Study of origin of metabasites from high-pressure metamorphic terrains

高压变质岩地形变碱岩成因研究

• 批准号: 02640633
• 负责人: ISHIZUKA Hideo
• 金额: $ 1.41万
• 依托单位: Kochi 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: 1990
• 资助国家: 日本
• 起止时间: 1990 至 1991
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-02640633/
• 关键词: Kamuikotan zone; Sanbagawa zone; metabasites; bulk rock chemistry; tectonic setting; 低温高圧型変成帯; 変成塩基性岩; 全岩化学分析

Field surveyes and chemical analyses(major, minor and rare earth elemenys) were done for metabasites from the high-pressure Kamuikotan zone in Hokkaido and Sanbagawa zone in Shikoku in order to examine the tectonic setting of original rocks.The Kamuikotan metabasites usually form close-packed pillow lavas and rarely isolated or brecciated pillow lavas and massive lavas, and occur as various sized- and shaped-blocks within pelitic matrix, forming a melange. The Sanbagawa metabasites occur as close-packed pillow lavas, isolated or brecciated pillow lavas, and massive lavas, and are commonly coherent with surrounding metasediments mainly derived from mudstones.On the basis of the chemical analyses, there are two types of metabasites in the Kamuikotan zone ; one is an ocean plateau type of basalts and the other an ocean island type of basalts, of which the former is more abundant in the field. This suggests that the Kamuikotan metabasites were derived from an ocean plateau-island complex. Also, the Sanbagawa metabasites are chemically divided into two types ; one is a N-type MORB(Mid-Ocean Ridge Basalt)with a back-arc basin affinity and the other a E-type MORB commonly found as shills within sediments in back-arc basins, of which the former occurs in the lowest level of the stratigraphic sequence. This indicates that the Sanbagawa metabasites were derived from a back-arc basin such as the Philippine Sea.Such difference of the tectonic setting of original rocks from the Kamuikotan and Sanbagawa zones may be related with the difference of the metamorphic conditions, especially the conditions of temperature. It is, therefore, suggested that the temperature of metamorphism is higher in the Sanbagawa zone than in the Kamuikotan zone.

实地调查和化学分析为了研究岩石形成的构造环境，对北海道高压釜湖带和四国三宝川带的变基性岩进行了主、次、稀土元素的对比分析。釜湖带的变基性岩通常形成密集的枕状熔岩，很少形成孤立或角砾状枕状熔岩和块状熔岩，在泥质基质中呈大小不等的块状产出，形成美琅脂。三坝川变基性岩以紧密堆积的枕状熔岩、孤立或角砾状枕状熔岩和块状熔岩的形式产出，通常与周围以泥岩为主的变沉积物相结合。一种是洋坪型玄武岩，另一种是洋岛型玄武岩，其中洋坪型玄武岩在野外更为丰富。这表明，Kamuikotan变基性岩来自海洋高原-岛屿复合体。此外，三坝川变基性岩的化学分为两种类型;一种是N型MORB（洋中脊玄武岩）与弧后盆地的亲和力和其他的E型MORB通常被发现为在弧后盆地的沉积物中的shills，其中前者发生在地层层序的最低水平。这表明三坝川变质基性岩来自于菲律宾海等弧后盆地，而鸭尾湖带和三坝川带原岩构造环境的差异可能与变质条件特别是温度条件的差异有关。因此，这表明，在三坝川带的变质温度高于Kamuikotan带。