DOCSLIB.ORG

Influence of Décollement Friction on Anisotropy of Magnetic

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Influence of Décollement Friction on Anisotropy of Magnetic Journal of Structural Geology 144 (2021) 104274 Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: http://www.elsevier.com/locate/jsg Influenceof d´ecollement friction on anisotropy of magnetic susceptibility in a fold-and-thrust belt model Thorben Schofisch¨ *, Hemin Koyi, Bjarne Almqvist Hans Ramberg Tectonic Laboratory, Department of Earth Sciences, Uppsala University, Villavagen¨ 16, 752 36, Uppsala, Sweden ARTICLE INFO ABSTRACT Keywords: Anisotropy of magnetic susceptibility can provide insights into strain distribution in models simulating fold-and- Analogue modelling thrust belts. Models with layers of sand and magnetite mixture shortened above adjacent d´ecollements with high Anisotropy of magnetic susceptibility and low friction, are used to study the effect of d´ecollement friction on the magnetic fabric. Above high-friction Fold-and-thrust belt d´ecollement, an imbricate stack produced a ‘tectonic’ fabric with magnetic foliation parallel to thrusts. In Basal friction contrast, above the low-friction d´ecollement deformation propagated farther into the foreland, and deformation D´ecollement intensity is gradual from the foreland to the hinterland by defining a transition zone in between. In this zone, magnetic lineation rotated parallel to the deformation front, whereas in the hinterland the principal axes do not show a preferred orientation due to different deformation mechanisms between “thrust-affected” and “pene­ trative-strain affected” area. Above both decollement´ types, the principal axes of susceptibility developed tighter clustering with depth. Along the boundary between the two d´ecollements, a deflection zone formed where rotation of surface markers and magnetic fabric reflect the transition between structures formed above the different decollements.´ Through quantifying magnetic fabric, this study reemphasises the clear link between d´ecollement friction, strain distribution and magnitude in fold-and-thrust belts. 1. Introduction results to the salt range in Pakistan, Cotton and Koyi (2000) concluded that the structures that develop in such deflection zones may trend Many models have addressed the influence of basal friction on the parallel to the shortening direction. Strain in such FTB models can be geometric, kinematic and dynamic evolution of fold-and-thrust belts estimated using passive markers at the surface (e.g. Nilforoushan and (FTB) (e.g. Davis et al., 1983; Dahlen et al., 1984; Colletta et al., 1991; Koyi, 2007), topographic change and laser scanning (e.g. Nilforoushan Huiqi et al., 1992; Mulugeta and Koyi, 1992; Willet, 1992; Gutscher et al., 2008) or other optical methods as summarized in Schellart and et al., 1996; Cotton and Koyi, 2000; Koyi et al., 2000; Agarwal and Strak (2016). In addition, taking sections during subsequent stages of Agrawal, 2002; Costa and Vendeville, 2002; Bahroudi and Koyi, 2003; deformation provides further information on internal deformation Koyi and Vendeville, 2003; Koyi and Cotton, 2004; Nilforoushan and across the model and displays the 4D evolution of the model (Colletta Koyi, 2007; Nilforoushan et al., 2008; Vidal-Royo et al., 2009). These et al., 1991; Mulugeta and Koyi, 1992). studies have shown that the structural style of a FTB depends on the The three main components of deformation in a FTB are faulting, d´ecollement friction. For example, above a low-friction d´ecollement (i) folding and layer-parallel shortening. The latter, which includes shortened layers form a wedge that possesses a gentler taper, (ii) the compaction by grain rearrangement and rotation, is not easy to estimate deformation front propagates farther, and (iii) both fore- and back­ in nature, but is of major significance for understanding the dynamic thrusts develop (Davis and Engelder, 1985; Cotton and Koyi, 2000). In evolution of a FTB, porosity reduction, and creation of balanced cross contrast, above a high-friction d´ecollement a stack of imbricates form, sections (Koyi et al., 2003; Sans et al., 2003). However, anisotropy of that consists of mainly forethrusts with a steeper taper wedge (Mulu­ magnetic susceptibility (AMS), which is a potentially useful tool to geta, 1988). Cotton and Koyi (2000) showed additionally that a describe details of grain reorientation and deformation in different deflectionzone forms in cover layers at the boundary between adjacent tectonic regimes (e.g. Graham, 1966; Borradaile and Henry, 1997; Pares,´ d´ecollements of contrasting low- and high-friction. Applying their 2015) can also be used to decipher this component of deformation. * Corresponding author. E-mail addresses: [email protected] (T. Schofisch),¨ [email protected] (H. Koyi), [email protected] (B. Almqvist). https://doi.org/10.1016/j.jsg.2020.104274 Received 1 September 2020; Received in revised form 21 December 2020; Accepted 23 December 2020 Available online 31 December 2020 0191-8141/© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). T. Schofisch¨ et al. Journal of Structural Geology 144 (2021) 104274 Recently, Almqvist and Koyi (2018) applied AMS analysis to definethe AMS ellipsoid, which is described by the shape factor T with a analogue models to describe the general strain evolution in a FTB. They spectrum ranges from T = +1 for oblate, T = 0 for neutral to T = 1 for outlined strain partitioning in different shortened models and repro­ prolate ellipsoids and the corrected degree of anisotropy Pj, which de­ duced their AMS patterns, which were comparable to AMS fabric evo­ scribes the degree of anisotropy of the ellipsoid. The mathematical ex­ lution in natural FTBs (e.g. Kligfieldet al., 1981; Borradaile and Henry, pressions for T and Pj use the natural logarithms (n) of the three 1997; Weil and Yonkee, 2009). In this study, we use the same method­ principal susceptibility axes (Jelinek, 1981), as shown in the following ology as Almqvist and Koyi (2018), to outline the AMS pattern in a equations: model simulating a FTB shortened above two different frictional sub­ 2 nint nmax nmin strates in order to evaluate the influence of d´ecollement friction on T = (1) nmax nmin magnetic fabric, strain distribution and intensity at surface and depth. q̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅]}̅ Pj = exp f 2 [( n n )2 + (n n )2 + (n n )2 (2) 2. Experimental setup and anisotropy of magnetic susceptibility max mean int mean min mean = ( ) = ( ) = ( ) = ( + Loose quartz sand (0.124–0.356 mm), which was used to build the with nmax ln kmax , nint ln kint , nmin ln kmin , and nmean nmax + )= layers of the model, was mixed homogenously with blocky, subangular nint nmin 3. magnetite grains of same size range (<0.1 vol%) to facilitate AMS an­ Plotting both parameters (T and Pj) provides a distribution of ellip­ alyses of samples taken from the deformed model. This granular mixture soid shapes, which describes a strain path of the AMS dataset (Jelinek, (cohesion μ = 0.49) is scraped from the backstop (north) to the ‘model 1981; Hrouda, 1982; Borradaile, 1988, 1991; Borradaile and Henry, south’ to a 2.5 cm thick layer within a 67 × 60 cm large sandbox and 1997). shortened above two adjacent substrates simulating different frictional d´ecollements (sandpaper with μ = 0.71, and fibre glass with μ = 0.29) 3. Results (Fig. 1). To decrease the influence of the backstop, a 7-cm long sand ◦ wedge with a 28 taper was built on top of the model next to the 3.1. Structural evolution backstop (Fig. 1). A passive marker of circles with a different colour sand was printed on the surface of the model to monitor surface deformation. Shortening of the model above two different frictional decollements´ After a total of 17 cm (26% of length) bulk shortening, the model was resulted in a differential propagation of the deformation front and pat­ carefully wetted and sampled systematically for AMS analysis. Wetting terns of different strain (Figs. 2 and 3). Above the high-friction of the model was made through adsorption of water through the porous decollement,´ an imbricate stack formed, which increased the model sand, in order to preserve the fabric and not cause physical disturbance height next to the backstop by a factor of three compared to its initial of the sand. Sequential sectioning was performed, and oriented cubic undeformed state (Fig. 3). Here, forethrusts dip with angles between 15 ◦ samples (volume of 2.2 cm3) were taken at the surface and at depth and 40 towards the backstop. In contrast, above the low-friction along the sections in the wetted model. AMS was measured with a decollement,´ three boxfolds with major backthrusts and several fore­ ◦ MFK1-FA Kappabridge (Agico Inc.) using an AC fieldstrength of 200 A/ thrusts developed, with dips between 35 and 50 and a gentle wedge m with a frequency of 976 Hz. The measurements provide the average slope. In addition, on this side of the model, deformation propagated orientation and degree of alignment of all grains within a sample, based farther (ca. 10 cm) into the foreland compared to that on the high- ´ on principal axes of susceptibility, kmax ≥ kint ≥ kmin, which are calcu­ friction decollement (Fig. 3). Ahead of the frontal thrust within the lated from the magnetic susceptibility second rank symmetric tensor. foreland of the low-friction domain, circular strain markers at the sur­ The orientations of the principal susceptibility
Load more

Recommended publications
  • Tectonic Imbrication and Foredeep Development in the Penokean
    Tectonic Imbrication and Foredeep Development in the Penokean Orogen, East-Central Minnesota An Interpretation Based on Regional Geophysics and the Results of Test-Drilling The Penokean Orogeny in Minnesota and Upper Michigan A Comparison of Structural Geology U.S. GEOLOGICAL SURVEY BULLETIN 1904-C, D AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the cur­ rent-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Sur­ vey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated month­ ly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, Box 25425, Denver, CO 80225. Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. Order U.S. Geological Survey publications by mail or over the counter from the offices given below. BY MAIL OVER THE COUNTER Books Books Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications of general in­ Books of the U.S.
    [Show full text]
  • Strike and Dip Refer to the Orientation Or Attitude of a Geologic Feature. The
    Name__________________________________ 89.325 – Geology for Engineers Faults, Folds, Outcrop Patterns and Geologic Maps I. Properties of Earth Materials When rocks are subjected to differential stress the resulting build-up in strain can cause deformation. Depending on the material properties the result can either be elastic deformation which can ultimately lead to the breaking of the rock material (faults) or ductile deformation which can lead to the development of folds. In this exercise we will look at the various types of deformation and how geologists use geologic maps to understand this deformation. II. Strike and Dip Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature, is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented parallel to the strike line. Strike (or strike angle) can be given as either a quadrant compass bearing of the strike line (N25°E for example) or in terms of east or west of true north or south, a single three digit number representing the azimuth, where the lower number is usually given (where the example of N25°E would simply be 025), or the azimuth number followed by the degree sign (example of N25°E would be 025°). The dip gives the steepest angle of descent of a tilted bed or feature relative to a horizontal plane, and is given by the number (0°-90°) as well as a letter (N, S, E, W) with rough direction in which the bed is dipping.
    [Show full text]
  • Patricia Persaud
    A bottom-driven mechanism for distributed faulting in the Gulf of California Rift Patricia Persaud1, Eh Tan2, Juan Contreras3 and Luc Lavier4 2017 GeoPRISMS Theoretical and Experimental Institute on Rift Initiation and Evolution [email protected], Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803; 2 Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan; 3 Centro de Investigación Científca y de Educación Superior de Ensenada, Ensenada, BC, Mexico; 4 University of Texas Austin, Institute for Geophysics, Austin, TX 78712 Introduction Modeling strain partitioning and distribution of deformation in Application to the Northern Gulf Observations in the continent-ocean transition of the Gulf • Our model with an obliquity of 0.7, and linear basal velocity of California (GOC) show multiple oblique-slip faults oblique rifts boundary conditions reveals a delocalized fault pattern of distributed in a 200x70 km2 area (Fig. 4). In contrast, north contemporaneously active faults, multiple rift basins and and south of this broad pull-apart structure, major transform variable fault dips representative of faulting in the N. Gulf. faults accommodate plate motion. We propose that the FIG. 9 • The r=0.7 model is able to predict the broad geometrical mechanism for distributed faulting results from the boundary arrangement of the two Upper Delfn, Lower Delfn and conditions present in the GOC, where basal shear is Wagner basins as segmented basins with tilted fault blocks, distributed between the southernmost fault of the San and multiple oblique-slip bounding faults characteristic of Andreas system and the Ballenas Transform fault. FIG. 8 incomplete strain-partitioning. We also confrm with our We hypothesize that in oblique-extensional settings numerical results that numerous oblique-slip faults whether deformation is partitioned in a few dip-slip and accommodate slip in the study area instead of throughgoing strike-slip faults, or in numerous oblique-slip faults may large-offset transform faults.
    [Show full text]
  • Non-Cylindrical Parasitic Folding and Strain Partitioning
    Solid Earth Discuss., https://doi.org/10.5194/se-2018-6 Manuscript under review for journal Solid Earth Discussion started: 6 February 2018 c Author(s) 2018. CC BY 4.0 License. Non-cylindrical parasitic folding and strain partitioning during the Pan-African Lufilian orogeny in the Chambishi-Nkana Basin, Central African Copperbelt Koen Torremans1, Philippe Muchez1, Manuel Sintubin2 5 1KU Leuven, Department of Earth and Environmental Sciences, Geodynamics and Geofluids Research Group, Celestijnenlaan 200E, 3001 Leuven, Belgium. 2Present address: Irish Centre for Research in Applied Geosciences, University College Dublin, Dublin 4, Ireland. Correspondence to: Koen Torremans ([email protected]) 1 Solid Earth Discuss., https://doi.org/10.5194/se-2018-6 Manuscript under review for journal Solid Earth Discussion started: 6 February 2018 c Author(s) 2018. CC BY 4.0 License. Abstract. A structural analysis has been carried out along the southeast margin of the Chambishi-Nkana Basin in the Central African Copperbelt, hosting the world-class Cu-Co Nkana orebody. The geometrically complex structural architecture is interpreted to have been generated during a single NE-SW oriented compressional event, clearly linked to the Pan-African 5 Lufilian orogeny. This progressive deformation resulted primarily in asymmetric multiscale parasitic fold assemblages, characterized by non-cylindrical NW-SE elongated, periclinal folds that strongly interfere laterally, leading to fold linkage and bifurcation. The vergence and amplitude of these folds consistently reflect their position along an inclined limb of a NW plunging megascale first-order fold. A clear relation is observed between development of parasitic folds and certain lithofacies assemblages in the Copperbelt Orebody Member, which hosts most of the ore.
    [Show full text]
  • 7.5 X 11.5.Doubleline.P65
    Cambridge University Press 978-0-521-84404-8 - Deformation of Earth Materials: An Introduction to the Rheology of Solid Earth Shun-ichiro Karato Index More information Materials index Ag, 55 hydrogen, 104, 127, 129, 144, 149, 181, 183, 193, 195, akimotoite, 409 209, 287 Al2O3, 127, 134, 142, 375, 378 hydrogen-related defect, 82 albite, 27, 53 hydrous mineral, 318 alkali halide, 54, 171 anorthite, 27, 172, 241 ice, 53, 55, 274, 275 Au, 55 iron, 23, 28, 209, 275, 316 a–iron, 55, 209 basalt, 254, 315, 317, 345 "-iron, 53, 362, 410 ferric iron, 28, 128 CaIrO3, 410 ferrous iron, 28, 128 calcite, 62, 190, 209, 226, 245, 266, 378 carbon, 193 KBr, 172 carbon dioxide, 20, 102 KCl, 55, 172 carbonaceous chondrite, 316 CaTiO3, 209 lherzolite, 241 CaTiO3 perovskite, 410 garnet lherzolite, 319 clinopyroxene, 84, 186, 190, 345, 351 spinel lherzolite, 319 cobalt, 275 coesite, 272 magnesiowu¨stite, 27, 215, 274, 282, 386, corundum, 65 405, 409 CsCl, 171, 172, 274 magnetite, 28 Cu, 55 majorite, 319, 359, 375, 409 majorite-pyrope, 69 diabase, 254, 345, 346, 348 metal diopside, 53, 241, 347 bcc metal, 84 dunite, 189 fcc metal, 84 hcp metal, 71, 84 eclogite, 314, 318, 348, 405 meteorite, 305 enstatite, 55, 65, 347 Mg, 245 Mg2SiO4, 26, 70, 71, 81, 127, 134, 203 Fe2SiO4,26 MgO, 53, 54, 81, 82, 126, 132, 133, 134, 142, 171, 172, 209, 337, feldspar, 190, 215, 245, 347 375, 378, 406 forsterite, 55, 65 MgSiO3, 26, 81, 82 mica, 215 gabbro, 254, 317, 345 mid-ocean ridge basalt, 315 garnet, 26, 53, 69, 84, 172, 186, 190, 215, 318, 319, 347 MORB, 315 garnetite, 405
    [Show full text]
  • Deepwater Niger Delta Fold-And-Thrust Belt Modeled As a Critical-Taper Wedge: the Influence of a Weak Detachment on Styles of Fault-Related Folds
    Deepwater Niger Delta fold-and-thrust belt modeled as a critical-taper wedge: The influence of a weak detachment on styles of fault-related folds Frank Bilotti1, Chris Guzofski1, John H. Shaw2 1 Chevron 2Harvard University GeoPrisms Rift Initiation and Evolution Scientific Planning Workshop Niger delta “outer” fold-and-thrust belt very low taper Odd fault-related folds “Ductile” thickening Forethrusts and backthrusts in close proximity GeoPrisms Rift Initiation and Evolution Scientific Planning Workshop Outline • The nature of the toe of the Niger Delta • Basics of critical-taper wedge theory • The Niger Delta outer fold-and-thrust belt is at critical taper • Model parameters and results (high basal fluid pressure) • Applicability in 3D & subsequent work • Implications of high basal fluid pressure for contractional fault-related folds GeoPrisms Rift Initiation and Evolution Scientific Planning Workshop Niger Delta Bathymetry Slope fold-and-thrust belt deepwater fold-and-thrust belt GeoPrisms Rift Initiation and Evolution Scientific Planning Workshop Fold-and-thrust belts of the Niger Delta GeoPrisms Rift Initiation and Evolution Scientific Planning Workshop Regional Geologic Setting Inner Fold and Outer Fold and Thrust belt 1 i Thrust belt Detachment fold belt Extensional Growth Faults t 3250 Lobia-1 0 k m a 0 k m . l m p 4 m . numerouscr estal crestal growthfaults growth faults numerous growthfaults ? ( 3 ma ? mudd apir (?) ? 5 m P n i e i y R it u x c : e n d her s d 5 l 1 0 5 m l l i 2 5 mud diapr (?) 2 m N m s t i 5 k m velocty sag(?) 5 k m e 2 m a .5 ma s u i basal detachment a .0 i 5 a as e veoct y ag(?) velocty sag(?) .
    [Show full text]
  • Accommodation of Penetrative Strain During Deformation Above a Ductile Décollement
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Earth and Atmospheric Sciences, Department Papers in the Earth and Atmospheric Sciences of 2016 Accommodation of penetrative strain during deformation above a ductile décollement Bailey A. Lathrop Caroline M. Burberry Follow this and additional works at: https://digitalcommons.unl.edu/geosciencefacpub Part of the Earth Sciences Commons This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Accommodation of penetrative strain during deformation above a ductile décollement Bailey A. Lathrop* and Caroline M. Burberry* DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES, UNIVERSITY OF NEBRASKA-LINCOLN, 214 BESSEY HALL, LINCOLN, NEBRASKA 68588, USA ABSTRACT The accommodation of shortening by penetrative strain is widely considered as an important process during contraction, but the distribu- tion and magnitude of penetrative strain in a contractional system with a ductile décollement are not well understood. Penetrative strain constitutes the proportion of the total shortening across an orogen that is not accommodated by the development of macroscale structures, such as folds and thrusts. In order to create a framework for understanding penetrative strain in a brittle system above a ductile décollement, eight analog models, each with the same initial configuration, were shortened to different amounts in a deformation apparatus. Models consisted of a silicon polymer base layer overlain by three fine-grained sand layers. A grid was imprinted on the surface to track penetra- tive strain during shortening.
    [Show full text]
  • Early Cenozoic Eurekan Strain Partitioning and Decoupling in Central Spitsbergen, Svalbard
    Solid Earth, 12, 1025–1049, 2021 https://doi.org/10.5194/se-12-1025-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Early Cenozoic Eurekan strain partitioning and decoupling in central Spitsbergen, Svalbard Jean-Baptiste P. Koehl1,2,3,4 1Centre for Earth Evolution and Dynamics (CEED), University of Oslo, P.O. Box 1028 Blindern, 0315 Oslo, Norway 2Department of Geosciences, UiT The Arctic University of Norway in Tromsø, 9037 Tromsø, Norway 3Research Centre for Arctic Petroleum Exploration (ARCEx), University of Tromsø, 9037 Tromsø, Norway 4CAGE – Centre for Arctic Gas Hydrate, Environment and Climate, 9037 Tromsø, Norway Correspondence: Jean-Baptiste P. Koehl ([email protected]) Received: 30 September 2020 – Discussion started: 19 October 2020 Revised: 22 March 2021 – Accepted: 6 April 2021 – Published: 10 May 2021 Abstract. The present study of field, petrological, explo- Group and Mimerdalen Subgroup might be preserved east ration well, and seismic data describes backward-dipping of the Billefjorden Fault Zone, suggesting that the Billefjor- duplexes comprised of phyllitic coal and bedding-parallel den Fault Zone did not accommodate reverse movement in décollements and thrusts localized along lithological tran- the Late Devonian. Hence, the thrusting of Proterozoic base- sitions in tectonically thickened Lower Devonian to lower- ment rocks over Lower Devonian sedimentary rocks along most Upper Devonian; uppermost Devonian–Mississippian; the Balliolbreen Fault and fold structures within strata of the and uppermost Pennsylvanian–lowermost Permian sedimen- Andrée Land Group and Mimerdalen Subgroup in central tary strata of the Wood Bay and/or Wijde Bay and/or Spitsbergen may be explained by a combination of down-east Grey Hoek formations; of the Billefjorden Group; and Carboniferous normal faulting with associated footwall rota- of the Wordiekammen Formation, respectively.
    [Show full text]
  • PLANE DIP and STRIKE, LINEATION PLUNGE and TREND, STRUCTURAL MEASURMENT CONVENTIONS, the BRUNTON COMPASS, FIELD BOOK, and NJGS FMS
    PLANE DIP and STRIKE, LINEATION PLUNGE and TREND, STRUCTURAL MEASURMENT CONVENTIONS, THE BRUNTON COMPASS, FIELD BOOK, and NJGS FMS The word azimuth stems from an Arabic word meaning "direction“, and means an angular measurement in a spherical coordinate system. In structural geology, we primarily deal with land navigation and directional readings on two-dimensional maps of the Earth surface, and azimuth commonly refers to incremental measures in a circular (0- 360 °) and horizontal reference frame relative to land surface. Sources: Lisle, R. J., 2004, Geological Structures and Maps, A Practical Guide, Third edition http://www.geo.utexas.edu/courses/420k/PDF_files/Brunton_Compass_09.pdf http://en.wikipedia.org/wiki/Azimuth http://en.wikipedia.org/wiki/Brunton_compass FLASH DRIVE/Rider/PDFs/Holcombe_conv_and_meas.pdf http://www.state.nj.us/dep/njgs/geodata/fmsdoc/fmsuser.htm Brunton Pocket Transit Rider Structural Geology 310 2012 GCHERMAN 1 PlanePlane DipDip andand LinearLinear PlungePlunge horizontal dddooo Dip = dddooo Bedding and other geological layers and planes that are not horizontal are said to dip. The dip is the slope of a geological surface. There are two aspects to the dip of a plane: (a) the direction of dip , which is the compass direction towards which the plane slopes; and (b) the angle of dip , which is the angle that the plane makes with a horizontal plane (Fig. 2.3). The direction of dip can be visualized as the direction in which water would flow if poured onto the plane. The angle of dip is an angle between 0 ° (for horizontal planes) and 90 ° (for vertical planes). To record the dip of a plane all that is needed are two numbers; the angle of dip followed by the direction (or azimuth) of dip, e.g.
    [Show full text]
  • Deformation of Rocks
    DeformationDeformation ofof RocksRocks Rock Deformation Large scale deformation of the Earth’s crust = Plate Tectonics Smaller scale deformation = structural geology 1 Deformation of rocks Folds and faults are geologic structures Structural geology is the study of the deformation of rocks and the effects of this movement Small-Scale Folds 2 Small-Scale Faults Deformation – Stress vs. Strain Changes in volume or shape of a rock body = strain 3 Stress The force that acts on a rock unit to change its shape and/or its volume Causes strain or deformation Types of directed Stress include Compression Tension Shear Compression Action of coincident oppositely directed forces acting towards each other 4 Tension Action of coincident oppositely directed forces acting away from each other Shear Action of coincident oppositely directed forces acting parallel to each other across a surface Right Lateral Movement Left Lateral Movement 5 Differential stress Strength • Ability of an object to resist deformation •Compressive •Capacity of a material to withstand axially directed pushing forces – when the limit of compressive strength is reached, materials are crushed •Tensile •Measures the force required to pull something such as rope, wire, or a rock to the point where it breaks 6 Strain Any change in original shape or size of an object in response to stress acting on the object Kinds of deformation Elastic vs Plastic Brittle vs Ductile 7 Elastic Deformation Temporary change in shape or size that is recovered when the deforming force is removed
    [Show full text]
  • Joints, Folds, and Faults
    Structural Geology Rocks in the Crust Are Bent, Stretched, and Broken … …by directed stresses that cause Deformation. Types of Differential Stress Tensional, Compressive, and Shear Strain is the change in shape and or volume of a rock caused by Stress. Joints, Folds, and Faults Strain occurs in 3 stages: elastic deformation, ductile deformation, brittle deformation 1 Type of Strain Dependent on … • Temperature • Confining Pressure • Rate of Strain • Presence of Water • Composition of the Rock Dip-Slip and Strike-Slip Faults Are the Most Common Types of Faults. Major Fault Types 2 Fault Block Horst and Graben BASIN AND Crustal Extension Formed the RANGE PROVINCE Basin and Range Province. • Decompression melting and high heat developed above a subducted rift zone. • Former margin of Farallon and Pacific plates. • Thickening, uplift ,and tensional stress caused normal faults. • Horst and Graben structures developed. Fold Terminology 3 Open Anticline – convex upward arch with older rocks in the center of the fold (symmetrical) Isoclinal Asymmetrical Overturned Recumbent Evolution Simple Folds of a fold into a reverse fault An eroded anticline will have older beds in the middle An eroded syncline will have younger beds in middle Outcrop patterns 4 • The Strike of a body of rock is a line representing the intersection of A layer of tilted that feature with the plane of the horizon (always measured perpendicular to the Dip). rock can be • Dip is the angle below the horizontal of a geologic feature. represented with a plane. o 30 The orientation of that plane in space is defined with Strike-and- Dip notation. Maps are two- Geologic Map Showing Topography, Lithology, and dimensional Age of Rock Units in “Map View”.
    [Show full text]
  • Evolution of Stress and Fault Patterns in Oblique Rift Systems: 3-D Numerical Lithospheric-Scale Experiments from Rift to Breakup
    Originally published as: Brune, S. (2014): Evolution of stress and fault patterns in oblique rift systems: 3-D numerical lithospheric-scale experiments from rift to breakup. - Geochemistry Geophysics Geosystems (G3), 15, 8, p. 3392-3415. DOI: http://doi.org/10.1002/2014GC005446 PUBLICATIONS Geochemistry, Geophysics, Geosystems RESEARCH ARTICLE Evolution of stress and fault patterns in oblique rift systems: 10.1002/2014GC005446 3-D numerical lithospheric-scale experiments from rift to Key Points: breakup 3-D numerical rift models are conducted covering the entire Sascha Brune1,2 obliquity spectrum 1 A constant extension direction can Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Geodynamic Modelling Section, Potsdam, generate multiphase fault Germany, 2School of Geosciences, University of Sydney, EarthByte Group, Sydney, Australia orientations A characteristic evolution of fault patterns from rift to breakup is identified Abstract Rifting involves complex normal faulting that is controlled by extension direction, reactivation of prerift structures, sedimentation, and dyke dynamics. The relative impact of these factors on the Supporting Information: observed fault pattern, however, is difficult to deduce from field-based studies alone. This study provides Readme insight in crustal stress patterns and fault orientations by employing a laterally homogeneous, 3-D rift setup Supplementary Figures S1–S5 with constant extension velocity. The presented numerical forward experiments cover the whole spectrum Alpha A1–A7 of oblique extension. They are conducted using an elastoviscoplastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Despite recent advances, Correspondence to: S. Brune, 3-D numerical experiments still require relatively coarse resolution so that individual faults are poorly [email protected] resolved.
    [Show full text]