Geochemical features of trace and rare earth elements of pumice in middle Okinawa Trough and its indication of magmatic process

Zhai, Shikui; Guo, Kun; Zong, Tong; Yu, Zhigang; Wang, Shujie; Cai, Zongwei; Zhang, Xia

doi:10.1007/s11802-017-3131-0

Cited by 7 publications

(5 citation statements)

References 15 publications

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“…Pumice is the most widely distributed volcanic rock in the MOT (Zhai et al, ); this magmatism represents the most extensive magmatism in the MOT. Although this pumice has been studied since the 1980s, the differences in the origins and magma compositions of the white and black pumice remain controversial due to the lack of the available data (especially Pb isotopic data) and representative samples.…”

Section: Discussionmentioning

confidence: 99%

Different magma sources and evolutions of white and black pumice from the middle Okinawa Trough: Evidence from major, trace elements and Sr–Nd–Pb isotopes

et al. 2018

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The Okinawa Trough (OT) is a back-arc, initial marginal sea basin that is located behind the Ryukyu arc-trench system. Pumice, including both white and black pumice, is the most widely distributed magmatic rock in the OT. Here, the major and trace element concentrations and Sr-Nd-Pb isotopic compositions of the white and black pumice from the middle OT (MOT) are presented and combined with previously published elemental data for volcanic rocks from the MOT.

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Section: Discussionmentioning

confidence: 99%

Different magma sources and evolutions of white and black pumice from the middle Okinawa Trough: Evidence from major, trace elements and Sr–Nd–Pb isotopes

et al. 2018

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“…These features imply that abundant subvolcanic magma chambers, which provide space for the storage and evolution of magma (e.g., Lai et al, 2016;Shinjo & Kato, 2000) and/or heat sources for hydrothermal systems (e.g., Hou, Ai, Qu, Zhang, & Tang, 1999;Tsuji et al, 2012), probably exist in the upper crust of the OT. Over the past several decades, many investigations have attempted to reveal the petrogenesis of the OT rhyolites (e.g., Guo, Zhai, Yu, Cai, & Zhang, 2016;Honma et al, 1991;Huang et al, 2006;Shinjo & Kato, 2000;Zhai et al, 2017;, but only a few have focused on the magmatic evolution processes in the magma chamber beneath the OT. Some researchers have proposed a doublelayered magma chamber model, in which two magma chambers exist in the lower crust and upper crust of the OT, respectively (Liao, Huang, & Hu, 2016;Shinjo & Kato, 2000;Zhai, Chen, Wang, & Gan, 1997).…”

Section: Introductionmentioning

confidence: 99%

“…Unlike many intraoceanic back-arc basins, the OT has abundant rhyolites, especially in the northern and middle regions of the trough (Yan & Shi, 2014). Moreover, many of these rhyolites are highly vesicular pumices (e.g., Huang, Li, & Jiang, 2006;Ishikawa et al, 1991;Shinjo & Kato, 2000;Yu, Zhai, Guo, Zhou, & Zong, 2016;Zhai, 1986;Zhai et al, 2017;Y. X. Zhang, Zeng, Qi, et al, 2017), which are generally considered to represent the products of relatively vigorous eruptions of evolved volatile-rich magma (Fiske, Naka, Iizasa, Yuasa, & Klaus, 2001;Kano, 2003;Klug, Cashman, & Bacon, 2002).…”

Section: Introductionmentioning

confidence: 99%

Petrology and mineralogy of pumice from the Iheya North Knoll, Okinawa Trough: Implications for the differentiation of crystal‐poor and volatile‐rich melts in the magma chamber

et al. 2018

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The Iheya North Knoll is a submarine hill that is covered with pumice in the Okinawa Trough. The petrology and mineralogy of the crystal‐poor rhyolitic pumice collected from two sampling sites (T3 and T6) on the knoll were analysed in this article. The T6 pumice, which contains some mafic minerals (e.g., clinopyroxene, orthopyroxene), is slightly more crystal‐rich (<5 vol.%) than the T3 pumice (<2 vol.%). However, both types of pumice are high‐potassium rhyolites with similar Nd isotopic ratios and rare earth element patterns, as well as similar glass compositions, which indicates that they may fall along a line of descent of comagmatic evolution. The T6 pumice contains some xenomorphic clinopyroxenes that are not in equilibrium with their whole‐rock composition, which suggests that the crystal‐poor melt was extracted from a more mafic source. The T3 pumice features a flow structure, and its matrix glass records higher Cl concentrations and a lower total mass than the T6 pumice, which implies that the T3 melt has a higher volatile content and lower viscosity. The distinct petrographic characteristics but similar matrix glass compositions of the T3 and T6 pumice suggest that the extracted melt was physically differentiated during ascent, with the more crystal‐poor and volatile‐rich T3 melt reaching a higher lever in the magma chamber. Meanwhile, simulation calculations indicate that the melt experienced near‐adiabatic decompression‐driven chemical differentiation, which led to the growth of sodium‐rich plagioclase but not quartz in the pumice.

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“…Accordingly, the OT has extremely high heat flow values (Kong et al, ; Yamano, Uyeda, Foucher, & Sibuet, ; Zhang, Luan, Zeng, & Liu, ) and has active volcanism and hydrothermal activities. Many submarine volcanoes have been recognized in the OT (Sibuet et al, ), with volcanic eruptions ranging compositionally from tholeiitic basalt to calc‐alkaline rhyolite, which were generated from a depleted mantle source and affected by subduction components and/or upper crustal components (e.g., Chen et al, ; Guo et al, , ; Guo, Zhai, Yu, Cai, & Zhang, ; X. H. Li et al, , ; Shinjo & Kato, ; Shinjo, Chung, Kato, & Kimura, ; Shu et al, ; Shu, Zeng, Yin, Wang, & Chen, ; Yu, Zhai, Guo, Zhou, & Zong, ; Zhai et al, ; Zhang et al, ; Zhang, Zhai, Yu, Guo, & Wang, ; Zhao, Luo, Lai, Tian, & Xu, ). Numerous seafloor hydrothermal active sites and massive sulfide deposits have also been discovered in the OT (e.g., Glasby & Notsu, ; Halbach, Pracejus, & Marten, ; Ishibashi & Urabe, ; Kawagucci et al, ; Suzuki et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

Amphibole perspective to unravel the rhyolite as a potential fertile source for the Yonaguni Knoll IV hydrothermal system in the southwestern Okinawa Trough

Chen

Zeng

et al. 2019

Geological Journal

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Yonaguni Knoll IV is an active seafloor hydrothermal system containing massive Zn-Pb sulfides located in the southwestern OkinawaTrough. Previous research has suggested that the metal elements Zn and Pb were dominantly derived from the local volcanic rocks via water-rock interactions. However, it is not known whether or why the volcanic rocks are rich in these metals. Here, we performed a detailed in situ analysis of the major and trace elements in amphiboles in the rhyolite from the hydrothermal field to decipher the physical-chemical conditions of the silicic magma, including temperature (T), pressure (P), oxygen fugacity (fO 2 ), volatile contents (Cl, H 2 O) and metal contents (Pb, Zn), and investigate the behavior of the metals (Zn and Pb) during melt evolution. Our results show that the amphiboles are euhedral calcic magnesiohornblende and are in equilibrium with the hydrous and oxidized host rhyolitic melt characterized by high H 2 O melt (~5.8-6.5 wt.%), fO 2 (NNO +0.1 to +0.6) and SiO 2 melt (~71.73-72.62 wt.%) values at 761-797°C and 102-137 MPa, corresponding to an approximate depth of 3.9-5.2 km. In addition, the rare earth element (REE) patterns of the melt reconstructed from the amphiboles are analogous to those of cold-wetoxidized rhyolites. Thus, the amphiboles crystallized in a cold-wet-oxidized shallow silicic magma chamber. The high oxygen fugacity is inferred to have favored sulfur and metal enrichment in the melt. The most abundant metal in the amphiboles is Zn (237-294 ppm), and the concentrations of Pb are much lower (0.86-3.32 ppm), suggesting that Zn preferentially entered the amphibole and that Pb was retained in the melt. The Cl content of the amphiboles ranges from 0.11 to 0.25 wt.%, and accordingly, the Cl melt content estimated from the amphiboles varies from 0.15 to 0.28 wt. %. The low (Cl/H 2 O) melt ratios, which are <0.05 (i.e.,~0.02-0.04), suggest that the melt exsolved an H 2 O-rich vapor rather than a hydrosaline fluid with insufficient Cl to transport metals (e.g., Pb and Zn) into the vapor phase during degassing both in the magma chamber and during ascent. The lack of exsolved hydrosaline fluid and the high oxidation conditions resulted in the metal elements Pb and Zn remaining dissolved in the rhyolitic melt and/or partitioning into crystalline minerals upon eruption. Thus, the large volumes of rhyolitic magma that intruded into the upper crust of the Yonaguni Knoll IV hydrothermal field are a potential fertile source of these elements via leaching by heated seawater.

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Geochemical features of trace and rare earth elements of pumice in middle Okinawa Trough and its indication of magmatic process

Cited by 7 publications

References 15 publications

Different magma sources and evolutions of white and black pumice from the middle Okinawa Trough: Evidence from major, trace elements and Sr–Nd–Pb isotopes

Different magma sources and evolutions of white and black pumice from the middle Okinawa Trough: Evidence from major, trace elements and Sr–Nd–Pb isotopes

Petrology and mineralogy of pumice from the Iheya North Knoll, Okinawa Trough: Implications for the differentiation of crystal‐poor and volatile‐rich melts in the magma chamber

Amphibole perspective to unravel the rhyolite as a potential fertile source for the Yonaguni Knoll IV hydrothermal system in the southwestern Okinawa Trough

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