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 paper, K/Ar dating and geochemical analyses have been carried out on the WNW-ESE elongated oceanic island of S. Jorge to reconstruct the volcanic evolution of a linear ridge developed close to the Azores triple junction.
74 citations
TL;DR: In this article, the authors present a review of the Azores deep seismic structure as inferred from recent global and regional studies, which reveals a negative anomaly under the archipelago confined within the upper 250-300 km.
68 citations
Additional excerpts
...The formation of the plateau began around 20 My and ended around 7 My. The plateau was subsequently rifted from north to south by the Mid-Atlantic Ridge (for a review, see Gente et al., 2003 )....
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...Based on the raregas signature, the Azores hotspot is presently located on the eastern side of the MAR under the central group of islands (see Gente et al., 2003, for a review)....
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...reflect typical ridge–hotspot interaction (e.g., Schilling, 1991), from elevated spreading ridge, basalt geochemistry and gravity anomaly (see Gente et al., 2003, for a recent review)....
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TL;DR: In this paper, the authors investigate the interactions between mantle dynamics and lithospheric deformation in relation to short-term plate reconfiguration and suggest that magma generation results from decompression melt- ing of a heterogeneously fertilized mantle.
66 citations
Cites background from "Interaction between the Mid-Atlanti..."
...The Azores plateau, especially, is generally interpreted as a large igneous province (LIP), formed during a plume-derived episode of enhanced melt production centered on the Mid-Atlantic Ridge (MAR) between 20 and 7Maago (e.g. Cannat et al., 1999; Gente et al., 2003)....
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TL;DR: The Oceanography 20, 1, 1 (2007): 102-115 as discussed by the authors is the most cited work in this category, and is published by Oceanography Society for personal use, not for redistribution.
Abstract: Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 1 (2007): 102-115.
62 citations
Cites background from "Interaction between the Mid-Atlanti..."
..., 2003), Azores (Cannat et al., 1999; Gente et al., 2003), Easter (Kingsley and Schilling, 1998), Foundation (Maia et al....
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TL;DR: In this paper, the authors derived the first chronologically detailed model of Eurasia-North America plate motion since 20 Ma from ship and airplane surveys of the well-expressed magnetic lineations along this slowly spreading plate boundary, including previously unavailable Russian magnetic data from the southern Reykjanes Ridge and northern Mid-Atlantic ridge near the Charlie Gibbs fracture zone.
Abstract: SUMMARY We derive the first chronologically detailed model of Eurasia‐North America plate motion since 20 Ma from ship and airplane surveys of the well-expressed magnetic lineations along this slowly spreading plate boundary, including previously unavailable dense Russian magnetic data from the southern Reykjanes Ridge and northern Mid-Atlantic ridge near the Charlie Gibbs fracture zone. From more than 7000 crossings of 21 magnetic anomalies from Anomaly 1n (0.78 Ma) to Anomaly 6n (19.7 Ma), we estimate best-fitting finite rotations and realistic uncertainties. Linear regressions of total opening distances versus their reversal ages at different locations along the plate boundary show that reversal boundaries are shifted systematically outwards from the spreading axis with respect to their idealized locations, with the outward shift ranging from more than 5 km between Iceland and the Charlie Gibbs fracture zone to ∼2 km elsewhere. This outward displacement, which is a consequence of the finite zone of seafloor accretion, degrades estimates of the underlying plate motion and is thus removed for the ensuing kinematic analysis. The corrected plate motion rotations reveal surprising, previously unrecognized features in the relative motions of these two plates. Within the uncertainties, motion was steady from 20 to 8 Ma around a pole that was located ∼600 km north of the present pole, with seafloor spreading rates that changed by no more than 5 per cent (1 mm yr −1 ) along the Reykjanes Ridge during this period. Seafloor spreading rates decreased abruptly by 20 ± 2 per cent at 7.5‐6.5 Ma, coinciding with rapid southward migration of the pole of rotation and a5 ◦ ‐10 ◦ counter-clockwise change in the plate slip direction. Eurasia‐North America plate motion since 6.7 Ma has remained remarkably steady, with an apparently stationary axis of rotation and upper limit of ±2 per cent on any variations in the rate of angular rotation during this period. Based on the good agreement between seismotectonic constraints on present deformation in northeast Asia and directions of motion that are predicted by our 6.7 Ma to present pole, we hypothesize that motion has remained steady to the present and attempt to test this hypothesis with published GPS estimates for Eurasia‐North America motion. We find, however, that GPS estimates that are tied to recent versions of the international geodetic reference frame and rely principally on station velocities from Europe give implausible estimates of recent motion, with the most recently published GPS model predicting convergence along the southern Gakkel Ridge and in the Laptev Sea, where seafloor spreading occurs. An alternative GPS estimate that is not tied to the international terrestrial reference frame and employs GPS station velocities from northeastern Asia is marginally consistent with our 6.7‐0 Ma motion estimate.
61 citations
Cites methods from "Interaction between the Mid-Atlanti..."
...S3), we extracted magnetic anomaly crossings from the dense TRIATNORD survey (Goslin et al. 1999; Gente et al. 2003), from surveys archived at the NGDC, and from two dense Canadian surveys of the ridge from 45◦N to 46◦N (Verhoef et al. 1996; S. Dehler 2000, personal communication)....
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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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