“C型埃达克岩”:一个基于误解的概念?  

The "C-type Adakite":A Concept Based on Misunderstanding?

作　　者：汪洋[1] 程素华[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《矿物岩石地球化学通报》2010年第3期284-292,298,共10页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金资助项目(90814006;40972125;40572128;40376013;40104003);国家重点基础研究发展规划项目(2008CB425704);中央高校基本科研业务费专项资金资助项目(2010ZY23;2010ZD15)

摘　　要：原始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。现有的失水部分熔融实验岩石学表明,中等富钾程度的贫硅(高Mg#值)玄武质源岩的低比例部分熔融条件下可以形成酸性"C型埃达克岩";玄武质源岩部分熔融不会形成那些SiO2含量中等而又不具备高度富碱特征的"C型埃达克岩"。高Sr低Y特征并非判别"C型埃达克岩"高压(p≥1.5 GPa)熔融成因的决定性标志,仅仅基于高Sr低Y特征而认为"C型埃达克岩"形成于高压熔融的成岩机制是值得商榷的。The original defined adakites are sodic igneous rocks,they are tonalite,trondhjemite or（plagioclase-rich） granodiorite in whole-rock chemistry;however,the K-rich ＂C-type adakites＂ defined by Chinese scholars are potassic igneous rocks,they belong to granite（s.s.）,quartz monzonite and（alkali feldspar-rich） granodiorite,etc.The fluid-absent melting experiments indicate that the acid ＂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.Otherwise,these experiments do not support the assumption that the intermediate ＂C-type＂ adakite,which does not have high alkali contents,is originated from the melting of basaltic source-rock.The characteristics of high Sr and low Y is not a key proxy to indicate the high pressure（p≥1.5 GPa） melting origin of ＂C-type adakites＂.Accordingly,it is not properly to assume the high pressure melting regime for ＂C-type adakites＂ just based on the high Sr and low Y characteristics.

关 键 词：C型埃达克岩 钠质 钾质 实验岩石学 部分熔融 Sr/Y值 

分 类 号：P588.1213[天文地球—岩石学]