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66-753: The Rio Grande rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east. The rift extends from central Colorado in the north to the state of Chihuahua , Mexico , in the south. The rift zone consists of four basins that have an average width of 50 kilometres (31 mi). The rift can be observed on location at Rio Grande National Forest , White Sands National Park , Santa Fe National Forest , and Cibola National Forest , among other locations. The Rio Grande rift has been an important site for humans for

132-475: A cobalt-60 interior acting as a radioactive heat source. This should take half a year to reach the oceanic Moho . Exploration can also be aided through computer simulations of the evolution of the mantle. In 2009, a supercomputer application provided new insight into the distribution of mineral deposits, especially isotopes of iron, from when the mantle developed 4.5 billion years ago. In 2023 JOIDES Resolution recovered cores of what appeared to be rock from

198-449: A lacustrine environment or in a restricted marine environment, although not all rifts contain such sequences. Reservoir rocks may be developed in pre-rift, syn-rift and post-rift sequences. Effective regional seals may be present within the post-rift sequence if mudstones or evaporites are deposited. Just over half of estimated oil reserves are found associated with rifts containing marine syn-rift and post-rift sequences, just under

264-466: A deeper discontinuity in colder regions and a shallower discontinuity in hotter regions. This discontinuity is generally linked to the transition from ringwoodite to bridgmanite and periclase . This is thermodynamically an endothermic reaction and creates a viscosity jump. Both characteristics cause this phase transition to play an important role in geodynamical models. There is another major phase transition predicted at 520 km (320 mi) for

330-414: A density of about 3.33 g/cm (0.120 lb/cu in) Upper mantle material that has come up onto the surface comprises about 55% olivine and 35% pyroxene, and 5 to 10% of calcium oxide and aluminum oxide . The upper mantle is dominantly peridotite , composed primarily of variable proportions of the minerals olivine, clinopyroxene , orthopyroxene , and an aluminous phase. The aluminous phase

396-429: A downward hinge on the other. Which side of the basin has the major fault or the hinge alternates along the rift. The alternation between these half-grabens occurs along transfer faults, which trend across the rift to connect the major basin-bounding faults and occur between basins or, in places, within basins. The Precambrian basement changes relief sharply in this area, from 8,700 metres (28,500 ft) below sea level at

462-403: A kind of orogeneses in extensional settings, which is referred as to rifting orogeny. Once rifting ceases, the mantle beneath the rift cools and this is accompanied by a broad area of post-rift subsidence. The amount of subsidence is directly related to the amount of thinning during the rifting phase calculated as the beta factor (initial crustal thickness divided by final crustal thickness), but

528-452: A long time, because it provides a north–south route that follows a major river. The Rio Grande follows the course of the rift from southern Colorado to El Paso, where it turns southeast and flows toward the Gulf of Mexico . Important cities, including Albuquerque , Santa Fe , Taos , Española , Las Cruces , El Paso , and Ciudad Juárez , lie within the rift. The Rio Grande rift represents

594-438: A mid-oceanic ridge and a set of conjugate margins separated by an oceanic basin. Rifting may be active, and controlled by mantle convection . It may also be passive, and driven by far-field tectonic forces that stretch the lithosphere. Margin architecture develops due to spatial and temporal relationships between extensional deformation phases. Margin segmentation eventually leads to the formation of rift domains with variations of

660-408: A pure-shear rifting mechanism, in which both sides of the rift pull apart evenly and slowly, with the lower crust and upper mantle (the lithosphere ) stretching like taffy . This extension is associated with very low seismic velocities in the upper mantle above approximately 400 kilometres (250 mi) depth associated with relatively hot mantle and low degrees of partial melting. This intrusion of

726-403: A quarter in rifts with a non-marine syn-rift and post-rift, and an eighth in non-marine syn-rift with a marine post-rift. Upper mantle (Earth) The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about 10 km (6.2 mi) under the oceans and about 35 km (22 mi) under the continents) and ends at the top of

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792-837: A result of the coupling between the subducting Farallon plate and the overlying North American Plate . Crustal thickening occurred due to Laramide compression. After the Laramide Orogeny and until 20 Ma, a major period of volcanic activity occurred throughout the southwestern United States. Injection of hot magmas weakened the lithosphere and allowed for later extension of the region. Cenozoic extension started about 30 million years ago (Ma). There are two phases of extension observed: late Oligocene and middle Miocene . The first period of extension produced broad, shallow basins bounded by low-angle faults. The crust may have been extended as much as 50% during this episode. Widespread magmatism in mid- Cenozoic time suggests that

858-717: A simple relay ramp at the overlap between two major faults of the same polarity, to zones of high structural complexity, particularly where the segments have opposite polarity. Accommodation zones may be located where older crustal structures intersect the rift axis. In the Gulf of Suez rift, the Zaafarana accommodation zone is located where a shear zone in the Arabian-Nubian Shield meets the rift. Rift flanks or shoulders are elevated areas around rifts. Rift shoulders are typically about 70 km wide. Contrary to what

924-513: A world record for total length for a vertical drilling string of 10,062 m (33,011 ft). The previous record was held by the U.S. vessel Glomar Challenger , which in 1978 drilled to 7,049.5 meters (23,130 feet) below sea level in the Mariana Trench . On 6 September 2012, Scientific deep-sea drilling vessel Chikyū set a new world record by drilling down and obtaining rock samples from deeper than 2,111 metres (6,926 ft) below

990-412: Is a conversion to a more dense mineral structure, the seismic velocity rises abruptly and creates a discontinuity. At the top of the transition zone, olivine undergoes isochemical phase transitions to wadsleyite and ringwoodite . Unlike nominally anhydrous olivine, these high-pressure olivine polymorphs have a large capacity to store water in their crystal structure. This has led to the hypothesis that

1056-402: Is also affected by the degree to which the rift basin is filled at each stage, due to the greater density of sediments in contrast to water. The simple 'McKenzie model' of rifting, which considers the rifting stage to be instantaneous, provides a good first order estimate of the amount of crustal thinning from observations of the amount of post-rift subsidence. This has generally been replaced by

1122-466: Is an abrupt increase of P -wave and S -wave velocities at a depth of 220 km (140 mi) (Note that this is a different "Lehmann discontinuity" than the one between the Earth's inner and outer cores labeled in the image on the right.) The transition zone is located between the upper mantle and the lower mantle between a depth of 410 km (250 mi) and 670 km (420 mi). This

1188-431: Is determined by the velocity of seismic waves. Density increases progressively in each layer, largely due to compression of the rock at increased depths. Abrupt changes in density occur where the material composition changes. The upper mantle begins just beneath the crust and ends at the top of the lower mantle. The upper mantle causes the tectonic plates to move. Crust and mantle are distinguished by composition, while

1254-536: Is in the south. The crustal thickness underneath the rift is on average 30–35 kilometres (19–22 mi), thinner by 10–15 kilometres (6.2–9.3 mi) than the Colorado Plateau on the west and the Great Plains to the east. Formation of the rift began with significant deformation and faulting with offsets of many kilometers starting about 35 Ma. The largest-scale manifestation of rifting involves

1320-691: Is intersected in northern New Mexico by the NE-SW trending Jemez Lineament which extends well into Arizona . The lineament is defined by aligned volcanic fields and several calderas in the area, including the Valles Caldera National Preserve in the Jemez Mountains . The Jemez Lineament is thought to be a hydrous subduction zone scar, separating Precambrian basement rock of the Yavapai - Mazatzal transition zone from

1386-415: Is plagioclase in the uppermost mantle, then spinel, and then garnet below about 100 kilometres (62 mi). Gradually through the upper mantle, pyroxenes become less stable and transform into majoritic garnet . Experiments on olivines and pyroxenes show that these minerals change the structure as pressure increases at greater depth, which explains why the density curves are not perfectly smooth. When there

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1452-547: Is responsible for anomalously high earthquake activity in the vicinity, including the largest rift-associated earthquakes in historic times (two events of approximately magnitude 5.8) in July and November 1906. Earth and space-based geodetic measurements indicate ongoing surface uplift above the Socorro magma body at approximately 2 mm/year. The Rio Grande rift's tectonic evolution is fairly complex. The fundamental change in

1518-518: Is the most complex discontinuity and marks the boundary between the upper and lower mantle. It appears in PP precursors (a wave that reflects off the discontinuity once) only in certain regions but is always apparent in SS precursors. It is seen as single and double reflections in receiver functions for P to S conversions over a broad range of depths (640–720 km, or 397–447 mi). The Clapeyron slope predicts

1584-454: Is the oldest of the three major basins, and contains 7,350 metres (24,110 ft) of Paleogene clastic sediments deposited on Precambrian basement. The southernmost Albuquerque basin contains pre-rift volcanic deposits , while the central and northern portions contain volcanics erupted during rifting. In cross-section, the geometry of the basins within the rift are asymmetrical half-grabens , with major fault boundaries on one side and

1650-429: Is thought to occur as a result of the rearrangement of grains in olivine to form a denser crystal structure as a result of the increase in pressure with increasing depth. Below a depth of 670 km (420 mi), due to pressure changes, ringwoodite minerals change into two new denser phases, bridgmanite and periclase. This can be seen using body waves from earthquakes , which are converted, reflected, or refracted at

1716-473: The Moho topography, including proximal domain with fault-rotated crustal blocks, necking zone with thinning of crustal basement , distal domain with deep sag basins, ocean-continent transition and oceanic domain. Deformation and magmatism interact during rift evolution. Magma-rich and magma-poor rifted margins may be formed. Magma-rich margins include major volcanic features. Globally, volcanic margins represent

1782-670: The asthenosphere into the lithosphere and continental crust is thought to be responsible for nearly all of the volcanism associated with the Rio Grande rift. The sedimentary fill of the basins consists largely of alluvial fan and mafic volcanic flows. The most alkalic lavas erupted outside the rift. The sediments that were deposited during rifting are commonly known as the Santa Fe Group . This group contains sandstones , conglomerates , and volcanics. Aeolian deposits are also present in some basins. The Rio Grande rift

1848-471: The lithosphere and asthenosphere are defined by a change in mechanical properties. The top of the mantle is defined by a sudden increase in the speed of seismic waves, which Andrija Mohorovičić first noted in 1909; this boundary is now referred to as the Mohorovičić discontinuity or "Moho." The Moho defines the base of the crust and varies from 10 km (6.2 mi) to 70 km (43 mi) below

1914-403: The lithosphere was hot, the brittle-ductile transition was relatively shallow. There is evidence that the second period of extension began earlier in the central and northern Rio Grande rift than in the south. A third period of extension may have begun in the early Pliocene . One theory is that the Colorado Plateau acts as a semi-independent microplate and one way of explaining the creation of

1980-528: The lower mantle at 670 km (420 mi). Temperatures range from approximately 500 K (227 °C; 440 °F) at the upper boundary with the crust to approximately 1,200 K (930 °C; 1,700 °F) at the boundary with the lower mantle. Upper mantle material that has come up onto the surface comprises about 55% olivine , 35% pyroxene , and 5 to 10% of calcium oxide and aluminum oxide minerals such as plagioclase , spinel , or garnet , depending upon depth. The density profile through Earth

2046-659: The 'flexural cantilever model', which takes into account the geometry of the rift faults and the flexural isostasy of the upper part of the crust. Some rifts show a complex and prolonged history of rifting, with several distinct phases. The North Sea rift shows evidence of several separate rift phases from the Permian through to the Earliest Cretaceous , a period of over 100 million years. Rifting may lead to continental breakup and formation of oceanic basins. Successful rifting leads to seafloor spreading along

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2112-431: The Earth's surface and outer core and the ability of the crystalline rocks at high pressure and temperature to undergo slow, creeping, viscous-like deformation over millions of years, there is a convective material circulation in the mantle. Hot material upwells , while cooler (and heavier) material sinks downward. Downward motion of material occurs at convergent plate boundaries called subduction zones . Locations on

2178-644: The Japanese vessel Chikyū to drill up to 7,000 m (23,000 ft) below the seabed. On 27 April 2012, Chikyū drilled to a depth of 7,740 metres (25,390 ft) below sea level, setting a new world record for deep-sea drilling. This record has since been surpassed by the ill-fated Deepwater Horizon mobile offshore drilling unit, operating on the Tiber prospect in the Mississippi Canyon Field, United States Gulf of Mexico, when it achieved

2244-660: The Mazaztl Province proper. Also on the Colorado Plateau but further north lies the San Juan volcanic field in the San Juan Mountains of Colorado. The youngest eruptions in the rift region are in the Valley of Fires , New Mexico, and are approximately 5,400 years old. The Socorro, New Mexico , region of the central rift hosts an inflating mid-crustal sill-like magma body at a depth of 19 km that

2310-422: The Rio Grande rift is by the simple rotation of the Colorado Plateau 1-1.5° in a clockwise direction relative to the North American craton. Other explanations that have been offered are that the extension is driven by mantle forces, such as large-scale mantle upwelling or small-scale mantle convection at the edge of the stable craton; collapse of over-thickened continental crust; initiation of transform faulting along

2376-671: The San Luis is roughly 120 by 80 kilometres (75 by 50 mi). These basins may contain smaller units within them, such as the Alamosa basin within the San Luis, which is bounded by the San Juan and Tusas mountains on the west and the Sangre de Cristo Mountains in the east. The Albuquerque basin is the largest of the three basins, spanning 160 kilometres (99 mi) north–south and 86 kilometres (53 mi) east–west at its widest points. It

2442-452: The axis of the rift the position, and in some cases the polarity (the dip direction), of the main rift bounding fault changes from segment to segment. Segment boundaries often have a more complex structure and generally cross the rift axis at a high angle. These segment boundary zones accommodate the differences in fault displacement between the segments and are therefore known as accommodation zones. Accommodation zones take various forms, from

2508-417: The base of the transition zone, ringwoodite decomposes into bridgmanite (formerly called magnesium silicate perovskite), and ferropericlase . Garnet also becomes unstable at or slightly below the base of the transition zone. Kimberlites explode from the earth's interior and sometimes carry rock fragments. Some of these xenolithic fragments are diamonds that can only come from the higher pressures below

2574-499: The bottom of the Albuquerque basin to 3,300 metres (10,800 ft) above sea level in the nearby Sandia Mountains , which flanks the Albuquerque basin to the east. Flanking mountains are generally taller along the east side of the rift (although some of this relief may be Laramide in origin). The thickness of the crust increases to the north beneath the rift, where it may be as much as 5 kilometres (3.1 mi) thicker than it

2640-557: The boundary, and predicted from mineral physics , as the phase changes are temperature and density-dependent and hence depth-dependent. A single peak is seen in all seismological data at 410 km (250 mi), which is predicted by the single transition from α- to β- Mg 2 SiO 4 (olivine to wadsleyite ). From the Clapeyron slope this discontinuity is expected to be shallower in cold regions, such as subducting slabs, and deeper in warmer regions, such as mantle plumes . This

2706-474: The core-mantle boundary. The highest temperature of the upper mantle is 1,200 K (930 °C; 1,700 °F). Although the high temperature far exceeds the melting points of the mantle rocks at the surface, the mantle is almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents melting because the temperature at which melting begins (the solidus ) increases with pressure. Pressure increases as depth increases since

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2772-423: The crust. The rocks that come with this are ultramafic nodules and peridotite. The composition seems to be very similar to the crust. One difference is that rocks and minerals of the mantle tend to have more magnesium and less silicon and aluminum than the crust. The first four most abundant elements in the upper mantle are oxygen, magnesium, silicon, and iron. Exploration of the mantle is generally conducted at

2838-469: The development of isolated basins. In subaerial rifts, for example, drainage at the onset of rifting is generally internal, with no element of through drainage. As the rift evolves, some of the individual fault segments grow, eventually becoming linked together to form the larger bounding faults. Subsequent extension becomes concentrated on these faults. The longer faults and wider fault spacing leads to more continuous areas of fault-related subsidence along

2904-532: The easternmost manifestation of widespread extension in the western U.S. during the past 35 million years. The rift consists of three major basins and many smaller basins, less than 100 square kilometres (39 sq mi). The three major basins (from northernmost to southernmost) are the San Luis , Española , and Albuquerque basins. The rift's northern extent is delineated by the upper Arkansas River basin between Leadville and Salida, Colorado . Further south,

2970-508: The linear zone characteristic of rifts. The individual rift segments have a dominantly half-graben geometry, controlled by a single basin-bounding fault. Segment lengths vary between rifts, depending on the elastic thickness of the lithosphere. Areas of thick colder lithosphere, such as the Baikal Rift have segment lengths in excess of 80 km, while in areas of warmer thin lithosphere, segment lengths may be less than 30 km. Along

3036-567: The majority of passive continental margins. Magma-starved rifted margins are affected by large-scale faulting and crustal hyperextension. As a consequence, upper mantle peridotites and gabbros are commonly exposed and serpentinized along extensional detachments at the seafloor. Many rifts are the sites of at least minor magmatic activity , particularly in the early stages of rifting. Alkali basalts and bimodal volcanism are common products of rift-related magmatism. Recent studies indicate that post-collisional granites in collisional orogens are

3102-611: The material beneath has to support the weight of all the material above it. The entire mantle is thought to deform like a fluid on long timescales, with permanent plastic deformation. The highest pressure of the upper mantle is 24.0 GPa (237,000 atm) compared to the bottom of the mantle, which is 136 GPa (1,340,000 atm). Estimates for the viscosity of the upper mantle range between 10 and 10 Pa·s , depending on depth, temperature, composition, state of stress, and numerous other factors. The upper mantle can only flow very slowly. However, when large forces are applied to

3168-404: The product of rifting magmatism at converged plate margins. The sedimentary rocks associated with continental rifts host important deposits of both minerals and hydrocarbons . SedEx mineral deposits are found mainly in continental rift settings. They form within post-rift sequences when hydrothermal fluids associated with magmatic activity are expelled at the seabed. Continental rifts are

3234-408: The result of continental rifting that failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a triple junction where three converging rifts meet over a hotspot . Two of these evolve to the point of seafloor spreading, while the third ultimately fails, becoming an aulacogen . Most rifts consist of a series of separate segments that together form

3300-432: The rift axis. Significant uplift of the rift shoulders develops at this stage, strongly influencing drainage and sedimentation in the rift basins. During the climax of lithospheric rifting, as the crust is thinned, the Earth's surface subsides and the Moho becomes correspondingly raised. At the same time, the mantle lithosphere becomes thinned, causing a rise of the top of the asthenosphere. This brings high heat flow from

3366-525: The rift is defined by a network of smaller, less topographically distinct alternating basins and ranges. The distinction between these smaller basins and those of the Basin and Range Province becomes blurred in northern Mexico . Basin size generally decreases to the north in the rift, though the Española covers approximately 120 kilometres (75 mi) north–south and 40 kilometres (25 mi) east–west, and

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3432-413: The seabed rather than on land because of the oceanic crust's relative thinness as compared to the significantly thicker continental crust. The first attempt at mantle exploration, known as Project Mohole , was abandoned in 1966 after repeated failures and cost overruns. The deepest penetration was approximately 180 m (590 ft). In 2005 an oceanic borehole reached 1,416 metres (4,646 ft) below

3498-747: The seafloor from the ocean drilling vessel JOIDES Resolution . On 5 March 2007, a team of scientists on board the RRS James Cook embarked on a voyage to an area of the Atlantic seafloor where the mantle lies exposed without any crust covering, midway between the Cape Verde Islands and the Caribbean Sea . The exposed site lies approximately 3 kilometres (1.9 mi) beneath the ocean surface and covers thousands of square kilometers. The Chikyu Hakken mission attempted to use

3564-553: The seafloor off the Shimokita Peninsula of Japan in the northwest Pacific Ocean. A novel method of exploring the uppermost few hundred kilometers of the Earth was proposed in 2005, consisting of a small, dense, heat-generating probe that melts its way down through the crust and mantle while its position and progress are tracked by acoustic signals generated in the rocks. The probe consists of an outer sphere of tungsten about 1 metre (3 ft 3 in) in diameter with

3630-471: The sites of significant oil and gas accumulations, such as the Viking Graben and the Gulf of Suez Rift . Thirty percent of giant oil and gas fields are found within such a setting. In 1999 it was estimated that there were 200 billion barrels of recoverable oil reserves hosted in rifts. Source rocks are often developed within the sediments filling the active rift ( syn-rift ), forming either in

3696-511: The surface of the Earth. Oceanic crust is thinner than continental crust and is generally less than 10 km (6.2 mi) thick. Continental crust is about 35 km (22 mi) thick, but the large crustal root under the Tibetan Plateau is approximately 70 km (43 mi) thick. The thickness of the upper mantle is about 640 km (400 mi). The entire mantle is about 2,900 km (1,800 mi) thick, which means

3762-403: The surface that lie over plumes are predicted to have high elevation (because of the buoyancy of the hotter, less-dense plume beneath) and to exhibit hot spot volcanism . The seismic data is not sufficient to determine the composition of the mantle. Observations of rocks exposed on the surface and other evidence reveal that the upper mantle is mafic minerals olivine and pyroxene, and it has

3828-403: The transition of olivine (β to γ) and garnet in the pyrolite mantle. This one has only sporadically been observed in seismological data. Other non-global phase transitions have been suggested at a range of depths. Temperatures range from approximately 500 K (227 °C; 440 °F) at the upper boundary with the crust to approximately 4,200 K (3,930 °C; 7,100 °F) at

3894-510: The transition zone may host a large quantity of water. In Earth's interior, olivine occurs in the upper mantle at depths less than 410 kilometres (250 mi), and ringwoodite is inferred within the transition zone from about 520 to 670 kilometres (320 to 420 mi) depth. Seismic activity discontinuities at about 410 kilometres (250 mi), 520 kilometres (320 mi), and 670 kilometres (420 mi) depth have been attributed to phase changes involving olivine and its polymorphs . At

3960-474: The upper mantle after drilling only a few hundred meters into the Atlantis Massif . The borehole reached a maximum depth of 1,268 meters and recovered 886 meters of rock samples consisting of primarily peridotite . There is debate over the extent to which the samples represent the upper mantle with some arguing the effects of seawater on the samples situates them as examples of deep lower crust. However,

4026-510: The upper mantle is only about 20% of the total mantle thickness. The boundary between the upper and lower mantle is a 670 km (420 mi) discontinuity. Earthquakes at shallow depths result from strike-slip faulting ; however, below about 50 km (31 mi), the hot, high-pressure conditions inhibit further seismicity. The mantle is viscous and incapable of faulting . However, in subduction zones , earthquakes are observed down to 670 km (420 mi). The Lehmann discontinuity

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4092-420: The uppermost mantle, it can become weaker, and this effect is thought to be important in allowing the formation of tectonic plate boundaries. Although there is a tendency to larger viscosity at greater depth, this relation is far from linear and shows layers with dramatically decreased viscosity, in particular in the upper mantle and at the boundary with the core. Because of the temperature difference between

4158-491: The upwelling asthenosphere into the thinning lithosphere, heating the orogenic lithosphere for dehydration melting, typically causing extreme metamorphism at high thermal gradients of greater than 30 °C. The metamorphic products are high to ultrahigh temperature granulites and their associated migmatite and granites in collisional orogens, with possible emplacement of metamorphic core complexes in continental rift zones but oceanic core complexes in spreading ridges. This leads to

4224-580: The western margin of the North American plate from one of subduction to a transform boundary occurred during Cenozoic time. The Farallon plate continued to be subducted beneath western North America for at least 100 million years during Late Mesozoic and early Cenozoic time. Compressional and transpressional deformation incurred by the Laramide Orogeny lasted until about 40  Ma in New Mexico. This deformation may have been

4290-465: The western margin of the North American plate; or detachment of a fragment of the Farallon plate beneath the Rio Grande region that enhanced asthenospheric upwelling in the slab window. Rift Major rifts occur along the central axis of most mid-ocean ridges , where new oceanic crust and lithosphere is created along a divergent boundary between two tectonic plates . Failed rifts are

4356-549: Was previously thought, elevated passive continental margins (EPCM) such as the Brazilian Highlands , the Scandinavian Mountains and India's Western Ghats , are not rift shoulders. The formation of rift basins and strain localization reflects rift maturity. At the onset of rifting, the upper part of the lithosphere starts to extend on a series of initially unconnected normal faults , leading to

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