Changes

Subduction zone is one of the most critical tectonic phenomena on Earth. Its correlation to the formation of volcanic arc, deep earthquake, and basins attract the minds of geologists. Profound role of subduction zone emerges as methods in geophysics reveal the structure and composition of materials deep beneath the Earth’s surface.

Subduction zone is one of the most critical tectonic phenomena on Earth. Its correlation to the formation of volcanic arc, deep earthquake, and basins attract the minds of geologists. Profound role of subduction zone emerges as methods in geophysics reveal the structure and composition of materials deep beneath the Earth’s surface.

Principally, subduction zone is the area of the Earth where two plates colliding and the one sinking inside the Earth. The primary cause of subducting slab beside compression is density. Crust with higher density tends to move inside the Earth. According to the types of involved crust, subduction zone has two separate types: island-arc and active continental margin (ACM). Island-arc only involves oceanic crust, while ACM encompasses both continental and oceanic crust.

Principally, subduction zone is the area of the Earth where two plates colliding and the one sinking inside the Earth. The primary cause of subducting slab beside compression is density. Crust with higher density tends to move inside the Earth. According to the types of involved crust, subduction zone has two separate types: island-arc and active [[continental margin]] (ACM). Island-arc only involves oceanic crust, while ACM encompasses both continental and oceanic crust.

==The Earth’s Crust==

==The Earth’s Crust==

====Forearc Basin====

====Forearc Basin====

Forearc basin forms between the volcanic arc and the trench. Volcanic arc and accretionary prism borders the edge of forearc basin. Dimension of forearc basin depends on the arc-trench gap. Continental margin or oceanic crust may form the base of forearc basin. Concerning its capacity to accumulate sediments, rate of subsidence of forearc basin is controlled by sediment loading.

Forearc basin forms between the volcanic arc and the trench. Volcanic arc and accretionary prism borders the edge of forearc basin. Dimension of forearc basin depends on the arc-trench gap. [[Continental margin]] or oceanic crust may form the base of forearc basin. Concerning its capacity to accumulate sediments, rate of subsidence of forearc basin is controlled by sediment loading.

On sedimentological aspects, forearc basin essentially has volcanic arc as provenance and change in depositional environment may occur. Volcanic materials may always exist in successions deposited in forearc basin. Macdonald and Butterworth (1990) in Boggs<ref name=Boggs /> explains that depositional environment in forearc basin may evolove from deep-water deposit, shallow-marine deposit, deltaic deposit, and fluvial deposit on top.

On sedimentological aspects, forearc basin essentially has volcanic arc as provenance and change in depositional environment may occur. Volcanic materials may always exist in successions deposited in forearc basin. Macdonald and Butterworth (1990) in Boggs<ref name=Boggs /> explains that depositional environment in forearc basin may evolove from deep-water deposit, shallow-marine deposit, deltaic deposit, and fluvial deposit on top.

====Active Continental Margin====

====Active Continental Margin====

Active continental margin becomes the most complicated site of magma generation of Earth. As discussed in previous section, magma generation begins at the slab and [[mantle]] wedge. Partial melting of mantle wedge generates basaltic primitive magma. In island-arc, primitive magma rises to the surface and builds basaltic or andesitic volcano. Igneous processes in island-arc differ with active continental margin in assimilation and fractional crystallization.

Active [[continental margin]] becomes the most complicated site of magma generation of Earth. As discussed in previous section, magma generation begins at the slab and [[mantle]] wedge. Partial melting of mantle wedge generates basaltic primitive magma. In island-arc, primitive magma rises to the surface and builds basaltic or andesitic volcano. Igneous processes in island-arc differ with active continental margin in assimilation and fractional crystallization.

Primitive magma generated from the mantle wedge ascent to the boundary of crust and mantle. Due to density contrast, magma from mantle wedge underplates at the base of crust and experiences melting, assimilation, storage, and homogenization (MASH). Assimilation occurs because the crust is molten and enriching the composition of ascending magma. Winter<ref name=Winter>Winter, J. D. 2001, An Introduction to Igneous and Metamorphic Petrology. New Jersey: Prentice-Hall Inc.</ref> defines fractionation as mechanical separation of materials with distinct phases. Simplified explanation of fractional crystallization is represented in Bowen reaction series. Magma will ascent from the base of the crust when faults creating fractures for magma migration. This requirement may occur in thinning area.

Primitive magma generated from the mantle wedge ascent to the boundary of crust and mantle. Due to density contrast, magma from mantle wedge underplates at the base of crust and experiences melting, assimilation, storage, and homogenization (MASH). Assimilation occurs because the crust is molten and enriching the composition of ascending magma. Winter<ref name=Winter>Winter, J. D. 2001, An Introduction to Igneous and Metamorphic Petrology. New Jersey: Prentice-Hall Inc.</ref> defines fractionation as mechanical separation of materials with distinct phases. Simplified explanation of fractional crystallization is represented in Bowen reaction series. Magma will ascent from the base of the crust when faults creating fractures for magma migration. This requirement may occur in thinning area.