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- Broska, Igor, et al.
(author)
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Alpine stacking of two Variscan granite blocks recognised from mineral stabilities, age and structural data (Western Carpathians)
- 2024
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In: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 648
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Journal article (peer-reviewed)abstract
- This study presents petrological, geochemical, geochronological and structural data that serve to identify two different Alpine tectonic units formed from the Variscan-aged Tribeč-Zobor granitic rocks. The proposed model for juxtaposition of two granite blocks in the Tribeč-Zobor basement during the Alpine orogeny is based on the degree of granite alteration, particularly related to differences in monazite stabilities of the S-type granitic rocks along the studied NW- SE profile through the Tribeč-Zobor mountain range. Along the cross-section, the Variscan crystalline basement in the mountain crest is composed of hydrothermally altered and metamorphosed S-type monzogranite (zircon age: 355.2 ± 1.2 Ma). Below this monzogranite there are hypidiomorphic non-altered granitic rocks with ages spanning from 357.8 ± 0.66 Ma to 351.2 ± 0.7 Ma for northeast S-type and 358.2 ± 0.85 Ma to 347.9 ± 0.94 Ma for I-type on southwest part of profile. U-Th-Pb dating revealed both low- and high-Y types of monazite in the S-type granites. Low-Y monazite from both the structurally lower unaltered, and the structurally upper, metamorphosed S-type granitic rocks provides Tournaisian Variscan ages in the range of 354–349 Ma. The high-Y monazite from the same rocks records Visean ages in the range of 348–335 Ma, likely indicating later-staged thermal rock overprinting. Monazites from non-altered S-type granodiorites are stable due to rapid emplacement in the upper crustal position. In contrast, the monazites in the overlying metamorphosed S-type granites are retrogressed to allanite as a result of slower, nearly isobaric cooling of the granites emplaced at deeper crustal levels. Thus, monazite behaviour indicate two different Variscan granite blocks, similar in age but with different emplacement depths. The conditions for metamorphism (450–500 °C, 750–800 MPa) of the structurally upper granites are inferred from phase equilibrium thermodynamic modelling, occurring during the Alpine orogeny. These metamorphic conditions are similar to those calculated for granites of the Western Carpathians that were pervasively reworked during Alpine orogenesis, indicating that structurally upper granites have an affinity to the Alpine Fatric Unit, whereas the lower granite is rather related to the Tatric Unit. An Alpine date of c. 78 Ma yielded by single grain fusion 40Ar/39Ar geochronology of muscovite is interpreted to post-date Alpine thrusting. The present position of the metamorphosed Variscan Fatric granitic rock in the Tribeč-Zobor crystalline basement, overlying both S- and I- non-altered Tatric granites, resulted from large-scale, north-directed Alpine thrusting. The geometry of the thrust, elucidated by tectonic elements from mylonites and hydrothermally altered Triassic quartzites deposited on Fatric granites, is inclined 20–40° to the northwest.
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| 2. |
- Broska, Igor, et al.
(author)
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Devonian/Mississippian I-type granitoids in the Western Carpathians : A subduction-related hybrid magmatism
- 2013
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In: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 162, s. 27-36
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Journal article (peer-reviewed)abstract
- SIMS zircon U-Pb dating of I-type granitoids from four Variscan crystalline basement outcrops in the Western Carpathians (Tribec, Nizke Tatry, Cierna Hora and Slovenske Rudohorie Mts.) implies that they originated between 367 and 353 Ma. Therefore, they belong to the earliest Variscan I-type granitoids. The oldest Devonian age at ca. 367-364 Ma is obtained from an enclave-bearing tonalite and associated dikes of the Tribe Mts. Several granodiorites from the Nizke Tatry, Vepor and Cierna Hora Mts. (353-357 Ma) show younger, Early Carboniferous ages. These data require a re-assessment of older models that explained the genesis of I-type granitoids in the Western Carpathians based on the assumption of younger, Middle to Upper Carboniferous ages. The I-type granite massifs of the Western Carpathians most probably originated in an arc-related environment within the Galatian superterrane, an assemblage of Gondwana derived fragments. The early age of I-type magmatism in the Western Carpathians marks the beginning of a north-dipping subduction of the Paleotethys ocean under Ibero-Ligerian and intra-Alpine terranes. We suggest a term "Proto-Tatricum" for that part of the Galatian superterrane where Devonian/Mississippian I-type granitoids were emplaced. Now the granitoids are incorporated as a part of crystalline basement into the Alpine Tatric and Veporic units within present West-Carpathian mountain chain.
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| 3. |
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| 4. |
- Maraszewska, Maria, et al.
(author)
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Multi-stage metamorphic and metasomatic imprints on apatite-monazite-xenotime assemblages in a set of small iron oxide-apatite (IOA) ore bodies, Prins Karls Forland, Svalbard
- 2023
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In: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 155
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Journal article (peer-reviewed)abstract
- On Prins Karls Forland, Svalbard Archipelago, a set of small iron oxide-apatite (IOA) ore bodies have been discovered within a crustal shear zone, which deformed the polymetamorphosed Neoproterozoic metasedimentary rocks. The ores have various styles and grades of deformation and distinct mineral assemblages whose compositions record a multi-stage tectonothermal and metasomatic history. These IOA ore bodies can be subdivided into fluorapatite-bearing and predominant low-Th monazite in the upper section of the shear zone and FCl apatite-bearing and predominant high Th-monazite in the structurally lower higher-grade deformed part. The first stage of alteration for these ore bodies resulted in metasomatic alteration of the apatite and liberation of REE and P redeposited as monazite and xenotime. The transport of dissolved REE and P was likely enhanced by deformation. The second stage of alteration had a distinct impact on the individual ore bodies, which resulted in the Th-enrichment of a small subset of the monazite grains in the upper section of the shear zone. In the lower section of the shear zone most of the monazite was replaced by high Th monazite. Here the original fluorapatite is enriched in Cl, Mn, and Sr, most probably due to interaction with CaCl2-rich fluids enriched in Sr and Mn that was scavenged from the hosting metasediments and altered metagabbros. Contrasting textures, mineral assemblages, and the geochemistry of the ores from distinct localities reflect involvement of compositionally different fluids from the gabbroic rocks and surrounding metasedimentary rocks during the protracted tectonothermal evolution of Prins Karls Forland. Therefore, it is concluded that the IOA ore bodies most likely resulted due to the fractionation of Fe, P, Ca, and REE from hypersaline fluids associated with the gabbros. Once deposited, these IOA ore bodies were subsequently altered during at least one and perhaps two later metamorphic events.
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