260 research outputs found
U-Pn geochronology of deformed metagranites in central Sutherland, Scotland: evidence for widespread late Silurian metamorphism and ductile deformation of the Moine Supergroup during the Caledonian orogeny
Within the Caledonides of central Sutherland, Scotland, the Neoproterozoic metasedimentary rocks of the Moine Supergroup record NW-directed D2 ductile thrusting and nappe assembly, accompanied by widespread tight-to-isoclinal folding and amphibolite-facies metamorphism. A series of metagranite sheets which were emplaced and penetratively deformed during D2 have been dated using SHRIMP UĆ¢Pb geochronology. Zircon ages of 424 8 Ma (Vagastie Bridge granite), 420 6 Ma (Klibreck granite) and 429 11 Ma (Strathnaver granite) are interpreted to date emplacement, and hence regional D2 deformation, during
mid- to late Silurian time. Titanite ages of 413 3 Ma (Vagastie Bridge granite) and 416 3 Ma (Klibreck granite) are thought to date post-metamorphic cooling through a blocking temperature of c. 550Ć¢ 500 8C. A mid- to late Silurian age for D2 deformation supports published models that have viewed the internal ductile thrusts of this part of the orogen as part of the same kinematically linked system of forelandpropagating thrusts as the marginal Moine Thrust Zone. The new data contrast with previous interpretations that have viewed the dominant structures and metamorphic assemblages within the Moine Supergroup as having formed during the early to mid-Ordovician Grampian arcĆ¢continent orogeny. The mid-to late Silurian D2 nappe stacking event in Sutherland is probably a result of the collision of Baltica with the Scottish segment of Laurentia
Patterns of Silurian deformation and magmatism during sinistral oblique convergence, northern Scottish Caledonides
Funding Information: Acknowledgments Fieldwork by RAS, REH and GIA was carried out in part during the remapping of BGS Scotland sheets 114E (Tongue), 108E (Loch Naver), 109E (Kildonan) and 109W (Badenloch) and funded under the NERC-BGS Academic Collaboration Programme. IMB acknowledges a PhD studentship funded by Oxford Brookes University (1990-93). Mark Witton is thanked for drafting. Rick Law, Fernando Corfu, Calvin Mako and Kathryn Goodenough contributed detailed comments that resulted in significant improvements to the paper. John Waldron and Rick Law are thanked for supplying editable versions of figures 1 and 3, respectively. Stephen Daly is thanked for efficient editorial handling.Peer reviewedPostprin
The Neoarchaean Uyea Gneiss Complex, Shetland: an onshore fragment of the Rae Craton on the European Plate
A tract of amphibolite facies granitic gneisses and metagabbros in northern Shetland, U.K., is here named the Uyea Gneiss Complex. Zircon UāPb dating indicates emplacement of the igneous protoliths of the complex c. 2746ā2726 Ma, at a later time than most of the Archaean protoliths of the Lewisian Gneiss Complex of mainland Scotland. Calc-alkaline geochemistry of the Uyea Gneiss Complex indicates arc-affinity and a strong genetic kinship among the mafic and felsic components. Zircon Hf compositions suggest an enriched mantle source and limited interaction with older crust during emplacement. Ductile fabrics developed soon after emplacement, with zircon rims at c. 2710 Ma, but there was little further deformation until Caledonian reworking east of the Uyea Shear Zone. There is no evidence for the Palaeoproterozoic reworking that dominates large tracts of the Lewisian Gneiss Complex and of the Nagssugtoqidian Orogen of East Greenland. The more northerly location of the Uyea Gneiss Complex and extensive offshore basement of similar age implies that, prior to the opening of the North Atlantic Ocean, these rocks were contiguous with the Archaean Rae Craton
Frustrated two-dimensional Josephson junction array near incommensurability
To study the properties of frustrated two-dimensional Josephson junction
arrays near incommensurability, we examine the current-voltage characteristics
of a square proximity-coupled Josephson junction array at a sequence of
frustrations f=3/8, 8/21, 0.382 , 2/5, and 5/12.
Detailed scaling analyses of the current-voltage characteristics reveal
approximately universal scaling behaviors for f=3/8, 8/21, 0.382, and 2/5. The
approximately universal scaling behaviors and high superconducting transition
temperatures indicate that both the nature of the superconducting transition
and the vortex configuration near the transition at the high-order rational
frustrations f=3/8, 8/21, and 0.382 are similar to those at the nearby simple
frustration f=2/5. This finding suggests that the behaviors of Josephson
junction arrays in the wide range of frustrations might be understood from
those of a few simple rational frustrations.Comment: RevTex4, 4 pages, 4 eps figures, to appear in Phys. Rev.
Signatures of the slow solar wind streams from active regions in the inner corona
Some of local sources of the slow solar wind can be associated with
spectroscopically detected plasma outflows at edges of active regions
accompanied with specific signatures in the inner corona. The EUV telescopes
(e.g. SPIRIT/CORONAS-F, TESIS/CORONAS-Photon and SWAP/PROBA2) sometimes
observed extended ray-like structures seen at the limb above active regions in
1MK iron emission lines and described as "coronal rays". To verify the
relationship between coronal rays and plasma outflows, we analyze an isolated
active region (AR) adjacent to small coronal hole (CH) observed by different
EUV instruments in the end of July - beginning of August 2009. On August 1 EIS
revealed in the AR two compact outflows with the Doppler velocities V =10-30
km/s accompanied with fan loops diverging from their regions. At the limb the
ARCH interface region produced coronal rays observed by EUVI/STEREO-A on July
31 as well as by TESIS on August 7. The rays were co-aligned with open magnetic
field lines expanded to the streamer stalks. Using the DEM analysis, it was
found that the fan loops diverged from the outflow regions had the dominant
temperature of ~1 MK, which is similar to that of the outgoing plasma streams.
Parameters of the solar wind measured by STEREO-B, ACE, WIND, STEREO-A were
conformed with identification of the ARCH as a source region at the
Wang-Sheeley-Arge map of derived coronal holes for CR 2086. The results of the
study support the suggestion that coronal rays can represent signatures of
outflows from ARs propagating in the inner corona along open field lines into
the heliosphere.Comment: Accepted for publication in Solar Physics; 31 Pages; 13 Figure
QUARTZ : QUantitative Analysis of Retinal Vessel Topology and size : an automated system for quantification of retinal vessels morphology
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Reconstruction and regional significance of the Coire Breac palaeoglacier, Glen Esk, eastern Grampian Highlands, Scotland
Chronic obstructive pulmonary disease and related phenotypes:polygenic risk scores in population-based and case-control cohorts
- ā¦