Date of Award

8-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

James Castle, Committee Chair

Committee Member

Scott Brame

Committee Member

John Garihan

Committee Member

Stephen Moysey

Abstract

Mapping of Six Mile quadrangle in the current study was restricted to the northern third and included comparison with lithologies mapped by Garihan (2005) in Sunset quadrangle. Following Garihan’s naming convention, six lithologic units were identified in Six Mile quadrangle: Walhalla hornblende gneiss, Table Rock gneiss, Tallulah Falls gneiss, Tallulah Falls schist, ultramafic rocks, and Quaternary alluvium. A major objective of this study was differentiating Table Rock gneiss from Tallulah Falls gneiss, undifferentiated previously within the study area. Age of rock units ranges from Early to Middle Cambrian (Tallulah Falls schist and gneiss; Hatcher, 2002) to Middle to Late Ordovician (Table Rock gneiss; Garihan, 2005). Age of Walhalla hornblende gneiss and ultramafic rocks is unknown.

Walhalla hornblende gneiss ranges from a white to gray to black, hornblende gneiss with foliation defined by aligned bands of hornblende and quartz-feldspar, to a fine- to medium-crystalline amphibolite dominated by hornblende. Amphibolite is defined in this work as having greater than fifty percent hornblende. Epidote is interfoliated locally with hornblende. Walhalla hornblende gneiss dominates the western portion of the study area as well as antiformal exposures in the central portion.

Table Rock gneiss is a leucocratic, fine- to medium-crystalline biotite gneiss that appears in stringers in the western part of the study area as well as in antiformal exposures in the central part. As mapped, Table Rock gneiss is surrounded by Walhalla hornblende gneiss. In this study, Walhalla hornblende gneiss and Table Rock gneiss are inferred to comprise the Walhalla nappe (Walhalla thrust sheet preferred usage).

Two of the three units of the Tallulah Falls Formation (Lower to Middle Cambrian; (Hatcher, 2002) occur in the study area: Tallulah Falls gneiss and Tallulah Falls schist. Tallulah Falls gneiss is a gray to black, medium- to coarse-crystalline, schistose, muscovite-biotite-porphyroclastic feldspathic gneiss. Tallulah Falls gneiss is found within synformal exposures in the central and eastern portions of the study area.

Tallulah Falls schist is a tan to red to purple to black, muscovite schist, ±garnet, sillimanite, biotite. Black, medium- to coarse-crystalline amphibolite is found within the unit and commonly as float. Tallulah Falls schist is commonly crenulated (wavelength= microscopic-2cm), with axial plane cleavage forming lineations on pavement exposures of schist. Tallulah Falls schist overlies Tallulah Falls gneiss and is found in the central and eastern portions of the study area. In this investigation, Tallulah Falls schist and Tallulah Falls gneiss are interpreted to be within the Six Mile thrust sheet. Amphibolite is also found as pods and float within Tallulah Falls schist and gneiss.

Two exposures of ultramafic rock were found in the study area. These ultramafic occurrences are 0.5-1.0m in size and include a green, schistose tremolite-clinochlore pod, and a white, talc-containing weathered hillslope exposure. Quartz-, feldspar-, and mica-rich, coarse-crystalline pegmatite is ubiquitous through the study area, but was not found at a mappable scale. Pegmatite was found concordant and discordant with rocks of the Six Mile thrust sheet and Walhalla thrust sheet. Quaternary alluvium was found in major and minor drainages in the study area and consisted of gray to tan to brown, silt to cobbles.

The Seneca fault, mapped by Garihan (2005) in Sunset quadrangle north of Six Mile quadrangle, is not visible in outcrop within the study area. However, location of the Seneca fault was interpreted within approximately 50m by mapping the transition from Walhalla hornblende gneiss and Table Rock gneiss of the Walhalla thrust sheet to Tallulah Falls gneiss and schist of the Six Mile thrust sheet. Ultramafic rocks occur within 500m of the interpreted Seneca fault.

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