Abstract
Planetary geologic maps are usually carried out following a morpho-stratigraphic approach where morphology is the dominant character guiding the remote sensing image interpretation. On the other hand, on Earth a more comprehensive stratigraphic approach is preferred, using lithology, overlapping relationship, genetic source, and ages as the main discriminants among the different geologic units. In this work we produced two different geologic maps of the Rembrandt basin of Mercury, following the morpho-stratigraphic methods and symbology adopted by many authors while mapping quadrangles on Mercury, and an integrated geo-stratigraphic approach, where geologic units were distinguished also on the basis of their false colors (derived by multispectral image data of the NASA MESSENGER mission), subsurface stratigraphic position (inferred by crater excavation) and model ages. We distinguished two different resurfacing events within the Rembrandt basin, after the impact event, and four other smooth plains units outside the basin itself. This provided the basis to estimate thicknesses, volumes, and ages of the smooth plains inside the basin. Results from thickness estimates obtained using different methodologies confirm the presence of two distinct volcanic events inside the Rembrandt basin, with a total thickness ranging between 1–1.5 km. Furthermore, model ages suggest that the volcanic infilling of the Rembrandt basin is among the ones that extended well into the mid-Calorian period, when Mercury’s effusive volcanism was previously thought to be largely over.
Highlights
Geologic maps of other planets are mainly based on units that are distinguished by surface geomorphology and stratigraphic relations [1], and only secondarily by their color variation
Results from the Model Production Function best fits display different model ages that can be associated with different geologic events related to the impact basin: 1. The age of 3.8 ± 0.1 Ga (Figure 11a) is likely to be associated with Rough Floor Terrain (RFT), mapped and interpreted as the bottom layer within the basin, i.e., a mixture of Low-Reflectance Material (LRM) and Intercrater Plains (IT) reworked in the early stages after the impact event and before the emplacement of the smooth plains
We link the age of 3.7 ± 0.1 Ga (Figure 11b) to the emplacement of the first smooth plain event, i.e., the Older interior smooth plains (OIP): this value falls within the fit error of the previous age, the two different fits are separated by a visible S-shape kink that occurs between 30–45 km
Summary
Geologic maps of other planets are mainly based on units that are distinguished by surface geomorphology (relief, texture) and stratigraphic relations [1], and only secondarily by their color variation. By ignoring or under-evaluating color variation, geologic mappers are inherently neglecting an important source of information Such information can improve understanding of the genesis and relative emplacement age of the different geologic units. Geologic maps of some quadrangles on Mercury [17,18,19,20] provide the most detailed cartographic products available for the planet up to date These maps focus on geologic units distinguished mainly on the basis of their morphology, texture (i.e., roughness) and crosscutting relationships with faults, but their stratigraphic relationship has been just barely defined by means of color variegation. We estimated the volume of the volcanic infilling of the Rembrandt basin
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