In this article, we will learn about magma characteristics, igneous rocks, and intrusive activity. Magma is the parent material of all igneous rocks. The molten material cools and solidifies. That’s gonna make our Rock.
Part of our global system is constantly changing and reshaping our world. The intrusive volcanic activity takes place beneath the earth’s surface when magma is forced to rise to the surface.
The majority of the magma is interrupted into the crust. When it solidifies and forms a range of features. Dykes are vertical inclusions that cut across the layers of rock.
Horizontal intrusions come to the different layers from erosion and can expose intrusive activity and bring it to the surface. They are formed deep below the earth’s surface when magma cools and solidifies forming large crystals.
Born out of tectonic plate movements and magma, volcanoes are the creator and destroyers of life on earth. They are formed by rising magma, originating in the core of the earth.
Let’s first introduce some of the factors that really help us understand some of these eruptions. So again remember, when referencing the differences between magma and lava, magma is deep underneath the surface and lava is what we see on top.
Now some of the general magma characteristics.
Let’s understand some characteristics of magma. It includes composition, temperature, and the last being the dissolved gases that are within that material.
Composition
Now moving into composition, we have three primary families. We have a fourth one which is considered ultra, ultramafic but that’s not very important.
The three that will be really focusing on will be felsic, intermediate, or mafic. so we’ll introduce what that means.
Temperature
The next step is looking at its temperature. It is once we consider it extremely hot and then considered as being cooler. Again the cool is still quite hot but there is a variation in those temperatures within those plumes and material.
Gases
Last is the dissolved gases. We find that when you have more dissolved gases in the material, as that material moves closer towards the surface in that convective current because of decreased pressure it can actually cause more of an explosion.
Viscosity
Let’s also talk about viscosity. Viscosity can be kind of challenging. But looking at the differences between honey and water, you know they’re both a liquid but they also move very differently.
They move very fluidly but one’s much slower, one is a lot quicker and so we’ll kind of talk about what they’re. So viscosity is the measure of a material’s resistance to flow or to measure its mobility.
Let’s look at something that may have high silica and ions. One that has high silica will also have high viscosity much like honey.
We’ll see that the temperature ranges between 650 and 900 degrees Celsius. These would be fake felsic lavas such as perhaps rhyolite.
Looking more at an intermediate zone the medium silica material that has intermediate viscosity will be between 800 degrees and 1050 degrees Celsius.
These types of materials we also identify as being andesite and then lastly low silica material will have low viscosity. Water does have low viscosity but in that sense of how it flows those will be between temperatures of one thousand to twelve hundred and fifty degrees Celsius.
So again when looking at viscosity we can see that there’s definitely a correlation between what is vicious or not based on its silica.
When talking about magma characteristics, it also includes Partial melting. Partial melting is the process in magma formation. that is going on down inside the earth. Now as magma reaches the surface. It is called lava.
Extrusives are the ones formed at the surface from magma. Ones that are formed at depths, due to the crystallization of magma are termed intrusive because they’re inside the earth.
An underwater volcano erupted off of Tonga’s main island. So that was back in 2009 so with the rocks that are created from this sort of eruption would they be intrusive or extrusive? They’re gonna be extrusive.
Even though it’s underwater, it’s still at the surface of the earth. So it’s gonna be producing those extrusive rocks. Kilauea eruption of Hawaii’s Mayen island at the top arrow that’s actually pointing to magma and inside the volcano. It’s intrusive rocks because they are inside the volcano.
The solids are any silicate minerals that were inside the magma chamber that is starting to crystallize out and then we have some of our different gaseous components.
We have carbon dioxide, water, and sulfur dioxide. Those are the three most common gases that you’re gonna find in magma. But there are plenty more and learn a little bit more about some of the gases you can expect in volcanoes.
Crystallization is another Magma characteristic. Here we’re gonna generate different types of silicate minerals. Just a little bit of a review of what exactly are silicate minerals.
Read: Learn about 3 different types of rocks
Remember they have to have silicon and oxygen. Now within that two different divisions. We have our Ferro magnesium and our non-Ferro magnesium silicate minerals.
But it just depends on their composition whether or not they have iron and magnesium.
The texture of the igneous rock is gained by mineral grains arrangement, size, and shape. The texture is gonna be a common term that we use for igneous, sedimentary, and metamorphic rocks. Hope you’re now clear with Magma’s characteristics.
Classification of igneous rocks
Slow cooling is gonna promote larger crystals. The faster it is, the smaller they are.
Another factor that affects the crystal size is the amount of silica present and the number of dissolved gases. Talking about the origin of magma is a pretty controversial topic among geologists. generating magma from solid rock.
So it’s produced when essentially a solid rock and the crust and upper mantle melt. So temperature increases with the Earth’s upper crust which is called the geothermal gradient when an average is between 20 degrees Celsius and 30 degrees Celsius per kilometer.
Near their melting points, additional heat actually causes the rocks to melt can come from friction at subduction zones heating. as rocks are descending down into the mantle and heat rises from hot mantle rocks.
Now the role of pressure is pretty important as well. so an increase in confining pressure. this conversely reducing the pressure will lower the melting temperature.