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the oceanic lithosphere to descend. The relationship between surface slope and subduction thrust also plays a huge role in the variation of forearc structure and deformation. A subduction wedge can be classified as either stable with little deformation or unstable with pervasive internal deformation (see section on Models). Some common deformation in forearc sediments are
151:
In general, the forearc topography (specifically in the trench region) is trying to achieve an equilibrium between buoyancy and tectonic forces caused by subduction. Upward motion of the forearc is related to buoyancy forces and the downward motion is associated with the tectonic forcing which causes
193:
The intense interaction between the overriding and underthrusting plates in the forearc regions have shown to evolve strong coupling mechanisms which result in megathrust earthquakes such as the Tohoku-oki earthquake which occurred off the
Pacific coast of Northeast Japan (Tian and Liu. 2013). These
180:
There are two models which characterize a forearc basin formation and deformation and are dependent on sediment deposition and subsidence (see figure). The first model represents a forearc basin formed with little to no sediment supply. Conversely, the second model represents a basin with a healthy
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One good example is the
Mariana forearc, where scientists have done extensive research. In this setting there is an erosive margin and forearc slope which consists of 2 km high and 30 km diameter serpentine- mud volcanoes. The erosive properties of these volcanoes are consistent with the
184:
The age of the oceanic crust along with the convergent velocity controls the coupling across the converging interface of the continental and oceanic crust. The strength of this coupling controls the deformation associated with the event and can be seen in the forearc region deformation signatures.
147:
The accretionary prism is located at the slope of the trench break where there is significantly decreased slope angle. Between the break and the magmatic arc, a sedimentary basin filled with erosive material from the volcanic arc and substrate can accumulate into a forearc basin which overlays the
53:
which may form a topographic ridge known as an outer arc ridge that parallels the volcanic arc. A forearc basin between the accretionary wedge and the volcanic arc can accumulate thick deposits of sediment, sometimes referred to as an outer arc trough. Due to collisional stresses as one tectonic
114:
Over geological time there is constant recycling of the forearc deposits due to erosion, deformation and sedimentary subduction. The constant circulation of material in the forearc region (accretionary prism, forearc basin and trench) generates a mixture of igneous, metamorphic and sedimentary
105:
Initial theories proposed that the oceanic trenches and magmatic arcs were the primary suppliers of the accretionary sedimentation wedges in the forearc regions. More recent discovery suggests that some of the accreted material in the forearc region is from a mantle source along with trench
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sediment supply. Basin depth depends on the supply of oceanic plate sediments, continentally derived clastic material and orthogonal convergence rates. The accretionary flux (sediment supply in and out) also determines the rate at which the sedimentation wedges grow within the forearc.
143:
At the surface, the forearc region can include a forearc basin(s), outer-arc high, accretionary prism and the trench itself. The forearc subduction interface can include a seismogenic zone, where megathrust earthquakes can occur, a decoupled zone, and a viscously coupled zone.
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sequences. In general, there is an increase in metamorphic grade from trench to arc where highest grade (blueschist to eclogite) is structurally uplifted (in the prisms) compared to the younger deposits (basins). Forearc regions are also where ophiolites are emplaced should
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driven by the down dip motion of the subducting slab. At the same time, the temperature of the mantle wedge closer to the trench is dominated by the denser and colder subducting slab, resulting in a cold, stagnant portion of the mantle wedge.
134:
collision, there is uplift and erosion of the accretionary prism and forearc basin. In the later stages of collision, the forearc region may be sutured, rotated and shortened which can form syn-collisional folds and thrust belts.
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derived from continental material. This theory holds due to evidence of pelagic sediments and continental crust being subducted in processes known as sediment subduction and subduction erosion respectively.
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mega thrust earthquakes may be correlated with low values of heat flow generally associated with forearc regions. Geothermal data shows a heat flow of ~30–40 mW/m, which indicates cold, strong mantle.
416:
Wada, Ikuko; Wang, Kelin; He, Jiangheng; Hyndman, Roy D. (2 April 2008). "Weakening of the subduction interface and its effects on surface heat flow, slab dehydration, and mantle wedge serpentinization".
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metamorphic grades (blueschists) expected for this region in the forearc. There is evidence from geothermal data and models which show the slab-mantle interface, levels of friction and the cool oceanic
452:
Uchida, Naoki; Nakajima, Junichi; Wang, Kelin; Takagi, Ryota; Yoshida, Keisuke; Nakayama, Takashi; Hino, Ryota; Okada, Tomomi; Asano, Youichi (10 November 2020).
539:
Brown, D.; Spadea, P (2013). "Processes of forearc and accretionary complex formation during arc-continent collision in the southern Ural
Mountains".
271:
90:. This area between the trench and the arc is called the forearc region, with the area behind the arc and away from the trench known as the
293:
Fuller, C. W; Willet, S.D.; Brandon, M.T. (2006). "Formation of forearc basins and their influence on subduction zone earthquakes".
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As tectonic plates converge, the closing of an ocean will result in the convergence of two landmasses, each of which is either an
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23:
Cross-section of a subduction zone and back-arc basin. The forearc is the region between the trench and the volcanic arc.
509:
Casey, J.; Dewey, J. (2013). "Arc/Forearc
Lengthening at Plate Triple junctions and the Formation of Ophiolitic Soles".
261:
227:
552:
454:"Stagnant forearc mantle wedge inferred from mapping of shear-wave anisotropy using S-net seafloor seismometers"
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and eponymously form 'in front of' the volcanic arcs that are characteristic of convergent plate margins. A
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The mantle region between the overriding plate and the subducting slab experiences corner flow near the
19:
607:
Tian, L.; Liu, Lucy (2013). "Geophysical properties and seismotectonics of the Tohoku forearc region".
374:"Mantle flow in subduction systems: The mantle wedge flow field and implications for wedge processes"
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plate subducts under another, forearc regions are sources for powerful earthquakes.
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occur, but such deposits are not continuous and can often be removed by erosion.
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130:, at which time the underthrusting oceanic crust slows down. In early stages of
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86:. The weight of the subducting slab flexes the overriding plate and creates an
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is a plate tectonic term referring to a region in a subduction zone between an
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plate is thrust below another tectonic plate, which can be oceanic or
568:"Advances in the thermal and petrologic modeling of subduction zones"
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or continental margin. When these two bodies collide, the result is
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The region between an oceanic trench and the associated volcanic arc
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351:(3rd ed.). Singapore by Moarkono: J. Wiley. pp. 1–400.
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Sedimentary Basins : Evolution, Facies, and
Sediment Budget
347:
Kearey, Philip; Klepeis, A. Keith; Fredrick, Vine J. (2009).
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10.1130/0091-7613(1999)027<0649:pofaac>2.3.co;2
74:. Water and other volatiles in the subducting plate cause
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oldest thrust slices in the wedge of the forearc region.
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372:Long, Maureen D.; Wirth, Erin A. (February 2013).
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46:is the companion region behind the volcanic arc.
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378:Journal of Geophysical Research: Solid Earth
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207:at the trench. Other good examples are:
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38:. Forearc regions are present along
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272:Forearc Basin Architecture, abstract
566:Peacock, Simon M. (1 August 2020).
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419:Journal of Geophysical Research
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511:Geological Research Abstracts
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629:10.1016/j.jseaes.2012.12.023
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160:, such as that seen in the
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609:Geological Survey of Japan
478:10.1038/s41467-020-19541-y
256:2nd ed., Ch. 12, Springer
154:synsedimentary deformation
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252:Einsele, Gerhard (2000)
211:Central Andean Forearc
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49:Many forearcs have an
24:
458:Nature Communications
230:and Peru-Chile Trench
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22:
439:10.1029/2007JB005190
621:2013JAESc..64..235T
584:2020Geosp..16.1647P
523:2013EGUGA..1513430C
470:2020NatCo..11.5676U
431:2008JGRB..113.4402W
390:2013JGRB..118..583L
307:2006Geo....34...65F
34:and the associated
593:10.1130/GES02213.1
399:10.1002/jgrb.50063
228:Western Cordillera
217:Savu-Wetar Forearc
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51:accretionary wedge
40:convergent margins
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358:978-1-4051-0777-8
220:Luzon arc-forearc
176:Types of forearcs
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315:10.1130/g21828.1
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164:forearc region.
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267:USGS definition
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241:Back-arc region
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92:back-arc region
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44:back-arc region
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578:(4): 936–952.
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547:(7): 649–652.
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384:(2): 583–606.
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223:Tohoku Forearc
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88:oceanic trench
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32:oceanic trench
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214:Banda Forearc
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158:olistostromes
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301:(2): 65–68.
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162:Magnitogorsk
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84:volcanic arc
80:upper mantle
76:flux melting
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36:volcanic arc
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615:: 235–244.
464:(1): 5676.
205:lithosphere
72:continental
659:Subduction
643:Categories
247:References
189:Seismicity
128:orogenesis
124:island arc
108:turbidites
64:subduction
572:Geosphere
517:: 13430.
139:Structure
117:obduction
58:Formation
496:33173070
235:See also
226:Between
198:Examples
99:back-arc
617:Bibcode
580:Bibcode
541:Geology
519:Bibcode
487:7655809
466:Bibcode
427:Bibcode
386:Bibcode
303:Bibcode
295:Geology
78:in the
68:oceanic
62:During
28:Forearc
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425:(B4).
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168:Models
66:, an
492:PMID
353:ISBN
258:ISBN
156:and
625:doi
588:doi
549:doi
482:PMC
474:doi
435:doi
423:113
394:doi
382:118
311:doi
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