12 Basin Evolution and Sediments
12.5 Deep-Sea Trenches,
Foreare, Backare, and
Retroarc Basins
12.5.1 Plate-Tectonic Overview
12.5.2 Deep-Sea Trenches and Accretionary Wedges
General Characteristics and Sediment Sources
Trench Fills and Sediment Accretion
(Qualitative Aspects)
Trench fills, Accretion and Subduction
ofSediment (Quantitative Aspects)
Sediment Budget ofModem Subduction
Complexes
Conclusions for the Sediment Budget
Specific Structures and Other Phenomena in
Accretionary Wedges
Tectonic Deformation
Melange, Wildflysch
Mud Diapirs and Mud Volcanoes
Examples of Arc-Trench Systems
Summary (Deep-Sea Trenches and
Sediment Accretion)
12.5.3 Forearc Basins
Basin Types and General Characteristics
Basin Evolution, Sediment Sources,
and Tectonic Overprint
Sediment Successions ofForearc Basins
Examples ofForearc Basins
Modern Forearc Basins on Continental Margins
Modern Intraoceanic Forearc Basins
Ancient Forearc Basins
Summary (Forearc Basins)
12.5.4 Backarc and Retroarc Basins
General Characteristics
Sediment Successions ofBackarc and
Retroarc Basins
Retroarc (Retro-Foreland) Basins on
Continental Crnst
Backarc Basins on Oceanic Crnst
Examples ofModern Backarc Basins
Summary (Backarc and Retroarc Basins)
12.5.5 Preservation and Recognition of
Ancient Subduction-Related Basins
12.5.1 Plate-Tectonic Overview
Arc-trench systems result either from the breakage of
a previously intact oceanic plate or from the activation of a passive continental margin (cf. Fig. 1.2, A
and B subduction). Intraoeeanie voleanogenie are
systems have oceanic lithosphere in both the forearc
and backarc regions. The island arc can be entirely
volcanic (e.g., present-day Tonga-Kermadoc Islands
and Mariana Islands) or comprise a continental sliver
(e.g., Japan). "Normal" subduction of oceanic plate
beneath an island arc is directed toward the continent
following behind the island arc and backarc basin;
reversed subduction (polarity reversal) affects
backarc basins, whose oceanic crust is subducted
oceanward, i.e., away from the continent. The minimum distance between arc and trench is ab out 100
km in modem oceanic arc systems; trenches are commonly smoothly arcuate, as for example the Sunda
trench (see below).
In contrast, the edges of rifted continental margins
tend to bt: jagged and to exhibit offsets and projections (Fig. 12.18a). Here, the subducting oceanic
plate cannot trace an these irregularities but tends to
adjust to the points of the crustal projections on the
continental block. Hence, oceanic and transitional
crnst is caught between the projections. The presence
of such thin, trapped crustal slivers is probably a prerequisite for the deep-water environment andJor large
subsidence and sediment thickness within the forearc
region. Similarly, backarc basins on oceanic or transitional crust have a higher potential for subsidence
and sediment accumulation than basins in the region
of continental crust: Additional subsidence may be
caused by crustal extension or compressional downfaulting.
The plate-tectonic evolution of arc-trench systems
is normally defined by two-dimensional cross sections (Fig. 12.18b,c). This is suitable for many cases
because of the wen developed longitudinal continuity
of these structures. However, oblique subduction and
irregularites in the subducting crust (e.g. oceanic
ridges or seamounts) may cause considerable complications.
The basic principles governing the structure and evolution
of arc-trench systems have been outlined by many authors
(e.g., Dickinson and Seely 1979) and are treated in many
modern text books on geodynamics (see also Busby and
Ingersoll 1995). The highly variable geotectonic settings of
12.5 Deep-Sea Trenches,
Foreare, Backare, and
Retroarc Basins
12.5.1 Plate-Tectonic Overview
12.5.2 Deep-Sea Trenches and Accretionary Wedges
General Characteristics and Sediment Sources
Trench Fills and Sediment Accretion
(Qualitative Aspects)
Trench fills, Accretion and Subduction
ofSediment (Quantitative Aspects)
Sediment Budget ofModem Subduction
Complexes
Conclusions for the Sediment Budget
Specific Structures and Other Phenomena in
Accretionary Wedges
Tectonic Deformation
Melange, Wildflysch
Mud Diapirs and Mud Volcanoes
Examples of Arc-Trench Systems
Summary (Deep-Sea Trenches and
Sediment Accretion)
12.5.3 Forearc Basins
Basin Types and General Characteristics
Basin Evolution, Sediment Sources,
and Tectonic Overprint
Sediment Successions ofForearc Basins
Examples ofForearc Basins
Modern Forearc Basins on Continental Margins
Modern Intraoceanic Forearc Basins
Ancient Forearc Basins
Summary (Forearc Basins)
12.5.4 Backarc and Retroarc Basins
General Characteristics
Sediment Successions ofBackarc and
Retroarc Basins
Retroarc (Retro-Foreland) Basins on
Continental Crnst
Backarc Basins on Oceanic Crnst
Examples ofModern Backarc Basins
Summary (Backarc and Retroarc Basins)
12.5.5 Preservation and Recognition of
Ancient Subduction-Related Basins
12.5.1 Plate-Tectonic Overview
Arc-trench systems result either from the breakage of
a previously intact oceanic plate or from the activation of a passive continental margin (cf. Fig. 1.2, A
and B subduction). Intraoeeanie voleanogenie are
systems have oceanic lithosphere in both the forearc
and backarc regions. The island arc can be entirely
volcanic (e.g., present-day Tonga-Kermadoc Islands
and Mariana Islands) or comprise a continental sliver
(e.g., Japan). "Normal" subduction of oceanic plate
beneath an island arc is directed toward the continent
following behind the island arc and backarc basin;
reversed subduction (polarity reversal) affects
backarc basins, whose oceanic crust is subducted
oceanward, i.e., away from the continent. The minimum distance between arc and trench is ab out 100
km in modem oceanic arc systems; trenches are commonly smoothly arcuate, as for example the Sunda
trench (see below).
In contrast, the edges of rifted continental margins
tend to bt: jagged and to exhibit offsets and projections (Fig. 12.18a). Here, the subducting oceanic
plate cannot trace an these irregularities but tends to
adjust to the points of the crustal projections on the
continental block. Hence, oceanic and transitional
crnst is caught between the projections. The presence
of such thin, trapped crustal slivers is probably a prerequisite for the deep-water environment andJor large
subsidence and sediment thickness within the forearc
region. Similarly, backarc basins on oceanic or transitional crust have a higher potential for subsidence
and sediment accumulation than basins in the region
of continental crust: Additional subsidence may be
caused by crustal extension or compressional downfaulting.
The plate-tectonic evolution of arc-trench systems
is normally defined by two-dimensional cross sections (Fig. 12.18b,c). This is suitable for many cases
because of the wen developed longitudinal continuity
of these structures. However, oblique subduction and
irregularites in the subducting crust (e.g. oceanic
ridges or seamounts) may cause considerable complications.
The basic principles governing the structure and evolution
of arc-trench systems have been outlined by many authors
(e.g., Dickinson and Seely 1979) and are treated in many
modern text books on geodynamics (see also Busby and
Ingersoll 1995). The highly variable geotectonic settings of