阿尔金奇克山斜长角闪岩同位素年龄及其地球化学特征
Geotectonica et Metallogenia(2017)
Abstract
阿尔金奇克山地区侵入于地层中的斜长角闪岩原岩为辉长岩,岩石地球化学组成显示斜长角闪岩的SiO2和Al2O3含量较高为49.29%~51.03%和12.27%~14.49%,Na2O+K2O含量低为2.35%~4.37%,MgO和Mg#值为6.48%~10.12%和48.7~59.6,具Eu负异常,样品的MgO对SiO2、Al2O3、TiO2及Cr-Rb和Rb/Nb-Rb/Zr关系图显示明显相关性,表明其为地幔岩浆经分异演化形成.岩石富集Rb、Th和U,亏损Nb、Sr和P,且Th/Ta为1.05~2.77>1,Nb/La为0.88~1.02,多小于1,显示岩石在演化过程中受到了地壳轻微混染,推断岩石形成于板内伸展环境.利用LA-ICP-MS微区原位定年获得斜长角闪岩206Pb/238U-207Pb/235U谐和年龄503±5 Ma和206Pb/238U加权平均年龄为479±6 Ma,该年龄段为阿尔金峰期变质阶段,指示岩石形成于479 Ma以前.
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Key words
amphibolite,genesis,isotopic age,Altyn Tagh,geochemistry
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