Interaction between the Mid-Atlantic Ridge and the Azores hot spot during the last 85 Myr: Emplacement and rifting of the hot spot-derived plateaus
TL;DR: In this paper, multiple and single-beam bathymetric data are compiled over the Azores plateau to produce a 1 km × 1 km grid between latitudes 32°N and 49°N, and longitudes 22°W and 43°W.
Abstract: [1] Multiple- and single-beam bathymetric data are compiled over the Azores plateau to produce a 1 km × 1 km grid between latitudes 32°N and 49°N and longitudes 22°W and 43°W. Mantle Bouguer anomalies are then calculated from this grid and the satellite-derived gravity. These grids provide new insights on the temporal and spatial variations of melt supply to the ridge axis. The elevated seafloor of the Azores plateau is interpreted as resulting from the interaction of a mantle plume with the Mid-Atlantic Ridge (MAR). The presence of a large region of elevated seafloor associated with a thick crust between the Great Meteor Seamounts and the Azores platform on the Africa plate, and less developed conjugate structures on the North America plate, favors genetic relations between these hot spot-derived structures. This suggests that a ridge-hot spot interaction has occurred in this region since 85 Ma. This interaction migrated northward along the ridge axis as a result of the SSE absolute motion of the Africa plate, following a direction grossly parallel to the orientation of the MAR. Kinematic reconstructions from chron 13 (∼35 Ma) to the present allow a proposal that the formation of the Azores plateau began around 20 Ma and ended around 7 Ma. A sharp bathymetric step is associated with the beginning of important melt supply around 20 Ma. The excess of melt production is controlled by the interaction of the ridge and hot spot melting zones. The geometry and distribution of the smaller-scale features on the plateau record episodic variations of the hot spot melt production. The periodicity of these variations is about 3–5 Myr. Following the rapid decrease of widespread volcanism, the plateau was subsequently rifted from north to south by the Mid-Atlantic Ridge since 7 Ma. This rifting begins when the MAR melting zone is progressively shifted away from the 200-km plume thermal anomaly. These results bear important consequences on the motion of the Africa plate relative to the Azores hot spot. They also provide an explanation to the asymmetric geochemical signature of the Azores hot spot along the Mid-Atlantic Ridge.
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TL;DR: In this article, the authors used the 40Ar/39Ar geochronology and Sr-Nd-Pb isotopes geochemistry of basalts from the New England Seamounts (NES) and the J-Anomaly Ridge (JAR) as these localities on the North American margin are still poorly investigated.
18 citations
TL;DR: In this article, the authors examined the distribution of strain and magmatism in the portion of the Terceira Rift (TR) making up the Nubia-Eurasia plate boundary.
Abstract: The evolution of hyperslow oceanic rifts, like the Terceira Rift (TR) in the Azores, is still poorly understood. Here we examine the distribution of strain and magmatism in the portion of the TR making up the Nubia-Eurasia plate boundary. We use Sao Miguel Island because it stretches most of the TR width, which allows to investigate the TR's architecture and shedding light on TR's age and mode of deformation. From topography and structural analysis, and new measurements of 380 faults and dikes, we show that (1) Sao Miguel has two main structural directions, N150 and N110, mostly concentrated in the eastern part of the island as an onshore continuation of the faults observed offshore in the NE (N110 faults) and SW (N140) TR walls; (2) a new N50-N80 fault system is identified in Sao Miguel; (3) fault and dike geometries indicate that eastern Sao Miguel comprises the TR's northern boundary, and the lack of major faults in central and western Sao Miguel indicates that rifting is mostly concentrated at master faults bounding the TR. Based on TR's geometry, structural observations and plate kinematics, we estimate that the TR initiated between 1.4 and 2.7 Ma ago and that there is no appreciable seafloor spreading associated with rifting. Based on plate kinematics, on the new structural data, and on Sao Miguel's structural and volcanic trends, we propose that the eastern two thirds of Sao Miguel lie along a main TR-related transform fault striking N70-N80, which connects two widely separated N130-N150 TR-trending segments.
18 citations
Cites background from "Interaction between the Mid-Atlanti..."
...Indeed, for some authors [Cannat et al., 1999; Gente et al., 2003] the plateau has formed by the eruption of underwater traps during the impact of a plume head of deep origin, around ~36Ma and between 20 and 10Ma, although tomographic data indicate shallow anomalies at the regional scale, Figure 1....
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...…a mantle plume (hot or wet) below the Azores has thus been proposed as an explanation for the excess of volcanism in the region [Vogt, 1976; Schilling, 1985; Thibauld et al., 1998; Gente et al., 2003; Métrich et al., 2014] and for the position of the Eurasia/Nubia rifting [Vogt and Jung, 2004]....
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...Indeed, for some authors [Cannat et al., 1999; Gente et al., 2003] the plateau has formed by the eruption of underwater traps during the impact of a plume head of deep origin, around ~36Ma and between 20 and 10Ma, although tomographic data indicate shallow anomalies at the regional scale, SIBRANT…...
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...[1980], Moreira [1985], Grimison and Chen [1986], Buforn et al....
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...The Azores region shows also significant excess in magmatism and an abnormal shallow and thick plateau, the so-called Azores Plateau [Searle, 1976; Detrick et al., 1995; Gente et al., 2003; Luís et al., 1998; Silveira et al., 2010], which cannot be explained by the geometry and configuration of the ATJ alone [Georgen and Sankar, 2010]....
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01 Jan 2019
TL;DR: In this paper, the authors studied the thermal and the mechanical properties of oceanic transform faults and their response to changes in plate motion, including the length of the offset and the magnitude of the change in the plate motion.
Abstract: Oceanic transform faults are fundamental features of the spreading processes and record changes in both the local-field and the far-field stresses, due to either local factors or plate motion changes. The study of the morphologic evidences of deformation they undergo due to these changes is key to understand the thermal and the mechanical structure of the oceanic lithosphere. Different features result from transform deformation. The large transverse ridges observed at several transforms form as a flexural response to extension at the transform or the fracture zone. The thermal heating of the lithosphere as well as the serpentinization of mantle rocks play a minor role in this uplift. Median ridges are also tectonic features formed due to compressive or extensional stresses inside the transform domain and serpentinization does not appear to play a major role in their uplift. At fast spreading ridges, extension inside the transform domain often results in the formation of “leaky transforms.” These morphologies are rare at slow spreading ridges, because the colder lithosphere does not favor the inception of intra-transform segments. However, large offset transforms, under severe changes in plate motions, may develop this geometry. Several factors will control the response of transform faults to changes in plate motion. A major one is the length of the offset, but the magnitude of the change in plate motion is also important. Minor changes will be easily accommodated by both small and large offset transforms, often through small deformations inside the transform valley. Conversely, larger changes may have small impact on small offset transforms but result in strong deformation at larger ones. Large offset transforms are slower to respond to kinematic changes than small offset ones. Mega-transforms may readjust even more slowly, thus forming a multifault complex boundary. At even larger offsets, the transform is no longer able to adjust to severe changes and will be abandoned. Local stresses such as mantle flow and thermal contraction of the lithosphere may induce significant topography at transform faults through small bends of the principal transform displacement zone (PTDZ) inside the transform domain, thus resulting in localized transpression and transtension.
18 citations
TL;DR: In this article, the authors examined magnetic anomalies over and around Ori Massif to obtain insights about the formation of this volcanic edifice and found that it is predominantly characterized by linear magnetic anomalies resulting from alternating normal and reversed polarity magnetization blocks, analogous to magnetic anomalies recorded by spreading-ridges.
18 citations
TL;DR: In this article, a detailed seafloor mapping with onshore studies is presented to gain a unique insight onto the evolution of volcanic island edifices and the processes that helped to shape their shelves, including the original shape and structure of volcanic edifice, the nature and age of the materials that compose its flanks, and the erosional, volcanic, tectonic and sedimentary processes that acted to form these shelves.
17 citations
References
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TL;DR: The Generic Mapping Tools (GMT) is introduced, which is a free, public domain software package that can be used to manipulate columns of tabular data, time series, and gridded data sets and to display these data in a variety of forms ranging from simple x-y plots to maps and color, perspective, and shaded-relief illustrations.
Abstract: When creating camera-ready figures, most scientists are familiar with the sequence of raw data → processing → final illustration and with the spending of large sums of money to finalize papers for submission to scientific journals, prepare proposals, and create overheads and slides for various presentations. This process can be tedious and is often done manually, since available commercial or in-house software usually can do only part of the job.
To expedite this process, we introduce the Generic Mapping Tools (GMT), which is a free, public domain software package that can be used to manipulate columns of tabular data, time series, and gridded data sets and to display these data in a variety of forms ranging from simple x-y plots to maps and color, perspective, and shaded-relief illustrations. GMT uses the PostScript page description language, which can create arbitrarily complex images in gray tones or 24-bit true color by superimposing multiple plot files. Line drawings, bitmapped images, and text can be easily combined in one illustration. PostScript plot files are device-independent, meaning the same file can be printed at 300 dots per inch (dpi) on an ordinary laserwriter or at 2470 dpi on a phototypesetter when ultimate quality is needed. GMT software is written as a set of UNIX tools and is totally self contained and fully documented. The system is offered free of charge to federal agencies and nonprofit educational organizations worldwide and is distributed over the computer network Internet.
4,128 citations
Additional excerpts
...0) [Wessel and Smith, 1991]....
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TL;DR: An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and Pliocene and with a new timescale for the Mesozoic.
Abstract: Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous/Paleogene boundary and in the Pliocene. An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and Pliocene and with a new timescale for the Mesozoic. The age of 66 Ma for the Cretaceous/Paleogene (K/P) boundary used for calibration in the geomagnetic polarity timescale of Cande and Kent (1992) (hereinafter referred to as CK92) was supported by high precision laser fusion Ar/Ar sanidine single crystal dates from nonmarine strata in Montana. However, these age determinations are now
3,582 citations
TL;DR: A global plate motion model, named NUVEL-1, which describes current plate motions between 12 rigid plates is described, with special attention given to the method, data, and assumptions used as discussed by the authors.
Abstract: A global plate motion model, named NUVEL-1, which describes current plate motions between 12 rigid plates is described, with special attention given to the method, data, and assumptions used Tectonic implications of the patterns that emerged from the results are discussed It is shown that wide plate boundary zones can form not only within the continental lithosphere but also within the oceanic lithosphere; eg, between the Indian and Australian plates and between the North American and South American plates Results of the model also suggest small but significant diffuse deformation of the oceanic lithosphere, which may be confined to small awkwardly shaped salients of major plates
3,409 citations
01 Jan 1988
TL;DR: In this paper, a new global model (NUVEL-1) was proposed to describe the geologically current motion between 12 assumed-rigid plates by inverting plate motion data.
Abstract: SUMMARY
We determine best-fitting Euler vectors, closure-fitting Euler vectors, and a new global model (NUVEL-1) describing the geologically current motion between 12 assumed-rigid plates by inverting plate motion data we have compiled, critically analysed, and tested for self-consistency. We treat Arabia, India and Australia, and North America and South America as distinct plates, but combine Nubia and Somalia into a single African plate because motion between them could not be reliably resolved. The 1122 data from 22 plate boundaries inverted to obtain NUVEL-1 consist of 277 spreading rates, 121 transform fault azimuths, and 724 earthquake slip vectors. We determined all rates over a uniform time interval of 3.0m.y., corresponding to the centre of the anomaly 2A sequence, by comparing synthetic magnetic anomalies with observed profiles. The model fits the data well. Unlike prior global plate motion models, which systematically misfit some spreading rates in the Indian Ocean by 8–12mm yr−1, the systematic misfits by NUVEL-1 nowhere exceed ∼3 mm yr−1. The model differs significantly from prior global plate motion models. For the 30 pairs of plates sharing a common boundary, 29 of 30 P071, and 25 of 30 RM2 Euler vectors lie outside the 99 per cent confidence limits of NUVEL-1. Differences are large in the Indian Ocean where NUVEL-1 plate motion data and plate geometry differ from those used in prior studies and in the Pacific Ocean where NUVEL-1 rates are systematically 5–20 mm yr−1 slower than those of prior models. The strikes of transform faults mapped with GLORIA and Seabeam along the Mid-Atlantic Ridge greatly improve the accuracy of estimates of the direction of plate motion. These data give Euler vectors differing significantly from those of prior studies, show that motion about the Azores triple junction is consistent with plate circuit closure, and better resolve motion between North America and South America. Motion of the Caribbean plate relative to North or South America is about 7 mm yr−1 slower than in prior global models. Trench slip vectors tend to be systematically misfit wherever convergence is oblique, and best-fitting poles determined only from trench slip vectors differ significantly from their corresponding closure-fitting Euler vectors. The direction of slip in trench earthquakes tends to be between the direction of plate motion and the normal to the trench strike. Part of this bias may be due to the neglect of lateral heterogeneities of seismic velocities caused by cold subducting slabs, but the larger part is likely caused by independent motion of fore-arc crust and lithosphere relative to the overriding plate.
3,328 citations
TL;DR: In this paper, a simple cooling model and the plate model were proposed to account for the variation in depth and heat flow with increasing age of the ocean floor. But the results were limited to the North Pacific and North Atlantic basins.
Abstract: Two models, a simple cooling model and the plate model, have been advanced to account for the variation in depth and heat flow with increasing age of the ocean floor. The simple cooling model predicts a linear relation between depth and t½, and heat flow and 1/t½, where t is the age of the ocean floor. We show that the same t½ dependence is implicit in the solutions for the plate model for sufficiently young ocean floor. For larger ages these relations break down, and depth and heat flow decay exponentially to constant values. The two forms of the solution are developed to provide a simple method of inverting the data to give the model parameters. The empirical depth versus age relation for the North Pacific and North Atlantic has been extended out to 160 m.y. B.P. The depth initially increases as t½, but between 60 and 80 m.y. B.P. the variation of depth with age departs from this simple relation. For older ocean floor the depth decays exponentially with age toward a constant asymptotic value. Such characteristics would be produced by a thermal structure close to that of the plate model. Inverting the data gives a plate thickness of 125±10 km, a bottom boundary temperature of 1350°±275°C, and a thermal expansion coefficient of (3.2±1.1) × 10−5°C−1. Between 0 and 70 m.y. B.P. the depth can be represented by the relation d(t) = 2500 + 350t½ m, with t in m.y. B.P., and for regions older than 20 m.y. B.P. by the relation d(t) = 6400 - 3200 exp (−t/62.8) m. The heat flow data were treated in a similar, but less extensive manner. Although the data are compatible with the same model that accounts for the topography, their scatter prevents their use in the same quantitative fashion. Our analysis shows that the heat flow only responds to the bottom boundary at approximately twice the age at which the depth does. Within the scatter of the data, from 0 to 120 m.y. B.P., the heat flow pan be represented by the relation q(t) = 11.3/t½ μcal cm−2s−1. The previously accepted view that the heat flow observations approach a constant asymptotic value in the old ocean basins needs to be tested more stringently. The above results imply that a mechanism is required to supply heat at the base of the plate.
2,667 citations
"Interaction between the Mid-Atlanti..." refers background or methods in this paper
...where t is the age in Myr and S is the subsidence in kilometers [Parsons and Sclater, 1977]....
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...The expected subsidence of the seafloor is calculated using the relation S ¼ 0:35 sqrt tð Þ where t is the age in Myr and S is the subsidence in kilometers [Parsons and Sclater, 1977]....
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