Here's a breakdown of what that means:
* Granodiorite: This is a type of igneous rock that is rich in both quartz and feldspar, with a moderate amount of other minerals like mica and hornblende. It's a relatively light-colored and hard rock.
* Composition: Granodiorite, and therefore the continental crust, is made up primarily of:
* Silica (SiO2): Approximately 60-70%
* Alumina (Al2O3): Approximately 15%
* Sodium Oxide (Na2O) and Potassium Oxide (K2O): These contribute to the feldspar content.
* Calcium Oxide (CaO): This contributes to the plagioclase feldspar content.
* Iron Oxide (FeO) and Magnesium Oxide (MgO): These are present in smaller amounts and contribute to the mafic minerals like hornblende.
Why granodiorite?
* Formation: Continental crust is formed through a complex process called plate tectonics. When oceanic and continental plates collide, the denser oceanic plate subducts (sinks) beneath the continental plate. This process melts the oceanic crust and some of the upper mantle, producing magma that rises and erupts, ultimately forming granitic rocks like granodiorite.
* Abundance: Granodiorite is one of the most abundant types of rocks found in the continental crust.
Important note: While granodiorite represents the *average* composition, the continental crust is highly heterogeneous. There are large variations in rock types and compositions depending on location and geological history.
