Magma Reservoir Formation and Evolution at a Slow-Spreading Center (Atlantis Bank, Southwest Indian Ridge)

Boulanger, Marine; France, Lydéric; Deans, J. R.; Ferrando, Carlotta; Lissenberg, C. Johan; Handt, Anette von der

doi:10.3389/feart.2020.554598

Cited by 31 publications

(66 citation statements)

References 99 publications

(182 reference statements)

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Section: Fig 2: Velocity Models: (A)mentioning

confidence: 99%

“…A more than 1500-m of the lower crustal gabbro was drilled during the Ocean Drilling Program Hole 735B 30,31 , containing several layered units of >250 m thickness. Analysis of a geochemical unit in the lower gabbro 31 suggests that it constitutes of a single magma reservoir but is separated in two parts. The lower part is formed by a stack of repeated recharge of primitive thin melt sills, whereas the upper part consists of a homogeneous evolved magma mush formed by upward reactive porous flow, progressive differentiation and accumulation 31,32 .…”

Section: Fig 2: Velocity Models: (A)mentioning

confidence: 99%

“…Analysis of a geochemical unit in the lower gabbro 31 suggests that it constitutes of a single magma reservoir but is separated in two parts. The lower part is formed by a stack of repeated recharge of primitive thin melt sills, whereas the upper part consists of a homogeneous evolved magma mush formed by upward reactive porous flow, progressive differentiation and accumulation 31,32 . This process would lead to a layering in the lower crust, containing olivine-rich gabbro and troctolites at the base with a distinct boundary separating more evolved olivine and olivine-bearing gabbro with decreasing olivine and increasing plagioclase 31 .…”

Section: Fig 2: Velocity Models: (A)mentioning

confidence: 99%

“…Observations from IODP/ODP drilling and ophiolites [28][29][30][31][32][33] indicate that the lower crustal gabbroic rocks are mainly composed of olivine (Ol), clinopyroxene (Cpx), and plagioclase (Pl), with seismic velocities VOl > VCpx > VPl (Table S1), where V represents the velocity.…”

Section: Fig 2: Velocity Models: (A)mentioning

confidence: 99%

“…The high-velocity layers are likely to be formed from primitive melt intrusions at the base of a magma reservoir, whereas the low-velocity layers can be produced by the fractional crystallisation and accumulation of more-evolved, upwardmigrated melt residue (mush). In situ crystallisation requires extensive seawater circulation down to the Moho depth along the sides of crystal-rich mush zone beneath the magma chambers for cooling 34 , which can be provided through well-developed faults in the slowspreading environment 31 . Moreover, the hydrothermal activities and the magmatic reaction with host rocks could lead to remelting and assimilation, altering the petrological constituents of igneous rocks 31,32 , hence changing the rock properties further.…”

Section: Fig 2: Velocity Models: (A)mentioning

confidence: 99%

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In situ lower crustal accretion by melt sill injection revealed by seismic layering

Guo

Singh

Vaddineni

et al. 2021

Preprint

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Oceanic crust is formed at mid-ocean spreading centres by a combination of magmatic, tectonic and hydrothermal processes. The crust formed by magmatic process consists of an upper crust generally composed of basaltic dikes and lava flows and a lower crust presumed to mainly contain homogeneous gabbro whereas that by tectonic process can be very heterogeneous and may even contain mantle rocks. Although the formation and evolution of the upper crust are well known from geophysical and drilling results, those for the lower crust remain a matter of debate. Using a full waveform inversion method applied to wide-angle seismic data, here we report the presence of layering in the lower oceanic crust formed at the slow spreading Mid-Atlantic Ridge, ~7-12 Ma in age, revealing that the lower crust is formed mainly by in situ cooling and crystallisation of melt sills at different depths by the injection of magma from the mantle. These layers are 400-600 m thick with alternate high and low velocities, with ± 100-200 m/s velocity variation, and cover over a million-year old crust, suggesting that the crustal accretion by melt sill intrusions beneath the ridge axis is a stable process. We also find that the upper crust is ~400 m thinner than that from conventional travel-time analysis. Taken together, these discoveries suggest that the magmatism plays more important roles in the crustal accretion process at slow spreading ridges than previously realised, and that in-situ lower crustal accretion is the main process for the formation of lower oceanic crust.

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Section: Fig 2: Velocity Models: (A)mentioning

confidence: 99%