| 岩浆母质对蚀变粘土矿物的约束:以贵州新民剖面P-T界线附近火山灰层为例 |
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| 引用本文： | 洪汉烈,方谦,王朝文,宫旎娜,赵璐璐.岩浆母质对蚀变粘土矿物的约束:以贵州新民剖面P-T界线附近火山灰层为例[J].地球科学,2017,42(2):161-172. |
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| 作者姓名： | 洪汉烈 方谦 王朝文 宫旎娜 赵璐璐 |
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| 作者单位： | 1.中国地质大学生物地质与环境地质国家重点实验室，湖北武汉 430074 |
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| 基金项目： | 国家自然科学基金项目41272053国家自然科学基金项目41472041 |
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| 摘 要： | 目前对于粘土层中伊蒙混层矿物的堆垛结构、单元层含量与岩浆母质及环境条件关系的了解等，仍然十分匮乏.一定沉积环境下火山灰层中粘土矿物组合、以及伊蒙混层堆垛方式精细结构特征，可能记录了沉积(包括成岩作用) 环境对火山物质蚀变产物的影响.采用X射线衍射(XRD)、扫描电子显微镜(SEM)、元素地球化学分析、氧同位素分析方法等方法，对贵州新民深海相二叠系-三叠系(P-T) 界线附近蚀变火山灰层的地球化学特征、粘土矿物精细结构特征等进行了深入研究.结果表明，4个火山灰粘土层均含有2种具有R3结构、不同混层比的伊蒙混层矿物相，且均出现粘土矿物集合体取代原先的火山碎屑颗粒或在颗粒表面生长的现象，粘土矿物形成于沉积-成岩阶段因而其泥质结构被保留；样品XM-5-1和XM-5-2的Fe3+原子数分别为0.16和0.17个且具有明显Eu负异常和较低的K2O含量，而XM-5-3和XM-5-4的Fe3+原子数均为0.14个，说明相对于前2个粘土层，后2个的岩浆母质更加偏向酸性而表现为成岩蚀变程度更强.粘土矿物的氧同位素组成为17.3‰~18.1‰，与常温下蒙脱石与海水的平衡数值相近，表明粘土矿物化学组成与海底成岩蚀变环境有关，而不同火山灰层的粘土矿物学特征则主要取决于岩浆岩母质以及成岩蚀变强度.
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| 关 键 词： | 二叠系-三叠系界线 火山灰 粘土矿物 晶体化学 稳定氧同位素 地球化学 |
| 收稿时间： | 2016-11-15 |
Constraints of Parent Magma on Altered Clay Minerals: A Case Study on the Ashes near the Permin-Triassic Boundary in Xinmin Section,Guizhou Province |
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| Abstract: | The study on the influence of sedimentary environments on the altered clay mineralogy facilitates accurate stratigraphical correlation using volcanic ashes as marked beds. However, the relationships among the stacking ordering, illite layer contents, parent magma and environmental condition are still poorly known. A case study on altered vocalnic materials near the Permian-Triassic boundary in the Xinmin section, Guizhou province was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), geochemical analysis, and oxygen isotope analysis methods. Results show that all the four volcanic ash layers contain two phases of mixed-layered illite/smectite (I/S) with R3 structure and varied layer contents, and clay mineral aggregates were found having replaced the volcaniclastic particles or have grown on the surfaces of volcaniclastic particles. It can be inferred that clay minerals formed in sedimentary to early diagenesis periods since the materials preserve argillaceous texture when clay minerals were produced. The number of Fe3+ atoms are 0.16 and 0.17 respectively in the samples XM-5-1 and XM-5-2, and 0.14 in both samples XM-5-3 and XM-5-4, indicating that parent magmas of the latter ones were more of meta acid compared with the former two. It is indicative of more intense alteration of the latter two volcanic ash layers, together with the apparent Eu negative anomaly and less K2O contents. Oxygen isotopic composition of the volcanic ashes ranges narrowly from 17.3‰ to 18.1‰, consistent with the equilibrium value between smectite and ocean water at 25 ℃, suggesting that chemical composition of the Xinmin clay minerals is related to conditions of submarine diagenesis alteration since the clay mineralogy of different volcanic ash layer depends on its parent magma and degree of diagenesis alteration. |
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