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

在新喀里多尼亚，在西海岸的Nepoui和中部山区的cold ' Amieu发现了boninites。在Rouge河和Kiwanis的蛇纹岩山上发现了角砾岩。后者含有丰富的斜辉石斑晶。斜立辉石的Mg值为90 ~ 88；正辉石的Mg值为87，鸽石的Mg值为70。冷亚米尤硼长岩除斜辉长岩外，还含辉长岩和假晶岩。辉长岩位于宝钢岩下方，含泵状辉长岩和前辉长岩。在博长岩上覆有橄榄玄武岩，有辉长石和斜长石。玄武岩组的火山岩主要由橄榄玄武岩组成，偶有正辉石。在新西兰，第三纪的怀拉考安山岩和第四纪的陶波和基维塔希火山带都发现了镁质安山岩。汤加里罗火山中心有大量镁质安山岩。镁质安山岩采集自Poutu damsite、Mahuia Rapids、Pukeonake和Ohakune。来自普图丹岩的样品含有丰富的辉石晶体，直径可达1厘米。这些镁质安山岩可能是由橄榄石和辉石斑晶堆积而成。对白岛镁质安山岩的组成矿物进行了电子探针研究。橄榄石在Fo 92.1 ~ Fo 82.9呈正分带，斜辉石、正辉石及斜长石呈反分带。斜辉石岩心Mg值为78.7 ~ 75.2，岩缘Mg值为83.9 ~ 79.7。正辉石岩心Mg值为76.6 ~ 73.8，岩辋Mg值为81.6 ~ 70.3。橄榄石和辉石岩芯之间的成分差距表明，这些矿物不是从一个共同的、单一的岩浆中结晶出来的。白岛镁质安山岩可能是高镁岩浆与低镁高硅岩浆混合的产物。

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.