| 冀东-辽西中-晚三叠世柏杖子花岗质侵入岩地球化学、Sr-Nd-Hf同位素特征及岩石成因 |
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| 引用本文： | 熊乐,石文杰,李欢,田宁,陈冲,周红智,赵少卿,李鹏宇.冀东-辽西中-晚三叠世柏杖子花岗质侵入岩地球化学、Sr-Nd-Hf同位素特征及岩石成因[J].地球科学,2017,42(2):207-222. |
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| 作者姓名： | 熊乐 石文杰 李欢 田宁 陈冲 周红智 赵少卿 李鹏宇 |
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| 作者单位： | 1.中国地质大学资源学院，湖北武汉 430074 |
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| 基金项目： | 中国黄金集团地质科研项目2012M521493 |
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| 摘 要： | 关于冀东-辽西中-晚三叠世具有埃达克质岩石特征的花岗质岩石的源区性质，存在较大争议，且以往对位于其北东向隆起区内的柏杖子岩体的成因研究程度低.对柏杖子花岗质侵入岩进行了系统的年代学、地球化学、Sr-Nd-Hf同位素研究，结果显示:柏杖子岩体结晶年龄为233±3 Ma，岩石具有低MgO、Mg#和Co、Ni、Cr含量；富集大离子亲石元素，亏损高场强元素，显示明显的Pb、Th正异常和Nb、Ta、Ti、P负异常；轻、重稀土元素分馏明显；87Sr/86Sr (t) 为0.704 45~0.705 24，εNd(t) 值为-7.3~-1.7；锆石εHf(t) 为-13.4~-5.9.综合分析认为，高Sr/Y比值和低Y含量的柏杖子岩体属于华北克拉通正常厚度镁铁质下地壳熔融的产物，岩石高Sr/Y比值、低Y含量和Nb-Ta负异常特征为继承的华北克拉通下地壳内在性质，并具有与太古宙-古元古代TTG岩石系列相一致的Nb-Ta解耦特征，表明柏杖子岩体源区物质有TTG岩石的贡献；岩石Sr-Nd-Hf同位素组成和低相容元素含量特征同样表明岩浆来源于受改造的下地壳熔融.早中生代玄武岩底侵过程中幔源组分的加入对华北克拉通下地壳形成改造，同时提供热源诱发下地壳物质熔融，形成的熔体向浅表侵位，经历一定程度的斜长石分离结晶，并最终形成柏杖子岩体.
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| 关 键 词： | 柏杖子花岗质侵入岩 冀东-辽西 三叠纪 岩浆源区 地质年代学 地球化学 |
| 收稿时间： | 2016-07-28 |
Geochemistry,Sr-Nd-Hf Isotopes and Petrogenesis of Mid-Late Triassic Baizhangzi Granitic Intrusive Rocks in Eastern Hebei-Western Liaoning Province |
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| Abstract: | The source of the Mid-Late Triassic adakitic rocks remains controversial in the eastern Hebei-western Liaoning Province in recent years, and there is a lack of petrogenesis studies on the Baizhangzi granitic rocks within this NE-striking uplift. Zircon U-Pb and Hf isotope data, whole rock major and trace element and Sr, Nd isotope data are presented for the Baizhangzi graniticintrusive rocks in this paper.Zircon U-Pb datingyields a weighted mean age of 233±3 Ma. The granitic rocks are featured with the high contentof MgO and Mg#, and low content of Cr, Co, Ni. The granitic intrusive rocks are enriched in large-ion lithophile elements, depleted in high-field-strength elements (e.g. Nb, Ta, Ti, P), and display strong positive Pb, Th anomalies and negative Nb, Ta, Ti, P anomalies. Rare earth elements (REE) display right-dipping chondrite-normalized REE patterns, indicating significant fractionation between light REE and heavy REE. The initial 87Sr/86Sr ratios and εNd(t) values vary from 0.704 45 to 0.705 24 and -7.3 to -1.7, respectively. The εHf(t) values of zircons vary from -13.4 to -5.9. It is concluded that the Baizhangzi granitic rocks were derived from partial melting of mafic lower continental crust of the NCC. The high Sr/Y, low Y and negative Nb-Ta anomalies are intrinsic characteristics of the lower continental crust. The Baizhangzi granitic rocks have decoupled Nb-Ta characteristics similar to the Archean-Paleoproterozoic TTG suites, which indicates that the Archean-Paleoproterozoic TTG rocks might have been involved in the magma source. The nonradiogenic Sr, scattered Nd-Hf isotopic compositions and low compatible trace element contents also suggest that the granitic rocks were derived from modified lower continental crust. The mafic lower continental crust has experienced modification by basaltic underplating during the Early Mesozoic, which led to formation of some juvenile crust materials. At the same time, melts produced by melting of the lower continental crust induced by basaltic underplating experienced fractional crystallization of plagioclase to some extent and intruded into the supercrust. |
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