Emplacement conditions of lunar impact melt flows

Lev, Einat; Hamilton, C. W.; Voigt, Joana; Stadermann, A. C.; Zhan, Y.; Neish, C. D.

doi:10.1016/j.icarus.2021.114578

Cited by 8 publications

(3 citation statements)

References 65 publications

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“…The lower temperature estimates (<2,000°C) have been argued to be a function of the entrainment of large volumes of cold material (i.e., lithic clast or block entrainment) within the melt sheet. For example, 15%–20% clast content in the melt could result in lowering the impact melt sheet temperature by 400°C, and 50% clast content would result in the solidification of the impact melt sheet much more rapidly than clast‐free melt (Bray et al., 2010; Lev et al., 2021; Simonds et al., 1976).…”

Section: Discussionmentioning

confidence: 99%

“…Impact melt sheets can have initial temperatures that are super‐heated far above the liquidus temperatures for most silicate rocks. However, establishing the range of initial impact melt temperature remains a subject of active debate (Bray et al., 2010; Lev et al., 2021; Timms et al., 2017; Tolometti et al., 2020). A wide range of initial temperatures have been estimated, ranging from >2,300°C based on samples from Mistastin Lake, Canada and Apollo 17 sample 76535, to 1,450°C in impact melts from Apollo 17 (Samples 76015; 76315; 76215; Simonds et al., 1976) and ∼1,800°C in the Ries and Sudbury craters (El Goresy, 1965; Prevec & Cawthorn, 2002).…”

Section: Discussionmentioning

confidence: 99%

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Using Lunar Granulites to Constrain Re‐Equilibration Timescales of Contact Thermal Metamorphism on the Moon

2023

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Rocks of the lunar granulite suite are the product of high‐temperature metamorphism within the Moon's crust. However, to date, their formation conditions have few constraints. Here, we combine Ti‐in‐pyroxene element diffusion modeling and two‐pyroxene thermometry with thermal modeling of the lunar crust in order to assess potential heat sources that could generate granulite metamorphism within the lunar highland crust. For the samples investigated in this study, the pyroxene crystals experienced peak metamorphic temperatures between ∼1,027 and 1,091°C over timescales ranging from ∼153 years to ∼15.1 Kyrs. To best satisfy these temperature and timescale constraints, hot (∼2,300°C) impact melt sheets with thickness ranging from 350 m to 3.35 km—equating to impact crater diameters between ∼60 and 280 km—have the potential to heat the underlying anorthositic crust. Deep (>20 km) igneous bodies, such as the large (>10 km thick) sills observed by the GRAIL mission near the base of the lunar crust, also have the potential to generate the required peak metamorphic temperatures; however, the thermal equilibration timescales in this scenario are modeled to be much larger (>100 Kyrs) than was witnessed by the granulites investigated. Our modeling highlights that while lunar granulites are only a minor component within the Apollo and meteorite collection, they are likely an important and ubiquitous lithology within the lunar highland crust.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Using Lunar Granulites to Constrain Re‐Equilibration Timescales of Contact Thermal Metamorphism on the Moon

2023

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“…Since the K 1 is known to plunge up flow (e.g., Callot et al., 2004; Cañón‐Tapia & Mendoza‐Borunda, 2014; Hillhouse & Wells, 1991), we suggest that the general flow direction of the impact melt was eastward. Thus, IM1, IM3, IM4, IM5, and IM6 outcrops present crater inward flow, which possibly is downslope and gravity‐driven (e.g., Bray et al., 2018; Lev et al., 2021; Stopar et al., 2014). In contrast, IM2 presents crater outward flow, which may suggest that this site recorded the initial outwards‐directed movement of impact melt during the excavation flow stage of crater formation, with the rest of the sites recording the later inwards movement during crater modification (e.g., Grieve, 1988; Oberbeck, 1975; Osinski, 2006; Osinski et al., 2005; Stöffler et al., 2004; Zhang et al., 2011).…”

Section: Discussionmentioning

confidence: 99%

On the Emplacement of the Impact Melt at the Dhala Impact Structure, India

et al. 2023

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We investigate the magnetic fabrics and magnetic mineralogy of the impact melt rock at the Dhala impact structure to understand its emplacement mechanism. Pseudo‐single domains of Ti‐poor magnetite and Ti‐hematite are the prime magnetic carriers in the impact melt rock. The magnetic foliations show a range of dip amounts. The overall trend of the magnetic foliation of the impact melt rock draws a resemblance with the flood basalts or lava flows. A well‐developed magnetic lineation (K1) indicates the strong alignment of Ti‐poor magnetite grains. Therefore, the magnetic carriers may have crystallized and aligned themselves along the flow direction before the emplacement. It may be possible that after the crystallization of the magnetic carriers, the impact melt moved in a semi‐molten state similar to lava flows with temperatures below c. 1,500°C, which is the melting point of Ti‐magnetite and was emplaced as crater‐fill deposits. Among the three principal magnetic susceptibility axes, K1 aligns best with the mesoscopic flow indicators. K1 of individual specimens' trends between NW and SW, while the mean K1 at all the sites trends westward. Thus, at the studied sites, the impact melt flow was dominantly eastward. In the sites located to the NW and W, the eastward flow could be due to gravity‐driven crater inward flow toward the center. At site IM2, which is located to E, the eastward flow of the impact melt is possibly due to crater outward excavation flow.

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