What effect does temperature have on the characteristics of magama?

Answer 1

This is quite a complicated question because one needs to consider the temperature at which the magma forms and the temperature st which it intrudes/erupts.

First let us consider the formation of magma, to make it you must melt a preexisting solid rock made up a bunch of chemical held together as minerals. Obviously if you were to melt it entirely then the overall composition would be the same as that of the rock being melted. However, when one starts to heat a rock some bits of it melt first to form a magma. Rather like how antifreeze melts ice a specific melt composition forms first (this is called a eutectic composition. If the melt then flows out of the rock, different magma will be formed from the remaining rock at higher melting temperature.

The eutectic melt determines the composition of the main magma types (basalt, andesite, granite, etc) depending on the composition of the source rocks.

Thus the first point is at given a certain start point chemistry, certain temperatures will produce specific magma chemistries.

OK, having generated a magma, this will move up in the crust and cool. if the temperature reduces slowly as it cools then a course grained rock, if it cools fast then it will form a fine grained rock.

Also the hotter the magma, the more "runny" it is when intruded or erupted.