Nano- to micro-scale decompression products in ultrahigh-pressure phengite: HRTEM and AEM study, and some petrological implications
-
Cristiano Ferraris
,
Christian Chopin
Abstract
Samples of phengite-3T, (K0.93Na0.01)(Al1.44Mg0.56Ti0.02)(Si3.54Al0.46)O10(OH1.93F0.07), which formed at about 3 GPa and 1000 K in ultrahigh-pressure metamorphic rocks of the Dora-Maira Massif (Western Alps, Italy), were investigated by HRTEM, AEM, EMPA, and SEM. The matrix of phengite- 3T, which is almost free of stacking faults, contains single-crystal α-quartz platelets 100-700 Å thick that are confined by (001) planes of phengite. In the vicinity of quartz, the 30 Å period of the phengite-3T matrix is faulted by short sequences with about 19 Å periodicity, interpreted as talc-2M. The occurrence of these phases is not connected with any defects in the host phengite nor is their spatial distribution homogeneous on the TEM scale. The shape control exerted by phengite on the quartz crystals, the absence of deformation around them, and the nearby presence of an interlayered 19 Å phase, suggest that quartz and talc may have been produced within mica by a reaction of the type:
3 alumino-celadonite + 2 H+ = 1 muscovite + 1 talc + 5 quartz + 2 H2O + 2 K+
which leads to a less celadonite-rich phengite during decompression, after the rock had left the coesite stability field. In addition, examination by optical microscopy along [001] of “thick” sections of the Dora-Maira phengite and of phengite samples from other high-pressure terranes (Monte Mucrone and Sesia Zone in the Italian Western Alps, Dabie Mountains in central China), revealed the presence of micrometer-wide, amoeboid platelets of quartz interlayered at various depths parallel to (001) of micas. In spite of the different observation scale, these are interpreted as the same reaction product as identified by HRTEM. These new observations show that high-pressure white micas may not be homogeneous and should be examined more carefully. Some consequences for thermobarometry of such heterogeneity and intracrystalline re-organization during decompression are considered; they depend on the resolution of the analytical method employed. Implications for thermochronometry still have to be evaluated.
© 2015 by Walter de Gruyter Berlin/Boston
Artikel in diesem Heft
- Measurement of crystal size distributions
- Pressure dependence of the solubility of Ar and Kr in melts of the system SiO2-NaAlSi2O6
- Solubility behavior of water in haploandesitic melts at high pressure and high temperature
- Proton-containing defects at forsterite {010} tilt grain boundaries and stepped surfaces
- Incorporation of Fe3+ into forsterite and wadsleyite
- Molecular dynamics simulation of Al/Si-ordered plagioclase feldspar
- Cation ordering and structural variations with temperature in MgAl2O4 spinel: An X-ray single-crystal study
- Aluminium coordination in tektites: A XANES study
- Crystal structure of Cr-mullite
- Structure of synthetic 2-line ferrihydrite by electron nanodiffraction
- Transmission electron microscopy study of gaudefroyite, Ca8Mn6 3+[(BO3)6(CO3)2O6]
- Nano- to micro-scale decompression products in ultrahigh-pressure phengite: HRTEM and AEM study, and some petrological implications
- New insights into the mechanism for chloritization of biotite using polytype analysis
- The dissolution of hectorite: In-situ, real-time observations using atomic force microscopy
- Quantification of minor phases in growth kinetics experiments with powder X-ray diffraction
- Illite-smectite structural changes during metamorphism in black Cambrian Alum shales from the Baltic area
- The tremolite-actinolite-ferro–actinolite series: Systematic relationships among cell parameters, composition, optical properties, and habit, and evidence of discontinuities
- Cordierite I: The coordination of Fe2+
- Cordierite II: The role of CO2 and H2O
- Crystal chemical variations in Li- and Fe-rich micas from Pikes Peak batholith (central Colorado)
- The crystal structure of TlAlSiO4: The role of inert pairs in exclusion of Tl from silicate minerals
- The structure of agrinierite: a Sr-containing uranyl oxide hydrate mineral
- The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry
- The crystal structure of pararobertsite and its relationship to mitridatite
- Description and crystal structure of cabalzarite Ca(Mg,Al,Fe)2(AsO4)2(H2O,OH)2, a new mineral of the tsumcorite group
- Tegengrenite, a new, rhombohedral spinel-related Sb mineral from the Jakobsberg Fe-Mn deposit, Värmland, Sweden
Artikel in diesem Heft
- Measurement of crystal size distributions
- Pressure dependence of the solubility of Ar and Kr in melts of the system SiO2-NaAlSi2O6
- Solubility behavior of water in haploandesitic melts at high pressure and high temperature
- Proton-containing defects at forsterite {010} tilt grain boundaries and stepped surfaces
- Incorporation of Fe3+ into forsterite and wadsleyite
- Molecular dynamics simulation of Al/Si-ordered plagioclase feldspar
- Cation ordering and structural variations with temperature in MgAl2O4 spinel: An X-ray single-crystal study
- Aluminium coordination in tektites: A XANES study
- Crystal structure of Cr-mullite
- Structure of synthetic 2-line ferrihydrite by electron nanodiffraction
- Transmission electron microscopy study of gaudefroyite, Ca8Mn6 3+[(BO3)6(CO3)2O6]
- Nano- to micro-scale decompression products in ultrahigh-pressure phengite: HRTEM and AEM study, and some petrological implications
- New insights into the mechanism for chloritization of biotite using polytype analysis
- The dissolution of hectorite: In-situ, real-time observations using atomic force microscopy
- Quantification of minor phases in growth kinetics experiments with powder X-ray diffraction
- Illite-smectite structural changes during metamorphism in black Cambrian Alum shales from the Baltic area
- The tremolite-actinolite-ferro–actinolite series: Systematic relationships among cell parameters, composition, optical properties, and habit, and evidence of discontinuities
- Cordierite I: The coordination of Fe2+
- Cordierite II: The role of CO2 and H2O
- Crystal chemical variations in Li- and Fe-rich micas from Pikes Peak batholith (central Colorado)
- The crystal structure of TlAlSiO4: The role of inert pairs in exclusion of Tl from silicate minerals
- The structure of agrinierite: a Sr-containing uranyl oxide hydrate mineral
- The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry
- The crystal structure of pararobertsite and its relationship to mitridatite
- Description and crystal structure of cabalzarite Ca(Mg,Al,Fe)2(AsO4)2(H2O,OH)2, a new mineral of the tsumcorite group
- Tegengrenite, a new, rhombohedral spinel-related Sb mineral from the Jakobsberg Fe-Mn deposit, Värmland, Sweden
