The Southwest Indian Ridge: Remelting the Gondwanan Mantle

<正>The Southwest Indian Ridge is an ultraslow spreading ridge(~14-mm/yr)that formed~150 Ma with the breakup of Gondwana.It extends 7700 km from the Bouvet to the Rodriguez Triple Junction,crossing over the flank of the large southern Geoid high centered over Marion and Crozet islands and the Conrad Rise.There is a     

Mineral chemical provenance of Neolithic pitchstone artefacts from Ballygalley,County Antrim,Northern Ireland

A large number of pitchstone fragments and artefacts have recently been discovered at a Neolithic settlement site in Ballygalley, Co. Antrim, Northern Ireland. They consist predominantly of flakes and un‐reworked lumps and cores, with only one complete tool being found. Since no sources of workable pitchstone exist in Ireland, the source must have been the abundant pitchstone volcanic rocks found on the Hebridean Islands of northwest Scotland. The composition of the glass from a number of artefacts is highly siliceous, indicating that they were derived from pitchstones on the Island of Arran; pitchstones from all other Scottish locations are less silica‐rich. In addition, analysis of pyroxene and amphibole microcrystallites within the pitchstone suggests that the Corriegills area of Arran is the most likely source of the Ballygalley artefacts, although the precise outcrop has proved elusive. These finds, and others across Ireland, show that raw materials were being transported and probably traded over considerable distances despite there being suitable alternative sources of material for making tools (flint, etc.) available in the local area. This suggests that the pitchstone had a very specialist use. © 2002 Wiley Periodicals, Inc.     

Regional magma plumbing and emplacement mechanisms of the Faroe‐Shetland Sill Complex: implications for magma transport and petroleum systems within sedimentary basins

The movement of magma through the shallow crust and the impact of subsurface sill complexes on the hydrocarbon systems of prospective sedimentary basins has long been an area of interest and debate. Based on 3D seismic reflection and well data, we present a regional analysis of the emplacement and magmatic plumbing system of the Palaeogene Faroe‐Shetland Sill Complex (FSSC), which is intruded into the Mesozoic and Cenozoic sequences of the Faroe‐Shetland Basin (FSB). Identification of magma flow directions through detailed seismic interpretation of approximately 100 sills indicates that the main magma input zones into the FSB were controlled primarily by the NE–SW basin structure that compartmentalise the FSB into its constituent sub‐basins. An analysis of well data shows that potentially up to 88% of sills in the FSSC are <40 m in thickness, and thus below the vertical resolution limit of seismic data at depths at which most sills occur. This resolution limitation suggests that caution needs to be exercised when interpreting magmatic systems from seismic data alone, as a large amount of intrusive material could potentially be missed. The interaction of the FSSC with the petroleum systems of the FSB is not well understood. Given the close association between the FSSC and potential petroleum migration routes into some of the oil/gas fields (e.g. Tormore), the role the intrusions may have played in compartmentalisation of basin fill needs to be taken fully into account to further unlock the future petroleum potential of the FSB.     

Observation-based evaluation of surface wave effects on currents and trajectory forecasts

Knowledge of upper ocean currents is needed for trajectory forecasts and is essential for search and rescue operations and oil spill mitigation. This paper addresses effects of surface waves on ocean currents and drifter trajectories using in situ observations. The data set includes colocated measurements of directional wave spectra from a wave rider buoy, ocean currents measured by acoustic Doppler current profilers (ADCPs), as well as data from two types of tracking buoys that sample the currents at two different depths. The ADCP measures the Eulerian current at one point, as modelled by an ocean general circulation model, while the tracking buoys are advected by the Lagrangian current that includes the wave-induced Stokes drift. Based on our observations, we assess the importance of two different wave effects: (a) forcing of the ocean current by wave-induced surface fluxes and the Coriolis–Stokes force, and (b) advection of surface drifters by wave motion, that is the Stokes drift. Recent theoretical developments provide a framework for including these wave effects in ocean model systems. The order of magnitude of the Stokes drift is the same as the Eulerian current judging from the available data. The wave-induced momentum and turbulent kinetic energy fluxes are estimated and shown to be significant. Similarly, the wave-induced Coriolis–Stokes force is significant over time scales related to the inertial period. Surface drifter trajectories were analysed and could be reproduced using the observations of currents, waves and wind. Waves were found to have a significant contribution to the trajectories, and we conclude that adding wave effects in ocean model systems is likely to increase predictability of surface drifter trajectories. The relative importance of the Stokes drift was twice as large as the direct wind drag for the used surface drifter.

     

Design constraints and error analysis of the temporal correlationlog

The basic principles of spatial and of temporal correlation sonar for velocity measurement of both surface vessels and autonomous underwear vehicles are considered, showing the advantages of using a pulsed temporal correlation log. To achieve correlation, the conditions for waveform invariance must be met, and there is a velocity-depth limitation to be observed; these are described in detail. Practical design constraints such as the effects of different transducer sizes/geometry and carrier frequencies are also considered     

Evidence for microbial activity in British and Irish Ordovician pillow lavas

Pyrite is consistently found in modern seafloor vesicular basalts and has a sulphur isotopic composition consistent with microbial activity. We present S isotope data from pyrite in Ordovician pillow lavas at localities across the British Isles, which yield a range of δ³⁴S compositions consistent with two components of sulphur: groundmass pyrite (~0 ± 4‰) and ³²S‐enriched pyrite in the vesicles (−8‰ to −27‰). The latter are recorded from vesicular lavas in four different terranes, representing different settings at the margins of the Iapetus Ocean. Whereas a component of magmatic sulphate is recognized in the groundmass values, the isotopically light data in the vesicles are consistent with microbial reduction of seawater sulphate in sub‐seafloor lavas. This is consistent with modern examples and indicates considerable longevity for this sub‐seafloor microbial habitat. Copyright © 2014 John Wiley & Sons, Ltd.