四川万州中侏罗统上沙溪庙组粘土岩中火山灰的岩矿和地球化学证据

四川万州中侏罗统上沙溪庙组粘土岩中火山灰的岩矿和地球化学证据

张超1, 马昌前1, 佘振兵2, 殷坤龙3

1. 中国地质大学,地球科学学院,武汉, 430074; 2. 中国地质大学,研究生院,武汉, 430074; 3. 中国地质大学,工程学院,武汉, 430074

收稿日期:2005-09-20 修回日期:2005-09-20 出版日期:2005-09-20 发布日期:2005-09-20

Volcanic Ash in the Clay Rocks from Upper Shaximiao Formation of Middle Jurassic, Northeast of Sichuan Basin： Evidence from Petrology, Mineralogy and Geochemistry

ZHANG Chao1, MA Chang-qian1, SHE Zhen-bing2, YIN Kun-long3

1. Graduate School, China University of Geosciences, Wuhan 430074, China; 2. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China; 3. Faculty of Engineering, China University of Geosciences, Wuhan 430074, China

Received:2005-09-20 Revised:2005-09-20 Online:2005-09-20 Published:2005-09-20

摘要/Abstract

摘要： 四川盆地东北缘万州地区中侏罗世上沙溪庙组产出稳定层状浅色粘土岩。利用X射线、X荧光光谱、等离子光谱（ICP）等方法对矿物成分、常量、微量和稀土元素进行了测试分析,粘土岩主要矿物为蒙脱石、伊利石和绿泥石。通过与澳大利亚后太古代平均页岩（PAAS）、北美平均页岩（NASC）、地壳粘土岩背景值以及其它具有代表性岩石的对比发现,本区粘土岩微量元素具有明显的低V,低Ti和低铁族元素的特点,高Al2O3／TiO2比值和低Ti／Th比值特征显著,某些层位具有明显的Eu负异常。推断本区粘土岩沉积物源具有火山灰和陆源碎屑的二元混合成因,各层位成分的差异显示了不同沉积时间内二者的混合比例发生变化。区域对比和地球化学资料显示火山灰可能来自于西部600km远的特提斯洋岛弧火山。

Abstract: The gray montmorillenite-rich beds （clay rocks）, discovered in the Upper Shaximiao formation of Middle Jurassic, Wanzhou City, were studied mineralogically and chemically. The clay minerals in the clay rocks are typically montmorillonite, illite and chlorite. Based on the comparison with post-Archean Australian shale （PAAS）, north American average shale （ NASC）, background value of earth crust clay and other typical rocks, the studied clay rocks are characterized by low abundances of V, Ti, and Fe group dements, and high Al2O3/TiO2 and Ti/Th ratios. Some beds have clear negative Eu anomalies. The sources of clay rocks are interpreted as mixtures of volcanic ash and continental debris. The variation of compositions in different beds shows different mixing ratios at different times when the Sichuan basin was formed. It is suggested that the volcanic ash might come from the middle Jurassic volcanic arc in the Tethys which was about 600 km to the west.

张超, 马昌前, 佘振兵, 殷坤龙. 四川万州中侏罗统上沙溪庙组粘土岩中火山灰的岩矿和地球化学证据[J]. J4.

ZHANG Chao1, MA Chang-qian1, SHE Zhen-bing2, YIN Kun-long3. Volcanic Ash in the Clay Rocks from Upper Shaximiao Formation of Middle Jurassic, Northeast of Sichuan Basin： Evidence from Petrology, Mineralogy and Geochemistry[J]. J4.