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: Small-scale volcanic systems are commonly monogenetic in the sense that they are represented at the Earth's surface by fields of small volcanoes, each the product of a temporally restricted eruption of a compositionally distinct batch of magma, and this is in contrast to relatively large edifices built by multiple eruptions over longer periods of time involving magmas with diverse origins.
Abstract: Abstract Small-scale volcanic systems are the most widespread type of volcanism on Earth and occur in all of the main tectonic settings. Most commonly, these systems erupt basaltic magmas within a wide compositional range from strongly silica undersaturated to saturated and oversaturated; less commonly, the spectrum includes more siliceous compositions. Small-scale volcanic systems are commonly monogenetic in the sense that they are represented at the Earth's surface by fields of small volcanoes, each the product of a temporally restricted eruption of a compositionally distinct batch of magma, and this is in contrast to polygenetic systems characterized by relatively large edifices built by multiple eruptions over longer periods of time involving magmas with diverse origins. Eruption styles of small-scale volcanoes range from pyroclastic to effusive, and are strongly controlled by the relative influence of the characteristics of the magmatic system and the surface environment.
115 citations
Cites background from "Interaction between the Mid-Atlanti..."
...At the less productive oceanic hotspots of the Azores (Gente et al. 2003) and Canary Islands (Fullea et al....
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...At the less productive oceanic hotspots of the Azores (Gente et al. 2003) and Canary Islands (Fullea et al. 2015), clinopyroxene–melt barometry and petrographical observations show that magma batches partially crystallize and mix with preexisting magma batches in a zone of temporary magma storage…...
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...At the less productive oceanic hotspots of the Azores (Gente et al. 2003) and Canary Islands (Fullea et al. 2015), clinopyroxene–melt barometry and petrographical observations show that magma batches partially crystallize and mix with preexisting magma batches in a zone of temporary magma storage at near and sub-Moho depths of 15–40 km (Hansteen et al. 1998; Schwarz et al. 2004; Klugel et al. 2005; Galipp et al. 2006; Longpré et al. 2009; Stroncik et al. 2009)....
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TL;DR: In this article, He isotope and major, trace and volatile element compositions for basaltic scoriae from five monogenetic cones emplaced along the fissure zone of Pico Island, the youngest island of the Azores archipelago.
Abstract: The concept of an 'Azores mantle plume' has been widely debated, and the existence of an Azores hotspot questioned. In an effort to shed new light on this controversy, we present He isotope and major, trace and volatile element compositions for basaltic scoriae from five monogenetic cones emplaced along the fissure zone of Pico Island, the youngest island of the Azores archipelago. The bulk scoriae and lavas are moderately alkaline basalts, and their He isotope ratios, determined on olivine crystals, vary between 10*2 and 11*1 ± 0*1 Ra. In contrast, melt inclusions hosted in olivine (Fo76-83*5) span a large range of compositions (K2O = 0*7-1*7 wt %; Ce = 32-65 ppm; Nb = 21-94 ppm), which extends the compositional field of lavas erupted along the Pico fissure zone. This chemical evolution is predominantly controlled by polybaric fractional crystallization. Most melt inclusions share similar enrichments in large ion lithophile and light rare earth elements, and trace element ratios (La/Sm, La/Yb, Sr/Nd, Ta/Th, Zr/Y) with their bulk-rocks. Only a few of them differ in their lower contents of incompatible elements and La/Sm, Li/Ta and Na/K ratios, a feature that is ascribed to distinct conditions of melting. As a whole, the melt inclusions preserve high and variable volatile contents, and contain up to 1*8-2*0 wt % of H2O and 0*4 wt % of CO2. The total fluid pressures, retrieved from the dissolved CO2 and H2O concentrations, and the PCO2 from fluid inclusions, indicate magma ponding and crystallization at the crust-mantle boundary (ca. 18 km deep). The H2O/Cl and H2O/Ce ratios in the inferred parental undegassed basalts of the Pico fissure zone average 0*036 ± 0*006 and 259 ± 21, respectively. The latter value is significantly higher than that reported for typical mid-ocean ridge basalts from the southern Mid-Atlantic Ridge, but is similar to published ratios for submarine undegassed basalts from the Azores platform. Combining the calculated compositions of Pico primary magmas formed by low degrees of melting with recent geophysical data for the Azores, we propose a model for Azores magma generation involving the decompression melting of a water-enriched mantle domain (H2O = 680-570 ppm) with an estimated temperature excess of ≤120°C with respect to the Mid-Atlantic Ridge.
92 citations
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...At the junction between three major lithospheric platesçthe North American, African and Eurasian platesçthe Azores islands are thus located in a complex tectonic setting characterized by anomalously thick crust ( 8 km; Luis et al., 1998; Gente et al., 2003; Dias et al., 2007; Georgen & Sankar, 2010; Silveira et al., 2010) and the presence of ‘V-shaped’ ridges along the adjacent MAR (e....
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...…platesçthe Azores islands are thus located in a complex tectonic setting characterized by anomalously thick crust ( 8 km; Luis et al., 1998; Gente et al., 2003; Dias et al., 2007; Georgen & Sankar, 2010; Silveira et al., 2010) and the presence of ‘V-shaped’ ridges along the adjacent MAR…...
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Lamont–Doherty Earth Observatory1, University of Bristol2, Tokyo Institute of Technology3, University of Lisbon4, United States Geological Survey5, University of Münster6, University of the Azores7, Leibniz Center for Tropical Marine Ecology8, University of North Carolina at Wilmington9, University of Porto10
TL;DR: In this paper, the authors reconstruct the evolutionary history of Santa Maria with respect to the timing and magnitude of its vertical movements, using detailed field work and 40Ar/39Ar geochronology.
Abstract: The growth and decay of ocean-island volcanoes are intrinsically linked to vertical movements. While the causes for subsidence are better understood, uplift mechanisms remain enigmatic. Santa Maria Island in the Azores Archipelago is an ocean-island volcano resting on top of young lithosphere, barely 480 km away from the Mid-Atlantic Ridge. Like most other Azorean islands, Santa Maria should be experiencing subsidence. Yet, several features indicate an uplift trend instead. In this paper, we reconstruct the evolutionary history of Santa Maria with respect to the timing and magnitude of its vertical movements, using detailed field work and 40Ar/39Ar geochronology. Our investigations revealed a complex evolutionary history spanning ∼6 m.y., with subsidence up to ca. 3.5 Ma followed by uplift extending to the present day. The fact that an island located in young lithosphere experienced a pronounced uplift trend is remarkable and raises important questions concerning possible uplift mechanisms. Localized uplift in response to the tectonic regime affecting the southeastern tip of the Azores Plateau is unlikely, since the area is under transtension. Our analysis shows that the only viable mechanism able to explain the uplift is crustal thickening by basal intrusions, suggesting that intrusive processes play a significant role even on islands standing on young lithosphere, such as in the Azores.
83 citations
TL;DR: In this paper, the authors used bathymetry and high-resolution seismic reflection profiles to characterize the morphology of the insular shelves adjacent to each volcanic edifice of Terceira Island in order to improve the understanding of its evolution.
Abstract: Shelves from volcanic ocean islands result from the competition between two main processes, wave erosion that forms and enlarges them and volcanic progradation that reduces their dimension. In places where erosion dominates over volcanism, shelf width can be used as a proxy for the relative age of the subaerial volcanic edifices and reconstruction of their extents prior to erosion can be achieved. In this study, new multibeam bathymetry and high-resolution seismic reflection profiles are exploited to characterize the morphology of the insular shelves adjacent to each volcanic edifice of Terceira Island in order to improve the understanding of its evolution. Subaerial morphological and geological/stratigraphic data were also used to establish the connection between the onshore and offshore evolution. Shelf width contiguous to each main volcanic edifice is consistent with the known subaerial geological history of the island; most of the older edifices have wider shelves than younger ones. The shelf edge proved to be a very useful indicator in revealing the original extent of each volcanic edifice in plan view. Its depth was also used to reconstruct vertical movements, showing that older edifices like Serra do Cume-Ribeirinha, Guilherme Moniz, and Pico Alto have subsided while more recent ones have not. The morphology of the shelf (namely the absence/presence of fresh lava flow morphologies and several types of erosional, depositional, and tectonic features) integrated with the analysis of the coastline morphology allowed us to better constrain previous geological interpretations of the island evolution.
79 citations
Cites background from "Interaction between the Mid-Atlanti..."
...…interaction between the triple junction of the Eurasian (Eu), Nubian (Nu), and North American (NA) plates [e.g., Laughton and Whitmarsh, 1974; Saemundsson, 1986], and a magmatic anomaly that some authors consider to be the Azores hotspot [Cannat et al., 1999; Gente et al., 2003; Schilling, 1975]....
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TL;DR: In this paper, the authors used the satellite-derived gravity anomaly to predict the bathymetry for different values of Te, which is a proxy for the long-term strength of the lithosphere.
Abstract: [1] The seafloor is characterized by numerous seamounts and oceanic islands which are mainly volcanic in origin. Relatively few of these features (<∼0.1%), however, have been dated, and so little is known about their tectonic setting. One parameter that is sensitive to whether a seamount formed on, near, or far from a mid-ocean ridge is the elastic thickness, Te, which is a proxy for the long-term strength of the lithosphere. Most previous studies are based on using the bathymetry to calculate the gravity anomaly for different values of Te and then comparing the calculated and observed gravity anomaly. The problem with such an approach is that bathymetry data are usually limited to single-beam echo sounder data acquired along a ship track and these data are too sparse to define seamount shape. We therefore use the satellite-derived gravity anomaly to predict the bathymetry for different values of Te. By comparing the predicted bathymetry to actual shipboard soundings in the vicinity of each locality in the Wessel global seamount database, we have obtained 9758 Te estimates from a wide range of submarine volcanic features in the Pacific, Indian, and Atlantic oceans. Comparisons where there are previous estimates show that bathymetric prediction is a robust way to estimate Te and its upper and lower bounds. Te at sites where there is both a sample and crustal age show considerable scatter, however, and there is no simple relationship between Te and age. Nevertheless, we are able to tentatively assign a tectonic setting to each Te estimate. The most striking results are in the Pacific Ocean where a broad swath of “on-ridge” volcanism extends from the Foundation seamounts and Ducie Island/Easter Island ridge in the southeast, across the equator, to the Shatsky and Hess rises in the northwest. Interspersed among the on-ridge volcanism are “flank ridge” and “off-ridge” features. The Indian and Atlantic oceans also show a mix of tectonic settings. Off-ridge volcanism dominates in the eastern North Atlantic and northeast Indian oceans, while flank ridge volcanism dominates the northeastern Indian and western south Atlantic oceans. We have been unable to assign the flank ridge and off-ridge estimates an age, but the on-ridge estimates generally reflect, we believe, the age of the underlying oceanic crust. We estimate the volume of on-ridge volcanism to be ∼1.1 × 106 km3 which implies a mean seamount addition rate of ∼0.007 km3 yr−1. Rates appear to have varied through geological time, reaching their peak during the Late/Early Cretaceous and then declining to the present-day.
75 citations
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TL;DR: In this paper, a detailed aeromagnetic survey covering both sides of the Mid-Atlantic Ridge between 37°N and 40°30′N is used to identify magnetic anomalies up to anomaly 5, allowing careful modelling of the kinematics of this region for the past 10 Ma and thus establishing a coherent framework for the design of geophysical models for the Azores Triple Junction.
124 citations
TL;DR: In this article, helium and lead isotopic data for basalts from the Azores archipelago (North Atlantic) were used to detect the coexistence of two mantle components, which are identified by data from Sao Miguel and Terceira.
122 citations
TL;DR: In this paper, the authors analyzed bathymetric and gravity anomalies along present and paleoaxes of oceanic spreading centers influenced by the Iceland, Azores, Galapagos, Tristan, and Easter hotspots.
Abstract: We analyzed bathymetric and gravity anomalies along present and paleoaxes of oceanic spreading centers influenced by the Iceland, Azores, Galapagos, Tristan, and Easter hotspots. Residual bathymetry (up to 4.7 km) and mantle Bouguer gravity (up to −340 km) anomalies are maximum at on-axis hotspots and decrease with increasing ridge-hotspot separation distance (D) , until becoming insignificant at D ∼500 km. Along-isochron widths of bathymetric anomalies (up to 2700 km) depend inversely on paleo–spreading rate, reflecting the extent to which plume material will flow along axis before being swept away by the spreading lithosphere. Flux balance arguments suggest that the five hotspots feed material to ridges with comparable fluxes of ∼2.2 × 106 km3/m.y. Assuming that the amplitudes of these geophysical anomalies reflect temperature-dependent crustal thickness and mantle density variations, we suggest that ridge temperature anomalies are maximum (150–225 ° C) when plumes are ridge centered and decrease with increasing ridge-hotspot distance due to cooling of the ridgeward-migrating plume material.
116 citations
"Interaction between the Mid-Atlanti..." refers background in this paper
...However, it is estimated that the Azores hot spot is located about 150–200 km east of the MAR [Ito and Lin, 1995], probably centered under the Central Group of islands [Moreira et al., 1999], on the boundary of the Africa and Eurasia plates....
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...5 of 23 MAR, under the group of islands between Faial and Terceira [Ito and Lin, 1995; Moreira et al., 1999]....
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TL;DR: In this paper, multibeam bathymetry data obtained along a 2400 km long section of the Mid-Atlantic Ridge (MAR) from 15°N to the Azores platform (40°N) and satellite-derived gravity data were used to calculate the mantle Bouguer anomaly (MBA) along this portion of the MAR.
Abstract: Multibeam bathymetry data obtained along a 2400 km long section of the Mid-Atlantic Ridge (MAR) from 15°N to the Azores platform (40°N) and satellite-derived gravity data were used to calculate the mantle Bouguer anomaly (MBA) along this portion of the MAR. Both data sets were used to determine the relations between gravity anomalies and topographic variations and discuss these in terms of thermal difference. A long-wavelength influence of the Azores hot spot is characterized by a gentle, continuous slope of the average ridge axial depth and a general gradient in the along-axis MBA profile. This thermal influence of the Azores hot spot controls a systematic southward propagation of the spreading segments at least to 26°30′N. South of 26°30′N, the direction of the segment propagation is controlled by the local difference in thermal state between adjacent segments. Except on the Azores platform, the systematic along-axis 11–90 km long wavelength segmentation is independent of the long-wavelength influence of the Azores. At the segment center, the axial morphology is linked to the thermal state of the segments between: (1) “Hotter segments” characterized by a smooth axial morphology, a well-defined shallow ”inner valley”, high ΔMBA and a long length;(2) “colder segments” which present a rough axial morphology with a deep, wide and well-defined rift valley, a low ΔMBA and a small length. For ”hotter segments” the formation of the abyssal hills is mainly due to a magmato-tectonic cycle over periods of 0.3 to 1 Myr, whereas on “colder segments” the axial morphology is mainly controlled by a tectonic rift valley formation. We propose that these different segment types correspond to a temporal evolution of the rift valley morphology over periods of several million years.
112 citations
"Interaction between the Mid-Atlanti..." refers background in this paper
...…elevated spreading ridge [Vogt, 1976; Schilling, 1985; Gente, 1987; Thibaud et al., 1998], basalt geochemistry [Schilling, 1975; White et al., 1976; Bougault and Treuil, 1980; Schilling et al., 1983; Dosso et al., 1999], and gravity anomalies [Detrick et al., 1995; Thibaud et al., 1998] (Figure 2)....
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...[11] Over the study area, shipborne and satellitederived free-air anomalies are roughly equivalent at wavelengths longer than 30 km, as shown by our previous work on the MAR segmentation between 15 and 40 N [Thibaud et al., 1998]....
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...…along the MAR (Figure 2), including ridge-axis elevation [Anderson et al., 1973; Le Douaran and Francheteau, 1981; Vogt, 1976; Gente, 1987; Thibaud et al., 1998], geoid topography [Bowin et al., 1984; Cazenave et al., 1992] and geochemical anomalies [Schilling, 1975; White and Schilling,…...
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...Except for the longest and most robust segment centered on 39 N [Detrick et al., 1995; Thibaud et al., 1998], the segmentation along the MAR axis has similar wavelengths and axial relief north and south of the Azores (Figure 2) [Thibaud et al., 1998; Goslin et al., 1999]....
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...…numerous authors to reflect a typical ridge-hot spot interaction because of an elevated spreading ridge [Vogt, 1976; Schilling, 1985; Gente, 1987; Thibaud et al., 1998], basalt geochemistry [Schilling, 1975; White et al., 1976; Bougault and Treuil, 1980; Schilling et al., 1983; Dosso et al.,…...
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TL;DR: In this article, the authors used gravity and bathymetry data collected during the SudAcores cruise (1998) to provide constraints on the rate of propagation of these melt anomalies and on the variations in melt production along the axis and in time.
Abstract: V-shaped ridges propagating along the Mid-Atlantic Ridge axis south of the Azores and Iceland hot spots indicate that ridge-hot spot interactions produce temporal and spatial variations in melt supply to the ridge axis. Estimates of relative crustal thickness variations associated with the ridges south of the Azores hot spots, based on gravity and bathymetry data collected during the SudAcores cruise (1998), provide constraints on the rate of propagation of these melt anomalies and on the variations in melt production along the axis and in time. The maximum apparent crustal thickness along the Azores V ridge is ∼14 km near the Azores, decreasing to normal crustal thickness of ∼6 km toward the south. This crustal thickness variation may be explained by enhanced melt production associated with the propagation of a mantle temperature anomaly that initiated ∼10 Myr ago at the Azores hot spot. The temperature anomaly decreased as it propagated southward, reaching ambient mantle temperatures at the present time at its predicted location under the axis. The excess melt was emplaced on axis forming discrete, shallow (<1000 m) oceanic plateaus (∼100 km in diameter at ∼37.5°N) that are isostatically compensated. The numerous seamounts, lack of normal faults, and smooth basement at the summit of these plateaus suggest high effusion rates that persisted for ∼5 Myr or less, with little or no tectonic strain. As the melt anomaly propagated along axis, the magmatic activity at the plateaus ceased, resulting in rifting of the plateau and onset of normal seafloor spreading. The variations in crustal thickness inferred for the V ridges south of the Azores are at least twice that inferred for the Iceland structures. In both cases the V ridges record temporal variations in temperature and/or mantle flux that affect melt production under the ridge axis, but the fluctuations are larger for the Azores than for the Iceland hot spot.
110 citations
"Interaction between the Mid-Atlanti..." refers background in this paper
...…and thus the thickest crust, are located within the Azores archipelago itself, with a maximum MBA contrast of about 100 mGal between the ridges and adjacent seafloor at the latitudes of Princess Alice Bank [Cannat et al., 1999; Escartin et al., 2001] or Pico and Faial islands [Luis et al., 1998]....
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...…of elevated topography with an overall triangular shape in map-view (Figure 3), including the Azores archipelago itself east of the MAR and the conjugate Faial and Corvo-Flores ridges which extend as far as 36 300N to the south [Vogt, 1976; Cannat et al., 1999; Escartin et al., 2001] (Figure 4)....
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