Official journal of Japan Association of Mineralogical Sciences (JAMS), focusing on mineralogical and petrological sciences and their related fields. Journal of Mineralogical and Petrological Sciences (JMPS) is the successor journal to both “Journal of Mineralogy, Petrology and Economic Geology” and “Mineralogical Journal”. Journal of Mineralogical and Petrological Sciences (JMPS) is indexed in the ISI database (Thomson Reuters), the Science Citation Index-Expanded, Current Contents/Physical, Chemical & Earth Sciences, and ISI Alerting Services.
The three–dimensional (3–D) structure of crystals around the interface between massive potassium (K)–feldspar and quartz–feldspar intergrowth (graphic granite) of two samples collected from a pegmatite body in Ishikawa town, Fukushima Prefecture, Japan, was determined by X–ray computed tomography (CT). Based on the results and additional information obtained by serial thin section and polarizing observations, the formation processes of graphic granite and pegmatite bodies are discussed. The most important finding of the 3–D observation using X–ray CT is the very flat spatial distribution of the tips of the quartz crystals. The sharp interface between the graphic and single–phase parts suggests that the change from graphic granite to massive K–feldspar crystallization corresponds to the transition of the thermodynamic conditions at the growth front from non–equilibrium to equilibrium. This indication leads to a new model for the pegmatite genesis, that is, graphic granite forms at the marginal zone under non–equilibrium conditions shortly after the intrusion of magma due to rapid cooling by the cold host rock body and, subsequently, the crystallization of massive K–feldspar starts when the conditions at the crystal growth front reenter the ‘feldspar + melt’ field in the phase diagram due to the relaxation of the conditions. Other results related to the conditions of the growth environment with coexisting aqueous fluid, such as the connectivity of the quartz crystals, are also discussed, for example, the influence of the supercritical state on the nucleation of quartz crystals.
We report on in situ high–pressure Raman spectroscopic study of hydrogrossular, katoite Ca3Al2(O4H4)3, in a diamond–anvil cell under hydrostatic conditions at room temperature. The variations of vibration modes were analyzed theoretically by factor group analysis. Three characteristic Raman peaks observed at 341, 541, and 3649 cm−1 at 1.3 GPa were obtained continuously up to 8.3 GPa. The Raman peak at 3649 cm−1 was assigned to the O–H stretching vibration modes of A1g + Eg symmetry at 3634 cm−1 and F2g symmetry at 3656 cm−1. The pressure dependence of the two O–H stretching vibration modes showed negative pressure shifts, indicating that hydrogen bond became shorter and stronger with compression. The most striking characteristic was that above 5.1 GPa pressure derivative of the O–H stretching vibration mode of F2g symmetry started to decrease significantly. This change suggests that symmetry of the H4O4 tetrahedron changes at 5.1 GPa, implying the phase transition of katoite to its high–pressure phase. Pressure derivatives of the two O–H stretching vibration modes of A1g + Eg and F2g symmetries are −7.2 and −1.1 cm−1/GPa, respectively, which yields negative Grüneisen parameters. In the frequency region of lattice mode, the lower frequency peak observed at 341 cm−1 was assigned to librational R(O4H4) vibration mode of A1g symmetry, whose frequency increased continuously up to 5.1 GPa with pressure derivatives of 6.5 cm−1/GPa. Meanwhile, the higher frequency peak at 541 cm−1 was assigned to T(OH) motions of A1g + Eg symmetry at 523 cm−1 and F2g symmetry at 545 cm−1, whose frequencies increased with pressure derivatives of 4.4 and 4.9 cm−1/GPa, respectively. These pressure coefficients in the lattice mode lead to the isothermal mode Grüneisen parameters varying from 0.49 to 1.11. Values of the full width at half maximum (FWHM) of all observed Raman bands were continuously increased up to 5.1 GPa, but their increasing rates became higher above this pressure. The result is also indicative that katoite transforms to the high–pressure phase above 5.1 GPa.
Retrograde pumpellyite was newly found in garnet blueschist that is Mg–rich equivalent of late Paleozoic retrograde eclogite of the Yunotani Valley in the Omi area, Hida–Gaien Belt. The pumpellyite with high Al/(Al + Mg + Fe) occurs in pressure shadows around garnets; it is associated with secondary glaucophane, epidote, chlorite, titanite, phengite, albite, and quartz, which all characterize a retrograde blueschist–facies mineral assemblage after peak eclogite–facies mineral assemblage. This feature is comparable with retrograde pumpellyite in late Paleozoic garnet blueschist (with relict eclogite–facies mineral assemblage) in the Osayama area of the Chugoku Mountains. Equilibrium phase calculation confirmed that the pumpellyite is stable at a low temperature and pressure portion of the lawsonite–blueschist–facies. T–bulk–composition (Mg) pseudosection suggests that pumpellyite appears preferentially in high Mg/(Mg + Fe) bulk composition. The limited occurrence of retrograde pumpellyite in the Yunotani garnet blueschist and retrograde eclogite would be explained by Mg–rich bulk compositions. Also, the limited occurrence in pressure shadows around garnets suggests that the fluid trapped in the pressure shadows might have enhanced growth (or precipitation) of pumpellyite. This finding provides a strong evidence that the deeply subducted (eclogite–facies) metabasaltic rocks both in the Hida–Gaien Belt and the Chugoku Mountains were subjected to a very similar blueschist–facies overprinting locally reached the pumpellyite stability field. The ‘Franciscan–type’ cooling path suggests a ‘steady–state’ underflow of the paleo–Pacific oceanic plate in late Paleozoic at a convergent margin of the South China Craton.
Chemically heterogeneous amphibole, ranging in composition from magnesio–riebeckite through ferri–ghoseite to clino–suenoite, was found in a specimen of Sanbagawa quartz schist from the Iimori region of the western Kii Peninsula, central Japan. The amphibole exhibits a continuous solid solution between BNa and BMn2+ (BMn2+ = 0–1.82 atoms per formula unit). Most of the amphibole crystals comprise a Mn–poor core and a Mn–rich rim, and ferri–ghoseite often occurs near the boundary between core and rim. The crystal structure of a single crystal fragment of ferri–ghoseite, which has an averaged composition of A(Na0.16K0.02)Σ0.18B(Na0.83Ca0.09Mn2+1.08)Σ2.00C(Mg3.78Mn2+0.52Fe3+0.66
Al0.04)Σ5.00T(Si7.95Al0.05)Σ8.00O22W[(OH)1.90F0.10]Σ2.00 based on electron–microprobe analyses, was refined to a R1 of 6.7%, has unit cell parameters of a = 9.6389(7), b = 18.0534(10), c = 5.3138(3) Å, and β = 102.896(2)°, and is in space group C2/m with Z = 2. The site populations for B cations of the ferri–ghoseite are M4(Na0.83Ca0.09)M4’Mn2+1.08, which also confirms the B(Na,Mn2+) solid solution. Sector–zoned aegirine occurs in the amphibole–bearing quartz schist from Iimori, and it is assumed that most of the metamorphic minerals in the quartz schist formed under non–equilibrium conditions. Therefore, taking into account the miscibility gap between sodium amphibole and clino–suenoite, the solid solution between BNa and BMn2+ in the amphibole can be inferred to have resulted from rapid, non–equilibrium crystallization rather than high–T equilibrium crystallization.
The viscosity of melt of soda melilite (CaNaAlSi2O7) composition was measured using the falling sphere method with synchrotron X–ray radiography. This composition of melt was used as a model basalt, because the ratio of the non–bridging oxygen (NBO) and the tetrahedrally coordinated (T) cation is 0.67. We observed a viscosity minimum between 2 and 4 GPa. This finding shows that the partially depolymerized melt (NBO/T = 0.67) has a viscosity minimum under high pressure.
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