Detailed geologic mapping of portions of the Banoak, Reepsville, Lincolnton West, and Cherryville 7.5-minute quadrangles has confirmed the easternmost exposure of the Brindle Creek fault, which frames the Newton window. The Brindle Creek fault is a terrane boundary that separates the overlying Siluro-Devonian assemblage of metasedimentary rocks and Devonian-Mississippian anatectic plutons of the Cat Square terrane from the Neoproterozoic(?)-Ordovician metasedimentary and igneous rocks of the Tugaloo terrane. Structures related to six deformational events have been identified in this portion of the Inner Piedmont. The Brindle Creek fault has been folded multiple times, resulting in a sinuous outcrop pattern and the formation of the Newton window and smaller Howards Creek window. Portions of three map-scale sheath folds have been identified by map patterns and orientation of dominant mineral lineations, fold axes, and shear-sense indicators. The discontinuity of map-scale bodies of metagraywacke, mafic complexes, and amphibolite is attributed to extension during sheath fold formation. Dominant foliation, mineral lineation, and fold-axis orientations suggest north-northwest directed flow occurred in this portion of the Inner Piedmont. Zircon geochronology data indicate crystallization of the Vale charnockite at 366.4 ± 3.1 Ma and the enclosing Walker Top Granite at 356.5 ± 5.3 Ma. Zircon saturation thermometry estimates minimum magmatic temperatures for the granitoids at 800-840⁰ C. Whole-rock geochemical and isotopic data indicate the Vale charnockite and Walker Top Granite are genetically related and were derived from deep crustal melting of largely Proterozoic-affinity metasediments in an arc environment. Both granitoids crystallized from the same parent magma; the Vale charnockite is an autolith, or early crystallization of the melt, incorporated into the later crystallizing Walker Top Granite. Geochemical analyses of Cat Square terrane mafic complexes west of the Newton window suggest these bodies represent vestiges of oceanic crust formed in a back-arc basin setting or from both MORB and volcanic-arc sources as characterized by mixed N-MORB and calc-alkaline volcanic-arc signatures. This back-arc basin likely formed from east-dipping subduction during the development of Ordovician volcanic arcs outboard of Laurentia.

Although karst processes in south central Kentucky have been studied extensively, the Haney Limestone Member of the Golconda Formation has not been studied in detail in contrast to limestones stratigraphically below it that are thicker. In addition, the relationship between petrographic features of the Haney Limestone and the formation of caves and karst features has not been studied extensively compared to lithographic, petrographic, or structural variables Petrographic data were collected using core and surface exposures across the study area of south central Kentucky from northern Logan and Warren counties up toward the Rough Creek Graben region, and stratigraphic columns were constructed. Twenty-three petrographic thin-sections were made from samples collected at these sites, described, and photo documented. These studies have revealed that grain size and silica content play a role in how the Haney weathers both in surface exposure and in a cave setting. Petrographic thin-section analysis suggests that the Haney possesses a complex diagenetic history that involves several generations of calcite cementation, dolomitization, silicification, and pressure-dissolution features in the form of microstylolites and stylolites. A basal shale in the Big Clifty occurs commonly at the Big Clifty/Haney contact and acts as a confining hydrogeologic unit, which is favorable for the development of springs and caves. Studying the Haney Limestone petrographically provides an opportunity not only to study a lesser known unit, but also in the context of relating petrographic influences or controls on the morphology of Haney cave-passage development under both vadose and phreatic hydrologic regimens. Heretofore, the vast majority of cave morphological studies have only linked the hydrologic regimen to formation of cave passages, but such studies have not considered petrographic variance. This study not only relates karst features to petrographic variance, but also provides a petrographical description of the Haney across south central Kentucky, whereas many previous studies focused on Illinois and Indiana. Understanding Haney petrographic characteristics also provides context for potential carbonate hydrocarbon reservoirs and groundwater resources in the Illinois Basin region.

The Ruby-Humboldt Range in Northeastern Nevada exposes the deepest crust in the western portion of the Sevier Hinterland. The product of unique brittle and ductile accommodations, this block of lower crustal rock is a window into the processes of continental thickening and extension. The structure of the northern tip of the Ruby-Humboldt Range core complex is dominated by a large recumbent fold nappe with a southward closeure cored by Paleoproterozoic-Archean gneissic complexes with complex interdigitated field relationships that record polyphase continental metamorphism. Amphibolite-grade metapelitic rocks within the core and Winchell Lake nappe record a wide range of zircon age dates of metamorphic events the oldest of which at ~2.5 Ga is recorded in adjacent orthogneiss as a crystallization age. At least two younger metamorphic events are recorded within this orthogneiss, most significantly at 1.7-1.8 Ga, an event previously unpublished for this region that links it to Wyoming province activity in addition to inherited component of detrital cores up to 3.7 Ga in age that is among the oldest ages reported in Nevada. The youngest overprint of cretaceous metamorphic overgrowth ranges fro 60-90 Ma in age based on zircon rims in the aforementioned units as well as three garnet amphibolites that intrude the core of the nappe and are interpreted to be metabasic bodies.

The Silurian-Devonian metasedimentary rocks of the Connecticut Valley-Gaspé trough (CVGT) were subjected to multiple deformational and metamorphic events during the Acadian orogeny in the Middle-Late Devonian. Plutons intruding the Devonian Waits River and Gile Mountain Formations have been considered post-tectonic, but microstructural studies of the intrusions and their metamorphic aureoles indicate some of these plutons intruded syntectonically. This study investigates the relationship between Acadian deformation and intrusion of the Knox Mountain pluton (KMP) of central Vermont. Structural and geochronological data were collected along a c. 15 km transect from the western limit of the CVGT, where the unconformable Richardson Memorial Contact coincides with the Dog River Fault Zone, into the margin of the KMP in the east. Field and microstructural observations indicate the KMP intruded syntectonically. Evidence for Acadian deformation post-dating intrusion includes folded and boudinaged granitic dikes at the margin of the KMP, and microstructures such as flame perthite, myrmekite, deformation twins, and textures associated with grain-boundary migration recrystallization in the granite. In the metamorphic aureole, biotite porphyroblasts overgrow S3, the earliest Acadian secondary foliation, and were deformed during S4 crenulation cleavage development. The KMP intruded at 377±5.2 Ma based on a U-Th-total Pb monazite crystallization age, which is concordant with the published age of the nearby Barre granite. The timing of S4 foliation development in the CVGT is constrained locally by 40Ar/39Ar geochronology at ~365 Ma, consistent with the microstructurally-inferred relative-age relationships. Plateau/weighted mean 40Ar/39Ar ages from across the transect and minimum ages from argon-loss profiles show a general trend of younging towards the east, suggesting these rocks have been affected by Alleghanian and Mesozoic deformation and exhumation.

The geology of Ethiopia is dominated by the Ethiopian Plateau that is similar in elevation to, but aerially larger than, the Colorado Plateau. Several rivers have incised through the plateau, creating gorges that reach up to 1.5 km in depth. The plateau uplifted to its current elevation and was subsequently incised sometime after the Oligocene flood basalt event that signaled the arrival of the African Superplume below Kenya and Ethiopia. Due to its size and extent, published climate modeling has indicated that Late Cenozoic plateau formation could have been a driving force in the East African Cenozoic climate changes. Although uplift timing has potentially far-reaching impacts to several scientific disciplines, uplift is not well constrained, and several published studies present contradictory data. This study aims to elucidate the uplift timing of the Ethiopian Plateau through the use of river incision timing as a proxy for uplift. Methods employed to accomplish incision timing include low temperature apatite fission track and (U-Th)/He thermochronology, thermal modeling, and scanning electron microscopy backscatter electron detection (SEM-BSE). Basement samples for thermochronologic dating were collected from the Didessa River Canyon near Nekemte. (U-Th)/He dating was conducted at the Arizona State University Group 18 Laboratory where 17 apatite grains were dated, while GeoSeps Services LLC performed the apatite fission track analysis. Results indicate that after crystallization between 797-630 Ma during the East African Orogen, the rocks experienced rapid exhumation to within 1400-3000 m of the surface in the Jurassic. The Cenozoic flood basalt event at 31-29 Ma caused a massive outpouring of basalts that forced the lowest sample into the partial retention zone where it remained for an extended period of time while accumulating radiation damage. Rapid cooling from 8 Ma to present represents a recent exhumation history of the Ethiopian Plateau, suggesting that the plateau’s high elevation gain was achieved within the last 10 Ma. This integrated apatite (U-Th)/He and fission track study is the first of its kind addressing East African Cenozoic tectonics.

Understanding how mountain landscapes respond to variations in tectonic forcing over a range of temporal scales in active mountain belts remains as a prominent challenge in tectonic and geomorphological studies. Although a number of empirical and numerical studies have examined this problem, many of them were complicated by issues of scale and climatic variability. More specifically, the relative efficiencies of fluvial and glacial erosion, which are presumably controlled by climate, are difficult to unravel. The Teton Range in Wyoming, which results from motion on the crustal-scale Teton fault, is an ideal natural laboratory for addressing this challenge as the tectonic uplift boundary condition and the variation of uplift along strike is well-documented by previous studies and due to its relatively small size, climate can be reasonably expected to vary consistently along strike. Here, we present the results from a study that examines how the Teton landscape responds across the longest (106-7 yrs) and shortest (102-4 yrs) temporal scales. Long-term canyon incision rates determined from apatite (U-Th)/He (AHe) analysis of major drainages are highest (0.24 mm yr-1) where measured uplift rates and duration are highest (near Mount Moran), leading us to propose that tectonic forcing operates as the first order control on long-term Teton erosion. Short-term denudation rates, which are derived by determining sediment volumes in Moran Bay that are deposited in catchments generated during the most recent glacial interval (Pinedale, ~15.5 ka), are 0.00303 – 0.4672 mm yr-1. We compare these rates to previous work, which found that high rock fall rates (1.13-1.14 mm yr-1) deposit large talus volumes in Avalanche and Moran Canyons. Despite their magnitude, such high rates of mass wasting are not sustained over long periods of time, as measured lake sediment volumes (0.007 km3) are. We conclude that the Tetons are transport limited during the interglacial and large volumes of canyon sediment generated during this time cannot be moved absent the advance of valley glaciers. That is, fluvial systems in small mountain systems are substantially less effective than glaciers in denuding mountain topography.

The Garlock Fault consists of three distinct segments, known as western, central, and eastern, together reaching approximately 260 km from the San Andreas Fault to the southern end of Death Valley. Although published slip rates are available along the western and central Garlock Fault segments, little is currently known of the Garlock Fault earthquake history or slip rate farther east. Using LiDAR and satellite imagery, the central and eastern Garlock Fault segments were analyzed for visibly offset, fault-adjacent, geomorphic surfaces that may potentially be used for estimating slip rate. Qualitative methods of assessing preserved alluvial surface maturity were adapted and used to establish unit age categories. Qualitative comparisons of late Pleistocene-Holocene surfaces reveal that the total offset at sites along the eastern Garlock Fault are less than half that of sites of comparable age along the central Garlock Fault, suggesting a significant reduction in slip rate across the intersection of the Brown Mountain, Owl Lake, and Garlock Faults. Digitally-measured offsets and their age groups were plotted in order to achieve preliminary slip-rate estimates. The resulting plot shows an eastward decrease in late Pleistocene-Holocene slip rate at sites along the central and eastern Garlock Fault segments. The central Garlock Fault slip-rate estimate taken from Slate Range West and Slate Range East sites in Pilot Knob Valley is approximately 4.2 mm/yr, within the error (but on the low side) of previously published rates. The slip-rate estimate from the Quail Mountains site, at the easternmost extent of the central Garlock Fault, is approximately 2.7 mm/yr. The slip-rate estimate from the Avawatz section of the eastern Garlock Fault is approximately 1.0 mm/yr.

Rocks of the western and eastern Inner Piedmont, along with the eastern Blue Ridge, comprise the Neoacadian metamorphic core of the southern Appalachians. The composite Inner Piedmont consists of the eastern Tugaloo (western Inner Piedmont) and Cat Square (eastern Inner Piedmont) terranes, which are separated by the Brindle Creek fault. Geochronologic evidence established the Brindle Creek fault as a terrane boundary within the Inner Piedmont, separating terranes of Laurentian and mixed Laurentian/Avalonian (peri-Gondwanan) zircon suites. The Newton window exposes Tugaloo terrane rocks of the Tallulah Falls Formation in the footwall of the Brindle Creek thrust sheet. Detailed geologic mapping in the western Newton window revealed structural and metamorphic similarities between rocks across the Brindle Creek fault. Peak metamorphism occurred contemporaneously with peak deformation, reaching upper amphibolite facies across both terranes. Peak Neoacadian metamorphism occurred between 360 and 345 Ma. Electron microprobe analyses of Cat Square terrane core and rim garnet-biotite and garnet-plagioclase pairs indicate an average temperature and pressure of 620 C, 3.6 kbar and 710 C, 6.1 kbar, respectively. Temperature and pressure estimates from the lower Tallulah Falls Formation core and rim analyses yield conditions of 570 C, 4.1 kbar and 690 C, 5.9 kbar, respectively. The maximum burial depth for both Cat Square and Tugaloo terrane rocks is ~20 km. The range in metamorphic ages suggests subduction and accretion occurred at a rate of 1 kilometer per 1.75 million years. Six deformational events shaped the western Newton window. D1 features are limited to amphibolite boudins of the Tugaloo terrane. D2 regional penetrative structures such as high-temperature foliations, mineral stretching lineations, and curved fold axes are the product of Neoacadian tectonism. The dominant S2 foliation trends north-northwest and dips moderately to the west-southwest. North-northwest-trending L2 mineral lineations parallel F2 fold axes, creating a curved map pattern recording crustal flow in an ancient orogenic channel. D3 resulted in open folding. The D4 event produced regional open folds. D5 and D6 features occur as joints, cataclasis, and diabase intrusion.

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 structural framework of the northern Gulf of Mexico coastal zone is characterized by numerous growth fault systems. Neotectonic processes in coastal marshes in this region have been shown to be important drivers of relative sea-level rise as well as having significant influence on marsh accretion processes. One active growth fault has been identified at East Matagorda Peninsula, Texas. To characterize the Holocene behavior of this fault and the consequent sedimentary responses, a suite of fallout radionuclides (7Be, 137Cs, 210Pb) and radiocarbon, supplemented by sediment physical property data have been used to determine sediment mixing depths, rates of accumulation, and geochronology. Correlation of time-equivalent stratigraphic boundaries reveals a maximum total Holocene offset of ~1 meter. Determination of slip rates from these values reveals a linear trend of displacement as a function of distance along the fault trace with maximum slip occurring to the southwest and minimum slip to the northeast. Sediment accumulation rates from the downthrown station nearest to the fault trace display a dramatic increase over the last 30 years. Sediment bulk density and grain size data suggest an interaction between fault-driven geomorphic change and sedimentation where a migrating land-water interface has influenced the type of sediment accumulation here.