Lecture Notes for the Final
Second order of relief: gigantic features and the dominant processes
shaping the martian surface
- Previously, we discussed the great impact craters of Mars.
- The next second order features are endogenic in character, originating
from tectonic processes (if not plate tectonics), that is, processes internal
to the planet, which tend to increase topographic contrast:
- Volcanic processes: The other great volcanic rise (Elysium)
- Rifting: Valles Marineris
- Under consideration now are gradational processes: floods and mud!
- See Viewgraphs:
"2nd order: Chryse Trough, Kasei Valles, Thaumasia"
-
Chryse Trough
- A large arc of locally depressed topography loosely rings the Tharsis
Rise, most likely the result of the loading of lava on the lithosphere below
the Tharsis volcanoes.
-
Timothy Parker in 1985 suggested that this depression east of Tharsis, dubbed
the Chryse Trough, might have housed an actual channel for catastrophic
flooding, comprising several tributary channels flowing from near the South
Polar Ice Cap into Argyre.
- From a presumed lake in Argyre, the flow would move through Uzboi Vallis
into a chain of smaller craters linked by channels that flowed into
Margaritifer Terra east of Valles Marineris. From there, drainage would move
into Chryse Planitia and the proposed northern lowlands ocean.
- The topographic resolution of even the best imagery was too coarse and
the elevational uncertainty too great for testing of the direction of flows in
the proposed system until MOLA data arrived (1997-2006).
- The resulting high resolution topographical information seems to confirm
the existence of an 8,000 km drainage system
- Two valley networks originate in Dorsa Argentea around 320°. near the
South Polar Cap and, along with a third network, lead to Argyre Planitia.
- An outflow channel with steep walls and great depth, Uzboi Vallis, runs
out of Argyre to the northeast, cutting into the rim of Holden Crater, where
signs of a delta or alluvial fan are found.
- The northeast rim of Holden Crater is blunted and forms a ramp leading
down to Ladon Basin where the channel structure, now called Ladon Bellis,
disappears into what may have
been a lake.
- En route to Ladon Basin, however, fluids leaving Holden Crater would
enter another, smaller crater, named Eberswalde Crater, which also seems to
have held a lake. Eberswalde Crater has a just spectacular delta structure!
- The channel morphology re-appears as Morava Valles leading out of Ladon
Basin to the
northeast into large outflow channels in Margaritifer Terra.
- These channels, now called Margaritifer Valles, then debouch into Chryse
Planitia,
forming a possible delta structure at the higher of Parker's two proposed
shorelines, Contact 1 or the Arabia shoreline.
- If, in fact, this system did move water or other fluids from the area
around the South Polar Cap to Chryse Planitia, even as a sporadic and perhaps
not continuously connected drainage, at some 8,000 km in length, the
Chryse Trough would constitute the longest fluvial network in the solar
system.
-
Massive outflow: Kasei Valles
- Kasei Valles is the enormous channel that seems to erupt out of Echus
Chasma to the north of Valles Marineris, flow due north, and then make a
nearly right angle turn to divide into two main branches that debouch into
Chryse Planitia to the northeast.
- Its northern channels are fringed with chaos terrain, too, such as Sacra
Fossæ.
- The channel could carry a staggering amount of fluid, dwarfing the
outflow channel in Ares Valles, not to mention the most gigantic
jökulhlaup floods on Earth (e.g., the Missoula and the Bonneville
floods).
- Kasei Valles cuts across the Hesperian lavas of eastern Tharsis and of
Lunæ Planum (forming the western boundary of Lunæ Planum).
- There is evidence of subsequent lava or pyroclastic flows into Kasei
Valles on its western edge, creating a marked softening of the edge there.
- This flow may have come from Tharsis Tholus, the easternmost volcano of
Tharsis Rise.
- The northermost of the Tharsis Montes proper, Ascræus Mons, the lava flows from which seem nearly to bury Tharsis Tholus, might alternatively be the culprit.
- Another possibility is that the source, whether fissure or vent/edifice, might be somewhere on Tharsis near Tharsis Tholus, but completely now buried by subsequent lava flows from Ascræus Mons or another source the way Tharsis Tholus appears to be partially engulfed.
-
Thaumasia Block: Plate or Megalandslide?
- A distinctive wedge- or lozenge-shaped plateau region on the
southeasternmost part
of the Tharsis Rise.
- To its north is Valles Marineris (it is sometimes bounded by Valles
Marineris, though some consider it to extend just beyond Vallis Marineris)
- To its south lie the Thaumasia Highlands, the only folded/faulted
mountain ranges on Mars that resemble the most common types of mountains on
Earth (e.g., Central Coast Ranges of California).
- These continue east as Coprates Rise.
- Claritas Fossæ lie to the west between Tharsis
Montes/Dædalia
Planum and the Thaumasia feature. Claritas Fossæ run about 1,800 km and
the terrain is fractures by a series of north-south striking normal faults and
graben, some of them offset, reflecting tensional and some shear stress
associated with the uplift of Tharsis.
- North of Claritas Fossæ and west of Valles Marineris is the
distinctive Noctis Labyrinthus chaotic terrain.
- Internally, Thaumasia is divided into:
- Syria Planum, the highest elevation portion at the northwest
corner of
Thaumasia, enclosed within the arch of Noctis Labyrinthus and north of the
beginnings of Claritas Fossæ
- Sinai Planum lies to the east of Syria Planum, south of the
junction of
Noctis Labythinthus and Valles Marineris
- Solis Planum is a large, flat expanse dominating the center of
Thaumasia,
characterized by northeast-southwest trending wrinkle ridges,
indicative of
compressional stress crumpling the thin lava beds of Solis, stresses from the
uplift of the Syria Planum and Claritas Fossæ areas to the northwest
- Thaumasia Planum or Thaumasia Minor, is a circular planum
south of
Coprates Chasma in Valles Marineris and west of the Coprates Rise. There's
some evidence that it contains a large buried crater: http://plate-
tectonic.narod.ru/watters_2006-02-01123a_figure4_l.jpg.
- The slight rise forming the western edge of Thaumasia Planum and the
eastern border of Solis Planum is sometimes called Melas Dorsa and
other times Melas Fossæ.
- Analogies with Earth plate tectonic features early suggested incipient
plate tectonics, with Valles Marineris the rift zone and possible divergent
boundary and Thaumasia Highlands and Coprates Rise the subduction zone
features.
-
Plate tectonics, even of the most incipient variety, is not the
consensus view today. Most workers consider Mars to be a one-plate planet,
with
tectonic uplift concentrated almost exclusively in a single mantle plume
rising up under Tharsis.
-
Plate tectonics is not completely out of the picture, however. Work by
An Yin at UCLA (2012) argues that the rounded southeastern boundary of Melas
Chasma
is, in fact, a large crater. The crater is missing its northern rim. Yin
points to a rounded structure in northwestern Melas Chasma that may be its
displaced northern rim. If so, there has been about 150 km of left-lateral
movement along what he argues is a shear fault boundary, like our own
San
Andreas Fault (a right-lateral fault). Could, then, Valles Marineris divide
adjacent plates, the way
the San Andreas divides the Pacific and North American plates?
- An argument by Montgomery et al. in 2009 (doi:10.1130/B26307.1) and by Andrews-Hanna in 2009 (doi: 10.1038/ngeo483) proposed that
Thaumasia constitutes a "mega-slide." This would result from
"thin-skinned" deformation
of multiple shallow layers of lava on top of deeply impact-shattered
regolith. This regolith contains mixtures, not only of basaltic impact
gardening debris, but of ices and evaporite beds as well.
- A lot of the subsurface is Noachian, meaning it could well have had
streams and ponds with evaporite beds forming in any local depressions.
- Evaporites often concentrate salts, and salts form materials that are
much less resistant to shear stresses than regular crustal rocks are and
capable of viscous flow in response to stresses (especially if water or brine
gets in there).
- Magma intrusion under subterranean ices, especially in Syria Planum
closest to Tharsis Montes, could create highly confined supercritical aquifers
(water unable to boil because of the confinement of subterranean water under
high pressure). A bomb waiting to go off.
- Shear-induced detachments could allow movement of these thin layers,
while the size of Thaumasia (and the low gravity of Mars and the low angle of
Thaumasia) implies this process of detachment must go down quite far, to
enable deep detachments to let the whole Thaumasia complex begin to move.
- Meanwhile, Tharsis, the source of subterranean heat, would continue its
upward movement, creating tremendous tensional stress around Thaumasia's
highest point, Syria Planum. That would account for the normal faulting seen
around Noctis Labyrinthus and the original rifting of Valles Marineris, as
well as the graben of Claritas Fossæ and their slight right lateral
motion (as Thaumasia began to detach and slide southward).
- The creation of some of these rifts could explosively liberate the
trapped supercritical fluids in the subsurface, possibly accounting for the
megaoutflows associated with Valles Marineris and the chaos terrain of the
undermined Noctis Labyrinthus.
- As the megaslide moved along its various detachments, crumpling would
occur in the thin lava layers as they experienced compressional stress between
the moving slide and the stationary terrains of Aonia Terra and Noachis Terra
to the south and east, respectively. This compressional stress is visible in
the many wrinkle ridges in the middle and lower reaches of the proposed
megaslide, running in quasi-parallel "waves" from east-northeast to
west-southwest. You can easily see them in Google Mars, through much of Solis
Planum and Thaumasia Planum to the immediate east of Solis Planum.
- The toe of the proposed megaslide would be the folded and thrust-faulted
mountain ranges of the Thaumasia Highlands and Coprates Rise.
- So, the large Thaumasia "lozenge" that is so conspicuous in MOLA maps
might be a second order expression of yet another mega geological process:
landsliding on an epic scale.
- Of course, Mars has that "yes, but..." quality, so the megaslide account has been called into question by a geochemical analysis by Hood et al. in 2016 (doi: 10.1002/2016JE005046). They used Mars Odyssey's Gamma Ray Spectrometer to perform geochemical analysis of Thaumasia and surrounding areas and could find no evidence of a salt-lubrication system that is a core part of the Montgomery et al, proposed mechanism allowing such movement on a planet with such low gravity and low slopes.
|
![[ orthographic image of Mars on a black background ]](https://home.csulb.edu/~rodrigue/mars/marsblackbg.jpg)
![[ Olympus Mons seen at oblique angle that gives a 3-d sense ]](https://home.csulb.edu/~rodrigue/mars/olympusmons3d.jpg)
![[ Mars explorer ]](https://home.csulb.edu/~rodrigue/mars/marsexplorerpainting.jpg)
|
|
![[ image of Mars ]](https://home.csulb.edu/~rodrigue/mars/marsatlas.gif)
