¹Chao Li et al. (>10)
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117349]
¹Institute of Natural Resources Survey, China University of Geosciences, Wuhan 430074, China

Copyright Elsevier

The elemental geochemical characteristics analyzed by the Mars Odyssey Gamma-Ray Spectrometer (GRS) have played a key role in understanding Mars geology and geochemical processes. However, GRS data are typical compositional data with a closure effect, which may introduce uncertainty in mapping Martian elemental geochemical provinces. We present a compositional data analysis (CoDA) based on centered log-ratio (clr) and isometric log-ratio (ilr) transformations to address these problems. Based on CoDA, we sequentially applied Exploratory Data Analysis (EDA), Correlation Analysis (CA), Principal Component Analysis (PCA), and Robust Principal Component Analysis (RPCA) to process the 1451 map bins that included Al, K, Fe, Si, Ca, H₂O, Cl, and S. The EDA analysis shows that the internal structure of the data after the clr transformation is closer to a normal distribution. Only clr-based CA analysis indicates consistently negative correlations between each of the key rock-forming elements (Si, Fe, Ca, Al) and each of the volatile elements (H₂O, Cl, S) at the global scale. When considering the closure effect and outliers in the GRS data, we used ilr-based RPCA to obtain the first three robust principal components that better reflect the multivariate geochemical information of the Martian surface. In particular, the geochemical anomalies revealed by RPC1 for the H₂O-S-Cl and Ca-K-Si-Al-Fe are more closely consistent with the distribution characteristics of low thermal inertia–high albedo and high thermal inertia–low albedo, respectively. Exploratory Hierarchical Cluster Analysis (HCA) based on the first three robust principal components revealed that when the number of clusters was set to five, elemental geochemical provinces better reflected the enrichment patterns of elements on the Martian surface. The element abundance statistics and Modified Box-and-Whisker (MBW) analysis for the seven representative sub-provinces across five geochemical provinces reveal more detailed characteristics of element enrichment and depletion. Some sub-provinces have significantly higher S, Cl, H₂O, and Si contents than the global average due to volcanism (e.g., Olympus Mons, Tharsis Montes, and Elysium Mons) and historical groundwater activity regions (e.g., Meridiani Planum); some are consistent with high-density distribution regions of aqueous minerals. Martian element provinces mapped using the CoDA analysis can be combined with other types of data and geological information for further research.