5. Choose the appropriate melting mechanism associated with the following enviro

Question

5. Choose the appropriate melting mechanism associated with the following environments of igneous activity by putting one of the following letters in the four blanks below (note that not all of the mechanisms may be appropriate melting mechanisms): IC=injection of molten material from Earth's core =D decompression melting (decrease in pressure), T= temperature increase melting, F= fluid fluxed melting, S=Dissolving of solid rock in water,

Upper Mantle beneath magmatic arcs______________

Upper Mantle beneath midocean ridge___________

Continental crust over hot spot__________________

6. True (T) or false (F): Most of the mantle is molten.

7. After each write "C" if it is a convergent plate boundary; D" if it is a divergent plate boundary; T if it is a transform plate boundary: (a) Southwest Indian Ridge:_____ (b) East Pacific Rise: _______(c) Andean Are:_________ (d):San Andreas fault system: _______(e) lzu-Bonin Are: _______(f)Mid-Atlantic Ridge:________.

8. which of the following INCREASES the potential explosiveness of a volcanic eruption? (circle best answer): (a) higher magma temperature(b) Higher silica content of magmas(c) lower silica content of magma; (e) lower viscosity of magma; (f) none of the above.

Explanation / Answer

5.A. F= fluid fluxed melting

This is caused when subduction at the convergent plate boundaries. Subduction at convergent plate boundaries introduces water into the mantlee and causes flux melting of the mantle to produce basaltic magmas. The magmas when reach the surface build island arcs.

5.B. D = decompression melting (decrease in pressure) at mid oceanic ridge. Partial decompression melting

5.C. D = decompression melting ( decreasing in pressure) due to rising mantle plume causing hotspots.

6. Mantle is has layers - Lithospere, Aesthanospere, Mesosphere. only Aestahnosphere is motlen or plastic, Mesosphere and lithosphere are rigid or solid. Hence, when question says "most of the mantle is molten", it is FALSE.

7. a) D = divergent plate boundary

b) East pacific rise is an mid oceanic ridge at the D= divergent plate boundary.

c) C= convergent plate boundaries that cause subduction forms volcanic andean belt.

d) Transform Fault, hence T= Transform plate boundary

e) Izu Bonin Mariana arc system is a convergent plate boundary system.

8. (B) high silica content. more the silica content more the explosiveness. Felsic magma has high silica content(70%) than mafic and intermediate and so is more explosive than the mafic and intermediate.

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