TY - JOUR

T1 - A reference section through fast‐spread lower oceanic crust, Wadi Gideah, Samail Ophiolite (Sultanate of Oman): Insights from Crystallographic Preferred Orientations

AU - Mock, Dominik Nicolas

AU - Ildefonse, Benoit

AU - Müller, Tim

AU - Koepke, Jürgen

N1 - Funding Information: The authors wish to thank J. Feige, C. Nevado, and D. Delmas for careful thin section preparation. F. Barou is acknowledged for helpful assistance during EBSD measurements. The authors thank Maël Allard and David Mainprice for their help with MTEX. We acknowledge Michael Denis Higgins for providing the CSDCorrections 1.60 software we used to calculate crystal size distributions. The support of the Sultan Qaboos University (Prof. Sobhi Nasir), as well as the friendly cooperation established in Oman with the Public Authority for Mining (Department of Geological Research, Dr. A. Al Rajhi, Dr. M. Al-Battashi, Dr. M. Alaraimi) are acknowledged. The submitted version of the paper improved by the helpful revisions of David Jousselin, Jill VanTongeren, an anonymous reviewer and the associate editor. This study was funded by DFG projects KO 1723/16-1, KO 1723/21-1, and KO 1723/25-1. Open access funding enabled and organized by Projekt DEAL. Funding Information: The authors wish to thank J. Feige, C. Nevado, and D. Delmas for careful thin section preparation. F. Barou is acknowledged for helpful assistance during EBSD measurements. The authors thank Maël Allard and David Mainprice for their help with MTEX. We acknowledge Michael Denis Higgins for providing the CSDCorrections 1.60 software we used to calculate crystal size distributions. The support of the Sultan Qaboos University (Prof. Sobhi Nasir), as well as the friendly cooperation established in Oman with the Public Authority for Mining (Department of Geological Research, Dr. A. Al Rajhi, Dr. M. Al‐Battashi, Dr. M. Alaraimi) are acknowledged. The submitted version of the paper improved by the helpful revisions of David Jousselin, Jill VanTongeren, an anonymous reviewer and the associate editor. This study was funded by DFG projects KO 1723/16‐1, KO 1723/21‐1, and KO 1723/25‐1. Open access funding enabled and organized by Projekt DEAL.

PY - 2021/6/24

Y1 - 2021/6/24

N2 - We established a 5,000 m thick profile through the paleo lower oceanic crust of the Samail ophiolite (Sultanate of Oman, Wadi Gideah), in order to investigate accretion processes beneath fast-spreading mid-ocean ridges. The Samail ophiolite is regarded as best on-land analog for fast-spread oceanic crust, and Wadi Gideah allows sampling of the entire lower crust along the Wadi bed. Here, we provide microstructural constraints to lower crustal accretion beneath fast-spreading mid-ocean ridges, which reveal changing microstructures and fabrics with depth. Grain size coarsening occurs from the foliated to the layered gabbro section. A ∼350 m thick zone of gabbroic rocks from the profile top, interpreted as frozen fillings of the axial melt lens and defined as varitextured gabbros, shows intergranular textures without crystallographic preferred orientations. Rocks from the varitextured/foliated gabbro transition (∼500 m thick) and from the upper foliated gabbros (∼600 m) are foliated and lineated. The lineation is absent or very weak in the underlying ∼800 m thick lower foliated gabbros. In layered gabbros, the fabric gradually strengthens and becomes more lineated down section with local scattering at small spatial scales. This implies distinct accretion mechanisms in the deep and shallow plutonic crust. For the layered and lower foliated gabbros, our data suggest in-situ crystallizing individual magma reservoirs. Dominant lineation in the upper foliated gabbros and the varitextured/foliated gabbro transition suggests vertically transported crystal-laden melts or mushes being consistent with subsiding crystal mushes from the axial melt lens, and/or crystallizing upward migrating melt expelled from the crystal mush beneath.

AB - We established a 5,000 m thick profile through the paleo lower oceanic crust of the Samail ophiolite (Sultanate of Oman, Wadi Gideah), in order to investigate accretion processes beneath fast-spreading mid-ocean ridges. The Samail ophiolite is regarded as best on-land analog for fast-spread oceanic crust, and Wadi Gideah allows sampling of the entire lower crust along the Wadi bed. Here, we provide microstructural constraints to lower crustal accretion beneath fast-spreading mid-ocean ridges, which reveal changing microstructures and fabrics with depth. Grain size coarsening occurs from the foliated to the layered gabbro section. A ∼350 m thick zone of gabbroic rocks from the profile top, interpreted as frozen fillings of the axial melt lens and defined as varitextured gabbros, shows intergranular textures without crystallographic preferred orientations. Rocks from the varitextured/foliated gabbro transition (∼500 m thick) and from the upper foliated gabbros (∼600 m) are foliated and lineated. The lineation is absent or very weak in the underlying ∼800 m thick lower foliated gabbros. In layered gabbros, the fabric gradually strengthens and becomes more lineated down section with local scattering at small spatial scales. This implies distinct accretion mechanisms in the deep and shallow plutonic crust. For the layered and lower foliated gabbros, our data suggest in-situ crystallizing individual magma reservoirs. Dominant lineation in the upper foliated gabbros and the varitextured/foliated gabbro transition suggests vertically transported crystal-laden melts or mushes being consistent with subsiding crystal mushes from the axial melt lens, and/or crystallizing upward migrating melt expelled from the crystal mush beneath.

KW - Oman ophiolite

KW - crystal size distributions

KW - crystallographic preferred orientations

KW - lower oceanic crust

UR - http://www.scopus.com/inward/record.url?scp=85109199030&partnerID=8YFLogxK

U2 - 10.1029/2021JB021864

DO - 10.1029/2021JB021864

M3 - Article

VL - 126

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 6

M1 - e2021JB021864

ER -