TY - JOUR

T1 - A Reference Section Through Fast-Spread Lower Oceanic Crust, Wadi Gideah, Samail Ophiolite (Sultanate of Oman)

T2 - Whole Rock Geochemistry

AU - Garbe-Schönberg, Dieter

AU - Koepke, Jürgen

AU - Müller, Samuel

AU - Mock, Dominik

AU - Müller, Tim

N1 - Funding Information: The study benefitted greatly from critical and constructive reviews by John Lassiter and one anonymous reviewer who is kindly acknowledged. The authors highly appreciate the support of the Oman Public Authority for Mining for permission of conducting fieldwork in Oman. Special thanks go to Dr. Ali Al Rajhi, Dr. Mohamed Al Batashi, and Dr. Mohamed Al Araimi. We kindly thank Prof. Dr. Sobhi Nasir, Geology Department of Sultan Quaboos University for generous assistance during planning and conducting fieldwork, and shipping samples. Help from Ulrike Westernströer with ICP-MS and LA-ICP-MS, Karen Bremer with ICP-OES, and Leewe Schönberg with LA-ICPMS is highly appreciated. Jasper Berndt-Gerdes (U Münster) provided access to his strip heater facility and Stefan Jung (U Hamburg) contributed to XRF data. This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) by a grant given to DGS and JK, Project No.: 214851514, GA 1960/11-2, KO 1723/21-2. Open Access funding enabled and organized by Projekt DEAL.

PY - 2022/6/17

Y1 - 2022/6/17

N2 - Due to its inaccessibility, no complete and coherent data set exists for the composition of modern fast-spreading oceanic crust. We sampled outcrops through 6,500 m of fossil oceanic crust in the Oman Ophiolite (Wadi Gideah Transect) that is regarded as best analogue of fast-spreading crust on land. Here we report a complete set of whole-rock major and trace element data displaying systematic and contrasting compositional trends in lower and upper gabbros being correlated with stratigraphic depth. A significant discontinuity in crystallization regime is observed at ∼3,525 m above the mantle-crust boundary: gabbros below ∼3,525 m have in general very low incompatible element mass fractions which develop upwards in a barely noticeable way to more differentiated compositions while Mg# decreases. More pronounced trends indicating progressive fractionation of ascending melts can be observed for incompatible elements and their element ratios as a consequence of in situ crystallization. Locally, more variable compositions within narrow depth intervals testify for advanced differentiation in situ within individual sills. Gabbros above ∼3,525 m become significantly more evolved and show considerable variations in composition. Fractional crystallization and mixing processes in a transient axial melt lens control the composition of isotropic “varitextured” gabbros and sheeted dike basalts where fractionation of high field strength elemental ratios is minor. New average compositions of fast-spread (paleo) oceanic crust are reported for major and 38 trace elements. Comparison with new data from Wadi Khafifah close to Wadi Gideah suggests robustness of crustal accretion processes in both space and time.

AB - Due to its inaccessibility, no complete and coherent data set exists for the composition of modern fast-spreading oceanic crust. We sampled outcrops through 6,500 m of fossil oceanic crust in the Oman Ophiolite (Wadi Gideah Transect) that is regarded as best analogue of fast-spreading crust on land. Here we report a complete set of whole-rock major and trace element data displaying systematic and contrasting compositional trends in lower and upper gabbros being correlated with stratigraphic depth. A significant discontinuity in crystallization regime is observed at ∼3,525 m above the mantle-crust boundary: gabbros below ∼3,525 m have in general very low incompatible element mass fractions which develop upwards in a barely noticeable way to more differentiated compositions while Mg# decreases. More pronounced trends indicating progressive fractionation of ascending melts can be observed for incompatible elements and their element ratios as a consequence of in situ crystallization. Locally, more variable compositions within narrow depth intervals testify for advanced differentiation in situ within individual sills. Gabbros above ∼3,525 m become significantly more evolved and show considerable variations in composition. Fractional crystallization and mixing processes in a transient axial melt lens control the composition of isotropic “varitextured” gabbros and sheeted dike basalts where fractionation of high field strength elemental ratios is minor. New average compositions of fast-spread (paleo) oceanic crust are reported for major and 38 trace elements. Comparison with new data from Wadi Khafifah close to Wadi Gideah suggests robustness of crustal accretion processes in both space and time.

KW - oceanic crust

KW - Oman drilling project

KW - Samail ophiolite

KW - trace elements

KW - Wadi Gideah transect

KW - whole rock geochemistry

UR - http://www.scopus.com/inward/record.url?scp=85132874756&partnerID=8YFLogxK

U2 - 10.1029/2021JB022734

DO - 10.1029/2021JB022734

M3 - Article

AN - SCOPUS:85132874756

VL - 127

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 6

M1 - e2021JB022734

ER -