Earth crust temperature
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Earth Crust Temperature: Gradients and Influencing Factors
Temperature Gradient in the Earth's Crust
The temperature in the Earth's crust increases with depth, a trend known as the geothermal gradient. A commonly cited average is about 3°C for every 100 meters of depth, though this can vary depending on local geology and heat flow conditions . Near the surface, temperatures are influenced by daily and annual cycles, but below about 50 meters, the temperature becomes stable and reflects the mean annual surface temperature, typically ranging from 5–8°C in some regions .
Deep Crustal Temperatures and Extreme Conditions
At greater depths, especially in thickened continental crust found in mountain belts, temperatures can reach ultrahigh values of 900–1000°C. These extreme temperatures are often associated with tectonic processes such as crustal thickening, high concentrations of heat-producing elements, and low erosion rates. Additional heating can occur in already-hot back-arc basins and through mechanical deformation in ductile shear zones . In some regions, such as the lower crust beneath the Rio Grande Rift, temperatures can exceed 900°C, with the lowermost crust reaching ultrahigh-temperature conditions due to enhanced conductive heat transfer from the mantle .
Heat Transport Mechanisms in the Crust
Heat in the Earth's crust is transported mainly by conduction, except in areas where fluid flow allows for heat advection. The dominant sources of heat are the original heat from Earth's formation and the decay of radioactive isotopes. Heat conduction is the primary process, but in rocks above 1200°C, heat radiation can also become significant . The thermal properties of crustal rocks, such as thermal diffusivity and conductivity, decrease with increasing temperature, making the hot middle and lower crust more effective at insulating heat than previously thought . This insulation can lead to positive feedback, where heating and partial melting further increase insulation and crustal temperatures .
Regional and Temporal Variations
Temperature distributions in the crust can vary significantly by region and over geological time. For example, in Southeastern Australia, Precambrian rocks can reach temperatures of about 650°C at depth due to higher rates of heat production, while Phanerozoic crust in the same area may only reach 520°C at the base of the crust . In the Archean era, the average temperature of the crust and mantle was similar to or slightly higher than today, with mantle potential temperatures estimated between 1450–1600°C, influencing the formation and differentiation of early continental crust 89.
Surface Temperature Effects
Surface temperature changes, such as daily and annual cycles, mainly affect the uppermost layers of the crust. These variations can cause stress and deformation in the shallow crust, but their influence diminishes rapidly with depth . Models show that cyclic surface temperature changes can induce stress changes up to 50 MPa in the near-surface crust .
Conclusion
The temperature of the Earth's crust is controlled by a combination of surface conditions, internal heat sources, and the physical properties of rocks. While surface temperatures stabilize below about 50 meters, deeper crustal temperatures rise steadily, reaching hundreds to over a thousand degrees Celsius in certain tectonic settings. The efficiency of heat transport and insulation in the crust is strongly influenced by rock properties, tectonic activity, and the presence of heat-producing elements, leading to significant regional and temporal variations in crustal temperature profiles 12456789+1 MORE.
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