Abrupt transition in H2O activity in the melt-present zone of a thermal aureole: Evidence from H2O contents of cordierites

Moazzen, Mohssen; Droop, G. T. R.; Harte, B.

doi:10.1130/0091-7613(2001)029<0311:atihoa>2.0.co;2

Cited by 6 publications

(39 citation statements)

References 23 publications

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“…If Reaction 8 consumed all available water, subsequent melting reactions must have been water-undersaturated. The data of Moazzen et al (2001); Rigby (2006) on H 2 0 contents of Etive cordierites provide supporting evidence for waterundersaturated conditions in the inner aureole. Contact-metamorphic garnet is associated with leucosomes in rare quartz-bearing samples from the Sillimanite Zone.…”

Section: Quartz-bearing Assemblagesmentioning

confidence: 59%

“…Na contents are low (<0.1 apfu). SIMS analysis indicates a significant decrease in the channel-site molecular H 2 0 occupancy from c. 0.5 pfu in Zone V to c. 0.3 pfu in Zone VI (Moazzen et al 2001). …”

Section: Cordieritementioning

confidence: 95%

“…fValues of n(H 2 0), determined by SIMS, are mean values for cordierites in the same rocks as the analyses listed (data from Moazzen et al 2001). …”

Section: Quartz-bearing Assemblagesmentioning

confidence: 99%

“…The relationship between metamorphism, melting, and the physical form of H 2 0 , the principal volatile component, will also be addressed. A preliminary study by Moazzen et al (2001) on the H 2 0 contents of Etive cordierites concluded that there was an abrupt transition from fluid-present conditions in the middle aureole to fluidabsent conditions in the melt-present inner aureole, but was hampered by a small sample set and poorly constrained P-T conditions. The present study will touch on this question with reference to dehydration equilibria, but will also furnish a much more detailed petrological framework for ongoing studies of the volatile contents of Etive cordierites.…”

Section: Introductionmentioning

confidence: 96%

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Contact metamorphism and partial melting of Dalradian pelites and semipelites in the southern sector of the Etive aureole

Droop

Moazzen

2007

SJG

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SynopsisContact-metamorphic mineral assemblages are described from Dalradian non-graphitic pelites and semipelites in the southern sector of the Etive thermal aureole, adjacent to the Quarry Diorite ring intrusion. Six metamorphic zones were mapped on the basis of incoming index minerals: I, Biotite; II, Cordierite; III, Andalusite+K-feldspar; IV, Corundum; V, Spinel; VI, Sillimanite. Garnet and orthopyroxene occur locally in high-grade quartz-bearing assemblages. Rocks of the Biotite and Cordierite zones retain their regional-metamorphic textures to a large extent, particularly S 2 crenulation cleavage. Above the Andalusite+K-feldspar isograd the rocks are hornfelses, but relict features of S 2 persist. Rocks of the upper Spinel and Sillimanite zones are agmatic/stromatic migmatites which preserve evidence of local partial melting in the form of S 2 -parallel leucosomes and thin fracture-filling vein leucosomes. All leucosomes are K-feldspar-rich. Vein leucosomes consist mainly of leucogranite with a metaluminous composition and, in the Sillimanite Zone, locally contain crystals of peritectic orthopyroxene and/or cordierite.The compositions of coexisting minerals, determined by EPMA, were used to constrain metamorphic reactions and, with equilibrium thermodynamic calculations, to refine estimates of the P-T conditions of metamorphism. Isograd reactions can generally be modelled satisfactorily in the CNKFMASH system as an isobaric sequence at P=2.2 kbar. An exception is the spinel isograd which occurs at anomalously low T due to the partitioning of Zn into spinel. Estimated isograd temperatures for the And+Kfs, Crn, Spl, melt and Sil isograds are 610°C, 630°C, 660°C, 680°C and 705°C, respectively. Calculated dehydration equilibria yield low values of water activity in the Sillimanite Zone, confirming that partial melting in the innermost aureole occurred under fluid-absent conditions. Leucosome textures and structures suggest that the siliceous microlithons of the former S 2 differentiated crenulation cleavage were the likely sites of melting and provided channels for the movement of melt into brittle fractures to form the vein leucosomes.

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Section: Quartz-bearing Assemblagesmentioning

confidence: 59%

Section: Cordieritementioning

confidence: 95%

“…fValues of n(H 2 0), determined by SIMS, are mean values for cordierites in the same rocks as the analyses listed (data from Moazzen et al 2001). …”

Section: Quartz-bearing Assemblagesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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Contact metamorphism and partial melting of Dalradian pelites and semipelites in the southern sector of the Etive aureole

Droop

Moazzen

2007

SJG

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“…It is imperative that both the air-jet and cold-finger are given sufficient time (-1 hr) to cool and/or stabilize. Cordierite standard AMNH (used by Carrington and Harley, 1996;Moazzen et al, 2001 andHarley et al, 2002 has XMg = 0.87; U¡O -1.56 +/-0.08 wt %; and CO¿ " 0.70 +/-0.05 wt %) was employed as the oxygen standard. The volatile contents of AMNH were determined independently by stepped-heating mass spectrometry (Harify pers.conim).…”

Section: Epma Of Oxygen In Cordieritementioning

confidence: 99%

Electron probe micro-analysis of oxygen in cordierite: potential implications for the analysis of volatiles in minerals

Rigby

Droop

Plant

et al. 2008

South African Journal of Geology

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The oxygen content of cordierite was analysed in 30, well-characterised samples, using electron probe micro-analysis (EPMA). The major elements were assumed to be stoichiometric and therefore any remaining oxygen from the analyses can be attributed to volatile oxygen, which is defined as the oxygen in HjO and/or COi within cordierite's channel .structure. The EPMA volatile oxygen contents were compared Iu volatile oxygen contents obtained from the same samples using seconttiry-ion nia.ss spectrometry (SIMS) and Fourier-transform infra-red spectroscopy (FTIR). There is a correlation between the data obtained by EPMA and the inik'pendcnt techniques. The data suggests that light-elements, .such a.s oxygen, can lie analyzed routinely on the electron microprobe with a degree of accuracy approaching the levels obtained by other, well-established methcxi.s, EPMA of oxygen, in addition to the major cations, provide.s a valuable tool for analyzing the HiO/OH" and/or volatile oxygen content of minerals such as amphilxiles, micas and cordierite. The assumption implicit in thi.s method, however, relies upon the fact ihat oxygen is stoichiometric with tiie major cations. If non-stoichiometry does apply ilien the method for calculating either H^O or volatile oxygen is rendered inadequate.

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Migmatite microstructures and partial melting of Hamadan metapelitic rocks, Alvand contact aureole, western Iran

Saki

Moazzen

Baharifar

2011

International Geology Review

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Abrupt transition in H2O activity in the melt-present zone of a thermal aureole: Evidence from H2O contents of cordierites

Cited by 6 publications

References 23 publications

Contact metamorphism and partial melting of Dalradian pelites and semipelites in the southern sector of the Etive aureole

Contact metamorphism and partial melting of Dalradian pelites and semipelites in the southern sector of the Etive aureole

Electron probe micro-analysis of oxygen in cordierite: potential implications for the analysis of volatiles in minerals

Migmatite microstructures and partial melting of Hamadan metapelitic rocks, Alvand contact aureole, western Iran

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