|
Felix Gorbatsevich, Geological Institute of the Kola Science Centre RAS (Russian Federation)
Felix Mitrofanov, Geological Institute of the Kola Science Centre RAS (Russian Federation)
Yury Yakovlev, Scientific Industrial Centre of the Kola Superdeep (Russian Federation)
Antonina Yakovleva, Scientific Industrial Centre of the Kola Superdeep (Russian Federation)
Petr Skuf'in, Geological Institute of the Kola Science Centre RAS (Russian Federation)
|
|
The rhythmic stratigraphic sketch of the Archaean complex structure in the SG-3 section (6842-12262 m) suggested before has not been corroborated by recent detailed investigations. A detailed analysis for the influence of the natural factors (the mode of rock occurrence, physical properties of rocks, tectonic and metamorphic transformations etc.) on the trajectory, shape and sizes of the SG-3 section led us to the conclusion about the presence of five differently oriented blocks (or plates) within the intersected Archaean complex.
1. 6.84-7.6 km, rock strike NW 300-320°;
2. 7.6-8.6 km, rock strike NE 60-70°;
3. 8.6-10.15 km, rock strike NE 35-45°
4. 10.15-11.1 km, rock strike ∼ NW 300°;
5. 11.1-12.26 km, rock strike NE 30-40°.
Conjunction zones of all blocks are 100-300 m thick, tectonic, and some of them (between the second and third, the third and fourth blocks) are characterized by an increased amphibolite (metabasite) content - up to 60-75% of the thickness of the corresponding intervals, while on the whole they account for ∼ 30% in the Archaean complex. Contact zones between individual blocks were likely to be most permeable for basic-ultrabasic melts.
The fourth block occupies a particular position - it is turned nearly by 90° to the third and fifth blocks. The rocks strike in this block is close to that in the first one, but their dip is reverse. The new data are supported by a distribution of age characteristics for protoliths of gneiss and amphibolite in the section. The fourth block has the greatest values of the model age and the most ancient age of the protoliths - 3.15 Ga was obtained for apoultrabasic rocks from the contact zone between the second and third blocks.
The data on 3He distribution in the section obtained before show its increased concentration not only in the Luchlompolo fault zone and in the contact zone between the Proterozoic and Archaean complexes but also in the conjunction zone between the third and fourth blocks in the Archaean complex. A peculiar position of the fourth block (plate) is also fixed by the maximum concentration of the crystal structure defects in the rock forming minerals.
Besides, generation of such a thick rift zone as Pechenga-Imandra-Varzuga included not only a deep depression of the Archaean basement but also its splitting into blocks and plates along the longitudinal and transversal tectonic dislocations that are fixed by various geological and geophysical methods.
The work was performed within project 1 07-05-00100-à of the Russian Foundation for Basic Research.
|
