A Study of the Potash Felspar Gneisses of Connemara and Felspar Comparison with the Galway Granite

1966 ◽  
Vol 103 (6) ◽  
pp. 522-533 ◽  
Author(s):  
P. J. Leggo
Keyword(s):  
Amphibolite Facies ◽  
Facies Metamorphism ◽  
Potash Felspar

AbstractEighteen potash felspars from the potash felspar gneisses of the Connemara migmatite belt have been partially analysed and the associated plagioclase optically determined. Comparisons have been made with seventeen similar felspar pairs from the Galway Granite. Albite components are expressed graphically in an attempt to illustrate sodium distribution between associated felspar phases. On such a plot it is possible to contrast the “magmatic” felspars of the Galway Granite with those of the migmatitic gneisses; the separation of the two fields being a function of total rock chemistry. Crystallization temperatures have been determined by the two felspar method and the range 460 to 480° C. is thought to represent retrograde amphibolite conditions in the migmatitic gneisses, while petrographic evidence supports 550° C. as the temperature of amphibolite facies metamorphism in these rocks. Triclinicity measurements have also been made on the analysed potash felspars.

DIVING DEEPER INTO THE PICURIS OROGEN: UPPER AMPHIBOLITE FACIES METAMORPHISM AND BRITTLE DEFORMATION ALONG THE PLOMO SHEAR ZONE

2020 ◽  
Author(s):  
Adrian E. Castro ◽  
◽  
Chloe Bonamici ◽  
Christopher G. Daniel ◽  
Danielle Shannon Sulthaus
Keyword(s):  
Shear Zone ◽  
Amphibolite Facies ◽  
Brittle Deformation ◽  
Facies Metamorphism

scholarly journals Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

2003 ◽  
Vol 75 (3) ◽  
pp. 393-403 ◽  
Author(s):  
Léo A. Hartmann ◽  
João O.S. Santos ◽  
Jayme A.D. Leite ◽  
Carla C. Porcher ◽  
Neal J. Mcnaughton
Keyword(s):  
Ultramafic Rock ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Rio De La Plata ◽  
Metamorphic Evolution ◽  
Río De La Plata ◽  
La Plata ◽  
Shrimp Geochronology ◽  
Facies Metamorphism ◽  
Magnesian Basalt

The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizário ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702±21 Ma during a greenschist facies eventM2; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257±12 Ma) and Camboriú Orogeny (~ 1989 Ma) of the Trans-Amazonian Cycle, followed by an orogenic event (702±21 Ma) of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma) corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton.

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.

scholarly journals Mapping in the Fiskefjord area, southern West Greenland

1982 ◽  
Vol 110 ◽  
pp. 55-57
Author(s):  
A.A Garde ◽  
V.R McGregor
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Supracrustal Rock ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Geological Work ◽  
Age Determinations

Previous geological work on the 1:100000 map sheet 64 V.l N (fig. 15) includes published maps of smaller areas by Berthelsen (1960, 1962) and Lauerma (1964), mapping by Kryolitselskabet Øresund A/S (Bridgwater et al., 1976) and mapping by GGU geologists for the 1:500000 map sheet Frederikshåb Isblink - Søndre Strømfjord (Allaart et al., 1977, 1978). The Amltsoq and Niik gneisses and Malene supracrustal rock units south and east of Godthåbsfjord have not so far been correlated with rocks in the Fiskefjord area. Godthåbsfjord separates the granulite facies gneisses in Nordlandet from amphibolite facies Nûk gneisses on Sadelø and Bjørneøen; the granulite facies metamorphism occurred at about 2850 m.y. (Black et al., 1973), while no published isotopic age determinations from the Fiskefjord area itself are available.

Penetrative ductile deformation and amphibolite-facies metamorphism prior to 1851Ma in the western part of the Svecofennian orogen, Fennoscandian Shield

2007 ◽  
Vol 153 (1-2) ◽  
pp. 29-45 ◽  
Author(s):  
Tobias Hermansson ◽  
Michael B. Stephens ◽  
Fernando Corfu ◽  
Jenny Andersson ◽  
Laurence Page
Keyword(s):  
Fennoscandian Shield ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Facies Metamorphism

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.

Archean rocks from the eastern Lac Seul region of the English River Gneiss Belt, northwestern Ontario, part 1. Petrology, chemistry, and metamorphism

1976 ◽  
Vol 13 (9) ◽  
pp. 1201-1211 ◽  
Author(s):  
N. B. W. Harris ◽  
A. M. Goodwin
Keyword(s):  
Complex Structure ◽  
Granulite Facies ◽  
Metamorphic Grade ◽  
Amphibolite Facies ◽  
Northwestern Ontario ◽  
Southern Margin ◽  
Field Evidence ◽  
Facies Metamorphism

The eastern Lac Seul region of the English River Gneiss Belt is divided into two domains defined by contrasting petrology and structure. The northern domain is underlain by east-trending, steeply south-dipping, migmatized metasediments, intruded by occasional granite sills, and the southern domain by gneissic tonalite and trondhjemite, with abundant amphibolite inclusions, intruded by granite dykes and diapirs: this domain has a complex structure with gently east-plunging open folds of about 5 km wavelength. Field evidence suggests that metasediments of the northern domain have been deposited on the tonalite trondhjemite basement, which was subsequently mobilized, thereby producing the steeply dipping paragneiss belt of the northern domain.The grade of metamorphism throughout the region lies in the upper amphibolite facies, rising locally to the granulite facies. Within 15 km of the southern margin of the gneiss belt, the metamorphic grade decreases to the greenschist facies.U–Pb dating of zircons indicates that the tonalite gneiss was emplaced at least 3040 m.y. ago, and the granite plutons at 2660 m.y., coeval with migmatization and upper amphibolite facies metamorphism. Late pegmatites were emplaced at 2560 m.y.

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