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Title:
Correlation Between Archean Rocks From Fhe Kola Superdeep Borehole and Their Surface Analogues: On The Data of Structural-petrological and Petrophysical Studies
Authors:
Lobanov, K.; Kazansky, V.
Publication:
EGS XXVII General Assembly, Nice, 21-26 April 2002, abstract #3349
Publication Date:
00/2002
Origin:
EGU
Bibliographic Code:
2002EGSGA..27.3349L

Abstract

The results of complex structural-petrological and petrophysical studies on core sam- ples from the Kola Superdeep borehole (SG-3) and their surface analogous are evi- dence in favour of choosing Mustantunturi site for correlation between Archean rocks of Kola series from the depths of 8-10 km and from the surface. The samples of the both groups show similarity in the mode of occurrence, mineral composition, tex- ture character and formation conditions. Using the data of the SG-3 investigations it was found that the degree of rock anisotropy has been increasing with depth, but such variations were not linear, being controlled by a combination of different fac- tors. It also depended on initial composition, intensities of plastic deformations syn- chronous with Early-Proterozoic zonal progressive metamorphism. Later overprinted fragile strains and regressive processes led to its decrease. Data on the northern flank of the Pechenga structure and its setting are in conflict with these observations, but generally, anisotropy of longitudinal waves at the surface is lower than that at the depth. This conclusion is verified by Avp determinations on reference gneiss and am- phibolite samples and their surface analogues. The investigations illuminate the con- tinuously debated issue of the anomalously high rock porosity and the anomalously low elastic wave velocities at the deep levels of the ancient continental crust cut by SG-3. The results of petrophysical and experimental study on the reference core sam- ples and their surface analogues show that the gneisses and amphibolites at the depths of 8-11 are characterized by normal values of density (2,71-2,74 and 3,05-3,06 g/cm3, respectively) typical for such rocks and by velocities of longitudinal (5,57-5,83 and 6,29-6,50 km/s) and shear (2,72-3,18 and 3,31-3,45 km/s) elastic waves. With lifting to the surface from the depth more than 7 km core undergo decompression and that leads to softening and loosening of rock material. As a result, the value of rock poros- ity may comprise 0,5- 0,8 %. The results of our petrophysical study give reason to believe that in situ porosity of the Archean gneisses and amphibolites is 0,5 % and permeability values are from 10-20 to 10-18 m2. This study was supported by the RFBR (projects nos. 01-05-64294, 01-05-64295).
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