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Study on Mantle Origin Magnesian Andesite from the Southern Pacific Region.

南太平洋地区地幔成因镁质安山岩研究。

基本信息

批准号：
63041068
负责人：
URANO Hayaomi
金额：
$ 3.2万
依托单位：
Aichi University of Education
依托单位国家：
日本
项目类别：
Grant-in-Aid for Overseas Scientific Research
财政年份：
1988
资助国家：
日本
起止时间：
1988 至无数据
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63041068/
关键词：
Boninite Magnesian Andesite New Caledonia New Zealand Island Arc Andesite Volcanic Rocks 超苦鉄質岩

项目摘要

In New Caledonia boninites have been found in Nepoui on the west coast and Col d' Amieu in the central mountains. New occurrences of boninites were found as breccias on the Rouge River and on the serpentinite hill of Kiwanis. The latter contains abundant clinoenstatite phenocrysts. The clinoenstatite has Mg values of 90-88 ; Mg values of the orthopyroxene are 87 and those of pigeonite 70. The Col d' Amieu boninite contains augite and pseudomorphs after clinoenstatite. A metagabbro with pumpellyite and prehnite occurs below the boninite. Overlying the boninite is an olivine basalt having augite and plagioclase. The volcanic rocks of the Basaltic formation consist mainly of olivine basalts containing occasionally orthopyroxene.In New Zealand magnesian andesites have been found in the Tertiary Wairakau andesites and in the Quaternary Taupo and Kiwitahi volcanic belts. A large amount of magnesian andesite occurs in the Tongariro volcanic centre. Magnesian andesites were collected from Poutu damsite, Mahuia Rapids, Pukeonake and Ohakune. Samples from Poutu damsite contain abundant pyroxene crystals up to 1 cm across. These magnesian andesites may have been formed by accumulation of olivine and pyroxene phenocrysts. An electron probe study was made on constituent minerals in amagnesian andesite from White Island. Olivine shows normal zoning ranging from Fo 92.1 to Fo 82.9, while clino-and ortho-pyroxenes, as well as plagioclase, show reverse zoning. Mg values in the cores of clinopyroxene are 78.7-75.2 and those in the rims 83.9-79.7. The orthopyroxene cores have Mg values of 76.6 to 73.8 and the rims Mg values of 81.6 to 70.3. The compositional gap between olivine and pyroxene cores suggests that these minerals have not crystallized from a common, single magma. The White Island magnesian andesite would be a mixing product of high-Mg magma with low-Mg, high-Si one.

在新喀里多尼亚，在西海岸的Nepoui和中部山脉的Col d' Amieu发现了玻尼岩。在胭脂河和基瓦尼斯的蛇纹岩山上发现了新的玻尼岩角砾岩。后者含有丰富的斜顽辉石斑晶。斜顽火辉石的Mg值为90-88 ;斜方辉石的Mg值为87，褐变岩的Mg值为70。Amieu山玻安岩中含有斜顽火辉石和假像。在玻安岩之下，出现了一种由绿纤石和葡萄石组成的变辉长岩。上覆玻安岩的是含有普通辉石和斜长石的橄榄玄武岩。玄武岩建造的火山岩主要由橄榄石玄武岩组成，偶尔含有斜方辉石。在新西兰，在第三纪Wairakau安山岩和第四纪Taupo和Kiwitahi火山带中发现了镁质安山岩。大量的镁安山岩产于汤加里罗火山中心。从Poutu坝址、Mahuia急流、Pukeonake和Ohakune采集镁安山岩。Poutu坝址的样品含有大量的辉石晶体，直径可达1厘米。这些镁安山岩可能是由橄榄石和辉石斑晶堆积而成。对白色岛富镁安山岩的组成矿物进行了电子探针研究。橄榄石显示正常分带，范围从Fo 92.1到Fo 82.9，而斜辉石和正辉石，以及斜长石，显示反向分带。单斜辉石核部的Mg值为78.7-75.2，边缘部的Mg值为83.9-79.7。斜方辉石核的Mg值为76.6至73.8，边缘的Mg值为81.6至70.3。橄榄石和辉石核之间的成分差距表明，这些矿物没有从一个共同的，单一的岩浆结晶。白色岛镁安山岩是高镁岩浆与低镁、高硅岩浆的混合产物。