滇东地区晚二叠世含煤岩系中磁绿泥石的成因、演化及其地质意义

Berthierine is a kind of clay mineral that similar to chamosite, but belongs to the serpentine family, it often occures in the marine environment. And berthierine is generally more stable in the <200 ℃ low temperature reducing environment, with the increase of temperature, it will be transformed to chamosite, and in a certain temperature range occurs as the form of interstified minerals. Although clay minerals are the main minerals in most coal, the output of berthierine is very rare in coal-bearing strata, and interstified berthierine/chamosite is even more rarely reported. This study choose the berthierine and interstified berthierine/chamosite as research subject, which are commonly occurred in the coal-bearing strata in eastern Yunnan, to deeply studied the distribution and modes of occurrence in different kinds of samples (coal seams, host rocks, partings and clay rocks altered from volcanic ash, etc.). A couple of geological factors will be comprehensive studied: including sediment sources, coal-forming depositional environment, volcanic ash, magma and hydrothermal activity and others. Accordingly, the sources and main controlling factors of berthierine and interstified berthierine/chamosite will be revealed, the evolution mechanism of berthierine and interstified berthierine/chamosite in the coal-bearing rock strata will be elucidated. The research is expected to develop and enrich the sedimentary environment of berthierine.

磁绿泥石化学成分类似于鲕绿泥石，但是属于蛇纹石族的一种黏土矿物，常产出于海相环境中，一般在<200℃低温还原环境中较为稳定，随着温度的升高，磁绿泥石会向鲕绿泥石发生转化，并且在一定的温度范围内以间层矿物的形式存在。黏土矿物虽然是大多数煤中最主要的矿物，但是磁绿泥石的产出在含煤岩系却非常罕见，而对于磁绿泥石/鲕绿泥石间层矿物则鲜有报道。本课题以滇东地区含煤岩系中普遍产出的磁绿泥石及磁绿泥石/鲕绿泥石间层矿物为研究对象，深入研究磁绿泥石和磁/鲕绿泥石在不同样品（煤、顶底板、夹矸和火山灰蚀变黏土岩等）中的时空分布规律以及赋存状态，综合分析物源供给、成煤介质环境、火山灰、岩浆和热液活动等多种地质作用，查明磁绿泥石及磁/鲕绿泥石的物质来源及形成的主控因素，阐明在含煤岩系中磁绿泥石和磁/鲕绿泥石的演化机制，发展并丰富了对磁绿泥石的产出环境的认识。

磁绿泥石，一种蛇纹石族黏土矿物，化学成分类似于鲕绿泥石，常产出于海相环境中，一般在<200℃低温还原环境中较为稳定，随着温度的升高，磁绿泥石会向鲕绿泥石发生转化，并且在一定的温度范围内以间层矿物的形式存在。研究区晚二叠世含煤岩系中普遍产出磁绿泥石及磁/鲕绿泥石，磁/鲕绿泥石的鉴定特征是较宽广的14Å衍射峰和尖锐的7Å衍射峰。磁绿泥石与滇东其他地区发现的鲕绿泥石相比更富Fe贫Mg。磁/鲕绿泥石是C1煤层中煤中最主要的黏土矿物，其在顶板中含量差别较大，在部分顶板、所有底板和酸性火山灰成因的Tonstein中则未检出；而磁绿泥石和磁/鲕绿泥石在碱性火山灰和基性火山灰蚀变黏土岩中均有产出，二者在纵向剖面呈现轻微互补的现象，即磁绿泥石主要产出于钻孔的中上部，而磁/鲕绿泥石产出于钻孔的下部。磁绿泥石（磁/鲕绿泥石）的赋存形态和成因主要分为两种：一种为碎屑状或尖角状，属于火山成因，由火山玻璃蚀变形成；另一种则包含产出于胞腔中，纤维状或胶体状以及交代蠕虫状高岭石等多种形态，均属于热液流体成因，表明其沉淀自富Fe-Mg的热液流体，或是富Fe-Mg的热液流体与高岭石反应的产物。经推断研究区晚二叠世沉积盆地中所侵入的是一种低温热液流体，推测磁绿泥石的形成温度大概在100℃左右，并且随着温度升高向磁/鲕绿泥石转变，最高温度不超过180℃。本次研究无论是对磁绿泥石产出于陆相沉积环境还是含煤岩系中均具有非常重要的参考意义。