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全文: "バルティカ大陸"
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  • 門田 康弘, 平島 崇男
    日本鉱物科学会年会講演要旨集
    2016年 2016 巻 R8-P04
    発行日: 2016年
    公開日: 2020/01/15
    会議録・要旨集 フリー
    トロムセ・ナップに産する正片麻岩の主要構成鉱物はざくろ石、白雲母、斜長石、石英である。ざくろ石は自形性がよく数十μmから1mm程度で、組成累帯構造が認められる;(1) Caに乏しくYに富み、包有物を多数含むコア、(2) CaとYに乏しく包有物をほとんど含まないリム、(3) Caに富みYに乏しい外部リム。コアの包有物は石英、白雲母、ジルコン、ルチルと稀に藍晶石が認められる。X線マッピング像によるCaやYの不連続面をコア‐リム境界と考えた。また不連続面の輪郭は丸みを帯びており、コア形成後にざくろ石が一旦溶融し、その後に再成長した可能性を示唆している。斜長石はCaに富むコアとCaに乏しいリムからなる。斜長石のリムはザクロ石の外部リムへのCaの供給源とみなすことができる。ざくろ石の形成過程について発表を行う。
  • 柏木 洋彦
    地学雑誌
    2017年 126 巻 4 号 513-531
    発行日: 2017/08/20
    公開日: 2017/09/27
    ジャーナル フリー

     Weathering is deeply related to global climate change. In the carbon cycle, silicate weathering, especially volcanic rock weathering, transfers carbon in the atmosphere (as CO2) to the lithosphere, and oxidative weathering of organic matter releases carbon (as CO2) from the biosphere to the atmosphere. Moreover, as an indirect effect of weathering on climate change, negative feedback in the climate system, which results from the dependence of weathering rate on temperature and evolution of terrestrial plants, is crucial. It has stabilized the long-term global climate throughout the Phanerozoic. Weathering rate is controlled by several geochemical external factors: tectonic forces such as lithology, continental uplift, and continental drift (paleogeography); climate forces such as temperature, runoff, and glaciations; and, biological forces such as terrestrial plant evolution. Regarding biological forces, accelerated weathering assisted by ectomycorrhizal fungi (EM fungi) and arbuscular mycorrhizal fungi (AM fungi), as well as vascular plants of gymnosperms and angiosperm, are emphasized. Variations of global weathering in the geological past are estimated using experimental approaches, such as isotope analysis (e.g., 87Sr/86Sr, 187Os/186Os, δ7Li), and theoretical approaches, such as numerical simulations (e.g., carbon cycle model). Each is used differently according the purpose of a study. Based on these estimates, geological past climate changes in the Phanerozoic are found to be closely related to weathering. For example, on the order of magnitude of 107 years, changes in weathering patterns due to continental drift (paleogeography) have resulted in variations of atmospheric CO2, hence climate change. On the order of magnitude of 106 years, it is suggested that a decrease in atmospheric CO2 from the mid- to late Cretaceous was caused by enhanced weathering according to terrestrial plant evolution and that variations of atmospheric CO2 in the late Cenozoic were regulated by weathering directly or indirectly influenced by continental uplift. Additionally, contributions of weathering to global climate change involved in oceanic anoxic events in the Mesozoic have been investigated.

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