Dike intrusion as a possible cause of linear Martian magnetic anomalies

Abstract

A model in which the ancient, 100-200-km-wide magnetic lineations in the southern hemisphere of Mars are formed by repeated dike intrusion is proposed. On the basis of magnetizations observed at terrestrial mid-ocean ridges, a likely upper bound on the Martian crustal magnetization is about 15 A m-1. This upper bound gives a minimum magnetized layer thickness of 35-60 km. Because the magnetic material is likely to be magnetite, the long-term stability of the anomalies probably requires ilmenite lamellae to have exsolved from the magnetite. This exsolution process provides an upper bound on the cooling time available of 10 2-10 5 yr. These bounds can be satisfied if the magnetic anomalies are created by successive intrusion of dikes from 20 to 2000 m wide. Production of a Martian crust 35-60 km thick by rifting requires either mantle potential temperatures in excess of 1430°C or stretching factors greater than 5.

Local spectral variability and the origin of the Martian crustal magnetic field

“…This average shell depth, near the crustal midpoint, may indicate an actual magnetized zone encompassing much of the vertical extent of the crust. If so, this is consistent with an intrusive model whereby magmatic dikes penetrate much of the crust and acquire thermo-remanent magnetization [Nimmo, 2000]. In contrast, chemical remanent magnetization models based on hydrothermal alteration predict a fairly consistent magnetized zone in the permeable upper $10 km of the crust [Scott and Fuller, 2004;Lillis et al, 2008].…”

Distribution of crustal magnetic fields on Mars: Shock effects of basin‐forming impacts

“…Recently, Robinson et al [2002] have proposed that terrestrial rocks containing finely exsolved lamellae of hematite-ilmenite (Fe 2 O 3 -FeTiO 3 ) may suggest an explanation for magnetic anomalies such as those found on Mars. In addition, it is possible that martian rocks may undergo magnetite-ilmenite exsolution [e.g., Nimmo, 2000]. Finally, pyrrhotite (Fe 7 S 8 ) has recently been advocated by Rochette et al [2001Rochette et al [ , 2002.…”

Thermal demagnetization of Martian upper crust by magma intrusion

“…Therefore, the magnetic signature of Martian volcanoes should show signs of demagnetization, and magnetic anomalies due to remagnetization should be absent or very weak. Hydrothermal circulation is potentially a dominant cause of demagnetization at Martian volcanoes [e.g., Nimmo, 2000;Harrison and Grimm, 2002;Smrekaret al, 2004;Solomon et al, 2005]. Away from volcanoes, impacts [Mohit and Arkani-Hamed, 2004] and low-temperature hydration [e.g., Bliel and Petersen, 1983] may instead dominate demagnetization of the shallow crust.…”