published_or_final_version / Earth Sciences / Master / Master of Philosophy

The Pioneer Mountains of Idaho expose a lower plate core of Precambrian and Ordovician metasedimentary rocks, which are intruded by Cretaceous and Eocene plutonic bodies. The core is separated by a detachment fault from a surrounding upper plate of Paleozoic and Tertiary sedimentary and volcanic units. The detachment system developed during a Tertiary extensional event which overprinted Paleozoic and Mesozoic east-directed compressional features, and exhibits both brittle and ductile (mylonitic) deformation. Stretching lineations in the mylonite and striations along the detachment surface both cluster around N65W. Composite planar fabrics (s- and c-surfaces) in the mylonite and limited development of a mylonitic front along the NW side of the core both suggest a top-to-the-west sense of shear. Minimum translation is estimated at about 17 km. The Pioneer structural complex is one of a number of metamorphic core complexes present along the North American Cordillera. All exhibit Tertiary extensional deformation, expressed as detachment faults structurally adjacent to ductile mylonitic shear zones. Extension directions, as indicated by stretching lineations within mylonite and striations along detachment faults, fall into regional groups in which the directions are similar in trend throughout each group. Asymmetric fabrics on both small and large scales give senses of shear and indicate that tectonic vergence within each group is directed outward from a central axis. The regional consistency of extension directions implies a regional control of extension in metamorphic core complexes. Much of central Idaho, and possibly a large part of eastern Idaho as well, may be riding on the upper part of an extensive detachment terrane, of which the Pioneer complex exposes the deeper levels. The Pioneer complex, and other core complexes, owes its present elevation to isostatic uplift over an overthickened crustal welt of local scale. Larger-scale uplift may be due to a similar isostatic adjustment over a broad zone of crustal thickening from Mesozoic compressional tectonics and intrusion.

No description available.

No description available.

No description available.

An improved method has been developed for carrying out 2-plate reconstructions, in which fracture zone locations are fitted to synthetic flowlines and magnetic anomaly picks are rotated and fitted to great circles representing other, not necessarily conjugate, anomaly isochrons. This enables the determination of finite rotation poles for regions with sparse data coverage, or where much of one or both plates has been subducted. Misfits and partial derivatives are calculated for each type of data, and combined in a single iterative inversion, allowing the direct calculation of confidence intervals. This method is then extended to a 3-plate reconstruction, taking closure into consideration. The South American - African - Antarctic plate system is then studied. Fracture zone locations are identified from a gravity map constructed from GEOSAT altimeter data, and magnetic anomalies are identified from ship profiles. Two-plate reconstructions are carried out for each plate pair, giving good fits to the observed data, and then all three datasets are combined in a 3-plate reconstruction. Comparison of the results reveals a discontinuity in spreading in the Weddell Sea, believed to be related to pseudo-asymmetric spreading caused by ridge re-organisation in the Paleocene and early Eocene. A revised 3-plate inversion, taking this discontinuity into account, produces an internally consistent set of poles, indicating a closed 3-plate system since anomaly 34 (83Ma), with no evidence for a Malvinas Plate extending into the Weddell Sea in the Late Cretaceous. Disruption to the system from anomaly 32 (71Ma) until anomaly 24 (52Ma), appears to be related to the collision of Africa with Eurasia. A study of the past motion, configuration and stability of the Bouvet Triple junction suggests that for the majority of the past 50Ma it has been in a RFF configuration, in theory considerably less stable than RRR, the other possible configuration.

A minor eruption of Mount Saint Helens in Washington State U. S. A. in 1984, triggered the formation of a debris flow in the headwaters of the North Fork Toutle River. As the debris flow progressed downstream it transformed through the incorporation of water and the loss of sediment and within 34 kilometres became a muddy flood. The deposits produced by the transforming flow and associated recessional flows that followed in its wake, exhibited a coarse grained depositional continuum from debris flow to stream flow, including deposits with intermediate sedimentological characteristics termed "hyperconcentrated flow deposits".The systematic and detailed sedimentological analysis of these deposits, combined with information concerning the characteristics of the flow, has allowed the delineation of hyperconcentrated flow deposits within the debris flow/stream flow depositional continuum and hence the establishment of criteria for the recognition of coarse grained hyperconcentrated flow deposits in the volcaniclastic environment of Mount Saint Helens. Hyperconcentrated flow deposits are generally homogeneous, matrix-supported, unstratified (except where defined by sub units), have sorting characteristics intermediate between debris flow and stream flow and can exhibit a bimodal, generally non imbricate, clast fabric as a function of clast size. Coarse-tail inverse grading may occur but it is weak, or restricted to sub units. Use of these criteria enabled the recognition of hyperconcentrated flow deposits within depositional sequences produced earlier in the eruptive history of Mount Saint Helens.The analysis of Permo-Triassic alluvial fan deposits on the Isle of Lewis Scotland, revealed that elements of the debris flow/stream flow depositional continuum could be recognised by the application of the criteria established in the volcaniclastic environment of Mount Saint Helens.

The Australian-Pacific plate boundary is an uncomplicated structure along most of its length in the South Island, New Zealand. In South Westland, south of the Arawata River, however, several terranes converge onto the Alpine fault. Inherent anisotropies arising from the position of pre-existing fault structures, lithological contacts and rheological heterogeneities within these give rise to an atypically diffuse and complex zone, the overall geometry of which resembles a regional scale transpressive flower structure. The flower structure is a broad deformation zone 60 km in length extending approximately 7 km from the Alpine fault to its eastern limit, the Dun Mountain Ophiolite Belt. Integral parts of the structure are the Hollyford Fault System and the Livingstone Fault System. The area is characterised by an array of left-stepping, subparallel faults with an average 060� strike linked by 020� striking structures. All fault traces offset Quaternary features. Fractions of the total interplate slip are partitioned across the reactivated structures. Additionally, kinematic indicators reveal partitioning of strike-slip and oblique/dip-slip deformation across the related secondary fault zones. The behaviour of the plate boundary zone in South Westland is fundamentally controlled by reactivation of the Hollyford Fault System and the Livingstone Fault System which partition slip away from the Alpine fault. As a consequence, the eastward transferral of slip onto the curved geometry of the converging fault systems has ultimately created a left-stepping contractional regime, the equivalent of a restraining bend in the plate boundary zone. The competent Dun Mountain Ophiolite Belt controls the geometry and evolution of the reactivated structures. It also acts as an indenter and imposes additional boundary conditions adding to the shortening component in the region and the onset of complex transpressional strain patterns. The geometry and kinematics of the flower structure in the upper crust is mimicked in the ductile mid to lower crust. Upper greenschist facies mylonites reveal a complex fold pattern developed in response to contemporaneous non-coaxial and coaxial deformation. The folding formed during a continuation of deformation associated with mylonitisation at depths within the fault system. The fact that strain localisation and transpressive strain patterns in the brittle crust continue into the ductile zones suggests there is a feedback relationship between the two regimes. The reactivation of pre-existing structures and the influence of rheological factors are considered as first order factors controlling strain partitioning in the plate boundary zone. Recognition of local strain partitioning is important for assessing slip rates and earthquake recurrence. Similarly, the faults extend down below the seismogenic zone so that interaction of the different structures with each other may produce changes in fault behaviour which affects earthquake nucleation. Although the Alpine fault is a major structure in the South Island of New Zealand with over 400 km of dextral movement, the reactivated structures still exert a degree of control locally on the structure and kinematics of the plate boundary zone. Reactivation of inherent fault structures has important implications for the initiation of plate boundary faults and the alteration of the plate boundary geometry with evolving deformation.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 121-130) Also available in print.

Thesis (M.S.)--University of North Carolina at Wilmington, 2004. / Includes bibliographical references (leaves : 70-72).