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Detrital zircon U-Pb geochronology of a metasomatic calc-silicate in the Tsäkkok Lens, Scandinavian Caledonides

Barnes Cristopher J., Majka Jarosław, Bukała Michał, Nääs Erika, Rousku Sabine

Geology, Geophysics and Environment

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2021

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Vol. 47, no. 1

21--31

EN

The Tsäkkok Lens of the Seve Nappe Complex in the Scandinavian Caledonides comprises eclogite bodies hosted within metasedimentary rocks. These rocks are thought to be derived from the outermost margin of Baltica along the periphery of the Iapetus Ocean, but detrital records from the sedimentary rocks are lacking. Many metasedimentary outcrops within the lens expose both well-foliated metapelitic rocks and massive calc-silicates. The contacts between these two lithologies are irregular and are observed to trend at all angles to the high-pressure foliation in the metapelites. Where folding is present in the metapelites, the calc-silicate rocks are also locally folded. These relationships suggest metasomatism of the metapelites during the Caledonian orogenesis. Zircon U-Pb geochronology was conducted on sixty-one zircon grains from a calc-silicate sample to investigate if they recorded the metasomatic event and to assess the detrital zircon populations. Zircon grains predominantly show oscillatory zoning, sometimes with thin, homogeneous rims that have embayed contacts with the oscillatory-zoned cores. The zircon cores yielded prominent early Stenian, Calymmian, and Statherian populations with a subordinate number of Tonian grains. The zircon rims exhibit dissolution-reprecipitation of the cores or new growth and provide ages that span similar time frames, indicating overprinting of successive tectonic events. Altogether, the zircon record of the calc-silicate suggests that the Tsäkkok Lens may be correlated to Neoproterozoic basins that are preserved in allochthonous positions within the northern extents of the Caledonian Orogen.

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Petrograficzne odmiany skały kwarcowej z rejonu Wądroża Wielkiego (blok przedsudecki) w nowych odsłonięciach

Wołkowicz K.

Biuletyn Państwowego Instytutu Geologicznego

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2016

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nr 466

343--359

PL

W skale kwarcowej z Wądroża Wielkiego, na podstawie charakterystycznych cech strukturalno-teksturalnych, wyróżniono cztery podstawowe typy: skałę kwarcową o strukturze nierównokrystalicznej, skałę drobnokrystaliczną, porowatą z dużymi kryształami kwarcu, kwarc żyłowy w zrostach wielkokrystalicznych i kwarc żyłowy w zrostach heterogranularnych. Wspólną cechą wszystkich odmian skały kwarcowej jest wieloetapowy rozwój. Jest on widoczny w narastaniu kolejnych generacji kwarcu na starszych kryształach lub ich fragmentach i w zabliźnianiu młodszym kwarcem różnego rodzaju spękań. W różny sposób przejawia się metasomatyczna geneza skały. Oprócz skupień drobnego kwarcu, serycytu i reliktów starszej mineralizacji kwarcowej, pospolite są drobne wpryśnięcia kalcytu w kwarcu. Geneza skały kwarcowej z Wądroża Wielkiego jest związana z roztworami hydrotermalnymi – z krystalizacją z tych roztworów oraz z ich metasomatycznym oddziaływaniem na skały wcześniejsze.

EN

As evidenced by specific structural and textural features, the quartz rock from Wądroże Wielkie is represented by four basic petrographic types: (1) inequicrystalline quartz rock, (2) finely crystalline porous rock with large quartz crystals, (2) vein quartz in macro¬crystalline intergrowths, and (4) vein quartz in heterogranular intergrowths. A common feature of all types of quartz rock is a multistage development. It is visible on the growing succeeding quartz generations on the older crystals and their fragments and in the fills of different kinds of fissures by the younger quartz. The metasomatic origin of the quartz rock is manifested in different ways. Small calcite inclusions in the quartz are common, accompanied by fine quartz, sericite and relics of earlier quartz mineralization. The origin of the quartz rock is related to the circulation of hydrothermal solutions and their metasomatic effect on the pre-existing rocks.

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Przeobrażenia amfiboli w porfirach ryodacytowych z Zalasu koło Krakowa

Marszałek M., Czerny J.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

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2009

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T. 35, z. 2/1

159-166

EN

The study was aimed at alteration of amphibole phenocrysts in the porphyries from Zalas. The alteration processes took place at the magmatic stage: development of orthopyroxenes and biotitization, and at the postmagmatic one: chloritization followed by argillitization and formation of feldspars, carbonate minerals, quartz, ilmenite, magnetite and hematite. Post-magmatic alteration resulted from hydrothermal processes of the metasomatic character.