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Gsp5 chapter 9 answers8/3/2023 In volcanic areas (yellow dashed line on top), the geothermal gradient is more like 40 to 50 ☌/km, so the temperature rises much faster as you go down. In other words, if you go 1,000 m down into a mine, the temperature will be roughly 30 ☌ warmer than the average temperature at the surface. In most areas (green dashed line on right), the rate of increase in temperature with depth is 30 ☌/km. Recall that the geothermal gradient describes how rapidly the temperature increases with depth in Earth. The yellow, green, and blue dashed lines represent the geothermal gradients in different environments. Source: Karla Panchuk (2018) CC BY 4.0, modified after Steven Earle (2016) CC BY 4.0 view sourceĪnother feature to notice in the diagram are the many dashed lines. Letters correspond to the types of metamorphism shown in Figure 6.36. The metamorphic rocks formed from a mudrock protolith under regional metamorphism with a typical geothermal gradient are listed. Figure 6.35 Metamorphic facies and types of metamorphism shown in the context of depth and temperature. Metamorphic facies are named for rocks that form under specific conditions (e.g., eclogite facies, amphibolite facies etc.), but those names don’t mean that the facies is limited to that one rock type. Each patch of color represents a range of temperature and pressure conditions where particular types of metamorphic rocks will form. The axes on the diagram are temperature and depth the depth within the Earth will determine how much pressure a rock is under, so the vertical depth axis is also a pressure axis. In other words, a given metamorphic facies groups together metamorphic rocks that form under the same pressure and temperature conditions, but which have different protoliths.įigure 6.35 shows the different metamorphic facies as patches of different colors. A convenient way to indicate the range of possible metamorphic rocks in a particular setting is to group those possibilities into metamorphic facies. While these rocks will be exposed to the same range of pressure and temperatures conditions within that setting, the metamorphic rock that results will depend on the protolith. In any given metamorphic setting there can be a variety of protolith types exposed to metamorphism. 6.5 Metamorphic Facies and Index Minerals Metamorphic Facies
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