Analytical study of mineral parageneses of the Abukuma metamorphic rocks

阿武隈变质岩矿物共生分析研究

• 批准号: 61540586
• 负责人: HIROI Yoshikuni
• 金额: $ 1.41万
• 依托单位: Chiba University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1986
• 资助国家: 日本
• 起止时间: 1986 至 1987
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-61540586/
• 关键词: Abukuma metamorphic rocks; Gosaisyo series; Takanuki series; P-T-t paths of rocks; Isothermal loading; Overthrusting; 衡上運動; ジュラ記放敬虫; 接触変成作用; 衝上断層; ジュラ紀の放散虫化石; 輝石ホルンフェルス相; ザクロ石斑状変晶; 累帯構造

Geological and petrological studies has been carried out on the Abukuma metamorphic rocks (the Gosaisyo series and the Takanuki series), northeastern Japan, to reveal their P(pressure)-T(temperature) evolution.Jurassic radiolarian fossils were found for the first time in a Fe-Mn-rich metachert of the Gosaisyo series and, thus, the age of original rocks of the Gosaisyo series was confirmed to be Jurassic. Consequently, the Abukuma regional metamorphism took place after Jurassic and before the emplacement of the Cretaceous intrusive complexes about 120 Ma ago.Rocks of the Gosaisyo series have not shown any evidence of high- to mediumpressure metamorphism. On the contrary, textures and compositions of garnet and plagioclase suggest low-pressure conditions during metamorphism.The Takanuki pelitic rocks are characterized by the occurrence of garnet porphyroblasts showing complex chemical zoning and a sector structure. Their P-T-t paths based on the compositions of garnet, plagioclase, and biotite suggest nearly isothermal loading at high-temperatures at an early stage of regional metamorphism. The high-temperature loading is also evidenced by the occurrence of sillimanite and hercynite along with staurolite within almandine and corundum in the Takanuki lareritic rocks. It may be due to the overthrusting of the Gosaisyo series on the Takanuki series.

通过对日本东北部阿武熊变质岩系（五斋所统和高贯统）的地质和岩石学研究，揭示了它们的P（压力）-T（温度）演化，首次在五斋所统的富铁锰变混杂岩中发现了侏罗纪放射虫化石，从而确定了五斋所统原岩的时代为侏罗纪。因此，阿武熊区域变质作用发生在侏罗纪之后，白垩纪侵入杂岩侵位之前，距今约120 Ma。石榴子石和斜长石的结构和成分反映了变质过程中的低压环境。高贯泥质岩以石榴子石变斑晶产出为特征，具有复杂的化学分带和扇形结构。根据石榴石、斜长石和黑云母的成分，它们的P-T-t轨迹表明，在区域变质作用的早期阶段，它们在高温下受到了近等温的加载。高温负荷也被证明是由硅线石和铁铝尖晶石沿着与十字石中的铁铝榴石和铁铝榴石在Takanuki红土岩石的出现。这可能是由于高贯岩系上的五斋洲岩系的逆冲作用。

项目成果

Yoshikuni,Hiroi: "Evolution of Metamorphic Belts"Special publication of the Geological Society of London.

广井吉国：《变质带的演化》伦敦地质学会特别出版物。

Yoshikuni, Hiroi: "P-T evolution of Abukuma metamorphic rocks in Northeast Japan-metamorphic evidence of oceanic crust obduction ?" "Evolution of Metamorphic Belts" Special publication of the Geological Society of London.

广井吉国：“日本东北部阿武隈变质岩的 P-T 演化——洋壳仰冲的变质证据？”

Yoshikuni,Hiroi: Journal of the Geological Society of Japan. 93. 445-448 (1987)

广井吉国：日本地质学会杂志。

Yoshikuni, Hiroi: "Discovery of Jurassic radiolaria from acmite-rhodonite-bearing metachert of the Gosaisyo metamorphic rocks in the Abukuma terrane, northeastern Japan" Journal of the Geological Society of Japan. 93. 445-448 (1987)

Yoshikuni, Hiroi：“从日本东北部阿武隈地体的 Gosaisyo 变质岩中发现侏罗纪放射虫”，日本地质学会杂志。