Within Hess Deep, litho-sphere generated at the north-south-trending East Pacific Rise (EPR) is being dismembered by the westward propagation of the Cocos-Nazca spreading axis at a rate that matches the 65 km/m.y. Exposed on the rift-valley walls and on fault blocks within the rift are ultramafic and gabbroic rocks, sheeted dikes, and pillow lavas, which formed at the East Pacific Rise at an inferred half spread- ing rate of 65 mm/yr (Francheteau et al., 1990). The rift valley is 1 to 3 km deep, about the depth and width of the Grand Canyon. Use the widths of the color bands (marked by the Problem 6 placemarks) representing seafloor ages on either side of this mid-ocean ridge to determine which side is moving faster. Tectonics of the East Pacific Rise, 5⁰ to 12⁰S Sometime between 30- and 20 million years ago the north American tectonic plate overrode a spreading center called the East Pacific Rise. The axial trough is only 5 to 20 meters deep and is where most of the eruption of lavas takes place. PDF East Pacific Rise Crest: A Near-Bottom Geophysical Profile Competing effects of spreading rate, crystal fractionation ... Late Tertiary history of hydrothermal deposition at the ... Understanding plate motions [This Dynamic Earth, USGS] PDF Asymmetric Mantle Dynamics in the MELT Region of the East ... What does the spreading rate matter? This produces volcanic eruptions and earthquakes; it also produces circulation of ocean water into the deep crust and back out through high-temperature hydrothermal vents, which are home to exotic life forms that may hold secrets about the origins of life . Some divergent boundaries spread at different rates. It spreads about 6-16 centimeters (3-6 inches) every year. East Pacific Rise - Hyperleap A Science Odyssey: You Try It: Plate Tectonics: Floor Spread In 1982 we undertook a seismic refraction experiment, known as the MAGMA expedition, to examine the detailed structure of the East Pacific Rise near 12°50'N. This segment of the rise, where the full spreading rate is about 110 mm/yr, is near the projected trace of the O'Gorman fracture zone and is the site of an overlapping spreading center as well as "black smoker" hydrothermal activity. Also beneath the rise axis is a narrow (less than 1 kilometer wide) melt sill that is in . It spread apart at rates of 2 to 5 cm per year, and at these relatively slow spreading rates, the ridge has a deep rift valley along its crest. A local estimate of the spread-ing rate of ~140 km Ma 1 (Nicolas and Boudier, 2015) has been derived from zircon dating of gabbros (Rio-ux et al., 2012). Key words: East Pacific Rise, multibeam sonar surveying, Mid- Ocean Ridge, magmatic plumbing system Abstract. During the Naudur cruise in December 1993, 23 dives using the French submersible Nautile were conducted on the axis of the East Pacific Rise between 17° and 19°S where the spreading rate is among the fastest in the ocean (14 to 16 cm/yr). Respective contributions of source heterogeneity and magma differentiation leading to this diversity, however, remain elusive. In contrast, the East Pacific Rise spreads fast at rates of 6 to 16 cm per year (more than 20 cm per year in the past). The rate of motion of the Pacific plate is generally the half-spresading rate for the East Pacific Rise. described evidence for recent volcanism . at fast spreading rates which allows for the maintenance of a steady state chamber along most of the length of the rise. flow and subsidence rates on the ridge flanks [e.g., Davis and Lister, 1974; Parker and Oldenburg, 1973; Parsons and Sclater, 1977]. In all three regions, the spreading axis of the EPR is defined by a topographic block 300 to 350 m high and about 15 km wide. Easter Island monolith [80 k] Evidence of past rates of plate movement also can be obtained from geologic mapping studies. In contrast, the East Pacific Rise spreads fast, at rates of 6 to 16 centimeters (3 to 6 inches) per year. Is the spreading rate greater on the East Pacific Rise or the Mid-Atlantic Ridge? East Pacific Rise The oceanic ridge which separates the Pacific Plate from the Antarctic, Nazca, and Cocos Plates.The East Pacific Rise is a fast-spreading ridge with a maximum half-spreading rate calculated at 4.4 cm/yr, and its topographic profile is relatively smooth compared with slow-spreading ridges, e.g. Lewis [1981, 1982, 1983] was able to force a thermal subsidence curve to match the crestal high on profiles across the East Pacific Rise by varying the values chosen for the of the fast-spreading East Pacific Rise (EPR) between 9ø12'N and 9ø54'N (full spreading rate is equal to 11 cm/yr; [Klitgord and Mammerickx, 1982]). The East Pacific Rise (EPR) 8°-10°N is an archetype for fast-spreading mid-ocean ridge (MOR), and has been one of the most comprehensively studied MOR sections for over four decades. Seismic observations clarify the roles of magma pressure and tectonic stress in the development of seafloor spreading during the most recent eruption at the East Pacific Rise. flow and subsidence rates on the ridge flanks [e.g., Davis and Lister, 1974; Parker and Oldenburg, 1973; Parsons and Sclater, 1977]. We examined Hess The portion of the East Pacific Rise (EPR) between 5° and 12°S can be subdivided into three areas by fracture zones that offset the rise axis at about 6.5°S and 9°S. equatorial eastern Pacific Ocean (Fig. Dynamics of a seafloor-spreading episode at the East Pacific Rise Yen 1Joe 1Tan 1, Maya 2Tolstoy , Felix Waldhauser & William S. D. Wilcock Seafloor spreading is largely unobserved because 98 per cent of the global mid-ocean-ridge system is below the ocean surface. The axis of the East Pacific Rise is defined by a topographic block about 15 km wide and 300 to 350 m high which is flanked by abyssal hills 100 to 200 m high and 3 to 5 km wide. Instead, the data show large variations in crustal thickness at slow spreading ridges (3 - 8 km for half rates < 20 mm/yr) and small . The spreading rate of the North Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80-145 mm/yr. This compares with 145 km Ma 1 in the fastest spread-ing segments of the East Pacific Rise (EPR) (The MELT Seismic Team, 1998). Mid-Atlantic Ridge East Pacific Rise 1,500 Magnetic reversals are found worldwide, so magnetic anomaly stripes should be the same width in every ocean if the rate of seafloor spreading were the same at all mid-ocean ridges. Because seafloor is produced to both sides of the midocean ridges, the full spreading rate is about twice that to one side, or the half-spreading rate. The East Pacific Rise is considered as a fast spreading center that spreads about 3-6 inches every year as compared to Mid-Atlantic Ridge that spreads 1-2 inches every year. the Mid-Atlantic Ridge. We wish here to compare The oceanic crust is moving away from the East Pacific Rise to either side. Here, the East Pacific Rise is the boundary between the Pacific and Cocos plates, which separate at a 'fast' rate of 110mmy 1. Correct answers: 2 question: Divergent Boundary Spreading Rates - East Pacific Rise. 16 Ma, 17 to 18 Ma, and 23-to-27 Ma. Argo I video and sonar data were used to create distribution maps for most of the second-order ridge segment between the Clipperton transform and the The main portion of the rise lies generally about 2,000 miles (3,200 km) off the coast. Click on a fe ature to learn more. . the average rate of seafloor spreading occurring in the Atlantic Ocean and in the Pacific Ocean at the East Pacific Rise? the average rate of seafloor spreading occurring in the Atlantic Ocean and in the Pacific Ocean at the East Pacific Rise? R = d/t or R = 9.5 * 107 cm / 6.5 * 107 years = 1.46 cm/yr. These hills often are tilted such that their steep slopes face the axis. Figure 6.10 is a map of the magnetic reversals (also called magnetic lineations) between the Gofar Fracture Zone (FZ . Geologists believe the amount of heat and . The East Pacific Rise is perhaps the best studied fast-spreading mid-ocean ridge. A local estimate of the spread-ing rate of ~140 km Ma 1 (Nicolas and Boudier, 2015) has been derived from zircon dating of gabbros (Rio-ux et al., 2012). The Mid-Atlantic Ridge runs down the center of the Atlantic Ocean, slowly spreading at a rate of 2 to 5 centimeters (0.8 to 2 inches) per year and forming a rift valley that is about the depth and width of the Grand Canyon. This implies that lower crust formed at fast spreading rates remains hot in the . The Mid-Atlantic Ridge separates at a rate of 1 - 2 cm (0.4 to 0.8 inches)/year compared to the East Pacific Rise, a fast moving spreading center that separates at an average rate of 6 to 8 cm (2.4 to 3.1 inches)/year. The topography across fast-spreading mid-ocean ridges is less pronounced relative to slow-spreading mid-ocean ridges. Is the spreading rate greater on the East Pacific Rise or the Mid-Atlantic Ridge? the rate is about 2.2 inches (3.6 cm) per year. The Arctic Ridge has the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr). The islands are a manifestation of intersecting plate boundaries—the spreading center of the East Pacific Rise, which traces south from the Gulf of California, and the subduction zone that consumes the Cocos plate beneath southern Mexico. The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 145 +/- 4 mm/yr between the Pacific and Nazca plates. The two straight lines on figure 6.11 provide a visual comparison between the spreading rates of the East Pacific Rise and the Mid-Atlantic Ridge. We undertook to simply this problem by mapping the distribution of hydrothermally produced thermal anomalies and light attenuation anomalies along the crest of the East Pacific Rise (EPR) 1.9°N-6.1°S, a fast-rate spreading center with segments of markedly differing morphology. Figure 6.10 is a map of the magnetic reversals (also called magnetic lineations) between the Gofar Fracture Zone . N. J. Kusznir, Thermal evolution of the oceanic crust; its dependence on spreading . The two straight lines on figure 6.11 provide a visual comparison between the spreading rates of the East Pacific Rise and the Mid-Atlantic Ridge. This study investigates the iron isotope systematics in basalts from the ultraslow spreading Gakkel Ridge in the Arctic Ocean and compares them to existing data from the fast spreading East Pacific Rise ridge. A GLORI-B and Sea Beam 2000 side scan/bathymetry survey, together with other geophysical data collection, was conducted aboard the R/V Melville covering an approximately 5° by 5° area . 1. Three seismic refraction profiles have been recorded on the East Pacific Rise near the Siqueiros fracture zone. The Juan de Fuca Ridge and Southwest Indian Ridge are classed as INTERMEDIATE-rate ridges (6 to 9 cm/yr, full rate), and the . Seismic reflection data from the East Pacific Rise at lat 16°N, which is spreading at the high end of intermediate rates, suggest that the depths at which axial magma chambers reside do not vary smoothly as a function of spreading rate. [12] Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges [3] [13] (e.g., the Gakkel Ridge in the Arctic Ocean and . Seafloor spreading is separating the Pacific Plate from the Cocos Plate at a rate of 11 centimeters (about 5 inches) every year. Dive & Discover's 2nd voyage takes you about 500 miles south of Manzanillo, Mexico to the crest of the East Pacific Rise, a volcanic ridge where the crust of the Earth is being constantly created. Seismic observations clarify the roles of magma pressure and tectonic stress in the development of seafloor spreading during the most recent eruption at the East Pacific Rise. Ultraslow eastern volcanic zone vs ultrafast east pacific rise. Auzende et al. The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 145 +/- 4 mm/yr between the Pacific and Nazca plates. of the spreading rate in this region over the past 1 or 2 million years, then the spreading rate coupled with average sediment thickness at various distances from the center of the rise crest should yield a reasonable sedimentation rate for the equatorial Pacific. At slow . In terms of plate kinematics, the East Pacific Rise here represents the accreting edge of the Pacific and Cocos plates. The southern East Pacific Rise (SEPR) has the fastest spreading rate and the highest magmatic budget of any ridge in the global mid-ocean ridge system ().Due to its elevated magmatism, the SEPR has over 50 known active vent sites from 5°S to 37°S (), consistent with the global trend in plume incidence versus magmatic budget for ridges spanning a range of spreading rates (5, 7). same average rate, and the direction of sea-floor spreading is usually approximately perpendicular to the ridge. The 18-Ma anomaly is the largest and is associated with the jump in spreading from the fossil Mendoza Ridge to the East Pacific Rise, whereas the 23-to-27-Ma anomaly is correlated with the birth of the Galapagos Spreading Center and resultant ridge reorganization. Oman ophiolite was a fast-spreading ridge. at the East Pacific Rise crest near 31S . use . The cooling history of the lowermost ocean crust formed at the East Pacific Rise and exposed at the Hess Deep Rift is constrained using fresh primitive olivine gabbro and troctolite cores recently recovered by Integrated Ocean Drilling Program Expedition 345. . (B) Shaded relief map of a 1000km stretch of the East Pacific Rise extending from 83 to 173N. Yen Tan et al. Although spreading rates at the East Pacific Rise and its predecessor, the Mendoza Rise, have varied by only 50% in the last 30 million years, we found certain episodes, at about 25, 18, 14, and 9 million years ago, of hydrothermal manganese deposition as much as a factor of 20 higher than equivalent Holocene accumulation. The setting supports numerous hydrothermal vent fields that respond to frequent earthquakes and occasional volcanic eruptions. use . Twenty hydrothermal fluids located at the topographic high of each segment in the axial domain were collected between 2573 and 2669 m depth on three . The East Pacific Rise, on the other hand, is a fast spreading center. The asymmetry reverses just south of 17ø15'S, so that the Nazca Plate is spreading eastward at a half-rate of 80 mm/yr, roughly 20 mm/yr faster than the Pacific plate half-rate [Cormier et al., Towards the west, the East Pacific rise exhibits the fastest current spreading rates on the planet, ranging from 120 +/- 3 mm/yr near the Galapagos triple junction to 145+/-4 mm/yr near the Chile Triple junction (Norabuena et al., 1999; De Mets et al., 2010). The map reveals two kinds of Yen Tan et al. SA narrow (50-300 meter wide) cleft at the axis of a fast-spreading mid-ocean ridge like the East Pacific Rise at 9-10°N Latitude. Our results are approximately consistent with Phipps Morgan and Chen (1993a) and show that if the change in magma- Since 1 Ma, the Pacific plate has been spreading slightly faster than the Nazca plate north of 17ø15'S, at a half-rate of 75 mm/yr versus 65 mm/yr. Notes: Ranges of Spreading throughout the world's oceans: 1cm/yr to 10 cm/yr. . fast-spreading, southern East Pacific Rise [1-6]. The 12-to-16-Ma and 8.5-to-10.5-Ma anomalies are The ridge segment that creates the Nazca and Pacific plates moves up to 5.6 inches (142 mm) each year. The rate is equivalent to 3 cm/year. The East Pacific Rise forms part of the circumglobal system of active volcanic ridges, all of which define the position of diverging plates where new crust is being created. [4] The results of the French-American Nautile Dorsale Ultra-Rapide (NAUDUR) program of 1993 [Auzende et al., 1994, 1996] indicated that the southern East Pacific Rise, between 17° and 19°S is an ideal place to investigate eruptive processes at the high end of the spreading rate spectrum. Taking recent studies of the fast-spreading East Pacific Rise and slow-spreading Mid-Atlantic Ridge, I have compiled a list of properties (summarized in Table 1) which distinguish the two spreading centers. Mid-ocean ridge Harry Hammond Hess Robert S. Dietz Continental drift Plate tectonics. A compilation of oceanic crustal thickness from seismic observations collected over the past two decades shows that the average crustal thickness, away from plateaus, is 6 km; no systematic increase of crustal thickness with spreading rate is observed. These islands are biologically important: they comprise the Islas Marias Biosphere Reserve and contain . Our understanding of the dynamic processes that control seafloor 78 LOCAL AXIAL MIGRATION AND SPREADING RATE VARIATIONS, EAST PACIFIC RISE, 31 1 DAVID K. REA Department of Atmospheric and Oceanic Science, The University of Michigan, Ann Arbor, Mich. 48109 (USA) Received October 7, 1976 Revised version received November 29, 1976 Mapping and analysis of marine magnetic anomalies generated during the past 3.78 m.y. half-spreading rate of the EPR (Hey et al., 1977; Lonsdale, 1988; Fig. Seismic data from the ultrafast-spreading (150 to 162 millimeters per year) southern East Pacific Rise show that the rise axis is underlain by a thin (less than 200 meters thick) extrusive volcanic layer (seismic layer 2A) that thickens rapidly off axis. same average rate, and the direction of sea-floor spreading is usually approximately perpendicular to the ridge. The Eastern Volcanic Zone (EVZ) displays the slowest spreading rates (< 10 mm/a) of the entire the Gakkel Ridge and is characterised . Seismic and electromagnetic measurements demonstrated that the Near Easter Island the rate is over 150 mm (6 in) per year which is the fastest in the world. Along the East Pacific Rise, third-order discontinuities usually consist of overlapping spreading centers that offset the ridge by less than three kilometers. There is not an ocean trench at the East Pacific Rise, because the seafloor spreading is too rapid for one to develop! Use the above equation to calculate spreading rate. On the eastern side of the rise the eastward moving Cocos and Nazca plates meet the westward moving South American Plate and the . Sample localities for eastern Pacific Bathymodiolus are marked by a color filled circle in accordance with the following regions: NEPR denotes the northern East Pacific Rise; SEPR = southern East Pacific Rise; GAR = Galápagos Rift; and PAR = Pacific-Antarctic Ridge. 3] Two aspects of the southern East Pacific Rise (SEPR) near 17 300S make this area particularly useful for the study of lava flows at high spatial and temporal resolution. The East Pacific Rise (EPR) along the western edge of the Nazca plate is the most rapidly spreading portion of the oceanic ridge system having an average whole rate of accretion of about 160 mm/yr (Table . Very high spreading rate ( 146 mm/a, where a is years) [Naar and Hey, 1989] corresponds with high eruption frequency of generally low-volume single eruptive episodes These profiles have been interpreted using both travel‐time analysis and waveform and amplitude studies with the aid of synthetic seismograms. If a particular anomaly stripe is wider in one ocean than in another, however, the difference must result from faster . The East Pacific Rise (EPR) 26°-32°S, located between the Easter microplate and the Juan Fernandez microplate, has the world's fastest spreading rate and tectonics characterized by dueling ridge propagation. Detailed bathymetric data from a Hydrosweep multi- beam sonar survey of a 250 km-long portion of the 'superfast'- spreading southern East Pacific Rise crest and flanks show that Lewis [1981, 1982, 1983] was able to force a thermal subsidence curve to match the crestal high on profiles across the East Pacific Rise by varying the values chosen for the These islands are biologically important: they comprise the Islas Marias Biosphere Reserve and contain . The islands are a manifestation of intersecting plate boundaries—the spreading center of the East Pacific Rise, which traces south from the Gulf of California, and the subduction zone that consumes the Cocos plate beneath southern Mexico. 1. 1). This compares with 145 km Ma 1 in the fastest spread-ing segments of the East Pacific Rise (EPR) (The MELT Seismic Team, 1998). Segments defined by third-order discontinuities are from 30 to 100 kilometers long. The rate of seafloor spreading at the Mid-Atlantic Ridge is 2 centimeters per year, whereas the rate of seafloor spreading at the East Pacific Rise is 15 centimeters per year. As nearly as we can determine, the spread-ing has remained uniform and symmetric with respect to the rise axis for at least the past several million years, Pressure-release melting of the upwelling mantle produces magma that migrates to the surface to form a layer of new crust at the spreading center about 6 km thick [7]. Mid-ocean ridge Harry Hammond Hess Robert S. Dietz Continental drift Plate tectonics. To the south, the Nazca plate is diverging from the Antarctic plate at rates of 50 mm . The Mid-Atlantic Ridge separates at a rate of 1 - 2 cm (0.4 to 0.8 inches)/year compared to the East Pacific Rise, a fast moving spreading center that separates at an average rate of 6 to 8 cm (2.4 to 3.1 inches)/year. Volcanic mound fields on the East Pacific Rise, 16 -19 S: Low effusion rate eruptions at overlapping spreading centers for the past 1 Myr Scott M. White1 and Ken C. Macdonald Department of Geological Sciences and Marine Science Institute, University of California, Santa Barbara, California, USA Oman ophiolite was a fast-spreading ridge. In contrast, the East Pacific Rise spreads fast at rates of 6 to 16 cm per year (more than 20 cm per year in the past). The rate of seafloor spreading at the Mid-Atlantic Ridge is 2 centimeters per year, whereas the rate of seafloor spreading at the East Pacific Rise is 15 centimeters per year. However, on the northern end, it is much slower at only roughly 60 mm (2 + 1 ⁄ 2 in) per year. The East Pacific Rise is part of the world's mid-ocean ridge system, where new crust is formed as earth's tectonic plates spread apart. Some of our recent research involves hydrothermal and structural investigations along Earth's fastest seafloor spreading center, the 28°S-32°S East Pacific Rise. That region experiences high spreading rate where more tectonic plate slab . Measure from the center of the spreading center to a known age point on the plate rather than from 65 Ma on the eastern plate to 65 Ma on the western plate. East Pacific Rise spreading axis (Lonsdale, 1988; Francheteau et al., 1990). It covers all orders of ridge discontinuities: first-order transform faults, second-order overlapping spreading centers, third-order small offset tectonic . The fastest present-day seafloor spreading, ~150 km/Myr, occurs along the Pacific-Nazca boundary between the Easter and Juan Fernandez microplates . Such ridges represent the locus of global shallow-water earthquakes. In all three regions, the spreading axis of the EPR is defined by a topographic block 300 to 350 m high and about 15 km wide. This area is similar to the spreading center of the Mid-Atlantic ridge that gradually separated Africa from South American, and Europe from North America. [11] The highest known rate is over 200 mm/yr in the Miocene on the East Pacific Rise. It is also where much of the hydrothermal venting is occuring. 1). Numbers indicate spreading rates of ridge segments in mm/year. For example, the East Pacific Rise (EPR) is known as a fast-spreading ridge where oceanic plates are moving apart at a rate of around ten centimeters per year. Rise (the Pacific plate) and the Siqueiros fracture zone region. The portion of the East Pacific Rise (EPR) between 5° and 12°S can be subdivided into three areas by fracture zones that offset the rise axis at about 6.5°S and 9°S. Location of the profile across the East Pacific . The Sea Floor Spread. At the East Pacific rise, which is pushing a plate into the west coast of South America, the rate is 12.6 inches (32.2 cm . We wish here to compare Such a cal-3 JANUARY 1969 Fig. Furthermore, what is the spreading rate for the East Pacific Rise in kilometers per million years? Spreading added an equal width of oceanic crust to a plate on the other side of the mid-ocean ridge, so the total rate of spreading across the ridge was 60 km . are comparable to those observed for the East Pacific Rise at lat 9°N, where spreading rates are 30% faster (Kent et al., 1993) and are only ~300-400 m deeper than those for the superfast-spreading ridges. The Mid-Atlantic Ridge is a slow-spreading center, while the East Pacific Rise is an example of fast spreading. Tectonic plate slab pulls at subduction zones is responsible for the faster rate of spreading. An empirical model explaining these features combines axial extrusion to form the central block and rotational faulting to lower the shoulders . The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 145 +/- 4 mm/yr between the Pacific and Nazca plates. It spreads about 6-16 centimeters (3-6 inches) every year.
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