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Fluid-rock history of granulite facies humite-marbles from Ambasamudram, southern India. (2001)

Satish-Kumar, M. ; Wada, H. ; Santosh, M. ; [weitere]

Oxford, UK : Blackwell Science Inc

Journal of metamorphic geology 19 (2001), S. 0

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ISSN: 1525-1314

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: An extensive humite-bearing marble horizon within a supracrustal sequence at Ambasamudram, southern India, was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics. At peak metamorphic temperatures of 775±73°C, based on calcite-graphite carbon isotope thermometry, the mineral assemblages suggest layer-by-layer control of fluid compositions. Clinohumite + calcite-bearing assemblages suggest XCO2 〈 0.4 (at 700°C and 5 kbar), calcite + forsterite + K-feldspar-bearing assemblages suggest XCO2〉0.9 (at 790°C); and local wollastonite + scapolite + grossular-bearing zones formed at XCO2 of c. 0.3. Retrograde reaction textures such as scapolite + quartz symplectites after feldspar and calcite and replacement of dolomite + diopside or tremolite+dolomite after calcite+forsterite or calcite+clinohumite are indicative of retrogression under high XCO2 conditions. Calcite preserves late Proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration, while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting. Isotopic zonation of calcite and graphite grains was likely produced by localized CO2 fluid infiltration during retrogression. Contrary to the widespread occurrence of humite-marbles related to retrograde aqueous fluid infiltration, the Ambasamudram humite-marbles record a prograde-to-peak metamorphic humite formation and retrogression under conditions of low XH2O.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.0263-4929.2001.00318.x

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Digitale Medien

Giant magnetocaloric effect of MnAs1−xSbx (2001)

Wada, H. ; Tanabe, Y.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 79 (2001), S. 3302-3304

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A giant magnetocaloric effect was found in MnAs, which undergoes a first-order ferromagnetic to paramagnetic transition at 318 K. The magnetic entropy change caused by a magnetic field of 5 T is as large as 30 J/K kg at the maximum value, which exceeds that of conventional magnetic refrigerant materials by a factor of 2–4. The adiabatic temperature change reaches 13 K in a field change of 5 T. The substitution of 10% Sb for As reduces the thermal hysteresis and lowers the Curie temperature to 280 K, while the giant magnetocaloric properties are retained. © 2001 American Institute of Physics.