Two Processes of Anglesite Formation and a Model of Secondary Supergene Enrichment of Bi and Ag in Seafloor Hydrothermal Sulfide Deposits

The in situ element concentrations and the sulfur (S), and lead (Pb) isotopic compositions in anglesite were investigated for samples from seafloor hydrothermal fields in the Okinawa Trough (OT), Western Pacific. The anglesite grains are of two kinds: (1) low Pb/high S primary hydrothermal anglesite (PHA), which is formed by mixing of fluid and seawater, and (2) high Pb/low S secondary supergene anglesite (SSA), which is the product of low-temperature (<100 °C) alteration of galena in the seawater environment. The Ag and Bi in the SSA go through a second enrichment process during the formation of high Pb/low S anglesite by galena alteration, indicating that the SSA and galena, which may be the major minerals host for considerable quantities of Ag and Bi, are potentially Ag-Bi-enriched in the back-arc hydrothermal field. Moreover, REEs, S and Pb in the OT anglesite are likely to have been leached by fluids from local sub-seafloor volcanic rocks and/or sediments. A knowledge of the anglesite is useful for understanding the influence of volcanic rocks, sediments and altered subducted oceanic plate in hydrothermal systems, showing how trace metals behave during the formation of secondary minerals.

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Zircon record of an Archaean crustal fragment and supercontinent amalgamation in quaternary back-arc volcanic rocks

Scientific Reports ◽

10.1038/s41598-021-90578-9 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Zhi-gang Zeng ◽

Zu-xing Chen ◽

Yu-xiang Zhang

Keyword(s):

Continental Crust ◽

Okinawa Trough ◽

Volcanic Rocks ◽

Parental Magma ◽

The Okinawa Trough ◽

O Isotopes ◽

Back Arc ◽

First Time ◽

Integrated Study

AbstractMagmatism has profoundly influenced the evolution of the geosphere, hydrosphere, atmosphere, and biosphere in back-arc basins. However, the timing of the magmatism in the Okinawa Trough (OT) is not well constrained by the age spectra of zircons. Here, for the first time, we carry out an integrated study combining in situ analysis of zircon U–Th–Pb and Hf–O isotopes, and trace element compositions of zircons from the volcanic rocks from the southernmost part of the OT. We found that the young (< 100 ka) zircons in these volcanic rocks have old (108 Ma to 2.7 Ga) inherited cores, which were captured as the magma ascended through the rifting continental crust. In particular, the inherited Archean zircons strongly suggest that remnants of the old East Asian continental blocks underlie the embryonic crustal rifting zone. Moreover, the ages of most of the inherited zircons correspond to five supercontinent amalgamation events. Specifically, the Archaean inherited zircons, which have positive εHf(t) and low δ18O values, correspond to the formation of juvenile continental crust. In contrast, the negative εHf(t) and high δ18O values of the post-Archaean inherited zircons indicate that their parental magma contained recycled older crust due to the enhanced crust-mantle interactions during the evolution of the early continental crust. Therefore, the inherited zircons in the back-arc volcanic rocks not only reflect the evolution of the local magmatism, but they also contain a record of the Archaean crustal fragment and of several global continental amalgamation events.

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Zircon Record of Supercontinent Amalgamation in Back-arc Volcanic Rocks

10.21203/rs.3.rs-109172/v1 ◽

2020 ◽

Author(s):

Zhigang Zeng ◽

Zuxing Chen ◽

Yuxiang Zhang

Keyword(s):

Continental Crust ◽

Detrital Zircon ◽

Okinawa Trough ◽

Volcanic Rocks ◽

Parental Magma ◽

Crustal Thickening ◽

The Okinawa Trough ◽

Global Age ◽

Back Arc

Abstract Episodic supercontinental amalgamation has profoundly influenced the evolution of the geosphere, hydrosphere, atmosphere and biosphere. However, the timing of supercontinent formation has mainly been constrained by the global age spectra of detrital zircon. Here, we show that the zircons in back-arc volcanic rocks not only reflect the evolution of local magmatism but also contain a record of global continental amalgamation events. We found that the young (<100 ka) zircons in volcanic rocks from the Okinawa Trough have old (108 Ma to 2.7 Ga) inherited zircon, which were captured as the magma ascended through the rifting continental crust. Moreover, the ages of the inherited zircons correspond to five supercontinent amalgamation events. Specifically, the Archaean inherited zircons, which have positive ɛHf(t) and low δ18O values, correspond to the formation of juvenile global continental crust. In contrast, the negative ɛHf(t) and high δ18O values of post-Archaean inherited zircons indicate that their parental magma contained recycled, old crust due to the enhanced crustal thickening and crust-mantle interactions during supercontinent assembly. Therefore, inherited zircons in back-arc volcanic rocks not only reflect the evolution of local magmatism but also contain a record of global supercontinental amalgamation events.

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Geochemical and Sr-Nd isotopic characteristics of volcanic rocks from the Okinawa Trough and Ryukyu Arc: Implications for the evolution of a young, intracontinental back arc basin

Journal of Geophysical Research Atmospheres ◽

10.1029/1999jb900040 ◽

1999 ◽

Vol 104 (B5) ◽

pp. 10591-10608 ◽

Cited By ~ 242

Author(s):

Ryuichi Shinjo ◽

Sun-Lin Chung ◽

Yuzo Kato ◽

Masaaki Kimura

Keyword(s):

Okinawa Trough ◽

Volcanic Rocks ◽

The Okinawa Trough ◽

Ryukyu Arc ◽

Back Arc

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A Systematic Assessment of Stable Sr Isotopic Compositions of Vent Fluids in Arc/Back-Arc Hydrothermal Systems: Effects of Host Rock Type, Phase Separation, and Overlying Sediment

Frontiers in Earth Science ◽

10.3389/feart.2020.591711 ◽

2020 ◽

Vol 8 ◽

Author(s):

Toshihiro Yoshimura ◽

Shigeyuki Wakaki ◽

Tsuyoshi Ishikawa ◽

Toshitaka Gamo ◽

Daisuke Araoka ◽

...

Keyword(s):

Host Rock ◽

Okinawa Trough ◽

Volcanic Rocks ◽

Hydrothermal Systems ◽

Systematic Assessment ◽

Average Value ◽

Carbonate Sedimentation ◽

The North ◽

Back Arc ◽

Hydrothermal Fields

Variations in the stable isotopic composition of seawater Sr (δ88Sr) is a new tool for estimating the rates of global carbonate sedimentation over geologic time, yet the isotope compositions of the major sources and sinks of Sr to the world oceans are still in need of further constraint. We report δ88Sr values of vent fluids from arc/back-arc seafloor hydrothermal systems in the western Pacific. In the sediment-starved hydrothermal fields of the Manus Basin, Izu-Bonin Arc, and Mariana Trough, the δ88Sr values of end-member fluids for each site showed little variation (0.29–0.30‰) and were close to the average value of oceanic volcanic rocks, reflecting dissolved Sr sourced from host rocks. Chlorine-depleted fluids from phase-separated hydrothermal systems in the North Fiji Basin had the end-member δ88Sr values of 0.26, 0.28, and 0.29‰. Thus, both sediment-starved and phase-separated vent fluids had the end-member δ88Sr values indistinguishable from or very close to the range of oceanic volcanic rocks. Therefore, the δ88Sr compositions in these hydrothermal sites are controlled predominantly by Sr sourced from host rock with a small influence from secondary mineral precipitation/re-dissolution. Fluids from the sediment-hosted hydrothermal fields of the Okinawa Trough, however, were characterized by low δ88Sr values of approximately 0.22‰ and high 87Sr/86Sr ratios, indicating interactions with sedimentary carbonates. As for the modern oceanic δ88Sr budget, the sediment-hosted sites lower the global hydrothermal δ88Sr. Since both sediment-starved and -hosted hydrothermal systems provide a long-term control on the global Sr cycle, the end-member δ88Sr value is an important constraint on the evolution of Sr cycling in past oceans.

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