(Fig.35)
Graphite along the steeply dipping fault systems is responsible for the observed highly anomalous self-potential at the surface. You will see the measured and the calculated data, and altogether this is a summary of the electrochemical properties of the crust. The bulk electrical resistivity of the continental crust is relatively high; it's increasing with depth. There are numerous intermediate zones of very low resistivity - that is, high conductivity - which are all clearly related to graphite- containing shear zones.
(Fig.36,37)
The super-deep bore reached a predicted highly conductive layer which was predicted to occur at a depth of around 10 km, and this could be shown by a large-scale dipole-dipole electrical experiment. Electric current was injected at variable distances from the KTB drill site up to 60 km apart and on two perpendicular profiles. So the data clearly showed that we reached this highly conducting layer and we believe that this is the reflection of the present-day brittle-ductile boundary.
(Fig.38)
The borehole was located above a pronounced magnetic anomaly, and one of the questions was what the nature of this anomalous magnetic behaviour was. It turned out surprisingly that pyrrhotite is the dominant carrier of rock magnetism. It occurs in all lithologies which were encountered. Interestingly, the present-day Curie-isotherm of pyrrhotite was reached so we had the chance to study the famous Hopkinson Effect. There are a number of mineralogical transformations - there are different modifications of pyrrhotite found in the borehole which can be used to estimate the paleo-oxygen-fugacity in the basement rocks.
(Fig.39)
Magnetite was restricted to only a very few horizons at depth below 7,000 meters. However, the magnetic anomalies produced by magnetite are much stronger than those produced by pyrrhotite and what we actually see at the surface is the magnetic anomalies produced by the deep-seated magnetite layers. That is, for the first time it could be demonstrated that magnetite anomalies are due to very deep-seated, or can be due to deep-seated, magnetite-containing bodies.
(Fig.40)
With an integrated stress measurement strategy, including a variety of methods, a number of hydrofrac experiments and relaxation measurements could be performed for the first time. The complete stress tensor of the continental crust from the surface down to mid-crustal levels could be obtained. This is some of the quantitative data. What is important is that the upper crust is strong, it is stress loaded, and it is capable of sustaining and transmitting forces comparable to those responsible for plate-driving processes.
(Fig.42,43)
This is the downward distribution of the least principal stress component and the vertical stress component. This is the maximum horizontal stress - horizontal stress component - maximum horizontal stress component, with the vertical stresses here, and what you see here is that the upper continental crust is obviously in frictional equilibrium. The data, the differential stresses, are shown here; show that the differential stress measured throughout the upper crust down to 9 km. almost equals the frictional strength of the crust, which means that only a small stress change should induce earthquakes, and this was the rationale behind a large-scale very expensive experiment that we conducted after the drilling was completed at the bottom of the main borehole.
