Magma mush dynamics during oceanic crust accretion
Laboratoire CRPG – Thème MAGMAS & FLUIDS PROFONDS
Encadrement – Directeur : Lydéric France (MCf-HDR) lyderic.france@univ-lorraine.fr
Co-directeur : Pierre Bouilhol (MCf) pierre.bouilhol@univ-lorraine.fr
Project Summary :
Nearly 2/3 of the Earth’s surface is covered by oceanic crust formed at mid-ocean ridges where over 70% of the total magmatic budget is concentrated. Over the last few decades, it has been shown that the magmatic system present at both fast- (FSR) and slow-spreading ridges (SSR), which was long considered as an essentially molten system (and therefore mobilizable to feed other reservoirs and/or eruptions on the seafloor), is instead formed of a crystal-rich medium (the mush): a magmatic ensemble with a high crystalline fraction making it non-mobilizable. This ultimately influence the expected thermal regime, magma migration patterns, and magmatic processes that shape the crust through differentiation, and magma migration and emplacement. Specifically, the first order igneous processes that govern the modes of differentiation, and that have been considered for decades to be mainly fractional crystallization (operating in crystal-poor environments) are now being re-assessed in the light of a reactive porous flow (RPF) model which remains ill constrained [1-6] . The objectives of this PhD project will be 1/ to provide new constraints on the early evolution of these systems (is there an initial crystal-poor phase during which magmas would be mobile, and fractional crystallization likely to occur?), and 2/ to provide quantitative assessment on the differentiation process that seems to govern crustal differentiation: reactive porous flow.
The project will rely on a quantitative petrographic and geochemical approach focusing on mineral phase morphologies, rock textures, and phase compositions. A high resolution petrological approach will provide new constraints on the RPF using in-situ chemical mapping, coupling major-minor elements [EPMA], and trace elements [LA-ICP-MS] data, allowing an unprecedented insight into the modus operandi of RPF. Samples previously identified as key in the study of RPFs in the oceanic domain (Oman, East-Pacific Rise, SW Indian Ridge, Mid-Atlantic Ridge) will be used for this purpose. In a second step, thermodynamic modeling (PerpleX) will provide a thorough evaluation of the identified processes, allowing an in-depth quantification of the fate of melt forming oceanic crust. We foresee that the results of this PhD project will have broader implications for the magmatic petrology community as reactive processes (RPFs) seems to govern magmatic systems in general [7-10] , anchoring this project as strong foundations for future studies on magmatic plumbing systems.
Candidate Profile & Applications:
Master’s degree in Geosciences. Research project experience in igneous petrology. Profiles with thermodynamic modeling and/or analytical skills will be appreciated. Applications are done directly via the ADUM website, but do not hesitate to contact the supervisors before applying.
References :
[1] Lissenberg CJ, Dick HJB (2008) Melt–rock reaction in the lower oceanic crust and its implications for the genesis of mid-ocean ridge basalt. Earth and Planetary Science Letters, 271, 311–325.
[2] Drouin M., Godard M., Ildefonse B., Bruguier O., Garrido C.J. (2009) Geochemical and petrographic evidence for magmatic impregnation in the oceanic lithosphere at Atlantis Massif, Mid-Atlantic Ridge (IODP Hole U1309D, 30°N). Chem. Geol. 264: 71–88.
[3] Sanfilippo A., Tribuzio R., Tiepolo M., Berno D. (2015) Reactive flow as dominant evolution process in the lowermost oceanic crust: evidence from olivine of the Pineto ophiolite (Corsica). Contributions to Mineralogy and Petrology, 170(4), 38.
[4] Lissenberg C.J. MacLeod C.J., Bennett E.N. (2019) Consequences of a crystal mush dominated magma plumbing system: a mid-ocean ridge perspective. Philosophical Transactions of the Royal Society A, 377(2139), 20180014.
[5] Boulanger M, France L, Deans JR, Ferrando C, Lissenberg CJ, von der Handt A (2020) Magma reservoir formation and evolution at a slow-spreading center (Atlantis Bank, Southwest Indian Ridge). Frontiers in Earth Science
[6]Boulanger M, France L (2023) Cumulate formation and melt extraction from mush-dominated magma reservoirs: The melt flush process exemplified at Mid-ocean ridges. Journal of Petrology 64:1-20.
[7] Leuthold J., Müntener O., Baumgartner L.P., Putlitz B. (2014) Petrological constraints on the recycling of mafic crystal mushes and intrusion of braided sills in the Torres del Paine mafic complex (Patagonia). J. Petrol. 55, 917–949.
[8] Bouilhol, P., Schmidt, M. W., & Burg, J. P. (2015). Magma transfer and evolution in channels within the arc crust: the pyroxenitic feeder pipes of Sapat (Kohistan, Pakistan). Journal of Petrology, 56(7), 1309-1342.
[9] Bachmann O, Huber C (2016) Silicic Magma reservoirs in the Earth’s Crust. Am. Mineral., 101, 2377–2404.
[10] Cashman KV, Sparks RSJ, Blundy JD (2017) Vertically extensive and unstable magmatic systems: a unified view of igneous processes. Science, 355-6331.