| Al_2O_3/Ti:风化与蚀变过程中的原岩示踪 |
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| 引用本文： | 严桃桃,龚庆杰,李金哲,陈晶,周伟伟,李睿堃.Al_2O_3/Ti:风化与蚀变过程中的原岩示踪[J].岩石学报,2016,32(8):2425-2432. |
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| 作者姓名： | 严桃桃 龚庆杰 李金哲 陈晶 周伟伟 李睿堃 |
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| 作者单位： | 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083,中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083,中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083,中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083,中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083,中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083 |
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| 基金项目： | 本文受国家自然科学基金重点项目（41230311）和国家科技支撑计划课题（2011BAB04B09）联合资助. |
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| 摘 要： | Al_2O_3和Ti在风化和热液蚀变等地球化学过程中通常被认为是不活动元素,两者的比值Al_2O_3/Ti常被用来指示地球化学作用过程。通过对中国157件火成岩样品元素含量平均值的统计发现,火成岩样品中Al_2O_3/Ti与SiO_2含量值之间存在着较好的幂函数关系:ln(Al_2O_3/Ti)=0.073×SiO_2-0.89,式中Al_2O_3和SiO_2和Ti含量单位均为%。本文基于得到的经验方程和TAS图解构建了一个新的判别岩石类型的图解——Al_2O_3-Ti图解。该图解可以区分酸性岩、中酸性岩、中性岩、中基性岩-基性岩四类岩性。通过对三个火成岩风化剖面的研究发现,花岗岩风化剖面从新鲜基岩到风化形成的土壤在Al_2O_3-Ti图解中均落在酸性岩区,花岗闪长岩风化剖面从新鲜基岩到风化形成的土壤样品均落在中酸性岩区,玄武质安山岩风化剖面从新鲜基岩到风化形成的土壤样品均落在中基性岩-基性岩区。不同风化程度的风化产物与其母岩在Al_2O_3-Ti图解中所在的区域一致,即Al_2O_3-Ti图解可以用来追溯火成岩风化产物的母岩岩性。通过对胶东焦家金矿和豫西牛头沟金矿两个矿区岩石的研究发现,黑云母花岗岩从新鲜岩石到其蚀变岩及其形成矿石的样品在Al_2O_3-Ti图解中均落在酸性岩区。玄武质安山岩从新鲜岩石到其蚀变岩及其形成矿石的样品在Al_2O_3-Ti图解中均落在中基性岩-基性岩区。即不同蚀变程度的蚀变产物与其原岩在Al_2O_3-Ti图解中所在的区域一致,这表明新构建的Al_2O_3-Ti图解可以用来示踪蚀变岩的原岩性质。
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| 关 键 词： | 不活动元素 Al2O3-Ti图解 火成岩 风化剖面 蚀变岩 原岩判别 |
| 收稿时间： | 2016/2/23 0:00:00 |
| 修稿时间： | 2016/5/17 0:00:00 |
Al2O3/Ti: Protoliths tracer in the process of weathering and alteration |
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| YAN TaoTao,GONG QingJie,LI JinZhe,CHEN Jing,ZHOU WeiWei and LI RuiKun.Al2O3/Ti: Protoliths tracer in the process of weathering and alteration[J].Acta Petrologica Sinica,2016,32(8):2425-2432. |
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| Authors: | YAN TaoTao GONG QingJie LI JinZhe CHEN Jing ZHOU WeiWei and LI RuiKun |
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| Institution: | State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China,State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China,State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China,State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China,State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China and State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China |
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| Abstract: | Al2O3 and Ti were usually considered as immobile elements during the process of weathering and alteration. The ratios between Al2O3 and Ti can be used to trace geochemical processes. On the basis of statistically analyzing the average chemical compositions of 157 igneous rocks from China, we found that there was a good power function relationship between their SiO2 abundances and Al2O3/Ti values as ln(Al2O3/Ti)=0.073×SiO2-0.89, units of Al2O3, SiO2 and Ti are in%. Combined with the total-alkali vs. SiO2 (TAS) diagram, a new diagram of Al2O3 vs. Ti to distinguish rock type had been proposed in this study. This diagram is able to differentiate four types of igneous rocks including felsic rocks, intermediate-felsic rocks, intermediate rocks, and intermediate-mafic & mafic rocks. On the new constructed Al2O3-Ti diagram, both the fresh granites and their weathering products from the Jiaodong weathering profile located in the eastern China were plotted in the area of felsic rocks; both the fresh granodiorite and their weathering products from the Zhoukoudian weathering profile located in the northern China were plotted in the area of intermediate-felsic rocks; both the fresh basaltic andesites and their weathering products from the Xiongershan weathering profile located in the central China were plotted in the area of intermediate-mafic & mafic rocks. As a result, the Al2O3-Ti diagram could be used to trace the protoliths of weathering rocks. On the new constructed Al2O3-Ti diagram, all samples from the fresh, altered and mineralized biotite granite in the Jiaojia gold deposit were plotted in the region of felsic rocks; all of the fresh, altered and mineralized basaltic andesites in the Niutougou gold deposit were plotted in the region of intermediate-mafic & mafic rocks. Therefore, the Al2O3-Ti diagram could be used to trace their parent rocks on altered samples. |
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| Keywords: | Immobile element Al2O3-Ti diagram Igneous rock Weathering profile Altered rock Provenance |
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