Paweł Boroń

Lucjan Chmielarz
email: chmielar@chemia.uj.edu.pl

Stanislaw Dzwigaj
email: stanislaw.dzwigaj@upmc.fr

Influence of Cu on the catalytic activity of FeBEA zeolites in SCR of NO with NH 3

Keywords: iron, copper, BEA zeolite, ammonia, SCR of NO

fx1 Highlights  Cu and Fe were incorporated into BEA framework as shown by XRD and DR UV-vis.  In FeSiBEA and CuSiBEA mainly pseudo-tetrahedral Fe(III) and Cu(II) were formed.

 These catalysts showed very high activity in SCR of NO with NH 3 .

 100 % NO conversion and 90 % selectivity toward N 2 at 450-700 K were observed.

 Introduction of Cu in FeBEA had a significant influence on the catalytic activity.

Introduction

Worldwide environmental regulations regarding NO x emissions from diesel engines have become significantly more stringent leading to innovative applications of new technologies to resolve this environmental problem. As a potent technology, the selective catalytic reduction (SCR) of NO has been studied intensively [1][2][3][4]. Iron and copper based zeolite catalysts are widely employed in selective catalytic reduction of NO with ammonia due to their high temperature durability compared to vanadium based catalysts [5].

Hence, the focus has shifted to the Fe-and Cu-based zeolite catalysts, both of which have demonstrated very high NO reduction efficiencies at high space velocities. The Cu-based catalysts are particularly effective at lower temperatures (< 620 K) [6,7]. Moreover, NO removal efficiencies over the Cu-based catalysts are found to be rather insensitive of the amount of NO 2 in the feed at lower temperatures [7]. On the other hand, the Fe-based catalysts are active at higher temperatures (> 620 K) and give very high NO reduction efficiencies even at very high temperatures (up to 870-970 K) [8,9]. Given the differences in activities of the Cu-and Fe-based catalysts, it seems plausible that a combination of the Fezeolite and Cu-zeolite catalysts might achieve high NO conversions over a broader temperature range than the individual catalysts.

A few literature studies considered such combined Fe-and Cu-zeolite systems [10,11,12,13]. Metkar et al. [10,11] studied the combined Fe-and Cu-zeolite monolithic catalysts. The Fe/Cu dual layer catalyst exhibited superior performance for the SCR reaction.

Krocher and Elsener [12], who studied double bed catalytic reactors for the SCR reaction, have found that a Fe-zeolite section followed by a Cu-zeolite bed gives higher NO conversion efficiencies. Girard et al. [13] carried out similar studies on combinations of Fe-and Cuzeolite monolith. They found that the series combinations of (33%) Fe-zeolite followed by (67%) Cu-zeolite gives the highest NO reduction efficiency throughout the studied temperature range. Similar studies on the series of the Fe and Cu-zeolite catalysts with [START_REF] Theis | CLEERS Conference[END_REF]. The approach of the combining of two or more distinct catalysts to achieve the improved performance has been considered in the other reaction systems [e.g . 15]. The other studies [e. g. 16] reported the use of the so-called dual layer monolithic catalysts for SCR of NO with hydrocarbons (e.g. propene) as reducing agents.

Even though the previous studies showed improvements in NO conversion over the Cu and Fe co-exchanged catalysts [10][11][12][13][START_REF] Theis | CLEERS Conference[END_REF][START_REF] Obuchi | [END_REF][16], the effect of the preparation method and state of transition metal present in the zeolite structure is not well documented. Usually, transition metal ions are introduced in the extra-framework position of the zeolite structure by ion exchange method. The objective of the earlier studies [10][11][12][13][START_REF] Theis | CLEERS Conference[END_REF][START_REF] Obuchi | [END_REF][16] was to determine if the duallayer Fe/Cu zeolite catalysts can exhibit improved performance for lean NO reduction.

Examination of various combinations of the sequential brick and dual layer catalysts was deeply investigated [10,11]. The general aim of the earlier studies [10,11,16] was to systematically vary the lengths of the Fe-and Cu-zeolite monoliths in order to identify superior axial configurations, along the lines of the pioneering studies of Ford Motor Company [START_REF] Gandhi | Catalyst system for the reduction of NO x and NH 3 emissions[END_REF].

Unfortunately, there are only few recent reports that have been focused on the single layer Fe/Cu-catalysts in SCR-NO using NH 3 as a reducing agent. It is worth to note that zeolite containing simultaneously two metal cations was attempted for broadening of the NO conversion temperature window [10,11]. Even though, the previous studies showed improvements in NO conversion over the Cu and Fe co-exchanged catalyst, the effect of variation of Cu/Fe ratio and preparation method is still not well documented. Thus, in contrast to the previous studies [e.g. 10,11,16], in which the dual layer catalysts were thoroughly investigated, our approach is to obtain single zeolite containing simultaneously two metal cations (Cu and Fe) by two-step postsynthesis and conventional wet impregnation procedures. As it was earlier shown [START_REF] Boroń | [END_REF]19] for iron and copper, it is possible to

A C C E P T E D M A N U S C R I P T
control the incorporation of Fe or Cu into the framework of BEA zeolite using the two-step postsynthesis method. The catalytic activities of FeCuSiBEA and FeCuHAlBEA in SCR-NO with ammonia were compared with the single metal (Fe or Cu) catalysts. The speciation of transition metals in FeCuSiBEA and FeCuHAlBEA zeolites was determined in order to evidence a "structure-properties" relationship in the selective catalytic reduction of NO with NH 3 .

Experimental

Materials

Two series of Cu and/or Fe-containing zeolites were prepared by two-step postsynthesis and conventional wet impregnation procedures. Fe x SiBEA, Cu x SiBEA and Fe x Cu x SiBEA zeolites (where x = 1.0 wt % of Fe or Cu, respectively) were prepared by the two-step postsynthesis procedure reported earlier [START_REF] Boroń | [END_REF]19]. In the first step, 2 g of HAlBEA zeolite, obtained by calcination in air at 823 K for 15 h of tetraethylammonium form of BEA (TEABEA) zeolite (Si/Al = 12.5), provided by RIPP (China) was treated with 13 mol L -1 HNO 3 solution under stirring (4 h, 353 K) to remove aluminium from the zeolite structure. In the second step, 2 g of resulting SiBEA (Si/Al = 1000) obtained after filtration were dispersed in aqueous solutions (pH = 2.5) containing 1.8 × 10 -3 mol L -1 of Fe(NO 3 ) 3 • 9 H 2 O and/or 1.5 × 10 -3 mol L -1 of Cu(NO 3 ) 2 • 3 H 2 O and stirred at room temperature for 24 h. Then, the obtained suspensions were stirred in evaporator under vacuum of a water pump in air at 353 K for 2 h until water was evaporated. The solids with the iron or copper content of 1.0 wt % were labelled as Fe 1.0 SiBEA, Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 SiBEA, respectively. Fe x HAlBEA, Cu x HAlBEA and Fe x Cu x HAlBEA zeolites (where x = 1.0 wt % of Fe or Cu, respectively) were prepared by conventional wet impregnation method. Firstly, NH 4 AlBEA was calcined in air at 773 K for 3 h to obtain the acidic form of BEA zeolite (HAlBEA). Secondly, 2 g of HAlBEA were dispersed in aqueous solutions (pH = 3.0)

A C C E P T E D M A N U S C R I P T Cu(NO 3 ) 2 • 3 H 2 O
and stirred at room temperature for 24 h. Then, the suspensions were stirred in evaporator under vacuum of a water pump in air at 353 K for 2 h until water was evaporated. The solids with iron or copper content of 1.0 wt % were labelled as Fe 1.0 HAlBEA, Cu 1.0 HAlBEA and Fe 1.0 Cu 1.0 HAlBEA, respectively.

Techniques

The structure of the studied samples was determined by powder X-ray diffraction.

Diffraction patterns were obtained by a PW 3710 Philips X'pert (Philips X'pert APD) diffractometer using Ni-filtered Cu Kα radiation (λ = 1.54056 Å). The measurements were performed in the range of 2Θ from 5 to 50° with a 0.02° step.

Textural properties of the samples were determined by adsorption of nitrogen at 77 K using a Micromeretics ASAP 2010 apparatus. Prior to nitrogen adsorption all the samples were outgassed, first at room temperature and then at 623 K. The specific surface areas were determined from nitrogen adsorption isotherms in the relative pressure (P/P 0 ) ranging from 0.05 to 0.16 using BET method, while the micropore volume was determined from the P/P 0 below 0.2.

The DR UV-Vis spectra were recorded using an Evolution 600 (Thermo) spectrophotometer. The measurements were performed in the range of 200-800 nm with a resolution of 2 nm. DR UV-Vis spectroscopy was applied to determine chemical nature of iron and/or copper species in the zeolite structure.

Hydrogen temperature-programmed reduction (TPR) was carried out in a flow of 5% of H 2 in Ar (25 ml/min). The sample was placed in a quartz microreactor and the quantitative consumption of H 2 from 300 to 1120 K (7.5 K/min) was monitored by a TCD detector. The minimum detectable partial pressure is about 5 •10 -11 Torr. Prior to the reaction, each sample (100 mg) of the catalyst was outgassed in a flow of pure helium at 823 K for 30 min.

Catalytic tests

The following composition of the gas mixture was used:

[NO] = [NH 3 ] = 0.25 vol. %, [O 2 ] =
2.5 vol. % and [He] = 97 vol. %. The reaction was studied in the temperature range between 373 K and 823 K. Total flow rate of the reaction mixture was 40 mL min -1 , with a weight hourly space velocity (WHSV) of about 24000 mL h -1 g -1 .

Results and Discussion

Introduction of iron and copper into BEA zeolite

X-ray diffraction

Figures 1A and 1B present X-ray diffraction patterns of SiBEA, Fe 1.0 SiBEA, Cu 1.0 SiBEA, Fe 1.0 Cu 1.0 SiBEA (Fig. 1A), HAlBEA, Fe 1.0 HAlBEA, Cu 1.0 HAlBEA and Fe 1.0 Cu 1.0 HAlBEA (Fig. 1B). The XRD patterns of all the samples are similar and characteristic of BEA zeolite. The crystallinity is preserved after dealumination and the samples do not show any evidence of extra framework crystalline compounds or long-range amorphization of the zeolite structure, as reported earlier [20,21]. Similar XRD diffractograms recorded for all the samples show that introduction of iron and/or copper ions into zeolites do not induce any significant changes in the BEA structure. [19,20,21,23]. In spite of this expansion, Fe 1.0 SiBEA and Cu 1.0 SiBEA exhibit similar intensity of diffraction lines as that observed for SiBEA, suggesting that incorporation of Fe and Cu ions into the zeolite framework does not affect their crystallinity. It should be noted that incorporation of both Fe and Cu into SiBEA zeolite results in an increase of the d 302 spacing from 3.888 Å (2Θ=22.85°) for SiBEA to 3.936 Å (2Θ=22.57°) for Fe 1.0 Cu 1.0 SiBEA and also proves that iron and copper are incorporated into the BEA zeolite framework.

An introduction of 1.0 wt % of iron or copper into HAlBEA zeolite does not lead to such significant increase in the d 302 spacing as it was observed upon incorporation of iron ions into SiBEA zeolite (Fig. 1B). In this case, a small increase in the d 302 spacing from 3.934 Å (2Θ=22.58°) for HAlBEA to 3.946 Å (2Θ=22.51°) for Fe 1.0 HAlBEA and 3.951 Å (2Θ=22.48°) for Cu 1.0 HAlBEA, respectively (Fig. 1B) suggests that only some amounts of iron or copper have been incorporated into the framework of HAlBEA zeolite. It should be noted that all materials have similar high BET surface area (620-780 m 2 g -1 ) and micropore volume (0.19-0.25 cm 3 g -1 ) characteristic for the BEA structure indicating that textural properties of BEA zeolite are preserved upon dealumination and introduction of iron or copper into BEA structure by two-step postsynthesis procedure as well as by conventional wet impregnation.

The incorporation of both iron and copper ions into

Nature and environment of iron and copper species in FeBEA, CuBEA and FeCuBEA zeolites

Diffuse reflectance UV-vis spectroscopy

The nature and environment of iron and copper present in obtained materials have been studied by DR UV-vis spectroscopy (Fig. 2). The white Fe 1.0 SiBEA sample exhibits one band at 248 nm, assigned to oxygen-to-metal charge transfer (CT) transitions involving pseudo-tetrahedral Fe(III), what is in line with earlier results [24][25][26][27][28][29]. The absence of a broad band near 500 nm, suggests that FeO x oligomers are not present in Fe 1.0 SiBEA [24][25][26]. The DR UV-vis spectra of Cu 1.0 SiBEA are composed of a broad and intense band around 845 nm and another band at about 283 nm (Fig. 2A). These bands may be assigned to d-d Cu 2+ (3d 9 ) and charge transfer (CT) O 2-→ Cu 2+ transitions, respectively, of isolated Cu(II) in pseudotetrahedral coordination, taking into account earlier works on copper in different coordination, environment and crystal field [30][31][32]. The absence of DR UV-vis bands in the range 300-600 nm, assigned to O 2-→ Cu 2+ CT transition and/or d-d transition of octa-coordinated Cu(II)

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indicates that such copper species are probably not present in Cu 1.0 SiBEA, in line with earlier works [33,34]. For Fe 1.0 Cu 1.0 SiBEA absorption bands at 275 and 845 nm can be assigned to pseudo-tetrahedral Fe(III) and Cu(II), respectively. It suggests that upon preparation of this sample by two-step postsynthesis method almost all Fe and Cu ions are incorporated in the SiBEA zeolite framework. Fig. 2B shows the DR UV-vis spectra recorded at room temperature for the HAlBEA, Fe 1.0 HAlBEA, Cu 1.0 HAlBEA and Fe 1.0 Cu 1.0 HAlBEA samples.

The Fe 1.0 HAlBEA sample exhibits one band at 280 nm assigned to oxygen-to-metal charge transfer (CT) transitions involving pseudo-tetrahedral Fe(III) [24][25][26]. Moreover, for this sample a broad band near 400-550 nm is not observed what proves that extra-framework FeO x oligomers and/or iron oxide are not present. It is in line with earlier studies [35,36]. The DR UV-vis spectrum of Cu 1.0 HAlBEA is composed of a broad band around 845 nm and another less intensive band at 285 nm (Fig. 2B). These bands proves the presence of different kinds of mononuclear Cu(II) [30][31][32]. The absence of DR UV-vis band in the range 300-600 nm assigned to CT transition of binuclear [32,37] or trinuclear [33] copper-oxygen complexes suggests that such polynuclear complexes are probably not present in Cu 1.0 HAlBEA. For Fe 1.0 Cu 1.0 HAlBEA, large bands at 280 and 845 nm are observed. These DR UV-vis results

show that the catalyst with 1.0 wt % of iron and copper, contains mainly isolated pseudotetrahedral Fe(III) and Cu(II) in the framework of BEA zeolite.

Temperature-programmed reduction (TPR)

The reducibility of the Fe(III) and Cu(II) present in Fe 1.0 SiBEA, Cu 1.0 SiBEA, Fe 1.0 Cu 1.0 SiBEA (Fig. 3A), Fe 1.0 HAlBEA, Cu 1.0 HAlBEA and Fe 1.0 Cu 1.0 HAlBEA (Fig. 3B) has been investigated by temperature-programmed reduction (TPR) under flowing hydrogen (5 vol % H 2 in Ar). Only one peak at 697 K, probably attributed to the reduction of framework pseudo-tetrahedral iron species from Fe(III) to Fe(II) oxidation state appears for Fe 1.0 SiBEA (Fig. 3A), what is in line with earlier reports [38]. The TPR profile of Fe 1.0 HAlBEA (Fig. 3B) shows two zones of hydrogen consumption: 513-753 K and > 953 K.

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As it was reported in previous studies of Fe-ZSM-5 [39], Fe-Y [40] and Fe-BEA [41], the first peak of hydrogen consumption (at 616 K) would correspond to reduction of Fe 3+ (bare Fe 3+ cations, and oxo-or hydroxycations) into Fe 2+ . The high-temperature reduction peak (at 914 K) is ascribed to the reduction of Fe 2+ to Fe 0 . H 2 -TPR profiles of Cu 1.0 SiBEA and Cu 1.0 HAlBEA are given in Figures 3A and3B. Two reduction peaks at around 477 and 590 K are detected for Cu 1.0 SiBEA, assigned to reduction of Cu 2+ to Cu + and Cu + to Co 0 [42], respectively. While the Cu 1.0 HAlBEA catalyst shows two reduction peaks around 515 and 653 K (Fig. 3B), that can be attributed to one step reduction of Cu 2+ directly to Cu 0 and reduction of Cu + to Cu 0 [42], respectively. Fe 1.0 Cu 1.0 SiBEA displays a very similar TPR profile as that recorded for Cu 1.0 SiBEA, constituted by a good visible peak centered at ca. 472 K, which proves reduction of Cu 2+ to Cu + . Moreover, the TPR profile of the catalyst, prepared by two-step postsynthesis method, shows an additional small peak at 624 K corresponding to reduction of Cu + to Cu 0 and/ or Fe 3+ into Fe 2+ . In contrast three main and unresolved peaks at 517, 546 and 590 K, observed for Fe 1.0 Cu 1.0 HAlBEA prepared by wet impregnation procedure (Fig. 3B), could be attributed to reduction of Cu 2+ directly to Cu 0 , framework tetrahedral Fe(III) to Fe(II) and Cu + to Cu 0 , respectively, in line with earlier work [38,43]. The two additional TPR peaks appearing from 753 to 953 K could be attributed to the reduction of small clusters of Fe 3 O 4 to FeO, and then FeO to Fe 0 , at ca. 777 and 877 K, respectively. The comparison of Figs 3A and 3B reveals that the presence of Cu along with Fe seems to decrease the reducibility of iron as seen from the TPR profiles of the It should be noted that the physicochemical properties (textural properties, nature of transition metals) determined for all the studied catalysts are collected in Table 1.

SCR of NO with NH

3 A C C E P T E D M A N U S C R I P T
reduction of NO with ammonia. Nitrogen and water vapour are desired products of this process, while N 2 O is a side-product. The results of the studies performed for both series of the catalysts are presented in Figs 4 and5. As it was earlier reported [START_REF] Boroń | [END_REF], dealuminated SiBEA shows a very low activity and the NO conversion does not exceed 7% in the whole studied temperature range. The NO conversion substantially increases after incorporation of iron in the framework of SiBEA zeolite as pseudo-tetrahedral Fe(III), as shown for Fe 1.0 SiBEA (Fig. 4). It suggests that pseudo-tetrahedral Fe(III), evidenced by DR UV-vis in Fe 1.0 SiBEA (Fig. 2), are responsible for high activity of the catalyst in the SCR of NO process, what is in line with earlier studies [START_REF] Boroń | [END_REF]44,45]. For Fe 1.0 SiBEA, the NO conversion reaches 100 % with the selectivity to N 2 above 90 % at temperature higher than 673 K. It should be noted that the modification of SiBEA support with copper significantly increases its catalytic activity in the SCR-NO process. The incorporation of Cu into SiBEA leads to its significant catalytic activation (Fig. 4). For the catalyst with 1 wt % of Cu (Cu 1.0 SiBEA), the reaction starts already at 400 K and NO conversion gradually increases with reaction temperature, as shown in Fig. 4. These results confirm that the presence of copper ions in the framework of zeolite is necessary to promote the activity in SCR of NO, in line with earlier report [19]. The incorporation of Cu into SiBEA as isolated pseudo-tetrahedral Cu(II), evidenced by DR UV-vis and TPR investigations (Figs. 2 and3), leads to obtain a more active catalyst and the main reaction route is the reduction of NO toward N 2 . Indeed, for Cu 1.0 SiBEA, a substantial increase of the SCR of NO activity is observed with a maximum NO conversion of 100 % and selectivity to N 2 above 90 % at temperature higher than 473 K. 4). Fe 1.0 Cu 1.0 SiBEA shows very high NO conversion in a broad temperature range of 473-623 K. It should be noted that a commercial catalysts for this process, based on V 2 O 5 -TiO 2 oxide system, operate in a significantly narrower temperature range of 523-673 K [46]. Therefore, these preliminary results obtained in our studies, especially for Fe 1.0 Cu 1.0 SiBEA are very promising. It should be underline that two-step postsynthesis method applied in this work leads to obtain well-define catalysts, containing isolated framework Fe (III) and Cu (II) sites that play a major role in SCR-NO reaction, as showed earlier [47,48]. Moreover, for Fe 1.0 Cu 1.0 SiBEA the effect of direct ammonia oxidation is less significant than for Cu 1.0 SiBEA.

Figure 5 shows the NO conversion as a function of the reaction temperature for all catalysts prepared by conventional wet impregnation of HAlBEA (Fe 1.0 HAlBEA, Cu 1.0 HAlBEA and Fe 1.0 Cu 1.0 HAlBEA). As typical for SCR-NO reaction, a maximum of NO conversion can be found for all these catalysts in a wide temperature window. First of all, it should be noted that the catalytic activity of zeolite without iron (HAlBEA) is rather good, but only in the high temperature region. The NO conversion exceeds ~ 70% with the selectivity to N 2 above 80% at temperature higher than 773 K. The modification of HAlBEA support with iron (1 wt %) in the form of pseudo-tetrahedral Fe (III), significantly increases its catalytic activity in the SCR-NO process. For Fe 1.0 HAlBEA, the NO conversion reaches 100 % with selectivity to N 2 above 90 % at temperature higher than 553 K. The close reaction performance of the Fe 1.0 SiBEA and Fe 1.0 HAlBEA catalysts is in concordance with the similar reducibility of Fe species, deduced from the H 2 -TPR experiments (Fig. 3). Results obtained for the sample modified with copper by conventional wet impregnation method are presented in Fig. 5. The Cu 1.0 HAlBEA catalyst achieved 100% NO conversion at temperature 553 K. In agreement with other authors [5,6] The results obtained for all the catalysts allow comparing their activity in the SCR-NO process. The catalytic activities of all the Fe and/or Cu-containing zeolite catalysts are high, however, it should be noted that Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA are the most active in the low temperature region (T < 473 K), while the catalysts containing only 1.0 Fe wt % or 1.0 Cu wt %, (especially Fe 1.0 SiBEA and Fe 1.0 HAlBEA), show higher activity at elevated temperatures (T > 673 K) (Figs 4,5). As evidenced by DR UV-vis spectroscopy the Fecontaining zeolite catalysts, obtained by conventional wet impregnation, contain pseudotetrahedral Fe(III), while the Cu-containing BEA catalysts contain mainly pseudo-tetrahedral Cu(II) species. Thus, it seems that the presence of these species (isolated framework Fe (III) and Cu (II) in pseudo-tetrahedral coordination) in both kinds of the catalysts (Fe 1.0 SiBEA, Cu 1.0 SiBEA or Fe 1.0 HAlBEA, Cu 1.0 HAlBEA) is responsible for similarity in their high catalytic activity. Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA zeolites effectively operate in the low and medium temperature range (473-673 K). Additionally, the selectivity towards

A C C E P T E D M A N U S C R I P T
nitrogen, measured for these catalysts, is higher than that observed for the samples modified with iron only (Fe 1.0 SiBEA, Fe 1.0 HAlBEA).

It should be underline that the Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA catalysts show a very high NO conversion in a broad temperature range of 473-623 K. The results of the catalytic tests in SCR-NO provided by Metkar et al., [10,11] and other authors [12,13,[START_REF] Theis | CLEERS Conference[END_REF][START_REF] Obuchi | [END_REF]16] are characterized by a very similar performance of the dual-layer and dualbrick catalysts. However, it should be noted that the reaction conditions are different in both cases. The Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA samples achieve high NO conversions over a broader temperature range and seems to be strong alternative to the dual-layer or sequential brick, catalysts reported earlier [10][11][12][13][START_REF] Theis | CLEERS Conference[END_REF][START_REF] Obuchi | [END_REF][16]. Analysis of the catalytic results of Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA in SCR-NO with NH 3 (Fig. 4,5), have shown that postsynthesis as well as wet impregnation procedure allow to obtain the high-performance single-bed catalysts. It is proved that 1 wt % of transition metals, are optimal to incorporate iron and copper in the zeolite structure as pseudo-tetrahedral Fe(III) or Cu(II) that are responsible for high catalytic efficiency in the SCR-NO process. Moreover, the catalytic performance of studied Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA, in contradiction to the duallayer or dual-brick catalysts [10,11], is not decreased by diffusion limitations.

Although the transition metal ions (Fe, Cu) introduces redox properties into the catalysts and modified their acidic properties [52,53], also the reducibility of the metal ions determines degree of NO conversion over the SCR-NO catalysts [54]. The easier is the reduction of the metal species the higher is its oxidation ability. It is worth to notice that the presence of copper along with iron in the Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA catalysts seems to increase the reducibility of iron species as seen from the TPR profiles (Fig. 3). It is well recognized that in the metal exchanged zeolite catalysts, the reducibility of metal ions determines the extent of the low-temperature NO conversion [55] temperature NO conversion is desired, the presence of copper species seems to be important, whereas for the high-temperature conversion the presence of iron species is desired. As discussed above low temperature NO conversion is mostly determined by the ease of reduction of metal ions, and NH 3 storage has inconsiderable role.

It is suggested in many reports [e.g. 58,59,60] that the oxidation of NO to NO 2 is the rate-limiting step for the SCR-NO reaction. Moreover, according to earlier results [59], the Fe 3+ ions seem to be responsible for increasing the oxidation rate of NO to NO 2 . The earlier published results of NO oxidation by O 2 in the presence of the FeBEA catalysts, obtained by postsynthesis and wet impregnation methods, with framework pseudo-tetrahedral Fe(III) [44] (not shown), proves that the formation of NO 2 is not detected in the studied temperature range (373 to 823 K). Thus, it seems that the reaction step of NO to NO 2 oxidation in the SCR-NO reaction over these catalysts does not play an important role. According to earlier works [45,50,61] and literature data [60,62], it is likely that the SCR-NO reaction mechanism on probably responsible for SCR of NO toward N 2 on the studied catalysts, which is in line with earlier report on Co x SiEA [61]. The recent experimental data obtained by us shows that the nitroethane and acetonitrile adsorbed on FeBEA [45] and CoBEA [61] zeolites are very active and selective in the NO conversion to N 2 and seems to be one of the most probable Noxygenated intermediate species.

There is still discussion related to possible mechanism of SCR of NO including chemisorption and activation of ammonia molecules as well the nature of active N-complexes. For this reason, further studies are undertaken to determine the mechanism and the role of framework Cu and Fe sites in SCR of NO by temperature programmed studies (e.g. NH 3 -TPD-NO, NO-TPD-NH 3 , NH 3 -TPD, NO-TPD, TPSR and FTIR spectroscopy of adsorbed NO and NH 3 ). Results of these studies will be presented as a continuation of the current studies.

Conclusions

Two series of Fe and/or Cu-containing BEA zeolites prepared by two-step postsynthesis and conventional wet impregnation methods were prepared. Transition metals (Cu or Fe) were incorporated into the framework of BEA zeolite as a framework pseudotetrahedral Fe(III) or Cu(II), as proved by XRD, DR UV-vis and TPR investigations.

The catalysts containing simultaneously both iron and copper, Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA, have been found to efficiently operate in the SCR-NO process in much broader temperature range comparing to the catalysts modified with only one transition metal (Fe or Cu). Moreover, the selectivity to nitrogen obtained over these catalysts was higher than for the process performed in the presence of the other catalysts. It is proved by the analysis of SCR-NO performance that reducibility of obtained catalysts play an important role in the catalytic process.

  different individual catalyst lengths were carried out by Theis and McCabe

Fe 1 .

 1 0 SiBEA, Cu 1.0 SiBEA, Fe 1.0 Cu 1.0 SiBEA, Fe 1.0 HAlBEA, Cu 1.0 HAlBEA and Fe 1.0 Cu 1.0 HAlBEA were studied as catalysts for SCR of NO with ammonia. Catalytic experiments were performed in a fixed-bed flow microreactor system. The reactant concentrations were continuously measured using a quadrupole mass spectrometer RGA 200 Prevac, with Faraday cup (FC) detector, connected directly to the reactor outlet. Sensitivity of the detector is equal 2•10 -4 A/Torr (measured with N 2 28 amu with 1 amu full peak width 10% height, 70 eV electron energy, 12 eV ion energy and 1 mA electron emission current).

  The absence of reflections characteristics of extra-framework iron and/or copper oxides in Fe x SiBEA, Cu x SiBEA and Fe x Cu x SiBEA indicates a good dispersion of both Fe and Cu transition metals. It has been reported[22] that a narrow diffraction peak near 22-23° can be used to compare qualitatively lattice contraction/expansion of the BEA structure. An increase of the d 302 spacing from 3.888 Å (2Θ=22.85°) for SiBEA to 3.939 Å (2Θ=22.55°) and 3.931 Å (2Θ=22.60°) for Cu 1.0 SiBEA upon introduction of 1.0 wt % of Fe and Cu into SiBEA (Fig.1A) indicates expansion of the matrix as a result of the reaction of iron or copper ions with OH groups of vacant T-atom sites (T = Si or Al) and their incorporation into the framework positions of BEA zeolite, as reported earlier

  HAlBEA zeolites leads also to a small increase in the interlayer distance in BEA matrix, what results in a shift of a narrow diffraction peak near 22-23° to lower values of 2 theta, from 2Θ=22.58° (d 302 = 3.934 Å) for HAlBEA to 2Θ=22.53° (d 302 = 3.943 Å) for Fe 1.0 Cu 1.0 HAlBEA (Fig. 1B). This effect is A C C E P T E D M A N U S C R I P T related to the reaction of iron and/or copper ions with OH groups of vacant T-atom sites and their partial incorporation into the framework positions of BEA zeolite. Moreover, X-ray diffractogram recorded for each sample contains (302) reflection of similar intensity, suggesting that an introduction of Fe and/or Cu into zeolites does not affect their crystallinity.

Fe 1 . 0

 10 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA catalysts.

For the Fe 1 . 0

 10 SiBEA and Cu 1.0 SiBEA catalysts a decrease in effectiveness of NO conversion observed in the high temperature region (above 773 K) is related to the side reaction of direct ammonia oxidation by oxygen, present in the reaction mixture. The Fe 1.0 Cu 1.0 SiBEA catalyst containing framework pseudo-tetrahedral Fe(III) and Cu(II) (as shown in Fig. 2), presents I P T much better catalytic activity in SCR of NO than the Fe 1.0 SiBEA and Cu 1.0 SiBEA catalysts (Fig.

  , Cu 1.0 HAlBEA shows maximum activity at lower temperatures (523-723 K) in comparison with Fe 1.0 HAlBEA (623-783 K). Selectivity to nitrogen, measured for the Cu 1.0 HAlBEA catalyst, is above 95 %. The activity of Fe 1.0 HAlBEA and Cu 1.0 HAlBEA zeolites is probably related to the presence in both catalyst simultaneously acidic sites and isolated pseudo-tetrahedral Fe(III) or Cu(II) species, as evidenced by TPR and DR UV-vis investigations (Figs. 2, 3) [19,46,49,50,51]. The activity of Fe 1.0 Cu 1.0 HAlBEA in the SCR-NO process are presented in Fig. 5. For the Fe 1.0 Cu 1.0 HAlBEA catalyst, NO conversion strongly increases with reaction temperatures and NO is completely converted in the reaction mixture in the range of 473-673 K, with selectivity toward N 2 exceeding 97%. The activity of Fe 1.0 Cu 1.0 HAlBEA in the reduction of NO with ammonia is influenced by specific iron and copper species, created during modification of HAlBEA zeolite. The framework Cu(II) and Fe(III) present in Fe 1.0 Cu 1.0 HAlBEA selectively catalyze the formation of nitrogen without undesirable oxidation of ammonia with oxygen at 773 K and at lower temperature, where its activity and selectivity are stable.

  (Figs 3, 4 and 5).

  easily reducible copper species found in the studied catalysts leads to lower NO conversion at high temperatures due to competing undesired NH 3 oxidation reaction (Fig.4,5). The nitrogen oxide conversion trends in SCR-NO over observed for Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA are in good agreement with earlier literature reports [56,57]. It should be noted that the presence of Fe and Cu in Fe 1.0 Cu 1.0 SiBEA or Fe 1.0 Cu 1.0 HAlBEA, shows different reducibility compared with Fe 1.0 SiBEA, Fe 1.0 HAlBEA or Cu 1.0 SiBEA, Cu 1.0 HAlBEA 3A, 3B). It seems that temperature window of NO conversion can be controlled by adjusting the reducibility of the studied catalysts. If the low-

FeBEA

  and CuBEA involves the preliminary adsorption of NO that is oxidized by O 2 forming an adsorbed NO x species (x = 2, 3) bound to a Fe(III) and/or Cu(II) sites. Framework mononuclear Fe(III) and Cu (II) species present in the Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA catalysts could activate ammonia molecule by abstracting hydrogen atom and then forming an N-oxygenated intermediate species [61]. This active intermediate is

  The higher activity for the Fe 1.0 Cu 1.0 HAlBEA catalyst compared to Fe 1.0 Cu 1.0 SiBEA obtained by two-step postsynthesis method, suggested that Fe(III) and Cu (II) species present in the former catalyst, were possibly close to lattice Al, which make them more catalytically active than Fe(III) or Cu (II) species present in siliceous Fe 1.0 Cu 1.0 SiBEA zeolite. Simultaneous presence of Cu and Fe in Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA strongly increases the low temperature NO conversion. Results of SCR-NO with ammonia for Fe 1.0 Cu 1.0 SiBEA and Fe 1.0 Cu 1.0 HAlBEA revealed that 1 wt % Cu loading is enough to improve the low-temperature NO conversion. It seems that by varying the amount of Cu and Fe in the catalysts the location of the temperature window of efficient NO conversion could be controlled.Further studies are underway on the FeCuSiBEA and FeCuHAlBEA catalysts with a higher Cu and Fe content to verify this phenomenon.

  Figure captions

Figure 1 .

 1 Figure 1. XRD patterns recorded at room temperature of SiBEA, Fe 1.0 SiBEA, Cu 1.0 SiBEA,

Figure 2 .

 2 Figure 2. DR UV-vis spectra recorded at ambient atmosphere of SiBEA, Fe 1.0 SiBEA,

Figure 3 .

 3 Figure 3. H 2 -TPR profiles of SiBEA, Fe 1.0 SiBEA, Cu 1.0 SiBEA, Fe 1.0 Cu 1.0 SiBEA (A), and

Figure 4 .

 4 Figure 4. NO conversion and N 2 selectivity in SCR of NO with NH 3 on SiBEA, Fe 1.0 SiBEA,

Figure 5 .

 5 Figure 5. NO conversion and N 2 selectivity in SCR of NO with NH 3 on HAlBEA,

  Fig.1

Table 1 .

 1 The physicochemical properties of studied catalysts.

	SAMPLE	Specific surface area SBET (m 2 /g)	t-plote Micropore Area (m 2 /g)	t-plote Micropore Volume (cm 3 /g)	wt % of Fe	wt % of Cu	Nature of Fe/Cu species
	SiBEA	789.7	625.7	0.24	0.019	0.002	-
	Fe1.0SiBEA	714.2	537.5	0.21	1.000	-	pseudo-Td Fe 3+
	Cu1.0SiBEA	764.0	588.2	0.23	-	1.000	pseudo-Td Cu 2+
	Fe1.0Cu1.0SiBEA	660.6	508.7	0.20	1.000	1.000	framework pseudo-Td Fe 3+ and Cu 2+
	HAlBEA	727.8	565.0	0.22	0.027	0.002	-
	Fe1.0HAlBEA	647.1	522.3	0.21	1.000	-	pseudo-Td Fe 3+
	Cu1.0HAlBEA	635.0	490.8	0.19	-	1.000	mononuclear Cu 2+
	Fe1.0Cu1.0HAlBEA	616.9	497.2	0.20	1.000	1.000	pseudo-Td Fe 3+ and Cu 2+

Acknowledgements

This research has received funding from the Marian Smoluchowski Kraków Research Consortium -a Leading National Research Centre KNOW supported by the Ministry of Science and Higher Education. Part of the research was done with equipment purchased in the frame of European Regional Development Fund (Polish Innovation Economy Operational Program -contract no. POIG.02.01.00-12-023/08).

The presented studies were performed in the frame of GDRI programme.


Alain Bonneville
email: bonneville@ipgp.jussieu.fr

Laure Dosso

Anthony Hildenbrand

Temporal Evolution and Geochemical Variability of the South-Pacific Superplume Activity

Keywords: mantle plume, South Pacific Superswell, geochemical sources, seamount ages, Cook-Austral, hotspot

We are presenting a new set of K/Ar ages and geochemical analyses obtained on deep-sea samples dredged in 1999 on several seamounts of the Cook-Austral volcanic chains in the Pacific Ocean. The new geochemical results, together with published data on island samples, allow us to reveal a time evolution of the mantle source composition as well as an increase in geochemical variability of the superplume responsible for the regional South Pacific Superswell. Three identified volcanic stages of 58-40 Ma, 33-20 Ma and 20-0 Ma are identified with signatures of mantle reservoir composition varying from close to C to N-MORB-types and C/HIMU-type respectively. Using a geodynamic reconstruction for the most recent volcanic period, from 20 Ma to present, three hotspot tracks are needed to explain the several volcanic episodes observed within the limited geographical area of the central part of the Cook-Austral chains. At the scale of a single volcano, different magmatic phases can also be identified with different ages and geochemical signatures, emphasizing the importance of structural control, either crustal or lithospheric, in the location of the magmatic outputs. These observations, taken together, are in good agreement with a model where each hot spot could sample a small volume of the large very heterogeneous plume responsible for the regional South Pacific Superswell.

-Introduction

The Cook-Austral volcanic chain is located on the southern part of the Pacific Plate, in a region of anomalous shallow seafloor known as the South Pacific Superswell [START_REF] Mcnutt | The south Pacific Superswell[END_REF]. This region of anomalously high bathymetry is also geochemically anomalous and known as the location of the South Pacific Isotope and Thermal Anomaly, SOPITA [START_REF] Staudigel | The longevity of the South Pacific isotopic and thermal anomaly[END_REF]. The Cook-Austral chain signature, based essentially on island sampling, is often attributed to a "HIMU"-type mantle source characterized by Mid-Ocean Ridge Basalt (MORB) -like Sr isotopic ratios and highly radiogenic Pb isotopic ratios (see review in [START_REF] Schiano | Correlated Os-Pb-Nd-Sr isotopes in the Austral-Cook chain basalts: the nature of mantle components in plume sources[END_REF]). Deep-sea samples of the Austral chain were collected during the ZEPOLYF2 cruise that took place in July 1999 between 22°S and 28°S latitude and 143°W and 155°W longitude (Figures 1 and2). Geophysical data including multibeam bathymetry, acoustic imagery, seismic reflection, gravity and magnetic data were also collected. 31 seamounts were mapped and 24 dredges recovered volcanoclastic sediments, altered and fresh pillow basalts, hyaloclastites and ferromanganese crusts. We present here geochemical data obtained on 17 samples selected from these dredges on the basis of their petrographic freshness. Two additional basaltic samples were included in this study (PLD07 and PLD09, Figure 2); they were collected in March 1998 during the POLYDRAG1 cruise (chief scientist, A. Bonneville) on the Tarava Seamount chain located between the Society island and the Austral islands chains [START_REF] Clouard | The Tarava seamounts: a new but exinct hotspot chain on the South Pacific Superswell[END_REF]. This collection of submarine basalt samples has been dated by K/Ar techniques. These new geochemical results, together with published data on island samples, allow us to explore the link between the volcanic activity observed at the Earth surface and deep mantle processes.

-Geological setting

The Cook-Austral chain extends from the island of Aitutaki (140°W, 29°S) to the active submarine volcano Macdonald (160°W,19°S) in a band more than 2200 km long and 240 km wide, oriented N115°E (Figures 1 and2). The chain is composed of several dozens of seamounts and of 11 islands and 2 atolls with little area above sea level (70 km 2 for the largest island). The Austral Fracture Zone (FZ) cuts the chain between the islands of Tubuai and Raivavae. Although oriented roughly in the direction of present Pacific plate motion ( 11 cm.y -1 along a N115° direction), the spatial and temporal pattern of both the aerial and submarine volcanoes is rather complex. The age of the oceanic crust along the chain ranges from about 39 Ma to 84 Ma [START_REF] Mayes | Tectonic history and new isochron chart of the South Pacific[END_REF] (Figure 2). Several K/Ar or Ar/Ar ages are available on almost all the islands of the Cook-Austral chain and on seamounts in the Taukina and Ngatemato seamount chains [START_REF] Mcnutt | Failure of plume theory to explain midplate volcanism in the Southern Austral islands[END_REF], but to date no seamount in the northern Austral region has been dated yet. The particular geometry and morphology of the chain have suggested so far two distinct but parallel alignments [START_REF] Baudry | Alignements volcaniques dans les iles Australes: Analyse et interprétation des données SEASAT et Seabeam[END_REF]. In 1997, McNutt et al. [START_REF] Mcnutt | Failure of plume theory to explain midplate volcanism in the Southern Austral islands[END_REF] determined the existence of two additional chains of volcanoes near the active Macdonald seamount at the southeast end of the chain, 20-34 m.y. older than the Macdonald volcanism. Both recent and old ages recorded on Aitutaki, and Rurutu islands basaltic samples [START_REF] Turner | K/Ar dating of the Cook Austral island chain; a test of the hot spot hypothesis[END_REF][START_REF] Barsczus | Two magmatic sources at Rurutu Island (Austral Islands, French Polynesia) and the Austral "hotline[END_REF] suggest the existence of two other hotspots (Rarotonga and Rurutu) and in 2002, Bonneville et al. [START_REF] Bonneville | Arago Seamount : The missing hot spot found in the Austral Islands[END_REF] proposed that the most recent volcanic stage of Rurutu be attributed to Arago Seamount, a very shallow seamount located 120 km east-southward of Rurutu and sampled during the ZEPOLYF2 cruise. To summarize up to 6 distinct hotspot tracks have been identified so far : from northwest to southeast, Rarotonga, Arago, Tubuai, Macdonald, Taukina and Ngatemato of which three are probably still active, Rarotonga, Arago and Macdonald.

-K-Ar dating of the dredged samples

During the ZEPOLYF2 cruise, 24 successful dredges were performed (Figure 2). Most of them were on lava flows covering the seamount slopes and most of them are very altered. They are classical pillow basalts with a major glassy phase in which the microlitic content increases towards the core. They contain some early crystallized phenocrysts, often altered, with inherited radiogenic Argon in various proportions. They also contain secondary mineral phases like zeolites due to fluid circulation. Moreover, right or immediately after the emplacement of the flow, the matrix is devitrified yielding to formation of mainly clay minerals. Some basaltic samples have a very low K and high Ca content. Despite the low K, K/Ar method remains the most appropriate one to date basalts younger than 60 Ma, if applied to a mineral phase representative of the lava flow emplacement [START_REF] Dalrymple | Potassium-Argon Dating. Principles, techniques and applications to geochronology[END_REF][START_REF] Gillot | The Cassignol technique for potassium-argon dating, precision and accuracy: examples from late Pleistocene to recent volcanics from southern Italy[END_REF][START_REF] Mcdougall | Geochronology and Thermochronology by the 40Ar/39Ar Method[END_REF]. Our samples contain different mineral assemblages corresponding to the successive stages of the lava history: (1) evolution in the magma chamber, (2) solidification on the seafloor, (3) hydrothermal circulation and finally, (4) in situ alteration. The chronometer is, thus, very questionable, and the whole rock dating of such lavas is unsuitable. Even though 40 Ar/ 39 Ar technique allows a distinction between phases to be made using a step heating procedure on whole rock grains [START_REF] Mcdougall | Geochronology and Thermochronology by the 40Ar/39Ar Method[END_REF], we chose to work with a single phase technique. The selection of the correct phase is critical to get the age of the lava flow, i.e. stage [START_REF] Staudigel | The longevity of the South Pacific isotopic and thermal anomaly[END_REF]. This phase in our samples is generally microlitic plagioclase and occasionally nepheline. The rapid cooling of the pillow-basalt, however, limits the size of these microlites to some tens of microns. This small size precludes the use of the 40 Ar/ 39 Ar dating technique because of the recoil of 39 Ar during the neutron activation. Moreover, the very high Ca content of plagioclase restricts the applicability of 40 Ar/ 39 Ar dating technique, especially for younger rocks for which the radiogenic 40 Ar content is very low. Considering these limitations, we decided to use a K-Ar dating technique devoted to detect very low radiogenic 40 Ar contents: the Cassignol technique [START_REF] Gillot | The Cassignol technique for potassium-argon dating, precision and accuracy: examples from late Pleistocene to recent volcanics from southern Italy[END_REF][START_REF] Cassignol | Range and effectiveness of unspiked potassium-argon dating: Experimental groundwork and applications[END_REF]. This technique has been previously applied successfully to submarine basalts from various settings, and yielded ages coherent with the stratigraphic and geodynamic constraints [START_REF] Clouard | The Tarava seamounts: a new but exinct hotspot chain on the South Pacific Superswell[END_REF].

Sample preparation

The inner part of the pillows is systematically used for dating. A specific technique is applied to extract the pure microlitic plagioclase phase when preserved. First, the rocks are crushed and sieved to a 125 to 500 µm size fraction. Heavy liquids are used to remove all phenocrysts and to select the pure microlitic groundmass. Then, the groundmass is crushed again to a smaller size such as to isolate pure plagioclase microlites (generally around 30 to 50 µm). Finally, a magnetic separator is used to separate pure plagioclase from the altered glass and other microlites. The different microlitic sizes extracted from the various samples are summarized in Table 1. When possible, different mineral phases are isolated: plagioclase microlites, plagioclase phenocrysts, nepheline (Figure 3) and groundmass. They constitute independent phases which are important to check for internal consistency of a given sample. This is illustrated in pillow-lavas DR07B and DR24-02 (Figure 4) for which both plagioclase crystals (125-250 µm) and microlites (30-50 µm) have been separated and analyzed. Note that the double separation is not necessary for the freshest samples DR02, DR04 and DR14-03, because their groundmass is fresh and well preserved. Finally, special attention has been given to the highly under-saturated glassy pillow-lava DR07 which contains small cubic crystals of nepheline. For this sample, dating has been done both on this particularly K-rich phase and on the preserved glassy groundmass, since the separated nepheline quantities were small. Most samples have been dated twice and Table 1 summarizes the results :

• for samples with duplicate dates on the same mineral phase (DR01, DR02, DR04, DR05, DR14, DR16, DR18, DR24), ages are perfectly reproducible; • for DR23 and DR07B, a slight discrepancy can be observed between the dating made on two different phases: (1) microlites and (2) plagioclase phenocrysts; • for DR07, the dating made on the nepheline phase and on the groundmass are different (by 0.2 Ma) but they are coherent. Both give a very recent age for the sample; however the age based on the nepheline phase is preferred because of the higher K content and of the lower Ar contamination level. In a few cases very different ages are obtained within a single dredge. This indicates that different volcanic episodes have been sampled along the dredge haul. This can be seen in particular for DR07 and suspected for DR14 and DR23 (see below). A large range of ages, between 0.23 Ma and 58.1 Ma, is observed with a maximum uncertainty of 2%. These new results bring important constraints to the geodynamical evolution of this region as further discussed in sections 5 and 6.

-Geochemical analytical techniques and results

Major, trace element and isotope data are presented in Table 2.

Sample preparation

Aboard the ship, all samples are crushed to centimeter size fragments. Pieces of glass or chips from the inner part of lava flows or pillow lavas are handpicked to avoid (1) Fe-Mn coatings, which could be a potential source of Pb and Nd contamination (2) altered surfaces which could have an effect on Sr isotope compositions. All samples (either glasses or rock chips) are washed in an ultrasonic bath of 2M HCl, followed by double quartz distilled water before further crushing in an agate mortar for major and trace element analysis. For Sr and Nd isotope analyses, the powder is further leached to remove seawater alteration with 0.1N HCl for a few minutes in an ultrasonic bath and rinsed in deionized water. The Sr-Nd separations are done according to the procedure described in [START_REF] Dosso | Geochemical morphology of the North Mid-Atlantic Ridge, 10°-24°N: Trace element-isotopes complementarity[END_REF]. Pb separation is performed on a separate aliquot of the powdered sample leached with 6M HCl at 140°C for an hour and rinsed up to 6 times with deionized water and dried. Such a procedure gives reliable Pb isotope ratios on whole rock powders as shown by Regelous et al [START_REF] Regelous | Geochemistry of lavas from the Emperor Seamounts, and the geochemical evolution of Hawaiian magmatism from 85 to 42 Ma[END_REF]. Sr and Nd ratios were measured on a Finnigan MAT261 multicollector instrument, in dynamic mode and were corrected for mass fractionation to a value of 8.375209 for 88 Sr/ 86 Sr and 0.721903 for 146 Nd/ 144 Nd. Standards NBS987, La Jolla and JNdi-1 analyzed during the sample measurement period gave values of 0.71025±2 (n=20), 0.511852±10 (n=34) and 0.512104±4 (n=15). High-resolution Pb analyses were made using the double spike technique with the calibrated Southampton-Brest 207/204 spike [START_REF] Ishizuka | Fluid-mantle interaction in an intra-oceanic arc: constraints from high-precision Pb isotopes[END_REF]. Replicate analyses of the Pb isotope standard NBS981 gave an average of 16.9431±33, 15.5001±39, 36.7317±11 (2sd, n=28) for 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb respectively. Pb blanks were about 30 pg and thus negligible.

Major Elements

Most samples are alkali basalts and basanites (Figure 5). Some samples have severe alteration features such as a high loss of ignition. DR14-4 is a basaltic breccia rich in clinopyroxenes.

Trace Elements 5/17

The South Pacific Superswell activity July 15 th , 2005 The data are presented in Figure 6. The rare earth diagrams are extended to include Th, Nb, Ta, Zr, Hf and Y. The concentrations are normalized to the primitive mantle values [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF], shown in parenthesis after the element name, in Table 2. It is important to note that the samples have been affected by seawater alteration. During such low temperature alteration, however, Nb, Ta, Zr, and Hf remain in the basalt whereas Y and the trivalent REE are partially removed [START_REF] Bienvenu | MORB alteration : rare-earth element/non rare-earth hygromagmaphile element fractionation[END_REF]. Therefore concentration ratios of elements such as Zr, Nb, Hf and Ta are considered to be insensitive to alteration. As described above in the sample preparation, more efficient alteration removal has been applied to samples for isotope analyses.

Most samples have light REE enriched patterns, like typical intraplate volcanic lavas (Figure 6). In detail, however, there seems to be a temporal evolution of the sample patterns. Sample DR14-4, the clinopyroxene rich sample is not included in this discussion as, due to its low K content, it could not be dated and its extended REE pattern is dominated by clinopyroxenes and thus does not represent the basalt. The oldest group of samples (40-58 Ma) has enrichment in light REE (LREE) relative to heavy REE with (La/Sm) N between 1.0 and 4.2.

The second group [START_REF] Chauvel | Contrasting old and young volcanism in Rurutu Island, Austral chain[END_REF][START_REF] Hanan | Lead and Helium Isotope Evidence from Oceanic Basalts for a Common Deep Source of Mantle Plumes[END_REF][START_REF] Hart | Mantle plumes and entrainment: isotopic evidence[END_REF][START_REF] Wessel | A geometric technique for relocating hotspots and refining absolute plate motions[END_REF][START_REF] Yan | A plate tectonic reconstruction of the Southwest Pacific, 0-100 Ma[END_REF][START_REF] Duncan | Sr isotopic evidence for an old mantle source region for French Polynesian volcanism[END_REF][START_REF] Davaille | Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle[END_REF][START_REF] Le Maitre | A classification of igneous rocks and glossary of terms[END_REF][START_REF] Macdonald | Chemical composition of hawaiian lavas[END_REF][START_REF] Nakamura | Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes[END_REF][START_REF] Palacz | Coupled trace element and isotope enrichment in the Cook-Austral-Samoa islands, southwest Pacific[END_REF][START_REF] Hauri | Re Os isotope systematics of HIMU and EMII oceanic island basalts from the South Pacific Ocean[END_REF][START_REF] Kogiso | High µ (HIMU) ocean Island Basalts in Southern Polynesia: New Evidence for Whole Mantle Scale Recycling of Subducted Oceanic Crust[END_REF][START_REF] Hemond | Source compositions and melting processes in the Society and Austral plumes (South Pacific Ocean); element and isotope (Sr, Nd, Pb, Th) geochemistry[END_REF] has LREE depleted patterns such as found in N-MORB (Normal Mid-Ocean Ridge Basalts) with (La/Sm) N between 0.7 and 1.4. The REE patterns of transitional basalts DR20-2 and DR23-2 have negative Nb anomalies and fractionated Nb-Ta and Zr-Hf ratios. Both features are similar to those of depleted MORB basalts. Finally, the youngest group (0-20 Ma) includes LREE patterns as commonly described in intraplate volcanic samples. It shows the largest enrichments and concentration variations of all groups with (La/Sm) N between 2.2 and 5.0. DR23-3, unfortunately too altered to be dated, is plotted with the youngest group on the basis of its isotopic composition. Although such trace element groupings seem tentative, the isotope data also show similar distinction as is discussed below.

Isotopes

The isotopic data are not corrected for post-emplacement decay because the Rb/Sr (as can be estimated from the extended REE patterns) and Sm/Nd ratios are small enough that changes in Sr-Nd isotopic ratios are negligible over the considered time period. In the same way, we will assume a negligible evolution of Pb isotopic compositions. The data are therefore compared directly to available data from the literature on samples collected in the same area including Pacific mid-ocean ridge basalt data. All Sr-Nd data from the literature have been normalized to the same standard values of 0.71025 for NBS987 and 0.511852 for La Jolla. In all diagrams (Figures 7 to 9), the most remarkable feature of the new data is heterogeneity. However it should be remembered that this data set not only includes samples from a wide geographical area but also from a large temporal range (from 58 Ma to present). The values range from very depleted (Sr, Pb) MORB values found in basalts south of the Austral FZ between Rapa and Raivavae (DR18-DR20-DR23) to very radiogenic values. Such depleted MORB-type values (Sr isotopic ratio as low as 0.70258) in intraplate volcanic samples have not been previously reported. The most radiogenic Sr value is found south of the Austral FZ in a basaltic sample (0.70434 -DR14-3). This value is similar to those found in Rarotonga and Aitutaki samples (Figure 7). Intermediate Sr-Nd values include HIMU-type values similar to those found for Tubuai and Mangaia basalts (DR01-DR04-DR21). Large Sr-Nd isotopic heterogeneity is found within single dredges such as DR14 and DR23. DR14-3 has extreme Sr-Nd compositions towards EM-type mantle sources whereas DR14-4 has Sr-Nd compositions that are close to the HIMU field of compositions. DR23-2 has Sr-Nd isotopic characteristics of Pacific MORB samples whereas DR23-3 has an isotope composition similar to the young volcanic lavas from Rurutu. Examination of Pb-Pb diagrams (Figures 8 and9) reinforces these observations. The 206 Pb/ 204 Pb isotopic compositions display a very wide range, from 17.59 to 20.87. We note that the most depleted samples located on the edge of the Pacific MORB field, have higher 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios than the Northern Hemisphere Regression Line, (NHRL), whereas the most radiogenic samples are located below the NHRL, and are of HIMU-type within the Tubuai-Rimatara field (DR04-2 10), the different age groups can also be identified.

-Discussion

The new geochemical data presented in this paper, based on sampling of seamounts of different ages, clearly illustrate the large heterogeneity of mantle sources at the regional scale of the Cook-Austral island chain between 58 Ma and present.

Temporal evolution of mantle source composition

This large mantle heterogeneity is seen in isotopes as well as in trace elements. However, the data set appears to be coherent in terms of age, isotope compositions and XREE data :

• Between 58 and 40 Ma, the tapped source presents enriched XREE patterns with a small variation in 206 Pb/ 204 Pb (18.4-9.0) and with a range in 143 Nd/ 144 Nd from 0.51280 to 0.51295. This area of the isotopic field is close to what has been referred to as the Common mantle component "C" zone [START_REF] Hanan | Lead and Helium Isotope Evidence from Oceanic Basalts for a Common Deep Source of Mantle Plumes[END_REF] or FOZO (FOcus ZOne) [START_REF] Hart | Mantle plumes and entrainment: isotopic evidence[END_REF] and could represent the material found between the enriched blobs in a "marble cake" mantle. Both groups are characterized by (La/Sm) N between 0.7 and 4.2 and Th/Ta ratios between 0.7 and 0.9.

• Between 20 Ma and present time, the geochemical heterogeneity is larger. The rare earth patterns are the most enriched of all three age groups with (La/Sm) N between 2.2 and 5.0 and Th/Ta ratios between 1 and 1.9. Isotopically, it is also the most heterogeneous group with 206 Pb/ 204 Pb ranging from 19.0 to 20.9 and 143 Nd/ 144 Nd ranging from 0.51269 to 0.51293. In terms of mantle source-types, C to HIMU-types are found. Local heterogeneity can also be observed at the dredge scale, like in DR14 where DR14-3, the only dated sample, and DR14-4 have widely different isotopic ratios. Most likely these two samples are from two different volcanic stages as already pointed out above in the case of DR23. To summarize, from 58 Ma to 40 Ma, the mantle source is close to C type, between 33 Ma and 20 Ma, the mantle source is of N-MORB type, between 20 Ma and present time, the source could be a mixture between C and HIMU type sources. During this last time period, hot spot tracks can be reconstructed. Hotspot track reconstruction (0-20 Ma) Three hotspot tracks have been recognized using a method coupling geodynamical reconstruction and the new K/Ar ages obtained on these samples added to the already available ages on islands. To reconstruct the apparent path followed by a hotspot on the seafloor, we have moved the hotspot present location back in time by using the set of stage poles proposed by Wessel and Kroenke [START_REF] Wessel | A geometric technique for relocating hotspots and refining absolute plate motions[END_REF]. This data set represents the most updated synthesis for the absolute Pacific plate motion since 145 Ma. However, for the last interval (0-3 Ma), we have chosen to use the pole previously proposed by Yan and Kroenke [START_REF] Yan | A plate tectonic reconstruction of the Southwest Pacific, 0-100 Ma[END_REF]. The apparent hot spot tracks are determined for the past 20 m.y. with this set of absolute stage poles (Figure 11). If we use a 100-km-wide track as representative of the zone of influence of a given hotspot source, we clearly see that the Macdonald hotspot could not have generated the northern Austral Islands. Furthermore, the Macdonald hotspot track fits well with the 19 Ma age of Mangaia and with the K-Ar age of 8.8 Ma obtained on the seamount ZEP2-19 (DR14-3). On the other hand, the northern Austral Islands can be well explained by a hotspot source that probably stopped producing magma at Raivavae ca. 6.5 Ma. This solution has also the advantage of linking together islands with isotopic signatures clearly different from those of Macdonald. President Thiers bank to the east is a guyot and probably much older. Finally, by using the same stage poles, the Arago track is drawn. It fits quite well with Rurutu and Cook Island ages. Note that volcanoes are often not located along the track axis, which we think emphasizes the importance of lithospheric control over a change in the mantle source location.

Mantle source variation along hotspot track

When looking at individual hotspot tracks in the last 20 Ma determined above and identified in Figure 10 with different colors, one can reveal specific characteristics of each of the sources with all tracks including "C" compositions. The three volcanic tracks are from north to south: (1) the Raivavae track (green line and symbols) from Raivavae Island (6.5 Ma) to Rurutu Island and nearby seamounts (12 Ma), (2) the Arago track (blue line and symbols) from Arago seamount (0.2 Ma) to Atiu Island (8 Ma) and (3) the Macdonald track (red line and symbols) from Macdonald seamount (0 Ma) to Mangaia (19 Ma).

(1) The Raivavae track extends from Raivavae-type (6.5 Ma) to old Rurutu type (12 Ma) towards the HIMU Mangaia-type. Tubuai Island and DR04-2, a sample dredged on a seamount eastward of Rurutu Island, belong to the old Rurutu field. DR07B, a sample dredged on Arago seamount, and dated at 8.2 Ma, has a Raivavae signature as well as DR22, a sample dredged on the northeast flank of Raivavae Island. If we extend the track eastward in order to find the youngest event, we find President Thiers guyot where DR21 was collected. Its isotopic signature is not far from that of the Raivavae field but only a radiometric age will settle the question.

(2) The Arago (DR7) track appears more homogeneous and could be related to the young Rurutu volcanic episode (1 Ma). Along this track, DR2 (2.6 Ma), a sample dredged on a seamount westward of Rimatara Island, has the same signature. Rimatara Island samples, although dated at 27 Ma [START_REF] Turner | K/Ar dating of the Cook Austral island chain; a test of the hot spot hypothesis[END_REF], are clearly belonging to the Young Rurutu episode. The Rimatara Island is thus likely belonging to this track and we think that the existing radiometric age already questioned by several authors is definitively an error. At the oldest end of the track, Atiu and Mauke, have less radiogenic Nd isotopes and their belonging to the track is thus more questionable, although one Mauke sample is close to the young Rurutu field.

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The South Pacific Superswell activity July 15 th , 2005

(3) The Macdonald track source is more heterogeneous than the other tracks, at the scale of the track as well as at the scale of each volcano. The volcano scale heterogeneity is seen especially in Nd isotopes in samples from Macdonald, Rapa, Marotiri and DR14-3, dated at 8.8 Ma. The track heterogeneity is illustrated by the difference in isotopic signature between Macdonald (0 Ma) and Mangaia whose age (19 Ma) is in agreement with the age along the track.

From the above description of mantle isotopic characteristics associated with each of these three hot spot tracks, it can be deduced that the mantle tapped in the last 20 Ma is more radiogenic and more heterogeneous than earlier. Further detailed work on identifying the different volcanic episodes present in the different volcanoes in correlation with basement ages would be needed to raise reasonable hypotheses about the causes of such heterogeneities.

We certainly can assume that the superplume mantle source was heterogeneous to start with 20 Ma ago. And we can safely state that mixing of sources combined with crustal assimilation would increase the observed degree of heterogeneity within each hotspot track.

Lithospheric control

As described earlier, geochemical heterogeneities are present even at the scale of a single volcano. On some island or seamount, important differences in geochemical signatures can be pointed out. These signatures however clearly belong to different volcanic stages separated in time by several millions of years. This is well known on Rurutu Island [START_REF] Duncan | Sr isotopic evidence for an old mantle source region for French Polynesian volcanism[END_REF] with two stages dated at 12 Ma (old Rurutu stage) and 1 Ma (Young Rurutu stage). Furthermore, if we consider the nearby Lotus bank with a sample dated at 54.8 Ma, we can conclude that at least three different stages have occurred in the same area. The present study also reveals that Arago Seamount experienced two volcanic stages separated by 8.7 m.y. (DR7 and DR7b samples) with distinct isotopic signatures. On the other hand, DR14 and DR23 samples are presenting different isotopic signatures but we don't know their difference in ages. We can therefore assume that each of them has sampled two separate episodes of volcanism in the same way as two volcanic stages have been identified in Rurutu island or Arago Seamount. During such a time interval (around 10 m.y.), the Pacific plate has moved 1200 km to the Northwest and the volcanic activity cannot correspond to the same mantle source. To explain such reoccurrence of volcanism at the same location, we have to assume that the lithosphere is weakened along the path taken by the magma to reach the surface. This weakened area then acts as the preferential pathway for subsequent magmatic events that bring magma from new plume sources to the surface.

-Conclusion

Based on the most complete to date oceanic sampling of the Cook-Austral volcanic chains, we have shown:

• a huge heterogeneity in mantle sources at the regional scale;

• a chemical grouping of the mantle sources during the three identified volcanic stages of 58-40 Ma, 33-20 Ma and 20-0 Ma with signatures of mantle reservoir composition from close to C to N-MORB-types and C/HIMU-type respectively. • a mantle heterogeneity along each hotspot track during the most recent volcanic period of 0-20 Ma; • an heterogeneity at the scale of a volcano due to the occurrence of different magmatic phases at the same location; • the importance of the structural control, either crustal or lithospheric, in the location of magma outputs. These observations taken together are in good agreement with a model where each hot spot could sample one volume of the large and very heterogeneous plume responsible for the regional swell of the seafloor topography [START_REF] Mcnutt | The south Pacific Superswell[END_REF]. It has been proposed that this small scale convection (100 km in surface expression compared to the 2000 km of the Superswell) could be due to secondary instabilities developing at the surface of the larger plume in the transition

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zone [START_REF] Davaille | Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle[END_REF]. The time constants of these phenomena should give us constraints to infer the size of the mantle heterogeneities described in this study. At the regional scale, the challenge is to decipher the dynamics of the super-plume responsible for the Superswell, given the time evolution of the mantle source composition.

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The South Pacific Superswell activity July 15 th , 2005 2 data. The field boundaries are from [START_REF] Le Maitre | A classification of igneous rocks and glossary of terms[END_REF] and [START_REF] Macdonald | Chemical composition of hawaiian lavas[END_REF] for the dashed line. DR14-4 is a basaltic breccia rich in clinopyroxenes shown by a slashed circle.

Figure 6:

Primitive-mantle normalized extended rare earth patterns for analyzed samples shown in Table 2. The elements are in decreasing incompatibility order for mantle derived melts. Open symbols are used for non-rare earth elements, Th, Ta, Nb and Zr, Hf [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]. The samples are organized in age groups according to absolute dating or estimated age when italic fonts are used. Grey areas include samples that have similar patterns. [START_REF] Schiano | Correlated Os-Pb-Nd-Sr isotopes in the Austral-Cook chain basalts: the nature of mantle components in plume sources[END_REF][START_REF] Chauvel | Contrasting old and young volcanism in Rurutu Island, Austral chain[END_REF][START_REF] Nakamura | Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes[END_REF][START_REF] Palacz | Coupled trace element and isotope enrichment in the Cook-Austral-Samoa islands, southwest Pacific[END_REF][START_REF] Hauri | Re Os isotope systematics of HIMU and EMII oceanic island basalts from the South Pacific Ocean[END_REF][START_REF] Kogiso | High µ (HIMU) ocean Island Basalts in Southern Polynesia: New Evidence for Whole Mantle Scale Recycling of Subducted Oceanic Crust[END_REF][START_REF] Hemond | Source compositions and melting processes in the Society and Austral plumes (South Pacific Ocean); element and isotope (Sr, Nd, Pb, Th) geochemistry[END_REF][START_REF] Woodhead | Extreme HIMU in an oceanic setting; the geochemistry of Mangaia Island (Polynesia), and temporal evolution of the Cook-Austral hotspot[END_REF] and Marquesas [START_REF] Desonie | Temporal and geochemical variability of volcanic products of the Marquesas hotspot[END_REF][START_REF] Liotard | Geochemistry and origin of basaltic lavas from Marquesas Archipelago, French Polynesia[END_REF][START_REF] Duncan | Plume versus lithospheric sources for melts at Ua Pou, Marquesas Islands[END_REF][START_REF] Vidal | Large mantle heterogeneity beneath French Polynesia[END_REF][START_REF] Woodhead | Temporal geochemical evolution in oceanic intra-plate volcanics; a case study from the Marquesas (French Polynesia) and comparison with other hotspots[END_REF][START_REF] Cheng | Geochemical studies of Tahiti, Teahitia and Mehetia, Society Island Chain[END_REF], Society [START_REF] Hemond | Source compositions and melting processes in the Society and Austral plumes (South Pacific Ocean); element and isotope (Sr, Nd, Pb, Th) geochemistry[END_REF][START_REF] Cheng | Geochemical studies of Tahiti, Teahitia and Mehetia, Society Island Chain[END_REF] and Pitcairn [START_REF] Woodhead | Geochemistry of the Pitcairn Seamounts .1. Source Character and Temporal Trends[END_REF][START_REF] Woodhead | Ancient seafloor signals in Pitcairn Island lavas and evidence for large amplitude, small length-scale mantle heterogeneities[END_REF][START_REF] Dupuy | Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia); geochemical dependence on the age of the lithosphere[END_REF][START_REF] Eisele | The role of sediment recycling in EM-1 inferred from Os, Pb, Hf, Nd, Sr isotope and trace element systematics of the Pitcairn hotspot[END_REF] islands as well as Pacific mid-ocean ridge basalts [45-47, 48 , 49-65] and main mantle reservoirs HIMU, EMI and EMII. The numbers in the inset refer to ZEPOLYF2 and POLYDRAG samples. Analytical errors are smaller than symbol sizes. All samples are represented by circles, black for old [START_REF] Cheng | Geochemical studies of Tahiti, Teahitia and Mehetia, Society Island Chain[END_REF][START_REF] Woodhead | Geochemistry of the Pitcairn Seamounts .1. Source Character and Temporal Trends[END_REF][START_REF] Woodhead | Ancient seafloor signals in Pitcairn Island lavas and evidence for large amplitude, small length-scale mantle heterogeneities[END_REF][START_REF] Dupuy | Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia); geochemical dependence on the age of the lithosphere[END_REF][START_REF] Eisele | The role of sediment recycling in EM-1 inferred from Os, Pb, Hf, Nd, Sr isotope and trace element systematics of the Pitcairn hotspot[END_REF][START_REF] White | Isotope geochemistry of Pacific Mid-Ocean Ridge Basalt[END_REF][START_REF] Mahoney | Isotope and trace element characteristics of a super-fast spreading ridge: East Pacific rise, 13-23°S[END_REF][START_REF] Niu | Mantle source heterogeneity and melting processes beneath seafloor spreading centers: The East Pacific Rise, 18 degrees-19S[END_REF][START_REF] Bach | Chemical and Isotopic Variations Along the Superfast Spreading East Pacific Rise from 6 degrees S to 30 degrees S[END_REF][START_REF] Macdougall | Sr and Nd isotopes in basalts from the East Pacific Rise: significance for mantle heterogeneity[END_REF][START_REF] Ito | Nd and Pb isotope geochemistry of MORB[END_REF][START_REF] White | Sr and Nd isotope geochemistry of oceanic basalts and mantle evolution[END_REF][START_REF] Cohen | U-Pb, Sm-Nd and Rb-Sr systematics of mid-ocean ridge basalt glasses[END_REF][START_REF] Cohen | The lead, neodymium and strontium isotopic structure of ocean ridge basalts[END_REF][START_REF] Hegner | Sr, and Nd isotopes in basalts and sulfides from the Juan de Fuca Ridge[END_REF][START_REF] Prinzhofer | Stochastic melting of the marble cake mantle: evidence from local study of the East Pacific Rise at 12°50[END_REF][START_REF] Schiano | Osmium-strontium-neodymium-lead isotopic covariations in mid-ocean ridge basalt glasses and the heterogeneity of the upper mantle[END_REF][START_REF] Verma | Neodynium isotopic evidence for Galapagos hotspot-spreading centre system evolution[END_REF][START_REF] Bach | Unusually large Nb-Ta depletions in North Chile ridge basalts at 36 degrees 50' to 38 degrees 56'S: Major element, trace element, and isotopic data[END_REF], grey for middle age [START_REF] Chauvel | Contrasting old and young volcanism in Rurutu Island, Austral chain[END_REF][START_REF] Hanan | Lead and Helium Isotope Evidence from Oceanic Basalts for a Common Deep Source of Mantle Plumes[END_REF][START_REF] Hart | Mantle plumes and entrainment: isotopic evidence[END_REF][START_REF] Wessel | A geometric technique for relocating hotspots and refining absolute plate motions[END_REF][START_REF] Yan | A plate tectonic reconstruction of the Southwest Pacific, 0-100 Ma[END_REF][START_REF] Duncan | Sr isotopic evidence for an old mantle source region for French Polynesian volcanism[END_REF][START_REF] Davaille | Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle[END_REF][START_REF] Le Maitre | A classification of igneous rocks and glossary of terms[END_REF][START_REF] Macdonald | Chemical composition of hawaiian lavas[END_REF][START_REF] Nakamura | Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes[END_REF][START_REF] Palacz | Coupled trace element and isotope enrichment in the Cook-Austral-Samoa islands, southwest Pacific[END_REF][START_REF] Hauri | Re Os isotope systematics of HIMU and EMII oceanic island basalts from the South Pacific Ocean[END_REF][START_REF] Kogiso | High µ (HIMU) ocean Island Basalts in Southern Polynesia: New Evidence for Whole Mantle Scale Recycling of Subducted Oceanic Crust[END_REF][START_REF] Hemond | Source compositions and melting processes in the Society and Austral plumes (South Pacific Ocean); element and isotope (Sr, Nd, Pb, Th) geochemistry[END_REF] and white for young (0-20 Ma). DR14-4 dominated by clinopyroxene has a slashed circle as a symbol.

Figure 8:

Pb-Pb diagrams with available data from the literature as specified in Figure 7 caption and additional references [START_REF] Dupré | Limitations on the scale of mantle heterogeneities under oceanic ridges[END_REF][START_REF] Church | Lead isotope relations in oceanic ridge basalts from the Juan de Fuca-Gorda Ridge area, N.E. Pacific Ocean[END_REF][START_REF] Sun | Lead isotopic study of young volcanic rocks from mid-ocean ridges, ocean islands and island arcs[END_REF][START_REF] Fontignie | 87 Sr/ 86 Sr and REE variations along the Easter Microplate boundaries (south Pacific): Application of multivariate statistical analyses to ridge segmentation[END_REF][START_REF] Hanan | Easter microplate evolution: Pb isotope evidence[END_REF] for Pacific mid-ocean ridge basalts. NHRL stands for Northern Hemisphere Line [START_REF] Hart | A large scale isotope anomaly in the Southern Hemisphere mantle[END_REF]. The numbers in the insets refer to ZEPOLYF2 and POLYDRAG samples. Analytical errors are smaller than symbol sizes. Symbols are defined in Figure 7.

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The South Pacific Superswell activity July 15 th , 2005

Figure 11: Bathymetric map with hotspot-track reconstruction for the three groups of volcanoes (see text). Map projection is made along direction of present motion of Pacific plate (from right to left). White italic numbers indicate time in Ma along each track. Note that northernmost track starts at 6.5 Ma for last volcanic event known on this track. A black star represents active Macdonald seamount. The new K-Ar ages obtained in the present study are in black and their exact location are given by the symbols defined in Figure 10. The known ages of islands are given in Figure 2.

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The South Pacific Superswell activity July 15 th , 2005

Tables Table 1 : Results of the K-Ar dating

Figure 1 :

 1 Figure 1: Location of the Cook-Austral Islands in the southwest Pacific with indication of the main structural features and names of main sampled islands. The box corresponds to the studied area displayed in Figure 2.

Figure 2 :

 2 Figure 2:Ages of seafloor and island volcanoes reported on a shaded view of seafloor topography for the Cook-Austral region. The 34j anomaly (84 Ma) marks the beginning of the Cretaceous quiet zone and west of this anomaly (~ 1ongitude 152°W), the crust has an age comprised between 84 and 118 Ma. White lines represent crustal magnetic anomalies, and their corresponding age is in white numbers (Ma). Black diamonds represent places where K-Ar or Ar/Ar ages (Ma, in black italic) are known. Dredge location and sample numbers are in red.

Figure 3 :

 3 Figure 3: (a) and (b) DR07 pillow lava observed in thin section. (c) nepheline phenocrysts can be observed within the vesicular altered groundmass.

Figure 4 :

 4 Figure 4: Extraction of the microlitic plagioclase from DR24-02 basalt, using the double separation technique: (a) crushing at an appropriate size to remove unsuitable phenocrysts; (b) re-crushing and sieving at a smaller size to extract the plagioclase microlites (c).

Figure 5 :

 5 Figure 5: SiO 2 vs. Na 2 O+K 2 O for Table2data. The field boundaries are from[START_REF] Le Maitre | A classification of igneous rocks and glossary of terms[END_REF] and[START_REF] Macdonald | Chemical composition of hawaiian lavas[END_REF] for the dashed line. DR14-4 is a basaltic breccia rich in clinopyroxenes shown by a slashed circle.

Figure 7 :

 7 Figure 7: Nd vs. Sr isotopic diagram for published data from the Austral islands[3, 20, 29- 34] and Marquesas[START_REF] Desonie | Temporal and geochemical variability of volcanic products of the Marquesas hotspot[END_REF][START_REF] Liotard | Geochemistry and origin of basaltic lavas from Marquesas Archipelago, French Polynesia[END_REF][START_REF] Duncan | Plume versus lithospheric sources for melts at Ua Pou, Marquesas Islands[END_REF][START_REF] Vidal | Large mantle heterogeneity beneath French Polynesia[END_REF][START_REF] Woodhead | Temporal geochemical evolution in oceanic intra-plate volcanics; a case study from the Marquesas (French Polynesia) and comparison with other hotspots[END_REF][START_REF] Cheng | Geochemical studies of Tahiti, Teahitia and Mehetia, Society Island Chain[END_REF], Society[START_REF] Hemond | Source compositions and melting processes in the Society and Austral plumes (South Pacific Ocean); element and isotope (Sr, Nd, Pb, Th) geochemistry[END_REF][START_REF] Cheng | Geochemical studies of Tahiti, Teahitia and Mehetia, Society Island Chain[END_REF] and Pitcairn[START_REF] Woodhead | Geochemistry of the Pitcairn Seamounts .1. Source Character and Temporal Trends[END_REF][START_REF] Woodhead | Ancient seafloor signals in Pitcairn Island lavas and evidence for large amplitude, small length-scale mantle heterogeneities[END_REF][START_REF] Dupuy | Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia); geochemical dependence on the age of the lithosphere[END_REF][START_REF] Eisele | The role of sediment recycling in EM-1 inferred from Os, Pb, Hf, Nd, Sr isotope and trace element systematics of the Pitcairn hotspot[END_REF] islands as well as Pacific mid-ocean ridge basalts[45-47, 48 , 49-65] and main mantle reservoirs HIMU, EMI and EMII. The numbers in the inset refer to ZEPOLYF2 and POLYDRAG samples. Analytical errors are smaller than symbol sizes. All samples are represented by circles, black for old[START_REF] Cheng | Geochemical studies of Tahiti, Teahitia and Mehetia, Society Island Chain[END_REF][START_REF] Woodhead | Geochemistry of the Pitcairn Seamounts .1. Source Character and Temporal Trends[END_REF][START_REF] Woodhead | Ancient seafloor signals in Pitcairn Island lavas and evidence for large amplitude, small length-scale mantle heterogeneities[END_REF][START_REF] Dupuy | Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia); geochemical dependence on the age of the lithosphere[END_REF][START_REF] Eisele | The role of sediment recycling in EM-1 inferred from Os, Pb, Hf, Nd, Sr isotope and trace element systematics of the Pitcairn hotspot[END_REF][START_REF] White | Isotope geochemistry of Pacific Mid-Ocean Ridge Basalt[END_REF][START_REF] Mahoney | Isotope and trace element characteristics of a super-fast spreading ridge: East Pacific rise, 13-23°S[END_REF][START_REF] Niu | Mantle source heterogeneity and melting processes beneath seafloor spreading centers: The East Pacific Rise, 18 degrees-19S[END_REF][START_REF] Bach | Chemical and Isotopic Variations Along the Superfast Spreading East Pacific Rise from 6 degrees S to 30 degrees S[END_REF][START_REF] Macdougall | Sr and Nd isotopes in basalts from the East Pacific Rise: significance for mantle heterogeneity[END_REF][START_REF] Ito | Nd and Pb isotope geochemistry of MORB[END_REF][START_REF] White | Sr and Nd isotope geochemistry of oceanic basalts and mantle evolution[END_REF][START_REF] Cohen | U-Pb, Sm-Nd and Rb-Sr systematics of mid-ocean ridge basalt glasses[END_REF][START_REF] Cohen | The lead, neodymium and strontium isotopic structure of ocean ridge basalts[END_REF][START_REF] Hegner | Sr, and Nd isotopes in basalts and sulfides from the Juan de Fuca Ridge[END_REF][START_REF] Prinzhofer | Stochastic melting of the marble cake mantle: evidence from local study of the East Pacific Rise at 12°50[END_REF][START_REF] Schiano | Osmium-strontium-neodymium-lead isotopic covariations in mid-ocean ridge basalt glasses and the heterogeneity of the upper mantle[END_REF][START_REF] Verma | Neodynium isotopic evidence for Galapagos hotspot-spreading centre system evolution[END_REF][START_REF] Bach | Unusually large Nb-Ta depletions in North Chile ridge basalts at 36 degrees 50' to 38 degrees 56'S: Major element, trace element, and isotopic data[END_REF], grey for middle age[START_REF] Chauvel | Contrasting old and young volcanism in Rurutu Island, Austral chain[END_REF][START_REF] Hanan | Lead and Helium Isotope Evidence from Oceanic Basalts for a Common Deep Source of Mantle Plumes[END_REF][START_REF] Hart | Mantle plumes and entrainment: isotopic evidence[END_REF][START_REF] Wessel | A geometric technique for relocating hotspots and refining absolute plate motions[END_REF][START_REF] Yan | A plate tectonic reconstruction of the Southwest Pacific, 0-100 Ma[END_REF][START_REF] Duncan | Sr isotopic evidence for an old mantle source region for French Polynesian volcanism[END_REF][START_REF] Davaille | Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle[END_REF][START_REF] Le Maitre | A classification of igneous rocks and glossary of terms[END_REF][START_REF] Macdonald | Chemical composition of hawaiian lavas[END_REF][START_REF] Nakamura | Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes[END_REF][START_REF] Palacz | Coupled trace element and isotope enrichment in the Cook-Austral-Samoa islands, southwest Pacific[END_REF][START_REF] Hauri | Re Os isotope systematics of HIMU and EMII oceanic island basalts from the South Pacific Ocean[END_REF][START_REF] Kogiso | High µ (HIMU) ocean Island Basalts in Southern Polynesia: New Evidence for Whole Mantle Scale Recycling of Subducted Oceanic Crust[END_REF][START_REF] Hemond | Source compositions and melting processes in the Society and Austral plumes (South Pacific Ocean); element and isotope (Sr, Nd, Pb, Th) geochemistry[END_REF] and white for young (0-20 Ma). DR14-4 dominated by clinopyroxene has a slashed circle as a symbol.

Figure 9 :

 9 Figure 9: (a) 208 Pb/ 206 Pb vs. 207 Pb/ 206 Pb diagram with available data from the literature as specified in Figures 7 and 8. (b) 206 Pb/ 204 Pb and c) ∆ 207 Pb/ 204 Pb (deviation from NHRL [71]) versus Th/Ta for studied samples. Symbols are defined in Figure 7.

Figure 10 :

 10 Figure 10: 143 Nd/ 144 Nd vs. 206 Pb/ 204 Pb diagram with available data from the literature as specified in Figures 7 and 8 captions. Green, blue and red symbols are used for samples belonging to hotspot tracks shown in Figure 11. Black circles are used for samples dated between 40 and 58 Ma. Yellow squares are used for 33 to 20 Ma samples. The stippled area indicates samples from 0-20 Ma.

Figure 1

 1 Figure 1 Bonneville et al., 2005

  Figure 2 Bonneville et al., 2005

  Raivavae and Rurutu island volcanics (Figures8 and 9a). In Figure9a,208 Pb/206 Pb is plotted against207 Pb/ 206 Pb. We note that the extreme isotopic heterogeneity that was pointed out within a single same dredge is confirmed in Pb-Pb systematics both for DR14 and DR23. Pb-Pb diagrams (Figures8 and 9a) suggest that the whole sample set might be divided into three groups according to age: 0-20 Ma, 20-33 Ma and 40-58 Ma, consistent with the classification based on the extended rare earth patterns presented above. The youngest group, the most radiogenic in Pb, includes samples with enriched trace element patterns only. The 20-33 Ma age group has MORB isotopic characteristics and includes samples with slightly enriched to depleted XREE patterns. Finally, the 40-58 Ma group includes only trace element enriched samples. These groups are also clearly separated when a key trace element ratio that is diagnostic of mantle source composition such as Th/Ta (insensitive to variable degrees of partial melting) is combined with Pb isotopic information such as 206 Pb/ 204 Pb (Figure9b) or the distance to the reference line NHRL, ∆ 207 Pb/ 204 Pb (Figure9c). DR14-3, dated at 8.8 Ma, is outside either group as is also shown by its peculiar Nd-Sr isotopic characteristics. A sample with unusual isotopic ratios (Nd composition of 0.51278) was also found in Rurutu island (74-394) and ignored in the discussion[START_REF] Chauvel | Contrasting old and young volcanism in Rurutu Island, Austral chain[END_REF]. DR14-4, the clinopyroxene rich basaltic breccia, could not be dated but its geochemical characteristics suggest that it belongs to the 20-33 Ma age group. Samples from a single dredge (DR23) show a very large heterogeneity: 206 Pb/ 204 Pb ratios vary from 18.0 to 20.3 for DR23-2 and DR23-3 respectively. However DR23-2 is a glassy sample that has been dated at 33 Ma whereas no age is available for DR23-3. These two samples from the same dredge most likely belong to different stages of volcanism. The isotopic characteristics of DR23-3 place it rather in the 0-20 Ma group of samples.

). Other samples have Pb isotopic ratios which vary between Pacific MORB sample values to values 6/17 The South Pacific Superswell activity July 15 th , 2005 typical of those found in Rarotonga-Aitutaki, Macdonald-In a Nd vs. Pb isotopic diagram (Figure

•

  Between 33 and 20 Ma, the isotopic field describing the source has rather depleted characteristics with almost constant MORB-type Nd values around 0.5131 whereas 206 Pb/ 204 Pb values range from 17.6 to 18.2. Samples in this age group present depleted to slightly enriched extended rare earth patterns.

Table 2 : Major, trace element and isotopic composition of analyzed samples.

 2 Major and trace element composition analyzed by XRF (Brest), ICP-MS (C.R.P.G. Nancy) and microprobe (Brest) when in italic. All Sr isotopic measurements are obtained with 2 σ M errors of less than 20 and Nd measurements are obtained with 2σ M errors of less than 15. Pb isotope measurements are done by double spike technique (see text). Normalization values used to present the data in the extended rare earth patterns of Figure6are given in parenthesis after the element name. Ages are K-Ar dates from Table1or estimated when shown in italic.

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The South Pacific Superswell activity July 15 th , 2005

Acknowledgments

The authors wish to thank Sophie Bernard, Marcel Bohn, Claire Bollinger, Henri Bougault, Joël Etoubleau, Philip Janney and Raymond Le Suavé for their help with data acquisition, analytical work and discussions. This paper has been greatly improved thanks to the detailed comments of reviewers P. Castillo and G. Ito. The ZEPOLYF2 cruise was funded by the government of French Polynesia in the framework of the ZEPOLYF program. Analytical work was financed by INSU-CNRS and IFREMER. This is IPGP contribution number 2077 and IUEM contribution number 980.

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