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Article

Using Apatite to Track Volatile Evolution in the Shallow Magma Chamber below the Yonaguni Knoll IV Hydrothermal Field in the Southwestern Okinawa Trough

by
Zuxing Chen
1,2,3,*,
Landry Soh Tamehe
4,
Haiyan Qi
1,3,
Yuxiang Zhang
1,2,3,
Zhigang Zeng
1,2,3,5,* and
Mingjiang Cai
6
1
CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
2
Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
3
Center for Ocean Mega-Science, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China
4
China Nonferrous Metals (Guilin) Geology and Mining Co. Ltd., Guilin 541004, China
5
College of Marine Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
6
School of Resources and Environmental Science, Quanzhou Normal University, Quanzhou 362000, China
*
Authors to whom correspondence should be addressed.
J. Mar. Sci. Eng. 2023, 11(3), 583; https://doi.org/10.3390/jmse11030583
Submission received: 27 January 2023 / Revised: 17 February 2023 / Accepted: 6 March 2023 / Published: 9 March 2023
(This article belongs to the Special Issue Research on Submarine Hydrothermal Activity and Its Material Circulation, Magmatic Setting, and Seawater, Sedimentary, Biologic Effects)
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Abstract

:
The Yonaguni Knoll IV is an active seafloor hydrothermal system associated with submarine silicic volcanism located in the “cross back-arc volcanic trail” (CBVT) in the southwestern Okinawa Trough. However, the behavior of volatiles during magmatic differentiation in the shallow silicic magma chamber is unclear. Here, the volatile contents of apatite inclusions trapped in different phenocrysts (orthopyroxene and amphibole) and microphenocrysts in the rhyolite from the Yonaguni Knoll IV hydrothermal field were analyzed by using electron microprobe analysis, which aims to track the behavior of volatiles in the shallow magma chamber. Notably, the ‘texturally constrained’ apatites showed a decreasing trend of XCl/XOH and XF/XCl ratios. Based on the geochemical analyses in combination with thermodynamic modeling, we found that the studied apatites were consistent with the mode of volatile-undersaturated crystallization. Therefore, volatiles were not saturated in the early stage of magmatic differentiation in the shallow rhyolitic magma chamber, and consequently, the metal elements were retained in the rhyolitic melt and partitioned into crystalline magmatic sulfides. Additionally, previous studies suggested that the shallow rhyolitic magma chamber was long-lived and periodically replenished by mafic magma. The injection of volatile-rich and oxidized subduction-related mafic magmas can supply abundant volatiles and dissolve magmatic sulfide in the shallow magma chamber. These processes are important for the later-stage of volatile exsolution, while the forming metal-rich magmatic fluids contribute to the overlying Yonaguni Knoll IV hydrothermal system.

1. Introduction

Volatiles (halogens, H2O, CO2, and S) are minor elements in magmas but important in volcanic processes [1,2,3,4,5], which influence the physical properties of silicate melts [6,7,8] and control the eruptive styles [9,10,11,12]. Furthermore, Cl and S are fundamental for transporting metals (e.g., Cu and Zn) from silicic magmas to exsolved hydrothermal fluids for formatting active hydrothermal systems and related ore deposits within active volcanoes [13,14]. Nevertheless, it is not easily demonstrated that any particular magmatic system has evolved an aqueous phase [15].
Apatite, Ca5(PO4)3(OH, F, Cl), is a ubiquitous accessory mineral in volcanic rocks [5], and its crystal structure can contain common magmatic volatile species such as H2O, F, Cl, and S [16]. Thus, apatite is a useful magmatic volatile ‘witness’ and can reliably record the melt volatile compositions [16,17,18]. Accordingly, the halogen contents in apatite can be used to estimate the F, Cl, and H2O compositions of the host melt [19,20,21,22,23]. Moreover, the variation trend in the halogen ratios in apatite can be evaluated whether the host melt is saturated in volatiles or not [15,16,17,24,25,26,27,28]. Specifically, the F:Cl:OH ratio of apatite remains approximately constant in vapor-undersaturated magma. In contrast, the Cl/F ratio of apatite decreases sharply when a vapor is exsolved [15,16,17,29]. Combined with the textural features of apatite, these trends in apatite are useful for tracking the vapor evolution in magmatic systems [16,17].
In this study, the volatile contents of apatites that are hosted in the groundmass and phenocryst phases (orthopyroxene and amphibole) of the rhyolite from the Yonaguni Knoll IV hydrothermal field of the southern Okinawa Trough were analyzed. According to the thermodynamic models of Candela [15], Stock et al. [16,17], and Piccoli and Candela [30], the ‘texturally constrained’ apatites reveal the magmatic volatile behavior in the rhyolitic magma chamber below the Yonaguni Knoll IV hydrothermal field. Furthermore, the implications for magmatic contribution to the overlying hydrothermal system are discussed.

2. Geological Setting

The Okinawa Trough (OT) is a present-day active back-arc basin of the Ryukyu subduction zone with affinities to the subduction of the Philippine Sea Plate beneath the Eurasian Plate at a velocity of ~5 to ~7 cm/year [31,32]. In the southwestern Okinawa Trough, an area of anomalous volcanism has been identified at the cross back-arc volcanic trail (CBVT) [32]. A cluster of more than 70 submarine volcanoes is distributed along the CBVT [33,34]. The abnormally voluminous volcanoes of CBVT might be related to the subduction of the Gagua Ridge on the Philippine seafloor since the early Pleistocene (Figure 1) [32,34]. Volcanic products of this region are dominated by rhyolites and dacites [35,36,37,38]. These silicic magmas are influenced by crustal assimilation and magma mixing [38,39,40,41].
The Yonaguni Knoll IV hydrothermal field (24°51′N, 122°42′E) is situated in an elongated valley within the CBVT zone [36,42]. Hydrothermal mineralization at the Yonaguni Knoll IV includes Zn–Pb–Cu sulfides, anhydrite-rich chimneys, Ba–As chimneys, Mn-rich chimneys, and native sulfur or barite [42,43]. The diverse range of mineralization reflects the contributions of organic-rich continent-derived sediment and the volatile-rich silicic magma [42,43].

3. Sampling and Methods

3.1. Sample and Petrography

The studied rhyolite was collected at the station HOBAB3-T9′ (122°41′55.877″E, 24°50′57.774″N) in the Yonaguni Knoll IV hydrothermal field (Figure 1) by using a TV grab during the R/V Kexue Hao cruise in 2014. The rhyolite sample has been well-studied and has a porphyritic texture with a mineral assemblage consisting of plagioclase, quartz, amphibole, Fe–Ti oxides, and orthopyroxene. Apatite and zircon are common accessory minerals in the rhyolite [36,38,39,44]. Chen et al. [38] reported the bulk-rock major elements, trace elements, and isotopic compositions of the rhyolite. The mineral chemistry of phenocrysts (e.g., orthopyroxene, amphibole, and plagioclase) and accessory minerals (i.e., zircon) were also analyzed for this rock [36,39,44]. Here, we made thin sections of the rhyolite for petrologic textural analysis and in situ chemical analyses of the apatite grains. In the studied rhyolite, apatite occurred as microphenocrysts within the groundmass and as inclusions within the phenocrysts composed of orthopyroxene and amphibole (Figure 2).

3.2. Analytical Methods

Polished thin sections of the rhyolite were first observed using a VEGA3 scanning electron microscope at the Institute of Oceanology, Chinese Academy of Sciences. Carbon coated polished sections were prepared to identify different texturally-constrained apatites. BSE images were obtained by using a scanning electron microscope operating with an acceleration voltage of 15 keV.
After detailed observation, apatites were analyzed for major elements in the same thin sections. All apatite analyses were made close to the center of the mineral grains. The major element compositions of apatites were determined using a JXA-8230 electron microprobe (EMP) at the State Key Laboratory of Continental Dynamics, Northwest University, Xian, China. The instrument was operated at an acceleration voltage of 15 kV, a beam current of 10 nA, and a beam diameter of 2 μm. The following standards were used: apatite (Ca, P), diopside (Si), almandine (Fe), fluorite (F), and NaCl (Cl). Analytical precision was ±0.01 wt.% for Cl and F, and 0.01–0.2 wt.% for the other elements.

4. Results

A total of 65 analyses were performed on 65 grains to identify the chemical composition of apatites in the studied rhyolite. The compositional data for all apatites are reported in Table 1, Table 2 and Table 3. Apatites have high concentrations of CaO (50.82 to 54.98 wt.%) and P2O5 (38.62 to 42.59 wt.%). They are fluorapatites exhibiting F and Cl contents ranging from 1.76 to 3.08 wt.% and from 0.50 to 0.73 wt.%, respectively (Table 1, Table 2 and Table 3).
Orthopyroxene-hosted apatite inclusions exhibited F and Cl concentrations ranging from 2.07 to 3.08 wt.% (XF = 0.55 to 0.82) and from 0.58 to 0.71 wt.% (XCl = 0.09 to 0.10), respectively (Table 1). XOH ranged from 0.09 to 0.36. Correspondingly, the XCl/XOH, XF/XOH, and XF/XCl ratios varied from 0.24 to 1.05, 1.53 to 9.25, and 5.50 to 8.79 (where XF, XCl, and XOH are the mole fractions of F, Cl, and OH, respectively) (Figure 3; Table 1).
The amphibole-hosted apatite inclusions had F and Cl contents ranging from 2.14 to 3.02 wt.% (XF = 0.57 to 0.80) and 0.50 to 0.72 wt.% (XCl = 0.07 to 0.11), respectively (Table 2). XOH ranged from 0.10 to 0.33. Correspondingly, the XCl/XOH, XF/XOH, and XF/XCl ratios varied from 0.29 to 0.91, 1.71 to 7.70, and 5.58 to 9.33, respectively (Table 2; Figure 3).
The apatite microphenocrysts displayed a large compositional range of F (1.76 to 3.08 wt.%; XF = 0.47 to 0.82), Cl (0.58 to 0.74 wt.%; XCl = 0.09 to 0.11), and XOH (0.09 to 0.43) compared with the apatite inclusions (Figure 3; Table 3). Correspondingly, the XCl/XOH, XF/XOH, and XF/XCl ratios ranged from 0.24 to 1.01, 1.09 to 8.95, and 4.50 to 8.82, respectively (Table 3). Apatite microphenocrysts were plotted on the same compositional trends with the apatite inclusions, but typically extended to more FeO-depleted compositions (Figure 3).

5. Discussion

5.1. Crystallization Sequence of the Texturally Constrained Apatites

Experiments have demonstrated that apatite crystallization is primarily a function of the SiO2 and P2O5 concentrations and temperature in silicate melts [5,45]. The saturation temperature of apatite calculated from the bulk rock compositions provides the minimum estimates of the initial temperature when apatite crystallized from the magma [5]. Based on the calculation formula of Piccoli and Candela [5], the apatite-saturation temperature of the rhyolite (SiO2 = 73.06 wt.% and P2O5 = 0.03 wt.%; [38]) was 824 °C, which was higher than the crystallization temperature of amphiboles in the rhyolite (761–797 °C; [36]). Moreover, quartz–amphibole intergrowth in the rhyolite [39] suggests that amphibole crystallized at a relatively late stage during magmatic differentiation. The orthopyroxene phenocrysts were in equilibrium with the host rhyolitic magma, having a crystallization temperature ranging between 792 and 838 °C [39]. Therefore, orthopyroxene began crystallizing before the amphibole. As orthopyroxene is enriched in FeO content (~34 wt.%, [39]), orthopyroxene fractional crystallization results in the residual melt toward decreasing FeO. On the whole, apatite microphenocrysts have lower FeO contents than those of apatite inclusions in orthopyroxene and amphibole phenocrysts (Figure 3), which is consistent with a comparative decrease in the melt FeO contents during magmatic differentiation. Thus, apatite hosted in phenocrysts generally crystallized earlier than their equivalents in the groundmass.

5.2. Behavior of the Volatiles during the Rhyolitic Magmatic Differentiation

The volatile contents of ‘texturally constrained’ apatites are a useful tracer for volatile evolution in the shallow magma chamber [16,17]. The factors controlling the variation trend of the F/Cl ratio in magmatic apatites during magma evolution include: (1) temperature and pressure conditions in open systems; (2) fractional crystallization; and (3) variable degrees of degassing or fluid exsolution [15,16,17,30]. We discuss these factors in the following sections.

5.2.1. Influence of Cooling and Decompression on Compositional Variability of Apatite Volatiles

Since temperature and pressure affect the halogen–OH exchange coefficients between apatite and melt [30,46], the volatile compositions of apatite are likely variable in the constant melt composition [17]. To model the apatite volatile compositional evolution during cooling or decompression at a given melt composition (Figure 4), we used the method according to Piccoli and Candela [5] and Stock et al. [16].
As shown in Figure 4a, the XCl/XOH and XF/XOH ratios of apatite strongly increased with decreasing temperature, which is consistent with the experimental results of a preference for the OH end-member in apatite at higher temperatures [46]. In contrast, pressure had little effect on the apatite volatile compositions at constant melt composition [30,46], with depressurization causing a slight increase in the Cl component, corresponding to an almost exclusive increase in the XCl/XOH ratios [16,30]. As apatite inclusions generally crystallized earlier than their equivalents in groundmass and thus displayed a decreased trend of XCl/XOH and XF/XOH ratios during magmatic evolution (Figure 4a), this suggests that cooling or depressurization is not the major control in driving the volatile composition variations of apatites. Although the injection of a mantle-derived basaltic magma into the shallow rhyolitic magma chamber and subsequent magma mixing is likely to lead to temporary heating and pressurization [22,35,38], the unzoned composition of apatite-hosted phenocrysts (amphibole and orthopyroxene) [36,39] suggests the crystallization of apatite under decreasing temperature. Collectively, the volatile composition trend in the studied apatites was not attributed to temperature and pressure variations. Alternatively, the progressive variation in the melt volatile composition during magmatic differentiation might explain the volatile composition trend observed in the studied apatites.

5.2.2. Compositional Variability of Apatite Volatiles during Magmatic Differentiation

As magmatic differentiation progressively increases the volatile contents of the residual melt, the volatile-rich subduction-related magmas may exsolve an aqueous fluid phase in the shallow magma chamber [15]. Before volatile unsaturation, the halogens (e.g., F and Cl) and H2O in a silicate melt were incompatible [15,17]. In contrast, when H2O was saturated, Cl will preferably partition into the fluid while F will be retained in the coexisting silicate melt [10,15,27,30]. For example, Cl partition coefficients between the fluid and silicate melt varied from 10 to over 200 in contrast to 0.7 for F [17,27] (Figure 4b). Thus, fluid-present magmatic differentiation can cause a strong fractionation of F from Cl in the residual melt [47]. Correspondingly, the volatile ratios of apatite (e.g., XF/XCl) are sensitive to aqueous fluid exsolution during magmatic evolution [15,16,17,24,26,27]. We then used the two-step thermodynamic model of Stock et al. [17] to constrain the volatile behaviors of the studied apatites during magmatic differentiation.
As shown in Figure 4, the XF/XOH and XF/XCl ratios of apatite typically displayed a decreasing trend during H2O-undersaturated crystallization. However, the XCl/XOH ratios of apatite either decreased or increased, which is controlled by the exact values of the F, Cl, and OH partition coefficients between apatite and the melt (Figure 4b). In contrast, the XF/XCl ratios of apatite strongly increased during H2O-saturated crystallization (Figure 4b). The decreased trend in the XCl/XOH and XF/XOH ratios of the studied apatites was consistent with the mode of H2O-undersaturated crystallization [48] (Figure 4b). Therefore, the rhyolitic magma in a shallow magma chamber was H2O-unsaturated during the period of apatite crystallization.

5.3. Implications for Magmatic Contribution to Hydrothermal System

Generally, there are at least two hypotheses for the origin of the metals in submarine massive sulfide deposits. One hypothesis is that the magmatic intrusion in the hydrothermal zone was leached by heated seawater, thereby indirectly contributing metal elements to the hydrothermal system [49,50,51]. The other view suggests that an evolved magma system can exsolve metal-rich magmatic fluids, thereby directly supplying metallic elements to the overlying hydrothermal system [52,53,54]. Moreover, the model of contribution of metal-rich magmatic fluids to the OT hydrothermal systems has been proposed by several scholars [41,55,56]. Nevertheless, it remains unclear whether and how the silicic magma exsolve metal-rich magmatic fluids.
As volatiles are ligands of metals transported in a magmatic–hydrothermal system [57], volatile exsolution is an essential precondition for the formation of metal-rich magmatic fluids [57,58]. The volatile exsolution from a silicate melt is expected to be recorded in the apatite with a drastic increase in the XF/XCl ratios (Figure 4b). Apatite occurs as inclusions in orthopyroxene and amphibole phenocrysts in the studied rhyolite (Figure 2), thus suggesting an early apatite saturation in the melt during magmatic differentiation [22]. However, the decreasing trend of XCl/XOH and XF/XCl ratios of the studied apatites in the rhyolite argues against H2O-saturated crystallization (Figure 4b). Therefore, the volatiles were not saturated and thus lacked exsolution of the metal-rich magmatic fluids in the early stage of magmatic differentiation in the shallow rhyolitic magma chamber. Metallic elements (e.g., Cu) are generally incompatible with silicate minerals but highly compatible with magmatic sulfides [57,58]. Consequently, the metal elements were partitioned into crystalline magmatic sulfides and/or dissolved in the rhyolitic melt [36,41]. Correspondingly, magmatic sulfide is common in silicic rocks from the CBVT region [41]. Additionally, the low Cu content of the rhyolite (13 μg/g; [55]) also indicates that magmatic sulfide was saturated during the rhyolitic magma evolution.
The prolonged zircon U–Th ages in the rhyolite reveal a long-lived (at least 100 ka) silicic magma chamber beneath the Yonaguni Knoll IV hydrothermal field [44]. The occurrence of mafic magmatic enclaves and compositional zoned plagioclase in the rhyolite [38,39] suggest multi-stages of mafic magma injection into the silicic magma chamber [22,35,40]. As subduction-related mafic magmas are enriched in volatiles [59], periodic injection of mafic magma can supply abundant volatiles into the shallow magma chamber, which is essential for the later-stage of volatile exsolution. Since subduction-related mafic magmas are oxidized [60,61], the injection of oxidized mafic magmas into the shallow rhyolitic magma chamber may lead to the oxidative dissolution of the earlier magmatic sulfides [41,55]. Consistently, the rhyolite magma has high oxygen fugacity at around QFM + 1 (where QFM is a quartz–fayalite–magnetite buffer) [36]. The phenomenon of magmatic sulfide dissolution is common in silicic rocks from the CBVT region [41]. Because magmatic sulfide is a significant sink of ore metals, the oxidative dissolution process facilitates the formation of metal-rich magmatic fluids [55,62,63]. Collectively, there is a lack of metal-rich magmatic fluid exsolved from the rhyolitic melt during the early stage of magmatic differentiation, but the subsequent periodic injection of volatile-rich and oxidized mafic magmas into the rhyolitic magma chamber, accompanied by the exsolution of metal-rich magmatic fluids, contribute to the submarine hydrothermal systems.

6. Conclusions

Apatites trapped in orthopyroxene and amphibole phenocrysts suggest early apatite saturation during the rhyolitic magmatic differentiation. The decreasing trend in the XCl/XOH and XF/XCl ratios of the apatite inclusions and microphenocrysts revealed that the magma chamber beneath the Yonaguni Knoll IV hydrothermal systems remained water-undersaturated during the early stage of magmatic differentiation. The lack of magmatic fluid exsolution resulted in the metal elements remaining dissolved in the rhyolitic melt and partitioning into magmatic sulfides. Subsequently, the injection of volatile-rich and oxidized basaltic magmas into the shallow rhyolitic magma chamber promoted the later-stage of volatile exsolution and forming metal-rich magmatic fluids to contribute to the overlying Yonaguni Knoll IV submarine hydrothermal system.

Author Contributions

Z.C.—Conceptualization, data curation, formal analysis, validation, writing and editing. L.S.T.—review and editing. H.Q.—Data curation, methodology. Y.Z.—Review and editing. Z.Z.—project administration and funding acquisition. M.C.—Review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the National Natural Science Foundation of China (Grant Nos. 42106083 and 91958213), the Open Fund of the Key Laboratory of Marine Geology and Environment, the Chinese Academy of Sciences (Grant Nos. MGE2022KG10 and MGE2020KG11), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB42020402), the Shandong Provincial Natural Science Foundation, China (Grant Nos. ZR2020QD069 and ZR2020MD068), the National Basic Research Program of China (Grant No. 2013CB429700), and the Special Fund for the Taishan Scholar Program of Shandong Province (Grant No. ts201511061).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data can be obtained from the corresponding author and are available in the main text.

Acknowledgments

We would like to thank the crews of the R/V Kexue during the HOBAB 3 cruise for their help with the sample collection. The authors thank Wenqiang Yang for his assistance in the EPMA analysis. We are grateful to three anonymous reviewers for their detailed and constructive comments and suggestions, which greatly improved an earlier version of the manuscript. We thank the MDPI editors for their efficient handling of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Regional and local bathymetric map showing the location of the studied rhyolite collected in the Yonaguni Knoll IV hydrothermal vent field of the southwestern Okinawa Trough.
Figure 1. Regional and local bathymetric map showing the location of the studied rhyolite collected in the Yonaguni Knoll IV hydrothermal vent field of the southwestern Okinawa Trough.
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Figure 2. Backscattered-electron (BSE) images displaying orthopyroxene (a) and amphibole (b) phenocrysts, and apatite microphenocrysts (c). (d–f) Sketch map showing the progressive growth of orthopyroxene and amphibole with the entrapment of apatite inclusions through time during cooling; (g) t1–t3 refer to the onset of crystallization of minerals (opx-in, ap-in, and amp-in), while t4 refers to the end of the crystallization of amphibole. The crystallization temperatures of minerals are according to previous studies [36,39]. Ap, apatite; Opx, orthopyroxene; Amp, amphibole; GM, groundmass.
Figure 2. Backscattered-electron (BSE) images displaying orthopyroxene (a) and amphibole (b) phenocrysts, and apatite microphenocrysts (c). (d–f) Sketch map showing the progressive growth of orthopyroxene and amphibole with the entrapment of apatite inclusions through time during cooling; (g) t1–t3 refer to the onset of crystallization of minerals (opx-in, ap-in, and amp-in), while t4 refers to the end of the crystallization of amphibole. The crystallization temperatures of minerals are according to previous studies [36,39]. Ap, apatite; Opx, orthopyroxene; Amp, amphibole; GM, groundmass.
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Figure 3. Volatile compositions of orthopyroxene- and amphibole-hosted apatite inclusions and apatite microphenocrysts in the rhyolite from the Yonaguni Knoll IV hydrothermal field. Data are depicted in the ternary diagram of Cl–OH–F (a) and binary plots of XCl/XOH vs. XF/XOH (b), and XF/XCl vs FeO (c).
Figure 3. Volatile compositions of orthopyroxene- and amphibole-hosted apatite inclusions and apatite microphenocrysts in the rhyolite from the Yonaguni Knoll IV hydrothermal field. Data are depicted in the ternary diagram of Cl–OH–F (a) and binary plots of XCl/XOH vs. XF/XOH (b), and XF/XCl vs FeO (c).
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Figure 4. Volatile compositions of apatites in the studied rhyolite. (a) XF/XOH versus XCl/XOH. Purple and blue arrows are the modeled trends of apatite compositional evolution at a constant melt composition under isothermal decompression and isobaric cooling conditions, respectively. The approach outlined by Stock et al. [16] was used to model the effects of physical processes such as the cooling and decompression on apatite compositions. (b) XF/XCl versus XCl/XOH. Arrows show the modeled trends of apatite composition during 80% volatile undersaturated crystallization, followed by 20% H2O-saturated crystallization. The various fluid–melt partition coefficients (DClf/m) in the thermodynamic modeling during H2O-undersaturated and saturated crystallization were according to Stock et al. [17]. Although the modeled results may not be quantitatively robust, these calculations provide a reference frame to outline the different processes on the apatite compositions.
Figure 4. Volatile compositions of apatites in the studied rhyolite. (a) XF/XOH versus XCl/XOH. Purple and blue arrows are the modeled trends of apatite compositional evolution at a constant melt composition under isothermal decompression and isobaric cooling conditions, respectively. The approach outlined by Stock et al. [16] was used to model the effects of physical processes such as the cooling and decompression on apatite compositions. (b) XF/XCl versus XCl/XOH. Arrows show the modeled trends of apatite composition during 80% volatile undersaturated crystallization, followed by 20% H2O-saturated crystallization. The various fluid–melt partition coefficients (DClf/m) in the thermodynamic modeling during H2O-undersaturated and saturated crystallization were according to Stock et al. [17]. Although the modeled results may not be quantitatively robust, these calculations provide a reference frame to outline the different processes on the apatite compositions.
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Table
Table 1. Major and volatile element analyses of the orthopyroxene-hosted apatite inclusions (wt.%).
Table 1. Major and volatile element analyses of the orthopyroxene-hosted apatite inclusions (wt.%).
AP1AP2AP3AP4AP5AP6AP7AP8AP9AP10AP11AP12AP13
P2O542.4741.7740.1939.9442.1638.6641.1840.9942.0841.8741.7341.6842.07
CaO53.9354.2153.8853.0653.8350.8253.6653.2852.9353.2654.1954.1154.28
SiO20.250.600.550.320.473.900.160.470.750.220.250.270.35
FeO1.031.171.481.251.231.331.141.151.420.961.170.881.37
F2.893.012.632.352.702.082.132.072.512.082.363.082.32
Cl0.640.640.650.580.710.670.700.670.690.580.610.630.68
Total101.46101.5899.5197.66101.3097.7199.1698.75100.5899.10100.49100.84101.15
1 XF0.770.800.700.620.720.550.560.550.670.550.630.820.62
2 XCl0.090.090.100.090.100.100.100.100.100.090.090.090.10
3 XOH0.140.110.210.290.180.350.330.350.230.360.280.090.28
XF/OH5.517.603.402.154.031.591.701.572.871.532.219.252.17
XCl/OH0.670.900.470.300.590.280.310.280.440.240.311.050.35
XF/Cl8.238.467.277.286.845.625.505.566.536.447.028.796.13
1−3 XF, XCl, and XOH are the mole fractions of the F-, Cl-, and OH-apatites, respectively (XF = CF/3.767, XCl = CCl/6.809, XOH = 1− XF − XCl; where CF and CCl are the contents of F and Cl in apatite in wt %). The calculations of the apatite mole fractions of the end-members are according to Piccoli and Candela [5].
Table
Table 2. Major and volatile element analyses of the amphibole-hosted apatite inclusions (wt.%).
Table 2. Major and volatile element analyses of the amphibole-hosted apatite inclusions (wt.%).
AP1AP2AP3AP4AP5AP6AP7AP8AP9AP10AP11AP12AP13
P2O541.5940.6740.6940.9541.3040.3939.1441.2940.8741.1242.5941.7241.46
CaO53.8854.2854.5654.0653.2153.5751.6754.4952.8753.4654.3453.8353.60
SiO20.430.610.640.510.500.462.060.440.910.470.370.410.42
FeO0.690.930.920.760.980.961.380.901.160.980.881.020.93
F2.212.982.592.452.332.332.142.842.282.592.672.342.16
Cl0.720.610.500.660.720.640.670.680.660.670.570.670.66
Total99.52100.0799.9099.3999.0498.3497.08100.6598.7699.28101.4299.9999.23
XF0.590.790.690.650.620.620.570.750.600.690.710.620.57
XCl0.110.090.070.100.110.090.100.100.100.100.080.100.10
XOH0.310.120.240.250.280.290.330.150.300.220.210.280.33
XF/OH1.916.602.882.592.242.161.715.192.023.203.412.211.73
XCl/OH0.340.750.310.390.380.320.300.690.320.460.400.350.29
XF/Cl5.588.789.336.705.876.645.767.516.247.018.496.355.89
AP14AP15AP16AP17AP18AP19AP20AP21AP22AP23AP24AP25AP26
P2O540.5440.8041.4740.8241.0842.1442.0541.3341.3840.9341.2742.1541.15
CaO53.4354.0554.0653.5553.5554.9854.8353.7954.0253.9154.7354.7354.65
SiO20.560.440.530.320.770.440.380.310.310.370.230.240.78
FeO0.950.660.720.691.161.000.780.790.620.670.900.930.87
F2.282.742.532.382.632.532.532.492.242.403.022.952.86
Cl0.660.660.700.660.670.620.590.680.680.690.640.700.64
Total98.4299.35100.0198.4299.86101.70101.1599.3899.2598.96100.78101.70100.95
XF0.610.730.670.630.700.670.670.660.600.640.800.780.76
XCl0.100.100.100.100.100.090.090.100.100.100.090.100.09
XOH0.300.180.230.270.200.240.240.240.310.260.100.110.15
XF/OH2.044.152.972.333.422.802.772.761.952.427.706.865.17
XCl/OH0.330.560.450.360.480.380.360.420.330.380.890.910.64
XF/Cl6.247.476.566.547.147.427.766.655.996.318.617.578.11
Table
Table 3. The major and volatile element analyses of the apatite microphenocrysts (wt.%).
Table 3. The major and volatile element analyses of the apatite microphenocrysts (wt.%).
AP1AP2AP3AP4AP5AP6AP7AP8AP9AP10AP11AP12AP13
P2O541.2142.3142.2241.0241.5141.7641.3641.2541.5541.7941.0242.3242.27
CaO53.3854.0853.9153.6753.1953.8852.8253.3353.3352.7953.3253.5053.54
SiO20.480.510.610.240.35 0.200.320.270.320.540.220.370.35
FeO0.790.630.800.500.390.660.440.550.350.900.470.740.46
F2.042.212.192.182.142.192.282.222.472.232.422.322.12
Cl0.700.720.670.710.700.660.710.680.700.710.710.700.70
Total98.70100.57100.5098.5098.4399.5098.0198.4998.9699.1498.37100.0699.61
XF0.540.590.580.580.570.580.600.590.660.590.640.620.56
XCl0.100.110.100.100.100.100.100.100.10 0.100.100.100.10
XOH0.360.310.320.320.330.320.290.310.240.300.250.280.33
XF/OH1.521.911.811.831.721.812.071.892.721.952.542.191.69
XCl/OH0.290.340.310.330.310.300.360.320.420.340.410.360.31
XF/Cl5.295.555.915.545.486.055.785.926.415.706.216.025.50
AP14AP15AP16AP17AP18AP19AP20AP21AP22AP23AP24AP25AP26
P2O540.0241.6939.9040.2041.2541.2940.3240.9440.4840.4539.7641.4438.62
CaO52.8052.9053.4953.0853.0254.0252.8653.8552.8253.3152.7553.9152.07
SiO20.340.420.630.890.430.410.630.380.620.481.630.332.13
FeO0.480.780.560.330.480.480.850.780.260.270.280.940.88
F1.762.312.762.642.212.762.393.082.14 2.222.332.542.65
Cl0.710.710.640.580.610.710.710.630.730.650.670.640.62
Total96.2998.9798.1097.9298.1399.8297.94 99.7697.2697.4297.60100.1197.21
XF0.470.610.730.700.590.730.630.820.570.59 0.620.670.70
XCl0.100.100.090.090.090.100.100.090.110.10 0.100.090.09
XOH0.430.280.170.210.320.160.260.090.320.32 0.280.230.21
XF/OH1.092.184.233.281.814.482.428.951.751.87 2.192.883.41
XCl/OH0.240.370.550.400.280.640.401.010.330.300.350.400.44
XF/Cl4.505.877.748.176.557.046.108.825.326.176.317.207.69
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Chen, Z.; Soh Tamehe, L.; Qi, H.; Zhang, Y.; Zeng, Z.; Cai, M. Using Apatite to Track Volatile Evolution in the Shallow Magma Chamber below the Yonaguni Knoll IV Hydrothermal Field in the Southwestern Okinawa Trough. J. Mar. Sci. Eng. 2023, 11, 583. https://doi.org/10.3390/jmse11030583

AMA Style

Chen Z, Soh Tamehe L, Qi H, Zhang Y, Zeng Z, Cai M. Using Apatite to Track Volatile Evolution in the Shallow Magma Chamber below the Yonaguni Knoll IV Hydrothermal Field in the Southwestern Okinawa Trough. Journal of Marine Science and Engineering. 2023; 11(3):583. https://doi.org/10.3390/jmse11030583

Chicago/Turabian Style

Chen, Zuxing, Landry Soh Tamehe, Haiyan Qi, Yuxiang Zhang, Zhigang Zeng, and Mingjiang Cai. 2023. "Using Apatite to Track Volatile Evolution in the Shallow Magma Chamber below the Yonaguni Knoll IV Hydrothermal Field in the Southwestern Okinawa Trough" Journal of Marine Science and Engineering 11, no. 3: 583. https://doi.org/10.3390/jmse11030583

APA Style

Chen, Z., Soh Tamehe, L., Qi, H., Zhang, Y., Zeng, Z., & Cai, M. (2023). Using Apatite to Track Volatile Evolution in the Shallow Magma Chamber below the Yonaguni Knoll IV Hydrothermal Field in the Southwestern Okinawa Trough. Journal of Marine Science and Engineering, 11(3), 583. https://doi.org/10.3390/jmse11030583

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