Impact vesiculation – a new trigger for volcanic bubble growth and degassing

We highlight a potentially important trigger for bubble growth and degassing in volcanic bombs. We have successfully triggered bubble growth in previously unvesiculated samples of silicate melt during experiments to simulate volcanic bomb impact, by firing pellets at, and dropping weights onto, melt samples. We call this phenomenon "impact vesiculation". Further work is required on real volcanic bombs to establish the extent to which impact vesiculation occurs in nature. However, our experiments are sufficient to demonstrate that impact vesiculation is a viable processes and should be borne in mind in analysis of bubble populations and degassing histories of bombs and spatter-fed lava flows. Degassing caused by impact vesiculation can occur only at ground-level, so any attempt to calculate the amount of erupted gas available for transport high into the atmosphere by convection above the source of a fountain-fed lava flow that is based on subtracting the volatile content of fluid inclusions from the volatile content of the resulting lava flow would be an overestimate if significant impact vesiculation has occurred

Geological Mapping of the Debussy Quadrangle (H-14) Preliminary Results

Geological mapping of Mercury is crucial to build an understanding of the history of the planet and to set the context for BepiColombo’s observations [1]. Geo-logical mapping of the Debussy quadrangle (H-14) is now underway as part of a program to map the entire planet at a scale of 1:3M using MESSENGER data [2]. The quadrangle is located in the southern hemisphere of Mercury at 0o – 90o E and 22.5o – 65o S. This will be the first high resolution map of the quadrangle as it was not imaged by Mariner 10

Candidate constructional volcanic edifices on Mercury

[Introduction] Studies using MESSENGER data suggest that Mercury’s crust is predominantly a product of effusive volcanism that occurred in the first billion years following the planet’s formation. Despite this planet-wide effusive volcanism, no constructional volcanic edifices, characterized by a topographic rise, have hitherto been robustly identified on Mercury, whereas constructional volcanoes are common on other planetary bodies in the solar system with volcanic histories. Here, we describe two candidate constructional volcanic edifices we have found on Mercury and discuss how these edifices may have formed

Preliminary findings from geological mapping of the Hokusai (H5) quadrangle of Mercury

Quadrangle geological maps from Mariner 10 data cover 45% of the surface of Mercury at 1:5M scale. Orbital MESSENGER data, which cover the entire planetary surface, can now be used to produce finer scale geological maps, including regions unseen by Mariner 10. Hokusai quadrangle (0–90° E; 22.5–66° N) is in the hemisphere unmapped by Mariner 10. It contains prominent features which are already being studied, including: Rachmaninoff basin, volcanic vents within and around Rachmaninoff, much of the Northern Plains and abundant wrinkle ridges. Its northern latitude makes it a prime candidate for regional geological mapping since compositional and topographical data, as well as Mercury Dual Imaging System (MDIS) data, are available for geological interpretation. This work aims to produce a map at 1:2M scale, compatible with other new quadrangle maps and to complement a global map now in progress

Spatial distribution and morphometric measurements of circum-Caloris knobs on Mercury: Application of novel shadow measurements

The Caloris basin (1550 km diameter) is the largest, well-preserved impact feature on Mercury. Its impact ejecta, excavated from the lower crust and uppermost mantle, provides an opportunity to investigate the interior materials of the planet. Based on Mariner 10 data, which cover only the eastern third of the basin, ‘hummocky plains’, associated with Caloris, consisting of ‘low, closely spaced to scattered hills 0.3-1 km across’ were interpreted as Caloris impact ejecta. These plains were subsequently named the Odin Formation, and the knobs associated with them were interpreted as degraded ejecta blocks. To test for an impact ejecta origin for the circum-Caloris knobs, we have mapped their locations and made morphometric measurements and high-resolution observations

Preliminary observations of Rustaveli basin, Mercury

Rustaveli basin on Mercury (82.76° E, 52.39° N) is a 200.5 km diameter peak-ring basin. Since the approval of its name on April 24, 2012, it has not featured prominently in the literature. It is a large and important feature within the Hokusai (H5) quadrangle of which we are currently producing a 1:2M scale geological map. Here, we describe our first observations of Rustaveli

Beagle Rupes – evidence for a basal decollement of regional extent in Mercury's lithosphere

Thanks to its location at low latitude and close to the terminator in the outbound view of Mercury obtained during MESSENGER's first flyby, the Beagle Rupes lobate scarp on Mercury has been particularly clearly imaged. This enables us to interpret it as a component of a linked fault system, consisting of a frontal scarp terminated by transpressive lateral ramps. The terrain bounded by these surface manifestations of faulting is the hanging-wall block of a thrust sheet and must be underlain by a basal decollement (a detachment horizon) constituting the fault zone at depth. The decollement must extend a minimum of 150 km eastwards from the frontal scarp, and at least 400 km if displacement is transferred to features interpreted as out-of-sequence thrusts and offset lateral ramps that appear to continue the linked fault system to the east. The depth of the basal decollement could be controlled by crustal stratigraphy or by rheological change within, or at the base of, the lithosphere. Previous interpretations of mercurian lobate scarps regard their thrusts as uniformly dipping and dying out at depth, lacking lateral ramps and any extensive detachment horizon. Anticipated improvements in image resolution and lighting geometry should make it possible to document what percentage of lobate scarps share the Beagle Rupes style of tectonics

Small smooth units (‘young’ lavas?) abutting lobate scarps on Mercury

We have identified small units abutting, and so stratigraphy younger than, lobate scarps. This post dates the end of large scale smooth plains formation at the onset of global contraction. This elaborates the history of volcanism on Mercury

Potential Identification of sublimation-driven downslope mass movement on Mercury

We have identified a further example of mass movement, in addition to the previously identified example in the pyroclastic vent NE of Rachmaninoff. Both examples show evidence of hollow sublimation being a cause of the mass movements

1:3M Geological Mapping of the Derain (H-10) Quadrangle of Mercury

We are making a high resolution geological map of the Derain quadrangle of Mercury. This is part of a coordinated project to create a global set of geological maps for BepiColombo