Magmatism refers to the movement or activity of magma, which is molten rock formed from rocks melted under high temperature and pressure. It can occur through processes such as subduction, hot-spot volcanism, and along rift zones, with specific conditions required for magma formation including decompression melting, flux melting, and heat transfer melting. Understanding these processes and conditions is essential for studying geological formations and volcanic activity.

1. MAGMATISM

2. Magmatism is the activity or the
motion of the magma. Rocks that
are subjected to high
temperature and pressure
melt and become the
magma. Magma is a semi-liquid
molten rock mixture that can be
found in the lower portion of the
crust and the upper part of the
mantle.

3. Types of Magma Generation
A. Subduction
The geodynamic process of one plate
sliding beneath another which occurs
along deep-sea trenches

4. B. Hot-spot Volcanism
A "hot spot" represents a region
of volcanism above a relatively
stationary region of intense
heat within the Earth's mantle,
a so-called mantle plume.

5. C. Magmatism along rift zones
The less spectacular formation of
mountains, involving magma addition
into the Earth’s surface, occurs along
with incipient spreading centers,
oceanic ridges, and (continental) rifts.

6. Special conditions required for the formation of magma
(Marshak, et al, Essentials of Geology, 2013):
a. Crust and mantle are almost entirely solid, indicating that
magma only forms in special places where pre-existing solid
rocks undergo melting.
b. Melting due to decrease in pressure (decompression
melting): The decrease in pressure affecting a hot mantle
rock at a constant temperature permits melting forming
magma. This process of hot mantle rock rising to shallower
depths in the Earth occurs in mantle plumes, beneath rifts
and beneath mid- ocean ridges.

7. c. Melting as a result of the addition of volatiles (flux
melting): When volatiles mix with hot, dry rock, the
volatile decreases the rock’s melting point and they help
break the chemical bonds in the rock to allow melting.
d. Melting resulting from heat transfer from rising
magma (heat transfer melting): A rising magma from
the mantle brings heat with it that can melt the
surrounding rocks at the shallower depths.

8. Table 3. Summary of the conditions for magma
generation and the areas it occurs