Is the Asthenosphere the same as the Mohorovicic Discontinuity?
1 Answer
No. The Mohorovicic Discontinuity is a change in composition of the rock, but it lies largely within the rigid lithosphere. The plastic asthenosphere is further down.
Explanation:
The Mohorovicic Discontuity is the boundary between the crust and mantle, where the basalt present in the crust gives way to heavier silicate rocks such as periodotite and dunite, which are characteristic of the upper mantle.
But the mantle rock is still rigid until you go further down where you have higher temperature. That is what makes the rock start to behave plastically; just as warm taffy is easier to pull than cold taffy, so it is with rock. But "warm" in the case of the upper mantle's rock means roughly 1300°C, and the lithosphere-asthenosphere boundary (LAB) is conventionally an isotherm in the mantle at that temperature.
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