Deformation Mechanisms, Rheology and Tectonics Geological Society Special Publications Series Editor J
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GEO 2008 Conference Abstracts, Bahrain GEO 2008 Conference Abstracts
GEO 2008 conference abstracts, Bahrain GEO 2008 Conference Abstracts he abstracts of the GEO 2008 Conference presentations (3-5 March 2008, Bahrain) are published in Talphabetical order based on the last name of the first author. Only those abstracts that were accepted by the GEO 2008 Program Committee are published here, and were subsequently edited by GeoArabia Editors and proof-read by the corresponding author. Several names of companies and institutions to which presenters are affiliated have been abbreviated (see page 262). For convenience, all subsidiary companies are listed as the parent company. (#117804) Sandstone-body geometry, facies existing data sets and improve exploration decision architecture and depositional model of making. The results of a recent 3-D seismic reprocessing Ordovician Barik Sandstone, Oman effort over approximately 1,800 square km of data from the Mediterranean Sea has brought renewed interest in Iftikhar A. Abbasi (Sultan Qaboos University, Oman) deep, pre-Messinian structures. Historically, the reservoir and Abdulrahman Al-Harthy (Sultan Qaboos targets in the southern Mediterranean Sea have been the University, Oman <[email protected]>) Pliocene-Pleistocene and Messinian/Pre-Messinian gas sands. These are readily identifiable as anomalousbright The Lower Paleozoic siliciclastics sediments of the amplitudes on the seismic data. The key to enhancing the Haima Supergroup in the Al-Haushi-Huqf area of cen- deeper structure is multiple and noise attenuation. The tral Oman are subdivided into a number of formations Miocene and older targets are overlain by a Messinian- and members based on lithological characteristics of aged, structurally complex anhydrite layer, the Rosetta various rock sequences. -
Faults and Joints
133 JOINTS Joints (also termed extensional fractures) are planes of separation on which no or undetectable shear displacement has taken place. The two walls of the resulting tiny opening typically remain in tight (matching) contact. Joints may result from regional tectonics (i.e. the compressive stresses in front of a mountain belt), folding (due to curvature of bedding), faulting, or internal stress release during uplift or cooling. They often form under high fluid pressure (i.e. low effective stress), perpendicular to the smallest principal stress. The aperture of a joint is the space between its two walls measured perpendicularly to the mean plane. Apertures can be open (resulting in permeability enhancement) or occluded by mineral cement (resulting in permeability reduction). A joint with a large aperture (> few mm) is a fissure. The mechanical layer thickness of the deforming rock controls joint growth. If present in sufficient number, open joints may provide adequate porosity and permeability such that an otherwise impermeable rock may become a productive fractured reservoir. In quarrying, the largest block size depends on joint frequency; abundant fractures are desirable for quarrying crushed rock and gravel. Joint sets and systems Joints are ubiquitous features of rock exposures and often form families of straight to curviplanar fractures typically perpendicular to the layer boundaries in sedimentary rocks. A set is a group of joints with similar orientation and morphology. Several sets usually occur at the same place with no apparent interaction, giving exposures a blocky or fragmented appearance. Two or more sets of joints present together in an exposure compose a joint system. -
Mechanical Stratigraphic Controls on Natural Fracture Spacing and Penetration
Journal of Structural Geology 95 (2017) 160e170 Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg Mechanical stratigraphic controls on natural fracture spacing and penetration * Ronald N. McGinnis a, , David A. Ferrill a, Alan P. Morris a, Kevin J. Smart a, Daniel Lehrmann b a Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166, USA b Geoscience Department, Trinity University, One Trinity Place, San Antonio, TX 78212, USA article info abstract Article history: Fine-grained low permeability sedimentary rocks, such as shale and mudrock, have drawn attention as Received 20 July 2016 unconventional hydrocarbon reservoirs. Fracturing e both natural and induced e is extremely important Received in revised form for increasing permeability in otherwise low-permeability rock. We analyze natural extension fracture 21 December 2016 networks within a complete measured outcrop section of the Ernst Member of the Boquillas Formation Accepted 7 January 2017 in Big Bend National Park, west Texas. Results of bed-center, dip-parallel scanline surveys demonstrate Available online 8 January 2017 nearly identical fracture strikes and slight variation in dip between mudrock, chalk, and limestone beds. Fracture spacing tends to increase proportional to bed thickness in limestone and chalk beds; however, Keywords: Mechanical stratigraphy dramatic differences in fracture spacing are observed in mudrock. A direct relationship is observed be- Natural fractures tween fracture spacing/thickness ratio and rock competence. Vertical fracture penetrations measured Fracture spacing from the middle of chalk and limestone beds generally extend to and often beyond bed boundaries into Fracture penetration the vertically adjacent mudrock beds. -
The Role of Pressure Solution Seam and Joint Assemblages In
THE ROLE OF PRESSURE SOLUTION SEAM AND JOINT ASSEMBLAGES IN THE FORMATION OF STRIKE-SLIP AND THRUST FAULTS IN A COMPRESSIVE TECTONIC SETTING; THE VARISCAN OF SOUTHWESTERN IRELAND Filippo Nenna and Atilla Aydin Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 e-mail: [email protected] scale such as strike-slip faults and thrust-cored folds in Abstract various stages of their development. In this study we focus on the initiation and development of strike-slip The Ross Sandstone in County Clare, Ireland, was faults by shearing of the initial JVs and PSSs and deformed by an approximately north-south compression formation of thrust faults by exploiting weak shale during the end-Carboniferous Variscan orogeny. horizons and the strike-parallel PSSs in the adjacent Orthogonal sets of fundamental structures form the sandstone intervals. initial assemblage; mutually abutting arrays of 170˚ Development of faults from shearing of initial oriented set 1 joints/veins (JVs) and approximately 75˚ fundamental structural elements with either opening or pressure solution seams (PSSs) that formed under the closing modes in a wide range of structural settings has same stress conditions. Orientations of set 2 (splay) JVs been extensively reported. Segall and Pollard (1983), and PSSs suggest a clockwise remote stress rotation of Martel and Pollard (1989) and Martel (1990) have about 35˚ responsible for the contemporaneous described strike-slip faults formed by shearing of shearing of the set 1 arrays. Prominent strike-slip faults thermal fractures in granitic rocks. Myers and Aydin are sub-parallel to set 1 JVs and form by the linkage of (2004) and Flodin and Aydin (2004) reported strike-slip en-echelon segments with broad damage zones faulting formed by shearing of joints formed by an responsible for strike-slip offsets of hundreds of metres. -
Sedimentary Stylolite Networks and Connectivity in Limestone
Sedimentary stylolite networks and connectivity in Limestone: Large-scale field observations and implications for structure evolution Leehee Laronne Ben-Itzhak, Einat Aharonov, Ziv Karcz, Maor Kaduri, Renaud Toussaint To cite this version: Leehee Laronne Ben-Itzhak, Einat Aharonov, Ziv Karcz, Maor Kaduri, Renaud Toussaint. Sed- imentary stylolite networks and connectivity in Limestone: Large-scale field observations and implications for structure evolution. Journal of Structural Geology, Elsevier, 2014, pp.online first. <10.1016/j.jsg.2014.02.010>. <hal-00961075v2> HAL Id: hal-00961075 https://hal.archives-ouvertes.fr/hal-00961075v2 Submitted on 19 Mar 2014 HAL is a multi-disciplinary open access L'archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destin´eeau d´ep^otet `ala diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publi´esou non, lished or not. The documents may come from ´emanant des ´etablissements d'enseignement et de teaching and research institutions in France or recherche fran¸caisou ´etrangers,des laboratoires abroad, or from public or private research centers. publics ou priv´es. 1 2 Sedimentary stylolite networks and connectivity in 3 Limestone: Large-scale field observations and 4 implications for structure evolution 5 6 Laronne Ben-Itzhak L.1, Aharonov E.1, Karcz Z.2,*, 7 Kaduri M.1,** and Toussaint R.3,4 8 9 1 Institute of Earth Sciences, The Hebrew University, Jerusalem, 91904, Israel 10 2 ExxonMobil Upstream Research Company, Houston TX, 77027, U.S.A 11 3 Institut de Physique du Globe de Strasbourg, University of Strasbourg/EOST, CNRS, 5 rue 12 Descartes, F-67084 Strasbourg Cedex, France. -
Deformation at the Microscale
Deformation at the Microscale Deformation processes occur at the microscale and lead to changes in the internal structure, shape or volume of a rock. Brittle versus Plastic deformation mechanisms is a function of: • Pressure – increasing pressure favors plastic deformation • Temperature – increasing temperature favors plastic deformation • Rheology of the deforming minerals (for example quartz vs feldspar) • Availability of fluids – favors brittle deformation • Strain rate – lower strain rate favors plastic deformation Given the different rheology of different minerals, brittle and plastic deformation mechanisms can occur in the same sample under the same conditions. The controlling deformation mechanism determines whether the deformation belongs to the brittle or plastic regime. Brittle deformation mechanisms operative at shallow depths. Crystal-plastic Deformation Mechanisms Mechanical twining – mechanical bending or kinking of the crystal structure. Mechanical twins in calcite Deformation (glide) twins in a calcite crystal. Stress is ideally at 45o to the shear In the case of calcite, the 38o angle (glide plane). Dark lamellae turns the twin plane into a mirror have been sheared (simple plane. The amount of strain shear). associated with a single kink is fixed by this angle. Crystal Defects • Point defects – due to vacancies or impurities in the crystal structure. • Line defects (dislocations) – a mobile line defect that causes intracrystalline deformation via slip. The slip plane is usually the place in a crystal that has the highest density of atoms. • Plane defects – grain boundaries, subgrain boundaries, and twin planes. Migration of vacancies Types of defects – vacancy, through a crystal structure by substitution, interstitial diffusion. The movement of dislocations occurs in the plane or direction which requires the least energy. -
Stress and Fluid Control on De Collement Within Competent Limestone
Journal of Structural Geology 22 (2000) 349±371 www.elsevier.nl/locate/jstrugeo Stress and ¯uid control on de collement within competent limestone Antonio Teixell a,*, David W. Durney b, Maria-Luisa Arboleya a aDepartament de Geologia, Universitat AutoÁnoma de Barcelona, 08193 Bellaterra, Spain bDepartment of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia Received 5 October 1998; accepted 23 September 1999 Abstract The Larra thrust of the Pyrenees is a bedding-parallel de collement located within a competent limestone unit. It forms the ¯oor of a thrust system of hectometric-scale imbrications developed beneath a synorogenic basin. The fault rock at the de collement is a dense stack of mainly bedding-parallel calcite veins with variable internal deformation by twinning and recrystallization. Veins developed as extension fractures parallel to a horizontal maximum compressive stress, cemented by cavity-type crystals. Conditions during vein formation are interpreted in terms of a compressional model where crack-arrays develop at applied stresses approaching the shear strength of the rock and at ¯uid pressures equal to or less than the overburden pressure. The cracks developed in response to high dierential stress, which was channelled in the strong limestone, and high ¯uid pressure in or below the thrust plane. Ductile deformation, although conspicuous, cannot account for the kilometric displacement of the thrust, which was mostly accommodated by slip on water sills constituted by open cracks. A model of cyclic dierential brittle contraction, stress reorientation, slip and ductile relaxation at a rheological step in the limestone is proposed as a mechanism for episodic de collement movement. -
Stylolites: Characteristics and Origin
• STYLOLITES: CHARACTERISTICS AND ORIGIN Joseph M. Montello A senior thesis submitted to fulfill the requirements for the degree of B.S. in Geology and Mineralogy • Winter Quarter, 1984 The Ohio State University ~2.~r·Thesis Advisor Department of Geology and Mineralogy Abstract • Stylolites are alternating interpenetrating columns of stone that form irregular interlocking partings or sutures in rock strata. They are most common along bedding planes of limestone but some are oblique or even perpendicular to bedding . Although the vast majority of stylolites occur in calcareous rocks, stylolites have been found in sandstone, quartzite and gypsum. The word "stylolite" refers to each individual column of stone. A cross section of a group of stylolites parallel to their length presents a rough, jagged line called a "stylolite seam" that resembles the sutures of a human skull. Stylolites always have a dark colored "clay" cap at the ends of the columns. The sides of the columns are typically discolored with a thin film of clay and show parallel flutings or striations that parallel their length. The shapes of individual stylolites vary greatly from broad flat • topped columns to pointed, jagged and tapering forms. After much controversy concerning the origin of stylolites, it is generally believed that they form by a process of chemical solution under pressure in lithified rock along some crack or seam. The interteething is produced because of differential solubilities and pressures within the rock unit. The clay cap on the stylolites is the non-soluble residue of the dissolved rock. Stylolites are only one of the possible end products in the spectrum of limestone responses to stress. -
Post-Seismic Deformation Mechanism of the July 2015 MW 6.5 Pishan
www.nature.com/scientificreports OPEN Post‑seismic deformation mechanism of the July 2015 MW 6.5 Pishan earthquake revealed by Sentinel‑1A InSAR observation Sijia Wang1*, Yongzhi Zhang1,2*, Yipeng Wang1, Jiashuang Jiao 1, Zongtong Ji1 & Ming Han1 On 3 July 2015, the Mw 6.5 Pishan earthquake occurred at the junction of the southwestern margin of the Tarim Basin and the northwestern margin of the Tibetan Plateau. To understand the seismogenic mechanism and the post‑seismic deformation behavior, we investigated the characteristics of the post‑seismic deformation felds in the seismic area, using 9 Sentinel‑1A TOPS synthetic aperture radar (SAR) images acquired from 18 July 2015 to 22 September 2016 with the Small Baseline Subset Interferometric SAR (SBAS‑InSAR) technique. Postseismic LOS deformation displayed logarithmic behavior, and the temporal evolution of the post‑seismic deformation is consistent with the aftershock sequence. The main driving mechanism of near‑feld post‑seismic displacement was most likely to be afterslip on the fault and the entire creep process consists of three creeping stages. Afterward, we used the steepest descent method to invert the afterslip evolution process and analyzed the relationship between post‑seismic afterslip and co‑seismic slip. The results witness that 447 days after the mainshock (22 September 2016), the afterslip was concentrated within one principal slip center. It was located 5–25 km along the fault strike, 0–10 km along with the fault dip, with a cumulative peak slip of 0.18 m. The 447 days afterslip seismic moment was approximately 2.65 × 1017 N m, accounting for approximately 4.1% of the co‑seismic geodetic moment. -
LIBRO GEOLOGIA 30.Qxd:Maquetaciûn 1
Trabajos de Geología, Universidad de Oviedo, 30 : 163-168 (2010) Peek inside the black box of calcite twinning paleostress analysis J. REZ1* AND R. MELICHAR1 1Department of Geological Sciences, Faculty of Science, Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic. *e-mail: [email protected] Abstract: Calcite e-twinning has been used for stress inversion purposes since the fifties. The common- ly used technique is the Etchecopar method (e.g. Laurent et al., 1981), based on testing of 500-1000 randomly generated reduced stress tensors using a penalization function fL. A systematic search of all possible reduced stress tensors with a new penalization function fR double checked with a spatial dis- tribution plot is suggested. Keywords: stress inversion, paleostress analysis, calcite, mechanical twinning. Extensive research of the deformation mechanisms of sion is 10 MPa, which was experimentally determined τ calcite monocrystals and polycrystalline aggregates by Turner et al. (1954). The magnitude of c is inde- during the last century provided evidence of several pendent of normal stress σ, magnitude and tempera- glide and twinning systems present in calcite. Twelve ture (e.g. Turner et al., 1954; De Bresser and Spiers, different glide systems on five different crystallo- 1997; figure 1b). In order to cause twinning, the graphic planes and three different twinning systems stress tensor acting upon an e-plane must have appro- have been defined (Bestmann and Prior, 2003). Only priate principal direction orientation and sufficient twinning systems are suitable for stress inversion pur- differential component. The magnitude of the shear poses because they are easy to observe under an opti- stress is controlled by the Schmid criterion μ, which σ cal microscope, their orientation can be measured is a function of the orientation of the 1 vector σ using either a universal stage or EBSD and only one (Handin and Griggs, 1951; figure 1c). -
Stylolite Compaction and Stress Models
Geophysical Research Abstracts, Vol. 11, EGU2009-1720, 2009 EGU General Assembly 2009 © Author(s) 2009 Stylolite compaction and stress models D. Koehn (1), M. Ebner (1), F. Renard (2), and R. Toussaint (3) (1) University of Mainz, Department of Geology, Mainz, Germany ([email protected]), (2) LGIT-CNRS-Observatoire, University of Grenoble, France, (3) Institut de Physique du Globe de Strasbourg, University of Strasbourg, France Stylolites are rough dissolution seams that develop during pressure solution in the Earth’s crust. Especially in limestone quarries they exhibit a spectacular roughness with spikes and large columns. They are visible as dark lines of residual clays and other non-dissolvable components in the white limestone. The roughening phenomena seems to be universal since stylolites can also be found in quarzites, mylonites and all kinds of rocks that undergo pressure solution. The genesis of stylolites is not well understood even though they have been used to estimate compaction and to determine the direction of the main compressive stress. We have developed a numerical model to study the dynamic development of the roughness and its dependence on stress. Based on the model we present estimates of finite strain and depth of burial. The numerical stylolites are studied in two ways: the temporal evolution of the roughness on one hand and the fractal characteristics of the roughness on the other hand. In addition we vary the noise in the model and illustrate the importance of the grain size on the roughening process. Surface energies are dominant for small wavelengths and the initial stylolite growth is non-linear and as slow as a diffusive process. -
Deformation Mechanism of Kink-Step Distorted Coherent Twin Boundaries in Copper Nanowire
AIMS Materials Science, 4(1): 102-117. DOI: 10.3934/matersci.2017.1.102 Received: 08 November 2016 Accepted: 27 December 2016 Published: 05 January 2017 http://www.aimspress.com/journal/Materials Research article Deformation mechanism of kink-step distorted coherent twin boundaries in copper nanowire Bobin Xing 1, Shaohua Yan 1, Wugui Jiang 2, and Qing H. Qin 1,* 1 Research School of Engineering, Australian National University, Acton, ACT 2601, Australia 2 School of Aeronautical Manufacturing Engineering, Nanchang Hangkong University, Nanchang 330063, China * Correspondence: Email: [email protected]; Tel: +61-0261258274; Fax: +61-0261255476. Abstract: In the construction of nanotwinned (NT) copper, inherent kink-like steps are formed on growth twin boundaries (TBs). Such imperfections in TBs play a crucial role in the yielding mechanism and plastic deformation of NT copper. Here, we used the molecular dynamic (MD) method to examine the influence of kink-step characteristics in depth, including kink density and kink-step height, on mechanical behavior of copper nanowire (NW) in uniaxial tension. The results showed that the kink-step, a stress-concentrated region, is preferential in nucleating and emitting stress-induced partial dislocations. Mixed dislocation of hard mode I and II and hard mode II dislocation were nucleated from kink-step and surface atoms, respectively. Kink-step height and kink density substantially affected the yielding mechanism and plastic behavior, with the yielding stress functional-related to kink-step height. However, intense kink density (1 kink per 4.4 nm) encourages dislocation nucleation at kink-steps without any significant decline in tensile stress. Defective nanowires with low kink-step height or high kink density offered minimal resistance to kink migration, which has been identified as one of the primary mechanisms of plastic deformation.