The break-up of continents and the formation of new ocean basins

Rifted continental margins are the product of stretching, thinning and ultimate break-up of a continental plate into smaller fragments, and the rocks lying beneath them store a record of this rifting process. Earth scientists can read this record by careful sampling and with remote geophysical techniques. These experimental studies have been complemented by theoretical analyses of continental extension and associated magmatism. Some rifted margins show evidence for extensive volcanic activity and uplift during rifting; at these margins, the record of the final stages of rifting is removed by erosion and obscured by the thick volcanic cover. Other margins were underwater throughout their formation and showed rather little volcanic activity; here the ongoing deposition of sediment provides a clearer record. During the last decade, vast areas of exhumed mantle rocks have been discovered at such margins between continental and oceanic crust. This observation conflicts with the well-established idea that the mantle melts to produce new crust when it is brought close to the Earth's surface. In contrast to the steeply dipping faults commonly seen in zones of extension within continental interiors, faults with very shallow dips play a key role in the deformation immediately preceding continental break-up. Future progress in the study of continental break-up will depend on studies of pairs of margins which were once joined and on the development of computer models which can handle rigorously the complex transition from distributed continental deformation to sea-floor spreading focused at a mid-ocean ridge

Geophysical characterisation of the ocean–continent transition at magma-poor rifted margins

Geophysical characterisation of the ocean-continent transition (OCT) at magma-poor riftedmargins has focused primarily on the determination of P wave velocities using wide-angleseismic techniques. Such experiments have shown that the OCT is heterogeneous, but thattypically velocities increase gradually with depth from ~5.0 km/s at top basement to ~8.0km/s at ~5 km deeper, without a large and abrupt Moho transition. The velocity variationwith depth is similar to that of old fracture zone crust, and appears to differ from that ofoceanic crust formed at ultra-slow spreading rates, though sampling of the latter is limited.Typically, the OCT is characterised by weakly lineated, low amplitude magnetic anomalies;the interpretation of these anomalies remains controversial. The oceanward limit of the OCTremains poorly defined on many margins

The microstructure of sediment-hosted hydrates: evidence from effective medium modelling of laboratory and borehole seismic data

Much of our knowledge of hydrate distribution in the subsurface comes frominterpretations of remote seismic measurements. A key step in such interpretations isan effective medium theory that relates the seismic properties of a given sediment toits hydrate content. A variety of such theories have been developed; these theoriesgenerally give similar results if the same assumptions are made about the extent towhich hydrate contributes to the load-bearing sediment frame. We have furtherdeveloped and modified one such theory, the self-consistentapproximation/differential effective medium approach, to incorporate additionalempirical parameters describing the extent to which both the sediment matrix material(clay or quartz) and the hydrate are load-bearing. We find that a single choice ofthese parameters allows us to match well both P and S wave velocity measurementsfrom both laboratory and in situ datasets, and that the inferred proportion of hydratethat is load-bearing varies approximately linearly with hydrate saturation. Thisproportion appears to decrease with increasing hydrate saturation for gas-richlaboratory environments, but increase with hydrate saturation when hydrate is formedfrom solution and for an in situ example

Seismic constraints on the three-dimensional geometry of low-angle intracrustal reflectors in the Southern Iberia Abyssal Plain

Several lines of evidence suggest that simple shear rifting of the continental crust, in the formof low-angle detachment faulting, occurred during the final stages of continental breakupbetween West Iberia and the Grand Banks. The primary evidence for such faulting is theoccurrence of low-angle, high amplitude reflectors within the basement adjacent to the ocean–continent transition zone. Here we present a series of intersecting, depth migrated seismicreflection profiles that image one such reflector, the H-reflector, located on the southern edgeof Galicia Bank. ‘H’ lies beneath several boreholes drilled during ODP Legs 149 and 173,in a region where the oceanward extent of extended continental crust steps at least 150 kmwestward from its location in the southern Iberia Abyssal Plain to its location off the relativelyshallow Galicia Bank. In our profiles ‘H’ appears to define a surface that extends over a regionof at least 200 km2 and that dips down ?19? to the north, towards Galicia Bank. The profilesshow that a close affinity exists between ‘H’ and the most seaward continental crust. Based ongeophysical data and ODP drilling results, we infer that the basement above ‘H’ is composedof continental crust deformed by extensional faults into a series of wedge-shaped blocks andthin slivers. These basement wedges have a complex 3-D geometry. ‘H’ rises to the basementsurface on a number of the seismic profiles and appears to define locally the oceanward extentof continental fault blocks

Lithospheric controls on melt production during continental breakup at slow rates of extension: Application to the North Atlantic

Rifted margins form from extension and breakup of the continentallithosphere. If this extension is coeval with a region of hotter lithosphere,then it is generally assumed that a volcanic margin would follow. Herewe present the results of numerical simulations of rift margin evolution byextending continental lithosphere above a thermal anomaly. We find that unlessthe lithosphere is thinned prior to the arrival of the thermal anomalyor half spreading rates are more than ? 50mmyr?1, the lithosphere actsas a lid to the hot material. The thermal anomaly cools significantly by conductionbefore having an effect on decompression melt production. If the lithosphereis thinned by the formation of extensional basins then the thermalanomaly advects into the thinned region and leads to enhanced decompressionmelting. In the North Atlantic a series of extensional basins off the coastof northwest Europe and Greenland provide the required thinning. This observationsuggests that volcanic margins that show slow rates of extension,only occur where there is the combination of a thermal anomaly and previousregional thinning of the lithosphere

Joint angle affects volitional and magnetically-evoked neuromuscular performance differentially

This study examined the volitional and magnetically-evoked neuromuscular performance of the quadriceps femoris at functional knee joint angles adjacent to full extension. Indices of volitional and magnetically-evoked neuromuscular performance (N= 15 healthy males; 23.5 ± 2.9 years; 71.5 ± 5.4 kg; 176.5 ± 5.5 cm) were obtained at 25°; 35° and 45° of knee flexion. Results showed that volitional and magnetically-evoked peak force (PFV; PTFE, respectively) and electromechanical delay (EMDV; EMDE, respectively) were enhanced by increased knee flexion. However, greater relative improvements in volitional compared to evoked indices of neuromuscular performance were observed with increasing flexion from 25° to 45° (e.g. EMDV; EMDE: 36% vs. 11% improvement, respectively; F[2,14] = 6.8; p < 0.05). There were no significant correlations between EMDV and EMDE or PFV and PTFE, respectively at analogous joint positions. These findings suggest that the extent of the relative differential between volitional and evoked neuromuscular performance capabilities is joint angle-specific and not correlated with performance capabilities at adjacent angles, but tends to be smaller with increased flexion. As such, effective prediction of volitional from evoked performance capabilities at both analogous and adjacent knee joint positions would lack robustness

Invisible Trojan-horse attack

We demonstrate the experimental feasibility of a Trojan-horse attack that remains nearly invisible to the single-photon detectors employed in practical quantum key distribution (QKD) systems, such as Clavis2 from ID Quantique. We perform a detailed numerical comparison of the attack performance against Scarani-Acin-Ribordy-Gisin (SARG04) QKD protocol at 1924nm versus that at 1536nm. The attack strategy was proposed earlier but found to be unsuccessful at the latter wavelength, as reported in N.~Jain et al., New J. Phys. 16, 123030 (2014). However at 1924nm, we show experimentally that the noise response of the detectors to bright pulses is greatly reduced, and show by modeling that the same attack will succeed. The invisible nature of the attack poses a threat to the security of practical QKD if proper countermeasures are not adopted.Comment: 8 pages, 3 figures, due to problem in the compilation of bibliography, we are uploading a corrected versio

An Examination of the Definitive Terms Used in the Biblical Doctrine of the Atonement

Evangelicals have always regarded the Bible as the ultimate source of doctrine as well as morale. This attitude applies, of course, to its teaching on the Atonement of Christ. This scriptural teaching on this subject is described by a number of definitive terms, the meaning of which is crucial to the formulation of a biblical doctrine of the Atonement. These terms, however, have never been studied in a comprehensive manner, and in no case has evidence been presented to show their meaning in relation to each other

Influence of surgery and rehabilitation conditioning on psychophysiological fitness

The purpose of this study was to assess changes in psychophysiological fitness following reconstructive knee surgery and early phase (2.5 months) physical rehabilitation. Nine patients (7 male, 2 female; mean age, 29.9 years) electing to undergo anterior cruciate ligament reconstructive surgery (central third, bone-patella tendon-bone graft) were assessed on four separate assessment occasions post-surgery. Repeated measures ANOVAs showed significant condition (injured/non-injured leg) by test occasion (2 weeks pre-surgery and 6, 8 and 10 weeks post-surgery) interactions for knee ligamentous compliance (anterior tibiofemoral displacement), peak force and electromechanical delay associated with the knee flexors of the injured and noninjured legs (F3,24 = 4.7 to 6.6; p < 0.01), together with individualized emotional profile disturbance scores that were significantly less at 10 weeks post-surgery compared to pre-surgery, 6 weeks and 8 weeks post-surgery (F3,24 = 7.6; p < 0.01). Spearman rank correlation coefficients identified significant relationships between musculoskeletal fitness and emotional profile scores at pre-surgery (r = 0.69–0.72; p < 0.05) and at 8 weeks post-surgery (r = 0.70–0.73; p < 0.05). The 6 Bi-POMS subscales and the 12 ERAIQ responses found inconsistent patterns of response and relationships across the assessment occasions. Overall, the patterning of changes and associations amongst emotional performance profile discrepancy scores in conjunction with those scores from indices of musculoskeletal fitness performance capability offered important support for the efficacy of an approach which integrates self-perceptive and objective measurements of fitness capability during rehabilitation following surgery to a synovial joint