Fig. 3

(A) First order reversal curve (FORC) diagram of the hematite-rich fault mirror HL008 (layer Hem). (B) FORC diagram of proximal goethite-rich (layer Gth). C. FORC diagram of distal goethite-rich layer. (D–F) Stereonet of bootstrapped AMS principal axes for sample HL011 in the geographic reference framework (for raw data see Supplementary Figure S5)—(D) slab 1, hematite-rich fault mirror; (E) slab 2, goethite-rich fault mirror; (F) slab3, goethite-rich fault mirror. Both bootstrapped and raw directional data are spatially homogeneous and show magnetic fabric consistency at the scale of a few centimeters. For the fault mirror (F) in which AMS is controlled by SP hematite, K₃ axes, poles to magnetic foliation, plot close to the normal to the fault plane (N120°, 66° SW) and K₁ axes, magnetic lineations (N198°, 58°) plot close to the slickenlines direction (N210°, 66°). (G) Thermomagnetic experiment on fault layer 1 (proximal Gth-rich) showing the high Curie temperature (570 °C) related to low-Ti hematite. The magnetic susceptibility decrease up to 400 °C is attributed to goethite dehydration. Between 400 and 570 °C, carbonate breakdown releases CO₂ which in turn buffers fO₂ and hence resulting in formation of small amounts of maghemite or magnetite and in a slight increase in magnetic susceptibility. At ~ 570 °C, the magnetic susceptibility sharply drops at a Néel temperature consistent with presence of a low-Ti hematite. (H) Stepwise flash heating experiment at intervals of 25 °C for 2 min in air atmosphere showing minor decrease in magnetic susceptibility caused by goethite dehydration up to 400 °C followed by transformation of goethite to hematite and decrease in magnetic susceptibility from 460 to 700 °C. Temperatures in the thermomagnetic experiments are determined through thermocouples with an accuracy of 2 °C.