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| Titel |
Varena suite in the crystalline crust of the Southern Lithuania: implication to the genesis and mineralization |
| VerfasserIn |
Vaida Kirkliauskaite, Gediminas Motuza, Raminta Skipitytė |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250136779
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| Publikation (Nr.) |
 EGU/EGU2016-17891.pdf |
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| Zusammenfassung |
| Keywords: Lithuania, Proterozoic, Varena suite, rare earth elements, metasomatosis.
Crystalline crust in Southern Lithuania is covered by 200-500 m thick sedimentary cover
and is investigated by potential field mapping and drilling. It is composed by amphibolites
(metabasalts), biotite-quartz-plagioclase gneisses (metapsammites and porphyry
metadacite and metaandesite) of Orosirian period. Each lithology is predominant in
alternating bands extended NNE-SSW. Supracrustals are metamorphosed on the level of
amphibolite facies and migmatized. Intrusive rocks are represented by coeval rare bodies
of gabbro, peridotite and widespread Calymmian granitic plutons. Varena suite
comprises olivine, enstatite, diopside, olivine-magnetite, magnetite, apatite-bearing, and
presumably also dolomite rocks. They form integrated bodies few sq. km large,
concentrated in the ∼300 km2area extended in N-S direction.Bodies of particular rocks
from Varena suite fixed in the boreholes are few tenths up to few hundred meters
thick, except apatite-bearing rocks, forming decimeter up to meter scale lenses and
veins.
Rocks of Varena suite are affected by strong metasomatic alteration. Olivine is substituted
by serpentine, and phlogopite, pyroxenes with amphibols (hornblende, actinolite, tremolite,
rarely richterite). The country rocks (amphibolites, metaporphyres) also affected by
alkaline (mainly sodic) metasomatosis manifested by formation of scapolite, albite,
clynopyroxene (often sodic), phlogopite, carbonates. The mineralization of REE
(up to 2759-3100 ppm of La and Ce respectively), Th, U, P hosted by monazite,
apatite, allanite is spatially related to the Varena suite and some metasomatized
supracrustals.
The views on the genesis of Varena suite are contradicting. By various authors they are
regarded as skarns, presuming metasomatic origin, as layered intrusions or products of
alkaline and carbonatitic magmatism.
In this presentation the genetic model is reviewed based on reinterpretation of structural,
geochemical, petrographical data, and new isotopic studies of O, C, Sr in the rocks of Varena
suite. According to preliminary data in carbonate rocks δ13CPDB ranges from -0.49 to +0.99
‰ and δ18OSMOW - from +13,7 to +18,6 ‰ respectively. These values are compatible with
Kola, Tamazert, Alnio carbonatites isotopic composition. 87Sr/86Sr in pyroxenic and
carbonate rock is close to ones derived from mantle source. Isotopical data, imprints of K-Na
metasomatosis, favourable tectonic setting of the research area and age constraints shows
similarities of this suite to fenitic areols inherent to alkaline and carbonatitic intrusions. |
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