Thesis (Ph. D.)--University of Wyoming, 2007. / Title from PDF title page (viewed on June 16, 2008). Includes bibliographical references.

Thesis (Ph.D.)--University of Melbourne, School of Earth Sciences, 2009. / Typescript. Includes bibliographical references.

The Cathaysia Block, located in southeastern China, is characterized by a widespread magmatic belt, prominent NE-striking fault zones and numerous rifted basins filled by Cretaceous-Eocene sediments. The geology denotes a transition from an active to a passive margin, which led to rapid modifications of crustal stress configuration and reactivation of older faults in the Cathaysia Block. However, the timing and kinematics of the active-passive margin transition need to be better constrained. The SW Cathaysia Block, near the coastal area of the South China Sea, is selected for studying the transition. There are two major geological units in this region: the Nanling Range and the Yunkai Terrane. The Nanling Range is a magmatic belt composed of granitic plutons with formation ages ranging from Caledonian to Cretaceous. The Yunkai Terrane is a metamorphic terrane of Caledonian age. Thirty zircon fission-track (ZFT) data and thirty apatite fission-track (AFT) data were obtained from the granitic plutons in the SW Cathaysia Block. The distribution of ZFT ages shows two episodes of exhumation of the granitic plutons: the first episode is found to occur during 170 Ma – 120 Ma and affect the SW part of the Nanling Range; the second episode, a more regional exhumation event, occurred during 115 Ma- 70 Ma. The AFT dating results show a general cooling sequence from south to north during Late Cretaceous – middle Eocene, contrary to the conventional passive margin model. Numerical geodynamic modeling of subduction zone indicates that (1) high slab dip angle, high geothermal gradient of lithosphere and low convergence velocity favor the subduction process and the reversal of crustal stress state from compression to extension in the upper plate; (2) the late Mesozoic magmatism in South China was probably caused by a slab roll-back; and (3) crustal extension could have occurred prior to the cessation of plate subduction. The numerical model results of lithospheric deformation associated with subduction process reveal that granitic crust is easily deformed compared to gneissic crust. The results could be used to explain the observation that the granite-dominant Nanling Range was exhumed earlier than the gneiss-dominant Yunkai Terrane. In addition to the difference in geology between Yunkai and Nanling, the heating from Jurassic- Early Cretaceous magmatism in the Nanling Range may have softened the upper crust, causing the area to exhume more readily. On the other hand, the numerical models of crustal extension with pre-existing faults dipping ocean-ward demonstrate a trend of fault reactivation sequence from south to north. Assuming that granite exhumation in the Cathaysia Block was mainly a product of rifting and fault reactivation, the numerical models support the AFT results. The integrated FT dating and numerical model results suggest that roll-back of the subducting paleo-Pacific Plate slab during Late Cretaceous is likely to be the driving force of the transition from Mesozoic subduction to Cenozoic extension in the Cathaysia Block. The timing of the transition is suggested to have taken place at ~ 92 Ma, according to a rapid cooling as revealed by the thermal history modeling of AFT length data. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Continental growth may be accomplished at active convergent margins through tectonic accretion and orogeny. Accretionary processes believed to add material to continents include the collision of island arcs and other unsubductable crustal blocks. Using the Intermontane belt as a case study for assessing accretionary processes, it is concluded that island-arc collision and accretion was the principal mechanism for continental growth with relatively minor contributions from 'sliced-off oceanic seamounts and/or plateaux. Fold and thrust belt formation in the northern Intermontane belt records a Middle Jurassic orogenic event that can be attributed to the collision of island-arc highlighting the importance of island-arc collision for causing orogenesis in the North American Cordillera. However, not all orogenic events in the North American Cordillera can be readily attributed to a collisional event. The leading model for driving Laramide orogenesis in the United States is flat-slab subduction, and thermal modelling indicates that subduction of a relatively buoyant oceanic plateau/aseismic ridge may have been responsible for the shallow trajectory. In the Canadian and Mexican portions of the Laramide, the coeval development of a magmatic arc within 300 km of the trench refutes the existence of flat-slab subduction in these regions, and therefore the processes responsible for this orogeny remain enigmatic and require resolution.

Maps in pocket.

A Dissertation Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in Fulfilment of the Requirements of the Degree of Doctor of Philosophy. / The Gariep Belt is an arcuate north-south trending tectonic unit extending ;along the western coast of southern Namibia and northwestern South Africa. It forms part of the Pan-African Damara Oragert, which consists of a north-south trending coastal branch (Kaoko and Gariep Belts) and an east-west trending inland branch. The Gariep Belt is subdivided into an eastern parautochthonous passive continental margin on the western edge of the Kalahari Craton, the Port Nolloth Zone, and a western allochthonous ophiolitic terrane, the Marmora Superterrane, thrusted on the Port Nolloth Zone. The sedimentary evolution of the Gariep Belt was initiated with the deposition of sediments of the Rosh Pinah Formation into fluvial, alluvial and lacustrine depositional systems, which are associated with bimodal volcanic activity and related Zn-Pb-Cu-Ag- (+Ba) sulphide mineralization. The overlying mixed continental/shallow marine deposits of the Gumchavib Formation are overlain by the carbonate dominated Pickelhaube Formation, which was deposited in shallow marine to pelagic depositional settings. The Rosh Pinah, Gumchavib and lower Pickelhaube Formations are intruded by basic volcanic sills of the "Gannakouriep dyke swarm", The conformably overlying Obib Peak Formation was deposited into a fluvial/alluvial palaeoenvlronrnent, The Numees Formation unconformably overlies the underlying stratigraphic units and consists predominantly of glaciomarine massive diamictites and occasionally interbedded iron formations, which are occasionally interbedded with interglacial sediments and volcanics. The regional structural pattern is characterized by three phases of deformation. The earliest deformational event, D1, comprises intrafolial small scale recumbent and isoclinal F1 folds, a penetratlve beddlnq-subparatel 81 cleavage and a preferred elongation of boulders, pebbles, grains and minerals (11). Associated with D1 are bedding-subparallel thrust faults. The D2 deformational phase is characterized by small to large scale, north to northwest trending F2 folds with a generally easterly vergence, which can change into a westerly direction due to backfolding. The F2 folds are associated with a penetrative axial planar S2 cleavage. Thrusting continued during the D2 deformational phase. The latest deformational event, D3, is characterized by small to large scale open F3 folds with southerly to south-westerly trending fold axes. The metamorphic evolution of the Gariep Belt during the Damara Orogeny was associated with barrovtan-type metamorphism with a geothermal gradient of about 20oC/km, reaching greenschist to lower amphibolite facies metamorphism. The sedimentological and structural features are explained in a tectono-sedimentery model, which started with rift initiation during the deposition of Rosh Plnah Formation lithologies along old tectonic weakness zones of Middle Proterozoic age at about 780Ma. Supercontinenta! breakup is documented by the initial transgression of Gumchavib Formation sediments and the continuous trensgression of the Pickelhaube Formation, which is related to thermal subsidence after the initiation of oceanic spreading of the Adamastor Ocean. Renewed rifting and/or glacial outwash heralding' the advance of the Numees glaciation and associated seale': :'changes may be responsible for the sudden break in marine sedimentation during the deposition of the Ohio Peak Formation. The Numees glaciation is probably contemporaneous with the 670Ma old Varangian glacial and the Rapitan glacial episodes and provides a minimum age for the deposition of Gariep Group lithologies. Rifting and spreading was followed by the closure of the Adamastor Ocean, associated with. a southeastward directed subduction. of oceanic crust under the Kalahari Craton and was accompanied by intense southeastward and subsequently eastward directed tectonic transport during 01 and D2. During D3, a late Sinistral movement developed along tre defined fault zones in the late stages of the Adamastor Orogeny.Metamorphic ages from the Nama and Vanrhynsdorp Groups indicate that that the tectonic evolution of the Gariep Belt only ceased at about 500Ma. / Andrew Chakane 2018

Magnetic, gravity and bathymetry data were collected on an extended cruise of the R/V Yaquina in 1969. The last set of data was obtained from those track lines leaving the Panama Basin. The area covered is mainly the Cocos plate (Molnar and Sykes, 1969). The data is analyzed and compared with results of previous workers and the geophysical implications considered. Generally speaking, from the magnetic part of the data, both direct and indirect methods show support of Vine and Matthew's (1963) hypothesis of sea-floor spreading and the subsequent principles of new global tectonics. The most northern magnetic anomaly profile across the East Pacific rise (at 18.3°N) shows a spreading rate about 3 cm/yr. and the most southern one (at 12.8°N) shows a rate about 5.2 cm/yr. The Cocos plate has been assumed to move in a northeast-southwest direction (N30°E to N45°E), and rotate with respect to the Pacific plate about a pole at 40°N, 110°W with an angular velocity of 19.6x10⁻⁷ deg./yr. (Larson and Chase, 1970). New material comes up from the west boundary - the East Pacific rise, and the south boundary - the Galapogos rift, causing the Cocos plate to underthrust the Americans plate at the middle American arc. Some of the points of new global tectonics can not be detected from this set of data; further detailed study of more track lines and sea bottom core samples are needed. The results of both analytical methods for determining the magnitude of induced and remanent magnetization in the second layer shows some consistence with the work of Schaeffer and Schwarz (1970), and Irving et al. (1970) at the Mid-Atlantic ridge near 45°N, in which a thinner magnetization layer at the ridge and the attenuation of magnetization intensity away from the ridge axis are suggested. Free-air gravity anomaly profiles have been employed to determine the crustal structure of two sections1 a ridge section at 12.8°N and a trench section at 14°N. For the ridge section, if the anomalous mantle was converted from normal mantle, the extension of anomalous mantle into the normal mantle requires some uplift and/or lateral expansion in the rise crest area. The tensional configuration suggested in the trench crustal section agrees with the model proposed by Elsasser (1968) for the differential movement between two lithospheric blocks. This work gives some speculations that evidence which supports the present new global tectonics theory is limited to a certain degree of accuracy. Further study of the theory based upon physics, its mechanism, and measurement techniques that would give more reliable evidence have to be developed before it can be ascertained what really happens beneath this wild, wild world. / Graduation date: 1971

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (April 26, 2007) Vita. Includes bibliographical references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Maps in pocket. Vita. Abstract. Includes bibliographical references (leaves 186-189). Also available via the Internet.

Thesis (M.S.)--Central Connecticut State University, 2001. / Thesis advisor: Charles W. Dimmick. " ... in partial fulfillment of the requirements for the degree of Master of Science in Physics and Earth Sciences." Includes bibliographical references (leaves 60-64). Also available via the World Wide Web.