How does magma change as crystallization occurs?
We said before that different minerals have different melting points. So, when rock heats up, different minerals melt sooner or later. The different minerals also affect what happens when rock cools. The liquid minerals with the highest melting point will solidify into crystals first. As a result, the chemical composition of the remaining magma is different. See Figure 4.10. • What happens when two magmas come together? You don’t have to worry about this section. It’s very interesting. We think that magmas probably combine more than we imagine. Sometimes, the combination is explosive. • What are zoned plutons? You can skip. Study questions • We do not find any ultramafic volcanic rocks younger than 2.5 billion years old. What does that tell us about the internal temperature of the Earth in the past? • Why are most explosive volcanoes near subduction zones? [Compared to say, volcanoes at divergent plate boundaries or hot spots?] • List some fluids that have a high viscosity. List some f
