Age dating of an extensive thrust system on Mercury: Implications for the planet's thermal evolution

The tectonic evolution of Mercury is dominated at a global scale by contractional features such as lobate scarps that are widely distributed across the planet. These structures are thought to be the consequence of the secular cooling of Mercury. Therefore, dating these features is essential to place constraints on the timing of planetary cooling, which is important for understanding the thermal evolution of Mercury. In this work, we date an extended thrust system, which we term the Blossom Thrust System, located between 80°E and 100°E, and 30°N and 15°S, and which consists of several individual lobate scarps exhibiting a north-south orientation and a westward vergence. The age of the system was determined using several different methods. Traditional stratigraphic analysis was accompanied by crater counting of units that overlap the thrust system and by using the buffered crater-counting technique, allowing us to determine an absolute model age for the tectonic feature. These complementary methods give consistent results, implying that activity on the thrust ended between 3.5 and 3.7 Ga, depending on the adopted absolute-age model. These data provide an important insight into this portion of Mercury's crust, which may have implications for models of the thermal evolution of the planet as a whole.