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Geologic evolution of the Martian dichotomy in the Ismenius area of Mars and implications for plains magnetization

Show simple item record Smrekar, S. E. McGill, G. E. Raymond, C. A. Dimitriou, A. M. 2008-06-16T20:58:59Z 2008-06-16T20:58:59Z 2004-11-13
dc.identifier.citation Journal of Geophysical Research, Vol. 109, E11002, doi:10.1029/2004JE002260, 2004 en_US
dc.description.abstract The origin of the Martian dichotomy, which divides highlands from lowlands, is unknown. We examine a section of the dichotomy ( 50 - 90E) defined by steep scarps and normal faults. Stratigraphy and age relationships preclude the formation of the 2.5 km high boundary via erosion. The abrupt disappearance of topographic knobs similar to 300 - 500 km to the northeast is interpreted as a buried fault. Alignment of the buried fault with grabens, stratigraphy, and age determinations using crater counts indicate that the lowland bench is down faulted highlands crust. The estimated local strain (3.5%) and fault pattern are broadly consistent with gravitational relaxation of a plateau boundary. Magnetic and gravity anomalies occur on either side of the buried fault. Admittance analysis indicates isostatic compensation. Although nonunique, a model with a 10 km thick intracrustal block under the lowland bench, a 20 km thick block under the plains, and an excess density of 200 kg/m(3) provides a good fit to the isostatic anomaly. A good fit to a profile of the magnetic field perpendicular to the dichotomy is produced using uniformly polarized intracrustal blocks 10 - 20 km thick, an intensity of 6 Am/m, a field inclination of -30 degrees, and gaps aligned with the isostatic anomalies. One interpretation is that high-density intrusions demagnetized the crust after dynamo cessation and that low-lying magnetized areas could be down faulted highlands crust. Another model (inclination of 30 degrees) has magnetized crust beneath the isostatic anomalies, separated by gaps. The gaps could result from hydrothermal alteration of the crust along fault zones. en_US
dc.description.sponsorship NASA/JPL en_US
dc.language.iso en_US en_US
dc.publisher American Geophysical Union en_US
dc.subject Mars en_US
dc.subject dichotomy en_US
dc.subject crustal magnetism en_US
dc.subject gravity anomalies en_US
dc.subject isostasy en_US
dc.subject faulting en_US
dc.subject gravitational relaxation en_US
dc.subject extension en_US
dc.subject structural geology
dc.title Geologic evolution of the Martian dichotomy in the Ismenius area of Mars and implications for plains magnetization en_US
dc.type Article en_US

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