Abstract

Magnetic properties of sedimentary rocks have been commonly exploited to determine the tectonic and chemical evolution of sedimentary basins. We here propose the use of the anisotropy of the anhysteretic remanent magnetization (ARM) to infer the orientation of magnetite grains formed during remagnetization stages, and hence to obtain the tectonic regime during the magnetization period, whose age can also be constrained by paleomagnetic methods. The anisotropy of ARM technique is here applied to remagnetized Jurassic limestones from the Central High Atlas (North Africa). These rocks were remagnetized at ca. 100 Ma during the Cretaceous Normal Superchron in an extensional tectonic setting. The magnetic fabric carried by authigenic magnetite (which is also the carrier of the remagnetization) shows a consistent orientation after a partial bedding correction, which precisely corresponds with the attitude of strata at the time of remagnetization. The anisotropy of the ARM tensor shows a well-defined horizontal lineation parallel to the Mesozoic regional extension, and a horizontal magnetic foliation perpendicular to the lithostatic maximum stress axis. Therefore, our results demonstrate that (1) the magnetite grain growth was consistent with the stress conditions and did not follow any preexisting fabric of the rock, and (2) these grains did not rotate during the subsequent compressional events.

You do not currently have access to this article.