【摘要】 北山早古生代火山岩发育,其中尤以志留纪火山岩出露最为广泛。本文选择对志留纪公婆泉群火山岩的地球化学特征以及Sr-Nd同位素进行系统研究。结果显示:志留纪公婆泉群火山岩除东七一山矿南样品主要落入钙碱系列外,其余各处大多数属拉斑系列。公婆泉群火山岩均表现为轻稀土富集、重稀土亏损型,伊哈托里火山岩相对于东七一山矿南、大狐狸山、四顶黑山以及双沟山北等地的火山岩而言,轻重稀土分馏程度较低。公婆泉群火山岩的大离子亲石元素（LILE）K、Rb、Ba等显示一定程度的富集,高场强元素（HFSE）如Ta、Nb、Ti等相对亏损（尤其是伊哈托里火山岩）,显示了与俯冲有关的火山岩特征。样品的εNd（t）值较高且集中,均为正值,而(⁸⁷Sr/⁸⁶Sr)t值则较低（0.70340⁰.70519）,部分样品Sr同位素比值明显增高的主要原因是源区中俯冲洋壳变质脱水流体的加入。研究表明北山志留纪公婆泉群火山岩的岩浆源区应为受俯冲洋壳板片沉积物流体及板片熔体双重交代的楔形亏损地幔源区。结合区域构造演化分析,认为北山北部伊哈托里火山岩与北山中部火山岩的构造环境存在明显差异,前者形成于岛弧环境,后者则形成于大陆边缘弧。更多还原

【Abstract】 Geochemistry,Sr-Nd isotopic compositions of the volcanic rocks have been studied in this paper.The samples collected from Silurian Gongpoquan Group mainly belong to tholeiite series,except Dongqiyishan samples which belong to calc-alkaline series.The volcanic rocks are chatacterized by enrichment in LREE and LILE（K,Rb and Ba）,and have negative anomaly in Nb,Ta,Ti（especially Yihatuoli）,which suggest a characteristic of volcanic rocks related to subduction.PositiveεNd（t）and lower(⁸⁷Sr/⁸⁶Sr)tvalues（0.70340⁰.70519）suggest that both fluid-sediments and silicate melts derived from subducted oceanic slab are involved in the genesis of volcanic rocks in Gongpoquan Group.The tectonic settings of volcanic rocks collected from Yihatuoli are different from that of the central Beishan in Gansu,the former were formed in island arc setting and the latter were formed in the setting of a continental marginal arc.更多还原