ABSTRACT

In this paper the results of experimentally determined physical and mechanical properties of rocks samples representing two various stratigraphic units of the Kola Superdeep Borehole SG-3, Proterozoic and Archean, and their surface analogues are presented. The density and grain density, porosity, strength and deformational characteristics for all rock samples were found and mutual comparison of the results was carried out.

INTRODUCTION

The Kola Superdeep Borehole (SG-3) represents the deepest borehole in the world reaching final depth of 12262 m.lt intersects sedimentary-volcanic sequences of the Lower Proterozoic North Pechenga Series, stratigraphically Karelian Complex (0 to 6842 m) and the underlying granitic-metamorphic Archean Kola Series, stratigraphically Kola-Belomorian Complex (Orlov & Laverov 1998).

This study presents physical and mechanical properties of several rocks from various depths of the Kola Superdeep borehole (SG-3) and their surface analogues experimentally determined by the methods of the rock mechanics. The data include grain and bulk density, porosity, compressive strengths and axial, lateral and volumetric strains. The comparative Investigations between values obtained on the core samples from the various depth in the borehole cross Section and their surface analogues can give valuable information about changes of these properties as a. function of depth. These experimental results pro- vide also important additions to the physical properties or rock samples from the Kola Superdeep Borehole obtained so far by similar methods or various indirect methods. Furthermore, they help to increase our understanding the nature of the differences between the Properties of similar rocks recovered from different depths and from surface.

ROCK SAMPLES

Nine Core samples of the Kola Superdeep borehole, free of visible fractures, were selected for the laboratory investigation (Trek ova et al. 2002a, b, Trčkova &

(Table in full paper)

Živor 2004, Gorbatsevich et al. in press). List of all samples of the borehole core that we have at disposal are given in the Table 1.

Three of the core samples belonging to the Kolasjoki suite of the North Pechenga Series were recovered from depths of3043 m, 3530 m and 4389 m. The other six samples of recovered from a depth of 6849 m, 7913 m, 7951 m, 8411 m, 8942 m and 9904 m represent the Archean Kola Series. Three of them belong among amphibolites and other three among gneisses (in Table 1–8 highlighted by gray color). Core fragmentation, caused by the drilling method and fracturing during core lifting from great depths to the surface, makes collection of rocks samples large enough for standard rock mechanics laboratory tests very difficult.

The sample analogues of the Proterozoic rocks of the and the sample analogues of the Archean rocks were collected on surface the site of the Kola Peninsula. In this case, the surface analogues are rocks that primarily belonged to the same rock complexes, i.e. rocks formed at the same time in similar geodynamic environment with similar structure and average chemical and normative mineral compositions.

LABORATORY TESTS

The physical and mechanical properties of core samples and their surface analogues were determined by the static method

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