Prograde P–T path of medium‐pressure granulite facies calc‐silicate rocks, Higo metamorphic terrane, central Kyushu, Japan

Abstract

Prograde P-T path of medium-pressure granulite facies calc-silicate rocks, Higo metamorphic terrane, ABSTRACT This paper reports an occurrence of medium-pressure granulite facies calc-silicate rocks intercalated with pelitic gneisses in the Higo metamorphic terrane, central Kyushu, Japan, which is classified as a low-P ⁄ high-T (andalusite-sillimanite type) metamorphic belt. Three equilibrium stages are recognized in the calc-silicate rock based on reaction textures: M1 stage characterized by an assemblage of porphyroblastic garnet + coarse-grained clinopyroxene + plagioclase included in the clinopyroxene; M2 stage by two kinds of breakdown products of garnet, one is plagioclase + coronitic clinopyroxene within garnet and the other is plagioclase + vermicular clinopyroxene surrounding garnet; and M3 stage by amphibole replacing clinopyroxene. The key assemblage in the calc-silicate rock common to M1 and M2 stages is Grt + Cpx + Pl ± Qtz, which constrains the pressure and temperature (P-T) conditions for these stages by Fe-Mg exchange reaction and the two univariant net-transfer reactions: 2Grs + Alm + 3Qtz = 3Hd + 3An or 2Grs + Prp + 3Qtz = 3Di + 3An. The P-T conditions for M1 and M2 stages were estimated to be about 8.4 ± 1.9 kbar and 680 ± 122°C, and 6.7 ± 1.9 to 8.9 ± 2.2 kbar and 700 ± 130 to 820 ± 160°C, respectively. Estimates are consistent with an isobaric heating P-T path. The high peak temperature conditions at normal crustal depths and the prograde isobaric heating path probably require heat advection due to melt migration during the high-T metamorphism.Key words: an isobaric heating P-T path; calc-silicate rock; Higo metamorphic terrane; low-pressure and high-temperature metamorphism; pervasive melt migration.

Recent progress in lower crustal process:

“…1992, , 1983Obata et al, 1994;, 1996;Osanai et al, 1998Osanai et al, , 2006aMiyazaki, 2004;Maki et al, 2009Maki et al, , 2014 Bt-Ms , Bt , Grt-Bt , Grt-Crd-Bt , Grt-Opx -1 Spr-Spl GASP -3 900 950°C 0.8 GPa Fig. 8d , , 1986;Osanai et al, 1998Osanai et al, , 2006aHamamoto et al, 1999 , Brown, 1998Brown, , 2007Santosh et al, 2011, Santosh and Kusky, 2010Santosh et al, 2011Santosh et al, , 2012 Tsunogae, T. and Santosh, M., 2004, Sapphirine and corundum bearing ultrahigh temperature rocks from the Palghat-Cauvery Shear System, southern India.…”

Spinifex‐like textured metaperidotites from the Higo Metamorphic Rocks, Japan, a possible high‐pressure dehydration product of antigorite serpentinite

“…The metamorphic field gradients estimated by Miyazaki (thin solid arrows) and Osanai et al(a dashed arrow) are both low-pressure gradients, typical of andalusite-sillimanite type metamorphism in the sense ofMiyashiro (1961). The medium-P granulite described byMaki et al (2009) represents pressure conditions higher than the above two estimates, but it is a rare example Osanai et al (2006). estimated the prograde path (a dotted arrow) of the D zone gneiss (in their definition), and ascribed it to the effect of intrusion of hornblende gabbro at 250 Ma.…”

“…Occurrences of garnet-amphibolite (Karakida & Yamamoto, 1982), staurolite-bearing pelitic gneisses (Maki et al, 2004;Osanai, Hamamoto, Maishima, & Kagami, 1998), and kyanite from river sand (Kano & Uruno, 1995) are indicative of medium-P metamorphism. Osanai et al (1998Osanai et al ( , 2006 found sapphirine-bearing granulites ( 0.9 GPa and 950 C) in the western part of the HMR, and Maki, Fukunaga, Nishiyama, and Mori (2009) reported a calc-silicate granulite ( 0.9 GPa and 820 ±160 C) in the eastern part. Maki et al (2014) studied migmatites and associated high-grade pelitic gneisses and estimated the P-T condition as 0.9-1.2 GPa and 800-900 C. Maki et al (2014) considered that some parts of the HMR reached a pressure condition higher than that thought by earlier workers (e.g., Miyazaki, 2004;Obata et al, 1994), implying that the HMR may have experienced a middle to deep crustal condition.…”

“…We indicate that the spinifex-like textured metaperidotites from the HMR may represent a product of deep subduction, then the tectonic significance of our finding resides in their occurrences in the low P/T type gneisses. Figure 12 shows the pressure-temperature conditions of the HMR compiled from earlier studies (Maki et al, 2009;Miyazaki, 2004;Osanai et al, 2006) west Japan (Miyashiro, 1961), and has been traditionally correlated to the HMR (Yamamoto, 1962). The Ryoke belt, however, does not contain such allochthonous rock bodies (e.g.…”

Zircon U–Pb ages of the Higo plutonic complex: Implication for migration of Cretaceous igneous activity in Kyushu, southwest Japan

“…The HMC are andalusite‐sillimanite type metamorphic rocks whose metamorphic grade increases toward the south as high as granulite facies, and cut into several blocks by high‐angle faults that trend E–W and NNE–SSW (e.g., Maki et al, 2004; Maki et al, 2009; Miyazaki, 2004; Obata et al, 1994; Osanai et al, 1998; Tsuji, 1967; Yamamoto, 1962). Biotite, muscovite and hornblende K‐Ar and Rb‐Sr ages of the HMC range from 97.9 ± 2.2 Ma to 109.8 ± 2.4 Ma (Hamamoto et al, 1999; Nagakawa et al, 1997; Nakajima et al, 1995; Shibata & Yamamoto, 1965; Yamaguchi & Minamishin, 1986), and most of them are concentrated around 101–107 Ma.…”