Tectonic evolution identified by regional and local structures within Danielson crater, Arabia Terra: Testifying to the waning of pseudo plate tectonics on Mars?
Authors: Schmidt Gene , Trullo Adriano , Salvini Francesco , Apuzzo Andrea 
Published: September 2022

&lt;p&gt;&lt;strong&gt;Introduction&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;The nature of the stress regime of the martian lithosphere that was active in the Late Noachian-Early Hesperian is a topic of ongoing debate [1]. The duality between the northern lowlands and southern highlands is thought to be a major relic of the early tectonic regime of Mars, however their exact origins and geological history is not fully constrained. Arabia Terra is a region that spans 4850 km across and is located in the transitional zone between the lowlands and highlands. It is known for widespread deposition of layered deposits [2, 3] within craters which are associated with past water activity [4]. Danielson is a 60 km diameter, 2 km deep, crater located in western Arabia Terra and centered at 8&amp;#176;N, 353&amp;#176;E (Figure 1A). The crater is dominated by the presence of a massive layered deposit which exhibits intense faulting and several large folds (e.g. Figure 1B, 1C, 1D).&lt;/p&gt;
&lt;p&gt;Danielson is unique to other craters in the region due to its quadrangular shape (Figure 1A and 1B). This shape cannot be easily explained by an impact event. Due to faulting that offsets the layered deposits and the crater rim, and high dips and folds, the crater likely has undergone extensive deformation. Since the deposition of these deposits is considered to have taken place in the Early Hesperian [5], we propose that the quadrangle shape of the crater rim, combined with post-depositional deformational structures, reflects the waning tectonic regimes during the Noachian-Middle Hesperian transition which was possibly a vestige of pseudo plate tectonics that never fully formed. The faulting and folding process may reflect the new successive tectonic regime that post-dates the closure of a pseudo plate tectonic era.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Methodology&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;An HRSC composite DEM [6] forms the base dataset of our study. We utilized three HiRISE DEMs and one HiRISE image for detailed measurements. 52 layer attitude measurements were obtained using Orion software and evaluated statistically based on strike and dip frequency (Figure 1D). Faults were identified by the lateral offset of layers and linear features. Folds were identified by interpreting large scale structures within layer sequences based on dip directions and 3D scenes.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Results&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;High layer dips, folds, and widespread faulting were identified and measured within Danielson. Two sets of dips, 4.5&amp;#176; and 19.2&amp;#176;, are present with a maximum dip of 44&amp;#176; (Figure 1D). At least 12 folds were identified, each collinear and alternating from syncline to anticline (e.g. Figure 1E). All folds plunge to the southwest. Fold limbs are approximately 200 m long and contain on average 20 layers. Axial traces have a preferred northeast-southwest orientation. Over a hundred faults have been identified, many propagating through fold hinges (e.g. Figure 1E). Faults have two preferred orientations, northeast-southwest and northwest-southeast. Faults generally offset layering several meters, with some reaching 400 m.&lt;/p&gt;
&lt;p&gt;Danielson has a quadrangle shaped crater rim which does not conform to a circle or an oval (Figure 1B). Several regional faults pass through the crater and cross-cut the crater rim. The quadrangle shape and the fault/fold trend are not coaxial, suggesting a rotation in the tectonic stress regime between the two events.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Discussion&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;Dips are often above the angle of repose for material with a grain size that could be deposited by air or fluid-expulsion (34&amp;#176;). Although there are many factors that contribute to the angle of repose (e.g., grain shape and moisture) [7], we interpret high dips as non syndepositional (i.e. not draping) and representative of a unique post-depositional history. Furthermore, the presence of tight folding in combination with widespread faulting demonstrates a period of intense deformation which possibly indicates regional extension and compression. Subsidence may have had a role in the observed deposit deformation because complex craters have a period of collapse and even uplift after impact, however the timescale of collapse is thought to be shorter in comparison with the accumulation rate of sediments [8].&lt;/p&gt;
&lt;p&gt;The quadrangle shape of the crater can be produced by the interaction of the impact stress and the stress regime of the lithosphere present at the time of impact (Middle-Late Noachian; 4.1-3.8 Gya) [9]. In this case it would be expected that the regional stress is characterized by northeast-southwest maximum horizontal extension and northwest-southeast maximum horizontal compression as explained by the contrast of the crater rim slightly changing from round to straight, normal to the extension direction (Figure 1B).&lt;br /&gt;&lt;br /&gt;This is further contested by the identification of faults and folds of the younger Early Hesperian aged (3.8 Gya) deposits within the crater that have preferred orientations north-northeast and south-southwest. It is likely that these structures are related to the tectonic regime which was present after the ending of the horizontal movement which produced the quadrangular shape of the crater. This change in the tectonic evolution of the region may well reflect the change from a type of plate tectonics regime to the present static stress.&lt;/p&gt;
&lt;p&gt;The stress regime revealed by the asymmetry of the crater can be a reflection of the last global tectonic (i.e. pseudo plate tectonics) framework which at the time of impact was ending. At the time of impact there was likely still a residual stress regime due to the horizontal movement at the boundary of the lowlands and highlands.&lt;/p&gt;
&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;1059&quot; height=&quot;1145&quot; /&gt;&lt;/p&gt;
&lt;p&gt;Figure 1.&lt;/p&gt;
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