Magmatic Zoisite and Epidote in Tonalite of the Ryoke Belt, Central Japan

Eur. J. Mineral. 2014, 26, 279–291 Published online February 2014

Magmatic zoisite and epidote in tonalite of the Ryoke belt, central Japan

1 1,2, 3 1 YOSUKE MASUMOTO ,MASAKI ENAMI *,MOTOHIRO TSUBOI and MEI HONG

1 Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464–8601, Japan 2 Present address: Center for Chronological Research, Nagoya University, Nagoya 464–8602, Japan *Corresponding author, e-mail: [email protected] 3 Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669–1337, Japan

Abstract: Magmatic epidote and zoisite commonly occur in Cretaceous tonalite of the Hazu area in the Ryoke belt, central Japan. The tonalite is mainly composed of amphibole, biotite, plagioclase, quartz, and epidote/zoisite with minor ilmenite, magnetite, pyrite, zircon, and apatite. Small amounts of K-feldspar occur as an interstitial phase between other felsic phases or perthitic patches in plagioclase. Epidote occurs as inclusions in plagioclase, as interstitial phase in the matrix, and as 3þ 3þ secondary phase in chlorite pseudomorphs after biotite, and in saussuritized plagioclase. The XFe [¼ Fe /(Al þ Fe )] value of the secondary epidote ranges from 0.27 to 0.39. Epidote inclusions in plagioclase and interstitial grains contain less Fe3þ 3þ (XFe ¼ 0.08–0.29), Fe -poor epidote with XFe , 0.18 occurs only as inclusion. Zoisite with XFe value of 0.01–0.07 occurs 3þ only as inclusions in plagioclase, and usually has thin lamella-like layers of Fe -poor epidote with XFe ¼ 0.09–0.14. The 3þ Fe -poor epidote with XFe , 0.20 and zoisite included in plagioclase occasionally form aggregates with K-feldspar and quartz. A thin sodic plagioclase zone develops at the boundary between the Fe3þ-poor epidote and zoisite inclusions and their host plagioclase. Such a reaction texture is not observed at the boundary between Fe3þ-richer epidote inclusions with XFe . 0.20 and their host plagioclase. Epidote grains with XFe . 0.20 in plagioclase and the matrix are a magmatic phase 3þ that crystallized directly from the tonalite magma. The Fe -poor epidote (XFe , 0.20) and zoisite were probably formed by a local reaction between the trapped melt and its host plagioclase, and these are considered not to have been in equilibrium with the tonalite magma. Compositions of amphibole-plagioclase assemblages allowed for temperature estimates in the range of 730–770 C and minimum pressures of 0.47–0.57 GPa for the epidote/zoisite-bearing tonalites of the Hazu area. Epidote/ zoisite-free tonalites occur in other areas of the Ryoke belt. There may be several tonalite bodies that record different intrusion processes and solidification depths in the Ryoke belt. Key-words: magmatic zoisite, magmatic epidote, tonalite, Ryoke belt, Japan.

1. Introduction magma was fed from a magma chamber at a depth corresponding to 0.8–1.3 GPa. Subsequently, magmatic epidote The petrological significance of magmatic epidote was was also described from monzogranite and diorite, as experimentally and petrographically demonstrated in the reviewed by Schmidt & Poli (2004); Schmidt & Thompson 1980s (Schmidt & Poli, 2004). Naney (1983) showed that (1996) experimentally showed that the epidote-in curve is epidote can coexist with a melt phase at 0.8 GPa in granitic positioned on the slightly higher temperature side for tonalite and granodioritic systems, and suggested that the presence of compositions than for granodiorite compositions, and it shifts magmatic epidote is almost-certain evidence for high- towards the lower pressure (P)/temperature (T)sidewith pressure crystallization of silicate magma. Zen & increasing oxygen fugacity. Furthermore, zoisite was reported Hammarstrom (1984) identified epidote as an important mag- from high-P migmatites and pegmatites derived from eclo- matic constituent of tonalite and granodiorite within the gites (Nicollet et al., 1979; Franz & Smelik, 1995). These mobile belt extending from northern California to southern petrographical and experimental studies clearly suggest that Alaska, and suggested that epidote indicates a minimum epidote-group minerals are an index phase that implies rela- intrusive pressure of about 0.5–0.6 GPa. Evans & Vance tively high-P solidification of a silicic melt, and the stability (1987) reported elongate phenocrysts of epidote, which tex- conditions for epidote-group minerals depend slightly on the turally ensures the magmatic origin, from rhyodacitic dikes in melt composition and increase towards the low P/T side with 3þ 3þ Colorado, and considered that the epidote-bearing dike an increase in their XFe [¼ Fe /(Al þ Fe )] values.

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Magmatic zoisite and clinozoisite-epidote (referred to as mainly composed of pelitic, psammitic, and siliceous litholo- epidote hereafter) commonly occur in a tonalitic pluton, a gies, with minor amounts of metabasite. The metamorphic member of the Ryoke belt, from the Hazu area, central grade generally increases from the chlorite–biotite zone in the Japan. The purpose of this paper is to document the mineral northwest, through the K-feldspar–cordierite zone, to the chemistry and petrological characteristics of the zoisite/ sillimanite–K-feldspar/garnet–cordierite zones in the south- epidote-bearing samples and to interpret their depths of east, and then locally decreases towards the MTL (Ikeda, crystallization based on the stabilities of zoisite/epidote 1998; Miyazaki, 2010). The low-grade part of the Ryoke and pressure estimations using the hornblende metamorphic rocks passes into the unmetamorphosed geobarometer. Jurassic accretionary complex of the Mino terrane. Chemical U-Th Total-Pb Isochron Method (CHIME) monazite ages from 98.0 3.2to100.7 3.2 Ma were reported as 2. Outline of Geology peak metamorphic ages of the Ryoke metamorphism (Suzuki et al., 1996a, 1996; Suzuki & Adachi, 1998). Granitoids in the The Ryoke belt, which consists of low-P/T metamorphic Ryoke belt of central Japan are categorized into fifteen plu- rocks originating from the Mesozoic accretionary complexes tons from the oldest Kamihara tonalite (94.5 3.1 – 94.9 and Cretaceous granitoid plutons, stretches throughout the 4.9 Ma CHIME monazite age: Nakai & Suzuki, 1996) to Inner Zone (the Japan Sea side) of southwest Japan over a the youngest Naegi granite (67.2 3.2 – 68.3 1.8 Ma: length of roughly 600 km (Fig. 1). The south of the Ryoke belt Suzuki et al., 1994b; Suzuki & Adachi, 1998), based on their is bounded by the Sanbagawa belt, which is a high-P/T sub- intrusive relations (Ryoke Research Group, 1972) and radio- duction metamorphic belt of Cretaceous age. These two belts metric ages (Suzuki & Adachi, 1998). The Kamihara tonalites form perhaps the best-known example of paired metamorphic defined by the Ryoke Research Group (1972) occur as three belts (Miyashiro, 1961). The boundary between the Ryoke major bodies in the Hazu, Shimoyama, and Tenryu areas and Sanbagawa belts is a major strike-slip fault, the Median (e.g., Suzuki & Adachi, 1998). Tectonic Line (MTL). Members of the Ryoke belt are dis- The Hazu area, from which the tonalite samples were tributed widely in central Japan, in which the Hazu area collected, is situated at the southwestern margin of the studied in this paper is located. Ryoke belt in central Japan (Fig. 1a). In the northern part of The geological configuration of the Ryoke belt in central the Hazu area, the Ryoke metamorphic rocks are distributed Japan is summarized in Suzuki & Adachi (1998), including widely, whereas tonalite occurs along the southern coastline the distributions of the Ryoke metamorphic rocks and a series (Fig. 1b). The Ryoke metamorphic rocks in the Hazu area are of granitoid plutons. The Ryoke metamorphic rocks are divided into sillimanite and sillimanite–K-feldspar zones in

(a) 36°N Japan Sea (b) R247 Nagoya ISTL Honshu Ryoke belt

Osaka

MTL Fig. 1b Shikoku Pacific Ocean

Kyushu 132°E 134°E 136°E 200 km

MT2503 MT1703 YM2910A MT1704 YM2907B YM2906 Mt. Hara

YM2911

Mikawa Bay Quaternary sediments 34°46’ N YM2912 Kamihara tonalite

Ryoke metamorphic rocks 1 km 137°10’ N

Fig. 1. (a) Distribution of the Ryoke belt in southwest Japan and (b) geological sketch map of the Hazu area, central Japan (simplified part of Geological Survey of Japan AIST, 2010). Abbreviations used are as follows: MTL, Median Tectonic Line; ISTL, Itoigawa-Shizuoka Tectonic Line.

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the northern and southern parts, respectively (Asami, 1977). (Fig. 2a and b). The host plagioclase around the zoisite The typical mineral assemblage of metapelite in the sillima- inclusions is locally modified in composition, and a thin nite zone is biotite þ muscovite þ sillimanite þ plagioclase zone with less calcic plagioclase characteristically devel- þ quartz. Andalusite occurs in the lower-grade part of the ops between the inclusions and the host phase (Fig. 2a). sillimanite zone. Staurolite is reported to occur sporadically Epidote in plagioclase also occurs as a single grain. A less in this zone (Asami, 1977). Metapelite in the sillimanite–K- calcic plagioclase zone is usually observed also around feldspar zone is mainly composed of biotite, muscovite, epidote inclusions with XFe, 0.2. On the other hand, sillimanite, K-feldspar, plagioclase, and quartz. The modal there is no obvious compositional modification of plagio- amount of muscovite in the sillimanite–K-feldspar zone is clase around most of the epidote inclusions with XFe. 0.2 lower than that in the sillimanite zone and tends to decrease (Fig. 2c). Although epidote/zoisite is not observed as inclu- with distance from the sillimanite–K-feldspar isograd, and sions in biotite and amphibole, these three phases coexist thus, in the higher-grade part of the sillimanite–K-feldspar as inclusions in a plagioclase grain. K-feldspar occurs zone, metapelite sometimes lacks primary muscovite interstitially in the matrix or as exsolution lamellae in (Asami, 1977; Asami et al., 1982). Garnet occurs sporadi- plagioclase. Secondary chlorite and titanite replace biotite. cally throughout the two mineral zones. Asami (1977) and Asami et al. (1982) considered that the metamorphic pressure condition of the Hazu area was slightly higher than that of the rest of the Ryoke area, based on the occurrence of 4. Whole-rock chemical composition staurolite in the Hazu area and the difference in temperature at which aluminum silicate þ K-feldspar becomes stable. The whole-rock major and trace element compositions The tonalite in the Hazu area intrudes into metasedimentary (Table 2) were determined by X-ray fluorescence spectro- rocks of the sillimanite–K-feldspar zone. metry (XRF) using a Shimadzu XRF-1800 spectrometer at Kwansei Gakuin University. The rhodium-target X-ray tube was energized at 40 kV and a current of 70 mA for the major-element analysis. Details and discussion of the 3. Petrography XRF analytical methods used in this study can be found in Morishita & Suzuki (1993) and Nakazaki et al. (2004). Most tonalite samples in the Hazu area are composed of The ‘‘Kamihara tonalite’’ reported in the literature, primarily biotite, calcic amphibole, plagioclase, and which includes tonalite samples from the Hazu, quartz, with subordinate amounts of K-feldspar, titanite, Shimoyama, and Tenryu areas, shows variable SiO2 con- ilmenite, magnetite, pyrite, zircon, and apatite (Table 1). tents (57.8–69.9 wt%) and modified alkali-lime index Biotite exhibits a dark-brownish to brownish Z-axial col- (MALI) values (–2.79–4.55), and belongs to the calc-alka- our. Calcic amphibole is pale brownish green to green in lic and calcic series of Frost et al. (2001) (Fig. 3a). With colour. Plagioclase usually occurs as subhedral forms and increasing SiO2 content, the aluminum-saturation index exhibits albite and pericline twins. Epidote occurs as inclu- (ASI) (e.g., Chappell & White, 1974) of the ‘‘Kamihara sions in plagioclase (Fig. 2 a–c), interstitial phases in the tonalite’’ increases from 0.82 to 1.22, suggesting wide matrix, as secondary phases after biotite (Fig. 2d), and in variations in the whole-rock composition from metalumi- saussuritized plagioclase. Zoisite is observed only as inclu- nous to peraluminous groups (Fig. 3b). sions in plagioclase, and usually shows twin textures with The studied Hazu samples are less silicic narrow epidote layers (Fig. 2a and b), similar to that (SiO2 ¼ 53.6–60.2 wt%) and have lower MALI reported for a high-P pegmatite in the Mu¨nchberg (–1.50–0.44) and ASI (0.89–1.06) values than most other Massif, Germany (Franz & Smelik, 1995). Zoisite usually tonalites reported in the literature. The Hazu samples, forms an aggregate with quartz, K-feldspar, and epidote however, share similar compositional trends with the

Table 1. Mineral assemblages of tonalites from the Hazu area, Ryoke belt.

Qz Pl* Kfs* Amp Bt Zo Ep Chl Ttn Mag Ilm Py Zrn Ap MT1703 þ 46(4) 94(1) i/m i/m i i/s s m/s þþþþþ MT1704 þ 45(2) 94(1) i/m i/m i/s s m/s þþþþþ YM2906 þ 47(3) 96(1) i/m i/m i i/m/s s m/s þþþþþ YM2907B þ 42(2) i i/m m/s s m/s þþþþþ YM2910A þ 48(4) 94(1) i/m i/m s m/s þþþþþ MT2503 þ 46(6) 93(2) i/m i/m i i/s s m/s þþþþþ YM2911 þ 44(2) i/m i/m s m/s þþþþþ YM2912 þ 45(5) 91(2) i/m i/m i s m/s þþþþþ

* Anorthite and orthoclase contents of plagioclase and K-feldspar, respectively. Parenthetic number indicates standard deviation for 1s level. Abbreviations are: þ, present; i, inclusion phase in plagioclase; m, matrix phase; s, pseudomorph after biotite and/or amphibole; Qz, quartz; Pl, plagioclase; Kfs, K-feldspar; Amp, amphibole; Zo, zoisite; Ep, epidote; Chl; chlorite; Ttn, titanite; Mag, magnetite; Ilm, ilmenite; Py, pyrite; Zrn, zircon: Ap, apatite.

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(a) BSI (b) FeKα high Pl (An ) 18 Ep

Kfs Ep Pl (An51)

100 µm 100 µm low

Chl Ep Qz Pl Ep Ep Bt Pl 10 µm 500 µm

Fig. 2. (a and c) Back-scattered electron images, and (b) Fe-Ka X-ray map of epidote-group minerals included in plagioclase, and (d) photomicrograph of secondary epidote in chlorite pseudomorph after biotite. Abbreviations: An, anorthite content; Bt, biotite; Chl, chlorite; Ep, epidote; Kfs, K-feldspar: Pl, plagioclase; Qz, quartz; Zo, zoisite.

Table 2. Whole-rock analyses of tonalite from the Hazu area, Ryoke belt.

Epidote-bearing Epidote-free MT1703 MT1704 YM2906 YM2907B MT2503 YM2912 YM2910A YM2911

SiO2 56.45 56.52 55.43 60.16 58.36 53.60 57.00 59.64 TiO2 1.02 1.04 1.02 0.80 0.80 1.14 0.84 0.87 Al2O3 18.23 19.48 20.02 18.12 15.89 17.61 17.85 15.47 FeO* 6.21 6.22 6.07 4.90 6.55 8.20 6.36 6.50 MnO 0.14 0.13 0.12 0.15 0.13 0.16 0.13 0.13 MgO 1.96 1.93 1.72 1.65 3.30 3.38 2.85 2.69 CaO 6.43 6.67 6.98 5.42 6.12 6.84 6.55 5.05 Na2O 3.77 4.00 4.28 3.31 2.90 3.22 3.61 3.14 K2O 1.58 1.47 1.31 1.87 1.72 2.12 1.50 2.35 P2O5 0.28 0.28 0.25 0.19 0.18 0.28 0.20 0.19 Total 96.07 97.74 97.20 96.57 95.95 96.55 96.89 96.03

* Total iron as FeO.

other ‘‘Kamihara tonalite’’ on the MALI–SiO2 and University. The accelerating voltage and beam current ASI–SiO2 diagrams, and mostly belong to the calc-alkalic were kept at 15 kV and 12 nA on the Faraday cup, respec- series metaluminous group. tively. A beam diameter of 5 mm was used for analyses of biotite and feldspars, and 2–3 mm for analyses of all other phases. Well-characterized natural and synthetic phases, 5. Mineral chemistry including synthetic REEP5O14, were used as standards (REE: rare-earth elements). Detection limits of La2O3, Chemical analyses of major constituent minerals were Ce2O3 and Nd2O3 were 0.02 wt% for the 1s level. The carried out using an electron probe microanalyzer factors calculated by Kato (2005) were employed for the (EPMA) with wavelength- and energy-dispersive X-ray matrix correction. Total iron of zoisite/epidote was treated spectrometer systems (JXA-8900R) at Nagoya as Fe2O3. Amphibole compositions for the mineral

12 (a) (b) 1.4

8 peraluminous group

alkalic series alkali-calcic series 1.2 calc-alkalic series 4

1.0 ASI MALI 0 calcic series 0.8 metaluminous group -4 Ep-bearing sample Hazu area Ep-free sample 0.6 Ep-free sample (in literature) -8 50 60 70 80 50 60 70 80

SiO2 (wt%) SiO2 (wt%)

Fig. 3. Variations of the whole-rock compositions of the ‘‘Kamihara tonalite’’ in the (a) modified alkali-lime index (MALI) vs. SiO2 diagram (Frost et al., 2001) and (b) aluminum-saturation index (ASI) vs. SiO2 diagram (Zen, 1986). Literature data are from Sakakibara (1967), Shibata (1967), Kagami (1968), Kutsukake (1970), Nakai (1976), Kutsukake (1993), Morishita & Suzuki (1993), Kutsukake (2002), and Tsuboi & Asahara (2009).

descriptions are given using an average of the maximum 5.1. Zoisite–epidote and minimum Fe3þ/Fe2þ estimates (Leake et al., 1997). Total iron of the other phases is assumed to be FeO. Most epidote grains consist of a REE-poor solid solu- Selected analyses of zoisite/epidote, amphibole, and bio- tion (total REE2O3 , 0.3 wt%), except for a slightly tite are listed in Tables 3, 4, and 5, respectively. REE-enriched core (up to 0.79, 1.67, and 0.59 wt% of

Table 3. Representative analyses of zoisite and epidote in tonalite from the Hazu area, Ryoke belt.

MT1703 MT1704 YM2906 YM2907B MT2503 YM2912 Zo Ep Ep Ep Ep Ep Ep Zo Ep Ep Ep Ep inc inc inc inc mat pseud mat inc inc mat pseud inc

SiO2 39.0 38.5 37.2 37.6 37.2 36.9 37.0 38.8 37.6 37.4 36.2 37.3 TiO2 0.01 0.32 0.24 0.13 0.39 0.15 0.11 0.07 0.06 0.23 0.42 0.02 Al2O3 33.0 28.1 23.7 25.8 23.6 20.9 22.6 32.8 27.5 22.5 18.5 22.8 Fe2O3* 0.48 6.96 12.2 9.36 12.1 15.9 13.6 1.13 7.07 13.5 18.1 14.0 Mn2O3** 0.01 0.42 0.58 0.00 0.32 0.00 0.32 0.00 0.01 0.19 0.11 0.00 MgO 0.00 0.00 0.02 0.04 0.04 0.02 0.00 0.26 0.16 0.02 0.06 0.03 CaO 24.1 23.3 23.0 23.3 22.6 22.7 22.7 24.6 23.7 23.2 22.8 22.9 Total 96.6 97.6 96.9 96.2 96.3 96.6 96.3 97.7 96.1 97.0 96.2 97.1 Formula (O ¼ 12.5) Si 3.00 3.00 2.99 3.00 3.00 3.01 3.00 2.96 2.98 3.01 3.00 3.00 Ti 0.00 0.02 0.01 0.01 0.02 0.01 0.01 0.00 0.00 0.01 0.03 0.00 Al 2.99 2.58 2.24 2.43 2.24 2.01 2.16 2.95 2.57 2.14 1.81 2.16 Fe3þ* 0.03 0.41 0.74 0.56 0.73 0.98 0.83 0.07 0.42 0.82 1.13 0.85 Mn3þ** 0.00 0.03 0.04 0.00 0.02 0.00 0.02 0.00 0.00 0.01 0.01 0.00 Mg 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.03 0.02 0.00 0.01 0.00 Ca 1.98 1.95 1.98 1.99 1.95 1.98 1.97 2.01 2.02 2.00 2.03 1.98 XFe† 0.01 0.14 0.25 0.19 0.25 0.33 0.28 0.02 0.14 0.28 0.38 0.28

*Total iron as Fe2O3. **Total manganese as Mn2O3. †Fe3þ/(Al þ Fe3þ). Abbreviations are: Zo, zoisite; Ep, epidote; inc, inclusion in plagioclase; mat, interstitial phase in matrix; pseud, pseudomorph after biotite.

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Table 4. Representative analyses of amphibole in tonalite from the Hazu area, Ryoke belt. Formulae on a 23 oxygen basis.

Epidote-bearing tonalite Epidote-free tonalite MT1703 MT1704 MT2503 YM2910A matrix matrix matrix matrix core riminclusion core riminclusion core riminclusion core rim inclusion

SiO2 41.3 39.7 41.4 42.5 39.9 41.7 43.1 41.9 43.1 43.9 41.4 43.3 TiO2 1.14 0.74 1.28 1.51 0.81 1.01 1.09 0.68 0.82 1.47 0.66 0.96 Al2O3 10.7 12.2 10.6 9.82 12.5 10.9 9.97 11.2 10.3 8.57 11.4 10.4 FeO* 21.9 22.9 21.8 21.1 22.8 21.9 18.3 19.2 18.0 18.9 20.3 19.9 MnO 0.61 0.60 0.58 0.66 0.56 0.54 0.48 0.46 0.45 0.53 0.45 0.48 MgO 7.14 6.44 7.02 7.82 6.33 6.90 9.66 8.96 9.70 9.55 8.21 8.51 CaO 11.3 11.5 11.0 10.8 11.5 11.2 11.6 11.8 11.8 11.2 11.6 11.5 Na2O 1.06 1.11 1.11 1.18 1.15 1.04 1.08 1.08 1.01 1.14 1.23 1.15 K2O 1.02 1.18 0.99 0.68 1.10 0.85 0.97 1.12 0.97 0.65 0.96 0.85 Total 96.2 96.4 95.8 96.1 96.7 96.0 96.3 96.4 96.2 95.9 96.2 97.1

Si 6.40 6.17 6.44 6.55 6.18 6.46 6.56 6.39 6.55 6.71 6.36 6.58 Ti 0.13 0.09 0.15 0.18 0.09 0.12 0.13 0.08 0.09 0.17 0.08 0.11 Al 1.96 2.24 1.94 1.78 2.28 1.99 1.79 2.01 1.85 1.54 2.06 1.86 Fe3þ** 0.59 0.77 0.52 0.53 0.71 0.53 0.46 0.58 0.46 0.42 0.61 0.41 Fe2þ** 2.25 2.20 2.32 2.19 2.25 2.31 1.87 1.87 1.83 2.00 2.00 2.12 Mn 0.08 0.08 0.08 0.09 0.07 0.07 0.06 0.06 0.06 0.07 0.06 0.06 Mg 1.65 1.49 1.63 1.80 1.46 1.59 2.19 2.04 2.20 2.18 1.88 1.93 Ca 1.88 1.92 1.83 1.78 1.91 1.86 1.89 1.93 1.92 1.83 1.91 1.87 Na 0.32 0.34 0.34 0.35 0.35 0.31 0.32 0.32 0.30 0.34 0.37 0.34 K 0.20 0.23 0.20 0.13 0.22 0.17 0.19 0.22 0.19 0.13 0.19 0.17

*Total iron as FeO. **Calculated values (see text).

Table 5. Representative analyses of biotite in tonalite from the Hazu area, Ryoke belt. Formulae on an 11 oxygen basis.

MT1703 MT1704 MT2503 YM2906 YM2910A YM2912 inclusion matrix inclusion matrix inclusion matrix matrix inclusion matrix inclusion matrix

SiO2 35.0 34.7 35.0 34.6 35.9 35.9 34.6 35.4 35.1 34.8 34.9 TiO2 2.38 3.37 3.21 3.21 2.55 2.46 2.96 3.20 3.31 2.67 3.90 Al2O3 15.6 15.2 15.1 15.2 15.4 15.4 15.4 14.8 14.8 15.2 14.5 FeO* 23.3 23.7 23.7 23.2 19.8 19.7 23.6 20.7 21.2 21.6 21.9 MnO 0.35 0.40 0.30 0.28 0.32 0.31 0.26 0.27 0.28 0.32 0.31 MgO 8.11 7.98 8.01 8.09 10.6 10.8 8.30 9.94 9.65 9.29 8.91 BaO 0.13 0.26 0.25 0.68 0.29 0.23 0.20 0.30 0.28 0.25 0.30 CaO 0.02 0.03 0.03 0.03 0.04 0.03 0.06 0.06 0.06 0.04 0.03 Na2O 0.12 0.12 0.10 0.11 0.10 0.10 0.12 0.13 0.12 0.13 0.13 K2O 9.18 9.29 9.47 9.34 9.26 9.31 9.16 9.33 9.42 9.41 9.45 Total 94.2 95.1 95.2 94.7 94.3 94.2 94.7 94.1 94.2 93.7 94.3

Si 2.77 2.74 2.75 2.74 2.79 2.79 2.73 2.77 2.76 2.76 2.75 Ti 0.14 0.20 0.19 0.19 0.15 0.14 0.18 0.19 0.20 0.16 0.23 Al 1.45 1.41 1.40 1.42 1.41 1.41 1.43 1.37 1.37 1.42 1.35 Fe2þ* 1.54 1.56 1.56 1.54 1.29 1.28 1.56 1.36 1.39 1.43 1.45 Mn 0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Mg 0.96 0.94 0.94 0.96 1.23 1.25 0.98 1.16 1.13 1.10 1.05 Ba 0.00 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Ca 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.00 Na 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 K 0.93 0.93 0.95 0.94 0.92 0.92 0.92 0.93 0.94 0.95 0.95

*Total iron as FeO.

La2O3,Ce2O3,andNd2O3, respectively) of zoned epi- Chemical compositions of zoisite/epidote are variable, dote included in plagioclase in sample YM2906. The and are closely related to their modes of occurrence total REE2O3 content of zoisite is less than 0.05 wt%. (Fig. 4). Zoisite grains occurring as inclusions in

5 5 (a) MT1703 (b) MT1704 4 4

3 3

2 2

1 1

0 0 25 20 (c) YM2906 (d) YM2907B 20 15 15 10 10

5 5

0 0 30 10 (e) MT2503 (f) YM2912 25 8 inclusion 20 matrix 6 pseudomorph 15 4 Frequency10 Frequency Frequency 5 2 0 0 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 XFe XFe

Fig. 4. Frequency distribution of XFe values of epidote-group minerals in some tonalite samples from the Hazu area.

plagioclase have XFe valuesrangingfrom0.01to0.07, phases: Si ¼ 6.40–6.58 pfu, Al ¼ 1.70–2.12 pfu, whereas epidote included in plagioclase has Ca ¼ 1.83–1.95 pfu, [A](K þ Na) ¼ 0.40–0.47 pfu, and XFe ¼ 0.08–0.29. Matrix epidote grains tend to be mg# ¼ 0.40–0.55. richer in Fe2O3,withXFe varying from 0.18 to 0.29. Amphibole crystals in epidote-free tonalites have a zonal Secondary epidote is distinctly enriched in Fe2O3 structure similar to those in the epidote-bearing tonalites, but (0.27 , XFe 0.39). with a less aluminous core (Fig. 6d): Si ¼ 6.54–6.71 pfu, Al ¼ 1.54–1.77 pfu, Ca ¼ 1.82–1.84 pfu, [A](K þ Na) ¼ 0.38–0.49 pfu, and mg# ¼ 0.46–0.52 in the 5.2. Amphibole core; and Si ¼ 6.37 pfu, Al ¼ 2.06 pfu, Ca ¼ 1.91 pfu, [A](K þ Na) ¼ 0.51 pfu, and mg# ¼ 0.48 in the rim. The Most amphibole crystals exhibit a relatively homogeneous composition of the inclusion amphibole in the epidote-free core and a thin Al- and K-richer rim. Al-richer amphibole tonalite is Si ¼ 6.57 pfu, Al ¼ 1.86 pfu, Ca ¼ 1.88 pfu, similar to the rim also develops along the cleavage (Fig. 5a, c, [A](K þ Na) ¼ 0.44 pfu, and mg# ¼ 0.48. and d). They have magnesiohornblende/hornblende–tschermakite/ferrotschermakite–pargasite/ferropargasite compositions (Fig. 6). Some grains are retrogressively rimmed by 5.3. Biotite Al-poor ferrohornblende/ferro-actinolite. The homogeneous core of amphibole in epidote-bearing tonalites has the follow- Biotite in epidote-bearing tonalites is relatively homoge- ing average compositions: Si ¼ 6.40–6.58 per formula unit neous, with crystals in the matrix (Si ¼ 2.73–2.79 pfu and (pfu), Al ¼ 1.70–1.95 pfu, Ca ¼ 1.78–1.90 pfu, mg# ¼ 0.38–0.49) similar to those enclosed by plagioclase [A](K þ Na) ¼ 0.7–0.48 pfu, and mg# [¼ Mg/ (Si ¼ 2.75–2.79 pfu and mg# ¼ 0.38–0.49). Biotite in (Mg þ Fe2þ)] ¼ 0.42–0.54, where [A](K þ Na) indicates epidote-free tonalites has similar Si contents alkaline contents at the 10-coordinated A-site (Fig. 6a–c). The (2.77–2.80 pfu in the matrix, 2.76 pfu in plagioclase) and Al-rich rim has average compositions of Si ¼ 6.17–6.40 pfu, mg# values (0.44–0.46 in the matrix, 0.45 in plagioclase) Al ¼ 2.01–2.35 pfu, Ca ¼ 1.90–1.94 pfu, to those in epidote-bearing tonalites. TiO2 and BaO con- [A](K þ Na) ¼ 0.50–0.55 pfu, and mg# ¼ 0.38–0.52. tents are up to 4.1 wt% and 1.2 wt% in the epidote-bearing Amphibole inclusions in plagioclase are homogeneous and samples and up to 4.0 wt% and 0.4 wt% in the epidote-free have similar compositions to those of the core of the matrix samples, respectively.

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(a) Al Kα YM2910A(b) CaKα YM2910A

Amp

Pl Qz

Bt Bt

Pl 500 µm 500 µm (c) Al Kα YM2906 (d) Al Kα YM2912 Pl Qz Pl Qz Bt Pl Amp

Amp Pl Pl Pl Bt Pl Qz 200 µm 200 µm

Fig. 5. (a, c, and d) Al-Ka and (b) Ca-Ka X-ray maps of amphibole and other constituent minerals of tonalites from the Hazu area. Abbreviations: Amp, amphibole; Bt, biotite; Pl, plagioclase; Qz, quartz.

5.4. Feldspars

Plagioclase crystals are slightly saussuritized, and those edenite þ quartz ¼ tremolite þ albite that survived saussuritization show normal zoning, with decreasing anorthite content from the core towards the and margin (Fig. 5b). The average anorthite content of the edenite þ albite ¼ richterite þ anorthite unsaussuritized calcic core is An42(2)–47(3) in epidote- bearing tonalites and An44(2)–48(4) in epidote-free tona- Pressure conditions were calculated using the empirical lites (value in parenthesis is the 1s-standard deviation). Al-in hornblende igneous geobarometers calibrated by K-feldspar grains are generally homogeneous and have Hammarstrom & Zen (1986); Hollister et al. (1987); orthoclase contents of 92–96% and 93–94% in epidote- Johnson & Rutherford (1989); Blundy & Holland (1990); bearing and epidote-free tonalites, respectively. The Schmidt (1992), and Anderson & Smith (1995). standard deviation is less than 2% on the 1s level. As the amphibole is chemically heterogeneous, with an BaO contents are up to 2.5 and 0.8 wt% in epidote- Al-richer zone as rim and along cracks and/or cleavages bearing and epidote-free tonalites, respectively. (Fig. 5), the core composition was employed for the P–T estimates of the solidification stage. The combination of the amphibole-bearing geothermobarometers gives P-T 6. Pressure-temperature estimates conditions of 0.47–0.57 GPa/730–770 C for the epidote- bearing tonalites. On the other hand, amphibole in the The amphibole–plagioclase thermometry of Holland & epidote-free tonalites has a slightly Al-poorer composition Blundy (1994) as defined by the following two equations (Al ¼ 1.54–1.77 pfu) than in the epidote-bearing tonalites was applied to estimate the temperature of tonalite solidi- (1.70–1.95 pfu), implying slightly lower P conditions of fication in the Hazu area: 0.37–0.48 GPa (Fig. 7).

1 1 (a) MT1703 (Zo/Ep-bearing) (b) MT1704 (Ep-bearing)

matrix inclusion Fed Fprg Fed Fprg

0.5 0.5 (Na + K) (phu) (Na + K) (phu) [A] [A] Hbl Fts Hbl Fts

Fac Fac

0 0 8 7.5 7 6.5 6 8 7.5 7 6.5 6 Si (pfu) Si (pfu)

1 1 (c) MT2503 (Zo/Ep-bearing) (d) YM2910A

Ed Prg Fed Fprg

0.5 0.5 (Na + K) (phu) (Na + K) (phu) [A] [A] Mhb Ts Mhb/Hbl Fts

Act Act/Fac 0 0 8 7.5 7 6.5 6 8 7.5 7 6.5 6 Si (pfu) Si (pfu)

Fig. 6. Compositional variation of amphibole in some tonalite samples from the Hazu area. Abbreviations: Act, actinolite; Ed, edenite; Ep, epidote; Fac, ferro-actinolite; Fed, ferro-edenite; Fprg, ferropargasite; Fts, ferrotschermakite; Hbl, hornblende; Mhb, magnesiohornblende; Prg, pargasite; Ts, tschermakite; Zo, zoisite.

7. Discussion 2004). The epidote-group minerals are generally a solid 3þ solution of Ca2Al3Si3O12(OH) and Ca2Al2Fe Si3 Epidote-group minerals in the tonalites from the Hazu area O12(OH), with a molar Al2O3/CaO value ranging from occur as three types: as inclusions in plagioclase, as inter- 0.5 to 0.75. Thus, magmatic epidote is probably stabilized stitial phase in the matrix, and as pseudomorph after bio- more easily in metaluminous melts than in peraluminous tite. The pseudomorph epidote characteristically has a high melts. However, the ‘‘Kamihara tonalite’’ has a wide dis- XFe (0.27–0.39). On the other hand, the inclusion and tribution of whole-rock compositions ranging from meta- interstitial epidote grains are less ferric, and all zoisite luminous to peraluminous groups, and some epidote-free and epidote grains with XFe , 0.18 occur as the inclusions tonalite samples have distinctly more metaluminous com- only (Figs. 4 and 8). These textural and compositional positions than the epidote-bearing Hazu tonalites (Fig. 3). characteristics suggest that zoisite and epidote included Thus, the occurrence of magmatic epidote in the tonalites in plagioclase and most epidote grains occurring as inter- of the Hazu area is not simply a result of the whole-rock stitial phases represent primary products and are probably composition of their host rocks, and is probably controlled of magmatic origin, and that the oxygen fugacity and/or by the oxygen fugacity and/or P–T conditions during crys- Fe2O3/Al2O3 value of magma have systematically tallization of the melt. increased during crystallization. The stability relations of magmatic epidote in the tona- The stability of magmatic epidote is controlled by var- lite composition (Schmidt & Thompson, 1996) show that ious factors, including melt composition, oxygen fugacity, the minimum P stability of the epidote þ melt assemblage and P–T conditions during crystallization (Schmidt & Poli, (1) is 0.5 GPa and 0.3 GPa at 680 C for NNO- and QFM-

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1.0 buffered oxygen fugacities, respectively, and (2) increases with increasing temperature. Schmidt (1993) conducted Qz systematic experiments on the relationship between the Or Ky Solidus Sill composition and stability of epidote in the tonalite composition and showed that the lower-P stability limit of the Cpx epidote þ melt assemblage increases with decreasing XFe ST96 value of epidote at constant T, and exceeds 1.0 GPa for 3þ Fe -poor epidote with XFe , 0.12–0.13 (Fig. 8a). The Pl Bt fields of possible coexistence of zoisite þ quartz þ melt in 0.5 the K O–CaO–Al O –SiO –H O and K O–CaO–MgO Ep (NNO) 2 2 3 2 2 2 –Al2O3–SiO2–H2O systems were explored experimentally Pressure (GPa) by Schliestedt & Johannes (1984) and Hoschek (1990), Ep-bearing Ep-free respectively, showing that this assemblage is more stable L73 Ep (HM) MT1703 YM2910A MT1704 YM2911 at higher P than at 0.7 GPa. Sil YM2906 And The P conditions of the Hazu tonalites, 0.47–0.57 GPa YM2907B for the epidote-bearing samples and 0.37–0.48 GPa for the H72 MT2503 YM2912 epidote-free samples, were estimated using Al-in hornble- 0 nde geobarometer. This geobarometer was suggested to 600 700 800 900 use for granitoid intrusions containing a limiting assem- Temperature (°C) blage of quartz, K-feldspar, plagioclase, biotite, and Fig. 7. Relationship between pressure-temperature estimates for tona- amphibole (Hammarstrom & Zen, 1986; Hollister et al., lites from the Hazu area and epidote-out reactions for various oxygen 1987), and thus, Al content of amphibole is probably con- fugacities (NNO ¼ nickel–bunsenite and HM ¼ hematite–magnetite). trolled by the following reactions: Data for epidote-out reactions are from Holdaway (1972: H72), Liou (1973: L73), and Schmidt & Thompson (1996: ST96). The P-T dia- phlogopite þ anorthite þ quartz ¼ tschermakite þ gram for tonalite melting under water-saturated conditions with oxy- K-feldspar (Hollister et al., 1987) gen fugacity buffered by NNO is modified from figure 2 of Schmidt & Thompson (1996). Abbreviations: And, andalusite; Bt, biotite; Cpx, and clinopyroxene; Ep, epidote; Ky, kyanite; Or, orthoclase; Pl, plagioclase; Qz, quartz; Sil, sillimanite. tremolite þ phlogopite þ anorthite þ albite = pargasite þ K-feldspar þ quartz (Ma¨der & Berman, 1992).

XFe The Hazu tonalites, however, contain K-feldspar only as 0 0.1 0.2 0.3 0.4 minor and interstitial phases in the matrix and as exsolved 1.5 (a) phase in plagioclase. The estimated T conditions (730–770 C) are far higher than the K-feldspar–in temperature of tonalitic composition (about 680 C at 0.5 GPa: 1.0 Schmidt & Thompson, 1996). Thus, the K-feldspar was probably a late-stage product during solidification of the Hazu tonalites, and was not stable during the major stage of crystallization of amphibole and plagioclase. The Al-con- 0.5

Pressure (GPa) trol reactions described above have gentle and positive DP/ DT slopes, and the K-feldspar–bearing right-hand sides are stable at higher P. Therefore, the estimated P conditions 0 for the epidote-bearing tonalites (0.47–0.57 GPa) probably zoisite clinozoisite - epidote indicate a lower P limit. The amphibole and biotite 50 50 employed for the P–T estimations coexist with epidote as (b) inclusions in plagioclase, and thus epidote grains were 40 40 inclusion crystallized at a pressure 0.47–0.57 GPa. 30 interstitial 30 The magmatic epidote-group minerals in tonalite from 20 20 the Hazu area show a wide compositional range from

Frequency (%) Frequency zoisite to epidote with an XFe value of 0.29. However, 10 10 most epidote grains have Fe3þ-rich compositions with 3þ 0 0 XFe . 0.24. The occurrence of such Fe -rich magmatic 0 0.1 0.2 0.3 0.4 epidote is not inconsistent with the lower P limit of mag- XFe matic epidote-bearing tonalite formation (0.47–0.57 GPa). 3þ Fig. 8. (a) Relationship between magmatic epidote composition and These Fe -rich magmatic epidote grains occur both as pressure condition for tonalitic system (Schmidt, 1993), and (b) interstitial phases in the matrix and as inclusions in plagi- frequency distribution of XFe value of magmatic epidote-group oclase, and the host plagioclase around the inclusions minerals in tonalites from the Hazu area. shows no textural evidence suggesting a reaction relation

between the two phases (Fig. 2c). Therefore, these Fe3þ- crystallization, which is revealed by systematic increase rich epidote grains were probably in equilibrium with of XFe in epidote from inclusion to matrix crystals, prob- plagioclase and crystallized directly from tonalitic ably stabilized the magmatic epidote in the matrix of the magma. On the other hand, the presence of Fe3þ-poor Hazu tonalites. epidote with XFe, 0.20 and zoisite implies an unusual Amphibole-bearing tonalites occur as intrusive bodies in high-P condition above 0.7 GPa, if they were in equili- the Ryoke metamorphic rocks of the Shimoyama and brium with the tonalitic melt. However, the Ryoke meta- Tenryu areas (e.g., Ryoke Research Group, 1972; Suzuki morphic country rocks of the tonalite are considered to & Adachi, 1998). The Shimoyama and Tenryu tonalites have recrystallized under sillimanite-stable conditions of show wide ranges of whole-rock compositions, from meta- 0.21–0.76 GPa at 700 C (Fig. 7), and thus, such high-P lumious to peraluminous, with some of them having simi- estimates are not expected for the melt solidification. lar compositions to those of the Hazu tonalites. Magmatic These Fe3þ-poor epidote and zoisite grains all occur as epidote, however, has not even been reported as either inclusions in plagioclase, unlike the Fe3þ-rich epidote. inclusions in plagioclase or in the matrix of tonalite in the Furthermore, the zoisite and Fe3þ-poor epidote included Shimoyama and Tenryu areas (e.g., Tsuboi & Asahara, in plagioclase sometimes form aggregates with K-feldspar 2009). We cannot completely deny the possibility that and other phases, and a thin zone of sodic plagioclase epidote in the Shimoyama and Tenryu tonalites was crys- 3þ (An15–19) characteristically develops between the Fe - tallized only as an interstitial phase, before being dissolved poor epidote and zoisite inclusions and their host plagio- by the host magma with decreasing P during emplacement. clase (Fig. 2a). Zoisite usually forms a lamellar texture However, the Al contents of amphibole in the Shimoyama with thin layers of Fe3þ-poor epidote (Fig. 2b), implying and Tenryu tonalites (usually Al ,1.4 pfu: Enami et al., an exsolution phenomenon during the cooling stage due to unpublished data) are distinctly lower than those in the the miscibility gap between the orthorhombic and mono- Hazu tonalites. Thus, the Shimoyama and Tenryu tonalites clinic phases (Enami & Banno, 1980; Prunier & Hewitt, possibly solidified under epidote-unstable P-T conditions, 1985; Brunsmann et al., 2002). These textural character- which are probably lower P and/or P/T conditions than for istics most likely indicate that local re-equilibration the Hazu tonalites. In other words, the tonalite magma in between the inclusion and host phases and that modifica- the Shimoyama and Tenryu areas was probably intruded tions of chemical compositions and species of minerals into the Ryoke metamorphic rocks and solidified at a occurred after the formation of the inclusion–host textural shallower level than in the Hazu area. The tonalites in the relation. The most probable interpretation of these textural Hazu, Shimoyama, and Tenryu areas have been considered characteristics, thus, is that (1) the inclusion aggregate was to share the same parent magma and intrusive and solidi- formed by a local reaction between a melt inclusion and its fication processes, and therefore are collectively called host plagioclase, (2) the Fe3þ-poor epidote and zoisite ‘‘Kamihara tonalite’’ (e.g., Ryoke Research Group, were not in equilibrium with the tonalitic melt, and (3) 1972). The occurrence of epidote-group minerals in their formation was controlled by local characteristics of ‘‘Kamihara tonalite’’ possibly indicates that tonalites in the chemical system. the Hazu area underwent intrusion processes that were Sial et al. (1999) particularly investigated modes of distinct from those in the Shimoyama and Tenryu areas. occurrence of magmatic epidote in granitoids from five Neoproterozoic tectonostratigraphic terranes in northeastern Brazil, Early Palaeozoic calc-alkalic granitoids in Acknowledgements: The authors are deeply indebted to northwestern Argentina, and from three batholiths in A.N. Sial, R. Giere´ and an anonymous reviewer for their Chile. They documented that the magmatic epidote occurs careful reading and constructive suggestions, which led to only as inclusions in biotite and K-feldspar, and concluded significant improvements in this manuscript. This research that the inclusion phase survived, whereas the matrix crys- was partially supported by grants from the Japan Society tals were probably dissolved by the host melt. In the Hazu for Promotion of Science Nos. 14540448, 18340172, tonalites, magmatic epidote grains mostly occur as inclu- 19654080, and 25400511 (ME), and 19540510 (MT). sions in plagioclase, but not in biotite and amphibole. However, individual plagioclase grains in many cases include biotite and amphibole, suggesting that these two inclusion phases coexisted with epidote, plagioclase, and References melt in equilibrium. Thus, a combination of the inclusion and matrix phases probably suggests that crystallization of Anderson, J.L. & Smith, D.R. (1995): The effect of temperature and the magmatic epidote has started at a relatively early stage fO2 on the Al-in hornblende barometer. Am. Mineral., 80, of solidification and continued until near-solidus stage. 549–559. Brasilino et al. (2011), studying magmatic epidote-bearing Asami, M. 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