TY - JOUR

T1 - Magma-Mush Interactions in the Lower Oceanic Crust

T2 - Insights From Atlantis Bank Layered Series (Southwest Indian Ridge)

AU - Boulanger, M.

AU - France, L.

AU - Ferrando, C.

AU - Ildefonse, B.

AU - Ghosh, B.

AU - Sanfilippo, A.

AU - Liu, C. Z.

AU - Morishita, T.

AU - Koepke, J.

AU - Bruguier, O.

N1 - Funding Information: The authors express our warm thanks to the various people involved at different technical stages in this work: C. Nevado and D. Delmas (Geosciences Montpellier) for their high quality thin sections, and Jean‐Luc Devidal (LMV) and Fabrice Barou (Geosciences Montpellier) for their assistance during EPMA and EBSD measurements, respectively. This research used data provided by the International Ocean Discovery Program (IODP). The authors gratefully acknowledge the Captain and shipboard crew of IODP Expedition 360 for their assistance in data collection at sea. The authors wish to thank the Scientific Party of IODP Expedition 360 for fruitful discussions during the cruise and post‐cruise meeting. This study also benefited from discussions with David Jousselin (CRPG), and Kathi Faak (RUB), and from thorough comments by M. Edmonds, L. A. Coogan, G. Borghini, B. Hayes, J. H. Bédard, and two anonymous reviewers. The authors thank Robert Dennen for English phrasing improvements. This is CRPG contribution number 2797. This research was supported by CNRS‐INSU and IODP‐France. M. Boulanger's PhD project was funded by the French Ministry of Research (MESRI).

PY - 2021/9/12

Y1 - 2021/9/12

N2 - Magma migration and differentiation processes are key to understanding the development and evolution of oceanic magma reservoirs. To provide new quantitative geochemical constraints on these processes, we applied a high-resolution approach to study an interlayered section of the lower oceanic crust sampled at Atlantis Bank, on the (ultra)slow-spreading Southwest Indian Ridge. The section is characterized by sharp grain-size layering between fine- and coarse-grained olivine gabbros that is representative of other layered structures described at the Atlantis Bank oceanic core complex. The textures and fabrics of the layers and the nature of their contacts indicate formation by intrusion of a magma (i.e., crystal-bearing) into an almost solidified coarse-grained mush. Petrographic observations and in situ incompatible trace element signatures indicate that the fine- and coarse-grained layers record reactive porous migration of melts. Widespread reactive porous flow occurred prior to intrusion within the coarse-grained gabbro, producing mineral compositions enriched in incompatible elements. The intrusive fine-grained lithology records a late stage event of localized reactive melt percolation in cm-scale structures, which lead to strong light rare earth elements depletion relative to heavy rare earth elements. In addition, we highlight the occurrence of interactions at the contacts between layers and partial modification in compositions of the intruded lithology. This layered section likely represents a contact between two larger magma bodies emplaced within the lower crust during accretion, where the type of melt migration (intrusion or porous flow) and the modalities of melt percolation (widespread or localized) strongly govern the composition of the crustal lithologies.

AB - Magma migration and differentiation processes are key to understanding the development and evolution of oceanic magma reservoirs. To provide new quantitative geochemical constraints on these processes, we applied a high-resolution approach to study an interlayered section of the lower oceanic crust sampled at Atlantis Bank, on the (ultra)slow-spreading Southwest Indian Ridge. The section is characterized by sharp grain-size layering between fine- and coarse-grained olivine gabbros that is representative of other layered structures described at the Atlantis Bank oceanic core complex. The textures and fabrics of the layers and the nature of their contacts indicate formation by intrusion of a magma (i.e., crystal-bearing) into an almost solidified coarse-grained mush. Petrographic observations and in situ incompatible trace element signatures indicate that the fine- and coarse-grained layers record reactive porous migration of melts. Widespread reactive porous flow occurred prior to intrusion within the coarse-grained gabbro, producing mineral compositions enriched in incompatible elements. The intrusive fine-grained lithology records a late stage event of localized reactive melt percolation in cm-scale structures, which lead to strong light rare earth elements depletion relative to heavy rare earth elements. In addition, we highlight the occurrence of interactions at the contacts between layers and partial modification in compositions of the intruded lithology. This layered section likely represents a contact between two larger magma bodies emplaced within the lower crust during accretion, where the type of melt migration (intrusion or porous flow) and the modalities of melt percolation (widespread or localized) strongly govern the composition of the crustal lithologies.

KW - assimilation—fractional crystallization

KW - crystal mush

KW - lower oceanic crust

KW - magma intrusion

KW - magmatic flow

KW - reactive porous flow

UR - http://www.scopus.com/inward/record.url?scp=85115812987&partnerID=8YFLogxK

U2 - 10.1029/2021JB022331

DO - 10.1029/2021JB022331

M3 - Article

AN - SCOPUS:85115812987

VL - 126

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 9

M1 - e2021JB022331

ER -