Boron isotope systematics of a fossil hydrothermal system from the Troodos ophiolite, Cyprus: Water–rock interactions in the oceanic crust and subseafloor ore deposits

Yamaoka, Kyoko; Matsukura, S.; Ishikawa, Tsuyoshi; Kawahata, Hodaka

doi:10.1016/j.chemgeo.2014.12.023

Cited by 17 publications

(9 citation statements)

References 64 publications

(108 reference statements)

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“…8.4) High-temperature altered Layer-3 samples from the Troodos and Oman ophiolites range from slightly depleted to strongly enriched in boron (0.25-11.6 lg/g; Table 8.1) with respect to fresh MORB, and they show significantly elevated d 11 B values of À1:7 to +18.6‰, but mostly between þ 8 and +18‰ ( Fig. 8.4; Smith et al 1995;Yamaoka et al 2012Yamaoka et al , 2015b.…”

Section: Alteration Of the Igneous Crustmentioning

confidence: 99%

Boron Isotopes in the Ocean Floor Realm and the Mantle

Marschall

2017

Boron Isotopes

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This chapter reviews the boron isotopic composition of the ocean floor, including pristine igneous oceanic crust such as mid-ocean ridge basalts and ocean island basalts and their implications for the B isotopic composition of the mantle. The chapter further discusses the B isotopic effects of assimilation of altered crustal materials in mantle-derived magmas. The systematics of seawater alteration on oceanic rocks are discussed, including sediments, igneous crust and serpentinization of ultramafic rocks and the respective marine hydrothermal vent fluids. The chapter concludes with a discussion of the secular evolution of the B isotopic composition of seawater.

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Section: Alteration Of the Igneous Crustmentioning

confidence: 99%

Boron Isotopes in the Ocean Floor Realm and the Mantle

Marschall

2017

Boron Isotopes

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“…It is hard to quantify the uncertainty in our estimate beyond the standard deviation of the sample mean, but we suggest [B] and δ 11 B are likely to be within the range of data in Table 1 . We emphasise that the values from the Oman and Troodos ophiolites 39 , 40 are much more likely to be representative of lower gabbroic crust at fast spreading ridges away from major fault zones.…”

Section: Resultsmentioning

confidence: 93%

“…The only previous data for [B] and δ 11 B in oceanic gabbros comes from the Oman and Troodos ophiolites 39 , 40 , and from ODP Hole 735B 41 on the Southwest Indian Ridge. Oman data (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…We have shown that downward movement of seawater alone (one-pass circulation) is very unlikely to add significant boron to either the upper mantle or the olivine-rich lower oceanic crust. Data from the Oman and Troodos ophiolites 39 , 40 suggest that heavy B is introduced into unfaulted lower oceanic crust, but only at relatively low concentrations. Multipass circulation driven by thermal convection is required to introduce higher [B].…”

Section: Discussionmentioning

confidence: 99%

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No significant boron in the hydrated mantle of most subducting slabs

et al. 2018

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Boron has become the principle proxy for the release of seawater-derived fluids into arc volcanics, linked to cross-arc variations in boron content and isotopic ratio. Because all ocean floor serpentinites so far analysed are strongly enriched in boron, it is generally assumed that if the uppermost slab mantle is hydrated, it will also be enriched in boron. Here we present the first measurements of boron and boron isotopes in fast-spread oceanic gabbros in the Pacific, showing strong take-up of seawater-derived boron during alteration. We show that in one-pass hydration of the upper mantle, as proposed for bend fault serpentinisation, boron will not reach the hydrated slab mantle. Only prolonged hydrothermal circulation, for example in a long-lived transform fault, can add significant boron to the slab mantle. We conclude that hydrated mantle in subducting slabs will only rarely contribute to boron enrichment in arc volcanics, or to deep mantle recycling.

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“…and at this point original mafic assemblages are replaced by epidote-quartz +/-titanite. Fluid inclusion (Bendnarz and Schmincke, 1990) and isotopic studies (Bickle and Teagle, 1992;Yamaoka et al, 2015) support the pervasive and high temperature nature of hydrothermal alteration in the SDC.…”

Section: 1: Regional Geologymentioning

confidence: 87%

Extreme enrichment of selenium in the Apliki Cyprus-type VMS deposit, Troodos, Cyprus

et al. 2018

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The Troodos ophiolite Cyprus hosts the type locality for Cyprus-type, mafic volcanogenic massive sulfide (VMS) deposits. Regional soil geochemical data for Troodos are highly variable with the Solea graben, one of three regional graben structures on Cyprus, showing enrichment in Te and Se. Of the three VMS sampled within the Solea graben, Apliki exhibits the most significant enrichment in Se. Samples from the South Apliki Breccia Zone; a zone of hematite-rich breccia containing euhedral pyrite and chalcopyrite, contain up to 4953 and 3956 ppm Se in pyrite and chalcopyrite, respectively. Four paragenetic stages are identified at Apliki and different generations of pyrite are distinguishable using trace-element chemistry analysed via laser ablation inductively coupled plasma mass spectrometry. Results indicate stage I pyrite formed under reduced conditions at high temperatures >280°C and contains 182 ppm (n = 22 σ = 253) Se. Late stage III pyrite which is euhedral and overprints chalcopyrite and hematite is enriched in Se (averaging 1862 ppm; n = 23 σ = 1394). Sulfide dissolution and hematite formation displaced large amounts of Se as hematite cannot accommodate high concentrations of Se in its crystal structure. The mechanisms proposed to explain the pronounced change in redox are twofold. Fault movement leading to localized seawater ingress coupled with a decreasing magmatic flux that generated locally oxidizing conditions and promoted sulfide dissolution. A Se/S ratio of 9280 indicates a probable magmatic component for late stage III pyrite, which is suggested as a mechanism explaining the transition from oxidizing back to reduced conditions. This study highlights the significance of changes in redox which promote sulfide dissolution, mobilization and enrichment of Se.

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Boron isotope systematics of a fossil hydrothermal system from the Troodos ophiolite, Cyprus: Water–rock interactions in the oceanic crust and subseafloor ore deposits

Cited by 17 publications

References 64 publications

Boron Isotopes in the Ocean Floor Realm and the Mantle

Boron Isotopes in the Ocean Floor Realm and the Mantle

No significant boron in the hydrated mantle of most subducting slabs

Extreme enrichment of selenium in the Apliki Cyprus-type VMS deposit, Troodos, Cyprus

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