Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordovician magmatic events in the Variscan foldbelt

Tichomirowa, Marion; Berger, Hans-Jürgen; Koch, E.A.; Belyatski, Boris; Götze, Jens; Kempe, Ulf; Nasdala, Lutz; Schaltegger, Urs

doi:10.1016/s0024-4937(00)00066-9

Cited by 94 publications

(64 citation statements)

References 27 publications

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“…475 Ma for both granofels and granulite (Zulauf et al, 2002;Konopásek et al, 2014), suggesting that they are derived from granitoid protolith of the same age. These ages are similar to other orthogneisses throughout the Saxothuringian domain (e.g., Tichomirowa et al, 2001;Košler et al, 2004). The high-P metamorphism was dated as 342 ± 1 Ma for the banded orthogneiss (U-Pb monazite ages; Zulauf et al, 2002) and as 339 ± 1.5 Ma and 342 ± 10 Ma for the granulites (U-Pb zircon ages; Kotková et al, 1996;Konopásek et al, 2014).…”

Section: Geological Settingsupporting

confidence: 79%

Role of strain localization and melt flow on exhumation of deeply subducted continental crust

et al. 2018

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A section of anatectic felsic rocks from a high-pressure (>13 kbar) continental crust (Variscan Bohemian Massif) preserves unique evidence for coupled melt flow and heterogeneous deformation during continental subduction. The section reveals layers of migmatitic granofels interlayered with anatectic banded orthogneiss and other rock types within a single deformation fabric related to the prograde metamorphism. Granofels layers represent high strain zones and have traces of localized porous melt flow that infiltrated the host banded orthogneiss and crystallized granitic melt in the grain interstices. This process is inferred from: (1) gradational contacts between orthogneiss and granofels layers; (2) grain size decrease and crystallographic preferred orientation of major phases, compatible with oriented growth of crystals from interstitial melt during granular flow, accommodated by melt-assisted grain boundary diffusion creep mechanisms; and (3) pressuretemperature equilibria modeling showing that the melts were not generated in situ. We further argue that this porous melt flow, focused along the deformation layering, significantly decreases the strength of the crustal section of the subducting continental lithosphere. As a result, detachment folds develop that decouple the shallower parts of the layered anatectic sequence from the underlying and continuously subducting continental plate, which triggers exhumation of this anatectic sequence.

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Section: Geological Settingsupporting

confidence: 79%

Role of strain localization and melt flow on exhumation of deeply subducted continental crust

et al. 2018

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“…Zircons in these HP gneisses were previously dated with ages of 340.5Ô1.1 (2s), 341.3Ô1.1, and 341.6Ô1.1 Ma (Kröner and Willner, 1998: Pb-Pb evaporation). Tichomirowa et al (2005) also reported zircons from GEU gneisses with U-Pb ages of~340 Ma. However, analyses of zircon cores from orthogneisses of the GEU resulted in protolith ages of 470À500 Ma.…”

Section: Introductionmentioning

confidence: 89%

Dating of zircon and monazite from diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge – hints at burial and exhumation velocities

et al. 2007

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ABSTR ACTIn order to better understand the formation and evolution processes of ultrahigh pressure (UHP) felsic rocks, we determined the ages of various domains of zircon and monazite crystals from the diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge. According to cathodoluminescence imagery and Th/U ratios, three zircon zones were distinguished. Each zone was dated using several spot analyses from a sensitive high-resolution ion microprobe (SHRIMP) analysing Pb, U and Th isotopes. The results were: (1) By combining the defined ages with previously published P-T conditions, minimum velocities for burial and exhumation were estimated. In addition, we present a likely geodynamic scenario involving age data from the literature as well as this study: starting 340 million years ago, gneisses at the base of a thickened continental crust (~1.8 GPa, 650ºC) were transported to depths of at least 130 km, possibly as deep as 250 km. They were heated (>1050ºC), partially melted and as a result began to rise quickly. The burial and following ascent back to a depth of 50 km, where zircon rims and monazite formed, took only a few million years and perhaps significantly less.

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“…The Neoproterozoic protolith ages of 540-580 Ma are typical of granitoids and orthogneisses of the Brunovistulian (van Breemen et al 1982;Scharbert and Batík 1985;Fritz et al 1996;Friedl et al 2000Friedl et al , 2004; see Leichmann and Höck 2008 for review) as well as Saxothuringian and Lugian domains (Hegner and Kröner 2000;Tichomirowa et al 2001;Linnemann et al 2008 and references therein) and they only rarely appear as protolith ages of Moldanubian orthogneisses (Schulmann et al 2005). Importantly, Cambrian ages of 500-520 Ma are absent in the Moravo-Silesian Domain (Brunia), but they are known as the most frequent protolith ages of the Moldanubian orthogneisses, as well as of some ortho gneisses in the Saxothuringian and Lugian domains (Vrána and Kröner 1995;Hegner and Kröner 2000;Tichomirowa et al 2001;Friedl et al 2004;Schulmann et al 2005). Zircons of this age found in the studied samples can be interpreted either as clastic grains coming directly from eroded Cambrian granitoids or volcanics, or they represent recycled crystals from sediments rich in clastic material of Cambrian age.…”

Section: Geochronological Datamentioning

confidence: 99%

“…Zircons of this age found in the studied samples can be interpreted either as clastic grains coming directly from eroded Cambrian granitoids or volcanics, or they represent recycled crystals from sediments rich in clastic material of Cambrian age. Ages older than 650 Ma are known from xenocrystic cores of younger zircons in Brunovistulian, Saxothuringian and Lugian orthogneisses as well as from orthogneisses and granulites of the Moldanubian Domain (Hegner and Kröner 2000;Kröner et al 2000;Tichomirowa et al 2001;Friedl et al 2004 and references therein).…”

Section: Geochronological Datamentioning

confidence: 99%

Metamorphic history of skarns, origin of their protolith and implications for genetic interpretation; an example from three units of the Bohemian Massif

Pertoldová¹,

Týcová²,

Verner³

et al. 2012

Jour. Geosci.

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Skarns in the Svratka Unit, in the neighbouring part of the Moldanubian Zone and in the Kutná Hora Complex were studied with respect to their metamorphic evolution, major-and trace-element geochemistry, oxygen isotopic composition and zircon ages. Skarns form competent lenses and layers in metamorphosed siliciclastic rocks and preserve some early deformation structures and several equilibrium assemblages representing the products of successive metamorphic reactions. The main rock-forming minerals, garnet and clinopyroxene, are accompanied by less abundant magnetite, amphibole, plagioclase, epidote ± quartz. In the Svratka Unit the early prograde M 1 , prograde/peak M 2 , and retrograde M 3 metamorphic stages have been distinguished. Metamorphic conditions in skarns of the Moldanubian Zone are limited to a relatively narrow interval of amphibolite facies. The prograde and retrograde events in the Kutná Hora Complex skarns probably took place under amphibolite-facies conditions. The presence of magnetite and the increasing proportion of the andradite component in the garnet indicate locally increased oxygen fugacity. Skarn geochemistry does not show systematic differences in the skarn composition among the three units. The regional variations are exceeded by differences among samples from individual localities. The Al 2 O 3 /TiO 2 , Al 2 O 3 /Zr, TiO 2 /Nb ratios point to the variable proportion of the detrital material, combined in skarn protoliths with CaO and FeO, the major non-detrital components. The skarns exhibit elevated abundances of Cu, Zn, Sn and As. The Eu/Eu* ratio varies in the range of 0.5-8.6, the total REE contents vary from 8 to 345 ppm. The lowest ΣREE values (< 100 ppm) occur in skarns with magnetite mineralization. The wide intervals of ΣREE and Eu/Eu* values are interpreted to indicate variations in the temperature and redox conditions among layers of the same locality and at various localities. The oxygen isotope compositions of garnets, pyroxenes and amphiboles from skarns of the Svratka Unit exhibit a range of δ 18 O = 0.1 to 4.1 ‰. In situ (laser-ablation ICP-MS) U-Pb dating of zircon from one of the Svratka Unit skarn bodies yielded a wide range of ages (0.5-2.6 Ga), supporting the detrital origin of this zircon population. The skarn protoliths were probably rocks of mixed detrital-exhalative origin deposited on the sea floor. The geological position of skarns, with their structural and metamorphic record, probably reflect tectono-metamorphic evolution shared with that of their host rocks. The geochemical characteristics, including oxygen isotopic compositions and the presence of detrital zircons with a wide range of ages exclude metasomatic, and point to a sedimentary-exhalative mode of origin for the studied skarns.

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Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordovician magmatic events in the Variscan foldbelt

Cited by 94 publications

References 27 publications

Role of strain localization and melt flow on exhumation of deeply subducted continental crust

Role of strain localization and melt flow on exhumation of deeply subducted continental crust

Dating of zircon and monazite from diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge – hints at burial and exhumation velocities

Metamorphic history of skarns, origin of their protolith and implications for genetic interpretation; an example from three units of the Bohemian Massif

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