Editing Noctis Labyrinthus (section)

==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 [[basalt]]ic composition.<ref name=thollot2012 /> The valleys of Noctis Labyrinthus fractured into three distinct trends (NNE/SSW, ENE/WSW, WNW/ESE) in an interlinked pattern that has been compared to the terrestrial fault systems that have formed over terrestrial [[dome (geology)|domes]].<ref name=masson1980 /> The formation of the fracture zone have been dated to the Late Hesperian based on [[crater counting]] age dates, concurrent with the formation of the lava plains of the adjacent Syria Planum province.<ref name=thollot2012 /> Some researchers have modeled the formation of such chasmata on Mars on the propagation of simple graben underlain with [[dike (geology)|dikes]]. As the underlying magma body drains, the chamber's pressure decreases and it begins to deflate. A [[crater chain|chain of crater-like depressions]] forms, where the extent of the collapse dictated by how deeply the magma body is located. Noctis Labyrinthus is estimated to have experienced collapses from the drainage of magma chambers up to 5&nbsp;km below the chasmata floors.<ref name=mege2003 /> In Noctis Labyrinthus in particular, some researchers have speculated that the fracture zone's corridors may connect deeper [[intrusive rock|intrusive]] structures, forming a plumbing network more akin to the terrestrial Thulean [[mantle plume]], which was responsible for the formation of the [[North Atlantic Igneous Province]].<ref name=mege2003>{{cite journal |last1=Mège |first1=D |last2=Cook |first2=AC |last3=Garel |first3=E |last4=Lagabrielle |first4=Y |last5=Cormier |first5=M-H |date=2003 |title=Volcanic rifting at Martian grabens |url= http://pure.aber.ac.uk/ws/files/89581/2002JE001852.pdf|journal=Journal of Geophysical Research |volume=108 |issue=E5 |page=5044 |doi=10.1029/2002JE001852 |bibcode=2003JGRE..108.5044M |doi-access=free }}</ref> 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.<ref name=mege2003 />

Other authors have proposed an alternate origin for Noctis Labyrinthus, linking its formation to the Valles Marineris and likening its initial formation to the expansion and collapse of a dense lava tube network.<ref name=leone2014>{{cite journal |last1=Leone |first1=G |date=2014 |title=A network of lava tubes as the origin of Labyrinthus Noctis and Valles Marineris on Mars |journal=Journal of Volcanology and Geothermal Research |volume=277 |pages=1–8 |doi= 10.1016/j.jvolgeores.2014.01.011|bibcode=2014JVGR..277....1L }}</ref> 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.<ref name=leone2014 /> Critics of a purely tectonic hypothesis have also noted that although pit crater chains (central to the diking hypothesis) are generally aligned and coincident with graben, they are occasionally found to bifurcate and to cross coeval graben in a perpendicular direction in the vicinity of Noctis Labyrinthus.<ref name=leone2014 /> Some authors have also proposed that Noctis Labyrinthus's chasmata may have formed due to extensional faulting in weakened rocks composed of interlayered [[tuff]] and lava flows, known to produce pit crater chains parallel to graben.<ref name=leone2014 />

Other authors have suggested that [[phreatomagmatic eruption|phreatomagmatic]] processes were associated with the formation of the Noctis Labyrinthus chasmata. This hypothesis is not widely favored because [[chaos terrain]] morphology, proposed to form from this mechanism, is not found in the Noctis Labyrinthus fracture network. Chasmata and pit crater chains like those of Noctis Labyrinthus are likewise also not observed near areas where phreatomagmatic activity is strongly believed to have occurred, such as the [[Sisyphi Montes]].<ref name=leone2014 /> Others have proposed that the chasmata of Noctis Labyrinthus are collapse features of a [[karst]]ic nature, in which constituent [[carbonate rock]] is dissolved by [[meteoric water]] that has been acidified by  acids originating in volcanic gases. This hypothesis has been challenged because carbonate spectral signatures have not been detected in the Noctis Labyrinthus network.<ref name=leone2014 />

The walls of the valleys of Noctis Labyrinthus have been widened significantly by [[slump (geology)|slumps]] that have canvassed the valley floors with debris taking the form of mudflows and boulders. Some authors have attributed the steady collapse of the valley walls to [[downhill creep|creep]] tied to [[temperature cycling|thermal cycling]], which could cause the repeated freezing and thawing of ground ice.<ref name=masson1980 /> Because of its location at the center of the Tharsis uplift, the melting associated with this creep could have been facilitated by increased heat flow to this area during periods of increased magmatic activity.<ref name=thollot2012 /> No evidence of fluvial or aeolian erosion is observed in this region.<ref name=masson1980 />

===Mineralogical diversity===

An unnamed depression near the southernmost extent of the Noctis Labyrinthus system, near the divide of [[Syria Planum]] and [[Sinai Planum]] and at the western end of the [[Valles Marineris]], was found to be one of the most mineralogically diverse sites yet observed on the planet. These deposits, dated to the late Hesperian, post-date most Martian deposits of hydrated minerals.<ref name=thollot2012>{{cite journal |last1=Thollot |first1=P |last2=Mangold |first2=N |last3=Ansan |first3= V |last4=Le Mouélic |first4=S. |last5=Milliken |first5=RE |last6=Bishop |first6=JL |last7=Weitz |first7=CM |last8=Roach |first8=LH |last9=Mustard |first9=JF |last10=Murchie |first10=SL|s2cid=6739191 |date=2012 |title=Most Mars minerals in a nutshell: Various alteration phases formed in a single environment in Noctis Labyrinthus |journal=Journal of Geophysical Research |volume=117 |issue=E00J06 |pages= n/a|doi=10.1029/2011JE004028 |bibcode=2012JGRE..117.0J06T |doi-access=free }}</ref> Based on [[Compact Reconnaissance Imaging Spectrometer for Mars|CRISM]] spectral imagery, authors studying this depression have interpretatively identified the presence of:
*iron-rich minerals such as [[hematite]] and [[goethite]]<ref name=thollot2012 />
*Polyhydrated iron sulfates ([[copiapite]] and [[coquimbite]]), monohydrated iron sulfates ([[szomolnokite]] and possibly [[kieserite]]), hydroxylated iron sulfates ([[melanterite]] and hydronium [[jarosite]]), and possibly anhydrous iron sulfates ([[mikasaite]]).<ref name=thollot2012 />
*aluminum [[phyllosilicates]] ([[kaolinite]]s like hydrated [[halloysite]]/endeillite, or perhaps a combination of kaolinite and [[montmorillonite]])<ref name=thollot2012 />
*iron [[smectite]]s ([[nontronite]])<ref name=thollot2012 />
*[[opal#Noncrystalline opal|opaline silica]] (opal-A to the [[diagenesis|diagenetically]]-altered opal-CT), found to be comparable in spectral signature to some [[Iceland]]ic volcanic glass [[lapilli]]<ref name=thollot2012 />

Of the hydrated iron sulfate minerals observed in the basin, some of them - such as [[copiapite|ferricopiapite]] - are not stable in modern Martian conditions. However, researchers have suggested that they appear to coexist because the different deposits may have been exposed to the open atmosphere at different times, and some of these minerals do only fully dehydrate under Martian conditions over the course of many years.<ref name=thollot2012 /> Furthermore, opaline silica deposits observed within this depression display spectra that may occasionally suggest interpersal with the iron sulfate mineral [[jarosite]] and the phyllosilicate mineral montmorillonite. The latter material is interpreted as such from an unusual doublet shape resolved on its spectra.<ref name=thollot2012 />

The minerals in this basin were most likely formed as a result of an initially acidic [[hydrothermal alteration]] of basaltic terrain, with the dissolution of [[plagioclase]] and calcium-rich pyroxenes increasing the pH steadily and causing the other minerals to precipitate. In this basin in particular, the [[mafic]] smectite layer overlays sulfates, aluminum phyllosilicate clays, and opaline silica deposits. The order of this layering is unique to the unnamed depression and is typically reversed in most Martian contexts, with the mafic smectites forming the bottom [[Noachian]]-age layer.<ref name=thollot2012 /> Some researchers have counterproposed that rather than a sequentially reversed depositional event, this basin formed in a single, highly heterogeneous event. This is not necessarily indicative of a global alterational phenomenon, but is most likely tied to a localized heat source such as a volcano or an impact crater.<ref name=thollot2012 /> In 2024, scientists Pascal Lee and Sourabh Shubham found evidence from CRISM, the [[HiRISE]] camera, and the [[Mars Orbital Laser Altimeter]] that this heat source was a volcano near the northeast end of the labyrinthus that they dubbed '''Noctis Mons''', which would be the seventh-highest mountain on Mars at {{cvt|9028|m|ft}}, and that the eastern part of its base was home to multiple [[glacier]]s with potential for hosting life, which could make it a highly valuable candidate target for [[astrobiology]] missions.<ref name="SETI Institute 2024">{{cite web | title=Giant Volcano Discovered on Mars | website=SETI Institute | date=March 13, 2024 | url=https://www.seti.org/press-release/giant-volcano-discovered-mars | access-date=March 20, 2024}}</ref><ref name="SETI Institute 2023">{{cite web | title=Remains of a Modern Glacier Found Near Mars’ Equator Implies Water Ice Possibly Present at Low Latitudes on Mars Even Today | website=SETI Institute | date=March 15, 2023 | url=https://www.seti.org/press-release/remains-modern-glacier-found-near-mars-equator-implies-water-ice-possibly-present-low-latitudes | access-date=March 20, 2024}}</ref>

Calcium-rich [[pyroxene]]s have been spectrally observed elsewhere in the northern reaches of the Noctis Labyrinthus fracture zone.<ref name=thollot2012 />