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THE STUDY OF GABBROS ASSOCIATED WITH THE CRETACEOUS GRANITIC ROCKS, KITAKAMI MOUNTAINS

与北上山白垩纪花岗岩相关的辉长岩研究

基本信息

批准号：
62540611
负责人：
KANISAWA Satoshi
金额：
$ 1.28万
依托单位：
Tohoku 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-62540611/
关键词：
Kitakami Mountains Cretaceous Igneous Activities Granitic Rocks Gabbroic Rocks Trace Elements Island Arc Igneous Activities 深成岩マグマの成因マグマ溜まり

项目摘要

The Early Cretaceous granites in the Kitakami Mountains are divided into six zones VIa, namely I to VI, and the last of which is divided further into subzones VIa and VIb(Katada 1974, Kanisawa and Katada,1988).1) Two kinds of gabbroic rocks associated with granitic plutons are recognized in the district,i.e., (1) olivine-pyroxene-hornblende gabbro series characterized by the association of An-rich plagioclase, olivine and pargasitic hornblende, and (2)biotite-olivine-pyroxene gabbro series characterized by the assemblage of relatively An-poor plagioclase, biotite and olivine with or without K-feldspar.2) Rocks of the olivine-pyroxene-hornblende gabbro series are associated with the plutons of Zones 1, 11 and V, and usually composed of hornblende gabbro, pyroxene-hornblende gabbro, and small amount of olivine-pyroxene-hornblende gabbro. Whereas, rocks of the biotite -pyroxene-hornblende gabbro series are composed of biotite-olivine-pyroxene gabbro/monzo- gabbro, biotite-pyroxene-hornblende gabbro/monzogabbro and associated with the plutons of Zones Ill, IV and VIb.3) Trace element patterns for granitic rocks indicate that they are rich in LILE and depleted in HFSE and show negative Nb anomaly similar to those of rocks of the island arc and active continental margins, but those of gabbroic rocks are irregular due to differences in modal proportions of minerals(Kanisawa and Katada,1988; Kanisawa and Yoshida,1989).4) Tectonic discrimination : Major element chemistry of the Cretaceous plutonic rocks of the district show continental are granites(CAG). Trace element characteristics, such as Y-, Rb- and Nb-SiO2, and Nb-Y, Rb-(Y+Nb) relations indicate those of the volcanic arc granites(VAG).5) The isotopic data are necessary to clarify the petrogenesis of granitic and gabbroic rocks. Further, it is considered that some of gabbro bodies indicate the sub-volcanic structure, so the detailed study on suitable body is necessary at this point.

北上山早白垩世花岗岩可划分为六个带VIa，即I至VI，最后一个带又可进一步划分为VIa和VIb亚带（Katada 1974，Kanisawa and Katada，1988）。(1)橄榄-辉石-角闪石辉长岩系列，以富An斜长石、橄榄石和部分气化角闪石的组合为特征;（2）黑云母-橄榄-辉石辉长岩系列，以相对贫An斜长石、黑云母和橄榄石的组合为特征，含或不含钾长石。通常由角闪石辉长岩、辉石角闪石辉长岩和少量橄榄辉石角闪石辉长岩组成。而黑云母-辉石-角闪石辉长岩系岩石由黑云母-橄榄石-辉石辉长岩/二长辉长岩、黑云母-辉石-角闪石辉长岩/二长辉长岩组成，与Ⅲ、Ⅳ、Ⅵ b带岩体共生。3）花岗质岩石微量元素模式显示富LILE，亏损HFSE，表现出与岛弧和活动大陆边缘岩石相似的Nb负异常，而辉长岩的主元素化学特征因矿物模态比例的不同而不规则（Kanisawa and Katada，1988; Kanisawa and Yoshida，1989）。4）构造判别：本区白垩纪深成岩的主元素化学特征显示为大陆弧花岗岩（CAG）。微量元素特征，如Y-、Rb-、Nb-SiO_2和Nb-Y、Rb-（Y+Nb）关系等，表明了火山弧花岗岩（VAG）的特征。同时，认为部分辉长岩体指示了次火山构造，因此有必要对适宜的辉长岩体进行详细的研究。