Temperature of the crust of the earth
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Temperature of the Earth's Crust
Understanding the temperature distribution within the Earth's crust is crucial for various geological and geophysical studies. This article synthesizes research findings on the temperature variations and factors influencing the thermal state of the Earth's crust.
Temperature Variations in the Earth's Crust
Surface to Deep Crust Temperature Gradient
The temperature of the Earth's crust increases with depth, a phenomenon well-documented through geothermal gradients. At the surface, temperatures average between 10-20°C, but this can vary significantly in polar regions and high mountains where it is much colder, or in deep mines where it becomes too hot to work for extended periods . The temperature change with depth can be plotted to create a geotherm, which shows a continuous increase in temperature as one moves deeper into the crust .
Ultrahigh Temperatures in the Continental Crust
In certain geological settings, the continental crust can reach ultrahigh temperatures of 900-1000°C. These extreme temperatures are often associated with thickened crust in collisional mountain belts and the production of large volumes of magma. Factors contributing to these high temperatures include high internal concentrations of heat-producing elements, low erosion rates, and mechanical heating by deformation in ductile shear zones . Numerical modeling suggests that long-lived mountain plateaus are the most likely settings for such conditions .
Temperature at the Mohorovičić Discontinuity
The Mohorovičić Discontinuity, or Moho, marks the boundary between the Earth's crust and mantle. The temperature at the base of the continental crust at this discontinuity is estimated to be between 500-600°C, while in the sub-oceanic regions, it ranges from 150-200°C . This layer is also under significant compressive stress, which influences its thermal properties .
High-Temperature Metamorphism and Crustal Differentiation
High- to ultrahigh-temperature metamorphism, ranging from 700°C to over 900°C, plays a critical role in the differentiation and stabilization of the Earth's continental crust. This process redistributes key elements between the crust and mantle, leading to the formation of more differentiated and cooler continents. Studies of lower-crustal xenoliths from regions like the Rio Grande Rift show that the lower 10 km of the crust can reside at granulite-facies conditions, with the lowermost 2 km experiencing ultrahigh temperatures . These conditions are indicative of significant conductive heat transfer from the mantle into the crust, facilitated by a thin lithospheric mantle lid .
Conclusion
The temperature of the Earth's crust varies significantly with depth and geological setting. From surface temperatures averaging 10-20°C to ultrahigh temperatures of 900-1000°C in specific regions, the thermal state of the crust is influenced by a range of factors including geothermal gradients, tectonic activity, and the presence of heat-producing elements. Understanding these variations is essential for insights into crustal formation, stability, and the dynamic processes shaping our planet.
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