Crystallisation in flow Part I: paleo-circulation track by texture analysis and magnetic fabrics.
Résumé
In order to better define the dependence of the mineral texture on flow, Anisotropy of Magnetic Susceptibility (AMS) and microscopic observations have been performed on calcite rich precipitations occurring in a horizontal pipe where the flow direction is clearly defined. Sixty-five cubes were cut from 5 slices, magnetic studies identified-pseudo-single domain magnetite as the major AMS carrier. Horizontal foliation characterizes the magnetic fabrics and the lineation is parallel to the pipe axis, i.e. the flow direction. The origin of this lineation is discussed and is interpreted to be mainly the consequence of elongated pseudo single domain magnetite. To complete the magnetic fabric studies, shape preferred orientation statistics were performed on 563 calcite sections in the (0001) calcite plane. It shows elongated shapes with a general orientation parallel to the pipe axis. The mean shape orientation is the average of two distinct sub-populations that deviated slightly from the pipe axis. Observation on calcite shapes and the direction of the magnetic lineation are coherent, suggesting that it is possible to track hydrothermal paleo-circulation using magnetic lineation and petrographic fabrics.
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