Understanding the Rock Cycle, Magmatism, and Mountain Formation

The Rock Cycle

The eroded rock reliefs acquiesce.

In areas of collision, mountains arise, and rocks undergo a process of metamorphosis.

The succession of these phenomena is the rock cycle.

The surface rocks are altered by physical or chemical processes to form sedimentary rocks.

In the depths of the crust, in subduction zones, by varying the temperature and pressure, metamorphic rocks occur.

Igneous rocks are formed by the cooling of magma from the melting of solid materials from the mantle or crust. If cooling is slow, the structure of the rock is plutonic; if it's fast, it's volcanic.

Magmatism

Magmatism on the Ridges

There are cracks in the ridges where basaltic magma rises, which solidifies at the bottom of the sea.

Magmatism in Subduction Zones

In the process of subduction, the material of the oceanic plate and continental crust melts. The magma is andesitic type, leading to explosive-type volcanoes at the edge of the continental plate, forming ridges or volcanic island arcs.

Intraplate Magmatism

Magmatic activity within the oceanic and continental plates occurs in hot spots, where mantle material rises.

Hawaiian Archipelago

As the Pacific plate moves northwest, the older volcanoes become extinct, and new ones appear, creating a succession of volcanic islands.

Mountain Ranges

Mountain ranges are formed at plate boundaries as a result of compression when plates collide. Evidence of this includes:

• Deformation of rocks
• Sedimentary rocks that bend if the temperature allows plastic behavior, and fracture if they exceed the limit of plasticity
• Presence of rocks and marine fossils at the top of the mountain ranges
• Metamorphosis in the rocks

Mountain Chain Formation

Mountain ranges are formed by the collision of plates. This can occur through:

• Convergence of continental plates: The Himalayan range is the result of the collision of India with the Eurasian continent.
• Convergence of oceanic-continental plates: The Andes are formed by the collision of the oceanic Nazca plate and the South American continental plate. The oceanic plate subducts under the continental plate.

Evolution of Mountain Chains

Mountain chains take a long time to form and are also destroyed by erosion.

The chains undergo two main effects:

• Destruction of the relief by weathering and erosion.
• Isostatic adjustment due to the different densities between the root of the Andes and the surrounding mantle.

When the root of the mountain chain has disappeared through erosion, a peneplain appears.

Transform Faults

The different rates between areas of the plates give rise to the appearance of transform faults. These are large fractures that cut perpendicularly through the back, moving horizontally. Most transform faults are underwater.