Crust temperature
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Crust Temperature: Insights from Recent Research
Ultrahigh Temperature in Continental Crust
Research has shown that the Earth's continental crust can reach ultrahigh temperatures (UHT) of 900-1000°C. These extreme temperatures are often found in thickened crust within collisional mountain belts and are associated with significant magma production. Numerical models suggest that a long-lived mountain plateau with high internal heat-producing elements and low erosion rates is the most likely setting for such conditions. Additionally, the preferential thickening of already-hot back-arc basins and mechanical heating by deformation in ductile shear zones can also contribute to these elevated temperatures 17.
Temperature Estimation in the Tibetan Crust
In the Tibetan crust, precise temperature estimation has been achieved through the seismic detection of the α-β quartz transition (ABQT). This transition occurs at temperatures of 700°C or higher in quartz-rich felsic rocks. Seismic features of the ABQT have been identified at depths of 18 km and 32 km in different regions of Tibet, corresponding to temperatures of 700°C and 800°C, respectively. These findings suggest that recent geological processes, rather than lithologic boundaries, are responsible for these high temperatures .
Cold Crust in Hot Spots
Contrary to expectations, the lower crust in some hot spots, such as Iceland, exhibits significantly lower temperatures than predicted by existing models of crustal accretion. Shear wave studies indicate that the temperature of the lower crust in these regions is at least 250-325°C below the solidus of gabbro, which is around 875-950°C. This discrepancy suggests that the lower crust in these areas is much cooler than previously thought .
Factors Influencing Crustal Metamorphism
The development of regional metamorphism in thickened continental crust is influenced by several factors, including radiogenic heat supply, mantle heat input, thermal conductivity, and erosion rates. During orogenic episodes, crustal thickening is followed by a phase of erosion, leading to thermal relaxation and subsequent cooling. The extent of heating and the timing of cooling are governed by the degree of crustal thickening and the duration before the rock is exhumed. This process can result in significant melting of the continental crust .
Conclusion
The temperature of the Earth's crust varies significantly depending on geological settings and processes. Ultrahigh temperatures are common in thickened crust within mountain belts, while some hot spots exhibit unexpectedly low temperatures. Precise temperature estimation techniques, such as seismic detection of the ABQT, provide valuable insights into crustal dynamics. Understanding these temperature variations is crucial for comprehending the thermal and tectonic evolution of the Earth's crust.
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