For most igneous rocks on earth, melting originally occurred in; a. the surface
ID: 159287 • Letter: F
Question
For most igneous rocks on earth, melting originally occurred in;
a. the surface of the earth
b. in the lower crust
c. in the middle continental crust
d. in the upper crust
e. in the lower most mantle
f. in the inner core
g. in the upper mantle
h. in the lowest part of the crust
i. on another planetary body
Which of the following processes do not influence changes in magma composition after intial partial melting?
a. mixing of the magma in the atmosphere
b. crystal fractionation
c. melting in assimilation of adjacent continental crust
Explanation / Answer
(1) For most igneous rocks on earth, melting originally occurred in
Answer :: (g) in the upper mantle
|Magma origination|
The Earth's crust is about 35 kilometers (22 miles) thick under the continents, but averages only some 7 kilometers (4.3 miles) beneath the oceans. It is made up of rocks which have a relatively low density, and beneath the crust there is the denser rock of the mantle, which extends to a depth of nearly 3,000 kilometers (1,860 miles). Most of the magma which forms igneous rocks is generated within the upper parts of the mantle at temperatures estimated between 600 to 1600 °C.
(2) Which of the following processes do not influence changes in magma composition after intial partial melting?
answer:: (c) melting in assimilation of adjacent continental crust
If magmas are related to each other by some processes, that process would have to be one that causes magma composition to change. Any process that causes magma composition to change is called magmatic differentiation. Over the years, various process have been suggested to explain the variation of magma compositions observed within small regions. Among the processes are:
Initially, researchers attempted to show that one or the other of these process acted exclusively to cause magmatic differentiation. With historical perspective, we now realize that if any of them are possible, then any or all of these processes could act at the same time to produce chemical change, and thus combinations of these processes are possible.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.