Late Variscan (315 Ma) subduction or deceptive zircon REE patterns and U–Pb dates from migmatite-hosted eclogites? (Montagne Noire, France)

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00025798%3A_____%2F22%3A00000027" target="_blank" >RIV/00025798:_____/22:00000027 - isvavai.cz</a>

Result on the web

<a href="https://onlinelibrary.wiley.com/doi/10.1111/jmg.12609" target="_blank" >https://onlinelibrary.wiley.com/doi/10.1111/jmg.12609</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1111/jmg.12609" target="_blank" >10.1111/jmg.12609</a>

Result language

angličtina

Original language name

Late Variscan (315 Ma) subduction or deceptive zircon REE patterns and U–Pb dates from migmatite-hosted eclogites? (Montagne Noire, France)

Original language description

Eclogites hosted in sillimanite-bearing migmatites in the Montagne Noire dome (French Massif Central) have an oceanic protolith and recorded a prograde P–T path from ~19.5 kbar, 700°C to the pressure peak at ~21 kbar, 750°C (pseudosection modelling), suggesting metamorphism in a subduction setting. Subsequent exhumation to low-P high-T (LP–HT) conditions (~6 kbar, 730°C) is constrained by the equilibration conditions of the embedding migmatite. In samples of a fresh and a retrogressed eclogite, all zircon crystals but one display similar REE patterns (no Eu anomaly, flat HREE), usually ascribed to crystallization under eclogite-facies conditions. Yet, the U–Pb apparent ages of zircon crystals from both eclogites spread from c. 360 Ma to a dominant data cluster at c. 315 Ma. The c. 315–310 Ma zircon U–Pb dates obtained from the embedding migmatite are interpreted as the age of crystallization of the partial melt during the LP–HT metamorphic stage. First-order geological evidence, in particular the sedimentary record, excludes the existence of a subduction zone in the region at this period. Unless calling upon a major reappraisal of the tectonics of the European Variscan orogen, this suggests an ambiguous relation between REE patterns and U–Pb dates in the zircon population. Various scenarios that could account for the observations are discussed. Combining our data with the results of a previously published Sm–Nd dating of garnet, and regional considerations, we consider that 360 Ma is the best approximation of the minimum age of the eclogite-facies event. We hypothesize that the eclogites formed farther north and were transferred to their present location by lower-crustal flow. It is inferred that during the subsequent exhumation, eclogite-facies zircon grains recrystallized and underwent partial to total resetting of their U–Pb system, whereas the REE system remained mostly unmodified. These results caution against the use of REE patterns as the only criterion to associate a specific zircon age with HP metamorphism in eclogites occurring in migmatitic domes.

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

—

Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2022

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

—

Volume of the periodical

40

Issue of the periodical within the volume

1

Country of publishing house

GB - UNITED KINGDOM

Number of pages

27

Pages from-to

39-65

UT code for WoS article

000660098400001

EID of the result in the Scopus database

2-s2.0-85107784305