Mariana Tomás-Laura Rial-Gabriela Varela

Characteristics of Igneous Rocks

Igneous rocks are produced by the crystallization and solidification of molten magma. Magma forms when rock is heated to high temperatures (between 625 and 1200° Celsius) beneath the Earth's surface. The exact temperature needed to melt rock is controlled by several factors. Chemistry of the rock material, pressure, presence of gases (like water vapor) all influence when melting occurs. Most of the heat required to melt rock into magma comes from the Earth's central internal region known as the core. Scientists estimate that the temperature of the Earth's core is about 5000° Celsius. Heat moves from the Earth's core towards the solid outer crust by convection and conduction. Convection moves hot  plumes of magma vertically from the lower mantle to the upper mantle. Some of these plumes melt through the Earth's solid lithosphere and can produce intrusive igneous features and extrusive igneous features on the surface. Heat can also be generated in the lower lithosphere through friction. The tectonic movement of subducted crustal plates can generate enough heat (and pressure) to melt rock. This fact explains the presence of volcanoes along the margin of some continental plates.