Geothermometry and geobarometry in the contact aureoles of the Nain complex, Labrador

• Main Author: Meltz, Robert E.
• Other Authors: Berg, Jonathan H., Department of Geology
• Format: Thesis
• Language: English
• Published: Northern Illinois University 1982
• Subjects: Petrology > Newfoundland > Labrador; Rocks > Thermal properties; Anorthosite > Newfoundland > Labrador; Newfoundland; Nain
• Online Access: https://commons.lib.niu.edu/handle/10843/19009

Includes bibliographical references. Includes illustrations and maps. The contact aureoles of the Naln Anorthosite Complex contain numerous mineral assemblages from which quantitative pressure and temperature estimates can be made. These estimates can be used to ascertain the conditions surrounding the emplacement of the Nain plutonic bodies. Two-feldspar thermometry, based on the graphical expressions of Brown and Parsons (1981) and Whitney and Stormer (1977). gives temperatures for the Klglapait contact aureole which are in good agreement with the temperature profile of Berg and Docka (in press). Garnet-orthopyroxene-plagioclase barometry (Newton and Perkins, 1982) and two-feldspar thermometry of garnet- cord ier it e-orthopyroxene-plagioclase-orthoclase-quartz assemblages give results which are in rather good agreement with the corrected garnet-cordierite data of Berg (1977)- Discrepancies which are present can best be explained as being a result of preferential re-equilibration between the feldspars in response to subsequent meta- morphisms or retrograde effects. The data from this study neither support nor refute the existence of a WNW-ESE trending arch in the ancient pressure surface (Berg, 1977)* With the exception of two samples, the pressures from both barometers range from 2.2 to ^.9 kbars. These low pres- sures support the conclusion of Berg (1977) that anorthosite emplacement need not be associated with conditions of deep-seated granulite facies metamorphism. Two-feldspar thermometry performed on lamellae and host from numerous perthites and antiperthites indicates that antiperthites yield lower equilibration temperatures than perthites from the same sample. This is interpreted to be a function of faster cation diffusion in alkali feldspar than in plagloclase, which results in alkali feldspar lamellae in antiperthites re-equilibrating during cooling to a greater extent than plagloclase lamellae in perthite. M.S. (Master of Science)