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Isotopic variation in Semail Ophiolite lower crust reveals crustal-level melt aggregation

M.N. Jansen1,2,

1School of Earth and Ocean Sciences, Cardiff University, Cardiff, United Kingdom
2Faculty of Science, Vrije Universiteit, Amsterdam, the Netherlands

C.J. Lissenberg1,

1School of Earth and Ocean Sciences, Cardiff University, Cardiff, United Kingdom

M. Klaver3,

3School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom

S.J. de Graaff2,4,

2Faculty of Science, Vrije Universiteit, Amsterdam, the Netherlands
4Department of Analytical and Environmental Geochemistry, Vrije Universiteit Brussel, Brussels, Belgium

J.M. Koornneef2,

2Faculty of Science, Vrije Universiteit, Amsterdam, the Netherlands

R.J. Smeets2,

2Faculty of Science, Vrije Universiteit, Amsterdam, the Netherlands

C.J. MacLeod1,

1School of Earth and Ocean Sciences, Cardiff University, Cardiff, United Kingdom

G.R. Davies2

2Faculty of Science, Vrije Universiteit, Amsterdam, the Netherlands

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Jansen, M.N., Lissenberg, C.J., Klaver, M., de Graaff, S.J., Koornneef, J.M., Smeets, R.J., MacLeod, C.J., Davies, G.R. (2018) Isotopic variation in Semail Ophiolite lower crust reveals crustal-level melt aggregation. Geochem. Persp. Let. 8, 37–42.

MSc project at de Vrije Universiteit Amsterdam

Geochemical Perspectives Letters v8  |  doi: 10.7185/geochemlet.1827
Received 15 April 2018  |  Accepted 10 October 2018  |  Published 5 November 2018
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY 4.0




Figure 1 (a) Geological map of the lower crustal section at Wadi Abyad, in the Semail Ophiolite, Oman, with sample locations indicated (after MacLeod and Yaouancq, 2000

MacLeod, C.J., Yaouancq, G. (2000) A fossil melt lens in the Oman ophiolite: Implications for magma chamber processes at fast spreading ridges. Earth and Planetary Science Letters 176, 357-373.

; sample names were shortened by omitting the numerals ‘95’ preceding the letters ‘OC’ and ‘OG’ and ‘14’ preceding ‘OM’). (b) An outcrop at the base of the layered gabbros was sampled at ~15 cm intervals (one sample per modal layer).
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Figure 2 Age-corrected 143Nd/144Ndi of (a) single clinopyroxene and (b) plagioclase crystals in the Abyad section. Clinopyroxene has a near uniform composition whereas plagioclase shows variability outside analytical uncertainty. Grey and white alternating bars at the base of the section indicate the individual modal layers of the sampled layered gabbro outcrop (not to scale). Coloured bars at the bottom of the figure represent the uncertainty for the two most extreme samples.
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Figure 3 (a) Age-corrected 143Nd/144Ndi and 87Sr/86Sr compositions of plagioclase samples. Indian Ocean MORB data from the PetDB database and age-corrected to 96 Ma using model Sm/Nd and Rb/Sr ratios for depleted MORB mantle (Workman and Hart, 2005

Workman, R.K., Hart, S.R. (2005) Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231, 53-72.

). The ranges of whole rock age-corrected Sr and Nd isotope analyses of the plutonic and extrusive series of the Semail Ophiolite are shown in the inset (McCulloch et al., 1980

McCulloch, M.T., Gregory, R.T., Wasserburg, G.J., Taylor Jr, H.P. (1980) A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust. Earth and Planetary Science Letters 46, 201-211.

; Godard et al., 2006; Rioux et al., 2012

Rioux, M., Bowring, S., Kelemen, P., Gordon, S., Dudás, F., Miller, R. (2012) Rapid crustal accretion and magma assimilation in the Oman-U.A.E. ophiolite: High precision U-Pb zircon geochronology of the gabbroic crust. Journal of Geophysical Research: Solid Earth 117, B07201.

, 2013

Rioux, M., Bowring, S., Kelemen, P., Gordon, S., Miller, R., Dudas, F. (2013) Tectonic development of the Samail ophiolite: High‐precision U‐Pb zircon geochronology and Sm‐Nd isotopic constraints on crustal growth and emplacement. Journal of Geophysical Research: Solid Earth 118, 2085-2101.

; de Graaff, 2016

De Graaff, S. (2016) Did the Oman Ophiolite form above a subduction zone? Evidence from widespread later-stage intrusions in the Central and Southeastern Semail Ophiolite. MSc thesis, Vrije Universiteit Amsterdam, 42 pp.

). (b) Age-corrected 143Nd/144Ndi and 147Sm/144Nd ratios show no correlation, whereas the present day Indian Ocean MORB array, shown for comparison, displays a broad positive correlation. Coloured bars in the centre panel represent the uncertainty in 143Nd/144Ndi for the two most extreme samples.
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Figure 4 Comparison of the ranges in Nd isotopes found in this study with previous results of the Semail Ophiolite (McCulloch et al., 1980

McCulloch, M.T., Gregory, R.T., Wasserburg, G.J., Taylor Jr, H.P. (1980) A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust. Earth and Planetary Science Letters 46, 201-211.

; Benoit et al., 1996

Benoit, M., Polvé, M., Ceuleneer, G. (1996) Trace element and isotopic characterization of mafic cumulates in a fossil mantle diapir (Oman ophiolite). Chemical Geology 134, 199-214.

; Godard et al., 2006; Rioux et al., 2012

Rioux, M., Bowring, S., Kelemen, P., Gordon, S., Dudás, F., Miller, R. (2012) Rapid crustal accretion and magma assimilation in the Oman-U.A.E. ophiolite: High precision U-Pb zircon geochronology of the gabbroic crust. Journal of Geophysical Research: Solid Earth 117, B07201.

, 2013

Rioux, M., Bowring, S., Kelemen, P., Gordon, S., Miller, R., Dudas, F. (2013) Tectonic development of the Samail ophiolite: High‐precision U‐Pb zircon geochronology and Sm‐Nd isotopic constraints on crustal growth and emplacement. Journal of Geophysical Research: Solid Earth 118, 2085-2101.

; de Graaff, 2016

De Graaff, S. (2016) Did the Oman Ophiolite form above a subduction zone? Evidence from widespread later-stage intrusions in the Central and Southeastern Semail Ophiolite. MSc thesis, Vrije Universiteit Amsterdam, 42 pp.

). Range for repeated analyses of BCR-2 reference material is indicated by the green (1.9-2.6 ng Nd) and blue (0.15-0.34 ng Nd) bars (displayed at an arbitrary position on the x-axis).
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