New Insights Into Subsurface Stratigraphy Northwest of Ascraeus Mons, Mars, Using the SHARAD and MARSIS Radar Sounders

Abstract

The Tharsis Montes volcanoes on Mars are the source of laterally extensive lava flows and other volcanic deposits generating a complex stratigraphy throughout the Tharsis Volcanic Province. We use SHAllow RADar (SHARAD) and Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) observations in a region northwest of Ascraeus Mons to determine the composition, density, thickness, and spatial distribution of these emplaced volcanic materials. We identified subsurface reflectors along 43 SHARAD and five MARSIS observations. Reflectors in the volcanic plains are interpreted to be sequences of basaltic lava flows with interspersed pyroclastic material, dust, or regolith during a hiatus in activity. Others correspond to the base of three major flow fields. Several plain reflectors were detected by both MARSIS and SHARAD. Other notable reflectors were identified near Ascraeus' flank where lava buried glacially derived sediment. We derived thickness and other material properties for flows using their distinct topographic boundary visible in the radar images. Permittivity ranged from 7.0 to 11.2 corresponding to lava flow densities of 3.20–3.52 g/cm3. Flow thicknesses ranged from 19.8 to 60.2 m. Loss tangents were low for the flow fields ranging from 0.024 to 0.043. Loss tangents in the plains ranged from 0.010 to 0.076. Higher loss tangents correspond to lossier regions that may have higher concentrations of radar absorbing minerals like hematite. Surface roughness controls where reflectors are detected. SHARAD detects the base of three out of the four flow fields in this region with muted surface roughness from dust mantling and erosion.

RIMFAX Ground Penetrating Radar Reveals Dielectric Permittivity and Rock Density of Shallow Martian Subsurface

“…The permittivity is consistent with permittivities found in dry, basaltic lava flows on Earth (Campbell & Ulrichs, 1969;F. Ulaby et al, 1990), as well as with orbital radar derived values for lava flows on Mars (Carter, Campbell, Holt, et al, 2009;Shoemaker et al, 2022;Simon et al, 2014). We infer that the scattering structures are likely comprised of sharp edges or cavities within lava flow regimes.…”

“…From orbit, the permittivity can be determined in regions where an independent measurement of the thickness of a particular layer is available. SHARAD (20 MHz center frequency) and MARSIS (1.8, 3, 4, and 5 MHz sounding modes) have estimated the permittivity of layers within the polar ice caps, buried ice deposits across Mars, and that of dry rocky materials such as lava flows and pyroclastic deposits (e.g., Carter, Campbell, Holt, et al., 2009; Carter, Campbell, Watters, et al., 2009; Ganesh et al., 2020; Shoemaker et al., 2022; Simon et al., 2014; Watters et al., 2007). Given the suggested igneous surface material of Jezero, the orbital permittivity studies for lava flows on Mars are most relevant for comparison with RIMFAX findings.…”

“…The thicknesses of basaltic lava flows near Ascraeus Mons in the Tharsis Volcanic Province were measured and permittivity was inferred to range from 6.2 to 17.3 and later reestimated to range from 7.6 ± 2.3 to 11.6 ± 4.2 with an average of 9.6 (Carter, Campbell, Holt, et al., 2009; Simon et al., 2014). Another study used additional SHARAD coverage to refine this range from 7 to 11.2 with an average of 9.7, using a different methodology to infer flow thickness (Shoemaker et al., 2022). These orbital measurements are in good agreement with the permittivity of terrestrial, laboratory derived values: dense, dry, and basaltic lava flows appear to range between 7 and 11, while for pyroclastic material (i.e., ash and tephra), the permittivity is found to be as low as 3 (Campbell & Ulrichs, 1969; F. Ulaby et al., 1990).…”

Revealing Elysium Planitia's Young Geologic History: Constraints on Lava Emplacement, Areas, and Volumes

“…The values inferred in this study are on the lower to middle end of the permittivities found by Carter et al (2009) and Shoemaker et al (2022) who investigated the properties of the flows west and northwest of Ascraeus Mons. Carter et al (2009) found that the northern flow has permittivity values between 6.2 and 17.3, with an average of 12.2.…”

“…(2009) and Shoemaker et al. (2022) who investigated the properties of the flows west and northwest of Ascraeus Mons. Carter et al.…”