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
Cites background from "Interaction between the Mid-Atlanti..."
...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
References
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01 Jan 1972
TL;DR: In this article, the authors examined more than 100 fault plane solutions for earthquakes within the Alpide belt between the Mid-Atlantic ridge and Eastern Iran and found that the deformation at present occurring is the result of small continental plates moving away from Eastern Turkey and Western Iran.
Abstract: Summary Examination of more than 100 fault plane solutions for earthquakes within the Alpide belt between the Mid-Atlantic ridge and Eastern Iran shows that the deformation at present occurring is the result of small continental plates moving away from Eastern Turkey and Western Iran. This pattern of movement avoids thickening the continental crust over much of Turkey by consuming the Eastern Mediterranean sea floor instead. The rates of relative motion of two of the small plates involved, the Aegean and the Turkish plates, are estimated, but are only within perhaps 50 per cent of the true values. These estimates are then used to reconstruct the geometry of the Mediterranean 10 million years ago. The principal difference from the present geometry is the smooth curved coast which then formed the southern coast of Yugoslavia, Greece and Turkey. This coast has since been distorted by the motion of the two small plates. Similar complications have probably been common in older mountain belts, and therefore local geological features may not have been formed by the motion between major plates. A curious feature of several of the large shocks for which fault plane solutions could be obtained for the main shock and one major aftershock was that the two often had different mechanisms.
2,378 citations
TL;DR: In this paper, the authors examined more than 100 fault plane solutions for earthquakes within the Alpide belt between the Mid-Atlantic ridge and Eastern Iran and found that the deformation at present occurring is the result of small continental plates moving away from Eastern Turkey and Western Iran.
Abstract: Summary Examination of more than 100 fault plane solutions for earthquakes within the Alpide belt between the Mid-Atlantic ridge and Eastern Iran shows that the deformation at present occurring is the result of small continental plates moving away from Eastern Turkey and Western Iran. This pattern of movement avoids thickening the continental crust over much of Turkey by consuming the Eastern Mediterranean sea floor instead. The rates of relative motion of two of the small plates involved, the Aegean and the Turkish plates, are estimated, but are only within perhaps 50 per cent of the true values. These estimates are then used to reconstruct the geometry of the Mediterranean 10 million years ago. The principal difference from the present geometry is the smooth curved coast which then formed the southern coast of Yugoslavia, Greece and Turkey. This coast has since been distorted by the motion of the two small plates. Similar complications have probably been common in older mountain belts, and therefore local geological features may not have been formed by the motion between major plates. A curious feature of several of the large shocks for which fault plane solutions could be obtained for the main shock and one major aftershock was that the two often had different mechanisms.
2,342 citations
01 Nov 1977
TL;DR: A data set comprising 110 spreading rates, 78 transform fault azimuths, and 142 earthquake slip vectors has been inverted to yield a new instantaneous plate motion model, designated Relative Motion 2 (RM2).
Abstract: A data set comprising 110 spreading rates, 78 transform fault azimuths, and 142 earthquake slip vectors has been inverted to yield a new instantaneous plate motion model, designated Relative Motion 2 (RM2). The model represents a considerable improvement over our previous estimate, RM1 [Minster et al., 1974]. The mean averaging interval for the spreading rate data has been reduced to less than 3 m.y. A detailed comparison of RM2 with angular velocity vectors which best fit the data along individual plate boundaries indicates that RM2 performs close to optimally in most regions, with several notable exceptions. The model systematically misfits data along the India-Antarctica and Pacific-India plate boundaries. We hypothesize that these discrepancies are manifestations of internal deformation within the Indian plate; the data are compatible with northwest-southeast compression across the Ninetyeast Ridge at a rate of about 1 cm/yr. RM2 also fails to satisfy the east-west trending transform fault azimuths observed in the French-American Mid-Ocean Undersea Study area, which is shown to be a consequence of closure constraints about the Azores triple junction. Slow movement between North and South America is required by the data set, although the angular velocity vector describing this motion remains poorly constrained. The existence of a Bering plate, postulated in our previous study, is not necessary if we accept the proposal of Engdahl and others that the Aleutian slip vector data are biased by slab effects. Absolute motion models are derived from several kinematical hypotheses and compared with the data from hot spot traces younger than 10 m.y. Although some of the models are inconsistent with the Wilson-Morgan hypothesis, the overall resolving power of the hot spot data is poor, and the directions of absolute motion for the several slower-moving plates are not usefully constrained.
2,013 citations
"Interaction between the Mid-Atlanti..." refers background in this paper
...Global present-day plate kinematic models of the Azores region imply a right lateral transtensional regime with an extensional component of 3–4 km/Myr [Minster and Jordan, 1978; DeMets et al., 1990]....
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...…in the Indian Ocean and the Tristan da Cunha hot spot in the South Atlantic Ocean, both located in its southern part for ages older than 30 Ma, while only the Reunion hot spot track is used for ages younger than 30 Myr [Minster and Jordan, 1978; Müller et al., 1993a; Gripp and Gordon, 1990, 2002]....
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TL;DR: In this article, a data set comprising 110 spreading rates, 78 transform fault azimuths and 142 earthquake slip vectors was inverted to yield a new instantaneous plate motion model, designated RM2.
Abstract: A data set comprising 110 spreading rates, 78 transform fault azimuths and 142 earthquake slip vectors was inverted to yield a new instantaneous plate motion model, designated RM2. The mean averaging interval for the relative motion data was reduced to less than 3 My. A detailed comparison of RM2 with angular velocity vectors which best fit the data along individual plate boundaries indicates that RM2 performs close to optimally in most regions, with several notable exceptions. On the other hand, a previous estimate (RM1) failed to satisfy an extensive set of new data collected in the South Atlantic Ocean. It is shown that RM1 incorrectly predicts the plate kinematics in the South Atlantic because the presently available data are inconsistent with the plate geometry assumed in deriving RM1. It is demonstrated that this inconsistency can be remedied by postulating the existence of internal deformation with the Indian plate, although alternate explanations are possible.
2,005 citations
TL;DR: In this article, a combination of high-density data from the dense mapping phases of Geosat and ERS 1 along with lower-density but higher-accuracy profiles from their repeat orbit phases is used to construct gravity anomalies from the two vertical deflection grids.
Abstract: Closely spaced satellite altimeter profiles collected during the Geosat Geodetic Mission (-6 km) and the ERS 1 Geodetic Phase (8 km) are easily converted to grids of vertical gravity gradient and gravity anomaly. The long-wavelength radial orbit error is suppressed below the noise level of the altimeter by taking the along-track derivative of each profile. Ascending and descending slope profiles are then interpolated onto separate uniform grids. These four grids are combined to form comparable grids of east and north vertical deflection using an iteration scheme that interpolates data gaps with minimum curvature. The vertical gravity gradient is calculated directly from the derivatives of the vertical deflection grids, while Fourier analysis is required to construct gravity anomalies from the two vertical deflection grids. These techniques are applied to a combination of high-density data from the dense mapping phases of Geosat and ERS 1 along with lower-density but higher-accuracy profiles from their repeat orbit phases. A comparison with shipboard gravity data shows the accuracy of the satellite- derived gravity anomaly is about 4-7 mGal for random ship tracks. The accuracy improves to 3 mGal when the ship track follows a Geosat Exact Repeat Mission track line. These data provide the first view of the ocean floor structures in many remote areas of the Earth. Some applications include inertial navigation, prediction of seafloor depth, planning shipboard surveys, plate tectonics, isostasy of volcanoes and spreading ridges, and petroleum exploration.
1,695 citations
"Interaction between the Mid-Atlanti..." refers background or methods in this paper
...In the Central and North Atlantic near the Azores, their work mostly relies on the studies of Klitgord and Schouten [1986], Müller et al. [1993b], and Srivastava and Tapscott [1986]....
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...This age map had been compiled before the detailed satellite-derived gravity anomaly maps [Sandwell and Smith, 1997] were published, and while the age map of Müller et al. [1997] is a good first-order approximation, a closer look reveals some inconsistencies at a regional scale....
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...Satellitederived free-air gravity anomaly data [Sandwell and Smith, 1997], with regionally homogeneous coverage and quality, are much easier to handle than the uneven shipborne gravity data available...
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...Free air anomaly map of the North Atlantic [Sandwell and Smith, 1997] with locations of the different structures discussed in this paper....
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...A complete reassessment of the magnetic anomalies in the Central and North Atlantic Ocean would therefore be required to derive more accurate plate kinematics around the Azores triple junction....
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