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| Titel |
Understanding Subduction Erosion Through Scaled Sandbox Analogue Experiments |
| VerfasserIn |
F. Albert, N. Kukowski, A. Tassara, O. Oncken  |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250058869
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| Zusammenfassung |
| The removal of material by tectonic erosion at ~60% of the Earth’s convergent margins is a
significant but still poorly understood process. We explored mass transfer processes and the
structural evolution of erosive systems in a series of 2D sandbox experiments. A
wedge-shaped sand body with an initial wedge geometry of 125 cm (length) x 30 cm (height)
x 20 cm (width) represented the forearc in a sandbox 3 m long. A conveyor belt with a rough
surface at the base simulated subducting oceanic crust. The initial slope angle α was set to
13.5º, the basal angle β to zero. For the system to develop dynamics similar to
those observed in nature, the mechanical properties of the materials were properly
scaled.
Our study explored the role of a controlled volume of sediment leaving the sand wedge on
its mechanics and dynamics by varying the width of the subduction window (Global Capacity
GC) at the base of the back wall. We quantified our results, including frontal erosion
(removing material from the tip of the slope), basal erosion (detachments from
the base of the forearc, causing surface subsidence), subsidence, accretion and tip
retreat, and compared them to natural examples of erosive convergent margins.
Basal erosion, subsidence and frontal prism evolution are related to subduction
channel (SC) characteristics. Volumes of frontal and basal erosion decrease as GC
decreases. Basal erosion can amount to up to twice the frontal erosion in case of a
sufficiently wide subduction window. As a consequence, wedges with large GCs
produced erosion ratios (basal erosion/frontal erosion) > 1, in agreement with estimates
from natural forearcs. Total erosion (i.e., frontal plus basal erosion) was favored by
wide GCs. Commonly, the size of the frontal prism varied in size with the GC.
“Accretionary” systems evolved in erosive systems by varying the GC, without adding
sediment to the toe. Thinner GCs developed a higher number of backthrusts at the
frontal slope. We identified three segments along the wedge and the SC, related
to the mass transfer modes. At the toe, the total sediment entering the channel is
restricted by the inlet capacity (IC). Volumes of eroded material correlate with
the IC/GC-ratio. If IC -¤ GC, frontal erosion is controlled by GC; if IC > GC, by
IC. In addition, the IC/GC-ratio also controlled basal erosion: when IC/GC>>1,
basal erosion was very low; in contrast, when IC/GC |
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