Ultramafic and gabbroic exposures at the Mid-Atlantic Ridge: geological mapping in the 15°N region

Cannat, Mathilde; Lagabrielle, Yves; Bougault, Henri; Casey, Jack; Coutures, Nathalie de; Dmitriev, L. V.; Fouquet, Yves

doi:10.1016/s0040-1951(97)00113-3

Cited by 173 publications

(149 citation statements)

References 25 publications

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“…Similarly, at 23°N on the MAR gabbro complexes intruded into mantle peridotite were mapped by dredging 34 and then confirmed and extended by seismic refraction 35 . A series of ODP holes in MAR tectonic windows at 14°-16°N 36 also confirm a plum pudding model of gabbro intrusions in serpentinized mantle 37 constructed from bathymetry, dredging and diving. In these holes abundant gabbro veins and dikes were consistent precursors of larger gabbro bodies.…”

Section: Crustal Architecturesupporting

confidence: 57%

Thin crust as evidence for depleted mantle supporting the Marion Rise

Zhou

Dick

2013

Nature

137

106

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The global ridge system is dominated by oceanic rises reflecting large variations in axial depth associated with mantle hotspots. The little studied Marion Rise is as large as the Icelandic, considering length and depth, but has an axial rift rather than a high nearly its entire length. Uniquely, along the SW Indian Ridge systematic sampling allows direct examination of crustal architecture over its full length. Unlike Iceland, peridotites are extensively exposed high over the rise. This shows for the 1 st time that the crust is generally thin, and often missing over a rifted rise. Thus the rise must be largely an isostatic response to ancient melting events that created low-density depleted mantle beneath the ridge rather than thickened crust and/or a large thermal anomaly. The likely origin for the depleted mantle is that emplaced into the African asthenosphere during the Karoo and Madagascar flood basalt events. Following Morgan1 , common wisdom equates oceanic rises to a hot fertile mantle plume producing a flow of plume-derived mantle to the ridge and down the sub-axial asthenospheric channel, resulting in elevated mantle temperature, ridge topography, and thickened igneous crust (the mantle wedge hypothesis, e.g.:2 ). Studies of the Reykjanes Ridge support this, with seismic crust thickening from ~6 km near the Gibbs FZ for 1600 km to ~18 km at the Reykjanes Peninsula e.g.: 3 . The Icelandic Rise, also has a long axial high consistent with such robust magmatism 4 (Table 1). The current consensus is the igneous crust thickens from east to west up the Marion Rise, and indeed up all rises (e.g.: 5 6 ). Basalt sodium contents, like other rises, decrease systematically towards Marion, and are interpreted to represent higher degrees of mantle melting and thicker crust 7 . Dick et al. 8 , however, point out that such correlations can be due to variable mantle temperature, or an increasingly depleted mantle source composition, and do not require thicker crust. The Marion Rise, in particular, has numerous large-offset transforms that would block sub-axial asthenospheric flow (e.g.: 9 ), and its deep rift valley indicates anemic rather than robust magmatism 4 . Niu and O'Hara 10 , though assuming thick crust over rises, suggest the global correlation of basalt chemistry and ridge depth is best explained by mantle composition variations, with many rises supported by depleted chemically buoyant mantle as first proposed by O'hara 11 for the Iceland Rise and Presnall and Helsley 12 for the Azores.2 14 . c) Maximum and minimum elevations are measured from shallowest point on axis, or midpoint of Iceland plateau to the rift valley axis point where average depth stabilizes or blocking transform. d) The 200-km average represents average elevation about the highest or lowest point. e) Iceland average plateau height; crest of Azores Rise, SWIR @ 36°15Ed) MAR @ Charlie Gibbs FZ; axial valley floor, MAR @ 24°N, axial valley floor @61°45'E. e) Depth anomaly calculated for the 200-km averages to eliminate local topographic e...

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Section: Crustal Architecturesupporting

confidence: 57%

Thin crust as evidence for depleted mantle supporting the Marion Rise

Zhou

Dick

2013

Nature

137

106

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“…The ultramafic rocks recovered from these fault surfaces have been used to invoke a limited role of magmatism during core complex formation, leading to the development of many "amagmatic" models of oceanic detachment faulting (Tucholke and Lin 1994;Tucholke et al 1998;Escartín et al 2003). In contrast, the detachment-fault surfaces of the Atlantis Bank (SWIR) and Kane (MAR) core complexes are dominated by gabbroic and troctolitic rocks and fault schists (Karson and Lawrence 1997;MacLeod et al 1998;Arai et al 2000;Kinoshita et al 2001;Matsumoto et al 2002), leading to models of core complex development that emphasize moderate levels of magmatism during detachment faulting (Dick et al 1992Cannat et al 1997;Karson 1999;MacLeod et al 2003;Ildefonse et al 2007). However, recent deep drilling of two core complexes thought to have developed during reduced magma supply, the Atlantis Massif and the 15Њ45ЈN, has revealed long sections (∼1400 and ∼200 m, respectively) of gabbroic rocks in the footwalls of both massifs Kelemen et al 2007).…”

Section: Structure Of Oceanic Core Complexes and Current Modelsmentioning

confidence: 99%

Oceanic Core Complex Development in Modern and Ancient Oceanic Lithosphere: Gabbro‐Localized versus Peridotite‐Localized Detachment Models

Miranda¹,

Dilek²

2010

The Journal of Geology

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A B S T R A C TDrilling and submersible studies of the Atlantis Bank (Southwest Indian Ridge) and the Atlantis Massif (Mid-Atlantic Ridge) oceanic core complexes reveal "gabbro-localized" and "peridotite-localized" end-member models of strain localization and deformation during core complex development, in which the gabbroic fault rocks exhibit extensive and rare high-temperature ductile-deformation fabrics, respectively. Both models emphasize a footwall cored by gabbroic intrusions, therefore precluding an amagmatic origin of core complex formation. We test these models by using relict oceanic core complexes preserved in the western Mirdita Ophiolite in Albania. The Puka and Krabbi massifs display traits of the peridotite-localized detachment model, whereby amagmatic tectonic extension is not required for the formation of this category of core complexes.

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“…org/IRvents). Mantle rock can outcrop at slow-spreading ridges because of their extensional tectonics [Aumento and Loubat, 1971;Bonatti, 1976;Dick, 1989;Cannat et al, 1995Cannat et al, , 1997. This enables hydration of olivine and pyroxene minerals by fluids circulating in the crust to form serpentine, magnetite and hydrogen.…”

Section: Introductionmentioning

confidence: 99%

A note on the fluxes of abiogenic methane and hydrogen from mid‐ocean ridges

Keir¹

2010

Geophysical Research Letters

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[1] The concentrations of methane and hydrogen in hydrothermal vent fluids issuing from mid-ocean ridges tend to fall into two groups, one with high concentrations of these gases in ultramafic-hosted vent fields and a second group with relatively lower concentrations in basalt-hosted vent fluids. Ultramafic-hosted systems, however, appear to be restricted to slow-spreading ridges and constitute only a fraction of the hydrothermal systems found there. In this note, the hydrothermal fluxes of methane and hydrogen have been calculated by estimating the percentages of the total subsurface hydrothermal circulation that circulate through each type of host rock. Even though the percentage of the total subsurface flow that is affected by serpentinization appears to be rather small (8%), it still appears that this process produces about 70% of the total mid-ocean flux of these gases. The total production of methane and hydrogen is calculated to be about 20 × 10 9 mol yr −1 and 190 × 10 9 mol yr −1 , respectively. The hydrogen flux is comparable to that most recently calculated on the basis of the rate of hydration of mantle rock in newly formed crust and the stoichiometry of the serpentinization reaction. This suggests that, except for the production of methane, a major portion of the hydrogen produced in the subsurface is not consumed before venting. Citation: Keir, R. S.(2010), A note on the fluxes of abiogenic methane and hydrogen from mid-ocean ridges, Geophys.

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Ultramafic and gabbroic exposures at the Mid-Atlantic Ridge: geological mapping in the 15°N region

Cited by 173 publications

References 25 publications

Thin crust as evidence for depleted mantle supporting the Marion Rise

Thin crust as evidence for depleted mantle supporting the Marion Rise

Oceanic Core Complex Development in Modern and Ancient Oceanic Lithosphere: Gabbro‐Localized versus Peridotite‐Localized Detachment Models

A note on the fluxes of abiogenic methane and hydrogen from mid‐ocean ridges

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