Dike intrusion as a possible cause of linear Martian magnetic anomalies

A model in which the ancient, 100-200-km-wide magnetic lineations in the so uthern 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 15A 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 sta bility of the anomalies probably requires ilmenite lamellae to have exsolve d from the magnetite. This exsolution process provides an upper bound on th e cooling time available of 10(2)-10(5) yr. These bounds can be satisfied i f 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 degrees C o r stretching factors greater than 5.