A Magnetic Survey of the Southwest Pacific Ocean

<p>The design and construction of a free precession proton magnetometer which give a reading of the field directly in gamma is described. This instrument has been used to obtain magnetic profiles across the Southwest Pacific Ocean during the 1963-65 summer Antarctic supply cruises of H.M.N.Z.S. Endeavour. The magnetic and bathymetric profiler obtained on these cruises have been analysed to determine the nature and structure of the oceanic crust in this region. The region is divided into four divisions. (l) The New Zealand Plateau, with an almost continental crustal thickness. (2) The Southwest Pacific Basin, at a depth of 3,000 fathoms. (3) The Pacific-Antarctic Ridge, pert of the world encircling mind-ocean ridge system. (4) The Ross Sea, an epicontinental sea across the Antarctic continental shelf. Subtraction of the regional field form the magnetic results has enabled a regional field map of the area to be drawn. Comparison with earlier results indicates a westward drift of the earth's field of approximately 0.25 degrees /yr. Some discussion of regional anomalies (~ 100 miles period) has been given. Because of the excellent correlation of magnetic anomalies from track to track across the basin it has been possible to draw an anomaly contour map of this part. This map illustrates the predominantly east-west trend of features over the basin. To the north the features parallel the edge of the New Zealand Plateau. To the south the features swing more towards the Pacific-Antarctic Ridge. A major discontinuity is indicated along a direction 9 degrees E of S meeting the Plateau just southwest of Antipodes Islands. If this discontinuity is extrapolated south to the ridge it meets it at approximately 180 degrees E, where the ridge turns N-E towards Easter Island. Across the ridge the magnetic pattern shows three distinct regions. Over the northern flanks large anomalies are evident but the correlation of anomalies from track to track is very poor. Further south, across the upper flanks, the magnetic records are very much subdued. The extent of this region varies appreciably from track to track. Over the axis of the ridge large, steep-sided anomalies are obtained. These correlate well over part of the region studied. The southern flanks of the ridge are hidden by the Balleny Plateau which seems to form a link between Antarctica and the ridge in this region. The bathymetry records obtained indicate a step-type formation over the ridge. A narrow median valley appears to exist along the axis of the ridge. Some preliminary experimentation has been carried out with continual seismic profiling techniques over the region. The equipment that has been developed and the preliminary results obtained with it are discussed.</p>

A Magnetic Survey of the Southwest Pacific Ocean

<p>The design and construction of a free precession proton magnetometer which give a reading of the field directly in gamma is described. This instrument has been used to obtain magnetic profiles across the Southwest Pacific Ocean during the 1963-65 summer Antarctic supply cruises of H.M.N.Z.S. Endeavour. The magnetic and bathymetric profiler obtained on these cruises have been analysed to determine the nature and structure of the oceanic crust in this region. The region is divided into four divisions. (l) The New Zealand Plateau, with an almost continental crustal thickness. (2) The Southwest Pacific Basin, at a depth of 3,000 fathoms. (3) The Pacific-Antarctic Ridge, pert of the world encircling mind-ocean ridge system. (4) The Ross Sea, an epicontinental sea across the Antarctic continental shelf. Subtraction of the regional field form the magnetic results has enabled a regional field map of the area to be drawn. Comparison with earlier results indicates a westward drift of the earth's field of approximately 0.25 degrees /yr. Some discussion of regional anomalies (~ 100 miles period) has been given. Because of the excellent correlation of magnetic anomalies from track to track across the basin it has been possible to draw an anomaly contour map of this part. This map illustrates the predominantly east-west trend of features over the basin. To the north the features parallel the edge of the New Zealand Plateau. To the south the features swing more towards the Pacific-Antarctic Ridge. A major discontinuity is indicated along a direction 9 degrees E of S meeting the Plateau just southwest of Antipodes Islands. If this discontinuity is extrapolated south to the ridge it meets it at approximately 180 degrees E, where the ridge turns N-E towards Easter Island. Across the ridge the magnetic pattern shows three distinct regions. Over the northern flanks large anomalies are evident but the correlation of anomalies from track to track is very poor. Further south, across the upper flanks, the magnetic records are very much subdued. The extent of this region varies appreciably from track to track. Over the axis of the ridge large, steep-sided anomalies are obtained. These correlate well over part of the region studied. The southern flanks of the ridge are hidden by the Balleny Plateau which seems to form a link between Antarctica and the ridge in this region. The bathymetry records obtained indicate a step-type formation over the ridge. A narrow median valley appears to exist along the axis of the ridge. Some preliminary experimentation has been carried out with continual seismic profiling techniques over the region. The equipment that has been developed and the preliminary results obtained with it are discussed.</p>

Gauge invariant and gauge dependent aspects of topological walking colloidal bipeds

Paramagnetic colloidal spheres assemble to colloidal bipeds of various length in an external magnetic field and walk on a magnetic pattern.

Simultaneous polydirectional transport of colloidal bipeds

Detailed control over the motion of colloidal particles is relevant in many applications in colloidal science such as lab-on-a-chip devices. Here, we use an external magnetic field to assemble paramagnetic colloidal spheres into colloidal rods of several lengths. The rods reside above a square magnetic pattern and are transported via modulation of the direction of the external magnetic field. The rods behave like bipeds walking above the pattern. Depending on their length, the bipeds perform topologically distinct classes of protected walks. We design parallel polydirectional modulation loops of the external field that command up to six classes of bipeds to walk on distinct predesigned paths. Using such loops, we induce the collision of reactant bipeds, their polymerization addition reaction to larger bipeds, the separation of product bipeds from the educts, the sorting of different product bipeds, and also the parallel writing of a word consisting of several letters. Our ideas and methodology might be transferred to other systems for which topological protection is at work.

Integrated interpretation of reflection seismic and aeromagnetic data in a marine geological complex area: a case study.

&lt;p&gt;This paper presents an integrated seismic and aeromagnetic approach applied in the geological complex area of the Cagliari Gulf in the southern Sardinian margin (Western Mediterranean). The investigated area represents the southern extreme part of the main branch of the Sardinian Rift (SR) (Western Mediterranean) that is made up here of a sub-basin bounded by approximately NW faults. The study was also integrated by complementary information deduced from the GNSS network in southern Sardinia.&lt;/p&gt;&lt;p&gt;The aim of this study was to give a contribution on the knowledge of the tectonic evolution and volcanism of the investigated area. For this purpose we used an integrated interpretation of two-dimensional reflection seismic sections and aeromagnetic data. In the same area a well drilled for oil prospection was used for calibrating the seismic interpretation up to approximately 1.8 sec.. It is worth noting that the interpretation of the seismic data can be problematic in structurally complex areas where volcanic formations occur, but it can be assisted effectively by magnetic interpretation.&amp;#160;An interesting magnetic pattern represented by a strong, well-localized positive magnetic anomaly extending N-S for approximately 35 km is present in the western part of the Gulf. Its width in the W-E direction is of almost 20 km. The anomaly seems to be linked with the magnetic anomalies that characterize the southern Sardinian Rift in correspondence to the Campidano Graben. In fact, a set of localized high-gradient anomalies generally corresponding to the Oligo-Miocene andesitic calc-alkaline complexes is present in this Graben. The aeromagnetic interpretation was carried out to explain the origin of the above strong elongated magnetic anomaly that has never been quantitatively interpreted. In this work, this anomaly has been interpreted by means of Euler deconvolution, the analytical signal and by a delineation technique based on the maxima of the radial horizontal derivative of the total magnetic field.&amp;#160;The geological knowledge of the area by means of earlier studies also on land contributed to give a petrographic meaning to the magnetic sources, while by the magnetic and seismic integrated interpretation it was possible to carry out a spatial reconstruction of the volcanic source body and to give an useful contribution to the knowledge on the volcano-tectonic evolution of the area. Recently the area of the Gulf of Cagliari was affected in its western sector by a weak earthquake with hypocenter at around 10 km of depth, localized by Istituto Nazionale di Geofisica e Vulcanologia (INGV). The results of this study also provided new elements of knowledge which have contributed to understand this seismic event.&lt;/p&gt;&lt;p&gt;Acknowledgements: This work was partially supported by FIR (Fondi integrativi per la Ricerca) funded by the University of Cagliari (Italy) and by RAS/FBS (grant number: F71/17000190002) grants for funding.&lt;/p&gt;

3D gravity and magnetic model of the Rogaland Igneous Complex in southwest Norway: a tank for ilmenite, apatite and magnetite resources

&lt;p&gt;The Rogaland Igneous Complex (RIC), in southwest Norway, is well known for its iron-titanium ore deposits (i.e. Storgangen and Tellnes), and potential apatite and vanadium-rich magnetite deposits. A better understanding of the subsurface structure of the complex and surrounding anorthosites will help to locate new mineral deposits, and in estimating the extent of the known mineralized zones. The RIC consists of anorthosites, leuconorites, mangerites, and the Bjerkreim-Sokndal (BK) layered intrusion. These igneous rocks were intruded into granulite facies rocks at 0.93-0.92 Ga, during the late-stage of the Sveconorwegian orogeny.&lt;/p&gt;&lt;p&gt;There is a strong correlation between the geology of the RIC and the magnetic and gravity anomaly patterns, with contrasting signatures between the three large anorthosite bodies (Egersund-Ogna, Haland-Helleren, and Ana-Sira) and the extensive BK layered intrusion.&lt;/p&gt;&lt;p&gt;Particularly, the Bouguer gravity map shows gravity lows over the anorthosites and the granulites, while a positive gravity anomaly ranging from 10 to 30 mGal correlates with the norite and mangerite rocks. In the aeromagnetic anomaly map, the anorthosites correlate with moderate to strong negative magnetic anomalies (below background) while mangerites and granulites have positive anomalies. More complex is the magnetic pattern over the BK layered intrusion. The latter is made up by 6 mega-cyclic units subdivided into a sequence of zones, defined by the presence or absence of certain index minerals which control the magnetic properties of the rocks and the magnetic pattern. This is clearly visible in the striking negative anomaly observed on the east limb of the Bjerkrem Lobe at Heskestad, with amplitude of -13000 nT in a high-resolution helicopter survey, and below -30000 nT in ground magnetic survey.&lt;/p&gt;&lt;p&gt;This area has long been explored, and a large set of geophysical data have been collected during multiple campaigns including gravity, seismic, airborne magnetic and radiometric data. Recently acquired ground magnetic data over the BK layered intrusion complement these data. Here, we used the geophysical data, and an extensive petrophysical dataset of over 1000 samples to investigate the shallow and deep structure of the RIC. A 3D gravity and magnetic model of the study area, built across multiple cross-sections, is presented. The BK layered intrusion is modeled in a doubly-plunging syncline structure and has a preliminary depth extent of approximately 4 km which agrees with previous seismic interpretations indicating the base at 4 to 5 km.&lt;/p&gt;