Serpentinization of olivine in troctolites and olivine gabbros from the Hess Deep Rift

Nozaka, Toshio; Wintsch, Robert P.; Meyer, R.

doi:10.1016/j.lithos.2016.12.032

Cited by 21 publications

(31 citation statements)

References 47 publications

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“…Thus, the activity components in the mineral phase equilibrium diagram (Figure b) were simulated for reactions in Stage 3 according to the six‐component system of FeO‐MgO‐CaO‐SiO 2 ‐H 2 O‐O 2 . Although prehnite was generated at Stage 3 in a previous report (Nozaka et al, ), prehnite is not found in AUMRs, which can be interpreted by Equation . Also, prehnite was possibly altered into chlorite with the loss of Ca 2+ (Komor, Elthon, & Casey, ; Mével, ).…”

Section: Discussionmentioning

confidence: 71%

“…In Equation of Stage 2, in order to investigate the mechanism of magnetite precipitation, Fe was assumed to isomorphically substitute for Mg in isomorphism (Nozaka et al, ). Additionally, Equation was assumed to be under ideal conditions, in which Fe 3 Si 2 O 5 (OH) 4 represent greenalite and Fe 3 O 4 represent magnetite.…”

Section: Discussionmentioning

confidence: 99%

“…In particular, the SiO 2 activity is one important factor (Figures and ). With respect to modern oceanic crustal ultramafic rocks, Nozaka et al () found that the relatively high SiO 2 activity in the reaction system restricted the generation of brucite. During the serpentinisation of AUMRs, the desilication of diopside could provide significant SiO 2 to the system (Viti, Mellini, & Rumori, ), as also seen in Equations and , which enhanced the SiO 2 activity and inhibited the generation of brucite.…”

Section: Discussionmentioning

confidence: 99%

“…The Mg# of serpentinite is positively related to the volume of magnetite precipitation (Nozaka et al, ). The range of Mg# of serpentine in the AUMRs is 77–95, suggesting the potential for small amount of magnetite precipitation (shaded area in Figure a).…”

Section: Discussionmentioning

confidence: 99%

“…Nevertheless, the geochemical conditions that affect serpentinisation and magnetite mineralisation remain equivocal. The serpentinisation of ultramafic rocks can be broadly divided into different stages based on petrography (Katayama et al, ), compositions in serpentine veins (Frost et al, ), and mineral phase equilibria (Nozaka et al, ). Thermodynamic modelling can also bring out the influence of silica activity and temperature on the precipitation of magnetite (Fujii et al, ; Lafay et al, ; Malvoisin, Carlut, & Brunet, ; Seyfried, Foustoukos, & Fu, ), as also verified by experimental studies (Klein et al, ; Klein, Bach, & McCollom, ).…”

Section: Introductionmentioning

confidence: 99%

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Serpentinisation and magnetite formation in the Angwu ultramafic rocks from the central Bangong–Nujiang suture zone, Tibetan Plateau

Liu

Tao

et al. 2019

Geological Journal

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Serpentinised ultramafic rocks are widely distributed in the Bangong–Nujiang suture zone (BNSZ) and show close relationship with the regional mineralisation. Here, we investigate the serpentinised ultramafic rocks from Angwu in the central segment of the BNSZ, where the primary minerals include olivine, clinopyroxene, chromite, lizardite, magnetite, and chlorite. Based on a comprehensive analysis of the results from petrography, back‐scattered electron images (BSE), and energy dispersive spectrographs (EDS), as well as electron probe microanalysis (EPMA), the alteration process of the ultramafic rocks, including serpentinisation, can be divided into three stages: 1, formation of relatively Fe‐rich serpentine (Mg#, 0.82), with no precipitation of magnetite; 2, formation of relatively Mg‐rich serpentine (Mg#, 0.93), with precipitation of magnetite in serpentine veins; and 3, alteration of serpentine into chlorite. We computed the reactions associated with alteration process for the above stages. In addition, thermodynamic modelling in multicomponent mineral equilibrium phase diagrams indicate that during the serpentinisation process, the desilication of pyroxene in caused the enhancement of SiO2 activity and restricted the transformation from olivine to magnetite. The reaction temperature for the serpentinisation of these rocks was relatively high, and within this temperature interval (100–300°C), lizardite was stable, and precipitation of magnetite was not favoured. We also evaluate the factors influencing magnetite precipitation during serpentinisation of ultramafic rocks including the composition of primitive rocks and the activity of SiO2 and temperature. Our study provides insights on the mechanism of magnetite mineralisation associated with the serpentinisation of ultramafic rocks.

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Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Serpentinisation and magnetite formation in the Angwu ultramafic rocks from the central Bangong–Nujiang suture zone, Tibetan Plateau

Liu

Tao

et al. 2019

Geological Journal

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New Rock Magnetic Analysis of Ultramafic Cores from the Oman Drilling Project and Its Implications for Alteration of Lower Crust and Upper Mantle

Hong

Till

Greve

et al. 2022

Preprint

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The Semail ophiolite, covering over 500 km of the eastern coast of Oman and the United Arab Emirates, is considered one of the most extensive and well-preserved ophiolite complexes on Earth. In general, the emplacement of the Semail ophiolite on land is thought to have occurred around 95 Ma (Kelemen et al., 2013;Rioux et al., 2012). The complex is well known for its overthrust structures, which preserve the remnants of Mid-Late Cretaceous oceanic lithosphere (Pearce et al., 1981;Wilson, 2000). The Semail ophiolite exposes diverse lithospheric units, including sheeted dike complexes, layered gabbro, and ultramafic mantle rocks. Some considered the ophiolite to be a modern-day analog of young oceanic crusts near a mid-ocean ridge (e.g., Nicolas et al., 2000). On the other hand, others argued that it reflects the collision of a volcanic arc into a continental margin in a supra-subduction setting (e.g., Tamura & Arai., 2006).

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Volcanic succession, petrology, and geochemistry of the Sujiagou komatiite from the North China Craton

et al. 2019

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The~2.7-GaTaishan greenstone belt from the Eastern Block of the North China Craton has well-exposed komatiite sections. The komatiite outcrops at Sujiagou have wellpreserved primary volcanic texture although they have experienced amphibolitefacies metamorphism. Two komatiite lava flows are identified in the Sujiagou outcrops: "Flow Ι," with a thickness of 55 m, is characterized by poly-sutured crust at the top, spinifex texture in the middle, and olivine cumulates at the flow bottom. "Flow ΙΙ" consists of abundant pahoehoe lava lobes with no interstitial materials. These volcanic characteristics, as well as the interbedding with terrestrial sediments, suggest that the Sujiagou komatiite erupted in a subaerial continental environment. The olivinechromite geothermometer gives peak metamorphic temperatures from 684°C to 764°C. Phase equilibria modelling suggests that the mineral proportions and mineral compositions are consistent with a retrograde temperature of~488°C, at which the komatiite would have low olivine Fo (79-89) and high bulk-rock Mg # (83-90). Linear mixing of the in situ trace element compositions of the metamorphic olivine, augite, tremolite, serpentine, and chlorite from Sujiagou komatiite samples can reproduce the trace elements of representative komatiite compositions, suggesting that later metamorphism and fluid-rock interactions played key roles in trace element variationsin the bulk-rock komatiite samples. These results also imply that the "arc signature" of the Sujiagou komatiite may be an overprint from posteruption fluid alteration rather than a primary subduction geochemical feature. Therefore, the Sujiagou komatiites may belong to a part of the global plume-related greenstone belts at~2.7 Ga.

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Serpentinization of olivine in troctolites and olivine gabbros from the Hess Deep Rift

Cited by 21 publications

References 47 publications

Serpentinisation and magnetite formation in the Angwu ultramafic rocks from the central Bangong–Nujiang suture zone, Tibetan Plateau

Serpentinisation and magnetite formation in the Angwu ultramafic rocks from the central Bangong–Nujiang suture zone, Tibetan Plateau

New Rock Magnetic Analysis of Ultramafic Cores from the Oman Drilling Project and Its Implications for Alteration of Lower Crust and Upper Mantle

Volcanic succession, petrology, and geochemistry of the Sujiagou komatiite from the North China Craton

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