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Mid-ocean ridge

About: Mid-ocean ridge is a research topic. Over the lifetime, 4190 publications have been published within this topic receiving 262361 citations. The topic is also known as: mid-ocean ridges & ridge.


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Journal ArticleDOI
TL;DR: In this paper, a new evaluation is made of parental magma compositions that would crystallize olivines with the maximum forsterite contents observed in lava flows, consistent with the plume model.
Abstract: Several methods have been developed to assess the thermal state of the mantle below oceanic ridges, islands, and plateaus, on the basis of the petrology and geochemistry of erupted lavas. One leads to the conclusion that mantle potential temperature (i.e., TP) of ambient mantle below oceanic ridges is 1430°C, the same as Hawaii. Another has ridges with a large range in ambient mantle potential temperature (i.e., TP = 1300–1570°C), comparable in some cases to hot spots (Klein and Langmuir, 1987; Langmuir et al., 1992). A third has uniformly low temperatures for ambient mantle below ridges, ∼1300°C, with localized 250°C anomalies associated with mantle plumes. All methods involve assumptions and uncertainties that we critically evaluate. A new evaluation is made of parental magma compositions that would crystallize olivines with the maximum forsterite contents observed in lava flows. These are generally in good agreement with primary magma compositions calculated using the mass balance method of Herzberg and O'Hara (2002), and differences reflect the well-known effects of fractional crystallization. Results of primary magma compositions we obtain for mid-ocean ridge basalts and various oceanic islands and plateaus generally favor the third type of model but with ambient mantle potential temperatures in the range 1280–1400°C and thermal anomalies that can be 200–300°C above this background. Our results are consistent with the plume model.

808 citations

Journal ArticleDOI
TL;DR: In this article, the authors determined the relative motion of the Cocos plate and the Caribbean plate with respect to the surrounding regions or plates and determined the focal mechanisms of 70 earthquakes in these regions.
Abstract: Seismic data strongly support recent theories of tectonics in which large plates of lithosphere move coherently with respect to one another as nearly rigid bodies, spreading apart at ocean ridges, sliding past one another at transform faults, and underthrusting at island arcs. Boundaries between adjacent plates of lithosphere are defined by belts of high seismic activity. Redetermination of more than 600 hypocenters in the Middle America region and previous studies in the Galapagos and Caribbean regions define the boundaries of two relatively small, nearly aseismic plates in the region of interest. The first, the Cocos plate, is bordered by the East Pacific rise, the Galapagos rift zone, the north-trending Panama fracture zone near 82° W., and the Middle America arc; the second, the Caribbean plate, underlies the Caribbean Sea and is bounded by the Middle America arc, the Cayman trough, the West Indies arc, and the seismic zone through northern South America. Focal mechanisms of 70 earthquakes in these regions were determined to ascertain the relative motion of these two plates with respect to the surrounding regions or plates. The results show underthrusting of the Cocos plate beneath Mexico and Guatemala in a northeasterly direction and beneath the rest of Central America in a more north-northeasterly direction. The Cocos plate is spreading away from the rest of the Pacific floor at the East Pacific rise and at the Galapagos rift zone. Motion is right-lateral strike-slip along the Panama fracture zone, a transform fault connecting the Galapagos rift zone and the Middle America arc. At the same time, the Caribbean plate is moving easterly with respect to the Americas plate, which is here taken to include both North and South America and the western Atlantic. Left-lateral strike-slip motion along steeply dipping fault planes is observed on the Cayman trough. The Americas plate is underthrusting the Caribbean in a westerly direction at the Lesser Antilles and near Puerto Rico. Unlike the Lesser Antilles, however, motion at present is not perpendicular to the Puerto Rico trench but instead is almost parallel to the trench along nearly horizontal fault planes. Computations of rates of motion indicate that underthrusting is at a higher rate in southeastern Mexico and Guatemala than in western Mexico and that the Caribbean is moving at a lower rate relative to North America than is the Cocos plate.

786 citations

Journal ArticleDOI
19 Mar 1999-Science
TL;DR: A boundary between compositionally distinct regions at a depth of about 1600 kilometers may explain the seismological observations pertaining to Earth's lower mantle, produce the isotopic signatures of mid-ocean ridge basalts and oceanic island basalts, and reconcile the discrepancy between the observed heat flux and the heat production of the mid-Ocean ridge basalt source region.
Abstract: A boundary between compositionally distinct regions at a depth of about 1600 kilometers may explain the seismological observations pertaining to Earth's lower mantle, produce the isotopic signatures of mid-ocean ridge basalts and oceanic island basalts, and reconcile the discrepancy between the observed heat flux and the heat production of the mid-ocean ridge basalt source region. Numerical models of thermochemical convection imply that a layer of material that is intrinsically about 4 percent more dense than the overlying mantle is dynamically stable. Because the deep layer is hot, its net density is only slightly greater than adiabatic and its surface develops substantial topography.

781 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarize the evolution of the greater Red Sea-Gulf of Aden rift system, which includes the Gulfs of Suez and Aqaba, the Red Sea and Gulf of Aden marine basins and their continental margins, and the Afar region.

774 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the composition of the melt lens is mainly moderately fractionated ferrobasalt, which is consistent with a model that effectively separates the processes of magma mixing and fractionation into different parts of a composite magma chamber.
Abstract: Geophysical evidence precludes the existence of a large, mainly molten magma chamber beneath portions of the East Pacific Rise (EPR). A reasonable model, consistent with these data, involves a thin (tens to hundreds of meters high), narrow (<1–2 km wide) melt lens overlying a zone of crystal mush that is in turn surrounded by a transition zone of mostly solidified crust with isolated pockets of magma. Evidence from the superfast spreading portion of the EPR suggests that the composition of the melt lens is mainly moderately fractionated ferrobasalt. These results have important implications for magmatic processes occurring beneath mid-ocean ridges and are consistent with a model that effectively separates the processes of magma mixing and fractionation into different parts of a composite magma chamber. Magma mixing, as evidenced by disequilibrium relations between host liquids and included phenocrysts, is especially apparent in samples from low magma supply ridges and probably mainly arises from interactions between crystals of the mush zone and new injections of primitive magma rising out of the mantle. Magmatic differentiation beneath mid-ocean ridges occurs in two parts. Migration of melts through the transition and mush zones can produce chemical trends consistent with in situ fractionation processes. Segregation of melt into molten horizons near the top of a composite magma chamber promotes the more extensive differentiation characteristic of fast spreading ridges. The optimum conditions for the formation of highly differentiated abyssal lavas is where small, discontinuous melt lenses occur, such as at intermediate spreading rates, in the vicinity of propagating rifts, and near ridge offsets at fast spreading ridges. Along-axis homogenization of subaxial magma is inhibited by the thin, high aspect ratio of the melt lens and by the high viscosities expected in the mush and transition zones. Low magma supply ridges are unlikely to be underlain by eruptable magma in a steady state sense, and eruptions at slow spreading ridges are likely to be closely coupled in time to injection events of new magma from the mantle. Extensional events at high magma supply ridges, which are more likely to be underlain by significant volumes of low-viscosity melt, can produce eruptions without requiring associated injection events. The critical magma supply necessary for the development of a melt lens near the top of a composite magma chamber is similar to that of normal ridges spreading at rates of about 50–70 mm/yr, a rate approximately corresponding to that marking an abrupt change in the morphology and gravity signal at the ridge axis. A composite magma chamber model can explain several previous enigmas concerning mid-ocean ridge basalts, including why slow spreading ridges dominantly erupt a narrow range of relatively undifferentiated lavas, why magma mixing is most evident in lavas erupted from slow spreading ridges, why fast spreading ridges erupt a wide range of generally more differentiated compositions, why bimodal lava populations occur in the vicinity of some propagating rifts, and how along-axis geochemical segmentation can occur at a scale shorter than the major tectonic segmentation of ridge axes.

759 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202338
202294
202157
202066
201980
201863