Changes

===Subduction-related Basins===

===Subduction-related Basins===

Subduction zone generates zone of accumulation of sediments in the trench and on overriding plate. Trench becomes sites of deposition for marine sediments and also for sediments brought by the downgoing plate. Characteristic deposit in trench is mélange. Boggs (2011) defines mélange as mixed assemblage of rock consisting of brecciated blocks in a highly shear matrix. Zone of accumulation on the overriding plate includes forearc, backarc, intraarc, and retro-arc basins. The formation of extensional regime in subduction zone is related to the angle of downgoing plate. As discussed before, subduction zone with steep angle of downgoing plate generates extensional forces on the overriding plate.

Subduction zone generates zone of accumulation of sediments in the trench and on overriding plate. Trench becomes sites of deposition for marine sediments and also for sediments brought by the downgoing plate. Characteristic deposit in trench is mélange. Boggs<ref name=Boggs>Boggs, Sam, Jr., 2011, Principles of Sedimentology and Stratigraphy Fifth Edition. New Jersey: Pearson Prentice Hall.</ref>defines mélange as mixed assemblage of rock consisting of brecciated blocks in a highly shear matrix. Zone of accumulation on the overriding plate includes forearc, backarc, intraarc, and retro-arc basins. The formation of extensional regime in subduction zone is related to the angle of downgoing plate. As discussed before, subduction zone with steep angle of downgoing plate generates extensional forces on the overriding plate.

====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 (2011) 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.

====Backarc Basin====

====Backarc Basin====

====Provenance of Sedimentary Rock in Subduction Zone====

====Provenance of Sedimentary Rock in Subduction Zone====

Provenance of sedimentary rocks can be divided in three types (Boggs, 2011): continental block provenances, recycled orogen provenances, and magmatic arc provenances. Sediments in continental block provenances come from the interior of the plate. Sediments may come from plutonic igneous rocks, metamorphic rocks, and pre-existing sedimentary rocks. Volcanic rocks take part less than other sources. Recycled orogen provenances occur in plate collision. The uplift caused by this process generates various types of rock as sediment source. Conclusively, types of sediment source in recycled orogen are derived from components of oceanic and continental crust: ultramafic rocks, basalt, limestone, shale, and others.

Provenance of sedimentary rocks can be divided in three types:<ref name=Boggs /> continental block provenances, recycled orogen provenances, and magmatic arc provenances. Sediments in continental block provenances come from the interior of the plate. Sediments may come from plutonic igneous rocks, metamorphic rocks, and pre-existing sedimentary rocks. Volcanic rocks take part less than other sources. Recycled orogen provenances occur in plate collision. The uplift caused by this process generates various types of rock as sediment source. Conclusively, types of sediment source in recycled orogen are derived from components of oceanic and continental crust: ultramafic rocks, basalt, limestone, shale, and others.

Provenance of sedimentary rocks in subduction zone originates from magmatic-arc. Sediment sources in magmatic-arc provenances come primarily from volcanic rocks. Geochemistry of igneous rock generated in subduction zone depends of the types of crust involved. Island-arc and active continental margin settings provide different proportions of types of minerals. Island-arc tends to produce basalt and andesite, while active continental margin generate volcanic rocks based on degree of assimilation and fractional crystallization of primitive magma.

Provenance of sedimentary rocks in subduction zone originates from magmatic-arc. Sediment sources in magmatic-arc provenances come primarily from volcanic rocks. Geochemistry of igneous rock generated in subduction zone depends of the types of crust involved. Island-arc and active continental margin settings provide different proportions of types of minerals. Island-arc tends to produce basalt and andesite, while active continental margin generate volcanic rocks based on degree of assimilation and fractional crystallization of primitive magma.

Dickinson et. al. (1983) in Boggs (2011) builds two classifications of provenances based on mineral composition in sandstone. Total quatzose grain, feldspar, and total unstable lithic fragments form one classification, and monocrystalline quartz, feldspar, and unstable clasts plus polycrystalline quartz. The detail of this classification can be reached in Fig. 10.

Dickinson et. al. (1983) in Boggs<ref name=Boggs /> builds two classifications of provenances based on mineral composition in sandstone. Total quatzose grain, feldspar, and total unstable lithic fragments form one classification, and monocrystalline quartz, feldspar, and unstable clasts plus polycrystalline quartz. The detail of this classification can be reached in Fig. 10.

Magmatic-arc provenances encompass undissected arc, transitional arc, and dissected arc. Undissected arc provides sediments from volcanogenic highlands, where the volcano has not been eroded intensively. Major composition of sandstone from this source is unstable lithic fragments. As volcanism ceases and plutonic rock exposed, undissected arc turns out to be dissected arc. Dissected arc has higher proportion of quarzose grains and feldspar than undissected arc. Transitional arc lies between the two.

Magmatic-arc provenances encompass undissected arc, transitional arc, and dissected arc. Undissected arc provides sediments from volcanogenic highlands, where the volcano has not been eroded intensively. Major composition of sandstone from this source is unstable lithic fragments. As volcanism ceases and plutonic rock exposed, undissected arc turns out to be dissected arc. Dissected arc has higher proportion of quarzose grains and feldspar than undissected arc. Transitional arc lies between the two.

File:Subduction Fig-7.png|Fig. 7. Plot of A = K2O + Na2O, F = FeO + 0,9Fe2O3, and M = MgO to Differentiate between Tholeiitic and Calc-alkaline Magma Series (Derived from Wilson, 2007)

File:Subduction Fig-7.png|Fig. 7. Plot of A = K2O + Na2O, F = FeO + 0,9Fe2O3, and M = MgO to Differentiate between Tholeiitic and Calc-alkaline Magma Series (Derived from Wilson, 2007)

File:Subduction Fig-8.png|Fig. 8. Schematic Model of Subduction Zone in Active Continental Margin (Derived from Winter, 2001)

File:Subduction Fig-8.png|Fig. 8. Schematic Model of Subduction Zone in Active Continental Margin (Derived from Winter, 2001)

File:Subduction Fig-9.png|Fig. 9. Classification of Tectonic Settings based on Mineral Composition in Sandstone (Derived from Dickinson et. al. (1983) in Boggs (2011))

File:Subduction Fig-9.png|Fig. 9. Classification of Tectonic Settings based on Mineral Composition in Sandstone (Derived from Dickinson et. al. (1983) in Boggs<ref name=Boggs />)

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==References==

==References==

* Jolivet, Laurent, and Nataf, Henri-Claude. 2001. Geodynamics. Dunod: A. A. Balkema.

* Jolivet, Laurent, and Nataf, Henri-Claude. 2001. Geodynamics. Dunod: A. A. Balkema.

* Keary, Philip and Vine, Frederick J. 1994. Geoscience Texts: Global Tectonics. Oxford: Blackwell Scientific Publications.

* Keary, Philip and Vine, Frederick J. 1994. Geoscience Texts: Global Tectonics. Oxford: Blackwell Scientific Publications.