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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Gurmeet Singh posted an Question
October 10, 2020 • 20:06 pm
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30 points
30 points
- IIT JAM
- Geology (GG)
Sir please explain the last 4 lines ( question given in paragraph).
Eduncre Geology (Petrology Partial melting of the asthenosphere takes place, resulting in a mafic magma. In most cases, melting occurs because the subducted oceanic crust releases water into the asthenosphere. The water collected in the oceanic crust when it was beneath the ocean and is driven out as the descending plate is heated. The water lowers the melting temperature of the ultramafic rocks in this part of the mantle. Partial melting produces a mafic magma. But how can we keep producing magma from ultramafic rock ? after those rocks have been depleted of the constituents of the mafic magma ? The answer is that hot asthenospheric rock continues to flow into the zone of partial melting. As shown in figure above asthenospheric ultramafic rock is dragged downward by the descending lithospheric slab. More ultramafic 1 alhaia tonaco the descending material. A continuous flow of hot, "fertile" (containing the
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Rahul kumar Best Answer
Last 4 lines discuss about the melt production in subduction zone. As the lithospheric plate goes down into the asthenosphere with subduction, the volatile constituents in the subducting slab comes out. As a result of volatile influx, the asthenosphere starts melting and in turn magma produced. The composition of asthenosphere is mainly ultramafic and with continued subduction of lithospheric plates; the melting continues because of increasing temperature with depth. Even after the depletion of constituents, due to increasing temperature with depth the melting process continues.
but sir asthenosphere is already in melt state.
it itself can't strt rising?
No, asthenosphere is not completely melt. Asthenosphere is partially melted and melt amount is very low which cannot start rising itself. Volatile influx melting will produce sufficient amount of melt and once melt will be sufficient, it will start rising.