Site BT1: fluid and mass exchange on a subduction zone plate boundary

Kelemen, P. B.; Matter, J. M.; Teagle, D.A.H.; Coggon, J. A.

doi:10.14379/omandp.proc.113.2020

Cited by 6 publications

(46 citation statements)

References 6 publications

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“…The bulk chemistry and proportions of magnesite and quartz can vary significantly on a small scale (Okazaki et al, 2021), but at the meter scale they are consistent with overall isochemical replacement of peridotite and minor addition of fluid-mobile elements (Godard et al, 2021;Kelemen et al, 2020b). Massive listvenite domains show two main types of pervasive microstructures: (i) zoned, ellipsoidal to spheroidal magnesite particles with euhedral to dendritic habit in a finer-grained quartz matrix (Beinlich et al, 2020b;Menzel et al, 2022) and (ii) variably large quartz (± fuchsite) aggregates with microstructures resembling those of orthopyroxene or bastite surrounded by a matrix of vermicular, mesh-like magnesitequartz intergrowths (Kelemen et al, 2020b;Menzel et al, 2022). Trace element geochemistry suggests that the protolith of the BT1B listvenites was part of the banded peridotite unit commonly found at the base of the Samail ophiolite, with compositions of fuchsite-bearing listvenite overlapping with amphibole-bearing basal lherzolite and fuchsitefree listvenite similar to the composition of refractory peridotite (Godard et al, 2021).…”

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 95%

“…Hole BT1B consists in its upper part of listvenite intercalated with two serpentinite layers separated by a fault at 200 m down-hole depth from underlying greenschist-facies metamafic rocks of the metamorphic sole (Fig. 1e) (Kelemen et al, 2020b). At site BT1, magnesite predominates, while dolomite and calcite are common in listvenites further north in the Fanjah area.…”

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

“…Based on data from underlying carbonate sediments (Grobe et al, 2019) and a plausible ophiolite thickness of 8-10 km, pressure was at least ∼ 0.3 GPa, while the P -T conditions recorded by the metamorphic sole set an upper bound of 0.7-1.0 GPa (Kotowski et al, 2021;Soret et al, 2017). Except for some dolomite-enriched intervals, especially close to the basal fault, most BT1B listvenites are composed of magnesite, quartz, minor Cr spinel, and locally Fe (hydr)oxides or Cr-bearing muscovite (fuchsite) (Kelemen et al, 2020b). The bulk chemistry and proportions of magnesite and quartz can vary significantly on a small scale (Okazaki et al, 2021), but at the meter scale they are consistent with overall isochemical replacement of peridotite and minor addition of fluid-mobile elements (Godard et al, 2021;Kelemen et al, 2020b).…”

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

“…Except for some dolomite-enriched intervals, especially close to the basal fault, most BT1B listvenites are composed of magnesite, quartz, minor Cr spinel, and locally Fe (hydr)oxides or Cr-bearing muscovite (fuchsite) (Kelemen et al, 2020b). The bulk chemistry and proportions of magnesite and quartz can vary significantly on a small scale (Okazaki et al, 2021), but at the meter scale they are consistent with overall isochemical replacement of peridotite and minor addition of fluid-mobile elements (Godard et al, 2021;Kelemen et al, 2020b). Massive listvenite domains show two main types of pervasive microstructures: (i) zoned, ellipsoidal to spheroidal magnesite particles with euhedral to dendritic habit in a finer-grained quartz matrix (Beinlich et al, 2020b;Menzel et al, 2022) and (ii) variably large quartz (± fuchsite) aggregates with microstructures resembling those of orthopyroxene or bastite surrounded by a matrix of vermicular, mesh-like magnesitequartz intergrowths (Kelemen et al, 2020b;Menzel et al, 2022).…”

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

“…Visual core logging by the OmanDP science team showed that veins are abundant in serpentinite and listvenite, with densities of > 200 veins per meter of core for veins < 1 mm wide and 50-200 veins per meter for veins > 1 mm (Kelemen et al, 2020b). In serpentinites, the vein logging team distinguished between four main vein types, with a narrow (< 0.1 mm) serpentine vein network that defines a mesh texture being the earliest generation.…”

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

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Progressive veining during peridotite carbonation: insights from listvenites in Hole BT1B, Samail ophiolite (Oman)

et al. 2022

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Abstract. The reaction of serpentinized peridotite with CO2-bearing fluids to form listvenite (quartz–carbonate rock) requires massive fluid flux and significant permeability despite an increase in solid volume. Listvenite and serpentinite samples from Hole BT1B of the Oman Drilling Project help to understand mechanisms and feedbacks during vein formation in this process. Samples analyzed in this study contain abundant magnesite veins in closely spaced, parallel sets and younger quartz-rich veins. Cross-cutting relationships suggest that antitaxial, zoned magnesite veins with elongated grains growing from a median zone towards the wall rock are among the earliest structures to form during carbonation of serpentinite. Their bisymmetric chemical zoning of variable Ca and Fe contents, a systematic distribution of SiO2 and Fe-oxide inclusions in these zones, and cross-cutting relations with Fe oxides and Cr spinel indicate that they record progress of reaction fronts during replacement of serpentine by carbonate in addition to dilatant vein growth. Euhedral terminations and growth textures of magnesite vein fill, together with local dolomite precipitation and voids along the vein–wall rock interface, suggest that these veins acted as preferred fluid pathways allowing infiltration of CO2-rich fluids necessary for carbonation to progress. Fracturing and fluid flow were probably further enabled by external tectonic stress, as indicated by closely spaced sets of subparallel carbonate veins. Despite widespread subsequent quartz mineralization in the rock matrix and veins, which most likely caused a reduction in the permeability network, carbonation proceeded to completion within listvenite horizons.

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Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 95%

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

Section: Serpentinites and Listvenites Of Hole Bt1bmentioning

confidence: 99%

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Progressive veining during peridotite carbonation: insights from listvenites in Hole BT1B, Samail ophiolite (Oman)

et al. 2022

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Major mineral fraction and physical properties of carbonated peridotite (listvenite) from ICDP Oman Drilling Project Hole BT1B inferred from X-ray CT core images

Okazaki

Michibayashi

Hatakeyama

et al. 2021

Preprint

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We evaluated the mineral fractions of listvenite (completely carbonated peridotite) in Hole BT1B drilled by the ICDP Oman Drilling Project from 3D X-ray Computed Tomography (XCT) images. Total >250,000 XCT images from continuous ˜200 m listvenite core samples were analyzed. Histograms of the intensity of X-ray attenuation (XCT number) of each XCT core-slice image were fitted assuming that the CT histogram is composed of magnesite, quartz, and dolomite peaks. These mineral peaks were confirmed by comparison of XCT numbers with chemical mapping data obtained using an XRF core scanner. In most core sections, XCT data indicate that listvenite matrix is composed of magnesite and quartz, consistent with discrete XRD and XRF data. Veins are composed mostly of dolomite. The mean abundance of dolomite in listvenite from BT1B is 11 vol.%, whereas that in core sections within 15 m of the basal thrust is >50 vol.%, suggesting that the basal thrust acted as a pathway for Ca-and CO fraction than that of Oman peridotite (39:60:1), indicating enrichment of Si during carbonation. P-and S-wave velocities and density of listvenite is close to that of peridotite while higher than that of serpentinites. These results suggest that limited material transfer during carbonation and hydration of the Oman Ophiolite, except for Si, Ca, CO 2 and H 2 O, but potential as an overlooked carrier of CO 2 into the deep of Earth's interior.

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Brittle Deformation of Carbonated Peridotite—Insights From Listvenites of the Samail Ophiolite (Oman Drilling Project Hole BT1B)

et al. 2020

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Hole BT1B of the Oman Drilling Project provides a continuous sampling from listvenite into the metamorphic sole that preserves the deformation, hydration, and carbonation processes of oceanic mantle peridotite at the base of the Samail ophiolite, Oman. We present evidence of multistage brittle deformation in listvenites and serpentinites based on field observations, visual core logging and petrography. About 10 vol% of listvenite and serpentinite in Hole BT1B is composed of cataclasite bands. Cataclasites contain lithic clasts of listvenite with spheroidal, zoned magnesite and quartz, and fragments of chalcedony-carbonate veins that elsewhere crosscut listvenite-showing that cataclasis postdates listvenite formation. Locally the cataclasites are reworked and cut by thin, sharp faults, pointing to repeated reactivation of brittle structures. SEM-EDS mapping shows that cataclasis was related to dissolution of carbonate and/or silica cementation. Dolomite veins crosscut cataclasites and breccias, suggesting that part of the Ca gain in BT1B is related to late fluids after listvenite formation. These results indicate a multistage tectonic overprint after peridotite carbonation and listvenite formation, which may be related to the tectonic history of the deformed continental margin under the ophiolite. These relatively late brittle structures should be excluded when trying to understand the carbonation of peridotite to listvenite.

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Site BT1: fluid and mass exchange on a subduction zone plate boundary

Cited by 6 publications

References 6 publications

Progressive veining during peridotite carbonation: insights from listvenites in Hole BT1B, Samail ophiolite (Oman)

Progressive veining during peridotite carbonation: insights from listvenites in Hole BT1B, Samail ophiolite (Oman)

Major mineral fraction and physical properties of carbonated peridotite (listvenite) from ICDP Oman Drilling Project Hole BT1B inferred from X-ray CT core images

Brittle Deformation of Carbonated Peridotite—Insights From Listvenites of the Samail Ophiolite (Oman Drilling Project Hole BT1B)

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