Examining the processes that control diffuse flow in seafloor hydrothermal systems can provide insight into what is happening below the seafloor at mid-ocean ridges. The diffuse flow could be either entrained seafloor fluids mixed with hot, upwelling fluids, or diffuse flow could be driven by sidewall heating across some low permeability barrier. This barrier would separate the diffuse flow fluids from the high temperature fluids, effectively preventing mixing. Three parameters were manipulated through a numerical model based on the single-pass model, and the fluid and heat flow results analyzed and compared to observed hydrothermal systems. These three parameters are depth of the extrusive layer at the top of the system, the permeability of the extrusive layer, and the existence of a low permeability barrier separating the high-temperature output from the induced diffuse flow.

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Passive margins along the eastern seaboard of North America formed during early Mesozoic continental rifting and seafloor spreading, tectonic processes that are not fully understood. Seismic refraction and reflection data at the northeastern and north-central Gulf of Mexico and the Grand Banks of Newfoundland, Canada, are used to interpret the deep seismic velocity structure of sediments, crust, and mantle. These interpretations allow for a better understanding of continental rifting, mantle upwelling, magmatism, and seafloor spreading. Magma-poor rifting of the Newfoundland-Iberian margin developed a wide continent-ocean transition zone (COT). I present an analysis of 2-D marine seismic refraction and reflection data from the SCREECH project, including a shear velocity model to constrain the composition of the Newfoundland COT. Comparing SCREECH Line 2 Vp/Vs ratios with depth to potential lithologies supports a COT comprised of hyperextended continental crust and serpentinized mantle. Reconstructions of the opening of the Gulf of Mexico basin are impeded by a lack of seafloor magnetic anomalies and an abundance of sediments that obscure acquisition of seismic refraction datasets. Accordingly, the roles of mantle upwelling, magmatism, and lithospheric extension in this small ocean basin are poorly known. I present new 2-D marine seismic refraction data from the U.S. Gulf of Mexico collected during the 2010 GUMBO project. Rifting in the eastern Gulf of Mexico developed above a zone of anomalously high mantle potential temperatures that led to abundant magmatism. Syn-rift basins in continental crust, high velocity lower crust, a narrow zone of crustal thinning, and seaward-dipping reflectors support this interpretation. Oceanic crust here is thick despite slow seafloor-spreading rates, implying continuation of a thermal anomaly after rifting. In the north-central Gulf of Mexico, transitional crust is consistently thin (~10 km) across a wide zone. Velocity-depth comparisons, asymmetry of the north-central Gulf with the Yucatán margin, and dating of onshore xenoliths support either stretched and magmatically intruded continental crust or a multi-stage episode of seafloor spreading with ridge jumps. I contend that although tectonic inheritance may ultimately influence the location of a passive margin, the rifting process is largely controlled by mantle potential temperature and upwelling rate. / text

Extraction of metals from the seafloor has been considered for decades, beginning with manganese nodules in the 1970s. Today, the targets are massive sulphide deposits rich in copper, zinc, gold, and silver that are associated with hydrothermal vents or black smoker chimneys that occur at divergent and convergent plate margins such as mid-ocean ridges and volcanic island arcs respectively. A recent objective of the mining industry is to develop industry practices that coincide with concepts of sustainability or sustainable development. This objective, known by some as sustainable mining, has indeed become an essential part of the commissioning of any new project, regardless of geographical location. While there has been much work on sustainable mining practice for terrestrial mining, these frameworks are not directly applicable to seafloor projects. There are two problems facing the development of a seabed mining industry. First, there is a regulatory vacuum when considering the mining of seabed deposits, leading to important policy issues. Second, the economic, environmental, and social impacts of a seabed mining project are theoretical, and the real impacts are unknown. Thus, the identification, characterization, and analysis of the sustainability issues facing a seabed mining project are essential steps. To assist with performing these three steps, this thesis provides a process model based on the IDEF0 (Integration DEFinition) standard to assess seafloor massive sulphide mining projects from sustainable mining perspectives. This adaptation of IDEF0 provides a clear, visual representation of a hierarchical framework that can be used to identify “go no-go” sustainability criteria to assist decision makers interested in the potential development of an ore body. / Thesis (Master, Mining Engineering) -- Queen's University, 2011-12-12 12:54:28.436

Hydrothermal discharge on the seafloor results in significant accumulation of base- and precious-metal-rich sulfide material. Technological advances as well as elevated metal prices have led to a growing interest in the direct mining of these deposits from the modern ocean floor. The research presented in this thesis details an investigation of the size, grades, distribution, and accumulation rates of these deposits on the seafloor. A three-part resource assessment, originally designed for land-based ore deposits, was used to generate a predictive framework for the global seafloor sulfide resource. Using detailed descriptions of sizes, grades and locations for 92 known deposits, a resource estimate was generated that predicts a total of ~1,000 deposits and a total global abundance of 600 Mt of sulfide within the neovolcanic zones of the modern ocean floor. A detailed study of the hydrothermal sulfide deposits along the Endeavour Segment of the Juan de Fuca Ridge was carried out to investigate the processes of sulfide accumulation at the ridge-segment scale. Results of 226Ra/Ba dating of barite within the deposits indicate that hydrothermal activity has been ongoing for ~6,000 years and venting has been continuous at the Main Endeavour and High Rise vent fields for ~2,300 and 850 years, respectively. Abundant older sulfide samples from inactive sites outside of the main vent fields indicate a complex history of venting along the ridge segment. Analysis of high-resolution bathymetry of the Endeavour Segment, generated from eight autonomous underwater vehicle surveys, revealed the location of 581 individual hydrothermal sulfide edifices along 15 km of ridge length. Using GIS-based software, the volume of each edifice was calculated, and the total amount of sulfide at Endeavour is estimated to be 1.2 Mt. This estimate is the first comprehensive resource evaluation on the seafloor at this scale. Sulfide has been accumulating within the Endeavour axial valley at a rate of ~400 tonnes per year, which is similar to estimates for the TAG deposit on the Mid-Atlantic Ridge. Using endmember hydrothermal fluid chemistry data and estimates of fluid discharge rates, the mass accumulation rate calculated for Endeavour corresponds to a sulfide depositional efficiency of 6%.

Hydrothermal discharge on the seafloor results in significant accumulation of base- and precious-metal-rich sulfide material. Technological advances as well as elevated metal prices have led to a growing interest in the direct mining of these deposits from the modern ocean floor. The research presented in this thesis details an investigation of the size, grades, distribution, and accumulation rates of these deposits on the seafloor. A three-part resource assessment, originally designed for land-based ore deposits, was used to generate a predictive framework for the global seafloor sulfide resource. Using detailed descriptions of sizes, grades and locations for 92 known deposits, a resource estimate was generated that predicts a total of ~1,000 deposits and a total global abundance of 600 Mt of sulfide within the neovolcanic zones of the modern ocean floor. A detailed study of the hydrothermal sulfide deposits along the Endeavour Segment of the Juan de Fuca Ridge was carried out to investigate the processes of sulfide accumulation at the ridge-segment scale. Results of 226Ra/Ba dating of barite within the deposits indicate that hydrothermal activity has been ongoing for ~6,000 years and venting has been continuous at the Main Endeavour and High Rise vent fields for ~2,300 and 850 years, respectively. Abundant older sulfide samples from inactive sites outside of the main vent fields indicate a complex history of venting along the ridge segment. Analysis of high-resolution bathymetry of the Endeavour Segment, generated from eight autonomous underwater vehicle surveys, revealed the location of 581 individual hydrothermal sulfide edifices along 15 km of ridge length. Using GIS-based software, the volume of each edifice was calculated, and the total amount of sulfide at Endeavour is estimated to be 1.2 Mt. This estimate is the first comprehensive resource evaluation on the seafloor at this scale. Sulfide has been accumulating within the Endeavour axial valley at a rate of ~400 tonnes per year, which is similar to estimates for the TAG deposit on the Mid-Atlantic Ridge. Using endmember hydrothermal fluid chemistry data and estimates of fluid discharge rates, the mass accumulation rate calculated for Endeavour corresponds to a sulfide depositional efficiency of 6%.

The Tonga-Kermadec arc in the SW Pacific comprises a chain of more than 90 volcanic complexes. A continuous 400-km long chain of volcanic activity along the central portion of the Tonga arc has become the focus of intensive research, extending previous studies that have focused on the southern Kermadec chain. Earlier interpretations of the Tonga arc have focused on a perceived lack of volcanism between ~21°S and ~27°S, adjacent to a bend in the trench caused by the collision of the subducting Louisville Seamount Chain (LSC). During swath mapping in 2002, it was revealed that this portion of the arc, including the Louisville and Monowai segments, is in fact one of the most volcanically active parts of the Tonga-Kermadec system. At this location, a combination of oblique convergence of the Pacific Plate and southward compression due to the collision of the LSC has resulted in left-lateral strike-slip faulting and rifting of the arc crust. This has produced a series of left-stepping arc transverse graben and horst structures that localize the voluminous volcanic activity. For this study, a new 1:250,000 scale geological map of the Louisville and Monowai segments has been constructed as a framework for a quantitative analysis of arc volcanism and the eruptive history of these segments. Two types of volcanoes dominate the arc front: deep caldera systems (collapse structures formed due to the evacuation of magma) within the arc rifts, and smaller volcanic cones between the rifts. The cone volcanoes tend to have small summit craters (<10 km3) whereas the large caldera volcanoes have major depressions of up to 50 km3. The cones are relatively undeformed, whereas the larger calderas are affected by multiple stages of collapse, asymmetric subsidence, and distortion caused by regional stresses. Surveys of the crater walls of the cone volcanoes show a predominance of volcaniclastic deposits, whereas the caldera volcanoes contain a high proportion of coherent lava flows. The caldera volcanoes also show a prevalence of basaltic melts compared to the more andesitic and dacitic cones. The largest caldera volcano is the Monowai volcanic complex (25°53’S) occupying a deep depression (Monowai Rift Graben) that crosses the arc front. The volcanic complex consists of a large caldera (12 km wide, 1600 m deep) and an adjacent stratovolcano (Monowai Cone) rising nearly to sea level. We suggest that the different types of volcanoes along the Louisville and Monowai segments reflect the influence of deep structures within the arc crust that have localized strikeslip and normal faulting.

Various porous media were tested with biosurfactant solutions (rhamnolipid or Emulsan) at concentrations ranging from 0 ppm to 1000 ppm. The biosurfactant solutions in the presence of porous media often showed substantial gas hydrate catalyzation, localization on selected surfaces, and/or specific hydrate form (massive, stratified, dispersed.) At 1000-ppm concentrations of rhamnolipid, all porous media surfaces exhibited the same hydrate formation rate increase of 187% over the control. The curves generated for rhamnolipid or Emulsan concentration versus peak hydrate formation rate resembled certain classical adsorption curves. Bentonite and aragonite showed hydrate catalyzation properties with or without biosurfactants. The preference for hydrate formation on porous media surfaces (no surfactant) was: Bentonite/nontronite > aragonite/stainless steel > Ottawa sand/kaolinite. Porous media/biosurfactant concentration combinations play marked roles in the types of gas hydrates formed: massive, dendritic, or needle-like. The research helps to explain the vast occurrence of gas hydrates in ocean sediments.

The different between Remotely Operated Vehicle (ROV) and Autonomous Underwater Vehicle (AUV) is that ROV is connected with the main computer by the electronic cable, so the operator can control the vehicle depending on the environment showing on the monitor; However, AUV is dependent on the received data to autonomously respond the condition via controlling program. In our research, we wanted to use the General Purpose Controller, which had been developed in the previous experiment, in the mission-mode to construct our AUV system for remaining the original ROV controlling system and switching mode between AUV system and ROV system. The mission was divided into primary and secondary mission written by the txt file which is known as mission script, including execute time, target, and mission type etc. In addition, we used the Watch Dog Timer (WDT) in our AUV for the security procedure. When the mission is failed or over the setting time, the AUV will change to the security mode and go forward to the water surface. The other topic in this research wanted to use the Seafloor Laser Scanner (SLS), which was mounted on the AUV, to improve the scanning efficiency. However, when the scanner was working, the AUV had to maintain the stable altitude to the sea floor, so the accurately output power of thruster is needed to be considered and tested. In this part, we found out the properly controlling way in the small water tank first, and then checked the attitude and scanning system in the swimmer pool and towing tank in NCKU respectively, to prove the ability of SLS of AUV system.

This study presents the applications of plastic limit analysis to offshore foundations and anchors, including the drag embedment anchors (DEAs) for mobile offshore drilling units (MODU’s) and spudcan foundations for jack-up platforms. In deep waters, drag embedment anchors are an attractive option for mooring of semisubmersible platforms due to low installation cost and high holding capacity; on the other hand, jack-up platforms are more stable than semisubmersible platforms but only can be placed in shallow waters. The analyses of anchor capacities are developed for an idealized anchor comprising a rectangular fluke, a cylindrical shank, and a metal chain connected to the shank at the padeye. The anchor trajectory prediction during drag embedment is also developed by considering anchor behavior in conjunction with the mechanics of the anchor line. The results of simulations show that anchors approach at equilibrium condition rapidly during the embedment and both the normalized holding capacity and the anchor line uplift angle remain constants in this stage. Besides the geometry of the fluke, the properties of the shank and soil are also crucial factors in the anchor-soil interaction behavior. Partial failure of mooring systems for floating structures will subject drag anchors to loads having an appreciable component outside of the intended plane of loading. Partial failure of mooring systems during hurricanes in recent years have generated an interest in understanding drag anchor performance under these conditions. The analysis presents the simulations of three dimensional trajectories of an anchor system subjected to an out-of-plane load component. For the conditions simulated in the example analyses, the anchor experienced a modest amount of continued embedment following partial failure of the mooring system; however, the ultimate embedment and capacity of the anchor is much less than what would have developed if the anchor had continued in its original trajectory within the plane of intended loading. The analyses of the spudcan foundation of jack-up units include preloading, bearing capacity, and the displacement assessment. When the contribution of the soil moment resistance is considered, a three-stage assessment procedure is recommended: superposing environmental forces on the plot of yield surface, determining the value of yield function corresponding to the external forces, and computing the factor of safety of the spudcan. The results of the assessment may be ambiguous while the different yield functions are employed to analyze the spudcan in soft clay.