| 冀西北姚家庄超镁铁岩-正长岩杂岩体中辉石的环带特征及意义 |
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| 引用本文： | 刘鑫,汤艳杰.冀西北姚家庄超镁铁岩-正长岩杂岩体中辉石的环带特征及意义[J].岩石学报,2018,34(11):3315-3326. |
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| 作者姓名： | 刘鑫 汤艳杰 |
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| 作者单位： | 中国科学院地质与地球物理研究所岩石圈演化国家重点实验室, 北京 100029;中国科学院大学, 北京 100049,中国科学院地质与地球物理研究所岩石圈演化国家重点实验室, 北京 100029 |
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| 基金项目： | 本文受国家重点研发计划"深地资源勘查开采"重点专项（2016YFC0600109）和国家自然科学基金项目（41725014）联合资助. |
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| 摘 要： | 冀西北姚家庄存在一套晚三叠世的超镁铁岩-正长岩杂岩体,岩体内发育具有环带特征的单斜辉石。辉石的环带有两种:简单环带和复杂环带。简单环带一般为正环带,辉石核部的MgO和Cr2O3含量高,Si O2、Fe O和Na2O含量低;边部的主要氧化物含量与核部刚好相反。简单正环带可以分为两类,其中核边接触带平滑、由核到边化学成分具有渐变特征的正环带辉石可能是岩浆在分离结晶或地壳混染过程中形成。而核边接触带有熔蚀结构、由核到边化学成分突变的正环带辉石可能是早期结晶的辉石颗粒受到晚期低镁岩浆的溶蚀改造而成的。复杂环带具有核-幔-边结构,其中,核部低镁高铁、幔部高镁低铁、边部与核部相似,但其Mg#更低,这些特征暗示了岩浆混合作用的存在,形成辉石核部的母岩浆可能来自富集的岩石圈地幔,幔部高Mg#的特征指示了软流圈地幔物质的贡献,其边部低Mg#的特征则指示了地壳物质的加入。具有韵律环带的复杂辉石是在岩浆多期侵入的过程中形成的。辉石环带的组成特征表明,姚家庄杂岩体是由岩浆多期侵位形成的,后期侵入的岩浆与前期就位的岩浆不断反应,形成了具有多种不同环带特征的辉石,并最终形成了空间上由外到内依次为辉石岩、辉石正长岩和正长岩的环状杂岩体。结合前人的研究成果,推测形成姚家庄岩体的岩浆主要来源于富集的岩石圈地幔,并由少量地壳组分和软流圈物质的贡献。
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| 关 键 词： | 冀西北 晚三叠世 成分环带 单斜辉石 岩浆混合 |
| 收稿时间： | 2018/2/2 0:00:00 |
| 修稿时间： | 2018/5/5 0:00:00 |
The characteristics and implication of the zonation in clinopyroxene phenocrysts from the Yaojiazhuang ultramafic-syenitic complex, northwestern Hebei Province |
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| LIU Xin and TANG YanJie.The characteristics and implication of the zonation in clinopyroxene phenocrysts from the Yaojiazhuang ultramafic-syenitic complex, northwestern Hebei Province[J].Acta Petrologica Sinica,2018,34(11):3315-3326. |
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| Authors: | LIU Xin and TANG YanJie |
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| Institution: | State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;University of Chinese Academy of Sciences, Beijing 100049, China and State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | Ultramafic-syenitic complex in the Yaojiazhuang, northwestern Hebei Province, contains abundant clinopyroxene phenocrysts with compositional zonations, which can be divided into two kind of patterns:simple zoning and complex zoning. All the simple zonings are in normal pattern. The cores of the grains show high contents of the Al2O3, FeO, Na2O and low contents of MgO and Cr2O3, while the rims of zonation are opposite to the cores. Two different kind of simple zonations are recognized. The chemical composition of some clinopyroxene phenocrysts changed gradually from the core to the rim of grains, which could be crystallized from the host magma of varying compositions caused by the assimilation of crustal materials or crystal fractionation. Whereas, other phenocrysts show compositional variation in an abrupt change from core to rim of grains with corrosion texture, possibly caused by the modification of early-crystallized clinopyroxenes by later magmas. The clinopyroxene phenocrysts with complex zoning have core-mantle-rim texture. The core of zonation is relatively low in Mg#, but high in FeO content, while the mantle of zonation is clearly high in Mg# and low in FeO content. The rim of zonation is lower in Mg# values than the core. These observations indicate the mixing of different magmas. The core of zonation could crystallize from the host magma derived from metasomatized lithospheric mantle. The high-Mg# mantle of zonation indicates the contribution of the asthenospheric melt, and the low-Mg# rim of clinopyroxene phenocrysts could be resulted from the addition of crustal materials. In conclusion, the zonations of clinopyroxene phenocrysts suggest that the Yaojiazhuang complex could be formed by multiple stage magmatic intrusion. The later magmas continuously intruded and reacted with the former host magma. As a result, abundant clinopyroxene phenocrysts with compositional zonations formed, and the pyroxenite, pyroxenite-syenite, and syenite occurred in sequence. Combined with the previous studies, the parent magma of Yaojiazhuang complex could originate from the enriched lithospheric mantle, with minor contributions of asthenosphere and crustal materials. |
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| Keywords: | Northwestern Hebei Province Late Triassic Compositional zonation Clinopyroxene Magma mixing |
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