September 2004 LIP of the Month

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Large igneous provinces on Mars: Ascraeus Mons

H. Hiesinger
Dept. of Geological Sciences,
Brown University,
Providence RI, 02912
Dept. of Physics and Earth Sciences,
Central Connecticut State University,
New Britain, CT 06050

J.W. Head III
Dept. of Geological Sciences,
Brown University,
Providence, RI, 02912

Large igneous provinces (LIPs) are common on most of the terrestrial planets, including the Earth, Mars, Venus and the Moon. However, there are fundamental differences in the characteristics of large igneous provinces on these planetary bodies. For example, while large shield volcanoes are absent on the Moon, Mars is characterized by extremely large shields that have formed on the stable lithosphere. Venus on the other hand shows evidence for a rapid, planet-wide and catastrophic resurfacing event and Head and Coffin [1997] argued that such an event could be the equivalent of a planet-wide large igneous province. LIPs are characterized by voluminous emplacement of mostly mafic plutonic and volcanic rocks that are not related to seafloor spreading. Rather, large igneous provinces such as the Deccan basalts or the Columbia River basalts are formed by transient large-scale activity occurring in geologic settings such as continental flood basalt provinces, volcanic passive margins, oceanic plateaus, ocean basin flood basalts, and large seamount chains [Head and Coffin, 1997]. Numerous studies indicate that large igneous provinces are closely linked to mantle dynamics [e.g., Coffin and Eldholm, 1994], but details such as emplacement rate, relationship to tectonism, and crustal processes remain under discussion.

On a dynamic planet such as Earth with its constantly moving plates and renewal of the lithosphere, mantle plume dynamics are often obscured. In contrast, one-plate planetary objects such as the Moon, Mars, Mercury and Venus can illustrate the long-term influences of mantle plumes and their variations under different thermal condition in space and time [Solomon, 1977]. Because the lithosphere is not recycled on these planets, we have a very long geologic record that allows one to investigate the chronology and episodicity of large igneous events and provinces. For these reasons, Head and Coffin [1997] argued that the planetary examples of large igneous provinces, in concert with detailed studies of terrestrial large igneous provinces, should help to develop and test models for the origin, formation, and emplacement of LIPs, and to decipher the influence of plate tectonics and deeper mantle and core processes on LIPs.

Mars is the focal point of numerous recent space missions, including Pathfinder, Mars Global Surveyor (MGS), Mars Odyssey, Mars Express, and the two MER rovers. In concert with early spacecraft data from the Mariner and Viking missions, the returned data indicate that 58% of the surface of Mars, an area of ~0.084 billion km2, are covered with volcanic material [Tanaka et al., 1988]. Greeley et al. [1987] estimated that approximately 0.2 billion km3 of volcanic rocks were emplaced on the surface of Mars. Stratigraphic studies show that most of the geologic surface activity, including volcanism, took place in the first half of the solar system history, with some volcanism and eolian and glacial activity continuing well into more recent times. In fact, the most recent spacecraft data show evidence that some lava flows might be as young as 10 - 100 million years [Hartman and Neukum, 2001]. Today Mars is characterized by the largest known volcanoes in the solar system. A large number of them sit on top of an extremely large volcanic rise that covers about 20% of the planet's surface. The Tharsis rise forms a broad dome of ~4000 km in diameter, rises as much as 10 km above the surrounding terrain, and covers an area of >6.5 million km2 [Head and Coffin, 1997]. Detailed mapping of the Tharsis rise indicates that it formed over 0.1- 1 billion years, a much longer period of time relative to many terrestrial LIPs, which formed over 0.1 - 1 million years. The Tharsis bulge is commonly interpreted to be the result of a long-lasting large mantle diapir that due to the lack of plate tectonics on Mars, had enough time to uplift the lithosphere and initiate tectonic faulting and volcanism [e.g., Banerdt et al., 1992; Breuer et al., 1996; Harder, 1998; Smith et al., 1999; Zuber et al, 2000; and references therein].

Topography of Mars from Mars Orbital Laser Altimeter (MOLA) on board Mars Global Surveyor spacecraft.

Credit: MOLA Science Team

A comparison of Olympus Mons, the largest volcano of the Tharsis rise, with the Hawaiian shield illustrates the enormous dimensions of this volcano. Its base is several hundreds of kilometers wide, approximately the size of Arizona, and its summit is at more than 20 km elevation, three times as high as Hawaii. Its volume of 2 million km3 (above its base) is an order of magnitude larger than that of Hawaii (0.1 million km3), which is composed of several individual shields. In addition to Olympus Mons, there exist numerous other large volcanoes on Mars, including the three Tharsis Montes, Ascraeus, Pavonis, and Arsia Mons, as well as Alba Patera, Elysium Mons Hadriaca Patera, and Amphitrites Patera, to name only a few. Very often these volcanoes exhibit a wide range of rift zone development, internal deformation related to lithospheric loading and flexure, flank and slope failure, and summit caldera development [Carr, 1973, 1981; Hodges and Moore, 1994; Head and Wilson, 1994; Crumpler et al., 1996].

How do we account for these unique characteristics of Martian shield volcanoes? On Mars, a one-plate planet, the lithosphere has been stable and has not moved laterally over very long times in Martian history. Thus the regions of melting in the mantle concentrated their effusive products in a single area, rather than having them spread out in a conveyor-belt-like fashion, as in the case of Hawaii. Over time, these melt products accreted vertically into huge accumulations that loaded the lithosphere and caused flexure, deformation and edifice flank failure. [Carr, 1973, Head and Coffin, 1997]. Another factor contributing to the large height of the Martian volcanoes is the very thick elastic lithosphere associated with these volcanoes; the volcanic load and the underlying lithosphere did not subside at a rate that would limit their heights.

New high-resolution multispectral stereo data from the HRSC camera on board the European Mars Express mission allow us to take a very detailed look at Martian large igneous provinces. The HRSC camera is a linescan camera with 9 CCD lines (blue green, red, IR, 3 stereo channels, 2 photometric channels) oriented perpendicular to the flight direction. The HRSC camera acquires images at spatial resolutions of about 10 m/pixel and is complemented by a Super Resolution Channel (SRC) with a 1024 x 1032 pixel frame CCD, which obtains images of about 2.3 m/pixel from an altitude of 250 km at periapsis. The latest HRSC images can be found at We used HRSC data from orbit 16 to investigate lava flows on Ascraeus Mons, one of the three Tharsis Montes [Hiesinger et al. 2004]. The Tharsis Montes are the locations of some of the youngest volcanic deposits on Mars [Scott and Tanaka, 1986]. Compared to earlier studies, the high spatial resolution of the HRSC data allowed us to map 25 late-stage lava flows and to measure their dimensions, as well as their morphological characteristics in greater detail. In the HRSC images we observe several lava flows with well-defined leveed channels on the flanks of Ascraeus Mons, some of which are truncated by the collapse of the calderas and extend for tens of kilometers downslope. On the basis of morphologic similarities between terrains on Ascraeus Mons and terrestrial shield volcanoes, Zimbelman and McAllister [1985] proposed that individual prominent flows on Ascraeus Mons are a'a flows and the planar areas adjacent the flows are pahoehoe flows. Our estimates of the yield strengths for the young flows are on the order of ~28 x thousand Pa. These values are comparable to estimates for terrestrial basaltic lava flows, and are in good agreement with estimates of Zimbelman [1985] derived for a small number of lava flows on Ascraeus Mons. Our investigation indicates that the effusion rates for the studied Ascraeus flows are consistent with findings of Zimbelman [1985] that indicate effusion rates of 18-60 m3 per second, with an average of 35 m3 per second. On the basis of our estimates of the effusion rates and the measured dimensions of the flows, we calculated that the time necessary to emplace the flows is on average on the order of hundreds of days. Viscosities were estimated on the basis of yield strengths and effusion rates, yielding average values of 0.5 to 6 million Pa per second.

In summary, with the new data we have the opportunity to better understand the environments, associations and styles of emplacement of LIPs on Mars and also to gain a better understanding of the relations to the internal structure and the implications for the plume structure. In addition, the new data allow us to estimate more precisely the areas and volumes of LIPs, the duration and rates of their emplacement, their petrologic evolution, their relation to the geologic history of Mars and their influence on the atmosphere and the environment.

References: Banerdt et al. [1992], in Mars, Univ. of Arizona Press, 249-297; Breuer et al. [1996], J. Geophys. Res. 101, 7531-7542; Carr [1973], J. Geophys. Res. 78, 4049-4062; Carr [1981] Surface of Mars, Yale Univ. Press; Coffin and Eldholm [1994], Rev. Geophys. 32, 1-36; Crumpler et al. [1996], in Volcano Instability on the Earth and Other Planets, Spec. Publ. 110, Geol. Soc. London; Greeley et al. [1987], Science 236, 1653-1654; Harder [1998], J. Geophys. Res. 103, 16775-16798; Hartman and Neukum [2001], in Chronology and Evolution of Mars, Kluwer Academic Press; Head and Coffin [1997], Geophys. Monogr. 100, 411-438; Head and Wilson [1994], LPSC XXV, 527-528; Hiesinger, Head and the HRSC Imaging Team [2004], (in prep.); Hodges and Moore [1994], Atlas of Volcanic Landforms on Mars, US Geol. Surv. Prof. Paper 1534; Scott and Tanaka [1986], US Geol. Surv. I-1802A; Smith et al. [1999], Science 284, 1495-1503; Solomon [1977], Phys. Earth Planet. Inter. 15, 135-145; Zimbelman [1985], Proc. LPSC 16, 157-162; Zimbelman and McAllister [1985] LPSC XVI, 936-937; Zuber et al. [2000], Science 287, 1788-1793.