Thermodynamics of the amphiboles: Anthophyllite-ferroanthophyllite and the ortho-clino phase loop

Evans, Bernard W.; Ghiorso, Mark S.; Yang, Hexiong; Medenbach, Olaf

doi:10.2138/am-2001-5-605

Cited by 17 publications

(13 citation statements)

References 45 publications

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“…The introduction of water must have followed the initiation of the thermal pulse as enstatite formed fi rst and was then rimmed by anthophyllite. Anthophyllite and the assemblage phlogopite+quartz are both at their limits of stability at around 790 °C (Chernosky et al, 1985;Evans et al, 2001;Bohlen et al, 1983), in good agreement with estimates for titanite geothermometry reported above (787-817 °C). Since enstatite forms the cores of the porphyoblasts it appears that water activity was initially low and with fl uid infi ltration anthophyllite eventually formed.…”

Section: Origin Of the Contact Rockssupporting

confidence: 76%

Differentiating Shawinigan and Ottawan orogenesis in the Central Adirondacks

et al. 2011

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The rocks at Chimney Mountain provide a rare glimpse into primary intrusive relations and exceptionally well-preserved pre-Shawinigan metasedimentary rocks in the Adirondack Highlands despite a strong Ottawan thermal overprint. A near vertical contact between granite (ca. 1172 Ma) and a shallowly dipping and structurally intact sequence of quartzose to calc-silicate metasedimentary rocks is exposed on the southern fl ank of Chimney Mountain in the Central Adirondacks. The contact is marked by foliation truncation and a metasomatic aureole with randomly orientated porphyro blasts of enstatite rimmed by anthophyllite (max. 5 cm) and phlogopite (max. 2 cm), and a zone of granular, quartzrich rock. The granite is non-to weakly foliated and has a shallow, north-plunging, mineral lineation as do the metasedimentary rocks. Zircons separated from a diopsidebearing quartzite (82% SiO 2 ; 0.75 m thick) are of variable size (up to 400 µm), equant, and contain, on average, >1000 ppm uranium. Scanning electron microscope investigation indicates that there is little variation in a uniformly dark cathodoluminescence response, no discernible cores or rims, few inclusions, and partially faceted to round morphologies. Zircon U-Pb sensitive highresolution ion microprobe (SHRIMP II) ages of 1042 ± 4 Ma and 1073 ± 15 Ma are coincident with Ottawan metamorphic ages from the Adirondack Highlands. Zircons from the intrusive granite yield large cores with typical anorthosite-mangerite-charnockitegranite (AMCG) ages (ca. 1171.6 ± 6.3 Ma) and sparse, thin younger rims (ca. 1060-1090 Ma) readily distinguishable by cathodoluminescence. Despite the younger zircon ages, the metasedimentary rocks and their fabric must predate the crosscutting granite. The thermal effect of the Ottawan event was likely enhanced by volatile fl uxing and resulted in recrystallization and resetting of zircons in the metasedimentary rocks. However, it had limited effects on zircons in the granite and produced only thin metamorphic rims emphasizing the importance of local geochemical conditions to the response of zircon to metamorphism. Elzevirian or Shawinigan fabrics are preserved as the dominant foliation; the lineation and folding is likely late (post-1170 Ma) Shawinigan or Ottawan (ca. 1050 Ma). Titanites from the same metasedimentary sequence yield a range of 238 U / 206 Pb ages from 969 to 1077 Ma, with a maximum probability age of 1035 Ma, similar to other titanites in the Adirondack Highlands. Ottawan paleotemperatures, estimated by zirconium in titanite thermometry, range from 787 to 818 °C.For permission to copy, contact editing@geosociety.org

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Section: Origin Of the Contact Rockssupporting

confidence: 76%

Differentiating Shawinigan and Ottawan orogenesis in the Central Adirondacks

et al. 2011

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“…At these temperatures with sufficient water present, one would expect mineral assemblages with Fe-Mg amphibole rather than the olivine and orthopyroxene that are observed ( Fig. 9; Evans et al, 2001). Perhaps the minerals totally exchanged the Mg/Fe during cooling, or the thermometer may be miscalibrated for metamorphic T.…”

Section: Fe-mg-spinel-olivine-orthopyroxenementioning

confidence: 97%

The LaPaz Icefield 04840 meteorite: Mineralogy, metamorphism, and origin of an amphibole- and biotite-bearing R chondrite

McCanta

Treiman

Dyar

et al. 2008

Geochimica et Cosmochimica Acta

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“…Considering the similarity between the anthophyllite–ferroanthophyllite and cummingtonite–grunerite series, it is reasonable to assume that the ordering of Fe and Mg in anthophyllite–ferroanthophyllite is identical to that in cummingtonite–grunerite (Evans et al. , 2001).…”

Section: Formulation and Calibration Of The Orthoamphibolesmentioning

confidence: 99%

A new thermodynamic model for clino‐ and orthoamphiboles in the system Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–O

Diener

Powell

White

et al. 2007

Journal Metamorphic Geology

460

305

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A recent thermodynamic model for the Na-Ca clinoamphiboles in the system Na 2 O-CaO-FeO-MgOAl 2 O 3 -SiO 2 -H 2 O-O (NCFMASHO), is improved, and extended to include cummingtonite-grunerite and the orthoamphiboles, anthophyllite and gedrite. The clinoamphibole model in NCMASH is adopted, but the extension into the FeO-and Fe 2 O 3 -bearing systems is revised to provide thermodynamic consistency and better agreement with natural assemblage data. The new model involves order-disorder of Fe-Mg between the M2, M13 and M4 sites in the amphibole structure, calibrated using the experimental data on site distributions in cummingtonite-grunerite. In the independent set of end-members used to represent the thermodynamics, grunerite (rather than ferroactinolite) is used for FeO, with two ordered Fe-Mg end-members, and magnesioriebeckite (rather than ferritschermakite) is used for Fe 2 O 3 . Natural assemblage data for coexisting clinoamphiboles are used to constrain the interaction energies between the various amphibole end-members. For orthamphibole, the assumption is made that the site distributions and the non-ideal formulation is the same as for clinoamphibole. The data set end-members anthophyllite, ferroanthophyllite and gedrite, are used; for the others, they are based on the clinoamphibole end-members, with the necessary adjustments to their enthalpies constrained by natural assemblage data for coexisting clino-and orthoamphiboles. The efficacy of the models is illustrated with P-T grids and various pseudosections, with a particular emphasis on the prediction of mineral assemblages in ferric-bearing systems.

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Thermodynamics of the amphiboles: Anthophyllite-ferroanthophyllite and the ortho-clino phase loop

Cited by 17 publications

References 45 publications

Differentiating Shawinigan and Ottawan orogenesis in the Central Adirondacks

Differentiating Shawinigan and Ottawan orogenesis in the Central Adirondacks

The LaPaz Icefield 04840 meteorite: Mineralogy, metamorphism, and origin of an amphibole- and biotite-bearing R chondrite

A new thermodynamic model for clino‐ and orthoamphiboles in the system Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–O

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Thermodynamics of the amphiboles: Anthophyllite-ferroanthophyllite and the ortho-clino phase loop

Cited by 17 publications

References 45 publications

Differentiating Shawinigan and Ottawan orogenesis in the Central Adirondacks

Differentiating Shawinigan and Ottawan orogenesis in the Central Adirondacks

The LaPaz Icefield 04840 meteorite: Mineralogy, metamorphism, and origin of an amphibole- and biotite-bearing R chondrite

A new thermodynamic model for clino‐ and orthoamphiboles in the system Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O

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A new thermodynamic model for clino‐ and orthoamphiboles in the system Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–O