ESCI 214: Mars: What and Where. (Survey of Major Geologic Features) Patrick J. McGovern Lunar and Planetary Institute Thursday’s presentation will be… Mars: How it all got there.

Crustal Dichotomy Martian Southern Hemisphere Heavily Cratered, topographically rough High elevation, thick crust. Contains several Large Impact Basins (Hellas, Argyre, Isidis). Networks of apparently water-cut valleys. Highland Paterae: low eroded volcanoes. High-intensity magnetic bands.

Crustal Dichotomy Northern Hemisphere Low elevations, thin crust. Topographically smooth surface. Apparent crater density much lower than Southern Highlands: surface units much younger. HOWEVER: “Stealth Craters” and buried basins are evident in topography. Densities comparable to those in Southern Highlands. Northern basement comparable in age to Southern Highlands

Tharsis Huge volcano-tectonic province. Roughly centered on Equator (240 E). Broad rise up to 10 km in elevation. Tall, young shield volcanoes. Rise and volcanoes covered by basaltic flows. Somewhat older: Plains with wrinkle ridges (thrust faults). Numerous graben: radial orientations. Some “swarms” exposed in very old terrain.

Tharsis Components: Volcanoes Olympus Mons: Tallest (NOT NECESSARILY “LARGEST”!!!) volcano in the solar system. 600 km in diameter, 23 km height above base. Covered by young basaltic lava flows. Central caldera system.. Basal escarpment up to 10 km high. Aureole deposits surrounding flanks to North and West: likely landslides from flank failure (Hawaii analogue: see Prof. Morgan).

Intro to Olympus (MOLA-style) Edifice Basal Scarp (variable) Aureole Lobes (“Deposits”)

Comparison: Hawai’i

Tharsis Components: Volcanoes Tharsis Montes: Ascraeus, Pavonis and Arsia Montes. 400 km in diameter, 15 km height above base. Edifices aligned NE-SW along crest of Tharsis Rise. Covered by basaltic lava flows, circumferential normal faults (Pav. and Ars.) Rifts oriented NE-SW through each edifice.

Tharsis Components: Volcanoes Alba Patera. 6 km height above base, flat-topped dome. Lava flows extend well into northern plains. Annulus of normal faults surrounds summit, linear bands of radial faults on lower flanks. Topography, faults probably due to intrusion of magma into edifice. Similarities to some Venusian coronae.

Tharsis Components: Faults Valles Marineris. Canyon system 4000 km long, 700 km wide, up to 10 km deep. ESE-WSW trend, roughly radial to Tharsis. Eroded fault scarps evident at base of walls. Suggests rift origin. Abundant layering seen in walls. Noctis Labyrinthus chasms at head of VM (eastern Tharsis).

The “Other Volcanic Rise” Elysium Rise 6000 km E, 1000 km N of Tharsis. Broad rise with 3 superimposed shield volcanoes (similar to Tharsis). 6 km height above base, flat-topped dome (similar to Alba Patera). Radial lower flank faults, annular near-summit faults (similar to Alba Patera).

Catastrophic Floods Chaotic Terrain: source regions for catastrophic floods issuing from Southern Highlands. Prominent near Chryse Basin, mouth of Valles Marineris, and elsewhere near dichotomy boundary. Downdropped blocks from removal of ground ice. Outflow channels: carry flood materials into Northern Lowlands.

Polar Caps North cap South cap Mostly water ice. Main cap surrounded by ice/dust mixture. South cap Mostly carbon dioxide on surface. However, CO2 too weak to support observed topography (interior must be water ice).

Eolian Features Dunes. Slope Streaks. Dust Storms. Gullies. Dust covers large fraction of Mars Surface. Gullies. Usually considered fluid-activated. Alternative: dry debris avalanches.