The inferred temperature at the interface between the stiffer mantle and the asthenosphere is closest to what temperature?
The correct answer and explanation is :
The inferred temperature at the interface between the stiffer mantle (lithospheric mantle) and the asthenosphere is approximately 1300°C (or 1500 K).
Explanation (Approx. 300 words):
The Earth’s interior is composed of several layers: the crust, the mantle, and the core. The mantle itself is subdivided into the upper mantle (which includes the lithospheric mantle and the asthenosphere) and the lower mantle. The lithosphere is the rigid outer part of the Earth, encompassing the crust and the uppermost portion of the mantle. Beneath it lies the asthenosphere, a relatively ductile and partially molten layer that behaves plastically over geological timescales, allowing tectonic plates to move.
The temperature at the boundary between the stiffer lithospheric mantle and the more ductile asthenosphere is crucial for understanding plate tectonics. This boundary is not marked by a sharp compositional change but rather by a difference in mechanical behavior—primarily due to temperature and pressure conditions.
Studies using seismic tomography, heat flow measurements, and experimental petrology suggest that the transition from the rigid lithosphere to the ductile asthenosphere occurs at around 1300°C. This temperature is significant because it is roughly the solidus temperature for peridotite, the dominant rock type in the upper mantle. At this temperature, the rock begins to partially melt or significantly weaken, allowing for the ductile flow observed in the asthenosphere.
This 1300°C isotherm is often used to define the lithosphere-asthenosphere boundary (LAB). The precise depth of this boundary varies depending on the tectonic setting: it may be as shallow as 50 km beneath oceanic lithosphere and as deep as 200 km beneath stable continental interiors. Nonetheless, the temperature remains relatively constant because it is tied to the material properties of mantle rocks.
In summary, the inferred temperature at the interface between the stiffer mantle and the asthenosphere is about 1300°C, marking the transition from brittle to ductile behavior in Earth’s upper mantle.
