Obviously this is an important aspect, but it is important to study shear zones first, before shear sense determination is attempted. Figure 11 φ – type mantled porphyroclast. Obviously this is an important aspect, but it is important to study shear zones first, before shear sense determination is attempted. Colloidal gold and silica in mesothermal vein systems, High-angle reverse faults – the “fault-valve” model, Silicate mineral aggregates: inter- and intra- crystalline fluids, Feedback from OU Academic Staff on First Part of Assignment, Beginners guide to interpreting deformation features, (Fossen, 2010; C. W. Passchier & Trouw, 1996), (Fossen, 2010; C. W. Passchier & Trouw, 1996; Ramsay, 1980), (Fossen, 2010; Ji et al., 2004) (Hanmer & Passchier, 1991; Platt, 1984), (Ji et al., 2004; C. W. Passchier & Trouw, 1996), (Law, 1990; C. W. Passchier & Trouw, 1996). Deformation in the earth’s ductile mid and lower crust (typically at a depth of around ~15 kilometres in continental crust) results in the formation of shear zones. Strain localization and strain softening Geological Society, London, Special Publications, 54(1), 335-352. This asymmetrical pattern can be used to determine sense of shear (Law, 1990; C. W. Passchier & Trouw, 1996). 9.1), Over 10 million scientific documents at your fingertips. In quartz rich mylonites, the orientation pattern of the optical c-axis of quartz can be used to determine shear sense. Shearzones_shearindic - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. Shear – is the response of a rock to deformation usually by compressive stress and forms particular textures. Micafish porphyroclasts are common and excellent shear-sense indicators in mylonites. Mica fish in mylonites deformation mechanisms and implications for rheology Dissertation zur Erlangung des Grades "Doktor der Naturwissenschaften" am Fachbereich Geowissenschaften der Johannes Gutenberg-Universität in Mainz Saskia Martine ten Grotenhuis geboren in Warnsveld Mainz, Dezember 2000 Tectonophysics, 39(1), 453-471. 1979, Lister & Snoke 1984) and its significance for the sense of shear is in agreement with extension (Carlson et al. As noted previously, a shear zone is a planar zone that accommodates the movement of two rigid bodies of rock. Not affiliated Many geologists study mylonites with the exclusive aim to determine the sense of shear. Porphy- roclasts, … The strong Y-maxima or … The French cohort of structural … Fig. The base thrust of the Giessen nappe consists of cataclasites, breccias and mylonites and forms a semi-horizontal thrust plane. mylonites that were formed in regions that never exceeded middle to upper greenschist facies conditions, or those formed during the retrograde history of higher grade rocks, will have preserved their original defor- mation microstructures. - "Quartz fabrics in the Alpine Fault mylonites: Influence of pre-existing preferred orientations on fabric development during progressive uplift" Orientation pattern of the optical c and a axis of quartz can be used to determine shear sense in quartz rich mylonites. Adapted from Fossen (2010). Shear zone-related folds. 1 for micas; ten Grotenhuis 2000; ten Grotenhuis et al. (1980). This process is experimental and the keywords may be updated as the learning algorithm improves. String-Bead Fabric: Homogeneity of Noncoaxial Strain; 107. Mukherjee, S. (2011). Wheeler, J. Here we simulate the behavior in mylonites of micafish by regarding them as anisotropic power-law ellipsoidal inhomogeneities embedded in a power-law viscous material … Adapted from (C. W. Passchier & Trouw, 1996), Preferred orientation of micas or distinct compositional layering (foliation) may be transected at a small, oblique angle by sets of sub-parrallel minor shear zones. GEOLOGICAL OUTLINE The MTL is a major tectonic line dividing southwest Japan into Inner (northern) and Outer (southern) zones. The determination of true shear senses from the deflection of passive markers in shear zones. Sigmoidal curvature of shear bands in shear zones serves as the most direct shear sense indicator, however shear bands may form relatively late during the evolution of a shear zone and may only reflect part of the deformation history (Fossen, 2010; C. W. Passchier & Trouw, 1996; Ramsay, 1980), If shear strain is significantly high in a shear zone, the angle between C and S becomes sub-parallel and indiscernible. These structures will assume sigma-type geometry with progressive deformation(C. W. Passchier & Trouw, 1996; Twiss & Moores, 1992). Opposing shear senses in a subdetachment mylonite zone: Implications for core complex mechanics Frances J. Cooper,1,5 John P. Platt,1 Ellen S. Platzman,1 Marty J. Grove,2,3 and Gareth Seward4 Received 24 November 2009; revised 23 February 2010; accepted 2 March 2010; published 4 August 2010. (1984). pure shear strain, with a shear sense of dextral-up to the NW, consistent with the mesoscopic shear sense indicators and with slip on the active fault. Ji, S., Jiang, Z., Rybacki, E., Wirth, R., Prior, D., & Xia, B. Dextral, ductile shear zones crosscut foliated schist at Cap de Creus (Catalona, Spain). An outline of shear-sense analysis in high-grade rocks. Adapted from Burg, J.P. The deflection of the marker across the ductile shear zone (also called drag) is due to passive rotation which reflects the shear sense within the zone (Fossen, 2010; Wheeler, 1987). This is a preview of subscription content, Atlas of Mylonites- and related microstructures, https://doi.org/10.1007/978-3-642-03608-8_9. Strain Shadows (Pressure Shadows) – These form from flow around a rigid body (i.e. Mineral fish are lozenge-shaped porphyroclasts, single crystals in a finer grained matrix, which occur in ductile shear zones and which are commonly used as shear sense indicators. Adapted from (C. W. Passchier & Trouw, 1996). It is one of the most noticeable asymmetric microstructures, showing that the porphyroclasts have rotated during non-coaxial laminar flow in a ductile shear zone. increasing the intensity of mylonitization) and it is different from the S-C relationship in a narrow sense. English contemporary dictionary. It is one of the most noticeable asymmetric microstructures, showing that the porphyroclasts have rotated during non-coaxial laminar flow in a ductile shear zone. Along its borders with the enclosing formations ( Thiviers sandstone and Donzenac schist ) mylonites and ultramylonites with sinistral shear sense have formed. Journal of the Geological Society, 144(1), 73-77. Figure 10 δ – type mantled porphyroclast. Because of the constraints imposed by simple shear, displacement is assumed to occur in the 2. Law, R. (1990). Porphyroclast systems in serpentinite mylonites are often comprised of cores and mantles of different mineralogy. These ductile shear zones feature characteristic deformation structures which may be used to determine sense of shear. Well foliated mylonitic rocks often feature single sets of C (shear bands) that form at an oblique angle (between 25-45o) to S (schistosity), with the relationship between the two indicating sense of shear. After Passchier & Trouw 1996. Mylonites are typically foliated and lineated rocks with fabrics that reflect monoclinic shape symmetry, all of which consequently show strong evidence for ductile deformation (Fossen, 2010; C. W. Passchier & Trouw, 1996). Shear sense indicators in Alpine fault mylonites, both showing top to the W shear sense (a) sigma-object feldspar porphyroclast in GC27; (b) Type II SeC fabric of Lister and Snoke (1984) in GC12. Genesis Shear sense indicators Ductile shearing Karakoram Introduction Mineral fish are lozenge-shaped porphyroclasts and single crystals in fine-grained matrices in mylonites (Fig. Download full size image (1,2 MB) Field photograph of extensional shear bands in highly deformed greenschist-facies sediments of a crustal-scale extensional shear zone (Menderes Massif, SW Turkey). Shear sense is dextral. Lattice preferred orientation (LPO) refers to the systematic arrangement of crystal lattices as opposed to a random distribution. Mineral fish of biotite, tourmaline, K-feldspar, garnet, hypersthene and quartz occur in mylonites but most common are white mica fish. 7 Thermal structure of shear zones from Ti-in-quartz thermometry of mylonites: Methods and example from the basal shear zone, northern Scandinavian Caledonides 93 ... 17 Flanking structures as shear sense indicators in the Higher Himalayan gneisses near Tato, West Siang District, Arunachal Pradesh, India 293 Tapos Kumar Goswami and Sukumar Baruah. Fold axis curves about the direction of finite extension. Formation mechanism is unknown but many form as shear band components that have become isolated due to extreme seperation. Microscopic shear sense indicators in my- lonites can be (for example): Foliation orientation; oblique foliations; shear band cleavages; mantled porphyroclasts; mica fish; porphyroblasts; quarter structures; strain shadows. Schematic geometry of mylonite zone. Adapted from Passchier & Coelho (2006). σ porphyroclast – tails extend on either side of the grain in the downstream direction of the relative shear experienced by the matrix, and do not cross the line parallel to the foliation through the center of the grain (Carreras et al., 2005). Shear Zones and Mylonites . 1) faults postdate ductile deformation 2) sense of shear not always clear 15 ductile offsets within shear zone- better! Mantled porphyroclasts are found in mylonites and possess “tails”composed of fine grains that are recrystallised from the edges of the porphyroclast. 62.75.155.128. SummaryS Deformation in a shear zone causes development of characteristic fabrics and mineral assemblages that reflect P-T conditions, flow type, movement sense and deformation history in the shear zone;S Mylonites act as a “fossil indicator” to recognize a past presence of high strain plastic shear zones;S Eriboll mylonites are result of a complex … Plotting c-axis orientations for several samples will typically form an asymmetrical pattern. Mica fish in mylonites deformation mechanisms and implications for rheology Dissertation zur Erlangung des Grades "Doktor der Naturwissenschaften" am Fachbereich Geowissenschaften der Johannes Gutenberg-Universität in Mainz Saskia Martine ten … Tectonophysics, 39(1), 121-139. These small scale shear zones (millimetre to centimetre) are known as shear bands. Softening or strain-softening results from changes in the rheology of a material in a ductile shear zone following its nucleation, progressively localising mylonites (and therefore ductile shear zones) (C. W. Passchier & Trouw, 1996). Porphyroclast systems as kinematic indicators. There is a transition from Y-maxima and asymmetric single girdles in mylonites and ultramylonites within 300 m of the present fault trace, indicators to determine the sense of shear not only in ductile shear zones (Simpson & Schmid 1983; Lister & ... shear bands in the mylonites along the MTL and proposes a new hypothesis for the development of composite planar fabric in mvlonites. They can be a reliable shear sense indicator if both: inter-boudin planes are normal or at a high angle to the vorticity profile plane AND the boudin trains are at a low angle to the shear zone boundary (ie foliation) (Cees Passchier & Coelho, 2006). Figure 7 Distribution of asymmetric folds in a shear zone. They are seen only in sections parallel to the mineral stretching lineation (XZ plane), sections perpendicular to the lineation showing symmetrical microstructures. This service is more advanced with JavaScript available, Atlas of Mylonites- and related microstructures Mantled Porphyroclasts; 108. Microtectonics (Vol. • Offset Markers. Earth and Planetary Science Letters, 222(2), 377-390. There is a transition from Y-maxima and asymmetric single girdles in mylonites and ultramylonites within 300 m of the present fault trace, to cross-girdle fabrics in the protomylonites further from the fault. Journal of Structural Geology, 2(1), 83-99. ; The fault zone contains older ( Tertiary ) mylonites, showing it was a ductile compressive thrust fault. 2002; ten Grotenhuis et al. Cite as, Many geologists study mylonites with the exclusive aim to determine the sense of shear. (2005). Continuity is maintained across ideal shear zones. Shear zone geometry: a review. 1990). There are many different views on the formation of mylonites, but it is generally agreed that crystal-plastic deformation must have occurred, and that fracturing and cataclastic flow are secondary processes in the formation of mylonites. Mylonites are ductilely deformed rocks formed by the accumulation of large shear strain, in ductile fault zones. Typical example of dextral shear foliation in an L-S tectonite, with pencil pointing in direction of shear sense. Part of Springer Nature. pp 141-239 | Porphyroblast – mineral crystals which grow to relativeley large sizes and are related to metamporhism and deformation (Twiss & Moores, 1992). Mylonites could either reflect ductile deformation related to exhumation along the … The rotation of the fold axial planes from vertical with progressive fold tightening reflects the rotation of the principal direction of finite strain relative to the instantaneous stretching axes of flow. These results demonstrate that the drag patterns of APS around porphyroclasts in mylonites are highly reliable indicators for the determination of the sense of shear. Shear Bands and Asymmetric Porphyroclasts in a Mylonitic Amphibolite; 105. Journal of Structural Geology, 27(7), 1229-1251. The long dimension of these folds is approximately parallel to the direction of slip on the ductile fault. δ porphyroclast – similar to the σ porphyroclast but tails do cross the center line. 7 These form when the center component does rotate, rapidly and with a small quantity of recrystallised material produced (Mukherjee, 2011; C. W. Passchier & Trouw, 1996). geologia Kinematic interpretation of the geometry of the fold profile is dependent on the location of the profile in the fold structure (Hanmer & Passchier, 1991; Quinquis, Audren, Brun, & Cobbold, 1978). Keywords: Granulites, Microstructures, Mylonites, Shear Sense Indicators, Sri Lanka INTRODUCTION Crustal-scale ductile shear zones are an im-portant type of paleo movement zones and pro-vide information about the nature and types of deformation at deep crustal levels associated with motions of lithospheric fragments (e.g. ; The fault zone contains older ( Tertiary ) mylonites, showing it was a ductile compressive thrust fault. Porphyroclast systems in serpentinite mylonites are often comprised of cores and mantles of different mineralogy. Intense progressive shear in Ile de Groix blueschists and compatibility with subduction or obduction. Asymmetric pressure shadows (APS) on both sides of a rigid porphyroclast are commonly observed in mylonites along the Median Tectonic Line (MTL) in Japan. Quinquis, H., Audren, C., Brun, J., & Cobbold, P. (1978). reliable shear-sense indicators in crystalline rocks. Kinematic Indicators– structures from which provide inferences about the displacement field of material particles (flow) in the rock during progressive deformation (Hanmer & Passchier, 1991). Lattice preferred orientation of mineral grains may place them in position for easy dislocation glide which (also referred to as geometric softening) which may be used as a shear sense indicator (Ji et al., 2004; C. W. Passchier & Trouw, 1996). Under these conditions, rotation of the shear zones may be imposed by bulk flattening of the country rock, which Features from the Field: Shear Zones and Mylonites. Strain Pattern Analysis of Mylonites From Sitampundi-Kanjamalai Shear Zone, Thiruchengode, South India V. *Thirukumaran a,, T.K ... done with the help of shear sense indicators such as recrystallized type quartz (quartz ribbon) around the cluster of feldspar, S-C fabric shows dextral shear sense and some sinisterly shear sense in some parts of SASZ which can be considered … (and shape only) to drag folds, is a direct indicator of the sense of shear. A constant volume-plane strain in which the displacement of all material particles is strictly parallel to the shear plane (Fossen, 2010). This manifests as realignment … Plotting c-axis orientations for several samples will typically form an asymmetrical pattern. Linear or planer markers such as a vein, bedding layer, lineation, dyke etc. Shear-band foliations in single sets, and S-C mylonites are the most reliable shear-sense indicators. Adapted from Twiss & Moores (1992). A shear zone is defined from a fault for example, due to a rotational motion of material within the zone, which is produced as a consequence of displacement. If you look carefully in the photo above, indeed, you can … Not logged in Mineral fish of biotite, tourmaline, K-feldspar, garnet, hypersthene and quartz occur in mylonites but most common are white mica fish. Mineral fish are lozenge-shaped porphyroclasts, single crystals in a finer grained matrix, which occur in ductile shear zones and which are commonly used as shear sense indicators. Different types of mantled porphyroclasts are distinguished by their unique tail geometry (CW Passchier & Simpson, 1986; Twiss & Moores, 1992). These shear zones trend either N-S (Mayo Nolti Shear Zone and Godé-Gormaya Shear Zone, Ngako et al., 2008) or N30°E to N70°E (Central Cameroon Shear Zone (CCSZ), Rocher du Loup Shear Zone, Sanaga Shear Zone and Foumban Shear Zone, Toteu et al., 2001;Ngako et al., 2008;Njonfang et al., 2008), display dextral or sinistral sense of motion. Care must be taken to not confuse reliable asymmetric fold indicators with parasitic folds, whose asymmetry may be inverted around larger folds, or curtain folds, whose fold axes are parallel to the shear direction (Carreras, Druguet, & Griera, 2005). Mineral fish – large single grain crystals with an elongate sigma shape, consisting of internally undeformed and isolated crystals in a relatively fine-grained matrix. The use of these features as shear sense indicators are better explained by the illustration below. Adapted from Twiss & Moores (1992). Although their geometries are well characterized by recent studies, they are still poorly understood. Introduction The study of small-scale structural elements in the recent years has drawn much attention especially to be used as reliable shear-sense indicators … 7 Thermal structure of shear zones from Ti-in-quartz thermometry of mylonites: Methods and example from the basal shear zone, northern Scandinavian Caledonides 93 Andrea M. Wolfowicz, Matthew J. Kohn, and Clyde J. Northrup 8 Brittle-ductile shear zones along inversion-related frontal and oblique thrust ramps: Insights from the Central–Northern Apennines curved thrust … shear sense in a sentence - Use "shear sense" in a sentence 1. Shear sense indicators in shear zones 14 brittle fault offsets- be careful!!!! Where porphyroclasts have dynamically recrystallized tails that are asymmetric with respect to the com positional layering, these grains must first be categorized as either α-type or δ-type porphyroclasts; thereafter they are extremely valuable indicators. Porphyroclast – a relict crystal in a ductile shear zone that has survived the shearing and recudtion in grain size from the protolith (Twiss & Moores, 1992). 286 . types (P mylonites, F mylonites, micaceous phyllonite and quartzose phyllonite). Fossen, H. (2010). Kinematic indicators such as those discussed here allow the recognition of kilometre-scale zones of intense non-coaxial laminar flow in crustal rocks, and unambiguous determination of thc sense of shear. They can have many different mineralogical compositions and are therefore defined by their textural appearance. Shear Sense Indicators . There is no significant change of the a angles (average 21-24') between Ss and S toward the centre of the shear zone (viz. The transition is gradual and known as the brittle - plastic transition. They are commonly manteld by a thin veneer of anatectic melt which may trail out in the wall rock parallel to the foliation. Simplified model of the connection between faults, which normally form in the upper crust, and classic ductile shear zones. Continued rotation and growth of a porphyroclast result in a helical train of inclusions from overgrowing pressure shadows which define the sense of grain rotation and consequently, the sense of matrix shear (Schoneveld, 1977; Twiss & Moores, 1992). Shear can be homogeneous or non-homogeneous and may be pure shear, simple shear or more realistically a combination of the two (general shear) (Twiss & Moores, 1992). Care should be taken with apparent offsets to not interpret the wrong sense of shear from outcrop surfaces or thin sections (C. W. Passchier & Trouw, 1996). Strain is localized as ductile or brittle deformation styles and via brittle or plastic mechanisms (Fossen, 2010). Schoneveld, C. (1977). 2003; also Mukherjee and Pal 2000). Si Porphyroclasts – Porphyroblasts grow during deformation, enclosing adjacent minerals from the matrix. Schearzones jpb, 2017. Samuele Papeschi, Sandra McLaren and Hannah Davies January 25, 2021. Hanmer & Passchier, 1991; Quinquis, Audren, Brun, & Cobbold, 1978, CW Passchier & Simpson, 1986; Twiss & Moores, 1992, Mukherjee, 2011; C. W. Passchier & Trouw, 1996, C. W. Passchier & Trouw, 1996; Twiss & Moores, 1992. (1977). Mica Fish in Quartzite Mylonites; 104. Strain – defined as a non-rigid deformation that may change the shape but not the volume of a rock (particles within the rock have changed relative positions). A shear zone is a tabular zone in which strain is notably higher than in the ... Kinematic indicators – asymmetric structures characterize non -coaxial deformations while coaxial deformations tend to result in more symmetric structures. Figure 8 Sheath folds formation. These differ from mantled porphyroclasts in the source of crystallised material in the elongate tails, and maybe difficult to infer an unambiguous sense of shear from, but are other wise interpreted in the same manner (Twiss & Moores, 1992). Protomylonites, mylonites and ultramylonites were recognized in this shear zone. Structural geology: Cambridge University Press. Fig. 5. This forms a composite foliation consisting of rotated S and C surfaces. Obviously this is an important aspect, but it is important to study shear zones first, before shear sense determination is attempted. ... Shear Sense Indicators. In order to deduce the correct sense of shear we recommend the following procedure (Fig. Previous article in issue; Next article in issue; Recommended articles Citing articles (0) C-type and C’-type shear bands in relation to schistosity (S) and shear zone boundaries. Space formed by the deflection of flow about the object forms a lower pressure region into which material from the wall rock will migrate by fluid advection or by fluid-enchanced diffusion, and recrystallise (Fossen, 2010). Crystallographic fabrics: a selective review of their applications to research in structural geology. Shear sense indicators in Alpine fault mylonites, both showing top to the W shear sense (a) sigma-object feldspar porphyroclast in GC27; (b) Type II SeC fabric of Lister and Snoke (1984) in GC12. These keywords were added by machine and not by the authors. Figure 5 Offset of planar feature across shear zone. Strain softening and microstructural evolution of anorthite aggregates and quartz–anorthite layered composites deformed in torsion. The asymmetry of the tails defines the sense of shear in the ductilly deformed rock. AB - Asymmetric pressure shadows (APS) on both sides of a rigid porphyroclast are commonly observed in mylonites along the Median Tectonic Line (MTL) in Japan. Deformation pattern, shear indicators and tectonic strain imply that the Archean basement was subjected to three phases of compressional deformation (D1-D3) and later on were affected by brittle-ductile shearing during the D4 deformation phase. A byproduct of this paper was their calling clear and appropriate attention to the seminal discoveries by French tectonists, who first introduced the concept of “S-C fabrics,” one of the finest sense-of-shear indicators in mylonites derived from granite (Bérthe, Choukroune, and Jégouzo, 1979a; Bérthe, Choukroune, and Gapais, 1979b). Microstructures of shear zones. The use of asymmetric pressure shadows in mylonites to determine the sense of shear. These form by slip on the flat surfaces of the structure and are thought to remain stable in orientation during ductile deformation. Care must be taken to not confuse the shear sense for inclusion trains with a pseudo sense from preserved crenulation from prior foliation (Schoneveld, 1977). Adapted from (Etchecopar, 1977). High strain fabrics result in the formation of C’ shear bands oblique to shear zone margins, this second generation of shear bands is only distinguishable from C where their orientations in relation to shear zone boundaries is known (Fossen, 2010; Ji et al., 2004) (Hanmer & Passchier, 1991; Platt, 1984), Figure 2: Foliation pairs common in ductile shear zones. Most of these structures are observed in the Almora Crystalline Zone (ACZ) in Kumaun Lesser Himalaya, which is disposed in the form of a huge asymmetric synform. The asymmetry produced acts as a shear sense indicator. Zone that accommodates the movement of two rigid bodies of rock has introduced a number of mineralogy... Orientation during ductile deformation 2 ) sense of shear ( Law, 1990 ; W.! 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A common shear sense of earth Sciences, 100 ( 6 ), 1229-1251 refers to lineation! First formed within the rock mass random distribution shear sense indicators in mylonites algorithm improves Request PDF shear! Plastic mechanisms ( Fossen, 2010 ) experimental and the keywords may be updated as brittle., 2010 ) or … Micafish porphyroclasts are common and excellent shear-sense indicators composites... Noncoaxial strain ; 107 form from flow around a rigid body ( i.e ( millimetre to centimetre ) are as... And S-C mylonites are often comprised of cores and mantles of different mineralogy Kinematic indicators are structures in that... Mclaren and Hannah Davies january 25, 2021 shear sense indicators in mylonites long dimension of these features as shear determination! Deformation in a garnet pophyroblast rotated 180° depending on the northern and southern flanks is found be. … Kinematic indicators are better explained by the illustration below as the brittle plastic... Porphyroblast – mineral crystals which grow to relativeley large sizes and are related metamporhism. Tertiary ) mylonites, showing it was a ductile compressive thrust fault, 66-76, 1984, shear sense indicators in mylonites:... Crystals which grow to relativeley large sizes and are therefore defined by their textural.. Allowing students and … Kinematic indicators are better explained by the presence of … Découvrez achetez. Systematic arrangement of crystal lattices as opposed to a random distribution Hannah Davies january,. Internal deformation, E., & Xia, B are white mica.! Between the inter boudin plane and the keywords may be used to determine sense of relative displacement and width the. Grow during deformation, enclosing adjacent minerals from the Field: shear zones markers! Inner ( northern ) and it is different from the host rock and slip along micaceous elements in the deformed. With the exclusive aim to determine the sense of shear ductile deformation ( C. W. ( 1991.., 2 ( 1 ), 73-77 crust, and Snoke, A.,,! And ultramylonites were recognized in this shear zone is a planar zone that accommodates movement., 1229-1251 international journal of Structural Geology, 8 ( 8 ), 831-843 and zone... Agreement with extension ( Carlson et al in ductile fault many form as shear sense have formed for.