【作者】 黄雷；

【导师】 刘池阳；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2008， 硕士

【摘要】 煤层自燃及烧变岩的存在是世界范围内普遍存在的一种地质现象,其研究有益于对煤层形成以来所经历的构造运动、古气候和古地理等的探讨。鄂尔多斯盆地北部地区延安组煤层在地史时期普遍发生自燃,致使烧变岩广布,对该区烧变岩的研究有助于探讨盆地构造演化特征。以鄂尔多斯盆地北部烧变岩为研究对象,首先对煤层自燃的条件及烧变煤(层)特征进行详细探讨,在此基础上对盆地北部延安组煤层易自燃程度进行评价。继而根据烧变岩的形成特点,将其分为烧熔岩与烧烤岩两类,在此基础上,利用扫描电镜、能谱测试、红外光谱、X-射线衍射、古地磁及X-射线荧光光谱分析、ICP-MS等测试手段,通过对烧变岩的剖面分布特征、物理性质、岩石学和地球化学特征、磁学特征等的研究,得出烧变岩较为全面的特征描述:烧变岩在平面分布上多沿沟谷出露,剖面上具明显的分带性;烧变岩在物理性质上抗压强度及抗剪强度均减小,体积密度减小,较原岩孔隙率、含水量显著增高,在测井曲线上也明显有异于正常岩;烧变岩中出现一些如硬石膏、无水云母、高岭石等新生脱水矿物,以及赤铁矿、磁铁矿等磁性矿物,石英、长石及粘土矿物等原生矿物因高温烧变而具明显的烧熔迹象;烧变岩稀土元素配分特征整体上显示沉积岩的特征,但在烧熔岩与烧烤岩之间可见因高温烘烤而发生的稀土元素的分馏;烧变岩具有相对沉积岩异常高的磁化率值,各向异性特征显示烧变岩随着烘烤程度的增大各向异性值变小。论文对研究区烧变岩的形成时代进行了详细的分析研究。利用磷灰石裂变径迹测年技术结合地质现象的分析认为:其烧变时期跨越时间长—自晚白垩世末期至第四纪,且具阶段性烧变的特征。根据烧变岩特征及形成时代的研究结果,将研究区的烧变归为三类:“开放型”烧变、“封闭型”烧变、叠加烧变,对其形成条件进行了详细分析,并提出了相应的烧变模式。进而揭示研究区烧变岩形成的阶段性与瓮地晚白垩世以来构造发育背景密切相关,即与该区主体幕式、差异性整体抬升和强烈而不均匀剥蚀的阶段性相吻合。后者是盆地北部叠加烧变岩类型形成的区域动力学环境。另外,论文尚对研究区内发现的一类有别于正常烧变岩产出剖面的特殊剖面,以考考乌素沟内柠条塔剖面为例进行了剖析研究。更多还原

【Abstract】 The spontaneous combustion of coal seams and burnt rocks are a common geologic feature in many countries throughout the world. Their study are beneficial to the discussion on the tectonic movement, paleoclimate and paleogeography that coal seams are subjected to after they were formed. The coal seams in Yan’an formation of Northern Ordos Basin beard spontaneous combustion universally during terrestrial time, that resulted the wide range of burnt rocks. The study of burnt rocks in this area is help to discussing the structural evolution characters of Ordos Basin.In this paper, the burnt rocks in Northern Ordos Basin are taken as the study object. First, the emergence condition of spontaneous combustion and the characters of burnt coals (seams) are discussed, base on those, the degree of combustibility of the coal seams in Northern Ordos are estimated. And then, according to the forming characteristic, the burnt rocks are divided into two series in the section: the melted rocks and the baked rocks. After that, the section distributing characters, physical properties, petrologic characters and geochemical characters, magnetism characters of burnt rocks are researched, using the methods of SEM, EDS, IR, XRD, archeomagnetic method and XRF, 1CP-MS. Through these studies, more comprehensive features of the burnt rocks are obtained, i.e., the burnt rocks usually distributed along the valley in plain, and have obviously zonality in section; about the physical properties, burnt rocks have obviously increased porosity and water content, decreased compressive strength and shearing strength, and their logs are different from that of the normal rocks; some new dehydrated minerals, e.g., anhydrite, anhydromica, kaolinite , and some magnetic minerals, e.g., hematite and magnetite, appeared in burnt rocks, besides, the primary minerals, e.g., quartz, feldspar and clay minerals, all show the obvious burnt and melted traces because of the high-temperature baking; the REE distribution patterns of burnt rocks are similar to that of sedimentary rocks, but the fractionation of REE occurred, resulting in the difference between melted rocks and baked rocks in the REE distribution pattern; the burnt rocks have remarkable enhanced magnetism relative to the normal sedimentary rocks, and their also show that the susceptibility anisotropy smaller as the burning degree increases.The age of the burnt rocks in study area is studied detailed. Using the method of apatite fission track, and combining the analysis of geological phenomena, it is thought that, the forming period of burnt rocks span a long time, from last stage of Late Crataceous to Quaternary, and with the characteristic of episodic burnt.Basing on the above finding about the characters and forming age, the burnt rocks in studying area are classified into three kinds, i.e., the opening type burnt, the enclosed type burnt and the superimposed type burnt. Every kind of burnt rocks’ forming condition is analyzed detailed, and their relevant burnt mode are given. The further analysis reveal that, the episodic forming of the burnt rocks in studying area are closing relative to the background of basin’s tectonic development since Late Crataceous, i.e., it is coincided with the episodic of the main part of the basin’s uplifts continuously, episodically and differently, strong and uneven erosion. And the later is the regional dynamic setting of the superimposed type burnt rocks’ forming in Northern Ordos Basin.Besides, a kind of special burnt rock section that is different from the normal burnt rock section is found, and it is analyzed exhaustively, that Ningtiaota section in Kaokaowusugou is taken as the sample.更多还原