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Native silver in the eastern part of the Karkonosze granitoid pluton, Lower Silesia, Poland

Kozłowski Andrzej, Matyszczak Witold

Acta Geologica Polonica

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2023

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Vol. 73, no. 2

223--245

EN

This article describes silver specimens of the size of tenths to a few millimetres, found in small pegmatites and quartz veinlets of the porphyritic granitoid area in 22 sites in the eastern part of the Variscan granitoid Karkonosze pluton, from 20 of which native silver occurrences were previously not known. The sites are scattered on the whole surface of the granitoid. The native silver occurred in wire, rod, platy, dendritic, anhedral granular and euhedral cubic and octahedral habits; in some specimens twins and fenster faces were also found. Associated with native silver small amounts of acanthite crystallized commonly, sometimes apparently formed by sulphur diffusion into silver. Inclusions of native gold, electrum, galena, chalcopyrite and pyrite occurred in the native silver. The parent fluids of the specimens were epithermal, because the homogenization temperature (Th) of inclusions in quartz, calcite and cleavelandite that were the host minerals of the native silver was generally 91–165ºC and for individual samples the Th range was 4–11ºC. The total salinity of the fluid was 2.4–7.2 wt. % with Na and Ca (hydro)carbonates as the main dissolved components and admixtures of K, Mg, Fe, Al, S, Cl and F. The parent granitoid contains Ag in trace amounts (0.034–0.056 ppm) and was probably the source of this element for the crystals of native silver. Migration of Ag was made easier by the presence of fluoride ions in fluids.

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W poszukiwaniu fragmentów najstarszej skorupy kontynentalnej na Labradorze

Kusiak M. A., Sałacińska A.

Przegląd Geologiczny

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2016

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Vol. 64, nr 11

896--901

EN

There are few unresolved questions in the Earth Sciences which generate as much debate as the nature of the Hadean Earth: i.e. the rock record between the Earth’s formation and about 3.8 billion years ago. Current knowledge of the nature and origin of the earliest crust comes largely from studies of the mineral zircon (ZrSiO4). The oldest zircon grains on Earth (4.46 Ga) are found in Jack Hills, Australia. They represent a time capsule of what the Earth was like from ca. 4.4-4.0 Ga during the Hadean. The other ancien rocks (>3.8 Ga) are preserved in Antarctica, Canada, China, Greenland, Labrador, Western Australia and Swaziland, with the oldest known rochi on Earth from the Acasta gneiss in Northern Canada, dated at 4.03 Ga. Most likely, the second oldest rock record in the world (>3.9 Ga) may be derivedfrom the Nanok gneiss in the Nain Complex of the Saglek-Hebron area in the northern part of the Labrador Peninsula. Extensive investigation of these rocks will allowfurther characterizing the nature of the earliest preserved crust.

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Geochronology of plutonic rocks from the Sanandaj-Sirjan zone, Iran and new zircon and titanite U-Th-Pb ages for granitoids from the Marivan pluton

Sepahi A. A., Shahbazi H., Siebel W., Ranin A.

Geochronometria

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2014

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Vol. 41, no. 3

207--215

EN

The Sanandaj-Sirjan zone of Iran is a metamorphic belt consisting of rocks which were metamorphosed under different pressure and temperature conditions and intruded by various plutons ranging in composition from gabbro to granite. The majority of these granitoids formed along the an-cient active continental margin of the Neo-Tethyan ocean at the southeastern edge of the central Ira-nian microplate. Geochronological data published in recent years indicate periodic plutonism lasting from Carboniferous through Mesozoic to late-Paleogene times (from ca. 300 to ca. 35 Ma) with cli-max activity during the mid- and late-Jurassic. The age constraints for plutonic complexes, such as Siah-Kouh, Kolah-Ghazi, Golpayegan (Muteh), Azna, Aligoodarz, Astaneh, Borujerd, Malayer (Samen), Alvand, Almogholagh, Ghorveh, Saqqez, Marivan, Naqadeh and Urumieh, clearly indicate the periodic nature of magmatism. Therefore, the Sanandaj-Sirjan zone preserves the record of mag-matic activity of a complete orogenic cycle related to (1) Permocarboniferous(?) rifting of Gondwana and opening of the Neo-Tethyan ocean, (2) subduction of the oceanic crust, (3) continental collision and (4) post-collision/post-orogenic activities. The formation of the Marivan granitoids, northwestern Sanandaj-Sirjan zone, for which we present U-Pb zircon and titanite ages of ca. 38 Ma, can be related to the collisional and post-collisional stages of this orogenic cycle.

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Preliminary palaeomagnetic study of the High Tatra granites, Central Western Carpathians, Poland

Grabowski J., Gawęda A.

Kwartalnik Geologiczny

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1999

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Vol. 43, Nr 3

263-276

EN

Variscan granitoids of the High Tatra Mts. in Poland were the subject of palaeomagnetic, petrographical and rock magnetic investigations. The sampled rocks were granodiorites, rarely tonalites showing weak hydrothermal alterations (chloritisation, epidotisation). 31 hand samples from 7 localities were palaeomagnetically investigated. Stable palaeomagnetic directions of Late Palaeozoic age were isolated in four localities (mean direction: D = 193°, I = 17°, a95 = 12, k = 59, palaeopole: 4°E, 31°S). The stable magnetisation resides in hematite. This mineral occurs in hematite-ilmenite intergrowths that exsolved in high temperatures (670-720°C) and as secondary hematite of hydrothermal origin. Because of heterogeneity of magnetic carriers it is possible that the characteristic magnetisation is shifted in time between localities. Question of tectonic tilt of the High Tatra granite is discussed. The age of characteristic magnetisation based on palaeoinclination estimations apparently fits the isotopic cooling age of the intrusion (330-300 Ma) if tectonic correction is not applied. The palaeopole is situated between the European and African Apparent Polar Wander Paths (APWP) and could be matched with both reference curves. After tectonic correction the palaeopole could be matched only with the African APWP at the point ca. 360 Ma. In this case the magnetisation related to the high temperature hematite would preceed the cooling ages recorded by Ar-Ar method.

PL

Przeprowadzono badania paleomagnetyczne waryscyjskich granitoidów polskiej części Tatr Wysokich. Pobrano 31 próbek ręcznych z nastepujących 7 stanowisk: próg między kotliną Morskiego Oka i kotliną Czarnego Stawu (stanowiska M0l i M02), ściana Świstówki Roztockiej w Dolinie Roztoki (RZ), Wodogrzmoty Mickiewicza (WM), Dolinka za Mnichem (M), rejon Kościelca(K) i próg powyżej Czarnego Stawu w Dolinie Gąsienicowej (HG). Badane skały maja skład granodiorytów i tonalitów, ze śladami przeobrażeń hydrotermalnych (epidotyzacja, chlorytyzacja). We wszystkich stanowiskach stwierdzono obecność lineacji magnetycznej o przebiegu W-E. Granitoidy tatrzańskie wykazują duże zróżnicowanie własności magnetycznych. Stabilne kierunki paleomagnetyczne wieku późnopaleozoicznego wyróżniono w stanowiskach M0I, M02, RZ i WM (kierunek średni: D = 193°, l= 17°, (alfa 95) = 12, k = 59, paleobiegun: 4°E, 31°S). Kierunki te są oparte na hematycie, który występuje jako przerosty w dwufazowych ziarnach hematytowo-ilmenitowych, odmierzanych w wysokich temperaturach (670720°C) oraz jako minerał hydrotermalny. Średnie kierunki z poszczególnych stanowisk różnią się nieco i nie można wykluczyć, że namagnesowanie nie jest jednoczasowe. Wydaje się, że istnieje pewna korelacja między wiekiem namagnesowania a składem mineralnym granitoidu (kierunki starsze występują w granitoidach o składzie tonalitu), problem ten wymaga jednak dalszych badań. Interpretacja wieku namagnesowania zależy od zastosowania korekcji tektonicznej. Wiek charakterystycznego kierunku namagnesowania, określony na podstawie parametru paleoinklinacji, wykazuje lepszą zgodność z wiekiem izotopowym stygnięcia intruzji tatrzańskiej (330-300 mln lat) bez stosowania korekcji tektonicznej. Paleobiegun leży między środkowo/późnokarbońskimi odcinkami krzywych referencyjnych dla płyty europejskiej i afrykańskiej i, po uwzględnieniu niewielkich rotacji wokół osi pionowej, może być dopasowany do obu krzywych na odcinku 340-320 mln lat. Po zastosowaniu korekcji tektonicznej (określonej na podstawie zapadania warstw dolnego triasu autochtonicznej pokrywy trzonu krystalicznego na jego północnej krawędzi) paleobiegun można dopasować jedynie do krzywej afrykańskiej w punkcie 360 mln lat. Interpretacji takiej nie można jednoznacznie odrzucić, gdyż namagnesowanie związane z przerostami hematytowo-ilmenitowymi mogło utrwalić się znacząco wcześniej niż zamknięcie systemu 4°Ar-39Ar, wykazujące wiek stygnięcia intruzji (300-350°C). Jednoznaczna interpretacja wyników badań paleomagnetycznych granitoidu tatrzańskiego nie jest możliwa bez określenia wieku radiometrycznego badanych próbek.

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Granitoids of the Odra Fault Zone: late- to post-orogenic Variscan intrusions in the Saxothuringian Zone, SW Poland

Oberc-Dziedzic T., Żelaźniewicz A., Cwojdziński S.

Geologia Sudetica

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1999

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Vol. 32, nr 1

55-71

EN

There are 5 occurrences of granodioritic to monzogranitic rocks found subsurface along the Odra Fault Zone a Permo-Mesozoic horst defining the northeastern edge of the Bohemian Massif. These are generally unfoliated, I-type granitoids with low A/CNK and initial Sr/Sr ratios making them geochemically and petrographically akin to late- to post-kinematic Variscan granitoids of the West Sudetes, being closest to those of the eastern part of the Fore-Sudetic Block (Strzelin, Niemcza). They represent late/post-orogenic, collisional intrusives of Early-Late Carboniferous age which are widespread throughout the Saxothuringian and Moldanubian zones in the Bohemian Massif. The country rocks to the granitoids are mica schists and paragneisses attaining staurolite-grade. The granitoids lack evidence of ductile or brittle strike-slip movement of Late Carboniferous-Permian age along the Odra Fault Zone, which thus has to be taken as a dip-slip fault zone, rather than a late Variscan dextral strike-slip feature. Brittle to semi-brittle deformation of the Odra granitoids relates to the formation of the horst during Permo-Mesozoic times. A Silurian-Early Devonian magmatic arc of the Mid-German Crystalline Rise, identified further to the west in Germany, probably does not have an easterly prolongation into Poland because there is no evidence for arc-related magmatism of that age in the Sudetes and Fore-Sudetic Block.