Eclogite-facies metamorphism at the eastern margin of the Bohemian Massif subduction prior to continental underthrusting?

2002 ◽  
Vol 14 (4) ◽  
pp. 701-713 ◽  
Author(s):  
Jiří Schulmann Konopásek ◽  
Věra Johan
Keyword(s):  
Bohemian Massif ◽  
Eastern Margin ◽  
Facies Metamorphism ◽  
Eclogite Facies

Zircon geochronology and trace element characteristics of eclogites and granulites from the Orlica-Śnieżnik complex, Bohemian Massif

2009 ◽  
Vol 147 (3) ◽  
pp. 339-362 ◽  
Author(s):  
MICHAEL BRÖCKER ◽  
REINER KLEMD ◽  
ELLEN KOOIJMAN ◽  
JASPER BERNDT ◽  
ALEXANDER LARIONOV
Keyword(s):  
Trace Element ◽  
Bohemian Massif ◽  
Trace Element Analysis ◽  
Amphibolite Facies ◽  
Zircon Geochronology ◽  
Metamorphic Zircon ◽  
Element Analysis ◽  
Large Variability ◽  
Facies Metamorphism ◽  
Eclogite Facies

AbstractU–Pb zircon geochronology and trace element analysis was applied to eclogites and (ultra)high-pressure granulites that occur as volumetrically subordinate rock bodies within orthogneisses of the Orlica-Śnieżnik complex, Bohemian Massif. Under favourable circumstances such data may help to unravel protolith ages and yet-undetermined aspects of the metamorphic evolution, for example, the time span over which eclogite-facies conditions were attained. By means of ion-probe and laser ablation techniques, a comprehensive database was compiled for samples collected from prominent eclogite and granulite occurrences. The 206Pb/238U dates for zircons of all samples show a large variability, and no single age can be calculated. The protolith ages remain unresolved due to the lack of coherent age groups at the upper end of the zircon age spectra. The spread in apparent ages is interpreted to be mainly caused by variable and possibly multi-stage Pb-loss. Further complexities are added by metamorphic zircon growth and re-equilibration processes, the unknown relevance of inherited components and possible mixing of different aged domains during analysis. A reliable interpretation of igneous crystallization ages is not yet possible. Previous studies and the new data document the importance of a Carboniferous metamorphic event at c. 340 Ma. The geological significance of this age group is controversial. Such ages have previously either been related to peak (U)HP conditions, the waning stages of eclogite-facies metamorphism or the amphibolite-facies overprint. This study provides new arguments for this discussion because, in both rock types, metamorphic zircon is characterized by very low total REE abundances, flat HREE patterns and the absence of an Eu anomaly. These features strongly suggest contemporaneous crystallization of zircon and garnet and strengthen interpretations proposing that the Carboniferous ages document late-stage eclogite-facies metamorphism, and not amphibolite-facies overprinting.

scholarly journals Absence of evidence for Palaeoproterozoic eclogite-facies metamorphism in East Antarctica: no record of subduction orogenesis during Nuna development

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Dillon A. Brown ◽  
Laura J. Morrissey ◽  
John W. Goodge ◽  
Martin Hand
Keyword(s):  
Plate Boundary ◽  
South Australia ◽  
East Antarctica ◽  
Geological Evidence ◽  
Crustal Shortening ◽  
Eastern Margin ◽  
Facies Metamorphism ◽  
Eclogite Facies ◽  
Early Palaeozoic ◽  
Collisional Orogenesis

AbstractThe cratonic elements of proto-Australia, East Antarctica, and Laurentia constitute the nucleus of the Palaeo-Mesoproterozoic supercontinent Nuna, with the eastern margin of the Mawson Continent (South Australia and East Antarctica) positioned adjacent to the western margin of Laurentia. Such reconstructions of Nuna fundamentally rely on palaeomagnetic and geological evidence. In the geological record, eclogite-facies rocks are irrefutable indicators of subduction and collisional orogenesis, yet occurrences of eclogites in the ancient Earth (> 1.5 Ga) are rare. Models for Palaeoproterozoic amalgamation between Australia, East Antarctica, and Laurentia are based in part on an interpretation that eclogite-facies metamorphism and, therefore, collisional orogenesis, occurred in the Nimrod Complex of the central Transantarctic Mountains at c. 1.7 Ga. However, new zircon petrochronological data from relict eclogite preserved in the Nimrod Complex indicate that high-pressure metamorphism did not occur in the Palaeoproterozoic, but instead occurred during early Palaeozoic Ross orogenesis along the active convergent margin of East Gondwana. Relict c. 1.7 Ga zircons from the eclogites have trace-element characteristics reflecting the original igneous precursor, thereby casting doubt on evidence for a Palaeoproterozoic convergent plate boundary along the current eastern margin of the Mawson Continent. Therefore, rather than a Palaeoproterozoic (c. 1.7 Ga) history involving subduction-related continental collision, a pattern of crustal shortening, magmatism, and high thermal gradient metamorphism connected cratons in Australia, East Antarctica, and western Laurentia at that time, leading eventually to amalgamation of Nuna at c. 1.6 Ga.

AGE OF ECLOGITE-FACIES METAMORPHISM AND EXHUMATION IN NORTHWESTERN BHUTAN

2016 ◽  
Author(s):  
David J. Young ◽  
◽  
Daniele Regis ◽  
Clare Warren ◽  
Andrew R.C. Kylander-Clark
Keyword(s):  
Facies Metamorphism ◽  
Eclogite Facies

scholarly journals Zircon U–Pb Dating and Lu-Hf Isotope of the Retrograded Eclogite from Chicheng, Northern Hebei Province, China

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xu Kong ◽  
Xueyuan Qi ◽  
Wentian Mi ◽  
Xiaoxin Dong
Keyword(s):  
Regional Metamorphism ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Metamorphic Event ◽  
Isotopic Data ◽  
Metamorphic Condition ◽  
Eu Anomaly ◽  
Facies Metamorphism ◽  
Eclogite Facies ◽  
Plagioclase Gneiss

We report zircon U–Pb ages and Lu-Hf isotopic data from two sample of the retrograded eclogite in the Chicheng area. Two groups of the metamorphic zircons from the Chicheng retrograded eclogite were identified: group one shows characteristics of depletion in LREE and flat in HREE curves and exhibit no significant Eu anomaly, and this may imply that they may form under eclogite facies metamorphic condition; group two is rich in HREE and shows slight negative Eu anomaly indicated that they may form under amphibolite facies metamorphic condition. Zircon Lu-Hf isotopic of εHf from the Chicheng eclogite has larger span range from 6.0 to 18.0, which suggests that the magma of the eclogite protolith may be mixed with partial crustal components. The peak eclogite facies metamorphism of Chicheng eclogite may occur at 348.5–344.2 Ma and its retrograde metamorphism of amphibolite fancies may occur at ca. 325.0 Ma. The Hongqiyingzi Complex may experience multistage metamorphic events mainly including Late Archean (2494–2448 Ma), Late Paleoproterozoic (1900–1734 Ma, peak age = 1824.6 Ma), and Phanerozoic (495–234 Ma, peak age = 323.7 Ma). Thus, the metamorphic event (348.5–325 Ma) of the Chicheng eclogite is in accordance with the Phanerozoic metamorphic event of the Hongqiyingzi Complex. The eclogite facies metamorphic age of the eclogite is in accordance with the metamorphism (granulite facies or amphibolite facies) of its surrounding rocks, which implied that the tectonic subduction and exhumation of the retrograded eclogite may cause the regional metamorphism of garnet biotite plagioclase gneiss.

Structural relations at the eastern margin of the Shuswap Complex, near Revelstoke, southeastern British Columbia

1968 ◽  
Vol 5 (4) ◽  
pp. 831-849 ◽  
Author(s):  
John V. Ross
Keyword(s):  
British Columbia ◽  
Granite Gneiss ◽  
Early Paleozoic ◽  
Final Phase ◽  
Late Proterozoic ◽  
Eastern Margin ◽  
Deformational History ◽  
Facies Metamorphism ◽  
Absolute Age ◽  
Paleozoic Rocks

Three major phases of folding affected rocks of Late Proterozoic and Early Paleozoic age and members long assigned to the Shuswap Complex of southeastern British Columbia. The main and first phase of folding produced a large recumbent anticline, having a northerly trend, overturned to the east, that contains an exotic wedge of granite-gneiss within its core. This gneiss was mechanically emplaced into the Late Proterozoic and Early Paleozoic sediments, and already had a metamorphic and deformational history prior to its emplacement. Its age is possible Hudsonian equivalent. Metamorphism during this recumbent phase of folding was greenschist facies.Phase 2 folding was accompanied by amphibolite facies metamorphism, and caused refolding of the earlier composite recumbent anticline into open folds along southeasterly axes.A third and final phase of folding, associated with waning metamorphism, gave rise to folds along southeasterly striking axial-planes that dip steeply to the northeast. Thus, phase three folds caused tightening-up of the previously formed folds.The absolute age of these deformations is not yet known, but the Shuswap Complex, at its eastern margin, is shown to include Paleozoic rocks and some older gneisses, possibly of Hudsonian age.

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