| 河北矾山杂岩体中单斜辉石的研究 |
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| 引用本文： | 牛晓露,陈斌,马旭.河北矾山杂岩体中单斜辉石的研究[J].岩石学报,2009,25(2):359-373. |
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| 作者姓名： | 牛晓露 陈斌 马旭 |
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| 作者单位： | 造山带及地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京,100871 |
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| 基金项目： | 国家科技部973项目（2006CB403501）和国家自然科学基金（40625005） |
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| 摘 要： | 河北矾山杂岩体属于二氧化硅不饱和的超钾质碱性-过碱性岩浆系列，由单斜辉石岩、辉石正长岩和碱长正长岩等不同类型岩石组成。各类型岩石主要组成矿物为单斜辉石、黑云母、石榴石和正长石。本文利用电子探针对单斜辉石进行了详细研究，发现所有单斜辉石属于高钙透辉石，随着岩浆的演化，主要表现为Fe2+对Mg2+的替代关系，结晶趋势为透辉石→钙铁辉石，这揭示矾山杂岩体岩浆体系的特点是高温、中等大小的氧逸度、贫硅、富碱（尤其是钾）。辉石中的AlIV含量取决于岩浆的硅饱和度，硅越不饱和，AlIV含量越高；AlVI含量则与体系中的Al含量呈正相关关系。由Al对Si的替代引起的电荷不平衡主要由八面体位置的Fe3+来补偿，其次为少量的Ti4+和更少量的Al3+。体系中的Ti含量与体系的温度呈正相关关系，而Na含量则与辉石中的Ti和Fe3+含量成正相关关系。不同类型岩石中单斜辉石从核部到边部随着Mg#的降低，Al、Ti含量呈现不同的演化趋势，这是因为它们于岩浆演化的不同阶段开始结晶，经历了不同的岩浆演化史。碱性岩中高钙辉石的出现和成分环带的普遍发育是由岩浆的贫硅富钾特征决定的。单斜辉石的成分不仅受控于结晶时的温度、压力条件，也受控于岩浆的总成分及其变异。
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| 关 键 词： | 单斜辉石 岩浆演化 过钾质碱性岩 矾山杂岩体 河北 |
| 收稿时间： | 2008/12/5 0:00:00 |
| 修稿时间： | 2008/12/13 0:00:00 |
Clinopyroxenes from the Fanshan pluton, Hebei |
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| NIU XiaoLu,CHEN Bin and MA Xu.Clinopyroxenes from the Fanshan pluton, Hebei[J].Acta Petrologica Sinica,2009,25(2):359-373. |
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| Authors: | NIU XiaoLu CHEN Bin and MA Xu |
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| Institution: | Key Laboratory of Orogenic Belts and Crustal Evolution; School of Earth and Space Sciences, Peking University, Beijing 100871, China;Key Laboratory of Orogenic Belts and Crustal Evolution; School of Earth and Space Sciences, Peking University, Beijing 100871, China;Key Laboratory of Orogenic Belts and Crustal Evolution; School of Earth and Space Sciences, Peking University, Beijing 100871, China |
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| Abstract: | The Fanshan complex from northern Hebei is an ultrapotassic alkaline-peralkaline pluton (silica-undersaturated), including clinopyroxenites, pyroxene-bearing syenites and alkali feldspar syenite. All the rocks mainly consist of clinopyroxenes, biotites, garnets and orthoclases. The clinopyroxenes have been studied in detail using microprobe in this paper. All of them are diopside belonging to Ca-rich clinopyroxene. Crystallization trend from diopside to hedenbergite, related to the replacement of Mg2+ by Fe2+ during magma evolution, is recognized from these clinopyroxexes. The features of clinopyroxenes above reflect that the magma system of the Fanshan pluton is characterized by high temperature, moderate oxygen fugacity, silica-undersaturated and high alkalis (especially potassium). The AlIV contents in clinopyroxene from the Fanshan pluton depend on SiO2 concentrations in magma system; AlIV contents increase with decreasing SiO2. AlVI contents are mainly controlled by Al concentrations in magma system. The excess of the negative charge caused by the Si-Al substitution is mainly compensated by the entrance of Fe3+ in the octahedral position, then by minor Ti4+ and much lesser Al3+. The Ti contents of clinopyroxenes are positively related to the temperature of the magma system; also, Na contents show positive relationship with the contents of Ti and Fe3+ of clinopyroxenes. The evolution trends of the Al and Ti contents from core to rim with decreasing Mg# are different in individual clinopyroxene grains from rocks of different types, and this is because the clinopyroxenes crystallized at different stages of magma evolution. That is, different clinopyroxene grains experienced different magma evolution history. The appearance of Ca-rich clinopyroxenes and the development of zoned clinopyroxenes in alkaline rocks are all caused by the characters of impoverished silica and enriched potassium of magma system. Clinopyroxene compositions are controlled not only by the P-T conditions when it crystallizes, but also the total magma compositions and its variations. |
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| Keywords: | Clinopyroxene Magma evolution Ultrapotassic alkaline rocks Fanshan pluton Hebei |
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