Sea-floor tectonics and submarine hydrothermal systems

The discovery of metal-depositing hot springs on the sea floor, and especially their link to chemosynthetic life, was among the most compelling and significant scientific advances of the twentieth century. More than 300 sites of hydrothermal activity and sea-floor mineralization are known on the ocean floor. About 100 of these are sites of high-temperature venting and polymetallic sulfide deposits. They occur at mid-ocean ridges (65%), in back-arc basins (22%), and on submarine volcanic arcs (12%). Although high-temperature, 350°C, black smoker vents are the most recognizable features of sea-floor hydrothermal activity, a wide range of different styles of mineralization has been found. Different volcanic substrates, including mid-ocean ridge basalt, ultramafic intrusive rocks, and more evolved volcanic suites in both oceanic and continental crust, as well as temperature-dependent solubility controls, account for the main geochemical associations found in the deposits. Although end-member hydrothermal fluids mainly originate in the deep volcanic basement, the presence of sediments and other substrates can have a large effect on the compositions of the vent fluids. In arc and backarc settings, vent fluid compositions are broadly similar to those at mid-ocean ridges, but the arc magmas also supply a number of components to the hydrothermal fluids. The majority of known black smoker vents occur on fast-spreading mid-ocean ridges, but the largest massive sulfide deposits are located at intermediate- and slow-spreading centers, at ridge-axis volcanoes, in deep backarc basins, and in sedimented rifts adjacent to continental margins. The range of deposit sizes in these settings is similar to that of ancient volcanic-associated massive sulfide (VMS) deposits. Detailed mapping, and in some cases drilling, indicates that a number of deposits contain 1 to 5 million tons (Mt) of massive sulfide (e.g., TAG hydrothermal field on the Mid-Atlantic Ridge, deposits of the Galapagos Rift, and at 13°N on the East Pacific Rise). Two sediment-hosted deposits, at Middle Valley on the Juan de Fuca Ridge and in the Atlantis II Deep of the Red Sea, are much larger (up to 15 and 90 Mt, respectively). In the western Pacific, high-temperature hydrothermal systems occur mainly at intraoceanic back-arc spreading centers (e.g., Lau basin, North Fiji basin, Mariana trough) and in arc-related rifts at continental margins (e.g., Okinawa trough). In contrast to the mid-ocean ridges, convergent margin settings are characterized by a range of different crustal thicknesses and compositions, variable heat flow regimes, and diverse magma types. These variations result in major differences in the compositions and isotopic systematics of the hydrothermal fluids and the mineralogy and bulk compositions of the associated mineral deposits. Intraoceanic back-arc basin spreading centers host black smoker vents that, for the most part, are very similar to those on the mid-ocean ridges. However, isotopic data from both the volcanic rocks and the sulfide deposits highlight the importance of subduction recycling in the origin of the magmas and hydrothermal fluids. Back-arc rifts in continental margin settings are typically sediment-filled basins, which derive their sediment load from the adjacent continental shelf. This has an insulating effect that enhances the high heat flow associated with rifting of the continental crust and also helps to preserve the contained sulfide deposits. Large hydrothermal systems have developed where initial rifting of continental crust or locally thickened arc crust has formed large calderalike sea-floor depressions, similar to those that contained major VMS-forming systems in the geologic record. Hydrothermal vents also occur in the summit calderas of submarine volcanoes at the volcanic fronts of arcs. However, this contrasts with the interpreted settings of most ancient VMS deposits, which are considered to have formed mainly during arc rifting. Hydrothermal vents associated with arc volcanoes show clear evidence of the direct input of magmatic volatiles, similar to magmatic-hydrothermal systems in subaerial volcanic arcs. Several compelling examples of submarine epithermal-style mineralization, including gold-base metal veins, have been found on submarine arc volcanoes,and this type of mineralization may be more common than is presently recognized. Mapping and sampling of the sea floor has dramatically improved geodynamic models of different submarine volcanic and tectonic settings and has helped to establish a framework for the characterization of many similar ancient terranes. Deposits forming at convergent margins are considered to be the closest analogs of ancient VMS. However, black smokers on the mid-ocean ridges continue to provide critically important information about metal transport and deposition in sea-floor hydrothermal systems of all types. Ongoing sea-floor exploration in other settings is providing clues to the diversity of mineral deposit types that occur in different environments and the conditions that are favorable for their formation

Further studies of methods for reducing community noise around airports

A simplified method of analysis was used in which all flights at a 'simulated' airport were assumed to operate from one runway in a single direction. For this simulated airport, contours of noise exposure forecast were obtained and evaluated. A flight schedule of the simulated airport which is representative of the 23 major U. S. airports was used. The effect of banning night-time operations by four-engine, narrow-body aircraft in combination with other noise reduction options was studied. The reductions in noise which would occur of two- and three-engine, narrow-body aircraft equipped with a refanned engine was examined. A detailed comparison of the effects of engine cutback on takeoff versus the effects of retrofitting quiet nacelles for narrow-body aircraft was also examined. A method of presenting the effects of various noise reduction options was treated

Turbojet blade vibration data acquisition design and feasibility testing

A turbojet blade vibration data acquisition system was designed to allow the measurement of blade vibration. The data acquisition system utilizing 96 microprocessors to gather data from optical probes, store, sort and transmit to the central computer is described. Areas of high technical risk were identified and a two-microprocessor system was breadboarded and tested to investigate these areas. Results show that the system was feasible and that low technical risk would be involved in proceeding with the complete system fabrication

Agricultural land use mapping

The author has identified the following significant results. Agricultural areas were selected or analysis in southeastern Pennsylvania, north central Montana, and southern Texas. These three sites represent a broad range of soils, soil parent materials, climate, modes of agricultural operation, crops, and field sizes. In each of these three sites, ERTS-1 digital data were processed to determine the feasibility of automatically mapping agricultural land use. In Pennsylvania, forest land, cultivated land, and water were separable within a 25,000 acre area. Four classes of water were also classified and identified, using ground truth. A less complex land use pattern was analyzed in Hill County, Montana. A land use map was prepared shown alternating patterns of summer fallow and stubble fields. The location of farmsteads could be inferred, along with that of a railroad line. A river and a creek flowing into the river were discernible. Six categories of water, related to sediment content and depth, were defined in the reservoir held by the Fresno dam. These classifications were completed on a 150 square mile area. Analysis of the data from Texas is in its formative stages. A test site has been selected and a brightness map has been produced

Techniques for delineation and portrayal of land cover types using ERTS-1 data

The author has identified the following significant results. ERTS data was used to map land cover in agricultural areas, although in some parts of Pennsylvania, with small irregular fields, many of the pixels overlap field boundaries and cause difficulties in classification. Various techniques and devices were used to display the results of these land cover analyses. The most promising approach would be a user-interactive color monitor interfaced with a large computer so that classification results could be displayed on the CRT and these results output by a hard complete copier

Relation of lineaments to sulfide deposits: Bald Eagle Mountain, Centre County, Pennsylvania

The author has identified the following significant results. Discrete areas of finely-fractured and brecciated sandstone float are present along the crest of Bald Mountain and are commonly sites of sulfide mineralization, as evidenced by the presence of barite and limonite gossans. The frequency distributions of the brecciated float as the negative binomial distribution supports the interpretation of a separate population of intensely fractured material. Such zones of concentrated breccia float have an average width of one kilometer with a range from 0.4 to 1.6 kilometers and were observed in a quarry face to have subvertical dips. Direct spatial correlation of the Landsat-derived lineaments to the fractured areas on the ridge is low; however, the mineralized and fracture zones are commonly assymetrical to the lineament positions. Such a systematic dislocation might result from an inherent bias in the float population or could be the product of the relative erosional resistance of the silicified material in the mineralized areas in relation to the erosionally weak material at the stream gaps

A delta Scuti distance to the Large Magellanic Cloud

We present results from a well studied delta Scuti star discovered in the LMC. The absolute magnitude of the variable was determined from the PL relation for Galactic delta Scuti stars and from the theoretical modeling of the observed B,V,I light curves. The two methods give distance moduli for the LMC of 18.46+-0.19 and 18.48+-0.15, respectively, for a consistent value of the stellar reddening of E(B-V)=0.08+-0.02. We have also analyzed 24 delta Scuti candidates discovered in the OGLE II survey of the LMC, and 7 variables identified in the open cluster LW 55 and in the galaxy disk by Kaluzny et al. (2003, 2006). We find that the LMC delta Scuti stars define a PL relation whose slope is very similar to that defined by the Galactic delta Scuti variables, and yield a distance modulus for the LMC of 18.50+-0.22 mag. We compare the results obtained from the delta Scuti variables with those derived from the LMC RR Lyrae stars and Cepheids. Within the observational uncertainties, the three groups of pulsating stars yield very similar distance moduli. These moduli are all consistent with the "long" astronomical distance scale for the Large Magellanic Cloud.Comment: Accepted for publication on A