss each of these contradictory data and interpretations and summarize the requirements for magma ascent and eruption models that might account for young RMDS ages. We conclude with a discussion of the tests and future research and exploration that might help resolve the RMDS age and mode of emplacement conundrum.

AB - Ring-moat dome structures (RMDSs) are small circular mounds of diameter typically about 200 m and ∼3–4 m in height, surrounded by narrow, shallow moats. They occur in clusters, are widespread in ancient Imbrian-aged mare basalt host units and show mineralogies comparable to those of their host units. Based on these close associations and similarities, a model has been proposed for the formation of RMDS as the result of late-stage flow inflation, with second boiling releasing quantities of magmatic volatiles that migrate to the top of the flow as magmatic foams and extrude through cracks in the cooled upper part of the flow to produce the small RMDS domes and surrounding moats. In contrast to this model advocating a contemporaneous emplacement of RMDSs and their host lava flows, a range of observations suggests that the RMDS formed significantly after the emplacement and cooling of their host lava flows, perhaps as recently as in the Copernican Period (∼1.1 Ga to the present). These observations include: (a) stratigraphic embayment of domes into post-lava flow emplacement impact craters; (b) young crater degradation age estimates for the underlying embayed craters; (c) regolith development models that predict thicknesses in excess of the observed topography of domes and moats; (d) landform diffusional degradation models that predict very young ages for mounds and moats; (e) suggestions of fewer superposed craters on the mounds than on the adjacent host lava flows, and (f) observations of superposed craters that suggest that the mound substrate does not have the properties predicted by the magmatic foam model. Together, these observations are consistent with the RMDS formation occurring during the period after the extrusion and solidification of the host lava flows, up to and including the geologically recent Late Copernican, that is, the last few hundreds of millions of years of lunar history. We present and discuss each of these contradictory data and interpretations and summarize the requirements for magma ascent and eruption models that might account for young RMDS ages. We conclude with a discussion of the tests and future research and exploration that might help resolve the RMDS age and mode of emplacement conundrum.

KW - Crater diffusional degradational process

KW - Morphology

KW - Stratigraphy

KW - the Moon

KW - Thermal Evolution

KW - Volcanism

KW - emplacement

KW - lava flow

KW - lunar crust

KW - lunar mantle

KW - Moon

KW - satellite data

KW - satellite imagery

KW - volcanism

U2 - 10.1029/2021JE006880

DO - 10.1029/2021JE006880

M3 - Journal article

VL - 126

JO - Journal of Geophysical Research: Planets

JF - Journal of Geophysical Research: Planets

SN - 2169-9100

IS - 8

M1 - e2021JE006880

ER -