Evidence of different structures in magnesium silicate liquids: coordination changes in forsterite- to enstatite-composition glasses

Wilding, Martin C.; Benmore, C. J.; Tangeman, Jean A.; Sampath, Sujatha

doi:10.1016/j.chemgeo.2004.08.055

Cited by 83 publications

(95 citation statements)

References 29 publications

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“…S-1b). The lighter Mg isotopic composition of olivine and orthopyroxene as compared with basaltic melt is broadly consistent with stable isotope theory (Wilding et al, 2004;Henderson et al, 2006), given that Mg is in six-fold and five-fold coordination in olivine-orthopyroxene crystals and silicate melts, respectively. Moreover, the high MgO contents of large degree melts of the vestan silicate mantle along with the lower pressure crystallisation on this protoplanet are predicted to result in even lower Mg coordination in vestan silicate melts than terrestrial magmas (Wilding et al, 2004).…”

Section: Figuresupporting

confidence: 58%

Tracking the formation of magma oceans in the Solar System using stable magnesium isotopes

Schiller¹,

Dallas²,

Creech³

et al. 2017

Geochem. Persp. Let.

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Vesta (Greenwood et al., 2005), or giant impacts such as the Moon-forming event in the case of the Earth and Moon (Tonks and Melosh, 1993). As such, finding robust geochemical fingerprints of these ancient magma oceans is important for understanding the earliest stages of planetary evolution.A range of newly developed stable isotope systems are yielding novel insights into planetary accretion, differentiation and evolution (e.g., Greenwood et al., 2005;Georg et al., 2007). However, many of these systems are multiply affected by a range of processes, potentially including core formation and crystallisation of accessory minerals, which makes interpretation of such data challenging. The lithophile, major element magnesium (Mg) is almost unique in this regard, as stable isotope fractionation in magmatic systems will be almost entirely controlled by crystallisation of high-Mg, mafic minerals, assuming isotopic fractionations exist between such minerals and magma.The large degree of planetary melting required to generate a magma ocean would produce highly magnesian magmas, which would then subsequently crystallise large amounts of mafic, Mg-rich minerals such as olivine. Small Mg stable isotope fractionations exist between co-existing terrestrial mantle olivine, orthopyroxene and clinopyroxene, with olivine being the isotopically lightest phase (Handler et al., 2009;Young et al., 2009;Pogge von Strandmann et al., 2011;Xiao et al., 2013). Consequently, it should also be possible to detect progressive Mg isotope changes in the products of a crystallising magma ocean.Vesta is the second largest asteroid in the Solar System and comprises a metal core, silicate mantle and crust (Russell et al., 2012). Based on spectral observations and the Dawn Mission, the howardite-eucrite-diogenite (HED) meteorite suite is inferred to come from Vesta (McCord et al., 1970;Binzel and Xu, 1993; Russell et al., 2012). Most HED meteorites also share common nucleosynthetic isotope signatures for some elements that demonstrate their genetic affinity (Greenwood et al., 2005). These lithologically diverse meteorites provide a unique archive of the timing and processes of protoplanet formation and differentiation. Diogenites are mostly orthopyroxenites, and are conventionally viewed as cumulate igneous rocks formed in a magma ocean or bodies on Vesta, whereas eucrites are basaltic and gabbroic rocks predominantly composed of pigeonite and plagioclase (Mittlefehldt, 2014).Despite many decades of petrological, geochemical and chronological study, the petrogenesis of eucrites and diogenites and the relationship between them remain enigmatic. End-member models include limited partial melting or extensive (i.e. magma ocean) melting of Vesta (Stolper, 1977; Mandler and ElkinsTanton, 2013;Mittlefehldt, 2014). Nearly all models are difficult to reconcile with the large range of incompatible trace element concentrations in diogenites and eucrites. However, a recent study by Mandler and Elkins-Tanton (2013) has used both chemical and physical arguments to ...

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Section: Figuresupporting

confidence: 58%

Tracking the formation of magma oceans in the Solar System using stable magnesium isotopes

Schiller¹,

Dallas²,

Creech³

et al. 2017

Geochem. Persp. Let.

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“…It appears in both the F Ti (Q) and F noTi (Q) functions, indicating that it is also associated with the organization of both Ti atoms and the alumino-silicate network. [32]. The intense peak at 2.66Å is mainly due to O-O correlations, as is the peak at 5.1Å.…”

Section: Neutron Diffraction Datamentioning

confidence: 99%

Environment of titanium and aluminum in a magnesium alumino-silicate glass

Guignard

Cormier

Montouillout

et al. 2009

J. Phys.: Condens. Matter

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The structure of the glass 2MgO-2Al 2 O 3 -5SiO 2 -TiO 2 was investigated using neutron diffraction with isotopic substitution. Reverse Monte Carlo (RMC) modeling was used to reproduce experimental structure factors derived from diffraction experiments. The local environment of titanium atoms was determined and it corresponds to an average of 5.4 ± 0.2 oxygen atoms at a mean distance of 1.86 ± 0.02Å. This coordination number agrees with the predominance of fivefold coordination, with the coexistence of four-and sixfold coordination in similar amounts. 27 Al nuclear magnetic resonance (NMR) results revealed that the proportion of highly coordinated aluminum atoms in this titanium-bearing glass was higher than in the titanium-free sample. RMC modeling was used to interpret the structural role of these [5] Al species and we show a trend for preferential bonding between [5] Al and Ti atoms. This favored linkage is important to understand the role of titanium dioxide as a nucleating agent in inorganic glass-ceramics fabrication.

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“…Liquid II lacks a silicate network. In MgOSiO 2 glasses there is an increase in area of the Mg-O correlation at 2.0 Å in the glasses between 38% and 33% SiO 2 an increase in coordination number from 4.5 to 5.0 [17,18]. Kohara [23] has used combined neutron and highenergy diffraction data in reverse Monte Carlo models of the 33% SiO 2 (forsterite) glass structure to suggest that Mg-O forms a distorted MgO n (n = 4, 5, 6) polyhedron edge shared with other Mg-O polyhedra to form a percolation domain.…”

Section: The Structure Of Mgo-sio 2 Liquidsmentioning

confidence: 99%

“…Glasses produced in the MgO-SiO 2 system between the compositions of the two important mantle minerals forsterite and enstatite show changes in structure [17,18] that coincides with changes in the relaxation properties of these glasses [19,20]. These rheological changes reflect differences in the configurational entropy of the liquid and in the terminology of Angell this is a change in the liquid fragility [7,21,22].…”

Section: Introductionmentioning

confidence: 99%

In situ diffraction studies of magnesium silicate liquids

2008

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Primitive MgO-SiO 2 liquids dominate the early history of the Earth and Terrestrial planets. The structures of these liquids and structure-dependent properties, such as viscosity and diffusion, are considered important in the evolution of these planets, however, MgO-SiO 2 liquids are refractory and do not form glasses easily and it is difficult to measure the structure of these liquids. Container-less synthesis techniques have been used to produce glasses that range in composition from 50 to 33% SiO 2 , corresponding to the compositions of two important mantle minerals: enstatite and forsterite. The structure of these glasses has been determined using combined neutron and high-energy diffraction and show changes in the short-range order as a function of composition. These changes include a jump in Mg-O coordination number at the limit to the formation of the silicate network in forsterite composition glass. These results imply a similar change in the structure of the liquid. Accordingly, the structures of forsterite and enstatite liquids have been determined using high-energy X-rays and a specialized sample environment, a containerless levitator. The main qualitative structural differences between MgSiO 3 and Mg 2 SiO 4 glasses are also observed in the melt. Liquid MgSiO 3 is interpreted as forming a relatively 'strong' network of SiO 4 tetrahedra, whereas the Mg 2 SiO 4 liquid is ''fragile'' and dominated MgO n (n = 4, 5, 6) polyhedra and highly mobile oxygen ions. The results differ significantly from previously reported X-ray diffraction data for liquid MgSiO 3 .

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Evidence of different structures in magnesium silicate liquids: coordination changes in forsterite- to enstatite-composition glasses

Cited by 83 publications

References 29 publications

Tracking the formation of magma oceans in the Solar System using stable magnesium isotopes

Tracking the formation of magma oceans in the Solar System using stable magnesium isotopes

Environment of titanium and aluminum in a magnesium alumino-silicate glass

In situ diffraction studies of magnesium silicate liquids

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