Lunar and Planetary Science XXXIII (2002)
1747.pdf
EXHUMATION OF INTRUSIVE IGNEOUS COMPLEXES ON THE MARGINS OF MARTIAN IMPACT BASINS.
E. F. Albin 1 and J. D. King2, 1Department of Space Sciences, Fernbank Science Center, Atlanta, Georgia 30307
([email protected]); 2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta,
Georgia 30332 ([email protected]).
Introduction: Impact basins are significant sites of
volcanism in the cratered uplands of Mars. For ni stance, lava plains and patera volcanoes occur adjacent
to the rims of ancient impact structures. Locating the
source vents for ridged plains units, interpreted to be
flood basalt flows, has proven difficult until the recent
acquisition of high resolution Mars Orbiter Camera
(MOC) imagery [1]. A search along the margins of martian impact basins has revealed the occurrence of features interpreted as igneous intrusive volcanics. Evidence includes the presence of dikes, sills, and laccoliths. These igneous complexes are interpreted as resistant intrusives left behind after the exhumation of
overlying non-indurated basin ejecta deposits.
Sill
Laccolith
Dikes
500 m
Figure 1. An intrusive igneous complex on the southwestern
exterior margin of the Cassini impact basin (MOC Image
M2200180).
Intrusive Volcanic Features: A preliminary search
for intrusive volcanics has revealed promising features
along the interior / exterior margins of several martian
impact basins (Figures 1 – 4). Thin linear ridges interpreted as dike remnants have been identified in association with at least three impact basins: southwestern
exterior rim of Cassini, northeastern interior rim of
Schiaparelli, and the northeastern floor of Huygens.
Domes thought to be exhumed laccoliths occur exterior
to the margins of Argyre and Cassini but within the
rims Isidis and Hellas basins. These domes range from
~ 200 m to 2.5 km in diameter. The Cassini basin exhibits flat “resistant” structures that may be analogous to
igneous sills.
500 m
Figure 2. Domes, possibly exhumed laccoliths, exterior to the
northeastern rim of Argyre impact basin (MOC Image
M2001626).
Lunar and Planetary Science XXXIII (2002)
1747.pdf
INSTRUSIVE IGNEOUS COMPLEXES: E. F. Albin and J. D. King
Discussion: During the late Noachian period, at
least 30 major impact basins, larger than 200 km in diameter, were produced in what is now the ancient cratered highlands. Sites for volcanism were created by
basin associated extensional tectonics [2]. It has been
previously suggested that volcanic loci, in the form of
fissure vents, occur in places were older basin rings
tangentially intersect basin-centered radial fractures [3].
Resulting volcanism began sometime after the impact
event as the tectonics adjusted to non-equilibrium
conditions established by impact. Most basins show
evidence of the emplacement of ridged plains (voluminous lava plains) both within and peripheral to the basin rim. These plains are interpreted as “simple” volcanic flows based on the occurrence of mare-like wrinkle ridges, their smooth appearance, and extensive aerial distribution. Such flows are likely flood basalts that
erupted from fissure systems sometime after basin formation.
were eventually buried and thus removed from view by
their own eruptive products [4]. Over time, the friable
and easily weathered basin ejecta deposits were removed (by wind, water, and mass wasting processes) in
places, exposing resistant underlying instrusive volcanic units – including igneous dikes, sills, and laccoliths. It is unlikely that fissure-like vents will ever be
found, but these other expressions of basin related
volcanism, in the form of intrusive igneous complexes,
appear discernible on recent high resolution MOC imagery. Future works includes a continued search for
such features along the margins of other martian impact
basins.
1.0 km
1.0 km
Figure 3. Several linear dike remnants on the northeastern
floor of the Schiaparelli basin just inside the rim (MOC Image
AB102303).
These vents easily penetrated overlying non-indurated
basin ejecta deposits and produced the vast lava
plains. The fissures that gave rise to the plains units
Figure 4. Domes found within the interior southern rim of the
Isidis impact basin (MOC Image M0300028).
References: [1] Albin E. F. (2001) LPSC XXXII,
1972. [2] Solomon S. C. and Head J. W. (1980) Rev.
Geophys. Space Phys., 18, 107-141. [3] Schultz P. H.
(1984) LPSC, XV, 728-729. [4] Ward A. W. and Spudis
P. D. (1984) LPSC, XV, 886-887.