辽西黄半吉沟早白垩世义县组高镁安山岩的成因  

Petrogenesis of Huangbanjigou high magensiun andesite in Early Cretaceous Yixian Formation,western Liaoning

作　　者：洪路兵[1,2] 张银慧[2,3] 任钟元[2] 徐义刚[2] 颜文[1] HONG LuBing ZHANG YinHui REN ZhongYuan XU YiGang YAN Wen(CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China University of Chinese Academy of Sciences, Beijing 100049, China)

机构地区：[1]中国科学院南海海洋研究所、中国科学院边缘海地质重点实验室,广州510301 [2]中国科学院广州地球化学研究所、同位素地球化学国家重点实验室,广州510640 [3]中国科学院大学,北京100049

出　　处：《岩石学报》2017年第1期41-55,共15页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41403024、91214202、41273042);中国科学院广州地球化学研究所135项目(Y234051001)联合资助

摘　　要：利用橄榄石和熔体包裹体,结合全岩的方法对辽西地区早白垩世义县组黄半吉沟火山岩的成因进行了研究。黄半吉沟火山岩SiO_2=53.41%~53.74%,MgO=8.15%~8.23%,Mg#=~70(Mg#=mol Mg/(Mg+Fe2+)),为高镁安山岩;全岩在TAS图解上,落在玄武安山岩范围内,属于亚碱性系列;它们具有较高Ni(119×10-6~125×10-6)和高Cr(467×10-6~521×10-6),显示幔源岩浆特征;在微量元素组成上,黄半吉沟高镁安山岩Sr=920×10-6~930×10-6,Y=16.1×10-6~16.4×10-6,Sr/Y=57~58;在微量元素原始地幔标准化蛛网图上,黄半吉沟高镁安山岩显示轻重稀土分异,明显的Nb-Ta-Ti和弱的Zr-Hf负异常,Ba、Sr和Pb正异常,这些特征与大陆下地壳非常相似。熔体包裹体MgO为6.5%~9.7%,SiO_2为51%~53%,不符合典型高镁安山岩的定义;在TAS图解上它们落在玄武粗安岩内,属于碱性系列;MgO与其它主量元素成分呈明显或者弱的负相关关系,说明它们的成分主要受控于橄榄石结晶分离过程。黄半吉沟高镁安山岩的橄榄石Fo值为75~91;CaO含量为0.10%~0.18%,NiO为0.05%~0.41%,Fe/Mn比值为60~80。黄半吉沟高镁安山岩的全岩和熔体包裹体成分存在显著差异,如熔体包裹体具有更高的Al2O3和更低的SiO_2。结合全岩微量元素特征,我们认为黄半吉沟高镁安山岩在地壳深度的岩浆演化过程中加入了来自下地壳的酸性熔体,是壳幔相互作用的结果。全岩较低Ni高Mg#,熔体包裹体低CaO并落在CATS-Olivine-Quartz相图的热障碍边界线富硅一侧,以及橄榄石低Ca和陡倾的Fo-Ni关系,指示黄半吉沟高镁安山岩的幔源岩浆是来自以斜方辉石为主辉石岩的源区。我们认为广泛发育于辽西地区的早白垩世义县组高镁安山岩可能经历了壳幔相互作用,因而不能作为拆沉作用导致岩石圈大规模减薄的重要证据。Olivine-hosted melt inclusions and their hosts, together with the bulk rocks were used to investigate the petrogenesis of the Huangbanjigou volcanic rocks in the Early Cretaceous Yixian Formation, western Liaoning Province. The Huangbanjigou volcanic rocks show the features of high magnesium andesite, such as SiO2=53.41%~53.74%, MgO=8.15%~8.23%, Mg#=~70 （Mg#=mol Mg/（Mg＋Fe2＋））. They are sub-alkaline series, ploting in the field of basaltic andesite in the TAS diagram. They also exhibit the characteristics of the mantle attributions, such as moderately high Ni （119×10-6~125×10-6） and high Cr （467×10-6~521×10-6）. The Huangbanjigou high magnesium andesites have 920×10-6~930×10-6 Sr, 16.1×10-6~16.4×10-6 Y and 57~58 Sr/Y. In the mantle primitive-normalized spider diagram, the Huangbanjigou high magnesium andesites show fractionation from light to heavy rare earth elements, significant and slight negative anomalies of Nb-Ta-Ti and Zr-Hf, respectively, and positive anomalies of Ba-Sr-Pb; all these features resemble that of the continental lower crust. The olivine-hosted melt inclusions have 6.5%~9.7% MgO and 51%~53% SiO2, unlike those of the typical high magnesium andesite. They are alkaline series, falling in the field of basaltic trachyandesite in the TAS plot. There are significant or slight negative relationships between MgO and other major element oxides, pointing to the olivine-controlled fractionation. Olivine crystals of the Huangbanjigou high magnesium andesites have Fo=75~91, CaO=0.10%~0.18%, NiO=0.05%~0.41%, Fe/Mn=60~80. There are large compositional discrepancies between the bulk rocks and the melt inclusions of the Huangbanjigou high magnesium andesites, such as the melt inclusions with higher Al2O3 and lower SiO2. Together with their similar trace element features to those of the continental lower crust, we suggest that the Huangbanjigou high magnesium andesites is the product of the crust-mantle interaction; they must assimilate an acid silicate melt from the lower crust during

关 键 词：橄榄石 熔体包裹体 高镁安山岩 壳幔相互作用 辉石岩 辽西黄半吉沟 

分 类 号：P588.144[天文地球—岩石学]