Contrasted Liquid Lines of Descent Revealed by Olivine-hosted Melt Inclusions and the External Magma

Abstract

To better understand the significance of the chemical compositions of forsterite-hosted melt inclusions, dynamic crystallization experiments were performed at atmospheric pressure and a low cooling rate (28C h À1 ) on a starting glass material with a composition in the CMAS system (12·21wt % CaO, 28·48 wt % MgO, 11·96 wt % Al 2 O 3 , 47·32 wt % SiO 2 ). Experiments were quenched at various temperatures, both above and below the theoretical solidus. Olivine is the liquidus phase and the mesostasis may exhibit a second crystalline phase corresponding to a metastable Al-rich pyroxene. Olivine crystal morphologies change from polyhedral to skeletal, depending on the quenching temperature. Regardless of the quenching temperature, the chemical compositions of liquids trapped in melt (now glass) inclusions in the olivines do not contain the boundary layer that should result from rapid growth of these crystals. The liquid compositions also show that down to temperatures far below the theoretical solidus, olivine is the only phase that crystallizes on the walls of these inclusions. Glass inclusion analyses can therefore be used to determine the chemical evolution of a liquid in metastable equilibrium with the host olivine, irrespective of the quenching temperature. Melt inclusions therefore follow their own liquid line of descent distinct from that of the whole charge. This experimental study suggests that it should be possible to (1) draw the metastable extensions of the liquidus from natural glass inclusions and (2) determine the real supersaturation degrees of the residual magmas.

Martian meteorite Tissint records unique petrogenesis among the depleted shergottites

“…However, it has been observed in terrestrial and lunar samples and through experimental studies that under metastable conditions pyroxene may have Al‐excess (Grove and Bence ; Shearer et al. ; Faure and Tissandier ). For example, Al‐enrichment in late‐stage pyroxene took place in the mare basalt 15499 due to rapid rate of crystallization and that delayed plagioclase saturation (Shearer et al.…”

Out-of-sequence skeletal growth causing oscillatory zoning in arc olivines

“…The immature olivines of group 3 described above represent a textural maturation analogous to morphologies that develop during stage 1 and 2. Crystals of similar morphology have been experimentally obtained by Faure and Tissandier 44 .…”

“…Some of the zones of Ni depletions are not totally filled and that explains the occurrence of elongated cavities that parallel the external crystal faces and ultimately may conform elongated melt inclusions; as frequently observed in natural and experimental crystals of olivine (e.g., ref. 12 , 14 , 15 , 44 ).…”

Early silica crust formation in planetesimals by metastable silica-rich liquid immiscibility or cristobalite crystallisation: the possible origin of silica-rich chondrules

“…I performed slow-cooling experiments (1-2 °C/h to ensure that the crystals and liquid remained under near-equilibrium conditions 18 ) on a liquid with a simplified CaO-MgO-Al 2 O 3 -SiO 2 composition (referred to here as CI*) that mimics the CI chondrite composition (see Methods for justification of this simplified iron-free starting composition). The experimental conditions and results are detailed in Supplementary Tables S1-S4.…”

“…Therefore, in the case of low degrees of melting, crystallisation of the generated magmas would produce only an olivine-dominated "mantle" and basaltic "crust" according to thermodynamic calculations. However, the most important parameter controlling the delay of pyroxene nucleation is the degree of superheating with respect to this second phase 18 . In these experiments, the degree of superheating relative to the pyroxene liquidus was around 50 °C for both the CI* and SF compositions.…”