Research Collection Doctoral Thesis Active deformation and landscape evolution of the Makran Accretionary Wedge (SE-Iran) New constraints from surface exposure dating of fluvial terraces Author(s): Haghipour, Negar Publication Date: 2013 Permanent Link: https://doi.org/10.3929/ethz-a-009795617 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library DISS. ETH No. 20994 Active deformation and landscape evolution of the Makran Accretionary Wedge (SE-Iran) New constraints from surface exposure dating of fluvial terraces A dissertation submitted to ETH Zurich For the degree of Doctor of Sciences Presented by Negar HAGHIPOUR M.Sc. in Geology. Azad University, Tehran-North branch (Iran) born 17.05.1977 citizen of Iran Accepted on the recommendation of Prof. Dr. Jean-Pierre Burg ETH Zurich Examiner PD Dr. Susan Ivy-Ochs ETH Zurich Co-examiner Dr. Florian Kober ETH Zurich Co-examiner Prof. Dr. Mark T. Brandon Yale University Co-examiner 2013 I have not failed. I've just found 10,000 ways that won't work. Thomas A. Edison Table of contents Abstract i - ii Zusammenfassung iii - iv Chapter I: Introduction 1- Study area 6 1-1 Geological setting 6 1-2 Geodynamic and seismicity 8 1-3 Overviews of previous work 11 Inland Makran 11 Coastal Makran 12 1-4 Remaining problems and aims 12 2 Morphometric analysis and methods 13 2-1 Fluvial systems 14 2-2 Morphometric tools 15 3 Terrestrial Cosmogenic Nuclides (TCNs) 16 3-1 Principles 16 3-2 Terrestrial Cosmogenic Nuclide (TCN) application to active tectonics research 18 3-3 Depth profile (surface erosion and inheritance) 19 4 Outline of the thesis 20 Chapter II: Geomorphological analysis 1-Introduction 26 2-Setting 27 2-1- Tectonic and geological setting 27 2-2- Regional climate 29 2-3- Drainage system on the Makran Accretionary Wedge 29 3- Analytical methods 30 3-1- Local relief and swath profiles 31 3-2- Longitudinal stream profile 31 3-3- Channel steepness index 32 3-4 Steady-state river profile reconstruction 32 4- Results 31 4-1- General topographic features 34 4-2- Stream profiles characteristics 36 4-3- Synthesis of results 51 5- Discussion and interpretation 51 5-1- Knickpoints and causes of transient incision 51 5-2- Quaternary uplift 52 5-3- Regional variation in topographic growth and tectonic activity 52 5-4- Comparison with other accretionary wedges 53 5-5- Possible drivers of morphometric variations along the Makran Accretionary Wedge 54 5-6- Coupled erosion and deformation model 55 6-Conclusion 56 Acknowledgements 57 Chapter III: Cosmogenic nuclide dating Abstract 61 1. Introduction 62 2. Setting 62 2.1. Geological setting 62 2.2. Seismicity – Active tectonics 65 2.3. Climate setting 65 3. Methods 66 3.1. Field observation and surveying 66 3.2. Channel steepness indices 67 3.3. Cosmogenic nuclide dating and sampling (10Be and 26Al) 69 3.4. Radiocarbon dating 74 3.5. Calculating incision and uplift rate 74 4. Site description of dated fluvial terraces 77 4.1. Sedij catchment 77 4.2. Fanuj catchment 78 4.3. Nikshahr catchment 80 4.4. Pishin catchment 82 5. Results 85 5.1. 10Be abandonment ages and rates of fluvial incision 85 5.2. 14C dating result and coastal uplift 86 5.3. Comparison between incision rate and river gradient 88 6. Discussion 89 6.1. Age uncertainties and resolution 89 6.2 Age distribution and modeled ages 93 6.3. Correlation with Marine Isotopic Stages 94 6.4. Uplift rates 95 Conclusion 92 Acknowledgements 96 Chapter IV Crustal shortening Introduction 100 1- Setting 100 1-1 Tectonic setting 100 1-2 Seismicity and geodesy background 101 1-3 Structural background of onshore, Central Makran 102 2- Methods 104 2-1 Mapping and surveying 104 2-2 Sampling - Terrace description 106 2-3 10Be terrestrial cosmogenic nuclide surface exposure dating 108 2-4 Uplift and shortening estimation 111 3- Results 112 3-1 Sites A and B: Sedij River 112 3-2 Sites C and D: Nikshahr River 113 3-3 Sites E and F: Sarbaz River – Pishin catchment 114 4- Discussion 117 4-1 10Be age uncertainties 117 4-2 Quaternary folding: Insight from fluvial terraces 118 4-3 Bulk horizontal shortening and shortening rate deduced from mass conservation119 4-4 Seismotectonic Implications 121 5- Conclusion 121 Acknowledgements 122 Chapter V Conclusion 5-1 Along strike variation of tectonic activity inferred from the river morphology 125 5-2 Surface exposure dating 126 Climatic influence 126 Tectonic implication 126 5-3 Rate of crustal shortening 127 5-4 Outlook 127 Bibliography i Abstract The topographic evolution of mountain belts results from complex coupling between tectonics, climate and surface processes. However, our ability to infer tectonic information from surface observations is hampered by a lack of quantification of the causal links between tectonic activity and topography. Therefore, a set of methodological tools quantifying landscape evolution has been recently developed to constrain forcing processes over temporal (103-106 a) and spatial (1-100 km) scales characteristic of orogenic systems. For this thesis the first systematic assessment of the landscape response to deformation of the onshore Makran Accretionary Wedge (MAW), in SE Iran, was carried out. First, we give a general introduction to the scientific problem, to the tectonic setting of the field area, and to the methodology employed in the thesis. Then, we present the quantitative assessment of the river pattern and link the characteristics of drainage basins and channel length profiles with fluvial incision as a marker of surface uplift. Surface uplift is essentially caused by recent crustal deformation of the wedge. The variations in channel steepness and concavity allow determining a background, regional picture and identifying focused incision where active folds and thrusts are growing. It also indicates a difference in behavior between western and eastern Makran. The first absolute ages of fluvial terraces over a large part of onshore MAW were obtained using 10Be exposure dating. The 13-379 ka spread of ages offers the chance to clarify whether the formation and abandonments of the studied terraces are associated with climatic cycles or/and tectonic forces. The most widespread levels (at ca 20 and 100 ka) are linked to Marine Isotopes Stages MIS 2-5. The new ages further permit calculating rates of both the regional background and the localized incisions. The regional ‘background’ incision rate, used as a proxy of surface uplift, is relatively moderate and homogeneous (0.3 mm/a). It fits previous estimates from uplifted marine terraces. This general uplift rate is confirmed by ages we obtained with 14C (radiocarbon) and 10Be methods on newly dated marine terraces. Local incision/uplift rates reach up to 0.8-1 mm/a. The regional, uniformly distributed incision rate is attributed to the steady growth of the MAW. The locally high incision rates indicate that, however, perfect steady-state is unlikely on short-length scales, local instabilities depict localized deformation. Folded fluvial terraces taken as passive markers on growing folds and fold trains help constraining the dynamics of both distributed and localized deformation due to shortening/convergence across the onshore MAW. The results are compared to interseismic deformation documented by published GPS data. The calculated average shortening rate due to folding on the millennial time scale accounts for 10-15% of the shortening rate given by kinematic GPS measurements across the Iranian part of the MAW. Active folding depicted in this work shows that the generally accepted concept of ‘Coulomb’ accretionary wedges is ii an excellent, long-term approximation that requires refinements in terms of bulk rheology to account for shortening mechanisms additional to discrete fault movements. The noticeable spatial variation in recent deformation, denoting increasingly stronger impact of Quaternary deformation towards the east, is attributed to eastward increasing convergence, hence subduction rates. Our results emphasize the link between surficial and deeper crustal processes in active orogenic systems. iii Zusammenfassung Die topographische Entwicklung eines Gebirges erfolgt aus dem komplexen Zusammenspiel zwischen Tektonik, Klima und Oberflächenprozessen. Die Möglichkeit aus Beobachtungen der Erdoberfläche, Informationen über tekonische Prozesse zu erhalten, wird aufgrund fehlender Quantifizierung der Zusammenhänge zwischen tektonischer Aktivität und Topographie geschmälert. Daher wurde kürzlich eine Anzahl methodologischer Werkzeuge, die die Landschaftsentwicklung quantifizieren, entwickelt, um die, für ein Gebirgssystem zeitlich (103-106 a) und räumlich (1-100 km) charakteristischen, treibenden Kräfte einzugrenzen. Im Zuge dieser Arbeit wurde die erste systematische Erfassung der Landschaftsentwicklung aufgrund der Verformung des landwärtigen Makran Akkretionskeils (MAK), im Südosten des Irans, durchgeführt. Zuerst wird eine allgemeine Einleitung zur wissenschaftlichen Fragestellung, zur tektonischen Situation des Feldgebiets und zur, in der Arbeit angewandten, Methodik präsentiert. Daraufhin wird die quantitative Bewertung des Flussmusters vorgestellt und die Eigenschaften von Einzugsgebieten und Profilen der Kanallängen werden mit dem Einschneiden von Flüssen, das als Marker für Oberflächenhebung dient, in Zusammenhang gebracht. Oberflächenhebung wird hauptsächlich durch rezente krustale Verformung des Keils verursacht.