Arabia Terra Layered Deposit Stratigraphy and Distribution: Evidence for Early Martian Explosive Volcanism?

Several large paterae, irregularly shaped depressions, in Arabia Terra have been suggested to be calderas that produced colossal explosive eruptions (i.e., supereruptions) that would have been among the largest to ever occur on Mars. If these features are indeed explosive calderas, ash dispersion modeling and comparisons to caldera forming eruptions on Earth suggestextensive ash deposits, carried by ancient westerlies, should be common throughout the region. Recent orbiting missions to Mars have returned high-resolution near infrared and hyperspectral images of the surface. These images enable a search in Arabia Terra for prodigious deposits of minerals that form as alteration products of volcanic ash. The identification of such deposits is evidence that large, explosive volcanic eruptions did take place in this area. Characterizing the morphology of these deposits and identifying widespread, regional units could connect these deposits to the purported calderas in western Arabia Terra.

Using hyperspectral data from the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars, onboard Mars Reconnaissance Orbiter) instrument, we have identified exposed strata that contains jarosite, smectite, and zeolites at distances of 500-3000 km from the paterae. We interpret these minerals to be altered products of volcanic ash. To verify this, we have produced terrain models (DTMs) of the surfaces encompassing these CRISM images using Context Imager (CTX) and High-Resolution Imaging Science Experiment (HiRISE) stereoimages. These DTMs are used to measure layer thicknesses of strata that contain altered ash deposits. We have found 20 to 40 m thick cliff forming units in stacks up to 300 m thick, consistent with explosive volcanic deposits. We compare these deposits to ignimbrite packages in the American southwest and the Chilean Atacama to interpret the morphology of the deposits and the infer eruption conditions and alteration environment.

Alone, neither the mineralogical nor the morphological study can definitively distinguish volcanic layers from other types of rock. Therefore, our team is also assessing layer spatial variability. Using these three aspects together our team is evaluating the hypothesis of calderas in Arabia Terra.