摘要
含煤地层中广泛分布的火山灰蚀变成因的高岭石黏土岩被称为Tonstein。少数情况下,煤系蚀变火山灰层的黏土矿物以蒙脱石和伊蒙混层矿物为主,则分别称为斑脱岩和钾质斑脱岩。尽管中外学者对煤系火山灰蚀变黏土岩已有大量研究,然而,迄今为止这几个术语在定义和使用上在国内外科学界仍然存在争议。煤中火山灰的淋滤作用会对煤的地球化学组成产生重要影响。含煤地层中这类岩石因为分布广泛可以被用作等时标志层,提供地层对比的依据,其中的原生矿物还可以提供绝对年龄信息。有的碱性火山灰层具有找矿指示意义。煤中火山灰蚀变黏土岩夹矸中化学性质相对稳定的元素可以用来推断原始火山灰的组成,提供原始岩浆的成分以及区域地质历史演化方面的信息。
Tonsteins, and less commonly bentonites and K-bentonites, are known to occur in many different coal-bearing formations in the world throughout geological time, although the actual definition of tonsteins is still regarded in some cases as controversial. Leaching of the precursor volcanic ash by ground waters and organic acids in the peat-forming environment would be expected to result in enrichment of some elements that were released from the ash and accumulated as minerals or organometallic compounds in the immediately adjacent coal. The occurrence of such minerals may therefore be indicative of volcanic influence during peat accumulation and coal formation. Tonsteins are thought to provide geochronological markers, with a widespread distribution that enables stratigraphic correlation. The primary minerals in tonsteins, if preserved, may also provide opportunities for absolute age determination. Some alkaline tonsteins are indicators for the discovering of rare metal ore deposits. The geochemical characteristics of tonsteins serve as indicators of magma affinities and volcanotectonic settings.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2016年第3期103-112,共10页
Earth Science Frontiers
基金
国家重点基础研究发展计划'973'项目(2014CB238904)
国家自然科学基金项目(41302128
41420104001)
中央高校基本科研业务费项目(2014QM01)
