The Volcanic Evolution of Syrtis Major Planum, Mars

This thesis explores the geological history of the Syrtis Major Planum volcanic province on Mars. The primary aims are (i) to differentiate the various units that make up the lava plain of Syrtis Major Planum, (ii) to investigate the formation of the central caldera complex, and (iii) to understand how the volcanic architecture has evolved over time in the regional contex. The methodology applied is that of planetary geological mapping using remote sensing data. Two new morpho-stratigraphic maps of Syrtis Major Planum have been produced. Map 1, a 1:2,000,000 scale map, uses 100 m/pixel THEMIS data as the base layer, and draws on 6 m/pixel CTX data to provide additional information. Map 2 is a 1:250,000 scale map of the Nili Patera caldera and uses base layer mosaics of CTX data and CTX Digital Terrain Models. The mapping shows that there were two major phases of magmatism at Syrtis Major. The first phase (~3.6 Ga – ~3.2 Ga) consisted of tube-fed lava plains interleaved with giant (>300 km) tabular lava flows emplaced from the centre of the planum. By the end of this phase, a fractionally crystallised magma reservoir, partially melting the hydrated sediments of the underlying Noachian highlands, had developed. The eruptive products of this magma reservoir include an ignimbrite, now exposed in Nili Patera. The second phase of magmatism (~2.7 Ga - ~2.2 Ga) consisted of temporally sporadic volcanism, spatially concentrated in the central caldera complex, and includes two examples of high-silica lava units. These derived from partial melting of the fractionally crystallised magma reservoir in the presence of hydrothermal fluids. The evolution of lava emplacement style and composition over time is best explained by the interaction between the waxing to waning stages of a mantle plume with the underlying Noachian terrain. This interaction led to the distinctive morphology of the volcanic shield, the explosive formation of the calderas, and the unusual compositions found within the central caldera complex. The volcanism of Syrtis Major is therefore defined both by the epoch in which it occurred, and the composition of the crust in which it formed

Syrtis Major volcano evolution characterised from a terrestrial analogue

New developments in 3D visualisation software enable interrogation of volcanic architecture by analysis of surface morphology and composition. We apply this remote sensing approach using Geovisionary™ software to investigate volcano evolution in the Manda-Hararo rift segment, Afar, (Ethiopia) and compare this with the Syrtis Major volcanic complex on Mars. In Afar, extensive exposure and low erosion rates in arid conditions allow comparison to Mars using remote sensing data sets of similar resolution. We use this comparison to understand the evolution of the Syrtis Major low-angle basaltic shield volcano – an edifice measuring 1500 km by 1000 km, formed in the early Hesperian (3.7 – 3.0 Ga). The complex is capped by calderas containing evolved volcanic products. Extensional fault systems and fissures, probably resulting from lack of buttressing on its ENE side, are aligned to the NNW-SSE these are comparable in morphology to the central part of Afar’s Manda-Hararo rift segment. We present results of an initial field campaign at the Manda-Hararo rift segment and an initial survey of the Syrtis Major calderas. In Afar oblique views of lava flow surface morphologies and cross-sections through successive lava flows reveal details of the relationships between lavas, topography and local structure. Lobes range in scale from 0.1 m to 10 m wide and are typically 1.5 m thick. Most lavas in this rift segment are pāhoehoe, emplaced as inflating lobes. Cross-sectional surfaces, exposed in fault scarps, show interfingered lava flows. Some very recent low volume (< 0.5 km3) rubbly pāhoehoe lavas occur at the rift axis. Distinct ‘a’ā lava flows originating from Dabbahu volcano are faulted and interfingered with lavas from a rift axial source. MRO data has been interrogated for similar morphologies. We examine evidence of similarities in emplacement style and the interaction of lavas from both Syrtis Major calderas, using Geovisonary™. Insights gained from the Manda-Hararo rift segment study will guide us in producing an architectural model of the evolution of the Syrtis Major complex, with the aid of further high resolution Mars imaging, including newly requested data from the Mars Reconnaissance Orbiter spacecraft

Amazonian-aged fluvial system and associated ice-related features in Terra Cimmeria, Mars

The Martian climate throughout the Amazonian is widely believed to have been cold and hyper-arid, very similar to the current conditions. However, ubiquitous evidence of aqueous and glacial activity has been recently reported, including channels that can be tens to hundreds of kilometres long, alluvial and fluvial deposits, ice-rich mantles, and glacial and periglacial landforms. Here we study a ∼340 km-long fluvial system located in the Terra Cimmeria region, in the southern mid-latitudes of Mars. The fluvial system is composed of an upstream catchment system with narrow glaciofluvial valleys and remnants of ice-rich deposits. We observe depositional features including fan-shaped deposits, and erosional features such as scour marks and streamlined islands. At the downstream section of this fluvial system is an outflow channel named Kārūn Valles, which displays a unique braided alluvial fan and terminates on the floor of the Ariadnes Colles basin. Our observations point to surface runoff of ice/snow melt as the water source for this fluvial activity. According to our crater size–frequency distribution analysis the entire fluvial system formed during early to middle Amazonian, between ∼1.8+0.2 −0.2 Ga to 510+40 −40 Ma. Hydraulic modelling indicates that the Kārūn Valles and consequently the alluvial fan formation took place in geologically short-term event(s). We conclude that liquid water was present in Terra Cimmeria during the early to middle Amazonian, and that Mars during that time may have undergone several episodic glacial-related events

The Hypanis Valles delta: The last highstand of a sea on early Mars?

One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars' dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km2). This has an extensive catchment (4.6 x 105 km2) incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (∼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend ∼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia – an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perhaps even an ocean that filled the northern plains of Mars

Impact crater degradation, Oxia Planum, Mars

The main goal of the European Space Agency (ESA) and Roscosmos ExoMars rover mission is to collect samples from the near-subsurface of Mars. The rover will look for any physical or chemical evidence of ancient life in the near subsurface. This map shows the distribution of impact craters at this proposed landing site in Oxia Planum on Mars. The map records 1199 impact craters > 500 m in diameter in a 5.0° × 2.5° region around Oxia Planum. The impact craters are symbolised based on the way different aspects of their morphology have degraded since their formation. The distribution of degradation and burial morphologies of impact craters can be used to determine where burial and erosion processes have occurred. Because the formation of impact craters is well constrained, occurs instantly and with a predictable flux, future studies could use this knowledge and our dataset to constrain when these events occurred

A Diverse Array of Fluvial Depositional Systems in Arabia Terra: Evidence for mid‐Noachian to Early Hesperian Rivers on Mars

Branching to sinuous ridges systems, 100s of kilometers in length and comprising layered strata, are present across much of Arabia Terra, Mars. These ridges are interpreted as depositional fluvial channels, now preserved as inverted topography. Here we use high resolution image and topographic datasets to investigate the morphology of these depositional systems and show key examples of their relationships to associated fluvial landforms. The inverted channel systems likely comprise indurated conglomerate, sandstone, and mudstone bodies, which form a multi‐storey channel stratigraphy. The channel systems intersect local basins and indurated sedimentary mounds, that we interpret as paleolake deposits. Some inverted channels are located within erosional valley networks, which have regional and local catchments. Inverted channels are typically found in downslope sections of valley networks, sometimes at the margins of basins, and numerous different transition morphologies are observed. These relationships indicate a complex history of erosion and deposition, possibly controlled by changes in water or sediment flux, or base level variation. Other inverted channel systems have no clear preserved catchment; likely lost due to regional resurfacing of upland areas. Sediment may have been transported through Arabia Terra towards the dichotomy and stored in local and regional‐scale basins. Regional stratigraphic relations suggest these systems were active between the mid‐Noachian and early Hesperian. The morphology of these systems is supportive of an early Mars climate which was characterized by prolonged precipitation and runoff

The evolution of ancient fluvial systems in Memnonia Sucli, Mars: impact crater damming, aggradation, and a large water body on the dichotomy?

There is conflicting evidence for an ancient ocean which occupied the northern hemispheric basin on Mars. Along different regions of the dichotomy boundary, sediment fans have been interpreted as either forming into a large water body or a series of smaller paleolake basins. Here, we investigate fluvial systems in the Memnonia Sucli region of Mars, set along the dichotomy, which comprise erosional valley networks, paleolake basins, inverted channel systems, and sediment fans. We focus our analysis on the evolution of the upslope catchment and characterizing the ancient environment of a large, downslope basin, bound by the topographic dichotomy and the Medusae Fossae Formation. The catchment fluvial systems comprise highly degraded valley networks and show a complex history of incision and filling, influenced by paleolake basin overflow, impact crater damming, aggradation, and possibly a downstream water body. The morphology of the sediment fans is consistent with either fluvial fans or deltas and they form at discrete elevations, rather than a common elevation plane. Our analysis is consistent with the sediment fans forming into a series of paleolake basins set along the dichotomy, rather than into a large inner sea or ocean-sized water body. The fluvial systems were likely active between the mid Noachian and early Hesperian periods. Our results demonstrate the complex, multi-phase evolution of fluvial systems on ancient Mars and highlight the importance of regional and local studies when characterising ancient regions of the dichotomy

Geologic mapping of Mawrth Vallis, Mars

Mawrth Vallis, generally counted among Mars’ giant outflow channels, has an atypical geomorphology that is less well-studied than its coinciding, thick (>150m) clay-bearing deposits. Here, we present ongoing work as part of the PLANMAP project to map the geomorphic features along the length of Mawrth Vallis in addition to a detailed map of the channel adjacent to the ExoMars 2018 landing ellipse to establish its history of erosion and deposition and relationship with the clay-bearing deposits