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Global Distribution and Volume of Cryptomare and Visible Mare on the Moon From Gravity and Dark Halo Craters.

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Title: Global Distribution and Volume of Cryptomare and Visible Mare on the Moon From Gravity and Dark Halo Craters.
Authors: Izquierdo, Kristel1 (AUTHOR) kig@purdue.edu, Sori, Michael M.1 (AUTHOR), Checketts, Brianne1 (AUTHOR), Hampton, Isabella1 (AUTHOR), Johnson, Brandon C.1,2 (AUTHOR), Soderblom, Jason M.3 (AUTHOR)
Source: Journal of Geophysical Research. Planets. Feb2024, Vol. 129 Issue 2, p1-19. 19p.
Subject Terms: Lunar craters, Lunar maria, Topographic maps, Moon, Volcanism, Laser altimeters, Gravity
Abstract: The present‐day distribution of mare basalts on the Moon is an important constraint on the timing, duration, and flux of volcanism on the Moon. In this work, we find the global distribution of visible mares and cryptomares using the effective density (ρeff) of the Moon, which is sensitive to the vertical density distribution of the crust. We compute ρeff using the Gravity Recovery and Interior Laboratory (GRAIL) data and the Lunar Orbiter Laser Altimeter (LOLA) topography data. We apply this ρeff approach to the search of cryptomare for the first time, and we use a higher resolution grid and larger search area to constrain visible mare thicknesses compared to previous work. We use a Bayesian approach to find the distribution of mare thicknesses and density gradients of the underlying crust that is consistent with the localized ρeff. Assuming a bulk density of the mare basalts of 3,460 kg/m3, we find a mean visible mare thickness of 0.7−0.1+0.2 ${0.7}_{-0.1}^{+0.2}$ km which is consistent with previous work. We find a candidate cryptomare volume of 3.6−1.1+1.7×106 ${3.6}_{-1.1}^{+1.7}\times {10}^{6}$ km3 representing more than half of the total mare volume on Moon. This volume is consistent with the higher end of the previously proposed values. Finally, we search for dark halo craters (DHC) globally to obtain geologic evidence of cryptomares and find 258 craters. Our results are consistent with extensive ancient volcanism, which explains the previously identified discrepancy between the early high volcanic flux predicted by thermal models of the Moon and the dearth of ancient volcanic deposits currently exposed. Plain Language Summary: Mare basalts are the most abundant type of lava that erupted on the Moon. It is important to constrain the distribution of basalts to understand the timing, duration, and flux of volcanism on the Moon. We can observe that 16% of the surface is covered by mare basalts but additional mare deposits exist, covered by a thin layer of lighter‐looking material. These hidden mare deposits are called cryptomaria and they are likely older than the exposed mare. We use gravity and topography data to map the global distribution of visible mares and cryptomares. These data are sensitive to the density signature of mare basalts. We obtain a higher resolution map of mare thicknesses than provided before, over a larger area, and uncertainties on these values. Additionally, we map dark halo craters (DHCs), which are considered geologic evidence of cryptomares because they expose underlying cryptomares as part of their ejecta material. Combining our gravitationally inferred cryptomare distribution and the distribution of DHCs, we find a total volume of mare of 6.8 × 106 km3 with 50% of this volume being cryptomare. Our results are consistent with a more extensive ancient volcanism than previously thought. Key Points: We constrain the global distribution of visible and hidden mare basalts on the Moon using gravity and topography dataAssuming a bulk density of 3,460 kg/m3, we find a total mare volume of 7.0 × 106 km3, with over 50% of cryptomareWe find new cryptomare regions, and our results are consistent with a higher volume of ancient mares than previously thought [ABSTRACT FROM AUTHOR]
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Abstract:The present‐day distribution of mare basalts on the Moon is an important constraint on the timing, duration, and flux of volcanism on the Moon. In this work, we find the global distribution of visible mares and cryptomares using the effective density (ρeff) of the Moon, which is sensitive to the vertical density distribution of the crust. We compute ρeff using the Gravity Recovery and Interior Laboratory (GRAIL) data and the Lunar Orbiter Laser Altimeter (LOLA) topography data. We apply this ρeff approach to the search of cryptomare for the first time, and we use a higher resolution grid and larger search area to constrain visible mare thicknesses compared to previous work. We use a Bayesian approach to find the distribution of mare thicknesses and density gradients of the underlying crust that is consistent with the localized ρeff. Assuming a bulk density of the mare basalts of 3,460 kg/m3, we find a mean visible mare thickness of 0.7−0.1+0.2 ${0.7}_{-0.1}^{+0.2}$ km which is consistent with previous work. We find a candidate cryptomare volume of 3.6−1.1+1.7×106 ${3.6}_{-1.1}^{+1.7}\times {10}^{6}$ km3 representing more than half of the total mare volume on Moon. This volume is consistent with the higher end of the previously proposed values. Finally, we search for dark halo craters (DHC) globally to obtain geologic evidence of cryptomares and find 258 craters. Our results are consistent with extensive ancient volcanism, which explains the previously identified discrepancy between the early high volcanic flux predicted by thermal models of the Moon and the dearth of ancient volcanic deposits currently exposed. Plain Language Summary: Mare basalts are the most abundant type of lava that erupted on the Moon. It is important to constrain the distribution of basalts to understand the timing, duration, and flux of volcanism on the Moon. We can observe that 16% of the surface is covered by mare basalts but additional mare deposits exist, covered by a thin layer of lighter‐looking material. These hidden mare deposits are called cryptomaria and they are likely older than the exposed mare. We use gravity and topography data to map the global distribution of visible mares and cryptomares. These data are sensitive to the density signature of mare basalts. We obtain a higher resolution map of mare thicknesses than provided before, over a larger area, and uncertainties on these values. Additionally, we map dark halo craters (DHCs), which are considered geologic evidence of cryptomares because they expose underlying cryptomares as part of their ejecta material. Combining our gravitationally inferred cryptomare distribution and the distribution of DHCs, we find a total volume of mare of 6.8 × 106 km3 with 50% of this volume being cryptomare. Our results are consistent with a more extensive ancient volcanism than previously thought. Key Points: We constrain the global distribution of visible and hidden mare basalts on the Moon using gravity and topography dataAssuming a bulk density of 3,460 kg/m3, we find a total mare volume of 7.0 × 106 km3, with over 50% of cryptomareWe find new cryptomare regions, and our results are consistent with a higher volume of ancient mares than previously thought [ABSTRACT FROM AUTHOR]
ISSN:21699097
DOI:10.1029/2023JE007867