Middle and Upper Ordovician strata in the southernmost Appalachians document initial collision along the southeastern margin of Laurentia during the Blountian orogeny, an early phase of the Taconic orogeny. Coeval drowning and exposure of different parts of the former platform and variations in stratal architecture have been attributed to tectonic and depositional loading along the collisional margin. Stratigraphic correlations, using a bentonite-graptoliteconodont time framework, a palinspastic map, and a map of subsurface basement structures, suggest that basement-fault reactivation, flexural subsidence, and eustasy variously controlled uplift, subsidence, and deposition at different sites within the peripheral foreland basin. This dissertation documents how pre-existing structures in the continental margin and interior affected subsidence, deposition, diagenesis, and composition of foreland strata, and deformation in tectonic loads. Stratigraphic correlations document an early episode of basementfault inversion in the distal foreland, and heterogeneous subsidence and provenance patterns in the middle and proximal foreland. Abrupt variations in depth of erosion of passive-margin strata and in thickness of distal foreland deposits coincide with the boundaries of the intraplate Birmingham graben. Inversion of the former graben increased the magnitude of erosion on inverted upthrown blocks; increased tectonic subsidence in adjacent blocks; supplied chert and quartz detritus to shallow-marine carbonate depocenters; and facilitated influx of meteoric water to aquifers in shallow-marine limestones. Tectonic subsidence of middle and proximal foreland deposits reflects local irregularities in the foreland subsidence and different rates of migration of the flexural wave along strike. Differential subsidence between embayments and promontories may have caused reactivation of transverse basement faults. Relief produced by reactivation of transverse basement faults and flexural normal reactivation of basement faults may provide sources for local conglomerates interbedded with deep-water shales. Differences in orogenicbelt deformation are reflected in provenance analyses that suggest exposure of dominantly feldspar-bearing basement rocks in the orogenic belt adjacent to the promontory and exposure of basement rocks and sedimentary cover in the orogenic belt adjacent to the embayment. Results of this study reveal the importance of considering the effects of pre-existing structures in the interpretation of along- and across-strike variations of foreland strata. Therefore, geodynamic modeling of the Blountian foreland basin needs to consider along-strike variations in the geometry of tectonic loads and reactivation of different basement structures.

Thesis advisor: Yvette D. Kuiper / The Paleoproterozoic Foxe Fold Belt (FFB) is composed of the Penrhyn Group, a Paleoproterozoic passive margin sequence, and supracrustal Archean basement. These units were interfolded and metamorphosed at amphibolite to lower granulite facies conditions during the 1883-1865 Ma Foxe orogeny, a part of the Trans-Hudson orogeny. The purpose of this study was to constrain the timing of metamorphism and deformation within the Penrhyn Group, in order to determine the role of the Foxe orogeny within the Trans-Hudson orogeny. Petrographic analysis, P-T-X pseudosections, monazite composition, and in-situ electron microprobe U-Th-Pb geochronology from sampled metapelites were used to determine the age and significance of metamorphic and deformation events related to monazite age populations. Population 1 is composed of 1926 ± 8 Ma monazite interpreted as detrital. Population 2 consists of 1892 ± 9 Ma monazite, the youngest detrital ages seen in the Penrhyn Group. Population 3 is composed of 1853 ± 5 Ma high-Y + HREE monazite predating an episode of pervasive garnet growth. Population 4 contains 1839 ± 8 Ma lower-Y + HREE monazite related to pervasive garnet growth. Population 5 is 1819 ± 16 Ma lowest-Y + HREE monazite with high LREE and Th/U, linked to the interpreted peak reaction: Bt + Sil + Pl = Grt + Crd + Kfs + melt. Monazite constraints on deformation fabrics indicate that deformation was ongoing locally as early as 1853 ± 9 Ma and continued until at least 1814 ± 14 Ma, pre- to syn-peak metamorphism. Rare 1794-1776 Ma monazite is interpreted to constrain the age of retrograde metamorphism as the Trans-Hudson orogeny waned. These data support interpreted clockwise P-T-t-D paths consistent with metamorphism initiated by crustal thickening in an orogenic belt. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

At collisional mountain ranges the tectonic history of crustal shortening and subsequent post-collisional erosion is preserved in the form of the presently observed gravity anomalies. In this study, models of erosion and isostatic rebound at various stages of collision illustrate the evolution of crustal structure, topography, and resulting gravity anomalies. The Ouachita Mountains of Arkansas, which show a low/high Bouguer gravity couple characteristic of the initial stages of collision, have undergone just 8 km of erosion during the process of completely rebounding the syn-orogenic crustal root. This minor rebound means that the Ouachitas retain a crustal geometry similar to the continental margin prior to collision, including thin transitional and oceanic crust. At more advances stages of collision Bouguer gravity anomalies show a broad low reflecting a thickened crustal root. The width of this low, which relates directly to the amount of crustal shortening, is retained during subsequent erosion and elastic rebound, but the amplitude decays gradually. Thus, the width and amplitude of the low can be used to estimate the degree of convergence and amount of erosion, respectively, for a specific mountain range. For the Scandinavian Caledonides results are consistent with 20 km of erosion following 200 km of crustal shortening. Following a larger magnitude of convergence, about 300 km, the southern Appalachians are estimated to have undergone 28 km of post-collisional erosion. Bouguer gravity profiles across the recently-active Alps compare with a model of 200 km of crustal shortening and 8 to 12 km of erosion. While the Alps have undergone a similar amount of shortening as that estimated for the Caledonides, erosion and post-collisional rebound is at an initial stage, such that a thick section of exotic crust still overlies the underthrusted European Platform. The results of these model comparisons suggest that the crustal geometry ofa collisional mountain range should be viewed as a consequence of the degree of crustal shortening as well as the amount of erosion and isostatic rebound. In models at moderate to advanced stages of shortening ( 200 km), and mature stages of erosion (e.g., Caledonides, Appalachians), the geometry of the crustal "suture" between overthrusting and underthrusting crusts is present as a shallow, subhorizontal de collement beneath the foreland. In the hinterland the suture abruptly steepens, a result of differential uplift during isostatic rebound. This crustal geometry, characteristic of seismic-reflection profiles across many ancient mountain belts, suggests: (1) that the "low angle detachment" observed beneath collisional mountain ranges was originally much deeper and steeper than it is at present; and (2) that steep-dipping seismic reflectors towards the hinterland represent the thrusted contact between converging crustal blocks, but have been steepened as a result of isostatic uplift following erosion. / Graduation date: 1992

Data from three refraction profiles of the 1993 LITHOPROBE refraction experiment were used to investigate the structure of the lithosphere of the Trans-Hudson Orogen. Novel digital processing of the wide-angle reflections arrivals with standard type reflection processing techniques revealed significant crustal thickness and Moho reflectivity variations within the orogenic belt. The obtained information was than complemented with the results of near-vertical incidence seismic sections to estimate the crustal thickness variations over the entire study area. The detected crustal thickness and Moho reflectivity changes could not be correlated to the location and extent of geological domains; they appear to reflect the complex deformation and metamorphic history of the orogen. The P-wave velocity image of the crust and upper mantle was established through ray-tracing and inverse modelling of the primary and secondary crustal and mantle arrivals. Successful modelling of the observation required the incorporation of non-standard inversion techniques into the processing sequence. Although the detected crustal velocity variations appear to correlate well with the changes of Moho reflectivity. These variations in the property of the crust are interpreted to be a consequence of differences between the tectonic evolution of orogenic units in the north-western and south-eastern parts of the study area. The transition belt separating these two areas appear to coincide with an anomalous zone located in the upper mantle. This mantle region exhibits strong P-wave velocity anisotropy, determined primarily from modelling of the mantle refraction arrivals. I interpret this anomalous mantle region as a highly deformed zone, a possibly suture, between the two collided Archean plates of the orogen. Additional information on the structure of the mantle was obtained by analyzing the secondary mantle phases, observed at offsets larger than 400 km on the shot records. The broad structure of this deeper mantle region was established by incorporating the results of regional teleseismic studies into the velocity models and refining the models with raytracing. Detailed acoustic properties of the mantle were investigated after introducing random perturbations into the models and comparing the computed finite-difference synthetic-seismic responses to the observations.

Thesis (M.S.)--Western Washington University, 2010. / Includes bibliographical references (leaves 98-102). Also issued online.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains vi, 21, [24] p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 20-21).

Extensive studies have been undertaking in exploring the tectonic evolution of the Himalayan Orogen. Various tectonic models were developed to explain and constraint spatially and temporally critical events including the collision of Indian Plate with the Eurasia Plate, crustal thickening in association with the indentation, crustal spreading of the Tibetan Plateau. Recent study by King et al., 2011 identified two distinct leucogranite suites which were formed by contrasting tectonic actions at Sakya. They are Equigranular Anastomosing Leucogranite (AEG) formed under prograde fluidpresent condition while the Discrete Porphyritic Pluton Leucogranite (DPP) formed with retro-grade fluid-absent environment. Based on the characteristics of AEG and DPP, this study started with the acquisition of geochemistry data of rock samples collected for researches at various locations of the Himalaya Orogen. The two leucogranite suites were characterized through the study of their geochemistry comprised major elements, trace elements and rare earth elements models. Results of the studies concluded the existence of AEGs and DPPs distributed over the eastern area of the Himalaya Orogen beyond longitude 85 degree East. DPPs are also found at the far West location of the orogen. AEGs are typically formed from around 38Ma to 23Ma, while DPPs are of young age from 23Ma to 15Ma. Based on the observation of missing, or paucity in data for AEG and DPPs available to the west of longitude 85 degree East, it is hypothesized that recent collision of the Arabia plate to the Iran Domain inhibited the northward indentation movement of the Indian plate that not only caused the anticlockwise rotation of the Indian plate but also decreased the rate of tectonic movement of the Indian plate in the West relative to Eurasia plate. The slow rate of tectonic movement may result in insufficient thickening/energy developed within the crustal layer to cause any melting. Further studies to examine and development of the hypothesis is recommended. / published_or_final_version / Applied Geosciences / Master / Master of Science

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.

Thèse (M.sc.A.)-- Université du Québec à Chicoutimi, 1981. / "Thèse présentée à Chicoutimi en vue de l'obtention d'une maîtrise en science appliqué (géologie)" CaQCU Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Sc.A.)---Université du Québec à Chicoutimi, 1984. / 3 cartes pliees dans une pochette. "Mémoire présenté en vue de l'obtention du diplôme de maîtrise en sciences appliquées (géologie)" CaQCU CaQCU Document électronique également accessible en format PDF. CaQCU