| 华北克拉通岩石圈减薄机制: 来自山东白垩纪基性-中基性岩浆岩Re-Os同位素地球化学特征的制约 |
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| 引用本文： | 杨红梅,凌文黎,张军波,段瑞春,高永娟,邱啸飞,卢山松.华北克拉通岩石圈减薄机制: 来自山东白垩纪基性-中基性岩浆岩Re-Os同位素地球化学特征的制约[J].地球科学,2013,38(3):529-540. |
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| 作者姓名： | 杨红梅 凌文黎 张军波 段瑞春 高永娟 邱啸飞 卢山松 |
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| 作者单位： | 1.国土资源部武汉地质矿产研究所同位素地球化学研究室, 湖北武汉 430223 |
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| 基金项目： | 国家自然科学基金委创新研究群体科学基金，国家自然科学基金重点项目，教育部和国家外国专家局高等学校学科创新引智计划，地质过程与矿产资源国家重点实验室开放基金，国土资源部公益性行业科研专项，中国地质调查局地质调查评价专项 |
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| 摘 要： | 对华北山东地区不同构造单元中生代白垩纪基性-中基性岩浆岩进行了系统的Re-Os同位素研究.侵入岩样品采自鲁西济南岩体、鲁中沂南岩体和胶东的观水岩墙群, 火山岩样品采自鲁西蒙阴、费县、方城青山群和鲁中安丘青山群.所有样品均以低Re(0.076×10-9~0.711×10-9)和Os(0.006×10-9~1.030×10-9)含量以及高放射成因Os同位素比值为特征, 其相应的初始187Os/188Os比值和γOs(t)值分别为0.131 6~0.529 1和4.30~319.00(安丘粗面安山岩分别高达1.463和1 060.000), 并具有较大变化范围(0.125~2.090 Ga)的Os同位素模式年龄.在Os-Nd和Os-Sr同位素关系图上, 这些样品分布于典型的岩石圈地幔与地壳端元组成之间, 显示壳-幔源岩浆混合特征.然而, 除1件观水岩体(MGS0610)和费县玄武岩之外, 各地质单元样品之间或所有的中生代岩浆岩作为整体, 样品的γOs(t)与(La/Ta)N和(Th/Nb)N比值间缺乏明显的相关关系, 说明样品的混源Os同位素并非来自岩浆作用过程中的地壳围岩混染.区内基性岩浆岩Os同位素模式年龄TMA明显小于古生代地幔橄榄岩包体的Re亏损模式年龄(TRD), 可能为地幔条件下源岩与再循环地壳物质发生交代作用后Re/Os比值升高所致.蒙阴高镁安山岩和沂南闪长岩在Yb-Re/Yb图解中大致位于中生代辉石岩包体与地壳端元之间, 也指示了下地壳拆沉后产生的熔体与地幔岩石可能发生了交代作用.蒙阴安山岩MMY-12(SiO2=56.4%)具有古老壳源特征的Os同位素模式年龄(2.090 Ga)、高Mg#(64.6)和高Os含量(0.089×10-9), 为这一解释提供了有力的佐证.
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| 关 键 词： | 华北克拉通 山东 中生代基性-中基性岩浆岩 Re-Os同位素 岩石圈减薄机制 地球化学 |
| 收稿时间： | 2012-04-17 |
The Lithospheric Thinning Mechanism of North China Craton: Re-Os Isotopic Geochemistry Constraint from the Cretaceous Basic to Intermediate Basic Igneous Rocks in Shandong Province |
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| YANG Hong-mei,LING Wen-li,ZHANG Jun-bo,DUAN Rui-chun,GAO Yong-juan,QIU Xiao-fei,LU Shan-song.The Lithospheric Thinning Mechanism of North China Craton: Re-Os Isotopic Geochemistry Constraint from the Cretaceous Basic to Intermediate Basic Igneous Rocks in Shandong Province[J].Earth Science-Journal of China University of Geosciences,2013,38(3):529-540. |
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| Authors: | YANG Hong-mei LING Wen-li ZHANG Jun-bo DUAN Rui-chun GAO Yong-juan QIU Xiao-fei LU Shan-song |
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| Institution: | 1.Isotope Geochemistry Lab.,Wuhan Institute of Geology and Mineral Resources,Ministry of Land and Resources,Wuhan 430223,China 2.State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China |
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| Abstract: | A Re-Os isotopic study of Mesozoic igneous basic to intermediate basic rocks from the western-, eastern- and Yishu fault belt tectonic units in Shandong province, North China Craton (NCC), is carried out. The samples consists of 13 intrusive rocks from the Jinan, Yinan plutons and Guanshui dykes, and 13 volcanic rocks from the Anqiu, Mengyin, Feixian and Fangcheng volcanic successions. Most samples have relatively low Re (0.076×10-9-0.711×10-9) and Os (0.006×10-9-1.030×10-9) contents and high radiogenic 187Os/188Os ratios, with corresponding initial 187Os/188Os ratio of 0.131 6-0.529 1 and γOs(t) of 4.30-319.00, except for rock MAQ0609 of the Anqiu trachyandesite with initial 187Os/188Os ratio of 1.463 and γOs(t) of 1 060.000. The igneous rocks show a wide range of 0.125 to 2.090 Ga in Os isotope modal age (TMA). On the γOs(t) vs. εNd(t) and (87Sr/86Sr)i vs. γOs(t) diagrams, these rocks are positioned between the lithospheric mantle and crust fields, indicative of a crust-mantle interaction-related origin. All but one Guanshui gabbro (MGS0610) and Feixian basalts of the samples display no clear positive correlation between γOs(t) and (La/Ta)N or (Th/Nb)N, which suggests that the role of crustal assimilation or contamination during the magma ascending was insignificant. Compared with the Paleozoic mantle xenoliths, these mantle-derived rocks have evidently younger Os modal ages, higher Re/Os and 187Os/188Os ratios. These crustal signs are likely to have been resulted from interactions of partial melts derived from delaminated lower crust rocks with ambient mantle under an upper mantle depth. Besides, on the Re/Yb vs. Yb diagram, samples of the Mengyin andesites and Yinan diorites are plotted between the Mesozoic pyroxene xenoliths and crust components, which may be best explained by mantle source rocks metasomatized by partial melts of delaminated eclogitic lower crust. Furthermore, a Mengyin andesite MMY-12 (SiO2=56.4%) has a modal age as old as 2.090 Ga, and high Mg# (64.6) and Os content (0.089×10-9), which provides an additional evidence for lithospheric thinning-related interaction between the delaminated lower crust and the convecting upper mantle. |
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