Geophysical Journal | 2000 volume 22 Ή3

A petromagnetic model of the Indian ocean's lithosphere

© Lebedev T.S., Savenko B.Y.

For the first time a model of the magnetoactive layer of the Indian Ocean lithosphere has been set up. As the geologic - geophysical parameters of the mineral formations of the lithosphere depend on its age, the model consists of two genetically related elements that characterize the whole process of the evolution of the magnetization of the crust and upper mantle crystalline rocks. The first of them is represented by a 2-D section of the magnetoactive layer of the lithosphere of the Aravian-Indian midoceanic ridge to 10 m y old. The second one is an 1-D column of the magnetoactive layer of the normal lithosphere (40-80 m y) of a deep-water trough where, unlike the midoceanic ridge, the time dependence of the magnetic parameters vanishes. The model considers the recent information on the formation conditions, composition and thermobaric regime of the oceanic lithosphere and uses magnetic parameters obtained for the first time by the authors in laboratory experiments under in - situ PT, conditions of the rocks of the ridge and the deep-water trough. The model demonstrates the change of the magnetization of the mineral components with their removal from the rift valley and deepening. The petromagnetic model is presented as a multilayered structure characterized by a definite set of high-temperature mineral formations with features of magnetization, composition and evolution of ferromagnetic substance inherent only to them. A regular relation of the magnetic properties of rocks with different stages of the lithosphere evolution differing in thermodynamic and tectonic conditions has been established. The new information obtained may be used for specifying the nature of the observed magnetic anomalies and the oceanic lithosphere structure.

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