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Einsichten durch 2D physikalischen Simulationen
No full textTitelblatt, Inhaltsverzeichnis, Summary, Zusammenfassung v
1. Introduction 1
2. Orogen-scale erosion 5
3. Continental collision zones 13
3.1. Kinematic concepts of bivergent orogens 13
3.2. Kinematic models of fold and thrust belts 13
3.3. The Critical Coulomb Wedge concept 17
3.4. The minimum work concept of mountain building 23
4. Experimental method 25
4.1. Physical properties of analogue materials 26
4.2. Experimental setup 29
4.3. Data acquisition and processing with Particle Image Velocimetry 34
4.4. Data mining and its limitations 36
5. Kinematic boundary conditions and their influence on bivergent wedge evolution 41
5.1. Reference experiment 41
5.2. Experiments with other kinematic boundary conditions 50
5.3. Discussion 65
5.3.1. Four-staged evolutionary model for bivergent sand-wedges 65
5.3.2. Strain transfer in bivergent wedges 66
5.3.3. The timing of thrust initiation 72
5.3.4. The spacing of thrusts 72
5.3.5. Frontal accretion in the retro-wedge 73
5.3.6. Parameter combinations 75
5.3.7. Self-similar growth 76
5.4. Implications and predictions for natural bivergent wedges 77
5.5. Implications for erosion experiments 82
6. The influence of erosion on bivergent wedge evolution 83
6.1. Reference experiment without erosion 83
6.2. Experiments with erosion 86
6.3. Discussion 95
6.3.1. Concepts of bivergent wedge evolution and the accretion cycle 95
6.3.2. Discrete erosion versus continuous deformation 95
6.3.3. Influence of erosion on bivergent wedge kinematics 98
6.4. Implications and predictions for natural orogens 100
7. Deformation versus erosion 103
8. Foreland basin evolution and the growth of an orogenic wedge 105
8.1. Introduction 105
8.2. Method 106
8.3. Results and discussion 107
9 Perspectives 111
Acknowledgements 113
References 115
Appendices 129Bivergent wedges result from the interaction between deformation, flexure and
surface processes. Based on 2D sandbox simulations in conjunction with PIV,
this study investigates the influence of these processes on the spatio-
temporal evolution of strain-partitioning within, and the associated surface
uplift of, bivergent wedges. To facilitate interpretation and to successfully
communicate results, two new display types, i.e., the surface uplift and the
evolution of deformation map are introduced. Experimental results suggest a
four-staged evolutionary pathway for bivergent wedges: an initial pop-up
(stage I) or backfold is followed by a proto pro-wedge, in which frontal
accretion dominates (stage II). Basal accretion commences if a mid-level
detachment is present (stage III). Frontal accretion within the retro-wedge
occurs during stage IV. Furthermore, a conceptual model of cyclic accretion
within bivergent wedges is proposed, whereby each cycle consists of a thrust
initiation, an underthrusting and a re-activation phase. The latter determine
the location and magnitude of deformation within, and surface uplift of, a
bivergent wedge. Therefore, the accretion cycle is considered as an internal
clock for wedge-scaled deformation and surface uplift. We also demonstrate
that the geometry of the deformation front as well as the spatial distribution
of surface uplift are indicative for the currently active phase within an
accretion cycle. During the course of an accretion cycle, surface uplift of
the axial-zone and the retro-wedge may reach up to 1/2 of the thickness of the
incoming layer. Cycle duration is estimated to range between 104 to 105 years
and is thus in a similar range as climatic cycles. This conceptual model
provides also an explanation for the transient behaviour of deformation and
surface uplift and for the discrepancy between geodetic and geologic estimates
of fault slip. We found that retro-wedge erosion amplifies the displacement of
the basally accreted material, whereas pro-wedge erosion accelerates and
additionally redirects the particle flow of the frontally accreted material.
Pro- and retro-wedge erosion retard the propagation of deformation into the
foreland. This effect is stronger for pro-wedge erosion. Retro-wedge erosion
amplifies vertical growth and leads to increased strain accumulation along the
retro shear-zone and the mid-level detachment. Thus, cause (retro-wedge
erosion) and response (pro-wedge deformation) are significantly offset in
space. Since pro-wedge erosion evokes a complete decoupling of the retro-wedge
from the pro-wedge, cause and response are spatially more closely related. We
also found that more focused erosion is associated with a more focused
tectonic response. Implications of these results are finally used to explore
the evolution of foreland basins. Thereby, special emphasis is devoted to the
Flysch to Molasse transition as well as to the occurrence of hydrocarbon and
MVT deposits.Bivergente Orogene werden durch das Zusammenwirken von Deformation, Isostasie
und Oberflächenprozessen kontrolliert. Ziel der vorliegenden Arbeit ist es,
den Einfluss dieser Prozesse auf die räumlich-zeitliche Verteilung von
Deformation und Oberflächenhebung, in bivergenten Orogenen, zu analysieren.
Dazu werden physikalische (Sand) 2D Simulationen unter Einbindung von PIV
genutzt. Experimentergebnisse deuten eine vierphasige Entwicklung von
bivergenten Orogenen an, welche durch das Auftreten bestimmter Akkretionsmodi
gekennzeichnet ist. Phase I ist durch die Bildung eines pop-up gekennzeichnet,
wobei in Phase II frontale Akkretion zur Herausbildung eines Proto-Prokeiles
führt. Sofern ein interner Abscherhorizont vorhanden ist, kommt es in Phase
III zur basalen Akkretion. Frontale Akkretion im Retrokeil markiert den Beginn
der Phase IV. Des Weiteren wird das konzeptionelle Modell für zyklische,
frontale Akkretion in bivergenten Orogenen vorgestellt. Demnach besteht jeder
Zyklus aus einer Initiierungs-, einer Überschiebungs- und einer
Reaktivierungsphase, wobei letztere den Ort als auch die Magnitude von
Deformation und Oberflächenhebung bestimmen. Der Akkretionszyklus stellt somit
eine interne Uhr für orogene Deformation und Oberflächenhebung dar. Wir
postulieren, dass sich die jeweils aktive Phase an Hand der Geometrie der
Deformationsfront als auch mittels der Verteilung der Oberflächenhebung
erkennen lässt. Dieses konzeptionelle Modell liefert auch eine Erklärung für
die oft beobachtete Diskrepanz zwischen geodätischen und geologischen
Versatzraten von Störungen. Während eines Zyklus kann die Hebung in der
Axialzone als auch im Retrokeil bis zu 50% der Mächtigkeit der
Vorlandsequenzen betragen. Die Zyklendauer variiert zwischen 104 und 105
Jahren und beweget sich somit in einem ähnlichen Rahmen wie klimatische
Zyklen. Prokeilerosion beschleunigt den Massenfluß der frontalen Akkretion und
führt zu einer deutlichen Versteilung der Partikelpfade im Prokeil. Hingegen
beschleunigt Retrokeilerosion nur den Massenfluß der basalen Akkretion. Sowohl
Pro- als auch Retrokeilerosion verzögern die Propagation von Deformation,
wobei dieser Effekt bei ersterer stärker ist. Retrokeilerosion steigert das
vertikale Wachstum bivergenter Orogene und führt zu einer erhöhten
Akkumulation von Deformation entlang der Retroscherzone und des internen
Abscherhorizontes. Somit evoziert Retrokeilerosion eine räumliche Entkoppelung
von Ursache (Retrokeilerosion) und Wirkung (Deformation im Prokeil). Da
Prokeilerosion den Prokeil vom Retrokeil entkoppelt, stehen Ursache und
Wirkung in einer engeren räumlichen Beziehung. Experimentergebnisse zeigen
auch, fokussierte Erosion auch eine fokussierte Deformation zur Folge hat.
Obige Resultate werden genutzt, um die Entwicklung von Vorsenken zu
beleuchten. Besonderes Augenmerk liegt dabei auf dem Flysch-Molasse Übergang
als auch auf der Genese von Kohlenwasserstoff- und MVT-Lagerstätten
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Deformation, erosion and natural resources in continental collision zones insight from scaled sandbox simulations
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