Picrite basalt（苦橄玄武岩）zz

转载于 2012-11-21 17:56:00 发布 · 111 阅读

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原文链接：http://www.cnblogs.com/heaventian/archive/2012/11/21/2781140.html

本文介绍了镁橄玄武岩（Picrite basalt），一种富含橄榄石矿物的高镁玄武岩。其特征为含有20%-50%的黄色绿色橄榄石晶体及黑色至深棕色角闪石。这种岩石在夏威夷基拉韦厄火山等地发现，是橄榄石晶体积累的结果。

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cited from wiki:http://en.wikipedia.org/wiki/Picrite_basalt

Picrite basalt, picrobasalt or oceanite[citation needed] is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20 to 50%) and black to dark brown pyroxene, mostly augite.

The olivine-rich picrite basalts that occur with the more common tholeiitic basalts（拉板玄武岩） of Kīlauea and other volcanoes of the Hawaiian Islands are the result of accumulation of olivine crystals either in a portion of the magma chamber or in a caldera lava lake.[1] The compositions of these rocks are well represented by mixes of olivine and more typical tholeiitic basalt.

The name "picrite" can also be applied to an olivine-rich alkali basalt: such picrite consists largely of phenocrysts of olivine and titanium-rich augite pyroxene with minor plagioclase set in a groundmass of augite and more sodic plagioclase and perhaps analcite and biotite.

Picrites and komatiites are somewhat similar chemically, but differ in that komatiite lavas are products of more magnesium-rich melts, and good examples exhibit the spinifex texture.[2] In contrast, picrites are magnesium-rich because crystals of olivine have accumulated in more normal melts by magmatic processes. Komatiites are largely restricted to the Archean.

When the term oceanite was apparently first proposed by Antoine Lacroix, he used the term to apply only to basalts with more than 50% olivine content (an extremely rare occurrence). Picrite basalt is found in the lavas of Mauna Kea and Mauna Loa in Hawaiʻi[3], Curaçao, in the Piton de la Fournaise[4] volcano on Réunion Island and various other oceanic island volcanoes.