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, the authors show that the alkalic basalt suites from Flores and Corvo lie on a single liquid line of descent, and they are derived from the same mantle plume as is responsible for the eastern Azores islands.
Abstract: The islands of Flores and Corvo in the Azores archipelago are the only two of nine subaerial volcanic edifices lying west of the Mid-Atlantic Ridge (MAR). This makes them important for constraining the evolution of this young (5 40 Ma) oceanic plateau. The alkalic basalt suites from Flores and Corvo lie on a single liquid line of descent. Ankaramitic cumulates, with MgO contents up to � 18 wt %, result from clinopyroxene-dominated polybaric crystallization. The parental magmas (MgO � 11wt %) are inferred to be low-degree partial melts (F ¼ 3^5%) of enriched peridotite generated at depths of � 80^90 km. These primary magmas commenced crystallizing at the lithosphere^asthenosphere boundary and this continued in conduits over a pressure range of � 0·6^1·2 GPa. Only lavas with MgO53 wt % fractionated at shallow crustal levels. Nd and Sr isotope data reveal variations in the source of both magmatic systems, suggesting variable contributions from both enriched (E-) and depleted (D-) mid-ocean ridge basalt (MORB)-source mantle components. This is supported by the greater variability of incompatible trace-element ratios within the Flores lavas (e.g. Ba/Nd, La/Sm, Th/Nd), whereas those from Corvo exhibit a good correlation between key trace-element ratios [e.g. (La/Sm)N,Th/Nd] and Sr isotope ratios. Lavas from Flores display a greater variability in Sr and Nd isotope compositions and define a mixing array between an E-MORB source and a common Azores mantle source.The latter signature is restricted to lava suites from the north and east of Flores. We concur with the generally accepted notion that Flores and Corvo are derived from the same mantle plume as is responsible for the eastern Azores islands. However, there is evidence (different Nb/Zr, Ta/Hf and La/Sm, but homogeneous Sr and Nd isotopic composition) that these two islands are dominated by a source component that is not as evident in the eastern archipelago.
37 citations
Cites background from "Interaction between the Mid-Atlanti..."
...The thickened oceanic crust on each flank of the MAR has a similar thickness ( 8^10 km) across the plateau (Krause & Watkins, 1970; Searle, 1980; Gente et al., 2003; Nunes et al., 2006; Beier et al., 2008; Georgen & Sankar, 2010)....
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...The subsidence-corrected topography (Gente et al., 2003) suggests at least one set of two seamounts roughly 50 km west of Flores and Corvo....
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..., 1999) or potentially in the vicinity of the island of Faial (Cannat et al., 1999; Gente et al., 2003; Shorttle et al., 2010), but in either case on the eastern plateau, 150^200 km away from the MAR....
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...However, numerous workers have emphasized the potential that lies in these nine islands and the nearby Mid-Atlantic Ridge (MAR) to study the dynamics associated with plume^ ridge interaction (e.g. Bourdon et al., 1996; Gente et al., 2003; Madureira et al., 2005; Shorttle et al., 2010)....
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...The magnetic stripes on the ocean floor north and south of the Azores plateau suggest that Flores and Corvo emerged from oceanic crust that is slightly younger than 10 Ma (Gente et al., 2003)....
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TL;DR: In this paper, the authors investigated the relationship between the hotspot-ridge interaction and the formation of oceanic plateaus and seamounts in the Southwest Indian Ocean and revealed that the activities of the Marion hotspot can be divided into three main phases: interaction with the paleo-Rodrigues triple junction (73.6-68.5 Ma), interaction with SWIR (68.7-42.7 Ma), and intra-plate volcanism (42.3-0 Ma).
Abstract: This study investigates the relationship between the hotspot-ridge interaction and the formation of oceanic plateaus and seamounts in the Southwest Indian Ocean. We first calculated the relative distance between the Southwest Indian Ridge (SWIR) and relevant hotspots on the basis of models of plate reconstruction, and then calculated the corresponding excess magmatic anomalies of the hotspots on the basis of residual bathymetry and Airy isostasy. The results reveal that the activities of the Marion hotspot can be divided into three main phases: interaction with the paleo-Rodrigues triple junction (73.6-68.5 Ma), interaction with the SWIR (68.5-42.7 Ma), and intra-plate volcanism (42.7-0 Ma). These three phases correspond to the formation of the eastern, central, and western parts of the Del Cano Rise, respectively. The magnitude and apparent periodicity of the magmatic volume flux of the Marion hotspot appear to be dominated by the hotspot-ridge distance. The periodicity of the Marion hotspot is about 25 Ma, which is much longer than that of the Hawaii and Iceland hotspots (about 15 Ma).
36 citations
01 Jan 2007
TL;DR: In this paper, the authors classify at least 13 chains as having long-lived (>50-My) age progressive volcanism, at least eight chains with short-lived (<20-my) age progression, and a number of hot spots with complex or no age progression.
Abstract: Volcanic hot spots are regions of intraplate volcanism or excess volcanism at plate margins that are not adequately explained by the plate tectonic paradigm. Hot spots have been associated with topographic swells, distinct radiogenic isotope characteristics, flood basalt events, and age-progressive volcanism, consistent with the movement of plates over relatively fixed point sources of magma. We classify at least 13 chains as having long-lived (>50 My) age progressive volcanism, at least eight chains with short-lived (<20 My) age progression, and a number of hot spots with complex or no age progression. Broad topographic swells commonly surround hot-spot volcanoes; they tend to subside with age and are generally absent around volcanoes older than ∼50–70 Ma. The large Pacific chains appear to be formed by hot spots that are nearly stationary with respect to each other, but prior to ∼50 Ma, could have moved with respect to the geomagnetic poles and the Atlantic and Indian hot spots. The oldest volcanism of some, but not all, hot-spot tracks is in the form of voluminous eruptions characterizing large igneous provinces. The connection between volcano chains and large igneous provinces is most clear for cases in which flood volcanism starts on or near continental margins, but the connection is weak or non-existent for other flood basalt provinces. The Sr–Pb–He isotope geochemistry of oceanic islands, with few exceptions, is significantly more diverse than, and distinguishably different from that of mid-oceanic ridges. Seismic studies of some prominent hot spots reveal anomalously low seismic wave speeds in the upper mantle and unusually thin mantle transition zones, which together suggest elevated mantle temperatures. Studies of the dynamical origin of hot spots are complemented by laboratory and theoretical modeling. Melt can be generated by variations in temperature, composition, and mantle upwelling. While there is a variety of petrologic and geophysical evidence for the magmatism at hot spots such as Hawaii, Galapagos, and Iceland being caused by large increases in mantle potential temperature, significant amounts of water or more mafic lithologies could allow for a lower temperature increase. Predictions of basic fluid dynamics and observations of topographic swells provide strong arguments for swells originating from buoyant upwellings below many hot-spot regions. These upwelling features are expected to be abundant in the convecting mantle but their forms, evolution, and depths of origin are likely to be much more diverse than originally conceived. Causes for hot spots that may originate above the lower mantle remain poorly understood. Unraveling the dynamics of both shallow and deep sources will require considering the interplay among factors such as thermal buoyancy, compositional buoyancy, variable fusability due to lithologic heterogeneity, and strongly varying rheology in the Earth’s mantle.
34 citations
TL;DR: In this paper, the pre-eruptive magma plumbing system of the 10 young, intra-caldera, sub-Plinian, trachytic eruptions of the Upper Furnas Group (UFG) is investigated via whole rock major and trace element geochemistry, mineral chemistry, thermobarometry, and petrogenetic modelling.
Abstract: Furnas is one of three active central volcanoes on Sao Miguel Island, Azores, and is considered to be one of the most hazardous in the archipelago. In this study, the pre-eruptive magma plumbing system of the 10 young (<5 ka), intra-caldera, sub-Plinian, trachytic eruptions of the Upper Furnas Group (UFG) is investigated via whole rock major and trace element geochemistry, mineral chemistry, thermobarometry, and petrogenetic modelling. The main aim of this work is to elucidate the petrogenesis of the Furnas trachytes, constrain the P–T–fO2 conditions under which they evolve, and investigate the temporal evolution of the magma plumbing system. Results indicate that the trachytes are derived predominantly from extended fractional crystallisation of alkali basalt parental magmas, at depths between ~3 and 4 km. This is considered to take place in a density-stratified reservoir, with alkali basalt magmas at the base and hydrous trachytes forming an upper cap or cupola. The presence of this reservoir at shallow crustal depths beneath the caldera likely inhibits the ascent and subsequent eruption of mafic magmas, generating a compositional Daly Gap. Rare syenitic ejecta represent in situ crystallisation of trachytic magmas in the thermal boundary zone at the top of the reservoir. Trachytic enclaves within these syenites, in addition to banded pumices and ubiquitous clinopyroxene antecrysts in the UFG pumice falls, provide evidence for mingling/mixing processes within the magmatic system. Despite relatively uniform major element compositions, systematic trace element variations within individual eruptions highlight the importance of fractional crystallisation during late-stage evolution of the trachytes. This is facilitated by the accumulation of water and the development of mild peralkalinity, which contribute to low pre-eruptive melt viscosities and efficient crystal settling. Compositional zoning patterns between individual eruptions cannot be accounted for by periodic tapping of a single magma batch undergoing fractional crystallisation. Instead, up to four individual cycles are recognised, in which a zoned cap of eruptible trachytic magma, formed at the top of the reservoir, was erupted in one or more eruptions and was re-established via intermittent replenishment and subsequent fractional crystallisation.
33 citations
Cites background from "Interaction between the Mid-Atlanti..."
...…the emergent portions of large volcanic centres that rise from the Azores Plateau, a bathymetric and gravitational anomaly associated with a morphologically complex area (~5.8 × 106 km2) of thickened oceanic crust that formed between 20 and 7 Ma (Kaula 1970; Ridley et al. 1974; Gente et al. 2003)....
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...8 × 10(6) km(2)) of thickened oceanic crust that formed between 20 and 7 Ma (Kaula 1970; Ridley et al. 1974; Gente et al. 2003)....
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TL;DR: In this paper, the authors investigated the surface expression of faulting close to the Azores triple junction, by the systematic mapping of MAR-generated abyssal hills, and showed that there is always a finite triple junction area, highly tectonized, in which size is dependent on the angle between the two faster arms and, consequently, on the relative spreading velocity of the slower arm.
33 citations
Cites background from "Interaction between the Mid-Atlanti..."
...The prominent tectonic character of that distributed deformation zone, coincides with the main rifting stage of the Azores plateau (Gente et al., 2003)....
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...…at the timeof chron C4a between a “mantle-dominated” period, associated with the uplift of the plateau and a “lithospheric-dominated” period where rifting by the MAR splits the previous unique plateau into western and eastern plateaus, in the same line as described by Gente et al. (2003)....
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...Gente et al., 2003) still showed large limitations close to the Azores....
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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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