Carved Stone Fragment of Sanidine Trachyte from the Viljandi Castle

This article examines the medieval carved stone fragment found in the course of archaeological excavations from a stable boys’ house in the third bailey of the Castle of the Teutonic Order in Viljandi (Estonia), which was built during the Middle Ages. It is likely that the piece of carved stone ended up in the layer of ruins when the buildings in the third bailey were demolished. Based thereon, no conclusions can be drawn about the original location of the carved stone – it may have been brought from somewhere in the vicinity. However, based on the place it was buried it is clear that the stone was carved before the second half of the 16th century.The carved stone fragment is a wedge-shaped piece of light grey limestone-like stone, which is few centimetres thick, 6–9 cm long and 5–8 cm wide, with carved profiling still visible on its sides. This mineralogicalpetrographical picture of carved stone fragment is characteristic of alkali volcanic rock trachyte, and considering the relationships of main minerals, it is more precisely characteristic of porphyritic sanidine trachyte from the Drachenfels Hill in Germany.Carved stone fragment is extremely small and seriously damaged, but the fine profiling is clearly visible. It is more likely that it comes from a small form. Since, in the Estonian context, this is a rare material, it is more believable that was a precious, rather than a mundane, object. First off, one would assume that it was a sacrament niche, but naturally there are other possibilities

The crystalline basement of Estonia: rock complexes of the Palaeoproterozoic Orosirian and Statherian and Mesoproterozoic Calymmian periods, and regional correlations

New data on the Fennoscandian Shield and the Baltic area suggest a need for reinterpretation of the stratigraphy of Estonian Precambrian rock complexes. The rocks of the Tallinn Zone formed in the framework of the Fennian orogeny at the margin of the Bergslagen microcontinent 1.90–1.88 Ga ago. The precise age of the Alutaguse Zone is not known. It may have formed either during the 1.93–1.91 Ga Lapland–Savo orogeny or as a rifted eastern part of the Tallinn Zone in the Fennian orogeny. The granulites of western and southern Estonia belong to the volcanic arcs inside the 1.84–1.80 Ga Svecobaltic orogenic belt and show peak metamorphic conditions of 1.78 Ga. Small shoshonitic plutons formed 1.83–1.63 Ga, the small granitic plutons of the Wiborg Rapakivi Subprovince 1.67–1.62 Ga, and the Riga pluton 1.59–1.54 Ga ago

Illitization of early paleozoic k-bentonites in the baltic basin : Decoupling of burial- and fluid-driven processes

The mineralogical characteristics of Ordovician and Silurian K-bentonites in the Baltic Basin were investigated in order to understand better the diagenetic development of these sediments and to link illitization with the tectonothermal evolution of the Basin. The driving mechanisms of illitization in the Baltic Basin are still not fully understood. The organic material thermal alteration indices are in conflict with the illite content in mixed-layer minerals. The clay fraction of the bentonites is mainly characterized by mixed-layered illite-smectite and kaolinite except in the Upper Ordovician Katian K-bentonites where mixed-layer chlorite-smectite (corrensite) occurs. The variation in expandability plus other geological data suggest that the illitization of Ordovician and Silurian K-bentonites in the Baltic Basin was controlled by a combination of burial and fluid driven processes. The illitization in the south and southwest sectors of the basin was effected mainly by burial processes. The influence of the burial process decreases with decreasing maximum burial towards the central part of the basin. The advanced illitization of the shallowburied succession in the north and northwest sectors of the basin was enhanced by the prolonged flushing of K-rich fluids in relation to the latest phase of development of the Scandinavian Caledonides ~420-400 Ma

Using a titanium-in-quartz geothermometer for crystallization temperature estimation of the Palaeoproterozoic Suursaari quartz porphyry

The Suursaari volcanic sequence represents volcanic activity related to Wiborg Batholith rapakivi intrusions in the southern part of the Fennoscandian Shield. The estimated pressure conditions for batholith granitic rocks are 1–5 kbar and crystallization temperatures range from 670 to 890 °C. To describe the temperature regime of the Suursaari volcanic system, a rock sample was taken from the Mäkiinpäällys Mountain outcrop and analysed with laser ablation inductively coupled plasma mass spectrometry. Sample spots were selected from quartz phenocrysts and groundmass. Quartz crystallization temperatures were calculated by the Ti-in-quartz method that takes into account rutile equilibrium and Ti activity in each phase. The calculated crystallization temperatures of the Suursaari quartz porphyry are in the range of 647–738 °C. The results show that the Suursaari quartz porphyry contains two generations of quartz which can be distinguished on the basis of crystallization temperatures: phenocrysts crystallized at higher and groundmass quartz at lower temperature

Hornblende alteration and fluid inclusions in Kärdla impact crater, Estonia: Evidence for impact-induced hydrothermal activity

The well-preserved Kärdla impact crater, on Hiiumaa Island, Estonia, is a 4-km diameter structure formed in a shallow Ordovician sea about 455 Ma ago into a target composed of thin (~150 m) unconsolidated sedimentary layer above a crystalline basement composed of migmatite granites, amphibolites and gneisses. The fractured and crushed amphibolites in the crater area are strongly altered and replaced with secondary chloritic minerals. The most intensive chloritization is found in permeable breccias and heavily shattered basement around and above the central uplift. Alteration is believed to have resulted from convective flow of hydrothermal fluids through the central areas of the crater. Chloritic mineral associations suggest formation temperatures of 100-300 degrees C, in agreement with the most frequent quartz fluid inclusion homogenization temperatures of 150-300 degrees C in allochthonous breccia. The rather low salinity of fluids in Kärdla crater (<13 wt% NaCleq) suggests that the hydrothermal system was recharged either by infiltration of meteoric waters from the cater rim walls raised above sea level after the impact, or by invasion of sea water through the disturbed sedimentary cover and fractured crystalline basement. The well developed hydrothermal system in Kärdla crater shows that the thermal history of the shock heated and uplifted rocks in the central crater area, rather than cooling of impact-melt or suevite sheets, controlled the distribution and intensity of the impact-induced hydrothermal processes.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Detrital zircon ages of Cambrian and Devonian sandstones from Estonia, central Baltica: a possible link to Avalonia during the Late Neoproterozoic

<div><p>Detrital zircon U–Pb ages of Lower Cambrian and Middle Devonian have been determined for sandstone in Estonia through LA-ICP-MS (Nu instruments, Wrexham, UK). Both sandstones have a similar zircon age spectrum with distinct age clusters that reflect the basement geology of Baltica, i.e. 2800–2700 Ma (Kola–Karelia), 1900–1700 Ma (Svecofennian), 1600–1500 Ma (Rapakivi) and 1200–1000 Ma (Sveconorwegian). Noteworthy is a cluster at 750–550 Ma, because rocks of such age are absent within the core of Baltica. The present results suggest a possible link between Baltica and Avalonia/Cadomia during the Late Neoproterozoic.</p></div