Partial melting

Partial melting is the phenomenon that occurs when a rock is subjected to temperatures high enough to cause certain minerals to melt, but not all of them. Partial melting is an important part of the formation of all igneous rocks and some metamorphic rocks (e.g., migmatites), as evidenced by a multitude of geochemical, geophysical and petrological studies. The parameters that influence partial melting include the composition of the source rock, the pressure and temperature of the environment, and the availability of water or other fluids. As for the mechanisms that govern partial melting, the main are decompression melting and flux melting. Decompression melting occurs when rocks are brought from higher to lower pressure zones in the Earth's crust, lowering the melting point of its mineral components, thus generating a partial melt. Flux melting, on the other hand, occurs when water and other volatiles get in contact with hot rock, reducing the melting point of miner

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Weekly to monthly time scale of melt inclusion entrapment prior to eruption recorded by phosphorus distribution in olivine from mid-ocean ridges

Lukas Baumgartner, Stéphane Laurent Escrig, Mélina Manzini, Anders Meibom

Melt inclusions (MIs) hosted in euhedral olivine have been proposed to represent droplets of primary melt, protected from processes occurring near Earth's surface during eruption. The complex zoning of phosphorus (P) in some olivines and the presence of a P-depleted zone around MIs indicate a complex history for the host-MI system. We analyzed P in olivine and MIs from two mid-oceanic ridge basalt (MORB) samples from the Mid-Atlantic Ridge (MAR) by electron probe microanalyzer, secondary ion mass spectrometry (SIMS), and NanoSIMS. Phosphorus dendrites in olivine suggest an initial fast olivine growth followed by a stage of slower growth. Dissolution textures around some MIs were identified and were probably caused by adiabatic decompression melting. Based on diffusion modeling of P in olivine, we infer that olivine beneath the MAR remains in the system (1) for days to weeks after crystallization of P-rich lamellae, and (2) for a few hours after recrystallization of dissolved olivine. Dissolution and reprecipitation of olivine containing boundary layers suggests that most MIs might be affected by late post-entrapment processes.

Geological Soc Amer, Inc2017

Re-Os isotopic evidence for long-lived heterogeneity and equilibration processes in the Earth's upper mantle

Reto Frei, Anders Meibom

The geochemical composition of the Earth's upper mantle(1-3) is thought to reflect 4.5 billion years of melt extraction, as well as the recycling of crustal materials. The fractionation of rhenium and osmium during partial melting in the upper mantle makes the Re-Os isotopic system well suited for tracing the extraction of melt and recycling of the resulting mid-ocean-ridge basalt(3). Here we report osmium isotope compositions of more than 700 osmium-rich platinum-group element alloys derived from the upper mantle. The osmium isotopic data form a wide, essentially gaussian distribution, demonstrating that, with respect to Re-Os isotope systematics, the upper mantle is extremely heterogeneous. As depleted and enriched domains can apparently remain unequilibrated on a timescale of billions of years, effective equilibration seems to require high degrees of partial melting, such as occur under mid-ocean ridges or in back-arc settings, where percolating melts enhance the mobility of both osmium and rhenium. We infer that the gaussian shape of the osmium isotope distribution is the signature of a random mixing process between depleted and enriched domains, resulting from a 'plum pudding' distribution in the upper mantle, rather than from individual melt depletion events.

2002

Are high He-3/He-4 ratios in oceanic basalts an indicator of deep-mantle plume components?

Reto Frei, Anders Meibom

The existence of a primordial, undegassed lower mantle reservoir characterized by high concentration of He-3 and high He-3/He-4 ratios is a cornerstone assumption in modern geochemistry. It has become standard practice to interpret high He-3/He-4 ratios in oceanic basalts as a signature of deep-rooted plumes. The unfiltered He isotope data set for oceanic spreading centers displays a wide, nearly Gaussian, distribution qualitatively similar to the Os isotope (Os-187/Os-188) distribution of mantle-derived Os-rich alloys. We propose that both distributions are produced by shallow mantle processes involving mixing between different proportions of recycled, variably aged (.) radiogenic and unradiogenic domains under varying degrees of partial melting. In the case of the Re-Os isotopic system, radiogenic mid-ocean ridge basalt (MORB)-rich and unradiogenic (depleted mantle residue) endmembers are constantly produced during partial melting events. In the case of the (U+Th)-He isotope system, effective capture of He-rich bubbles during growth of phenocryst olivine in crystallizing magma chambers provides one mechanism for 'freezing in' unradiogenic (i.e. high He-3/He-4) He isotope ratios, while the higher than chondritic (U+Th)/He elemental ratio in the evolving and partially degassed MORB melt provides the radiogenic (i.e. low He-3/He-4) endmember. If this scenario is correct, the use of He isotopic signatures as a fingerprint of plume components in oceanic basalts is not justified. Published by Elsevier Science B.V.

2003

Subduction

Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a

Igneous rock

Igneous rock (igneous ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma o

Basalt

Basalt (UKˈbæsɔːlt,_-əlt; USbəˈsɔːlt,_ˈbeɪsɔːlt) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava)

CIVIL-211: Geology

Les ingénieurs civils exercent leurs activités en constante interaction avec le sous-sol. Le cours de géologie donne aux étudiants les bases en Géosciences nécessaires à une ingénierie bien intégrée dans le contexte de notre planète.

MICRO-470: Scaling laws & simulations in micro & nanosystems

This class combines an analytical and finite elements modeling (FEM) simulations approach to scaling laws in MEMS/NEMS. The dominant physical effects and scaling effects when downsizing sensors and actuators in microsystems are discussed, across a broad range of actuation principles.