Silicon Superconducting Quantum Interference Device

We have studied a Superconducting Quantum Interference SQUID device made from a single layer thin film of superconducting silicon. The superconducting layer is obtained by heavily doping a silicon wafer with boron atoms using the Gas Immersion Laser Doping (GILD) technique. The SQUID device is composed of two nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at low temperature and low magnetic field. The overall behavior shows very good agreement with numerical simulations based on the Ginzburg-Landau equations.Comment: Published in Applied Physics Letters (August 2015

Protracted timescales of lower crustal growth at the fast-spreading East Pacific Rise

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Geoscience 5 (2012): 275-278, doi:10.1038/ngeo1378.Formation of the oceanic crust at mid-ocean ridges is a fundamental component of plate tectonics. A majority of the crust at many ridges is composed of plutonic rocks that form by crystallization of mantle-derived magmas within the crust. Recent application of U/Pb dating to samples from in-situ oceanic crust has begun to provide exciting new insight into the timing, duration and distribution of magmatism during formation of the plutonic crust1-4. Previous studies have focused on samples from slow-spreading ridges, however, the time scales and processes of crustal growth are expected to vary with plate spreading rate. Here we present the first high-precision dates from plutonic crust formed at the fast-spreading East Pacific Rise (EPR). Individual zircon minerals yielded dates from 1.420–1.271 million years ago, with uncertainties of ± 0.006–0.081 million years. Within individual samples, zircons record a range of dates of up to ~0.124 million years, consistent with protracted crystallization or assimilation of older zircons from adjacent rocks. The variability in dates is comparable to data from the Vema lithospheric section on the Mid-Atlantic Ridge (MAR)3, suggesting that time scales of magmatic processes in the lower crust may be similar at slow- and fast-spreading ridges.This research was partially funded by NSF grant OCE-0727914 (SAB), a Cardiff University International Collaboration Award (CJL) and NERC grant NE/C509023/1 (CJM).2012-07-2

Constructing the crust along the Galapagos Spreading Center 91.3°–95.5°W : correlation of seismic layer 2A with axial magma lens and topographic characteristics

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): B10310, doi:10.1029/2004JB003066.Multichannel seismic reflection data are used to infer crustal accretion processes along the intermediate spreading Galapagos Spreading Center. East of 92.5°W, we image a magma lens beneath the ridge axis that is relatively shallow (1.0–2.5 km below the seafloor) and narrow (∼0.5–1.5 km, cross-axis width). We also image a thin seismic layer 2A (0.24–0.42 km) that thickens away from the ridge axis by as much as 150%. West of 92.7°W, the magma lens is deeper (2.5–4.5 km) and wider (0.7–2.4 km), and layer 2A is thicker (0.36–0.66 km) and thickens off axis by <40%. The positive correlation between layer 2A thickness and magma lens depth supports the interpretation of layer 2A as the extrusive volcanic layer with thickness controlled by the pressure on the magma lens and its ability to push magma to the surface. Our findings also suggest that narrower magma lenses focus diking close the ridge axis such that lava flowing away from the ridge axis will blanket older flows and thicken the extrusive crust off axis. Flow of lava away from the ridge axis is probably promoted by the slope of the axial bathymetric high, which is largest east of 92.5°W. West of ∼94°W the “transitional” axial morphology lacks a prominent bathymetric high and layer 2A no longer thickens off axis. We detect no magma lens west of 94.7°W where a small axial valley appears. The above changes can be linked to the westward decrease in the magma and heat flux associated with the fading influence of the Galapagos hot spot on the Galapagos Spreading Center.This project was funded by NSF-OCE- 0002189

Primitive layered gabbros from fast-spreading lower oceanic crust

Three-quarters of the oceanic crust formed at fast-spreading ridges is composed of plutonic rocks whose mineral assemblages, textures and compositions record the history of melt transport and crystallization between the mantle and the sea floor. Despite the importance of these rocks, sampling them in situ is extremely challenging owing to the overlying dykes and lavas. This means that models for understanding the formation of the lower crust are based largely on geophysical studies and ancient analogues (ophiolites) that did not form at typical mid-ocean ridges. Here we describe cored intervals of primitive, modally layered gabbroic rocks from the lower plutonic crust formed at a fast-spreading ridge, sampled by the Integrated Ocean Drilling Program at the Hess Deep rift. Centimetre-scale, modally layered rocks, some of which have a strong layering-parallel foliation, confirm a long-held belief that such rocks are a key constituent of the lower oceanic crust formed at fast-spreading ridges. Geochemical analysis of these primitive lower plutonic rocks-in combination with previous geochemical data for shallow-level plutonic rocks, sheeted dykes and lavas-provides the most completely constrained estimate of the bulk composition of fast-spreading oceanic crust so far. Simple crystallization models using this bulk crustal composition as the parental melt accurately predict the bulk composition of both the lavas and the plutonic rocks. However, the recovered plutonic rocks show early crystallization of orthopyroxene, which is not predicted by current models of melt extraction from the mantle and mid-ocean-ridge basalt differentiation. The simplest explanation of this observation is that compositionally diverse melts are extracted from the mantle and partly crystallize before mixing to produce the more homogeneous magmas that erupt

Accretion, structure and hydrology of intermediate spreading-rate oceanic crust from drillhole experiments and seafloor observations

Downhole measurements recorded in the context of the Ocean Drilling Program in Hole 504B, the deepest hole drilled yet into the oceanic crust, are analyzed in terms of accretion processes of the upper oceanic crust at intermediate spreading-rate. The upper part of the crust is found to support the non steady-state models of crustal accretion developed from seafloor observations (Kappel and Ryan, 1986; Gente, 1987). The continuous and vertical nature of borehole measurements provides stratigraphic and structural data that cannot be obtained solely from seafloor studies and, in turn, these models define a framework to analyze the structural, hydrological, and mineralogical observations made in the hole over the past decade.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43190/1/11001_2005_Article_BF01204282.pd

Bathymetric Reconstruction Method: Application to the Central Atlantic Basin between 10°N and 40°N

It is well known that a general relationship exists between the age of the earth's crust at mid-ocean ridges and its depth (Menard, 1969; Sclater and Francheteau, 1970; Sclater et al., 1971). Depths increase from 2500 300 meters at a spreading center, to 5800 5300 meters in oceanic crust of Early Cretaceous to Late Jurassic age (Figure 1; Sclater et al., 1971). The 3 km deepening of the oceanic crust can be satisfactorily explained by simple models involving the thermal structure of the oceanic lithosphere during its spreading from the axis of ridges to the adjacent oceanic basins (Sclater and Francheteau, 1970; Davis and Lister, 1974). It has also been suggested that structural highs like aseismic ridges, which have not come about by accretion, nevertheless follow the subsidence law of normal oceanic crust since they ride "piggy-back" on top of the oceanic lithosphere immediately after their creation at or close to spreading centers (Detrick et al., 1977). [NOT CONTROLLED OCR

Gravity study of the Pitcairn-Easter hotline

International audienceShipboard free air gravity and bathymetric anomalies with an extension of 400 km were identified across the Pitcairn-Easter hotline in the South Pacific. The anomalies are associated with one of the positive geoid undulations observed in the area from satellite data. Several smaller topographic features , volcano-tectonic ridges oriented N65øE, are superimposed on the topographic high. Admittance computations and direct modeling show that the swell topography is compensated by a low density zone within the lithosphere, 4 to 8 km below the crust The volcano tectonic ridges are locally compensated in a classical Airy sense. The swell and the associated ridges were probably created by the action of a thermal anomaly resulting from the interaction of the Easter Island hotspot and of the Easter Microplate accretion centers

Large Rotation of the Easter Microplate as Evidenced by Oriented Paleomagnetic Samples from the Ocean Floor

One of the goals of the Pito93 cruise along the perimeter of the Easter microplate was to obtain oriented rock samples from the ocean floor for paleomagnetic study. Using a new orienting device, the Geocompass, 14 oriented blocks were obtained during 6 dives conducted using the Ifremer DSRV Nautile. Paleomagnetic analysis shows that 13 of these 14 blocks give consistent results in thermal and AF demagnetizations, and reveals a mean Characteristic Remanent Magnetization (ChRM) direction within each block, with both normal and reverse polarities. After elimination of data from 5 blocks situated outside the microplate, and one block which bears an anomalous direction, we have computed a mean ChRM direction at Dm = 49.0°, Im = −39.0° (k = 10.2, α95 = 19.8 °, n = 7). Although the mean inclination is in agreement with the inclination of the recent dipole magnetic field (D = 0°, I = −43°), the average declination is significantly different from this direction, which we interpret as due to a bulk clockwise rotation of 48.5° ± 11° (after the bivariate average) of the Easter microplate over the past 2–3 Ma. This value is in excellent agreement with previous estimates based on remote geophysical measurements and models

Hydrothermal deposits sampled by diving saucer in transform fault "a" near 37°n on the mid-atlantic ridge, famous area

Deep-sea hydrothermal deposits were observed, mapped and sampled in situ with the submersible "Cyana" in the Famous area of the Mid-Atlantic Ridge.Two neighbouring fields, each covering an area of about 600 m2, are associated with low, E-W trending sediment-covered ridges that lie at a depth of about 2 700 m close to the axis of Transform Fault "A".In each field the deposits are thicker (up to about 1 m) close to the small, fissure-like vents through which they were evidently delivered. Despite their heterogeneous composition, their mineralogical and chemical variations have an orderly pattern.The principal constituents are a green clay-rich material, and Fe-Mn oxides in the form of black concretions. The relative abundances of these products vary with distance from the source-vent.The green clay-rich material, abundant near the vent, consists of hydromica, smectite and an amorphous Fe-Si compound.Further away, the Fe-Mn concretions, made up of rancieite and todorokite, are the dominant components. [NOT CONTROLLED OCR]La soucoupe plongeante " Cyana » a permis d'observer, de cartographier et d'échantillonner in situ des dépôts hydrothermaux dans la zone Famous de la dorsale médio-atlantique.Deux sites voisins, chacun recouvrant une surface d'environ 600 m2 forment des monticules très peu sédimentés et allongés dans une direction E-W à une profondeur d'environ 2 700 m au voisinage de l'axe de la Faille Transformante "A".Dans chaque site les dépôts sont plus épais (ils atteignent 1 m) près des griffons en forme de fissures. Les dépôts sont formés soit d'argile, en général de couleur verte, soit de concrétions noires de fer et de manganèse.Malgré leurs caractères hétérogènes la minéralogie et la chimie des dépôts montrent une zonation.L'abondance relative des dépôts varie avec la distance aux griffons : les dépôts de couleur verte enrichis en argile (smectite, hydromica et matériel amorphe enrichi en Fe-Si), sont abondants près des sorties; les concrétions de Fe-Mn deviennent abondantes au fur et à mesure que l'on s'en éloigne. Parmi les principaux produits de Fe-Mn notons la todorokite et la rancieite. [OCR NON CONTRÔLE

Chemical analyses of hydrothermal deposits and associated material from Transform fault 'A' on the Mid-Atlantic Ridge, FAMOUS area

Sampled hydrothermal deposits from Transform fault 'A' on the Mid-Atlantic Ridge have been classified into two main categories according to the relative proportion of the black Fe-Mn concretions with respect to the clay-rich fraction: clay-rich hydrothermal material and black Fe-Mn concretions (nodules). These materials have been analysed for their chemical composition by arc spectrometry using an ARL quantometer were made at the University of Strasbourg. This method consists of melting the sample in a mixture of lithium tetraborate and then introducing the melt into in a glycolated solvent prior analysis. Trace elements were determined using graphite discs . Na and K were determined by emission spectrometry (precision of +- 2.0%)