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Fusion of Torridonian Sandstone by a Picrite Sill in Soay (Hebrides)

Wyllie, P. J. (1961) Fusion of Torridonian Sandstone by a Picrite Sill in Soay (Hebrides). Journal of Petrology, 2 (1). pp. 1-37. ISSN 0022-3530. doi:10.1093/petrology/2.1.1.

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Up to 92 per cent of the original minerals were fused during progressive metamorphism of Torridonian sediment by a picrite sill. The liquid precipitated microlites of tridymite, cordierite, hypersthene, and magnetite until that remaining quenched to a glass. Stages of fusion were determined by petrographic methods. After decomposition of sericite and reduction of haematite, liquid developed by fusion of feldspar and quartz. The composition of liquid in a fused xenolith at various stages was calculated from chemical and modal analyses. The chemical analysis indicates that fusion occurred in the presence of excess water-vapour. The melting and crystallization processes compare closely with the behaviour of similar compositions in the system NaAlSi_3O_8-KalSi_3O_8-SiO_2-H_2O. Liquidus temperatures corresponding to the calculated liquids provide temperature estimates. An upper pressure limit is given by the quartz-tridymite PT curve. It is estimated that the liquid crystallized between 1,025°C and 935°C at a water-vapour pressure of 430 kg/cm^2. Reaction between picrite and fused sediment indicates that maximum fusion occurred when crystallization of the picrite was almost completed. The estimated picrite intrusion temperature is at least 1,175°C.

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Additional Information:© 1961 Oxford University Press. The writer wishes to thank Dr. H. I. Drever and Mr. R. Johnston for their co-operation and assistance. Drever discovered the fused sediments and suggested this detailed study, and Johnston was a stimulating companion on Soay. Both provided critical comments which have led to improvements in the paper. The laboratory work was completed in the Geology Department, University of St. Andrews, and in the Department of Geophysics and Geochemistry, The Pennsylvania State University. The field work was partly financed by the Shell Petroleum Company.
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Shell Petroleum CompanyUNSPECIFIED
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Record Number:CaltechAUTHORS:20160112-131343995
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Official Citation:P. J. WYLLIE Fusion of Torridonian Sandstone by a Picrite Sill in Soay (Hebrides) J. Petrology (1961) 2 (1): 1-37 doi:10.1093/petrology/2.1.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63596
Deposited By: Tony Diaz
Deposited On:12 Jan 2016 22:15
Last Modified:10 Nov 2021 23:18

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