Séminaire de Koenraad de Jong (Seoul National University, Seoul)


 AHLeGall    29/04/2016 : 23:55

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Le vendredi 29 avril 2016 à 10:30, en salle de conf de l'OSUR (campus de Beaulieu, bât.14B, RDC), Koenraad de Jong propose un séminaire intitulé Geochronological ans structural constraints on tectonic evolution of the Korean collision belt and links with the central China orogen

Le vendredi 29 avril 2016 à 10:30, en salle de conf de l'OSUR (campus de Beaulieu, bât.14B, RDC), Koenraad de Jong propose un séminaire intitulé Geochronological ans structural constraints on tectonic evolution of the Korean collision belt and links with the central China orogen


Cette présentation est proposée dans le cadre du cycle des séminaires de Géosciences Rennes

Présentation :

The Korean Peninsula forms part of the East Asian large-scale tectonic system where Late Palaeozoic to middle Cretaceous deformation, metamorphism and magmatism combined to create great complexity. We present an integrated view of the Korean collision belt using recent 40Ar/39Ar laser-probe stepheating single grain ages from the uppermost Gyeonggi Massif, central Korea's Palaeoproterozoic highgrade granite-gneiss terrane affected by Permo-Triassic metamorphism, the bordering Hongseong zone and the overlying Imjingang belt and the correlative Taean Formation, as well as SHRIMP isotopic ages of detrital zircons from meta-sandstones from the latter metamorphic marine turbidite sequences. We show that early Paleozoic isolated exotic terranes form part of the collision belt and were reworked in Permo-Triassic time.
Age spectra of zircons from mature meta-sandstones in the Misan Formation (Imjingang Belt) and Taean Formation do not match the age distribution of the Gyeonggi Massif, to which both are usually assigned, as they show only subordinate 1.9–1.8 Ga and ~2.5 Ga age modes but dominant 441–426 Ma and 978–919 Ma peaks. Much of the sediment appears to have been derived from distant, exotic middle Paleozoic and Early Neoproterozoic magmatic sources, not present in Gyeonggi or other Korean basement massifs. The youngest concordant zircon ages are: 394, 398 and 402 Ma, showing that both formations are at least of Early Devonian age. Terranes with a substratum with Early Neoproterozoic and Silurian-Devonian granitoids are present in the Qinling Terrane (Central China Orogen). Both formations may, hence, represent the submarine fan part of a routing system and a delta-shelf system originally situated in China.
The Taean Formation and Imjingang Belt are thus exotic Paleozoic terranes tectonically emplaced in the Korean collision belt. Muscovite, biotite and amphibole from different units of the Imjingang Belt yielded tightly clustered 40Ar/39Ar plateau ages between 255±1 and 249±1 Ma, dating fast cooling after peak temperature conditions. Slightly younger 243±1 and 240±1 Ma muscovite plateau ages in strongly retrogressed mylonites in the top of the Gyeonggi Massif and 241–237 Ma age components (Taean Formation) point to collisional tectonism. Concordant 233–229 Ma isotopic ages of titanite, hornblende and mica in Hongseong zone and Taean Formation, and detrital muscovite in Jurassic Gimpo sandstones reveal a regional thermal event affecting large portions of the peninsula's crust, also manifested in widespread 237–226 Ma mantle-sourced Mg-rich potassic magmatism and associated mafic dykes truncating folds and tectonic foliations. The Late Triassic thermal pulse implies rapid advective-conductive asthenospheric heat transport promoted by extension and magmatic underplating during post- or latecollisional lower crust and uppermost mantle delamination and/or oceanic slab break-off. The efficiency of cooling is underlined by identical biotite (228±1 Ma) and hornblende (230±1 Ma) plateau ages in Hongseong amphibolites that are comparable to 243–229 Ma (average: 234.6 Ma) U–Pb ages in zircon rims in high-temperature metamorphic, anatectic and magmatic rocks in the Gyeonggi Massif and the Hongseong zone. This shows that the Gyeonggi Massif is a Late Triassic core complex.

Semin Koen De Jong 29avril2016


Contact :
Koenraad de Jong (Seoul National University, Seoul)

Contact OSUR :
Philippe Steer (Géosciences Rennes)
Benjamin Guillaume (Géosciences Rennes)