A new ‘microstructural mapping’ methodology for the identification, analysis and interpretation of polyphase deformation within subglacial sediments
A new ‘microstructural mapping’ methodology for the identification, analysis and interpretation of polyphase deformation within subglacial sediments
复制标题
一种新的“微观结构绘图”方法，用于识别、分析和解释冰下沉积物内的多相变形
DOI：
10.1016/j.quascirev.2011.04.024
复制
发表时间：
2011
影响因子：
4
通讯作者：
A. Ferguson
中科院分区：
文献类型：
--
作者：
E. Phillips;J. Meer;A. Ferguson
尽管综合碎屑宏观和微观结构研究已被用来提供古冰流动方向的证据，区分沉积在不同沉积环境中的重聚体，并模拟冰碛物对冰下变形的响应，但这些研究通常只检查了重聚体中发育的“块状”结构，很大程度上忽略了这些典型的多变形沉积物中结构发育的几个阶段的潜力。我们提出了一种新的图形方法，用于识别、描述和分析多变形耕地中的碎屑微纤维。该方法利用导入到标准计算机图形包中的定向薄片的高分辨率数字扫描来测量耕耘机中包含的碎屑（骨架）颗粒的长轴方向。然后，使用这些数据来识别耕斗内存在的主要碎屑微纤维，从而描绘碎屑微纤维区域，其中细长颗粒具有相似的优选方向。这个过程导致了识别、表征，最重要的是，确定了各代微织物之间的相互关系。还可以检查这些碎屑微织物和其他微结构（例如质织物、涡轮结构、剪切、折叠、断层等）之间的关系，提供薄片的详细微织物-微结构图。将针对薄片的不同部分收集的碎屑长轴方向数据绘制在一系列玫瑰图上，从而以图形方式显示碎屑微织物方向的变化。还提出了一套用于描述碎屑微纤维的新术语，该术语基于变质岩石学家使用的系统。对更新世和现在的冰下沉积物中存在的织物进行的三个案例研究被用作如何应用这种方法的示例。
Although integrated clast macro and microfabric studies have been used to provide evidence of palaeo-ice flow directions, to discriminate between diamictons deposited in differing sedimentary environments, and to model the response of tills to subglacial deformation, such studies have typically only examined the ‘bulk’ fabric developed within the diamicton, largely ignoring the potential for several phases of fabric development within these typically polydeformed deposits. We present a new graphical method for the identification, description and analysis of clast microfabrics in polydeformed tills. This method utilises high resolution digital scans of orientated thin sections imported into a standard computer graphics package to measure the orientation of long axes of detrital (skeleton) grains included within the till. These data are then used to identify the main clast microfabrics present within the till, allowing the delineation of clast microfabric domains in which elongate grains share a similar preferred orientation. This process leads to the identification, characterisation and, most importantly, the interrelationships between the various generations of microfabrics. The relationships between these clast microfabrics and other microstructures (e.g. plasmic fabrics, turbate structures, shears, folds, faults…etc) can also be examined, providing a detailed microfabric-microstructural map of the thin section. Clast long axis orientation data collected for different parts of a thin section are plotted on a series of rose diagrams allowing the variation in clast microfabric orientation to be displayed graphically. A new set of terminology for the description of clast microfabrics in tills, which is based upon the system used by metamorphic petrologists, is also presented. Three case studies of the fabrics present within subglacial sediments of Pleistocene age as well as the present are used as examples of how to apply this methodology.