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Vol. 10 (2007 year), No. 1

Nikitina L.P., Ovchinnikov N.O., Babushkina M.S., Yakovleva A.K., Yakovlev Yu.N., Chernova O.G., Goilo E.A.
Do Fe-Mg micas from the Archaean rocks of the Kola Superdeep Borehole preserve information about the crystalline substance state during their extraction to the surface in the course of drilling?

A comparative analysis of structural and spectroscopic peculiarities of the rock forming minerals in the SG-3 rocks and their homologues in the Pechenga structure framing allowed obtaining some new results concerning the specific character of buried Archaean units and constructing correlations between deep and surface formations. The investigations were performed with the use of the EPR data on vacancy defects (Р•1-centres) and defects related to the isomorphous incorporation of Al-, Ge-, Ti-ions into the lattice of the rock forming quartz and the X-ray luminescence (XRL) data on the proper and admixture defects in plagioclase. Rank correlations between the qualitative composition of the plagioclase XRL patterns and petrogenetic characteristics of host rocks have been found. Dependence of the system of admixture and proper structural defects in the rock forming minerals along the SG-3 section vs the depth of occurrence and petrogenesis of the Precambrian host rocks has been estimated. Our study showed that the admixture structural defects in the rock forming quartz can serve as a genetic mark of metamorphic rocks in the Precambrian structural-formational complexes. They are one of the criteria for typization and correlation of deeply metamorphosed Early Precambrian units penetrated by SG-3.

(in Russian, стр.13, fig. 8, tables. 6, ref 34, Adobe PDF, Adobe PDF 0 Kb)

Vol. 10 (2007 year), No. 1

Nikitina L.P., Babushkina M.S., Chernova O.G., Ovchinnikov N.O., Yakovleva A.K., Yakovlev Yu.N., Goilo E.A.
Structural state of amphibole from the Archaean rocks of the Kola Superdeep Borehole and their homologues at the surface

Trioctahedral ferromagnesium micas from the SG-3 Archaean rocks and their surface homologues constituting the amphibolite-gneiss complex in the Pechenga structure southern framing (Allarechka block) have been studied. The mineral structure, the nature and degree of structural defects have been investigated by X-ray powder diffractometry, infrared and Mossbauer spectroscopy. The chemical composition of micas was determined by the wet chemistry and microprobe methods. The study showed that with the same fm values, the mica structures from the SG-3 Archaean rocks have higher values of the unit cell volume over those for synthetic micas of the phlogopite-annite series. This is evidence of the mica structural "looseness" and is unexpected for a mineral from deep zones (7900-11350 m) taking into account the presence of trivalent cations to 0.5 AU in the mica octahedral layer. The presence of defects related to the composition non-stoichiometry (the presence of crystalline hydrate water molecules in the alkaline cation site and availability of vacancies in the octahedral sites M1) and defects of "order-disorder" type have been established. Non-stoichiometry of the composition is equally typical of the micas from the SG-3 Archaean rocks and surface homologues and is likely to reflect the metamorphism specific regime of the Archaean complex under amphibolite facies conditions (increased partial water pressure, lack of alkalies). At the same time the content of crystalline hydrate water molecules in the mica structure from the SG-3 Archaean rocks decreases slowly with depth. A various degree of cation order in the octahedral sites of the mica structure from the SG-3 Archaean rocks (disorder or close to disorder distribution) and from the homologous rocks (order distribution with prevailing ferrous iron occupation of the sites M1) has been established. The difference in the order degree most likely results from the different velocity of the Archaean rocks lift in the process of drilling as well as from the erosion processes. This fact supports the assumption that some structural peculiarities of minerals do not alter when extracting the core from the borehole. This provides preservation of the information on the crystalline substance state at depths of the Archaean complex cut by the borehole.

(in Russian, стр.11, fig. 3, tables. 8, ref 13, Adobe PDF, Adobe PDF 0 Kb)