thumb|right|High resolution [[Thermal Emission Imaging System|THEMIS daytime infrared image mosaic of Noctis Labyrinthus and its surroundings. The area is crisscrossed by multiple sets of graben running in different directions. The shield volcano Pavonis Mons is at upper left.]]
thumb|right|[[Mariner 9 view of the Noctis Labyrinthus "labyrinth" at the western end of Valles Marineris on Mars. Linear graben, grooves, and crater chains dominate this region, along with a number of flat-topped mesas. The image is roughly 400 km across, centered at 6 S, 105 W, at the edge of the Tharsis bulge. North is up. Image located in Phoenicis Lacus quadrangle]]
is a region of Mars located in the Phoenicis Lacus quadrangle, between Valles Marineris and the Tharsis upland. The region is notable for its maze-like system of deep, steep-walled valleys. The valleys and canyons of this region formed by faulting and many show classic features of grabens, with the upland plain surface preserved on the valley floor. In some places the valley floors are rougher, disturbed by landslides, and there are places where the land appears to have sunk down into pit-like formations. It is thought that this faulting was triggered by volcanic activity in the Tharsis region. Research described in December 2009 found a variety of minerals, including clays, sulfates, and hydrated silicas, in some of the layers.
Context
Noctis Labyrinthus is located in the heart of Tharsis at the western end of the Valles Marineris, manifesting as a network of graben that extends in a spider-like network before coalescing into a coherent, relatively shallow graben swarm that curves in a semicircular fashion towards the south into the Claritas Rise. The graben are known as the Claritas Fossae beyond this point.
Geology
The Noctis Labyrinthus fracture zone is centered at the heart of the Tharsis Rise, dividing a plateau of Hesperian-Noachian age that is understood to be of a basaltic composition. In the chasmata of Noctis Labyrinthus, these pit crater chain collapse zones propagate directionally with a V-shaped tip, and can be used as an indicator of the direction into which magma withdraws from its underlying chamber. These V-tipped morphologies are generally found to propagate away from the center of the Tharsis Rise. Supporters of the lava tube hypothesis note that no evidence of lateral lava flows from the chasmata have been observed, suggesting against the notion that dikes must be required to underlie the surface of the modern-day collapse features as there is no evidence that such a near-surface intrusion has breached the surface in the Noctis Labyrinthus region. Based on CRISM spectral imagery, authors studying this depression have interpretatively identified the presence of:
- iron-rich minerals such as hematite and goethite
Calcium-rich pyroxenes have been spectrally observed elsewhere in the northern reaches of the Noctis Labyrinthus fracture zone.