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

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

Nov 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004jgre..10911002s&link_type=abstract

Journal of Geophysical Research, Volume 109, Issue E11, CiteID E11002

Other

12

Planetology: Solar System Objects: Mars, Geodesy And Gravity: Local Gravity Anomalies And Crustal Structure, Geomagnetism And Paleomagnetism: Magnetic Anomaly Modeling, Planetology: Solid Surface Planets: Tectonics (8149), Structural Geology: Fractures And Faults

Scientific paper

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 ~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/m3 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°, 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°) has magnetized crust beneath the isostatic anomalies, separated by gaps. The gaps could result from hydrothermal alteration of the crust along fault zones.

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