Multi-phase activity on Ganymede's dark terrain: Tectonic evolution of Galileo Regio

Widespread brittle deformation characterizes the surface of Ganymede. In dark terrain regions, tectonic-related structures occur and represent linear to curvilinear kilometer-scale troughs. Such structures are called furrows and are pivotal to understand the early history of the satellite, the tectonics that affected the dark terrain, and the transition or possible future generation of light terrain. The dark terrain of Galileo Regio shows the highest density of furrows on the satellite at the resolution of Voyager and Galileo imagery. Currently, the origin of such structures is still poorly constrained and strictly related to impact cratering that occurred during Ganymede's geologic history. However, evidence from structural geology interpretation suggests an endogenic origin. In this work, we investigate the structural setting of furrows and deformation structures on Galileo Regio to understand the tectonic regimes responsible for their formation and their relative chronological evolution. Furrows that deform Galileo Regio represent evidence for a multiphase tectonic activity that affected the study area. We perform structural mapping and geostatistical analyses, which allow us to recognize a total of four systems that deform Galileo Regio at both regional-and local-scale. Our analyses allow to understand their azimuthal dis-tribution, deformation intensity and to obtain paleo-stress tensors that show the orientations of the maximum and minimum horizontal stress axes (SHmax/Shmin). The obtained results allow to propose a tectonic model that frames five phases affecting Galileo Regio, which followed a deformation history starting from an impact origin to a tectonic remodeling. Such evolutionary phases refer to a total of three different extensional regimes with Shmin trending i) NW-SE, ii) NE-SW and iii) NNE-SSW, and two strike-slip processes related to iv) NNW-SSE and v) NW-SE trending kinematics. Several phases of the proposed model are consistent with the activity of the adjacent light terrain of Uruk Sulcus and suggest its tectonic control over the dark terrain of Galileo Regio by leading to the formation of two systems. In addition, the last phase of the model shows the current setting on Galileo Regio and suggests possible rejuvenation sites of the dark terrain by the Precursor structures, considered as key elements for the dark/light transition.