CONSTRAINING EFFUSIVE ERUPTION STYLES THROUGHOUT ELYSIUM PLANITIA, MARS. J.R.C. Voigt1 and C.W. Hamilton1. 1Lunar and Planetary

50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2620.pdf

CONSTRAINING EFFUSIVE ERUPTION STYLES THROUGHOUT ELYSIUM PLANITIA, MARS. J.R.C. Voigt1 and C.W. Hamilton1. 1Lunar and Planetary Laboratory, University of Arizona, 1629 E. Universi- ty Blvd., Tucson, AZ 85721 USA ([email protected]).

Introduction: Elysium Planitia includes several through Marte Vallis and onto the Amazonis Plani- of the youngest lava flow fields on Mars [e.g., 1–5] tia (Figure 1). Effusion rates associated with this and thus represents a crucial location for constrain- event were high (103–4 m3/s [8]), but still two to ing the late volcanic history of the planet. The low- three orders of magnitude lower than for the Aav lying volcanic plain, designated as the Cerberus eruption—even through the eruption volumes may Fossae 3 unit (AEc3 [1, 2]), is bounded in the north be comparable [9]. Additionally, lava flow mor- by the Elysium Rise unit (AEc3 [1, 2]) and in the phologies in the distal end of the Marte Vallis flows south by the equatorial Medusa Fossae Formation. resemble terrestrial sheet-like lava lobes produced Flows within AEc3 include: the 5–20 Ma Athabasca through a process of lava flow inflation, and sug- Valles lava (Aav [3]); and a succession of older la- gesting an emplacement duration of years to decades va, but still young (<50 Ma) flows that occupy the [9]. central part of the Cerberus Basin [4] (Figure 1). We conjecture that high effusion rate eruptions, Determining the similarities and differences be- like the one that formed the Aav flood basalt, erupt tween these two groups is critical for determining more volatile rich magma over a short period of how eruption styles have evolved on Mars during time from deeply-sourced reservoirs, whereas the the geologically recent past. For instance, are all other lava flows within central Elysium Planitia may major eruptions in this region characterized by high be fed by more volatile-depleted magmas erupted effusion rate, short duration eruptions, like the Aav over longer periods of time from shallower crustal flood basalt, or do there exist a wider range of erup- reservoirs. tion styles that reflect different magmatic storage To develop improved models for how magmatic regions throughout Elysium Planitia? If so, have source regions are related to effusive eruption styles magmatic source depths, eruption styles, and em- within Elysium Planitia, we are developing a new placement durations changed in a systematic way inventory of eruptions within this region by system- through time? This study addresses these issues. atically mapping the area of major flow units and Background: The Aav flood basalt may have using thickness estimates, based of stereo-derived been emplaced as recently as 5–20 Ma [6, 7], mak- topography and radar sounding data, to infer flow ing it the youngest and best preserved major lava volume. Combining this information with detailed flows on Mars. Aav occupies the western part of descriptions of flow morphology this information Elysium Planitia and includes two main branches. will be used to run and validate eruption scenarios The larger of the two branches infilled Cerberus for magma batches erupted at different depths with- Palus, overtopped its confinement to the south, and in Mars. Predictions of inferred magmatic source continued to flow northwest through a trough region can also be compared to measurements by formed by the erosional retreat of the Medusa Fos- the Heat Flow and Physical Properties Package 3 sae Formation from the AEc3 unit. However, Aav (HP ) and Seismic Experiment for Interior Structure also includes an eastern branch that overlies older (SEIS) instruments onboard InSight (Interior Explo- AEc3 lava within the central part of the Cerberus ration using Seismic Investigations, Geodesy and Basin. Heat transport) lander [10, 11]. For the first time, The Aav flood basalt is interpreted to have been this will provide the opportunity to evaluate predict- emplaced turbulently at high effusion rates of 5–20 ed magma sources based on geomorphological ob- × 106 m3/s over a relatively short amount of time. servations and compare them with heat flow data For instance Jaeger et al., (2010) [3] suggest that the and seismic signals on Mars. bulk of the erupted volume pay have been emplaced Data and Methods: This study utilizes or- over a period of only several weeks. thoimages from the Context (CTX; 6 m/pixel [12]) In contrast to the Aav flood basalt, other flows camera and High Resolution Imaging Science Ex- within the AEc3 may have been emplaced more periment (HiRISE; 0.3 m/pixel [13]) camera gradually. While the total number of flows within onboard the Mars Reconnaissance Orbiter (MRO) the Cerberus Basin remains poorly constrained, as well as High Resolution Stereo Camera (HRSC; some of the youngest major flow units debouched 12.5 m/pixel [14]) onboard Mars Express. Topo- 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2620.pdf

graphical analyzes are based on the Mars Orbiter Comparing these results with seismic signals and Laser Altimeter (MOLA) on the Mars Global Sur- surface heat flow measurements from the InSight veyor (MGS) spacecraft [15]. Combining or- mission allows for better constraining the thermal thoimages and subsurface radar reflectors obtained evolution of the planet. from the MRO SHAllow RADar (SHARAD) allow References: [1] Tanaka et al. (2005) U.S. Geo- to infer the thickness of the lava flows [16]. logical Survey Sci. Inv. Map 28888. [2] Tanaka et al. To measure the spatial area and thus infer the (2014) U.S. Geological Survey Sci. Inv. Maps. [3] volume of the emplaced lava flows the Environmen- Jaeger et al. (2010) Icarus, 205, 230–243. [4] tal Systems Research Institute (ESRI) software Vaucher et al. (2009) Icarus, 2004, 418–442. [5] ArcGIS 10.5.1 is used to digitize the lava flow mar- Voigt and Hamilton (2018) Icarus, 309, 389–410. gins. The discharge rate defines the ratio of lava [6] Berman and Hartman (2002) Icarus, 159, 1–17, volume per time which can be determined by calcu- [7] Murray et al. (2005) Nature, 434, 352–356, [8] lating the average flow velocity for a laminar New- Gregg and Sakimoto (2000) Lunar Planet. Sci. 31, tonian flow or turbulent flow, as summarized by Abstract 1758. [9] Keszthelyi et al. (2000) JGR: Jaeger et al., (2010) [3]. Planets, 105, 15027–15049. [10] Spohn et al. (2018) Conclusion: This study investigates the critical Space Sci. Rev., 214, p. 96. [11] Lognonné et al. question whether eruption styles have changed over (2015) Lunar Planet. Sci. 46, Abstract 2272. [12] the late history in Elysium Planitia on Mars. Sys- Malin et al. (2007) JGR: Planets, 112, E05S04. [13] tematically comparing two groups of lava flow McEwen et al. (2007) JGR: Planets, 112, E05S02. fields (see Figure 1) according to their morphologi- [14] Jaumann et al. (2007) Planet. Space Sci., 55, cal characteristics, volumes, and effusion rates pro- 928–952. [15] Smith et al. (2001) JGR: Planets, vides insight into the evolution of magma reservoirs 106, 23689–23722. [16] Seu et al. (2004) Planet. within the geological recent past. Space Sci., 52, p. 157.

Figure 1. This figure shows an overview of Elysium Planitia, with the Cerberus Fossae 3 unit denoted in translucent white. It inundates the central Cerberus Basin and debouches through Marte Vallis and onto Amazonis Planitia in the Northeast. The unit shown in solid white represents the Athabasca Val- les lava with the black star indicating its source. The black lines mark the Cerberus Fossae graben.