Reconstructing Displacement Histories at Fault–Crater Intersections on Mercury.

Introduction

Mercury is a contracting planet that has undergone a global contraction of about 7 km [1]. This contraction has produced ubiquitous compressional landforms—including lobate scarps, high-relief ridges, and wrinkle ridges—that have been active since the Early Calorian period [2] and possibly into the present day [3].

Mercurian faults, like their terrestrial counterparts, likely initiate as small segments that later coalesce into longer, more continuous structures [e.g., 4]. Terrestrial faults typically exhibit bell-shaped displacement profiles, with peak displacement at the center and tapering toward the tips [e.g., 5]. However, observations on Mercury reveal anomalies in this trend, especially near intersections with impact craters, where displacement first drops at the crater rim and then slightly peaks at the crater floor. These deviations suggest syn-tectonic crater formation.

This study investigates such anomalies in three key fault systems—segments of the Victoria System, Discovery Rupes, and Enterprise System—to reconstruct their original displacement profiles and constrain the relative chronology of fault evolution and crater formation.

Data and Methods

Our analysis integrates the MESSENGER/MDIS BDR global basemap (166 m/px), the global DEM [6], and the global structural map [7]. We focus on four fault–crater intersections: the Victoria System at Geddes and Donne craters, the Enterprise System at Karsh crater, and Discovery Rupes at Rameau crater.

Displacement profiles were extracted along multiple cross-fault transects both within and outside the craters. Scarp heights measured along these profiles were plotted against fault length, derived from cumulative transect spacing. Peaks in these plots indicate discrete fault segments. To reconstruct the original (pre-crater) displacement profiles, we linearly interpolated the segment flanks and used their intersection points to estimate the expected maximum displacement. The average y-values of these intersections provided a rough displacement estimation.

By combining the reconstructed profiles with published chronologies [8–11], we derived average slip rates and estimated crater ages based on the modelled displacement accumulation.

Results and Interpretation

Victoria System (Geddes crater): The fault segment cutting Geddes crater displays slight asymmetry between its two major segments. Despite some erosion likely caused by the impact, both segments suggest comparable original displacement. Tectonic activity spanned 3.8–2.4 Ga [8], with 2.43 km of total displacement, yielding a slip rate of ~170 cm/Myr. The observed 1.15 km of displacement within the crater accumulated over ~0.68 Gyr, suggesting a crater age of ~3.1 Ga (Mid Calorian).

Victoria System (Donne crater): The Donne segment features a nearly symmetrical profile adjacent to the crater, indicating undisturbed fault growth. With 1.09 km of total displacement and a slip rate of 78 cm/Myr, the central 0.9 km peak implies 1.15 Gyr of growth. This places Donne Crater’s formation at ~3.55 Ga (Early Calorian), during the fault’s early activity.

Enterprise System (Karsh crater): The Enterprise System is one of the longest fault systems on Mercury, extending over 900 km. With tectonic activity spanning 3.8–0.95 Ga [8] and a maximum displacement of 3.7 km, it yields an average slip rate of 130 cm/Myr. The 0.9 km displacement within Karsh Crater likely developed ~710 Myr before the end of the fault’s tectonic activity, suggesting a crater age of ~1.66 Ga (Late Calorian).

Discovery Rupes (Rameau crater): Absolute dating for Discovery Rupes is unavailable, but it is estimated to have remained active into the Mansurian period (1.7–0.3 Ga) [9]. Assuming faulting began in the Early Calorian (3.85 Ga) [2], the total 1.34 km displacement implies a slip rate of 38 cm/Myr. The 0.6 km displacement within Rameau likely accrued over 1.58 Gyr, suggesting a crater age of ~1.88 Ga (Late Calorian).

Conclusions and Future Work

Our results highlight the diagnostic potential of displacement profiles in reconstructing fault evolution and offer insights into the timing and dynamics of tectonic activity when faults intersect syn-tectonic craters.

Our age estimates for Geddes, Donne, and Karsh craters are consistent with published morphological dating [10], supporting the robustness of our modelling. While the approach is promising, uncertainties remain—especially where long tectonic histories blur temporal resolution (as in the case of Discovery Rupes and Rameau Crater). Ongoing work will systematically date all fault–crater intersections on Mercury, enabling a more comprehensive reconstruction of the planet’s global contraction history.

References: [1] Byrne et al. (2014). Nature Geoscience, 7, 301–307. [2] Crane & Klimczak (2017). Geophysical Research Letters, 44(7), 3082-3089. [3] Tosi et al. (2013). JGR: Planets, 118(12), 2474-2487. [4] Klimczak et al. (2013). JGR: Planets, 118, 2030-2044. [5] Kim & Sanderson (2005). Earth-Sci. Rev., 68(3-4), 317-334. [6] Becker et al. (2016). LPSC Contrib., 1903. [7] Man et al. (2023). Nature Geoscience, 16, 856–862. [8] Galluzzi et al. (2019). JGR: Planets, 124, 2543-2562. [9] Giacomini et al. (2020). Geoscience Frontiers, 18, 15187. [10] Clark et al. (2024). LPSC Contrib. No. 3040. [11] Kinczyk et al. (2020). Icarus, 341, 113637.

Acknowledgements: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2024-18-HH.0.
This research is also supported by INAF through RSN3 Mini-Grant “Investigation of Mercury’s Tectonics (iMeT)”