Assessing the geologic evolution of Greater Thaumasia, Mars

Abstract

The Greater Thaumasia region consists of three chemical provinces that include Syria, Solis, and Thaumasia Planae, the Corprates Rise, part of the Thaumasia Highlands, and the transition zone northwest of the Argyre basin. Chemical signatures obtained from the Mars Odyssey Gamma Ray Spectrometer suggest low abundances of K and Th to the west, with low H abundances and high Si abundances to the east, relative to the bulk Martian crust at midlatitudes. These observations are confirmed and quantified with a modified box and whisker analysis that simultaneously captures the degree of deviation and significance of the regionally anomalous chemistry. Motivated by regionally unique chemistry, as well as its diverse geological history, we characterize Greater Thaumasia in terms of chemistry, mineralogy, and mapped geology to determine how such complementary data record the evolution of this region. Our observations are inconsistent with a proposed salt‐lubricated landslide origin, particularly given the lack of chemical or mineralogical signatures to support near‐surface salt deposits that should arise over geological timescales. Our observations instead support magmatic processes, such as mantle evolution over geological time, which may impart the Si‐enriched signature of the eastern portion of Greater Thaumasia as well as the K and Th depletion of the southeastern flank of Syria Planum. While the observed trend of decreasing K and Th from Noachian to Hesperian lavas is inconsistent with previous models of Martian mantle evolution, we see an increase in Ca content at the Noachian‐Hesperian boundary, consistent with predictions from thermodynamic modeling.

Consolidated Chemical Provinces on Mars: Implications for Geologic Interpretations

“…However, that mantle evolution model also predicts high Th abundances, not seen in our study. Overall, the LP likely follows the same volcanic evolution trends as identified in the Greater Thaumasia area, that is, low H 2 O abundance and temporally decreasing K and Th, maybe a part of the same evolving volcanic province (Hood et al., 2016). Furthermore, higher K and Th abundance within LP relative to Greater Thaumasia could place it as the oldest member of an underlying volcanic series.…”

Amagmatic hydrothermal systems on Mars from radiogenic heat

“…While that introduces a conceptual uncertainty as the age or provenance of the bulk regolith relative to that of the underlying crust is not well known, prior works show that regolith chemistry can serve as an informative proxy for crustal processes 83 , 87 . That is notably true when mapped geology overlaps with distinct geochemistry 60 , 69 , 88 as for Eridania, albeit with greater uncertainty in areas of thick mantles of fine siliciclastics (i.e., dust) 89 . Further, ejecta from Hellas and Argyre are expected to have only thinly mantled the highlands of Terra Cimmeria and Terra Sirenum; thus, the Eridania surrounding region may represent the pre-Hellas surface better than most other regions on Mars 90 .…”

“…The relative concentration of the two elements, placed in the context of overall geochemical trends in Eridania relative to the martian crust, helps resolve that uncertainty. To avoid analytical distributional bias, we use a non-parametric modified box-and-whisker (MBW) method developed expressly for planetary data 68 , 69 , as shown in Fig. 3 .…”

Multiphase Volatilization of Halogens at the Soil‐Atmosphere Interface on Mars

“…As a graphical nonparametric statistical method, we use the modified box‐and‐whisker (MBW) method to describe the general distribution of element concentrations and mass fraction ratios in surface and subsurface soils sampled across the three landing sites. The MBW is a robust graphical method for summarizing pairwise compositional variation among locations previously used in Mars geochemical data analysis (Hood et al., 2016; Karunatillake et al., 2011; Ojha et al., 2021; Susko et al., 2017). In a typical MBW plot (Figure 3), the lower boundary and upper boundary of a box are the low excursion (represented 25th/75th percentile ratio) and the high excursion (75th/25th percentile ratio), respectively relative to a reference set; the box bounds the range of relative variation (interquartile range; IQR) for the pair.…”