Aqueous alteration of the Vastitas Borealis Formation at the Tianwen-1 landing site

Abstract The Vastitas Borealis Formation is a Hesperian-aged sedimentary unit that mainly covers the Martian northern plains. Its environment of formation uncertain but may be related to an ancient ocean, outflow channel deposits, compaction and drainage activities, or subsurface ice-related processes. Here we investigate geological evolution using geochemical mineralogical data acquired by Mars Surface Composition Detector on board Zhurong rover at Tianwen-1 landing site. We find fine-grained soil very similar ubiquitous surface dust other sites mixed with calcium-rich magnesium-poor local materials. These materials are mostly igneous minerals allophane imogolite/opal appear have low degree chemical alteration. suggest these deposits likely formed alteration extensive volcaniclastic soils in limited ephemeral water under cold conditions, which largely supports hypotheses frozen ocean sublimation.