| 华北克拉通北缘早二叠世堆晶岩及其构造意义 |
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| 引用本文： | 邵济安,田伟,张吉衡.华北克拉通北缘早二叠世堆晶岩及其构造意义[J].地球科学,2015,40(9):1441-1457. |
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| 作者姓名： | 邵济安 田伟 张吉衡 |
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| 作者单位： | 1.北京大学造山带与地壳演化教育部重点实验室, 北京 100871 |
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| 基金项目： | 国家自然科学基金项目41172196 |
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| 摘 要： | 目前对华北克拉通北缘早二叠世基性-超基性岩成因有不同认识, 其中, 一种流行的观点是它们与"安第斯型大陆边缘"的活动有关.通过对冀东地区堆晶岩的研究对这一观点进行了讨论.华北克拉通北缘断续分布了受丰宁-隆化岩石圈断裂控制的早二叠世基性-超基性堆晶岩, 堆晶岩的SHRIMP锆石U-Pb年龄为280~300 Ma.通过岩相学的研究, 确认这是一套由纯橄岩、橄辉岩、辉石岩、角闪岩、辉长岩、闪长岩、斜长岩等不同岩性组成的堆晶岩, 进一步可分为层状堆晶岩和环状堆晶岩, 它们有着明显的堆晶结构.矿物学研究显示堆晶岩中角闪石、辉石、金云母等均具有高镁、高铬的幔源组分特征.不同组分堆晶岩的Sr/Ba比值不随熔融程度变化, 具有分离结晶的趋势.相近的稀土配分形式和过渡族元素组成显示了它们的同源性.从本区晚古生代和早中生代堆晶岩的对比中, 结果表明早二叠世这期堆晶岩具有初始裂谷岩浆的特征, 它传递了华北克拉通陆壳从稳定向活动转化的最早信息.从区域角度看, 这期活动有着更大范围的深部动力学背景.
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| 关 键 词： | 华北克拉通北缘 早二叠世 堆晶岩 壳幔过渡带 伸展背景 构造 |
| 收稿时间： | 2015-05-18 |
Early Permian Cumulates in Northern Margin of North China Craton and Their Tectonic Significances |
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| Abstract: | Understanding about genesis of the Early Permian basic-ultrabasic rocks in the northern margin of North China craton are varied, with one of the influential viewpoints suggesting that they are related with activities of "Andes-type continental margin", which is discussed in this paper based on researches of the cumulates in east Hebei Province. Early Permian basic-ultrabasic cumulates controlled by Fengning-Longhua lithospheric faults are distributed discontinuously in the northern margin of North China craton. The SHRIMP Zircon U-Pb ages from cumulates are 280-300 Ma. Petrographic studies confirm that the complexes consist of a suite of cumulates including dunite, pyroxenite, amphibolite, gabbro, diorite, anorthosite, and so on, which in turn can be further divided into layered and circular ones, both with obvious cumulate texture. Mineralogical studies show that hornblende, pyroxene, and phlogolite in cumulates all are characterized by mantle sourced components of high Mg and high Cr. Sr/Ba ratio of cumulates with different components does not change with their melting degrees, showing that cumulates possess a fractional crystallization trend. Similar REE patterns and transition group elements reveal their consanguinity. Comparison of cumulates of the Late Paleozoic with those of the Early Mesozoic from the concerned area indicates that these Early Permian cumulates have characteristics of an initial-rift magma, which offers the earliest evidence of the transformation from the stable to the active one of continental crust of North China craton. Viewed from broader regions, activities of this period in this area are driven by deeper geodynamics. |
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