 | |
| Feature type | Fracture system |
|---|---|
| Location | Tharsis quadrangle |
| Coordinates | 29°12′N251°00′E / 29.2°N 251°E /29.2; 251[1] |
| Discoverer | Mariner 9 |
TheCeraunius Fossae are a set of fractures in the northernTharsis region ofMars. They lie directly south of the largevolcanoAlba Mons and consist of numerous parallelfaults and tension cracks that deform the ancient highland crust.[2] In places, youngerlava flows cover the fractured terrain, dividing it into several large patches or islands.[3] They are found in theTharsis quadrangle.
The faults are mainly narrow, north-south orientedgraben. Graben (the name is both singular and plural) are long, narrow troughs bound by two inward-facing normalfaults that enclose a downfaulted block of crust. The graben in the Ceraunius Fossae are commonly several kilometers wide, between 100 and slightly over 1000 m deep,[4] and very closely spaced, giving the terrain a rugged ridge and groovetopography.[5] Many of the graben are hundreds of kilometers long[6] and have walls with complex scalloped segments.[2] Some containpit crater chains (catenae) at their bottoms, suggesting the presence of deep-seated tension cracks into which surface material has drained.[3][5]
The term Ceraunius is from analbedo feature at lat. 19.78°N, long. 267°E. It was named by Greek AstronomerE. M. Antoniadi in 1930 for theCeraunian Mountains on the coast ofEpirus,Greece[7] (now southwesternAlbania).Fossa (pl.fossae) isLatin for ditch and is adescriptor term used inplanetary geology for a long, narrow depression or trench.[8] TheInternational Astronomical Union (IAU) formally adopted the term Ceraunius Fossae in 1973.[1] The name Ceraunius Fossae is plural and translates into "the Ceraunian trenches".
Most of the Ceraunius Fossae are located in the northernTharsis quadrangle. A portion extend northward into the southwestern part of theArcadia quadrangle where the fossae diverge around the flanks of Alba Mons to form the Alba andTantalus Fossae systems. The area stretches from lat. 18.9° to 38°N and from long. 247° to 255°E. The entire feature has a north-south length of 1137 km.[1][9]
The Ceraunius Fossae lie on a broad topographic ridge up to 1.5 km high,[10] called the Ceraunius rise.[11] The ridge projects from the southern edge of Alba Mons and extends southward for a distance of over 1000 km. The southern half of the Alba Mons volcano is built over the northern extension of this ridge.[10]
The Ceraunius Fossae aretectonic features indicatingstresses in the planet'slithosphere. The fractures form when the stresses exceed theyield strength of rock, resulting in deformation of surface materials. Typically, this deformation is manifested as slip on faults that are recognizable in images from orbit.[5] Most of the tectonic features in the western hemisphere of Mars are explained by crustal deformation from theTharsis bulge (a huge volcanic mass up to 7 km high that covers nearly a quarter of the planet’s surface). Among the processes proposed to explain the tectonic features associated with Tharsis are domal uplifting,magmaticintrusion, and volcanic loading (deformation due to the large, sagging weight of the volcanic mass).[12]
The Ceraunius Fossae fractures areextensional features produced when the crust is stretched apart. The fractures are oriented north-south, radial to an early center of volcano-tectonic activity inSyria Planum, a region in southern Tharsis.[6][13] A large number of extensional structures, includinggraben andrifts, radiate outward from the center of Tharsis.Mechanical studies indicate that a regional pattern of radiating graben and rifts is consistent with stresses caused by loading of the lithosphere by the enormous weight of the Tharsis bulge.[5] The immenseValles Marineris is probably the best known example of a rift system that lies radial to Tharsis. Several generations of grabens with slightly different orientations are present in Ceraunius Fossae, indicating thatstress fields have changed somewhat over time.[2]
In addition to producing normal faults and graben, extensional stresses can produce dilatant fractures or tension cracks that can open up subsurface voids. When surface material slides into the void, a pit crater may form. Pit craters are distinguishable from impact craters in lacking raised rims and surroundingejecta blankets. On Mars, individual pit craters can coalesce to formcrater chains (catenae) or troughs with scalloped edges.[14][15]
Evidence also exists that some of the graben and crater chains in the Ceraunius Fossae may have been formed by the intrusion ofmagma, which forms large undergrounddikes. The migration of the magma exploits or opens up fractures in the subsurface, causing a crack or pit crater chain to form at the surface.[16]
Knowledge of the locations and formation mechanisms of pit craters and fossae is important for the future colonization of Mars because subsurface fractures may act as conduits or reservoirs for water and ice.[14]
