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Upper Cretaceous volcanoclastic deposits from the Haţeg basin, south Carpathians (Romania): K-Ar ages and intrabasinal correlation

Bojar A.-V., Halas S., Bojar H.-P., Grigorescu D., Vasile S.

Geochronometria

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2011

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Vol. 38, no. 2

182-188

EN

In order to constrain the age of the Upper Cretaceous continental Densuş-Ciula Formation from the Haţeg basin, South Carpathians, and correlate it with the other continental unit that occurs in the region, the Sânpetru Formation, we separated and dated by the K-Ar method biotites and amphi-boles from volcanoclastic deposits. The mineral phases analysed are from two tuff layers and volcanic bombs cropping out near Rachitova village. Two tuff layers from the Densuş-Ciula Formation give early Maastrichtian ages of 69.8š1.3 and 71.3š1.6 Ma, respectively. The ages determined for the tuff layers constrain the age of deposition for the Densuş-Ciula Formation and enable further correlations with the available palaeomagnetic data from the deposits occurring along the Sibişel Valley that be-long to the Sânpetru Formation. The volcanic bombs collected near to Răchitova village are andesites and dacites. The age determined by K-Ar method on hornblende separated from a volcanic bomb is 82.7š1.5 Ma, which is older than the underlying Campanian marine deposits in turbidite facies. This suggests that the volcanic bombs were re-deposited during the early Maastrichtian. Thus, the volcan-ics found at Răchitova have at least two origins: one type is related to an explosive synsedimentary volcanic activity, and the other type is represented by older andesitic/dacitic bombs, which most probably originate from a volcanic centre situated in the Haţeg region.

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Sulphur and oxygen isotope signatures of late Permian Zechstein anhydrites, West Poland: seawater evolution and diagenetic constraints

Peryt T. M., Halas S., Petrivna Hryniv S.

Geological Quarterly

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2010

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Vol. 54, No 4

387-400

EN

The stable oxygen and sulphur isotope ratios of 52 anhydrite samples from three Zechstein anhydrite units (Lower Anhydrite, Upper Anhydrite and Basal Anhydrite) of West Poland show d18O values vs. VSMOW in the range of 9.4 to 15.5% (mean of 12.6 š1.3%), and d34S values vs. VCDT between 9.6 to 12.6%o (mean of 11.4 š0.6%o). A generally uniform distribution pattern of both isotopic values throughout the section, although with some random variation, implies that sulphate ions were sufficiently supplied and the basin was open during sulphate deposition. There is a slight stratigraphic differentiation of both the d18O and d34S values: the highest mean values are shown by the Upper Anhydrite and the lowest average values occur in the Basal Anhydrite. The correlation between d18 O and 8 S values is statistically significant only in case of the Basal Anhydrite. A wide range of oxygen isotopic ratios (from 11.6 to 25. l%o), with only several samples having d18O values that fall within the range of late Permian seawater, have been recorded in anhydrite cements and nodules that occur in the Main Dolomite rocks. Sulphur isotope ratios of anhydrite cements (range of 7.6 to 12.9%o, average of 10.7 š1.4%o) tend to reflect the late Permian sulphur isotopic signature of sulphate in seawater. The higher ranges of d18O and d34S values of anhydrite cements and nodules in the Main Dolomite compared to the underlying and overlying anhydrites are due to diagenetic resetting. The conversion of gypsum to anhydrite (often very early and under negligible cover) evidently did not affect the primary marine stratigraphic sulphur isotope composition of the sulphate deposits.

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Study on the possible existence of water on the Moon

Robens E., Halas S.

Geochronometria

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2009

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Vol. 33

23-31

EN

Aim of an extensive research project is an analysis of surface properties of Moon’s regolith covering and the assessment of the possible existence of usable water on the Moon. In the present paper a short historical survey on Moon’s exploration and recent and planned missions is given. Recent recognitions are discussed on the basis of origin and history of the Moon and the import of water from other celestial bodies. Characteristic data and chemical composition of the Moon’s surface are summarised with respect to possible water or ice preservation. Experimental investigations have been made on three typical lunar regolith powder samples from the Apollo 11, 12 and 16 missions. The experiments include spectroscopic and thermal analysis, density measurements and sorptometry. In the present paper we give a survey on measuring methods applied and discuss some results. The measurements confirm results of investigations made with less sensitive equipment shortly after the missions. With regard to water occurrence we found that the regolith cover of the Moon surface is rather hydrophobic and can hardly store water as adsorbed layers.

4

Stable isotopes (H, C, S) and the origin of Baltic amber

Gaigalas A., Halas S.

Geochronometria

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2009

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Vol. 33

33-36

EN

New results of isotope analysis of light elements (H, C and S) of a dozen Baltic amber samples are described and discussed. Carbon isotope composition was nearly constant (ca. -23‰), whereas sulphur and hydrogen varied in their isotope compositions from +4 to -28‰ and from -171 to -213‰, respectively. The formation and subsequent evolution of this material since its origin in Paleogene time until present is outlined.

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Radiometric age analyses of rocks from the northern envelope of the Karkonosze massif, the Sudetes, Poland: a comparative geochronological study

Jarmołowicz-Szulc K., Halas S., Wójtowicz A.

Geochronometria

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2009

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Vol. 34

33-39

EN

K-Ar determinations have been conducted on the background of the earlier radiometric data in the eastern part of the northern Karkonosze-Izera envelope of the granite massif, composed of different varieties of granites, gneisses and mica schists. The values of the K-Ar age for minerals and rocks from the Karkonosze-Izera block lie in the wide interval ranging from 226.0 ± 6.7 Ma to 386.1 ± 3.0 Ma. The K-Ar age data obtained by volumetric method oscillate between 308 ± 21 and 372 ± 26 Ma. Most biotite K-Ar age values of the Izera granite-gneisses complex give an average age of 316.1 ± 3.3 Ma. They correspond to the cooling age of the Karkonosze pluton while the data below 300 Ma are minimum age values that postdate the last granite intrusion of the Krkonoše-Jizera pluton. The obtained results over 300 Ma are mixed apparent ages between the age of the Karkonosze and the Izera granite ages. The K-Ar dates in the studied region have been compared with fission-track (FT) ages of zircon and titanite in the same area which display another distribution pattern.

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Petrology of gabbroides and isotope signature of sulfide mineralization from Fedorov-Pansky layered mafic intrusion, Kola Peninsula, Russia

Huber M., Halas S., Piestrzyński A.

Geochronometria

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2009

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Vol. 33

19-22

EN

Samples from Fiodoro-Pansky massif were investigated by polarized light microscopy, EDS electron microscopy and isotope ratio mass spectrometry. We have observed four-stage ore mineralization: (1) magmatic Fe-Ti-oxides, (2) sulfide-ferrous oxide, (3) hydrothermal Cu-Ni-sulfide with haycokite, talnakhite and galena admixture, (4) tiosulfates formed from pyrrhotite. A few sulfide samples from generations (2) and (4) were investigated isotopically. The second generation is isotopically homogenous with δ34S close to zero, whilst the third generation shows significantly negative δ34S values.

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Argon stable isotope concentrations in lunar regolith

Halas S., Wójtowicz A., Czarnacki M., Robens E.

Geochronometria

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2009

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Vol. 33

37-39

EN

We performed stepwise heating experiments for determination of the two stable isotope ratios of argon fractions and total concentrations of the three stable isotopes 36Ar, 38Ar and 40Ar in lunar regolith acquired from the Apollo 11, Apollo 12 and Apollo16 missions. Also the concentration of in situ formed radiogenic 40Ar was estimated on the basis of known ages and potassium concentrations determined by isotope dilution method. The observed excess of 40Ar concentration is interpreted to be due to variable (over geological time) flux of solar energetic particles which were implanted into the material at the Moon surface.

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Physical foundations of rhenium-osmium method - a review

Dąbek J., Halas S.

Geochronometria

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2007

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Vol. 27

23-26

EN

A newly acquired mass spectrometer MI 1201 by the Mass Spectrometry Laboratory will be adapted to determine rhenium and osmium isotope concentrations using negative thermal ionization mass spectrometry (NTIMS). We describe the principle of the Re-Os dating technique and the thermal ionization phenomena which lead to high precision isotope analysis on NTIMS.

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New K-Ar cooling ages of granitoids from the Strzegom Sobótka Massif, SW Poland

Turniak K., Halas S., Wójtowicz A.

Geochronometria

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2007

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Vol. 27

5-9

EN

The Strzegom-Sobótka Variscan Massif (Fore-Sudetic Block, NE Bohemian Massif) consists of various post-kinematic Variscan granitoids emplaced into Palaeozoic low grade metamorphic rocks. Biotite from five samples representing the hornblende-biotite monzogranite, biotite monzogranite and biotite granodiorite has been dated using the K-Ar method for two size-fractions (0.25-0.35 and 0.35-0.5 mm). Finer fractions show more intense chloritization and therefore the results for them were rejected in further discussion. Coarser fractions with higher potassium content were accepted as yielding a maximum estimate approaching the true K-Ar biotite cooling ages. The results are clustered in two groups. The older age group (308.8 ±4.6 Ma and 305.5 ±4.3 Ma) comprises results obtained from the biotite granodiorites. They are generally consistent with the zircon crystallization age of 308.4 ±1.7 Ma reported by Turniak et al. (2005) and imply rapid cooling of the biotite granodiorite from magmatic temperatures down to the closure temperature of K-Ar isotopic system in biotite. The younger group is defined by 291.0 ±4.4 Ma and 298.7 ±5.2 Ma ages for the hornblende-biotite monzogranite and 294.2 ±4.3 Ma age for the biotite monzogranite. In the absence of precise U-Pb or Pb-Pb zircon data further geochronological studies are needed to decipher precisely the cooling history of the monzogranites.

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New data on the post-impact material in radiolarian horizons in Outer Flysh Carpathians and search for a source crater

Paul Z., Halas S., Wójtowicz A.

Geochronometria

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2007

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Vol. 27

17-22

EN

In the Outer Carpathians in Barnasiówka radiolarian shale formation, there is an intercalation underlied by bentonite. There were found very rare elements and minerals in this intercalation. It was recognized that this horizon has been filled with products of a big object collision with Earth. The age of the manganese-iron intercalation was determined by potassium-argon (K-Ar) dating of illites to be (89.3±1.2) Ma. Similar age, (85.2±0.6) Ma, was found for the post-impact glass from the Boltysh crater in Ukraine. It was concluded that the formation of this intercalation was synchronous with the Boltysh crater formation at the Cenomanian/Turonian boundary. The research for the K-Ar age of the crater creation in Logoisk (Belarus) established its formation to (124.2±1.2) Ma ago.

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Low-blank crucible for argon extraction from minerals at temperatures up to 1550 C degrees

Halas S.

Geochronometria

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2007

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Vol. 27

1-3

EN

The new version of a double-vacuum crucible for fusion of small samples of refractory minerals has been described recently by Halas (2006). This novel type of high temperature crucible was further improved in the following important points: (1) The expensive material, tantalum, was replaced by much cheaper molybdenum which also appears to be significantly less corrosive in the presence of hot boron nitride ceramic used as the insulator, and (2) a versatile temperature controller was assembled from commercially available components.