Twenty‐year weathering remeasurements at St Paul's Cathedral,London

Microerosion meter (MEM) measurements of the surface height of the balustrade of St Paul's Cathedral, London, have been repeated in the year 2000 following earlier measurements in 1980, 1981, 1985 and 1990. Methodological sources of error mean that while the measurements were made to 0·0001 mm, the data are reliable to two decimal places. There was a reduction in the mean erosion rate on horizontal sites from 0·045 mm a^?1 in the period 1980–1990 to 0·025 mm a^?1 in 1990–2000. Decreases in atmospheric SO₂ levels from 20–25 ppb in 1980–1982 to around 10 ppb in 1990–2000, offer a causal explanation. The surface topography evolved more erratically in 1990–2000 than before, with much, but not all, of the more microelevated areas showing greater, and often more variable erosion. There are also indications of less erosion and more surface rises in low‐lying microareas on horizontal sites which is interpreted as possible deposition and/or microfloral growth in wetter depressions, the pattern being largely absent on a well drained vertical site. Copyright © 2001 John Wiley & Sons, Ltd.     

Measurement of Ejecta from Normal Incident Hypervelocity Impact on Lunar Regolith Simulant

The National Aeronautics and Space Administration (NASA) continues to make progress toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment. A subject for further definition is the lunar impact ejecta environment. The document NASA SP-8013 was developed for the Apollo program and is the latest definition of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA’s Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powered pumice targets, simulating unconsolidated lunar regolith. The Ames Vertical Gun Range (AVGR) was used to accelerate spherical Pyrex projectiles of 0.29g to velocities ranging between 2.5 and 5.18 km/s. Impact on the pumice target occurred at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the pumice target in a 0.5 Torr vacuum. A simplistic technique to characterize the ejected particles was formulated. Improvements to this technique will be discussed for implementation in future tests.     

Stone movement on hillslopes in the Mojave Desert,California: A 16-year record

Previous research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the American Southwest. This study analyses the movement over 16 years of painted stones on two hillslopes in the central Mojave Desert to ascertain which of these two processes dominate in this region. The distance moved (M) is found to be directly related to length of overland flow (X) and hillslope gradient (S), and inversely related to particle size (D). The fact that M is more highly correlated with X than with S suggests that hydraulic action rather than creep is the dominant process. It is concluded that this is probably the case over most of the Mojave and Sonoran Deserts on slopes up to at least 24°, and that it is only at higher elevations where winters are more severe that creep may become dominant.     

Everywhere different? Globalisation and the impact of international migration on Sydney and Melbourne

Using a new approach to classifying migrant group concentrations, we test for evidence of the effects of globalisation, associated by some with ‘protopostmodernity’, on two Australian cities. Sydney is characterised as an emergent world city and a focus of ‘new economy’ activities. Melbourne is associated with ‘old economy’ activities, dominated by manufacturing. In the Australian context, the onset of globalisation also coincided with significant changes to immigration policy: the end of a ‘white Australia’ policy in the early 1970s in favour of a skills-based policy, regardless of race or ethnicity. We argue that the evidence of the spatial behaviour of ethnic groups for these two cities highlights the essential continuity of ethnic segregation and spatial assimilation processes in two cities where segregation levels and experience are fundamentally different from many overseas examples. We further argue for a need to recognise that context, and the ethnic experience, are everywhere different, both intra- and internationally.     

Porphyry fertility in the Northparkes district: indicators from whole-rock geochemistry

Abstract

Four economic porphyry Cu–Au deposits and several prospects have been investigated in the Northparkes district, part of the Ordovician to early Silurian Junee–Narromine Belt of the Macquarie Arc, New whole-rock geochemical data from the Northparkes porphyry Cu–Au district, NSW, indicate that the mineralising intrusive complexes exhibit distinct arc signatures that are transitional from high-K calc-alkaline to silica-saturated alkalic. Based on ratios of Sr/Y vs Y (e.g. Sr/Y > ～20 and Y < ～17?ppm) the mineralising intrusions are interpreted to have crystallised from fractionated hydrous melts indicating the suppression of plagioclase crystallisation in favour of hydrous mineral phases. This interpretation is supported by listric-shaped rare earth element curves and the presence of primary hornblende phenocrysts indicating elevated magmatic water contents. There is an association of mineralising intrusions with a low Zr trend both in the mineralised Northparkes district intrusive rocks and in mineralised porphyry-related intrusive rocks globally. A newly developed fertility indicator ratio Zr/Y ～10% is more accurate at identifying the mineralised rocks at Northparkes than the conventional Sr/Y vs Y fertility indicator diagram, successfully identifying 92% of the mineralising intrusions, mainly owing to the fact that it is less affected by hydrothermal alteration. The insensitivity of Zr–Y to alteration makes this indicator a useful new tool that may lead to enhanced probabilities for future discoveries in the Northparkes district, broader Macquarie Arc and altered rocks globally.

1. KEY POINTS

2. Mineralising intrusions in the Northparkes district have distinct Zr vs Y concentrations.

3. The Zr vs Y indicator of magmatic fertility is less sensitive to alteration than Sr-based indicators.

4. The Zr vs Y magmatic fertility indicator identified at Northparkes is not unique and identifies mineralising intrusions in other porphyry fields.