Abstract
Pityusa Patera is the southernmost of four paterae in the 1.2 × 106 km2 wrinkle-ridged plains-dominated Malea Planum region of Mars. Based on their texture, morphology, and uniqueness to Pityusa Patera, we interpret layered, folded massifs as pyroclastic deposits emplaced during patera formation as a collapse caldera. Such deposits would not be expected in a previously suggested scenario of patera formation by subsidence from lithospheric loading. Our structural measurements and modeling indicate that the folding and high relief of the massifs resulted from ~1.3%–6.9% of shortening, which we show to be a reasonable value for a central plug sagging down into an assumed piston-type caldera. According to a previously published axisymmetric finite-element model, the extent of shortening structures on a caldera floor relative to its total diameter is controlled by the roof depth of the collapsed magma chamber beneath it, which would imply Pityusa Patera formed above a chamber at 57.5–69 km depth. We interpret this value to indicate a magma chamber at the crust-mantle interface, which is in agreement with crust-penetrating ring fractures and mantle flows expected from the formation of the Hellas basin. As such, the folded massifs in Pityusa Patera, which are partially superposed by ca. 3.8 Ga wrinkle-ridged plains, should consist of primordial mantle material, a theory that might be assessed by future hyperspectral observations. In conclusion, we do not favor a formation by load-induced lithospheric subsidence but suggest Pityusa Patera to be one of the oldest extant volcanic landforms on Mars and one of the largest calderas in the solar system, which makes the folded, likely mantle-derived deposits on its floor a prime target for future exploration.
Highlights
AND SETTING The Malea Planum region is an ∼1.2 × 106km2 physiographic domain defined by Noachian to early Hesperian wrinkle-ridged plains located in Mars’ southern hemisphere, southwest of the Hellas basin (Fig. 1A; Peterson, 1978; Tanaka and Scott, 1987; Williams et al, 2009, 2010a, 2010b; Tanaka et al, 2014)
Recent mapping by Bernhardt and Williams (2021) showed that Pityusa Patera is superposed by the younger, ubiquitous wrinkle-ridged plains characterizing the Malea Planum region (Fig. 1D, unit Npr—Noachian ridged plains), explaining the apparent lack of tectonic and volcanic landforms expected for calderas
We present new observations including the analyses of previously undescribed massifs of folded, potentially pyroclastic deposits as well as structural investigations based on modeling by Zuber and Mouginis-Mark (1992) that indicate Pityusa Patera to have formed not by loading-induced lithospheric subsidence, but as an actual volcanic mega-caldera from collapse of a magma chamber, potentially at the crustmantle interface
Summary
AND SETTING The Malea Planum region is an ∼1.2 × 106km2 physiographic domain defined by Noachian to early Hesperian wrinkle-ridged plains (including Malea Planum) located in Mars’ southern hemisphere, southwest of the Hellas basin (Fig. 1A; Peterson, 1978; Tanaka and Scott, 1987; Williams et al, 2009, 2010a, 2010b; Tanaka et al, 2014). Recent mapping by Bernhardt and Williams (2021) showed that Pityusa Patera is superposed by the younger, ubiquitous wrinkle-ridged plains characterizing the Malea Planum region (Fig. 1D, unit Npr—Noachian ridged plains), explaining the apparent lack of tectonic and volcanic landforms expected for calderas.
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