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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Shivam Sharma posted an Question
September 05, 2020 • 14:31 pm
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30 points
30 points
- CSIR NET
- Earth Sciences
(a) (i) felsic magmas are more likely to give rise to hydrothermal deposits than mafic magmas. why? name two metals that form deposits associated with felsic ma
(a) (i) Felsic magmas are more likely to give rise to hydrothermal deposits than mafic magmas. Why? Name two metals that form deposits associated with felsic magmatism. (6)
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Veer vikram singh
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Felsic magma are produced at end stage of magmatic differentiation. Water and some elements like Rubidium, Caesium, Potassium etc are incompatible in mafic melts. During evolution of melt by differentiation, first mafic minerals such as olivine and pyroxene forms. And remaining melt become more felsic and enriched with incompatible elements. On further melting more mafic minerals such as amphiboles crystallize and remaining melt become more felsic and further enriched with incompatible elements. At end stage of magmatic evolution the melt is highly felsic and contains high amount of these incompatible elements which get segregated from the melt and forms a water rich fluid called as hydrothermal fluid and forms hydrothermal deposit along with felsic rocks. mafic rocks simply do not have high concentration of water and incompatible elements to form hydrothermal deposits.
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Rahul kumar Best Answer
Felsic magma are viscous in comparison with magic magma and can holds a large amount of fluids (water and gases) inside it under subsurface condition. When felsic magma comes to the surface; due to sudden decrease of pressure the fluids come out and can give rise to hydrothermal deposits. The fluids are very enriched in rare elements because felsic magma forms at end stage of magmatic differentiation. The example of hydrothermal deposits generated from felsic magma is Pegmatite deposits which is very enrich in rare minerals like spodumene, beryl etc.