Kinetics and duration of metamorphic mineral growth in a subduction complex: zircon and phengite in the Nagasaki metamorphic complex, western Kyushu, Japan

Abstract

We applied interface-controlled kinetics, including interface-controlled Ostwald ripening and non-hydrostatic dissolutionprecipitation, to metamorphic zircon and phengite growth in a high-pressure (high-P) metamorphic complex. This kinetic modeling yields the growth duration of metamorphic zircon, based on the assumption that dissolution and precipitation of zircon is much slower than that of phengite. The model was applied to zircon and phengite growth in the Nishisonogi unit of the high-P Nagasaki metamorphic complex, western Kyushu, Japan. Given that detrital zircons that are tens of microns in size remain after metamorphism, our model assumption is justified. Our results show that the duration of metamorphic zircon growth in an individual rock ranges from 10 to 20 Myr. In general, the duration of metamorphic zircon growth in the whole Nishisonogi unit is ca. 30 Myr. This prolonged duration implies that high-P metamorphism is sustained by continuous subduction of hydrated oceanic crust and overlying trench-fill sediments. The continuous subduction and accretion of these materials may supply the metamorphic fluid into the high-P metamorphic domain in the deeper part of the accretionary prism, thereby contributing to interface-controlled kinetics in the metamorphic complex.

Kinetics and pulses of zircon growth in migmatites beneath a volcanic arc: An example from the high‐T Ryoke Complex, southwest Japan

“…To formulate interface-and diffusion-controlled growth rates, we introduced supersaturation Δξ i of a component i as a measure of disequilibrium. Δξ i is defined as follows (Miyazaki et al, 2019):…”

“…where C i eq (mol/m 3 ) and C i m (mol/m 3 ) are concentrations of the component i in diffusional medium at equilibrium with zircon and those distant from growing zircon, respectively. Using the supersaturation Δξ i , radial growth rate (dr/dt) for diffusion-controlled kinetics becomes as follows (Miyazaki et al, 2019):…”

“…For example, if we use component i = Zr, n i for zircon (ZrSiO 4 ) becomes 1. The radial growth rate (dr/dt) for interface-controlled kinetics becomes as follows (Miyazaki et al, 2019):…”

The basement geology of Japan from A to Z

“…Lenses and blocks of serpentinite are also found scattered throughout the higher grade regions. Mica Ar and zircon U-Pb dating shows that sedimentation and metamorphism occurred in the Cretaceous (Miyazaki, Suga, et al, 2019;Nishimura, Hirota, Shiokai, Nakahara, & Itaya, 2004;Tsutsumi, Horie, Miyashita, & Shiraishi, 2011). The foliation is gently dipping in all areas and the stretching lineation is approximately north−south.…”

Secular Variation of Early Cretaceous Granitoids in Kyushu, SW Japan: The Role of Mélange Rocks as a Possible Magma Source

“…Metamorphic age data (K-Ar, 40 Ar/ 39 Ar, U-Pb) from the pelitic and psammitic schists range from 85 to 60 Ma (Hattori and Shibata, 1982;Faure et al, 1988;Miyazaki et al, 2019), 85-65 Ma ( 40 Ar/ 39 Ar, U-Pb) for the jadeitites (Mori et al, 2007(Mori et al, , 2011Yui et al, 2012), and 108-105 Ma (U-Pb) for the rodingites (Fukuyama et al, 2014). The youngest detrital zircon ages and metamorphism duration were estimated to be 97-79 Ma and 10 to 20 Myr, respectively (Miyazaki et al, 2019).…”