GLONASS Broadcast Orbit Computation

The potential 48-satellite constellation offered by the combination of observations from both the GPS and GLONASS positioning systems has created considerable interest among existing GPS users. In the published literature, a considerable amount of work has been devoted to the theoretical issue of algorithm design for combined GPS/GLONASS positioning solutions. Little work has been published, however, on the practical conversion of existing GPS software to include GLONASS observations. This paper considers the computation issues pertaining to the GLONASS broadcast ephemeris for inclusion of GLONASS observations into existing GPS software. The format of the GLONASS broadcast ephemeris is discussed and theory of satellite orbits and their stepwise numerical integration is reviewed. Finally, a strategy for GLONASS broadcast ephemeris computation is proposed to facilitate combination of GPS and GLONASS observations. ? 1998 John Wiley & Sons, Inc.     

Sedimentary thickness variations and deformation intensity during basin inversion in the Flinders Ranges, South Australia

The central and northern parts of the Adelaide fold belt in the Flinders Ranges, South Australia, consist of a sequence of Neo-Proterozoic–Cambrian sediments overlying a Meso-Proterozoic basement complex, both of which were mildly deformed in an intracratonic setting during the 500 Ma Delamerian orogeny. The fold belt lies within a prominent heat flow anomaly (average heat flows of 90 mWm⁻²) reflecting extraordinary enrichments in heat producing elements in the Meso-Proterozoic basement, suggesting that anomalous thermal regimes may have been significant in localising Delamerian deformation. However, spatial variations in deformation intensity correlate more closely with variations in the thickness of the sedimentary sequence than with observed variations in heat flow, suggesting that the thickness of the sedimentary blanket plays a crucial role in localising Delamerian deformation during basin inversion. We use simple numerical models of lithospheric strength to investigate the potential role of sedimentary thickness variations on the distribution and style of deformation, focussing on the impact of a variable thickness sediment pile deposited above a ‘radioactive’ basement. We show that for thermal parameters appropriate to the Flinders Ranges, Moho temperatures may vary by 25–30°C for every additional kilometre of sediment. For a ‘Brace–Goetze’ lithospheric rheology, controlled by a combination of temperature-dependent creep processes and frictional sliding, the observed variations in thickness of the sedimentary pile are sufficient to cause dramatic reductions in the vertically-integrated strength of the lithosphere (by many orders of magnitude), thereby providing a plausible explanation for observed correlation between sediment thickness and deformation intensity during basin inversion.     

Understanding and managing climate change: the UK experience

Climate change has emerged over the last 25 years not just as a physical reality, affecting global and regional climates, but also as a socio-cultural phenomenon – an icon of a globalizing world which is increasingly altering the physical fabric of our planet and at the same time demanding new forms of global governance. The UK, both through its scientific research activity and through its development of climate change policy initiatives, has been at the forefront of this emergence. This review traces some of this history from a UK perspective, with an emphasis on the last 10 years. The relationship between climate change science and policy has become increasingly reflexive, leading to new forms of research and institutional structures. The academic discipline of geography has been rather marginalized from this process.     

New horizons for astronomy

Mike Edmunds summarizes an exciting and inspiring RAS Discussion Meeting which looked forward to the new world of powerful astronomical instruments that are becoming available to UK researchers, through GEMINI and ESO.     

Standing Conference of Astronomy Professors

Phil Charles and Mike Bode present the minutes of the 13th Standing Conference of Astronomy Professors (SCAP) meeting held at the NAM in Bristol on 12 April. Thirteen universities/groups were represented.     

Global Change and Health — The Good, The Bad and The Evidence

Debates over the merits and demerits of globalisation for health are increasingly polarised. Conclusions range from globalisation being essentially positive for health, albeit with a need to smooth out some rough edges, to one of utter condemnation, with adverse effects on the majority of the world's population. Anyone wading into this debate is immediately confronted by seemingly irreconcilable differences in ideology, opinion and interests. Both camps agree that global changes are occurring, and with them many of the determinants of population health status. While some skepticism persists about whether “globalisation” has value beyond being a fashionable buzzword, most agree that we need better understanding of these changes. Two difficult questions arise: (i) What are the health impacts of these changes; and (ii) how can we respond more effectively to them? To move beyond the stand-offs that have already formed within the health community, this paper reviews the main empirical evidence that currently exists, summarises key points of debate that remain, and suggests some ways forward for the research and policy communities. In particular, there is need for an informed and inclusive debate about the positive and negative health consequences of globalisation.     

Hydrothermal Alteration and Cu-Au Mineralization at Nena High Sulfidation-type Deposit, Frieda River, Papua New Guinea

Abstract. The Nena Cu‐Au deposit, located in the Frieda River mineral district of northwestern mainland Papua New Guinea, is a composite structurally‐lithologically controlled high sulfidation (HS) system. Its hydrothermal alteration and Cu‐Au mineralization are presented in this paper. Initially propylitized andesitic volcanics veined by epithermal quartz were pervasively superimposed by zoned HS alteration. The zonation grades from vuggy silica core to sulfur‐rich, pyritic silica‐alunite halo followed by pyrophyllite‐dickite‐kaolinite interval and finally to thin illite‐smectite margin, suggesting progressive decrease in temperature and increase in pH. This zonation is enveloped by chlorite‐epidote‐calcite‐gypsum alteration. The acid altered rocks were then invaded by multiple phases of pyrite, subsequently crosscut by quartz, vein alunite and barite. Then sequential deposition of bladed covellite, enargite, luzonite and stibioluzonite occurred from the NW to the SE portions of the deposit, forming a zonation suggestive of progressive decrease in temperature, sulfur fugacity and sulfidation stage. Most ore mineralization occurs in the vuggy silica core. Gold mineralization commenced from the transition of enargite to luzonite and continued throughout the stibioluzonite stage. Associated with gold deposition are Au‐rich pyrite, tennantite‐tetrahedrite, chalcopyrite‐bornite, native tellurium, electrum, calaverite, bismuthinite and galena. Native sulfur occupied the remaining cavities and represents the waning stage of the hydrothermal system. Fluid inclusions studies distinguished magmatic (>300–350d?C, 9–15 wt% NaCl equiv.) and meteoric (<150–200d?C, 1–2 wt% NaCl equiv.) fluids (Holzberger et al., 1996). Temperatures and salinities of fluid inclusions from barite associated with Cu sulfides show a general decrease from NW (330d?C, 9–15 wt% NaCl equiv.) to SE (172d?C, 10 wt% NaCl equiv.) parts of the deposit, indicating gradual entrainment of ground water (Hitchman and Espi, 1997). Interaction of magmatic fluids with meteoric water accompanied by changes in temperature, salinity, acidity and oxidation state of the resultant fluids is interpreted to have been the main cause of metal precipitation. Finally, supergene processes generated Au zone with an underlying chalcocite‐covellite‐digenite blanket over the primary sulfides at depth. Gold occurs as lattice constituent in scorodite, limonite‐goethite and jarosite. Chalcocite is more abundant and widespread than other Cu sulfides. Acidic fluids deposited powdery alunite and kaolinite, vein alunite and amorphous silica. Weakly secondary biotite‐quartz altered porphyry located below the known HS Cu‐Au deposit contains chalcopyrite‐bornite and is overprinted by quartz‐alunite‐pyro‐phyllite‐pyrite assemblage. This feature indicates close temporal, spatial and genetic relation between the two deposit types.