Independent Project at the Department of Earth Sciences
Självständigt arbete vid Institutionen för geovetenskaper
2015: 8
Pit Craters of Arsia Mons Volcano,
Mars, and Their Relation to Regional
Volcano-Tectonism
Kollapskratrar på vulkanen Arsia Mons, Mars, och
deras relation till regional vulkantektonism
Jesper Perälä
DE PA R TM E N T O F
EA R TH S CI E N CE S
INSTITUTIONEN FÖR
GEOVETENSKAPER
Independent Project at the Department of Earth Sciences
Självständigt arbete vid Institutionen för geovetenskaper
2015: 8
Pit Craters of Arsia Mons Volcano,
Mars, and Their Relation to Regional
Volcano-Tectonism
Kollapskratrar på vulkanen Arsia Mons, Mars, och
deras relation till regional vulkantektonism
Jesper Perälä
Copyright © Jesper Perälä and the Department of Earth Sciences, Uppsala University
Published at Department of Earth Sciences, Uppsala University (www.geo.uu.se),
Uppsala, 2015
Sammanfattning
Kollapskratrar på vulkanen Arsia Mons, Mars, och deras relation till regional
vulkantektonism
Jesper Perälä
Kollapskratrar och kraterkedjor relaterade till vulkanen Arsia Mons på Mars har
karterats för att analysera deras spatiala mönster och för att komma till slutsatser för
deras tillblivelse. Högupplösta satellitbilder tagna av Mars Express-sonden har
använts för karteringen. Fördelningen av de karterade kraterkedjorna jämfördes med
typiska fördelningar av magmatiska gångbergarter från vulkaner på jorden.
Resultaten visar att fördelningen av kollapskratrar och kraterkedjor överensstämmer
enligt förväntningarna och påvisar en relation mellan kollapskratrar och magmatiska
gångbergarter på Mars.
Nyckelord: Strukturgeologi, kollapskratrar, kraterkedjor, Arsia Mons, Mars
Självständigt arbete i geovetenskap, 1GV029, 15 hp, 2015
Handledare: Michael Krumbholz och Steffi Burchardt
Institutionen för geovetenskaper, Uppsala universitet, Villavägen 16, 752 36 Uppsala
(www.geo.uu.se)
Hela publikationen finns tillgänglig på www.diva-portal.org
Abstract
Pit Craters of Arsia Mons Volcano, Mars, and Their Relation to Regional
Volcano-Tectonism
Jesper Perälä
Pit crater and pit crater chains associated to the volcano Arsia Mons on Mars have
been mapped to analyse their spatial pattern and to conclude about their formation.
For the mapping, high resolution satellite data gathered during the Mars Express
mission were used. The spatial distribution of the pit craters was then compared with
typical patterns of magmatic sheet intrusions within volcanoes as they are known
from Earth. The results show that the pattern of the mapped pit craters and pit crater
chains are in good agreement with these sheet intrusions and are therefore likely
related to Martian sheet intrusions.
Key words: Structural geology, pit craters, crater chains, Arsia Mons, Mars
Independent Project in Earth Science, 1GV029, 15 credits, 2015
Supervisors: Michael Krumbholz and Steffi Burchardt
Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36
Uppsala (www.geo.uu.se)
The whole document is available at www.diva-portal.org
Table of Contents
Introduction
Geological background
The Martian dichotomy
Geological ages of Mars
Martian volcanism
Arsia Mons volcano
Pit craters on Mars
Sinuous rilles
Method
1
1
1
2
3
4
4
5
6
Results
Discussion
Patterns
Terrestrial analogues
Formation mechanisms
Acknowledgements
7
10
10
12
12
14
References
Online resources
14
17
Introduction
Among the planets of our solar-system, Mars has possibly caught the most attention
over the years. The first flyby of the planet by Mariner 4 in 1965 scored the first closeup satellite images taken of the planet, and ever since, satellites and landers have
provided pictures and data with increasing quality. Since very few Martian meteorites
have been found on Earth, most of the knowledge of Mars’s geology is based on
remote sensing. The aim of this study is to improve the understanding of the
formation of pit craters and pit crater chains on Mars. The volcano Arsia Mons,
located in the Tharsis region of Mars, was chosen as study region (Figure 1). The
hypothesis is that pit crater chains are related to magmatic sheet intrusions (dykes).
Dykes arrange in typical patterns within a given stress-field as e.g. regional dykes,
cone sheets and radial dykes. If the typical pattern of dykes on Earth coincides with
the patterns formed by the pit craters on Mars, this would give strong evidence for the
pit craters to be dyke-related structures.
So far several mechanisms are suggested for the formation of pit craters
and pit crater chains on Mars. These can be categorized into four groups: carbonate
dissolution related, related to opening mode fractures, lava tubes and related to
dykes. Carbonate related mechanisms include dissolution of equatorial carbonates
by water available during early greenhouse conditions on Mars, or by water released
by volcanism (Spencer & Fanale, 1990). The opening mode fracture-related models
suggest that the pit craters are related to graben formation in the Martian crust
(Tanaka & Golombek, 1989). A different model based on opening mode fractures
conclude that during faulting void space is created in the subsurface, which
consequently lead to the observed pit craters (Ferrill & Morris, 2003). Another
mechanism is based on roof collapse of evacuated lava tubes and subsequent pit
crater formation (Cushing et al., 2007). Dyke-related formation of pit craters include
four different models. Pit craters could be formed when dykes interact with the
hydrosphere or cryosphere, resulting in a steam blast (Mège & Masson, 1996).
Smaller pits are proposed to be formed when volatiles escape from a newly formed
dyke, thus creating a void space, in which material collapses (Scott & Wilson, 2002).
Larger pit structures are suggested to be formed as a result of Plinian-style eruptions
(Scott & Wilson, 2002). Another explanation reported from Mège & Masson (1996) is
that pits are formed above giant dyke swarms which are connected to a collapsing or
deflating major magma chamber causing an evacuation of the associated dykes.
Geological background
The Martian dichotomy
One of the first impressions when investigating the Mars surface is the great
dichotomy dividing the planet roughly by the hemispheres (Figure 1). The southern
hemisphere of Mars is topographically higher, more cratered, and older compared to
the northern hemisphere. There are still disagreements about the cause of these
topographic differences. Neumann et al. (2004) suggest mantle convection as a
mechanism for the formation of the duality of Martian topography. Wilhelms &
Squyres (1984) and Marinova et al. (2008), in contrast, suggest that the northern
plains are caused by an impact event. Another explanation for the formation of the
northern basin is that of a paleo-ocean (Villanueva et al., 2015).
1
Figure 1. Topographical map of Mars based on Mars Orbiter Laser Altimeter data. Arsia
Mons shown in the inset. The three aligned Tharsis Montes are Arsia Mons (A), Pavonis
Mons (B), Ascraeus Mons (C). Other notable features include Olympus Mons (D), Valles
Marineris (E) and the Hellas basin (F) (NASA, 2007).
Geological ages of Mars
The geological timescale of Mars is divided into four periods: Pre-Noachian,
Noachian, Hesperian and Amazonian. Dating of these periods was carried out by a
combination of meteorite dating and meteorite cratering chronology. Cratering
chronology is based on comparing the size and frequency distribution of impact
craters of different areas. Geologically older areas are more likely to have been
impacted by larger meteorites and over longer periods of time. The periods have
estimated ranges, based on the ages of Martian type localities (Hartmann & Neukum,
2001; Carr & Head, 2010). The Pre-Noachian age includes the formation and
differentiation of the planet until the formation of the Hellas impact basin (Carr &
Head, 2010). The Noachian period covers the time between 4.1-3.8 and 3.7 Ga,
while the age of the Hesperian period is specified to range from 3.7 to 2.9-3.3 Ga.
The Amazonian-Hesperian period boundary lies at around 1.4-2.1 Ga, and is the
most uncertain due to limitations of the crater chronology. These limitations results
from the fact that most small craters on Mars may be secondary craters (McEwen et
al., 2005), formed from debris of larger impacts, thus decreasing the accuracy of the
crater chronology for more recent periods.
Another timescale is suggested by Bibring et al. (2006) based on mineral
alterations. The Phyllocian era lies around the Noachian period and is defined by the
phyllosilicates found, which indicate alteration of minerals by water interaction. The
second era, called Theiikian, begins in the late Noachian to Hesperian. It is
characterized by the presence of sulfate minerals deposited. The Siderikian era
reaches until the present, defined by the presence of anhydrous ferric oxides formed
without the presence of water.
2
Martian volcanism
As early as 1973 it was suggested that Mars has a stationary crust, lacking plate
tectonics and subduction as known from Earth (Carr, 1973). Recent studies suggest
a weak form of plate tectonics for the Valles Marineris formation (Figure 1; Yin,
2012b). Volcanism on the other hand, is prominent and characteristic for many areas
of Mars. Hodges & Moore (1994) list and describe 46 different volcanic features in
their Atlas of volcanic landforms on Mars. The largest volcanoes on Mars can be
found in the Tharsis region (Figure 2). The Tharsis rise is a topographical highground situated in the equatorial part of the western hemisphere. The Tharsis region
hosts a number of gigantic volcanoes, among them Olympus Mons, the largest
volcano of our solar system (Figure 1; Hodges & Moore, 1994). In the centre of the
Tharsis region, the three volcanoes Arsia Mons, Pavonis Mons and Ascreus Mons
form a NE-SW trending line (Carr, 1973). The alignment of the Tharsis Montes has
given rise to theories of a common origin. A single source of magma for the later
stages of eruptions is suggested by Bleacher et al. (2007). Mège and Masson (1996)
provide a model where a mantle plume serves as the source for the early
development of the Tharsis region. Yin (2012a) on the other hand proposes a model
where episodic subduction explains the formation of the Tharsis rise.
Based on spectroscopic evidence it was concluded that Martian rocks
are mostly basaltic (Platz et al., 2015) with felsic rock being uncommon (Bandfield,
2002). In some places an andesitic signature was identified which is interpreted to
origin from basaltic rocks weathered by interaction with water (Wyatt & McSween,
2002).
Figure 2. Oblique angle view of the eastern Tharsis rise with the three Tharsis Montes,
Arsia, Pavonis, Ascraeus as seen from above Valles Marineris (NASA, 2000).
3
Arsia Mons volcano
Arsia Mons is the southernmost volcano of the three Tharsis Montes and is expected
to be the oldest of the trio. It has a basal diameter of 430 kilometres in NNE-SSW
direction and a summit altitude of 17.7 kilometres. It is a shield volcano with convex
flanks (Hodges & Moore, 1994). The centre of the volcano is dominated by a caldera,
with a diameter of 130 kilometres and a depth of 1.3 kilometres (Plescia, 2004).
Smaller shield-volcanoes have been found inside the caldera of Arsia Mons (Carr et
al., 1977; Mouginis-Mark, 2003). Fan-shaped lava flows are found, oriented toward
the NE and SW from vents high up on the volcano. Lava flows, lava channels, and
lava tubes concentrate in the north and south of Arsia Mons. Pit crater chains are
common on the volcano’s flanks.
The evolution of Arsia Mons volcano probably took place in three stages,
as was suggested by Crumpler & Auberle (1978). The earliest stage includes the
regional volcanism and shield-building phase. It was followed by caldera formation
with possible parasitic volcanism from vents and concentric grabens on the NE and
SW flanks. The end of the last succession is marked by fissure and vent volcanism in
the NE and SW flanks with extensive lava flows. More recently another evolutionary
sequence has been suggested for Ascraeus Mons by Byrne et al. (2012), which also
could be applicable for Arsia Mons due to the similarities of the three Montes. This
progression has also been divided into three stages. The first stage includes shieldbuilding and caldera collapse with basement flexure and flank terrace formation. The
second stage comprises the formation of rift aprons, enormous overlapping lava
flows. Finally, summit volcanism with extensional tectonism and formation of more rift
aprons, arcuate grabens, sinuous rilles and pit craters mark the end of the volcanotectonic evolution. The former report (Crumpler & Auberle, 1978) also suggested that
the Tharsis Montes could be represented by the three different phases of the volcano
triplet. Ascraeus Mons as the youngest and least developed part, Pavonis Mons
represents the second intermediate stage and Arsia Mons as the third and most
developed part. Byrne et al. (2012) note that Ascraeus Mons shows well developed
features in line with the ones seen on Arsia and Pavonis Mons and suggest that all
three Montes have undergone a similar structural evolution.
Pit craters on Mars
Pit craters are typical features associated with Martian volcanism, but also found on
other planetary bodies, including Earth (Okubo & Martel, 1998) and Venus
(Bleamaster & Hansen, 2001). They are rimless craters with sizes of individual
craters ranging from 1 to 4.5 kilometres in diameter (Wyrick et al., 2004). Pit crater
shapes are circular to elliptical with conical, U-shaped or flat floors (Smart et al.,
2011; Byrne et al., 2012). They can occur solitary, as crater chains (with at least 3
aligned craters) or troughs. Suggestions that pit craters can have a convex-upward
morphology have also been made from comparing sun incidence to slope angle
(Wyrick et al., 2004) and through numerical modelling (Smart et al., 2011). The idea
that pit craters on Mars are formed by collapse of surface material into a subsurface
void is generally supported, but the mechanism behind formation of the void has
been widely discussed. Wyrick et al. (2004), categorized the proposed mechanisms
into 8 groups.
(1) Karst dissolution. The formation of pit craters in the Valles Marineris
are proposed to be associated to carbonates in the region. After deposition of
4
carbonates, three mechanisms for carbonate dissolution were suggested by Spencer
& Fanale (1990). Removal of carbonates by carbonic acid from atmospheric CO2, by
acids of a magmatic source such as carbonic, sulphuric or chlorine acids or removal
of carbonates by calc-silicate mineral formation.
(2) Tension fracturing. Extensional deformation of basement rocks with
resulting graben formation followed by pit crater formation. This occurs when material
collapses into void spaces due to horizontal extension (Tanaka & Golombek, 1989).
(3) Dilational faulting. Competent rock layers e.g. of magmatic origin are
suggested to be interlayered with less competent layers consisting of volcanic ash or
aeolian sediments. Extensional deformation would create dilational faults
predominantly in the competent layers causing steep voids into which unconsolidated
material collapses (Ferrill et al., 2003).
(4) Lava tube sky lights. Lava tubes form when lava channels are
emptied and ultimately form roofs made of encrusted lava. Lava tubes form from
basaltic lavas on the slopes of volcanoes, and roof sky lights may form when a part of
the lava tube roof collapses (Lockwood & Hazlett, 2010). Possible Martian sky lights
have been discussed by Cushing et al. (2007) and related to the formation of pit
craters.
(5) Dykes interacting with the hydrosphere or cryosphere. Mège &
Masson (1996) relate the formation of linear troughs and pit craters with dykes at
different depths. Dykes at medium depths could increase the temperature of water in
the hydrosphere or cryosphere enough to let the water escape laterally to form linear
troughs. Dykes that come in direct contact with the hydrosphere or cryosphere could
lead to phreatomagmatic eruptions and the creation of pit crater structures (Mège &
Masson, 1996).
(6) Dykes with exsolved volatiles. Smaller pit craters are proposed to be
formed passively by dykes that do not reach the surface. When the magma degasses
at the tip of the dykes, void space would be created with subsequent collapse and pit
crater formation (Scott & Wilson, 2002).
(7) Dykes with Plinian-style eruptions. Larger pit structures could be
formed by very high initial gas escape from dykes. This would lead to an eruption of
Plinian type which continues until the walls collapse into the magma conduit, thus
creating a larger pit crater. The collapse is expected to remove evidence of
pyroclastic deposits, which are not found in the vicinity of the pit craters (Scott &
Wilson, 2002).
(8) Deflation of magma chambers. The Tharsis region is suggested to be
placed above a gigantic elongated magma body. Deflation or compaction of the
magma body could induce magma flow-back within the dykes which then could
collapse along the dykes. The collapse could then have created the grabens and pit
craters associated with the Tharsis region (Mège & Masson, 1996; Mège et al.,
2000).
Sinuous rilles
Sinuous rilles are rimless channels, which on Ascraeus Mons are found on the northeastern embayments (Byrne et al., 2012). It is expected that these are found on Arsia
Mons in a similar fashion. There are several suggested explanations for the formation
of these channels, in which a fluid agent is key to all of them. Erosion by pyroclastic
flows (Cameron, 1964), collapse of lava tubes (Greeley, 1971), incision by lava flows
(Carr, 1974), mud flows or lahars (Murray et al., 2010). Pit craters have been shown
5
to crosscut sinuous rilles on Ascraeus Mons (Murray et al., 2010; Byrne et al., 2012).
Byrne et al. (2012) suggest that the orientations of sinuous rilles are primarily
influenced by gravity and secondarily by subsurface structures. They discuss tectonic
influence to explain the sudden change of orientation in some of the rilles examined.
Another explanation in which grabens, normal faults, pit craters and sinuous rilles all
primarily are under structural control by local to regional stress fields is suggested by
Pozzabon et al. (2010).
Figure 3. (A) White arrow indicate transition from single pit craters to coalesced trough. The
red arrow points out a small impact crater with a raised rim, in comparison to the rimless pit
craters. (B) White arrow showing pit crater formation in relation to a graben on the southeastern flank of Arsia Mons. The red arrow indicates normal faulting associated with graben
formation. (C) White arrow shows pit crater chain extending radially from Arsia Mons’
caldera, slightly west of the northern rift fissure. (D) Structure interpreted as a sinuous rille,
showing similar morphological features to pit crater troughs.
Method
Pit crater chains and troughs were mapped in the proximity of Arsia Mons volcano
(extending 300 kilometres north, 265 kilometres south, 175 kilometres east and 200
kilometres west from the caldera centre). Aerial photographs used in the mapping
were photo-mosaics from the High Resolution Stereo Camera from the Mars Express
mission by the European Space Agency. A total of eight images was used to produce
a map covering most of Arsia Mons. The images have a resolution of 6 and 12
meters/pixel and use the Mars coordinate system with a sinusoidal projection.
Mapping was carried out with ArcMap 10.3 GIS software.
6
Guidelines to distinguishing pit craters from impact craters and sinuous
rilles are adapted from Wyrick et al. (2004): “a pit crater does not have a raised rim
(to distinguish from impact craters); a chain must consist of at least three separate
pits in alignment, or two coalesced pits in alignment; pits that occur within a collapsed
through are considered the same pit crater chain”. The mapping was done at a
consistent view scale of 1:100 000. This scale was chosen due to difficulties
distinguishing the raised rim of craters less than 300 metres in diameter. Polylines
were created following the extent of crater-chains or troughs. These were then
assigned to one of five groups. These five groups comprise pit craters or troughs
which could correspond to the following three types of magmatic intrusions: cone
sheets, regional dykes or radial dykes. The fourth group includes pit crater chains
that show strong similarities to sinuous rilles and could consequently not be assigned
to any certain type of magmatic sheets. The fifth group include crater chains that
could not be assigned to any of the previous groups with sufficient certainty. Craters
and troughs which were interpreted to belong to the same feature were grouped
together. The length and azimuth of the polylines were calculated using Field
calculator and EasyCalculate 10 (http://www.ian-ko.com/free/EC10/EC10_main.htm)
add-in for ArcMap 10.3. Additional control measurements were made with the
Measure/Angle tool add-in, to validate the azimuth calculations made by
EasyCalculate 10. For further analysis the attribute tables were exported to Microsoft
Excel 2013 to create tables and graphs. The azimuth data were analysed with Rosediagrams using Stereo31 1.0.1 (http://www.ruhr-unibochum.de/hardrock/downloads.html).
Results
A total of 336 polylines were produced using ArcMap 10.3, following the extent of
structures interpreted as pit crater chains or troughs (Table 1). There is a general
absence of crater chains in the eastern and south-eastern flank of Arsia Mons, as
well as on the western to north-western flank. A small portion of the volcanoes
western flank is not included in the satellite photographs, as seen in Figure 5, A-F.
The cone sheet group comprises 104 structures. The Rose-diagram
shows that the azimuth varies greatly, with a mean azimuth of 65° (Figure 5-B). The
maximum count in the Rose-diagram is 6. The crater chains are mostly 4000-10 000
metres in length (Figure 4).
Regional dyke group includes 131 structures. The mean azimuth of the
group is approximately 15°, displaying a trend in the NNE direction (Figure 5-C). The
maximum count in the Rose-diagram is 15. The majority of the crater chains are
4000-8000 metres in length (Figure 4).
36 structures are classified as radial dykes. They populate an area of the
north-western flank of Arsia Mons. The Rose-diagram show a trend toward NNW and
a mean azimuth of 345° (Figure 5-D). The maximum count in the Rose-diagram is
4.5. The length of the crater chains are mainly in the 2000-6000 metres interval
(Figure 4).
There are 36 structures in the sinuous rille-like pit crater group. A trend is
seen toward the NE in the Rose-diagram, with a mean azimuth of 35° (Figure 5-E).
The maximum count in the Rose-diagram is 5. The majority of these crater chains are
up to 8000 metres in length (Figure 4).
29 structures are included in the uncategorized group. The mean
azimuth of the group is 10°, trending towards NNE as shown in the Rose-diagram
7
(Figure 5-F). The maximum count in the Rose-diagram is 2.5. All crater chains in
Group 4 are shorter than 10 000 metres (Figure 4).
Table 1. Summary of results.
Group
Quantity
1
104
2
131
3
36
4
36
5
29
Mean azimuth
65°
15°
345°
35°
10°
Maximum count
6
15
4.5
5
2.5
Mean length
7240 m
5696 m
6970 m
7079 m
4931 m
Figure 4. Histograms showing the length distribution of the mapped pit crater chains.
8
Figure 5. Continuing on the next page
9
Figure 5. Mapping results including Rose-diagrams with the orientations of the mapped
structures. (A) Measurements including all 5 groups, the maximum count in the Rosediagram is 22.5. (B) Cone sheet-like structures, the maximum count in the Rose-diagram is
6. (C) Regional dyke-like structures, the maximum count in the rose diagram is 15. (D) Radial
dyke-like structures, the maximum count in the Rose-diagram is 4.5. (E) Sinuous rille-like
structures, the maximum count in the Rose-diagram is 5. (F) Unspecified pit crater group, the
maximum count in the Rose-diagram is 2.5. 10° bin sizes in the Rose-diagrams. Mars
sinusoidal coordinate system with sinusoidal projection.
Discussion
Patterns
Magmatic sheet intrusions can occur as dykes, sills and cone sheets (Figure 6).
Sheet intrusions arrange within the stress field, in which they occur. Regional dykes
are expected to follow the same orientation on a regional scale. Radial dykes would
orient themselves radially from the magmatic centre. Cone sheets are oriented in a
circumferential fashion around the magma reservoir.
10
Figure 6. Schematic image of a shallow magma body feeding both dykes (blue) and cone
sheets (red). Modified from Galland et al. (2014). Under copyright by John Wiley & Sons, Inc.
Reproduced under permission number 3630200087527.
When analysing the results of the pit crater mapping of Arsia Mons
typical trends can be distinguished, while the orientation of the total of all mapped pit
crater chains is mainly NE-SW.
The crater chains of the cone-sheet group were expected to show an
even distribution toward all directions in the Rose-diagram. This is not the case,
although the maximum amount in the Rose-diagram was merely 6. The lack of an
even distribution of the cone sheet-like crater chains could be explained by the
general absence of crater chains on the north-western and south-eastern flanks of
Arsia Mons and should therefore not be taken as an argument against a cone-sheet
like pattern. The visual appearance of the pattern of this group strongly correlates
with that expected to be formed from cone-sheets.
The regional dyke-like group show a mean azimuth of 15°. This group
includes the greatest amount of pit crater chains. The pattern can be explained by
the alignment of the pit craters within the regional stress field, in a similar fashion as
observed in regional dykes found in the Mull swarm (Jolly & Sanderson, 1995) and
the Cuillins Intrusive Complex, Scotland (Bistacchi et al., 2012) and coincide with the
pit crater chain orientations on the other Tharsis Montes, which is strong evidence for
a regional control on the orientation of the crater chains.
The radial dyke-like group shows a mean azimuth of 345°, which is not in
line with the overall trend of the other mapped pit crater groups. Instead, the strike of
this group points towards the centre of the volcano, therefore they could be explained
as a population of radial dykes.
The sinuous rille-like group includes pit crater chains that generally follow
the NE-SW trend. The crater chains in this group are close to sinuous rilles, and do in
some cases change direction. Structural control by local changes in the stress field
could be the cause of such alterations (Pozzabon et al., 2010).
11
The unspecified group is aligned with a mean azimuth of 10°. The pit
craters do not directly sort into any of the three groups above. The alignment of these
pit crater chains could be influenced by both the stress field of the volcano and the
regional stress field.
Terrestrial analogues
The Cuillins Intrusive Complex found on Isle of Skye, Scotland, offers an example
where a proximal population of cone sheets is found as well as regional dykes.
Bistacchi et al. (2012), showed that an oblate magma chamber can produce the
pattern of dykes found on the Isle of Skye. An oblate magma chamber was used as a
model by Pozzabon et al. (2010) to describe grabens, normal faults, crater chains
and sinuous rilles of Ascraeus Mons. Such a model could be related to the model by
Bleacher et al. (2007), suggesting a shared magma source for the Tharsis Montes. A
shared source would most likely be elongated along the orientation of the three
volcanoes.
Eruptive fissure vents were mapped across the Fernandina and Isabela
islands, Galapagos, by Chadwick Jr & Howard (1991), showing a pattern where
circumferential fissures are located close to the summits of the volcanoes and radial
to regional fissures are located at an increasing distances from the central calderas.
The pattern is similar to the observed pit crater chains but contrasts as eruptional
deposits are not found near pit craters (Byrne et al., 2012). Mège & Masson (1996)
expect dyke swarms related to grabens and pit craters in the Tharsis region not to
breach the surface.
A model for the Mull swarm in Scotland postulated by Jolly & Sanderson
(1995) may give insight into the distribution pattern. The dykes are more influenced
by the regional stress field with increasing distance from the magma chamber. At
closer range the opening angles of the dykes, in relation to the source, are highly
variable whereas the dykes are more aligned farther away from the magma source.
This could be reflected by the regional dyke-like pit craters, which are highly aligned,
as shown by the Rose-diagram in Figure 5-C. The radial dyke-like and unspecified
group pit craters could represent an intermediate form, where the stresses from Arsia
Mons and the regional stresses are overlap, whereas cone sheet-like pit craters are
highly influenced by Arsia Mons’ stress field.
Formation mechanisms
As described above, there are several hypotheses for the formation of pit craters on
Mars. How well they fit the patterns observed on Arsia Mons is discussed in the
following section.
The mechanisms for carbonate dissolution and subsequent pit crater
formation is mainly proposed for Martian equatorial basins (Spencer & Fanale, 1990).
As Arsia Mons is a large shield volcano that consists of basaltic rocks, it is difficult to
explain the occurrence of large amounts of carbonates. Karst dissolution thus seems
to be an unlikely explanation for the pit craters of Arsia Mons.
Tension fracturing mechanisms are not conflicting with the pit crater
patterns seen on Arsia Mons. Magma chamber inflation for example could produce
extensional fractures in agreement with the cone sheets and regional dykes. Dykes
themselves can be considered tensional fractures (Rubin, 1993). The suggestion by
12
Tanaka & Golombek (1989), that magma withdrawal produced grabens and pit
craters, supports the explanation that pit craters can be related to dykes.
Pit craters related to graben formation during dilational faulting is
expected during local to regional extension (Wyrick et al., 2004). Regional scale
extension is expected to require some form of tectonism as driving force. Such
tectonism is described by Anderson et al. (2001). Byrne et al. (2012) expect pit crater
formation late in the evolution of the Tharsis Montes during extension caused by
magmatic upwelling in the Amazonian, explaining the circumferential patterns of the
pit crater chains. Wyrick et al. (2004) suggest dyke intrusion into pre-existing faults.
Dilational faulting cannot be fully excluded as explanation for the formation of pit
craters on Arsia Mons.
Lava tubes form when lava flows downslope in a channel which narrows
to form the lava tubes (Lockwood & Hazlett, 2010). This downslope pattern does not
explain the circumferential patterns in which pit crater chains are often found.
Dykes interacting with the hydrosphere or cryosphere on Mars could
explain the patterns, in which pit crater chains have been observed. Hydrovolcanic
eruptions are explosive (Lockwood & Hazlett, 2010), which would be expected to
leave a crater rim or ejecta around the pit craters, which is not supported by
observations as pit craters are by definition rimless. However, wider dispersion of ash
due to the lower Martian gravity and dust storm erosion are suggested to remove
evidence of ejecta (Mège & Masson, 1996).
Degassing of magma in dykes could be in agreement with some of the
patterns observed, as they are suggested to form smaller pit craters. The nonexplosive process would not produce ejecta debris (Scott & Wilson, 2002), but does
not explain the larger pit craters observed.
Plinian eruption is a suggested mechanism for larger pit craters. The
underlying dykes could explain the pit crater patterns observed. Ejecta debris
produced by the explosion is explained to be by the large collapse around the
eruption. On Earth, Plinian eruptions are common for rhyolitic volcanoes and less
typical for basaltic volcanoes. As Arsia Mons produced predominantly basaltic lavas,
the probability of large enough degassing events can be debated. Scott & Wilson
(2002) provide calculations which support this theory in which the Martian gravity and
the, compared to Earth, lower density of the Martian crust is used.
Deflation of a major magma chamber with subsequent pit crater chains
forming over dykes could explain the dyke-like patterns of the pit craters. The
deflation may be explained by the late Amazonian magmatic upwelling suggested by
Bleacher et al. (2007) and the subsequent termination of the upwelling.
Of the aforementioned formational mechanisms, some are more readily
in agreement to the dyke related patterns. Lava tubes and carbonate dissolution do
not fully explain all pit crater patterns. Extensional faulting could be in agreement with
the observations and is not excluded. Mechanisms which rely on dykes in some
fashion could provide explanations for the observations. Passive formation related to
dykes, such as magma degassing or magma chamber deflation supports that positive
structures are not found in relation to pit craters and are suggested as explanation for
the results of this report.
13
Acknowledgements
I would like to express my gratitude to Dr. Michael Krumbholz for his help and neverending patience while guiding me through all stages of this study. I would also like to
thank Dr. Steffi Burchardt for useful discussions and reviewing my work. Additional
gratitude go to the DPS Geoscience Node of Washington University in St. Louis for
hosting the data needed for this report and especially to Dr. Paul Byrne for providing
links to all the data needed for this study.
References
Anderson, R. C., Dohm, J. M., Golombek, M. P., Haldemann, A. F. C., Franklin, B. J.,
Tanaka, K. L., Lias, J. & Peer, B. (2001). Primary craters and secondary
concentration of tectonic activity through time in the western hemisphere of
Mars. Journal of Geophysical Research, 106(E6), pp 20563–20585.
Bandfield, J. L. (2002). Global mineral distributions on Mars. Journal of Geophysical
Research [online], 107(E6). pp 1-21. Available from:
http://doi.wiley.com/10.1029/2001JE001510. [Accessed 2015-05-13].
Bibring, J.-P., Langevin, Y., Mustard, J. F., Poulet, F., Arvidson, R., Gendrin, A.,
Gondet, B., Mangold, N., Pinet, P., Forget, F. & the OMEGA team (2006).
Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars
Express Data. Science, 312(5772), pp 400–404.
Bistacchi, A., Tibaldi, A., Pasquarè, F. A. & Rust, D. (2012). The association of cone–
sheets and radial dykes: Data from the Isle of Skye (UK), numerical modelling,
and implications for shallow magma chambers. Earth and Planetary Science
Letters, 339-340, pp 46–56.
Bleacher, J. E., Greeley, R., Williams, D. A., Cave, S. R. & Neukum, G. (2007).
Trends in effusive style at the Tharsis Montes, Mars, and implications for the
development of the Tharsis province. Journal of Geophysical Research
[online], 112(E9), E09005. Available from:
http://doi.wiley.com/10.1029/2006JE002873. [Accessed 2015-04-09].
Bleamaster, L. F. & Hansen, V. L. (2001). The Kuanja/Vir-Ava Chasmata: A Coherent
Intrusive Complex on Venus [online], Proceedings of Lunar and Planetary
Science XXXII, Houston, TX 2001. Available from:
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1316.pdf. [Accessed 2016-0616].
Byrne, P. K., van Wyk de Vries, B., Murray, J. B. & Troll, V. R. (2012). A
volcanotectonic survey of Ascraeus Mons, Mars. Journal of Geophysical
Research [online], 117(E1), E01004. Available from:
http://doi.wiley.com/10.1029/2011JE003825. [Accessed 2015-04-09].
Cameron, W. S. (1964). An Interpretation of Schröter’s Valley and Other Lunar
Sinuous Rills. Journal of Geophysical Research, 69(12), pp 2423–2430.
Carr, M. H. (1973). Volcanism on Mars. Journal of Geophysical Research, 78(20), pp
4049-4062.
Carr, M. H. (1974). The role of lava erosion in the formation of lunar rilles and Martian
channels. Icarus, 22(1), pp 1–23.
Carr, M. H., Greeley, R., Blasius, K. R., Guest, J. E. & Murray, J. B. (1977). Some
Martian Volcanic Features as Viewed From the Viking Orbiters. Journal of
Geophysical Research, 82(28), pp 3985-4015.
14
Carr, M. H. & Head, J. W. (2010). Geologic history of Mars. Earth and Planetary
Science Letters, 294(3-4), pp 185–203.
Chadwick Jr, W. W. & Howard, K. A. (1991). The pattern of circumferential and radial
eruptive fissures on the volcanoes of Fernandina and Isabela islands,
Galapagos. Bulletin of Volcanology, 53, pp 259–275.
Crumpler, L. S. & Auberle, J. C. (1978). Structural Evolution of Arsia Mons, Pavonis
Mons, and Ascraeus Mons: Tharsis Region of Mars. Icarus, 1978(34), pp 496–
511.
Cushing, G. E., Titus, T. N., Wynne, J. J. & Christensen, P. R. (2007). THEMIS
observes possible cave skylights on Mars. Geophysical Research Letters
[online], 34(17), L17201. Available from:
http://doi.wiley.com/10.1029/2007GL030709. [Accessed 2015-04-23].
Ferrill, D. A. & Morris, A. P. (2003). Dilational normal faults. Journal of Structural
Geology, 25(2), pp 183–196.
Galland, O., Burchardt, S., Hallot, E., Mourgues, R. & Bulois, C. (2014). Dynamics of
dikes versus cone sheets in volcanic systems. Journal of Geophysical
Research: Solid Earth, 119(8), pp 6178–6192.
Greeley, R. (1971). Lunar Hadley Rille: Considerations of Its Origin. Science,
172(3984), pp 722–725.
Hartmann, W. K. & Neukum, G. (2001). Cratering Chronology and the Evolution of
Mars. Space Science Reviews, 96, pp 165–194.
Hodges, C. A. & Moore, H. J. (1994). Atlas of Volcanic Landforms on Mars [online].
Washington: United States Department of the Interior/United States Geological
Survey. Available from: http://pubs.er.usgs.gov/publication/pp1534. [Accessed
2015-06-13].
Jolly, R. J. H. & Sanderson, D. J. (1995). Variation in the form and distribution of
dykes in the Mull swarm, Scotland. Journal of Structural Geology, 17(11), pp
1543–1557.
Lockwood, J. P. & Hazlett, R. W. (2010). Volcanoes: global perspectives. Hoboken,
NJ: Wiley-Blackwell. ISBN 9781405162494.
Marinova, M. M., Aharonson, O. & Asphaug, E. (2008). Mega-impact formation of the
Mars hemispheric dichotomy. Nature, 453(7199), pp 1216–1219.
McEwen, A., Preblich, B., Turtle, E., Artemieva, N., Golombek, M., Hurst, M., Kirk, R.,
Burr, D. & Christensen, P. (2005). The rayed crater Zunil and interpretations of
small impact craters on Mars. Icarus, 176(2), pp 351–381.
Mège, D., Lagabrielle, Y., Garel, E., Cormier, M.-H. & Cook, A. C. (2000). Collapse
features and narrow grabens on Mars and Venus: dike emplacement and
deflation of underlying magma chamber [online]. Proceedings of Lunar and
Planetary Science XXXI, Houston, TX 2000. Available from:
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1854.pdf. [Accessed 2016-0616].
Mège, D. & Masson, P. (1996). A plume tectonics model for the Tharsis province,
Mars. Planetary and Space Science, 44(12), pp 1499–1546.
Mouginis-Mark, P. J. (2003). New Observations of the Diversity of Eruption Styles
Along the SW Rift Zone of Arsia Mons, Mars [online]. Proceedings of Sixth
International Conference on Mars. Pasadena, CA 2003. Available from:
http://www.lpi.usra.edu/meetings/sixthmars2003/pdf/3001.pdf. [Accessed
2016-06-16].
Murray, J. B., van Wyk de Vries, B., Marquez, A., Williams, D. A., Byrne, P., Muller,
J.-P. & Kim, J.-R. (2010). Late-stage water eruptions from Ascraeus Mons
15
volcano, Mars: Implications for its structure and history. Earth and Planetary
Science Letters, 294(3-4), pp 479–491.
Neumann, G. A., Zuber, M. T., Wieczorek, M. A., McGovern, P. J., Lemoine, F. G. &
Smith, D. E. (2004). Crustal structure of Mars from gravity and topography.
Journal of Geophysical Research [online], 109(E8), pp 1-18. Available from:
http://doi.wiley.com/10.1029/2004JE002262. [Accessed 2015-04-01].
Okubo, C. H. & Martel, S. J. (1998). Pit crater formation on Kilauea volcano, Hawaii.
Journal of volcanology and geothermal research, 86, pp 1–18.
Platz, T., Byrne, P. K., Massironi, M. & Hiesinger, H. (2015). Volcanism and
tectonism across the inner solar system: an overview. Geological Society,
London, Special Publications, 401(1), pp 1–56.
Plescia, J. B. (2004). Morphometric properties of Martian volcanoes. Journal of
Geophysical Research [online], 109(E3), E03003. Available from:
http://doi.wiley.com/10.1029/2002JE002031. [Accessed 2015-04-01].
Pozzabon, R., Bistacchi, A., Simioni, E., Massironi, M. & Cremonese, G. (2010).
Association of late cone sheets and radial dykes on Ascraeus Mons [online].
Proceedings of European Planetary Science Congress 2010, Rome, Italy
2010. Available from:
http://meetingorganizer.copernicus.org/EPSC2010/EPSC2010-743.pdf.
[Accessed 2015-06-16].
Rubin, A. M. (1993). Tensile Fracture of Rock at High Confining Pressure:
Implications for Dike Propagation. Journal of Geophysical Research, 98(B9),
pp 15919–15935.
Scott, E. D. & Wilson, L. (2002). Plinian eruptions and passive collapse events as
mechanisms of formation for Martian pit chain craters. Journal of Geophysical
Research [online], 107(E4), pp 1-11. Available from:
http://doi.wiley.com/10.1029/2000JE001432. [Accessed 2015-04-01].
Smart, K. J., Wyrick, D. Y. & Ferrill, D. A. (2011). Discrete element modeling of
Martian pit crater formation in response to extensional fracturing and dilational
normal faulting. Journal of Geophysical Research [online], 116(E4), pp 1-10.
Available from: http://doi.wiley.com/10.1029/2010JE003742. [Accessed 201504-01].
Spencer, J. R. & Fanale, F. P. (1990). New Models for the Origin of Valles Marineris
Closed Depressions. Journal of Geophysical Research, 95(B9), pp 14301–
14313.
Tanaka, K. L. & Golombek, M. P. (1989). Martian Tension Fractures and the
Formation of Grabens and Collapse Features at Valles Marineris [online].
Proceedings of Proceedings of the 19th Lunar and Planetary Science
Conference, pp 383–396. Houston, TX 1989. Available from:
http://adsabs.harvard.edu/full/1989LPSC...19..383T. [Accessed 2015-06-16].
Villanueva, G. L., Mumma, M. J., Novak, R. E., Kaufl, H. U., Hartogh, P., Encrenaz,
T., Tokunaga, A., Khayat, A. & Smith, M. D. (2015). Strong water isotopic
anomalies in the martian atmosphere: Probing current and ancient reservoirs.
Science, 348(6231), pp 218–221.
Wilhelms, D. E. & Squyres, S. W. (1984). The martian hemisphere dichotomy may be
due to a giant impact. Nature, 309, pp 138–140.
Wyatt, M. B. & McSween, H. Y. J. (2002). Spectral evidence for weathered basalt as
an alternative to andesite in the northern lowlands on Mars. Nature, (417), pp
263–266.
16
Wyrick, D., Morris, A. P., Colton, S. L. & Sims, D. W. (2004). Distribution,
morphology, and origins of Martian pit crater chains. Journal of Geophysical
Research [online], 109(E6), pp 1-20. Available from:
http://doi.wiley.com/10.1029/2004JE002240. [Accessed 2015-05-15].
Yin, A. (2012a). An episodic slab-rollback model for the origin of the Tharsis rise on
Mars: Implications for initiation of local plate subduction and final unification of
a kinematically linked global plate-tectonic network on Earth. Lithosphere,
4(6), pp 553–593.
Yin, A. (2012b). Structural analysis of the Valles Marineris fault zone: Possible
evidence for large-scale strike-slip faulting on Mars. Lithosphere, 4(4), pp 286–
330.
Online resources
ET Spatial Techniques, EasyCalculate 10
http://www.ian-ko.com/free/EC10/EC10_main.htm [2015-05-05]
National Aeronautics and Space Administration (NASA): Photojournal, PIA02987:
Photomosaic of the Tharsis Region (2000)
http://photojournal.jpl.nasa.gov/catalog/PIA02987 [2015-05-16]
National Aeronautics and Space Administration (NASA): The Mars Orbiter Laser
Altimeter, Images (2007)
http://mola.gsfc.nasa.gov/images.html [2015-05-16]
Ruhr-Universität Bochum, Downloads
http://www.ruhr-uni-bochum.de/hardrock/downloads.html [2015-05-05]
Washington University in St. Louis: PDS Geoscience Node, Mars Express HRSC
Data
http://pds-geosciences.wustl.edu/mex/mex-m-hrsc-5-refdr-mapprojectedv2/mexhrsc_1001/data/ [2015-05-17]
17