Melt inclusions

Thomas JB, Bodnar RJ, Shimizu N, Sinha AK (2002) Determination of zircon/melt trace element partition coefficients from SIMS analysis of melt inclusions in zircon. Geochim Cosmochim Acta 66 2887-2901 Thompson GM, Malpas J (2000) Mineral/melt partition coefficients of oceanic alkali basalts determined on natural samples using laser ablation-inductively eouple plasma-mass spectrometry (LAM-ICP-MS). Mineral Mag 64 85-94... 

Roedder E. and Wieblen P W. (1971). Lunar petrology of silicate melt inclusions, Apollo 11 rocks. Proc. Apollo 11 Lunar Scl Conf, 1 801-837. 

The change of melt inclusion composition by diffusion through the host mineral... 

Figure 3-3c displays the steady-state concentration profile for a spherical shell. One application of this solution is for a spinel crystal inside a magma chamber, where the spinel contains a large melt inclusion at its core. The diffusion profile in the spinel (which is a spherical shell) in equilibrium with the melt inclusion and the outside melt reservoir would follow Equation 3-3 Ig. 

For simplicity, the melt inclusion is assumed to be (i) spherical, and (ii) concentric with the spherical crystal shell (Figure 4-33). Furthermore, the host mineral is assumed to be isotropic in terms of diffusion. The concentric assumption and the isotropic assumption are rarely satisfied. Nonetheless, for order of magnitude estimate, these assumptions make the problem easy to treat. 

Because diffusion in the melt inclusion is orders of magnitude faster than in the crystal, we assume that the melt composition is uniform. The inclusion radius is Ri, and the outer radius of the host is Rz- For the component under consideration, the concentration in the melt inclusion is Q, the concentration in the outside melt (bulk melt) is Cg. The partition coefficient between the crystal and melt is K so that the concentration of the component in the mineral host is Ci=KCi at r = Ri (inclusion-host interface) and C2=KC at r=f 2- The partition coefficient K may be larger or smaller than 1. 

Two end-member cases of approximate treatments are considered. In one end-member case, the extra mass of the component in the melt inclusion is not very high compared to the mass of the component in the crystal (i.e., K is not... 

Figure 4-33 A schematic diagram showing a melt inclusion inside a host mineral. For simplicity, the inclusion and the host are assumed to be concentric.

In the other end-member scenario, the mass of the component in the host mineral is negligible. A quasi-steady-state diffusion profile is established in the host crystal and the melt inclusion maintains the concentration on the inner surface. The steady-state concentration profile would be (Equation 3-3 Ig)... 

The timescale for the melt inclusion to move significantly toward equilibrium is max(Ti, tz)- The exact percentage toward equilibrium at f = max(ri, xz) is not quantified above, but is expected to be significant, e.g., between 20 and 80%. 

Example 4.2. Consider H2O in a rhyolite melt inclusion in quartz. The radius of the inclusion is 100/ m. The quartz radius is 1mm. The partition coefficient between quartz and melt is estimated to be 10 . Assume that the diffusivity of H2O in quartz is 10 °m /s. Find the re-equilibration timescale. 

A melt inclusion and its olivine host are concentric spheres of radius R- and / 2. Consider H2O in the melt inclusion and its re-equilibration with ambient melt outside olivine. Ignore anisotropy of olivine. If / i=0.1mm, / 2 = 1 mm, H2O diffusivity in olivine is D = 10 " m /s, K=0.000, find the reequilibration timescale. 

Consider Ca in a basaltic melt inclusion concentric with the host mineral olivine. The radius of the inclusion is SOfim. The olivine radius is 1 mm. The Ca partition... 

Thomas R. (2000) Determination of water contents of granite melt inclusions by confocal laser Raman microprobe spectroscopy. Am. Mineral. 85, 868-872. 

De Astis et al. (2000) and Calanchi et al. (2002b) noticed that calc-alkaline and HKCA basalts at Vulcano and Panarea have distinct trace element ratios (e.g. La/U, Rb/Zr, Zr/Nb) compared to the associated sho-shonitic and KS mafic volcanics. However, the rocks of the Calabro-Peloritano basement underlying the Aeolian volcanoes show compositions that resemble the calc-alkaline rather than shoshonitic and KS rocks this was interpreted to exclude a derivation of potassic rocks from calc-alkaline parents via crustal assimilation. The same conclusion was drawn by Frez-zotti et al. (2004), who modelled magma contamination processes using melt inclusions entrapped in metamorphic xenoliths as contaminants. 

REE patterns are fractionated for all the rocks, but tholeiites show lower La/Yb ratios than alkaline products (Fig. 8.5a). Incompatible element patterns normalised to primordial mantle compositions for mafic rocks are very different from the Aeolian arc and central-southern Italian peninsula. Both tholeiitic and alkaline basalts show a marked upward convexity, with negative spikes of K (Fig. 8.5b). Note, however, that there are also negative anomalies for Hf and Ti, which are uncommon in most Na-alkaline basalts from intraplate settings (e.g. Wilson 1989). Overall, the Etna magmas have been found to be more enriched in volatile components than common intraplate magmas, and water contents up to 3-4 wt % have been found by melt inclusion studies (Corsaro and Pompilio 2004 Pompilio, personal communication). 

Frezzotti ML, Peccerillo A, Bonelli R (2003) Magma ascent rates and depths of crustal magma reservoirs beneath the Aeolian volcanic arc (Italy) inferences from fluid and melt inclusions in xenoliths. In De Vivo B, Bodnar RJ (eds) Melt Inclusions in Volcanic Systems Methods, Applications and Problems. Elsevier, Amsterdam, pp 185-205... 

Along with studies of melt inclusions, the study of mantle xenoliths (samples of mantle material entrained and brought to the surface in eruption magmas) and exhumed mantle rocks is one of the most common applications of SIMS for trace element analysis. SIMS is ideally suited to this task, as there is no need to try to make mineral separates from what are often limited amounts of sample, alteration can be prevented, and zoning easily studied. 

De Vivo, B., Lima, A., Kamenetsky, V. S., and Danyushevsky, L. V. (2006). Fluid and melt inclusions in the sub-volcanic environments from volcanic systems Examples from the Neapolitan area and Pontine islands (Italy). In Melt Inclusions in Plutonic Rocks (J. D. Webster, ed.), pp. 211-237. Mineralogical Association of Canada Short Course 36, Montreal, Quebec. 

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