This is commonly associated with the boundaries of convergent plate and mountain range formation. 16. All of the important processes of metamorphism that we are familiar with can be directly related to geological processes caused by plate tectonics. Regional metamorphism during the Cenozoic Era is linked to plate tectonics. Water within the crust is forced to rise in the area close to the source of volcanic heat, and this draws more water in from farther out, which eventually creates a convective system where cold seawater is drawn into the crust and then out again onto the sea floor near the ridge. In most parts of southern Canada, the average surface temperature is about 10°C, so at 1,000 m depth, it will be about 40°C. A. Because the oceanic crust is typically relatively cool by the time it reaches the subduction zone, especially along its sea-floor upper surface, it does not heat up quickly, and the subducting rock remains several hundreds of degrees cooler than the surrounding mantle (Figure 6.1.5 right). Most feldspars are stable up to between 1000°C and 1200°C. Some minerals will crystallize into different polymorphs (same composition, but different crystalline structure) depending on the temperature and pressure. Regional metamorphism refers to large-scale metamorphism, such as what happens to continental crust along convergent tectonic margins (where plates collide). One of the results of directed pressure and shear stress is that rocks become foliated—meaning that they’ll develop a foliation or directional fabric. Most regional metamorphism takes place within the continental crust. Regional metamorphism largely occurs at convergent plate boundaries. Most blueschist forms in subduction zones, continues to be subducted, turns into eclogite at about 35 kilometres depth, and then eventually sinks deep into the mantle—never to be seen again because that rock will eventually melt. Creative Commons Attribution 4.0 International License. Sedimentary or igneous rocks can be considered the parent rocks for metamorphic rocks. The three heavy dotted lines on this diagram represent Earth’s geothermal gradients under different conditions. Contents. The various types of metamorphism described above are represented in Figure 7.20 with the same letters (a through e) used in Figures 7.14 to 7.17 and 7.19. The type of plate boundary that regional metamorphism is associated with convergent plate boundaries. Figure 6.1.6 shows the types of rock that might form from a mudrock protolith at various points along the curve of the “typical” geothermal gradient (dotted green line). For this reason, it is very difficult to study metamorphic processes in a lab. At a 10 kilometre depth, the temperature is about 300°C and at 20 kilometres it’s about 600°C. Regional metamorphism is a type of metamorphism where the formation of a metamorphic rock occurs in a wide area. Paired metamorphic belts are sets of parallel linear rock units that display contrasting metamorphic mineral assemblages.These paired belts develop along convergent plate boundaries where subduction is active. The conditions under which they were metamorphosed are those of regional metamorphism. When rocks are buried deep in the crust, regional metamorphism occurs. Regional metamorphism. For example, the growth of new minerals within a rock during metamorphism has been estimated to be about 1 millimetre per million years. In only a few places in the world, where the subduction process has been interrupted by some tectonic process, has partially subducted blueschist rock returned to the surface. Figures 6.1.1, 6.1.2, 6.1.4, 6.1.5, 6.1.6: © Steven Earle. The rate of increase of temperature with depth in the Earth (typically around 30˚ C/km within the crust). Beyond 25 km depth in this setting, we cross the partial melting line for granite (or gneiss) with water present, and so we can expect migmatite to form. In most parts of southern Canada, the average surface temperature is about 10°C, so at a 1,000 metre depth, it will be about 40°C. Each pair consists of one belt with a low-temperature, high-pressure metamorphic mineral assemblage, and another characterized by high-temperature, low-pressure metamorphic minerals. The collisions result in the formation of long mountain ranges, like those along the western coast of North America. 2.1 Electrons, Protons, Neutrons, and Atoms, 4.5 Monitoring Volcanoes and Predicting Eruptions, 5.3 The Products of Weathering and Erosion, Chapter 6 Sediments and Sedimentary Rocks, 6.3 Depositional Environments and Sedimentary Basins, Chapter 7 Metamorphism and Metamorphic Rocks, 7.5 Contact Metamorphism and Hydrothermal Processes, 9.1 Understanding Earth through Seismology, 10.1 Alfred Wegener — the Father of Plate Tectonics, 10.2 Global Geological Models of the Early 20th Century, 10.3 Geological Renaissance of the Mid-20th Century, 10.4 Plates, Plate Motions, and Plate-Boundary Processes, 11.5 Forecasting Earthquakes and Minimizing Damage and Casualties, 15.1 Factors That Control Slope Stability, 15.3 Preventing, Delaying, Monitoring, and Mitigating Mass Wasting, Chapter 21 Geological History of Western Canada, 21.2 Western Canada during the Precambrian, Chapter 22 The Origin of Earth and the Solar System, 22.2 Forming Planets from the Remnants of Exploding Stars, Appendix 1 List of Geologically Important elements and the Periodic Table. There are relatively few terrains for which any investigation of the source of the heat for regional metamorphism has been made (Richardson and Powell, 1976), and, on theoretical and observational grounds, sources internal and ex¬ ternal to the metamorphic pile would both appear possible in appropriate areas. Chlorite ((Mg5Al)(AlSi3)O10(OH)8) and serpentine ((Mg, Fe)3Si2O5(OH)4) are both “hydrated minerals” meaning that they have water (as OH) in their chemical formulas. Metamorphism also occurs at subduction zones, where oceanic crust is forced down into the hot mantle. Pressure is important in metamorphic processes for two main reasons. The critical feature of the parent rock is its mineral composition because it is the stability of minerals that counts when metamorphism takes place. In most areas, the rate of increase in temperature with depth is 30°C/km. If there is water present, it will be lower. Such magma bodies, at temperatures of around 1000°C, heat up the surrounding rock, leading to contact metamorphism (Figure 7.19). Most metamorphism results from the burial of igneous, sedimentary, or pre-existing metamorphic rocks to the point where they experience different pressures and temperatures than those at which they formed. Another way to understand metamorphism is by using a diagram that shows temperature on one axis and depth—which is equivalent to pressure—on the other (Figure 6.1.6). For example, when there are two convergent plates pushing together, there will be immense pressure at the fault in between. In most areas, the rate of increase in temperature with depth is 30°C per kilometre. The three heavy dotted lines on this diagram represent Earth’s geothermal gradients under different conditions. So, while the water doesn’t necessarily change the outcome of a metamorphic process, it speeds the process up so metamorphism might take place over a shorter time period, or metamorphic processes that might not otherwise have had time to be completed are completed. Regional metamorphism: We find metamorphic rocks exposed over regions of the Earth's surface, either in the cores of mountain belts or the roots of what were once mountain belts. While rocks can be metamorphosed at depth in most areas, the potential for metamorphism is greatest in the roots of mountain ranges where there is a strong likelihood for burial of relatively young sedimentary rock to … Along subduction zones, as described above, the cold oceanic crust keeps temperatures low, so the gradient is typically less than 10°C/km. 4. regional metamorphism:results from mountain building and plate tectonic collisions. Dynamic metamorphism is associated with zones of high to moderate strain such as … The various types of metamorphism described above are represented in Figure 6.1.6 with the same letters (a through e) used in Figures 6.1.4 and 6.1.5. As a result higher grades of metamorphism can take place closer to surface than is the case in other areas (Figure 7.19). Nevertheless, the cleavage front and the front of regional metamorphism can be found near its western and southern boundaries, in the transition to the more internal parts of the orogen and in relation with the early stages of deformation. While rocks can be metamorphosed at depth in most areas, the potential for metamorphism is greatest in the roots of mountain ranges where there is a strong likelihood for burial of relatively young sedimentary rock to great depths, as depicted in Figure 7.15. Because burial to 10 to 20 kilometers is required, the areas affected tend … In volcanic areas, the geothermal gradient is more like 40° to 50°C/km, so the temperature at 10 km depth is in the 400° to 500°C range. a blue-coloured sodium-magnesium bearing amphibole mineral that forms during metamorphism at high pressures and relatively low pressures, typically within a subduction zone, a metamorphic facies characterized by relatively low temperatures and high pressures, such as can exist within a subduction zone, a garnet-pyroxene-glaucophane bearing rock that is the product of high-pressure metamorphism of oceanic crustal rock (e.g., basalt), typically within a subduction zone. Contact processes work by raising the local temperature and producing hornfels. Results in foliated rocks (convergent plate boundary) Metamorphic rocks are classified basesd on their texture and composition. Magma is produced at convergent boundaries and rises toward the surface, where it can form magma bodies in the upper part of the crust. Regional metamorphism occurs over wide areas, affects large volumes of rocks, and is associated with tectonic processes such as plate collision and crustal thickening (orogenic metamorphism) and ocean-floor spreading (ocean-floor metamorphism). One such place is the area around San Francisco; the rock is known as the Franciscan Complex (Figure 7.18). Describe the three general classes of metamorphic textures, draw them, and give examples of each. Also, some areas can be found locally within the C.Z. This metamorphism creates rocks like gneiss and schist. Beyond a depth of 25 kilometres in this setting, we cross the partial melting line for granite (or gneiss) with water present, and so we can expect migmatite to form. Skip to content. The force of the collision causes rocks to be folded, broken, and stacked on each other, so not only is there the squeezing force from the collision, but from the weight of stacked rocks. Regional metamorphism also takes place within volcanic-arc mountain ranges, and because of the extra heat associated with the volcanism, the geothermal gradient is typically a little steeper in these settings (somewhere between 40° and 50°C/km). Studies linking tectonic environments to types of metamorphic rocks, with key examples from the Pacific Rim and Alpine regions, were published as plate tectonic theory became widely accepted (e.g., Miyashiro, 1967, 1973; Ernst, 1971). Metamorphism occurs along a more-or-less stable geothermal gradient; the resulting metamorphic mineral assemblages are characterized by low recrystallization temperatures and an absence o… Burial metamorphism mostly affects sedimentary strata in sedimentary basins as a result of compaction due to burial of sediments by overlying sediments. Based on the approximate average diameter of the garnets visible, estimate how long this metamorphic process might have taken. This is commonly associated with convergent plate boundaries and the formation of mountain ranges. zones of regional metamorphism. For example, quartz is stable from environmental temperatures (whatever the weather can throw at it) all the way up to about 1800°C. the amount and type of pressure during metamorphism, the types of fluids (mostly water) that are present during metamorphism, and. 1. The main factors that control metamorphic processes are: The protolith, or “parent rock”, is the rock that exists before metamorphism starts. Most regional metamorphism takes place within continental crust. For example, one important metamorphic setting is many kilometres deep within the roots of mountain ranges. The zone of contact metamorphism around an intrusion is very small (typically metres to tens of metres) compared with the extent of regional metamorphism in other settings (tens of thousands of square kilometres). In volcanic areas, the geothermal gradient is more like 40° to 50°C per kilometre, so the temperature at a 10 kilometre depth is in the 400° to 500°C range. At this continent-continent convergent boundary, sedimentary rocks have been both thrust up to great heights (nearly 9,000 metres above sea level) and also buried to great depths. What are the defining features of metamorphic textures? Chapter 1 Introduction to Geology Exercise 7.3 Metamorphic Rocks in Areas with Higher Geothermal Gradients. At 10 km to 15 km, we are in the greenschist zone (where chlorite would form in mafic volcanic rock) and very fine micas form in mudrock, to produce phyllite. regional metamorphism takes place within the continental crust. Are certain types of metamorphic rocks indicative of particular plate boundaries or tectonic settings? Another way to understand metamorphism is by using a diagram that shows temperature on one axis and depth (which is equivalent to pressure) on the other (Figure 7.20). Practice Exercise 6.2 Metamorphic rocks in areas with higher geothermal gradients. The deeper rocks are within the stack, the higher the pre… The presence of water is important for two main reasons. In areas of plate convergence, for example, the pressure in one direction (perpendicular to the direction of convergence) is typically greater than in the other directions (Figure 6.1.2b). Contact metamorphism is common at both convergent and divergent plate boundaries, in areas where molten rock is produced. CC BY. Regional metamorphism is associated with the major events of Earth dynamics, and the vast majority of metamorphic rocks are so produced.They are the rocks involved in the cyclic processes of erosion, sedimentation, burial, metamorphism, and mountain building (), events that are all related to major convective processes in Earth’s mantle.

regional metamorphism and plate boundaries

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