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| Titel |
Effects of Oblique Extension and Inherited Structure Geometry on Transfer Zone Development in Continental Rifts: A 4D Analogue Modeling Approach |
| VerfasserIn |
Frank Zwaan, Guido Schreurs |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101916
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| Publikation (Nr.) |
 EGU/EGU2015-1474.pdf |
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| Zusammenfassung |
| INTRODUCTION
Inherited structures in the crust form weak zones along which deformation will focus
during rifting. Along-strike connection of rift segments may occur along transfer zones, as
observed in East Africa. Previous studies have focused on numerical and analog modeling of
transfer zones (e.g. Acocella et al., 1999, Allken et al., 2012). We elaborate upon those by
investigating the effects of 1) oblique extension and 2) the geometry of linked and
non-linked inherited structures on the development of transfer zones. A further
improvement is the use of X-ray Computer Tomography (CT) for detailed internal
analysis.
METHODS
The experimental set-up (see Schreurs & Colleta, 1998) contains two sidewalls with a
base of compressed foam and plexiglass bars stacked in between. Decompressing this base
results in distributed deformation of the overlying model materials. Deforming the model
laterally with a mobile base plate produces the strike-slip components for oblique extension.
Divergence velocities are in the order of 5 mm/h, translating to ca. 5 mm/Ma in nature, and 1
cm represents 10 km. A 2 cm thick layer of viscous silicone represents the ductile lower crust
and a 2 cm quartz sand layer the brittle upper crust. Inherited structures are created with thin
lines of silicon laid down on top of the basal silicone layer. Several models were run in
a CT-scanner to reveal the 3D evolution of internal structures with time, hence
4D.
RESULTS
Localization of deformation along the pre-defined structures works well. The models
show that the structural style changes with extension obliquity, from wide rift structures to
narrower rifts with internal oblique-slip and finally strike-slip structures. Furthermore, rift
offset is an important parameter influencing the occurrence of linkage: increasing rift offset
decreases linkage as previously observed by Allken et al. (2012). However, increasing
divergence obliquity promotes transfer zone formation, as does the presence of
rift-connecting inherited zones, whose strike is at an angle of >15°with respect to the
divergence direction.
CT-analysis indicates that faulting initiated shortly after the start of the experiments,
while structures become only clearly visible at the surface only after 1:30h (4% extension).
Rift boundary fault angles tend to decrease from an initial 70°to ca. 55°after 4:00h (10%
extension). Further CT-analysis will reveal the 3D evolution of the transform zones in more
detail.
REFERENCES
Acocella, V., Faccenna, C., Funiciello, R., Rossetti, F., 1999. Sand-box modelling of
basement-controlled transfer zones in extensional domains. Terra Nova, Vol. 11, No. 4, pp
149-156
Allken, V., Huismans, R. S., Thieulot, C., 2012. Factors controlling the mode of rift
interaction in brittle-ductile coupled systems: A 3D numerical study, Geochem. Geophys.
Geosyst. Vol. 13, Q05010
Schreurs, G., Colletta, B. (1998) Analogue modelling of faulting in zones of continental
transpression and transtension. In: Holdsworth, R. E., Strachan R. A., Dewey, J. F., (eds.)
1998. Continental Transpressional and Transtensional Tectonics. Geological Society, London,
Special Publications. No. 135, pp 59-79 |
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