The Reaction Antigorite → Olivine + Talc + H2O in the Bergell Aureole, N. Italy

R. H. Worden*, G. T. R. Droop and P. E. Champness
Department of Geology, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
*Present address: BP International Limited, Sunbury Research Centre, Chertsey Road, Sunbury-on-Thames, Middlesex TW16 7LN, U.K.

Abstract: The low-grade contact metamorphic decomposition of antigorite serpentine to olivine and talc has been studied using TEM. The reaction was more complex than has been assumed by previous workers in that (i) FeO played a significant role in controlling the temperature of reaction, and (ii) minor amounts of an aluminous phase (chlorite) were probably produced. The reaction occurred over a range of temperatures within which the assemblage antigorite + talc + olivine was stable and the antigorite became progressively more Mg-rich as the reaction proceeded. Oriented nucleation of talc occurred within the antigorite. However, the olivine breakdown product did not require nucleation; rather it appears to have grown on pre-existing olivine grains. Communication between the sites of reaction was probably facilitated by an ubiquitous grain-boundary fluid.

Keywords: antigorite • olivine • talc • TEM • contact metamorphism • Bergell aureole

Mineralogical Magazine; September 1991 v. 55; no. 380; p. 367-377; DOI: 10.1180/minmag.1991.055.380.07
© 1991, The Mineralogical Society
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