Depletion of Heat Producing Elements in the Martian Mantle

Abstract

Heat is primarily generated in planetary interiors by the decay of long‐lived heat producing elements (HPE). Planetary heat flow estimates can thus provide critical insights into the thermal state of a planet and the bulk distribution of the HPE. The lack of appreciable lithospheric deflection in the north polar region of Mars by the weight of the polar ice cap is suggestive of low heat flow. Here we model the deflection of the Martian lithosphere and show that the present‐day mantle heat flow cannot exceed 7 mW m−2 in the north polar region of Mars. Our mantle heat flow estimate is notably lower than the heat flow expected from a chondritic mantle suggesting the Martian mantle to be depleted in HPE. If our result is globally representative, lower levels of heat generation in the planet's mantle may have inhibited widespread late‐stage volcanism on Mars.

Martian Mantle Heat Flow Estimate From the Lack of Lithospheric Flexure in the South Pole of Mars: Implications for Planetary Evolution and Basal Melting

“…The surficial downwarping underneath the SPLD is likely less than our conservative estimate of 1 km (e.g., Plaut et al., 2007). If surficial downwarping is ∼500 m, the mantle heat flow may be lower than 7 mW/m 2 , similar to our estimate of mantle heat flow in the north polar region (Ojha et al., 2019). Thus, reasonable variations in radar mapping of the basal surface do not notably change our upper limit on q b at the south polar region.…”

“…The viscoelastic response of the Martian lithosphere to the SPLD was modeled using the finite element package Marc‐Mentat. Here, we only summarize the methodology, and interested readers are referred to several previous works (e.g., Karimi & Dombard, 2016; Karimi et al., 2016; Ojha et al., 2019) for a detailed description.…”

Flexure of the Lithosphere Beneath the North Polar Cap of Mars: Implications for Ice Composition and Heat Flow

“…This discrepancy is largely the result of their having mistook previously reported relative 10.1029/2019GL086746 deflections between two points with the maximum absolute deflection below the deposit (see Figure S7). For example, the maximum deflection at the center of the cap, as predicted by both Phillips et al (2008) and this study, is about 350-400 m. Ojha, Karimi, et al (2019) however used a value of 200 m, but this value (Selvans et al, 2010) represents only the relative deflection from the edge of the cap to about half-way to the center of the polar cap.…”

“…Using previously reported MARSIS and SHARAD radar constraints on the amount of lithospheric deflection beneath the north polar cap, Ojha, Karimi, et al (2019), however, inferred a considerably lower mantle heat flow of 7 mW m −2 . This discrepancy is largely the result of their having mistook previously reported relative 10.1029/2019GL086746 deflections between two points with the maximum absolute deflection below the deposit (see Figure S7).…”

“…Our results imply a maximum absolute deflection of 400 m at the center of the polar cap and 250 m below Gemina Lingula. From Figure 2 of Ojha, Karimi, et al (2019), our constraints require the mantle heat flow to be 13 to 20 mW m −2 .…”