Plate Boundaries and Igneous Process

Plate boundaries are the interface between two tectonic plates.
There are three types of plate boundaries: divergent, convergent, and transform.

Divergent boundaries occur when two tectonic plates move apart.
These boundaries are generally found at the crests of mid-ocean ridges and are characterised by seismic activity.
They are associated with sea-floor spreading, volcanic activity, and the creation of new crust from magma that rise from the mantle, cools and solidifies.

Convergent boundaries occur when two tectonic plates move towards each other.
They can lead to the formation of mountains, oceanic trenches, and volcanic arcs.
The heavier plate, generally the oceanic plate, is subducted beneath the lighter plate, often leading to volcanic activity.
Convergent boundaries are associated with powerful seismic activity.

Transform boundaries involve two plates sliding horizontally past each other.
They do not result in the creation or destruction of the lithosphere, but are associated with seismic activity.
Notable examples include the San Andreas Fault in California.

Igneous processes involve the cooling and solidification of magma or lava to form igneous rocks.
At divergent boundaries, the resultant rocks are primarily basaltic in nature due to the partial melting of mantle peridotite.
At convergent boundaries, the rocks formed can vary. The subducted oceanic plate results in an increased pressure and reduced temperature, causing the formation of rocks like andesite and diorite.
Igneous intrusions, such as dykes, sills, and batholiths, are also common at convergent boundaries and can lead to the creation of large bodies of granite.
Volcanism at both convergent and divergent boundaries contribute greatly to the formation of the Earth’s crust and to the geochemical evolution of the Earth.

Bowen’s Reaction Series describes the sequence in which different types of igneous rocks form as a result of cooling magma.
Minerals crystallise in a systematic fashion based on their melting points.
Minerals crystallise in the order of olivine, pyroxene, amphibole, and biotite mica. This is followed by potassium feldspar, muscovite mica, and quartz.
This series can be used to understand the mineralogy of igneous rocks in relation to their formation conditions.