C.M. Rodrigue, 2014 Geography, CSULB Mars: First Order Landscapes The Great Crustal Dichotomy Geography 441/541 S/14 Dr. Christine M. Rodrigue

C.M. Rodrigue, 2014Geography, CSULB

Mars: First Order LandscapesThe Great Crustal Dichotomy

Geography 441/541S/14

Dr. Christine M. Rodrigue


Mars: First Order Landscapes





• The “Orders of Relief” for Martian Landscapes– On Earth, the orders of relief scheme

• Is sometimes seen in geography textbooks• Organizes topographic variation in a scale-dependent manner• Geographers often focus on

_ Spatial analysis of particular phenomena_ Regional synthesis to integrate assemblages of phenomena_ Scales at which processes and regional patterns operate_ The interactions among phenomena at different scales



• The “Orders of Relief” for Martian Landscapes– Examples of interactions among scales

_ In spatial statistics: the Modifiable Areal Unit Problem (MAUP) _ In human geography: local cultural and political responses to

global economic and political processes _ Biogeography: alpha, beta, and gamma measures of biodiversity _ Geomorphology: "megageomorphology" has emerged as remote

sensing technology has made the simultaneous examination of form and process at large scale (small map scale) possible



• The “Orders of Relief” for Martian Landscapes– For Mars, a handy descriptive scheme for handling the

regional variations in Mars’ physical landscapes• The “First Order of Relief” = the crustal dichotomy

□ The northern lowlands: Vastitas Borealis□ The southern highlands

• If Earth’s oceans evaporated (which they will …), there would remain a crustal dichotomy here

Former ocean basins: low elevation, thin crust, basaltic, with a veneer of pelagic sediments

Former continents: high elevation, thick crust, granitic rocks and their extrusive igneous, sedimentary, and metamorphic derivatives



• The “Orders of Relief” for Martian Landscapes– Vastitas Borealis

• Regional subdivisions:_ Utopia Planitia _ North Polar Basin_ Embayments:

_ Acidalia Planitia_ Chryse Planitia_ Amazonis Planitia_ Arcadia Planitia_ Isidis Planitia




• Relatively young surface– Smooth with few craters– This is exactly what you’d expect if Mars had had an ocean

_ It could be expected to receive sediments from rivers, floods, and coastal processes and create terrigenous sediments nearshore

_ They would be turned into minerals that would eventually precipitate out of the water column onto the abyssal floor

_ The oceans would thus cover the underlying original rock surface, much as pelagic sediments here do




• Further suggestions of an ocean:_ Drainage of Martian outflow channels and valley

networks_ This is also exactly what you’d expect if Mars had had an

ocean to serve as base level for stream networks


Mars: First Order Landscapes• The “Orders of Relief” for Martian Landscapes

– Vastitas Borealis• Drainage:

_ Valles Marineris' outflow channels, which drain into Chryse Planitia_ Nanedis north of Ganges_ Ares and Aram Chaos _ Argyre to Aram and Ares






• Even better: Coastlines!?– Transition between the southern highlands and the

northern lowlands is quite abrupt






• Even better: Coastlines!?– Terraces on the Arcadia side of Alba Patera




• Even better: Coastlines!?– Tim Parker’s analysis of Viking imagery




• Even better: Coastlines!?_ Tim Parker’s analysis of Viking imagery (1994)_ His and others’ re-analysis using MOC imagery seemed

to debunk his argument, which even he admitted in 2001_ But it’s as though the new imagery is so fine in resolution

that it can’t detect the coarser scale at which this putative ocean’s coastline features might exist

_ MOLA suggests that, in fact, at least one of the “coastlines” is at the same elevation (water seeks a level constant with respect to the geoid)




• Plot complication_ That "ocean" floor is dominated by andesitic rock_ Not sediments with minerologies consistent with

precipitation out of water. _ No carbonates! No ocean?




• About those andesites_ "Surface Type 1"

(basalts dominating the southern highlands)

_ "Surface Type 2" (andesites and andesitic basalts dominating the northern lowlands)






• Rampart craters



• The “Orders of Relief” for Martian Landscapes– The Southern Highlands

_ Mostly 1-5 km above the mean Martian geoid _ Versus 0-3 km below for the northern lowlands_ Sharp ~1 km scarp dividing the two



• The “Orders of Relief” for Martian Landscapes– Ancient, battered terrain

• Arabia Terra




_ Noachis Terra is another old land (for which “Noachian era” named)

_ West of Hellas, east of Argyre

_ Signs of water or fluid_ Channels_ Softened terrain




• Hellas, with Isidis and Utopia from the Northern Lowlands beyond




• Noachis Terra, Holden Crater, Vallis Uzboi




• Noachis Terra, Holden Crater, alluvial fan/bajada?




• Syrtis Major Planum, volcanic province, basaltic, not dusty




• Terra Tyrrhena, battered basalt, fluvial dissection, mineral precipitation (sulfates?), wind deposition




• Promethei Terra, east of Hellas, basaltic, landslides, dust devils




• Cimmeria Terra, basaltic, cratered, E of Hellas, S of Elysium, SW of Tharsis, Ma’adim Valles



– Ancient, battered terrain• Margaritifer Terra, basaltic, cratered, fluvial alteration, chaos terrain,

east of Valles Marineris outflow, west of Meridiani



– Basalt terrain and dust dominate the Southern Highlands_ Spectra showing high proportions of basalt shown in the green_ Andesite shown in the red channel_ Hæmatite shown in blue (small area)_ Dust-dominated areas come out brown

Documents

C.M. Rodrigue, 2014 Geography, CSULB Mars: First Order Landscapes The Great Crustal Dichotomy Geography 441/541 S/14 Dr. Christine M. Rodrigue