Active Tectonics of the Dasht-E Bayaz Fault (Ene Iran)

UNIVERSITE AIX-MARSEILLE

Centre Européen de Recherche et d’Enseignement en Géosciences de l’Environnement N° attribué par la bibliothèque :

ACTIVE TECTONICS OF THE DASHT-E BAYAZ FAULT (ENE IRAN)

Tectonique active de la faille de Dasht-é Bayaz (ENE de l’Iran) THESE Pour obtenir le grade de DOCTEUR DE L’UNIVERSITE AIX-MARSEILLE Faculté des Sciences et Techniques Discipline : Géosciences de l’environnement

Présentée et soutenue publiquement par Fariborz BANIADAM Le 16 Juillet 2019 au CEREGE

Directeurs de thèse Olivier BELLIER et Esmaeil SHABANIAN Ecole Doctorale : Sciences de l’Environnement

Jury Dr. Christine AUTHEMAYOU, MCF, Université de Bretagne occidentale Rapporteure Pr. Carole PETIT, Université de Nice Sophia Antipolis, UMR Géoazur Rapporteure Pr. Federico ROSSETTI, Université Roma III Examinateur Dr. Lucilla BENEDETTI, Dr CNRS, CEREGE Présidente Pr. Olivier BELLIER, Université Aix-Marseille, CEREGE Directeur Dr. Esmaeil SHABANIAN, Assistant professor, Institute for Advanced Studies in Basic Sciences, Zanjan Co-Directeur

ANNEE: 2019 Tectonique active de la faille de Dasht-é Bayaz (ENE de l’Iran)

Résumé

La convergence entre l’Arabie et l’Eurasie est accommodée à travers tout le plateau iranien et particulièrement le long de chaînes de montagnes qui localement structurent le Plateau. Les failles décrochantes ont un rôle principal dans la déformation du plateau iranien et dans l’accommodation de la convergence. Elles sont d’autre part responsables de plusieurs séismes majeurs à l’Est de l’Iran. Le rôle de la faille senestre décrochante et activement séismique de Dasht-e Bayaz qui est perpendiculaire aux mouvements du plateau, a été souvent débattu dans l’accommodation de la convergence d’Arabie-Eurasie.

Mon travail se concentre sur les aspects fragiles et récent de la déformation (cinématique et régimes de contraintes récents, vitesse de glissement actuel) le long de la faille de Dasht- e Bayaz afin d’expliquer le rôle de cette faille dans géodynamique de l’ENE de l’Iran. Afin de distinguer la cinématique des déformations et les états de contraintes plio-quaternaires, nous avons utilisé l’inversion des données séismiques (mécanismes aux foyers) et de cinématiques de faille mesurée autour et le long de la faille de Dasht-e Bayaz. Nos résultats indiquent une direction de compression de N133±17°E (contrainte maximale σ1) pour l’état de contrainte ancien associé à un régime tectonique en compression. L’état de contrainte le plus récent « moderne » est lui caractérisé par une contrainte maximale σ1 NE-SW, parfaitement cohérente avec la direction N050±05°E déduite de l’inversion des mécanismes au foyer des séismes représentant l’état actuel de contrainte.

Notre analyse structurale montre qu’en deux points, la faille décrochante d’orientation E- W de Dasht-e Bayaz croise les failles décrochantes de Mahyar et de Korizan d’orientation de N-S, et forme un système classique des failles conjuguées. Nos estimations la vitesse moyenne de glissement de la faille de Dasht- Bayaz en combinant des âges de cônes alluviaux déterminés à partir de l’analyse de nucléides cosmogéniques et la reconstruction morphotectonique des cônes alluviaux qui ont été décalés par cette faille, ont mené à un taux de 0.9±0.14 mm/an. Taux qui semble presque stable depuis ~160 ka, dans la limite des incertitudes attribuées aux décalages (rejets) et aux âges.

D’après notre discussion géodynamique, le cisaillement (décrochement) d’orientation N- S, responsable de l’accommodation de la convergence à l’Est de l’Iran, s’interrompt à la latitude de 34°N et ne se continue pas vers le Nord. Au Nord de cette latitude le système décrochant est remplacé par un mécanisme purement compressif (chevauchement et failles inverses), qui se transforme à la latitude ~ 36°N en cisaillement d’orientation NW. Nous avons proposé le fait que dans le Nord of 34°N, la convergence est principalement accommodée par du raccourcissement crustal qui se traduit par des systèmes de chevauchements et failles inverses. Dans ce contexte, au NE de l’Iran, la convergence est majoritairement absorbée (accommodée) par du raccourcissement crustal pure le long des failles inverses, alors que les failles senestres d’orientation E-W qui se situent entre les failles inverses tels que Ferdows, Jangal et le segment à l’Est de la faille de Doruneh ont un rôle complémentaire dans l’accommodation de la convergence. Ce scenario est confirmé par le faible taux de la vitesse de glissement qui a été obtenu pour la faille de Dasht-e Bayaz, et qui minimise le rôle de cette dernière dans l’accommodation de la convergence à l’échelle de la Tectonique des Plaques.

Mots clés: Faille de Dasht-e Bayaz ; bloc de Lut; morphotectonique; décrochement; états de contraintes; collision Arabie-Eurasie; datation par nucléides cosmogéniques; vitesse de glissement.

III

ACTIVE TECTONICS OF THE DASHT-E BAYAZ FAULT

(E-NE IRAN)

The sinistral Dasht-e Bayaz fault is characterized by conspicuous seismic and geological activities, while the geodynamic role of the fault in the accommodation of active convergence is still debated. This dissertation focuses on two aspects of brittle deformation (kinematics and rate of movement) along the Dasht-e Bayaz fault in order to describe and discuss the role of the fault in the geodynamics of the E-NE Iranian regions. Characterizing the Pliocene-Quaternary to present-day states of stress in the region, affected by the Dasht- e Bayaz fault, we applied the fault-slip inversion technique to both kinds of seismologic and geological fault slip data gathered around the Dasht-e Bayaz fault. The inversion results indicate a mean N045±5°E trending horizontal σ1 in the modern stress field, coherent with the present-day strike-slip tectonic regime (regional N050±05°E trending σ1) deduced from the inversion of earthquake focal mechanism data. The paleostress state is characterized by a homogeneous N125±05°E trending mean σ1, with a compressional stress regime, which shows that E-W faults of this region like Dasht-e Bayaz has been right-lateral in certain periods of their activity.

In view of geodynamics, lithospheric right-lateral shear between the Iranian plateau and fixed Eurasia is interrupted between 34°N and 36°N and is mainly replaced by reverse/thrust faulting before being accommodated, farther north, by dextral faulting along NNW faults of the Kopeh Dagh. According to our geodynamic model, the region between Lut and Kopeh Dagh is divided by the Doruneh fault into two tectonic domains. In the northern domain, active convergence is taken up by the extrusion of fault-bounded blocks while, in the southern domain the convergence is accommodated through E-W sinistral faults such as Dasht-e Bayaz and NW-striking reverse/thrust faults. In this context, the E- W sinistral faults are situated between NW striking reverse/thrust faults like the Ferdows, Jangal and Khaf as well as the eastern termination of Doruneh, playing their complementary role in the crustal shortening at the converging edges of the north going blocks of Lut – Central Iran. The different tectonic role of the Dasht-e Bayaz fault with respect to the Doruneh fault (as a major block bounding structure) is reflected in their rates of slip such that the Doruneh Fault slips, at least, five times faster than the Dasht-e Bayaz fault.

Keywords: Lut block; morphotectonics; strike-slip faulting; state of stress; Arabia- Eurasia collision; cosmogenic nuclides; slip rate.

Discipline: Géosciences de l’Environnement

Laboratoire: CEREGE UMR 7330 Europôle de l’Arbois, BP 80 13545, Aix-en-Provence Cedex 4

Remerciements

Ayant accompli la fin de ce projet de recherche, j’ai le plaisir de pouvoir remercier toutes les personnes qui m’ont accompagné durant ce parcours. Ainsi, j’ai l’honneur de présenter mes remerciements aux collègues et aux professeurs envers qui je suis reconnaissant grâce à leur assistance et collaboration scientifique mais aussi aux amis et aux proches qui m’ont grandement aidé et soutenu.

Premièrement, je remercie grandement Olivier Bellier et Esmaeil Shabanian mon directeur et co-directeur de thèse. Je remercie Olivier Bellier d’avoir accepté ce projet et de m'avoir fait confiance dans le cadre de ce travail de recherche. C’est grâce à l’encouragement et aux efforts de Esmaeil, un cher ami avec qui je partage beaucoup de beaux souvenirs depuis la jeunesse, que j’ai pu commencer ce travail et rencontrer Olivier. C’est grâce à eux, leur assistance et leur contribution scientifique que j’ai pu accomplir ce travail. Je dois avouer que cette coopération m’était une joie et un plaisir et ceci était dû à la relation professionnelle, communicative et collaborative que nous avons pu construire grâce à leurs soutiens et aides fournis en permanence.

Ce travail ne serait pas possible sans la coopération et la collaboration de mes collègues et amis iraniens. De ce fait, je présente mes remerciements au Service Géologique National de l’Iran (GSI), mon lieu de travail pendant 19 ans. Un lieu qui m’a permis de m’épanouir et donc de poursuivre mes études. Je remercie particulièrement Monsieur Mohammad Taghi Korei, l’ancien président de GSI. Pareillement, je remercie mon très cher ami et collègue Vahid Fotovati. Il a beaucoup contribué à ce travail, non seulement par son amitié sincère et son soutien sympathique pendant des années partagées comme collègues, mais aussi en facilitant nos travaux en terrain, en nous offrant des outils de travail et en nous aidant avec les affaires administratives. J’ai bénéficié de trois années de bourse de couverture sociale par l’intermédiaire de l’Ambassade de France en Iran. Ainsi, je remercie profondément les employés de l’ambassade de France en Iran. Je tiens particulièrement à remercier Monsieur Pierre- André Lhôte et Mesdames Zohreh Mirbaha et Délaram Zandieh pour leurs efforts et leur aide professionnelle. Je dois une grande partie de l’accomplissement de ce travail aux personnes incroyables que j’ai eu l’honneur de rencontrer en France. Ainsi, je suis spécialement reconnaissant envers mes formidables amies Nadia, Hélène, Michèle et Marie. Des amies qui ont rendu mon séjour en France beaucoup plus agréable, aisé et aimable en m’offrant

VI leur aide et leur amitié qui m’est la plus chère. De ce fait, j’adresse mes remerciements à mes chères amies pour l’appui et le soutien qu’elles m’ont prêtés en permanence. Je tiens à remercier vivement tous les gens formidables que j’ai rencontrés au CEREGE dont le soutien était indispensable pour ce parcours. De ce fait, je remercie particulièrement mon très cher ami et collègue Jules Fleury et sa femme Yassaman, qui m’ont toujours encouragé et aidé en facilitant mon séjour en France et en m’assistant dans ma soutenance de thèse. Pareillement, je remercie Morteza Djamali et Madjid Shah Hosseini, des amis qui m’ont énormément aidé surtout au début de mon séjour en France. De la même manière, je remercie Régis Braucher pour ses conseils concernant l’analyse d’échantillons et leurs interprétations scientifiques. Je présente également mes remerciements à Valery Guillou qui m’a beaucoup appris et aidé au laboratoire 10Be. J’aimerais également présenter mes remerciements à Isabelle Hammad qui m’a patiemment aidé dans les démarches administratives.

Je tiens également à remercier les membres du jury, Dr. Christine Authemayou, Pr. Carole Petit, Pr. Federico Rosseti et Dr. Lucilla Benedetti d’avoir accepté d’examiner et de juger ce travail de thèse.

Je présente mes remercîments à mon cher oncle Morteza Baniadam qui a beaucoup contribué à mon intégration en France. Finalement, je suis heureux de pouvoir exprimer ma plus profonde reconnaissance à ma chère famille, ma femme Maryam et mes deux filles Romina et Hosna qui m’ont énormément assisté dans toutes les étapes de ce parcours. Je remercie particulièrement mes filles de m’avoir aidé dans la rédaction de ma thèse en anglais au niveau linguistique. De plus, bien que ces cinq années de travail soient dures pour ma famille, elle a tout fait pour me faciliter ce parcours avec son soutien affectif et désintéressé.

VII

Contents INTRODUCTION 1

CHAPTER I

GENERAL PRESENTATION, PROBLEM STATEMENT &METHODOLOGY 6

1.1. Geodynamic framework 7 1.2. Previous studies about Dasht-e Bayaz fault and around area 16 1.3. Explanatory statement of the problems 18 1.3.1. Situation of present-day kinematic in the northern Lut, state of stress and tectonic regime change in plio-Quaternary 18

1.3.2. morpho-tectonic discussions and structural characteristics of Dasht-e Bayaz fault, evolution, segmentation, total offset and relationships and interactions with the adjacent faults 23

1.3.3. Challenges and questions about geodynamic of northern Lut and role of the Dasht-e Bayaz fault in the context of the Arabia-Eurasian convergence 26

1.3.4. Questions about the rate of slipping along the Dasht-e Bayaz fault 29 1.4. Methodology 35

1.4.1. Structural and geomorphic studies along the Dasht-e Bayaz fault 35 1.4.2. Fault kinematics and states of stress studies 35

References 49

CHAPTER II

THE KINEMATICS OF DASHT-E BAYAZ FAULT DURING PLIO-QUATERNARY IMPLICATIONS FOR THE GEODYNAMICS OF EASTERN CENTRAL IRAN 59 Abstract 60

1. Introduction 61

2. Kinematic Background and tectonic setting 66 2.1. Late Cenozoic stress fields in the Iranian plateau 66

VIII

2.2. Geodynamic and seismotectonic framework 68

3. Methodology: inversion method, chronology and data separation, stress tensor quality 73

3.1. Inversion of fault-slip data 73 3.2. Chronology and data separation 76

3.3. Inversion of earthquake focal mechanism data 79

4. Fault kinematics and states of stress in the Dasht-e Bayaz area 84

4.1. Modern state of stress 85

4.2. Paleostress state 88

4.3. The present-day state of stress deducted from inversion of earthquake focal mechanisms

5. Discussion 91

5.1. Integration of our results in the regional geodynamic context 91

5.2. Kinematic implications along the Dasht-e Bayaz fault 96

5.3. Interpretation of structural and geomorphic features 97

5.4. Tectonic implications of results and geodynamic model 105

7. Conclusion 111

References 114

CHAPTER III

QUATERNARY SLIP RATES ALONG THE DASHT-E BAYAZ FAULT 130

Abstract 131

1. Introduction 132

2. Geodynamic and Tectonic setting 134

3. Sequential cumulative offsets along the Dasht-e Bayaz fault 136 4. Cosmogenic exposure dating of alluvial surfaces offset along the Dasht-e Bayaz Fault 138 4.1. Methodologies 138 IX

4.2. Geomorphic mapping and site selection 139

4.3. Sampling strategy and analytical approach for cosmogenic dating 140

4.4 Cosmogenic 10Be results 142 4.4.1. Estimation of inheritance and denudation rates 142

4.4.2. 10Be cosmogenic dating results and timing of abandonment of Qt2 surfaces 145

4.4.3. 10Be cosmogenic dating results and timing of abandonment in Qt3 surfaces 148

4.4.4. Surface 10Be cosmogenic dating results and timing of abandonment in Qt4 surface 149

4.4.5. Surface 10Be cosmogenic dating results and timing of abandonment in Qt5 surface 155

5. Quaternary slip-rate of the Dasht-e Bayaz fault 158

6. Discussion 158 6.1. Erosion versus inheritance and their influences on CRE ages of alluvial fans 159

6.2. Tectonic implication of results 163

6.3. Geological versus geodetic slip rates of the Dasht-e Bayaz fault 165

6.4. Consistency of our results with previous slip-rate estimates along the Dasht-e Bayaz fault

166

7. Conclusion 168

References 170

CHAPTER IV

DISCUSSION and CONCLUSIONS 178

4.1. The Kinematics of deformation in the Dasht-e Bayaz area 179

4.2. Morphotectonic and structural characteristics of Dasht-e Bayaz fault, evolution, segmentation, total offset and relationships and interactions with the adjacent faults 183

4.3. The role of Dasht-e Bayaz fault in the context of Arabia-Eurasian convergence 194

4.4. The rate of slip along the Dasht-e Bayaz fault 202 X

References 214

CONCLUSION, SYNTHESE FRANÇAISE

TECTONIQUE ACTIVE DE LA FAILLE DE DASHT-E BAYAZ (E-NE DE L’IRAN) 220 1. Introduction 221

2. Contexte géodynamique 221

3. Etude structurale et géométrie de faille 226

4. étude cinématique 226

5. Quantification de la déformation : déplacement fini et vitesse de déplacement 227

6. Rôle géodynamique 228

7. Conclusions et perspectives 231

Bibliographies 233

INTRODUCTION

Introduction The convergence between Arabia and Eurasia is responsible for current deformation in Iran. Nearly all the convergence is accommodated across the Iranian plateau and the surrounding mountain ranges such as the Zagros, Alborz and Kopeh Dagh ranges; the collision boundaries approximately match the political borders of Iran. The Makran tectonic province is the surface expression of the active subduction of Arabia beneath the Iranian micro-continent (Fig.1).

Figure 1. General tectonic map of the east and northeast of Iran. (A) The upper left inset shows the location in the Arabia–Eurasia collision framework (after Shabanian et al., 2010). Grey arrows and associated numbers represent Arabia–Eurasia plate velocities (mm/yr) after Reilinger et al. (2006). (B) GTOPO30 topographic image showing the regional tectonic setting and the major active faults (red lines) in E and NE Iran. The study area of Dasht-e Bayaz is marked by the black dashed rectangle.

INTRODUCTION

Strike-slip faults play significant roles in current deformation of the Iranian plateau and were responsible for several moderate to large earthquakes especially in east of Iran [e.g.,

31 August 1968 Dasht-e Bayaz (Mw 7.1), 27 November 1979 Bam earthquake, 10 May

1997 Zirkuh earthquake (Mw 7.2); 27 November 1979 Koli-Boniabad earthquake (Mw 7.1);

7 December 1979 Kalat-e Shur earthquake (Mw 5.9); 26 December 2003 Bam earthquake

(Mw 6.5); 20 November 1989 South of Golbaf earthquake (Mw 7.1)].

After the destructive 1968 Mw 7.1 earthquake, the Dasht-e Bayaz area has been one of the most seismically active domains in Iran (Fig. 2). The 31 August 1968 earthquake of Dasht-e Bayaz has been considered as a trigger for the reactivation of the east segment of the Dasht-e Bayaz fault, Ferdows thrust zone and Korizan fault and was responsible for a sequence of earthquakes (e.g., the Zirkuh, Koli-Boniabad and Ferdows earthquakes). The most remarkable seismic events occurred just 20 hour after the Dasht-e Bayaz main shock during Ferdows earthquakes of 1st (and 4th) September 1968 (Mw6.3 & Mw5.5) about 70 km west of Dasht-e Bayaz.

The series of earthquakes occurred between 1968 and 1997 in Dasht-e-Bayaz, Ferdows and Zirkuh area present one of the most remarkable examples of temporally clustered continental seismic activity in the world (Fig. 2). The later active tectonic and seismological studies conducted in the Dasht-e Bayaz and around area show that active faults responsible for numerous seismic activities in the area are temporally and mechanically in a close interaction.

INTRODUCTION

Figure 2. Landsat ETM imagery (RGB 741) and the major active faults around the Dasht-e Bayaz area. Fault-plane solutions belong to the major earthquakes of the study area (redrafted from waveform modelling of Walker et al., 2004, 2011).

In the Lut block and central Iran, the role of the N-trending faults and fault systems (e.g., Nayband, Zahedan, Abiz faults and Neh fault systems) are properly known and established in the accommodation of convergence so as there is not much debate on this subject. The function of thrust fault systems such as the Tabas and Ferdows thrusts and their role in the crust shortening are well accepted in the absorption of Arabia-Eurasian convergence. However, the role of E trending strike-slip faults such as the Doruneh and Dasht-e Bayaz faults perpendicular to plate motion is not well understood.

Determination of the slip rate and kinematics of this fault has been done with the help of morphotectonic studies of offset Quaternary alluvial fans, in-situ produced cosmogenic

INTRODUCTION dating and the inversion of fault slip data measured in the field. The determination of the geodynamic role of the Dasht-e Bayaz fault along the kinematic studies on this area were two other important objectives of this study. The methodology used in this study, the collected data, associated interpretations and the discussion are arranged in the four following chapters.

 CHAPTER I GENERAL PRESENTATION, PROBLEM STATEMENT &

METHODOLOGY

An introduction to the tectonic and geodynamic framework of eastern Iran, the northern Lut block and the Dasht-e Bayaz area, the previous studies and seismic history of the area, the explanatory statement of the problems, the objectives of the study and the main questions that we try to answer and finally the methodology of our research along the Dasht-e Bayaz fault have been explained in the chapter I.

 CHAPTER II THE KINEMATICS OF THE DASHT-E BAYAZ FAULT DURING

PLIO-QUATERNARY: IMPLICATION FOR THE GEODYNAMICS OF EASTERN

CENTRAL IRAN

The study of fault kinematic data along the Dasht-e Bayaz fault, the chronological classification of the resulting stress regimes, the structural complexities and implications along the fault, the study of the interactions of this fault with adjusting faults, as well as the geodynamic model of the Northern Lut and the role of the Dasht-e Bayaz fault in the accommodation of Arabia-Eurasian convergence has been discussed in this chapter.

 CHAPTER III QUATERNARY SLIP RATES ALONG THE DASHT-E BAYAZ

FAULT

INTRODUCTION

A systematic measurement of cumulative offsets in the Quaternary alluvial fans according to morphotectonic reconstructions of geomorphic markers, determination of abandonment age of reconstructed surfaces based-on analysis of in-situ produced cosmogenic 10Be concentrations in the quartz clasts collected from alluvial surfaces and consequently calculated slip rates and the earthquake recurrence interval along the Dasht- e Bayaz fault has been presented in this chapter.

 CHAPTER IV DISCUSSION, CONCLUSION & PERSPECTIVES The main results and conclusions of our study of the Dasht-e Bayaz fault in form of detailed answers to the main questions having been discussed in the first chapter, are presented in this chapter.

CHAPTER I

GENERAL PRESENTATION,

PROBLEM STATEMENT &

METHODOLOGY

CHAPTER I

1.1. Geodynamic framework

The Dasht-e Bayaz fault (Fig. 3) is located in the northern parts of the Lut Block in NNE of Iran. The Lut Block (Fig. 1, 4) is an N-trending elongated rectangular area in the eastern Iranian plateau. This block is bounded by the Doruneh fault system (to the north), Nayband, Gowk (to the west), Korizan fault and Sistan suture zone (to the east) and Jazmurian depression to the south.

Figure 3. East looking field view of Dasht-e Bayaz fault trace, which has been reactivated during 31 August 1968 earthquake.

The eastern margin of Lut block is bounded by a fault zone, with more than 500 km long and comprising nearly parallel NNW trending right-lateral faults (Fig. 1, 4). In the extreme north of the eastern boundary of Lut block, the Dasht-e Bayaz fault intersects with

CHAPTER I the Korizan fault, which is the northern segment of the Abiz fault (Fig. 2) and has been responsible for the 7 December 1979 Kalat-e-Shur (Mw 5.9), the 14 November 1979

Korizan (Mw 6.6) and the 10 May 1997 Zirkuh (Mw 7.2) destructive earthquakes (Berberian et al., 1999). The Korizan fault terminates to the north after intersection with the Dasht-e Bayaz fault (Fig. 5). Its continuation to the south is through a zone of several strike-slip and reverse faults including the Gazik, Avaz, Birjand and Purang faults.

Figure 4. Tectonic map and the major active faults (white lines) in Iran in the border with Eurasia, superimposed on the 30-m SRTM Digital Elevation Model (SRTM30 PLUS; http://topex.ucsd.edu/WWW_html/srtm30_plus.html). The Dasht-e Bayaz study area was shown as black quadrangle.

CHAPTER I

Farther south, the faults continue as the two nearly parallel East and West Nehbandan (Neh) faults. West Neh fault overlaps in some parts with the East Neh, Asagie and Zahedan faults and links in the south to the Kahrak and Nosratabad faults. The right-lateral shear between the Iranian plateau and Afghan block is accommodated by this complex fault zone. Although few reverse component and folding has been reported along and around the Zahedan fault (Walker and Jackson, 2004), most of the above mentioned fault system accommodate the convergence through right-lateral strike slip faulting. the amount of dextral offset along this fault system has been discussed by different workers (Freund, 1970; Tirrul et al., 1983; Saidi, 1989; Eftekhar-Nezhad, 1990/1991; Sahandi, 1992; Vahdati Daneshmand, 1992; Walker and Jackson, 2004; Meyer and Le Dortz, 2007; Walpersdorf et al., 2014) and several displacement values have been proposed (see Walker and Jackson, 2004 and Meyer and Le Dortz, 2007 for detailed discussion). The importance and geodynamic role of the East Lut fault system in Arabia-Eurasian convergence is well known and it is approved by geologic and geodetic studies (e.g., Tirrul et al., 1983; Walker and Jackson, 2002; Walker et al, 2004; Walker and Jackson 2004; Vernant et al., 2004; Meyer and Le Dortz, 2007; Walpersdorf et al., 2014); a large portion of shear between the Iranian plateau and Afghanistan is accommodated by this fault system.

CHAPTER I

Figure 5. Map of the major active faults around the Dasht-e Bayaz area.

The eastern part of the Doruneh fault forms the northern limit of the Lut block and separates it from the Binalud and the Kopeh Dagh mountains (Fig. 1). The Doruneh fault has a total length of 400 km (Farbod et al., 2011) and together with the Great Kavir fault is considered as the longest strike-slip fault system (a sum of 600 km length) through the Iranian plateau (e.g., Wellman, 1966; Fattahi et al., 2007; Farbod et al., 2011). Despite clear Quaternary activity of the Doruneh Fault, no historical and instrumental earthquakes of magnitudes M ≥ 6 (Ambraseys and Melville, 1982; Jackson and McKenzie, 1984; Farbod et al., 2011) have been recorded along this major fault.

CHAPTER I

The structural and geomorphic investigation of Farbod et al. (2011) reveals that the curved shape of the DFS is a structural assemblage of three distinct western (WFZ), central (CFZ) and eastern (EFZ) fault zones, instead a ~400-km-long uniform structure. Each fault zone has individual structural, geomorphic and kinematic characteristics. While the CFZ is pure left-lateral strike-slip, the WFZ is reverse left-lateral oblique-slip and the EFZ is predominantly reverse. Consequently, they proposed that this fault should not be regarded as a unique, continuous structure.

Taking into consideration the mechanism and geometry of faulting, western margin of the Lut block has a boundary more or less similar to the eastern one. This boundary involves a long N-trending, right-lateral fault system with roughly straight geometry. This fault system, 290 km in length, separates the Lut block in the east from the relatively high block of Tabas in the west; to the north in 33°N it links with the south dipping Cheshmeh Rostam reverse fault and the Tabas fault system. The west Lut fault has been divided into five segments and includes some bends, a pull-apart basin and the well-known Gandom-e Berian Quaternary basaltic plateau along it length (see Foroutan et al., 2014; Walker et al., 2009 for details). Further to the south, the Nayband fault is linked to the Gowk fault while the south junction of this fault is very complex and involves terminations of the Kuh-Banan and Lakarkuh faults, an intense deformation zone and numerous reverse faults. The seismological and geological observations of the Gowk fault shows that it has right-lateral strike-slip mechanism and has been responsible for several destructive earthquakes (e.g., Berberian et al., 2001).

In the recent years active tectonic studies tried to clarify the rate and kinematics of movement along the plateau bounding and intra continental faults. Strike-slip faults play significant roles in current deformation of the Iranian plateau and were responsible for several moderate to large earthquakes especially in east of Iran. In the Lut block and Central

CHAPTER I

Iran, the role of the N-trending faults (e.g., Nayband, Zahedan, Abiz faults and Neh fault systems- Fig. 5) is properly known and established in the accommodation of convergence so as there is no major debate on this subject. The function of reverse fault systems such as the Tabas and Ferdows faults and their role in the crustal shortening are well accepted in the accommodation of Arabia-Eurasian convergence.

Figure 6. Focal mechanisms for earthquakes in in Iran in the border with Eurasia (lower hemisphere projections) from Harvard catalog, 1976 to January 2005 (Re-drafted from Reilinger et al., 2006). Base map is as in Fig. 4.

CHAPTER I

In the southern limit of the plateau, the convergence zone is limited by active subduction in the Makran region. To the west, the Main Recent Fault of Zagros forms a dextral strike-slip boundary between the Arabian plate and Central Iran. Most of the shortening occurs at the southern and northern edges of the collision zone, in the Zagros and in the Alborz and Kopeh Dagh mountains, respectively (e.g., Walpersdorf et al. 2014).

Jackson and McKenzie (1984), according to earthquake focal solutions in the northeastern Iran had been proposed that few arrows showing the probable slip vectors toward northeast and east. They also emphasized the seismic activity of eastern Iran decreases abruptly east of about 61°E (Fig. 6), which roughly corresponds the border of Arabia- Eurasian collision.

Thanks to recent GPS measurements (e.g., Nilforoushan et al., 2003; Vernant et al., 2004a, 2004b; Masson et al., 2005, 2007; Walpersdorf et al., 2006; Tavakoli, 2007; Tavakoli et al., 2008) we know more about the present-day deformation and our quantitative knowledge of convergence has progressed. The results of GPS measurements showed that the slip vectors are more inclined to the north (almost N-S, e.g., Vernant et al., 2004; Masson et al., 2007) than have been presumed by Jackson and McKenzie (1984). As well, not a significant movement had been measured in the GPS stations of YAZT and ZABO in the east of Sistan suture zone confirmed the seismologic-based presumed structural border between Iranian plateau and Afghan block of Jackson and McKenzie (1984) and allowed Masson et al. (2005) to conclude that the Afghan block belongs to the stable Eurasia.

These data show a northward motion of the Arabian Plate relative to Eurasia at a rate of 22 ± 2 mm/yr at the longitude of 50.6°E. According to these geodetic studies, the Arabia- Eurasia convergence is mostly accommodated at the Iran block borders by the Zagros (6.5

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± 2 mm/yr) to the southwest and the Alborz (8 ± 2 mm/yr) to the north of the collision zone, by the Makran subduction zone (19.5 ± 2 mm/yr) to the southeast and by the Kopeh Dagh Mountains (6.5 ± 2 mm/yr) to the east of the Arabia-Eurasia convergence zone (Vernant et al., 2004).

Based-on the GPS-derived velocity field that were yielded from GPS stations and using seismic records, Reilinger et al. (2006) suggested an elastic block model with a northward movement of the Lut block respect to the Eurasia at a rate of 7 mm/yr (Fig. 1A). The differential motion of the HB and LB blocks results (Walpersdorf et al., 2014) in a right- lateral slip operating at 5.6 ± 0.6 mm/yr along the east Lut ~ N12°E mean strike. The right- lateral slip rate is roughly constant along the fault, ranging from 5.6 ± 0.6 mm/yr in its southern part to 5.8 ± 0.7 mm/yr in the north.

The GPS-inferred LB and NB differential motion induces a roughly constant 4.4 ± 0.4 mm/yr right-lateral slip rate on the west Lut fault (Walpersdorf et al., 2014). This geodetic rate of slipping is more similar to 3.8 ± 0.7 mm/yr (Walker et al., 2010) geologic slip rates estimations have been done on the southern Gowk segment but has discrepancy with 1.4 ± 0.5 mm/yr (Walker et al., 2009) and 1.8 ± 0.7 mm/yr (Foroutan et al., 2014) on the northern Nayband segment.

About the Doruneh fault it seems that because of a sparse and unevenly distributed arrangement of GPS stations in the north and south of the fault (Walpersdorf et al., 2014), GPS measurements could not help to have a general view about present-day rate of slipping along this fault, specially that it has a curved geometry and the strike of the fault varies outstandingly along its length. According to Walpersdorf et al. (2014), the current lateral slip rate on the Doruneh fault is not well constrained yet and they find it to be in the range 0.5–2.1 mm/yr on the average N077°E strike of the fault. Additionally, it might vary along

CHAPTER I the fault from 2.6 ± 0.5 mm/yr in the west to 0.8 ± 0.6 mm/yr in the east. The relative NDR and SDR motion more robustly constrains a fault perpendicular shortening of 2.1 ± 0.4 mm/yr. The across-strike compressive component slightly increases toward the east.

This complexity is also the case for the geologic slip rates that have been estimated by the different researchers. From the measurement and the dating of one offset alluvial terrace at one fault site, a local Holocene slip rate of 2.4 ± 0.3 mm/yr is estimated (Fattahi et al., 2007), reaching ~3.0 mm/yr at a nearby site (R. Walker, personal communication with Walpersdorf, see Walpersdorf et al., 2014). It seems that the questioning of Farbod et al., 2016 is reasonable as this slip rate has been estimated in one location, while, it is well known that horizontal offsets and consequently the slip rate may significantly vary along the strike of long strike-slip faults (e.g., Deng et al., 1986). Specially that the Doruneh fault is a very long curved fault and as concluded by Farbod et al., (2011) even not considering great Kavir fault, it is a complicated fault system and involves three fault strands with completely different mechanisms. Consequently, without consideration of the complexities and slip distribution along the Doruneh fault, a single slip rate could not be representative of the overall fault slip.

Another interesting issue has been discussed recently by Walpersdorf et al. (2014) in eastern Iran concerns the understanding of the relationships between “major” and “secondary” faults. They proposed that in a seismologic point of view the importance of “secondary faults” such as Shahdad fault, Mohammadabad fault, Bam fault, Dustabad fault, Chahak fault, Dasht-e Bayaz fault, Lakarkuh fault and Zahedan fault have been more than “major faults” such as Nayband, East Neh, West Neh, Anar, Dehshir, Kahurak and Nosratabad faults. Meanwhile, it is presumed that the “major faults” accommodate more strain than “secondary faults” and in fact the second category are structurally associated to the “major faults”. While these secondary faults are likely to accommodate less strain and

CHAPTER I slip at lower rates than the major faults, a number of them broke in large devastating earthquakes in historical times whereas the major faults were basically quiescent (e.g., earthquakes of Mohammadabad 1941, Dustabad 1947, Ferdows 1968 and Tabas 1978, South Golbaf, Sefidabeh 1994, Chahar-Farsakh 1998, Bam 2003, Dahuyieh (Zarand) 2005, and Konarak 2010; see Walpersdorf et al., 2014 and references therein).

Although the general process of convergence are well-identified, a number of key questions remains unanswered and need to be answered in the future.

- the total offset and geological slip rate in both sides of Lut block are not equal.

- the total offset and geological slip rate in each of fault systems, particularly in eastern boundary of Lut block that coincides with the convergence boundary, are totally different and no convincing reason has not been proposed for it.

- the discrepancy between geological and geodetic slip rates in eastern Iranian active faults is another unanswered question. Although some answers and solutions such as the switching of activity between parallel active faults, has been suggested (Walker et al., 2009) to answer this discrepancy.

- the role of sinistral E-W trending left-lateral strike-slip faults perpendicular to plate motion in the northern Lut, despite some proposed and discussed models and solutions (e.g., Jackson and McKenzie, 1984; Jackson et al., 1995; Walker and Jackson, 2004; Farbod et al., 2011) has not been well understood and has been debated in the recent years.

1.2. Previous studies about Dasht-e Bayaz fault and around area

After the destructive 1968 Mw 7.1 earthquake (Fig. 7), the Dasht-e Bayaz area has been one of the most seismically active domains in Iran. Right after the Dasht-e Bayaz main

CHAPTER I shock in 1968, this area was studied by numerous researchers from different points of view. The first studies focused on mapping of coseismic rupture and post-earthquake observations (e.g., Ambraseys and Tchalenko, 1969; Eftekhar-nezhad et al., 1968; Tchalenko and Ambraseys, 1970; Tchalenko and Berberian, 1975; Berberian and yeast, 1999), while more recent studies focused on modeling, seismology and active tectonics of the Dasht-e Bayaz and surrounding area in the context of Arabia-Eurasian convergence (e.g., Walker et al., 2004; Fattahi et al., 2011, 2015). Berberian (2014) is one of the best resources covering this area.

Figure 7. Four pictures of 31 August 1968 Dasht-e Bayaz earthquake. Upper Left the Dasht-e Bayaz village and upper right coseismic displacement in the south of Boskabad, lower left another coseismic displacement in the north of Nimboluk plain and lower right, coseismic depression basin around the Salayani village (All of pictures taken by A. Haghipour)

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1.3. Explanatory statement of the problems

The objective of this study is to answer the fundamental questions about the Dasht-e Bayaz fault and northern Lut block. For this reason first we explain the questions and challenges and after a historical and critical discussion about existing complexities, we describe the questions that should be answered. In the last section (conclusion) and after the two major parts of our study we will try to explain the results of this study by answering the confronting questions and challenges that are discussed here.

1.3.1. Situation of present-day kinematic in the northern Lut, state of stress and tectonic regime change in plio-Quaternary

One of the most interesting issues about the accommodation of Arabia-Eurasian convergence in Iranian plateau is the history of stress regime change during Plio- Quaternary. Thanks to modern techniques like inversion of focal mechanism of earthquakes, our knowledge of present-day state of stress data has progressed. Whereas there is still some ambiguity left in the interpretation of long-term stress regime, their changes and transition in between.

Temporal changes in the Alborz mountain chains, Kopeh Dagh mountains and North of Lut block have been reported by authors (e.g., Abbassi and Farbod, 2009; Guest et al., 2006; Landgraf et al., 2009; Yassaghi and Madanipour, 2008; Zanchi et al., 2006). The rate and style of deformation in north and northeast of Iran have significantly changed during the late Cenozoic (e.g., Ritz et al., 2006; Shabanian et al., 2010). The next fault kinematics studies showed that these changes have not been gradual and on the contrary were drastic (e.g., Shabanian et al., 2010; Javidfakhr et al., 2011)

In each newer situation the nature of change and transtension is tightly associated with the geometry of pre-existing faults (see Ritz et al., 2006). Some of strike-slip faults have

CHAPTER I possessed vertical component or reversed and in some cases the change in direction of compression temporally coincides with critical events like beginning of volcanic activity of Damavand volcano (see Ritz et al., 2006).

Temporal changes in stress regime for first time in Iran was reported by Tchalenko et al. (1974) during Tectonic studies in Tehran region. Based on structural observations and the style of folding and faulting in the alluvial formations they noticed the existence of an N-S to NE-SW orientated compression in post-Pleistocene times (see Tchalenko et al., 1974). Abbassi and Shabanian (1999) during the paleostress studies in the same region were obtained three distinct stress states with help of inversion of fault kinematics data, which have been collected from the 167 fault slip data and 57 tension gashes. They could also determine the chronology of temporal changes and direction of rotation of stress field based on the relative ages of involving alluvial formations. According to this research, stress direction trending NW-SE affected just A-formation as the oldest Quaternary deposits so they were the oldest generation and N-S and NE-SW directed stress tension affected only B-formation that is overlaying younger unit, so they resulted a clock-wise rotation in the stress field during plio-quaternary.

In 2001 another interesting research involving U/Pb, 40Ar/39Ar, and (U-Th)/He analysis and structural geology studies in west-central Alborz more explained the details of the consequences and chronology of this stress regime change and contributed to a better understanding of Cenozoic tectonic evolution of Iranian plateau in the context of Arabia- Eurasian collision zone. After crystallization and thermal histories studies of intrusions, cooling and exhumation of Akapol and Alamkuh plutons they properly related their temporal coincidence with a chain of other more widespread occurrences and Tectonic changes at ca. 5 Ma including reorganization of the Dead Sea transform and onset of oceanic spreading in the Red Sea along two boundaries of the Arabian plate (Garfunkel,

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1987) and possible initiation of extrusion of western Turkey from between the North and East Anatolian faults (Westaway, 1994). While pointing out to affecting the interior basin of Alborz by a dextral transpressional movements between 56 Ma and 7 Ma they result that the modern tectonic regime including sinistral faulting, overthrusting and north trending folding probably began ca. 3.4 Ma (when those folds began to grow, Devlin et al., 1999). Evidences of an N-S compressional regime has also been reported in western Alborz (Jackson et al., 2002; Allen et al., 2003).

In continue Ritz et al. (2006) based on morphotectonics and structural analyses suggested that the South Caspian Basin northwestward motion to Eurasia and/or its clockwise rotation started in Pleistocene. They also found that this motion had been contemporaneous with events like change from a general N-S compression to a general NNE-SSW transpression in Alborz and also the expression of transtension in the internal domain of the range and maybe in succession creating of Damavand volcano in one of this transtensional domains between 1 and 1.5 Ma.

The inversion of fault kinematics data in Kopeh Dagh mountain range measured from 39 sites revealed temporal clock-wise change and three distinct state of stress including N140±10°E, N180±10°E and N30±15°E trending horizontal σ1 as older, medium and modern state of stress since 5 Ma (Shabanian et al. 2010).

Similar drastic temporal changes and maximum horizontal σ1 trending were reported (Javidfakhr et al., 2011) in NE of Iran including eastern Alborz and western Kopeh Dagh mountains. Fault kinematic measurements and statistical calculations in 48 sites in this transitional zone attain to three group of homogenous transpressional tectonic regime with clock-wise rejuvenation involving N135±20°E, N185±15°E and N36±20°E trending horizontal σ1.

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The inversion results along the Doruneh fault system (Farbod et al., 2011) showed transpression states of stress as N150±20°E and N45±15°E trending horizontal σ1 as paleostress and modern stress during Plio-Quaternary, respectively. The other research approving changes in stress field this time in northwest of Iran was done in Mianeh- Mahneshan sedimentary basin (Aflaki et al., 2017, in Persian). The red beds folded at the end of middle-Miocene have been overprinted and deformed by a younger generation of NE-SW oriented folds in a time interval between Pliocene to Quaternary. Inversion of fault kinematics data in this region affirm that a compressional paleostress (Plio-Quaternary) with N138°E trending horizontal σ1 has affected the area before dominance of NE-SW oriented present-day stress regime.

In one of the most recent studies, Tadayon et al. (2017), tried to clarify this temporal change by combining the structural results with thermochronology investigations around the middle parts of Doruneh fault in NE of Iran. Based on this study, switch from an early NW-SE oriented maximum paleo-σ1 direction to N-S started in Miocene-Pliocene boundary (at about 5-6 Ma) and this change had been source of an important cooling/exhumation in the area. They also suggested that the previous deformation and exhumation in the area started at early Miocene (22-18 Ma), this age approximately corresponds with the time of dominance of NW-SE oriented stress regime that was cause of first generation of folding and deformation of the red beds in Mahneshan region (Aflaki et al., 2017, in Persian) in NW of Iran.

Finally we discuss the results of Jentzer et al. (2017) in Sistan belt of eastern Iran that its kinematics results especially in the domain of regional geodynamic are debatable and ambiguous. They obtained three distinct compressional stages during late Cenozoic including (1) an E-W (N87±5°E direction of σ1) probably late Miocene, (2) a late Pliocene ENE-WSW (N59±8°E direction of σ1) and (3) an oblique late Pliocene to present-day

CHAPTER I almost NNE-SSW (N26±8°E direction of σ1) in their study area and it has been mentioned that within the last ~10–5 Myr, the main stress direction rotated about 60° counterclockwise in Sistan. There is no other kinematics studies results accessible in Sistan belt for comparing and reviewing the consistency.

Regardless of accuracy and precision of the results in the interior of study area of Sistan belt, the results should not be necessarily in agreement with other parts of Iranian plateau and the results can be analysed independently. But this research tried to compare and generalise the results to all of Iran while they were not in agreement with most of them in Alborz, Kopeh Dagh and north of Lut block (e.g. Tchalenko et al. 1974; Shabanian et al., 2010; Farbod et al., 2011; Javadi et al., 2013; Javidfakhr et al., 2011; Aflaki et al., 2017; Tadayon et al., 2017). In fact, the problem comes back to the lack of attention in data gathering and prepared stress comparison maps so each map misses important results even from cited papers that mentioned in description below the maps. Although compression of modern state of stress (N26±8°E direction of σ1) is generally coherent with expected direction but it is more inclined to the north in comparison with previous studies conducted in south (N51°E) and north (N38°E) of study area (see Zarifi et al., 2014) and mean trend of N39°E of inversion of earthquake focal mechanism is more inclined to north. It is worth considering this ambiguities in the geodynamic interpretations of the east of Iran.

o What is the main question regarding the Kinematics of deformation in the Dasht-e Bayaz area?

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i. What is the present-day state of stress around the Dasht-e Bayaz fault in the northern Lut? Is the present pattern of kinematics of deformation in this part of the convergence/collision zone the same as other parts of Iranian plateau such as Kopeh Dagh and Alborz? ii. The tectonic regime change discussed above is the case for Dasht-e Bayaz area? If yes, would the mechanism and directions of the main stress be the same as in the previous studies?

1.3.2. morpho-tectonic discussions and structural characteristics of Dasht-e Bayaz fault, evolution, segmentation, total offset and relationships and interactions with the adjacent faults

Considering the previous works and the situation of the Dasht-e Bayaz active fault in the northern Lut, detailed morpho-tectonic investigations along the fault can present new ideas and interpretations. Detailed structural studies along an active fault, segmentation, total and cumulative displacement, and its interaction with adjacent faults are very important. Accordingly, detailed geological and structural map involves particularly Plio- Quaternary features, geomorphologic would properly help to find answers to important questions and challenges encountered along the fault and can even explain kinematic and structural complexity of the region in geodynamic scale.

Although some dispersed discussions have been made by the recent studies, it seems that they did not go further than pointing out some general structural aspects along the

CHAPTER I fault. As there are similarities in the sinistral mechanism of fault and location in the northern Lut we refer to some determining results about Doruneh fault system.

Total and cumulative offset along the Dasht-e Bayaz fault:

Maximum cumulative displacement of 4 km has been measured by Tchalenko and Berberian (1975) based on outcrop of black limestone in the Khidbas area and this amount presented as conjectural total offset in this paper. They pointed out also to another much smaller displacement as such as 400 m near the Darreh Sefid area in the east of abovementioned Khidbas region based on limestone marker beds contained in Eocene volcanic rocks (Tchalenko and Berberian, 1975, personal communication with H. Behzadi). They referred to amount of 8 to 28m left-lateral slip movements that was documented by displaced stream channels in different parts of the Dasht-e Bayaz fault.

There is no report concerning cumulative offset of Quaternary fans, which have been displaced by the Dasht-e Bayaz fault. Fattahi et al. (2015) during a study with aim of slip rate determination of Dasht-e Bayaz fault referring to existence of “no measurable relief” along the fault. This subject leaded the authors to choose a measurement site based-on streams in the dry lake-bed sediments in a flat area without any Quaternary fan. Accordingly, in the absence of Quaternary alluvial fans and/or any other geomorphic marker, no convincing reason has been presented for consideration of one of streams offsets and rejection of two others as displacement factor in the calculation of slip rate.

o What is the main question about morpho-tectonic and structural characteristics of Dasht-e Bayaz fault, evolution, segmentation, total offset and relationships and interactions with the adjacent faults? 24

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i. How is the situation of interaction of this fault with adjacent faults? Is there a phenomenon of slip partitioning around this fault? ii. The segmentation and the probable existence of strike-slip related structural features such as pull-apart basins and en-echelon folds placed between the main questions of this section. iii. The total and cumulative displacement along the Dasht-e Bayaz fault exceed to which amount? Are there any measurable displaced alluvial fans that are necessary for slip rate calculations? If yes, how much is displacement of geomorphic markers in this (or these) alluvial fan(s)?

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1.3.3. Challenges and questions about geodynamic of northern Lut and role of Dasht-e Bayaz fault in the context of the Arabia-Eurasian convergence

In East of Iran, strike-slip faults have a main role in accommodation of the convergence. According to the geological investigations and geodetic GPS measurements done in the two last decades (e.g., Berberian et al., 1999; Walker and Jackson, 2004; Vernant et al., 2004; Mayer and Le Dortz, 2007; Foroutan et al., 2012, Walpersdorf et al., 2014), the N-trending right-lateral fault systems in central Iran and specially on both the west and east sides of the Lut block, accommodate the northward component of Eurasia- Arabia convergence as right-lateral shear between central Iran and Afghanistan. Distribution of historic records and earthquake epicenters and GPS measurements show that convergence is accommodated mainly along the fault systems and fault bounded blocks (like Lut block) that are almost aseismic (e.g., Vernant et al., 2004; Walker and Jackson, 2004).

This crustal-scale right-lateral shear continues up to the latitude 34°N, where the E-W left-lateral faults like Dasht-e Bayaz and Doruneh (further north) are present. At this latitude, the change in geology is accompanied by a change in the active faulting from the N-S right-lateral faults of Sistan to a system dominated by E-W left-lateral strike-slip faults (Berberian et al., 1999). The role of these crustal faults in the accommodation of active deformation perpendicular to the N-S dextral shear was a matter of debate since at least thirty years ago (e.g. Jackson and McKenzie, 1984; Berberian et al., 1999; Walker and Jackson, 2004; Farbod et al., 2011, 2016).

Based on one of the proposed models, much of N–S right-lateral shear between Iranian plateau and stable western Afghanistan and the present-day deformation is concentrated along the eastern margin of Iran (e.g., Jackson and McKenzie, 1984; Walker and Jackson

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2004). Therefore an uneven distribution of shear and a westward decrease in cumulative N–S right-lateral shear caused a clockwise rotation of fault bounded blocks in north of Lut and central Iran (north of 34N). This model tried to interpret particular features in north of Lut and central Iran like:

- Left-lateral movements of Doruneh and Dasht-e Bayaz fault. North of 34N, deformation is accommodated on left-lateral strike-slip faults that must rotate clockwise if they are to take up N–S right-lateral shear (e.g., Jackson and McKenzie, 1984; Walker et al., 2004)

- The prominent curvature of the Doruneh fault. This phenomena could be due to larger finite rotations in the eastern part of the fault because more rotation is required in the east than in the west.

- Limited extent of the Dasht-e-Bayaz fault. The left-lateral Dasht-e-Bayaz fault occurs only east of 58E, in the region where the Doruneh fault has an ESE–WNW trend (e.g.,

Walker and Jackson, 2014)

However, the structural pattern and kinematics of deformation at this intracontinental boundary cannot be explained by this simple geometric model specially that the proposers of this model “in absence of enough data to test several of the key assumptions and hypotheses” accept ambiguities in their model and they consider it as “speculative kinematic model” (e.g., Walker and Jackson, 2004).

The idea of block rotation model proposed by Walker and Jackson (2004) was questioned for its lack of clarity, necessity of subsistence of rigid blocks in both sides of Doruneh and absence of any evidence indicating Doruneh had initially been an straight E- trending of fault (Farbod et al., 2011).

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o What is the main question about the role of Dasht-e Bayaz fault in the context of Arabia-Eurasian convergence? i. According to above discussion, a main unanswered geodynamic question is the role of this E-W seismogenic sinistral fault in accommodation of the N-S convergence of central Iran–Eurasia. Clarifying the geodynamic role of Dasht- e Bayaz fault perpendicular to plate motion in the context of a geodynamic model could help us to find better answers to the questions about the structural features in the northern Lut.

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1.3.4. Questions about the rate of slipping along the Dasht-e Bayaz fault

The slip rate is one of the most important characteristics of an active fault as it is a well- defined and unambiguous criteria to recognize how active a fault is. Estimation of slip rate had been subject of a lot of studies in the Central Iran, Kopeh Dagh and the Lut block in the recent years (e.g., Berberian and Yeats, 1999; Le Dortz et al., 2009, 2011, 2012; Walker et al., 2009; Shabanian et al., 2009; Rizza et al., 2011; Fattahi et al., 2011, 2015; Foroutan et al., 2014; Farbod et al., 2016). Three methods of in-situ cosmogenic nuclide analysis (e.g., Shabanian et al., 2009; Farbod et al., 2016), optically stimulated luminescence (e.g., Fattahi et al., 2011, 2015; Le Dortz et al., 2009; Foroutan et al., 2014) and infrared stimulated luminescence /IRSL (e.g., Fattahi 2006, 2007; Fattahi and Walker, 2007; Rizza et al., 2011) that have been used by most studies for dating of displaced alluvial surfaces. Also the GPS data has been extensively applied to determine the slip rate of the active faults in all over Iranian plateau was using the GPS data (e.g., Walpersdorf et al., 2006; Tavakoli et al., 2008; Vernant et al., 2004; Masson et al. (2007); Peyret et al., 2009; Djamour et al. (2010); Mousavi et al., 2013; Walpersdorf et al., 2014). The interferometry methods using InSAR data to measure the rate of interseismic strain accumulation has been used for slip rate determination in some areas in the NE of Iran (e.g., Walters et al., 2013; Mousavi et al., 2015). In some particular cases, displacement along the man-made qanat lines have been applied by Berberian and Yeats (1999) for estimation of slip rate along the Dasht-e Bayaz fault and Walker et al., (2009) used displaced river courses incised in the Quaternary basaltic lavas and 40Ar/39Ar dating for the calculation of slip rate of Nayband fault in the limit of Central Iran and the Lut block.

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Challenges about slip rate estimations of major faults around the Lut Block

The review of slip rate estimations done in the recent years in eastern Iranian plateau show that there have been complexities in the interpretation of the results.

However, there are difficulties and ambiguities mostly in level of total cumulative offset and the amount of slip rate that may complicate the geodynamic and tectonic interpretations. We review some of the challenges and questions concern Lut block and around area in brief as below:

-Walker and Jackson (2004) discuss that the maximum right-lateral 70-95 km offset calculated by the total of parallel or sub-parallel Zahedan (13-20km), East Neh (65 km) and West Neh (10 km) as the main active faults of Sistan suture zone cannot be followed in none of northern and southern sole faults (e.g. Abiz, Gazik, Avaz and Nosratabad faults).

- Furthermore they discuss that while large-scale geomorphologic reconstruction of East Iranian range requires at least 150 km of cumulative right-lateral displacement, this reconstruction will juxtapose rocks of the Ratuk complex with those of the Neh complex that are in fact separate structural entities of different ages (see Walker and Jackson, 2004 and references there in).

- As we saw in the case of Sistan suture zone in some parts there are parallel or sub- parallel overlapped active faults that each one accommodates a part of convergence. Therefore the total amount of cumulative offset in these cases is obtained by the addition of individual offset of concerned faults. The Gowk fault is in the contrary of its equivalent parallel faults of Sistan suture zone in the west of Lut block, is the only major structure in the same latitude that can transmit strain to the Nayband fault in the north. While the additional minimum amount of 70-95 km fault displacement of Sistan suture zone in the

CHAPTER I eastern Lut is much larger than 12-15 km of cumulative right-lateral slip estimated for the Gowk fault to the west of the Dasht-e-Lut (Walker and Jackson, 2002, 2004).

- Considerable discrepancies are seen between geodetic and geologic rates of faulting in different parts of eastern and central Iran. During study of slip rate along the Doruneh fault system, Farbod et al. (2016) considered that there is no consistency between instantaneous geodetic and moderate to long-term geologic slip rates. They explained the reasons of this discrepancy to be cases such as fault slip behavior, temporal scale of measurements, the arrangement and distribution of geodetic arrays relative to geological structures, boundary conditions for rigid block models. As we will see about Dasht-e Bayaz fault (see section of 4.4 of this study), the positioning of GPS stations around this fault has led to complexities in the results. The Pleistocene-Holocene geological slip rate of the Nayband fault determined as 1.8 ± 0.7 mm/y (Foroutan et al., 2014) and 1.4 ± 0.5 mm/y (Walker et al., 2009) is discrepant with the GPS rate of 4.4 ± 0.4 mm/y (Walpersdorf et al., 2014) derived from this new GPS deformation field. There is no regularity in this issue and therefore these discrepancies between the results of two methods are not predictable especially that those discrepancies are not necessarily observed everywhere.

Meyer and Le Dortz (2007) based-on assumption of coeval occurrence of alluvial fans of the last climatic drastic change (onset of Holocene) with the latest regional incision in the Iranian plateau, estimated the slip rates (over the last 12 ± 2 ka) for the Anar, East Neh, West Neh and Asagie faults equal to 0.5–0.75 mm/y, 1.75–2.5 mm/y, 1–5 mm/y and 1– 2.5 mm/y, respectively. Meyer and Le Dortz (2007) estimated that the Holocene total rate of faulting across the East Neh and West Neh faults would be about 2.75 – 7.5 mm/y near 30.5N. Additionally, they discussed the Zahedan fault should have been slipped at least in 6.5 mm/y during the Holocene to reach the 14 mm/y suggested by Walker and Jackson (2004) for the Eastern Lut fault system. They believe that as it is unlikely to rely (or count)

CHAPTER I on Zahedan or hidden faults inside the Lut block, had been slipped at such a rate. Meyer and Le Dortz (2007) then conclude that the total rates on the faults surrounding the Dasht- e-Lut during the Holocene are considerably less than short-term rates of faulting derived from GPS data and therefore “the GPS shear-rate across the Lut may not extrapolate over the Holocene”. Afterwards, in a complementary explanation walker et al. (2009) referring to results of Meyer and Le Dortz (2007) and the discussion of alternative changes in the slip rate in a region of strike-slip faulting as a result of the switching of activity between parallel active faults (Dolan et al., 2007) proposed “Testing whether fault slip rates in Iran are constant or variable requires detailed information on the rates of faults averaged over various timescales”.

- The geologic and geodetic rates of faulting have decreased to the north.

- The GPS velocities extrapolation over geologic timescales has been questioned by Meyer and Le Dortz, 2007 because

- A significant difference between long-term geological and short-term geologic slip rates has been reported in some of studies (e.g., Meyer and Le Dortz, 2007; Farbod et al., 2016).

- slip rate and total offset base yielded age of N-trending faulting in east and west of north and south of the Lut block are different and could not suggest a distinct timing of initiation. Time of initiation proposed as 8-22 Ma, (Meyer and Le Dortz, 2007), 5-7 Ma (Walker and Jackson, 2004), 3.3-4.8 Ma (walker et al., 2010), ∼5 Ma (Westaway, 1994; Lyberis and Manby, 1999; Allen et al., 2004).

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Previous slip rate estimations along the Dasht-e Bayaz fault and the questions

First attempt to estimate the slip rate of Dasht-e Bayaz fault has been done according to qanat line displacement along the Dasht-e Bayaz fault. Ten meters of left-lateral displacement measured by Ambraseys and Tchalenko (1969) in the old qanats of Miam qanat system allowed Berberian and Yeats (1999) to determine minimum slip rate of Dasht- e Bayaz fault. By applying the dating results of Mehryar and Kabiri (1986) equal to 4000 years that have been done in the Semnan area they calculated the minimum slip rate of Dasht-e Bayaz fault, as much as 2.5 mm/y.

In the second estimation of slip rate of the Dasht-e Bayaz fault, Fattahi et al. (2015) dated two OSL samples of lake-bed sediments from northern Nimboluk plain as 8.6±0.6 and 8.5±1.0 ka. They applied 26±2 m of displacement in “small streams” that have been displaced along the Dasht-e Bayaz fault in the east of Khezri and estimated the minimum slip rate of this fault as 2.6 mm/y.

In the one of the recent studies, Walpersdorf et al. (2014) working on present-day fault kinematics and slip rates derived from eleven years of GPS data in eastern Iran, beside the other faults tried to estimate the present-day slip rate of Dasht-e Bayaz fault. Four stations around the Dasht-e Bayaz fault were used for processing and as a result, they obtained a N-S extension of 1.2 ± 0.3 mm/y combined with a dextral E-W lateral slip of 0.2 ± 0.1 mm/y.

o What is the main question about the rate of slipping along the Dasht-e Bayaz fault? i. The primary objective is to estimate the slip rate of the Dasht-e Bayaz fault for the long-term as long as possible according to geomorphic markers of displaced alluvial deposits and absolute age of abandonment of these alluvial fans.

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ii. The study of coherency of new results with the previous estimations should be done. iii. As it was mentioned by Walpersdorf et al., (2014), dextral sense of movement has been obtained for this fault is contradictory with the observations while the Dasht-e Bayaz fault is unambiguously left-lateral. As it was emphasized “we cannot explain the discrepancy between the actual sense of slip and that observed in the GPS data” in this research, it is expected from our slip rate results to have interpretations about this complexity.

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1.4. Methodology

The multidisciplinary character of our present research required a data base involving satellite images and previous studied done in the Dasht-e Bayaz area. After preparation of the required data and resources we arranged them in the function of usage. The satellite images and geological maps were necessary almost in all of field and office works were integrated in a Geographic Information System.

1.4.1. Structural and geomorphic studies along the Dasht-e Bayaz fault

The Dasht-e Bayaz fault is typical seismic fault and it has not been long since the last earthquake took place and therefore with a clear-cut and distinct fault trace, mapping the fault was not very difficult. In the northern Nimboluk plain almost most parts of fault trace has been removed because of cultivation and human activities and we used the coseismic mapping of Ambraseys and Tchalenko (1969), Eftekhar-nezhad et al. (1968), Tchalenko and Ambraseys (1970) and Tchalenko and Berberian (1975). We used different satellite images for structural and morphologic analysis. ETM, ASTER and SPOT high resolution images were used during the mapping the fault trace, preparing Quaternary alluvial maps and structural and morphologic analysis. The Quaternary fans around the fault trace were mapped and everywhere they have been displaced by the fault, the geomorphic markers have been measured and registered as well. Conjunction of the Dasht-e Bayaz fault with cross-cutting faults and the other structural features were studied and mapped correctly.

1.4.2. Fault kinematics and states of stress studies

 Inversion of fault slip data:

We used fault Kinematics data inversions to identify state of stress during Plio- Quaternary by the method originally proposed by Carey and Brunier (1974). Principal inputs are geologically measured (or seismologically determined) fault slip data including

CHAPTER I spatial orientation (e.g., strike/dip/dip quadrant) of striated fault planes in addition to the pitch and movement of the faults striation.

Computer programs (faille software in our study) compute a mean best fitting deviatoric stress tensor from a group of fault striations by minimizing the angular deviation (misfit angle) between the observed striation and the shear stress resolved on the fault plane (Carey and Brunier, 1974, Carey; 1979; Angelier, 1990). We revised and refined repeatedly the inversion results to reach to smallest misfit angle with involving of highest possible number of measured homogenous fault slip data.

The main outputs of this method are orientations (trend and plunge) of principal stress axes σ1≥ σ2≥ σ3 (corresponding maximum, intermediate and minimum stresses, respectively) and “R= (σ2-σ1)/(σ3-σ1)”. This linear parameter (R) equal to 1−φ, φ being another commonly used stress ratio (e.g., Angelier, 1979; Zoback, 1989; Ritz and Taboada, 1993), and describes relative stress magnitudes ranging from 0 to 1 (e.g., Carey and Brunier, 1974; Mercier et al., 1991; Bellier and Zoback, 1995, Shabanian et al., 2010). A combination of Andersonian stress arrangements and R value leads to determine the stress regime in individual sites (e.g., Ritz and Taboada, 1993; Shabanian et al., 2010).

All of 11 visited and measured outcrops we measured the fault kinematics data were displaced by major faults that were reactivated recently during late Quaternary such as Ferdows thrust zone and Dasht-e Bayaz, Korizan faults. We used crosscutting relationship methods to separate different generations and finally the measured fault slip data were separated into three homogeneous groups of slip generations.

After calculation of stress regime in each site, tectonic regime of area has been statistically calculated by Stereonet V. 10.0, Richard W. Allmendinger © 2011-2018) and presented as paleostress, intermediate and modern state of stress.

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 Inversion of earthquake focal mechanism data:

We determined the present-day state of stress in Dasht-e Bayaz through inversion of focal mechanisms of medium to large (7.1>M>5.5) earthquakes applying the method described by Carey-Gailhardis and Mercier (1987); these earthquakes have occurred between 1968 and 1997 comprising the Dasht-e Bayaz main shock. We only used focal mechanism solutions that had been relocated and modeled using body wave by Walker et al. (2004) and Walker et al. (2011). In this method, we analyzed two orthogonal nodal planes for each earthquake focal solution taking into account that only one plane was reactivated during the earthquake due to a regional stress state. The final selection among each pairs of nodal planes can be done by (1) direct observation of the surface rupture of earthquake, (2) seismological investigations of the rupture process, (3) the spatial distribution of aftershocks and (4) the inverse computation by selecting the nodal plane that results in the greatest consistency with the inferred stress field (Carey-Gailhardis and Mercier, 1987). For some of the main shocks, we had direct information on the rupture geometry from field observations (e.g. Ambraseys and Tchalenko, 1969; Eftekhar-nezhad et al., 1968; Tchalenko and Ambraseys, 1970) otherwise we used inverse computation of nodal plane with the greatest consistency with the inferred stress field method.

1.4.3. Determination of rate of slipping of the Dasht-e Bayaz fault

The slip rate of a given fault is a quantitative value and is calculated through the division of displacement by absolute age, indicating the starting-point of the displacement.

Different methods of measurement of slip rate through different time domains have been presented in Fig. 8. Geodetic data obtained from GPS stations provides slip rates over the most recent five to ten years, while morpho-tectonic & exposure age based

CHAPTER I investigations yield slip rates over tens of thousands of years and the geological slip rates commonly average over millions of years. Taking into consideration the determining factors, morpho-tectonic slip rate integrate many earthquake cycles, while geodetic methods can be more sensitive to interseismic strain (Benedetti and van der Woerd, 2014).

Figure 8. Methods available for measuring slip rates on active faults over different time windows. Geodetic measurements can generate decadal slip rate determinations; morpho-chronology, based mainly on cosmogenic nuclide surface-exposure dating, can yield slip rates over tens of thousands of years; and geology reveals slip rates over millions of years. Geomorphic measurements integrate many earthquake cycles, while geodetic methods can be more sensitive to interseismic strain (image and explications from Benedetti and van der Woerd, 2014)

In the last decades thanks to the growth of technology of measurements of minor elements, different methods of surface exposure dating has been initiated and used mainly

CHAPTER I in the study of evolution of landscapes and particularly in the Quaternary geochronology. According to an important essential of the surface exposure dating, concentration of cosmogenic nuclides in the certain minerals increases with passing of time when they expose to cosmic rays. As the cosmogenic nuclides build-up predictably, by measuring their concentrations we estimate how long the rocks have been exposed at (or near) the surface of the Earth (see Ivy-Ochs and Kober, 2008 and references therein). The radionuclides 10Be, 14C, 26Al and 36Cl and the stable noble gases 3He and 21Ne are the most common nuclides have been utilized in the recent years in the surface exposure dating studies.

The above subjects explained the fundaments of surface exposure dating but practically when we use this method in study area, there are some individual limiting factors should be considered as local factors as bellow:

i. The production rate of cosmic nuclides are dependent on altitude and latitude (Fig. 9). Because of deflective and impeditive function of the earth’s magnetic field, cosmic ray intensity and therefore nuclide production is higher at the poles than at the equator. Accordingly, at low latitude, production rates are lower than at high latitude moreover, production rates increase exponentially with increasing altitude.

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Figure 9. Production of rate of 10Be in quartz as a function of geomagnetic latitude and altitude (based on Stone, 2000). The production rates have been normalized to sea level and high latitude. At low latitude, production rates are lower than at high latitude. Production rates increase exponentially with increasing altitude (image and explications from Ivy-Ochs and Kober, 2008).

ii. Shielding by surrounding hill slopes and mountains reduces the cosmic ray ﬂux to the sampling site leading to lower production of cosmogenic nuclides.

Therefore the production rate is scaled for site latitude, altitude, as well as, sample thickness, and topographic shielding by doing appropriate corrections have been proposed by the researchers (e.g., Lal, 1991; Dunne et al., 1999; Dunai, 2000, 2001; Stone, 2000; Desilets and Zreda, 2001; Pigati and Lifton, 2004; Muzikar, 2005; Desilets et al., 2006).

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Figure 10. Production rate of 10Be in quartz as a function of depth at sea level and high latitude. The total production is a composite of the production by neutron spallation, stopped muons, and fast muons (image and explications from Ivy-Ochs and Kober, 2008).

iii. Cosmogenic nuclides build-up in an exposed rock surface is a value in a function of depth (Fig. 10) so as Production rate decreases exponentially with depth (Lal, 1991).

It remains two crucial considerations in the application of surface exposure dating. First, the amount of inheritance is important as the clasts may have a pre-depositional history of exposure before deposition in the studied alluvial fans. It is clear that the presence of inherited nuclide concentrations will yield ages older than the true age.

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Figure 11. Use of cosmogenic radionuclide concentration profile to deduce both inheritance and surface age. Dated surface is the Stockton bar of Lake Bonneville, associated with the latest high stand of the lake, at roughly 14.5 ka. Grayed box represents the concentration due to inheritance of cosmogenic radionuclides by the quartzite clasts prior to deposition in the bar. Best-fit line is exponential shifted to account for inheritance. Age deduced from this method is 15 ka. If inheritance were not accounted for, and a single surface sample were used to deduce age, the estimated age would have been ∼26 ka, too old by roughly 11 ka (image and explications from Burbank and Anderson, 2012).

Second point to consider is the rate of denudation, as after abandonment of alluvial fan the outermost layers of fragments with the highest concentrations of cosmogenic nuclides are removed. This phenomenon causes a decrease in the concentration of cosmic nuclides and consequently, the calculated exposure age will be lower than true age. For these reasons a depth profile sampling and modelling have been used to estimate probable inheritance and denudation rate (Fig. 11) of studied areas (e.g., Anderson et al., 1996; Siame et al., 2004; Braucher et al., 2009; Le Dortz et al., 2009,2011,2012; Oskin et al., 2008; Hidy et al., 2010).

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The surface exposure dating and the use of in-situ produced cosmogenic nuclide is done by considering the basic assumptions as bellow (Ivy-Ochs and Kober, 2008):

o the half-life of the radionuclide is known, o production pathways and production rates including their variation in space (including with depth into the rock or sediment) are known, o the initial nuclide concentration (inheritance) is zero or can be determined or estimated, o the mineral has remained a closed system, i.e. there has been no gain or loss of the nuclide except due to production or decay (or through erosion).

Considering the existence of quartz debris in the alluvial fans and in the absence of calcareous minerals, all of the samples were collected in order to analyzing of in-situ produced 10Be contents. These debris come from right after the northern contact of alluvial fans with Jurassic sedimentary rocks have been intruded by pure quartz veinlets.

After the site selection, surface sampling were done in two phases, a number of 26 samples were collected. As the quartz fragments were mainly in pebble sized, the majority of samples were collected as amalgamated and some of them in the form of individual cobbles, if available. In the amalgamated samples, the thickness did not exceed 5 cm and in case of existing of cobble sized, we picked up an individual piece of quartz or a cobble sized rock fragment included quartz mineral. Avoiding broken and eventually rooted rocks, we took care to collect well-embedded pebbles and/or cobbles to ensure their long‐term stability. During the sampling we preferred relatively flat and more preserved areas in the top of fans surfaces and as far as possible we avoided the slops, the edge of fans and eroded areas.

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For obtaining the quantitative information on inheritance and denudation rates in the studied alluvial surfaces, we dug a soil pit in one of the oldest fans with depth of 1.65 meters and we collected 8 the samples.

In this study we applied the calculated exposure age according to in-situ 10Be concentration in quartz debris of different generations of alluvial fans. Practically we consider the obtained age as abandonment age of the given alluvial fan. This attribution that will attain to amount of slip rate of the fault have been done according to the assumptions as below:

o transport, burial, and reworking of material was sufficiently rapid in active fans for little cosmogenic nuclide accumulation to occur o little loss of cosmogenic nuclides due to erosion occurred subsequent to fan abandonment.

Under these conditions, the concentration of an in-situ–produced cosmogenic nuclide is directly related to the time since abandonment of a surface and hence to the initiation of its offset from its upslope sediment source (Ritz et al., 1995). Any change in the assumed conditions could have already affected the exposure in front of cosmic ray and this will be reflected in the measured concentration of in-situ cosmic nuclides in the sample.

In theory, by doing latitude, altitude, sample thickness and, inheritance and denudation rate obtained by the depth profile, an absolute age is calculated for each sample and by statistics a distinct age is attributed to the alluvial fans. In the other words, the ideal case occurs when the distribution of the age results are like a narrow Gaussian curve. But in practice, the age results are not often homogenous and because of unexpected discrepancies between the obtained ages of the same surface, they are sometimes scattered

CHAPTER I and need to be modelled. The age modelling demand the definition of age clusters and the rejection of outliers, this process is often very delicate.

Which technics we can do for age modelling?

If we come back to the basics of cosmogenic dating, in cosmogenic dating, we measure in-situ produced cosmogenic nuclides that have been produced after the rock started to place at or near the surface. As cosmogenic nuclides build up predictably with time, measuring their concentrations allows us to determine how long a rock surface or sediment exposed at the surface (e.g., Gosse and Phillips, 2001). Hence in theory after the analysis we are capable to calculate the absolute age of objective surface according to cosmogenic nuclide concentrations. But in practice, the age results are not often homogenous and hence they need to be modelled. The most usual complexity rises when unexpected amount of discrepancy in the cosmogenic nuclide concentrations is observed in the samples were collected on the same surface. The distribution of ages could be in the form of multimodal clusters or in the more complicated state, scattered ages without possibility of any classification. Age modelling often requires defining cluster borders and rejecting the outliers. The definition of age clusters and the rejection of outliers are done during age modelling are often controversial, especially when the sample distribution, which may, or may not, appear Gaussian (Le Béon et al., 2010). Typically, outliers are excluded visually (e.g., Van der Woerd et al., 1998; Le Béon et al., 2010) or by using Chauvenet’s criterion (Mériaux et al., 2004, 2009) (see le Béon et al., 2010 and references therein for detail). The complexities in the cosmogenic exposure ages have been reported by Ward et al. (2005), Philips et al. (1998), Matmon et al. (2005), Van der Woerd et al. (2006), Le Dortz et al. (2009,2012), Behr et al. (2010), Le Béon et al. (2010), Schmidt et al. (2011), Farbod et al. (2016).

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Matmon et al. (2005) during the offset and slip rate studies of San Andreas fault, California by cosmogenic 10Be and 26Al method, observed the exposed boulders yielded ages ranging from 16 to 413 ka. Although fan age determinations are accompanied by large uncertainties, they explained a clear trend of increasing fan ages with increasing distance from their source at the mouth of Little Rock Creek. And finally they concluded that after deposition in the fans, surface processes such as boulder erosion, fan surface lowering, and soil development operate, and each boulder acquires a unique exposure history. Thus, the complex environment results in large uncertainties in boulder erosion rate and boulder cosmogenic nuclide inheritance. Together with the large uncertainties associated with exposure and burial age dating, fan age determinations are, therefore, accompanied by large uncertainties (Matmon et al., 2005).

Dating is a statistical process and therefore the number of samples is a determinant factor. In this point of view, taking enough samples in each alluvial surface is strictly needed for having a reasonable and acceptable analysis about it. It should note that although the statistical analysis helps us to analyze the dating results, it will not solve by itself the problems that arise in using cosmogenic exposure dating. As properly explained by Matmon et al. (2005) each sample can have a unique exposure history and for finding the most appropriate age is attributed to an alluvial surface, various scenario should be considered and studied for the samples. These scenarios will help to decrease and narrowing the large uncertainties and approach us to real age of abandonment of alluvial surfaces. In this subject we are agree with final conclusion of Matmon et al. (2005) “a simple interpretation of measured cosmogenic nuclide concentrations in boulders residing on fan surfaces is likely to result in misinterpretation of the geologic history of a studied site. For each individual site, it is critical to understand field relations, climatic conditions,

CHAPTER I and surface processes in order to interpret cosmogenic nuclide concentrations in a meaningful way” (see Matmon et al., 2005 for detail).

Behr et al. (2010) during the study of “uncertainties in slip rate estimates for the Mission Creek strand of the southern San Andreas Fault” observed that existing scatter in the concentration and age prevents to attribute a unique age for the studied alluvial surface. For explaining, they considered detailed characteristics of samples such as;

-the role mechanical anisotropy (e.g. foliation in the metamorphosed samples) in progressive decrease in concentration of cosmogenic nuclides because of acceleration of weathering

-orientation of deposition and re-deposition of rocks

-the role of size of sampled rocks (cobble/boulder)

-self-shielding phenomena in the boulders

-different transport speeds of large boulders and smaller cobbles

-different approaches to the clasts of first and second generation of deposition

-the role of surface lowering and post-depositional evolution of studied fan

-correlation the boulder top ages systematically correlate with height above the current fan surface such that the shortest boulders yield the youngest ages, and the ages increase progressively with boulder height up to at least 1 m

By considering above explanations they explained why they exclude some of samples from statistics and finally even after these considerations they obtained a range of 45 ka and 54 ka. Considering geological uncertainties in determination of offset, they suggested

CHAPTER I a minimum, maximum and preferred amount of slip rate along the study area of Mission Creek strand of the southern San Andreas Fault (see Behr et al., 2010 for detail)

A wide range cosmic nuclides dating ages have been observed on the Quaternary surface along the southern San Andreas Fault at Indio. In this case, slight distinction between 10Be concentrations in upstream and downstream and also between cobble and boulder top samples has been observed. Even though this distinction is not very sharp, it has permitted Van der Woerd et al. (2006) to exclude certain age results and to classify the others in two distinct age groups. (See Benedetti and van der Woerd, 2014 and references therein for more detail)

In our case, after reviewing some of similar complexities in the Iranian plateau and other parts of the world, we tried to do age modelling by considering the individual exposure history of the samples. The slip rate of Dasht-e Bayaz fault at the end was determined by means of morpho-tectonic reconstruction of Quaternary alluvial fans and measurements of in-situ 10Be content in quartz debris.

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CHAPTER II

THE KINEMATICS OF DASHT-E BAYAZ

FAULT DURING PLIO-QUATERNARY:

IMPLICATIONS FOR THE GEODYNAMICS OF

EASTERN CENTRAL IRAN

CHAPTER II

The kinematics of the Dasht-e Bayaz earthquake fault during Plio-Quaternary: implications for the geodynamics of eastern Central Iran Fariborz Baniadama b, Esmaeil Shabanianc, Olivier Belliera a Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France, [email protected] b Geological Survey of Iran, Tehran, Iran, corresponding author: E-mail address: [email protected]; [email protected] c Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran, [email protected]; [email protected]

Keywords: Fault kinematic analysis; Stress state; Active tectonics; Dasht-e Bayaz Fault; Lut Block

Abstract The convergence between Arabia and Eurasia is accommodated across the Iranian plateau and surrounding mountain ranges. Strike-slip faults play significant roles in the current deformation of the Iranian plateau and were responsible for several moderate to large earthquakes. The sinistral Dasht-e Bayaz fault is characterized by conspicuous seismic and geological activities, while the role of the fault in the accommodation of active convergence is still debated. This paper focuses on the Pliocene-Quaternary to present-day states of stress in the region, affected by the Dasht-e Bayaz fault. We applied the fault-slip inversion technique to seismologic and geological fault slip data gathered around the Dasht-e Bayaz fault. The inversion results indicate a mean N045±5°E trending horizontal σ1 in the modern stress field, which agrees with the present-day strike-slip tectonic regime (regional N050±05°E trending σ1) deduced from the inversion of earthquake focal mechanism data. The paleostress state is characterized by a homogeneous N125±05°E trending mean σ1, with a compressional stress regime, showing that E-W faults of this region like Dasht-e Bayaz has been right-lateral in certain periods of their activity. Our

CHAPTER II mapping of fault intersection areas highlights the cross-cutting relationship between N-S dextral and E-W sinistral faults forming a typical crosswise to conjugate fault arrangement in the central part and the eastern end of the Dasht-e Bayaz fault trace. Integrating our original data in a larger regional scale, we present a kinematic scheme about the northeastern border of the Arabia-Eurasian convergence zone in which the region between Lut and Kopeh Dagh is divided by the Doruneh fault into two tectonic domains. In the northern domain, active convergence is taken up by the reverse thrust faulting along with the extrusion of fault-bounded blocks while, in the southern domain the convergence is accommodated through the reverse/thrust faulting in confining wedges accompanied by crosswise strike-slip faulting.

1. Introduction The convergence between Arabia and Eurasia is responsible for the current deformation in Iran. Nearly all the convergence is accommodated across the Iranian plateau and surrounding mountain ranges such as Zagros, Alborz and Kopeh Dagh; the collision boundaries correspond approximately to the political borders of Iran (e.g., Walker and Jackson, 2004). The Makran tectonic province is the surface expression of the active subduction of Arabia beneath the Iranian micro-continent (e.g., Walpersdorf et al., 2014; Burg, 2018). In recent decades, different parts of the Arabia-Eurasia convergence zone have been studied in detail; the pieces of the puzzle of this convergence are progressively fitting together. Numerous studies have attempted to describe the role of strike-slip faults in the active tectonics of the collision zone (e.g., Hessami et al., 2003; Talebian and Jackson, 2004; Walker and Jackson, 2004; Karakhanian et al., 2004; Regard et al., 2005, 2006; Authemayou et al., 2006; Meyer and Le Dortz, 2007; Shabanian et al., 2009a, 2009b;

CHAPTER II

Molnar and Dayem, 2010; Farbod et al., 2011, 2016; Calzolari et al., 2015, 2016, 2018). According to these studies, strike-slip faults play a significant role in the current deformation of the Iranian plateau and had been responsible for several moderate to large earthquakes especially in eastern Iran (e.g., Dasht-e Bayaz 31 August 1968, Koli-Buniabad 27 November 1979 and Zirkuh-Qayen 10 May 1997). Since the Pliocene (5.3-2.6 Ma), the dominant tectonic regime in the Iranian plateau and the surrounding deformation belts has changed from compressional to strike-slip (Regard et al., 2005, 2006; Authemayou et al., 2006; Shabanian et al., 2009a, 2009b, 2010; Farbod et al., 2011, 2016; Ghods et al., 2015; Tadayon et al., 2017, 2018; Taghipour et al., 2018). Even in thrust-fold domains such as the Zagros and Alborz belts, where the main way of accommodation of the convergence is crustal shortening, the role of strike-slip faulting is determinant (e.g., Talebian and Jackson, 2004; Authemayou et al., 2006, 2009). The role of major strike-slip faults, such as the North Tabriz fault in northwestern Iran (e.g., Cisternas and Philip, 1997; Karakhanian et al., 2004; Ghods et al., 2015), the Main Recent Fault in the Zagros (Tchalenko et al., 1974; Braud and Ricou, 1975; Ricou et al., 1977; Berberian, 1995; Talebian and Jackson, 2004), the Minab-Zendan-Palami fault zone at the Zagros – Makran transition (Regard et al., 2005) and the Bakharden-Quchan Fault System in the Kopeh Dagh (Shabanian et al., 2009a, 2009b) as well as the faults that reactivate the Sistan suture zone in eastern Iran, (e.g., Vernant et al., 2004; Walker and Jackson, 2004) in the accommodation of the Arabia-Eurasian convergence is rather well- known. These strike-slip faults act as plate or block boundaries and are in charge of block translation in accordance with the overall deformation in the Arabia – Eurasia collision zone (e.g., Walpersdorf et al., 2006, 2014; Tavakoli et al., 2008; Shabanian et al., 2009b; Mousavi et al., 2013; Ghods et al., 2015).

CHAPTER II

Figure 1. General tectonic map of the east and northeast of Iran. (A) The upper left inset shows the location in the Arabia–Eurasia collision framework (after Shabanian et al., 2010) and the dotted rectangle implies the study area. Grey arrows and associated numbers represent Arabia–Eurasia plate velocities (mm/yr) after Reilinger et al. (2006). Solid lines are boundaries of plates or major blocks. (B) GTOPO30 topographic image showing the regional tectonic setting and the major active faults (red lines) in E and NE Iran. The study area of Dasht-e Bayaz is marked by the black dashed rectangle. Reverse/thrust faults are marked by small triangles pointing to the fault hanging wall. The fault map is based on Hessami et al. (2003), Walker and Jackson (2004), Shabanian et al. (2010), Farbod et al. (2011), Nozaem et al. (2013), Calzolari et al., 2015 and this study. 63

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Recent geodetic (e.g., Vernant et al., 2004; Reilinger et al., 2006; Mousavi et al., 2013; Walpersdorf et al., 2014) and geological studies (Shabanian et al., 2009a, 2009b, 2010, 2012; Farbod et al., 2011, 2016) in NE Iran have revealed that active deformation is localized along block-bounding crustal faults. In the Central Iran, GPS-derived velocity fields (Walpersdorf et al., 2014) and GPS block modeling (Reilinger et al., 2006; Walpersdorf et al., 2014) show that about 90 percent of the 5.7 mm/yr northward motion of the Lut block – Eurasia is transferred to the north of the E-W Doruneh fault (Fig. 1). To the north, the Bakharden-Quchan Fault System takes up 4.1 - 4.6 mm/yr of this dextral faulting across the Kopeh Dagh Mountains (Shabanian et al., 2009a, 2009b, 2012; Mousavi et al., 2013). Thus, north of 37°N this fault system accommodates 80% of the Central Iran- Eurasia convergence (~5.1 mm/yr). In this tectonic context, there are other strike-slip faults, such as the Doruneh and Dasht-e Bayaz faults, which affect the Iranian plateau and are characterized by conspicuous seismic and/or geological activities. Nevertheless, the role of these faults in the accommodation of the active convergence has been a matter of debate. Interestingly, these E-W strike-slip faults are perpendicular to the active block motions and separate the N-S dextral strike-slip faults of Lut – Central Iran (the Nayband and Sistan suture zone) to the south from the NW-trending structures of the Binalud and Kopeh Dagh deformation domains to the north (Fig. 1). Our understanding of the processes involved in the plate convergence improves progressively, but we still need to know more about (1) the pattern and kinematics of deformation in each part of the convergence/collision zone and (2) the role of intracontinental crustal faults in the accommodation of this deformation within the plateau. During the last century, areas such as the Dasht-e Bayaz, Tabas, and Bam, which were considered as stable areas in the interior of rigid blocks, have been affected by large destructive earthquakes occurring on mostly unknown faults (e.g., Walker et al., 2011;

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Berberian, 2014). After the destructive 31 August 1968 Mw 7.1 earthquake, for instance, the Dasht-e Bayaz area has been one of the most seismically active domains in Iran. Right after the Dasht-e Bayaz main shock in 1968, this area has been studied from different points of view. The first studies focused on mapping the coseismic rupture and post-earthquake observations (e.g. Ambraseys and Tchalenko, 1969; Tchalenko and Ambraseys, 1970; Tchalenko and Berberian, 1975). Meanwhile, more recent studies have focused on the seismology and the active tectonics of the Dasht-e Bayaz and surrounding areas in the context of Arabia-Eurasian convergence (Walker et al., 2004; Walker and Jackson, 2004; Walker et al., 2011). However, the main unanswered question concerns the role of E-W sinistral faults, such as the Dasht-e Bayaz fault, in accommodation of the NNE-trending plate motion (e.g., Vernant et al., 2004; Walpersdorf et al., 2014). This question can be answered partly through an investigation of the spatio-temporal kinematic evolution of the Dasht-e Bayaz fault and its kinematic interaction with other major structures constituting the Sistan suture zone. It is also important to know whether the stress field in eastern Iran is preferably caused by stress transfer from the Arabia – Central Iran collision, or is influenced by individual block motions in eastern Iran (e.g., Jentzer et al., 2017). This paper focuses on the Pliocene-Quaternary to the present-day states of stress (the last 5 Ma) in the region affected by the Dasht-e Bayaz fault in east-northeastern Iran (Fig. 1). We applied the inversion technique to fault slip data, provided by the focal mechanism of earthquakes, and also acquired from geological fault planes. We have then put our results in a larger framework, which we have reconstructed using available kinematic data and results from east and northeastern Iran. This has enabled us to discuss the possible interaction of the Dasht-e Bayaz fault with other active faults of the region. The level of consistency of our results has been discussed in the light of previous studies on the late Cenozoic stress field of the Iranian plateau and surrounding deformation belts. We have

CHAPTER II also discussed the structural and geomorphic features along the Dasht-e Bayaz fault and finally, we have proposed a tectonic scheme to describe the role of reverse/thrust and strike- slip faulting in the accommodation of active convergence in ENE Iran.

2. Kinematic background and tectonic setting 2.1. Late Cenozoic stress fields in the Iranian Plateau One of the most interesting issues concerning the accommodation of Arabia-Eurasian convergence in the Iranian plateau is the history of stress regimes during the Pliocene and Quaternary. Thanks to application of modern techniques, such as the inversion of focal mechanisms of earthquakes, our knowledge about the present-day state of stress in the Iranian plateau has progressed. Whereas, there is still some ambiguity left concerning the situation of the stress regime, its probable changes and the way of transition in the late Cenozoic. Temporal changes in the stress field of the Alborz and Kopeh Dagh Mountains, north of the Lut block, as well as northwestern Iran have been reported by several authors (e.g., Tchalenko et al., 1974; Abbassi and Shabanian, 1999; Jackson et al., 2002; Allen et al., 2003; Guest et al., 2006; Zanchi et al., 2006; Yassaghi and Madanipour, 2008; Abbassi and Farbod, 2009; Landgraf et al., 2009; Shabanian et al., 2010, 2012; Farbod et al., 2011; Javidfakhr et al., 2011; Tadayon et al., 2017; Aflaki et al., 2018a, 2018b). Tchalenko et al. (1974), during tectonic studies in the Tehran region, have suggested the possible occurrence of a post-Pleistocene change in the direction of compression from NW to NE, based on the pattern of post Eocene dikes and the style of folding and faulting in alluvial formations. In the same region, Abbassi and Shabanian (1999) have found three distinct states of stress and a clockwise rotation in the stress field through the inversion of fault slip data mostly measured in young alluviums. According to this research, the oldest stress field

CHAPTER II had been characterized by a NW-trending compression that has changed into a N-S and then, into a NE-directed compression, affecting the Plio-quaternary alluvial deposits. Another interesting research involving U/Pb, 40Ar/39Ar, and (U-Th)/He analysis, complemented by structural geological studies in west-central Alborz (Axen et al., 2001), has led to the attainment of the first chronological framework for a major tectonic reorganization in the Alborz Mountains. The occurrence of a dextral transpressional movement along the main faults before the onset (ca. 3.4 Ma) of modern sinistral faulting on these faults, parallel to the range, has been reported. According to morphotectonic analyses along the Mosha and Taleghan faults in the Alborz, Ritz et al. (2006) suggested that the change from a N-S compression (compressional tectonic regime) to the present- day NNE-trending compression should has occurred between 1 and 1.5 Ma. In the Kopeh Dagh and Binalud Mountains, the inversion of fault slip data, measured in 39 sites, have revealed temporal clockwise changes in the state of stress since 3.6 Ma; those include the horizontal σ1 oriented N140±10°E, N180±10°E and N30±15°E for the paleostress, intermediate and modern states of stress, respectively (Shabanian et al., 2010). Similar drastic temporal changes have been reported in NNE Iran, including eastern Alborz and western Kopeh Dagh Mountains by Javidfakhr et al. (2011). The analysis of fault slip data in 48 sites has led the authors to characterize the three homogenous stress fields as a maximum horizontal stress σ1 orientated N135±20°E (paleostress), N185±15°E (intermediate) and N36±20°E (modern stress) in this transitional zone. Farther south, Farbod et al. (2011) have shown that a Plio-Quaternary older state of stress, with a σ1 orientated N150±20°E, had been changed into a modern compression of N45±15°E, responsible for the active sinistral kinematics along the Doruneh Fault System. Tadayon et al. (2018) have suggested that the switch from the early NW-oriented σ1 to the penultimate

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N-S compression has started at the Miocene-Pliocene boundary (5-6 Ma) and this change has been the source of important cooling/exhumation in the Doruneh Fault region. The other research approves the same pattern of change in the stress field of northwestern Iran (the Mianeh-Mahneshan basin; Aflaki et al., 2018a). The NW-trending fold axes in the Upper Red Formation, folded at the end of Middle Miocene, have been superimposed by two younger generations of NE and NW trending folds in a time interval between the Pliocene and Quaternary. The results of the inversion of fault slip data in this region confirm that a compressional paleostress (Plio-Quaternary), with a N138°E trending horizontal σ1, has affected the area before the dominance of the present-day NE-oriented compression. The recent study in the Sistan belt of eastern Iran (Jentzer et al., 2017) has reported three distinct compressional stages during late Cenozoic, including (1) an E-W (N87±5°E) direction of σ1 probably in the Late Miocene, (2) a late Pliocene ENE-WSW (N59±8°E) direction of σ1 and (3) a late Pliocene to present-day compression (N26±8°E). They have mentioned that during the last ~10–5 Ma, the direction of compression has rotated about 60° counterclockwise in Sistan. The kinematics of this region, especially from a regional geologic and geodynamic point of view, is debatable. However, there is no other similar study in the Sistan belt enabling a comparison and an evaluation of the accuracy of their results. Finally, even though several studies confirm the occurrence of drastic changes in the kinematics of north, east and northeastern Iran, these results are geographically sparse and need absolute age-based dating in order to enable the drawing of firm conclusions in the context of Arabia-Eurasia convergence.

2.2. Geodynamic and seismotectonic framework

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According to geological investigations (e.g., Berberian et al., 1999; Walker and Jackson, 2004; Meyer and Le Dortz, 2007; Foroutan et al., 2014) and geodetic Global Positioning System (GPS) measurements (e.g., Vernant et al., 2004; Walpersdorf et al., 2014), the N-trending right-lateral faults in Central Iran, especially on both sides of the Lut block, accommodate the northward motion of central Iran relative to Eurasia (Helmand block in Afghanistan). The Distribution of historic records and instrumental earthquake epicenters, as well as the GPS velocity field show that the convergence is mainly accommodated along the block boundaries, while the interior of the blocks (e.g., Lut block) is almost rigid (e.g., Vernant et al., 2004; Walker and Jackson, 2004; Walpersdorf et al., 2014), with low rates of deformation. The crustal-scale dextral shear continues up to 34°N, north of which E-W left-lateral faults like the Dasht-e Bayaz, Niazabad and Doruneh (further north) are present (Fig. 1). At this latitude, the change in geology is accompanied by a change in active faulting from the N-S dextral faults of the Sistan suture zone to a system mainly constituted by E-W sinistral strike-slip faults (e.g., Berberian et al., 1999). The role of these crustal faults in the accommodation of active deformation perpendicular to the N-S dextral shear has been a matter of debate since, at least, thirty years ago (e.g. Jackson and McKenzie, 1984; Berberian et al., 1999; Walker and Jackson, 2004; Farbod et al., 2011, 2016; Aflaki et al., 2019). Active tectonic and seismological studies conducted in Dasht-e Bayaz and the surrounding areas documented that the active faults, responsible for numerous seismic shocks in the area, are temporally and mechanically in close interaction (e.g., Berberian et al., 1999; Walker et al., 2004; Walker et al., 2011). On 31 August 1968, a destructive earthquake (Mw 7.1) shocked the area and produced a 70 km E-W coseismic rupture; the maximum coseismic displacement (4.5 m left-lateral and 2.5 m vertical) was measured in

CHAPTER II north of the Nimboluk plain (Tchalenko and Ambraseys, 1970; Tchalenko and Berberian, 1975).

Figure 2. Shaded-relief topographic map and the major active faults around the Dasht-e Bayaz area. (A) Major fault zone and their structural interactions in the area of interest. Fault-plane solutions belong to the major earthquakes of the study area (redrafted from waveform modelling of Walker et al., 2004, 2011) (B) LANDSAT ETM satellite overview (RGB, 541) of the area emphasizing the western termination of left-lateral Dasht-e Bayaz, Kabutarkuh and Avash faults.

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The most remarkable seismic events occurred just 20 hours after the Dasht-e Bayaz main shock during the Ferdows earthquakes of 1st and 4th September 1968 (Mw 6.3 and Mw 5.5, respectively) about 70 km west of the Dasht-e Bayaz village. The close proximity (or even overlap) between the domains of impact of the Dasht-e Bayaz and Ferdows earthquakes has prevented researchers from separating their field effects (e.g., Berberian, 2014). Several authors, based on field observations, suggested that the two earthquakes of 1 and 4 September occurred on the NW–trending Ferdows reverse fault (Figs. 1 and 2); the reverse focal mechanisms of the earthquakes were also compatible with this fault (see Berberian, 2014 and references therein). After 11 years and during less than one month, three other destructive earthquakes of Korizan (14.11.1979), Koli-Buniabad (27.11.1979 - e.g., Haghipour and Amidi, 1980) and Kalateh Shur (07.12.1979 - e.g., Haghipour and Amidi, 1980; Ambraseys and Melville, 1982) occurred along the northern part of the Abiz fault, the eastern segment of the Dasht-e Bayaz fault and at the intersection of these faults, respectively. The Zirkuh earthquake of 1997 May 10 (Mw 7.2), caused by the northern segment of the NNW-striking Abiz fault (Fig. 1), has also been considered as a sequence of seismic events triggered by the Dasht-e Bayaz main shock on 31 August 1968 (e.g., Berberian et al., 1999). The 125-km-long surface faulting which, with dextral strike-slip mechanism, has occurred during the Zirkuh earthquake is known as the longest surface rupture associated with an Iranian earthquake (e.g., Berberian et al., 1999). This NNW- striking fault segment changes into a NNE-SSW trend (causative fault of the November 14, 1979 Korizan earthquake; see above) near the eastern end of the Dasht-e Bayaz fault and provides the dextral pair of a conjugate-like arrangement (see 5.3; Fig. 3). The 1968, 31 August earthquake of Dasht-e Bayaz is considered as a likely trigger for the reactivation of the east segment of the Dasht-e Bayaz fault, the Ferdows reverse fault zone and the Korizan fault, causing a sequence of earthquakes (e.g. the Zirkuh, Koli-

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Buniabad and Ferdows earthquakes). The 1968.09.11, 1979.01.16 and 1997.06.25 events did not rupture the surface (e.g. Berberian et al., 1999). The 1979.01.16 event showed NW- striking reverse faulting and 1997.06.25 event has produced both the possibilities of N-S right-lateral or E-W left-lateral faulting (Berberian et al., 1999). The calibrated relocations and the body-wave modeling of Walker et al. (2011) showed that the epicenter of the 1979.01.16 earthquake is centered on an SW–dipping reverse fault. As for the 1997.06.25 event, Walker et al. (2011) also proposed that, through InSAR results, the rupture had occurred on the N–S trending dextral fault plane without the possibility to attribute it to any of the Boznabad or Pavak faults (Fig. 2). Regarding this brief history of seismicity, it is concluded that the Dasht-e Bayaz and nearby faults are amazingly in close kinematic interaction to accommodate the active deformation of the area. This sequence of the Dasht-e-Bayaz, Ferdows and Zirkuh earthquakes (occurred between 1968 and 1997) presents one of the most remarkable examples of temporally clustered continental seismicity in the world (e.g., Berberian et al., 1999; Walker et al., 2011). These consecutive destructive earthquakes could have been triggered by the 31 August 1968 Dasht-e Bayaz main shock (e.g., Berberian et al., 1999 and references therein) and occurred along faults with different kinematics. All these faults are optimally oriented with respect to the far-field stress field allowing the accommodation of convergence in this part of the Arabia-Eurasian convergence. The study of recent seismic events in addition to the results of inversion of fault kinematics data and interpretation of structural and geomorphic observations that we will discuss, allowed us to suggest a tectonic scheme about the northeastern border of Arabia-Eurasia convergence zone.

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Figure 3. Simplified geological map of the Dasht-e Bayaz area based on published geological maps of the area (Alavi Naini and Behruzi, 1983; Fauvelet and Eftekhar Nezhad, 1991). Fault traces were extracted from satellite images complemented by field observations; we used Tchalenko and Berberian (1975) maps for the co-seismic ruptures in the northern Nimboluk plain, which currently is under cultivation. The numbers imply the fault kinematic measurement sites of Fig. 6.

3. Methodology: inversion method, chronology and data separation, stress tensor quality 3.1. Inversion of fault-slip data Following the method proposed by Carey and Brunier (1974), determination of a deviatoric stress tensor from fault slip data is based on the stress-slip relationship described by Wallace (1951) and Bott (1959). Computer programs, developed for the inversion of fault slip data, compute a mean best fitting deviatoric stress tensor from a group of striated fault planes by minimizing the angular deviation (misfit angle) between the observed

CHAPTER II striation and the shear stress resolved on the fault plane (Carey and Brunier, 1974, Carey; 1979; Angelier, 1990). The inversion results are revised and refined iteratively to reach the smallest misfit angle while involving the highest possible number of measured homogenous fault slip data. The meaningful process of stress determination (deviatoric reduced stress tensor) from both geological and seismological fault slip data is a delicate challenge requiring good quality of data, meticulous observations and data separation as well as adequate knowledge on both kinematics and mechanics of faulting (see Allmendinger et al., 1989; Shabanian et al., 2010; Hippolyte et al., 2012; Tranos, 2018). A blind use of abundant computer programs (whatever software is used) seems very simple, but it would lead to mathematic results without geological significance (see Hippolyte et al., 2012 and Tranos, 2018 for details). Principal inputs are fault-slip data from geological faults measured in the field or seismologically determined focal mechanism of earthquakes including attitudes (e.g., strike/dip/dip quadrant) of striated fault planes and associated striations with well-known sense of movement. As a great advantage, acquisition of field data is feasible almost everywhere and a careful inversion analysis of good quality fault slip data would lead to a reliable reconstruction of the kinematic history of the area (e.g., Angelier, 1984; Carey- Gailhardis and Mercier, 1992; Hippolyte et al., 1993; Bellier and Zoback, 1995; Regard et al., 2005; Shabanian et al., 2010). The main outputs of this method are orientations (trend and plunge) of principal stress axes σ1≥ σ2≥ σ3 (corresponding maximum, intermediate and minimum stresses, respectively) and “R= (σ2-σ1)/(σ3-σ1)”. This linear parameter (R) equals 1−φ, φ being another commonly used stress ratio (e.g., Angelier, 1979; Zoback, 1989; Ritz and Taboada, 1993), and describes relative stress magnitudes ranging from 0 to 1 (e.g., Carey and Brunier, 1974; Mercier et al., 1991; Bellier and Zoback, 1995, Shabanian et al., 2010 and references therein). Different combinations of Andersonian stress

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arrangements (vertical principal stress axes of 1, 2 and 3 for pure extensional, strike- slip and reverse faulting, respectively) and R values lead to various stress regimes responsible for different kinds of faulting (see Ritz and Taboada, 1993; Shabanian et al., 2010 for more details). We used the method originally proposed by Carey (1979); the results deduced from inversion of fault-slip data measured in individual sites along the Dasht-e Bayaz fault and nearby areas are presented in Table 1.

Figure 4. Distinct fault slips related to the modern and intermediate states of stress and a summary of data separation strategy applied in this study. (A) SE looking field photograph a fault plane (site 7) that includes two generations of striations and (B) a stereoplot of these striations. (1) and (2) refer to older and

CHAPTER II younger relative chronologies, respectively, of the striations on the fault plane in the Neogene mudstone. This site is along the western end of the Dasht-e Bayaz fault where it merges the Ferdows reverse fault zone. (C) The schmidt lower hemisphere stereographic projection of the fault slip data measured in site 7. (D) The lower hemisphere stereographic projection of the fault slip data measured in site 3. The middle diagram is non-separated data set including all fault slip data. (1) and (2) refer to the older and younger relative chronology of the striations. The stereograms (1) and (2) indicate relative chronology of two distinct sets of data. The relative chronology of striations is according to cross-cutting relationships observed on fault planes (colored as red). This strategy is applied to other sites for separation of fault slip data into homogenous data sets.

3.2. Chronology and data separation According to an important assumption accepted in fault kinematic inversion methods, a distinct stress deviator (σ1≥ σ2≥ σ3 and “R”) can create only one slip direction on a given fault plane. The complications of data separation are normally revealed when different sets of heterogeneous fault-slip data are collected from fault planes. Several generations of striae on a single fault plane are surely the result of changes in angular relationships between the fault plane and principal stress axes. Nevertheless, the nature of such changes could either be due to temporal variations in the stress field or could imply the rotation of the fault plane during deformation. In both cases, the chronology of striae is usually determined through the crosscutting relationships of striations and/or fault planes complemented by geological field observations. Except for some possible mistakes in measurements and individual cases of local rotations due to progressive deformation, the fault slip data are classified into homogenous sub-groups. In some of recent studies, the automatic or semi-automatic methods have also been proposed or utilized to separate heterogeneous fault slip data (e.g., Nemcok and Lisle, 1995; Salvini and Storti, 1999; Fry, 1999; Rossetti et al., 2002; Shan et al., 2003; Tranos, 2015, 2018), however, in this study

CHAPTER II we preferred to take advantage of techniques concerning data separation based on geological observations and kinematic rules (see Shabanian et al., 2010). Figure 4 shows an example of this strategy which is based on crosscutting relationships, filed observations and kinematic considerations. The kinematic sites were inspected in outcrops of different formation ages ranging from the Triassic to Quaternary (Fig. 5); almost half of the measurements were done on fault planes affecting the Pliocene and Quaternary deposits (see Table 1). The relative chronologies of different generations of striations on a fault plane or in an outcrop have been determined while considering the superposition of successive striations and/or the crosscutting relationship between fault planes affecting the outcrop. In a given outcrop there are often a few fault planes revealing the above-mentioned direct chronological indicators which could enable us to distinguish the chronological order of different generations of striations. Meanwhile, the majority of planes solely reveal one generation of striations with an unknown relative chronology (see Shabanian et al., 2010 for more details). In such cases, the fault slip data have primarily been separated using well-known relative chronologies and then, other planes with single striations have been added to each data set, taking their kinematic and mechanical compatibilities as well as their geological field notes into consideration (Fig. 3). The final chronology of the resolved deviatoric stress states (defined as paleo, intermediate or modern stresses) has been determined while considering the age of the youngest rock units, affected by each stress state, and chronological cross-relations between different stress tensors.

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Figure 5. Field photographs of some of sites we have inspected for the measurement of fault slip data along the Dasht-e Bayaz fault. (a) Site 2 at the northern margin of the Chah Deraz pull-apart basin. (b) Closeup view of the fault plane and the associated sinistral striation in site 2. (c) general view of the Dashte- Bayaz earthquake rupture to the west of the intersection zone. (d) structural evidence of an ancient dextral faulting along the main trace of the Dasht-e Bayaz fault in the Chah Deraz pull-apart basin. (e) and (f) fault plane and striation of the fault measued along the coseismic rupture. (g) An outcrop of the northern continuation of the Korizan fault in site 1. (h) The reverse-sinistral fault trace in Neogene deposits in site 6. (i) a fault plane with two distinct generation of striations in site 10. (j) a metric scale sinistral fault plane along the main fault zone in site 9.

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Certain criteria should be met in order to determine reliable stress solutions (e.g. Etchecopar, 1984; Carey-Gailhardis and Mercier, 1992; Bellier and Zoback, 1995; Shabanian et al., 2010): (1) we need at least 4 fault planes with different attitudes that are well-distributed in space. A higher number of fault planes and a good spatial distribution will result in a more constrained stress solution, (2) the inversion results will theoretically be reliable when at least 80 percent of deviation angles are under 20°, (3) the measured fault planes must show good mechanical compatibility with the stress tensor solution, for instance, a set of transtensional faults cannot be explained by a compressional stress tensor, (4) a reliable stress solution needs fault slip data of good quality; it greatly depends on the details of field observations, the tectonic history of the measurement site and user’s experiences of data measurement and inversion analysis. Considering these criteria, A, B and C were assigned to well-constrained, constrained and poorly-constrained stress tensor solutions, respectively. For solutions from less than four well-distributed fault planes, we used a fixed solution (Bellier and Zoback, 1995) in which, one principal stress axis is fixed as vertical. In this study the quality of fixed solutions has been considered the same as C and they were marked as CF; the stress ratio “R” is not valid for these kind of solutions.

3.3. Inversion of earthquake focal mechanism data We determined the present-day state of stress in the Dasht-e Bayaz area through the inversion of focal mechanisms of medium to large (7.1>M>5.5) earthquakes applying the method described by Carey-Gailhardis and Mercier (1987). These earthquakes have occurred between 1968 and 1997 comprising the Dasht-e Bayaz main shocks. We have only used focal mechanism solutions that had been relocated and modeled using body waves by Walker et al. (2004, 2011). With this method, we analyzed two orthogonal nodal planes for each earthquake focal solution taking into account that only one plane was

CHAPTER II reactivated during the earthquake due to the regional stress state. The final selection among each pair of nodal planes can be done by (1) direct observation of the surface rupture of the earthquake, (2) seismological investigations of the rupture process, (3) the spatial distribution of aftershocks and (4) the inverse computation by selecting the nodal plane that results in greater consistency with the regional stress field (Carey-Gailhardis and Mercier, 1987). For determining the regional state of stress, the importance of the main shocks (even a single datum) is significantly greater than that of the aftershocks because small earthquakes would probably reflect kinematic instabilities due to heterogeneous deformation and independent faulting in small-scale bodies (e.g. Carey-Gailhardis and Mercier, 1992). For some of the main shocks, we have direct information on the rupture geometry from field observations (Tchalenko and Ambraseys, 1970; Berberian et al., 1999). This serves as a reference for evaluating the compatibility (in a geometric sense) of other events using inverse computation. This method was successfully applied to determine the causative fault plane of the second event of August 2012 earthquake doublet (Mw 6.4, 6.2), that had occurred in the Ahar-Varzaghan complex fault system in NW Iran (see Ghods et al., 2015 and Momeni and Tatar, 2018).

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Table 1 The fault kinematic inversion results characterizing the Plio-Quaternary stress regimes in the Dasht-e Bayaz area. Site Long. Lat. Paleostress Modern Stress Intermediate Stress Lithology Age

(°E) (°N) Stress axis(trend/plunge) R N Q Rm Stress axis(trend/plunge) R N Q Rm Stress axis(trend/plunge) R N Q Rm

σ1 σ2 σ3 σ1 σ2 σ3 σ1 σ2 σ3

1 59.807 34.013 152/00 62/00 295/90 0.595 4 CF C 28/03 293/61 119/29 0.51 10 B S ------Andesite Paleo-Eocene

2 59.101 34.041 120/01 210/01 345/89 0.500 4 CF C 53/05 157/70 321/19 0.47 12 A S ------Sandstone Triassic

3 58.931 34.048 ------40/11 176/75 308/10 0.55 8 A S 357/9 250/60 92/28 0.44 6 C S Conglomerate Quaternary

4 59.248 34.026 127/00 303/90 37/00 0.327 4 CF S 240/15 43/75 149/04 0.43 12 A S ------Andesite Paleo-Eocene

5A 58.977 34.043 ------218/03 116/76 308/14 0.66 12 A S ------Conglomerate Quaternary

5B 58.977 34.043 ------256/01 354/83 166/07 0.714 8 A S ------Conglomerate Quaternary

6 58.738 34.028 119/05 212/28 19/62 0.452 4 C C 73/06 343/01 241/84 0.23 14 B C 20/15 112/07 227/74 0.12 6 A C Conglomerate Pliocene

7 58.561 34.017 161/06 252/12 46/76 0.696 5 B C 230/02 320/05 124/85 0.78 14 A C ------Conglomerate Pliocene

8 59.281 34.032 ------41/07 279/76 133/11 0.96 10 A S ------Tuff Paleocene

9 59.168 34.027 ------40/07 232/82 130/2 0.530 14 A S ------Dolomite Triassic

10 59.274 34.028 120/00 210/00 354/90 0.6 5 CF C 217/00 103/89 307/01 0.624 15 A S ------Limestone Paleocene

Site numbers and their geographic coordination refer to Figure 8. The results of inversion of fault slip data are including trend and plunge of principal stress axes (σ1, σ2, σ3 (matching maximum, intermediate and minimum stress axes, respectively) and stress ratio “R= (σ2-σ1) / (σ3-σ1)” shows the relative stress magnitude. N, number of fault slip data involved in stress calculations; Rm points out to stress regimes: C, compressional; S, strike-slip; Q is different states of quality of stress tensors: A, well- constrained; B, constrained; C, poorly-constrained solutions. CF quality represents data sets consist of less than four spatially well-distributed fault slip data, for this kind of data sets a “fixed” solutions (Bellier and Zoback, 1995) is used, in which the principal stress axes were fixed to lie in horizontal and vertical planes. In site 5, two deviatoric stress tensors (5A and 5B) obtained in modern state of stress.

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Figure 6. Reconstruction of the Plio-Quaternary stress fields in the Dasht-e Bayaz area, the base is ASTER image (RGB, 321). Direction of Maximum horizontal stress axis (σ1) for different stress fields showing dominant stress regimes including strike-slip, compressional and extensional deducted from inversions of fault kinematics data in each sites (see Table 2). (A) Modern state of stress (B) Intermediate state of stress (C) Paleostress state of stress.

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Figure 7. Lower hemisphere stereograms of fault slip data with inversion results of the modern state of stress presented in Table 1. Fault planes and measured slip vectors (arrows on fault planes) are plotted.

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Large arrows outside stereograms represent the direction of minimum (σ3, divergent, white arrows) and maximum (σ1) horizontal stress axes. Histograms show distribution of deviation angles between the measured and calculated slip vectors (e.g., Bellier and Zoback, 1995). Numbers on top left of stereograms refer to site marked in Figure 6 as well as in Table 1. MFP refers to result of inversion of major fault plane data (see 4.1).

4. Fault kinematics and states of stress in the Dasht-e Bayaz area In this research, we measured the fault slip data in Triassic to late Quaternary age deposits. All the ten outcrops (Fig. 6), where the fault slip data has been measured, are cut by major faults that had been reactivated during late Quaternary (Dasht-e Bayaz fault, Korizan fault and Ferdows reverse fault zone). Specially, five sites that include fault planes with three generations of fault slip data have been inspected in deposits Pliocene to Quaternary in age. In the two Pliocene sites, the kinematic signatures of the all generations (older, intermediate and younger) were present, while in the two Quaternary sites we have measures striations related to the intermediate and younger generations. This measurement strategy helped us to exclude the fault slip data, predating Pliocene – Quaternary tectonic regimes in our data sets. According to the method explained in section 3, the measured fault slip data were separated into three homogeneous groups of slip generations and were analyzed to reach the results presented in Figures 6 to 10. This analysis has provided basic information for describing the kinematic evolution of the Dasht-e Bayaz fault during the Pliocene and Quaternary times. We compared the pattern of kinematic changes along the Dasht-e Bayaz fault with recent similar studies in nearby regions in E and NE Iran (e.g. Shabanian et al., 2010; Farbod et al., 2011; Javidfakhr et al., 2011; Jentzer et al., 2017; Tadayon et al., 2017), which has permitted us to place our results in a larger geodynamic scale.

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4.1. Modern state of stress The analysis of the youngest group of fault slip data, measured in ten sites (Table 1, Fig. 6A) including the last coseismic kinematics of the Dasht-e Bayaz fault, led us to characterize the modern state of stress dominated in the region. Except for sites 5b, 6 and 4, the maximum horizontal stress axis (σ1) has the average trend of N045±5°E (Fig. 10C). These deviatoric stress tensors indicate a homogenous strike-slip stress field in the area including the Dasht-e Bayaz fault (Fig. 6A). The trend of the σ1 axis locally changes in sites 5b, 6 and 4, with an orientation of ~N070°E. The strike-slip stress regime deduced along the eastern and central parts of the Dasht- e Bayaz fault changes into a compressional stress regime at the western end of the fault (sites 7 in Figs. 6 and 7). These two distinct stress regimes are completely coherent with different structural settings of the resolved stress tensors. Despite the strike-slip character of the fault that is clearly expressed along its eastern and central portions (e.g., Tchalenko and Ambraseys, 1970), the kinematics of the Dasht-e Bayaz fault change to oblique-slip sinistral reverse at its western end. In fact, the strike-slip character of the Dasht-e Bayaz fault disappears near the NW-SE Ferdows thrust (Berberian, 1981, 2014) where the E-W strike of the fault turns into NW. This change in strike is in accordance with the compressional stress regime obtained from site 7. As for site 6, it is inspected along a pressure ridge formed along a branch of the main fault. In that area, the fault branch locally accommodates the contractional deformation induced by left-lateral faulting along the main fault trend. In other words, this compressional stress regime expresses the local variation in regional stress at structural complexities along the fault. To avoid the local stress changes caused by structural complexities along the fault, we have separately analyzed the youngest set of fault-slip data measured on main fault planes (MFP), which had been inspected in different sites distributed along the Dasht-e

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Bayaz and the northern Korizan faults. The inversion analysis of such a particular dataset leads to a mean regional stress state responsible for the reactivation of different fault trends, regardless of the geographic location and structural setting. The resulting main fault plane (MFP) stress tensor specifies a mean regional strike-slip stress regime characterized by a N42±05°E σ1 axis (Fig. 7- MFP stress tensor). This mean regional compression is very close to the average orientation of N45±05°E for σ1 that we have obtained in 8 individual sites and we presented it as modern state of stress (see above).

Figure 8. Lower hemisphere stereograms of fault slip data with inversion results of the paleostress state presented in Table 1. Numbers on top left of stereograms refer to site marked in Figure 6 as well as in Table 1. The stereograms indicated by asterisk are the “fixed” solutions (Bellier and Zoback, 1995) for fault data populations comprised of less than four well-distributed fault directions. See the caption of Figure 7 for stereoplot descriptions. 86

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Figure 9. Lower hemisphere stereograms of fault slip data with inversion results of the intermediate state of stress presented in Table 1. Numbers on top left of stereograms refer to site marked in Figure 6 as well as in Table 1. See the caption of Figure 7 for stereoplot descriptions.

Figure 10. Statistical analysis of kinematic inversion results. Lower hemisphere stereograms showing direction of maximum horizontal stress axes (σ1) corresponding to (A) paleostress state (N125 ±05°E), (B) intermediate state of stress (N09±12.5°E) and (C) modern state of stress (N45±05°E), and in the Dasht-e Bayaz area all calculated in PBT axes method (Marrett and Allmendinger, 1990; Allmendinger et al., 2013). Blue and red arrows indicate the mean direction of σ1 and σ3, respectively.

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4.2. Paleostress state In more than half of the Kinematic measurement sites of the study area, we considered the oldest generation of fault slip data representative of a paleostress field. These older data, which were naturally fewer than the younger data, were carefully differentiated and analyzed. In six out of ten sites, which are well distributed over the study area, the oldest data sets comprise sufficient data to give independent deviatoric stress tensors (Figs 6C, 8 and Table 1). The paleostress state is characterized by a homogeneous N125±05°E trending mean σ1, with a compressional stress regime (Fig. 10A). This stress regime obtained from the E-W fault planes positioned on the reactivated main fault plane (or in the ones placed in parallel with the reactivated fault planes) implies dextral oblique kinematics activity during the dominance of this stress field. In addition to the mentioned results representing the modern and paleostress state of stress, the signature of an intermediate stress field was also measured in two sites along the Dasht-e Bayaz fault (Figs 6B, 9 and Table 1). This intermediate stress (if existed) is characterized by a ~N009°E mean σ1 and a strike slip stress regime (Fig. 10B). However, the insufficient number of stress solutions for this stress state precludes us from considering this stress state as an independent regional stress field (see 5.1).

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Table 2 Earthquake source parameters used in the focal mechanism inversion.

Date Time (UTC) Y X Depth (km) Magnitude (Mw) Strike Dip Rake Reference 1968.08.31 10:47 34.068 59.018 17 7.1m 254 84 5 5 1968.08.31 10:47 34.068 59.018 10 6.4 320 70 90 5 1968.09.01 07:27 34.099 58.155 9 6.3 115 54 85 3 1968.09.04 23:24 34.042 58.244 9 5.5 148 56 81 3 1968.09.11 19:17 34.031 59.472 6 5.6 78 90 16 1 1976.11.07 04:00 33.836 59.171 8 6.0m 84 79 12 1,4 1976.11.07 04:00 33.836 59.171 10 67 52 -7 1 1979.01.16 09:50 33.961 59.501 11 6.5m 293 34 46 1,4 1979.01.16 09:50 33.961 59.501 13 257 88 5 1 1979.11.14 02:21 34.017 59.78 10 6.6m 160 89 -177 1,4 1979.11.14 02:21 34.017 59.78 6 85 85 1 1 1979.11.27 17:10 34.056 59.769 8 7.1m 261 82 8 5 1979.12.07 09:24 34.13 59.889 10 5.9 113 84 21 1 1997.05.10 07:57 33.88 59.815 13 7.2 156 89 -160 2 1997.06.25 19:38 33.972 59.459 8 5.7 181 87 170 2

In this research we used the source parameters of instrumentally recorded earthquakes in the Dasht-e Bayaz region that have been modelled by Walker et al. (2004) with body wave methods. References are the same as they used in their modeling, including: (1) Baker (1993), (2) Berberian et al. (1999), (3) Walker et al. (2003), (4) Jackson (2001) and (5) Walker et al. (2004). An (m) after of some of Mw means a multiple event. For more information see Table 1 of Walker et al. (2011).

4.3. The present-day state of stress obtained from inversion of earthquake focal mechanisms We have used 15 earthquake focal mechanisms that have been recorded in the Dasht- e Bayaz region and nearby areas and that have been modeled by Walker et al. (2004, 2011), using body wave modeling (Table 2). The final stress tensor was prepared through the inversion of fault slip data reactivated during several earthquakes, affecting a vast area around the Dasht-e Bayaz fault and is therefore representative of the present-day regional state of stress in the northern Lut block. This solution indicates a single strike-slip tectonic regime, characterized by a regional N050±05°E trending σ1 (Fig. 11), responsible for the active deformation (whatever reverse or strike-slip fault mechanisms) throughout the region. This result is in total agreement with the modern state of stress (a N045±05°E

CHAPTER II compression with strike-slip regime) deduced from the analysis of the youngest generation of fault slip data principally measured in Pliocene and Quaternary deposits.

Figure 11. Stress map of the Iranian plateau and surrounding mountain belts. (A) SHmax orientations deriving from some of earthquake focal mechanisms in the Iranian plateau created by online stress map creator: http://www.world-stress-map.org/casmo/ (see Heidbach et al., 2016 and references therein). TF, thrust faulting; SS, strike-slip; NF, normal faulting; U, unknown. Different tectonic regimes are characterized by different symbol colors. NF and NS data is printed in red, SS data in green, and TF and TS data in blue. Data with an unknown regime is printed in black. (B) Our inversion results (N050±05°E trending σ1) showing the present-day state of stress in Dasht-e Bayaz area, source parameters were used from instrumentally recorded earthquakes that have been modeled using body waves (Walker et al., 2004), see the caption of Table 2 for more explanations. We put into practice inversion of focal mechanisms by using moderate to large earthquakes (7.1>M>5.7) and employing the method proposed by Carey-Gailhardis and Mercier (1987).

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5. Discussion 5.1. Integration of our kinematic results in the geodynamic context In section 2.1, we have presented a brief history of the related studies on the evolution of Late Cenozoic stress state in the north, east and northeast of Iran. Here, we put our results in a regional tectonic context in order to evaluate the consistency of the results with other similar studies in the north, northwest and west of the Dasht-e Bayaz area. The results of inversion on both geological and seismological fault slip data indicate the dominance of an active strike-slip tectonic regime characterized by a N45±05°E trending 1 in the Dasht-e

Bayaz area. There is a good consistency between this stress regime and the modern state of stress with an average compression of N045°E reported along the Doruneh fault (Farbod et al., 2011). Farther north, Shabanian et al. (2010) reported a modern state of stress in the Kopeh Dagh and Allah Dagh-Binalud Mountains characterized by a mean regional ~N030°E trending horizontal σ1 axis. According to the results of Javidfakhr et al. (2011), this modern state of stress prevails on eastern Alborz and western Kopeh Dagh Mountains (mean regional ~N036°E trending horizontal σ1 axis). Interestingly, the results mentioned above cover geological domains with different structural patterns, geological histories and active tectonics, while except for some local perturbations due to structural complexities, the modern state of stress remains homogenous throughout the region. As for the intermediate stress regime in the Dasht-e Bayaz area, the related maximum horizontal compression obtained in two sites was oriented as ~N009°E. Even though the insufficient number of stress solutions for this stress state prevented us from considering this stress state as an independent regional stress field, at a larger scale our results are completely in accordance with other studies done in the northeast of Iran (N180±10°E - Shabanian et al., 2010; Javidfakhr et al., 2011). Although there is no report of intermediate state of stress by Farbod et al. (2011) along the Doruneh, Tadayon et al. (2017) presented

CHAPTER II structural evidences for the prevalence of a penultimate N-S compression during the Plio- Quaternary time (see also Tadayon et al., 2018).

We have obtained a compressional N125±05°E trending mean σ1 as paleostress state, indicating that the currently left-lateral Dasht-e Bayaz fault had been right-lateral during a certain period of time. This result is very similar to that reported in the Kopeh Dagh and the transition zone between the Alborz and Kopeh Dagh Mountains (N140±10°E trending σ1 - Shabanian et al., 2010; Javidfakhr et al., 2011). A close stress orientation (N150±20°E trending σ1) and structural configuration were also determined along the Doruneh fault (Farbod et al., 2011; see also Javadi et al., 2013, 2015). The general consistency between the results on the kinematic history of the east, northeast and north of the Arabia-Eurasia collision zone (Abbassi and Shabanian, 1999; Abbassi and Farbod, 2009; Shabanian et al., 2010, 2012; Farbod et al., 2011; Javidfakhr et al., 2011; Javadi et al., 2013, 2015; Tadayon et al., 2017, 2018; Aflaki et al., 2017; this study) implies a homogenous transfer of stress during different periods of time, regardless of the geodynamic boundaries. Our results confirm that the Zagros collision zone, and its hinterland domain were mechanically coupled during, at least, late Miocene-Quaternary times (e.g., Tadayon et al., 2018). Such kinds of systematic regional change in the late Miocene to present-day states of stress and kinematics of crustal-scale faults discard the possibility of systematic block rotations around vertical axes in the region between Dasht‐ e‐Bayaz, Doruneh and Kopeh Dagh; a rotation of almost 30 degrees clockwise in the south and 30 degrees anticlockwise in the north produces 60 degrees of differential rotation in every linear structural element of the region (e.g., Jackson and McKenzie, 1984; Walker et al., 2004; Hollingsworth et al., 2006; see also Shabanian et al., 2009 and Farbod et al., 2011 for details).

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Despite the coherencies between our results and those obtained in the northern regions, the history of stress changes along the Dasht-e Bayaz and the northern end of the Abiz fault differs from what is recently obtained along the Sistan suture zone (Jentzer et al., 2017). They presented different sets of fault slip data related to three successive stress states. Their anticlockwise rotation history of compression is contrary to the history we found around the Dasht-e Bayaz and Abiz faults. Considering the good quality and the spatial distribution of data sets used by Jentzer et al. (2017), the discrepancy between the results cannot be explained through structural rotations due to progressive deformation along the fault zone. Hence, a more relevant geodynamic cause should be envisaged. Explaining this particular configuration, Jentzer et al. (2017) supposed that from the Miocene to late Pliocene, regions sufficiently close to the Zagros (i.e., within ~750 km: central Alborz, Central Iran, and Sistan) were stressed by the Zagros collision, and that this stress later spread, between late Pliocene to Quaternary, to more remote areas (e.g., Kopeh Dagh). However, more relevant observations are needed in the regions around the Sistan suture zone in order to reach a firm conclusion on the geodynamic cause of this particular pattern. As for the age, there is no general consensus on the timing of the aforesaid changes in the stress state; for example, Shabanian et al. (2012) showed geological evidence for late Cenozoic volcanism (dikes and volcanic domes) coeval with the prevalence of the paleostress state (a NW trending compression) in the Meshkan transition zone (between the Kopeh Dagh and Binalud Mountains). The last phase of volcanism was dated at 2.4 Ma (Ar-Ar dating of dacitic volcanic domes) and subsequently, a volcanic dome has been right- laterally displaced by the N-S Chakaneh Fault, reactivated in the intermediate stress state, with an N-S compression (Shabanian et al., 2009, 2012). Accordingly, they proposed a maximum age of 2.4 Ma (close to the border of Pliocene and Quaternary) for the change

CHAPTER II from NW trending paleo-1 to N-S intermediate 1. In the Mahneshan area (NW Iran),

Aflaki et al. (2018a) proposed that the last drastic change in the stress regime into the present-day stress state (a NE trending compression) has taken place at the Pliocene- Quaternary boundary. Around the Doruneh fault (north of the Lut Block), however, the shift in the regional maximum compression direction from NW to NS is placed at the Miocene–Pliocene boundary (Tadayon et al., 2018). Nowadays, a drastic change in the Plio-Quaternary tectonic regime throughout the Iranian plateau and the surrounding deformation domains is a geological fact, thanks to different researches carried out during the last two decades (e.g., Abbassi and Shabanian, 1999; Regard et al., 2005; Shabanian et al., 2010, 2012; Javidfakhr et al., 2011; Farbod et al., 2011; Tadayon et al., 2017; Jentzer et al., 2017; Aflaki et al., 2018a). The regional extent of these similar changes in distanced Plio-Quaternary stress fields clearly discards the possibility of block/stress rotation during progressive deformation. However, the possible causes of change in stress regime, especially in E and N of Iran, have not been identified yet. This change may be due to the onset of the northward subduction of the South Caspian Basin, and/or changes in the structural configuration or in the lithospheric characteristics of N and NE Iran during an evolving collisional convergence (Shabanian et al., 2012). In other words, it may correspond to a major regional reorganization of the plate boundary, following the transition from an infant to a mature stage of continental collision (Tadayon et al., 2018).

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Figure 12. Morpho-structural map of the central intersection zone along the Dasht-e Bayaz fault. (A) Detailed fault map of the interaction zone of the Mahyar and the Dasht-e Bayaz faults. Solid black line is geological fault; inferred fault is shown by dashed black line. Red solid line is the coseismic rupture of the Dasht-e Bayaz 1968 (west of the Mahyar fault) and 1979 (east of the Mahyar fault) earthquakes. The N-S dextral and E-W sinistral fault zones displaced each other in the sense of their movement of about 1.5 km; see Figure 17 for more details on the structural configuration of this zone. The lower right rose diagram (rosette) indicates the frequency of orientations of post-folding dikes (cut by strike-slip faults) concentrated around the intersection zone; note that the overall orientation of N330±10°E does not significantly vary along the strike- slip faults. Two topographic profiles across the contractional (P1) and extensional (P2) quadrants are shown. 95

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5.2. Kinematic implications along the Dasht-e Bayaz fault In the kinematic analysis, an important issue is the possibility of structural rotations due to progressive deformation. In order to evaluate such a possibility, we used arrays of dikes intruded in the folded strata of the area (post folding dikes). In the central part of the study area and around the intersection zone of the Dasht-e Bayaz and Mahyar faults (Fig. 12), different sets of dioritic and andesitic dikes have intruded in folded rocks of Jurassic to Eocene ages (Alavi Naini and Behruzi, 1983; Fauvelet and Eftekhar-Nezhad, 1991; Mohammadi Gharetapeh et al., 2014). The clear crosscutting relationships of the dikes show two generations of which the oldest set (microdioritic dikes) is the most frequent, with a dominant orientation of N325±10°E (Fig. 12). A younger minor population of pyroxene andesitic dikes (N345±15°E) are less abundant in the area and clearly cut through the oldest generation (Mohammadi Gharetapeh et al., 2014). The relative chronology suggests the age of post Eocene and pre-Pliocene as they have not intruded in the Plio- Quaternary alluvial deposits which outcropped in the proximity of the dike intruded zone. We have mapped 379 dikes through the analysis of Bing Map (SAS Planet©) satellite images of the area (Fig. 12). Aside for the existence of the same NW trend of both generations of dikes and the paleo-compression we have obtained (σhmax: N315±15°E), the overall orientation of the dikes does not significantly vary along and across the trace of both the Mahyar and Dasht-e Bayaz faults (Fig. 12). The same orientations of the first set of dikes close to, and beyond the main fault traces indicate insignificant structural rotations due to the post injection strike-slip faulting. Accordingly, the absence of any sign of gradual change in geological markers such as post Eocene pre-Pliocene dikes, indicates that the change in the regional state of stress has been drastic. In other words, this evidence along with the results of inversion of kinematic data (see 4.1 and 4.2) suggests a “kinematic switch” from dextral to sinistral displacement during the Pliocene-Quaternary.

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Based on the inversion of different sets of earthquake focal mechanisms that have been taken place in the last decades, the present-day state of stress in the Dasht-e Bayaz area is characterized by a mean regional N050±05°E trending σ1 accommodated by strike-slip tectonics. In this study we also obtained modern state of stress through the inversion of fault slip data measured in youngest geological outcrops in ten sites along the Dasht-e Bayaz fault. The latter concerns the fault planes affecting the Quaternary rock units (the youngest rock unit includes the modern generation of fault slip data) and thus involve much longer period of time. The high degree of consistency between modern and present-day results reveals three important inferences; (1) the absence of remarkable change in the modern state of stress during the late Quaternary time, (2) the prevalence of a homogeneous stress field in the brittle crust (above the ~17 km depth of seismogenic layer) of the Dasht- e Bayaz region and (3) the lack of stress perturbation due to the activity of the Dasht-e Bayaz fault.

5.3. Interpretation of structural and geomorphic features The Dasht-e Bayaz fault is a 120-km-long sinistral fault in the north of the Lut block (Fig. 1). The E-W Dasht-e Bayaz fault, with a rather straight geometry, is a structural assemblage of several fault strands with different orientations ranging from N070°E to N110°E (e.g., Tchalenko and Ambraseys, 1970; Fig. 3). Two western and eastern parts or segments are mainly considered for the Dasht-e Bayaz earthquake fault (e.g., Walker et al., 2004) are separating by N-trending Mahyar fault (Berberian, 2014). The western segment with ~70 km in length has been reactivated during the 31 August 1968 main shock, while the eastern segment of the Dasht-e Bayaz fault with the same trend attracted attention subsequent to the reactivation of its 55 km length extension to the east after 27 November 1979 Mw 7.1 Koli-Buniabad earthquake (e.g., Berberian et al., 1999).

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This particular structural arrangement forms various contractional and extensional mesoscale structures and morphotectonic landforms such as pull-apart basins, pressure ridges and en-echelon folds at different scales along the fault zone; the same structural patterns were coseismically created during the 31 August 1968 Dasht-e Bayaz main shock (Tchalenko and Ambraseys, 1970; Berberian et al., 1999). In addition to these variations in the fault geometry, the Dasht-e Bayaz fault is affected by N-S dextral faults, which are in close interaction with the main fault (Figs. 2 and 3). At the eastern end, the Dasht-e Bayaz fault intersects the NNE-striking Korizan segment of the Abiz fault (Fig. 2). In the south of 34°N, the N-S dextral faults are dominant and cut both the E-W sinistral and the NW-SE reverse faults of the region (e.g., Berberian et al., 1999). However, near this latitude it is difficult for instance to define any relative dominance of the N-S Korizan or the E-W Dasht-e Bayaz faults. Near the village of Buniabad, in the south of Kheybar Kuh-e Kuchek (i.e., Little Kheybar Mountain), these faults join together into a single ENE-WSW trend (Fig. 2). Farther northeast, however, the sinistral Niazabad fault runs in parallel with the Dasht-e Bayaz fault and looks like a left- hand stepping segment in a larger E-W sinistral fault system (Fig. 2). The northern parts of the Korizan fault are partly covered by eolian deposits, while the overall fault trace in the south of Buniabad village (Fig. 2) cuts the Quaternary alluvial fan surfaces. Our mapping of the intersection area shows a deforming wedge between the main traces of the Dasht-e Bayaz and Korizan faults (Fig. 3A); the conjugate arrangement of the main faults implies active contraction inside the wedge. Interestingly, N-S fault traces appear again in a discontinuous way in the northern side of the Dasht-e Bayaz fault trace, cutting the bedrock hence, there is no way to evaluate their Quaternary activity (see Walker et al., 2011). Nevertheless, systematic dextral geomorphic offsets of main streams along these faults could indicate their activity during, at least, the Pliocene time.

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Figure 13. Bing Map image (SAS.Planet© 2015-2017) centered on the western termination of the East Dasht-e Bayaz fault. See Figure 3 for location. (A) Detailed fault map of the area. Solid white lines are coseismic rupture traces and dashed white lines are geological faults not reactivated during the 1979 Dasht-e Bayaz earthquake. (B) Close-up view of the sinistral rupture that terminates in a NE-dipping reverse segment. (C) Close-up view of the northern end of the reverse fault segment due to intersection with a SW-trending sinistral segment.

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Another structural node along the Dasht-e Bayaz fault occurs where it intersects with the N-S Mahyar fault (Fig. 3). In fact, the western and eastern earthquake segments of the Dasht-e Bayaz fault (ruptures of the 31 August 1968 and 27 November 1979 earthquakes) are separated by the Mahyar fault (Berberian, 2014). Our detailed mapping (Fig. 12) shows that the cross-cutting N-trending dextral Mahyar and the E-trending sinistral Dasht-e Bayaz faults form a typical crosswise fault arrangement in their intersection area. These coexisting faults have displaced each other in the sense of their movement for ~1.5 km (Fig. 12). Following the opposite shear senses of the crosswise faults, double-coupled extensional and contractional domains have been formed in the quarters of this intersection. In the NW and SE extensional quarters, there are two relatively lowlands with an average elevation of 1300 m, while the adjacent NE and SW contractional quarters occupy higher areas with the average elevation of 1400 m (Fig. 12). The NE contractional quarter is occupied by nearly E-dipping reverse faults which join the main trace of the eastern Dasht-e Bayaz fault (Fig. 12). Our mapping of the 1979 earthquake rupture reveals that the main trace of the coseismic rupture dies out westward into a N-S reverse fault zone, with a dextral component of faulting (Figs 12 and 13). Other parallel reverse/thrust faults are observed in the NE quarter, but they have not been picked up by the coseismic rupture (Fig. 13). In contrast, the adjacent NW extensional quadrant hosts the extensional termination of the 1968 coseismic rupture (Fig. 13). In this area, the E-W trend of the 1968 rupture dies out eastwards into a NE-striking normal fault zone, of which a 615-m-long array of surface rupture can be mapped in satellite images (Figs. 12 and 13). The alignment of several SE-facing landslides (with fresh free-faces recognizable on images) along this part of the rupture is coherent with the extensional character of the rupture termination. The active crosswise pattern of the faults and the almost symmetrical deformation in the four quadrants around the intersection zone indicate a rather similar

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CHAPTER II structural significance for the N-S Mahyar fault and the E-W Dasht-e Bayaz fault. However, the simultaneous activity of these crosswise to conjugate fault sets is mechanically impossible hence, the fault sets must logically reactivate one after another (e.g., Freund, 1974). The succession of recent seismic events, producing sinistral faulting along both the western (e.g., 31.08.1968 Dasht-e Bayaz main earthquake, Mw 7.1) and eastern (e.g., 11.09.1968 Dasht-e Bayaz earthquake aftershock sequence, Mw 5.6 and 27.11.1979 Koli-Buniabad earthquake, Mw 7.1) segments of the Dasht-e Bayaz fault and right-lateral faulting in the southeast of this system (e.g., 25.06.1997 Boznabad earthquake, Mw 5.9; see Berberian et al., 1999 and Walker et al., 2011), could confirm that the deformation in this area is taking place under the influence of alternate reactivation of the above-mentioned right-lateral and left-lateral fault sets. Farther to the west, an E-W pull-apart basin (the Chah Deraz pull-apart basin, see also Walker et al., 2004), with ~3900 m in length and ~870 m in width can be recognized easily thanks to its particular geomorphology in the southern side of the Dasht-e Bayaz fault trace. The almond-shaped geometry of the pull-apart basin, in addition to its symmetric curved boundaries (Fig. 14) suggest that the basin was formed in a releasing bend (e.g., Dooley and Schreurs, 2012). Taking into account the results of Aydin and Nur (1982), which indicate the maximum frequency of length-width ratio of the pull-apart basins varies between 3 and 4, the Chah Deraz pull-apart basin having a length to width ratio ~4.5, can be considered as an elongated basin, slightly more than usual. The study of these basins shows (e.g., Bellier and Sébrier, 1994; Dooley and Schreurs, 2012) that their propagation is limited and eventually at a certain point of their evolutionary period, the creation of a shortcut fault renders the moving apart fault strands (stepovers or restraining bends) inactive and henceforth the basin only displaces in the sense of movement of the strike-slip fault. Considering the lack of recent activity along the southern border of the

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CHAPTER II basin and the coseismic reactivation of the northern master fault during the 31 August 1968 earthquake (Fig. 14), we suggest that the Chah Deraz pull-apart basin has entered a new stage of evolution by a shift in its active extension from the central part to the northwest margin of the basin (Fig. 14) and probably does not propagate anymore.

Figure 14. SPOT image of the Chah Deraz pull-apart basin along the west Dasht-e Bayaz fault. (A) the active trace of the fault passes at the northern margin of the basin, while the southern one is inactive. (B) close-up view of the coseismic rupture (1968 Dasht-e Bayaz earthquke) at the northen margin of the basin.

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Figure 15. Tectonic features of the western portion of the west Dasht-e Bayz fault. (A) Shaded relief image of the northwestern Nimboluk plain and structural map of this area including different fault branches of the Dasht-e Bayaz fault. The hatched polygon shows areas involved in en-echelon folding and pressure ridges. (B) and (C) SPOT image of the northwestern Nimboluk plain. Fold axes shown as yellow lines. (D) West looking photographs and reconstructed section across the Rahmatabad fault branch and associated folding of Plio-Quaternary deposits in the footwall.

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Further to the west, the Dasht-e Bayaz fault controls the contact between Quaternary deposits and Mesozoic sedimentary rocks. In northwestern Nimboluk plain, there are outcrops of Miocene marls armored by Quaternary deposits; the dense cultivation and human-made changes in the Quaternary surfaces, cut by the fault, precluded us from following the trace of the coseismic rupture. The detailed rupture maps of Tchalenko and Ambraseys (1970) and Tchalenko and Berberian (1975) show that about 12 km westwards from the Chah Deraz pull-apart, the fault trace encounters another structural complexity. In the northwestern Nimboluk plain, the Dasht-e Bayaz fault could not be followed as an individual fault trace (Fig. 15A). Our observations and mapping show that in addition to Golbiz and Mozdabad fault branches, which have been mentioned in previous studies (e.g., Berberian, 2014), the Dasht-e Bayaz fault has another northern fault branch, which we imply it as Rahmatabad fault branch. As shown in Fig. 15D, the road trench reveals a cross-section of the Rahmatabad fault branch and a folding that has been formed in its footwall in the Plio- Quaternary conglomerates. The observation of satellite imagery and our fieldworks show that this fold is not alone and a series of parallel and sub-parallel en-echelon folds (Fig. 15) have been formed wholly in the Miocene gypsiferous marls and Plio-Quaternary deposits due to several restraining curvatures along the Dasht-e Bayaz fault and attached fault branches. The Golbiz fault branch of the Dasht-e Bayaz fault continues toward Maysur Mountain to the NW trending N100E (Berberian 2014) and joins the north dipping reverse faults in the middle of Kuh-e Kamarkhid Mountain (Fig. 15A). Fresh surface faulting with 30–50 cm left-lateral and 30 cm vertical coseismic displacements has been reported along this fault branch (See Berberian, 2014 and references therein). The coseismic main rupture of the Dasht-e Bayaz fault cuts across between the villages of Dasht-e Bayaz and Khezri and after 10 km, while joining the Mozdabad fault branch, bends southwestwards. In the

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CHAPTER II western termination of the Dasht-e Bayaz fault, the NE-trending Mozdabad fault branch with 6 km length joins the Ferdows reverse fault array at the western flank of the Kuh-e Kamarkhid and Kuh-e Kalat Mountains (Fig. 15A). Reactivation of 1.5 km along this fault branch with small left-lateral coseismic offset has been reported by Ambraseys and Tchalenko (1969).

5.4. Geodynamic implications and tectonic scenario According to the model frequently applied in the east and northeast of Iran, originally proposed by Jackson and McKenzie, (1984), an uneven distribution of N-S right-lateral shear between central Iran and Afghanistan and its westward decrease has caused a clockwise rotation of fault bounded blocks in the north of ~34°N (Walker et al., 2004; Walker and Jackson, 2004). The model tends to explain the structural features of the northern Lut block by the concept of clockwise rotation around vertical axes. It seems that as a generalized paradigm, the structural deflections and internal deformation, due to local dragging or compression caused by faults or thrust zones, have usually been interpreted as systematic block rotations around vertical axes (e.g., Walker et al., 2004).

This block rotation model was questioned about its lack of ability in explaining the prominent curvature and other complexities along the Doruneh Fault System (see Farbod et al., 2011 for more details). For example, Farbod et al. (2011), showed that to attain the present-day geometry of the DFS, the fault trace needs to rotate clockwise in the eastern part and counterclockwise in the western part. While the occurrence of pre‐Pliocene dextral faulting on E-W trends distributed across Central Iran (Javadi et al., 2013, 2015; Nozaem et al., 2013; Bagheri et al., 2016; Calzolari et al., 2016, 2018; Tadayon et al., 2017) and the Quaternary kinematic shifts along the Doruneh and Dasht-e Bayaz faults (Farbod et al., 2011; Javadi et al., 2015; this study), which clearly indicate a homogenous regional stress

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CHAPTER II field distribution and coeval evolution of the intracontinental deformation in Central Iran, are not coherent with the block rotation model (see Tadayon et al., 2018 for discussion).

Figure 16. A brief explanation of our model about the northern Lut block and the southern Kopeh Dagh domain. (A) Up to 34° N the most of convergence is accommodated by right-lateral shear between Iranian plateau and fixed Eurasia. In the north of 34° N, an interruption in right- lateral shear takes place and in the absence of right-lateral shear, accommodation of convergence is assigned to reverse/thrust faulting. (B) Schematic model emphasizing the role of separated thrust zones, as confining wedges at the termination of N-S dextral fault, in accommodation of the Arabia-Eurasia convergence. See text for more information.

The paleomagnetic data of Mattei et al. (2012) does not indicate any systematic clockwise rotation over the Neogene in the region. The most recent study by Mattei et al. (2019) provides new paleomagnetic data on the Kopeh Dagh Mountains. They reported that paleomagnetic rotations (the mean of 11.3±9.4 clockwise rotation during ~4 Ma)

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CHAPTER II occurred in the Kopeh Dagh belt between ≈6–4 Ma and ≈2 Ma, before the beginning of the westward extrusion of the South Caspian Block. Mattei et al. (2017, 2019) pointed out that their oroclinal model does not correspond to the present-day kinematics of the studied areas (Alborz and Kopeh Dagh) and the rotation was stopped before the onset of the present-day kinematics at ~2 Ma. Nevertheless, a mean “clockwise” rotation rate of ~2.5°/Ma can explain neither the 30° of anticlockwise rotation in the Kopeh Dagh, nor the 30° clockwise rotation (Walker et al., 2004) in the north of Lut due to the active kinematics of the region.

Based-on this model, if the Dasht-e Bayaz fault transfers right-lateral shear between central Iran and Afghanistan to the mountains of northern Iran, it must do so by rotating clockwise about a vertical axis (see Walker et al., 2004 and references therein). Instead, we propose another tectonic scheme that we believe can better explain the complexities of northeastern Iran and the role of the Dasht-e Bayaz fault in this context. It is worth mentioning that this scheme generally concerns the northeastern border of Arabia-Eurasian collision zone and it is clear that it does not involve the other regions such as eastern Alborz and the internal blocks of the Central Iran.

According to our tectonic scheme (Fig. 16), the right-lateral shear is the main mechanism for the accommodation of the Arabia-Eurasian convergence and the GPS velocity vectors show a northward (N013°E) block motion in the Lut Block with respect to Eurasia (Walpersdorf et al., 2014), but it is not necessarily the case everywhere in E and NE Iran. In the north of 34°N (corresponding to the E-trending Dasht-e Bayaz fault), the N-trending right-lateral shear is interrupted and does not continue to the north. Beyond this latitude, the convergence is mainly accommodated by crustal shortening across NW- trending reverse/thrust faults. In the north of 34°N, there is no dextral N-S strike-slip fault, while the NW-trending parallel reverse/thrust faults are abundant in the region. The Ferdows reverse fault zone, the Jangal and Khaf thrust faults and the eastern termination

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CHAPTER II of the Doruneh fault (Farbod et al., 2011) as well as the restraining fault terminations in the southern flank of Binalud (Shabanian et al., 2012) and the thrusts of the Fariman area (Aflaki et al., 2019) are among the most important NW-trending contractional faults confirming our geodynamic scenario in northeastern Iran.

Southeastern Binalud and Kopeh Dagh Mountains is occupied by a soft-linking restraining relay zone (Binalud-Fariman-Torbat-e Jam; Aflaki et al., 2019) in which the mechanism of faulting is preferably reverse to reverse dextral, while farther north in the Kopeh Dagh, it is pure dextral strike-slip. Accordingly the N-S right-lateral shear between Iran and Afghanistan that had been interrupted in the latitude 34° N (corresponding to the Dasht-e Bayaz fault) is recuperated gradually near the latitude of ~36°N, but this time along the NW-trending faults with respect to the Turan platform instead of the Helmand block (Afghanistan).

The integrated geological, seismological and InSAR investigations done by Aflaki et al. (2019), in the area affected by the 5th April 2017 Sefid Sang earthquake (Mw 6), showed that the dextral shear along the NNW-striking faults (i.e., Bakharden-Quchan and Hezar Masjed fault systems) is transferred southeast into WNW-striking transpressional terminations in the region between the Binalud Mountains and Doruneh fault. The CMT and the first polarity solution of the main shock and the two aftershocks of this seismic event, which occurred close to the southern termination of the Hezar Masjed fault system near the town of Fariman, indicate a mainly reverse mechanism with a small dextral component (See Aflaki et al., 2019 for details). This event clearly reveals the dominance of reverse faulting in the southeastern end of Kopeh Dagh and the eastern termination of the Doruneh fault.

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Figure 17. Details on the processes involved in the accommodation of Lut – Eurasia convergence in the NE and E Iranian regions. (A) The process of wedge confining at the edges of north-going blocks and the associated secondary sinistral faulting along E-W faults such as the Dasht-e Bayaz and Niazabad. The overall N013°E direction of Lut – Eurasia motion (Walpersdorf et al., 2014) is mainly taken up by lithospheric N-S dextral shear translating the southern tectonic domain (STD) northwards. Shortening at the opposing edges of the main blocks (STD against ER) is accommodated through contractional faulting in a restraining relay zone (RRZ in “A”; Farbod, 2011; Aflaki et al., 2019), while internal deformations due to sub-block adjustments is taken up by crosswise dextral and sinistral faulting accompanied by contractional deformation at their terminations (CW, confining wedge). (B) And (C) Site-scale examples for the evolution of crosswise faulting; (B) illustrates the initial stage of crosswise faulting and (C) shows the structural configuration of crosswise dextral and sinistral faults after development of contractional quadrants. “TL” is the length of the main thrust fault zone developed perpendicular to the compression and is proportional to the amount of dextral (DD) and sinistral (SD) displacements of the main crosswise fault traces. (D) Is the intersection zone between the Dasht-e Bayaz and Mahyar faults; note to the analogy between this structural configuration and the typical crosswise faulting illustrated in (C). Such the kind of kinematic interaction accommodates the overall convergence oblique to the faults without a need for rotations of faults and blocks around vertical axes. 109

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For instance, the Khaf and Jangal thrusts have been considered as probable sources for the Zuzan historical destructive earthquakes (Berberian, 2014) of 19 and 21 October of

1336 A.D., respectively. The 1 and 4 September 1968 Ferdows earthquakes (MW 6.8 and

MW 5.5) also indicate significant tectonic activity of the Ferdows reverse fault zone. The observations show creation of new reverse faults in the west of Kuh-e Kalat Mountain at Ferdows (e.g., Walker et al., 2004; Rashid et al., 2015) indicate the high activity of thrust/faulting in this area. The study of magnetic foliation vertical and oblique to the bedding of post Miocene folds in the Ferdows fault zone (Rashid et al., 2015) suggests that a cleavage system, not visible at the outcrop scale, has been developed as a consequence of recent shortening related to the activity of this thrust zone. All these observations reveal that, in the northern Lut, the NW-trending reverse/thrust fault zones accommodates significant portion of the active deformation perpendicular to their strikes.

Between the latitudes 34° N and ~36° N, an interruption in the N-trending right-lateral shear between Iran and Afghanistan takes place and instead, the reverse/thrust faulting has the principal role in the accommodation of convergence. In this tectonic scheme, the secondary role of E-W sinistral faults such as the Dasht-e Bayaz and Niazabad faults in accommodation of the convergence can be explained through their structural setting between two reverse/thrust zones. In the northeastern Lut block, the main left-lateral strike- slip displacement occurs between the convergence point of the Doruneh (we discuss only about eastern termination of the Doruneh fault) and Niazabad faults and the meeting point of Dasht-e Bayaz fault with the Ferdows thrust zone and is completely controlled by the activity of these confining parallel thrust zones (Fig. 17).

Regarding both the structural configuration and the present-day relative velocity field (Eurasia fixed) in east-northeastern Iran, the Doruneh fault is a major boundary separating two distinct northern and southern domains (Fig. 16). Angular relationships between

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CHAPTER II dextral and sinistral faults obviously change in these tectonic domains; the northern domain is characterized by NNW-striking dextral and ENE-striking sinistral faults (e.g., Tchalenko and Berberian, 1975; Shabanian et al., 2009a, 2010; Javidfakhr et al., 2011). This structural pattern leads to the NNW extrusion of both Central Iran and western Kopeh Dagh towards the South Caspian Basin (Hollingsworth et al., 2006; Shabanian et al., 2009). Therefore, in our tectonic scheme’s point of view, the method of absorption of convergence has some differences in northern Lut and southern Kopeh Dagh, which are being separated by the Doruneh fault system. In the north of the Doruneh fault system, active convergence is taken up by the reverse thrust faulting along with the extrusion of fault-bounded blocks, while in the southern domain the convergence is accommodated through the reverse/thrust faulting in confining wedges accompanied by crosswise strike-slip faulting, without a need for the systematic block rotation around a vertical axis. The details of these different processes are shown in Figure 17. The process of wedge confining at the edges of north-going blocks (due to a NE-trending compression) allows accommodating the internal deformation, which has not been absorbed during the lithospheric scale northwards motion of Central Iran relative to Eurasia (Fig. 17a). The accommodation of this internal deformation is done through crosswise faulting along N-S dextral and E-W sinistral faults (Fig. 17b-d). This later has leaded to the development of contractional (reverse/thrust) fault zones perpendicular to the overall direction of Arabia – Eurasia convergence and those faults accommodate the eastward component of the convergence (Fig. 17).

6. Conclusion Our inversion analysis of fault kinematics data revealed signatures of two distinct stress fields in the Dasht-e Bayaz area during Plio-Quaternary. Before the modern state of stress (N45±05°E trending compression, σ1) which controls the active deformation in the area,

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CHAPTER II an old stress state characterized by a N125±05°E trending compression (σ1) was responsible for the dextral transpressional movements before the onset of the active left- lateral faulting along the Dasht-e Bayaz fault. The Dasht-e Bayaz main fault plane, contains several roughly E-W fault strands characterized by a coseismic sinistral mechanism superimposing the older dextral reverse kinematics of the main fault.

The consistency between the inversion results of both modern geological fault slip data and the earthquake focal mechanisms reveals: (1) the absence of remarkable change in the modern state of stress during the late Quaternary time, (2) the prevalence of a homogeneous stress field in the brittle crust (above the ~17 km depth of seismogenic layer) of the Dasht-e Bayaz region and (3) the lack of long-term stress perturbation due to the activity of the Dasht-e Bayaz fault. The general consistency between the results on the kinematic history of the east, northeast and north of the Arabia – Eurasia collision zone implies that a homogenous transfer of stress during, at least, late Miocene – Quaternary times, has taken place due to the mechanical coupling of the Zagros collision and its hinterland domains. We suggest that the region between Lut and Kopeh Dagh is divided by the Doruneh fault into two northern and southern distinct tectonic domains. The northern domain is characterized by the extrusion of fault-bounded blocks towards the north-northwest, while in the southern domain, the northward motion of the central Iranian blocks occurs through structural and kinematic interactions between N-S dextral, E-W sinistral and NW-striking reverse/thrust faults at the block boundaries without a need for symmetric block rotations around vertical axes.

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Acknowledgements We would like to thank the Geological Survey of Iran especially thanks to Mr. Koreie and Mr. Fotovati for their support and logistic assistance. We are grateful to the municipality of Khezri-Dasht-e Bayaz and Sangan Iron Ore Complex for their support during field trips. We thank Mr. Lhôte and the staff of French Embassy in Tehran. We thank A. Ghods and F. Sobouti in the Institute for Advanced Studies in Basic Sciences in Zanjan.

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QUATERNARY SLIP RATES ALONG THE

DASHT-E BAYAZ FAULT

CHAPTER III

Quaternary slip rates along the Dasht-e Bayaz Fault (NEE Iran)

Fariborz Baniadam ab, Olivier Bellier a, Esmaeil Shabanian c, Régis Braucher a, Valéry Guillou a, ASTER team a

a Aix Marseille Univ., CNRS, IRD, INRA, Coll. France, CEREGE, Aix-en-Provence, France, [email protected] b Geological Survey of Iran, Tehran, Iran, corresponding author: E-mail address: [email protected]; [email protected] c Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran, [email protected]; [email protected]

Abstract

The Dasht-e Bayaz fault is located in the northern part of the Lut block in the east of Iran. After the destructive 1968 Mw 7.1 earthquake, the Dasht-e Bayaz area has been one of the most seismically active domain in Iran. The occurrence of this earthquake was followed by numerous destructive earthquakes which renders this area a suitable reference of world class earthquake clustering. Despite the conspicuous seismic activity of the fault, the lack of detailed information about its slip rate, has precluded the determination of the geodynamic significance of the fault in the accommodation of active deformation in the context of the Arabia-Eurasia convergence. In this research, we investigate the long-term slip rate through studding Quaternary cumulative offsets along the Dasht-e Bayaz fault. We have recognized five successive generations of Quaternary alluvial fans (Qt1, Qt2, Qt3, Qt4 and Qt5, from the oldest to the youngest) some of which have been displaced along the Dasht-e Bayaz fault. A number of 57 samples were collected in four sites and all have been dated using the CRE 10Be dating method. The abandonment ages of Qt2, Qt3 and Qt4 Quaternary alluvial fans were obtained as 159.0 ± 5.0, 88.6 ± 3.7 and 19.5 ± 0.7 ka,

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CHAPTER III respectively. Assigning these abandonment ages to the geomorphic offsets recorded by the alluvial fans yields to an average slip-rate of 0.9 ±0.14 mm/yr for the western Dasht-e Bayaz fault. This slip rate has probably remained constant since at least 159 ka ago and is lower than what was previously presented (2.5 to 2.6 mm/yr). In spite of recent highlighted seismic activity, our results indicate an insignificant geodynamic role for the Dasht-e Bayaz fault in the accommodation of internal deformation in the Iranian plateau. These results emphasize the seismic potential of slow slipping active faults in the interior of continental regions, with low rates of deformation.

1. Introduction

The rate of fault slip is one of the most important characteristics of an active fault and if well-defined, it is an unambiguous criterion to evaluate both the activity and geodynamic role of the fault. During the last two decades, the slip rate estimations have been the subject of several studies in Central Iran, Zagros and Kopeh Dagh, as well as the Lut block (e.g., Regard et al., 2005; Authemayou et al., 2009; Le Dortz et al., 2009, 2011 and 2012; Shabanian et al., 2009a, 2009b and 2012; Walker et al., 2009; Rizza et al., 2011; Fattahi et al., 2014 and 2015; Foroutan et al., 2014; Farbod et al., 2016). Four geochronological methods of cosmic ray exposure (CRE) dating (e.g., Shabanian et al., 2009a; Javidfakhr et al., 2011; Farbod et al., 2016), optically stimulated luminescence (OSL - e.g., Fattahi et al., 2014, 2015; Le Dortz et al., 2009; Foroutan et al., 2014) and infrared stimulated luminescence (IRSL – e.g., Fattahi et al., 2006, 2007; Fattahi and Walker, 2007; Rizza et al., 2011) as well as 40Ar/39Ar dating (Shabanian et al., 2009a; Walker et al., 2009) have been used to determine the absolute ages of Quaternary geomorphic surfaces, offset along the main faults of the Iranian plateau and the surrounding deformation belts. Since 2004,

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CHAPTER III the GPS data has been extensively applied to determine the slip rate of active faults along the Iranian plateau (e.g., Vernant et al., 2004; Masson et al., 2007; Walpersdorf et al., 2006; Tavakoli et al., 2008; Peyret et al., 2009; Djamour et al., 2010; Mousavi et al., 2013; Walpersdorf et al., 2014). Interferometry methods, using InSAR data to measure the rate of interseismic strain accumulation, have been used for slip rate determination in some areas in NE Iran (e.g., Walters et al., 2013; Mousavi et al., 2015). In particular cases, the displacements of the man-made qanat lines were used (Trifonov, 1978; Berberian and Yeats, 1999) to calculate the slip rate of the faults. The information concerning the slip rates of an active fault enables one (1) to describe the geodynamic role of the fault, (2) to constrain the seismogenic behavior of the fault and (3) to determine the kinematics of deformation in continental regions.

The Dasht-e Bayaz fault is one of the main E-W active faults, in the Iranian plateau, that has been causative fault of the two destructive earthquakes of 31 August 1968 Dasht- e Bayaz Mw 7.1 and 27 November 1979 Mw 7.1 Khuli-Buniabad earthquakes. The E- trending sinistral Dasht-e Bayaz fault accommodates the Arabia-Eurasia convergence despite the fact that it is perpendicular to the northward motion of central Iran relative to Eurasia. The kinematics and geodynamic role of the Dasht-e Bayaz fault have been fully discussed by Baniadam et al. (2019). According to their tectonic model, the Dasht-e Bayaz fault has a minor role in the accommodation of this deformation, while the parallel Doruneh fault plays a significant role as a boundary fault separating the two distinct tectonic domains of northeast and east-central Iran. The Doruneh fault slips at ~5 mm/yr (Farbod et al., 2016), however there is no consensus on the rate of slip along the Dasht-e Bayaz fault. The knowledge of slip rate of the Dasht-e Bayaz fault would allow one to evaluate the tectonic models proposed for the region north of the Lut block (Walker and Jackson, 2004;

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Baniadam et al., 2019) and provides key information for the assessment of seismic hazards in the region.

This paper aims to estimate the slip rate of the Dasht-e Bayaz fault for a time period as long as possible. In this paper we use 10Be CRE dating along with cumulative offsets of Quaternary alluvial fans displaced along the Dasht-e Bayaz fault to determine the slip rate of this fault during Quaternary. We have analyzed 55 samples collected from four successive alluvial surfaces offset by the fault. The reconstruction of geomorphic offsets was done through the analysis of satellite images. The slip rate of the fault was determined using the geomorphic offsets and their assigned CRE ages. We will discuss the tectonic implications of the results integrating our results in a larger regional scale.

2. Geodynamic and Tectonic setting

The Dasht-e Bayaz fault is located in the northern parts of the Lut Block in the NNE of Iran (Fig. 1). The Lut Block is an N-trending elongated rectangular-shaped area in eastern Iranian plateau. This block is bounded by the Doruneh fault system to the north, Nayband, Gowk to the west, Korizan fault and Sistan suture zone to the east and Jazmurian depression zone to the south. Arabia-Eurasian convergence is accommodated mainly by the northward translation of the Lut block and active deformation along the surrounding active faults. In the recent years, active tectonic studies have mainly concentrated on the determination of the rates and kinematics of movements along the block bounding faults and the faults located in the interior of the Iranian plateau, as well as describing the role of these faults in the accommodation of active deformation.

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Fig. 1. (A) The upper left (after Shabanian et al. 2010) inset corresponds to the location of the study area in the Arabia–Eurasian collision framework. The grey arrows and the associated numbers represent the Arabia–Eurasian plate velocities (mm/yr) after Reilinger et al., 2006. (B)The GTOPO30 topographic image presents the regional tectonic setting and the major active faults In E and NE Iran. The Dasht-e Bayaz study area has been marked through the black dotted quadrangle.

The Dasht-e Bayaz fault interacts actively with N-S dextral faults of the region, such as the Mahyar and Abiz fault zones (Baniadam et al., 2019). At its eastern termination, the Dasht-e Bayaz fault intersects the Korizan fault, which is included by the northern portion of the Abiz fault zone. The Korizan fault caused the 7 December 1979 Kalat-e-Shur (Mw

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5.9), the 14 November 1979 Korizan (Mw 6.6) and the 10 May 1997 Zirkuh (Mw 7.2) destructive earthquakes (Berberian et al., 1999). The importance and geodynamic role of the Sistan suture zone, in the east of Lut, in the accommodation of Arabia-Eurasian convergence is well known and is approved by both geologic and geodetic studies, (e.g., Tirrul et al., 1983; Walker and Jackson, 2002; Walker et al, 2004; Walker and Jackson, 2004; Vernant et al., 2004; Meyer and Le Dortz, 2007; Walpersdorf et al., 2014) indicating that a large portion of the dextral shear between the Iranian plateau and Afghanistan is accommodated by this fault system. This fault system is interrupted to the north by the E- W sinistral Dasht-e Bayaz fault.

3. Sequential cumulative offsets along the Dasht-e Bayaz fault

The only estimation concerning the maximum total geological offset of the Dasht-e Bayaz fault was done by Tchalenko and Berberian (1975) according to a mass of black Cretaceous limestone, which crops out in the Khidbas region and was dragged for about 4 km along the fault. However, like the Doruneh fault (Farbod et al., 2011; Tadayon et al., 2017), the Dasht-e Bayaz fault has a complex history of evolution, (differential uplift, erosion and lateral displacement) leading to the elimination of the southern counter part of rock units cropped out in the northern side of the fault. This has precluded a convincing estimation of total sinistral displacements along the fault.

In order to determine the maximum Quaternary offset along the fault, the entire length of the fault was carefully mapped by means of satellite images of the area. We distinguished five distinct Quaternary surfaces classified as Qt1, Qt2, Qt3, Qt4 and Qt5, from the oldest to the youngest one. These geomorphic surfaces are the abandoned alluvial fans which

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CHAPTER III sequentially inset each other and are characterized by different topographic levels, distinct surface geomorphology, depth of incision and density of streams.

Fig. 2. Site DB1, the Qt1 fan surface offset by the Dasht-e Bayaz fault. The SPOT imagery of the Qt1 surface at the south of the Chahnow village in the central parts of the Dasht-e Bayaz fault. We found 265 ± 10 meters of cumulative offset in this site.

As the largest Quaternary cumulative offset, we have measured a left-lateral cumulative offset of 265 ± 10 meters along the Dasht-e Bayaz fault based on the geomorphic reconstruction of the shape of a Qt1 alluvial fan and its associated streams in the site DB1 (Fig. 2) The largest cumulative offset recorded by a Qt2 surface is observed in site DB2 (about 11 km northeast of Khezri) and corresponds to a typical cone-shaped alluvial fan cut by the Dasht-e Bayaz fault. The original height of this cone has been approximately 440 m and the base is 210 m (Fig. 5). There is no stream incising the surface, but the reconstruction of initial form of the alluvial fan allows one to partially match the eroded edges of this cone after the restoration of 165±15 m of left-lateral offset (Fig. 5a).

The cumulative offset in a Qt3 surface has been measured in site DB3 (12 km east of Khezri village - Fig. 6a). In this site, the Qt3 surface involves a piedmont alluvial fan which

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CHAPTER III is elevated relative to the other surrounding fans, while it has properly preserved its original shape. The detailed reconstruction of the overall fan geomorphology and its streams yields to a left-lateral cumulative offset of 71 ± 5 m, postdating the abandonment of the Qt3 alluvial surface.

In the western proximity of the DB3 site, a Qt4 surface insets the older Qt3 alluvial fan, mentioned above. That is a rhomboidal alluvial fan extended in the N-S direction and lays 15 – 20 m lower than the Qt3 surface (Fig. 8a). The Qt4 surface is cut distinctly by the Dasht-e Bayaz fault in its middle parts so that their incising streams show systematic offset/deflection along the fault. The geomorphic restoration of this sinistral offset through the reconstruction of both fan borders and streams indicates an offset value of 20 ± 3 meters since the abandonment of the Qt4 alluvial fan.

In the site DB5 we tried to measure left-lateral offset along the fault in the Qt5 surface as youngest generation of Quaternary alluvial surfaces (Fig. 9). Our observations indicates that this surface has not incised enough and probably has not abandoned completely, and therefore there is no possibility to measure the cumulative offset on its surface.

4. Cosmogenic exposure dating of alluvial surfaces offset along the Dasht-e Bayaz Fault

4.1. Methodologies

In the second stage of this study, we have looked for the age of abandonment of alluvial fans, offset by the Dasht-e Bayaz fault. Our objective is to find how much time is elapsed since the onset of the cumulative offsets recorded by different generations of alluvial surfaces. The absolute age of abandonment is determined by calculating the time necessary for achieving the concentrations of in situ–produced cosmogenic nuclides, measured in the clasts (boulders, pebbles or amalgamated samples) which were originally disposed on each

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CHAPTER III surface, due to the last alluvial/fluvial deposition on the surface. The assignment of abandonment ages to the geomorphic offsets recorded by the abandonment surfaces is usually a delicate job (e.g., Cowgill, 2007) and requires two principal assumptions of low amounts of inheritance and low rates of erosion (Ritz et al., 1995). Under these conditions, the concentration of an in situ–produced cosmogenic nuclide is directly related to the amount of time passed since the abandonment of a surface (Ritz et al., 1995). Any change in the assumed conditions could affect the time of exposure of the surficial clasts and is reflected in the concentration of in situ–produced cosmogenic nuclides measured in the sample collected from the geomorphic surface.

4.2. Geomorphic mapping and site selection

We have verified all Quaternary alluvial fans around the Dasht-e Bayaz fault using SPOT5 satellite images, in order to find well-preserved alluvial fans suitable for CRE dating. The western part of the fault, around the Khezri and Dasht-e Bayaz, is covered by cultivated and inhabited areas, while in the eastern part there is no abandoned alluvial fan mostly because of the eolian character of geomorphic features and the relatively smooth topography of the area. Along the entire length of the fault, we have found six sites, with well-preserved surfaces and holding the possibility of fault offset reconstruction, all situated in the middle part of the fault. We have selected four western sites for sampling since they possessed more suitable criteria. These sites include four generations of alluvial fans including Qt2, Qt3, Qt4 and Qt5. There was one outcrop of Qt1 along the fault in the south of Chahnow village but sampling was not done in this alluvial fan because of the excessive amount of topographic slope. Regardless of the CRE sampling, quaternary alluvial deposits were mapped precisely and geomorphic reconstruction was done in every possible area.

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4.3. Sampling strategy and analytical approach for cosmogenic dating

Cosmic Ray Exposure (CRE) dating is based on the accumulation of certain cosmogenic nuclides in the surficial materials (few top meters of the crust) exposed to cosmic radiation (see review by Gosse and Philips, 2001; Dunaï, 2010; Benedetti and van der Woerd, 2014).

In order to estimate the CRE ages of alluvial fan surfaces offset along the Dasht-e Bayaz Fault, CRE dating has been done in four sites along the western Dasht-e Bayaz Fault by measuring the concentrations of the in situ-produced 10Be cosmogenic nuclide accumulated in quartz-rich clasts. After the site selection, surface sampling was done in the first phase (28 samples) and in the second phase, a number of 29 samples were collected in order to increase the accuracy of our dating calculations.

In the sampling sites of DB2 to DB5, like major parts of the study area, Quaternary alluvial fans have been fed from rock units in the north of the fault. The geomorphology and lithology of alluvial fans in the sampling areas show that their forming particles have mainly derived from the surrounding outcrops of the Jurassic sedimentary rocks which contain pure quartz veinlets. In all 4 sampling sites (DB2-DB5) we used these quartz fragments for CRE dating and determining the abandonment age of Quaternary alluvial fans displaced by the Dasht-e Bayaz fault.

As the quartz fragments are mainly pebble sized, the majority of the samples were collected as amalgamated and only some individual cobbles were found for sampling. In the amalgamated samples, the thickness did not exceed 3 cm and in the case of cobble sized samples, we picked up an individual piece of quartz or a cobble sized rock fragment including quartz minerals. Avoiding broken and eventually rooted rocks, we took care to

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CHAPTER III collect well-embedded pebbles and/or cobbles to ensure their long-term stability. During the sampling we preferred relatively flat and more preserved areas at the top of the fan surfaces and we avoided the slops, the edge of the fans and eroded areas, as far as possible.

The morphology of the fans and lithological evidences show that the watersheds, recognised as the source of the sampled alluvial fans, are short and that the forming clasts have neither been carried over long distances nor for a long time. Therefore, we considered that the inheritance of in situ-produced 10Be during the transportation from sources to the first generation of alluvial fans is negligible.

The quartz-rich samples were prepared for AMS 10Be measurements following chemical procedures adapted from Brown et al. (1991) and Merchel and Herpers (1999). All 10Be concentrations are normalized to 10Be/9Be SRM 4325 NIST reference material

-11 10 6 with an assigned value of (2.79 ± 0.03) ×10 . The Be half-life of (1.39 ± 0.01) × 10 years used is that recently recommended by Korschinek et al. (2010) and Chmeleff et al. (2010) according to their two independent measurements. Two chemical blanks, prepared with the samples, yield a 10Be/9Be ratio of (4.98 ± 16.2) × 10-15 and (1.85 ± ?.?) ×10-15. In order to determine production rates, scaling factors for latitude and altitude corrections were calculated according to Stone (2000), using a modern 10Be spallation production rate at sea level and a high latitude of 4.5 ± 0.3 atoms/g-SiO2/yr, in order to account for the reevaluation of the absolute calibration of 10Be AMS standards proposed by Nishiizumi et al. (2007). For all sampling sites, shielding effects created by the surrounding topography, snow cover and sample geometry, following Dunne et al. (1999), have negligible impact on the surface production rates. The in situ-produced 10Be concentrations accompanied by two sets of ages are calculated assuming no denudation and the denudation rate of 1 m/Ma obtained in this study (see 4.4.1) and presented in the Tables 1-4.

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4.4 Cosmogenic 10Be results

4.4.1. Estimation of inheritance and denudation rates

Surface samples are collected to be analyzed by the CRE method and the obtained ages will finally be considered as the abandonment age of the alluvial surface. This age will later be used in order to determine the slip-rates of the fault. Meanwhile, there are two crucial points to be considered in the application of the surface CRE ages in the mentioned process. First, the amount of inheritance is important as clasts may have a pre-depositional history of exposure before their deposition in alluvial fans. It is clear that the presence of inherited nuclide concentrations will yield ages older than the true age. On the other hand, the lowering of the original surface, caused mainly as a result of erosion (denudation), decreases the total concentration of cosmogenic nuclides in clasts exposed at the surface. This leads to the obtainment of CRE ages younger than the true ages of the surface abandonment. For these reasons, depth profile sampling and modelling is used to estimate a probable inheritance and denudation rate (e.g., Anderson et al., 1996; Siame et al., 2004; Braucher et al., 2009; Le Dortz et al., 2009, 2011 and 2012; Oskin et al., 2008; Hidy et al., 2010). The rate of erosion/aggradation and the amount of inheritance are two determinant factors in the shape of the curve of the diagram of concentration versus depth. For testing and minimising the difference between the measured and modelled concentrations a Chi- square inversion has been developed, based-on the difference between generated depth profiles for the given and ideal quadruplet (time–denudation–density and inheritance by Siame et al. (2004) and Braucher et al. (2009). Although the model can help one to provide a unique solution for the quadruplet, it will always be necessary for the user to consider the geological evidence to evaluate the model’s output (Braucher et al., 2009).

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A critical assumption of the depth profile method is that nuclide inheritance is uniform throughout the profile (Philips et al., 1998). In addition, since the data normally includes uncertainties and because landforms were subjected to post-depositional processes (bio- cryoturbation, compaction, etc.), the natural data never exactly fits the model (e.g., Siame et al., 2004). Therefore, curves which are fitted to these data could show some difference from the ideal shape of profiles and hence best fitting curve technics are used (e.g., Siame et al., 2004; Braucher et al., 2009).

Fig 3. An outcrop of siliceous veinlets in the volcanic host rock in the catchment of Quaternary fans in the Northern parts of the Dasht-e Bayaz fault trace. These quartz veinlets have been dispersed mainly as pebble-sized, rarely as cobble-sized and never as boulder-sized fragments throughout the Quaternary alluvial fans of the region. These quartz fragments are well distributed, distinguishable and easy to sample within all the Quaternary surfaces that have been formed in the north of the Nimboluk plain.

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We used a depth profile in order to obtain quantitative information concerning the inheritance and denudation rates in the studied alluvial surfaces. In order to calculate a maximum erosion rate, we dug a pit and collected eight depth samples in a Qt2 alluvial surface near the Dasht-e Bayaz fault. The distribution diagram of cosmogenic 10Be concentrations versus depth with their uncertainties are shown in Fig. 3. The best-fitting curves (Braucher et al., 2009 model) based on a 2.5 g/cm3 density of Quartz fragments and 10Be concentrations of samples yielded a 1 m/Ma denudation rate (Fig. 4).

Fig. 4. 10Be concentrations vs. depth (expressed as depth g/cm2) considering the 2.5 g/cm3 density of the approximately pure quartz pebbles. The Error bars represent the concentration and depth uncertainties. The brown curve corresponds to the best-fitting model according to the 1σ confidence zone and reveals a 1m/Ma denudation rate.

Our soil pit had a maximum depth of 1.65 meters and three of the eight samples that had been taken from deeper parts of the pit were ignored during the preparation process and were not analysed because of the lack of Sio2. Therefore, we are not able to quantify the inheritance in the Qt2 alluvial fan based-on the profile. On the other hand, a well-known source of quartz fragments (Fig. 3) and its adjacency with the studied Quaternary surfaces,

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CHAPTER III suggest that the Quartz fragments have not undergone a complex and long transport history. Moreover, the 2,930 years exposure ages measured in one of the samples (sample No. F18, Table 4) collected from the Qt5 alluvial surface confirm that there is an insignificant pre- depositional inheritance in the Quartz fragments dispersed on the Quaternary alluvial fans around the study area.

Our denudation rate estimation (1 m/Ma) is very close to the mean rate of 1.4 m/Ma reported in a similar hyper-arid climatic and strike-slip tectonic regime in Central Iran (Le Dortz et al., 2011). These rates are also in close agreement with the <1 m/Ma denudation rates determined for the Sahara-Arabia Deserts (Matmon et al., 2009).

Table 1. 10Be Exposure Dating: 10Be Concentrations and Model Ages in the DB2 site. Age (Zero Erosion) Age (1m/Ma) Longitude Latitude Elevation 10 Sample Surface Be (Atom/gSiO2) (°E) (°N) (m) Age (ka) Uncert. ± Age (ka) Uncert. ± F4 58.93153 34.04673 1524 Qt2 2,196,335 ± 66945 141,468 4,468 166,515 5,075 F5 58.93161 34.04651 1525 Qt2 2,213,178 ± 54579 142,475 3,642 167,897 4,140 F6 58.93107 34.04655 1527 Qt2 1,976,469 ± 59644 126,536 3,942 146,481 4,420 F24 58.93123 34.04765 1534 Qt2 2,331,158 ± 163722 149,255 10,883 177,300 12,452 F33 58.92848 34.04492 1518 Qt2 2,013,852 ± 59974 129,965 3,999 150,940 4,495 F53 58.931056 34.04731 1518 Qt2 2,129,721 ± 49033 140,385 3,232 160,384 3,693 F32 58.93145 34.04807 1528 Qt2 1,189,572 ± 41695 75,098 2,682 82,411 2,889 F3 58.93215 34.04493 1519 Qt2 1,566,459 ± 43658 100,270 2,866 112,843 3,145 F1 58.9329 34.04488 1519 Qt2 1,595,127 ± 48641 102,152 3,196 115,186 3,512 F2 58.93247 34.04487 1518 Qt2 1,663,265 ± 50719 106,721 3,343 120,913 3,687 F34 58.92735 34.04444 1517 Qt3 1,607,650 ± 44161 103,147 2,908 116,344 3,196 F30 58.93131 34.04814 1516 Qt3 2,021,619 ± 52008 130,694 3,474 151,950 3,909 F29 58.92865 34.04428 1520 Qt3 1,539,406 ± 47683 98,417 3,125 110,546 3,424 In situ-produced 10Be concentrations and uncertainty, sample locations, calculated ages of the samples accompanied by the age uncertainties (Uncert. ±). The modelled ages calculated based on a zero denudation rate and the 1m/Ma denudation rate obtained in this study.

4.4.2. 10Be cosmogenic dating results and timing of abandonment of Qt2 surfaces

In order to date the abandonment age in the DB2 site, we collected 10 samples from the Qt2 surfaces exposed at both sides of the fault and 3 samples from a Qt3 surface at its western proximity (Fig. 5). All the samples were analysed by the 10Be method and consequently the age modelling has been done while applying the geologic and

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CHAPTER III geomorphological considerations of the studied fan and the surrounding area (Table 1). The measured cumulative offset, the location of the samples, the field image of the site and finally the diagram showing the 10Be dating results and model have been presented in Fig.9.

In the Qt2 surface, sample No. 32 is visually rejected as outlier. As seen in the Fig. 6, on the Qt2 surface two populations of ages are observed in the diagram. Considering the general slope of the fan and the higher amount of erosion in the southern parts of the fault trace, we did not include samples no. F1, F2 and F3 in the age calculations. Accordingly, based-on 6 samples taken from northern part of the fault trace, and considering a conservative uncertainty of (2σ) and a denudation rate of 1m/Ma, we calculated an average age of 159.0 ± 5.0 ka for Qt2 surface.

Fig. 5. Morphotectonic reconstruction and CRE dating in order to determine the abandonment age of the Qt2 alluvial surface, offset by the Dasht-e Bayaz fault. A. SPOT imagery of the DB2 site, morpho-tectonic interpretations, cumulative offset, sample locations and obtained exposure ages for each sample. B. Field image, showing the Qt3 surface inset by the Qt2 alluvial fan in the south of the Dasht-e Bayaz fault trace, confirms the possibility of the re-deposition of the previously exposed samples in this area.

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In Figs. 9a and 9b the location of samples F29, F30 and F34 are shown. The ages and location of those samples in the downstream of the Qt2 surface suggest that they have been re-deposited from the Qt2 alluvial surface. As discussed, two populations of exposure ages have been measured in the Qt2 surface. The obtained ages of samples collected in the Qt3 surface indicates that the sample F30, inherited from the older generation of quartz grains populated in the north of fault trace, whereas the samples F29 and F34 have been re- deposited from quartz grains previously exposed in the southern part of the fault trace (see section 6.1 for more detailed explanations).

Fig. 6. Age modelling according to in-situ 10Be concentrations that have been measured in the DB2 site. Sample no. F32 (in grey) has been rejected as outlier. The blue dashed line and the coloured area represent the average exposure age and 2σ uncertainty, respectively. The grey vertical dashed line separates the samples that have been taken from the north of the fault trace from the three samples that have been collected from the south of the fault trace. (See text). The three samples collected from the Qt3 surface, properly confirm the re-deposition of the two categories of samples, previously exposed on the Qt2 surface.

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4.4.3. 10Be cosmogenic dating results and timing of abandonment in Qt3 surfaces

We found a very well-preserved Qt3 fan surface in site DB3. We collected 8 quartz samples from Qt3 surfaces at both sides of the fault (Fig. 7). Four boulder samples with sizes between 8×10×6 and 20×10×8 cm were collected from the Qt3 alluvial fan in the north of the fault. This Qt3 surface was, in the southern parts of the fault, sampled as four amalgam samples including pure quartz pebbles. The sample locations, the field photograph of the Qt3 surface in site DB3 and the age model are presented in Fig.7.

The Sample No. F14 was visually excluded because of a notable difference in exposure age with the other samples. The samples No. F16 and F17 also did not participated in the age modeling as they had exposure ages slightly lower than the other five samples that have been placed statistically in an acceptable range between 83.4 ± 2.6 and 96.4 ± 2.9 ka (Fig. 7D). As a consequence, considering a conservative uncertainty of (2σ) and a denudation rate of 1m/Ma an average age of 88.6 ± 3.7 ka is assigned to the Qt3 alluvial fan in the site DB3.

Table 2. 10Be Exposure Dating: 10Be Concentrations and Model Ages in the DB3 site

Age (Zero Erosion) Age (1m/Ma) Longitude Latitude Elevation Sample Surface 10 Be (Atom/gSiO ) (°E) (°N) (m) 2 Age (ka) Uncert. ± Age (ka) Uncert. ± F15 58.9793 34.04267 1534 Qt3 1285397 ± 40007 80,889 2,569 89,301 2,779 F28 58.9796 34.04042 1520 Qt3 1195511 ± 36669 75,978 2,375 83,449 2,560 F55 58.97926 34.04053 1512 Qt3 1247853 ± 34871 79,887 2,278 88,047 2,460 F56 58.97936 34.03995 1524 Qt3 1352997 ± 42178 85,926 2,737 95,318 2,971 F57 58.97891 34.03929 1514 Qt3 1356247 ± 40919 86,838 2,678 96,353 2,907 F14 58.97942 34.04295 1534 Qt3 622145 ± 37225 38,743 2,341 41,081 2,458 F16 58.97831 34.04222 1529 Qt3 942018 ± 32753 59,196 2,089 63,976 2,224 F17 58.97911 34.04244 1536 Qt3 1033065 ± 35811 64,646 2,278 70,243 2,435 In situ-produced 10Be concentrations and uncertainty, sample locations, calculated ages of the samples accompanied by the age uncertainties (Uncert. ±). The modelled ages calculated based on a zero denudation rate and the 1m/Ma denudation rate obtained in this study.

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Fig. 7. Morphotectonic reconstruction and CRE dating in order to determine the abandonment age of the Qt3 alluvial surface, offset by the Dasht-e Bayaz fault. A. SPOT imagery of the DB3 site, morpho-tectonic interpretations, cumulative offset, sample locations and obtained exposure ages for each sample. B. A field image showing the Qt3 fan surfaces in the south of the Dasht-e Bayaz fault trace and around the location of sample no. F55. C. A Google maps 3D satellite image of the DB3 site after the reconstruction and the effectuation of a 67 ± 5 m displacement. D. Age modelling according to the in-situ 10Be concentrations that have been measured in the DB3 site. Samples no. F14, F16 and F17 (in grey) have been rejected as outlier. The samples numbered in black have been included in the age modelling. The blue dashed line and the coloured area represent the average age and 2σ uncertainty, respectively.

4.4.4. Surface 10Be cosmogenic dating results and timing of abandonment in Qt4 surface

Farther west from site DB3, we selected site DB4 for Cosmo-nuclide dating because of the presence of a well-preserved Qt4 alluvial fan surface which has been displaced by the Dasht-e Bayaz fault. Our geomorphic offset reconstruction of this 4th generation of

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Quaternary alluvial fan shows a cumulative offset of 20 ± 3 meters after its abandonment. We tried to obtain the abandonment age of this fan by means of relatively dense sampling and measurement of 10Be concentrations in quartz fragments, calculation of exposure age following geological and geomorphological interpretations.

Table 3. 10Be Exposure Dating: 10Be Concentrations and Model Ages in the DB4 site Age (Zero Erosion) Age (1m/Ma) Longitude Latitude Elevation 10 Sample Surface Be (Atom/gSiO2) (°E) (°N) (m) Age (ka) Uncert. ± Age (ka) Uncert. ± F7 58.9734 34.0415 1524 Qt4 365606 ± 11147 22,859 701 23,888 728 F11 58.97403 34.04125 1525 Qt4 263769 ± 8841 16,452 554 17,096 573 F12 58.97403 34.04125 1525 Qt4 329323 ± 16053 20,562 1,007 21,444 1,045 F13 58.97386 34.04101 1523 Qt4 287551 ± 8901 17,971 559 18,698 579 F8 58.97297 34.04149 1521 Qt4 487304 ± 15241 30,599 964 32,198 1,007 F46 58.970334 34.04258 1516 Qt4 461479 ± 15724 29,082 998 30,532 1,040 F47 58.970603 34.04330 1519 Qt4 498597 ± 16358 31,390 1,038 33,032 1,084 F48 58.973778 34.04252 1529 Qt4 466182 ± 14844 29,077 933 30,557 973 F49 58.973586 34.04226 1532 Qt4 390616 ± 12237 24,277 765 25,399 796 F50 58.973175 34.04197 1531 Qt4 443183 ± 13448 27,588 843 28,950 878 F9 58.97297 34.04149 1521 Qt4 1297146 ± 40233 82,510 2,613 91,212 2,829 F25 58.97074 34.04407 1528 Qt4 1193842 ± 31921 75,387 2,054 82,761 2,213 F26 58.97136 34.04445 1528 Qt4 1273882 ± 39310 80,543 2,536 88,875 2,743 F27 58.97161 34.04402 1529 Qt4 1295538 ± 42237 81,875 2,725 90,466 2,949 F54 58.97285 34.04119 1522 Qt4 1266000 ± 35056 80,423 2,272 88,689 2,456 F31 58.97141 34.04061 1524 Qt4 1390347 ± 35733 90,981 2,338 98,758 2,538 F10 58.97398 34.04126 1524 Qt4 1927343 ± 59515 123,553 3,935 142,583 4,403 F52 58.971129 34.04109 1516 Qt5 424284 ± 13806 26,722 875 28,009 911 F51 58.971827 34.04214 1530 Qt5 410454 ± 12721 25,559 797 26,774 830 In situ-produced 10Be concentrations and uncertainty, sample locations, calculated ages of the samples accompanied by the age uncertainties (Uncert. ±). The modelled ages calculated based on a zero denudation rate and the 1m/Ma denudation rate obtained in this study.

In the site DB4 we collected 16 samples from a Qt4 surface and 3 samples from a Qt5 surface which is inset in the former. The exposure ages were calculated considering 0 and 1m/Ma (see 4.4.1) of denudation rates (Table 3). The obtained exposure ages of the quartz samples are graphically presented in Fig. 8 (taking into account 1m/Ma of denudation rate). The sample F10 shows a great difference from the other samples and is considered as outlier. Considering the other samples (Fig. 8D), two age populations are clearly distinguishable in the graph. It is obvious that the obtainment of two exposure ages from one alluvial fan presenting such a difference is not reasonable. The age classification of the

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CHAPTER III calculated exposure ages shows an older generation range between 82.8 ± 2.2 and 91.2 ± 2.8 ka whereas, the younger generation shows a range between 17.1 ± 0.6 and 33.0 ± 1.1 ka. Considering the geomorphic setting of the alluvial surfaces, the sampled Qt4 alluvial fan in site DB4 should have an abandonment age remarkably younger than that of the Qt3 surface. Meanwhile, the age modeling in the site DB4 shows that the average age of the older cluster of exposure ages in the Qt4 surface is equal to 87.8 ± 2.3 ka, which is very close to the abandonment age of 88.6 ± 3.7 ka for the Qt3 surface in site DB3 (see 4.4.3). Considering that Qt4 is inset by the Qt3 surface, the most likely scenario is the re- deposition of the clasts previously exposed on the Qt3 surface, in the Qt4 fan. Accordingly, the older age cluster (87.8±2.3 ka) concerns the clasts that have been removed from the Qt3 surface and re-deposited later on in the younger lower fan. Therefore, the exposure age of these re-deposited samples has not been used in the final age modeling of the Qt4 fan surface.

After removing the older age population, the resting 10 samples show a slight scattered pattern with a range of ages from 17.1 ± 0.6 and 33.0 ± 1.1 ka (Fig. 8D). One of the issues that should be discussed concerns the reason for the scattered nature of the younger cluster; the other important issue is the finding of a practical solution to the narrowing of the age range which will enable the obtainment of a more acceptable age modeling from a statistical point of view. While resolving the first issue, our observations show that this phenomenon is related to proximity and later surficial mixing of both generations of pre- exposed and no pre-exposed generations of quartz fragments. In fact, the key point is that in some parts on the Qt4 alluvial fan, the re-deposited quartz fragments have been placed beside the other clasts with a simple transport/deposition history. The subsequent fragmentation of these clasts with different depositional histories has produced a heterogeneous clast pavement including fragments with different exposure histories. Most

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CHAPTER III of our samples were unavoidably collected as amalgamated quartz pebbles and are thus sensitive to such a complex exposure history. In other words and according to our presumed scenario we call it in this paper “fragment contamination scenario”, the 10Be content of some of our amalgamated samples is proportionally increased depending on the amount of pre-exposed fragments included in this sample.

In order to examine this presumed scenario, in the second phase of sampling we tried to find and analyze individual cobbles in the proximity of amalgamated samples. The comparison between their ages, was expected to help us to attain a better understanding of the exposure history of the clasts on this alluvial surface. In two points we could collect both individual cobbles besides the amalgamated quartz samples. The CRE ages of 3 samples collected from the Qt4 surface (58.97403 E, 34.04125 N) amazingly confirm the proposed fragment contamination scenario. Two cobble samples F10 and F11 yielded the exposure ages of 142.6 ± 4.4 ka (10Be 1,927,343 ± 59,515 atom/g) and 17.1 ± 0.6 ka (10Be 263,769 ± 8,841 atom/g) respectively, while the amalgamated sample of F12 gives an exposure age of 21.4 ± 1.0 ka (10Be 329323 ± 16053 atom/g). The 10Be ages of these samples prove that an amalgamated sample collected in proximity of the pre-exposed clasts would show an exposure age slightly older than the true age of surface exposure, as a result of the increase in the 10Be concentrations, due to the partial mixing of the two generations of clasts. – This reasoning is valid if the cobble age (F11) being younger than the amalgamated (F12); otherwise is confusing!

The samples F8 (amalgamated) and F9 (quartz cobble), collected in the same location, yield 32.2 ± 1.0 and 91.2 ± 2.8 ka exposure ages, respectively. According to the abovementioned fragment contamination scenario, the exposure age of the F8 amalgamated sample has increased because it partially contained fragments separated from the initial F9 quartz cobble.

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Fig. 8. Morphotectonic reconstruction and CRE dating in order to determine the abandonment age of the Qt4 alluvial surface, offset by the Dasht-e Bayaz fault. A. SPOT imagery of the DB4 site, morpho-tectonic interpretations, cumulative offset, sample locations and obtained exposure ages for each sample. B. A Google maps 3D satellite image of the DB4 site after reconstruction and the effectuation of a 20 ± 3 m displacement. C. A field image showing the Qt4 fan surfaces in the south of the Dasht-e Bayaz fault trace. D. Age modelling according to in-situ 10Be concentrations that have been measured in the DB4 site. Sample no. F10 (in grey) has been rejected as outlier. The samples numbered in blue are samples collected from the Qt3 surface in the DB3 site. The green coloured numbers, represent the quartz fragments previously pre-exposed on the Qt3 surface and transferred later on to the Qt4 alluvial surface. This phenomenon is logically possible as the Qt4 surface is inset by the Qt3 alluvial surface in the DB4 site. The samples in violet involve the samples that basically belong to the Qt4 surface however, their 10Be concentrations and CRE ages have slightly increased as a result of their partial mixing with the quartz samples previously pre-exposed on the Qt3 alluvial fan (fragment contamination scenario, see text). The samples numbered in red have been involved in the age modelling, the dashed blue line and the coloured area represent the average exposure age and 2σ uncertainty, respectively. The numbers in black represent the samples that have been collected from the Qt5 surface in the

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DB4 site. As the Qt5 surface is inset by the Qt3 and Qt4 surfaces, sample no. F31 can be re- deposited directly from the Qt3 surface or indirectly after a certain amount of re-exposition time on the Qt4 surface. Sample no. F51 and F52, collected from quartz fragments, have been reworked from the Qt4 alluvial surface and have been re-deposited on the Qt5 surface.

This kind of surficial fragment contamination happens when the clasts of both pebble generations are placed in close proximity or pre-exposed pebbles settle in upstream and those fragments are transported downstream under the influence of gravity or seasonal floods mixing with clasts originally deposited on the fan surface. For instance, the samples F46 and F47, placed downhill from the pre-exposed F25, show the signature of 10Be concentrations inherited from upstream older clasts such as F25 (See Fig. 8D) .

In order to resolve the second issue discussed above aiming to narrow the age range, we consider the individual cobble sample F7 (CRE age of 23.9 ± 0.7 ka) as the oldest sample not contaminated by quartz fragments of pre-exposed history, while the youngest exposure age of 17.1 ± 0.6 belongs to the cobble sample F11. Considering the mentioned interpretation, we used the F7 and F11 border determining samples, accompanied by the F12 and F13 samples whose exposure ages are placed in between, in order to obtain the modeled age of the Qt4 alluvial fan.

Finally considering the above interpretations, we removed the sample F10 as outlier, the samples F9, F25, F26, F27 and F54 based re-deposition scenario and the samples F8, F46, F47, F48, F49 and F50 according to fragment contamination scenario and by participating the samples F7, F11, F12 and F13 in the age modeling, we obtained the abandonment age of 19.5 ± 0.7 ka for the Qt4 alluvial surface in the site DB4.

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4.4.5. Surface 10Be cosmogenic dating results and timing of abandonment in Qt5 surface

The Qt5 unit corresponds to the youngest abandonment surface comprising relatively flat alluvial fan surfaces that have not been deeply incised by streams. This generation of alluvial surfaces is inset in older Qt4 and/or Qt3 geomorphic surfaces. The particular geomorphic setting of the Qt5 surfaces worsens the problem of inheritance because the main portion of the fans were fed by alluviums reworked from older upstream alluvial fans. This problem has precluded us from determining the age of abandonment of this series of surfaces. In the two sites of DB4 and DB5 we collected quartz samples from Qt5 surface.

Table 4. 10Be Exposure Dating: 10Be Concentrations and Model Ages in the DB5 site

Longitude Latitude Elevation 10 Be Age (Zero Erosion) Age (1m/Ma) Sample Surface (°E) (°N) (m) (Atom/gSiO2) Age (ka) Uncert. ± Age (ka) Uncert. ± F19 58.99377 34.04061 1538 Qt5 65598 ± 8430 4,037 519 4,151 533 F20 58.99284 34.04143 1544 Qt5 68496 ± 4731 4,195 290 4,315 298 F23 58.99275 34.0416 1538 Qt5 64886 ± 2449 3,993 151 4,106 155 F38 58.99371 34.04427 1541 Qt5 72244 ± 3336 4,435 205 4,562 211 F18 58.99376 34.04063 1539 Qt5 47118 ± 1469 2,896 90 2,903 91 F21 58.99281 34.04134 1537 Qt5 250839 ± 13037 15,492 808 16,089 836 F36 58.99347 34.04415 1549 Qt5 210942± 7432 12,896 456 13,359 471 F22 58.99271 34.04171 1538 Qt5 148155 ± 5377 9,128 332 9,428 342 F37 58.99362 34.04422 1541 Qt5 157239 ± 4938 9,666 304 9,988 314 F40 58.99376 34.04443 1541 Qt5 146909 ± 4622 9,030 285 9,321 293 F43 58.99380 34.04107 1526 Qt5 122093 ± 3895 7,591 243 7,824 250 F35 58.99346 34.04409 1551 Qt5 128302 ± 4773 7,822 292 8,068 300 F44 58.99382 34.04090 1529 Qt5 112028 ± 4582 6,948 285 7,158 293 F41 58.99387 34.0446 1550 Qt5 110374 ± 4055 6,732 248 6,939 255 F39 58.99379 34.04438 1542 Qt5 95488 ± 4424 5,860 272 6,035 280 F42 58.99372 34.04437 1544 Qt5 89028 ± 3764 5,454 231 5,615 237 F45 58.99383 34.04084 1527 Qt5 89075 ± 5642 5,534 351 5,691 360 In situ-produced 10Be concentrations and uncertainty, sample locations, calculated ages of the samples accompanied by the age uncertainties (Uncert. ±). The modelled ages calculated based on a zero denudation rate and the 1m/Ma denudation rate obtained in this study.

In the DB4 site, the three samples (F31, F51 and F52) collected from a Qt5 alluvial surface reveal the CRE ages of 95.7 ± 2.7, 26.1 ± 0.8 and 27.3 ± 0.9 ka, respectively (Fig. 8, Table 3). Considering that the Qt5 fan is inset in the older Qt3 and Qt4 alluvial fans, the re-deposition of pre-exposed samples is the most plausible cause for this age dispersion.

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The exposure ages of samples F51 and F52 are close to the abandonment age of the Qt4 surface, while the exposure age of F51 sample is close to the average age of the samples collected from the Qt3 surface. This similarity in ages of samples with different geomorphic settings indicate that these samples were reworked from the Qt3 and Qt4 surfaces to their present position on Qt3 due to the erosion of materials from the uphill alluvial fans.

Fig. 9. A. SPOT imagery of the DB5 site, sample locations and obtained exposure ages for each sample. This surface has not been deeply incised and thus the cumulative offset in this surface could not be measured. The CRE ages measured on this surface show a scattered pattern therefore they prevent us from assigning a reasonable abandonment age to the Qt5 alluvial surface placed in the DB5 site. The yellow arrows show the probable way of the arrival of pre-exposed quartz samples (e.g. because of seasonal floods) responsible for the scattered pattern of CRE ages measured on the Qt5 alluvial surface. A field image showing the Qt5 fan surfaces in the south of the Dasht-e Bayaz fault trace.

In the site DB5, we collected 17 samples in two separated area all on the youngest alluvial surface of Qt5 (Fig. 9). The CRE analysis of these samples show a scattered pattern, ranging from 3.0 ± 0.1 to 16.1 ± 0.8 ka (Fig. 10; Table 4). Our observations do not show an immediate inset of Qt5 alluvial surface by the older alluvial fans, meanwhile it seems that location of Qt5 surfaces in the site DB5 and its probable affection by the transporting

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CHAPTER III materials of drainages during the seasonal floods has been main factor of this scattered pattern of exposure ages in quartz pebbles. In the other words as these fans located in the proximity of main drainages, they could be affected by seasonal floods of two existing drainages in this site. For this reason, they involve various generations of quartz fragments some of them such as samples no. F18 and F19 belong to the Qt5 fragments have been exposed recently and some others such as samples no. F21 and F36, have a more complex exposure history and come from upper parts, have been previously exposed in an older quaternary surface. If accepting this interpretation, the Qt5 alluvial fan in the site DB5, contain quartz fragments with different history of exposure, coming from upper parts of the catchment basin. Regardless of the reason of this phenomenon, we could not find any acceptable criteria for narrowing the age range by means of rejecting and excluding the outliers and/or pre-exposed samples.

Fig 10. Diagram showing CRE exposure ages that have been measured through the samples collected from the DB5 site. As the ages and their uncertainties are highly scattered and we were unable to find a reasonable criteria for the rejection of the irrelevant samples and the narrowing of the age range of the selected samples, we were unable to attribute an abandonment age to the Qt5 surface. 157

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5. Quaternary slip-rate of the Dasht-e Bayaz fault

Both coseismic and cumulative displacements along faults are not constant and may significantly vary along the strike. Meanwhile, the rate of slip is a time-depended quantitative criterion permitting one to describe how active a fault is. Geological slip rates are averaged over relatively long periods of time (several thousand to millions of years) and, if reasonably determined, are more representative than short-term geodetic slip rates. An accurate estimation of a slip rate along a fault requires the characterization of the displacement pattern and the spatial variation of the cumulative slip in order to determine the pattern of slip along the fault strike; so that a single slip rate determined at one point is not representative of the global behavior of the fault. In the absence of suitable geomorphic features offset by the fault, individual slip rates determined far from the fault terminations can be considered as the average slip rate of the fault. In this study, datable geomorphic features are localized along the central portion of the western Dasht-e Bayaz fault. Because of this condition, the determined slip rates are considered as the average slip rate along the Dasht-e Bayaz fault.

Fig. 11. Calculated slip rates in the Qt2, Qt3 and Qt4 alluvial surfaces and the most probable amount of slip rate along the Dasht-e Bayaz fault.

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We are aware that both the cumulative displacement and the absolute age involve uncertainties and therefore the calculated slip rate vitiate in a domain depending on the amount of the mentioned uncertainties. In order to calculate individual maximum slip rates, we divided the maximum cumulative offsets by minimum exposure ages assigned to offset markers. Accordingly, we calculated independent slip rates of 1.1 ± 0.2 mm/yr, 0.8 ± 0.1 mm/yr and 1.1 ± 0.3 mm/yr for Qt2, Qt3 and Qt4 alluvial surfaces, respectively (Fig. 11). These amounts of slip rates are independently determined from fault offsets with different ages and show a narrow range of variation in the past 155 ka. Considering this consistency, the average slip rate of 0.9 ± 0.14 mm/yr is determined along the western Dasht-e Bayaz fault since at least 159 ka ago (Fig. 11).

6. Discussion

6.1. Erosion versus inheritance and their influences on CRE ages of alluvial fans

The ideal case when the distribution of the ages is like a narrow Gaussian curve which statistically gives us a most probable age close to the true age of the surface abandonment with its associated uncertainty. But, in some cases, especially when surface denudation and inheritance play their roles, the age results are not often homogenous and hence they need to be modelled. The most usual complexity rises when large discrepancies in the cosmogenic nuclide concentrations is observed in the samples were collected on the same surface. The distribution of ages could appear as multimodal clusters or in the more complicated state, scattered ages without any meaningful clustering. The complexities in the cosmogenic exposure ages have been reported by Ward et al. (2005), Philips et al. (1998), Matmon et al. (2005), Van der Woerd et al. (2006), Behr et al. (2010), Le Béon et al. (2010), Schmidt et al. (2011), Le Dortz et al. (2009/2012), Farbod et al. (2016). Age modelling often requires defining cluster borders and rejecting the outliers. The definition

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CHAPTER III of age clusters and the rejection of outliers are done during age modelling are often controversial, especially when the sample distribution, which may, or may not, appear Gaussian (Le Béon et al., 2010). Typically, outliers are excluded visually (e.g., Van der Woerd et al., 1998; Le Béon et al., 2010) or by using Chauvenet’s criterion (Mériaux et al., 2004/2009) (see Le Béon et al., 2010 and references therein for detail). Matmon et al. (2005) during the offset and slip-rate studies of San Andreas fault, California by cosmogenic 10Be and 26Al method, observed the exposed boulders yielded ages ranging from 16 to 413 ka. Although fan age determinations are accompanied by large uncertainties, they explained a clear trend of increasing fan ages with increasing distance from their source at the mouth of Little Rock Creek. Finally, they concluded that after deposition in the fans, surface processes such as boulder erosion, fan surface lowering, and soil development operate, and each boulder acquires a unique exposure history. Thus, the complex environment results in large uncertainties in boulder erosion rate and boulder cosmogenic nuclide inheritance. Together with the large uncertainties associated with exposure and burial age dating, fan age determinations are sometimes accompanied by large uncertainties (Matmon et al., 2005).

It should be noted that although the statistical analysis helps us to analyze the dating results, it will not solve by itself the problems. As explained by Matmon et al. (2005) each sample can have a unique exposure history and for finding the most appropriate age is attributed to an alluvial surface, various scenarios should be considered in order to decrease large uncertainties and approaching to the true age of abandonment of alluvial surfaces. For interpreting age populations, however, it is critical to understand field geomorphology of sampling sites, climatic conditions, and surface processes in order to interpret cosmogenic nuclide concentrations in a meaningful way” (see Matmon et al., 2005 for detail).

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A typical bimodal pattern of CRE ages distribution has been observed by Farbod et al. (2016) along the Doruneh fault at the northern margin of the Lut block, north of the Dasht-e Bayaz fault. They took advantage of inset scenario to explain the bimodal distribution of the ages of abandonment alluvial surfaces. In continue, referring to some of previous researches (e.g., Le Dortz et al., 2009/2011; Schmidt et al., 2011; Le Béon et al., 2010; Ritz et al., 2006) they showed that in the Doruneh area the inset surface pattern allowed the clasts initially exposed on upper surfaces to be detached from older alluvial fans due to stream channel incision, gravitational movements, or during occasional flooding periods and to form lower inset surfaces.

Fig. 12. SPOT imagery of two Quaternary fans in the north of the Nimboluk plain offset by the Dasht-e Bayaz fault. In the both image, major parts of the alluvial fans in the south side of the fault has been eliminated because of higher amount of erosion in compare with northern parts of the fault trace.

In this study, after a preparatory statistical screening, we excluded visually obvious outliers (the grey samples in the prepared diagrams). In site DB2, we have nearly distinct bimodal age populations while in site DB4, the age modeling is more complicated such that, for each sample, we have individually considered both field geomorphology and

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CHAPTER III deposition/exposure history. The uneven erosion of the Qt2 surface at both sides of the Dasht-e Bayaz fault has caused some complexities for the interpretation of the results of the cosmogenic ages of site DB2. Post-earthquake reports (e.g., Tchalenko and Berberian, 1975) and our field observations along the western parts of the Dasht-e Bayaz fault shows that the south part of the fault subsides progressively. This situation has removed most parts of the Quaternary fans downhill from the fault (Fig. 12) and decreased the total concentration of 10Be nuclides in quartz pebbles exposed in the downhill part of Qt2 alluvial fan due to lowering the surface (samples No. F1, F2 and F3).

The bimodal pattern of 10Be CRE ages in site DB4 can be explained in a different way. The Quaternary fan of Qt3 includes two generations of quartz clasts with different deposition/exposure histories. As for the Qt4 fan surface that is inset in older Qt3 alluvial surface, the sample CRE ages are clearly classified into two separated groups because of pre-depositional 10Be inheritance in the collected quartz pebbles. This inheritance belongs to the period of exposure the clasts experienced on the Qt3 older surface before being displaced into lower Qt4 surfaces. The complexity of this scenario is that over the time, with gradual degradation of the Qt4 fan surface, mixing of reworked and in situ clasts has leaded to partial increasing of 10Be concentration in the samples collected in site DB4. As each amalgamated quartz sample could involve a proportion of pre-exposed quartz fragments, age distribution for the younger age cluster are dispersed. We suggest that the level of age dispersions depend on the fraction of reworked clasts in amalgamated samples. Therefore, we have used the effect of both single reworked samples and contamination in amalgamated samples to select/reject the sample ages in our age modeling. For instance, in the Qt2 alluvial surface we have sampled, the geomorphic setting and erosion/deposition relationships described above suggest that the samples collected from northern side of the fault, represent sample CRE ages closer to the true age of abandonment of the surface. In

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CHAPTER III contrast, for the samples collected in the Qt4 alluvial surface, the youngest age cluster was participated in the statistics of age models avoiding the effect of contamination in amalgamated samples which included quartz fragments with complex exposure history.

6.2. Tectonic implication of results

North of 34°N, the Dasht-e Bayaz fault interrupts the N-S shear at the eastern boundary of the Lut against the Helmand block (belonging to Eurasia). In that latitude, the E-W Dasht-e Bayaz fault is almost perpendicular to the overall trend (N013°E) of active convergence (Walpersdorf et al., 2014). This particular orthogonal relation has raised up important questions concerning the geodynamic role of the Dasht-e Bayaz, Niazabad and Doruneh sinistral faults (Walker and Jackson, 2004; Farbod et al., 2011 and Baniadam et al., 2019). The most recent tectonic model proposed by Baniadam et al. (2019) explains the role of the E-W sinistral faults in the accommodation of the active convergence by two different kinematics. The Doruneh fault divides the regions of E and NE Iran into two distinct domains: (1) the northern domain which is characterized by fault-bounded blocks extruding WNW along NNW dextral and ENE sinistral faults like the western Doruneh, Farhadan and Shahrud, and (2) the southern domain in which E-W sinistral faults accommodate differential deformation caused by wedge confinement at the intersection zones between sinistral and N-S dextral faults (Baniadam et al., 2019). This model only explains the geometric relationships between the diagonal sets of sinistral and dextral faults. Meanwhile a question about the kinematic significance of the sinistral faults remains unanswered. According to this model, the Doruneh fault acts as a boundary condition between two tectonic domains and takes up its part in the WNW tectonic extrusion, while the activity of the Dasht-e Bayaz fault is only due to contractional faulting at the northern

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CHAPTER III edges of north-going blocks of eastern Iran. The different kinematic roles of these two E- W sinistral faults imply that the Dasht-e Bayaz fault slips more slowly with respect to the Doruneh fault. The study of Quaternary slip rate of the Dasht-e Bayaz fault in this study provides information necessary to evaluate the kinematic aspect of this model.

The geological slip rate of the Doruneh fault during Holocene is in the order of ~5 mm/yr (Farbod et al., 2016), while according to our study, the Dasht-e Bayaz fault should slip at ~1 mm/yr since 155 ka ago. This drastic difference in the slip rates of these two faults seems reasonable considering the different kinematic roles of these faults described in the tectonic model proposed by Baniadam et al. (2019). Interestingly, the Quaternary slip rates of these faults have been estimated using the same strategy of sampling, CRE technique and nearly the same sequence of alluvial fan surfaces. Despite these similarities in technical aspects, both the mapped geomorphic offsets and the offset/age derived slip rates are significantly different and give three important implications: (1) the geological slip rate of the Doruneh fault (Farbod et al., 2016) was not overestimated and the difference with the GPS-derived low rates of slip (Mousavi et al., 2013) have to be explained through further geodetic investigations involving more sophisticated geodetic techniques (well-designed GPS profiles or local networks, as well as long-period InSAR analysis), (2) the Dasht-e Bayaz fault does not play a major role in the accommodation of active convergence and as proposed by Baniadam et al. (2019), it takes up the differential deformation across the confining wedges at the intersection areas of the Dasht-e Bayaz fault with the N-S dextral faults of Mahyar and Abiz (Fig. 1), and (3) the different rates of deformation along the main E-W sinistral faults of Lut-Central Iran imply that strike-slip faulting in this region cannot be explained by systematic block rotations around vertical axes (e.g., Jackson and McKenzie, 1984; Walker et al., 2004). As explained by Baniadam et al. (2019), such kinds of structural rotations need systematic

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CHAPTER III rotations, with constant amounts of slip on the boundary faults of both the deformation zone and the rotating blocks.

6.3. Geological versus geodetic slip rates of the Dasht-e Bayaz fault

Recently, Walpersdorf et al. (2014) have discussed the present-day fault kinematics and slip-rates derived from eleven years of GPS measurements as well as block modeling in eastern Iran. As for the Dasht-e Bayaz fault, they used four stations around the fault and obtained an across fault extension of 1.2 ± 0.3 mm/y combined with a dextral slip of 0.2 ± 0.1 mm/y along the fault. Walpersdorf et al. (2014) have explained that the dextral sense of movement is contradictory to the unambiguous sinistral kinematics of the Dasht-e Bayaz fault.

We suggest that considering the location of GPS stations around the Dasht-e Bayaz fault, the dextral sense of movement obtained by Walpersdorf et al. (2014) can be explained by local deformation within an interacting fault network, with different kinematics. Fig. 5 shows the location of GPS stations around the Dasht-e Bayaz area. BAJE and GONA stations are located within the Ferdows thrust zone while QAEN and QAE2 stations are located in the southern side of the Dasht-e Bayaz fault. The QAEN and QAE2 stations are under the influence of the Avash left-lateral earthquake fault which is also responsible for the 7 November 1976 Mw 6.03 Vandik event (e.g., Baker, 1993; Berberian et al., 1999; Walker et al., 2004). If we ignore the relative movement of the Avash fault, the relative extensional dextral movement observed by GPS could be due to the displacement of BAJE and GONA stations towards the northeast with respect to the relatively fixed southern block of the Dasht-e Bayaz fault. It is worthy to note that such an inconsistency has been reported

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CHAPTER III by Farbod et al. (2016) between instantaneous geodetic and moderate- to long-term geologic slip rates of the Doruneh Fault System (see section 2).

6.4. Consistency of our results with previous slip-rate estimates along the Dasht-e Bayaz fault

The first attempt at estimating the slip-rate of the Dasht-e Bayaz fault has been done according to the displacement of the qanat line along the Dasht-e Bayaz fault. Ten meters of left-lateral displacement had been measured by Ambraseys and Tchalenko (1969) in the old qanat lines of the Miam village. In the absence of any absolute age and dating of the Miam qanat system, Berberian and Yeats (1999) tried to use the age of the Semnan qanats in the north of Iran, constructed in the second millennium B.C. according to the estimations of Mehryar and Kabiri (1986) based on archeological evidences. Assuming that the Miam Qanats has the same age as the Semnan qanats, Berberian and Yeats (1999) considered the age of the Miam qanats as old as 4000 years and by applying the 10-meter offset reported by Ambraseys and Tchalenko (1969), they estimated a minimum slip-rate of 2.5 mm/yr for the Dasht-e Bayaz fault.

In the first tentative for dating of Miam qanats in vicinity of Dasht-e Bayaz village, Fattahi et al. (2011) obtained two different sample ages of 15.8±1 and 22.1±2.7 ka for the time of construction of the oldest qanats of Miam, through the OSL dating method. The obtained ages were rejected by the authors because of their contradiction with the results of archeological investigations. In the next study, Fattahi (2015) analyzed two other samples by the OSL method and proposed a reconstruction time between 3.6 and 4.3 ka for the Miam qanats without discussing the slip rate. However, by replacing the construction age of the Semnan qanats that have been used by Berberian and Yeats (1999)

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CHAPTER III with the dating results of Fattahi (2015), a slip rate of 2.33-2.78 mm/yr can be found along the Dasht-e Bayaz fault.

Basically, this kind of estimation is also based on the assumption that the construction of the qanat has been done right before the previous earthquake that has been displaced it, while there is the possibility that this system of irrigation has been created long (e.g., centuries or more than a thousand of years) before the earthquake. In the other words, the qanats is normally constructed in an unknown time between two earthquake recurrence intervals that is not known. Therefore, it should pay attention to the point that the obtained slip rate in this way is not very precise because other than usual displacement/age uncertainties it always includes an uncertainty related to time of construction of qanats inside the time period between two consequent earthquakes. Aside for the age ambiguity of the Miam qanats, there is also no detail concerning the uncertainty of displacement in the report of Ambraseys and Tchalenko (1969). Interestingly, the ten-meter displacement has been cited exactly by the next researches (e.g., Berberian and Yeast, 1999; Fattahi et al., 2015) in order to calculate the slip-rate. As seen in the aerial photo of the area (e.g., Fattahi, 2015; Fig.3) the Miam qanat is a complex system comprising several qanat lines naturally with different ages of construction (and/or reconstruction) which have not been mentioned or discussed in the previous studies.

Fattahi et al. (2015) have dated two OSL samples (8.6±0.6 and 8.5±1.0 ka) of lake-bed sediments from the northern Nimboluk plain in order to determine the slip rate of Dasht-e Bayaz fault. Emphasizing on the absence of a “measurable relief” for dating and measuring the offset, they used the fault offset of 26±2 m recorded in “small streams” not incised inside a quaternary fan in the east of Khezri and estimated the minimum slip-rate of 2.6 mm/y for the Dasht-e Bayaz fault. Nevertheless, based on our field observations and the geomorphic analysis of satellite images, it seems that the age/offset relationship in the site

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CHAPTER III studied by Fattahi et al. (2015) is not as straightforward as assumed by the authors to determine the slip rate of the Dasht-e Bayaz fault.

In summary, we suggest that the Dasht-e Bayaz fault is a relatively slow slipping earthquake fault with an average slip rate of ~1 mm/yr, which has likely been constant since at least 159 ka ago.

7. Conclusion

The geomorphologic investigations in this study reveal a Quaternary succession of five alluvial fan surfaces (being younger from Q1 to Q5), with inset arrangement, all which have been cut and displaced along the Dasht-e Bayaz fault. According to the 10Be CRE ages of 52 quartz samples collected from 4 sites, the abandonment ages of Qt2, Qt3 and Qt4 Quaternary alluvial fans have been obtained as 155.6 ± 10.8, 87.7 ± 5.2 and 19.8 ± 2.9 ka, respectively. Assigning these abandonment ages to the geomorphic offsets recorded by the alluvial fans yields an average slip rate of 0.9 ± 0.14 mm/yr for the western Dasht-e Bayaz fault. This slip rate has likely been constant since at least 159 ka ago.

The significantly lower slip rate of the Dasht-e Bayaz fault with respect to the Doruneh fault, as a well-known active fault in the north of the Lut block, confirms the different geodynamic roles of these E-W sinistral faults as proposed by Baniadam et al. (2019). Despite this insignificant geodynamic role, the Dasht-e Bayaz fault is responsible for the accommodation of internal deformation in the Iranian plateau and is characterized by highlighted seismic activity. These results emphasize the seismic potential of slow slipping active faults in the interior of continental regions, with low rates of deformation.

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Acknowledgements

We would like to thank the Geological Survey of Iran, especially M. Koreie and M. Fotovati for their support and logistic assistance. We are grateful to the municipality of the Khezri-Dasht-e Bayaz town and the Sangan Iron Ore Complex for their support during the 2014-2016 field trips. We thank Mr. Lhôte and the staff of the French Embassy in Tehran. We appreciate M. Ghods and M. Sobouti working in the Institute for Advanced Studies in Basic Sciences in Zanjan.

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DISCUSSION and CONCLUSION

CHAPTER IV

This dissertation focuses on the active tectonics of the Dasht-e Bayaz Fault, NE Iran. In the first chapter, we discussed the geological setting and geodynamic framework of the area, the encountered questions and our methodology of research.

The second and third chapters involved the main body of our research and the work that we have done in the Dasht-e Bayaz area.

In this part we will conclude by answering the fundamental questions discussed in section 1.2.

4.1. The Kinematics of deformation in the Dasht-e Bayaz area

What is the present-day state of stress around the Dasht-e Bayaz fault in the northern Lut? Is the present pattern of kinematics of deformation in this part of the convergence/collision zone the same as other parts of the Iranian plateau such as Kopeh Dagh and Alborz?

The analyses of the youngest group of fault slip data, measured in ten sites including the last coseismic kinematics of the Dasht-e Bayaz fault, led us to characterize the modern state of stress dominated in the region. The average of inversions of the newest generation of fault slip data in Dasht-e Bayaz area yielded the maximum horizontal stress axis (σ1) as trend of N045±5°E. Avoiding local changes in the stress state caused by structural complexities along the fault, we separately computed the fault kinematic data measured in main fault planes (MFP) of study area in an individual solution and we obtained the amount of N042±5°E as the maximum horizontal stress axis (σ1).

There is no result of fault kinematic studies around the Dasht-e Bayaz area for comparing, however the direction of maximum horizontal stress axis of our results has a good consistency with modern stress regime reported along the Doruneh fault, with an average compression of N045°E (Farbod et al., 2011), in Kopeh Dagh and Allah Dash- 179

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Binalud mountains with an average of ~N030°E (Shabanian et al., 2010) and a regional mean ~N036°E trending horizontal σ1 axis has been averaged from the solutions obtained from a wide area of north and northeast of Iran covering eastern Alborz and western Kopeh Dagh (Javidfakhr et al., 2011).

We have used 15 focal mechanism solutions of earthquakes recorded in the Dasht-e Bayaz region and nearby areas; these focal solutions were obtained by Walker et al. (2004) using body wave modeling. Our prepared solution, resulted from the inversion of fault slip data reactivated in several earthquakes affecting the Dasht-e Bayaz area, indicates a homogenous strike-slip tectonic regime characterized by a regional N050±05°E trending σ1 as present-day state of stress. This result is in total agreement with our modern state of stress (a compression of N045±05°E, with strike-slip regime) obtained from the analysis of the youngest generation of faults slip data principally measured in Quaternary deposits. We compare our result with the results of the same method obtained in the same study area as bellow:

One of the studies performed with the method of inversion of earthquake focal mechanism, covering the area of Dasht-e-Bayaz, is Naimi-Ghassabian et al. (2015). They divided their study area in North Eastern of Iran in seven sub-regions and calculated the maximum compression of the region with the method of inversion of focal mechanism. Their calculations were done using two methods; improved Right Dihedron method and Rotational Optimization method we preferred to compare our results with the latter due to the use of similar criteria. Area No. 2 and 3.2 of this research overlap with the western and eastern part of Dasht-e Bayaz fault respectively. Based on this research the area No.2 with one degree of difference is exactly consistent with our results (N49±9°E) whereas the results in area No.3.2 indicating NE-SW direction and orientation of N28±8°E σ1 was deviated as much as 22 degrees from our calculations for all of Dasht-e Bayaz area.

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Considering that the source of the selected earthquakes was almost similar, it seems that the main reason for this difference of results in eastern parts of Dasht-e Bayaz fault is the selection of different auxiliary plains during the application of inversion of focal mechanism. In the mentioned research, other areas situated in east, north east and north of Dasht-e Bayaz area, except of one other debatable amount of N10°E in central parts of the Doruneh Fault System, calculated orientations of σ1 close to our results in a range between N33°E and N56°E.

. Is the tectonic regime change discussed above also the case for Dasht-e Bayaz area? If yes, would the mechanism and directions of the main stress be the same as in the previous studies?

In this study, the spatiotemporal changes in the state of stress were investigated through the inversion of fault slip data measured in ten sites along the Dasht-e Bayaz fault. Our inversion analysis of fault kinematics data showed three distinct states of stress in Dasht-e Bayaz area during Plio-Quaternary. The cross-cutting relationships observed in fault planes helped us to determine the chronology of the three obtained generations of states of stress.

The modern state of stress based on youngest generations of fault slip data was determined as N45±5°E trending horizontal σ1. Stress solutions show that dominant tectonic regime in most of the study area is strike-slip but in western parts changes to compressional stress regime. The older state of stress field in this area is characterized by homogenous regional N133 ±17 °E trending horizontal σ1 with a compressional tectonic regime. An N trending stress field was distinguished in this area is placed between older and modern states of stress with direction of N09±12.5°E trending horizontal σ1 we implied it intermediate state of stress. There were not halfway solutions and any evidences

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CHAPTER IV of gradual changes between three states of stress that have been responsible for deformations in Dasht-e Bayaz and around area during Plio-Quaternary.

In the section we discussed the history of tectonic regime change referring to previous studies in different parts of Iranian plateau. Here we compare our results with some of them.

In the Kopeh Dagh and Binalud mountains, the inversion of fault kinematics data measured from 39 sites revealed temporal clockwise changes in the state of stress since 3.6 Ma; those include the horizontal σ1 oriented N140±10°E, N180±10°E and N30±15°E for the paleostress, intermediate and modern states of stress, respectively (Shabanian et al., 2010). Similar drastic temporal changes were reported in NNE Iran including the eastern Alborz and western Kopeh Dagh mountains (Javidfakhr et al., 2011). The analysis of fault slip data in 48 sites lead to characterizing three homogenous stress fields with the maximum horizontal stress σ1 orientated N135±20°E (paleostress), N185±15°E intermediate) and N36±20°E (modern stress) in this transitional zone. In the north adjacency of our study area, Farbod et al. (2011) showed that a Plio-Quaternary older state of stress, with a σ1 orientated N150±20°E, was changed into a modern compression of N45±15°E responsible for the active sinistral kinematics along the Doruneh fault system. Tadayon et al. (2018) suggested that switch from this early NW-oriented σ1 to the penultimate N-S compression started at the Miocene-Pliocene boundary (5-6 Ma) and this change had been source of an important cooling/exhumation in the area. The other research approves the same pattern of changes in the stress field of northwest Iran (the Mianeh- Mahneshan basin; Aflaki et al., 2017). The NW-trending fold axes in the Upper Red Formation, folded at the end of Middle Miocene, have been superimposed by two younger generations of NE and NW trending folds in a time interval between Pliocene to Quaternary. Inversion of fault slip data in this region affirms that a compressional

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CHAPTER IV paleostress (Plio-Quaternary) with a N138°E trending horizontal σ1 has affected the area before dominance of the NE-oriented present-day compression.

4.2. Morphotectonic and structural characteristics of Dasht-e Bayaz fault, evolution, segmentation, total offset and relationships and interactions with the adjacent faults

. How is the situation of interaction of the Dasht-e Bayaz fault with adjacent faults?

Two important nodes of the Dasht-e Bayaz fault exist in the junction of this fault with NNW-striking right-lateral strike-slip faults. In the both of these junctions a systematic and typical interaction between both sides is seen. At the eastern termination, the Dasht-e Bayaz fault intersects the NNE-striking Korizan segment of the Abiz fault.

The Abiz fault is the northern end of the very long fault system that occupies the right- lateral shear between Lut block and Fixed Afghan block. The NNW-SSE trend of Northern segment of Abiz fault under the effect of conjugate intersection with eastern end of Dasht- e Bayaz changes to NNE-SSW. Three consecutive earthquakes of Korizan (14.11.1979), Koli-Boniabad (27.11.1979, e.g. Haghipour and Amidi 1980) and Kalat-e Shur (07.12.1979, e.g. Haghipour and Amidi 1980; Ambraseys and Melville, 1982) has occurred in a short period of time (23 days) in northern Abiz, eastern segment of Dasht-e Bayaz and intersection of two faults, respectively and confirm the structural interaction of mentioned faults.

As for the N-S faults, for example, Sudhaus and Jónsson (2011) during the source modeling of JERS and ERS InSAR observations on the 10 May 1997 Zirkuh earthquake (Mw 7.2) have noticed linear changes in dip and sense of fault plane and subsequently 183

CHAPTER IV linear changes in mechanism of faulting along northern parts of the Abiz fault. According to their findings, Abiz fault plane has a westerly dip along the northern parts, is nearly vertical in the center and gradually changes to an easterly tilted plane in the south; subsequently the fault mechanism changes from contractional (east-dipping reverse) in the south to almost pure strike-slip in the center and transpression (west dipping reverse dextral) in the north. In the other words, the south block of Dasht-e Bayaz fault thrusts gently over the western block of Korizan fault in the intersection area that coherent with eastward displacement of the northern termination of Korizan fault.

Our mapping of the intersection area shows a deforming wedge between the main traces of the Dasht-e Bayaz and Korizan faults; the conjugate arrangement of the main faults implies active contraction in the interior of the wedge.

Another structural node along the Dasht-e Bayaz fault occurs where it intersects with the N-S Mahyar fault. This intersection has been the border ruptures of two main earthquakes of 31 August 1968 and 27 November 1979 and has been discussed as border of western and eastern segments of the Dasht-e Bayaz fault (Berberian, 2014).

Our detailed mapping of the intersection area shows that the cross-cutting dextral Mahyar fault and the sinistral Dasht-e Bayaz fault form a typical crosswise to conjugate fault arrangement in the middle part of the Dasht-e Bayaz fault trace. These coexisting faults have displaced each other in the sense of their movement of about 1.5 km. Following the opposite shear senses of the crosswise faults, double-coupled extensional and contractional domains have been formed in the quarters of this intersection. In the NW and SE extensional quarters including two relatively lowlands, while the adjacent NE and SW contractional quarters occupy areas with higher elevations. The NE contractional quarter

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CHAPTER IV is occupied by nearly E-dipping reverse faults which join the main trace of the eastern Dasht-e Bayaz fault, southwards (Fig. 3).

Our observed and mentioned evidences show that N-S dextral faults such as Mahyar and Korizan have the same structural significance as the E-W Dasht-e Bayaz fault. The sequence of recent seismic activities, producing sinistral faulting (e.g., 1968.08.31; 1968.09.11) along both the western and eastern segments of the Dasht-e Bayaz fault and N-trending right-lateral faulting (e.g., 1997.06.25 event) in the south of this junction, confirm that this system of interaction is still active (see Berberian et al., 1999; Walker et al., 2011, and the next subject of this study).

. Does slip partitioning occur around this fault?

The1968 31 August earthquake of Dasht-e Bayaz has been considered as a trigger for reactivation of east segment of Dasht-e Bayaz fault, Ferdows thrust zone and Korizan fault that was cause of a sequence of earthquakes (e.g. the Zirkuh, Koli-Boniabad and Ferdows earthquakes). East segment of Dasht-e Bayaz fault and its southern block in SE of central conjugate system (Boznabad plain) has shocked at least 4 times. Fig. 1 shows the location of epicenters in the proximity of Dasht-e Bayaz and Boznabad faults. Three 1968.09.11, 1979.01.16 and 1997.06.25 events did not have surface rupture and could not attributed to particular faults (e.g. Berberian et al., 1999). In the Boznabad plain there was a complicated double event (Baker, 1993), the 1997.06.25 event could be considered as N-S right-lateral or E-W left-lateral strike-slip and 1979.01.16 showed NW-striking reverse faulting (Berberian et al., 1999).

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Figure 1. SPOT image and structrul map of of middle parts of Dasht-e Bayaz fault. The joint of Dasht- e Bayaz and Mahyar faults is critical point in bouth faults while they displaced each other in the sense of their movement of about 1.5 km. The Western and eastern segments of the Dasht-e Bayaz fault are separated by Mahyar right-lateral, strike-slip fault and seismic evidences confirm this segmentation (see discussion for more detail). The fault plane solutions of seismic events in this figure have been prepared by Walker et al., 2011 (See Fig. 15 of this paper anf the references therein for detail) and involving oblique reverse, right- lateral and left-lateral faultings, clearly show phenomenon of partitioning of slip between strike-slip and parallel thrust faults.

Berberian et al. (1999) during the study of aftershock sequence of the 1997 Zirkuh event from the distribution of seismic intensities and epicentral determinations, suggest that both of earthquakes probably occurred on the N–S trending faults such as the Boznabad and Pavak faults rather than on the E-W Dasht-e-Bayaz fault. Afterwards the calibrated relocations and body-wave modelling of Walker et al. (2011) showed that epicenter of the 1979.01.16 earthquake is centered on an E–W north-facing scarp that

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CHAPTER IV actually is an SW–dipping reverse fault. Considering the existence of too much N-S and E-W structures in the area, distinguishing between E-W and N-S nodal planes of the 1997.06.25 earthquake had been very complicated for Walker et al. (2011) and by using the other techniques such as interferometry they proposed that the rupture had occurred on the N–S trending dextral fault plane without possibility to attribute it to any Boznabad our Pavak faults.

Regardless of attribution of the 1997.06.25 earthquake to each of Boznabad or Pavak faults, the structural and the seismic studies in the Boznabad plain show how a unique stress field can influence and re-activate the different pre-existing structures in various manners and mechanisms of faulting and therefore, the co-existence of right-lateral, left- lateral strike slip and reverse faulting is comprehensible in the procedure of accommodation of convergence. Beside the structural evidences along the right-lateral Mahyar fault, the N–S trending and dextral mechanism of 1997.06.25 confirm that the right-lateral shear in this region between eastern and western segments of the Dasht-e Bayaz fault is still active and continue to accommodate the convergence.

. The segmentation and the probable existence of strike-slip related structural features such as pull-apart basins and en-echelon folds placed between the main questions of this section.

As we explained before, the Dasht-e Bayaz fault has two principal segments that are separated by Mahyar N-trending right-lateral fault. The main criteria for this segmentation has been seismic rupture of the main earthquakes of 1968.09.11 and 1968.08.31 (Berberian, 2014). We agree with this segmentation, however we believe that the western segment of

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CHAPTER IV the Dasht-e Bayaz fault involves also other fault strands that can be discussed from other points of view.

In the central parts of the Dasht-e Bayaz fault and right after to the west of the Mahyar N-trending fault, the previous active strand of this fault that has been bypassed because of south-ward trace migration of the fault (Fig. 2).

Figure 2. SPOT imagerie of middle parts of Dasht-e Bayaz faul. Present and old fault trace of the Dasht-e Bayaz fault, showed as contnious red line and red triangles, respectively. The fault trace has migerated southward and bypassed by present fault trace.

Farther west, the Dasht-e Bayaz fault reaches an E-W, pull-apart basin (the Chah Deraz pull-apart basin), with ~3900 m length and ~870 m width. The almond-shaped geometry of the pull-apart basin, in addition to its symmetric curved boundaries (Figs. 3 and 4), imply that the basin was formed in a releasing bend (e.g., Dooley and Schreurs, 2012). Considering the lack of Quaternary activity along the southern border of the basin and the coseismic reactivation of the northern principal fault during the 31 August 1968 earthquake, we suggest that the pull-apart basin is not active anymore. Some case studies have showed that the pull-apart basins usually die after creation of a shortcut fault between two, or along one of the master faults (e.g., Belier and Sébrier, 1994). 188

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Figure 3. SPOT image of Chah deraz pull-apart basin in the western segment of Dasht-e Bayaz fault showing a possible creation model of this basin. Red lines represent the previous fault trace and the blue line is present fault trace (shortcut fault) was re-activated during the 31 August Dasht-e Bayaz earthquake.

Figure 4. West waching scenery of the Chah deraz pull-apart basin, showing northern fault trace that has been reactivated during 31 August Dasht-e Bayaz earthquake. 189

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In northeastern Nimboluk plain, there are outcrops of Miocene marls armored by Quaternary deposits; the dense cultivation and human-made changes in the Quaternary surfaces were done after 31 August 1968 earthquake. The detailed rupture maps of Tchalenko and Ambraseys (1970) and Tchalenko and Berberian (1975) show that about 12 km westwards from the Chah Deraz pull-apart, the fault trace continues to the west as two fault braches. These two fault branches have been reported and mapped as Golbiz and Mozdabad fault branches in the previous studies, (see Berberian, 2014 and references therein). Our observations and mapping show that the Dasht-e Bayaz fault has another northern fault branch bends to the northwest and continues around Kakhk village that we imply it as Rahmatabad fault branch (Fig. 5).

Figure 5. Field photographs of a site along the Rahmatabad branch of the Dasht-e Bayaz fault. (A) Southeast looking view of a main fault plain (MFP) of Dasht-e Bayaz in the contact between Cretaceous limestone and Plio-Quaternary conglomerates in the northeastern Nimboluk plain. (B) Northeast looking scenery of fault plane, shows striations indicating pure left-lateral movement. Two fault striations are shown in (C). 190

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The Northeastern Nimboluk plain because of some geological characteristics is host of two important structural phenomena of remarkable segmentation and consequently a series of en-echelon pressure ridges and folds. The northeastern Nimboluk plain has covered by outcrops of the Miocene gypsiferous marls, siltstone, sandstone, Plio-Quaternary conglomerates and sandstones. The satellite image and our field observations show that a collection of parallel and sub-parallel folds have been formed wholly in the Miocene gypsiferous marls and Plio-Quaternary deposits around/and between the fault branches due to existing restraining curvatures. Although the folding is mostly seen around the curvatures along the fault branches, but some of them have been formed in the spaces between two fault branches.

Figure 6. Summary diagram illustrating typical restraining stepover geometry formed across weak bodies. (a) Riedel shears propagate toward the weak body and gradually diverge from the trace of the basement fault. (b) Linked faults form restraining stepover centred on the weak body (Fig. 73 of Dooley and Schreurs, 2012).

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It is discussable, why such a barely segmented fault with a straight geometry divides into several fault branches in the northeastern Nimboluk plain. In order to answer to this question we refer to Dooley and Schreurs (2012) that studied in detail the development of main faults in an evolutionary model by employing varied analogue experimental models. The various proposed models emphasize on the role of a high-level weak layer above a basement strike-slip fault (Fig. 6) in the development of main strike-slip faults. According to these models, separated faults propagate around a weak-layer (or weak body) and in a period of structural evolution of the main fault, a newly formed shortcut fault connects the separated fault branches. Depending on various geometrical possibilities, a local transpressional (en echelon folds) or transtensional (pull-apart) basin can be created in the space between weak-layer surrounding faults (see Dooley and Schreurs, 2012 for details).

Accordingly, the fault trace in northeastern Nimboluk plain is confronted with complexities such as the parallel or sup-parallel folds and notable segmentation of the fault that coincide with the folded Miocene gypsiferous marls. Considering the evolutionary models proposed by Dooley and Schreurs (2012), we propose that Miocene gypsiferous marls could play the role of weak bodies and the present fault rupture can be shortcut faults have linked each of previously independent faults branches like Mozdabad, Golbiz or Rahmatabad faults to the main Dasht-e Bayaz fault.

Taking into consideration the above discussion along with models proposed by Dooley and Schreurs (2012), each of the Chah Deraz pull-apart and northeastern Nimboluk plain are nodal points, which separate three fault strands composing the western segment of the Dasht-e Bayaz fault.

. The total and cumulative displacement along the Dasht-e Bayaz fault exceed to which amount? Are there any measurable displaced alluvial fans that are

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necessary for slip rate calculations? If yes, how much is the displacement of geomorphic markers in this (or these) alluvial fan(s)?

Because of bedrock outcrops and geomorphological complexities, well-founded and demonstrated estimation of total displacement along the Dasht-e Bayaz fault has not been reported yet. Emphasizing on conjectural nature of estimation, maximum total offset of Dasht-e Bayaz fault proposed by Tchalenko and Berberian (1975). According to a black Cretaceous limestone mass was dragged along the fault and crops out in Khidbas region in the middle parts of fault, they proposed that this fault may have total displacement ~4 km.

In other estimation of total offset along the Dasht-e Bayaz fault Tchalenko and Berberian (1975) pointed out to another much smaller displacement as such as 400 m near the Darreh Sefid area in the east of abovementioned Khidbas region based on limestone marker beds contained in Eocene volcanic rocks (Tchalenko and Berberian, 1975, personal communication with H. Behzadi). They also pointed out to amount of 8 to 28m left-lateral slip movements was documented by displaced stream channels in different parts of the Dasht-e Bayaz fault.

The other reported displacements are mainly devoted to co-seismic offset along the 30 August 1968 Dasht-e Bayaz rupture (e.g., Ambraseys and Tchalenko, 1969; Tchalenko and Berberian, 1975). The Maximum left-lateral and vertical offset has been measured in the Northern Nimboluk plain in amount of 4.5m and 2.5m, respectively (See Berberian, 2014, All of the reported co-seismic displacements have been properly exposed in Fig. 13.1 of this report). As Tchalenko and Berberian (1975) emphasized the conjectural nature of the 4 km maximum total displacement along the Dasht-e Bayaz fault, we prefer to report the 1.5 km displacement of Mahyar fault caused by left-lateral movement of the Dasht-e Bayaz fault as maximum certain total offset of this fault.

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About the displacement in the Quaternary alluvial fans, for the first time we studied four measurable alluvial fan, which have been displaced by the Dasht-e Bayaz fault as much as 265±10 m, 165±15 m, 71±5 m and 20±3m for Qt1, Qt2, Qt3 and Qt4, respectively. (Sites DB1-DB4, see chapter 3). These alluvial surfaces have been dated and reconstructed in order to determine the slip rate of the Dasht-e Bayaz fault (see chapter 2).

4.3. The role of Dasht-e Bayaz fault in the context of Arabia-Eurasian convergence

. According to the subjects discussed in the section 1.3.3, a main unanswered geodynamic question is the role of this E-W seismogenic sinistral fault in accommodation of the N-S convergence of central Iran–Eurasia. Clarifying the geodynamic role of Dasht-e Bayaz fault perpendicular to plate motion in the context of a geodynamic model could help us to find better answers to the questions about the structural features in the northern Lut.

The study area is located in the northeastern Lut block in the border of Arabia-Eurasia collision zone. In the east of Iran such as the other parts the geomorphology is under the influence of active faulting and the way of accommodation of Arabia-Eurasian convergence. The structural (e.g., Jackson and McKenzie, 1984; Walker and Jackson, 2004; Berberian, 2014) and geodetic studies (Vernant et al., 2004; Reilinger et al., 2006; Walpersdorf et al., 2014) showed that a major part of convergence, accommodates along the eastern Lut block as a N-trending right-lateral shear. The mechanism of accommodation is more or less well-known along the Sistan suture zone, while in the north of latitude 34, the mechanism of accommodation of convergence become more complicated. The manner of accommodation has been discussed in some of recent studies in northeastern Iran (Jackson and McKenzie, 1984; Walker and Jackson, 2004; Farbod et al., 2011; Nozaem et al., 2013; Calzolari et al., 2015).

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As discussed before, the pre-existing regional geodynamic model (Jackson and McKenzie, 1984; Walker et al., 2004; Walker and Jackson, 2004) frequently referenced in east and northeast of Iran, prefers to focus on curvature and interpret the role of left-lateral faulting in rotation of blocks. Based on this model, the convergence in the northeastern Lut block is being accommodated by clockwise rotation of block, preferably situated between the Doruneh fault system and Dasht-e Bayaz fault. The block rotation model believes that uneven distribution of N–S right-lateral shear on the fault systems of central Iran (Anar and Dehshir), the Gowk-Nayband fault system and the active faults of the Sistan suture zone has been cause of structural complexities in the Northern Lut. According to this model, from west to east, an increase in cumulative N–S right-lateral shear is reflected in the orientation of the Doruneh fault, as it rotates clockwise to accommodate the right-lateral shear, accordingly more rotation is required in the east than in the west (Walker and Jackson, 2004). This model has been challenged by Farbod et al. (2011) during the structural studies around the Doruneh Fault System. They discussed about the structural evidence could interpret some of the issues around this Fault system, in other point of view.

In our research we tried to study the correctness of the rotation model by verifying its conformity with different evidences along the Dasht-e Bayaz fault and particularly by concentrating on the relationships of this fault with other structural phenomena. Our observations and interpretations focused on the evidences that had been ignored in previous studies. We showed that although right-lateral shear is considered as mechanism of accommodation of Arabia-Eurasian convergence and the GPS vectors show a northward plate motion almost everywhere in the Lut Block, where is located in the front of collision, however this is not necessarily the case in all of the Arabia-Eurasian front zone. In continue, we proposed that in the north of latitude of 34° N (E-trending Dasht-e Bayaz fault), the right-lateral shear interrupts and does not continue to the north. We discussed

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CHAPTER IV that in the north of 34° N, the convergence is mainly accommodated by crustal shortening method and more precise by the mechanism of inverse/thrust faulting. In the north of 34° N, we do not observe any strike-slip fault parallel or sub-parallel to plate motion and instead, the evidences show the dominance of the NW-trending parallel thrust faults in the region. The Ferdows thrust zone, Jangal thrust, and southeastern faults of Kopeh Dagh Mountain are the most important thrust faults confirm our geodynamic scenario in the northeastern Iran. The reverse mechanism of eastern segment of the Doruneh fault approves the dominance of compressive tectonic regime in the form of reverse/thrust faulting in this domain, because the Doruneh strike slip fault in this domain is influenced by the dominant tectonic regime and simultaneous to changing the strike, converts to a typical thrust fault parallel to N-trending above-mentioned thrust faults.

Figure 7. A brief explanation of our model about the northern Lut block and the southern Kopeh Dagh domain. (A) Up to 34° N the most of convergence is accommodated by right-lateral shear between Iranian plateau and fixed Eurasia. In the north of 34° N, an interruption in right-lateral shear takes place and in the absence of right-lateral shear, accommodation of convergence is assigned to reverse/thrust faulting. (B) Schematic model emphasizing the role of separated thrust zones, as confining wedges at the termination of N-S dextral fault, in accommodation of the Arabia-Eurasia convergence. See text for more information. 196

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Figure 8. Shaded relief image of the northern Lut block and structural map of the study area. The strike-slip and thrust faults play the main role in this part of convergence zone showed as bold lines. The blue points imply the GPS stations and the numbers in the parenthesis are the measured VE and VN speed of the stations (mm/yr), respectively (data from Walpersdorf et al., 2013). The FERD accompanied by the BAJE and GONA, are influenced by the previous, which measured the maximum speed in northern Lut block, particularly in compare with KHAF and BAKH stations. This extent of difference beside the other structural characteristics can explain the existence of the Dasht-e Bayaz fault. This proposed model also explains how the Dasht-e Bayaz left-lateral strike-slip fault accommodates the convergence, perpendicular to the plate motion in the context of Arabia-Eurasia collision.

To the north and after latitude ~36° N, the right-lateral shear retrieves between Arabia and Eurasia front zone, accompanied by changing of trend from N to NW and continues in Kopeh Dagh mountains. According to seismological evidences we referred them in our study (Sefid Sang Mw 6 event, see Aflaki et al., 2019) the long NW-trending strike-slip faults of Kopeh Dagh mountains show reverse mechanism with a small dextral component

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CHAPTER IV of faulting in the extreme southeast and therefore we found that the recuperation of right- lateral shear occurs gradually so by approaching northwestern parts of the Kopeh Dagh mountain, the strike-slip component of faults increases. In the other words considering NW and SE of Kopeh Dagh and Binalud mountains as a two ends of a long mountain range, the mechanism of faulting in the extreme southeast is preferably reverse or dextral revers while in the extreme NW parts is almost absolutely strike-slip. Therefore the N-trending right- lateral shear between Iran and Afghanistan that had been interrupted in the latitude 34° N (equal to the level of Dasht-e Bayaz fault) recuperates in the latitude ~36° N, but this time in a NW direction and in opposition to the Turan platform instead of Afghan block.

Accepting this tectonic model, the role of E-W sinistral strike-slip faults, such as the Dasht-e Bayaz, Niazabad, Gonabad and Avash faults can be explained through their position, being situated between the NW striking Ferdows thrust zone and the eastern termination of the Doruneh fault, Jangal and Khaf thrusts. The Khaf and Jangal thrusts have been considered as probable causative of Zuzan historical destructive earthquakes (Berberian, 2014) of 19 and 21 October of 1336 A.D., respectively. The mentioned historical events and the 1 and 4 September 1968 Ferdows earthquakes (MW 6.8 and MW 5.5) indicate both of the thrust fault zones are active.

The structural map of northern Lut block, the location of GPS stations and northward and eastward components of speed, which have been measured in the last years (Walpersdorf et al., 2013) on these stations has been presented in Fig. 8. As the GPS speeds show, the stations located in the Ferdows thrust zone or influenced by this zone have the most amount of speeds. Considering this quantity as a suitable criteria representing the real amount of activity of the faults, it would be reasonable if we consider the Ferdows thrust zone as the most active fault system in compare with the adjacent thrust faults. Taking into account the GPS data of the Fig.1, while the VN speed in FERD station exceeds to the

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CHAPTER IV amount of 7.73 mm/yr (the highest amount in the whole region), the speed in the same direction in KHAF and BAKH stations has been measured as inconsiderable rate of 0.49 and - 0.01 mm/yr, respectively (Fig. 8). This remarkable difference between the activities of two parallel and adjacent thrust zone, imply the thrust zones are converging parallel to NE trending stress field and perpendicular to the strike of the both parallel thrust zones. In addition, the structural map of Dasht-e Bayaz area confirms that the Gonabad plain has been surrounded in the eastern and western sides by active thrusts and involves a compressional basin. This condition could re-activate any pre-existing structures that are in accordance with absorption of the stress field in this area (see below).

Figure 9. The structural map of the northern Lut block that only involves thrust faults influence the activity of the left-lateral faults, which is located in between. According to this scenario, the higher rate of slip in the Ferdows thrust zone in compare with Eastern termination of the Doruneh fault, Khaf and Jangal thrusts have caused a convergence between two thrust zones, which could be the main cause of the left- lateral displacement of the Dasht-e Bayaz and the Niazabad faults.

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In the northern Lut block, the left-lateral strike-slip displacement occurs between the convergence point of the Doruneh and Niazabad faults and the meeting point of Dasht-e Bayaz fault with the Ferdows thrust zone and is completely controlled by these confining parallel thrust zones (Fig. 9). In the absence of ductile or major brittle structures needed to absorb this convergence and depending on geometry and positioning of the confining thrust zones, the E-W trending structures, have been re-activated. Re-arraying and joining together of the independent fault segments in geologic time scale has led the Dasht-e Bayaz fault (and Niazabad fault) fault to its present form and it seems to continue evolving. This scenario can explain the outstanding interaction of the main fault systems undertaking the accommodation of Arabia-Eurasian convergence in the northern Lut block.

The E-W strike-slip faults such as the Dasht-e Bayaz and Niazabad faults therefore retain their secondary role in the crustal shortening which is dominant in this area. We believe that in the northern Lut, the major portion of the convergence is accommodated by the thrust faults such as Ferdows thrust zone and the E-W strike-slip faults undertake a minor portion of the convergence. Thus, the role of E-trending faults such as the Dasht-e Bayaz fault that are perpendicular to northward plate motion is significant when they have been considered retaining a secondary role in the context of the thrust/ reverse faulting, which is dominant in this region.

Lastly, in view of our tectonic scheme, the method of absorption of convergence has some differences in the region northern Lut and southern Kopeh Dagh, which are being separated by the Doruneh fault system. In the north of the Doruneh fault system, active convergence is taken up through the NW-striking thrust faults accompanied by the extrusion of fault-bounded blocks, while, in the southern domain the convergence is absorbed mainly through the NW-striking reverse/thrust faults and to a lesser extent by the E-W striking left-lateral faults.

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The results of our research based-on in-situ 10Be analysis showed that the slip rate of the Dasht-e Bayaz fault (1 mm/yr, see chapter 3) that represent the actual amount of activity of this fault, has been lower than estimated and was considered before (2.5 mm/yr; see Berberian and Yeats, 1999; Fattahi et al., 2015). Consideration of the slip rate result of our study in the context of geodynamic of northeastern Lut block, will help us to evaluate some of issues have been discussed in the proposed models (e.g., Jackson and McKenzie, 1984; Walker et al., 2004; Nozaem et al., 2013; Calzolari et al., 2015).

According to the rotation model, the Doruneh and Dasht-e Bayaz faults are considered to be dominant structures in the north of 34°N, which create a clockwise rotation by a left- lateral displacement (walker et al., 2004) and in this manner accommodate the right lateral shear between Iran and Afghanistan. Our research shows that the activity of the Dasht-e Bayaz fault slipping 1mm/yr does not correspond with Doruneh fault system with slip rate of ~5 mm/yr (Farbod et al., 2016). By accepting the existence of a rotating block, approximately similar amounts of slip rate expected for the Doruneh and the Dasht- Bayaz faults as the presumed rotation would occur along these peripheral faults. Consequently, five times of differences in the rate of slipping of these two faults prevent us from considering a similar kinematic role in accommodation of convergence.

By the other point of view and in the northwest edge of Lut block, Nozaem et al. (2013) and Calzolari et al. (2015) during the studies along the Kuh-e Sarhangi and Kuh- Faghan faults have discussed about the role of the Dasht-e Bayaz fault in the right-lateral shear among these faults and proposed almost similar models. Nozaem et al., (2013) beside the other scenarios “tentatively propose that the post-Neogene slip of the Kuh-e Sarhangi fault occurred in response of tectonic reactivation of the northeastward prosecution of the Kashmar–Kerman Tectonic Zone, as a consequence of an excess dextral shear generated in the intrafault block bordered by the Doruneh Fault to the north and the Dasht-e–Bayaz

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Fault to the south, respectively”. Furthermore, they discussed about the factors such as excess dextral shear caused by the faster westward propagation of the Dasht-e Bayaz fault because of higher slip rate with respect to Doruneh fault that consecutively induced the right-lateral reactivation of the Kashmar–Kerman Tectonic Zone during Late Neogene– Quaternary. According to this scenario, the Ferdows thrust fault and associated deformation structures partly accommodated the tectonic stresses in the intrafault block.

We agree with Nozaem et al., (2013) as they emphasized that their proposed scenarios “needs to be improved and validated by further studies to be carried out along the northern margin of the Lut block” especially there is no quantitative data such as absolute age based slip rates or GPS data available. We believe that these data are necessary to realize the intensity of current and the Quaternary activity along the Kuh-e Sarhangi and Kuh-e Faghan faults and to be aware of the role of these faults in the accommodation of Arabia- Eurasia convergence. However, as far as their scenario concerns the Dasht-e Bayaz fault, their postulate about the faster westward propagation of this fault with respect to the Doruneh fault, is not in accordance with our slip rate results.

4.4. The rate of slip along the Dasht-e Bayaz fault

. The primary objective is to estimate the slip rate of the Dasht-e Bayaz fault for the long-term as long as possible according to geomorphic markers of displaced alluvial deposits and absolute age of abandonment of these alluvial fans.

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CHAPTER IV et al., 2009; Shabanian et al., 2009; Rizza et al., 2011; Fattahi et al., 2011, 2015; Foroutan et al., 2014; Farbod et al., 2016).

Different methods have been used by the researchers to determine the rate of slipping in eastern and central Iran. For example:

- in-situ produced cosmogenic nuclide analysis (e.g., Farbod et al., 2016; Shabanian et al., 2009; Javidfakhr et al., 2011), optically stimulated luminescence (e.g., Fattahi et al., 2011, 2015; Le Dortz et al., 2009; Foroutan et al., 2014) and Infrared stimulated luminescence /IRSL (e.g., Fattahi et al., 2006, 2007; Fattahi and Walker, 2007; Rizza et al., 2011) have been used for dating of displaced alluvial surfaces.

- The interferometry methods using InSAR data to measure the rate of interseismic strain accumulation has been used for slip rate determination in some areas in the NE of Iran (e.g., Walters et al., 2013; Mousavi et al., 2015).

- In some particular cases, displacement along the man-made qanat lines have been applied by Berberian and Yeats (1999) for estimation of slip rate along the Dasht-e Bayaz fault and Walker et al. (2009) used displaced river courses incised in the Quaternary basaltic lavas and 40Ar/39Ar dating for calculation of slip rate of Nayband fault in the limit of Central Iran and the Lut block.

- current situation and the rate slipping has been one of the most favorite subject of studies and the GPS data has been extensively applied to determine the slip rate of the active faults in all over Iranian plateau (e.g., Walpersdorf et al., 2006; Tavakoli et al., 2008; Vernant et al., 2004; Masson et al., 2007; Mousavi et al., 2013; Walpersdorf et al., 2014).

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 In our study we tried to estimate rate of slipping of the Dasht-e Bayaz fault by analyzing of in-situ produced 10Be cosmogenic nuclides in quartz clasts on the Quaternary alluvial fans and morphotectonics reconstruction of these fans have been displaced by this fault. The result of our research showed that the Dasht-e Bayaz fault slips at 0.9 ±0.14 mm/yr, which has been almost steady from ~160 ka. As we explain later, this amount is remarkably lower than estimated before and changes the ideas about the role of this fault in geodynamic of northeastern Iran.

Next, we explain about our viewpoints about some of complexities about slip rate of major faults in eastern Iran.

In the section 1.3.4., we discussed the main challenges about slip rate estimations of major faults around the Lut Block. Some of the mentioned challenges are:

- Difference between geodetic and geologic rate of slipping is observed in some parts:

Too many reasons for this kind of discrepancy could be discussed, however as we will explain, our experience about the Dasht- Bayaz fault showed that the GPS stations positioning and their location considering dominant tectonic regime has a determinant role in the modeling and the consecutive interpretations (see the next subjects of this section for more detailed).

- A significant difference between long-term geological and short-term geologic slip rates has been reported in some of studies (e.g., Meyer and Le Dortz, 2007; Farbod et al., 2016). The complexities in slip rate and total offset in both side of Lut block and a change from south to the north.

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As the obtained slip rates about each of Q2, Qt3 and Qt4 alluvial fans were notably overlapped and placed almost in the same range, we conclude almost an invariable history of activity at least from ~160 ka. Therefore our results about the rate of slipping along the Dasht-e Bayaz fault in long-term cannot directly help to answer this question. The complexities of various slip rates along the fault also is not observed in our study area. However our finding about the structural complexities along the Dasht-e Bayaz fault allow us to discuss about some probable reasons for these kinds of challenges in eastern Iran. At the end we will point out that we believe that under some conditions, these complexities could be the case for the Dasht-e Bayaz fault also.

We believe that one of the reasons for these complexities in the total offset and slip rate comes back to the reality that most of faults are very long (e.g., Doruneh fault system, Nayband fault, Abiz fault). Although most of these faults apparently have a relatively simple and straight geometry, in fact they are more complicated than they appear. We explained in the case of the Dasht-e Bayaz fault although it seems as a simple straight geometry, indeed in three points (at least) there are evidences of segmentation or junctions. The junction of Dasht-e Bayaz and Mahyar fault, Chah Deraz pull-apart basin and northern Nimboluk plain are three critical parts along the Dasht-e Bayaz fault. All of four segments of the Dasht-e Bayaz fault did not have necessarily the same history of faulting in the geologic time. Accordingly if the quaternary alluvial fans have been selected for dating and morphotectonic reconstructions placed in different segments, we could have slip rate amounts with remarkable discrepancy. We discussed also about a southward trace migration in the middle parts of the Dasht-e Bayaz fault (Fig. 2). It is clear that any estimation of offset and slip rate in such a complex area without paying attention to the structural complexities doing not attain a reasonable and acceptable result.

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Such a segmentations including transpressional basin (e.g. Kuh-e Hori Mountain) and transtensional basin (e.g. Nehbandan and Sahlabad subsidence zone) in conjunction of West Neh and Esmailabad Faults have been reported in middle of Sistan suture zone (Nabavi et al., 2018). According to the experimental models of Dooley and Schreurs, (2012), the strike-slip faults are produced during the re-arraying of surface short or long faults above a basement fault and in long-term. Therefore the faults particularly in the beginning stages of creation, should be considered as developing and evolving systems so normally the different parts of a fault may manifest various offset or slip rates. Accordingly, structures such as pull-apart basins and en-echelon folds could be very important critical points in the evolution of the faults so as both segments forming a pull- apart basin did not have necessarily the same history of faulting. Considering such a complexities and paying attention to possible different structural history along the probable segmentation of mentioned structures may help to explain for instance the discrepancy of slip rate and total off-set in eastern Iran.

At the end of this section, as it is sometimes natural that we obtain different results in the length of the fault, it is better the offset and slip rate results to be attributed to the studied segment of the fault.

Although the Dasht-e Bayaz fault is an E-striking fault and cannot directly help to above-mentioned complexities however, any estimation of time of initiation can be useful

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CHAPTER IV in the regional tectonic interpretations. As Tchalenko and Berberian (1975) emphasized the conjectural nature of the 4 km maximum total displacement along the Dasht-e Bayaz fault, we prefer to use 1.5 km displacement of Mahyar fault caused by left-lateral movement of the Dasht-e Bayaz fault as maximum certain total offset of this fault. Considering ~1mm/yr of slip rate obtained in this study, we propose the Dasht-e Bayaz fault has been started its actual left-lateral displacement at least from 1.5 Ma. This time of initiation is remarkably more recent in compare with the above-mentioned proposed initiation times for N-trending faults in both sides of the Lut block.

. The study of coherency of new results with the previous estimations should be done.

Up to now two slip rate amount has been reported for Dasht-e Bayaz fault. In the first attempt and in the absence of any absolute age about the determinant factors of geodetic or geologic slip rates, Berberian and Yeats (1999) tried to present a roughly estimate of this fault. As the Dasht-e Bayaz fault had displaced the man-made qanats and there were several perturbations had been done by the fault in the vicinity of Miam village, they used the 10 meters of displacement of these qanat lines, had been reported by Ambraseys and Tchalenko (1969). In the absence of any absolute age about the time of creation of these qanat lines, Berberian and Yeats (1999) applied the time of creation of Semnan qanats locate in the North east of Tehran, that have been reported by Mehryar and Kabiri (1986) based-on archeological estimations. As a result, a slip rate as much as 2.5 mm/yr estimated for the Dasht-e Bayaz fault.

Two main critics about the slip rate estimation of Berberian and Yeats (1999):

- The calculated absolute age of the qanats belong to qanats of Semnan area,

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- the age of Semnan qanats have been obtained by archeological methods that are not suitable for fault slip rate estimations, because the age has been reported as 2000 B.C. millennium.

In the report of Ambraseys and Tchalenko (1969) the uncertainty of measured displacement has not been implied. There is no detailed image of displaced referenced qanat lines for doing next interpretations based on high resolution satellite images. This ten meters of measurement has been referenced exactly by the next researches (e.g., Berberian and yeast, 1999; Fattahi et al., 2011) for calculation of the slip rate of Dasht-e Bayaz fault. As seen in the aerial photo of the area (e.g., Fig.3 of Fattahi, 2011) there are complexities in the Miam qanat system that have not been mentioned and discussed in the previous studies. For example the existence of another qanat line exactly on the Dasht-e Bayaz fault trace and other qanat lines in the north and south side of the fault trace on the contrary of our expectance regarding the left-lateral displacement of the fault, require a detail map of the qanat system that precisely determines the relative chronology of the various generations of the qanat lines. While the possibility of re-construction of different generation of qanats should be considered in the prepared detailed maps. This will make clear the precision of ten meters of displacement measured along the fault and will obtain possibility of another estimations of slip rate based on newer generations of qanat lines.

We believe this rough estimate at the time of publication has been useful as it could give the researchers an approximate idea about the activity of the Dasht-e Bayaz fault, but in fact it seems that some of the next researches have been influenced by the result.

In the second estimation of slip rate of the Dasht-e Bayaz fault, Fattahi et al. (2015) dated two OSL samples of lake-bed sediments in order to determine the abandonment age of Nimboluk dry lake. These two samples have been collected from northern Nimboluk

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CHAPTER IV plain yielded an age as much as 8.6±0.6 and 8.5±1.0 ka. Assuming the abandonment of Nimboluk dry lake and beginning of incision of the streams has been simultaneous, they applied 26±2 m of displacement in “small streams” have been displaced along the Dasht-e Bayaz fault in the east of Khezri and estimated the minimum slip rate of this fault as 2.6 mm/y.

Some of assumptions, discussions, methodologies and results of this study are debatable or do not agree with the observations in the Dasht-e Bayaz area. There are complexities about sampling site that could have affected the result of dating. We believe the sampling site for OSL dating is very close to the fault zone and naturally could been affected by the fault. Fattahi et al. (2015) has implied the northern part of the fault has been uplifted because of a small component of vertical slip on the Dasht-e-Bayaz fault while, as we discussed in chapter 2, the both sides of the Dasht-e Bayaz fault around the sampling site of Fattahi et al. (2015), the layers have folded generally in NW-trending. Although there are not many displaced Quaternary fans along the Dasht-e Bayaz fault, but the observations are not agree with the expression “no measurable relief” and “overall lack of relief across it” that has been mentioned in Fattahi et al. (2015). The mentioned expression is inacceptable concerning the presence of at least four quaternary fans in the western parts of Dasht-e Bayaz fault that have been sampled and dated in our research. This incorrect idea have leaded the authors to choose an unsuitable displacement measurement site in the flat area without any quaternary fan. Accordingly, between three offset measurements of 26±2 m, 26±2 m and 26±2 m have been presented in this study it have not been clarified that based-on which convincing geomorphologic marker, two of measurements have been put aside and the amount of 26±2 m has been considered as cumulative displacement since the abandonment of the Nimboluk dry lake. Considering application of a weak methodology, it seems that for Fattahi et al. (2015) the consistency of obtained slip rate

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CHAPTER IV with the previous studies (2.5 mm/y, Berberian and Yeats, 1975) had been enough to propose the new results.

We believe that an important point has been ignored in the recent studies in the estimation of Dasht-e Bayaz fault according to displacement of qanat lines. Basically this kind of estimation has an assumption so that the construction of qanat has been done right after an earthquake. In these estimations, theoretically the measured qanat displacement attributed to displacement along the fault while in fact there is possibility that discussing qanats have been created long time (e.g. centuries or more than a thousand of years) after the last displacement along the fault (Fig. 10). Therefore we suggest, an uncertainty equivalent to the length of earthquake recurrence interval of the fault should be considered to the age factor in the slip rate calculations based on qanat displacements.

Figure 10. A schematic conjectural image for explaining the complexity of determination of slip rate by displacement in qanat lines. The yellow qanat wheels have created in 3700, and the white circles in 2700 years ago along the same fault. We assume an earthquake took place in 3900 years ago and the recurrence interval is 1300 years. Accordingly the slip rate based-on yellow and white qanats yields 2.7 mm/y and 3.7 mm/y, respectively while the actual slip rate is 2.5 mm/y.

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. As it was mentioned by Walpersdorf et al., (2014), dextral sense of movement has obtained for the Dasht-e Bayaz fault is contradictory with the observations while the Dasht-e Bayaz fault is unambiguously left-lateral. As it was emphasized by Walpersdorf et al., (2014): “we cannot explain the discrepancy between the actual sense of slip and that observed in the GPS data”, it is expected from our slip rate results to have interpretations about this complexity.

In one of the recent studies, Walpersdorf et al. (2014) working on present-day fault kinematics and slip rates derived from eleven years of GPS data in eastern Iran, beside the other faults tried to estimate the present-day slip rate of Dasht-e Bayaz fault. Four stations around the Dasht-e Bayaz fault were used for processing and as a result, they obtained a N-S extension of 1.2 ± 0.3 mm/y combined with a dextral E-W lateral slip of 0.2 ± 0.1 mm/y. As it was mentioned in this study, dextral sense of movement obtained for this fault is obviously contradictory with the observations because the Dasht-e Bayaz fault is unambiguously left-lateral (e.g., Tchalenko and Berberian, 1975; walker et al., 2004; Berberian, 2014, and this study). With emphasizing on “we cannot explain the discrepancy between the actual sense of slip and that observed in the GPS data” they expressed “our data only suggest that the current left-lateral slip on the Dasht-e-Bayaz fault is likely to be small”.

Our proposed tectonic model about the northeastern Lut block could properly explain the cause of the observed discrepancy. In fact, considering the positioning of GPS stations around the Dasht-e Bayaz fault, the dextral sense of movement has been initially obtained by Walpersdorf et al. (2014) for this fault is justifiable.

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Figure 11. LANDSAT ETM satellite overview (RGB 741) of the Dasht-e Bayaz area, major faults of the area. The blue triangles are the GPS stations have been used by Walpersdorf et al., 2014 for study of estimation of current slip rate of the Dasht-e Bayaz fault (see text).

Fig. 11 shows the location of GPS stations around the Dasht-e Bayaz area. BAJE and GONA stations are located in Ferdows thrust while QAEN and QAE2 stations are installed in the south side of the Dasht-e Bayaz fault around Qayen. Although the QAEN and QAE2 stations are located in the south side of Dasht-e Bayaz fault, these stations are under the influence of Avash left-lateral earthquake fault responsible of 7 November 1976 Mw 6.03 Vandik event (e.g., Baker, 1993; Berberian et al., 1999; Walker et al., 2004), also. If we ignore the relative displacement of Avash fault, we believe that this relative dextral movement is because of higher rate of slipping in the Ferdows thrust zone in compare with strike-slip rating along the Dasht-e Bayaz fault. Accordingly, the measured E-W slip of 0.2 ± 0.1 mm/y (Walpersdorf et al., 2014) is difference between east-west components of slip rates between two above mentioned fault systems. Quicker eastward movement of the GPS stations (BAJE and GONA) located on Ferdows thrust in comparison with the stations

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CHAPTER IV located on the south side of Dasht-e Bayaz fault (QAEN and QAEN2), has been the cause of concluded relative dextral sense of movement.

The amount of 1.2 ± 0.3 mm/y N-S extension measured by GPS data is explained by persistence of difference in northward movement speed between Dasht-e Bayaz and Ferdows zones. In this part, Ferdows zone also moves northward more rapidly because of higher amount of slip rate and this difference appears as extension between the GPS stations as reported by Walpersdorf et al. (2014). Therefore the more important role of NE- trending thrusts in accommodation of Arabia-Eurasian convergence can be concluded from this inference.

As we see here about the Dasht-e Bayaz fault, the GPS measurements are sometimes influenced preferably by regional geology more than general plate motion. Although the GPS stations are not spatially and geographically very far, they have not been installed in the areas with the same stress regime. Accordingly they are under the influence of two different kinds of faulting and slip rates with different mechanism of accommodation of convergence. Therefore paying attention to the positioning in the convergence zone without paying attention to geodynamic role of the involving region can rise complexities in the interpretations. In the case of the Dasht-e Bayaz fault the sense of movement was obviously at odds with the observations and thus attracted the attentions while if the sense of movement was not inverse, it could be showed as unambiguity such as the discrepancy between instantaneous geodetic and moderate- to long-term geologic rate of slipping as it was reported in the eastern Iran (e.g., Meyer and Le Dortz, 2007; Farbod et al., 2016)

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Tectonique active de la faille de Dasht-é Bayaz (ENE de l’Iran)

1. Introduction

Cette thèse porte sur une des failles décrochante active et majeure de l’ENE de l’Iran, la faille de Dasht-é Bayaz (Fig. 1). Elle est située dans le NE du bloc de Lut, au Sud de la zone de collision entre l’Arabie et l’Eurasie. Nous avons tenté dans ce travail de définir la cinématique et ainsi que le rôle géodynamique de cette structure dans ce contexte de convergence Arabie-Eurasie. Notre étude tectonique et géomorphologique est basée sur l'analyse d’images satellitaires, de modèles numériques de terrain et de cartes géologiques, complétée par des observations de terrain ainsi que par des mesures de cinématique de faille et de datation par l’analyse de cosmo nucléides produits in situ.

Nous avons confronté les résultats de notre analyse avec les données de sismicité instrumentale et historique disponibles, ainsi qu’avec les vitesses de déplacement déduites des mesures GPS. En combinant l’ensemble de ces données indépendantes, nous proposons un cadre tectonique cohérent du système de faille de Dasht-é Bayaz, intégré dans un nouveau modèle géodynamique du NE de l’Iran.

2. Contexte géodynamique

La convergence entre l’Arabie et l’Eurasie est responsable de la déformation actuelle en Iran. Presque toute la convergence est accommodée à travers tout le plateau iranien, ainsi que par les chaînes de montagnes bordant des blocs pseudo-rigides telles que les chaines du Zagros, de l’Alborz et du Kopeh Dagh. Les frontières de collision à l’Est et au Nord Est de l’Iran, correspondent approximativement aux frontières politiques de l’Iran.

A l’Est de l’Iran, les failles décrochantes ont un rôle majeur dans l’accommodation de la convergence. D’après les investigations géologiques et les mesures géodésiques (GPS,

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InSAR) effectuées au cours des dernières décennies (e.g., Berberian et al., 1999; Walker and Jackson, 2004; Vernant et al., 2004; Meyer and Le Dortz, 2007; Foroutan et al., 2012 ; Walpersdorf et al., 2014), les systèmes de failles dextres d’orientation N, situés au centre de l’Iran et surtout à l’Est et à l’Ouest du bloc de Lut, accommodent les composantes vers le Nord de la convergence Arabie-Eurasie sous forme d’une zone de cisaillement dextre entre l’Iran Central et le bloc de Helmand (Afghanistan).

Figure 1. Une photo de terrain de la trace de la faille de Dasht-e Bayaz, qui a été réactivée par le séisme du 31 aout 1968 (vers E)

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La distribution des épicentres des séismes ainsi que les mesures GPS montrent que l’accommodation de la convergence est principalement localisée le long du système de failles alors que les blocs sont relativement a- séismique et non déformable, tel que le bloc de Lut (e.g., Vernant et al., 2004; Walker and Jackson, 2004).

Les études géodésiques et structurales montrent qu’une partie principale de la convergence, se traduit par une zone de cisaillement dextre à l’Est de bloc de Lut et le long de zone de suture du Sistan (e.g., Berberian et al., 1999 ; Walker et al., 2004). Le mécanisme de l’accommodation est plus ou moins connu tout au long des failles de deux côtés de bloc de Lut, cependant au nord de la latitude 34°N, l’accommodation de la convergence est plus complexe. Le fonctionnement de l’accommodation au Nord du bloc de Lut a été abordé dans certaines études récentes du Nord-Est de l’Iran. (Jackson and McKenzie, 1984; Walker and Jackson, 2004; Farbod et al., 2011; 204; Nozaem et al., 2013; Calzolari et al., 2015). Selon un modèle géodynamique régional proposé et très cité au Nord-Est de l’Iran, au Nord de la latitude 34°N, un taux croissant vers l’Est de cisaillement dextre a créé une rotation rigide de blocs au Nord-est de l’Iran (e.g., Jackson and McKenzie, 1984; Walker and Jackson, 2004). Ce modèle implique la courbure de la faille du Doruneh et propose une explication pour les rôles des failles senestres de Doruneh et de Dasht-e Bayaz.

Selon ce modèle, une rotation horaire (e.g., Walker et al., 2004;) se déroule le long des faille de Doruneh et de Dasht-e Bayaz afin d’accommoder le cisaillement dextre qui se fait le long des failles majeures d’orientation N-S au sud de latitude 34°N (e.g., failles de Dehshir, Anar, Nayband et zone de suture de Sistan). Le modèle de rotation du bloc suppose que la distribution inégale du cisaillement dextre d’orientation N-S au Nord du bloc de Lut est la cause principale des mouvements senestres des failles de Doruneh et

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Dasht-e Bayaz, de la courbure de la faille de Doruneh et de la longueur de la faille de Dasht-e Bayaz.

Ce modèle a été remis en cause par Farbod et al. (2011) au moyen de différents arguments essentiellement structuraux aux alentours du système de failles de Doruneh. Ils ont suggéré que toutes les questions géologiques au nord du bloc de Lut ne peuvent pas forcement s’expliquer par des modèles régionaux impliquant des rotations rigides. Farbod et al. (2011) ont privilégié l’hypothèse que la courbure de la faille de Doruneh peut s’expliquer par un nouveau modèle de segmentation de la faille et ses zones de relais avec des failles connectées.

Dans notre travail nous avons souligné le rôle de la faille de Dasht-e Bayaz dans la géodynamique du Nord-Est de l’Iran, et son implication par rapport aux modèles de déformation proposés préalablement. Nous avons également abordé d’autres questions dont les plus importantes sont évoquées ci-dessous:

- Quels sont les états de contraintes autour de la faille de Dasht-e Bayaz et dans le Nord du bloc de Lut?

Nous avons donc étudié la cinématique des déformations et les champs de contrainte plio- quaternaires qui ont été responsables des déformations de Dasht-e Bayaz et dans la région environnante pendant le Plio-Quaternaire.

- Nous avons également étudié l’évolution de la segmentation de cette faille et notamment l’existence et le rôle de bassin pull-apart et de plis en-échelon et l’interaction de cette faille avec les failles adjacentes.

- Existe-t-il un phénomène du partitionnement de la déformation autour de cette faille?

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- Existent-t-ils des cônes alluvial déplacés et mesurables qui sont nécessaires aux calculs de vitesse? Quel est la quantité de déplacement de ces cônes alluviaux et des marqueurs géomorphologiques associés à ces cônes?

- Quelle est la vitesse de glissement de la faille de Dasht-e Bayaz ?

- Quel est le rôle de la faille senestre décrochante de Dasht-e Bayaz qui est perpendiculaire aux mouvements du plateau, dans l’accommodation de la convergence Arabie-Eurasie?

Durant ce travail de thèse, nous avons donc cherché à hiérarchiser ces différentes questions et tenté d’y répondre, en appliquant une méthodologie rigoureuse et en suivant les objectifs successifs présentés ci-dessous :

1- Établir une cartographie suffisamment détaillée des zones de failles actives afin de pouvoir faire les reconstructions des déplacements des cônes alluvial et d’en déduire une carte de segmentation ainsi qu’un schéma structural rigoureux.

2- Mesurer les déplacements ainsi que les vitesses de glissement le long de la faille de Dasht-e Bayaz.

3- Déterminer la cinématique des déformations plio-quaternaires et en déduire les états de contraintes responsables de la déformation afin de discuter le régime tectonique régional et de l’intégrer dans le nouveau modèle géodynamique que nous proposons.

Ces différents objectifs scientifiques ont été poursuivis grâce à une approche pluridisciplinaire combinant une étude de géologie structurale, de morphotectonique, de géomorphologie quantitative et des datations par des nucléides cosmogéniques. Les principaux résultats obtenus dans ce travail sont synthétisés ci-dessous.

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3. Étude structurale et géométrie de la Faille

L’une des objectives de notre recherche était d’étudier l’aspect structural tels que la segmentation de la faille, l’existence et l’évolution d’un bassin pull-apart régional et de plis en-échelon autour de la faille. Par conséquent, nous avons cartographié la trace de la faille. Nous avons établi une carte détaillée de la géométrie, dont nous avons déduis les principales caractéristiques structurales du domaine de déformation le long de la faille. Notre analyse structurale montre qu’en deux points, la faille décrochante d’orientation E- W de Dasht-e Bayaz interagit (croise) avec les failles décrochantes de Mahyar et de Korizan d’orientation N-S. Par conséquent, cette situation ainsi que cette interaction de la faille de Dasht-e Bayaz avec les failles adjacentes ont été étudiées.

D’un point de vue sismogénique, la faille de Dasht-e Bayaz comprend des segments de l'Ouest et de l’Est qui se sont séparées par la faille de Mahyar d’orientation N-S (Berberian, 2014). Notre recherche montre que si nous considérons les aspects structuraux, tels que le bassin en pull-apart de Chah Deraz et les plis en échelon du Nimboluk au Nord, nous remarquons qu’à l’Ouest, la Faille de Dasht-e Bayaz comprend trois segments de failles alignées qui sont en train d’évoluer. Nous avons démontré une migration de la déformation vers le Sud dans la zone centrale de la faille de Dasht-e Bayaz.

4. étude cinématique et régime tectonique plio-quaternaire

Dans cette étude, nous avons déterminé les variations spatiales et temporelles de l’état de contrainte appréhendé au moyen de mesures et de l’interprétation des cinématiques de faille mesurées dans secteur de déformation de la Faille de Dasht-e Bayaz. Dix sites ont été mesurés le long de la zone de Faille et le domaine environnant. Notre l’analyse des données de cinématiques de faille et leur inversion ont révélé deux états de contraintes distincts dans la zone de Dasht-e Bayaz pendant Plio-Quaternaire. Les inter- relations entre les différentes

226

CONCLUSION, SYNTHESE cinématiques (recoupement, recouvrement de stries, etc.) observées sur les plans de la faille nous ont aidés à déterminer l'occurrence et la chronologie des 2 générations d’états de contrainte obtenues en relations avec 3 régimes tectoniques distincts locaux/régionaux.

L’état de contrainte le plus récent que l’on a défini comme « moderne », basé sur la génération la plus jeune des données cinématique a été déterminé un régime de contrainte caractérisé par une direction moyenne de contrainte maximale : σ1 N45°±5°E. Les champs de contrainte montrent que le régime tectonique dominant est décrochant (σ2 vertical) notamment dans la partie principale de la zone d’étude, cependant il change dans les régions à l’Ouest avec un régime compressif local (σ3 vertical). Le plus ancien état de contrainte Plio-Quaternaire de cette zone est caractérisé par une direction moyenne de contrainte maximale σ1 N133±17°E. C’est un régime tectonique purement compressif (σ3 vertical).

En conclusion, nous avons essayé d’intégrer nos résultats à l’échelle régional, et discuté l’histoire du changement du régime tectonique en les comparant avec les résultats des études précédentes dans les différentes parties du plateau iranien, et plus particulièrement dans l’Est de l’Iran.

5. Quantification de la déformation : déplacement fini et vitesse de déplacement

Concernant le déplacement de cônes alluviaux quaternaires, nous avons étudié pour la première fois 4 systèmes de cônes alluviaux déplacés par la faille de Dasht-e Bayaz. Ces déplacement sont de l’ordre de : 265±10 m, 165±15 m, 71±5 m and 20±3m pour Qt1, Qt2, Qt3 et Qt4 (du plus vieux au plus jeune), respectivement.

La vitesse de glissement est une des caractéristiques importantes d’une faille active vu qu’elle est un critère bien défini et non ambigu à l’évaluation de l’activité d’une faille. En terme télésismique c’est un paramètre fondamental car en première approximation c’est la

227

CONCLUSION, SYNTHESE vitesse moyenne de la faille qui va prédéfinir le temps de retour des séismes (la récurrence). L’estimation de la vitesse de glissement a été le sujet de plusieurs études au centre de l’Iran, à travers le Kopeh Dagh et plus récemment dans le Nord du bloc de Lut dans les années récentes. (e.g., Le Dortz et al., 2009, 2011, 2012; Walker et al., 2009; Shabanian et al., 2009; Rizza et al., 2011; Fattahi et al., 2015, Foroutan et al., 2014; Farbod et al., 2016).

Dans notre étude nous avons tenté de faire une estimation de la vitesse de glissement de la faille de Dasht-e Bayaz au moyen de datations par des analyses des nucléides cosmogéniques et de la reconstruction morphotectonique des cônes alluvial qui ont été décalés par cette faille. Notre étude a permis de déterminer une vitesse moyenne, intégrée sur les derniers ~160 ka, de la faille de Dasht-e Bayaz d’environ 0.9±0.14 mm/an. Ce taux semble avoir été stable sur la période considérée, en tenant compte des incertitudes respectives de nos âges de cône relativement élevées.

6. Rôle géodynamique

Dans notre recherche sur la géodynamique du Nord du bloc de Lut, nos observations et interprétations ce sont concentrées sur les arguments de géologie structurale que nous avons répertoriée et analysés de manière détaillées dans la région d’étude. Nous avons montré que malgré le fait que le cisaillement dextre est considéré comme un mécanisme d’accommodation de convergence de l’Arabie-Eurasie entre les blocs de Lut et Afghan, ce qui n’est pas nécessairement le cas dans toute la zone de bordure. Nous avons proposé qu’au Nord de la latitude 34°N (niveau de la faille de Dasht-e Bayaz), ce cisaillement d’orientation N-S s’interrompt et ne se continue pas vers le Nord.

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CONCLUSION, SYNTHESE

Figure 2. Une explication brève de notre modèle concernant le Nord du bloc de Lut et le Sud du domaine de Kopeh Dagh. Au Nord de 34°N, la convergence est principalement accommodée par du raccourcissement crustal sous forme de inverse/chevauchement.

Par conséquent au Nord de 34°N, la convergence est principalement accommodée par du raccourcissement crustal (Fig. 2) de direction de compression parallèle à la convergence qui se traduit essentiellement par du chevauchement (Failles inverses). Dans ce domaine, nous n’avons observé aucune faille décrochante parallèle ou subparallèle aux mouvements vers le nord du plateau, en revanche nous relatons une dominance de failles parallèles de mécanisme inverse/chevauchement et d’orientation NW dans la région. La zone de chevauchement de Ferdows, la faille inverse de Jangal et Khaf, ainsi que les failles inverses de la Binalud du Sud-Est sont les failles inverses les plus importantes, ce qui confirme

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CONCLUSION, SYNTHESE notre scénario géodynamique au Nord-Est de l’Iran.Le mécanisme inverse du segment de l’Est de la faille de Doruneh (EFZ) confirme la dominance d’un régime tectonique et compressif sous forme d’inverse/chevauchement dans ce domaine, car la faille décrochante de Doruneh dans ce domaine est influencée par le régime dominant, et se convertit à une faille inverse d’orientation NW parallèle aux failles inverses déjà mentionnées.

Figure 3. La carte structurale du Nord du bloc de Lut s’intéresse seulement aux failles inverses responsables de la réactivation de la faille de Dasht-e Bayaz et de Niazabad.

Vers le Nord et au Nord de la latitude ~36°N, le cisaillement dextre se localise entre l’Arabie et l’Eurasie. On y observe un changement d’orientation de la zone de déformation de N à NW. Nous croyons que dans le nord du 34°N, une grande partie de la convergence

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CONCLUSION, SYNTHESE et de la déformation est absorbée par des systèmes de failles inverses (telles que la faille d’inverse de Ferdows) et en revanche les failles décrochantes d’orientation E-W, telles que la faille de Dasht-e Bayaz n’absorbent qu’une petite partie de la convergence. Le faible taux de vitesse de glissement, qui a été obtenu pour la faille de Dasht-e Bayaz dans cette étude confirme cette idée, malgré son potentiel sismogénique important.

Au Nord du bloc de Lut, le déplacement sénestre a lieu entre le lieu de convergence des failles de Doruneh et de Niazabad et le point d’intersection des failles de Dasht-e Bayaz et de la faille d’inverse de Ferdows. Par conséquent, ce déplacement sénestre est complètement contrôlé par l’activité de ces zones de confinement parallèles (Fig. 3).

7. Conclusions et perspectives

Dans cette recherche, nous avons révisé les études précédentes et les modèles proposés. Nous avons ensuite expliqué nos travaux de terrain, nos observations, les prélèvements d’échantillons et les résultats des analyses faites au laboratoire. Finalement, nos résultats et leur interprétation, nos points de vue et notre modèle géodynamique sont présentés sous forme de réponses aux questions principales concernant le Nord du bloc de Lut.

Notre analyse de cinématiques de faille a permis de déterminer un état de contrainte compressif caractérisé par une direction de compression (contrainte maximale σ1) N133±17°E. Nous avons également déterminé un régime de contrainte décrochant plus récent de direction de contrainte maximale σ1, N45±5°E. Ces états de contrainte «ancienne» et «moderne» déterminé dans notre étude, sont parfaitement cohérents avec les résultats des études similaires effectuées au Nord et Nord-Est de l’Iran.

Durant nos études structurales le long de la faille, nous avons étudié la segmentation et avons discuté le rôle d’un bassin pull-apart (bassin de Chah Deraz), un system des plis en- 231

CONCLUSION, SYNTHESE

échelon, une migration vers le Sud de la trace de la faille au centre de la faille de

Dasht-e Bayaz et nous avons proposé un schéma d’interprétation (modèle régional). A partir des données sismiques recensées et interprétés, nous avons montré qu’il existe un système classique de partitionnement de la déformation qui est actif dans les parties centrales de la faille de Dasht-e Bayaz.

Nous avons étudié 4 systèmes de cônes alluviaux décalés par la Faille de Dasht-e Bayaz de 265±10 m, 165±15 m, 71±5 m et 20±3m pour Qt1, Qt2, Qt3 et Qt4, respectivement.

En conclusion, nous avons proposé des estimations de la vitesse moyenne de glissement de la Faille de Dasht- Bayaz en analysant des nucléides cosmogéniques et de la reconstruction morphotectonique des cônes alluvial qui ont été décalés par cette faille. Le résultat de notre recherche montre que la faille de Dasht-e Bayaz a une vitesse de glissement de 0.9±0.14 mm/an, vitesse stable depuis ~160 ka. Ce taux est significativement inférieur à ceux estimés précédemment, et limite donc rôle joué par cette faille dans les géodynamiques du Nord-Est de l’Iran.

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CONCLUSION, SYNTHESE

Bibliographies

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(E-NE IRAN)

Our mapping of fault intersection areas highlights the cross-cutting relationship between N-S dextral and E-W sinistral faults forming a typical coexisting crosswise to conjugate fault arrangement in the middle part and the eastern end of the Dasht-e Bayaz fault trace. The morphotectonic studies complemented by Cosmic Ray Exposure (CRE) dating of quartz clasts collected from abandoned Quaternary alluvial surfaces offset by the fault allowed determining the slip rate of the Dasht-e Bayaz fault at 0.9±0.14 mm/yr; this rate has been almost constant since ~160 ka. In view of geodynamics, lithospheric right-lateral shear between the Iranian plateau and fixed Eurasia is interrupted between 34°N and 36°N and is mainly replaced by reverse/thrust faulting before being accommodated, farther north, by dextral faulting along NNW faults of the Kopeh Dagh. According to our geodynamic model, the region between Lut and Kopeh Dagh is divided by the Doruneh fault into two tectonic domains. In the northern domain, active convergence is taken up by the extrusion of fault-bounded blocks while, in the southern domain the convergence is accommodated through E-W sinistral faults such as Dasht-e Bayaz and NW-striking reverse/thrust faults. In this context, the E- W sinistral faults are situated between NW striking reverse/thrust faults like the Ferdows, Jangal and Khaf as well as the eastern termination of Doruneh, playing their complementary role in the crustal shortening at the converging edges of the north going blocks of Lut – Central Iran. The different tectonic role of the Dasht-e Bayaz fault with respect to the Doruneh fault (as a major block bounding structure) is reflected in their rates of slip such that the Doruneh Fault slips, at least, five times faster than the Dasht-e Bayaz fault.

Keywords: Lut block; morphotectonics; strike-slip faulting; state of stress; Arabia- Eurasia collision; cosmogenic nuclides; slip rate.

Discipline: Géosciences de l’Environnement

Laboratoire: CEREGE UMR 7330 Europôle de l’Arbois, BP 80 13545, Aix-en-Provence Cedex 4