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ORIGIN OF MIOCENE ACIDIC VOLCANIC ROCKS IN SETOUCHI AREA

濑户内地区中新世酸性火山岩的成因

基本信息

批准号：
07640605
负责人：
TAZAKI Koichi
金额：
$ 1.41万
依托单位：
EHIME UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07640605/
关键词：
Setouchi dacite rhyolite Miocene REE Sr isotope Ishizuchi group pyroclastic rock 黒森峠安山岩岩石化学

项目摘要

Regional volcanic activities of high magnesian andesite during the late stage of Japan Sea opening were widely extended in the circum Seto Inland Sea area. In the northwest of Shikoku, calcalkaline volcanism which was related to the magmatism of Ishizuchi cauldron spread thick dacitic pyroclastic flow westward followed by calcalkaline Kuromoritoge andesite. The dacitic pyroclastic flow called Takano pyroclastic rock comprises lower pumice and fragment rich layr and upper fine ash rich sediments.Various rhyo-dacitic intrusion such as pottasium rich Taisanji-type acidic volcanic rocks, per-aluminous Myojinyama-type acidic volcanic rocks and K-feldspar bearing Misakatoge rhyolite are also exposed in the area. Rhyo-dacitic pyroclastic volcanism was also antecedent to high magnesian magmatism in Goshikidai.Chondrite normarized REE patterns of rhyo-dacitic to rhyolite rocks of the area exhibit LREE enrichment and steep inclination to HREE side and the most of the pattern exhibit negative Eu anomaly. Specific patterns which reflect magma source are also present. The potassium rich Taisanji-type rocks are enriched in REE and indicate relative mild inclination, whereas Misakatoge rhyolites are relatively poor in HREE and show steep inclination. Not distinctive negative Eu anomaly in the Kuromoritoge andesite suggests a least fractionation of magma. Variation of Inital Sr isotope ratios of these rocks are accordant with REE characteristics.

日本海开闭后期高镁安山岩的区域性火山活动在濑户内海周边地区广泛扩展。在国西北地区，与石穴大锅岩浆活动有关的钙碱性火山作用向西扩散厚的英质火山碎屑流，随后是钙碱性黑森里安山岩。高野火山碎屑流由下部富浮石和碎屑层和上部富细灰分沉积物组成。区内还出露富钾太三集型酸性火山岩、全铝型myojinyama型酸性火山岩和含钾长石Misakatoge流纹岩等各种流纹岩。高镁质岩浆活动发生于五石台的流英质火山碎屑作用之前。该地区流纹岩-流纹岩球粒陨石归一化稀土模式表现为LREE富集和向HREE侧倾斜，大部分模式表现为负Eu异常。还存在反映岩浆来源的特殊模式。富钾的太三基型岩石稀土元素富集，倾斜程度相对较轻，而三宅寺流纹岩稀土元素相对较弱，倾斜程度较陡。黑森内安山岩中Eu负异常不明显，表明岩浆分异作用最小。岩石初始Sr同位素比值的变化与稀土元素特征一致。