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| Titel |
Quantitative analysis of surface deformation and ductile flow in complex
analogue geodynamic models based on PIV method. |
| VerfasserIn |
Ondřej Krýza, Ondrej Lexa, Prokop Závada, Karel Schulmann, Denis Gapais, John Cosgrove |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151116
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| Publikation (Nr.) |
 EGU/EGU2017-15666.pdf |
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| Zusammenfassung |
| Recently, a PIV (particle image velocimetry) analysis method is optical method abundantly
used in many technical branches where material flow visualization and quantification is
important. Typical examples are studies of liquid flow through complex channel system, gas
spreading or combustion problematics.
In our current research we used this method for investigation of two types of
complex analogue geodynamic and tectonic experiments. First class of experiments is
aimed to model large-scale oroclinal buckling as an analogue of late Paleozoic
to early Mesozoic evolution of Central Asian Orogenic Belt (CAOB) resulting
from nortward drift of the North-China craton towards the Siberian craton. Here
we studied relationship between lower crustal and lithospheric mantle flows and
upper crustal deformation respectively. A second class of experiments is focused to
more general study of a lower crustal flow in indentation systems that represent a
major component of some large hot orogens (e.g. Bohemian massif). The most of
simulations in both cases shows a strong dependency of a brittle structures shape, that are
situated in upper crust, on folding style of a middle and lower ductile layers which is
influenced by rheological, geometrical and thermal conditions of different parts
across shortened domain. The purpose of PIV application is to quantify material
redistribution in critical domains of the model. The derivation of flow direction and
calculation of strain-rate and total displacement field in analogue experiments is
generally difficult and time-expensive or often performed only on a base of visual
evaluations.
PIV method operates with set of images, where small tracer particles are seeded within
modeled domain and are assumed to faithfully follow the material flow. On base of pixel
coordinates estimation the material displacement field, velocity field, strain-rate, vorticity,
tortuosity etc. are calculated.
In our experiments we used velocity field divergence to quantify the redistribution and
flow of anatectic lower crust and to evaluate upper crust thickenning and topography
evolution. As this method is very sensitive to resolution and color contrast of obtained images
and used materials are mostly uniform within individual rheological layers and domains, we
utilized various markers as flakes of a fluorescent wax or glitter to increase overall
sensitivity.
Applying this method to oroclinal buckling experiments we derived velocity field
divergence associated with upper crustal deformation and evolution of topography. Scaled,
dimensionless negative values of divergence reach minimum (∼ -1) in two elongated domains
propagating from inflection area of modeled orocline. These values correlate with significant
upper crust material removing and-or with redistribution of crustal material associated with
formed pop-up and pop-down structures. Maximum positive values (∼ 0.1) correspond with
material spreading alongside forming platforms that are situated in foreland of maximum
elevations.
Application of PIV method on lateral view, where ductile middle and lower crust is
vertically folded during lithosphere shortening and indentation, revealed possibility to track
melt migration from base of lower crust through interlimb area towards hinge zone of
individual folds. Simultaneously with folds locking and material accumulation, whole
structures are exhumed at the middle crust level. Melt flow and heat exchange with
surrounding environment is responsible for increased plasticity of the middle crust marked by
higher strain-rates observed inside fold envelope. It is also responsible for significant
elevation above hinges during later stages of model evolution. Heterogeneous nature of
deformation is well documented by heterogeneities in derived divergence field within folds
interiors.
Our results show distinct advantages of PIV method for post-processing of geodynamic
and tectonic analogue models and demonstrate great potential of this method for quantitative
processing of wide spectrum of analogue approaches to different natural systems. |
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