The fate of zircon during UHT-UHP metamorphism: isotopic (U/Pb, δ18O, Hf) and trace element constraints

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00025798%3A_____%2F16%3A00000253" target="_blank" >RIV/00025798:_____/16:00000253 - isvavai.cz</a>

Result on the web

<a href="http://onlinelibrary.wiley.com/doi/10.1111/jmg.12206/full" target="_blank" >http://onlinelibrary.wiley.com/doi/10.1111/jmg.12206/full</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1111/jmg.12206" target="_blank" >10.1111/jmg.12206</a>

Result language

angličtina

Original language name

The fate of zircon during UHT-UHP metamorphism: isotopic (U/Pb, δ18O, Hf) and trace element constraints

Original language description

Garnet-clinopyroxene ultrahigh-pressure rocks from N Bohemian Massif contain zircons with micro-diamond inclusions. Trace element concentrations, oxygen and hafnium isotopic composition and U-Pb age of distinct textural domains in zircons characterize their growth conditions and temporal evolution. Uniform Th/U ratios (c. 0.1-0.2), high Ti contents (110-190 ppm), and preserved steep HREE patterns with a weak negative Eu anomaly of the diamond-bearing zircon mantle domains with relics of oscillatory zoning are consistent with crystallization from a melt under UHP/UHT conditions. The bright-CL rims with Th/U ratios of c. 0.3-0.4), lower Ti contents (20-40ppm), flat HREE patterns and negative Eu anomalies have formed through recrystallization in solid state during the exhumation of the rock, when garnet and plagioclase are stable. The three zircon domains, i.e. cores, mantles and rims, yield U-Pb concordia ages of 340.9 ± 1.5 Ma, 340.3 ± 1.5 Ma and 341.2 ± 3.4 Ma, respectively. When linked to the previously reconstructed P-T path of the rock, the error limits of the zircon mantle and rim ages constrain the exhumation of the rocks from depth of c. 140 km (UHP) to c. 80 km (HP) to a minimum rate of 1.5 cm/year. The scattering εHf values (-15.7 to +4.8) possibly reflect the presence of a heterogeneous population of old zircons. The uniform and young 238U/206Pb ages may thus represent (near-)complete resetting of the U-Pb geochronometer during the UHP-UHT event at ca. 340 Ma through dissolution-reprecipitation process. In contrast to Hf, the oxygen isotope composition of zircons is homogeneous, ranging between 7.8 and 9.6 ‰ VSMOW, reflecting a source containing upper crustal material and homogenization at UHP-UHT conditions. Our study documents that continental crust was subducted to mantle depths at c. 340 Ma during the Variscan orogeny and subsequent very rapidly exhumed, implying that the sequence of events was faster than can be resolved by the SIMS technique.

Czech name

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Czech description

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Type

J_x - Unclassified - Peer-reviewed scientific article (Jimp, Jsc and Jost)

CEP classification

DB - Geology and mineralogy

OECD FORD branch

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Project

<a href="/en/project/GA13-21450S" target="_blank" >GA13-21450S: Diamond and coesite-bearing North Bohemian granulites: study of diamond-forming media in a deep subduction zone and consequences for geodynamic models</a><br>

Continuities

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Publication year

2016

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

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Volume of the periodical

34

Issue of the periodical within the volume

7

Country of publishing house

GB - UNITED KINGDOM

Number of pages

20

Pages from-to

719-739

UT code for WoS article

000382959200005

EID of the result in the Scopus database

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