医巫闾山变质核杂岩核部晚中生代花岗岩成因及地质意义
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P588.12+1;P588.3

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国家自然科学基金项目(41662014)


The genesis of the Late Mesozoic granitoids in the core of the Yiwulüshan metamorphic core complex and its geological significance
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    摘要:

    位于华北克拉通北缘的医巫闾山变质核杂岩是中生代东北亚大陆大规模伸展变形的一个代表。本文在系统收集该区已有数据的基础上,对医巫闾山变质核杂岩核部晚中生代花岗岩的主量元素、微量元素以及Sr-Nd同位素进行了测试分析和特征总结,进而讨论其成因及地质意义。研究结果显示,医巫闾山花岗岩主要为一套由黑云母二长花岗岩和花岗闪长岩等组成的杂岩体,总体上富硅(SiO2=61.17%~75.21%)、富碱(K2O+Na2O=7.34%~9.03%),呈准铝质-过铝质(A/CNK=0.96~1.08),属于高钾钙碱性,与I型花岗岩特征相一致;大部分花岗岩具有弱的负Eu异常(δEu=0.71~1.63),富集大离子亲石元素(Rb、Ba、Sr)和轻稀土元素,亏损高场强元素(Nb、Ta、Ti)和重稀土元素,高Sr (308×10-6~1 414×10-6,平均709×10-6),低Y (3.17×10-6~13.30×10-6,平均7.86×10-6)和Yb (0.45×10-6~1.32×10-6,平均0.78×10-6),具有埃达克质岩的特征;同位素分析结果显示,早期同侵位花岗岩具有变化较大的(87Sr/86Sr)i值(0.695 966~0.707 869)和较低的εNd (t)值(-21.72~-18.32),表明其物源为古老地壳,应是加厚下地壳在区域伸展减压背景下部分熔融的产物,晚期变形后侵位花岗岩的(87Sr/86Sr)i值为0.705 909~0.706 774,εNd (t)值为-20.60~-16.99,与晚中生代华北克拉通伸展减薄相关。

    Abstract:

    The Yiwulüshan metamorphic core complex (MCC) within the northern margin of the North China Craton is a typical representative of large-scale Mesozoic extensional deformation in Northeast Asia continent. Many studies including the fabric characteristics, shear-sense indicators, strain, kinematic vorticity and deformation age have been intensively conducted. However, some problems concerning geochemistry, isotopic characteristics and genesis of the granite within the core of this MCC remain unanswered. The granite of the core within the MCC is composed of biotite monzogranite and granodiorite. Based on previous research, together with the major elements,trace elements and Sr-Nd isotopic data, the paper presents the results of the data and discusses the genesis and geological significance. According to the results obtained, the granite of Yiwulüshan MCC granite is characterized by high silicon and alkali content (SiO2 =61.17%~75.21%, K2O+ Na2O=7.34%~9.03%), thus belonging to metaluminous and peraluminous (A/CNK=0.96~1.08) and can be assigned to genetic type of high-k-calc-alkaline series, suggesting characteristics of I type granites; most granites have weak negative Eu anomaly (δEu=0.71~1.63), enrichment of large ion lithophile elements (e. g., Rb, Ba and Sr) and light rare earth elements, depletion of high field strength elements (e. g., Nb,Ta and Ti) and heavy rare earth elements, high Sr (308×10-6~1 414×10-6, averaging 709×10-6), low Y (3.17×10-6~13.30×10-6, averaging 7.86×10-6) and Yb (0.45×10-6~1.32×10-6, averaging 0.78×10-6), showing the characteristics of adakitic rocks; isotopic data show that the early co-emplacement granites have a wide range of (87Sr/86Sr)i values (0.695 966 ~ 0.707 869) and a lower εNd(t) values (-21.72~-18.32) and were derived from ancient crust and attributed to the partial melting of the thickened lower crust under the background of regional extension; the isotopic data of the later post-emplacement granites range from 0.705 909 to 0.706 774, and have negative εNd(t) values (-20.60~-16.99), which indicates that the post-emplacement granite resulted from the North China Craton extension thinning during the Late Mesozoic.

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梁键婷,欧阳志侠,张莹,李建波,曾涛,周智超,2021,医巫闾山变质核杂岩核部晚中生代花岗岩成因及地质意义[J].岩石矿物学杂志,40(4):671~686.

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  • 收稿日期:2020-04-22
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  • 在线发布日期: 2021-07-16
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