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Aluminum-rich and Si-poor calcium amphibole [~3.9 Al atoms per formula unit (apfu) and ~5.5 Si apfu for 23 O] occur in the quartz-bearing eclogites from the Donghai area, Sulu ultrahigh-pressure metamorphic belt, eastern China. Most of the aluminous amphibole phases are retrograde products from the exhumation and hydration stage and are texturally divided into a mantle phase around a porphyroblastic garnet and a crack-filling (vein) phase of a garnet. Less aluminous amphibole occurs as symplectite phase with plagioclase after omphacite. The formation process of the aluminous amphibole in the quartz-bearing samples is discussed on the basis of the analytical data by EPMA, FIB-TEM, and EBSD.

Growth histories recorded in garnet grains in metasedimentary rocks from the Sanbagawa belt in Japan and the Mogok belt in Myanmar were analyzed using an effective combination of electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) data. Garnet in the Sanbagawa metapelite has inner and outer zones that formed in the eclogite and epidote-amphibolite facies stages, respectively. Based on EPMA element mapping, this garnet appears to have grown as a single crystal with a temporal break in growth between the inner and outer zones that occurred during exhumation. The EBSD data, however, document that the garnet grain is composed of four domains. The misorientation angles of crystallographic orientations between the domains are as large as 59°, and domain boundaries crosscut the growth zoning and the compositional boundary between the inner and outer zones. Sets of quartz grains included in the garnets on either side of the domain boundaries sometimes share the same crystallographic orientation with misorientation angles less than 4°. The garnet grains formed via a three-step process of prograde crystallization of polycrystalline garnet during the eclogite facies stage (inner zone) → resorption around garnet rims and along domain boundaries during exhumation → crystallization of the outer zone and in the domain boundaries during the prograde epidote-amphibolite facies stage.

Raman spectra of quartz inclusions in garnet hosts of low-pressure/temperature metamorphic rocks from the Yanai district in the Ryoke belt (around 0.1-0.3 GPa/500-600 °C), Southwest Japan, exhibit frequency (peak position) shifts toward lower wavenumbers as compared to those of a quartz standard measured at ambient conditions. The observed negative frequency shifts indicate that tensile normal stress is exerted on the quartz-garnet boundary and therefore, quartz inclusions are subjected to negative residual pressure. Elastic modeling that assumed the constant elastic properties of minerals cannot explain this negative residual pressure. This study estimated the residual pressure based on a new scheme of elastic modeling with equation of state (EOS) of quartz and garnet, which takes into account the pressure- and temperature-dependency of compressibility and expansivity. The calculated residual pressure was converted into frequency shifts of quartz Raman spectrum based on the experimentally determined relation. The results showed that the quartz inclusions in garnets retain residual pressure of about -0.3 GPa, and logically reproduced the observed frequency shifts in the direction of lower wavenumbers. The new elastic modeling also simulates positive frequency shifts retained by quartz inclusions in garnets of high-pressure metamorphic rocks from the Sambagawa metamorphic belt in Southwest Japan, and from the Motagua fault zone in Guatemala. The degree and direction of Raman frequency shifts of quartz inclusion in garnet depend on metamorphic conditions when the quartz was included in the host garnet. Conversely, the metamorphic conditions prevailing when a set of a quartz inclusion and garnet host was recrystallized can be inferred from Raman frequency shifts of quartz inclusion in garnet. The proposed Raman spectroscopic analysis should be a powerful and useful tool to decipher information at earlier stage of garnet growth even in samples of highly recrystallized matrix phases during exhumation and retrograde stages.

AbstractRaman spectra of quartz inclusions in garnet hosts of low-pressure/temperature metamorphic rocks from the Yanai district in the Ryoke belt (around 0.1-0.3 GPa/500-600 °C), Southwest Japan, exhibit frequency (peak position) shifts toward lower wavenumbers as compared to those of a quartz standard measured at ambient conditions. The observed negative frequency shifts indicate that tensile normal stress is exerted on the quartz-garnet boundary and therefore, quartz inclusions are subjected to negative residual pressure. Elastic modeling that assumed the constant elastic properties of minerals cannot explain this negative residual pressure. This study estimated the residual pressure based on a new scheme of elastic modeling with equation of state (EOS) of quartz and garnet, which takes into account the pressure- and temperature-dependency of compressibility and expansivity. The calculated residual pressure was converted into frequency shifts of quartz Raman spectrum based on the experimentally determined relation. The results showed that the quartz inclusions in garnets retain residual pressure of about -0.3 GPa, and logically reproduced the observed frequency shifts in the direction of lower wavenumbers. The new elastic modeling also simulates positive frequency shifts retained by quartz inclusions in garnets of high-pressure metamorphic rocks from the Sambagawa metamorphic belt in Southwest Japan, and from the Motagua fault zone in Guatemala. The degree and direction of Raman frequency shifts of quartz inclusion in garnet depend on metamorphic conditions when the quartz was included in the host garnet. Conversely, the metamorphic conditions prevailing when a set of a quartz inclusion and garnet host was recrystallized can be inferred from Raman frequency shifts of quartz inclusion in garnet. The proposed Raman spectroscopic analysis should be a powerful and useful tool to decipher information at earlier stage of garnet growth even in samples of highly recrystallized matrix phases during exhumation and retrograde stages.

Indentation testing of natural single-crystal α-quartz parallel to the crystallographic c axis, using a triangular pyramidal diamond indenter at a maximum load of 500 mN, produced a very small residual volume of less than 1 μm3 in which α-quartz is highly stressed. Laser Raman microspectroscopy across the indentation at room temperature and pressure revealed a shift in the Raman bands, interpreted to reflect the residual stress field generated within the α-quartz. Based on the observed Raman shift, we identified a steep gradient in the residual non-hydrostatic stress field after complete unloading in quartz near the impression formed by indentation. At the center of the indentation, the maximum compressive stress and tensile stress were inferred to be higher than 2.2 and 0.1 GPa, respectively

A Laser Raman microspectrometry method was applied to metamorphic quartz in quartz-eclogite-, epidote-amphibolite-, and amphibolite-facies rocks to assess the quantitative correlation between the Raman frequency shift and metamorphic pressure. Quartz crystals sealed in garnet and other phases have a higher frequency shift than those in the matrix. Furthermore, the quartz inclusions show a frequency shift specific to the individual host crystals in eclogites (garnet ≈ kyanite > omphacite ≈ epidote). These observations imply that the residual pressures retained by quartz inclusions depend on elastic parameters of the host crystals, as discussed by previous researchers. The Raman frequency shift of quartz inclusions in garnet systematically increases with increasing peak metamorphic pressures from the amphibolite facies (0.30-0.55 GPa/470-570°C), through the epidote-amphibolite facies (0.8-1.1 GPa/470-635°C) to the quartz-eclogite facies (2.1-2.5 GPa/660-710°C). Calibrations based on experimental work suggest that the measured Raman frequency shifts signify residual pressures of 0.1-0.2, 0.4-0.6, and 0.8-1.0 GPa for these three groups of metamorphic rocks, respectively. Normal stresses (internal pressures) of quartz inclusions in garnet, numerically simulated with an elastic model, and inferred pressure-temperature conditions at peak metamorphic stage are compatible with the residual pressures estimated from the frequency shifts. Laser Raman microspectroscopic analysis of quartz is a simple and effective method for (1) comparison of pressure conditions in metamorphic rocks formed under various pressure-temperature conditions, and (2) detection of a higher-pressure signature in metamorphic rocks extensively recrystallized during the subsequent exhumation and hydration stage

Chromian dissakisite-(Ce), a Cr-enriched Mg analogue of allanite-(Ce), is found in a garnet lherzolite from the Su-Lu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. Major minerals of the lherzolite are olivine [XMg= Mg/(Mg + Fe) = 0.92], pyrope-rich garnet (Prp70.1-73.2Alm11.3- 13.4Grs6.9-8.3Uvr3.6-5.1Anr0-0.4Sps0.7-1.7), orthopyroxene (XMg= 0.92-0.93), and clinopyroxene (XMg = 0.92-0.95). The chromian dissakisite-(Ce) occurs as a single-crystal inclusion in a clinopyroxene neoblast that also contains several irregularly shaped olivine grains. It is partly metamict, and there is intensive radial cracking in the surrounding clinopyroxene. Its composition is represented by the averaged formula: (Ca0.86Na0.03)0.89(REE0.86Th0.04)0.90(Mg0.98Fe2+ 0.20Fe3+0.21Cr0.36Al1.39Ti0.04)Si3.03O12(OH), with Ce2O3, MgO and Cr2O3contents up to 13.1, 7.3, and 5.4 wt%, respectively. Because the M3 site in the chromian dissakisite-(Ce) is fully occupied by Mg and Fe2+, Fe3+and Cr can only occupy the smaller M1 site. Similar site occupancy is noted for a chromian allanite from the Sanbagawa metamorphic belt, Japan, which contains up to 0.547 Cr atoms per formula unit (apfu). Such compositional characteristics of the chromian dissakisite/allanite and existing polarized absorption data on Cr-bearing epidote suggest the existence of possible end-members, “CeCa(Mg,Fe)CrAlSi3O12(OH),” for the epidote-group minerals, which may form solid solution with Ca2Al3Si3O12(OH) through coupled substitutions of REEMgCa-1Al-1, REEFeCa-1Al-1, and CrAl-1. The rare earth elements (REE), Ca, and Na total 1.79 apfu, implying that Mn and Fe2+are also present on the nine-coordinated A1 site. The high REE abundance, the presence of minor Na, and the Mg and Cr-enriched characteristics of the mineral suggest that it was formed as a result of reaction between the host lherzolite and crustderived melt/fluid at UHP conditions. Textural relations suggest that the chromian dissakisite-(Ce) was unstable in the garnet lherzolite and reacted with olivine to form clinopyroxene. Dissakisite- (REE) in subducted ultramafic rocks can transport rare earth elements into the Earth’s mantle.

Chromian dissakisite-(Ce), a Cr-enriched Mg analogue of allanite-(Ce), is found in a garnet lherzolite from the Su-Lu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. Major minerals of the lherzolite are olivine [XMg= Mg/(Mg + Fe) = 0.92], pyrope-rich garnet (Prp70.1-73.2Alm11.3- 13.4Grs6.9-8.3Uvr3.6-5.1Anr0-0.4Sps0.7-1.7), orthopyroxene (XMg= 0.92-0.93), and clinopyroxene (XMg = 0.92-0.95). The chromian dissakisite-(Ce) occurs as a single-crystal inclusion in a clinopyroxene neoblast that also contains several irregularly shaped olivine grains. It is partly metamict, and there is intensive radial cracking in the surrounding clinopyroxene. Its composition is represented by the averaged formula: (Ca0.86Na0.03)0.89(REE0.86Th0.04)0.90(Mg0.98Fe2+ 0.20Fe3+0.21Cr0.36Al1.39Ti0.04)Si3.03O12(OH), with Ce2O3, MgO and Cr2O3contents up to 13.1, 7.3, and 5.4 wt%, respectively. Because the M3 site in the chromian dissakisite-(Ce) is fully occupied by Mg and Fe2+, Fe3+and Cr can only occupy the smaller M1 site. Similar site occupancy is noted for a chromian allanite from the Sanbagawa metamorphic belt, Japan, which contains up to 0.547 Cr atoms per formula unit (apfu). Such compositional characteristics of the chromian dissakisite/allanite and existing polarized absorption data on Cr-bearing epidote suggest the existence of possible end-members, “CeCa(Mg,Fe)CrAlSi3O12(OH),” for the epidote-group minerals, which may form solid solution with Ca2Al3Si3O12(OH) through coupled substitutions of REEMgCa-1Al-1, REEFeCa-1Al-1, and CrAl-1. The rare earth elements (REE), Ca, and Na total 1.79 apfu, implying that Mn and Fe2+are also present on the nine-coordinated A1 site. The high REE abundance, the presence of minor Na, and the Mg and Cr-enriched characteristics of the mineral suggest that it was formed as a result of reaction between the host lherzolite and crustderived melt/fluid at UHP conditions. Textural relations suggest that the chromian dissakisite-(Ce) was unstable in the garnet lherzolite and reacted with olivine to form clinopyroxene. Dissakisite- (REE) in subducted ultramafic rocks can transport rare earth elements into the Earth’s mantle.

Coexisting minerals of the hollandite-cryptomelane series, piemontite-group, and abswurmbachite-braunite series occur as a small nodule in a quartzose schist (metachert) from the epidote-amphibolite facies area of the Sanbagawa metamorphic belt, central Shikoku, Japan. Stron­tium, Ba. K. and Pb contents of the hollandite-cryptomelane minerals are 0.00-0.42, 0.07-0.99, 0.00-0.75 and 0.00-0.05 apfu (atoms per formula unit: O = 16), respectively. The piemontite-group minerals can be divided into common piemontite (Ca > Sr in the ten-coordinated A2-site) and strontiopiemontite (Sr > Ca). Strontium. Ba and Pb contents of the strontiopiemontite reach 0.71, 0.26 and 0.20 apfu (O = 12.5), respectively, suggesting the existence of two possible new end- members for epidote-group minerals: “Ba-piemontite [BaCa(Mn3+, Fe3+, Al)3Si3O12(OH)]” and "Pb- piemontite [PbCa(Mn3+, Fe3+, Al)3Si3O12(OH)]”. The abswunnbachite-braunite series minerals (Cu = 0.30-0.53 apfu: O = 12) contain up to 0.34 apfu Mg, indicating the exchange Mg(Mn2+, Cu)-1. Distribution coefficients for Sr between the hollandite-cryptomelane series and the piemontite-group minerals are up to 20. implying that the hollandite-type structure with its large open tunnel is more suitable for incorporation of Sr than the A2-site of the piemontite-group minerals. A synthetic alumi­nosilicate analogue of the hollandite-cryptomelane compound is stable under P > 8-10 GPa. and suggests the hollandite-type aluminosilicate may be a reservoir of Sr and other large-ion-lithophile elements in the upper mantle.

Coexisting minerals of the hollandite-cryptomelane series, piemontite-group, and abswurmbachite-braunite series occur as a small nodule in a quartzose schist (metachert) from the epidote-amphibolite facies area of the Sanbagawa metamorphic belt, central Shikoku, Japan. Stron­tium, Ba. K. and Pb contents of the hollandite-cryptomelane minerals are 0.00-0.42, 0.07-0.99, 0.00-0.75 and 0.00-0.05 apfu (atoms per formula unit: O = 16), respectively. The piemontite-group minerals can be divided into common piemontite (Ca > Sr in the ten-coordinated A2-site) and strontiopiemontite (Sr > Ca). Strontium. Ba and Pb contents of the strontiopiemontite reach 0.71, 0.26 and 0.20 apfu (O = 12.5), respectively, suggesting the existence of two possible new end- members for epidote-group minerals: “Ba-piemontite [BaCa(Mn3+, Fe3+, Al)3Si3O12(OH)]” and "Pb- piemontite [PbCa(Mn3+, Fe3+, Al)3Si3O12(OH)]”. The abswunnbachite-braunite series minerals (Cu = 0.30-0.53 apfu: O = 12) contain up to 0.34 apfu Mg, indicating the exchange Mg(Mn2+, Cu)-1. Distribution coefficients for Sr between the hollandite-cryptomelane series and the piemontite-group minerals are up to 20. implying that the hollandite-type structure with its large open tunnel is more suitable for incorporation of Sr than the A2-site of the piemontite-group minerals. A synthetic alumi­nosilicate analogue of the hollandite-cryptomelane compound is stable under P > 8-10 GPa. and suggests the hollandite-type aluminosilicate may be a reservoir of Sr and other large-ion-lithophile elements in the upper mantle.

Jadeitic pyroxenes in two Franciscan samples, one, a possible segregation vein in metabasite, and another, a metabasite, both from Ward Creek, Cazadero area, western California, were examined with the electron microprobe. The samples were collected from the area of Type III rocks, the highestgrade portion of the pumpellyite zone. Jadeitic pyroxenes from both samples are very heterogeneous and cannot be ascribed to crystallization under conditions of surface equilibrium with the coexisting phases. Two possibilities for their origin are suggested: one is as tectonic blocks, and the other as the highest-grade rocks from the zone that crystallized close to or within the P-T stability field of pure jadeite + quartz

This paper reviews chemical characteristics of common minerals in ultrahigh-pressure (UHP) metamorphic rocks. Garnet in UHP metamorphic rocks belongs to the almandine-pyrope-grossular series and has a wide compositional range in Xalm (up to 0.73), Xprp (0.98), and Xgrs (0.92). Garnet with pyroxene exsolution microstructures reported from the Western Gneiss Region, Norway, shows relicts of majoritic garnet formed under P = 6 to 7 GPa. Most clinopyroxenes are Na-Ca groups and their Xjd ranges from 0.0 to 0.89. Members of the clinoenstatite-clinohypersthene (P21/c) were reported from peridotites in UHP terranes, and are considered to have been originally the high-pressure polymorph (C2/c) formed under P > 7 to 8 GPa. The presence of sodium in garnet and of potassium in clinopyroxene characterizes UHP equilibrium. Attention is drawn to minerals of the epidote group as strontium and REE containers, to amphibole as a sensor of metamorphic fluid composition, and to phengite as a geobarometer.

Petrological and isotopic evidence suggests that the protolith of the Sulu ultrahigh-pressure (UHP) terrane was Precambrian continental crust consisting of granite, granodiorite, gabbro, marble, and basic dikes, with local granulite-facies assemblages. Around 220 Ma this unit of continental rocks was buried to depths up of ∼120 km within the mantle. Structures formed during exhumation suggest highly mobile behavior of acidic rocks, even under conditions of very low water activity. Petrological studies show that the Sulu terrane underwent isothermal decompression, which implies relatively rapid exhumation, and suggests that the role of melting during exhumation may have been underestimated. The later stages of exhumation are associated with NW-SE-directed tectonic transport and the formation of at least one major normal detachment.

Abstract: Coexisting sodic augite and omphacite were found in a zoisite amphibolite from the Iratsu epidote amphibolite mass in the Sanbagawa metamorphic terrain of central Shikoku, Japan. The occurrences of the sodic augite-omphacite pairs are classified into four types by texture: independent, composite, intergrowth and exsolution types. Sodic augite and omphacite of the independent and composite types (pair A) have X Na (=Na/(Na + Ca)) = 0.15 and 0.35, respectively, and were stable in the epidote amphibolite facies during the Sanbagawa progressive metamorphism. On the other hand, X Na values of sodic augite and omphacite of the intergrowth and exsolution types (pair B) are 0.10 and 0.44, respectively. The Na-poor augite and Na-rich omphacite of the pair B were formed by re-equilibration of the pair A at lower temperature. The pair A of the Iratsu sample suggests that a compositional gap lies between sodic augite and C2/c omphacite under epidote amphibolite facies conditions, and is in marked contrast to the coexistence of sodic augite and P2/n omphacite reported from some low-grade, high-pressure metamorphic terrains. A possible phase diagram to explain the chemistry and mode of occurrence of the coexisting sodic pyroxenes is proposed.

Sodic pyroxene (jadeite content Xjd=0.1–0.3) occurs locally as small inclusions within, albite porphyroblasts and in the matrix of hematite-bearing quartz schists in the Sanbagawa (Sambagawa) metamorphic belt, central Shikoku, Japan. The sodic, pyroxene-bearing samples are characteristically free from chlorite and their typical mineral assemblage is sodic pyroxene+subcalcic (or sodic) amphibole+phengitic mica+albite+quartz+hematite+titanite±epidote. Spessartine-rich garnet occurs in Mn-rich samples. Sodic pyroxene in epidote-bearing samples tends to be poorer in acmite content (average XAcm=0.26–0.50) than that in the epidote-free samples (XAcm=0.45–0.47). XJd shows no systematic relationship to metamorphic grade, and is different among the three sampling regions [Saruta-gawa, Asemi-gawa and Bessi (Besshi)]. The average XJd of the Saruta-gawa samples (0.21–0.29) is higher than that of the Asemi-gawa (0.13–0.17) and Bessi (0.14–0.23). The P-T conditions of the Asemi-gawa and Bessi regions are estimated at 5.5–6.5 kbar, >360°C in the chlorite zone, 7–8.5 kbar, 440±15°C in the garnet zone and 8–9.5 kbar, 520±25°C in the albite-biotite zone. Metamorphic pressure of the Saruta-gawa region is systematically 1–1.5 kbar higher than that of the Asemi-gawa and Bessi regions, and materials of the Saruta-gawa region have been subducted to a level 3–5 km deeper than materials that underwent metamorphism at equivalent temperatures and are now exposed in the Asemi-gawa and Bessi regions. Pressure slightly increases toward the north (structurally high levels) through the Sanbagawa belt of central shikoku. Two types of zonal structure were observed in relatively coarse-grained sodic pyroxenes in the matrix. One type is characterized by increasing XJd from core to rim, the other type by decreasing XJd from core to rim. Both types of zoned pyroxenes show an increase in XFe2+[=Fe2+/(Fe2++Mg)] from core to rim. The first type of zoning was observed in a sample from the chlorite zone of lowest grade, whereas the latter occurs in the garnet and albite-biotite zones of higher grade. The contrast in zonal structure implies that dP/dT during prograde metamorphism decreased with increasing metamorphic grade and may have been negative in some samples from the higher-grade zones. The estimated dP/dT of the prograde stage of the chlorite zone is 3.2 kbar/100°C, and that of the garnet and albite-biotite zones is -1.8 to 0.9 kbar/100°C. The variation of dP/dT at shallow and deep levels of a subduction system probably reflects the difference of heating duration and/or change in thermal gradient of the subduction zone by continuous cooling of the surrounding mantle.

AbstractChlorine-rich potassium hastingsite occurs in a calcareous pegmatite, a replacement zone and an amphibolite lens within hornblende gneiss on West Ongul Island, Lützow-Holm Bay, East Antarctica. The amphibolite lens and hornblende gneiss were metamorphosed to the kyanite-sillimanite grade of the granulite facies during Proterozoic metamorphism. Chemical analysis (3.27 wt.% Cl), unit cell parameters and optical properties of the Cl-rich potassium hastingsite are given. Cl-rich (> 3 wt.%) calcic amphiboles reported from various rock types are mostly more than 0.9 in (Na+ K) content, more than 0.4 in K/(Na + K) ratio, more than 0.75 in Fe2+/(Fe2++ Mg + Mn) ratio and more than 1.9 in AlIVcontent (total iron as FeO and O = 23). The unit cell volume of Cl-rich hastingsite is distinctly larger than that of Cl-poor hastingsite.

SummaryCoexisting zoisite and clinozoisite in seventeen specimens from six localities in Japan have been studied with the electron-probe microanalyser. Zoisite and clinozoisite are commonly zoned, but compositional gaps between them are systematic. Referring to the metamorphic grade of the host rocks, a temporary and schematic phase-diagram for the system Ca2Al3Si3O12-(OH)-Ca2Al2Fe3+Si3O12(OH) is presented. With increasing temperature, in the range of low- to medium-grade metamorphism, the compositional gap between the two epidote-group minerals shifts towards higher Fe3+compositions.

Sodian and yttrian (Na-Y) garnet occurs in orthogneisses of the Su-Lu terrane of eastern China with major quartz, microcline, and albite and subordinate biotite, titanite, hematite, and zircon. Acmite-rich pyroxene, muscovite, epidote, allanite, and hastingsitic amphibole occur in a few of the samples. The Na- Y garnet can be divided into almandine-spessartinegrossular [Al > 1.6 per formula unit (pfu) for O = 12, hereafter denoted as Al-garnet], and andradite-spessartine (Fe3+> 1.3 pfu, hereafter denoted as Fe3+-garnet) groups. Average composition of the Al-garnet in each sample ranges from Alm35Sps13Prp1Grs49Adr2to Alm21Sps67Prp0Grs5Adr7. The Fe3+-garnet contains a calderite component (Cdr) and its composition is Alm4-7Sps10-21Prp1-2Adr59-81Cdr3-12. Na, Y, and Yb contents of the Al-rich garnet reach 0.37, 1.46, and 0.42 oxide wt%, respectively, and Na/(Y + Yb) = 0.99 ± 0.16. The Fe3+-garnet contains up to 0.11,2.1, and 0.48 wt% of Na2O, Y2O3, and Yb2O3, respectively, and its Na/(Y + Yb) value (0.17 ± 0.1) is lower than that of the Al-garnet. We conclude that Na, Y, and Yb are incorporated in the Al-rich garnet by the [8]Na[8](Y,Yb)(Ca,Mn)-2substitution, whereas in the Fe3+-garnet, Y and Yb are dominantly incorporated by the [8](Y,Yb)[4](Al,Fe3+)(Ca,Mn)-1Si-1substitution with up to 3 mol% Y + Yb for Ca + Mn. Comparison ofNa/(Y + Yb) of garnets in the orthogneisses and in some pegmatites implies that increasing pressure favors incorporation of Na with Y and Yb, and that under the albite-epidote amphibolite facies or higher-pressure conditions, Y and Yb probably substitute into the garnet structure by [8]Na[8](Y,Yb)(Ca,Mn)-2, instead of the [8](Y,Yb)[4](Al,Fe3+)(Ca,Mn)-1S-1-type substitution effective under lower-pressure conditions.

Sr-bearing zoisite and epidote are common constituents of eclogites and associated paraschists throughout the Su-Lu ultra-high pressure (UHP) province, eastern China. The SrO content of prograde zoisite and epidote reaches 3.2 wt% in crystal cores and generally decreases toward crystal margins. Retrograde epidote is poorer in SrO (<0.1 wt%). Preliminary rare earth element (REE) analyses of epidote give La2O3(up to 2.9 wt%), Ce2O3(5.9 wt%), and Nd2O3(3.0 wt%). REE contents of zoisite are distinctly lower (La2O3up to 0.16 wt%, Ce2O3up to 0.26 wt%, and Nd2O3up to 0.16 wt%) than coexisting epidote. Apatite is always more depleted in SrO (0.10-0.59 wt% on average) than coexisting zoisite and epidote, and Sr-Ca partition coefficients for zoisite and epidote and apatite [(Sr/Ca)zo/ep-ap] range from 5 to 20. SrO content of K-white mica (0.012-0.044 wt%) is an order of magnitude lower than that of apatite. An evaluation of the SrO content in zoisite and epidote and their modal abundances in seven samples indicates that >70% of the whole-rock SrO is contained in these minerals. Apatite and K-white mica are only minor reservoirs for SrO in these rocks. Zoisite and epidote are thus regarded as the most important Sr reservoirs at UHP conditions where calcic plagioclase and titanite are unstable.

Summary Zn-Mn ilmenite occurs as a principal constituent of the miarolitic cavities in the Kuiqi granite from Fuzhou. In the cavities potassium feldspar, albite, quartz, fluorite, aegirine and arfvedsonite also occur with accessory zircon, magnetite, hematite and sphalerite. Zn-Mn ilmenite forms a trigonal platy euhedral crystal up to 30 mm in length. Its chemical composition ranges from 37.3 to 63.8 mol.% FeTiO3 (ilmenite molecule), 61.1 to 22.4 mol.% MnTiO3 (pyrophanite molecule) and 0.6 to 15.3 mol.% ZnTiO3 (Znmetatitanate molecule). ZnO content ranges from 0.34 wt.% to 7.63 wt.%. Zonal structure is noticeable in the Zn-Mn ilmenite. FeTiO3 and ZnTiO3 molecules increase towards the crystal rim, while MnTiO3 molecule decreases towards the rim. Unit cell parameters of the rim and the core area = 5.092(6)Å,c = 14.08(2)Å,V = 316.1Å3 anda = 5.106(7)Å,c = 14.02(3)Å,V = 316.6Å3, respectively. Coexisting minerals, except for arfvedsonite and sphalerite, are very low in ZnO content. It is suggested that complete isomorphous replacement between FeTiO3 MnTiO3 and ZnTiO3 may be possible. Oxygen fugacity conditions for crystallization of Zn-Mn ilmenite are considered to be in the vicinity of the magnetite-hematite and quartz-fayalite-magnetite buffers.

Abstract Aluminous titanites occur in low-grade metasediments from the Salton Sea geothermal system, U.S.A., and in granitoids and associated fluorite-bearing skarns from southwest Japan. Average (Al + Fe3+) content of the metamorphic titanites in the Salton Sea geothermal system decreases systematically with increasing temperature and depth from 0.21-0.37 per formula unit (pfu.) in the chlorite-calcite zone (T = 180-320°C), through 0.12-0.23 pfu. in the biotite zone (320-340°C), to 0.12-0.13 pfu. in the clinopyroxene zone (340-360°C). Fluorine content varies from 0.0 to 0.20 pfu., and average XF [= F/(F + Cl + OH)] is less than 0.5 in all samples. Titanites in the granitoids are divided into magmatic titanites occurring as discrete grains in the matrix or as inclusions in plagioclase, and secondary titanites occurring as tiny granules in chlorite that alters biotite. The (Al + Fe3+) content and F contents are, respectively, 0.18 ± 0.03 and 0.14 ± 0.04 pfu. for the magmatic titanites and 0.45 ± 0.05 and 0.35 ± 0.08 pfu. for the secondary titanites. The (Al + Fe3+) content and F contents of titanites in fluorite-bearing skarns are 0.21 ± 0.05 and 0.16 ± 0.06 pfu., respectively. The titanites in the granitoids and skarns have high XF of 0.77 ±0.17 and 0.75 ± 0.16, respectively. The low-grade metamorphic and secondary titanites have variable Al content and XF; their compositions are controlled by both substitutions (Al, Fe3+)FTi-iO-i and (Al, Fe3+)(OH)Ti-iO-i. The Ca(Al, Fe3+)(OH)Si04 component of titanites was preferentially decomposed with increasing temperature and the (Al, Fe3+)FTi-iO-i substitution mainly controls Al content of titanite under high-temperature conditions. On the other hand, the Ca(Al, Fe3+)FSiO4 component increases with increasing pressure at fixed temperature, and stabilizes titanite in high-temperature and high-pressure conditions such as eclogite-facies metamorphism

Abstract Aluminian subsilicic orthopyroxene (AI2O3 =16.8 wt% maximum) was found in pseudomorphs after garnet megacrysts in alkali basaltic rocks occurring at the Mt. Huangyishan, Liaoning province and at Mt. Chishan, Shandong province of northeast China. The orthopyroxene-bearing pseudomorphs are mainly composed of finegrained (usually less than 2-3 µm in size) orthopyroxene, spinel and anorthite crystals. The pseudomorphs have many internal cracks, and aggregates of coarser-grained (20-300 µm in size) orthopyroxene, spinel and anorthite occur sporadically along the cracks. Olivine or clinopyroxene occurs rarely in the coarser-grained aggregates of a Huangyishan megacryst. In this sample, orthopyroxenes in the olivine- or clinopyroxene-bearing coarser-grained aggregates have fairly restricted Al2O3 contents of 10.5 ±1.2 and 10.7 ± 1.2 wt%, respectively, and that in the olivine- and clinopyroxene-free aggregates is richer in AI2O3 (12.3 ± 1.2 wt%). The Al enrichment of orthopyroxene is strongly controlled by the Tschermaks substitution [4]Al[6]Al(Mg, Fe)-1Si-1. The equilibrium conditions of the orthopyroxene-bearing assemblages are estimated at T = 1180-1270°C and P = 9-15 kbar. The orthopyroxene-bearing pseudomorphs have been formed by solid-state and isochemical breakdown of original garnet megacrysts during the transportation by the alkali basaltic magma. The transportation speed was high and is estimated at 3.5-7.0 km/h from a calculation of the velocities of the host magma ascent and gravitational sedimentation of the garnet megacryst. This suggests that the transportation time of the garnet megacryst from the garnet-stable depth to the surface was about 6-14 hours, which is probably sufficient for its partial decomposition.

Abstract Coesite in a granulite host-rock is reported from Weihai City, northeastern Shandong Province, China. Coesite occurs as inclusions in garnet, which is separated from the fine-grained matrix of quartz + clinopyroxene + hornblende by a zoned corona of plagioclase + clinopyroxene + orthopyroxene + hornblende. Petrological evidence shows that the coesite-bearing granulite is retrograded from eclogite. Three stages in the metamorphic history of the granulite have been recognized, (i) Coesite-eclogite stage: The assemblage reconstructed from the inclusions in garnet is Mg-rich garnet + omphacite + coesite + rutile. (ii) During the granulite stage, these minerals reacted to form quartz + clinopyroxene + hornblende (in the matrix), clinopyroxene + albite (omphacite pseudomorphs) and plagioclase + clinopyroxene + orthopyroxene + hornblende (as corona around garnet), (iii) Amphibolite stage: Earlier minerals were replaced by biotite, epidote and hornblende. The P-T conditions estimated with various geothermobarometers show a T-increasing and P-decreasing path from the eclogite stage (T ~ 720°C, P > 28 kbar) to the granulite stage (T ~ 850°C, P ~ 10 kbar). Thus the exhumation of the ultra-high-pressure rocks in Weihai proceeded under increasing temperature, and may not have been as fast as it was thought before