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‘Decompressional’ reaction textures formed by isobaric heating: an example from the thermal aureole of the Taylor Brook Gabbro Complex, western Newfoundland

Published online by Cambridge University Press:  05 July 2018

S. J. Ings  and
J. V. Owen
S. J. Ings
Affiliation:
Department of Geology, Saint Mary's University, Halifax, Nova Scotia, Canada B3H 3C3
J. V. Owen*
Affiliation:
Department of Geology, Saint Mary's University, Halifax, Nova Scotia, Canada B3H 3C3
*
*E-mail: victor.owen@stmarys.ca
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Abstract

Reaction textures including corona structures in granulites from the Proterozoic Long Range Inlier of western Newfoundland are spatially associated with a Silurian (0.34 Ga) mafic intrusion, the Taylor Brook Gabbro Complex. They comprise, in metabasites and tonalitic gneiss, coronal orthopyroxene and plagioclase on garnet and, in metapelites, cordierite and spinel formed at the expense of sillimanite, garnet and quartz. Although generally interpreted to indicate near-isothermal decompression (ITD) following regional metamorphism, which in the inlier occurred at ˜1.10–1.03 Ga, these features appear to be absent elsewhere. Therefore they are interpreted to be products of contact metamorphism (near-isobaric heating – IBH) within the thermal aureole of the gabbro. Thus, there is a ˜0.7 Ga difference (i.e. mid-Proterozoic vs. mid-Silurian) between the age of the regional metamorphic mineral assemblages and the contact aureole assemblages. The observation that classic ITD features occur in this aureole environment underscores the fact that P-sensitive reactions can progress during IBH as well as by pressure release.

Keywords

coronaNewfoundlandCanadaTaylor Brook Gabbro Complexisothermal decompressionisobaric heating
Type
Research Article
Information
Mineralogical Magazine , Volume 66 , Issue 6 , December 2002 , pp. 941 - 951
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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