THE ELLICOTT METEORITE

Two individual specimens (total weight 15.7 kg) of a new medium octahedrite were found near Ellicott, El Paso County, Colorado. The find is only 1.2 km from the find (in 1890) of the Franceville medium octahedrite. Ellicott and Franceville are distinct meteorites, the latter exhibiting pronounced differences in shock features, kamacite band width, and Ni, Ga, Ge, and Ir contents. Ellicott is a group IA iron while Franceville is in group IIIA.     

A paleomagnetic study of the Mull lava succession

Summary. A paleomagnetic study has been made of a succession of 139 non-overlapping basaltic lavas, representing 91 per cent of the longest remaining succession of flows associated with the Paleogene Mull volcano. All the lavas have experienced considerable hydrothermal alteration, probably at up to several million years after initial magnetization and frequently with alteration to the opaque minerals and the production of new potentially magnetic phases. The question of whether directional remagnetization has taken place while preserving within-unit directional consistency and discreteness of unit mean direction is discussed. Extensive directional remagnetization is excluded as an explanation for the data. If stable directions obtained by alternating field remanence cleaning coincide with original TRM directions then a mean pole position for all temporally independent lava directions from the British Tertiary igneous province is at 71.9° N, 167.2° E, with k:22 and α₉₅:3.0°. This pole is significantly different from the geographic pole. If the difference in palaeomagnetic and geographic poles is interpreted in terms of absolute plate motion, then 2010 km of northwards motion of the western part of the Eurasian Plate, at 3.7 cm/yr, has taken place over the last 55 Myr. This motion has implications for the geological history of the Arctic and for the complexity of mantle motions.     

A virtual surface concept for nested yield surface plasticity

A return mapping algorithm based on the concept of virtual surfaces is presented for stress integration in the numerical solution of boundary value problems using an elastoplastic multiple yield surface model. Both kinematic hardening and isotropic softening yield surfaces are addressed. With the implementation of virtual surfaces, the active yield surface is located before a stress update is implemented. The return mapping algorithm consists of only two steps. The first step consists of performing the intermediate update of the trial stress corresponding to the translation of all yield surfaces inside the active yield surface. Little calculation is involved in this step. The second step consists of performing the conventional explicit one-step radial return mapping of the updated trial stress on the corresponding active yield surface. The algorithm efficiency resides in the virtual surface based return mapping which preserves the elastic predictor representation of the updated trial stress, and limits iterations to at most two steps.     

MAVIS–an upper crustal seismic refraction experiment in the Midland Valley of Scotland

The results of the Midland Valley Investigation by Seismology (MAVIS) are described. The experiment consists of three refraction profiles of between 80 and 100 km length across the Upper Palaeozoic basins of the Scottish Midland Valley.
Three refractors are recognized, thus defining four upper crustal layers. The top two layers are interpreted as Carboniferous plus Upper Old Red Sandstone, and Lower Old Red Sandstone plus Lower Palaeozoic. The structure of the refractor, an unconformity, separating the two layers mirrors surface structure. Deeper refractors, associated with Midland Valley crystalline basement, show no correlation with surface structure. The MAVIS survey allows the refinement of earlier gross interpretation of upper crustal structure in the Midland Valley, but confirms the existence of anomalously shallow (6.4 km s^–1) basement, and shows, in conjunction with results of previous work, that a large area of the central and southern Midland Valley is characterized by one velocity signature, probably indicative of a single terrane.     

Electron-impact excitation of the Cameron system (a3π → X1Σ)of CO

We have studied the excitation of the Cameron bands of carbon monoxide (a³π → X¹Σ⁺) by electron impact on CO and CO₂. This investigation was prompted by a recent study of the Martian airglow by Conway (1981) who concluded that the cross section for the dissociative excitation of the Cameron bands is seven times larger than the laboratory value reported by Ajello (1971a) and by a perplexing inconsistency between the optical cross section and CO(a³π) time-of-flight experiments. We have found now that three factors have contributed to these discrepancies: (1) spectral contamination of the (1,4) Cameron band used by Ajello to normalize the entire Cameron band cross section, (2) major revisions in the magnitude of the CO(a³π) radiative lifetime, and (3) new insights into the effects of the CO(a³π) velocity distribution on the field of view of the emission experiments. The new results largely reconcile the TOF and emission measurements, but they also suggest that the calculated photoelectron fluxes in the Martian atmosphere may be too large by a factor of 3.     

VRI photometry of late dwarf common proper motion stars

Summary From the photometric observations of a sample of late dwarf common proper motion pairs it may be inferred that about 30%–50% of such systems contain one or more additional stellar components. A small fraction of such systems have separations in excess of 5000 A.U.     

FOUR NEW IRON METEORITE FINDS

Four new irons are described; Buenaventura (IIIB) from Chihuahua, Mexico: mass 114 kg; Denver City (anomalous) from Texas, USA: mass 26.1 kg; Kinsella (IIIB) from Alberta, Canada: mass 3.7 kg; and Tacoma (IA) from Washington, USA: mass 17 g. Denver City is unique, i.e., not related to any other known iron. Tacoma is the smallest iron meteorite recorded. All were purchased for the UCLA collection following a publicity drive for new meteorites     

The British Tertiary igneous province: palaeomagnetism of the dyke swarm along the Sleat coast of Skye

Summary. A palaeomagnetic investigation has been made of a swarm of more than 400 dykes along the south coast of Skye, Scotland, by the Sound of Sleat.
Seven red lamprophyre dykes have palaeomagnetic directions inconsistent with Tertiary age, and not inconsistent with their previously held Caledonian age. The remaining 409 dykes have palaeomagnetic directions that are consistent with a Lower Tertiary age. We present evidence suggesting that the Tertiary dykes might have been emplaced during a short time, over which the geomagnetic polarity occupied as few as three polarity intervals (NRN or RNR).
Certain 'intermediate' directions of magnetization have also been found, and are presented here.