NationMaster - Encyclopedia: Structural geology

Structural geology is the study of the three dimensional distribution of rock bodies and their planar or folded surfaces, and their internal fabrics.

Structural geology includes features of and overlaps with facets of geomorphology, metamorphism and geotechnical studies. By studying the three dimensional structure of rocks and regions, inferences on tectonic history, past geological environments and deformation events can be made. These can be fixed in time using stratigraphical controls as well as geochronology, to determine when the structural features formed. Surface of the Earth Geomorphology is the study of landforms, including their origin and evolution, and the processes that shape them. ... Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i. ... Geotechnical engineering is concerned with the engineering properties of earth materials. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Geochronology is the science of determining the age of rocks, fossils, and sediments. ...

More formally stated it is the branch of geology that deals with the geological processes through which the application of a force results in the transformation of a shape, arrangement or internal fabric of the rock into another shape, arrangement or internal fabric. Petroleum structural geologists can interpret prospect or basin scale geology using several techniques. These techniques include the interpretation of surface data, well data, remote sensing data and seismic data. With varied data sources many structural geologists and petroleum service companies now use 3D software programs. This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... This balancing rock, Steamboat Rock stands in Garden of the Gods park in Colorado Springs, CO The rocky side of a mountain creek near OrosÃ, Costa Rica. ...

Use and importance

The study of geologic structures has been of prime importance in economic geology, both petroleum geology and mining geology. Folded and faulted rock strata commonly form traps for the accumulation and concentration of fluids such as petroleum and natural gas. Faulted and structurally complex areas are notable as permeable zones for hydrothermal fluids and the resulting concentration areas for base and precious metal ore deposits. Veins of minerals containing various metals commonly occupy faults and fractures in structurally complex areas. These structurally fractured and faulted zones often occur in association with intrusive igneous rocks. They often also occur around geologic reef complexes and collapse features such as ancient sinkholes. Deposits of gold, silver, copper, lead, zinc, and other metals, are commonly located in structurally complex areas. Economic geology is concerned with earth materials that can be utilized for economic and/or industrial purposes. ... Petroleum geology is a term used to refer to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration). ... Chuquicamata, the second largest open pit copper mine in the world, Chile. ... For other uses, see strata (novel) and strata title. ... Pumpjack pumping an oil well near Lubbock, Texas Ignacy Åukasiewicz - inventor of the refining of kerosene from crude oil. ... For other uses, see Natural gas (disambiguation). ... Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ... Iron ore (Banded iron formation) Manganese ore Lead ore Gold ore An ore is a volume of rock containing components or minerals in a mode of occurrence which renders it valuable for mining. ... Pluton redirects here. ... Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... A reef surrounding an islet. ... Devils Hole near Hawthorne, Florida, USA. A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or cenote, is a natural depression or hole in the surface topography caused by the removal of soil or bedrock, often both, by water. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Standard atomic weight 107. ... For other uses, see Copper (disambiguation). ... For Pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ...

Structural geology is a critical part of engineering geology, which is concerned with the physical and mechanical properties of natural rocks. Structural fabrics and defects such as faults, folds, foliations and joints are internal weaknesses of rocks which may affect the stability of human engineered structures such as dams, road cuts, open pit mines and underground mines or road tunnels. Engineering Geology is the application of the science of geology to the understanding of geologic phenomena and the engineering solution of geologic hazards and other geologic problems for society. ... Columnar jointed basalt in Turkey Columnar jointing in the basalt of the Giants Causeway in Ireland A joint is a generally planar fracture formed in a rock as a result of extensional stress. ... This article does not cite any references or sources. ... Open Pit is the name of a brand of sauces marketed by Pinnacle Foods. ... Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals such as those containing metals like gold, copper, zinc, nickel and lead or gems such as diamonds. ... A disused railway tunnel now converted to pedestrian and bicycle use, near Houyet, Belgium A tunnel is an underground passage. ...

Geotechnical risk, including earthquake risk can only be investigated by inspecting a combination of structural geology and geomorphology. In addition areas of karst landscapes which are underlain by underground caverns and potential sinkholes or collapse features are of importance for these scientists. In addition, areas of steep slopes are potential collapse or landslide hazards. Geotechnical engineering is concerned with the engineering properties of earth materials. ... An earthquake is the result of a sudden release of stored energy in the Earths crust that creates seismic waves. ... Surface of the Earth Geomorphology is the study of landforms, including their origin and evolution, and the processes that shape them. ... Karst topography is a three-dimensional landscape shaped by the dissolution of a soluble layer or layers of bedrock, usually carbonate rock such as limestone or dolomite. ... Devils Hole near Hawthorne, Florida, USA. A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or cenote, is a natural depression or hole in the surface topography caused by the removal of soil or bedrock, often both, by water. ...

Environmental geologists and hydrogeologists or hydrologists need to understand structural geology because structures are sites of groundwater flow and penetration, which may affect, for instance, seepage of toxic substances from waste dumps, or seepage of salty water into aquifers. Environmental geology, like hydrogeology, is a multidisciplinary field of applied science and is closely related to engineering geology and somewhat related to environmental geography. ... Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earths crust, (commonly in aquifers). ... Water covers 70% of the Earths surface. ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ... An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. ...

Plate tectonics is structural geology on a large scale, usually referring to the structural effects of plate collisions and other plate tectonic features. The tectonic plates of the world were mapped in the second half of the 20th century. ...

Rock macro-structures

On a large scale, structural geology is the study of the three dimensional relationships of stratigraphic units to one another within terranes of rock or within geological regions. A terrane in paleogeography is an accretion that has collided with a continental nucleus, or craton but can be recognized by the foreign origin of its rock strata. ...

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. Old fault exposed by roadcut near Harrisburg, Pennsylvania. ... Very tight folds. ... Foliation is any penetrative planar fabric present in rocks. ...

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. // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within... The tectonic plates of the world were mapped in the second half of the 20th century. ... Pumpjack pumping an oil well near Lubbock, Texas Ignacy Åukasiewicz - inventor of the refining of kerosene from crude oil. ... This article does not cite any references or sources. ... A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. ... There is a billion year gap in the geologic record where this 500 million year old dolomite unconformably overlays 1. ... Iron ore (Banded iron formation) Manganese ore Lead ore Gold ore An ore is a volume of rock containing components or minerals in a mode of occurrence which renders it valuable for mining. ...

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 in the deep crust. Seismic tomography uses digital seismographic records to image the interior of the Earth. ... Seismology (from the Greek seismos = earthquake and logos = word) is the scientific study of earthquakes and the movement of waves through the Earth. ... â€¹ The template below has been proposed for deletion. ... Gravity is a force of attraction that acts between bodies that have mass. ...

Old fault exposed by roadcut near Harrisburg, Pennsylvania. ... Very tight folds. ... Columnar jointed basalt in Turkey Columnar jointing in the basalt of the Giants Causeway in Ireland A joint is a generally planar fracture formed in a rock as a result of extensional stress. ... Figure 1. ...

Rock microstructures

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. Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means change in form, derived from the Greek words meta, change, and morphe, form. The protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound... Two types of sedimentary rock: limey shale overlaid by limestone. ... Foliation is any penetrative planar fabric present in rocks. ... Crenulation is a texture formed in metamorphic rocks such as phyllite, schist and some gneiss by two or more stress directions resulting in superimposed foliations. ... Petrography is the description of rocks and their textures. ...

Main article: rock microstructure Rock microstructure includes the texture of a rock and the small scale rock structures. ...

Principles of structural geology

Measurement conventions

The inclination of a planar structure in geology is measured by strike and dip. The strike is the line of intersection between the planar feature and a horizontal plane, taken according to the right hand convention, and the dip is the magnitude of the inclination, below horizontal, at right angles to strike. For example; striking 25 degrees East of North, dipping 45 degrees Southeast, recorded as N25E,45SE.
Alternatively, dip and dip direction may be used as this is absolute. Dip direction is measured in 360 degrees, generally clockwise from North. For example, a dip of 45 degrees towards 75 degrees azimuth, recorded as 45/75. Note that this is the same as above. Strike and dip refer to the orientation or attitude of a geologic feature. ...

Fold axis plunge is measured in dip and dip direction (strictly, plunge and azimuth of plunge). The orientation of a fold axial plane is measured in strike and dip or dip and dip direction.

Lineations are measured in terms of dip and dip direction, if possible. Often lineations occur expressed on a planar surface and cannot be measured directly. In this case, the lineation may be measured as a rake upon the surface. Lineations in structural geology are linear structural features within rocks. ...

Rake is measured by placing a protractor flat on the planar surface, with the flat edge horizontal and measuring the angle of the lineation clockwise from horizontal. The orientation of the lineation can then be calculated from the rake and strike-dip information of the plane it was measured from.

If a fault has lineations formed by movement on the plane, eg; slickensides, this is recorded as a lineation, with a rake, and annotated as to the indication of throw on the fault.

Generally it is easier to record strike and dip information of planar structures in dip/dip direction format as this will match all the other structural information you may be recording about folds, lineations, et cetera.

Plane, fabric, fold and deformation conventions

The convention for analysing structural geology is to identify the planar structures, often called planar fabrics because this implies a textural formation, the linear structures and, from analysis of these, unravel deformations. Rock microstructure includes the texture of a rock and the small scale rock structures. ...

Planar structures are named according to their order of formation, with original sedimentary layering the lowest at S0. Often it is impossible to identify S0 in highly deformed rocks, so numbering may be started at an arbitrary number or given a letter (S_A, for instance). In cases where there is a bedding-plane foliation caused by burial metamorphism or diagenesis this may be enumerated as S0a. In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism. ...

If there are folds, these are numbered as F₁, F₂, etc. Generally the axial plane foliation or cleavage of a fold is created during folding, and the number convention should match. For example, an F₂ fold should have an S₂ axial foliation.

Deformations are numbered according to their order of formation with the letter D denoting a deformation event. For example D₁, D₂, D₃. Folds and foliations, because they are formed by deformation events, should correlate with these events. For example an F₂ fold, with an S₂ axial plane foliation would be the result of a D₂ deformation.

Metamorphic events may span multiple deformations. Sometimes it is useful to identify them similarly to the structural features for which they are responsible, eg; M₂. 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. A porphyroblast is a large mineral crystal of metamorphic origin which has grown within the finer grained groundmass of a metamorphic rock as a response to the stresses or heat of metamorphism. ... Geochronology is the science of determining the age of rocks, fossils, and sediments. ...

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 S₁ 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, eg; L₁, L₂. 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

Stereographic projection of structural strike and dip measurements is a powerful method for analyzing the nature and orientation of deformation stresses, lithological units and penetrative fabrics. Stereographic projection of a circle of radius R onto the x axis. ...

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