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| 胶北荆山群富铝岩系石榴石扩散环带特征及其成因指示意义 | |
| 引用本文： | 周喜文,魏春景,董永胜,卢良兆.胶北荆山群富铝岩系石榴石扩散环带特征及其成因指示意义[J].岩石学报,2003,19(4):752-760. |
| 作者姓名： | 周喜文 魏春景 董永胜 卢良兆 |
| 作者单位： | 1. 北京大学地球与空间科学学院,北京,100871;吉林大学地球科学学院,长春,130061 2. 北京大学地球与空间科学学院,北京,100871 3. 吉林大学地球科学学院,长春,130061 |
| 基金项目： | 国家自然科学基金项目(编号:40172031,40142006)资助. |
| 摘 要： | 通过详细的微区成分测定，发现胶北荆山群富铝岩系中石榴石普遍发育扩散环带，但扩散环带的发育程度及样式很不均匀，明显受与其相邻矿物的控制。与黑云母接触时，石榴石晶体边部的镁含量最低，环带最为发育，与堇青石接触时次之，与长英质矿物接触时则环带发育较弱或不发育。这种特征的石榴石扩散环带样式与传统认识有很大差异，反映降温过程中石榴石与黑云母等镁铁矿物之间的Fe-Mg交换作用主要是通过彼此接触的界面来实现，粒间流体对组分的传输作用有限。但是当岩石中黑云母大量存在而石榴石含量又较低时，由于体系水活度增高，粒间流体也会传输一定的Fe、Mg组分，导致与长英质矿物相邻的石榴石晶体边部发育微弱的扩散环带。通过分析，确定粒径大于1500斗m的石榴石晶体核部可以保存变质峰期的平衡成分，基质中远离石榴石等镁铁矿物处于长英质矿物之间的大颗粒黑云母颗粒核部也基本可以保存变质峰期的平衡成分。 |
| 关 键 词： | 石榴石扩散环带 粒间流体 变质峰期成分 富铝岩系 胶北荆山群 |
| 文章编号： | 1000-0569/2003/019(04)-0752-60 |
| 修稿时间： | 2002年12月10 |
Characteristics and genetic implications of diffusion zoning in garnet from Al-rich rock series of the Jingshan group in north Jiaodong |
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| ZHOU XiWen,WEI Chunjing,DONG YongSheng and LU LiangZhao School of Earth and Space Sciences,Peking University,Beijing,China College of Earth Sciences,Jilin University,Changchun,China.Characteristics and genetic implications of diffusion zoning in garnet from Al-rich rock series of the Jingshan group in north Jiaodong[J].Acta Petrologica Sinica,2003,19(4):752-760. | |
| Authors: | ZHOU XiWen WEI Chunjing DONG YongSheng and LU LiangZhao School of Earth and Space Sciences Peking University Beijing China College of Earth Sciences Jilin University Changchun China |
| Abstract: | The detailed EPMA analysis indicates that the diffusion zoning is ubiquitous in garnets from Al-rich rock series of the Jingshan group in northern Jiaodong. However, the intensity and pattern of the garnet zoning are rather different. The rim of garnet has the lowest Mg content and shows a well-developed diffusion zoning when contacting biotite, a slightly higher Mg content and less-developed diffusion zoning by contacting cordierte, and nearly same Mg content, as that in the core of garnet, and the poor-developed diffusion zoning adjacent to felsic minerals. The characteristics of Mg zoning of garnet is different from the conventional knowledge, and indicates that the Fe-Mg exchange between garnet and biotite or other mafic minerals is resulted from the transfer of interface contact. The grain-boundary fluid seems playing less important role on the process of Fe-Mg exchange. However, Fe and Mg also could be transferred through grain-boundary fluid owing to increasing H2O activity in the rocks and the presence of large volume of biotite and low garnet content. As a result, the weak diffusion zoning could be formed in the garnet rim even though they contact felsic minerals. The metamorphic peak composition of the garnet could be persevered in the core of the grains over 1500 um in size. Accordingly, the core of large biotite away from garnet and among felsic minerals might also have kept peak composition. |
| Keywords: | Garnet diffusion zoning Grain-boundary fluid Peak composition Al-rich rock series Jingshan group in northJiaodong |
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