The distribution and origin of smooth plains on Mercury

Abstract

[1] Orbital images from the MESSENGER spacecraft show that~27% of Mercury's surface is covered by smooth plains, the majority (>65%) of which are interpreted to be volcanic in origin. Most smooth plains share the spectral characteristics of Mercury's northern smooth plains, suggesting they also share their magnesian alkali-basalt-like composition. A smaller fraction of smooth plains interpreted to be volcanic in nature have a lower reflectance and shallower spectral slope, suggesting more ultramafic compositions, an inference that implies high temperatures and high degrees of partial melting in magma source regions persisted through most of the duration of smooth plains formation. The knobby and hummocky plains surrounding the Caloris basin, known as Odin-type plains, occupy an additional 2% of Mercury's surface. The morphology of these plains and their color and stratigraphic relationships suggest that they formed as Caloris ejecta, although such an origin is in conflict with a straightforward interpretation of crater size-frequency distributions. If some fraction is volcanic, this added area would substantially increase the abundance of relatively young effusive deposits inferred to have more mafic compositions. Smooth plains are widespread on Mercury, but they are more heavily concentrated in the north and in the hemisphere surrounding Caloris. No simple relationship between plains distribution and crustal thickness or radioactive element distribution is observed. A likely volcanic origin for some older terrain on Mercury suggests that the uneven distribution of smooth plains may indicate differences in the emplacement age of large-scale volcanic deposits rather than differences in crustal formational process.

Geology of the Victoria quadrangle (H02), Mercury

“…In the western region of H02, IMP are approximately located inside the high-Mg region described by Weider et al (2015). In the eastern region, IMP correspond approximately to an area previously mapped as SP by Denevi et al (2013), p. 894, which is characterised by high Al abundance (Weider et al, 2015). Whitten et al (2014) state that IMP show similar ages to ICP of Tolstojan and Pre-Tolstojan period, though the lower crater density and superposition relationships (where apparent) confirm that IMP is younger than ICP.…”

“…However, recent work concludes that there is no clear contrast between IMP and ICP, which seem to have a 'patchy' distribution, and the adjacent terrains (Denevi et al, 2013;Whitten et al, 2014). Despite the similarity with ICP at a regional scale, our mapping scale (i.e.…”

“…Recently their volcanic nature was confirmed due to evidence of flow and sharp colour contrasts with adjacent units (Denevi et al, 2013). In the north polar region of Mercury, SP are known as the 'Northern smooth plains' (SPn, Denevi et al, 2013;Ostrach et al, 2015); inside the H02 quadrangle most of the mapped SP pertain to this unit ( Figure 6).…”

“…In the north polar region of Mercury, SP are known as the 'Northern smooth plains' (SPn, Denevi et al, 2013;Ostrach et al, 2015); inside the H02 quadrangle most of the mapped SP pertain to this unit ( Figure 6). Several authors believe SP belong to the Calorian period estimating an age of 3.7-3.9 Ga based on crater density distribution (Denevi et al, 2013;Fassett et al, 2009;Head et al, 2011;Ostrach, Robinson, Denevi, & Thomas, 2011;Strom, Chapman, Merline, Solomon, & Head, 2008, 2011.…”

Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

“…S4) and the assumption that Mercurian lavas were sulfide saturated when they erupted (see text for details). The thin black lines represent the limits of the smooth plains as mapped by Denevi et al (2013) We considered three potential bulk sulfur contents for Mercury (3, 4 and 5 wt.%), a bulk Fe content of 65 ± 5 wt.% and that the thickness of the mantle is 420 ± 30 km. Grey fields below the red, blue and green curves show the result of iterative calculations of the amount of sulfur that does not dissolve in the metallic core and contributes to the formation of a FeS external core.…”