Abstract
Marble has a great potential to understand a history of various geological events occurring during tectonic processes. In order to decode metamorphic–metasomatic records on C–O isotope compositions of marble at mid-crustal conditions, we con-ducted a C–O–Sr isotope study on upper amphibolite-facies marbles and a carbonate–silicate rock from the Hida Belt, which was once a part of the crustal basement of the East Asian continental margin. Carbon and oxygen isotope analyses of calcite from marbles (Kamioka area) and a carbonate–silicate rock (Wadagawa area) show a large variation of δ13 C [VPDB] and δ18 O [VSMOW] values (from −4.4 to +4.2 ‰ and +1.6 to +20.8 ‰, respectively). The low δ13C values of calcites from the carbonate–silicate rock (from −4.4 to −2.9 ‰) can be explained by decarbon-ation (CO2 releasing) reactions; carbon–oxygen isotope modeling suggests that a decrease of δ13 C strongly depends on the amount of silicate reacting with carbon-ates. The occurrence of metamorphic clinopyroxene in marbles indicates that all samples have been affected by decarbonation reactions. All δ18O values of calcites are remarkably lower than the marine-carbonate values. The large δ18 O variation can be explained by the isotope exchange via interactions between marble, external fluids, and/or silicates. Remarkably low δ18 O values of marbles that are lower than mantle value (∼+5 ‰) suggest the interaction with meteoric water at a later stage. Sr isotope ratios (87 Sr/86 Sr = 0.707255–0.708220) might be close to their protolith values. One zircon associated with wollastonite in a marble thin-section yields a U–Pb age of 222 ± 3 Ma, which represents the timing of the recrystallization of marble, triggered by H2O-rich fluid infiltration at a relatively high-temperature condition. Our isotope study implies that the upper amphibolite-facies condition, like the Hida Belt, might be appropriate to cause decarbonation reactions which can modify original isotope compositions of marble if carbonates react with silicates.
Original language | English |
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Article number | e12389 |
Pages (from-to) | 1-23 |
Number of pages | 23 |
Journal | Island Arc |
Volume | 30 |
Issue number | 1 |
DOIs | |
Publication status | Published - Jan 1 2021 |
Keywords
- Carbon isotope
- Decarbonation reaction
- Hida Belt
- Marble
- Oxygen isotope
- Strontium isotope
- Zircon U–Pb age
ASJC Scopus subject areas
- Geology