Atlas of Structural Geology

Soumyajit Mukherjee

• Publisher: Elsevier
• Year: 2015
• eBook ISBN: 9780124202061
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Atlas of Structural Geology features a broad and inclusive range of high-quality meso- and micro-scale full-color photographs, descriptions, and captions related to the deformation of rocks and geologic structures. It is a multi-contributed, comprehensive reference that includes submissions from many of the world's leading structural geologists, making it the most thorough and comprehensive reference available to the scientific community. All types of structures are featured, including structures related to ductile and brittle shear zones, sigma- and delta-structures, mineral fish, duplexes and trapezoids, shear related folds, and flanking structures in meso- and micro-scales. A stunning collection of the world's most beautiful and arresting geologic structures, the Atlas of Structural Geology is the ideal aid in the retention of key concepts in geology. - Presents more than 250 top-quality, full-color photographs contributed by the world's most respected structural geologists - Features a broad range of morphological variations of geologic structures, making it the most up-to-date and inclusive reference of its kind - Edited by a structural geologist with 14 years of experience in related research and instruction - Aids researchers in developing mathematical and analogue models on the peculiarity and uniqueness of the world's most iconic structures

Chapter 1

Folds

Abstract

Two of the most intensely studied aspects in structural geology are morphology and genesis of folds. Of particular importance is whether folds found inside ductile shear zones are related to ductile shear. This chapter presents folds of different geometries and generations, some related with ductile shear zones, from different scales.

Keywords

Folds; Folds not related to shear zones; Overturned fold; Shear zone related fold; Sheath fold; Superposed fold

Two of the most intensely studied aspects in structural geology are morphology and genesis of folds (see Ramsay, 1967; Hudleston and Lan, 1993; Ez, 2000; Harris et al., 2002; Harris, 2003; Alsop and Holdsworth, 2004; Mandal et al., 2004; Carreras et al., 2005; Bell, 2010; Hudleston and Treagus, 2010; Godin et al., 2011; Harris et al., 2012a,b; Llorens et al., 2013; Mukherjee et al., in press). Of particular importance is whether folds found inside ductile shear zones are related to ductile shear (e.g., Mandal et al., 2004; Carreras et al., 2005; Bell, 2010). This chapter presents folds of different geometries and generations, some related with ductile shear zones, from different scales (Figures 1.1–1.87).

Figure 1.1 Upright folds and folded boudins resulting from continental collision of East and West Gondwana.

The boudins of dark-colored amphibolite (Fb) in light-colored biotite-hornblende gneiss have originally pancake shapes with flattening parallel to compositional layering of gneiss, and resulted from the layer-parallel extension and thinning of crustal rocks within 640–600 Ma (Toyoshima et al., 1995). The folds with wavelengths of 20–30 m are parasitic upright folds of larger-scale upright fold related to 600–560 Ma sinistral transpression and crustal shortening during the collision (Toyoshima et al., 2013). The boudins (Fb) folded by the parasitic folds suggest that the tectonic regime changed from layer-normal to layer-parallel compression (Toyoshima et al., 2013). Osanai et al. (2013) presented SHRIMP U–PB ages for metamorphic rocks from the Sør Rondane Mountains, East Antarctica, and recognized periods of ultrahigh-temperature metamorphism (pre-main metamorphic stage) during 750–700 Ma and granulite- to amphibolite-facies metamorphism during 640–600 Ma. Location: 72°09′42″S, 25°31′50″E, the southern part of Salen in the Sør Rondane Mountains, East Antarctica. (Tsuyoshi Toyoshima, Masaaki Owada, Kazuyuki Shiraishi)

Figure 1.2 Fault-bend-fold viewed along NNW-SSE section within Tethyan Himalayan succession.

Compression in the Tethyan Himalaya indicated. Width of view: ∼80 ft. The fold is developed within thinly bedded, presumably less viscous, argillaceous rocks of Lower Cretaceous age. North vergent folding in the Tethyan Himalaya resulted from strong drag induced by channel flow extrusion of the Greater Himalaya at south, as Godin et al. (2011) proposed from Nepal Himalaya. Note opposite senses of normal drag (Grasemann et al., 2005; Mukherjee, 2007; Mukherjee and Koyi, 2009; Mukherjee, 2010, 2011a, 2014a,b) across the fault plane. Latitude 32°19′54″N, Longitude 78°0′29″E. Kibber village, Spiti, Himachal Pradesh, India. (Mainak Choudhuri)

Figure 1.3 Tri-shear fault-propagation folding.

Greater Himalayan gneissic rocks. The fold axis trends N330°. Location: 28°32′48.61″N; 94°13′47.24″E. Scale: Hammer (white circled). (George Mathew, Dnyanada Salvi)

Figure 1.4 (a) Full section and (b) zoomed into an excellent outcrop-scale example of an “out-of-syncline” fold accommodation fault (Mitra, 2002; Deng et al., 2013), Triassic limestones, Spiti valley, near Losar village, Himachal Pradesh, India. Fold accommodation faults accommodate strain on the fold limbs. Here the synform is present to the SW. Its NE limb accommodated strain. Location: 32°23′47.63″N, 77°57′2.09″E. (Achyuta Ayan Misra)

Figure 1.5 Fault-bend fold.

The fault plane is not perfectly straight. Presuming a “normal drag,” reverse faulting deciphered. Thinly bedded meta-siltstone. 15-mm pencil for scale. Location: Chail Group, SE of Shimla, Himachal Pradesh, India. (Subhadip Mandal)

Figure 1.6 The Eocene limestone–shale sequences of the Siang fold-and-thrust belt, Arunachal Pradesh, India.

The sequence is bounded by parallel and arcuate thrusts at N (Acharyya and Saha, 2008). The southward propagating Eocene sequence is thrusted...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Acknowledgments
• Chapter 1. Folds
• Chapter 2. Ductile Shear Zones
• Chapter 3. Brittle Faults
• Chapter 4. Boudins and Mullions
• Chapter 5. Veins
• Chapter 6. Various Structures
• Author Index
• Subject Index