DOCSLIB.ORG

Shear Zones – a Review MARK ⁎ Haakon Fossena,B, , Geane Carolina G

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Shear Zones – a Review MARK ⁎ Haakon Fossena,B, , Geane Carolina G Earth-Science Reviews 171 (2017) 434–455 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Shear zones – A review MARK ⁎ Haakon Fossena,b, , Geane Carolina G. Cavalcantec a Department of Earth Science/Museum of Natural History, University of Bergen, Allégaten 41, N-5007 Bergen, Norway b Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, Cidade Universitária, São Paulo, SP CEP 05508-080, Brazil c Departmento de Geologia, Universidade Federal do Paraná, Av. Cel. Francisco Heráclito dos Santos, s/n, Centro Politécnico, 81531-980, Curitiba, PR CEP 81531-980, Brazil ARTICLE INFO ABSTRACT Keywords: Strain in the lithosphere localizes into tabular zones known as shear zones that grow from small outcrop-size Shear zones individual zones to large composite structures. Nucleation is related to distributed microscale flaws or mesoscale Kinematics structures such as fractures and dikes, and they soon establish displacement profiles similar to faults. Also similar Strain localization to faults, they grow in width and length primarily by segment linkage as they accumulate strain and displace- Vorticity ment, and this process typically results in shear zone networks. Consequently, mature shear zones are hetero- Crustal deformation geneous and composite zones characterized by anastomosing patterns and local variations in thickness and finite strain. Kinematic vorticity estimates suggest that most shear zones deviate from simple shear, and even if subsimple shear may be a useful reference model in many cases, finite strain data indicate that many shear zones involve three-dimensional combinations of coaxial and non-coaxial deformation, such as transpression and transtension. Strain geometry and kinematic vorticity can vary significantly within shear zone networks, which makes it difficult to estimate the bulk deformation type for a composite shear zone or shear zone network. However, perhaps the most challenging aspect is that of progressive deformation, i.e. to what extent and how flow parameters change during deformation (non-steady state deformation), which needs to be addressed by a combination of detailed field observations and numerical modeling. 1. Introduction during rifting (Powell and Glendinning, 1990; Butler et al., 2008; Bird et al., 2015; Phillips et al., 2016) and are important components in the The majority of strain accumulated in the mostly plastic or viscous context of plate tectonics (Bercovici and Ricard, 2012). part of the lithosphere, both in the crust and the mantle (e.g., Vauchez High-strain zones have been recognized in naturally deformed rocks et al., 2012; Snyder and Kjarsgaard, 2013), localizes into zones that since the 19th century (e.g., Reusch, 1888), and particularly since the show large variations in orientation, length, thickness, displacement, theory of thrusting was introduced (e.g., Bertrand, 1884; Geike, 1884; strain geometry, coaxiality, and deformation mechanisms. Such zones Törnebohm, 1888; Peach et al., 1907). However, even though strain in typically involve a significant component of simple shear, and are deformed rocks was discussed relatively early on (e.g., Harker, 1885), therefore called shear zones (Ramsay and Graham, 1970; Sibson, 1977; sound and quantitative analysis of shear zones in terms of geometry, Simpson and De Paor, 1993; Ramsay, 1980), although a component of strain and kinematics founded in mathematical analysis is relatively coaxial deformation (e.g., pure shear) is also commonly involved new, and basic aspects of such analyses were presented in a systematic (Ramberg, 1975a,b; Coward and Kim, 1981; Fossen and Tikoff, 1993; way by Ramsay (1967) and in a series of papers in the 1970s and1980s, Northrup, 1996). Shear zones separate less strained or unstrained notably Ramsay and Graham (1970), Ramberg (1975a,b), Coward portions of the lithosphere, and are the deeper counterparts to upper (1976), Cobbold (1977a,b), Berthé et al. (1979), Lister and Williams crustal faults and fault zones in contractional (thrust), extensional and (1979), Mandl et al. (1977), Sibson (1977), Ramsay (1980), Cobbold strike-slip settings alike (e.g., Sibson, 1977; Scholz, 1988; Wernicke, and Quinquis (1980), and Lister and Snoke (1984). The typical ap- 1985; Godin et al., 2006; Fossen, 2010; Ganade de Araujo et al., 2013; proach during this era was that of simple shear with or without addi- Cottle et al., 2015). They also represent rheological and mechanical tional shortening/dilation across the shear zone. Pure shear was then anomalies that may be reactivated or otherwise influence the structural combined with simple shear to create more general subsimple shear evolution during later stages or phases of deformation, for example zones, first in the pioneering work by Ramberg (1975a,b) and later by ⁎ Corresponding author at: Department of Earth Science/Museum of Natural History, University of Bergen, Allégaten 41, N-5007 Bergen, Norway. E-mail address: [email protected] (H. Fossen). http://dx.doi.org/10.1016/j.earscirev.2017.05.002 Received 19 January 2017; Received in revised form 6 May 2017; Accepted 6 May 2017 Available online 08 May 2017 0012-8252/ © 2017 Elsevier B.V. All rights reserved. H. Fossen, G.C.G. Cavalcante Earth-Science Reviews 171 (2017) 434–455 Fig. 1. Two shear zones at micro- and mapscale. a) Shear band in highly porous sandstone (thin section of core from the Njord Field, offshore central Norway). Deformation oc- curred at shallow (few hundred meters) depth under un- consolidated conditions. b) Great Slave Lake shear zone (Canada), showing deflection of the Thelon-Taltson Magmatic Zone (TTMZ). Based on USGS map (2005). Passchier (1986), Tikoff and Fossen (1993), and Simpson and De Paor fabric (Figs. 1 and 2a). The geometry, orientation and relative move- (1993), and then to combine pure and simple shear in a three-dimen- ment of the walls are the boundary conditions that control the de- sional way, particularly in the framework of transpression and trans- formation within the zone. However, several processes may change the tension (Sanderson and Marchini, 1984). In this work we will review boundary conditions over time, for example changes in compaction the most useful and fundamental aspects of shear zones, their evolution caused by pressure solution and related loss of material in the zone from incipient to large structures, and discuss challenges that need to be (thinning), strain localization where margins are left inactive (thin- studied in the future. ning), inclusion of larger or smaller portions of wall rocks (widening), and interaction between adjacent shear zones (widening by linkage). 2. Definition and classification Hence, terms such as widening, constant thickness and thinning shear zones are commonly used. A shear zone is a zone in which strain is clearly higher than in the A significant distinction can be made between plane strain zones and wall rock, and whose margins are defined by a change in strain, typi- non-plane strain zones, i.e. zones involving two- and three-dimensional cally seen by rotation of preexisting markers or formation of a new strain, respectively. Plane strain implies no change in length along the Fig. 2. a) Schematic illustration of a simple shear zone, showing strain ellipses, new-formed foliation and two marker layers assumed to behave passively. b) Shear strain profile through the zone. c) Graph showing relationships between shear strain (horizontal axis) and the orientation of the strain ellipse and the two markers shown in (a) as well as strain (R). d) Natural shear zone (based on photo by Giorgio Pennacchioni) from deformed granitoid rock in the Tauern Window, Italian Alps, and e) a shear strain map with three shear strain profiles estimated from foliation orientation, assuming simple shear. Displacement d is given in terms of the local shear zone thickness. 435 H. Fossen, G.C.G. Cavalcante Earth-Science Reviews 171 (2017) 434–455 intermediate (Y) principal strain axis, and thus many aspects of plane Correspondingly, a brittle shear zone shows discontinuous deformation strain can conveniently be dealt with by considering the plane con- where originally continuous markers are broken up by slip surfaces taining the maximum and minimum principal strain axes (X and Z) (shear fractures) that cause discontinuities in the displacement field (only the rotation of preexisting line and plane markers requires 3D (Fig. 4b). A completely brittle shear zone would have undeformed considerations in this case). Plane strain, whether simple, sub-simple or portions of rock between these slip surfaces. Ductile-brittle shear zones pure shear, plots along the diagonal of the Flinn diagram (Flinn, 1962), contain both continuous and discontinuous deformation. In this sense, while 3D deformations produce off-diagonal constrictional or flattening drag associated with faulting creates a ductile-brittle shear zone, even if strains. However, if volume change occurs by compaction across the the deformation mechanisms involved are purely frictional (e.g., shear zone in combination with a plane strain deformation (such as Homberg et al., 2017). simple shear), the resulting plane strain will plot in the flattening field (Ramsay and Woods, 1973). 3. From simple shear zones to zones of 3D strain Shear zones can further be classified according to their dominant micro-scale deformation mechanism, where plastic (or crystal-plastic) 3.1. Simple shear and the ideal (Ramsay-type) shear zone shear zones, also referred to
Load more

Recommended publications
  • The Alpstein in Three Dimensions: Fold-And-Thrust Belt Visualization in the Helvetic Zone, Eastern Switzerland
    Swiss J Geosci (2014) 107:177–195 DOI 10.1007/s00015-014-0168-6 The Alpstein in three dimensions: fold-and-thrust belt visualization in the Helvetic zone, eastern Switzerland Paola Sala • O. Adrian Pfiffner • Marcel Frehner Received: 14 August 2013 / Accepted: 9 September 2014 / Published online: 11 December 2014 Ó Swiss Geological Society 2014 Abstract To investigate the geometrical relationships determined from line-length balancing. The model also between folding and thrust faulting, we built a 3D geo- clearly shows the lateral extension, the trend, and the logical model of the Helvetic fold-and-thrust belt in eastern variation in displacement along the principal faults. The Switzerland from several existing and two newly drawn reconstruction of horizons in 3D allows the investigation of cross-sections in the Sa¨ntis area. We partly redrew existing cross-sections in any given direction. The 3D model is cross-sections and validated them by checking for line useful for developing and understanding how the internal length balance; to fill areas with no data we drew additional nappe structures, namely folds and thrust faults, change cross-sections. The model was built based on surface along strike due to palaeogeographic and stratigraphic interpolation of the formation interfaces and thrusts variations. Lateral stratigraphy variations correlate with between the cross-sections, which allowed generating eight different deformation responses of the nappe. Changes can main surfaces. In addition, we used cave data to validate occur either abruptly across transverse faults or in a more the final model in depth. The main structural elements in gradual manner. the Sa¨ntis area, the Sa¨ntis Thrust and the Sax-Schwende Fault, are also implemented in the model.
    [Show full text]
  • Chapter 8 Large Strains
    Chapter 8 Large Strains Introduction Most geological deformation, whether distorted fossils or fold and thrust belt shortening, accrues over a long period of time and can no longer be analyzed with the assumptions of infinitesimal strain. Fortunately, these large, or finite strains have the same starting point that infinitesimal strain does: the deformation and dis- placement gradient tensors. However, we must clearly distinguish between gradi- ents in position or displacement with respect to the initial (material) or to the final (spatial) state and several assumptions from the last Chapter — small angles, addi- tion of successive phases or steps in the deformation — no longer hold. Finite strain can get complicated very quickly with many different tensors to worry about. Most of our emphasis here will be on the practical measurement of finite strain rather than the details of the theory but we do have to review a few basic concepts first, so that we can appreciate the differences between finite and infinitesimal strain. Some of these differences have a profound impact on how we analyze de- formation. CHAPTER 8 FINITE STRAIN Comparison to Infinitesimal Strain A Plethora of Finite Strain Tensors There are lots of finite strain tensors and they come in pairs: one referenced to the initial state and the other referenced to the final state. The derivation of these tensors is usually based on Figure 7.3 and is tedious but straightforward; we will skip the derivation here but you can see it in Allmendinger et al. (2012) or any good continuum mechanics text. The first tensor is the Lagrangian strain tensor: 1 ⎡ ∂ui ∂u j ∂uk ∂uk ⎤ 1 " Lij = ⎢ + + ⎥ = ⎣⎡Eij + E ji + EkiEkj ⎦⎤ (8.1) 2 ⎣∂ X j ∂ Xi ∂ Xi ∂ X j ⎦ 2 where Eij is the displacement gradient tensor from the last Chapter.
    [Show full text]
  • Gy403 Structural Geology Kinematic Analysis Kinematics
    GY403 STRUCTURAL GEOLOGY KINEMATIC ANALYSIS KINEMATICS • Translation- described by a vector quantity • Rotation- described by: • Axis of rotation point • Magnitude of rotation (degrees) • Sense of rotation (reference frame; clockwise or anticlockwise) • Dilation- volume change • Loss of volume = negative dilation • Increase of volume = positive dilation • Distortion- change in original shape RIGID VS. NON-RIGID BODY DEFORMATION • Rigid Body Deformation • Translation: fault slip • Rotation: rotational fault • Non-rigid Body Deformation • Dilation: burial of sediment/rock • Distortion: ductile deformation (permanent shape change) TRANSLATION EXAMPLES • Slip along a planar fault • 360 meters left lateral slip • 50 meters normal dip slip • Classification: normal left-lateral slip fault 30 Net Slip Vector X(S) 40 70 N 50m dip slip X(N) 360m strike slip 30 40 0 100m ROTATIONAL FAULT • Fault slip is described by an axis of rotation • Rotation is anticlockwise as viewed from the south fault block • Amount of rotation is 50 degrees Axis W E 50 FAULT SEPARATION VS. SLIP • Fault separation: the apparent slip as viewed on a planar outcrop. • Fault slip: must be measured with net slip vector using a linear feature offset by the fault. 70 40 150m D U 40 STRAIN ELLIPSOID X • A three-dimensional ellipsoid that describes the magnitude of dilational and distortional strain. • Assume a perfect sphere before deformation. • Three mutually perpendicular axes X, Y, and Z. • X is maximum stretch (S ) and Z is minimum stretch (S ). X Z Y Z • There are unique directions
    [Show full text]
  • Fluid Flow and Rock Alteration Along the Glarus Thrust
    1661-8726/08/020251-18 Swiss J. Geosci. 101 (2008) 251–268 DOI 10.1007/s00015-008-1265-1 Birkhäuser Verlag, Basel, 2008 Fluid flow and rock alteration along the Glarus thrust JEAN-PIERRE HÜRZELER 1 & RAINER ABART 2 Key words: Glarus thrust, rock alteration, strain localization, Lochseiten calc tectonite ABSTRACT Chemical alteration of rocks along the Glarus overthrust reflects different the footwall units. In the northern sections of the thrust, the Lochseiten calc- stages of fluid rock interaction associated with thrusting. At the base of the tectonite has a distinct chemical and stable isotope signature, which suggests Verrucano in the hanging wall of the thrust, sodium was largely removed dur- that it is largely derived from Infrahelvetic slices, i.e. decapitated fragments of ing an early stage of fluid-rock interaction, which is ascribed to thrust-paral- the footwall limestone from the southern sections of the thrust, which were lel fluid flow in a damage zone immediately above the thrust. This alteration tectonically emplaced along the thrust further north. Only at the Lochseiten leads to the formation of white mica at the expense of albite-rich plagioclase type locality the original chemical and stable isotope signatures of the calc- and potassium feldspar. This probably enhanced mechanical weakening of the tectonite were completely obliterated during intense reworking by dissolution Verrucano base allowing for progressive strain localization. At a later stage and re-precipitation. of thrusting, fluid-mediated chemical exchange between the footwall and the hanging wall lithologies produced a second generation of alteration phenom- ena. Reduction of ferric iron oxides at the base of the Verrucano indicates DEDICATION fluid supply from the underlying flysch units in the northern section of the thrust.
    [Show full text]
  • Ductile Deformation - Concepts of Finite Strain
    327 Ductile deformation - Concepts of finite strain Deformation includes any process that results in a change in shape, size or location of a body. A solid body subjected to external forces tends to move or change its displacement. These displacements can involve four distinct component patterns: - 1) A body is forced to change its position; it undergoes translation. - 2) A body is forced to change its orientation; it undergoes rotation. - 3) A body is forced to change size; it undergoes dilation. - 4) A body is forced to change shape; it undergoes distortion. These movement components are often described in terms of slip or flow. The distinction is scale- dependent, slip describing movement on a discrete plane, whereas flow is a penetrative movement that involves the whole of the rock. The four basic movements may be combined. - During rigid body deformation, rocks are translated and/or rotated but the original size and shape are preserved. - If instead of moving, the body absorbs some or all the forces, it becomes stressed. The forces then cause particle displacement within the body so that the body changes its shape and/or size; it becomes deformed. Deformation describes the complete transformation from the initial to the final geometry and location of a body. Deformation produces discontinuities in brittle rocks. In ductile rocks, deformation is macroscopically continuous, distributed within the mass of the rock. Instead, brittle deformation essentially involves relative movements between undeformed (but displaced) blocks. Finite strain jpb, 2019 328 Strain describes the non-rigid body deformation, i.e. the amount of movement caused by stresses between parts of a body.
    [Show full text]
  • Actually Consists of 2 Cleavages
    Types of foliations • Crenulation Cleavage- – Actually consists of 2 cleavages – The first may be a slaty cleavage or schistosity that becomes microfolded – Fold axial planes typically form at high angle to the σ1 of the second compressional phase 1 Progressive development (a → c) of a crenulation cleavage for both asymmetric (top) and symmetric (bottom) situations. From Spry (1969) Metamorphic Textures. Pergamon. Oxford. 2 Figure 23.24a. Symmetrical crenulation cleavages in amphibole-quartz-rich schist. Note concentration of quartz in hinge areas. From Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag. 3 Figure 23.24b. Asymmetric crenulation cleavages in mica-quartz-rich schist. Note horizontal compositional layering (relict bedding) and preferential dissolution of quartz from one limb of the folds. From Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag. 4 Figure 23.25. Stages in the development of crenulation cleavage as a function of temperature and intensity of the second deformation. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag. Development of S2 micas depends upon T and the intensity of the second deformation 5 Types of lineations a. Preferred orientation of elongated mineral aggregates b. Preferred orientation of elongate minerals c. Lineation defined by platy minerals d. Fold axes (especially of crenulations) e. Intersecting planar elements. Figure 23.26. Types of fabric elements that define a lineation. From Turner and Weiss (1963) Structural 6 Analysis of Metamorphic Tectonites. McGraw Hill. Analysis of Deformed Rocks • If two or more geometric elements are present, we can add a numeric subscript to denote the chronological sequence in which they were developed and superimposed- • Deformational events: D1 D2 D3 … • Metamorphic events: M1 M2 M3 … • Foliations: So S1 S2 S3 … • Lineations: Lo L1 L2 L3 … • Plot on a metamorphism-deformation-time plot showing the crystallization of each mineral 7 Deformation vs.
    [Show full text]
  • The Glarus Thrust: Excursion Guide and Report of a Field Trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14.–16
    1661-8726/08/020323-18 Swiss J. Geosci. 101 (2008) 323–340 DOI 10.1007/s00015-008-1259-z Birkhäuser Verlag, Basel, 2008 The Glarus thrust: excursion guide and report of a field trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14.–16. 09. 2006) MARCO HERWEGH 1, *, JEAN-PIERRE HÜRZELER 2, O. ADRIAN PFIFFNER 1, STEFAN M. SCHMID 2, RAINER ABART 3 & ANDREAS EBERT 1 Key words: Helvetics, Glarus thrust, deformation mechanism, mylonite, brittle deformation, geochemical alteration, fluid pathway PARTICIPANTS Ansorge Jörg (ETHZ) Nyffenegger Franziska (Fachhochschule Burgdorf, University of Bern) den Brok Bas (EAWAG-EMPA) Pfiffner Adrian (University of Bern) Dèzes Pierre (SANW) Schreurs Guido (University of Bern) Gonzalez Laura (University of Bern) Schmalholz Stefan (ETHZ) Herwegh Marco (University of Bern) Schmid Stefan (University of Basel) Hürzeler Jean-Pierre (University of Basel) Wiederkehr Michael (University of Basel) Imper David (GeoPark) Wilson Christopher (Melbourne University) Mancktelow Neil (ETHZ) Wilson Lilian (Melbourne University) Mullis Josef (University of Basel) ABSTRACT This excursion guide results form a field trip to the Glarus nappe complex or- and fluid flow, and (iii) the link between large-scale structures, microstruc- ganized by the Swiss Tectonic Studies Group in 2006. The aim of the excursion tures, and geochemical aspects. Despite 150 years of research in the Glarus was to discuss old and recent concepts related to the evolution of the Glarus nappe complex and the new results discussed during the excursion,
    [Show full text]
  • Geometry and Kinematics of Bivergent Extension in the Southern Cycladic Archipelago: Constraining an Extensional Hinge Zone on S
    RESEARCH ARTICLE Geometry and Kinematics of Bivergent Extension in 10.1029/2020TC006641 the Southern Cycladic Archipelago: Constraining an Key Points: Extensional Hinge Zone on Sikinos Island, Aegean Sea, • New and novel (re)interpretation of extension-related structures in Greece Cycladic Blueschist Unit • Extensional structures resulted from Uwe Ring1 and Johannes Glodny2 high degree of pure-shear flattening during general-shear deformation 1Department of Geological Sciences, Stockholm University, Stockholm, Sweden, 2GFZ German Research Centre for • Structures are interpreted to reflect Geosciences, Potsdam, Germany an extensional hinge zone in southern Cyclades Abstract We report the results of a field study on Sikinos Island in the Aegean extensional province Supporting Information: of Greece and propose a hinge zone controlling incipient bivergent extension in the southern Cyclades. Supporting Information may be found A first deformation event led to top-S thrusting of the Cycladic Blueschist Unit (CBU) onto the Cycladic in the online version of this article. basement in the Oligocene. The mean kinematic vorticity number (Wm) during this event is between 0.56 and 0.63 in the CBU, and 0.72 to 0.84 in the basement, indicating general-shear deformation with about Correspondence to: equal components of pure and simple shear. The strain geometry was close to plane strain. Subsequent U. Ring, [email protected] lower-greenschist-facies extensional shearing was also by general-shear deformation; however, the pure- shear component was distinctly greater (Wm = 0.3–0.41). The degree of subvertical pure-shear flattening Citation: increases structurally upward and explains alternating top-N and top-S shear senses over large parts of Ring, U., & Glodny, J.
    [Show full text]
  • 2 Review of Stress, Linear Strain and Elastic Stress- Strain Relations
    2 Review of Stress, Linear Strain and Elastic Stress- Strain Relations 2.1 Introduction In metal forming and machining processes, the work piece is subjected to external forces in order to achieve a certain desired shape. Under the action of these forces, the work piece undergoes displacements and deformation and develops internal forces. A measure of deformation is defined as strain. The intensity of internal forces is called as stress. The displacements, strains and stresses in a deformable body are interlinked. Additionally, they all depend on the geometry and material of the work piece, external forces and supports. Therefore, to estimate the external forces required for achieving the desired shape, one needs to determine the displacements, strains and stresses in the work piece. This involves solving the following set of governing equations : (i) strain-displacement relations, (ii) stress- strain relations and (iii) equations of motion. In this chapter, we develop the governing equations for the case of small deformation of linearly elastic materials. While developing these equations, we disregard the molecular structure of the material and assume the body to be a continuum. This enables us to define the displacements, strains and stresses at every point of the body. We begin our discussion on governing equations with the concept of stress at a point. Then, we carry out the analysis of stress at a point to develop the ideas of stress invariants, principal stresses, maximum shear stress, octahedral stresses and the hydrostatic and deviatoric parts of stress. These ideas will be used in the next chapter to develop the theory of plasticity.
    [Show full text]
  • Faults (Shear Zones) in the Earth's Mantle
    Tectonophysics 558-559 (2012) 1–27 Contents lists available at SciVerse ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Review Article Faults (shear zones) in the Earth's mantle Alain Vauchez ⁎, Andréa Tommasi, David Mainprice Geosciences Montpellier, CNRS & Univ. Montpellier 2, Univ. Montpellier 2, cc. 60, Pl. E. Bataillon, F-34095 Montpellier cedex5, France article info abstract Article history: Geodetic data support a short-term continental deformation localized in faults bounding lithospheric blocks. Received 23 April 2011 Whether major “faults” observed at the surface affect the lithospheric mantle and, if so, how strain is distrib- Received in revised form 3 May 2012 uted are major issues for understanding the mechanical behavior of lithospheric plates. A variety of evidence, Accepted 3 June 2012 from direct observations of deformed peridotites in orogenic massifs, ophiolites, and mantle xenoliths to seis- Available online 15 June 2012 mic reflectors and seismic anisotropy beneath major fault zones, consistently supports prolongation of major faults into the lithospheric mantle. This review highlights that many aspects of the lithospheric mantle defor- Keywords: Faults/shear-zones mation remain however poorly understood. Coupling between deformation in frictional faults in the upper- Lithospheric mantle most crust and localized shearing in the ductile crust and mantle is required to explain the post-seismic Field observations deformation, but mantle viscosities deduced from geodetic data and extrapolated from laboratory experi- Seismic reflection and anisotropy ments are only reconciled if temperatures in the shallow lithospheric mantle are high (>800 °C at the Rheology Moho). Seismic anisotropy, especially shear wave splitting, provides strong evidence for coherent deforma- Strain localization tion over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults.
    [Show full text]
  • Download Download
    e-ISSN 2580 - 0752 BULLETIN OF GEOLOGY Fakultas Ilmu dan Teknologi Kebumian (FITB) Institut Teknologi Bandung (ITB) STRUCTURAL CONTROL RELATED WITH MEDIUM-TO-VERY HIGH Au GRADE AT PIT B EAST AND B WEST, TUJUH BUKIT MINE, EAST JAVA ILHAM AJI DERMAWAN1, ANDRI SLAMET SUBANDRIO1, ALFEND RUDYAWAN1, ARYA DWI SANJAYA2, RAMA MAHARIEF2, KRISMA ANDITYA2, RIZFAN HASNUR2, M. SATYA MUTTAQIEN2, CICIH LARASATI WIDYA FITRI2, ANDI PAHLEVI2, DEDY DAULAY2, AGUS PURWANTO2, ADI ADRIANSYAH SJOEKRI2 1. Program Studi Teknik Geologi, Fakultas Ilmu dan Teknologi Kebumian, Institut Teknologi Bandung (ITB), Jl. Ganesha No.10, Bandung, Jawa Barat, Indonesia. Email: [email protected] 2. PT Bumi Suksesindo, Desa Sumberagung, Kecamatan Pesanggaran, Kabupaten Banyuwangi, Provinsi Jawa Timur, Indonesia. Sari – Tujuh Bukit secara umum disusun oleh batuan vulkanik dan vulkaniklastik Formasi Batuampar berumur Oligosen Akhir sampai Miosen Tengah. Setelah terjadi aktivitas tektonomagmatisme pada Pliosen, satuan tersebut teralterasi dan menjadi host rock bagi mineralisasi ekonomis yang juga terbentuk pada Pliosen. Daerah penelitian berada di tambang terbuka Pit B East dan B West. Kavling yang mencakup kedua pit tersebut memiliki luas ± 700 x 500 m2, terletak pada koordinat ± 9045100 – 9045600 mU dan ± 174400 – 175100 mT sistem proyeksi koordinat UTM WGS 1984 zona 50S. Penelitian ini membahas tentang kontrol struktur yang berperan dalam pembentukan karakteristik alterasi dan mineralisasi Au sistem epitermal sulfidasi tinggi yang berkembang di Pit B East dan B West, tambang Tujuh Bukit. Struktur geologi yang dominan berkembang berupa sistem sesar mendatar berumur Pliosen, berarah relatif NW-SE dan N-S, dengan arah tegasan utama NNW-SSE mengikuti model pure shear. Terdapat pula sesar normal berarah relatif NW-SE dan sesar naik berarah relatif ENE-WSW.
    [Show full text]
  • Kinematic and Vorticity Analyses of the Western Idaho Shear Zone, USA
    THEMED ISSUE: EarthScope IDOR project (Deformation and Magmatic Modification of a Steep Continental Margin, Western Idaho–Eastern Oregon) Kinematic and vorticity analyses of the western Idaho shear zone, USA Scott Giorgis1,*, Zach Michels2, Laura Dair1, Nicole Braudy2, and Basil Tikoff2 1DEPARTMENT OF GEOLOGICAL SCIENCES, STATE UNIVERSITY OF NEW YORK AT GENESEO, 1 COLLEGE CIRCLE, GENESEO, NEW YORK 14454, USA 2DEPARTMENT OF GEOSCIENCE, UNIVERSITY OF WISCONSIN–MADISON, 1215 W DAYTON STREET, MADISON, WISCONSIN 53706, USA ABSTRACT The western Idaho shear zone (WISZ) is a Late Cretaceous, mid-crustal exposure of intense shear localized in the Cordillera of western North America. This shear zone is characterized by transpressional fabrics, i.e., downdip stretching lineations and vertical foliations. Folded and boudinaged late-stage dikes indicate a dextral sense of shear. The vorticity-normal section is identified by examining the three-dimensional shape preferred orientation of feldspar populations and the intragranular lattice rotation in quartz grains in deformed quartzites. The short axes of the shape preferred orientation ellipsoid gather on a plane perpendicular to the vorticity vector. In western Idaho this plane dips gently to the west, suggesting a vertical vorticity vector. Similarly, sample-scale crystallographic vorticity axis analysis of quartzite tectonites provides an independent assessment of vorticity and also indicates a subvertical vorticity vector. Constraints on the magnitude of vorticity are provided by field fabrics and porphyroclasts with strain shadows. Together these data indicate that the McCall segment of the WISZ dis- plays dextral transpression with a vertical vorticity vector and an angle of oblique convergence ≥60°. North and south of McCall, movement is coeval on the Owyhee segment of the WISZ and the Ahsahka shear zone.
    [Show full text]