Geochemical characterization of highly diverse hydrothermal fluids from volcanic vent systems of the Kermadec intraoceanic arc

Chemical Geology 528 (2019) 119289

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Geochemical characterization of highly diverse hydrothermal fluids from volcanic vent systems of the Kermadec intraoceanic arc

T

Charlotte Kleinta,b, , Wolfgang Bachb,c, Alexander Diehlb,c, Nico Fröhberga, Dieter Garbe-Schönbergd, Jan F. Hartmanna,e, Cornel E.J. de Rondef, Sylvia G. Sanderg,h, Harald Straussi, Valerie K. Stuckerf, Janis Thalb,c, Rebecca Zitoung, Andrea Koschinskya,b ⁎

a

Department of Physics and Earth Sciences, Jacobs University Bremen, 28759 Bremen, Germany Center for Marine Environmental Sciences (MARUM), University of Bremen, 28359 Bremen, Germany c Department for Geosciences, University of Bremen, 28359 Bremen, Germany d Institute of Geosciences, Kiel University, 24118 Kiel, Germany e Institute of Earth Sciences, Heidelberg University, 69115 Heidelberg, Germany f Department of Marine Sciences, GNS Science, Lower Hutt 5040, New Zealand g Department of Chemistry, University of Otago, Dunedin 9016, New Zealand h Marine Environmental Studies Laboratory, International Atomic Energy Agency - Nuclear Applications, 98000, Monaco, Monaco i Department for Geology and Palaeontology, University of Münster, 48149 Münster, Germany b

ARTICLE INFO

ABSTRACT

Editor: Karen Johannesson

During the R/V Sonne cruise SO253 in 2016/2017, hydrothermal vent sites along the Kermadec intraoceanic arc were sampled for hydrothermal fluids at four active volcanoes: Macauley, Haungaroa, Brothers and Rumble III, respectively. Water depths ranged between 290 m and 1700 m. A new vent field was discovered at Haungaroa. The samples were taken from diffuse-flow sites as well as from white and black smokers – rich in metals and gases – with discharge temperatures as high as 311 °C. Their fluid composition is very variable but basically divides into two types: one that indicates distinct magmatic input and another that shows evidence for intense water-rock interaction under hot, acidic conditions. Fluid samples from Macauley, the shallowest sampling site (~300 m), had Fe concentrations as high as 1.7 mM, Al concentrations up to 122 μM and H2S up to 10 mM at a pH of only 1.2. At Brothers, the deepest sampling site (down to 1600 m), we identified two different fluid types: 1) A magmatically-influenced type at the Upper and Lower Cone with highest temperatures of 115 °C, up to 95.6 mM Mg (the highest Mg concentration measured in fluids from intraoceanic arc systems so far), elevated SO42− (76.9 mM), high H2S (5.0 mM), but Fe concentrations of only 15 μM and 2) A fluid with low Mg (5.4 mM), low H2S (1.1 mM), temperatures reaching 311 °C and high Fe contents (12.4 mM) at the Upper Caldera and NW Caldera Wall, typical of a black smoker fluid. Chloride concentrations in all fluids were similar, or highly enriched when compared to seawater (e.g. up to 787 mM, brine fluids), with also one low-chlorinity vapor-phase fluid sample recovered, indicating that phase separation is occurring at Brothers. Unusual highly elevated Mg concentrations in fluids from the Brothers Lower Cone (95.6 mM, compared to 53.2 mM in ambient seawater) combined with highly elevated concentrations of SO42− (76.9 mM, compared to 29.0 mM in ambient seawater) indicate dissolution of Mg- and SO42−-bearing minerals in the subsurface, such as caminite. Our data show how highly diverse and variable island arc systems can be with respect to their fluid chemistry, both spatially and temporally. It adds to the still limited data set of arc systems compared to mid-ocean ridges and supplies an important contribution towards a better understanding of geochemical processes along arc volcanoes. The higher range in fluid chemistry together with shallower water depth implies that the fluids from intraoceanic arcs may contribute a significant fraction of dissolved metals not only to the global oceanic biogeochemical cycle but also into the photic zone, the area of highest bioproductivity.

Keywords: Hydrothermalism at intraoceanic arcs High-chlorinity acid-sulfate fluids High Mg-fluids Kermadec arc Trace metals

⁎

Corresponding author at: Department of Physics and Earth Sciences, Jacobs University Bremen, 28759 Bremen, Germany. E-mail address: [email protected] (C. Kleint).

https://doi.org/10.1016/j.chemgeo.2019.119289 Received 6 February 2019; Received in revised form 15 August 2019; Accepted 28 August 2019 Available online 03 September 2019 0009-2541/ © 2019 Elsevier B.V. All rights reserved.

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1. Introduction

Elements, such as e.g. calcium, (Ca) iron (Fe), silica (Si) and manganese (Mn) as well as different gases (He, H2, CO2 and CH4) are usually enriched in the emitting fluid compared to ambient seawater. Phase separation is common at many seafloor hydrothermal systems, separating the fluid into a volatile-rich “vapor” phase and a metal-rich “brine” phase (Bischoff, 1991; Butterfield et al., 1990; Von Damm, 1995). If the fluid keeps below the critical point of seawater at 407 °C and 298 bar (~3000 m water depth), a gas-rich vapor phase of very low chlorinity and density is formed, as well as a liquid phase of essentially unmodified chlorinity, known as subcritical phase separation. Above the critical point, however, supercritical phase separation will take place characterized by the condensation of a high-salinity brine droplet, which produces a residual phase that is generally referred to as vapor. So far, supercritical phase separation occurring at the seafloor, has only been observed at the 5°S hydrothermal vent field, at the Mid-Atlantic-Ridge (Koschinsky et al., 2008). As the water depth, and thereby pressure, in shallower island arc settings is much lower

Volcanic arcs and their associated hydrothermal systems span ∼21,700 km of the Earth's surface, about 1/3rd of mid-ocean ridges (MORs; de Ronde and Stucker, 2015). Arc systems may be of real significance in terms of metal flux into the surface oceans, as they are typically located in shallow water depth (< 1800 m) with more than half of them at < 500 m (de Ronde et al., 2003). To develop a convective seawater-derived submarine hydrothermal environment, cold seawater needs to seep through cracks and faults into the oceanic crust where it is exposed to a heat source. With increasing proximity to the heat source, the seawater gets heated, potentially to temperatures above 450 °C (Mills, 1995) and the precipitation of different minerals occurs, such as anhydrite, resulting in a fluid depleted in sulfate (SO42−); or clay minerals (such as smectite), depleting the fluid in magnesium (Mg). A pure end-member fluid would therefore contain 0 mM Mg and 0 mM SO42− (Mottl and Holland, 1978).

Fig. 1. Map showing the active and inactive hydrothermal sites along the Kermadec arc with the working areas of research cruise SO253 (Macauley, Haungaroa, Brothers and Rumble III) highlighted by dashed boxes. Adapted from GNS-Science (2017). 2

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than at MORs, phase separation will most-likely be subcritical. In addition to the differences in water depth, the host rocks of arc systems typically have a more evolved to intermediate to felsic (i.e. rhyolitic to rhyodacitic or andesitic) composition compared to mostly basaltic and ultramafic host rocks at MORs (Hannington et al., 2005; Keith et al., 2016). Hydrothermal activity releases large amounts of various elements into the ocean, with the fluid composition dependent on several factors such as temperature, pressure, tectonic setting and magmatic activity. Arc, as well as back-arc volcanoes show a large range of water depth (approx. 300 m to 1800 m water depth), a high variability in host-rock composition and a potential magmatic volatile input, which leads to a high compositional fluid diversity (e.g., the Manus Basin (Craddock et al., 2010; Gamo et al., 1997; Reeves et al., 2011; Seewald et al., 2019, 2015), the Lau Basin (Baker et al., 2005; German et al., 2006; Mottl et al., 2011; Takai et al., 2008), the Mariana arc (Baker et al., 2008; Embley et al., 2007; Resing et al., 2007), the North Fiji Basin (Grimaud et al., 1991), the New Hebrides arc (Schmidt et al., 2017) or the Kermadec arc (de Ronde et al., 2001, 2007)). Here, we present results on the diverse fluid chemical compositions, including significant small scale variations of four different submarine hydrothermal systems, all located along the Kermadec intraoceanic arc, with implications for their role in elemental fluxes into the ocean as well as subsurface processes such as phase separation and mineralization. Thus, we consider our findings as an important contribution towards a better understanding of geochemical processes as well as the related fluid composition along arc environments, adding to the still limited data set of such systems.

1.1.3. Brothers volcano Brothers volcano is the hydrothermally most active and so far beststudied of the four working areas (de Ronde et al., 2012 and references therein). The area is comprised of a ~3 km wide silicic caldera with two resurgent cones located in the southern part of the caldera. Hydrothermal activity at Brothers is concentrated in several areas but especially at the Upper Caldera, NW Caldera Wall, Upper Cone and Lower Cone, and to a lesser degree at the W Caldera and SE Caldera (Fig. 4). At the Upper Cone (four fluid samples), diffuse hydrothermal venting is common in ~1200 m water depth, while white smoker venting is common at the Lower Cone (six fluid samples) in ~1300 m water depth. Black smokers of several meters height expel high-temperature, focused fluids at the Upper Caldera (three samples) and NW Caldera Wall (24 fluid samples) in water depths of ~1370 m and 1600 m, respectively.

1.1. Geological setting and working areas

2.1. Sampling devices

The Kermadec intraoceanic arc is located northeast of New Zealand, where the Pacific plate is subducted beneath the Australian plate. It stretches from White Island up through Tonga where it becomes the Tofua arc, combined forming 2500 km of intraoceanic arc (de Ronde et al., 2003). The whole arc is host to around 80 submarine volcanoes of which around 80% in the Kermadec section are hydrothermally active and has a density of active volcanic centers of 1.4/100 km of arc length (de Ronde et al., 2001). Four working areas along the southern and middle Kermadec intraoceanic arc were selected during the research cruise SO253: Macauley, Haungaroa, Brothers and Rumble III (Fig. 1).

All hydrothermal fluid samples were collected during R/V Sonne cruise SO253 between December 2016 and January 2017 using the remotely operated vehicle (ROV) MARUM-QUEST 4000 (University of Bremen). For the direct sampling of hot, focused fluids from the high-temperature vents, two Isobaric Gas Tight (IGT) samplers (150 mL each (Seewald et al., 2002)) as well as two Titanium Syringe Samplers (major samplers, 750 mL each (Von Damm et al., 1985)) were deployed on the ROV. In contrast to the major sampler, the IGT fluid sampler keeps the sample at seafloor pressure (up to 450 bar) before and during sample withdrawal in the laboratory, which enables subsampling nearly under in-situ conditions without degassing of the fluid. Larger volumes of lower temperature and diffuse hydrothermal fluids were collected by the fully remotely controlled flow-through fluid sampling system KIPS (Kiel Pumping System, KIPS-4; Garbe-Schönberg et al., 2006) made entirely of inert materials, such as perfluoralkoxy (PFA) and high-purity titanium (4 bottles, 750 mL each). An ambient background seawater sample was collected in an area not affected by hydrothermal venting using a trace metal rosette (TMR) in 1250 m water depth (Table 1).

1.1.4. Rumble III volcano Rumble III (Fig. 5) is a stratovolcano that is seismically active with morphological changes having occurred over the past 20–30 years. A slope collapse created a talus field of volcanic rocks surrounding a pronounced vertical volcanic edifice of coherent lava, reminiscent of a volcanic spine. Rumble III has been reported to be hydrothermally active due to the presence of relatively shallow hydrothermal plumes (de Ronde et al., 2001). During our expedition, hydrothermal activity was seen as diffuse fluids emitting through rocks (five fluid samples were collected); black smoke was visible in the water column although no focused black smoker venting was found. 2. Samples and methods

1.1.1. Macauley volcano Macauley is a caldera volcano 10 km in diameter and is comprised of a silicic cone/basalt dome-shield (Wright et al., 2006) with known hydrothermal activity being located near the summit of a cone within the caldera at only ~290 m water depth (Fig. 2). Venting at Macauley occurs within the summit pit crater of the cone (45 m deep and 80 m across) located in the southern part of the caldera. It is present as white fluids including single gas bubbles emitted directly out of rocks with elemental sulfur around the vent outlet. Wright et al. (2006) sampled lavas that comprised aphyric and sparsely plagioclase-phyric dacite. Ten separate fluid samples from two areas were collected.

2.2. Methods 2.2.1. On-board measurements Once on-board, aliquots of all samples were analyzed for pH, redox potential (Eh) and salinity with a WTW pH/Cond 340i multimeter. Sensors used were a SenTix ORP platinum electrode with 3 M KCl reference electrolyte for Eh, a SenTix 41 pH probe and a WTW TetraCon 325 conductivity probe to determine salinity. Sulfide (H2S) concentrations were determined on-board photometrically following the methylene blue method described by Cline (1969). A first determination of total Fe and Fe(II) concentration was conducted on-board using a visual Fe CHEMets© field kit (classic chelating ligand: 1,10-phenanthroline). The method is described in more detail in

1.1.2. Haungaroa volcano Haungaroa (Fig. 3) is a stratovolcano and prior to SO253, no dives had been carried out at this site. At Haungaroa, focused high-temperature venting as well as diffuse venting through large fields of barnacles and mussels occurs in a 170 by 60 m area north of the summit at 675 to 688 m water depth. The hydrothermally active area is near the summit of the cone and is hosted by a phyric and sparsely plagioclasephyric basaltic andesite, similar to the lava that forms the main volcanic edifice (Wright et al., 2006). Twelve fluid samples were collected at Haungaroa. 3

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Fig. 2. A) Bathymetric map showing the Macauley volcano including the two sampling sites. B) White hydrothermal fluids being expelled from a mound of whitishyellow rocks covered with elemental sulfur.

Kleint et al. (2015). An overview on all fluid samples taken with IGTs, Majors and KIPS, the ambient seawater (SW) sample, as well as the parameters that were measured on-board after retrieval of the samples is shown in Table 1. While Major and IGT samples are mostly from focused venting, KIPS samples rather represent diffuse venting and are therefore typically diluted by seawater.

clean container through 0.2 μm HEPA filters. Concentrations of major and minor elements were determined by inductively coupled plasma - optical emission spectrometry (ICP-OES, Spectro Ciros) after matrix-matched calibration, while trace elements, including the rare earth elements and yttrium, were determined by inductively coupled plasma – mass spectrometry (ICP-MS, Perkin Elmer NexION), at Jacobs University Bremen. To confirm unusual high Mg concentrations as well as to rule out any methodological flaws, the samples were re-measured by ICP-OES (Spectro Ciros) at the University of Kiel, Germany. As results were comparable (deviations below 5%), the Mg concentrations are considered as true and correct. Concentrations of the anions sulfate and chloride were determined at the New Zealand Geothermal Analytical Laboratory, GNS Science, using a Dionex ICS 5000 ion chromatograph equipped with AG- and AS-11 columns. Samples were diluted 50–100× and standards were run every

2.2.2. Major, minor and trace metals For major, minor and trace metal analysis, the samples were pressure-filtered (99.99% nitrogen) through 0.2 μm Nuclepore polycarbonate (PC) membrane filters in a Sartorius filtration unit installed in a laminar flow bench, acidified with suprapure HCl to pH ~2 and stored in acid cleaned PE bottles at 4 °C until further analysis. The background seawater sample was collected with a TMR and filtered in a

Fig. 3. A) Bathymetric map showing the Haungaroa volcano including the sampling site. B) Diffuse venting as given by shimmering water. 4

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Fig. 4. A) Bathymetric map showing the Brothers volcano including the two sampling sites at the Caldera Wall (Upper Caldera and NW Caldera Wall) as well as the two cone sites (Lower Cone and Upper Cone). B) High-temperature, black smoker venting at the NW Caldera Wall site of Brothers volcano. C) White smoker venting at the Lower Cone.

Fig. 5. A) Bathymetric map showing the Rumble III volcano including the sampling site. B and C) Warm and diffuse fluids emitting from a crack with surrounding rocks covered by white fluffy bacterial mats.

10 samples and verified to be within 5% of expected value. Accuracy for minor and major elements was monitored with IAPSO standard seawater (supplied by Ocean Scientific International Ltd. along with the concentrations of major and minor elements). Additionally, as quality control for trace metals, the seawater reference material NASS-7 from the National Research Council Canada was measured along with the samples. The analytical errors for IAPSO and NASS-7 were within ± 5% of the reference/recommended values.

2.2.3. Comparison of derived Fe concentrations by CHEMets© field kit vs. ICP-OES A first determination of the Fe concentration in all fluid samples was done on-board using the CHEMets© field kit (with a measuring range of ~0.001 mM–1.8 mM Fe). A comparison of the results obtained by this colorimetric on-board analysis of Fe to ICP-OES measurements performed in the lab results in a very good agreement between the two methods (Fig. 6). The highest offset is observed for samples with the highest Fe concentrations. Upon sample recovery, no information on the actual Fe concentration in the sample was available. Therefore, samples were 5

Brothers (Cones)

Haungaroa

SW Macauley

045ROV

048ROV

Lower Cone

Upper Cone

035ROV

030ROV

018ROV 023ROV 026ROV

013ROV

080TMR 009ROV

Station 4 2F 3F 4F 12F 2F 3F 4F 5F 5F 4F/5F 4F 5F 9F 10F/11F 2F/3F 10F 11F 16F 5F 7F 8F 17F–19F 3F 4F 5F/6F 9F/10F 11F 12F 2F 4F 5F 10F

Sample no. TMR IGT Major Major KIPS IGT IGT Major Major KIPS KIPS IGT Major Major KIPS KIPS IGT Major Major Major IGT Major KIPS IGT Major KIPS KIPS IGT Major IGT Major KIPS IGT

Sampling device 1250 336 337 337 291 336 336 335 335 686 685 679 679 662 674 675 677 677 688 683 684 684 613 1318 1318 1318 1332 1331 1331 1217 1217 1217 1218

Water depth [m] 35° 30° 30° 30° 30° 30° 30° 30° 30° 30° 30° 32° 32° 32° 32° 32° 32° 32° 32° 32° 32° 32° 32° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34°

15.50100′ 12.77455′ 12.77527′ 12.77535′ 12.72972′ 12.77463′ 12.77479′ 12.77478′ 12.77469′ 12.96689′ 12.96451′ 36.99614′ 36.99614′ 36.97765′ 36.96667′ 36.94558′ 36.94573′ 36.94573′ 36.94726′ 36.95220′ 36.95061′ 36.95061′ 36.96892′ 52.73418′ 52.73400′ 52.73383′ 52.73116′ 52.73184′ 52.73187′ 52.93231′ 52.93231′ 52.93756′ 52.95167′

Latitude S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S

178° 178° 178° 178° 178° 178° 178° 178° 178° 178° 178° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179°

46.62500′ 26.94008′ 26.93843′ 26.93919′ 26.98012′ 26.93295′ 26.93186′ 26.93143′ 26.93080′ 27.84233′ 27.84386′ 37.55880′ 37.55880′ 37.55288′ 37.52404′ 37.39238′ 37.46876′ 37.46876′ 37.45933′ 37.43188′ 37.46704′ 37.46704′ 37.52847′ 04.26340′ 04.26351′ 04.26386′ 04.27879′ 04.27910′ 04.27945′ 04.10221′ 04.10221′ 04.09600′ 04.09824′

Longitude E W W W W W W W W W W W W W W W W W W W W W W E E E E E E E E E E

– 90 – – – 112 112 – – – – 23 – – 13 13–18 210 – – – 267 – 13 67 – 70 77.5 83 – 115 – 15–23 83

T [°C] 7.8 1.5 2.3 2.0 7.0 1.2 1.6 1.6 1.6 7.9 7.8 6.1 6.3 6.5 7.8 7.6 3.9 5.1 5.1 3.4 3.7 5.2 6.1 4.8 4.4 4.5 4.5 3.8 4.4 2.4 2.4 5.7 2.1

pH 328 – 130 138 108 205 185 189 176 370 315 141 90 90 324 280 77 57 73 144 100 77 55 −1 2 6 26 39 32 190 176 69 170

Eh [mV] 32.6 – 39.3 44.2 33.5 50.5 49.6 50.2 50.1 32.8 32.8 33 32.8 32.8 32.5 32.6 28.3 31.8 34.2 36.0 27.4 31.8 32.7 34.1 33.7 33.9 33.5 34.8 33.5 33.6 33.3 33.0 34.8

Salinity [‰] – – – 8.12 0.073 9.91 8.89 9.31 10.4 – – 0.004 0.004 – – b.d. 2.06 0.521 0.437 1.19 1.57 0.349 0.105 4.49 5.06 – – 4.98 3.61 1.53 1.28 0.271 2.31

6

b.d. – – 1.07 0.002 1.61 1.43 1.79 1.61 – b.d 0.014 0.007 0.004 b.d. b.d. 0.107 0.018 0.107 0.358 0.269 0.027 b.d. 0.036 0.001 0.002 0.004 0.013 b.d. 0.013 0.007 0.002 0.023

Fe2+ [mM]

b.d. – – 1.07 0.004 1.61 1.43 1.79 1.61 – b.d 0.016 0.007 0.011 b.d. b.d. 0.107 0.018 0.107 0.358 0.269 0.027 b.d. 0.036 0.001 0.002 0.004 0.013 b.d. 0.013 0.007 0.002 0.023

Fetotal [mM]

(continued on next page)

H2S [mM]

Table 1 Overview of all fluid samples collected during SO253 together with parameters that were analyzed directly on-board. Note that the concentrations shown for Fe were determined by a visual Fe CHEMets© field kit. b.d.: below detection, −: not analyzed or no temperature measured.

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Rumble III

Brothers (NW Caldera & Upper Caldera)

Table 1 (continued)

7

078ROV

074ROV

085ROV

085ROV

081ROV

Upper C Upper C Upper C 072ROV

067ROV

064ROV

061ROV

Station 2F 3F 4F 7F 8F 13F–15F 4F 5F 11F 13F/14F 1F/2F 5F 10F 11F 12F 4F 5F 7F 2F 3F 4F 10F 12F 14F 15F 16F 17F 1F 2F 3F 6F 5F

Sample no. IGT Major Major Major Major KIPS IGT Major IGT KIPS KIPS KIPS IGT Major Major Major Major IGT IGT Major Major Major KIPS IGT Major Major KIPS IGT Major Major KIPS KIPS

Sampling device 1670 1670 1670 1658 1658 1643 1590 1600 1600 1609 1580 1579 1374 1374 1374 1617 1617 1610 1619 1619 1619 1658 1658 1616 1616 1616 1616 346 346 346 346 392

Water depth [m] 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 34° 35° 35° 35° 35° 35°

51.76637′ S 51.76671′ S 51.76664′ S 51.75002′ S 51.74997′ S 51.73661′ S 51.66120′ S 51.66177′ S 51.66383′ S 51.66875′ S 51.66083′ S 51.66062′ S 51.55044′ S 51.55070′ S 51.55096′ S 51.74469′ S 51.74392′ S 51.71182′ S 51.67705′ S 51.67681′ S 51.67703′ S 51.76858′ S 51.76858′ S 51.66975′ S 51.67037′ S 51.66935′ S 51.66723′ S 44.38214′ S 44.38214′ S 44.38214′ S 44.38214′ S 44.38492′ S

Latitude 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 179° 178° 178° 178° 178° 178°

03.49132′ E 03.49137′ E 03.49140′ E 03.47542′ E 03.47553′ E 03.45883′ E 03.45858′ E 03.45984′ E 03.46248′ E 03.46327′ E 03.43270′ E 03.43550′ E 03.13760′ E 03.13736′ E 03.13748′ E 03.43967′ E 03.44107′ E 03.44803′ E 03.46658′ E 03.46649′ E 03.46668′ E 03.47813′ E 03.47813′ E 03.47456′ E 03.47436′ E 03.47437′ E 03.47645′ E 29.79202′ E 29.79202′ E 29.79202′ E 29.79202′ E 29.83686′ E

Longitude 248 – – – – 13–21 264 – 170 – – – 311 – – – – 170 305 – – – – 220 – – – 25 – – 25 13

T [°C] 3.9 3.4 5.3 3.6 4.2 6.5 4.4 3.5 3.5 7.0 7.5 7.3 3.2 3.2 3.1 3.1 3.1 3.7 3.3 3.5 3.4 5.7 5.6 3.3 5.3 3.2 2.8 5.0 5.1 5.3 5.1 7.1

pH 153 186 180 162 169 153 12 133 27 68 192 84 184 211 220 176 133 −2 197 153 212 247 246 162 40 170 179 102 102 340 111 258

Eh [mV] 33.4 33.7 33.0 34.6 34.8 32.8 42.2 43.1 18.1 32.5 32.7 32.6 45.3 45.1 44.9 36.0 36.4 40.6 34.4 43.0 41.3 33.7 33.4 36.6 34.1 36.8 38.1 33.6 33.7 34.0 33.8 33.3

Salinity [‰] 0.199 0.275 0.043 0.496 0.191 0.015 – – – – 0.002 0.031 1.11 1.05 1.05 0.800 0.987 2.35 – – – 0.002 0.001 – 0.834 2.66 5.91 – – – – –

H2S [mM] 1.61 1.61 0.448 3.13 3.13 0.179 6.45 5.37 2.69 0.004 b.d. 0.001 10.74 9.59 10.74 4.30 6.45 6.45 6.45 6.45 4.30 0.448 0.448 4.30 1.79 4.30 6.45 0.036 0.036 0.001 0.036 0.004

Fe2+ [mM] 1.61 2.42 0.537 4.03 4.03 0.269 8.06 8.06 4.03 0.004 0.002 0.001 12.89 9.67 16.12 6.45 9.67 7.52 9.67 6.45 6.45 0.806 0.448 4.30 1.79 4.30 6.45 0.036 0.036 0.018 0.036 0.004

Fetotal [mM]

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contrasted by an even stronger enrichment in bromide (up to 73%). Sulfate concentrations are similar to that of seawater, with slightly elevated concentrations in the least diluted samples. Sulfide concentrations vary between 8 and 10.5 mM, making fluids from Macauley the sulfide-richest samples in this study. With the exception of Sr, all cations analyzed in this study are enriched in Macauley vent fluids when compared to ambient seawater (Table 3, Fig. 7). The most pronounced enrichments are found for Pb (1.2 μM), Al (122 μM), Fe (1.71 mM), Mn (866 μM) and Zn (243 μM). In particular, the hydrothermal fluids are characterized by unusually high concentrations of Mg (up to 69.6 mM; seawater at 53.1 mM). In addition, the fluids are enriched in U (up to 32.3 nM; seawater at 11.5 nM) which, like Mg, is depleted in most other hydrothermal vent fluids. Rare Earth Elements (REE) and yttrium (then REYs) in the fluids from Macauley show the highest concentrations for all samples from the four hydrothermal vent sites studied. The sum of all REEs reached concentrations up to 2264 nM. Chondrite normalized REY distribution patterns are comparable to the Lower Cone pattern and similar to those of fluids from other white smoker vent fluids, such as fluids from the Manus Basin (Fig. 8), with the heavier REEs being more enriched than the lighter ones. In addition, the patterns show a characteristic small negative Eu anomaly.

Fig. 6. Comparison of on-board Fe determination using the CHEMets© field kit and Fe data determined at the laboratories of Jacobs University Bremen with ICP-OES.

first measured undiluted and afterwards, if necessary, diluted to different degrees, thus insufficient dilution factors might be one reason for the offsets. Additionally, as the color intensity of the sample is only visually compared to the standards contained in the kit, which then corresponds to a Fe concentration, variations caused by subjective views may occur. Nevertheless, an overall good correlation confirms the viability of the Fe CHEMets© colorimetric kit as a fast and easy method for immediate, onboard characterization of fluid samples with Fe concentrations in the range measurable by the method (Kleint et al., 2017).

3.3. Haungaroa vent fluids The clear to light-gray fluids that were sampled have pH values down to 3.4 and temperatures between 210 and 267 °C (Table 1). Least diluted fluids sampled at Haungaroa show Mg concentrations down to 7.0 mM (87% end-member, Table 3). All samples had chloride contents (489–601 mM) similar to that of ambient seawater (559 mM). With the exception of SO42−, Mg and U, all measured elements are enriched in the fluids from Haungaroa over seawater, with concentrations pertaining to B, Ca, Li, Mn and Si (Fig. 7). Sulfide concentrations are highly variable with values up to 2 mM in the least diluted end-member fluids. With a low pH of 3.4, the highest Fe concentration measured was only 0.396 mM in sample 035ROV05F. Concentrations for REEs are comparatively low, reaching maximum values of 8.39 nM, with several of the REE below the limit of detection (Table 4). Three diffuse vent fluids were collected from a small mound north of the main vent field. These samples had temperatures up to 23 °C and slightly lower concentrations of Mg and SO4 and increased concentrations of Ca, Si, Mn, Fe, Li.

3. Results 3.1. End-member composition The vent fluids collected fall into two categories: (1) Mg-depleted, black and gray smoker fluids at Haungaroa and Brothers NW Caldera and Upper Caldera, and (2) acid-sulfate, white smoker fluids at the Brothers Cone sites, Macauley and Rumble III. Based on the low Mg concentration in fluids from Haungaroa and Brothers Caldera sites (7.0 and 3.2 mM Mg, respectively), when compared to 53.1 mM in ambient seawater, we assume that at these sites pure endmember fluids contain 0 mM Mg, resulting from Mg-precipitation upon heating and Mg-removal during water-rock interactions (Mottl and Holland, 1978). Based on this Mg depletion, the end-member composition of such hydrothermal fluids can be calculated using a linear least squares regression extrapolated between 0 mM Mg and the ambient seawater concentration. However, this method is not appropriate for determining the endmember concentrations of the white-smoker fluids at Macauley and Brothers Lower and Upper Cones, as these fluids have Mg contents greater than seawater. Thus, a zero-Mg end-member fluid cannot be assumed. Fluid end-member concentrations were therefore calculated only for samples from Haungaroa and Brothers NW Caldera and Upper Caldera that had at least ≥80% end-member (based on the lowest Mg concentration, ≤10 mM Mg) and are given in Table 2.

3.4. Brothers vent fluids Four different vent sites were sampled at Brothers volcano: white smoker venting at the Upper Cone and Lower Cone sites, and black smoker venting at the NW Caldera Wall and Upper Caldera site. The compositional data revealed distinct differences between the four sites in geochemical characteristics of the fluids (Tables 1 and 3). 3.4.1. NW Caldera Wall and Upper Caldera The two Caldera sites at Brothers volcano are characterized by hydrothermal venting in the form of black smokers discharging fluids with temperatures up to 311 °C and highest H2S concentrations of ~6 mM. Hydrothermal fluids were sampled from vents at depths ranging between 1371 (Upper Caldera) and 1670 m (NW Caldera Wall). The deeper sites on the caldera wall coincide with vent fields sampled previously (de Ronde et al., 2011). The shallowest site is on top of the caldera rim at the base of a small volcanic edifice in a vent site known as the Upper Caldera site. This newly discovered vent field comprises a group of up to 20-m tall chimneys that vent up to 305 °C black smoker fluids. Samples from the NW Caldera Wall and the Upper Caldera showed rather moderate acidity with a minimum measured pH value of 2.8. Generally, the fluids from the both Caldera sites are enriched in all

3.2. Macauley vent fluids Extremely low pH values of 1.2 and a maximum temperature of 112 °C were measured in white smoker fluids issuing from a sulfur mound at a water depth of 336 m (Fig. 2, Table 1). Hydrothermal fluids sampled with IGTs and major samplers show a clear enrichment in chloride concentration (up to 787 mM) when compared to seawater (559 mM). This 40% enrichment in chloride is 8

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Table 2 Calculated end-member compositions of hydrothermal fluids (for samples that have at least ≥85% end-member) from Haungaroa, Brothers Upper Caldera (in italics) and NW Caldera Wall. Ambient background seawater concentrations are given for comparison. TMR: trace metal rosette, b.d.: below detection, n.a.: not analyzed.

Seawater Haungaroa Brothers NW Caldera Wall & Upper Caldera

080TMR 035ROV05F 035ROV07F 064ROV04F 064ROV05F 064ROV11F 067ROV10F 067ROV11F 067ROV12F 081ROV02F 081ROV03F 085ROV17F

Al

Ba

B

Br

Ca

Cl

Fe

K

Mn

Si

Sr

Li

U

Zn

H2S

SO42−

[μM]

[μM]

[μM]

[mM]

[mM]

[mM]

[mM]

[mM]

[μM]

[mM]

[μM]

[μM]

[nM]

[mM]

[mM]

[mM]

9.04 39.8 32.7 41.5 33.2 18.3 45.6 43.9 43.1 38.5 39.3 33.0

0.15 11.5 6.99 5.75 38.4 3.43 35.7 45.0 44.9 57.0 12.5 47.8

400 1003 810 1325 1347 763 1246 1204 1182 1390 1393 1274

0.834 0.94 0.73 1.17 1.19 0.50 1.33 1.29 1.26 1.20 1.18 1.06

10.6 63.5 47.2 54.1 48.7 24.5 62.1 58.9 58.9 51.0 50.2 44.3

559 608 511 692 714 286 773 748 765 722 722 644

10−6 0.47 0.30 8.80 8.93 3.61 13.8 13.1 13.2 9.12 8.96 7.24

10.5 37.9 27.9 66.0 68.9 28.7 74.5 70.5 71.1 72.9 70.7 63.9

b.d. 1198 849 654 682 284 2686 2513 2491 719 701 617

0.056 10.3 7.41 13.7 14.4 6.54 17.1 16.3 16.4 15.4 14.5 13.5

94.4 156 107 215 185 84.5 253 238 246 197 181 175

27.3 11.5 576 0.53 405 −0.19 817 1.07 857 1.35 378 0.51 836 2.29 817 2.42 754 2.03 866 1.31 904 0.66 915 1.35

n.a. 106 20.7 3.3 17.4 3.28 11.1 20.9 20.9 6.38 17.7 78.9

b.d. 1.40 1.81 – – – 1.24 1.16 1.16 – – 6.30

29.0 −2.01 −4.17 9.39 −0.38 3.60 −2.50 −2.51 −2.73 −1.33 −1.28 −1.60

measured elements compared to seawater, except for Mg, SO42− and U. Full end-member concentrations were calculated for four sites at Brothers, ranging from 91 to 94% endmember hydrothermal fluids in the samples (Table 3). The lowest Mg concentration (3.2 mM) was measured in sample 081ROV, where a 94% end-member was sampled. The Upper Caldera area, where three samples could be retrieved (067ROV10F-12F), produces the most iron-rich fluids of the four volcanoes sampled, with a maximum concentration of 12.4 mM (Fig. 7). The high Fe contents combined with the relatively low H2S concentrations result in an unusually high Fe/H2S ratio of 11.2. Most fluid samples have high salinities, with a maximum measured Cl concentration of 746 mM (067ROV12F), compared to 559 mM in ambient seawater. One sample, however, has a significantly reduced chlorinity of 310 mM (064ROV11F). This fluid is also less enriched in metals than the high-chlorinity fluids (Table 3). Chondrite-normalized REY distribution patterns are uniformly enriched in light REEs over heavier REEs, and show a positive Eu anomaly (Fig. 9). Samples from station 085ROV are different in that they show light REE depletion. The total REE concentrations add up to a maximum of 413 nM in sample 064 ROV04F (Fig. 9).

3.4.3. Upper Cone Active venting at the Upper Cone of Brothers volcano was found in depths of around 1217 m with maximum temperatures of 115 °C and a minimum pH of 2.1. In contrast to the vents at the Lower Cone, the fluids from Upper Cone show no Mg enrichment. Instead, Mg concentrations are similar to that of seawater, which is also the case for sulfate concentrations. Despite the low pH, Fe concentration are ≤15 μM (Table 1) and thus not nearly as high as in other acid-sulfate vents, such as Macauley. Notably, U concentrations in the Upper Cone fluids are elevated (up to 19.8 nM) when compared to seawater (11.5 nM), the enrichment being similar to that of the Macauley fluids. Total REE concentrations reach up to 238 nM. The chondrite-normalized REY distribution pattern is very similar to that of the Lower Cone and Macauley fluids. However, the light REEs show lower concentrations that the Lower Cone fluids; conversely, the heavy REEs are more enriched than in the Lower Cone white smoker fluids (Fig. 8). 3.5. Rumble III vent fluids Diffuse venting was observed through cracks of coherent lava and in places through a talus field, hydrothermal fluids were sampled in two areas within the talus field. A total of five diffuse hydrothermal fluid samples were collected in water depths between 346 m and 392 m, with a maximum recorded temperature of 25 °C and minimum pH value of 5.0 (Tables 1 & 3). All fluid samples showed chlorinities similar to that of seawater with elevated concentrations of Mn, Ca and SO42−. Uranium is the only element showing a clear depletion, with maximum concentrations of 1.72 nM (11.5 nM in seawater). Despite the low concentrations of most elements, concentrations of the REEs in the fluids from Rumble III are comparatively high and have a maximum concentration of 113 nM (sample 074ROV06F). Chondrite-normalized REY distribution patterns are similar to those from the acid-sulfate fluids from Macauley and both Brothers Cone fluids (Fig. 8).

3.4.2. Lower Cone Hydrothermal venting at the Lower Cone of Brothers volcano was found in depths of 1318 m to 1332 m with maximum temperatures of 83 °C, minimum pH of 3.8, and H2S concentrations up to 5 mM. Only small variations in chlorinity were detected. Highly unusual are the markedly elevated Mg concentrations of up to 95.6 mM, which is 80% higher than seawater values (Table 3). Similarly, SO42− concentrations are elevated with respect to seawater (i.e., up to 76.9 mM, or 165% of ambient seawater values) (Fig. 7, Table 3). With a maximum of 41 μM, Fe is still highly elevated compared to seawater but is only 0.3% of the maximum Fe concentration recorded at the Upper Caldera site. However, Mn concentrations are highly elevated with maximum concentrations of 1 mM, resulting in the lowest Fe/Mn ratio (0.014) of all fluid samples investigated in this study. Strontium and U are significantly depleted in fluid samples that have high Mg concentrations. While all other vent fluids collected during SO253 show a typical Ca enrichment, the Lower Cone fluids reveal an unusual Ca depletion, with concentrations as low as 7.3 mM compared to 10.6 mM in ambient seawater. The chondrite normalized REY distribution patterns are comparable to those of the Macauley fluids and other white smoker vent systems in arcs, such as fluids from the Manus Basin (Fig. 8). Compared to Macauley, the Lower Cone fluids have lower concentrations of total REE, with a maximum value of 141 nM.

4. Discussion 4.1. Site-specific geochemical trends 4.1.1. Macauley Fluid compositions from Macauley are distinct from those of other vent fluids from the southern Kermadec arc based on the highly-elevated concentrations of Al, Fe, U, Zn and Mg; the enrichment of Mg is discussed in a separate section (Section 4.2). The extremely low pH values encountered at Macauley are inconsistent with the presence of feldspars in the equilibrium mineral assemblage in the reservoir zone of the vent fluids (Reed, 1997). Both, the low pH and the high chlorinity of the vent fluid will facilitate leaching 9

Brothers (Cones)

Haungaroa

SW Macauley

10

045ROV

048ROV

Lower Cone

Upper Cone

035ROV

030ROV

018ROV 023ROV 026ROV

013ROV

080TMR 009ROV

Station

4 2F 3F 4F 12F 2F 3F 4F 5F 5F 4F/5F 4F 5F 9F 10F/11F 2F/3F 10F 11F 16F 5F 7F 8F 17F–19F 3F 4F 5F/6F 9F/10F 11F 12F 2F 4F 5F 10F

Sample

– – – – – – – – – – 6 6 5 1 – 72 18 18 85 87 13 3 – – – – – – – – – –

EM [%] 7.8 1.5 2.3 2.0 7.0 1.2 1.6 1.6 1.6 7.9 7.8 6.1 6.3 6.5 7.8 7.6 3.9 5.1 5.1 3.4 3.7 5.2 6.1 4.8 4.4 4.5 4.5 3.8 4.4 2.4 2.4 5.7 2.1

pH

9.04 119 46.3 84.8 8.52 122 118 120 121 7.7 8.37 9.89 9 8.63 7.85 8.04 25.6 11.7 14.2 35.2 29.6 10.5 8.59 9.78 9.52 9.78 8.44 9.07 8.44 9.67 9.67 8.67 12.5

Al [μM] b.d. 2.59 2.62 3.15 b.d. 2.36 2.64 1.76 1.87 b.d. b.d. 0.47 0.29 0.2 b.d. b.d. 11.3 1.88 2.01 9.83 6.09 1.45 0.15 0.56 0.64 0.5 0.32 0.5 0.43 1.93 1.99 0.44 2.68

Ba [μM] 400 594 452 523 389 609 602 597 601 375 384 401 385 385 379 383 690 437 483 913 756 417 387 429 419 418 402 428 397 415 401 377 458

B [μM] 0.834 1.400 0.974 1.190 0.795 1.360 1.410 1.410 1.440 0.766 0.796 0.805 0.766 0.768 0.772 0.790 0.792 0.772 0.814 0.920 0.747 0.771 0.776 0.770 0.814 0.814 0.800 0.829 0.787 0.788 0.785 0.770 0.822

Br [mM] 10.6 16.6 12.4 14.7 11.0 16.4 16.4 16.5 16.4 10.7 11.1 13.4 12.0 11.9 10.8 10.8 36.9 16.2 20.2 55.6 42.4 14.5 11.4 8.1 7.7 8.3 8.9 7.3 8.4 10.2 10.0 10.5 10.2

Ca [mM] 559 786 639 692 568 780 787 783 769 534 540 546 540 549 545 535 489 525 558 601 517 526 540 528 533 528 522 519 529 544 538 540 545

Cl [mM] b.d. 1.49 0.505 1.01 b.d. 1.68 1.64 1.68 1.71 b.d. b.d. *17 *9 n.a. *4.80 n.a. 0.12 *26 0.100 0.396 0.263 *29 b.d. *41 n.a. b.d. b.d. *15 *33.6 *15 n.a. n.a. n.a.

Fe [mM] *[μM] 10.5 15.5 11.4 13.7 10.2 15.4 15.3 15.1 15.2 10.0 10.1 11.4 10.6 10.4 10.0 10.1 24.0 12.6 14.6 33.8 25.6 11.6 10.3 13.2 12.8 13.1 12.0 13.7 11.8 12.4 11.7 10.2 14.5

K [mM] 53.1 66.8 57.4 62.5 54.5 68.9 69.6 68.9 68.9 53.1 53.1 49.8 49.8 50.5 52.7 53.1 15.0 43.7 43.3 7.9 7.0 46.2 51.6 82.6 79.0 79.0 75.4 95.6 76.1 52.7 52.0 52.4 55.3

Mg [mM] b.d. 833 282 579 b.d. 840 831 859 866 b.d b.d. 15.6 9.3 b.d. b.d b.d. 607 121 190 1020 737 83.5 5.73 842 835 792 526 1040 607 210 176 30.7 358

Mn [μM] 0.056 6.98 2.79 4.48 0.096 6.87 6.73 7.12 7.05 b.d. b.d. 0.82 0.50 0.46 b.d. b.d. 8.40 1.79 1.83 8.79 6.44 0.87 0.29 4.80 4.91 4.52 3.11 5.98 3.59 2.46 2.06 0.40 4.70

Si [mM] 94.4 67.1 76.5 75.9 87.9 55.1 69.1 67.2 66.9 82.3 89.3 91.1 86.9 87.1 87 88.1 106 88.2 97 147 105 85.7 87.1 51.6 49.7 50.2 55.4 42.8 52.2 70.1 71.8 83.7 62.4

Sr [μM] 27.3 102 47.3 64.9 25.3 94.4 88.3 84.5 84.2 24.2 26.7 48.9 36.9 34.3 22.0 87.5 323 87.5 112 494 355 57.5 30.0 56.1 55.8 56.9 43.8 60.4 52.9 45.4 42.4 33.0 64.9

Li [μM] 11.5 32.3 15.6 18.8 12.8 26.1 22.7 18.6 19.7 12.1 11.8 1.73 6.14 7.83 12.7 8.57 2.57 8.57 8.55 2.16 1.35 10.0 0.28 0.75 0.83 0.23 b.d. 1.56 5.59 16.2 14.9 12.8 19.8

U [nM] b.d. 197 81 138 b.d. 243 185 187 191 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 23 b.d. b.d. 90 18 b.d. b.d. 3.0 b.d. b.d. b.d. 2.0 b.d. 30 19 b.d. 42

Zn [μM]

29.0 29.4 28.7 28.5 28.2 30.3 30.2 30.1 29.8 n.a. n.a. 26.5 26.6 27.3 28.0 27.4 4.3 22.4 23.2 2.6 0.2 24.1 27.6 61.0 64.8 60.4 52.8 76.9 58.1 27.3 27.1 28.0 28.4

SO42− [mM]

(continued on next page)

n.a. 1235 453 108 b.d. 545 569 181 158 b.d. b.d. 5.91 4.10 b.d. b.d. 9.80 44.4 9.80 b.d. 15.1 107 7.49 8.96 23.0 0.61 1.12 6.10 21.4 b.d. 278 52.3 1.24 305

Pb [nM]

Table 3 Major, minor and trace element concentrations measured with ICP-OES, ICP-MS and data for SO42− in hydrothermal fluids from the Kermadec arc. TMR: trace metal rosette; SW: Seawater; EM: endmember; b.d.: below the limit of detection; n.a.: not analyzed. Note: Fe concentrations with * are given in μM!

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Rumble III

Brothers (NW Caldera Wall & Upper Caldera)

Table 3 (continued)

11

078ROV Detection limits (n = 4)

074ROV

085ROV

081ROV

Upper C Upper C Upper C 072ROV

067ROV

064ROV

061ROV

Station

2F 3F 4F 7F 8F 13F–15F 4F 5F 11F 13F/14F 1F/2F 5F 10F 11F 12F 4F 5F 7F 2F 3F 4F 10F 12F 14F 15F 16F 17F 1F 2F 3F 6F 5F –

Sample

50 59 16 53 49 3 81 92 91 – 1 3 90 91 91 66 66 67 94 85 68 10 11 63 23 74 94 1 – 7 1 4 –

EM [%] 3.9 3.4 5.3 3.6 4.2 6.5 4.4 3.5 3.5 7.0 7.5 7.3 3.2 3.2 3.1 3.1 3.1 3.7 3.3 3.5 3.4 5.7 5.6 3.3 5.3 3.2 2.8 5.0 5.1 5.3 5.1 7.1 –

pH

18.3 15.4 9.70 15.3 14.7 8.33 38.5 31.2 17.5 8.19 8.07 7.78 41.9 40.7 40.1 22.8 24.2 13.7 36.7 34.6 31.9 11.0 12.5 24.1 14.9 26.3 31.5 13.4 13.7 12.0 13.6 7.81 2.08

Al [μM] 6.02 14.5 2.96 10.4 4.22 2.14 5.23 35.3 3.15 b.d. b.d. b.d. 32.1 40.9 40.8 7.5 5.06 1.73 53.6 10.6 5.99 1.18 1.23 6.92 2.36 9.83 44.8 0.76 0.45 0.43 0.39 b.d. 0.17

Ba [μM] 839 889 503 820 791 392 1240 1270 732 387 365 366 1160 1130 1110 889 981 437 1330 1240 1060 508 493 950 591 981 1220 389 394 364 393 368 33.8

B [μM] 0.907 0.904 0.815 0.944 0.926 0.772 1.140 1.160 0.529 0.804 0.771 0.772 1.280 1.250 1.220 0.980 0.996 1.070 1.180 1.130 1.080 0.837 0.816 0.972 0.861 0.979 1.044 0.815 0.822 0.766 0.827 0.771 0.058

Br [mM] 18.2 18.7 12.6 17.7 17.1 10.9 50.1 45.6 23.3 10.8 10.6 10.7 56.9 54.4 54.4 26.9 27.2 30.9 48.6 44.1 38.4 15.2 14.2 32.7 19.0 34.9 42.2 17.4 17.4 15.8 17.6 11.0 0.027

Ca [mM] 561 560 549 568 574 548 680 701 310 542 533 533 751 731 746 608 602 650 712 697 673 548 483 596 558 595 639 554 539 541 545 534 7.29

Cl [mM] 1.53 1.71 0.448 3.82 3.53 *19 7.99 8.21 3.30 0.008 b.d. b.d. 12.4 11.9 12.0 6.34 n.a. 7.71 8.57 7.56 6.33 0.362 0.323 4.78 1.47 5.14 6.79 *37 *31 n.a. *32 n.a. *6.76

Fe [mM] *[μM] 33.5 35.8 16.5 34.3 32.7 11.0 60.9 64.2 27.1 10.0 10.0 10.0 68.0 65.0 65.5 40.7 49.6 51.2 69.1 61.4 54.5 17.4 15.7 45.2 22.8 47.3 60.6 10.6 10.6 9.8 10.6 10.1 0.089

K [mM] 26.8 21.8 44.4 25.2 27.1 51.6 10.2 4.3 4.6 53.4 52.4 51.6 5.4 4.9 4.9 18.2 18.1 17.4 3.2 8.2 16.8 47.6 47.3 19.4 40.8 14.4 3.3 52.4 53.1 49.5 52.4 50.9 0.042

Mg [mM] 362 408 105 344 318 12.8 594 627 259 b.d. b.d. 1.1 2413 2281 2261 434 443 486 676 593 504 106 85 4141 151 443 579 208 221.1 185.7 222.1 7.5 5.15

Mn [μM] 8.79 10.1 2.64 10.6 9.96 0.537 12.4 13.2 5.98 0.103 0.116 0.176 15.4 14.8 14.9 10.7 10.8 10.4 14.5 12.3 11.0 2.02 1.69 9.32 3.47 10.0 12.7 1.01 1.05 0.893 1.06 – 0.054

Si [mM] 90.4 95.4 85.7 98.2 97.6 85.6 204 178 85.4 88.9 85.6 83.4 237 225 232 122 127 139 191 168 168 101 96.9 131 105 142 170 96.7 98.2 89 98.3 84.9 14.5

Sr [μM]

U [nM]

399 2.25 509 0.87 145 7.85 455 3.32 423 3.74 43.5 12.45 744 2.03 790 2.17 348 1.46 26.3 15.1 25.6 12.2 24.7 11.6 754 3.23 744 3.26 687 2.90 526 3.66 563 3.26 696 6.93 815 1.92 769 2.33 702 4.00 146 4.04 104 6.69 591 4.32 223 8.76 658 4.62 860 1.98 30.3 1.33 29.9 0.90 27.7 1.72 33.7 0.89 26.3 13.4 0.291 0.37

Li [μM] 4063 b.d. b.d. b.d. b.d. b.d. 9.73 b.d. 13.8 b.d. b.d. b.d. 59.2 b.d. 1.32 b.d. b.d. 29.4 97.3 b.d. 1.14 b.d. 2.09 13.4 b.d. b.d. b.d. 2.08 b.d. 0.49 b.d. b.d. 0.45

Pb [nM] 80 69 b.d. 46 37 b.d. 3.0 16 3.0 b.d. b.d. b.d. 10 19 19 58 60 11 6.0 15 51 b.d. b.d. b.d. b.d. 14 74 b.d. b.d. b.d. b.d. b.d. 1.58

Zn [μM] 5.3 1.8 20.9 4.7 6.3 26.9 11.2 2.0 5.8 27.7 27.3 26.8 0.7 0.4 0.2 4.7 4.0 6.0 0.5 3.4 7.5 22.0 n.a. n.a. 19.6 22.1 0.3 33.5 32.9 32.7 33.3 13.9 –

SO42− [mM]

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Fig. 7. Measured element concentrations versus Mg concentrations for all fluid samples collected during research cruise SO253. The dashed line represents the seawater concentration of each respective element (Mg concentration of ambient background seawater: 53.1 mM).

of metals from the host rocks. For instance, we suggest that the highly elevated Al concentrations likely reflect proton-promoted leaching and the presence of hydrothermal alteration minerals, such as kaolinite or pyrophyllite that undergo reaction to alunite or natroalunite (Inoue, 1995; Seewald et al., 2019, 2015). High fluid mobility of elements

implies that the basement rocks in the flow path of the fluid may become depleted in fluid-mobile elements (such as e.g. Li and B), given long enough time-integrated water/rock ratios. The high concentration of Li and B indicate that pronounced leaching of these elements from the basement has not taken place, which may indicate that the vent 12

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Fig. 7. (continued)

system at Macauley is relatively young, or has a low fluid discharge rate. The 40% enrichment in chloride in the fluids is contrasted by an even stronger enrichment in bromide (up to 73%), indicating that the two elements were fractionated from each other. This fractionation is likely caused by phase separation, as the brine phase is expected to have elevated Br/Cl ratios relative to seawater (Liebscher et al., 2006).

Although they are briny, the fluids have high concentrations of H2S (10.4 mM), they have a very low pH of 1.2 and are slightly enriched in SO42− (30.3 mM). This acid-sulfate characteristic would traditionally be interpreted as influx of SO2-rich magmatic vapors and disproportionation of SO2 at decreasing temperatures to create sulfuric acid and sulfide as well as sulfur (Butterfield et al., 2011; Gamo et al., 1997; Resing et al., 2007; Seewald et al., 2015). However, it is also 13

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Fig. 8. Chondrite-normalized REY distribution in the fluids sampled by IGTs and major samplers from the magmatic systems at Macauley, Brothers Upper and Lower Cone, as well as Rumble III compared to seawater and fluids from other island arcs (Alibo and Nozaki, 1999; Cole et al., 2014; Craddock et al., 2010). SW*100: seawater multiplied by a factor of 100.

possible that the increased sulfate and low pH are due to dissolution of alunite in the basement (Seewald et al., 2019) The chondrite-normalized REY distribution pattern of the Macauley fluids shows a comparable flat pattern compared to those of acid-sulfate fluids found in the Manus Basin (Fig. 8) (Craddock et al., 2010). The heavy REE show concentrations that are significantly greater than those of high-temperature black smoker fluids from the NW Caldera Wall and Upper Caldera. This, again, can be attributed to the low pH, which aids the dissolution of high-field strength elements that tend to hydrolyze at high pH. The presence of sulfate as a complexing agent will facilitate the development of flat, undifferentiated REE patterns because it has similar complex-stabilities for all REE (Bach et al., 2003; Craddock et al., 2010; Migdisov et al., 2016). A slightly negative Eu anomaly may reflect the pattern of the host rocks, which have experienced magmatic differentiation by fractional crystallization of plagioclase (amongst other liquid phases). Given the overall very high concentrations of REEs, we thus do not consider the small negative Eu anomaly to be inherited from seawater. Total REE concentrations in the fluids from Macauley range from around 2000 nM to maximum concentrations of 2264 nM and are therefore significantly greater than those reported from the Manus Basin acid-sulfate fluids (Craddock et al., 2010). The lower-than-seawater Sr concentrations are inconsistent with enhanced leaching of other metals; it may point to sub-seafloor precipitation of anhydrite. Anhydrite precipitation would also remove sulfate; the sulfate concentrations of the source fluids may thus be higher than in the analyzed seafloor fluids, corroborating the hypothesis of magmatic SO2 input and subsequent disproportionation and sulfuric acid production. As for Al, we suggest that Fe and Zn (and perhaps U) were most likely leached out of the surrounding rocks by the very acidic fluids.

The Fe concentrations in samples 030ROV and 035ROV are much lower than the corresponding Mn concentrations, resulting in unusually low Fe/Mn values (0.19–1.1). In most other high-temperature hydrothermal systems, Fe and Mn exhibit a similar pH- and temperaturedependent mobility and rather high Fe/Mn values (Seewald and Seyfried, 1990). Given that Fe preferentially precipitates relative to Mn as the fluid cools, the low Fe/Mn values may suggest that the Haungaroa fluids have cooled during upflow (cf. James et al., 2014; Seyfried and Ding, 1993), which may then lead to a precipitation of Fe-sulfides in the sub-seafloor and removal of Fe from the fluid. Despite the still relatively high temperatures (267 °C) of the low-Mg fluids (7.0 mM Mg), REE concentrations were mostly below the limit of detection, which might be due to the rather moderate pH, the cooling processes occurring during upflow and/or mixing with seawater in the subseafloor. Anhydrite (CaSO4) precipitation is a common product of subseafloor mixing between high-temperature fluids and locally entrained seawater and can incorporate significant amounts of REEs, leading to the expelled fluid being depleted in REE (Humphris and Bach, 2005; Mills and Elderfield, 1995; Tivey et al., 1998). The only chondrite-normalized REY distribution pattern obtained from sample 030ROV10F is similar to those from high-temperature black smoker fluids at Brothers with a higher enrichment in LREE over HREE as well as the characteristic pronounced positive Eu anomaly. 4.1.3. Brothers 4.1.3.1. NW Caldera Wall and Upper Caldera. The compositions of vent fluids from the NW Caldera Wall and Upper Caldera site are typical for high-temperature black smoker fluids based on their low Mg, SO42 and U contents and enrichments of all fluid-mobile elements. Chloride concentrations in fluids from Brothers Caldera site reach to 751 mM and indicate that the fluids have undergone phase separation (de Ronde et al., 2011). Only one fluid with a low chlorinity (310 mM Cl) was recovered at the Brothers NW Caldera Wall site (064ROV). The least-diluted samples with 3.2 mM Mg (94% end-member) have the lowest pH and values of SO42− near 0 mM. The concurrence of highest temperature and highest chloride concentrations indicate that these samples have not mixed substantially with seawater prior to venting. Although Cl may be leached from basement rocks (Mottl et al., 2011; Seewald et al., 2019), we suggest that the large range in chlorinity observed is due to phase separation. We hence consider the most plausible explanation for the fluids with increased chlorinity that they represent the ‘brine’ portion of a phase-separated fluid. With total REE concentrations of 413 nM, the vent fluids from both

4.1.2. Haungaroa Hydrothermal fluid compositions from the Haungaroa vent field are similar to typical high-temperature black smoker fluids from mid-ocean ridges, i.e., the fluids are being enriched in all fluid-mobile elements compared to seawater, but depleted in Mg, U and SO42−. Chloride variability (489–601 mM) that occurs in response to phase separation has a relatively minor effect on the solubility of metals, but instead pH and temperature are probably more important in controlling metal solubility (Butterfield et al., 1994). This is further supported by looking at the calculated end-member concentration, such as that for sample 035ROV07F, where a calculated Cl concentration of 511 mM is only slightly below that of ambient seawater (Table 2). 14

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Table 4 Rare earth element and yttrium (REY) concentrations measured with ICP-MS in hydrothermal fluids from the Kermadec arc. b.d.: below the limit of detection. SW: seawater from 1000 m water depth, values for SW are * 100 (SW data from Alibo and Nozaki (1999)).

SW*100 Macauley

Station

Sample

009ROV

2F 3F 4F 12F 2F 3F 4F 5F 5F 4F/5F 4F 5F 9F 10F/11F 2F/3F 10F 11F 16F 5F 7F 8F 17F–19F 3F 4F 5F/6F 9F/10F 11F 12F 2F 4F 5F 10F 2F 3F 4F 7F 8F 13F–15F 4F 5F 11F 13F/14F 1F/2F 5F 10F 11F 12F 4F 5F 7F 2F 3F 4F 10F 12F 14F 15F 16F 17F 1F 2F 3F 6F 5F –

013ROV

018ROV 023ROV 026ROV

Haungaroa

030ROV

035ROV

Brothers (Cones)

Lower Cone

Upper Cone Brothers (NW Caldera Wall & Upper Caldera)

035ROV 035ROV 045ROV

048ROV

061ROV

064ROV

067ROV Upper C Upper C Upper C 072ROV 081ROV 081ROV 085ROV

Rumble III

074ROV

078ROV Detection limits (n = 9)

Y [nM]

La [nM]

Ce [nM]

Pr [nM]

Nd [nM]

Sm [nM]

Eu [nM]

Gd [nM]

Tb [nM]

Dy [nM]

Ho [nM]

Er [nM]

Tm [nM]

Yb [nM]

Lu [nM]

La/Yb

47.2 3282 3333 2317 77.6 3439 3504 4977 2610 67.4 68.3 682 389 317 71.5 72.3 16,742 2375 7033 13,811 10,650 1581 197 936 921 762 503 736 671 2446 2601 544 2636 – 34,522 2765 20,865 3273 2382 6919 64,631 6753 259 229 239 47,161 210,887 196,440 14,320 24,034 8614 97,429 42,088 5604 1667 1719 13,461 2037 9110 57,311 955 529 579 537 66.6 0.36

3.19 77.5 29.2 52.4 b.d. 74.4 73.1 77.5 76.7 b.d. b.d. b.d. b.d. 0.19 b.d. b.d. 1.71 b.d. b.d. b.d. 0.47 b.d. b.d. 6.59 4.86 4.94 2.16 4.43 2.74 0.99 0.57 0.35 3.19 0.26 0.11 0.13 0.15 0.35 b.d. 61.4 32.8 26.2 b.d. b.d. b.d. 16.2 16.1 15.9 b.d. 0.39 2.02 32.2 22.8 20.4 b.d. b.d. 0.63 b.d. 1.48 0.65 3.36 4.00 3.62 4.78 b.d. 0.15

0.47 315 108 217 b.d. 298 309 300 288 b.d. b.d. b.d. b.d. 7.60 b.d. b.d. 3.44 b.d. b.d. b.d. 0.97 b.d. b.d. 17.9 17.1 17.6 9.32 16.5 12.1 4.78 2.79 0.79 11.2 b.d. b.d. b.d. b.d. b.d. b.d. 139 61.2 65.0 b.d. b.d. b.d. 21.2 21.3 19.7 b.d. b.d. 5.24 65.2 45.1 42.4 b.d. b.d. 2.02 b.d. 3.52 1.99 10.2 14.4 12.1 17.1 b.d. 0.77

0.39 65.2 22.2 44.3 b.d. 62.9 64.2 60.1 63.6 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.36 b.d. b.d. b.d. 0.19 b.d. b.d. 3.51 3.68 3.92 2.47 4.12 2.79 1.62 1.09 0.27 2.92 b.d. b.d. b.d. b.d. b.d. b.d. 23.4 8.28 11.1 b.d. b.d. b.d. 2.49 2.35 2.17 b.d. b.d. 1.01 8.69 5.91 5.63 b.d. b.d. 0.42 b.d. 0.72 0.58 2.12 2.99 2.28 3.71 b.d. 0.17

1.72 418 141 270 b.d. 378 379 378 383 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.21 b.d. b.d. b.d. b.d. b.d. 0.51 23.4 25.6 27.5 16.3 29.4 19.7 17.0 12.7 2.56 27.1 b.d. 0.33 b.d. b.d. 0.49 b.d. 112 35.8 51.1 b.d. b.d. b.d. 11.1 8.99 8.45 b.d. 0.64 b.d. 33.2 23.8 22.9 b.d. b.d. 2.81 1.18 4.68 5.24 13.0 18.9 15.0 22.6 b.d. 0.21

0.37 171 56.3 117 b.d. 164 157 162 159 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.23 8.00 9.95 10.5 6.52 11.4 7.77 15.9 13.1 2.72 26.9 0.32 b.d. b.d. b.d. b.d. b.d. 27.9 8.14 12.8 b.d. b.d. b.d. 2.68 2.38 1.95 0.14 0.29 2.64 7.28 4.64 4.49 b.d. b.d. 2.14 1.11 3.56 4.76 4.40 6.65 4.62 7.43 b.d. 0.13

0.09 49.2 16.5 33.1 b.d. 46.8 46.2 45.7 47.0 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.43 b.d. b.d. b.d. b.d. b.d. 0.11 2.11 2.47 2.61 1.66 2.86 1.99 5.37 4.22 0.78 8.4 b.d. 0.18 b.d. b.d. 0.25 b.d. 8.78 8.10 3.58 b.d. b.d. b.d. 23.7 24.0 24.0 0.93 1.25 9.05 7.47 5.92 4.41 b.d. b.d. 3.34 1.63 5.16 7.22 1.74 2.25 1.63 2.79 b.d. 0.12

0.52 266 92.6 178 b.d. 252 254 245 254 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.41 b.d. b.d. 0.49 13.2 14.9 15.3 9.46 17.3 11.9 28.4 22.3 4.05 41.9 0.20 0.24 b.d. 0.25 b.d. b.d. 22.8 6.35 10.7 b.d. b.d. b.d. 2.36 1.84 1.75 0.37 0.65 2.37 6.59 3.56 3.51 b.d. b.d. 2.70 1.45 4.50 6.11 8.74 11.3 8.72 13.1 b.d. 0.11

0.08 47.9 16.9 33.5 b.d. 46.6 44.5 45.4 46.2 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.13 b.d. b.d. 0.08 2.13 2.40 2.58 1.66 2.86 1.86 4.77 3.77 0.66 7.33 b.d. b.d. 0.09 b.d. b.d. b.d. 2.61 0.74 1.35 b.d. b.d. b.d. 0.28 0.21 0.18 b.d. 0.09 0.29 0.91 0.42 0.45 b.d. b.d. 0.34 0.19 0.58 0.75 1.42 1.98 1.44 2.19 b.d. 0.08

0.63 347 117 236 b.d. 312. 315 320 317 b.d. b.d. 0.15 0.10 b.d. b.d. b.d. 0.48 b.d. b.d. 0.63 b.d. b.d. 0.58 14.2 16.4 16.9 10.6 19.7 13.4 29.7 23.7 4.61 48.7 b.d. b.d. b.d. b.d. 0.12 b.d. 10.7 3.09 6.20 b.d. b.d. b.d. b.d. 0.88 0.79 0.29 0.52 1.35 5.12 2.10 1.92 b.d. b.d. 1.67 0.81 2.59 3.13 10.1 13.8 10.2 14.8 b.d. 0.11

0.18 69.8 23.6 47.0 b.d. 66.0 65.2 64.3 66.3 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.13 b.d. b.d. 0.12 b.d. b.d. 0.136 3.24 3.63 3.78 2.37 4.28 2.87 6.01 4.44 0.83 9.21 b.d. b.d. b.d. b.d. b.d. b.d. 1.28 0.39 0.79 b.d. b.d. b.d. 0.14 0.11 0.09 b.d. b.d. 0.20 0.82 0.31 0.29 b.d. b.d. 0.24 0.11 0.32 0.39 2.46 3.13 2.43 3.48 b.d. 0.09

0.61 210 70.6 134 b.d. 195 193 192 192 b.d. b.d. b.d. b.d. 0.07 b.d. b.d. 0.28 b.d. b.d. 0.35 b.d. b.d. 0.39 9.9 10.9 11.1 6.84 12.8 8.40 16.1 12.9 2.31 24.8 b.d. b.d. b.d. b.d. b.d. 0.06 2.22 0.77 1.50 b.d. b.d. b.d. 0.29 b.d. 0.22 0.06 b.d. 0.53 2.33 0.62 0.60 b.d. b.d. 0.55 0.21 0.67 b.d. 7.51 9.41 6.82 10.1 b.d. 0.07

0.09 29.3 9.47 19.1 b.d. 26.4 26.2 25.9 27.5 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.05 1.37 1.50 1.59 0.97 1.82 1.23 2.09 1.66 0.26 3.47 b.d. b.d. b.d. b.d. b.d. b.d. 0.16 b.d. 0.12 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.12 0.28 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.91 1.22 0.95 1.40 b.d. 0.10

0.61 173 61.3 116 b.d. 168 165 156 165 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.23 b.d. b.d. 0.28 b.d. b.d. 0.34 8.91 10.2 10.4 6.22 12.0 7.84 12.1 9.06 1.59 19.8 b.d. b.d. b.d. b.d. b.d. b.d. 0.78 b.d. 0.53 b.d. b.d. b.d. b.d. 0.13 b.d. b.d. b.d. b.d. 1.70 0.30 0.30 b.d. b.d. 0.38 0.12 0.40 0.44 5.83 7.72 5.76 8.33 b.d. 0.08

0.11 25.6 8.65 16.8 b.d. 22.2 22.1 22.1 21.9 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.05 1.39 1.54 1.63 0.97 1.77 1.19 1.64 1.24 0.18 2.61 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.09 0.23 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.84 1.05 0.78 1.22 b.d. 0.08

5.26 0.45 0.48 0.45 – 0.44 0.44 0.50 0.46 – – – – – – – 7.57 – – – – – – 0.74 0.48 0.48 0.35 0.37 0.35 0.08 0.06 0.22 0.16 – – – – – – 78.3 – 49.3 – – – – 121 – – – – 18.9 75.0 67.5 – – 1.66 – 3.68 1.47 0.58 0.52 0.76 0.57 – –

15

REE Σ [nM] 2264 773 1514 – 2112 2113 2093 2107 – – 0.15 0.10 7.86 – – 8.26 – – 1.91 1.63 – 2.97 116 125 130 78 141 96 147 114 22 238 0.76 0.86 0.22 0.41 1.21 0.06 413 166 191 – – – 80 78 75 1.8 3.83 25 172 116 107 – – 17 6.81 28 31 73 99 76 113 – –

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Fig. 9. Chondrite-normalized REY distribution in the fluids sampled with IGTs and major samplers from the water/rock dominated systems at Haungaroa, Brothers Upper Caldera and NW Caldera Wall. For comparison, seawater and other water/rock dominated fluids from the Mid Atlantic Ridge and the Juan de Fuca Ridge are shown (Alibo and Nozaki, 1999; Bao et al., 2008; Douville et al., 2002). SW*100: seawater multiplied by a factor of 100.

Brothers Caldera sites are clearly enriched in these elements (compared to seawater); however, the REEs are not as enriched as in the fluids from Macauley. Chondrite-normalized REY distribution patterns display an enrichment of LREE over HREE, as well as a positive Eu anomaly and lie well within the range of black smoker fluids from basalt-hosted MORs, while the degree of LREE/HREE fractionation (see Table 4 for La/Yb values) and the size of the positive Eu anomaly is smaller when compared to MORs (Fig. 9). We suggest that the patterns reflect higher mobility of the LREE relative to HREE and that the divalent Eu is more mobile (fluid soluble) than the neighboring trivalent REE that are preferentially incorporated into secondary alteration minerals such as chlorite and smectite (cf. Allen and Seyfried, 2005; Bach and Irber, 1998; Bau et al., 1998). Calculated end-member concentrations for the fluids from the NW Caldera are highly elevated in all elements, especially in K and Fe, with negative concentrations for SO42−. The negative values have been used as evidence of subsurface precipitation of sulfate minerals in the subseafloor (Von Damm, 2000) (Table 2). The high potassium content most likely reflects the high K concentrations of the dacitic basement of Brothers volcano along with efficient K-leaching via water-rock interaction (de Ronde et al., 2011). The high calculated end-member concentrations of Fe up to 13.8 mM Fe at the Upper Caldera are distinct amongst all the other sites sampled during the expedition. In addition, Fe/H2S values are higher (up to 11.3) than in most arc hydrothermal vents (up to 5) (detailed Fe/H2S values for several arc volcanoes can be found in e.g. de Ronde and Stucker, 2015), suggesting that large quantities of dissolved Fe cannot be precipitated as Fe-sulfides near the vent and instead may escape into the water column. Vents with high Fe/H2S ratios may hence contribute strongly to the budget of dissolved Fe in the ocean (e.g., Yücel et al., 2011).

however, they are about one order of magnitude lower than those of vent fluids from Macauley. This could be a result of a more moderate pH for the Lower Cone fluids. The chondrite-normalized REY distribution pattern is consistent with that of other acid-sulfate fluids that also have flat patterns and a small negative Eu anomaly. Like for the Macauley fluids, we interpret the flat pattern and the negative Eu anomaly as inherited from magmatically differentiated host rock. 4.1.3.3. Upper Cone. In contrast to the Lower Cone fluids, no enrichment in Mg or SO42− is observed in fluids collected from the Upper Cone. However, as the fluids are also not depleted in Mg and SO42−, when compared to seawater, they must be added to the fluid, probably either by seawater entrainment, or by mineral dissolution in the subsurface. Uranium also appears to have been added to the fluids, reaching concentrations up to 19.8 nM (11.5 nM for seawater). This is very unusual for hydrothermal systems, as U is commonly removed from seawater during high-temperature hydrothermal circulation, for example by incorporation into secondary minerals such as calcium carbonate or palagonite (Chen et al., 1986). We suggest that the high U contents of the fluids might be due to leaching of U from the surrounding rocks, consistent with the low pH of 2.1 (similar to Macauley fluids). Rare Earth Element concentrations are similar to the ones for the Lower Cone. LREE are more depleted and the HREE more enriched than at Lower Cone, but overall the REY distribution shows a similar chondrite-normalized distribution pattern. 4.1.3.4. Comparison with previous studies. Comparison between Brothers fluid chemistry presented here with that of vent fluids collected from Brothers in 2004 and 2005 (de Ronde et al., 2011) shows similarities but also some distinct differences in fluid chemistry over the 12–13 years between sampling. Similar to our observations, de Ronde et al. (2005, 2011) described different chemical characteristics for vents fluids collected from the different sites at Brothers. These workers also highlighted the predominance of black smoker discharge at the Caldera vent fields and white smokers or more clear fluid discharging from the Upper and Lower Cone sites, respectively. The most distinct difference between the two data sets is that fluids collected from the Lower Cone in 2004 and 2005 contain Mg and SO42− concentrations very similar compared to seawater (max: 52.3 mM and 28.9 mM, respectively), while fluids sampled during this project show a clear enrichment in these elements (max: 95.6 mM and 76.9 mM,

4.1.3.2. Lower Cone. The most notable chemical differences between the fluids of the Lower Cone and all other fluids collected during this study are the unusual, highly elevated concentrations for Mg (up to 95.6 mM) and SO42− (up to 76.9 mM) relative to seawater. This is discussed in more detail in Section 4.2. Given the limited range in chlorinity of 519 to 533 mM, as well as lower temperatures, phase separation does not appear to have played a significant role with respect to the geochemical composition of these fluids. Strontium, and to a lesser degree Ca, are significantly depleted in the fluid samples, suggesting that anhydrite precipitation may have taken place. Concentrations of REE are highly elevated compared to seawater; 16

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Table 5 Comparison of Brothers hydrothermal fluid composition collected by de Ronde et al. (2011) with data collected during this study, In this study, only samples taken with IGT and Major samplers with end-member concentrations > 50% are shown. The three samples from the Upper Caldera Site are not included within this table.

de Ronde et al. (2011)

Lower Cone Upper Cone NW Caldera

This study

Lower Cone Upper Cone NW Caldera

Min Max Min Max Min Max Min Max Min Max Min Max

Depth

T

[m]

[°C]

1306 1336 1213 1227 1572 1670 1318 1332 1217 1218 1590 1670

46 68 60 122 274 302 67 83 83 115 170 305

pH

5.1 5.2 1.9 5.9 2.8 3.8 3.8 4.8 2.1 2.4 2.8 4.4

Mg

Cl

Si

Fe

Mn

K

Ca

SO42−

Al

[mM]

[mM]

[mM]

[mM]

[mM]

[mM]

[mM]

[mM]

[μM]

45.5 52.3 50.5 53.5 3.40 22.3 75.4 95.6 52.0 55.3 3.20 27.1

497 544 539 547 506 724 519 533 538 545 310 712

0.94 4.32 0.24 3.92 7.44 13.0 3.11 5.98 62.4 71.8 5.98 14.5

0.03 0.04 0.03 1.14 2.70 6.61 0.02 0.04 0.02 0.02 1.53 8.6

0.19 0.39 0.01 0.17 0.36 0.70 0.53 1.04 0.18 0.36 0.26 4.14

11.0 18.5 10.1 14.8 35.4 68.0 11.8 13.7 11.7 14.5 27.1 69.1

7.20 9.90 9.70 10.9 24.5 42.0 7.30 8.90 10.0 10.2 17.1 50.1

24.3 28.9 25.4 39.4 0.20 11.4 52.8 76.9 27.1 28.4 0.30 22.1

10.0 46.7 75.9 116 3.10 64.8 8.4 9.8 9.7 12.5 13.7 38.5

respectively) (Table 5). Over the same interval of time, the maximum measured temperatures at the Lower Cone have increased from 68 °C in 2004 to 83 °C in this study, while the lowest measured pH decreased from 5.1 to 3.8. The reason for the differences in Mg and SO42−is not clear, but could reflect a continuous dissolution of Mg- and SO42−-bearing minerals, enriching the fluids in Mg and SO42, respectively (see below). Maximum measured temperatures at the Upper Cone are overall similar, but slightly higher temperatures of 122 °C were reached in 2004 compared to the 115 °C measured 13 years later. Another temporal change in the fluid compositions is apparent in the Al concentration in fluids collected from both the Cone sites. While de Ronde et al. (2011) reported maximum Al concentrations of 116 μM for the Upper Cone, similar to those measured at Macauley in samples of this study, our samples collected from both Brothers Cone sites show only very little enrichment of Al compared to seawater, with a maximum concentration of 12.5 μM. While measured temperatures at the NW Caldera site have remained relatively constant over time, the most noticeable difference in the fluid compositions between 2004 and 2016/2017 is the Mn concentration, which has increased from maximum measured concentrations of 0.7 mM Mn to 4.1 mM Mn over 12–13 years. Iron increased from 6.6 mM to 8.6 mM, while concentrations up to 12.4 mM Fe were measured at the Upper Caldera in this study. However, as the Upper Caldera vent site was not sampled in 2004, concentrations from that vent site are not included in Table 5.

fluid-mobile elements, as these would precipitate in the fluid upflow zone during conductive cooling. However, cooling processes cannot explain the similar-to-seawater Mg concentrations as well as the slightly enriched SO42− concentrations. Despite the rather low temperatures of only 25 °C, REY concentrations are highly enriched compared to ambient seawater and show concentrations in the range of the Brothers Upper Cone fluids. By looking at the chondrite-normalized distribution pattern, it becomes obvious that the fluids from Rumble III are showing flat patterns, characteristic of acid-sulfate fluids and comparable to the ones observed in the Brothers Cone fluids (Fig. 8). This may explain the elevated SO42− concentrations, which, together with the REE contents, indicate that the vent fluids at Rumble III may represent diluted acidsulfate fluids. 4.2. Magnesium enrichment in fluids at Macauley and Brothers Lower Cone In many hydrothermal systems, Mg is removed upon heating by the formation of different clay minerals (Inoue, 1995; Mottl and Holland, 1978) such as brucite (Mg(OH)2) or minerals of the chlorite group. A pure end-member fluid would therefore contain zero mM Mg and all Mg measured in hydrothermal fluid samples can normally be assumed to be introduced by mixing with seawater (either in the sub-seafloor or during sampling) as Mg concentrations compared to other elements will plot on a linear function intercepting the zero point on dilution (German and von Damm, 2003). Although fluids from two sites at Macauley (009ROV & 013ROV) and the Lower Cone at Brothers (045ROV) are highly enriched in Mg relative to seawater (up to 69.6 mM measured at Macauley and up to 95.6 mM at Brothers Cone cf. 53.1 mM for seawater, Table 3), they show distinctively different characteristics when comparing Mg concentrations to chlorinity. For example, the range of Mg/Cl values for Macauley of 0.084 to 0.095 is only slightly lower than that of seawater (0.095). Based on the high Cl concentrations of up to 787 mM, it is most likely that the hydrothermal fluids at Macauley are subject to significant phase separation, resulting in a high-salinity fluid (brine phase). All elements (bar Sr) show a positive linear correlation with magnesium and chloride (Fig. 7) indicating that Mg appears to be leached just as Fe and Mn. The very low pH of only 1.2 in the Macauley fluids may be responsible for the unusual leaching of Mg, which is then being released back in the hydrothermal fluid (Hannington et al., 2005). By contrast, fluids from site 045ROV of the Brothers Lower Cone show Mg/Cl values far above that of seawater (up to 0.184). Phase separation processes cannot explain this enrichment, as those could not enrich the fluid in Mg relative to chloride. As seen in the very small variation of chlorinity for fluid samples from Brothers Cone (Table 2, Fig. 7), phase separation processes only seem to play a minor role in the

4.1.4. Rumble III Vent fluid compositions measured from Rumble III fluids are different to those from all other sites sampled in this study. The sampled fluids have only moderate enrichments of fluid-mobile elements at the maximum measured temperature of 25 °C, although still registering a minimum pH of 5.0, suggesting an acidic end-member fluid. Small deviations in Mg, Cl and SO42− concentration imply only little impacts of phase separation and Mg-mineral precipitation processes. However, elevated concentrations of Al, Ca, Mn and Si, when compared to background seawater, indicate hydrothermal enrichment processes that are most likely pH- and T-dependent, rather than being controlled by phase separation. Additionally, the near zero concentration of U indicates that the sampled fluids are not substantially mixed with seawater prior to venting, as that would directly increase U proportionally to the seawater content (Chen et al., 1986). Instead, the fluid must have cooled during upflow, as it is also partly suggested for fluids from Haungaroa. Like at Haungaroa, at Rumble III the Fe/Mn ratio is unusually low (0.14–0.18) and would further support a cooling process, removing Fe from solution relative to Mn (Seyfried and Ding, 1993). Cooling would also explain the overall low concentrations of 17

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dissolution is feasible. 5. Summary and conclusions The chemical compositions of vents fluids sampled from four different hydrothermally active volcanoes along the Kermadec intraoceanic arc (i.e., Macauley, Haungaroa, Brothers, Rumble III) have been determined during this study. Distinct differences between the compositions of fluids show that processes including water/rock interaction and phase separation, as well as inputs of acidic magmatic components from SO2 degassing, strongly influence hydrothermal fluid compositions along the Kermadec arc (cf. de Ronde et al., 2014, 2011, 2001). At Macauley, Rumble III and the Brothers Cone sites, discharge of magmatic fluids may explain some of the compositional characteristics, such as high REE contents and SO42−. Haungaroa and the Brothers NW Caldera Wall as well as the Upper Caldera site, in contrast, vent high-temperature black smoker fluids with typical chondrite-normalized REY patterns. We sampled low-Mg fluids at the Brothers Caldera sites (3.2 mM) and fluids that have highly enriched Mg concentrations (95.6 mM) at the Brothers Lower Cone site, when compared to seawater (53.1 mM), implying for the latter an addition of Mg either by mineral dissolution or subcritical phase separation. To our knowledge, no other hydrothermal vent fluids having such high Mg concentrations have ever been previously reported. At Macauley, we sampled low pH, acid-sulfate fluids with chlorinities much higher than seawater. This is the first report of briny acid-sulfate fluids. Apart from the range in fluid compositions between the different hydrothermal fields, temporal changes were also observed. While de Ronde et al. (2011) found enriched Al but seawater-like Mg and SO42− concentrations in fluids from the Brothers Lower Cone site, we found high Mg, high sulfate but low Al concentrations, implying temporal changes in subsurface magmatic activity as well as on-going mineral dissolution processes. Thus, our data show how highly diverse and variable island arc systems can be with respect to their fluid chemistry, spatially and temporally. The high Fe/H2S ratios at the Brothers Caldera sites are also uncommon for vent fluids in arcs. Such fluids may allow large quantities of dissolved Fe to escape into the water column and contribute to the biogeochemical Fe cycle far beyond the volcanic arc. Additionally, Fe and Al concentrations in the fluids from the shallower sites at Macauley, venting at only 330 m water depth, are highly enriched when compared to seawater and may serve either as essential micronutrients (Fe) or as potential toxins (Al) for microorganisms in the photic zone, in which bioproductivity is highest, but Fe usually limited.

Fig. 10. Modeling approach showing the heating of seawater and the associated precipitation temperatures of anhydrite and caminite. (Geochemists Work Bench (GWB)).

hydrothermal circulation at this site. However, as all samples that show a Mg enrichment combined with enriched SO42− concentrations, we hypothesize that the dissolution of sulfate-bearing minerals and magnesium-hydroxide-sulfate-hydrateminerals, such as anhydrite and caminite (Mg1.4(SO4)(OH)0.8·0.2H2O), respectively, might occur in the subsurface, resulting in the unusual high concentrations of Mg and SO42− in the fluids. Studies along the East Pacific Rise have proven that caminite precipitates in hydrothermal vent systems and that it was found intergrown with anhydrite in the wall of a black-smoker chimney (Haymon and Kastner, 1986). Thermodynamic computations show that heating seawater to 350 °C should have both phases precipitate, caminite at T > 240 °C and anhydrite at T > 130 °C (Fig. 10). In turn, theses phases would be dissolving upon cooling of the system below the respective temperatures. This would suggest that the hydrothermal system of the Lower Cone was exposed to temperatures of at least 240 °C in the past. de Ronde et al. (2005) have suggested, based on mineral assemblages at the Cone sites, that vent fluids must have reached temperatures of up to 300 °C, which would be consistent with precipitation of caminite, which could subsequently dissolve. This would also be consistent with the moderate acidity of these fluids with pH values between 3.8 and 4.8, as the dissolution of caminite will consume protons and hence increase the pH of the fluid (Table 1). Fluids from other magmatic-dominated vent sites, such as DESMOS and SuSuKnolls in the Manus Basin, show high SO42− values up to 132 mM, but the associated Mg concentrations did not exceed 50.4 mM (Craddock et al., 2010; Seewald et al., 2015). To our knowledge, such high Mg concentrations as measured in fluids from the Brothers Lower Cone (95.6 mM) during this study have never been observed before. Our preferred interpretation is that caminite-dissolution is responsible for the elevated Mg and SO42− contents in moderate-pH fluids. Caminite-dissolution is expected to be a transient feature, which would explain why the enrichment of the fluid in Mg and SO42− observed in our study was not observed in fluids sampled in 2004 and 2005 from the Lower Cone site (de Ronde et al., 2011). Caminite-dissolution was not proposed to affect fluid compositions before, but it appears a plausible mechanism to explain the unusual composition of the Lower Cone fluids. Anhydrite-dissolution is more common (e.g., Reeves et al., 2011), but both phases are expected to precipitate, so caminite-

Declaration of competing interest None. Acknowledgements We thank Captain L. Mallon and his crew for their skilled support of the scientific work onboard the R/V Sonne and we acknowledge the excellent cooperation with the ROV MARUM Quest 4000 team. We also thank all scientific members of SO253 for help during sampling, especially Annika Moje for handling the KIPS sampling during the expedition. Funding of this project (03G0253) was provided by the BMBF (German Federal Ministry of Education and Research) and is gratefully acknowledged. The IAEA is grateful to the Government of the Principality of Monaco for the support provided to its Environment Laboratories. This study received financial support from the University of Otago Grant. The New Zealand authorities are thanked for permission to work along the Kermadec arc. We thank Dr. M. Keith and Dr. J. Seewald for constructive revisions, which helped to improve the manuscript. 18

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References

Pacific). Chem. Geol. 93, 209–218. Hannington, M.D., de Ronde, C.E.J., Petersen, S., 2005. Sea-floor tectonics and submarine hydrothermal systems. In: Econ. Geol. 100th Anniv, vol. 111–141. Haymon, R.M., Kastner, M., 1986. Caminite: a new magnesium-hydroxide-sulfate-hydrate mineral found in a submarine hydrothermal deposit, East Pacific Rise, 21°N. Am. Mineral. 71, 819–825. Humphris, S.E., Bach, W., 2005. On the Sr isotope and REE compositions of anhydrites from the TAG seafloor hydrothermal system. Geochim. Cosmochim. Acta 69, 1511–1525. https://doi.org/10.1016/j.gca.2004.10.004. Inoue, A., 1995. Formation of clay minerals in hydrothermal environments. In: Velde, B. (Ed.), Origin and Mineralogy of Clays. Springer, Berlin Heidelberg, Berlin, Heidelberg, pp. 268–329. https://doi.org/10.1007/978-3-662-12648-6. James, R.H., Green, D.R.H., Stock, M.J., Alker, B.J., Banerjee, N.R., Cole, C., German, C.R., Huvenne, V.A.I., Powell, A.M., Connelly, D.P., 2014. Composition of hydrothermal fluids and mineralogy of associated chimney material on the East Scotia Ridge back-arc spreading centre. Geochim. Cosmochim. Acta 139, 47–71. https://doi. org/10.1016/j.gca.2014.04.024. Keith, M., Häckel, F., Haase, K.M., Schwarz-Schampera, U., Klemd, R., 2016. Trace element systematics of pyrite from submarine hydrothermal vents. Ore Geol. Rev. 72, 728–745. https://doi.org/10.1016/j.oregeorev.2015.07.012. Kleint, C., Kuzmanovski, S., Powell, Z., Bühring, S.I., Sander, S.G., Koschinsky, A., 2015. Organic Cu-complexation at the shallow marine hydrothermal vent fields off the coast of Milos (Greece), Dominica (Lesser Antilles) and the Bay of Plenty (New Zealand). Mar. Chem. 173, 244–252. https://doi.org/10.1016/j.marchem.2014.10. 012. Kleint, C., Pichler, T., Koschinsky, A., 2017. Geochemical characteristics, speciation and size-fractionation of iron (Fe) in two marine shallow-water hydrothermal systems, Dominica, Lesser Antilles. Chem. Geol. 454, 44–53. https://doi.org/10.1016/j. chemgeo.2017.02.021. Koschinsky, A., Garbe-Schönberg, D., Sander, S., Schmidt, K., Gennerich, H.-H., Strauss, H., 2008. Hydrothermal venting at pressure-temperature conditions above the critical point of seawater, 5°S on the Mid-Atlantic Ridge. Geology 36, 615. https://doi.org/ 10.1130/G24726A.1. Liebscher, A., Lüders, V., Heinrich, W., Schettler, G., 2006. Br/Cl signature of hydrothermal fluids: liquid-vapour fractionation of bromine revisited. Geofluids 6, 113–121. https://doi.org/10.1111/j.1468-8123.2006.00135.x. Migdisov, A., Williams-Jones, A.E., Brugger, J., Caporuscio, F.A., 2016. Hydrothermal transport, deposition, and fractionation of the REE: experimental data and thermodynamic calculations. Chem. Geol. 439, 13–42. https://doi.org/10.1016/j.chemgeo. 2016.06.005. Mills, R.A., 1995. Hydrothermal deposits and metalliferous sediments from TAG, 26 N Mid-Atlantic Ridge. Geol. Soc. Lond. Spec. Publ. 87, 121–132. https://doi.org/10. 1144/GSL.SP.1995.087.01.11. Mills, R.A., Elderfield, H., 1995. Rare earth element geochemistry of hydrothermal deposits from the active TAG Mound, 26°N Mid-Atlantic Ridge. Geochim. Cosmochim. Acta 59, 3511–3524. https://doi.org/10.1016/0016-7037(95)00224-N. Mottl, M.J., Holland, H.D., 1978. Chemical exchange during hydrothermal alteration of basalt by seawater-I. Experimental results for major and minor components of seawater. Geochim. Cosmochim. Acta 42, 1103–1115. https://doi.org/10.1016/00167037(78)90107-2. Mottl, M.J., Seewald, J.S., Wheat, C.G., Tivey, M.K., Michael, P.J., Proskurowski, G., McCollom, T.M., Reeves, E., Sharkey, J., You, C.F., Chan, L.H., Pichler, T., 2011. Chemistry of hot springs along the Eastern Lau spreading center. Geochim. Cosmochim. Acta 75, 1013–1038. https://doi.org/10.1016/j.gca.2010.12.008. Reed, M.H., 1997. Hydrothermal alteration and its relationship to ore fluid composition. In: Geochemistry of Hydrothermal Ore Deposits, pp. 303–365. Reeves, E.P., Seewald, J.S., Saccocia, P., Bach, W., Craddock, P.R., Shanks, W.C., Sylva, S.P., Walsh, E., Pichler, T., Rosner, M., 2011. Geochemistry of hydrothermal fluids from the PACMANUS, Northeast Pual and Vienna Woods hydrothermal fields, Manus Basin, Papua New Guinea. Geochim. Cosmochim. Acta 75, 1088–1123. https://doi. org/10.1016/j.gca.2010.11.008. Resing, J.A., Lebon, G., Baker, E.T., Lupton, J.E., Embley, R.W., Massoth, G.J., Chadwick, W.W., de Ronde, C.E.J., 2007. Venting of acid-sulfate fluids in a high-sulfidation setting at NW Rota-1 submarine volcano on the Mariana Arc. Econ. Geol. 102, 1047–1061. https://doi.org/10.2113/gsecongeo.102.6.1047. de Ronde, C.E.J., Stucker, V.K., 2015. Seafloor hydrothermal venting at volcanic arcs and backarcs. In: The Encyclopedia of Volcanoes. Elsevier, pp. 823–849. https://doi.org/ 10.1016/B978-0-12-385938-9.00047-X. de Ronde, C.E.J., Baker, E.T., Massoth, G.J., Lupton, J.E., Wright, I.C., Feely, R.A., Greene, R.R., 2001. Intra-oceanic subduction-related hydrothermal venting, Kermadec volcanic arc, New Zealand. Earth Planet. Sci. Lett. 193, 359–369. https:// doi.org/10.1016/S0012-821X(01)00534-9. de Ronde, C.E., Massoth, G.J., Baker, E.T., Lupton, J.E., 2003. Submarine hydrothermal venting related to volcanic arcs. In: Simmons, S.F., Graham, I.J. (Eds.), Volcanic, Geothermal, and Ore-Forming Fluids: Rulers and Witnesses of Processes Within the Earth. Society of Economic Geologists. Special publication/Society of Economic Geologists, Littleton, Colo, pp. 91–109. https://doi.org/10.5382/SP.10. de Ronde, C.E.J., Hannington, M.D., Stoffers, P., Wright, I.C., Ditchburn, R.G., Reyes, A.G., Al, E., 2005. Evolution of a submarine magmatic-hydrothermal system: Brothers Volcano, Southern Kermadec Arc, New Zealand. Econ. Geol. 100, 1097–1133. de Ronde, C.E.J, Baker, E.T., Massoth, G.J., Lupton, J.E., Wright, I.C., Sparks, R.J., Bannister, S.C., Reyners, M.E., Walker, S.L., Greene, R.R., Ishibashi, J., Faure, K., Resing, J.A., Lebon, G.T., 2007. Submarine hydrothermal activity along the midKermadec Arc, New Zealand: Large-scale effects on venting. Geochem. Geophys. Geosyst. 8 (7). https://doi.org/10.1029/2006GC001495. de Ronde, C.E.J., Massoth, G.J., Butterfield, D.A., Christenson, B.W., Ishibashi, J.,

Alibo, D.S., Nozaki, Y., 1999. Rare earth elements in seawater: particle association, shalenormalization, and Ce oxidation. Geochim. Cosmochim. Acta 63, 363–372. https:// doi.org/10.1016/S0016-7037(98)00279-8. Allen, D.E., Seyfried, W.E., 2005. REE controls in ultramafic hosted MOR hydrothermal systems: an experimental study at elevated temperature and pressure. Geochim. Cosmochim. Acta 69, 675–683. https://doi.org/10.1016/j.gca.2004.07.016. Bach, W., Irber, W., 1998. Rare earth element mobility in the oceanic lower sheeted dyke complex: evidence from geochemical data and leaching experiments. Chem. Geol. 151, 309–326. https://doi.org/10.1016/S0009-2541(98)00087-4. Bach, W., Roberts, S., Vanko, D.A., Binns, R.A., Yeats, C.J., Craddock, P.R., Humphris, S.E., 2003. Controls of fluid chemistry and complexation on rare-earth element contents of anhydrite from the Pacmanus subseafloor hydrothermal system, Manus Basin, Papua New Guinea. Miner. Depos. 38, 916–935. https://doi.org/10.1007/ s00126-002-0325-0. Baker, E.T., Massoth, G.J., Nakamura, K., Embley, R.W., de Ronde, C.E.J., Arculus, R.J., 2005. Hydrothermal activity on near-arc sections of back-arc ridges: results from the Mariana Trough and Lau Basin. Geochem. Geophys. Geosyst. 6https://doi.org/10. 1029/2005GC000948. n/a-n/a. Baker, E.T., Embley, R.W., Walker, S.L., Resing, J.A., Lupton, J.E., Nakamura, K., de Ronde, C.E.J., Massoth, G.J., 2008. Hydrothermal activity and volcano distribution along the Mariana arc. J. Geophys. Res. 113, B08S09. https://doi.org/10.1029/ 2007JB005423. Bao, S.X., Zhou, H.Y., Peng, X.T., Ji, F.W., Yao, H.Q., 2008. Geochemistry of REE and yttrium in hydrothermal fluids from the Endeavour segment, Juan de Fuca Ridge. Geochem. J. 42, 359–370. https://doi.org/10.2343/geochemj.42.359. Bau, M., Usui, A., Pracejus, B., Mita, N., Kanai, Y., Irber, W., Dulski, P., 1998. Geochemistry of low-temperature water-rock interaction: evidence from natural waters, andesite, and iron-oxyhydroxide precipitates at Nishiki-numa iron-spring, Hokkaido, Japan. Chem. Geol. 151, 293–307. https://doi.org/10.1016/S00092541(98)00086-2. Bischoff, J.L., 1991. Densities of liquids and vapors in boiling NaCl-H2O solutions; a PVTx summary from 300 degrees to 500 degrees C. Am. J. Sci. 291, 309–338. https://doi. org/10.2475/ajs.291.4.309. Butterfield, D.A., Massoth, G.J., McDuff, R.E., Lupton, J.E., Lilley, M.D., 1990. Geochemistry of hydrothermal fluids from Axial Seamount hydrothermal emissions study vent field, Juan de Fuca Ridge: subseafloor boiling and subsequent fluid-rock interaction. J. Geophys. Res. 95, 12895. https://doi.org/10.1029/JB095iB08p12895. Butterfield, D.A., McDuff, R.E., Mottl, M.J., Lilley, M.D., Lupton, J.E., Massoth, G.J., 1994. Gradients in the composition of hydrothermal fluids from the endeavor segment vent field - phase-separation and brine loss. J. Geophys. Res. Earth 99, 9561–9583. https://doi.org/10.1029/93jb03132. Butterfield, D.A., Nakamura, K.I., Takano, B., Lilley, M.D., Lupton, J.E., Resing, J.A., Roe, K.K., 2011. High SO2 flux, sulfur accumulation, and gas fractionation at an erupting submarine volcano. Geology 39, 803–806. https://doi.org/10.1130/G31901.1. Chen, J.H., Wasserburg, G.J., von Damm, K.L., Edmond, J.M., 1986. The U-Th-Pb systematics in hot springs on the East Pacific Rise at 21°N and Guaymas Basin. Geochim. Cosmochim. Acta 50, 2467–2479. https://doi.org/10.1016/0016-7037(86)90030-X. Cline, J.D., 1969. Spectrophotometric determination of hydrogen sulfide in natural waters. Limnol. Oceanogr. 14, 454–458. https://doi.org/10.4319/lo.1969.14.3.0454. Cole, C.S., James, R.H., Connelly, D.P., Hathorne, Ed C., 2014. Rare earth elements as indicators of hydrothermal processes within the East Scotia subduction zone system. Geochim. Cosmochim. Acta 140, 20–38. https://doi.org/10.1016/j.gca.2014.05.018. Craddock, P.R., Bach, W., Seewald, J.S., Rouxel, O.J., Reeves, E., Tivey, M.K., 2010. Rare earth element abundances in hydrothermal fluids from the Manus Basin, Papua New Guinea: indicators of sub-seafloor hydrothermal processes in back-arc basins. Geochim. Cosmochim. Acta 74, 5494–5513. https://doi.org/10.1016/j.gca.2010.07. 003. Douville, E., Charlou, J., Oelkers, E., Bienvenu, P., Jove Colon, C., Donval, J., Fouquet, Y., Prieur, D., Appriou, P., 2002. The rainbow vent fluids (36°14′N, MAR): the influence of ultramafic rocks and phase separation on trace metal content in Mid-Atlantic Ridge hydrothermal fluids. Chem. Geol. 184, 37–48. https://doi.org/10.1016/S00092541(01)00351-5. Embley, R., Baker, E., Butterfield, D., Chadwick, W., Lupton, J., Resing, J., de Ronde, C., Nakamura, K., Tunnicliffe, V., Dower, J., Merle, S., 2007. Exploring the submarine ring of fire: Mariana Arc - Western Pacific. Oceanography 20, 68–79. https://doi.org/ 10.5670/oceanog.2007.07. Gamo, T., Okamura, K., Charlou, J.-L., Urabe, T., Auzende, J.-M., Ishibashi, J., Shitashima, K., Chiba, H., Shipboard Scientific Party of the ManusFlux Cruise, 1997. Acidic and sulfate-rich hydrothermal fluids from the Manus back-arc basin, Papua New Guinea. Geology 25, 139–142. https://doi.org/10.1130/0091-7613(1997) 025<0139:AASRHF>2.3.CO;2. Garbe-Schönberg, D., Koschinsky, A., Ratmeyer, V., Jähmlich, H., Westernstroeer, U., 2006. KIPS – a new multiport valve-based all-Teflon fluid sampling system for ROVs. Geophys. Res. Abstr. 8, 07032 (doi:SRef-ID: 1607-7962/gra/EGU06-A-07032). German, C.R., von Damm, K.L., 2003. Hydrothermal processes. In: Holland, H., Turekian, K. (Eds.), The Oceans and Marine Geochemistry (Treatise on Geochemistry Series, Vol. 6). Elsevier, pp. 182–222. German, C.R., Baker, E.T., Connelly, D.P., Lupton, J.E., Resing, J., Prien, R.D., Walker, S.L., Edmonds, H.N., Langmuir, C.H., 2006. Hydrothermal exploration of the Fonualei Rift and spreading center and the Northeast Lau spreading center. Geochem. Geophys. Geosyst. 7https://doi.org/10.1029/2006GC001324. n/a-n/a. Grimaud, D., Ishibashi, J.-I., Lagabrielle, Y., Auzende, J.-M., Urabe, T., 1991. Chemistry of hydrothermal fluids from the 17 ° S active site on the North Fiji Basin Ridge (SW

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C. Kleint, et al. Ditchburn, R.G., Hannington, M.D., Brathwaite, R.L., Lupton, J.E., Kamenetsky, V.S., Graham, I.J., Zellmer, G.F., Dziak, R.P., Embley, R.W., Dekov, V.M., Munnik, F., Lahr, J., Evans, L.J., Takai, K., 2011. Submarine hydrothermal activity and gold-rich mineralization at Brothers Volcano, Kermadec Arc, New Zealand. Miner. Depos. 46, 541–584. https://doi.org/10.1007/s00126-011-0345-8. de Ronde, C.E.J., Butterfield, D.A., Leybourne, M.I., 2012. Metallogenesis and mineralization of intraoceanic arcs I: Kermadec Arc-introduction. Econ. Geol. 107, 1521–1525. https://doi.org/10.2113/econgeo.107.8.1521. de Ronde, C.E.J., Walker, S.L., Ditchburn, R.G., Tontini, F.C., Hannington, M.D., Merle, S.G., Timm, C., Handler, M.R., Wysoczanski, R.J., Dekov, V.M., Kamenov, G.D., Baker, E.T., Embley, R.W., Lupton, J.E., Stoffers, P., 2014. The anatomy of a buried submarine hydrothermal system, Clark Volcano, Kermadec Arc, New Zealand. Econ. Geol. 109, 2261–2292. https://doi.org/10.2113/econgeo.109.8.2261. Schmidt, K., Garbe-Schönberg, D., Hannington, M.D., Anderson, M.O., Bühring, B., Haase, K., Haruel, C., Lupton, J., Koschinsky, A., 2017. Boiling vapour-type fluids from the Nifonea vent field (New Hebrides Back-Arc, Vanuatu, SW Pacific): geochemistry of an early-stage, post-eruptive hydrothermal system. Geochim. Cosmochim. Acta 207, 185–209. https://doi.org/10.1016/j.gca.2017.03.016. Seewald, J.S., Seyfried, W.E., 1990. The effect of temperature on metal mobility in subseafloor hydrothermal systems: constraints from basalt alteration experiments. Earth Planet. Sci. Lett. 101, 388–403. https://doi.org/10.1016/0012-821X(90)90168-W. Seewald, J.S., Doherty, K.W., Hammar, T.R., Liberatore, S.P., 2002. A new gas-tight isobaric sampler for hydrothermal fluids. Deep. Res. Part I Oceanogr. Res. Pap. 49, 189–196. https://doi.org/10.1016/S0967-0637(01)00046-2. Seewald, J.S., Reeves, E.P., Bach, W., Saccocia, P.J., Craddock, P.R., Shanks, W.C., Sylva, S.P., Pichler, T., Rosner, M., Walsh, E., 2015. Submarine venting of magmatic volatiles in the Eastern Manus Basin, Papua New Guinea. Geochim. Cosmochim. Acta 163, 178–199. https://doi.org/10.1016/j.gca.2015.04.023. Seewald, J.S., Reeves, E.P., Bach, W., Saccocia, P.J., Craddock, P.R., Walsh, E., Shanks, W.C., Sylva, S.P., Pichler, T., Rosner, M., 2019. Geochemistry of hot-springs at the SuSu Knolls hydrothermal field, Eastern Manus Basin: advanced argillic alteration and vent fluid acidity. Geochim. Cosmochim. Acta 255, 25–48. https://doi.org/10.

1016/j.gca.2019.03.034. Seyfried, W.E., Ding, K., 1993. The effect of redox on the relative solubilities of copper and iron in Cl-bearing aqueous fluids at elevated temperatures and pressures: an experimental study with application to subseafloor hydrothermal systems. Geochim. Cosmochim. Acta 57, 1905–1917. https://doi.org/10.1016/0016-7037(93)90083-9. Takai, K., Nunoura, T., Ishibashi, J.I., Lupton, J., Suzuki, R., Hamasaki, H., Ueno, Y., Kawagucci, S., Gamo, T., Suzuki, Y., Hirayama, H., Horikoshi, K., 2008. Variability in the microbial communities and hydrothermal fluid chemistry at the newly discovered Mariner hydrothermal field, southern Lau Basin. J. Geophys. Res. Biogeosci. 113. https://doi.org/10.1029/2007JG000636. Tivey, M.K., Mills, R.A., Teagle, D.A.H., 1998. Temperature and salinity of fluid inclusions in anhydrite as indicators of seawater entrainment and heating in the TAG active mound. In: Proc. Ocean Drill. Program, 158 Sci. Results 158, https://doi.org/10. 2973/odp.proc.sr.158.211.1998. Von Damm, K.L., 1995. Controls on the chemistry and temporal variability of seafloor hydrothermal fluids. In: Seafloor Hydrothermal Systems: Physical, Chemical, Biological, and Geological Interactions, pp. 222–247. https://doi.org/10.1029/ GM091p0222. Von Damm, K.L., 2000. Chemistry of hydrothermal vent fluids from 9 degrees-10 degrees N, East Pacific Rise: “time zero,” the immediate posteruptive period. J. Geophys. Res. Earth 105, 11203–11222. https://doi.org/10.1029/1999jb900414. Von Damm, K., Edmond, J., Grant, B., Measures, C., Walden, B., Weiss, R., 1985. Chemistry of submarine hydrothermal solutions at 21 °N, East Pacific Rise. Geochim. Cosmochim. Acta 49, 2197–2220. https://doi.org/10.1016/0016-7037(85)90222-4. Wright, I.C., Worthington, T.J., Gamble, J.A., 2006. New multibeam mapping and geochemistry of the 30°–35° S sector, and overview, of southern Kermadec arc volcanism. J. Volcanol. Geotherm. Res. 149, 263–296. https://doi.org/10.1016/j.jvolgeores. 2005.03.021. Yücel, M., Gartman, A., Chan, C.S., Luther, G.W., 2011. Hydrothermal vents as a kinetically stable source of iron-sulphide-bearing nanoparticles to the ocean. Nat. Geosci. 4, 367–371. https://doi.org/10.1038/ngeo1148.

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