Lunar floor‐fractured craters: Evidence for viscous relaxation of crater topography

Hall, Jeffery L.; Solomon, Sean C.; Head, J. W.

doi:10.1029/jb086ib10p09537

Cited by 60 publications

(63 citation statements)

References 24 publications

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“…On the Moon, fractures on crater floors have been interpreted to form either by viscous relaxation (22) or the intrusion of sills and uplift of crater floors (23). The presence of floor-fractured craters was suspected from Mariner 10 data (24), and the MESSENGER data confirm their presence (Fig.…”

supporting

confidence: 56%

Volcanism on Mercury: Evidence from the First MESSENGER Flyby

Head

Murchie

Prockter

et al. 2008

Science

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the LRM are also seen in the MASCS data (30). From these observations and previous work (2-7, 10, 18, 21), we propose that Mercury's crust is composed of iron-poor calcium-magnesium silicates (e.g., plagioclase, enstatite, pigeonite, and diopside) with a detectable component of spectrally neutral opaque minerals. Ilmenite (FeTiO 3 ) is the most likely candidate based on lunar analogy and cosmochemical abundance considerations. This lithology is broadly basaltic to gabbroic, with nearly all ferrous iron contained in opaque minerals and not in silicates, requiring redox conditions at or near the iron-wüstite buffer. An alternative to ilmenite is native iron metal, but such a material is relatively red at typical lunar regolith grain sizes (29, 31) and implies more reducing conditions than iron-wüstite. The distinctively red smooth plains (HRP) appear to be large-scale volcanic deposits stratigraphically equivalent to the lunar maria (20), and their spectral properties (steeper spectral slope) are consistent with magma depleted in opaque materials. The large areal extent (>10 6 km 2 ) of the Caloris HRP is inconsistent with the hypothesis that volcanism was probably shallow and local (10); rather, such volcanism was likely a product of extensive partial melting of the upper mantle. The origin of plains on Mercury, whether by volcanic flooding or impact ejecta ponding, has been controversial since the Mariner 10 flybys . High-resolution images (down to 150 meters per pixel) obtained during the first MESSENGER flyby show evidence for volcanic vents around the Caloris basin inner margin and demonstrate that plains were emplaced sequentially inside and adjacent to numerous large impact craters, to thicknesses in excess of several kilometers. Radial graben and a floor-fractured crater may indicate intrusive activity. These observations, coupled with additional evidence from color images and impact crater size-frequency distributions, support a volcanic origin for several regions of plains and substantiate the important role of volcanism in the geological history of Mercury.

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supporting

confidence: 56%

Volcanism on Mercury: Evidence from the First MESSENGER Flyby

Head

Murchie

Prockter

et al. 2008

Science

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“…In calculating this number, we first calculate the average gravitational anomaly from our model CrustAnom within the main crater rim, i.e. within a circular region defined by its radius D/2 where D is the crater diameter reported by Head et al (2010) and Jozwiak et al (2012). We then subtract from this value the average value of the gravity field in an annulus extending from the crater rim to a radius of one crater diameter D ( Supplementary Fig.…”

Section: Crater Gravitational Signaturesmentioning

confidence: 99%

“…We use the dataset of Head et al (2010) as a reference catalog for normal craters and the dataset of Jozwiak et al (2012) as a reference catalog for floor-fractured craters. We consider only complex craters and thus use a minimum crater diameter of 20 km, which is the transitional crater diameter between simple and complex lunar craters (Pike, 1974(Pike, , 1980.…”

Section: Normal and Floor-fractured Crater Populationsmentioning

confidence: 99%

Gravitational signatures of lunar floor-fractured craters

Thorey

Michaut

Wieczorek

2015

Earth and Planetary Science Letters

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“…Laccolith intrusions can result in uplift and flexural bending of the overlying material (Supplementary Note S6). This mechanism has been proposed to account for uplift and extension in lunar floor-fractured craters [22][23][24][25] (Supplementary Note S1). It must be noted, however, that there is currently no direct evidence of young (<100 Myr) extrusive volcanism on the Moon 17,18,26 that would substantiate this mechanism.…”

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confidence: 99%

Recent extensional tectonics on the Moon revealed by the Lunar Reconnaissance Orbiter Camera

et al. 2012

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Large-scale expressions of lunar tectonics-contractional wrinkle ridges and extensional rilles or graben-are directly related to stresses induced by mare basalt-filled basins 1,2 . Basin-related extensional tectonic activity ceased about 3.6 Gyr ago, whereas contractional tectonics continued until about 1.2 Gyr ago 2 . In the lunar highlands, relatively young contractional lobate scarps, less than 1 Gyr in age, were first identified in Apollo-era photographs 3 . However, no evidence of extensional landforms was found beyond the influence of mare basalt-filled basins and floor-fractured craters. Here we identify previously undetected small-scale graben in the farside highlands and in the mare basalts in images from the Lunar Reconnaissance Orbiter Camera. Crosscut impact craters with diameters as small as about 10 m, a lack of superposed craters, and graben depths as shallow as ∼1 m suggest these pristine-appearing graben are less than 50 Myr old. Thus, the young graben indicate recent extensional tectonic activity on the Moon where extensional stresses locally exceeded compressional stresses. We propose that these findings may be inconsistent with a totally molten early Moon, given that thermal history models for this scenario predict a high level of late-stage compressional stress [4][5][6] that might be expected to completely suppress the formation of graben.Basin-localized lunar tectonics resulted in both basin-radial and basin-concentric graben and wrinkle ridges. Typically, basinlocalized graben are found near basin margins and in the adjacent highlands whereas wrinkle ridges are restricted to the basin interior (ref. 2, plate 6) (Supplementary Note S1). The dominant contractional tectonic landform found outside of mare basins are lobate scarps 2,3 . These small-scale scarps are thought to be the surface expression of thrust faults 3 . Crosscutting relations with Copernican-age, small-diameter impact craters indicate the lobate scarps are relatively young, less than 1 Gyr old (ref. 3).Small-scale graben revealed in 0.5-2.0 m/pixel Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images are often associated with lobate scarps (Supplementary Note S2). These graben were first found in the back-limb area of the Lee-Lincoln scarp 3,7 (∼20.3• N, 30.5• E) and are spatially correlated with a narrow rise along the crest of the scarp face and the elevated back-limb terrain 3 . Newly detected graben found in the back-limb terrain of the Madler scarp (∼10.8• S, 31.8 • E; Supplementary Fig. S1) are located ∼2.5 km from the scarp face (Fig. 1a). The orientation of these graben is roughly perpendicular to the trend of the scarp. The dimensions of the graben vary, with the largest being ∼40 m wide and ∼500 m long. Graben in the back-limb area of the Pasteur scarp (∼8.6• S, 100.6 • E; Supplementary Fig. S1) are ∼1.2 km from the scarp face (Fig. 1b). Unlike the Madler graben, the orientation of the Pasteur graben are subparallel to the scarp and extend for ∼1.5 km, with the largest ∼300 m in length and 2...

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Lunar floor‐fractured craters: Evidence for viscous relaxation of crater topography

Cited by 60 publications

References 24 publications

Volcanism on Mercury: Evidence from the First MESSENGER Flyby

Volcanism on Mercury: Evidence from the First MESSENGER Flyby

Gravitational signatures of lunar floor-fractured craters

Recent extensional tectonics on the Moon revealed by the Lunar Reconnaissance Orbiter Camera

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