鲁西地块晚中生代中—基性岩地球化学和Sr-Nd-Pb同位素组成特征  

Geochemistry and Sr-Nd-Pb Isotopic Composition of Late Mesozoic Intermediate-basic Rock in Western Shandong Block

作　　者：宁培松[1,2] 龙群[1,2] 程婷[1,2] 胡昭平[1,2] 陈福坤[1,2] 

机构地区：[1]中国科学技术大学地球和空间科学学院,安徽合肥230026 [2]中国科学院壳幔物质与环境重点实验室,安徽合肥230026

出　　处：《地球科学与环境学报》2013年第4期62-76,共15页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(40973042;41090372)

摘　　要：报道了鲁西地块西北部晚中生代中—基性岩锆石U-Pb年龄、全岩主微量元素含量和Sr-Nd-Pb同位素组成特征。样品分别采集自济南、邹平、泰安和章丘4个地区,这些中—基性岩富集大离子亲石元素,亏损高场强元素,轻、重稀土元素分异显著,Sr含量高,Y、Yb含量低,具有岛弧岩石的地球化学特征。锆石U-Pb定年结果显示,章丘和泰安中—基性岩形成年龄为124;128 Ma。4个地区中—基性岩表现出相似的、相对富集的Sr-Nd同位素组成,其二阶段Nd模式年龄集中在1.85 Ga。在Pb同位素组成上,邹平中—基性岩类似于洋脊玄武岩特征,而其他3个地区岩石有明显的类似于古老地壳物质特征,暗示岩浆源自受过华北陆块古老的地壳物质改造的富集地幔源区。这些岩石可能是在晚中生代太平洋板块向华北陆块俯冲作用过程中,古老的华北地壳物质重新循环进入地幔,产生富集型熔/流体交代上覆的华北岩石圈地幔,富集型地幔橄榄岩发生部分熔融形成鲁西地块晚中生代中—基性岩侵入体。Zircon U-Pb ages, major and trace element contents and Sr-Nd-Pb isotopic composition of whole-rocks from Late Mesozoic intermediate-basic rocks exposed in the northwestern part of western Shandong block were measured. The samples were collected in Jinan, Zouping, Tai＇an and Zhangqiu areas. The results show that geochemical characteristics of these intermediate-basic rocks, which are enriched in large-ion lithosphile elements, depleted in highqield strength elements, and have strong fractionation in light and heavy rare-earth elements, high contents of Sr and low contents of Y and Yb, are similar to that of arc magmatic rocks; according to the results of zircon U-Pb dating, the formation ages of intermediate-basic rocks in Zhangqiu and Tai＇an areas are 124-128 Ma; Sr-Nd isotopic compositions of intermediate-basic rocks collected in the four areas are similar and relatively enriched, and the two-stage Nd model ages focus on 1.85 Ga;Pb isotopic composition of intermediate-basic rock in Zouping area is similar with that of MORB, whereas the rocks in other three areas are significantly similar with ancient crustal material, so that the characteristics probably indicate that the magmas are derived from enriched mantle source transformed by ancient crustal materials of North China block. Possible tectonic scenario for the magma formation of intermediate-basic rock is that during the subduction of Late Mesozoic Pacific plate beneath North China block, the recycle of ancient crustal material of North China block is deep into mantle, and the metasomatism of enriched melting/fluid and overlying North China lithospheric mantle happens, and then partial melting of peridotite from the enriched mantle produces intrusion of Late Mesozoic intermediate-basic rocks in western Shandong block.

关 键 词：地球化学 Sr—Nd—Pb同位素 晚中生代 中-基性岩 锆石U—Pb年龄 岩石成因 鲁西地块 

分 类 号：P584[天文地球—岩石学] P588.12[天文地球—地质学]