Petrography and petrology of "unakites" located in the Mount Rogers area, southwestern Virginia

Mount Rogers, located in southwestern Virginia, approximately 36 miles east of Bristol, Virginia, on the Smyth-Grayson county line, is in the Blue Ridge physiographic province. This area is underlain by the Mount Rogers volcanic series which consists of a complex series of tuffaceous sediments, arkoses, basalts, and rhyolites of late Precambrian age. An older Precambrian "injection complex" of granite, gneiss, and unakite is exposed in the area. Two unakites are present in the area of this study and will be called the Azen unakite and the Elk Garden Ridge unakite. These unakites are older than the Mount Rogers group and are thought to be erosional highs of the "injection complex". The Azen unakite consists of: quartz, 36.5 per cent; potassium feldspar, 41.2 per cent; epidote, 22.3 per cent; and traces of ilmenite and hematite. Texture and mineral composition indicate this rock to be a hypersolvus unakite. Evidence favoring a primary origin for the epidote includes: 1) inclusion of euhedral epidote grains in primary quartz, 2) epidote inclusions in earlier, high temperature minerals but its exclusion from lower temperature minerals, and 3) lack of relict structure or residual mafic constituents of a primary mineral which has been altered to epidote. The Elk Garden Ridge unakite consists of: quartz, 27.7 per cent; plagioclase, 27.3 per cent; epidote, 43.6 per cent; potassium feldspar, 1.4 per cent; and traces of ilmenite, hematite, and magnetite. Continuous magmatic crystallization of an initially hypersolvus magma is evidenced by the continued crystallization of epidote and the initiation of plagioclase crystallization. Thus the Azen unakite is the high temperature counterpoint for the Elk Garden Ridge unakite which initiated crystallization hypersolvus but later crossed the solvus into the two feldspar region. Evidences for dynamic metamorphism are interpreted to have resulted from autometamorphism during magmatic intrusion. The feldspars show dislocation and epidote is granulated.

Name thesis:degree_name

M.S.

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Geological Sciences

Department dc:contributor.department

Geological Sciences

Grantor dc:publisher

Virginia Polytechnic Institute

Year dc:date.issued

1967

Author dc:creator

• McTague, Stephen Bartholomew

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10919/118533

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/118533