Low-voluminous, mafic-dominated volcanism in Claritas Fossae, Thaumasia region on Mars
Authors: Pieterek Bartosz , Brož Petr , Hauber Ernst 
Published: February 2023

The majority of Tharsis is covered by relatively young and low-viscous widespread lava plains, being of basaltic composition. They likely buried older volcanic landforms which could have provided important data about ancient eruptive style and magma composition. However, several fractured regions forming topographic raises survived regional resurfacing, and they are providing an insight into the volcanic history of the planet. To date, these Noachian/Hesperian-aged fractured terrains revealed the presence of putative scoria cones in Ulysses (Bro&#382; and Hauber, 2012) and Noctis Fossaes (Pieterek et al., 2022) supporting a hypothesis that the volcanic activity differed in the past from waste eruptions of young low-viscous lavas. Here, we present results of mapping that focused on the edifices superimposed on the Noachian-age fractured crust within the Claritas Fossae region. The aim was to decipher their origin and provide additional constraints on the volcanism emplaced on the ancient terrains.In the studied region, we mapped 39 topographically positive edifices of constructional character. They are spread on the ancient crust showing NW-SE trending alignment over an area of 170 x 500 km. Based on the CTX observations, we noted that their majority is characterized by elongated (WNW-trending) to irregular or circular outlines and relatively steep-appearing flanks without associated flow-like units. Among these edifices, one circular-shaped edifice located in the easternmost part of the studied area is associated with short-distance flow-like units and rimmed by a caldera-like structure. We also determined the mineralogical composition for several edifices with available CRISM spectral data. This showed that edifices are spatially associated with high concentrations of igneous-origin low-calcium pyroxenes (LCP). Based on the relative stratigraphy, we showed that volcanic activity postdates the fracturing, the age of which has been estimated to space between ~3.4 to ~2.6 Ga and likely predates the formation of Thaumasia graben (Late Hesperian/Early Amazonian).The shapes, sizes, distribution pattern, and mineralogical composition of the mapped edifices are consistent with putative volcanic origin. Therefore, we argue that Claritas Fossae&#8217;s field mainly experienced effusive eruptions characterized by highly viscous, volatile-poor magma(s). Such composition limited the ability of the effused lavas to spread from the site into the surroundings. The elongation and spatial distribution of the edifices together with their LCP-rich composition indicate volcanic eruptions might be controlled by the migration of subsurface dike(s) from the shallow magma chamber(s). Altogether the comprehensive study of the volcanic evolution of the Thaumasia region showed that the studied edifices might express the late-stage dike migration of LCP-rich magmas that used the reactivated WNW-ESE tectonic pathways.Besides the effusive-origin edifices, the area might contain one of the best-preserved kilometer-sized, explosive-type volcanic edifice emplaced within the putative caldera-like rim known from Mars.This research was funded by the &#8220;GEO-INTER-APLIKACJE&#8221; project no. POWR.03.02.00-00-I027/17.ReferencesBro&#382;, P., Hauber, E., 2012. A unique volcanic field in Tharsis, Mars: Pyroclastic cones as evidence for explosive eruptions. Icarus 218, 88&#8211;99. https://doi.org/10.1016/j.icarus.2011.11.030Pieterek, B., Laban, M., Ci&#261;&#380;ela, J., Muszy&#324;ski, A., 2022. Explosive volcanism in Noctis Fossae on Mars. Icarus 375, 114851. https://doi.org/doi.org/10.1016/j.icarus.2021.11485