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Geochemistry International

, Volume 57, Issue 6, pp 668–681 | Cite as

Geochemistry of Sillimanite–Magnetite–Kaolinite Metasomatic Rocks on Great Tyuters Island, Gulf of Finland, Russia

  • T. F. ShcherbakovaEmail author
  • E. N. TerekhovEmail author
Article
  • 11 Downloads

Abstract

Secondary quartzites on Tyuters Island in the Gulf of Finland host long linear zones, up to 3 m thick, that are easily discernible in detailed satellite imagery. The zones consist of sillimanite–magnetite–kaolinite metasomatites, rocks that were first found in these zones. The metasomatites were produced at shattering of the quartzites and subsequent fluid introduction of material enriched in various components. The metasomatites are enriched in Al2O3 (16–23 wt %, as compared to 2–5 wt % in the quartzites). In contrast to the quartzites, iron in the metasomatic is contained mostly in the form of ferric oxide (whereas it occurs dominantly as ferrous oxide in the quartzites). The metasomatites contain practically no alkalis and alkali-earth elements and are enriched in Zn (146–199 ppm) and some other trace elements, including REE, first of all Ce (34 ppm) and La (17 ppm). Both the metasomatites and the quartzites show similar and insignificant REE fractionation: (La/Yb)n = 6.55 and 6.17. The metasomatites consist of the same minerals as the quartzites, but the proportions of these minerals and their composition in these rock types are different. It is worth mentioning magnetite of the metasomatites: it hosts abundant quartz inclusions with kaolinite rims. The quartz inclusions host, in turn, inclusions of magnetite crystallites. The metasomatites were produced in a number of stages of a metasomatic process, with changes in the fluid composition and its pH. The development of the metasomatites in the linear zones, the disintegration of their protolithic quartzites, and the high kaolinite contents in the rocks make these metasomatites similar, in a sense, to weathering crusts. However, the facts that the metasomatites and their protolithic quartzites consist of the same minerals, that the metasomatites contain absolutely no sulfides and sulfur but contain magnetite with complicated mineral inclusions make these rocks different from classic weathering crusts.

Keywords:

metasomatite quartzite linear zone aluminous minerals weathering crust magnetite hosting double mineral inclusions 

Notes

ACKNOWLEDGMENTS

The authors thank V.A. Utenkov (Ordzonikidze Russian State Geological Prospecting University) for assistance with the identification of minerals. The Russian Geographical Society (RGS) is thanked for the organization of the expedition to Great Tyuters Island. The general sponsor, the United Energy System Federal Grid Company, is thanked for help for conducting the RGS 2015 fieldwork. This study was financially supported by the Russian Foundation for Basic Research, project no. 18 05 00485 and the Presidium of the Russian Academy of Sciences, Program 19, project 0135-2018-0040.

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Copyright information

© Pleiades Publishing, Ltd. 2019

Authors and Affiliations

  1. 1.Geological Institute (GIN), Russian Academy of SciencesMoscowRussia

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