Spinifex-like textured metaperidotites from the Higo Metamorphic Rocks (HMR), west-central Kyushu, Japan, may be formed by high-pressure dehydration of antigorite, and may indicate deep subduction of serpentinite reaching a pressuretemperature condition of 1.6 GPa and 740-750 C. Three rock types have been identified based on mineral assemblage and rock texture: Type I (L) consisting of medium-grained (1-5 cm long) olivine + enstatite + chromite ±tremolite with secondary talc and anthophyllite that occurs in low-grade metamorphic rocks of the biotite zone, Type I (H) of coarse-grained (up to 10 cm long) olivine + enstatite (with clinoenstatite lamella) + chromite ±tremolite with secondary talc that occurs in highgrade metamorphic rocks of the garnet-cordierite zone, and Type II composed of Alspinel + chlorite + olivine + apatite + ilmenite with minor sodic gedrite in the garnetcordierite zone together with Type I (H). Olivines in all rock types are mostly serpentinized during exhumation. The chromite-olivine thermometer gives 560-690 C for Type I (L) rocks, and the spinel-olivine thermometer gives 610-740 C for Type II rocks. The peak metamorphic pressure will be higher than 1.6 GPa based on the location of the experimentally determined invariant point (P = 1.6 GPa and T = 670 C) of antigorite + forsterite + enstatite + talc + H 2 O. This estimate is consistent with the occurrence of chlorite in Type II rocks, which is stable up to 890 C at 2.0 GPa. The spinifex-like textured metaperidotites occur as small bodies in the low P/T type gneisses, implying tectonic juxtaposition of them probably during exhumation of the HMR. Recent findings of medium pressure (0.9-1.2 GPa) granulites and gneisses from the HMR may indicate that the HMR has a deep root into the wedge mantle from which the spinifex-like textured metaperidotites have derived.
This paper presents the temperature and pressure dependence of the minimum binary diffusivity in granitic melts. The minimum diffusivities are determined by monitoring the temporal development of the diffusion -controlled melt layer(DCM) in granitic systems (albite (Ab) -quartz (Qtz) -H 2 O and orthoclase (Or) -Qtz -H 2 O) gathered during 31 melting experiments under conditions of 800 -900 °C and 100 -200 MPa for durations of 19 -72 h. The DCM is formed between single crystals (Ab or Or crystals) and powdered quartz in all runs and is characterized by a distinct concentration gradient. The maximum thickness of the DCM increases systematically with temperature, pressure, and run duration. Temporal development of the DCM obeys the parabolic growth rate law, using which the diffusivity can be estimated. Plots of concentrations along the diffusion paths in ternary diagrams (Na 2 O -Al 2 O 3 -SiO 2 diagram for the Ab -Qtz -H 2 O system and K 2 O -Al 2 O 3 -SiO 2 diagram for the Or -Qtz -H 2 O system) show linear trends rather than S -shaped trends, indicating that binary nature of diffusion occurs in these systems. Therefore, the diffusive component can be interpreted as an albite component or orthoclase and quartz components (SiO 2 ) rather than an oxide or a cation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.