Geology and Tectonic Significance of the Late Precambrian Eastern Blue Ridge Cover Sequence in Central Virginia

The Late Precambrian cover sequence in the Blue Ridge of central Virginia includes rocks of the Moneta Formation and the overlying Lynchburg Group. The Moneta Formation comprises arnphibolites, felsites and biotite gneisses that unconformably overlie the Grenville basement. The Lynchburg Group in central Virginia is divided into three formations. Lynchburg I is made up of massive to thick bedded coarse-grained feldspathic arenites and conglomerates, which are interpreted as slope-apron deposits. Lynchburg IT contains mainly medium to fine grained feldspathic arenites and graphitic schist (black shales) with subordinate conglomeratic rocks. These are believed to be channelized submarine fan turbidites formed in an anoxic environment. Lynchburg ill consists of fine to medium grained feldspathic quartz arenites and a minor amount of conglomeratic rocks, which are considered to be channelized submarine turbidites with a more open marine environment and wider shelf. Three metamorphic facies and two deformation events are recognized in the cover sequence of the study area. The current tectonic models tend to view most of the mafic-ultramafic rocks and the host sedimentary rocks of the Lynchburg as ophiolitic melange, thus creating a suture, of Precambrian to Ordovician age. Detailed field mapping shows that the Lynchburg Group does not have the characteristics of melange and the mafic-ultramafic rocks in it do not resemble ophiolite. Rather, the cover sequence is related to the Late Precambrian Iapetan rifting event. Some tectonomagmatic discriminant diagrams have been used to support the current tectonic model and they are considered one of the most important arguments for ophiolites. These diagrams were tested by plotting samples from Jurassic rift basalts-diabases of eastern North America (ENA). The ENA samples, as well as the post Grenville mafic rocks in the Blue Ridge, tend to plot outside the within-plate field. It is clear that geochemical data alone may give a wrong tectonic classification, and that a knowledge of field relations is of paramount importance for interpretation.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Geosciences

Department dc:contributor.department

Geosciences

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1991

Author dc:creator

• Wang, Ping

Chair dc:contributor.committeechair

• Glover, Lynn III

Committee members dc:contributor.committeemember

• Tracy, Robert J.
• Eriksson, Kenneth A.
• Law, Richard D.
• Craig, James R.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

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

Language dc:language.iso

en

Dc Identifier Other

etd-06062008-142355

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/37945