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学科主题: 地理学::自然地理学
题名: 慕士塔格地区冰川沉积组构特征研究
作者: 朱志勇
答辩日期: 2009-06-05
导师: 易朝路
专业: 自然地理学
授予单位: 中国科学院研究生院
授予地点: 北京
学位: 博士
关键词: 慕士塔格冰川 ;  冰川沉积 ;  组构发育 ;  特征值和特征向量
索取号: S000024
部门归属: 图书馆
摘要: 组构分析已经被广泛的应用于地球科学之中,是传统、有效的冰川沉积研究方法之一。冰碛物内砾石的优选特征被认为是研究冰川运动方向、冰川沉积过程和环境特征的重要依据,能够将冰川动力学和沉积记录有机的结合起来。由于冰下压力对多数沉积物产生应力,并导致颗粒发育具体的组构排列,因此可以通过对冰碛物组构特征来反映冰川搬运、堆积和变形过程,恢复古冰碛形成时期冰川运动的方向,也可以用来对冰川混杂岩的识别与分类,对未知冰碛类型进行区分。同时,使用组构证据能否判断冰川的成因类型也存在着争议,学者又指出运用单一的模型来解释沉积环境是不可靠也不实际的,必须结合其他沉积学证据,进而从多指标方法确定其沉积环境。慕士塔格地区发育了大量的现代冰川,其古冰川遗迹的分布比较广泛,山西侧的洋布拉克冰川末端下伸至海拔4320米,是慕士塔格峰西坡下伸最低的冰川,是研究山谷型冰川冰碛石组构特征的理想地区。本文运用组构特征向量(eigenvector)和特征值(eigenvalue)统计方法,对研究区的各种冰川成因类型冰碛物的组构特征进行研究,并与其他大型山谷冰川和大陆性冰川环境下组构发育特征进行了对比,并讨论了山谷冰川下运用组构特征解释冰碛成因类型的意义,结果表明以下几点特征:(1)在冰碛物中,砾石组构中AB面的组构强度要高于A轴的组构强度,也就是说冰碛物中,冰碛砾石的AB面定向排列性要高于A轴的定向排列性;(2)不同的冰碛类型,其组构特征也不尽相同,经过冰下作用的底碛,其组构强度较高;而冰上融出碛,组构强度比底碛的组构强度低。这主要可能是二者所经历的动力过程不同而导致的结果。经过冰下作用的冰碛物,经历了剪切、推挤和挤压等动力过程,使得砾石的定向排列性明显受到冰下动力的影响,其组构强度偏高。而冰上融出碛在沉积过程中仅仅部分受到了冰川动力作用以及表面过程,其砾石排列也被地表、山谷形态所控制着,这些多样的控制因素也是导致冰上融出碛组构强度偏弱的因素;(3)冰碛砾石AB面定向排列的方向与冰川运动方向近平行,A轴与冰川运动方向存在较低的夹角,基本可以反映冰川的运动方向,但同时A轴受地形、山谷形态等因素的变化要比AB面敏感;(4)随着与现代冰川距离的增加,砾石的A轴组构也存在着一定的规律。离现代冰川越远,其组构强度越高,反映了砾石A轴组构与冰川规模存在一定的联系,即冰川规模越大,厚度越大,其组构强度越强,而靠近现代冰川的冰碛物中,冰川规模相对小,冰川厚度也小,受到冰川动力作用弱,因此冰碛物轴砾石组构强度也偏低;(5)在与大陆冰盖相比时,山谷冰川A轴最大优选方位强度要明显低于大陆冰盖冰川A轴最大优选方位的强度。这是由于两者的冰川性质存在明显的区别,大陆冰盖冰川其规模较大,冰川较厚,冰川作用强,因此其砾石定向排列性明显;而山谷冰川中,冰川规模小,受到冰川作用相对低,其组构强度也偏小;(6)在研究组构发育特征时,有必要建立最佳的范围和确立组构强度与轴向比值,碎屑大小和形态之间的联系;(7)在运用组构特征解释沉积动力过程必须谨慎,这是因为在埋藏期间沉积过程及很可能经历了后期再沉积的变化。同时由于不同过程的组构特征值也存在着叠加,也使得组构特征的判别意义必须与其他方法相结合,才能更好的使得组构特征解释沉积过程。同时运用单一的模型来解释沉积环境是不可靠也不实际的,必须结合其他沉积学数据(如岩相分析等),从多指标方法确定其沉积环境。
英文摘要: Fabric analysis has been widely applied in material sciences and geosciences. Up to now, in-situ fabric measuring is one of the most effective and traditional methods to study glacigenic diamictons. Till fabrics provide important evidence on glacier movement orientation, sedimentary process and environmental conditions. It provides a potential link between glacier dynamics and the sedimentary record. Particles can develop specific fabric arrangements as a response to bulk sediment strain driven by effective stress at the bed of a glacier. As such, fabric analysis has been used to try and understand the paleo-ice-flow, and studies have shown that clast orientations differ in genetically different deposits. Today, clast-fabric analysis has been as a diagnostic tool to distinguish glacigenic diamictions of unknown origin, and can be used to catalogue till genesis type. In contrast, it is argued that fabric data argue unable to independently determine origin of tills. Their results indicate that the application of one uniform model in explaining till fabric is neither reliable nor practical. Multiple criteria including structural, lithologic, and stone morphologic data from the till must also be considered before drawing conclusions on till genesis. The well preserved moraine successions and valley fills that are present in the Muzag Ata area. The Yangbulak glacier which located west of Muzag Ata Mount is considered to be an ideal area to study the glacigenic clast-fabric characters for the alpine glaciers. With the developments in the analysis of till fabric have been facilitated by the application of vector and eigenvector statistics, we study the general characteristics of fabrics in different genesis type till, and compare these data with the fabrics on the large mountain glaciers and ice sheets. Meanwhile, we discuss the reliable for using the measurement and analysis of till fabrics to interpret unknown glacigenic diamictons. Some conclusions are displayed as follows: (1) All profiles have strong a-b plane fabrics, and the S1 value indicates that the fabric of the a-b plane of till clasts is stronger than that of a-axis. (2) Clast fabrics vary with different genesis till type. Results of eigenvector / eigenvalue analysis of clast fabrics suggest that the fabrics of the subglacial tills is stronger than that of supraglacial one. (3) The a-b plane fabrics are near-parallel to the former ice flow direction. The a-axis intersects former ice flow direction, and is more sensitive than is the a-b plane to the variation of local relief and the morphology of valley. (4) Results of fabric analysis from glacial area different far from modern glacier show that the tills far away modern glaciers have stronger a-axis fabrics than that of tills near the modern glaciers. (5) Comparison with continental glaciers, the S1 values of a-axis in the valley glaciers are smaller than those in ice sheets. It is mainly because of the different characteristics of two kinds of glaciers. In the continental glaciers, thickness and strong glaciation, have stronger a-axis fabrics. In contrast, the valley glaciers have smaller a-axis fabrics. (6) Further work is necessary to establish an optimal range and to ascertain possible relations between fabric strength, axial ratio, clast size and shape. (7) It must be careful to use the fabric analysis to distinguish glacigenic diamictions of unknown origin. Multiple criteria including structural, lithologic, and stone morphologic data from the till must also be considered before drawing conclusions on till genesis.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.itpcas.ac.cn/handle/131C11/1240
Appears in Collections:图书馆_学位论文

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Recommended Citation:
朱志勇.慕士塔格地区冰川沉积组构特征研究[博士].北京.中国科学院研究生院.2009
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