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Geological and petrological study of the middle Miocene regional basalts from the Japan Sea side in the NE Japan arc

日本东北弧日本海一侧中新世区域玄武岩的地质和岩石学研究

基本信息

批准号：
62540617
负责人：
SHUTO Kenji
金额：
$ 1.09万
依托单位：
Niigata 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：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-62540617/
关键词：
The Northeast Japan Arc Lateral Variation of LIL Elements Non Island Arc-Type Volcanic Rock Late Miocene (8-6 Ma) Volcanic Rock Pliocene (4-2 Ma) Volcanic Rock Middle Miocene (16-14 Ma) Volcanic Rock Plate Subduction Mantle Diapir 後期中新世(8〜

项目摘要

Abundances of major elements and seven trace elements, Rb, Sr, Nb, Y, Zr, Ni and Cr were determined by X-ray fluorescence analysis for 111 samples from twelve Pliocene volcanic centers in the NE Japan are. The petrographical and analytical results in this study and the published ones on other Pliocene volcanic rocks indicate that systematic zonal variation of petrological features, i.e., mafic phenocryst assemblages and rock series, as well as gradual increase in K_2O, Rb and Sr contents are recognized in the Pliocene volcanic rocks from the Pacific Ocean side to the Japan Sea side across the NE Japan arc. Furthermore, systematic across-arc variation of chemical compositions and petrological features, similar to those in the Pliocene to Quaternary volcanic rocks, are also observed in the late Miocene (8-6 Ma) volcanic rocks throughout the NE Japan arc.Similarity of across-arc variation. with regard to both the petrological and geochemical features among the volcanic rocks from the late … More Miocene to Quaternary through Pliocene time suggests that igneous activity which is related to a mechanism for magma generation determined by plate subduction bas been continuous in the NE Japan arc at least during 8 Ma ago to the present.On the other hand, the NE Japan arc of the middle Miocene (16-14 Ma) are characterized by occurrence of rocks of non island arc-type volcanic rocks such as E-type MORB like basalt which is enriched in Ti and other HFS elements, basaltic rocks hailing intermediate nature between the island arc tholeiite and the back arc basin basalt in bulk rock chemistry and icelandite like andesite and dacite, in association with volcanics of the island arc tholeiite series and calc-alkaline series. These volcanic rocks increase gradually in K_2O from the Japan Sea side toward the Pacific Ocean side across the NE Japan arc, indicating the lateral variations dissimilar to the case of volcanic rocks produced during 8 Ma ago to the present.It is possible that such non island arc-type volcanics were derived from a upper mantle material which is different from the present one in the NE Japan arc. These volcanics could have been generated from a mantle diapir ascending from asthenosphere during the spreading of the Japan Sea. The middle Miocene volcanics of island arc tholeiite series and calc-alkaline series in the NE Japan arc may have been originated from partial melting of upper mantle and lower crust heated by the ascending mantle diapir. Less

本文用x射线荧光法测定了日本东北部12个上新世火山中心111个样品的主元素和7种微量元素Rb、Sr、Nb、Y、Zr、Ni、Cr的丰度。本研究的岩石学和分析结果与已发表的其他上新世火山岩的岩石学和分析结果表明，上新世火山岩的岩石学特征，即基性斑晶组合和岩石系列的系统地带性变化，以及K_2O， Rb和Sr含量的逐渐增加，从太平洋一侧到日本海一侧穿过日本东北弧。此外，日本东北弧的晚中新世（8-6 Ma）火山岩的化学成分和岩石学特征也具有与上新世至第四纪火山岩相似的系统弧间变化。弧间变化的相似性。晚中新世至第四纪至上新世火山岩的岩石学和地球化学特征表明，至少在8 Ma以前到现在，日本东北弧的火成岩活动是连续的，火成岩活动与板块俯冲决定的岩浆生成机制有关。中中新世（16-14 Ma）日本东北弧发育非岛弧型火山岩，如富Ti等HFS元素的e型MORB型玄武岩、块状岩石化学性质介于岛弧拉斑岩与弧后盆地玄武岩之间的玄武岩、冰岛岩类安山岩和英安岩等，并与岛弧拉斑岩系列和钙碱性系列火山相结合。这些火山岩的K_2O含量从日本海一侧向太平洋一侧逐渐增加，穿过日本东北弧，表明其横向变化与8 Ma以前至现在的火山岩不同。这种非岛弧型火山可能起源于与现今日本东北弧不同的上地幔物质。这些火山可能是在日本海扩张期间由软流圈上升的地幔底辟形成的。日本东北弧中新世中期的岛弧拉斑岩系列和钙碱性系列火山活动可能是由于上地幔和下地壳在上升的地幔底喷流加热下部分熔融而形成的。少