Complex geochronological record of an emblematic Variscan eclogite (Haut-Allier, French Massif Central)

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00025798%3A_____%2F23%3A10168703" target="_blank" >RIV/00025798:_____/23:10168703 - isvavai.cz</a>

Result on the web

<a href="https://doi.org/10.1111/jmg.12733" target="_blank" >https://doi.org/10.1111/jmg.12733</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1111/jmg.12733" target="_blank" >10.1111/jmg.12733</a>

Result language

angličtina

Original language name

Complex geochronological record of an emblematic Variscan eclogite (Haut-Allier, French Massif Central)

Original language description

Two eclogite samples from the Haut-Allier record a prograde evolution from similar to 20 kbar, 650 degrees C to 750 degrees C, 22-23 kbar followed by heating up to 850-875 degrees C and partial melting. Incipient decompression in high-pressure granulite facies conditions (19.5 kbar, 875 degrees C) was followed by exhumation to high-temperature amphibolite facies conditions (&lt;9 kbar, 750-850 degrees C). Following a detailed geochemical, petrological, and geochronological investigation using trace-element data and laser ablation inductively coupled plasma mass spectrometry U-Pb dating of zircon, apatite, and rutile, the eclogites reveal an Ordovician (c. 490 Ma) rifting event followed by Devonian (c. 370-360 Ma) subduction and Carboniferous (c. 350 Ma) exhumation in this part of the French Massif Central. The previously proposed Silurian age for the subduction, which strongly influenced many tectonic models, is definitively rejected. In the light of other geological data from the French Massif Central, including the lithological and geochemical zoning of calc-alkaline Devonian volcanism, we propose a southward polarity of the subduction and question the very existence of the so-called Massif Central Ocean. Furthermore, we infer that following subduction, the eclogites were relaminated to the upper plate and exhumed at the rear of the magmatic arc pointing to similarities with the geodynamics of the Bohemian Massif. The petrochronological record of zircon is particularly complex. Metamorphic zircon with clear eclogitic rare-earth elements patterns (no Eu anomaly and flat heavy rare-earth elements) and inclusions (garnet, rutile, and omphacite) shows concordant apparent ages that spread from c. 380 down to c. 310 Ma. This apparent age pattern strongly contrasts with the well-defined age of apatite and rutile of c. 350 Ma. Apparent zircon ages younger than 350 Ma unequivocally testify that zircon can recrystallize outside the conditions of the eclogite facies, which resets the U-Pb while preserving an apparent eclogitic signature. Local fractures filled by analcite, thomsonite, plagioclase, and biotite testify to late interaction of the eclogites with alkaline fluids at relatively low temperatures. This interaction, possibly at c. 310 Ma or later, could lead to the recrystallization of zircon while leaving apatite unaffected.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

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OECD FORD branch

10505 - Geology

Project

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Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2023

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Journal of Metamorphic Geology

ISSN

0263-4929

e-ISSN

1525-1314

Volume of the periodical

41

Issue of the periodical within the volume

7

Country of publishing house

GB - UNITED KINGDOM

Number of pages

29

Pages from-to

967-995

UT code for WoS article

001000038100001

EID of the result in the Scopus database

2-s2.0-85161455100