Paolo Mancinelli

Geology of the Raditladi quadrangle, Mercury (H04)

ABSTRACT In this work, we present a 1:3,000,000-scale geologic map of the Raditladi quadrangle (H04) of Mercury. The area covers nearly 7% of the entire planet and encompasses several features of interest such as the Caloris basin, the Raditladi basin, hollow clusters and volcanic features. The mapping took advantage of the data produced during MESSENGERs orbital phase. The mapped deposits include impact-related units observed at several scales from the Caloris basin to the secondary crater chains. The Smooth Plains unit covers the majority of the area, mantling the older Intercrater Plains and Bright Intercrater Plains units. Results show that the emplacement of all the main units and the Caloris impact event, representing the main geologic events in the quadrangle, were concentrated between 3.96 and 3.72 Ga. After this intense phase, the geologic framework was modified only by local events such as impact craters and hollow formation. This map is among the first products for the detailed geologic characterization of Mercury at such a scale. It will contribute as a constraint and a support for both further local investigation and mapping, and targeting of the forthcoming BepiColombo ESA/JAXA joint exploration mission to Mercury.

Experimental constraints on the rheology, eruption and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains

We present new viscosity measurements of a synthetic silicate system considered an analogue for the lava erupted on the surface of Mercury. In particular, we focus on the northern volcanic plains (NVP), which correspond to the largest lava flows on Mercury and possibly in the Solar System. High-temperature viscosity measurements were performed at both superliquidus (up to 1736 K) and subliquidus conditions (1569–1502 K) to constrain the viscosity variations as a function of crystallinity (from 0 to 28%) and shear rate (from 0.1 to 5 s-1). Melt viscosity shows moderate variations (4 –16 Pa s) in the temperature range 1736–1600 K. Experiments performed below the liquidus temperature show an increase in viscosity as shear rate increases from 0.1 to 5 s-1, resulting in a shear thinning behaviour, with a decrease in viscosity of ca. 1 log unit. The low viscosity of the studied composition may explain the ability of NVP lavas to cover long distances, on the order of hundreds of kilometres in a turbulent flow regime. Using our experimental data we estimate that lava flows with thickness of 1, 5 and 10 m are likely to have velocities of 4.8, 6.5 and 7.2 m/s respectively, on a 5° ground slope. Numerical modelling incorporating both the heat loss of the lavas and its possible crystallization during emplacement allows us to infer that high effusion rates (> 10000 m3/s) are necessary to cover the large distances indicated by satellite data from the MESSENGER spacecraft.

Mercury's Caloris basin: Continuity between the interior and exterior plains

The smooth plains on the floor of Mercurys Caloris basin and those almost entirely surrounding it beyond its rim are usually accepted to be younger than the rim materials and to be lava flows rather than impact melt. High-resolution imaging shows that the emplacement of interior and exterior plains was concurrent, with evidence of both inward and outward flow while they were being emplaced. The Caloris rim is breached in two places by continuous smooth plains that seamlessly connect interior and exterior plains. The gross-scale spectral and compositional distinctiveness of interior and exterior plains is blurred on a scale of several tens of kilometers, which could reflect interfingering of flow units less than a few hundred kilometers long that tapped melt sources of different composition and/or depth inside and outside the basin followed by local mixing of regolith. Flows occurring both inside and outside the basin should be included in estimates of the total erupted volume.

A downscaling approach for geological characterization of the Raditladi basin of Mercury

Abstract In this work, we combined multi-scale geological maps of Mercury to produce a new global map where geological units are classified based on albedo, crater density and morphological relationships with other units. To create this map, we used the 250 m/pixel mosaic of images acquired by the narrow- and wide-angle cameras onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during its orbital phase. The geological mapping is supported by digital terrain model data and surface mineralogical variation from the global mosaic of MESSENGER Mercury Atmospheric and Surface Composition Spectrometer observations. This map comprises the global-scale intercrater plains, smooth plains and Odin-type units as reported in previous studies, as well as units we term bright intercrater plains, Caloris rough ejecta and dark material deposits. We mapped a portion of the Raditladi quadrangle (19–35°N, 106–133°E) at a regional scale at a resolution of 166 m/pixel. We characterized the geological context of the area and evaluated the stratigraphic relationships between the units. To obtain a representative geological section, we analysed and corrected available topographical data. The geological cross-section derived from our regional mapping suggests that volcanic emplacement of Raditladis inner plains followed the topography of the basin after the deposition of impact-related units (i.e. melts, breccias and rim collapse) and was driven by low-viscosity flows. Hollows that appear on Raditladis peak ring were possibly formed from low-reflectance intercrater plains materials exposed through the peak ring unit. Supplementary material: Cleaner, larger version of the global-scale geological map and a local-scale map for comparison are available at http://www.geolsoc.org.uk/SUP18741.

Fractal Dimension of Geologically Constrained Crater Populations of Mercury

Data gathered during the Mariner10 and MESSENGER missions are collated in this paper to classify craters into four geo-chronological units constrained to the geological map produced after MESSENGER’s flybys. From the global catalogue, we classify craters, constraining them to the geological information derived from the map. We produce a size frequency distribution (SFD) finding that all crater classes show fractal behaviour: with the number of craters inversely proportional to their diameter, the exponent of the SFD (i.e., the fractal dimension of each class) shows a variation among classes. We discuss this observation as possibly being caused by endogenic and/or exogenic phenomena. Finally, we produce an interpretative scenario where, assuming a constant flux of impactors, the slope variation could be representative of rheological changes in the target materials.