Stresses along the metastable wedge of olivine in a subducting slab: possible explanation for the Tonga double seismic layer

A numerical calculation of the stresses associated with changes in volume during phase transitions of olivine in a descending slab results in a double layer of high shear stress along the metastable olivine wedge in the depth range 350-460 km. Stress in the upper layer is in-plane tensional and stress in the lower layer is down-dip compressional. The modeled stress field agrees with observations of stress in the Tonga double seismic zone. High shear stress also exists in the slab at depths below the metastable wedge. This stress distribution involves down-dip compression and trench-parallel tension, which agrees with about half of the focal mechanisms in the Tonga slab at depths of 460-690 km. The model supports the idea that at least two possible stress release mechanisms for deep earthquakes may act in the Tonga subducting slab. One, transformational faulting, is restricted to the metastable wedge while the other one acts below the metastable wedge.     

Using 'the body' as an 'instrument of research': kimch'i and pavlova

Often researchers position themselves in relation to race, age and gender, but the body is less often discussed as an actual 'instrument of research'. We aim to extend thinking on this point by reflecting on a project we conducted on migrant women and food in New Zealand. We present a vignette as an example of how we used our bodies as 'instruments of research' at a 'shared lunch' attended by new migrants from a range of different countries. At the lunch some combined on their plates spicy dishes such as kimch'i (fermented vegetables) and sweet dishes such as pavlova (a meringue dessert). For others this combination prompted feelings of disgust. We conclude that the body is a primary tool through which all interactions and emotions filter in accessing research subjects and their geographies.     

Compositional and temporal investigation of exposed lunar basalts in the Mare Imbrium region

This paper presents an updated stratigraphical and compositional study of the exposed maria within the Imbrium basin on the Moon. Clementine multispectral data were employed to derive TiO₂ and FeO wt% abundance estimates of potentially distinct basaltic flows. Additionally, NASA Lunar Orbiter images were used to estimate flow ages using crater count statistics. Mare Imbrium shows evidence of a complex suite of low to high-Ti basaltic lava units infilling the basin over an 800 million year timescale. More than a third (37%) of identified mare basalts were found to contain 1-3 wt% TiO₂. Two other major mare lithological units (representing about 25% of the surface each) show TiO₂ values between 3-5 and 7-9 wt%. The dominant fraction (55%) of the sampled maria contain FeO between 16 and 18 wt%, followed by 27% of maria having 18-20 wt% and the remaining 18%, 14-16 wt% FeO. A crater frequency count (for diameters >500 m) shows that in three quarters of the sampled mare crater counts range between 3.5 and 5.5×¹⁰⁻² per km², which translates, according to a lunar cratering model chronology, into estimated emplacement ages between ∼3.3 and 2.5 Ga. A compositional convergence trend between the variations of iron and titanium oxides was identified, in particular for materials with TiO₂ and FeO content broadly above 5 and 17 wt%, respectively, suggesting a related petrogenesis and evolution. According to these findings, three major periods of mare infill are exposed in the Imbrium basin; despite each period showing a range of basaltic compositions (classified according to their TiO₂ content), it is apparent that, at least within these local geological settings, the igneous petrogenesis generally evolved through time towards more TiO₂- and FeO-rich melts.     

Origin of the Olympus Mons aureole and perimeter scarp

The aureole materials that form an annulus of corrugated terrain surrounding Olympus Mons are considered to be the product of mass movement. The scarp at the mountain's foot formed as a result of this massive removal of material from the volcano's outer flanks. This interpretation is supported by a comparison of the amount of material originally available before scarp formation, and the present volume of aureole materials. On the basis of distribution, surface textures and theoretical considerations it is considered that the aureole was produced by a series of megaslides, rather than by a flow mechanism. Production of the megaslides may have been assisted by a period of widespread melting of permafrost.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.     

Gender, immigration policies and accreditation: valuing the skills of professional women migrants

Human capital is the most important form of wealth for a modern nation and countries with the most intellectual resources are achieving the highest rates of economic growth. In the drive for human capital, many industrialised countries are giving priority to policies aimed at attracting highly skilled immigrants. The number of skilled immigrants who settle permanently in these countries is not rising but there is a significant level of temporary movement of highly skilled labour from developing countries, particularly in information technology (IT), medicine, nursing and teaching. Women now account for an increased proportion of highly skilled migrants but there are still few analyses of their economic participation. Immigration selection and occupational entry policies are crucial for an understanding of the gendered experiences of migration for skilled migrants. This article draws together material from empirical work and reports/other literature on the situation facing professional women compared to men, both permanent and temporary, in the selection processes for migration and the post-arrival processes of accreditation and recognition.