Synsedimentary volcanic-ash-derived illite tonsteins in Late Permian coal-bearing formations of southwestern China
Synsedimentary volcanic-ash-derived illite tonsteins in Late Permian coal-bearing formations of southwestern China
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DOI：
10.1016/0166-5162(90)90071-6
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发表时间：
1990-08
影响因子：
5.6
通讯作者：
K. Burger;Yiping Zhou;Dazhong Tang
中科院分区：
文献类型：
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作者：
K. Burger;Yiping Zhou;Dazhong Tang
中国西南地区晚二叠世含煤建造中伊利石粘土岩发育，分布广泛。在过去的几十年里，人们已经认识到，它们是同沉积火山灰-瀑布的起源本文通过对蚀变凝灰岩的地层地理分布、岩石类型、化学成分、副矿物组合及形态特征的综合研究，矿物学和岩石学鉴定以及X射线衍射分析进一步表明，根据粘土矿物组成，它们主要可分为三类：高岭石、高岭石-伊利石（过渡型）和伊利石。在大多数情况下，这些不同类型的夹煤岩在区域尺度上表现出明显的带状分布。它们的矿物组成在后生成岩作用过程中受到多种因素的综合影响而发生了深刻的变化，如相邻煤层挥发分百分比（VM）的变化所示（VM是在可燃组分的基础上计算的）。VM > 10%的煤中插层煤岩以高岭石为主。但当煤的挥发分从10%降低到8%时，它们的伊利石含量增加，而高岭石含量减少。当VM降至8%以下时，这些灰岩中的粘土矿物几乎全部为伊利石，并伴有某种绿泥石化。从区域角度来看，这些灰岩中粘土矿物组成的变化显然是对地质作用的持续和渐进变化的响应。除温度和压力条件外，溶液中一定量的碱金属离子和亚铁离子的存在也是控制因素之一。
Illite claystones (tonsteins) of Late permian coal-bearing formations are well developed and extensively distributed in southwestern China. Over the past decades it has been recognized that they are synsedimentary volcanic ash-falls in origin (altered tuff beds), based on the data derived from the comprehensive investigations on their stratigraphic and geographic distribution, petrographic types, chemical composition, accessory-mineral assemblage, as well as on their morphological characteristics.Recently, mineralogical and petrological identifications and X-ray diffraction analyses on these peculiar tonsteins further suggest that they can be classified mainly into three categories based on their clay-mineral constitution: kaolinitic, kaolinitic-illitic (transitional type), and illitic. As coal partings in most cases, these different types of tonsteins show a distinct zonal distribution on a regional scale. Their mineral constitution is profoundly modified by the combined effects of many factors during deuterogenic diagenesis, as indicated by the variation in volatile-component percentage (VM) of the adjacent coal seams (VM is calculated on a combustible-component basis). Those tonsteins intercalated in coal with a VM > 10% are dominated by kaolinite. But they contain increasing amount of illite at the expense of kaolinite when VM of coal decreases from 10% to 8%. When VM declines to less than 8% the clay minerals in these tonsteins are almost entirely illite with some sort of accompanying chloritization.It is clear that, from a regional point of view, the variation in clay-mineral constitution of these tonsteins is in response to the continual and progressive change in geological processes. In addition to the temperature and pressure conditions, the existence of a certain amount of alkali-metal ions and ferrous ions in solution is one of the controlling factors.