Why is the electrical resistivity around the KTB hole so low

The low-resistivity anomaly close to the KTB borehole coincides with both a self-potential and a static magnetic anomaly. If this coincidence is not accidental, it may yield information about the conditions required for the existence of low-resistivity anomalies in the deeper crust. A possible answer to the question in the title of this paper is that the oxygen fugacity in the crust around the KTB hole must be low enough to stabilize graphite on a grain boundary scale. This could partially explain the extremely low resistivities of the graphitized cataclastic zones, the formation of magnetic pyrrhotite from ∼ 250 to 4000 m deep and the large self-potential anomaly. The latter requires a large vertical gradient of the oxygen fugacity and a continuous graphitic conductor through this gradient zone.