Graduation date: 1968

The opening of the South Atlantic between 140 and 90 m. y. B. P. occurred about two poles of rotation. The initial pole of rotation was maintained until Africa and South America were completely separated. The subsequent removal of restraints imposed by the pre-existing structure of Africa and South America on the early spreading direction permitted a northward migration of the pole of rotation and concomitant reorientation of spreading direction, The NNE trending Cameroon-Gabon and southern Angola coastlines which offset the generally SSE trend of the west African margin between 5°N and the Walvis Ridge are proposed as initial transform offsets of the South Atlantic proto-rift. Location of these initial offsets was controlled by lineations of the Precambrian/Early Paleozoic belts of thermotectonic activity which occur between older, stable cratonic nuclei of Gondwana. Shorter offsets of the continental margin south of the Walvis Ridge and the two major offsets of the west African coastline north of the Walvis Ridge define a pole of rotation at 5°N, 26°w for the initial South Atlantic opening. A set of magnetic anomaly lineations near the continental margins of Angola and southwest Africa is described and named the Benguela sequence. These anomalies were formed during the initial phase of spreading and are displaced right-laterally almost 1000 kilometers across an extension of the continental offset along the southern Angola margin. This offset is named the Benguela Fracture Zone. The Benguela anomalies are correlated with anomalies of the Lynch sequence in the western North Atlantic. The change in direction between the two pre-Cenozoic phases of South Atlantic spreading is dated at roughly 120 m. y. B. P. based upon an extrapolation of the ages of anomalies in the Lynch sequence to the time of reorientation in the South Atlantic. Formation of the South Atlantic quiet zones occurred by sea-floor spreading about a pole of rotation at 21. 5°N, 14. 0°W during the second phase of opening. The present structure of the Walvis Ridge is controlled by nearly orthogonal NE and NW trending faults shown by seismic reflection profiling. The NE trending set of faults approximate small circles of the pole of rotation at 21. 5°N, 14. 0°W and appear to offset the Walvis Ridge topography in a right-lateral sense. Reorientation of spreading would have produced extension across the Benguela Fracture Zone; development of short offset spreading centers along the Benguela Fracture Zone during this reorientation is proposed to explain the right-lateral offsets of the Walvis Ridge topography. Lack of geophysical information on the lower crustal structure prevents a direct explanation of the present elevation of the Walvis Ridge. However the Walvis Ridge is probably underlain by a low density root produced by alteration of the lower crust and upper mantle materials beneath the Benguela Fracture Zone which began during the spreading reorientation. Asymmetric spreading over the Walvis Ridge may have permitted the zone of crustal accretion to remain near the older Benguela Fracture Zone long enough to allow the creation of an anomalously broad low-density root which is responsible for the uplift of the Walvis Ridge. / Graduation date: 1974

The thermal regime of a postulated descending lithospheric slab is calculated. The gravity anomaly associated with such a structure is large in amplitude and long in wavelengh. Observed free-air gravity anomalies in the Pacific Northwest do not indicate a gravitational effect due to a descending slab. Two hypothetical compensation models proposed may mask the effects of the slab. However, a more complex form of compensation seems required. Extraction of long wavelength signals from the gravity record using matched filters is demonstrated. Caution in the interpretation of potential field records by this class of filters is recommended. / Graduation date: 1975

The continental margin off southern Oregon, which includes the shelf and slope from Cape Blanco to the Oregon-California border, exhibits a distinctive marginal-plateau structural pattern which divides the margin into the continental shelf, the upper continental slope and its associated benches, and the lower continental slope. Lutum transport and deposition have dominated the sedimentary processes on the margin since the start of Holocene time. The structure of the southern Oregon margin is characterized by north-south trending compressional folds, and near-vertical faults which have been down-dropped to the west. Large-scale folds on the upper slope have ponded sediments behind them resulting in the formation of the Klamath Plateau, Cape Blanco Bench, and other bench-like features. Development of the structural pattern is most likely a result of the compressive underthrusting of the oceanic lithospheric plate beneath the southernmost Oregon-northern California margin and the crustal extension which exists throughout the nearby continent and ocean basin. Useful stratigraphic horizons within the late Pleistocene and Holocene margin deposits include Mazama Ash (6600 years B.P.) and several recognizable shifts in the abundance of Radiolaria and planktonic Foraminifera, particularly one dating from 5000-4000 years B.P. Holocene sedimentation rates vary from an average of 10 cm/ 1000 years on the upper slope to an average of 50 cm/1000 years on the lower slope, indicating that the lower slope is out-building and up-building more rapidly than the upper slope. The paleo-depth range of Pliocene fauna in sedimentary rocks from the margin suggests that subsequent to their deposition both uplift and subsidence occurred on the southern Oregon margin. Sediments from the southern Oregon margin consist primarily of olive gray lutite, gray lutite, and sand-silt layers. Olive gray lutite is Holocene in age and is ubiquitous on the margin, with the thickest accumulation (10 m average) found on the lower slope, while the distribution of Holocene lutite on the upper slope is thin and patchy (3-4 m or less). The gray lutite appears to be a late Pleistocene deposit, and the sand-silt layers reflect both ages. The surface sediment distribution pattern on the shelf consists of modern inner shelf sand, modern central shelf mud, and mixed deposits of both types. Relict deposits are present at the shelf edge. The lower slope consists entirely of modern mud, but the surface sediment on the upper slope and benches consists of both modern and relict deposits, and mixtures of the two. The mineralogy of the unconsolidated and consolidated sediments from the margin indicates that the Klamath Mountains have been the dominant source for these deposits since early Tertiary time. This is reflected in the abundance of blue-green hornblende and other heavy minerals indicative of the Mesozoic rocks of the Klamath Mountains; the same source is suggested for the abundant chlorite found in the clay fraction of margin sediments and rocks. There are indications in the mineralogy of lower slope sediments which suggest that the Tertiary strata of the southern Oregon Coast Ranges may be a secondary source for the deposits in this environment. When compared to the upper slope sediments, those from the lower slope have a higher feldspar content, a higher pyroxene-to-amphibole ratio, and an apparently higher illite content. As a result of the Holocene rise in sea level, the deposition of coarse clastics on the southern Oregon margin has been restricted to the inner shelf. Consequently, only the fine-grained lutum discharged from rivers is deposited on the outer margin environments. Submarine topography, oceanographic conditions, and gravity are important factors which effect transport and deposition of lutum on the margin. A model of modern lutum transport by bottom turbid layers and fine-particle suspensate is proposed for the southern Oregon margin. Long-period swell is believed to be responsible for much of the formation of bottom turbid layers on the shelf. Once formed, these turbid layers move north and west over the shelf under the influence of shelf currents, alternating tidal action, and gravity; upon reaching the slope they are funneled into submarine valleys and deposited on the lower slope and adjacent deep sea. Lutum deposited on the upper slope is eventually re-suspended and transported by southerly bottom currents into down-slope valleys; very little lutum remains behind on the upper slope. Deposition of the fine-particle suspensate as well as slumping and other gravitational processes contribute to the lower slope sediments. The end result of modern lutum transport is the continual up-building and out-building of the lower slope. / Graduation date: 1971

Thesis (M. Sc.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 65-66)

Thesis (Ph. D.) - Oregon State University, 1968. / Bibliography: leaves 205-222.

The purpose of this project is to investigate the feasibility of and methodology for the development of a set of environmental analogs of operational Undersea Warfare (USW) areas within fleet training areas. It is primarily a discussion of the identification of parameters that characterize the tactical USW environment, prioritization of these parameters, identification of existing databases that contain these parameters and an outline of the processes required to extract the desired data from the databases. An example of two operational areas with probable analogous training areas is discussed in terms of the methodology proposed. Among the environmental parameters considered are: bathymetry, sediment type, sound velocity profiles, acoustic response of the environment across a broad frequency spectrum (for both active and passive sonar), ambient noise, shipping density, bioluminescent properties, evaporation duct height, atmospheric surface duct height and gravitational anomalies. The project focus is primarily on acoustic oceanographic features but non-acoustic and atmospheric features are considered. There is an expectation that this project is the starting point for further research, software product development, data extraction, analog identification and promulgation of a tailored product to the fleet. The ultimate goal is to train for USW across the fleet in areas as much like the areas the Navy fights in as possible.

The work presented in this dissertation depicts past and present signatures of melt distribution at fast and intermediate spreading centers. The primary goal of the studies included in this thesis is to provide better understanding of melt distribution and variation in melt physical properties within and at the base of oceanic crust formed at these spreading centers. Furthermore, this work examines effects that melt presence might have on formation and structural characteristics of oceanic crust. To explore the above we use geophysical data collected during two expeditions conducted along the Juan de Fuca Ridge (intermediate) and the East Pacific Rise (fast). The major part of the thesis is based on the work conducted on high resolution reflection seismic data that investigate present day intracrustal melt distribution along the East Pacific Rise (EPR) axis extending between 8º20’ and 10º10’N. Here, the character of the melt reservoir is examined from different aspects and by using different seismic data analysis methods. By systematic analysis of the seismic reflection data, we show that the axial melt lens (AML) is segmented at different segment scales. Locations of the mapped disruptions in the AML correspond to previously identified tectonic discontinuities well expressed in the seafloor bathymetry. The above result corroborates genetic relationship between tectonic and magmatic segmentation. To examine melt distribution along the EPR, here for the first time we use amplitude variation with angle of incidence (AVA) crossplotting technique that was developed by oil and gas industry experts to look for presence of hydrocarbons. Further data examination for the first time for the mid-ocean ridges show presence of deeper lenses (lenses that are present below the AML). Presence of gaps in these sub-events and their collocation with what is believed to be the location of origin of the last documented eruption occurred in 2005-06, may shed light on the mechanisms behind the mid-ocean ridges volcanic processes. To explore variation in crustal structure and melt distribution at present day along the Juan de Fuca Ridge and relicts of past melt presence near ridge propagators wakes, a combination of gravity and multi-channel seismic data was used. Gravity modeling, constrained by seismic data, showed that robust topography (shallow axial depth and wide axial high) and thicker crust observed for the southern portion of this ridge system originate from enhanced melt supply at the base of the crust. In addition, prominent crustal thickening on the younger crust side of the inner propagators wakes (now on the ridge flanks) is brought into relationship with collocated frozen magma lenses imaged at the base of the crust. Spatial relationship of the two argues for their causal relationship at the time of the crustal formation on the axis. Our study suggests that these frozen lenses represent the record of once molten reservoir that most probably actively participated in the formation of the thicker crust.

Two thirds of the Earth's lithosphere is covered by the ocean. The oceanic lithosphere is formed at mid-ocean ridges, evolves and interacts with the overlying ocean for millions of years, and is eventually consumed at subduction zones. In this thesis, I use 2D and 3D multichannel seismic (MCS) data to investigate the accretionary and hydrothermal process on the ridge flank of the fast-spreading East Pacific Rise (EPR) at 9°37-40'N and the structure of the downgoing Juan de Fuca plate at the Cascadia subduction zone offshore Oregon and Washington. Using 3D multichannel seismic (MCS) data, I image a series of off-axis magma lenses (OAML) in the middle or lower crust, 2 -10 km from the ridge axis at EPR 9°37-40'N. The large OAMLs are associated with Moho travel time anomalies and local volcanic edifices above them, indicating off-axis magmatism contributes to crustal accretion though both intrusion and eruption (Chapter 1). To assess the effect of OAMLs on the upper crustal structure, I conduct 2-D travel time tomography on downward continued MCS data along two across-axis lines above a prominent OAML in our study area. I find higher upper crustal velocity in a region ~ 2 km wide above this OAML compared with the surrounding crust. I attribute these local anomalies to enhanced precipitation of alteration minerals in the pore space of upper crust associated with high-temperature off-axis hydrothermal circulation driven by the OAML (Chapter 2). At Cascadia, a young and hot end-member of the global subduction system, the state of hydration of the downgoing Juan de Fuca (JdF) plate is important to a number of subduction processes, yet is poorly known. As local zones of higher porosity and permeability, faults constitute primary conduits for seawater to enter the crust and potentially uppermost mantle. From pre-stack time migrated MCS images, I observe pervasive faulting in the sediment section up to 200 km from the deformation front. Yet faults with large throw and bright fault plane reflections that are developed under subduction bending are confined to a region 50-60 km wide offshore Oregon and less than ~45 km wide offshore Washington. Near the deformation front of Oregon margin, bending-related faults cut through the crust and extend to ~6-7 km in the mantle, whereas at Washington margin, faults are confined to upper and middle crust, indicating that Oregon margin has experienced more extensive bend faulting and related alteration. These observations argue against pervasive serpentinization in the slab mantle beneath Washington and suggest mechanisms other than dehydration embrittlement need to be considered to explain the intermediate depth earthquakes found along the Washington margin (Chapter 3). Using MCS images of a ~400 km along-strike profile ~10-15 km from the deformation front, I investigate the along-trench variation of the structure of downgoing JdF plate and its relation to the regional segmentation of Cascadia subduction zone. I observe that the propagator wakes within the oceanic plate are associated with anomalous basement topography and crustal reflectivity. Further landward, segment boundaries of ETS recurrence interval and relative timing align with the propagator traces within the subducting plate. I propose while the upper plate structure or composition may determine the threshold of fluid pore pressure at which ETS occur, the propagators may define barriers for ETS events that occur at the same time. I also observe a change in crustal structure near 45.8°N that is consistent with an increase in bend-faulting and hydration south of 45.8°N;. In addition, four previously mapped oblique strike-slip faults are associated with changes in Moho reflection, indicating that they transect the entire crust and may cause localized mantle hydration (Chapter 4).

Graduation date: 1967