Possible Tuff Rings in the Beagle 2 Landing Area and Implications for Sub-surface Volatiles

Details Possible Tuff Rings in the Beagle 2 Landing Area and Implications for Sub-surface Volatiles Possible Tuff Rings in the Beagle 2 Landing Area and Implications for Sub-surface Volatiles

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p31b..10r&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #P31B-10

Astronomy and Astrophysics

Astrophysics

5480 Volcanism (8450), 6225 Mars

Scientific paper

Isidis Planitia, which contains the December 2003 landing site for Beagle 2, is a basin at the edge of the northern hemisphere martian lowlands. Crater counts date most of this plains material at close to the Hesperian-Amazonian boundary. There is a dearth of small craters (<120m) that presumably reflects mainly aeolian erosion and/or burial. Superimposed on this surface are tens of thousands of cones, sometimes occurring singly but often in chains. Individual cones are several hundred metres across and up to 300m high. Summits are about half the diameter of the base, and are often occupied by an apparently shallow summit crater. Where most abundant, cones occupy about 10% of the surface area of Isidis. The cones show a wide variety of degradation, ranging from apparently pristine to severely eroded. Such differences can be noted even in adjacent edifices, but there is also a basin-wide trend towards more degraded morphology from SW to NE. The range in morphologies presumably reflects an age-range, and we think it unlikely that the cones can have been produced as mud volcanoes in response to catastrophic sediment loading of the basin because this would have led to a relatively brief single episode of cone formation. We therefore prefer a volcanic origin. We reject the rootless cone hypothesis, because, in contrast to examples elsewhere on Mars, the Isidis cones do not appear to be built on a lava surface. Lack of identifiable lava flows emanating from any of the studied cones makes a scoria cone origin unliklely. Instead, we suggest that the cones are analogs to tuff cones. These are produced on Earth when magma encounters a wet subsoil, leading to an explosive eruption with a water:magma ratio of about 10:1. On Mars, the volatile trapped at depth within the Isidis sediments could be either water or carbon dioxide. Further arguments in favor of a volcanic origin for the cones are the chains that could reflect deep-seated fractures through which magma was supplied, and the presence of a few sharp narrow ridges that could be exhumed dykes.

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