Understanding axial melt lens dynamics and lower crust accretion at fast-spreading mid-ocean ridges: new insights from drill cores obtained by the ICDP Oman Drilling Project
Mineralogy, Petrology and Geochemistry
Final Report Abstract
The Oman ophiolite (Samail massif; Sultanate Oman) is the largest sub-aerial exposure of oceanic lithosphere on Earth and provides the opportunity to study the accretion and alteration of oceanic lithosphere formed under fast-spreading conditions. This ophiolite was target for the drilling campaign Oman Drilling Project in the frame of ICDP, where three 400 m long cores have been drilled in order to penetrate the paleocrust of the ophiolite (GT1, GT2, and GT3). Based on samples of these drill cores and on surface samples collected in the Wadi Gideah of the Wadi-Tayin-Massif of the Oman Ophiolite, we started a research project, which focuses on four main scientific targets: (1) exploring of axial melt lens dynamics at the gabbro/dike transition, (2) investigating the nature of the transition between layered and foliated gabbro in the mid-crust (3) understanding the mechanisms of layer-forming processes in the deep, layered crust, and (4) testing the hypothesis that amphibole-bearing patches/veins formed in the magmatic-metamorphic regime are the results of initial cooling of the deep crust. It was one aim of the project to integrate petrographical, petrological, geochemical and micro-structural work (lattice preferred orientation using electron backscattering diffraction) on layered, foliated and varitextured gabbros. One significant outcome of the project, is the establishing of a ~5,000 m thick profile through the paleo lower oceanic crust of the Samail ophiolite with an exceptional spatial resolution, which serves as a reference profile though the lower crust of fast-spreading mid-ocean ridge systems. The main results are summarized as follows. Concerning understanding the process of layer formation in the layered gabbros of the lower crust, we performed an outcrop study applying a multidisciplinary approach and presented two layer formation models, as a function of the style of layering. For the formation of decimeter‐ scale modal layers we concluded that gravitational sorting in density currents is the key process. For creating millimeter‐scale olivine‐rich bands, we suggested cyclical nucleation and growth of large crystals at the expense of smaller ones as formation model. Concerning the Wadi Gideah reference profile, depth profiles of mineral compositions combined with petrological modeling, as well as microstructures analyzed by EBSD reveal insights into the mode of magmatic formation of fast-spreading lower oceanic crust, implying a hybrid accretion mechanism. The lower two thirds of the crust, mainly consisting of layered gabbros, formed via the injection of melt sills and in situ crystallization. Here, upward moving fractionated melts mixed with more primitive melts through melt replenishments, resulting in a slight but distinct upward differentiation trend. The upper third of the gabbroic crust is significantly more differentiated, in accord with a model of downward differentiation of a primitive parental melt originated from the axial melt lens located at the top of the gabbroic crust. Our hybrid model for crustal accretion requires a system to cool the deep crust, which was established by hydrothermal fault zones, initially formed on-axis at very high temperatures. Moreover, detailed investigations applying a multidisciplinary methodological approach on ICDP OmanDP crustal drill cores GT1 and GT2 provide new, profound insights into the magmatic accretion process of fast-spreading oceanic crust, with an unique spatial resolution of ~ 2m for the 400 m long cores, which has been not reached so far in gabbros of fast-spreading ocean crust. The data enable the identification of individual fractionation cycles in the decameter dimensions after replenishments, revealing incredible details of the fractionation/crystallization process in the deep fast-spreading crust, clearly showing that the accretion mode is in-situ crystallization within individual sills, and ruling out an accretion mode by subsiding crystal mushes from the axial melt lens sandwiched between the gabbro and the sheeted dike sequence (gabbro glacier model). The investigation of 36 varitextured gabbros of the OmanDP drill core GT3 provided new insights into the magmatic dynamics of the axial melt lens sandwiched between the gabbros and the sheeted dikes. The result revealed a complex formation with several evolution stages, with insitu crystallization as major process. Poikilitic domains formed first, corresponding to an early crystallization stage, where only plagioclase and clinopyroxene of more primitive composition crystallized. Later, domains of granular textures containing also interstitial amphibole and Fe-Ti oxide have been formed. The observed processes are very similar as those observed at IODP Site 1256 in the Eastern Equatorial Pacific, were, for the first time in IODP history, an intact dike/gabbro transition has been penetrated.
Publications
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Understanding lower crust accretion at fastspreading mid-ocean ridges: new insights from drill cores obtained by the ICDP Oman Drilling Project: First Results. DFG IODP/ICDP Colloquium 2018
D. Mock; B. Ildefonse; D. Garbe-Schönberg; S. Müller; D.A. Neave; J. Koepke & the Oman Drilling Project Phase 1 Science Party
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Wadi Gideah (Sumail Ophiolite, Sultanate Oman): A reference section through the lower fast-spreading oceanic crust. GeoBonn 2018
J. Koepke; D. Garbe-Schönerg; T. Müller; S. Müller; D. Mock; H. Strauss; S. Schuth & B. Ildefonse
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What Causes the Layering of Gabbros? – A Microanalytical and Microstructural Investigation on the Layering of two Gabbro Sections in the Oman Ophiolite. Annual DMG Meeting GeoBonn 2018
D. Mock; B. Ildefonse; D. Garbe-Schönberg; S. Müller; K. Faak; O. Namur & J. Koepke
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Dynamics at the roof of an oceanic magma chamber: Oman Drilling Project GT3 site survey. EGU 2019
C. Berthold; L. France; D. Mock; B. Ildefonse; D. Garbe-Schönberg; S. Müller; D.A. Neave & J. Koepke
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New Insights into Lower Crustal Accretion at Fast- Spreading Mid-Ocean Ridges – Petrological and Microstructural Results from the ICDP Oman Drilling Project. DFG IODP/ICDP Colloquium 2019
D. Mock; B. Ildefonse; D. Garbe-Schönberg; S. Müller; D.A. N eave; J. Koepke & the Oman Drilling Project Phase 1 Science Party
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On the formation of oceanic layered gabbros: drillcore GT1 of the ICDP Oman Drilling Project. Annual DMG Meeting GeoMünster 2019
D. Mock; B. Ildefonse; D. Garbe-Schönberg; S. Müller; D. A. Neave & J. Koepke
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Oxide gabbro intrusions of the dike-gabbro transition, Hole GT3A, Oman Drilling Project. EGU 2019
A. Jesus; J. Koepke & J. Mata
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The ICDP Oman Drilling Project: a status report. GeoMünster 2019
J. Koepke; D. Garbe-Schönerg; D. Mock & S. Müller
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A Reference Section through the lower crust in the Wadi Gideah (Sumail ophiolite, Sultanate Oman): the crustal drill sites within the ICDP OmanDP and related work. International Conference on Ophiolites and Oceanic Lithosphere, Muscat, 2020
J. Koepke; D. Garbe-Schönerg; T. Müller; D. Mock; S. Müller; S. Schuth & B. Ildefonse
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Crystallographic preferred orientations in Wadi Gideah (Oman) – refining a reference profile along lower oceanic crust. AGU conference 2020
D. Mock; B. Ildefonse; T. Müller; J. Koepke & the Oman Drilling Project Science Team
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Drillcore GT1 of the ICDP Oman Drilling Project: Implications from the Layered Gabbros on the Accretion of Lower Oceanic Crust. International Conference on Ophiolites and Oceanic Lithosphere, Muscat, 2020
D. Mock; B. Ildefonse; D. Garbe-Schönberg; S. Müller; D.A. Neave; J. Koepke & the Oman Drilling Project Phase 1 Science Party
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Drillcore GT1 of the ICDP Oman Drilling Project: insights into magmatic processes beneath fast-spreading mid-ocean ridges. GeoUtrecht 2020
D. Mock; B. Ildefonse; D. Garbe-Schönberg; S. Müller; D.A. Neave; J. Koepke & the Oman Drilling Project Phase 1 Science Party
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How does layering in lower oceanic crust form? A high-resolution study. DMG virtual poster session 2020
D. Mock; D.A. Neave; S. Müller; D. Garbe-Schönberg; O. Namur; B. Ildefonse & J. Koepke
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A profile through ancient fast-spreading oceanic crust in the Wadi Gideah, Oman ophiolite – reference frame for the crustal drillings within the ICDP Oman Drilling Project. GeoKarlsruhe 2021
J. Koepke; D. Garbe-Schönerg; D. Mock & S. Müller
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A Reference Section Through Fast‐Spread Lower Oceanic Crust, Wadi Gideah, Samail Ophiolite (Sultanate of Oman): Insights From Crystallographic Preferred Orientations. Journal of Geophysical Research: Solid Earth, 126(6).
Mock, Dominik; Ildefonse, Benoît; Müller, Tim & Koepke, Jürgen
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Accretion of fast-spread lower oceanic crust: drill core GT1 from the ICDP Oman Drilling Project. American Geophysical Union (AGU).
Mock Dominik, Neave David Axford; Müller Samuel, Garbe-Schönberg Dieter; Ildefonse Benoit, Koepke Jürgen & Science Team Oman Drilling Project
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Formation of Igneous Layering in the Lower Oceanic Crust From the Samail Ophiolite, Sultanate of Oman. Journal of Geophysical Research: Solid Earth, 126(1).
Mock, D.; Neave, D. A.; Müller, S.; Garbe‐Schönberg, D.; Namur, O.; Ildefonse, B. & Koepke, J.
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Rhythmic fracionation trends in lower layered gabbros: Evidence from hole GT1 Oman Drilling Project. DMG Annual meeting of the section Petrology and Petrophysics 2021
D. Mock; D.A.; Neave; S. Müller; D. Garbe-Schönberg; B. Ildefonse & J. Koepke
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Sill intrusions in lower oceanic crust: Implications from drill core GT1 of the Oman Drilling Project. European Mineralogical Conference 2021
D. Mock; D. A. Neave; S. Müller; D. Garbe-Schönberg; B. Ildefonse; J. Koepke & the Oman Drilling Project Science Team
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The ICDP Oman Drilling Project – Implications from drill core GT1 on magmatic processes beneath fast-spreading mid-ocean ridges. GeoKarlsruhe 2021
D. Mock; D. A. Neave; S. Müller; D. Garbe-Schönberg; B. Ildefonse; J. Koepke & the Oman Drilling Project Science Team
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Wet magmatic processes during the accretion of the deep crust of the Oman Ophiolite paleoridge: Phase diagrams and petrological records. Tectonophysics, 817(c(2021, 10)), 229051.
Koepke, J.; Feig, S.T.; Berndt, J. & Neave, D.A.
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A profile through fast-spreading oceanic crust in the Oman ophiolite: reference frame for the crustal drillings within the ICDP Oman Drilling Project . American Geophysical Union (AGU).
Koepke, Jürgen; Garbe-Schönberg, Dieter; Mock, Dominik & Müller; Samuel
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A Reference Section Through Fast‐Spread Lower Oceanic Crust, Wadi Gideah, Samail Ophiolite (Sultanate of Oman): Petrography and Petrology. Journal of Geophysical Research: Solid Earth, 127(1).
Koepke, J.; Garbe‐Schönberg, D.; Müller, T.; Mock, D.; Müller, S. & Nasir, S.
