 |
| Titel |
Slab stagnation and buckling in the mantle transition zone: Rheology, phase transition, trench migration, and seismic structure |
| VerfasserIn |
Craig Bina, Hana Cizkova |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093290
|
| Publikation (Nr.) |
 EGU/EGU2014-7889.pdf |
|
|
|
|
|
| Zusammenfassung |
| Subducting slabs may exhibit buckling instabilities and consequent folding behavior in the
mantle transition zone for various combinations of dynamical parameters, accompanied by
temporal variations in dip angle, plate velocity, and trench retreat. Parameters governing such
behavior include both viscous forces (slab and mantle rheology) and buoyancy forces (slab
thermal structure and mineral phase relations). 2D numerical experiments show that many
parameter sets lead to slab deflection at the base of the transition zone, typically accompanied
by quasi-periodic oscillations (consistent with previous scaling analyses) in largely
anticorrelated plate and rollback velocities, resulting in undulating stagnant slabs as buckle
folds accumulate subhorizontally atop the lower mantle. Slab interactions with mantle phase
transitions are important components of this process (Bina and Kawakatsu, 2010; Äížková
and Bina, 2013).
For terrestrial parameter sets, trench retreat is found to be nearly ubiquitous, and trench
advance is quite rare – due to both rheological structure and ridge-push effects (Äížková and
Bina, 2013). Recent analyses of global plate motions indicate that significant trench advance
is also rare on Earth, being largely restricted to the Izu-Bonin arc (Matthews et al., 2013).
Consequently, we explore the conditions necessary for terrestrial trench advance through
dynamical models involving the unusual geometry associated with the Philippine Sea
region.
Detailed images of buckled stagnant slabs are difficult to resolve due to smoothing effects
inherent in seismic tomography, but velocity structures computed for compositionally layered
slabs, using laboratory data on relevant mineral assemblages, can be spatially low-pass
filtered for comparison with tomographic images of corresponding resolution. When applied
to P-wave velocity anomalies from stagnant slab material beneath northeast China,
model slabs which undulate due to compound buckling fit observations better than
a flat-lying slab (Zhang et al., 2013). Earthquake hypocentral distributions and
focal mechanisms may provide clearer insights into slab buckling, as they appear to
vary systematically across regions of slab stagnation (Fukao and Obayashi, 2013).
Stress fields computed from our dynamical models may help to illuminate such
observations.
References:
Bina, C.R., and H. Kawakatsu, Buoyancy, bending, and seismic visibility in deep slab
stagnation, Phys. Earth Planet. Inter., 183, 330-340, 2010.
Äížková, H., and C.R. Bina, Effects of mantle and subduction-interface rheologies on
slab stagnation and trench rollback, Earth Planet. Sci. Lett., 379, 95-103, 2013.
Fukao, Y., and M. Obayashi, Deepest hypocentral distributions associated with stagnant
slabs and penetrated slabs, Fall Meeting Abstracts, AGU, DI14A-01, 2013.
Li, Z.-H., and N.M. Ribe, Dynamics of free subduction from 3-D boundary element
modeling, J. Geophys. Res., 117, B06408.
Matthews, D.C., L. Zheng, and R.G. Gordon, Do trenches advance? Fall Meeting
Abstracts, AGU, T43D-2682, 2013.
Zhang, Y., Y. Wang, Y. Wu, C. Bina, Z. Jin, and S. Dong, Phase transitions of harzburgite
and buckled slab under eastern China, Geochem. Geophys. Geosys., 14, 1182-1199, 2013. |
|
|
|
|
|
|