Origin of the dunitic mantle-crust transition zone in the Oman ophiolite: The interplay between percolating magmas and high-temperature hydrous fluids

Rospabé, Mathieu; Ceuleneer, Georges; Benoît, Mathieu; Abily, Bénédicte; Pinet, P.

doi:10.1130/g38778.1

Cited by 45 publications

(106 citation statements)

References 35 publications

(36 reference statements)

Supporting

Mentioning

103

Contrasting

Order By: Relevance

“…The chromite grains scattered in the DTZ share the same abundant mineral inclusions than the chromite grains from chromitites (e.g. Borisova et al, 2012;Rospabé et al, 2017). Consequently, both dunite and chromitite appear to be, in this context, two associated products formed at the expense of harzburgite following melt-or magma-peridotite reactions (Arai and Yurimoto, 1994;Borisova et al, 2012;Zhou et al, 1994).…”

Section: Introductionmentioning

confidence: 95%

Multi-scale development of a stratiform chromite ore body at the base of the dunitic mantle-crust transition zone (Maqsad diapir, Oman ophiolite): The role of repeated melt and fluid influxes

Rospabé

Ceuleneer

Granier

et al. 2019

Lithos

Self Cite

View full text Add to dashboard Cite

A stratiform chromite ore body crops out in the lower part of the dunitic mantle-crust transition zone (DTZ) that developed at the top of a mantle diapir in the Maqsad area in the Oman ophiolite. It is made of layers ranging in thickness from a few mm to a maximum of 3 m, and in modal composition from massive to antinodular and disseminated ore. The ore body is about 50 m thick and its lateral extent does not exceed several hundred meters. The layering dips gently to the southeast, parallel to that of the overlying gabbroic cumulates. The chromite composition is typical of a MORB kindred-moderate XCr (100 × Cr/(Cr + Al) atomic ratio), ranging from 48 to 60, and relatively high TiO 2 content, ranging from about 0.3 to 0.5 wt%-, a characteristic shared by most lithologies issued from the igneous activity of the Maqsad diapir. The silicate matrix is essentially made of slightly serpentinized olivine with minor clinopyroxene and rare pargasitic amphibole, orthopyroxene and garnet. This strongly contrasts with the nature of the mineral inclusions mostly made of the assemblage amphibole-orthopyroxene-mica, enclosed in the chromite grains and represented in abundance all along the ore body whatever the ore grade. The inclusions demonstrate the involvement of a silica-and water-rich melt and/or fluid, in addition to MORB, in the early stages of chromite crystallization. The chemical composition of chromite, silicate matrix, together with the one of silicate inclusions display well-defined evolutions vertically along the stratiform chromitite. At the scale of the ore body, the compositional trends are independent of the ore concentration but the major kinks in these trends are well-correlated with levels of magmatic breccias. This shows that abrupt chemical changes can be attributed to sudden melt +/-fluids injection events followed mainly by melt-fluid-rock interaction and in a lesser extent by quieter evolution by fractional crystallization. At the thin section scale, second order chemical variations, essentially in the Mg# (100 × Mg/(Mg + Fe 2+) atomic ratio) of chromite and Fo of olivine, are clearly attributable to re-equilibration between these two solid phases, possibly in the presence of an interstitial melt/fluid.

show abstract

Section: Introductionmentioning

confidence: 95%

Multi-scale development of a stratiform chromite ore body at the base of the dunitic mantle-crust transition zone (Maqsad diapir, Oman ophiolite): The role of repeated melt and fluid influxes

Rospabé

Ceuleneer

Granier

et al. 2019

Lithos

Self Cite

View full text Add to dashboard Cite

show abstract

“…Based on modeling these trends at different water contents, MacLeod et al (2013) deduced that axial spreading was accompanied by hydrous input from a subducting slab along the length of the ophiolite. However, these deductions partly rely on elements susceptible to hydrothermal mobilization, which renders them suspect for some workers (e.g., Kusano et al, 2017), whereas others view the hydrous input as having been derived from deeply circulated seawater (e.g., Rospabé et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Subduction-zone contributions to axial volcanism in the Oman–U.A.E. ophiolite

Belgrano

Diamond

2019

Lithosphere

View full text Add to dashboard Cite

Over four decades of research on the Semail ophiolite (Oman-U.A.E.) has greatly influenced our understanding of processes occurring at fast-spreading ocean ridges. While the well-developed sheeted dike complex and comagmatic lower pillow lavas indicate that the early Semail crust formed at a spreading axis, the precise tectonic setting of this axis-whether true mid-ocean ridge, back-arc or "proto"-arcis contentious. This is largely because the tectonic implications of the geochemistry of the main axial volcanic unit (Geotimes/V1) are disputed. We bypass this hurdle by focusing on intercalations of primitive lavas that are depleted relative to mid-ocean-ridge basalt and that are deeply intercalated within the early Geotimes axial volcanostratigraphy throughout the northern ophiolite. Our analyses of these intercalations show a clear trace-element influence from a subducting slab. We interpret the depleted axial melts to have formed by localized, high-degree partial melting assisted by a high-Th/Nb slab fluid. These results confirm a deep subduction influence on the entire axial spreading phase of the world's largest ophiolite. Considered in the context of later hydrous and boninitic Alley volcanism and of insight from modern tectonic environments, our observations support a proto-arc, subduction-initiation setting for the origin of the Semail ophiolite.

show abstract

“…Indeed, the highest known water contents of the Kane Megamullion south of the Kane Fracture Zone along the Mid-Atlantic Ridge were recorded in MORB samples (up to 1.8 wt% in glass, and up to 2.7 wt% in bulk rocks)(Ciazela et al, 2017). These MORB magmas are considered to assimilate significant volume of the host serpentinite at lithospheric conditions, whereas most MORB glasses sampled at the surface are degassed.It is now established that hydrothermal circulation during oceanic spreading reaches mantle peridotite at and below the petrologic Moho(Python et al, 2007;Rospabé et al, 2017; 2019a,b). The serpentinized peridotite or/and dehydrated serpentinite mantle are characterized by an excess of H2O, Cl (e.g.,Bonifacie et al, 2008), 4 He, 36 Ar (Kendrick et al, 2013) and radiogenic 87 Sr/ 86 Sr (e.g., Harvey et al, 2014).…”

mentioning

confidence: 99%

Hydrated Peridotite–Basaltic Melt Interaction Part II: Fast Assimilation of Serpentinized Mantle by Basaltic Magma

et al. 2020

Self Cite

View full text Add to dashboard Cite

The most abundant terrestrial lavas, mid-ocean ridge and ocean island basalt (MORB and OIB), are commonly considered to be derived from a depleted MORB-mantle component (DMM) and more specific, variably enriched mantle plume sources. However, findings of oceanic lavas and mafic cumulates issued from melts, enriched in chlorine and having a radiogenic 87 Sr/ 86 Sr ratio, can be attributed to an interaction between the asthenosphere-derived melts and lithospheric peridotite variably hydrated due to penetration of hydrothermal water down to and below Moho level. To constrain mechanisms and rates responsible for the interaction, we report results of 15 experiments of reaction between serpentinite and tholeiitic basaltic melt at 0.2 -1.0 GPa and 1250 -1300°C. Results show that the reaction proceeds via a multi-stage mechanism: (i) transformation of serpentinite into Cr-rich spinel-bearing harzburgite (Fo92-95 mol.%) containing pore fluid, (ii) partial melting and dissolution of the harzburgite assemblage with formation of interstitial hydrous melts (up to 57 -60 wt% of SiO2 contents at 0.5 GPa pressure), and (iii) final assimilation of the Cr-rich spinel-bearing harzburgite/dunite and formation of hybrid basaltic melts with 12 -13 wt.% of MgO and elevated Cr (up to ~500 ppm) and Ni (up to ~200 ppm) contents. Assimilation of serpentinite by basaltic melt may occur under elevated melt/rock ratios (>2) and may lead to chromitite formation. We show that hybrid magmas produced by the progressive assimilation of serpentinized lithospheric mantle may be recognized by high Mg-numbers and high Cr and Ni contents of olivine and pyroxenes, an excess of SiO2, H2O and halogens in the melts, and some unusual isotopic composition (e.g., radiogenic 87 Sr/ 86 Sr, non-mantle δ 18 O and low 3 He/ 4 He). Our experiments provide evidence that MORB and high-Mg-Cr orthopyroxene-rich cumulates depleted in incompatible elements can be produced from common mid-ocean ridge basaltic melts modified by reaction with hydrated lithospheric peridotite. We established that the rate of assimilation of serpentinized peridotite is controlled by silica diffusion in the reacting hydrous basaltic melt. Our study challenges 3 traditional interpretation of the variations in MORB and OIB chemical and isotopic composition in terms of deep mantle plume source heterogeneities or/and degrees of partial melting.

show abstract

Origin of the dunitic mantle-crust transition zone in the Oman ophiolite: The interplay between percolating magmas and high-temperature hydrous fluids

Cited by 45 publications

References 35 publications

Multi-scale development of a stratiform chromite ore body at the base of the dunitic mantle-crust transition zone (Maqsad diapir, Oman ophiolite): The role of repeated melt and fluid influxes

Multi-scale development of a stratiform chromite ore body at the base of the dunitic mantle-crust transition zone (Maqsad diapir, Oman ophiolite): The role of repeated melt and fluid influxes

Subduction-zone contributions to axial volcanism in the Oman–U.A.E. ophiolite

Hydrated Peridotite–Basaltic Melt Interaction Part II: Fast Assimilation of Serpentinized Mantle by Basaltic Magma

Contact Info

Product

Resources

About