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The polymetamorphic evolution path of metapelites characteristic of the Algyo-Ferencszállás Metamorphic Complex of the Békés-Codru Unit (SE Hungary) is presented on the basis of microstructural and mineral paragenetic features, mineral chemical data and geothermobarometric calculations. The first (Variscan?) metamorphic event recorded by the Ca-rich part of zoned garnets from the Ferencszállás area is poorly defined, yielding conditions of 520-560 oC and 820-1010 MPa. This event was followed by a new tectonometamorphic phase that began with the formation of garnet, kyanite, muscovite, plagioclase and biotite. This younger (Alpine) event is marked by the decomposition of staurolite and biotite, and an increase in temperature and pressure. Peak metamorphic conditions reached c. 650 oC and 900 MPa in the Ferencszállás and Újszentiván areas. This P-T peak was followed by continuous decrease in temperature and pressure to c. 500-560 oC and 400-530 MPa. The P-T path calculations from the progressively zoned garnets of the Algyo area show an increase in temperature and pressure similar to the Ferencszállás area – but in shallower crustal depth – and yield 650-680 oC and 500-600 MPa for the metamorphic peak. This study, in combination with recently published geochronological data, presents the first record of Alpine amphibolite facies metamorphic overprint of the basement of the Tisza Unit, which was considered as not affected by medium-grade metamorphism younger than Variscan until now.

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Abstract

A detailed petrographic and mineral-chemical study on metapelites from the Meliatic accretionary wedge complex (Bôrka Nappe, Western Carpathians, Slovak Republic) reveals the HP character of the samples using quantitative phase diagrams contoured with mineral composition, H2O mode isopleths and garnet-phengite thermometry. The presented PT pseudosections prove that small-scale differences in bulk rock composition are responsible for the variations in the mineral assemblages formed at the same PT conditions. The peak conditions indicate blueschist facies metamorphism (520–620 °C, 11–14 kbar) and are correlated with the 150–165 Ma subduction of the Mesozoic Meliata Oceanic branch of the Neotethys. Continuous decrease of P and T from peak conditions enabled the metapelitic rocks to preserve their HP assemblages. The presented HP conditions and retrograde PT path with decreasing P and T are characteristic of subduction zone tectonic settings which are in agreement with most of the geodynamic and tectonic reconstructions for the area.

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The heavy mineral assemblages and chemistry of detrital spinel grains from the Senonian basin of the Transdanubian Range (TR) were examined and compared with previous results from Jurassic and Lower Cretaceous successions of the Gerecse Mountains of the Transdanubian Range Unit. The heavy minerals recorded that in the area of Transdanubian Range the sedimentary cover, low-grade metamorphic and granitic rocks of the continental crust were eroded in the Coniacian and Santonian. Detritus of high-grade metamorphics was transported to the bathyal basin during Campanian time. The ophiolitic source area indicated by the presence of chrome spinel, ilmenite and magnetite still existed and persisted through the Late Cretaceous.  Compared to the low TiO2 content (lower than 0.2 wt%) of detrital spinels from Jurassic and Lower Cretaceous sediments of the Gerecse Mountains, the most characteristic features of spinels in the Senonian sediments are as follows: exceptionally high TiO2 content (about 0.5-4.7 wt%), relatively high amount of Cr2O3 (about 33-50.8 wt%) and high total iron (sumFeO=15-36 wt%). The data on detrital spinels from the Ajka Coal and Csehbánya Formations suggests that xenoliths (mainly dunites), which previously enclosed the spinel grains, may have been formed from alkalic-tholeiitic magma as crystal accumulates. This was the potential source rock of high TiO2-bearing spinel grains.

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New mineral paragenetic, illite Kübler index, chlorite “crystallinity”, apparent crystallite thickness, lattice strain, and K-white mica geobarometric data proved that the Eoalpine (Paleozoic-Mesozoic) metamorphic complex was affected by medium-pressure, high-temperature anchizonal regional metamorphism, whereas the Jurassic ophiolitic mélange and the Late Cretaceous-Paleocene sedimentary sequence of Mt. Medvednica were diagenetically altered. Mineral chemical investigations carried out on phyllosilicate flakes found in various microstructural positions revealed complete mineral chemical homogenization of chlorite and K-white mica of selected slate samples from the Eoalpine (Paleozoic-Mesozoic) metamorphic complex. One possible explanation of this feature is an Alpine (Cretaceous) regional metamorphic event with polyphase deformational history. Variscan low-temperature metamorphism overprinted by an Alpine (Cretaceous) event, with temperatures at least as high as those of the Variscan one, may be an alternative, although more complicated explanation. However, no isotope geochronological evidence supports this assumption. At present only one metamorphic event can be detected. Its physical conditions were ca. 350-400 °C on the basis of illite Kübler index and chlorite Al(IV) empirical thermometers and 3-4 kbar using K-white mica b cell dimension measurements.

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Abstract

Metamorphic mineral assemblages in low-temperature metaclastic rocks often contain paragonite and/or its precursor metastable phase (mixed K-Na-white mica). Relationships between the bulk rock major element chemistries and the formation of paragonite at seven localities from Central and SE-Europe were studied, comparing the bulk chemical characteristics with mineral assemblage, mineral chemical and metamorphic petrological data. Considerable overlaps between the projection fields of bulk chemistries of the Pg-free and Pg-bearing metaclastic rocks indicate significant differences between the actual (as analyzed) and effective bulk chemical compositions. Where inherited, clastic, inert phases/constituents were excluded, it was found that a decrease in Na/(Na+Al*) and in K/(K+Al*) ratios of rocks favors the formation and occurrence of Pg and its precursor phases (Al* denotes here the atomic quantity of aluminum in feldspars, white micas and “pure” hydrous or anhydrous aluminosilicates). In contrast to earlier suggestions, enrichment in Na and/or an increase in Na/K ratio by themselves do not lead to formation of paragonite. Bulk rock chemistries favorable to formation of paragonite and its precursor phases are characterized by enrichment in Al and depletion in Na, K, Ca (and also, Mg and Fe2+). Such bulk rock chemistries are characteristic of chemically “mature” (strongly weathered) source rocks of the pelites and may also be formed by synand post-sedimentary magmatism-related hydrothermal (leaching) activity. What part of the whole rock is active in determining the effective bulk chemistry was investigated by textural examination of diagenetic and anchizone-grade samples. It is hypothesized that although solid phases act as local sources and sinks, transport of elements such as Na through the grain boundaries have much larger communication distances. Sodium-rich white micas nucleate heterogeneously using existing phyllosilicates as templates and are distributed widely on the thin section scale. The results of modeling by THERMOCALC suggest that paragonite preferably forms at higher pressures in low-T metapelites. The stability fields of Pg-bearing assemblages increase, the Pg-in reaction line is shifted towards lower pressures, while the stability field of the Chl-Ms-Ab-Qtz assemblage decreases and is shifted towards higher temperatures with increasing Al* content and decreasing Na/(Na+Al*) and K/(K+Al*) ratios.

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Néhány potenciálisan mérgező fém frakcióinak meghatározására alkalmazott analitikai módszer értékelése eltérő fizikai talajféleségű mintákon

Evaluation of analytical methods for the determination of different potentially toxic metal fractions in soils with different physical properties

Agrokémia és Talajtan
Authors:
Katalin Kovács
,
Márk Horváth
,
Gábor Halász
,
Anita Takács
,
György Heltai
,
Norbert Boros
,
Péter Sipos
, and
Zoltán Győri

Munkánk során potenciálisan toxikus fémek frakcióinak meghatározására alkalmazott analitikai módszereket kívántunk értékelni, azok talajféleségtől való függése alapján.

A talajféleségtől való függés mértéke döntően megszabja a módszer használhatóságát. Jelen dolgozat célja, hogy a Cu, a Zn, a Fe és a Ni környezeti mobilitása szempontjából értékelje a vizsgálatba vont egy- és többlépéses kioldásos módszereket.

Vizsgálatainkhoz a TIM adatbázisból származó négy, eltérő fizikai talajféleségű mintát választottunk (homok-, homokos vályog-, vályog- és agyag-talaj sorrendjében növekvő agyag- és humusztartalommal és pH-val).

Öt különböző kivonószerrel végzett egylépéses extrakciót és kétféle szekvens, azaz 3+1 lépéses egymás utáni extrakciós vizsgálatot végeztünk (BCR és McGrath módszerekkel).

Elvégeztük a minták Magyar Szabvány (MSZ 21470-50) szerinti, mikrohullámú kezeléssel egybekötött, H2O2+HNO3 eleggyel való roncsolását is. Az így megállapított elemtartalom környezetvédelmi szempontból teljes („összes”) elemtartalomnak tekinthető.

A mérési eredmények alapján megkíséreltük kiválasztani a vizsgálatba vont módszerek közül azokat, amelyek a talajból már biztonsággal meghatározható mennyiségű elemet vonnak ki, de a kivont mennyiség még nem a teljes elemtartalommal arányos.

A mikrohullámú feltárással kapott Zn-, Cu-, Fe- és Ni-tartalmak, a homok-, homokos vályog-, vályog- és agyag-talaj sorrendben, vagyis az agyag- és humusztartalmukkal, valamint pH-jukkal párhuzamosan nő. Egy olyan összetett rendszerben, mint a talaj, az egyes talajtulajdonságok, így az agyag- és humusztartalom, valamint a pH hatása vizsgálataink alapján nem különíthető el, de mint várható volt, a nagyobb agyag- és humusztartalmú és magasabb pH-jú talajok ezekből az elemekből többet halmoztak fel.

Mivel a kelátképzőket tartalmazó kivonószerek az összes réztartalomnak mintegy harmadát kivonták, a kivont mennyiség a réztartalommal volt arányos, vagyis a réztartalom növekedésével párhuzamosan nőtt.

Ezek a kivonószerek tehát Cu esetében kevésbé alkalmasak az egyes talajféleségek toxicitása közti különbségek kimutatására.

A rézzel ellentétben, a másik három elemnél az egyes talajféleségeknél kivont kis elemmennyiségek esetenként nagyságrendileg is különböztek, így az elméleti meggondolásunknak megfelelően feltételezhető, hogy az egyes talajféleségek toxicitása közti különbséget mutatják.

A két szekvens módszernél a vasnál kapott mérési eredményeket azok szórása miatt nem lehetett értékelni.

Megállapítható, hogy a BCR agresszívebb kivonószereket használ, mint a McGrath módszer, ennek megfelelően a BCR módszerrel a talajok átlagában az elemek 36, a McGrath módszerrel pedig csak 9%-át vontuk ki.

A BCR módszernél nincs vízszerű gyenge kivonószer, amiből a különböző talajok összes elemtartalmából felszabaduló ionok mennyiségére lehetne következtetni. Az ecetsav, a leggyengébb kivonószer, de a kicserélhető elemtartalom mellett kivonja a karbonátokhoz kötött, vagyis biztosan nem szabad ionos elemtartalmat is.

Mivel a BCR módszer minden kivonószerével sok elemet vonunk ki, nincs érdemi különbség az elemek egyes talajoknál mért kivonási százaléka között, ami figyelembe véve, hogy a talajok elemtartalma a homoktól az agyagtalajig nő, azt jelenti, hogy a kivont mennyiség az összes elemtartalommal arányos.

Lényegében ugyanezt mondhatjuk a McGrath módszer két agresszívebb kivonószeréről is, annak ellenére, hogy lényegesen kevesebb elemet vonnak ki. Ezzel szemben a módszer leírása szerint, a 0,1 mólos kalcium-kloridos kivonatból a vízoldható és kicserélhető elemtartalomra lehet következtetni, így minden bizonnyal a talajok toxicitását mutatja.

In this study, we aimed to evaluate some analytical methods used to determine the fractions of potentially toxic metals, based on their dependence on soil type.

The degree of dependence on soil type determines the applicability of the method. The aim of the present paper is to evaluate the single- and multi-step extraction methods included in the study in terms of the environmental mobility of Cu, Zn, Fe and Ni.

For the studies, we selected four samples with different physical soil types from the Soil Information and Monitoring System database.

In order to establish trends, soil samples were selected so that their clay and humus content, i.e., their adsorption capacity as well as their pH increased in the order of sand, sandy loam, loam and clay soils.

One-step extractions with five different extractants and two sequential extraction analyses including 3+1 steps were performed (BCR and McGrath methods).

We also performed the digestion of the samples with H2O2 + HNO3 solvent combined with microwave treatment according to the Hungarian Standard (MSZ 21470-50). The element content determined in this way can be considered as the "total" element content from the environmental point of view.

Based on the results of the analyses, we tried to select from the methods included in the study those that already extract a safe amount of elements from the soil, but the extracted amount is not yet proportional to the total element content.

The Zn, Cu, Fe and Ni contents resulting from microwave digestion increased in the order of sand, sandy loam, loam and clay soils, i.e. in parallel with the clay and humus content and pH of the soils.

As the extractants containing chelating agents extracted about one-third of the total copper content, the amount extracted was proportional to the copper content, i.e. it increased in parallel with the increase in copper content. Thus, in the case of copper, these extractants are less suitable for detecting differences in the toxicity of different soil types.

In contrast to copper, in the case of the other three elements, the small amounts extracted from each soil type also differed in order of magnitude, so according to our theoretical consideration, it can be assumed that they show a difference between the toxicity of each soil type.

The results obtained with iron using the two sequential methods could not be evaluated due to their standard deviation.

It can be stated that BCR uses more aggressive extractants than the McGrath method, accordingly, the BCR method extracted 36%, whereas the McGrath method only 9% of the elements on average of the soils.

The BCR method does not have an aqueous weak extractant, which would indicate the amount of ions released from the total element content of the different soils. Acetic acid is the weakest extractant, but in addition to the exchangeable element content, it also extracts the ionic element content bound to carbonates, which is certainly not free.

Because a large amount of elements is extracted with each extractant in the BCR method, there is no significant difference in the percentage of elements extracted for each soil, which, given that soil element content increases from sand to clay soil, means that the extracted amount is proportional to total element content.

Basically, the same can be said for the two more aggressive extractants of the McGrath method, despite the fact that they extract significantly less amount of elements. In contrast, as described in the method, the water-soluble and exchangeable element content can be inferred from the 0.1 M calcium chloride extract, thus it certainly indicates soil toxicity.

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