14. May 2020
Mars Express mission

Up­arch­ing, stress and strain on Mars – the horst and graben land­scape of As­curis Planum

Vertical plan view of the horst and graben landscape of Ascuris Planum
Ver­ti­cal plan view of the horst and graben land­scape of As­curis Planum
Image 1/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Vertical plan view of the horst and graben landscape of Ascuris Planum

This 200 by 80-kilo­me­tre sec­tion of As­curis Planum is a text­book ex­am­ple of the par­al­lel ridges re­ferred to as a ‘horst and graben’ struc­ture. These are cre­at­ed by tec­ton­ic forces. If a rigid, brit­tle rock crust is stretched, due to ris­ing sub­sur­face ma­te­ri­al, for ex­am­ple, the sur­face above un­der­goes ten­sion. If the ten­sile stress ris­es above a cer­tain lim­it, the crust breaks up along steeply slop­ing frac­ture sur­faces, cre­at­ing a ‘fault zone’. If the crust con­tin­ues to ex­pand, large blocks of rock slide down the frac­ture sur­faces sev­er­al hun­dred me­tres, or even one to two thou­sand me­tres, form­ing a tec­ton­ic graben. The blocks left stand­ing on both sides now tow­er above the land­scape and form the as­so­ci­at­ed horsts.
Oblique perspective view of horsts and grabens in Ascuris Planum
Oblique per­spec­tive view of horsts and grabens in As­curis Planum
Image 2/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Oblique perspective view of horsts and grabens in Ascuris Planum

Tec­ton­ic forces have cre­at­ed a char­ac­ter­is­tic pat­tern of par­al­lel, lin­ear frac­ture struc­tures in As­curis Planum, the north­ern­most part of the Tempe Ter­ra re­gion to the north­east of the Thar­sis Ridge. As a re­sult of ris­ing mag­ma pock­ets, the Mar­tian crust was stretched, caus­ing crustal blocks to sub­side along frac­ture sur­faces and form tec­ton­ic grabens. In be­tween, the horsts re­mained as raised crustal blocks. The grabens are part­ly filled by de­bris-cov­ered glaciers, which are char­ac­ter­is­tic of all steep­er slopes at these lat­i­tudes. The eject­ed ma­te­ri­al of a small crater (cen­tre right of the im­age) ris­es like a plat­form above the sur­round­ing land­scape. Such crater sur­round­ings are formed when the eject­ed ma­te­ri­al is much more re­sis­tant to ero­sion pro­cess­es than the sur­face rock. They form an ero­sion-re­sis­tant lay­er which, af­ter the sur­round­ing ma­te­ri­al has been re­moved, cre­ate a plateau around the crater.
Topographic image map of the tectonic structures of Ascuris Planum
To­po­graph­ic im­age map of the tec­ton­ic struc­tures of As­curis Planum
Image 3/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Topographic image map of the tectonic structures of Ascuris Planum

Us­ing im­age strips ac­quired by the High Res­o­lu­tion HRSC cam­era sys­tem on Mars Ex­press, which were im­aged from dif­fer­ent an­gles, re­searchers from DLR and Freie Uni­ver­sität Berlin have com­put­ed Dig­i­tal Ter­rain Mod­els (DTMs) of the Mar­tian sur­face, which con­tain el­e­va­tion in­for­ma­tion for each pix­el. The colour cod­ing of the DTM (leg­end in the top right-hand cor­ner) pro­vides in­for­ma­tion about dif­fer­ences in al­ti­tude in As­curis Planum, the north­ern­most part of the Tempe Ter­ra re­gion. The mod­el ar­ti­fi­cial­ly high­lights the horst and graben struc­ture, which is the re­sult of tec­ton­ic stress pro­cess­es. When these pro­cess­es oc­cur, crustal blocks sub­side by sev­er­al hun­dred me­tres down steep, al­most ver­ti­cal frac­ture sur­faces, and grabens form be­tween the re­main­ing horsts. Some small­er graben frac­tures, which cut the pre­vail­ing stress regime di­ag­o­nal­ly, ev­i­dence a change in the di­rec­tion of ac­tion of the sub­sur­face forces.
3D view of Ascuris Planum in the Tempe Terra region
3D view of As­curis Planum in the Tempe Ter­ra re­gion
Image 4/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

3D view of Ascuris Planum in the Tempe Terra region

Anaglyph im­ages can be gen­er­at­ed us­ing da­ta ac­quired by the nadir chan­nel of the High Res­o­lu­tion Cam­era Sys­tem (HRSC), which is di­rect­ed per­pen­dic­u­lar­ly to the sur­face of Mars, and one of the four oblique­ly view­ing stereo chan­nels. When us­ing red-blue or red-green glass­es, they pro­vide a re­al­is­tic, three-di­men­sion­al view of the land­scape. North is on the right of the im­age. The vari­a­tions in al­ti­tude in this land­scape, which is called a horst and graben struc­ture, are strik­ing. They range from sev­er­al hun­dred me­tres to al­most one kilo­me­tre. The grabens are the re­sult of sub­sid­ing crustal blocks caused by stretch­ing of the Mar­tian crust. The ter­rain blocks left be­tween the grabens are called horsts.
The Tempe Terra region, shaped by tectonic forces
The Tempe Ter­ra re­gion, shaped by tec­ton­ic forces
Image 5/5, Credit: NASA/JPL (MOLA); FU Berlin

The Tempe Terra region, shaped by tectonic forces

Lo­cat­ed to the north­east of the large vol­canic re­gion Thar­sis on Mars, Tempe Ter­ra is an area that has been strong­ly in­flu­enced by tec­ton­ic forces. Dur­ing the up­lift­ing and stress­ing of the litho­sphere by vol­canic and plu­ton­ic rocks over bil­lions of years, enor­mous ten­sile stress­es in the Mar­tian crust trans­formed large re­gions in­to what are re­ferred to as ‘horst and graben’ land­scapes. The sur­face is char­ac­terised by nu­mer­ous tec­ton­ic stress struc­tures, shield vol­ca­noes, so­lid­i­fied la­va flows and glacial struc­tures. The frac­ture struc­tures (small rect­an­gle), shown here in im­ages ac­quired by the High Res­o­lu­tion Stereo Cam­era in Septem­ber 2019, dur­ing or­bit 19,913, show the south­west­ern foothills of the Tempe Fos­sae grabens. These are over 1000 kilo­me­tres long and they can be com­pared to that of the Kenya Rift on Earth, part of the East African Rift.
  • These images of Mars, acquired by the HRSC camera operated by DLR, show signs of enormous tectonic forces acting on the planetary surface.
  • The imaged area is located northeast of the large volcanic region of Tharsis, a magmatic bulge approximately five kilometres high. During its formation, enormous tensile stresses occurred in the Martian crust, transforming large regions into horst and graben landscapes.
  • The fault structures shown here are extensions of the Tempe Fossae troughs. These are over 1000 kilometres long, and their characteristics are strikingly similar to the Kenya rift.

These images show a landscape deformed by strong tectonic activity in the area north of Labeatis Fossae in the Tempe Terra region of Mars. They were acquired by the High Resolution Stereo Camera (HRSC), operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), on board ESA's Mars Express spacecraft. Here, the results of the enormous forces that once affected the Martian crust as large magma pockets rose from below can be seen. These pockets lifted the crust upwards and triggered volcanic and tectonic activity. HRSC has been mapping the Red Planet since 2004, as part of ESA's Mars Express mission. It was developed and is operated by DLR.

The area depicted is located northeast of the large volcanic region of Tharsis, where there are many other similar geological structures. The Tharsis region has a diameter of several thousand kilometres, making it almost as large as Europe. Tharsis is a magmatic bulge, approximately five kilometres tall, and was formed over the course of several billion years. During the gradual upwelling and stressing of the lithosphere by volcanic and plutonic rocks, enormous tensile stresses occurred in the Martian crust, transforming large regions into 'horst and graben' landscapes.

Tempe Terra is the northernmost highland region on Mars. The landscape is characterised by numerous tectonic expansion structures, shield volcanoes and solidified lava flows. The fracture structures shown here are in the south-western foothills of the Tempe Fossae troughs, which are over 1000 kilometres long and whose characteristics can be compared to that of the Kenya Rift on Earth, which is a part of the East African Rift.

How do horst and graben structures develop?

The region shown in these HRSC images is a textbook example of horst and graben tectonics. If a rigid, brittle rock crust is stretched, for example when the ground below it is raised, the surface experiences tension. If the tensile stress rises above the tolerable limit for the rock, the crust breaks up along somewhat steeply sloping fracture surfaces and a 'fault zone' is created. If the crust continues to expand, large blocks of rock slide down along the fracture surfaces for hundreds of metres, and even up to 1000 or 2000 metres in places. Over many millions of years, tectonic grabens develop. The regions left standing on both sides now tower above the landscape and form the corresponding horsts. The word pair 'horst and graben' have their origins in early medieval miners' German and were incorporated into many languages following geology’s establishment as an 'Earth science'.

A change in the stress regime

Tempe Terra is a part of the Martian crust that must have experienced high tectonic stress over a very long period of Martian history. The grabens run mostly parallel from northeast to southwest. However, there are also grabens that cut across this primary direction. This indicates a change in the orientation of the stress field. Particularly in the south (to the left of Image 1), some fractures run almost perpendicular to the prevailing direction of the faults.

Varied landscape

In the north (to the right of image 1), the landscape has a much smoother profile. The grabens are partly filled by debris-covered glaciers, which are characteristic of all steeper slopes at these latitudes. What are referred to as 'wrinkle ridges' can be seen at the top of the image. These were formed in the Tempe Terra region by compressive stress and form a concentric ring around the entirety of Tharsis. Erosion processes have also shaped this northern part of the region. The ejected material of a small crater (on the right of Image 1 and the upper right of the perspective view) rises like a platform above the surrounding landscape. These types of crater are formed whenever the ejecta are significantly more resistant to erosion processes than the surface rock. They form an erosion-resistant layer which, after the surrounding material has been removed, creates a plateau around the crater.

  • Image processing

The images were acquired by the High Resolution Stereo Camera (HRSC) on 30 September 2019 during Mars Express orbit 19,913. The image resolution is approximately 15 metres per pixel. The image centre is located at 279 degrees east and 36 degrees north. The perpendicular colour view was generated from the data acquired by the HRSC nadir channel, which is directed perpendicular to the Martian surface, and the colour channels. The oblique perspective view was computed using a Digital Terrain Model (DTM) and data from the nadir and colour channels of HRSC. The anaglyph image, which gives a three-dimensional impression of the landscape when viewed with red-blue or red-green glasses, was derived from data acquired by the nadir channel and the stereo channels. The colour-coded image map is based on a DTM of the region, from which the topography of the landscape can be derived. The reference body for the HRSC DTM is an equipotential surface of Mars (areoid).

HRSC was developed and is operated by the German Aerospace Center (DLR). The systematic processing of the camera data was performed at the DLR Institute of Planetary Research in Berlin-Adlershof. Personnel at the Department of Planetary Sciences and Remote Sensing at Freie Universität Berlin used these data to create the image products shown here.

  • The HRSC experiment on Mars Express

The High Resolution Stereo Camera (HRSC) was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and built in collaboration with partners in industry (EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The science team, which is headed by Principal Investigator (PI) Ralf Jaumann, consists of 50 co-investigators from 35 institutions in 11 countries. The camera is operated by the DLR Institute of Planetary Research in Berlin-Adlershof.

Contact
  • Elke Heinemann
    Ger­man Aerospace Cen­ter (DLR)
    Pub­lic Af­fairs and Com­mu­ni­ca­tions
    Telephone: +49 2203 601-2867
    Fax: +49 2203 601-3249

    Contact
  • Daniela Tirsch
    Ger­man Aerospace Cen­ter (DLR)

    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-488
    Fax: +49 30 67055-402
    Linder Höhe
    51147 Köln
    Contact
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
    Contact
  • Prof.Dr. Ralf Jaumann
    Freie Uni­ver­sität Berlin
    In­sti­tute of Ge­o­log­i­cal Sci­ences
    Plan­e­tary Sci­ences and Re­mote Sens­ing
    Telephone: +49-172-2355864
    Malteserstr. 74-100
    12249 Berlin
    Contact

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