新潟県北部、葡萄山塊に分布する岩船花崗岩類中の斑状黒雲母花崗岩の2段階分別結晶作用

フォーマット:

論文(リポジトリ)

責任表示:

加々島, 慎一 ; 志村, 俊昭

出版情報:

日本地質学会, 2001-08

掲載情報:

地質学雑誌 — 地質学雑誌

ISSN:

00167630      

著者名:

• 加々島, 慎一
• 志村, 俊昭

巻:

107

通号:

8

開始ページ:

515

終了ページ:

530

概要:

The Late Cretaceous to Paleogene Iwafune granitoids of are distributed around the border between Niigata and Yamagata Prefectures, Japan. The Budo Mountains is located in northern part of Niigata Prefecture and is exposed in an area coverin … g more than 250 square kilometers. It consists of Iwafune granitoids, which are divided into six lithological types ; porphyritic biotite granite (PBG), biotite granite (BG), garnet two-mica granite (GTMG), two-mica granite (TMG), quartz diorite (QD) and granodiorite (GD). The six rock types can be assigned to three rock groups on the basis of petrological observations as follows : biotite granite group(BG-group ; PBG and BG), and tow－mica granite group (TMG-group；GTMG and TMG) and diorite group (D-group；QD and GD). Most of the granitoids in this area are attributed to BG-group. This group is composed of quartz, plagioclase, potassium feldspar, biotite and minor amounts of accessory minerals. Especially, the PBG contains potassium feldspar megacrysts and sometimes shows schlieren layering owing to the concentration of biotite and plagioclase. BG-group has medium SiO_2 content ranging from 69 to 77 weight percent and is peraluminous. Modal and bulk chemical compositions show that BG－group has curved trend. Mass balance calculation indicates that the BG-series magma can be derived from common parental magma through two-stage fractional crystallization of potassium feldspar, biotite and plagioclase. The first stage is characterized by plagioclase- and biotite-rich fractionation, and the second stage is characterized by fractionation of biotite and potassium feldspar more than plagioclase.<br />新潟県北部の蒲萄山塊には，後期白亜紀から古第三紀の岩船花崗岩類が分布する．蒲萄山塊南部の岩船花崗岩類は，斑状黒雲母花崗岩，黒雲母花崗岩，ざくろ石両雲母花崗岩，両雲母花崗岩，石英閃緑岩，花崗閃緑岩に区分された．これらは産状，構成鉱物，全岩-鉱物組成から3つの岩類に分けられる．主要岩相である斑状黒雲母花崗岩の結晶作用を検討した．モード組成および全岩化学組成から屈曲したトレンドが得られ，2段階の分別結晶作用が考えられる．マスバランス計算により，第1段階では斜長石と黒雲母が主な分別鉱物であり，第2段階では斜長石よりもカリ長石＋黒雲母の分別が多かったことが導き出された． 続きを見る

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