DOCSLIB.ORG

Cross-Section Restoration and Balancing

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Cross-Section Restoration and Balancing Salt Tectonics The following notes are abbreviated versions of Mark Rowan’s three-day industry short course on salt tectonics. Introduction Diapirs and diapirism Diapir initiation during differential Distribution and origin of salt basins loading Diapir initiation during extension or Mechanics of salt deformation contraction Active and passive diapirism Salt withdrawal structures and welds Reactivation of diapirs during Turtle structures extension or contraction Expulsion rollovers Diapir interiors and margins Welds Near-diapir deformation - folding and faulting Tectonic styles of salt deformation Thick-skinned extension Collisional mountain belts 1 INTRODUCTION There has been an enormous revolution in our understanding of salt tectonics in the past decade or so Structural restoration. The technique of cross- (see Jackson, 1995, for an excellent history of salt section restoration was first applied to salt tectonics research). The beginnings of the revolution date structures in the late 1980s (e.g., Worrall and back a little farther within some of the exploration Snelson, 1989). In the past decade, numerous companies, but their ideas only became public starting in people have used restoration to reconstruct the about 1989. Our increased understanding of the history of salt movement and associated geometry and evolution of salt bodies and associated deformation of surrounding strata. strata is due in large part to the fortuitous convergence of advances in four areas: Field studies. Armed with new ideas, various researchers have reexamined exposed salt basins Seismic imaging. There has been a steady improvement throughout the world, leading to improved in seismic data acquisition and processing over the years. But with the advent of such techniques as pre- understanding of the processes of salt-related stack depth migration, images of salt bodies became deformation. much clearer, with improved pictures of the bases of salt In this course, we will concentrate on the new sheets and overhangs and the steep flanks of many ideas about salt tectonics. Many of the illustrations diapirs (e.g., Ratcliff, 1993). used here are examples of the four areas of Experimental and numerical modeling. Attempts to advance listed above. Much of the work has been model salt deformation have been made for many concentrated in the northern Gulf of Mexico, but decades (e.g., Nettleton, 1934), but until fairly recently, the impact of the advances has spread to salt both salt and its overburden were modeled as viscous basins worldwide. Thus, we will also examine the fluids. Starting in the late 1980s, however, B. Vendeville and coworkers started modeling the overburden as a geometries and structural styles of salt from such brittle material, more in keeping with the known places as the North Sea, the Red Sea, offshore mechanical behavior. The results demonstrated salt’s West Africa, offshore Brazil, the Precaspian more passive role of reacting to, rather than causing, Basin, and onshore Mexico. deformation (e.g., Vendeville and Jackson, 1992a, b) and fundamentally changed the ways most people look at salt deformation. 2 DISTRIBUTION AND ORIGIN OF SALT BASINS SE oriented transfer faults. The rift geometry, coupled with the rate of sedimentation and the relative time of Salt basins are found throughout the world (Fig. 1), but a evaporite formation, determines the areal extent and quick look will show that they occur primarily in rift thickness distribution of evaporites. Salt may be restricted basins and along passive margins, as well as in their to individual half-grabens (Fig. 5 it may be regionally deformed counterparts, such as the Alpine/Himalayan tabular (Fig. 6), or it may have an intermediate geometry, system. According to a review by Jackson and Vendeville with a regional distribution but significant thickness (1994), many salt deposits were formed during the early variations (Fig. 7). postrift phase, including the basins of offshore Brazil, offshore West Africa, the U.S. Gulf Coast, and the Red Salt commonly occurs in paired basins on either side of Sea (Fig. 2). Others were formed either during rifting or oceanic crust, such as across the Gulf of Mexico, the South during lulls between distinct rift episodes, for example Atlantic, and the North Atlantic. Thus, it has generally many of the basins on either side of the northern Atlantic been thought that evaporite deposition occurs only on Ocean (Fig. 2). Finally, a few salt basins appear to be older continental crust, with subsequent oceanic spreading than rifting, namely those in the North Sea and Persian separating a once contiguous basin into two parts (Fig. 8). Gulf (Fig. 2). Many passive margins have seaward-dipping reflectors, or SDRs (Fig. 9) – wells show that these consist of subaerial Many rift basins have a similar history, one that is basalts that are considered the initial expression of oceanic conducive to evaporite deposition. They form during spreading. Autochthonous salt in parts of offshore Brazil extension of the continental crust, and grabens are initially occurs at a stratigraphic level above the SDRs, leading to a filled with nonmarine clastics because of the high heat model in which salt deposition postdates the onset of flow and associated regional uplift during rifting. oceanic spreading (Fig. 10). Salt in the South Atlantic Subsidence of the grabens, either during rifting or, more (offshore West Africa or Brazil) is interpreted to occur typically, during postrift thermal and loading subsidence, above the breakup unconformity and thus is underlain by a leads to marine incursion. If the climatic conditions are combination of landward continental crust and basinward appropriate, it is during the transition from nonmarine to oceanic crust (Fig. 11). There is then a transition to marine environments that evaporites are formed (often shallow-water carbonates and then deeper-water facies. episodically). In the typical (but not universal) scenario, The interbedded nature of the salt-carbonate transition and continued subsidence leads to true marine conditions. the similar seismic velocities means that there is typically Rift basins have a distinct basement architecture made a low acoustic impedance contrast and thus no good top- up of grabens and half-grabens segmented by transverse salt reflector for the autochthonous salt layer. In contrast, structures such as accommodation zones or transfer faults the salt is usually in contact with underlying clastic (Fig. 3). An example from the Brazilian margin is shown redbeds or basement so that there is a good base-salt in Figure 4, where the rift system includes a series of NW- reflector. 3 The evolution for the northern Gulf of Mexico is shown in The Precaspian Basin example nicely shows the kinds of Figure 12. Initial rifting during the Early Jurassic resulted vertical and lateral facies variations commonly found in in the SSW movement of Yucatan away from N. America, evaporite basins. Although salt dominates the basin center, whereas oceanic spreading resulted in southern movement there is also interbedded anhydrite that becomes more and rotation about a nearby pole. This means that dominant towards the northern margin. There can also be basement structures will have different orientations in the significant components of both carbonates and thinned continental crust and the oceanic crust. The siliciclastics that are concentrated along basin margins. boundary between the two is interpreted to be in the Another example is provided by the central North Sea, approximate position of the present-day shelf edge, so that where non-salt facies in the proximal part of the basin most of the deepwater province is underlain by oceanic disappear towards the center (Fig. 16). Of course, the crust (Fig. 13). So instead of one salt basin on continental presence of other lithologies means that there can be crust that was subsequently split by spreading (Fig. 12), significant, even coherent, reflectivity within the evaporite there were most likely two salt basins with the downdip layer (Fig. 17). edges defined by the incipient spreading center (Fig. 13). Although most salt basins are closely associated with rifting, salt deposits can form anytime conditions are appropriate for evaporite formation. Thus, any restricted basin with an arid climate is a potential salt basin. The modern examples are the sabkha deposits of the Arabian peninsula, but these are rare in the geologic record and, similarly, the types of salt basins common in the past are not observed today (Warren, 1999). One ancient setting for evaporite deposition is a basin with an open marine connection that gets closed off. This will lead to the development of various evaporite facies as the basin essentially dries up (Fig. 14). Examples include basins with narrow entrances that become emergent during major sea-level drops, such as the Mediterranean (Messinian salinity crisis) and the Red Sea. Another example is when plate tectonic motions close off a basin, as in the case of the Precaspian Basin during the Permian (Fig. 15). 4 Figure 1. Locations of salt basins around the world (Jackson and Talbot, 1991). 5 Figure 3. 3-D block diagram of basement rift architecture with offset grabens separated by an accommodation zone (Stonely, 1981). Note that more asymmetric rift geometries are also possible. 6 Figure 5. Example from east Africa where the salt is isolated within a single half-graben (Malek-Aslani, 1985). 7 Figure 6. Example from west Africa, where salt is high enough in the section to form a regionally continuous, tabular salt body (Perrodon, 1981). 8 Figure 7. Model for the onshore northern Gulf of Mexico, where the salt is continuous but of highly variable thickness because it partially fills in the rift-basin architecture (Adams, 1989). 9 Figure 11. Regional cross section across Angolan margin showing salt deposition above both continental and oceanic crust (Jackson et al., 2000). 10 Figure 12. Present-day geometry of the Gulf of Mexico and three reconstructions to the Early Jurassic (beginning of rifting), Late Jurassic (onset of seafloor spreading), and Early Cretaceous (end of 11 seafloor spreading) (Pindell et al., 2000).
Load more

Recommended publications
  • Structural Modeling Based on Sequential Restoration of Gravitational Salt Deformation in the Santos Basin (Brazil)
    Marine and Petroleum Geology xxx (2012) 1e17 Contents lists available at SciVerse ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo Structural modeling based on sequential restoration of gravitational salt deformation in the Santos Basin (Brazil) Sávio Francis de Melo Garcia a,*, Jean Letouzey b, Jean-Luc Rudkiewicz b, André Danderfer Filho c, Dominique Frizon de Lamotte d a Petrobras E&P-EXP, Rio de Janeiro, Brazil b IFP Energies Nouvelles, France c Universidade Federal de Ouro Preto, Ouro Preto/MG, Brazil d Université de Cergy-Pontoise, France article info abstract Article history: The structural restoration of two parallel cross-sections in the central portion of the Santos Basin enables Received 8 December 2010 a first understanding of existent 3D geological complexities. Santos Basin is one of the most proliferous Received in revised form basins along the South Atlantic Brazilian margin. Due to the halokinesis, geological structures present 22 November 2011 significant horizontal tectonic transport. The two geological cross-sections extend from the continental shelf Accepted 2 February 2012 to deep waters, in areas where salt tectonics is simple enough to be solved by 2D restoration. Such cross- Available online xxx sections display both extensional and compressional deformation. Paleobathymetry, isostatic regional compensation, salt volume control and overall aspects related to structural style were used to constrain basic Keywords: fl Salt tectonics boundary conditions. Several restoration
    [Show full text]
  • The Confusion Range, West-Central Utah: Fold-Thrust Deformation and a Western Utah Thrust Belt in the Sevier Hinterland
    The Confusion Range, west-central Utah: Fold-thrust deformation and a western Utah thrust belt in the Sevier hinterland David C. Greene* Department of Geosciences, Denison University, Granville, Ohio 43023, USA ABSTRACT INTRODUCTION tions together while delineating the lateral and oblique thrust ramps that form a signifi cant The Confusion Range in west-central Utah The Confusion Range is a collection of ridges complicating factor in the structure of the fold- has been considered a broad structural trough and small ranges that together form a low moun- thrust system. Together, these fi ve cross sections or synclinorium with little overall shorten- tain range in western Utah, between the more total almost 300 km in map length. Enlarged ing. However, new structural studies indicate imposing Snake Range on the west and House versions of the cross sections at a scale of that the Confusion Range is more accurately Range on the east (Figs. 1 and 2). The range is 1:50,000, along with a discussion of the petro- characterized as an east-vergent, fold-thrust named for its “rugged isolation and confusing leum potential of the region, may be found in system with ~10 km of horizontal shortening topography” (Van Cott, 1990). The Confusion Greene and Herring (2013). during Late Jurassic to Eocene Cordilleran Range exposes ~5000 m of Ordovician through Similar structural style and fold-thrust struc- contractional deformation. For this study, Triassic strata in what has been considered a tures are continuous southward throughout the four balanced and retrodeformable cross broad structural trough or synclinorium (e.g., length of the originally proposed synclinorium, sections across the Confusion Range and Hose, 1977; Anderson, 1983; Hintze and Davis, forming a fold-thrust belt more than 130 km in adjacent Tule Valley were constructed using 2003; Rowley et al., 2009).
    [Show full text]
  • Structural and Metamorphic Investigation of the Cathedral Rock – Drew Hill Area, Olary Domain, South Australia
    STRUCTURAL AND METAMORPHIC INVESTIGATION OF THE CATHEDRAL ROCK – DREW HILL AREA, OLARY DOMAIN, SOUTH AUSTRALIA. Jonathan Clark (B.Sc.) Department of Geology and Geophysics University of Adelaide This thesis is submitted as a partial fulfilment for the Honours Degree of a Bachelor of Science November 1999 Australian National Grid Reference (SI 54-2) 1:250 000 i ABSTRACT The Cathedral Rock – Drew Hill area represents a typical Proterozoic high-grade gneiss terrain, and provides an excellent basis for the study of the structural and metamorphic geology in early earth history. Rocks from this are comprised of Willyama Supergroup metasediments, which have been subjected to polydeformation. The highly strained nature of the area has been attributed to three deformations. These have been superimposed into a single structure, the Cathedral Rock synform, which represents a second-generation fold that refolds the F1 axial surface. Pervasive deformation with a northwest transport direction firstly resulted in the formation of a thin-skinned duplex terrain. Crustal thickening in the middle to lower crust led to the reactivation of basement normal faults in a reverse sense. Further compression, led to more intense folding and thrusting associated with the later part of the Olarian Orogeny. Strain analysis has shown that the region of greatest strain occurs between the Cathedral Rock and Drew Hill shear zones. Cross section restoration showed that this area has undergone approximately 65% shortening. Further analysis showed that strain fluctuated across the area and was affected by the competence of different lithologies and the degree of recrystallisation. ii Contents Abstract (ii) List of Plates, Tables and Figures (v) Acknowledgments (vi) CHAPTER 1:INTRODUCTION 1 1.1.
    [Show full text]
  • Contractional Tectonics: Investigations of Ongoing Construction of The
    Louisiana State University LSU Digital Commons LSU Doctoral Dissertations Graduate School 2014 Contractional Tectonics: Investigations of Ongoing Construction of the Himalaya Fold-thrust Belt and the Trishear Model of Fault-propagation Folding Hongjiao Yu Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_dissertations Part of the Earth Sciences Commons Recommended Citation Yu, Hongjiao, "Contractional Tectonics: Investigations of Ongoing Construction of the Himalaya Fold-thrust Belt and the Trishear Model of Fault-propagation Folding" (2014). LSU Doctoral Dissertations. 2683. https://digitalcommons.lsu.edu/gradschool_dissertations/2683 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Doctoral Dissertations by an authorized graduate school editor of LSU Digital Commons. For more information, please [email protected]. CONTRACTIONAL TECTONICS: INVESTIGATIONS OF ONGOING CONSTRUCTION OF THE HIMALAYAN FOLD-THRUST BELT AND THE TRISHEAR MODEL OF FAULT-PROPAGATION FOLDING A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Geology and Geophysics by Hongjiao Yu B.S., China University of Petroleum, 2006 M.S., Peking University, 2009 August 2014 ACKNOWLEDGMENTS I have had a wonderful five-year adventure in the Department of Geology and Geophysics at Louisiana State University. I owe a lot of gratitude to many people and I would not have been able to complete my PhD research without the support and help from them.
    [Show full text]
  • Structural and Kinematic Analyses of the Basement Window Within the Hinterland Fold-And-Thrust Belt of the Zagros Orogen, Iran
    Geol. Mag.: page 1 of 18 c Cambridge University Press 2016 1 doi:10.1017/S0016756816000558 Structural and kinematic analyses of the basement window within the hinterland fold-and-thrust belt of the Zagros orogen, Iran ∗ KHALIL SARKARINEJAD & SOMAYE DERIKVAND Department of Earth Sciences, College of Sciences, Shiraz University, Shiraz 71454, Iran (Received 1 December 2015; accepted 18 May 2016) Abstract – The Zagros hinterland fold-and-thrust belt is located in the central portion of the Zagros Thrust System and consists of the exhumed basement windows associated with NW-striking and NE-dipping flexural duplex structures that contain in-sequence thrusting and related folds. Mylonitic nappes of the basement were exhumed along deep-seated sole thrusts of the Zagros Thrust System. Lattice preferred orientation (LPO) c-axes of quartz show asymmetric type-1 crossed girdles that demonstrate a non-coaxial deformation under plane strain conditions. Based on the opening angles of quartz c-axis fabric skeletons, deformation temperatures vary from 425 ± 50 °C to 540 ± 50 °C, indicating amphibolite facies conditions. The estimated mean kinematic vorticity evaluated from quartz c-axis of the quartzo-feldspathic mylonites (Wm = 0.55 ± 0.06) indicates the degree of non- coaxiality during mylonite exhumation. The estimated angle θ between the maximum instantaneous strain axis (ISA1) and the transpressional zone boundary is 17°, and the angle of oblique convergence is 57° in the M2 nappe of the basement involved. This indicates that the mylonitic nappe was formed by a combination of 62 % pure shear and 38 % simple shear during oblique convergence. Keywords: transpressional zone, mylonitic nappe, vorticity, quartz c-axis, Zagros orogenic belt.
    [Show full text]
  • CONTACT AUREOLE RHEOLOGY of the WHITE HORSE PLUTON By
    CONTACT AUREOLE RHEOLOGY OF THE WHITE HORSE PLUTON by WAYNE THEODORE MARKO, B.S. A THESIS IN GEOSCIENCE Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved •—.—• «^ Chairperson of the Committee Accepted Dean of the Graduate School August, 2004 ACKNOWLDGEMENTS This work would was made possible with funding provided by the NSF grant for contact aureole research awarded to Dr. Aaron Yoshinobu at Texas Tech University as well as by teaching assistantships provided by the Texas Tech Geosciences Department. 1 would like extend thanks to my committee members, Dr. Aaron Yoshinobu, Dr. Calvin Barnes and Dr. George Asquith for their insightful observations and guidance with various aspects of this work. Lastly, I thank my family and friends for their support and camaraderie during the course of the project. n ABSTRACT The 160 Ma White Horse pluton intruded a thick sequence of miogeoclinal Paleozoic carbonate rocks in the northeastern Great Basin Region, Nevada. The dominantly quartz monzonite pluton (-16 km^ of exposure) lacks internal fabric, concentric zoning, and stoped blocks, but hosts several smaller granite and granodiorite bodies as well as numerous microdiorite mafic enclaves. The structural aureole extends 7 km along the eastern side of the elliptical intrusive body. Continuous and discontinuous spaced axial planner foliations and harmonic to disharmonic, tight to isoclinal folds wrap around the western margin of the pluton. Folds verge toward and away from the pluton and a rim anticline is preserved along the pluton margin. In several locations fold axes are cut by the pluton host rock contact.
    [Show full text]
  • The Structure and Kinematics of the Southeastern Zagros Fold-Thrust Belt, Iran : from Thin-Skinned to Thick-Skinned Tectonics M
    The structure and kinematics of the southeastern Zagros fold-thrust belt, Iran : From thin-skinned to thick-skinned tectonics M. Molinaro, Pascale Leturmy, Jean-Claude Guezou, Dominique Frizon de Lamotte To cite this version: M. Molinaro, Pascale Leturmy, Jean-Claude Guezou, Dominique Frizon de Lamotte. The struc- ture and kinematics of the southeastern Zagros fold-thrust belt, Iran : From thin-skinned to thick- skinned tectonics. Tectonics, American Geophysical Union (AGU), 2005, 24 (3), pp.TC3007. 10.1029/2004TC001633. hal-00022420 HAL Id: hal-00022420 https://hal.archives-ouvertes.fr/hal-00022420 Submitted on 20 May 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. TECTONICS, VOL. 24, TC3007, doi:10.1029/2004TC001633, 2005 The structure and kinematics of the southeastern Zagros fold- thrust belt, Iran: From thin-skinned to thick-skinned tectonics M. Molinaro, P. Leturmy, J.-C. Guezou, and D. Frizon de Lamotte De´partement des Sciences de la Terre et de l’Environnement, UMR 7072, CNRS, Universite´ de Cergy-Pontoise, Cergy, France S. A. Eshraghi Geological Survey of Iran, Tehran, Iran Received 17 February 2004; revised 14 February 2005; accepted 11 March 2005; published 15 June 2005.
    [Show full text]
  • Palinspastic Restoration of an Exhumed Deep-Water System: a Workflow to Improve Paleogeographic Reconstructions
    This is a repository copy of Palinspastic restoration of an exhumed deep-water system: a workflow to improve paleogeographic reconstructions. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/87196/ Article: Spikings, AL, Hodgson, DM, Paton, DA et al. (1 more author) (2015) Palinspastic restoration of an exhumed deep-water system: a workflow to improve paleogeographic reconstructions. Interpretation, 3 (4). pp. 71-87. ISSN 2324-8858 https://doi.org/10.1190/INT-2015-0015.1 Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Interpretation 1 Palinspastic restoration of an exhumed deep-water system: a workflow to improve paleogeographic reconstructions Spikings, A.L., Hodgson, D.M., Paton, D.A., Spychala, Y.T. School of Earth & Environment, University of Leeds, Leeds, LS2 9JT 2 ABSTRACT The Permian Laingsburg depocenter, Karoo Basin, South Africa is the focus of sedimentological and stratigraphic research as an exhumed analogue for offshore hydrocarbon reservoirs in deep- water basins.
    [Show full text]
  • Gautam Mitra Curriculum Vitae February 2018
    Gautam Mitra Curriculum Vitae February 2018 CONTACT INFORMATION Department of Earth & Environmental Sciences, University of Rochester Rochester, New York 14627 Telephone: (585) 275-5816 e-mail: [email protected] RESEARCH INTERESTS Structural mapping and kinematic analysis. Application of strain analysis and microstructural studies to understanding strain histories and crustal rheology. Geometry and mechanics of fold-thrust belts and foreland uplfts. Critical wedge theory. Thermal and mechanical modeling. Fracture network development and implications for fluid flow. Cataclastic flow in fault zones and within thrust sheets. Brittle fault zones and ductile shear zones in continental crust -- implications for the brittle-ductile transition. Basement - cover relationships in mountain belts. EDUCATION 1977 Ph.D. (Geology), The Johns Hopkins University, Baltimore, MD Advisor: David Elliott 1970 M.Sc. (Geology) University of Calcutta, India Advisor: Dhruba Mukhopadhyay 1968 B.Sc. (Geology) University of Calcutta, India EMPLOYMENT HISTORY 1992 -present Professor of Geological Sciences, University of Rochester, Rochester, NY. 1984 - 1992 Associate Professor of Geological Sciences, University of Rochester. 1981 - 1984 Assistant Professor of Geological Sciences, University of Rochester. 1977 - 1981 Assistant Professor of Geology, University of Wyoming, Laramie, WY. 1976 - 1977 Assistant Professor (part-time), Morgan State University, Baltimore, MD. AWARDS 2012 Lifetime Achievement Award in Graduate Education, University of Rochester 1996 Elected Fellow, Geological Society of America 1970 University of Calcutta gold medal (for best M.Sc. student in Geology). 1968 Chandranath Moitra medal, Hemchandra Dasgupta medal, Jubilee Prize, and Government of India National Scholarship (all for best B.Sc. Student in Geology, University of Calcutta). PROFESSIONAL SERVICES Committees 2010 Executive Council Member, Structural Geology & Tectonics Studies Group – India.
    [Show full text]
  • Controls on Structural Styles and Decoupling in Stratigraphic Sequences
    Manuscript submitted to Journal of Structural Geoloy 1 Controls on structural styles and decoupling in stratigraphic sequences 2 with double décollements during thin-skinned contractional tectonics: 3 insights from numerical modelling 4 Qingfeng Meng*1, David Hodgetts 5 School of Earth and Environmental Sciences, University of Manchester, M13 9PL, UK 6 Abstract 7 Six series of particle-based numerical experiments were performed to simulate thin-skinned 8 contractional tectonics in stratigraphic sequences with double décollements during horizontal 9 shortening. The models were assigned with varying rock competence, depth and thickness of the 10 upper décollement, which resulted in significantly different styles of deformation and decoupling 11 characteristics above and below the upper décollement. The models composed of the least 12 competent material produced distributed sinusoidal detachment folds, with many shallow 13 structures profoundly decoupled from the deep-seated folds. The models composed of a more 14 competent material are dominated by faulted, diapir-cored box folds, with minor disharmonic folds 15 developed in their limbs. Differently, the results of models composed of the most competent 16 material are characterised by localised piggyback thrusts, fault-bend folds and pop-up structures 17 with tensile fractures developed in fold hinges. Depth of the upper décollements also plays an 18 important role in controlling structural decoupling, i.e. the shallower the upper décollements, the 19 higher the degree of decoupling becomes. Thicker upper décollements can provide sufficient 20 mobile materials to fill fold cores, and contribute to the formation of secondary disharmonic folds, 21 helping enhance structural decoupling. Our modelling results are comparable to the structural 1 *Corresponding author.
    [Show full text]
  • Fold-Accommodation Faults
    Fold-accommodation faults AUTHOR Shankar Mitra ϳ School of Geology and Shankar Mitra Geophysics, University of Oklahoma, Norman, Oklahoma, 73019; [email protected] Shankar Mitra holds the Monnett Chair and Professorship of Energy Resources at the ABSTRACT University of Oklahoma. He received his Ph.D. Fold-accommodation faults are secondary faults that accommodate in structural geology from Johns Hopkins strain variations related to structural and stratigraphic position dur- University in 1977. He spent 19 years at ing fold evolution. Four main types of fold-accommodation faults ARCO Research and Exploration as senior and are commonly found. Out-of-syncline and into-anticline thrusts principal research geologist, director of form primarily because of an increase in bed curvature within fold Structural Geology, manager of Geological cores, although differential layer-parallel strain at different scales Research, and senior exploration research also contributes to fault slip. Depending on the kinematic evolution advisor. His primary research interests are in the development of structural concepts and of the major fold, the thrusts may propagate along the steep or methods and their application to exploration gentle limb of an asymmetric fold or along the hinge of symmetric and production problems. He is a recipient of folds. Wedge thrusts are primarily formed in competent units be- AAPG’s Wallace Pratt and Cam Sproule cause of variations in penetrative layer-parallel strain between ad- awards. jacent units. Limb wedges occur as hanging-wall and/or footwall fault-bend and fault-tip folds, whereas hinge wedges occur as mul- tiple nested faults that tend to thicken the more competent units.
    [Show full text]
  • A Serial Cross-Section Analysis of the Lewiston Structure
    A SERIAL CROSS-SECTION ANALYSIS OF THE LEWISTON STRUCTURE, CLARKSTON, WASHINGTON By MICHAEL ROBERT ALLOWAY A Thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN GEOLOGY WASHINGTON STATE UNIVERSITY School of Earth and Environmental Sciences December 2010 To the Faculty of Washington State University The members of the Committee appointed to examine the thesis of MICHAEL ROBERT ALLOWAY find it satisfactory and recommend that it be accepted. ______________________________ A. John Watkinson, Ph.D., Chair ______________________________ Simon A. Kattenhorn, Ph.D. ______________________________ John A. Wolff, Ph.D. ii ACKNOWLEDGMENTS First and foremost I would like to thank Dr. A. John Watkinson not only for serving as chair on my committee, but for his patience, guidance, friendship, and mentorship throughout my graduate career. I am grateful to Dr. Watkinson for thorough edits and constructive criticism during the development of the final manuscript. I also thank committee members Dr. Simon A. Kattenhorn and Dr. John A. Wolff for reviewing the initial manuscript and providing helpful suggestions. Special thanks to Dr. Kattenhorn for teaching me the most valuable lesson I have learned during my graduate education: to trust and have confidence in my intuition. Thanks to Dr. Wolff for his help with the chemical analysis. I would like to express extreme gratitude to Dr. Stephen P. Reidel for help in the field, help with chemical data, allowing me to borrow his personal fluxgate magnetometer, constant email correspondence, sponsoring my abstract for AGU, providing helpful references, and editing figures and tables. Thank you Dr. Victor E. Camp, Dr.
    [Show full text]