Chronology of transpression, magmatism, and sedimentation in the Thompson Nickel Belt (Manitoba, Canada) and timing of Trans-Hudson Orogen – Superior Province collisionThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

The Thompson Nickel Belt marks the boundary between the Archean Superior Province and the Trans-Hudson Orogen in Canada. It comprises Archean gneisses, and Paleoproterozoic rocks with metasediments and metavolcanites (Ospwagan Group) and intrusions. The gneisses are frequently migmatitic and host numerous pegmatites. The western belt boundary is a fault contact with the Kisseynew Domain of the Reindeer Zone. In the south, the transition zone between the belt and the Kisseynew Domain comprises granitoids and a detrital sequence (Grass River Group), part of which grades into turbidites in the Kisseynew Domain. The eastern belt boundary is a diffuse zone where the Archean east–west (E–W) structural trend changes into the north-northeast (NNE) trend of the belt. This paper presents U–Pb ages for granitoids and 207Pb/206Pb detrital zircon ages from the Ospwagan and Grass River groups. Ages and a comparison of events in the belt and in the eastern Reindeer Zone have major implications. The change from stable platform deposits to syn-tectonic filling and emplacement of mafic intrusions in the Ospwagan Group are attributed to the convergence between the Reindeer Zone and the Superior Province at 1891–1885 Ma. At ca. 1850 Ma, continuing convergence led to drowning of marginal basins of the Superior craton and to the development of a transpressive regime in the belt, the onset of which could be as old as ca. 1885 Ma. Metamorphic ages of 1818–1785 record closure of the Kisseynew basin and crustal thickening. Collision of the new continental block with the Superior Province was accommodated by transpression until 1750–1720 Ma.

Spatiotemporal Patterns of Excitation and Inhibition Evoked by the Horizontal Network in Layer 2/3 of Ferret Visual Cortex

The horizontal network in visual cortex layer 2/3 is implicated in numerous psychophysical and physiological properties. To investigate the spatial and temporal distribution of excitation and inhibition evoked by this network, we used voltage-sensitive dyes to image the responses to focal electrical stimulation in tangential slices of ferret visual cortex layer 2/3. The resulting optical patterns included a diffuse zone of activation near the stimulation site and numerous ovoid domains throughout the slice. In contrast to the fixed anatomy of the horizontal connections, substantial shifts in both space and time were evident in the distribution of population-based neuronal activity during stimulus trains. Both of these shifts relied on inhibitory synaptic potentials, suggesting that inhibition driven by horizontal connections sculpts the distribution of activity in this cortical network.

A Study of the Interface Between THM Grown MCT Crystals and Cdte Seeds.

ABSTRACTHgCdTe crystals have been grown from CdTe seeds by the travelling heater method (THM). Three different kinds of interfaces between the growing crystal and the seed were found: a sharp planar interface; a non-planar interface which is caused by meltback near the ampoule walls; a diffuse zone, where an interface cannot be discerned. A correlation was found between the initial growth parameters and the interface structure. Microprobe analysis revealed a boundary layer which, in the case of the planar interface, had an unusual shape. This layer had a thickness varying from 400 to 800 microns. It consisted mostly of HgTe, and contained holes as defects.

Structure and Tectonics of the Continental Slope West of Southern Vancouver Island

The lower continental slope west of southern Vancouver Island consists of a series of ridges formed by folding, faulting, and uplift of Cascadia Basin deposits; underlying oceanic basement, at least initially, is not involved in this deformation. The middle and upper continental slope has probably formed by the same process, combined with deposition of overlying material coming directly from the continent. This compressive deformation is postulated to be a result of underthrusting of the America Plate by the Juan de Fuca Plate. Linear magnetic anomalies produced at the Juan de Fuca spreading center can be traced under the slope for at least 40 km, further evidence for underthrusting. Anomaly source depth calculations indicate that oceanic basement dips beneath the continental slope at an angle of more than 10°. A diffuse zone of earthquake epicenters extending northeast from the northern tip of Juan de Fuca Ridge may mark the present northern margin of the Juan de Fuca Plate.

The Molecular Structure and Arrangement in Stretched Natural Rubber

Although there are still some minor discrepancies to be resolved, the appearance of the diffuse-zone electron-diffraction pattern arising from thin films of stretched natural rubber is adequately explained on the basis of the thermal oscillations of the long-chain rubber molecules in the crystalline regions, this pattern being analogous to that which would be given by a stream of oriented molecules in a pseudo-gaseous condition. As Charlesby, Finch and Wilman pointed out, the diffuse-zone pattern has distinct advantages in the examination of complex molecules, since it gives a direct indication of the configuration of the molecule, independent of its mode of fitting into any particular crystalline lattice. In spite of the diffuseness of the patterns with which we are dealing a study of the diffuse zone or molecular pattern has shown that it is possible to discriminate decisively between two postulated atomic configurations which do not differ greatly. In the case of natural rubber, neither of the two configurations investigated agrees in every respect with experiment, but the evidence brought forward above supports the view that the atomic arrangement in the stretched rubber molecule approximates to a simple form having planar units and standard bond lengths and angles, rather than to the more complex form hitherto considered.