Petrogenesis of subduction-related lavas from the southern Tonga arc

Journal Pre-proofs Petrogenesis of subduction-related lavas from the southern Tonga arc Bora Myeong, Jonguk Kim, Jung Hoon Kim, Yun Deuk Jang PII: DOI: Reference:

S1367-9120(19)30441-9 https://doi.org/10.1016/j.jseaes.2019.104089 JAES 104089

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Journal of Asian Earth Sciences

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1 November 2018 4 October 2019 18 October 2019

Please cite this article as: Myeong, B., Kim, J., Kim, J.H., Jang, Y.D., Petrogenesis of subduction-related lavas from the southern Tonga arc, Journal of Asian Earth Sciences (2019), doi: https://doi.org/10.1016/j.jseaes. 2019.104089

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Petrogenesis of subduction-related lavas from the southern Tonga arc

Bora Myeong1,2 • Jonguk Kim1* • Jung Hoon Kim3 • Yun Deuk Jang2

1Deep-Sea

and Seabed Mineral Resources Research Center,

Korea Institute of Ocean Science & Technology (KIOST), Busan, 49111, South Korea 2Department 3Division

of Geology, Kyungpook National University, Daegu, 41566, South Korea

of Environment Policy, Gyeongsangbuk-Do, Andong, 36759, South Korea

*Corresponding

author: [email protected]

Declarations of interest: none

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Abstract: We present new whole-rock geochemical data for volcanic rocks dredged from active submarine volcanoes TA15, TA16, and TA19 that mark the southern part of the Tonga Arc near Ata island. The lava samples show a wide range of compositions from basalt to dacite within the low-K tholeiitic series, and geochemical data indicate fractional crystallization of olivine, orthopyroxene, clinopyroxene, and plagioclase. The origin of magmas in the southern Tonga Arc can be explained by the mixing of three components: a depleted mantle wedge, a melt derived from the partial melting of subducted pelagic sediments (PS) and sediments of the subducted Louisville Seamount Chain (LSC), and a fluid produced during subduction by the dehydration of altered oceanic crust (AOC). Our geochemical modeling suggests that mafic magmas in the study area can be generated by 10%–25% partial melting of a depleted mantle that had been metasomatized by ~1% AOC fluids as well as ~1% melts derived from a 40:60 mixture of LSC and PS sedimentary components. On the other hand, volcanoes V, U, and Monowai, located farther south near the present LSC–Tonga Trench intersection, can be generated by 15%–25% partial melting of a depleted mantle that had been metasomatized by ~0.5% AOC fluids as well as ~1.5% sediment-derived melts (a 90:10 mixture of LSC and PS). These results are consistent with previous proposals that the influence of the LSC-derived components was stronger in the southerly volcanoes V, U, and Monowai than in the volcanoes near Ata.

Keywords: southern Tonga Arc, mantle source, subduction component, Louisville Seamount Chain, pelagic sediment, altered oceanic crust

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1. Introduction Arc magma at a subduction zone is generated in response to the subduction of altered oceanic crust (AOC) and sediment into the mantle, as a result of which dehydration reactions occur in the AOC, thus driving fluids into the overlying wedge and lowering the peridotite solidus to promote melting (e.g., Tatsumi et al., 1986; Tatsumi, 1989; Davies and Bickle, 1991). Island arc magmas are therefore characterized by higher abundances of large ion lithophile elements (LILEs) and lower contents of high field strength elements (HFSEs) than intraplate and midocean ridge magmas. These geochemical signatures depend mostly on the components derived from altered oceanic crust (AOC) and sediment as a result of their subduction (Plank and Langmuir, 1993; Elliott et al., 1997; Elliott, 2003; Plank, 2005). For some of the volcanoes in the Tonga–Kermadec Arc (e.g., Ata, and volcanoes V, U, and Monowai), the sedimentary component can be further divided into components from the Louisville Seamount Chain (LSC) sediments and pelagic sediments (PS) (Regelous et al., 2010; Timm et al., 2012, 2013; Li et al., 2015). The LSC consists mainly of guyots and a number of smaller seamounts, and it has been subducted beneath the Tonga–Kermadec Arc. Although the subducted seamounts contribute to the element budget in the subduction zone, the extent and mechanism of the recycling of seamount components and their role in subduction zone processes are not well known. The Tonga–Kermadec Arc is therefore a good location for studying the effects of seamount subduction on arc magmatism. Previous work has focused on defining the geochemical characteristics of LSC components in lavas dredged from the southern Tonga Arc. Escrig et al. (2009) reported that young lavas dredged from Ata have the geochemical imprints of a LSC component, such as high values of 206Pb/204Pb, 208Pb/204Pb, and 86Sr/87Sr, and Timm et al. (2013) proposed that the enrichment of radiogenic isotopes in lavas from volcanoes V, U, and Monowai at ~25°S can

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be attributed to the recent influence of materials derived from the LSC. Timm et al. (2013) did not rule out the influence of LSC subduction in the case of Ata, and they suggested that Ata may have been affected by an early stage of LSC subduction. The Pb and Sr isotopic compositions of Ata lavas can be explained by ~5–8 wt% addition of an LSC component into a mantle with a composition similar to that of the northern Havre Trough–Lau Basin (Timm et al., 2013). The presence of subducted LSC materials in the Ata lavas has therefore been well reported, but the quantity of such materials, including the trace elements, is poorly constrained. In this paper, we report on the major and trace element compositions of volcanic lavas from seamounts close to Ata, and we use trace element modeling to evaluate the contribution made by subduction components, especially those derived from the LSC, during the genesis of the magmas.

2. Geological setting The intra-oceanic Tonga–Kermadec Arc has a total length of 2,800 km and is located to the east of the Lau Basin and the Havre Trough (Fig. 1). The Tonga–Kermadec Arc system has formed since the Oligocene in response to the westwards subduction of the oceanic Pacific Plate beneath the oceanic Indian–Australian Plate, and it is the margin with the highest rate of convergence in the world, with a convergence rate of as much as 240 mm/yr at the northern Tonga Arc (Bevis et al., 1995; Arculus, 2005; Castillo et al., 2009). The convergence rate increases from the south (50 mm/y) to the north (240 mm/y) (Bevis et al., 1995). The dip of the Benioff Zone is ~14°–30° to a depth of ~60 km (Isacks and Barazangi, 1977; Contreras– Reyes et al., 2011; Bassett et al., 2016). The volcanoes in this arc lie on a volcanic basement that makes up a crust with a thickness of 7 to 20 km (Contreras–Reyes et al., 2011). This basement consists mainly of stratovolcanoes that exhibit structures such as calderas and volcanic cones.

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At 25.36°S, the LSC intersects the zone where the Pacific Plate is being subducted under the Tonga Arc and the Indian–Australian Plate. The LSC is a chain of seamounts approximately 4,200 km-long on the Pacific Plate, and it is positioned to the southeast of Samoa and east of the Tonga Trench (Fig. 1). Together with the Hawaiian and Easter Islands, the LSC is recognized as one of the few primary Pacific hotspots (Courtillot et al., 2003), based on its linear morphology and its long-lived age-progressive volcanism (Koppers et al., 2004, 2011). LSC lavas are alkalic, and they have homogeneous trace element and isotopic compositions (Cheng et al., 1987; Beier et al., 2012; Li et al., 2015). The LSC includes two layers of sediment: an upper layer of pelagic deposits (100 m thick) and a lower layer of volcanoclastic sediments that represent a 50-m-thick apron of material erupted from the LSC (Turner et al., 1997). Two models have been proposed to explain how the subduction of the LSC took place. According to one model, the LSC was subducted at the northern Tonga Trench at ~4 Ma, and LSC-derived materials reached the subarc magma generation zone beneath the northernmost part of the Tonga Arc at ~3 Ma. LSC subduction then migrated southwards to its current position at 25.36°S (Ruellan et al., 2003). The elevated values of 206Pb/204Pb and 208Pb/204Pb in volcanic rocks from the northern (i.e., at Tafahi and Niuatoputapu) and southern (i.e., Ata) Tonga Arc have been attributed to LSC subduction based on this model (Regelous et al., 1997, 2010; Turner and Hawkesworth, 1997; Turner et al., 1997; Wendt et al., 1997; Ewart et al., 1998; Escrig et al., 2009). However, in another model (Timm et al., 2013; Li et al., 2015), it was proposed that the geochemical characteristics of the northern Tonga Arc lavas were derived from the partial melting of a locally enriched mantle with ocean island type affinities. In this second model, the counterclockwise rotation of the LSC was a consequence of the change in plate motion at ~80 Ma at the Hawaii Emperor Seamount Chain, and the subduction of the Osbourn Seamount at 76.7 Ma suggests counterclockwise bending of the subducted LSC near the Osbourn Seamount. According to this second model, the enrichment of radiogenic

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isotopes in lavas from Ata and the volcanoes V, U, and Monowai can be attributed to material derived from the LSC. Therefore, in both of these models, the LSC was subducted beneath the Ata region. Ata (176°W; 22°S) is the only subaerial volcano in the southern Tonga Arc, and it was thought by Johnstone (1978) to be an eroded remnant of a previously much larger island. Ata is part of a large composite seamount that contains two similarly sized and closely spaced groups of seamounts to the north, according to satellite-derived bathymetry (Fig. 2; Chase, 1985; Tagudin and Scholl, 1994; Smith and Sandwell, 1997). Here, we designate the western group of seamounts to the north as the TA15 group, and the eastern group as the TA16 group. TA15 and TA16, along with Ata itself, have been designated as the Ata volcanic complex in previous work (Stoffers et al., 2003), and we assume, therefore, that TA15 and TA16 were formed during the same stage of volcanism. We refer to them in this paper as TA15–16. TA19 (176.2°W; 22.5°S) is located ~80 km to the south of the Ata volcanic complex (Fig. 2).

3. Samples and analytical techniques For this study, samples of lava were collected during 14 rock dredge operations at the summits and flanks of TA15–16 and TA19 in the southern Tonga Arc region. The collected samples vary in composition from basaltic andesite to dacite. We selected 16 representative rock samples for whole-rock analyses. Samples were crushed into chips, sonicated in distilled water, and hand-picked under a microscope to remove altered material. The samples were then leached in 1 M HCl for 10 minutes to remove carbonate before being ground in an agate mortar. Major and trace element compositions were determined by inductively coupled plasma–atomic emission spectrometry (ICP–AES; Thermo Jarrell–Ash ENVIRO II) at Activation Laboratories, Canada, and by inductively coupled plasma–mass spectrometry (ICP–MS; Agilent 7700) at the Korea Institute

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of Ocean Science and Technology (KIOST). The samples were prepared and analyzed in a batch system that included a method reagent blank and certified reference material. The samples were ignited and fused in LiBO2 and Li2B4O7 for the major element analyses, and digested in HF–HNO3–HClO4 for the trace element analyses. Samples of the standard material were analyzed as an unknown during the analysis of every group of 5–6 samples. The replicate analyses for every sample yielded average relative standard deviations (RSD, n = 3) of 5% on average for major elements (excluding K2O and P2O5, which were both 10%, due to the closeness to the detection limits) and <5% for trace elements. The uncertainty in the external reproducibility of the trace element analyses was generally within ±5% except for some trace elements (less than ±10% for V, Zn, and Rb, and less than ±15% for Nb and Pb) (Table 1).

4. Results The major and trace element compositions of lavas recovered from TA15–16 and TA19 are listed in Table 1. On a TAS diagram (Fig. 3a), the analyzed samples from TA15–16 fall in a range from basaltic andesite to dacite, and those from TA19 fall in a range from basaltic andesite to andesite. These variations represent the successive fractionations of magma in the study area. The lavas belong to a low-K tholeiite series, and they exhibit an initial trend of iron enrichment followed by silica and alkali enrichment (Fig. 3b, c). Variation diagrams of a number of oxides against MgO (Fig. 4) show trends of increasing SiO2, Na2O, and K2O, and decreasing CaO, FeO(T), and Al2O3 against decreasing MgO, and these variations are consistent with fractional crystallization. We note, too, that there is commonly an inflection in the trend lines at MgO = 3 wt%, and this could have been caused by crystal fractionation of olivine and clinopyroxene in the early stage (MgO > 3 wt%) followed by crystal fractionation of plagioclase, orthopyroxene, and clinopyroxene in the later stage (MgO < 3 wt%) (Dorendorf et al., 2000). Figure 5 shows variation diagrams of selected trace elements against MgO

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contents. Ni decreases with decreasing MgO content, which shows the magma was affected by olivine crystallization, and the decreasing Cr content with decreasing MgO indicates the influence of spinel crystallization with olivine. The decrease in Co content with decreasing MgO content can be attributed to the crystallization of Fe–Ti oxides such as magnetite and ilmenite, and the decrease in Sc content with decreasing MgO can be explained by the crystallization of clinopyroxene with Fe–Ti oxides. Multi-element variation diagrams, normalized to N-MORB, show enrichments in fluid-mobile large ion lithophile elements (LILEs) and depletions in relatively fluid-immobile high field strength elements (HFSEs), which is a typical pattern for arc magmas (Fig. 6a). In chondrite-normalized REE diagrams (Sun and McDonough, 1989), the lavas from TA15–16 and TA19 show flat or slightly LREE depleted REE patterns, with contents that are several to ten times higher than chondrite values (Fig. 6b).

5. Discussion 5.1. Petrogenesis of the southern Tonga Arc lavas Quantitative modeling of the elemental variations of the arc magmas in this subduction zone suggests that at least three independent components were involved in their petrogenesis (Ellam and Hawkesworth, 1988; Hawkesworth et al., 1997a, 1997b; Turner et al., 1997; Haase et al., 2002; Kimura and Yoshida, 2006). In a detailed geodynamic and quantitative three-component model for lavas in the northern Tonga and Kermadec arcs, Turner et al. (1997) and Timm et al. (2012) described the three components as mantle wedge, melt derived from a mix of LSC sediments and pelagic sediments (PS), and fluid that originated from the dehydration of subducted altered oceanic crust (AOC). Considering that our study area is located between the northern Tonga Arc and the Kermadec Arc, we discuss the petrogenesis of the study area (the southern Tonga Arc) using the three components described above.

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According to their geochemical behavior, trace elements can be divided into relatively subduction-immobile elements (Nb, Ta, Zr, Hf, Ti, and HREEs) and subduction-mobile elements (Rb, Ba, Sr, K, Th, U, LREEs, middle-REEs, P, and Pb) with respect to the supercritical fluid or melt derived from subducted oceanic crust and sediment at high temperatures. Among the subduction-mobile elements, some elements (i.e., Rb, Ba, K, Sr, and Pb) are further considered to be fluid-mobile elements, as they can be contained in the aqueous fluid released from subducted crust and sediment at low temperatures (Pearce et al., 2005; Pearce and Stern, 2006). As the analyzed lavas have various SiO2 contents (i.e., different degrees of fractionation), we first calculated the fractionation-corrected values for selected trace elements, normalized to a common 8% MgO (i.e., Nb(8), Yb(8), Ba(8), and Th(8)) using the method suggested by Till (1974), before evaluating the influence of various subduction components.

5.1.1. Mantle wedge The geochemistry of arc lavas depends on the mantle composition and the nature of the subduction components derived from the subducted slab (Pearce and Peate, 1995; Langmuir et al., 2006; Pearce and Stern, 2006). Assuming that the composition of the mantle wedge is homogeneous, the geochemical variation in the arc lava is controlled by the variable influx of subduction components. However, the mantle wedge does not always show a homogeneous composition, mostly because of mantle flow beneath the arc and back-arc settings. Therefore, we first examined the mantle wedge composition of the southern Tonga Arc. Since the composition of a volcanic arc is affected not only by the mantle source but by the subduction components, the Sr and Pb isotopic compositions may not solely reflect the composition of the mantle source. Nd, however, is less mobile during subduction (Tatsumi et al., 1986; Hoogewerff et al., 1997), and by using the values of

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143Nd/144Nd

in the lavas from

the Lau spreading center (i.e., from CLSC, ELSC, and VFR, as reported by Peate et al., 2001; Pearce et al., 2007; Tian et al., 2008; Escrig et al., 2009; Yan et al., 2012), we can constrain the composition of the mantle wedge beneath the Lau spreading center near TA15–16 and TA19 (i.e., CLSC, ELSC, and VFR). The results show that the variations in the values of 143Nd/144Nd in the mantle wedge beneath the volcanic arc from 18°S to 23°S are insignificant (Fig. 7b). However, beneath the southern volcanoes V, U, and Monowai, which are located between 25°S and 26°S, there is no spreading center, and so the mantle wedge beneath 18°S to 23°S cannot be directly compared with the wedge beneath the area from 25°S to 26°S. Instead, we compared the mantle fertility using the relatively subduction-immobile trace elements. Because both Nb and Yb are relatively immobile during subduction, the value of the Nb/Yb ratio is widely used as a proxy to indicate the degree of mantle fertility, and this proxy is applicable to arc lavas affected by subducted materials (Pearce et al., 2005; Pearce and Stern, 2006). As mentioned above, we used the values of Nb(8)/Yb(8), which had been corrected for the effects of fractional crystallization. The average value of Nb(8)/Yb(8) for lavas from TA15–16 and TA19 is 0.20. Other volcanoes previously reported in the southern Tonga Arc between 18°S and 25°S show values of Nb(8)/Yb(8) that range from 0.14 in Volcano V to 0.38 in Hunga (Fig. 7a). The fairly uniform trace element ratios for the arc volcanoes and the uniform Nd isotopic composition of the adjacent spreading center lavas suggest that the mantle composition is relatively homogeneous in the southern Tonga Arc region. We suggest, therefore, that any observed geochemical variations in the volcanic rocks of the southern Tonga Arc were controlled by subduction components rather than by mantle wedge compositions. 5.1.2. Subduction components: altered oceanic crust (AOC) fluids and sediment-derived melts The analyzed lavas have typical arc-like trace and minor element compositions, including negative Nb anomalies (less pronounced negative anomalies for Zr and Hf) and significant

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enrichments in LILEs (Fig. 6), all of which indicates the addition of a slab-derived fluid component to the mantle wedge in the source area of the southern Tonga Arc magmas. These characteristics are normal for lavas in the Tonga Arc (Timm et al., 2012, 2013; Li et al., 2015). Furthermore, it is known that lavas from the southern Lau Basin–Havre Trough have been slightly (∼3%) influenced by hydrous melts derived from sediments in the deep parts of the subducting slab (Todd et al., 2010). We therefore need to consider both fluid and melt subduction components. Incompatible elemental ratios such as Ba/Th and Th/Nb are useful fractionationindependent proxies for identifying subduction components. Because Ba, Th, and Nb have similar partition coefficients during mantle melting and fractional crystallization, their ratios can reflect the source composition (Pearce et al., 2005; Pearce and Stern, 2006). However, the elements have different mobilities during subduction. Ba, but not Th, is significantly mobile in aqueous fluids derived from the subduction zone, while both Ba and Th can be partitioned into siliceous melts (Keppler, 1996; Johnson and Plank, 2000). In contrast, Nb is relatively mobile in slab melts at high temperatures (Ryerson and Watson, 1987; Ayers and Watson, 1993; Brenan et al., 1994). Thus, the values of Ba/Th are widely used as proxies for dehydration fluids, and the values of Th/Nb for sediment-derived melts. The relative contributions of the two different subduction components (i.e., fluids derived by dehydration and sediment-derived melts) in Tonga Arc magmatism are shown on the plot of Ba/Th versus Th/Nb in Fig. 8. Some arc volcanoes, such as Fonualei, Late, Kao, Tofua, and Hunga, were enriched by a fluid component and plot within the compositional range of the Tonga Arc. On the other hand, TA15–16 and TA19 and other volcanoes known to be affected by the LSC component, including Ata and volcanoes U, V, and Monowai (Regelous et al., 1997, 2010; Turner and Hawkesworth, 1997; Turner et al., 1997; Wendt et al., 1997; Ewart et al., 1998; Escrig et al., 2009; Timm et al., 2012; Li et al., 2015), define another trend

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that lies outside the compositional bounds of published Tonga Arc data. The linear trends of the volcanoes with a higher contribution of a sedimentary component indicate that this component can be further divided into PS and LSC. Fig. 8 indicates a lower LSC melt influence but a higher PS melt influence in Ata, TA15–16, and TA19 compared with volcanoes V, U, and Monowai. We proceed, therefore, to assess these influences further by using trace element modeling in the following section.

5.2. Geochemical modeling of the southern Tonga Arc lavas The results of trace element modeling, using Th, La, and REEs in the seamounts along the southern Tonga Arc, are shown in Figs. 9 and 10. Th is one of the most important elements indicating the effects of LSC sediments (Li et al., 2015). However, Th contents can be influenced by fractionation in a basaltic melt, and for this reason, La, with its similar partition coefficient (Kd) in clinopyroxene (Arth, 1976; Fujimaki et al., 1984), garnet (Hauri et al., 1994; Johnson, 1994), olivine (McKenzie and O’Nions, 1991), and plagioclase (Bindeman et al., 1998; Aigner–Torres et al., 2007), is used instead of Th as the denominator. More depleted compositions in arc-front lavas than back-arc lavas can be generated by prior partial melting of their mantle source in the back-arc region, followed by corner flow in the mantle wedge, as reported for the New Britain Arc front lavas and the related Manus back-arc lavas (Woodhead et al., 1998). Similarly, the basalts in the southern Tonga Arc are more depleted in HFSEs than are the VFR lavas in the southern Lau Basin (Fig. 6a), suggesting that HFSE depletion in these volcanic rocks reflects melt extraction. In the trace element modeling, we used a primitive mantle with ~5% previous melt extraction for the composition of the depleted mantle, as suggested by Timm et al. (2012) (Table 2). Based on the quantitative model of Turner et al. (1997), the mantle wedge may be enriched first by the addition of a melt derived from a mixture of the LSC sediments and PS at

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relatively low pressures. We used the experimental results for element partitioning suggested by Johnson and Plank (2000) at 2 GPa and 800 °C to model this process (Table 3), based on the fact that the uppermost layer of sediment begins to melt at ~750 °C and pressures greater than 2 GPa (Johnson and Plank, 2000; Kelemen et al., 2004). We used the compositions of the LSC and PS in the southern Tonga Arc, as reported by Turner et al. (1997) and Falloon et al. (2007), and we assumed that the sediment-derived melts was formed by 20% partial melting of the mixture of sediments (Table 3). The mantle wedge is then dragged down to greater depths by the viscous drag induced by the subducting slab. Eventually, suitable conditions are reached for the dehydration reaction of amphibole to produce fluids from the AOC, and the fluids are then transported into the mantle wedge to initiate partial melting. These fluids traverse the wedge until the amphibole peridotite solidus (~1000 °C isotherm) is reached (Green, 1973; Wyllie, 1979; Turner and Hawkesworth, 1997). We used the experimental results of Kessel et al. (2005) for element partitioning at 6 GPa and 1000 °C to model this process (Table 3). We used the actual eclogite bulk composition of Kessel et al. (2005) for the AOC composition, and we assumed that the AOC fluid was produced by 30% dehydration of the AOC (Table 3). In modeling the Th and La compositions of lava samples from TA15–16 and TA19, we assumed the mantle wedge had first been modified by the addition of 1% sediment-derived melts (LSC:PS = 40:60), and then modified further by the addition of 1% AOC fluid. The observed Th and La compositions of TA15–16 and TA19 match well the results of 10%–25% melting of the modified mantle wedge source (F = 0.1–0.25) (Fig. 9a). In the case of volcanoes V, U, and Monowai, the arc lavas could be formed by 15%–25% partial melting of a mantle wedge source (F = 0.15–0.25) that had been modified by the addition of 1.5% sediment-derived melts (LSC:PS = 90:10) and 0.5% AOC fluid (Fig. 9b).

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REE modeling using the same end-members, mineral compositions, and degrees of partial melting and mixing, also shows good agreement with the results of Th and La modeling. As seen in Fig. 10a and b, the REE patterns of the modeled values and analyzed data for the southern Tonga Arc fit consistently, implying the conditions and hypothesis outlined above are highly plausible. The modeling results show that the influences of sediment-derived melts were relatively high for volcanoes V, U, and Monowai compared with TA15–16, Ata, and TA19, which were more strongly affected by AOC fluids. In the southern Tonga Arc, the sedimentderived melts were a mixture of partial melts of the pelagic sediments (PS) and LSC sediments. In the models, we used an LSC:PS ratio of 40:60 for TA15–16, Ata, and TA19, and a ratio of 90:10 for volcanoes V, U, and Monowai. The model results are consistent with the whole-rock data for the southern Tonga Arc (Figs. 8–10). We suggest, therefore, that volcanoes V, U, and Monowai were more strongly affected by LSC material than were TA15–16, Ata, and TA19, although the general influence of LSC is widespread in the southern Tonga Arc region. According to the subduction model of Ruellan et al. (2003), subduction of the LSC began at the northernmost part of the Tonga Arc and migrated southwards to its current location at 25°S. Timm et al. (2013) suggested that the LSC signature is better represented in volcanoes V, U, Monowai near the subducted LSC than in Ata, based on the high values of 206Pb/204Pb and 208Pb/204Pb. However, taking into account previous models and our modeling results, we conclude that although the LSC signature is widespread in the southern Tonga Arc region (i.e., in Ata and the volcanoes V, U, and Monowai), the volcanoes near 25°S (i.e., volcanoes V, U, and Monowai) were more strongly affected by the LSC component than those near 22°S (i.e., TA15–16, Ata, and TA19).

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6. Conclusions We compared the geochemical evolution of subduction-related lavas recovered from submarine volcanoes TA15–16 and TA19 on the southern Tonga Arc with lavas from volcanoes V, U, and Monowai farther south on the southern Tonga Arc. The petrogenesis of the southern Tonga Arc, as represented by TA15–16 and TA19, can be explained in terms of the influence of three components: (1) a mantle wedge source, (2) melts derived from a mixture of subducted sediments including pelagic sediments (PS) and sediments in the Louisville Seamount Chain (LSC), and (3) fluids derived as a result of dehydration of the altered oceanic crust (AOC). Trace element modeling shows that the influence of LSC-derived materials during subduction was widespread, both in the volcanoes at 22°S (i.e., TA15–16, Ata, and TA19) and those at 25°S (volcanoes V, U, and Monowai). Our models further indicate that the most primitive TA15–16, TA19, and Ata magmas were less affected by LSC sediment-derived melts and more affected by AOC-derived fluids than the magmas of volcanoes V, U, and Monowai. The relatively weak LSC signature observed in the volcanoes at 22°S can be attributed to the early subduction process, while the volcanoes near 25°S were more affected by LSC material as a result of the present westerly subduction of the LSC.

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Acknowledgments This work was supported by the Ministry of Oceans and Fisheries of Korea (Grant Nos. 19992001 and 20170411). We thank the scientists and crew of the R/V Onnuri for their support during the sampling and collection of data during the Tonga Arc cruises. We also thank three reviewers (Pat Castillo, Alexandra Yang, and an anonymous reviewer) and journal editor for their constructive and inspiring comments.

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Stoffers, P., Worthington, T., Ackermand, D., Fretzdorff, S., 2003. Cruise Report SONNE 167 Louisville Ridge: Dynamics and magmatism of a mantle plume and its influence on the Tonga‐Kermadec subduction system. Institut für Geowissenschaften, ChristianAlbrechts-Universität, Kiel, Germany, 276 pp. Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes, In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins. Geological Society of London, pp. 313-345. Tagudin, J. E., Scholl, D. W., 1994. The westward migration of the Tofua volcanic arc towards the Lau Basin, In: Herzer, R. H., Ballance, P.F., Stevenson, A.J. (Eds.), Geology and Resources of the Tonga-Lau-Fiji Region. SOPAC Technical Bulletin, pp. 81-100. Tatsumi, Y., 1989. Migration of fluid phases and genesis of basalt magmas in subduction zones. Journal of Geophysical Research: Solid Earth 94, 4697-4707. Tatsumi, Y., Hamilton, D.L., Nesbitt, R.W., 1986. Chemical characteristics of fluid phase released from a subducted lithosphere and origin of arc magmas: Evidence from highpressure experiments and natural rocks. Journal of Volcanology and Geothermal Research 29, 293-309. Tian, L., Castillo, P.R., Hawkins, J.W., Hilton, D.R., Hanan, B.B., Pietruszka, A.J., 2008. Major and trace element and Sr-Nd isotope signatures of lavas from the Central Lau Basin: Implications for the nature and influence of subduction components in the back-arc mantle. Journal of Volcanology and Geothermal Research 178, 657-670. Till, R., 1974. Statistical Methods for the Earth Scientist: An Introduction. John Wiley, New York, 154 pp. Timm, C., Bassett, D., Graham, I.J., Leybourne, M.I., De Ronde, C.E.J., Woodhead, J., LaytonMatthews, D., Watts, A.B., 2013. Louisville seamount subduction and its implication on

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mantle flow beneath the central Tonga-Kermadec arc. Nature communications 4, 17201728. Timm, C., Graham, I.J., De Ronde, C.E.J., Leybourne, M.I., Woodhead, J., 2012. Geochemical evolution of Monowai volcanic center: New insights into the northern Kermadec arc subduction system, SW Pacific. Geochemistry, Geophysics, Geosystems 12, Q0AF01. Todd, E., Gill, J.B., Wysoczanski, R.J., Handler, M.R., Wright, I.C., Gamble, J.A., 2010. Sources of constructional cross-chain volcanism in the southern Havre Trough: New insights from HFSE and REE concentration and isotope systematics. Geochemistry, Geophysics, Geosystems 11, Q04009. Turner, S., Hawkesworth, C., 1997. Constraints on flux rates and mantle dynamics beneath island arcs from Tonga-Kermadec lava geochemistry. Nature 389, 568-573. Turner, S., Hawkesworth, C., Rogers, N., Bartlett, J., Worthington, T., Hergt, J., Pearce, J., Smith, I., 1997. 238U-230Th disequilibria, magma petrogenesis, and flux rates beneath the depleted Tonga-Kermadec island arc. Geochimica et Cosmochimica Acta 61, 4855-4884. Wendt, J.I., Regelous, M., Collerson, K.D., Ewart, A., 1997. Evidence for a contribution from two mantle plumes to island-arc lavas from northern Tonga. Geology 25, 611-614. Woodhead, J.D., Eggins, S.M., Johnson, R.W., 1998. Magma genesis in the New Britain island arc: further insights into melting and mass transfer processes. Journal of Petrology 39, 1641-1668. Wyllie, P.J., 1979. Magmas and volatile components. American Mineralogist 64, 469-500. Yan, Q., Castillo, P.R., Shi, X., 2012. Geochemistry of basaltic lavas from the southern Lau Basin: Input of compositionally variable subduction components. International Geology Review 54, 1456-1474.

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Figure captions Fig. 1. Bathymetric map of: (a) the southern Pacific; and (b) the Tonga arc-Lau Basin (both from GeoMapApp). Back-arc spreading centers include: the Central Lau Spreading Center (CLSC); Intermediate Lau Spreading Center (ILSC); Eastern Lau Spreading Center (ELSC); and Valu Fa Ridge (VFR). The symbols indicate the locations of volcanoes discussed in this study. Fig. 2. Bathymetry map of TA15-16 and TA19, showing sampling locations (yellow circles). For satellite data in the background, refer to SRTM30+ version 11 (Becker et al., 2009). Contour interval is 200 m. Fig. 3. (a) TAS (Total Alkali versus Silica) diagram of analyzed lava samples from the study area. The samples show varying SiO2 content, from basalt andesite to dacite, which is consistent with a continuous fractionation trend. (b) AFM (Alkali-FeO-MgO) diagram, showing the boundary between the calc-alkaline field and the tholeiitic field. All samples from TA15-16 and TA19 are plotted in the tholeiitic field. (c) K2O versus SiO2 diagram, indicating that the samples belong to the low-K series. Data source for Tonga arc volcanic samples is GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/). Fig. 4. Variation diagrams against MgO (wt%) of major elements for the volcanic rocks, showing the Liquid Line of Descent (LLD) (the dashed lines). The fractional crystallization of olivine (ol), clinopyroxene (cpx), orthopyroxene (opx), and plagioclase (plag) (all marked with a minus sign) are required to explain the composition of TA15-16 and TA19. Fig. 5. Variation diagrams against MgO (wt%) of the some compatible elements for the volcanic rocks showing the Liquid Line of Descent (LLD) (the dashed lines). The fractional crystallization of olivine (ol), clinopyroxene (cpx), spinel (spl), magnetite (mag), and ilmenite (ilm) (all marked with a minus sign) are required to explain the composition of TA15-16 and TA19.

26

Fig. 6. (a) N-MORB-normalized incompatible trace element patterns for volcanic rocks from TA15-16, TA19, and Valu Fa Ridge (VFR) lavas (gray area) in the southern Tonga Arc. The data for VFR lavas were reported by Peate et al (2001), Escrig et al (2009), and Yan et al (2012). (b) Chondrite-normalized REE patterns for volcanic rocks from TA15-16 and TA19. Normalizing value is from Sun and McDonough (1989). Fig. 7. (a) Latitudinal variation of Nb(8)/Yb(8) in volcanic arcs located north and south of the study area. We used fractionation-corrected Nb and Yb value, which are labeled as Nb(8) and Yb(8) (i.e., Nb and Yb content at MgO of 8 wt%), considering the varying SiO2 content in samples. Because of the lack of data with >8 wt% MgO, Nb(8) and Yb(8) are extrapolated their composition at MgO of 8 wt% using the reduced major axis regression technique outlined in Till (1974) with at least five data points between 1 and 6 wt% MgO. Data for Fonualei, Late, Kao, Tofua, Hunga, Ata, V, U, and Monowai are whole rocks from the GEOROC database. (b) Along-axis variation of Nd isotopic data for the Lau Spreading center, including the Central Lau Spreading Center (CLSC), Eastern Lau Spreading Center (ELSC), and Valu Fa Ridge (VFR). These data are from Peate et al (2001), Tian et al (2008), Escrig et al (2009), and Yan et al (2012). Fig. 8. Ba/Th versus Th/Nb in volcanic arcs located north and south of the study area. We used fractionation-corrected Ba, Th, and Nb value (i.e., Ba, Th, and Nb concentration at MgO of 8 wt%) for study area (TA15-16, Ata, TA19, Volcano V, U, and Monowai) and representative volcanoes (Kao, Tofua, and Hunga) as well as relatively mafic data (i.e., MgO > 5 wt%) for published Tonga Arc. We used three end-members (i.e., sediment-derived melts with LSC and PS, and AOC fluid) and the mixing line with LSC and PS to evaluate the effects for subduction components. There are two trends (one is sediment-dominated, and the other is fluid-dominated trend) in Tonga Arc. The arrows indicate that the volcanoes with sediment-dominated trend have affected by more LSC and PS mixture than others, and show a lower influence of the LSC

27

sediment and higher PS melts in Ata, TA15-16, and TA19 than in volcanoes V, U and Monowai. See Table 3 for detailed parameters of three end-members. Fig. 9. Trace element modeling using Th and La content. (a) TA15-16, Ata, and TA19; (b) V, U, and Monowai. The end-members in the models are composed of the mantle wedge, the AOC fluid, made by 30% partial melting of the AOC, and the sediment melt, formed by 20% partial melting of a sediment mixture ((a) LSC:PS = 40:60, (b) LSC:PS = 90:10). Th and La content of relatively mafic samples (i.e., MgO > 5 wt%) are used in the models. See Table 2 and 3 for detailed modeling parameters. Fig. 10. REE modeling of: (a) TA15-16, Ata, and TA19; and (b) V, U, and Monowai. REE patterns of the three end-members, which are equal to those in trace element modeling, and the modified mantle wedge, resulted from mixing of the end-members. REE concentration of relatively mafic samples (i.e., MgO > 5 wt%) are used in the models. See Table 2 and 3 for detailed modeling parameters.

28

Graphical abstract

29

Highlights

 Southern Tonga Arc volcanic rocks show geochemical variation affected by subduction components.  Influence of Louisville Seamount Chain (LSC) is widely shown in volcanoes between 22°S and 25°S.  Contribution of subduction components is evaluated by using trace element modeling.  Volcanic rocks at 25°S are more affected by LSC material than those at 22°S.

30

31

32

33

34

35

36

37

38

39

40

Table 1. The major and trace element composition for southern Tonga Arc Sample Edifice Rock type

Dacite

Latitude(S) Longitude(E) Water depth (mbsl)

22.03 176.13

LB070602 TA15-16 Basaltic andesite 22.03 176.13

407.5

407.5

SiO2(%)

67.21

56.66

56.2

55.87

69.41

59.78

62.05

54.01

Al2O3

13.08

14.93

15.06

14.79

12.99

13.74

14.59

16.98

6.2

10.32

10.48

10.36

5.91

10.14

9.45

11.82

MnO

0.139

0.161

0.163

0.162

0.134

0.158

0.154

0.201

MgO

1.51

3.05

3.4

3.05

1.21

2.18

2.32

5.94

CaO

5.62

10.23

10.42

10.01

5.18

8.5

7.46

9.91

Na2O

2.64

1.75

1.73

1.84

2.83

1.9

2.46

2.03

K2O

0.78

0.29

0.35

0.26

0.61

0.44

0.62

0.48

TiO2

0.461

0.591

0.555

0.586

0.476

0.635

0.709

0.69

P2O5

0.13

0.08

0.09

0.08

0.16

0.1

0.14

0.14

Fe2O3(T)

LB070601 TA15-16

LB070603 TA15-16 Basaltic andesite 22.03 176.13

LB070604 TA15-16 Basaltic andesite 22.03 176.13

LB070605 TA15-16

LB070701 TA15-16

LB070803 TA15-16

Dacite

Andesite

Andesite

22.03 176.13

22.04 176.14

22.08 176.14

LB071401 TA15-16 Basaltic andesite 22.05 176.05

407.5

407.5

407.5

689

352.5

730.5

LOI

1.61

-0.1

-0.19

-0.09

0.06

-0.03

0.01

-0.21

Total

99.37

100.1

100.2

99.03

98.98

98.85

99.97

99.81

Sc(ppm)

29

43

52

45

25

42

39

52

V

98

385

442

406

68

396

331

403

Cr

13

23

12

13

4

4

7

104

Co

14

29

35

29

10

26

25

43

Ni

4

12

9

7

1

4

5

36

Cu

40

162

198

188

33

117

138

147

Zn

101

88

99

92

80

100

101

98

Ga

14

15

17

16

14

16

16

16

Rb

12

3

2

2

11

6

7

5

Sr

164

168

184

168

169

177

196

258

Y

27

18

17

16

26

20

25

17

Zr

41

27

25

20

40

26

48

27

Nb

0.4

0.24

0.51

0.08

0.73

0.53

0.26

0.39

Cs

0.39

0.09

0.04

0.11

0.15

0.29

0.34

0.21

Ba

202

146

134

118

199

147

192

147

Hf

1.38

0.92

0.79

0.73

1.42

0.96

1.48

0.87

Pb

2.49

0.94

0.87

1.08

2.59

1.99

2.15

1.49

Th

0.32

0.22

0.17

0.15

0.38

0.2

0.31

0.31

U

0.18

0.14

0.1

0.1

0.19

0.12

0.18

0.14

La

3.12

2.21

1.81

1.59

3.1

2.04

3.4

3.19

Ce

7.8

5.47

4.49

3.98

7.92

5.08

8.98

7.87

Pr

1.22

0.85

0.71

0.65

1.24

0.8

1.36

1.18

Nd

6.56

4.53

3.95

3.61

6.65

4.48

7.25

6.1

Sm

2.34

1.56

1.42

1.33

2.37

1.65

2.41

1.94

Eu

0.78

0.57

0.55

0.53

0.81

0.63

0.82

0.73

Gd

3.12

2.09

1.89

1.91

3.15

2.3

3.08

2.35

Tb

0.58

0.39

0.36

0.36

0.6

0.44

0.56

0.41

Dy

4.06

2.7

2.55

2.56

4.14

3.12

3.76

2.8

Ho

0.9

0.6

0.56

0.57

0.93

0.71

0.83

0.59

Er

2.79

1.88

1.72

1.73

2.87

2.19

2.59

1.76

Tm

0.41

0.28

0.26

0.26

0.43

0.32

0.39

0.26

41

Yb

2.83

1.9

1.71

1.76

2.89

2.26

2.57

1.7

Lu

0.46

0.3

0.27

0.28

0.47

0.35

0.4

0.26

LB071402 TA15-16 Basaltic andesite 22.05 176.05

LB073301 TA19-1 Basaltic andesite 22.42 176.23

LB073302 TA19-1

730.5

SiO2(%)

Table 1. Continued Sample Edifice

22.42 176.23

LB081101 TA19-2 Basaltic andesite 22.50 176.22

LB081102 TA19-2 Basaltic andesite 22.50 176.22

LB081103 TA19-2 Basaltic andesite 22.50 176.22

LB081104 TA19-2 Basaltic andesite 22.50 176.22

LB081108 TA19-2 Basaltic andesite 22.50 176.22

566

566

740.5

740.5

740.5

740.5

740.5

54.82

55.4

57.82

56.33

55.16

56.7

56.24

53.99

Al2O3

15.08

16.52

15.23

16.18

14.57

14.82

14.63

16.86

Fe2O3(T)

11.7

12.44

8.7

12.31

10.34

10.41

10.43

10.48

MnO

0.202

0.204

0.146

0.194

0.161

0.181

0.163

0.175

MgO

5.01

4.25

3.52

4.02

2.9

3.45

2.99

5.97

CaO

9.35

9.89

9.14

8.9

9.64

9.48

9.41

10.83

Na2O

2.2

2.08

2.33

2.3

2.22

2.22

2.33

1.79

Rock type Latitude(S) Longitude(E) Water depth (mbsl)

Andesite

K2O

0.55

0.36

0.39

0.5

0.37

0.47

0.45

0.39

TiO2

0.712

0.858

0.702

0.868

0.744

0.706

0.752

0.593

P2O5

0.14

0.09

0.13

0.12

0.1

0.12

0.11

0.07

LOI

-0.12

0.4

-0.07

-0.41

-0.34

-0.43

-0.43

-0.38

Total

99.65

100.6

99.67

99.98

98

99.47

98.96

99.16

Sc(ppm)

53

53

36

44

41

42

43

48

V

441

475

278

432

398

360

408

349

Cr

49

10

20

13

12

9

16

44

Co

42

39

28

38

32

31

32

41

Ni

21

15

11

14

8

9

9

24

Cu

181

172

123

181

157

167

170

86

Zn

106

108

88

108

98

95

100

91

Ga

17

16

17

17

19

17

19

16

Rb

6

3

3

5

9

6

5

2

Sr

287

207

240

217

246

229

254

198

Y

19

21

23

22

23

20

25

16

Zr

33

34

47

46

47

42

56

32

Nb

0.31

0.15

0.23

0.22

0.23

0.35

0.38

0.18

Cs

0.22

0.24

0.22

0.3

0.27

0.31

0.3

0.17

Ba

164

133

162

174

167

173

185

122

Hf

0.98

1.08

1.42

1.39

1.4

1.26

1.61

0.93

Pb

1.58

1.58

1.31

1.95

1.83

1.9

1.97

1.29

Th

0.31

0.17

0.31

0.32

0.34

0.31

0.32

0.18

U

0.13

0.1

0.24

0.17

0.14

0.15

0.16

0.08

La

3.42

1.97

3.04

3.09

2.97

2.92

3.23

1.92

Ce

8.57

5.36

8.2

8.15

7.94

7.51

8.82

5.01

Pr

1.27

0.92

1.3

1.28

1.27

1.18

1.39

0.82

Nd

6.64

5.22

7.03

6.88

6.8

6.23

7.51

4.49

Sm

2.16

1.94

2.38

2.32

2.29

2.09

2.49

1.57

Eu

0.81

0.75

0.86

0.82

0.84

0.76

0.9

0.59

Gd

2.65

2.55

3.06

2.9

2.98

2.61

3.21

1.95

Tb

0.46

0.49

0.56

0.52

0.54

0.47

0.57

0.35

Dy

3.03

3.37

3.62

3.5

3.6

3.15

3.77

2.47

Ho

0.65

0.73

0.79

0.76

0.79

0.69

0.83

0.54

Er

1.9

2.25

2.42

2.28

2.41

2.05

2.49

1.62

42

Tm

0.27

0.32

0.35

0.33

0.36

0.3

0.37

0.23

Yb

1.85

2.13

2.32

2.26

2.33

1.98

2.5

1.59

Lu

0.29

0.33

0.36

0.34

0.35

0.32

0.38

0.25

Table 1. Continued Sample

BIR-1a (n = 3)

DNC-1 (n = 3)

W-2a (n = 3)

BCR-2 (n = 3)

Edifice

Standard

Standard

Standard

Standard

This study

Published (Jochum et al., 2016)

This study

Published (Govindaraj u, 1994)

This study

Published (Jochum et al., 2016)

This study

Published (Jochum et al., 2016)

48.3

47.79

47.07

47.04

52.51

52.57

Al2O3

15.7

15.51

18.53

18.3

15.19

15.38

Fe2O3(T)

11.59

11.4

9.91

9.93

10.97

10.8

MnO

0.171

0.1731

0.147

0.149

0.165

0.1658

MgO

9.55

9.689

9.87

10.05

6.31

6.431

CaO

13.52

13.29

11.38

11.27

11.13

10.91

Na2O

1.82

1.832

1.89

1.87

2.17

2.196

K2O

< 0.01

0.029

0.2

0.229

0.63

0.6242

TiO2

0.971

0.9587

0.491

0.48

1.076

1.064

P2O5

0.02

0.03

0.08

0.085

0.15

0.1362

Sc(ppm)

32.11

33.53

V

447.95

417.6

Cr

15.98

15.85

Co

37.14

37.33

Ni

12.01

12.57

Cu

19.55

19.66

Zn

141.33

129.5

Ga

22.46

22.07

Rb

48.76

46.02

Sr

349.96

337.4

Y

34.53

36.07

Zr

185.08

186.5

Nb

10.53

12.44

Cs

1.18

1.16

Ba

668.66

683.9

Hf

4.71

4.972

Pb

9.095

10.59

Th

5.78

5.828

U

1.68

1.683

La

24.43

25.08

Ce

51.12

53.12

Pr

6.67

6.827

Nd

28.19

28.26

Sm

6.56

6.547

Eu

2.05

1.989

Gd

6.91

6.811

Tb

1.05

1.077

Dy

6.28

6.424

Ho

1.28

1.313

Er

3.68

3.67

SiO2(%)

LOI Total

43

Tm

0.51

Yb

3.25

0.5341 3.392

Lu

0.49

0.5049

Table 2. The partial melting parameter of primitive mantle. The mineral mode of primitive mantle is as follows: olivine = 65%; orthopyroxene (opx) = 25%; clinopyroxene (cpx) = 8%; spinel = 2% Partition coefficients

DOlivine

DOPX

DCPX

DSpinel

Bulk Kd

Primitive mantle

Mantle wedge

5% partial melting of PM

a=

Th

0.0001a

0.00026a

0.0001

0.085

0.0002

La

0.00007b

0.0005b

0.0536b

0.0006b

0.0106

0.687

0.1209

Ce

0.0001b

0.0009b

0.0858b

0.0006b

0.0169

1.775

0.4544

Nd

0.0007b

0.009b

0.1873b

0.0006b

0.0386

1.354

0.6031

Sm

0.007b

0.02b

0.291b

0.0006b

0.0645

0.444

0.2574

Eu

0.00095b

0.03b

0.35b

0.0006b

0.0746

0.168

0.1037

Gd

0.0012b

0.04b

0.4b

0.0006b

0.0865

0.596

0.3900

Dy

0.004b

0.06b

0.442b

0.0015b

0.1003

0.737

0.5088

Er

0.009b

0.07b

0.387b

0.003b

0.0946

0.48

0.3246

Yb

0.023b

0.1b

0.43b

0.0045b

0.1170

0.493

0.3579

Lu

0.0015a

0.06a

1c

0.01a

0.2075

0.025

0.0570d

McKenzie and O'Nions (1991); b = Kelemen et al (1993); c = Gaetani (2004); d = Assumed in Timm et al (2012);

PM = Primitive mantle

44

Table 3. End-member composition used in subduction proxies (i.e., Ba/Th and Th/Nb) and modelings for the petrogenesis for volcanoes at 22°S in the southern Tonga Arc.

a

Mantle wedge

Tonga Pelagic sediment

Louisville seamount chain sediment

90:10a Sediment mix

40:60 Sediment mix

Oceanic crust

D1b

D2c

D3d

Cmelt Sediment mix

Cfluid Oceanic crust

Modified mantle wedgee

Ba

-

850

195

-

-

38

-

1.64

47

-

-

-

Th

0.0002

9

1.47

2.223

5.988

0.2

0.0001

1.45

62

1.635

0.005

0.049

Nb

-

11

18.8

-

-

2

-

3

173

-

-

-

La

0.1209

104

15

23.9

68.4

3.34

0.0043

2.47

74

10.983

0.064

0.443

Ce

0.4544

184

34

49

124

11.48

0.0069

2.97

35

19.022

0.463

1.006

Nd

0.6031

122

19.7

29.93

81.08

10.15

0.0171

4.41

19.6

8.028

0.724

0.825

Sm

0.2574

27

4.88

7.092

18.152

3.43

0.0319

4.17

3.8

2.006

1.159

0.318

Eu

0.1037

6.6

1.59

2.091

4.596

1.23

0.0349

8.11

2.05

0.313

0.709

0.116

Gd

0.3900

29

4.96

7.364

19.384

4.68

0.0413

8.67

1.03

1.032

4.584

0.451

Dy

0.5088

26

4.2

6.38

17.28

5.53

0.0513

10

0.301

0.778

10.828

0.620

Er

0.3246

15

2.01

3.309

9.804

3.52

0.0528

10.1

0.14

0.4

8.844

0.412

Yb

0.3579

13

1.68

2.812

8.472

2.75

0.0726

9.68

0.092

0.354

7.547

0.430

Lu

0.0570f

2

0.24

0.416

1.296

0.45

0.0929

9.28

0.077

0.055

1.272

0.069

= Model mix is based on the quantitative model suggested by Turner et al (1997), comprising 90% Louisville

Seamount Chain sediments and 10% pelagic sediments; b = for partial melting modeling of the modified mantle wedge having a mineral mode of 55% olivine, 21% orthopyroxene, 20% clinopyroxene and 4% spinel and the modeling uses the same partition coefficients as listed in Table 3; c = Sediment melt partition coefficients from Johnson and Plank (2000) d = Bulk distribution coefficients for eclogite-fluid equilibria from Kessel et al (2005); e

= Addition of ~ 3% sediment mix melt and ~ 1% AOC fluid to mantle wedge; f = Assumed in Timm et al (2012)

45