Mare Domes in Mare Tranquillitatis: Identification, Characterization, and Implications for Their Origin. Issue 9 (13th September 2021)

• Record Type: Journal Article
• Authors: Qiao, Le; Head, James W.; Wilson, Lionel; Chen, Jian; Ling, Zongcheng
• Is Part Of: Journal of geophysical research. Volume 126:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-13
• Subjects: mare domes -- small shield volcano -- Mare Tranquillitatis -- mare volcanism -- lunar/Moon; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2021JE006888
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Mare domes, small shield volcanoes typically <∼30 km diameter, are part of the spectrum of lunar volcanic features that characterize extrusive basalt deposits. We used new spacecraft data to document these in Mare Tranquillitatis, among the oldest maria and the site commonly interpreted as an ancient degraded non‐mascon impact basin. We found 283 known and suspected mare domes, with the majority ( n = 229) concentrated on a broad, ∼450 km circular topographic rise in eastern Mare Tranquillitatis. The domes (median diameter 5.6 km, height 68 m, volume 0.7 km 3 ) contain summit pits (74%; median diameter 0.8 km), and exhibit minor compositional variability between domes and surrounding flows, suggesting that domes both supply and are embayed by these flows. Based on their characteristics and associations, we interpret the small shield volcanoes to have been built from individual low‐volume (<∼10–100 km 3 ), low volatile content, short duration, cooling‐limited eruptions. The ∼450 km broad volcanic rise is ∼920 m high (volume ∼1.6 × 10 5 km 3 ) and is interpreted to be built from multiple occurrences of small shield eruptions, a shield plains volcanism style. This implies a shallow mantle source region capable of supplying distributed dike‐emplacement and eruption events over an area of 1.75 × 10 5 km 2 early in mare volcanism history (∼3.7 Ga). The difference between Mare Tranquillitatis and younger mare‐filled mascon basins is attributed to the more ancient thermal state and crustal structure of the viscously relaxed Tranquillitatis basin, and a shallower broad magma source region present in earlier lunar thermal history. Plain Language Summary: Lunar mare volcanic activity spans several billion years in early middle lunar history and involves melting in the mantle, ascent in blade‐like cracks (dikes) and eruption to the surface to form basaltic lava flows. The features surrounding the eruption vent (e.g., flows, channels, sinuous rilles, cones, domes, pyroclastics, etc.) provide important information about eruption conditions (e.g., magma volume, rate of eruption, cooling behavior, composition, volatile content, etc.). The array of these features in specific mare locations and with differing ages provides critical information on the evolution of mantle source regions and the thermal evolution of the Moon. We studied ∼3.7 Ga‐aged lava deposits in Mare Tranquillitatis and found over 200 small shield volcanoes clustered in a ∼450 km broad volcanic rise, and formed from a series of eruptions in a distinctive shield plains volcanism style. Missing or rare were other types of volcanic features (sinuous rilles, steep flow fronts, pyroclastics, cones, lava channels). Individual small shield volcanos are interpreted to have formed from relatively low‐volume, low‐volatile content, short‐duration, cooling‐limited eruptions. This unusual concentration in eastern Mare Tranquillitatis implies broad, relatively shallow source regions below this possible ancient, non‐mascon impact basin, in contrast to later mascon‐basin maria (Crisium, Serenitatis, and Imbrium). Key Points: The distribution of over 200 mare domes in Mare Tranquillitatis shows a concentration in a broad rise in eastern Tranquillitatis The broad volcanic rise was formed by shield plains volcanism, differing from volcanism in younger mascon basins Differences between Mare Tranquillitatis and younger maria are due to greater ages of the basin and mare, and a shallower source region