A Planetary Example of Tectonic Inversion:Folding and Thrusting in Valles Marineris, Mars

Daniel MEGEJean-Pierre PEULVASTPhilippe MASSON

Planetology and Geodynamics Lab, University of NantesGeography Institute, University of Paris-SorbonneIDES, University of Paris-Sud, Orsay

INSU

Blasius, Cutts, Guest, and Masursky, 1977Geology of the Valles Marineris: First Analysis of Imaging from the Viking 1 Orbiter Primary Mission, Journal of Geophysical Research

10 km

N

• Fractured anticline/syncline axes oblique to graben trend

Interpretation

Suggests transpressionMEGE, Ph.D. thesis, 1994PEULVAST et al., Geomorphology, 2001

10 km

strain partitioning

1

1

Hmin

Hmin

Themis image mosaic of Valles Marineris

Study area

Data used

•Themis imagery

• MOC imagery

• MOLA DEM

200 km

NASA/JPL/Arizona State University

IUS CHASMA

GERYON MONTES

1 Themis IR image2 Themis VIS images2 MOC images

Imagery

Viking image

N

GERYON MONTES

S

PLATEAU IUS CHASMA

1 km

South-dipping layer

horizontal layer

MOLA profile

N S

horizontal floor

truncatedlayerstruncatedlayers spursspurs

thrust planethrust plane

truncated layersspurs

top layer

thick central layerinner layer

Northern slope

N

NE

Fold layers

W

top layer

inner layer thrust fault

1 km

1 km

11°

11°

Southern slope

moat

floor deposits

N S

SW

NE

unloading ofwater-saturated

walls?

Origin of shortening

Sackung

ridge top splitting

gravitational unloading

landsliding

Reconstruction: from stretching to shortening

1 Rifting initiation

GERYON MONTES IUS CHASMA SOLIS PLANUM

SN

2 Rifting

SN

(1 - previous stage)

SN

3Spur and gully developmentOnset of detrital sedimentation (monocline layers?)

(2 - previous stage)

SN

SN

4 Wall sappingWater level loweringChannel development on graben floor

(3 - previous stage)

SN

SN

MO

C E

18

01

11

1upper foldlayer

oldest, exhumeddeposits (monoclinelayers, innermostfold layer?)

5 Late-stage stretching

(4 - previous stage)

SN

SN

6Dry erosional processes (mass wasting, aeolian activity)Sabkha deposits

(5 - previous stage)

SN

SN

7Geomorphological processes dominated by sackung

(6 - previous stage)

SN

SN

8Sackung and associated debris slopeStructural inversionAeolian reworking (sand dunes, deflation patterns)

SN

NASA/JPL/Arizona State University

20 km

Perspectives

Look for similar features in other places in Valles Marineris

Other sackung featuresin Coprates Chasma

ridge topsplitting

landslide

Perspectives

• Constrain rheology at depth from this and from composition of rock units as from OMEGA

• Model slope stability and failure through sackung

• Try to quantify stretching in order to estimate shortening

• Use shortening quantification and observed fold structure to determine thrust plane geometry and displacement

Intepretation of geologicunits

6

5

4

3

2

1

Dune fields (reworking of Fms 3-5)

Sabkhas (on Fms 3 and 4)

Dark, resistant floor material

Weak, thinly layered deposits

Exhumed resistant layers

Wallrock material