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nerally the axial plane foliation or cleavage of a fold is created during folding and the number convention should match for example an f 2 fold should have an s 2 axial foliation deformations are numbered according to their order of formation with the letter d denoting a deformation event for example d 1 d 2 d 3 folds and foliations because they are formed by deformation events should correlate with these events for example an f 2 fold with an s 2 axial plane foliation would be the result of a d 2 deformation metamorphic events may span multiple deformations sometimes it is useful to identify them similarly to the structural features for which they are responsible e g m 2 this may be possible by observing porphyroblast formation in cleavages of known deformation age by identifying metamorphic mineral assemblages created by different events or via geochronology intersection lineations in rocks as they are the product of the intersection of two planar structures are named according to the two planar structures from which they are formed for instance the intersection lineation of a s 1 cleavage and bedding is the l 1 0 intersection lineation also known as the cleavage bedding lineation stretching lineations may be difficult to quantify especially in highly stretched ductile rocks where minimal foliation information is preserved where possible when correlated with deformations as few are formed in folds and many are not strictly associated with planar foliations they may be identified similar to planar surfaces and folds e g l 1 l 2 for convenience some geologists prefer to annotate them with a subscript s for example l s1 to differentiate them from intersection lineations though this is generally redundant stereographic projections edit diagram showing the use of lower hemisphere stereographic projection in structural geology using an example of a fault plane and a slickenside lineation observed within the fault plane stereographic projection is a method for analyzing the nature and orientation of deformation stresses lithological units and penetrative fabrics wherein linear and planar features structural strike and dip readings typically taken using a compass clinometer passing through an imagined sphere are plotted on a two dimensional grid projection facilitating more holistic analysis of a set of measurements stereonet 4 developed by richard w allmendinger is widely used in the structural geology community rock macro structures edit on a large scale structural geology is the study of the three dimensional interaction and relationships of stratigraphic units within terranes of rock or geological regions this branch of structural geology deals mainly with the orientation deformation and relationships of stratigraphy bedding which may have been faulted folded or given a foliation by some tectonic event this is mainly a geometric science from which cross sections and three dimensional block models of rocks regions terranes and parts of the earth s crust can be generated study of regional structure is important in understanding orogeny plate tectonics and more specifically in the oil gas and mineral exploration industries as structures such as faults folds and unconformities are primary controls on ore mineralisation and oil traps modern regional structure is being investigated using seismic tomography and seismic reflection in three dimensions providing unrivaled images of the earth s interior its faults and the deep crust further information from geophysics such as gravity and airborne magnetics can provide information on the nature of rocks imaged to be in the deep crust rock microstructures edit main article texture geology rock microstructure or texture of rocks is studied by structural geologists on a small scale to provide detailed information mainly about metamorphic rocks and some features of sedimentary rocks most often if they have been folded textural study involves measurement and characterisation of foliations crenulations metamorphic minerals and timing relationships between these structural features and mineralogical features usually this involves collection of hand specimens which may be cut to provide petrographic thin sections which are analysed under a petrographic microscope kinematics edit geologists use rock geometry measurements to understand the history of strain in rocks strain can take the form of brittle faulting and ductile folding and shearing brittle deformation takes place in the shallow crust and ductile deformation takes place in the deeper crust where temperatures and pressures are higher stress fields edit by understanding the constitutive relationships between stress and strain in rocks geologists can translate the observed patterns of rock deformation into a stress field during the geologic past the following list of features are typically used to determine stress fields from deformational structures in perfectly brittle rocks faulting occurs at 30 to the greatest compressional stress according to byerlee s law the greatest compressive stress is normal to fold axial planes modeling edit for economic geology such as petroleum and mineral development as well as research modeling of structural geology is becoming increasingly important 2d and 3d models of structural systems such as anticlines synclines fold and thrust belts and other features can help better understand the evolution of a structure through time without modeling or interpretation of the subsurface geologists are limited to their knowledge of the surface geological mapping if only reliant on the surface geology major economic potential could be missed by overlooking the structural and tectonic history of the area characterization of the mechanical properties of rock edit the mechanical properties of rock play a vital role in the structures that form during deformation deep below the earth s crust the conditions in which a rock is present will result in different structures that geologists observe above ground in the field the field of structural geology tries to relate the formations that humans see to the changes the rock went through to get to that final structure knowing the conditions of deformation that lead to such structures can illuminate the history of the deformation of the rock temperature and pressure play a huge role in the deformation of rock at the conditions under the earth s crust of extreme high temperature and pressure rocks are ductile they can bend fold or break other vital conditions that contribute to the formation of structure of rock under the earth are the stress and strain fields stress strain curve edit stress is a pressure defined as a directional force over area when a rock is subjected to stresses it changes shape when the stress is released the rock may or may not return to its original shape that change in shape is quantified by strain the change in length over the original length of the material in one dimension stress induces strain which ultimately results in a changed structure elastic deformation refers to a reversible deformation in other words when stress on the rock is released the rock returns to its original shape reversible linear elasticity involves the stretching compressing or distortion of atomic bonds because there is no breaking of bonds the material springs back when the force is released this type of deformation is modeled using a linear relationship between stress and strain i e a hookean relationship ϵ σ e displaystyle epsilon frac sigma e where σ denotes stress ϵ displaystyle epsilon denotes strain and e is the elastic modulus which is material dependent the elastic modulus is in effect a measure of the strength of atomic bonds plastic deformation refers to non reversible deformation the relationship between stress and strain for permanent deformation is nonlinear stress has caused permanent change of shape in the material by involving the breaking of bonds one mechanism of plastic deformation is the movement of dislocations by an applied stress because rocks are essentially aggregates of minerals we can think of them as poly crystalline materials dislocations are a type of crystallographic defect which consists of an extra or missing half plane of atoms in the periodic array of atoms that make up a crystal lattice dislocations are present in all real crystallographic materials hardness edit hardness is difficult to quantify it is a measure of resistance to deformation specifically permanent deformation there is precedent for hardness as a surface quality a measure of the abrasiveness or surface scratching resistance of a material if the material being tested however is uniform in composition and structure then the surface of the material is only a few atomic layers thick and measurements are of the bulk material thus simple surface measurements yield information about the bulk properties ways to measure hardness include mohs scale dorry abrasion test deval abrasion test indentation hardness indentation hardness is used often in metallurgy and materials science and can be thought of as resistance to penetration by an indenter toughness edit toughness can be described best by a material s resistance to cracking during plastic deformation a material absorbs energy until fracture occurs the area under the stress strain curve is the work required to fracture the material the toughness modulus is defined as m t 2 3 σ u t s ϵ f displaystyle m_ t frac 2 3 sigma _ uts epsilon _ f where σ u t s displaystyle sigma _ uts is the ultimate tensile strength and ϵ f displaystyle epsilon _ f is the strain at failure the modulus is the maximum amount of energy per unit volume a material can absorb without fracturing from the equation for modulus for large toughness high strength and high ductility are needed these two properties are usually mutually exclusive brittle materials have low toughness because low plastic deformation decreases the strain low ductility ways to measure toughness include page impact machine and charpy impact test resilience edit resilience is a measure of the elastic energy absorbed of a material under stress in other words the external work performed on a material during deformation the area under the elastic portion of the stress strain curve is the strain energy absorbed per unit volume the resilience modulus is defined as m r σ y 2 2 e displaystyle m_ r frac sigma _ y 2 2e where σ y displaystyle sigma _ y is the yield strength of the material and e is the elastic modulus of the material to increase resilience one needs increased elastic yield strength and decreased modulus of elasticity see also edit earth science portal crenulation list of rock textures section restoration stereographic projection tectonophysics vergence geology hydrogeology references edit russell william l 1955 1 introduction structural geology for petroleum geologists new york mcgraw hill p 1 plate tectonics and people usgs livaccari richard f burke kevin scedilengör a m c 1981 was the laramide orogeny related to subduction of an oceanic plateau nature 289 5795 276 278 bibcode 1981natur 289 276l doi 10 1038 289276a0 s2cid 27153755 stereonet rick allmendinger s stuff retrieved 2022 12 23 further reading edit m king hubbert 1972 structural geology hafner publishing company g h davis and s j reynolds 1996 the structural geology of rocks and regions 2nd ed wiley isbn 0 471 52621 5 c w passchier and r a j trouw 1998 microtectonics berlin springer isbn 3 540 58713 6 b a van der pluijm and s marshak 2004 earth structure an introduction to structural geology and tectonics 2nd ed new york w w norton p 656 isbn 0 393 92467 x d u deere and r p miller 1966 engineering classification and index properties for intact rock technical report no afwl tr 65 116 air force weapons laboratory v t e structural geology underlying theory deformation mechanism lamé s stress ellipsoid mohr coulomb theory mohr s circle overburden pressure rock mechanics strain strain partitioning stress stress field tension measurement conventions brunton compass inclinometer orthographic projection rake stereographic projection strike and dip large scale tectonics accretionary wedge allochthon autochthon back arc basin continental collision convergent boundary décollement divergent boundary extensional tectonics fault block fenster fold and thrust belt fold mountains foreland basin graben half graben horse horst horst and graben intra arc basin inversion klippe list of tectonic plate interactions mélange mountain formation nappe obduction orogeny passive margin plate tectonics pull apart basin rift valley rift saddle strike slip tectonics structural basin suture syneclise terrane thick skinned deformation thin skinned deformation thrust tectonics fracturing columnar jointing dike exfoliation joint fissure joint vein faulting asperity cataclasite cataclastic rock detachment fault disturbance fault friction fault mechanics fault scarp fault trace thrust fault transfer zone transform fault foliation and lineation cleavage compaction crenulation fissility oblique foliation pressure solution rock microstructure slickenside stylolite tectonic phase tectonite folding anticline chevron detachment fold dome homocline monocline syncline vergence boudinage competence kinematic analysis 3d fold evolution paleostress inversion paleostress section restoration shear zone mylonite pure shear shear category v t e geology overviews outline of geology glossary of geology history of geology index of geology articles history of geology geochronology geological history of earth timeline of geology composition and structure cosmochemistry crystallography geochemistry mineralogy petrology sedimentology historical geology stratigraphy paleontology paleoclimatology palaeogeography dynamic earth structural geology geodynamics plate tectonics geomorphology volcanology water glaciology hydrogeology marine geology geodesy cartography earth s orbit geodetic astronomy geomatics gravity of earth planetary geodesy remote sensing geopositioning geophysics geomagnetism geophysical survey planetary geophysics seismology tectonophysics applications biogeology economic geology engineering geology environmental geology planetary geology geobiology geologic modelling forensic geology forensic geophysics meteoritics mining geology mineral physics occupations geologist petroleum geologist volcanologist geology portal geology geology authority control databases international gnd national japan czech republic retrieved from https en wikipedia org w index php title structural_geology oldid 1320275654 category structural geology hidden categories articles with short description short description is different from wikidata articles needing additional references from october 2008 all articles needing additional references this page was last edited on 3 november 2025 at 19 32 utc page was rendered with parsoid text is available under 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