Mechanism of Origin of Chains of Cones in Cryse PLanitia

Introduction: Small cones are common on Mars [1]. Some are concentrated in large fields or form long chains of several dozen kilometers long. Similar cones and chains are observed on Earth in volcanic zones (e.g., Iceland).

The origin of cones on Mars is discussed in many papers [e.g., 2-5]. [2] investigated cones in Chryse  Planitia. They believe that the cones are mostly results of mud volcanism and/or evaporite deposition.

 

Considered region: We analyzed the region on  Chryse Planitia centered in ~38^o13’ N and ~40^o35’W - Figs 1 and 2. The region is at the boundary of a smooth plain (AHcs) and a complex unit (AHcc). AHcs is the Amazoniam-Hesperian smooth plain. A small region of another type (HNck in Fig.1) is: “older knobby material” [6]. All of considered forms are composed of lacustrine deposits. They are thick enough to cover possible underlying wrinkle ridges – [6]. These ridges could be a source of hot lava or pyroclastic falls. 

Figure 1

Our region under study at Chryse Planitia (the white square) is at the boundary of smooth plain (AHcs) and complex unit (AHcc). HNck is the “older knobby material” – [6].

Figure 2

The considered region (see also Fig. 1). The chains of cones are indicated by solid black arrows and labeled by numbers 1, 2, 3, 4, 5. According to our hypothesis, the chains are formed along outcrops of sediment layers with high content of volatiles.

 

Proposed mechanisms of formation of chains: Our hypothesis assumes that the investigated region had been covered with several layers of lacustrine deposits with the layers of sediments rich in volatiles separated by layers with small amount of volatiles – Fig. 3.

Figure 3

The scenario, leading to formation chains of cones. Legend:1 – rich volatiles deposits, 2 - fissures, 3 – low volatile deposits, 4 – cones.

 

Figure 4

Apparent Thermal Inertia (ATI) map calculated from three pairs of THEMIS thermal bands (I11560003-I36037011, I47513003-I05775011 and I11560003=I36037011) and CTX based albedo (CTXP19_008417 - gray scale image).

 

Apparent thermal inertia (ATI):

It approximates thermal inertia and is often useful in remote sensing – Fig.4. The fundamental equation is ATI=(1-A)/∆T, where ΔT is the  diurnal temperature difference (in K), and A is the Lambertian albedo. ΔT is obtained from THEMIS images (in this study: I11560003-I36037011). Albedo is derived from CTX images. Geometric, topographic and atmospheric corrections are applied. The ATI values range from 397.3 to 1134.4 with the arithmetic mean of  510.6 and median value of 496.9 J m^-2 K^-1 s^-1/2. These values indicate the presence of sand and gravel.

 

Hypothesis of mud volcanoes:

. The ‘Martian version’ of mud volcanism could be substantially different than its terrestrial counterpart [7]. Note first, that the temperature of the boiling water on Mars was (for most of its history) substantially lower than in terrestrial atmosphere. We have assumed that some sedimentary layers contained substantial amount of water or ice. The stability of these layers depends on the pressure. A fissure, extending from the surface of Mars to the layer containing volatiles, could lead to the drop of pressure and release of gases. The gas release had led to development a chain of conical structures along the outcrop – Fig. 3.

    Hydrocarbon stored in clathrates could be important for this process. The clathrates could release volatiles along outcrops at the temperature substantially lower than temperature of water. Probably, on Earth there have never been similar global processes (see however [8]).

 

Hypothesis of rootless cones:

                The size and shape of the considered cones are not substantially different than many terrestrial rootless cones. The rootless cones are often generated when hot lava is interacting with water or ice. If lava flows through glacier or wetlands then it produces explosive outgassing. The blisters of water vapor could break through the lava and cause a so-called hydro-volcanic explosion, eventually forming pseudo-craters. Because the lava cools quickly, it does not spill around the cone.

Terrestrial rootless cones are of the shape and size similar to the cones on Chryse Planitia. The scenario leading to the origin of rootless cones in the considered region of Chryse Planitia requires the interaction of volatile-rich deposits from the outcrops with some hot matter. This hot matter could be a result of a rejuvenation of volcanic processes in a ridge adjacent to the considered area.

 

Conclusions:

1.We have presented the hypothesis explaining the origin of the cones chains in the chosen region of Chryse Planitia.

2.1 The ‘mud volcano mechanism’ assumes that the volatiles in the sediment layer are warm enough to be unstable. High temperature can be a result of increased heat flow of late magma intrusion below lacustrine deposits.

2.2 The ‘rootless cones mechanism’ requires hot volcanic material to come into contact with volatile-rich sediments. 

Acknowledgments: This study was supported by statutory project of Institute of Geophysics of University of Warsaw.

 References:

[1] Frey H., and Jarosewich, M., (1982) J. Geophys. Res. 87, 9867-9879. [2] Fagents, S., and Thordarson, T., (2007) https: //www.researchgate.net/publication /252418640._ [3] Farrand, W. H., et al., (2005), J. Geophys. Res.,110, E05005. [4] Gallinger, C.L. and Ghent, R.R,. (2016) 47th LPSC  2767.pdf. [5] Ghent, R. R., et al. (2012) Icarus 217, 1, 169-183. [6] Rotto, S., and K. L. Tanaka, (1995) Geologic/geomorphologic map of the Chryse Planitia: region of Mars. USGS. [7] Allen, C. C.; et al. (2008) Astrobiology, 8, 6, 1093-1112. [8] Allen. C.C., et al., (2013) Icarus 224, 424–432. [9] Orosei, R., et al., (2018). Science, vol. 361, 6401,  490-493. [10] Brož, P., et al., (2014) Earth and Planet. Sci. Let. 406, 14-23.