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Lab 10 Geologic Structures

Lab 10 Geologic Structures - As we go through the Computer...

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Geologic structures Introduction Geologists typically show the distributions and orientations of discrete rock units at the Earth's surface on so-called geologic maps, and they are skilled at interpreting map patterns. Geologists prepare such maps to provide detailed information about the type and age of rocks exposed at the Earth's surface. However, the map patterns also contain information about the underlying structures formed when rocks respond to stresses (i.e., forces) operating below the surface. This response of rocks to stress is called deformation. Thus, geologic maps are useful not only for identifying geologic structures, and their causes, but also for locating natural resources such oil, gas, and groundwater. They can also help us to identify potential areas prone to landslides. This lab will acquaint you with how rocks behave in response to external forces acting upon them. It will also develop your 3-D thinking by showing you how rock-unit patterns observed at the surface can be used to predict their continuation beneath the surface. Such knowledge is useful for both reconstructing Earth history and searching for natural resources. Figure 1. A. Picture of a fold in a road cut section, B. Picture of a fault in a road cut section. Note the sense of relative movement of the blocks of rocks in either sides of the faults are marked by black arrow. A B A B
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Types of Structures in Rocks Geologic structures known as faults and folds are produced when rocks break or bend, respectively, due to applied stresses operating within the Earth. That is, rocks are said to deform. Plate tectonics and sediment burial are examples processes that can lead to rock deformation. A. Faults Breaks or ruptures in rock along which movement has occurred are called faults. Faulting displaces the rocks on one side of the break, which is called the fault plane, relative to those on the other side. The 2 fault blocks associated with the fault plane were given colorful names by early miners, who recognized that some ore deposits are concentrated in fault zones. Thus, they named the bottom side of the fault plane that they could stand on while excavating as the footwall . Likewise, they named the upper side of the fault plane the hanging wall , because the overhang provided a place to hang a lantern while excavating. See figure 2 below. Figure 2. Diagram showing main fault components and relative movement of adjacent fault blocks. There are 2 general classes of faults, those having vertical movement and those having mostly horizontal (lateral) movement. Vertical-motion faults are of two types: normal faults and reverse faults. These are distinguished by noting the sense of motion of the top block relative to the bottom block, irrespective of which block actually moved. In fact, we cannot tell exactly which block(s)
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