Sm–Nd isotopic mapping of lithospheric growth and stabilization in the eastern Kaapvaal craton

Whole-rock Sm–Nd isotope systematics of 79 Archean granitoids from the eastern Kaapvaal craton, southern Africa, are used to delineate lithospheric boundaries and to constrain the timescale of crustal growth, assembly and geochemical differentiation c. 3.66–2.70 Ga. Offsets in ε_Nd values for 3.2–3.3 Ga granitoids across the Barberton greenstone belt (BGB) are consistent with existing models for c. 3.23 Ga accretion of newly formed lithosphere north of the BGB onto pre-existing c. 3.66 Ga lithosphere south of the BGB along a doubly verging subduction margin. The Nd isotopic signature of c. 3.3–3.2 Ga magmatic rocks show that significant crustal growth occurred during subduction–accretion. After c. 3.2 Ga, however, the Nd signature of intrusive rocks c. 3.1 and 2.7 Ga is dominated by intracrustal recycling rather than by new additions from the mantle, signalling cratonic stability.     

Modeling input errors to improve uncertainty estimates for one-dimensional sediment transport models

Stochastic Environmental Research and Risk Assessment - Bayesian methods have recently been applied to one-dimensional sediment transport models to assess the uncertainty in model predictions due...     

Sedimentology of the debris-flow-dominated Warm Spring Canyon alluvial fan, Death Valley, California

Facies analysis of widely distributed exposures of the 32·6 km² and 8·1-km-long Warm Spring Canyon fan, central Death Valley, shows that it has been built principally by debris-flow deposits. These deposits were derived from a mature Panamint Range catchment mostly underlain by Precambrian mudrock, quartzite and dolomite. Stacked, clast-rich and matrix-supported debris-flow lobes of slightly bouldery, muddy, pebble–cobble gravel in beds 20–150 cm thick dominate the fan from apex to toe, accounting for 75–98% of most exposures. Interstratified with the debris flows are less abundant (2–25% of cuts), thinner (5–30 cm) and more discontinuous beds of clast-supported and imbricated, pebble–cobble gravel deposited by overland flows and gully flows. This facies formed by the surficial fine-fraction water winnowing of the debris flows primarily during recessional flood stage of the debris-flow events. Two other facies associations make up a small part of the fan. The incised-channel tract consists of a 250-m-wide clast-supported ribbon of irregularly to thickly bedded, boulder, pebble, cobble gravel nested within debris-flow deposits. This channel fill is oriented generally perpendicular to the Panamint range front. It formed by extensive erosion and winnowing of debris flows deposited within the incised channel, into which all water discharge from the catchment is funnelled. The limited presence of this facies only straddling the present incised channel indicates that this channel overall has maintained a consistent position on the fan except for slight lateral shifts, some caused by strike-slip offset. Fault offset temporarily closed the upper incised channel, causing recessional debris-flow mud to be ponded behind the dam. The other local facies assemblage consists of subrounded to rounded, moderately sorted pebble gravel in low-angle cross-beds that slope both basinwards and fanwards. This gravel was deposited in beachface, backshore and shoreface barrier-spit environments that developed where Lake Manly impinged on the Warm Spring fan during late Pleistocene time. These deposits straddle headcuts into, and were derived from, erosion of the debris-flow deposits. Wave energy sorted finer sediment from the shore zone, concentrated coarser sediment and rounded the coarse to very coarse pebble fraction by selective reworking.     

Polarization and amplitude attributes of reflected plane and spherical waves

The characteristics of a reflected spherical wave at a free surface are investigated by numerical methods; in particular, the polarization angles and amplitude coefficients of a reflected spherical wave are studied. The classical case of the reflection of a plane P wave from a free surface is revisited in order to establish our terminology, and the classical results are recast in a way which is more suited for the study undertaken. The polarization angle of a plane P wave, for a given angle of incidence, is shown to be 90° minus twice the angle of reflection of the reflected S wave. For a Poisson's ratio less than 1/3, there is a non-normal incident angle for which both amplification coefficients are 2 precisely; for this incident angle the direction of the particle motion at the free surface is also the direction of the incident wave. For a wave emanating from a spherical source, the polarization angle, for all angles of incidence, is always less than, or equal to, the polarization angle of a plane P wave. The vector amplification coefficient of a spherical wave, for all angles of incidence, is always greater than the vector amplification coefficient of a plane P wave. As expected, the results for a spherical wave approach the results for a plane P wave in the far field. Furthermore, there was a good agreement between the theoretical modelling and the numerical modelling using the dynamic finite element method (DFEM).     

ASCA observations of deep ROSAT fields — III. The discovery of an obscured Type 2 AGN at z = 0.67

We report on the discovery of a narrow-emission-line object at z  = 0.672 detected in a deep ASCA survey. The object, AXJ 0341.4–4453, has a flux in the 2–10 keV band of 1.1 ± 0.27 × 10⁻¹³ erg s⁻¹ cm⁻², corresponding to a luminosity of 1.8 × 10⁴⁴ erg s⁻¹ ( q ₀ = 0.5, H ₀ = 50 km s⁻¹ Mpc⁻¹). It is also marginally detected in the ROSAT 0.5–2 keV band with a flux 5.8 × 10⁻¹⁵ erg s⁻¹ cm⁻². Both the ASCA data alone and the combined ROSAT/ASCA data show a very hard X-ray spectrum, consistent with either a flat power law (α < 0.1) or photoelectric absorption with a column of n _H > 4 × 10²² cm⁻² (α = 1). The optical spectrum shows the high-ionization, narrow emission lines typical of a Seyfert 2 galaxy. We suggest that this object may be typical of the hard sources required to explain the remainder of the X-ray background at hard energies.     

A data analysis approach for detecting gravitational waves from PSR 0437–4715

A search for gravitational waves from the millisecond pulsar PSR 0437-4715 has been initiated using the bar detector NIOBE which is located at the University of Western Australia. We present a detailed report on the data analysis algorithm, called phase plane rotation , which will be used in this search. A discussion of the actual implementation of the algorithm is presented. The data analysis algorithm mentioned above has the advantage that it requires minimal changes to the already-existing data acquisition facility of NIOBE but, at the same time, it is as efficient as optimal filtering in detecting a signal. This search involves a very long coherent integration of the bar output which may stretch over a few years. With some planned improvements in the detector, a three-year integration should be able to put an upper limit of h  ∼ 10⁻²⁶ on the signal amplitude.     

Reviews

THE DICTIONARY OF HUMAN GEOGRAPHY edited by R. J. Johnston. 20 x 13 cm, xix and 411 pages. Blackwell: Oxford 1983 (ISBN 0 631 13465 4) $A13.95 (limp).

THE GEOGRAPHY OF AUSTRALIAN CORPORATE POWER edited by Michael Taylor. 22 x 14 cm, ix and 230 pages. Croom Helm Australia: Sydney 1984 (ISBN 0 949614 06 8) $A24.95 (cloth).

MULTINATIONALS AS MUTUAL INVADERS: Intra‐industry Direct Foreign Investment edited by A. Erdilek. 14 x 22 cm, xii and 217 pages. Croom Helm: London 1985 (ISBN 0 7099 0935 7) $A39.95 (cloth).

UNEVEN DEVELOPMENT: Nature, Capital and the Production of Space by N. Smith. 15 x 22 cm, xv and 198 pages. Basil Blackwell: Oxford 1984 (ISBN 0 631 13564 2) $A59.95 (cloth); (ISBN 0 631 13685 1) $A18.95 (limp).

SOCIAL THEORY AND THE AUSTRALIAN CITY (Studies in Society No. 26) by L. Kilmartin, D. Thorns and T. Burke. 14 x 21 cm, ix and 218 pages. George Allen and Unwin: Sydney 1985 (ISBN 0 86861 405) $A24.95 (cloth); (ISBN 0 86861 413 0) $A12.95 (limp).

THE FUTURE OF URBAN FORM: The Impact of New Technology edited by J. Brotchie, P. Newton, P. Hall and P. Nijkamp. 14 x 22 cm, xiii and 374 pages. Croom Helm: London 1985 (ISBN 0 7099 3255 3) $A44.95 (cloth).     

Short-period temperature variability at Winnipeg, Canada, 1872–1993: Characteristics and trends

Summary Temperature variability in Winnipeg, Canada, was assessed by determining average and extreme temperature ranges over 1, 2, 5, 10, and 15-day intervals, on a monthly basis, for the period of 1872–1993. Trends in the monthly averages for each of the intervals were also examined.The results show that Winnipeg experiences a very large amount of short-term temperature variability, especially over 2, 5, 10 and 15 days. The monthly average diurnal ranges vary from about 9 to 14 °C, while the 15-day average ranges are about two to three times as large. In general, average temperature ranges over the two shortest intervals (1 and 2 days) are slightly greater in the warm-season months than in the cold-season months, but the averages for the three longest intervals are inversely related to mean monthly temperature, as are the largest ranges observed in each of the months.Average temperature variability in the months of November through March was found to have decreased quite significantly, and rapidly, during the first two decades of this century. This decrease was likely associated with a decrease in the meridionality of the atmospheric circulation. It also occurred during a time when the average maximum and minimum temperatures in Winnipeg were rising, lending support to the conjecture that a warmer global climate will result in less 1–15 day temperature variability. The rapidity of the change also supports the hypothesis that climate changes tend to be non-linear.With 5 Figures     

Modelling of meander migration in an incised channel

An updated linear computer model for meandering rivers with incision has been developed. The model simulates the bed topography, flow field, and bank erosion rate in an incised meandering channel. In a scenario where the upstream sediment load decreases （e.g., after dam closure or soil conservation）, alluvial river experiences cross section deepening and slope flattening. The channel migration rate might be affected in two ways： decreased channel slope and steeped bank height. The proposed numerical model combines the traditional one-dimensional （1D） sediment transport model in simulating the channel erosion and the linear model for channel meandering. A non-equilibrium sediment transport model is used to update the channel bed elevation and gradations. A linear meandering model was used to calculate the channel alignment and bank erosion/accretion, which in turn was used by the 1D sediment transport model. In the 1D sediment transport model, the channel bed elevation and gradations are represented in each channel cross section. In the meandering model, the bed elevation and gradations are stored in two dimensional （2D） cells to represent the channel and terrain properties （elevation and gradation）. A new method is proposed to exchange information regarding bed elevations and bed material fractions between 1D river geometry and 2D channel and terrain. The ability of the model is demonstrated using the simulation of the laboratory channel migration of Friedkin in which channel incision occurs at the upstream end.     

Local economic development and the academy

This brief introduction highlights the various ways the Academy approaches local economic development (LED). It shows that the Academy is not always been favorable to the advancement of LED as its practical demands often transcend the tightly defined disciplines of a typical university structure. Caught between disciplines, LED to often neglected by theorists as the subject matter is difficult to model and depends heavily on the social fabric of the regional economy. The paper concludes with a brief outline of this special issue. The papers in this volume show the diversity of approaches and topics that characterize the practice of LED. They are multidisciplinary and depict a variety of approaches from the more theoretical to the applied.