Geological History of the Dichotomy in the Southern Utopia Planitia of Mars

Abstract

The Martian crustal dichotomy represents a fundamental geological boundary, separating the ancient Noachian highlands in the south from the relatively younger lowlands to the north, which may host sediments derived from a putative northern ocean. To investigate the tectonic and hydrologic evolution of this transition, we produced a high-resolution geologic map of the southern Utopia Planitia region (5°–30°N, 105°–115°E), identifying 20 stratigraphic units grouped into highland, transitional, lowland, Amenthes region, and impact-related categories. Chronostratigraphic constraints based on crater size-frequency distributions and cross-cutting/super-positional relationships allow division of the regional geologic history into five stages, encompassing two major extrusive episodes, two regional volcanic pulses, and one intrusive event. Wrinkle ridges concentrated in the central and southern mapping areas reflect compressional stresses likely associated with these volcanic events (e.g., Watters, 1988, https://doi.org/10.1029/jb093ib09p10236; Yin et al., 2023, https://doi.org/10.26464/epp2023031), suggesting that magmatic activity was a dominant driver of Noachian–Hesperian tectonic evolution. In contrast, Hesperian and Amazonian units in the northern region are interpreted as water-related deposits, consistent with emplacement in a volatile-rich environment. Among these, the AHul₂ unit satisfies both engineering and scientific criteria for landing, highlighting it as a favorable site for China's Tianwen-3 sample return mission. This study refines our understanding of the geological evolution across the dichotomy boundary and informs future exploration strategies.