@article{oai:niigata-u.repo.nii.ac.jp:00003227, author = {高橋, 俊郎 and 周藤, 賢治}, issue = {11}, journal = {地質学雑誌, 地質学雑誌}, month = {Nov}, note = {The Early Miocene volcanic rocks (the Iwaine Formation) are widely distributed in the Hokuriku Green Tuff Province. The volcanic rocks in the Iwaine Formation in the southern part of Toyama Prefecture can be divided into two groups in the FeO^*/MgO-SiO_2 diagram;andesite group I has a tholeiitic trend showing enrichment in FeO^*/MgO ratio from mafic to felsic andesite, whereas andesite group II has a calc-alkaline trend on which SiO_2 content increases from about 54 to 68 wt.% despite a little variation in FeO^*/MgO. Petrographic and chemical data indicate that andesite group I was formed from tholeiitic basalt magma by fractional crystallization of its phenocryst minerals. Andesite group II is composed mainly of calc-alkaline andesite with subordinate amounts of high-magnesian andesite and adakitic andesite. Most phenocrystic plagioclases in calc-alkaline andesite are dusy and show reverse zoning in terms of Ca, suggesting that the andesite was of magma mixing origin. Adakitic andesite is characterized by higher Sr and lower Y contents, and higher Sr/Y ratio than common andesites in island arcs, and is also characterized by higher MgO, Ni and Cr contents compared with typical adakite. The high-magnesian andesite shows lower K_2O and Rb contents, and higher Sr/Y ratio than the Setouchi high-magnesian andesite and boninite. Adakitic andesite may result from modification of felsic (adakitic) magma generated by partial melting of the subducted oceanic crust, due to interaction with the overlying mantle peridotite or mixing with mafic magma during its rise to the surface. The high-magnesian andesite seems to have a genetical close relation to adakitic andesite. K_2O content of basaltic magmas in the Iwaine Formation tends to increase from the study area (eastern margin of the Hokuriku Green Tuff Province) to the western area. Thus, it is possible to consider that the study area occupied the volcanic front in the Early Miocene Hokuriku Green Tuff Province., 富山県南部に分布する中新統岩稲累層の安山岩類は,8タイプの安山岩~デイサイトに分けられ,それらはFeO^*/MgO-SiO_2図中で,ソレアイト系列の領域を占めるもの(グループ-1)と,カルクアルカリ系列~高マグネシア安山岩の領域を占めるもの(グループ-II)とに区分される.グループ-IIの安山岩はカルクアルカリ系列の安山岩,アダカイト質の安山岩,高マグネシア安山岩からなる.これらの安山岩類の成因は以下のように考えられる.グループ-Iの安山岩;低アルカリソレアイト質の玄武岩質マグマの分別結晶作用,グループ-IIのカルクアルカリ系列の安山岩;安山岩質マグマと玄武岩質マグマとの混合,アダカイト質の安山岩;沈み込んだ海洋地殻に由来するアダカイト質マグマと,マントルカンラン岩との反応あるいは玄武岩質マグマとの混合,高マグネシア安山岩;成因的にアダカイト質の安山岩と関連する,また,本地域は岩稲累層の火山活動域の火山フロントに相当する可能性があることを議論した.}, pages = {789--809}, title = {富山県南部の中新統岩稲累層のアダカイト質安山岩、高マグネシア安山岩、カルクアルカリ系列安山岩およびソレアイト系列安山岩の成因}, volume = {105}, year = {1999} }