Metamorphism – the invisible life of the rocks

Three types of metamorphism are developed on the metamorphic complexes of the Rhodope Massif: a, widespread regional; b, high thermobaric in shear zones of friction and c, metasomatism, each with its own thermodynamic system. Friction generates energy that deforms, disintegrates and destroys minerals, subsequently recrystallized into new rocks.

Deformation and structural evolution of metamorphic complexes of the Taldyk antiform in the East Mugodzhar zone of Urals (West Kazakhstan)

The study is focused on mesostructural folded parageneses of the Taldyk antiform (a.k.a. Taldyk block) located in the East Mugodzhar zone. The sequence of their formation is established; the structural evolution of the study area is investigated, and four stages of deformation are identified. The NW-trending folds F1 with SE-vergence formed during the first stage of deformation, DI. The geodynamics and timeline of this stage remain unclear. The W-E-trending folds F2 with E-vergence are related to tectonic movements that took place at stage DII. In the western limb of the antiform, stage DII is evidenced by folds overturned towards the south-east. In the eastern limb, folds plunge to the east and northeast. These fold structures are probably related to the Devonian subduction-obduction processes. At stage DIII, thrusting of the Taldyk antiform over the West Mugodzhar zone and folding F3 with W-vergence is related to the Ural continental collision in the Late Paleozoic, which completed the geodynamic evolution of the Ural paleo-ocean. At stage DIV, postcollisional shearing is evidenced by folds F4 with steeply dipping hinges, which completed the structural evolution of the study area.

Structure, composition and conditions of formation of Quaternary sediments in the Keltmin burial canyon (southeast of the Komi Republic)

Our lithological study of the Quaternary strata in the section of the well 17843 resulted in identification of three sediments sequences of various thickness and composition. In the lower part of the well, at depths of 43.2—27 m (layers 5, 4d and 4c), the sediments were formed probably in fluvioglacial conditions. The sediments are characterized by high content of ilmenite — 7—14 %, and group of titanium minerals — 7—12 %, where concentrations of leucoxene and titanite are increased. The content of chromespinellides increases downwards from 2 to 4.4 %. In the depth interval 25.9—23.6 m (lay 4b), a dense, poorly-sorted silty clay without clastic material is exposed; its genesis is unclear. Clay is characterized by the highest amount of heavy fraction in the section — 1.91 %, and contains an abnormally high amount of magnetite — on average 31 %. The upper 22 m of the sequence (layers 4a and 3—1) are represented by alluvium — well-sorted medium-fine-grained sand with amphibole-ilmenite-garnet-epidote association of heavy minerals and increased amounts of metamorphic minerals — 7—10 %, chromespinellides — 4—6 %, and magnetite — 4—8 %. Such complex of heavy minerals in the sediments, forming the canyon, testifies to the participation of the Ural magmatic and metamorphic complexes in their formation; the supply of minerals from the Kama seems to be very problematic. Palynological analysis data obtained from layers 5, 4d, and 4b reflect a regular vegetation change of the final stages during the interglacial. Spruce-pine forests with fir, cedar, treelike and dwarf birches, alder and willow were gradually replaced by tundra plant communities, where, along with bog-tundra formations, there were xerophytic communities with wormwood Artemisia sp., Chenopodiaceae, and rare Ephedra sp.