Diverse Mineral Compositions, Textures, and Metamorphic Pâ€“T

Journal of Asian Earth Sciences 63 (2013) 218–233

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Journal of Asian Earth Sciences

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Diverse mineral compositions, textures, and metamorphic P–T conditions of the glaucophane-bearing rocks in the Tamayen mélange, Yuli belt, eastern Taiwan ⇑ Chin-Ho Tsai a, , Yoshiyuki Iizuka b, W.G. Ernst c a Department of Natural Resources and Environmental Studies, National Dong Hwa University, Shoufeng, Hualien 97401, Taiwan b Institute of Earth Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan c Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA article info abstract

Article history: This paper presents new petrologic data for high-pressure, low-temperature (HP–LT) metamorphic rocks Available online 28 September 2012 at Juisui. We reinterpret the so-called ‘‘Tamayen block’’ (Yang and Wang, 1985) or ‘‘Juisui block’’ (Liou, 1981; Beyssac et al., 2008) as a tectonic mélange. It is not a coherent sheet but rather a mixture domi- Keywords: nated by greenschist and pelitic schist with pods of serpentinite, epidote amphibolite, and rare blueschist. Glaucophane Four types of glaucophane-bearing rocks are newly recognized in this mélange. Type I is in contact with Epidote blueschist greenschist lacking glaucophane and garnet. Glaucophane is present only as rare inclusions within parg- HP–LT metamorphism asite. This type records metamorphic evolution from epidote blueschists-, epidote amphibolite-, to green- Amphibole zoning schist-facies. Type II contains characteristic zoned amphiboles from barroisite core to Mg-katophorite Yuli belt Tananao Complex mantle and glaucophane rim, implying an epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Type III includes winchite and indicates P–T conditions of about 6–8 kbar, approaching 400 °C. Type IV contains paragonite but lacks garnet; amphibole shows a Na–Ca core surrounded by a glaucophane rim. This type shows a high-pressure (?) epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Amphibole zoning trends and mineral assemblages imply contradictory P–T paths for the four types of glaucophane-bearing rocks—consistent with the nat- ure of a tectonic mélange. The new P–T constraints and petrologic ﬁndings differ from previous studies (Liou et al., 1975; Beyssac et al., 2008). Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Pliocene arc-continent collision mentioned above (Ernst and Jahn, 1987; Huang et al., 2006; Beyssac et al., 2008). The Yuli terrane The Yuli and Tailuko metamorphic belts in eastern Taiwan con- is thus as one of the youngest recognized blueschist belts in the stitute the Tananao Complex (Fig. 1), a pre-Tertiary polymetamor- World (Ota and Kaneko, 2010). However, the HP–LT metamorphic phosed basement sequence overprinted by a late Cenozoic record is not evident in either the in situ metasedimentary schists tectono-metamorphic event (Liou and Ernst, 1984; Lo and Onstott, of the Yuli belt (Lin, 1985), or in the landward Tailuko belt. More- 1995; Lo and Yui, 1996; Tsao et al., 1996). The young regional over, the P–T evolution of this HP–LT event and its tectonic impli- recrystallization is probably related to accretion/collision of the Lu- cations have not been well constrained by previous studies. zon volcanic arc with the Asian passive margin (Ernst and Jahn, Due to heavy vegetation and surface weathering in most of the 1987; Simoes et al., 2012). The presence of a sodic amphibole-bear- Yuli belt, the glaucophane-bearing exposures are extremely poor. ing assemblage in the so-called Tamayen or Juisui ‘‘tectonic block’’ Most previous workers collected boulders in creeks transecting (Liou et al., 1975; Liou, 1981; Yang and Wang, 1985; Sun et al., this Tamayen ‘‘block’’, and were unable to report a clear occurrence 1998; Fig. 2) implies a subduction event (Liou and Ernst, 1984; of glaucophane schist or its contact relation with adjacent Ernst and Jahn, 1987; Beyssac et al., 2008). Geochronologic data rocks (Yen, 1966; Beyssac et al., 2008). A classic petrologic paper indicate that this HP–LT metamorphism occurred during the late Liou et al. (1975) described three representative rock types: Miocene (8–14 Ma) (Jahn and Liou, 1977; Jahn et al., 1981; Lo glaucophane schist, garnet epidote amphibolite, and epidote amphib- and Yui, 1996), slightly predating the latest Miocene–earliest olite. Liou et al. speculated that the ﬁrst two might be genetically related, although no ﬁeld relationship was described. The epidote amphibolite may record two stages of metamorphism because two contrasting geochronologic data were obtained: one Rb–Sr mineral isochron age was about 79 Ma and the other was about ⇑ Corresponding author. Fax: +886 3 8633260. 5Ma(Jahn and Liou, 1977; Jahn et al., 1981). E-mail address: [email protected] (C.-H. Tsai).

Fig. 1. Simplified geologic map of a part of the Tananao Complex, eastern Taiwan (modified after Chen et al. (2000)). The Coastal Range and other Taiwan Central Range map units are neglected. Note that the Tailuko belt also contains very minor metamafic–ultramfic rocks but they are located further north and out of view in this map.

We restudied the Tamayen HP–LT occurrence by investigating with blob-like or irregular shapes on geologic maps (Yen, 1966; the field relationships, petrographic characteristcs, mineral Liou et al., 1975; Yang and Wang, 1985; Sun et al., 1998; Chen compositions, and P–T implications. We use the term glauco- et al., 2000). Previous geochemical studies indicate that these phane-bearing rocks rather than glaucophane schist as common in exotic metamafic/ultramafic rocks are likely oceanic crust proto- the literature because the studied samples are mostly massive liths (Liou et al., 1975; Jahn et al., 1981; Liou, 1981; Sun et al., rather than schistose, and several different rock types contain 1998). glaucophane. P–T conditions of glaucophane-bearing rocks in this The stratigraphically coherent in situ schists in the Juisui area area were previously estimated as 5–6 kbar, 350–400 °C(Liou, have been divided into three metasedimentary units from structu- 1981) or 10–12 kbar, 430–530 °C(Beyssac et al., 2008). ally lower to higher (a) Hongyeh unit = metapelitic schist, metapsammitic schist, and phyllite; (b) Juisui unit = albite ‘‘spotted’’ 2. Geologic setting schist, including thin layers of greenschist and garnet-mica schist, as well as serpentinite pods; and (c) Hutoushan unit = metapsam- The Tananao Complex consists of two metamorphic terranes, mitic schist intercalcated with thin layers of metapelitic schist and the Tailuko belt in the west and the Yuli belt in the east (Fig. 1; greenschist (Yang and Wang, 1985; Fig. 2). Due to lack of index Yen, 1963). These two terranes contrast in terms of rock types, minerals such as Al-silicates, metamorphic conditions of the structural patterns, peak metamorphic conditions, and ages of in situ schists are not well constrained. Metacarbonates and metag- recrystallization (Jahn et al., 1981; Liou and Ernst, 1984; Ernst ranitoids are absent from the oceanic Yuli terrane, whereas they and Jahn, 1987; Lo and Yui, 1996; Yui et al., 2009). The Tailuko belt are abundant in the continental Tailuko belt. is dominated by schists (including pelitic and psammitic schist, We reinterpret the so-called Tamayen or Juisui ‘‘tectonic block’’ and greenschist), marbles, and metagranitoids. Minor amphibolites (Liou et al., 1975; Yang and Wang, 1985; Sun et al., 1998)asa and rare serpentinite also occur. This belt was subjected to poly- mélange covering an area of about 20 km2 (Fig. 2). It is dominated metamorphic stages of greenschist- and amphibolite-facies condi- by greenschist (greenstone) and pelitic schist (blackschist), includ- tions (Liou and Ernst, 1984; Chen and Wang, 1995). The Shoufeng ing pods or blocks of (garnet) epidote amphibolites, serpentinite fault (Yen, 1963) separates these two belts, and probably repre- and glaucophane-bearing rocks (Yen, 1966; Liou et al., 1975; Yang sents a major suture (Ernst and Jahn, 1987). The Yuli belt consists and Wang, 1985; our observations). Apparent pillow strutures are mainly of a range of metapelitic, metapsammitic, and chlorite- preserved in the massive to foliated greenschist. Minor lenticular bearing schists (greenschists). Exotic lithotypes, dominant metab- or irregular exotic serpentinite pods (some brecciated) are interca- asites and/or serpentinites, also occur in the Fengtien, Wanjung, lated with the metabasites (Liou et al., 1975; Hsu, 1983). Glauco- Juisui, and Chinsuishi areas (Liou et al., 1975; Lin et al., 1984; Yang phane-bearing rocks are rare and have been reported only from and Wang, 1985; Yui and Lo, 1989; Lin, 1999). The Juisui metama- the Tamayen mélange but not the in situ schists in the Juisui area. fic/ultramafic rocks have been interpreted as ‘‘tectonic blocks’’ and We collected samples mainly from an outcrop in the southwestern marked as several isolated but coherent thrust sheets or bodies margin of this mélange (Fig. 2). 220 C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233

Fig. 2. Simplified geologic map of the Tamayan area (modified after Yen (1966), Liou et al. (1975), Hsu (1983), Yi et al. (2012); and present authors). Red crosses denote glaucophane outcrops of Yen (1966). Drill hole HJ-1 (solid triangle) revealed that a thick layer of amphibole-bearing meta-mafic rock is intercalated with metapelites in the Hongyeh unit (Hsu, 1983). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3a. A slump block in locality 1 (Fig. 2) with garnet-rich, glaucophane-bearing rock (Type I) on the left and garnet-free mafic greenschist on the right. Note that the Fig. 3b. Garnet-free mafic greenstone with flattened pillow structures on the left horizontal quartz vein on the left is truncated by a near vertical boundary in the and garnet-rich glaucophane-bearing rock (Type I) on the right. The medial middle, implying that recrystallization of the mafic greenschist might have boundary zone is enriched in coarse-grained, dark-green calcic amphibole and fine- postdated that of the Type I glaucophane-bearing rock. (For interpretation of the grained yellowish epidote as thin folded layers. Vertical dimension of this view is references to colour in this figure legend, the reader is referred to the web version of about 4 m. (For interpretation of the references to colour in this figure legend, the this article.) reader is referred to the web version of this article.) C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 221

3. Field occurrences of glaucophane-bearing rocks

Although the outcrop conditions in the Tamayen area are extremely poor as mentioned above, previous studies described a few possible glaucophane-bearing occurrences. Yen (1959) reported that glaucophane-bearing rocks might be intercalated with albite ‘‘spotted’’ schist, which equals to the Juisui unit schist in this study. According to Yen (1966) and Liou et al. (1975), glaucophane- bearing rocks occur as small lenses or layers (about 0.2–5.0 m thick and 2–50 m long) enclosed by a thick metabasaltic sequence, including epidote amphibolites and greenschists (both ± white mica), with grain-size variation and bands of metamorphic differ- entiation. We found that some serpentinite bodies (a few to tens of meters in dimensions) are sandwiched within non-ophiolitic rocks such as garnet-bearing mica-quartz schist, which apparently belong to the Yuli belt in situ schists. Such an occurrence implies that these serpentinitic or peridotitic pods might have been included in the protolithic sediments before the late Cenozoic Fig. 4b. Photomicrograph in reflected light showing two grains of chalcopyrite (ccp, regional metamorphism. An alternative interpretation is that these bright yellow within grain) overgrown by bornite (bn, orange in mantle) and ultramafics might represent fragments of mantle wedge. chalcocite (cct, bluish grey in rim) in Type I rock. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of We have identified several types of glaucophane-bearing rocks this article.) with different mineral modes, textures, and grainsizes (especially amphiboles) at both outcrop and hand-sample scales. In general, glaucophane-bearing rocks occur as layers or irreguar masses (tens of cetimeters to <10 m) surrounded by greenschist or greenstone. Several meter-scale boulders of the in situ metasedimentary and metabasaltic rocks in locality 1 (Fig. 2) show that garnet-rich glaucophane-bearing rocks (Type I) are in direct contact with garnet- free mafic greenschist (Fig. 3a). In some cases, a thin contact zone of coarse-grained dark amphibole and yellow-greenish epidote lies between Type I garnet-glaucophane-bearing rock and greenschist; the latter preserves pillow structures (Fig. 3b). These occurrences implies that protoliths of the Type I glaucophane-bearing rocks might have been an interlayer in the pillow lava. In contrast, pre- vioius studies suggested that some glaucophane-bearing rocks might have been volcanic materials mixed with Mn-rich marine sediments (Liou et al., 1975; Jahn et al., 1981). Pillow-structured greenschist occurs both within and outside the Tamayan mélange, as abundant large boulders (3–7 m in long dimension) were found along the Hongyeh River.

From a poorly exposed surface of about 12 m horizon- Fig. 4c. Photomicrograph in plane polarized light of zoned amphibole porphyro- tally Â 7 m vertically in a quarry at locality 1 (Fig. 2), from the cen- blast in Type II sample showing pale core (barroisite, brs), bluish-green mantle (Mg- ter of the outcrop outwards, rocks vary from glaucophane-bearing katophorite/taramite, Mg-ktp/trm) and lavender blue rim (glaucophane, gln). Note (Type III) to glaucophane-free epidote/hornblende-rich, whereas that the core contains abundant tiny inclusions whereas the mantle is inclusion- the texture remains similar. This glaucophane-free rock is less poor. Matrix minerals shown are mainly garnet (high-relief), phengite, epidote, quartz, biotite (yellow-brownish), and opaques. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.)

mafic but contains larger porphyroblastic pinkish garnet and more abundant epidote. Type II rocks are apparently coarser and seem to occur in between these two lithotypes. Amphibole grainsize in the glaucophane-bearing rocks varies from fine-grained (longest dimension <1 mm) to coarse-grained (>5 mm), but, except for Type I, no direct contact relations can be observed in field. Locally, quartz-rich veins and pockets (±epidote and amphibole) crosscut the glaucophane-bearing and glaucophane-free rocks. A different kind of glaucophane-bearing rock (Type IV) was collected at locality 2 (Fig. 2). It is a float sample but certainly was derived from the Tamayen mélange. Its relationship with the other three types remains unknown.

4. Petrography Fig. 4a. BSE image of inclusions in a Type I amphibole porphyroblast. Glaucophane (gln) appears to be a relict phase within the pargasitic amphibole host (prg). Note the thin actinolitic rim (act) in the upper-left corner of this photo (grt: garnet; ilm: We determined the petrographic features of the minerals and ilmenite; act: actinolite; ep: epidote; qz: quartz). their host rocks using a polarizing microscope and a SEM (JEOL 222 C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233

Fig. 4d. Photomicrograph in plane polarized light of glaucophane (gln) is included Fig. 4f. Photomicrograph in plane polarized light of yellowish-green amphibole within a bluish-green katophorite (ktp) rim overgrowth on a pale barroisite (brs) (katophorite, ktp, or taramite, trm) surrounded by lavender blue glaucophane (gln) core in a Type II subgroup sample. The matrix shown is mostly epidote and quartz. in a Type IV sample. This rock lacks garnet but contains paragonite (pg). (For (For interpretation of the references to colour in this ﬁgure legend, the reader is interpretation of the references to colour in this ﬁgure legend, the reader is referred referred to the web version of this article.) to the web version of this article.)

4.1. Type I

Major phases are amphibole (42%), quartz (24%), epidote (21%), and garnet (11%). In these rocks, glaucophane occurs only as rare inclusions within porphyrobastic bluish-green pargasitic amphibole. Other inclusions are epidote, garnet, quartz, ilmenite, and rutile. Pargasitic crystals are surrounded by thin actinolite rims (Fig. 4a). The porphyroblasts show significant grain-size variation even at the thin section scale. Some garnet grains are euhedral, but some grains are rounded. These rounded grains have been resorbed. Accessory matrix phases include titanite, apatite, Cu sulfides, rutile, ilmenite, and zircon. The sulfides exhibit a three- stage zonation texture with chalcopyrite overgrown by bornite and chalcocite (Fig. 4b). Three metamorphic stages are inferred by mineral assemblages: (I) gln + qz ± grt ± ep; (II) prg + qz + grt + ep + rt ± ilm; (III) act + qz + ep + chl + ttn.

Fig. 4e. Photomicrograph in plane polarized light of lavender blue glaucophane (gln) rimmed by bluish-green amphibole (winchite, wnc) in Type III rock. An euhedral garnet lies in the center of the slide. The matrix phases are mainly epidote 4.2. Type II and quartz. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) This type contains phengite (33%), amphiboles (20%), quartz (14%), garnet (10%), chlorite (10%), and epidote (8%). Accessory JSM-6380LV) outfitted with an energy-dispersive spectrometer phases (5%) are titanite, biotite, albite, apatite, and magnetite. Rare (EDS; Oxford INCA 350) at National Dong Hwa Univeristy, Hualien, rutile and ilmenite occur as inclusions in titanite, epidote, amphi- Taiwan. SEM analytical conditions were 15 kV acceleration voltage bole, or magnetite. Porphyroblastic amphibole mostly has a colore- and 0.18 nA beam current. Back-scattered electron (BSE) images less barroisite core, a bluish-green Mg-taramite/katophorite were obtained from polished thin sections or epoxy discs. Amphi- mantle, and a lavender-blue glaucophane rim (Fig. 4c). This rock bole nomenclature follows Leake et al. (1997) on the basis of EDS type is probably the same as the glaucophane schist of Liou et al. and/or electron microprobe data. Mineral abbreviation follows (1975) and Jahn et al. (1981). In some samples the barroisitic core Whitney and Evans (2010). is absent. The core, mantle, and rim may contain finer grained The most characteristic feature of the glaucophane-bearing inclusions of garnet, epidote, and quartz. In some cases, glauco- rocks is that dark amphibole occurs as elongated prisms in a light phane also occurs as inclusions within the amphibole porphyrob- matrix of variously-dominant garnet, epdiote, quartz, and/or white lastic core and mantle. Such a feature is difficult to interpret (cf. mica. The texture resembles the common scene of bamboo leaves Chen and Yang, 1997). Locally, rims of the zoned porphyroblast in Chinese paintings, and local people refer to such rocks as are surrounded by a corona or symplectite of biotite ± quartz. Gar- ‘‘Chu-Yeh Shi’’ (bamboo-leaf stone). We divided the glaucophane- net tends to be concentrated in phengite-rich domains but is rare bearing samples into four sub-types on the basis of occurrence, in late-stage, quartz-rich domains. Three metamorphic stages are texture, and mineral composition. All contain amphiboles, garnet inferred by mineral assemblages: (I) qz + grt + ep ± gln ± chl ± rt ± (except for Type IV), quartz, epidote, chlorite, titanite, and albite. bt; (II) brs/ktp/trm + qz + grt + ep + ph + chl + rt + ttn ± ilm ± ab; Rocks associated with the glaucophane-bearing lithologies are (III) gln + qz + ep + ph + chl + ab + ttn ± bt. A Type II subgroup lacks briefly described as well. A more detailed characterization of these white mica, and glaucophane does not occur as a rim phase but is glaucophane-free rocks will be presented in another paper in included within green Na–Ca amphibole mantling the barroisitic preparation. core (Fig. 4d). C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 223

Table 1 Selected amphibole compositions analyzed by EPMA.

Rock type Type I Type II Sample 10-23 1804 10-24 10-30 1801A Texture Inc Host Rim Core Mantle Rim Mantle Rim Inc Core Mantle Rim Core Mantle

SiO2 54.83 43.29 52.76 46.80 44.59 54.44 47.74 54.21 56.81 49.50 48.38 54.03 49.19 46.48

TiO2 0.03 0.48 0.01 0.14 0.35 0.00 0.07 0.03 0.03 0.13 0.12 0.04 0.16 0.32

Al2O3 9.05 14.05 2.59 10.33 11.86 8.67 9.28 8.52 11.34 8.55 8.35 8.30 7.60 10.69

Cr2O3 0.01 0.00 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 FeO 14.04 16.03 15.09 20.10 20.17 18.99 15.78 20.83 8.14 7.37 13.98 20.66 9.65 17.52 MnO 0.29 0.27 0.63 0.20 0.06 0.11 0.33 0.13 0.42 1.52 0.79 0.09 1.29 0.46 MgO 10.14 9.72 14.11 7.45 7.31 6.34 11.46 6.14 12.32 16.95 12.99 6.13 15.72 9.55 CaO 1.89 9.55 10.19 6.28 7.23 0.94 7.83 1.28 1.71 8.82 7.72 0.96 9.19 8.87

Na2O 5.96 3.39 1.30 4.65 4.51 6.45 3.77 6.48 6.34 3.05 3.86 6.35 2.91 3.41

K2O 0.00 0.35 0.05 0.23 0.32 0.00 0.17 0.04 0.00 0.15 0.22 0.01 0.19 0.38 Total 96.24 97.13 96.73 96.18 96.43 95.94 96.43 97.66 97.11 96.04 96.41 96.57 95.90 97.71 O=23 Si 7.694 6.371 7.621 6.980 6.689 7.856 6.952 7.749 7.715 6.965 6.984 7.777 7.037 6.819 IVAl 0.306 1.629 0.379 1.020 1.311 0.144 1.048 0.251 0.285 1.035 1.016 0.223 0.963 1.181 VIAl 1.191 0.809 0.062 0.796 0.785 1.331 0.544 1.183 1.530 0.383 0.406 1.184 0.319 0.666 Ti 0.003 0.053 0.001 0.016 0.039 0.000 0.007 0.003 0.003 0.013 0.013 0.004 0.017 0.035 Cr 0.001 0.000 0.000 0.000 0.003 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.003 Fe3+ 0.899 0.659 0.775 0.782 0.734 0.707 0.930 0.851 0.573 0.868 1.048 0.942 0.933 0.605 Fe2+ 0.748 1.313 1.047 1.725 1.796 1.584 0.991 1.638 0.351 0.000 0.640 1.545 0.222 1.545 Mn 0.035 0.034 0.077 0.025 0.008 0.014 0.040 0.016 0.049 0.181 0.097 0.011 0.156 0.057 Mg 2.122 2.132 3.038 1.656 1.634 1.364 2.487 1.309 2.494 3.555 2.796 1.314 3.354 2.089 Ca 0.284 1.506 1.577 1.004 1.162 0.146 1.222 0.196 0.249 1.330 1.195 0.148 1.408 1.393 Na 1.620 0.966 0.363 1.345 1.312 1.803 1.064 1.796 1.670 0.832 1.081 1.771 0.807 0.971 K 0.001 0.066 0.008 0.043 0.062 0.000 0.031 0.007 0.000 0.027 0.040 0.001 0.034 0.071 Total 14.904 15.538 14.948 15.392 15.535 14.949 15.316 14.999 14.919 15.189 15.316 14.920 15.250 15.435 (B)Na 1.620 0.494 0.363 0.996 0.838 1.803 0.778 1.796 1.670 0.670 0.805 1.771 0.592 0.607 (A)Na 0.000 0.472 0.000 0.349 0.474 0.000 0.286 0.000 0.000 0.162 0.276 0.000 0.215 0.364 XMg 0.739 0.619 0.744 0.490 0.476 0.463 0.715 0.444 0.876 1.000 0.814 0.460 0.938 0.575 XFe3+ 0.430 0.449 0.926 0.496 0.483 0.347 0.631 0.418 0.273 0.694 0.721 0.443 0.745 0.476 Name Gln Prg Act Fbrs Ktp Fgl Brs Fgl Gln Brs Brs Fgl Brs Brs Type II Type III Type IV Grt-amp rock Greenschista 1801A 110408 100602 1806 100202 FD CD Rim Inc Rim Core Rim Host Rim Host Rim

SiO2 53.32 55.33 56.15 51.97 52.47 43.96 54.70 43.64 44.89 56.12 52.26 54.75 52.17 54.67

TiO2 0.04 0.06 0.06 0.08 0.05 0.43 0.08 0.56 0.37 0.17 0.19 0.09 0.00 0.00

Al2O3 4.34 8.37 8.65 3.80 3.14 13.30 8.84 14.57 12.93 8.93 5.95 3.90 6.44 4.77

Cr2O3 0.00 0.01 0.00 0.00 0.00 0.02 0.06 0.00 0.05 0.11 0.00 0.00 0.00 0.00 FeO 14.71 14.37 12.88 17.44 15.78 20.11 16.48 15.46 14.81 13.66 9.46 9.26 9.56 9.45 MnO 0.40 0.26 0.46 0.74 0.68 0.17 0.11 0.18 0.24 0.18 0.63 0.61 0.00 0.00 MgO 13.14 9.43 10.21 11.82 13.00 7.20 8.10 9.77 10.14 9.80 16.45 17.11 15.71 16.09 CaO 8.79 1.44 1.81 9.03 9.77 8.22 2.22 9.92 9.02 2.37 10.89 10.94 13.19 12.23

Na2O 2.57 6.51 6.54 2.26 1.81 4.17 6.19 3.12 3.74 6.31 1.84 1.37 1.47 1.51

K2O 0.05 0.00 0.00 0.12 0.08 0.29 0.01 0.28 0.24 0.03 0.12 0.08 0.00 0.00 Total 97.36 95.78 96.76 97.26 96.78 97.87 96.79 97.50 96.43 97.68 97.79 98.11 98.54 98.72 O=23 Si 7.643 7.858 7.868 7.563 7.634 6.519 7.799 6.383 6.620 7.842 7.354 7.639 7.439 7.710 IVAl 0.357 0.142 0.132 0.437 0.366 1.481 0.201 1.617 1.380 0.158 0.646 0.361 0.561 0.290 VIAl 0.376 1.259 1.298 0.214 0.172 0.844 1.284 0.895 0.866 1.313 0.341 0.279 0.521 0.503 Ti 0.004 0.007 0.006 0.008 0.005 0.048 0.009 0.061 0.041 0.018 0.020 0.009 0.000 0.000 Cr 0.000 0.001 0.000 0.000 0.000 0.002 0.007 0.000 0.006 0.012 0.000 0.000 0.000 0.000 Fe3+ 0.545 0.631 0.495 0.718 0.607 0.667 0.498 0.546 0.457 0.369 0.452 0.405 0.000 0.000 Fe2+ 1.218 1.075 1.014 1.404 1.313 1.827 1.467 1.345 1.369 1.227 0.661 0.675 1.140 1.114 Mn 0.049 0.031 0.054 0.091 0.084 0.021 0.013 0.022 0.030 0.021 0.076 0.073 0.000 0.000 Mg 2.808 1.996 2.133 2.564 2.820 1.592 1.722 2.130 2.229 2.041 3.450 3.559 3.339 3.383 Ca 1.349 0.218 0.272 1.408 1.523 1.305 0.338 1.554 1.425 0.355 1.642 1.635 2.015 1.848 Na 0.713 1.791 1.777 0.638 0.509 1.197 1.711 0.886 1.069 1.710 0.502 0.371 0.406 0.413 K 0.010 0.001 0.000 0.023 0.014 0.054 0.001 0.053 0.044 0.006 0.022 0.014 0.000 0.000 Total 15.072 15.010 15.049 15.068 15.047 15.557 15.050 15.492 15.536 15.072 15.166 15.020 15.421 15.261 (B)Na 0.651 1.782 1.728 0.592 0.477 0.695 1.662 0.446 0.575 1.645 0.358 0.365 0.00 0.15 (A)Na 0.062 0.010 0.049 0.046 0.032 0.503 0.049 0.440 0.494 0.065 0.144 0.006 0.41 0.26 XMg 0.697 0.650 0.678 0.646 0.682 0.466 0.540 0.613 0.619 0.624 0.84 0.84 0.75 0.75 XFe3+ 0.592 0.334 0.276 0.770 0.780 0.441 0.280 0.379 0.346 0.219 0.57 0.59 0.00 0.00 Name Wnc Gln Gln Wnc Act Ktp Gln Ts Mkt Gln Mhb Act Mhb Act

XMg = Mg/(Mg + Fe2+), XFe3+ =Fe3+/(Fe3++VIAl). Inc: inclusion; Gln: glaucophane; Prg: pargasite; Act: actinolite; Ktp: katophorite; Brs: barroisite; Fgl: Fe-glaucophane; Fbrs: Fe-barroisite; Wnc: winchite; Ts: tschermakite; Mkt: Mg-katophorite; Mhb: Mg-hornblende. a EDS data. 224 C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233

4.3. Type III whereas the rim is actinolite. White mica occurs only locally. Rutile is enclosed in titanite. Since rutile is not stable in greenschist facies This rock type is significantly finer grained than the two de- conditions, the existence of rutile prior to titanite may imply an scribed above. It is intercalated with glaucophane-free epidote-rich earlier stage of high-pressure metamorphism (Ernst and Liu, garnet-amphibole rocks (see below) at the outcrop locality 1 1998; Diener et al., 2007). (Fig. 2). Major phases are amphiboles (40%), epidote (19%), garnet (12%), and quartz + albite (27%). Accessory phases include chlorite, 4.6. Paragonite-bearing garnet-epidote amphibolite titanite, hematite, rutile, apatite, and zircon. Garnet is euhedral and zoned. Quartz, epidote, and rare dolomite are present in garnet This type contains amphibole, garnet, paragonite, epidote, chlo- cores. The textural relationships among amphiboles are ambigu- rite, rutile, ilmenite, muscovite, and zircon. Euhedral garnet occurs ous, although bluish-green to green amphiboles (barroisite, win- sporadically and tends to be concentrated in layers; it lacks signif- chite, actinolite) tend to surround blue glaucophane (Fig. 4e). icant zoning and is Fe-rich (up to Alm65) and Mn-poor (less than Patchy bluish-green amphibole also occurs within blue amphibole. Sps10). Mg and Ca contents are about Prp10 and Grs18 respectively. The garnet composition is slightly different from the other two Amphibole is calcic and unzoned. Rutile is included in ilmenite. In types (see Section 5). Three metamorphic stages are inferred by contrast to the glaucophane-bearing rocks, this higher metamor- mineral assemblages: (I) qz + grt + ep + gln ± rt; (II) wnc/ phic grade rock lacks titanite (cf. Ernst and Liu, 1998). brs + qz + grt + ep + ttn; (III) act + qz + ep + ab + chl + ttn. 4.7. Epidote-rich garnet-amphibole rock 4.4. Type IV This rock is pale-yellowish in hand specimen and is relatively fi- This garnet-absent rock type contains paragonite and is quite ner grained than glaucophane-bearing rocks. It contains epidote rare. This rock is more mafic (basaltic) than the three other types, (53%), calcic amphibole (25%), quartz (14%), garnet (4%), titanite which are intermediate (andesitic) in bulk composition (cf. Jahn (2%), apatite, and zircon. Garnet is euhedral, pinkish, and signifi- et al., 1981; Sun et al., 1998). Glaucophane appears to surround cantly coarser than those of glaucophane-bearing rocks. Garnet, green Na–Ca katophorite (Fig. 4f). The studied sample has a glauco- epidote, and amphibole all are zoned. Amphible shows a magnesio- phane-bearing part separated from a glaucophane-free part by epi- hornblende core and an actinolite rim. dote-rich veinlets. In the lighter colored glaucophane-bearing part, major phases are amphiboles (45%), epidote (24%), paragonite (10%), and quartz + albite (18%). Minor and accessory minerals in- 5. Mineral compositions clude muscovite, chlorite, rutile, ilmenite, Cr-rich magnetite, hematite, apatite, titanite, calcite, and zircon. The glaucophane- We determined mineral compositions using an electron probe free dark part is relatively coarse-grained, and contains yellow- micro-analyzer (EPMA; JEOL JXA-8900R) equipped with four ish-green amphibole, muscovite, chlorite, and albite. Two meta- wave-length dispersive spectrometers (WDS) at the Institute of morphic stages are inferred by mineral assemblages: (I) qz + ktp/ Earth Sciences, Academia Sinica in Taipei. For quantitative analysis, trm + pg + ep + rt ± ab; (II) gln + qz + ep + ph + chl + ab. This Type a2lm defocused beam was operated at 15 kV acceleration voltage IV rock is more mafic than the other three types. and 12 nA beam current. The measured X-ray intensities were cor- rected by the ZAF method using standard analytical and calibration 4.5. Greenschist and/or greenstone techniques.

This rock is greenish with or without foliation. It contains chlo- 5.1. Amphibole rite, epidote, albite, quartz, calcic amphibole, titanite, and white mica. Both amphibole and epidote show two stages of recrystalli- Amphibole formula recalculation follows Leake et al. (1997) and zation. The amphibole core is magneisohornblende or edenite, the results are classiﬁed in the Ca, Na–Ca, and Na groups. The

Fig. 5. Sodic amphibole compositions plotted in the Mg/(Mg + Fe2+) vs. Fe3+/(Fe3++VIAl) diagram. Ranges denoting amphibole blueschist and greenschist environments are from Bousquet et al. (2008). The hematite/magnetite buffer is from Okay (1980). (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 225

Fig. 6a. [B]Na–IVAl diagram of representative amphibole compositions. The colored arrows show core-to-mantle variations of Type II, III, and IV. The amphibole compositions of Type III and glaucophane-free garnet-amphibole rock are signiﬁcantly different from those of the other three rock types. The isobaric curves are based on the Fig. 10 in Brown (1977). Amphibole names allocated in this diagram follow the usage in Tsujimori et al. (2006). (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.)

Fig. 6c. A rim-to-core compositional proﬁle expressed as per-formula-unit values of IVAl and [B]Na vs. distance for a zoned amphibole in Type II (same sample as Fig. 6b). Fig. 6b. BSE image of a zoned amphibole in a Type II rock. Note that the core– mantle transition is gradational whereas the mantle–rim boundary is sharp.

IMA-abandoned sodic amphibole term crossite is used for compar- ison of our data with those from the literature. Most amphiboles are zoned and reveal a wide range of compositional variation (Ta- ble 1, Figs. 5 and 6). Sodic amphibole compositions in all rock types are mostly glaucophane ± minor ferroglaucophane. According to the compilation by Bousquet et al. (2008), sodic amphibole compositions of the Tamayen rocks fall within the range of blueschist terranes world- wide (Fig. 5). Sodic-calcic amphibole compositions in all types (except Type I) lie within the ﬁeld of barroisite and Mg-taramite/ katophorite (Fig. 6a). Calcic amphibole compositions are within the range of magnesiohornblende, edenite, pargasite, and actinolite. In Type I, porphyroblastic amphibole compositions plot near the boundary between pargasite and taramite (Fig. 6a). This Fig. 6d. A rim-to-core compositional proﬁle for another zoned Type II amphibole. 226 C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 pargasite overprinting might have caused the disappearance of Na–Ca group, are new data and have never been reported before glaucophane in adjacent rocks as the observed occurrence de- (cf. Lan, 1993; Beyssac et al., 2008). scribed earlier. In Type II, the core–mantle transition is gradational, IV whereas the mantle–rim boundary is sharp (Fig. 6b). The Al con- 5.2. Garnet tent is relatively homogeneous in the core, slightly enriched in the [B] mantle, and dramatically depleted in the rim, whereas the Na Garnets of Type I and II samples are relatively Fe-rich (up to content is homogeneous in core–mantle but abruptly enriched in Alm66), whereas Type III garnet is Mn-rich (up to Sps70)(Table 2; IV the rim (Fig. 6c). In some other Type II samples, the Al content Fig. 7a). Spassertine contents are about 20% in Type I, 10–50% in in the core and mantle shows a variation similar to oscillatory zon- Type II, and 40–70% in Type III. Type I garnet is generally homoge- ing (Fig. 6d). Many of the amphibole compositions, especially the neous. Type II garnet shows complex zoning with an atoll-shaped

Table 2 Selected garnet compositions analyzed by EPMA.

Rock type Type I Type II Type III Grt-amp rock Sample 10-23 1804 10-24 10-30 1801A 110408 1806 Texture Core Rim Core Rim Core Rim Core Rim Core Rim Core Rim

SiO2 37.80 36.11 36.34 37.36 38.54 38.42 38.05 37.88 37.71 38.97 37.15 37.95 38.07 37.93 38.28

TiO2 0.07 0.01 0.30 0.06 0.20 0.09 0.20 0.08 0.26 0.28 0.27 0.02 0.29 0.06 0.08

Al2O3 20.73 20.36 19.67 21.32 20.58 21.70 20.62 20.94 20.65 19.8 20.49 20.75 19.32 20.85 21.36 FeO 25.70 25.37 24.98 28.08 29.80 28.71 13.33 24.88 12.28 21.29 3.49 16.19 8.57 11.45 17.49 MnO 7.62 7.37 9.70 6.35 6.00 5.15 20.13 10.34 19.58 12.31 29.53 15.47 19.94 19.12 14.01 MgO 2.32 3.23 1.46 2.13 1.08 2.09 1.88 2.00 2.5 1.67 1.98 1.68 0.92 1.70 1.82 CaO 6.73 5.90 7.04 5.34 6.57 5.93 7.01 4.97 6.99 7.38 6.56 8.07 12.76 9.20 8.18 Total 100.97 98.35 99.49 100.64 102.77 102.09 101.22 101.09 99.97 101.70 99.47 100.13 99.87 100.31 101.22 O=12 Si 3.005 2.951 2.972 2.984 3.035 3.011 3.017 3.015 3.009 3.077 2.996 3.028 3.049 3.015 3.015 Ti 0.004 0.001 0.019 0.004 0.012 0.005 0.012 0.005 0.016 0.017 0.016 0.001 0.017 0.003 0.005 Al 1.942 1.961 1.896 2.007 1.910 2.003 1.927 1.964 1.942 1.843 1.947 1.951 1.824 1.953 1.982 Fe2+ 1.708 1.734 1.708 1.875 1.962 1.880 0.884 1.656 0.819 1.406 0.235 1.080 0.574 0.761 1.151 Mn 0.513 0.510 0.672 0.429 0.400 0.342 1.351 0.697 1.323 0.823 2.016 1.045 1.353 1.287 0.934 Mg 0.274 0.394 0.178 0.253 0.126 0.243 0.222 0.237 0.297 0.196 0.238 0.199 0.110 0.201 0.214 Ca 0.573 0.516 0.617 0.457 0.554 0.498 0.595 0.423 0.598 0.624 0.567 0.689 1.095 0.784 0.690 Total 8.019 8.067 8.062 8.009 7.999 7.982 8.008 7.997 8.004 7.986 8.015 7.993 8.022 8.004 7.991 Prp91368487810687477 Alm 56 55 54 62 65 64 29 55 27 46 8 35 18 25 39 Sps 16 16 21 14 13 11 44 23 43 27 66 35 43 42 31 Grs 19 16 19 15 18 17 20 14 20 21 18 23 35 26 23

Prp: pyrope; alm: almandine; sps: spessartine; grs: grossular.

Fig. 7a. Garnet compositions plotted in endmember ternary diagrams. Note that the garnet of the glaucophane-free garnet-amphibole-epidote rock is signiﬁcantly different from those of the glaucophane-bearing rocks. C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 227 mantle domain of high Mn content (Fig. 7b). Most grains in the is absent from Type I and Type III lithologies. Those in Type IV in- Type II show core–rim zoning with very slight Prp increasing and clude paragonite and muscovite, but the former occurs as relics in- Grs decreasing, which might suggest a P–T increasing process cluded in the latter. (Wei et al., 2009; Wei and Clarke, 2011). But the zoning trend is not continuous. Type III garnet also shows zoning, with the highest 5.5. Biotite Mn content in the core–mantle (Fig. 7c). Garnet from glaucophane- free epidote-rich garnet-amphibole rock is Mn-rich (up to Sps58). In Biotite was not reported by previous workers (Liou et al., 1975; the Type I, II and III rocks, compositions of garnet inclusions in Lan and Liou, 1984; Beyssac et al., 2008). We discovered it only in amphibole and those in matrix are similar. In general, Grs contents Type II rocks, where it occurs as (a) inclusions in porphyroblastic in these three rock types are low, implying that the XCO2 might be amphibole; (b) intergrown with quartz in a symplectite after high during the garnet crystallization (Wei and Clarke, 2011). amphibole; (c) in coronas surrounding zoned amphibole porphyroblasts and grading continuously into matrix phengite; (d) in 5.3. Epidote straight contact with phengitic mica in the groundmass. Biotite compositions are listed in Table 4. Epidote exhibits zoning in most of the samples studied. Selected epidote compositions are listed in Table 3. Compositional ranges 5.6. Chlorite are expressed as Fe3+/(Fe3++Al) and are summarized in Fig. 8. Epi- dote zoning trends of the Type III, the glaucophane-free garnet- Chlorite mostly is a late-stage, retrograde phase replacing por- amphibole rock, and greenschist are the opposite of those from phyroblastic calcic, sodic-calcic, and sodic amphiboles. Less com- the other three glaucophane-bearing types (cf. Maruyama and monly, chlorite occurs as inclusions in Type II amphiboles and Liou, 1988), implying that these rocks might have undergone dif- exhibits different compositions from those with mica in the matrix ferent P–T evolutions. (Table 5).

5.4. White mica 5.7. Plagioclase

White mica in Type II rocks is phengitic (Table 4), and appears All analyzed plagiclase crystals from the glaucophane-bearing to be in textural equilibrium with garnet and biotite. White mica rocks are pure albite (

Fig. 7b. Element mapping of garnet in a Type II rock by EPMA. Warmer color represents higher content. Note the atoll-shaped high Mn domain in mantle. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 228 C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 detected. Albite in greenschist is slightly enriched in Ca compared core to rim in a single grain: Type I = glaucophane ? pargasitic/sodic- to analogues in glaucophane-bearing rocks (cf. Lan and Liou, 1984). calcic amphibole ? actinolite; Type II = barroisite ? Mg-katophorite/taramite ? glaucophane; Type III = glaucophane ? barroisite/ 5.8. Ti-rich phases winchite ? actinolite; Type IV = katophorite ? glaucophane. At least two different P–T paths can be inferred from the different In Type I and Type II rocks, rutile and ilmenite are included in zoning trends, judging by the experimentally-bracketed or empir- amphibole porphyroblasts, whereas titanite is mainly confined to ically-calibrated stability fields of amphiboles (Ernst, 1979; Otsuki the matrix. One of our analyzed ilmenites contains substantial and Banno, 1990). One is clockwise (Type I and Type III) and the MnO (up to 7.8 wt.%). All three Ti-rich phases coexist in Type IV other is counter-clockwise (Type II and Type IV) (Fig. 9). samples. Rutile is also enclosed within titanite in the greenschist, In general, the peak-pressure stage is represented by the assem- but is absent in the epidote-rich garnet-amphibole rock. blage glaucophane–epidote–garnet–phengite–albite, which probably was produced under the epidote blueschist or epidote 5.9. Fe-oxides amphibolite facies conditions (Evans, 1990; Zhang et al., 2009). The Al2O3 content of sodic amphibole in a low-variance, buffered Type I lacks Fe-oxide. Type II contains magnetite. Type III con- assemblage is a potential geobarometer (Maruyama et al., 1986). tains hematite. Type IV contains hematite and rare Mn–Al-bearing We applied this geobarometer to Type III sodic amphiboles, which Cr-rich magnetite. Both magnetite and hematite have been re- possess the highest Al2O3 content (10.0 wt.%), yielding a nominal ported in previous studies (Liou et al., 1975; Liou, 1981). pressure of 6–7 kbar. This value is consistent with the stability field of chl–gln–ep–ab in a P–T pseudosection for common basalt 6. P–T conditions compositions calculated by Dale et al. (2005). If the empirical semi-quantitative geobarometer of Brown (1977) is applied, the Mineral zoning in metamorphic rocks generally reflects chang- pressure is slightly over 7 kbar (Fig. 6). Accordingly, we tentatively ing chemical environments and/or contrasting P–T conditions assign a pressure of 6–8 kbar for the studied Type III glaucophane- (Trzcienski et al., 1984; Hosotani and Banno, 1986; Sperlich, bearing rocks. Due to the lack of suitable thermometers, it is more 1988; Banno, 2000). In some phase assemblages, sodic amphibole difficult to constrain metamorphic temperatures. We estimated zoning may reflect a change in oxygen fugacity during metamor- the temperatures and P–T paths of the four types of glauco- phism (Okay, 1980). Amphibole compositional variations in the phane-bearing rocks on the basis of amphibole zoning trends rela- Tamayen glaucophane-bearing rocks are summarized below. From tive to stability fields, calculated phase diagrams (Evans, 1990),

Fig. 7c. Element mapping of garnet in a Type III rock by EPMA. Warmer color represents higher content. Note the exquisite euhedral shape of the crystal and the sharp Mn- depletion zone in the thin outer rim. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 229

Table 3 Selected epidote compositions analyzed by EPMA.

Rock type Type I Type II Sample 10-23 1804 10-24 10-30 1801A Texture C R C O-C M C R C O-C M C O-C M

SiO2 37.76 37.66 37.78 34.64 37.53 37.57 37.70 36.69 34.80 38.03 38.26 35.37 37.77

TiO2 0.00 0.05 0.00 0.00 0.02 0.00 0.10 0.00 0.00 0.08 0.11 0.05 0.10

Al2O3 24.40 22.19 23.47 19.59 22.30 23.24 21.93 21.90 20.30 23.02 23.80 23.23 23.17

Cr2O3 0.00 0.00 0.03 0.02 0.01 0.00 0.00 0.04 0.02 0.00 0.00 0.05 0.00

Fe2O3 12.67 15.81 12.22 13.33 13.95 13.53 15.59 12.23 12.12 13.42 12.48 13.06 13.53 MnO 0.64 0.45 1.51 0.93 0.27 1.18 0.44 1.31 1.26 0.15 0.06 1.19 0.68 MgO 0.05 0.00 0.12 0.49 0.04 0.15 0.00 0.38 0.68 0.02 0.02 0.05 0.05 CaO 22.37 22.84 21.50 16.68 22.16 21.22 22.41 19.34 17.77 22.91 23.70 22.25 22.57

Na2O 0.02 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.01

K2O 0.00 0.00 0.00 0.00 0.01 0.00 0.03 0.02 0.05 0.03 0.00 0.00 0.00 Total 97.91 99.00 96.63 85.72 96.29 96.89 98.20 91.91 87.00 97.67 98.43 95.26 97.88 O = 12.5 Si 2.996 2.993 3.040 3.128 3.040 3.021 3.017 3.091 3.099 3.034 3.023 2.917 3.013 IVAl 0.004 0.007 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.083 0.000 VIAl 2.278 2.072 2.226 2.086 2.130 2.203 2.069 2.176 2.132 2.165 2.216 2.176 2.179 Ti 0.000 0.001 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.001 0.002 0.001 0.002 Cr 0.000 0.000 0.002 0.001 0.000 0.000 0.000 0.002 0.001 0.000 0.000 0.003 0.000 Fe3+ 0.756 0.946 0.740 0.906 0.851 0.819 0.939 0.776 0.812 0.806 0.742 0.811 0.812 Mn 0.043 0.030 0.103 0.071 0.018 0.080 0.030 0.094 0.095 0.010 0.004 0.083 0.046 Mg 0.005 0.000 0.014 0.065 0.005 0.018 0.000 0.047 0.090 0.002 0.003 0.007 0.006 Ca 1.901 1.945 1.853 1.614 1.924 1.828 1.921 1.746 1.696 1.958 2.006 1.966 1.930 Na 0.003 0.000 0.000 0.007 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.001 0.002 K 0.000 0.000 0.000 0.000 0.001 0.000 0.003 0.002 0.006 0.003 0.000 0.000 0.000 Total 7.986 7.994 7.978 7.878 7.969 7.969 7.980 7.934 7.931 7.980 7.996 8.048 7.990 YFe3+ 0.25 0.31 0.25 0.30 0.29 0.27 0.31 0.26 0.28 0.27 0.25 0.26 0.27 Type III Type IV Grt-amp rock Greenschista 110408 100602 1806 100202 CRCRCRCR

SiO2 38.45 38.73 39.49 38.71 38.34 37.35 38.92 38.97

TiO2 0.08 0.12 0.15 0.63 0.07 0.17 0.00 0.00

Al2O3 22.52 23.97 24.51 22.03 21.06 24.60 21.72 24.41

Cr2O3 0.03 0.02 0.12 1.10 b.d. b.d. 0.00 0.00

Fe2O3 13.46 11.41 10.50 13.56 15.47 11.05 13.85 10.65 MnO 0.88 0.39 0.12 0.29 0.96 0.46 0.00 0.00 MgO 0.02 0.02 0.06 0.02 0.08 0.04 2.37 1.77 CaO 22.50 23.24 23.49 22.52 22.67 23.34 21.77 22.60 Total 97.94 97.90 98.44 98.86 98.65 97.01 98.63 98.4 O = 12.5 Si 3.064 3.063 3.090 3.070 3.060 2.989 3.065 3.045 IVAl 0.000 0.000 0.000 0.000 0.000 0.011 0.000 0.000 VIAl 2.116 2.235 2.262 2.060 1.981 2.310 2.016 2.249 Ti 0.001 0.002 0.002 0.009 0.001 0.002 0.000 0.000 Fe3+ 0.807 0.679 0.618 0.810 0.929 0.666 0.821 0.626 Cr 0.002 0.001 0.007 0.067 0.000 0.000 0.000 0.000 Mn 0.059 0.026 0.008 0.019 0.065 0.031 0.000 0.000 Mg 0.002 0.002 0.007 0.002 0.009 0.004 0.278 0.206 Ca 1.921 1.969 1.970 1.914 1.938 2.002 1.837 1.892 Total 7.972 7.977 7.964 7.951 7.983 8.015 8.017 8.018 YFe3+ 0.28 0.23 0.21 0.28 0.32 0.22 0.29 0.22

YFe3+ =Fe3+/(Fe3++totalAl). C: core, R: rim, M: mantle, O-C: outer-core. Some of the outer-core data are low total because they contain rare-earth elements (not shown). a EDS data. and pseudosections (Dale et al., 2005). Four schematic P–T paths pressure of the Type IV rock must be higher than those of the other are shown in Fig. 9. A pseudosection modeling on a typical MORB three types, because the former contains rutile and ilmenite but composition by Diener et al. (2007) indicates that the Type IV rock lacks titanite. might have been metamophosed under conditions of =12 kbar and =500 °C, assuming hornblendic amphibole and rutile are among the equilibrium phases. However, pseudosction calculations are 7. Discussion highly affected by whole-rock chemistry. The Si content (up to 6.67 p.f.u for O = 22) of Type IV’s phengitic mica also implies pres- 7.1. Epidote blueschist-facies rocks associated with greenschist-facies sure conditions of 12–16 kbar according to another pseudosection metabasites calculated by Wei et al. (2009), although the observed assemblage in Type IV is not the same as the predicted assemblage in the It is well known that blueschist and greenschist assemblages pseudosection diagram. In either case, metamorphic grade or may be interlayered at the outcrop or even at the thin-section scale 230 C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233

Fig. 8. Compositional ranges of epidotes from the studied glaucophane-bearing rocks, glaucophane-free garnet-amphibole rock, and greenschist. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.)

Table 4 Selected mica compositions analyzed by EPMA.

Rock type Type II Type IV Sample 1804 10-24 10-30 100602 Ms Bt Ms Bt Bt Ms Bt Bt Bt Bt Ms Pg Texture Cor Sym Matrix Inc Sym Cor Matrix

SiO2 47.72 37.51 47.49 38.00 36.97 49.74 39.49 37.61 37.31 37.01 49.12 46.88

TiO2 0.29 0.07 0.19 0.07 1.10 0.18 0.81 0.17 0.32 0.82 0.46 0.11

Al2O3 26.96 14.52 29.72 15.17 14.87 26.28 12.37 13.84 15.40 14.72 27.83 36.85 FeO 5.43 21.34 5.16 20.78 20.85 3.75 16.23 19.28 20.30 19.72 4.22 1.21

Cr2O3 0.02 0.00 0.04 0.04 0.10 0.03 0.11 0.00 0.03 0.23 0.34 0.06 MnO 0.13 0.60 0.06 0.61 0.59 0.00 0.71 0.68 0.61 0.56 0.00 0.00 MgO 2.05 11.09 1.78 11.07 11.25 3.06 13.87 11.29 11.68 11.18 2.14 0.08 CaO 0.00 0.12 0.05 0.05 0.01 0.00 0.14 0.01 0.06 0.12 0.05 0.37

Na2O 0.73 0.08 1.21 0.14 0.09 0.26 0.03 0.03 0.10 0.03 0.88 6.98

K2O 9.15 8.00 8.78 8.81 8.41 10.11 8.37 8.94 8.42 7.23 9.35 0.49 Total 92.48 93.33 94.48 94.74 94.24 93.41 92.13 91.85 94.23 91.62 94.39 93.03 O=22 Si 6.652 5.853 6.461 5.839 5.721 6.812 6.094 5.943 5.749 5.819 6.665 6.148 IVAl 1.348 2.147 1.539 2.161 2.279 1.188 1.906 2.057 2.251 2.181 1.335 1.852 VIAl 3.082 0.524 3.228 0.586 0.433 3.054 0.344 0.521 0.545 0.546 3.116 3.845 Ti 0.031 0.008 0.019 0.008 0.128 0.018 0.094 0.020 0.037 0.096 0.047 0.011 Cr 0.002 0.000 0.004 0.005 0.012 0.003 0.013 0.000 0.004 0.028 0.037 0.006 Fe2+ 0.633 2.785 0.587 2.671 2.698 0.430 2.095 2.548 2.616 2.592 0.479 0.133 Mn 0.016 0.079 0.007 0.079 0.077 0.000 0.092 0.091 0.079 0.075 0.000 0.000 Mg 0.426 2.579 0.362 2.537 2.596 0.624 3.191 2.660 2.682 2.620 0.433 0.016 Ca 0.001 0.020 0.008 0.007 0.001 0.000 0.023 0.002 0.010 0.020 0.008 0.051 Na 0.197 0.023 0.318 0.040 0.026 0.070 0.010 0.010 0.029 0.009 0.231 1.774 K 1.627 1.593 1.523 1.727 1.660 1.766 1.647 1.802 1.654 1.450 1.618 0.082 Total 14.015 15.611 14.056 15.660 15.631 13.965 15.509 15.654 15.656 15.436 13.969 13.918 XMg 0.40 0.48 0.38 0.49 0.49 0.59 0.60 0.51 0.51 0.50 0.48 0.11 XNa 0.11 0.01 0.17 0.02 0.02 0.04 0.01 0.01 0.02 0.01 0.12 0.96

XMg = Mg/(Mg + Fe3+), XNa = Na/(Na + K). Bt: biotite; ms: muscovite/phengite; pg: paragonite; cor: corona, sym: symplectite, inc: inclusion.

(Maruyama et al., 1986; Barrientos and Selverstone, 1993; Baziotis ologic assemblage to reach—or maintain—equilibrium over a com- et al., 2009). Such associations reﬂect: (a) coexisting equilibrium mon set of physical conditions. In the case of the Tamayen samples, mineral assemblages stabilized by contrasting bulk-rock composi- glaucophane-bearing rocks are surrounded by greenschist-facies tions; (b) lithologic mélanges formed under differing P–T condi- metabasite assemblages (albite, epidote, chlorite, calcic amphibole, tions and subsequently juxtaposed by sedimentary and/or titanite). This suggests that earlier formed HP–LT blueschist associ- tectonic processes; or (c) preserved due to sluggish kinetics, ations were metastably preserved during decompression toward involving the failure of spatially disparate portions of a single lith- lower pressure greenschist conditions. C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233 231

Table 5 Selected chlorite compositions analyzed by EPMA.

Rock type Type I Type II Type III Type IV Sample 10–23 1804 10-24 10-30 1801A 110408 100602 Texture Inc Matrix Sym Inc Sym Inc Inc FD CD

SiO2 26.91 26.21 26.08 26.14 27.57 29.09 27.11 32.34 27.31 27.35 26.95 28.06

TiO2 0.02 0.03 0.03 0.08 0.01 0.08 0.04 0.07 0.06 0.02 0.04 0.06

Al2O3 18.74 18.34 19.19 18.59 18.21 20.14 18.13 16.51 18.71 19.03 19.63 18.50

Cr2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.15 FeO 24.05 26.36 26.29 25.33 23.67 13.93 25.92 17.54 25.80 21.37 25.82 21.93 MnO 0.92 0.83 0.97 1.23 1.16 0.96 1.18 0.87 1.20 0.88 0.11 0.27 MgO 16.55 14.78 14.95 15.47 15.72 22.76 14.66 18.04 14.40 17.84 13.94 17.82 CaO 0.00 0.03 0.00 0.00 0.06 0.12 0.08 1.10 0.08 0.10 0.01 0.02

Na2O 0.02 0.04 0.00 0.04 0.06 0.00 0.05 0.17 0.05 0.07 0.04 0.01

K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 87.21 86.62 87.51 86.88 86.46 87.08 87.17 86.64 87.61 86.66 86.56 86.82 O=28 Si 5.682 5.650 5.561 5.595 5.846 5.781 5.784 6.510 5.778 5.716 5.727 5.837 IVAl 2.318 2.350 2.439 2.405 2.154 2.219 2.216 1.490 2.222 2.284 2.273 2.163 VIAl 2.347 2.316 2.387 2.293 2.409 2.514 2.350 2.468 2.457 2.411 2.664 2.384 Ti 0.003 0.006 0.005 0.012 0.002 0.012 0.007 0.011 0.009 0.004 0.006 0.009 Cr 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.004 0.025 Fe3+ 0.017 0.000 0.000 0.000 0.133 0.178 0.073 0.531 0.131 0.062 0.218 0.144 Fe2+ 4.230 4.768 4.706 4.576 4.064 2.138 4.553 2.421 4.435 3.672 4.370 3.670 Mn 0.164 0.151 0.175 0.223 0.208 0.161 0.213 0.149 0.215 0.156 0.020 0.047 Mg 5.209 4.752 4.752 4.935 4.969 6.745 4.664 5.413 4.542 5.557 4.416 5.524 Ca 0.000 0.008 0.000 0.000 0.014 0.026 0.019 0.238 0.017 0.021 0.003 0.005 Na 0.013 0.034 0.000 0.035 0.049 0.000 0.041 0.134 0.044 0.057 0.035 0.010 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Total 19.983 20.035 20.025 20.074 19.848 19.774 19.920 19.365 19.850 19.940 19.736 19.818 XFe 0.45 0.50 0.50 0.48 0.46 0.26 0.50 0.35 0.50 0.40 0.51 0.41

XFe = Fe2+/(Fe2++Mg). Sym: symplectite, inc: inclusion, FD: ﬁne-grained domain, CD: coarse-grained domain.

in a small outcrop area, we propose two possibilities that may explain such features. (1) Multiple stages of HP–LT subduction- related metamorphism are recorded in the Tamayen lithotypes, as previously suggested in a few studies (Liou, 1981; Liou and Ernst, 1984). (2) Factors other than P–T such as contrasting bulk- rock compositions (Baziotis et al., 2009), local availabity of ﬂuids (Barrientos and Selverstone, 1993), and/or sluggish kinetics might have played important roles in controlling the mineral compositions, zoning patterns, and assemblages. In either explanation, the Tamayen rock suite represents a mélange of oceanic and continental-margin rock types. Because of poor exposures, it is not possible to determine from presently available evidence whether the mélange originated as a sedimentary olistostrome or as a tectonic mixture of unrelated lithotypes—or in fact as a deformed olistostrome (cf. Lin et al., 1984; Yang and Wang, 1985). In any case, multiple sheets of cha- otic oceanic rocks are sequestered in the in situ metasedimentary section at Juisui, as documented by drill hole HJ-1 performed by the Industrial Technology Research Institute and reported by Hsu (1983).

Fig. 9. Schematic P–T paths of Tamayen glaucophane-bearing rock types. Meta- morphic facies abbreviations: BS: blueschist; EA: epidote amphibolite; GS: green- 8. Conclusions schist; AM: amphibolite; Amp-EC: amphibole eclogite. Facies boundaries after Liou et al. (2004). The reaction line of tr + chl + ab = cz + gl + qz + H2O after Maruyama 1. This study provides new, detailed petrochemical characteriza- et al. (1986); winchite stability after Otsuki and Banno (1990); barroisite stability after Ernst (1979). (For interpretation of the references to colour in this figure tion of constituent minerals in the Tamayen glaucophane- legend, the reader is referred to the web version of this article.) bearing rocks of the Juisui area. We identified four types of glaucophane-bearing rocks, which show diverse textures and 7.2. Tectonic setting of the Tamayen rocks and its relation to the Yuli contrasting mineral compositions. In particular, sodic, sodic- belt calcic, and calcic amphibole compositions display significant variations and complex zoning trends. These features were pro- Judging from the diverse mineral compositions, chemical zon- duced by varying P–T conditions, bulk-rock + fluid chemical ing trends, assemblages, and textures in the Tamayen rocks present evolutions, oxygen fugacity changes, and/or deformation. 232 C.-H. Tsai et al. / Journal of Asian Earth Sciences 63 (2013) 218–233

2. We estimate the peak pressure of Type III glaucophane-bearing Ernst, W.G., Liu, J., 1998. Experimental phase-equilibrium study of Al- and Ti- rocks as 6–8 kbar, whereas the attending temperature could contents of calcic amphibole in MORB – a semiquantitative thermobarometer. American Mineralogist 83, 952–969. have been near 400 °C. Amphibole zoning trends imply contra- Evans, B.W., 1990. Phase relations of epidote-blueschists. Lithos 25, 3–23. dictory P–T paths for the four types of glaucophane-bearing Hosotani, H., Banno, S., 1986. Amphibole composition as an indicator of subtle grade rocks. Type I and Type III show a clockwise a P–T trajectory, variation in epidote-glaucophane schists. Journal of Metamorphic Geology 4, 23–35. whereas Type II and Type IV reveal a counter-clockwise one. Huang, C.Y., Yuan, P.B., Tsao, S.J., 2006. Temporal and spatial records of active arc- The findings differ from previous studies (e.g. Liou et al., continent collision in Taiwan: a synthesis. Bulletin of Geological Society of 1975; Beyssac et al., 2008). American 118, 274–288. Hsu, J.-B., 1983. Geothermal geology and a model for formation of hot springs in the 3. The studied Tamayen rocks apparently are of different meta- Juisui area, Hualien. Mining Technology 21, 12–24 (in Chinese). morphic grades and were subjected to at least two different Jahn, B.M., Liou, J.G., 1977. Age and geochemical constraints of glaucophane schists types of P–T paths. Based on field relations and petrographic of Taiwan. Memoir of the Geological Society of China 2, 129–140. Jahn, B.M., Liou, J.G., Nagasawa, H., 1981. High-pressure metamorphic rocks of observations, the so-called Tamayen ‘‘block’’ evidently is a Taiwan: REE geochemistry, Rb–Sr ages and tectonic implications. Memoir of the mélange. The host Yuli belt is probably at least partly a sedi- Geological Society of China 4, 497–520. mentary mélange, involving olistostromal and tectonic pro- Lan, C.-Y., 1993. Reviews of amphiboles in the metamorphic terranes of Taiwan. cesses at different stages of formation. Special Publication of the Central Geological Survey 7, 1–30. Lan, C.-Y., Liou, J.G., 1984. Mineral chemistry of metamorphosed oceanic rocks in the Yuli belt of the Tananao Schist, Taiwan. Memoir of the Geological Society of China 6, 153–178. Leake, B.E., Woolley, A.R., Arps, C.E.S., Birch, W.D., Gilbert, M.C., Grice, J.D., Acknowledgements Hawthorne, F.C., Kato, A., Kisch, H.J., Krivovichev, V.G., Linthout, K., Laird, J., Mandarino, J., Maresch, W.V., Nickel, E.H., Tock, N.M.S., Schumacher, J.C., Smith, D.C., Stephenson, N.C.N., Ungaretti, L., Whittaker, E.J.W., Youzhi, G., 1997. This paper salutes Prof. Bor-ming Jahn’s contributions to the Nomenclature of amphiboles: report of the Subcommittee on amphiboles of the study of HP metamorphic rocks in Taiwan. We thank Linda Hsu International Mineralogical Association Commission on new minerals and and Hui-Ho Hsieh for assistance in the analytical work of SEM- mineral names. Canadian Mineralogist 35, 219–246. Lin, M.-L., 1985. Amphiboles in greenschist of the Yuli belt, Juisui area, eastern EDS and EPMA, data processing, and figure drafting. We are grate- Taiwan. Acta Geologica Taiwanica 23, 99–109. ful to Jin-Tsuen Lin, Tz-Huei Yeh, Huei-Ting Huang, Jia-Wei Huang, Lin, M.L., 1999. Litho-stratigraphy and structural geology of Wanjung area, eastern and Yun-Jie Lo for help with field work, to Bor-ming Jahn, Yu Wang, Taiwan and their implications. Journal of the Geological Society of China 42, 247–267. and Xiaochun Liu for generous support of thin-section making. Lin, M.-L., Yang, C.-N., Wang, Y., 1984. Petrotectonic study on the Yuli belt of the Comments by two anonymous reviewers and the handling guest Tananao Schist in the Chinshuichi area, eastern Taiwan. Acta Geologica editor Dr. L.F. 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