Saturday, October 27, 2012

Gremyakha-Vyrmes, Kola peninsula. Field trip 2012.

This is short report about field trip with Vernadsky Institute, RAS to proterozoic massif Gremyakha-Vyrmes.
The massif consist of three main complexes: 1) ultramafic-mafic rocks 2) foidolites 3) alkali granites and syenogranites [Polkanov et al., 1967]. Interpretation of sequence is complicated because of late tectonic and metamorphic processes that are occurred here intensive.
To view the location on the map click here. It is wonderful, you can see faults in granite complex form satellite.
Our object of study were alkaline rocks, particularly alkaline granites. Some authors do not recognize alkaline granite as the product of the same source as for ultramafic and basic alkaline complexes. They consider granites and layered ultramafic-alkaline pluton separately. It is difficult to belive because of emplacement and the similar age (?) of all rocks.
I will not publish our geological schemes because of their incompleteness.
Geological scheme of Gremyakha-Vyrmes massif. Alkaline granites located on the North (elongated crosses). (Kukharenko et al., 1971)

Granites consist of two alkaline feldspars, quartz, aegirine, arfvedsonite, aenigmatite. They are distinguished from others similar granites by its age, setting and chemistry. 
In some old ditches we found uranium-molybdenum occurrence with anomaly high radiation. There is a video demonstrating this.

Materials of prospecting work in 1970's.
I should say that vegetation covers all the territory and it took a lot for observing outcrops.

Aegirinite. Alkaline metasomatic rock.
Old prospecting ditch.

Saturday, October 13, 2012

High aluminous metamorphic rock, Keivy. Al2[SiO4]O phases.

Short post about the thin section of biotite-kyanite carbonaceous schist from Keivy, Kola peninsula, Russia. The rock was invloved in processes of muscovitization, staurolitization, alteration, retrogressive metamorphism etc. I would like to show several pictures of Al2[SiO4]O modifications and high aluminous phases.

Fig. 1. All three Al2[SiO4]O modifications that has been formed due to different processes occured here.  Kyanite as a paramorphose after andalusite, sillimanite as a product of thermal reaction, andalusite as relict in newly formed muscovite aggregate. XPL.

Fig. 2. The same field, PPL.

Fig. 3. Staurolitization. Staurolite replaces kyanite crystal. PPL.

Fig. 4. Fibrous sillimanite aggregate, muscovitization and chloritization of biotite. PPL.
The pictures show complex and multi-step process of metamorphism of highly aluminous metasediments. 

Saturday, October 6, 2012

XXIX International Conference. Ore Potential of Alkaline, Kimberlite and Carbonatite Magmatism.

 "Geochemistry of Alkaline Rocks" School

The conference was held in Sudak, Ukraine. This event is organized annually by laboratory of alkaline magmatism, Vernadsky Institute RAS.
The place was chosen very properly. The beauty of nature, historical places and The Black Sea helped to support positive atmosphere during the whole conference.
Theconference was opened with first words by L.N. Kogarko and E.M. Sheremet