Enhancing Structural Geology Enhancing Structural Geology Using Mars Data?Using Mars Data?

You Bet! You Bet!

Eric B. GrosfilsEric B. Grosfils

Geology DepartmentGeology Department

Pomona CollegePomona College

Structural Geology in a Typical Structural Geology in a Typical Undergraduate CurriculumUndergraduate Curriculum

PHYSICAL GEOLOGY (INTRO) COURSEPHYSICAL GEOLOGY (INTRO) COURSE• Basic Styles/Types… folding, faulting, Basic Styles/Types… folding, faulting,

jointing, tilting. Stratigraphy interpretations.jointing, tilting. Stratigraphy interpretations.• Illustrated by block diagrams, field examplesIllustrated by block diagrams, field examples

Opportunities to use Mars examples for Opportunities to use Mars examples for illustration and for teaching stratigraphic illustration and for teaching stratigraphic relationships are abundant!relationships are abundant!

• Mars mission web sites often organize Mars mission web sites often organize collections of “best images” topically, so collections of “best images” topically, so tracking down examples is straightforward.tracking down examples is straightforward. http://themis.asu.edu/zoom-20050613Ahttp://themis.asu.edu/zoom-20050613A

50 km50 km

Arsia Mons CalderaArsia Mons Caldera

Structural Geology in a Typical Structural Geology in a Typical Undergraduate CurriculumUndergraduate Curriculum

STRUCTURAL GEOLOGY (UPPER LEVEL)STRUCTURAL GEOLOGY (UPPER LEVEL)• FundamentalsFundamentals

– e.g., force and stress, deformation mechanisms e.g., force and stress, deformation mechanisms and strain, rheologyand strain, rheology

• Brittle Deformation Processes and StructuresBrittle Deformation Processes and Structures– e.g., joints and veins, faults, failure criteria, pore e.g., joints and veins, faults, failure criteria, pore

pressure effectspressure effects

• Ductile Deformation and StructuresDuctile Deformation and Structures– e.g., folds and fold mechanics, foliations and e.g., folds and fold mechanics, foliations and

lineations, ductile shearlineations, ductile shear

• Tectonics and Regional DeformationTectonics and Regional Deformation

Structural geology is both Structural geology is both quantitativequantitative and and visualvisual – the topic is – the topic is perfectperfect for integration of available Mars datasets! for integration of available Mars datasets!

50 km50 km

V.E. = 5xV.E. = 5x

Wrinkle ridge topography and origin

Cerberus FossaeCerberus Fossae

5 km5 kmhttp://themis.asu.edu/zoom-20031029a

• It has been proposed by It has been proposed by many researchers that the many researchers that the Cerberus fractures that Cerberus fractures that extend SE from Elysium extend SE from Elysium Mons are underlain by Mons are underlain by dikes.dikes.

• Theoretical, experimental Theoretical, experimental and field data indicate that and field data indicate that the width of dike-induced the width of dike-induced fracturing at the surface is fracturing at the surface is ~twice the depth to the ~twice the depth to the top of the dike (cf. top of the dike (cf. Mastin Mastin and Pollard, JGR, 1988and Pollard, JGR, 1988).).

• Does the dike hypothesis Does the dike hypothesis for the Cerberus Fossa at for the Cerberus Fossa at left pass this test?left pass this test?

Cerberus FossaCerberus FossaDike Underlain?Dike Underlain?

You test and decideYou test and decide!!

5 km5 kmhttp://themis.asu.edu/zoom-20031029a

RememberRemember

The width of dike-The width of dike-induced fracturing at induced fracturing at the surface is ~twice the surface is ~twice

the depth to the top of the depth to the top of the dike…the dike…

http://www.nearingzero.net/

Cerberus Fossa – Dike Underlain?Cerberus Fossa – Dike Underlain?

5 km5 kmhttp://themis.asu.edu/zoom-20031029a

~400 m~400 m

~1300 m~1300 m

• Typical fracture width on Typical fracture width on the plains, ~400 m, suggests the plains, ~400 m, suggests depth to dike top is depth to dike top is ~200 m~200 m

• For the topographic peak, For the topographic peak, 1300 m width suggests that 1300 m width suggests that the depth to the dike top is the depth to the dike top is on the order of on the order of 650 m650 m

• But, need to calculate the But, need to calculate the height of the topographic height of the topographic peak at the measurement site peak at the measurement site to complete the test! to complete the test!

Cerberus Fossa – Dike?Cerberus Fossa – Dike?

5 km5 kmhttp://themis.asu.edu/zoom-20031029a

~1300 m~1300 m

• Shadow length is ~1900 m Shadow length is ~1900 m at measurement locationat measurement location

• From trigonometry, peak is From trigonometry, peak is ~450 m tall~450 m tall

• Hypothesis passes the test: Hypothesis passes the test: 200 m200 m (below fracture) + (below fracture) + 450 m450 m (height of peak) = (height of peak) = 650 m650 m (below peak) (below peak)

N58.6EN58.6E

13.4°

1900 m

x

Incidence Angle is 76.6°Incidence Angle is 76.6°(sun is 13.4° above horizon)(sun is 13.4° above horizon)

Solar Azimuth is 148.6°Solar Azimuth is 148.6°(measured cw from E, so sun shining toward N58.6E)(measured cw from E, so sun shining toward N58.6E)

Pit Chain FormationPit Chain Formation

http://themis.asu.edu/zoom-20041119a

• In some places on Mars, many In some places on Mars, many grabens have chains of pits centered grabens have chains of pits centered within them and aggregated along within them and aggregated along bounding normal faults.bounding normal faults.

• One mechanism proposed for their One mechanism proposed for their formation (e.g., formation (e.g., Ferrill et al., GSA Ferrill et al., GSA Today, 2004Today, 2004) is that the pits form ) is that the pits form when low cohesion surface materials when low cohesion surface materials collapse into void spaces created collapse into void spaces created during dilational fault slip.during dilational fault slip.

• Such features are not seen all over Such features are not seen all over the place on Earth… why not?the place on Earth… why not?

• Testing the collapse hypothesis from Testing the collapse hypothesis from a structural standpoint and thinking a structural standpoint and thinking about the Earth-Mars difference about the Earth-Mars difference promotes analog experiments, Mohr promotes analog experiments, Mohr Circle analysis, etc.!Circle analysis, etc.!5 km5 km

CENTEREDCENTEREDPITPIT

““SWALLOWSWALLOWHOLE”HOLE”

PIT ALONGPIT ALONGNORMAL FAULTNORMAL FAULT

Figure 5 of Ferrill et al., GSA Today, Oct. 2004.Figure 5 of Ferrill et al., GSA Today, Oct. 2004.Photo in (A) taken by George McGill 7/3/1976.Photo in (A) taken by George McGill 7/3/1976.

Pit chain deforming gravels above basalt Pit chain deforming gravels above basalt basement in NE Iceland. Region shown basement in NE Iceland. Region shown in the air photos is part of the western in the air photos is part of the western bounding fault system for a reactivated bounding fault system for a reactivated graben 1 km wide. The event produced graben 1 km wide. The event produced 1.5 m of horizontal extension and 1 m of 1.5 m of horizontal extension and 1 m of vertical throw. Pits formed are orders of vertical throw. Pits formed are orders of magnitude smaller than on Mars.magnitude smaller than on Mars.

Figures 2 and 4 of Ferrill et al., GSA Today, Oct. 2004.Figures 2 and 4 of Ferrill et al., GSA Today, Oct. 2004.

Set up an analog models, explore if/how Set up an analog models, explore if/how parameters such as thickness of the parameters such as thickness of the unconsolidated layer will affect the pit unconsolidated layer will affect the pit chain geometries produced!chain geometries produced!

Figure 6a and 6b of Ferrill et al., GSA Today, Oct. 2004. (c) is derived from Figure 6c of Ferrill et al., 2004.Figure 6a and 6b of Ferrill et al., GSA Today, Oct. 2004. (c) is derived from Figure 6c of Ferrill et al., 2004.

• Mohr circle analysis can be used to explore the conditions consistent with dilational faulting (tensile Mohr circle analysis can be used to explore the conditions consistent with dilational faulting (tensile and hybrid faults, stated by and hybrid faults, stated by Ferrill et al.Ferrill et al. to have fault dips for basalt >78°). to have fault dips for basalt >78°).

• For the Earth, such faults will occur in upper 2 km or so (under lithostatic loading), but pits formed are For the Earth, such faults will occur in upper 2 km or so (under lithostatic loading), but pits formed are readily eroded (i.e., by stream in Iceland example) and don’t survive very long.readily eroded (i.e., by stream in Iceland example) and don’t survive very long.

• On Mars, lower gravity means that dilational faulting can occur in upper 5 km or so. Larger pits may On Mars, lower gravity means that dilational faulting can occur in upper 5 km or so. Larger pits may form due to thickness of low-cohesion surface layer (test with analog model!), greater depth extent of form due to thickness of low-cohesion surface layer (test with analog model!), greater depth extent of dilation, less rapid erosion, and net accumulation of dilation volume via multiple fault reactivations.dilation, less rapid erosion, and net accumulation of dilation volume via multiple fault reactivations.

One could go on to calculate (a) the amount of dilation required to account for drained volumes, (b) how these dilations compare with the fault dips/offsets observed to test for consistency…

156°

Hoek-Brown Failureenvelope for an

“average” basalt

1 ≈ 50 MPa5 km depth, Mars2 km depth, Earth

Galle “Happy Face” Crater in YellowGalle “Happy Face” Crater in Yellow(51.1°S, 31.3°W; 215 km across)(51.1°S, 31.3°W; 215 km across)

Elliptical (Strained?) Crater in Blue to NEElliptical (Strained?) Crater in Blue to NE

Calculate strain Calculate strain using impact using impact

crater crater deformation!deformation!

( But beware of ( But beware of oblique impacts… )oblique impacts… )

Arcuate Arcuate FaultFault

Systems?Systems?

http://themis.asu.edu/zoom-20050324a

5 km5 km

5 km5 km

http://www.mines.edu/academic/http://www.mines.edu/academic/geology/faculty/btrudgil/research.htmlgeology/faculty/btrudgil/research.html

Canyonlands National Canyonlands National Park DEMPark DEM

Rotated Fault Rotated Fault Blocks?Blocks?

http://www.geosci.usyd.edu.au/users/prey/Teaching/Geol-1002/HTML.Lect6/sld010.htm

A Few Other Seed Ideas…A Few Other Seed Ideas…• Fault Length-Displacement Analyses Fault Length-Displacement Analyses (cf. papers by R.A. Schultz & colleagues)(cf. papers by R.A. Schultz & colleagues)

• Regional Strain Calculations Using Fault Displacement Regional Strain Calculations Using Fault Displacement MeasurementsMeasurements

• Analysis of Joints/Fractures Seen in MER ImagesAnalysis of Joints/Fractures Seen in MER Images

• Constraining Wrinkle Ridge Origin Using TopographyConstraining Wrinkle Ridge Origin Using Topography

– Fault-bend folds? Fault-bend folds? (cf. work by Okubo & colleagues; by Golombek & colleagues)(cf. work by Okubo & colleagues; by Golombek & colleagues)

– Fault-propagation folding? Fault-propagation folding? (investigate using PC/MAC freeware written by Allmendinger?)(investigate using PC/MAC freeware written by Allmendinger?)

– Thin- or thick-skinned deformation?Thin- or thick-skinned deformation?

• Graben/Rift Topo - purely tectonic? Graben/Rift Topo - purely tectonic? (cf. papers by Rubin ; Schultz; Goudy)(cf. papers by Rubin ; Schultz; Goudy)

• Polygonal Fracturing -- constrain thickness and type of material in Polygonal Fracturing -- constrain thickness and type of material in the northern plains (Utopia Basin) burying old impact craters and the northern plains (Utopia Basin) burying old impact craters and forming drape folds forming drape folds (cf. papers by Buczkowski & colleagues)(cf. papers by Buczkowski & colleagues)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Now, What Are Now, What Are YouYou Going to Try? Going to Try?

http://marsrovers.jpl.nasa.gov/gallery/press/opportunity/20060307a/Sol744B_P2351_L257F-B744R1.jpg