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Zircon geochemistry of Mid-Miocene adakites in the southern Patagonian province

Yuji ORIHASHI 1), Akihisa MOTOK1 2), Daiji HIRATA 3), Tsutomu OHTA 4), Meguel HALLER 5), Hideto YOSHIDA 6) and Ryo ANMA 7)

1) Earthquake research Institute, 113-0032, Japan, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyoku, Tokyo, 113-0032, Japan. 2) Rio de Janeiro State Univ., 3) Kanagawa Pref. Museum, 4) TITech, 5) Patagonian national Univ., 6) Fac. Science, Univ. of Tokyo, 7)Tsukuba Univ.

Corresponding author: Yuji Orihashi

Japan-Korea joint meeting of isotope ration mass spectrometry, 13.

Archaean juvenile continental crust has been mostly characterized in TTG (Tonalite, Trondhjemite Granodiorite), of which geochemical signature shows high Sr concentration, high Sr/Y and La/Yb ratios with non-Eu anomaly on REE pattern normalized to chondrite value (e.g., Martin, 1986; Defant and Drummond, 1990).

The experimental petrological results suggest that this geochemical signature can produce partial melting of tholeiitic rocks trans formed into garnet bearing amphibolite or eclogite (e.g., Rapp et al., 1991). On the Cenozoic arc volcanic fields, adakitic rocks, which are very similar geochemical signature to TTG, occur in subduction of young oceanic crust or young subduction zone, i.e., Alutians, Austral Chile, Cascade, and so on (e.g., Martin, 1999). Study of these adakitic magmatism is very important key to understand not only generation of slab melting and interaction process between mantle wedge and slab melting, but also formation and growth of the Archaean juvenile continental crust.

Because of these, our study group has extensively investigated and sampled the Cenozoic volcanic and plutonic rocks related to the Chile ridge subduction, Patagonian province. In this presentation, we reveal behavior of zircon crystal during slab melting using "typical" Mid-Miocene adakites in Cerro Pampa and Puesto Nuevo on the Because zircon geochemistry possibly becomes a powerful tool to reveal the petrogenesis of adakitic magma.

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