Alteration heterogeneities in peridotites exhumed on the southern wall of the Atlantis Massif (IODP Expedition 357)

The IODP Expedition 357 Science Party

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Serpentinized and metasomatized peridotites intruded by gabbros and dolerites have been drilled on the southern wall of the Atlantis Massif (Mid-Atlantic Ridge, 30°N) during International Ocean Discovery Program (IODP) Expedition 357. They occur in seven holes from five sites making up an east-west-trending, spreading-parallel profile that crosscuts this exhumed detachment footwall. Here we have taken advantage of this sampling to study heterogeneities of alteration at scales less than a kilometer. We combine textural and mineralogical observations made on 77 samples with in situ major and trace element analyses in primary and serpentine minerals to provide a conceptual model for the development of alteration heterogeneities at the Atlantis Massif. Textural sequences and mineralogical assemblages reveal a transition between an initial pervasive phase of serpentinization and subsequent serpentinization and metasomatism focused along localized pathways preferentially used by hydrothermal fluids. We propose that these localized pathways are interconnected and form 100 m- to 1 km-sized cells in the detachment footwall. This change in fluid pathway distribution is accompanied by variable trace element enrichments in the serpentine textures: deep, syn-serpentinization fluid-peridotite interactions are considered the source of Cu, As, and Sb enrichments, whereas U and Sr enrichments are interpreted as markers of later, shallower fluid- serpentinized peridotite interaction. Alteration of gabbros and dolerites emplaced in the peridotite at different lithospheric levels leads to the development of amphibole-, chlorite- and/or talc-bearing textures as well as enrichments in light rare earth elements, Nb, Y, Th, and Ta in the serpentine textures of the surrounding peridotites. Combining these observations, we propose a model that places the drill holes in a conceptual frame involving mafic intrusions in the peridotites and heterogeneities during progressive alteration and emplacement on the seafloor.

Original languageEnglish
Pages (from-to)1329-1358
Number of pages30
JournalJournal of Petrology
Volume59
Issue number7
DOIs
Publication statusPublished - 2018 Jul 1

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expeditions
serpentinization
peridotite
oceans
Fluids
textures
Textures
fluids
texture
Trace Elements
ocean
footwall
diabase
detachment
trace elements
fluid
Bearings (structural)
Amphibole Asbestos
trace element
Serpentine Asbestos

Keywords

  • Atlantis Massif
  • Fluid-rock interaction
  • International Ocean Discovery Program (IODP)
  • Serpentinization

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Alteration heterogeneities in peridotites exhumed on the southern wall of the Atlantis Massif (IODP Expedition 357). / The IODP Expedition 357 Science Party.

In: Journal of Petrology, Vol. 59, No. 7, 01.07.2018, p. 1329-1358.

Research output: Contribution to journalArticle

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abstract = "Serpentinized and metasomatized peridotites intruded by gabbros and dolerites have been drilled on the southern wall of the Atlantis Massif (Mid-Atlantic Ridge, 30°N) during International Ocean Discovery Program (IODP) Expedition 357. They occur in seven holes from five sites making up an east-west-trending, spreading-parallel profile that crosscuts this exhumed detachment footwall. Here we have taken advantage of this sampling to study heterogeneities of alteration at scales less than a kilometer. We combine textural and mineralogical observations made on 77 samples with in situ major and trace element analyses in primary and serpentine minerals to provide a conceptual model for the development of alteration heterogeneities at the Atlantis Massif. Textural sequences and mineralogical assemblages reveal a transition between an initial pervasive phase of serpentinization and subsequent serpentinization and metasomatism focused along localized pathways preferentially used by hydrothermal fluids. We propose that these localized pathways are interconnected and form 100 m- to 1 km-sized cells in the detachment footwall. This change in fluid pathway distribution is accompanied by variable trace element enrichments in the serpentine textures: deep, syn-serpentinization fluid-peridotite interactions are considered the source of Cu, As, and Sb enrichments, whereas U and Sr enrichments are interpreted as markers of later, shallower fluid- serpentinized peridotite interaction. Alteration of gabbros and dolerites emplaced in the peridotite at different lithospheric levels leads to the development of amphibole-, chlorite- and/or talc-bearing textures as well as enrichments in light rare earth elements, Nb, Y, Th, and Ta in the serpentine textures of the surrounding peridotites. Combining these observations, we propose a model that places the drill holes in a conceptual frame involving mafic intrusions in the peridotites and heterogeneities during progressive alteration and emplacement on the seafloor.",
keywords = "Atlantis Massif, Fluid-rock interaction, International Ocean Discovery Program (IODP), Serpentinization",
author = "{The IODP Expedition 357 Science Party} and St{\'e}phane Roum{\'e}jon and Fr{\"u}h-Green, {Gretchen L.} and Orcutt, {Beth N.} and Sophie Green and Carol Cotterill and Sally Morgan and Norikatsu Akizawa and Gaye Bayrakci and Behrmann, {Jan Hinrich} and Emilio Herrero-Bervera and Chiara Boschi and William Brazelton and Mathilde Cannat and Dunkel, {Kristina G.} and Javier Escartin and Michelle Harris and Kirsten Hesse and Barbara John and Lang, {Susan Q.} and Marvin Lilley and Liu, {Hai Quan} and Lisa Mayhew and Andrew McCaig and Benedicte Menez and Yuki Morono and Marianne Qu{\'e}m{\'e}neur and Ratnayake, {Amila Sandaruwan} and Matthew Schrenk and Esther Schwarzenbach and Katrina Twing and Dominique Weis and Whattam, {Scott A.} and Morgan Williams and Rui Zhao",
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AU - Früh-Green, Gretchen L.

AU - Orcutt, Beth N.

AU - Green, Sophie

AU - Cotterill, Carol

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AU - Akizawa, Norikatsu

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AU - Hesse, Kirsten

AU - John, Barbara

AU - Lang, Susan Q.

AU - Lilley, Marvin

AU - Liu, Hai Quan

AU - Mayhew, Lisa

AU - McCaig, Andrew

AU - Menez, Benedicte

AU - Morono, Yuki

AU - Quéméneur, Marianne

AU - Ratnayake, Amila Sandaruwan

AU - Schrenk, Matthew

AU - Schwarzenbach, Esther

AU - Twing, Katrina

AU - Weis, Dominique

AU - Whattam, Scott A.

AU - Williams, Morgan

AU - Zhao, Rui

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N2 - Serpentinized and metasomatized peridotites intruded by gabbros and dolerites have been drilled on the southern wall of the Atlantis Massif (Mid-Atlantic Ridge, 30°N) during International Ocean Discovery Program (IODP) Expedition 357. They occur in seven holes from five sites making up an east-west-trending, spreading-parallel profile that crosscuts this exhumed detachment footwall. Here we have taken advantage of this sampling to study heterogeneities of alteration at scales less than a kilometer. We combine textural and mineralogical observations made on 77 samples with in situ major and trace element analyses in primary and serpentine minerals to provide a conceptual model for the development of alteration heterogeneities at the Atlantis Massif. Textural sequences and mineralogical assemblages reveal a transition between an initial pervasive phase of serpentinization and subsequent serpentinization and metasomatism focused along localized pathways preferentially used by hydrothermal fluids. We propose that these localized pathways are interconnected and form 100 m- to 1 km-sized cells in the detachment footwall. This change in fluid pathway distribution is accompanied by variable trace element enrichments in the serpentine textures: deep, syn-serpentinization fluid-peridotite interactions are considered the source of Cu, As, and Sb enrichments, whereas U and Sr enrichments are interpreted as markers of later, shallower fluid- serpentinized peridotite interaction. Alteration of gabbros and dolerites emplaced in the peridotite at different lithospheric levels leads to the development of amphibole-, chlorite- and/or talc-bearing textures as well as enrichments in light rare earth elements, Nb, Y, Th, and Ta in the serpentine textures of the surrounding peridotites. Combining these observations, we propose a model that places the drill holes in a conceptual frame involving mafic intrusions in the peridotites and heterogeneities during progressive alteration and emplacement on the seafloor.

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KW - Atlantis Massif

KW - Fluid-rock interaction

KW - International Ocean Discovery Program (IODP)

KW - Serpentinization

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