Geological Complexity of Glinka Crater (Mercury): A Hybrid Mapping Approach Based on Spectral and Morphological Analysis

INTRODUCTION

Mercury's surface has undergone intense modification by impact cratering and space weathering, which makes delineating distinct geological units particularly complex. In this study, we focus on Glinka crater (Fig. 1), situated in the Beethoven quadrangle (H-07), an area marked by diverse spectral and morphological features including impact structures, a candidate pyroclastic vent [1], tectonic ridges [2], and hollows [3] [4]. Our objective is to identify and classify surface units by applying an integrated methodology that combines compositional information from spectral data with detailed morphological and structural analysis. This hybrid approach is intended to enhance the geological interpretation of the crater and provide insights into the interplay between impact, volcanic, and tectonic activity.

 

METHODS

The analysis is based on a combination of MESSENGER MDIS datasets and derived topographic products. We produced a 121 m/pixel monochromatic NAC mosaic and two higher-resolution ones (56 and 14 m/pixel) for detailed mapping. Spectral data were derived from a WAC 8-filter multispectral cube [6] (268 m/pixel), while topographic derivatives were extracted from a DEM at 222 m/pixel [7]. The data were processed using ISIS3 employing the Kaasalainen–Shkuratov photometric correction model considering the parameters derived by [8] and analyzed in ENVI and GIS environments.

Four spectral parameters were selected [9]: R750, global slope, NIR slope, and UV/VIS slope. Each was classified into five intervals using k-means clustering. The combined classification led to the extraction of over 400 initial spectral units, subsequently filtered and merged into ten representative SUs. These were then correlated with morpho-structural features, allowing the construction of a hybrid map that integrates both spectral and geological observations.

 

RESULTS

The classification identified ten distinct spectral units (SUs), each defined by unique combinations of reflectance and spectral slope values (Fig.1). Some units display high reflectance and low slopes (e.g., SU 3 and SU 8), while others show steep slopes, especially in the visible or NIR range (e.g., SU 5, SU 7, SU 10). A hybrid geological map (Fig. 2) was constructed by integrating these spectral units with geomorphological elements such as crater rims, terraces, central uplifts, and tectonic ridges.

In the hybrid geological map, the spectral units were grouped into seven hybrid units (A–G), each associated with specific morphologic or structural contexts.

Unit A (SU 2) is the most spatially widespread unit in the study area. It is characterized by the lowest reflectance among all SUs, along with high global and IR slopes and moderate UV/VIS slope. It forms spectrally homogeneous surfaces over broad, morphologically indistinct regions.

Unit B (SU 1) appears scattered across the study area and does not correspond to a single ejecta blanket, unlike other ejecta-related units (e.g., Units C and D).
Unit C (SU 3) is optically bright and spectrally flat, arranged in radial patterns around impact craters, consistent with fresh ejecta blankets.
Unit D (SU 4) shows an ejecta-like distribution but differs spectrally from other ejecta units due to its steeper slopes.

Unit E (SU 7), one of the brightest and spectrally steepest units, exhibits an irregular lobate morphology resembling ejecta and is spatially located above parts of Unit D. Interestingly, SU 7 spectral behaviour is also present in Unit G (SU 7 + 10), which surrounds the central vent and forms a compact, circular deposit. This recurrence highlights a spectral similarity across units with different geological context spatial configurations.

 

DISCUSSION AND ONGOING WORK

Preliminary spatial relationships between hybrid units reveal potential stratigraphic links. Unit E appears to partially overlie Unit D, suggesting a relative sequence between two spectrally distinct surfaces. While both display ejecta-like morphologies, the higher reflectance and steeper spectral slopes of Unit E set it apart from the underlying Unit D. This configuration may reflect differences in composition or emplacement history and will be further explored through stratigraphic and contextual mapping.

Unit G, located at the centre of the crater and surrounding the presumed pyroclastic vent, stands out for its spatial and spectral coherence. Its confinement to the vent area and extreme spectral characteristics support its interpretation as a unique, compositionally distinct surface unit.

Crater counting (CSFD) is currently underway on selected ROIs to estimate the relative age of key units and distinguish potentially coeval from diachronous deposits. Unit B, a spectrally neutral ejecta-like unit with scattered distribution, is under investigation to determine whether it includes ejecta from multiple impacts. Its subdivision is being approached through a combination of crater counts, morphologic context, and analysis of adjacent areas.

Current analyses are also addressing the recurrence of SU 7 spectral characteristics across different geological contexts. This spectral configuration appears both in an ejecta-like deposit (Unit E) and in the vent-associated Unit G. We are working to clarify whether this similarity reflects comparable compositions, distinct emplacement mechanisms, or post-depositional alterations.

We are also investigating potential interactions between pyroclastic and tectonic processes. Specifically, we are analyzing spatial and stratigraphic relationships between spectrally red-bright units surrounding the vent and the compressional ridges that intersect it. These investigations aim to reconstruct the relative timing of magmatic and tectonic events and evaluate possible genetic connections.

 

Acknowledgements  

M.I. and G.M. acknowledges support from the Italian Space Agency (2022-16-HH.1-2024).

 

References

[1] Kerber L. et al. (2011) PSS 59, 1895-1909.
[2] Thomas R. J. et al. (2014) Icarus 229, 221-235.

[3] De Toffoli B. et al. (2024) Earth Space Sci. 11.

[4] Man B. et al. (2023) Nat.Geosci. 16, 856-862.

[5] Hawkins S.E. et al. (2007), Space Sci. Rev. 131, 247-338.

[6] MESSENGER MDIS Data Users’ Workshop (2015), LPSC XLVI.

[7] Domingue D. L. et al. (2016) Icarus 268, 172-203.

[8] Preusker F. et al. (2017) PSS 142, 26-37.

[9] Zambon F. et al. (2022) JGR:Planets 127.

 

 

Figure 1. Spectral map

 

 

Figure 2. Hybrid map