Introduction to Structural Geology

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8/19/2016 What is Structural Geology? Geol 341 Structural Geology Introduction Goals Topics and Logistics • 1. Understand Earth’s structures and • http://www.geo.wvu.edu/~jtoro the processes that create them. • 2. Learn skills used to analyze and interpret geological structures How do Tool to Measure Strike and Dip we explain the major You need to buy one now features of SUUNTO MC2 Navigator the Earth? or Brunton TRUARC15 Mirror Compass with clinometer, Azimuth (360o) $40 to $50 Or a smartphone app (Lambert) Earth Field Notebook $8 each Moon 1 8/19/2016 Why are there mountains? How do faults relate to earthquakes? Active mountain front, Basin and Matterhorn, Swiss Alps Range Province, Nevada Interaction between Structural and It all starts with field observations Sedimentary Processes Brooks Range Foothills, AK Erosion Tectonic Burial Sedimentary burial Basal heat flux A basic tool: the geologic map A structural cross section: Interpret deep structure from surface data 2 8/19/2016 How can solid rock flow like taffy? Strain Field in a Shear Zone Morcles Nappe, Swiss Alps From Ramsay and Hubert, 1983 Microscopic view: How is deformation accomplished? Study structures at all scales 5 mm Looking inside the Earth Seismic Reflection Data from Santos Basin (Brazil) Seismic Acquisition Fossen, 2010 3 8/19/2016 Practical applications of Structure Methods of Structural Geology Where is the oil field? Experiments with Analogue Materials Salt H.M. Cadell, 1887 Mechanics: What happens to the stress field Stress Components when you drill a well? Or when a fault forms? zz z zx xz xz xx xx zx zz x Fracture systems and their role in fluid flow Preparation for Field Camp 4 8/19/2016 Orientation of a Plane Apparent Horizontality Elements of Geology, Lyell 1871 True Dip vs Apparent Dip True Dip vs Apparent Dip Map View N d= true dip True 20 a= apparent dip Dip Apparent True b= angle between strike (d) Line of section and line of section b tan a= tan d . sin b 50o a= atan (tan d . sin b) Line of Strike Apparent Dip Table Take Home Points a b • Structural Geology ranges from field observations to quantitative models and has broad applications • You need to buy a geological compass • Strike and dip describe the orientation and tilt of rock layers • Apparent dip is the tilt seen on a plane that is NOT 90o to strike. It is always less than true dip 5.

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Linking Megathrust Earthquakes to Brittle Deformation in a Fossil Accretionary Complex
ARTICLE Received 9 Dec 2014 | Accepted 13 May 2015 | Published 24 Jun 2015 DOI: 10.1038/ncomms8504 OPEN Linking megathrust earthquakes to brittle deformation in a fossil accretionary complex Armin Dielforder1, Hauke Vollstaedt1,2, Torsten Vennemann3, Alfons Berger1 & Marco Herwegh1 Seismological data from recent subduction earthquakes suggest that megathrust earthquakes induce transient stress changes in the upper plate that shift accretionary wedges into an unstable state. These stress changes have, however, never been linked to geological structures preserved in fossil accretionary complexes. The importance of coseismically induced wedge failure has therefore remained largely elusive. Here we show that brittle faulting and vein formation in the palaeo-accretionary complex of the European Alps record stress changes generated by subduction-related earthquakes. Early veins formed at shallow levels by bedding-parallel shear during coseismic compression of the outer wedge. In contrast, subsequent vein formation occurred by normal faulting and extensional fracturing at deeper levels in response to coseismic extension of the inner wedge. Our study demonstrates how mineral veins can be used to reveal the dynamics of outer and inner wedges, which respond in opposite ways to megathrust earthquakes by compressional and extensional faulting, respectively. 1 Institute of Geological Sciences, University of Bern, Baltzerstrasse 1 þ 3, Bern CH-3012, Switzerland. 2 Center for Space and Habitability, University of Bern, Sidlerstrasse 5, Bern CH-3012, Switzerland. 3 Institute of Earth Surface Dynamics, University of Lausanne, Geˆopolis 4634, Lausanne CH-1015, Switzerland. Correspondence and requests for materials should be addressed to A.D. (email: [email protected]). NATURE COMMUNICATIONS | 6:7504 | DOI: 10.1038/ncomms8504 | www.nature.com/naturecommunications 1 & 2015 Macmillan Publishers Limited.
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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.
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Significance of Brittle Deformation in the Footwall
Journal of Structural Geology 64 (2014) 79e98 Contents lists available at SciVerse ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg Significance of brittle deformation in the footwall of the Alpine Fault, New Zealand: Smithy Creek Fault zone J.-E. Lund Snee a,*,1, V.G. Toy a, K. Gessner b a Geology Department, University of Otago, PO Box 56, Dunedin 9016, New Zealand b Western Australian Geothermal Centre of Excellence, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia article info abstract Article history: The Smithy Creek Fault represents a rare exposure of a brittle fault zone within Australian Plate rocks that Received 28 January 2013 constitute the footwall of the Alpine Fault zone in Westland, New Zealand. Outcrop mapping and Received in revised form paleostress analysis of the Smithy Creek Fault were conducted to characterize deformation and miner- 22 May 2013 alization in the footwall of the nearby Alpine Fault, and the timing of these processes relative to the Accepted 4 June 2013 modern tectonic regime. While unfavorably oriented, the dextral oblique Smithy Creek thrust has Available online 18 June 2013 kinematics compatible with slip in the current stress regime and offsets a basement unconformity beneath Holocene glaciofluvial sediments. A greater than 100 m wide damage zone and more than 8 m Keywords: Fault zone wide, extensively fractured fault core are consistent with total displacement on the kilometer scale. e Fluid flow Based on our observations we propose that an asymmetric damage zone containing quartz carbonate Hydrofracture echloriteeepidote veins is focused in the footwall.
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Wakabayashi Intgeolr
International Geology Review ISSN: 0020-6814 (Print) 1938-2839 (Online) Journal homepage: http://www.tandfonline.com/loi/tigr20 Whither the megathrust? Localization of large- scale subduction slip along the contact of a mélange John Wakabayashi & Christie D. Rowe To cite this article: John Wakabayashi & Christie D. Rowe (2015) Whither the megathrust? Localization of large-scale subduction slip along the contact of a mélange, International Geology Review, 57:5-8, 854-870, DOI: 10.1080/00206814.2015.1020453 To link to this article: http://dx.doi.org/10.1080/00206814.2015.1020453 Published online: 09 Mar 2015. Submit your article to this journal Article views: 189 View related articles View Crossmark data Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tigr20 Download by: [University of California, Berkeley] Date: 04 April 2016, At: 09:19 International Geology Review, 2015 Vol. 57, Nos. 5–8, 854–870, http://dx.doi.org/10.1080/00206814.2015.1020453 Whither the megathrust? Localization of large-scale subduction slip along the contact of a mélange John Wakabayashia* and Christie D. Roweb aDepartment of Earth and Environmental Sciences, California State University, Fresno, CA, USA; bDepartment of Earth and Planetary Sciences, McGill University, Montreal, Canada (Received 13 February 2015; accepted 14 February 2015) Long-lived subduction complexes, such as the Franciscan Complex of California, include tectonic contacts that represent exhumed megathrust horizons that collectively accommodated thousands of kilometres of slip. The chaotic nature of mélanges in subduction complexes has spawned proposals that these mélanges form as a result of megathrust displacement.
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Silica Gel Formation During Fault Slip: Evidence from The
*Manuscript Publisher: GSA Journal: GEOL: Geology Article ID: G34483 1 Silica gel formation during fault slip: Evidence from the 2 rock record 3 J.D. Kirkpatrick1*, C.D. Rowe2, J.C. White3, and E.E. Brodsky1 4 1Earth & Planetary Sciences Department, University of California–Santa Cruz, 1156 5 High Street, Santa Cruz, California 95064, USA 6 2Department of Earth & Planetary Sciences, McGill University, 3450 University Street, 7 Montréal, QC H3A 0E8, Canada 8 3Department of Earth Sciences, University of New Brunswick, 2 Bailey Drive, 9 Fredericton, New Brunswick E3B 5A3, Canada 10 *Current address: Department of Geosciences, Colorado State University, 1482 Campus 11 Delivery, Fort Collins, Colorado 80523, USA. 12 ABSTRACT 13 Dynamic reduction of fault strength is a key process during earthquake rupture. 14 Many mechanisms causing coseismic weakening have been proposed based on theory 15 and laboratory experiments, including silica gel lubrication. However, few have been 16 observed in nature. Here we report on the first documented occurrence of a natural silica 17 gel coating a fault surface. The Corona Heights fault slickenside in San Francisco, 18 California, is covered by a shiny layer of translucent silica. Microstructures in this layer 19 show flow banding, armored clasts and extreme comminution compared to adjacent 20 cataclasites. The layer is composed of ~100 nm to 1 µm grains of quartz, hydrous 21 crystalline silica, and amorphous silica, with 10–100 nm inclusions of Fe oxides and 22 ellipsoidal silica colloids. Kinematic indicators and mixing with adjacent cataclasites Page 1 of 15 Publisher: GSA Journal: GEOL: Geology Article ID: G34483 23 suggest the shiny layer was fluid during fault slip.
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Stylolites and Crack-Seal Veins in Finnmark, North Norway Textures Shear Zones Stylolites
Stylolites and crack-seal veins in Finnmark, north Norway NICHOLASJ. MILTON Milton, N. J.: Stylolites and crack-sea! veins in Finnmark, north Norway, Norsk Geologisk Tidsskrift, Vol. 60, pp. 219-221. Oslo 1980. ISSN 0029-196X. Sediments of the Cambro-Ordovician Digermul Group on Digermulhalvøya, north Norway, are locally deform ed below the tectonically emplaced Caledonian Laksefjord Nappe. The rocks contain stylolite seams, crackseal veins, and conjugate shear surfaces, suggesting that deformation took place largely by pressure solution, Iocal transport, and redeposition of quartz. An X : Z strain ratio of approximately 1.25 was achieved by this mechanism. N. J. Milton, B.N.O.C, 150 St. Vincent Street, Glasgow, G 25 U, Great Britain. In tht. valley Kistedalen on Digermulhalvøya, of quartz veins, and, perpendicular to these, a Finnmark, north Norway, the metamorphic series of stylolite seams (Fig. lA). Caledonian Laksefjord Nappe rests tectonically above folded but unmetamorphosed Cambro Shear zones Ordovician sediments of the Digermul Group (Reading 1965). The sediments of the Digermul The sample (Fig lB) is crossed by two conjugate Group are strongly altered within a zone up to 20 sets of shear zones which intersect at 112 de m below the basal Laksefjord thrust. The other grees. These shears give rise to the cleavage wise pale to dark sandstones and shales develop observed in the field. In thin section they appear a dark charred appearance and a metallic surface as dark concentrations of opaque minerals, and sheen. At the same time a poor cleavage, sub sites for nucleation of brown mica. The concen parallel to the Laksefjord thrust, is developed, tration of opaque minerals is responsible for the and minor folds (with sub-horizontal axial metallic sheen seen on the shear surfaces.
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Towards a Nappe Theory
https://doi.org/10.5194/se-2019-130 Preprint. Discussion started: 26 August 2019 c Author(s) 2019. CC BY 4.0 License. Towards a nappe theory: Thermo-mechanical simulations of nappe detachment, transport and stacking in the Helvetic Nappe System, Switzerland Dániel Kiss1, Thibault Duretz2,1, and Stefan M. Schmalholz1 1Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland 2Univ. Rennes, CNRS, Géosciences Rennes - UMR 6118, F-35000 Rennes, France Correspondence: Dániel Kiss ([email protected]) Abstract. Tectonic nappes are observed for more than a hundred years. Although geological studies often refer to a “nappe theory”, the physical mechanisms of nappe formation are still incompletely understood. We apply two-dimensional numerical simulations of shortening of a passive margin, to investigate the thermo-mechanical processes of detachment, transport and stacking of 5 nappes. We use a visco-elasto-plastic model with standard creep ﬂow laws and Drucker-Prager yield criterion. We consider tectonic inheritance with two initial mechanical heterogeneities: (1) lateral heterogeneity of the basement-cover interface due to half-grabens and horsts and (2) vertical heterogeneities due to layering of mechanically strong and weak sedimentary units. The model shows detachment and horizontal transport of a thrust nappe and stacking of this thrust nappe above a fold nappe. The detachment of the thrust sheet is triggered by stress concentrations around the sediment-basement contact and the resulting 10 brittle-plastic shear band formation. The horizontal transport is facilitated by a basal shear zone just above the basement-cover contact, composed of thin, weak sediments. Fold nappe formation occurs by a dominantly ductile closure of a half-graben and the associated extrusion of the half-graben ﬁll.
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A Partial Glossary of Spanish Geological Terms Exclusive of Most Cognates
U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY A Partial Glossary of Spanish Geological Terms Exclusive of Most Cognates by Keith R. Long Open-File Report 91-0579 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 1991 Preface In recent years, almost all countries in Latin America have adopted democratic political systems and liberal economic policies. The resulting favorable investment climate has spurred a new wave of North American investment in Latin American mineral resources and has improved cooperation between geoscience organizations on both continents. The U.S. Geological Survey (USGS) has responded to the new situation through cooperative mineral resource investigations with a number of countries in Latin America. These activities are now being coordinated by the USGS's Center for Inter-American Mineral Resource Investigations (CIMRI), recently established in Tucson, Arizona. In the course of CIMRI's work, we have found a need for a compilation of Spanish geological and mining terminology that goes beyond the few Spanish-English geological dictionaries available. Even geologists who are fluent in Spanish often encounter local terminology oijerga that is unfamiliar. These terms, which have grown out of five centuries of mining tradition in Latin America, and frequently draw on native languages, usually cannot be found in standard dictionaries. There are, of course, many geological terms which can be recognized even by geologists who speak little or no Spanish.
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The Processes of Underthrusting and Underplating in The
GEOLOGICAL JOURNAL Geol. J. (2009) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/gj.1144 The processes of underthrusting and underplating in the geologic record: structural diversity between the Franciscan Complex (California), the Kodiak Complex (Alaska) and the Internal Ligurian Units (Italy) F. MENEGHINI 1,2*, M. MARRONI 1,3, J.C. MOORE 2, L. PANDOLFI 1,3 and C.D. ROWE 4 1Dipartimento di Scienze della Terra, Universita` di Pisa, Pisa, Italy 2Earth and Planetary Sciences Department, University of California at Santa Cruz, CA., USA 3C.N.R., Istituto di Geoscienze e Georisorse, Pisa, Italy 4Department of Geological Sciences, University of Cape Town, South Africa Existing studies on active subduction margins have documented the wide diversity in structural style between accretionary prisms, both in space and time. Together with physical boundary conditions of the margins, the thickness of sedimentary successions carried by the lower plate seems to play a key role in controlling the deformation and fluid flow during accretion. We have tested the influence of the subducting sedimentary section by comparing the structural style and fluid-related structures of four units from three fossil accretionary complexes characterized by similar physical conditions but different subducting sediment thicknesses: (1) the Franciscan Complex of California, (2) the Internal Ligurian Units of Italy and (3) the Kodiak Complex, Alaska. Subducting plates bearing a thick sedimentary cover generally result in coherent accretion through polyphase deformation represented by folding and thin thrusting events, while underplating of sediment-starved oceanic sections results in diffuse deformation and me´lange formation. These two structural styles can alternate through time in a single complex with a long record of accretion such as Kodiak.
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Geodynamics of Wedges
1 DRIVING MECHANISMS OF THRUST SYSTEMS Dynamics of accretionary, orogenic wedges Tens of kilometres long displacements are reported for only a few thousands meters thick thrust sheets. With accepted values of frictional resistance, stresses necessary to push a thrust sheet on a horizontal or slightly up-inclined basal thrust exceed the failure strength of intact rocks. Accordingly, hinterlands should deform and crush before fronts of thrust sheets would move. This mechanical paradox has triggered formulation of a few working hypotheses. The question is still not fully resolved, possibly because all envisioned mechanisms are involved on a scale-dependent importance. Concepts and definitions Thrust systems are common in converging settings, resulting from compressional deformation of rocks once the shear strength along weak layers or planes is exceeded. In convergent plate boundaries, thrusts cutting through accretionary wedges are virtually splays of the subduction plane. This mechanism, where the accretionary hanging wall is deformed while the subducting footwall plate descends undeformed, is typical of thin-skinned tectonics depicted in mountain systems. Therefore, mechanics developed from accretionary wedges are often applied to foreland fold-and-thrust belts and even to orogenic belts (see lecture on thrust systems). Geometry A thrust sheet (or nappe; distinguish from fold nappe = large recumbent fold) is an allochthonous unit that has been transported and lies almost horizontally, away from its original position, on an autochthonous substratum. The bottom boundary is an originally shallow-dipping thrust fault or shear zone along which most of the displacement has taken place. The frontal part in the direction of movement is the leading edge.
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Glossary of Thrust Tectonics Terms
Glossary of thrust tectonics terms K.R. McClay Department of Geology, Royal Holloway and Bedford New College, University of London, Egham, Surrey, England, TW20 OEX This glossary aims to illustrate, and to define where possible, recognise the difficulty in precisely defining many of the some of the more widely used terms in thrust tectonics. It is terms used in thrust tectonics as individual usages and pref presented on a thematic basis - individual thrust faults and erences vary widely. related structures, thrust systems, thrust fault related folds, 3- D thrust geometries, thrust sequences, models of thrust sys tems, and thrusts in inversion tectonics. Fundamental terms Thrust faults are defined first, followed by an alphabetical listing of related structures. Where appropriate key references are given. Thrust fault: A contraction fault that shortens a datum surface, usually bedding in upper crustal rocks or a regional Since some of the best studied thrust terranes such as the foliation surface in more highly metamorphosed rocks. Canadian Rocky Mountains, the Appalachians, the Pyrenees, and the Moine thrust zone are relatively high level foreland This section of the glossary defines terms applied to indi fold and thrust belts it is inevitable that much of thrust vidual thrust faults (after McClay 1981; Butler 1982; Boyer tectonics terminology is concerned with structures found in & Elliott 1982; Diegel 1986). the external zones of these belts. These thrustbelts character istically consist of platform sediments deformed by thrust Backthrust: A thrust fault which has an opposite vergence faults which have a ramp-flat trajectories (Bally et al. 1966; to that of the main thrust system or thrust belt (Fig.
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Late Neoproterozoic–Silurian Tectonic Evolution of the Rödingsfjället Nappe Complex, Orogen-Scale Correlations and Implications for the Scandian Suture
Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 Late Neoproterozoic–Silurian tectonic evolution of the Rödingsfjället Nappe Complex, orogen-scale correlations and implications for the Scandian suture Trond Slagstad1*, Kerstin Saalmann1, Chris L. Kirkland2, Anne B. Høyen3, Bergliot K. Storruste4, Nolwenn Coint1, Christian Pin5, Mogens Marker1, Terje Bjerkgård1, Allan Krill4, Arne Solli1, Rognvald Boyd1, Tine Larsen Angvik1 and Rune B. Larsen4 1Geological Survey of Norway, Trondheim, Norway 2Centre for Exploration Targeting Curtin Node, School of Earth and Planetary Sciences, Curtin University, Perth, Australia 3Department of Geology and Mineral Resources Engineering, Norwegian University of Science and Technology, Trondheim, Norway 4Department of Geosciences and Petroleum, Norwegian University of Science and Technology, Trondheim, Norway 5Département de Géologie, C.N.R.S. & Université Blaise Pascal, 5 rue Kessler, 63038 Clermont-Ferrand, France TS, 0000-0002-8059-2426; CLK, 0000-0003-3367-8961; NC, 0000-0003-0058-722X; AK, 0000-0002-5431-3972; RBL, 0000-0001-9856-3845 Present addresses: ABH, The Norwegian Directorate of Mining, Trondheim, Norway; BKS, Brønnøy Kalk, Velfjord, Norway *Correspondence: [email protected] Abstract: The Scandinavian Caledonides consist of disparate nappes of Baltican and exotic heritage, thrust southeastwards onto Baltica during the Mid-Silurian Scandian continent–continent collision, with structurally higher nappes inferred to have originated at increasingly distal positions to Baltica. New U–Pb zircon geochro- nological and whole-rock geochemical and Sm–Nd isotopic data from the Rödingsfjället Nappe Complex reveal 623 Ma high-grade metamorphism followed by continental rifting and emplacement of the Umbukta gabbro at 578 Ma, followed by intermittent magmatic activity at 541, 510, 501, 484 and 465 Ma.
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