The temporal variability of hydrothermal activity of Wocan hydrothermal field, Carlsberg Ridge, northwest Indian Ocean

doi:10.1016/j.oregeorev.2021.103999

Ore Geology Reviews

Volume 132, May 2021, 103999

https://doi.org/10.1016/j.oregeorev.2021.103999 Get rights and content

Highlights

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Wocan-1 sediments are mainly derived from hydrothermal inputs, while Wocan-2 sediments are dominated by biogenic inputs.
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The intensity of hydrothermal activity at the Wocan-1 site has been extremely strong over the past ~1069 years.
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The Wocan-2 site has been inactive since 4864 ± 114 yr BP but still contained weak hydrothermal signatures.

Abstract

The Wocan is a basalt-hosted hydrothermal field on the slow-spreading Carlsberg Ridge (CR), northwest Indian Ocean. It consists of two hydrothermal sites: Wocan-1 which is active, and Wocan-2 which is inactive. Three push-cores collected by the manned submersible Jiaolong from these two sites were investigated on their mineralogy, geochemistry, Pb-Sr isotopes, and chronology to understand the characteristics of hydrothermal sediments and their hydrothermal history. Core JL125-S17 (26-cm long) was collected from the Wocan-1 site with its lithology characterized by metalliferous sediments, mainly composed of sulfides, sulfates, Fe-oxides, and Fe-oxyhydroxides. Cores JL123-S03 (18-cm long) and JL124-S04 (20 cm long) were retrieved from the Wocan-2 site, mainly composed of calcareous oozes. Geochemically, Wocan-1 sediments exhibit strong metal and S enrichment. Ag, As, Cd, Co, Cu, Fe, Mg, Pb, Zn, and S are mainly incorporated into sulfides, while As, Ga, Mo, P, U, and V are mainly scavenged from seawater by Fe-Mn oxyhydroxides. In contrast, Wocan-2 sediments are rich in Ca and have much lower heavy metal content. The temporal variations of hydrothermal metal fluxes, which corrected for lithogenic input with Ti show that the intensity of hydrothermal activity at the Wocan-1 site has been extremely strong over the past ~1069 years, with hydrothermal Fe (Fe_H) fluxes varying from 9483 to 10834 mg·cm⁻²·kyr⁻¹. During this period, 699–1069 yr BP and 0–411 yr BP represent two stages of increased hydrothermal activity. The Wocan-2 site has been inactive since 4864 ± 114 years before present (yr BP) but the cores still contained weak hydrothermal signatures evidenced by a slightly elevated flux of Fe_H at the base of the cores, which could be explained by the mineralization of low-temperature diffuse flow and distal plume fall-out from Wocan-1.

Graphical abstract

Introduction

Submarine hydrothermal systems at mid-ocean ridges play a critical role in the heat budgets and chemical and isotopic compositions of the oceanic crust and seawater (Edmond et al., 1979, Elderfield and Schultz, 1996, Hannington, 2013). Hydrothermal sediments are products of seafloor hydrothermal activities and are distinguished from pelagic sediments by their distinct mineralogical and geochemical characteristics (Miller et al., 1966, Baturin et al., 1969). The accumulation rate of hydrothermal metal-bearing matter in hydrothermal sediments reflects the intensity of hydrothermal activity and the amount of mineral deposition (Metz et al., 1988). A continuous and well-dated sediment core from the hydrothermal field can be used to reconstruct the history of hydrothermal activity. In the past two decades, reconstructions of the history of hydrothermal activity based on the studies of sediment cores have been conducted on the Mid-Atlantic Ridge (e.g., Cave et al., 2002), Juan de Fuca Ridge (e.g., Costa et al., 2017), Central Indian Ridge (e.g., Kuhn et al., 2000), and the Southeast Indian Ridge (e.g., Kuhn et al., 2000). However, a similar study has not been conducted on the Carlsberg Ridge (CR), northwest Indian Ocean.

Seafloor hydrothermal activity in slow-spreading ridges is usually long-lived and episodic, and has the potential to host large seafloor massive sulfide deposits (Hannington et al., 2011). Deciphering the hydrothermal history is of great significance for assessing the extent of hydrothermal mineralization. The Wocan hydrothermal field on the slow-spreading CR was discovered by the R/V Zhukezhen in 2013 during the Chinese DY 28th cruise (Wang et al., 2017) and revisited in 2017 by the manned submersible Jiaolong during the Chinese DY 38th cruise (Qiu et al., 2017). It consists of two hydrothermal sites: Wocan-1 which is active, and Wocan-2 which is inactive. Recent studies of massive sulfides and metalliferous sediments collected from Wocan-1 and Wocan-2 using a TV-grab have detailed their mineralogical and geochemical properties (Wang et al., 2017, Popoola et al., 2019a, Popoola et al., 2019b). However, little is known about the characteristics of hydrothermal activities in the Wocan field and how they have evolved with time.

In this paper, we first present the mineralogy, geochemistry, Pb-Sr isotopic compositions, and ¹⁴C ages of near-vent sediment cores taken from the Wocan-1 and Wocan-2 hydrothermal sites. By comparing with other hydrothermal sites, we aim to reveal the hydrothermal signatures, the fluxes of major hydrothermal elements, and the hydrothermal histories recorded by the sediment cores.

Section snippets

Geological setting

The CR, which separates the Indian and Somalia tectonic plates in the northwest Indian Ocean, is a slow-spreading ridge with half spreading rates of 11–16 mm/yr (Kamesh Raju et al., 2008). The basalt-hosted Wocan hydrothermal field is located on the CR on a NW-SE oriented axial volcanic ridge (Fig. 1). It consists of two hydrothermal sites: Wocan-1 covering an area of ~ 450 × 400 m near the center of the axial volcanic ridge at a water depth of ~ 3000 m, and Wocan-2 situated 2.7 km northwest of

Methods

Three sediment cores were retrieved from the Wocan hydrothermal field with the manned submersible Jiaolong using a 30 cm “push-corer.” Cores JL123-S03 and JL124-S04 were collected 219 m and 412 m east of the inactive Wocan-2, respectively. Core JL125-S17 was collected 208 m west of the active Wocan-1 (Fig. 1). Cores JL123-S03 and JL124-S04 were extruded using a precision screw device and sliced at 1-cm intervals onboard. Core JL125-S17 was split lengthwise, photographed, and sliced into 1-cm

Lithology

Core JL125-S17 (26 cm long) was collected in the active Wocan-1 vent field. The core can be divided into five layers based on color and texture, combined with the mineralogical and chemical composition (Fig. 2). Layers 1 (0–3 cm) and 3 (8–14 cm) were composed mainly of greenish-brown metalliferous sediments with red to yellow patches. Layers 2 (3–8 cm) and 4 (14–25 cm) were mainly yellowish-brown to reddish-brown with patches and lenses of greenish-brown color. Layer 5 (25–26 cm) was brown to

Identification and estimation of different sedimentary components

In order to differentiate the different components of the sediments, PCA was conducted on the major and trace elements of the Wocan sediments. The analysis produced three principal component factors with an eigenvalue > 1.00 (PC1–PC3), cumulatively explaining 93.9% of the variance in the major and trace elements (Fig. 9).

PC1 accounted for 71.2% of the variance in the data set and showed high positive Ag, As, Cd, Co, Cu, Fe, Mg, Pb, Zn, and S loadings and high negative Al, Ca, Cr, K, Mn, Na, Ni,

Conclusions

Wocan-1 sediments are mainly derived from hydrothermal inputs, with negligible biogenic and detrital components. Their mineral composition is mainly pyrite, chalcopyrite, isocubanite, pyrrhotite, sphalerite, barite, covellite, Fe-oxides, and Fe-oxyhydroxides, with minor talc. Geochemically, Wocan-1 sediments exhibit strong metal and S enrichment. Ag, As, Cd, Co, Cu, Fe, Mg, Pb, Zn, and S are mainly incorporated into sulfides, while As, Ga, Mo, P, U, and V are mainly scavenged from seawater by

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors appreciate the captain and crew of the R/V Xiangyanghong 9 for their support in the investigation and sampling during the Chinese DY 38^th Cruise. This study was funded by the National Key Research and Development Program of China (2018YFC0309903), the National Natural Science Foundation of China (No. 41976075), the China Ocean Mineral Resources R&D Association project (DY135-S2-1-03), and the Fundamental Research Funds for National Non-profit Institute Grant (No. JG1802). We

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Citation Excerpt :
In particular, Cu and Co have respective contents up to 1900 and 100 times those of the average shales, indicating strong inputs of hydrothermal components (Fig. 2). The Cu, Mg, Co and Ni contents (Cu: 4.4–8.7%, Mg: 3.0–7.7%, Co: 241–1860 ppm, Ni: 133–743 ppm) and Cu/Fe ratios (0.25–0.35) are significantly higher than those in the metalliferous sediments of the basalt-hosted hydrothermal field at the CR (e.g., Wocan-1 (208 m from the vent): Cu: < 5.0%, Mg: < 2.4%, Co: < 162 ppm, Ni: < 10 ppm, Cu/Fe: < 0.13; Qiu et al., 2021), which can be explained by the leaching of ultramafic rocks and Cl complexation under low-pH and high-temperature conditions (Fouquet et al., 2010). The 33I-TVG07 sediment has low Al and Ca contents (0.7 wt% and 1.1 wt%, respectively), indicating trace amounts of detrital and biogenic inputs.
Tianxiu is the only ultramafic-hosted hydrothermal field that has been discovered on the slow-spreading Carlsberg Ridge (CR), northwest Indian Ocean. Sequential extraction has been performed on the surface sediments from the near-vent and far-field of Tianxiu to characterize the compositions of metalliferous sediments, the speciation of selected metals and the potential risks of metal mobility. The near-vent sediments of Tianxiu are mainly derived from hydrothermal inputs and are enriched in Fe, Zn, P, Pb, Mo and especially Cu, Mg, Co and Ni with significantly higher contents compared to metalliferous sediments formed in basalt-hosted hydrothermal systems. Most of the ore-forming elements (Fe, Cu, Zn, Mn, Co and Ni) and rare-earth elements (REEs) exist in the residual fraction and FeMn oxide fraction, followed by the carbonate fraction and organic fraction. The chondrite-normalized REE pattern in each phase is characterized by relative enrichment in light (L)REEs and positive Eu anomalies, consistent with the REE patterns of hydrothermal fluids. The far-field sediments of Tianxiu are mainly derived from background pelagic sedimentation while the sediments at some sites are influenced by a small amount of hydrothermal plume fallout. The investigated elements mainly exist in the FeMn oxide fraction, residual fraction and carbonate fraction. In particular, ore-forming elements Cu, Pb, Mn, Co and Ni are mostly enriched in the FeMn oxide fraction, which is attributed to their adsorption by hydrothermal particulates in the plumes. The potential mobility of each metal is evaluated in terms of its total content in the unstable phases, which reveals that most of the heavy metals (e.g., Cu, Zn, Mn and Pb) in the metalliferous sediments have high potential mobility (> 50%).

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The temporal variability of hydrothermal activity of Wocan hydrothermal field, Carlsberg Ridge, northwest Indian Ocean

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Geological setting

Methods

Lithology

Identification and estimation of different sedimentary components

Conclusions

Declaration of Competing Interest

Acknowledgments

Geochim. Cosmochim. Acta

Earth Planet Sci. Lett.

Earth Planet. Sci. Lett.

Mar. Geol.

Chem. Geol.

Geochim. Cosmochim. Acta

Chem. Geol.

Chem. Geol.

Deep Sea Res. Part I

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Mar. Geol.

Geochim. Cosmochim. Acta

Mar. Geol.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Mar. Chem.

Geochim. Cosmochim. Acta

J. Mar. Syst.

Ore Geol. Rev.

Quality evaluation of River Chanchaga using metal pollution index and principal component analysis

J. Geogr. Geol.

Composition and origin of iron-ore sediments and hot brines in the Red Sea

Okeanologiya (Oceanology)