WEATHERING AND CHEMICAL ALTERATION IN WRIGHT VALLEY, ANTARCTICA, AS AN ANALOG FOR ALTERATION ON MARS

Two ponds in Wright Valley, Antarctica , Don Juan Pond (DJP) and Don Quixote Pond (DQP), are in a landscape that has experienced moderate Pliocene expansion of local alpine glaciers paired with continuous cold-desert conditions. The basins of DJP and DQP in the South and North Forks of the valley have experienced alteration over the past 2 million years that they have been ice-free. A detailed comparison of processes of the DJP and DQP microenvironments demonstrates their potential as analogs for understanding alteration processes on Mars. We investigated trends in i) major and trace elements, ii) mineralogy (from reflectance spectra and XRD), and iii) soluble ions in the soils from the surface, sediment cores, and trenches as a function of depth and location in the basins to evaluate the effects of physical and chemical alteration. Differences in multiple parameters of three cores from the DJP saltpan reveal inversely related chemical and physical alteration gradients as a function of distance to the pond. For example, average sulfate and chloride salt abundances decrease from about 20% to less than 5% over 300 m. No such gradient is observed in radially collected surface samples of the DQP basin. While sulfate and chloride salt abundances are consistently around 5% in samples close to and far away from DQP, the salt abundances at a radial distance between 16 and 28 m of a 50 m sampling traverse are at about 15%. At DJP basin light rare earth element abundances decrease significantly towards the pond as does variability with depths, arguing strongly for increasing chemical alteration towards the pond. Rare earth element abundances in DQP basin are grouped closer and do not illustrate the spread found at DJP, indicating a lower level of chemical alteration. The difference in degree of alteration between the two microenvironments of similar soil composition and exposure time is attributed to the sources of liquid water. DJP sources include upwelling groundwater, temporary stream input, and active layer transport atop the permafrost table within the colluvium end of the pond. For DQP only shallow groundwater has been identified as a liquid water source. Our study provides complex and graded aqueous alteration scenarios under cold and dry desert conditions with strong potential for analogous aqueous processes on Mars, past or present.