Figure 10.22a: If the hanging wall slips downward relative to the footwall, the fault is defined as a normal fault. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Folds & Faults. 1. N 10o W) and plunge (e.g. Maps of these geologic structures are linked to a database containing detailed descriptions and … 3. Rocks deep within the crust under high confining pressures deform by folding. Figure 10.22c: Shear forces typically produce strike-slip faults where one block slips horizontally past the another. Folds are most visible in rocks that layered (also known as sedimentary rocks). 1. Figure 10.4: The orientations of rock layers, folds, fractures and faults can all be measured in three dimensional space using strike and dip. •Define and describe synclines, anticlines, and other types of folds. Figure 10.22: A fault is a plane of dislocation where rocks on one side of the fault have moved relative to rocks on the other side. Larger faults are mostly from action occuring in earth's plates. Silly Putty™ allows students to discover that the structure we see in rocks provides evidence for they type of stress that formed. If the axis is not horizontal, the structure is said to be a plunging fold. When tectonic forces acting on sedimentary rocks are a number of characteristic forms. Rock layers dip away from the fold axis in anticlines, but dip toward the fold axis in synclines. Fig. Confining pressures within the earth are caused by the weight of the overlying rock pushing downward and from all sides. Joints can form as a result of expansion and contraction of rocks. Figures 10.10 & 10.11: The two sides of a fold are referred to as limbs. Performance & security by Cloudflare, Please complete the security check to access. There are three or four primary fault types: Normal fault. ; Geosyncline: a large-scale depression in the earth’s crust containing very thick deposits. Start studying Chapter 9: Folds, Faults, and Geologic Maps. The rock below the joints fell, leaving scars in this hillside. 1. Sedimentary rocks are more flexible than the metamorphic, and when the thrust is not intense enough to move them fold as if they were a pie… The dip is measured at right angles to the strike and is a measure of the angle at which the surface tilts relative to a horizontal surface. Start studying A-Level Geology Edquas - Faults and Folds. In general, the greater asymmetry in the fold, the more intense the deformation. Tensional forces common along extensional plate boundaries such as mid-ocean ridges. Based on the direction of slip, faults can be categorized as: Holes drilled within the earth’s crust tend to remain open at shallow depths, but at greater depths holes tend to squeeze shut due to the increase in confining pressure. The fracture itself is called a fault plane.When it is exposed at the Earth's surface, it may form a cliff or steep slope … ; They are the loftiest mountains, and they are generally concentrated along continental margins. Figure 10.10: A fold can be divided by an imaginary surface called the axial plane. Faults may be vertical, horizontal, or inclined at any angle. The type of strain (deformation) that develops in a rock depends on the tectonic force. (d) Once this information is obtained, the geologist can employ the principles of geometry and trigonometry to determine the orientation of the axial plane and also whether the fold plunges. Figure 10.5: For anticlines, the surface rock exposures become progressively older towards the fold axis. Fold mountains are formed when sedimentary rock strata in geosynclines are subjected to compressive forces. Structural Geology 2. Similarly, rocks with Folds are classified by their size, fold shape, tightness, dip of the axial plane. Introduction • Structural geology is the study of factors such as origin, occurrence, classification, type and effects of various secondary structures like folds, faults, joints, rock cleavage and are different from those primary structures such as bedding and vesicular structure, which develop in rocks at the time of their formation. Buy Folds, Faults and Fossils - Exploring Geology in Pembrokeshire by Downes, John (ISBN: 9781845241728) from Amazon's Book Store. Spectacular folding of Palaeozoic carbonate strata in Scapegoat Mountain, Montana. Folding is caused due to compressive stresses. 4. The two limbs come together to form an imaginary line called the fold axis. Rock exposures become progressively younger towards the axis of synclines. Strata on one side of the joint align with strata on the other side. Tethys geosyncline. Compressive forces are common along convergent plate boundaries resulting in mountain ranges. CHAPTER 10: Folds, Faults and Rock Deformation. 3. 6. Rocks under low confining pressures near the earth’s surface therefore generally deform through fracturing and faulting. 8. 1. 1. The direction in which the fold axis points indicates the strike of the fold. 10.6c: Shearing forces cause rocks to slide horizontally past one another such as along transform plate boundaries to produce extensive fault systems. Folds constitute the twists and bends in rocks. Figure 10.9: Folds are a result of ductile deformation of rocks in response to external forces. 3. which refers to a surface across which there is a discontinuity in displacement, strain, and/or fold style. 5. Figure 10.23: A reverse fault in which the dip of the fault plane is so small as to be almost horizontal is called a thrust fault. A dip-slip fault in which the block above the fault has moved downward relative to the block below. The strike of a surface is the direction of a line formed by the intersection of a rock layer with a horizonal surface. 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