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Field of formation of Besshi-type deposits-Their geochemical characterization

别子型矿床形成场-地球化学特征

基本信息

批准号：
06640617
负责人：
WATANABE Makoto
金额：
$ 0.64万
依托单位：
HIROSHIMA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06640617/
关键词：
Besshi-type deposits Primary features Metamorphic features Geochemical characteristics Field of formation Sanbagawa belt Rb-Sr, Sm-Nd, K-Ar and S isotopes Rb-Sr, Sm-Nd, K-Ar,イオウ同位体生成場緑色岩類地球化学四万十帯丹波帯希土類元素微量元素同位体比

项目摘要

Besshi-type deposits have hitherto been studied mainly on those in the Sanbagawa belt. They underwent regional metamorphism up to eipdote-amphibolite facies, making it difficult to unravel their geological and geochemical primary features. Namely, ore deposits in the Sanbagawa belt are suitable for study of metamorphic features. Measurements of sulfur isotope fractionation between pyrite and chalcopyrite from the Besshi-type deposits in the Sanbagawa belt and some other weakly and non-metamorphosd terrains have revealed that highly metamorphosed deposits have a more uniform fractionation than weakly metamorphosed deposits (Watanabe et al., in print). Our recent laser-ablation analyzes showed that delta<@D134@>D1S values of sulfides in non-metamorphosed deposit are similar to those of hydrothermal deposits associated with oceanic ridges (Watanabe et al., in prep). Measured Rb-Sr and Sm-Nd isotope ratios of pillowed basalts metamorphosed in pumpellyite-actinolite facies condition yielded a Rb-Sr whole-rock isochron age of 107 (]SY.+-。[) 15 Ma with an initial ratio of 0.70401 (]SY.+-。[) 0.00006. This age is regarded as the metamorphic age. Initial epsilon values at T=107 Ma suggest that the most likely source for the basalts is considered as depleted oceanic mantle with an oceanic island-type isotopic signature (Watanabe et al., submitted). K-Ar ages were determined for mineral separates, ranging from ca.60 to 112 Ma, with the highest mode of ca.80 Ma (Watanabe et al., ditto). The Besshi-type mineralization in the Inner zone occurred related to basaltic volcanism in a back-arc basin under the influence of an island-arc in Late Carboniferous to Early Permian times, while that in the Outer zone did associated with basaltic volcanism in an intra-oceanic plate in Late triassic to Cretaceous times (Watanabe et al., submitted).

迄今为止，对别石型矿床的研究主要集中在三八川带。它们经历了区域变质作用直至斜闪岩-角闪岩相，使其地质和地球化学基本特征难以揭示。即三八川带的矿床适合研究变质特征。对三八川带和其他弱变质和非变质地形的贝什型矿床中黄铁矿和黄铜矿硫同位素分异的测量表明，高度变质的矿床比弱变质的矿床具有更均匀的分异（Watanabe et al., in print）。我们最近的激光烧蚀分析表明，非变质矿床中硫化物的δ <@D134@>D1S值与与洋脊相关的热液矿床相似（Watanabe et al., in prep）。在泵柱岩-放光石相条件下变质的枕状玄武岩的Rb-Sr和Sm-Nd同位素比值测定结果表明，整个岩石的Rb-Sr等时线年龄为107 （]SY.+-）。[] 15 Ma，初始比值0.70401 (]SY.+-。(0.00006)。这个时代被认为是变质时代。T=107 Ma的初始epsilon值表明，玄武岩最可能的来源被认为是具有海洋岛屿型同位素特征的枯竭海洋地幔（Watanabe et al.，提交）。测定了矿物分离物的K-Ar年龄，范围为ca.60 ~ 112 Ma，最高模式为ca.80 Ma （Watanabe et al.，同上）。内带贝什型矿化与晚石炭世—早二叠世岛弧影响下的弧后盆地玄武岩火山作用有关，外带贝什型矿化与晚三叠世—白垩世洋内板块玄武岩火山作用有关（Watanabe et al.，提交）。