Indicator minerals of diamond in the lamproitic diatreme, Kostomuksha region, KareliaGor’kovets, V.; Rudashevskii, N.; Rudashevskii, V.; Popov, M.; Antonov, A.
doi: 10.1134/S1028334X13050024pmid: N/A
The mineralogy of a new lamproitic diatreme 200–250 m in diameter and 3 ga in area is studied in detail. The chemical and 3-D mineralogical analysis identify the diatreme rocks as strongly altered olivine lamproites with a large volume (50–60%) of xenoliths of strongly altered spinel (garnet) lherzolites and harzburgites-dunites. Numerous grains-xenocrysts of indicator minerals of diamond have been extracted from the heavy concentrates (the weight of the initial product is 742 g and the size is 100–500 μm) as a result of hydroseparation: (1) subcalcium (CaO av. 2.6 wt %) high-Cr (Cr 2 O 3 av. 5.3 wt %) pyrope (50 grains); (2) chrome diopside (7 and 8 mol % of kosmochlor and jadeite components, respectively, >40 grains); (3) high-Cr chromite (Cr 2 O 3 > 62 wt %); and (4) picroilmenite (MgO 12–13.8 wt %) and Cr-rutile (Cr 2 O 3 1.1 wt %). Xenocrysts prove the mantle endogene (the level of garnet lherzolites) source of the magmatic center of lamproites and forecast the diamond potential of the new diatreme in the Kostomuksha ore district.
Age of blastomilonites of the Yenisei regional shear zone as evidence of the Vendian accretionary-collision events at the western margin of the Siberian CratonLikhanov, I.; Reverdatto, V.; Zinov’ev, S.; Nozhkin, A.
doi: 10.1134/S1028334X13050115pmid: N/A
The age of the latest impulse of dynamometamorphic structural-compositional transformations (603–615 Ma) was established from the 40 Ar- 39 Ar age of micas from balstomilonites of the Garevka metamorphic complex of the Yenisei Ridge confined to the Priyenisei shear zone. The age of these tectonic-thermal events marks the final stage of the Neoproterozoic evolution of the Yenisei Ridge related to the accretion of the Isakovka terrane to the western margin of the Siberian Craton. These results are in agreement with the age of metamorphic rocks of northwestern Prisayany, which are incorporated into the Sayany-Yenisei accretionary belt along with Yenisei Ridge. The conformable data on two regions indicate a global Vendian accretionary-collision event, which led to the formation of the Sayany-Yenisei accretionary belt, lateral thickening of the continental crust to the southwestern margin of the Siberian Craton, and its subsequent tectonic reworking. The synchronous Vendian orogenesis and consequence of the tectonic-thermal events along the periphery of the large Precambrian cratons of the Baltic and Siberia confirm their close spatial relation about 800 Ma ago, which agrees with contemporary paleomagnetic reconstructions.
Age and sources of late precambrian sedimentary sequences of the Southern Baikal Region: Results of the U-Pb LA-ICP-MS dating of detrital zirconsGladkochub, D.; Nicoll, G.; Stanevich, A.; Mazukabzov, A.; Sklyarov, E.; Pisarevsky, S.; Donskaya, T.; Tait, J.
doi: 10.1134/S1028334X13050097pmid: N/A
The first data on the age of detrital zircons are given for Late Precambrian terrigenous rocks of the Baikal Group and Ushakovka Formation of the southern flank of the Siberian Craton. The ages obtained for 348 zircons cover the Paleoarchean to Late Ediacaran period, demonstrate the dynamics of change of sources of the clastic material in the sedimentation basin, and mark the changes of the Late Precambrian tectonic regimes. The age of the youngest group of detrital zircons extracted from the rocks of the Kachergat Formation allows us to restrict the upper age limit of accumulation of the rocks of the Baikal Group to the Late Ediacaran (Late Vendian).
Geochemistry of terricolous lichens in the White Sea catchment areaShevchenko, V.; Pokrovsky, O.; Starodymova, D.; Vasyukova, E.; Lisitzin, A.; Drovnina, S.; Zamber, N.; Makhnovich, N.; Savvichev, A.; Sonke, J.
doi: 10.1134/S1028334X13050073pmid: N/A
This paper presents new data on the multielemental composition of terricolous lichens in the White Sea catchment area. The content of 51 chemical elements was determined in 31 samples using modern analytical methods. It was shown that the chemical composition of terricolous lichens varies widely and depends on many factors. The lithogenic dust plays the main role in accumulation of Ti, Cr, Co, Ga, Fe, Zr, Nb, Ga, Th, U, and REE. Long-range transport from remote pollution sources is important for Pb, Zn, Cd, Bi, Hg, and Se. The Kostomuksha ore dressing mill provides the local enrichment of the lichens in Fe, whereas the Monchegorsk copper-nickel enterprise affects large distances and additionally enriches the lichens in Cu, Ni, Co, Pb, and Cd in comparison with the background regions. The marine impact is reflected in elevated contents and enrichment factors in Na, Mg, and the Na/K ratio.