Oxygen isotopic constraints on the geneses of the Miocene Outer Zone granitoids in Japan
書誌事項
- 公開日
- 1999-03
- 権利情報
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- https://www.elsevier.com/tdm/userlicense/1.0/
- DOI
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- 10.1016/s0024-4937(98)00081-4
- 公開者
- Elsevier BV
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説明
Abstract Miocene ilmenite-series granitoids of the Outer Zone of southwest Japan have been classified mineralogically into the southern S-type and the northern I-type. Oxygen isotopic ratios, δ 18 O SMOW , were determined on 45 representative samples from 17 granitic plutons. The results indicate that the Outer Zone granitoids have much higher δ 18 O values than magnetite-series granitoids of similar ages, confirming a contribution from crustal sediments to the genesis of the ilmenite-series granitoids, and that S-type granitoids are higher than I-type, with separation at 10.5‰, which is slightly higher than the 9.7‰ boundary in the Lachlan Fold Belt of Australia. Assuming the granitoids originated from mixtures of basaltic magmas from the upper mantle and sedimentary rocks of the accretionary complex from the fore-arc basin, mixing ratios were calculated. The S-type granitoids have sedimentary contributions of 64–45 wt.% with one exception, while I-type granitoids have that of 43–30 wt.%. Two trends are typically observed in the δ 18 O–SiO 2 diagram: (i) granitoids having large variation in δ 18 O values but little variation in SiO2 contents; and (ii) vice versa. The former granitoids solidified from heterogeneous magmas containing restite fragments, but the latter crystallized from a completely homogenized magma with magmatic fractionation. This type is associated with mineralization.
収録刊行物
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- Lithos
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Lithos 46 (3), 523-534, 1999-03
Elsevier BV