Pull-apart basin

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In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend create an area of crustal extension undergoing tension, which causes the basin to sink down. Frequently, the basins are rhombic or sigmoidal in shape. Dimensionally, basins are limited to the distance between the faults and the length of overlap. [1]

Contents

Mechanics and fault configuration

Diagram of a pull-apart basin redrawn from Frisch et al. 2010 Pull apart basin.jpg
Diagram of a pull-apart basin redrawn from Frisch et al. 2010

The inhomogeneity and structural complexity of continental crust causes faults to deviate from a straight course and frequently causes bends or step-overs in fault paths. Bends and step-overs of adjacent faults become favorable locations for extensional and compressional stress or transtension and transpression stress, if the shear motion is oblique. Pull-apart basins form in extensional to transtensional environments along fault bends or between two adjacent left-lateral faults or two right-lateral faults. The step-over or bend in the fault must be the same direction as sense of motion on the fault otherwise the area will be subject to transpression. [1]

For example, two overlapping left lateral fault must have a left-step-over to create a pull-apart basin. This is illustrated in the accompanying figures.

A regional strike slip fault is referred to as a principle displacement zone (PDZ). Connecting the tips of step over faults to the opposite fault are bounding basin sidewall faults. The tectonic subsidence of strike-slip basins is mainly episodic, short lived (typically less than 10 Ma), and end abruptly with commonly very high tectonic subsidence rates (greater than 0.5 km/Ma) compared to all other basin types. [2] [3] Recent sandbox models have shown that the geometry and evolution of pull-apart basins varies greatly in pure-strike slip situations versus transtensional settings. Transtensional settings are believed to generate greater surface subsidence than pure-strike slip alone. [4]

Examples

Famous localities for continental pull-apart basins are the Dead Sea, the Salton Sea, and the Sea of Marmara. [1] Pull-apart basins are amenable to research because sediments deposited in the basin provide a timeline of activity along the fault. The Salton Trough is an active pull-apart located in a step-over between the dextral San Andreas Fault and the Imperial Fault. [5] Displacement on the fault is approximately 6 cm/yr. [1] The current transtensional state generates normal growth faults and some strike slip motion. The growth faults in the region strike N15E, have steep dips (~70 deg), and vertical displacements of 1–4 mm/yr. Eight large slip events have occurred on these faults with throw ranging from 0.2–1.0 meters. These produce earthquakes greater than magnitude six and are responsible for the majority of extension in the basin and consequently thermal anomalies, subsidence, and localization of rhyolite buttes such as the Salton Buttes. [5] [6]

Economic significance

Pull-apart basins represent an important exploration target for oil and gas, porphyry copper mineralisation, and geothermal fields. The Matzen fault system in the Matzen oil field has been recast as extensional grabens produced by pull-apart basins of the Vienna Basin. [7] The Dead Sea has been studied extensively and thinning of the crust in pull-aparts may generate differential loading and instigate salt diapirs to rise, [8] a frequent trap for hydrocarbons. Likewise intense deformation and rapid subsidence and deposition in pull-aparts creates numerous structural and stratigraphic traps, enhancing their viability as hydrocarbon reservoirs. [9]

The shallow extensional regime of pull-apart basins also facilitates the emplacement of felsic intrusive rocks with high copper mineralisation. It is believed to be the main structural control on the giant Escondida deposit in Chile. [10] Geothermal fields are located in pull-aparts for the same reason due to the high heat flow associated with rising magmas. [11]

Related Research Articles

<span class="mw-page-title-main">Sedimentary basin</span> Regions of long-term subsidence creating space for infilling by sediments

Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence creates a regional depression that provides accommodation space for accumulation of sediments. Over millions or tens or hundreds of millions of years the deposition of sediment, primarily gravity-driven transportation of water-borne eroded material, acts to fill the depression. As the sediments are buried, they are subject to increasing pressure and begin the processes of compaction and lithification that transform them into sedimentary rock.

<span class="mw-page-title-main">Rift</span> Geological linear zone where the lithosphere is being pulled apart

In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting and rift-flank uplifts mainly on one side. Where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake. The axis of the rift area may contain volcanic rocks, and active volcanism is a part of many, but not all, active rift systems.

<span class="mw-page-title-main">Salt dome</span> Structural dome formed of salt or halite

A salt dome is a type of structural dome formed when salt intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered using techniques such as seismic reflection. They are important in petroleum geology as they can function as petroleum traps.

<span class="mw-page-title-main">Los Angeles Basin</span> Sedimentary basin located along the coast of southern California

The Los Angeles Basin is a sedimentary basin located in Southern California, in a region known as the Peninsular Ranges. The basin is also connected to an anomalous group of east-west trending chains of mountains collectively known as the Transverse Ranges. The present basin is a coastal lowland area, whose floor is marked by elongate low ridges and groups of hills that is located on the edge of the Pacific Plate. The Los Angeles Basin, along with the Santa Barbara Channel, the Ventura Basin, the San Fernando Valley, and the San Gabriel Basin, lies within the greater Southern California region. The majority of the jurisdictional land area of the city of Los Angeles physically lies within this basin.

<span class="mw-page-title-main">Passive margin</span> Transition between oceanic and continental lithosphere that is not an active plate margin

A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting forms new ocean basins. Eventually the continental rift forms a mid-ocean ridge and the locus of extension moves away from the continent-ocean boundary. The transition between the continental and oceanic lithosphere that was originally formed by rifting is known as a passive margin.

Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere.

<span class="mw-page-title-main">Transpression</span> Type of strike-slip deformation

In geology, transpression is a type of strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. This movement ends up resulting in oblique shear. It is generally very unlikely that a deforming body will experience "pure" shortening or "pure" strike-slip. The relative amounts of shortening and strike-slip can be expressed in the convergence angle alpha which ranges from zero to 90 degrees. During shortening, unless material is lost, transpression produces vertical thickening in the crust. Transpression that occurs on a regional scale along plate boundaries is characterized by oblique convergence. More locally, transpression occurs within restraining bends in strike-slip fault zones.

<span class="mw-page-title-main">Thrust tectonics</span> Concept in structural geology

Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, the others being extensional tectonics and strike-slip tectonics. These match the three types of plate boundary, convergent (thrust), divergent (extensional) and transform (strike-slip). There are two main types of thrust tectonics, thin-skinned and thick-skinned, depending on whether or not basement rocks are involved in the deformation. The principle geological environments where thrust tectonics is observed are zones of continental collision, restraining bends on strike-slip faults and as part of detached fault systems on some passive margins.

Strike-slip tectonics or wrench tectonics is a type of tectonics that is dominated by lateral (horizontal) movements within the Earth's crust. Where a zone of strike-slip tectonics forms the boundary between two tectonic plates, this is known as a transform or conservative plate boundary. Areas of strike-slip tectonics are characterised by particular deformation styles including: stepovers, Riedel shears, flower structures and strike-slip duplexes. Where the displacement along a zone of strike-slip deviates from parallelism with the zone itself, the style becomes either transpressional or transtensional depending on the sense of deviation. Strike-slip tectonics is characteristic of several geological environments, including oceanic and continental transform faults, zones of oblique collision and the deforming foreland of zones of continental collision.

<span class="mw-page-title-main">Inversion (geology)</span> Relative uplift of a sedimentary basin or similar structure as a result of crustal shortening

In structural geology inversion or basin inversion relates to the relative uplift of a sedimentary basin or similar structure as a result of crustal shortening. This normally excludes uplift developed in the footwalls of later extensional faults, or uplift caused by mantle plumes. "Inversion" can also refer to individual faults, where an extensional fault is reactivated in the opposite direction to its original movement.

Transtension is the state in which a rock mass or area of the Earth's crust experiences both extensive and transtensive shear. As such, transtensional regions are characterised by both extensional structures and wrench structures. In general, many tectonic regimes that were previously defined as simple strike-slip shear zones are actually transtensional. It is unlikely that a deforming body will experience 'pure' extension or 'pure' strike-slip.

<span class="mw-page-title-main">Jeanne d'Arc Basin</span>

The Jeanne d'Arc Basin is an offshore sedimentary basin located about 340 kilometres to the basin centre, east-southeast of St. John's, Newfoundland and Labrador. This basin formed in response to the large scale plate tectonic forces that ripped apart the super-continent Pangea and also led to sea-floor spreading in the North Atlantic Ocean. This basin is one of a series of rift basins that are located on the broad, shallow promontory of continental crust known as the Grand Banks of Newfoundland off Canada's east coast. The basin was named after a purported 20 metres shoal labelled as "Ste. Jeanne d'Arc" on out-dated bathymetric charts and which was once thought to represent a local exposure of basement rocks similar to the Virgin Rocks.

Tectonic subsidence is the sinking of the Earth's crust on a large scale, relative to crustal-scale features or the geoid. The movement of crustal plates and accommodation spaces produced by faulting brought about subsidence on a large scale in a variety of environments, including passive margins, aulacogens, fore-arc basins, foreland basins, intercontinental basins and pull-apart basins. Three mechanisms are common in the tectonic environments in which subsidence occurs: extension, cooling and loading.

The South China Sea Basin is one of the largest marginal basins in Asia. South China Sea is located to the east of Vietnam, west of Philippines and the Luzon Strait, and north of Borneo. Tectonically, it is surrounded by the Indochina Block on the west, Philippine Sea Plate on the east, Yangtze Block to the north. A subduction boundary exists between the Philippine Sea Plate and the Asian Plate. The formation of the South China Sea Basin was closely related with the collision between the Indian Plate and Eurasian Plates. The collision thickened the continental crust and changed the elevation of the topography from the Himalayan orogenic zone to the South China Sea, especially around the Tibetan Plateau. The location of the South China Sea makes it a product of several tectonic events. All the plates around the South China Sea Basin underwent clockwise rotation, subduction and experienced an extrusion process from the early Cenozoic to the Late Miocene.

<span class="mw-page-title-main">Yinggehai basin</span>

The Yinggehai-Song Hong Basin is located on the northwest of the South China Sea, between Hainan island and the coast of northern Vietnam. It is a large extensional pull-part basin in extensional continental marginal setting, developed along the Red River fault zone, which located at the suture of the Indochina Plate and Yangtze Plate.

<span class="mw-page-title-main">Northern North Sea basin</span>

The North Sea is part of the Atlantic Ocean in northern Europe. It is located between Norway and Denmark in the east, Scotland and England in the west, Germany, the Netherlands, Belgium and France in the south.

<span class="mw-page-title-main">Geology of the southern North Sea</span> Largest gas producing basin

The North Sea basin is located in northern Europe and lies between the United Kingdom, and Norway just north of The Netherlands and can be divided into many sub-basins. The Southern North Sea basin is the largest gas producing basin in the UK continental shelf, with production coming from the lower Permian sandstones which are sealed by the upper Zechstein salt. The evolution of the North Sea basin occurred through multiple stages throughout the geologic timeline. First the creation of the Sub-Cambrian peneplain, followed by the Caledonian Orogeny in the late Silurian and early Devonian. Rift phases occurred in the late Paleozoic and early Mesozoic which allowed the opening of the northeastern Atlantic. Differential uplift occurred in the late Paleogene and Neogene. The geology of the Southern North Sea basin has a complex history of basinal subsidence that had occurred in the Paleozoic, Mesozoic, and Cenozoic. Uplift events occurred which were then followed by crustal extension which allowed rocks to become folded and faulted late in the Paleozoic. Tectonic movements allowed for halokinesis to occur with more uplift in the Mesozoic followed by a major phase of inversion occurred in the Cenozoic affecting many basins in northwestern Europe. The overall saucer-shaped geometry of the southern North Sea Basin indicates that the major faults have not been actively controlling sediment distribution.

<span class="mw-page-title-main">Wessex Basin</span> Petroliferous geological area on the southern coast of England and the English Channel

The Wessex Basin is a petroleum-bearing geological area located along the southern coast of England and extending into the English Channel. The onshore part of the basin covers approximately 20,000 km2 and the area that encompasses the English Channel is of similar size. The basin is a rift basin that was created during the Permian to early Cretaceous in response to movement of the African plate relative to the Eurasian plate. In the late Cretaceous, and again in the Cenozoic, the basin was inverted as a distant effect of the Alpine orogeny. The basin is usually divided into 3 main sub-basins including the Winterborne-Kingston Trough, Channel Basin, and Vale of Pewsey Basin. The area is also rich in hydrocarbons with several offshore wells in the area. With the large interest in the hydrocarbon exploration of the area, data became more readily available, which improved the understanding of the type of inversion tectonics that characterize this basin.

The Otway Basin is a northwest trending sedimentary basin located along the southern coast of Australia. The basin covers an area of 150,000 square kilometers and spans from southeastern South Australia to southwestern Victoria, with 80% lying offshore in water depths ranging from 50-3,000 meters. Otway represents a passive margin rift basin and is one of a series of basins located along the Australian Southern Rift System. The basin dates from the late Jurassic to late Cretaceous periods and formed by multi-stage rifting during the breakup of Gondwana and the separation of the Antarctic and Australian plates. The basin contains a significant amount of natural gas and is a current source of commercial extraction.

Magmatism along strike-slip faults is the process of rock melting, magma ascent and emplacement, associated with the tectonics and geometry of various strike-slip settings, most commonly occurring along transform boundaries at mid-ocean ridge spreading centres and at strike-slip systems parallel to oblique subduction zones. Strike-slip faults have a direct effect on magmatism. They can either induce magmatism, act as a conduit to magmatism and magmatic flow, or block magmatic flow. In contrast, magmatism can also directly impact on strike-slip faults by determining fault formation, propagation and slip. Both magma and strike-slip faults coexist and affect one another.

References

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  2. Xie,X., Heller, P.L. "Plate tectonics and basin subsidence history" GSA Bulletin 121 (2009): 55-64. https://doi.org/10.1130/B26398.1
  3. Lee, E.Y., Wagreich, M. "Polyphase tectonic subsidence evolution of the Vienna Basin inferred from quantitative subsidence analysis of the northern and central parts" International Journal of Earth Sciences 106 (2017): 687-705. https://doi.org/10.1007/s00531-016-1329-9
  4. Wu, Jonathan E., Ken McClay, Paul Whitehouse, and Tim Dooley. "4D analogue modelling of transtensional pull-apart basins." Marine and Petroleum Geology 26, no. 8 (2009): 1608–1623.
  5. 1 2 Brothers, D. S., N. W. Driscoll, G. M. Kent, A. J. Harding, J. M. Babcock, and R. L. Baskin. "Tectonic evolution of the Salton Sea inferred from seismic reflection data." Nature Geoscience 2, no. 8 (2009): 581–584.
  6. Brothers, Daniel, Debi Kilb, Karen Luttrell, Neal Driscoll, and Graham Kent. "Loading of the San Andreas fault by flood-induced rupture of faults beneath the Salton Sea." Nature Geoscience 4, no. 7 (2011): 486–492.
  7. Fuchs, Reinhard, and Walter Hamilton. "New depositional architecture for an old giant: the Matzen Field, Austria." (2006): 205–219.
  8. Al-Zoubi, Abdallah, and Uri S. ten Brink. "Salt diapirs in the Dead Sea basin and their relationship to Quaternary extensional tectonics." Marine and Petroleum Geology 18, no. 7 (2001): 779–797.
  9. Brister, Brian S., William C. Stephens, and Gregg A. Norman. "Structure, stratigraphy, and hydrocarbon system of a Pennsylvanian pull-apart basin in north-central Texas." AAPG bulletin 86, no. 1 (2002): 1–20.
  10. Richards, Jeremy P., Adrian J. Boyce, and Malcolm S. Pringle. "Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization." Economic Geology 96, no. 2 (2001): 271–305.
  11. Monastero, F. C., A. M. Katzenstein, J. S. Miller, J. R. Unruh, M. C. Adams, and Keith Richards-Dinger. "The Coso geothermal field: A nascent metamorphic core complex." Geological Society of America Bulletin 117, no. 11–12 (2005): 1534–1553.

Further reading