Chemical and chronologic complexity in the convecting upper mantle: Evidence from the Taitao ophiolite, southern Chile

Exposure of the ca. 6 Ma Taitao ophiolite, Chile, located 50 km south of the Chile Triple Junction, allows detailed chemical and isotopic study of rocks that were recently extracted from the depleted mantle source of mid-ocean ridge basalts (DMM). Ultramafic and mafic rocks are examined for isotopic (Os, Sr, Nd, and O), and major and trace element compositions, including the highly siderophile elements (HSE). Taitao peridotites have compositions indicative of variable extents of partial melting and melt extraction. Low δ¹⁸O values for most whole rock samples suggest some open-system, high-temperature water–rock interaction, most likely during serpentinization, but relict olivine grains have δ¹⁸O values consistent with primary mantle values. Most of the peridotites analyzed for Nd–Sr isotopes have compositions consistent with estimates for the modern DMM, although several samples are characterized by ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd indicative of crustal contamination, most likely via interactions with seawater. The peridotites have initial ¹⁸⁷Os/¹⁸⁸Os ratios that range widely from 0.1168 to 0.1288 (γ_Os = −8.0 to +1.1), averaging 0.1239 (γ_Os = −2.4), which is comparable to the average for modern abyssal peridotites. A negative correlation between the Mg^# of relict olivine grains and Os isotopic compositions of whole rock peridotites suggests that the Os isotopic compositions reflect primary mantle Re/Os fractionation produced by variable extents of partial melting at approximately 1.6 Ga. Recent re-melting at or near the spatially associated Chile Ridge further modified these rocks, and Re, and minor Pt and Pd were subsequently added back into some rocks by late-stage melt–rock or fluid–rock interactions.In contrast to the peridotites, approximately half of the mafic rocks examined have whole rock δ¹⁸O values within the range of mantle compositions, and their Nd and Sr isotopic compositions are all generally within the range of modern DMM. These rocks have initial ¹⁸⁷Os/¹⁸⁸Os ratios, calculated for 6 Ma, that range from 0.126 (γ_Os = −1) to as high as 0.561 (γ_Os = +342). The Os isotopic systematics of each of these rocks may reflect derivation from mixed lithologies that include the peridotites, but may also include pyroxenites with considerably more radiogenic Os than the peridotites. This observation supports the view that suprachondritic Os present in MORB derives from mixed mantle source lithologies, accounting for some of the worldwide dichotomy in ¹⁸⁷Os/¹⁸⁸Os between MORB and abyssal peridotites.The collective results of this study suggest that this >500 km³ block of the mantle underwent at least two stages of melting. The first stage occurred at 1.6 Ga, after which the block remained isolated and unmixed within the DMM. A final stage of melting recently occurred at or near the Chile Ridge, resulting in the production of at least some of the mafic rocks. Convective stirring of this mantle domain during a >1 Ga period was remarkably inefficient, at least with regard to Os isotopes.     

Multivariate Analysis of Incomplete Mapped Data

Classical multivariate analyses are based on matrix algebra and enable the analysis of a table containing measurements of a set of variables for a set of sites. Incomplete mapped data consist of measurements of a set of variables recorded for the same geographical region but for different zonal systems and with only a partial sampling of this zone. This kind of data cannot be analysed with usual multivariate methods because there is no common system of sites for all variables. We propose a new approach using GIS technology and NIPALS, an iterative multivariate method, to analyse the spatial patterns of this kind of data. Moreover, an extension of our method is that it can be used for areal interpolation purposes. We illustrate the method in analysing data concerning the distribution of roe deer weights over several years in a reserve.     

Historical sand injections on the Mediterranean shore of Israel: evidence for liquefaction hazard

The abundant silt and sand along the coastal plain of Israel have long been considered susceptible to liquefaction, but previous searches have failed to find field evidence for it. We report the first finding of typical liquefaction features and silty sand injections in trenches that were excavated behind a fourth century Byzantine dam on the Taninim Creek, some 850 m inland of the Mediterranean shore. The trenches revealed a series of flame-shape injections of silty sand that penetrate the overlying clay-rich soil. The injections are largest and most frequent within several meters of the point where the dam is badly damaged on the seaward side, which we interpret as a possible result of a large wave. Three features make the sand injections special: (1) their lower extent is commonly asymmetric with dominant southeastward vergence, away from the breach in the dam, (2) zigzag shapes characterize the upper parts of many injections, and (3) the size and frequency of the injections diminish gradually with distance from the dam until they completely disappear some 100 m away from it. We suggest that the sand injections can be explained by overpressure that was induced either directly by earthquake shaking or by a tsunami wave that breached the dam, filled the reservoir behind the dam and increased the pressure on the water-saturated silt and sand layers and triggered liquefied sand injections. The movement of water sloshing back and forth in the lake accounts for the zigzag shape of the injections. The similarity to structures that were observed in Thailand after the great 2004 tsunami and other palaeotsunami observations lead us to prefer the tsunami origin of the liquefaction features. Based on the stratigraphic position, the archeological context, and the historical accounts, we suggest that an earthquake of November 25, 1759 is the most plausible trigger of the sand injections, either directly or via earthquake-induced tsunami. The observations demonstrate the vulnerability of the densely populated coastal plain to liquefaction.     

Book reviews

The weather and climate of Australia and New Zealand

A.P. Sturman & N.J. Tapper, 1996

Oxford University Press, Melbourne

18 × 24 cm, xi + 476pp., ISBN 0–19–553393–3, A$55.00 (soft)

Australians and the environment

W. McLennan, 1996

Australian Bureau of Statistics (Catalogue No. 4601.0), Melbourne

21 × 30 cm, viii + 415pp., ISBN 0–642–20690–2, A$44.00 (soft)

The information age: economy, society and culture. Vol.1—The rise of the network society

M. Castells, 1996

Blackwell, Cambridge MA/Oxford

15 × 23 cm, xvii + 556 pp., ISBN 1–155786–617–1, US$25.95/£15.99 (soft)

Retailing, consumption and capital: towards the new retail geography

N. Wrigley & M. Lowe (eds), 1996

Longman, Harlow

16 × 23 cm, vi + 352 pp., ISBN 0–582–22824–7, £17.99 (soft)     

After the Supernova: Runaway Stars and Massive X-ray Binary Populations with Metallicity

One of the main pathways by which massive runaways are thought to be produced is by the disruption of a binary system after the supernova (SN) of one of its components. Under such a scenario, the populations of runaway stars in different phases should reflect the input binary population and its evolution. Conversely, if the system stays together after the SN, a High Mass X-Ray Binary (HMXB) may result. We present simulations exploring the behaviour of such runaway and HMXB populations with metallicity, and compare them to observations. As many as two-thirds of massive runaway stars may be produced by supernovae in binaries. Decreasing metallicity lowers the fraction of O stars which are runaway, but increases the Wolf-Rayet runaway fractions and the number of potential HMXBs.     

Carbon leakage in aviation policy

ABSTRACT

The inherently global, connected nature of aviation means that carbon leakage from aviation policy does not necessarily behave similarly to leakage from other sectors. We model carbon leakage from a range of aviation policy test cases applied to a specific country (the United Kingdom), motivated by a desire to reduce aviation CO₂ faster than achievable by currently-planned global mitigation efforts in pursuit of a year-2050 net zero CO₂ target. We find that there are two main components to leakage: one related to passenger behaviour, which tends to result in emissions reductions outside the policy area (negative leakage), and one related to airline behaviour, which tends to result in emissions increases outside the policy area (positive leakage). The overall leakage impact of a policy, and whether it is positive or negative, depends on the balance of these two components and the geographic scope used, and varies for different policy types. In our simulations, carbon pricing-type policies were associated with leakage of between +50 and ?150% depending on what is assumed about scope and the values of uncertain parameters. Mandatory biofuel use was associated with positive leakage of around 0–40%, and changes in airport landing costs to promote more fuel-efficient aircraft were associated with positive leakage of 50–150%.

Key policy insights

• Carbon leakage in aviation policy arises from airline responses (typically positive leakage) and passenger responses (typically negative leakage).

• Depending on the geographical scope, policy type and values for uncertain parameters, leakage may be between around ?150 to +150%.

• Of the policies investigated in this study, leakage was typically most negative for carbon pricing and most positive for environmental landing charges.

• Absolute values of leakage are smallest where policies are considered on the basis of all arriving and departing flights.