Origin of waters responsible for serpentinization of the Izu-Ogasawara-Mariana forearc seamounts in view of hydrogen and oxygen isotope ratios

Sakai, Ryutaro; Kusakabe, Minoru; Noto, Masami; Ishii, Teruaki

doi:10.1016/0012-821x(90)90192-z

Cited by 66 publications

(45 citation statements)

References 34 publications

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“…7 through 9; Table 11). The values lie within the range of published D/H ratios of oceanic serpentine (Wenner and Taylor, 1973;Sheppard, 1980;Sakai et al, 1990) and are similar to the values reported by Agrinier et al (in press) from Hess Deep ultramafic rocks. The D/H ratios of vein-serpentine separates scatter over a range of 22%o, with δD values from -46%o to -68%o.…”

Section: Stable Isotope Ratios Of Serpentinesupporting

confidence: 91%

“…7 through 9; Table 11). They are very similar to previously measured values in Hess Deep ultramafic rocks (Agrinier et al, in press), and are consistent with a large number of oceanic serpentinites examined to date (Wenner and Taylor, 1973;Sheppard, 1980;Sakai et al, 1990 (Table 11).…”

Section: Stable Isotope Ratios Of Serpentinesupporting

confidence: 90%

“…In spite of uncertainties in the serpentine-water fractionation curves (in particular for hydrogen; see discussions in Wenner and Taylor, 1971, 1973Sakai and Tsutsumi, 1978;Kyser, 1987;Sakai et al, 1990), the oxygen and hydrogen isotope signatures of the Hess Deep peridotites, as well as thermal decomposition experiments carried out on two pervasively serpentinized peridotites, provide important information on the origin of the serpentinizing fluids and the extent of seawater penetration and fluid-rock interaction in the shallow mantle. The combination of stable isotope geochemistry and petrologic data may further constrain the role of serpentinization in the exhumation of the lower crustal-shallow mantle sequence and allow the two models proposed by Francheteau et al (1990) for the tectonic evolution of the Hess Deep to be evaluated.…”

Section: Ultramafic Rocksmentioning

confidence: 99%

“…A minimum F/R ratio of 0.3 atom percent is dictated by the stoichiometric amount of H 2 O in the serpentine structure. The effects of temperature and fluid/rock ratios on hydrogen and oxygen ratios can be evaluated by considering the open system model for serpentinization proposed by Sakai et al (1990), as shown in Figure 7. This model predicts that serpentinization at relatively low fluid/rock ratio results in more deuterium-rich compositions, and would thus increase the discrepancy between predicted and measured values of the Hess Deep samples (Fig.…”

Section: A Depletion Inmentioning

confidence: 99%

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Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Früh-Green¹,

Plas²,

Lécuyer³

1996

Proceedings of the Ocean Drilling Program

106

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Leg 147 of the Ocean Drilling Program recovered sections of the East Pacific Rise lower crust and shallow mantle ( l Ma), tectonically exposed at the western end of the Cocos-Nazca propagator of the Hess Deep Rift Valley. These rocks record a polyphase history of hydrothermal alteration and provide new constraints on the depth and mechanisms of hydrothermal circulation at fast-spreading ridges. A complex sequence of harzburgite-dunite-troctolite-gabbro recovered at Site 895 is considered to be the result of processes of melt migration and wall-rock reaction close to the mantle/crust boundary. The peridotites are extensively serpentinized (50%-100%) and are cut by multiple generations of fracture-filling veins. In the gabbros, progressive alteration under greenschist to zeolite facies conditions is characterized by tremolite + chlorite + diopside + anorthjte ± prehnite assemblages in the least altered samples, and incipient rodingitization to prehnite + hydrogrossular + zeolite + clays as Cataclastic deformation and veining increases.Oxygen isotope ratios of mineral separates from the gabbros and peridotites from Site 895 show a depletion in I8O relative to mantle values and are consistent with high-temperature exchange with aqueous fluids. Dunite/harzburgite ratios of chlorite, serpentine, and tremolite, together with δ' 3 C values of CO 2 extracted from completely serpentinized dunites, suggest at least two, but possibly three, components of the hydrothermal fluids: hydrothermally altered seawater; magmatic volatiles; and H 2 released during serpentinization. These data combined with structural data imply that penetration of seawater and high-temperature hydrothermal alteration produced a low 18 O shallow mantle sequence at some distance off-axis of the East Pacific Rise, but at an early stage in the propagation of the Cocos-Nazca rift and formation of the Hess Deep Rift Valley. Mineral assemblages in the gabbroic rocks and the presence of antigorite at Hess Deep, combined with oxygen isotope ratios, suggest that faulting associated with the Cocos-Nazca propagator enhanced seawater penetration and hydrothermal alteration at temperatures above 350°C in this segment of the East Pacific Rise oceanic lithosphere. The results of this study suggest that seawaterperidotite interactions and high-temperature serpentinization processes may be an important contribution to the overall 18 Obudget in the oceanic lithosphere nd may represent a significant sink for mantle CO 2 and source of H 2 .

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Section: Stable Isotope Ratios Of Serpentinesupporting

confidence: 91%

Section: Stable Isotope Ratios Of Serpentinesupporting

confidence: 90%

Section: Ultramafic Rocksmentioning

confidence: 99%

Section: A Depletion Inmentioning

confidence: 99%

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Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Früh-Green¹,

Plas²,

Lécuyer³

1996

Proceedings of the Ocean Drilling Program

106

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“…Because the aqueous fluids that serpentinized the peridotites may have a slab-derived component (Leg 125 Shipboard Scientific Party, 1989;Sakai et al, 1990) it is feasible that the latter two enrichment processes are strongly interrelated.…”

Section: Causes Of Lree Zr and Sr Enrichmentmentioning

confidence: 99%

Trace Element Geochemistry of Peridotites from the Izu-Bonin-Mariana Forearc, Leg 125

Parkinson¹,

Pearce²,

Thirlwall³

et al. 1992

Proceedings of the Ocean Drilling Program

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Trace element analyses (first-series transition elements, Ti, Rb, Sr, Zr, Y, Nb, and REE) were carried out on whole rocks and minerals from 10 peridotite samples from both Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu-Bonin forearc using a combination of XRF, ID-MS, ICP-MS, and ion microprobe. The concentrations of incompatible trace elements are generally low, reflecting the highly residual nature of the peridotites and their low clinopyroxene content (<2%). Chondrite-normalized REE patterns show extreme U shapes with (La/Sm) n ratios in the range of 5.03-250.0 and (Sm/Yb) n ratios in the range of 0.05-0.25; several samples show possible small positive Eu anomalies. LREE enrichment is common to both seamounts, although the peridotites from Conical Seamount have higher (La/Ce) n ratios on extended chondrite-normalized plots, in which both REEs and other trace elements are organized according to their incompatibility with respect to a harzburgitic mantle. Comparison with abyssal peridotite patterns suggests that the LREEs, Rb, Nb, Sr, Sm, and Eu are all enriched in the Leg 125 peridotites, but Ti and the HREEs exhibit no obvious enrichment. The peridotites also give positive anomalies for Zr and Sr relative to their neighboring REEs. Covariation diagrams based on clinopyroxene data show that Ti and the HREEs plot on an extension of an abyssal peridotite trend to more residual compositions. However, the LREEs, Rb, Sr, Sm, and Eu are displaced off this trend toward higher values, suggesting that these elements were introduced during an enrichment event. The axis of dispersion on these plots further suggests that enrichment took place during or after melting and thus was not a characteristic of the lithosphere before subduction.Compared with boninites sampled from the Izu-Bonin-Mariana forearc, the peridotites are significantly more enriched in LREEs. Modeling of the melting process indicates that if they represent the most depleted residues of the melting events that generated forearc boninites they must have experienced subsolidus enrichment in these elements, as well as in Rb, Sr, Zr, Nb, Sm, and Eu. The lack of any correlation with the degree of serpentinization suggests that low-temperature fluids were not the prime cause of enrichment. The enrichment in the high-field-strength elements also suggests that at least some of this enrichment may have involved melts rather than aqueous fluids. Moreover, the presence of the hydrous minerals magnesio-hornblende and tremolite and the common resorption of orthopyroxene indicate that this high-temperature peridotite-fluid interaction may have taken place in a water-rich environment in the forearc following the melting event that produced the boninites. The peridotites from Leg 125 may therefore contain a record of an important flux of elements into the mantle wedge during the initial formation of forearc lithosphere. Ophiolitic peridotites with these characteristics have not yet been reported, perhaps because the precise equiva...

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Tectonic structure, lithology, and hydrothermal signature of the Rainbow massif (Mid-Atlantic Ridge 36°14′N)

Andréani

Escartı́n

Delacour

et al. 2014

Geochem. Geophys. Geosyst.

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Rainbow is a dome-shaped massif at the 36 14 0 N nontransform offset along the Mid-AtlanticRidge. It hosts three ultramafic-hosted hydrothermal sites: Rainbow is active and high temperature; Clamstone and Ghost City are fossil and low temperature. The MoMARDREAM cruises (2007, 2008) presented here provided extensive rock sampling throughout the massif that constrains the geological setting of hydrothermal activity. The lithology is heterogeneous with abundant serpentinites surrounding gabbros, troctolites, chromitites, plagiogranites, and basalts. We propose that a W dipping detachment fault, now inactive, uplifted the massif and exhumed these deep-seated rocks. Present-day deformation is accommodated by SSW-NNE faults and fissures, consistent with oblique teleseismic focal mechanisms and stress rotation across the discontinuity. Faults localize fluid flow and control the location of fossil and active hydrothermal fields that appear to be ephemeral and lacking in spatiotemporal progression. Markers of high-temperature hydrothermal activity (350 C) are restricted to some samples from the active field while a more diffuse, lower temperature hydrothermal activity (<220 C) is inferred at various locations through anomalously high As, Sb, and Pb contents, attributed to element incorporation in serpentines or microscalesulfide precipitation. Petrographic and geochemical analyses show that the dominant basement alteration is pervasive peridotite serpentinization at 160-260 C, attributed to fluids chemically similar to those venting at Rainbow, and controlled by concomitant alteration of mafic-ultramafic units at depth. Rainbow provides a model for fluid circulation, possibly applicable to hydrothermalism at oceanic detachments elsewhere, where both low-temperature serpentinization and magmatic-driven high-temperature outflow develop contemporaneously, channeled by faults in the footwall and not along the detachment fault.

show abstract

Origin of waters responsible for serpentinization of the Izu-Ogasawara-Mariana forearc seamounts in view of hydrogen and oxygen isotope ratios

Cited by 66 publications

References 34 publications

Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Trace Element Geochemistry of Peridotites from the Izu-Bonin-Mariana Forearc, Leg 125

Tectonic structure, lithology, and hydrothermal signature of the Rainbow massif (Mid-Atlantic Ridge 36°14′N)

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