2:30 PM - 2:45 PM
[SMP24-14] An experiment to reproduce the textural change from partially molten rock to plutonic rock
Keywords:partial melting rock, rock experiment, rock texture
The diversity in plutonic rock structures is believed to reflect the transformation process from partial melt rock structures to plutonic rock structures. Therefore, there is a possibility to extract information such as geological time from the non-equilibrium state of natural rock structures. Initially, we experimentally investigated the transformation process from partial melt rock to plutonic rock structure.
We synthesized a polycrystalline sample by adding 5 wt.% spinel (MgAl2O4) to fine-grained (about 10 µm) forsterite (Mg2SiO4) + 5 vol% enstatite (MgSiO3) + 5 vol% diopside (MgCaSi2O6) (melting point = 1,316 ℃) using the vacuum sintering method (Koizumi et al. 2010). In the experiment, to reproduce the partial melt rock structure, we partially melted it at atmospheric pressure at 1,400 ℃ for 5 hours, then held it at 1,220 ℃ for different times to reproduce the transformation process under sub-solidus conditions, and then rapidly cooled it to room temperature. After the experiment, we performed chemical analysis and microstructure observation of the samples using a scanning electron microscope (JSM-7800F PRIME) equipped with an energy-dispersive X-ray spectrometer (JEOL JED-2300F).
Chemical analysis revealed the presence of augite ((MgCa)2Si2O6) and anorthite (CaAl2Si2O8) with a range of Ca concentrations in the crystallized partial melt areas (referred to as ex-liquid phase parts). Microstructure observation showed that in samples with a holding time at 1,220 ℃ of less than 30 minutes, the ex-liquid phase parts present at the particle triple points had an inwardly curved structure (fig. 1), preserving the shape determined by the liquid-solid interfacial tension. After 37 hours of holding, the shape of the ex-liquid phase parts began to deform, and after 130 hours of holding, they began to have a wavy shape (fig. 2), adopting a structure that seemed to respond to the solid-solid interfacial tension. Even after 500 hours, the ex-liquid phase parts did not reach a complete solid-solid equilibrium shape (fig. 3).
Using fine-grained samples and efficiently advancing the diffusion necessary for structural changes, we successfully reproduced the transformation process from partial melt rock to plutonic rock structure, which takes geological time. The structural changes followed the transition from the equilibrium shape according to the liquid-solid interfacial tension to the equilibrium shape according to the solid-solid interfacial tension. In the future, we will proceed with quantifying the shape change of the ex-liquid phase parts and investigate the relationship with the holding time under sub-solidus conditions.
We synthesized a polycrystalline sample by adding 5 wt.% spinel (MgAl2O4) to fine-grained (about 10 µm) forsterite (Mg2SiO4) + 5 vol% enstatite (MgSiO3) + 5 vol% diopside (MgCaSi2O6) (melting point = 1,316 ℃) using the vacuum sintering method (Koizumi et al. 2010). In the experiment, to reproduce the partial melt rock structure, we partially melted it at atmospheric pressure at 1,400 ℃ for 5 hours, then held it at 1,220 ℃ for different times to reproduce the transformation process under sub-solidus conditions, and then rapidly cooled it to room temperature. After the experiment, we performed chemical analysis and microstructure observation of the samples using a scanning electron microscope (JSM-7800F PRIME) equipped with an energy-dispersive X-ray spectrometer (JEOL JED-2300F).
Chemical analysis revealed the presence of augite ((MgCa)2Si2O6) and anorthite (CaAl2Si2O8) with a range of Ca concentrations in the crystallized partial melt areas (referred to as ex-liquid phase parts). Microstructure observation showed that in samples with a holding time at 1,220 ℃ of less than 30 minutes, the ex-liquid phase parts present at the particle triple points had an inwardly curved structure (fig. 1), preserving the shape determined by the liquid-solid interfacial tension. After 37 hours of holding, the shape of the ex-liquid phase parts began to deform, and after 130 hours of holding, they began to have a wavy shape (fig. 2), adopting a structure that seemed to respond to the solid-solid interfacial tension. Even after 500 hours, the ex-liquid phase parts did not reach a complete solid-solid equilibrium shape (fig. 3).
Using fine-grained samples and efficiently advancing the diffusion necessary for structural changes, we successfully reproduced the transformation process from partial melt rock to plutonic rock structure, which takes geological time. The structural changes followed the transition from the equilibrium shape according to the liquid-solid interfacial tension to the equilibrium shape according to the solid-solid interfacial tension. In the future, we will proceed with quantifying the shape change of the ex-liquid phase parts and investigate the relationship with the holding time under sub-solidus conditions.