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![Predicted bathymetry of the Foundation Seamount chain [Smith and Sandwell, 1997]. Selected contour interval is 1000 m. The dashed blue isobath depicts the 4000 m depth while the green one represents the 3000 m depth. Volcanoes above 1000 m are colored in dark pink. The location of the Pacific-Antarctic Ridge (PAR) and other ridge axes (red lines) are derived from Lonsdale [1994] and from the interpretation of the bathymetric data collected during the Foundation Hotline cruise [Maia et al., 2000]. Absolute motion vectors were calculated using the HS2-NUVEL-1 model [Gripp and Gordon, 1990]. Blue vectors indicate the absolute motions for Pacific and Antarctic plates, and the orange vector shows the absolute motion of the PAR in the hot spot reference frame. FR, failed rift; SM, Selkirk paleomicroplate; and FZ, fracture zone. Boxes show the limits of the studied areas, depicted in Figures 3 and 6. Some of the volcanoes of the Foundation chain are named (light brown rectangles) to help in the location of the areas discussed in the paper.](profile/Marcia-Maia-3/publication/248820641/figure/fig1/AS:641308578304001@1529911288576/Predicted-bathymetry-of-the-Foundation-Seamount-chain-Smith-and-Sandwell-1997.png)
Predicted bathymetry of the Foundation Seamount chain [Smith and Sandwell, 1997]. Selected contour interval is 1000 m. The dashed blue isobath depicts the 4000 m depth while the green one represents the 3000 m depth. Volcanoes above 1000 m are colored in dark pink. The location of the Pacific-Antarctic Ridge (PAR) and other ridge axes (red lines) are derived from Lonsdale [1994] and from the interpretation of the bathymetric data collected during the Foundation Hotline cruise [Maia et al., 2000]. Absolute motion vectors were calculated using the HS2-NUVEL-1 model [Gripp and Gordon, 1990]. Blue vectors indicate the absolute motions for Pacific and Antarctic plates, and the orange vector shows the absolute motion of the PAR in the hot spot reference frame. FR, failed rift; SM, Selkirk paleomicroplate; and FZ, fracture zone. Boxes show the limits of the studied areas, depicted in Figures 3 and 6. Some of the volcanoes of the Foundation chain are named (light brown rectangles) to help in the location of the areas discussed in the paper.
Source publication
The Foundation Seamounts are a volcanic chain formed during the last 21
m.y. by the action of a hot spot, presently located near the axis of the
Pacific-Antarctic Ridge. The western part of the chain is formed by
volcanoes with ages ranging from 21 to 16 m.y., spatially distributed
along two parallel lines roughly 200 km apart. The shape and
distri...
Contexts in source publication
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... Foundation-PAR system, where a series of narrow, elongated ridges nearly join the PAR axis [Mammerickx, 1992;Devey et al., 1997] and where the geochemical gradient between a plume source and a MORB-type source was clearly established Hékinian et al., 1997], is the best exam- ple of a ridge approaching a hot spot. [4] The Foundation Seamounts (Figure 1) form a volcanic chain located between 338S, 1318W and 388S, 1118W, roughly following the 1008N trend for the absolute motion of the Pacific plate [Mammerickx, 1992]. Ages decrease pro-gressively, from 21 m.y. at the westernmost seamount to very recent ages near the PAR axis [O'Connor et al., 1998]. ...
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... decrease pro-gressively, from 21 m.y. at the westernmost seamount to very recent ages near the PAR axis [O'Connor et al., 1998]. The main body of the chain (Figure 1), between 338S, 1258W and 368S, 1158W is made of well-individualized, elevated volcanoes, sometimes grouped into clusters of two or three edifices . Rocks from these volcanoes display a chemical composition typical of intraplate hot spot samples [Hémond and Devey, 1996;Devey et al., 1997;Hékinian et al., 1997]. ...
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... volcanoes and volcanic ridges are observed over a 300-km-wide area west of this failed axis in what will be called hereafter the ''western province.'' [6] In this paper, we will focus on the analysis of the spatial distribution of trace element and lead isotopes and of geophysical and morphostruc- tural data of both the ''western province'' and the ''ridge-hot spot interaction zone'' (boxes in Figure 1). The main body of the Foundation Seamount chain, located between these two areas and composed of the central volcanoes of the chain, will not be studied in this paper. ...
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... The first volcanoes of the Foundation Sea- mounts are located south of the Resolution fracture zone (FZ) (Figures 1 and 3). Ages decrease from 21 m.y. at Ampère seamount to 16 m.y. at Becquerel seamount [O'Connor et al., 1998] and are consistent with the age regression toward the younger Foundation Sea- mounts to the east. ...
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... whether the westernmost Foundation Seamounts are the product of an incipient hot spot or of the reactivation of an older one, they represent the beginning of an important magmatic pulse of the plume. South of these edifices of the main chain, volcanism is distributed along two different trends (Figures 1 and 3): the Del Cano ridge and a southern E-W line of elongated edifices. ...
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... The Del Cano ridge (Figures 1 and 3) is an elongated high roughly parallel to the direction of the neighboring fracture zones [Mammerickx, 1992;Tebbens and Cande, 1997]. It was inter- preted either as the wall of a fracture zone [Mammerickx, 1992] or as a chain of small off- axis volcanoes following the relative plate motion direction [Tebbens and Cande, 1997]. ...
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... survey reveals that the structure of the Del Cano ridge is far more complex than previously suggested by satellite altimetry, where the ridge appears as a quasi-continuous feature, com- posed of two large segments (Figure 1). Only the eastern segment was surveyed ( Figure 4) 204 Pb ratios are presented. ...
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... The present-day ridge-hot spot interaction zone (Figures 1 and 6) extends 400 km away from the PAR axis and across a 200-90-km- wide band. The edifice morphologies vary, but average summit depths increase toward the PAR while the total volume of the edifices decreases. ...
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... spot interaction: Second magmatic episode [33] Reconstructions using different published rotation poles [Lonsdale, 1988;Yan and Kroenke, 1993;Géli et al., 1999] and ages published by O' Connor et al. [1998] show that all the volcanic constructions of the western area could have been emplaced as the result of the movement of the Pacific plate over a sta- tionary hot spot. Figure 10 shows a possible emplacement sketch of the edifices of the second magmatic phase, which began around 21 m.y. ago at $500 km to the west of the failed rift. ...
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... G 3 G emplaced roughly 500 km away. The nearest active ridge axis, located north of the Resolution fracture zone (Figure 10) was located far away from the hot spot ($300 km). Moreover, the distance between both did not vary significantly during the time of the building of these edifices, and an important variation in distance is required to explain the compositional trend. ...
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... We therefore suggest that the whole area was influenced by the hot spot to various extents ( Figure 11). Ampère seamount, which was located on the northern edge of the hot spot footprint, is derived from an asthenosphere- lithosphere which was moderately contami- nated, probably by some of the first melts released by the plume pulse. ...
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... extended activity would have ceased only when hot-spot-derived material was no longer entrained toward the weak lithospheric zone underneath the failed axis, $9 m.y. ago ( Figure 11). This is consis- tent with the existence of hot spot material channeling as proposed by Schilling [1985Schilling [ , 1991 when a ridge is moving away from a hot spot. ...
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... may have been drained by the slope of the lithosphere for $4 m.y. until the distance between plume and rift was large enough to end the connection. The age of Galilei sea- mount, 9 Ma [O' Connor et al., 1998], 300 km to the east (see Figure 1 for map location), tells us where the plume was located when Buffon's activity ceased. ...
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... observed differences in volume are also consistent with a northerly location of the hot spot, where the most vigo- rous melting regime, and therefore the larger lava production, would have occurred. Figure 12 shows a sketch representing the evolution of the ridge-hot spot interaction over the past 5 ...
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... lack of volcanism north of the northern line could be explained by the presence of the Resolution-Challenger FZ, which could release at least part of the flexural stresses and prevent fracturing of the plate. The sketch presented in Figure 12 also shows that in the past the hot spot could have been located slightly to the south of the northern main volcanic line, there- fore explaining the asymmetry of the flexural arch volcanism. In this case, the double system of the Foundation is analogous to the Taukina- Ngatemato ridges mapped by McNutt et al. [1997] at the southeastern end of the Austral chain. ...
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... Mohorovicic seamount and eastward, lavas become heterogeneous and never as hot-spot- like as those at Mendel. This observation and the kinematic reconstruction ( Figure 12) show that this mixing started only around 4 Ma. A drop of cumulated magmatic volume of the volcanoes, at $2 Ma age of loading, signifies the partial capture of the hot spot magmatic production by the spreading axis. ...
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... The observed chemical pattern of the whole area shows that the interactions between the hot spot and the spreading axis started fairly recently. For example, a volcano as young as Mendel (4.5 Ma) does not show traces of mixing with ridge-derived products. From Mohorovicic seamount and eastward, lavas become heterogeneous and never as hot-spot- like as those at Mendel. This observation and the kinematic reconstruction ( Figure 12) show that this mixing started only around 4 Ma. A drop of cumulated magmatic volume of the volcanoes, at $2 Ma age of loading, signifies the partial capture of the hot spot magmatic production by the spreading axis. This is sup- ported by the observation that the oceanic crust is thicker by 1-1.5 km on the eastern flank of the PAR at least up to 1 Ma [ Maia et al., ...
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... survey reveals that the structure of the Del Cano ridge is far more complex than previously suggested by satellite altimetry, where the ridge appears as a quasi-continuous feature, com- posed of two large segments (Figure 1). Only the eastern segment was surveyed ( Figure 4) 204 Pb ratios are presented. These data were obtained using a Finnigan MAT 261 mass spectrometer in static mode. The measurements were performed from Pb fractions obtained by digestion of sample chips and separation and purification of the Pb using a chemical procedure described by Manhès et al. [1984]. Pb mass fractionation during mass spectrometry analysis was corrected by 0.10%. This value was calculated by comparing the mean of 29 analyses of the NBS 981 standard done during the course of this study and loaded by the same operator with the value of the same standard given by Todt et al. [1996]. Our NBS 981 standard mean was 16.904 ± 0.014 (n = 29 and the error in the 2s of the mean). Pb isotope data represent the average of duplicate or triplicate analyses. A complete isotope data set will be published and discussed in a paper where the isotopic characterization of the Foundation plume will be discussed in full ...
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... We therefore suggest that the whole area was influenced by the hot spot to various extents ( Figure 11). Ampère seamount, which was located on the northern edge of the hot spot footprint, is derived from an asthenosphere- lithosphere which was moderately contami- nated, probably by some of the first melts released by the plume pulse. Ampère lavas could then result from partial melting of this contaminated asthenosphere-lithosphere heated from below. This process may have been ini- tiated through heat transfer from the rising plume to the lithosphere. The first melts derived from the plume are likely to have fertilized the asthenosphere-lithosphere in order to account for the chemical characteristics of the lavas. Aristotelis lavas could be generated by the same process, the seamount being located farther north and consequently less influenced by the hot spot. Becquerel's heterogeneous results may Other numbers represent crustal ages. Active volcanoes are depicted by the red triangles, and extinct ones are painted blue. SM stands for Selkirk paleomicroplate. All vertical and horizontal distances are ...
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... G 3 G emplaced roughly 500 km away. The nearest active ridge axis, located north of the Resolution fracture zone (Figure 10) was located far away from the hot spot ($300 km). Moreover, the distance between both did not vary significantly during the time of the building of these edifices, and an important variation in distance is required to explain the compositional ...
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... The first volcanoes of the Foundation Sea- mounts are located south of the Resolution fracture zone (FZ) (Figures 1 and 3). Ages decrease from 21 m.y. at Ampère seamount to 16 m.y. at Becquerel seamount [O'Connor et al., 1998] and are consistent with the age regression toward the younger Foundation Sea- mounts to the east. Some of the volcanoes tend to form elongated ridges. These westernmost Foundation Seamounts appear to be the oldest volcanoes of the chain since no significant volcanic structures can be clearly identified from satellite maps between them and the Aus- tral chain. A recent work [McNutt et al., 1997] reports ages for volcanic ridges at the south- eastern end of the Austral chain which could be consistent with an ancient activity of the Foun- dation hot spot. Geochemical evidence, such as elevated Pb isotopes, is still required to confirm this. Nevertheless, whether the westernmost Foundation Seamounts are the product of an incipient hot spot or of the reactivation of an older one, they represent the beginning of an important magmatic pulse of the plume. South of these edifices of the main chain, volcanism is distributed along two different trends (Figures 1 and 3): the Del Cano ridge and a southern E-W line of elongated ...
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... The first volcanoes of the Foundation Sea- mounts are located south of the Resolution fracture zone (FZ) (Figures 1 and 3). Ages decrease from 21 m.y. at Ampère seamount to 16 m.y. at Becquerel seamount [O'Connor et al., 1998] and are consistent with the age regression toward the younger Foundation Sea- mounts to the east. Some of the volcanoes tend to form elongated ridges. These westernmost Foundation Seamounts appear to be the oldest volcanoes of the chain since no significant volcanic structures can be clearly identified from satellite maps between them and the Aus- tral chain. A recent work [McNutt et al., 1997] reports ages for volcanic ridges at the south- eastern end of the Austral chain which could be consistent with an ancient activity of the Foun- dation hot spot. Geochemical evidence, such as elevated Pb isotopes, is still required to confirm this. Nevertheless, whether the westernmost Foundation Seamounts are the product of an incipient hot spot or of the reactivation of an older one, they represent the beginning of an important magmatic pulse of the plume. South of these edifices of the main chain, volcanism is distributed along two different trends (Figures 1 and 3): the Del Cano ridge and a southern E-W line of elongated ...
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... Both the size and the anomalous age of Buffon seamount (9 Ma) may be related to its location on a very weak zone of the lithosphere. Its samples present ages which are too young compared to the neighboring edifices [O' Connor et al., 1998]. This is possible only if the samples represent late activity of a volcano whose construction started contemporaneously with the neighboring seamounts, i.e., around 16-13 Ma and/or during the final phase of extension of the failed rift (around 20 Ma). It is indeed possible that this seamount was built during three successive or near-continuous phases of volcanism. This long activity may be linked with the location of Buffon seamount, which sits right on the failed western axis of the Selkirk paleomicroplate. Its extended activity would have ceased only when hot-spot-derived material was no longer entrained toward the weak lithospheric zone underneath the failed axis, $9 m.y. ago ( Figure 11). This is consis- tent with the existence of hot spot material channeling as proposed by Schilling [1985Schilling [ , 1991 when a ridge is moving away from a hot spot. Its chemistry undoubtedly shows input of hot-spot-derived material in its source. Magmas may have been drained by the slope of the lithosphere for $4 m.y. until the distance between plume and rift was large enough to end the connection. The age of Galilei sea- mount, 9 Ma [O' Connor et al., 1998], 300 km to the east (see Figure 1 for map location), tells us where the plume was located when Buffon's activity ...
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... Both the size and the anomalous age of Buffon seamount (9 Ma) may be related to its location on a very weak zone of the lithosphere. Its samples present ages which are too young compared to the neighboring edifices [O' Connor et al., 1998]. This is possible only if the samples represent late activity of a volcano whose construction started contemporaneously with the neighboring seamounts, i.e., around 16-13 Ma and/or during the final phase of extension of the failed rift (around 20 Ma). It is indeed possible that this seamount was built during three successive or near-continuous phases of volcanism. This long activity may be linked with the location of Buffon seamount, which sits right on the failed western axis of the Selkirk paleomicroplate. Its extended activity would have ceased only when hot-spot-derived material was no longer entrained toward the weak lithospheric zone underneath the failed axis, $9 m.y. ago ( Figure 11). This is consis- tent with the existence of hot spot material channeling as proposed by Schilling [1985Schilling [ , 1991 when a ridge is moving away from a hot spot. Its chemistry undoubtedly shows input of hot-spot-derived material in its source. Magmas may have been drained by the slope of the lithosphere for $4 m.y. until the distance between plume and rift was large enough to end the connection. The age of Galilei sea- mount, 9 Ma [O' Connor et al., 1998], 300 km to the east (see Figure 1 for map location), tells us where the plume was located when Buffon's activity ...
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... The Del Cano ridge (Figures 1 and 3) is an elongated high roughly parallel to the direction of the neighboring fracture zones [Mammerickx, 1992;Tebbens and Cande, 1997]. It was inter- preted either as the wall of a fracture zone [Mammerickx, 1992] or as a chain of small off- axis volcanoes following the relative plate motion direction [Tebbens and Cande, ...
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... The spatial distribution and morphological evolution of the volcanic ridges in the youngest part of the Foundation chain show that hetero- geneity in the strength of the lithosphere partly controls the surface expression of the hot spot volcanism. Several observations indicate that the emplacement of the southern volcanic line was controlled by the flexural response of the lithospheric plate to the loading of the northern line. First, the ridges form two subparallel systems, emplaced nearly simultaneously and separated by a distance that decreases toward the PAR. Both systems display the same mor- phological evolution from tall cones to small dome-shaped volcanoes. Edifices belonging to the south system are elongated, suggesting emplacement along fissures or cracks. More- over, the volume of volcanic products differs between the two lines, the southern one being significantly smaller than the northern one. Second, the local maximum of the geoid ( Figure 8) is located over the two smooth ridges of the north line, west of the PAR axis, which strongly implies a location of the Foundation hot spot beneath the north system. This is consistent with the observation that this north system lies in the prolongation of the older seamounts of the chain, while the south line formed only recently (<5 Ma). The observed differences in volume are also consistent with a northerly location of the hot spot, where the most vigo- rous melting regime, and therefore the larger lava production, would have occurred. Figure 12 shows a sketch representing the evolution of the ridge-hot spot interaction over the past ...
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... The present-day ridge-hot spot interaction zone (Figures 1 and 6) extends 400 km away from the PAR axis and across a 200-90-km- wide band. The edifice morphologies vary, but average summit depths increase toward the PAR while the total volume of the edifices decreases. The largest volcanoes are grouped into oblique- striking ridges. Volcanism is organized along two roughly parallel lines, the distance between them diminishing toward the PAR from $130 km to $80 km. A rough estimation of volcanic output volume for the north line yields 2-3 times the volume of the south line, suggesting that the northern line, which lies in the prolon- gation of the older Foundation volcanoes, is the main locus of volcanism. Magnetic modeling of the volcanoes shows that the emplacement of both lines was synchronous and that the edifices become progressively younger toward the PAR, in agreement with published radiometric ages [O' Connor et al., ...
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... lack of volcanism north of the northern line could be explained by the presence of the Resolution-Challenger FZ, which could release at least part of the flexural stresses and prevent fracturing of the plate. The sketch presented in Figure 12 also shows that in the past the hot spot could have been located slightly to the south of the northern main volcanic line, there- fore explaining the asymmetry of the flexural arch volcanism. In this case, the double system of the Foundation is analogous to the Taukina- Ngatemato ridges mapped by McNutt et al. [1997] at the southeastern end of the Austral chain. According to these authors the Taukina ridge was emplaced on the flexural arch of the bending produced by the Ngatemato ridge. It is worth noting that the Taukina is considerably smaller than the Ngatemato ridge in both vol- ume and size of the edifices, in a striking analogy to the differences between the north and the south lines of the ...
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... Plate-hot spot interaction: Second magmatic episode [33] Reconstructions using different published rotation poles [Lonsdale, 1988;Yan and Kroenke, 1993;Géli et al., 1999] and ages published by O' Connor et al. [1998] show that all the volcanic constructions of the western area could have been emplaced as the result of the movement of the Pacific plate over a sta- tionary hot spot. Figure 10 shows a possible emplacement sketch of the edifices of the second magmatic phase, which began around 21 m.y. ago at $500 km to the west of the failed rift. Ampère, Archimidis, as well as Laplace seamounts lie in a trend coherent with the main body of the Foundation chain (Cel- sius-Linnè seamounts, 13-5 Ma age range, [O'Connor et al., 1998]), although Ampère and Archimidis are located slightly north of the hot spot center. Aristotelis, Becquerel, Buf- fon, and Celsius seamounts lie on the northern edge of the hot spot track (see Figure 9). Boltzmann seamount is located near its south- ern edge. The apparent draining of plume material by weak zones inherited from intra- plate deformation can explain the irregularity of the trend as well as the widespread volcanism along this old part of the chain. [34] From the spatial distribution of the (Nb/Zr) N and 206 Pb/ 204 Pb ratios (Figure 4) we can infer that the influence of the hot spot has progres- sively increased between 21 Ma (Ampère) and 13 Ma (Celsius). The compositions of the south- ern seamounts are more enriched than those of the northern ones and suggest that they contain more of the enriched component brought by the plume. This complex pattern cannot result from the decreasing influence on these melts of a neighboring spreading ridge axis as proposed by Devey et al. [1997] and Hékinian et al. [1997,1999]. The Selkirk paleomicroplate western axis was already extinct when most of these volca- noes formed, except for Ampère ...
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... of the interaction processes between mid-oceanic ridges and hot spots have advanced significantly since the early works of Schilling [1973], Vogt [1976], and Morgan and Rodri- guez [1978]. Vogt [1971], Johnson [1975, 1976], and Schilling [1973] discussed the possibilities and implications of a flow along the axis of a mid-oceanic ridge under the influence of an underlying hot spot, while Morgan [1978] suggested that the proximity between a ridge and an off-axis hot spot could generate an asthenospheric flow between the two melting zones. Based on morphological and geochemical (isotopes and trace elements) observations, J.-G. Schilling and coworkers [e.g., Schilling, 1985;Schilling et al., 1985;Hanan et al., 1986] developed the so-called mantle plume source-migrating ridge sink (MPS-MRS) model, where the mid-oceanic ridge acts as a line sink, draining the material of the plume along a sublithospheric channel. For a ridge-centered plume the preferential flow direction is along the axis. When it migrates away from the plume, the ridge continues to be fed by a nonradial flow, directed toward it. According to this model the along-axis exten- sion of the geochemical and topographic anomalies is related to the distance between the hot spot and the spreading center, and the connection could still be effective at distances larger than 1700 km [Schilling, 1985]. Off-axis, volcanism located between the spreading ridge and the plume and showing a linear trend of chemical mixing between the ridge mid-ocean- ridge-basalt-like (MORB-like) pole and the plume source is observed. This suggests that exchanges can occur along the asthenospheric channel linking the ridge and the hot spot [Kingsley and Schilling, 1998;Pan and Batiza, 1998]. The mixing trends were interpreted either as a two-way flux between the plume and the ridge [Haase et al., 1996] or as a mixing between the plume and the asthenospheric materials along the sublithospheric channel, the plume signature being diluted progressively as the distance from the hot spot increases [Kingsley and Schilling, 1998]. Numerical experiments [ Ito et al., 1997;Ribe and Delattre, 1998] showed that the onset of an astheno- spheric flow connecting plume and ridge is strongly controlled by the relative movement between the ridge and the hot spot. In a system where a spreading axis moves toward a mantle plume the additional drag created by the faster plate speed will hinder the connection. On the contrary, in systems where a ridge is moving away from a plume the slower plate speed will contribute to maintain the flow. As a conse- quence, ridge-hot spot interactions in the first case will be delayed, while in the second case, they will remain active at large distances. [3] Linear features and small cones or lava flows grouped along narrow bands support the idea of narrow channels underlying weakened ther- mally thinned plates [Morgan, 1978;Rappaport et al., 1997]. However, all the studied cases considered either the situation of a ridge centered above a plume or of a ridge moving away from a plume. The case of a ridge approaching a hot spot was given much less attention because the only known examples are the Louisville hot spot- Pacific-Antarctic Ridge (PAR) and Foundation hot spot-PAR systems. Recently, the narrow and linear Hollister ridge, thought initially to repre- sent the channeling flow between the Louisville hot spot and the PAR [Small, 1995], was shown to be of a more complex nature [Géli et al., 1999]. Therefore no morphological connection between the Louisville hot spot (the location of which is still controversial [Géli et al., 1999]) and the PAR can be observed on satellite gravity data. The Foundation-PAR system, where a series of narrow, elongated ridges nearly join the PAR axis [Mammerickx, 1992;Devey et al., 1997] and where the geochemical gradient between a plume source and a MORB-type source was clearly established Hékinian et al., 1997], is the best exam- ple of a ridge approaching a hot spot. [4] The Foundation Seamounts (Figure 1) form a volcanic chain located between 338S, 1318W and 388S, 1118W, roughly following the 1008N trend for the absolute motion of the Pacific plate [Mammerickx, 1992]. Ages decrease pro-gressively, from 21 m.y. at the westernmost seamount to very recent ages near the PAR axis [O'Connor et al., 1998]. The main body of the chain (Figure 1), between 338S, 1258W and 368S, 1158W is made of well-individualized, elevated volcanoes, sometimes grouped into clusters of two or three edifices . Rocks from these volcanoes display a chemical composition typical of intraplate hot spot samples [Hémond and Devey, 1996;Devey et al., 1997;Hékinian et al., 1997]. At its eastern end the Foundation chain joins the PAR. Lava compositions show that 400 km away from the PAR axis, near 1158W, hot-spot- and ridge-derived materials start to mix Hémond and Devey, 1996] in what we call the ''ridge-hot spot interaction zone.'' [5] A paleomicroplate is located between 1258 and 1218W [Mammerickx, 1992]. It probably formed between 23.4 and 20 m.y. [Tebbens and Cande, 1997], when the southern Pacific-Far- allon spreading axis propagated northward cre- ating the eastern spreading ridge of the microplate. Its western boundary, the former northern Pacific-Farallon ridge axis, corre- sponds to a failed rift, located near 1258W, where the spreading ceased roughly 20 m.y. ago [Tebbens and Cande, 1997;Blais et al., 1999]. Isolated volcanoes and volcanic ridges are observed over a 300-km-wide area west of this failed axis in what will be called hereafter the ''western province.'' [6] In this paper, we will focus on the analysis of the spatial distribution of trace element and lead isotopes and of geophysical and morphostruc- tural data of both the ''western province'' and the ''ridge-hot spot interaction zone'' (boxes in Figure 1). The main body of the Foundation Seamount chain, located between these two areas and composed of the central volcanoes of the chain, will not be studied in this paper. These volcanoes represent the truly intraplate expres- sion of the Foundation hot spot (see Figure 2 for the composition) and will be the subject of a specific paper. Trace element data will be dis- cussed as (Nb/Zr) N ratios which characterize the nature (enriched or depleted) of the chemical composition of the lavas. 206 Pb/ 204 Pb isotopic ratios will be also used because they are an isotopic tool sensitive to magma mixing and source contamination when dealing with a high-m-(HIMU)-like hot spot such as Foundation [Hémond and Devey, 1996]. This isotopic ratio will be used only to confirm that the variations observed in the (Nb/Zr) N ratio are essentially source features, rather than a magmatic differ- entiation effect (Figure 2). The objectives are twofold. First, to understand the temporal evo- lution of the interaction between the Foundation plume and the lithosphere by analyzing both the spatial distribution of the volcanism and the lithospheric control on the formation of the volcanoes. Second, to understand the temporal evolution of the interaction between the plume, the upper mantle, and the spreading ridge by analyzing the spatial distribution of the lava composition. Finally, the Foundation hot spot- PAR system will be compared with accepted models for ridge-hot spot ...
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... of the interaction processes between mid-oceanic ridges and hot spots have advanced significantly since the early works of Schilling [1973], Vogt [1976], and Morgan and Rodri- guez [1978]. Vogt [1971], Johnson [1975, 1976], and Schilling [1973] discussed the possibilities and implications of a flow along the axis of a mid-oceanic ridge under the influence of an underlying hot spot, while Morgan [1978] suggested that the proximity between a ridge and an off-axis hot spot could generate an asthenospheric flow between the two melting zones. Based on morphological and geochemical (isotopes and trace elements) observations, J.-G. Schilling and coworkers [e.g., Schilling, 1985;Schilling et al., 1985;Hanan et al., 1986] developed the so-called mantle plume source-migrating ridge sink (MPS-MRS) model, where the mid-oceanic ridge acts as a line sink, draining the material of the plume along a sublithospheric channel. For a ridge-centered plume the preferential flow direction is along the axis. When it migrates away from the plume, the ridge continues to be fed by a nonradial flow, directed toward it. According to this model the along-axis exten- sion of the geochemical and topographic anomalies is related to the distance between the hot spot and the spreading center, and the connection could still be effective at distances larger than 1700 km [Schilling, 1985]. Off-axis, volcanism located between the spreading ridge and the plume and showing a linear trend of chemical mixing between the ridge mid-ocean- ridge-basalt-like (MORB-like) pole and the plume source is observed. This suggests that exchanges can occur along the asthenospheric channel linking the ridge and the hot spot [Kingsley and Schilling, 1998;Pan and Batiza, 1998]. The mixing trends were interpreted either as a two-way flux between the plume and the ridge [Haase et al., 1996] or as a mixing between the plume and the asthenospheric materials along the sublithospheric channel, the plume signature being diluted progressively as the distance from the hot spot increases [Kingsley and Schilling, 1998]. Numerical experiments [ Ito et al., 1997;Ribe and Delattre, 1998] showed that the onset of an astheno- spheric flow connecting plume and ridge is strongly controlled by the relative movement between the ridge and the hot spot. In a system where a spreading axis moves toward a mantle plume the additional drag created by the faster plate speed will hinder the connection. On the contrary, in systems where a ridge is moving away from a plume the slower plate speed will contribute to maintain the flow. As a conse- quence, ridge-hot spot interactions in the first case will be delayed, while in the second case, they will remain active at large distances. [3] Linear features and small cones or lava flows grouped along narrow bands support the idea of narrow channels underlying weakened ther- mally thinned plates [Morgan, 1978;Rappaport et al., 1997]. However, all the studied cases considered either the situation of a ridge centered above a plume or of a ridge moving away from a plume. The case of a ridge approaching a hot spot was given much less attention because the only known examples are the Louisville hot spot- Pacific-Antarctic Ridge (PAR) and Foundation hot spot-PAR systems. Recently, the narrow and linear Hollister ridge, thought initially to repre- sent the channeling flow between the Louisville hot spot and the PAR [Small, 1995], was shown to be of a more complex nature [Géli et al., 1999]. Therefore no morphological connection between the Louisville hot spot (the location of which is still controversial [Géli et al., 1999]) and the PAR can be observed on satellite gravity data. The Foundation-PAR system, where a series of narrow, elongated ridges nearly join the PAR axis [Mammerickx, 1992;Devey et al., 1997] and where the geochemical gradient between a plume source and a MORB-type source was clearly established Hékinian et al., 1997], is the best exam- ple of a ridge approaching a hot spot. [4] The Foundation Seamounts (Figure 1) form a volcanic chain located between 338S, 1318W and 388S, 1118W, roughly following the 1008N trend for the absolute motion of the Pacific plate [Mammerickx, 1992]. Ages decrease pro-gressively, from 21 m.y. at the westernmost seamount to very recent ages near the PAR axis [O'Connor et al., 1998]. The main body of the chain (Figure 1), between 338S, 1258W and 368S, 1158W is made of well-individualized, elevated volcanoes, sometimes grouped into clusters of two or three edifices . Rocks from these volcanoes display a chemical composition typical of intraplate hot spot samples [Hémond and Devey, 1996;Devey et al., 1997;Hékinian et al., 1997]. At its eastern end the Foundation chain joins the PAR. Lava compositions show that 400 km away from the PAR axis, near 1158W, hot-spot- and ridge-derived materials start to mix Hémond and Devey, 1996] in what we call the ''ridge-hot spot interaction zone.'' [5] A paleomicroplate is located between 1258 and 1218W [Mammerickx, 1992]. It probably formed between 23.4 and 20 m.y. [Tebbens and Cande, 1997], when the southern Pacific-Far- allon spreading axis propagated northward cre- ating the eastern spreading ridge of the microplate. Its western boundary, the former northern Pacific-Farallon ridge axis, corre- sponds to a failed rift, located near 1258W, where the spreading ceased roughly 20 m.y. ago [Tebbens and Cande, 1997;Blais et al., 1999]. Isolated volcanoes and volcanic ridges are observed over a 300-km-wide area west of this failed axis in what will be called hereafter the ''western province.'' [6] In this paper, we will focus on the analysis of the spatial distribution of trace element and lead isotopes and of geophysical and morphostruc- tural data of both the ''western province'' and the ''ridge-hot spot interaction zone'' (boxes in Figure 1). The main body of the Foundation Seamount chain, located between these two areas and composed of the central volcanoes of the chain, will not be studied in this paper. These volcanoes represent the truly intraplate expres- sion of the Foundation hot spot (see Figure 2 for the composition) and will be the subject of a specific paper. Trace element data will be dis- cussed as (Nb/Zr) N ratios which characterize the nature (enriched or depleted) of the chemical composition of the lavas. 206 Pb/ 204 Pb isotopic ratios will be also used because they are an isotopic tool sensitive to magma mixing and source contamination when dealing with a high-m-(HIMU)-like hot spot such as Foundation [Hémond and Devey, 1996]. This isotopic ratio will be used only to confirm that the variations observed in the (Nb/Zr) N ratio are essentially source features, rather than a magmatic differ- entiation effect (Figure 2). The objectives are twofold. First, to understand the temporal evo- lution of the interaction between the Foundation plume and the lithosphere by analyzing both the spatial distribution of the volcanism and the lithospheric control on the formation of the volcanoes. Second, to understand the temporal evolution of the interaction between the plume, the upper mantle, and the spreading ridge by analyzing the spatial distribution of the lava composition. Finally, the Foundation hot spot- PAR system will be compared with accepted models for ridge-hot spot ...
Context 32
... of the interaction processes between mid-oceanic ridges and hot spots have advanced significantly since the early works of Schilling [1973], Vogt [1976], and Morgan and Rodri- guez [1978]. Vogt [1971], Johnson [1975, 1976], and Schilling [1973] discussed the possibilities and implications of a flow along the axis of a mid-oceanic ridge under the influence of an underlying hot spot, while Morgan [1978] suggested that the proximity between a ridge and an off-axis hot spot could generate an asthenospheric flow between the two melting zones. Based on morphological and geochemical (isotopes and trace elements) observations, J.-G. Schilling and coworkers [e.g., Schilling, 1985;Schilling et al., 1985;Hanan et al., 1986] developed the so-called mantle plume source-migrating ridge sink (MPS-MRS) model, where the mid-oceanic ridge acts as a line sink, draining the material of the plume along a sublithospheric channel. For a ridge-centered plume the preferential flow direction is along the axis. When it migrates away from the plume, the ridge continues to be fed by a nonradial flow, directed toward it. According to this model the along-axis exten- sion of the geochemical and topographic anomalies is related to the distance between the hot spot and the spreading center, and the connection could still be effective at distances larger than 1700 km [Schilling, 1985]. Off-axis, volcanism located between the spreading ridge and the plume and showing a linear trend of chemical mixing between the ridge mid-ocean- ridge-basalt-like (MORB-like) pole and the plume source is observed. This suggests that exchanges can occur along the asthenospheric channel linking the ridge and the hot spot [Kingsley and Schilling, 1998;Pan and Batiza, 1998]. The mixing trends were interpreted either as a two-way flux between the plume and the ridge [Haase et al., 1996] or as a mixing between the plume and the asthenospheric materials along the sublithospheric channel, the plume signature being diluted progressively as the distance from the hot spot increases [Kingsley and Schilling, 1998]. Numerical experiments [ Ito et al., 1997;Ribe and Delattre, 1998] showed that the onset of an astheno- spheric flow connecting plume and ridge is strongly controlled by the relative movement between the ridge and the hot spot. In a system where a spreading axis moves toward a mantle plume the additional drag created by the faster plate speed will hinder the connection. On the contrary, in systems where a ridge is moving away from a plume the slower plate speed will contribute to maintain the flow. As a conse- quence, ridge-hot spot interactions in the first case will be delayed, while in the second case, they will remain active at large distances. [3] Linear features and small cones or lava flows grouped along narrow bands support the idea of narrow channels underlying weakened ther- mally thinned plates [Morgan, 1978;Rappaport et al., 1997]. However, all the studied cases considered either the situation of a ridge centered above a plume or of a ridge moving away from a plume. The case of a ridge approaching a hot spot was given much less attention because the only known examples are the Louisville hot spot- Pacific-Antarctic Ridge (PAR) and Foundation hot spot-PAR systems. Recently, the narrow and linear Hollister ridge, thought initially to repre- sent the channeling flow between the Louisville hot spot and the PAR [Small, 1995], was shown to be of a more complex nature [Géli et al., 1999]. Therefore no morphological connection between the Louisville hot spot (the location of which is still controversial [Géli et al., 1999]) and the PAR can be observed on satellite gravity data. The Foundation-PAR system, where a series of narrow, elongated ridges nearly join the PAR axis [Mammerickx, 1992;Devey et al., 1997] and where the geochemical gradient between a plume source and a MORB-type source was clearly established Hékinian et al., 1997], is the best exam- ple of a ridge approaching a hot spot. [4] The Foundation Seamounts (Figure 1) form a volcanic chain located between 338S, 1318W and 388S, 1118W, roughly following the 1008N trend for the absolute motion of the Pacific plate [Mammerickx, 1992]. Ages decrease pro-gressively, from 21 m.y. at the westernmost seamount to very recent ages near the PAR axis [O'Connor et al., 1998]. The main body of the chain (Figure 1), between 338S, 1258W and 368S, 1158W is made of well-individualized, elevated volcanoes, sometimes grouped into clusters of two or three edifices . Rocks from these volcanoes display a chemical composition typical of intraplate hot spot samples [Hémond and Devey, 1996;Devey et al., 1997;Hékinian et al., 1997]. At its eastern end the Foundation chain joins the PAR. Lava compositions show that 400 km away from the PAR axis, near 1158W, hot-spot- and ridge-derived materials start to mix Hémond and Devey, 1996] in what we call the ''ridge-hot spot interaction zone.'' [5] A paleomicroplate is located between 1258 and 1218W [Mammerickx, 1992]. It probably formed between 23.4 and 20 m.y. [Tebbens and Cande, 1997], when the southern Pacific-Far- allon spreading axis propagated northward cre- ating the eastern spreading ridge of the microplate. Its western boundary, the former northern Pacific-Farallon ridge axis, corre- sponds to a failed rift, located near 1258W, where the spreading ceased roughly 20 m.y. ago [Tebbens and Cande, 1997;Blais et al., 1999]. Isolated volcanoes and volcanic ridges are observed over a 300-km-wide area west of this failed axis in what will be called hereafter the ''western province.'' [6] In this paper, we will focus on the analysis of the spatial distribution of trace element and lead isotopes and of geophysical and morphostruc- tural data of both the ''western province'' and the ''ridge-hot spot interaction zone'' (boxes in Figure 1). The main body of the Foundation Seamount chain, located between these two areas and composed of the central volcanoes of the chain, will not be studied in this paper. These volcanoes represent the truly intraplate expres- sion of the Foundation hot spot (see Figure 2 for the composition) and will be the subject of a specific paper. Trace element data will be dis- cussed as (Nb/Zr) N ratios which characterize the nature (enriched or depleted) of the chemical composition of the lavas. 206 Pb/ 204 Pb isotopic ratios will be also used because they are an isotopic tool sensitive to magma mixing and source contamination when dealing with a high-m-(HIMU)-like hot spot such as Foundation [Hémond and Devey, 1996]. This isotopic ratio will be used only to confirm that the variations observed in the (Nb/Zr) N ratio are essentially source features, rather than a magmatic differ- entiation effect (Figure 2). The objectives are twofold. First, to understand the temporal evo- lution of the interaction between the Foundation plume and the lithosphere by analyzing both the spatial distribution of the volcanism and the lithospheric control on the formation of the volcanoes. Second, to understand the temporal evolution of the interaction between the plume, the upper mantle, and the spreading ridge by analyzing the spatial distribution of the lava composition. Finally, the Foundation hot spot- PAR system will be compared with accepted models for ridge-hot spot ...
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... We also used two additional geyserite opal-A samples (sample 85.27 from White Terrace, New Zealand) and opal-CT (sample 24.349 from Reykjanes, Iceland). Nine additional samples are volcanic glasses: Gi1900 and Obs_3 (Mexico), Obs_2 (Iceland), Obs_1 (unknown provenance), WD3 (dacitic glass, Milos, Greece), SO100-86DS and SO100-91DS and SO100-92DS (andesitic glasses from the Pacific-Antarctic Ridge, for more information see Maia et al., 2001 andFreund et al., 2013 studies) and Shosho (highly alkaline felsic glass of the shoshonitic series, Argentina; for more information on shoshonitic rock associations see Morrison, 1980 paper). Chemical analyses are available in Annex 1, for samples Obs_3, SO100-86DS, SO100-91DS, SO100-92DS, and Shosho. ...
... J o u r n a l P r e -p r o o f 2 for more information see Maia et al. (2001), Freund et al. (2013) and Annex 1 * samples used for FTIR measurements at Mars-relevant atmospheric pressure ...
Hydrated silica detected on the martian surface, from both orbital and in-situ data, is an indicator of past aqueous conditions. On Earth, several near infrared (NIR) spectral criteria can be used to discriminate silica phases (e.g. opal-A, opal-CT and chalcedony) and their formation processes. We have applied these spectral criteria to Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data in order to investigate the geological origin of hydrated silica on Mars. We used two spectral criteria: (i) the crystallinity spectral criteria on the 1.4- and 1.9 μm absorption bands to distinguish between amorphous (opal-A and hydrated glasses) and more crystalline (opal-CT and chalcedony) varieties of silica, and (ii) the Concavity-Ratio-Criterion (CRC) to differentiate opals of hydrothermal origin from weathering origin. We first adapted the CRC measurements on terrestrial samples to make them comparable to CRISM measurements on Mars: we resampled our terrestrial spectra down to the CRISM resolution, and tested the martian pressure effect on spectral signatures. Then, we selected several areas over nine sites where hydrated silica has been detected on Mars, on the basis of good quality detections. Our results show that two main types of spectra can be distinguished, and these are consistent with two distinct geomorphological contexts proposed by Sun and Milliken (2018): amorphous and/or dehydrated silica-bearing bedrock deposits, and more crystalline and/or hydrated silica-bearing aeolian deposits. The concavity criterion also indicates silica origins that are in agreement with most of the hypothesized geological origins proposed in the literature. Although these results need further strengthening, they are promising for the use of NIR signatures as means of investigating the processes of hydrated silica on Mars.
... Indeed, maximum interaction distance is predicted to be higher for a ridge receding from a plume than for a ridge approaching a plume (Ito et al., 1997;Ribe & Delattre, 1998;Schilling, 1985). Studies of the interaction between the Foundation Seamounts mantle plume and the Pacific-Antarctic ridge where the ridge is currently approaching the plume confirm the model results (Maia et al., 2000(Maia et al., , 2001. Consequently, for a given plume-ridge distance, the connection is stronger (i.e., more plume material reaches the axis) when the ridge is migrating away from the plume and this will generate a thicker crust. ...
The Amsterdam‐St. Paul (ASP) Plateau formed by interaction between the South East Indian Ridge (SEIR) and the ASP mantle plume during the last 10 Myr. The combined bathymetry and gravity‐derived crustal thickness anomalies along the present and paleoaxes of the SEIR atop the plateau indicate: (1) a thicker crust and shallower water depth along the southern part of segment I2 during much of the last 10 Myr; (2) an earlier decrease (~1.4 Ma) in crustal thickness along the southern part of I2 compared to the northern part (~0.9 Ma) during the most recent period of reduced magmatism; (3) a topographic transition at ~0.7 Ma and during the last 0.1 Myr; and (4) an approximately uniform crustal thickness (8 km) along the entire I2 segment today. These observations require spatial and temporal variations in magma production during construction of the ASP Plateau over the last 3 Myr. We propose that during periods of weaker plume magma flux, spatial variations in upper mantle temperature and composition are small, and lead to small variations in crustal thickness along‐axis. In contrast, during periods of stronger plume magma flux, spatial contrasts in upper mantle temperature and composition (fertility) are large, leading to significant variations in crustal thickness. Along‐axis variations of ³He/⁴He, Δ8/4Pb, K/Ti, and Na8 in “zero‐age” basalts indicate that there is a gradient in the underlying mantle material, from a “common” mantle plume component (Δ8/4Pb~60) stronger in the north to a DUPAL component (Δ8/4Pb~110) dominating in the south.
... Melts sampling EM (Enriched Mantle) reservoirs are known to be depleted in H 2 O and Cl relative to lithophile elements of similar mantle incompatibility, consistent with the presence of dehydrated sediment or continental crustal material in EM sources 2,4,[11][12][13] . However, the volatile content of the HIMU mantle end-member and the relative proportions of recycled versus primordial water in the mantle remain poorly constrained 2,4,[11][12][13][14][15] . ...
... The current study combines new and published F, Cl, Br, I and H 2 O analyses for a suite of globally distributed submarine glasses representing melts formed from all the major mantle end-member reservoirs (Figs 1 and S1, electronic supplement). The new samples include submarine HIMU glasses dredged from around St Helena Island in the southern Atlantic 9,14 , and from the Foundation Seamount chain in the SE Pacific 15 . The latter samples show variable trace element and 206 Pb/ 204 Pb enrichment that result from interaction between the Foundation HIMU component and the Pacific Antarctic Ridge (Fig 1) 15,16 . ...
... The new samples include submarine HIMU glasses dredged from around St Helena Island in the southern Atlantic 9,14 , and from the Foundation Seamount chain in the SE Pacific 15 . The latter samples show variable trace element and 206 Pb/ 204 Pb enrichment that result from interaction between the Foundation HIMU component and the Pacific Antarctic Ridge (Fig 1) 15,16 . New glasses were also selected from the East Pacific Rise, Mid Atlantic Ridge, Southwest and Southeast Indian Ocean Ridges, Ontong Java Plateau and Reunion Island. ...
The extent to which water and halogens in Earth’s mantle have primordial origins, or are dominated by seawater-derived components introduced by subduction is debated. About 90% of non-radiogenic xenon in the Earth’s mantle has a subducted atmospheric origin, but the degree to which atmospheric gases and other seawater components are coupled during subduction is unclear. Here we present the concentrations of water and halogens in samples of magmatic glasses collected from mid-ocean ridges and ocean islands globally. We show that water and halogen enrichment is unexpectedly associated with trace element signatures characteristic of dehydrated oceanic crust, and that the most incompatible halogens have relatively uniform abundance ratios that are different from primitive mantle values. Taken together, these results imply that Ear th’s mantle is highly processed and that most of its water and halogens were introduced by the subduction of serpentinized lithospheric mantle associated with dehydrated oceanic crust
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... The geochemical features of the northern zone are thus susceptible to result from a localized plume-ridge interaction. Maia et al. (2001) Chauvel et al. (1992) and Rehkamper and Hofmann (1997). Between 58 and 98 % of Pb must be lost during slab dehydration to generate the high 206 Pb/ 204 Pb with time (Chauvel et al., 1992;Kelley et al., 2005). ...
To better address how Mid-Ocean Ridge Basalt (MORB) sulfur isotope composition can be modified by assimilation and/or by immiscible sulfide fractionation, we report sulfur (S), chlorine (Cl) and copper (Cu) abundances together with multiple sulfur isotope composition for 38 fresh basaltic glasses collected on the Pacific-Antarctic ridge. All the studied glasses - with the exception of 8 off-axis samples - exhibit relatively high Cl/K, as the result of pervasive Cl-rich fluid assimilation. This sample set hence offers an opportunity to document both the upper mantle S isotope composition and the effect of hydrothermal fluids assimilation on the S isotope composition of erupted basalts along segments that are devoid of plume influence.
... The summit trough is approximately 200 m wide with abundant signs of recent volcanic and hydrothermal activities (Lonsdale, 1994;Hekinian et al., 1997). The time-progressive Foundation seamount chain intersects the PAR between~37 and~38°S, probably reflecting the interaction of the PAR with a deep mantle plume (O'Connor et al., 1998;Maia et al., 2001). The PAR lavas close to the Foundation seamounts are slightly enriched in incompatible elements but towards the south, the compositions progressively change to depleted MORB with distance from the intersection with the hotspot (Hekinian et al., 1997;Hekinian et al., 1999). ...
... The PAR lavas show a significant range of Nd isotopes, Nb/Zr and (Ce/Yb) N ratios with the lavas closest to the Foundation Seamount being most enriched in terms of incompatible elements (Figs. 2, 6). This systematic variation along the PAR reflects the inflow of enriched material from the Foundation plume (Hekinian et al., 1997(Hekinian et al., , 1999Maia et al., 2001). However, although the samples along the 300 km long portion of the PAR have different mantle sources, we find that basaltic and evolved lavas occurring in close proximity have similar sources as reflected by similar Nd isotope ratios. ...
... The clinopyroxenes in the evolved lavas are in disequilibrium with the liquid composition (glass) and thus cannot be used for thermobarometry. The barometric results indicate that the basaltic melts started crystallising at 9 (±3) km depth which is in agreement with a slightly thickened crust of 9 km at 37°S due to the increased melt production close to the Foundation Hotspot (Maia et al., 2001). We suggest therefore, that the basaltic liquids stagnate in a deep melt lens, fractionate olivine, plagioclase and clinopyroxene, and periodically inject melts into shallower levels in the crust where AFC leads to the formation of the FeTi basalts towards silicic magmas. ...
... For Gente et al. (2003), the plateau results from the interaction between the MAR and the plume, followed by the progressive southward rifting of the plateau after 7 Ma. According to different authors the beginning of the enhanced volcanism occurred around 10 Ma, and ended between 3 and 7 Ma depending upon latitude (Cannat et al., 1999; Escartín et al., 2001; Gente et al., 2003; Maia et al., Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/epsl 2001). ...
... [3] The plume/ridge interactions can be described by three successive and possible geometries: (1) a ridge approaching a plume, (2) a ridge above a plume, and (3) a ridge moving away from a plume. The latter geometry has long-term consequences on the interaction dynamics as ridge and plume melting zones may remain connected for a long time [Ito et al., 1997;Ribe and Delattre, 1998;Maia et al., 2001]. When a ridge is located above a plume, the excess heat results in enhanced melting and longer and more voluminous magmatic production. ...
... [9] Literature data belong to the most recent part of the ASP plateau (ridge axis, islands and nearby seamounts [Graham et al., 1999;Burnard et al., 2002;Doucet et al., 2004;Nicolaysen et al., 2007]) whereas the ASP hot spot/SEIR interaction system results from a much longer period of activity of the plateau (presently in the early stage of breakup [Maia et al., 2001]). The Chain of Dead Poets (CDP) may also be due to ASP hot spot activity and has to be taken into account to understand the dynamics of such interaction and its evolution. ...
The Amsterdam-St Paul (ASP) oceanic plateau results from the interaction
between the ASP hot spot and the Southeast Indian ridge. A volcanic
chain, named the Chain of the Dead Poets (CDP), lies to its northward
tip and is related to the hot spot intraplate activity. The ASP plateau
and CDP study reveals that ASP plume composition is inherited from
oceanic crust and pelagic sediments recycled in the mantle through a 1.5
Ga subduction process. The ASP plateau lavas have a composition (major
and trace elements and Sr-Nd-Pb-Hf isotopes) reflecting the interaction
between ASP plume and the Indian MORB mantle, including some clear DUPAL
input. The Indian upper mantle below ASP plateau is heterogeneous and
made of a depleted mantle with lower continental crust (LCC) fragments
probably delaminated during the Gondwana break-up. The lower continental
crust is one of the possible reservoirs for the DUPAL anomaly origin
that our data support. The range of magnitude of each end-member
required in ASP plateau samples is (1) 45% to 75% of ASP plume and (2)
25% to 55% of Indian DM within 0% to a maximum of 6% of LCC layers
included within. The three end-members involved (plume, upper mantle and
lower continental crust) and their mixing in different proportions
enhances the geochemical variability in the plateau lavas. Consequently,
the apparent composition homogeneity of Amsterdam Island, an aerial
summit of the plateau, may result from the presence of intermediate
magmatic chambers into the plateau structure.
... (Small, 1995). Le cas de dorsale s'approchant d'un point chaud est moins commun, et concerne par exemple le système de Fondation Maia et al. (2000Maia et al. ( , 2001. L'exemple le plus étudié du cas de la dorsale à l'aplomb du point chaud est celui de l'Islande (Schilling, 1973;Vogt, 1976). ...
... la Réunion) résultant en des anomalies plus faibles au niveau de l'axe de la dorsale. Ainsi, selon Goslin et al. (1998) dans les systèmes d'interaction entre points chauds et dorsales (Small, 1995;Maia et al., 2000Maia et al., , 2001Shorttle et al., 2010). ...
... Le magma du point chaud est contaminé par celui de la dorsale, la signature géochimique des roches est une mélange entre le pôle de type OIB du point chaud et celui de type N-MORB de la dorsale (Schilling, 1991). Comme observé dans le système Fondation -dorsale Pacifique-Antartique (Maia et al., 2000(Maia et al., , 2001 ; Étape 3, la dorsale est à l'aplomb du point chaud. L'excès de magmatisme dû au flux thermique du point chaud occasionne un fort épaississement crustal, ce qui résulte potentiellement en un plateau axial ou même une île volcanique. ...
In this work we have studied the space and time evolution of the Tristan hotspot and south Mid-Atlantic Ridge interaction system. The Tristan hotspot and its associated bathymetrical features (i.e. Walvis Ridge in the African plate and Rio Grande Rise in the South American plate) are ones of the most significant features of the South Atlantic Ocean. However, this system is not as well studied as the systems in the North Atlantic (e.g. Azores and Iceland), and their origin and evolution is an open subject. Data compilation of the available surveys from the National Geophysical Data Center (NGDC) and satellite-derived bathymetry were treated to generate a Digital Elevation Model (DEM) for the entire South Atlantic Ocean. Satellite-derived free-air anomaly data and sediment thickness data were used to calculate the mantle Bouguer anomaly (MBA) and digital isochrons of the ocean floor were used to calculate the residual mantle Bouguer anomaly (RMBA), residual bathymetry and new poles for the South America and Africa relative plate motions. Satellite-derived geoid data and the Earth Gravitational Model - EGM2008 were used for the separation of the different components in the geoid data with the calculation of filters using different levels and degree of spherical harmonics. From kinematic reconstructions based on new rotation poles calculated in this work and using the most accepted hypothesis for the current position of the hotspot, as the volcanic island of Tristan da Cunha, the chronology of the emplacement of the volcanic structures could be detailed. This highlighted the existence of several axes jumps and periodic variations in the magma supply to the axis resulting in a periodic alternation between periods of construction and axial ruptures of the axial plateau. The detailed comparison of the estimated position for the Tristan da Cunha hotspot and the location of the volcanic structures of the Walvis Ridge whose ages are known, underlined that the formation of the Walvis Ridge cannot be explained in its entirety by the evolution model involving an interaction between the South Atlantic Mid Ocean Ridge and a hotspot whose current position is in the island of Tristan da Cunha. Next, we evaluated the temporal evolution of the influence of the hotspot to the South Atlantic Mid-Ocean Ridge axis with respect to changes in the residual bathymetry (RB) and the residual mantle Bouguer anomaly (RMBA) with the analysis of variations in the spreading rate and the hotspot-ridge distance. For the early stages of the South Atlantic opening, the RMBA and BR anomalies are stronger for the African plate then for the South American plate. This suggests that the position of the hotspot was beneath the African plate since the beginning of the opening of the South Atlantic Ocean. In summary, there are three different periods for the Tristan da Cunha hotspot and South Atlantic Mid-Ocean Ridge interaction system. A period of rapprochement of the ridge to the hotspot between 115 Ma and 100 Ma, in which it is observed the influence of the hotspot on the ridge axis for at least the distance of 150 km. Then, between 95 Ma and 60 Ma, we observed that the ridge is directly above or very close (<50 km) of the hot spot. Then, since 60 Ma, it is observed a gradual and progressive separation of the ridge from the hotspot position. Have been shown that in periods of rapprochement and ridge directly above of the hotspot the observed periodic variations of the magmatic contribution are related to changes in the flux of the plume. From the analysis of the evolution of volcanic structures, together with the free-air anomaly and geochemistry data, the volcanic structures have been divided into two groups. A group formed by the NW border of the Walvis Ridge was called first phase, consistent with the evolution of structures from a context of the mid-ocean ridge directly above the hotspot to the emplacement of the intraplate situation, in agreement with the three periods, rapprochement, directly above and displacement, as described above. The other group, formed by the SE border of the Walvis Ridge was called second phase and shows a gravity signature that is characteristic of intraplate setting up even for structures with ages in which the position of the mid-ocean ridge was directly above the hotspot. The two groups have different geochemical signatures, Zr/Nd ratio and Ti abundance. Then, from the comparative analysis of different degrees of spherical harmonics of the geoid and the new results available in the literature for the seismic tomography, we have shown the existence of an deep association between the plume responsible for the volcanic structures of the Rio Grande Rise and Walvis ridge with the African superplume. The identification of three mantle anomalies close to the islands of Gough and RSA seem a better alternative for the hotspot actual position than the location of the island of Tristan da Cunha accepted today.
... The ridge absolute migration rate (relative velocity between the ridge and the hot spot) can also be an important factor. A fast migration rate, when the ridge is moving toward the hot spot, can result in the overriding plate dragging part of the hot spot material away from the ridge [Ribe and Delattre, 1998;Maia et al., 2000Maia et al., , 2001, thus reducing the amount of excess melting at the axis and reducing or delaying the possibility of plateau formation. A subsidiary question concerns the early phase of the interaction between the ridge and the hot spot. ...
... A subsidiary question concerns the early phase of the interaction between the ridge and the hot spot. Studies of a fast ridge rapidly migrating toward a hot spot show that off-axis volcanoes may be present very close to the ridge axis [Maia et al., 2000[Maia et al., , 2001. The absence of other studies, covering different spreading rates or ridge migration rates, prevents a thorough understanding of the transition between the intraplate phase, characterized by the building of off-axis volcanoes, and the axial phase, when the hot spot influence at the ridge axis increases, with or without construction of a plateau. ...
... [28] Plateaus are built when enough hot spot material is drained toward the ridge axis to allow a large increase of crust production. The connection is established when the two melting zones are close enough to interact or when the slope at the base of the lithosphere becomes steep enough to act as a drain [Maia et al., 2001;Sleep, 2002]. The distance at which it begins relates to the size of the hot spot source and to both the ridge spreading rate (which shapes the slope of the bottom of the lithosphere) and the velocity of the ridge-hot spot relative movement. ...
The Amsterdam-Saint Paul plateau results from a 10 Myr interaction between the South East Indian Ridge and the Amsterdam-Saint Paul hot spot. During this period of time, the structure of the plateau changed as a consequence of changes in both the ridge-hot spot relative distance and in the strength of the hot spot source. The joint analysis of gravity-derived crust thickness and bathymetry reveals that the plateau started to form at ∼10 Ma by an increase of the crustal production at the ridge axis, due to the nearby hot spot. This phase, which lasted 3-4 Myr, corresponds to a period of a strong hot spot source, maybe due to a high temperature or material flux, and decreasing ridge-hot spot distance. A second phase, between ∼6 and ∼3 Ma, corresponds to a decrease in the ridge crustal production. During this period, the hot spot center was close to the ridge axis and this reduced magmatic activity suggests a weak hot spot source. At ∼3 Ma, the ridge was located approximately above the hot spot center. An increase in the hot spot source strength then resulted in the building of the shallower part of the plateau. The variations of the melt production at the ridge axis through time resulted in variations in crustal thickness but also in changes in the ridge morphology. The two periods of increased melt production correspond to smooth ridge morphology, characterized by axial highs, while the intermediate period corresponds to a rougher, rift-valley morphology. These variations reveal changes in axial thermal structure due to higher melting production rates and temperatures.
... Concurrently, the Foundation lavas became both progressively depleted in most mantle incompatible elements (reaching values even lower than local MORB) and lost their primitive He and Ne isotope signatures ( Fig. 1; Supplementary Tables S1 and S2). Sr, Nd and Pb isotope ratios, in contrast, show no equivalent pattern 15 . ...
... If similar mixing processes were occurring beneath the near-axis seamounts then they should show similar He and Ne isotope patterns, which they do not. To produce He and Ne isotopic patterns showing no evidence of the plume endmember, the He and Ne contents of the plume melt contributing to the near-axis seamount magmas must be lower than those in the on-axis magmas, as the amount of plume material in near-axis magmas is larger or at least similar (as indicated by the Pb isotope values of both systems [15][16][17] to that in the on-axis magmas. There are three possible methods to lower He and Ne contents of a melt before mixing: (1) higher melting degrees, (2) magmatic degassing and (3) prior melting leaving a depleted residue. ...
Lavas erupted within plate interiors above upwelling mantle plumes have chemical signatures that are distinct from mid-ocean ridge lavas. When a plume interacts with a mid-ocean ridge, the compositions of both their lavas changes, but there is no consensus as to how this interaction occurs. For the past 15Myr, the Pacific-Antarctic mid-ocean ridge has been approaching the Foundation hotspot and erupted lavas have formed seamounts. Here we analyse the noble gas isotope and trace element signature of lava samples collected from the seamounts. We find that both intraplate and on-axis lavas have noble gas isotope signatures consistent with the contribution from a primitive plume source. In contrast, near-axis lavas show no primitive noble gas isotope signatures, but are enriched in strontium and lead, indicative of subducted former oceanic lower crust melting within the plume source. We propose that, in a near-ridge setting, primitive, plume-sourced magmas formed deep in the plume are preferentially channelled to and erupted at the ridge-axis. The remaining residue continues to rise and melt, forming the near-axis seamounts. With the deep melts removed, the geochemical signature of subduction contained within the residue becomes apparent. Lavas with strontium and lead enrichments are found worldwide where plumes meet mid-ocean ridges, suggesting that subducted lower crust is an important but previously unrecognised plume component.
