北山地区辉长岩类的地球化学特征及其深部信息  

Geochemical Characteristics of Gabbros in Beishan Area and Their Deep Setting Implications

作　　者：范育新[1] 白云来 陈发虎[1] 

机构地区：[1]兰州大学西部环境教育部重点实验室,甘肃兰州730000 [2]西北石油地质研究所,甘肃兰州730000

出　　处：《地球学报》2005年第B09期61-66,共6页Acta Geoscientica Sinica

基　　金：本文由科技部国际合作重点项目（编号：2002CB714004）资助.

摘　　要：据稀土元素配分曲线可将北山辉长岩类分为3组，第1组∑REE较大，LREE富集且发生了较大程度的分馏；第2组轻稀土未发生明显的分馏，曲线较为平坦，∑REE较低；第3组LREE亏损，∑REE较低。Nb亏损，指示北山辉长岩类形成于俯冲相关的构造环境，εNd（0）εNd（t）均大于0，指示来源于亏损型地幔源区。本文认为北山地区辉长岩产出于活动大陆边缘的不同次一级构造环境；原始岩浆在上升途中遭受了陆壳混染；Sm-Nd模式年龄不代表岩石的形成年龄。Being the main type of mafic and ultramafic rocks in Beishan area, the gabbros can be divided into three groups according to the rare earth element patterns. The first group has high concentration of total REE, with the enrichment and obvious fractionation of LREE. The second group with the lower total REE content than the first group has a smooth REE pattern. The third group is slightly depleted in LREE and has the low total REE concentration. The gabbros from Beishan area are obviously enriched in LILE such as Cs, U and Pb and depleted in HFSE like Nb （some samples are depleted in Ta, Ti and Zr）, which implies that gabbros are somewhat subduction-related. Both εNd（0） and εNd（t） are positive, suggesting that the primary magma was derived from sources of depleted mantle. The obvious linear correlation between ratios of Th/Sm and Th/Nb shows continental hybrid processes. Geochemical characteristics indicate that gabbros were formed at different sub-settings along the active continental margin. The primary magma assimilated the continental wall rock during its migration to the present site, which changed the composition of the primary magma. The gabbros resulted from the evolution of the hybrid magma. The Sm-Nd model age of the depleted mantle （tDM） can not represent the chronological age of the gabbros.

关 键 词：微量元素 构造环境 辉长岩类 北山地区 地球化学特征 深部信息 岩类 活动大陆边缘 ND模式年龄 REE 

分 类 号：P618.51[天文地球—矿床学] P588.2[天文地球—地质学]