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The Blue Ridge Province of western North Carolina contains a wide variety of metamorphosed igneous and sedimentary rocks that record the tectonic effects of Precambrian and Paleozoic orogenic cycles. Tectonic interpretations of the events that led to the present configuration are varied and often conflicting. This investigation examines metamorphosed mafic rocks that are widely interpreted to have formed during the closure of ocean basins. Metabasites, and specifically eclogites, have a tendency to mark tectonic sutures and frequently preserve pressure (P), temperature (T), and age data (t) that can be gleaned from mineral equilibria and U-Pb isotopic compositions. As such, the examination of the metabasites is considered the key to understanding the orogenic history of the southern Blue Ridge where these metabasites occur. Chapter 2 is an investigation of the retrograde reactions related to the decompression of sodic pyroxenes that react to form diopside-plagioclase-hornblende-quartz symplectites as stability fields are overstepped during isothermal decompression. In Chapter 3 metabasites from the central and eastern Blue Ridge are re-examined and P-T pathways of these lithologies are determined. The argument is made that the Taconic orogeny of the Blue Ridge is the result of a continent-continent collision event that culminated in a mega-mélange that coincides with the Cullowhee terrane and the eastern Blue Ridge mélange of western North Carolina. Chapter 4 contains the results of a geochronological investigation of the Precambrian basement complex of the eastern Great Smoky Mountains. Chapter 5 is a whole rock geochemical study of the same basement complex. In Chapter 6, a potential lithologic correlation between the southern Blue Ridge basement and the Arequipa- Antofalla block of Peru is discussed. The geologic history of western South America from the Mesoproterozoic through Cambrian is summarized, a potential isotope-based lithologic correlation is proposed, and the early tectonic history of the central Blue Ridge is discussed. Chapter 7 contains brief summaries of Chapters 1-6.

The Springfield pluton intrudes the Wissahickon schist in the southeast Pennsylvania Piedmont. The mineralogy of the pluton. in order of decreasing abundance is plagioclase, quartz, microcline, biotite, epidote (often with allanite cores) and trace amounts of hornblende. Accessory minerals include sphene, magnetite, apatite and zircon. The magmatic assemblage of quartz+two feldspars+biotite+sphene+hornblende+magnetite permits its utilization of AI-in-hornblende as a geobarometer (Schmidt, 1992) and yields a pressure estimate of 9 kbars. The initial 87Sr/86Sr ratio of 0.708, suggests an evolved source for the magma with respect to mantle compositions, while a Rb-Sr whole rock age of 457 ± 9 Ma suggests a link between peak metamorphic conditions (Crawford and Crawford, 1980; Crawford and Mark, 1987, Sinha, 1988) and magmatism. The pluton is metaluminous to weakly peraluminous, with the aluminum saturation index (ASI) < 1.15. Si02 contents range from 64.1 to 75.1 wt. percent, with all other elements showing a correlation (either positive or negative) with the Si02. The pluton is correlated with two similar bodies to the south, Ellicott City, Maryland and Ellisville, Virginia. The spatial and temporal relationships of the plutons, including the two mica Gunpowder granite, Maryland record a magmatic axis associated with high pressures (>5.0 kb) of emplacement of magmas. / Master of Science

Near Burlington, Vermont, the Champlain Thrust fault placed massive Cambrian dolostones over calcareous shales of Ordovician age during the Ordovician Taconic Orogeny. Although the Champlain Thrust has been studied previously throughout the Champlain Valley, the architecture and structural evolution of its fault zone have never been systematically defined. To document these fault zone characteristics, a detailed structural analysis of multiple outcrops was completed along a 51 km transect between South Hero and Ferrisburgh, Vermont. The Champlain Thrust fault zone is predominately within the footwall and preserves at least four distinct events that are heterogeneous is both style and slip direction. The oldest stage of structures—stage 1—are bedding parallel thrust faults that record a slip direction of top-to-the-W and generated localized fault propagation folds of bedding and discontinuous cleavages. This stage defines the protolith zone and has a maximum upper boundary of 205 meters below the Champlain Thrust fault surface. Stage 2 structures define the damage zone and form two sets of subsidiary faults form thrust duplexes that truncate older recumbent folds of bedding planes and early bedding-parallel thrusts. Slickenlines along stage 2 faults record a change in slip direction from top-to-the-W to top-to-the-NW. The damage zone is ~197 meters thick with its upper boundary marking the lower boundary of the fault core. The core, which is ~8 meters thick, is marked by the appearance of mylonite, phyllitic shales, fault gouge, fault breccia, and cataclastic lined faults. In addition, stage 3 sheath folds of bedding and cleavage are preserved as well as tight folds of stage 2 faults. Stage 3 faults include thrusts that record slip as top-to-the-NW and -SW and coeval normal faults that record slip as top-to-the-N and -S. The Champlain Thrust surface is the youngest event as it cuts all previous structures, and records fault reactivation with any top-to-the-W slip direction and a later top-to-the-S slip. Axes of mullions on this surface trend to the SE and do not parallel slickenlines. The Champlain Thrust fault zone evolved asymmetrically across its principal slip surface through the process of strain localization and fault reactivation. Strain localization is characterized by the changes in relative age, motion direction along faults, and style of structures preserved within the fault zone. Reactivation of the Champlain Thrust surface and the corresponding change in slip direction was due to the influence of pre-existing structures at depth. This study defines the architecture of the Champlain Thrust fault zone and documents the importance of comparing the structural architecture of the fault zone core, damage zone, and protolith to determine the comprehensive fault zone evolution.

ABSTRACT The Central Blue Ridge sub-province of the southern Appalachian Mountains preserves an unique and complex geologic history. The Cartoogechaye terrane is the westernmost terrane of the Central Blue Ridge sub-province, and is characterized by extensive olistostromal sequences, including mafic-ultramafic massifs, isolated mafic units, and block-in-matrix structures of varying scales. This study investigates the genetic and tectonic relationships, and regional chemical and metamorphic trends of the amphibolitic rocks entrained within units of the Cartoogechaye and nearby terranes, toward constraining the origins of these regional sequences, and examining the rationale for the current Blue Ridge terrane designations. A distinct compositional variation exists between the northern and southern portions of the Cartoogechaye terrane, evident in the mafic rocks of the terrane. The amphibolite blocks and mega-blocks of the Willets-Addie mafic unit, in the northeastern portion of the Cartoogechaye terrane, indicate igneous rock protoliths of a calc-alkaline composition that are different from the mafic-origin amphibolitic massifs of the southwestern Cartoogechaye terrane (Ryan et al., 2005). Amphibolitic blocks of the Tathams Creek/Sylva area, immediately southwest of the Willets-Addie study site, show rare earth element systematics indistinguishable from the more mafic rocks in the Willets-Addie area, albeit with some chemical variation related most likely to variable migmatization of the rocks regionally. Mafic rocks in the adjoining Mars Hill terrane to the northwest show similar chemical trends, even though the Mars Hill terrane is recognized as different from the Cartoogechaye terrane, based on dating results from enclosing granitiods and migmatitic segregations. In the southwestern Cartoogechaye terrane, the Carroll Knob mafic complex preserves chemical signatures suggestive of ocean crustal origins, similar to the Buck Creek mafic-ultramafic suite (Berger et al. 2001, Peterson et al., 2009). However, the amphibolites in the Carroll Knob complex indicate pyroxene-rich cumulate and gabbroic protoliths consistent with an active oceanic magma system undergoing continuous magmatic replenishment and crystallization. West of the Carroll Knob complex, the Kimsey Bald mafic body includes amphibolites with protoliths comparable to the MORB-like, high-Ti amphibolites of the Buck Creek suite. The few amphibolite samples from the Lake Chatuge complex examined in this study also shows ocean crustal affinities, similar to those in the Buck Creek, Kimsey Bald, and Carroll Knob complexes. The chemical distinctions among these amphibolite suites, and the differences in the inferred crustal ages among their enclosing crustal units point to a possible boundary between the northern and southern regions of the Cartoogechaye terrane, one related either to likely crustal protoliths, or to a change in tectonic environment. The varied types of blocks comprising the Tathams Creek and associated Cartoogechaye units may indicate a transitional zone between the upper plate-derived accretionary sequences observed to the northeast and dominantly lower oceanic plate lithologies exposed in the southwestern extent of the terrane.

Late Ordovician (Cincinnatian) strata of the central Appalachians provide an opportunity to study the effects of both tectonics and eustasy within a foreland-basin setting. The Juniata Formation consists of red sandstones, siltstones, and shales that were deposited as part of an extensive siliciclastic basin-fill that resulted from the Taconic Orogeny. This study attempts to resolve some of the questions regarding tectonic and eustatic influences on sedimentation by (1) reconstructing the paleogeographic environment of the Juniata Formation and (2) examining the stratigraphic architecture of the Juniata Formation. A combination of both outcrop and subsurface data was analyzed. Seven facies were identified in this study, including: (1) "proto-vertisols", (2) red shale/mudstone, (3) siltstone/silty mudstone with interbedded sandstones, (4) quartz arenite and sublithic arenite, (5) argillaceous sandstone, (6) hummocky-bedded sandstones and siltstones, and (7) lithic sandstones and conglomerates. These facies are grouped into four facies associations (A–D), which are interpreted to be deposited from the inner shelf to the upper shoreface. Isopach and paleocurrent data suggest the shoreline was oriented NE–SW and detrital sediment was dispersed west and southwest across the basin. Tectonics controlled the 2nd-Order basin-fill pattern, and these patterns vary along the strike of the basin. Eustatic changes are expressed in two 3rd-Order sequences that were identified in the formation, and possibly in the 4th-Order (?) cycles of Facies Association A. The Ordovician–Silurian boundary is expressed as an unconformity throughout the study area, and along-strike variations in the structural setting of the basin were important in its development. / Master of Science

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