Strike-slip tectonics
Encyclopedia
Strike-slip tectonics is concerned with the structures formed by, and the tectonic
processes associated with, zones of lateral displacement within the crust
or lithosphere
.
rocks produces characteristic fault structures within the overlying cover. This will also be the case where an active strike-slip zone lies within an area of continuing sedimentation. At low levels of strain the overall simple shear
causes a set of small faults to form. The dominant set, known as R shears, form at about 15° to the underlying fault with the same shear sense. The R shears are then linked by a second set, the R' shear that form at about 75° to the main fault trace. These two fault orientations can be understood as conjugate fault sets at 30° to the short axis of the instantaneous strain ellipse associated with the simple shear strain field caused by the displacements applied at the base of the cover sequence. With further displacement the Riedel fault segments will tend to become fully linked, often with the development of a further set of shears known as 'P shears', which are roughly symmetrical to the R shears with respect to the overall shear direction, until a throughgoing fault is formed. The somewhat oblique segments will link downwards into the fault at the base of the cover sequence with a helicoidal geometry.
Areas of strike-slip tectonics are associated with:
s. The active part of the transform links the two ridge segments. Some of these transforms can be very large, such as the Romanche fracture zone
, whose active portion extends for about 300 km.
, the Dead Sea Transform
, the North Anatolian Fault
and the Alpine Fault
.
the relative movement of the plates is oblique to the plate boundary itself. The deformation along the boundary is normally partitioned into dip-slip contractional structures in the foreland with a single large strike-slip structure in the hinterland accommodating all the strike-slip component along the boundary. Examples include the Main Recent Fault along the boundary between the Arabian
and Eurasian plates behind the Zagros fold and thrust belt, the Liquiñe-Ofqui Fault
that runs through Chile
and the Great Sumatran fault
that runs parallel to the subduction
zone along the Sunda Trench
.
, occurs during a collisional event where one of the plates deforms internally along a system of strike-slip faults. The best known active example is the system of strike-slip structures observed in the Eurasian plate
as it responds to collision with the Indian plate, such as the Kunlun fault
and Altyn Tagh fault.
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
processes associated with, zones of lateral displacement within the crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
or lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
.
Deformation styles
Riedel shear structures
In the early stages of strike-slip fault formation displacement within basementBasement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
rocks produces characteristic fault structures within the overlying cover. This will also be the case where an active strike-slip zone lies within an area of continuing sedimentation. At low levels of strain the overall simple shear
Simple shear
In fluid mechanics, simple shear is a special case of deformation where only one component of velocity vectors has a non-zero value:\ V_x=f\ V_y=V_z=0And the gradient of velocity is constant and perpendicular to the velocity itself:...
causes a set of small faults to form. The dominant set, known as R shears, form at about 15° to the underlying fault with the same shear sense. The R shears are then linked by a second set, the R' shear that form at about 75° to the main fault trace. These two fault orientations can be understood as conjugate fault sets at 30° to the short axis of the instantaneous strain ellipse associated with the simple shear strain field caused by the displacements applied at the base of the cover sequence. With further displacement the Riedel fault segments will tend to become fully linked, often with the development of a further set of shears known as 'P shears', which are roughly symmetrical to the R shears with respect to the overall shear direction, until a throughgoing fault is formed. The somewhat oblique segments will link downwards into the fault at the base of the cover sequence with a helicoidal geometry.
Flower structures
In detail many strike-slip faults at surface consist of en echelon and/or braided segments in many cases probably inherited from previously formed riedel shears. In cross-section the displacements are dominantly reverse or normal in type depending on whether the overall fault geometry is transpressional (i.e. with a small component of shortening) or transtensional (with a small component of extension). As the faults tend to join downwards onto a single strand in basement, the geometry has led to these being termed flower structure. Fault zones with dominantly reverse faulting are known as positive flowers, those with dominantly normal offsets are known as negative flowers. The identification of such structures, particularly where positive and negative flowers are developed on different segments of the same fault, are regarded as reliable indicators of strike-slip.Geological environments associated with strike-slip tectonics
Oceanic transform boundaries
Mid-ocean ridges are broken into segments offset from each other by transform faultTransform fault
A transform fault or transform boundary, also known as conservative plate boundary since these faults neither create nor destroy lithosphere, is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction. Furthermore, transform faults end abruptly...
s. The active part of the transform links the two ridge segments. Some of these transforms can be very large, such as the Romanche fracture zone
Romanche Trench
The Romanche Trench, also called the Romanche Furrow or Romanche Gap, is the third deepest of the major trenches of the Atlantic Ocean, after the Puerto Rico Trench and the South Sandwich Trench. It bisects the Mid-Atlantic Ridge just north of the equator at the narrowest part of the Atlantic...
, whose active portion extends for about 300 km.
Continental transform boundaries
Transform faults within continental plates include some of the best known examples of strike-slip structures, such as the San Andreas FaultSan Andreas Fault
The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...
, the Dead Sea Transform
Dead Sea Transform
The Dead Sea Transform fault system, also sometimes referred to as the Dead Sea Rift, is a geologic fault which runs from the Maras Triple Junction to the northern end of the Red Sea Rift...
, the North Anatolian Fault
North Anatolian Fault
The North Anatolian Fault is a major active right lateral-moving strike-slip fault in northern Anatolia which runs along the transform boundary between the Eurasian Plate and the Anatolian Plate. The fault extends westward from a junction with the East Anatolian Fault at the Karliova Triple...
and the Alpine Fault
Alpine Fault
The Alpine Fault is a geological fault, more specifically known as a right-lateral strike-slip fault, that runs almost the entire length of New Zealand's South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the...
.
Lateral ramps in areas of extensional or contractional tectonics
Major lateral offsets between large extensional or thrust faults are normally connected by diffuse or discrete zones of strike-slip deformation allowing transfer of the overall displacement between the structures.Zones of oblique collision
In most zones of continent-continent collisionContinental collision
Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains produced, and two continents sutured together...
the relative movement of the plates is oblique to the plate boundary itself. The deformation along the boundary is normally partitioned into dip-slip contractional structures in the foreland with a single large strike-slip structure in the hinterland accommodating all the strike-slip component along the boundary. Examples include the Main Recent Fault along the boundary between the Arabian
Arabian Plate
The Arabian Plate is one of three tectonic plates which have been moving northward over millions of years and colliding with the Eurasian Plate...
and Eurasian plates behind the Zagros fold and thrust belt, the Liquiñe-Ofqui Fault
Liquiñe-Ofqui Fault
The Liquiñe-Ofqui Fault is major geological fault that runs a length of roughly 1000 km in a north-south direction and exhibits current seismicity . It is located in the Chilean northern patagonean Andes. It is a dextral intra-arc transform fault...
that runs through Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
and the Great Sumatran fault
Great Sumatran fault
The Indonesian island of Sumatra is located in a highly seismic area of the world. In addition to the subduction zone and the associated Sunda Arc off the west coast of the island, Sumatra also has a large strike-slip fault, the so-called Great Sumatran Fault, running the entire length of the island...
that runs parallel to the subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
zone along the Sunda Trench
Java Trench
The Sunda Trench, earlier known as, and sometimes still indicated as the Java Trench, located in the northeastern Indian Ocean, with a length of and a maximum depth of , is the second-deepest point in the Indian Ocean after Diamantina Trench, which is 8,047 metres deep...
.
The deforming foreland of a zone of continent-continent collision
The process sometimes known as escape tectonics, first elucidated by Paul TapponnierPaul Tapponnier
Paul Tapponnier was born on January 6, 1947 in Annecy, France. He became an engineer from the prestigious Ecole Nationale Superieure des Mines de Paris in 1970. He started his career at the Universite du Languedoc, in Montpellier, and trained as a research fellow at the Massachusetts Institute of...
, occurs during a collisional event where one of the plates deforms internally along a system of strike-slip faults. The best known active example is the system of strike-slip structures observed in the Eurasian plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
as it responds to collision with the Indian plate, such as the Kunlun fault
Kunlun fault
The Kunlun fault is a strike slip fault to the north side of Tibet. Slippage along the long fault has occurred at a constant rate for the last 40,000 years. This has resulted in a cumulative offset of more than . The fault is seismically active, most recently causing the magnitude 7.8 2001 Kunlun...
and Altyn Tagh fault.