gabbro; ophiolite; MORB; crystal-melt reaction; experimental petrology; spreading ridges
Leuthold Julien, Gilli Adrian (2019), Translating Scientific Articles to the Non-scientific Public Using the Wikipedia Encyclopedia, in Frontiers in Education
, 4, 1-10.
Ewing Tanya, Müntener Othmar, Leuthold Julien, Ramírez de Arellano Cristóbal, Baumgartner Lukas P, Schaltegger Urs (2018), The zircon Hf isotope archive of rapidly changing mantle sources in the south Patagonian retro-arc, in Geochimica et Cosmochimica Acta
, 131(3-4), 587-608.
Rezeau Hervé, Leuthold Julien, Tayan Rodrik, Hovakimyan Samvel, Kouzmanov Kalin, Moritz Robert (2018), Incremental growth of mid- to upper-crustal magma bodies during Arabia-Eurasia convergence and collision: A petrological study of the calc-alkaline to shoshonitic Meghri-Ordubad Pluton, in Journal of Petrology
, 59(5), 931-966.
Leuthold Julien, Lissenberg C. Johan, O'Driscoll Brian, Karakas Ozge, Falloon Trevor, Klimentyeva Dina N., Ulmer Peter (2018), Partial Melting of Lower Oceanic Crust Gabbro: Constraints From Poikilitic Clinopyroxene Primocrysts, in Frontiers in Earth Science
, 6, 1-20.
Rickli Jörg, Hindshaw Ruth S., Leuthold Julien, Wadham Jemma L., Burton Kevin W., Vance Derek (2017), Impact of glacial activity on the weathering of Hf isotopes – Observations from Southwest Greenland, in Geochimica et Cosmochimica Acta
, 215, 295-316.
Rezeau Hervé, Moritz Robert, Leuthold Julien, Hovakimyan Samvel, Tayan Rodrik, Chiaradia Massimo (2017), 30 Myr of Cenozoic magmatism along the Tethyan margin during Arabia–Eurasia accretionary orogenesis (Meghri–Ordubad pluton, southernmost Lesser Caucasus), in Lithos
, 288-289, 108-124.
Fiedrich Alina M., Bachmann Olivier, Ulmer Peter, Deearing Chad D., Kunze Karsten, Leuthold Julien (2017), Mineralogical, geochemical, and textural indicators of crystal accumulation in the Adamello Batholith (Northern Italy), in American Mineralogist
, 102, 2467-2483.
MORB (i.e. Mid Ocean Ridge Basalt, erupted along spreading ridges) covers 70% of the Earth surface. Its composition is used to estimate the mantle source partial melting conditions and composition. However, closely associated lavas and melt inclusions may cover a very wide geochemical range. Expensive 1D drilling projects in active spreading ridges and studies on ophiolites (i.e. obducted [i.e. lifted in a mountain chain] fossil oceanic crust and mantle) provide important constrains on spreading ridges processes. The original complexity in structures and lithologies is additionally complicated by cumulate-liquid reactions, resulting in significant mineralogical, textural and chemical variations of cumulate rocks and percolating liquid. Although this has important implications, it is frequently neglected. Along spreading ridges, successive mantle-derived melt batches intrude, percolate and react with the oceanic lithosphere. Current models state that mantle rocks react with ascending, percolating mantle-derived pyroxene-undersaturated melt that are responsible for the formation of the dunitic transition zone (i.e. a hundreds of meter thick olivine-rich rocks layer below the Moho [i.e. the mantle - crust interface]). Trapped mantle-derived melt crystallizes as gabbro (i.e. olivine + plagioclase + clinopyroxene-rich rocks) lenses similar to the lower crustal layered gabbro, and clinopyroxene and Cr-spinel saturated melts (pyroxenite, wehrlite, chromitite) intrudes the lower crust. Dunite and troctolite also occur within the lower oceanic crust. Their petrogenesis is strongly debated. In the analogue successively replenished Rum shallow layered intrusion, Leuthold et al. (2014a) have recently demonstrated and quantified gabbro partial melting and mixing with intruded reactive picrite (i.e. hot mafic basalt). The products are clinopyroxene-poor gabbro, troctolite and dunite restites and clinopyroxene- and Cr-enriched liquids. The latter crystallized abundant chemically distinct clinopyroxene rims around partly resorbed clinopyroxene relics in melt channels, veins of pyroxenite and spinel, as illustrated by the following reaction: initial rock (Olivine1 +Plagioclase1 +Clinopyroxene1) + hot reactive melt (picrite) = restite (Olivine1 ±Plagioclase1 relics) + modified melt (Clinopyroxene-rich basalt) = modified rock (Olivine2 +Plagioclase2 +Clinopyroxene2 +Spinel)Applying our model to (fast-)spreading ridges, I suggest: 1) Some lower oceanic crust and dunitic transition zone dunites and troctolites formed by olivine ± plagioclase fractionation from hot picrite, from gabbroic crystal mush re-heating and from gabbro cumulate partial melting; 2) Late stage clinopyroxenite, gabbronorite and wehrlite (i.e. olivine + pyroxene ± plagioclase-rich rocks) crystallized from pyroxene-saturated gabbro partial melts mixed with invading mantle-derived hot melt. MORB liquid represents fractionated mantle-derived melt, hybridized during percolation through the oceanic crust filter. For the first time, I will use experimental petrology, combined with field observations, mineral micro-textures, bulk rock and mineral geochemistry and numerical modelling, to quantify melt-rock interactions in the lower oceanic crust. I will start with field campaigns to the world´s best studied Oman ophiolite, and the distinctly fresh Leka ophiolite (Norway). I will acquire micro-textural and micro-analytical data on collected and lent samples to testify melt-rock interactions evidenced by reactions and distinct mineral generations. The preliminary results are very promising. I will run and analyse three sets of experiments at ETHZ, in collaboration with Prof. Peter Ulmer: (1) phase equilibria experiments of mantle-derived melt at lower crust pressure, (2) experiments of mantle-derived melt equilibrated with gabbro and (3) kinetic experiments of mantle-derived melt percolation into gabbro. Thanks to a multi-disciplinary approach, I will produce a robust quantitative numerical model about reactive liquid flow in the oceanic lower crust and its effect on the MORB liquid line of descent and the percolated lower oceanic crust. The outcomes will offer a new vision on the evolution of mantle-derived melt, with important consequences for spreading ridges processes and mantle geochemistry.