Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references (leaves 163-171) / Microfiche. / xi, 171 leaves, bound ill., maps 29 cm

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

The West Iberia (WIM) and Newfoundland (NFM) continental margins formed over a succession of rift events related to the opening of the North Atlantic between the Late Triassic and the Early Cretaceous. They are characterized by a variable width Ocean- Continent Transition (Zone) where exhumed and serpentinized mantle has been cored. Results from 1-D well backstripping along the Portuguese shelf suggest 40-45% greater extension factors (β) than previous estimates. In addition, the age and duration of both the Late Triassic-earliest Jurassic and the Late Jurassic rifting episodes have been better constrained. It appears, for example, that the Late Jurassic rift propagates northwards along the margin, as inferred for the continental break-up during the Early Cretaceous. Combined backstripping and gravity modelling techniques (POGM), together with new bathymetry and sediment thickness grids, have been used to estimate the effective elastic thickness, T_e, of the lithosphere. Results along closely space profiles in the WIM reveal that T_e decreases from 15-40 km over unthinned Variscan basement to ≤ 15 km over stretched continental and transitional crust. Along strike, a good correlation is found between the modelled mechanical structure and the segmentation of the Variscan basement onshore. Discrepancies between observed and calculated anomalies are discussed in terms of other processes that affected the margin, such as serpentinization and inversion. Thermo-mechanical rheological modelling techniques have also been tested. The compiled software inputs the β's constrained from POGM to determine the thermal structure of the margin, which, in turn, has been used to construct models of rheology and, hence, T_e. The models predict an increase in the T_e of thinned continental lithosphere with age since rifting, between < 20 and > 35 km, and suggest that processes such as ductile shearing and mantle serpentinization might have permanently weakened the lithosphere. Results from POGM along conjugate profiles off WI and NF reveal a greater longterm strength of extended continental and transitional basement in the NFM (T_e's of 10-40 km). This analysis further supports the hypothesis that the low T_e's modelled in the WIM might be related to its complex structural framework. In order to explain the large asymmetries observed in the amount of basement subsidence (500-1300 in) between the WI and NF margins a lithospheric-scale "simple shear" rift model is proposed for the latest stages of rifting and continental break-up.

The southeastern Brazilian continental margin has a debated evolution regarding postrift events and formation of topography. Apatite fission track (AFT) and apatite U-Th/He (AHe) analysis ages for the N-S transect between Rio de Janeiro and Três Rios range between 98.5±11.9 and 54.1±4.2 Ma. Ages are younger towards the coast and increase progressively inland. Highest samples (around 1500 m above sea level) have older AFT ages. A wide range of ages was not found in the area, contrasting with the large AFT age span found by other studies in adjacent portions of the Brazilian continental margin, where age ranges of up to ~200 Ma from the coast to the innermost sample in the continent have been reported. The cooling ages and the thermal history models produced with software QTQt corroborate a uniform and continuous cooling process for the rifted margin, with total depths of denudation between 2.5 and 4.4 km, attesting to the absence of post-Cretaceous rift reburial in the area. Towards the continental interior, at the back of the Serra do Mar escarpment, thermal history models point to a change in cooling rate in the Upper Cretaceous, compatible with reported reactivation of the regional Neoproterozoic structures which led to the formation of the Cenozoic Rift System of Southeastern Brazil. Collision episodes in the western margin of W Gondwana have important role on platewide stress distribution, inducing regional structure reactivation and creation throughout the South American Platform. The plate-wide deformation arising from the western plate margin collisions is possibly responsible for the formation of the many Paleozoic grabens, which were the precursors of the cratonic basins of the South American continent. Among those, evidence from zircon U-Pb detrital provenance indicates that the Ordovician Piranhas Graben in central Brazil is in fact an early manifestation of the Paraná Basin, since its progressive increase in catchment area matches the sediment sources of the Silurian Vila Maria and Devonian Ponta Grossa formations of the Paraná Basin. The present-day landscape is mainly a result of isostatic rebound due to erosional unloading, although combined with post-rift magmatism and regional structure reactivation. The post-rift continuous uplift of the southeastern Brazilian margin supplied vast volumes of clastic sediments to the Santos and Campos basins during the late Cretaceous and Cenozoic, generating high quality reservoirs for hydrocarbons.

Continental passive margins exhibit high elevation topography in many localities across the globe. The source and age of much of this topography remains a subject of great debate within the wider community, with numerous theories being presented, including significant post-rift uplift and isostatically preserved rift anks. Establishing the mechanisms that generate topography and the onshore evolution across passive margins is vital in understanding regional geological histories and their wider development. The passive margins of the NW Atlantic realm exhibit high elevation topography topped with low relief summits. The origin of this topography is debated, with both 3 km of uplift in the post-rift stage and the isostatic preservation of Cretaceous rift anks being suggested within the literature. The work of this thesis aims to resolve this debate by establishing the timing and source of uplift across the region and determining the onshore evolution prior to, during and after rifting with the application of apatite low temperature thermochronology. Contemporary analytical and modelling techniques are utilised to generate thermal histories from across both central West Greenland and SE Baffin Island, helping to de ne how the modern landscape has formed. Results from this work outline an onshore history dominated by uplift in the Cretaceous and exhumation throughout the Cenozoic. Basement samples from SW Greenland exhibit protracted cooling throughout the Mesozoic and Cenozoic, implying low rates of exhumation have been apparent throughout. Within the Nuussuaq Basin, centralWest Greenland, thermal histories display reheating i through the Late Cretaceous/Palaeogene and cooling to present, consistent with events outlined in the basin's stratigraphy and implying uplift of the topography is likely the result of extrusive volcanism and an isostatic response to the unroo ng of the lithosphere. Spatial trends in data and thermal histories across SE Ba n Island imply much of the landscape is shaped by rift ank uplift along its SE coastline, driving exhumation of the region throughout the Cenozoic. Collectively these results suggest the elevated topography of the NW Atlantic realm is the result of rift related uplift in the Cretaceous, magmatism and widespread exhumation throughout the Cenozoic, preserved by isostatic exure. This interpretation of the region's onshore history contributes greatly to our understanding of the NW Atlantic's geological evolution. The results highlight the role of extensional tectonism, exhumation and isostasy in shaping both margin's landscapes and helps to determine the principal characteristics of the wider extensional system and the evolution of the o shore domain. Moreover, these conclusions have a wider relevance to the evolution of passive margins across the North Atlantic, improving our understanding of how topography across other margins, such as of East Greenland, Norway and the UK, has formed.

Thesis--Woods Hole Oceanographic Institution/Massachusetts Institute of Technology Joint Program in Oceanography, 1978. / Grant 04-7-158-44104 and 04-8-M01-149. Includes bibliographical references (p. 163-184).

Thesis (doctoral)--Göteborgs universitet, 1992. / Added t.p. with thesis statement inserted. Includes bibliographical references (p. 141-150).

Thesis (Ph. D.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 195-211). Also available on the World Wide Web.

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