The investigation drill hole Outokumpu is located in SE Finland near the worked-out deposit bearing the same name. It reached a final depth of 2516 m. Basic rocks are presented by mica and black schist, biotite gneiss, serpentinite and pegmatite granite. The boundary separating Proterozoic rocks from the Archaean basement is at a depth of 1.2-1.3 km.
Rock density, such parameters of elastic anisotropy as a number and spatial orientation of symmetry elements, their symmetry type were determined by means of experimental methods. Part of determinations were made by the acoustopolariscopy method. Subsequently the values of compression (VP) and shear (VS) velocities and their pressure dependence were measured. The average (isotropic) elastic properties were obtained by the calculation method. The essence of the calculation method is in defining VP and VS from the specific mineral composition of a sample.
Judging from the acoustopolarigrams, the main part of the rocks along the drill hole section are strongly anisotropic. One can find greatly ordered (in terms of elastic anisotropy) structures of rocks. These rocks are concentrated in the upper drill hole section, down to ∼1300 m. Below, where pegmatite rocks occur, elastic properties of rocks are strongly influenced by heterogeneities. The elastic symmetry of rocks is mainly orthorhombic.
Most important palaeogeodynamic events in the Outokumpu drill hole section took place at depths of about 800, 1330-1360, 1460 m and in the range of 1650-2300 m. Displacement of the rock individual blocks in the course of palaeogeodynamics was likely to occur in these ranges.
The samples from the deep Outokumpu drill hole display the effects of linear acoustic anisotropic absorption (LAAA) and depolarization of shear waves. The LAAA effect, as a rule, is related to the oriented arrangement of the crystallographic directions in the grains of minerals, such as biotite, muscovite, plagioclase and microcline. First the manifestation of these effects was discovered in the samples from the Kola Superdeep Borehole SG-3 in Russia.
This work was financially supported by the Russian Foundation for Basic Research, grant 07-05-00100-a.
