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Folding, Faulting and the Brittle/Ductile Transition Zone Overarching concept: Fractals Key concepts: Fold Fault Stress Strain Mantle Crust Plastic deformation Brittle deformation Instructional Objective Compare and contrast the processes of faulting and folding Engage Active participation demonstration using layers of different colored clay (both pliable and brittle). Show students that some of the clay layers are stiff, while some are flexible. Have them write out a hypothesis filling in the following statement: If I apply stress on either side of these layers of clay… Then teacher places two boards, or books, on either side of the layers and apply pressure in the horizontal direction. The pliable layers should fold, while the brittle layers should fracture, or fault. Explore Have students use their textbook and other resources they deem appropriate to relate the demonstration to geology. Using their textbooks to be able to use the correct terminology and relate it to the earth, have students design two of their own demonstrations: one that would represent folding, one representing faulting. Investigative questions to be answered in all experiments: What, in the Earth would behave like the flexible clay? (answer: rocks below the brittle/ductile transition zone) What would behave like the brittle clay? (answer: rocks located at a shallower depth) Is there a relation of depth in Earth as to where rocks may be more ductile than brittle? Explain Have students swap experiments with each other. Once they have performed each others' experiments they should have a strong concept of the difference between the two processes. Ask for a student volunteer to draw three columns on the board. Label one brittle, one ductile, and one brittle/ductile. Have students call out individual examples or characteristics that fit into each column. After they have supplied examples and characteristics regarding depth and heat, label the ductile column with Fold, brittle column with Fault, and leave the third column as Brittle/Ductile. Teacher then goes over the defining characteristics of faults and folds, using the information the students supplied and other missing components. This discussion should stem from an introduction (or revisiting) of the concept of fractals in the earth system. Using fractals to group concepts in geology emphasizes that geologic processes are complex at all scales. Large scale features mimic smaller scale features, and so on. Folds, for example, can be seen from space (see image below, of the Appalachian Mountain belt in Pennsylvania) and are the result of massive tectonic events. However, look at the image of Massanutten Mountain below, this is an example of a fold on a smaller order. Next, look at the image above the evaluate section, this of a fold in outcrop scale, at an even smaller scale yet. If examined closer still, this outcrop-scale fold would have the same structures (called z or s-folds) that can be seen in the image of the Appalachian Mountains. This concept of the fractal nature of geology is crucial to understanding geologic systems. In addition, make sure to mention the brittle/ductile transition zone in regards to where rocks behave more plastically versus where they tend to break and fracture. Also, in the column that has characteristics of both faults and folds, add notes about faultrelated folding. Image of Appalachian Mountain Belt (Tectonic scale) Outcrop Scale Image Massanutten Mountain (regional scale) Extend Using Google Earth or WhirlWind and pictures of outcrops in cross-section view, supply students with coordinates of exposed faults and folds. Ask them to fly to the coordinates and work together to classify which coordinates or images are faults and which are folds. Typical locations would be Massanutten Mountain (see image above), the San Andreas Fault, the fault block mountains in California, and the Appalachian Mountains. These locations are exceptional exposures of features that are typically subsurface and have been uplifted or tilted. A discussion of how they came to be should accompany students' exploration of each location. Evaluate Using the activities outlined above, have each student come up with a written definition of folding and one of faulting. These definitions must be extensive, covering the depth and nature of each process. Students must hand these two definitions to the teacher and either get them approved or have to revise them before leaving the classroom. Connections Throughout this lesson the teacher will emphasize the fractal nature of folding and faulting. Specifically, that these are smaller scale geologic processes that are a result of larger scale tectonic processes like those discussed in previous lessons. Also, this lesson will be connected to future lessons concerning earthquakes and metamorphism. Reflections This lesson is akin to my constructivist nature. Students are using examples and their own characteristics to develop a definition of the terms folding and faulting. Also, I am a strong proponent of concept-based teaching. As you may have noticed, many of my lessons mention systems and complex system principles like fractals or cycles. I believe that it is important to view the earth as a system with many defining and interrelated parts. Teaching in this manner allows students the ability to continually relate individual concepts back to a broad overarching concept, the earth system. The final summative project will assess the success of this lesson. It is very inquiry based and open-ended, therefore it may be difficult to tell how well the students understood the material until the results of the final summative project are in.