Peridotite-melt interaction under transitional conditions between the spinel and plagioclase facies beneath the Mid-Atlantic Ridge: Insight from peridotites at 13°N

Pertsev, A. N.; Бортников, Н. С.; Aranovich, L. Ya.; Vlasov, E. A.; Bel’tenev, V. E.; Ivanov, V.N.; Симакин, С. Г.

doi:10.1134/s0869591109020027

Cited by 10 publications

(6 citation statements)

References 29 publications

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“…A wide range of lithologies including gabbros, peridotites, basalts, and deformed fault rocks and mass-wasted rubble have been sampled at, or at shallow depth beneath, the seabed (MacLeod et al, 2009;Pertsev et al, 2009;Escartin et al, 2017), similar to those observed from the OCCs of the 15°20'N (Albers et al, 2019) and 16°30'N (Sanfilippo et al, 2019) areas of the MAR. Geochemical analysis of the basalts recovered from the 13°N region reveals a change in magmatic activity from a magma-poor phase at the initiation of detachment faulting, to an apparently more magma-rich phase at the present time (Wilson et al, 2013).…”

Section: Geological Settingmentioning

confidence: 82%

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Peirce

Robinson

Funnell

et al. 2020

Geophysical Journal International

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SUMMARY A region of oceanic core complexes (OCCs) exists at 13°N on the Mid-Atlantic Ridge that is regarded as a type site. This site includes two OCCs at 13°20′N and 13°30′N, thought to be in the active and dying stages of evolution, and two together called the Ashadze Complex (centred at 13°05′N) that are considered to be relict. Here we describe the results of S-wave seismic modelling along an ∼200-km-long 2-D transect traversing, south-to-north, through both the Mercurius and Marathon fracture zones, the southern outside corner of the 13°N segment, the OCCs, the ridge axis deviation in trend centred at 13°35′N, and the youngest oceanic crust of the eastern ridge flank to the north. Our inversion model, and the corresponding Vp/Vs ratio, show that the majority of the crust beneath the 13°30′N OCC comprises metamorphosed lithologies that have been exhumed to the shallowest subseabed level, while basaltic lithologies underlie the 13°20′N OCC. The transition between these contrasting crustal structures occurs over a distance of <5 km, and extends to at least ∼2 km depth below seafloor. The northern and southern OCCs of the Ashadze Complex have contrasting structures at shallow depth, with the northern OCC having a faster S-wave velocity in the upper crust. A Vp/Vs ratio of >1.9 (and equivalent Poisson's ratio of >0.3) indicates exhumed and/or metamorphosed lithologies beneath the bathymetric depression between them and within the crust beneath the southern OCC. Between the northern and southern flanks of the Marathon fracture zone and northern flank of Mercurius fracture zone, the lower crust has a relatively low Vp/Vs ratio suggesting that the deformation associated with Marathon fracture zone, which facilitates fluid ingress, extends laterally within the lower crust. Marathon fracture zone itself is underlain by a broad zone of low S-wave velocity (∼2.0 km s−1) up to ∼20 km wide from the seabed to at least the mid-crust, that is mirrored in a high Vp/Vs ratio and lower density, particularly deeper than ∼1 km below seabed within its bathymetric footprint. Volcanic domains are highlighted by a low Vp/Vs ratio of <1.6 (and equivalent Poisson's ratio of <0.15). Our combined seismic and density models favour the localized model of OCC evolution. They also show a considerable ridge-parallel variability in the amount and distribution of magmatic versus metamorphosed crust. Our results suggest that the current focus of magmatism lies to the north of the 13°20′N OCC, where the magmatic accretion-type seabed morphology observed is mirrored in the pattern of microseismicity, suggesting that its inward-facing median-valley-wall fault may link to the 13°20′N OCC detachment surface. Magmatism and active faulting behind (to the west) the footwall breakaway of the 13°30′N OCC, and the microseismicity concentrated in a band along its southern flank, suggest a readjustment of ridge geometry along axis is underway. As part of this, a transform offset is forming that will ultimately accommodate the 13°30′N OCC in its inside corner on the eastern flank of the ridge axis to the north.

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Section: Geological Settingmentioning

confidence: 82%

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Peirce

Robinson

Funnell

et al. 2020

Geophysical Journal International

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“…We are not aware of direct evidence (from melt inclusions) for such a scenario, but it was often proposed in case studies to explain compositional gradients of mineral phases around late-stage mafic dikes (e.g. Pertsev et al 2009;Warren and Shimizu 2010). In our schematic Fig.…”

Section: Comparison With Natural Quenched Liquidsmentioning

confidence: 91%

Melt variability in percolated peridotite: an experimental study applied to reactive migration of tholeiitic basalt in the upper mantle

Bleeken

Müntener

Ulmer³

2010

Contrib Mineral Petrol

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Melt-rock reaction in the upper mantle is recorded in a variety of ultramafic rocks and is an important process in modifying melt composition on its way from the source region towards the surface. This experimental study evaluates the compositional variability of tholeiitic basalts upon reaction with depleted peridotite at uppermost-mantle conditions. Infiltration-reaction processes are simulated by employing a three-layered set-up: primitive basaltic powder ('melt layer') is overlain by a 'peridotite layer' and a layer of vitreous carbon spheres ('melt trap'). Melt from the melt layer is forced to move through the peridotite layer into the melt trap. Experiments were conducted at 0.65 and 0.8 GPa in the temperature range 1,170-1,290°C. In this P-T range, representing conditions encountered in the transition zone (thermal boundary layer) between the asthenosphere and the lithosphere underneath oceanic spreading centres, the melt is subjected to fractionation, and the peridotite is partially melting (T s * 1,260°C). The effect of reaction between melt and peridotite on the melt composition was investigated across each experimental charge. Quenched melts in the peridotite layers display larger compositional variations than melt layer glasses. A difference between glasses in the melt and peridotite layer becomes more important at decreasing temperature through a combination of enrichment in incompatible elements in the melt layer and less efficient diffusive equilibration in the melt phase. At 1,290°C, preferential dissolution of pyroxenes enriches the melt in silica and dilutes it in incompatible elements. Moreover, liquids become increasingly enriched in Cr 2 O 3 at higher temperatures due to the dissolution of spinel. Silica contents of liquids decrease at 1,260°C, whereas incompatible elements start to concentrate in the melt due to increasing levels of crystallization. At the lowest temperatures investigated, increasing alkali contents cause silica to increase as a consequence of reactive fractionation. Pervasive percolation of tholeiitic basalt through an upper-mantle thermal boundary layer can thus impose a high-Si 'low-pressure' signature on MORB. This could explain opx ? plag enrichment in shallow plagioclase peridotites and prolonged formation of olivine gabbros.

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“…Dredge, TV‐grab sampling, and seafloor rock drilling at these detachments faults yielded a wide range in rock types, consistent with the exposure of deep‐seated rocks (gabbro and peridotite), in addition to basalt/diabase, and including fault rocks [ MacLeod et al ., ; Pertsev et al ., ]. The geochemistry of basalts recovered has been also interpreted as an indicator of a change in magmatic activity from a period of low supply of magma to the ridge axis at the initiation of detachment faulting, to more robust axial melt supply at the present time [ Wilson et al ., ].…”

Section: Geological Setting and Prior Workmentioning

confidence: 99%

Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N, Mid Atlantic Ridge)

Escartı́n

Mével

Petersen

et al. 2017

Geochem Geophys Geosyst

100

179

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Microbathymetry data, in situ observations, and sampling along the 13°20′N and 13°20′N oceanic core complexes (OCCs) reveal mechanisms of detachment fault denudation at the seafloor, links between tectonic extension and mass wasting, and expose the nature of corrugations, ubiquitous at OCCs. In the initial stages of detachment faulting and high‐angle fault, scarps show extensive mass wasting that reduces their slope. Flexural rotation further lowers scarp slope, hinders mass wasting, resulting in morphologically complex chaotic terrain between the breakaway and the denuded corrugated surface. Extension and drag along the fault plane uplifts a wedge of hangingwall material (apron). The detachment surface emerges along a continuous moat that sheds rocks and covers it with unconsolidated rubble, while local slumping emplaces rubble ridges overlying corrugations. The detachment fault zone is a set of anostomosed slip planes, elongated in the along‐extension direction. Slip planes bind fault rock bodies defining the corrugations observed in microbathymetry and sonar. Fault planes with extension‐parallel stria are exposed along corrugation flanks, where the rubble cover is shed. Detachment fault rocks are primarily basalt fault breccia at 13°20′N OCC, and gabbro and peridotite at 13°30′N, demonstrating that brittle strain localization in shallow lithosphere form corrugations, regardless of lithologies in the detachment zone. Finally, faulting and volcanism dismember the 13°30′N OCC, with widespread present and past hydrothermal activity (Semenov fields), while the Irinovskoe hydrothermal field at the 13°20′N core complex suggests a magmatic source within the footwall. These results confirm the ubiquitous relationship between hydrothermal activity and oceanic detachment formation and evolution.

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Peridotite-melt interaction under transitional conditions between the spinel and plagioclase facies beneath the Mid-Atlantic Ridge: Insight from peridotites at 13°N

Cited by 10 publications

References 29 publications

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Melt variability in percolated peridotite: an experimental study applied to reactive migration of tholeiitic basalt in the upper mantle

Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N, Mid Atlantic Ridge)

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