浅议埃达克岩的几个问题
首发时间:2010-01-12
摘要:最初定义的埃达克岩是钠质火成岩,其全岩化学成分相当于英云闪长岩、奥长花岗岩和(富斜长石的)花岗闪长岩(TTG);而富钾的“C型埃达克岩”全岩化学成分相当于(狭义)花岗岩、石英二长岩和(富碱性长石的)花岗闪长岩。目前的实验岩石学结果不支持玄武质源岩部分熔融形成SiO2含量中等(56 ~ 67 %)的“C型埃达克岩”的假设。但中等富钾程度的贫硅(或高Mg#值)玄武质源岩在相对高压低比例部分熔融条件下可以形成酸性(SiO2 > 70%)“C型埃达克岩”。
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On some problems about the adakite
Abstract:The original defined adakitesare sodium igneous rocks, they are tonalite, trondhjemite or (plagioclase-rich) granodiorite in whole-rock chemistry; however, the K-rich “C-type” adakite defined by Chinese scholars are potassic igneous rocks, they are granite (s.s.), quartz monzonite and (alkali feldspar-rich) granodiorite, etc. The fluid-absent melting experiments of amphibolite do not support the assumption that, the intermediate “C-type” adakite (with SiO2 contents of 56 ~ 67 %) is originated from the melting of basaltic source-rock. Otherwise, the acid (SiO2 > 70%) “C-type” adakite can be generated by low portion melting of the basaltic source-rock that has intermediate potassic and low silicic contents (or high Mg#) under higher pressure.
Keywords: adakite experimental petrology partial melting
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